JP2002198568A - Light projecting unit and photoelectric sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light projecting unit which outputs parallel light whose light intensity is uniform without attenuating the quantity of the radiated light outputted from a light emitting means, and a photoelectric sensor. SOLUTION: The photoelectric sensor 1 is constituted of the light projecting unit 6 provided with an LED 4 as a light emitting means and a collimator lens 5, a light receiving unit 11, and a light shaded state detecting circuit as a light shaded state detecting means. In the photoelectric sensor 1, curvature of the collimator lens 5 included in the light projecting unit 6 is so set that the quantity of the radiated light is made constant against the radiated light from the LED 4 in accordance with a parallel light outputted from a unit area in an output surface of the collimator lens 5, in order to make the quantity of the parallel light outputted from the unit area uniform. As a result, light intensity distribution can be made uniform in the output surface without attenuating the quantity of the parallel light outputted from the light projecting unit 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light projecting unit for emitting parallel light having a uniform light amount per unit area on an exit surface, and a measuring optical path for transmitting and receiving parallel light using the light projecting unit. The present invention relates to a photoelectric sensor that measures a position, a size, and the like of a detected object by detecting a light blocking state of the detected object.

[0002]

2. Description of the Related Art Conventionally, based on detecting a light blocking state when an object to be detected is placed on a measurement optical path for transmitting and receiving parallel light, a photoelectric sensor for measuring the position and size of the object to be detected is used. There are sensors. For example, FIG. 9 shows a configuration of a photoelectric sensor 100 for measuring a height dimension of an object. In FIG. 9, the light emitting unit 101 has an LED.
102 and a collimating lens 103 are provided,
The radiated light emitted from the LED 102 is collimated by passing through the collimating lens 103 and is emitted as parallel light.

The light receiving unit 104 is provided with a slit 105 having a rectangular opening, a condenser lens 106, and a photodiode 107. Of the parallel light, the light passing through the slit 105 is condensed by the condenser lens 106. In this state, the light is received by the photodiode 107,
The photodiode 107 outputs an electric signal that has been photoelectrically converted according to the amount of received light. The signal processing unit (not shown) is composed of an electric circuit mainly composed of a microcomputer, and the relative relationship between the amount of received light and the height of the detected object is previously recorded as data. Then, the amount of light received by the photodiode 107 is detected based on the electric signal, and the height of the detected object is measured based on a comparison between the amount of received light and the relative relationship data.

[0004]

By the way, in general, L
The ED 102 emits radiated light having a light intensity distribution such that the light intensity increases near the optical axis and decreases as the emission angle increases (see FIG. 10). Therefore, the light intensity distribution of the parallel light that passes through the collimator lens 103 and travels on the measurement optical path is also substantially non-uniform, and therefore, when this parallel light is represented by a light beam 108, as shown in FIG. The center is dense and sparse toward the outer edge.

Accordingly, when measuring the height dimensions of the detected object having different height dimensions, the rate of change in the height direction of the detected object and the ratio of the amount of light that is blocked by the detected object and no longer passes through the slit 105 ( (Light-shielding ratio) is not proportional to the light-receiving amount of the photodiode 107, and the light-shielding ratio is not proportional to the light-shielding ratio, and the measurement accuracy of the height dimension is reduced. For this reason,
In Japanese Unexamined Patent Publication No. 3-12403 and Japanese Unexamined Patent Publication No. Hei 8-240412, for example, as shown in FIG.
By making the opening width of the aperture 9 narrower toward the denser portion of the parallel light beam 108 (see FIG. 9), the amount of the parallel light passing through the slit 109 becomes uniform in the direction perpendicular to the optical axis. The light amount was adjusted. This allows
For example, in the case of a box-shaped object to be detected, the relationship between the rate of change in the height direction of the object to be detected and the light blocking rate can be made a proportional relationship,
Measurement accuracy of the height dimension can be improved.

However, such a slit 109
Is a method of attenuating the amount of light per unit area passing through the central portion so as to be equal to the amount of light per unit area passing through the outer edge, so that the amount of light received by the photodiode 107 is reduced. , The SN ratio decreases. In addition, as shown in FIG. 12, for example, when the detection objects 110 and 111 having a spherical shape with the same curvature and different heights are placed on the measurement optical path, as shown in FIG. IX and the amount of light IY transmitted through the shaded portion Y have a relationship of IX <IY, and the change rate in the height direction of the object to be detected and the light blocking ratio are not proportional to each other. There was also a problem of lowering. Further, there is a disadvantage that it is difficult to perform an alignment operation for aligning the center of the slit 109 with the optical axis of the emitted light, and since the slit 109 having a special shape must be manufactured,
There is also a disadvantage that the manufacturing cost is increased.

