How to achieve precise control of the servo - News - Global IC Trade Starts Here.

1. Discussion:

1) Is there any motor or control method in the world that can start and stop precisely on a command pulse?

2) For example, the servo theory discussed above requires that the motor can accurately rotate through 1/10 of a revolution, 1/100, 1/1000, 1/10000, etc., with just one command pulse.

2. How to Achieve Servo Control:

1) Alternating current has a zero-crossing issue, so it can be controlled by a half-cycle pulse.

2) AC motors have magnetic poles and phase issues; reversing in units of pole-phase groups allows for accurate phase band control.

3) DC motors reverse in coil units, allowing precise control at the slot level.

4) These are the fundamental principles behind our servo motor control systems.

5) Everyone knows that to achieve servo control, people developed stepper motors and pulse motors.

6) The core of servo control is enabling the motor to step. A motor without stepping cannot perform precise servo control.

8. Stepper Servo Control Principle:

1) For a DC motor, a pulse current in the number of slots causes the rotor to rotate by an angle equal to 360 divided by the number of slots.

2) For an AC motor, a pulse current in pole-phase units causes the rotor to rotate by an angle equal to 360 divided by (number of poles × number of phases).

3) Although we can't achieve fractions like 1/10, 1/100, 1/1000, or 1/10000 of a revolution, we can achieve precise DC motor control with a pulse that moves the rotor over 1/16 of a revolution (if the motor has 16 slots).

4) Similarly, for an AC motor, we can achieve a precise rotation of 1/12 of a revolution when using a 4-pole, 3-phase motor.

5) Of course, a stepping motor can achieve even finer control, such as rotating 1/36 of a revolution or more with each pulse.

6) So, how do we achieve high-precision translation control of a workpiece?

7) We all know that manual adjustment knobs have coarse and fine settings.

8) And we also know about precision measuring tools like micrometers.

9) Using this knowledge, we can precisely control workpiece movement by using an AC pulse that rotates the motor accurately by 1/12 of a revolution.

1) Drive the motor through a gear reducer to increase the number of revolutions, allowing a single pulse to rotate the lead screw by 1/10, 1/100, 1/1000, or even 1/10000 of a revolution, achieving precise control.

2) For example, a 4-pole, 3-phase AC motor, with a three-phase AC sequence, completes one full revolution per 12 half-cycles of the AC signal.

3) If the reduction ratio between the motor and the lead screw is 500, then each 12×500 half-cycles of the AC pulse will rotate the motor 500 times, causing the lead screw to turn once.

4) When the lead screw turns once, the workpiece translates by one pitch, which is 6 mm.

5) Therefore, one AC pulse that rotates the lead screw by 12×500 = 1/6000 of a revolution results in a workpiece movement of 6 mm / 6000 = 0.001 mm.

6) Thus, we have achieved precise 0.001 mm translation of the workpiece with a single current pulse.

10) Another example of precise control that everyone sees every day is the second hand of a clock. Let’s calculate: every second, the second hand moves 360° / 60 = 6°. How many degrees does the minute hand move? And the hour hand?

11) The second hand moves 6° per second. The minute hand moves 1/10°, and the hour hand moves 1/120° per second.

12) To achieve precise 1-second control, people use mechanical spring pendulums, gravity pendulums, electronic crystal oscillators, and other methods.