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The fields of static balancing and tensegrity structures are combined into statically balanced tensegrity mechanisms. This combination results in a new class of prestressed structures that behave like mechanisms: although member lengths and orientations change, they can be deformed into a wide range of positions, while continuously remaining in equilibrium; in other words, the structures have zero stiffness. The key to these structures is the use of zero-free-length springs as tension members. The tools of structural engineering were used to search for, and understand, zero-stiffness modes in the tangent stiffness matrix of prestressed pin-jointed bar frameworks. To this end the recently uncovered parallels between structural engineering and mathematical rigidity theory were exploited. Mathematical literature described that affine transformations preserve the equilibrium of a tensegrity structure; these findings gained value when translated from a mathematical concept into the engineering terms rigid-body motions, shear and dilation. Not only did these transformations prove to be instrumental for describing zero stiffness, but it also provided new insight in the form-finding methods for tensegrity structures: the minimum nullity requirement for the stress matrix is formed by the affine transformations. In this research it was shown that affine transformations of the structure that preserve the length of conventional members are zero-stiffness modes valid over finite displacements: these are statically balanced zero-stiffness modes. What is more, for prestress stable structures with a positive semi-definite stress matrix of maximal rank -- meaning there are only affine transformations in its nullspace -- those are the only possible zero-stiffness modes. The length-preserving affine transformations exist if and only if the directions of the conventional members lie on a conic at infinity. If all conventional member directions lie on a conic, the number of independent length-preserving affine transformations can then be found with a simple counting rule. A systematic analysis of the zero-stiffness modes in the tangent stiffness matrix of a prestressed pin-jointed bar framework yielded several interesting scenarios that warrant further attention, as they cannot be fully described within the currently developed framework. Finally, a demonstration prototype was designed and constructed to illustrate the properties of statically balanced tensegrity mechanisms; the prototype serves as a proof of concept, not as a practically applicable design. Prior to construction, the range of motion of the tensegrity used for the prototype was extensively analysed using the analytic equilibrium conditions. The results were instrumental in dimensioning the prototype.

This study describes a method for the identification of Time-Varying joint admittance. The method transforms the time signals into a time--frequency representation using the wavelet transform, from which the Time--Varying frequency response function (TV--FRF) is estimated, and the model parameters are derived. Analysis of the performance of the developed method is established by simulation of the human arm. The study showed that increasing the observation time, increase the confidence regions of the estimate. The study showed that smoothing is needed, but it comes with a trade-off between precision and response time. Increasing the time smoothing increases the precision but decreases the response time. The developed method showed promising results by estimating the properties of the simulated model, giving the bases for a posterior study using experimental data.

Meniscectomy is a medical procedure where ruptured meniscal tissue is removed within the knee joint. The con- ventional cutters fail to reach the entire meniscus. Therefore, the focus of this study is to create a cutter with a steerable tip, which allows sideway steering to increase the reacha- bility within the knee joint. Additionally, this steerable joint is required to be robust to transmit a cutting force of up to 190N. The mechanism design is divided into the functions: steering and actuating cutting mechanism. The most promis- ing solution of each function was combined and resulted in the use of a crossed configuration of a Compliant Rolling- Contact Element for the instrument joint. Flexural Steering Beams actuate the rotation of the joint using the principle of a parallelogram mechanism. A prototype of this mechanism has a range of motion of +25 and -22 degrees with a steering stiffness at the handle side of 18Nmm/rad. An axial load of 200N on the tip corresponded with a parasitic deflection of 4 degrees. This unique type of a steerable joint shows poten- tial to be functional in a meniscectomy cutter due to its great robustness towards compression, yet allowing the instrument tip to deflect.

Blood flow and the associated shear forces have important biological effects on blood vessels. It has been suggested that blood flow abnormalities play a part in the development and the rupture of a deformed part of the wall of a brain artery, which is called an intracranial aneurysm, and thus in cerebral hemorrhages. Knowledge about the blood flow velocities and profiles in patient’s aneurysms is of major importance to understand their effect on the blood vessels. The Amsterdam Medical Center obtains blood flow velocities and profiles in the aneurysm region with a measurement technique called phase contrast MRI. There is a need for a validation of the measurement technique and protocol of the Amsterdam Medical Center. A common way of validation is the use of a flow phantom which is, in this case, a physical model of the circulation in the region of an aneurysm. In this project, the flow velocities and profiles in the aneurysm phantom are measured with phase contrast MRI and with Particle Image Velocimetry. The results of both measurement techniques are compared in order to contribute to the validation of blood flow measurements in intracranial aneurysms with phase contrast MRI.

