JPH073336B2 - Distance calculation method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a distance calculation method, and in particular, it uses the value of current output from electrodes located at both ends of a position detection light-receiving element and uses the principle of triangulation. The present invention relates to a distance calculation method capable of calculating a distance to an object to be measured.

[Conventional technology]

Optically measuring the spatial position coordinates of the object to be measured includes an image device such as a television image pickup tube or a solid-state image pickup device by electronic scanning,
Basically, most of the methods are based on image scanning technology, such as mechanical scanning of mirrors and reticles. In the case of such a scanning method, the sampling rate for measurement is determined by the number of images per second and is limited. As a method to detect the position of incident light without scanning the image, "Latera
l Light receiving element for position detection using "Photo Effect" (hereinafter P
(Abbreviated as SD) has been adopted.

The PSD obtains a signal including position information of incident light without scanning, and has a relatively simple structure and manufacturing method as compared with solid-state imaging devices such as CCD (charge coupled device) and MOS. Infinitely small pixels are considered to be innumerably distributed in a two-dimensional manner, and there is no dead zone between pixels, so that the pixel has extremely high position resolution. The calculation of the position signal and the driving of the element are relatively easy. A high sampling rate can be obtained. It is possible to easily measure the position of multiple points by turning on the light source attached to the measured point in a time-division manner (“O plus E”, March 1981).
Monthly non-scanning position sensor, Kazuo Kurasawa and others).

FIG. 3 shows an example of the cross section of the PSD. P on the surface of PSD
A mold resistance layer is provided, and the back surface is an n ⁺ layer. The substrate used is required to have as high a resistance as possible and a uniform specific resistance. By using a high resistance substrate, an element having a high response speed, low noise and excellent linearity can be obtained.
As the substrate, for example, a high resistance Si substrate is used.

Next, the operation principle will be described with reference to JP-B-58-42411 and Hamamatsu Photonics KK catalog-Principles and features of semiconductor position detecting elements.

When a light spot is incident on the PSD, an electric charge proportional to the incident energy is generated at the incident position. The generated charges pass as a photocurrent through the p-type resistance layer, and the currents I ₁ and I ₂ are extracted from the electrodes A and B, respectively. Electrode A of PSD
When the distance between B and B is 2L, the center of PSD is the origin, and the distance from the central axis of PSD to the light incident position is X _A Holds. When the one end of the PSD on the electrode A side is the origin and the distance from the electrode A to the light incident position is X _B , Holds. Therefore, the light incident position can be obtained from I ₁ and I ₂ .

On the other hand, as shown in FIG. 4, the distance from the light projecting lens 1 to the measured object 4 is a, the distance from the light receiving lens 2 to the light receiving surface of the PSD 3 is b, the optical axis of the light projecting lens 1 and the light receiving lens. Let B be the distance from the optical axis of 2 and X be the distance from the optical axis of the light receiving lens 2 to the light incident position 5 of the PSD 3. The mutual positional relationship among the light projecting lens 1, the light receiving lens 2 and the PSD 3 is fixed. Here, based on the principle of triangulation, Holds. Therefore, Is. Here, if the distance from the optical axis of the light receiving lens 2 to the right end of PSD3 is X _O and the distance from the right end of PSD3 to the light incident position 5 is X _B , then X = X _O + X _B (4). Therefore, since the light incident position can be obtained from the equation (1) or the equation (2), the distance to the measured object 4 can be obtained from the equations (3) and (4).
However, conventionally, since the setting position of PSD3 is not taken into consideration, the position error of PSD3 becomes large when the range to be measured becomes large, and there is a problem that the linearity of the output is poor.

In order to improve the linearity of the PSD output, a circuit near the broken line is added, or, for example, as shown in Japanese Patent Laid-Open No. 61-112902, the photocurrent output from the PSD is changed to (I ₁ ＋ KI ₂ )
By using / (I ₁ + KI ₂ ) or (I ₁ −I ₂ ) / (I ₁ + KI ₂ ) (K is a constant not equal to 1) for displacement output,
It has been proposed to improve linearity without providing a correction circuit. However, it was not possible to obtain good output linearity over a wide measurement range by a simple method.

[Problems to be Solved by the Invention]

Therefore, an object of the present invention is to solve the above-mentioned problems, to have linearity of output over a wide measurement range, and to measure an object to be measured from a current output from electrodes at both ends of a position detection light receiving element. It is to provide a distance calculation method capable of easily calculating a distance.

[Means for Solving the Problems]

In order to achieve such an object, the present invention projects a light beam on an object to be measured, and reflects light from the object to be measured on a light-receiving surface between the electrodes having electrodes at both ends. When light is received, currents I ₁ and I ₂ are output from each of the electrodes according to the distance between the light receiving position and the electrode. Or (In each formula, A, B, C, D, and E are constants determined by the structures of the light emitting / receiving system and the position detecting light receiving element), and the distance to the object to be measured is calculated.

[Action]

The principle of the present invention will be described. Based on the principle of triangulation, the distance a is Given in.

On the other hand, solving equation (2) for X _B Becomes Here, by substituting the above expression of X _{B into} the expression (4), Becomes Furthermore, if equation (5) is substituted into equation (3), Becomes X _O , b, B are constants determined by design,
Since L is a constant determined by PSD3 to be used, if X _O + L = A, L = B, b · B = C, then equation (6) becomes the following equation.

