JP3156515B2 - Optical encoder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical encoder used for measuring, for example, the angle and position of an object.

[0002]

2. Description of the Related Art An example of the above-mentioned conventional optical encoder will be described below with reference to the drawings.

FIG. 6 is a schematic view of a conventional optical encoder. In FIG. 6, reference numeral 21 denotes a light source such as an LED or an incandescent lamp, and reference numeral 22 denotes a collimator lens for converting light emitted from the light source 21 into parallel light.

Reference numeral 23 denotes a movable slit plate having slits arranged at a pitch p, and reference numeral 24 denotes a fixed slit plate which is disposed substantially parallel to the movable slit plate and has slits arranged at the same pitch as the movable slit plate 23. The slits of the moving slit plate 23 and the fixed slit plate 24 are parallel to each other.

[0005] Reference numeral 25 denotes a light receiving unit, which is a movable slit plate 2.
3. Detect the light passing through the fixed slit plate 24 and convert it to an electric signal.

The operation of the optical encoder configured as described above will be described below.

Light emitted from a light source 21 is collimated by a collimator lens 22 and illuminates a moving slit plate 23.
The fixed slit plate 2 is fixed by the slit of the movable slit plate 23.
4, a light-dark pattern occurs. The movement of the moving slit plate 23 also moves the light / dark pattern on the fixed slit plate 24.

Since the pitch of the fixed slit plate 24 is equal to and parallel to the slit of the movable slit plate 23, the amount of light emitted from the fixed slit plate 24 changes due to the movement of the light and dark pattern.

The position of the movable slit plate 23 can be detected by detecting the change in the amount of light by the light receiving section 25.

[0010]

However, in the above-described configuration, the light emitted from the collimator lens includes light beams in various directions because the light source light-emitting portion is wide. Therefore, when the angle of incidence of the light beam on the moving slit plate changes, the position of the light and dark pattern generated on the fixed slit plate changes, so that the phase of the signal at the light receiving unit changes.

The phase change of the signal is substantially proportional to the product of the angle of incidence of the light beam on the moving slit plate and the distance between the slit plates. When light beams having different incident angles are incident on the moving slit plate, signals are canceled in the light receiving unit, and the signal amplitude is reduced.

For this reason, conventionally, the distance between the slit plates has been narrowed to prevent the signal amplitude from decreasing at the light receiving section.

However, when the distance between the slit plates is reduced,
There has been a problem that the slit plate is damaged by contact of the slit plate due to impact, vibration, or the like, or mixing of foreign matter.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide an optical encoder which increases the distance between a movable slit plate and a fixed slit plate and is resistant to shock and vibration.

[0015]

According to a first aspect of the present invention, there is provided an optical encoder comprising: a light source; a collimator lens having the light source as a front focal point; and a light emitted from the collimator lens. A first slit plate having a plurality of slits arranged at equal intervals as incident light, and a plurality of slits being arranged at the same pitch as the slits of the first slit plate using the light emitted from the first slit plate as incident light. A second slit plate having a slit, and a light receiving unit that uses light emitted from the second slit plate as incident light; at least the first slit plate or the second slit plate is movable; When the focal length is f, the pitch of the first slit plate is p, and the distance between the first and second slit plates is g, the arrangement of the slits of the first slit plate is g. The dimension a of the light emitting portion of the light source in the direction in which the a <0.7fp / g.

An optical encoder according to a second aspect of the present invention includes a light source, a collimator lens having the light source as a front focal point, and a plurality of slits arranged at equal intervals with the light emitted from the collimator lens as incident light. A first slit plate, a second slit plate having a plurality of slits arranged in parallel with each other and at the same pitch as the slits of the first slit plate with the emission light of the first slit plate as incident light; A light-receiving unit for emitting light from the two-slit plate as incident light, at least the first slit plate or the second slit plate is movable, and the light-emitting unit of the light source in the arrangement direction of the slits of the first slit plate is provided. The dimension is a and the first
The pitch of the slit plate is p and the first slit plate and the second
When the distance between the slit plates is g and the aperture diameter of the collimator lens is d, the focal length f of the collimator lens is set to (1.43 ga / p) <f <2d.

[0017]

According to the optical encoder of the first aspect, the signal amplitude is reduced by reducing the size of the light emitting portion of the light source in the slit arrangement direction of the slit plate and improving the parallelism of the light beam illuminating the slit plate. Can be prevented, and the gap between the slit plates can be widened.

