2018 Volume 24 Pages 91-101
Powered prosthetic arm is a necessary device for person with bilateral shoulders disarticulation cause by accident or illness. In recent years, persons with bilateral shoulder disarticulation are challenging to operate multiple Degrees-of-Freedom (DOF) electrically powered artificial arm. However, the multiple DOF electrically powered artificial arms which are tested for practical use has unresolved contradicting fundamental problems on mechanism, DOF, and control. In this research, we propose and are developing hydraulic-electric type powered artificial arms. A wearable-type 5-DOF unit taking advantage of the remaining function of the upper extremity motion and a desktop non-wearable unit with 2-DOF external terminal are composed. Hydraulic Bilateral Servo Actuator, which combines the controllability of electric control and the high output of hydraulic system, are implemented in the powered artificial arm. The system significantly changes the previous design concepts of artificial upper limb by features of 1) highly rigid joint mechanism without using a gear reducer mechanism, 2) a bi-articular muscular hydraulic cylinder actuator that functions as upper arm frame structure and simultaneously and independently drives the shoulder and elbow, and 3) a forearm with rotary-type hydraulic actuators consisting a 3-DOF highly rigid joint mechanism. In addition, each digit on the 5-DOF hand is driven by a electric motor for precise positioning and the variable arch structure palm is capable of adjusting to grasping object shapes by its passive rigidness adapting function.