By measuring the outputs I ₁ and I ₂ of the PSD 3, the distance a from the light projecting lens 1 to the measured object 4 can be obtained from the equation (7).

In the present invention, as shown in the equation (5), since the calculation method takes into account the PSD mounting position, the linearity between the measured distance and the output is good.

The measured distance is obtained by the change of the light receiving position of PSD3, but if the light receiving position is largely deviated from the center, the linearity between the measured distance and the output is lost. The distance when the light receiving position is at the center of the PSD is called the center detection distance. In the conventional device, the range in which the output maintains linearity is about ± 12% with respect to the center detection distance of 16 mm, but according to the present invention, the measurement distance that can maintain the linearity of the output is the same center. It was possible to expand to a range of ± 100% for a detection distance of 16 mm.

〔Example〕

Hereinafter, embodiments to which the present invention is applied will be described in detail with reference to the drawings.

Embodiment 1 FIG. 1 is a block diagram showing an example of a circuit configuration for realizing the expression (7). The current I ₁ and the current I ₂ output from the PSD 3 are converted into voltages by the current-voltage converters 6A and 6B to be S (I ₁ ) and S (I ₂ ) signals.
The S (I ₁ ) signal and the S (I ₂ ) signal are input to the adder 7 and the subtractor 8, and are respectively S (I ₁ + I ₂ ) and S (I ₂ −
I ₁ ) signal is output. Next, the S (I ₁ + I ₂ ) signal is passed through an amplifier 9 which amplifies the signal C times, and the S (I ₁ + I ₂ ) signal is transferred to A
The signal is multiplied, and the S (I ₂ −I ₁ ) signal is multiplied by B and passed through an adder 10 for adding the two. S (C · (I ₁ + I ₂ )) signal and S
By inputting the (A (I ₁ + I ₂ ) + B (I ₂ −I ₁ ) signal to the divider 11, a can be obtained.

Dividing the denominator and numerator of equation (6) by X _O + L gives Therefore, A = 1 can be set, and the adjustment of the magnification can be reduced.

The numerator coefficient does not depend on (I ₁ + I ₂ ), in other words,
Determined by optical mechanical dimensions. Therefore, it is clear from the equation (6) that even if the coefficient of the numerator is set to 1, the output only changes n times in calculation and does not affect the calculation of the distance. Therefore, the amplifier 9 can be omitted.

Embodiment 2 FIG. 2 is a block diagram showing another embodiment to which the present invention is applied. If you pay off the brackets in the denominator of equation (6), Becomes If you divide the denominator and numerator by L, Becomes Here, if we put (b · B) / L = D, X _O / L = E, Becomes

First, the current I ₁ and the current I ₂ output from the PSD 3 are converted into voltages by the current-voltage converters 6A and 6B, respectively, and S
(I ₁ ) signal and S (I ₂ ) signal. The S (I ₁ ) signal and the S (I ₂ ) signal are passed through the adder 7 to obtain the S (I ₁ ) signal.
+ I ₂ ) signal is output.

On the other hand, the S (I ₂ ) signal is doubled by the amplifier 12 and S (2
I ₂ ) Signal. Next, the S (I ₁ + I ₂ ) signal is multiplied by E by the adder 13 and the S (E (I ₁ + I ₂ )) signal and the S (2I ₂ ) signal are added.

The S (I ₁ + I ₂ ) signal and S (E (I ₁ + I ₂ ) +2
I can be obtained by inputting the I ₂ ) signal and multiplying the output obtained by division by D.

In addition, A, B, C, D, E are amplified by the coefficient of the amplifier,
It is clear from the formula (8) that there is no problem even if the attenuator is used. Therefore, an attenuator may be used instead of the amplifier 9. Furthermore, it is clear that the adders 10 and 13 can be realized by weighted addition circuits of operational amplifier circuits.

In the conventional example, with respect to the center detection distance of 40 mm, the range in which the linearity between the measurement distance and the output was obtained was ± 5 mm, which was very narrow.
Despite the wide detection range of 16 mm to ± 8 mm, the linearity between the measured distance and the output was within ± 3%.

〔The invention's effect〕

As described above, according to the present invention, since the correction of the PSD mounting position is taken into consideration, there is an effect that the linearity between the measurement distance and the output can be obtained over a wide measurement range.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment to which the present invention is applied, FIG. 2 is a block diagram showing another embodiment to which the present invention is applied, and FIG. 3 is an explanatory view showing the principle of a position detecting light receiving element, FIG. 4 is an explanatory diagram showing how to obtain the distance to the measurement object. 1 ... Emitter lens, 2 ... Light receiving lens, 3 ... PSD, 4 ... Object to be measured, 5 ... Light incident position, 6A, 6B ... Current-voltage converter,
7 ... adder, 8 ... subtractor, 9 ... amplifier, 10 ... amplifying adder, 11 ... divider, 12 ... multiplier, 13 ... adder, 14 ... divider.

Claims (1)

[Claims] 1. A light receiving position when a light beam is projected onto an object to be measured and reflected light from the object to be measured is received by a light receiving surface between both electrodes having electrodes at both ends thereof. And currents I ₁ and I ₂ according to the distance between the electrodes are received by the position detection light receiving elements that output from each of the electrodes, Or (In each formula, A, B, C, D, and E are constants determined by the structures of the light emitting / receiving system and the position detecting light receiving element), and the distance calculating method is characterized by calculating the distance to the object to be measured.