A moving mirror control system for a dual-channel orthogonal interferometer

Abstract

The present invention discloses a dual-channel orthogonal interferometer moving mirror control system, wherein the dual-channel interferometer is used to obtain two laser interference signals with consistent intensity and phase at the light input port and the light output port; the phase shift unit is used to process the two laser interference signals obtained by the dual-channel interferometer into an orthogonal relationship; the interference pulse processing unit is used to perform frequency doubling processing on the two mutually orthogonal signals through an XOR operation; the zero position detection unit is used to detect the moving origin of the moving mirror; the voice coil motor is installed at the outer end of the swing arm K of the moving mirror support frame in the dual-channel interferometer, and is used to drive the moving mirror to swing at a uniform speed; the DSP motor control and drive unit controls the voice coil motor according to the preset moving mirror speed and displacement, and drives the moving mirror to swing at a uniform speed within a certain range. The internal structure of the above system is simple, and the movement stroke of the interferometer moving mirror can be continuously adjusted according to needs, and uniform speed movement can be performed within the set displacement.

Description

Technical Field

[0001] The invention relates to the technical field of infrared spectrometers, and in particular to a dual-channel orthogonal interferometer moving mirror control system. Background Art

[0002] Fourier transform infrared spectrometer has the characteristics of high spectral resolution, high light flux, wide measurement spectrum, etc. It is widely used in spectral analysis of solid, liquid and gas multi-state chemical substances. Its core device, time-modulated Michelson interferometer, is a necessary component for generating interference signals. The interference signal containing the infrared spectrum information of the object under test is generally collected in an equal optical path difference interval manner, so controlling the uniform motion of the moving mirror helps to reduce the distortion of the inverted spectrum. In addition, the spectral resolution of the infrared spectrometer depends on the maximum optical path difference between the two coherent lights that form the interference signal, and in order to make the resolution of the spectrometer variable, the position of the moving mirror needs to be continuously adjustable.

[0003] The movement of the moving mirror is generally driven by a voice coil motor. The position feedback of the voice coil motor in the existing Fourier transform infrared spectrometer generally uses a grating ruler position sensor. The grating ruler is installed inside the instrument, which increases the complexity of the instrument design and is not convenient for debugging. Another solution is to obtain the moving position of the moving mirror by counting the square wave pulses converted from a single-channel laser interference signal, and use a limit switch as a counting trigger signal at the positive and negative maximum optical path differences. However, the counting accuracy of the single-channel laser interference signal in this solution is low, and when the limit switch is used as the counting trigger signal, it is impossible to collect the bilateral interference signal with a continuously changing optical path difference according to the needs of the host computer. Summary of the invention

[0004] The purpose of the present invention is to provide a dual-channel orthogonal interferometer moving mirror control system, which has a simple internal structure and can continuously adjust the movement stroke of the interferometer moving mirror as needed, perform uniform motion within a set displacement, and realize continuous adjustment of the spectral resolution of an infrared spectrometer.

[0005] The objective of the present invention is achieved through the following technical solutions:

[0006] A dual-channel orthogonal interferometer moving mirror control system, the system comprises a dual-channel interferometer, a phase shift unit, an interference pulse processing unit, a zero position detection unit, a voice coil motor, a DSP motor control and drive unit, wherein:

[0007] The dual-channel interferometer is used to obtain two laser interference signals with consistent intensity and phase at the light input port and the light output port;

[0008] The zero position detection unit is used to detect the moving origin of the moving mirror in the dual-channel interferometer as the counting zero point of the moving displacement; specifically, a slot-type photoelectric switch is used as a zero position trigger signal at the zero optical path difference position of the moving mirror to facilitate bidirectional adjustment of the moving position of the moving mirror;

[0009] The voice coil motor is mounted on the outer end of the swing arm of the moving mirror support frame, and is used to drive the moving mirror to swing at a uniform speed;

[0010] The phase shift unit, interference pulse processing unit and DSP motor control and drive unit constitute the electronic signal processing part, wherein:

