Mark E. Dohring

Feasibility of a new application of noninvasive Brain Computer Interface (BCI): a case study of training for recovery of volitional motor control after stroke.

Background/Purpose: A large proportion of individuals with stroke have persistent deficits for which current interventions have not restored normal motor behavior. Noninvasive brain computer interfaces (BCIs) have potential advantages for restoration of function. There are also potential advantages for combining BCI with functional electrical stimulation (FES). We tested the feasibility of combined BCI + FES for motor learning after stroke. Case Description: The participant was a 43-year-old woman who was 10 months post-stroke. She was unable to produce isolated movement of any of the digits of her involved hand. With effort she exhibited simultaneous mass hyperextension of metacarpal phalangeal joints of all four fingers and thumb with simultaneous flexion of proximal interphalangeal and distal interphalangeal joints of all fingers. Intervention: Brain signals from the lesioned hemisphere were used to trigger FES for movement practice. The BCI + FES intervention consisted of trials of either attempted finger movement and relax conditions or imagined finger movement and relax conditions. The training was performed three times per week for three weeks (nine sessions total). Outcome: The participant exhibited highly accurate control of brain signal in the first session for attempted movement (97%), imagined movement (83%), and some difficulties with attempted relaxation (65%). By session 6, control of relaxation (deactivation of brain signal) improved to >80%. After nine sessions (three per week) of BCI + FES intervention, the participant demonstrated recovery of volitional isolated index finger extension. Discussion: BCI + FES training for motor learning after stroke was feasible. A highly accurate brain signal control was achieved, and this signal could be reliably used to trigger the FES device for isolated index finger extension. With training, volitional control of isolated finger extension was attained in a small number of sessions. The source of motor recovery could be attributable to BCI, FES, combined BCI + FES, or whole arm or hand motor task practice.

Response to upper-limb robotics and functional neuromuscular stimulation following stroke.

Twelve moderately to severely involved chronic stroke survivors (>12 mo) were randomized to one of two treatments: robotics and motor learning (ROB-ML) or functional neuromuscular stimulation and motor learning (FNS-ML). Treatment was 5 h/d, 5 d/wk for 12 wk. ROB-ML group had 1.5 h per session devoted to robotics shoulder and elbow (S/E) training. FNS-ML had 1.5 h per session devoted to functional neuromuscular stimulation (surface electrodes) for wrist and hand (W/H) flexors/extensors. The primary outcome measure was the functional measure Arm Motor Ability Test (AMAT). Secondary measures were AMAT-S/E and AMAT-W/H, Fugl-Meyer (FM) upper-limb coordination, and the motor control measures of target accuracy (TA) and smoothness of movement (SM). ROB-ML produced significant gains in AMAT, AMAT-S/E, FM upper-limb coordination, TA, and SM. FNS-ML produced significant gains in AMAT-W/H and FM upper-limb coordination.

Augmented impedance control: an approach to compliant control of kinematically redundant manipulators

A control method that achieves impedance control of redundant degree-of-freedom manipulators is proposed. The technique combines reduced-order impedance control with configuration control to achieve impedance control of the hand and integrable control of the redundancy. The resulting controlled dynamics is shown to present a passive physical equivalent impedance, thus guaranteeing stability in contact with arbitrary passive environment. In addition, it is shown that there are severe restrictions in choosing the desired hand inertia.<<ETX>>

Admittance enhancement in force feedback of dynamic systems

A limitation of high-speed contact operations, including robotic assembly, is the magnitude of contact forces resulting from inertial effects. Directly attempting to reduce the apparent inertia of interacting systems through force feedback results in instability. It is shown here that one can introduce a mechanical filter to alter the open-loop system dynamics, making feedback much more effective. Experimental results are presented showing a reduction in apparent inertia by nearly two orders of magnitude.

A load-dependent transmission friction model: theory and experiments

Mechanical transmission dynamics are a major source of motion disturbances and prospective instability in feedback. To overcome this problem, feed-forward compensation is often added to the control algorithm requiring an accurate friction model. A load-dependent friction model based on a wedge-like planar transmission is presented. The effects of load dependence, backlash, and tooth preload can be incorporated into the model. Derivation of the model is presented together with the results of experiments performed on a worn gear drive and a discussion of how the data fits the model.<<ETX>>

The passivity of natural admittance control implementations

Natural Admittance Control (NAC) has been proposed as a means of implementing responsive force control that is both gentle and rapid while maintaining an end-effector admittance that is passive. Practical implementations, however, must deviate from the ideal NAC formulation, impacting the passivity of the manipulator. Issues arise particularly in the case where NAC is retrofitted to an existing industrial robot controller. Command input may be restricted to only position commands, and the servo algorithm may be fixed. Direct torque control is often not possible, precluding the use of torque feed-forward. Finally, the feedback sensors signals themselves often contain filters. Each of these three effects is examined and their effects on NAC implementations are identified by considering a simplified, continuous-time model of a typical NAC implementation.

Preliminary Design and Testing of a Novel Robot Design for Metal Finishing Applications

We present a novel robot design concept intended for material removal in finishing operations. A key component of the design is a cable-driven transmission that exhibits low friction, negligible backlash and high linearity. Use of this transmission in a 2-DOF test rig demonstrated the capacity for stable, smooth performance in grinding and polishing operations. The prototype could be programmed quickly to remove surface flaws using compliant lead-through for teaching. During grinding, the robot was capable of measuring surface profiles to monitor grinding progress. A full-mobility design concept is proposed for an advanced surface-finishing robot.

Design of Robot Controllers for Cooperative Interactive Dynamics

Achieving autonomous competence in dynamic robotic operations involving physical interactions remains a challenge. Recent experimental evidence suggests a pathway to constructing controllers that embody generic skills of dynamic interaction. We describe a means to encode interactive skills in terms of a low-level impedance controller, parameters describing virtual dynamics as an interface to a discrete-event control layer, and the interpretation and synthesis of skills using atomic behaviors. Experimental results are described illustrating high levels of task competence in specific examples.