Abstract: The automobile four round position finder was a distributed computer observation system, this article introduced controlled the MSComm communication through the RS-485 main line and using VB 6.0 ActiveX to control, has realized in the automobile four round position finder single Taiwan PC machine and many monolithic integrated circuit’s communication functions.
Key word: RS-485; Serial communication; Four rounds localization; VB; Examination
1st, introduction
The automobile in the normal speed process, should have changes the operation facile and maintains automatically the straight line travel ability, simultaneously the wheering wheel should be the pure trundle as far as possible, reduces tire’s attrition and reduces the fuel oil consumption. The above request realizes usually is 4 parameters which locates through the wheering wheel (in king pin caster angle, king pin inclination angle, wheel camber angle and toe-in) guarantees. Because the present automobile uses the front wheel to change most, therefore the wheering wheel localization usually is called the front wheel alignment. The modern automobile not only front wheel has the location parameter, at present many passenger vehicle trailing wheels have also established the toe-, the flare and the thrust force angle three location parameters, before its goal is causes, trailing wheel’s to superpose as far as possible in road surface path, both has guaranteed the passenger vehicle high speed travel stability and the security, and is helpful in reduces the tire and the suspension fork various components attrition.
After the automobile moves one fixed time once in a while replaces certain components, four round location parameters will change, therefore needs prompt or carries on the examination regularly to the vehicles location parameter, if surpasses the normal value which the factory assigns, then should make the adjustment, restores vehicles’ travel stability, the security, the fuel oil efficiency, decreases the tire and the related part’s attrition.
The wheel alignment detection mode has the dynamic examination and the static state examines two methods. The dynamic examination use side-slipping test platform, uses for in the automobile rate process carries on the examination to automobile’s front wheel toe-in value and the wheel camber angle match situation. Its characteristic is the operation is simple, the speed is quick, very suitable to examine fast, but cannot determine the single item wheel alignment value, this detection mode examined in the automobile security check line or the synthesis on-line to obtain the widespread application. The static examination uses four rounds the position finder, its may in the automobile static state situation, determine wheel’s each kind of localization parameter value, applies the most widespread wheel alignment detection mode at present.
At present the domestic four round position finder’s form mainly has three kinds, namely back guy type, wireless survey wire transmission type and entire wireless -like. Because the back guy type four round position finder the operation is not convenient, affects the measuring accuracy the factor to be many, at present has been eliminated basically. Entire wireless -like the characteristic is uses optics non-contact type survey, between the main engine and the sensor uses the wireless intelligence transmission, the measuring accuracy is high, easy to operate. The wireless survey wire transmission type the main difference is uses the signal cable with entire wireless -like to transmit the examination data, although in the use aspect was inferior that entire wireless -like is convenient, but has the information transmission and the examination speed is quick, is reliable, does not have the replacement battery, the battery charge, the use cost low status merit, at present applies is similarly widespread.
The modern four round position finder uses the microcomputer control completely, is responsible to control and the management task superior machine (PC machine) with is responsible for the data acquisition duty through the field bus certain lower positions machine (monolithic integrated circuit) connected, the two have composed a distributed computer control and the measurement system. The communication system software and hardware’s design and the choice are one of four round position finder design key technologies, is big to system’s overall performance influence. The RS-232C serial communication connection is the PC machine standard layout, the connection is simple, the programming is convenient, but can only use between two microcomputer’s connections, cannot satisfy the multi-contact connection the need. We have used present in the industry observation system the quite popular RS-485 communication connection, and controlled MSComm through the VB 6.0 communications convenient to realize the many monolithic integrated circuit’s common controls and the data acquisition, in good solution four round position finder’s communication questions.
2nd, four round position finder’s system constitutions
Four round position finder’s system’s constitution as shown in Figure 1. The overall system and four lower positions machine is composed of a superior machine. The superior machine is the PC microcomputer, is responsible to the measuring process control, the read lower position machine examination data, the data processing and the computation as well as the result demonstration, the memory, the printing and the management and so on. Four lower positions machine of the monolithic integrated circuit system composition, the monolithic integrated circuit use AT89C51, uses in realizing various wheel alignment angle survey control and the data upload function. After before the monolithic integrated circuit is located at left separately, left, after before, right, and in right, nose’s shell, the nose and the clamping apparatus are connected, when survey the nose passes the clamping apparatus to fix separately to the automobile four wheel’s wheel felloes. The overall system has altogether used 14 sensors, in vertical plane angle (including in king pin caster angle, king pin inclination angle and wheel camber angle) the survey realizes before six precise inclination angle sensors (nose each two, latter nose each), eight PSD (Position Sensitive Detector) the optical sensor (around nose each two groups) use in surveying in the lateral plane the wheel each localization angle.
