JPH087044B2 - Displacement measuring device for pattern that crosses spatial filter detector and light receiving element - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the field of non-contact measurement, and in particular, constitutes a spatial filter detector composed of a plurality of light receiving element groups and is formed on this detector. The present invention relates to an adaptive spatial filter detector that detects movement of a regular or irregular pattern of an object to be measured and measures displacement, velocity, vibration, etc. of the object to be measured.

(Prior Art) In a basic spatial filter detector, a plurality of light receiving elements are arranged at equal intervals in a comb-tooth shape to form a set of detectors, and a pattern of an object to be measured formed on the detector is formed. The periodic output change detected each time each unit crosses the light receiving element and the repetition thereof are counted, and this is multiplied by the pitch of the comb to obtain the movement amount of the pattern in the direction orthogonal to the comb. However, since one set of comb-shaped detectors carries a large direct current component on the output, normally, in order to remove them, the difference between the two sets of comb-shaped detectors shown in FIG. Dynamic spatial filter detectors have been developed. Specifically, the pattern 70 formed by irradiating the measured object surface with light
The photodetector 71 is arranged on the surface of the pair of comb-shaped detectors 72, 73.
And each output accompanying the movement of the pattern is amplified by the differential amplifier 74, an output signal as shown in FIG. The movement amount of the pattern is obtained by counting the period of this signal and multiplying it by the pitch of the comb.

(Problems to be Solved by the Invention) However, although the differential spatial filter detector described above is suitable for measuring a regular pattern, for example, an irregular (random) pattern such as a speckle pattern is used. In the case of detecting the movement of, there may be a pattern that does not have the spatial frequency component selected by the spatial filter, so the output signal disappears at this time, and the amount of movement of the pattern can be measured. could not. Further, since the output shows the same change regardless of which direction the pattern moves with respect to the comb, the moving direction (sign) cannot be obtained. Therefore, the displacement, vibration, deformation, etc. of the object cannot be measured stably, and the measurement range is limited.

In view of the above problems of the conventional spatial filter detector, the present invention does not lose the output signal even when the random pattern generated from the measured object surface moves, its speed, displacement, vibration, etc. It is an object of the present invention to provide a new type of spatial filter that measures a high resolution.

(Means for Solving the Problem) The above problem is that a plurality of spatial filter detectors are configured by changing the combination of connections between outputs of light receiving elements arranged at equal intervals. This can be solved by comparing the amplitudes of the output signals and adopting the signal with the largest amplitude among them.

Further, in the spatial filter detector, the signals of the sine component and the cosine component detected by the movement of the pattern on each of the constituted detectors are taken out, the phase of the output signal is obtained from the arctangent of the ratio, and the square thereof is obtained. This can be solved by obtaining the amplitude of the output signal from the sum and then accumulating the phase increments of the signal having the largest amplitude to measure the movement amount and the movement direction of the pattern.

(Operation) Here, with respect to the respective light receiving sensitivities in which four types of differential outputs are taken out by changing the combination of the connections between the outputs composed of a plurality of slit-shaped light receiving elements arranged at equal intervals of the present invention,
This will be described with reference to the sensitivity distribution chart 30 in FIG.

As represents the sensitivity distribution of the conventional differential spatial filter detector. This can be represented as described above because two element arrays corresponding to positive and negative values are combined to take the differential between the outputs of the respective light receiving elements. In the present invention, this is
A spatial filter detector that gives three sensitivity distributions of c, Bs, and Bc is added, and a total of four types of output signals are processed to detect pattern movement with high accuracy. First, the combination of As and Ac outputs is SFD1, and the combination of Bs and Bc outputs is SFD2. The phase of the frequency response is deviated by π / 2 between As and Ac and Bs and Bc, respectively, and the sin component and cos of SFD1 and SFD2 respectively
Output the component. In addition, Bs and Bc are out of phase with each other by π compared to As: Ac. By shifting the phase from the middle in SFD2, the frequency response of SFD1 and SFD2 shifts, and when they disappear, the other usually remains. That is, when the pattern moves onto the detector, SFD1
Different signals can be taken out from SFD2 and SFD2, respectively, even if they have the same period. If one signal disappears, the other signal is compensated. That is, the problem of signal loss can be solved by extracting [SFD (1 + 2)] only for the larger amplitude of SFD1 and SFD2.

