JPS5814646B2 - distance measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a distance measuring device, particularly to a distance measuring device suitable for use in an automatic focusing device of a camera.

There are various types of automatic distance measuring devices, but the distance measuring device that is the object of the present invention is of a type that can be called a floodlight triangulation type.

FIG. 1 shows an embodiment of the present invention, and with reference to this figure, the principle of a floodlight triangulation type distance measuring device will first be explained.

Reference numeral 2 denotes a distance measuring lens which is oriented and fixed so that the center of the subject is located on its optical axis, and 6 is a projector whose direction can be changed.

The projector 6 includes a light source 8 and a lens 7 that converts the light into a parallel beam and projects it.

In order to avoid interference from external light, the light source 7 emits light of a specific wavelength, and a filter 1 is provided in front of the lens 2 to pass only the light of that wavelength.

The light beam projected from the projector hits an appropriate object and is reflected, and an image of the reflection point is created on the focal plane of the lens 2.
Generally, this image is formed at a position away from the optical axis of the lens 2.

When the projector 6 is rotated and the projected light beam is projected onto the center of the subject that the lens 2 is looking at, the image at the reflection point will be the lens 2.
It is located on the optical axis of the

Therefore, if a photoelectric element is placed at the focal point position on the optical axis to detect the image, the distance to the subject can be determined from the tilt of the projector 6.

In the above principle method, light enters the photoelectric element only when it is in focus;
In other cases, it does not enter, but for that reason, the floodlight 6
It is inconvenient for automatic distance measurement because it is difficult to tell whether the camera is facing closer or further away from the subject.

Therefore, it has been proposed to arrange two photoelectric elements 4 and 5 on both sides of the optical axis of the lens 2 as shown in FIG.

At the in-focus position, light enters the two electroluminescent elements 4 and 5 equally,
In other cases, more light enters into one of the photoelectric elements due to the tilt, so it can be determined whether the projector 6 is facing away from or closer to the subject depending on which element the light enters more.

FIG. 1 shows an embodiment in which the distance measuring device of the present invention is applied to an automatic focusing device of a camera, where 11 is a photographing lens, the optical axis of lens 2 is parallel to that of 11, and both lenses are used to focus on a subject at a considerable distance. They are staring at the same point.

The lens 11 is moved back and forth by a motor 13 via a gear train 12, the projector 6 is fixed to a gear 9, and the gear 9 is connected to the gear train 12 via a gear 10. Its direction is changed in conjunction with the forward and backward movement, and the motor 13 is stopped at the focused position.

To make the above focus judgment, it is sufficient to measure the difference between the outputs of both photoelectric elements and detect the positive and negative values and the point at which O is reached. If, for example, there is no object that reflects the light, the difference between the outputs of both photoelectric elements becomes 0 even though the lens is not in focus, which can be mistaken for an in-focus state.

The present invention aims to eliminate such misjudgments.

In order to achieve this purpose, in the present invention, in addition to the difference between the outputs of both photoelectric elements, the sum of the outputs is taken, and when this sum is not 0 and the difference is 0, it is determined that the state is in focus. .

The present invention will be explained below with reference to Examples.

FIG. 2 is a circuit diagram of one embodiment of the present invention.

The dotted line blocks with the symbols ``■■'' and ``■'' are signal processing circuits corresponding to the photoelectric elements 4 and 5 in FIG.

In the figure, only the structure shown in ■ is shown, and the inside of ■ is omitted.

The light source 8 is blinked at an appropriate frequency.

The output of photoelectric element 4 is applied to operational amplifier 17 via a high input impedance circuit consisting of FET 1 516.

The output of the operational amplifier 17 is applied to one input terminal of a subtraction circuit including the operational amplifier 24.

The amplified output of the photoelectric element 5 of block (2), which has the same configuration as block (2), is applied to the other input terminal of this subtraction circuit.

The operational amplifier 17 is provided with negative feedback via the FET 22, and the amount of negative feedback is controlled by the gate of the FET 22.
It is controlled by the output of 17 through 9, and the AC component is cut by the capacitor 23, so
The output of 17 is extremely stabilized in terms of direct current, and the alternating current component is extracted without attenuation.

A signal representing the difference between the outputs of the photoelectric elements 4 and 5 is obtained at the output terminal A of the operational amplifier 24.

In addition, an adder circuit is constituted by the operational amplifier 25 and the resistors around it, and the photoelectric elements 4 and 5 are amplified by the blocks ① and ②.
The outputs of are added.

26 is a bandpass filter consisting of an operational amplifier, a resistor, and a filter, which is matched to the blinking frequency of the light source 8, and the sum of the outputs of the photoelectric elements 4 and 5 is purely taken out to the output terminal B.

28 is also a bandpass filter, and the output terminal A (upper A) of the operational amplifier 24 is connected to the input terminal (lower A), and the output of this filter is connected to the source of the FET 29.

Since a pulse synchronized with the blinking of the light source 8 is applied to the gate of the FET 29, the difference between the outputs of the photoelectric elements 4 and 5 will be synchronously rectified by this X, and the light will be incident on either 4 or 5. The sign of the output of FET 2 9 is inverted depending on the condition.

The output of the FET 29 is applied to a differential amplifier consisting of transistors 30 and 31, and the two outputs of this amplifier are applied to amplifiers 32 and 33, respectively, and the light emitting diodes 37,
Controls the blinking of 3B.

When the difference between the outputs of the photoelectric elements 4 and 5 is 00, the transistor 30
, 310 inputs become equal, and at this time the light emitting diode 3
7 and 38 are not lit, and when light enters only one of the photoelectric elements 4 and 5, 37 and 38 are turned on depending on which one the light enters.
one of them flashes.

However, even if the current X is able to focus and display so-called front focus and rear focus, it is unclear whether it is actually in focus or not.

The outputs of the amplifiers 32 and 33 pass through an OR circuit 34 to open and close a gate 35.

The gate 35 is a light emitting diode 37. 38 is closed when any of them lights up.

In other words, it is closed when it is not in focus.

The gate 35 sends the sum of the outputs of the photoelectric elements 4 and 5 to the display unit 36, and is closed when the image is not in focus.
Conversely, when the difference between the outputs of the photoelectric elements 4 and 5 is O, the difference occurs, but in this case, if the sum of the outputs of the photoelectric elements 4 and 5 is also O
If this is the case, the in-focus state is not correct (for example, if the light source 8 is not lit), but since no force is applied to the display device 36, the display is displayed.The difference between the outputs of the photoelectric elements 4 and 5 is O. The display is made only when the sum has a certain value, indicating correct focus.

Eventually, the display device 36 displays the correct focus, and the light emitting diodes 37 and 38 display the front focus and rear focus.

A pulse signal synchronized with the blinking of the light source 8 applied to the gate of the FET 29 is applied to the output of the adder circuit 26 to the FET 27, a pulse signal synchronized with the blinking of the light source 8 is applied to the gate of this FET, and the drain of the FET 27 is connected to the drain of the FET 29. It is given by connecting to the gate.

Also, the sum signal of the photoelectric elements 4 and 5 sent to the gate 35 is also F.
This is the drain output of ET27.

This output is in the form of a pulse, but the outputs of the amplifiers 32 and 33 are also in the form of a pulse as a result of the synchronous rectification in the previous stage, and both are synchronous.

As described above, the distance measuring device of the present invention measures the sum and difference of the outputs of the two photoelectric elements, and determines the in-focus state when the sum is not 0 and the difference is O. It is possible to display the rear focus, eliminates the possibility of mistaking a case where the apparent difference is 0 as being in focus, and contributes to improving the reliability of distance measurement automation.

[Brief explanation of the drawing]

FIG. 1 is a plan view of an embodiment of the distance measuring device of the present invention, and FIG. 2 is a circuit diagram of the signal processing section. 2... Rangefinder lens, 4, 5... Photoelectric element, 6... Emitter, ■, ■... Output amplifier of photoelectric elements 4 and 5. , 24... Operational amplifier of the main part of the subtraction circuit, 26... Addition circuit, 37
．． 38... Light emitting diode for displaying front focus and rear focus, 36... Focus display unit.

Claims (1)

[Claims] 1. A light projector that projects light toward a distance measurement target, a distance measurement lens, two light receivers placed adjacent to each other across the optical axis behind the lens, and detects the output difference between both light receivers. a difference detection means, a sum detection means for detecting the sum of the outputs of both light receivers, and the outputs of both detection means are input, and when the output difference is substantially zero and the output sum is not substantially zero, , and a display unit that displays that distance measurement has been performed on the distance measurement target.