In Japanese Patent Application Laid-Open Nos. 7-209507 and 7-208939, an optical filter is proposed in which the same effect as the slit 109 is replaced by an optical filter. Although not shown, the optical filter is provided on a surface perpendicular to the optical axis of the parallel light emitted from the collimator lens, and the light transmittance of the light is reduced as the light flux of the parallel light becomes denser. The light amount is adjusted so that the light amount of the transmitted parallel light becomes uniform. In this case, the shape of the slit can be left rectangular. Moreover, regardless of the shape of the detected object, the rate of change in the height direction of the detected object and the light-shielding ratio are in a proportional relationship, and the measurement accuracy of the height dimension can be improved.

However, there is a problem that the total amount of light received by the photodiode is reduced and the SN ratio is reduced.
There are problems such as difficulty in alignment work and increase in manufacturing cost due to the addition of an optical filter, and there is room for improvement.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a light projecting device which emits parallel light having a uniform light intensity without attenuating the amount of radiation emitted from a light emitting means. An object of the present invention is to provide a unit and a photoelectric sensor including the light projecting unit.

[0010]

According to a first aspect of the present invention, there is provided a photoelectric sensor including a collimating lens for collimating radiation emitted from a light emitting means and having a light intensity distribution which becomes smaller as the radiation angle becomes larger, to emit parallel light. In the light projection unit provided, the curvature of the collimator lens is set such that the amount of the parallel light per unit area on the exit surface perpendicular to the optical axis is uniform.

According to such a configuration, unlike a method of emitting parallel light having a uniform light intensity distribution using, for example, a slit or an optical filter, a state in which a large intensity is maintained without attenuating the amount of emitted light. Thus, parallel light having a uniform light intensity distribution can be emitted. Moreover, since it is only necessary to adjust the curvature of the collimator lens without adding new optical components, it is possible to suppress an increase in the manufacturing cost of the light projecting unit.

According to a second aspect of the present invention, the curvature of the collimating lens is such that the amount of the radiated light incident from the light-emitting means corresponding to the parallel light emitted from a unit area on the emission surface is a constant value. It is characterized by being set based on an arithmetic expression such as

According to such a configuration, since the radiation light having a wider radiation angle range is condensed toward the periphery of the collimator lens, the parallel light having the same light intensity as the vicinity of the optical axis having the higher light intensity is emitted on the entire exit surface. Can be emitted.

According to a third aspect of the present invention, the curvature of the collimating lens is set such that an amount of attenuation due to reflection on the surface of the collimating lens is removed in advance in accordance with the radiation angle. I do.

According to such a configuration, the amount of attenuation due to the reflection on the surface of the collimator lens is canceled, so that the reflectivity changes according to the angle of incidence on the surface of the collimator lens, so that the light is condensed on the exit surface. It is possible to prevent the amount of light per unit area from becoming non-uniform,
The uniformity of the light intensity distribution of the parallel light can be further improved.

According to a fourth aspect of the present invention, a photoelectric sensor according to any one of the first to third aspects, and the parallel light emitted from the light emitting unit is condensed by a condenser lens.
A light receiving unit for receiving the condensed light by a light receiving unit, and detecting a light blocking state of a measuring optical path formed between the light projecting unit and the light receiving unit based on an amount of light received by the light receiving unit. A photoelectric sensor, comprising: a light-shielding state detecting unit.

According to such a configuration, since parallel light having a uniform light intensity distribution is emitted from the light projecting unit, it is possible to make the light blocking rate of the measuring optical path and the amount of light received by the light receiving means proportional. As a result, the detection accuracy of the light-shielded state can be improved. Moreover, since the light intensity of the parallel light is sufficiently large,
The S / N ratio can be improved. In addition, the work of aligning the light emitting unit and the light receiving unit can be simplified, and it is not necessary to add a new optical component, so that an increase in manufacturing cost can be suppressed.

