Abstract: The composition and working principle of the full digital electric actuator are introduced. The motor driving circuit of the full-digital motor Traveler Based on 80C196 single-chip computer is developed. The reliability of the lower computer of the full-digital motor traveler and the communication between the upper and lower computer based on CAN bus are studied.
Key word:Single-chip Computer CAN Bus for Electric Executor
Introduction
The all-digital electric executor designed in this paper is a further improvement based on the motor drive circuit of 9610R series of all-electronic electric executors in Xiangyi Electronic and Electrical Equipment Plant.We will replace the original analog control with the digital control based on 80C196 single-chip computer in order to improve the reliability of control and operation. At the same time, for debugging convenience, the function of infrared remote control and communication based on CAN bus are added to meet the needs of modern industrial control.
1 Features of original all-electronic electric actuator
The original 9610R series full-electronic electric executor uses 220V AC unidirectional power supply as the driving power, the driving motor uses unidirectional AC motor, and the position feedback uses high-performance conductive plastic potentiometer.
The principle of the servo amplifier is shown in Figure 1.
1 When UY=0,
K_= Uo/Ux=-[(R4+R5)/R5] × (R6/R1)
(2) When Ux = 0,
K+=Uo/UY=[R3/(R2+R3)] × [(R4+R5)/R5] × (1+R6/R1)
According to the principle of linear overlay, Uo=K+UY+K_ UX.
It can be seen from the above that the original 9610R electric actuator has the problem of asymmetric forward and reverse motor because it is difficult to match the resistance perfectly. The motor drive circuit is shown in Figure 2.
In Figure 2, Uo is the voltage signal from the server amplifier when Uo> At 0.7V, the motor turns forward; When Uo<- When 0.7V, the motor is reversed. C1 is the capacitance to control the motor operation.
The redesigned all-digital electric executor improves the drive circuit of the motor, controls the forward and reverse of the motor by the time of (+) 12V on-off signal, and achieves the function of power system and reverse cut-off of the electric executor. The new motor drive circuit is shown in Figure 3.
In Figure 3, Ukp and Ukn are the two high-speed pins of 80C196, and there are six photoisolators, T2-1/T2-2, T3-1/T3-2, T4-1/T4-2, T5-1/T5-2, T6-1/T6-2 and T7-1/T7-2, respectively. When Uk is at +5V high level, T2-1/T2-2 conducts, thus T*-1/T6-2 conducts the motor forward; When Uk changes from high level to low level, T4-1/T4-2 conducts instantaneously, which makes T7-1/T7-2 conducts instantaneously, the motor reverses instantaneously, and the motor stops when the capacitive discharge ends. Similarly, when Uk is 0V low level, the motor is inverted. This enables the forward and reverse control of the motor.
Figure 3 The newly designed motor drive circuit
The photoelectric isolation between the output of the system and the driving circuit is completely realized, which improves the anti-jamming ability and reliability of the system.
2 Control system structure
The control system structure of the full-digital electric executor with 80C196KC single-chip computer is shown in Figure 4. In Figure 4, in addition to 80C196KC single-chip computer, X25043 is selected to realize power-off protection, and MAX7219 is used to drive the LED digital tube to display the given value and feedback value of the valve position, as well as the status and control mode of the valve position. At the same time, the improved 4-20mA constant current circuit directly converts the threshold feedback signal to 4-20mA signal and sends it to the indoor analog secondary table to ensure its compatibility with analog and digital control. The A/D converter inside 80C196KC is used to convert the given signal of valve position feedback and valve position simulation into 10-bit digital signal. The software is used to judge the valve position fault (blocking, overrun), to handle the fault (alarm or shutdown), and to isolate the single-chip computer system from the motor drive circuit using MOC3061 photoelectric isolation at the control output and the fault handling end to achieve the purpose of anti-interference.
1838 infrared remote control receiving and decoding integrated chip is selected to receive infrared remote control signals from the remote control. The CAN controller uses Philips'SJA1000 integrated chip, CAN bus driver uses 82C250 integrated chip, and between SJA1000 and CAN bus driver 82C250, uses 6N137 fast light isolation to process the photoelectric isolation, and interacts with single-chip computer to realize the communication function between single-chip computer and upper computer.
The main hardware circuits of each part are described below.
(1) Improved 4~20mA constant current circuit
The whole constant current circuit consists of an integrated 4-channel operational amplifier LM324 and 6 precision resistors, a adjustable resistor, a ceramic capacitor and a diode. The circuit structure is very simple, as shown in Figure 5. In Fig. 5, R1=R2=R3=R4=R5=100k, R6=200, R7 is 0-100 adjustable resistance.
From the circuit of Fig. 5, we can see that under the condition that the four resistors R2, R3, R4, R5 are well matched, U1-U2=U1, and by adjusting R7 to make R6+R7=250_, Io=U1/250_achieves the purpose of converting 1-5V voltage to 4-20mA, and this relationship will not change, no matter how the output load changes, to achieve the purpose of constant current. In order to maximize the load that this constant current circuit can carry, the power supply for integrated operation and amplification LM324 is+18V.
(2) Infrared remote control receiving circuit
As an electric actuator, in the application of industrial process control, it is often difficult to debug the installation location. Using infrared remote control adjustment can be a good solution to avoid some work that needs to be done in regular debugging, such as opening the control box cover for debugging line changes and so on. The infrared remote control receiving chip uses the infrared remote control receiving and decoding integrated chip 1838. The circuit is shown in Figure 6.
