JP4501000B2 - Laser interference displacement measuring method and laser interference displacement measuring apparatus - Google Patents

Description

  The present invention relates to a laser interference displacement measuring method and a laser interference displacement measuring apparatus used to precisely set a displacement position of a workpiece, a cutting tool, a measurement object, etc., for example, in a precision processing machine or a precision measuring instrument.

  In general, this type of interferometer divides the light from the light source and reflects it to the surface of the object and the reference surface respectively, and then combines the object light from the surface of the object and the reference light from the reference surface. Interference optical system for causing interference and a photoelectric conversion means for converting the interference light obtained on the detection surface of the interference optical system into an electric signal, and converting the phase difference or optical path length difference between the two light waves into light intensity As a result, ultra-precise measurement in units of light wavelength has been realized. In particular, since non-contact measurement can be performed on an object, it is used as an effective measurement means in a processing site where a precision processing machine or a precision measuring instrument is used.

As such a displacement measuring device using an interferometer, for example, in Patent Document 1, an interference optical system using a semiconductor laser as a light source having a single wavelength is prepared, and the surface of an object is λ / 2 (λ is a semiconductor laser). There is disclosed a technique for minutely measuring the displacement of an object by utilizing the fact that the intensity of an interference signal obtained by a photoelectric conversion means changes by one period each time it is displaced by (oscillation wavelength).
JP-A-4-169817

  In the above-described displacement measuring apparatus, rather than using only a single wavelength in the interference optical system as in Patent Document 1, the wavelength of the laser light is continuously changed, and the displacement of the object is shifted by the phase due to the interference light. It is possible to measure the displacement more accurately when captured as. Therefore, conventionally, a sawtooth modulation current as shown in FIG. 7 is inputted as the injection current i (t) of the semiconductor laser, and an interference signal is obtained by modulating the oscillation frequency of the semiconductor laser.

  However, when the frequency fc of the modulation current input to the semiconductor laser is increased and the cycle Tc of the injection current i (t) shown in FIG. 7 is about 4 μSec (fc = 250 kHz), at the portion where the sawtooth wave suddenly falls. The interference signal corresponding to the modulation cannot be obtained, and there is a problem that the displacement cannot be measured at a higher speed.

  In view of the above problems, an object of the present invention is to provide a laser interference displacement measuring method and a laser interference displacement measuring apparatus capable of accurately measuring the displacement of an object at a higher speed than before.

The laser interference displacement measuring method according to claim 1 includes a first step of inputting an injection current modulated in a sine wave form into a laser light source, and generating light from the laser light source while changing the wavelength with time, and A second step of obtaining interference light by combining the object light from the surface of the object and the reference light from the reference surface after being divided and reflected on the surface and the reference surface of the object; and Based on the third step of converting the interference light into an electrical interference signal, and the sinusoidal modulation frequency as a reference , the interference signal is sampled and acquired at regular intervals with respect to one period of the modulation frequency . And a fourth step of measuring the displacement of the object by processing each signal.

In this case, the wavelength of light generated from the laser light source also changes to a sine wave by inputting an injection current modulated in a sine wave form into the laser light source. Light from the laser light source reflects and interferes with the surface of the object and the reference surface, respectively, and this interference light is converted into an electrical interference signal, but the injection current input to the laser light source is abrupt. Since the sinusoidal change without rising or falling is repeated, the interference signal can be correctly sampled and acquired even when the modulation frequency of the injected current is increased to, for example, about 1.5 MHz. Therefore, based on the sinusoidal modulation frequency, rather shorter than the time for displacement of the object, if the sampling get an interference signal at regular intervals to one period of the modulation frequency, the sampling obtained plurality of interference signals With this calculation process, the displacement of the object can be measured correctly.

Such an effect is obtained by dividing the light from the laser light source and reflecting the light on the surface of the object and the reference surface, respectively, and then the object light from the surface of the object and the reference light from the reference surface. An interference optical system that obtains interference light by combining the above, first photoelectric conversion means for converting the interference light obtained by the interference optical system into an electrical interference signal, and an injection current that is modulated into a sinusoidal shape in the laser light source And a modulation current generating means for generating a light whose wavelength changes with time from the laser light source, and sampling the interference signal at regular intervals with respect to one period of the modulation frequency with the sine wave modulation frequency as a reference The laser interference displacement measuring apparatus according to claim 5, further comprising: a signal processing unit that acquires and samples and acquires each sampled and acquired signal to measure the displacement of the object.

