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V. van der Wijk
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1
Development of Flexure-Driven Eversion Mechanisms
For Confined-Space Grasping
This dissertation explores the development and evaluation of mechanical grippers with flexure-driven eversion mechanism fingers, designed to address the challenges of grasping objects in confined spaces—a common issue in the agri-food and food processing industry that hinders robotic automation. Conventional mechanical grippers face significant difficulties in dense environments, such as within piles or plants, as their grasping process relies on positioning fingers around the object performing inward-outward movements from its sides. This approach requires considerable clearance, often obstructed by neighboring obstacles. To overcome this challenge, this research introduces in Chapter 1 a novel grasping approach in which the gripper fingers move tangentially along the surface of the object, utilized as flexure-driven eversion mechanisms, to set or release the grasp while reducing environmental disturbances. This approach significantly reduces the required space, as well as unwanted displacements and forces in the surroundings, and leverages environmental interactions to aid finger navigation.
The main objective is to develop and evaluate flexure-driven eversion mechanism fingers for mechanical grippers, aimed at grasping food in confined spaces, as presented in Chapter 1. The finger design incorporates a curved flexure as the structural backbone, which navigates along the object’s surface—displacing adjacent obstacles if necessary—and securely holds it once enclosed. The flexure is combined with the principles of eversion mechanisms to reduce friction forces during operation by ensuring zero relative speed differences with the environment.
This thesis is divided into two parts. The first part, presented in Chapter 2, investigates the applicability of flexures within the proposed finger concept by analyzing their ability to navigate predictably through multiple obstacles when driven from the base. A case study was conducted, modeling the kinematics and kinetics of a straight base-driven flexure, which bends and moves through two consecutive circular obstacles when pushed forward, using a pseudo-rigid-body modeling (PRBM) approach. This analysis required an extension of existing PRBM techniques, enabling the analysis of flexures in event-based scenarios (e.g., abrupt load changes) and with multiple loads at unknown locations along their length. This was achieved by systematically switching and stitching PRBM-topologies while maintaining the system’s potential energy within reasonable bounds. Experimental validation confirmed the compatibility of base-driven flexures with the proposed finger concept, demonstrating their ability to navigate through obstacles in a predictable manner, with both trajectory and interaction forces modeled with high accuracy for design purposes.
In the second part of this thesis, two finger designs were developed and manufactured as prototype grippers, which were experimentally validated based on defined performance criteria. Chapter 3 presents a preliminary gripper design with three fingers, each implemented as a Dual-Belt Curved-Flexure Eversion Mechanism (DBCF-EM)—a single curved base-driven flexure, with its inner and outer contours covered by two everting (outwardly unrolling) belts guided through rollers. Chapter 4 presents an evolved gripper design featuring Sleeved Concentric-Flexure Eversion Mechanisms (SCF-EM) as fingers—a base-driven channeled backbone comprising two concentric curved flexures, fully enclosed along its circumference by a latex sleeve with engineered stretchability, which everts from the channel. The design is completed by a cable-pulley system that synchronizes both movements.
The results showed that both grippers operated as intended, following the object’s surface and navigating adjacent obstacles, and successfully validated the proposed grasping method, enabling form-closed grasps of densely packed objects. Practical tests involving integration into a robotic set-up tasked with emptying a crate of tomatoes, one at a time, demonstrated an exceptionally high grasp success rate, previously unobserved. While the gripper with DBCF-EM fingers occasionally encountered issues such as mis-grasps, object damage, and hygiene concerns due to its open structure, the gripper with SCF-EM fingers achieved a 100% success rate in picking and placing tomatoes without damaging them or the surroundings. Additionally, the SCF-EM fingers offered improved hygiene compliance, durability, and robustness due to the enclosed eversion sleeve creating a barrier and a reduction in the number of mechanical components. Technical tests of both designs measured relatively low disturbance forces and sufficient holding forces. Comparative studies showed that the integration of the eversion mechanism reduced friction forces by around 90%, reducing both damage and mis-grasps.
In general, these findings demonstrate the effectiveness of the proposed finger designs for grasping objects in confined spaces and their suitability to gently and securely handle fragile agri-food products while accommodating natural variations, although additional engineering, testing, and refinement are required to ensure industrial readiness. Ultimately, the most important outcome is that this dissertation introduces flexure-driven eversion mechanisms for the first time and convincingly demonstrates their exceptional potential for navigation in complex and confined environments. This breakthrough constitutes the central scientific contribution of this work, arising from the need for alternative gripper methods for grasping tasks in tight spaces. This contribution provides a solid foundation for further applications in domains such as medical devices, search-and-rescue robotics, and inspection systems for hard-to-reach environments. ...
The main objective is to develop and evaluate flexure-driven eversion mechanism fingers for mechanical grippers, aimed at grasping food in confined spaces, as presented in Chapter 1. The finger design incorporates a curved flexure as the structural backbone, which navigates along the object’s surface—displacing adjacent obstacles if necessary—and securely holds it once enclosed. The flexure is combined with the principles of eversion mechanisms to reduce friction forces during operation by ensuring zero relative speed differences with the environment.
This thesis is divided into two parts. The first part, presented in Chapter 2, investigates the applicability of flexures within the proposed finger concept by analyzing their ability to navigate predictably through multiple obstacles when driven from the base. A case study was conducted, modeling the kinematics and kinetics of a straight base-driven flexure, which bends and moves through two consecutive circular obstacles when pushed forward, using a pseudo-rigid-body modeling (PRBM) approach. This analysis required an extension of existing PRBM techniques, enabling the analysis of flexures in event-based scenarios (e.g., abrupt load changes) and with multiple loads at unknown locations along their length. This was achieved by systematically switching and stitching PRBM-topologies while maintaining the system’s potential energy within reasonable bounds. Experimental validation confirmed the compatibility of base-driven flexures with the proposed finger concept, demonstrating their ability to navigate through obstacles in a predictable manner, with both trajectory and interaction forces modeled with high accuracy for design purposes.
In the second part of this thesis, two finger designs were developed and manufactured as prototype grippers, which were experimentally validated based on defined performance criteria. Chapter 3 presents a preliminary gripper design with three fingers, each implemented as a Dual-Belt Curved-Flexure Eversion Mechanism (DBCF-EM)—a single curved base-driven flexure, with its inner and outer contours covered by two everting (outwardly unrolling) belts guided through rollers. Chapter 4 presents an evolved gripper design featuring Sleeved Concentric-Flexure Eversion Mechanisms (SCF-EM) as fingers—a base-driven channeled backbone comprising two concentric curved flexures, fully enclosed along its circumference by a latex sleeve with engineered stretchability, which everts from the channel. The design is completed by a cable-pulley system that synchronizes both movements.
The results showed that both grippers operated as intended, following the object’s surface and navigating adjacent obstacles, and successfully validated the proposed grasping method, enabling form-closed grasps of densely packed objects. Practical tests involving integration into a robotic set-up tasked with emptying a crate of tomatoes, one at a time, demonstrated an exceptionally high grasp success rate, previously unobserved. While the gripper with DBCF-EM fingers occasionally encountered issues such as mis-grasps, object damage, and hygiene concerns due to its open structure, the gripper with SCF-EM fingers achieved a 100% success rate in picking and placing tomatoes without damaging them or the surroundings. Additionally, the SCF-EM fingers offered improved hygiene compliance, durability, and robustness due to the enclosed eversion sleeve creating a barrier and a reduction in the number of mechanical components. Technical tests of both designs measured relatively low disturbance forces and sufficient holding forces. Comparative studies showed that the integration of the eversion mechanism reduced friction forces by around 90%, reducing both damage and mis-grasps.
In general, these findings demonstrate the effectiveness of the proposed finger designs for grasping objects in confined spaces and their suitability to gently and securely handle fragile agri-food products while accommodating natural variations, although additional engineering, testing, and refinement are required to ensure industrial readiness. Ultimately, the most important outcome is that this dissertation introduces flexure-driven eversion mechanisms for the first time and convincingly demonstrates their exceptional potential for navigation in complex and confined environments. This breakthrough constitutes the central scientific contribution of this work, arising from the need for alternative gripper methods for grasping tasks in tight spaces. This contribution provides a solid foundation for further applications in domains such as medical devices, search-and-rescue robotics, and inspection systems for hard-to-reach environments. ...
