Marcia K. O’Malley

Shared Control in Haptic Systems for Performance Enhancement and Training

This paper presents a shared-control interaction paradigm for haptic interface systems, with experimental data from two user studies. Shared control, evolved from its initial telerobotics applications, is adapted as a form of haptic assistance in that the haptic device contributes to execution of a dynamic manual target-hitting task via force commands from an automatic controller. Compared to haptic virtual environments, which merely display the physics of the virtual system, or to passive methods of haptic assistance for performance enhancement based on virtual fixtures, the shared-control approach offers a method for actively demonstrating desired motions during virtual environment interactions. The paper presents a thorough review of the literature related to haptic assistance. In addition, two experiments were conducted to independently verify the efficacy of the shared-control approach for performance enhancement and improved training effectiveness of the task. In the first experiment, shared control is found to be as effective as virtual fixtures for performance enhancement, with both methods resulting in significantly better performance in terms of time between target hits for the manual target-hitting task than sessions where subjects feel only the forces arising from the mass-spring-damper system dynamics. Since shared control is more general than virtual fixtures, this approach may be extremely beneficial for performance enhancement in virtual environments. In terms of training enhancement, shared control and virtual fixtures were no better than practice in an unassisted mode. For manual control tasks, such as the one described in this paper, shared control is beneficial for performance enhancement, but may not be viable for enhancing training effectiveness.

Current Trends in Robot-Assisted Upper-Limb Stroke Rehabilitation: Promoting Patient Engagement in Therapy

Stroke is one of the leading causes of long-term disability today; therefore, many research efforts are focused on designing maximally effective and efficient treatment methods. In particular, robotic stroke rehabilitation has received significant attention for upper-limb therapy due to its ability to provide high-intensity repetitive movement therapy with less effort than would be required for traditional methods. Recent research has focused on increasing patient engagement in therapy, which has been shown to be important for inducing neural plasticity to facilitate recovery. Robotic therapy devices enable unique methods for promoting patient engagement by providing assistance only as needed and by detecting patient movement intent to drive to the device. Use of these methods has demonstrated improvements in functional outcomes, but careful comparisons between methods remain to be done. Future work should include controlled clinical trials and comparisons of effectiveness of different methods for patients with different abilities and needs in order to inform future development of patient-specific therapeutic protocols.

Disturbance-Observer-Based Force Estimation for Haptic Feedback

In this paper, we propose the use of a nonlinear disturbanceobserver for estimation of contact forces during haptic interactions. Most commonly used impedance-type haptic interfaces employ open-loop force control under the assumption of pseudostatic interactions. Advanced force control in such interfaces can increase simulation fidelity through improvement of the transparency of the device. However, closed-loop force feedback is limited both due to the bandwidth limitations of force sensing and the associated cost of force sensors required for its implementation. Using a disturbance-observer, we estimate contact forces at the tool tip, then use these estimates for closed-loop control of the haptic interface. Simulation and experimental results, utilizing a custom single degree-of-freedom haptic interface, are presented to demonstrate the efficacy of the proposed disturbance-observer (DO)-based control approach. This approach circumvents the traditional drawbacks of force sensing while exhibiting the advantages of closed-loop force control in haptic devices. Results show that the proposed disturbance-observer can reliably estimate contact forces at the human-robot interface. The DO-based control approach is experimentally shown to improve haptic interface fidelity over a purely open-loop display while maintaining stable and vibration-free interactions between the human user and virtual environment. DOI: 10.1115/1.4001274

Position Synchronization in Bilateral Teleoperation Under Time-Varying Communication Delays

Passivity-based approaches to bilateral teleoperation sacrifice performance to achieve robust stability against time-varying delays. Typically, force and velocity signals are exchanged in passivity-based bilateral teleoperation resulting in good velocity tracking, but may accrue a position drift. Recently, a power-based time domain passivity approach (TDPA) was proposed to passivate the communication channel in bilateral teleoperation with time-varying delays, which has the potential to be less conservative than other time-invariant passivity-based approaches. Several approaches have been proposed to address the problem of position drift in time-invariant passivity-based approaches to bilateral teleoperation, but the problem of position drift with power-based TDPA remains unsolved. We propose a feedback passivity-control-based scheme to achieve position synchronization in bilateral teleoperation with power-based TDPA. Our proposed method encodes position information with velocity to construct a composite signal, which is transmitted across the communication channel to attain position tracking. The proposed method utilizes time delay power network formulation, enabling extension to position-measured force bilateral teleoperation scheme. Simulations and experiments conducted on a custom one degree of freedom teleoperation setup demonstrate robust position tracking performance with our approach under time-varying communication delays and remote environment conditions.