According to a fifth aspect of the present invention, there is provided a photoelectric sensor including a collimating lens for collimating a radiated light emitted from the light emitting means and having a light intensity distribution that becomes smaller as the radiation angle becomes larger, and emitting the parallel light. A light-receiving unit that collects the parallel light emitted from the light-projecting unit with a condenser lens and receives the collected light with a light-receiving unit capable of detecting a light-receiving position, and is detected by the light-receiving unit. A light-shielding state detecting unit that detects a light-shielding state of an optical path formed between the light-emitting unit and the light-receiving unit based on the light-receiving position; A photoelectric sensor, wherein the amount of the condensed light per unit area on a surface is set to be uniform.

According to such a configuration, parallel light having sufficiently large light intensity and uniform light intensity distribution is emitted from the light projecting unit, and the state of blocking the parallel light by the detected object is set at the light receiving position of the light receiving means. Since they are associated with each other, it is possible to improve measurement accuracy such as recognition of the position, size, and shape of the detected object.

In the photoelectric sensor according to the sixth aspect, the curvature of the collimating lens may correspond to the amount of the radiated light incident from the light emitting unit corresponding to the condensed light incident on a unit area of the light receiving surface of the light receiving unit. Is set based on an arithmetic expression that makes a constant value. With such a configuration, the same effect as that of the second aspect can be obtained.

According to a seventh aspect of the present invention, the curvature of the collimating lens is set such that an amount of attenuation caused by reflection on the surfaces of the collimating lens and the condenser lens is removed in advance in accordance with the radiation angle. It is characterized by being.

According to such a configuration, the amount of attenuation due to reflection on the surfaces of the collimating lens and the condensing lens is canceled, so that the reflectivity changes in accordance with the angle of incidence on the surface of each lens. The amount of light per unit area condensed on the light receiving surface of the light receiving unit can be prevented from becoming non-uniform, so that the uniformity of the light intensity distribution of the condensed light on the light receiving surface of the light receiving means can be further improved. it can.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] FIGS. 1 to 6 show a first embodiment in which the photoelectric sensor of the present invention is applied to a photoelectric sensor for measuring the height of an object to be detected. It will be described with reference to FIG. FIG. 1 shows a configuration of the photoelectric sensor 1. In FIG. 1, a photoelectric sensor 1 is installed on the side of a line 2 through which objects to be detected having different heights flow, as follows.

First, a box-shaped case 3 is provided on one side of the line 2, and an LED 4 as a light emitting means is provided in the case 3. The LED 4 emits light when electric power is supplied from an external power supply (not shown), and emits radiated light whose light intensity distribution decreases as the radiation angle increases.

An opening 3b formed in the front of the case 3 has a biconvex collimating lens 5 whose center is located on the optical axis of the radiation emitted from the LED 4.
Is mounted, and the radiation emitted from the LED 4 is
The light is collimated by the collimating lens 5 and is emitted toward the line 2 as parallel light. The surface of the collimating lens 5 is provided with an anti-reflection film. The light emitting unit 6 is constituted by the LED 4 and the collimating lens 5.

Next, a box-shaped case 7 is provided on the other side of the line 2 facing the light projecting unit 6, and a front portion 7a of the case 7 has a longitudinal direction perpendicular to the longitudinal direction. A slit 8 is formed as a slit means which is oriented and is opened in a rectangular shape such that the center portion is located at the optical axis. Further, a biconvex condensing lens 9 is provided inside the case 7 so that the central portion is located on the extension of the optical axis.
Are disposed, and a photodiode 10 as a light receiving unit is positioned at the focal position of the condenser lens 9.

The surface of the condenser lens 9 is provided with an anti-reflection film. In the photodiode 10, all the parallel light passing through the slit 8 is collected, and an electric signal that is photoelectrically converted according to the light intensity of the collected light is output. The slit 8, the condenser lens 9 and the photodiode 10 constitute a light receiving unit 11.

Although not shown, the light-shielding state detecting circuit is constituted by an electric circuit mainly composed of a microcomputer, and measures the height of an object to be detected based on an electric signal received from the photodiode 10. Done. Then, information on the measured height of the detected object is transmitted to a line management device (not shown), and is used for controlling the division of the detected object. As described above, the photoelectric sensor 1 is configured by the light projecting unit 6, the light receiving unit 11, and the light blocking state detecting circuit.

<Description of Function of Photoelectric Sensor 1> Next, the function of the photoelectric sensor 1 will be described. First, the curvature of the collimating lens 5 attached to the light projecting unit 6 is such that the light intensity distribution of the parallel light is uniform on the exit surface 13 (see FIG. 2) perpendicular to the optical axis, which will be described later in detail. Is set to Therefore, when this parallel light is represented by a light beam, it becomes uniform with respect to the emission surface 13 as shown in FIG.

