A closed-loop and ergonomic control for prosthetic wrist rotation

Abstract

Beyond the ultimate goal of prosthetics, repairing all the capabilities of amputees, the development line of upperlimb prostheses control mainly relies on three aspects: the robustness, the intuitiveness and the reduction of mental fatigue. Many complex structures and algorithms are proposed but no one question a common open-loop nature, where the user is the one in charge of correcting errors. Yet, closing the control loop at the prosthetic level may help to improve the three main lines of research cited above. One major issue to build a closed-loop control is the definition of a reliable error signal; this paper proposes to use body compensations, naturally exhibited by prostheses users when the motion of their device is inaccurate, as such. The described control scheme measures these compensatory movements and makes the prosthesis move in order to bring back the user into an ergonomic posture. The function of the prosthesis is no longer to perform a given motion but rather to correct the posture of its user while s/he focus on performing an endpoint task. This concept was validated and compared to a standard open-loop scheme, for the control of a prosthetic wrist, with five healthy subjects completing a dedicated task with a customized transradial prosthesis. Results show that the presented closed-loop control allows for more intuitiveness and less mental burden without enhancing body compensation.

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;…”

“…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.…”

Controlling Upper-Limb Prostheses with Body Compensations

“…Note that this scheme is valid to control intermediate joints like wrist, elbow and shoulder, but not for hand since no body compensation substitutes grasping functions. This paradigm has already been explored and validated for the control of wrist pronosupination with able-bodied subjects [6]. In the work presented here, we extend this study to transradial amputated people, on a different task.…”

“…The control law implemented to servo the prosthetic wrist pronosupination to the user's compensatory motions is the same as the one presented in [6]; we briefly recall it below. To supplant wrist pronosupination, amputated subjects tend to use trunk and arm compensatory motions to change the hand orientation [4].…”