JP2939045B2 - Distance sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring sensor using a PSD or the like.

[0002]

2. Description of the Related Art PSD (Positive) as a light receiving element.
on Sensitive Photodetecto
r = semiconductor position detecting element) is a photodiode (PD)
This is a light spot position detection sensor to which the present invention is applied.

[0003] The PSD is the position of the incident light Supotsuto balance of the signal current _{I 1} and _{I 2} to be taken out is varied. FIG. 5 shows a detection principle diagram of a distance measuring sensor using a PSD.

[0004] As shown in FIG.
The light emitted by the (LED) is reflected by a detection object (a person, for example) 3 through a lens 2 and enters a PSD 5 through a lens 4. The position at which 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. When the detected object 3 is farther (when D is longer), the reflected light M1 is shown in FIG. 5, the spot position of the light incident on the PSD 5 also changes.
When the spot position of the light incident on the PSD 5 changes, the signal current I ₁ extracted from both ends of the PSD 5 correspondingly changes.
The balance of _{I 2} is changed with.

By detecting the balance between the signal currents I ₁ and I ₂ by a signal processing circuit, the distance between the detection object 3 and the sensor can be detected, so that the sensor can be used as a distance measuring sensor using the PSD 5. it can. In FIG. 5, 21 is a storage case, and 22 is a printed wiring board (PWB) on which a signal processing circuit and the like are formed.

FIG. 8 shows functional blocks of a conventional distance measuring sensor using a PSD. In FIG. 8, reference numeral 8 denotes a signal processing circuit, and 9 denotes an LED drive circuit unit.

Here, the principle of operation of the PSD will be described with reference to FIG. PSD5 is, as shown in FIG.
When the surface of the PSD 5 is irradiated with the light spot φ, the generated charges (carriers) have a resistance of p ^- layer on the front surface of the silicon chip, N ⁺ layer on the back surface, and I layer in the middle. 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 from the electrodes A and B as currents I ₁ and I ₂ .

Now, as shown in FIG. 7A, 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 value from the incident position P to the electrode A is R ₀₁ , the resistance value from the incident position P to the electrode B is R ₀₂ , the distance between the electrodes A and B is L, and the resistance value between the electrodes A and B is R. _T , electrodes A and B
Let I ₁ and I ₂ be the currents extracted from
The currents I ₁ and I ₂ are represented by the following equations (1) and (2).

[0009]

(Equation 1)

[0010] The surface resistance layer ^- so the distribution of the specific resistance _{R i} of (p layer) is uniform as shown in FIG. 7 of (B), the resistance _{R 01,
R02} is proportional to the distance from the incident point P to the electrodes A and B, and is expressed by the following equation.

[0011]

(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.

[0013]

(Equation 3)

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

[0015]

(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.

[0017] An example of the signal processing circuit 8 for processing the signal currents _{I 1} and _{I 2} of the PSD5 in FIG. In Figure _9, R 1 ~R ₇ is _resistance, P 1 to P ₅ denotes an amplifier. P
The signal currents I ₁ and I ₂ of SD5 are supplied to the current / voltage conversion circuit unit 1
At 1, conversion is made to voltages V ₀₁ and V ₀₂ . _V01 is V
_{01 = R 1 × I 1,} V 02 becomes _{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.

[0018]

(Equation 5)

In addition, V ₀₁ and V
₀₂ is added. In FIG. 9, V ₀₃ is represented by the following equation.

[0020]

(Equation 6)

The output _VOB corresponding to I ₁ + I ₂
Can be obtained. V _0B is represented by the following equation.

[0022]

(Equation 7)

The arithmetic operation of _VOA and _{VOB is performed} by a microcomputer or the like to obtain _VOA / _VOB . _V0A
/ V _0B is expressed by the following equation.

[0024]

(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 obtained by (I ₂ −I ₁ ) / (I ₁ + I ₂ ).
The spot position of the light incident on the PSD 5 can be found.

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

In this way, the signal current I _{1 of the} PSD ₅
And by processing the I ₂ in the signal processing circuit 8, it is possible to detect the sensor a distance of the detected object 3.

FIG. 10 shows an example of another signal processing circuit 8 of the PSD 5. In the circuit of FIG. 10, 15 is a logarithmic conversion circuit section, 16 is a differential amplifier circuit section, and 17 and 18 are logarithms.
The outputs V ₀₁ and V ₀₂ of the diode are represented by the following equations. Here, k is the Boltzmann constant, and T is the absolute temperature (°
K) and q are charge amounts of electrons.

[0029]

(Equation 9)

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

[0031]

(Equation 10)

With this circuit, an output corresponding to log (I ₁ / I ₂ ) can be obtained. _{I 1} / I ₂ is, PS
D corresponds to the spot position of light incident on D, and log
From (I ₁ / I ₂ ), the spot position of the light incident on the PSD can be determined. When the spot position of the light incident on the PSD 5 is known, the distance between the sensor and the detection object 3 can be detected as described above.