Now, the parallel light whose light intensity distribution emitted from the light projecting unit 6 is uniform on the exit surface 13 is represented by line 2.
The light is emitted toward the slit 8 of the light receiving unit 11 while forming a measurement optical path thereon. Then, only parallel light having the same width as the opening width of the slit 8 passes through the slit 8 and is condensed by the condensing lens 9, and this condensed light is
0 is received. Subsequently, in the photodiode 10, an electric signal photoelectrically converted according to the light intensity of the condensed light is output to the light-shielded state detection circuit.

In the light-shielded state detection circuit, the amount of light received by the photodiode 10 is detected based on the received electric signal. In this case, the light intensity distribution of the parallel light
Is uniform, the amount of light received by the photodiode 10 is proportional to the ratio of the amount of light that is shielded according to the height of the detected object when the detected object passes through the measurement optical path (light blocking ratio). I do. Then, assuming that the light reception rate of the light reception amount detected in a state where light is not blocked (a state where 100% of parallel light is incident on the slit 8) is 100%, a light reception rate detected when light is blocked by the detected object is determined. Thereby, the height dimension of the detected object is measured.

<Method of Setting Curvature of Collimating Lens 5>
Next, the curvature of the collimating lens 5 that collimates the radiated light emitted from the LED 4 and whose light intensity distribution becomes smaller as the radiation angle becomes larger, and emits parallel light so that the light intensity distribution becomes uniform on the emission surface 13. The setting method of will be described.

FIG. 2 shows an optical configuration of the aspherical collimating lens 5. As shown in FIG. Here, for the sake of simplicity, the LED 4 is assumed to be a point light source, and the light intensity of the emitted light is cos with respect to the emission angle θ with respect to the optical axis 12.
It changes with θ. A plane perpendicular to the optical axis near the collimating lens 5 on the side where parallel light is emitted is referred to as an emission surface 13. Further, the minute solid angle α at the incident angle θA
The radiation light incident at A is RA, the parallel light is HA (near the optical axis), the light flux is ΦA, the radiation light incident at a small solid angle αB at the incident angle θB is RB, and the parallel light is HB
(Near the middle between the optical axis and the peripheral end), the luminous flux is ΦB, and the radiated light incident at a small solid angle αC at the incident angle θC is R
C, the parallel light is HC (near the peripheral end), and the light flux is ΦC
And

First, the concept of the method of setting the curvature of the collimator lens 5 will be described. In order to make the light intensity distribution of the parallel light uniform on the exit surface 13, the amount of light per unit area of the exit surface 13 is required. Should be uniform.
That is, for example, assuming that the parallel light beams HA to HC are emitted from the unit area t of the emission surface 13 in FIG. For this purpose, first, the minute solid angles αA to αC such that the light amounts of the radiated lights RA to RC incident from the LED 4 corresponding to the parallel lights HA to HC emitted from the unit area t on the emission surface 13 become constant. Is determined. Then, the radiated lights RA to RC incident at the incident angles θA to θC and the minute solid angles αA to αC satisfy the relationship such that they are emitted as parallel lights HA to HC from the unit area t of the emission surface 13. , The curvature of the collimating lens 5 is set.

Next, a method of setting the curvature of the collimator lens 5 will be described with reference to a specific design example. First,
The design conditions of the collimating lens 5 are set as follows. Refractive index n = 1.486 (assuming that the refractive index of air is 1) Focal length F = 32.428 mm

Next, the light intensity of the radiated light R incident at a small solid angle α at a predetermined incident angle θ is I (α), the minute irradiation area when the radiated light R is incident on the collimating lens surface is ΔS, The unit area t of the emission surface 13 is determined by the radiation R.
Let ΔΦ be the luminous flux of the parallel light H emitted from, the following relational expression is derived between ΔΦ, I (α), and ΔS. ΔΦ = I (α) × ΔS (1)

For example, the relationship between the radiated lights RA to RC is expressed by the following equation based on the equation (1). I (αA) × ΔSA = I (αB) × ΔSB = I (αC) × ΔSC (2)

The curved surface equation of the aspherical collimator lens 5 is expressed by the following equation when the optical axis is the z-axis and the x and y axes are set on a plane perpendicular to the optical axis.

