If we're talking about the hottest topics right now, robots are definitely one of them. As a typical mechatronics technology-intensive product, how does a robot operate? It's understood that robot control falls into two main categories: mechanical body control and servo mechanism control. The servo control system is a crucial part of realizing both mechanical body control and servo mechanism control. Therefore, understanding the robot's operation inevitably involves the servo system.
Servo systems are products developed based on frequency conversion technology. They are automatic control systems that use mechanical position or angle as the controlled object. In addition to speed and torque control, servo systems can also perform precise, fast, and stable position control.
Generally, when we talk about robot servo systems, we are referring to precision servo systems used for multi-axis motion control. A multi-axis motion control system consists of a high-order motion controller and a low-order servo driver. The motion controller is responsible for decoding motion control commands, controlling the relative motion between the axes, acceleration and deceleration contour control, etc., and its main function is to reduce the path error of the overall system motion control. The servo driver is responsible for the position control of the servo motor, and its main function is to reduce the following error of the servo axis.
The figure below shows a simplified control block diagram of a dual-axis motion control system. Under normal circumstances, the dynamic response characteristics of the X-axis and Y-axis will be quite different, which will cause obvious errors in high-speed contour control. Therefore, a motion controller must be designed to solve this problem from a holistic perspective.
A servo system consists of three main parts: a servo motor, a servo driver, and a command mechanism. The servo motor is the actuator, which is used to achieve motion. The servo driver is the power source for the servo motor. The command mechanism sends pulses or provides speed signals to coordinate with the servo driver for normal operation.
The requirements for servo motors in robots are higher than those for the other two components. First, servo motors must have rapid response. The time it takes for the motor to complete the required working state from receiving a command signal should be short. The shorter the response time, the higher the sensitivity of the electric servo system and the better its rapid response performance. Generally, the electromechanical time constant of the servo motor is used to describe its rapid response performance. Second, the starting torque-to-inertia ratio of the servo motor must be large. When driving a load, the robot's servo motor needs a large starting torque and a small moment of inertia. Finally, the servo motor must have continuous and linear control characteristics. As the control signal changes, the motor speed must change continuously, and sometimes the speed needs to be directly proportional or approximately proportional to the control signal.
Of course, to fit the robot's size, the servo motors must be small in size, lightweight, and short in axial dimension. They must also withstand harsh operating conditions, be able to perform very frequent forward and reverse rotations and acceleration and deceleration, and be able to withstand several times the overload for a short period of time.
Servo drives are actuators that can directly or indirectly drive the robot body to obtain various movements by utilizing the torque and force generated by various motors. They have advantages such as high torque-to-inertia ratio, no brushes and no commutation sparks, and are widely used in robots.