Sometimes children are born with (part of) an arm missing. Next to congenital loss, children or adults can loose their arm due to an accident or illness. The missing arm can be replaced with a prosthesis, connected to the arm remnant by a socket. Existing sockets tend to have a hot and humid climate and some sockets are difficult to don and doff. The WILMER open socket is adjustable but looks bulky. All these disadvantages result in reduced wearing of the prosthesis. After the current prostheses are evaluated, the existing patents and available literature are investigated, a list of requirements was made for a new design. With the requirements, the problem can be solved by improving a current socket and designing new sockets. The application of new materials in prosthetics is evaluated, resulting in several new designs. The WILMER open socket is improved, resulting in another design. From these designs one concept is chosen and detailed. The chosen concept is made of stainless steel wire mesh, with an adjustable condyle brace and a standard forearm shell over the mesh.

The Dutch Shoulder and Elbow Model (DSEM) is a musculoskeletal model of the shoulder that can be used to predict internal shoulder loading (muscle forces, joint reaction forces, etc.). The DSEM uses an inverse optimisation method to predict muscle forces from net joint moments. In this study two new modes are presented that constrain the inverse optimisation with muscle force boundaries based on muscle dynamics (inverse forward dynamical mode) and boundaries based on EMG-recordings (EMG-assisted mode). The new modes were validated with measurements of two standardised movements (abduction and ante exion) from two subjects. A proof of concept has been given that both new modes work. It was concluded that DSEM predictions can be dominated by morphological differences between the subject and the cadaver on which the DSEM is based. Until better scaling routines are developed the IFDO mode is not very useful. When EMG-constraints are added, muscle and GH-joint reaction forces are predicted to be higher. Adding EMG for one muscle can predict cocontraction in other muscles. By adding EMG-based constraints, the DSEM can account for individual strategies in control strategy for the data that was analysed and is therefore an interesting topic for future research.

Indirect Heat Induced Attachment and Detachment (HIAD) is a promising concept for gripping delicate tissues in ophthalmic surgery. However, the optimal settings of attaching to and detaching from delicate tissues are unknown. This study presents the effects of the instrument heating properties and initial contact force on the adhesion force, detachment success and thermal damage. An instrument prototype was developed to test attachment and detachment for different combinations of generated heat (3.5-20.0mJ) and pulse length (0.25-2.50ms). Thermal tissue damage was estimated with electro-thermal FEM simulations and histological analysis. The adhesion force depended strongly on the amount of generated heat and contact force. Pulse length played a minor role. Detachment success was determined by the maximum instrument temperature. Thermal tissue damage was strongly related to the amount of generated heat, the effect of pulse length was marginal. In RPE-choroid graft analysis, the RPE cells were not affected by heat. HIAD proved sensitive to heating characteristics and tissue properties. Nevertheless, this principle creates potential to build better performing tissue manipulators.

This thesis work analyses, models and presents a new frame design for the Csiro electric drive for solar cars. The main objective is to determine whether Csiro motor (CM) is more efficient than the Biel motor (BM). To do that, performance tests were conducted and compared with both drives. Results showed that the CM is more efficient at low torques. The same results were used to derive and validate a steady state model for the CM. The Model is based on four major losses in the CM. Using the model it was possible to determine the areas where improvements were possible to boost the efficiency, to optimize the mechanical design and to calculate the losses and efficiency of the CM when subjected to some certain load.

Assessment of the sodium/potassium (Na/K) pump functioning can play an important role in the early diagnosis of several polyneuropathies. However, currently no method exists that allows in vivo testing of the Na/K pump. Therefore, this study developed a test based on repetitive nerve stimulation at single motor units. In order to evaluate the Na/K pump functioning, measurements were taken at various frequencies. Low frequency stimulation was applied to record the recovery cycle of a single motor unit at which no Na/K pump influence is expected. Stimulation trains of physiological frequency perturbed the Na/K pump and led to hyperpolarization of the membrane potential. Hence hyperpolarization leads to a decreased neural excitability, a threshold change can be recorded. Since both stimulation at physiological and low frequency led to a threshold change, a model was introduced to discriminate the influence of the Na/K pump. During the recordings at physiological stimulation frequency a remarkable phenomenon was noticed which was identified as neural bifurcation.