(Equation 1) Here, c represents the curvature of the collimating lens, and there is a relationship of c = 1 / r with the radius of curvature r. D,
e, f, g, and K are coefficients.

Subsequently, the design conditions of the collimating lens 5 and the relation (ie, equation (2)) that makes the left side of equation (1) constant are satisfied so that each coefficient c in equation (3) is satisfied. G and K are set to optimal values. It should be noted that this optimization can be easily performed in a short time by performing arithmetic processing on a computer using the quasi-Newton method or the like.

By this optimization, the collimating lens 5 is designed so that the radiated light having an incident angle of up to 30 ° as shown in FIG. 3 is taken in and parallel light having a radius of 15 mm is emitted.

<Method of Evaluating Uniformity of Light Intensity Distribution on Outgoing Surface 13 of Parallel Light> When the curvature of the collimating lens 5 is set as described above, the uniformity of light intensity distribution on the outgoing surface 13 of parallel light is determined. In order to evaluate, we introduce the concept of linearity error. This linearity error is also defined in Japanese Patent Application Laid-Open No. Hei 1-312403.

FIG. 4 shows the relationship between the light receiving rate and the light blocking rate in the photoelectric sensor 1. The light blocking ratio in this case is defined as a case where the slit 8 is blocked in the same direction from above or below. In FIG. 4, a straight line indicated by a one-dot chain line is a reference line 14 indicating a relationship between a light receiving ratio and a light shielding ratio with ideal parallel light whose light intensity distribution is completely uniform on the emission surface 13. On the other hand, a curve shown by a solid line is a light receiving ratio in a parallel light having a non-uniform light intensity distribution such that the center is dense and becomes sparse toward the outer edge as in the photoelectric sensor 100 shown in the conventional example. 7 is an actual measurement line 15 showing a relationship between the light-shielding ratio and the light-shielding ratio.

The linearity error ER is defined as PS with respect to the light receiving rate of the reference line 14 and P with the light receiving rate of the actual measurement line 15 at a predetermined light blocking rate, and the difference between PS and P as ΔP. The ratio of ΔP is defined as the following equation. ER = ΔP / PS × 100 (%) (4)

FIG. 5A shows a linearity error ER in the photoelectric sensor 1 when the collimating lens 5 is mounted on the light projecting unit 6. FIG.
6B shows, for comparison, a conventional collimating lens (plano-convex lens) 103 having the same design conditions as shown in FIG.
9 shows a linearity error ER in the photoelectric sensor 100 when the sensor is mounted on the optical sensor 100. Thus, it can be seen that the linearity error of the photoelectric sensor 1 of the present embodiment is much smaller than that of the conventional one. Moreover, in the case of the conventional collimating lens 103, the incident angle is 21.9.
Only synchrotron radiation up to ° is taken in (see Fig. 6).
Therefore, in the collimating lens 5 of the present embodiment, it can be seen that the radiation light of a wider range of radiation angles (incident angle 30 °, see FIG. 3) is taken in, thereby suppressing the radiation light attenuation.

As described above, in this embodiment, in order to make the amount of parallel light emitted from the unit area t on the exit surface 13 of the collimating lens 5 uniform, the parallel light emitted from the unit area t on the exit surface 13 is used. LED4 corresponding to light
The curvature of the collimator lens 5 is set so that the amount of the radiated light incident from the lens becomes constant. Then, the photoelectric sensor 1 configured to measure the height of the detected object by the light projecting unit 6, the light receiving unit 11, and the light shielding state detecting circuit having the collimating lens 5 is configured.

According to such a configuration, unlike a method of emitting parallel light having a uniform light intensity distribution using, for example, a slit or an optical filter, a state in which a large intensity is maintained without attenuating the amount of emitted light. As a result, parallel light having a uniform light intensity distribution on the emission surface can be emitted. Moreover, since it is only necessary to adjust the curvature of the collimator lens 5 without adding new optical components, it is possible to suppress an increase in the manufacturing cost of the light projecting unit 6.

Further, since the radiation light having a wider radiation angle range is condensed toward the periphery of the collimating lens 5, parallel light having the same light intensity as that near the optical axis where the light intensity is large is emitted from the entire exit surface 13. Can be.

