Optimal settings and designs for prosthetic parameters, such as knee stiffness, are required to achieve effective and stable sit-to-stand (STS) movements for individuals with lower limb prostheses but remain inadequately defined. One possible solution is prosthetic modeling and predictive simulations. However, current literature primarily focuses on inverse kinematics, inverse dynamics, and most likely, gait. There remains a gap in optimizing the parameters during STS movement through predictive simulation. By utilizing SCONE (Simulated Controller OptimizatioN Environment for predictive simulating), this study aims to find the optimized prosthetic parameters and investigate the effect of varying transfemoral prosthetic knee joint stiffness on biomechanics and validate this approach. A modified musculoskeletal model with a prosthesis and neuromuscular controllers are combined for predictive sit-to-stand simulation. The control parameters for neuromuscular controllers and the prosthetic parameters are optimized by SCONE with predefined objective functions to obtain energy-oriented results. The simulation results were analyzed in terms of joint load, stability, kinematics, and energy cost. Lastly, the results were validated by comparison with an existing experimental dataset. The simulations indicated that prosthetic knee stiffness affects joint loads, stability, kinematics, and energy expenditure during STS movements. Higher knee stiffness generally leads to increased prosthetic side joint loads and contribution but requires higher damping ratios to ensure a successful STS movement, while extreme stiffness should be avoided. Optimal stiffness settings were identified near 70 Nm/rad with the damping ratio of 22 Nms/rad. Validation shows the feasibility of this approach as well as its limitations. This study demonstrates the potential and insights of predictive simulations in optimizing prosthetic knee parameters. However, the current approach is limited by the model, methodological, theoretical, and practical issues. Therefore, further validation and refinement are necessary. Future work may focus on building complex and customized models and exploring other movements. ... Read more

Rehabilitation following a stroke plays a crucial role in functional recovery and the regaining of independence. Advanced rehabilitation robots such as the Lokomat, C-mill, Rysen, and ZeroG have become integral tools for gait rehabilitation. The MATE (Minimally Actuated Tendon-based Exercise Environment) is a novel rehabilitation device that could offer a wider range of motion compared to the Lokomat while providing support for leg movement, unlike the C-Mill, Rysen, and ZeroG. However, initial testing on the MATE indicated that this passive tendon-based rehabilitation device lacks a proper connection to the wearer. Consequently, this study was conducted to design and evaluate an attachment model, ensuring that the pulling forces are comfortably transferred to the body and that the MATE fulfills its purpose of supporting and enhancing the natural gait. The study compared two user-centred attachment designs based on user experience, comfort, usability, acceptance, ability to follow the natural gait, and the difference in pulling forces on the legs. The findings revealed that the bandage design exerted greater control over the legs, while the cuff design provided more guidance. Additionally, it was observed that adhering to the user’s natural gait greatly influenced comfort and that walking with the MATE became easier with practice. Although the bandage design was preferred, the results suggest further iterations to enhance gait support, comfort, and usability. ... Read more

Falling remains a large source of (traumatic) injuries and healthcare costs. Over the past years, different actuators have been developed in the field of wearable robotics to help prevent injuries from falling. To increase the wearability of these systems, the weight of power storage can be decreased with intermittent instead of continuous control. A fall detector is then needed for these systems to trigger the activation of the actuator to prevent the fall. A proof of concept for a model-based fall detector that is aimed at using only wearable sensor measurements is presented. The algorithm is based on a single inertial measurement unit placed on the lower back. The upper-body orientation and centre of mass velocity are estimated with two separate Kalman filters. The velocity is estimated with a gait model consisting of a spring-damper-legged point mass in three-dimensional space. The balance of the subject is evaluated with the velocity estimates and the extrapolated centre of mass method. The presented model is verified on a non-falling treadmill walking dataset of real humans and shows accurate estimates of the centre of mass velocity. Furthermore, a planar falling simulation is performed to show successful pre-impact fall detection. This resulted in no false alarms outside the initial estimation settling time, and a successful detection with a lead time of 680 ms. This lead time is long enough to provide a trigger for fall mitigation devices. ... Read more

