Development Of Automatic On-line Inner Diameter Detector

Automatic on-line inner diameter detector is mainly composed of the optical system, the photoelectric conversion system, the motor drive system and the data acquisition and processing system. On the basis of laser triangulation theory, when the laser beam processed by the optical system irradiates on the photosensitive surface of charge-coupled device (CCD), CCD outputs the video signals. Then through the pre-processing and binarization processing circuits, the analog video output signals are transformed into digital signals. Finally, the digital signals are sent into computer through USB interface for calculating and displaying. This detector can realize rapid, loss-free, high-precision and non-contact measurement of inner diameter size. The measuring precision is±10μm, the resolution is 4μm, the repeatability precision is±5μm, and the measuring range is from 15mm to 50mm.The following contents are mainly studied in this dissertation:1. The overall scheme argumentation. In this thesis, the overall scheme and the main components of automatic on-line inner diameter detector are analyzed and argued firstly, then the principle of laser triangulation diameter measurement based on CCD is expounded, and the mathematical model is established.2. Research on optical processing system. A kind of dual-beam system is designed to eliminate the drift of laser beam and improve the quality of the beam.3. Research on CCD drive circuit. On the basis of CCD working principle, CPLD technology is used to research CCD drive circuit, the output waveforms of which meet CCD timing requirements, and the drive circuit has shorter design cycles and high flexibility.4. Research on data acquisition and processing system. Firstly, the pre-processing circuit is designed which suppresses the circuit noise effectively and realizes the amplification of CCD output video signal. Then the method of floating threshold is taken to improve the precision of binarization processing circuit. Thirdly,8253 counter is adopted to count the widths of the binarization output pulses in order to determine the location of the mobile laser spot. At last, real-time processing, displaying, and storing of measurement results are done in host computer through USB communication interface between MCU and host computer.5. Design of software, including software design of CCD drive circuit, software design of single-chip controlling and signal processing, design of USB firmware and device driver, and implementaion of control interface for host computer.6. Measurement test and error analysis. Real-time measurement is done using this detector. The experimental data of automatic on-line inner diameter detector shows that the detector achieves the precision requirements of subject, and has higher reliability. Meanwhile, this thesis analyzes the error which may impact the measurement precision of the instrument, and introduces some processing methods such as the de-noising technology based on mathematical morphology to improve the instrument precision.7. Finally, the main research work of this thesis is summarized and the follow-up research of automatic on-line inner diameter detector is prospected.