  The laser interference displacement measuring method according to claim 2, wherein the fifth step of converting the light intensity change of the laser light source into an electrical detection signal, and the interference signal in the third step are divided by the detection signal, And a sixth step of obtaining an interference signal from which a change in optical light intensity is removed, wherein the fourth step samples the interference signal from which the temporal change in light intensity obtained in the sixth step is removed. It is characterized by acquisition.

  When an injection current modulated into a sine wave is input to the laser light source, not only the wavelength of light from the laser light source but also the intensity changes with time. Therefore, the change in the light intensity of this laser light source is converted into an electrical detection signal, the interference signal obtained from another interference light is divided by the detection signal, and the interference signal from which the temporal light intensity change has been removed is obtained. If it obtains, the influence of the light intensity change of the laser light source unnecessary for the displacement measurement of the object can be effectively eliminated.

  Such an effect is achieved by the second photoelectric conversion means for converting the light intensity change of the laser light source into an electrical detection signal, and the interference signal obtained by the first photoelectric conversion means as the second photoelectric conversion means. The laser interference displacement measuring apparatus according to claim 6, further comprising a divider that divides the detection signal obtained by the photoelectric conversion means and obtains an interference signal from which temporal light intensity change is removed.

The laser interferometric displacement measuring method in claim 3, before Symbol fourth step, the one of intervals of 8 minutes to 1 cycle of the modulation frequency contained in the interference signal, the value of the interference signal respectively sampled acquisition From these values, a feedback signal for variably controlling the amplitude of the injection current is generated so that the modulation amplitude included in the interference signal is constant, and the level of the interference signal is calculated from each sampled and acquired signal. seeking phase, it is characterized by measuring the displacement of the subject matter.

In this case, the injection current is modulated sinusoidally around the current reference value, the wave length of the laser light sources, varies sinusoidally with time. Here the value of the temporal change in light intensity interference signal removal of the, at one interval of 8 minutes to 1 cycle of the modulation frequency contained in the interference signal, and the angular frequency of the specific A sinusoidal modulation time, when it is omega _C and t, respectively, cos .omega _C value of t is 0, 1 / 2,1, if acquired as _{S 0, S 1, S 2} , S 3 respectively at the time of -1 / 2 , by a simple operation processing, obtains the position phase related to distance to the surface of the object from the reference plane, it is possible to measure the displacement of the object. Further, a feedback signal for variably controlling the amplitude of the injected current can be generated from each value of the sampled interference signal so that the modulation amplitude included in the interference signal is constant.

Then, such an effect is obtained by sampling and acquiring the value of the interference signal at an interval of 1/8 with respect to one period of the modulation frequency included in the interference signal. as modulation amplitude contained is constant, and generates a feedback signal for variably controlling the amplitude of the injection current, obtains the position phase of the interference signal from the signal the sampling acquisition, displacement of the subject matter It can also be realized by the laser interference displacement measuring apparatus according to claim 7 provided with a signal processing means for measuring.

A laser interference displacement measuring method according to a fourth aspect of the invention is characterized in that the fourth step further includes a seventh step of performing feedback control so that the value of the modulation amplitude becomes π .

In this case, in addition to the interference signal values S ₀ , S ₁ , S ₂ , S ₃ , the interference signal value S ₄ when cosω _C t is −1 is acquired, and (S ₄ −S ₂ ) / if the feedback control of the amount of the amplitude of the sinusoidal modulation so that the value of (S 3 _{-S 1)} is 0, the modulation amplitude is a constant value is a necessary condition for obtaining the position phase and (= [pi) Thus, it becomes possible to accurately measure the displacement of the object.

Such an effect can also be realized by the laser interference displacement measuring apparatus according to claim 8 provided with signal processing means for performing feedback control so that the value of the modulation amplitude becomes π .

  According to the laser interference displacement measuring method of claim 1 and the laser interference displacement measuring apparatus of claim 5, it is possible to correctly sample and acquire the interference signal even when the modulation frequency of the injection current is high, which is higher than in the prior art. The displacement of the object can be accurately measured at high speed.

  According to the laser interference displacement measuring method of claim 2 and the laser interference displacement measuring apparatus of claim 6, it is possible to effectively eliminate the influence of the light intensity change of the laser light source that is unnecessary for the displacement measurement of the object. it can.

According to the laser interference displacement measuring method of claim 3 and the laser interference displacement measuring apparatus of claim 7, the constants A and B are eliminated by a simple arithmetic processing to obtain the phase α related to the distance P, and the object It becomes possible to measure the displacement. Furthermore, a feedback signal that variably controls the amplitude of the injected current can be generated from each value of the sampled interference signal so that the modulation amplitude included in the interference signal is constant.

