An experimental study on open-loop position and speed control of a 3-RRR planar parallel mechanism

This paper describes design, construction and control of a 3-RRR planar parallel mechanism. The focus is on experimental control methods using inverse kinematic problem in order to gain more accuracy and smooth movement during the control process. Since there is no direct feedback sensor on the end-effector, all the foregoing control approaches could be regarded as open-loop control. In order to control the mechanism, two main control methods are used namely, position control and speed control. A Joy-stick is added to the system, in order to provide the ability for the user to control the mechanism directly. In addition, a Graphical User Interface is designed to help the user by three main control states. The first state is considered as off-line control, in which, the mechanism will follow a specific path defined in the program. In the second state, off-line control via Joy-stick, the mechanism will follow a path specified by the user via Joy-stick. As the third state, which is considered as the on-line control via Joy-stick, the mechanism will interactively follow a path specified by the user via the Joy-stick. All the programs are written in Qt creator in order to speed up data transmission from computer to the mechanism's actuators and vice versa. Results reveal that the mean error value of the actual and the desired angles of actuators is 0.68 degree, which illustrates that the mechanism has sufficient accuracy when the joints backlash are ignored.