Servo Motor: Definition, Working, Types & Repair

What is Servomotor?

A servo motor is a rotary actuator or linear actuator that allows for precise control of angular or linear position, velocity, and acceleration. It consists of a suitable motor coupled to a sensor for position feedback. It also requires a relatively sophisticated controller, often a dedicated module designed specifically for use with servomotors.

A servo motor is a general term for a specific type of linear or rotary actuator. Basically, the name servo motor refers to the term servo mechanism, which means that the motor is constantly monitored to control its motion.

Servomotors are used in applications such as robotics, CNC machines or automated manufacturing.

Servo motors are used in modern automobiles to control their speed. When the accelerator is depressed, it sends electrical signals to the car’s computer. The computer then processes this information and sends a signal to the servo attached to the throttle to adjust the engine speed.

How does a servo motor work?

A servo motor is an electromechanical device that generates torque and velocity based on the supplied current and voltage. A servo motor operates as part of closed-loop control, providing torque and velocity as commanded by a servo controller which uses a feedback device to close the loop.

The feedback device provides information such as current, velocity or position to the servo controller, which adjusts the motor action depending on the commanded parameters.

Servos are controlled by sending a variable width electrical pulse or pulse width modulation (PWM) over the control cable. There is a minimum heart rate, a maximum heart rate, and a repetition rate. A servo motor can normally only rotate 90 ° in each direction, which adds up to a total of 180 ° of movement.

The neutral position of the motor is defined as the position where the servo has the same potential rotation in both clockwise and counterclockwise directions. The PWM sent to the motor determines the position of the shaft and is based on the duration of the pulse sent over the control cable; the rotor turns into the desired position.

The servo motor expects a pulse every 20 milliseconds and the length of the pulse determines how far the motor turns. A pulse of 1.5ms, for example, causes the motor to turn to the 90 ° position.

For less than 1.5ms it moves counterclockwise towards the 0 ° position, and longer than 1.5ms rotates the servo clockwise towards the 180 ° position.

When a move command is given to these servos, they will move into position and hold that position. If an external force is pressing against the servo while the servo is holding a position, the servo will resist moving from that position.

The maximum force the servo can exert is called the servo’s torque. Servos won’t hold their position forever, however; The position pulse must be repeated to tell the servo to stay in position.

 servo motor Diagram

Types of servo motors

Servomotors come in many sizes and in three basic types. The three types include positional rotation, continuous rotation, and linear.

  • Positional Rotation Servos rotate 180 degrees. They also have stops in the gearbox to protect the output shaft from over-rotating.
  • A continuous rotation servo motor is a servo whose range of motion is not limited. Instead of letting the input signal determine which position the servo should turn, the continuous rotation of the servo relates the input to the speed of the output and the direction. The limitless movement of these motors allows them to move in both CW and CCW directions.
  • Linear servos use a rack and pinion mechanism to change their performance. The rack and pinion convert rotary motion into linear motion.

Servo Motor Repair

Step-1 Initial Evaluation

During an evaluation, a visual inspection is carried out to check parts such as the shaft, keyway, end bells, clamps, and connectors. After the inspection, a surge voltage comparison test or a short test is carried out to check whether the stator needs to be rewound.

Next, an insulation resistance test often referred to as the Megger test, is performed at each phase to ensure that the insulation is not broken.

The next test in the evaluation is the phase balance test, which uses an RMS meter to ensure the windings are balanced between phases; The brake is also checked here if the servomotor has one.

Step-2 Disassembly

First, the backplate is removed, followed by the encoder and encoder housing, while the cabling is carefully removed. Then the end bells are removed and the rotor pulled from the stator; here the rotor and shaft are visually inspected.

Next, the bearings and the bearing housing, as well as the brake, are removed.

Step-3 Cleaning

An alkaline washer is used as it is better for your motor than hand cleaning or pressure washing.  All of our motor parts are washed this way.

Step-4 Bearing Change

It is important to change every bearing every time as they are often the cause of failure in a motor. We only use high-quality bearings that meet or exceed all manufacturer’s specifications.  Once the bearings are changed the motor is reassembled.

Step-5 Final Testing

To ensure the motor is fully repaired, Next, a memory test is performed to ensure the realignment of the feedback device.  After the repair is fully tested and verified the motor is painted and is ready to send back to you, ready to use!

FAQs.

What is Servomotor?

A servo motor is a rotary actuator or linear actuator that allows for precise control of angular or linear position, velocity, and acceleration. It consists of a suitable motor coupled to a sensor for position feedback. It also requires a relatively sophisticated controller, often a dedicated module designed specifically for use with servomotors.

How does Servomotor work?

A servo motor is an electromechanical device that produces torque and velocity based on the supplied current and voltage. A servo motor works as part of a closed-loop system providing torque and velocity as commanded from a servo controller utilizing a feedback device to close the loop.

What are the types of servo motors?

Servo motors come in many sizes and in three basic types. The three types include positional rotation, continuous rotation, and linear. Positional Rotation servos rotate 180 degrees. They also have stops in the gear mechanism to protect the output shaft from over-rotating.