CN103063128B - Dynamic electronic signal phase measurement system for double-frequency laser interferometer - Google Patents

Abstract

A dynamic electronic signal phase measurement system for a dual-frequency laser interferometer, including an RS receiver, a field programmable gate array device, a pulse interval measurement chip, and a measurement calculation module; wherein the field programmable gate array device includes a real-time calculation The difference between the number of pulses passing through the logic unit per unit time between the reference signal and the measurement signal, the whole cycle counting unit, the pulse extraction unit for converting the input periodic reference signal and measurement signal into two sets of pulse signals, and the receiving pulse interval The phase measurement control unit and I/O control unit of the measurement results of the measurement unit; the pulse interval measurement chip is used to receive two sets of pulse signals output by the pulse extraction unit and convert the time interval between pulses into digital quantities; the measurement calculation module calculates the reference The moving distance of the target to be measured can be obtained by the phase difference between the signal and the measurement signal, and the invention can accurately measure the phase of the dynamic signal, thereby broadening the application occasions of the dual-frequency laser interferometer.

Description

Dynamic electronic signal phase measurement system for dual-frequency laser interferometer

technical field

The invention belongs to the technical field of laser interferometer signal phase and displacement measurement, in particular to a dynamic electronic signal phase measurement system for a dual-frequency laser interferometer.

Background technique

The dual-frequency laser interferometer is widely used in the field of high-precision displacement measurement due to its strong environmental adaptability and the measurement results can be traced to the laser wavelength. Usually, the optical system part of the dual-frequency laser interferometer used for measurement is a Michelson interferometer. The dual-frequency orthogonally polarized laser emitted by the dual-frequency laser is split by a polarization beam splitter prism and then incident on a fixed angle cone to form a reference arm. Incident to the target to be measured to form a measurement arm. The movement of the target to be measured will cause the frequency of the reflected light to superimpose the Doppler frequency shift introduced by the movement on the basis of the original frequency, thereby generating the frequency difference between the measurement arm signal and the reference arm signal. The phase difference of the signal can be obtained by integrating the frequency difference signal in the time domain. The photoelectric detector is used to receive the laser interference signal and convert it into an electrical signal, and the phase difference between the reference signal and the measurement signal is measured by the electronic system. Coupled with the periodicity of the laser interference signal, every 360° change in the phase difference between the reference signal and the measurement signal corresponds to a displacement to be measured that is half the wavelength of the laser light. Therefore, the dual-frequency laser interferometer can obtain the displacement of the target to be measured by accurately measuring the phase difference of the laser interference signal.

According to the working principle of the dual-frequency laser interferometer, in order to achieve high-precision displacement measurement, a reliable signal phase measurement method is required. The current signal processing systems capable of phase measurement of electronic signals can be divided into the following three categories. The first type is to obtain the result within 360° through high-frequency pulse filling, and then obtain the whole cycle result by counting the phase jump point (360° to 0°). The disadvantage of this method is that the whole period counting result will introduce counting errors due to the jitter of the optical signal, so the phase measurement result of this method is not reliable. The second type is to perform phase-locking and frequency multiplication on the input signal, measure the phase difference within 360° of the multiplied signal, and then multiply it by the frequency multiplication coefficient to obtain the phase difference between the measured and reference signals. The disadvantage of this method is that it cannot guarantee good phase-frequency characteristics while achieving a high multiplier, and is limited by the temperature drift and zero drift of the analog circuit, and the phase measurement accuracy is low. The third type of signal processing system is two-way differential digital phase detection. First, the reference signal and the measurement signal are XORed, and then the duration of the high level and low level is measured to obtain the phase value. The disadvantage of this method is that the measurement signal is required to have the same frequency as the reference signal, that is, the target to be measured is stationary, so dynamic signal processing and phase measurement during the moving process of the target to be measured cannot be realized.

