JPS62298704A - Optical length measuring apparatus - Google Patents

Abstract

PURPOSE:To simplify construction of a gauge, by measuring a relative displacement of a main scale basing upon a mutual action of bright-and-dark fringes formed by a lens array and the main scale. CONSTITUTION:A beam of light from a source 1 is collected by a lens array 7 and bright-and-dark fringes are formed as the result. By using said fringes in place of an index-scale, a mutual action is created with a main scale 5. By this arrangement, an optical signal of high contrast is irradiated onto a detecting apparatus 6 corresponding to a relative displacement of the main scale 5. By arithmetic operation of an output signal of the detecting apparatus 6, the relative displacement of the main scale 5 can be obtained.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an optical length measuring device that optically measures the moving distance of a moving table of a machine tool.

[Conventional technology]

Conventionally, as a device for optically measuring the amount of movement of a moving table or the like of a machine tool, a pair of optical gratings are arranged facing each other, and a light source and a photodetector are arranged so as to sandwich the pair of optical gratings. A length measuring device is used that measures the moving distance of an object by measuring the amount of relative movement of the optical grating.

FIG. 3 schematically shows the optical system of the length measuring device described above.

The optical system shown in FIG. 3 is assumed to be housed in a dark box (not shown) in order to eliminate the influence of external light.

In FIG. 3, light from a light source 1 such as a light emitting diode is converted into parallel light by a convex lens 2, and then enters an optical grating pair consisting of an index scale 3 and a main scale 5. The index scale 3 and the main scale 5 each have a grid formed of band-shaped opaque members 4 provided on transparent glass and extending in a direction perpendicular to the plane of the paper, and are relatively movable in parallel. It is located in The light passing through the main scale 5 is detected by a detector 6, converted into an electrical signal, and output.

Since the detector 6 is composed of two detectors whose pitch is shifted by 1/4 grid pitch, the electrical signal is a two-phase signal with a phase shift of 90'. When the main scale 5 moves in the direction of arrow a, a corresponding substantially periodic optical signal is incident on the detector 6.

The output signal of the detector 6 is processed by an arithmetic unit (not shown), and the relative movement amount and movement direction of the main scale 5 are determined.

[Problem that the invention seeks to solve]

By the way, index scale 3 and main scale 5
In an ideal state with no gap between main scale 5 and
The amount of light passing through changes as the main scale moves, as shown by the solid line A in FIG. However, in an actual device, a predetermined gap is provided between the index scale 3 and the main scale 5 in order to prevent the opaque portion 4 from being worn out due to friction. When the gap is increased, the light passing through the main scale 5 becomes as shown by the broken line B in FIG. 4, and the contrast decreases, making measurement impossible. Therefore, in practice, it is necessary to maintain the distance between the index scale 3 and the main scale 5 within a range of about 10μ+1 to 50μ−, and it is necessary to use extremely high-precision and expensive parts.

Furthermore, even when high-precision parts are used, some variation in dimensions occurs during the manufacturing process, and in the worst case, there is a problem that measurements cannot be made due to lack of contrast. In order to prevent this, it may be possible to make adjustments when assembling the parts, but this has the disadvantage of requiring extremely high skill and poor productivity.

Furthermore, in order to prevent a decrease in contrast, a configuration in which a projection lens is disposed between the index scale and the main scale can be considered, but this has the disadvantage that the aberration of the projection lens affects the contrast, and the optical system is complicated. It had the disadvantage of becoming

The present invention has been made in view of the above drawbacks, and an object of the present invention is to provide a highly accurate optical length measuring device that is not affected by variations in components.

(Means for Solving the Problem) The optical length measuring device of the present invention includes a lens array, a main scale disposed opposite to the lens array and movable relative to the lens array, and a main scale that is movable relative to the lens array. The apparatus includes a detector that detects light from a light source obtained through an array and the main scale, and a calculation unit that calculates a relative movement amount of the main scale based on an output signal of the detector.

[For production]

Light from a light source is focused by a lens array, resulting in the formation of light and dark stripes. The light and dark stripes are used instead of the index scale and interact with the main scale. As a result, a high-contrast optical signal corresponding to the relative movement of the main scale is incident on the detector. By processing the output signal of the detector, the relative movement amount of the main scale can be obtained.

〔Example〕

FIG. 1 is a diagram showing an embodiment of an optical system used in the optical length measuring device of the present invention. The optical system shown in FIG. 1 is housed in a dark box to eliminate the influence of external light.

