Compact in design and energy-efficient, servo motors are actuators that serve countless applications. These features enable them to operate remote-controlled or radio-controlled toy cars, robots, and aircraft. Furthermore, they find use in pharmaceutics, in-line manufacturing, and food services. Versatile in function, this blog will cover how they work and their importance.
The servo circuitry is constructed in the motor unit along with a positionable shaft that is fitted with a gear. The motor itself is controlled with an electrical signal that determines the amount of shaft movement in the assembly. Inside, the set-up is fairly simple, consisting of a small DC motor, potentiometer, and a control circuit.
The motor is attached to the control wheel via gears. As the motor rotates, the resistance of the potentiometer changes, allowing the control circuit to accurately regulate how much movement there is and in which direction. When the shaft is positioned properly, power supply to the motor is cut off. Moreover, the desired position is sent through electrical pulses via a signal wire.
It is important to note that the motor’s speed is proportional to the difference between its actual position and desired position. As such, if the motor is near the desired position, it will turn slowly, generating what is referred to as proportional control. That being said, the motor will only run with the power necessary to accomplish the task at hand.
In particular, servos are controlled by transmitting electrical pulses of variable widths, or pulse width modulation (PWM), via the control wire. These pulses are present as either a minimum pulse, a maximum pulse, or a repetition rate. Typically, a servo motor can turn 90 degrees in either direction, meaning it has the capacity to turn a total of 180 degrees. The motor’s neutral position is considered the position wherein the servo has the same amount of potential rotation in both clockwise and counterclockwise directions.
The function of the PWM that is sent via the wire is to determine the position of the shaft, allowing the rotor to turn to the desired position. The servo motor expects a pulse every 20 ms and the length of the pulse determines how far the motor runs. When servos are commanded to move, they will move to the desired position and maintain this position. Generally, they can resist external force so that they do not move, but they cannot hold a single position indefinitely.
Similar to other actuator types, servo motors are available in various types, shapes, and sizes. Servos are usually equipped with three parts: a motor, feedback device, and control electronics. If you require feedback, a potentiometer, tachometer, resolver, encoder, linear transducer, or any other sensor can be employed. The two common types that are widely used are AC and DC servos.
As AC servos have the capacity to handle more current surges, they find use in a variety of industrial machines. Meanwhile, DC servos are better suited for smaller applications since they cannot withstand a lot of power surges. However, DC motors are less expensive than their counterparts, making them a go-to choice for many operations. Regardless of the type one chooses, it is important to routinely check either servo motor type, ensuring the functionality of your assembly.
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