JP3479597B2 - Distance measuring device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active distance measuring device suitable for use in a camera or the like.

[0002]

2. Description of the Related Art Conventionally, as an active distance measuring device in a camera, a device shown in FIG. 14 has been known.
FIG. 14 is a configuration diagram of a distance measuring device according to a first conventional technique.

In the distance measuring device shown in this figure, the CPU 110
Under the control of, the driver 112 drives an infrared light emitting diode (hereinafter referred to as “IRED”) 114 to output infrared light, and the infrared light is projected by a projection lens (not shown).
The light is projected onto the object to be measured via. The infrared light reflected by the object to be measured is focused on a position detection element (hereinafter referred to as “PSD”) 116 through a light receiving lens (not shown), and PS
D116 outputs two signals I1 and I2 according to the position where the reflected infrared light is received. The first signal processing circuit 118 removes the stationary light component that is noise included in the signal I1, and the second signal processing circuit 120 removes the stationary light component that is noise included in the signal I2.

The arithmetic circuit 132 outputs the output ratio (I1 / (I) based on the signals I1 and I2 from which the stationary light component has been removed.
1 + I2)) is calculated and an output ratio signal corresponding to the distance to the object to be measured is output. The integrating circuit 134 integrates the output ratio signal output from the arithmetic circuit 132 a number of times in this way to improve the S / N ratio. This integration circuit 1
A signal output from 34 (hereinafter referred to as "AF signal")
Is according to the distance to the object to be measured. Then, the CPU 110 outputs A output from the integration circuit 134.
Based on the F signal, a predetermined calculation is performed to obtain a distance signal, and the lens drive circuit 136 is controlled based on this distance signal to move the lens 138 to the in-focus position.

FIG. 15 is a diagram showing the relationship between the AF signal output from the integrating circuit 134 of the first prior art and the distance to the object to be measured. In the graph shown in this figure, the horizontal axis is the reciprocal of the distance L to the object to be measured (1 / L)
And the vertical axis is the output ratio (I1 / (I1 + I2)), that is, the AF signal. As shown in this figure, a certain distance L
Below 4, the output ratio has a substantially linear relationship with the reciprocal of the distance L (1 / L), and the distance L is large (1 / L is small).
Then, the output ratio becomes smaller. However, above the distance L4, as the distance L increases, the influence of the noise component increases. When the noise component is In (In ≥0), the output ratio becomes (I1 + In) / (I1 + In + I2 + In), and the output ratio fluctuates in the direction of increasing beyond the distance L4. Moreover, since In occurs randomly, it becomes unstable depending on the distance measuring conditions. This is because as the distance L increases, the intensity of the reflected light received by the PSD 116 decreases and the noise component In relatively increases. When such a phenomenon occurs, the distance L to the object to be measured cannot be uniquely determined from the output ratio.

Therefore, the following devices are known as distance measuring devices for solving such a problem. FIG.
FIG. 4 is a configuration diagram of a distance measuring device according to a second conventional technique. In this figure, only the light receiving side is shown. In the range finder shown in this figure, the signals I1 and I2 output from the PSD 140 are transmitted by the stationary light removing circuits 142 and 14 respectively.
After the stationary light component is removed by each of the four, it is input to both the arithmetic circuits 146 and 148. Arithmetic circuit 146
On the basis of the signals I1 and I2 from which the stationary light component has been removed, the calculation of I1 / (I1 + I2) is performed to obtain the output ratio, and the integrating circuit 150 integrates the output ratio. On the other hand, the arithmetic circuit 148 calculates the light quantity by calculating I1 + I2, and the integrating circuit 152 integrates the light quantity. Then, the selection unit 160 selects one of the output ratio and the light amount and obtains the distance to the object to be measured based on this selection.
The selecting unit 160 is a process in the CPU.

FIG. 17 is a block diagram of a distance measuring device according to the third conventional technique. Note that, also in this figure, only the light receiving side is shown. In the range finder shown in this figure, the PSD 170
The signals I1 and I2 output from the respective circuits are input to one end of the switch 176 after the stationary light components are removed by the stationary light removal circuits 172 and 174, respectively. The switch 176 is controlled by the CPU to input the output of any one of the stationary light removing circuits 172 and 174 to the integrating circuit 178. The integrating circuit 178 integrates either one of the input signals I1 and I2, and the arithmetic unit 180 calculates I1 / (I1 +) based on the integration result.
I2) is calculated to obtain the output ratio, while the calculation unit 1
Reference numeral 82 calculates the amount of light by performing the calculation of I1 + I2. Then, the selection unit 184 selects one of the output ratio and the light amount, and based on this, calculates the distance to the object to be measured.
The calculation units 180 and 182 and the selection unit 184 are C
This is processing in the PU.

Both of the distance measuring devices according to the second and third prior arts (FIGS. 16 and 17) have an output ratio (I1 / (I1 + I2) when the distance L to the object is small.
)), The distance L is obtained, and when the distance L is large, the distance L is obtained based on the light quantity (I1 + I2). By doing so, the distance L can be uniquely determined. It is a thing.

