Do you know how the servo motor works? Today, Xinda will take you to systematically understand the servo motor.

　　What is the servo motor servomotor

　　The word "servo" comes from the Greek word for "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 is stationary; when the control signal is sent, the rotor rotates immediately; when the control signal disappears, the rotor can stop immediately.

　　Servo motors are micro motors used as actuators in automatic control devices, and their function is to convert electrical signals into angular displacement or angular velocity of a rotating shaft. Servo motors, also known as executive motors, are used as executive elements in automatic control systems to convert received electrical signals into angular displacement or angular velocity output on the motor shaft.

　　Classification of Servo Motors

　　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° on the stator, which are connected to a constant AC voltage, and the AC voltage or phase change applied to Wc is used to control the operation of the motor.

　　AC servo motors have the characteristics of stable operation, good controllability, fast response, high sensitivity, and strict non-linearity indicators of mechanical characteristics and adjustment characteristics (required less than 10% to 15% and less than 15% to 25%, respectively).

　　Advantages and disadvantages of DC servo motors

　　Advantages: Accurate speed control, very hard torque-speed characteristics, simple control principle, easy to use and cheap.

　　Disadvantages: brush commutation, speed limit, additional resistance, generation of wear particles (not suitable for dust-free and explosive environments).

　　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 armature back electromotive force, K is constant, j is magnetic flux per pole, Ua, Ia are armature voltage and armature current, Ra is 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. . The DC servo motor has good linear adjustment characteristics and fast time response.

　　Advantages and disadvantages of AC servo motors

　　Advantages: good speed control characteristics, smooth control in the entire speed range, almost no oscillation, high efficiency of more than 90%, less heat generation, high-speed control, high-precision position control (depending on encoder accuracy), rated operating area It can achieve constant torque, low inertia, low noise, no brush wear, and maintenance-free (suitable for dust-free and explosive environments).

　　Disadvantages: The control is more complicated, the drive parameters need to be adjusted on the spot to determine the PID parameters, and more connections are required.

　　DC servo motors are divided into brushed and brushless motors.

　　The brushed motor has low cost, simple structure, large starting torque, wide speed regulation range, easy control, and requires maintenance, but it is easy to maintain (replacement of carbon brushes), generates electromagnetic interference, has requirements for the use environment, and is usually used for cost-sensitive general industrial and civil occasions.

　　The brushless motor is small in size, light in weight, large in output and fast in response, high in speed, small in inertia, stable in torque and smooth in rotation, complex in control, intelligent, flexible in electronic commutation, can be commutated by square wave or sine wave, motor maintenance-free, high efficiency and energy saving , Small electromagnetic radiation, low temperature rise and long life, suitable for various environments.

　　The AC servo motor is also a brushless motor, which is divided into synchronous and asynchronous motors. At present, synchronous motors are generally used in motion control. They have a large power range, can achieve a large power, large inertia, and a low maximum speed. The speed increases with the power. Descending at a uniform speed, suitable for occasions where low-speed and stable operation is performed.

　　The rotor inside the servo motor is a permanent magnet. The driver controls the 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 rotation angle of the rotor. The accuracy of the servo motor is determined by the accuracy (number of lines) of the encoder.

　　What is the difference in performance between AC servo motors and brushless DC servo motors?

　　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 makes the DC servo system face the crisis of being eliminated[/p][p=30,2,left]Since the 1980s, with the development of integrated circuits, power electronics technology and AC variable speed drives With the development of technology, the permanent magnet AC servo drive technology has achieved outstanding development, and famous electrical manufacturers in various countries have successively 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 the DC servo motor, the permanent magnet AC servo motor has the following main advantages:

　　(1) Without brushes and commutators, the operation is more reliable and maintenance-free.

　　(2) The heating of the stator winding is greatly reduced.

　　(3) The inertia is small, and the system has good quick response.

　　(4) Good working condition at high speed and high torque.

　　(5) Small size and light weight under the same power.

　　How Servo Motors Work

　　The structure of the AC servo motor stator is basically similar to that of the capacitor split-phase single-phase asynchronous motor. The stator is equipped with two windings whose positions are different from each other by 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. Therefore, the AC servo motor is also called two servo motors.

　　The rotor of the AC servo motor is usually made of squirrel cage, but in order to make the servo motor have a wide speed regulation range, linear mechanical characteristics, no "rotation" 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: one is a squirrel-cage rotor with high resistivity bars made of conductive materials with high resistivity. In order to reduce the moment of inertia of the rotor, the rotor is made slender; 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 size of the control voltage. When the phase of the control voltage is opposite, the servo motor will reverse.

