JPH10274524A - Range finding device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine a distance uniformly in the small scale of a circuit in a short time even if a distance to a range-finding object is large by obtaining a distance signal from an power ratio signal according to a conversion expression which varies according to the reference value (threshold value) which discriminates whether a clamp is operated in a standard condition or not. SOLUTION: A far side signal 12 outputted from PSD(position detection element) 5 which receives reflected light from a range-finding object is inputted into a clamp circuit 13 through the second signal processing circuit 12, and a signal 12c of whichever level is larger, the far side signal 12 or a clamp signal Ic at a constant level is outputted from the clamp circuit 13. A power ratio (I1 /(I1 +I2c )) is obtained by a computing circuit 14 and an integrating circuit 15 which input a near side signal I1 outputted from the PSD 5, and the signal I2c outputted from the clamp circuit 13, a distance signal is obtained from the power ratio by a CPU 1 according to a conversion expression which varies with a threshold value which discriminates whether a clamp is operated or not.

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 As an active type distance measuring device in a camera, a device shown in FIG. 15 has been conventionally known.
FIG. 15 is a configuration diagram of a distance measuring apparatus according to the first related art.

In the distance measuring apparatus shown in FIG.
The driver 112 drives an infrared light emitting diode (hereinafter referred to as “IRED”) 114 to output infrared light, and transmits the infrared light to a projection lens (not shown).
Light is projected on the object to be measured via. The infrared light reflected by the object to be measured is condensed on a position detecting element (hereinafter, referred to as “PSD”) 116 via a light receiving lens (not shown), and is reflected by the PS.
D116 outputs two signals I1 and I2 according to the position where the reflected light of the infrared light is received. The first signal processing circuit 118 removes the stationary light component that becomes noise contained in the signal I1, and the second signal processing circuit 120 removes the stationary light component that becomes noise contained in the signal I2.

The arithmetic circuit 132 outputs an output ratio (I1 / (I1) 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 improves the S / N ratio by integrating the output ratio signal output from the arithmetic circuit 132 many times in this manner. This integration circuit 13
4 (hereinafter referred to as “AF signal”).
Is based on the distance to the object to be measured. Then, CPU 110 outputs A
Based on the F signal, a predetermined calculation is performed to obtain a distance signal, and based on the distance signal, the lens driving circuit 136 is controlled to move the lens 138 to a focus position.

FIG. 16 is a diagram showing the relationship between the AF signal output from the integration 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 (1 / L) of the distance L to the object to be measured.
The vertical axis represents the output ratio (I1 / (I1 + I2)), that is, the AF signal. As shown in this figure, a certain distance L4
Hereinafter, the output ratio has a substantially linear relationship with the reciprocal (1 / L) of the distance L, and the output ratio decreases as the distance L increases (1 / L decreases). However, above the distance L4,
Conversely, as the distance L increases, the influence of the noise component increases. Assuming that the noise component is In (In ≧ 0), the output ratio is (I1 + In) / (I1 + In + I2 + In), and the output ratio fluctuates in a direction larger than the distance L4.
In addition, since In occurs randomly, it becomes unstable depending on the distance measurement conditions. This means that if the distance L increases, the PSD
This is because the intensity of the reflected light received by 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 is known as a distance measuring device for solving such a problem. FIG.
FIG. 2 is a configuration diagram of a distance measuring apparatus according to a second related art. In this figure, only the light receiving side is shown. In the distance measuring apparatus shown in this figure, the signals I1 and I2 output from the PSD 140 are applied to the stationary light removing circuits 142 and 14 respectively.
After the steady light component is removed by each of the four, the signals are input to both the arithmetic circuits 146 and 148. Arithmetic circuit 146
Performs an operation of I1 / (I1 + I2) on the basis of the signals I1 and I2 from which the stationary light component has been removed to obtain an output ratio, and the integrating circuit 150 integrates the output ratio. on the other hand,
The arithmetic circuit 148 calculates I1 + I2 to obtain the light amount, and the integrating circuit 152 integrates the light amount. And
The selection unit 160 selects one of the output ratio and the light amount,
Based on this, the distance to the object to be measured is determined. In addition,
The selection unit 160 is a process in the CPU.