[0009]

As described above, the distance measuring devices according to the second and third conventional techniques (FIGS. 16 and 17).
Both can solve the problems of the distance measuring device according to the first conventional technique (FIG. 14). However, the distance measuring device according to the second related art (FIG. 16) needs to include two sets of the arithmetic circuit and the integrating circuit, which is compared with the distance measuring device according to the first related art (FIG. 14). Then, there is a problem that the circuit scale becomes large and the cost becomes high. On the other hand, the distance measuring device according to the third conventional technique (FIG. 17) has a smaller circuit scale, but the signal I1 from the PSD 170 is reduced.
Since it is not possible to detect both I and I2 at the same time, it takes twice as much time to obtain the distance L with the same S / N ratio as that of the distance measuring apparatus according to the second prior art (FIG. 16). .

Further, any of the distance measuring devices according to the prior arts described above is designed to operate properly when the ambient light luminance is within the standard range, but when the ambient light luminance becomes large, the stationary light component is removed. Circuit (the signal processing circuits 118 and 120 in FIG. 14, the stationary light removal circuit 1 in FIG. 16)
42 and 144, the stationary light removal circuit 17 in FIG.
2 and 174), it becomes impossible to sufficiently remove the stationary light component from the signals I1 and I2 output from the PSD. In such a case, the obtained distance measurement result includes an error, and an accurate distance measurement result cannot be obtained. This problem is particularly great when the distance to the object to be measured is large.

Further, in any of the distance measuring devices according to the related arts described above, the relative positional relationship between the IRED and the PSD may be different from the design value when the camera is assembled. In such a case, there is an error in the distance measuring result. Occurs. That is, as shown in FIG. 18, the relative positional relationship between IRED and PSD (see FIG.
8 (a)) is as designed (FIG. 18 (b)), the output signal from the PSD shows the actual distance, but the relative output of the PSD causes the output signal from the PSD to shift. , Indicates that the object for distance measurement is farther than it actually is (FIG. 18C), or indicates that it is closer than it actually is (FIG. 18D). Further, the influence of the external light luminance on the distance measurement result depends on the relative positional relationship between the IRED and the PSD, and the farther the PSD is, the greater the influence of the external light luminance is.

The present invention has been made in order to solve the above-mentioned problems, and the relative positional relationship between the IRED and the PSD can be achieved even if the external light luminance fluctuates in a short circuit scale and in a short time. An object of the present invention is to provide a distance measuring device capable of surely obtaining the distance even if the distance is not as designed, even when the distance to the object is large.

[0013]

A distance measuring apparatus according to the present invention comprises (1) a light emitting means for projecting a light beam toward an object to be measured, and (2) a light beam projected to the object to be measured. The reflected light is received at the light receiving position on the position detection element according to the distance to the object to be measured, and based on the light receiving position, if the received light amount is constant, the farther the distance is, the greater the value. The light receiving means that outputs the signal and the near-side signal that is larger as the distance is shorter if the received light amount is constant, and (3) The far-side signal is input and the magnitude of the clamp signal is compared to determine the far-side. When the signal level is equal to or higher than the clamp signal level, the far side signal is output as it is, otherwise the clamp means is output, and (4) the near side signal and the signal output from the clamp means. Calculation means to calculate the output ratio signal and output ratio signal, and (5) measure the external light brightness Luminance measuring means that, (6)
If the output ratio signal is closer to the clamp effect presence / absence reference level determined by the reference object reflectance, the first conversion formula is used. If not, the distance is regarded as infinity. Is a distance corresponding to the distance according to the second conversion equation depending on the magnitude relation between the external light luminance measured by the luminance measuring means and the luminance switching determination value set based on the position of the position detection element. And a conversion unit that converts the signal into a signal.

According to this distance measuring device, the luminous flux output from the light emitting means toward the object to be measured is reflected by the object to be measured, and the reflected light is transmitted to the object to be measured by the light receiving means. Light is received at the light receiving position on the position detection element according to the distance,
Based on the light receiving position, if the received light amount is constant, a far-side signal that is larger as the distance is longer, and if the received light amount is constant, a near-side signal that is larger as the distance is closer is output. . The far-side signal is compared with the level of the clamp signal by the clamp means, and when the level of the far-side signal is equal to or higher than the level of the clamp signal, the far-side signal is output as it is. The signal is output. The calculation means calculates the ratio between the near side signal and the signal output from the clamp means, and outputs the output ratio signal.

When the output ratio signal is closer to the clamp effect presence / absence reference level determined by the reference object reflectance by the converting means, according to the first conversion equation,
Otherwise, the value of the output ratio signal that regards the distance as infinity depends on the magnitude relationship between the external light luminance measured by the luminance measuring means and the luminance switching determination value set based on the position of the position detection element. According to the second conversion formula, the output ratio signal is converted into a distance signal according to the distance and is output. here,
Since the brightness switching determination value is set on the basis of the position of the position detection element of the light receiving means, the distance range in which the distance signal is uniquely determined and the outside light brightness range are wide.

Further, when the level of the clamp signal in the clamp means is variably set, the brightness switching determination value is preferably set also based on the level of the set clamp signal. Also in this case, the distance range and the external light luminance range in which the distance signal is uniquely determined are wide.

If this distance measuring device is built in a camera and used for automatic focusing, the focusing of the photographing lens is controlled based on the distance signal.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below 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.

