JPH0621789B2 - Distance detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention uses a semiconductor position detector that receives light from an object to be measured as a light spot and detects the position of this light spot. The present invention relates to a distance detecting device that detects a distance to an object to be measured based on an output from the.

[Conventional technology]

Conventionally, there is an active distance detecting device that projects light from a light source onto an object to be measured, receives reflected light with a semiconductor position detector provided at a position apart from the light source, and detects the distance to the object to be measured. Are known.

FIG. 4 is an explanatory diagram of an optical system of such a distance detecting device.
As shown in the figure, the light from the light source 1 such as a light emitting diode (LED) is irradiated onto the DUT 3 via the condenser lens 2. The reflected light from the DUT 3 is condensed by the light receiving lens 4 and is incident as a light spot of a light receiving portion (not shown) of the semiconductor position detector 5. Here, the baseline length is set to B, and the measured object 3
Is L, the distance between the light receiving lens 4 and the semiconductor position detector 5 (image forming distance) is f, and the light point position on the semiconductor position detector 5 from the optical axis of the light receiving lens 4 (concentration center position) S
When the distance to P (the amount of movement of the spot light) is x, the following formula (1) is established.

x = (f · B) / L (1) Therefore, if the values of x, f, and B are known in FIG. 4, the distance L to the DUT 3 can be obtained.

FIG. 5 is a detailed sectional configuration diagram of the one-dimensional semiconductor position detector 5 shown in FIG. As shown in the figure, the intrinsic (i
A p-type resistance layer 52 in which p-type impurities are uniformly diffused is formed on the surface side of a (type) silicon substrate 51 to form a light receiving portion as a pn junction diode. In addition, on the back surface side of the silicon substrate 51, n ⁺ which is a high concentration of n-type impurities diffused
A mold conductive layer 53 is formed, and an electrode 54 is in ohmic contact with this. The signal extraction electrodes 55a and 55b are integrally provided at both ends of the p-type resistance layer (light receiving portion) 52 on the front surface side, and the currents I _A and I _B are taken out therefrom.

Now, it is assumed that the light from the DUT 3 is incident on the position SP on the p-type resistance layer 52 as a light spot, and the position SP is separated from the electrode 55a by the distance x. Also, the electrodes 55a, 5
5b is C, the resistance value of the p-type resistance layer 52 between them is R _C , the resistance of the p-type resistance layer 52 between the position SP and the electrode 55a is R _x , When the generated photocurrent is I _O , the following equations hold for the currents I _A and I _B.

In _{I A = I O · (R} C -R x) / R C I B = I O · R x / R C ... (2) where the resistance value of the p-type resistive layer 52 from proportional to its length, The above equation (2) becomes the following equation (3).

I _A = I _O · (C−x) / C I _B = I _O · x / C (3) Therefore, from the above formula (3), (I _A −I _B ) / (I _A + I _B ) = 1-2x / C ...
(4) is obtained, the current I can be obtained regardless of the intensity of incident light.
_A, it is possible to calculate the incident position SP of the light from the value of I _B.

FIG. 6 is a diagram showing a distance detecting optical system when the distance measuring range is set from L _N to L _F. The luminous flux of the light source 1 is condensed by the condensing lens 2 to irradiate the DUT 3. The reflected light from the DUT 3 is condensed by the light receiving lens 4 which is arranged at a distance of the base line length B from the condensing lens 2. The semiconductor position detector 5 is arranged at a light collecting position (light spot position) at a distance f from the light receiving lens 4.

Here, the closest distance (limit on the short distance side) and the farthest distance (limit on the long distance side) in the distance measuring range are L _N and L _F , respectively, and the distance to the DUT 3 is L. Further, the distance from the optical axis of the light receiving lens 4 to the one end of the light receiving portion of the semiconductor position detector 5 and x _F, the distance x _N to the other end
And x is the distance from the light spot position SP at which the reflected light from the DUT 3 is condensed by the light receiving lens 4 to the optical axis of the light receiving lens 4, and the light receiving portion of the semiconductor position detector 5 from the light spot position SP. When the distance to _one end is x ₁ and the length of the light receiving portion of the semiconductor position detector 5 (interval between a pair of electrodes) is C, the following relational expressions hold.

Therefore, the following equation (7) is obtained from the above equations (5) and (6).

