Research On Errors Analysis And Precision Control In High-precision Convexity Measurement With Laser For Thin Sheet

With the development of economy and technology, the requirement ofthin sheet increased largely. Especially in aluminum industry, to realizehigh accuracy control of aluminum thin sheet's thickness, flatness andconvexity, the higher measurement precision of the on line measureequipment, and that will promote measure equipment become moreintelligent. But the actual measure equipment has shortage in economicand functional aspects.Funded by the National High Technology Research and DevelopmentProgram("863"Program) of China—"The On-line High-precisionConvexity Measurement Equipment for Thin Aluminum Sheet"(No.2002AA423190). An on-line high-precision convexity measurementequipment for thin aluminum sheet based on laser measurementtechnology. With theory analysis and experiment research, the error rulesof whole system and subsystem of high-precision convexity measurementequipment using a laser system are studied. The key technologies toguarantee and control the measuring precision of the measurement systemby use of finite element method and wavelet signal analysis andprocessing method, which includes error avoidance and error restraint.Combined with the high-speed thin-gauge roll casting industrialexperiment, the capabilities of high-precision sheet convexity using alaser measuring system are validated by the industry test. The experimentshows that the system has advantages of low-cost, high-precision andgood-stability, and that is very important to improve production quality ofdomestic aluminum sheet and boost up market competition ability. At thesame time, the theory and means are also used in other measurementequipment. All those study of this paper are very important both in theoryand application.In this paper, the main research work and achievement as follows:1. After errors analysis of whole system and subsystem ofhigh-precision convexity measurement equipment using a laser system,and compare different projects, according to the main program goal of moving and high-precision measurement, a scanning project to measurethe convexity of thin-sheet is developed, that is based on the differencemeasurement theory of a pair of laser beams, and the whole structure ofequipment is designed, which is C-frame structure. It is realized that sheetthickness and convexity are measured together with low-cost andhigh-precision.2. The automatic measurement strategy is studied, which is used torealize intelligent measurement for convexity measurement equipmentusing a laser system. The rule between sensor's position relation andmeasurement validity of difference measurement system with a pair oflaser beams is studied; the optimal position adjusting aim under differentthickness conditions of sheet to be measured is set up. According to thisaim, the adjustment strategy in sheet convexity measurement system withlaser is brought forward, and the differentia sensor's position adjustingmechanism is designed. The measurement simulation experimental showsthat automatic measurement strategy is feasibility.3. The static errors transfer rules of high-precision convexitymeasurement using a laser system is studied. The rule that is howhorizontal position errors of sensor and rotational angle errors of sensor,etc. caused by mechanism assembly precision affect system precision isstudied. The analysis model of errors caused by mechanism process andassembly precisions is set up, and the control rule of system processassembly is fashioned, which could provide the theory foundation ofsystem calibration and static errors modification.4. Based on experimental studies, which include the environmentvibrations testing experiment under industrial conditions, the experimentof the frame dynamics capability excited by the different vibrations, andthe rule experiment of how different scanning status affect measurementprecision, the rule of how vibrations with different parameters affect themeasurement is investigated, the dynamics errors analysis model is set up,which set up the foundation of guarantee measuring precision of themeasurement system by use of error avoidance and error restraint.5. After the rule of how static distortions, dynamic distortions and ill modes shapes of moving-frame affect the system's measuring precision isstudied, the method to guarantees the measuring precision of theequipment by structure optimization of the C-frame which is key part ofmeasurement system is brought forward. With the universal finite elementanalysis software-ANSYS, by the use of APDL language, the analysis ofthe frame's mechanics characteristic and dynamic structure optimizationof the frame is carried out, which include static (intensity and stiffness)optimum analysis, modal optimum analysis and dynamic responseanalysis, etc. The sensitivity analysis of design variable is also carried out.So that, the optimum structure of moving frame with C-shape is putforward.6. The method of vibration error restraint for sheet convexitymeasuring signal based on wavelet signal multi-resolution analysis isstudied. According to multi-frequency characteristic of sheet convexitymeasuring signal and by use of the wavelet multi-resolution analysismethod, with wavelet decomposition and restoration method, theconvexity measuring signal is decomposed into single components andafter a restraining algorithm is used, the wavelet restoration of validcomponents of the measured signal is carried out and vibration errors areeliminated. The optimum wavelet primary function and the optimumwavelet decomposition level number are determined. By the simulationtesting and experiment, it is showed that errors caused by vibration andsome environment disturbance could be reduced and measuring precisionis increased obviously.7. The errors compensation for sheet convexity measuring, which arecaused by the factor of scanning parameters is studied. According to thecharacteristic of multi-parameter coupling and non-linear, by use of neuralnetwork (NN) method, the non-linear NN model between scanningparameters and dynamic errors is created. By means of dynamic errorsforecasting, dynamic errors compensation is realized. By industrial testing,it is showed that errors caused by different scanning parameters areeliminated effectively and measurement precision is increased.8. The technology integration of high-precision convexity measurement using laser is carried out. The detailed analysis and study ofhardware composing and software structure for the measurementequipment are carried out. The device of convexity measurement withlaser for thin-gauge roll casting is designed and developed, which is firstone in our country. The application shows that the measurement precisionand the system functions of device can satisfy measurement and control ofthe convexity for thin-gauge roll casting and system.