Tadej Bajd

Standing-up of a healthy subject and a paraplegic patient

The joint torques in hip, knee and ankle were measured during the standing-up of a healthy subject. Force plate and stroboscopic photography were used in the experiment. It has been observed that the time courses of particular joint torques depend on the kind of standing-up. On the basis of these results a standing-up procedure for paraplegic patients was proposed. With the use of electrical stimulation to both paralyzed knee extensors and through use of the arm support, a completely paraplegic patient was able to rise independently from the wheel-chair. The same dual-channel stimulation also provides knee locking during standing of spinal cord injured patients.

Application of Model Reference Adaptive Control to Industrial Robot Impedance Control

The paper deals with the application of model reference adaptive control to robot impedance control, which is actually a technique of steering the end-effector on a prescribed path and satisfying a prescribed dynamic relationship between the force and the end-effector position. Due to unknown parameters of the environment (stiffness, exact position), a model reference algorithm is proposed which differs from classical algorithms in its method of excitation. The results of the proposed procedure are illustrated by implementation on the ASEA IRb 6 industrial robot.

Use of functional electrical stimulation in the rehabilitation of patients with incomplete spinal cord injuries

When patients enter the Rehabilitation Centre a therapeutic electrical stimulation programme is immediately initiated. Three groups of patients were identified: (i) those in whom an improvement of both voluntary and stimulated muscle force was observed, (ii) those with an increase in stimulation response only, and (iii) patients in whom no effect of electrical stimulation training could be recorded. Isometric measurement of voluntary and stimulated knee joint torque revealed that in a great number of patients one leg was severely paralysed while the other leg was under sufficient voluntary control. Unilateral two-channel stimulation of knee extensors and the peroneal nerve was proposed as an orthotic aid for this group of patients. Exaggerated extensor tone was observed by assessment of spasticity around the knee joint. A two-channel peroneal stimulator was found to be a useful approach in order to inhibit this tone and thereby help the patients to initiate a step.

Rehabilitation robotics

The paper presents the background, main achievements and components of rehabilitation robotics in a simple way, using non-technical terms. The introductory part looks at the development of robotic approaches in the rehabilitation of neurological patients and outlines the principles of robotic device interactions with patients. There follows a section on virtual reality in rehabilitation. Hapticity and interaction between robot and human are presented in order to understand the added value of robotics that cannot be exploited in other devices. The importance of passive exercise and active tasks is then discussed using the results of various clinical trials, followed by the place of upper and lower extremity robotic devices in rehabilitation practice. The closing section refers to the general importance of measurements in this area and stresses quantitative measurements as one of the advantages in using robotic devices.

Posture switching for prolonging functional electrical stimulation standing in paraplegic patients

The presently employed posture for Functional Electrical Stimulation (FES) assisted standing in spinal cord injury (SCI) patients utilises the active locking of knee joints by tetanically stimulating the quadriceps muscle. The hip joints are in hyper extension and the ankle joints remain free. The upper limbs are used for balancing. This posture requires minimal corrective forces exerted by the hands, the weight is transferred across the legs, while very limited forward-backward sway is permitted. Knee jack-knifing may occur in the instance when the gravity knee bending moment exceeds the moment generated by the quadriceps muscle. Because of these effects and fatiguing of the M. quadriceps the standing time is short, lasting from several minutes up to an hour, depending on the condition of the patients muscles. Cyclical FES with a duty cycle of 10-20 seconds (onjoff) fatigues muscle considerably less. The use of different postures for standing requiring activation of different muscles permits the application of cyclical FES. The cyclic FES results in prolonging standing times by a factor of two to five. Utilising this improvement some patients can stand for up to five hours at a time. This functional achievement is comparable to the standing time of a normal man. The incorporation of the principle of posture switching also prolongs standing in patients with weak muscles, because of the possibility of cyclical coactivation of different synergistic muscle assemblies. It is shown that posture switching can be carried out automatically and that patients adapt quickly to it. In addition using co-contraction of two or three muscles with posture switching does further expand the range of suitable patients and improves standing with an increased permissible range of body sway. Also, the FES antigravity action obtained raises hopes for substantially improving FES induced reciprocal gait.

