JP5595360B2 - Optical displacement measuring device - Google Patents

Description

  The present invention relates to an optical displacement measuring device that measures a minute displacement of incident light radiated from a light source using a light detection element.

  In order to measure a minute displacement of incident light, a spot light (incident light) is incident from a light source to a light detection element whose light receiving surface is divided into a plurality of regions, and the output from each region of the light detection element An apparatus for measuring the relative displacement of the spot light with respect to the light detection element based on the change is known. This utilizes the fact that the amount of light incident on each region changes in accordance with the change in the position of the spot light on the light detection element, and the output from each region changes in proportion to the amount of light.

  As such a device, a light beam (incident light) is made incident from a light emitting diode to a light receiver (photodetection element) whose light receiving surface is divided into a plurality of light receiving portions, and changes in the light reception output from each light receiving portion. Based on this, a displacement detection device that measures the two-dimensional displacement of the light beam is known (see, for example, Patent Documents 1 and 2).

Hereinafter, a conventional optical displacement measuring device will be described with reference to the drawings.
FIG. 6 is a perspective view showing a quadrant photodiode 50, which is a light detection element of a conventional optical displacement measuring device, together with a light source 60. In FIG. 6, spot light (incident light) 61 is incident on the four-divided photodiode 50 from a light source 60 configured by a light emitting diode (LED) and a pinhole cap.

  FIG. 7 is a configuration diagram showing an extracted light receiving surface of the quadrant photodiode 50 shown in FIG. In FIG. 7, the light receiving surface of the four-divided photodiode 50 is configured by four photodiodes (elements) 51 </ b> A to 51 </ b> D having the same area. That is, the quadrant photodiode 50 has a light receiving surface divided into four regions. The boundaries between the four photodiodes 51A to 51D are separated by a region called a gap that is insensitive to light.

  When light enters, the photodiode outputs a current corresponding to the amount of light. Therefore, when spot light is incident on the quadrant photodiode 50 from the light source 60, an output corresponding to the ratio of the amount of light incident on each of the photodiodes 51A to 51D is obtained. Here, the barycentric position of the spot light can be obtained by taking the ratio of the outputs from the photodiodes 51A to 51D.

  Thereby, the relative displacement of the spot light with respect to the quadrant photodiode 50 can be measured based on the change in the output from each of the photodiodes 51 </ b> A to 51 </ b> D. That is, an optical displacement measuring device that measures a minute displacement of the spot light emitted from the light source 60 can be configured.

  FIG. 8 is a schematic diagram showing a circuit configuration of a conventional optical displacement measuring device. With this circuit configuration, the horizontal and vertical displacements of the spot light can be obtained. In FIG. 8, this optical displacement measuring apparatus includes a four-division photodiode 50, a first-stage amplifying unit 52, a second-stage amplifying unit 53, and a third-stage amplifying unit 54 each having a light receiving surface composed of photodiodes 51A to 51D. It has.

  Each of the photodiodes 51A to 51D outputs a current corresponding to the amount of incident spotlight. The first-stage amplifying unit 52 converts the output signals from the photodiodes 51A to 51D into voltages and amplifies them using amplifiers provided corresponding to the photodiodes 51A to 51D, respectively.

  The second stage amplification unit 53 calculates the difference between the output signal from the photodiode 51A amplified by the first stage amplification unit 52 and the output signal from the photodiode 51C and is amplified by the first stage amplification unit 52. The difference between the output signal from the photodiode 51D and the output signal from the photodiode 51B is taken, and each output signal is amplified (differential amplification processing).

  The third stage amplifying unit 54 calculates the sum of the output signals from the second stage amplifying unit 53 (sum calculation) and calculates the difference between the output signals from the second stage amplifying unit 53 (difference calculation). . At this time, if necessary, the third stage amplifying unit 54 amplifies each output signal. Here, assuming that output signals from the photodiodes 51A to 51D are simply A to D, respectively, these processes eventually result in a signal obtained by amplifying A-B-C + D representing the lateral displacement of the spot light. A signal obtained by amplifying A + B−C−D representing the displacement in the vertical direction is obtained.

  Generally, in the initial state, the spot light is arranged at a position (center) where an equal output signal can be obtained from each of the photodiodes 51A to 51D. In this state, as shown in FIG. 9, the output signals A to D from the photodiodes 51A to 51D are equal to each other, and an output signal corresponding to the ratio of the amount of light incident on each of the photodiodes 51A to 51D is obtained. It is done. Here, since the respective output signals are equal, the output signal from the second stage amplifying unit 53 becomes 0 as a result of the difference between the output signals in the second stage amplifying unit 53.

