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

1. Discussion:

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

2) For example, in servo theory, we need a motor that can rotate precisely by 1/10, 1/100, 1/1000, or even 1/10000 of a revolution with each single command pulse.

2. How to Achieve Servo Control:

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

2) AC motors have magnetic poles and phase issues, but they can be reversed in pole-phase groups, enabling precise phase control.

3) DC motors reverse based on coil units, allowing control per slot.

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

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

6) The core of servo control is the ability for the motor to step. A motor without stepping cannot achieve true servo control.

8. Stepper Servo Control Principle:

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

2) For an AC motor, a pulse current in pole-phase units rotates the rotor 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, or 1/1000 of a rotation directly, we can achieve accurate control of a DC motor with a 1/16th rotation (when there are 16 slots).

4) Similarly, for an AC motor, we can achieve a 1/12th rotation when there are 4 poles and 3 phases.

5) Stepper motors, however, can rotate as precisely as 1/36th or even finer with each pulse.

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

7) As we all know, manual adjustment knobs often have coarse and fine adjustments.

8) We also use precision tools like micrometers to measure tiny distances.

9) Using this logic, we can accurately control the movement of a workpiece by controlling an AC motor's rotation with a precise 1/12th of a turn through an AC pulse.

1) By driving the motor through a reducer connected to a lead screw, we increase the number of revolutions, enabling precise control of the lead screw rotation—such as 1/10, 1/100, 1/1000, or even 1/10000 of a turn per pulse.

2) For example, a 4-pole, 3-phase AC motor completes one full rotation every 12 half-cycles of the AC pulse.

3) If the reduction ratio between the motor and the lead screw is 500, then each 12×500 AC half-cycles cause the motor to rotate 500 times, resulting in one full rotation of the lead screw.

4) Each full rotation of the lead screw moves the workpiece by 6 mm (the pitch of the screw).

5) Therefore, with a 12×500 = 6000 pulses, the lead screw turns 1/6000 of a rotation, moving the workpiece by 6 mm / 6000 = 0.001 mm.

6) This means we've achieved precise 0.001 mm movement of the workpiece with a single pulse.

10) Another example of precise control we see daily is the second hand of a clock.

11) Let’s calculate: the second hand moves 360° / 60 = 6° per second. How many degrees does the minute hand move? And the hour hand?

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

13) To achieve such accurate control of just 1 second, people have used mechanical pendulums, spring mechanisms, and electronic crystal oscillators over time.