  According to the laser interference displacement measuring method of claim 4 and the laser interference displacement measuring apparatus of claim 8, since the modulation amplitude Z becomes a constant value of Z = π which is a condition necessary for obtaining the phase α, It becomes possible to measure the displacement of the object.

  Hereinafter, preferred embodiments of a displacement measuring method and a displacement measuring apparatus using a laser interferometer according to the present invention will be described in detail with reference to the accompanying drawings. In FIG. 1 showing the overall configuration of the apparatus, reference numeral 1 denotes a laser interferometer that constitutes a Fizeau interference optical system. The laser interferometer 1 includes a semiconductor laser 10 that is a laser light source, and light emitted from the semiconductor laser 10. A lens 21 that collects light, a fiber 31 to 34 and a fiber coupler 35 that form an optical path, and a SELFOC lens 22 that is connected to the tip of the fiber 32 and is disposed to face the surface of the object O. Each has. Each of the fibers 31 to 34 has a base end connected to a fiber coupler 35 having a function of separating and coupling light, and the tip of the fiber 31 is disposed opposite to the lens 21, while the tips of the fibers 33 and 34 Are connected to photodiodes 41 and 42 which are photoelectric conversion means. In this embodiment, the optical fibers 31 to 34 are arranged in the optical path to constitute a flexible interference optical system in which the SELFOC lens 22 and the photodiodes 41 and 42 can be arranged at arbitrary positions. Alternatively, an interference optical system that does not use the fibers 31 to 34 may be used.

In the laser interferometer 1 in this embodiment, the light emitted from the semiconductor laser 10 is condensed on the end face of the fiber 31 by the lens 21 and distributed to the fibers 32 and 33 by the fiber coupler 35 through the fiber 31. Here, the light traveling through the fiber 32 is reflected part by the outgoing end face of the fiber 32 as the ginseng Thermen, the reference light. The light that has passed through the fiber 32 and the Selfoc lens 22 becomes parallel light and irradiates the surface of the object O, and the reflected light from the surface of the object O returns to the Selfoc lens 22 as object light. . The fiber 32, the fiber coupler 35, and the fiber 34 serve as a common transmission path for the object light and the reference light. On the detection surface of the photodiode 41 arranged on the end face of the fiber 34, the object light and the reference light are transmitted. It is supposed to interfere. On the other hand, the light passing through the fiber 33 distributed by the fiber coupler 35 reaches the detection surface of another photodiode 42 .

  The photodiode 41 corresponds to first photoelectric conversion means that captures interference light between the object light and reference light on a detection surface and obtains an interference signal S (t). Further, another photodiode 42 captures a part of the light emitted from the semiconductor laser 10 distributed by the fiber coupler 35 into the detection surface, and generates a detection signal indicating a temporal light intensity change I (t) of the semiconductor laser 10. This corresponds to the obtained second photoelectric conversion means. Each electric signal detected by the photodiodes 41 and 42 is input to a divider 43 described later.

Reference numeral 51 denotes a feedback control device that controls the injection current i (t) of the semiconductor laser 10 based on the detection results from the photodiodes 41 and 42. This feedback control device 51 divides the interference signal S (t) detected by the photodiode 41 by a detection signal representing the temporal light intensity change I (t), thereby obtaining a temporal light intensity change I. The divider 43 that outputs the interference signal S _D (t) from which the influence of (t) has been removed, and the phase α of the interference signal S _D (t) output from the divider 43 are obtained, and the output end face of the fiber 32 A change in the distance P between the object and the surface of the object O, that is, a displacement amount of the object O, and a change in the modulation amplitude Z included in the interference signal S _D (t) is detected. a signal processor 44 which generates a feedback signal SF in response to the change, the oscillation wavelength of the semiconductor laser 10 generates the injection current i (t) that varies sinusoidally, and by the feedback signal S _F, the distance P modulation amplitude Z of the interference signal S _D (t) is kept constant with respect to changes As such, a feedback controller 45 for feedback control of the amplitude a of the injection current i of the semiconductor laser 10 (t), the constructed.

  In the displacement measuring apparatus configured as described above, the laser interferometer 1 detects the interference light between the light emitted from the semiconductor laser 10 and the reflected light from the surface of the object O by the photodiode 41, while The present invention can be applied to any interference optical system in which a change in light intensity of the semiconductor laser 10 can be detected by another photodiode 42. Further, the photoelectric conversion element here is preferably a single photoelectric conversion element having good follow-up properties such as the photodiodes 41 and 42, as long as the light intensity changing with time can be measured in a short time.

