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A servo motor is a special negative feedback motor designed for use in CNC machines. Servomotors have fairly high speed characteristics, as well as high positioning accuracy.
A servo motor is an unpretentious working element that is part of industrial equipment. When used correctly, the servomotor can operate 24 hours a day.
Servo motor history
Modern servomotors have combined all the achievements of scientific and technological innovative progress, and therefore are capable of developing enormous rotation speeds with very high power. A large range of adjustment of the servomotor shaft rotation using software during significant acceleration or braking makes this equipment simply indispensable for use in machine tools or production lines and many other structures.
Comparison of Stepper Motors and Servo Motors
As you know, servomotors combine fairly high power and compactness. However, these motors can only function if an electronic unit is available. The combination of a servomotor and an electronic control module is called a servo drive. One of the main advantages of servomotors over stepper motors is, of course, smooth running. Presence feedback creates conditions for precise positioning of the position, as well as the speed of rotation of the servomotor shaft.
The difference between stepper motors
As a rule, stepper motors also require electronic units to control their operation, but unlike servomotors, they do not require feedback and operate in their own discrete mode. The stepper motor itself is an electric motor of a special design that converts the impulses that give it into discrete movement with a certain number of steps.
In general, stepper motors are used in cases where, due to the complete absence of a feedback module, it is necessary to reduce the cost of the drive. According to the principle of operation, servo motors and stepper motors are largely similar and in some cases can even use standard electronic devices.
Application of stepper motors
Stepper motors can be used in modern high-tech devices, because the accuracy of their operation is quite high. Therefore, even despite the intensity of the functions being implemented, they are unpretentious in operation, durable and very reliable. Stepper motors are integrated into various production automation systems, for example, from CNC (computer numerical control) machines to analytical instruments.
If there is no need for too high precision of the operating mechanism and smooth movement at “not” high feed rates, then purchasing a discrete device will significantly reduce equipment costs, thereby saving money, because the cost of a stepper motor together with the control unit is significantly lower than a servo drive .
Stepper motors are a type of brushless DC equipment. Therefore, like any engines without a commutator, they have fairly high reliability and a significant service life. Compared to the traditional inclusion of DC motors, stepper motors require the presence of electronic circuits switching special windings during operation. A stepper motor is a very, very expensive device, so if the positioning accuracy is not significant, it is best to use conventional commutator motors instead.
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This article discusses servos: their design, purpose, control of the servo, connecting the servo, types of servos and their comparison. Let's go ahead and start with what a servo is.
Servo concept
A servo drive is most often understood as a mechanism with an electric motor, which can be asked to turn to a given angle and hold this position. However, this is not a completely complete definition.
To be more precise, a servo drive is a drive controlled through negative feedback, allowing precise control of motion parameters. A servo drive is any type of mechanical drive that contains a sensor (position, speed, force, etc.) and a drive control unit that automatically maintains the necessary parameters on the sensor and device according to a given external value.
In other words:
The servo drive receives the value of the control parameter as input. For example, the rotation angle
The control unit compares this value with the value on its sensor
Based on the comparison result, the drive performs some action, for example: turning, accelerating or decelerating so that the value from the internal sensor becomes as close as possible to the value of the external control parameter
The most common are servos that hold a given angle and servos that maintain a given rotation speed.
A typical hobby servo is shown below.
How are servos designed?
Servo drive device
Servo drives have several components.
Drive - electric motor with gearbox. To convert electricity into mechanical rotation, you need electric motor. However, the motor rotation speed is often too high for practical use. Used to reduce speed gearbox: a gear mechanism that transmits and converts torque.
By turning the electric motor on and off, we can rotate the output shaft - the final gear of the servo, to which we can attach something that we want to control. However, in order for the position to be controlled by the device, it is necessary feedback sensor - 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, proportional to the angle of rotation. Thus, it can be used to determine the current position of the mechanism.
In addition to the electric motor, gearbox and potentiometer, the servo drive has electronic filling, which is responsible for reception external parameter, reading the values from the potentiometer, comparing them and turning the motor on/off. She is responsible for maintaining negative feedback.
There are three wires going to the servo. 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 a servo externally.