This study introduces a new design for the drivetrain of a robotic ball. An application for the robotic ball is a rehabilitation device for young children. With these children, movement can be stimulated in a more intuitive way when a robotic ball is used compared to other training programs. Since the ball will be kicked and played with, an important requirement is the ability to handle multiple impacts, i.e. the ball is impact-resistant. Additional requirements are the ability to roll like a normal ball (the center of gravity is in the center of the ball) and maintain low weight and cost. The final design is found through iterative testing and shape optimization of the individual components. The impact resistance of the final design is met by protecting from torque overload and the possibility of absorbing shocks, however, the latter still requires testing to confirm the drivetrain's impact resistance. The proposed design successfully fulfills the size and weight requirements for implementation in a robotic ball, representing a promising step toward creating a robotic ball with enhanced impact resistance. A subject for future research remains the development of the complete robotic ball, with a shell and suspension mechanism. ... Read more

A new type of mobility device that functions as both a walker and a scooter is being developed to address some issues of current mobility solutions. Some key design parameters for the scooter mode of this scooter-walker hybrid must be optimized. Through literature, a number of simulated "tests", mostly about safety and manoeuvrability, are developed, and 2100 different possible configurations for the device are generated, with each configuration being rated on the performance for each test using the Analytic Hierarchy Process. Some design parameters tend to affect the test outcomes more, particularly the width of the front of the device and the length. In general, larger dimensions lead to a higher stability, but a lower manoeuvrability. A set of optimized key design parameters is identified, but the methodological framework developed is a useful tool by itself as well. ... Read more

This thesis investigates the behavior of an elastomer spherical structure compressed by a small object compared to the cross-section of the structure. The study is based on the situation in which a child catches a ball multiple times with two hands. This was simplified to a situation where a hemisphere was cyclically compressed by a small object. The elastomer chosen was the cured resin Elastic 50A, which is manufactured by Formlabs. Stereo lithography was used to print the investigated structures. Layer-by-layer printing introduced the ability to print the same structure with different layering. Elastomers and rubbers cannot be described by a linear material model. Therefore, the non-linear behavior of the elastomer was obtained experimentally. Material behavior was described by performing a uni-axial tensile test with dumbbell specimens printed in three different directions according to ASTM D412. The dumbbell specimens were printed in the x-, y- and z-directions, representing upright, lateral and supine positions. A comparison between the specimen force-deflection responses and the finite-element analysis(FEA) responses showed that different models performed best for different print directions. Ansys Mechanical was used to calibrate the hyper-elastic material models available to describe a material with a single uni-axial test. The curve fitting tool of Ansys was used to acquire the Arruda-Boyce, Gent and Yeoh model constants. The 2nd-order Yeoh model performed best for the x-direction printed specimen. The 1st-order Yeoh model performed best for the y- and z-direction printed specimen. These models were used in the finite-element analysis on the elastomer hemispheres. The hemispheres were printed in the y- and z- direction, representing the upright and lateral positions. The experimentally obtained peak forces for the z-direction printed hemisphere were 19.61 and 17.76 N for the velocities of 50 and 500mm/min, respectively. The peak forces for the y-direction printed hemisphere were 19.40 and 17.51 N for the velocities of 50 and 500mm/min, respectively. The prediction of the finite- element analysis showed a higher peak force at 50mm/min of 33.78, 29 and 36.27 N for the x-, y- and z-direction models used, respectively. The prediction of the finite-element analysis showed a higher peak force at 500 mm/min of 33.62, 28.91 and 36.1 N for the x-, y- and z-direction models used, respectively. The hysteresis found during the compression test did not match the hysteresis found in the FEA. The experimentally obtained hysteresis was larger than the hysteresis predicted by finite-element analysis. Both hemispheres were able to support the loads without damage for ten cycles. ... Read more

Twisted and coiled polymer muscles (TCPMs) are a type of artificial muscle with a remarkable power-to-weight ratio. However, actuation dynamics are slow compared to other artificial muscles. This work aims to improve dynamic performance by incorporating redundancy. Specifically, this work examines if TCPM bundles of heterogeneous geometries containing high-force low-bandwidth actuators and low-force high-bandwidth actuators have a substantially better tracking performance than that of bundles of homogeneous geometries. First, a white-box model was created to simulate TCPM dynamics as a function of geometric parameters. The model revealed fiber diameter is the only geometric parameter that represents a trade-off between TCPM bandwidth and maximum realizable force for isometric force tracking. Next, an optimum feedforward controller was designed to distribute the reference among redundant actuators. Finally, a brute-force optimization was conducted to find the optimum configurations of heterogeneous and homogeneous TCPM bundles and the associated tracking performances. Optimal homogeneous configurations outperformed all heterogeneous configurations irrespective of number of TCPMs in parallel or reference signal. For unidirectional configurations, a nontrivial fiber diameter optimizes tracking performance. For antagonistic configurations, tracking performance improves monotonically with increasing fiber diameter. ... Read more