The goal of this study is to quantify the recovery of spinal reflexes at the elbow after neurosurgical intervention in patients with brachial plexus injuries. So far, main focus was on the recovery of muscle force and little on sensory- and reflex system. As reflexes play an important role during normal movement, it is of interest to determine to what extend reflexes have been restored after surgery. Arm admittance (dynamic relationship between displacements in a response to forces) at endpoint level (hand) was estimated using force perturbations in two directions (horizontal) applied by a two-joint robotic manipulator. Three different task instructions were used to provoke different intrinsic and reflexive behavior, being a position task (PT), a relax task (RT) and a force task (FT) where the subject was required to minimize hand displacements, not react to the perturbations and minimize force deviations (being compliant) respectively. Ten patients with brachial plexus lesions participated in this experiment and were suffering from varying degrees of arm dysfunction. All had successful recovery for the biceps (MRC grade 3 and higher) after surgical nerve repair of the n. musculocutaneous. Estimated intrinsic and reflexive parameters were compared to those of a control group (n = 10, age and sex matched). The task instructions had great influence on the admittance, especially between the PT and RT. In all patients, reflexive activity was found corresponding to assumed muscle spindles (velocity- and position feedback) and Golgi tendon organ (force feedback) function. For the PT, the difference in parameters between patients and control subjects was largest. Overall, patients exhibit more intrinsic stiffness at the shoulder and elbow than the control subjects, an indication of co-contraction, and less reflexive feedback at the elbow. There are two possible explanations for this: 1) The intrinsic and reflexive properties did not recover to the combination as before the injury and are not cooperating correctly, and 2) The patients are relying more on intrinsic control than on reflexive control (different control strategy). Whereas the control group uses an energy efficient approach, i.e. less intrinsic and more reflex activity, the patients appear to use a more maximal activation approach resulting in co-contraction. It is possible that the exercises performed during rehabilitation which focus on muscle force do not provoke enough reflexive behavior. More research, e.g. experiments that are designed to disable co-contraction, is needed to verify if the use of co-contraction is learnt or a necessity. Conclusion: reflexes do recover after surgery to severe Brachial plexus injuries, the amount of reflex function is less or less effective than for the control group.

Body powered prostheses have many advantages: They are reliable, lightweight and relatively cheap. The disadvantage is the need of a shoulder harness, which causes discomfort, pain and trouble donning and doffing the prosthesis. The goal of this thesis is to develop a body-powered prosthesis without the need for a shoulder harness. This is realized by making a design that uses passive wrist flexion of the prosthesis itself to operate the grasping mechanism. The force and displacement are converted to a grasping motion by using a hydraulic system. The grasping force is enhanced by a pressure intensifier and holding an object is achieved by including an automatic lock.

A gravity balancer is a mechanism that compensates the weight of a mass over a range of motion. When no friction is present, this gives an energy efficient mechanism and little effort is required to move an object. Conventional mechanisms have drawbacks due to the use of conventional rigid joints. Compliant joints do not have these disadvantages, can be made from fewer parts and can increase performance compared to rigid body joints. The goal of this paper is to develop a single degree of freedom gravity balancer where all the rigid joints are replaced with compliant joints. To reach this goal a new method has been developed. The method is based on connecting rigid links with compliant joints. With a constant potential energy as objective, the method allows new gravity balancers to be designed. It can be concluded that for the first time a gravity balancers has been constructed where all the rigid joints are replaced with compliant joints. The gravity balancer had a peak moment reduction of 93%. The presented method is extensible and allows others to understand and to further develop gravity balancers with compliant joints for other applications.