Further, in FIG. 6, a relational expression of x ₁ = x−x _F = f · B (1 / L−1 / L _F ) ... (8) is also obtained.

Next, the position resolution of the semiconductor position detector 5 is Δx and the distance L is
The distance resolutions at _N and L _F are ΔL _N and Δ, respectively.
And L _F, expressed the relationship of _{L N} and _{L F} with _{L F / L N = m ...} (9), the following relationship is obtained.

From equations (11) and (12), the distance resolutions ΔL _N and ΔL _F are as shown in equations (13) and (14), respectively.

ΔL _N = Δx · L ▲ ² _N ▼ / (Δx · L _N + f · B) ...
(13) ΔL _F = m ² · Δx · L ▲ ² _N ▼ / (m · Δx · L _N + f · B) ... (14) When the ratios of the expressions (13) and (14) are taken, the following ( 1
Equation 5) is obtained.

ΔL _F / ΔL _N = m ² · (Δx · L _N + f · B) / (m · Δx · L _n + f + B) (15) In the expression (15), m · Δx · L _N << f · B When is satisfied, this can be approximated by the following equation (16).

ΔL _F / ΔL _N ≈m ² (16) From the equation (16), it can be seen that the distance resolution ΔL _F on the far distance side is significantly deteriorated when m shown in the above equation (9) is large.

[Problems to be solved by the invention]

In other words, if the range from the shortest measurable distance to the farthest measurable distance is increased, the resolution at such a long distance decreases. Therefore, for example, a position detection device that is expected to have an optical resolution on the short distance side, such as a position detection on a processing part of a laser processing machine, can be used on a long distance side such as a position detection on an unmanned guided vehicle traveling. When applied to a device that requires a high resolution, there is a drawback that the desired resolution cannot be obtained.

Therefore, according to the present invention, the ratio of the far and near limit distances (L _F / L _N =
It is an object of the present invention to provide a distance detection device having a wide side distance range that can obtain high distance resolution on the far side even if m) is increased.

[Means for solving problems]

A distance detecting device according to the present invention forms a light receiving portion containing a first conductivity type impurity on a front surface side of a high-resistance semiconductor substrate, and forms a second conductivity type impurity layer on a back surface side of the light receiving portion to be measured. When a light from an object is incident as a light spot, it is equipped with a semiconductor position detector from which a photocurrent is taken out from signal extraction electrodes arranged at both ends of the light receiving part. A distance detecting device for detecting a distance to a measurement object, characterized by being configured as follows. That is, the above-mentioned light receiving section includes a plurality of light receiving areas each having a pair of signal output electrodes arranged at both ends, and the plurality of light receiving areas are arranged in a row so that one and the other of each pair of signal output electrodes are adjacent to each other. And the intervals between the signal extraction electrodes of the plurality of light receiving areas gradually increase from one to the other, and the intervals between the signal extraction electrodes of an arbitrary light receiving area and the other side adjacent to the arbitrary light receiving area The ratio of the light receiving area to the distance between the signal extraction electrodes is always constant. Further, the distance detecting device of the present invention is based on the photocurrent output from each pair of signal extraction electrodes of the plurality of light receiving areas, and a determining means for determining which light receiving area is most strongly exposed to light, Of the photocurrent output of the light receiving area of the light receiving area based on the discrimination result of the discriminating means, and the position of the light spot in the light receiving portion from the photocurrent output selected by the selecting means. And calculating means for calculating the distance to the object to be measured.

[Action]

According to the configuration of the present invention, the light from the object to be measured on the far distance side and the light from the object to be measured on the near distance side are incident on different light receiving areas as light spots, and accordingly, each photocurrent is received by each light receiving area. It is output from the signal extraction electrode of the area. And
Regarding the photocurrent output from each light receiving area, it is determined which one is most strongly exposed to the light. Therefore, the most suitable light receiving area is selected according to the distance to the object to be measured, and the distance is detected.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

FIG. 1 is a block diagram of a distance detecting device according to an embodiment, which has a semiconductor position detector and a signal processing circuit for processing an output signal thereof. As shown, in this embodiment, the first feature is that the light receiving portion of the semiconductor position detector is divided into a plurality of areas (light receiving areas), and the second feature is that the photocurrent output from each light receiving area is selected. The predetermined arithmetic processing is performed based on the photocurrent output from the light receiving area where the light is most intense.
Therefore, first, the structure and operation of the semiconductor position detector will be described in detail.

