JP3208502B2 - Distance measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring device.

[0002]

2. Description of the Related Art Conventionally, a distance measuring device as disclosed in Japanese Patent Application Laid-Open No. 1-260309 uses a double integral type A / D converter having a capacitor to obtain distance information as a digital signal. are doing. If a high dielectric constant capacitor such as an inexpensive ceramic capacitor is used for the double integration type A / D converter, dielectric polarization occurs when an initial voltage is applied, and the capacitance changes. Film capacitors have been generally used because of the inconvenience of causing errors in the distance measurement data.

[0003]

However, since the film capacitor is expensive, there has been a problem that the cost is high as a distance measuring device.

An object of the present invention is to provide a distance measuring device which is inexpensive and has excellent distance measuring accuracy.

[0005]

According to the present invention, there is provided a light projecting means for irradiating a subject with light, a light receiving means for receiving reflected light from the subject, and an output of the light receiving means according to a distance to the subject. A double integration type analog-to-digital conversion circuit for converting an output of the output generating means into a digital signal, and a voltage applying means for providing a high dielectric constant capacitor to the high dielectric constant capacitor. Control means for operating the light emitting means after a desired time has elapsed after applying a desired voltage,
The above objectives have been achieved.

Further, the above-mentioned object is achieved by setting the desired time to a time until dielectric polarization caused by application of a voltage to the high dielectric constant capacitor is stabilized.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to one embodiment shown in the drawings.

In FIG. 1, reference numeral 1 denotes a light projecting element constituting light projecting means. In this embodiment, infrared light is projected on a subject. Reference numeral 2 denotes a light emitting element driving circuit which drives the light emitting element 1. Reference numeral 3 denotes a light projecting lens which collects infrared light emitted from the light projecting element 1 and irradiates the infrared light to a subject. Reference numeral 4 denotes a light receiving lens which collects the infrared light reflected by the subject. Reference numeral 5 denotes a position detecting element constituting a light receiving means. In this example, a PSD (Position Sensitive) is used.
Device), a pair of output terminals that take out a photocurrent generated in accordance with the amount of infrared light projected on the light receiving surface and distribute the photocurrent in a ratio corresponding to the projection position of the infrared light. Have. Reference numerals 6 and 7 denote a stationary photocurrent extracting circuit which bypasses a stationary photocurrent generated by projecting the stationary light onto the position detecting element. Reference numerals 8 and 9 denote head amplifiers for amplifying and outputting an input signal. 10 and 11 are logarithmic compression circuits. Numeral 12 denotes an arithmetic circuit which constitutes an output generating means, which comprises a differential amplifier or the like, and has a logarithmic compression circuit 10 and a logarithmic compression circuit 11
And outputs an analog signal corresponding to the ratio of the input signals. Reference numeral 13 denotes a double integration type analog-to-digital conversion circuit, which has a high dielectric constant capacitor 14. The high dielectric constant capacitor 14 includes, for example, a ceramic capacitor and a barium titanate capacitor. In this example, a ceramic capacitor is used. Reference numeral 15 denotes a voltage application circuit that constitutes voltage application means, and applies a voltage (a reference voltage of 0.3 V in this example) to the high dielectric constant capacitor 14. Reference numeral 16 denotes a control circuit which constitutes control means and comprises a CPU, a ROM, a RAM, and the like, and controls the entire apparatus. 17 is a timer, 18
Is a counter.

Next, the operation will be specifically described with reference to FIG. Now, the light emitting element driving circuit 2, the steady light current extracting circuits 6, 7, the head amplifier units 8, 9, the arithmetic circuit 1
It is assumed that power is not supplied to the double-double integration type analog-to-digital conversion circuit 13 and the voltage application circuit 15 and the timer 17 and the counter 18 are cleared.

In this embodiment, the infrared light is projected 32 times from the light projecting element 1 during one distance measuring operation, and the distance to the subject is measured based on the result of the 32 times distance measuring. I do.

When a distance measurement start signal is input to the terminal A (step 2a), the control circuit 16 determines whether power is supplied to the double integration type analog-to-digital conversion circuit 13 (step 2b).

A double integration type analog / digital conversion circuit 13
When the power is not supplied to the control circuit 16, the control circuit 16 performs the double integration type analog / digital conversion circuit 13 and the voltage application circuit 1.
5, the voltage application circuit 15 applies a reference voltage (0.3 V in this example) to the high dielectric constant capacitor 14 to charge it (step 2c). FIG. 3 shows a change in the voltage of the high dielectric constant capacitor 14 at this time.

Subsequently, the control circuit 16 operates the timer 17 (step 2d).

The count value of the timer 17 is stored in the control circuit 16
If the count value matches the count value stored in the ROM (time required for stabilization of dielectric polarization caused by application of a voltage to the high dielectric constant capacitor 14, for example, 400 ms or more) (step 2e), the control circuit 16 The timer 17 is cleared (step 2f), and power is supplied to the light emitting element driving circuit 2, the steady-state photocurrent extraction circuits 6, 7, the head amplifiers 8, 9, and the arithmetic circuit 12 (step 2f).
g) Infrared light is projected from the light projecting element 1 toward the subject to start distance measurement (step 2h).

The control circuit 16 adds 1 to the count value of the counter 18 every time the light emitting element 1 outputs infrared light (step 2i). That is, the counter 18 is a light emitting element 1
The number of times of light emission is counted.

In this embodiment, since infrared light is emitted from the light emitting element 1 32 times during one distance measuring operation, the control circuit 16 determines whether or not the count value of the counter 18 is 32 (step). 2j) If not 32, the operation after step 2h is performed.