Laparoscopic surgery is a technique in which operations in the abdomen are performed with long slender instruments through small incisions (5-10 mm). Single port surgery is a form of laparoscopic surgery with possible advantages in which the surgeon operates almost exclusively through a single incision. In order to compensate for the limited freedom of motion of the used instruments, steerable instruments with articulating tips that can be steered in 2 DOF have been developed for use during laparoscopic or single port surgery. The freedom of motion provided by steerable instruments make single port surgery possible, but however introduces a number of problems (eye-hand coordination conflicts, incision widening). This paper presents the design of a new, multisteerable instrument that can be used for both laparoscopic as well as single port surgery.

To diagnose and treat colon cancer a colonoscopy is usually performed. Current colonoscopy is performed by advancing a colonoscope (scope) through the tortuous colon. However, the flexible scope often buckles when advanced. This can cause discomfort and pain for the patient and can make the examination of the colon difficult for the endoscopist. Guiding the scope, with an overtube that has a controllable rigidity, when the scope is advanced could reduce these problems. The rigidity of the overtube should be switched between a flexible state, that allows the insertion of the overtube, and a rigidified state that provides sufficient support to the scope. The PlastoLock overtube utilizes the glass transition of Purasorb© PLC 7015 (PLC). By changing the temperature of its PLC components from 43 to 5°C, the PlastoLock overtube is reversibly rigidified. A physical test model of the PlastoLock overtube shaft was developed and its stiffness at 43 and 5°C was determined. The tests showed a reliable, reversible and fast change in stiffness. The stiffness of the test model in flexible state is sufficiently low. However, the stiffness of the rigidified test model is insufficient. A larger change in stiffness was found when testing the test model submerged in water compared to passing water through the PLC components. The measured stiffnesses were considerably below expectation. Possible causes for this discrepancy were investigated, but require further testing to confirm. These future tests should also indicate whether the stiffness of the rigidified test model can be increased.

Assessing mechanisms of peripheral reflex control is important for understanding movement disorders after suprapsinal nerve lesions like stroke. In the present study, reflex provocation by ramp and hold rotations (R&H) was combined with Transcranial Magnetic Stimulation (TMS). In four subjects, subthreshold single pulses TMS were applied to the primary motor cortex at carefully timed intervals, while short and long latency EMG responses of the m. flexor carpi radialis were elicited by R&H rotations around the wrist joint. TMS was found to inhibit the long latency response with a maximum inhibition when TMS was calculated to arrive at 45ms after stretch onset in all subjects. Excitation was found at 60 ms in all subjects. An involvement of the primary motor cortex in peripheral reflex loop operation was demonstrated. This involvement may be either exictatory or inhibititory on the stretch reflex.

Static balancing is a useful concept to reduce operating effort in mechanisms. A statically balanced system which is designed to counterbalance a mass, is referred to as a gravity equilibrator. The potential energy in a gravity equilibrator is constant, which in most of the times is achieved by mechanical springs. Often helical springs are used, although these springs take a lot of space within the workspace of the mechanism. This paper presents the design of an adjustable gravity equilibrator using torsion bars, which saves space in the working area. Static balancing is achieved with a non-constant transmission (NCT). A new NCT design, and a general method to calculate the design parameters are presented. The stiffness of the torsion bars can be adapted by changing the active length. In this way it is possible to balance different masses with the same system.

When performing minimally invasive interventions, surgeons use grippers to grip and manipulate tissue. These grippers generally rely on their toothed profile and require pinching of the tissue for sufficient grip, entailing a risk of tissue damage. An solution should be found for this risk of damage. An alternative could be to manipulate the tissue without pinching or even touching it. Contactless gripping exists in the industrial field by using the principle of Bernoulli. This study explores the possibility of applying Bernoulli gripping for tissue manipulation during minimally invasive surgery. A medical gripper using the principle of Bernoulli was developed. Increasing the air flow, the radius of the gripper face and the radius of the nozzle has a positive effect on the lifting force. In order to prevent tissue damage, different variants are tested that change the direction of the air flow. In an exploring experiment, a deflector was selected out of seven variants as best solution to prevent damage from the air flow. The Bernoulli gripper was made expandable and collapsible for insertion in the body of the patient with a system of living hinges. The effect of Venturi channels and the position of a membrane for an airtight surface on the lifting force were tested. The lifting force generated on the object during gripping was measured using a tensile-strength tester. Bernoulli’s theory was compared to the results of the experiments and a discrepancy was found between theory and results. This study shows that a Bernoulli gripper is feasible to lift flexible tissue.

