Browsing by Author "McDonald, Craig G."
Now showing 1 - 5 of 5
Results Per Page
Sort Options
Item A cable-based series elastic actuator with conduit sensor for wearable exoskeletons(IEEE, 2017) Blumenschein, Laura H.; McDonald, Craig G.; O’Malley, Marcia K.There is currently a scarcity of wearable robotic devices that can practically provide physical assistance in a range of real world activities. Soft wearable exoskeletons, or exosuits, have the potential to be more portable and less restrictive than their rigid counterparts. In this paper, we present the design of an actuation system that has been optimized for use in a soft exosuit for the human arm. The selected design comprises a DC motor and gearbox, a flexible cable conduit transmission, and a custom series elastic force sensor. Placed in series with the transmission conduit, the custom compliant force sensor consists of a translational steel compression spring with a pair of Hall effect sensors for measuring deflection. The custom sensor is validated as an accurate means of measuring cable tension, and it is shown that it can be used in feedback to control the cable tension with high bandwidth. The dynamic effect of the cable-conduit transmission on the force felt at the user interface is characterized by backdriving the system as it renders a range of virtual impedances to the user. We conclude with recommendations for the integration of such an actuation system into a full wearable exosuit.Item A Review of Intent Detection, Arbitration, and Communication Aspects of Shared Control for Physical Human–Robot Interaction(ASME, 2018) Losey, Dylan P.; McDonald, Craig G.; Battaglia, Edoardo; O’Malley, Marcia K.As robotic devices are applied to problems beyond traditional manufacturing and industrial settings, we find that interaction between robots and humans, especially physical interaction, has become a fast developing field. Consider the application of robotics in healthcare, where we find telerobotic devices in the operating room facilitating dexterous surgical procedures, exoskeletons in the rehabilitation domain as walking aids and upper-limb movement assist devices, and even robotic limbs that are physically integrated with amputees who seek to restore their independence and mobility. In each of these scenarios, the physical coupling between human and robot, often termed physical human robot interaction (pHRI), facilitates new human performance capabilities and creates an opportunity to explore the sharing of task execution and control between humans and robots. In this review, we provide a unifying view of human and robot sharing task execution in scenarios where collaboration and cooperation between the two entities are necessary, and where the physical coupling of human and robot is a vital aspect. We define three key themes that emerge in these shared control scenarios, namely, intent detection, arbitration, and feedback. First, we explore methods for how the coupled pHRI system can detect what the human is trying to do, and how the physical coupling itself can be leveraged to detect intent. Second, once the human intent is known, we explore techniques for sharing and modulating control of the coupled system between robot and human operator. Finally, we survey methods for informing the human operator of the state of the coupled system, or the characteristics of the environment with which the pHRI system is interacting. At the conclusion of the survey, we present two case studies that exemplify shared control in pHRI systems, and specifically highlight the approaches used for the three key themes of intent detection, arbitration, and feedback for applications of upper limb robotic rehabilitation and haptic feedback from a robotic prosthesis for the upper limb.Item Characterization of surface electromyography patterns of healthy and incomplete spinal cord injury subjects interacting with an upper-extremity exoskeleton(IEEE, 2017) McDonald, Craig G.; Dennis, Troy A.; O’Malley, Marcia K.Rehabilitation exoskeletons may make use of myoelectric control to restore in patients with significant motor impairment following a spinal cord injury (SCI) a sense of volitional control over their limb - a crucial component for recovery of movement. Little investigation has been done into the feasibility of using surface electromyography (sEMG) as an exoskeleton control interface for SCI patients, whose impairment manifests in a highly variable way across the patient population. We have demonstrated that by using only a small subset of features extracted from eight bipolar electrodes recording on the upper arm and forearm muscles, we can achieve high predictive accuracy for the intended direction of motion. Five healthy subjects and two SCI subjects performed voluntary isometric contractions while wearing an exoskeleton for the wrist and elbow joints, generating six distinct single and multi-DoF motions in a total of sixteen possible directions. Using linear discriminant analysis, classification performance was then evaluated using randomly selected holdout test data from the same recording session. Commonalities across subjects, both healthy and SCI, were analyzed at