Training with bodyweight support (BWS) systems can improve the likelihood of regaining normal locomotor abilities for neurologically impaired patients. It is known that people alter their gait parameters when walking with BWS. However, it is unclear whether 2D (vertical and lateral support) and 3D (only vertical support) BWS systems affect these gait parameters differently. In this study, participants walked overground in both a 2D and a 3D BWS system to investigate the effects of this lateral support. To compare the contribution of the vestibular system between the different BWS systems, participants received galvanic vestibular stimulation (GVS). Motion capture and force plates were used to find the coupling between the GVS stimulus and the mediolateral ground reaction forces and to calculate the gait parameters. Differences in gait parameters were observed between the 2D and the 3D system. Compared to unsupported gait, participants increased their step width variability by ~10% in the 3D system. Contrarily, participants decreased step width variability by more than 15% in the 2D system. Mean step width decreased slightly in only the 3D system. The margin of stability did not change significantly in any condition. The coupling between the GVS signal and mediolateral ground reaction forces decreased in the 2D and 3D systems compared to unsupported gait, but no significant differences were observed between different BWS conditions. These results suggest that 2D and 3D BWS systems influence gait parameters differently and that they influence the contribution of the vestibular system to balance, but no significant differences between the systems can be observed in this aspect. ... Read more

Trunk motor control is essential for the proper functioning of the upper extremities and is an important predictor of gait capacity in children with delayed development. Early diagnosis and intervention can potentially increase the trunk motor capabilities in later life. However, current tools used to assess the level of trunk motor control are largely observation-based and lack the sensitivity to change required to accurately monitor progress and effects of therapy in children below the age of 4. To the best of our knowledge, this is the first attempt to use trunk-attached inertial measurement units (IMUs) to differentiate different levels of trunk motor control in this population. We performed experiments with seven children to examine the applicability of the RMS of jerk as an outcome metric for the level of trunk motor control. This study showed that the root mean square (RMS) of jerk decreases for ages up to 24 months, is relatively independent of data segment and length, and shows results similar to a more established method: the centre of pressure (COP) velocity. These findings suggest that the RMS of jerk shows potential as a metric for the differentiation of different trunk motor control levels. However, due to the small sample size, a follow-up study is necessary to verify and validate these results. ... Read more

Fluid-controlled actuators are widely used in lower limb prostheses. Most fluid-controlled actuators have valves integrated into the cylinder systems and require complex manufacturing steps, making these systems expensive. A cost-effective production method for these complex actuator valve systems is 3D-printing. The goal of this research is to study the possibility of creating a pneumatic and hydraulic cylinder with integrated valves using 3D-printing and evaluate their performance. A 3D-printed pneumatic cylinder with integrated valves was designed, manufactured and tested on static and dynamic leakage for different pressure levels on a designed test rig. To evaluate the performance, the leakage data was compared with the performance of a commercial pneumatic cylinder. A 3D-printed hydraulic cylinder was designed and built according to the earlier design insights. The 3D-printed hydraulic cylinder was tested on hysteresis and internal and external leakage in open and closed valve mode. Overall the commercial pneumatic cylinder performs better on static and dynamic leakage. In static leakage, a maximum pressure loss of 0.0095 MPa was measured at 0.6 MPa starting pressure after 20 minutes in the 3D-printed pneumatic cylinder. In dynamic leakage tests, a larger pressure difference of 0.035 MPa is measured at 0.5 MPa after 20 minutes in the 3Dprinted cylinder. The higher leakage profiles of the 3D-printed cylinder are caused by a difference in roughness and clearance of the sealing seatings causing movement of the seals. The 3D-printed hydraulic cylinder did not work as expected with 20 N force for moving the cylinder over its stroke, internal leakage of 0.007 MPa at a 0.01 MPa dynamic test and an average external leakage of 8.7 mL after 20 minutes. The tests gave important insights into sealing selection, which was not optimal for the hydraulic application. All in all, this study shows that it is possible to create functional 3D-printed pneumatic cylinders for static applications. Thereby it gives important design insights into improving the performance of 3D-printed pneumatic cylinders for dynamic applications and 3D-printed hydraulic cylinders. ... Read more

