JPS61501340A - Mirror scan speed control device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Mirror scan speed control device Bandou 2 Gong! The present invention uses infrared light to measure the spectral absorption properties of sample materials. spectral photometric measurements, and especially interferometers and interferometers to obtain spectral data. Concerning Fourier transform analysis of infrared absorption properties using lasers.

Oimame 2 1 A Fourier transform infrared (FT-IR) spectrophotometer consists of two basic parts. Ru. Namely (1) the light containing the interferometer through which the infrared light beam passes before passing through the sample; (2) to analyze the spectral information contained in the light emitted from the sample; It is a dedicated computer used. Improved equipment for FT-IR spectrophotometer The advantage is that it can detect the wavelength change of the infrared beam directed at the sample and determine the spectral characteristics. Benefits from using an interferometer rather than a diffraction grating or prism to measure It will be done. An interferometer can measure the complete spectral profile of a sample. The accuracy of the analysis is improved, and the preparation time is shortened.

In order to perform analysis by changing the wavelength of infrared light that passes through the sample, FT-IR spec The operation of Michelson interferometers, such as those used for torque photometry, is well known. this An interferometer consists of two orthogonal optical paths, each with an optical path that reflects the light passing through that path. A reflector, ie, a mirror, is disposed at the end of the mirror. Mirror in one optical path is fixed. The mirror in the other optical path moves vertically to increase the length of that optical path. increase or decrease. The infrared light beam entering the interferometer is split by a beam splitter. The individual components of the beam are optically separated into two components. The components will pass through each optical path. Each light beam component reflects its respective After reorienting along the optical path of Recombine and interfere constructively and destructively. The combined beam passes through the sample The light is focused on a photodetector, and the intensity and intensity changes in the frequency range of the emerging beam are measured. Ru.

The intensity characteristics of any selected frequency of the combined optical beam are determined by the beam components. It depends in part on the difference in the length of the optical path taken. In general, a movable mirror is moved axially at a constant speed. When moving, that is, scanning, the intensity of the emitted light beam passes through the interferometer. For any selected wavelength of light, it varies in a regular sinusoidal manner.

A typical infrared light beam coming out of an interferometer has a modulation frequency due to its polychromatic nature. It is a complex mixture of After passing through the sample material, the infrared light beam can be detected to determine the characteristic wavelength of light absorbed by the light. child is the regular sinusoidal intensity pattern expected when the light beam exits the interferometer. This is achieved by measuring the change in turns. The beam that comes out is made up of By measuring the differences in the characteristics of the sine curve pattern of each wavelength of light, Find out the wavelength of light absorbed by the sample. The measured infrared light absorption characteristics are spectra provides data from which the substances that make up the sample are determined.

The output signal of the detector, which measures the intensity modulation of the emerging light beam, is scanned by a movable mirror. can be recorded at very precise intervals throughout the session, so that the interface A blow, known as a program, is formed. The interferogram is is a function of the difference in optical path length taken by both components of the infrared beam passing through the interferometer. A record of data points showing the output signal produced by an infrared photodetector as a number be. Obtain an average interferodrum with improved signal-to-noise ratio characteristics For this purpose, the sample is scanned continuously. This average interferogram is Provides information and data on the spectral properties of sample materials. processed mathematically After that, Fourier transform calculations are performed on the sonointerferogram to obtain the sample construct. A spectral image is obtained. Compare the results with known reference data and sample the results. Determine the configuration of the file.

Most Fourier transform techniques require a large number of interferograms to obtain accurate results. The movable mirror must be scanned 32 to 50 times and the The measurements taken in between are averaged. The L interferograms are to maintain accuracy when averaging with interferograms that are accurately reproduced. It is very important to. The interferogram is formed as a function of mirror position. If you want to measure data points and form an interferogram, The more accurate the mirror position determination, the more accurate the interferogram and An applied Fourier transform will be obtained.

For accuracy and reproducibility when forming interferograms, data points are Both the component measurement ratio (sample ratio) and the mirror speed must be precisely controlled. In other words, when measuring a data point, the exact position of the mirror is determined. I have to.

Modern devices pass a laser beam through an interferometer and use a beam of infrared light. to obtain sample ratio and mirror speed control and/or mirror position measurements. Leh The beam directly measures the motion and/or position of the movable mirror to determine the length of the interferometer's optical path. used to accurately determine changes in Laser beam to beam splitter Therefore, it is split in the same way as the infrared light beam and passes through the same optical path changes. , the combined laser beam carries information about the mirror scanning speed of the movable mirror. This intensity interference shows a measurable monochromatic wavelength of light that displays an intensity interference pattern. The scanning pattern also shows the position of the mirror while scanning and Helps display and correlate collection of data points at uniform intervals of movement. stand.

In conventional devices, when a movable mirror moves at a constant speed, the optical path changes in length. Doppler frequency changes occur in the components of the laser beam. dotsupura – When the changed component combines with a component passing through a fixed length optical path, , a frequency modulated beam is formed that exhibits a measurable amplitude modulation or beat signal. intensity changes or stripe patterns that are analyzed to determine mirror position and/or velocity. cause a buzz. The frequency of the laser beam formed by many lasers is generally A beat signal is useful since it is too high to be measured by a detector.

Conventional equipment typically uses a 5KHz amplitude modulation or beat signal frequency in the emerging beam. Drive the movable mirror at a speed that produces a wave number. The beat signal frequency is around the Doppler equal to the magnitude of the wavenumber change, because it is the light beam component that is coupled This is because it is equal to the difference in frequency between them. As the mirror speed increases, the beat signal frequency The number increases to increase analysis power, while the beat signal decreases as the mirror speed decreases. Ru. The system based on this technology is maintained in one cycle out of 5,000 and is extremely accurate. Provide accurate speed and location information.

However, conventional equipment does not measure the Doppler frequency change of the light beam passing through the optical path. The movable mirror must be moving in order to obtain, therefore, the combined light beam Movement of the movable mirror is required to obtain a measurable beat signal frequency at Become. When the movable mirror is stationary, the beams traveling along adjacent optical paths of the interferometer The component light beams are combined to form a same frequency light beam. Because, This is because there was no Doppler frequency change in either component. be. The combined beam exhibits no intensity modulation or beat signal, and therefore: used to determine mirror position or mirror speed when the mirror is not moving. This information is not contained in the exiting laser beam, which means that the movable mirror as when it reaches the end of the scan and stops to go in the opposite direction.

