Use of a Delta robot as a walking machine. (1998)
AuthorsWong, Edward Ting Pingshow all
A 3 degree of freedom (dof) parallel Delta robot was built in the laboratory of the Mechanical Engineering Department, University of Canterbury. It possesses the similar characteristics and features as Clavel’s Delta 4 robot, which is well known for pick and place applications. Due to its parallel actuated mechanisms, this type of robot, so far, has been claimed as the fastest robot in the world. However, the Canterbury Delta robot in the laboratory suffered jerky motions when travelling along a prescribed continuous path. This was due to the use of 3 single axis step motor controllers (donated) rather than a single multi-axes control system. In order to improve the performance of the robot, the 3 existing control systems were replaced by a single chip DSP controller (TMS320F240). Under control of this powerful controller, the robot is able to perform point-to-point motion and continuous path motion under an open loop control mode. In order to use the Delta robot as a walking machine, a tripod foot was successfully developed and attached to the travelling platform of the delta robot. The result was a practical walking machine with 3 dof called Delta walker or Delta walking machine. It is based on parallel mechanisms and has a maximum allowable step length of 120mm. The step length and walking space of the Delta walking machine were studied and stimulated through a static forces analysis in Matlab1. It was found that the step length was constrained by the torque limit of the harmonic gear drives rather than the torque output by the stepping motors. An off-line optimal continuous path planning method was developed in Matlab for real time control at the joint level. The step walking path is approximated by a set of location nodes selected on the desired path. The motion control of the machine is provided by trajectory interpolation at the joint level. The pulse rates and the direction values are generated and sent to the DSP through an RS232 serial communication port.