A Subject-Adaptive Controller for Wrist Robotic Rehabilitation

Abstract

In order to derive maximum benefit from robotassisted rehabilitation, it is critical that the implemented control algorithms promote the participant's active engagement in therapy. Assist-as-needed (AAN) controllers address this need by providing only appropriate assistance during movement execution. Often, these controllers depend on the definition of an optimal movement profile, against which the participant's movements are compared. In this paper, we present a novel subject-adaptive controller, consisting of two main components: AAN control algorithm and online trajectory recalculation. First, the AAN control algorithm is based on an adaptive controller and introduces a novel feedback gain modification algorithm. Coupled with the uniformly ultimately bounded stability property of the resulting dynamic system, the developed controller is capable of changing the amount of error allowed during movement execution, while simultaneously estimating the forces provided by the participant that contribute to movement execution. Second, we present a real-time trajectory generation algorithm based on a physiologically optimal and experimentally validated asymmetric wrist movement profile. The feedback gain modification and trajectory generation algorithms are validated with the RiceWrist system in an experimental study involving five healthy subjects, with the modified AAN adaptive controller decreasing its feedback control action when a subject shifts his behavior from passively riding along with the robot during movement to actively engaging and initiating movements to the desired on-screen targets.

Robust Iterative Feedback Tuning Control of a Compliant Rehabilitation Robot for Repetitive Ankle Training

“…Thereby the shank's position will not be consistent during the operation, and the orientation of the robotic platform is thus unlikely to be the same as the actual rotation of ankle joint. Meanwhile, a majority of existing devices utilise rigid actuators such as electric motors or cylinders which are not back-driveable [7]. As a result of this, the human interaction environment is not fully compliant during operation of the devices.…”

Characterization of a hand-wrist exoskeleton, READAPT, via kinematic analysis of redundant pointing tasks

“…The robot possesses non-negligible inertial and friction characteristics that should alter movement. While models of wrist dynamics [15] show limited inertial effects on pointing movement dynamics, the inertia of the READAPT, approximately the same as the wrist module, [24] is nearly a five-fold increase over the inertia used in a biomechanical model, [15] which could have an effect on wrist pointing movements. Since static friction is not present in the model, it could have an even greater perturbing effect on kinematic couplings.…”

Design of a parallel-group balanced controlled trial to test the effects of assist-as-needed robotic therapy

“…1), we adapt the controller proposed in [14], which consists of three main components: subject ability estimation, feedback gain modification, and on-line trajectory recalculation. The subject ability estimation algorithm employed in this study was based on the adaptive controller [20], using the following adaptation law:θ…”

“…For this study, we extende our previous formulation by introducing direction dependency on the regressor matrix Y = Y (x,ẋ), considering that an impaired subject might have different levels of disability on their agonist and antagonist muscles. As in [14], we use Gaussian Radial Basis Functions (RBFs) as known functions included in the regressor matrix, but we doubled the set of RBFs for each DOF to account for direction dependence.…”

“…This lack of knowledge is surprising, especially if we consider the continuously increasing efforts that roboticists are devoting to the formalization and implementation of shared control modes to facilitate robot-assisted rehabilitation protocols [12]- [14]. A necessary condition for such research efforts to have translational significance is to test their effects in a clinical population.…”