Occurs whenever the mirror is stopped.

Furthermore, in conventional interferometry devices, the Doppler frequency generated by the scanning of the mirror The change in number produces the same intensity modulation effect in the combined light beam regardless of the direction of movement of the mirror. For example, if the mirror moves in either the forward or backward direction, the An amplitude modulation or beat frequency is obtained. Therefore, even if the difference between the optical paths increases or decreases, It is not possible to determine the direction of mirror movement from the emitted laser beam, even if only for a moment. However, this disadvantage is generally due to the fact that the mirror is Another circuit must be added to indicate the direction of motion.

Furthermore, in conventional devices, the scanning speed of the mirror is very slow, so the emerging light For example, the amplitude modulation or beat frequency of the beam becomes very difficult to measure. When moving at a speed of 0,3 Cm7 seconds, the emitted light beam has a beat of 5 KHz. A frequency arises. However, the mirror frequency became 0.5KHz, making it difficult to measure. Ru. Therefore, as the scan speed becomes slower, the modulation frequency of the combined light beam becomes It is difficult to measure with current electronic detectors, reducing accuracy and analytical power. become.

The FT-IR spectrophotometer forms and reproduces accurate interferograms. There is a limit to the analytical power of the sample, which is determined by the ability to analyze the sample. The important parts of optical equipment are This is the movable mirror of the interferometer. This part is where the spectrophotometer is Determine the accuracy of forming the ram. The accuracy with which a spectrophotometer can analyze a sample is , control the precision and repeatability of the interferogram and thus the speed and position of the movable mirror. It is directly related to the ability of the measuring instrument to determine.

The use of conventional laser references to control and determine the speed and position of moving mirrors Continuing to struggle with the limits of accuracy and control ability. Improvement of mirror position measurement accuracy and mirror speed The analytical accuracy of the sample material of the infrared spectrophotometer is necessarily improved by controlling the degree of It will be improved upon actual purchase.

ヱj] and transition The present invention provides a constant movable interferometer mirror in an infrared (rR) spectrophotometer. The position of the movable mirror over the entire scanning range is two frequencies, including an improved mirror scan controller that can more accurately determine A laser generating a laser beam with components and a standard Michelson In an rR spectrophotometer having an interferometer and a reference signal source, the invention is A closed-loop electronic servo controller controls the laser beam passing through the interferometer. scans the mirror by comparing the signal emitted by the system with a controlled frequency reference signal. Control speed. This laser has a a second closed-loop electronic servo controller that maintains a constant frequency difference between Therefore, it is stabilized. Mirror scanner interacting with laser servo controller The controller controls the output beam at the indicated modulation or beat signal frequency of the resulting light beam. Phase-locked control technology is used to control the scanning speed and position of the interferometer's movable mirror. A continuous information signal can be generated displaying the information.

Base? The S signal source is compatible with a first reference signal frequency sent to the laser servo controller. A second reference signal having a frequency corresponding to the second reference signal is generated. The other two reference signals are the movable mirror The calculated Doppler circumference that the camera reports when scanning at a selected constant speed. The frequency increases or decreases by a value corresponding to the wave number change. The second reference signal is the scan Changes in the intensity of the light beam sent to the servo controller and exiting the interferometer, i.e., the beat A control signal is issued to keep the scanning speed of the movable mirror constant. Ru. Is the scanning speed of the mirror the second one? ! ! of the signal and the beam coming out of the interferometer. Beat frequency obtained by intensity detection and characterized by Doppler frequency changes Control signals are sent and modified until phase lock is achieved with the signal indicating the number. . A phase lock between both of these signals maintains constant speed scanning of the moving mirror. , on the other hand, a well-known reference signal is used to obtain information corresponding to the scanning speed and position of the mirror. number is used.

further instructing the reference signal source to increase or decrease the frequency of the second reference signal; A direction control device is provided. Increasing or decreasing the frequency of the reference signal Thus, the direction as well as the velocity are determined, where the movable mirror is controlled by the scan servo controller. driven by position. The detection signal indicating the functional parameters of the movable mirror is generated by a laser sensor. locked to a common reference signal also used by the turbo controllers.

The mirror scan servo controller controls the heterodyne component of the laser beam. Accurate and stable control is achieved by analyzing intensity modulation.

By applying a magnetic field to a helium-neon laser, the frequency is slightly different2 A laser beam is obtained that accommodates two frequency components. This phenomenon is well known This is explained as the Zeeman split effect. Both components of the laser beam Special table of frequencies between components 1986-501340 (4) The difference is stabilized to a selected difference by the laser servo controller. By this In this case, a continuous beat signal with a constant frequency is generated by a is indicated by a change in the intensity of the light beam based on the mixture. Laser beam intensity The phase of the signal produced by the detection and representing the beat signal is determined by a frequency equal to the selected frequency difference between the Stabilization is achieved by locking to one reference signal.

A laser beam emitting components h with different frequencies that are selectively separated is It is oriented to pass through the traverse meter. Each frequency component of that beam After passing through each optical path of the interpolator, the polarization technique of light separates the opposite frequency components. component.

The resulting light beam is affected by the frequency difference between the components and the gap between the movable mirrors. equal to plus or minus the Doppler frequency change caused by the A laser beam with a circular frequency The beat frequency equal to the frequency difference between the components comes out of the hetero gain Appears in the beam. When the movable mirror scans in the first direction, the Doppler frequency The beat frequency increases due to the change, and the same as when the movable mirror scans in the other direction The beat frequency is reduced by the Doppler effect. Therefore, the frequency of the reference signal is the stop beat signal frequency detected in the laser beam and the beam generated by the beam. Move the movable mirror forward by making it larger or smaller than the rodine signal. It can be scanned in the direction or in the backward direction. 2 - drying using frequency laser mirror by allowing a continuously modulated beam of light to emerge from the intermeter. The scanning direction increases or decreases the reference signal frequency characterizing the laser beam. Easily determined and controlled by small changes.