  Here, consider the case where the position of the spot light is displaced in the right direction from this state as shown in FIG. At this time, the output signals A and D from the photodiodes 51A and 51D increase in accordance with the increase in the light amount, while the output signals B and D from the photodiodes 51B and 51C decrease in accordance with the decrease in the light amount. To do.

  Therefore, in the second stage amplifying unit 53, the difference between the output signal A and the output signal C is changed from 0 to positive, and the difference between the output signal D and the output signal B is also changed from 0 to positive. Accordingly, (A−C) + (D−B) becomes positive and (A−C) − (D−B) becomes 0 in the third stage amplification unit 54, so that the spot light is displaced in the right direction. Can be detected.

  Here, when a minute displacement of the spot light is to be measured, it is necessary to set a large amplification magnification in the amplification unit. In the circuit shown in FIG. 8, since there are three stages of amplifiers from the first stage amplifier 52 to the third stage amplifier 54, the output signal can be amplified in three steps.

  However, it is desirable to perform amplification with as few stages as possible. This is because, in addition to the amplified input signal, noise generated by processing in the amplifier is superimposed on the signal output from the amplifier. For this reason, in the subsequent stage amplifier, the noise superimposed by the previous stage amplifier is also amplified, so that the magnitude of the noise component in the signal increases each time amplification is repeated.

Therefore, it is considered to increase the amplification factor as much as possible in the first stage amplification unit 52. In general, an amplifier cannot output a voltage equal to or higher than its power supply voltage. Therefore, the relationship between the amplification factor G of the amplifier and the maximum amplification factor G _{max at} which the output does not go out of range is expressed as V _out , When the input signal is I _in , the power supply voltage is V _supply , the output signal V _out = 0 when the input signal I _in = 0, and the assumed maximum value of the input signal I _in is I _max , the following equation (1 ).

In the formula (1), the input signal I _in has a bias output I _b which together according to the amount that enters the photodiode before and after the displacement of the spot light, a photodiode when the spot light is displaced by a small displacement Δd And a displacement output ΔI from the sum (I _in = I _b + Δd). At this time, in the input signal I _in after the spot light is displaced, since I _b >> ΔI, it is understood that the bias output I _b occupies most of the input signal I _in .

Here, in the input signal I _in , since the displacement output ΔI is meaningful as an output, it is important to amplify this signal, but the input signal I _in including the bias output I _b is amplified, Since it is necessary that the output signal V _out does not exceed the power supply voltage V _supply , the maximum gain G _max cannot be increased. Therefore, in the second-stage amplifying section 53, by taking the difference between the output signals each other, to offset the amplification component of the bias output I _b, thereafter, it is amplified only components of the displacement output [Delta] I.

JP-A-1-2011129 Japanese Patent Laid-Open No. 5-60557

However, the prior art has the following problems.
When measuring the minute displacement of the spot light, the displacement output generated by the relative displacement of the spot light with respect to the photodiode, compared to the magnitude of the bias output constantly output from the photodiode before and after the displacement of the spot light. The size of is very small.

  Here, in the first stage amplification unit that amplifies the output signal from the photodiode, both the bias output and the displacement output are amplified. For this reason, the output limit of the first stage amplification unit is reached by the bias output, and the displacement output cannot be sufficiently amplified. Therefore, in the second stage amplification unit, it is necessary to perform amplification after canceling the bias output by processing such as obtaining a difference between output signals.

  As a result, there is a problem that noise superimposed on the output signal in the first stage amplification unit is amplified in the second and subsequent amplification units, and the S / N of the output signal is deteriorated. There is also a problem that the circuit configuration of the optical displacement measuring device increases due to an increase in the number of amplifier stages.

  The present invention has been made to solve the above-described problems. In measuring a minute displacement of incident light radiated from a light source, the S / N of an output signal is improved and a circuit configuration is improved. An object of the present invention is to obtain an optical displacement measuring device that can be miniaturized.

The optical displacement measuring apparatus according to the present invention causes incident light emitted from a light source to be incident on a light detection element whose light receiving surface is divided into a plurality of regions through a gap insensitive to light. An optical displacement measuring device that amplifies the output from each region of the detection element and measures the relative displacement of the incident light with respect to the light detection element based on the change in the amplified output. In each area, a dead area where no output is generated by incident light and a photosensitive area where output is generated by incident light are formed, and the insensitive area formed in each area is formed in each area for the entire photodetecting element. A reflector portion that reflects incident light in the direction of the light source is provided in the insensitive area formed in each area of the entire light detection element .

