The servo is the most advanced and modern type of motor. It is intended for use in motion control applications requiring high positioning accuracy. Knowing how a servo drive works allows us to understand its growing demand in industrial process automation and consumer technology.
Content
- Pre-digital era
- The evolution of precision
- Device and types
Pre-digital era
The name Le-Servomoteur was first used by Joseph Farco in 1868 to describe hydraulic and steam engines used in shipbuilding. The actual meaning of this word has been lost over time, but it can be assumed that it was a pun from the French cerveau (brain) and Latin servus (to serve). In a broad sense, this term was introduced not to emphasize the usefulness or complexity of motors, but focused on their ability to serve the commands of the propulsion control complex. That is, the drive has feedback with the rest of the system and responds to its signals.
In 1898 Tesla experimented with wireless control of ship models equipped with contactor servo motors, and in 1911 Hobart had already put the term "servo motor" in his vocabulary. By 1915, this word was firmly entrenched among English-speaking electrical engineers, despite its French origin.
. Further development of technology before World War II was more than rapid:- 1
916 - patented pneumatic torpedo, in which the steering wheel obeyed a servo mechanism; - 1922 - General Electric begins work on servos for controlling naval guns;
- 1925 - created an electronic gun servo, using proportional control and positive feedback;
- 1933 - DC servo tape recorder introduced.
- 1935 - the first stepper motor was tested as a remote repeater of the position of the compass and the sight of the gun.
The evolution of precision
Stepper motors were used in limited numbers during and after World War II. In the 60s of the last century, they experienced several improvements and were ubiquitous for more than two decades as irreplaceable unmanned control elements, indicators for sorting wagons and weighing stations, digital differential altimeters and computer periphery.
The first brushless motors were developed in the mid 50s. The elimination of mechanical brushes allowed them to operate for a surprisingly long time with high reliability. Stepper motors have a strong competitor. Brushless motors are indispensable in space exploration, which determined their rapid development.
The advent of affordable manufacturing methods for rare earth cobalt magnets in the 1960s became the main base for the technological breakthrough of DC motors. It is these, equipped with controlled feedback drives, that make up the majority of the servo motors produced in the world. Microprocessors broke into the automation market in the early 1970s and were able to provide near-perfect control over machine movement.
Device and types
A servo drive is a device designed to perform a mechanical action with high precision under continuous self-control of the target position and movement parameters. The presence of a feedback system with a sensitive device for correcting deviations from the set parameters distinguishes it from other types of drives. In a broader sense, this term refers to modern electric motors equipped with servo drives. Simplified, the servo device can be described as a closed system of four elements:
- sensor;
- engine;
- controller;
- feedback system.
The principle of operation of the servomotor looks like this: a command is sent to the device input to assign a new state (coordinates, speed, etc.) ), the device determines the current value, compares it with the received one and makes a control action on the motor to reduce their difference.
Due to their ability to maintain and control the set parameters, servos are considered to be the most advanced actuators. Modern devices have changed a lot compared to the first generations. Now these are smart devices, made using the latest advances in the production of magnets and processor technology. In the 21st century, progress made it possible to reduce the cost of simple devices several times without losing their qualities and to create technically sophisticated variable speed and high precision drives for demanding industries such as machine tool building.
In modern industry, two types of servo motors are used: linear and rotary. Linear allow you to achieve:
- high speeds and accelerations;
- high positioning accuracy.
They have undeniable advantages, but nevertheless, it is rotary servos that are popular. This is mainly due to the fact that linear tend to overheat. Heat causes unwanted expansion, placing stress on bearings, grease and sensors. Over time, this negatively affects the lifespan of the components.
Rotary motors are divided, in turn, into position and continuous rotation servos. Positional rotation devices are the most common type. The output shaft operates only in a sector of the circle, limited by physical stops to prevent rotation outside the design specified limits.
Continuous motors are very similar to positional motors with the difference that they have the ability to rotate in any direction at different speeds depending on the input signal.
The advantages of rotary servo motors, from a control point of view, are as follows:
- torque is proportional to current;
- the speed is proportional to the applied voltage.
Both the first and the second are in demand in applications ranging from children's toys to space robotics.
Servos, of course, continue to improve. They emerged and evolved as a result of the trend towards decentralization of automated systems. Reducing the cost of processors speeds up this process. The number of functions performed by modern servos is growing and will likely continue to grow. The newest devices are already endowed with the ability to self-adjust and optimize control parameters and can be manufactured with process controllers for remote installations.
It is quite possible that servo drives of the future will solve many related tasks in machines and mechanisms, helping to avoid the installation of additional equipment.