This dissertation explores the development and evaluation of mechanical grippers with flexure-driven eversion mechanism fingers, designed to address the challenges of grasping objects in confined spaces—a common issue in the agri-food and food processing industry that hinders robotic automation. Conventional mechanical grippers face significant difficulties in dense environments, such as within piles or plants, as their grasping process relies on positioning fingers around the object performing inward-outward movements from its sides. This approach requires considerable clearance, often obstructed by neighboring obstacles. To overcome this challenge, this research introduces in Chapter 1 a novel grasping approach in which the gripper fingers move tangentially along the surface of the object, utilized as flexure-driven eversion mechanisms, to set or release the grasp while reducing environmental disturbances. This approach significantly reduces the required space, as well as unwanted displacements and forces in the surroundings, and leverages environmental interactions to aid finger navigation.
The main objective is to develop and evaluate flexure-driven eversion mechanism fingers for mechanical grippers, aimed at grasping food in confined spaces, as presented in Chapter 1. The finger design incorporates a curved flexure as the structural backbone, which navigates along the object’s surface—displacing adjacent obstacles if necessary—and securely holds it once enclosed. The flexure is combined with the principles of eversion mechanisms to reduce friction forces during operation by ensuring zero relative speed differences with the environment.
This thesis is divided into two parts. The first part, presented in Chapter 2, investigates the applicability of flexures within the proposed finger concept by analyzing their ability to navigate predictably through multiple obstacles when driven from the base. A case study was conducted, modeling the kinematics and kinetics of a straight base-driven flexure, which bends and moves through two consecutive circular obstacles when pushed forward, using a pseudo-rigid-body modeling (PRBM) approach. This analysis required an extension of existing PRBM techniques, enabling the analysis of flexures in event-based scenarios (e.g., abrupt load changes) and with multiple loads at unknown locations along their length. This was achieved by systematically switching and stitching PRBM-topologies while maintaining the system’s potential energy within reasonable bounds. Experimental validation confirmed the compatibility of base-driven flexures with the proposed finger concept, demonstrating their ability to navigate through obstacles in a predictable manner, with both trajectory and interaction forces modeled with high accuracy for design purposes.
In the second part of this thesis, two finger designs were developed and manufactured as prototype grippers, which were experimentally validated based on defined performance criteria. Chapter 3 presents a preliminary gripper design with three fingers, each implemented as a Dual-Belt Curved-Flexure Eversion Mechanism (DBCF-EM)—a single curved base-driven flexure, with its inner and outer contours covered by two everting (outwardly unrolling) belts guided through rollers. Chapter 4 presents an evolved gripper design featuring Sleeved Concentric-Flexure Eversion Mechanisms (SCF-EM) as fingers—a base-driven channeled backbone comprising two concentric curved flexures, fully enclosed along its circumference by a latex sleeve with engineered stretchability, which everts from the channel. The design is completed by a cable-pulley system that synchronizes both movements.
The results showed that both grippers operated as intended, following the object’s surface and navigating adjacent obstacles, and successfully validated the proposed grasping method, enabling form-closed grasps of densely packed objects. Practical tests involving integration into a robotic set-up tasked with emptying a crate of tomatoes, one at a time, demonstrated an exceptionally high grasp success rate, previously unobserved. While the gripper with DBCF-EM fingers occasionally encountered issues such as mis-grasps, object damage, and hygiene concerns due to its open structure, the gripper with SCF-EM fingers achieved a 100% success rate in picking and placing tomatoes without damaging them or the surroundings. Additionally, the SCF-EM fingers offered improved hygiene compliance, durability, and robustness due to the enclosed eversion sleeve creating a barrier and a reduction in the number of mechanical components. Technical tests of both designs measured relatively low disturbance forces and sufficient holding forces. Comparative studies showed that the integration of the eversion mechanism reduced friction forces by around 90%, reducing both damage and mis-grasps.
In general, these findings demonstrate the effectiveness of the proposed finger designs for grasping objects in confined spaces and their suitability to gently and securely handle fragile agri-food products while accommodating natural variations, although additional engineering, testing, and refinement are required to ensure industrial readiness. Ultimately, the most important outcome is that this dissertation introduces flexure-driven eversion mechanisms for the first time and convincingly demonstrates their exceptional potential for navigation in complex and confined environments. This breakthrough constitutes the central scientific contribution of this work, arising from the need for alternative gripper methods for grasping tasks in tight spaces. This contribution provides a solid foundation for further applications in domains such as medical devices, search-and-rescue robotics, and inspection systems for hard-to-reach environments.
The main objective is to develop and evaluate flexure-driven eversion mechanism fingers for mechanical grippers, aimed at grasping food in confined spaces, as presented in Chapter 1. The finger design incorporates a curved flexure as the structural backbone, which navigates along the object’s surface—displacing adjacent obstacles if necessary—and securely holds it once enclosed. The flexure is combined with the principles of eversion mechanisms to reduce friction forces during operation by ensuring zero relative speed differences with the environment.
This thesis is divided into two parts. The first part, presented in Chapter 2, investigates the applicability of flexures within the proposed finger concept by analyzing their ability to navigate predictably through multiple obstacles when driven from the base. A case study was conducted, modeling the kinematics and kinetics of a straight base-driven flexure, which bends and moves through two consecutive circular obstacles when pushed forward, using a pseudo-rigid-body modeling (PRBM) approach. This analysis required an extension of existing PRBM techniques, enabling the analysis of flexures in event-based scenarios (e.g., abrupt load changes) and with multiple loads at unknown locations along their length. This was achieved by systematically switching and stitching PRBM-topologies while maintaining the system’s potential energy within reasonable bounds. Experimental validation confirmed the compatibility of base-driven flexures with the proposed finger concept, demonstrating their ability to navigate through obstacles in a predictable manner, with both trajectory and interaction forces modeled with high accuracy for design purposes.
In the second part of this thesis, two finger designs were developed and manufactured as prototype grippers, which were experimentally validated based on defined performance criteria. Chapter 3 presents a preliminary gripper design with three fingers, each implemented as a Dual-Belt Curved-Flexure Eversion Mechanism (DBCF-EM)—a single curved base-driven flexure, with its inner and outer contours covered by two everting (outwardly unrolling) belts guided through rollers. Chapter 4 presents an evolved gripper design featuring Sleeved Concentric-Flexure Eversion Mechanisms (SCF-EM) as fingers—a base-driven channeled backbone comprising two concentric curved flexures, fully enclosed along its circumference by a latex sleeve with engineered stretchability, which everts from the channel. The design is completed by a cable-pulley system that synchronizes both movements.
The results showed that both grippers operated as intended, following the object’s surface and navigating adjacent obstacles, and successfully validated the proposed grasping method, enabling form-closed grasps of densely packed objects. Practical tests involving integration into a robotic set-up tasked with emptying a crate of tomatoes, one at a time, demonstrated an exceptionally high grasp success rate, previously unobserved. While the gripper with DBCF-EM fingers occasionally encountered issues such as mis-grasps, object damage, and hygiene concerns due to its open structure, the gripper with SCF-EM fingers achieved a 100% success rate in picking and placing tomatoes without damaging them or the surroundings. Additionally, the SCF-EM fingers offered improved hygiene compliance, durability, and robustness due to the enclosed eversion sleeve creating a barrier and a reduction in the number of mechanical components. Technical tests of both designs measured relatively low disturbance forces and sufficient holding forces. Comparative studies showed that the integration of the eversion mechanism reduced friction forces by around 90%, reducing both damage and mis-grasps.
In general, these findings demonstrate the effectiveness of the proposed finger designs for grasping objects in confined spaces and their suitability to gently and securely handle fragile agri-food products while accommodating natural variations, although additional engineering, testing, and refinement are required to ensure industrial readiness. Ultimately, the most important outcome is that this dissertation introduces flexure-driven eversion mechanisms for the first time and convincingly demonstrates their exceptional potential for navigation in complex and confined environments. This breakthrough constitutes the central scientific contribution of this work, arising from the need for alternative gripper methods for grasping tasks in tight spaces. This contribution provides a solid foundation for further applications in domains such as medical devices, search-and-rescue robotics, and inspection systems for hard-to-reach environments.
