JP2942046B2 - Optical ranging sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical distance measuring sensor such as a PSD.

[0002]

2. Description of the Related Art PSD (Position Sensi)
The active Photodetector (semiconductor position detecting element) is a light spot position detecting sensor to which a photodiode (PD) is applied.

In this PSD, the balance between the extracted signal currents I ₁ and I ₂ changes depending on the position of the incident light spot. FIG. 2 shows a detection principle diagram of a distance measuring sensor using a PSD.

[0004] As shown in FIG.
The light emitted from the (LED) is reflected by a reflector (for example, a person) 3 through a lens 2 and is incident on a PSD 5 through a lens 4. The position where the reflected light M is incident on the PSD 5 (spot position of the light) changes depending on the distance D between the person 3 and the sensor, and when the reflection object 3 is farther (when D becomes longer), the reflected light M1 is shown in FIG. It looks like the dotted line in 2,
The spot position of the light incident on the PSD 5 also changes. PS
When Supotsuto position of light changes incident to D5, the signal current I ₁ and I ₂ to be taken out from both ends of PSD5 accordingly
The balance changes.

By detecting the balance between the signal currents I ₁ and I ₂ by a signal processing circuit, the distance between the reflector 3 and the sensor can be detected, and the sensor can be used as a distance measuring sensor using the PSD 5. it can. FIG. 5 shows functional blocks of a conventional distance measuring sensor using the PSD 5. As shown in FIG. In FIG. 5, reference numeral 8 denotes a signal processing circuit, and 9 denotes an LED drive circuit.

Here, the principle of operation of the PSD will be described with reference to FIG. PSD5 is, as shown in FIG.
The silicon chip is composed of a p ^- layer on the front surface, an n ⁺ layer on the back surface, and an I layer in the middle, and when the surface of the PSD 5 is irradiated with a light spot φ, the generated charges (carriers) are resistive. In the layer (p ^- layer), the light is divided in inverse proportion to the incident position of light and the distance to the extraction electrodes A and B, and the light is extracted as currents I ₁ and I ₂ from the electrodes A and B, respectively.

Now, as shown in FIG. 4A, the photocurrent I ₀ ,
The distance from the midpoint of the electrodes A and B to the light incident point P is x,
The resistance from the incident point P to the electrode A is R ₁ , the resistance from the incident point P to the electrode B is R ₂ , the distance between the electrodes A and B is L, and the resistance between the electrodes A and B is R. Assuming that the currents taken from _T and electrodes A and B are I ₁ and I ₂ , respectively, the current I
₁ and I ₂ are represented by the following equations (1) and (2).

[0008]

(Equation 1)

Since the distribution of the specific resistance R _i of the surface resistance layer (p ⁻ layer) is uniform as shown in FIG. 4B, the resistances R ₁ and R ₂ are changed from the incident point P to the electrodes A and B. It is proportional to the distance to and is expressed by the following equation.

[0010]

(Equation 2)

When this is substituted into the equations (1) and (2), the currents I ₁ and I ₂ extracted from the electrodes A and B are as follows.

[0012]

(Equation 3)

Here, the ratio of the sum and difference of the currents I ₁ and I ₂ is given by the following equation.

[0014]

(Equation 4)

As described above, when the PSD is used as the light receiving element, the position information can be directly obtained as an output.

FIG. 6 shows an example of the signal processing circuit 8 for processing the signal currents I ₁ and I ₂ of the PSD 5. In FIG.
R1~R7 resistance, P ₁ to P ₅ denotes an amplifier. PSD5
The signal currents I ₁ and I ₂ of
The signals are converted into voltages V ₀₁ and V ₀₂ . V ₀₁ is V ₀₁ = R ₁ × I ₁ , V
₀₂ is V ₀₂ = R ₁ × I ₂ . Next, the subtraction of V ₀₂ and V ₀₁ at subtraction circuit 12 to obtain an output voltage V _OA corresponding to I ₂ -I _1. V _0A is represented by the following equation.

[0017]

(Equation 5)

[0018] In addition, at the adder circuit unit 13, performs the addition of V ₀₁ and V _02. In FIG. 6, V ₀₃ is represented by the following equation.

[0019]

(Equation 6)

Then, an output V _OB corresponding to I ₁ + I ₂ can be obtained. V _0B is represented by the following equation.

[0021]

(Equation 7)

The V _OA and V _OB are processed by a microcomputer or the like to obtain V _OA / V _OB . V _0A / V _0B is represented by the following equation.

[0023]

(Equation 8)

Therefore, (I ₂ −I ₁ ) / (I ₁ + I ₂ )
Corresponds to the position of the light incident on the PSD 5 as described above, and is expressed by (I ₂ −I ₁ ) / (I ₁ + I ₂ ).
The position of the spot of the light incident on the spot is known.

When the spot position of the light incident on the PSD 5 is known, the distance between the sensor and the reflector 3 is known as described above.

As described above, the signal current I _{1 of the} PSD _{5 is obtained.}
And I ₂ are processed by the signal processing circuit 8, so that the distance between the sensor and the reflector 3 can be detected.

FIG. 7 shows an example of another signal processing circuit 8 of the PSD 5. In the circuit of FIG. 7, 15 is a logarithmic conversion circuit section, 16 is a differential amplifier circuit section, 17 and 18 are log diodes, and outputs V ₀₁ and V ₀₂ are represented by the following equations. Here, k is the Boltzmann constant, T is the absolute temperature (° K), and q is the amount of electron charge.

