JP3418234B2 - Length measuring device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a length measuring device capable of measuring the length of a standard scale with high accuracy.

[0002]

2. Description of the Related Art Conventionally, as a length measuring machine, for example, Japan Society for Precision Engineering Vol. 44, No. 2, "Laser interferometer for measuring 2 m standard scale (second
Report) ”. This will be described with reference to FIGS. 5 and 6. A detection optical system 15a is mounted on the movable table 10 and moves in the measurement direction. The amount of movement in this case is measured as follows. That is, the laser light from the laser light source 1 passes through the reflecting mirror 30 and the interferometer 3
Each laser light is branched by the reflecting mirrors 31 and 32 to the reference mirror 37 and the movable mirror 6 fixed to the movable table 10, passes through the same path again, interferes with the interferometer 3, and then is reflected by the reflecting mirror 33. It is measured by the detectors 8 and 9 via the prism 34. The image of the scale line engraved on the standard scale 13 from the detection optical system 15 is transmitted through the relay lens 36 to the slit 35.
And is detected by the photoelectric conversion element 38. The output of the photoelectric conversion element 38 is amplified by the amplifier 39 and differentiated by the differentiator 40.

In this case, by adjusting the width of the slit 35, a waveform as shown in FIG. 6 can be obtained, and the output of the differentiator 40 can determine the center of the scale line . In the example of FIG. 5, the movable mirror 6 and the standard scale 13 are not arranged on the same axis, and for the following reason, the Abbe (Ab
The basic theorem of be) is not satisfied. That is, the basic theorem is that in a laser length measuring machine or the like for measuring length, the length to be measured and the dividing scale line used as a scale should be arranged so as to be aligned on a straight line in the measuring direction. Is the theorem that minimizes the error.

However, in the example of FIG. 5, Abbe (Abb
The reason why the basic theorem of e) is not satisfied is that there is a drawback that the whole apparatus becomes large in size if it is configured to satisfy the basic theorem.

Therefore, in the example of FIG. 5, the distance from the standard scale 13 to the measurement axis, that is, the movable mirror 6, and the detection optical system 1
5 is matched with the focal length of a objective lens is made to satisfy the condition of the edge Ben Stein (Eppenstein).

[0006]

However, in the example of FIG. 5, it is necessary to adjust the width of the slit 35 by the image of the scale line, and fine adjustment is required. In addition, standard scale 1
Not all 3 scale line widths are manufactured to have the same line width, and variations in this scale line width cause an error.

Further, in order to satisfy the conditions of Ebbenstein, an objective lens having a long focal length is required, and it is conceivable that the apparatus becomes complicated and large-sized. The present invention has been made in order to solve the above-mentioned problems, can eliminate Abbe's error, does not cause an error due to fluctuation of the scale line width, enables highly accurate measurement, and requires adjustment of the slit interval or the like. It is an object of the present invention to provide a length measuring device which is easy to perform, and is suitable for higher speed.

[0008]

In order to achieve the above object, the invention according to claim 1 provides a movable table movable in a measuring direction of an object and an edge of the object image provided on the movable table. An edge detection optical system for detecting, a laser light source for emitting a laser beam, and the edge detection on the movable table.
The movement with respect to the measurement point of the subject by the output optical system
The positional relationship is symmetrical in the direction orthogonal to the moving direction of the platform.
A movable mirror arranged two sea urchin, the edge detection optical system
According to the measurement point of the subject,
Two pieces are arranged so as to have a symmetrical positional relationship with the direction orthogonal to the direction.
Is location, the and the moving base laser interferometer detecting a moving amount of photoelectrically converting an edge of the detected object image in the edge detection optical system based on the laser light from the laser light source reflected by the movable mirror , Latch signal generating means for generating a latch signal, and two position data obtained by the two laser interferometers based on the latch signal generated by the latch signal generating means, and these two positions A data processing means for averaging the data to obtain length measurement data is provided.

To achieve the above object, in the invention according to claim 2, the latch signal generating means includes a rising edge detecting section and a falling edge detecting section, and each of the detecting sections generates a latch signal. , A first position data is fetched from the latch signal by the rising edge detector
A laser interferometer, and a second laser interferometer that captures second position data from the latch signal by the fall detection unit,
It said first, averaging said second position data, the object scene
2. The length measuring apparatus according to claim 1, further comprising: a data processing unit for obtaining length measuring data of the body .

In order to achieve the above object, the invention according to claim 3 is that the latch signal generating means compares a threshold value and a detection area with a window comparator and the threshold value and the detection signal. a comparator for, the
A length measuring apparatus according to claim 1, characterized by including.