Transcranial direct current stimulation (tDCS) of the primary motor cortex and robot-assisted arm training in chronic incomplete cervical spinal cord injury: A proof of concept sham-randomized clinical study

BACKGROUND After cervical spinal cord injury, current options for treatment of upper extremity motor functions have been limited to traditional approaches. However, there is a substantial need to explore more rigorous alternative treatments to facilitate motor recovery. OBJECTIVE To demonstrate whether anodal-primary motor cortex (M1) excitability enhancement (with cathodal-supra orbital area) (atDCS) combined with robot-assisted arm training (R-AAT) will provide greater improvement in contralateral arm and hand motor functions compared to sham stimulation (stDCS) and R-AAT in patients with chronic, incomplete cervical spinal cord injury (iCSCI). METHODS In this parallel-group, double-blinded, randomized and sham-controlled trial, nine participants with chronic iCSCI (AIS C and D level) were randomized to receive 10 sessions of atDCS or stDSC combined with R-AAT. Feasibility and tolerability was assessed with attrition rate and occurrence of adverse events, Changes in arm and hand function were assessed with Jebson Taylor Hand Function Test (JTHFT). Amount of Use Scale of Motor Activity Log (AOU-MAL), American Spinal Injury Association Upper Extremity Motor Score and Modified Ashworth Scale (MAS) at baseline, after treatment, and at two-month follow-up. RESULTS None of the participants missed a treatment session or dropped-out due to adverse events related to the treatment protocol. Participants tended to perform better in JTHFT and AOU-MAL after treatment. Active group at post-treatment and two-month follow-up demonstrated better arm and hand performance compared to sham group. CONCLUSION These preliminary findings support that modulating excitatory input of the corticospinal tracts on spinal circuits may be a promising strategy in improving arm and hand functions in persons with incomplete tetraplegia. Further study is needed to explore the underlying mechanisms of recovery.

An exploration of grip force regulation with a low-impedance myoelectric prosthesis featuring referred haptic feedback

BackgroundHaptic display technologies are well suited to relay proprioceptive, force, and contact cues from a prosthetic terminal device back to the residual limb and thereby reduce reliance on visual feedback. The ease with which an amputee interprets these haptic cues, however, likely depends on whether their dynamic signal behavior corresponds to expected behaviors—behaviors consonant with a natural limb coupled to the environment. A highly geared motor in a terminal device along with the associated high back-drive impedance influences dynamic interactions with the environment, creating effects not encountered with a natural limb. Here we explore grasp and lift performance with a backdrivable (low backdrive impedance) terminal device placed under proportional myoelectric position control that features referred haptic feedback.MethodsWe fabricated a back-drivable terminal device that could be used by amputees and non-amputees alike and drove aperture (or grip force, when a stiff object was in its grasp) in proportion to a myoelectric signal drawn from a single muscle site in the forearm. In randomly ordered trials, we assessed the performance of N=10 participants (7 non-amputee, 3 amputee) attempting to grasp and lift an object using the terminal device under three feedback conditions (no feedback, vibrotactile feedback, and joint torque feedback), and two object weights that were indiscernible by vision.ResultsBoth non-amputee and amputee participants scaled their grip force according to the object weight. Our results showed only minor differences in grip force, grip/load force coordination, and slip as a function of sensory feedback condition, though the grip force at the point of lift-off for the heavier object was significantly greater for amputee participants in the presence of joint torque feedback. An examination of grip/load force phase plots revealed that our amputee participants used larger safety margins and demonstrated less coordination than our non-amputee participants.ConclusionsOur results suggest that a backdrivable terminal device may hold advantages over non-backdrivable devices by allowing grip/load force coordination consistent with behaviors observed in the natural limb. Likewise, the inconclusive effect of referred haptic feedback on grasp and lift performance suggests the need for additional testing that includes adequate training for participants.

On the Efficacy of Haptic Guidance Schemes for Human Motor Learning

This article investigates the efficacy of different haptic guidance schemes on human motor learning. In particular, the performances of four training protocols, virtual practice, virtual fixtures, fixed-gain error-reducing shared control, and progressive error-reducing shared control, are compared. The experimental results indicate that, if not designed carefully, haptic guidance protocols may be detrimental on motor learning, since such schemes actively interfere with the coupled system dynamics and cause participants to experience task dynamics that are altered from those of the real task. Results also show that the amount of assistance is an important factor, and fixed-gain assistance schemes may cause subjects to gain dependence on the existence of the guidance. Adjusting the amount of haptic guidance based on performance, utilizing progressive gains, is shown to increase the training effectiveness when compared to fixed gain controllers. Key parameters that influence the principles of motor learning in healthy human subjects may guide the design of more effective rehabilitation training protocols.