...
Dynamic balancing can offer significant benefits to applications where moving parts are present. It aims to reduce the reaction forces and moments due to inertia of the parts, thereby reducing vibrations. Dynamic balancing receives significant academic interest for planar and spatial applications, but limited attention for spherical mechanisms. This leads to the following goal of this thesis: Present novel force balanced spherical mechanisms design using inherent balancing planar pantograph theory for use in micro precision applications.
To achieve this goal, the thesis has been divided into three sub goals. First is defining the qualitative benefit of dynamic balancing for applications requiring micro-precision. This qualitative analysis looked into six different 'high speed precise' applications with motion and determined a potentially significant benefit exists for applications such as (space) telescopes, space manipulation, additive manufacturing, motions stages and beam steering. Engines and drives require new balancing methods to achieve significant benefit. However, the analysis also showed that many different aspects other then inertia also influence precision, thereby potentially reducing the gained benefit in precision. This is due to the addition of extra components or mass in most common dynamic balancing methods.
The second goal presents five new shaking force balanced spherical mechanisms using inherent balancing theory. Here the planar knowledge of inherently balanced shapes such as the pantograph as well as the use of projections are used to design three novel types of balanced spherical pantographs, namely the spherical pantograph, double spherical pantograph and the double S shaped mechanism with surrounding 4R four-bar linkage. Also, two additional variations of the spherical pantograph and the double spherical pantograph are presented, which leads to a total of five new designs. Each design has its required constraints and available design freedom described. Also, the balance conditions for the double spherical pantograph are presented.
The last goal shows ten novel force balanced remote center mechanisms, using the three types of inherently balanced spherical pantographs. These remote center mechanisms are either using a swivel joint or are a combination of spherical pantographs to form a parallel manipulator. This allows all end effectors to show spherical movement, around a fixed Center of Rotation. The pros and cons as well as feasible variations and constraints are also discussed.
To show the use case of a force balanced remote center mechanism, a realistic design has been made for a beam steering application, where a mirror can perform a tip/tilt movement around a shared center of rotation. The mechanism uses three scaled shifted double spherical pantographs as legs to form a parallel manipulator, with a mirrored surfaced attached to the end effector and positioned in the center of rotation. ...
To achieve this goal, the thesis has been divided into three sub goals. First is defining the qualitative benefit of dynamic balancing for applications requiring micro-precision. This qualitative analysis looked into six different 'high speed precise' applications with motion and determined a potentially significant benefit exists for applications such as (space) telescopes, space manipulation, additive manufacturing, motions stages and beam steering. Engines and drives require new balancing methods to achieve significant benefit. However, the analysis also showed that many different aspects other then inertia also influence precision, thereby potentially reducing the gained benefit in precision. This is due to the addition of extra components or mass in most common dynamic balancing methods.
The second goal presents five new shaking force balanced spherical mechanisms using inherent balancing theory. Here the planar knowledge of inherently balanced shapes such as the pantograph as well as the use of projections are used to design three novel types of balanced spherical pantographs, namely the spherical pantograph, double spherical pantograph and the double S shaped mechanism with surrounding 4R four-bar linkage. Also, two additional variations of the spherical pantograph and the double spherical pantograph are presented, which leads to a total of five new designs. Each design has its required constraints and available design freedom described. Also, the balance conditions for the double spherical pantograph are presented.
The last goal shows ten novel force balanced remote center mechanisms, using the three types of inherently balanced spherical pantographs. These remote center mechanisms are either using a swivel joint or are a combination of spherical pantographs to form a parallel manipulator. This allows all end effectors to show spherical movement, around a fixed Center of Rotation. The pros and cons as well as feasible variations and constraints are also discussed.
To show the use case of a force balanced remote center mechanism, a realistic design has been made for a beam steering application, where a mirror can perform a tip/tilt movement around a shared center of rotation. The mechanism uses three scaled shifted double spherical pantographs as legs to form a parallel manipulator, with a mirrored surfaced attached to the end effector and positioned in the center of rotation. ...
Dynamic balancing can offer significant benefits to applications where moving parts are present. It aims to reduce the reaction forces and moments due to inertia of the parts, thereby reducing vibrations. Dynamic balancing receives significant academic interest for planar and spatial applications, but limited attention for spherical mechanisms. This leads to the following goal of this thesis: Present novel force balanced spherical mechanisms design using inherent balancing planar pantograph theory for use in micro precision applications.
To achieve this goal, the thesis has been divided into three sub goals. First is defining the qualitative benefit of dynamic balancing for applications requiring micro-precision. This qualitative analysis looked into six different 'high speed precise' applications with motion and determined a potentially significant benefit exists for applications such as (space) telescopes, space manipulation, additive manufacturing, motions stages and beam steering. Engines and drives require new balancing methods to achieve significant benefit. However, the analysis also showed that many different aspects other then inertia also influence precision, thereby potentially reducing the gained benefit in precision. This is due to the addition of extra components or mass in most common dynamic balancing methods.
The second goal presents five new shaking force balanced spherical mechanisms using inherent balancing theory. Here the planar knowledge of inherently balanced shapes such as the pantograph as well as the use of projections are used to design three novel types of balanced spherical pantographs, namely the spherical pantograph, double spherical pantograph and the double S shaped mechanism with surrounding 4R four-bar linkage. Also, two additional variations of the spherical pantograph and the double spherical pantograph are presented, which leads to a total of five new designs. Each design has its required constraints and available design freedom described. Also, the balance conditions for the double spherical pantograph are presented.
The last goal shows ten novel force balanced remote center mechanisms, using the three types of inherently balanced spherical pantographs. These remote center mechanisms are either using a swivel joint or are a combination of spherical pantographs to form a parallel manipulator. This allows all end effectors to show spherical movement, around a fixed Center of Rotation. The pros and cons as well as feasible variations and constraints are also discussed.
To show the use case of a force balanced remote center mechanism, a realistic design has been made for a beam steering application, where a mirror can perform a tip/tilt movement around a shared center of rotation. The mechanism uses three scaled shifted double spherical pantographs as legs to form a parallel manipulator, with a mirrored surfaced attached to the end effector and positioned in the center of rotation.
To achieve this goal, the thesis has been divided into three sub goals. First is defining the qualitative benefit of dynamic balancing for applications requiring micro-precision. This qualitative analysis looked into six different 'high speed precise' applications with motion and determined a potentially significant benefit exists for applications such as (space) telescopes, space manipulation, additive manufacturing, motions stages and beam steering. Engines and drives require new balancing methods to achieve significant benefit. However, the analysis also showed that many different aspects other then inertia also influence precision, thereby potentially reducing the gained benefit in precision. This is due to the addition of extra components or mass in most common dynamic balancing methods.
The second goal presents five new shaking force balanced spherical mechanisms using inherent balancing theory. Here the planar knowledge of inherently balanced shapes such as the pantograph as well as the use of projections are used to design three novel types of balanced spherical pantographs, namely the spherical pantograph, double spherical pantograph and the double S shaped mechanism with surrounding 4R four-bar linkage. Also, two additional variations of the spherical pantograph and the double spherical pantograph are presented, which leads to a total of five new designs. Each design has its required constraints and available design freedom described. Also, the balance conditions for the double spherical pantograph are presented.
The last goal shows ten novel force balanced remote center mechanisms, using the three types of inherently balanced spherical pantographs. These remote center mechanisms are either using a swivel joint or are a combination of spherical pantographs to form a parallel manipulator. This allows all end effectors to show spherical movement, around a fixed Center of Rotation. The pros and cons as well as feasible variations and constraints are also discussed.
To show the use case of a force balanced remote center mechanism, a realistic design has been made for a beam steering application, where a mirror can perform a tip/tilt movement around a shared center of rotation. The mechanism uses three scaled shifted double spherical pantographs as legs to form a parallel manipulator, with a mirrored surfaced attached to the end effector and positioned in the center of rotation.
