Zlatko Matjacic

Universal Haptic Drive: A Robot for Arm and Wrist Rehabilitation

In this paper we present a universal haptic drive (UHD), a device that enables rehabilitation of either arm (“ARM” mode) or wrist (“WRIST” mode) movement in two degrees-of-freedom. The mode of training depends on the selected mechanical configuration, which depends on locking/unlocking of a passive universal joint. Actuation of the device is accomplished by utilizing a series elastic actuation principle, which enables use of off-the-shelf mechanical and actuation components. A proportional force control scheme, needed for implementation of impedance control based movement training, was implemented. The device performance in terms of achievable lower and upper bound of viable impedance range was evaluated through adequately chosen sinusoidal movement in eight directions of a planar movement for the “ARM” mode and in eight directions of a combined wrist flexion/extension and forearm pronation/supination movement for the “WRIST” mode. Additionally, suitability of the universal haptic drive for movement training was tested in a series of training sessions conducted with a chronic stroke subject. The results have shown that reliable and repeatable performance can be achieved in both modes of operation for all tested directions.

Foot-sole reflex receptive fields for human withdrawal reflexes in symmetrical standing position

Human withdrawal-reflex receptive fields were assessed in 10 healthy subjects during standing with even support on both legs. Two electrical-stimulus intensities (1.2 and 2.2 times the pain threshold, PTh) were used. The painful stimuli were delivered in random order to 12 positions distributed over the foot sole. Tibialis anterior (TA), soleus (SO), vastus lateralis (VL), semitendinosus (ST), and iliopsoas (IL) reflexes were recorded. Further, the vertical force was recorded and the center or pressure (CoP) was assessed in the frontal and sagittal planes on both legs. Reflexes were observed at both intensities with the strongest reflexes at the high intensity. Around the ankle joint, SO reflexes dominated, which is in contrast to previous observations for subjects sitting. An unloading of the limb was found on the stimulated leg associated with a simultaneous loading of the contralateral leg. The shift in load was most pronounced for stimulation of the heel. The flexors ST and IL also had strong reflexes with reflex patterns correlated to the pattern of unloading. The shift in vertical force was accomplished by a move of the CoP in the anterior direction on the stimulated limb (contraction of SO), which simultaneously caused a small movement of the CoP in the lateral direction. In the present standing conditions, the ankle extensor played a dominant role in the withdrawal pattern in contrast to previous studies during sitting, relaxed conditions.

Telerehabilitation using virtual reality task can improve balance in patients with stroke

Purpose: The objective of the telerehabilitation is a continuation of the rehabilitation process on patients’ home. The study also compares the balance training in clinical environment with the telerehabilitation approach when the physiotherapists and physicians can follow the progress remotely. Method: In this paper, the preliminary study of the pilot project with virtual reality (VR)-based tasks for dynamic standing frame supported balance training is presented. Six patients with stroke participated in the study. The patients performed the balance training 3 weeks, 2 weeks in the clinical settings and 1 week in the home environment, five times a week, and each time for up to 20 minutes. Objective effectiveness was demonstrated by parameters as track time, number of collisions and the clinical instruments Berg Balance Scale (BBS), Timed Up & Go (TUG), 10-m walk test and standing on the unaffected and affected extremity. The outcomes were compared to the balance training group without VR and telerehabilitation support. A 2-way ANOVA was used to explore the differences between the both stroke groups. Results: In patients who were subject to VR supported balance training, the BBS demonstrated improvement for 15%, the TUG for 29%, the 10-m walk for 26%, stance time on the affected and unaffected extremity for 200 and 67%, respectively. The follow-up demonstrated that the patients preserved the gained functional improvement. The VR task performance time and number of collisions decreased to 45 and 68%, respectively. Besides, no statistical differences were found between the telerehabilitation approach with VR supported balance training and conventional balance training in clinical settings either regarding the overall mean level or regarding the mean improvement. Conclusions: The telerehabilitation approach in VR supported balance training improved balance in stroke patients and had similar effect on patients’ postural functional improvement as conventional balance training in clinical settings. However, when balance training is continued on patient’s home instead of the hospital, it would eventually decrease the number of outpatients’ visits, reduce related costs and enable treatment of larger number of patients. Implications for Rehabilitation People suffering from stroke have severe problems with posture and balance. This study demonstrates that using target based tasks in a virtual environment can improve balance in stroke population. Telerehabilitation offers continuation of balance training in the remote centres or at home. The longer rehabilitation period improves functionality and therefore the quality of life.