FIG. 18 is a configuration diagram of a distance measuring apparatus according to a third prior art. In this figure, only the light receiving side is shown. In the distance measuring device shown in FIG.
After the steady light components are removed by the steady light removing circuits 172 and 174, respectively, the signals I1 and I2 output from are input to one end of the switch 176. The switch 176 is controlled by the CPU, and causes one of the outputs of the stationary light removal circuits 172 and 174 to be input to the integration circuit 178. An integrating circuit 178 integrates either one of the input signals I1 and I2, and a calculating section 180 calculates I1 / (I1 +
I2) is calculated to obtain the output ratio.
In step 82, the calculation of I1 + I2 is performed to obtain the light amount. Then, the selection unit 184 selects one of the output ratio and the light amount, and obtains a distance to the distance measurement target based on the selected one. The operation units 180 and 182 and the selection unit 184
This is the process in U.

The distance measuring devices (FIGS. 17 and 18) according to the second and third prior arts both have an output ratio (I1 / (I1 + I) when the distance L to the object to be measured is small.
2)), the distance L is obtained. When the distance L is large, the distance L is obtained based on the light amount (I1 + I2). By doing so, the distance L can be uniquely determined. Things.

[0009]

As described above, the distance measuring devices according to the second and third prior arts (FIGS. 17 and 18)
Can solve the problem of the distance measuring apparatus (FIG. 15) according to the first conventional technique. However, the distance measuring apparatus according to the second prior art (FIG. 17) needs to provide two sets of both an arithmetic circuit and an integrating circuit, which are compared with the distance measuring apparatus according to the first prior art (FIG. 15). Then, there is a problem that the circuit scale is increased and the cost is increased. On the other hand, in the distance measuring apparatus according to the third prior art (FIG. 18), although the circuit scale is small, the signal I1 from the PSD 170 is small.
And I2 cannot be detected at the same time, so it takes twice as long to obtain the distance L with the same S / N ratio as the distance measuring apparatus according to the second prior art (FIG. 17). .

SUMMARY OF THE INVENTION The present invention has been made to solve the above problem, and a unique circuit can be obtained with a small circuit scale in a short time even if the distance to the object to be measured is large. An object of the present invention is to provide a distance measuring device.

[0011]

A first distance measuring apparatus according to the present invention comprises: (1) light emitting means for outputting a light beam to a distance measuring object; and (2) light emitted to the distance measuring object. The reflected light of the luminous flux is received at a light receiving position corresponding to the distance to the object to be measured, and based on the light receiving position, if the received light amount is constant, a far-side signal having a larger value as the distance increases, If the received light amount is constant, the light receiving means that outputs a near-side signal that becomes larger as the distance is shorter, and (3) the far-side signal is input and compared with the clamp signal level to determine the level of the far-side signal If the signal is equal to or higher than the level of the clamp signal, the far-side signal is output as it is. Otherwise, the ratio of the clamp signal that outputs the clamp signal to (4) the ratio between the near-side signal and the signal output from the clamp means is calculated. Calculating means for calculating and outputting an output ratio signal; (5)
A conversion that converts the output ratio signal into a distance signal according to the distance according to different conversion formulas depending on whether or not the output ratio signal is farther than the reference level for determining whether or not the clamp effect is determined by the reference object reflectance. Means.

According to this distance measuring device, the light beam 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. At the light receiving position corresponding to the distance, light is received at a light receiving position. Based on the light receiving position, if the received light amount is constant, the far side signal is larger as the distance is longer. Is output. The clamp means compares the far-side signal with the clamp signal level. If the far-side signal level is equal to or higher than the clamp signal level, the far-side signal is output as it is. A signal is output. The calculating means calculates the ratio between the near-side signal and the signal output from the clamp means, and outputs an output ratio signal. According to the conversion means, the output ratio signal is a distance signal corresponding to the distance according to a conversion formula different from each other depending on whether or not the output ratio signal is on the far side from the reference level for determining the presence or absence of the clamp effect determined by the reference object reflectance. Is converted and output. And
If the distance measuring device is incorporated in a camera and used for automatic focusing, the focusing of the photographing lens is controlled based on the distance signal.