Servo drive control. Control signal interface
To indicate the desired position to the servomotor, a control signal must be sent along the wire provided for this purpose. The control signal is pulses of constant frequency and variable width.
What position the servo should take depends on the length of the pulses. When a signal enters the control circuit, the pulse generator present in it produces its own pulse, the duration of which is determined through a potentiometer. The other 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.
Most often, hobby servers produce pulses at a frequency of 50 Hz. This means that a pulse is emitted and received once every 20 ms. Typically, a pulse duration of 1520 µs means that the servo should take the middle position. Increasing or decreasing the pulse length will cause the servo to turn clockwise or counterclockwise, respectively. In this case, there are upper and lower limits on the pulse duration. In the Servo library for Arduino, the following pulse lengths are set by default: 544 μs for 0° and 2400 μs for 180°.
Please note that your specific device may not have factory default settings. Some servos use a pulse width of 760 µs. The middle position corresponds to 760 μs, similar to how in conventional servos the middle position corresponds to 1520 μs.
It's also worth noting that these are just generally accepted lengths. Even within the same servo model, there may be manufacturing tolerances that cause the operating range of pulse lengths to vary slightly. For accurate operation, each specific servo must be calibrated: through experimentation, it is necessary to select the correct range specific to it.
Something else worth paying attention to is the confusion in terminology. Often the method of controlling servos is called PWM/PWM (Pulse Width Modulation) or PPM (Pulse Position Modulation). This is not true, and using these methods may even damage the drive. The correct term is PDM (Pulse Duration Modulation). In it, the length of the pulses is extremely important and the frequency of their occurrence is not so important. 50 Hz is normal, but the servo will work correctly at both 40 and 60 Hz. The only thing you need to keep in mind is that if the frequency is greatly reduced, it can operate jerkily and at reduced power, and if the frequency is greatly increased (for example, 100 Hz), it can overheat and fail.
Servo Drive Characteristics
Now let's figure out what types of servos there are and what characteristics they have.
Torque and swing speed
First let's talk about two very important characteristics of a servo drive: o torque and about turning speed.
The moment of force, or torque, is a vector physical quantity equal to the product of the radius vector drawn from the axis of rotation to the point of application of the force and the vector of this force. Characterizes the rotational action of a force on a solid body.
Simply put, this characteristic shows how heavy a load the servo can hold at rest on a lever of a given length. If the torque of the servo drive is 5 kg×cm, then this means that the servo drive will hold a lever 1 cm long, on the free end of which 5 kg is suspended, in a horizontal position. Or, equivalently, a lever 5 cm long from which 1 kg is suspended.
Servo speed is measured by the amount of time it takes for the servo arm to rotate 60°. A characteristic of 0.1 s/60° means that the servo rotates 60° in 0.1 s. From it it is easy to calculate the speed in a more familiar value, revolutions per minute, but it so happens that when describing servos, such a unit is most often used.
It is worth noting that sometimes there is a trade-off between these two characteristics, since if we want a reliable, heavy-duty servo, we must be prepared for this mighty unit to turn slowly. And if we want a very fast drive, then it will be relatively easy to dislodge it from its equilibrium position. When using the same motor, the balance is determined by the configuration of the gears in the gearbox.
Of course, we can always take a unit that consumes more power, the main thing is that its characteristics meet our needs.
Form factor
Servos vary in size. And although there is no official classification, manufacturers have long adhered to several sizes with a generally accepted arrangement of fasteners. They can be divided into:
small
standard
They have the following characteristic dimensions:
There are also so-called “special type” servos with dimensions that do not fall into this classification, but the percentage of such servos is very small.
Internal interface
Servo drives are either analog or digital. So what are their differences, advantages and disadvantages?
Externally, they are no different: electric motors, gearboxes, potentiometers are the same, they differ only in the internal control electronics. Instead of a special analog servo microcircuit, the digital counterpart has a microprocessor on the board that receives pulses, analyzes them and controls the motor. Thus, in the physical design, the only difference is in the method of processing impulses and controlling the motor.