Next, the operation principle of the above configuration will be described. First, in order to modulate the sinusoidal oscillation wavelength of the semiconductor laser 10 at the angular frequency omega _c, feedback controller 45 applies an injection current i (t) as shown in the following Equation 1 to the semiconductor laser 10.

In the above equation, I ₀ is the current reference value, a is the amplitude, and t is the time, and the injection current i (t) to the semiconductor laser 10 has an upper limit value I ₀ + a and a lower limit value I ₀ -a depending on the time t. Changes sinusoidally in the range. Further, when the modulation efficiency is β, the wavelength λ (t) of the semiconductor laser 10 to which the injection current i (t) is given is expressed as the following equation 2 , which is also the upper limit value λ ₀ depending on the time t. It changes in a sine wave form within the range of + βa and the lower limit value λ ₀ −βa. As an example, when the injection current i (t) is changed by 80 ± 1 mA, the shift amount of the wavelength λ (t) (and thus the phase) of the semiconductor laser 10 is about 0.02 nm.

In Equation 2 , λ ₀ is the center wavelength. In the semiconductor laser 10, the wavelength λ (t), that is, the oscillation frequency changes with time as in the above equation, but the optical output intensity also changes with time. Since this temporal change in light intensity is an obstacle to the displacement measurement of the object O, it is removed by the divider 43 provided in the feedback control device 51 in the subsequent stage.

In the laser interferometer 1, when laser light is emitted from the semiconductor laser 10 to which the injection current i (t) is given, the emitted light is condensed on the end face of the fiber 31 by the lens 21, and the inside of the fiber coupler 35. Is distributed to the fibers 32 and 33, respectively. The light passing through the fiber 33 reaches the detection surface of the photodiode 42 as it is, and is converted into a detection signal indicating a temporal light intensity change I (t) of the semiconductor laser 10. On the other hand, the light that Tsutawa Fiber 32, becomes a part of the reference reflected light at the exit end face of the fiber 32, the remaining light passes through fiber 32 and SELFOC lens 22, the target is parallel light It reaches the surface of the object O. The light reflected from the surface of the object O returns to the fiber 32 from the Selfoc lens 22 together with the reference light as object light, passes through the fiber 34, and interferes on the detection surface of the photodiode 41. The photodiode 41 converts this interference light into an interference signal S (t) and outputs it.

The signal processor 44 constituting the feedback control device 51 measures a change in the distance P from the selfoc lens 22 to the surface of the object O from the interference signal S (t) detected by the photodiode 41. However, since the amplitude of the interference signal S (t) is affected by the temporal light intensity change I (t) of the semiconductor laser 10, the divider 43 serves as a pre-measurement step in the signal processor 44. The interference signal S (t) is divided by the temporal light intensity change I (t) to obtain an interference signal S _D (t) from which the influence of the temporal light intensity change I (t) is removed. This interference signal S _D (t) can be expressed by the following equation ( 3 ).

In the above formula, A and B are constants. Z is a modulation amplitude, and α is a conventional phase, which can be expressed as the following equation ( 4 ).

FIG. 2 is a graph showing the signal of the modulation frequency component Zcosω _C t in Equation 3 , and the value of Zcosω _C t changes in the range of Z to −Z in a sine wave shape. The feedback control device 51 here preferably samples and acquires the interference signal S _D (t) at an interval of 1/8 (for each ω _C t = π / 4) with respect to one period of the modulation frequency. More specifically, as shown in FIG. 2, the value _{S 0} of the interference signal in cosω _C t = 0, the value _{S 1} of the interference signal in cosω _C t = 1/2, the interference signal at cosω _C t = 1 Value S ₂ , an interference signal value S _{3 at} cosω _C t = −1 / 2, and an interference signal value S ₄ at cosω _C t = −1 are detected. At this time, the values of the interference signals S _{0 to} S ₄ are as follows.

Here, when Z = [pi _{is, S C = S 0 -S 2} = 2Bcosα _next, since the _{S S = S 3 -S 1 =} 2Bsinα, to clear the constant B from each value of _{S C} and _{S S} The phase α is obtained, and the displacement of the object O can be measured from the relationship between the phase α and the distance P in Equation 4 above. Further, since the modulation amplitude Z changes with the distance P as shown in Equation 4, even if the distance P changes, the value of the modulation amplitude Z becomes constant (preferably Z = π, The signal processor 44 calculates the amplitude a of the injection current i (t) to the semiconductor laser 10 from each value of the sampled interference signal S _D (t) so that the phase α is accurately obtained by the processor 44). generating a feedback signal S _F to variably control.