Further, a second distance measuring apparatus according to the present invention comprises:
(1) a light emitting means for outputting a light beam toward a distance measuring object,
(2) The reflected light of the light beam projected on the object to be measured is received at the light receiving position corresponding to the distance to the object to be measured, and based on the light receiving position, if the received light amount is constant, the distance is increased. A light receiving means for outputting a far-side signal having a larger value as the distance increases, and a near-side signal having a larger value as the distance decreases if the amount of received light is constant; and (4) clamping means for comparing the level with the level, outputting the far-side signal as it is when the level of the far-side signal is equal to or higher than the level of the clamp signal, and outputting the clamp signal otherwise.
Calculating means for calculating the ratio of the near-side signal to the signal output from the clamp means to output an output ratio signal; and (5) detecting whether or not the level of the far-side signal is equal to or higher than the level of the clamp signal. (6) conversion means for converting the output ratio signal into a distance signal corresponding to the distance in accordance with conversion formulas different from each other depending on the detection signal.

The functions of the light emitting means, light receiving means, clamp means and calculating means in this distance measuring device are the same as those of the first distance measuring device. Here, the detection unit outputs a detection signal indicating whether or not the level of the far-side signal is equal to or higher than the level of the clamp signal.
The output ratio signal is converted into a distance signal corresponding to the distance and output according to conversion equations different from each other depending on the detection signal.

[0015]

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

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

The CPU 1 controls the entire camera including the distance measuring device, and controls the entire camera including the distance measuring device based on programs and parameters stored in the EEPROM 2 in advance. In the distance measuring apparatus shown in FIG. 1, the CPU 1 controls the driver 3 to control the emission of infrared light from the IRED 4, and controls the operation of an automatic focusing IC (hereinafter, referred to as "AFIC") 10. , And an AF signal output from the AFIC 10.

The infrared light emitted from the IRED 4 is
The light is projected on a distance measuring object via a light projecting lens (not shown) disposed on the front of the ED 4, a part thereof is reflected, and the reflected light is received by a light receiving lens disposed on the front of the PSD 5. The light is received at any position on the light receiving surface of the PSD 5 via a not shown (not shown). The light receiving position corresponds to the distance to the object to be measured. Then, the PSD 5 outputs two signals I1 and I2 according to the light receiving position.
The signal I1 is a near-side signal having a larger value as the distance is shorter if the received light amount is constant, and the signal I2 is a far-side signal having a larger value as the distance is longer if the received light amount is constant, The sum of the signals I1 and I2 represents the amount of reflected light received by the PSD 5, 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. And the near side signal I1 is AFIC
10, the far-side signal I2 is input to the AFI terminal
Input to PSD10 terminal of C10. However, in practice,
Depending on external conditions, a signal in which a stationary light component I0 is added to each of the near-side signal I1 and the far-side signal I2 may be input to the AFIC 10.

The AFIC 10 is an integrated circuit (IC) and includes 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 receives the signal I1 + I0 output from the PSD 5, removes the stationary light component I0 included in the signal, and outputs the near-side signal I1. The circuit 12 receives the signal I2 + I0 output from the PSD 5, removes the steady light component I0 included in the signal, and outputs the far-side signal I2.

The clamp circuit 13 includes the second signal processing circuit 1
2, the level of the clamp signal Ic at a certain level and the level of the far side signal I2 are compared. If the former is larger, the clamp signal Ic is output. If not, the far side signal I2 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 substantially equal to the level of the far-side signal I2 corresponding to the distance L4 shown in FIG.

The arithmetic circuit 14 includes a near side signal I1 output from the first signal processing circuit 11 and a signal I2c (far side signal I2 and clamp signal I2c) output from the clamp circuit 13.
c) and output ratio (I1 / (I1 + I2)
c)) is calculated and the result is output. Integration circuit 15
Inputs the output ratio and integrates the output ratio with the integrating capacitor 6 connected to the _CINT terminal of the AFIC 10 many times, thereby improving the S / N ratio. Then, the integrated output ratio is represented by AFIC as an AF signal.
It is output from the SOUT terminal 10.

