Towards Safe Autonomy in Assistive Robots

Robots have the potential to support older adults and persons with disabilities on a direct and personal level. For example, a wearable robot may help a person stand up from a chair, or a robotic manipulator may aid a person with meal preparation and housework. Assistive robots can autonomously make decisions about how best to support a person. However, this autonomy is potentially dangerous; robots can cause collisions or falls which may lead to serious injury. Therefore, guaranteeing that assistive robots operate safely is imperative. This dissertation advances safe autonomy in assistive robots by developing a suite of tools for the tasks of perception, monitoring, manipulation and all prevention. Each tool provides a theoretical guarantee of its correct performance, adding a necessary layer of trust and protection when deploying assistive robots. The topic of interaction, or how a human responds to the decisions made by assistive robots, is left for future work. Perception: Assistive robots must accurately perceive the 3D position of a person's body to avoid collisions and build predictive models of how a person moves. This dissertation formulates the problem of 3D pose estimation from multi-view 2D pose estimates as a sum-of-squares optimization problem. Sparsity is leveraged to efficiently solve the problem, which includes explicit constraints on the link lengths connecting any two joints. The method certifies the global optimality of its solutions over 99 percent of the time, and matches or exceeds state-of-the-art accuracy while requiring less computation time and no 3D training data. Monitoring: Assistive robots may mitigate fall risk by monitoring changes to a person’s stability over time and predicting instabilities in real time. This dissertation presents Stability Basins which characterize stability during human motion, with a focus on sit-to-stand. An 11-person experiment was conducted in which subjects were pulled by motor-driven cables as they stood from a chair. Stability Basins correctly predicted instability (stepping or sitting) versus task success with over 90 percent accuracy across three distinct sit-to-stand strategies. Manipulation: Robotic manipulators can support many common activities like feeding, dressing, and cleaning. This dissertation details ARMTD (Autonomous Reachability-based Manipulator Trajectory Design) for receding-horizon planning of collision-free manipulator trajectories. ARMTD composes reachable sets of the manipulator through workspace from low dimensional trajectories of each joint. ARMTD creates strict collision-avoidance constraints from these sets, which are enforced within an online trajectory optimization. The method is demonstrated for real-time planning in simulation and on hardware on a Fetch Mobile Manipulator robot, where it never causes a collision. Fall Prevention: Wearable robots may prevent falls by quickly reacting when a user trips or slips. This dissertation presents TRIP-RTD (Trip Recovery in Prostheses via Reachability-based Trajectory Design), which extends the ARMTD framework to robotic prosthetic legs. TRIP-RTD uses predictions of a person’s response to a trip to plan recovery trajectories of a prosthetic leg. TRIP-RTD creates constraints for an online trajectory optimization which ensure the prosthetic foot is placed correctly across a range of plausible human responses. The approach is demonstrated in simulation using data of non-amputee subjects being tripped.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/169822/1/pdholmes_1.pd

‘Just Normal’: a grounded theory of prosthesis use

A significant number of individuals around the world live with limb absence and use prosthetic technologies to assist and enable them in various ways about their lives. The aim of this study was to enhance our understanding of prosthesis use through exploring a core concern of prosthesis users and to develop a theory of how this concern is managed. By employing classical Grounded Theory methodology (Glaser, 1978, 1992, 1998, 2001, 2003, 2005, 2009, 2011a, 2013, 2014; Glaser & Strauss, 1967), data from 24 participants that used upper- and/or lower-limb prostheses were collected and analysed. These individuals were interviewed using a flexible, unstructured interviewing style. In addition to interviews, data from internet forums, blogs and autobiographical texts were also included, all of which were analysed in accordance with the established procedures of Grounded Theory methodology, which included open and selective coding, theoretical memoing, and theoretical sampling. A main concern of being ‘just normal’ emerged through analyses, and the data were further explored in order to develop a theory of the resolving of this concern. Just normal is the condition of being and living in ways that persons variously perceive are ‘about right’; that are sufficient, that are fair, and generally how things ‘ought to be’ for them, as they see it. Three modes of just normal were identified, which were: preserving being just normal, where persons manage threats to their ability to be this way, redressing to just normal when this is judged to be lacking and so persons bring themselves into alignment with this, and persevering with just normal, accounting for how persons keep going with living just normally and despite difficulties that may accompany this. The theory provides a novel perspective on users of prostheses and elucidates the benefits and challenges of living with artificial limbs, as persons make efforts to live in ways they see as fitting with what they consider is just normal. Such an understanding has the potential to facilitate multidisciplinary teams involved in the appropriate fitting of prostheses, inform goal-setting in rehabilitation, and how to manage further consultations. The theory links to existing research and goes beyond this in providing an understanding of what compels prosthesis users to act in particular ways. It also has the transferrable potential to related areas of living with assistive technologies, the experience of disability more broadly, and beyond

Proceedings of the ECCOMAS Thematic Conference on Multibody Dynamics 2015

This volume contains the full papers accepted for presentation at the ECCOMAS Thematic Conference on Multibody Dynamics 2015 held in the Barcelona School of Industrial Engineering, Universitat Politècnica de Catalunya, on June 29 - July 2, 2015. The ECCOMAS Thematic Conference on Multibody Dynamics is an international meeting held once every two years in a European country. Continuing the very successful series of past conferences that have been organized in Lisbon (2003), Madrid (2005), Milan (2007), Warsaw (2009), Brussels (2011) and Zagreb (2013); this edition will once again serve as a meeting point for the international researchers, scientists and experts from academia, research laboratories and industry working in the area of multibody dynamics. Applications are related to many fields of contemporary engineering, such as vehicle and railway systems, aeronautical and space vehicles, robotic manipulators, mechatronic and autonomous systems, smart structures, biomechanical systems and nanotechnologies. The topics of the conference include, but are not restricted to: ● Formulations and Numerical Methods ● Efficient Methods and Real-Time Applications ● Flexible Multibody Dynamics ● Contact Dynamics and Constraints ● Multiphysics and Coupled Problems ● Control and Optimization ● Software Development and Computer Technology ● Aerospace and Maritime Applications ● Biomechanics ● Railroad Vehicle Dynamics ● Road Vehicle Dynamics ● Robotics ● Benchmark ProblemsPostprint (published version