2 is a perspective view of the semiconductor position detector, FIG. 3 (a) is a plan view thereof, and FIG. 3 (b) is a longitudinal sectional view thereof. What is characteristic of this compared with the conventional one is that the light receiving portion formed on the front surface side of the semiconductor substrate is formed by arranging a plurality of light receiving areas in a row. The n (n is an integer of 2 or more) light receiving areas 52 _{1 to} 52 _n are
It is formed by uniformly diffusing P-type impurities on the surface side of the high resistance silicon substrate 51.
The length of _{1 to} 52 _{n in} the longitudinal direction is sequentially increased. Then, a pair of signal extraction electrodes 55a _{1 to} 55 55 each having a sufficiently narrow width is provided at both ends of each of the light receiving areas 52 _{1 to} 52 _n.
a _n , 55b _{1 to} 55b _n are arranged, and C ₂ / C ₁ = C ₃ / C ₂ = ... for the lengths C _{1 to} C _n of the P-type resistance layer (light receiving area) between the pair of extraction electrodes. = relationship _{C n / C n-1 =} D ( constant) ... (17) is satisfied. In addition, each signal extraction electrode 55a ₁
～55A _n, the width W of _55b 1 _{~55b n} is assumed to be sufficiently narrow to the extent that can be regarded as a W _{"C 1.}

The distance measuring range is divided into n, and L ₁ , L ₂ , L ₃ ,
Assuming that L ₄ , ... L _n , when the semiconductor position detector 5 satisfies the above equation (17), the following equation (18) holds.

L ₁ / L ₂ = L ₂ / L ₃ = L ₃ / L ₄ = ... = L _n-1 / L _n = D (constant) ... (18) In the amplifier circuit connected to the semiconductor position detector 5, a semiconductor is used. The light incident on the position detector 5 includes ambient light (for example, sunlight) in addition to the signal light. In this case, the current −
It is common to use an AC coupling method using a voltage conversion resistor and a capacitor (see "Semiconductor Position Detector Catalog" P.14 issued by Hamamatsu Photonics KK). At this time, due to the difference in the temperature characteristics of the inter-electrode resistance R _C of the semiconductor position detector 5 and the current-voltage conversion resistance, an error occurs in the signal calculation output shown in the above equation (4). Therefore, the electrodes _55a 1 _{~55a n} on high-resistance silicon substrate 51 of the semiconductor position detector 5 shown in FIG. 2, the current in proximity to _55b 1 _{~55b n} - voltage converting resistor (not shown) By forming the resistors and aligning the temperature characteristics of the resistors, the error in the signal calculation output can be eliminated.

FIG. 1 is a block diagram of a semiconductor position detector 5 applied to the present invention and a signal processing circuit dedicated thereto. In this embodiment, the light receiving portion 51 of the semiconductor position detector 5 is separated from the separation layer 58.
_1, 58 ₂ by completely divided into three parts, the relationship of the aforementioned equation (17) is set to the following values.

C ₂ / C ₁ = C ₃ / C ₂ = 2 (19) Along with this, the division of the distance-measuring range becomes the following numerical value from the above-mentioned formula (18).

L ₁ / L ₂ = L ₂ / L ₃ = 2 (20) Each of the light receiving areas 52 _{1 to} 52 on the semiconductor position detector 5.
₃ signal extraction electrodes 55a _{1 to} 55a ₃ and 55b _{1 to} 55
b ₃ to contact a current - voltage conversion resistor r is formed.
Photocurrents I _A and I _B obtained by the incidence of light
Is converted into a voltage by this current-voltage conversion resistor r,
Only AC components are AC-coupled by the capacitor C and are sent to the amplifiers U _{1 to} U ₆ , and after amplification, they are transferred to the gate circuit 22 and the adding circuits U _{7 to} U ₉ . Addition circuit U ₇ calculates the sum of the AC components in the photocurrent light is obtained by entering the light receiving area 52 ₁ of the semiconductor position detector 5. Similarly, the adder circuits U ₈ and U ₉ calculate the sum of the AC components of the photocurrents obtained from the light receiving area 52 ₂ and the light receiving area 52 ₃ . The outputs of the adder circuits U _{7 to} U ₉ are given to the sample and hold circuits U _{10 to} U _12, and the signal level of the light reflected from the DUT 3 when the light source 1 is pulsed is held. It The sampling signal at this time is shown by symbol φ ₂ in FIG.