[0011] The phase shift unit is used to process the two laser interference signals obtained by the dual-channel interferometer into an orthogonal relationship, obtain two mutually orthogonal signals, and improve the displacement detection accuracy;

[0012] The interference pulse processing unit is used to perform frequency multiplication processing on the two mutually orthogonal signals processed by the phase shift unit through an exclusive OR operation, thereby improving the resolution of displacement measurement and also improving the sampling rate of the infrared interference signal;

[0013] The DSP motor control and drive unit is used to receive the zero position signal sent by the zero position detection unit and the orthogonal pulse signal processed by the interference pulse processing unit, and use the zero position signal as a reference point to count the orthogonal pulse signal to determine the current displacement and speed of the moving mirror; then control the voice coil motor according to the preset moving mirror speed and displacement to drive the moving mirror to swing at a uniform speed within a certain range.

[0014] It can be seen from the technical solution provided by the present invention that the internal structure of the above system is simple, and the movement stroke of the interferometer moving mirror can be continuously adjusted as needed, and uniform motion can be performed within the set displacement, thereby realizing continuous adjustment of the spectral resolution of the infrared spectrometer. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0016] Figure 1 A schematic diagram of the structure of a moving mirror control system for a dual-channel orthogonal interferometer provided in an embodiment of the present invention;

[0017] Figure 2 A schematic diagram of the laser signal processing process according to an embodiment of the present invention;

[0018] Figure 3 The figure is a specific circuit diagram of the phase shift unit described in the embodiment of the present invention. DETAILED DESCRIPTION

[0019] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments, which does not constitute a limitation of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] like Figure 1 The figure shows a schematic diagram of the structure of a dual-channel orthogonal interferometer moving mirror control system provided by an embodiment of the present invention. The system includes a dual-channel interferometer, a phase shift unit, an interference pulse processing unit, a zero position detection unit, a voice coil motor, and a DSP motor control and drive unit, wherein:

[0021] The dual-channel interferometer is used to obtain two laser interference signals with consistent intensity and phase at the light input and light output ports;

[0022] A zero position detection unit is used to detect the moving origin of the moving mirror in the dual-channel interferometer as the counting zero point of the moving displacement; specifically, a slot-type photoelectric switch OS1 is used as a zero position trigger signal at the zero optical path difference position of the moving mirror to facilitate bidirectional adjustment of the moving position of the moving mirror;

[0023] The voice coil motor is installed at the outer end of the swing arm K of the moving mirror support frame in the dual-channel interferometer, and is used to drive the moving mirror to swing at a uniform speed. Figure 1 VM1 in the figure is a voice coil motor;

[0024] The phase shift unit, interference pulse processing unit and DSP motor control and drive unit constitute the electronic signal processing part, such as Figure 2 FIG. 1 is a schematic diagram of a laser signal processing process according to an embodiment of the present invention, wherein:

[0025] The phase shift unit is used to process the two laser interference signals obtained by the dual-channel interferometer into an orthogonal relationship, obtain two mutually orthogonal signals, and improve the displacement detection accuracy;

[0026] An interference pulse processing unit is used to perform frequency doubling processing on the two mutually orthogonal signals processed by the phase shift unit through an exclusive-OR operation, thereby improving the resolution of displacement measurement and also improving the sampling rate of the infrared interference signal;

[0027] The DSP motor control and drive unit is used to receive the zero position signal sent by the zero position detection unit and the orthogonal pulse signal processed by the interference pulse processing unit, and use the zero position signal as a reference point to count the orthogonal pulse signal to determine the current displacement and speed of the moving mirror; and then control the voice coil motor according to the preset moving mirror speed and displacement to drive the moving mirror to swing at a uniform speed within a certain range.