Further, since parallel light having a uniform light intensity distribution is emitted from the light projecting unit 6, the light receiving rate and the light blocking rate can be made in a proportional relationship, and the detection accuracy of the light blocking state can be improved. . Moreover, since the light intensity of the parallel light is sufficiently large, the SN ratio can be improved. In addition, the work of aligning the light projecting unit 6 and the light receiving unit 11 is simplified, and it is not necessary to add a new optical component, so that an increase in manufacturing cost can be suppressed.

[Second Embodiment] Hereinafter, a second embodiment in which the photoelectric sensor of the present invention is applied to a photoelectric sensor for measuring the height of an object to be detected will be described with reference to FIGS. I do. The same parts as those in the first embodiment are denoted by the same reference numerals and the description thereof will be omitted, and only different parts will be described below.

As shown in FIG. 7, in the photoelectric sensor 20 according to the second embodiment, the curvature of the condenser lens 21 mounted on the light receiving unit 11 maintains the light intensity distribution of the parallel light passing through the slit 8. It is set to condense as it is (in a linear state). Incidentally, a conventional general condenser lens is set to such a curvature. Then, a one-dimensional light receiving element 22 is mounted on the side wall surface 7b as a light receiving means capable of detecting a light receiving position so that a longitudinal direction thereof is oriented in a vertical direction. The one-dimensional light receiving element 22 is configured such that N light receiving units are arranged in a line at equal intervals.

The curvature of the collimator lens 23 mounted on the light projecting unit 6 is set to be different from the curvature of the collimator lens 5 shown in the first embodiment, as will be described later in detail.

<Description of Operation of Photoelectric Sensor 20> Next, the operation of the photoelectric sensor 20 will be described. First, the curvature of the collimator lens 23 mounted on the light projecting unit 6 is set so that the light amount per unit area of the condensed light on the light receiving surface of the one-dimensional light receiving element 22 is uniform, which will be described later in detail. Have been.

The parallel light emitted from the light projecting unit 6 is applied to the slit 8 of the light receiving unit 11 while forming a measuring optical path on the line 2,
, And is condensed by the condensing lens 21, and the condensed light is received by the one-dimensional light receiving element 22. One-dimensional light receiving element 2
In the N light receiving units in 2, the received light amount is independently photoelectrically converted into an electric signal for each light receiving unit, and the electric signals from these N light receiving units are parallel-serial converted at a predetermined cycle,
It is output as a serial signal to the light shielding state detection circuit. In the light-shielded state detection circuit, the light receiving position of the condensed light is detected based on the received electric signal, and the detected object is located at a position corresponding to the light receiving position where the condensed light was not detected (ie, the light-shielded position). As a result, the height of the detected object is measured.

<Method of Setting Curvature of Collimating Lens 23> Next, a method of setting the curvature of the collimating lens 23 will be described. In the second embodiment, it is assumed that the surfaces of the collimator lens 23 and the condenser lens 21 are not provided with an antireflection film. In this case, the collimating lens 2
On the surface of the condenser lens 3 and the condenser lens 21, the larger the incident angle is, the larger the reflection rate is, and the more the light is attenuated. Therefore, when the light intensity distribution of the parallel light is made uniform on the exit surface, the unit of the condensed light on the light receiving surface of the one-dimensional light receiving element 22 is affected by the influence of the reflection when the light is condensed by the condenser lens 21. The luminous flux per area is dense at the center and sparse at the outer edge. Therefore, in the second embodiment, the attenuation of the light amount due to the surface reflection of the collimating lens 23 and the condensing lens 21 is canceled, and the light amount per unit area of the condensed light on the light receiving surface of the one-dimensional light receiving element 22 is reduced. The curvature of the collimator lens 23 is set so as to be uniform.

FIG. 8 shows an aspherical collimating lens 23.
2 illustrates an optical configuration of the condenser lens 21. Here, the same symbols as those in the first embodiment are used for the incident angle θ, the small solid angle α, the light flux Φ, the emitted light R, and the parallel light H. The condensed light condensed by the condensing lens 21 is referred to as SA to SC, respectively.

Now, in order to make the amount of condensed light per unit area on the light receiving surface of the one-dimensional light receiving element 22 uniform,
First, when parallel light is incident on the condenser lens 21, the amount of light attenuated by surface reflection according to the angle of incidence on the condenser lens 21 is canceled, and condensed light on the light receiving surface of the one-dimensional light receiving element 22 is canceled. The unit area t of the exit surface 13 of the collimating lens 23 is set so that the amount of light per unit area becomes uniform.
The light fluxes of the parallel lights HA to HC emitted from are determined.