Drones are increasingly used nowadays, primarily for visual inspection tasks facilitated by onboard cameras. The field of aerial manipulation tries to expand the capabilities of drones by attaching a manipulator, enabling physical interaction. Unfortunately, the usability of aerial manipulators is hindered by disturbances resulting from the movements of the manipulator. These disturbances, including reaction forces and a shifting centre of mass, not only affect manipulation accuracy but also pose safety risks by potentially destabilizing the drone. In this thesis, a design is presented that addresses this challenge by leveraging the theory of dynamic balance.
A new design approach of making a manipulator fly, instead of the common approach of mounting a manipulator arm to a drone was used. This new approach avoids interference with the drone's components, allowing to focus on the design of the manipulator arm. Furthermore, it made it possible to create a manipulator which can manipulate above, to the side and underneath itself. This makes the presented manipulator arm more versatile than common aerial manipulators whose workspace is mostly located only above or below the drone. The kinematics, workspace and balance conditions of the manipulator arm are presented. Furthermore, the design's workspace is optimised while the mass of the manipulator is minimized in a bilevel optimisation. Finally, the design is validated both by simulation and measurements performed with the built prototype.
The design presented is the first inherently fully dynamically balanced manipulator with omnidirectional workspace which can be used for aerial manipulation.
...
A new design approach of making a manipulator fly, instead of the common approach of mounting a manipulator arm to a drone was used. This new approach avoids interference with the drone's components, allowing to focus on the design of the manipulator arm. Furthermore, it made it possible to create a manipulator which can manipulate above, to the side and underneath itself. This makes the presented manipulator arm more versatile than common aerial manipulators whose workspace is mostly located only above or below the drone. The kinematics, workspace and balance conditions of the manipulator arm are presented. Furthermore, the design's workspace is optimised while the mass of the manipulator is minimized in a bilevel optimisation. Finally, the design is validated both by simulation and measurements performed with the built prototype.
The design presented is the first inherently fully dynamically balanced manipulator with omnidirectional workspace which can be used for aerial manipulation.
...
Drones are increasingly used nowadays, primarily for visual inspection tasks facilitated by onboard cameras. The field of aerial manipulation tries to expand the capabilities of drones by attaching a manipulator, enabling physical interaction. Unfortunately, the usability of aerial manipulators is hindered by disturbances resulting from the movements of the manipulator. These disturbances, including reaction forces and a shifting centre of mass, not only affect manipulation accuracy but also pose safety risks by potentially destabilizing the drone. In this thesis, a design is presented that addresses this challenge by leveraging the theory of dynamic balance.
A new design approach of making a manipulator fly, instead of the common approach of mounting a manipulator arm to a drone was used. This new approach avoids interference with the drone's components, allowing to focus on the design of the manipulator arm. Furthermore, it made it possible to create a manipulator which can manipulate above, to the side and underneath itself. This makes the presented manipulator arm more versatile than common aerial manipulators whose workspace is mostly located only above or below the drone. The kinematics, workspace and balance conditions of the manipulator arm are presented. Furthermore, the design's workspace is optimised while the mass of the manipulator is minimized in a bilevel optimisation. Finally, the design is validated both by simulation and measurements performed with the built prototype.
The design presented is the first inherently fully dynamically balanced manipulator with omnidirectional workspace which can be used for aerial manipulation.
A new design approach of making a manipulator fly, instead of the common approach of mounting a manipulator arm to a drone was used. This new approach avoids interference with the drone's components, allowing to focus on the design of the manipulator arm. Furthermore, it made it possible to create a manipulator which can manipulate above, to the side and underneath itself. This makes the presented manipulator arm more versatile than common aerial manipulators whose workspace is mostly located only above or below the drone. The kinematics, workspace and balance conditions of the manipulator arm are presented. Furthermore, the design's workspace is optimised while the mass of the manipulator is minimized in a bilevel optimisation. Finally, the design is validated both by simulation and measurements performed with the built prototype.
The design presented is the first inherently fully dynamically balanced manipulator with omnidirectional workspace which can be used for aerial manipulation.
In this work, we present the ADAPT, a novel reconfigurable force-balanced parallel manipulator with pantograph legs for spatial motions applied underneath a drone. The reconfigurable aspect allows different motion-based 3-DoF operation modes like translational, rotational, mixed, planar without disassembly. For the purpose of this study, the manipulator is used in translation mode only. A kinematic model is developed and validated for the manipulator. The design and motion capabilities are also validated both by conducting dynamics simulations of a simplified model on MSC ADAMS, and experiments on the physical setup.
The force-balanced nature of this novel design decouples the motion of the manipulator’s end-effector from the base, zeroing the reaction forces, making this design ideally suited for aerial manipulation in unmanned aerial vehicles (UAVs) applications, or generic floating-base applications. ...
The force-balanced nature of this novel design decouples the motion of the manipulator’s end-effector from the base, zeroing the reaction forces, making this design ideally suited for aerial manipulation in unmanned aerial vehicles (UAVs) applications, or generic floating-base applications. ...
In this work, we present the ADAPT, a novel reconfigurable force-balanced parallel manipulator with pantograph legs for spatial motions applied underneath a drone. The reconfigurable aspect allows different motion-based 3-DoF operation modes like translational, rotational, mixed, planar without disassembly. For the purpose of this study, the manipulator is used in translation mode only. A kinematic model is developed and validated for the manipulator. The design and motion capabilities are also validated both by conducting dynamics simulations of a simplified model on MSC ADAMS, and experiments on the physical setup.
The force-balanced nature of this novel design decouples the motion of the manipulator’s end-effector from the base, zeroing the reaction forces, making this design ideally suited for aerial manipulation in unmanned aerial vehicles (UAVs) applications, or generic floating-base applications.
The force-balanced nature of this novel design decouples the motion of the manipulator’s end-effector from the base, zeroing the reaction forces, making this design ideally suited for aerial manipulation in unmanned aerial vehicles (UAVs) applications, or generic floating-base applications.
Robotic manipulators are desired to keep their settling time as low as possible for the pick-and-place industry. If the settling time is lower, more cycles can be made, increasing productivity. For high-speed parallel manipulators, a significant vibration cause that increases the settling time is the movable mass and inertia. By dynamic balancing a manipulator, these vibrations can be eliminated. However, balancing a structure relies on adding mass and inertia to movable links, which decreases controllability. This thesis presents 2-DoF inherently dynamically balanced structures that make use of a constant inertia mechanism. Inherently balanced relies on structures that balance themself and do not need active counter-balancing, which is hard to control. A prototype of a 2-DoF, inherently dynamically balanced parallel manipulator is designed and optimized for controllability. By experimental verification, a reduction of 93.6% and 88.9% in shaking force and shaking moment, respectively, compared to the unbalanced case, is obtained for the first DoF and a 97.2% and 93.4% reduction, respectively, for the second DoF. The manipulator had a measured lowest eigenfrequency of 91 Hz and a workspace of about 20 cm. Up to 8 G of tip acceleration was achieved. So fully inherently dynamic balancing can be combined with high accelerations.
...
Robotic manipulators are desired to keep their settling time as low as possible for the pick-and-place industry. If the settling time is lower, more cycles can be made, increasing productivity. For high-speed parallel manipulators, a significant vibration cause that increases the settling time is the movable mass and inertia. By dynamic balancing a manipulator, these vibrations can be eliminated. However, balancing a structure relies on adding mass and inertia to movable links, which decreases controllability. This thesis presents 2-DoF inherently dynamically balanced structures that make use of a constant inertia mechanism. Inherently balanced relies on structures that balance themself and do not need active counter-balancing, which is hard to control. A prototype of a 2-DoF, inherently dynamically balanced parallel manipulator is designed and optimized for controllability. By experimental verification, a reduction of 93.6% and 88.9% in shaking force and shaking moment, respectively, compared to the unbalanced case, is obtained for the first DoF and a 97.2% and 93.4% reduction, respectively, for the second DoF. The manipulator had a measured lowest eigenfrequency of 91 Hz and a workspace of about 20 cm. Up to 8 G of tip acceleration was achieved. So fully inherently dynamic balancing can be combined with high accelerations.
