working principle
1. The servo mainly locates by the pulse, basically can understand like this, the servo motor receives 1 pulse, will rotate the angle corresponding to 1 pulse, thus realizes the displacement, because, the servo motor itself has the pulse function, therefore the servo Every time the motor rotates an angle, it will send out the corresponding number of pulses. This will form a echo with the pulse received by the servo motor, or a closed loop. In this way, the system will know how many pulses have been sent to the servo motor and how much it has received. The pulse is returned. In this way, the rotation of the motor can be accurately controlled, so that an accurate positioning can be achieved, which can reach 0.001 mm.
DC servo motors are divided into brushed and brushless motors. The brush motor has low cost, simple structure, large starting torque, wide speed range, easy control and maintenance, but easy maintenance (for carbon brush), electromagnetic interference, and environmental requirements. It can therefore be used in cost-sensitive general industrial and civil applications. The brushless motor is small in size, light in weight, large in output, fast in response, high in speed, small in inertia, smooth in rotation, and stable in torque. The control is complex and it is easy to realize intelligence. The electronic commutation mode is flexible, and it can be changed by square wave or sine wave. The motor is maintenance-free, high efficiency, low operating temperature, low electromagnetic radiation, long life, and can be used in various environments. 2. 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. Its power range is large, and it can achieve a large power. With high inertia, the maximum rotational speed is low, and it rapidly decreases with increasing power. Therefore, it is suitable for low speed and smooth operation. 3. The rotor inside the servo motor is a permanent magnet. The U/V/W three-phase power controlled by the driver forms an electromagnetic field. The rotor rotates under the action of this magnetic field. At the same time, the motor’s own encoder feedback signal to the driver, and the driver according to the feedback value. Compare with the target value and adjust the rotation angle of the rotor. The accuracy of the servo motor is determined by the encoder accuracy (number of lines). What is a servo motor? There are several types? What are the characteristics of the job? A: Servomotors, also known as executive motors, are used in automatic control systems as actuators to convert received electrical signals into angular or angular velocity outputs on the motor shaft. It is divided into two major categories of DC and AC servo motors. Its main feature is that when the signal voltage is zero, there is no rotation phenomenon, and the speed decreases with increasing torque. The AC servo motor and brushless DC servo motor are functionally functional. What’s the difference? Answer: AC servo is better because it is sine wave control and torque ripple is small. DC servo is a trapezoidal wave. However, the DC servo is relatively simple and inexpensive. Permanent-magnet AC servo motor Since the 1980s, with the development of integrated circuits, power electronics and AC variable-speed drive technology, permanent magnet AC servo drive technology has made remarkable progress, and well-known electrical companies in various countries have successively launched their own AC servos. The series of motors and servo drives are continuously improved and updated. The AC servo system has become the main development direction of the contemporary high-performance servo system, making the original DC servo face the crisis of being eliminated. After the 1990s, AC servo systems that have been commercialized in various countries all over the world are all digitally controlled sine-wave motor servo drives. The development of AC servo drives in the field of transmission is changing with each passing day. The permanent magnet AC servo motor is compared with the DC servo motor, the main advantages are: (1) No brush and commutator, so the work is reliable, and the maintenance and maintenance requirements are low. (2) The stator winding heat dissipation is more convenient. (3) Small inertia, easy to improve the rapidity of the system. (4) Adapt to high speed and high torque working conditions. (5) Smaller volume and weight at the same power. The principle of servo motor First, the structure of AC servo motor AC servo motor stator is basically similar to the capacitive phase-type single-phase asynchronous motor. The stator is equipped with two windings with a mutual difference of 90, one is the excitation winding Rf, it is always connected On the AC voltage Uf; the other is the control winding L, 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 into a squirrel cage type, but in order to enable the servo motor to have a wider speed range, linear mechanical characteristics, no “rotation” phenomenon and fast response performance, it should have a comparison with an ordinary motor. Rotor resistance and small moment of inertia of these two features. At present, there are two types of rotor structures that are widely used: one is a squirrel cage rotor made of a high-resistivity conductive material made of a high-resistivity conductive material. In order to reduce the rotor’s rotational inertia, the rotor is made slender; One is a hollow cup-shaped rotor made of aluminum alloy. The wall of the cup is very thin, only 0.2-0.3mm. In order to reduce the magnetic resistance of the magnetic circuit, a fixed inner stator is placed inside the hollow cup-shaped rotor. The rotary inertia of the rotor is very small, it responds