Paraplegic standing supported by FES-controlled ankle stiffness

The objective of this paper was to investigate whether a paraplegic subject is able to maintain balance during standing by means of voluntary and reflex activity of the upper body while being supported by closed loop controlled ankle stiffness using FES. The knees and hips of the subject were held in extended positions by a mechanical apparatus, which restricted movement to the sagittal plane. The subject underwent several training sessions where the appropriate level of stiffness around the ankles was maintained by the mechanical apparatus. This enabled the subject to learn how to use the upper body for balancing. After the subject gained adequate skills closed-loop FES was employed to regulate ankle stiffness, replacing the stiffness provided by the apparatus. A method to control antagonist muscle moment was implemented. In subsequent standing sessions, the subject had no difficulties in maintaining balance. When the FES support was withheld, the ability to balance was lost.

Control of posture with FES systems

One of the major obstacles in restoration of functional FES supported standing in paraplegia is the lack of knowledge of a suitable control strategy. The main issue is how to integrate the purposeful actions of the non-paralysed upper body when interacting with the environment while standing, and the actions of the artificial FES control system supporting the paralyzed lower extremities. In this paper we provide a review of our approach to solving this question, which focuses on three inter-related areas: investigations of the basic mechanisms of functional postural responses in neurologically intact subjects; re-training of the residual sensory-motor activities of the upper body in paralyzed individuals; and development of closed-loop FES control systems for support of the paralyzed joints.

Functional postural responses after perturbations in multiple directions in a standing man: a principle of decoupled control

The objective of this study was to assess functional postural responses by analyzing the net joint torques (NJT) in the ankles and the hips resulting from perturbations delivered in multiple directions to subjects standing quietly. A total of eight subjects were standing on two force platforms while an apparatus randomly delivered controlled perturbations at the level of the pelvis in eight directions: anterio-posterior (AP), medio-lateral (ML), and four combinations of these principal directions. Perturbations were repeated five times in each direction for six conditions (i.e., three different perturbation strengths and three different feet orientations). The comparison of the averaged ankle sum NJT (AP) responses showed that the time courses of the responses elicited by a perturbation acting only in the AP direction were identical to those elicited by a combination of two corresponding AP and ML perturbations. In contrast the observed averaged ankle NJT (ML) responses did not follow the same similarity. The comparison of the averaged ankle and hip sum NJT (ML) responses revealed that the time courses of the responses elicited by a perturbation acting only in the ML direction were identical to those elicited by a combination of two corresponding AP and ML perturbations. These findings were invariable of the experimental conditions and were consistent among all the eight subjects. Thereby, we conclude that the ankle sum NJT (AP) and the ankle and hip sum NJT (ML) are the global variables being controlled. This shows that CNS controls the recovery from the multiple direction perturbations of moderate strength by decoupling the AP-ML postural space into two orthogonal directions (AP and ML).