Both types of servo drive accept the same control pulses. The analog servo then decides whether to change the position and sends a signal to the motor if necessary. This usually happens with a frequency of 50 Hz. Thus, we get 20 ms - the minimum reaction time. At this time, any external influence can change the position of the servo drive. But this is not the only problem. In a state of rest, no voltage is supplied to the electric motor; in case of a slight deviation from equilibrium, voltage is supplied to the electric motor. short signal low power. The greater the deviation, the stronger the signal. Thus, with small deviations, the servo drive will not be able to quickly rotate the motor or develop a large torque. “Dead zones” are formed in time and distance.
These problems can be solved by increasing the reception frequency, signal processing and electric motor control. Digital servos use special processor, which receives control pulses, processes them and sends signals to the motor with a frequency of 200 Hz or more. It turns out that the digital servo drive is able to react faster to external influences, quickly develop the required speed and torque, which means it is better to hold a given position, which is good. Of course, it also consumes more electricity. Also, digital servos are more difficult to manufacture and therefore cost significantly more. Actually, these two disadvantages are all the disadvantages that digital servos. In technical terms, they unconditionally defeat analog servos.
Gear materials
Gears for servos come from different materials: plastic, carbon, metal. All of them are widely used, the choice depends on the specific application and what characteristics are required in the installation.
Plastic, most often nylon, gears are very light, not subject to wear, and are most common in servos. They do not withstand heavy loads, but if the loads are expected to be light, then nylon gears are the best choice.
Carbon gears are more durable, practically do not wear out, and are several times stronger than nylon ones. The main disadvantage is the high cost.
Metal gears are the heaviest, but they can withstand maximum loads. They wear out quite quickly, so you have to change the gears almost every season. Titanium gears are the favorite among metal gears, both in terms of technical characteristics and price. Unfortunately, they will cost you quite a lot.
Brushed and brushless motors
There are three types of servo motors: regular core motor, coreless motor, and brushless motor.
A conventional core motor (right) has a dense iron rotor with a wire winding and magnets around it. The rotor has multiple sections, so when the motor rotates, the rotor causes the motor to vibrate slightly as the sections pass the magnets, resulting in a servo that vibrates and is less accurate than a servo with a coreless motor. The hollow-rotor motor (left) has a single magnetic core with a cylinder or bell-shaped winding around the magnet. The coreless design is lighter in weight and has no sections, resulting in faster response and smooth, vibration-free operation. Such motors are more expensive, but they provide more high level control, torque and speed compared to standard ones.
Servo drives with brushless motors have appeared relatively recently. The advantages are the same as those of other brushless motors: there are no brushes, which means they do not create rotational resistance and do not wear out, the speed and torque are higher with a current consumption equal to brushed motors. Brushless motor servos are the most expensive servos, but they also offer best characteristics compared to servos with other types of motors.
Connecting to Arduino
Many servos can be connected to Arduino directly. To do this, a loop of three wires comes from them:
red - nutrition; connects to 5V pin or directly to power supply
brown or black - earth
yellow or white - signal; connects to the Arduino digital output.
To connect to Arduino, it will be convenient to use a port expander board such as Troyka Shield. Although with a few additional wires you can connect the servo via the breadboard or directly to the Arduino pins.
It is possible to generate control pulses yourself, but this is such a common task that there is a standard Servo library to simplify it.
Dietary restrictions
A typical hobby servo drive consumes more than 100 mA during operation. At the same time, Arduino is capable of delivering up to 500 mA. Therefore, if you need to use a powerful servo drive in a project, it makes sense to think about separating it into a circuit with additional power.
Let's look at the example of connecting a 12V servo drive: 
Limitation on the number of connected servos
On most Arduino boards, the Servo library supports control of a maximum of 12 servos; on the Arduino Mega, this number increases to 48. However, there is a small side effect of using this library: if you are not working with an Arduino Mega, then it becomes impossible to use the analogWrite() function on 9 and 10 pins regardless of whether servos are connected to these pins or not. You can connect up to 12 servos to the Arduino Mega without disrupting PWM/PWM functionality when using more servos, we will not be able to use analogWrite() on pins 11 and 12.