quickly, and it runs smoothly, so it is widely used. When the AC servo motor has no control voltage, only the pulsating magnetic field generated by the excitation windings 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. Under a constant load, the rotation speed of the motor varies with the magnitude of the control voltage. When the phase of the control voltage is opposite, the servo motor Will reverse. Although the operating principle of AC servo motor is similar to that of split-phase single-phase asynchronous motor, the rotor resistance of the former is much larger than that of the latter. Therefore, compared with single-motor asynchronous motor, servo motor has three notable features: 1. Large starting torque Due to the large rotor resistance, its torque characteristic curve is shown as curve 1 in Fig. 3, and there is a clear difference compared with the torque characteristic curve 2 of the ordinary asynchronous motor. It can make the critical slip S0 > 1, which not only makes the torque characteristics (mechanical characteristics) more linear, but also has a larger starting torque. Therefore, when the stator has a control voltage, the rotor rotates immediately, which means that it has a quick start and high sensitivity. 2, a wide range of operation 3, no rotation phenomenon Normal operation of the servo motor, as long as the loss of control voltage, the motor immediately stop running. When the servo motor loses the control voltage, it is in a single-phase operation state. Due to the large rotor resistance, two torque characteristics (T1-S1, T2-S2 curve) generated by the rotating magnetic field and the rotor acting in two opposite directions in the stator And synthetic torque characteristics (T-S curve) AC servo motor output power is generally 0.1-100W. When the power supply frequency is 50Hz, the voltage is 36V, 110V, 220, 380V; when the power supply frequency is 400Hz, the voltage has 20V, 26V, 36V, 115V and so on. The AC servo motor runs smoothly and with low noise. However, the control characteristics are non-linear, and because the rotor resistance is large, the loss is large and the efficiency is low. Therefore, compared with the DC servo motor with the same capacity, it is large and heavy, so it is only suitable for a low-power control system of 0.5-100W.
Edit this paragraph selection method
Compared with stepper motor performance
As an open-loop control system, stepper motors have an essential connection with modern digital control technology. In the current domestic digital control system, stepper motors are widely used. With the advent of all-digital AC servo systems, AC servo motors are also increasingly used in digital control systems. In order to adapt to the development trend of digital control, most of the motion control systems use stepper motors or all-digital AC servo motors as the execution motors. Although the two are similar in control mode (burst and direction signals), there is a big difference in performance and application. Now compare the performance of the two. First, the control accuracy is different Two-phase hybrid stepper motor step angle is generally 1.8, 0.9, five-phase hybrid stepper motor step angle is generally 0.72, 0.36. There are also some high performance stepper motors with smaller step angles after subdivision. For example, the stepping angle of a two-phase hybrid stepper motor manufactured by SANYO DENKI can be set to 1.8, 0.9, 0.72, 0.36, 0.18, 0.09, 0.072, 0.036 by the dial switch. It is compatible with the step angle of two-phase and five-phase hybrid stepping motors. AC servo motor control accuracy is guaranteed by a rotary encoder at the rear end of the motor shaft. Take Sanyo’s all-digital AC servo motor as an example. For a motor with a standard 2000 line encoder, the pulse equivalent is 360/8000 = 0.045 due to the quadruple frequency technology inside the driver. For a motor with a 17-bit encoder, the driver receives one revolution of 131,072 impulse motors per revolution, that is, its pulse equivalent is 360/131072=0.0027466. It is the pulse equivalent of a stepper motor with a step angle of 1.8. 1/655. Second, different low-frequency characteristics Stepper motor at low speed is prone to low frequency vibration phenomenon. The vibration frequency is related to load conditions and driver performance. It is generally believed that the vibration frequency is half of the motor’s no-load take-off frequency. This kind of low frequency vibration, which is determined by the working principle of the stepper motor, is very unfavorable to the normal operation of the machine. When the stepper motor operates at a low speed, damping techniques are generally used to overcome the low-frequency vibration phenomena, such as adding a damper to the motor, or using a subdivision technique on the driver. The AC servo motor operates very smoothly and does not vibrate even at low speeds. The AC servo system has a resonance suppression function that can cover the lack of mechanical rigidity, and the system has a frequency analysis function (FFT), which can detect the mechanical resonance point and facilitate system adjustment. Third, the characteristics of different torque characteristics Stepper motor output torque decreases with the increase in speed, and will decline sharply at higher speeds, so the maximum operating speed is generally 300 ~ 600RPM. The AC servo motor is constant torque output, that is, it can output rated torque within its rated speed (generally 2000RPM or 3000RPM), and it is constant power output above the rated speed. Fourth, different overload capabilities Stepper motors generally do not have the ability to overload. AC servo motor has strong overload capability. Take