The output of the sample-and-hold circuit U ₁₀ ~U ₁₂ is averaged by the filter circuit U ₁₃ ~U _15. The output of the filter circuit U ₁₃ ~U ₁₅ is supplied to the comparison circuit U ₁₆ ~U _18, wherein the light receiving area 52 _{1-52 3} of the signal light reflected from the object to be measured 3 is semiconductor position detector 5 It is determined which one of the light receiving areas is most strongly hit, and the result is output as gate signals G1, G2 and G3. Here, for example, when the optical signal is incident on the light receiving area 52 _1, a gate signal G1 is "H" (high level), and the gate signal G2 and G3 is set to "L" (a low level). These gate signals G1, G2 and G3
Thus, in the gate circuit 22, the signal line from the light receiving area where the signal light is most strongly incident is turned on, and the output is sent to the subtraction circuit 23 and the addition circuit 24.

The operation outputs of the subtraction circuit 23 and the addition circuit 24 are given to a signal component extraction circuit 25, where only the signal component superimposed on the disturbance light component is extracted. Here, the sampling signal φ ₁ is the voltage level immediately before the light source is pulsed.
The voltage level at the time of pulse lighting is recorded by the sampling signal φ ₂ . The signal component is extracted by taking the difference between the two recorded values. The output of the signal component extracting circuit 25 is given to the analog divider 26, where an arithmetic operation is executed and output in the form of an analog voltage. As a result, it is determined where the object to be measured is in the distance measuring range divided into three by the output states of the gate signals G1, G2 and G3, and the accurate distance to the object to be measured 3 is obtained by the analog voltage output. be able to.

Specifically, the analog calculation for detecting the distance can be performed by the above equations (3) and (4).
That is, when erasing the distance x from the equation (1) and _{(4), (I A -I B) /} (I A + B) = 1-2f · B / (C · L) ... (21) since the relationship is obtained, the current calculated value _(I a _-I B) /
It can be seen that (I _A + _B ) is inversely proportional to the distance L to the object to be measured, and therefore the distance L can be indirectly obtained.

Although not shown in the figure, of the output of the signal component extracting circuit 25, the level of the signal of I _A + _B is monitored, and the drive circuit (not shown) on the light source 1 side so that this voltage level becomes constant. By controlling (1), the calculation accuracy of the analog divider 26 can be improved.

Next, the above embodiment will be described in more detail with specific numerical values.

First, the optical conditions of the distance measuring device of the embodiment are set as follows.

f = 60 [mm] B = 200 [mm] L _N3 = 750 [mm] L _F3 = L _N2 1500 [mm] L _F2 = L _N1 3000 [mm] L _F1 = 6000 [mm] L _F1 / L _N1 = 2 C1 = f · B (1 / L _N1 −1 / L _F1 ) = 2 [mm] Δx = C1 / 500 = 4 [μm] The resolution of the semiconductor position detector 5 is the magnitude of the signal photocurrent based on the incident light. varies with, but the sum of the general signal photocurrent _(I a _{+ B)} is at 300 [nA], the resolution Δx is about 1/500 of the electrode spacing. Therefore, Δx = C1 /
Calculate as 500. Substituting the above numerical values into the above equation (14), the distance resolution ΔL _F of the farthest distance is as follows.

ΔL _F = 12 [mm] (19) On the other hand, when the conventional semiconductor position detector is used in the same optical system, the distance resolution of the farthest distance is similarly obtained as follows.

_{f · B = 12000 L N =} 750 (mm) L _F = 6000 [mm] _{L F / L N = 8 C} = f · B (1 / L N -1 / L F) = 14 [mm] [Delta] L _F = 83 [mm] (20) Then, comparing equations (19) and (20), the distance resolution in long-distance measurement is higher in this embodiment than in the case of using the conventional semiconductor position detector. Even with the same optical system, it is improved about 7 times. This effect can be further improved by increasing the number of divisions of the light receiving portion of the semiconductor position detector (the number of light receiving areas).

The present invention is not limited to the above embodiment, and various modifications can be made.

