Most of the existing service robots employ electric actuators with harmonic reducers to drive the upper arm joints. Due to the limited size of elbow joint and shoulder joint, such actuators need to be small. To match the capability of human arm, they also need to be powerful. Such requirements on the actuators lead to high cost. In this work, a new joint actuation system is presented. Based on biomimetic approach, the system is arranged along the length of the upper arm as well as in the upper body. The system represents the functions of human biceps and triceps for elbow joint and of the shoulder muscles including deltoid, pectoralis major, latissimus dorsi and etc. The space for the elbow muscles and the shoulder muscles is much larger than that of each joint. With relieved spatial constraint on the actuation system, economic design is possible with standard industrial components. The new system consists of gears, a timing belt, pulleys and a feed-drive (screw-nut). The feed drive offers high joint torque with high reduction as well as self-locking. Since friction loss is inherent to the feed drive, an attempt is made for design improvement with TRIZ approach. Technical contradiction analysis of TRIZ on the 1 st design suggests several invention principles including 'Nesting' that was implemented in the 2 nd design. Experiments show that the 2 nd design is about 330% more efficient than the 1 st design.
ABSTRACT:A manipulator for remote duplication of an operator's arm motion is presented. The focus of design is on the economic efficiency with limited payload, speed and accuracy ranges for a given application. The arm has eight degrees of freedom with upper arm, elbow, lower arm, wrist and end effector. The actuators employ screw-nut combination for maximum payload and self-locking feature with low cost geared motors. The end effector has three degrees of freedom for wrist and one degree of freedom for fingers. The three fingers are coupled by a triangular joint that offers approximately equal grasping forces among them and are operated by one actuator. The mechanism, which is composed of the combination of screw-nut-timing pulley, was designed for an upper arm. The motion range of the manipulator had been analyzed by a forward kinematics. The performance of the manipulator based on video motion capture of an operator had been verified by experiments.
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