This paper describes the development of a hydraulically actuated patient transfer device, utilizing a force amplifying passivity based control strategy. The patient transfer device is intended for moving mobility limited patients, for example, from a bed to a chair, from a wheelchair into a car, or from the floor into a wheelchair. Our needs assessment has indicated that a more powerful, more easily maneuverable device is needed which is operable by a single caregiver with one hand. For this purpose, we are proposing a coordinated force amplifying control strategy. The caregiver input to the device is measured from a force sensor mounted on the device near the patient. The output is the force applied by the device actuators in the same direction as the input; this force may be amplified to assist the caregiver. Passivity-based control provides a way to implement this force amplifying control to aid in stability, which is critical for a device that interacts directly with humans. This paper describes the implementation of this force amplifying passivity-based control on a simpler pre-prototype two DOF patient transfer device.

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