Inventive scan servo control is sent to moving mirror drive electronics The $1 control circuit, which includes a triple electronic control circuit that generates the scan control signal, The required mirror while scanning if the scanning speed of - Generates a position error signal indicating a change in position, allowing the mirror to move to the theoretical earthwork position at any time. Place it in the right place. This describes the Doppler frequency change in the beat signal frequency. The detection signal from the interferometer, which contains information on the mirror position through the a reference signal containing information that determines the theoretical mirror position for one hour. This is achieved by comparing.

The second control circuit maintains the required mirror scan speed during scanning. Generates an instantaneous velocity error signal that indicates a change in speed so that the scanning mirror remains constant. This leads to the theoretical desired speed to be maintained, which is the dop in the beat signal frequency. The detection signal from the interferometer contains information on the mirror velocity through the frequency variation of the mirror. and the output signal of the tracking voltage controlled oscillator circuit. can be obtained. Contains the rate of change of the scanning mirror's position with respect to its theoretical position. This velocity error signal is more quickly determined by the difference between the desired constant velocity scan and the mirror motion. Respond quickly. Therefore, this signal performs preliminary control of speed and Position the mirror in the perfect position above, reducing the reaction time of the scanning servo controller Provides a control effect to the position error signal to avoid over-driving the mirror when .

The third control circuit is detected by the detection signal that is the basis of mirror scan control, and Improper frequency difference between component frequency modes of split laser beam to compensate for errors formed by precise control. This is because this frequency difference is large. is the basis of the signal frequency and therefore of the measurement of the velocity and position of the mirror. , the discrepancy or error found in the frequency difference between the components is an erroneous scan. This results in a control signal being generated. Therefore, the actual error measured in frequency difference Compensating for eliminates a source of error that occurs in generating the scan control signal.

The position error signal, velocity error signal, and laser compensation signal are added together and selected. The summed signal is given the gain and filter applied to the movable mirror drive. to the dynamic electronics to control the mirror scan.

This scanning servo control device allows the mirror to be It is also possible to scan in both directions at a constant speed. This is a constant frequency basis. Directly allowing quasi-signals to be sent to the scan controller in each direction of mirror movement This is achieved by a phase lock controller. In this way, the sample moves forward on the movable mirror. and during backward scanning, enough to obtain accurate measurements and accurate analytical techniques. Effectively, the time required to obtain relevant data is substantially reduced. .

Additionally, generally known techniques can simply be used to increase or decrease the comparison signal phase. Just by counting, the forward scan is equal to the position of the movable mirror in both backward scans. position can be determined accurately. When the movable mirror moves, the laser beam that appears It depends on the number of cycles in which the phase of the signal representing the system moves forward or backward relative to the reference signal. Thus, the end position of the movable mirror within the scanning range is measured. In this way, the ratio scan range by summing the number of cycles changed between compared signals. Scan and measure data points for the exact position and change in position of a movable mirror. can be easily determined in all samples tested.

This improved scan control device eliminates the drawbacks of previous ° technology devices by continuously To provide accurate mirror position determination means and mirror scanning speed control means. is overcome by This scan controller uses a microsecond each time the scan is reversed. This eliminates the need for a separate optical device to reposition the mirror. This system The control servo device uses this to obtain interferogram data points. High resolution allows spectrophotometers to more accurately analyze sample materials . Continuous information signal formed by two frequency laser beams and high performance position control Thanks to the control means, the spectrophotometer carburetion is performed only once per series of scans. only a single analysis is required, thus providing the required data for accurate sample analysis. The complexity and amount of data is reduced.

Preferred embodiments of the invention Fourier transform infrared (FT-IR) spectrum with reference to Figures 1 and 1a. Explain the interferometer of a photometer. A portion of the incident light beam is divided into two orthogonal optical paths 11 and 1. A microphone having a beam splitter 10 positioned along each of the Explain the Runn interferometer. The beam splitter 10 is a magnetically influenced laser. - Receives the laser beam 16 and the infrared light beam from the i! generated by light source 22! It was shown as 20. in general.

The infrared beam 20 is reflected by a non-planar mirror 24, collimated, and enters the interferometer; , the laser beam 16 is directed directly through an aperture 26 disposed in the center of a non-planar mirror 24. Beams Brick 10 is used.

Beam splitter 10 splits the first component of each light beam 16 and 20 into a light beam guided along a first optical path 11 of constant length bounded by a mirror 12; 16 and 20 are reflected by the mirror 12 and sent to the beam splitter 1 along the light M11. Return to 0. The second component of each light beam 16 and 20 is connected to a beam splitter. 10 along a second optical path 13 bounded by a movable mirror 14. Ru. Movable mirror 14 moves longitudinally with respect to optical path 13 and is indicated by arrow 15 The length of the optical path can be varied within the selected scan range. movable mirror 14 is manufactured by Systems Magnetics, part number ES-1126. The mirror drive electronics 28 controlling the linear motor commercially available as 9. Therefore, it is driven.

The second component of the light beams 16 and 20 is reflected by the movable mirror 14 and the optical path 13 back to the beam splitter 10, where their components t± Recombining with the first component of light beams 16 and 20 returning along the first optical path, respectively. do. The combined first and second components of laser beam 16 are Caused by interference of different frequencies between one component and the second component A heterodyne containing information on the speed, position, and position of the movable mirror 14 by intensity modulation. A beam 30 is formed. The different frequencies of the first and second components are Frequency changes in the Doppler effect caused by an optical component passing through a changing optical path This is partly due to. The combined components of the infrared beam 20 are heterogeneous. An in-beam 32 is formed, the frequency of which is modulated at a customary ratio, to provide the signal to be analyzed. Provides a detectable frequency range of infrared light that can be applied to sample materials.

The combined lenser and infrared light beams 30 and 32 are similar to one reflector 24, respectively. 9 reflections ta, 34 guided along the exit passage 33 of the interferometer where the reflections ta, 34 of The projecting mirror 34 receives the parallel infrared beam 32 and reflects the beam to the sample chamfer. The light is focused by a member 36. The infrared beam 32 passes through a sample chamber 36. The light reaches the third mirror 38 and is reflected from there so as to be collected by the infrared light detector 40. Ru. A photodetector 40 receives an infrared beam modulated in intensity and frequency; The beam is modulated by the absorption properties of the sample material through which it passes.

Modulation of the light beam is the beam variation used to generate the interferogram. detected to form an electrical information signal proportional to the key.

