Derek G. Kamper

Finger impairment following stroke results in significant deficits in hand manipulation and the performance of everyday tasks. While recent advances in rehabilitation robotics have shown promise for facilitating functional improvement, it remains unclear how best to employ these devices to maximize benefits. Current devices for the hand, however, lack the capacity to fully explore the space of possible training paradigms. Particularly, they cannot provide the independent joint control and levels of velocity and torque required. To fill this need, we have developed a prototype for one digit, the cable actuated finger exoskeleton (CAFE), a three-degree-of-freedom robotic exoskeleton for the index finger. This paper presents the design and development of the CAFE, with performance testing results.

The purpose of this study was to examine force transmission from one of the major multi-articular muscles of the finger, flexor digitorum pro-fundus (FDP), to the index finger. Specifically, we examined whether the popular moment arm (MA)-joint torque technique of modeling muscle force transmission can accurately represent the effects of the FDP on finger movement. A dynamic finger model employing geometric MA values (model I) was compared with another model including realistic tendon force transformation mechanisms via pulley structures and joint reaction forces (model II). Finger flexion movements generated by these models were compared with those obtained from in vivo stimulation experiments. The model with the force transformation mechanisms (model II) resulted in more realistic joint spatial coordination (i.e., proximal interphalangeal > metacarpophalangeal ges distal interphalangeal) than the MA-based model (model I) in relation to the movement patterns evoked by stimulation. Also, the importance of the pulley structures and passive joint characteristics was confirmed in the model simulation; altering/eliminating these components significantly changed the spatial coordination of the joint angles during the resulting movements. The results of this study emphasize the functional importance of the force transformation through various biomechanical components, and suggest the importance of including these components when investigating finger motor control, such as for examining injury mechanisms or designing rehabilitation protocols.

Chronic hand impairment is common following stroke. While mass practice of movement has shown promise for rehabilitation, initial impairment of the hand may be too severe to permit even approximations of the desired movement. To facilitate movement, especially of pinch, we are building an exoskeleton to permit independent actuation of each of the three joints of the index finger. Separate actuators are used for flexion and extension, with closed-loop control of either force or position. In the future, a companion thumb exoskeleton will be developed to permit coordinated performance of pinch. This system will be used to assess strategies for optimizing rehabilitation of pinch and reach-to-pinch following stroke. The design of the actuated index finger exoskeleton is presented here.

In this paper, the effects of three visual factors: scene complexity, stereovision and motion parallax on correct perception of a virtual object's size were analyzed in an immersive virtual environment. We designed a controlled experiments set to incorporate visual conditions that reflected all twelve different configuration combinations of the three visual factors. Under each visual condition, subject performed the task of making judgments of the sizes of a virtual object displayed at five different distances from him/her. A total number of eighteen subjects participated in our study. The subjects' judgments and the corresponding actual sizes of the virtual object were recorded. Based on the collected data, two quantitative measures of subjects' performance were derived and analyzed. The results of our experiments were consistent across the majority of the subject population and suggested that scene complexity and stereovision could have significant impact on the performance of a user of virtual environments to make correct judgments on a virtual object's size. On the contrary, motion parallax, either produced by the virtual environment or by the observer, might not be a significant factor in determining that performance

The patterns of interlimb coupling were examined in 10 stroke survivors with chronic hand impairment. In particular, the potential roles of postural state and motor tasks in promoting the flexed posture of the upper extremity were assessed. Through the use of electromyography analysis, joint angle measurements and a novel biomechanical apparatus to perturb the digits of the hand into extension, measurements of muscle activity and joint position were compared during multiple postural states, locomotion and voluntary muscle activity. The results demonstrated a significant increase in flexion of the digits (P < 0.001) and elbow (P < 0.005), during walking as compared with standing, sitting or laying supine. These results were indicative of an overall excessive activation coupling between the upper and lower extremities after stroke. Indeed both voluntary finger flexion and voluntary leg extension produced significant activity in the other impaired extremity, leg and arm, respectively, in the stroke as compared with the control subjects. Thus, rectus femoris in the impaired leg was active during finger flexion of the impaired hand in the stroke survivors and all four tested muscles in the impaired arm were active during extension of the legs (P < 0.05). These findings suggest an interlimb coupling related to active motor tasks, contributing to an upper extremity flexion bias following stroke.

The goal of this research was to evaluate the usefulness of a wireless custom monitor in measuring real-time finger posture over an extended period of time as the wearer goes about daily life activities. One individual wore the device for 25 continuous hours in the research facility and at home. Initial data analysis methods have been presented to explore different aspects of hand activity over time. Evaluating mean flexion over five minute intervals reveals common hand postures assumed throughout the day, while total joint excursion over longer intervals highlights periods of inactivity associated with sleep or rest, as well as periods of higher intensity activities that can be used to evaluate compliance with physical therapy and home rehabilitation instructions

The goal of this research was to evaluate the usefulness of a wireless custom monitor in measuring real-time finger posture over an extended period of time as the wearer goes about daily life activities. One individual wore the device for 25 continuous hours in the research facility and at home. Initial data analysis methods have been presented to explore different aspects of hand activity over time. Evaluating mean flexion over five minute intervals reveals common hand postures assumed throughout the day, while total joint excursion over longer intervals highlights periods of inactivity associated with sleep or rest, as well as periods of higher intensity activities that can be used to evaluate compliance with physical therapy and home rehabilitation instructions