　　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 two notable characteristics:

　　1. Large starting torque: Due to the large rotor resistance, the torque characteristics (mechanical characteristics) are closer to linear, and it has a larger starting torque. Therefore, when the stator has a control voltage, the rotor rotates immediately, that is, it has the characteristics of fast starting and high sensitivity.

　　2. Wide operating range: stable operation and low noise.

　　3. No rotation phenomenon: As long as the servo motor in operation loses the control voltage, the motor will stop running immediately.

　　Precision transmission micro motor

　　"Precision transmission micro-motor" can quickly and correctly execute frequently-changing commands in the system, and drive the servo mechanism to complete the work expected by the command. 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, stepper motor), the control performance is good.

　　4. High reliability and high precision.

　　The categories of precision transmission micro-motors and their structure and performance comparisons are as follows:

　　AC Servo Motor

　　(1) Squirrel-type two-phase AC servo motor (slender squirrel-cage rotor, approximate 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 (hollow cup rotor, approximate linear mechanical characteristics, large volume and excitation current, low power servo, smooth operation at low speed).

　　(3) Ferromagnetic cup-type rotor two-phase AC servo motor (ferromagnetic material cup-type rotor, the mechanical characteristics are approximately linear, the rotor inertia moment is large, the cogging effect is small, and the operation is stable).

　　(4) Synchronous permanent magnet AC servo motor (consisting of permanent magnet synchronous motor, tachometer and position detection element coaxial integrated unit, stator is 3-phase or 2-phase, magnetic material rotor, must be equipped with driver; wide speed range, mechanical The characteristics are composed of constant torque area and constant power area, which can be continuously locked, fast response performance is good, output power is large, and torque fluctuation is small; there are two modes of square wave drive and sine wave drive, and the control performance is good. chemical products).

　　(5) Asynchronous three-phase AC servo motor (the rotor is similar to the squirrel asynchronous motor, it must be equipped with a driver, and the vector control is adopted, which expands the range of constant power speed regulation, and is mostly used in the machine tool spindle speed regulation system).

　　DC Servo Motor

　　(1) Printed winding DC servo motor (disk-shaped rotor, disk-shaped stator axially bonded with cylindrical magnetic steel, small rotor inertia, no cogging effect, no saturation effect, and large output torque).

　　(2) Wire-wound disc type DC servo motor (disc rotor, stator axially bonded with cylindrical magnetic steel, small rotor inertia, better control performance than other DC servo motors, high efficiency and large output torque).

　　(3) Cup-type armature permanent magnet DC motor (hollow cup rotor, small rotor inertia, suitable for incremental motion servo system).

　　(4) Brushless DC servo motor (stator is polyphase winding, rotor is permanent magnet type, with rotor position sensor , no spark interference, long life and low noise).

　　torque motor

　　(1) DC torque motor (flat structure, the number of poles and slots, the number of commutation sheets and the number of series conductors; the output torque is large, it can work continuously at low speed or locked rotor, the mechanical and adjustment characteristics are good, and the electromechanical time constant is small).

　　(2) Brushless DC torque motor (similar in structure to brushless DC servo motor, but flat, with a large number of poles, slots and series conductors; large output torque, good mechanical and adjustment characteristics, long life, no sparks, no noise Low).

　　(3) Spur-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, soft mechanical characteristics).

　　(4) Solid rotor AC torque motor (ferromagnetic material solid rotor, flat structure, large number of poles and slots, long-term locked rotor, smooth operation, soft mechanical properties).

　　stepper motor

　　(1) Reactive stepping motor (both the stator and the 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 frequencies are high, the step angle accuracy is low, no self-locking torque).

　　(2) Permanent magnet stepping motor (permanent magnet rotor, radial magnetization polarity; large step angle, low starting and running frequency, holding torque, and lower power consumption than reactive type, but positive and negative pulses must be supplied current).

　　(3) Hybrid stepping motor (permanent magnet rotor, axial magnetization polarity; high step angle accuracy, holding torque, small input current, and both the advantages of reactive and permanent magnets).

　　Switched reluctance motor (both stator and rotor are made of silicon steel sheets, both of which are salient pole type, similar in structure to large-step reactive stepper motors with similar pole numbers, with rotor position sensor, and the direction of torque has nothing to do with the direction of current. , 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 rails, 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).