Rehabilitation robots have been shown to be effective in post-stroke gait rehabilitation. However, these devices are usually expensive and suffer from high inertia which decreases transparency. The Minimally Actuated Tendon-based exercise Environment (MATE) is a tendon-based rehabilitation device, designed to be cost-effective and minimize inertia effects. The MATE must apply minimal forces to the wearer if the gait cycle is healthy to prevent deviation into an unhealthy gait. Previously a mathematical optimization was performed on the design of the MATE. This thesis aims to make a physical realization of the MATE to investigate the minimal forces during a healthy gait cycle with two experiments. The first experiment attached the tendons to a machine to investigate forces on a non-altering gait. HTC VIVE motion trackers were used to measure the position of the tendon attachments over time. To measure the tension, in each cable inline tension sensors were added. Comparing the measured forces to velocity-based thresholds indicates that the forces applied by the MATE are too high and would cause deviation. The second experiment involved a human walking with and without the MATE. Evaluating the gait cycle trajectory when walking with and without the MATE indicates that the MATE alters a healthy gait cycle, lowering the step height and causing drift. The forces acting on this gait also exceed the thresholds. The MATE in its current design alters a healthy gait. Redesigning the MATE with the suggestions from this thesis will likely show further improvements. ... Read more

Many wheelchair users, such as the elderly or children with Profound Intellectual and Multiple Disabilities (PIMD), rely on a caregiver to push them. The lack of eye contact between the wheelchair user and caregiver hinders communication and can even be dangerous, for example for children with epilepsy. Conventional wheelchairs place the caregiver behind the patient when pushing the wheelchair, but this position obstructs communication and makes it harder to assess the user's health.

To facilitate face-to-face communication while walking, Lucy Bennett recently proposed a steering compensation method at BME2021 using a banked castor wheel to allow the caregiver to walk next to the wheelchair. This thesis contains a mathematical model for a castor wheel to determine how the three-dimensional orientation of the castor swivel axis and wheel spin axis, and external parameters such as rolling resistance affect the steering compensation. Both the Lagrange and virtual power methods are used to find the equations of motion of the castor wheel.

The steering effect was quantified as the moment generated by the wheelchair around its center of mass in the up direction. The cant angle of the castor wheel has the strongest steering effect. In the future, the developed mathematical model can be applied to calculate the influence of design variables to build a better prototype. ... Read more

Robots can be powerful tools in post-stroke gait rehabilitation. However, state-of-the-art robots are often expensive machines containing rigid links with high inertia. Their expensiveness could limit their availability, and their high inertia reduces transparency, which could hinder rehabilitation progress. These factors raise the need for a minimalistic transparent robot that can effectively fill this gap. This research aims to design and validate such a device, a minimally actuated tendon-based exercise environment. The device is synthesized using an optimization algorithm that considers possible system configurations and optimizes both these configurations and their respective design parameters. Validation is done based on a reconstructed simulation of gait using motion capture on the optimal design to check whether it could be used for real-life rehabilitation. It was found that the most simplistic solution is not yet adequate for rehabilitation; thus, a slightly more complex design is required. While not providing the final solution, this research provides an important stepping stone towards designing a minimally actuated, simplistic, and transparent rehabilitation device. ... Read more

