Servo drives, also known as "servo controllers" and "servo amplifiers", are controllers used to control servo motors. They act like a frequency converter acting on a common AC motor and are part of the servo system. Mainly used in high precision positioning systems. Generally, the servo motor is controlled by three modes: position, speed and torque to realize high-precision transmission system positioning. At present, it is a high-end product of transmission technology.
working principleAt present, the mainstream servo drivers adopt digital signal processor (DSP) as the control core, which can realize more complicated control algorithms, realize digitalization, networking and intelligence. The power device generally adopts the driving circuit designed with the intelligent power module (IPM) as the core. The IPM integrates the driving circuit internally, and has fault detection and protection circuits such as overvoltage, overcurrent, overheat and undervoltage, and adds soft in the main loop. Start the circuit to reduce the impact of the startup process on the drive. The power driving unit first rectifies the input three-phase electric power or the commercial power through a three-phase full-bridge rectifying circuit to obtain a corresponding direct current power. After rectifying the three-phase electric or commercial power, the three-phase permanent-magnet synchronous AC servo motor is driven by the three-phase sinusoidal PWM voltage inverter. The entire process of the power drive unit can be simply the process of AC-DC-AC. The main topology circuit of the rectifier unit (AC-DC) is a three-phase full-bridge uncontrolled rectifier circuit.
With the large-scale application of servo system, servo drive use, servo drive debugging and servo drive repair are all important technical issues of servo drives. More and more industrial control service providers have carried out in-depth technical research on servo drives.
Servo drives are an important part of modern motion control and are widely used in automation equipment such as industrial robots and CNC machining centers. Especially for servo drives for controlling AC permanent magnet synchronous motors, it has become a research hotspot at home and abroad. The current, servo, and position 3 closed-loop control algorithms based on vector control are commonly used in current AC servo drive design. The speed closed-loop design in this algorithm is reasonable or not, which plays a key role in the performance of the entire servo control system, especially the speed control performance.
Servo feed system requirements
1, wide speed range
2, high positioning accuracy
3, there is enough transmission rigidity and high speed stability
4, fast response, no overshoot
In order to ensure the productivity and processing quality, in addition to the high positioning accuracy, it also requires good fast response characteristics, that is, the response of the tracking command signal is required to be fast, because the CNC system requires addition and subtraction during starting and braking. The acceleration is large enough to shorten the transition process time of the feed system and reduce the contour transition error.
5, low speed and large torque, strong overload capability
In general, the servo drive has an overload capacity of 1.5 times or more in a few minutes or even half an hour, and can be overloaded 4 to 6 times in a short time without being damaged.
6, high reliability
The feed drive system of CNC machine tools is required to have high reliability, good work stability, strong environmental adaptability such as temperature, humidity, vibration and strong anti-interference ability.
Motor requirements
1. The motor can run smoothly from the lowest speed to the highest speed. The torque fluctuation is small, especially at low speeds such as 0.1r/min or lower, there is still a smooth speed without creeping.
2. The motor should have a large overload capacity for a long time to meet the requirements of low speed and large torque. Generally, DC servo motors are required to be overloaded 4 to 6 times in a few minutes without damage.
3. In order to meet the requirements of fast response, the motor should have a small moment of inertia and a large stall torque, with the smallest possible time constant and starting voltage.
4. The motor should be able to withstand frequent starts, braking and reversal.
What are the characteristics of the servo drive?1. Servo driver software program mainly includes main program, interrupt service program and data exchange program.
2. The main program of the servo driver is mainly used to complete the initialization of the system, the LO interface control signal, and the setting of each control module register in the DSP.
3. After all the initialization work of the servo driver is completed, the main program enters the waiting state and waits for the interruption to occur, so as to adjust the current loop and the speed loop.
4. After all the initialization work of the servo driver is completed, the main program enters the waiting state and waits for the interruption to occur, so as to adjust the current loop and the speed loop.
5, servo drive initialization mainly includes DsP core initialization, current loop and speed loop cycle setting, PWM initialization, four M start, ADc initialization and start, QEP initialization, vector and permanent magnet synchronous motor rotor initial position initialization, multiple times Servo motor phase current sampling, zero offset of phase current, current and speed P regulation initialization, etc.
6, PWM timing interrupt program is used to sample the Hall current sensor A, B two-phase current ia, ib sampling, calibration, and according to the magnetic field orientation control principle, calculate the rotor magnetic field orientation angle, then angle, and then generate PWM The signal controls the position loop and the speed loop.
7. The power drive protection interrupt program is mainly used to detect the fault output of the intelligent power module.
8. The zero-pulse capture interrupt program of the photoelectric encoder can realize accurate and accurate capture of the encoder feedback zero pulse, so that the correction value of the vector transformation orientation angle of the AC permanent magnet synchronous motor can be obtained.
9. The data exchange program mainly includes the communication program with the host computer, the reading of the EEPRoM parameter, and the digital tube display program. The storage controller keyboard value for the parameter.
10. Servo driver software main program flow chart.
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