Servo library functionality
The Servo library allows software control of servos. For this purpose it starts type variable Servo. Management is carried out by the following functions:
attach() - attaches a variable to a specific pin. There are two syntax options for this function: servo.attach(pin) and servo.attach(pin, min, max) . In this case, pin is the number of the pin to which the servo drive is connected, min and max are the pulse lengths in microseconds, responsible for the rotation angles of 0° and 180°. By default, they are set to 544 μs and 2400 μs, respectively.
write() - commands the servo to accept some parameter value. The syntax is: servo.write(angle) where angle is the angle the servo should turn through.
writeMicroseconds() - gives a command to send a pulse of a certain length to the servo drive; it is a low-level analogue of the previous command. The syntax is: servo.writeMicroseconds(uS) , where uS is the pulse length in microseconds.
read() - reads the current value of the angle at which the servo is located. The syntax is: servo.read() , returning an integer value between 0 and 180.
attached() - checks whether a variable has been attached to a specific pin. The syntax is as follows: servo.attached() , returning logical true if the variable was attached to any pin, false otherwise.
detach() - performs the opposite action of attach() , that is, it detaches the variable from the pin to which it was assigned. The syntax is: servo.detach() .
All Servo2 library methods are the same as Servo methods.
Example of using the Servo library
Instead of a conclusion
Servo drives are different, some are better - others are cheaper, some are more reliable - others are more accurate. And before you buy a servo, it is worth keeping in mind that it may not have the best characteristics, as long as it is suitable for your project. Good luck in your endeavors!
Servo motors have the following characteristics:
High dynamics,
High positioning accuracy,
High overload capacity over a wide speed range.
In addition, servo motors have the following features:
High accuracy of maintaining the specified rotation speed;
Wide range of speed control;
Short acceleration time;
Short torque control time;
Large starting torque;
Low moment of inertia;
Light weight;
Compact design.
Rice. 1 Example of servo motors
The main design elements of the servomotor are:
Connection elements in the form of plug connectors or terminal box;
Feedback sensor.
1. Overview of modern servo motors
The servo motor family can be divided into the following groups:
Rice. 2 Servo Motors Overview
The most important distinctive features due to the following factors:
Motor design (stator, rotor);
Required regulatory systems;
Feedback system (sensors).
Until recently, brushless DC motors with permanent magnet excitation were used as servo drives. Control was provided by thyristor or transistor converter-regulators.
Thanks to technological progress in the field of power semiconductor devices and microcontrollers, the use of synchronous servomotors increased significantly in the nineties.
Today synchronous servomotors alternating current with permanent magnet excitation occupy a larger market segment than asynchronous servomotors. This is due to the characteristics of the engines.
In this article, the following terms are used to refer to engines:
Synchronous servo motor- synchronous AC servomotor with permanent magnet excitation.
Asynchronous servo motor- asynchronous motor with feedback sensor, specially designed to operate from a frequency converter.
Synchronous linear motor- linear synchronous AC servomotor with permanent magnet excitation.
2. Characteristics of synchronous and asynchronous servomotors
| Characteristics of synchronous servo motors | Characteristics of Asynchronous Servo Motors |
| High dynamics. | Medium...high dynamics. |
| Moderately good control characteristics at high load inertia moments. | Good control characteristics at high load inertia moments. |
| High overload capacity up to 6 MN (rated torque, depends on the type of engine). | High overload capacity (almost 3 times). |
| High permissible thermal load in continuous operation over the entire speed range. | High permissible thermal load in continuous operation depending on the rotation speed. |
| Cooling through convection, heat dissipation and thermal radiation. | Cooling by impeller on the shaft or forced. |
| High quality speed control. |
|
| Possibility of long-term operation with starting torque at low speeds. | Due to the high thermal load, long-term operation in the lower speed range without a forced cooling fan is not possible. |
| Wide range of rotation speed control, 1:5000 or more (depending on the converter). |
|
| Torque ripple (Cogging) at low speed. | Almost complete absence of torque pulsation (Cogging). |
3. Design of synchronous servomotors
The main design elements of a synchronous servomotor are:
Rotor with permanent magnets;
Stator with corresponding winding;
Connection elements in the form of a plug connector or terminal box;
Feedback sensor.
The following types of synchronous servomotors are available:
Version with housing - hull motors;
Version without housing - frameless motors.
The design without a housing means that the role of the motor housing is performed by a stack of stator plates. This allows the entire profile of the steel plate stack to be fully utilized.