[0028]

(Equation 9)

The output V ₀ from inside the amplifier circuit section 16
Is represented by the following equation.

[0030]

(Equation 10)

With this circuit, an output corresponding to log (I ₁ / I ₂ ) can be obtained. As described above, I ₁ / I ₂ corresponds to the spot position of the light incident on the PSD 5 , and the log (I ₁ / I ₂ ) indicates the spot position of the light incident on the PSD 5 . When the spot position of the light incident on the PSD 5 is known, as described above, the sensor and the reflector
3 can be detected.

[0032]

In the above prior art, as shown in FIG. 5, since the LED 1 is driven and controlled only by the drive circuit 9, the control of the light emission amount is constant regardless of the distance to the distance measuring object. It was. Therefore, for example, as shown in FIG. 2, when the PSD 5 is used, it is necessary to increase the amount of received light in order to measure a long distance.

However, when doing so, the PSD5 on the short distance side
Above the allowable photocurrent (FIG. 3), and the range of distance measurement is limited.

[0034] Incidentally, in FIG. 3 (A) shows an equivalent circuit of the PSD 5, (B) shows an equivalent circuit of the reverse bias V _R. The allowable photocurrent I in this circuit is represented by the following equation.

[0035]

[Equation 11]

Here, V _DF is a forward voltage of the diode.

In view of the above, it is an object of the present invention to provide a distance measuring sensor which can measure a long distance even if a PSD is used.

[0038]

SUMMARY OF THE INVENTION As shown in FIG. 1, the present invention monitors the amount of light incident on a PSD and controls the amount of light emission based on the output current of the PSD light. Try to expand the range.

[0039]

In the above means for solving the problems, when the light output current of the PSD 5 increases, the light emission amount is reduced so as not to exceed the allowable light current of the PSD 5.

[0040]

An embodiment of the present invention will be described below with reference to FIG.

In FIG. 1, reference numeral 1 denotes an LE as a light emitting element.
D and 5 are PSDs as light receiving units, and 8 is a signal processing circuit. These components have the same functions as those of the conventional one, and therefore description thereof is omitted.

In this embodiment, a light receiving amount detecting circuit 21 for detecting the light receiving amount of the PSD 5 is provided. This detection circuit 21 has a common terminal of the PSD 5,
Connected to the n-side terminal C of the pn diode shown
5 is to detect the photocurrent flowing through 5.

The signal from the detection circuit 21 is
Is input to a control circuit 22 for controlling the amount of light emitted from the light source. The control circuit 22 controls the light emission amount of the LED 1 so as not to exceed the allowable photocurrent of the PSD 5. That is, PSD5
If the light output current of the LED increases, the light emission amount decreases and the PSD
The allowable photocurrent of 5 is not exceeded.

In the above configuration, when measuring to a long distance, control is performed to increase the light emission amount. In this case, since the amount of light received from the reflecting object is not so large, PSD5
Does not exceed the allowable photocurrent.

When measuring a short distance, the amount of light emission is reduced so that the allowable photocurrent of the PSD 5 is not exceeded.

It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that many modifications and changes can be made to the above-described embodiment within the scope of the present invention.

[0047]

As is clear from the description above, according to the present invention, according <br/> to the onset bright, since the controlled amount of light emitted from the light emitting portion in accordance with the measurement distance, long distance not short distance only Can be measured.

Even if a semiconductor position detecting element (PSD) is used as the light receiving section, the light receiving amount is detected and the light emitting amount is controlled so as not to exceed the allowable photocurrent. There is an excellent effect that the measurement range at a long distance is expanded. Detecting the amount of light received by this semiconductor position detecting element
When the semiconductor position detection element which is the output signal from the common terminal
Detection based on the photocurrent flowing through the
Calculation is not required and the configuration of the received light amount detection circuit can be simplified.
You.

[Brief description of the drawings]

FIG. 1 is a functional block diagram of a distance measuring sensor according to the present invention.

FIG. 2 is a diagram showing the principle of detection by a distance measuring sensor.

3A is an equivalent circuit diagram of a PSD, and FIG. 3B is a PSD.
Equivalent circuit diagram with reverse bias

4A is a diagram illustrating the principle of operation of a PSD, and FIG. 4B is a distribution diagram of a specific resistance R _i of a surface resistance layer.

FIG. 5 is a functional block diagram of a conventional distance measuring sensor.

FIG. 6 is a signal processing circuit diagram of signal currents I ₁ and I ₂ of a conventional PSD.

FIG. 7 is another signal processing circuit diagram of signal currents I ₁ and I ₂ of a conventional PSD.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Infrared light emitting diode 2 Lens 3 Reflector 4 Lens 5 PSD 8 Signal processing circuit 21 Light reception amount detection circuit 22 Light emission amount control circuit

Claims (1)

(57) [Claims] 1. A light from a light emitting unit is applied to a detection object, the reflected light is received by a light receiving unit constituted by a semiconductor position detecting element, and a distance to the detection object is measured according to a light receiving position of the received light. In the optical distance measuring sensor, the amount of light received by the light receiving unit is changed from a common terminal of the semiconductor position detecting element.
A light reception amount detection circuit for detecting based on the output signal is provided, and based on a detection result from the light reception amount detection circuit, the light emitting unit outputs a light output current of the semiconductor position detection element so as not to exceed an allowable photocurrent. An optical distance measuring sensor comprising a control circuit for controlling the amount of light emitted from the optical distance measuring device.