The compliance (stiffness) of a human arm varies, depending on the task at hand. Some precise tasks require high stiffness, while others need a level of flexibility to deal with unknown disturbances. To describe this human behaviour a portable device is needed to give small force perturbations (input) while the resulting reaction of the arm (output) is measured. There are multiple state-of-the-art devices to choose from to provide such input. However, the majority of these devices either offer too little versatility or impede the free movement of the user. Implementation of a novel parallel mechanism allows for a lightweight (0.175kg) and compact device that can generate various signals in three degrees-of-freedom. Since the device is designed to be mounted around the wrist, it leaves your arm and hand unobstructed. A full-scale prototype is constructed and the concept is tested using a force sensor. Implementing powerful yet compact servo motors allows for controlled perturbations in the order of 4N, with bandwidths up to 12Hz.
...
The compliance (stiffness) of a human arm varies, depending on the task at hand. Some precise tasks require high stiffness, while others need a level of flexibility to deal with unknown disturbances. To describe this human behaviour a portable device is needed to give small force perturbations (input) while the resulting reaction of the arm (output) is measured. There are multiple state-of-the-art devices to choose from to provide such input. However, the majority of these devices either offer too little versatility or impede the free movement of the user. Implementation of a novel parallel mechanism allows for a lightweight (0.175kg) and compact device that can generate various signals in three degrees-of-freedom. Since the device is designed to be mounted around the wrist, it leaves your arm and hand unobstructed. A full-scale prototype is constructed and the concept is tested using a force sensor. Implementing powerful yet compact servo motors allows for controlled perturbations in the order of 4N, with bandwidths up to 12Hz.
The moving parts in a mechanical device often rely on rolling or sliding contacts such as in ball bearings to gain motion. These suffice in many applications, but the friction inherent to their working principle limits their motion repeatability and thereby their precision. Flexure mechanisms are a popular alternative in the field of precision engineering because they gain motion by elastic deformation of slender segments such as thin spring steel plates, resulting in a highly repeatable motion due to the absence of friction and play. Furthermore, they are lubricant-free and do not generate particles, which makes them suitable for applications in space, astronomy, the semiconductor industry, and healthcare. A drawback of flexure mechanisms is their limited range of motion compared to their build volume, which results in voluminous designs and which limits their application field. Their range is limited by material stress but also because at large displacements the stiffness in their support directions decreases significantly, and their actuation effort increases at large deflections, resulting in high energy consumption and heat generation. Increasing the motion range would highly benefit the field of precision engineering and could also lead to innovations in healthcare or space. The motivation for this thesis is the observation that the vast majority of flexure mechanisms consist of initially straight and stress-free flexures. Recent developments in fabrication methods such as the additive manufacturing of steel are providing the possibility to create more complex shapes, which could improve the range of motion of flexure mechanisms. The objective of this thesis is to provide design strategies to increase the motion range of flexure mechanisms. The thesis consists of two parts, of which the first (chapters 2-4) focuses on a new method to design stressed and curved flexures. The second part (chapters 5 and 6) further develops a recent strategy to increase the range of motion using torsion reinforcement structures.
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The moving parts in a mechanical device often rely on rolling or sliding contacts such as in ball bearings to gain motion. These suffice in many applications, but the friction inherent to their working principle limits their motion repeatability and thereby their precision. Flexure mechanisms are a popular alternative in the field of precision engineering because they gain motion by elastic deformation of slender segments such as thin spring steel plates, resulting in a highly repeatable motion due to the absence of friction and play. Furthermore, they are lubricant-free and do not generate particles, which makes them suitable for applications in space, astronomy, the semiconductor industry, and healthcare. A drawback of flexure mechanisms is their limited range of motion compared to their build volume, which results in voluminous designs and which limits their application field. Their range is limited by material stress but also because at large displacements the stiffness in their support directions decreases significantly, and their actuation effort increases at large deflections, resulting in high energy consumption and heat generation. Increasing the motion range would highly benefit the field of precision engineering and could also lead to innovations in healthcare or space. The motivation for this thesis is the observation that the vast majority of flexure mechanisms consist of initially straight and stress-free flexures. Recent developments in fabrication methods such as the additive manufacturing of steel are providing the possibility to create more complex shapes, which could improve the range of motion of flexure mechanisms. The objective of this thesis is to provide design strategies to increase the motion range of flexure mechanisms. The thesis consists of two parts, of which the first (chapters 2-4) focuses on a new method to design stressed and curved flexures. The second part (chapters 5 and 6) further develops a recent strategy to increase the range of motion using torsion reinforcement structures.
Cable Driven Parallel Robots, or CDPRs, might provide art historians and curators with an improved automated way of scanning 3D art objects. This application requires CDPRs to rotate around a 3D object with large panning and tilting, while avoiding collisions. While no designs exist for this purpose, this article investigates and proposes new cable robot geometries. First, we built a workspace model to quantify the performance of a design. A brainstorm and the ACCREx method then provided us with over 100 promising robot architectures. Their subsequent testing with the workspace model revealed the nine most promising architectures. Lastly, a geometry optimization resulted in the most favourable CDPR geometries. It appeared that mainly cable force limits, cable-statue and platform-statue collision are limiting the workspace of the CDPRs. In the end, the best enclosing and non-enclosing design are capable of reaching 29% and 16% respectively of the required 180 degrees workspace around the statue. Without extra panning and tilting these percentages are 79% and 66% respectively. Both designs show to which extend a statue can be scanned by a CDPR from one configuration.
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Cable Driven Parallel Robots, or CDPRs, might provide art historians and curators with an improved automated way of scanning 3D art objects. This application requires CDPRs to rotate around a 3D object with large panning and tilting, while avoiding collisions. While no designs exist for this purpose, this article investigates and proposes new cable robot geometries. First, we built a workspace model to quantify the performance of a design. A brainstorm and the ACCREx method then provided us with over 100 promising robot architectures. Their subsequent testing with the workspace model revealed the nine most promising architectures. Lastly, a geometry optimization resulted in the most favourable CDPR geometries. It appeared that mainly cable force limits, cable-statue and platform-statue collision are limiting the workspace of the CDPRs. In the end, the best enclosing and non-enclosing design are capable of reaching 29% and 16% respectively of the required 180 degrees workspace around the statue. Without extra panning and tilting these percentages are 79% and 66% respectively. Both designs show to which extend a statue can be scanned by a CDPR from one configuration.
Master thesis
(2021)
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P.I. van der Stigchel, V. van der Wijk, P.T. Tempel, J.L. Herder, M.W.E.M. Alfeld
In cable driven parallel robots (CDPRs), the end effector or moving platform is actuated by multiple cables in parallel that are wound on winches, which are located on a frame. Compared to classical parallel robots, such as the Delta robot, CDPRs have a lower inertia due to low cable masses. Therefore, they can perform high speed motions with a low power consumption. Additionally, the workspace of a CDPR is easily scalable as the cable lengths are hardly limited. Consequently, the CDPRs can potentially improve efficiency and reduce the cost of high speed pick and place operations, which are now often carried out by Delta robots. However, CDPRs have not yet been applied in the high speed pick and place industry. One of the reasons that CDPRs are not yet attractive for this industry is their limited orientation range. In pick and place applications it is often required to not only translate a product, but also reorient it about one axis for proper packaging. This motion is also known as a Schönflies motion. For full product reorientation, a rotation of 180 degrees is required, which can only be achieved with an additional axis on the moving platform. Several solutions for large rotations of CDPRs exist in literature, but none of them are designed, compared, modelled or tested for dynamic purposes. Therefore, this thesis proposes three concept designs of CDPRs that can perform a Schönflies motion, including a rotation of 180 degrees. These concept designs are compared with each other and on a state of the art Delta robot, based on their dynamic workspace. The dynamic workspace volume of each concept is optimized for their geometric parameters by the particle swarm algorithm, which showed that the concept that uses a cable loop to perform the rotation has the largest workspace for the smallest cable forces. Additionally, a prototype of this concept has been evaluated on a typical pick and place motion, which shows the feasibility of this concept. Nonetheless, stiffness should improve to reach the state of the art repeatability in future designs.