First, the overall configuration of the distance measuring device according to this embodiment will be described. FIG. 1 is a configuration diagram of a distance measuring device according to the present embodiment.

The CPU 1 controls the entire camera including this distance measuring device, and controls the entire camera including this distance measuring device based on a program and parameters stored in advance in the EEPROM 2. In the distance measuring device shown in this figure, the CPU 1 controls the driver 3 to control the emission of infrared light from the IRED (infrared light emitting diode) 4. Further, the CPU 1 is an autofocus IC
(Hereinafter referred to as “AFIC”) The operation of 10 is controlled, and the AF signal output from the AFIC 10 is input. Further, the CPU 1 inputs the value of the external light luminance measured by the photometric sensor 71.

The infrared light emitted from the IRED4 is IR
The light is projected onto the object to be measured through a light projecting lens (not shown) arranged on the front surface of the ED 4, a part of the light is reflected, and the reflected light is the front surface of the PSD (position detecting element) 5. The light is received at any position on the light receiving surface of the PSD 5 via a light receiving lens (not shown) disposed in the. This light receiving position is
This is according to the distance to the object to be measured. And P
SD5 outputs two signals I1 and I2 corresponding to the light receiving position. The signal I1 is a near-side signal that has a larger value as the distance is shorter if the received light amount is constant.
2 is a far-side signal that has a larger value as the distance is longer, if the amount of received light is constant. The sum of the signals I1 and I2 is P
It represents the amount of reflected light received by SD5, and the output ratio (I1 /
(I1 + I2)) represents the light receiving position on the light receiving surface of the PSD 5, that is, the distance to the object to be measured. Then, the near-side signal I1 is input to the PSDN terminal of the AFIC 10, and the far-side signal I2 is input to the PSDF terminal of the AFIC 10. However, in reality, there may be a case where a signal in which the stationary light component I0 is added to each of the near-side signal I1 and the far-side signal I2 is input to the AFIC 10 depending on external conditions.

The AFIC 10 is an integrated circuit (IC) and comprises a first signal processing circuit 11, a second signal processing circuit 12, a clamp circuit 13, an arithmetic circuit 14 and an integrating circuit 15. The first signal processing circuit 11 inputs the signal I1 + I0 output from the PSD 5, removes the stationary light component I0 contained in the signal, and outputs the near-side signal I1, and the second signal The processing circuit 12 receives the signal I2 + I0 output from the PSD 5, removes the stationary light component I0 contained in the signal, and outputs the far-side signal I2.

The clamp circuit 13 is the second signal processing circuit 1.
The far-side signal I2 output from 2 is input, and the levels of the clamp signal Ic and the far-side signal I2 of a certain constant level are compared in magnitude. When the former is large, the clamp signal Ic is output, and when not, the far side is output. The signal I2 is output as it is. Hereinafter, the signal output from the clamp circuit 13 is represented by I2c. Here, the clamp signal Ic
Is approximately the same as the level of the far-side signal I2 corresponding to the distance L4 shown in FIG.

The arithmetic circuit 14 outputs the near-side signal I1 output from the first signal processing circuit 11 and the signal I2c (far-side signal I2 and clamp signal I2) output from the clamp circuit 13.
Input either (c)) and output ratio (I1 / (I1 + I2
c)) is calculated and the result is output. Integrating circuit 15
Inputs its output ratio, integrates the output ratio with the integration capacitor 6 connected to the C _INT terminal of the AFIC 10 many times, and thereby improves the S / N ratio. Then, the integrated output ratio is used as an AF signal in the AFIC.
It is output from the S _OUT terminal of 10.

The CPU 1 inputs the AF signal output from the AFIC 10, performs a predetermined calculation to convert the AF signal into a distance signal, and sends the distance signal to the lens drive circuit 7. The lens drive circuit 7 causes the taking lens 8 to perform focusing operation based on the distance signal. The conversion calculation from the AF signal to the distance signal in the CPU 1 will be described later.

Next, the first signal processing circuit 1 of the AFIC 10
1, more specific circuit configurations of the clamp circuit 13 and the integrating circuit 15 will be described. FIG. 2 is a circuit diagram of the first signal processing circuit 11 and the integrating circuit 15 in the distance measuring device according to the present embodiment. Further, FIG. 3 is a circuit diagram of the clamp circuit 13 in the range finder according to the present embodiment. The second signal processing circuit 12 also has the same circuit configuration as the first signal processing circuit 11.

The circuit diagram of the first signal processing circuit 11 is shown in FIG. 2, in which the near-side signal I1 including the stationary light component I0 output from the PSD 5 is input, and the stationary light component I0 contained in the near-side signal I1. Is removed and the near-side signal I1 is output. The current output from the short-distance side terminal of PSD5 (I
1 + I0) is input to the − input terminal of the operational amplifier 20 of the first signal processing circuit 11 via the PSDN terminal of the AFIC 10. The output terminal of the operational amplifier 20 is the transistor 2
1 and the collector terminal of the transistor 21 is connected to the base terminal of the transistor 22. The negative terminal of the operational amplifier 23 is connected to the collector terminal of the transistor 22, and the arithmetic circuit 1
4 is connected. Further, the collector terminal of the transistor 22 is connected to the cathode terminal of the compression diode 24, and the + input terminal of the operational amplifier 23 is connected to the compression diode 2
The cathode terminals of 5 are connected to each other, and the first reference power supply 26 is connected to the anode terminals of each of the compression diodes 24 and 25.