The combined laser beam 30 exits the interferometer through an aperture 42 in reflector 34. The light beam 30 is directed to a detector 44 . Electrical signal formed by the detector 4 5 is used to measure the intensity modulation, i.e. the beat signal frequency exhibited by the light beam 30. It will be done. Detector 44 simply places a single photodetector in the center of emerging laser beam 30. It may also be possible to detect the intensity modulation by placing the

The resulting signal 45 is used to generate a mirror scan servo drive signal 52. - is sent to the scan servo control device 50. The drive signal 52 is a mirror drive voltage. The signal is sent to the child device 28 to control the speed and direction of movement of the movable mirror 14.

The He-Ne lasers 10 are separated by a measured rotational frequency difference, and each has an opposite A laser beam 16 with two component frequency modes with circular polarization It is subjected to magnetic action to form. different frequencies of those components and polarity are the continuous information signals of the heterogain laser beam 30 entering and exiting the interferometer. used to obtain the number. In Figure 2, two component frequency modes The laser beam 16, which is damped by the do. Quarter-wave plate 15 converts each of the circularly polarized components into linearly polarized light. In the drawing, one of the linearly polarized components is is indicated by a bar 17 in a plane parallel to the drawing and accommodates the frequency f1. linear polarized light The 82 components shown are in the plane perpendicular to the drawing and are indicated by point 19. The frequency aft is shown. This phenomenon is caused by the circular polarization of each of the light beam components. It comes from linearly polarized light. In this way, the light beams guided to the interferometer are each They are polarized because they are made up of two components with frequency and circular polarization. Optical technology provides two independent laser beams that are clearly distinguished from each other. Can provide optical signals.

A first component of the laser beam 16' reflected along an optical path 11 of constant length. The light 21 passes through the second quarter-wave plate 23, is reflected by the mirror 12, and is again divided into quarters. The beam passes through the one-wavelength plate 23 and returns to the beam splitter 10. 1st con of beam 16 21 passes through the quarter-wave plate 23 twice, each component The frequency mode polarization will be rotated 90 degrees about the axis of beam 16.

For example, when entering an optical path 11 of a certain length, the light is vertically polarized and is shown as a point 19. The first frequency component 17 having a frequency f, which It is horizontally polarized as indicated by ° and is sent to the beam splitter lO. Similarly, one It enters an optical path 11 of constant length and is horizontally polarized and has a frequency f2 indicated by bar 17. @2 frequency component is vertically polarized light as shown at point 19° from optical path 11. and R to the beam splitter 10.

The laser beam 16 passes through the beam splitter 10 and proceeds along the optical path 13. The second component 25 is reflected from the movable mirror 14 without changing its polarization.

However, each component frequency of the second component 25 of the laser beam The several mode is a doppler effect caused by the movement of the movable mirror 14. The frequency may be changed by a Tsuppler value Δf, thus the frequency with frequency f, The component changes frequency to f, ±Δf, and the frequency converter with frequency f2 When the frequency of the component changes to f2±Δf, it becomes blurred.

Only the unidirectionally polarized component of the light beam passes through beam splitter 10. Therefore, it has a frequency f] whose polarization is changed by 90 degrees once it crosses the first optical path 11. The frequency components of the laser beam are transmitted through the second optical path 13 with similar polarization. The frequency component of the laser beam with the frequency f2±Δf Doppler It will be combined with the Therefore, the combined light beams in one plane of polarization z7 The component has a vertical polarization that exhibits a frequency of fl-(fz ±Δf Doppler). The combined components of the light beam in the optical plane 29 are (f+±Δf Doppler )-fl indicates the frequency.

Light beam components in circularly polarized planes 27 and 29 with orthogonal polarizations are interferometered. and is guided through a polarizing plate (31). This polarizing plate has two polarized components. one of the components is filtered or removed. Therefore, the detector 44 , the combination of different frequency components of a laser beam that have passed through separate optical paths receives a beam of light with a frequency modulated by On the one hand, the Doppler change Δf Doppler that changes in frequency is It may occur. Doppler change in frequency Δf Doppler only occurs when the movable mirror 14 is moving. It should be noted that this occurs in the light beam components. Movable mirror 14 is stationary In the state, no Doppler effect occurs, so the mirror 14 is stationary. At the time, the frequency component having frequency f1 and passing through the optical path 11 is the beam splitter. The same polarization frequency components having different frequencies f2 in the liter 10 and passing through the second optical path 13 amplitude (intensity) modulation, i.e. the difference between both component frequencies, i.e. A heterodyne frequency optical beam exhibiting a beat signal with a frequency equal to f, -fl. This will cause problems. If the frequencies f1 and fl are equal, as in the prior art device, then No signal is generated.

For the Zeeman split component frequency mode used in the present invention When the frequency f1 is different from fl as shown in FIG. is the Doppler change in the frequency of one component Δ modulated by f Doppler.

Thus, photodetector 44 receives a light beam that produces a measurable continuous beat signal. and determine that the mirror is at rest when the frequency is equal to f, -fl. can be done. Even when the movable mirror 14 is stationary, the emerging light beam 3 The information signal is formed continuously by a continuous intensity modulation or beat signal indicated by 0; The information signal controls the speed and position of the mirror 14 over the entire scanning range. enable.

By monitoring the increase or decrease in beat signal frequency exhibited by the emerging light beam 30. Therefore, the scanning speed and time of the mirror can be easily controlled. when the mirror is stationary The frequency difference f, −f exhibited by the combined component frequency modes of the laser beam 2 Which frequency difference indicates the mirror speed, the beat signal frequency appears when the mirror is stopped By determining whether the indicated frequency ef+, is more or less than fz. Therefore, the direction of mirror movement can be determined. The movable mirror 14 moves at a constant speed. When moving during scanning, Doppler occurs at the beat signal frequency of the optical beam. The change Δf Doppler becomes constant.

This mirror scan servo controller is used to control the mirror scan speed It is this beat signal that does this.

The laser 18 affected by the m-air is driven by the difference between the frequencies of the component frequency modes. That is, it is stabilized so that f and -fl are constant. This is laser beam 1 A constant beat signal (intensity variation 7J4) frequency at 6 is maintained. stabilized The beat signal frequency increases the accuracy of mirror velocity and position analysis. can be predicted accurately The beat signal frequency is determined by accurately measuring the Doppler change frequency Δf frequency. Determine whether constant velocity scanning of mirror 14 is achieved, and determine A control signal can be generated based on the detected speed error.

