A robot electric servo drive system is an actuator that uses the torque and force generated by various electric motors to directly or indirectly drive the robot body to obtain various movements of the robot.
Classification of commonly used motor drive systems for industrial robots
For motors driving the joints of industrial robots, the requirements are: maximum power-to-weight ratio and torque-to-inertia ratio, high starting torque, low inertia, and a wide and smooth speed range. Especially for robot end effectors (grippers), motors with the smallest possible size and mass should be used. When rapid response is required, servo motors must possess high reliability and stability, as well as significant short-term overload capacity. These are prerequisites for the application of servo motors in industrial robots.
The main requirements for joint drive motors in robots are summarized as follows:
1. Speed
The time it takes for a motor to complete the required operating state after receiving a command signal should be short. The shorter the response time to the command signal, the higher the sensitivity of the servo system and the better its fast response performance. Generally, the electromechanical time constant of the servo motor is used to describe its fast response performance.
2. Large starting torque-to-inertia ratio
When driving a load, the robot's servo motor is required to have a large starting torque and a small moment of inertia.
3. Continuity and linearity of control characteristics: The motor speed can change continuously as the control signal changes, and sometimes the speed needs to be proportional or approximately proportional to the control signal.
4. Wide speed range.
It can be used in a speed range of 1:1000 to 10000.
5. Small size, light weight, and short axial dimension.
6. It can withstand harsh operating conditions, can perform very frequent forward and reverse and acceleration and deceleration operations, and can withstand overload for a short period of time.
Currently, due to the widespread use of AC and DC servo motors with high starting torque, large torque, and low inertia in industrial robots, most industrial robots with a load of less than 1000N (equivalent to 100kgf) employ electric servo drive systems. The joint drive motors used are mainly AC servo motors, stepper motors, and DC servo motors. Among them, AC servo motors, DC servo motors, and direct drive motors (DD) all employ closed-loop position control and are generally used in high-precision, high-speed robot drive systems. Stepper motor drive systems are mostly suitable for small, simple robot open-loop systems where precision and speed requirements are not high. AC servo motors, due to their electronic commutation and lack of commutation sparks, are widely used in flammable and explosive environments. The power range of robot joint drive motors is generally 0.1–10kW. These are the motors used in industrial robot drive systems.
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