Further, the CHF terminal of the AFIC 10 is externally provided with a stationary light removal capacitor 27, and this stationary light removal capacitor 27 is connected to the base terminal of a stationary light removal transistor 28 in the first signal processing circuit 11. Has been done. The stationary light removing capacitor 27 and the operational amplifier 23 are connected via a switch 29.
Is turned on / off by the CPU 1. The collector terminal of the stationary light removal transistor 28 is connected to the-input terminal of the operational amplifier 20, and the emitter terminal of the transistor 28 is connected to the resistor 30 whose other end is grounded.

The circuit diagram of the clamp circuit 13 is shown in FIG. The + input terminal of the determination comparator 37 of the clamp circuit 13 is connected to the collector terminal of the transistor 22 of the second signal processing circuit 12 and the input terminal of the arithmetic circuit 14 via the switch 38. On the other hand, the-input terminal of the judgment comparator 37 is +
Similar to the transistor 22 and the compression diode 24 connected to the input terminal, they are connected to the collector terminal of the transistor 51 and the cathode terminal of the compression diode 52, and to the input terminal of the arithmetic circuit 14 via the switch 39. ing.

A clamp current source 41 is connected to the base terminal of the transistor 51. The clamp current source 41 has a set of a constant current source and a switch connected in series, and a plurality of sets connected in parallel. Each switch is controlled by the CPU 1 to open and close. Then, the clamp current source 41 inputs the clamp current, which is the sum of the currents from the constant current sources corresponding to the closed switches, to the base terminal of the transistor 51. This clamp current becomes a base current of the transistor 51, and a collector potential corresponding to the magnitude thereof is input to the-input terminal of the determination comparator 37.

The output terminal of the judgment comparator 37 is connected to the switch 39, and the output signal of the judgment comparator 37 is input. Further, the output terminal of the determination comparator 37 is connected to the switch 38 via the inverter 40, and the output signal of the determination comparator 37 is inverted and then input. Therefore, the switches 38 and 39 have a relationship in which one of them is turned on by the output signal from the determination comparator 37 and the other is turned off.

The circuit configuration of the integrating circuit 15 is shown in FIG. The integration capacitor 6 externally attached to the C _INT terminal of the AFIC 10 is connected to the arithmetic circuit 1 via the switch 60.
4 is connected to the output terminal of the operational amplifier 6, the switch 62 is connected to the constant current source 63, and the switch 65 is connected to the operational amplifier 6
4 is connected to the output terminal, and the operational amplifier 64 is directly connected.
Is connected to the-input terminal of the
It is output from the S _OUT terminal of 10. These switches 6
0, 62 and 65 are controlled by a control signal from the CPU 1. In addition, the + input terminal of the operational amplifier 64 is
The second reference power source 66 is connected.

The operation of the AFIC 10 configured as described above will be described with reference to FIGS. 2 and 3.
When the CPU 1 is not causing the IRED 4 to emit light,
The switch 29 of the first signal processing circuit 11 is turned on. At this time, the stationary light component I0 output from the PSD 5
Is input to the first signal processing circuit 11, and the operational amplifier 20
Further, it is current-amplified by the current amplifier composed of the transistors 21 and 22 and logarithmically compressed by the compression diode 24 to be converted into a voltage signal, which is input to the-input terminal of the operational amplifier 23. Operational amplifier 2
When the signal input to 0 is large, the cathode potential of the compression diode 24 increases, so that the signal output from the operational amplifier 23 is large, and thus the capacitor 27 is charged. Then, since the base current is supplied to the transistor 28, the collector current flows through the transistor 28, and the signal I0 input to the first signal processing circuit 11 is input.
The signal input to the operational amplifier 20 becomes smaller. Then, when the operation of the closed loop is stable, all of the signal I0 input to the first signal processing circuit 11 flows to the transistor 28, and the capacitor 27 stores the electric charge corresponding to the base current at that time.

When the CPU 1 causes the IRED 4 to emit light and turns off the switch 29, the PSD
A stationary light component I0 of the signals I1 + I0 output from
Flows as a collector current to the transistor 28 to which the base potential is applied by the electric charge stored in the capacitor 27, and the near-side signal I1 is current-amplified by the current amplifier composed of the operational amplifier 20 and the transistors 21 and 22 and compressed. It is logarithmically compressed by the diode 24, converted into a voltage signal, and output. That is, the stationary signal I0 is removed from the first signal processing circuit 11 and only the near-side signal I1 is output, and the near-side signal I1 is input to the arithmetic circuit 14. On the other hand, the second signal processing circuit 12 also
Similar to the first signal processing circuit 11, the stationary light component I0 is removed and only the far-side signal I2 is output.
Is input to the clamp circuit 13.

