title: Compensation for the intrinsic dynamics of the InMotion2 robot.
abstract: The InMotion2 and other similarly designed robots, are commonly used for rehabilitation of neurological injuries and motor adaptation studies. These robots are used to simulate haptic environments; however, anisotropy in end-point impedance due to the intrinsic robot dynamics can compromise these experiments. The goal was to decrease the magnitude and anisotropy of the robot impedance using a dynamic compensation algorithm that reduces the forces normally felt by the user during rapid movements. We tested this algorithm with two different methods for real-time calculation of derivatives, a novel quadratic fit method (CQF) and the commonly used backward derivative method (CBD). Six subjects performed a series of point-to-point movements under three conditions (no compensation, CQF, CBD), in different directions at peak speeds of 50, 100 and 150 cm/s. Without compensation, tangential peak-to-peak forces were as large as 69 N in certain directions at the 150 cm/s speed. Both CQF and CBD significantly reduced tangential forces in all directions and speeds. CQF outperformed CBD in the directions with highest intrinsic impedance, reducing tangential forces by 64% in these directions. Compensation also significantly reduced forces normal to the movement direction, with CQF again outperforming CBD in several cases. Anisotropy was assessed by the range of tangential peak-to-peak forces across movement directions. In the no compensation condition, anisotropy was as high as 52.7 N at the 150 cm/s speed, but an average anisotropy reduction of 74% was achieved with CQF. The CQF method can significantly reduce impedance and anisotropy in this class of robot.
authors: Center for Applied Biomechanics and Rehabilitation Research at the National Rehabilitation Hospital, Washington, DC, USA.
authors: Hoi B
authors: HB
authors: Nguyen
authors: Peter S
authors: PS
authors: Lum
mesh_terms: D000328:Adult; D000465:Algorithms; D016880:Anisotropy; D001132:Arm / Q000294:innervation / Q000502:physiology; D001696:Biomechanical Phenomena; D017097:Electric Impedance; D005260:Female; D006801:Humans; D008297:Male; D009069:Movement Disorders / Q000534:rehabilitation; D011597:Psychomotor Performance; D012371:Robotics / Q000295:instrumentation; D019415:Torque; D055815:Young Adult