Further, in the optical encoder according to the present invention, the focal length of the collimator lens is lengthened, and the parallelism of the light beam illuminating the slit plate is improved, so that the signal amplitude is prevented from lowering and the gap between the slit plates is reduced. Can be spread.

[0019]

【Example】

(First Embodiment) An optical encoder according to a first embodiment of the present invention will be described below with reference to the drawings.

In this embodiment, by reducing the size of the light emitting portion of the light source, the degree of signal modulation at the light receiving portion is improved, the distance between slits is increased, and breakage of the slit due to vibration or impact is prevented.

FIG. 1 is a schematic view of an optical encoder according to this embodiment. In FIG. 1, 1 is an LED
Reference numeral 2 denotes a collimator lens having a focal length f, and the light source 1 is disposed at a front focal position.

Reference numeral 3 denotes a moving slit plate having slits arranged at a pitch p. The movement amount of the moving slit plate in the direction in which the slits are arranged is represented by t. Reference numeral 4 denotes a fixed slit plate which is arranged substantially parallel to the moving slit plate 3 and has slits arranged at the same pitch as the slits of the moving slit plate 3. The slits of the moving slit plate 3 and the fixed slit plate 4 are parallel to each other.

Reference numeral 5 denotes a light receiving section for detecting light passing through the movable slit plate 3 and the fixed slit plate 4 and converting the light into an electric signal. The light emitting portion of the light source 1 has a dimension a in the direction in which the slits of the movable slit plate 3 are arranged. At this time, the dimension a of the light emitting portion of the light source 1 satisfies a <0.7 fp / g.

The operation of the optical encoder configured as described above will be described. The light emitted from the light source 1 is collimated by the collimator lens 2,
Is irradiated. The light and dark pattern is generated on the fixed slit plate 4 by the slit of the movable slit plate 3. The movement of the moving slit plate 3 also moves the light / dark pattern on the fixed slit plate 4. Since the pitch of the fixed slit plate 4 is equal to and parallel to the pitch of the movable slit plate 3, the amount of light emitted from the fixed slit plate 4 changes due to the movement of the light / dark pattern. The position of the movable slit plate 3 can be detected by detecting the change in the amount of light by the light receiving unit.

Next, with respect to the focal length f of the collimator lens, the slit pitch p of the movable slit plate, and the distance between slits (the distance between the movable slit plate and the fixed slit plate) g,
A description will be given of the fact that a sufficient signal modulation degree in the light receiving unit can be obtained by setting the dimension a of the light emitting unit of the light source 1 to a <0.7 fp / g.

FIG. 2 shows the light emitted from the light source 1. Light emitted from a minute area at a distance s from the center of the light source light emitting unit is converted by the collimator lens 2 into a luminous flux having an angle θ = arctan (s / f).

FIG. 3 shows the light incident on the slit plate. When the light beam of the angle θ enters the moving slit plate 3,
The position of the light and dark pattern generated on the fixed slit plate 4 is e
= G × tan (θ).

If the distance between the movable slit plate 3 and the fixed slit plate 4 is extremely small, the signal waveform at the light receiving section becomes triangular because it is proportional to the opening area of the two slits.

However, if the distance between the slits increases, the signal waveform at the light receiving section becomes sinusoidal due to the influence of diffraction and the like.

Therefore, if the signal at the light receiving section is approximated and expressed by a sine wave, then Ab {sin {2π (te) / p} +1}. b is the amount of light emission per unit area in the light emitting section of the light source 1, and A is a constant.

When the dimension of the light emitting portion of the light source 1 in the direction perpendicular to the slit arrangement direction of the moving slit plate is defined as v, and a signal from the light emitting portion of the light source in the slit arrangement direction of the moving slit plate 3 is obtained (Equation 1). Becomes

[0032]

(Equation 1)

Assuming that the light emitting portion is sufficiently small, θ ≒ s / f, e
Integrating with approximation to ≒ gθ yields (Equation 2).

[0034]

(Equation 2)

Here, sinc (x) = {sin (x)}
/ X. Assuming that the total amount of light of the light emitting unit is c, c = abv and (Equation 3).