However, when the external light brightness is high, the collector current flowing through the transistor 28 fluctuates, and the stationary light component I0 becomes large. The distance to the object to be measured is far PSD
If such an error is added when the amount of the reflected light entering 5 is small, the output ratio signal approaches 50%, and the infinity determination accuracy deteriorates. The distance measuring device according to the present embodiment can obtain a reliable infinity determination result even in such a case.

Far side signal I2 input to the clamp circuit 13
Is input to the + input terminal of the determination comparator 37 of the clamp circuit 13. The clamp current output from the clamp current source 41 flows as a base current of the transistor 51, and the potential (clamp signal Ic) of the collector terminal of the transistor 51, which is generated as a result, is determined by the determination comparator 3.
Input to the-input terminal of 7. The far-side signal I2 and the clamp signal Ic are compared in magnitude by the determination comparator 37, and one of the switches 38 and 39 is turned on and the other is turned off according to the result. That is, when the far side signal I2 is larger than the clamp signal Ic, the switch 38 is turned on and the switch 39 is turned off, and the far side signal I is output as the output signal I2c of the clamp circuit 13.
2 is output. If the magnitude relationship is reversed, switch 3
8 is turned off, switch 39 is turned on,
The clamp signal I is output as the output signal I2c of the clamp circuit 13.
c is output.

The signal I2c output from the clamp circuit 13
And the near-side signal I output from the first signal processing circuit 11
1 is input to the arithmetic circuit 14, and the arithmetic circuit 14 calculates and outputs the output ratio (I1 / (I1 + I2c)),
The output ratio is input to the integrating circuit 15. When the IRED4 emits a pulsed light a predetermined number of times, the integrating circuit 15
The switch 60 is turned on, the switches 62 and 65 are turned off, and the output ratio signal output from the arithmetic circuit 14 is stored in the integrating capacitor 6. And
When the pulsed light emission of a predetermined number of times is completed, the switch 60 is turned off, the switch 65 is turned on, and the electric charge accumulated in the integrating capacitor 6 is changed by the electric charge of the reverse potential supplied from the output terminal of the operational amplifier 64. Will decrease. The CPU 1 monitors the potential of the integrating capacitor 6 to measure the time required to return to the original potential, obtains the AF signal based on the time, and further obtains the distance to the object to be measured.

FIG. 4 shows the relationship between the AF signal thus obtained and the distance L to the object to be measured. FIG. 4 is a diagram showing the relationship between the AF signal output from the integrating circuit of the distance measuring apparatus according to this embodiment and the distance to the object to be measured. In the graph shown in this figure, the horizontal axis is the reciprocal (1 / L) of the distance L to the object to be measured, and the vertical axis is the output ratio (I1
/ (I1 + I2)), that is, the AF signal. As shown in this figure, when the distance L to the object to be measured is a certain distance L4 or less (L≤L4), the signal output from the clamp circuit 13 is I2, and the output ratio is I1 / (I1 + I2). The output ratio has a substantially linear relationship with the reciprocal of the distance L (1 / L), and the output ratio decreases as the distance L increases (1 / L decreases). Further, the distance L is greater than or equal to the distance L4 (L ≧
In L4), the signal output from the clamp circuit 13 is I
c, and the output ratio is I1 / (I1 + Ic). In this case as well, the output ratio decreases as the distance L increases. As described above, by using the clamp circuit 13, the distance L to the object to be measured can be uniquely and stably determined from the output ratio (AF signal).

The CPU 1 uses the AF thus obtained.
Based on the signal, a distance signal representing the drive amount of the photographing lens 8 is calculated, and the distance signal is sent to the lens driving circuit 7 to cause the photographing lens 8 to perform a focusing operation. FIG. 5 is an explanatory diagram of conversion of an AF signal into a distance signal in the distance measuring device according to the present embodiment. In the graph shown in this figure, the horizontal axis is the reciprocal (1 / L) of the distance L to the object to be measured,
The left vertical axis is the AF signal, and the right vertical axis is the distance signal. Further, this graph shows the relationship between the distance L and the AF signal and the relationship between the distance L and the distance signal, respectively, and particularly, the distances L2, L3, L4 and L5 (where L2 <L3 <
For each of L4 <L5), the AF signals are y2, y3, y
4 and y5 respectively, and the distance signals are x2, x3, x4
And x5 respectively.

Here, the range of the distance L≤L4 and the distance L
In each range> L4, the AF signal has a substantially linear relationship with the reciprocal of the distance L (1 / L), and the distance L
In the entire range of, the distance signal is the reciprocal of the distance L (1 / L)
Is a substantially linear relationship with. Therefore, the distance L≤L4
And the distance L> L4 respectively, A
The relationship between the F signal and the distance signal is also a substantially linear relationship.

Therefore, the AF signal y can be converted into the distance signal x by using the conversion expression represented by the linear expression. Particularly in this embodiment, the reference object reflectance (36%)
Clamping effect presence / absence determination standard level COUNT_B
Is compared with the AF signal y, and the photometric sensor 71
External light luminance value Lv and luminance switching judgment value AE measured by
The magnitude of DATA is compared, and the AF signal y is converted into the distance signal x according to the conversion formula according to these comparison results. In addition,
In the case of the reference object reflectance (36%), the distance L corresponding to the clamp effect presence / absence determination reference level COUNT_B is L4, and the clamp effect presence / absence determination reference level COUNT_B is the distance y.
Equal to 4. The brightness switching determination value AEDATA is IRED.
4 and the PSD 5 are set based on the relative positional relationship, and when the clamp current supplied from the clamp power supply 41 of the clamp circuit 13 is variable, the clamp signal Ic (or the clamp current source 41 It is also set based on the level of the clamp current output from).

