JP2549514B2 - Photoelectric encoder reference point signal generation mechanism - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a reference point signal generation mechanism of an optical encoder used for rotation angle detection, linear position detection, and the like, and particularly for a photoelectric encoder.

(Prior Art) Conventionally, an absolute position is not possible with an incremental encoder, so a reference point is provided on the scale, and the rotation angle or moving position is detected by rotating or moving to the reference point at the time of initial setting. There is. In the optical encoder, one or a plurality of slits are provided as the reference point on the main scale and the index scale, respectively, and the fact that the output signal becomes maximum when the slits on both scales coincide is used as the reference point. A signal mechanism is used.

With each one slit for the reference point, the output signal when the slit provided in the main scale and the slit provided in the index scale do not match is zero as shown in the sixth figure, so S / The N ratio is infinite, which is ideal. However, since the output signal level is proportional to the amount of light passing through the slit, the output signal level obtained from the slit is very weak and not practical.

Therefore, generally, as shown in FIG. 7, the width of the reference point signal, the S / N ratio, and the level are set on the reference point signal generators (1) and (2) of the main scale and the index scale, respectively. Multiple slits with different width (6)
(7) is irregularly formed. Here, the width ls of the slits (6) and (7) of the slit groups formed in the reference point signal generators (1) and (2) of the main scale and the index scale and the distance lm between adjacent slits are set to the main scale. The width of the slits of the main signal slit group (not shown) provided and the distance between adjacent slits are basic multiples of these and are an integral multiple of these, and for the reference points provided on the main scale and the index scale. The slits (6) and (7) are arranged symmetrically.

In FIG. 7, (3) is a collimation lens, (4) is a light source, and (5) is a photoelectric conversion element.

The output signal obtained in the reference point generation mechanism is as schematically shown in FIG. 8, and the originally required signal level Vs and the unnecessary nozzle level V _N occur. The sum of the widths ls of the slits (6) and (7) is the distance lm between adjacent slits.
When the slits (6) and (7) are arranged irregularly, the ratio between the signal level Vs and the noise level V _N is 2: 1 at best, that is, the S / N ratio is 6 dB. The width W of the reference point signal is determined by making a rectangular wave using the level Vp of the reference light or electric signal which is set in advance. Here, the width W of the reference point signal needs to be less than two cycles of the main signal, and is generally set to the width of one cycle of the main signal.

(Problems to be Solved by the Invention) When trying to obtain a high-resolution optical encoder in the above-mentioned conventional optical encoder, the period of the main signal becomes short, and therefore the width of the slits (6) (7) for the reference point signal is reduced. The reference unit of ls also becomes small, and the influence of diffraction and interference of light from the light source (4) cannot be ignored.

Therefore, the light intensity distribution on the surface of the reference point signal slit (7) provided on the index scale, which is separated by the distance L of the light transmitted through the reference point signal slit (6) provided on the main scale, is Due to the influence of the diffraction and interference, the distribution is greatly different from the distribution calculated geometrically as shown in FIG. 9 and becomes as shown in FIG.

If the light intensity distribution in the reference point signal generator (2) of the index scale is as shown in FIG. 9, the output obtained by scanning this with the reference point signal generator (1) of the main scale is schematically shown. Although it is as shown in FIG. 8, as shown in FIG. 10 as described above, the output obtained by scanning the reference point signal generator (1) of the main scale with this light intensity distribution is the output shown in FIG. become that way.

When a reference point signal is obtained by converting from this output to a rectangular wave using a preset electric signal or reference light level Vp ₁ , the width W _{1 of} this signal is the width of the signal shown in FIG. W
However, there is a drawback in that the ratio between the level Vs ₁ of the reference point signal and the nozzle level V _N1 , that is, the S / N ratio, deteriorates.

It is an object of the present invention to provide a reference point signal generating mechanism for a photoelectric encoder, which can eliminate such conventional drawbacks without using a special additional mechanism.

