The Woodruff School

SUMMARY

A significant need has been identified for an improved device to assist in transferring mobility limited patients, particularly those who are heavier or bariatric. Typical transfers include moving between a bed, wheelchair, chair/couch, toileting chair or toilet, car, or the floor. Currently, clinicians suffer more disabling workplace injuries than construction workers or firefighters, many of which are attributable to moving patients. A new, cost effective, hydraulically actuated prototype patient transfer assist device has been developed and fabricated; hydraulic actuation has advantages in terms of force density over electrical actuators that are typically used at this power scale. More generally, improved methods for control of machines that work collaboratively with humans, sharing a task and a workspace, were developed in this work. It also aims to overcome some of the control challenges with these actuation systems in this type of application, such as non-ideal characteristics of the low cost actuation systems and management of a machine with large force capability operating in a home or clinical environment with humans in its workspace. With a powerful machine working in a relatively delicate environment, it is necessary for the controller to manage any external interaction forces, to keep them in a safe range, in addition to smoothly controlling motion. A significant challenge lies in implementation of interaction control with these electro-hydraulic pump controlled actuators, which are intrinsically stiff, have slow dynamics, and have many nonlinear or non-ideal features. An impedance control framework has been formulated and implemented, using redundant sensing of obstacles, with feedback of both external interaction forces and proximity. Operator control experiment results show that the interaction control results in statistically significant reductions in collision forces by an average of 53%, and greater reductions in cases where the machine is moving faster, with greater momentum and subsequently larger collision forces; similar controlled experiments in hardware with software inputs result in reductions in collision forces of 87%. Beyond the patient transfer application, this project aims to make steps toward improving control in the broader application set of machines that work collaboratively with humans, sharing a task and a workspace, for example, in construction, manufacturing, or distribution.

SUBJECT:	Ph.D. Dissertation Defense

BY:	Heather Humphreys

TIME:	Thursday, September 8, 2016, 12:00 p.m.

PLACE:	Love Building, 210

TITLE:	Caretaker-Machine Collaborative Manipulation with an Advanced Hydraulically Actuated Patient Transfer Assist Device

COMMITTEE:	Dr. Wayne Book, Chair (ME) Dr. Andrew Alleyne (ME, Univ. of Illinois) Dr. Thomas Kurfess (ME) Dr. Jun Ueda (ME) Dr. Christina Choi (Industrial Design)

SUMMARY A significant need has been identified for an improved device to assist in transferring mobility limited patients, particularly those who are heavier or bariatric. Typical transfers include moving between a bed, wheelchair, chair/couch, toileting chair or toilet, car, or the floor. Currently, clinicians suffer more disabling workplace injuries than construction workers or firefighters, many of which are attributable to moving patients. A new, cost effective, hydraulically actuated prototype patient transfer assist device has been developed and fabricated; hydraulic actuation has advantages in terms of force density over electrical actuators that are typically used at this power scale. More generally, improved methods for control of machines that work collaboratively with humans, sharing a task and a workspace, were developed in this work. It also aims to overcome some of the control challenges with these actuation systems in this type of application, such as non-ideal characteristics of the low cost actuation systems and management of a machine with large force capability operating in a home or clinical environment with humans in its workspace. With a powerful machine working in a relatively delicate environment, it is necessary for the controller to manage any external interaction forces, to keep them in a safe range, in addition to smoothly controlling motion. A significant challenge lies in implementation of interaction control with these electro-hydraulic pump controlled actuators, which are intrinsically stiff, have slow dynamics, and have many nonlinear or non-ideal features. An impedance control framework has been formulated and implemented, using redundant sensing of obstacles, with feedback of both external interaction forces and proximity. Operator control experiment results show that the interaction control results in statistically significant reductions in collision forces by an average of 53%, and greater reductions in cases where the machine is moving faster, with greater momentum and subsequently larger collision forces; similar controlled experiments in hardware with software inputs result in reductions in collision forces of 87%. Beyond the patient transfer application, this project aims to make steps toward improving control in the broader application set of machines that work collaboratively with humans, sharing a task and a workspace, for example, in construction, manufacturing, or distribution.