In Figure 6, resistors and capacitors form a decoupling circuit to suppress power supply interference. In addition, no external elements are required, and the center frequency is 38 kHz. However, due to the high growth of 1838 integrated chips, which are not adjustable and shielded, they are particularly vulnerable to external interference, so shielding measures must be taken. The solution is to use a metal material as a shield box and load 1838, leaving only the infrared interface outside.
We select a universal infrared remote control as the debugging device of the electric execution mechanism. 80C196KC single-chip computer first detects the command codes of each key of the remote control, and then gives them the debugging commands we need, which can greatly shorten the development cycle.
Figure 7 CAN bus communication interface circuit
(3) Communication between upper and lower computer
CAN (Cantrol Area Network) is short for controlling local area network. It was first introduced by the German BOSCH company for data communication between internal measurement and execution parts of automobiles. Its bus specification has been formulated as an international standard by ISO International Standards Organization and is widely used in the field of discrete control. The signal transmission medium is twisted pair. The communication rate is up to 1Mbps/40m, the direct transmission distance can be up to 10km/5kbps, and the hooked devices can be up to 110.
CAN uses a short frame structure for signal transmission, with 8 valid bytes per frame, which results in short transmission time and low probability of interference. When a node is in serious error, it has the function of auto-closing to disconnect the node from the bus, so that other nodes on the bus and their communication are not affected, and it has strong anti-interference ability. The CAN bus communication interface circuit is shown in Figure 7.
The AD15 port of 80C196KC acts as the chip selection signal of SJA1000, so the address occupied by CAN controller SJA1000 is: 8000H~80FFH. The purpose of using the CAN bus transceiver PCA82C250 is to further improve the drive capability of the CAN bus. Its operating mode is provided by the RS control pin, depending on the slope resistance (resistance value of 200 K adjustable resistance).
The upper computer monitors the instruments and control devices with CAN communication interface in the industrial field through a non-intelligent isolated communication board of HK-CAN30B PCI bus of a Chinese controlled company.
(4) Power-off protection and anti-interference measures
The components of the system for on-the-spot protection use Maxim X25043. The X25043 has three common functions: watchdog timer, voltage monitor and E2PROM, which are combined in a single package. The X25043 is ideal for systems that require minimal space on the printed circuit board, as shown in Figure 8.
The X25043 watchdog timer provides an independent protection system for the microcontroller 80C196. Optional timeout cycles are 1.4s, 600ms, 200ms or disabled. When the system fails, the X25043 watchdog will respond to the RESET signal to reset the system beyond the selected timeout period. The X25043 low VCC detection circuit protects the system from low voltage conditions. When the VCC drops to the minimum VCC detection level, RESET becomes low and resets the system until the VCC rises to the minimum VCC detection level of 200ms. In addition, X25043 has 512 × The 8-bit serial E2PROM makes it unnecessary for the system to extend the data memory RAM.
The anti-interference measures of the system include hardware and software measures. Hardware: 1) Photoelectric isolation is used for signal transmission in input and output channels, MOC3061 is used for motor drive circuit, and 6N137 is used for fast optical isolation in upper and lower computer communication circuit; 2. Place a 0.01 on each integrated circuit chip μ F's ceramic capacitance to eliminate most high frequency interference; Separated analogically from digitally; 4 In the CPU anti-interference measures, besides power-off protection circuit, artificial reset and automatic power-on reset circuit are also configured. Software: 1) Redundant instructions, insert two NOP instructions after some double- and three-byte instructions to ensure that the running program is quickly brought into the correct control track; 2 Use software traps to force captured programs to be directed to programs that handle program errors; 3. Enable the 80C196KC internal monitoring timer (watchdogtimer); A/D input signal is filtered by software digital filter.
Software Design of System 3
The program diagram of this system is shown in Figure 9. First, the initialization of the program, including the initialization of hardware and variables. Then, the program determines the global variable RUN, if RUN=0 indicates that the program terminates, it jumps to the end of the program to reset the watchdog, then jumps to the front of the program to determine the RUN flag, and loop execution; If RUN_0, the program executes the main loop and resets the watchdog. In this way, you can control program execution by setting RUN variables.
Only basic operations, such as data input and output, are handled in the interrupt program. Complex data processing, such as software filtering of input channels, is handled in the main loop. In the main program, each break is assigned a global variable as the break flag, which is set to 1 when an interrupt occurs. In the main loop, the program determines each flag bit in turn to determine whether to execute the corresponding subroutine, a procedure or function. After the interrupt service is processed in the main program, the corresponding interrupt flag should be cleared.
Functions of the main program include: determining the valve position and valve position status, LED display of the valve position and valve position status, valve position control output, judging whether the valve is blocked to protect the motor from overheating, decoding infrared remote control commands and remote control command control output. On the output of the valve position control, the valve position is controlled by controlling the time of the motor's forward and reverse, and the cycle of A/D sampling is controlled very short, such as 10ms or even shorter. The motor action is controlled by this production cycle, and the motor is kept inactive within the required valve position range of 0.5%, to ensure the accuracy of the valve position control and to avoid the vibration of the valve position back and forth.
4 Conclusion
By improving the motor drive circuit and 4~20mA constant current circuit of 9610R series full electronic electric actuator, the operability and reliability of the actuator in analog control are further improved. Improved control. Its intelligence makes remote maintenance possible. The development of its remote control system makes debugging of this electric executor more convenient.