FIG. 5 is an output waveform of SFD1 obtained by arithmetically processing As and Ac in the sensitivity distribution chart 30 in FIG. 3, and FIG.
Is an object displacement-amplitude, and FIG. 7B is an object displacement-phase diagram. Since As and Ac output the sin and cos components of SFD1, the amplitude of SFD1 is obtained from the square of each square sum, and the phase of SFD1 is obtained from the arctan of each ratio. In the area (A) where the amplitude is small (for example, where the object displacement is 2.6 to 2.7 mm, 3.7 to 3.8 mm), the spatial frequency component selected by the spatial filter detector disappears in the pattern on the detector. Since it is doing, at this time (B) in the same figure
The phase of is also disordered.

FIG. 6 is an output waveform of SFD2 obtained by arithmetically processing Bs and Bc as in FIG. Output of SFD1 in Figure 5 and 6
The outputs of SFD2 in the figure do not match when each output disappears even though the same pattern on the detector is detected. From this, it is understood that only the one having the larger amplitude needs to be extracted from the two signals SFD1 and SFD2. For example, when the object displacement is around 2.6 mm, SFD2 is adopted and 2.0
SFD1 is adopted in the vicinity of mm.

The phase of the obtained output signal gives the amount of movement of the pattern on the detector. Here, the amount of movement of the object can be obtained by successively comparing the amplitudes of the two signals SFD1 and SFD2, accumulating the larger phase increments, and converting the amount of change into the amount of movement of the object. Furthermore, the moving direction of the pattern can be determined by increasing or decreasing the phase with respect to the object displacement.

Since the detector of the present invention can be constructed only by changing the combination of the connections between the outputs of the slit-shaped light receiving elements, it is possible to use the same structure as the conventional spatial filter detector.

(Effects of the Invention) As described in detail above, the present invention arranges a plurality of sets of spatial filter detectors each including a light receiving element array, and selects the one having the largest amplitude from the obtained output signals. Since it is adopted, there is no problem of signal loss even if the pattern on the detector due to the movement of the object is a random pattern such as a speckle pattern. In the signal processing system,
Since the amount of movement of the pattern is changed to the amount of change of the phase, it is possible to measure with a resolution less than the pitch of the detector, and moreover, it becomes possible to easily obtain the movement direction of the pattern by increasing or decreasing the phase with respect to the object displacement.

The spatial filter detector of the present invention, in the spatial domain,
Real-time measurement is possible because the signals are processed in parallel. Further, by using the speckle pattern, the displacement or deformation amount of the object can be known. Furthermore, since the resolution is less than the pitch of the detector, by making the pitch between the light receiving elements finer, the resolution becomes higher and the measurement range becomes wider. Therefore, the adaptive spatial filter detector of the present invention has an extremely high industrial utility value.

(Example) Below, the Example of this invention is described in detail.

FIG. 1 is a block diagram of the entire apparatus for carrying out the present invention. Spot on the rough surface object 12 surface of the aluminum plate installed on the stepping motor moving table (10 μm / step) 11 that moves the laser beam emitted from the He-Ne laser light source 10 with the wavelength of 632.8 nm in the in-plane direction. With a diameter of 0.6 mm, speckles are generated in the diffusely reflected light, which is received by the spatial filter detector 13 of the present invention. The detector composed of the light receiving element is composed of a one-dimensional image sensor,
The pitch of the comb was 160 μm, and the number of element sets was 32. Since the speckle pattern moves along with the displacement of the rough surface object, the amount of movement of the object can be obtained by detecting this amount of movement. The processing system fetches the outputs of As, Ac, Bs, and Bc into the A / D converter 14, and the computer 15 processes the values thereof. The results obtained are recorded on plotter 16. Further, the stepping motor 17 receives a signal from the computer and drives at a minimum of 1 μm / step.