Procedure for generating the feedback signal S _F is as follows. First, each value of S _Z = S ₄ -S ₂ and S _SZ = S ₃ -S ₁ is calculated using interference signal values S _{1 to} S ₄ detected by sampling. Each value of S _Z and S _SZ can be derived from Equation 5 as follows.

_Then, if _{S SZ} ≠ 0, to obtain a feedback signal _{S F} which is obtained by dividing the value of _{S Z} by the value of _{S SZ.} That is, the feedback signal _SF is represented by the following formula.

Therefore, if feedback control is performed on the injection current i (t) of the semiconductor laser 10 so that the feedback signal S _F = 0, the relationship of Z = π is maintained regardless of the change in the distance P, and the above S _C and It becomes possible to correctly calculate the phase α from each value of S _S.

An example of the feedback control device 51 that enables calculation of the phase α is shown in FIG. In the figure, a signal processor 44 having a preferable configuration is obtained by sampling means 61 for sampling and acquiring the interference signal S _D (t) at an interval of 1/8 with respect to one period of the modulation frequency, and acquired by this sampling means 61. The amount α of the interference signal is obtained from the values S _{0 to} S _{3 of the} interference signal, the displacement amount calculating means 62 for calculating the displacement amount of the object O, and the value of the modulation amplitude Z become constant even if the distance P changes. Furthermore, an injection current adjusting means 63 for adjusting the amplitude a of the injection current i (t) for the semiconductor laser 10 is provided.

More specifically, the sampling means 61 has values of cosω _C t of 0, 1/2, 1, −1/2, −1 when modulating the wavelength λ (t) of the semiconductor laser 10 into a sine wave. At the time (for example, when the phase of the modulation frequency is 0, π / 4, π / 2, 3π / 4, π), the value of the interference signal S _D (t) is set to S ₀ , S ₁ , S ₂ , Sampling is acquired as S ₃ and S ₄ . Further, the displacement amount calculating means 62 includes a first subtracting means 65 for calculating a value of S _C (= S ₀ −S ₂ ) from each value of S ₀ and S ₂ , and each of S ₁ and S ₃ . from the _value, and second subtraction means 66 for calculating a value of _{S S (= S 3 -S 1} ), obtains a phase α to clear the constant B from each value of _{S C} and _{S S,} in Formula 4 Displacement amount calculating means 67 for calculating the displacement of the object O from the relationship between the phase α and the distance P is provided. Further, the injection current adjusting means 63 includes a third subtracting means 68 for calculating the value of S _Z (= S ₄ −S ₂ ) from each value of S ₂ and S ₄ , and each of S ₁ and S ₃ . The value of the feedback signal S _F (= S _Z / S _SZ ) is calculated when the fourth subtraction means 69 for calculating the value of S _SZ (= S ₃ −S ₁ ) from the value and S _SZ is not 0. a division unit 70, so that the value of the feedback signal S _F obtained in this division means 70 becomes zero, and a vibrating amount calculating means 71 for calculating an optimal value of the amplitude a. Since the second subtracting means 66 and the fourth subtracting means 69 calculate the same value (S ₃ -S ₁ ), they may be constituted by a common subtracting means. Further, the displacement amount of the object O obtained by the displacement amount calculation means 67 is output in an arbitrary form to a display means, a printing means, a notification means or the like.

Next, an example of an experimental result using the displacement measuring apparatus of the present embodiment is presented. In the experiment, a piezoelectric element such as PZT was attached to the object O in order to displace the object O in a pseudo manner. The semiconductor laser 10 used had a center wavelength λ ₀ of 690 nm and an optical output of 25 mW. When the distance P between the exit end face of the fiber 32 and the surface of the object O is reduced to 25 mm, the frequency of sinusoidal phase modulation that maintains the relationship of Z = π is f _c = ω _C / The upper limit is 2π. In the current experiment, the upper limit modulation frequency f _c is about 1.5 MHz. The value of the phase α is so determined by using the values S ₀ to S ₃ of the sampled interfering signals, 3/8 period of the measurement time limit modulation frequency f _c (0.25μSec), namely in terms of frequency, (8/3) × f _c = 4 MHz, and the displacement of the object O can be measured correctly in a much shorter time than conventional.