For example, the semiconductor position detector applied to the distance detecting device of the present invention is not limited to that shown in FIG. Further, the semiconductor substrate is not limited to silicon, and if gallium arsenide (GaAs) is used, for example, it can be used under higher temperature conditions.

〔The invention's effect〕

As described above in detail, according to the present invention, the light from the object to be measured for long-distance measurement and the light from the object to be measured for short-distance measurement are made incident on different light receiving areas as light spots, and accordingly, each light The current is output from the signal extraction electrode in each light receiving area. Then, since the photocurrent output from the light receiving area where the light is most intense is selected and the analog calculation is performed, even if the ratio of the far and near limit distances (L _F / L _N = m) is increased, It is possible to obtain a distance detection device having a wide distance measuring range and capable of obtaining high distance resolution on the far side.

[Brief description of drawings]

FIG. 1 is a block diagram of an essential part of a distance detecting device according to an embodiment of the present invention, FIG. 2 is a perspective view of a semiconductor position detector applied to the embodiment of the present invention, and FIG. 3 is shown in FIG. A plan view and a longitudinal sectional view of the semiconductor position detector, FIG. 4 is an explanatory view of an optical system of the distance detecting device, FIG. 5 is a sectional view of the semiconductor position detector applied to a conventional device, and FIG. 6 is a distance measuring device. Range L _N to L _F
FIG. 7 is an explanatory diagram of a distance detecting optical system when the setting is made. 1 ... Light source, 2 ... Condensing lens, 3 ... Object to be measured, 4 ...
... light receiving lens, 5 ... semiconductor position detector, 22 ... gate circuit, 23 ... subtraction circuit, 24 ... addition circuit, 25 ...
… Signal component sampling circuit, 26… Analog divider, 51…
... Silicon substrate, 52 ... Light receiving part (P-type resistance layer), 52
_{1 to} 52 _n ... light receiving area, 53 ... n ^{+ type} conductive layer, 5
_{5a, 55a 1 ~55a n, 55b} , 55b 1 ~55b
_n ...... signal extraction _electrodes, U 1 ~U ₆ ...... _amplifier, U 7 ~U
₉ ...... adder circuit, U ₁₀ ~U ₁₂ ...... sample and hold circuit, U ₁₃ ~U ₁₅ ...... filter circuit, U ₁₆ ~U ₁₈ ......
Comparison circuit (comparator).

Claims (4)

[Claims] 1. A high-resistance semiconductor substrate is provided with a light receiving portion containing a first conductivity type impurity on a front surface side thereof, and a second conductivity type impurity layer is formed on a back surface side of the high resistance semiconductor substrate. When light is incident as a light spot, a semiconductor position detector is provided from which a photocurrent is taken out from the signal extraction electrodes arranged at both ends of the light receiving part. In the distance detection device for detecting the distance to the DUT by obtaining the incident position, the light receiving unit includes a plurality of light receiving areas in which each pair of signal extraction electrodes is arranged at both ends, and the plurality of light receiving areas are One and the other of each of the pair of signal extraction electrodes are arranged in a row so as to be adjacent to each other, and the intervals between the signal extraction electrodes in the plurality of light receiving areas gradually increase from one to the other, and at the same time, receive any light. Area signal extraction The ratio of the distance between the electrodes and the distance between the signal extraction electrodes of the light reception area on the other side adjacent to the arbitrary light reception area is always constant, and the ratio from the pair of signal extraction electrodes of the plurality of light reception areas Based on the photocurrent output, a determination unit that determines which of the light receiving areas is most strongly exposed to light, and the one of the plurality of light receiving areas that is most strongly exposed to light is the determination unit of the determination unit. Selective means for selecting based on the discrimination result, and arithmetic means for calculating the distance to the object to be measured by obtaining the position of the light spot in the light receiving part from the photocurrent output selected by the selecting means. Distance detection device. 2. The distance detecting device according to claim 1, wherein the light receiving portion is divided into the plurality of light receiving areas via a separation layer formed on the semiconductor substrate. 3. The distance detecting device according to claim 1 or 2, wherein the signal extracting electrode is grounded via a resistor for current / voltage conversion. 4. The distance according to claim 1, wherein the discriminating means has a comparison circuit for comparing the photocurrent output levels of the plurality of light receiving areas. Detection device.