Design of Two Robotically Facilitated Simulations in Virtual Environments to Train the Hemiplegic Upper Extremity of Persons Post-Stroke

Qinyin Qiu MS, Gerard G. Fluet DPT, Alma S. Merians PT, PhD, Abraham Mathai MS, Sergei Adamovich PhD.

Current neuroscience has identified several constructs to increase the effectiveness of upper extremity rehabilitation. One is the use of progressive, skill acquisition-oriented training programs. This paper describes the design and feasibility testing of an impedance controlled robotic / virtual environment system designed to train the arm of persons who have had strokes.

The Haptic Master is a 3 degrees of freedom admittance controlled (force controlled) robot. 3 dimensional force sensors measure the external force exerted by the user on the robot. The acceleration, velocity and position are calculated in real time to generate reactive motion. The Haptic Master can be programmed to produce haptic effects, such as spring, damper and constant force. Virtual objects, including blocks, cylinders and spheres are also created. The Haptic Master records position and force in three dimensions at a rate of 100 Hz, allowing the movement arm to act as an interface between the participants and the virtual environments.

We designed several modalities to interface the paretic upper extremity of our subjects including a stationary 1.5 inch diameter sphere connected to the robot, a glove that secures the sphere at the end of the haptic master to the palm of the subject and a ball and socket joint attached to the palmar surface of a pre-fabricated resting hand splint.

2 simulations have been developed and tested in our lab, the Reach and Touch simulation focuses on improving the speed and accuracy of shoulder and elbow movements during aiming and reaching movements. This simulation presents a 3-dimensional stereo working space, using stereoscopic glasses, to enhance depth perception. Multiple haptic effects are used to assist subjects in accomplishing this activity. The first is a spring that draws the subject toward the target. A second haptic effect used to accommodate persons with strength impairments is a ramp, which provides an invisible tilted floor that goes through the starting point and the target. A third haptic effect, a range restriction, limits the participant’s ability to deviate from an ideal trajectory toward each target.

The goal of the Cup Reaching simulation is to improve general upper extremity strength and to improve reaching accuracy. The screen displays a three-dimensional room with haptically rendered shelves and table. The participant uses their virtual hand (hemiparetic side) to lift virtual cups and place them onto one of three spots on three shelves.Haptic feedback is employed in this simulation to provide feedback to shape trajectories performed by the participant. The “weight “of the haptic cups can be adjusted, which allows for weighted strengthening activities for less impaired as well as anti-gravity assisted movement for weaker subjects. A damping effect can be applied by the Haptic Master which opposes the subjects movement of the Haptic Master in 3 dimensions. The augmented force feedback provided by the damping effect reduces the need for the impaired user to grade forces as they must when the Haptic Master is moving freely.

Three subjects with chronic strokes performed 6 to 14 hours of training on the Haptic Master to establish its feasibility and safety. No adverse responses were experienced during or after training. All three pilot subjects experienced improvements in kinematic measures during their robotic training activities and all of them also demonstrated performance improvement on elements of clinical testing batteries, despite the fact that they were neurologically “stable” and in the chronic phase of their recovery from stroke.
This supports our assertion that this system is safe and that training with it is feasible and worthy of further study.