JP2001041730A - Linear scale - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate gap adjustment of a linear scale. SOLUTION: A reflecting plate 52 is mounted on a main scale substrate 50, and a reflector type detecting element 62 for gap adjustment is installed on a holder 60 movable along the main scale substrate 50. And, determination whether a gap (d) between the main scale substrate 50 and the holder 60 is in a proper range or not is executed, based on a detection output detected by the reflector type detecting element 62, and if the gap (d) is in the proper range, an indicator 63 is lit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear scale for measuring an amount of relative movement between two objects, and is particularly suitable for installation on a machine tool or the like.

[0002]

2. Description of the Related Art In a machine tool or the like, it is extremely important to accurately measure a relative movement amount of a tool with respect to a workpiece in performing precision machining, and various measuring devices have been commercialized. . Measuring devices used for precision machining include encoders that use a rotating mechanism that detects the amount of movement of the device to be measured, and optical devices that use moiré fringes obtained by superimposing two optical gratings. Expression scales and the like are conventionally known.

FIG. 8 shows an outline of a conventional measurement and display device combining an optical linear scale measuring device 110 and a display device for displaying the measurement results. In this figure, reference numeral 101 denotes a main scale provided with graduations in the longitudinal direction at fine intervals as described later.
An index scale, which will be described later, is provided so as to be relatively movable with respect to 01.

In such a measuring and displaying apparatus, moire fringes generated by the relative movement of the main scale 101 and the index scale are optically detected, and the moire fringes are converted into electric signals and arithmetic processing is performed. By providing a measuring device, an A-phase pulse signal and a B-phase pulse signal that finally interpolate within one pitch of the scale are output. Then, for example, the A-phase pulse signal and the B-phase pulse signal having a phase difference of φ (90 degrees) are transmitted to the transmission lines 114 a and 114.
The relative movement distance of the scale is known by inputting the number of pulses to the display device 120 via b and counting while adding and subtracting the number of pulses according to the phase difference between the A-phase pulse signal and the B-phase pulse signal. Like that. The A-phase pulse signal and the B-phase pulse signal are transmitted to the transmission lines 121A, 121A.
The data is input to the NC machine 130 and the like via the 21B and used as a servo reference or the like.

FIG. 9 is a view for explaining the principle of an optical linear scale using the above-described moire fringes. As shown in FIG. 9, the optical scale includes a main scale 101 in which a grid (notched line) is provided on one surface of a transparent glass scale 100 such that light transmitting portions and non-light transmitting portions are arranged at a predetermined pitch. On one surface of the transparent glass scale 102, there is provided an index scale 103 provided with a lattice (notched line) so that light-transmitting portions and non-light-transmitting portions are arranged at a predetermined pitch. As shown in FIG. This main scale 10
1, the index scale 103 is opposed to the index scale 103 at a small interval, and the grid of the index scale 103 is arranged so as to be inclined at a small angle with respect to the grid of the main scale 101 as shown in FIG.

The grating provided on the main scale 101 and the index scale 103 is a glass scale 1
Chromium (Cr) is vacuum-deposited on 00 and 102, and is formed by a lattice having the same pitch formed by etching. With this arrangement, moire fringes shown in FIG. 10 are generated. The interval between the moire fringes is W, and a dark portion or a bright portion occurs at each interval W. This dark or bright part is the main scale 101
On the other hand, the index scale 103 moves from top to bottom or from bottom to top depending on the direction in which the index scale 103 relatively moves left and right. In this case, assuming that the pitch of the grids of the main scale 101 and the index scale 103 is P, and the mutual inclination angle is θ [rad], the interval W between the moire fringes is expressed as follows: W = P / θ Means that the lattice spacing P is optically enlarged to 1 / θ times. Then, when the grating moves by one pitch P, the moire fringes are displaced by W, and by reading the change in transmitted light or reflected light of the slit in W, the amount of movement in one pitch P is accurately measured. Will be able to do it.

As shown in FIG. 11, a change in moiré fringes is obtained by providing a photoelectric conversion element 113 for optically detecting a change in moiré fringes on an index scale, and providing a light source on the opposite side of the main scale 101. Scale 10
The change in the current flowing through the photoelectric conversion element 113 is read while the index scale 103 is relatively moved with respect to 1.

