Controller Area Network CAN (Controller Area Network) is a fieldbus is an effective support for distributed control or real-time control of serial communication network, is recognized as one of the most promising field bus.


In industrial control systems, the electric actuator is a very important implementation of electronic control unit. Two in the circuit by the control circuit and the implementing agencies completely separate part of the composition, can receive the electrical signal from the regulator to be linearly converted to mechanical angle or linear displacement, is used to manipulate the throttle, baffle, valves and other regulatory agencies in order to achieve automatic control. In recent years, with the rapid development of microelectronics and control technology, electric actuators to obtain a rapid development, especially some foreign manufacturers in the past few years have launched a regular, intelligent electric actuators with fieldbus communication protocol , CAN intelligent electric actuator is the most development potential of a

This article describes the CAN intelligent electric actuators with brushless DC motor control, high control precision, digital valve position detection can improve the accuracy and reliability of the valve position measurement can replace the current commonly used potentiometers and differential transformer analog measurement method.
　　
Hardware design of the control circuit

CAN intelligent electric actuators of the principles of the structure shown in Figure 1.

图1 The principle block diagram of the CAN intelligent electric actuators
The entire circuit consists of five parts: microcontroller P89C58-based host part of the SJA1000, 82C250, photoelectric isolation circuit composed of the CAN bus control interface section of brushless DC motor control chip MC33035 motor control section,valve position detection part and the LCD display section.

1 CAN bus interface section

CAN bus control interface shown in Figure 2, including independent CAN communication controller SJA1000 CAN bus transceiver 82C250 and high-speed optocoupler 6N137.


MCU the P89C58 First on the SJA1000 initialization, control of the SJA1000 to realize data communication tasks. The SJA1000 AD0 ~ keeper on the AD7 connect to the P0 port 89C52 CS connected to the P2.0 port of the 89C52, the rest of the pin correspond linked.

图2 CAN总线及接口部分

In order to enhance the anti-jamming capability of the CAN bus node, of SJA1000 TX0 and the RX0 not directly connected with the 82C250 the TXD and RXD, but high-speed optocoupler 6N137 and then with the 82C250 connected so well to achieve the CAN buselectrical isolation between the nodes. 82C250 CAN bus interface is also used to a certain degree of security and anti-jamming measures, it CANH and CANL pin CAN bus between series a 5Ω resistor, so that may play a limiting role, the protection of the 82C250 from the impact of the stream; can also CANH and CANL pin parallel capacitance, played the role of high-frequency interference and anti-electromagnetic radiation on the filter bus. 82C250 of Rs feet, then a slope resistance, the resistor size can be appropriately adjusted according to the bus communication speed is generally between 16 ~ 140kΩ.

2 Motor control circuit

The electric actuator motor control chip uses a brushless DC motor controller of MC33035 Semiconductor has developed high-performance second-generation unit. The controller includes rotor position decoder for the correct rectifier timing, as well as on the sensor temperature compensation of the reference level; the same time, with a frequency programmable sawtooth oscillator, an error amplifier, a pulse modulator comparator, three open collector top drive output and three very high current totem pole bottom of the output drive power MOSFET.Motor control circuit schematic module shown in Figure 3。

图3 电机控制电路原理模块图

The motor control circuit functions include PWM open-loop speed control, enable control and reversing control. 4-10 bit decoder / drive 74LS145 function of motor speed control, gives the signal by the microcontroller P89C58 through the voltage divider circuit to provide voltage to pin speed to achieve.


Motor control and reversing the control signal is controlled by microcomputer, the issue level signal to the 89C2051, level conversion is output to the MC33035 corresponding pin to control the working status of the motor.

3 Valve position sensing, and LCD

In order to achieve the valve position detection, ADI's 16-bit Σ-△ (charge balanced) A / D converter the AD7705 is used in the A / D converter circuit. AD7705 buffer and programmable gain amplifier (PGA) front-end analog conditioning circuitry, sigma-delta modulator and programmable digital filter, directly to the sensor swing within the scope of signal amplification to A / D converter full-scale voltage is near, then the a / D converter 16 0.003% accuracy of the nonlinear error-free data output; gain and data output update rate can be programmed, but also to select the input analog buffer, and self-calibration and system calibration. Through an external high-precision conductive plastic potentiometer sensor, the partial pressure obtained by the reference voltage value of voltage values ​​that reflect the value of the valve position.


TRULY produced 128 × 64 dot matrix LCD, and all of its controller, the scanning circuit and display RAM integrated in the back of the LCD screen with LED backlight. The module uses a single power supply, large-scale dot matrix display controller KS0107, KS0108 of the array of LCD driver circuit, display memory and LCD screen, such as four parts.

Smart actuators software design

Software design mainly includes three aspects: CAN bus communication module, actuator control and LCD display.


CAN bus communication part of the SJA1000 initialization to return to normal operation after the completion of its initialization, the operation of the actuator through the bus up modem to send and operation from the host computer to issue control instructions to operate the device.


The control part of the electric actuator valve position control function, can also control the motor speed to control the valve closing speed. LCD display some of the major shows valve valve situation and the actuator of the work, can also be issued by the host computer to the actuator control signal.

The program flow of the system shown in Figure 4。

图4 系统程序流程图