FIG. 6 is a flow chart for explaining the conversion from the AF signal y to the distance signal x. In the range in which the AF signal y exceeds the clamp effect presence / absence determination reference level COUNT_B, that is, in the range in which the distance L is less than L4,

[Equation 1] AF signal y to distance signal x based on
To

[Equation 2] The conversion formula is

On the other hand, the range in which the AF signal y is below the clamp effect presence / absence determination reference level COUNT_B, that is, the distance L
Is above L4,

[Equation 3] AF signal y to distance signal x based on
To

[Equation 4] The conversion formula is Here, the above formulas (2) and (4) are conversion formulas different from each other.

If the AF signal y is less than the farthest AF signal value INFDATA corresponding to the farthest setting value of the taking lens 8, the distance signal x is set to the farthest setting value corresponding to the farthest setting value of the taking lens 8. By setting the distance signal value AFINF, more stable focusing control of the taking lens can be performed. That is,
Equation (4) above is

[Equation 5] Becomes Here, the farthest AF signal value INFDATA is a value according to the magnitude relationship between the external light luminance value Lv measured by the photometric sensor 71 and the luminance switching determination value AEDATA, and the luminance switching determination is performed from the external light luminance value Lv. The larger the result of subtracting the value AEDATA, the larger the value.

For example, the farthest AF signal value INFDATA may be one selected from two or more values according to the difference between the external light luminance value Lv and the luminance switching determination value AEDATA. Alternatively, it may be obtained by calculation based on the value of the difference between the external light luminance value Lv and the luminance switching determination value AEDATA. In the present embodiment, it is assumed that the farthest AF signal value INFDATA is selected from two values according to the magnitude relationship between the external light brightness value Lv and the brightness switching determination value AEDATA. When the brightness value Lv is less than the brightness switching determination value AEDATA, the farthest AF signal value INFDATA is set to INFDATA_a, and when the outside light brightness value Lv is the brightness switching determination value AEDATA or more, the farthest AF signal value INFDATA is set to INFDATA_a
INFDATA_b, which is a larger value.

The parameters A2, B2, A3 and B3, the brightness switching determination value AEDATA, the farthest AF signal value INFDATA_.
a and INFDATA_b, and the farthest signal value AFINF
Is obtained at the time of manufacture for each camera in which this distance measuring device is incorporated, and is stored in the EEPROM 2 or the like in advance. Then, these parameters are read by the CPU 1 at the time of distance measurement, and the calculation of the formula (2) or the formula (5) is performed and the AF
The signal y is converted to the distance signal x.

Next, a method of setting the brightness switching determination value AEDATA will be described. Brightness switching judgment value AEDATA is IRE
It is set based on the relative positional relationship between D4 and PSD5, and may be set based on the measurement result obtained by actually measuring the distance between IRED4 and PSD5. In addition, the brightness switching determination value AEDATA is IRED4 and PS.
It may be set based on a parameter determined based on the relative positional relationship with D5. An example of such a parameter is the farthest AF signal value INFDATA corresponding to the farthest set point of the taking lens 8. This is because when the AF signal value y is less than or equal to the farthest AF signal value INFDATA, the distance signal x
Is set to a value corresponding to the farthest set point of the taking lens 8, thereby performing more stable focusing control of the taking lens 8. Below, the clamp power supply 4 of the clamp circuit 13
A method of setting the luminance switching determination value AEDATA based on the farthest AF signal value INFDATA and the clamp current value when the clamp current supplied from 1 is variable will be described.

FIG. 7 shows the external light luminance when the distance L to the object to be measured is a constant distance of L4 or more for each of the clamp current values of 0.5 nA, 0.75 nA and 1 nA in the clamp circuit 13. 5 is a graph showing the relationship between the AF signal and the AF signal. As shown in this figure, the AF signal y is a quadratic expression of the external light luminance Lv.

[Equation 6] Is approximated by Here, the coefficient KKA and the coefficient K
Each KB is a constant value that does not depend on the clamp current value, and the coefficient KKC is a constant value that is determined according to the clamp current value.

Therefore, the values of the coefficients KKA and KKB, and the value of the coefficient KKC corresponding to each clamp current value are the external light luminance and the AF signal as shown in FIG. It is obtained in advance based on the relationship. Then, the farthest AF signal value INFDATA (INFDATA_a or INFDATA_b) is substituted into y in the equation (6), and the value of the outside light luminance Lv obtained at that time is set as the luminance switching determination value AEDATA. That is, the brightness switching determination value AEDATA
Is

[Equation 7] It is set by the formula.

Next, an example of calculation of the distance signal with respect to the distance to the object to be measured in the distance measuring apparatus according to this embodiment will be described with reference to FIGS. These figures show, as a comparative example for comparison with the present embodiment, an example of calculation of a distance signal when the brightness switching determination value AEDATA is set to a constant value 13.5 irrespective of the relative positional relationship between IRED4 and PSD5. Also shows. Further, each of the three two-dot chain lines in each drawing shows the upper limit of the allowable range, the theoretical value, and the lower limit of the allowable range.

