Design of actuator system for industrial robots

Abstract

Heavy-duty robots are used in a wide range of industrial applications. During the last years the handling capacity and a reduced cycle time requirements have been increased without compromising the robot quality. The purpose of this master thesis is to design and simulate an actuator system for motion control suitable for a three joint robot. Before analyzing the 3-DOF model, a theoretical kinematic and dynamic analysis is performed. This theoretical foundation gives the basis to later decide how the model will be implemented. The project work can be divided into two phases. The first one consists of developing the three joint robot model in Dymola. All the steps carried out to build up the mechanical structure and the actuator system are explained. After this, different scenarios are set to obtain the torques and accelerations in each joint. The results of the first phase show that the joint torque is highly influenced by the acceleration and the gear ratio. In the second phase, the electro mechanical actuator system is simulated in Matlab as a two mass flexible system. Developing the mechanical equations that describe the system a block diagram is obtained. The procedure is based on varying parameters such as the gear box elasticity, the gear ratio, the stiffness and the time constant of the motor; and analyzing the velocity response as well as the frequency response. The influence of these parameters on the system is discussed to obtain a response with fewer oscillations. The final model is composed by an acceleration feedback in order to reduce the oscillations and increase the controllability. The comparison of the driven actuators according to their characteristics, giving a large overview of pros and cons of both technologies studied: electric and hydraulic. This comparison leads to state that hydraulic actuators are an interesting alternative. Since they are not widely used on the market today, a future work could be to implement this technology in heavy-duty robots.