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In cable driven parallel robots (CDPRs), the end effector or moving platform is actuated by multiple cables in parallel that are wound on winches, which are located on a frame. Compared to classical parallel robots, such as the Delta robot, CDPRs have a lower inertia due to low cable masses. Therefore, they can perform high speed motions with a low power consumption. Additionally, the workspace of a CDPR is easily scalable as the cable lengths are hardly limited. Consequently, the CDPRs can potentially improve efficiency and reduce the cost of high speed pick and place operations, which are now often carried out by Delta robots. However, CDPRs have not yet been applied in the high speed pick and place industry. One of the reasons that CDPRs are not yet attractive for this industry is their limited orientation range. In pick and place applications it is often required to not only translate a product, but also reorient it about one axis for proper packaging. This motion is also known as a Schönflies motion. For full product reorientation, a rotation of 180 degrees is required, which can only be achieved with an additional axis on the moving platform. Several solutions for large rotations of CDPRs exist in literature, but none of them are designed, compared, modelled or tested for dynamic purposes. Therefore, this thesis proposes three concept designs of CDPRs that can perform a Schönflies motion, including a rotation of 180 degrees. These concept designs are compared with each other and on a state of the art Delta robot, based on their dynamic workspace. The dynamic workspace volume of each concept is optimized for their geometric parameters by the particle swarm algorithm, which showed that the concept that uses a cable loop to perform the rotation has the largest workspace for the smallest cable forces. Additionally, a prototype of this concept has been evaluated on a typical pick and place motion, which shows the feasibility of this concept. Nonetheless, stiffness should improve to reach the state of the art repeatability in future designs.
In mechanisms and machines, elements' motions can generate reaction forces and moments on the base of the mechanism, which are called shaking forces and shaking moments. These induce vibrations of the base, which create noise, wear and fatigue problems and reduce the accuracy of the systems. Dynamic balancing is a solution to eliminate these reaction forces and moments by generally introducing additional counterweights and counter-rotating elements. Mechanisms having zero shaking forces and moments are called, respectively, force balanced and moment balanced. Dynamically balanced mechanisms are both force and moment balanced. Since the introduction of additional elements increases the total mass and inertia of the mechanisms, the method of inherent dynamic balancing aims at designing dynamically balanced mechanisms which do not include additional elements. By considering dynamic balance as a design principle, all the links contribute to both the motion and the balance of the mechanisms. These are called inherently dynamically balanced mechanisms and can be synthesized from inherently force balanced linkage architectures, which are based on principal vectors. However, the design of these architectures consists in parallelogram linkages which can potentially compromise the force balance when their links become collinear. In addition, links can overlap and represent a potential limitation in real applications. This thesis presents techniques which modify the linkage architectures and can prevent the potential issues related to their original design. The number of degrees of freedom can be reduced and specific motions can be created by constraining links’ rotations and translations. Moreover, parallelograms’ sizes can be modified and links can be replaced by machine elements like sliders, gears, belt and chain drives. It will be shown how force balance is maintained after having modified the linkage architectures.
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In mechanisms and machines, elements' motions can generate reaction forces and moments on the base of the mechanism, which are called shaking forces and shaking moments. These induce vibrations of the base, which create noise, wear and fatigue problems and reduce the accuracy of the systems. Dynamic balancing is a solution to eliminate these reaction forces and moments by generally introducing additional counterweights and counter-rotating elements. Mechanisms having zero shaking forces and moments are called, respectively, force balanced and moment balanced. Dynamically balanced mechanisms are both force and moment balanced. Since the introduction of additional elements increases the total mass and inertia of the mechanisms, the method of inherent dynamic balancing aims at designing dynamically balanced mechanisms which do not include additional elements. By considering dynamic balance as a design principle, all the links contribute to both the motion and the balance of the mechanisms. These are called inherently dynamically balanced mechanisms and can be synthesized from inherently force balanced linkage architectures, which are based on principal vectors. However, the design of these architectures consists in parallelogram linkages which can potentially compromise the force balance when their links become collinear. In addition, links can overlap and represent a potential limitation in real applications. This thesis presents techniques which modify the linkage architectures and can prevent the potential issues related to their original design. The number of degrees of freedom can be reduced and specific motions can be created by constraining links’ rotations and translations. Moreover, parallelograms’ sizes can be modified and links can be replaced by machine elements like sliders, gears, belt and chain drives. It will be shown how force balance is maintained after having modified the linkage architectures.
Bicycle simulator research has been the subject of considerable research, however, few of these attempts have integrated direct balance control and enough freedom of motion to deliver a real-world kinematic cycling experience. In this study, the B.I.K.E. (Bicycle Intrinsic Kinematics Emulator) system, a kinematic bicycle simulator, is developed with the purpose of letting its users experience realistic kinematic motion, which are: steer, roll, yaw and sway motions. This study validates the developed simulator by performing a kinematic comparison of bicycle motion among 15 participants of varying age and mass, and performs an initial subjective study to investigate effects common to indoor vehicle simulation. Manoeuvres performed by the participants are straight-line cycling, at low (5 km/h) to high (40 km/h) velocities, as well as performing a zig-zagging motion. The results show that users can successfully rely on existing bicycle skills to use the simulator. They also show that, in the kinematic sense, the simulator performs similarly to an outdoor bicycle, particularly at velocities below 35 km/h, but more work is needed in improving the vehicle model and control algorithm to accurately cover low to high-velocity cycling. Subjectively speaking, the simulator performs better than existing static solutions, but more work will be required to make the riding experience feel like real outdoor cycling.
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Bicycle simulator research has been the subject of considerable research, however, few of these attempts have integrated direct balance control and enough freedom of motion to deliver a real-world kinematic cycling experience. In this study, the B.I.K.E. (Bicycle Intrinsic Kinematics Emulator) system, a kinematic bicycle simulator, is developed with the purpose of letting its users experience realistic kinematic motion, which are: steer, roll, yaw and sway motions. This study validates the developed simulator by performing a kinematic comparison of bicycle motion among 15 participants of varying age and mass, and performs an initial subjective study to investigate effects common to indoor vehicle simulation. Manoeuvres performed by the participants are straight-line cycling, at low (5 km/h) to high (40 km/h) velocities, as well as performing a zig-zagging motion. The results show that users can successfully rely on existing bicycle skills to use the simulator. They also show that, in the kinematic sense, the simulator performs similarly to an outdoor bicycle, particularly at velocities below 35 km/h, but more work is needed in improving the vehicle model and control algorithm to accurately cover low to high-velocity cycling. Subjectively speaking, the simulator performs better than existing static solutions, but more work will be required to make the riding experience feel like real outdoor cycling.
In aerial manipulation, Unmanned Aerial Vehicles (UAVs) are equipped with manipulators to perform a variety of tasks such as inspections of critical infrastructure at heights. A fundamental issue is that the shaking forces and moments of the manipulator cause the UAV to tip-over and become unstable. Control based methods have been applied in which the UAV provided a compensation force or moment at the propellers. However, the dynamic model required was too complex to compute on-board in real time and simplifications led to poor performance. This thesis resolves the issue of shaking forces and moments by creating a new manipulator using inherent dynamic balancing principles. The advantage of these principles is that the manipulator architecture achieves both functions of supporting and positioning the end effector as well as balancing. This helps to reduce the weight of the manipulator. The result of the synthesis work is a manipulator which is reactionless, lightweight, has 3 degrees of freedom, and is compatible with a UAV. First a manipulator is designed using inherently force balanced architectures. Next, active moment balancing is developed through a novel control scheme. Finally, a simulation is performed to prove the dynamic balancing and control method. It shows the manipulator is reactionless. However, the control scheme’s tracking still needs improvement. This work is useful to enable UAVs with manipulators to perform a variety of tasks such as inspections of surfaces at height.