When the counter value of the counter 18 becomes 32 during the operation of the step 2j, the control circuit 16 stops the emission of the infrared light from the light emitting element 1 and clears the counter 18 (step 2k). Return to operation.

When the PSD receives the infrared light reflected by the subject through the light receiving lens, the PSD outputs a photocurrent generated in accordance with the amount of the infrared light projected on the light receiving surface to the infrared light. , And are extracted at a ratio corresponding to the projection position of the image data and output as analog signals from a pair of output terminals B and C. Since the photocurrent includes the current output by the stationary light, the current output by the stationary light is excluded by the stationary photocurrent extraction circuits 6 and 7, respectively. Therefore, the current supplied to the terminals D and E is a photocurrent generated by the reflected light of the infrared light projected on the subject by the light projecting element 1. These two photocurrents are respectively supplied to the head amplifier unit 8,
9 are respectively amplified by logarithmic compression circuits 10 and 1
1 and logarithmically compressed and input to the arithmetic circuit 12.

The arithmetic circuit 12 receives the two analog signals input from the logarithmic compression circuits 10 and 11, and outputs an analog ranging signal corresponding to the ratio of the two input signals.

Double integration type analog-to-digital conversion circuit 13
Performs a first integration operation of discharging the charge of the high dielectric constant capacitor 14 according to the analog signal input from the arithmetic circuit 12 (see FIG. 3).

As described above, since the reference voltage is applied to the high-permittivity capacitor 14 and the first integration operation is performed after a lapse of time until the dielectric polarization stabilizes, the first integration operation is performed. Without being affected, the discharging operation of the high dielectric constant capacitor 14 can be performed accurately corresponding to the input analog signal.

When the above operation is performed 32 times, the double integration type analog-to-digital conversion circuit 13 performs the second integration, converts the analog ranging signal into a digital signal, and outputs the digital signal to the control circuit 16 ( (See FIG. 3).

When the distance measurement start signal is input to the terminal A again when the operation returns to the step 2a, the control circuit 16 performs the same operation as described above. Now, since power is supplied to the double integration type analog-to-digital conversion circuit 13, the control circuit 16 operates the voltage application circuit 15 to apply the reference voltage (0.3 V) to the high dielectric constant capacitor 14 ( Step 2m).

Hereinafter, the same operation as described above is performed.

When the distance measurement start signal is not input to the terminal A again when the operation returns to the step 2a, the control circuit 16 determines whether power is supplied to the double integration type analog-to-digital conversion circuit 13 (step 2a). 2n), if supplied, the light emitting element drive circuit 2, the steady photocurrent extraction circuit 6,
7, stopping the supply of power to the head amplifier units 8, 9, the arithmetic circuit 12, the double integration type analog-to-digital conversion circuit 13, and the voltage application circuit 15 (Step 2p), and Step 2a
Return to the operation of.

If power is not supplied to the double integral type analog-to-digital conversion circuit 13 during the step 2n operation,
The operation returns to step 2a.

In this embodiment, the infrared light is projected 32 times as one distance measurement, but the number of times the infrared light is projected is not limited to the above.

The reference voltage of the double integration type analog-to-digital conversion circuit 13 is not limited to 0.3 V, but can be changed as appropriate.

Further, it is desirable to use the distance measuring apparatus of the present invention in an automatic focusing mechanism of a camera.

[0030]

According to the present invention, there is provided a light projecting means for irradiating a subject with light, a light receiving means for receiving reflected light from the subject,
An output generating means for generating an analog signal according to the distance to the subject by an output of the light receiving means, and a double integral type analog-to-digital converter for converting an output of the output generating means into a digital signal, comprising a high dielectric constant capacitor Circuit and
A control means for operating the light projecting means after a desired time has elapsed since the application of a desired voltage to the high dielectric constant capacitor by the voltage applying means is provided. Since the use of the high-permittivity capacitor enables an inexpensive circuit configuration and is economical, the desired time should be the time until the dielectric polarization caused by applying a voltage to the high-permittivity capacitor stabilizes. Accordingly, it is possible to provide a distance measuring device having excellent distance measuring accuracy without being affected by a change in capacitance at the beginning of voltage application.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing an embodiment of the present invention.

FIG. 2 is a flowchart for explaining the operation of FIG. 1;

FIG. 3 is a voltage waveform diagram at the time of distance measurement of the high dielectric constant capacitor used in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Projecting means 5 Light receiving means 12 Output generating means 13 Double integration type analog-to-digital conversion circuit 14 High dielectric constant capacitor 16 Control means

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-199108 (JP, A) JP-A-2-67912 (JP, A) JP-A-4-363618 (JP, A) JP-A-4-199 363619 (JP, A) JP-A-5-172566 (JP, A) JP-A-5-273457 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01C 3/06 G02B 7 / 32

Claims (2)

(57) [Claims] 1. An active distance measuring device for irradiating a subject with light, receiving reflected light diffused by the subject and detecting a distance, a light projecting means for irradiating the subject with light, A light receiving means for receiving reflected light from the light source; an output generating means for generating an analog signal according to a distance to the subject by an output of the light receiving means; and a high dielectric constant capacitor, wherein the output of the output generating means is digital. A double integration type analog-to-digital conversion circuit for converting the signal into a signal; and control means for operating the light emitting means after a desired time has elapsed after applying a desired voltage to the high dielectric constant capacitor by voltage applying means. A distance measuring device characterized by the above-mentioned. 2. The distance measuring apparatus according to claim 1, wherein the desired time is a time until a dielectric polarization caused by applying a voltage to the high dielectric constant capacitor is stabilized.