Compensation for the intrinsic dynamics of the InMotion2 robot. 

<br/><br/> 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. Copyright  2013 Elsevier B.V. All rights reserved. 
<br/><br/><br/>English 
<br/><br/><label>ISSN: </label>0165-0270 
<br/><br/><label>Subjects--Topical Terms: </label><br/>*Robotics<br/>Adult<br/>Algorithms<br/>Anisotropy<br/>Arm/ir [Innervation]<br/>Arm/ph [Physiology]<br/>Biomechanics<br/>Electric Impedance<br/>Female<br/>Humans<br/>Male<br/>Movement Disorders/rh [Rehabilitation]<br/>Psychomotor Performance<br/>Robotics/is [Instrumentation]<br/>Torque<br/>Young Adult
<br/><br/><label>Subjects--Geographic Terms: </label><br/>MedStar National Rehabilitation Network
<br/><br/><label>Index Terms--Function: </label><br/>Journal Article<br/>Randomized Controlled Trial<br/>Research Support, U.S. Gov't, Non-P.H.S.