Some above the knee amputees take a smaller step with their prosthetic leg. A momentum exchange device (MED) can increase the step length by exchanging angular momentum between the device and the leg. However, there are no controllers for MEDs during regular gait. The goal of this study is to build a model predictive controller (MPC) that controls an MED to help the amputees achieve a certain step length. The MPC uses a model of an unimpaired walking human to predict its movement. Two different models are evaluated, a compass-gait biped (CGB) model and a neuromusculoskeletal (NMS) model. The parameters of the CGB model are estimated with a grey-box estimation method. An NMS model of an unimpaired human is used to simulate the controllers as well. For control, both linear and nonlinear hybrid model predictive control methods are used. By evaluating the behaviour of the controllers, insights are gained in whether the chosen models and control methods are suitable to achieve the goal. It is concluded that the prediction of the CGB model is insufficient for the control algorithm used. The model is capable of approximating the swing of the leg, but it is unable to accurately predict the future states. The NMS model may be more accurate, but is at this moment in time not practical for control. The model is computationally expensive, observing all its states is difficult and the model can currently not be initiated in any desired state, which is required for control. The results indicate that the chosen combinations of models and control methods are not well suitable to achieve the goal. Control with an unimpaired human model unfolded many difficulties and control of an impaired human is even more difficult. A control method that does not rely on an accurate step length prediction might be more suitable. However, the identified CGB model and the control methods contribute to further research on the subject or other applications within the field. ... Read more

Background Pneumatic actuators are widely used in applications like (medical) robots, or prosthetics. They require tight tolerances to keep them leakage-free. Over the last decade 3D-printing, or additive manufacturing, has emerged as a cost-effective production method in these applications.
Objective The goal of this research is to study the possibility of creating a pneumatic linear actuator with additive manufacturing. The focus is on finding sealing mechanisms which can have a positive influence on preventing leakage and friction force in the 3D-printed actuator. Furthermore we aimed to use the advantage of 3D-printing to create pneumatic actuators with a non-circular cross-section.
Methodology To evaluate the performance of a 3D-printed pneumatic actuator, a test setup is designed to measure the leakage and sliding friction force. Furthermore, we designed two pneumatic actuators with a non-conventional cross-sectional shape and validated their performance.
Results The choice for the optimal sealing mechanism in 3D-printed pneumatic actuators depends on the application in mind. For low-pressure situations the single-acting cup-shaped NAPN sealing is recommended, with a measured friction force of 6.7 N at a pressure of 0.1 MPa for one entire movement cycle (extending and retracting stroke together). For high pressure situations the double acting KDN sealing shows the lowest friction force while remaining leakage-free (13.5 N for the entire stroke at a pressure of 0.7 MPa). Furthermore, we have proven it possible to print pneumatic cylinders with a non-cylindrical cross section.
Conclusion We demonstrated a method to create leakage-free pneumatic linear actuators with additive manufacturing. For low pressure applications we showed first steps towards 3D-printed pneumatic actuators with non-circular cross-section of the piston, allowing more design freedom for these actuators. ... Read more

Due to neuromuscular capacity decline, sit-to-stand, an essential daily life activity, is increasingly difficult to perform for elderly. In practice, elderly frequently use compensatory arm-strategies in sit-to-stand. However, the specific advantages of these compensatory strategies are unclear. The focus of this research is to study the influence of thigh push-off, a common compensatory strategy, on the stability of sit-to-stand for both the young and elderly. Motion data was retrieved from 50 young and elderly participants who performed sit-to-stand with and without thigh push-off. To mimic realistic daily-life strategies, participants were not restricted in sit-to-stand style in any way but arm-use. The experimental sit-to-stand data was fitted to a pendulum model with feedforward and feedback control to simulate the stability limits of the observed sit-to-stand strategies. The model allows us to explore stability limits without the need of perturbation. For each arm-strategy and participant a stability basin, i.e. all potential trajectories of motion, was formed. We compared the stability basins between arm-strategies and between age-groups. The size of the computed stability basin for thigh push-off was larger than for no arm push-off implicating thigh push-off is a more stable sit-to-stand strategy. The difference between arm strategies was larger for the elderly than for the young participants. Overall, the stability basins of the elderly were larger compared to those of the young participants, for both arm strategies. The resulting stability basins suggest that thigh push-off increases the stability of sit-to-stand and thus could indeed be an effective compensatory strategy. Stability basin shape differences indicate that without thigh push-off elderly compensate for possible early sit-down and a step halfway sit-to-stand, and with the thigh push-off strategy only for early sit-down. The age-groups differences confirm stability basins quantify the stability of the observed movement strategy rather than the stability of the participants. We observed that elderly use more precautious sit-tot-stand movements. ... Read more

