The stepping motor is an induction motor. Its working principle is to use electronic circuit to supply power when the DC power is changed into components. The multi-phase timing control current is used to supply the stepping motor with this current, and the stepping motor can work normally. The driver is a time-sharing power supply for the stepper motor, multi-phase timing controller.
Although stepper motors have been widely used, stepper motors are not as conventional DC motors, and AC motors are used under normal conditions. It must be composed of a dual ring pulse signal, a power drive circuit, etc. to form a control system. Therefore, the use of stepper motors is not an easy task. It involves many professional knowledge such as machinery, motors, electronics and computers. As an actuator, stepper motor is one of the key products of mechatronics and is widely used in various automation control systems. With the development of microelectronics and computer technology, the demand for stepper motors is increasing day by day, and it has applications in various national economic fields.
Single pulse control and double pulse control of stepper motorThe control of the stepper motor has the distinction of single voltage and high and low voltage control;
The single voltage control uses a series of pulse signals to control the on and off of an electronic switch to control the power and power loss of the motor drive windings;
The high and low voltage control is based on the single voltage control, and another series of pulses is used to control the on and the half conduction of one electronic switch. The two switches are connected in series, and the two control pulses have the same frequency but different phases and widths. The purpose of achieving a full, half, and rapid shutdown of the supply voltage to the windings is achieved.
Open loop control of stepper motor
1. General composition of stepper motor open loop servo system
The number of armatures of the stepping motor and the order of energization of each phase determine the output angular displacement and the direction of motion. The control pulse distribution frequency can realize the speed control of the stepping motor. Therefore, the stepper motor control system generally adopts an open loop control mode. The picture shows the block diagram of the open-loop stepper motor control system. The system is mainly composed of controller, power amplifier and stepping motor.
2, stepper motor controller
1. Hardware control of stepper motor
The stepping motor rotates through a corresponding step angle under the action of a pulse, so that as long as a certain number of pulses is controlled, the corresponding angle of the stepping motor can be accurately controlled. However, the windings of the stepping motor must be energized in a certain order to operate correctly. This process of cycling the on/off sequence of the motor windings according to the control of the input pulses is called ring pulse distribution.
There are two ways to implement circular allocation. One is computer software distribution, which uses a table lookup or calculation method to cause the three output pins of the computer to sequentially output a circular distribution pulse signal that satisfies the speed and direction requirements. This method can make full use of computer software resources to reduce hardware costs, especially the pulse distribution of multi-phase motors shows its advantages. However, since the software operation will take up the running time of the computer, the total time of the interpolation operation will increase, thereby affecting the running speed of the stepping motor.
The other is hardware ring distribution, which uses digital circuit construction or dedicated ring distribution device to process continuous pulse signals through the circuit and output ring pulses. Ring distributors constructed using digital circuits are usually composed of discrete components (such as flip-flops, logic gates, etc.), which are characterized by large size, high cost, and poor reliability.
2. Microcomputer control of stepper motor:
At present, the digital control of the servo system is mostly a combination of hardware and software. The software control method is generally realized by a microcomputer. This is because the digital servo controller based on microcomputer has the following advantages compared with the analog servo controller:
(1) Significantly reduce controller hardware costs. A new generation of microprocessors with faster speeds and newer features are emerging, and hardware costs can be cheap. Small size, light weight and low energy consumption are their common advantages.
(2) Significantly improve the reliability of control. The mean time between failures (MTBF) of integrated circuits and large scale integrated circuits is much longer than that of discrete component electronic circuits.
(3) The temperature drift of the digital circuit is small, and there is no influence of parameters, and the stability is good.
(4) The hardware circuit is easy to standardize. In the circuit integration process, some shielding measures are adopted to avoid excessive transient current and voltage electromagnetic interference caused by voltage and electronic circuits, so the reliability is relatively high.
(5) Using the digital control of the microprocessor, the two-way transmission capability of the information is greatly enhanced, and it is easy to communicate with the upper system machine, and the control parameters can be changed at any time.