Acumen : an open-source testbed for cyber-physical systems research

Developing Cyber-Physical Systems requires methods and tools to support simulation and verification of hybrid (both continuous and discrete) models. The Acumen modeling and simulation language is an open source testbed for exploring the design space of what rigorous-but-practical next-generation tools can deliver to developers of Cyber-Physical Systems. Like verification tools, a design goal for Acumen is to provide rigorous results. Like simulation tools, it aims to be intuitive, practical, and scalable. However, it is far from evident whether these two goals can be achieved simultaneously. This paper explains the primary design goals for Acumen, the core challenges that must be addressed in order to achieve these goals, the “agile research method” taken by the project, the steps taken to realize these goals, the key lessons learned, and the emerging language design.

Improved Haptic Fidelity via Reduced Sampling Period With an FPGA-Based Real-Time Hardware Platform

Impedance based haptic interfaces face inherent challenges in displaying stiff virtual environments. Fidelity of a virtual environment is enhanced by stiff virtual walls combined with low damping and passive behavior of the interface. However, the stiffness of virtual walls displayed on an impedance based interface is limited by the damping inherent in the controller, the sampling rate of the control loop, and the quantization of the controller’s position. Attempting to display a stiffness larger than this limiting value destroys the passivity of the interface, leading to active controller behavior and eventually closed loop instability. We propose a method of increasing the fidelity of a PHANToM Premium 1.0 commercial haptic interface by controlling it via a Field Programmable Gate Array (FPGA) both alone and with a Real Time Operating System (RTOS) control system. This custom controller enjoys several benefits over the standard control achieved via a proprietary control card in a Multitasking OS, including reduced system overhead and deterministic loop rate timing. The performance of the proposed FPGA/RTOS controller compares favorably with the performance of an FPGA/Multitasking OS controller. The FPGA/RTOS controller achieves control loop rates an order of magnitude greater than that of the proprietary controller, allowing virtual walls to be displayed with greatly increased stiffnesses, while retaining the passivity and low damping of the PHANToM interface.Copyright

Effects of Assist-As-Needed Upper Extremity Robotic Therapy after Incomplete Spinal Cord Injury: A Parallel-Group Controlled Trial

Background Robotic rehabilitation of the upper limb following neurological injury has been supported through several large clinical studies for individuals with chronic stroke. The application of robotic rehabilitation to the treatment of other neurological injuries is less developed, despite indications that strategies successful for restoration of motor capability following stroke may benefit individuals with incomplete spinal cord injury (SCI) as well. Although recent studies suggest that robot-aided rehabilitation might be beneficial after incomplete SCI, it is still unclear what type of robot-aided intervention contributes to motor recovery. Methods We developed a novel assist-as-needed (AAN) robotic controller to adjust challenge and robotic assistance continuously during rehabilitation therapy delivered via an upper extremity exoskeleton, the MAHI Exo-II, to train independent elbow and wrist joint movements. We further enrolled seventeen patients with incomplete spinal cord injury (AIS C and D levels) in a parallel-group balanced controlled trial to test the efficacy of the AAN controller, compared to a subject-triggered (ST) controller that does not adjust assistance or challenge levels continuously during therapy. The conducted study is a stage two, development-of-concept pilot study. Results We validated the AAN controller in its capability of modulating assistance and challenge during therapy via analysis of longitudinal robotic metrics. For the selected primary outcome measure, the pre–post difference in ARAT score, no statistically significant change was measured in either group of subjects. Ancillary analysis of secondary outcome measures obtained via robotic testing indicates gradual improvement in movement quality during the therapy program in both groups, with the AAN controller affording greater increases in movement quality over the ST controller. Conclusion The present study demonstrates feasibility of subject-adaptive robotic therapy after incomplete spinal cord injury, but does not demonstrate gains in arm function occurring as a result of the robot-assisted rehabilitation program, nor differential gains obtained as a result of the developed AAN controller. Further research is warranted to better quantify the recovery potential provided by AAN control strategies for robotic rehabilitation of the upper limb following incomplete SCI. ClinicalTrials.gov registration number: NCT02803255.