SERVOMOTOR: WHAT IS IT, THE PRINCIPLE OF OPERATION, TYPES, AND WHAT IS IT USED FOR

The term “servo” comes from the Latin word servus, which translates as “servant” or “assistant.” And by definition, a servomotor is a rotating motor with a feedback sensor, which allows you to precisely control the angular position, speed, and acceleration of the actuator.

Servomotors are widely used in machine tools, the production of packaging, packaging and bottling machines, and in robotics etc. In general, these motors are used when high accuracy of movement of the executive body is required.

Servo device

Most modern servo drives are built on the same principle and consist of such components: output shaft, gears, DC motor, potentiometer, printed circuit board, and control electronics.

The gearbox, together with the motor, forms a drive. The electric motor is needed to convert electricity to the mechanical rotation. However, often the speed of the motor is too high for practical use. So, to reduce the speed, a gearbox is used: a gear mechanism that transmits and converts torque.

Turning the electric motor on and off, you can rotate the output shaft – the final gear of the servo drive, to which you can attach something that we want to control. However, for the position to be controlled by the device, a feedback sensor is required – an encoder, which will convert the angle of rotation back into an electrical signal. A potentiometer is often used for this. When you turn the slider of the potentiometer, its resistance changes in proportion to the angle of rotation. Thus, with its help, you can set the current position of the mechanism.

In addition to the electric motor, gearbox, and potentiometer, the servo drive has an electronic filling. The filling is responsible for receiving an external parameter, reading values ​​from the potentiometer, comparing them, and turning the motor on / off. It is also responsible for maintaining negative feedback.

Three wires reach the servo drive. Two of them are responsible for powering the motor, the third delivers a control signal, which is used to set the position of the device.

Now let’s see how to control the servo from the outside.

Servo control – Control signal interface

In order to indicate the desired position to the servo, a control signal must be sent along the wire intended for this purpose. The control signal is pulses of constant frequency and variable width.

Which position the servo drive should take, depends on the length of the pulses. When the signal enters the control circuit, the pulse generator available in it produces its own pulse, the duration of which is determined through the potentiometer. Another part of the circuit compares the duration of two pulses. If the duration is different, the electric motor turns on. The direction of rotation is determined by which of the pulses is shorter. If the pulse lengths are equal, the electric motor stops.

Main Servo Specifications

1. Torque (Force on the shaft).Measured in kg / cm. It is a product of force and the length of the lever. In practice, the torque is responsible for the acceleration of the output shaft and its ability to overcome the resistance to rotation. The higher the torque, the more opportunities the motor has to realize its potential.
2. Turning speed.Indicates the speed at which the output shaft of the servo changes its position. The angle of change of position is indicated in degrees.
3. Angle of rotation.This is the maximum angle that the output shaft can turn. The most common values ​​for this characteristic are 180 ° and 360 °.
4. Dimensions of the servo.Servos are small, standard and large. Standard servos are the most inexpensive. If the dimensions deviate from the standard values, the price, as a rule, changes in proportion to such a deviation.
5. Gear material.Servo gears are made of plastic, carbon, metal. Plastic gears are lightweight but not designed for heavy loads. Carbon gears are more durable, but also more expensive. Metal gears are the heaviest, ideal for maximum loads.

The evolution of Servos

Servos change and evolve. At the very beginning of their appearance, they possessed collector motors with windings on the rotor. Gradually, the number of windings increased, and the speed of rotation and acceleration enhanced too. Later, the windings began to be located outside the magnet, which also contributed to an increase in work efficiency. Further improvements allowed to abandon the collector and permanent rotor magnets began to be used. The most popular right now, are motion control servos that run on a programmable controller. This makes it possible to create high-precision instruments and modern technology.

Types of Servomotors

Servomotors are distinguished by their diversity in design and principle of operation. Models come with brushes and without brushes. The first category is represented by DC motors. Devices with brushes are more diverse – these include stepper motors and AC-powered ones. The last group is divided into two types – synchronous and asynchronous. Synchronous motors, depending on the characteristics of the work, can be rotating or linear.

The motors also use a servo amplifier – this is a structural element that provides power supply and motor control with permanent magnets. It can work offline if necessary, using a special program that is preloaded into the device’s memory.

Depending on the circuit diagram and design, servos can be electromechanical and electrohydromechanical. The first option, including the gearbox and motor, is characterized by low speed. In the second case, the action occurs very quickly due to the movement of the piston in the cylinder.

Application area

At the moment, servos are quite widespread. They can be found in precision instruments, automatic machines manufacturing various boards, programmable machines, industrial robots, and other mechanisms. Drives of this type have gained great popularity in the aircraft model sphere due to efficient energy consumption and uniform movement. Not only that, a servo drive is a necessary element in robotics, with the help of which many creative projects are embodied. This smart steered motor is designed to simulate motion. Using its functions is quite simple; many programs have already been written that can be used as a stencil for translating your own ideas.