[0036]

(Equation 3)

At this time, the signal modulation degree M is M = sin
(Πag / (pf)). However, the signal modulation degree M
Is M = (max−min) / (max + min) where the maximum value of the signal is max and the minimum value is min.

In general, the output of the light receiving unit is converted into a digital signal by cutting a DC component by taking a difference from a signal having a phase shift of 180 degrees, binarizing it at 0 level.

In equation (3), if t / p = x and the coefficient is omitted, the output signal of the light receiving section is 1 + Msin (2πx), and the signal shifted by 180 degrees is 1-Msin (2πx). Become. Here, the duty ratio of the signal when there is an output ratio of α between the two signals is obtained in consideration of the element sensitivity variation and the light source intensity distribution. The difference signal h becomes (Equation 4).

[0040]

(Equation 4)

When the range of x satisfying h> 0 is obtained (Equation 5)
Becomes

[0042]

(Equation 5)

FIG. 4 shows the relationship of (Equation 5). The left side of (Equation 5) is y = sin (2πx), and the right side is y = (1−
α) / {M (1 + α)}. Assuming h = 0,
When a solution x1 near x = 0 is obtained, it becomes (Equation 6).

[0044]

(Equation 6)

The solution x2 near x = 0.5 is given by (Equation 7).

[0046]

(Equation 7)

Therefore, the width of x satisfying h> 0 (x2-x
1) becomes (Equation 8).

[0048]

(Equation 8)

Since the cycle of the difference signal h is 1, the duty ratio is x2-x1, and the variation of the duty ratio is x
2-x1-0.5.

Generally, the sensitivity variation of the element in the light receiving section is about 10% for a pin diode or the like, and the light source has an intensity distribution, and about 10% of the light reception is provided between two signals 180 degrees out of phase. A difference in light amount occurs. Therefore, 2
The output ratio α between the signals is about 0.8 to 1.2.

Generally, in an encoder, 90
The moving direction of the device under test is detected based on the signals whose phase is shifted by one degree (A-phase signal and B-phase signal). Also, the resolution may be electrically increased (quadrupled) using the A-phase and B-phase signals. Therefore, the fluctuation of the signal duty ratio is set to about ± 10% or less.

Therefore, -0.1 <x2-x1-0.5 <
0.1, and when calculated using (Equation 8), (1−α) / {0.31 (1 + α)} <M and (α−1) / {0.31 (1 + α)} <M. To set α in the range of 0.8 to 1.2,
The signal modulation degree M needs to be about 0.36 or more.

Therefore, sinc (πag / (pf))>
0.36, which gives a <0.7 fp / g.

By the way, when the size of the light emitting portion of the light source is reduced, the temperature rise due to heat generation becomes large and the life of the light source is shortened. For this reason, the minimum size of the light emitting unit is 20 μm in practical use.
About.

For example, if the focal length of the collimator lens is 5 mm and the slit pitch of the movable slit plate 3 is p = 5
In order to set the distance between the moving slit plate 3 and the fixed slit plate 4 to be g = 0.3 mm, the dimension a of the light emitting portion of the light source in the slit arrangement direction of the moving slit plate should be 625 mm.
It may be set to μm or less.

As described above, according to the present embodiment, by setting the dimension a of the light emitting portion of the light source so as to satisfy a <0.75 fp / g, a sufficient distance between the slits can be obtained, so that the vibration And the damage of the slit due to the impact can be prevented.

In the present embodiment, the movable slit plate 3 is provided on the light source 1 side, but the fixed slit plate 4 may be provided on the light source side.

In this embodiment, the slits on the movable slit plate are arranged linearly. However, the movable slit plate and the fixed slit plate are disks, and the slits are arranged on the circumference to detect the rotation angle. You may do it.

(Second Embodiment) Hereinafter, an optical encoder according to a second embodiment of the present invention will be described with reference to the drawings.

In this embodiment, by increasing the focal length of the collimator lens, the degree of signal modulation at the light receiving section is improved, the distance between slits is increased, and breakage of the slit due to vibration or impact is prevented.

FIG. 5 is a schematic diagram showing an optical encoder according to this embodiment. 5, components having the same functions as in FIG. 1 are denoted by the same reference numerals as in FIG.

Reference numeral 6 denotes a light source such as an LED. The dimension of the light emitting unit in the slit arrangement direction of the movable slit plate 3 is defined as a. Reference numeral 7 denotes a collimator lens having a focal length f and an aperture diameter d, and the light source 1 is disposed at a front focal position.
3ga / p) <f <2d.

