How does a servo motor work?


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A servo motor is a motor that allows an input signal to control the rotation of the shaft to a specific angle. There are 2 types of servo motors - AC and DC.

Servos are controlled by a pulse width modulation signal (PWM) through the control wire. There is a minimum pulse width and a repetition rate. A servo motor can usually only turn 90° in either direction for a total of 180° movement. For example, when operating on DC, the axis position control uses PWM to rotate the shaft movement in the clockwise or counter-clockwise direction, depending on the pulse width of the signal as shown in the following figure:

  • When using a 1.5 ms pulse, set the axis at a 90 degree position or intermediate position.

  • The pulse width is less than 1.5ms (this example is set at 1 ms), which will rotate the axis 90 degrees clockwise;

  • When the pulse width is greater than 1.5ms (this example is set at 2 ms), the axis will be rotated 90 degrees counterclockwise;

  • A buffer is set between each pulse (this example is set at 20 ms, and the speed is controlled by the buffer time). The figure below shows the time of each location.

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If operating on AC, you can use phase shift and frequency change to control shaft steering and its speed; or use a signal generator, corresponding to the change of the PWM signal output at different frequencies, and then control the motor as shown by the above principle.

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