[0011]

According to the invention corresponding to claim 1, the moving amount of the moving table is measured by the two laser interferometers arranged so as to have a symmetrical positional relationship with respect to the measuring point, and the two measured values are measured. By averaging the data, the Abbe error due to the tilt of the moving table can be eliminated, so that the error due to the fluctuation of the scale line width does not occur, and highly accurate measurement is possible, and the slit interval is adjusted. The length can be easily measured without the need for.

According to the inventions corresponding to claims 2 and 3, the rising edge and the falling edge are detected separately, and the respective data are averaged to obtain the length measurement data, which is suitable for high speed operation. , Drift such as temperature can be minimized.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of one embodiment of the present invention, which is configured as follows. Guide members 14a and 14b arranged in parallel with each other in the measurement direction, a movable base 10 movable along the guide members 14a and 14b, and arranged on the movable base 10 in the measurement direction. and a movable mirror 6, an edge detecting optical system 15 to be described later is disposed on the moving table 10 for detecting the edge of the workpiece (end), standard scale 1 which is disposed in a substantially central portion of the moving base 10
3, a motor 11 for giving a moving force to a moving table 10 having such movable mirrors 6, 7, a standard scale 13, and an edge detecting optical system 15, and a rotating force of the motor 11 fixed to the moving table 10 for moving the moving table 10 A steel tape 12 for transmitting the laser beam from the laser light source 1, a beam splitter 2 for branching the laser light from the laser light source 1 to the movable mirror 6, and a beam bender 4 for guiding the light split by the beam splitter 2 to the movable mirror 7. A first laser interferometer 3 arranged between the beam splitter 2 and the movable mirror 6.
A second laser interferometer 5 arranged between the beam bender 4 and the movable mirror 7, a detector 8 for detecting the output of the laser interferometer 3, and an output of the laser interferometer 5. Detector 9 to detect
And a signal processing unit (not shown), which will be described later, for performing signal processing for inputting the detection outputs of the detectors 8 and 9 and outputting length measurement data.

The operation of the embodiment thus configured will be described below. The laser light from the laser light source 1 is split by the beam splitter 2 and is incident on the second laser interferometer 5 via the first laser interferometer 3 and the beam bender 4.

The laser light emitted from the interferometers 3 and 5 is
It is coincident with the measurement point in the height direction, and is line-symmetrically separated by an equal distance L1. 3,5 in total
The detector 8 and 9 detect the amount of movement of the movable table 10 by interfering with the reference light inside.

The movable table 10 is driven by a motor 11 and a steel tape 12 along guide members 14a and 14b which are arranged in parallel with each other in the measuring direction of the standard scale 13 at intervals.

In such a structure, for example, the moving table 1
Even if 0 moves while tilting in the direction of the arrow shown in FIG. 1 (the yawing direction), since the moving distance is measured at the line-symmetrical position at the same distance from the measurement point of the standard scale 13, two data are measured. By averaging, the Abbe error can be eliminated.

FIG. 2 is a view showing the schematic arrangement of the edge detection optical system 15, which includes a light source 16, a lens 17, and a half mirror 1.
8, objective lens 19, imaging lens 20, pinhole 2
1. The photoelectric conversion element 22.

Specifically, the light emitted from the light source 16 is
The light passing through the lens 17, bent by the half mirror 18, illuminated on the scale line of the standard scale 13 via the objective lens 19, and reflected from the scale line of the standard scale 13 enters the objective lens 19 again, Pinhole 2 by imaging lens 20
Projected onto 1. Then, the light passing through the pinhole 21 enters the photoelectric conversion element 22 and is converted into an electric signal.

FIG. 3 is a diagram showing a schematic structure of a signal processing means for processing the output of the photoelectric conversion element 22. The current-voltage conversion circuit (IV) 41 and the window comparator 4 are shown in FIG.
2, the comparator 43, the inverters 44 and 45, and the flip-flops 46 and 47.

Specifically, the output of the photoelectric conversion element 22 is
The voltage signal is converted by the current-voltage conversion circuit 41 and input to the window comparator 42 and the comparator 43. The signal input to the window comparator 42 is an arbitrary threshold value VT, that is, (Vmax + Vmi in FIG. 4).
n) ÷ 2 and the window width Vw, the detection enable signal is input to the clear terminals (CLR) of the flip-flops 46 and 47 via the inverter 44, and the window comparator 42 outputs the high level signal when the window is high. Edge detection is permitted when the level is (High).

The signal input to the comparator 43 is output as an edge signal binarized by an arbitrary threshold value. This edge signal is input to the clock terminal of the flip-flop 46 via the inverter 45. Then, the outputs of the flip-flops 46 and 47 are low (Lo) at the rising edge of the clock pulse as shown in FIG.
w) and becomes High when Low is input to the clear terminal. Therefore, the outputs of the flip-flops 46 and 47 become the rising latch signal and the falling latch signal, respectively, as shown in FIG.

