JP2004029030A - Ranging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately find a distance to a ranging object with a small circuit scale in a short period of time, even if the outside light luminance fluctuates, by finding a distance signal from an output ratio signal according to transformation having an INFDATA value depending on the presence of a clamp operation or outside light luminance, thereby reliably determine an infinite distance. <P>SOLUTION: A far-side signal 12, which is output from a PSD 5 receiving a reflected light from the ranging object, is input to a clamping circuit 13 through a second signal processing circuit 12, and a larger level signal I2c of either of a far-side signal I2 or a clamp signal Ic with a fixed level is output from the clamping circuit 13. An output ratio (I1/ (I1+I2c)) is found by an arithmetic circuit 14 and integrating circuit 15, which input a near-side signal I1 that is output from the PSD 5 and a signal I2c that is output from the clamping circuit 13. By a CPU 1, a distance signal is found from the output ratio according to the first transformation during non-clamp operation, and according to the second transformation having the INFDATA value depending on the outside luminance during clamp operation. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to an active distance measuring device suitable for use in a camera or the like.

Conventionally, as an active distance measuring device in a camera, the one shown in FIG. 10 is known. FIG. 10 is a configuration diagram of a distance measuring apparatus according to a first related art.

In the distance measuring apparatus shown in this figure, under the control of the CPU 110, the driver 112 drives an infrared light emitting diode (hereinafter referred to as "IRED") 114 to output infrared light, and emits the infrared light to a light projecting lens. (Not shown) to project light to the object to be measured. The infrared light reflected by the object to be measured is focused on a position detecting element (hereinafter, referred to as “PSD”) 116 via a light receiving lens (not shown), and the PSD 116 receives the reflected light of the infrared light. The two signals I1 and I2 are output in accordance with the positions thus set. 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 calculates an output ratio (I1 / (I1 + I2)) based on the signals I1 and I2 from which the stationary light component has been removed, and outputs an output ratio signal according to the distance to the object to be measured. . 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. The signal output from the integration circuit 134 (hereinafter, referred to as an “AF signal”) corresponds to the distance to the object to be measured. The CPU 110 performs a predetermined calculation based on the AF signal output from the integration circuit 134 to obtain a distance signal, and controls the lens driving circuit 136 based on the distance signal to move the lens 138 to the in-focus position. Move.

FIG. 11 is a diagram showing the relationship between the AF signal output from the integration circuit 134 of the first related 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, and the vertical axis is the output ratio (I1 / (I1 + I2)), that is, the AF signal. As shown in this figure, below a certain distance L4, the output ratio has a substantially linear relationship with the reciprocal (1 / L) of the distance L, and as the distance L increases (1 / L decreases), the output ratio increases. Become smaller. However, when the distance L is longer than the distance L4, the influence of the noise component becomes larger as the distance L 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. Moreover, since In occurs randomly, it becomes unstable depending on the distance measurement 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 is known as a distance measuring device for solving such a problem. FIG. 12 is a configuration diagram of a distance measuring apparatus according to a second conventional technique. 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 input to both the arithmetic circuits 146 and 148 after the stationary light components are removed by the stationary light removing circuits 142 and 144, respectively. The arithmetic circuit 146 calculates the output ratio I1 / (I1 + I2) based on the signals I1 and I2 from which the stationary light component has been removed, and the integration 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 selector 160 selects one of the output ratio and the light amount, and obtains the distance to the distance measurement target based on the selected one. The selection unit 160 is a process in the CPU.

FIG. 13 is a configuration diagram of a distance measuring apparatus according to a third conventional technique. 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 170 are input to one end of a switch 176 after the stationary light components are removed by the stationary light removing circuits 172 and 174, respectively. 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. The integration circuit 178 integrates either one of the input signals I1 and I2, and the operation unit 180 performs an operation of I1 / (I1 + I2) based on the integration result to obtain an output ratio. 182 calculates the light amount by performing an operation of I1 + I2. Then, the selection unit 184 selects one of the output ratio and the light amount, and obtains the distance to the distance measurement target based on the selected one. The calculation units 180 and 182 and the selection unit 184 are processes in the CPU.