When the distance P is 50 mm, the amplitude a of the injection current i (t) is adjusted so that an interference signal S _D (t) where Z = π is obtained, and at that time, the feedback signal S _F = 0. It was confirmed. It was also confirmed that the feedback signal S _F = 0 was maintained by feedback control when the distance P was changed in the range of 40 mm to 60 mm.

In the experiment, to a piezoelectric element attached to the object O, Yuki added stepwise voltage by V _{M /} 8 to 0 to V _M, given a change in each lambda _0/16 at a distance P, and the phase α It measured in the range of 0-2π. 4 to 6 show measurement results of the phase α when the distance P is 40 mm, 50 mm, and 60 mm, respectively. In the figure, the broken line is the theoretical value, and the solid line with the plot is the experimental value. As a result of obtaining the measurement accuracy from the difference between the experimental value and the theoretical value, it was ± 10 nm when the distance P = 50 mm, ± 18 nm when the distance P = 40 mm, and ± 20 nm when the distance P = 60 mm.

  Actually, by performing feedback control with a high modulation frequency of 1.5 MHz and a constant modulation amplitude Z, the displacement of the object O at a position where the distance P is 20 mm to 100 mm can be measured in a short measurement time of 0.25 μSec. It becomes possible to measure with high accuracy of 10 nm.

As described above, in the laser interference displacement measuring method in this embodiment, the injection current i (t) modulated in a sine wave shape is input to the laser light source 10, and the laser light source is changed while the wavelength λ (t) is changed with time. A first step of generating light (coherence light) from 10, and the light is divided and reflected by the surface of the object O and the exit end face of the fiber 32, which is the reference surface, A second step of combining the object light from the surface and the reference light from the emission end face of the fiber 32 to obtain interference light, and a third step of converting the interference light into an electrical interference signal S (t) With reference to the step and the sinusoidal modulation frequency, the interference signal S (t) obtained in the third step is sampled and acquired at regular intervals for one period of the modulation frequency, and the sampled and acquired signal is calculated. A fourth step of processing and measuring the displacement of the object O; It contains.

In order to realize this method, in the present embodiment, the light from the laser light source 10 is divided and reflected on the surface of the object O and the emission end face of the fiber 32, and then from the surface of the object O. The object light and the reference light from the output end face of the fiber 32 are combined to produce a laser interferometer 1 as an interference optical system for obtaining interference light, and the interference light obtained by the laser interferometer 1 is converted into an electrical interference signal S. A photodiode 41 as a first photoelectric conversion means for converting into (t) and an injection current i (t) modulated in a sine wave form are given to the laser light source 10 and light whose wavelength λ (t) varies with time is applied. The interference signal S (t) is sampled and acquired at regular intervals with respect to one period of the modulation frequency with reference to the feedback controller 45 as a modulation current generating means generated from the laser light source 10 and the sine wave modulation frequency. Get this sampling, Signals and processing has provided a signal processor 44 as a signal processing means for measuring the displacement of the object O, and the laser interferometric displacement measuring device provided with a.

According to the above method and apparatus, when the injection current i (t) modulated in a sine wave is input to the laser light source 10, the wavelength λ (t) of the light generated from the laser light source 10 is also changed to a sine wave. Become. The light from the laser light source 10 is reflected and interferes with the surface of the object O and the output end face of the fiber 32, and this interference light is converted into an electrical interference signal S (t) by the photodiode 41. Since the injection current i (t) input to the laser light source 10 repeats a sinusoidal change without a sudden rise or fall, the modulation frequency of the injection current i (t) increases to, for example, about 1.5 MHz. Also, the interference signal S (t) can be correctly sampled and acquired. Therefore, based on the sinusoidal modulation frequency, rather shorter than the time for displacement of the object O, if sampling obtain an interference signal S (t) at regular intervals with respect to one period of the modulation frequency, the sampling acquisition The displacement of the object O can be correctly measured by the arithmetic processing of the plurality of interference signals S (t).

Further, the laser interference displacement measuring method in the present embodiment includes the fifth step of converting the light intensity change I (t) of the laser light source 10 into an electrical detection signal and the interference signal S (t in the third step. ) By the detection signal obtained in the fifth step to obtain an interference signal S _D (t) from which the temporal light intensity change I (t) has been removed, and the fourth step, This step is characterized in that the interference signal S _D (t) obtained by removing the temporal light intensity change I (t) obtained in the sixth step is sampled and acquired.