Housing version: CMP engine;
Version with housing: CM/DS engine;
Version without housing: CMD motor.
3.1 CMP motor design
CMP servomotors are characterized by very high dynamics, low rotor inertia, compactness and high power density.
CMP servo motors are framed motors.
Rice. 3. Design of the CMP synchronous servomotor from SEW-EURODRIVE
1 - Compensation washer
2 - Radial ball bearing
4 - Radial ball bearing
5 - Signal plug connector SM/SB
6 - Power plug connector SM/SB
7 - Housing cover
8 - Gasket
9 - Resolver
10 - Rear bearing shield
11 - Housing with stator
13 - Cuff
CMP Engine Features and Options
Overload capacity up to 4.5*Mn (nominal torque).
Stator with tooth winding.
Variable arrangement of plug connectors.
3.2 CM/DS motor design
CM/DS servomotors are characterized by a wide torque range, good control characteristics at high load inertia moments, a powerful service brake and a variety of options.
CM/DS servo motors are motors with a housing.
Rice. 4. Design of the CM synchronous servomotor from SEW-EURODRIVE
2 - Bearing shield with flange
4 - Housing with stator
5 - Rear bearing shield
7 - Resolver
8 - Plug connector housing
9 - Power cable plug, assembled
10 - Signal cable plug, assembled
11 - Brake, assembled
CM/DS Engine Features and Options
Overload capacity up to 4*Mn (nominal torque).
Stator with template winding.
Possibility of mounting on standard gearboxes and gearboxes for servo drives via an adapter.
Possibility of direct mounting on the gearbox.
Possibility of installing a resolver or an absolute encoder with high resolution.
Plug connector or terminal box.
Forced cooling fan (optional).
Service brake (optional).
TF or KTY sensor for thermal motor protection. 2nd shaft on sensor side (optional).
Reinforced bearings (optional).
3.3 CMD motor design
CMD servomotors are particularly compact, have optimal speed selection and a range of options for installations with direct (gearless) drive.
CMD servo motors are motors without housing.
Rice. 5. Design of the CMD synchronous servomotor from SEW-EURODRIVE
2 - Bearing shield with flange
3 - Radial ball bearing
4 - Stator
5 - Rear bearing shield
6 - Radial ball bearing
7 - Resolver
8 - Signal cable connector
9 - Power cable connector
CMD Motor Features and Options
Almost 6 times overload capacity.
Stator with template winding.
Brake with 24 V coil (optional).
Possibility of installing a resolver or an absolute encoder with high resolution.
KTY sensor for thermal protection of the motor.
3.4 Rotor design
The rotor of synchronous servomotors is equipped with permanent magnets.
Rice. 6.
1 - Pasted magnets
These magnets are typically made from sintered rare earth material neodymium-iron-boron. The magnetic properties of this material significantly exceed those of conventional ferrite magnets. This allows for a more compact design with equal power output.
Servos and mechanisms are equipped with a sensor that monitors a specific parameter, such as force, position or speed, as well as a control unit in the form of an electronic device. The purpose of this device is to maintain required parameters V automatic mode during operation of the device, depending on the type of incoming signal from the sensor at certain periods of time.
Design and operation
A servo drive differs from a conventional electric motor in that it is possible to set the exact position of the shaft in degrees. Servo drives are any mechanical drives that include a sensor for some parameter and a control unit that is capable of automatically maintaining the required parameters corresponding to certain external values.
1 — Reducer gears
2 - Output shaft
3 - Bearing
4 - Lower bushing
5 - Potentiometer
6 - Control board
7 — Housing screw
8 - DC motor
9 – Electric motor gear
To convert electrical energy into mechanical movement, it is necessary. The drive is a gearbox with an electric motor. A gearbox is required to reduce the speed of the motor as the speed is too high for the application. The gearbox consists of a housing in which there are shafts with gears capable of converting and transmitting torque.
By starting and stopping the electric motor, the output shaft of the gearbox, which is connected to the servo gear, can be driven. A device or mechanism that needs to be controlled can be attached to the shaft. In addition, to control the position of the shaft, a feedback sensor is required. This sensor can convert the rotation angle back into an electrical current signal.
