The software realizes the data processing software of the virtual instrument is realized on the LabVIEW virtual instrument development platform of NI Company of the United States. It can conveniently construct the user interface of the virtual instrument, and there are a large number of common data processing algorithm modules, so that you can concentrate on Focus on the specific data processing algorithms required by the instrument.
How to accurately measure the frequency change of the signal is a difficult point in the design of the virtual instrument. The original idea was to use the spectrum analysis module in the LabVIEW virtual instrument development platform to convert the two signal segments into the time domain to the frequency domain, and then obtain the most important frequency components from the spectrum as the frequency of the corresponding time period, and the standard worm The frequency calculates the theoretical frequency of the measured gear according to equation (1). By comparing the theoretical frequency of the measured gear with the measured frequency, the error of the corresponding segment of the gear can be obtained. This scheme was rejected by experimental and theoretical analysis. If the spectrum analysis method is used, not only the calculation amount is large, but also the frequency leakage phenomenon caused by the truncation of the signal cannot obtain the exact frequency value of the original signal.
After analyzing the principle, the phase of the signal can accurately reflect the angular displacement of the corresponding gear. When the measured gear has no error, it can be obtained by formula (1): U1-U01tz1z2=U2-U02t(2)U1z1z2-U2=U01z1z2-U02=C1(3) where U1, U01, U2, U02 represent The angular displacement and initial angular displacement of the standard worm and the angular displacement and initial angular displacement of the measured gear; t is the measured time; z1, z2 are the number of teeth of the standard worm and the measured gear, respectively; C1 is a constant. And because the grating disk has 10800 reticle lines, the correspondence between the angular displacement U and the signal phase A is: U=A 2kP10800 (where k is a positive integer related to U) (4) Substituting equation (3) Main value: arg(A1 2k1P)z1z2-A2=arg(10800C1 2k2P)=C(5) It can be seen that when the angular displacement of the measured gear caused by the gear error changes less than P/5400, only the phase of the worm signal is needed. By performing an appropriate transformation and comparing with the phase of the measured gear signal, an accurate error value can be obtained. By counting the period of the measured gear signal, it can be checked that the angular displacement changes beyond P/5400, and the corresponding amount of 2P is added to obtain the corresponding error value. When programming, the standard worm is rotated at a constant speed, and its signal period is fixed. Only one cycle of the signal measurement value can be calculated for later phase comparison calculation. However, due to the calculation error, if all the phases are calculated from the beginning of the measurement, the calculation error will be accumulated to invalidate the calculation result. To this end, the signal of the measured gear is calculated for each period to obtain the difference between the measured phase of the measured point and the theoretical calculated phase, thereby obtaining the error of the point.
Conclusion Using software to simulate hardware functions instead of actual hardware is the biggest advantage of virtual instruments, and it is also the reason why virtual instruments have become the development direction of detection instruments. In this virtual instrument design, the original instrument function can be realized by software, and the precision is higher. Except for the original rack and the sensor, the other hardware components are all common, saving resources. However, in this instrument, a data acquisition card with a high sampling speed is required to obtain a correct measurement result, and the data storage amount is large due to the separation of data acquisition and processing. In the future, some simple signal processing circuits can be added to complete the frequency division and phase comparison functions, and then the data acquisition card is used to collect signals for data processing. This will simplify the program and at the same time reduce the requirements on the acquisition card, but at this time, The software's dependence on hardware has also increased.
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