The CPU 1 receives the AF signal output from the AFIC 10, performs a predetermined operation, converts the AF signal into a distance signal, and sends the distance signal to the lens driving circuit 7. The lens driving circuit 7 causes the taking lens 8 to perform a 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 integration 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 apparatus according to the present embodiment. FIG. 3 is a circuit diagram of the clamp circuit 13 in the distance measuring apparatus according to the present embodiment. Note that the second signal processing circuit 12 has the same circuit configuration as the first signal processing circuit 11.

FIG. 2 is a circuit diagram of the first signal processing circuit 11. The near-side signal I1 including the stationary light component I0 output from the PSD 5 is input to the first signal processing circuit 11, and the stationary light component I0 contained in the near-side signal I1 is included. And outputs the near side signal I1. The current (I
1 + I0) is input to the negative 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 a 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 potential of this collector terminal is connected to the arithmetic circuit 14. Further, a compression diode 24 is connected to the collector terminal of the transistor 22.
The cathode terminal of the compression diode 25 is connected to the + input terminal of the operational amplifier 23, and the first reference power supply 26 is connected to the anode terminal of each of the compression diodes 24 and 25. .

A stationary light removing capacitor 27 is externally connected to the CHF terminal of the AFIC 10, and is connected to a base terminal of a steady light removing transistor 28 in the first signal processing circuit 11. Have been. The steady light removing capacitor 27 and the operational amplifier 23 are connected via a switch 29, and the on / off of the switch 29 is controlled by the CPU 1. The collector terminal of the steady light removing transistor 28 is connected to the negative terminal of the operational amplifier 20.
The emitter terminal of the transistor 28 is connected to a 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 to the input terminal of the arithmetic circuit 14 via the switch 38. On the other hand, the − input terminal of the comparator for determination 37 is +
Like the transistor 22 and the compression diode 24 connected to the input terminals, the collector terminal of the transistor 51 and the cathode terminal of the compression diode 52 are connected to the input terminal of the arithmetic circuit 14 via the switch 39. ing.

Further, a constant current source 41 is connected to the base terminal of the transistor 51, whereby a predetermined clamp level is set, and a current of a predetermined magnitude is input to the base terminal of the transistor 51. . This current becomes the base current of the transistor 51, and the collector potential corresponding to the magnitude is input to the minus input terminal of the comparator 37 for determination.

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

The circuit configuration of the integration circuit 15 is shown in FIG. The integration capacitor 6 externally connected to the _CINT terminal of the AFIC 10
4, connected to a constant current source 63 via a switch 62, and connected to an operational amplifier 6 via a switch 65.
4 and connected directly to the operational amplifier 64
Of the AFIC
It is output from the SOUT terminal 10. These switches 6
0, 62 and 65 are controlled by a control signal from the CPU 1. Also, the + input terminal of the operational amplifier 64 includes:
The second reference power supply 66 is connected.

The operation of the AFIC 10 configured as described above will be described with reference to FIGS.
When the CPU 1 does not make the IRED 4 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
The current is amplified by a current amplifier composed of transistors 21 and 22, logarithmically compressed by a compression diode 24 and converted into a voltage signal, and this voltage signal is input to a negative input terminal of an operational amplifier 23. Operational amplifier 2
If the signal input to 0 is large, the VF of the compression diode increases, so that the signal output from the operational amplifier 23 is large, and the capacitor 27 is charged. Then, a base current is supplied to the transistor 28, so that a collector current flows through the transistor 28,
Of the signals I0 input to the first signal processing circuit 11, the signal input to the operational amplifier 20 becomes smaller. When the operation of this closed loop is stable, the first signal processing circuit 1
All of the signal I0 input to 1 flows into the transistor 28, and the capacitor 27 stores a charge corresponding to the base current at that time.

When the CPU 1 makes the IRED 4 emit light and turns off the switch 29, the PSD 1
5 of the signal I1 + I0 output from the stationary light component I0
Flows as a collector current through a transistor 28 to which a base potential is applied by the charge stored in the capacitor 27, and the near-side signal I1 is current-amplified by the operational amplifier 20 and a current amplifier including the transistors 21 and 22, and compressed. The data is logarithmically compressed by the diode 24, converted into a voltage signal, and output. That is, the first signal processing circuit 11 removes the stationary light component I0 and outputs only the near-side signal I1. The near-side signal I1 is input to the arithmetic circuit 14.