(6) It is possible to design a unified hardware circuit suitable for many power electronic systems, in which the software can be modularly designed and assembled to form control algorithms suitable for various application objects; to meet different purposes. Software modules can be easily added, changed, deleted, or completely updated as the actual system changes.
(7) Improve the ability of information storage, monitoring, diagnosis and hierarchical control, making the servo system more intelligent.
(8) With the continuous improvement of the computing speed and memory capacity of the microcomputer chip, the control strategy with excellent performance but complicated algorithm has the basis of realization.
3, stepper motor power drive circuit
In order for the stepping motor to output enough torque to drive the load, a stepper motor must be provided with a sufficient power control signal. The circuit that implements this function is called a stepper motor drive circuit. The driving circuit is actually a power switching circuit, and its function is to power-amplify the output signal of the ring distributor to obtain the pulse current required by the stepping motor to control the winding and the required pulse waveform. The operating characteristics of a stepper motor depend to a large extent on the performance of the power driver. For each phase winding, the ideal power driver should be such that the current pulses through the winding are as close as possible to the rectangular wave. However, since the stepper motor winding has a large inductance, it is difficult to do this.
There are two common stepper motor drive circuits:
Figure 4.6 Stepper motor drive circuit
(1) Single voltage drive circuit
This circuit is powered by a single power supply, has a simple structure and low cost, but has a poor current waveform, low efficiency, and small output torque. It is mainly used for driving small stepping motors with low speed requirements, as shown in Figure 6-19. One-phase winding drive circuit of the motor (the circuit of each phase winding is the same).
Pulse input signal when the ring distributor 
Low level (logic 0, about 1V), although VT1 
, 
The tubes are all turned on, but as long as they are properly selected 
Resistance value 
"0 (about -1V), then 
The tube is in an off state and the phase winding is de-energized. When input signal 
When the level is 3.6V (logic 1). 》0 (about 0.7V), 
The tube is saturated and the phase winding is energized.
(2) The dual voltage drive circuit, also known as the high and low voltage drive circuit, is powered by two high voltage and low voltage power supplies. When the stepping motor winding is just turned on, it is powered by the high voltage power supply to speed up the current rising speed, and after a delay, switch to the low voltage power supply. This circuit greatly improves the current waveform, output torque and operating frequency.
Pulse input signal when the ring distributor When it is high (requires the phase winding to be energized), the diode 
The base has a signal voltage input, so that Both are conductive. Then under the action of a high voltage power supply (the diode at this time) 
Both ends are subjected to a reverse voltage, which is in an off state, so that the low voltage power supply does not act on the winding. The winding current rises rapidly and the current front is steep. When the current reaches or slightly exceeds the rated steady-state current, it is cut off by means of a timing circuit or a current detector. 
The signal voltage on the base, so Deadline, but this time Still conductive, so the winding current is turned by the low voltage power supply through the diode supply. When the voltage at the output of the ring distributor When it is low (requires winding power off), The signal voltage on the base disappears, so Cutoff, the current in the winding passes through the diode 
And resistance 
When discharged to a high voltage power supply, the current drops rapidly. With this high and low voltage switching power supply, no series resistors are required on the motor windings or only a small resistor is required in series. 
(To balance the current of each phase), the power consumption of the power supply is relatively small. Since the voltage supply mode greatly improves the current waveform, the torque-frequency characteristic of the stepping motor is good, and the starting and running frequencies are greatly improved.
Closed loop control of stepper motor
Closed loop control has a number of advantages over open loop control systems. In the feedback control system, for whatever reason (external disturbance or internal system change), as long as the controlled amount deviates from the specified value, a corresponding control action is generated to eliminate the deviation. Therefore, it has the ability to suppress interference, is insensitive to changes in component characteristics, and can improve the response characteristics of the system. However, the introduction of the feedback loop increases the complexity of the system, and the gain selection may cause instability of the system. In order to improve the control accuracy, when the disturbance variable can be measured, the disturbance control (ie feedforward control) is often used as a supplement to the feedback control to form a composite control system.
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