In Figure 1, the basic device of the mirror scan servo control 'J device is the reference signal system. This is a synthesizer 54. A signal synthesizer 54 generates a reference signal, which signal is A component frequency 58 of laser beam 16 is applied. laser beam 16 The stable frequency difference between the frequency components of beam 16 is When the laser beams combine into the laser beam entering the interferometer, there is a constant intensity modulation, i.e. form a signal.

The reference signal 56 may also be applied to a dedicated computer (not shown). The beat signal frequency (laser beam intensity modulation) is required for data measurement analysis. Ru.

Signal synthesizer 54 also generates a second reference signal 60. This second @ issue is A first reference signal 56 having a theoretically selected increasing or decreasing frequency change Δf is shown. 0 What is the direction of increase or decrease in frequency change?

Directional control device 64 applies the signal to the synthesizer. Forward/reverse input signal 62. The magnitude of the theoretical frequency change Δf is programmable is determined by a scan speed selector 66. The second reference signal 60 is The mirror scan sensor is used as an absolute standard for controlling the scanning speed of the moving mirror 14. is applied to the turbo controller 50.

The reference signal synthesizer 54 generates a changed frequency signal and a variable frequency signal. For example, a frequency synthesizer consists of a digital electronic circuit generally known to those skilled in the art. The iser 54 is a crystal oscillator that generates a frequency stable signal with a uniform periodic waveform. The output signal of the crystal oscillator, which may include a reference signal 56, is The frequency may be varied, for example by a divider or multiplier circuit, to form 60 .

The frequency of reference signal 56 is selected within a range of frequencies. The range is Both component frequency modulations of the laser beam 16 through changes in laser operating parameters. determined by the difference in frequency shown between the two nodes. He-N influenced by magnetism For e-lasers, the range is typically 100-1500 KHz. current envoy More useful signals suitable for use with digital electronic components used It is preferable to choose frequencies at the lower level of this range to form 6 For example, the reference signal 56 is preferably controlled at a frequency of 250 KHz. , this can be done by selecting a collector frequency crystal oscillator, or is a multiplier/divider circuit applied to a higher frequency crystal oscillator. It can also be obtained by using some well-known frequency generators such as Ru.

The frequency of 250 KHz selected for reference signal 56 is Determine the exact frequency difference f, −f2 required between the component frequency modes. . This allows the use of phase-locked control loose and its frequency The difference in numbers is stabilized and a stable strength equal to the 250KHz frequency of the reference signal is created. A degree modulation or beat signal frequency is obtained. This stable 250KHz beat signal The station wavenumber is easily measured with a laser beam excited by conventional electronics. can do. It depends on the speed and position of the movable mirror 14 and the reference interferometry. provides useful information signals that can be used to determine gram data measurements.

The frequency of second reference signal 60 is based on the selected frequency of first reference signal 56. Therefore, the reference signal 60 is based on the frequency of 250 KHz of the first reference signal and is one revolution by a selected value equal to the theoretical Δf caused by the motion of the moving mirror 14. The wave number changes by increasing or decreasing. The absolute value of that frequency change is determined by the reference signal synthesizer can be programmed to Various times to obtain the selected frequency change in @ The methods and techniques are well known to those in the field of signal frequency synthesizers. Ru.

The reference signal 60 increases or decreases in frequency by 5 KHz, and the reference signal 60 is connected to the direction-specific control device. 245KHz or 255KHz signal as determined by Frequencies that are preferably added to or subtracted from the frequency of 250 KHz of the first reference signal 56 The variation accurately determines the scanning speed of the movable mirror 14 over the entire scanning range. The signal is applied to the mirror scan servo control device 50 in order to do this. This selected 5 The KHz frequency change scans the movable mirror 14 at a constant speed of 0.3 cm per second. It is used to drive the entire range in either a forward or backward direction.

The direction control W unit W164 uses a beat signal generated from a heterotine component frequency. (controlled at 250KHz) and a heterodyne laser coming out of the interferometer. Intensity modulation frequency detected from the beam (250KHz Doppler frequency change) You can have an up-down requalant array that sums the phase change between Wear. By keeping count of the number of phase changes that occur between these signals, we can -14 can determine the distance moved in one scan.

For example, an up-down counter array can be detected from an incoming laser beam. 68 in response to signal 68 to generate an increasing number of signals per cycle. the decrease signal detected from the input laser beam and the intensity modulation of the emitted laser beam. and a down count input responsive to signal 74 for generation. Therefore, The up-down counter array counters the number of phase changes that occur between these signals. maintain the The number of phase changes counted is the known position required during a full-length scan. It is compared with the phase number. When the movable mirror 14 moves through one scan, the 2 cm of mirror 14 exhibiting a phase change of approximately 6.3XIO' over a typical scan range. The number of phase changes caused by M shift is within the known total number of phase changes within the scanning range. By determining , the direction control device places mirror 1 at the end of the selected scan. Determine the position of the mirror within the scan range when 4 is reached. Mirror 14 When the end of the appeasement scan range is reached, i.e. when the selected number of phase changes is reached, the direction The controller generates a forward/reverse signal 62 which is input to the reference signal synthesizer 54. to change the frequency of the second reference signal 60 from an increasing value of theoretical Δf to a decreasing value, Or change from a decreased value to an increased value. The change in the second reference signal is caused by the shift of the movable mirror 14. instructs the mirror scan drive to change scan direction.

Up-down counter array described as having directional control device The design is generally known to those skilled in the art. The up-down counter array is Standard digital technology, as described in the related Motorola data pants left. It may be configured with a Motolow 90MO34029 counter, such as the one shown here.