Similarly, the laser interference displacement measuring apparatus according to the present embodiment includes a photodiode 42 as a second photoelectric conversion unit that converts a light intensity change I (t) of the laser light source 10 into an electrical detection signal, and a photodiode 41. Dividing the interference signal S (t) obtained in step 2 by the detection signal obtained by the photodiode 42, the division as a dividing means for obtaining the interference signal S _D (t) from which the temporal light intensity change I (t) has been removed. And an arithmetic unit 43.

In this case, when an injection current modulated in a sine wave shape is input to the laser light source 10, not only the wavelength λ (t) of the light from the laser light source 10 but also the intensity changes with time. Therefore, the light intensity change I (t) of the laser light source 10 is converted into an electrical detection signal by the photodiode 42, and the interference signal obtained from the interference light by another photodiode 41 is divided by the detection signal. Thus, if the interference signal S _D (t) from which the temporal light intensity change I (t) is removed is obtained, the influence of the light intensity change of the laser light source 10 which is unnecessary for the displacement measurement of the object O is eliminated. Can be effectively eliminated.

Further, in the laser interference displacement measuring method in the present embodiment, the injection current i (t) is expressed by the above equation 1 , the wavelength λ (t) of the laser light source 10 is expressed by the above equation 2 , and the time a when the interference signal light intensity change to remove S _D where (t) is expressed as in equation 3, in the fourth step, the cos .omega _C t is 0, 1 / 2,1, -1 / 2 the value _S 0 of the interference signal S _D (t) when _{the, S 1, S 2, S} 3 were respectively sampled acquisition, each of these values _{S 0,} S _1, S 2, interference from _{S 3} signal S _D ( included as modulation amplitude Z is constant in t), the amplitude a of the injection current i (t) to generate a feedback signal S _F to variably control, to erase the constants a, B contained in the equation (3) Thus, the phase α related to the distance P is obtained, and the displacement of the object O is measured.

Similarly, in the laser interference displacement measuring apparatus in the present embodiment, the values S ₀ , S ₁ , S of the interference signal S _D (t) when cosω _C t is 0, 1/2, 1, −1/2. _{2, S 3} were respectively sampled acquisition, as modulation amplitude Z is constant included from each of these values _{S 0,} S _1, S 2, _{S 3} to the interference signal S _D (t), the injection current i the amplitude a of the (t) to generate a feedback signal S _F to variably control, the constant a, and erases the B seeking the phase alpha, a signal processor 44 so as to measure the displacement of the object O I have.

In this case, the injection current i (t) is modulated in a sine wave shape with the current reference value I ₀ as the center, and the wavelength λ (t) of the laser light source also changes in a sine wave shape with time with the λ ₀ as the center wavelength. Here interference signal S _D to remove the temporal light intensity changing the value of (t), in 1 interval of 8 minutes to 1 cycle of the modulation frequency contained in the interference signal S _D (t), specifically Is obtained as S ₀ , S ₁ , S ₂ , and S ₃ when cosω _C t is 0, 1/2, 1, and −1/2, respectively, and constants A and B can be obtained by simple arithmetic processing. The phase α related to the distance P from the reference surface to the surface of the object O is obtained, and the displacement of the object O can be measured. Further, the respective values of the sampled interference signal S _D (t), as modulation amplitude Z contained in the interference signal S _D (t) is constant, variably controls the amplitude a of the injection current i (t) it is also possible to generate a feedback signal S _F.

Further, in the laser interference displacement measuring method in this embodiment, in the fourth step, the value S ₄ of the interference signal S _D (t) when the cosω _C t is −1 is further sampled and acquired (S by the value of _{4 -S 2) / (S 3} -S 1) is adjusted the amplitude a to be 0, always be further comprised seventh step of performing feedback control of the Z = [pi It is a feature .

Similarly, the laser interference displacement measuring apparatus in the present embodiment further samples and acquires the value S ₄ of the interference signal S _D (t) when the cos ω _C t is −1, and (S ₄ −S ₂ ) / There is provided a signal processor 44 that always performs feedback control such that Z = π by adjusting the amplitude a so that the value of (S ₃ -S ₁ ) becomes zero.

In this case, in addition to the value _{S 0,} S _1, S 2, _{S 3} of the interference signal _{S D (t), cosω C} t is acquired interference signal S value _{S 4} of the _D (t) when the -1 If the amount of the amplitude a of the injection current i (t) is feedback-controlled so that the value of the feedback signal _SF = (S ₄ -S ₂ ) / (S ₃ -S ₁ ) becomes 0, the modulation amplitude Z becomes a constant value (= π), which is a condition necessary for obtaining the phase α, and the displacement of the object O can be accurately measured.