FIG. 2 is an example of the spatial filter detector 13 of the present invention shown in FIG. 1, and is a configuration diagram of a detector showing a configuration of a light receiving element and a connecting portion between outputs from each element. The number of light receiving elements is 128, and the detector has the light receiving sensitivity in Fig. 3 As and A in Fig. 30.
The connections are c, Bs, and Bc. In FIG. 2, in the middle (element numbers 64 and 65) of the light receiving element row (element numbers 1-128).
(Dashed line portion), and each of the four elements, for example, element numbers 1 to 4 is combined to perform differential amplification of the first element and the third element and the second element and the fourth element. Is configured as follows. Since four elements are combined into one group, the number of element groups is 32. For example, the light receiving element in FIG.
In order to achieve this, differential amplification is performed with the second element (element number 2) being positive and the fourth element (element number 4) being negative on the left side and the right side from the middle of the light receiving element array. On the other hand, Bs
Is the same as As from the middle of the light receiving element row to the left side, but the second element (element number 66) is negative on the right side and is 4
Differential amplification is performed with the element number (element number 68) being positive. Ac,
The same applies to Bc. By configuring the combination of connections in this way, the light receiving element can be shifted from the middle by π.

FIG. 3 shows signals (As, As, detected by the detector of FIG. 2).
It is a block diagram showing a processing system of Ac, Bs, Bc). With SFD1
The amplitudes of SFD2 are compared and the larger phase component is accumulated.
The As and Ac signals are input to the squarers 31 and 31 ',
Calculate the amplitude of SFD1 by taking the sum of the two. In parallel with this, the ratio of As and Ac is taken, and this is input to the arctangent function generating circuit 32 to obtain the phase of SFD1. This phase and the immediately preceding phase are input to the subtractor 35 to obtain the phase increment.
The immediately preceding phase is obtained through the delay unit 33, and the subtractor 35 always outputs the phase increment of SFD1. The same process is performed for SFD2, and the subtractor 35 'always outputs the phase increment of SFD2. Here, the comparator 34 compares the amplitude of SFD1 with the amplitude of SFD2, and extracts only the larger phase increment. This is accumulated in the accumulator 36 and is output. The symbols 1 to 3 in FIG. 3 correspond to the symbols in FIGS. 5 (A) and 5 (B).

FIG. 4 shows the amount of movement of the speckle pattern on the detector measured by applying the detector having the configuration of the light receiving element shown in FIG. 2 to FIG. Rough surface object to be measured is 10 μm /
It is a measured value when the step is moved back and forth by 5 mm.
[SFD (1 + 2)] in the figure is the measurement result according to the present invention. For comparison, the measurement results of SFD1 and SFD2 alone were also recorded. As can be seen from the signal loss point a of SFD1 and the signal loss point b of SFD2 in the figure, it is clear from [SFD (1 + 2)] that if one cannot be measured, the other is compensated, and the measurement is performed accurately. It is understood that Also, during the measurement time of 5 to 10 seconds, the object is moving in the opposite direction, and since the phase is decreasing at this time, the moving direction of the measured object can be determined, so the absolute position of the object is measured. Is possible. That is, it was found from the figure that the displacement measurement can be performed faithfully by the adaptive spatial filter detector of the present invention by comparing with the movement amount of the stepping motor.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an entire apparatus for carrying out the present invention, FIG. 2 is a configuration example showing an array of light receiving elements and connections between respective outputs of the present invention, and FIG. 3 is a second example of the present invention. FIG. 4 is a block diagram showing a signal processing system detected by the detector shown in FIG. 4, FIG. 4 is a phase diagram showing a measurement result of the present invention performed using a rough surface object, and FIGS. 5 (A) and 5 (B) are sensitivity. Output waveforms of the distributions As and Ac and output waveforms of the SFD1 amplitude and phase obtained by calculating the output waveforms, FIGS. 6 (A) and (B) are the same as those in FIGS. 5 (A) and (B).
Output waveforms of s and Bc and SFD2 obtained by arithmetic processing
FIG. 7 (A) and FIG. 7 (B) are an output waveform diagram of the differential type spatial filter detector and its output waveform diagram. (Description of symbols) 10 …… Laser beam, 11 …… Stepping motor moving base, 12 …… Rough surface object, 13 …… Spatial filter detector, 14 …… A / D converter, 15 …… Computer, 16 …… Plotter , 17 ... Stepping motor, 30 ... Sensitivity distribution map (spatial filter detector), 31, 31 ', 37, 37' ... Squarer, 32, 32 '... Inverse tangent function generation circuit, 33, 33' …… Delay device, 34 …… Comparator, 35,35 ′ …… Subtractor, 36 …… Accumulator, 70 …… Pattern, 71 …… Light receiving element, 72,73 …… Combic spatial filter detector, 74 ...... Differential amplifier.