[0028] In the specific implementation, Figure 2 As shown, the laser light source passes through a dual-channel interferometer, and laser detectors D1 and D2 receive monochromatic laser interference signals with consistent phases;

[0029] The laser interference signal received by the laser detector D1 is subjected to transimpedance amplification and filtering preprocessing, and then subjected to hysteresis comparison by the interference pulse processing unit, so that the original interference signal is processed into a square wave signal S1;

[0030] At the same time, the laser interference signal received by the laser detector D2 is subjected to transimpedance amplification and filtering preprocessing, and then is subjected to phase shift processing by the phase shift unit, and then subjected to hysteresis comparison by the interference pulse processing unit, so as to process the original interference signal into a square wave signal S2; wherein the phase difference between the square wave signals S1 and S2 is 90°, and they are a set of orthogonal pulse signals;

[0031] The square wave signals S1 and S2, which are orthogonal to each other, are subjected to an XOR operation to obtain a frequency-doubled square wave signal S3 that is twice the frequency of the original signal.

[0032] The timer / counter counts the rising edges of the frequency-doubled square wave signal S3, which is set to N. The change in the optical path difference can be expressed as Where, λ is the wavelength of the laser light source;

[0033] When the input pin of the DSP motor control and drive unit detects the trigger signal of the slot-type photoelectric switch, it is enabled, and the timer / counter starts counting. When the trigger signal is detected again, the counting ends;

[0034] The value of the timer / counter is stored in a two-level deep FIFO stack. Before using the timer / counter, a clock needs to be set for it to record the time between two jumps on the pin, and thus calculate the current displacement and movement speed of the moving mirror;

[0035] Then, according to the preset moving mirror speed and displacement, the motion control amount is calculated through the scanning rate feedback control algorithm, and the motion control amount is converted into an analog signal. The voice coil motor is then controlled by the power amplifier circuit to drive the moving mirror to swing at a uniform speed within a certain range.

[0036] In the specific implementation, Figure 3FIG. 1 is a specific circuit diagram of the phase shift unit according to an embodiment of the present invention. Assume that the expression of the intensity I of the original laser interference signal received by the laser detector D2 and the optical path difference x is:

[0037] I(x)=A·cos(2πσx)

[0038] Where A is the amplitude of the laser interference signal; x is the optical path difference; σ is the wave number of the laser;

[0039] Then, the relationship between the signal voltage input to the phase shift unit and time can be expressed as:

[0040] U in =U m ·cos(ωt)

[0041] Among them, U m is the voltage amplitude; ω is the signal frequency;

[0042] The output signal voltage after being processed by the phase shift unit is expressed as:

[0043]

[0044] By setting the values ​​of the resistor R and capacitor C in the phase shift unit, When , a signal with constant amplitude and a phase lag of 90° compared to the input signal can be obtained.

[0045] like Figure 1 As shown, the dual-channel interferometer specifically includes a beam splitter BS, a first plane mirror M1, a second plane mirror M2, a double-sided mirror M3, a first right-angle mirror RM1, a second right-angle mirror RM2, a cross spring bearing S, a first laser detector D1, and a second laser detector D2, wherein:

[0046] The reference laser light source L passes through the beam splitter BS and is divided into reflected light L1 and transmitted light L2;

[0047] The reflected light L1 passes through the second plane reflector M2 and the double-sided reflector M3 in sequence and then enters the second right-angle reflector RM2, so that the light is offset by a certain amount in the Z-axis direction (perpendicular to the paper direction); then the second right-angle reflector RM2 returns the light to the double-sided reflector M3, and then reflects the light back to the beam splitter BS through the second plane reflector M2;

[0048] The transmitted light L2 passes through the first plane reflector M1 and the double-sided reflector M3 in sequence and then enters the first right-angle reflector RM1, causing the light to be offset by a certain amount in the Z-axis direction; then the first right-angle reflector RM1 returns the light to the double-sided reflector M3, and then reflects the light back to the beam splitter BS through the first plane reflector M1;

[0049] The first plane reflector M1 and the second plane reflector M2 are movable mirrors of the dual-channel interferometer, and swing around the cross spring bearing S to generate an optical path difference between the reflected light L1 and the transmitted light L2. The two coherent lights of the reflected light L1 and the transmitted light L2 with the optical path difference converge at the beam splitter BS to form a monochromatic laser interference light.