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In aerial manipulation, Unmanned Aerial Vehicles (UAVs) are equipped with manipulators to perform a variety of tasks such as inspections of critical infrastructure at heights. A fundamental issue is that the shaking forces and moments of the manipulator cause the UAV to tip-over and become unstable. Control based methods have been applied in which the UAV provided a compensation force or moment at the propellers. However, the dynamic model required was too complex to compute on-board in real time and simplifications led to poor performance. This thesis resolves the issue of shaking forces and moments by creating a new manipulator using inherent dynamic balancing principles. The advantage of these principles is that the manipulator architecture achieves both functions of supporting and positioning the end effector as well as balancing. This helps to reduce the weight of the manipulator. The result of the synthesis work is a manipulator which is reactionless, lightweight, has 3 degrees of freedom, and is compatible with a UAV. First a manipulator is designed using inherently force balanced architectures. Next, active moment balancing is developed through a novel control scheme. Finally, a simulation is performed to prove the dynamic balancing and control method. It shows the manipulator is reactionless. However, the control scheme’s tracking still needs improvement. This work is useful to enable UAVs with manipulators to perform a variety of tasks such as inspections of surfaces at height.
In the ever developing world that we live in, machines perform their task faster, better, more precise, cheaper, etc. every year. The improvements in a lot of mechanisms are inspired by the natural behavior of animals and humans. While falling off a balance beam, the human instinct let an arm or leg accelerate in the opposite direction of the fall to find balance. The principle that the vestibular system and muscles work together to keep the body static and dynamic actively balanced works quite well. Although, making a coloring page on a roller coaster is a challenge for the control system of the human body. Nowadays, mechanisms in the world around us are desired to perform even better than the human is doing.
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In the ever developing world that we live in, machines perform their task faster, better, more precise, cheaper, etc. every year. The improvements in a lot of mechanisms are inspired by the natural behavior of animals and humans. While falling off a balance beam, the human instinct let an arm or leg accelerate in the opposite direction of the fall to find balance. The principle that the vestibular system and muscles work together to keep the body static and dynamic actively balanced works quite well. Although, making a coloring page on a roller coaster is a challenge for the control system of the human body. Nowadays, mechanisms in the world around us are desired to perform even better than the human is doing.
In robotics, machine elements are accelerated in order for the machine to perform certain tasks, such as picking and placing objects. These accelerations result in inertia forces and inertia torques on the machine elements and on the base of the machine. These reaction forces and reaction torques on the base are called shaking forces and shaking moments. Shaking forces and shaking moments result in noise, vibration, wear and fatigue problems. Dynamic balancing eliminates shaking forces and shaking moments on the base, which results in low cycle times and high accuracy. However, the process of balancing a mechanism generally increases the masses, the moments of inertia, and the complexity of the mechanism.
The method of inherent dynamic balance aims at minimizing these drawbacks by considering the balancing prior to the kinematic synthesis. With the method of principal vectors, a large number of inherently shaking force balanced mechanisms has been found. However, the options for shaking moment balanced mechanisms are still limited.
In this thesis, an overview of current dynamic balancing methods is presented, along with a new method for the synthesis of inherently moment balanced mechanisms. This new method is used for the synthesis of inherently dynamically balanced 1-DoF pantographic linkages, where the desired motion of the end-effector is selected by the designer. This motion is defined as a set of precision positions. For this new method, the known method for RR chain synthesis from Burmester’s theory is combined with the shaking moment balancing condition. For the special case where the relationship between link angular velocities is linear, the shaking moment balancing condition is substituted into the RR chain design equation. For the general case where the relation between link angular velocities is non-linear, the equation of motion is numerically solved for a range of possible solutions in order to find the solution which reproduces the desired motion.
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The method of inherent dynamic balance aims at minimizing these drawbacks by considering the balancing prior to the kinematic synthesis. With the method of principal vectors, a large number of inherently shaking force balanced mechanisms has been found. However, the options for shaking moment balanced mechanisms are still limited.
In this thesis, an overview of current dynamic balancing methods is presented, along with a new method for the synthesis of inherently moment balanced mechanisms. This new method is used for the synthesis of inherently dynamically balanced 1-DoF pantographic linkages, where the desired motion of the end-effector is selected by the designer. This motion is defined as a set of precision positions. For this new method, the known method for RR chain synthesis from Burmester’s theory is combined with the shaking moment balancing condition. For the special case where the relationship between link angular velocities is linear, the shaking moment balancing condition is substituted into the RR chain design equation. For the general case where the relation between link angular velocities is non-linear, the equation of motion is numerically solved for a range of possible solutions in order to find the solution which reproduces the desired motion.
...
In robotics, machine elements are accelerated in order for the machine to perform certain tasks, such as picking and placing objects. These accelerations result in inertia forces and inertia torques on the machine elements and on the base of the machine. These reaction forces and reaction torques on the base are called shaking forces and shaking moments. Shaking forces and shaking moments result in noise, vibration, wear and fatigue problems. Dynamic balancing eliminates shaking forces and shaking moments on the base, which results in low cycle times and high accuracy. However, the process of balancing a mechanism generally increases the masses, the moments of inertia, and the complexity of the mechanism.
The method of inherent dynamic balance aims at minimizing these drawbacks by considering the balancing prior to the kinematic synthesis. With the method of principal vectors, a large number of inherently shaking force balanced mechanisms has been found. However, the options for shaking moment balanced mechanisms are still limited.
In this thesis, an overview of current dynamic balancing methods is presented, along with a new method for the synthesis of inherently moment balanced mechanisms. This new method is used for the synthesis of inherently dynamically balanced 1-DoF pantographic linkages, where the desired motion of the end-effector is selected by the designer. This motion is defined as a set of precision positions. For this new method, the known method for RR chain synthesis from Burmester’s theory is combined with the shaking moment balancing condition. For the special case where the relationship between link angular velocities is linear, the shaking moment balancing condition is substituted into the RR chain design equation. For the general case where the relation between link angular velocities is non-linear, the equation of motion is numerically solved for a range of possible solutions in order to find the solution which reproduces the desired motion.
The method of inherent dynamic balance aims at minimizing these drawbacks by considering the balancing prior to the kinematic synthesis. With the method of principal vectors, a large number of inherently shaking force balanced mechanisms has been found. However, the options for shaking moment balanced mechanisms are still limited.
In this thesis, an overview of current dynamic balancing methods is presented, along with a new method for the synthesis of inherently moment balanced mechanisms. This new method is used for the synthesis of inherently dynamically balanced 1-DoF pantographic linkages, where the desired motion of the end-effector is selected by the designer. This motion is defined as a set of precision positions. For this new method, the known method for RR chain synthesis from Burmester’s theory is combined with the shaking moment balancing condition. For the special case where the relationship between link angular velocities is linear, the shaking moment balancing condition is substituted into the RR chain design equation. For the general case where the relation between link angular velocities is non-linear, the equation of motion is numerically solved for a range of possible solutions in order to find the solution which reproduces the desired motion.
High accelerations in unbalanced robotic manipulators can induce significant base vibrations, which reduces precision and increases settling time. These vibrations are caused by fluctuating reaction forces and reaction moments exerted on the base by the manipulator. Dynamic balancing eliminates these fluctuations and therefore improves performance. However, dynamic balancing, in general, comes at the cost of additional moving mass in the manipulator, which reduces controllability. Combining balancing with optimal controllability therefore requires an integral design approach. In this thesis, the controllability of multiple balancing principles are compared. Based on these findings a design for a balanced rotatable link will be presented, which aims to combine dynamic balancing with optimal controllability. Experimental verification of the balanced design showed a reduction of 99.3% in reaction forces and 97.8% in reaction moments compared to the unbalanced mechanism. Transverse tip accelerations up to 21 G are achieved in experiments, showing the potential for high acceleration applications.
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High accelerations in unbalanced robotic manipulators can induce significant base vibrations, which reduces precision and increases settling time. These vibrations are caused by fluctuating reaction forces and reaction moments exerted on the base by the manipulator. Dynamic balancing eliminates these fluctuations and therefore improves performance. However, dynamic balancing, in general, comes at the cost of additional moving mass in the manipulator, which reduces controllability. Combining balancing with optimal controllability therefore requires an integral design approach. In this thesis, the controllability of multiple balancing principles are compared. Based on these findings a design for a balanced rotatable link will be presented, which aims to combine dynamic balancing with optimal controllability. Experimental verification of the balanced design showed a reduction of 99.3% in reaction forces and 97.8% in reaction moments compared to the unbalanced mechanism. Transverse tip accelerations up to 21 G are achieved in experiments, showing the potential for high acceleration applications.