In FIG. 1, the same parts as in FIG. 3 are given the same reference numerals. In FIG. 1, a lens array 7 is used instead of an index scale. As shown in FIG. 2(a), the semicylindrical lens array 7 is a lenticular lens array in which a plurality of columnar convex lenses are arranged side by side.

In FIG. 1, light from a light source 1 is converted into parallel light by a convex lens 2, and then enters a lens array 7. The light that has entered the lens array 7 is focused onto the main scale 5 by each convex lens, and then enters the detector 6.

The lens array 7 is composed of a plurality of columnar convex lenses, and since the axis of each convex lens is arranged parallel to the grating 4, light and dark stripes parallel to the grating are formed on the main scale 5. be done. Even when the main scale 5 is displaced toward or away from the lens array 7, a high-contrast optical signal is incident on the detector 6. Furthermore, since only the main scale is used as an optical grating, there is little loss of light, and the light utilization rate is approximately 100%, twice that of conventional optical systems.

By the way, the diameter of the light source 1 is A, the diameter of the image (bright part) formed on the main scale 5 by the lens array 7 is B,
If the focal length of the convex lens 2 is fc, and the focal length of each convex lens of the lens array 7 is f[, then B '' A-fR/
The relationship f c holds true. In addition, when a laser diode with a wavelength λ is used as the light source 1, and if the lens 1 has no aberration, the image diameter B can be expressed as a function of the numerical aperture NA of the lens array. , K:l
:0.4).

Therefore, based on the above equation, the pitch of the bright and dark stripes formed on the main scale 5 can be set to a predetermined value.

For example, if the diameter of the image formed by the lens array 7, that is, the convergent light, is set smaller than the grating pitch of the main scale 5, and the pitch of the convergent light is an integral multiple of the grating pitch, the main scale 5 is placed at the converging position. However, by moving this, an optical signal determined by the lattice constant and the moving distance can be obtained with higher contrast, similar to the optical system shown in FIG. 3. The amount of relative movement of the main scale 5 is determined by detecting the optical signal with the detector 6 and performing a calculation (not shown).

In this example, a lenticular lens array is used as a convex lens array to form bright and dark fringes parallel to the main scale grating. Moire fringes may be generated and detected.

Further, as the lens array 7, a lens array 7 consisting of circular convex lenses 8 to 11 as shown in FIG. 2(b) may be used. In that case, the lenses 8 and 9 are spaced at an integral multiple of the grating pitch of the main scale, and the lens 10
．． 11 is set to an interval that is an integral multiple of the grating pitch of the main scale, and lenses 10 and 11 are shifted from lenses 8 and 9 by 1/4 of the grating pitch. and lenses 8, 9
A first detector is provided corresponding to the lens 10.11, and a second detector is provided corresponding to the lens 10.11.
By obtaining two signals with a 90° phase shift from the detector, discrimination of the moving direction and highly accurate measurement can be realized. In addition, the columnar convex lens arrays 7 shown in FIG. 2(a) are arranged in two stages, upper and lower, shifted by 174 pitches of the lattice pitch of the main scale. One detector without pitch deviation may be provided for each. Furthermore, in the lens array shown in FIG. 2(b), a pyramid-shaped lens array, a prism, or the like may be used instead of the circular lens.

〔Effect of the invention〕

The optical length measuring device of the present invention measures the amount of relative movement of the main scale based on the interaction between the bright and dark fringes formed by the lens array and the main scale. High-contrast optical signals are obtained not only when the scale is misaligned toward the lens array, but also when it is misaligned away from the lens array, increasing the tolerance for the distance between the lens array and the main scale. It is extremely easy to manufacture. Furthermore, since only the main scale is used as an optical grating, the efficiency of light utilization is increased and a detector with low sensitivity can be used.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an optical system used in the present invention, FIG. 2 is a perspective view of a lens array used in the present invention, and FIG. 3 is a schematic diagram of an optical system used in the present invention.
FIG. 4, which is a schematic diagram of an optical system of a conventional optical length measuring device, is a characteristic diagram of the conventional optical length measuring device. 1... Light source 2... Convex lens 3... Index scale 5... Main scale 6... Detector 7.
...Lens array patent applicant Futaba Electronics Co., Ltd. Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] a lens array, a main scale arranged to face the lens array and movable relative to the lens array, and a detector that detects light from a light source obtained through the lens array and the main scale. and an arithmetic unit that calculates the relative movement amount of the main scale based on the output signal of the detector.