Servo motor basic knowledge
The word ”servo” comes from the Greek word ”slave”. “Servo motor” can be understood as a motor that absolutely obeys the command of the control signal: before the control signal is sent, the rotor stands still; when the control signal is sent, the rotor rotates immediately; when the control signal disappears, the rotor can stop immediately.
The servo motor is a micro motor used as an actuator in an automatic control device. Its function is to convert an electrical signal into an angular displacement or angular velocity of a rotating shaft.
Servo motors are divided into two categories: AC servo and DC servo
The basic structure of an AC servo motor is similar to that of an AC induction motor (asynchronous motor). There are two excitation windings Wf and control windings WcoWf with a phase space displacement of 90° electrical angle on the stator, connected to a constant AC voltage, and using the AC voltage or phase change applied to Wc to achieve the purpose of controlling the operation of the motor. AC servo motor has the characteristics of stable operation, good controllability, fast response, high sensitivity, and strict non -linearity indicators of mechanical characteristics and adjustment characteristics (required to be less than 10% to 15% and less than 15% to 25% respectively).
The basic structure of a DC servo motor is similar to that of a general DC motor. Motor speed n=E/K1j=(Ua-IaRa)/K1j, where E is the armature counter electromotive force, K is a constant, j is the magnetic flux per pole, Ua, Ia are the armature voltage and armature current, Ra is The armature resistance, changing Ua or changing φ can control the speed of the DC servo motor, but the method of controlling the armature voltage is generally used. In the permanent magnet DC servo motor, the excitation winding is replaced by a permanent magnet, and the magnetic flux φ is constant. . DC servo motor has good linear regulation characteristics and fast time response.
Advantages and Disadvantages of DC Servo Motors
Advantages: Accurate speed control, hard torque and speed characteristics, simple control principle, easy to use, and cheap price.
Disadvantages: brush commutation, speed limitation, additional resistance, and wear particles (not suitable for dust -free and explosive environments)
Advantages and disadvantages of AC servo motor
Advantages: good speed control characteristics, smooth control in the entire speed range, almost no oscillation, high efficiency above 90%, less heat generation, high -speed control, high-precision position control (depending on the encoder accuracy), rated operating area Inside, can achieve constant torque, low inertia, low noise, no brush wear, maintenance -free (suitable for dust -free, explosive environments)
Disadvantages: The control is more complicated, the drive parameters need to be adjusted on site to determine the PID parameters, and more connections are required.
DC servo motors are divided into brushed and brushless motors
Brushed motors are low in cost, simple in structure, large in starting torque, wide in speed regulation range, easy to control, need maintenance, but easy to maintain (replace carbon brush), generate electromagnetic interference, have requirements for the use environment, and are usually used for cost -sensitive Common industrial and civil occasions.
Brushless motors are small in size and light in weight, high in output and fast in response, high in speed and small in inertia, stable in torque and smooth in rotation, complex in control, intelligent, flexible in electronic commutation mode, can be commutated in square wave or sine wave, maintenance -free motor, high efficiency and energy saving , small electromagnetic radiation, low temperature rise and long life, suitable for various environments.
AC servo motors are also brushless motors, which are divided into synchronous and asynchronous motors. At present, synchronous motors are generally used in motion control. The power range is large, the power can be large, the inertia is large, the maximum speed is low, and the speed increases with the increase of power. Uniform -speed descent, suitable for low -speed and smooth running occasions.
The rotor inside the servo motor is a permanent magnet. The driver controls U/V/W three - phase electricity to form an electromagnetic field. The rotor rotates under the action of this magnetic field. At the same time, the encoder that comes with the motor transmits the feedback signal to the driver. Values are compared to adjust the angle of rotor rotation. The accuracy of the servo motor depends on the accuracy of the encoder (number of lines).
What is a servo motor? How many types are there? What are the working characteristics?
Answer: The servo motor, also known as the executive motor, is used as an actuator in the automatic control system to convert the received electrical signal into an angular displacement or angular velocity output on the motor shaft.