The operation of the optical encoder configured as described above will be described. The light emitted from the light source 6 is collimated by the collimator lens 7,
Is irradiated. Due to the slits of the movable slit plate 3, a light and dark pattern is generated on the fixed slit plate 4. The movement of the moving slit plate 3 also moves the light / dark pattern on the fixed slit plate 4.

Since the slits of the fixed slit plate 4 are equal in pitch and parallel to the slits of the movable slit plate 3, the amount of light emitted from the fixed slit plate 4 changes due to the movement of the light / dark pattern. The position of the movable slit plate 3 can be detected by detecting the change in the amount of light by the light receiving unit.

Next, a signal having a sufficient amplitude is obtained in the light receiving section with respect to the slit pitch p of the moving slit plate 3, the dimension a of the light emitting portion of the light source 6, and the distance g between the moving slit plate 3 and the fixed slit plate 4. For this purpose, it will be described below that the focal length f of the collimator lens should be set to (1.43 ga / p) <f <2d.

As shown in FIG. 2, the light emitted from the minute area at a distance s from the center of the light source light emitting section is converted into a light beam having an angle θ = arctan (s / f) by the collimator lens 2.

As shown in FIG. 3, when a light beam having an angle θ is incident on the movable slit plate 3, the position of the light and dark pattern generated on the fixed slit plate 4 is shifted by e = g × tan (θ).

If the distance between the movable slit plate 3 and the fixed slit plate 4 is extremely small, the signal waveform at the light receiving section becomes triangular because it is proportional to the opening area of the two slits.

However, if the distance between the slits increases, the signal waveform at the light receiving section becomes sinusoidal due to the influence of diffraction and the like.

Therefore, when the signal at the light receiving section is approximated and expressed by a sine wave, Ab {sin {2π (te) / p} +1}. b is the amount of light emission per unit area in the light emitting section of the light source 1, and A is a constant.

When the dimension of the light emitting portion of the light source 1 in the direction perpendicular to the slit arrangement direction of the moving slit plate is set to v, and the signal based on the light beam from the light source emitting portion in the slit arrangement direction of the moving slit plate 3 is obtained (Equation 1). Becomes

Assuming that the light emitting portion is sufficiently small, θ ≒ s / f, e
Integrating with approximation to ≒ gθ yields (Equation 2). Assuming that the total amount of light of the light emitting unit is c, c = abv and (Equation 3). The signal modulation degree M is sin (πag / (pf)).

In general, the output of the light receiving section is converted into a digital signal by cutting a DC component by taking a difference from a signal having a phase shift of 180 degrees, binarizing the output at a 0 level. In (Equation 3), if t / p = x and the coefficient is omitted, the output signal of the light receiving unit is 1 + Msin (2πx), and the signal shifted by 180 degrees is 1−Msin (2πx). Considering variations in element sensitivity and light source intensity distribution,
If there is an output ratio of α between the two signals, the difference signal h becomes (Equation 4). When the range of x satisfying h> 0 is obtained (Equation 5)
Becomes

FIG. 4 shows the relationship of (Expression 5). When h = 0 and the solution x1 near x = 0 is obtained, (Formula 6) is obtained, and the solution x2 near x = 0.5 is (Formula 7).

Therefore, the width of x satisfying h> 0 (x2-x
1) becomes (Equation 8). Since the cycle of the difference signal h is 1, the duty ratio is x2-x1, and the variation of the duty ratio is represented by x2-x1-0.5.

In general, the sensitivity variation of the element in the light receiving section is about 10% in a pin diode or the like, and the light source has an intensity distribution, and the light receiving section has about 10% light receiving between two signals having a phase shift of 180 degrees. A difference in light amount occurs. Therefore, 2
The output ratio α between the signals is about 0.8 to 1.2.

In general, in an encoder, 90
The moving direction of the device under test is detected based on the signals whose phase is shifted by one degree (A-phase signal and B-phase signal). Also, the resolution may be electrically increased (quadrupled) using the A-phase and B-phase signals. Therefore, the fluctuation of the signal duty ratio is set to about ± 10% or less.

