81 research outputs found
Functionality-Driven Musculature Retargeting
We present a novel retargeting algorithm that transfers the musculature of a
reference anatomical model to new bodies with different sizes, body
proportions, muscle capability, and joint range of motion while preserving the
functionality of the original musculature as closely as possible. The geometric
configuration and physiological parameters of musculotendon units are estimated
and optimized to adapt to new bodies. The range of motion around joints is
estimated from a motion capture dataset and edited further for individual
models. The retargeted model is simulation-ready, so we can physically simulate
muscle-actuated motor skills with the model. Our system is capable of
generating a wide variety of anatomical bodies that can be simulated to walk,
run, jump and dance while maintaining balance under gravity. We will also
demonstrate the construction of individualized musculoskeletal models from
bi-planar X-ray images and medical examinations.Comment: 15 pages, 20 figure
Reinforcement learning control of a biomechanical model of the upper extremity
Among the infinite number of possible movements that can be produced, humans
are commonly assumed to choose those that optimize criteria such as minimizing
movement time, subject to certain movement constraints like signal-dependent
and constant motor noise. While so far these assumptions have only been
evaluated for simplified point-mass or planar models, we address the question
of whether they can predict reaching movements in a full skeletal model of the
human upper extremity. We learn a control policy using a motor babbling
approach as implemented in reinforcement learning, using aimed movements of the
tip of the right index finger towards randomly placed 3D targets of varying
size. We use a state-of-the-art biomechanical model, which includes seven
actuated degrees of freedom. To deal with the curse of dimensionality, we use a
simplified second-order muscle model, acting at each degree of freedom instead
of individual muscles. The results confirm that the assumptions of
signal-dependent and constant motor noise, together with the objective of
movement time minimization, are sufficient for a state-of-the-art skeletal
model of the human upper extremity to reproduce complex phenomena of human
movement, in particular Fitts' Law and the 2/3 Power Law. This result supports
the notion that control of the complex human biomechanical system can plausibly
be determined by a set of simple assumptions and can easily be learned.Comment: 19 pages, 7 figure
Breathing Life Into Biomechanical User Models
Forward biomechanical simulation in HCI holds great promise as a tool for evaluation, design, and engineering of user interfaces. Although reinforcement learning (RL) has been used to simulate biomechanics in interaction, prior work has relied on unrealistic assumptions about the control problem involved, which limits the plausibility of emerging policies. These assumptions include direct torque actuation as opposed to muscle-based control; direct, privileged access to the external environment, instead of imperfect sensory observations; and lack of interaction with physical input devices. In this paper, we present a new approach for learning muscle-actuated control policies based on perceptual feedback in interaction tasks with physical input devices. This allows modelling of more realistic interaction tasks with cognitively plausible visuomotor control. We show that our simulated user model successfully learns a variety of tasks representing different interaction methods, and that the model exhibits characteristic movement regularities observed in studies of pointing. We provide an open-source implementation which can be extended with further biomechanical models, perception models, and interactive environments.publishedVersio
Advancing Medical Technology for Motor Impairment Rehabilitation: Tools, Protocols, and Devices
Excellent motor control skills are necessary to live a high-quality life. Activities such as walking, getting dressed, and feeding yourself may seem mundane, but injuries to the neuromuscular system can render these tasks difficult or even impossible to accomplish without assistance. Statistics indicate that well over 100 million people are affected by diseases or injuries, such as stroke, Parkinsonâs Disease, Multiple Sclerosis, Cerebral Palsy, peripheral nerve injury, spinal cord injury, and amputation, that negatively impact their motor abilities. This wide array of injuries presents a challenge to the medical field as optimal treatment paradigms are often difficult to implement due to a lack of availability of appropriate assessment tools, the inability for people to access the appropriate medical centers for treatment, or altogether gaps in technology for treating the underlying impairments causing the disability. Addressing each of these challenges will improve the treatment of movement impairments, provide more customized and continuous treatment to a larger number of patients, and advance rehabilitative and assistive device technology.
In my research, the key approach was to develop tools to assess and treat upper extremity movement impairment. In Chapter 2.1, I challenged a common biomechanical[GV1] modeling technique of the forearm. Comparing joint torque values through inverse dynamics simulation between two modeling platforms, I discovered that representing the forearm as a single cylindrical body was unable to capture the inertial parameters of a physiological forearm which is made up of two segments, the radius and ulna. I split the forearm segment into a proximal and distal segment, with the rationale being that the inertial parameters of the proximal segment could be tuned to those of the ulna and the inertial parameters of the distal segment could be tuned to those of the radius. Results showed a marked increase in joint torque calculation accuracy for those degrees of freedom that are affected by the inertial parameters of the radius and ulna. In Chapter 2.2, an inverse kinematic upper extremity model was developed for joint angle calculations from experimental motion capture data, with the rationale being that this would create an easy-to-use tool for clinicians and researchers to process their data. The results show accurate angle calculations when compared to algebraic solutions. Together, these chapters provide easy-to-use models and tools for processing movement assessment data. In Chapter 3.1, I developed a protocol to collect high-quality movement data in a virtual reality task that is used to assess hand function as part of a Box and Block Test. The goal of this chapter is to suggest a method to not only collect quality data in a research setting but can also be adapted for telehealth and at home movement assessment and rehabilitation. Results indicate that the data collected in this protocol are good and the virtual nature of this approach can make it a useful tool for continuous, data driven care in clinic or at home. In Chapter 3.2 I developed a high-density electromyography device for collecting motor unit action potentials of the arm. Traditional surface electromyography is limited by its ability to obtain signals from deep muscles and can also be time consuming to selectively place over appropriate muscles. With this high-density approach, muscle coverage is increased, placement time is decreased, and deep muscle activity can potentially be collected due to the high-density nature of the device[GV2] . Furthermore, the high-density electromyography device is built as a precursor to a high-density electromyography-electrical stimulation device for functional electrical stimulation. The customizable nature of the prototype in Chapter 3.2 allows for the implementation both recording and stimulating electrodes. Furthermore, signal results show that the electromyography data obtained from the device are of high quality and are correlated with gold standard surface electromyography sensors. One key factor in a device that can record and then stimulate based on the information from the recorded signals is an accurate movement intent decoder. High-quality movement decoders have been designed by closed-loop device controllers in the past, but they still struggle when the user interacts with objects of varying weight due to underlying alterations in muscle signals. In Chapter 4, I investigate this phenomenon by administering an experiment where participants perform a Box and Block Task with objects of 3 different weights, 0 kg, 0.02 kg, and 0.1 kg. Electromyography signals of the participants right arm were collected and co-contraction levels between antagonistic muscles were analyzed to uncover alterations in muscle forces and joint dynamics. Results indicated contraction differences between the conditions and also between movement stages (contraction levels before grabbing the block vs after touching the block) for each condition. This work builds a foundation for incorporating object weight estimates into closed-loop electromyography device movement decoders. Overall, we believe the chapters in this thesis provide a basis for increasing availability to movement assessment tools, increasing access to effective movement assessment and rehabilitation, and advance the medical device and technology field
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