Closing the Loop Between Body Compensations and Upper Limb Prosthetic Movements: A Feasibility Study

Abstract

To control the robotic joints of an upper limb prosthesis, most existing approaches rely on decoding the user motor intention from electrophysiological signals produced by the subject, and then executing the desired movement. This suffers from important limitations and requires extended training, particularly when a large number of prosthetic joints have to be controlled. Even when they master the control of their prosthesis, many amputees underuse the prosthetic mobility to the benefit of compensatory body movements, whose generation is less expensive and more natural from a cognitive point of view. Indeed, with an arm prosthesis, hand movements result from a combination of human and robotic joint motions. We propose in this paper to use these compensatory motions as an error signal to servo the robotic controller. This approach thus creates a coupling between body compensations and prosthetic movements.To study the feasibility of such a coupling, the concept is tested with ten able-bodied subjects wearing an emulated elbow prosthesis and one congenital arm amputee. The results validate the concept, which allows naive subjects to control the prosthetic joint with no or very short training period.Index Terms-Physical human-robot interaction, prosthetics and exoskeletons, human-in-the-loop and body compensations.

Multichannel haptic feedback unlocks prosthetic hand dexterity

“…This might lead to suboptimal grip forces applied to the objects, which could be ameliorated via a soft-synergy approach with mass-dependent variable gains 54 , or through a grasped object slip prevention algorithm 55 . Additionally, techniques to automate the shoulder, elbow, and wrist joints could be highly beneficial to reduce the cognitive burden on the amputee to multitask by sensing upper body compensatory motions 56 or shoulder kinematics with respect to the grasped object locations 57 to autonomously plan smooth prosthetic arm trajectories. These types of motion planning algorithms could reduce unnecessary oscillations in grip forces and corresponding haptic sensations during object transportation 58 while reflexive compensation for inertial loads during transport could be used to proactively prevent slip of the grasped objects 59 .…”

Simultaneous Control of 2DOF Upper-Limb Prosthesis With Body Compensations-Based Control: A Multiple Cases Study

“…Existing control schemes for upper-limb prosthesis do not provide efficient control for multiple degrees of freedom simultaneously, in any situation. The suggestion of this paper is to extend Compensations Cancellation Control, previously validated on single prosthetic DOF [18], [19], to transhumeral amputees controlling simultaneously two joints, the wrist pronosupination and the elbow flexion/extension. This concept lets the user focus on the end-effector task, while prosthesis motions aim at correcting human posture and cancelling body compensations.…”

“…As presented in [18] and [19], Compensations Cancellation Control (CCC) aims at cancelling the compensations exhibited by the user with prosthesis motions, through a kinematic coupling created between the human and the prosthetic device (see Figure 1). It operates in three steps: (i) analysis of the body posture to evaluate whether the user is currently compensating for an inadequate prosthesis configuration;…”

“…Hand orientation, hip and acromion positions, required in the control law, were measured with a motion capture system OptiTrack © (NaturalPoint, Inc.), and sent in real time to the prosthesis. Following the tuning performed in [19], λ was taken as 2s −1 for the elbow, and to homogenize wrist and elbow velocity during the task, λ was taken as 4s −1 for the wrist. The deadzone threshold vector q 0 was 5 5 deg.…”

“…The more the active prosthetic DOFs, the more complex the control sequence. To remove the need for voluntary control instructions, we have proposed in [18] and [19] to control upper-limb prostheses by cancelling the body compensations of the user. This approach relies on natural behaviours of prosthesis users, i.e.…”