That is, with respect to the main scale 101
Index scale 103 is in A state
And the amount of light irradiated on the photoelectric conversion element 113 is the largest.
Therefore, the current flowing through the photoelectric conversion element 113 has a maximum value I₁ Tona
You. Next, when it relatively moves to the state of B, photoelectric conversion is performed.
The amount of light applied to the element 113 is slightly reduced, and the current is
I_Two And further moves to the state of C, the photoelectric conversion element
The element 113 is irradiated with the least amount of light, and its current is also minimized.
Small I_Three Becomes And move further to the state of D
The amount of light applied to the photoelectric conversion element 113 slightly increases
And the current is I _Two And move until it becomes the state of E
Then, it becomes the position with the highest light intensity again, and the current becomes
Value I₁ Becomes Thus, the flow to the photoelectric conversion element 113
Current changes sinusoidally, and the change is one cycle
When the time elapses, the main scale 101 is separated from the main scale 101 by the lattice spacing P.
Index scale 103 relatively moved
become.

FIG. 12 shows the principle of a scale for detecting conversion of moiré fringes using a photoelectric conversion element. In this figure, one surface of an elongated main scale 101 has the same pitch formed by vapor-deposited chromium. The index scale 103 is provided on one side of a U-shaped holder 104 for holding the main scale 101.
Is fixed. On the surface of the index scale 103 facing the main scale 101, a grid of the same pitch formed by chromium deposited in the same manner as the main scale 101 is engraved, and the back side of the index scale 103 is photoelectrically converted. An element 113 is provided.

The index scale 103 is a main scale 101 of a U-shaped holder 104 as shown in FIG.
The light source 105 is arranged on a surface located on the side opposite to the above, and the light transmitted through the main scale 101 and the index scale 103 is detected by the photoelectric conversion element 113. The main scale 101 and the index scale 103 are movable with respect to each other. Note that a light source 105 is provided on the same side of the holder 104 as the photoelectric conversion element 113, and a moire fringe is received from the light reflected by the main scale 101, thereby detecting a change in the moire fringe as a change in the amount of current. It can also be a device.

Usually, two or three photoelectric conversion elements 113 are provided at positions where the detection positions are different, so that an A-phase pulse signal and a B-phase pulse signal having a phase difference of 90 ° from each other are output. The moving direction and the moving distance of the scale can be measured from the two signals of the A phase and the B phase.

[0012]

When an optical linear scale as described above is installed on a machine tool, for example, after the main scale 101 is installed, an encoder unit such as a photoelectric conversion element 113 is provided. A U-shaped holder 104 having an encoder head will be attached. In this case, a gap (gap) between the main scale 101 and the index scale 103 is set in an appropriate range (for example, 1 mm) so that an appropriate moire fringe can be detected by the photoelectric conversion element 113 provided in the U-shaped holder 104. (± 0.2 mm).

FIG. 14 is a view showing an example of a conventional gap adjusting method for an optical linear scale. FIG. 14 shows a reflection type optical linear scale. In this case, for example, the encoder head 11 provided on the main scale 101 side of the U-shaped holder 104
At 0, a photoelectric conversion element 113, a light source 105, and the like are provided. Light transmitted from the light source 105 is reflected by the main scale 101, and the reflected light is detected by the photoelectric conversion element 113.

In such a reflective linear scale, a main scale 101 and an index scale 10 are used.
3 is adjusted, the photoelectric conversion element 1 is used.
13 are input to the oscilloscope 200 from the terminal 111, and the oscilloscope 20
The gap adjustment is performed while watching the waveform displayed on the screen of No. 0. For example, if the gap d between the main scale 101 and the index scale 113 is within an appropriate range, A
Since the phase and B phase signals have a phase difference of 90 °, when the A and B phase signals are input to the oscilloscope 200,
The Lissajous waveform displayed on the oscilloscope 200 is
It becomes circular at a given level. However, at the position where the gap d deviates from the appropriate range, the detected pits of the moiré fringes deviate, so that the output levels of the A-phase and B-phase signals decrease, and the magnitude of the circular Lissajous waveform changes (reduces).
Become.

Therefore, when adjusting the gap of the optical linear scale, the operator checks the Lissajous waveform displayed on the oscilloscope 200 while checking the encoder head 110.
Is moved along the main scale 101 so that the gap d between the main scale 101 and the index scale 103 is adjusted within an appropriate range at all measurement positions of the main scale 101.

However, the conventional gap adjustment as described above needs to be performed while confirming with the oscilloscope 200 whether or not the gap d between the main scale 101 and the encoder head 110 is within an appropriate range. The encoder head 110 and the oscilloscope 200 must be connected by a cable 210. For this reason, when the linear scale is attached to a large machine tool, the adjustment work is very troublesome and may involve danger.

Accordingly, the present invention has been made in view of the above points, and an object of the present invention is to provide a linear scale that can easily adjust a gap between a main scale and a measuring unit.

[0018]

In order to achieve the above-mentioned object, a main scale provided with first scribed lines which are graduated at equal intervals in a length direction intersects with the first scribed line. An index scale provided with a second engraved line, and a moiré fringe generated by the first engraved line and the second engraved line are detected, and a relative moving distance between the main scale and the index scale is detected. In a linear scale that has a photoelectric conversion unit that detects the main scale and a measurement unit that is movably arranged with respect to the main scale, a gap detection unit that detects a gap between the main scale and the measurement unit A determination unit that determines whether a gap between the main scale and the measurement unit is within an appropriate range based on a detection output of the gap detection unit, and a display unit that displays a determination result of the determination unit. There.

The gap detecting means is constituted by a reflecting plate provided on the main scale and a light emitting / receiving means provided on the measuring section and receiving the reflected light of the light transmitted to the reflecting plate. .

According to the present invention, the determination means determines whether the gap between the main scale and the measurement section is within an appropriate range, based on the detection output of the gap detection means for detecting the gap between the main scale and the measurement section. Is performed and the determination result is displayed on the display means, so that the operator can determine whether the gap between the main scale and the measuring unit is within the appropriate range by looking at the display on the display means. Becomes possible.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a linear scale according to the present invention will be described below. The present invention can be applied to either a reflection type or a transmission type linear scale, but in the present embodiment, an example in which the invention is applied to a reflection type optical linear scale will be described. FIG. 1 is a perspective view showing an outline of an optical linear scale of the present embodiment. In FIG. 1, reference numeral 50 denotes a main scale substrate attached to a machine tool or the like, which is usually made of a glass plate having a small coefficient of thermal expansion. The main scale substrate 50 includes a main scale 51 that is continuous in a longitudinal direction for detecting a relative movement amount of the scale,
A reflector 52 used for adjusting the gap between the main scale substrate 50 and the holder 60 is attached. Since the linear scale of the present embodiment is of a reflection type, at least a part of the main scale 51 is formed of a reflective material. The shape may be any size as long as it can reflect light output from a light source to be described later and can be detected by the photoelectric conversion element, and any material can be used as long as an appropriate reflectance can be obtained. May be something.

Reference numeral 60 denotes a holder (not shown) which can be moved along a track provided along the main scale substrate 50. Reference numeral 61 denotes an index scale provided on the holder 60. At the height position corresponding to the engraved line of the main scale 51, the engraved line of the same pitch that is oblique to the engraved line of the main scale 51 detects at least one pitch of the moire fringe as described above with reference to FIG. It is formed so that it can be done. Reference numeral 62 denotes a reflection-type detection element used for adjusting a gap between the main scale substrate 50 and the holder 60.
2 and the reflection plate 52 of the main scale substrate 51
Receives the light reflected by the main scale substrate 5
The gap between 0 and the holder 60 is detected. 63 is a main scale substrate 51 and a holder 60
Indicates an indicator provided as a display means for displaying whether the gap between the main scale substrate 51 and the holder 60 is within an appropriate range. For example, when the gap between the main scale substrate 51 and the holder 60 is within the appropriate range, the indicator is turned on. I have.

FIG. 2 is a cross-sectional view for explaining the structure of the optical linear scale according to the present embodiment. As shown in FIG. 2, the index scale 6 is attached to the holder 60.
1, a photoelectric conversion element 64, a light source 65, and a measurement unit (not shown) for measuring a relative movement distance with respect to the main scale substrate 50 are provided. The configuration of the measuring unit will be described later. Photoelectric conversion element 6
The moiré fringes 4 are usually provided with two to three light receiving elements at different positions. The moiré fringes are generated from the light emitted from the light source 65 and reflected by the main scale 51 and the score line of the index scale 61. To obtain a current output corresponding to the change in the moiré fringes, and output the relative movement distance of the scale as A-phase and B-phase sinusoidal signals having a phase difference of 90 ° from each other.

Further, the holder 60 is provided with the above-mentioned reflection type detecting element 62 used for adjusting the gap between the main scale substrate 50 and the holder 60. The reflection-type detection element 62 includes a light-emitting element 62a made of, for example, a light-emitting diode and a light-receiving element 62b made of a phototransistor. When adjusting the gap d between the main scale substrate 50 and the holder 60, The light receiving element 62b receives the reflected light of the light emitting element 62a reflected by the reflecting plate 52 attached to the main scale substrate 50, and the main scale substrate 50 and the holder 6
It is detected whether or not the gap d between 0 and 0 is within an appropriate range. When the gap d between the main scale substrate 50 and the holder 60 is within an appropriate range, an indicator 63 not shown in the figure is turned on.

FIG. 3 shows the characteristics of a reflection type photosensor suitable for the reflection type detection element 62. The reflection-type photo sensor shown in FIG.
1001, CNB 1002) is an infrared light-emitting diode as a light-emitting element and a high-sensitivity phototransistor as a light-receiving element integrated into one resin package as shown in FIG. Is done. Also,
When such a reflection-type photosensor is used as the reflection-type detection element 62, the relationship between the gap d with the reflection surface and the relative output current output from the light-receiving element has the characteristic shown in FIG. It shall be shown. Therefore, when the reflection type photosensor as shown in FIG. 3 is used for the reflection type detection element 62 of the linear scale of the present embodiment, the gap d between the main scale substrate 50 and the holder 60 is set to an appropriate range (1 mm ± 0). .2 mm), a relatively large relative output current can be obtained with the light receiving element.

In this embodiment, the reflection type photo sensor as shown in FIG. 3 is applied. However, this is merely an example, and the reflection type detection element 62 is the reflection type photo sensor shown in FIG. It is not limited to sensors.

Therefore, in the linear scale of the present embodiment, the reflection type photosensor as shown in FIG. 3 is used for the reflection type detection element 62, and the light receiving element 6 as shown in FIG.
At a distance d1 ≦ d ≦ d2 where the gap d is within an appropriate range where the output of 2b is greater than or equal to a predetermined threshold value Th, a signal is output to turn on the indicator 63 (see FIG. 1). I try to light it.

The size of the reflection plate 52 may be such that the light output from the light emitting element 62a of the reflection type detection element 62 can be detected by the light receiving element 62b when the light is reflected. Any type may be used as long as a high reflectance can be obtained. However, when a reflection type photosensor as shown in FIG.
The material of the reflection plate 52 is preferably, for example, aluminum (Al).

As described above, in the linear scale of the present embodiment, the reflection plate 52 is provided on the main scale substrate 50 and the holder 60 can receive the reflected light of the light transmitted to the reflection plate 52. The reflection type detection element 62 is provided. Then, the reflection type detection element 62
It is determined whether the gap d between the main scale substrate 50 and the holder 60 is within an appropriate range based on the result of the light received by the indicator.
3 is turned on.

Thus, when adjusting the gap by installing the linear scale of this embodiment on a machine tool, the operator does not need to connect an oscilloscope as in the prior art.
The main scale substrate 50 and the holder 6 can be viewed only by seeing the lighting state of the indicator 63 provided on the holder 60.
Since it is possible to determine whether or not the gap d between 0 and 0 is within an appropriate range, the gap can be easily adjusted.

The linear scale of the present embodiment is
A reflector 52 is attached to the main scale substrate 50 in advance,
In addition, since the reflection type detection element 62 is provided on the holder 60, it is easy to check the undulation when the main scale substrate 50 is attached or to periodically adjust the gap after installing the linear scale, for example. become.

In this embodiment, the reflection type optical linear scale has been described as an example.
It is needless to say that the present invention can also be applied to a transmission type optical linear scale arranged on the opposite side of the main scale 51.

FIG. 5 is a diagram showing a configuration of main blocks of a linear scale according to the present embodiment. In FIG. 5, light emitted from a light source 65 such as a light emitting diode is reflected by a main scale 51, passes through a grid of a pitch P engraved on an index scale 63 (not shown), and is a photodiode as a photoelectric conversion element. 64 is received. The A-phase signal and the B-phase signal received by the photodiode 64 are amplified by the photoelectric conversion amplifier 3 and applied to the comparator 4 to be converted into binary data. Each time the position data backup counter 5 moves the pitch P, the binary data is incremented or decremented in accordance with the moving direction, and is supplied to the processing device (display device) 9 as position data in units of the pitch P. You.
Data for interpolating the pitch P described below is also supplied to the processing device 9 so that a more precise absolute value can be measured and displayed.