FIGS. 8 and 9 show calculation examples of the distance signal with respect to the distance to the object to be measured in the case where the PSD 5 is on the far side (FIG. 18 (c)), for the comparative example and this embodiment respectively. It is the figure shown. In this case, the brightness switching determination value AEDATA obtained by the above equation (7) in the distance measuring apparatus according to the present embodiment is 15.4. Figure 8 (a)
9A to 9C show calculation examples in the case of the comparative example, and FIG.
(C) shows an example of calculation in the case of the present embodiment. Also, FIG.
FIGS. 8A and 9A show calculation examples when the external light luminance Lv is less than 13.5, and FIG. 8B and FIG. 9B show the external light luminance Lv of 13.5 or more and 15. A calculation example in the case of less than 4 is shown, and FIG. 8C and FIG.
Here is an example of calculation in the case of 15.4 or more.

FIGS. 10 and 11 show examples of calculation of the distance signal with respect to the distance to the object to be measured in the case where the PSD 5 is at the center (FIG. 18B) for the comparative example and each of the embodiments. It is a figure. in this case,
The brightness switching determination value AEDATA obtained by the above equation (7) in the distance measuring device according to the present embodiment is 19.2. Figure 10
11A to 11C show calculation examples in the case of the comparative example, and FIG.
(A)-(c) shows the example of calculation in the case of this embodiment. 10 (a) and 11 (a) show calculation examples when the external light luminance Lv is less than 13.5, and FIGS. 10 (b) and 11 (b) show the external light luminance Lv of 13. 5 or more 19.2
An example of calculation in the case of less than is shown in FIG.
(C) shows a calculation example when the external light luminance Lv is 19.2 or more.

12 and 13 show calculation examples of the distance signal with respect to the distance to the object to be measured in the case where the PSD 5 is on the near side (FIG. 18 (d)), for the comparative example and this embodiment, respectively. It is the figure shown. in this case,
The brightness switching determination value AEDATA obtained by the above equation (7) in the distance measuring apparatus according to the present embodiment is 31.9. 12
13A to 13C show calculation examples in the case of the comparative example, and FIG.
(A)-(c) shows the example of calculation in the case of this embodiment. 12A and 13A show calculation examples when the external light luminance Lv is less than 13.5, and FIGS. 12B and 13B show the external light luminance Lv of 13. 5 or more 31.9
An example of calculation in the case of less than is shown in FIG.
(C) shows a calculation example when the external light luminance Lv is 31.9 or more.

As can be seen from these figures, in the case of the comparative example in which the brightness switching determination value AEDATA is a fixed value, the worst case PSD5 is on the far side (FIG. 18C). Since it is necessary to set and fix the brightness switching determination value AEDATA, the closer the PSD 5 is, the narrower the distance range in which the distance signal is uniquely determined. On the other hand, in the case of the present embodiment, the brightness switching determination value AEDATA set based on the position of the PSD 5 is large in comparison with the case of the comparative example, so that the distance range in which the distance signal is uniquely determined and The external light brightness range is wide. Therefore, according to the distance measuring device according to the present embodiment, even if the external light luminance changes, the accuracy of long distance measurement is excellent, and a reliable infinity determination can be performed.

The present invention is not limited to the above embodiment, but various modifications can be made. For example, in the above-described embodiment, two conversion formulas are switched using one brightness switching determination value AEDATA, but two or more brightness switching determination values are used.
AEDATA may be provided to switch three or more conversion expressions. Further, in the above embodiment, the farthest AF signal INFDATA
Although the position of the position detecting element is calculated using, an AF signal corresponding to an infinite distance or an AF signal corresponding to an arbitrary distance may be used, and a conversion formula (from the AF signal to the distance signal ( The position of the position detection element may be calculated using the value of (Equation (2)).

[0056]

As described in detail above, according to the present invention, the luminous flux output from the light emitting means toward the object to be measured is reflected by the object to be measured, and the reflected light is received by the light receiving means. , The far-side signal, which is a larger value as the distance is farther, when the light is received at the light-receiving position on the position detection element according to the distance to the object to be measured If the amount of light is constant, the near side signal, which has a larger value as the distance is shorter, is output. The far-side signal is compared with the level of the clamp signal by the clamp means, and when the level of the far-side signal is equal to or higher than the level of the clamp signal, the far-side signal is output as it is. The signal is output. The calculation means calculates the ratio between the near side signal and the signal output from the clamp means, and outputs the output ratio signal.

Then, when the output ratio signal is closer to the clamp effect presence / absence reference level determined by the reference object reflectance by the converting means, according to the first conversion equation,
Otherwise, the value of the output ratio signal that regards the distance as infinity depends on the magnitude relationship between the external light luminance measured by the luminance measuring means and the luminance switching determination value set based on the position of the position detection element. According to the second conversion formula, the output ratio signal is converted into a distance signal according to the distance and is output. If the distance measuring device is built in a camera and used for automatic focusing, the focusing of the photographing lens is controlled based on the distance signal.