Twisted and coiled polymer muscles (TCPMs) show promise to function as artificial muscles, because of their lightweight, low cost, large contraction, and respectively low hysteresis. A TCPM contracts when it is heated and extends when it is cooled. Different modeling and controlling techniques have been implemented. \cite{VanDerWeijde_2019} implemented a self-sensing model that does not need large apparatus for measurements of force and deflection. The goal of this thesis is to design a force controller that works with this model. Parameter estimation of the self-sensing model is done. The fit of the model is not high enough for control. A first order black-box model is estimated and used instead. A P and PI controller is simulated and tested on the setup. The force oscillates around the reference value. This is because the actual model is of order 2. A D-action needs to be added to dampen the oscillations. The integral action reduces the max to min and vice versa input behavior. The model parameter differs for each TCPM. The controller parameters have to be adjusted for each TCPM. This is impractical in large-scale applications. Further research can be done into using model-free controllers. ... Read more

Inspired by phenomena in the plant world, a
meteoro-sensitive rotational actuator is developed. The design
uses a hygro-active shell, whose water-based swelling is restricted
at selective locations to form a helicoid structure. The influence
of geometrical parameters on the performance is investigated
using a numerical analysis of various geometries, by looking at
resulting rotation and torque during this rotation. Prototypes
are built of five key geometries in the design space, to validate
the simulations and to investigate the real-life behaviour
of the design. These prototypes are submerged in water to
investigate their deformation, after which they are placed in
a torsion machine to investigate the torque during rotation.
The experiments result in similar rotations and torques as the
simulations. The designed Hygromorphic Rotational Actuator is
capable of passively rotating its own structure, thereby expanding
the possibilities of engineers and designers when designing passive
autonomous systems. ... Read more

This study proposes the creation of a multi-modal feedback system to guide humans towards ergonomic poses. A number of studies have tried to come up with methods where subjects are alerted upon crossing biomechanical or ergonomic thresholds while doing a task but not many have tried to successfully and efficiently guide users to ergonomic positions after having alerted them. Through this study we propose the creation of a multi-modal feedback system comprising of a visual and a speech based audio feedback and hypothesize that the proposed system will lead to a better performance as compared to the other feedback modalities when trying to guide users from one pose to another. During our study we have conducted two sets of experiments to carry out a comparative study between only audio, only visual and the proposed multi-modal feedback system to try and find the modality most effective and successful in guiding humans for pose corrections and a comparative study between two types of speech based audio feedbacks in joint space and end point space to motivate our choice for using the more desired one between the two for our proposed system.
Speech based feedback in joint space came out as the preferred audio feedback due to its ability to allow users to carry out efficient and coordinated inter-joint movements especially in cases of high redundancy whereas the proposed multi-modal feedback system successfully shows its superiority over the other feedback
modalities by showing equivalent results against the benchmark visual feedback when measured objectively and better results when measured subjectively due to its ability to successfully combine the advantages of audio and visual feedback and at the same time, avoid their limitations. ... Read more

The mechanisms that move plants can serve as biological role models for engineers, designers and architects. This practice is slowly being implemented in various engineering fields, with architects often being pioneers. Various methodologies have been written about the subject, but often only from an architectural point of view.
The classification presented in this paper provides a different perspective on the
subject. It is structured like a toolbox, containing a clear classification of the technical working principles that plants use to generate motion. With the working principles abstracted, it is no longer necessary to dive deep into the inner workings of plants.
The Scopus and Web of Science databases have been systematically searched for
compliant plant movements. Plants mainly move by reallocating water, either actively via osmosis or passively via hygroscopic tissue. In compliant plant mechanisms, these basic movement initiators bring about deformations of plant parts. These movements are classified according to their goal: does the plant move quasi-static or dynamic? And does the plant only use a mechanism or does it rely on the gradual storage and fast release of elastic energy as well? Quasi-static movements are often only mechanical and reversible, while dynamic movements rely on energy storage and are often irreversible due to their failure-based release. A bilayer structure in one form or another is present in almost all mechanisms, proving its large adaptability to various circumstances. This
adaptability is achieved by the various configurations of the two layers, including
fibre-orientation and cellular set-up.
Existing bio-inspired devices are classified according to the same system. This
enables identification of plant mechanisms that are already suited for implementation and exposes plant movements that are not yet used in the human world. Additionally, a lot could be gained from copying mechanisms on a cellular level rather than on a macroscopic level. Most importantly, a change in mindset needs to happen in order to fully benefit the intricate mechanisms that the plant world has to offer.
... Read more