Current evaluation of hydraulics to replace the cable force transmission system for body-powered upper-limb prostheses

Body-powered variable impedance: An approach to augmenting humans with a passive device by reshaping lifting posture

The movement patterns appropriate for exercise and manual labor do not always correspond to what people instinctively choose for better comfort. Without expert guidance, people can even increase the risk of injury by choosing a comfortable posture rather than the appropriate one, notably when lifting objects. Even in situations where squatting is accepted as a desirable lifting strategy, people tend to choose the more comfortable strategy of stooping or semisquatting. The common approach to correcting lifting posture, immobilizing vulnerable joints via fixation, is insufficient for preventing back injuries sustained from repetitive lifting. Instead, when lifting small but heavy objects, the entire kinetic chain should cooperate to achieve a series of squat-lifting patterns. Inspired by the observation that force fields affect the coordination of voluntary human motion, we devised a passive exosuit embedded with a body-powered variable-impedance mechanism. The exosuit adds impedance to the human joints according to how far the wearer's movement is from the squat-lifting trajectories so that it hinders stooping but facilitates squatting. In an experiment that entailed lifting a small 10-kg box, 10 first-time users changed their voluntary lifting motion closer to squatting on average. Simulation results based on recorded kinematic and kinetic data showed that this postural change reduced the compression force, shear force, and moment on the lumbosacral joint. Our work demonstrates the potential of using an exosuit to help people move in a desirable manner without requiring a complicated, bulky mechanical system.

Evaluation and Analysis of Push-Pull Cable Actuation System Used for Powered Orthoses

Cable-based actuation systems are preferred in rehabilitation robotics due to their adequate force transmission and the possibility of safely locating the motors away from the patient. In such applications, the cable dynamics represents the prescribing component for the system operating loads and control. A good understanding of the actuation, based on cable-conduit transmission, is therefore becoming mandatory. There are several types of cable-conduit configurations used for the actuation. Currently, there is lack of information in literature with regard to the push-pull cable type. Therefore, the main focus of this contribution is to evaluate push-pull cable-based actuation used within wearable robotic devices. This study includes working principle description of push-pull cable actuation with its characteristic advantages and drawbacks. The use of push-pull cables in bidirectional force transfer with remote actuation is investigated being integrated in a test-stand setup of a novel gait rehabilitation device. The experimental results and close analysis of the push-pull cable-based actuation system outline its performance, the overall dynamic behavior and the transmission efficiency of push-pull cables used for powered orthoses.

A passive wrist with switchable stiffness for a body-powered hydraulically actuated hand prosthesis

State of art upper limb prostheses lack several degrees of freedom (DoF) and force the individuals to compensate for them by changing the motions of their arms and body. Such movements often yield to articulation injuries, nonetheless these could be prevented by adding DoFs, for instance, an articulated passive wrist. Available stiff or compliant wrists with passive flexion/extension and/or radial/ulnar deviation are sub-optimal solutions. Indeed, stiff wrists induce the individuals wearing them to perform exaggerated compensatory movements during the reaching phase while compliant wrists proved to be unpractical while manipulating heavy objects. Here we present a wrist capable of combining the benefits of stiff and compliant wrists. It is provided with two switchable levels of passive compliance that are automatically selected. The prototype was integrated in a body-powered hydraulic hand prosthesis and actuated using the same hydraulic circuit of the hand. Detailed analysis of the parameters that affect the compliance, the critical load and the performance of the prosthesis are presented.

Evaluation of transradial body-powered prostheses using a robotic simulator

BACKGROUND

Transradial body-powered prostheses are extensively used by upper-limb amputees. This prosthesis requires large muscle forces and great concentration by the patient, often leading to discomfort, muscle fatigue, and skin breakdown, limiting the capacity of the amputee to conduct daily activities. Since body-powered prostheses are commonplace, understanding their optimal operation to mitigate these drawbacks would be clinically meaningful.

OBJECTIVES

To find the optimal operation of the prosthesis where the activation force is minimized and the grip force is maximized.

STUDY DESIGN

Experimental design.

METHODS

A computer-controlled robotic amputee simulator capable of rapidly testing multiple elbow, shoulder, and scapular combinations of the residual human arm was constructed. It was fitted with a transradial prosthesis and used to systematically test multiple configurations.

RESULTS

We found that increased shoulder flexion, scapular abduction, elbow extension, and the placement of the ring harness near the vertebra C7 correlate with higher gripper operation efficiency, defined as the ratio of grip force to cable tension.