An tele-operation, haptic feedback from the remote environment to the human is often limited, which has been shown to negatively influence the performance and required time of tasks. The conventional research focus is on improving the quality of the haptic feedback (transparency), which may have led to significant improvement, but is still imperfect, with many unresolved issues. The present study presents an alternative approach to improve tele-operated tasks: by offering haptic shared control in which both operator and support system apply the required forces at the input (master) device. It is hypothesized that virtual forces from well-designed shared control will improve required time and accuracy, with less control effort, and that these benefits exist for perfect transparency but even more so for imperfect transparency. In an experimental study haptic shared control was designed to aid operators (n=9) with performing a simple bolt-spanner task using a planar (2D, 3DOF) tele-operator setup. Haptic shared control was compared to normal operation for three types of control: the baseline condition of direct control at the master (perfect transparency), teleoperation with a simple PERR controller, and a PERR controller with feedback gains set to zero (no transparency). The experimental results provided evidence for the hypotheses, showing that all tested tele-manipulation tasks benefit from haptic shared control, for all three levels of transparency. Essentially, the presence of haptic shared control allows for a worse transparency without compromising accuracy or required time, and can even improve accuracy and required time during perfect transparency. Subjective results indicated that the shared control was perceived as helpful and beneficial.

The Delft Biorobotics Laboratory develops bipedal humanoid robots. One of these robots, called LEO, is designed to learn to walk using reinforcement learning. During learning, LEO will make mistakes and fall. These mistakes can cause serious dam- age to the system but are an integral part of the learning process. A likely solution is punishing the robot more severely for falling. However, punishing the robot too rigorously can lead to a robot that is too cautious to make a step. In this research, three methods were tested that reduce the amount of falls during learning, without restricting the possible solutions or increasing the learning time. We introduce Threshold Restricted Learning (TRL), a new method for action se- lection that, during exploration, makes the probability an action is chosen dependent on the expected reward for taking that action. Actions with expected rewards below the set threshold have a signifcant reduced probability of being chosen. The concept of TRL developed from the desire to optimize the use of a pre-learned solution. Hence, TRL was tested after pre-learning in simulation. The largest reduction in the amount of falls achieved by TRL in this research was 50% TRL did not increase the learning time. Without pre-learning the largest reduction was 7%. Softmax action selection is a well known but underused selection method. Combined with pre-learning it was able to reduce the amount of falls during learning with approximately 80% and did not increase the learning time either. Without pre-learning, Softmax could still achieve a reduction of approximately 20%. Sarsa2Q, another new method, stores expected rewards at different levels op generalization. The level with little generalization is used to store the expected total positive reward, while the level with more generalization is used to store the expected total negative reward. Sarsa2Q learned to avoid the failure states for the inverted pendulum problem faster than using a single level of generalization. This method does not use pre-learning. The highest achieved reduction in the amount of falls was approximately 20%. Sarsa2Q can have a broader use than just avoiding failure states. Rather than only using the coarse generalization for negative rewards, it can be used for all rewards that need less precision.

The concept of underactuation is increasingly applied to hand prostheses because it minimizes the number of actuators while the fingers are adaptive to the grasped objects. However, current underactuated grasp mechanisms suffer from an intrinsic stability problem which disables them to obtain a pinch grasp, hence they fail to grasp small objects. In an attempt to solve this problem joint locks are applied to an underactuated pulley-tendon driven hand. Joint locks might also have an effect on the power grasp strength. Therefore the effect of joint locks on the pinch grasp performance and power grasp strength of underactuated hand prostheses is investigated. This effect is quantified by two grasp performance metrics: the ability to pinch and the ability to hold. To find the optimal joint lock configurations for pinch grasp performance and power grasp strength, the effect of different joint lock configurations on both performance metrics is calculated using a static grasp model. The results of this model are validated by measurements on a prototype. Both the model and the measurements showed that joint locks do not have a significant effect on the pinch grasp performance when only the range of object sizes for which a pinch grasp equilibrium exists is considered. However, the measurements showed that a pinch grasp is more easily established with joint locks. Additionally, both the model and the measurements showed a significant increase in the power grasp strength.