JPH0228507A - Range finder for camera - Google Patents

Abstract

PURPOSE:To broaden a distance measuring range by calculating an object distance based on a signal from a light receiving means for receiving light, which is the light projected from 1st and 2nd light projection parts, reflected on an object. CONSTITUTION:In measuring the distance to the closest one B, the light projected by the light projection part 7a can be measured in terms of distance at the point 6c of the projected image 6 of a semiconductor position detector 2. When the object comes at a distance shorter than the distance B, that means, when the object exists at the closest distance C, the light projected to the object from the light projection part 7b reaches the point 5d of the projected image 5a of the detector 2 and it can be measured. By providing the light projection part 7a having the optical axis of projected light in parallel with that of a photographic lens and the light projection part 7b in parallel with said part 7a on a position where the light, which is the projected light, reflected on the object that exists at the desired closest distance can be made incident on the detector 2, the distance measuring range can be drastically broadened without lowering an ability for measuring the distance.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application of the Invention) The present invention relates to an improvement in a distance measuring device for an active camera that projects light onto a subject and measures the distance to the subject by receiving the reflected light. It is something.

(Background of the Invention) In this type of device, in order to widen the measurable range, it is conceivable to increase the length of the light receiving element in the base line length direction.

However, when the above-mentioned light-receiving element is composed of, for example, a PSD (semiconductor device detector), if the length of the element is increased in order to widen the measurable range as described above, the light-receiving area of the entire element will be reduced. This will increase the noise from outside light. However, since the light emitting energy from a light emitting element, such as a 1RED (infrared light emitting diode), does not change, the reflected light from the subject has the same energy, resulting in a poor S/N ratio as a whole and a decrease in distance measurement accuracy. Furthermore, when the light receiving area is expanded as described above, the amplifier circuit of the light receiving element is likely to be saturated due to the influence of sunlight and the like. This will be explained in more detail below using FIG. 4.

Figure 4 shows the arrangement of the light emitting and receiving systems in a conventional device, where 1 is the light emitting element 1RED, 2 is the light receiving element PSD, 3 is the light emitting lens, 4 is the light receiving lens, 5 is a projected image of PSD2 projected onto the subject side;
A is the baseline length, B is the closest distance that can be measured with the conventional device, C is the closest distance that can be measured when the light receiving surface 2a is extended to the position shown by 2b, D is the focal length of the light receiving lens 4,
E is the focal length of the projection lens 3, F is P at close range B
The length of the light receiving surface of SD 2, G is PSD 2 at close distance C
is the length of the light receiving surface.

In the conventional device, as shown in Fig. 4, when 1RED 1 is projected onto the subject, the projected image is at a distance F on PSD 2
The image is formed on the spot. This state can be considered as a point 6c on the image 6 when the PSD 2 is projected onto the subject.

Therefore, if the subject is at close range C, jRE
The projected image of Dl reaches the subject, but when viewed from the projected image 5 of PSD 2 onto the subject, it corresponds to point 5c,
At that position, the light receiving surface of PSD 2 has already disappeared. Therefore, in order to extend the measurable range to the closest distance C, it is necessary to extend PSD 2 to 2b, but extending it in this way will cause the problems described above.

(Objective of the Invention) An object of the present invention is to provide a distance measuring device for a camera that can solve the above-mentioned problems and expand the measurable range without reducing the distance measuring ability.

(Features of the Invention) In order to achieve the above object, the present invention includes a light receiving means for receiving reflected light from a subject, and a light receiving means for projecting light toward the subject, the projected light being at a distance beyond a first close distance. A first light-emitting device arranged at a position where the light is reflected by the subject and enters the light-receiving means.
a light projecting unit, a position where the projected light is reflected by a subject located between a second close distance that is closer than the first close distance and the first close distance and enters the light receiving means; a light projecting means having at least a second light projecting section disposed in the light projecting section; and the light receiving device receiving reflected light from the subject of the projected light from the first light projecting section or the second light projecting section. and calculation means for calculating the subject distance based on the signal from the means,
The light projecting section that allows the reflected light from the object to enter the light receiving means is used as the light projecting means at that time to perform distance measurement, as if the light receiving area of the light receiving means was extended in the baseline length direction. It is characterized by having the same configuration as that used for distance measurement.

(Embodiment of the Invention) FIG. 1 shows a light emitting/receiving system arranged in a distance measuring device according to an embodiment of the present invention, and the same parts as in FIG. 4 are denoted by the same reference numerals.

In FIG. 1, 7 is 1RED having two light projecting parts 7a and 7b, and H is the distance between the light emitting parts of the light projecting parts 7a and 7b.

In the above configuration, in distance measurement to the closest distance B,
The projected image by the light projecting unit 7a is the point 6 of the projected image 6 of the PSD 2.
Distance measurement becomes possible with c. When the subject becomes closer than the close distance B, for example, if the subject is at the close distance C, the light projected by the light projecting section 7a will not reach 58 parts of the projected image of the PSD 2. In that case, the second light projecting section 7b
When the light is projected onto the subject, the projected light reaches the point 5d of the projected image 5a of the PSD 2, making it possible to measure the distance.

FIG. 2 shows a block diagram of a distance measuring device having a light emitting/receiving system as described above.

In the figure, 11 is one output current of PSD 2 ＾
12 is a current-voltage conversion circuit consisting of an operational amplifier and a resistor that converts the other output current 1. of the PSD 2 into a voltage VA. A current-voltage conversion circuit 13 consisting of an operational amplifier and a resistor that converts the current-voltage conversion circuit 11 into a voltage VB inputs the output voltage vA of the current-voltage conversion circuit 11 and the output voltage Vδ of the current-voltage conversion circuit 12, and (Va-Vゎ) A subtraction circuit that performs the operation 14
(■, +
VS); 15 is the subtraction circuit 1;
3 and the output of the adder circuit 14 as inputs, (VA
-VB) / (VA +Ve), a division circuit 16 which performs the calculation: the output of the addition circuit 14 and the reference voltage V□
, a comparator 17 for comparing the dividing circuit 15 with
18 is a CPU that controls the distance measurement sequence; 19 is a switch that generates a trigger signal to start distance measurement; 20.21 is the CPU 18;
22 is a ROM that stores a table A showing the correspondence between the output of the A/D converter 17 and the subject distance when the light projecting section 7a is being driven; 23 is a light projector; This ROM stores a table B showing the correspondence between the output of the A/D converter 17 and the subject distance when the section 7b is driven.

Next, the operation will be explained according to the flowchart shown in FIG.

First, the CPU S determines whether the switch 19 is on or off. While the switch 19 is off, it is repeatedly determined whether the switch 19 is on or off. When the switch 19 is turned on, the CPU 18 turns on the transistor 20 in order to start the distance measuring operation.
It outputs a hetribe signal and drives the light projector 7a. The subsequent processing changes depending on the distance to the subject, so it will be explained separately below.

1) When the subject is located at a measurable distance that is farther than the close distance B in Fig. 1. In this case, light is emitted from the light projecting unit 7a through the light projecting lens 3, and the projected image reflected by the subject is transmitted to the light receiving lens. P through 4
An image is formed on SD2. Therefore, from the PSD 2, output currents ^ and ^ can be obtained at a rate depending on the image position. These are converted into voltages by current-voltage conversion circuits 11 and 12. ,
Converted to VB. The voltages V^ and VB are input to the subtraction circuit 13 and addition circuit 14, and (VA V+s) and (
An output of vA+Va) is obtained. And the output (VA+
VB) is input to the comparator 16 and the reference voltage VR
Compared to KF. As a result, the output of the comparator 16 becomes "H" (because the subject is located within the measurable distance of the light projector 7a), and this signal is input to the CPU 18.

As mentioned above, the CPU 18 receives “H” from the comparator 16.
Since a signal is input, the output from the A/D converter 17 is (Va Va ) / (VA +Va).
After inputting the D conversion value, driving of the light projecting section 7a is stopped. Since this A/D conversion value is the value when the light projector 7a is being driven, the CPU 18 refers to table A in the ROM 22 to determine the subject distance.

2) When the subject is located between the closest distance B and the closest distance C in FIG. 1 In this case, the light projected from the light projecting section 7a and reflected by the subject is not imaged on the PSD 2. Therefore P.S.D.
Since the output current, In, cannot be obtained from 2, the output (vA+V,) from the adder circuit 14 cannot be obtained either. Therefore, since the output of the comparator 16 is "L", the CPU 1
8 stops driving the light projecting section 7a, and now the transistor 2
1 to drive the other light projecting section 7b. When the light projecting section 7b is driven in this way, PS
Since the reflected light from the subject is imaged on D2, the P
From SD 2, the output current ﾆ, IB can be obtained.

Therefore, the output of the comparator 16 becomes "H", so
The CPU 18 receives the output from the A/D converter 17 (VA
Va )/(VA +Ve ) (7) Input the A/D conversion value, and then stop driving the light projecting section 7b. This A
Since the /D conversion value is the value when the light projector 7b is being driven, the CPU 18 refers to table B in the ROM 23 to determine the subject distance.

3) When the subject distance is infinite In this case, the light projected from the light projecting section 7a and the light projected from the light projecting section 7b are reflected onto the PSD 2 and do not return. The output of the comparator 16 becomes "L" in both cases. Therefore, after stopping the driving of the light projecting section 7a, the CPU 18 determines that the distance is infinite regardless of the A/D conversion output.

After making the above distance determination, the CPU 18 switches switch 1
Wait for 9 to turn off and return to the initial state.

According to this embodiment, the light projecting section 7a has a light projecting optical axis parallel to the optical axis of the photographic lens, and the light projecting section 7a is lined up with the light projecting section 7a to reflect the projected light of a desired subject at a close distance. Light is PSD
Since the light projecting section 7b is provided at a position where the light can be incident on the light beam 2, it is possible to significantly expand the measurable range without reducing the distance measurement ability (range measurement accuracy, resolution).

(Correspondence between the invention and the embodiments) In this embodiment, the PSD 2 is the light receiving means of the present invention,
The light projecting parts 7a and 7b are the first. In the second light projecting section, the current-voltage conversion circuit 11 to the CPU 18 correspond to calculation means.

(Modification) In this embodiment, distance measurement in the ω direction from the close distance B is performed by the light projecting unit 7.
a, and from close range B to C, the light emitting unit 7b is used. However, in order to perform distance measurement even closer than close range C, the number of light emitting units is further increased. This can be achieved without reducing the equivalent ranging ability.

Furthermore, if the distance H between the light projecting parts 7a and 7b in FIG. It may be convenient because they can be made almost the same.

(Effects of the Invention) As described above, according to the present invention, there is provided a light receiving means for receiving reflected light from a subject, and a light receiving means for projecting light toward the subject, the projected light being emitted from a first close distance. A first light-emitting device arranged at a position where the light is reflected by the subject and enters the light-receiving means.
a light projecting unit, a position where the projected light is reflected by a subject located between a second close distance that is closer than the first close distance and the first close distance and enters the light receiving means; a light projecting means having at least a second light projecting section disposed in the light projecting section; and the light receiving device receiving reflected light from the subject of the projected light from the first light projecting section or the second light projecting section. and calculation means for calculating the subject distance based on the signal from the means,
The light projecting section that allows the reflected light from the object to enter the light receiving means is used as the light projecting means at that time to perform distance measurement, as if the light receiving area of the light receiving means was extended in the baseline length direction. Since the configuration is the same as that used for measuring distances, it is possible to expand the measurable range without reducing the distance measuring ability.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the arrangement of the light emitting and receiving systems arranged in a device according to an embodiment of the present invention, FIG. 2 is a block diagram of a distance measuring device having the light projecting and receiving system shown in FIG. 1, and FIG. The flowchart, FIG. 4, is a diagram showing the arrangement of light emitting and receiving systems arranged in a conventional device. 2...-PSD, 7...1RED,
7 a, 7 b... Light projecting section, 11.12.
...Current voltage conversion circuit, 13... Subtraction circuit, 14... Addition circuit, 15 ---- Division circuit, 16 ... Comparator, 17・・・・・・
- A/D converter, 18...CPU. Patent applicant Canon Co., Ltd.

Claims (1)

[Claims] (1) A light-receiving means for receiving reflected light from a subject, and a position for projecting light toward the subject, where the projected light is reflected by a subject located at a distance other than a first close distance and enters the light-receiving means. a first light projecting unit disposed at a second close distance, which is further closer than the first close distance;
a light projecting means having at least a second light projecting section disposed at a position where the light is reflected by a subject located within close range of the object and entering the light receiving means; and the first light projecting section or the second light projecting section A distance measuring device for a camera, comprising: calculation means for calculating a subject distance based on a signal from the light receiving means that receives reflected light from the subject of light projected from a light section.