The operation of the embodiment described above will be described with reference to the timing chart of FIG. Now, it is assumed that the output waveform as shown in FIG. 4 is obtained from the photoelectric conversion element 22. In this case, when the edge detection optical system 15 passes through the scale line 13a of the standard scale 13, the threshold value VT is set at 50% where the voltage value difference appears due to the light and darkness due to the reflection of the scale line 13a.
Then, the edge of the scale line 13a can be detected.

The above is the graduation line 13b which is engraved on the standard scale 13 with a predetermined distance from the graduation line 13a.
Is also the same. Then, the rising latch signal obtained from the threshold value VT is used, for example, as the length measurement data of the laser interferometer 3, and the falling latch signal is used as the length measurement data of the laser interferometer 5. Then, by inputting these length measurement data to a data processing unit (not shown) and averaging the two length measurement data here, the center-to-center distance L between the scale line 13a and the scale line 13b can be obtained.

This center-to-center distance L eliminates the Abbe error due to the inclination of the moving table 10, and the scale lines 13a, 1
Even if 3b changes, the center-to-center distance L does not change, and highly accurate measurement can be performed.

Further, depending on the width of the scale lines 13a and 13b,
The work of adjusting the slit spacing, which was necessary in the past, is no longer necessary, and the length can be easily measured. Further, even for a minute scale line width, since the rising edge and the falling edge are detected separately, it is suitable for speeding up, and the drift of illumination, temperature, etc. can be minimized.

In the above-described embodiment, the threshold value VT is 50.
% And it was, but may be any value not a critical condition when measuring the center-to-center distance. Furthermore, in the embodiment, the edge detection optical system 15 is used for epi-illumination, but this may be performed for transmitted illumination. Further, the same effect can be obtained even if the pinhole 21 of the embodiment is formed of a slit.

[0028]

According to the present invention, the Abbe error can be eliminated, the error due to the fluctuation of the scale line width does not occur, the highly accurate measurement is possible, and the slit interval need not be adjusted.
It is possible to provide a length measuring device that can be easily performed and is suitable for higher speed.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a first embodiment of a length measuring device according to the present invention.

FIG. 2 is a diagram for explaining an edge detection optical system 15 of FIG.

FIG. 3 is a diagram for explaining the signal processing means of FIG.

FIG. 4 is a timing chart for explaining the operation of FIG.

FIG. 5 is a schematic configuration diagram showing an example of a conventional length measuring device.

6 is a diagram for explaining a circuit that processes an output signal of the photoelectric conversion element in FIG.

[Explanation of symbols]

1 ... Laser light source, 2 ... Beam splitter, 4 ... Beam bender, 3, 5 ... Laser interferometer, 6, 7 ... Movable mirror, 8, 9
... Detector, 10 ... Moving base, 11 ... Motor, 12 ... Steel tape, 13 ... Standard scale, 14a, 14b ... Guide member,
15 ... Edge detection optical system, 16 ... Light source, 17 ... Lens,
18 ... Half mirror, 19 ... Objective lens, 20 ... Imaging lens, 21 ... Pinhole, 22 ... Photoelectric conversion element.

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01B 9/00-11/30

Claims (3)

(57) [Claims] 1. A movable table movable in a measurement direction of an object, an edge detection optical system provided on the movable table for detecting an edge of the object image, a laser light source for emitting a laser beam, and the movable table. In the above, the object detected by the edge detection optical system is
The measurement point of the body is orthogonal to the moving direction of the movable table.
Two movable mirrors are arranged so as to have a symmetrical positional relationship with each other, and a measurement point of the subject by the edge detection optical system.
A position symmetrical with the direction orthogonal to the moving direction of the movable table.
Are arranged two such that the relationship, a laser interferometer for detecting the movable carriage moving amount based on the laser light from the laser light source reflected by the movable mirror, detected by the edge detecting optical system subject Latch signal generating means for photoelectrically converting the edge of the image to generate a latch signal, and two positions obtained by the two laser interferometers based on the latch signal generated by the latch signal generating means. > A data measuring device which takes in data and averages these two position data to obtain length measurement data. Wherein said latch signal generating means comprises a rising edge detector and the falling detection unit, respectively to generate a latch signal to the respective detector, the first position from the latch signal from the rising edge detector
A first laser interferometer capturing location data, a second laser interferometer incorporating a second position data <br/> data from the latch signal by the falling detection unit, said first, said second position data were averaged, the object scene
2. The length measuring device according to claim 1, further comprising: a data processing unit for obtaining length measuring data of the body . Wherein said latch signal generating means comprises claims, characterized and window comparator capable of setting thresholds and detection region, a comparator for comparing said detection signal with said threshold value, by comprising the 1. The length measuring device according to 1.