[0033]

In the conventional distance measuring sensor, if a noise source such as an inverter lamp is located near the sensor, noise is generated in the signal currents I ₁ and I _{2 of} the PSD 5 and the signal processing circuit 8 of the PSD 5. Nori, the signal current _{I 1} of PSD5
And the balance of I ₂ is not detected accurately. Then,
The distance between the detection object 3 and the distance measurement sensor is not accurately detected.

The storage case 21 is made of, for example, polycarbonate resin (linear expansion coefficient: 70 ppm / ° C.)
When the printed wiring board 22 such as the signal processing circuit 8 is made of a glass epoxy copper clad laminate (linear expansion coefficient: 13 ppm / ° C.), when the temperature changes, the light receiving lens 4 fixed to the storage case 21 and The relative positional relationship of the PSD 5 fixed to the printed wiring board 22 changes due to a difference in linear expansion coefficient. When the positional relationship between the light receiving lens 4 and the PSD 5, especially the lateral positional relationship, changes, the position of the light spot incident on the PSD 5 changes even if the distance D between the detection object 3 and the distance measuring sensor does not change. Then, the balance of the signal current I ₁ and I ₂ of PSD5 ends up changing, the detection accuracy of the distance measuring sensor is deteriorated.

FIG. 11 is a conventional temperature characteristic diagram. The set temperatures are -10 ° C, 7 ° C, 25 ° C,
At each temperature of 39 ° C. and 60 ° C., the distance characteristics with the detection object 3 are measured. From this, it can be seen that an output error occurs due to the temperature environment.

In view of the above problems, an object of the present invention is to provide a distance measuring sensor capable of preventing a deterioration in detection accuracy without changing a balance of a PSD signal current even when an ambient temperature changes.

[0037]

According to the first aspect of the present invention, as shown in FIG. 1, a light emitting element 1, a light receiving element 5, and a light receiving element 5 are fixed in a storage case 21. A wiring board 22 on which a signal processing circuit 8 for detecting the currents I ₁ and I ₂ is formed is housed, a light receiving lens 4 is fixed to the housing case 21, and light from the light emitting element 1 is applied to the detection object 3. In the distance measuring sensor that receives the reflected light by the light receiving element 5 and measures the distance to the detection object 3 based on the signal currents I ₁ and I ₂ , the storage case 21 has conductivity. grounded Te, and the wiring board 22 and the material used having an equivalent coefficient of linear expansion Rutotomoni, the wiring substrate 22 is one that was fixed.

The storage case 21 contains carbon.
The light receiving element 5 employs a semiconductor position detecting element for measuring the distance to a detection object based on the position of the incident light spot.

[0039]

According to the first and second aspects of the present invention, even if there is a noise source such as an inverter lamp nearby, the storage case 21 is grounded to provide a shielding effect and operate without being affected by noise. It becomes possible.

Even if the temperature changes, the storage case 21
Is made of a material having a coefficient of linear expansion equivalent to that of the wiring board 22, so that the light receiving lens 4 fixed to the storage case 21 is used.
And the PSD 5 fixed to the wiring board 22 changes position equivalently, and the relative position change between the light receiving lens 4 and the PSD 5 is small. Therefore, the position of the light spot incident on the PSD 5 hardly changes depending on the temperature.

[0041]

FIG. 1 is a sectional view of a distance measuring sensor according to an embodiment of the present invention.

In FIG. 1, 1 is an LED as a light emitting element,
Reference numerals 2 and 4 are lenses, 5 is a PSD as a light receiving element, 22 is a printed wiring board (PWB) on which a drive circuit of the LED 1 and a signal processing circuit 8 of the PSD 5 are formed, and these components have the same functions as the conventional ones Therefore, the description is omitted. Reference numeral 21 denotes a storage case for storing the wiring board 22 on which the two elements 1 and 5 are mounted while positioning the wiring board 22 with respect to the lenses 2 and 4.

In this embodiment, the storage case 2
As 1, a material having conductivity and a coefficient of linear expansion equivalent to that of the wiring board 22 is used.

Specifically, for example, when a glass epoxy copper clad laminate having a linear expansion coefficient of 13 ppm / ° C. is used for the wiring board 22,
A plastic of ３０30 ppm / ° C. is used.

The storage case 21 contains carbon for imparting conductivity, and is grounded to GND.
This provides a shielding effect and improves noise resistance, and even if there is a noise source such as an inverter lamp nearby, the distance measuring sensor operates without being affected by noise. Is accurately detected.

FIG. 2 is an output characteristic diagram when the storage case 21 is grounded, and FIG. 3 is an output characteristic diagram when the storage case 21 is not grounded. The distance measuring sensor used in the experiment has a detection range of 4 to 30 cm. As the detection object 3, a white object having a reflectance of 90% and a gray object having a reflectance of 18% were used. In the figure, the solid line indicates the separation distance characteristic from the detection object 3 when the inverter lamp is disposed at a position separated by about 20 cm, and the dotted line indicates the separation distance characteristic when the inverter lamp is not close. 2 and 3, it can be seen that the output error is smaller when the storage case 21 is grounded.

