Rahamim Seliktar

A Simple Technique to Passively Gravity-Balance Articulated Mechanisms

A simple method to counter the effects of gravity in articulated mechanisms is proposed. The scheme uses kinematics and linear springs to produce a nonlinear restoring force to oppose the gravitational moment. The method equilibrates a rotational mechanism for all postures. A solution for one link is obtained then general equations for n links are derived. The method is simpler than previous schemes and has applications in robotics, orthotics and a host of everyday mechanisms.

Passive Exoskeletons for Assisting Limb Movement

This article presents the state of the art in passive devices for enhancing limb movement in people with neuromuscular disabilities. Both upper- and lower-limb projects and devices are described. Special emphasis is placed on a passive functional upper-limb orthosis called the Wilmington Robotic Exoskeleton (WREX). The development and testing of the WREX with children with limited arm strength are described. The exoskeleton has two links and 4 degrees of freedom. It uses linear elastic elements that balance the effects of gravity in three dimensions. The experiences of five children with arthrogryposis who used the WREX are described.

Some Gait Characteristics of Below-Knee Amputees and Their Reflection on the Ground Reaction Forces

Human locomotion studies employing cinematography and force plates have been conducted during the last five decades with the goal of producing a clinically acceptable gait evaluation technique. The bulk of information contained in the kinetic studies was the major obstacle in achieving this goal. Our aim in this work was to explore the possibility of representing some locomotor abnormalities solely by their reflection on the ground reaction force characteristics. As a first stage towards the establishment of these relationships, the gait characteristics of below-knee amputees were examined.One hundred and thirty ground force test results as obtained on twenty three below-knee amputees were analysed. Different variables such as time durations of the various phases, peak forces, impulses, rate of change of the forces, and others, were examined. The conclusions suggest that some of these variables are suitable for evaluation of gait and some, such as small perturbations superimposed on the curve, may serve a...

Gait consistency test based on the impulse-momentum theorem

The kinematic and dynamic aspects of human locomotion have been investigated during the last eighty years. Significant contributions were made towards the understanding of the mechanics of movement and of the joints. As a consequence the field of Rehabilitation and Orthopaedic Biomechanics advanced considerably. However the complexity of the kinematic and dynamic data of locomotion prevented the various techniques from becoming clinically applicable. This paper attempts to develop a technique for clinical evaluation of gait by relatively simple means. For this purpose the six components of the ground reaction forces were chosen for an analysis. The major tool of the technique is the time integral of the forces. Since this is a quantitative parameter with a distinct physical definition, it can be very meaningful as far as investment of efforts in ambulation is concerned. As a first step towards the reinforcement of this thesis a consistency test was developed. The consistency test ensures that the use of dynamic forceplates do not impose a bias on the test procedure. The test is meant to indicate whether the results are valid for further processing. The concept of the test is based on the fact that the velocity vector is expected to be equal in two equivalent points of consecutive walk cycles. It therefore follows that the time-force integral which equals the difference of momentum between the two points should be zero. The advantage of this test is that it does not discriminate between normal and pathological gait. The theory was tested with 28 subjects and the results have provided sufficient evidence for its verification.

Alignment procedure for the optimal fitting of lower limb prostheses

Systematic methods for optimizing the fitting and alignment of artificial legs were developed in this study. The procedures were based on gait analysis and included the following aspects: stump-prosthesis interface or socket geometry, the selection of components from which the artificial leg was constructed, and dynamic alignment of the prosthesis. The amputees adaptation to deliberately imposed perturbations in his prosthesis, and the resulting compensatory mechanisms are also discussed.

Partial immobilization of the ankle and talar joints complex and its effect on the ground--foot force characteristics.

A combined qualitative–quantitative approach towards the analysis of the ground reaction forces is suggested so as to detect deficiencies and predict hazards in human locomotion. The population stu...

Using distraction forces to drive an autodistractor during limb lengthening

Distraction osteogenesis can result in high forces developing in the limb. To determine and control the distraction forces (DF), a motorized distractor driven by feedback from DF was developed and used to lengthen the tibiae of 6 sheep undergoing distraction osteogenesis. The forces were measured continually, and, in 4 of the sheep, a force threshold was set, above which an increase in rate was initiated. The rate kept increasing to a set limit if forces remained above the threshold; otherwise, the rate was decreased. Radiographs were acquired biweekly, and muscle samples were analyzed from both the operated and contralateral limbs upon termination of the experiment. Results demonstrated a drop in DF associated with increased lengthening rate, attributed to separation of the callus as indicated by radiography. Histological evidence of muscle damage generally correlated with higher DF levels. There was a significant decrease in muscle fiber diameter in lengthened relative to contralateral limbs. Collectively, the results demonstrated the use of a force-driven distraction system and support the need for considering force data in regulating distraction rates to achieve optimal clinical outcomes.

Study of the Vibromyographic Signal as a Means for Quantifying Muscular Effort

Abstract The present work describes an effort to quantify the level of muscular activation by monitoring and processing muscular vibrations under isometric conditions. The history and nature of vibromyography (VMG) are examined, and a brief review of current VMG literature is presented. In addition, preliminary results from an ongoing study are presented. Although several subjects were included in this feasibility study, the results from only one subject are presented here. The subject was asked to reach 25%, 50%, 75%, and 100% of his maximum isometric elbow extension. A uniaxial accelerometer was placed over his right triceps brachii and monitored the transverse component of the underlying muscles acceleration. Electromyographic (EMG) data were also recorded from the long and lateral heads of the same muscle. Results were then processed using traditional algorithms and the ability of VMG and EMG to discriminate among the four different effort levels were compared. The data indicated that VMG was able to discriminate between the 75% and 100% effort levels better than EMG. Currently, this protocol is being applied to additional subjects using more advanced signal processing as well as discriminant analyses to improve effort level discrimination as well as fatigue detection.

Force feedback in limb lengthening

A new variable-rate distraction system using a motorized distractor driven by feedback from the distraction force was designed. The distractor was mounted on a unilateral fixator and attached to the tibiae of 6 sheep that underwent distraction osteogenesis. The sheep were divided equally into 3 groups. In group 1, the forces were recorded but were not used to drive the lengthening rate. In group 2, force feedback was used and the desired distraction force level was set to 300 N and the initial rate was 1 mm/day. Group 3 also underwent force feedback with the desired force limit at 300 N, but the rate change was initiated earlier, at 200 N. The distraction force was recorded at 15 second intervals throughout the distraction phase and stored onboard the distractor.

Kinematic Analysis Of A 4 D.O.F. Prosthetic Arm Using Extended Physiological Proprioception

The propreoceptive properties of the human arm are emulated in a 4 degree of freedom arm prosthesis that utilizes shoulder movements as command inputs, while the power is external. The redundancy in going from 3 signals to 4 joints, was eliminated by introducing a kinematic constraint that yields arm motion that is cosmetically sound. Motion derived from minimizing the Euclidian norm of joint displacements was also investigated. Through Inverse Kinematics the joint variables, incorporating the constraint, were obtained. Experimental human motion analysis was performed, and results of actual joint trajectories in terms of position, velocity and acceleration were compared with results from the kinematic constraint and the Moore-Penrose pseudoinverse (minimizing Euclidean norm). Results from the kinematic constraint were in good agreement with actual data, suggesting the wlidity of the constraint employed.