Figure 1 four round position finder’s system constitution
3rd, system communication function hardware’s realization
The standard RS-232 connection can only use between two computer’s connections, PC machine two RS-232 connection COM1 and COM2 are most also can only connect two monolithic integrated circuits, if expands together the serial communication card again, causes four serial ports to be separately connected with four lower positions machine, not only then the price is high, moreover the structure is also complex. Therefore has used present in the distributional industry observation system the quite popular RS-485 main line. Compares the RS-485 connection with RS-232 to have the following characteristic:
(1) the connection level connection is lower than RS-232 the C, is not easy to damage interface circuit’s chip, and level and TTL level concurrently
Accommodates, may facilitate and the TTL electric circuit connection.
(2) the data transmission rate is high, the baudrate reaches as high as 10Mbps.
(3) uses is balanced the driver and the difference receiver, anti-syntype disturbance ability, namely the anti-noise jamming is good.
(4) the transmitting range is far, the maximum transmitting range is 4000 feet.
(5) on the main line may connect reaches 256 transceivers, namely has the multi-station ability, the user may use the sole RS-485 connection convenient establishment communication network.
In this system PC machine through the RS-232 connection, is connected after the RS-232/RS-485 transformation module with four noses, each nose’s monolithic integrated circuit also passes through the RS-485 interface module to hang on the main line, and is bestowed on distinguishes in the respective communication address the status. The monolithic integrated circuit uses RS-485 transceiver for US Letter Company’s MAX3082, this is one kind of high speed, has the expiration protection and limits the suspending rate function the transceiver chip. Such superior PC machine then can carry on the communication through the RS-485 main line with each nose’s monolithic integrated circuit, realizes to the location parameter data acquisition and the process control.
4th, system communication functional software’s realization
4.1 system’s communication ways
The PC computer’s selects the half-duplex method with various noses between communication, the communication baudrate is 9600bps, the communication form is: 1 outset position, 8 bit data positions, the non-parity check, 1 stop position, each nose entrusts with the only this aircraft address. The main engine starts a time communication and the data acquisition through the routing directive frame, from machine the receive after ordering the frame, the judgment call address with this aircraft address is whether same, if is the same, and the test result will pass to the main engine according to the order character execution corresponding data acquisition through the data frame; If different, according to the address and the order character judges whether to launch the survey light. The order frame’s form is as follows:
The first item for frame (STX), with symbolizes a start; The second item is from machine the address (ADDR); The third order character expression nose feedback’s data content either this examination content, fourth item of FCS is different or the verification, different or verifies and uses in the communication school for the front data being wrong.
Data frame’s form is as follows:
The data frame and the order frame besides the third item, other significances are the same, the data frame’s third content is from machine the order frame which sends out according to the main engine the location parameter examination data which sends out to the main engine.
4.2 VB6.0 MSComm controls and serial communication control realization
VB6.0 provided ActiveX to control - - Microsoft Communication Control, Version 6.0, was called MSComm to control, used it to be possible to carry on the computer serial port conveniently the communication management. MSComm controls to have many with the serial port related attribute, here no longer makes the detailed introduction.
The serial port receives when the information MSComm controls to provide two processing methods, one kind is the inquiry way, another kind responds the way for the event, namely uses SetCommEvent () the function establishment serial port response event. When the response event occurs, the system will activate OnComm () the event. () In the event increases the user processing code in OnComm, then may realize the similar interrupt serial port event processing, this system used the event to respond the way.
The PC machine communication software’s duty is controls the examination process and reads and the processing wheel alignment parameter real-time data. The receive and the transmission data use the text format, the main engine call from when machine does not have the reply, is equipped with the warning prompt facility. The following gave has controlled an initialization and the routing directive partial source code.
(1) controls a initialization:
MSComm1.CommPort=2 ’selects the COM2 mouth communication
MSComm1.Setting= “9600, N,8,1″ ‘establishment communication parameter
MSComm1.Inputlen=0 ‘read buffer complete content
MSComm1.InBufferSize=50 ‘establishment receive buffer size
MSComm1.OutBufferSize=20 ‘establishment transmission buffer size
MSComm1.InputMode=comInputModeText ‘by text form receive data
MSComm1.PortOpen=True ‘turns on the communication port
MSComm1.InBufferCount=0 ‘elimination receive buffer
MSComm1.OutbufferCount=0 ‘Clear to Send buffer
(2) orders transmission (take front wheel toe-in as example):
Dim Command, node, c, f As string
Dim i, fcs As integer
node=” 01″ ‘the node number, before expressing the right, nose
Command=” FT” ‘front wheel toe-in examination
c=” @” node Command
fcs=0
For i=1 To Len(c)
fcs=fcs Xor Asc(Mid$(c, i,1)) ‘frame verification code FCS
Next i
f=Hex$(fcs)
if Len(f)=1 Then f=” 0″ f
MSComm1.Output=c f
5th, conclusion
And used under VB6.0 through the RS-485 main line ActiveX to control to realize in the automobile four round position finder main engine PC machine and many from machine between communication, the practice card Ming dynasty printed books system’s communication function movement is reliable, rational design.
Reference
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