the levels of selected features and the values of commonly selected features. Future work will be to investigate group-specific classification of SCI subjects' intended movements for use in the real-time control of a rehabilitation exoskeleton.Item Myoelectric Sensing for Intent Detection and Assessment in Upper-Limb Robotic Rehabilitation(2020-04-24) McDonald, Craig G.; O'Malley, Marcia KThis thesis explores how surface electromyography (EMG) -- the measurement of muscle force through voltage changes at the skin surface – can be of use to the field of upper-limb robotic rehabilitation. We focus on two main aspects: detecting human intention from measured muscle activity and assessing human motor coordination through synchronous muscle activations known as muscle synergies – each examples of the bidirectional communication found in tightly integrated human-robot interaction. EMG-based intent detection presents an opportunity to examine and promote human engagement at the neuromuscular level, enabling new protocols for intervention that could be combined with robotic rehabilitation, particularly for the most impaired of users. Meanwhile, the latest research in motor control proposes that natural, healthy human movement can be characterized by the presence of certain muscle synergies, and that the alteration of these synergies indicates a disruption, from neurological impairment or some other physical constraints, in natural movement. Wearable robotic devices are capable of altering muscle synergies, and though the mechanisms are not yet understood, a focus on altering muscle synergies is a promising new approach to neurorehabilitation. This thesis employs a robotic exoskeleton for the elbow and wrist joints designed for research in robotic rehabilitation of individuals with neurological impairments and now integrated with a myoelectric control interface. We first demonstrate the ability of a myoelectric interface to discern the user’s intended direction of motion in single-degree-of-freedom (DoF) and multi-DoF control modes with 10 able-bodied participants and 4 participants with incomplete cervical spinal cord injury (SCI). Predictive accuracy was high for able-bodied participants (averages over 99% for single-DoF and near 90% for multi-DoF), and performance in the SCI group was promising (averages ranging from 85% to 95% for single-DoF, and variable multi-DoF performance averaging around 60%), which is encouraging for the future use of myoelectric interfaces in robotic rehabilitation for SCI. Second, we explore the identification of synchronous muscle synergies in the muscles controlling the elbow and wrist, and the possible effects of robot-imposed task constraints on the neural constrains represented by synergy patterns. Our results indicate that constraining the unused degrees of freedom during a single-DoF movement inside the exoskeleton does not have a significant effect on the underlying muscle synergies in the task, and that methodological choices in muscle synergy analysis also do not have a large effect on the outcome. With all of these findings, we have achieved a deeper understanding of the value myoelectric sensing can bring to upper-limb robotic rehabilitation, and how much potential it has to advance the field toward greater accessibility to individuals of all levels of impairment.Item Reflection on System Dynamics Principles Improves Student Performance in Haptic Paddle Labs(IEEE, 2018) Rose, Chad G.; McDonald, Craig G.; Clark, Janelle P.; O’Malley, Marcia K.Contribution: Significant effort has been placed on the development of laboratory exercises for mechanical engineering curricula. Often, however, the exercises are not structured to encourage students to see the labs as a scientific process, instead of a checklist to be completed. Facilitating reflective observation and abstract conceptualization during the concrete experience (CE) of the lab improves student performance. Background: Extensive work has been put into the development of simple, low-cost educational tools to improve learning by supplementing curricula with hands-on experiences. Several devices, including haptic paddles, have been developed to combine dynamics and mechatronics content which culminate in rendering virtual environments. Despite demonstrated student interest in haptic devices and the foundational role of CE in learning, experimental comparisons of learning outcomes over a broad range of devices have had mixed results. Intended Outcomes: Device design can only address the experience portions of the learning cycle--effort put into encouraging and mediating a reflection phase will improve student performance. To test this hypothesis, the performance was compared of groups receiving the standard haptic paddle lab curriculum or a curriculum intended to facilitate reflection. Findings: Students receiving the reflective curriculum had statistically significant higher scores on lab report grades than those receiving the standard, non-reflective curriculum. The increased performance across multiple student GPA quartiles suggests that even modest curriculum changes designed to encourage reflection can improve student performance.