[0050] The beam splitter BS splits it into two monochromatic laser interference lights, which are incident on the first laser detector D1 and the second laser detector D2 respectively to obtain two laser interference signals with consistent intensity and phase. In a specific implementation, using two laser detectors to simultaneously collect laser interference signals can minimize the phase error between the two laser signals caused by the processing circuit.

[0051] In a specific implementation, the zero position detection unit is implemented by a slot-type photoelectric switch, the slot of the slot-type photoelectric switch and the direction of the swing arm K of the moving mirror are perpendicular to each other in the state of zero optical path difference, and a baffle is installed on the swing arm K so that it just passes through the slot of the slot-type photoelectric switch;

[0052] When the moving mirror swings to the zero optical path difference position, the slot-type photoelectric switch OS1 will be triggered, and the pulse signal of the zero optical path difference position will be sent to the DSP motor control and drive unit for subsequent processing.

[0053] It is worth noting that the contents not described in detail in the embodiments of the present invention belong to the prior art known to professional and technical personnel in the field.

[0054] In summary, the system described in the embodiment of the present invention uses a set of orthogonal laser interference signals to control the motion of the moving mirror, and the two laser detectors simultaneously collect laser interference signals to reduce phase errors, reduce false counting rates, improve displacement measurement accuracy, and simplify the internal mechanical structure of the instrument; at the same time, the motion stroke of the interferometer moving mirror can be continuously adjusted as needed, and uniform motion can be performed within the set displacement, thereby realizing continuous adjustment of the spectral resolution of the infrared spectrometer.

[0055] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed in the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims. The information disclosed in the background technology section of this article is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as an admission or in any form that the information constitutes prior art known to those skilled in the art.