That is, the above-mentioned A-phase signal and B-phase signal output from the photoelectric conversion amplifier 3 are supplied to an absolute interpolation circuit 6, and the absolute interpolation circuit 6
To count the number of interpolation pulses that divide the lattice pitch P finely.
, And outputs the interpolation data obtained by dividing the pitch P to the processing device 9.

Further, an A / B phase signal generator 8 to which a signal phase-modulated by the absolute interpolation circuit 6 is applied.
Then, as will be described later, interpolation data obtained by dividing the pitch P is generated as an A-phase pulse signal and a B-phase pulse signal indicating the number and phase of pulses, and supplied to a numerical control (NC) device. ing. The control of the moving direction and the moving amount of the machine tool can be controlled by these pulse signals.

In the present embodiment, as described above, the reflection type photodetector 62 is provided as a reflection type detection element for adjusting the gap between the main scale substrate 50 and the holder 60. The detection output of the photodetector 62 is output to the gap determination unit 18 after being amplified by the amplifier 17. Gap determination unit 18
Determines whether the detection output from the photodetector 62 is equal to or higher than a predetermined threshold level Th, and turns on the indicator 63 when the detection output is equal to or higher than the predetermined threshold level Th. Such a signal is output.

In this embodiment, the main scale 5
When the interval P between 1 and the grid provided on the index scale 61 is 40 microns, 40 pulses are counted in one cycle of the A-phase signal or the B-phase signal input to the absolute interpolation circuit 6. And an optical scale with a resolution of 1 micron.

The absolute interpolation circuit 6 includes a phase modulation circuit 21 that applies a phase shift corresponding to the level of the input A-phase signal and B-phase signal to the carrier, and a phase-shifted output of the phase modulation circuit 21. A low-pass filter (LPF) 22 for extracting a fundamental wave of the signal; a comparator 23 for binarizing an output signal of the low-pass filter 22; counting is started at an edge of the binarized carrier wave; Counter 2 stops counting
5 and a clock generator 24 for generating a clock counted by the counter 25 and a clock for generating a carrier wave
And a frequency divider 2 for dividing the clock of the clock generator 24
6 and a carrier generator 27 that generates a carrier from the output of the frequency divider 26, and has a function of dividing the inside of the grating pitch P in order to improve the resolution.

The phase modulator 21 is disclosed in, for example, JP-A-62-1.
No. 32104, and
The detailed configuration is, as shown in FIG. 6, the input A-phase signal is supplied to the resistor network RT via the operational amplifier OP1 operating as a buffer, and is also inverted and supplied to the resistor network RT by the operational amplifier OP2. . The B-phase signal is supplied to the resistor network RT via the operational amplifier OP3 operating as a buffer, and is also inverted by the operational amplifier OP4 and supplied to the resistor network RT.

That is, the A-phase signal, the inverted A-phase signal, the B-phase signal, and the inverted B-phase signal are mixed and added by the resistor network RT to generate a mixed signal having the opposite voltage and the same voltage divided into eight. 8 input terminals (0) ~
(7). This multiplexer A
The selection signals A, B, and C shown in FIG. 6C are input to the M input terminals C1, C2, and C3.
, The input terminals (0) to (7) of the multiplexer AM are sequentially selected, and a step-like output signal S shown in FIG. 7A is output from the output terminal to. This multiplexer A
The frequency of the signal S output from M is the same as the cycle of the selection signal C as shown in FIG. 7, and as a result, the selection signal C is used as a carrier and its phase is the same as that of the A-phase signal (B-phase signal). The output signal S balanced-modulated by the level is output from the multiplexer AM. That is, a carrier wave whose phase has been shifted according to the level of the A-phase signal (B-phase signal) is output.

The carrier wave thus balanced is LPF
22 to form a smooth sinusoidal wave as shown in FIG. This signal is a signal represented by S = K · cos (ωt−2π · x / p) where ω is the angular velocity of the frequency of the carrier, p is the lattice interval, and x is the amount of movement. The ratio x / p of the pitch p is a signal indicated as a change in phase.

The following is a description of the Japanese Patent Application No. Hei.
As described in 320921, the comparator 23
The point at the zero level of the signal S is set as an edge 2
It is converted to a value signal.