Next, the unit area t on the emission surface 13
ΦA to ΦC of parallel light HA to HC emitted from
The small solid angles αA to αC of the radiated lights RA to RC incident on the collimating lens 23 from the LED 4 are determined in accordance with the following. Also in this case, when the radiated light enters, the small solid angle αA is set so that the amount of light attenuated by surface reflection according to the angle of incidence on the collimator lens 23 is canceled.
To αC. The specific setting method is the same as in the first embodiment (1) and (3).
The description may be omitted because it may be performed based on the equation.

As described above, in the second embodiment, the curvature of the collimating lens 23 is such that the light quantity attenuation due to the surface reflection of the collimating lens 23 and the condensing lens 21 is canceled, and then the light reception of the one-dimensional light receiving element 22 is performed. The amount of condensed light per unit area on the surface was set to be uniform.
The light projecting unit 6 having the collimating lens 23, the condensing lens 21 for condensing light while maintaining the light intensity distribution of the parallel light, and the one-dimensional light receiving element 2 for receiving the condensed light
2 and a photoelectric sensor 20 for measuring the height of the detected object by the light-shielding state detection circuit.

According to such a configuration, the light emitting unit 6
Since a parallel light having a sufficiently large light intensity and a uniform light intensity distribution is emitted from the device, and the light blocking state of the parallel light by the detected object is associated with the light receiving position of the one-dimensional light receiving element 22,
Measurement accuracy of the height dimension of the detected object can be improved.

Further, since the radiation light having a wider radiation angle range is condensed toward the periphery of the collimator lens 23, parallel light having the same light intensity as that near the optical axis where the light intensity is high is emitted from the entire exit surface 13. Can be.

Further, since the amount of attenuation of the light amount due to the surface reflection of the collimating lens 23 and the condensing lens 21 is canceled, the reflectance changes according to the angle of incidence on the surface of each of the lenses 21 and 23, so that the one-dimensional It is possible to prevent the amount of light per unit area condensed on the light receiving surface of the light receiving element 22 from becoming non-uniform. Therefore, the uniformity of the light intensity distribution of the condensed light on the light receiving surface of the one-dimensional light receiving element 22 can be prevented. Can be further improved.

The present invention is not limited to the embodiment described above and shown in the drawings.
Extension is possible. In the first embodiment of the present invention, the collimator lens is provided with the antireflection film.
The present invention is not limited to this. When the antireflection film is not provided, the curvature of the collimator lens may be set so that surface reflection according to the incident angle of the radiated light at the collimator lens is canceled. .

In the embodiment of the present invention, the light emitting means is applied to the LED. However, the present invention is not limited to this. For example, the light emitting means may be applied to a laser light source such as a semiconductor laser or a general light bulb. Also, for example, the present invention may be applied to a light source configured to emit radiation light from an optical fiber end.
Any device may be used as long as it emits radiated light whose light intensity distribution decreases as the radiation angle increases.

In the embodiment of the present invention, the photoelectric sensor is applied to a device for measuring a height dimension. However, the present invention is not limited to this, and may be applied to a device for measuring a length of an object to be detected. Further, the light receiving means in the second embodiment of the present invention is, for example, a two-dimensional light receiving element, so that the present invention can be applied to a device for measuring two-dimensional shape recognition of a detected object. Further, the light receiving means may be configured so that, for example, the light condensed by the condensing lens is once received by the optical fiber, and the light propagated by the optical fiber is received by the light receiving element.

In the embodiment of the present invention, the slit is provided at the position where the parallel light enters the light receiving unit. However, the present invention is not limited to this, and the slit is provided on the optical path formed between the light emitting means and the light receiving means. If necessary, it may be provided at any position. In addition, the slit may be provided as needed. In short, the optical system of the photoelectric sensor may be set so that the area of the parallel light received by the light receiving unit is restricted to a rectangular slit shape.

[0066]

As is apparent from the above description, in the light emitting unit of the present invention, by adjusting the curvature of the collimating lens, the light intensity distribution of the parallel light emitted from the light emitting unit is uniform on the emitting surface. Therefore, parallel light having a uniform light intensity distribution can be emitted while maintaining a large light intensity without attenuating the amount of radiation light emitted from the light emitting means. Since the light emitting unit, the light receiving unit and the light shielding state detecting means constitute a photoelectric sensor, the linearity error can be reduced and the measurement accuracy in the light shielding state can be improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a photoelectric sensor according to a first embodiment of the present invention.