A signal 68 having a frequency that characterizes the laser beam beat signal is A direction control device is detected from the output of a photodetector detecting a rearwardly directed portion 72 of the beam. Obtained at location i64. @ No. 68 is laser servo control m'? with ti158 The obtained signal is the same.

a signal having a characteristic frequency of the heterodyne component of the laser beam 30; No. 74 is a detector 44 that detects changes in the intensity of the laser beam 30 exiting the interferometer. obtained from the signal emitted by

The laser stability control device M58 controls the frequency between the component frequency modes of the laser beam. Stabilize the wave number difference f, -f2. This laser servo control device 58 has a phase lock Zero phase lock control loop stabilized by electronic control loop technology closed by applying a correction signal to the frequency that is tuning the 18 elements. , thereby precisely controlling the frequency difference exhibited by the laser beam. stable 25 Providing phase lock control to the laser using a 0 KHz reference signal 56 As a result, the beat signal frequency of the laser beam is stabilized at 250 KHz. growling belief Since the signal frequency is equal to the frequency difference between the frequency components, The frequency difference between the components of the laser beam also stabilizes at 250 KHz.

Laser servo control system! For the circuit and operation of 58, see Weintes and Berscher. A pending patent application filed on March 5, 1983 entitled "Laser Stability Control Device" No. 472,538.

Therefore, the beat signal frequency of the laser beam 16 entering the interferometer is 250K Stable at a known value of Hz. The laser beam 30 leaving the interferometer is also moved by the movable mirror 14. When is in a stationary state, that is, when there is no Doppler frequency change, the WI wavenumber is 250K. The beat signal frequency exhibited by a laser beam passing through an interferometer, representing a beat signal in Hz. By accurately controlling the wave number, the position of the movable mirror 14 can be directed, and the mirror This provides a highly accurate measuring instrument for controlling the scanning speed of the image. laser bee Because the two component frequency modes of the system are mixed, the laser beam It is impossible that the beat signal of the beam exists continuously regardless of the movement of the mirror. It's always effective.

The following measurements control the position and velocity of the mirror. The beam leaving the interferometer beat signal frequency of the beam and the beat signal frequency of the laser beam entering the interferometer The measurement of the number of phase changes occurring between Provides an accurate means of determining movement. This is the standard digital in direction control device 64. This is achieved by counting techniques. Beat signal frequency of the laser beam leaving the interferometer The difference in frequency between the wave number and the beat signal frequency of the laser beam entering the interferometer By measuring , the scanning mirror speed is accurately indicated. child This is achieved by phase comparison of the respective signals. Using the detected frequency difference By doing so, the scanning speed of the mirror can be kept constant.

The mirror scan servo control device includes two devices that generate mirror scan control signals 52. It consists of a phase-locked electronic control loop. The scan control device 50 controls the operation of the mirror 14. scan control signals 52 to mirror drive electronics (not shown) that control the motion of the mirror; supply. This scan control! J device 50 is schematically illustrated in FIG.

In FIG. 1, scan controller 50 includes an active laser beam that detector 44 receives. An electrical signal 80 is received from detector 44 in response to intensity variations in system 30 . Faith No. 80 is the beat signal frequency and the phase of the heterodyne optical beam coming out of the interferometer. Provide information on The signal 80 is a voltage signal, the voltage of which is It oscillates at a frequency equal to the intensity change of that portion of the Rogaine beam 30. Detector 4 4 is generally centered with respect to the cross-section of the beam, so that the detected light beam The portion of the frame will clearly define the required beat signal.

The detection signal 80 is connected to a first phase lock sensor, shown as a mirror position controller 84. control loop and a second phase lock, shown as mirror speed controller 86. sent to the servo control loop. Mirror position control device 84 and mirror speed control device 86 are highly efficient mirrors that interact with each other to drive the movable mirror 1. - form a scan control signal 52;

Detection signal 80 is shown at 81 before being applied to mirror position controller 84 is sent to a frequency divider 88 which divides the frequency by 16 values. similarly The reference signal 60 outputted from the reference signal synthesizer 54 determines the ideal mirror position and and speed information to the mirror position controller 84. The reference signal is Doppler frequency change Δf expected at 250KH2 plus or minus Indicates the frequency, and the sum of seven is also divided by 16 values to proportionally convert the frequency. The zero frequency is subtracted by both the detection signal 80 and the reference signal 60, and the mirror position controller The position comparison range using 84 increases. This is explained as follows. Immediately That is, each cycle of the signal sent to the mirror position controller 84 corresponds to the reference signal sent to it. This is equal to 16 times the actual frequency and therefore the actual phase of the signal and detection signal. By using an error detection signal that is multiplied by a factor of 16, there is no correction. The range covered is increased by a factor of 16.

The electronics of the mirror position control device 84 are schematically illustrated in the third part. Mi The error position controller includes a phase comparator 90, which has a frequency divided by 16. Detection signal 81 from divider 88 is received. Comparator 90 further divides by 16. The reference signal 60 from the reference signal synthesizer 54 is received. This phase comparator The data is proportional to the phase difference between the two signals by comparing the phases of the two signals received. An output signal 92 is generated. This output @%92 increases the voltage in response to the phase difference or is preferably lowered; signal 92 is therefore proportional to the difference in frequency between the input signals.

The output signal 92 is a position error signal, and the voltage of this signal is theoretically accurate information. At any time during the mirror scan, the theoretical It varies in relation to the difference in mirror position from the above required mirror position. This signal This can be used as a correction signal for the position of the movable mirror 14.

This phase detector 90 is a commercially available device manufactured by Motorola, part number MC1. Available as 4046B. More information about this phase detector can be found at Motro It is described on pages 7 to 124 of the CMOS data book.

The output signal 92 (position error signal) of the phase detector 90 is connected to the selected resistive network 9 3 to the desired voltage level, and with a 0.1m1C capacitor. A capacitance filter 94 is provided to filter out the peaks in the resulting signal. The zero position error signal 92 from which the selected average is then obtained is illustrated in FIG. selected gain and filter electronics 95, and then the differential The signal is sent to a dynamic amplifier 100.

Detection signal 80 is also sent to mirror speed controller 186. Illustrated schematically in Figure 4 As shown, the mirror speed controller 86 is a tracking voltage controlled oscillator circuit. It consists of In particular, a phase comparator 96 is arranged, which is connected to the detection signal 80. A 0-phase controller receives the output signal 97 of the voltage-controlled oscillator and outputs an output signal 98. The output signal 98 of the comparator is connected to a resistor circuit #199 and a capacitance filter. Via 101, a selected voltage range is provided. @ No. 98 then became 1! pressure Output signal of 0 phase comparator 96 applied to input of controlled oscillator 102 98 to the input of the voltage controlled oscillator 102, the oscillator 102 is activated. The regulator produces an output 97 whose frequency is controlled by the phase comparator output 98. driven to do so. The oscillator output 97 is thus The electronic control loop The phase comparator output 98 is varied to limit .

By using the output signal 98 of the phase comparator, it can be used as a speed error signal. An analog variable voltage control signal is formed that can be used as an analog variable voltage control signal. Speed error @ is movable It indicates the rate of change in position between the mirror position and the theoretically required position. signal 98 The voltage therefore consists of the theoretical mirror velocity and the actual mirror velocity at a given time point. – Varies in relation to the difference in speed. This signal responds to errors in mirror position. The scanning speed increases according to the position error signal issued from the mirror position control device 84. No. 92 acts to attenuate the control effect.

The phase comparator 96 installed in the mirror speed control device was also sent in the same way. Signals 80 and 97 are compared to generate an output signal proportional to the phase difference between them. child The phase detector 96 is manufactured by Motorola and sold as part number MC14046B. This is a commercially available device.

Further information about this phase detector can be found in the aforementioned brochure.

The voltage controlled oscillator 102 operates as a tracking voltage controlled oscillator circuit. This is also a commercially available device manufactured by Motorola, part number MC14. It is incorporated into 046B. More information about this device can also be found on Motorola CMOS The output signal 98 of the phase comparator 96 obtained from the data book is also differential amplifier 103. sent to.

Position errors output from the mirror position control device 84 and mirror speed control W device 186, respectively. - signal 92 and the speed error signal are sent to a differential amplifier 100 of appropriate polarity to generate a differential Amplifier 100 acts to sum the position and velocity error signals: The summed signal is sent as the mirror control signal 52 and is therefore always available. Contains the position error information of the moving mirror, and also the speed error of the mirror scan speed. Generate an expected signal. Signal 52 is sent to the mirror drive electronics.

A laser signal stability compensator 108 is disposed in the mirror scan servo control device. , in stabilizing the frequency difference between both component frequency modes of the laser beam Position error signal 9 from mirror position controller 84 for inaccuracies and errors in The difference in the zero frequency that compensates for These inaccuracies and errors can be corrected since is important. In FIG. 5, the laser signal stability compensator 108 is a four-phase compensator. 110, to which reference and laser detection signals 56 and 68 are sent. reference signal 56 is output from the reference signal synthesizer 54 and shows a stable frequency of 250KHz. 4. The frequency continuously separates both wavenumber components of the laser beam. This is the difference in frequencies that should be used. The laser detection signal 68 is the light beam emitted from the laser. is generated by detecting the intensity modulation or beat signal frequency of the should have a frequency of 250KHz. However, it is generally indicated as EL. The nine-phase converter will contain frequency errors due to inaccuracies in the control of the laser. The parator 110 compares the phases of the sent signals 56 and 68 and determines the phase between them. An output signal 112 is generated that is proportional to the difference. Therefore, the output of the 1-phase comparator 110 The force signal 112 is proportional to the frequency error found in the energized sense signal. The output signal °112 of the 0-phase comparator 110 is 1, for example, a variable addition signal. A selected voltage adjustment is made by the resistor reducer 113 to reduce the error in the laser frequency difference. generates a laser error signal used to compensate position error signal 92 for do. The laser error signal 112 is a position error signal 92 that has a gain and a filter error. It is summed with the position error signal before being sent to Lectronics.

When the interferometer is differentially moving and the movable mirror 14 is scanning, the mirror ski The sensor servo controller 50 receives a detection signal 80, reference signals 56 and 60, and a detection laser signal. By continuously comparing the phase relationship of No. 68, the mirror position, scan speed, and laser circumference are determined. A mirror scan control signal containing wave number control error information is generated. Control signal 52 incrementally increases or decreases the scan speed of the movable mirror 14 to increase or decrease its scan speed. mirror drive electronics to guide the motor to the theoretical desired parameters. can be used. The mirror scan control signal 52 is incrementally adjusted to match the detection signal. The above-mentioned phase relationship between the signal and the reference signal is ideal; Once a zero-phase lock is achieved that makes the scanning speed of the moving mirror accurate and constant, the mirror The scan control signal 52 is stably sent to the mirror drive electronics to scan the movable mirror. Indicates that the can speed is completely constant.

The selected scan speed generates reference signals with different frequency bases can be easily changed by programming the reference signal synthesizer 54 to Reference signals 56 and 60 of different frequencies can be launched to measure the beam. The movable mirror 14 is driven at different scanning speeds by being phase-locked to the intensity modulation generated by the and thus a Doppler corresponding to the selected theoretical frequency change in the reference signal. – Causes frequency changes.

When the movable mirror 14 reaches the end of the scan, the direction control device 64 adjusts the rotation of the reference signal. a reference signal synthesizer 5 for changing the wave number from an increasing value to a decreasing value or vice versa; 4. The change in sign of the reference frequency change is formed by the movable mirror 14. When the Doppler frequency changes, for example, the sign changes from +5 KHz to -5 KHz. request for change. This requires the mirror to change its scan direction. Therefore, mirror The mirror 14 is scanned in the opposite direction by phase comparison in the scan servo controller M50. Mirror scan control that instructs the mirror drive electronics to scan A signal 52 is formed. Bidirectional scan speed control is achieved by adding a separate Obtained by mirror scan servo control GL device 50 without additional circuitry . Beat signal frequency measured with reference signals 56 and 60 and heterodyne optical beam 30 Since the wave number is displayed continuously, the mirror scanning speed and position control can be performed using mirror scanning. Persistent throughout the can's direction change. This ensures greater accuracy and Additionally, the number of scans required to generate interferogram data is reduced. Ru. The usable portion of each mirror scan for which control maintenance is performed increases in real terms.

