Many people ask: servo - what is it? The classic design of the servo drive includes a motor, a position sensor and a three-loop control system (regulation of position, speed and current).
The word “servo” is of Latin origin “servus”, literally translated as “slave”, “assistant”, “servant”.
In the machine-building industry, devices acted as auxiliary components (feed drive in a machine, robot, etc.). However, today the situation has changed, and the main purpose of the servo drive is to implement in the field of servomechanisms.
The installation of a servo drive is justified when conventional frequency converters do not sufficiently regulate the accuracy.
The use of high-quality devices is necessary in equipment characterized by a high level of performance.
This article will talk about the servo, what it is and how it works.
Application Areas
In the modern world, when automation has taken a strong position in all areas of mechanical engineering, the design of all mechanisms has been noticeably unified. In this case, modern individual drives are used.
In order to understand the servo drive, what it is, you should know the scope of the device.
Devices contain precision designs to maintain speed in industrial robots and machine tools with high accuracy. They are mounted on drilling equipment, in various transport systems and auxiliary mechanisms.
The most widely used devices are in the following areas:
- paper and packaging manufacturing;
- the manufacture of metal sheets;
- material processing;
- production of transport equipment;
- woodworking industry ;
- manufacturing of building materials.
Servos on the trunk of a car
There are many models of servos for the trunk of a car from different manufacturers. Consider the functionality of such a device as a boot servo from the domestic manufacturer Avtozebra. The device is designed for Russian cars, but not only. For example, it can be used in a Renault Logan car.
According to user reviews, this design is convenient. It allows, without leaving the car, to open and close the trunk.
The device is controlled by a button mounted in the car interior or in the alarm key fob.
Reason for widespread use of the device
The reason for the frequent use of servos is:
- the ability to obtain control that is highly accurate and stable;
- wide range of speed control;
- high level of immunity to interference;
- small size and weight of the device.
The principle of operation of the servo
How does the device work? A servo drive, the principle of which is based on feedback from one or more system signals, controls the object. The output indicator of the device goes to the input, where there is a comparison with the setting action.
Mechanism features
The servo device has two main features:
- ability to increase power;
- providing feedback information.
Amplification is required for the purpose that the energy required at the output is very high (comes from an external source), and at the input its indicator is negligible.
Feedback is nothing more than a closed loop circuit in which signals are not matched at the input and output. This process is used for management.
This leads to the conclusion: the circuit in the forward direction serves as a transmitter of energy, and in the opposite direction, as a transmitter of information that is needed for control accuracy.
Power and pinout of device connectors
A servo drive, the principle of which is applicable in radio-controlled configurations, usually has three wires:
- Signaling. A control pulse is transmitted along it. As a rule, the wire is painted in white, yellow or red.
- Feeding. The power indicator is from 4.8 to 6 V. Often, this is a red wire.
- Grounding. The wire is black or brown.
Drive Dimensions
By size, units are divided into three categories:
- micro drives;
- standard modifications;
- large devices.
Servo drives are also found with other size indicators, however, the above types make up 95% of all devices.
Key Product Features
The servo drive is characterized by two main indicators: turning speed and shaft forces. The first value is an indicator of the time, which is measured in seconds. The force is measured in kg / cm, that is, what level of force the mechanism develops from the center of rotation.
In general, this parameter depends on the main purpose of the device, and only then on the number of gear reducers and the nodes used in the device.
As already mentioned, now they produce mechanisms that operate with a supply voltage indicator of 4.8 to 6 V. More often this indicator is 6 V. However, not all models are designed for a wide voltage range. Sometimes the servo motor works only at 4.8 V or only at 6 V (the latest configurations are extremely rare).
Analog and Digital Modifications
A few years ago, all servo circuits were analog. Now there are digital designs. What is the difference in their work? Let us turn to official information.
It follows from a Futaba report that over the past decade, servo drives have become distinguished by better technical performance than before, as well as by their small size, high level of rotation speed and torsion rate.
The latest round of development is the advent of the device on a digital basis. These units have significant advantages even over collector type motors. Although there are some disadvantages.
Externally, analog and digital devices are indistinguishable. Differences are recorded only on the device boards. Instead of a microcircuit on a digital unit, you can see a microprocessor that analyzes the receiver signal. He controls the engine.
It is completely wrong to say that analog and digital modifications are fundamentally different in operation. They can have the same motors, mechanisms and potentiometers (variable resistors).
The main difference is the method of processing the incoming signal of the receiver and engine control. Both servos receive the same power radio signal.
So it becomes clear, servo, what is it?
The principle of analog modification
In the analogue modification, the received signal is comparable with the current position of the servomotor, and then the amplifier receives a signal from the engine, causing the motor to move to a given position. The process frequency indicator is 50 times in one second. This is the minimum response time. If you reject the handle on the transmitter, then short pulses will begin to arrive at the servo drive, the interval between which will be equal to 20 m / s. Between pulses, nothing is supplied to the motor, and external influences can change the functioning of the device in any direction. This time period is called the "dead zone".
The principle of digital design
Digital devices use a special processor that operates at high frequencies. It processes the receiver signal and sends control pulses to the engine with a frequency index of 300 times per second. Since the frequency indicator is much higher, the reaction is much faster and holds the position better. This causes optimum centering and a high level of torsion. But this method requires a lot of energy, so the battery used in the analog mechanism in this design will be discharged much faster.
However, all users who have at least once encountered a digital model say that its difference with the analog design is so significant that they would never use the latter again.
Conclusion
Digital analogs will be your choice if you need:
- high level of resolution ;
- minimum number of "dead zones";
- exact level of positioning;
- quick reaction to the team;
- unchanged effort on a shaft when turning;
- high power level.
Now you know what a servo is and how to use it.