Shanyang AC servo system as an example, it has speed overload and torque overload capability. Its maximum torque is two to three times the rated torque and can be used to overcome the moment of inertia of the inertial load at the moment of starting. Because there is no such overload ability for the stepping motor, in order to overcome this kind of moment of inertia during selection, it is often necessary to select a motor with a relatively large torque, and when the machine does not require such large torque during normal operation, a torque occurs. Wasted phenomenon. Fifth, the performance of different stepper motor control is open-loop control, the starting frequency is too high or the load is too large prone to lost or blocked the phenomenon of rotation, stop the speed is too high overshoot phenomenon, so to ensure its control Accuracy should deal with problems of rising and falling speeds. The AC servo drive system is closed-loop control, and the drive can directly sample the feedback signal of the motor encoder. The position loop and the speed loop are internally formed. Generally, there is no phenomenon of lost or overshoot of the stepping motor, and the control performance is more reliable. Sixth, different speed response performance Stepper motor from static acceleration to working speed (usually hundreds of revolutions per minute) requires 200 to 400 milliseconds. Acceleration performance of the AC servo system is better. Take Sanyo 400W AC servo motor as an example. Acceleration from standstill to its rated speed of 3000 RPM only takes a few milliseconds. It can be used in control applications requiring fast start-stop. In summary, AC servo systems are superior to stepper motors in many aspects of performance. However, stepper motors are often used to perform the motor in some less demanding applications. Therefore, in the design process of the control system, various factors such as control requirements and costs should be comprehensively considered, and appropriate control motors should be selected.
Selection calculation method
First, the speed and encoder resolution confirmation. Second, the motor shaft load torque conversion and acceleration and deceleration torque calculations. Third, calculate the load inertia, inertia match, Yaskawa servo motor, for example, some product inertia matching up to 50 times, but the actual smaller the better, so that the accuracy and response speed. Fourth, the calculation and selection of the regenerative resistor, for the servo, generally more than 2kw, outside configuration. Fifth, cable selection, twisted shield encoder cable, for Yaskawa servo and other Japanese products absolute encoder is 6 core, incremental type is 4 core.
Edit this paragraph installation and use precautions
First, the protection of the servo motor oil and water A: Servo motor can be used in places that will be affected by water or oil droplets, but it is not fully waterproof or oil-proof. Therefore, servo motors should not be placed or used in water or oil-infiltrating environments. B: If the servo motor is connected to a reduction gear, the oil seal should be used when using the servo motor to prevent the oil of the reduction gear from entering the servo motor. C: The cable of the servo motor should not be submerged in oil or water. Second, the servo motor cable → reduce stress A: To ensure that the cable is not subject to external bending force or its own weight moment or vertical load, especially at the cable outlet or connection. B: In the case of servo motor movement, the cable (that is, the one configured with the motor) should be firmly fixed to a stationary part (relative to the motor) and should be extended with an additional cable installed in the cable holder. It so that bending stress can be minimized. C: The elbow radius of the cable is as large as possible. 3. Permissible shaft end load of servo motor A: Ensure that the radial and axial load control applied to the servo motor shaft during installation and operation is within the specified value of each model. B: Be extremely careful when installing a rigid coupling. In particular, excessive bending loads may cause damage or wear on the shaft end and the bearing. C: It is better to use a flexible coupling so that the radial load is lower than the allowable value. This object is designed for high mechanical strength servo motors. D: Regarding the permitted shaft load, refer to “Permissible Shaft Load Table” (Instruction Manual). Fourth, servo motor installation attention A: When installing/removing the coupling part to the shaft end of the servo motor, do not directly hit the shaft end with a hammer. (The hammer directly hits the shaft end, and the encoder on the other end of the servo motor shaft is to be knocked out.) B: Strive to align the shaft ends to the best condition (which may cause vibration or bearing damage).
Brushless DC Motor Features
Small moment of inertia, low starting voltage, and low no-load current; Abandoned contact type commutation system greatly increases the motor rotation speed, and the maximum speed is up to 100 000 rpm; When the servo motor is controlled by a brushless servo motor, speed and position can be achieved without an encoder. , Torque and other control; There is no brush wear, in addition to high speed, but also has a long life, low noise, no electromagnetic interference and other characteristics.
DC Brushed Servo Motor Features
1. Small size, quick response, high overload capacity, wide speed range 2. Low torque, small fluctuation, stable operation 3. Low noise, high efficiency 4. Rear encoder feedback (optional) constitutes DC servo Etc
Range of use
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