The basic introduction of the servo The characteristics of the servo point and the comparison of the stepper motor
1. What is a servo? Why use servo? Servo System Definition: A control system that implements output variables to accurately follow or replicate input variables. The demand for motion control is getting higher and higher, and servo control has emerged. 2. What is a servo motor? What are the characteristics? 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. Divided into two major categories of DC and AC servo motor, its main feature is that when the signal voltage is zero there is no rotation phenomenon, the speed decreases with the increase of torque and uniform speed. The characteristics of the servo point are more clear here compared to the stepper motor: 1. Different control accuracy The step angle of the two-phase hybrid stepping motor is generally 3.6° and 1.8°. The step angle of the five-phase hybrid stepping motor is generally 0.72° and 0.36°. There are also some high performance stepper motors with smaller step angles. For example, a step motor manufactured by Stone Company for use in a slow-moving wire machine has a step angle of 0.09°. The step angle of the three-phase hybrid stepper motor produced by BERGERLAHR in Germany can be dialed. The code switches are set to 1.8°, 0.9°, 0.72°, 0.36°, 0.18°, 0.09°, 0.072°, 0.036° and are compatible with step angles of two-phase and five-phase hybrid stepper motors. AC servo motor control accuracy is guaranteed by a rotary encoder at the rear end of the motor shaft. Taking Panasonic's all-digital AC servo motor as an example, for a motor with a standard 2500 line encoder, the pulse equivalent is 360°/10000=0.036° due to the quadruple frequency technology inside the driver. For a motor with a 17-bit encoder, the driver receives one revolution of 217=131,072 pulses per pulse, ie, its pulse equivalent is 360°/131072=9.89 seconds. It is 1/655 of the pulse equivalent of a stepping motor with a step angle of 1.8°. 2. Different low-frequency characteristics Stepper motors are prone to low-frequency vibration at low speeds. 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. 3, the characteristics of different torque characteristics Stepper motor output torque decreases with the increase in speed, and at high speeds will drop sharply, 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. 4. Different overload capacity Stepper motors generally do not have overload capability. AC servo motor has strong overload capability. Take Panasonic AC servo system as an example, it has speed overload and torque overload capability. Its maximum torque is 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. 5, the performance of different stepper motor control for open-loop control, start-up frequency is too high or the load is prone to loss of step or stalled phenomenon, 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. The drive can directly sample the feedback signal of the motor encoder. The position loop and the speed loop are internally formed. The phenomenon of lost or overshoot of the stepper motor generally does not occur, and the control performance is more likely. 6, 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 the Panasonic MSMA400W AC servo motor as an example. Acceleration from standstill to its rated speed of 3000 RPM takes only a few milliseconds. It can be used in control applications requiring fast start-stop. 3. What are the types of encoders? What are the applications? An encoder is a meter device that compiles or converts a signal or data into a signal that can be used for communication, transmission, and storage. 1, according to the different types of empty disk code: (The current encoder classification method, just say about the commonly used classification) (1) Absolute type encoder: There are several concentric encoders in the radial direction on its circular encoder. Each channel has light-transmitting and opaque sectors, and the sectors of the adjacent encoders are trees. It is a double relationship. The number of code channels on the code board is the number of digits of its binary digits. On one side of the disc is a light source, and on the other side there is a photosensitive element for each code channel. When the disc is in a different position, Each photosensitive element converts a corresponding level signal according to the illumination or not, forming a binary number. (2) Incremental encoder principle: Each revolution of the shaft sends out a pulse signal (also has a sine wave signal, and then subdivides it and chops out a higher pulse), usually A, B , C three-phase output, A, B two-phase pulse output delayed by 4 cycles can be judged according to the delay between positive and negative, by using the A phase, B phase of the rising edge, falling edge can be 2 times, 4 times the frequency processing The Z phase is a single turn pulse, which is one pulse per turn. 2. Classification by mechanical installation of encoders: (1) Axle type Axis type can be divided into clamping flange type, synchronous flange type, servo installation type, etc. (2) Shaft sleeve type Divided into half-empty, full-empty, large-caliber Encoder application The encoder is mainly used in CNC machine tools and machinery accessories, robots, automatic assembly machines, automatic production lines, elevators, textile machinery, sewing machinery, packaging machinery (fixed length), printing machinery (synchronous), woodworking machinery, plastic machinery (fixed number) , rubber and plastic machinery, drawing equipment, goniometers, therapeutic radars, etc. 4. How to achieve servo control? 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). 3.2V Battery Cells,Prismatic Phosphate Lithium Batteries,3.2V 202Ah,3.2v lifepo4 battery,3.2V LifePO4 Lithium Battery Pack Jiangsu Zhitai New Energy Technology Co.,Ltd , https://www.zt-tek.com
