SUMMARY

A new, advanced patient transfer device is being developed for moving mobility limited patients, for example, from a wheelchair to a bed or a floor into a chair. Current market patient lift devices are antiquated and insufficient for customer needs, with only one actuated degree of freedom. The high power to size ratio of hydraulic actuation makes it suitable for moving larger, heavier patients. A prototype electro-hydraulically actuated patient transfer device with four actuated degrees of freedom has been designed and fabricated. Current progress is toward developing a more intuitive and safe caretaker interface and control strategy. A revealing needs assessment has been performed, and key design requirements have been identified. The device must be capable of producing large forces and operating safely in a delicate home or clinical environment with humans in its workspace. So it is desirable for the controller to minimize any unintentional large external contact forces, and provide force feedback to the caretaker. In this system, the caretaker and device work together to maneuver a complex payload, a human body. A control scheme for coordinated collaborative manipulation is being developed, where the caretaker pushes on the device to guide the desired motion, and the machine lifts the weight of the patient. Several different forms of interaction controllers are being tested and incorporated into this collaborative control, to manage any undesirable external interaction forces, and avoid obstacles where possible. Furthermore, the device uses a pump controlled electro-hydraulic actuation system, with a separate reversible brushed DC motor and bidirectional fixed displacement pump for each degree of freedom.