“Aiming at the problem of insufficient torque and driving power of two coaxial stepping motors. An innovative design method for coaxial connection and drive of multi-stepper motors is proposed and successfully applied. This technology has been granted a Chinese national patent. This text gives the hardware and software design example of MCS-51 one-chip computer control.
Introduction: Aiming at the problem of insufficient torque and driving power of two coaxial stepping motors. An innovative design method for coaxial connection and drive of multi-stepper motors is proposed and successfully applied. This technology has been granted a Chinese national patent. This text gives the hardware and software design example of MCS-51 one-chip computer control.
Stepper motors are widely used in manipulators, printers and intelligent instruments. In the high-tech robotics technology, every action joint of the robot is inseparable from the stepper motor. But in some applications. Two coaxial stepping motors cannot meet the torque required by the actuator, and a single (or two) driver IC (integrated circuit) cannot provide the driving power required by the large torque. The innovative technology of multi-stepper motor coaxial coupling and driving device successfully solves the above problems.
2 Stepper motor and control driving principle
Stepper motors are different from other control motors. Its characteristic is that it is controlled by inputting pulse signals. The driving principle of the stepping motor is to make the motor rotate in a step-by-step manner through the sequential switching of the current in each phase coil. Each loses a regular pulse signal. The stepper motor rotates by a fixed angle. The total rotation angle is determined by the number of input pulses, and the speed of the stepping motor is determined by the frequency of the pulse signal. In this paper, the SB-2P stepping motor produced by Beijing Micro-motor Factory is used. Rated voltage: -24V: rated current: 0.2A; rated step distance: 3°; phase number: 3 phases). If A, B, C work in 3-phase 3-beat mode, the power-on sequence: forward rotation is ABCA…reverse rotation is ACBA….
In this 3-phase 3-beat energization sequence, when the pulse is switched, one phase winding is powered off before the other phase winding starts to energize, so that the stepper motor is prone to out-of-step or oscillation at the equilibrium position when the power is switched. Accuracy is not high. In order to improve the running performance of the progressive motor, the driving mode adopts 3-phase double 3-beat or 3-phase 6-beat mode. The power-on phase sequence table for 3-phase dual 3-beat operation is shown in Table 1.
3 Concept of coaxial connection and drive of multi-stepper motors
3.1 Coaxial connection of multi-stepper motors with double-ended shafts
Double-ended shaft, that is, each stepper motor has a motor shaft on both end faces. Schematic diagram of the coaxial connection structure of multi-stepper motors with double-ended shafts. As shown in Figure 1. After multiple stepper motors are coaxially connected, the torque can be multiplied. It is worth noting that the stepper motor with the same model and parameters must be used, and the stepper motor shaft must be coaxial.
3.2 Coaxial connection of multi-stepper motors with mixed single-ended and double-ended shafts
Single-ended shaft, that is, only one end of the two end faces of the stepper motor has a motor shaft. The structure diagram of the coaxial connection of multi-stepper motors with mixed single-ended and double-ended shafts is shown in Figure 2. The 1-support and 3-support stepper motors in the figure are single-ended shafts. The 2-support stepping motor is a double-ended shaft. Similarly, after connecting multiple stepping motors coaxially. Multiple increases in torque can be achieved. In addition to this method, it should be noted that stepper motors with the same model and parameters must be used. Since the rotation directions of the stepping motors on both sides of the main drive wheel are opposite, it is necessary to exchange the phases B (φ2) and φ3) of the 3# stepping motor with each other.
3.3 Drive of coaxial connection of multi-stepper motors
Stepper motors are different from other AC motors, and it is not enough to simply connect to the power supply: Feng barnyard sequence. work requirements, even if a pulse signal is input. The corresponding driver must also be connected for the ORG 2000H to work. To drive a plurality of coaxially connected stepping motors at the same time, the usual single-chip (or two-chip) power driver IC (integrated circuit) cannot provide the driving power required by the large torque. to this end. Multi-chip driver IC stacking and paralleling technology is adopted. It is realized by stacking and paralleling multiple driver IC chips one by one and welding them one by one according to the pin number. The schematic diagram of the multi-chip driver IC stacking and parallel structure is shown in Figure 3.
Special attention must be paid to the selection of ICs from the same manufacturer, same model, same parameters, and the same batch of production. Adopt multi-chip driver IC stacking and parallel technology. The driving power can be multiplied without increasing the area of the hardware circuit board. Reduced hardware costs.
4 Examples of hardware and software design
4.1 Hardware Design
Schematic diagram of the hardware circuit of multi-stepper motor coaxial connection and drive device. As shown in Figure 4. The P1.0, P1.1, and P1.2 ports of the 89C51 output the pulse signals for controlling the stepping motor, which are respectively connected to IN1, IN2, and IN3 of the 1413IC that are stacked and connected in parallel. Through inverse driving, OUT1, OUT2, OUT3 are respectively connected to φ1, φ2, φ3 of 1#, 2#, and 3# stepper motors, so as to realize the drive of 3 stepper motors at the same time.
In this example, the rated current of each phase of the stepper motor is 0.2A, then the rated current of each phase of the three stepper motors is:
Because when the 3-phase double 3-beat mode works, when each stepper motor rotates, 2 phases are energized at the same time, so the rated current of the 3 stepper motors is:
O. 2A*3*2=1.2A (2)
According to the relevant information, the maximum current of each stage of the MCl413 inverting driver IC is 0.5A. From the above formula (2), it can be seen that one (or two) MCl413 inverting driver IC cannot meet the requirements of driving multiple stepper motors at the same time. , and the driver cannot work at the maximum drive current state for a long time when in use. In order to meet the above requirements and leave room for it, 4 pieces of MCl413 inverting driver ICs are stacked and connected in parallel to form a driving circuit. In Figure 4, the diodes in the MCl413 IC play a role in releasing the back EMF in the stepper motor coil to protect the stepper motor and driver IC from damage. R1-R3 are current limiting resistors.
4.2 Software Design
The following program uses the MCS-51 assembly language program to realize the control of 3 coaxially connected stepping motors (double-ended shafts). After the program starts, the stepping motor rotates in the reverse direction for 100*3 beats (300 steps) and stops.The procedure is as follows
“Multi-stepper motor coaxial connection and drive device” has won the Chinese national patent (patent number: ZL03266939.9), and has been successfully applied to the simulation lifting device controlled by single chip microcomputer. The author’s innovation point: solves the practical problem that the required torque and driving power cannot be met when the dual stepper motors are coaxially connected and driven: the multi-chip driver IC stacking and parallel technology can be used without adding hardware circuit boards. On the basis of the area, the driving power is multiplied and the hardware cost is reduced. The patented technology can also be extended to the coaxial connection and drive of four stepping motors.