Servo motors are divided into two categories: DC and AC servo motors. Their main characteristics are that there is no self-rotation when the signal voltage is zero, and the speed decreases at a uniform speed with the increase of torque.
What is the difference in performance between an AC servo motor and a brushless DC servo motor?
Answer: The performance of the AC servo motor is better, because the AC servo is controlled by a sine wave and the torque ripple is small; while the brushless DC servo is controlled by a trapezoidal wave. But brushless DC servo control is relatively simple and cheap.
The rapid development of permanent magnet AC servo drive technology has made the DC servo system face the crisis of being eliminated. With the development of technology, permanent magnet AC servo drive technology has achieved outstanding development, and famous electrical manufacturers in various countries have continuously launched new series of AC servo motors and servo drives. The AC servo system has become the main development direction of the contemporary high-performance servo system, which makes the DC servo system face the crisis of being eliminated.
Compared with DC servo motors, permanent magnet AC servo motors have the following main advantages:
⑴Without brush and commutator, the operation is more reliable and maintenance -free.
(2) Stator winding heating is greatly reduced.
⑶ The inertia is small, and the system has good quick response.
⑷ High-speed and high -torque working condition is good.
⑸Small size and light weight under the same power.
Servo motor principle
The structure of the stator of the AC servo motor is basically similar to that of the capacitor split-phase single -phase asynchronous motor. The stator is equipped with two windings with a mutual difference of 90°, one is the excitation winding Rf, which is always connected to the AC voltage Uf; the other is the control winding L, which is connected to the control signal voltage Uc. So the AC servo motor is also called two servo motors.
The rotor of the AC servo motor is usually made into a squirrel cage, but in order to make the servo motor have a wide speed range, linear mechanical characteristics, no ”autorotation” phenomenon and fast response performance, compared with ordinary motors, it should have The rotor resistance is large and the moment of inertia is small. At present, there are two types of rotor structures that are widely used: one is the squirrel -cage rotor with high - resistivity guide bars made of high -resistivity conductive materials. In order to reduce the moment of inertia of the rotor, the rotor is made slender; the other One is a hollow cup - shaped rotor made of aluminum alloy, the cup wall is only 0.2 -0.3mm, the moment of inertia of the hollow cup -shaped rotor is small, the response is fast, and the operation is stable, so it is widely used.
When the AC servo motor has no control voltage, there is only the pulsating magnetic field generated by the excitation winding in the stator, and the rotor is stationary. When there is a control voltage, a rotating magnetic field is generated in the stator, and the rotor rotates in the direction of the rotating magnetic field. When the load is constant, the speed of the motor changes with the magnitude of the control voltage. When the phase of the control voltage is opposite, the servo motor will be reversed.
Although the working principle of the AC servo motor is similar to that of the capacitor - operated single -phase asynchronous motor, the rotor resistance of the former is much larger than that of the latter. Therefore, compared with the capacitor -operated asynchronous motor, the servo motor has three salient features:
1. Large starting torque: Due to the large rotor resistance, the torque characteristic (mechanical characteristic) is closer to linear, and has a larger starting torque. Therefore, when the stator has a control voltage, the rotor rotates immediately, which has the characteristics of fast starting and high sensitivity.
2. Wide operating range: stable operation and low noise. [/p][p=30, 2, left] 3. No self-rotation phenomenon: If the servo motor in operation loses the control voltage, the motor will stop running immediately.
What is ”precision transmission micro motor”?
“Precision transmission micro motor” can quickly and correctly execute frequently changing instructions in the system, and drive the servo mechanism to complete the work expected by the instruction, and most of them can meet the following requirements:
1. It can start, stop, brake, reverse and run at low speed frequently, and has high mechanical strength, high heat resistance level and high insulation level.
