Design and Control of a Chained Form Manipulator

Exploiting unique features of nonholonomic systems, innovative and advantageous mechanisms can be designed. We have proposed a nonholonomic manipulator which is a controllable n joint manipulator with only two actuators. In order to create its nonholonomic constraint, a special type of velocity transmission, called the nonholonomic gear, was developed. There are many possible alternatives for designing underactuated manipulators using the nonholonomic gear. In this paper, the chained form manipulator is designed not only to satisfy chained form convertibility, but also to achieve control simplicity. Design requirements are clarified, then we establish the mechanical design of the chained form manipulator. The chained form manipulator is designed with an innovative main power train as well as nonholonomic gears. For experimental verification, a prototype is fabricated. So far, various control strategies for nonholonomic systems have been proposed. In this paper, an efficient motion planning scheme for the chained form is presented to approximate any holonomic path with the feasible nonholonomic path. Furthermore, a new concept of motion planning is proposed through the analysis of the initialcondition sensitivity. Combining these two approaches, the motion planning scheme is constructed towards practical applications. Presented experimental results show the usefulness of the design and the applied control scheme. KEY WORDS—nonholonomic constraint, nonlinear control, underactuated system, chained form, nonholonomic motion planning The International Journal of Robotics Research Vol. 21, No. 5-6, May-June 2002, pp. 389-408, ©2002 Sage Publications