(Means for Solving Problems) The present invention, in order to achieve the above-mentioned object, a main scale having a reference signal generating slit group formed on a main surface,
An index scale that is movably opposed to the main scale and has a reference point signal transmission slit group formed at a position facing the reference point signal generation slit group, and a reference signal generation on the main scale. In the reference point signal generating mechanism of a photoelectric encoder having a light source for irradiating a slit group for use, and a photoelectric conversion element that is arranged to face the index scale and receives light transmitted through the slit group for transmitting a reference point signal, Each slit constituting the reference point signal generating slit group is arranged irregularly, the position where each slit constituting the reference point signal transmitting slit group is arranged is transmitted through the reference point signal generating slit group. , At a position corresponding to the peak of the intensity distribution formed on the index scale by the transmitted light affected by diffraction and interference. The width of each slit constituting the reference point signal transmissive slit group is characterized by a width corresponding to the magnitude of the intensity distribution.

(Operation) Since the transmitted light transmitted through the reference point signal generation slit group formed on the main scale is affected by light diffraction and interference, the light intensity distribution when the transmitted light is irradiated on the index scale Pattern does not match the distribution pattern of each slit of the reference point signal generating slit group on the main scale.

Therefore, passing through the reference point signal generating slit group,
Diffraction, each slit constituting the reference point signal transmission slit group is arranged at a position corresponding to the peak of the intensity distribution formed on the index scale by the transmitted light affected by interference, and the width thereof is set to the intensity. If it is configured to correspond to the size of the distribution, the S / N ratio of the signal output by the photoelectric conversion element can be increased.

(Example) Next, the Example of this invention is described with reference to drawings.

FIG. 1 shows a diagram of one embodiment of the present invention. In the figure, (1) is a reference point signal generator of the main scale, which is provided with a main signal slit (not shown), and is movable in the longitudinal direction. A reference point signal generator (2) is fixedly installed, and a light source (4) is arranged via a collimation lens (3) on the side opposite to the index scale. Further, a light source conversion element (5) is arranged so as to face the index reference point signal generator (2).

Each slit (6 ₁ ) (6 ₂ ) that constitutes the reference point signal generation slit group of the main scale reference point signal generation unit (1)
(6 ₆ ) is, as shown in FIG. 1 and FIG. 2 (B),
Like the conventional example, they are arranged irregularly, and the distance between each slit (6 ₁ ) to (6 ₆ ) and the slit is an integral multiple of the width of the main signal slit (not shown). Has been formed.

Each slit constituting the reference point signal generator of the index scale reference point signal transmission slit group (2) (7 ₁₎
(7 ₂ ) ... (7 ₆ ) is the transmitted light of the reference point signal generator (1) of the main scale as shown in FIG. 2 (A) in the reference point signal generator (2) of the index scale. It is determined based on the intensity distribution and, like the main scale, is formed to be an integral multiple of the width of the main signal slit. Explaining this in more detail, the intensity distribution of the transmitted light is such that each slit (6 ₁ ) forming a reference point signal generating slit group arranged in the reference point signal generating section ( ₁ ).
(6 ₂ ) ... (6 ₆ ) Based on the distance between adjacent slits, the wavelength of the light source (4) and the coherency, the light source degree at each slit is obtained by a known calculation method called Fresnel diffraction, and these are combined. Can be obtained at. Based on the intensity distribution as shown in FIG. 2 (A) thus obtained, that is, its peaks (8 ₁ ) (8 ₂ ) (8 ₃ ) ... (8 ₆ )
Slits (7 ₁ ) (7 ₂ ) …… (7 ₆ ) that make up the slit group for transmitting the reference point signal almost corresponding to the position and size of
The position and size of is determined. Here, the slits of the reference point signal generators (1) and (2) described above are manufactured by forming a light-shielding thin film such as chrome on a transparent substrate such as a glass plate.

Thus, when the reference point signal generator (1) of the main scale is scanned, an output as shown in FIG. 3 is obtained, and the width W is reduced from this output by using the electric signal or the reference light of the preset level Vp. A reference point signal with a large S / N ratio can be obtained.

In the above embodiment, the reference point signal generator of the main scale and the index scale (1) and the slit (2) (6 ₁₎ (6 ₂₎ (6 _6), (7 ₁₎ (7 ₂₎ ... The width of (7 ₆ ) is formed as an integral multiple of the width of the main signal slit,
If it is set not to be an integral multiple but to match the intensity distribution of FIG. 2 (A) as shown in FIG. 2 (D), the width of the reference point signal and the S / N ratio can be further improved. Is possible. Further, in this embodiment, the light source (4) is arranged so as to face the main scale and the photoelectric conversion element (5) is arranged so as to face the index scale, but this relationship may be reversed. In this case, a slit having a width facing the size of the peak is formed at the position of the main scale that corresponds to the peak of the intensity distribution of the transmitted light of the index scale on the main scale.