This sensor is called an encoder. A potentiometer can be used as an encoder. If the potentiometer slider is turned, its resistance will change. The value of this resistance is directly proportional to the angle of rotation of the potentiometer. Thus, it is possible to achieve a certain position of the mechanism.
In addition to the above-mentioned potentiometer, gearbox and electric motor, the servos are equipped with an electronic board that processes the incoming signal of the external parameter value from the potentiometer, compares it, and, in accordance with the comparison result, starts or stops the electric motor. In other words, this electronic filling is responsible for supporting negative feedback.
The servo drive is connected by three conductors, two of which supply power to the electric motor, and the third conductor receives a control signal, which is used to set the position of the motor shaft.
In addition to the electric motor, another mechanism can also play the role of a drive, for example a pneumatic cylinder with a rod. Angle rotation sensors are also used as feedback sensors, or . The control unit is a servo amplifier, an individual inverter. It may also contain a control signal sensor.
If it is necessary to create smooth braking or acceleration to prevent excessive dynamic loads on the engine, more complex control microcontroller circuits are used that can control the position of the working element much more accurately. The drive device for setting the position of the heads in computer hard drives is designed in a similar way.
Types of servos
If it is necessary to create control of several groups of servo drives, use CNC controllers, which are assembled in the diagrams programmable logical controllers. Such servos are capable of providing a torque of 50 N*m, with a power of up to 15 kilowatts.
Synchronous are able to set the rotation speed of the electric motor with great accuracy, as well as acceleration and rotation angle. Synchronous drive types can quickly reach rated speed.
Asynchronous able to accurately maintain speed even at very low speeds.
Servo drives are fundamentally divided into electromechanical And electrohydromechanical . Electromechanical drives consist of a gearbox and an electric motor. But their performance is much slower. In electrohydromechanical drives, motion is created by the movement of a piston in a cylinder, as a result of which the speed is at a very high level.
Servo Drive Characteristics
Let's consider the main parameters that characterize servos:
- Shaft force. This parameter is the torque. This is the most important parameter of the servo drive. The data sheet most often indicates several torque values for different voltage values.
- Turning speed is also important characteristic. It is indicated in terms of the equivalent time required to change the position of the actuator output shaft by 60 degrees. This parameter can also be specified for multiple voltage values.
- Servo type can be analog or digital.
- Nutrition . The main part of the servos operates at a voltage of 4.8-7.2 volts. Power is most often supplied through three conductors: white – control signal, red – operating voltage, black – common wire.
- Angle of rotation - this is the largest angle through which the output shaft can rotate. Most often this parameter is 180 or 360 degrees.
- Constant rotation . If necessary, a conventional servo can be retrofitted for continuous rotation.
- Material of manufacture Servo gearboxes can be of different types: carbon, metal, plastic, or a combination. Gears made of plastic cannot withstand shock loads, but have high wear resistance. Carbon gears are much stronger than plastic ones, but are more expensive. Metal gears can withstand significant loads and falls, but have low wear resistance. The output shaft of the gearbox is installed differently on different models: on sliding bushings or on ball bearings.
Advantages
- Ease and simplicity of installation of the structure.
- Reliability and reliability, which is important for critical devices.
- They do not create noise during operation.
- Precision and smooth movement is achieved even at low speeds. Depending on the task at hand, the resolution can be adjusted by the employee.
Flaws
- Difficult to set up.
- Increased cost.
Application
Servo drives are currently used quite widely. For example, they are used in various precision instruments, industrial robots, automatic production printed circuit boards, computer-controlled machines, various valves and gate valves.
High-speed drives have become the most popular in aircraft modeling. Servo motors have the advantage of efficient electrical energy consumption as well as uniform movement.
At the beginning of the appearance of servomotors, commutator three-pole motors with windings on the rotor and permanent magnets on the stator were used. In addition, the engine design included a unit with a commutator and brushes. Further, with technological progress, the number of motor windings increased to five, and the rotational torque increased, as well as the acceleration speed.
The next stage in the development of servo motors was the location of the windings outside the magnets. This reduced the mass of the rotor and reduced the acceleration time. At the same time, the cost of the engine has increased. As a result of further design of servomotors, it was decided to abandon the presence of a commutator in the motor design. Motors with permanent magnet rotors began to be used. The motor became brushless, its efficiency increased due to an increase in torque, speed and acceleration.
Recently, servomotors powered by a programmable controller (Arduino) have become the most popular. As a result, great opportunities have opened up for the design of precision machine tools, robotics, and aircraft manufacturing (quadcopters).
Since drives with motors without commutators have high functional characteristics, precise control, and increased efficiency, they are often used in industrial equipment, household appliances (powerful vacuum cleaners with filters), and even in children's toys.
Heating servo drive
Compared to mechanical adjustment of the heating system, electric servos are the most advanced and progressive technical devices ensuring the maintenance of space heating parameters.
1 - Power supply
2 - Room thermostats
3 - Switching block
4 - Servomotors
5 - Supply manifold
6 - Bypass
7 — Water heated floor
8 - Return manifold
9 — Water temperature sensor
10 - Circular pump
11 - Ball valve
12 — Control valve
13 - Two-way thermostatic valve
The heating system drive operates in conjunction with a wall-mounted thermostat. An electrically driven faucet is mounted on the coolant supply pipe, in front of the warm water floor collector. Next, connect the 220 volt power supply and set the operating mode thermostat.
The control system is equipped with two sensors. One of them is located in the floor, the other in the room. The sensors transmit signals to a thermostat that controls a servomotor that is connected to the faucet. You can increase the accuracy of adjustment by installing additional device outside the room, since climate conditions are constantly changing and affect the temperature in the room.
The actuator is mechanically connected to the valve to control it. Valves can be two- or three-way. A two-way valve can change the temperature of the water in the system. The three-way valve is able to maintain the temperature constant, but changes the consumption hot water, which is supplied to the circuits. The three-way valve device has two hot water inlets (supply pipes) and a return water outlet through which mixed water is supplied at a predetermined temperature.
Mixing of water occurs using a valve. At the same time, the supply of coolant to the collectors is adjusted. When one entrance opens, the other begins to close, and the water flow at the outlet does not change.
Trunk servos
Currently, modern cars are most often produced with an automatic trunk opening function. For this purpose, the servo drive design we discussed is used. Automakers use two methods to equip a vehicle with this feature.
Of course, the trunk pneumatic drive is more reliable, but its cost is quite high, so such a drive has not been used in cars.
The electric drive is available with different control methods:
- The handle is on the trunk lid.
- Button on the driver's door panel.
- From the alarm panel.
Opening the trunk manually is not always convenient. For example, in winter the castle tends to freeze. The servo drive additionally performs the function of protecting the car from unauthorized entry, as it is combined with the locking device.
Such trunk drives are used on some imported cars, however, it is possible to install such a mechanism on domestic cars, if desired.
There are trunk drives with magnetic plates, but they have not found application since their design is quite complex.
The most affordable ones are trunk servos, which only open. The closing function is not available for them. You can also choose a drive model design that has an inertial mechanism. It plays the role of blocking when an obstacle appears when the trunk moves.
Expensive models of servo drives include a mechanism for raising and lowering the trunk, a closer locking mechanism, sensors and a controller. They are usually installed on cars at the factory, however simple designs It is quite possible to install it yourself.
Many people ask the question: servo drive - what is it? The classic servo design includes a motor, a position sensor and a three-loop control system(position, speed and current regulation).
The word "servo" is of Latin origin "servus", literally translated as "slave", "helper", "servant".
In the mechanical engineering industry, devices acted as auxiliary components (feed drive in a machine tool, robot, etc.). However, today the situation has changed, and the main purpose of the servo drive lies in the implementation in the field of servomechanisms.
Installing a servo drive is justified in cases where conventional ones do not sufficiently regulate the accuracy of operation.
Application of devices High Quality necessary in equipment with a high level of performance.
This article will tell you about the servo drive, what it is and how it functions.
Areas of use of the device
IN modern world When automation took a strong position in all areas of mechanical engineering, the design of all mechanisms became noticeably unified. In this case, modern individual drives are used.
In order to understand what a servo drive is, you should know the scope of application of the device.
The devices contain precision designs to maintain speed in and machine tools with high accuracy. They are mounted on drilling equipment, in various systems transport and auxiliary mechanisms.
