Application of Virtual Instrument Technology in Automobile Inspection
Introduction Modern automotive test systems are complex and large. On a single station, there are often dozens of parameters that need to be tested and controlled. The detection of the automatic tightening of the three-station nut of the automobile connecting rod is part of this complicated system. It is in mass production of automobile shock absorbers. When the living rod is assembled, the nut on the head of the head is tightened to the standard torque, and then the piston rod is tightened. Special equipment for head hoe tightening to keep nut locking force unchanged. In the old system, the single parameter measurement and control is often realized by the test equipment with a large footprint. For example, the three-station automatic tightening test instrument before restructuring requires a large cabinet with many buttons (such as: start, test, print, etc.) and signal light displays on the panel. The operation is complex and the function is single. The virtualized test instrument requires only a PC with a built-in DAQ card, and all function keys, displays, and curves can be reconstructed on the CRT display. Its operation is simple, users can easily add and subtract modules, reconfigure the existing system to meet the new test requirements, not only lose the existing hardware and software resources, but also meet the constantly changing test requirements.
2. Auto-tightening system of three-station nut of automobile connecting rod
The connecting rod three-station nut automatic tightening hoeing device uses pneumatic as the power source, and the electric valve controls the movement of the cylinder. After reaching the working station, the microcomputer automatically controls the nut tightening. The whole equipment is a three-station rotary structure. The first station is for loading and unloading, the second station is for tightening the nut, and the third station is for offsetting the head of the piston rod. The phase difference of the three stations is 120 degrees, and the conversion between the three stations is driven by the rotary table cylinder. Its specific technical indicators are:
(1) The production cycle time is 0.25 minutes.
(2) The maximum tightening torque is 15N.m, and the tightening torque is required to be steplessly adjustable within the range of 10 ~ 15N.M, and the accuracy is within ± 2.5.
(3) The angle of rotation during the tightening torque from 8N.m to 15N-m should be relatively constant. The light spot encoder starts counting when the torque is 5N.m. When the torque reaches 12N.m, the angle of rotation is 5 degrees, which is qualified.
In actual operation, sometimes impurities such as iron filings penetrate into the thread, causing errors and resulting in defective products. Therefore, we propose a compound control method of torque-turn angle. After tightening to overcome the unevenness of the surface and withstanding a certain torque, a certain turn angle is tightened to improve product quality.
During the tightening process, how to control the constant speed of the spindle motor is the key to accurately measure the tightening torque. This system uses a DC motor with PWM speed control device, that is, pulse width modulation.
At the same time, install a photoelectric encoder on the spindle to measure the angle that the spindle turns when tightening the nut to ensure product quality.
3. Realization of virtualized test system
The birth of virtual instruments has changed the traditional hardware-based instruments into software-based instruments, which has made tremendous improvements in data calculation, results display, and productivity improvement.
The improved design of the virtualization of the automatic tightening and riveting device for the three-position nut of the automobile connecting rod adopts the analog output based on the PC and the built-in data acquisition card position resolution, which can perform analog / digital triggering and has ten programmable Function input port.
The system uses Labwindows / CVI of NI company as the software development platform, which is built on the open software architecture, and adopts engineering (plug-in DAQ) matching scheme to collect and process data. The combination of computer and DAQ series products can carry out real-time measurement and process control. In the production process, we no longer need to manually record data and enter the data into the analysis or display program. The built-in DAQ and appropriate software can automatically achieve these functions. The built-in DAQ scheme design mainly uses a DAQ board inserted inside the PC chassis, and uses software to process the entire measurement process and the actual analog / digital signals. A typical DAQ board includes one or more analog / digital converters (Converts), digital I / O ports, and counting / timing loops. These components are the interface between the computer and the actual analog, digital, and timed I / O signals, which provides convenience for us to read and write data.
In this system, we chose the AT-MIO-16E-2 from NI as the built-in DAQ board. Its main performance indicators are: 16 single-ended, 8 differential analog inputs, 12-bit sampling accuracy, sampling rate up to 500kS / s, each channel gain and range are independent of each other; 2 channels, 12 files as the subject framework, combining C ++ source files, header files, library files, target modules, user interface files, dynamic link library instrument drivers and other multi-functional components Integrated, and supports network functions such as dynamic data exchange (DDE) and TCP / IP.
4 Conclusion
Due to the use of PC-based, equipped with a built-in DAQ board, Labwindows / CVI as a software development platform for process monitoring and control, the virtualized design solution removes the original huge cabinet, which can be instantly convenient The results can be displayed in the same way, and the results can be saved as files such as Excel. Remote monitoring and data collection can also be performed, reducing the time required to analyze and process the data. Moreover, the graphical programming platform is much superior to the original system for the development and debugging of the system and the generation of executable programs. If the number of required measurement and control parameters is large, considering the electromagnetic shielding, system expansion and development, it is more appropriate to adopt the implementation scheme based on VXI bus.
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