Pneumatic Actuators for Climbing, Walking and Serpentine Robots

This chapter presents construction, control, advantages and disadvantages of various pneumatic actuators we have been using in several projects of climbing, walking and serpentine robots during last 13 years. We start with qualitative and quantitative analysis of different actuators. This part is mostly based on the literature review but augmented with our own experience related to these particular types of robots. We focus on pneumatic drives as very suitable for robots having permanent contact with unknown environment. Then we show a few constructions developed in our laboratory: starting from light weight manipulator for climbing robot, quadruped walker and climber, jumping and worm-like robots, see Fig. 1. We also present our contribution in development of the family of serpentine robots designed at the University of Michigan (UofM). There are some general requirements for joint actuators in mobile robots designed for regular contact with ground (obstacles). Listed here are the six most important ones: 1. Joint actuators should be capable of developing sufficient force to lift whole robot or its parts in order to climb or overcome obstacles, or to operate with load. 2. Joint angles should be controllable proportionally. 3. Another key requirement is that mobile robots should conform to the terrain compliantly. This assures correct propulsion and safe manipulation as well as dynamic isolation of main body (controller) from ground. Robots that don’t conform compliantly require complex sensor systems to measure contact forces and to command a momentary angle for each non-compliant joint accordingly. 4. At times it is necessary to increase the stiffness of a joint, for example to cross a gap or precisely track position trajectory. Alternatively, it may be necessary to adjust the stiffness to an intermediate level, for example to change jumping frequency. Thus, considered mobile robots and manipulators must be capable of adjusting the stiffness of every DOF individually and proportionally. 5. Joint actuators should be scalable to fit robots of different sizes. It is convenient to use the same technology in miniand macro-scale.