The devices are most widely used in the following areas:
- production of paper and packaging;
- production of metal sheets;
- materials processing;
- production of transport equipment;
- production of building materials.
Servo drives for car trunk
There are many models of car trunk servos from different manufacturers. Let's consider the functionality of such a device as the trunk servo drive 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 you to open and close the trunk without leaving the car.
The device is controlled via a button mounted inside the car or in
The reason for the widespread use of the device
The reasons for the frequent use of servos are:
- the ability to obtain control characterized by high accuracy and stable operation;
- wide range of speed control;
- high level of interference resistance;
- small size and weight of the device.
Operating principle of servo drive
How does the device work? A servo, whose operating principle is based on feedback from one or more system signals, regulates an object. The output indicator of the device is sent to the input, where it is compared with the setting action.
Features of the mechanism
The servo drive device has two main features:
- ability to increase power;
- providing feedback information.
Amplification is required for the purpose that the required output energy is very high (comes from external source), and at the input its indicator is insignificant.
Feedback is nothing more than a closed circuit loop in which the signals at the input and output are not matched. This process is used for management.
This leads to the following conclusion: in the forward direction, the circuit serves as an energy transmitter, and in the reverse direction, it serves as a transmitter of information that is needed for control accuracy.
Power supply and pinout of device connectors
The servo drive, the operating principle of which is applicable in radio-controlled configurations, usually has three wires:
- Signaling. The control impulse is transmitted through it. As a rule, the wire is painted white, yellow or red.
- Nourishing. Its power indicator ranges from 4.8 to 6 V. Often this is the red wire.
- Grounding. The wire is black or brown.
Drive sizes
By size, units are divided into three categories:
- microdrives;
- standard modifications;
- large devices.
There are servos with other size indicators, but the above types make up 95% of all devices.
Main characteristics of the product
The operation of a servo drive is characterized by two main indicators: the speed of rotation and the force on the shaft. The first value serves as an indicator of 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.
At all this parameter depends on the main purpose of the device, and only then on the number of gears of the gearbox and the components used in the device.
As already mentioned, mechanisms are now produced that operate at a supply voltage of 4.8 to 6 V. More often, this indicator is 6 V. However, not all models are designed for a wide range of voltages. Sometimes the servo motor operates at only 4.8 V or only at 6 V (the latter configurations are extremely rare).
Analog and digital modifications
A few years ago, all servo circuits were analog. Now digital designs have appeared. What is the difference between their work? Let's turn to official information.
From the Futaba report it follows that over the past decade, servos have become distinguished by better technical performance than before, as well as small sizes, high rotation speeds and torsional elements.
The latest round of development is the emergence of a digital device. These units have significant advantages even over commutator-type motors. Although there are some disadvantages.
Externally, analog and digital devices are indistinguishable. The differences are recorded only on the device boards. Instead of a microcircuit on the 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 functioning. They may have the same motors, mechanisms and potentiometers
The main difference is the method of processing the incoming receiver signal and motor control. Both servos receive the same power radio signal.
Thus, it becomes clear, what is a servo drive?
Operating principle of analog modification
In the analog modification, the received signal is compared with the current position of the servomotor, and then an amplifier signal is sent to the motor, causing the motor to move to a given position. The process frequency is 50 times per second. This is the minimum response time. If you tilt the handle on the transmitter, short pulses will begin to arrive at the servo drive, the interval between which will be 20 m/sec. 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”.
Working principle of digital design
Digital devices use a special processor that operates on high frequencies. It processes the receiver signal and sends control pulses to the engine at a frequency of 300 times per second. Since the frequency indicator is much higher, the reaction is noticeably faster and holds the position better. This causes optimal centering and a high level of torsion. But this method requires a lot of energy, so the battery used in the analog movement will drain much faster in this design.
However, all users who have at least once encountered a digital model say that its difference from an analog design is so significant that they would never use the latter again.
Conclusion
Digital analogues will be your choice if you require:
- high level ;
- minimum number of “dead zones”;
- precise positioning level;
- quick response to commands;
- constant force on the shaft when turning;
- high power level.
Now you know what a servo is and how to use it.