Here, since the brightness switching determination value is set based on the position of the position detecting element of the light receiving means, the distance range where the distance signal is uniquely determined and the outside light brightness range are widened. Further, when the level of the clamp signal in the clamp means is variably set, the brightness switching determination value is preferably set also based on the level of the set clamp signal. In this case In addition, the distance range in which the distance signal is uniquely determined and the external light luminance range are widened.

Therefore, even if the external light luminance fluctuates in a short time with a circuit scale smaller than that of the prior art,
Further, even when the position of the position detection element is not as designed, the distance can be reliably obtained even when the distance to the object to be measured is large.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a distance measuring device according to an embodiment.

FIG. 2 is a circuit diagram of a first signal processing circuit and an integrating circuit in the distance measuring device according to the present embodiment.

FIG. 3 is a circuit diagram of a clamp circuit in the distance measuring device according to the present embodiment.

FIG. 4 is a diagram showing a relationship between an AF signal output from an integrating circuit of the distance measuring apparatus according to the present embodiment and a distance to an object to be measured.

FIG. 5 is an explanatory diagram of conversion of an AF signal into a distance signal in the distance measuring apparatus according to the present embodiment.

FIG. 6 is a flowchart illustrating conversion from an AF signal y to a distance signal x.

FIG. 7 is a graph showing the relationship between the external light luminance and the AF signal when the distance L to the object to be measured is a certain fixed distance of L4 or more.

FIG. 8 is a diagram showing a calculation example of a distance signal with respect to a distance to an object to be measured when the PSD is on the far side, in the case of a comparative example.

FIG. 9 is a diagram showing a calculation example of a distance signal with respect to a distance to an object to be measured when the PSD is on the far side in the case of the present embodiment.

FIG. 10 is a diagram showing a calculation example of a distance signal with respect to a distance to an object to be measured when the PSD is at the center, in the case of a comparative example.

FIG. 11 is a diagram showing a calculation example of a distance signal with respect to a distance to an object to be measured when the PSD is at the center, in the case of the present embodiment.

FIG. 12 is a diagram showing a calculation example of a distance signal with respect to a distance to an object to be measured when the PSD is on the near side, in the case of a comparative example.

FIG. 13 is a diagram showing an example of calculation of a distance signal with respect to a distance to an object to be measured when the PSD is on the near side, in the case of the present embodiment.

FIG. 14 is a configuration diagram of a distance measuring device according to a first conventional technique.

FIG. 15: A output from the first prior art integrating circuit
It is a figure which shows the relationship between F signal and the distance to a ranging object.

FIG. 16 is a configuration diagram of a distance measuring device according to a second conventional technique.

FIG. 17 is a configuration diagram of a distance measuring device according to a third conventional technique.

FIG. 18 is an explanatory diagram of a measurement error due to a shift in relative positional relationship between IRED and PSD.

[Explanation of symbols]

1 ... CPU, 2 ... EEPROM, 3 ... driver, 4 ... I
RED (light emitting diode), 5 ... PSD (position detecting element), 6 ... Integrating capacitor, 7 ... Lens driving circuit, 8 ...
Photographic lens, 10 ... AFIC (IC for automatic focusing), 11
... 1st signal processing circuit, 12 ... 2nd signal processing circuit, 13 ...
Clamp circuit, 14 ... Arithmetic circuit, 15 ... Integrator circuit, 71
… Photometric sensor.

Continuation of the front page (56) Reference JP-A-6-109967 (JP, A) JP-A-8-94919 (JP, A) JP-A-8-94920 (JP, A) JP-A-8-54231 (JP , A) JP 5-281460 (JP, A) JP 4-62412 (JP, A) JP 8-254421 (JP, A) JP 3-64715 (JP, A) JP 10-281756 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01C 3/00-3/32 G02B ⁷ /28-7/40 G03B 13/32-13/36

Claims (2)

(57) [Claims] 1. A light emitting means for projecting a light beam toward an object to be measured, and a reflected light of the light beam projected to the object to be measured, at a position corresponding to the distance to the object to be measured. Light is received at the light receiving position on the detection element, and based on the light receiving position, the far side signal that is larger as the distance is longer when the received light amount is constant, and the closer the distance is when the received light amount is constant. A light receiving unit that outputs a near-side signal having a large value, and inputs the far-side signal and compares the magnitude with the level of the clamp signal. When the level of the far-side signal is equal to or higher than the level of the clamp signal, Calculation of outputting a far-side signal as it is, and calculating a ratio of the near-side signal and the signal output from the clamp means by outputting the output ratio signal by the clamp means that outputs the clamp signal otherwise. Means and measure the ambient light brightness Luminance measuring means, when the output ratio signal is a near side from the clamping effect presence determination reference level defined by the reference object reflectance first
In accordance with the conversion formula, the value of the output ratio signal that otherwise considers the distance as infinite is set based on the external light brightness measured by the brightness measuring means and the position of the position detection element. A distance measuring device, comprising: a conversion unit that converts the output ratio signal into a distance signal according to the distance according to a second conversion equation that depends on a magnitude relationship with the determination value. 2. The distance measuring device according to claim 1, wherein the brightness switching determination value is also set based on a level of the clamp signal in the clamp means.