According to the optical displacement measuring apparatus according to the present invention, in each area of the light detection element, a dead area where no output is generated by incident light and a photosensitive area where output is generated by incident light are formed. As a whole, the insensitive area formed in each area is surrounded by the photosensitive area formed in each area.
As a result, the ratio of the bias output corresponding to the amount of light incident on each area of the light detection element before and after the displacement of the incident light to the total output from each area of the light detection element is reduced, and the displacement of the incident light is reduced. The proportion of displacement output from each region of the corresponding light detection element increases. Therefore, the displacement output can be sufficiently amplified when the output from each region of the light detection element is amplified.
Therefore, when measuring a minute displacement of incident light radiated from the light source, an optical displacement measuring device capable of improving the S / N of the output signal and reducing the circuit configuration can be obtained.

It is a block diagram which extracts and shows the light-receiving surface of the photon detection element of the optical displacement measuring device which concerns on Embodiment 1 of this invention. It is explanatory drawing which shows the state in which the light has entered into the center of the photon detection element of the optical displacement measuring device concerning Embodiment 1 of this invention, and the output signal from each element at that time. It is explanatory drawing which shows the state which the light which injects into the photon detection element of the optical displacement measuring device concerning Embodiment 1 of this invention displaced to the right direction from the center, and the output signal from each element at that time. It is a block diagram which extracts and shows another light-receiving surface of the photon detection element of the optical displacement measuring device which concerns on Embodiment 1 of this invention. It is a block diagram which extracts and shows the light-receiving surface of the photon detection element of the optical displacement measuring device which concerns on Embodiment 2 of this invention. It is a perspective view which shows the photon detection element of the conventional optical displacement measuring device with a light source. It is a block diagram which extracts and shows the light-receiving surface of the photon detection element shown in FIG. It is the schematic which shows the circuit structure of the conventional optical displacement measuring device. It is explanatory drawing which shows the state in which the light has entered into the center of the photon detection element of the conventional optical displacement measuring apparatus, and the output signal from each element at that time. It is explanatory drawing which shows the state which the light which injects into the photon detection element of the conventional optical displacement measuring device displaced to the right direction from the center, and the output signal from each element at that time.

  Hereinafter, preferred embodiments of an optical displacement measuring device according to the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts will be described with the same reference numerals. In the optical displacement measuring device according to the present invention, incident light radiated from a light source is incident on a light detection element whose light receiving surface is divided into a plurality of regions, and the output from each region of the light detection element is amplified. Then, the relative displacement of the incident light with respect to the photodetecting element is measured based on the amplified output change.

  The optical displacement measuring device according to the present invention is used, for example, when measuring the displacement of a microstage. Moreover, the use of this optical displacement measuring apparatus is not limited to this, You may use for another use.

Embodiment 1 FIG.
FIG. 1 is a configuration diagram illustrating an extracted light receiving surface of a four-division photodiode 10 which is a light detection element of an optical displacement measuring apparatus according to Embodiment 1 of the present invention. In FIG. 1, spot light (incident light) 21 is incident on a four-divided photodiode 10 from a light source (not shown) configured by a light emitting diode (LED) and a pinhole cap.

  In addition, the light receiving surface of the four-divided photodiode 10 is configured by four photodiodes (elements) 11A to 11D having the same area. That is, the quadrant photodiode 10 has a light receiving surface divided into four regions. The boundaries between the four photodiodes 11A to 11D are separated by a region called a gap that is insensitive to light.

  Here, in each region of the photodiodes 11 </ b> A to 11 </ b> D, a dead region where no output is generated by the spot light and a photosensitive region where output is generated by the spot light are formed. Hereinafter, the insensitive areas formed in the respective areas of the photodiodes 11A to 11D are collectively referred to as the insensitive area 12, and the photosensitive areas formed in the respective areas of the photodiodes 11A to 11D are collectively referred to as the photosensitive area 13.

  The dead area 12 is formed in the central part of the photodiodes 11A to 11D, surrounded by the photosensitive area 13. This insensitive region 12 may be formed by creating a mask with a light shielding material on the surface of a normal multi-division photodiode in which the insensitive region 12 is not formed, or formed by applying a light shielding material. Also good. Further, the photodiode may be manufactured so that the insensitive region 12 is formed in advance.

  The circuit configuration of the optical displacement measuring device is substantially the same as that shown in FIG. However, if necessary, the second stage amplifying unit amplifies the difference between the output signal from the photodiode 11A amplified by the first stage amplifying unit and the output signal from the photodiode 11C, and the first stage amplifying unit. After taking the difference between the output signal from the photodiode 11D and the output signal from the photodiode 11B, the respective output signals are amplified.