Standing-up robot: an assistive rehabilitative device for training and assessment

In this paper a robotic assistive device is presented, aimed at assisting physically impaired individuals when rising from a sitting to a standing position. The robotic device is designed as a three degrees of freedom (3-DOF) mechanism supporting the subject under the buttocks. The device is driven by an electrohydraulic servosystem capable of operating in multiple control modes. It is instrumented with a sensory system providing information about the standing-up parameters. Evaluation of the standing up assistive device was accomplished in robot-supported rising trials of a paraplegic subject. The experiments demonstrated that stable risings in different standing – up manoeuvres were achieved. The measurement results revealed the role of the arm support and the support of the artificially evoked moments in the paralysed lower extremities during rising. The results show that the device can be used efficiently for training and evaluation of standing up manoeuvres.

A dynamic model of the ankle joint under functional electrical stimulation in free movement and isometric conditions

Abstract This paper describes a dynamic model of the ankle joint in which ago- and antagonistic muscle groups are under functional electrical stimulation. To the first approximation these muscles perform the dorsal and plantar flexion of the ankle. The model describes the behaviour of the joint in isometric and in free movement conditions. Considered are the delays between excitation and response, and three non-linearities, namely; the stimulating voltage threshold, the Coulomb friction in the joint, and different muscle behaviour during contraction and relaxation. The majority of model parameters were directly measured on from 3 to 10 normal subjects. The rest of parameters were determined by the brute-force method of parameter identification on one normal subject. The real system responses to different stimulating functions are compared to the respective responses of the model simulated on a digital computer. The response agreement is investigated in the frequency and time domains.

Quantitative Gait Evaluation of Hemiplegic Patients Using Electrical Stimulation Orthoses

Although the functional electrical stimulation orthosis is one of the most recent approaches to the rehabilitation of hemiplegic patients, the quantitative estimate of its influence on the patients walking is not satisfactorily solved. In this communication the variables necessary for gait evaluation are defined and two quantitative methods for their interpretation are given. The second method was tested on eight hemiplegic patients. The results show the applicability of the described techniques of evaluation.

Nonlinear modeling of FES-supported standing-up in paraplegia for selection of feedback sensors

This paper presents analysis of the standing-up manoeuvre in paraplegia considering the body supportive forces as a potential feedback source in functional electrical stimulation (FES)-assisted standing-up. The analysis investigates the significance of arm, feet, and seat reaction signals to the human body center-of-mass (COM) trajectory reconstruction. The standing-up behavior of eight paraplegic subjects was analyzed, measuring the motion kinematics and reaction forces to provide the data for modeling. Two nonlinear empirical modeling methods are implemented-Gaussian process (GP) priors and multilayer perceptron artificial neural networks (ANN)-and their performance in vertical and horizontal COM component reconstruction is compared. As the input, ten sensory configurations that incorporated different number of sensors were evaluated trading off the modeling performance for variables chosen and ease-of-use in everyday application. For the purpose of evaluation, the root-mean-square difference was calculated between the model output and the kinematics-based COM trajectory. Results show that the force feedback in COM assessment in FES assisted standing-up is comparable alternative to the kinematics measurement systems. It was demonstrated that the GP provided better modeling performance, at higher computational cost. Moreover, on the basis of averaged results, the use of a sensory system incorporating a six-dimensional handle force sensor and an instrumented foot insole is recommended. The configuration is practical for realization and with the GP model achieves an average accuracy of COM estimation 16 /spl plusmn/ 1.8 mm in horizontal and 39 /spl plusmn/ 3.7 mm in vertical direction. Some other configurations analyzed in the study exhibit better modeling accuracy, but are less practical for everyday usage.

Bending moments in lower extremity bones for two standing postures

The goal of this paper is to study how external gravitational forces stress the lower extremity bones and to ascertain and study how muscle activation compensates for the external load. For these purposes relatively accurate anatomical and biomechanical modelling is necessary. For a comparison of the calculated results to the naturally occurring muscular activity, seven-channel surface EMG activity was recorded. For simplicity a two-dimensional model was developed for the sagittal plane including 19 lower extremity muscles relevant to human standing and walking. In the calculation procedure of muscle forces an optimization procedure is also included. The results give rise to the expected assumption that muscle action is covered by two main requirements: first, to stabilize the joint actively (moment equilibrium) and, second, to compensate efficiently for bending moments produced by gravitational and external forces.