2. Good fast response ability, large torque, small moment of inertia and small time constant.
3. With driver and controller (such as servo motor, stepping motor), the control performance is good.
4. High reliability and high precision.
The category, structure and performance of ”precision transmission micro motor”
AC servo motor
(1) Cage -type two-phase AC servo motor (slender cage -type rotor, approximately linear mechanical characteristics, small volume and excitation current, low -power servo, low -speed operation is not smooth enough)
(2) Non -magnetic cup rotor two-phase AC servo motor (coreless rotor, nearly linear mechanical characteristics, large volume and excitation current, small power servo, smooth operation at low speed)
(3) Two-phase AC servo motor with ferromagnetic cup rotor (cup rotor made of ferromagnetic material, nearly linear mechanical characteristics, large moment of inertia of rotor, small cogging effect, stable operation)
(4) Synchronous permanent magnet AC servo motor (a coaxial integrated unit consisting of a permanent magnet synchronous motor, a tachometer and a position detection element, the stator is 3-phase or 2-phase, and the magnetic material rotor must be equipped with a drive; the speed range is wide and the mechanical The characteristics are composed of constant torque area and constant power area, which can be locked continuously, with good fast response performance, large output power, and small torque fluctuation; there are two modes of square wave drive and sine wave drive, good control performance, and an electromechanical integration chemical products)
(5) Asynchronous three -phase AC servo motor (the rotor is similar to the cage -type asynchronous motor, and must be equipped with a driver. It adopts vector control and expands the range of constant power speed regulation. It is mostly used in machine tool spindle speed regulation systems)
DC servo motor
(1) Printed winding DC servo motor (disc rotor and disc stator are axially bonded with cylindrical magnetic steel, the rotor moment of inertia is small, there is no cogging effect, no saturation effect, and the output torque is large)
(2) Wire -wound disk type DC servo motor (disc rotor and stator are axially bonded with cylindrical magnetic steel, the rotor moment of inertia is small, the control performance is better than other DC servo motors, the efficiency is high, and the output torque is large)
(3) Cup-type armature permanent magnet DC motor (coreless rotor, small rotor moment of inertia, suitable for incremental motion servo system)
(4) Brushless DC servo motor (the stator is multi -phase winding, the rotor is permanent magnet, with rotor position sensor, no spark interference, long life, low noise)
torque motor
(1) DC torque motor (flat structure, number of poles, number of slots, number of commutation pieces, number of series conductors; large output torque, continuous work at low speed or stalled, good mechanical and adjustment characteristics, small electromechanical time constant)
(2) Brushless DC torque motor (similar in structure to brushless DC servo motor, but flat, with many poles, slots and series conductors; large output torque, good mechanical and adjustment characteristics, long life, no sparks, no noise Low)
(3) Cage-type AC torque motor (cage -type rotor, flat structure, large number of poles and slots, large starting torque, small electromechanical time constant, long -term locked-rotor operation, and soft mechanical properties)
(4) Solid rotor AC torque motor (solid rotor made of ferromagnetic material, flat structure, large number of poles and slots, long -term locked-rotor, smooth operation, soft mechanical properties)
stepper motor
(1) Reactive stepping motor (the stator and rotor are made of silicon steel sheets, there is no winding on the rotor core, and there is a control winding on the stator; the step angle is small, the starting and running frequency is high, the step angle accuracy is low, and there is no self-locking torque)
(2) Permanent magnet stepping motor (permanent magnet rotor, radial magnetization polarity; large step angle, low starting and operating frequency, holding torque, and smaller power consumption than reactive type, but positive and negative pulses are required current)
(3) Hybrid stepping motor (permanent magnet rotor, axial magnetization polarity; high step angle accuracy, holding torque, small input current, both reactive and permanent magnet
advantages)
Switched reluctance motor (the stator and rotor are made of silicon steel sheets, both of which are salient pole type, and the structure is similar to the large -step reactive stepper motor with a similar number of poles, with a rotor position sensor, and the torque direction has nothing to do with the current direction , the speed range is small, the noise is large, and the mechanical characteristics are composed of three parts: constant torque area, constant power area, and series excitation characteristic area)
Linear motor (simple structure, guide rail, etc. can be used as secondary conductors, suitable for linear reciprocating motion; high -speed servo performance is good, power factor and efficiency are high, and constant speed operation performance is excellent)
Post time: Dec-19-2022