  Here, the state in which the spot light is incident on the center of the photodiodes 11A to 11D and the output signals from the respective elements at that time are shown in FIG. Compared with the case where the insensitive region 12 is not formed as shown in FIG. 9, the output decreases from the output from each element by the bias output corresponding to the area of the insensitive region 12 at the center of the photodiodes 11A to 11D. You can see that

  Next, FIG. 3 shows a state in which the spot light incident on the photodiodes 11A to 11D is displaced rightward from the center, and output signals from each element at that time. Compared to the case where the insensitive region 12 is not formed as shown in FIG. 10, although the output is reduced by the bias output corresponding to the area of the insensitive region 12 at the center of the photodiodes 11A to 11D, the spot light Since the area of each element changed by the displacement of is the same, it can be seen that the magnitude of the change in output is the same.

  From this, by forming the insensitive region 12 in the photodiodes 11A to 11D, the ratio of the displacement output corresponding to the displacement of the spot light with respect to the entire output from the photodiodes 11A to 11D can be increased. Therefore, when the output from each of the photodiodes 11 </ b> A to 11 </ b> D is amplified in the first stage amplification unit, a sufficiently large amplification can be applied to the displacement output.

  In the above-described conventional optical displacement measuring device, the arithmetic processing is performed with the analog signal up to the third-stage amplifying unit 54. However, in the optical displacement measuring device according to the first embodiment of the present invention, one-stage processing is performed. Since the displacement output can be sufficiently amplified by the eye amplifying unit, it can be converted into a digital signal immediately after the amplification by the first stage amplifying unit and the arithmetic processing can be performed. Therefore, the apparatus configuration can be simplified.

  Note that the size of the insensitive area 12 is preferably set to a size in which the insensitive area 12 is always included in the spot light area when the spot light is displaced within a range assumed to be measured. . That is, it is desirable that the insensitive region 12 is formed within a range where the spot light is continuously incident before and after the spot light is displaced.

  This is because if the insensitive region 12 comes out of the spot light region due to the displacement of the spot light, the output from the photodiodes 11 </ b> A to 11 </ b> D depends on whether the insensitive region 12 is formed or not. This is because the amount of change is different. In such a case, the correlation between the position change of the spot light and the displacement output is broken.

  In particular, for a photodiode whose output increases due to the displacement of the spot light, the increase in output does not change from that in which the insensitive region 12 is not formed, whereas a photodiode whose output decreases due to the displacement of the spot light. In the insensitive area 12 that protrudes from the spot light, the output does not change. For this reason, the balance between the increase and decrease of the output is out of order, and the linearity of the output change with respect to the displacement of the spot light is deteriorated.

  Therefore, by forming the insensitive region 12 within a range in which the spot light is continuously incident before and after the displacement of the spot light, the linearity of the output change with respect to the displacement of the spot light can be ensured.

  Here, when the spot light is a circle having a radius R and the rated displacement of the spot light is ± Δd in both the horizontal and vertical directions, a dead region 12 that can reduce the bias output from the photodiode most is formed. The light receiving surface of the four-divided photodiode 10 is shown in FIG. In FIG. 4, the insensitive region 12 is maximized under the condition that the spot light does not go out of the spot light region even when the spot light is displaced from the center of the photodiodes 11 </ b> A to 11 </ b> D by the rated displacement amount. .

  The bias output from the photodiode can be minimized by designing the shape and size of the dead region 12 according to the shape and size when the spot light is displaced to the limit of the rated displacement.

  However, in actuality, it is conceivable that the initial positions of the spot light and the four-divided photodiode 10 do not coincide with the insensitive areas 12 and the center positions of the photodiodes 11A to 11D and are installed with a certain amount of deviation. In such a case, in order to prevent the insensitive area 12 from going out of the spot light area, it is necessary to set the insensitive area 12 to be smaller by the amount of the initial position shift that can be assumed.

  This is because the initial position of the spot light and the four-divided photodiode 10 is shifted when the size of the insensitive area 12 is set to a marginal size calculated from the rated displacement amount of the spot light. This is to prevent the insensitive region 12 from unexpectedly coming out of the spot light region and deteriorating the linearity of the output change with respect to the spot light displacement.

