Design Evolution of an Actuation System for Manipulator Upper Arm Based on TRIZ

Abstract

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 1st design suggests several invention principles including ‘Nesting’ that was implemented in the 2nd design. Experiments show that the 2nd design is about 330% more efficient than the 1st design.