For example, the counting of the counter 25 is started by the edge of the carrier frequency obtained by dividing the output of the clock generator 24 by the divider 26, and the counter 25 is started by the rising edge of the binary output of the comparator 23.
Is stopped, the interpolation absolute value obtained by dividing the grid pitch P from the counter 25 can be detected as the count value.

The counted value is such that one pitch of the scale is 40.
When the coefficient is multiplied by the number of clocks, for example, 1/4
When the pitch shifts, 10 clocks are counted by the counter 2
5 counts. In addition, 20 clocks are shifted when moving by １ ／ pitch, and 30 clocks when shifted by ／ pitch.
The counter 25 counts the number of clocks.

As described above, if the frequency of the clock counted by the counter 25 is set to 40 times the carrier frequency,
Since the counter 25 counts one pulse each time it moves by an amount obtained by dividing the grating pitch P by 40, the resolution can be increased by a factor of 40. Therefore, when the grating pitch is 40 microns, the resolution can be 1 micron. That is, the number of interpolated pulses is “0 to 39”.
It will be. Note that the carrier wave generation circuit 27 is supplied with a clock frequency-divided by the frequency divider 26 whose frequency division ratio is set to “40”, and the frequency division ratio of the frequency divider 26 is set to, for example, “200”. , A resolution of 0.2 microns can be achieved.

[0046]

As described above, the linear scale according to the present invention uses the detection output of the gap detecting means for detecting the gap between the main scale and the measuring section to determine the gap between the main scale and the measuring section by the judging means. It is determined whether or not the gap is within an appropriate range, and the result of the determination is displayed on the display means. Therefore, at the time of adjusting the gap, it is possible to know whether or not the gap between the main scale and the measuring unit is within the appropriate range only by looking at the display on the display means, so that the gap can be easily adjusted.

Further, according to the present invention, as a gap detecting means,
Since the reflector is attached to the main scale in advance and the light emitting and receiving means is provided in the measuring unit, even after the linear scale is installed on the machine tool, for example, it is easy to periodically adjust the gap. There are advantages too.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an outline of a linear scale according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a structure of a linear scale according to the present embodiment.

FIG. 3 is a diagram showing a structure and characteristics of a reflective detection element for gap adjustment.

FIG. 4 is a diagram illustrating a determination method of a gap determination unit.

FIG. 5 is a block diagram of a main part of the linear scale according to the embodiment.

FIG. 6 is a circuit diagram of a phase modulation circuit.

FIG. 7 is a timing chart of the phase modulation circuit.

FIG. 8 is a schematic diagram showing an outline of a measurement display device using a linear scale.

FIG. 9 is a principle diagram of an optical scale.

FIG. 10 is an explanatory diagram of moire fringes.

FIG. 11 is a diagram showing movement of moiré fringes.

FIG. 12 is a perspective view of an optical scale.

FIG. 13 is a sectional view of an optical scale.

FIG. 14 is an explanatory diagram of a conventional gap adjusting method in an optical scale.

[Explanation of symbols]

2 Photodiode, 3 photoelectric conversion amplifier, 4 comparator, 5 position data backup counter, 6
Absolute interpolation circuit, 8 A / B phase signal generator, 9
Processing circuit (display unit), 17 amplifier, 18 gap determination unit, 50 main scale substrate, 51 main scale, 52 reflection plate, 60 holder, 61 index scale, 62 reflection type detection element (photodetector), 63 indicator, 64 photoelectric conversion Element (photodiode), 65 light source

Claims (2)

[Claims] 1. A first scale which is graduated at equal intervals in a longitudinal direction.
A main scale provided with an inscribed line, an index scale provided with a second inscribed line intersecting the first inscribed line, the first inscribed line and the second inscribed line A moire fringe generated by the main scale and a photoelectric conversion unit that detects a relative moving distance between the index scale, a measuring unit that is movably disposed with respect to the main scale, A gap detecting means for detecting a gap between the main scale and the measuring section; and a gap between the main scale and the measuring section by a detection output of the gap detecting means. A linear scale comprising: a determination unit that determines whether or not is within an appropriate range; and a display unit that displays a determination result of the determination unit. 2. The apparatus according to claim 1, wherein the gap detecting unit includes: a reflecting plate provided on the main scale; and a light emitting / receiving unit provided on the measuring unit and receiving reflected light of light transmitted to the reflecting plate. The linear scale according to claim 1, wherein the linear scale is configured.