FIG. 2 is an optical configuration diagram of a collimating lens.

FIG. 3 shows a design example of a collimating lens.

FIG. 4 is a diagram showing a relationship between a light receiving rate and a light blocking rate of a photoelectric sensor.

FIG. 5 is a diagram showing a linearity error of a photoelectric sensor.

FIG. 6 is a diagram corresponding to FIG. 3 showing a conventional example.

FIG. 7 is a view corresponding to FIG. 1, showing a second embodiment of the present invention;

FIG. 8 is an optical configuration diagram of a collimator lens and a condenser lens.

FIG. 9 is a diagram corresponding to FIG. 1 showing a conventional example.

FIG. 10 is a light intensity distribution diagram with respect to an emission angle of an LED.

FIG. 11 is a diagram showing a shape of a slit.

FIG. 12 is a diagram showing the relationship between the light shielding state of a slit and the amount of light passing therethrough.

[Explanation of symbols]

In the drawing, 1, 20 is a photoelectric sensor, 2 is a line, and 4 is LE
D (light emitting means), 5 is a collimating lens, 6 is a light emitting unit, 8 is a slit (slit means), 9 and 21 are condensing lenses, 10 is a photodiode (light receiving means), 11 is a light receiving unit, and 22 is a primary light. 1 shows a primary light receiving element (light receiving means).

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02B 3/00 G02B 19/00 5F089 3/02 H01L 31/12 D 19/00 G01J 1/02 P H01L 31 / 12 F21M 1/00 Q // G01J 1/02 F term (reference) 2F065 AA07 AA24 DD00 EE04 EE08 FF02 GG07 GG12 HH03 HH13 HH15 JJ02 JJ09 JJ25 LL00 LL28 QQ25 UU01 UU05 2G065 AB23 BA23 BA09 BA06 3K042 AA01 AC06 BC01 5F041 AA06 EE11 EE16 FF16 5F089 BB04 BC15 GA01

Claims (7)

[Claims] 1. A light-projecting unit comprising a collimating lens for collimating radiation emitted from a light-emitting means and having a light intensity distribution that becomes smaller as the radiation angle becomes larger and emitting parallel light, the curvature of the collimator lens is A light emitting unit, wherein the light quantity per unit area of the parallel light on the exit surface perpendicular to the optical axis is set to be uniform. 2. An arithmetic expression for calculating a curvature of the collimating lens such that an amount of the radiated light incident from the light emitting unit becomes a constant value corresponding to the parallel light emitted from a unit area on the emission surface. 2. The light projecting unit according to claim 1, wherein the light emitting unit is set based on: 3. The projection according to claim 2, wherein the curvature of the collimating lens is set in advance so as to remove an attenuation due to reflection on the surface of the collimating lens in accordance with the radiation angle. Light unit. 4. The light projecting unit according to claim 1, wherein the parallel light emitted from the light projecting unit is condensed by a condenser lens, and the condensed light is transmitted to a light receiving unit. Based on the amount of light received by the light receiving unit
A photoelectric sensor comprising: a light-shielding state detecting unit that detects a light-shielding state of a measurement optical path formed between the light projecting unit and the light receiving unit. 5. A light projecting unit having a collimating lens for collimating emitted light emitted from the light emitting means and having a light intensity distribution that becomes smaller as the radiation angle becomes larger and emitting parallel light, and emitting from the light projecting unit. A light receiving unit that collects the parallel light with a condenser lens, and receives the collected light with a light receiving unit capable of detecting a light receiving position, based on the light receiving position detected by the light receiving unit, A light-blocking state detection unit that detects a light-blocking state of an optical path formed between the light-emitting unit and the light-receiving unit; A photoelectric sensor, wherein the light amount per unit area is set to be uniform. 6. The curvature of the collimating lens is such that the amount of radiated light incident from the light emitting means has a constant value corresponding to the condensed light incident on a unit area of the light receiving surface of the light receiving means. The photoelectric sensor according to claim 5, wherein the photoelectric sensor is set based on an arithmetic expression. 7. The curvature of the collimating lens is set in advance so as to remove attenuation due to reflection on the surfaces of the collimating lens and the condenser lens according to the radiation angle. Item 7. The photoelectric sensor according to Item 6.