Efficient FES triggering applying Kalman filter during sensory supported treadmill walking

In this paper an algorithm for a functional electrical stimulation (FES) gait re-education system for incomplete spinal cord injured persons, providing efficient stimulation triggering, is presented. During neurological impaired gait FES was provided as motor augmentation support. Simultaneously the gait kinematics were recorded using the proposed sensory system, which is equipped with a dual-axial accelerometer and a gyroscope. The sensory device was placed at the shank of the paretic leg. The data assessed were input into a mathematical algorithm applied for shank angle estimation. The algorithm is based on the Kalman filter, estimating the angle error and correcting the actual measurement. Furthermore the information was combined with other kinematic data for the purpose of efficient and reliable stimulation triggering. The algorithm was tested with preliminary measurements on several neurologically intact persons during even terrain and treadmill walking. Trial measurements were verified with a contactless optical measurement system, with FES only simulated on controller output. Later on a treadmill training in combination with FES triggering was carried out. The outcome of the measurements shows that the use of sensory integration may successfully solve the problem of data assessment in dynamic movement where an inclinometer does not provide sufficient information for efficient control of FES.

Postural activity of constrained subject in response to disturbance in sagittal plane

The study examines postural activity of a constrained subject in response to various disturbances in the sagittal plane. Three different initial standing postures were examined. Each response to a perturbation was divided into three consecutive phases according to the intensity of the muscular activity. The relation of the ankle joint torque versus the ankle joint angle was studied. A linear relationship, resulting in constant ankle stiffness, was observed in each phase of the response. Only negligible differences in the stiffness values were observed among different phases. The results indicate an ankle stiffness value of 10 N m/o for the majority of initial stance postures and perturbation intensities.

Directionally Specific Objective Postural Response Assessment Tool for Treatment Evaluation in Stroke Patients

The aim of the research is to develop an objective evaluation tool for use in stroke rehabilitation clinical practice. Stroke patients are prone to particularly high risk of fall, which may differ for various directions of movement. An apparatus enabling perturbations and postural response assessment in eight directions in transversal plane during standing was used to assess data in seven neurologically intact volunteers and 10 stroke patients before and after the rehabilitation. Ground reaction force and center of pressure were acquired during the perturbation, signal processed and compared to Berg Balance Scale (BBS), a clinical outcome measure of balance. The results of the weight load ratio between the affected and unaffected lower extremity demonstrated objective positive outcomes of the rehabilitation and also correlated with the clinical instrument BBS. Additionally, the center of pressure ratio between the anterior/posterior and medial/lateral peak for each perturbation direction have shown identifiable postural response strategies in selected directions of transverse plane. The directional postural information can be helpful when identifying and evaluating the objective rehabilitation progress which can lead to application of targeted rehabilitation techniques. The directional indicator also demonstrated correlation with the BBS in directions indicating rehabilitation progress. When considering the common use with the clinical instrument, the proposed objective rehabilitation progress evaluation tool may also become helpful in directional fall risk indication. The proposed tool may become a powerful instrument, when the balance training and postural response assessment will move to remote or home environment as a telerehabilitation service.

Design of a series visco-elastic actuator for multi-purpose rehabilitation haptic device

BackgroundVariable structure parallel mechanisms, actuated with low-cost motors with serially added elasticity (series elastic actuator - SEA), has considerable potential in rehabilitation robotics. However, reflected masses of a SEA and variable structure parallel mechanism linked with a compliant actuator result in a potentially unstable coupled mechanical oscillator, which has not been addressed in previous studies.MethodsThe aim of this paper was to investigate through simulation, experimentation and theoretical analysis the necessary conditions that guarantee stability and passivity of a haptic device (based on a variable structure parallel mechanism driven by SEA actuators) when in contact with a human. We have analyzed an equivalent mechanical system where a dissipative element, a mechanical damper was placed in parallel to a spring in SEA.ResultsThe theoretical analysis yielded necessary conditions relating the damping coefficient, spring stiffness, both reflected masses, controllers gain and desired virtual impedance that needs to be fulfilled in order to obtain stable and passive behavior of the device when in contact with a human. The validity of the derived passivity conditions were confirmed in simulations and experimentally.ConclusionsThese results show that by properly designing variable structure parallel mechanisms actuated with SEA, versatile and affordable rehabilitation robotic devices can be conceived, which may facilitate their wide spread use in clinical and home environments.