Compliant Manipulator Design method
Applied for designing a 4-DoF manipulator with a TTTR-motion
Current multi-DoF compliant manipulators are still rarely implemented in the industry because their range of motion (ROM) is limited as their designs are heavy and bulky or obtained by a serial set of multiple stacked flexure systems, which limits their compactness. The goal of this article is to overcome these limitations by considering them as an integrated multi-DoF compliant joint, either serial or parallel, and setting up a new method the Compliant Manipulator Design (COMAD)-method and investigate its performance. This method will combine the "Type synthesis of legs"-technique to include parallel kinematic solutions for the desired motion pattern whereafter the complete compliant solution space is obtained using the FACT-method. The method is applied for designing a 4-DoF-manipulator with a TTTR-motion pattern resulting in four new concepts composed of compactly aggregated wire flexures. After the concept selection, a demonstrator is manufactured which excellently possesses four decoupled motions with a relatively large ROM. This can be seen as a new milestone for designing multi-DoF compliant manipulators as it permits a larger ROM and better stiffness capabilities than those obtained from conventional methods because all compliant topologies are deflecting in series due to the parallel kinematic couplings within the multi-DoF flexure systems.
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Current multi-DoF compliant manipulators are still rarely implemented in the industry because their range of motion (ROM) is limited as their designs are heavy and bulky or obtained by a serial set of multiple stacked flexure systems, which limits their compactness. The goal of this article is to overcome these limitations by considering them as an integrated multi-DoF compliant joint, either serial or parallel, and setting up a new method the Compliant Manipulator Design (COMAD)-method and investigate its performance. This method will combine the "Type synthesis of legs"-technique to include parallel kinematic solutions for the desired motion pattern whereafter the complete compliant solution space is obtained using the FACT-method. The method is applied for designing a 4-DoF-manipulator with a TTTR-motion pattern resulting in four new concepts composed of compactly aggregated wire flexures. After the concept selection, a demonstrator is manufactured which excellently possesses four decoupled motions with a relatively large ROM. This can be seen as a new milestone for designing multi-DoF compliant manipulators as it permits a larger ROM and better stiffness capabilities than those obtained from conventional methods because all compliant topologies are deflecting in series due to the parallel kinematic couplings within the multi-DoF flexure systems.
Design for additive manufacturing of decoupled compliant mechanisms
With an example of a monolithic adjustable mount
Master thesis
(2017)
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Marleen Meeuwsen, Winfred Mugge, Jantsje Pasma, Alfred Schouten, John van den Dobbelsteen, Volkert van der Wijk
Implementation of perturbation training for elderly requires a validated measure to quantify someone’s ability to recover
when encountering a perturbation. A quantified recovery performance has been constructed for the anteroposterior
(QRPAP) and for mediolateral (QRPML) plane, the QRPAP and QRPML reflect the amount of deviation of the center of
pressure trajectory from the unperturbed walking pattern. The QRPAP and QRPML were calculated for eleven elderly
subjects (>65 years), who experienced 66 perturbations (accelerations and decelerations) during treadmill walking.
The constructed QRPAP and QRPML were validated in this study (1) by comparing them to the rated recovery performance
(RRT) as provided by physiotherapists and (2) by studying how they were affected by an increased specified
difficulty (SpD) of perturbations. The used perturbation characteristics for the SpD’s were validated with the perceived
difficulty (PD) as reported by the subjects for each perturbation. A positive relation confirmed the increase of PD with
an increase of SpD. Both for the QRPAP and the QRPML a positive relation was found with the RRP and a negative relation
was found with the SpD. The QRPAP showed a stronger relation with the RRP and was found to be more sensitive
when compared to the QRPML. The relation of the QRPAP with the RRP was consistent across physiotherapists. Implementation of the QRPAP during perturbation training will decrease the attention demanded of physiotherapists and will remove the offset observed across physiotherapists. Progress can be monitored objectively and training difficulty can
be adjusted accordingly. ...
when encountering a perturbation. A quantified recovery performance has been constructed for the anteroposterior
(QRPAP) and for mediolateral (QRPML) plane, the QRPAP and QRPML reflect the amount of deviation of the center of
pressure trajectory from the unperturbed walking pattern. The QRPAP and QRPML were calculated for eleven elderly
subjects (>65 years), who experienced 66 perturbations (accelerations and decelerations) during treadmill walking.
The constructed QRPAP and QRPML were validated in this study (1) by comparing them to the rated recovery performance
(RRT) as provided by physiotherapists and (2) by studying how they were affected by an increased specified
difficulty (SpD) of perturbations. The used perturbation characteristics for the SpD’s were validated with the perceived
difficulty (PD) as reported by the subjects for each perturbation. A positive relation confirmed the increase of PD with
an increase of SpD. Both for the QRPAP and the QRPML a positive relation was found with the RRP and a negative relation
was found with the SpD. The QRPAP showed a stronger relation with the RRP and was found to be more sensitive
when compared to the QRPML. The relation of the QRPAP with the RRP was consistent across physiotherapists. Implementation of the QRPAP during perturbation training will decrease the attention demanded of physiotherapists and will remove the offset observed across physiotherapists. Progress can be monitored objectively and training difficulty can
be adjusted accordingly. ...
Implementation of perturbation training for elderly requires a validated measure to quantify someone’s ability to recover
when encountering a perturbation. A quantified recovery performance has been constructed for the anteroposterior
(QRPAP) and for mediolateral (QRPML) plane, the QRPAP and QRPML reflect the amount of deviation of the center of
pressure trajectory from the unperturbed walking pattern. The QRPAP and QRPML were calculated for eleven elderly
subjects (>65 years), who experienced 66 perturbations (accelerations and decelerations) during treadmill walking.
The constructed QRPAP and QRPML were validated in this study (1) by comparing them to the rated recovery performance
(RRT) as provided by physiotherapists and (2) by studying how they were affected by an increased specified
difficulty (SpD) of perturbations. The used perturbation characteristics for the SpD’s were validated with the perceived
difficulty (PD) as reported by the subjects for each perturbation. A positive relation confirmed the increase of PD with
an increase of SpD. Both for the QRPAP and the QRPML a positive relation was found with the RRP and a negative relation
was found with the SpD. The QRPAP showed a stronger relation with the RRP and was found to be more sensitive
when compared to the QRPML. The relation of the QRPAP with the RRP was consistent across physiotherapists. Implementation of the QRPAP during perturbation training will decrease the attention demanded of physiotherapists and will remove the offset observed across physiotherapists. Progress can be monitored objectively and training difficulty can
be adjusted accordingly.
when encountering a perturbation. A quantified recovery performance has been constructed for the anteroposterior
(QRPAP) and for mediolateral (QRPML) plane, the QRPAP and QRPML reflect the amount of deviation of the center of
pressure trajectory from the unperturbed walking pattern. The QRPAP and QRPML were calculated for eleven elderly
subjects (>65 years), who experienced 66 perturbations (accelerations and decelerations) during treadmill walking.
The constructed QRPAP and QRPML were validated in this study (1) by comparing them to the rated recovery performance
(RRT) as provided by physiotherapists and (2) by studying how they were affected by an increased specified
difficulty (SpD) of perturbations. The used perturbation characteristics for the SpD’s were validated with the perceived
difficulty (PD) as reported by the subjects for each perturbation. A positive relation confirmed the increase of PD with
an increase of SpD. Both for the QRPAP and the QRPML a positive relation was found with the RRP and a negative relation
was found with the SpD. The QRPAP showed a stronger relation with the RRP and was found to be more sensitive
when compared to the QRPML. The relation of the QRPAP with the RRP was consistent across physiotherapists. Implementation of the QRPAP during perturbation training will decrease the attention demanded of physiotherapists and will remove the offset observed across physiotherapists. Progress can be monitored objectively and training difficulty can
be adjusted accordingly.