Claims

1. A dual-channel orthogonal interferometer moving mirror control system, characterized in that: The system includes a dual-channel interferometer, a phase shift unit, an interference pulse processing unit, a zero position detection unit, a voice coil motor, a DSP motor control and drive unit, wherein: The dual-channel interferometer is used to obtain two laser interference signals with consistent intensity and phase at the light input port and the light output port; The zero position detection unit is used to detect the moving origin of the moving mirror in the dual-channel interferometer as the counting zero point of the moving displacement; specifically, a slot-type photoelectric switch is used as a zero position trigger signal at the zero optical path difference position of the moving mirror to facilitate bidirectional adjustment of the moving position of the moving mirror; The voice coil motor is mounted on the outer end of the swing arm of the moving mirror support frame, and is used to drive the moving mirror to swing at a uniform speed; The phase shift unit, interference pulse processing unit and DSP motor control and drive unit constitute the electronic signal processing part, wherein: The phase shift unit is used to process the two laser interference signals obtained by the dual-channel interferometer into an orthogonal relationship, obtain two mutually orthogonal signals, and improve the displacement detection accuracy; The interference pulse processing unit is used to perform frequency multiplication processing on the two mutually orthogonal signals processed by the phase shift unit through an exclusive OR operation, thereby improving the resolution of displacement measurement and also improving the sampling rate of the infrared interference signal; The DSP motor control and drive unit is used to receive the zero position signal sent by the zero position detection unit and the orthogonal pulse signal processed by the interference pulse processing unit, and use the zero position signal as a reference point to count the orthogonal pulse signal to determine the current displacement and speed of the moving mirror; and then control the voice coil motor according to the preset moving mirror speed and displacement to drive the moving mirror to swing at a uniform speed within a certain range; The dual-channel interferometer includes a beam splitter BS, a first plane reflector M1, a second plane reflector M2, a double-sided reflector M3, a first right-angle reflector RM1, a second right-angle reflector RM2, a cross spring bearing S, a first laser detector D1, and a second laser detector D2, wherein: The reference laser light source L passes through the beam splitter BS and is divided into reflected light L1 and transmitted light L2; The reflected light L1 passes through the second plane reflector M2 and the double-sided reflector M3 in sequence and then enters the second right-angle reflector RM2, so that the light is offset by a certain position in the Z-axis direction; then the second right-angle reflector RM2 returns the light to the double-sided reflector M3, and then reflects the light back to the beam splitter BS through the second plane reflector M2; The transmitted light L2 passes through the first plane reflector M1 and the double-sided reflector M3 in sequence and then enters the first right-angle reflector RM1, causing the light to be offset by a certain amount in the Z-axis direction; then the first right-angle reflector RM1 returns the light to the double-sided reflector M3, and then reflects the light back to the beam splitter BS through the first plane reflector M1; The first plane reflector M1 and the second plane reflector M2 are movable mirrors of the dual-channel interferometer, and swing around the cross spring bearing S to generate an optical path difference between the reflected light L1 and the transmitted light L2. The two coherent lights of the reflected light L1 and the transmitted light L2 with the optical path difference converge at the beam splitter BS to form a monochromatic laser interference light. The beam splitter BS splits it into two monochromatic laser interference lights, which are incident on the first laser detector D1 and the second laser detector D2 respectively, so as to obtain two laser interference signals with the same intensity and phase; The specific working process of the electronic signal processing part is: The laser light source passes through a dual-channel interferometer, and the first laser detector D1 and the second laser detector D2 receive monochromatic laser interference signals with consistent phases; The laser interference signal received by the first laser detector D1 is subjected to transimpedance amplification and filtering preprocessing, and then subjected to hysteresis comparison by the interference pulse processing unit, so that the original interference signal is processed into a square wave signal S1; At the same time, the laser interference signal received by the second laser detector D2 is subjected to transimpedance amplification and filtering preprocessing, and then is subjected to phase shift processing by the phase shift unit, and then subjected to hysteresis comparison by the interference pulse processing unit, so as to process the original interference signal into a square wave signal S2; wherein the phase difference between the square wave signals S1 and S2 is 90°, and they are a set of orthogonal pulse signals; The square wave signals S1 and S2, which are orthogonal to each other, are subjected to an XOR operation to obtain a frequency-doubled square wave signal S3 that is twice the frequency of the original signal. The timer / counter counts the rising edges of the frequency-doubled square wave signal S3, which is set to N. The change in the optical path difference can be expressed as Where, λ is the wavelength of the laser light source; When the input pin of the DSP motor control and drive unit detects the trigger signal of the slot-type photoelectric switch, it is enabled, and the timer / counter starts counting. When the trigger signal is detected again, the counting ends; The value of the timer / counter is stored in a two-level deep FIFO stack. Before using the timer / counter, a clock needs to be set for it to record the time between two jumps on the pin, and thus calculate the current displacement and movement speed of the moving mirror; Then, according to the preset moving mirror speed and displacement, the motion control amount is calculated through the scanning rate feedback control algorithm, and the motion control amount is converted into an analog signal. The voice coil motor is then controlled by the power amplifier circuit to drive the moving mirror to swing at a uniform speed within a certain range.

2. The dual-channel orthogonal interferometer moving mirror control system according to claim 1, characterized in that: The zero position detection unit is realized by a slot-type photoelectric switch, the slot of the slot-type photoelectric switch is perpendicular to the direction of the swing arm of the moving mirror in the state of zero optical path difference, and a baffle is installed on the swing arm so that it just passes through the slot of the slot-type photoelectric switch; When the moving mirror swings to the zero optical path difference position, the slot-type photoelectric switch will be triggered, and the pulse signal of the zero optical path difference position will be sent to the DSP motor control and drive unit for subsequent processing.

3. The dual-channel orthogonal interferometer moving mirror control system according to claim 1, characterized in that: The processing process of the phase shift unit is specifically as follows: Assume that the expression of the intensity I of the original laser interference signal received by the second laser detector D2 and the optical path difference x is: I(x)=A·cos(2πσx) Where A is the amplitude of the laser interference signal; x is the optical path difference; σ is the wave number of the laser; Then, the relationship between the signal voltage input to the phase shift unit and time can be expressed as: U in =U m ·cos(ωt) Among them, U m is the voltage amplitude; ω is the signal frequency; The output signal voltage after being processed by the phase shift unit is expressed as: By setting the values ​​of the resistor R and capacitor C in the phase shift unit, When , a signal with constant amplitude and a phase lag of 90° compared to the input signal can be obtained.

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