Therefore, -0.1 <x2-x1-0.5 <
0.1, and when calculated using (Equation 8), (1−α) / {0.31 (1 + α)} <M and (α−1) / {0.31 (1 + α)} <M.

In order for α to be in the range of 0.8 to 1.2, the signal modulation degree M needs to be about 0.36 or more.

Therefore, sinc (πag / (pf))>
0.36, which gives (1.43 ga / p) <f 2.

When the focal length f is longer than the aperture diameter d of the collimator lens, the light use efficiency is reduced.
The half-value angle of the emitted light of the LED is about 60 degrees, and when the lens focal length f is twice or more the aperture diameter d, the light use efficiency becomes 1
0% or less, the light amount at the light receiving unit becomes small, and there is a possibility that the signal cannot be detected. Therefore, the lens focal length f is set to (1.43 ga / p) <f <2d.

For example, when the size of the light source light emitting portion is 400 μm
m, the aperture diameter of the collimator lens is 4 mm, and when the slit pitch of the movable slit plate 3 is p = 50 μm, the distance between the movable slit plate 3 and the fixed slit plate 4 is set to g = 0.3 mm. Focal length f is 2.4
mm and 8 mm or less.

As described above, according to the present embodiment, by setting the focal length f of the collimator lens to satisfy (1.43 ga / p) <f <2d, the distance between the slits can be sufficiently secured. Therefore, breakage of the slit due to vibration or impact can be prevented.

In the present embodiment, the movable slit plate 3 is provided on the light source 1 side, but the fixed slit plate 4 may be provided on the light source side.

In this embodiment, the slits on the movable slit plate are arranged linearly. However, the movable slit plate and the fixed slit plate are formed as disks, and the slits are arranged on the circumference thereof to detect the rotation angle. You may do it.

[0086]

As described above, according to the present invention, the distance between the movable slit plate and the fixed slit plate can be sufficiently secured by setting the dimension a of the light emitting portion of the light source to satisfy a <0.7 fp / g. Therefore, it is possible to prevent the slit from being damaged by vibration and impact.

Alternatively, the focal length f of the collimator lens
Is satisfied so as to satisfy 1.43 ga / p <f <2d, the distance between the movable slit plate and the fixed slit plate can be sufficiently set, so that damage to the slit due to vibration and impact can be prevented.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a first embodiment of the present invention.

FIG. 2 is a view showing light emitted from a light source in the embodiment.

FIG. 3 is a diagram showing light incident on a moving slit plate and a fixed slit plate in the embodiment.

FIG. 4 is a diagram for explaining a signal duty in the embodiment.

FIG. 5 is a configuration diagram of a second embodiment of the present invention.

FIG. 6 is a schematic diagram of a conventional optical encoder.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source 2 Collimator lens 3 Moving slit plate 4 Fixed slit plate 5 Receiver

────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masaya Ito 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-5-40046 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G01D 5/26-5/38 G01B 11/00-11/30

Claims (2)

(57) [Claims] 1. A light source, a collimator lens having the light source as a front focal point, a first slit plate having a plurality of slits arranged at equal intervals using light emitted from the collimator lens as incident light, and the first slit A second slit plate having a plurality of slits arranged in parallel with the slits of the first slit plate and at the same pitch as the light emitted from the plate as incident light, and the emitted light of the second slit plate as incident light. A light receiving section, at least the first slit plate or the second slit plate is movable, and the focal length of the collimator lens is f, the pitch of the first slit plate is p, and the first slit plate and the second slit are When the distance between the plates is g, the dimension a of the light emitting portion of the light source in the arrangement direction of the slits of the first slit plate is a <0.7 fp / g. Manabu encoder. 2. A light source, a collimator lens having the light source as a front focal point, a first slit plate having a plurality of slits arranged at equal intervals with the light emitted from the collimator lens as incident light, and the first slit. A second slit plate having a plurality of slits arranged in parallel with the slits of the first slit plate and arranged at the same pitch with the light emitted from the plate as incident light, and the light emitted from the second slit plate as incident light A light receiving unit, wherein at least the first slit plate or the second slit plate is movable, and the dimension of the light emitting unit of the light source in the arrangement direction of the slits of the first slit plate is a, and the pitch of the first slit plate is When the distance between the first slit plate and the second slit plate is g and the aperture diameter of the collimator lens is d, the focal length f of the collimator lens is (1. 43 ga / p) <f <2d.