Contents of the invention

In order to overcome the shortcomings of the above-mentioned prior art, the object of the present invention is to provide a dynamic electronic signal phase measurement system for dual-frequency laser interferometers, which can accurately measure the phase of dynamic signals, thereby broadening the application of dual-frequency laser interferometers occasion.

In order to achieve the above object, the technical scheme adopted in the present invention is:

Dynamic electronic signal phase measurement system for dual-frequency laser interferometers, including:

RS485 receiver 1 for receiving reference signal and measurement signal;

A pulse interval measurement unit 6 for receiving two sets of pulse signals output by the pulse extraction unit 4 and converting the time interval between the pulses into a digital quantity;

A field programmable gate array FPGA device connected to the RS485 receiver 1 and the pulse interval measurement unit 6, the field programmable gate array FPGA device includes a pulse for real-time calculation of the reference signal and the measurement signal passing through the logic unit per unit time The difference value whole period counting unit 2 of the number, the pulse extraction unit 4 for converting the input periodic reference signal and measurement signal into two groups of pulse signals, the phase measurement control unit 3 receiving the measurement result of the pulse interval measurement unit 6, and The I/O control unit 5 for sending the measurement results of the difference whole cycle counting unit 2 and the phase measurement control unit 3 to the measurement calculation module 7;

The measurement calculation module 7 is used to calculate the phase difference between the reference signal and the measurement signal under the Windows operating system, and then calculate and display the moving distance of the target to be measured.

The RS485 receiver 1, the pulse interval measurement unit 6 and the field programmable gate array FPGA device are integrated into a dual-frequency laser interferometer dynamic measurement phase card.

The reference signal and the measurement signal are square wave signals input in differential form, which are converted into standard TTL level single-ended signals in the RS485 receiver 1 .

The phase measurement control unit 3 provides clock signals and control instructions to the pulse interval measurement unit 6, receives the feedback signal from the pulse interval measurement unit 6, activates the pulse extraction unit 4 according to the feedback signal, and finally receives the measurement result of the pulse interval measurement unit 6.

The pulse extraction unit 4 takes the time when the rising edge of the measurement signal arrives as the sampling time, and converts the input periodic reference signal and measurement signal into two groups of pulse signals: the first group of pulse signals carries the sampling time reference signal adjacent to the measurement signal The time interval information of the rising edge; the second group of pulse signals carries the information of the period value of the reference signal.

The measurement calculation module 7 receives the measurement results of the difference whole cycle counting unit 2 and the phase measurement control unit 3 according to the universal serial bus protocol.

The measurement calculation module 7 includes a data entry unit for entering data

The measurement calculation module 7 includes a data management unit for data management.

Compared with the prior art, the present invention has the advantages of:

1. Using the pulse extraction logic, the periodic signal is converted into a pulse signal containing the phase information at the sampling time, and cooperates with the high-precision pulse interval measurement unit to realize accurate measurement of the signal phase difference in the dynamic process.

2. The high-frequency clock inside the FPGA is replaced by a dedicated pulse interval measurement module, which removes the limitation of the high-frequency clock frequency inside the FPGA on the measurement accuracy of the digital phase measurement system, and achieves higher-precision phase measurement.

3. The digital phase measurement system is adopted. Compared with the analog phase measurement system, the structure is simple, the anti-interference ability is strong, and the development cost is low.

Description of drawings

Fig. 1 is a block diagram of the phase measurement system of the present invention.

Fig. 2 is a measurement diagram of the pulse time interval in the present invention.

Fig. 3 is a graph showing the test results of the long-time working stability of the phase measurement system of the present invention.

Fig. 4 is a diagram showing the test results of the phase measurement accuracy of the phase measurement system of the present invention.

Detailed ways

The implementation of the present invention will be described in detail below in conjunction with the drawings and examples.

As shown in Figure 1, the measurement system of the present invention comprises: RS485 receiver 1, difference value whole period counting unit 2, phase measurement control unit 3, pulse extraction unit 4, I/O control unit 5, pulse interval measurement unit 6 and Measurement calculation module7. Among them, the difference whole cycle counting unit 2, the phase measurement control unit 3, the pulse extraction unit 4, and the I/O control unit 5 are integrated in a field programmable gate array (FPGA) device.

The reference square wave and measurement square wave in differential form are used as the input signal of RS485 receiver 1. When the amplitude of the reference signal is 200mV higher than the amplitude of the measured signal, the output of the receiver is high level; otherwise, when the amplitude of the measured signal is higher than When the reference signal amplitude is 200mV, the receiver output is low level. In this way, the RS485 receiver 1 converts the differential input signal into a single-ended signal and feeds it into the FPGA. After the single-ended signal enters the FPGA, part of it enters the difference whole-period counting unit 2 , and the other part enters the pulse extraction unit 4 .

The difference whole-period counting unit 2 uses a 28-bit counter to calculate in real time the difference in the number of pulses passing through the logic unit between the reference signal and the measurement signal per unit time, denoted as N, and the corresponding phase difference is 360°×N. When the target to be measured is stationary, the frequency of the reference signal and the measurement signal are the same, and the output result of the difference whole cycle counting unit 2 is 0; when the target to be measured is moving, the frequency of the measurement signal and the reference signal are different due to the Doppler frequency shift, The difference whole cycle counting unit 2 performs addition or subtraction according to the output result of the internal sign discrimination logic.

The phase measurement control unit 3, the pulse extraction unit 4 and the pulse interval measurement unit 6 constitute a phase subdivision measurement unit. The pulse interval measurement unit 6 uses a time-to-digital conversion chip TDC-GP21. The chip uses its own internal gate delay to measure the time interval of the input pulse, using the measurement range 2 working mode, the resolution is 45ps, and the measurement range is 500ns~4ms. Under the control of the phase measurement control unit 3, the pulse interval measurement unit 6 completes power-on reset, self-calibration and other initialization procedures, and waits for input pulses. The phase measurement control unit 3 activates the pulse extraction unit 4 after receiving the feedback signal that the initialization of the pulse interval measurement unit 6 is completed. In the pulse extraction unit 4, the measurement signal and the reference signal are frequency-divided by a D flip-flop, and the frequency division coefficient is denoted as K. For the frequency-divided signal, the rising edge of the measurement signal is taken as the sampling time, and the frequency-divided signal is converted into two sets of pulse signals, as shown in Figure 2. This method can avoid the influence of TDC-GP21's 500ns measurement dead zone on the phase measurement range. The pulse interval measurement unit 6 measures the time interval Δt and T, and the corresponding phase difference

where K is the frequency division coefficient, the phase difference The positive and negative of is completed by the sign discrimination logic in the pulse extraction unit 4. The phase subdivision result contains part of the whole cycle value, which realizes the redundant measurement of the whole cycle value and improves the accuracy of the whole cycle measurement result.

The measurement software 7 under the Windows operating system extracts the measurement results latched in the difference whole cycle counting unit 2 and the phase measurement control unit 3 in the dynamic measurement phase card of the dual-frequency laser interferometer. This module synthesizes the phase difference ψ between the measurement signal and the reference signal according to the whole cycle counting and phase subdivision results, and then calculates the corresponding displacement of the target to be measured In addition to displaying the displacement of the target to be measured in real time, the application software also provides data recording and management functions.

In order to test the long-term working stability of the dynamic electronic signal phase measurement system for dual-frequency laser interferometer, the signal generated by Agilent's 33522A signal generator is used as the reference signal and the measurement signal, and the signal frequency is set to 1MHz, every 1 second One sampling is carried out, and the experimental results are shown in Figure 3. It can be seen from the experimental results that the stability of the display value of the phase card for dynamic measurement is guaranteed to be within the range of ±0.4°, the maximum positive jitter is 0.394845°, the maximum negative jitter is -0.34204°, and there is no There is a noticeable jump in the measurement result.

In order to test the phase measurement accuracy of the dynamic electronic signal phase measurement system for dual-frequency laser interferometer, Agilent's 33522A signal generator is used as the signal source, the phase adjustment range to be measured is 0~3600°, and sampling is performed every 90° For comparison, the signal frequency is 1MHz, and the experimental results are shown in Figure 4. The experimental results are converted into displacement representation, and the analysis of the experimental results shows that the regression equation of the phase measurement system is y=x-0.0004, and the maximum measurement deviation is 0.001062 μm.

In summary, through the cooperation of the entire period counting unit and the phase subdivision measurement unit based on dynamic pulse extraction, the dynamic electronic signal phase measurement system for dual-frequency laser interferometer can measure the instantaneous phase difference between the measurement signal and the reference signal The measurement is carried out, and then the real-time measurement of the displacement of the target to be measured during the movement process is realized.

Claims (7)

1., for the dynamic electron signal phase measuring system of two-frequency laser interferometer, it is characterized in that, comprising:

For receiving the RS485 receiver (1) of reference signal and measuring-signal;

The time interval between pulse is also converted into the pulse interval measurement unit (6) of digital quantity by the two group pulse signals exported for received pulse extraction unit (4);

Connect field programmable gate array (FPGA) device of RS485 receiver (1) and pulse interval measurement unit (6), described field programmable gate array (FPGA) device comprise for calculate described reference signal in real time and in the measuring-signal unit interval by difference counting unit complete cycle (2) of the pulse number of this logical block, for the periodic reference signal of input and measuring-signal being converted to the DISCHARGE PULSES EXTRACTION unit (4) of two group pulse signals, the phase measurement control module (3) of received pulse interval measurement unit (6) measurement result and the I/O control module (5) for difference counting unit complete cycle (2) and phase measurement control module (3) measurement result being sent to measuring and calculating module (7), described DISCHARGE PULSES EXTRACTION unit (4) arrives the moment as sampling instant using measuring-signal rising edge, the periodic reference signal of input and measuring-signal is converted to two group pulse signals: the first group pulse signal carries the time interval information of sampling instant reference signal and measuring-signal adjacent rising edges, second group pulse signal carries the information of cycle reference signal value,

For the phase differential of computing reference signal and measuring-signal under Windows operating system, then calculate and demonstrate the measuring and calculating module (7) of the displacement of target to be measured.

2. the dynamic electron signal phase measuring system for two-frequency laser interferometer according to claim 1, it is characterized in that, described RS485 receiver (1), pulse interval measurement unit (6) and field programmable gate array (FPGA) device are integrated into two-frequency laser interferometer kinetic measurement phase place card.

3. the dynamic electron signal phase measuring system for two-frequency laser interferometer according to claim 1, it is characterized in that, described reference signal and measuring-signal are with the square-wave signal of difference form input, are converted into the single-ended signal of standard Transistor-Transistor Logic level in RS485 receiver (1).

4. the dynamic electron signal phase measuring system for two-frequency laser interferometer according to claim 1, it is characterized in that, described phase measurement control module (3) provides clock signal and steering order to pulse interval measurement unit (6), the feedback signal of received pulse interval measurement unit (6), according to feedback signal starting impulse extraction unit (4), the measurement result of final received pulse interval measurement unit (6).

5. the dynamic electron signal phase measuring system for two-frequency laser interferometer according to claim 1, it is characterized in that, described measuring and calculating module (7), according to universal serial bus protocol, receives the measurement result of difference counting unit complete cycle (2) and phase measurement control module (3).

6. the dynamic electron signal phase measuring system for two-frequency laser interferometer according to claim 1, it is characterized in that, described measuring and calculating module (7) comprises the data entry element for logging data.

7. the dynamic electron signal phase measuring system for two-frequency laser interferometer according to claim 1 or 6, it is characterized in that, described measuring and calculating module (7) comprises the Data Management Unit for data management.