FIG. 4D shows a reference point signal generating mechanism 1 according to the present invention.
The measurement result of the output characteristic of an example is shown. The output characteristic is shown in FIG. 4 (B), which is a main scale reference point signal generator (1).
Intensity distribution on the reference point signal generator (2) of the index scale shown in FIG. 4 (C) of the transmitted light of FIG. 4 (A).
Are obtained by scanning the reference point signal generator (1). FIG. 5C shows the measurement result of the output characteristics of the conventional example. The output characteristic is the index scale shown in FIG. 5 (B) of the transmitted light of the reference point signal generator (1) of the main scale having the same configuration as in FIG. 5 (A), that is, FIG. 4 (B). The intensity distribution (FIG. 4 (A)) on the reference point signal generator (2) is obtained by scanning the reference point signal generator (1).

The distance between the main scale and index scale of the present invention shown in FIGS. 4 and 5 and the conventional example is 120 μm.
m, the wavelength of the light from the light source is 880 nm. As is clear by comparing the output characteristics of FIG. 4 (D) and FIG. 5 (C), the width and S / N ratio of the reference point signal of the present invention are superior to those of the conventional example.

(Effect of the Invention) As described above, according to the present invention, the width of the reference point signal can be narrowed without using a special additional mechanism,
It is possible to obtain a highly accurate reference point and to improve the S / N ratio.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the configuration of one embodiment of the present invention, and FIG.
FIG. 1A is a light intensity distribution chart of the one shown in FIG. 1, and FIGS. 2B and 2C are reference point signal generators (1) and (2) corresponding to the light intensity distribution of FIG. 2A. 2D is a schematic diagram of the modified side of the reference point signal generator (2) shown in FIG. 2C, and FIG. 3 is an output characteristic diagram of the one shown in FIG. (A) is a light intensity distribution chart of the present invention, FIGS. 4 (B) and (C) are schematic diagrams of the reference point signal generators (1) and (2), and FIG. 4 (D) is its output characteristic. Figure, fifth
FIGS. 4A and 4B are schematic diagrams of the reference point signal generators 1 and 2 of the conventional example corresponding to the present invention shown in FIGS. 4B and 4C, and FIG. 5C. ) Is the output characteristic diagram, No. 6
FIG. 7 is an output characteristic diagram of the conventional example, FIG. 7 is a schematic diagram of the conventional example, FIG. 8 is an output characteristic diagram of the one shown in FIG. 7, FIG. 9 is a light intensity distribution diagram of the one shown in FIG. 7, and FIG. FIG. 11 is a light intensity distribution chart in which light is diffracted and interfered, and FIG. 11 is an output characteristic chart in the light intensity distribution shown in FIG. (1) …… Main scale reference point signal generator (2) …… Index scale reference point signal generator (3) …… Light source (5) …… Photoelectric conversion element (6 ₁ ) (6 ₂ ) to ( 6 ₆₎ slits constituting the ...... reference point signal generating slit group ₍₇₁₎ (7 ₂₎ each of the slits constituting the ~ (7 ₆₎ ...... a reference point signal transmissive slit group

Claims (1)

(57) [Claims] 1. A main scale having a reference signal generating slit group formed on a main surface thereof, and a main scale which is disposed so as to be movable relative to the main scale so as to be opposed to the reference point signal generating slit group. An index scale formed with a slit group for transmitting a point signal, a light source for irradiating a slit group for generating a reference signal on the main scale, and a light source that is arranged so as to face the index scale and transmits through the slit group for transmitting a reference point signal. In a reference point signal generating mechanism of a photoelectric encoder having a photoelectric conversion element that receives light, each slit constituting the reference point signal generating slit group is arranged irregularly, and the reference point signal transmitting slit group is The position where each of the constituent slits is arranged is transmitted through the reference point signal generating slit group and is transmitted through the influence of diffraction and interference. The light is at a position corresponding to the peak of the intensity distribution formed on the index scale, and the width of each slit constituting the reference point signal transmission slit group is a width corresponding to the size of the intensity distribution. A reference point signal generation mechanism for a photoelectric encoder, characterized by: