Design of an underactuated parallelogram crawler module for an in-pipe robot

This paper presents a design method to determine the output ratio of a differential mechanism, which is installed in an in-pipe robot with three underactuated parallelogram crawler modules. The crawler module can automatically shift its shape to a parallelogram when encountering with obstacles. To clarify the requirements for the mechanism, two outputs of each crawler mechanism (torque of the arms and front pulley) are quasi-statically analyzed, and how the environmental and design parameters affect the system are verified.