On the other hand, similarly to the first signal processing circuit 11, the second signal processing circuit 12 removes the stationary light component I0 and outputs only the far-side signal I2. To enter. The 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 signal output from the constant current source 41 flows as the base current of the transistor 51, and the potential of the collector terminal of the transistor 51 (clamp signal Ic) generated by the signal flows to the determination comparator 37.
To the-input terminal. The near side signal I2 and the clamp signal Ic are compared in magnitude by the comparator 37, and one of the switches 38 and 39 is turned on and the other is turned off according to the comparison result. That is, when the near side signal I2 is larger than the clamp signal Ic, the switch 38 is turned on, the switch 39 is turned off, and the output signal I2c of the clamp circuit 13 becomes the near side signal I2c.
2 is output. If the magnitude relationship is reversed, switch 3
8 is turned off, the switch 39 is turned on,
The clamp signal 13 is used 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, where the output ratio (I1 / (I1 + I2c)) is calculated and output by the arithmetic circuit 14, and the output ratio is input to the integrating circuit 15. When the IRED 4 emits a predetermined number of pulses, the switch 60 of the integrating circuit 15 is turned on, and the switches 62 and 6 are turned on.
5 is turned off, and the output ratio signal output from the arithmetic circuit 14 is stored in the integrating capacitor 6. Then, when the pulse emission of the predetermined number of times is completed, the switch 60 is turned off, the switch 65 is turned on, and the electric charge stored in the integrating capacitor 6 has the opposite potential supplied from the output terminal of the operational amplifier 64. Decreases due to charge. The CPU 1 monitors the potential of the integrating capacitor 6, measures the time required to return to the original potential, determines the AF signal based on the time, and further determines the distance to the distance measurement target.

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 integration circuit of the distance measuring apparatus according to the present 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 less than a certain distance L4 (L≤L4), the signal output from the clamp circuit 13 is I2, and the output ratio is I1 / (I1 + I2). ), And the output ratio has a substantially linear relationship with the reciprocal (1 / L) of the distance L. The output ratio decreases as the distance L increases (1 / L decreases). Further, the distance L is equal to or greater than the distance L4 (L ≧
L4), the signal output from the clamp circuit 13 is
Ic, and the output ratio is I1 / (I1 + Ic). Also in this case, as the distance L increases, the output ratio decreases.
As described above, when the clamp circuit 13 is used, the distance L to the object to be measured can be uniquely and stably determined from the output ratio (AF signal).

The CPU 1 controls the AF thus obtained.
Based on the signal, a distance signal representing the driving amount of the photographing lens 8 is obtained by calculation, 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 from an AF signal to a distance signal in the distance measuring apparatus according to the present embodiment. In the graph shown in this figure, the horizontal axis represents 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. In particular, the distances L2, L3, L4, and L5 (where L2 <L3 <
L4 <L5), the AF signal is y2, y3, y
4 and y5, respectively, and the distance signal is x2, x3, x4
And x5 respectively.

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

Therefore, the reference levels COUNT_B and A for determining the presence or absence of the clamp effect determined by the reference object reflectance (36%)
The magnitude of the F signal y is compared with that of the F signal y, and the AF signal y is converted into the distance signal x by a different conversion formula depending on the result. In the case of the reference object reflectance, the distance L corresponding to the clamp effect presence / absence determination reference level COUNT_B is L4, and COUNT_B is equal to y4. That is, the distance L ≦ L4
In the range

[0038]

(Equation 1)

[0039]

(Equation 2) From the AF signal y to the distance signal x based on
To

[0040]

(Equation 3) It is calculated by the following conversion formula. In the range of distance L> L4,

(Equation 4)

[0041]

(Equation 5) From the AF signal y to the distance signal x based on
To

[0042]

(Equation 6) It is calculated by the following conversion formula. Note that the parameter A2 (equation (1)),
B2 (Equation (2)), A3 (Equation (4)) and B3 (Equation (5)) are obtained at the time of manufacture for each camera in which this distance measuring device is incorporated, and are stored in advance in the EEPROM 2 or the like. And
These parameters are read out by the CPU 1 at the time of distance measurement, and the calculation of the expression (3) or (6) is performed to obtain the AF signal y.
To a distance signal x.

