Design And Control Of Multiple Joint Robot Driven By Ultrasonic Motors

Robotic arms for space applications have a number of challenges. On the one hand, the motors should be high torque in low-speed and the mass and volume of them should be as low as possible. On the other hand, the motors should work well in the space conditions, such as vacuum, along with temperature in the range +80°C to -150°C and high radiation levels. These natural conditions of space can wreak havoc on electromagnetic motors.Ultrasonic motors (USMs) have a lot of advantages over commonly used brushed or brushless motors, such as, electromagnetically immune, high torque at low speeds, high torque per unit weight and a significant holding torque without power. Due to the above advantages, USMs have become one of promising motors for space applications. However, it is difficult to derive accurate mathematical model of an USM, so the control characteristics of USMs are complicated and highly nonlinear. There is no perfect control scheme for ultrasonic motors, especially in the precise speed and position servo systems. In order to examine USMs control strategies for the next generation of space robots, this paper developed a multiple joint robot driven by ultrasonic motors and the goals of the robot control are accurate tracking and smooth movement of the robot.Firstly, Virtual Prototyping Technology has been adopted in the design period of the robot. The multi-joint robot has been designed by means of SolidWorks, which is 3D mechanical design software. In order to ensure the performance of the robot, kinematic and kinetic simulation of the robot has been analyzed by means of Adams. After analysis and comparison of several designs, the most compact robot body has been determined eventually which can meet the need of the motions.Secondly, due to the very quick response of USMs, control strategies of electromagnetic motors are hard to be applied in the robot driven by USMs. After analysis and comparison several PID control strategies, the standard PID control strategy is chosen as the basic control method. Based on the large experiments of position feedback control and velocity feedback control, a velocity-position feedback control system has been proposed. This new control system is a kind of double-loop feedback control, which is on the basis of velocity feedback and assisted with position feedback. The experiment shows that the control system is effective to achieve the goals of robot control.Finally, to realize the motion control of online track planning, the kinematic equations of robot are given and the inverse kinematic solutions in closed form are generated. The working space of robot has also been calculated. On the above basis, the mapping of the input interface and working space of the robot has been realized. Eventually, the online planning motion control of robot and tracking of the arbitrary figures using a mouse as input device are implemented.