As described above, according to the first embodiment, in each area of the photodetecting element, the insensitive area where no output is generated by the incident light and the photosensitive area where the output is generated by the incident light are formed. As a whole, the insensitive area formed in each area is surrounded by the photosensitive area formed in each area.
As a result, the ratio of the bias output corresponding to the amount of light incident on each area of the light detection element before and after the displacement of the incident light to the total output from each area of the light detection element is reduced, and the displacement of the incident light is reduced. The proportion of displacement output from each region of the corresponding light detection element increases. Therefore, the displacement output can be sufficiently amplified when the output from each region of the light detection element is amplified.
Therefore, when measuring a minute displacement of incident light radiated from the light source, an optical displacement measuring device capable of improving the S / N of the output signal and reducing the circuit configuration can be obtained.

Embodiment 2. FIG.
In Embodiment 1 described above, it has been described that the insensitive region 12 where no output is generated by the spot light is formed at the center of the photodiodes 11A to 11D. In the second embodiment, a case will be described in which the insensitive region is provided with a reflector 14 so as to reflect the spot light incident on the insensitive region in the light source direction, as well as simply mask the insensitive region.

  FIG. 5 is a block diagram showing an extracted light receiving surface of the quadrant photodiode 10 of the optical displacement measuring apparatus according to Embodiment 2 of the present invention. In FIG. 5, a reflector portion 14 that reflects light is provided in a portion corresponding to the insensitive region 12 illustrated in FIG. 1. By providing the reflector unit 14, the spot light (incident light 22) radiated from the light source is reflected by the reflector unit 14 and returned to the light source (reflected light 23). The light enters the split photodiode 10.

  By repeating the reflection of the spot light, the spot light incident on the insensitive area is guided to the photosensitive area, so that the spot light emitted from the light source can be effectively used, and the outputs from the photodiodes 11A to 11D can be generated by the displacement of the light source. It is possible to increase the amount of light per unit area in the region where the change occurs. Therefore, even if the amount of spot light from the light source is the same, the output change with respect to the displacement of the spot light can be increased, and the S / N of the output signal can be improved.

  Note that it is conceivable that spot light is diffusely reflected by the reflector unit 14 and the reflected spot light is reflected back to the surroundings without returning to the light source as it is. In such a case, if the spot light from the light source returns to the photodiode in a region other than the originally incident photodiode, a constant output is generated as stray light regardless of the position of the spot light. Become. For this reason, the sensitivity of the output with respect to the displacement of the spot light may be reduced. Accordingly, it is desirable that the reflector unit 14 does not diffusely reflect light but reflects light straight in the direction of the light source.

In the first and second embodiments, the quadrant photodiode 10 is described as an example of the light detection element. However, the present invention is not limited to this, and the light detection surface of the light detection element is divided into two regions. Similar effects can be obtained even with a two-divided photodiode.
In addition, with respect to a multi-division photodetection element in which a certain vertex of each element of a plurality of divided areas is concentrated in a certain area, and spot light can be incident on each element simultaneously. The same effect can be obtained.
Furthermore, in the first and second embodiments, the photodiode is used as the light detection element. However, the present invention is not limited to this, and any light detection element that can obtain an output by the incidence of light, like the photodiode, can be used. The same effect can be obtained.

  10 quadrant photodiode (photodetection element), 11A to 11D photodiode, 12 insensitive area, 13 photosensitive area, 14 reflector section, 21 spot light, 22 incident light, 23 reflected light, 50 4-divided photodiode, 51A to 51D Photodiode, 52 1st stage amplification section, 53 2nd stage amplification section, 54 3rd stage amplification section, 60 light source, 61 spot light.

Claims (3)

Incident light emitted from a light source is incident on a photodetection element whose light-receiving surface is divided into a plurality of regions through a gap that is insensitive to light, and the output from each region of the photodetection element is amplified. An optical displacement measuring device that measures a relative displacement of the incident light with respect to the photodetecting element based on the amplified output change,
In each area of the photodetecting element, a dead area where no output is generated by the incident light and a photosensitive area where output is generated by the incident light are formed, and the entire photodetecting element is formed in each area. The insensitive area is surrounded by the photosensitive area formed in each area ,
An optical displacement measuring apparatus , wherein a reflector portion for reflecting the incident light in the direction of the light source is provided in the insensitive area formed in each area of the entire photodetecting element .   2. The insensitive region formed in each region of the entire photodetecting element is formed within a range in which the incident light continues to be incident before and after the displacement of the incident light. Optical displacement measuring device.   The size of the insensitive region formed in each region of the entire photodetection element is such that the incident light and the photodetection element from the outer edge of the range in which the incident light continues to enter before and after the displacement of the incident light. The optical displacement measuring device according to claim 1, wherein the optical displacement measuring device is reduced by an amount corresponding to a deviation of an initial position.

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