CONCLUSION

We conclude that force transmission efficiency is closely related to body posture configuration. These results could help guide practitioners in clinical practice as well as motivate future studies in optimizing the operation of a body-powered prosthesis. Clinical relevance The results from this study suggest that clinicians ought to place the ring harness inferior and to the sound side of the vertebra prominens in order to maximize grip efficiency. The results will also help clinicians better instruct patients in body posture during prosthesis operation to minimize strain.

Learning to use a body-powered prosthesis: changes in functionality and kinematics

BACKGROUND

Little is known about action-perception learning processes underlying prosthetic skills in body-powered prosthesis users. Body-powered prostheses are controlled through a harness connected by a cable that might provide for limited proprioceptive feedback. This study aims to test transfer of training basic tasks to functional tasks and to describe the changes over time in kinematics of basic tasks of novice body-powered prosthesis users.

METHODS

Thirty able-bodied participants and 17 controls participated in the study, using a body-powered prosthetic simulator. Participants in the training group were divided over four groups and practiced during a 2-week-period either direct grasping, indirect grasping, fixation, or a combination of these tasks. Deformable objects with different compliances had to be manipulated while kinematic variables and grip force control were assessed. Functional performance was measured with the Southampton Hand Assessment Procedure (SHAP) prior to and after the training sessions, and after 2 weeks and 3 months retention. The control group only performed the SHAP tests.

RESULTS

All four training groups and the control group improved on the SHAP, also after a period of non-use. Type of training had a small but significant influence on the improvements of the SHAP score. On a kinematic level movement times decreased and hook closing velocities increased over time. The indirect grasping group showed significantly shorter plateau times than the other training groups. Grip force control only improved a little over training.

CONCLUSIONS

Training action-perception couplings of body-powered prosthesis in basic tasks transferred to functional tasks and this lasted after a period of non-use. During training movement times decreased and the indirect grasping group showed advantages. It is advisable to start body-powered training with indirect grasping tasks but also to practice hook-object orientations.

The lightweight Delft Cylinder Hand: first multi-articulating hand that meets the basic user requirements

Rejection rates of upper limb prostheses are high (23%-45%). Amputees indicate that the highest design priority should be reduction of the mass of the prosthetic device. Despite all efforts, the mass of the new prosthetic hands is 35%-73% higher than that of older hands. Furthermore, current hands are thicker than a human hand, they operate slower and do not provide proprioceptive force and position feedback. This study presents the Delft Cylinder Hand, a body powered prosthetic hand which mass is 55%-68% lower than that of the lightest current prosthetic hands, operates faster, has an anthropomorphic shape, and provides proprioceptive force and position feedback. The hand has articulating fingers, actuated by miniature hydraulic cylinders. The articulating fingers adapt to the shape of the grasped object. Its functional scores are similar to that of current prosthetic devices. The hand has a higher mechanical performance than current body-powered hands. It requires 49%-162% less energy from the user and it can deliver a higher maximum pinch force (30-60 N).

Design and evaluation of two different finger concepts for body-powered prosthetic hand

The goal of this study was to find an efficient method of energy transmission for application in an anthropomorphic underactuated body-powered (BP) prosthetic hand. A pulley-cable finger and a hydraulic cylinder finger were designed and tested to compare the pulley-cable transmission principle with the hydraulic cylinder transmission principle. Both fingers had identical dimensions and a low mass. The only thing that differed between the fingers was the transmission principle. The input energy was measured for a number of tasks. The pulley-cable finger required more input energy than the hydraulic cylinder finger to perform the tasks. This was especially the case in tasks that required high pinch forces. The hydraulic cylinder transmission is therefore the more efficient transmission for application in BP prosthetic fingers.

Performance of above elbow body-powered prostheses in visually guided unconstrained motion tasks

The "classical" body-powered above elbow arm prosthesis continues to be used by a large majority of arm prosthesis users, even though many more modern devices are available. This paper presents a set of experiments designed to compare performance of unimpaired arms and body-powered prostheses of six unilateral amputees. The experiments were designed to measure quantitatively how well the body-powered prosthesis can be used to perform free-motion tasks, as well as to study the qualitative features of movement common to both the prosthesis and unimpaired arm. It was found that regular peaks in velocity were common to both the unimpaired arm and prosthesis movements, suggesting that movements were composed of a sequence of successive actions. In addition, it was found that the body-powered prosthesis generally required more movements than the unimpaired arm to meet an accuracy constraint and could not keep up with the unimpaired arm when a speed constraint was imposed, even though the body-powered prosthesis was able to match the unimpaired arm in a simple nondynamic task.