R7: a snake-like robot for 3-d visual inspection

Abstract

This article describes the design of an 8 degree of freedom snake-like robot, the R7 manipulator. The purpose of the device is to position a CCD camera and to rapidly acquire a sequence of images in an environment containing obstacles that may constrain the motion of the robot. Because of these requirements, it was desirable to minimize the manipulator's size and maximize its speed while preserving accuracy. These goals led to a unique design that is presented here. The device consists of four transmission modules. Each module has 2 degrees of freedom and contains a dual differential drive mechanism. Each module is a little more than 1.0" in diameter. The coordinated motion of these differential drives produces a prehensile motion of each transmission module. The range of motion of each module is /spl plusmn/90/spl deg/ in yaw and pitch. The smooth prehensile bending easily accommodate fragile cables and wiring harnesses. A benefit of using rigid links, as in this design, is an increase in stiffness of the mechanism. High stiffness aids in rapid positioning. One key feature of the mechanism is the use of low tension cable drive. Cables pass over a series of stationary sheaves and transmit power to transmission units located in each module. The use of a gear reducing transmission allows the use of low tension cables. This paper describes the design of the R7 manipulator and supporting electronics. Also discussed is the numerical solution to the inverse kinematics for this novel manipulator. The robot was built at Hughes Aircraft.<>