  In addition, this invention is not limited to said each Example, A various deformation | transformation implementation is possible. For example, various light sources other than the semiconductor laser 10 can be used as long as the oscillation wavelength λ (t) is changed by changing the injection current i (t). Further, the function as the divider 43 may be included in the signal processor 44.

It is a schematic explanatory drawing which shows the whole structure of the laser interference displacement measuring apparatus in one preferable Example of this invention. It is a graph which shows a time change of a phase modulation signal same as the above. It is a block diagram which shows the function structure of a signal processor same as the above. FIG. 6 is a graph showing the relationship between the voltage applied to the piezoelectric element and the phase α when the distance P = 40 mm. FIG. 6 is a graph showing the relationship between the voltage applied to the piezoelectric element and the phase α when the distance P = 50 mm. FIG. 6 is a graph showing the relationship between the voltage applied to the piezoelectric element and the phase α when the distance P = 60 mm. It is a graph which shows an example of the modulation signal with respect to the semiconductor laser which shows a prior art example.

1 Laser interferometer (interference optical system)
10 Laser light source
41 Photodiode (first photoelectric conversion means)
42 Photodiode (second photoelectric conversion means)
43 Divider (Division means)
44 Signal processor (Signal processing means)
45 Feedback controller (Modulation current generator)
O Object

Claims (8)

A first step of inputting a sinusoidally modulated injection current to a laser light source and generating light from the laser light source while changing the wavelength with time;
A second step of obtaining interference light by dividing the light and reflecting the light on the surface of the object and the reference surface, and then combining the object light from the surface of the object and the reference light from the reference surface When,
A third step of converting the interference light into an electrical interference signal;
Using the sinusoidal modulation frequency as a reference , the interference signal is sampled and acquired at regular intervals with respect to one period of the modulation frequency, and each sampled and acquired signal is arithmetically processed to measure the displacement of the object. And a step of measuring a laser interference displacement. A fifth step of converting the light intensity change of the laser light source into an electrical detection signal;
A sixth step of dividing the interference signal in the third step by the detection signal to obtain an interference signal from which the temporal light intensity change is removed, and
In the fourth step, the interference signal obtained by sampling the interference signal from which the temporal change in light intensity obtained in the sixth step is sampled and acquired. Before Symbol fourth step, at 1/8 of the interval for one period of the modulation frequency contained in the interference signal, the value of the interference signal, respectively sampled acquired from each of these values, the interfering signal as modulation amplitude includes a constant, the amplitude of the injection current to generate a feedback signal for variably controlling obtains a position phase of the interference signal from the signal the sampling acquisition, a displacement of the subject matter 3. The laser interference displacement measuring method according to claim 2, wherein measurement is performed. 4. The laser interference displacement measuring method according to claim 3, further comprising a seventh step of performing feedback control so that the value of the modulation amplitude becomes π in the fourth step. Interference to obtain interference light by dividing light from the laser light source and reflecting it to the surface of the object and the reference surface respectively, and then combining the object light from the object surface and the reference light from the reference surface Optical system,
First photoelectric conversion means for converting interference light obtained by the interference optical system into an electrical interference signal;
A modulation current generating means for applying a sinusoidally modulated injection current to the laser light source, and generating a light whose wavelength changes with time from the laser light source;
A signal for measuring the displacement of the object by sampling and acquiring the interference signal at regular intervals with respect to one period of the modulation frequency with the sinusoidal modulation frequency as a reference , and calculating and processing each sampled and acquired signal And a laser interference displacement measuring apparatus. Second photoelectric conversion means for converting a light intensity change of the laser light source into an electrical detection signal;
Dividing means for dividing the interference signal obtained by the first photoelectric conversion means by the detection signal obtained by the second photoelectric conversion means to obtain an interference signal from which temporal light intensity change has been removed, further comprising 6. The laser interference displacement measuring apparatus according to claim 5, wherein The signal processing means samples and acquires the value of the interference signal at an interval of 1/8 with respect to one period of the modulation frequency included in the interference signal, and is included in the interference signal from each of these values. as the modulation amplitude is constant, the amplitude of the injection current to generate a feedback signal for variably controlling obtains a position phase of the interference signal from the signal the sampling acquisition, measures the displacement of the subject matter The laser interference displacement measuring apparatus according to claim 6, wherein the apparatus is a laser interference displacement measuring apparatus. 8. The laser interference displacement measuring apparatus according to claim 7, wherein the signal processing means performs feedback control so that the value of the modulation amplitude becomes π .

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