Next, an example of calculation of the AF signal and the distance signal in the distance measuring apparatus according to the present embodiment will be described. 6 and 7 each show a distance L to a distance measurement target having a reflectance of 36%.
FIGS. 8 and 9 are graphs showing calculation results of an AF signal and a distance signal, respectively, with respect to a distance L to a distance measurement target having a reflectance of 9%. And FIG.
0 and FIG. 11 are graphs respectively showing the calculation results of the AF signal and the distance signal with respect to the distance L to the object to be measured having a reflectance of 90%. In each of FIGS. 7, 9 and 11, (a) shows the calculation result when the distance signal is calculated according to the present invention, and (b) shows the equations (1) to (3) over the entire range of the distance L. (C) shows a calculation result when a distance signal is calculated according to the equation (3), and (c) shows a calculation result when a distance signal is calculated by light amount ranging when the distance L increases.

First, looking at the distance dependency of the AF signal when the reflectivity of the object to be measured shown in FIG. 6 is 36% (that is, under the standard condition), the distance L (unit is:
When the reciprocal (1 / L) of m) is in the range of about 0.13 or more, the signal output from the clamp circuit 13 is the far-side signal I2, and the AF signal has a substantially linear relationship with 1 / L in this range. It is in. When 1 / L is about 0.13 or less, the signal output from the clamp circuit 13 is the clamp signal Ic.
Has a substantially linear relationship with.

Based on such AF signals, equations (1) through
When the distance signal is calculated according to the equation (6), a result as shown in FIG. 7A is obtained. When the result is compared with the result of the conventional method (FIG. 7C) which is used in combination with the light amount ranging, the result is well matched. The results obtained are as follows. In addition, 2 shown in the graph of FIG.
The broken line indicates the allowable range of the error of the distance measurement result derived from the circle of confusion caused by the photographing lens 8, and FIG.
The distance signals shown in (c) and (c) are within the allowable range. On the other hand, over the entire range of the distance L
When the distance signal is calculated according to the equations (1) to (3) (FIG. 7)
In (b)), when 1 / L becomes about 0.13 or less, the distance signal rapidly decreases, the error in the distance measurement result increases, and the distance measurement is out of the allowable range.

FIG. 6 shows the distance dependency of the AF signal when the reflectivity of the object to be measured shown in FIG. 8 is 9% (that is, when the reflectivity of the object to be measured is low). Where the distance L is smaller than (1 / L = about 0.27)
The signal output from the clamp circuit 13 is switched at the boundary. However, also in this case, the distance signal obtained according to the present invention (FIG. 9A) is in good agreement with the distance signal obtained by the conventional method used together with the light quantity measurement (FIG. 9C). The distance signals shown therein are within the allowable range. On the other hand, when the distance signal is calculated according to the equations (1) to (3) over the entire range of the distance L (FIG. 9).
In (b)), when 1 / L becomes about 0.26 or less, the distance signal sharply decreases and the error of the distance measurement result increases,
1 / L is about 0.25 or less, which is out of the allowable range.

FIG. 6 shows the distance dependency of the AF signal when the reflectance of the object to be measured shown in FIG. 10 is 90% (that is, when the reflectance of the object to be measured is high). (1 / L = about 0.0)
The signal output from the clamp circuit 13 is switched at the boundary of 8). However, also in this case, the distance signal (FIG. 11A) obtained according to the present invention is the distance signal (FIG. 11C) obtained by the conventional method which is used together with the light quantity ranging.
Relatively well, and the distance signals shown therein fall within the allowable range. Also, over the entire range of the distance L
When the distance signal is calculated according to the equations (1) to (3) (FIG. 1)
1 (b)), the mutation amounts are substantially the same. As described above, the calculation result of the distance signal according to the present invention shows a relatively good agreement with the light quantity and distance measurement combined method over a wide range where the reflectance of the distance measurement target is 9% to 90%. And it is within the allowable range.