When the distance L to the object to be measured is small, the distance measuring devices according to the second and third prior arts (FIGS. 12 and 13) both use the distance based on the output ratio (I1 / (I1 + I2)). L is obtained, and 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.

In addition to the above-described devices, there are, for example, the following Patent Documents related to a distance measuring device used for a camera or the like.
JP-A-3-64715

As described above, the distance measuring devices according to the second and third prior arts (FIGS. 12 and 13) can both solve the problems of the distance measuring device according to the first prior art (FIG. 10). Things. However, the distance measuring apparatus according to the second prior art (FIG. 12) 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. 10). Then, there is a problem that the circuit scale is increased and the cost is increased. On the other hand, the distance measuring apparatus according to the third prior art (FIG. 13) cannot detect both the signals I1 and I2 from the PSD 170 at the same time, although the circuit scale is small. It takes twice as long to obtain the distance L at the same S / N ratio as that of the distance measuring device (FIG. 12).

In addition, any of the distance measuring apparatuses according to the prior arts described above is designed to operate favorably when the external light luminance is within the standard range. Circuits for changing the amount of light and removing the stationary light component (signal processing circuits 118 and 120 in FIG. 10, stationary light removal circuits 142 and 144 in FIG. 12, and stationary light removal circuits 172 and 174 in FIG. 13). Cannot sufficiently remove the steady light component from the signals I1 and I2 output from the PSD, and the operation of the arithmetic circuit and the integrating circuit deviates from the design values. 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 serious when the distance to the object to be measured is large.

The present invention has been made in order to solve the above problems, a small circuit scale and in a short time, even if the distance to the object to be measured is large, and even if the external light luminance varies, An object of the present invention is to provide a distance measuring device capable of uniquely obtaining a distance.

A first distance measuring apparatus according to the present invention includes: (1) a light emitting unit that outputs a light beam toward a distance measuring object; and (2) a reflected light of the light beam projected on the distance measuring object, the distance measuring device Light is received at a light receiving position corresponding to the distance to the object, and based on the light receiving position, if the received light amount is constant, the far side signal, which increases as the distance increases, and if the received light amount is constant, the distance increases. (3) When the far side signal is input and compared with the level of the clamp signal, the level of the far side signal is greater than the level of the clamp signal. Outputs the far-side signal as is, otherwise outputs a clamp signal, and (4) calculates the ratio of the near-side signal to the signal output from the clamp means and outputs an output ratio signal Calculating means, (5) luminance measuring means for measuring external light luminance, and (6) output ratio signal. The value of the output ratio signal, which is closer to the clamp effect presence / absence determination reference level determined by the subject reflectance according to the first conversion formula, otherwise the distance is regarded as infinity, is determined by the luminance measuring means. Conversion means for converting the output ratio signal into a distance signal corresponding to the distance in accordance with a second conversion equation depending on the measured external light luminance, wherein the first conversion equation The value of the output ratio signal, which is set according to the light luminance and considers the distance to be infinity, is closer to the near side than the value set according to the second external light luminance, which is smaller than the first external light luminance. There is a feature.

According to the first distance measuring device, the light 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. 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, and if the received light amount is constant, the far side signal is larger. 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. When the output ratio signal is closer to the reference level for judging the presence or absence of the clamp effect determined by the reference reflectance of the object, the conversion unit uses the first conversion formula. Otherwise, the distance is set to infinity. The output ratio signal is converted into a distance signal corresponding to the distance and output according to a second conversion formula in which the value of the output ratio signal to be regarded depends on the external light luminance measured by the luminance measuring means.

A second distance measuring apparatus according to the present invention includes: (1) a light emitting unit that outputs a light beam toward a distance measurement target; Light is received at a light receiving position corresponding to the distance to the object, and based on the light receiving position, if the received light amount is constant, the far side signal, which increases as the distance increases, and if the received light amount is constant, the distance increases. (3) When the far side signal is input and compared with the level of the clamp signal, the level of the far side signal is greater than the level of the clamp signal. Outputs the far-side signal as is, otherwise outputs a clamp signal, and (4) calculates the ratio of the near-side signal to the signal output from the clamp means and outputs an output ratio signal Calculating means, (5) luminance measuring means for measuring the external light luminance, and (6) far-side signal level. (7) a detection means for outputting 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. According to the conversion formula of 1, otherwise, the value of the output ratio signal is regarded as being at infinity. According to the second conversion formula which depends on the external light luminance measured by the luminance measuring means, the output ratio signal is changed according to the distance. Conversion means for converting the distance into infinity, wherein the value of the output ratio signal, which is set according to the first external light luminance and which considers the distance to be infinity, is the second conversion formula of the conversion means. It is characterized by being closer to a value set according to a second external light luminance smaller than the first external light luminance.

In the second distance measuring device, the operations of the light emitting unit, the light receiving unit, the clamping unit, and the calculating unit are the same as those of the first distance measuring unit. A detection signal indicating whether or not the level is equal to or higher than the level is output, and when the detection signal indicates that the level of the far-side signal is equal to or higher than the level of the clamp signal, If not, the output ratio signal is converted to a distance signal corresponding to the distance in accordance with a second conversion formula in which the value of the output ratio signal that regards the distance as infinity depends on the external light luminance measured by the luminance measuring means. You.

If both of the first and second distance measuring devices are incorporated in a camera and used for automatic focusing, the focusing of the photographing lens is controlled based on the distance signal.

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 in accordance with the distance to the object to be measured. Based on the light receiving position, based on the light receiving position, if the amount of received light is constant, the far side signal is larger as the distance is longer, and if the amount of received light is constant, the near side signal is larger as the distance is shorter. 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.

When the level of the far-side signal is equal to or higher than the level of the clamp signal, the conversion means follows the first conversion formula; otherwise, the value of the output ratio signal (INFDATA value) that regards the distance as infinity Is converted into a distance signal corresponding to the distance in accordance with a second conversion formula depending on the external light luminance, and is output. Alternatively, 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, and the conversion unit detects that the level of the far-side signal is equal to or higher than the level of the clamp signal. Indicates that the output ratio signal is equal to the distance in accordance with the first conversion formula. Otherwise, the value of the output ratio signal is determined to be infinite according to the second conversion formula depending on the external light luminance. Is converted to a distance signal corresponding to In the second conversion equation, the value of the output ratio signal that is set according to the first external light luminance and that assumes that the distance is infinity is the second external light luminance that is smaller than the first external light luminance. Is closer to the value set according 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, it is possible to obtain the same distance measurement result as that of the conventional light amount and distance measurement combined method without increasing the circuit scale and in a short time, and it is unique even if the distance to the distance measurement object is large. The distance can be obtained accurately and stably. Further, even if there is a change in the external light luminance, the distance can be uniquely and stably obtained, the accuracy of the long distance measurement is excellent, and the infinity determination can be reliably performed.

Hereinafter, embodiments of the present invention will be described 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 this figure, the CPU 1 controls the driver 3 to control the emission of infrared light from the IRED 4, and also supplies the power supply voltage supplied to the driver 3 (or the power supply voltage supplied from the driver 3 to the IRED 4). (Power supply voltage obtained from the drive current). In addition, the CPU 1 controls the operation of the automatic focusing IC (hereinafter, referred to as “AFIC”) 10 and inputs an AF signal output from the AFIC 10. Further, the CPU 1 inputs the value of the external light luminance measured by the photometric sensor 71 and the value of the temperature measured by the temperature sensor 72. Note that the power supply voltage is not limited to the driver 3 and the IRED 4, and the voltage of the battery may be directly measured, or the voltage supplied to other components may be measured.

The infrared light emitted from the IRED 4 is projected on a distance measuring object via a light projecting lens (not shown) disposed on the front surface of the IRED 4, and a part of the reflected light is reflected. The light is received at any position on the light receiving surface of the PSD 5 via a light receiving lens (not shown) disposed on the front surface of the PSD 5. This 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 indicates the amount of reflected light received by the PSD 5, and the output ratio (I1 / (I1 + I2)) indicates the light receiving position on the light receiving surface of the PSD 5, that is, the distance to the object to be measured. 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, actually, 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 may be input to the AFIC 10 due to external conditions.

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 receives the far-side signal I2 output from the second signal processing circuit 12, compares the levels of the clamp signal Ic at a certain level and the level of the far-side signal I2 with each other. Ic is output, otherwise, the far-side signal I2 is output as it is. Hereinafter, the signal output from the clamp circuit 13 is represented by I2c. Here, the level of the clamp signal Ic is substantially the same as the level of the far-side signal I2 corresponding to the distance L4 shown in FIG.

The arithmetic circuit 14 receives the near-side signal I1 output from the first signal processing circuit 11 and the signal I2c (one of the far-side signal I2 and the clamp signal Ic) output from the clamp circuit 13, and outputs the output ratio. (I1 / (I1 + I2c)) is calculated and the result is output. The integration circuit 15 receives the output ratio and integrates the output ratio with the integration 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 output from the SOUT terminal of the AFIC 10 as an AF signal.

The CPU 1 receives the AF signal output from the AFIC 10, performs a predetermined calculation, 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, a more specific circuit configuration of the first signal processing circuit 11, the clamp circuit 13, and the integration circuit 15 of the AFIC 10 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. The second signal processing circuit 12 has the same circuit configuration as the first signal processing circuit 11.

The first signal processing circuit 11 receives the near-side signal I1 including the stationary light component I0 output from the PSD 5 and removes the stationary light component I0 included in the first signal processing circuit 11 as shown in FIG. And outputs the near side signal I1. The current (I1 + I0) output from the short-distance terminal of the PSD 5 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 connected to the base terminal of the transistor 21, 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, the cathode terminal of the compression diode 24 is connected to the collector terminal of the transistor 22, and the cathode terminal of the compression diode 25 is connected to the + input terminal of the operational amplifier 23. Is connected to a first reference power supply 26.

A stationary light removing capacitor 27 is externally connected to the CHF terminal of the AFIC 10, and the stationary light removing capacitor 27 is connected to a base terminal of a steady light removing transistor 28 in the first signal processing circuit 11. . The stationary 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 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.

(3) The circuit diagram of the clamp circuit 13 is shown in FIG. The + input terminal of the judgment 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 connected to the collector terminal of the transistor 51 and the cathode terminal of the compression diode 52, similarly to the transistor 22 and the compression diode 24 connected to the + input terminal. It is connected to the input terminal of the arithmetic circuit 14 via 39.

The constant current source 41 is connected to the base terminal of the transistor 51, so that 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 of the current is input to the-input terminal of the comparator 37 for determination.

The switch 39 is connected to the output terminal of the judgment comparator 37, and receives the output signal of the judgment comparator 37. 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 are in 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 integrating capacitor 6 externally connected to the CINT terminal of the AFIC 10 is connected to the output terminal of the arithmetic circuit 14 via the switch 60, connected to the constant current source 63 via the switch 62, and connected to the operational amplifier 64 via the switch 65. It is connected to the output terminal and is directly connected to the negative input terminal of the operational amplifier 64, and its potential is output from the SOUT terminal of the AFIC 10. These switches 60, 62 and 65 are controlled by a control signal from the CPU 1. A second reference power supply 66 is connected to the + input terminal of the operational amplifier 64.

The operation of the AFIC 10 configured as described above will be described with reference to FIGS. When the IRED 4 is not emitting light, the CPU 1 turns on the switch 29 of the first signal processing circuit 11. At this time, the steady light component I0 output from the PSD 5 is input to the first signal processing circuit 11, where the current is amplified by the operational amplifier 20 and the current amplifier including the transistors 21 and 22, and logarithmically compressed by the compression diode 24. Is converted into a voltage signal, and this voltage signal is input to the negative input terminal of the operational amplifier 23. If the signal input to the operational amplifier 20 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, the base current is supplied to the transistor 28, so that the collector current flows through the transistor 28, and the signal input to the operational amplifier 20 of the signal I0 input to the first signal processing circuit 11 becomes smaller. When the operation of the closed loop is stable, all of the signal I0 input to the first signal processing circuit 11 flows through the transistor 28, and the capacitor 27 stores a 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 stationary light component I0 of the signal I1 + I0 output from the PSD 5 at this time becomes the transistor 28 to which the base potential is applied by the electric charge stored in the capacitor 27. The near-side signal I1 is amplified by a current amplifier composed of an operational amplifier 20 and transistors 21 and 22, is logarithmically compressed by a compression diode 24, is converted into a voltage signal, and is 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. The far-side signal I2 is input to the clamp circuit 13. .

However, when the external light luminance is high, the collector current flowing through the transistor 28 fluctuates, and the steady light component I0 increases. When the temperature fluctuates, the amplifier gain and the amount of light emitted from the IRED 4 fluctuate, the noise component In increases, and the clamp current fluctuates. Further, when the power supply voltage fluctuates, the amount of light emitted from the IRED 4 fluctuates, and the noise component In increases. When the distance to the object to be measured is long and the amount of reflected light incident on the PSD 5 is small, if such an error is added, the output ratio signal approaches 50%, and the infinity determination accuracy is reduced. The distance measuring apparatus according to the present embodiment can obtain a reliable infinity determination result even in such a case.

(4) 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 thereby is input to the negative input terminal of the comparator 37 for determination. 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 near side signal I2 is output as the output signal I2c of the clamp circuit 13. When the magnitude relation is reversed, the switch 38 is turned off, the switch 39 is turned on, and the clamp signal Ic is output as the output signal I2c of the clamp circuit 13.

The signal I2c output from the clamp circuit 13 and the near-side signal I1 output from the first signal processing circuit 11 are input to an arithmetic circuit 14, where the output ratio (I1 / (I1 + I2c)) is calculated. The output is output, and the output ratio is input to the integration circuit 15. When the IRED 4 emits a predetermined number of pulses, the switch 60 of the integrating circuit 15 is turned on, the switches 62 and 65 are turned off, and the output ratio signal output from the arithmetic circuit 14 is supplied to the integrating capacitor 6. It is stored. 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 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 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). When 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). The output ratio becomes smaller. As described above, if 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 calculates a distance signal representing the driving amount of the photographing lens 8 based on the AF signal thus obtained, and sends the distance signal to the lens driving circuit 7 to focus the photographing lens 8 on a focusing operation. Let it. 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 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. In particular, the distances L2, L3, L4, and L5 (where L2 <L3 <L4 <L5) For each, the AF signal is y2, y3, y4 and y5 respectively, and the distance signal is x2, x3, x4
And x5 respectively.

Here, in each of the range of distance L ≦ L4 and the range of distance L> L4, the AF signal has a substantially linear relationship with the reciprocal (1 / L) of the distance L. The signal has a substantially linear relationship with the reciprocal (1 / L) of the distance L. Therefore, the relationship between the AF signal and the distance signal is also substantially linear in each of the range of distance L ≦ L4 and the range of distance L> L4.

Then, the magnitude of the AF signal y is compared with the reference level COUNT_B for judging the presence / absence of the clamp effect determined by the reference object reflectance (36%), and the AF signal y is converted by a conversion formula of a coefficient different depending on the result. Convert to a distance signal x. 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, in the range of distance L ≦ L4,

なるパラメータに基づいて、ＡＦ信号ｙから距離信号ｘを

Distance signal x from AF signal y based on

なる変換式で求める。一方、距離Ｌ＞Ｌ4 の範囲では、

It is calculated by the following conversion formula. On the other hand, in the range of distance L> L4,

なるパラメータに基づいて、ＡＦ信号ｙから距離信号ｘを

Distance signal x from AF signal y based on

なる変換式で求める。

It is calculated by the following conversion formula.

If the AF signal y is equal to or less than a certain value (for example, the AF signal value INFDATA corresponding to the farthest set point of the taking lens 8), the distance signal x is set to a certain value (for example, By setting the distance signal value AFINF) corresponding to the set point, more stable focusing control of the photographing lens 8 can be performed. That is, the above equation (6) is

となる。さらに、外光輝度、温度または電源電圧の値に応じてINFDATA値を切り替えた上で、ＡＦ信号ｙの値がそのINFDATA値以下となる場合に、距離信号ｘの値を一定値AFINF に固定させて安定させるのが好適である。

It becomes. Further, after switching the INFDATA value according to the value of the external light luminance, temperature, or power supply voltage, when the value of the AF signal y becomes equal to or less than the INFDATA value, the value of the distance signal x is fixed to a constant value AFINF. It is preferable to stabilize it.

Therefore, in the range of distance L> L4, the value of the external light luminance measured by the photometric sensor 71, the value of the temperature measured by the temperature sensor 72, or the value depending on the value of the power supply voltage input from the driver 3 is used. The distance signal x is obtained from the AF signal y in accordance with the conversion equation (7) having a certain INFDATA value. For example, the INFDATA value when all of the external light luminance, temperature and power supply voltage are within the standard range (hereinafter referred to as INFDATA_a value) and the INFDATA value when any of the external light luminance, temperature and power supply voltage are outside the standard range INFDATA values (hereinafter referred to as INFDATA_b values) are different from each other.

Note that the parameters A2 (equation (1)), B2 (equation (2)), A3 (equation (4)), B3 (equation (5)), the INFDATA_a and INFDATA_b values, the external light luminance, the temperature, and the power supply A standard range of each voltage (that is, a criterion for selecting which INFDATA value is selected) is obtained at the time of manufacture for each camera in which the distance measuring device is incorporated, and is stored in the EEPROM 2 or the like. Then, these parameters are read by the CPU 1 at the time of distance measurement, and the calculation of the expression (3) or (7) is performed to convert the AF signal y into the distance signal x. In this way, even if the external light luminance, the temperature, and the power supply voltage change, the distance can be uniquely obtained.

Next, a calculation example of the AF signal and the distance signal in the distance measuring apparatus according to the present embodiment will be described.

FIGS. 6 and 7 are graphs showing calculation results of the AF signal and the distance signal with respect to the distance L to the distance measuring object having high reflectance. FIG. 7A shows a result obtained by converting an AF signal into a distance signal in accordance with a conversion formula (where INFDATA_a = 305.608) represented by Expression (7) in a range of distance L> L4, and FIG. In the range of distance L> L4, the result of converting the AF signal into a distance signal in accordance with the conversion formula (7), where INFDATA_b = 820.4022, is shown. Here, a standard reflectance of 36% (the external light luminance at this time is defined as a second external light luminance) of the object to be measured has a reflectance of 90% (the external light luminance at this time is the first external light luminance). In other words, when the external light luminance is high, the level of the clamp signal Ic is set to 1.5 nA, and the near-side signal I1 output from the first signal processing circuit 11 and the second signal processing circuit 12 are output. It is assumed that an error signal of 0.2 nA is added to each of the far-side signals I2 output from.

As shown in these figures, an AF signal (FIG. 6) obtained when high-luminance external light is incident from a distance-measuring object having a reflectance of 90% is converted into an external-light luminance within a range of distance L> L4. When the distance signal is converted to a distance signal in accordance with the conversion formula expressed by the equation (7) using the INFDATA_a value when the temperature and the power supply voltage are all within the standard range, the distance signal The value is large, and the infinity determination is not performed (FIG. 7A). On the other hand, when the AF signal (FIG. 6) is converted into a distance signal in accordance with the conversion formula expressed by equation (7) using an INFDATA_b value different from the INFDATA_a value in a range of distance L> L4, the distance L becomes In a very large range, the value of the distance signal is small and a constant value AFINF (infinity determination) (FIG. 7B). As a result, even if the distance L is in a very large range, the distance signal does not increase, and the infinity determination can be reliably performed.

FIG. 8 is a graph showing a calculation result of a distance signal with respect to the distance L to the distance measurement target when the temperature fluctuates. FIG. 8A shows a result of converting an AF signal into a distance signal in accordance with the conversion formula (7) (Expression 7) in a range of distance L> L4, where INFDATA_a = 305.608. FIG. In the range of distance L> L4, the result of converting the AF signal into a distance signal in accordance with the conversion formula (7), where INFDATA_b = 820.4022, is shown. Here, when the temperature is −10 ° C. with respect to the standard temperature of 20 ° C., the amount of infrared light emitted from the IRED 4 becomes 1.25 times, and the level of the clamp signal Ic becomes 1.25 times. Shows the case where

As shown in this figure, the AF signal obtained when the temperature is lower than the standard temperature by 30 ° C. is such that the external light luminance, the temperature, and the power supply voltage are all within the standard range in the range of distance L> L4. When the value of INFDATA_a at that time is used as it is and converted into a distance signal according to the conversion formula expressed by equation (7), the value of the distance signal is large in a range where the distance L is very large, and the infinity determination is not made. (FIG. 8 (a)). On the other hand, when the AF signal is converted into a distance signal in accordance with the conversion formula expressed by the equation (7) using an INFDATA_b value different from the INFDATA_a value in a range of the distance L> L4, the range where the distance L is extremely large is obtained. In FIG. 8, the value of the distance signal is small and constant (infinity determination) (FIG. 8B).

FIG. 9 is a graph showing a calculation result of a distance signal with respect to the distance L to the distance measurement target when the power supply voltage fluctuates. FIG. 9A shows a result of converting an AF signal into a distance signal in accordance with a conversion formula (where INFDATA_a = 305.608) represented by Expression (7) in a range of distance L> L4, and FIG. In the range of distance L> L4, the result of converting the AF signal into a distance signal in accordance with the conversion formula (7), where INFDATA_b = 820.4022, is shown. Here, the case where the voltage is 3.2 V with respect to the standard voltage 2.85 V, the amount of infrared light emitted from the IRED 4 is 1.15 times, and the power supply noise is 0.15 nA is shown. ing.

As shown in this figure, the AF signal obtained when the voltage is higher than the standard voltage by 0.35 V is set such that the external light luminance, temperature, and power supply voltage are all within the standard range in the range of distance L> L4. When the value of the INFDATA_a at a certain time is used as it is and converted into a distance signal according to the conversion formula expressed by the expression (7), the value of the distance signal is large in a range where the distance L is very large, and the infinity determination is made. No (FIG. 9A). On the other hand, when the AF signal is converted into a distance signal using the INFDATA_b value different from the INFDATA_a value in the range of distance L> L4 in accordance with the conversion formula expressed by the equation (7), the distance L is extremely large. In FIG. 9, the value of the distance signal is small and constant (infinity determination) (FIG. 9B).

As described above, according to the distance measuring apparatus of the present embodiment, even when the external light luminance, the temperature, or the power supply voltage fluctuates, the accuracy of the long distance measurement is excellent, and the infinity determination can be reliably performed.

In the above embodiment, when the CPU 1 converts the AF signal y into the distance signal, the determination as to which of the expressions (3) and (7) is used is made based on the AF signal y being determined by 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. However, formulas (3) and (7) 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, the CPU 1 inputs an output signal from the determination comparator 37 in the clamp circuit 13 and selects one of the equations (3) and (7) based on this signal. Then, the AF signal y is converted into the distance signal y.

It is a lineblock diagram of a distance measuring device concerning this embodiment. FIG. 3 is a circuit diagram of a first signal processing circuit and an integrating circuit in the distance measuring apparatus according to the embodiment. It is a circuit diagram of a clamp circuit in the distance measuring device according to the present embodiment. FIG. 3 is a diagram illustrating a relationship between an AF signal output from an integration circuit of the distance measuring apparatus according to the embodiment and a distance to a distance measurement target. FIG. 4 is an explanatory diagram of conversion from an AF signal to a distance signal in the distance measuring apparatus according to the embodiment. 9 is a graph showing a calculation result of an AF signal with respect to a distance L to a distance measuring object having a high reflectance. It is a graph which shows the calculation result of the distance signal with respect to the distance L to the ranging object of a high reflectance. 7 is a graph showing a calculation result of a distance signal with respect to a distance L to a distance measurement target when a temperature fluctuates. 9 is a graph showing a calculation result of a distance signal with respect to a distance L to a distance measurement target when a power supply voltage changes. FIG. 2 is a configuration diagram of a distance measuring device according to a first related art. FIG. 7 is a diagram illustrating a relationship between an AF signal output from an integration circuit according to a first related art and a distance to an object to be measured. FIG. 9 is a configuration diagram of a distance measuring apparatus according to a second related art. FIG. 13 is a configuration diagram of a distance measuring apparatus according to a third conventional technique.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 ... CPU, 2 ... EEPROM, 3 ... driver, 4 ... IRED (light emitting diode), 5 ... PSD (position detection element), 6 ... integration capacitor, 7 ... lens drive circuit, 8 ... photographing lens, 10 ... AFIC (automatic Focusing IC), 11: first signal processing circuit, 12: second signal processing circuit, 13: clamp circuit, 14: arithmetic circuit, 15: integrating circuit.

Claims (2)

Light emitting means for outputting a light beam toward the object to be measured;
The reflected light of the luminous flux projected on the distance measuring object is received at a light receiving position corresponding to the distance to the distance measuring object, and based on the light receiving position, the distance is determined if the received light amount is constant. A far-side signal having a larger value as the distance increases, and a light-receiving unit that outputs a near-side signal having a larger value as the distance decreases if the amount of received light is constant,
The far-side signal is input and compared with the 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. Clamping means for outputting a signal;
Calculating means for calculating a ratio between the near-side signal and the signal output from the clamping means and outputting an output ratio signal;
Luminance measuring means for measuring external light luminance;
If the output ratio signal is closer to the reference level for determining whether or not the clamp effect is determined by the reference object reflectance, the output ratio is determined according to the first conversion formula; otherwise, the distance is regarded as infinity. Conversion means for converting the output ratio signal into a distance signal according to the distance, according to a second conversion formula whose signal value depends on the external light luminance measured by the luminance measurement means,
With
In the second conversion formula of the conversion means, a value of the output ratio signal that is set according to a first external light luminance and that considers the distance to be infinity is smaller than the first external light luminance. A distance measuring apparatus, which is closer to a value set according to a second external light luminance. Light emitting means for outputting a light beam toward the object to be measured;
The reflected light of the luminous flux projected on the distance measuring object is received at a light receiving position corresponding to the distance to the distance measuring object, and based on the light receiving position, the distance is determined if the received light amount is constant. A far-side signal having a larger value as the distance increases, and a light-receiving unit that outputs a near-side signal having a larger value as the distance decreases if the amount of received light is constant,
The far-side signal is input and compared with the 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. Clamping means for outputting a signal;
Calculating means for calculating a ratio between the near-side signal and the signal output from the clamping means and outputting an output ratio signal;
Luminance measuring means for measuring external light luminance;
Detecting means for outputting 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;
When the detection signal indicates that the level of the far-side signal is equal to or higher than the level of the clamp signal, the output ratio signal according to the first conversion formula; otherwise, the distance is regarded as infinity. Conversion means for converting the output ratio signal into a distance signal according to the distance, according to a second conversion formula whose value depends on the external light luminance measured by the luminance measurement means,
With
In the second conversion formula of the conversion means, a value of the output ratio signal that is set according to a first external light luminance and that considers the distance to be infinity is smaller than the first external light luminance. A distance measuring apparatus, which is closer to a value set according to a second external light luminance.

Images