Brief description of the drawing Figure 1 shows the interference part of an infrared spectrophotometer and especially the mirror scan made by the present invention. A schematic diagram of the servo control device, Figure 2 shows when a two-frequency laser beam passes through an interferometer. A spectrum showing the polarization relationships of the individual component frequency modes of that beam. Schematic diagram of the interference part of the Torr photometer, Figure 3 shows the mirror position control IJ device included in the mirror scan servo control device. Schematic diagram of Figure 4 shows an overview of the mirror speed control device included in the mirror scan servo control device. Schematic diagram, Figure 5 shows the laser signal stability compensator included in the mirror scan servo control device. is a schematic diagram Figure 1a Figure 3 Figure 5 No. 41 Missing 1 1 rigid - 1 mu・drunk δ＾＠amtr+4＾gang PCT/l, fs 85100382

Claims (10)

[Claims] 1. Controls the movement of the movable mirror of an interferometer used for spectroscopic measurements of sample specimens a closed-loop servo control device for determining the movement of said movable mirror; having one or more frequency components to generate a continuous modulation frequency of a first means for generating a laser beam that directs a constant rate of motion of said movable mirror; and generate a reference signal having frequency characteristics of the theoretical modulation of the laser beam. a second means for detecting a modulation frequency of the laser beam and transmitting an electric signal at the modulation frequency; a third means for obtaining a signal characteristic; and the reference signal from the second means and the third means. receiving the electrical signal from the stage and comparing the phase between the reference signal and the electrical signal; and a position error signal responsive to the phase difference between said two signals, and fourth means for generating a velocity error signal responsive to a rate of change of mirror position; When detected by the three means, it outputs an electrical signal whose phase is locked to the reference signal. a laser from said interferometer having a modulation frequency that determines the position-velocity linkage of the moving mirror; controlling the movement of the movable mirror in response to the error signal to obtain a beam; a closed-loop servo control device comprising: 2. The first means generates a laser having a continuous modulation frequency and has different frequencies. magnetic field to obtain a laser beam with multiple component frequency modes that become The servo according to claim 1, characterized in that it includes a laser influenced by Control device. 3. The third means is responsive to the modulation frequency of the laser beam. The servo control device according to claim 1, characterized in that it includes a photodetector. 4. The fourth means receives the reference signal from the second means and the reference signal from the third means. a first phase detector that generates an error signal proportional to the phase difference between the first phase detector and the electrical signal; an error proportional to the rate of change with respect to the electrical signal from the third means; A second phase detector generates a signal, and the error signals are added together to detect the mirror. and means for generating a control signal containing position and velocity information. A servo control device according to claim 1. 5. The reference frequency output from the second means is based on constant movement of the movable mirror. characterized in that the modulation rate is equal to the desired modulation frequency of said heterodyne laser beam. A closed loop servo control device according to claim 1. 6. Controls the movement of a movable mirror in an interferometer used for spectroscopic measurements of sample materials a closed-loop servo control device, the basis for determining the position and rate of motion of the movable mirror; a first means of generating a heterodyne laser beam with continuous amplitude modulation as the basis; , a first group having frequency characteristics of a desired modulation frequency of the heterodyne laser beam; quasi-signal and the frequency characteristics of the desired modulation frequency that indicates a constant rate of motion of the movable mirror. second means for generating a second reference signal having an electrical signal characteristic of the modulation frequency; detecting the modulation frequency of the laser beam exiting the interferometer to obtain third means; in response to the frequency of the signal, the reference signal from the second means; and the electric signal from the third means, and furthermore, it is possible to prevent an error in the mirror position at any time. a first characteristic indicating a difference and a velocity error of said mirror proportional to said difference at any time; output means for generating an output signal having a second characteristic indicative of a difference; and said movable mirror. the movable mirror in response to the output signal to increase or decrease the rate of motion of the mirror; and drive means for driving a closed loop servo control device. 7. A closed-loop server that drives the movable mirror of an interferometer used in spectroscopic measurements in two directions. a control device for generating a laser beam having a characteristic modulation frequency, and Changes in modulation frequency in response to the Doppler effect caused by the movement of a movable mirror directing said beam through said interferometer to provide said movable mirror; The beam is emitted from the interferometer using the modulation frequency characteristic of the scanning rate of the laser beam. means for adjusting the modulation frequency of the laser beam; 1 signal and a second signal having a frequency smaller than the modulation frequency of the laser beam. a reference signal generator that generates a constant frequency reference signal paired with the signal; detecting the exiting laser beam and determining the modulation frequency displayed by the laser beam; means for generating an electrical signal having a frequency proportional to said reference signal and said electrical signal; a phase comparator that receives a signal and compares the phase difference between the reference signal and the electrical signal; a detector for generating an output signal indicative of a positional error of said mirror having a voltage representing an example; forming a phase-locked control loop to control the mirror throughout the scan. A tracking voltage controlled oscillator is used to generate an output signal indicating the speed error of the a drive means for driving the movable mirror in two directions in response to the drive signal; , the driving means includes the phase coniparator and the tracking voltage controlled oscillator. in response to the output signal of the controller, the modulation frequency is adjusted to have the phase of the reference signal. In order to obtain a phase of mirror scanning, comprising driving the mirror in the laser beam as described above; Servo control device. 8. Controls the movement of a movable mirror in an interferometer used for spectroscopic measurements of sample materials A closed room control device, comprising a continuous variable as a basis for determining the movement of the movable mirror. a first means for generating a heterodyne laser beam having a harmonic frequency; The movable mirror has a frequency characteristic of the desired modulation frequency of the dyne laser beam. second means for generating a reference signal indicative of a constant rate of motion; and an electrical signal at said modulating frequency. third means for detecting the modulation frequency of the laser beam to obtain signal characteristics; receiving the reference signal from the second means and the electric signal from the three means; Compare the phase between the reference signal and the electrical signal, and determine the difference in frequency between the two signals. fourth means for generating an error signal in response to said electrical signal from said third means; and compares the phase with a frequency signal controlled in response to the output of the phase comparison; and fifth means for generating an error signal in response to the frequency difference between the two signals; generating an error signal in response to a change in the modulation frequency of the laser beam; a sixth means for controlling a rate of motion of the movable mirror in response to the error signal; and incrementally adjust the rate of motion to determine the motion of the movable mirror. and control means forming a control loop. 9. The second means generates a direction signal for increasing or decreasing the frequency of the reference signal. in response to the signal, and also determines the position of the movable mirror within the range of motion and issues a direction signal. The servo according to claim 7, further comprising means for generating Control device. 10. The second means further comprises: changing the frequency of the reference signal to a selected value; increasing or decreasing the reference signal with respect to the continuous modulation frequency of the laser beam; , comprising means for controlling the movable mirror in two directions. The servo control device according to item 15.