Since the storage case 21 is made of a material having a coefficient of linear expansion equivalent to that of the wiring board 22,
When the temperature changes, the position of the light receiving lens 4 fixed to the case 21 and the position of the PSD 5 fixed to the wiring board 22 change equally, and the relative position of the light receiving lens 4 and the PSD 5 changes little. The incident light spot position hardly changes with temperature. Therefore, the output of the distance measuring sensor hardly changes depending on the temperature.

FIG. 4 is a temperature characteristic diagram of the distance measuring sensor according to one embodiment of the present invention. It can be seen that the output error due to the temperature environment is reduced as compared with the conventional example of FIG.

As described above, the storage case 21 for the distance measuring sensor
Is made of a material which is conductive and has a linear expansion coefficient equivalent to that of the wiring board 22, thereby improving noise resistance and improving temperature characteristics.

Further, according to the present invention, it is only necessary to change the material for forming the case 21, and it is not necessary to change the process structure.

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.

For example, the storage case may be made of the same material as the printed wiring board mixed with a conductive agent such as carbon.

[0053]

As is apparent from the above description, according to the first and second aspects of the present invention, since the storage case is conductive and is further grounded, noise resistance is improved by the shielding effect. I do. Therefore, even if there is a noise source such as an inverter lamp nearby, the distance measuring sensor operates without being affected by the noise.

Further, since a material having a coefficient of linear expansion equivalent to that of the wiring board is used for the storage case, even if the temperature changes, the light receiving lens fixed to the case and the light receiving element fixed to the wiring board can be used. The position changes equally, and the relative position between the light receiving lens and the light receiving element changes less. Therefore, the position of the light spot incident on the light receiving element hardly changes with temperature, and the output of the distance measuring sensor hardly changes with temperature.

As described above, the storage case for holding the lens
Shield function and temperature simply by changing the material for fabricating
Compensation function can be added at the same time to change the process
No need for additional components
As a result, the detection accuracy of the distance measurement sensor is improved without increasing costs.
There is an excellent effect when it can be raised.

[Brief description of the drawings]

FIG. 1 is a sectional view of a distance measuring sensor according to an embodiment of the present invention.

FIG. 2 is an output characteristic diagram when a storage case of a distance measuring sensor according to an embodiment of the present invention is grounded.

FIG. 3 is an output characteristic diagram when the storage case of the distance measuring sensor according to one embodiment of the present invention is not grounded.

FIG. 4 is a temperature characteristic diagram of the distance measuring sensor according to one embodiment of the present invention.

FIG. 5 is a diagram illustrating a detection principle of a general distance measuring sensor.

FIG. 6A is an equivalent circuit diagram of a light receiving element, and FIG. 6B is an equivalent circuit diagram of the light receiving element with a reverse bias.

7A is a diagram illustrating the operation principle of the light receiving element, and FIG. 7B is a distribution diagram of the specific resistance of the surface resistance layer.

FIG. 8 is a functional block diagram of a conventional distance measuring sensor.

FIG. 9 is a signal processing circuit diagram of a signal current of a conventional light receiving element.

FIG. 10 is another signal processing circuit diagram of a signal current of a conventional light receiving element.

FIG. 11 is a temperature characteristic diagram of a conventional distance measuring sensor.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 light emitting element 2 lens 3 detection object 4 lens 5 light receiving element 8 signal processing circuit 21 storage case I ₁ , I ₂ signal current 22 wiring board

Continuation of the front page (56) References JP-A-3-28789 (JP, A) JP-A-61-1068 (JP, A) JP-A-3-145745 (JP, A) , U) Japanese Utility Model Showa 61-10588 (JP, U) Japanese Utility Model Application Hei 3-102743 (JP, U)

Claims (3)

(57) [Claims] A light-emitting element, a light-receiving element, and a wiring board on which the light-receiving element is fixed and on which a signal processing circuit for detecting a signal current is formed are stored in a storage case, and a light-receiving lens is provided in the storage case. Is fixed, the light from the light emitting element is applied to a detection object, the reflected light is received by the light receiving element, a distance measurement sensor that measures the distance to the detection object based on the signal current, wherein the storage case is is grounded is brought have a conductivity, and a material having the wiring board equivalent to the linear expansion coefficient is used Rutotomoni, the wiring
A distance measuring sensor having a substrate fixed . 2. The distance measuring sensor according to claim 1, wherein the storage case is made of carbon-containing plastic. 3. The distance measuring sensor according to claim 1, wherein the light receiving element is a semiconductor position detecting element that measures a distance to a detection object based on a position of an incident light spot.