Next, an example of actual measurement of an AF signal and a distance signal in the distance measuring apparatus according to the present embodiment will be described. FIG. 12 is a graph showing actual measurement results of a distance signal with respect to a distance L to a distance measurement target having a reflectance of 36%. In this figure, the solid line indicates the theoretical value of the distance signal, the symbols ▽ and △ indicate the upper limit and the lower limit of the allowable range of the error of the distance signal, and the symbol-indicates the number of times the distance signal L was measured 20 times. Of each of the measurement results, and the mark x indicates the average value of the measurement results of 20 times. As can be seen from this figure, not only the average value but also the actual measurement values of each of the 20 measurement results show good agreement with the theoretical values and fall within the allowable range.

In the above embodiment, when the CPU 1 converts the AF signal y into the distance signal, the CPU 1 determines whether to use the equations (3) and (6) based on whether the AF signal y is the reference object reflectance. This is based on whether or not it is farther than the reference level for judging the presence or absence of the clamp effect defined in the above. But,
Equations (3) and (6) may be selected based on whether or not the level of the far-side signal I2 is equal to or higher than the level of the clamp signal Ic. In this case, in FIGS. 1 and 3, CP
U1 is a comparator 37 for determination in the clamp circuit 13.
, And based on this signal, one of the equations (3) and (6) is selected, and the AF signal y is converted into the distance signal y. 13 and 14 show calculation examples of the distance signal in this case. FIG. 13 is a graph showing a calculation result of a distance signal with respect to a distance L to a distance measurement target having a reflectance of 9%, and FIG. 14 is a graph showing a reflectance of 90%.
9 is a graph showing a calculation result of a distance signal with respect to a distance L to a distance measurement target. 13 and FIG.
9 (a) and FIG. 11 (a),
It shows a relatively good match, and the distance signals shown here are within the allowable range.

[0050]

As described in detail above, according to the present invention, the light beam 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 reflected by the light receiving means. The far-side signal I2, which is greater at a longer distance if the amount of received light is constant, is received at a light-receiving position corresponding to the distance to the object to be measured, and based on the received light position, If there is, the near side signal I1 having a larger value as the distance is shorter is output. The far-side signal I2 is compared with the level Ic of the clamp signal by the clamp means, and the level of the far-side signal I2 is compared with the level Ic of the clamp signal.
In the above case, the far side signal I2 is output as it is, otherwise, the clamp signal Ic is output. The calculating means calculates the ratio between the near side signal I1 and the signal Ic2 output from the clamp means, and outputs an output ratio signal.

The conversion means converts the output ratio signal into a distance according to a different conversion formula depending on whether or not the output ratio signal is farther than a reference level for judging the presence or absence of a clamp effect determined by the reference reflectance of the object. Is output after being converted into a distance signal corresponding to. Alternatively, the detection means outputs a detection signal indicating whether or not the level of the far-side signal is equal to or higher than the level of the clamp signal, and the conversion means converts the output ratio signal into the distance according to a different conversion equation depending on the detection signal. Is output after being converted into a distance signal corresponding to. If the distance measuring device is incorporated in a camera and used for automatic focusing, the focusing of the photographing lens is controlled based on the distance signal.

With such a configuration, the same distance measurement result as that of the conventional light amount and distance measurement combined method can be obtained in a short time without increasing the circuit scale, and the distance to the distance measurement target is increased. However, the distance can be uniquely and stably obtained.

[Brief description of the drawings]

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

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

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

FIG. 4 is a diagram showing a relationship between an AF signal output from an integration circuit of the distance measuring apparatus according to the present embodiment and a distance to a distance measurement target.

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

FIG. 6 is a graph showing a calculation result of an AF signal with respect to a distance L to a distance measurement target having a reflectance of 36%.

FIG. 7 is a graph showing a calculation result of a distance signal with respect to a distance L to an object to be measured having a reflectance of 36%.
6 is a graph of a calculation result when a distance signal is calculated according to the present invention, and FIG. 7B is a graph of a calculation result when the distance signal is calculated according to the equations (1) to (3) over the entire range of the distance L. FIG. 8C is a graph of a calculation result when a distance signal is calculated by light amount ranging when the distance L increases.

FIG. 8 is a graph showing a calculation result of an AF signal with respect to a distance L to a distance measurement target having a reflectance of 9%.