Front page continued (72) Inventor Hidenori Nagayama 1-2-7-4 Yaguchi, Ota-ku, Tokyo Inside Ono Sokki Technical Center Co., Ltd. (56) Reference JP-A-2-278312 (JP, A) -67214 (JP, U)

Claims (2)

[Claims] 1. A first characteristic, As, in which light receiving elements arranged at equal intervals are provided, and a light receiving sensitivity characteristic with respect to a detection position changes periodically with an increase in the detection position, and a periodic change of the first characteristic. And the second characteristic Ac which changes by 90 degrees in phase
A third characteristic Bs that changes in the same manner as the first characteristic until reaching the predetermined detection position, and changes in a different phase when the predetermined detection position is exceeded, and the third detection position The spatial filter detector including a fourth characteristic Bc that changes in the same manner as the second characteristic up to the above, and changes in a different phase when the predetermined detection position is exceeded. 2. A first characteristic, As, in which light-receiving elements arranged at equal intervals are provided, and a light-receiving sensitivity characteristic with respect to a detection position periodically changes with an increase in the detection position, and a periodical change of this first characteristic. And the second characteristic Ac which changes by 90 degrees in phase
A third characteristic Bs that changes in the same manner as the first characteristic until reaching the predetermined detection position, and changes in a different phase when the predetermined detection position is exceeded, and the third detection position Up to the above-mentioned second characteristic, and a spatial filter detector including a fourth characteristic Bc which changes in a different phase when it exceeds the predetermined detection position. Connected to a container and having the first characteristic
A second square circuit 31 that squares the first output signal of As, a second square circuit 31 ′ that squares the second output signal of the second characteristic Ac, and a second square circuit 31 ′ of the third characteristic Bs. Third square circuit 37 squares the output signal of No. 3, fourth square circuit 37 'squares the fourth output signal of the fourth characteristic Bc, the first and second square circuits 31, A first adder circuit for adding the output signals of 31 ', a second adder circuit for adding the output signals of the third and fourth square circuits 37, 37', and the first and second adder circuits Comparing and discriminating circuit for discriminating which output is larger, a first dividing circuit for obtaining a ratio between the first output signal and the second output signal, and the third Second division circuit for obtaining the ratio of the output signal of the second output signal to the fourth output signal, a first arctangent function generation circuit connected to the first division circuit, and the second Second arctangent function generating circuit connected to the division circuit, first delay circuit 33 connected to the first arctangent function generating circuit, connected to the second arctangent function generating circuit A second delay circuit 33 ', a first subtraction circuit 35 connected to the first arc tangent function generating circuit and the first delay circuit, and a second arc tangent function generating A second subtraction circuit 35 'connected to the circuit and the second delay circuit, the comparison / determination circuit and the first and second subtraction circuits 35,
A switch circuit connected to 35 ', which selects the phase difference having the larger amplitude in response to the output of the comparison / discrimination circuit, and an accumulator circuit 36 connected to this switch circuit. Displacement measuring device that crosses the light receiving element.