Abstract: Introduced multiple motor control platforms based on single chip microcomputer C8051F020. The hardware circuit is simple and reliable. The power circuit is built by field effect tube. It has strong versatility. By rewriting the software, it can be directly used in the drive control system of other small power motors. .
introduction
Stepping motors are very suitable for open loop position control systems because of their low rotor inertia, high positioning accuracy, and no cumulative errors. DC motor is a commonly used motor in servo control. However, in actual systems, in order to satisfy different functions, there are often multiple moving parts at the same time. The common method is that an independent function corresponds to a control system. Although this has a good modularity, it takes up a lot of system resources and space. To a certain extent, the reliability of the system is reduced.
For example, there are 4 moving parts in a system, which are two three-phase reactive stepper motors, one DC motor and one four-phase stepper motor. In line with the idea of ​​improving system integration, this article uses only one control chip C8051F020 to complete the drive control of the above 4 motors. The circuit is simple and the reliability is high.
1 Overall design
The multi-motor control system platform based on Cygnal's MCU control chip C8051F020 can complete the control of four motors according to the control instructions. The composition block diagram is shown in Figure 1.
2 Hardware design
2. 1 main control chip selection
The C8051F020 single-chip microcomputer produced by Cygnal Company in the United States uses the CIP-51 microcontroller core. Compared with the standard 8051 structure, it has the following characteristics:
(1) The instruction execution speed has been greatly improved, and the peak speed has reached 25 MIPS;
(2) In addition to 4 standard 8051 ports, there are 4 additional ports, a total of 64 general-purpose I / O ports;
(3) All I / O ports can be configured as open-drain or push-pull outputs, further developing to low-power applications;
(4) Introduce digital crossbar switch, allowing users to combine common I / O ports and required digital resources by themselves;
(5) With two serial UART interfaces, five 16-bit general-purpose timers, and five comparison capture modules;
(6) With on-chip watchdog, on-chip temperature sensor, and on-chip VDD monitor, there is almost no external expansion when using;
(7) The software online debugging function can be realized through the JTAG interface.
C8051F020 single chip microcomputer has become an ideal choice for this multi-motor control system due to its obvious advantages in execution speed and system resources.
2. 2 Communication circuit design
According to the communication protocol with the host computer, the communication interface uses standard two-way differential RS-422 serial port communication, the operating voltage is 5 V, the baud rate is 38 400 bit / s. There are two enhanced full-duplex UARTs inside the C8051F020 series MCU, The communication protocol is RS-232, and the operating voltage is also 5 V. Therefore, the MAX490 device is selected, and the MAX490 chip can easily convert the RS422 differential signal of the host computer into the serial port signal of the single-chip computer. The specific circuit is shown in Figure 2.
2. 3 Stepper motor drive circuit design The control of the stepper motor can use serial control, using a ring distributor to complete the commutation. Parallel control can also be used, and the single-chip microcomputer completes the commutation of the stepper motor. When the system resources are sufficient, the parallel control can simplify the design of the circuit. This system adopts parallel control, and the I / O port of the single chip microcomputer is controlled by software to output PWM waves according to a certain time sequence to control the power on and off of the motor winding.
The motor is an inductive load, and the current in the motor winding cannot be abruptly changed. After the motor is changed from phase A to phase B, if there is no protection circuit, the current in the phase A winding will remain for a long time, so the motor operation is very unstable. In order to make the motor run smoothly, protection measures have been added to the system to quickly discharge the current in the winding coil to protect the motor. Figure 3 shows the control circuit of one phase of the motor.
In order to eliminate the crosstalk of the stepper motor, all the output signals of the single-chip microcomputer are isolated by optocouplers. The output signal of the single chip microcomputer is 3.3 V TTL level, which is not enough for the driving force of the motor, so the field effect tube is used to drive the motor after the power amplification circuit. The stepping motor of this system is driven by a single voltage drive. The advantages of this drive circuit are simple circuit, low cost, and good response at low frequencies. The disadvantage is that there is resonance and the load capacity of the high frequency band is reduced. The motor running speed required by the system is low, and the high-frequency load capacity is not considered. To solve the resonance problem, the PWM wave is used to supply power to the motor, and the purpose of reducing vibration is achieved by changing the resonance point of the motor.
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