How to realize the full closed-loop system composed of servo controller, servo motor and encoder

"How to realize a fully closed-loop system consisting of PLC + servo controller + servo motor (supporting equipment) + encoder (external equipment end)? My method is to have PLC give unlimited pulses to the servo. When the required process position is reached (the external encoder is connected to the PLC), the PLC stops the pulse output. However, the actual stop position is not accurate enough. This is probably because the stop signal after reaching the position will cause errors due to the deceleration and parking of the servo!!"

1. In the discussion of the original poster, it is believed that the "full closed-loop system composed of PLC + servo controller + servo motor (supporting equipment) + encoder (external equipment end)" is a system in which the operation of the motor is controlled by the pulses sent by the PLC. The motor starts to rotate when the PLC sends pulses. The faster the PLC sends pulses, the faster the motor rotates, etc.;

2. The original poster’s understanding is wrong. It is not only the original poster’s fault, but many “experts” also think so.

3. "Fully closed-loop system consisting of PLC + servo controller + servo motor (supporting equipment) + encoder (external equipment end)", the motor operation mode is:

Start → accelerate → keep constant speed → decelerate → stop;

4. The motor's "start, accelerate, keep constant speed, decelerate, stop" instructions are issued by comparing the number of command pulses with the number of encoder feedback pulses:

1) The number of command pulses > the number of encoder feedback pulses, and the motor starts;

2) Command pulse number = encoder feedback pulse number, the motor stops;

3) The number of command pulses >> the number of encoder feedback pulses, and the motor accelerates to the upper speed limit and moves at a constant speed;

4) The number of command pulses ≥ the number of encoder feedback pulses, and the motor decelerates to stop;

5. PLC does not send pulses. The number of command pulses is just a number calculated by the user based on the displacement and pulse equivalent, and the command pulse number is entered into the command pulse counter (or comparison counter);

6. The encoder feedback pulse reaches the encoder feedback pulse counter (or reaches the down count end of the comparison counter);

7. The command pulse counter and encoder feedback pulse counter are two counters of PLC. The numbers of the two counters are compared, and the motor's "start, accelerate, constant speed, decelerate, stop" instructions are generated according to the comparison results. These instructions are the instructions for the inverter (driver) to drive the motor to work;

8. Therefore, during the servo motion process, the PLC does not send pulses. The PLC counter and comparator only generate "start, accelerate, constant speed, decelerate, stop" instructions;

9. Therefore, during the servo motion process, the motor's motion "start, acceleration, constant speed, deceleration, and parking" is controlled by the inverter output;

10. The original poster said that after the PLC stops sending pulses, the motor decelerates and stops, so it cannot stop accurately. This is an illusion. In fact:

1) When the command pulse number ≥ encoder feedback pulse number, the motor decelerates to stop;

2) When stopping, the number of command pulses = the number of encoder feedback pulses;

11. Due to the "servo" control mode, the single pulse stepping control of the servo motor cannot be performed. If you don't believe it, input a command pulse and see how the motor will move? ? ? Will it move the displacement of a command pulse? ? ?

12. Of course, when the command pulse number = encoder feedback pulse number, the motor and its workpiece will not stop immediately due to inertia, so it cannot stop accurately;

13. Since the vehicle will not stop immediately due to inertia, the solution is:

1) Slow down before parking;

2) When parking, braking measures can be used;

14. This method of using an encoder to detect the angular displacement of the motor to control the position of the workpiece is defective because the relationship between the position of the workpiece and the angular displacement of the motor is often uncertain, such as the error caused by the gap in the mechanical transmission;

15. From this perspective, encoder control is not as accurate as position switch command control!