9 is a graph showing a calculation result of a distance signal with respect to a distance L to a distance measurement target having a reflectance of 9%, and FIG. 9A is a graph showing a calculation result when a distance signal is calculated according to the present invention; , (B) are graphs of calculation results when the distance signal is calculated according to the equations (1) to (3) over the entire range of the distance L, and (c) is a graph when the distance L is increased. 7 is a graph of a calculation result when a distance signal is calculated by light amount ranging.

FIG. 10 is a graph showing a calculation result of an AF signal with respect to a distance L to a distance measurement target having a reflectance of 90%.

11A and 11B are graphs showing calculation results of a distance signal with respect to a distance L to a distance measurement target having a reflectance of 90%, and FIG.
Is a graph of a calculation result when a distance signal is calculated according to the present invention, and FIG.
6 is a graph of a calculation result when a distance signal is calculated according to Expressions (1) to (3), and (c) is a calculation result when a distance signal is calculated by light amount ranging when the distance L increases. It is a graph of.

FIG. 12 is a graph showing actual measurement results of a distance signal with respect to a distance L to a distance measurement target having a reflectance of 36%.

FIG. 13 is a graph showing a calculation result of a distance signal with respect to a distance L to a distance measurement target having a reflectance of 9% when a conversion formula is selected based on a level of a far-side signal.

FIG. 14 shows a distance L to a distance measurement target having a reflectance of 90% when a conversion formula is selected based on the level of a far-side signal.
9 is a graph showing a calculation result of a distance signal with respect to.

FIG. 15 is a configuration diagram of a distance measuring apparatus according to a first related art.

FIG. 16 shows A output from the first prior art integration circuit;
FIG. 4 is a diagram illustrating a relationship between an F signal and a distance to a distance measurement target.

FIG. 17 is a configuration diagram of a distance measuring apparatus according to a second related art.

FIG. 18 is a configuration diagram of a distance measuring apparatus according to a third conventional technique.

[Description of Signs] 1 ... CPU, 2 ... EEPROM, 3 ... Driver, 4 ... I
RED (light emitting diode), 5 ... PSD (position detection element), 6 ... integration capacitor, 7 ... lens drive circuit, 8 ...
Shooting lens, 10 ... AFIC (autofocus IC), 11
... first signal processing circuit, 12 ... second signal processing circuit, 13 ...
Clamp circuit, 14 arithmetic circuit, 15 integration circuit.

Claims (2)

[Claims] A light emitting unit that outputs a light beam toward the object to be measured; and a light receiving position corresponding to a distance to the object to be measured, the reflected light of the light beam being projected onto the object to be measured. The far-side signal, which has a larger value as the distance increases if the amount of received light is constant, and the near-side signal, which increases as the distance decreases, if the amount of received light is constant, based on the light-receiving position. A light receiving means for outputting a signal and a signal of the far side, and comparing the level with a level of a clamp signal; if 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. If not, a clamp means for outputting the clamp signal; a calculation means for calculating a ratio between the near-side signal and the signal output from the clamp means to output an output ratio signal; Signal is reference object reflectance Conversion means for converting the output ratio signal into a distance signal according to the distance in accordance with conversion equations different from each other depending on whether or not the output level is on the far side from the determined clamping effect presence / absence determination reference level. Distance measuring device. 2. A light emitting means for outputting a light beam toward the object to be measured, and a light receiving position corresponding to a distance to the object to be measured, the reflected light of the light beam being projected onto the object to be measured. The far-side signal, which has a larger value as the distance increases if the amount of received light is constant, and the near-side signal, which increases as the distance decreases, if the amount of received light is constant, based on the light-receiving position. A light receiving means for outputting a signal and a signal of the far side, and comparing the level with a level of a clamp signal; if 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. And if not, a clamp means for outputting the clamp signal; a calculation means for calculating a ratio between the near-side signal and the signal output from the clamp means to output an output ratio signal; If the signal level is A detection unit that outputs a detection signal indicating whether or not the signal level is equal to or higher than a signal level; and a conversion unit that converts the output ratio signal into a distance signal corresponding to the distance, according to different conversion formulas depending on the detection signal. A distance measuring device comprising: