JPH0739954B2 - Ranging device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a distance measuring device such as a still camera and a video camera, more specifically, an infrared light projection type so-called active type distance measuring device, The present invention relates to a processing means under special conditions when A / D exchange of an analog signal obtained from an output of an optical sensor in the case of obtaining distance information from an output signal of an optical sensor having two outputs.

[Prior Art] Various methods have been already proposed for a method for calculating the output signal of an optical sensor having two outputs and obtaining the distance to a subject for photography with an active distance measuring device. Among them, a method of performing distance calculation after converting the obtained output signal into time through an analog IC to perform operational amplification of the output of the optical sensor, and further A / D converting it to a digital value. This is as described in the publication of the same applicant (Japanese Patent Laid-Open No. 61-231410).

In such an A / D converter, it is customary to count the number of clock pulses passing within the gate time by a counter and store the value. However, since the gate time is generated based on the amount of information obtained by the optical sensor, it may become unpredictably long under special conditions, that is, when the subject is extremely close or far. . As a result, the above-mentioned counter overflows, and there is a drawback that the distance measurement is completely erroneous.

[Purpose] The present invention has been made in view of such a problem, and an object thereof is to make an error even under a special condition such that the distance to a subject at the time of shooting is extremely short or far. It is to obtain an appropriate distance measurement result without distance measurement.

[Means for Achieving the Object] That is, in order to achieve the above object, the present invention is provided with a counter overflow detection circuit for A / D converting the time corresponding to the two output signal amounts of the optical sensor, Is under special conditions and the counter overflows, set a distance measurement signal to move the shooting lens to the closest step or a distance measurement signal to move the shooting lens to the farthest step. The lens is forcibly set to the distance.

[Examples] Hereinafter, details of the present invention will be described based on illustrated examples.

FIG. 1 shows an embodiment in which the distance measuring device of the present invention is applied to a camera. Number 1 in the drawing is a distance measuring circuit utilizing the principle of triangulation distance measurement, which is an optical device such as PSD. The currents i1 and i2 output from both ends of the sensor 2 are respectively I1 = k × i1 and I2 = k × i2 by the amplifiers 5a and 5b and the voltage / current converters 6a and 6b.
Is amplified to. 7a and 7b are changeover switches, which are turned on when the control lines 8a and 8b for the respective switches are "H" and cut off when they are "L". In the figure, 3 is a light emitting element, and 4a, 4
b indicates a condenser lens, respectively.

Now consider a system in which the optical axis of the received light and the electrical center position of the PCD coincide.

This distance measuring circuit 1 measures the distance to the subject as L, the length of PSD
When d is the base line length (lens interval) b, and the distance between the light spot formation position and the light receiving optical axis is x (Fig. 4), the output current from each PSD2 output terminal is i1 = (d + 2x) / 2d.・ F, i2 = (d-2x) /
It becomes 2d · F. (However, F is the intensity of the light spot determined by the distance to the subject and its reflectance.) On the other hand, the distance x between the light receiving optical axis and the light spot is on the light receiving optical axis from the lens 4d to the PSD light receiving surface. If the distance is f, it can be expressed as f · b / L, Becomes

Therefore, the distance L to the subject is equal to the amplified current I1 =
If k · i1, i2 = k · i2 Becomes

In the distance measuring circuit 1, when the distance L to the subject is a long distance, the intensity of the PSD light spot becomes very weak, and therefore i1 and i2 are minute currents.

Also, when the distance L to the subject is very close, x≈d / 2
And i2 = (d−2x) / 2d · F is a minute current.

The one-shot multivibrator 10 (hereinafter referred to as OST) is a pulse that is in inverse proportion to the currents I1 and I2 sent from the changeover switches 7a and 7b in time division in synchronization with the trigger signal sent from the output terminal 16 of the CPU. It is configured to output width. The clock oscillator 11 outputs a predetermined clock pulse and is connected to one input terminal of the AND gate 18. The output terminal of the OST is connected to the other input terminal of the AND gate 18, and the binary counter 1
At 2, the one-shot output pulse width is counted by the clock pulse. The output terminal of the OST is also connected to the input terminal of the CPU via the binary counter 12. The overflow detection means 13 is connected to a binary counter, and outputs an overflow detection signal to the CPU when the maximum value that can be counted by the binary counter 12 is exceeded. A signal that clears the OST and the binary counter is output from the output terminal 19 of the CPU. 14 is a lens drive circuit that receives an instruction from the CPU,
Stop the lens in place.

Next, the operation of the thus constructed apparatus will be described based on the embodiment shown in FIG. 1 and the flow chart shown in FIG. When, for example, the release button is pressed to measure the distance to the subject, the light emitting element 3 emits light, then the switch 7a is turned on, and the current signal I1 is input to the OST. When the trigger signal is output from the CPU output terminal 16 to the OST, the output terminal 17 of the OST outputs the capacitor 9, the current I1, and the OST threshold voltage V
The pulse width T1 of the time width determined by th is output. With this pulse width T1, the clock pulse CK1 output from 11 by opening the gate 18 is input to the binary counter 12, and the number of clock pulses matching the pulse width is counted by the binary counter 12. This pulse width T1 is Is represented by

At this time, when the subject is at a long distance, I1 becomes very small. Therefore, when T1 becomes long, the binary counter 12 exceeds the maximum value that can be counted, and when an overflow signal is sent from the overflow detection means 13 to the CPU, OST and 2 The advance counter is cleared by the signal output from the CPU output terminal 19, stops the measurement, and sets the condition of the farthest set distance.

When the overflow detection signal is not output and the output of the pulse width T1 is completed, the CPU reads the count value of the binary counter 12, turns off the changeover switch 7a, turns on 7b,
I2 is input to ST, and then a trigger pulse is output. This makes OST a time width inversely proportional to the current I2. The pulse width T2 of is output.

At this time, when the subject is in the vicinity, I2 becomes a minute current for the above reason, and therefore T2 becomes long, and when the overflow detection signal is output, the measurement is stopped and the set distance is set to the close distance.

When the overflow output signal is not detected and the output of the pulse width T2 is finished, the CPU reads the count value corresponding to T2.

The relationship between these pulse numbers P1 and P2 and the distance L to the subject is given by the following equation.

Needless to say, this relational expression does not include the factors of variations in C, Vth and intensities of light spots.

The CPU calculates (P2-P1) / (P1 + P2) and R
The (P2-P1) / (P1 + P2) corresponding to the distance to the subject is stored in the OM (READ ONLY MEMORY), and the set distance is determined by selecting the stored value from the calculated value.

Table 1 is an example in which (P2-P1) / (P1 + P2) is stored in the ROM of the CPU, and this step amount can be set arbitrarily.

Then, a signal corresponding to the set distance is input to the lens drive circuit 14, and the lens drive circuit drives a lens (not shown) to a predetermined position.

In this embodiment, the one-shot multivibrator is used, but it is not particularly limited to this.
For example, a pulse may be converted using a comparator.
Also, the optical sensor has been described using PSD as an example,
You may use SPD (silicon photodiode) of 2 divisions. Further, it goes without saying that the distance measuring apparatus is not limited to the camera of the above-described embodiment and can be applied to other devices.

[Effect] As is clear from the above description, according to the distance measuring apparatus of the present invention, the A / D conversion counter overflows for a subject that is extremely close to the object, so that the object is determined to be a long distance. On the contrary, it is possible to provide an excellent distance measuring device without erroneous distance measurement such that a far object is judged to be a short distance. Further, by mounting this distance measuring device on a camera, it is extremely effective in improving the accuracy for long distances and expanding the photographing range for short distances.

[Brief description of drawings]

1 is a circuit block diagram showing the distance measuring device of the present invention, FIG. 2 is a time chart for explaining the operation of the distance measuring device of FIG. 1, and FIG. 3 is a flowchart of the distance measuring device of the present invention. FIG. 4 is a diagram for explaining the principle of distance measurement. Explanation of main numbers 1 …… Distance measuring circuit 2 …… Optical sensor (PSD) 3 …… Light emitting element 4a, 4b …… Lens 5a, 5b …… Amplifier 7a, 7b …… Changeover switch 15 …… CPU

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Michio Taniwaki, 934-13 Shikato, Yotsukaido, Chiba, Ltd. Inside the Chiba Works, Seikosha Co., Ltd. (56) References

Claims (1)

[Claims] 1. A light-emitting element for projecting light toward an object, receiving a reflected light by an optical sensor having two outputs, and performing A / D conversion on a time corresponding to each output of the optical sensor. A distance measuring device having a counter, storing means for storing a count value corresponding to two outputs of an optical sensor counted by the counter, and calculating means for calculating the count value stored in the storage means, When the overflow detection signal of the counter is output by the first output of the output of the optical sensor, the arithmetic means determines the farthest distance, and outputs the optical sensor output. When the overflow output signal of the counter is output by the second output of the counter, the calculating means determines the short distance. That the distance measuring apparatus.