JP2912682B2 - Object speed detector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, for example, an apparatus for detecting a moving speed of a subject, and more particularly, to automatic focus photographing of a camera that drives a photographing lens to a focus position based on a focus detection output. The present invention relates to a moving speed detecting apparatus for a subject which detects a moving speed of a subject in order to prevent a focus shift accompanying a moving of the subject in a direction of an optical axis of the photographing lens.

[Prior Art] Conventionally, when an image of a subject moving in the direction of the optical axis of a photographing lens is to be photographed, there is a disadvantage that the subject is shifted during the release time lag, resulting in defocus.

In order to prevent this defocus, for example, Japanese Patent Application Laid-Open No. 63-159817 discloses a photographic lens in which a distance measurement operation is performed a plurality of times in response to a first release signal, and a position of a subject at the start of exposure is predicted. Is disclosed. In fields other than cameras, for example,
As disclosed in Japanese Patent Application Laid-Open No. 62-232571, a method has been proposed in which infrared rays are projected onto an object to be measured and a moving speed of the object to be measured is detected based on a reflected signal.

Here, a conventional speed detecting device will be described with reference to the above-mentioned Japanese Patent Application Laid-Open No. 63-159817.

In FIG. 5, reference numeral 1 denotes a subject, and reference numerals 2 to 4 denote a distance measuring optical system, a light emitting element drive circuit, and a distance calculation circuit, respectively, which constitute a distance measuring device.

That is, when the infrared light emitting diode (IRED) 2a included in the distance measuring optical system 2 is driven by the light emitting element driving circuit 3, light from the IRED 2a is projected on the subject 1 via the light projecting lens 2b. You. The light projected on the subject 1 is reflected there, then condensed by a light receiving lens 2c, and is imaged on a light position detecting element (PSD) 2d. Then, the signal currents I ₁ and I according to the incident position of the reflected signal light are output from the PSD 2d.
₂ is output. The distance to the subject 1 is obtained by processing the signal currents I ₁ and I ₂ by the distance calculation circuit 4.

In the speed detecting device, the distance measuring operation as described above is repeated at predetermined time intervals according to the timing circuit 5. Then, after each distance measurement result is stored in the distance data storage circuit 6, the movement speed is detected by calculating how much the position of the subject 1 has been displaced within a predetermined time.

In addition, this speed detecting device includes a dedicated function determining circuit 7 including an order determining circuit 7a, a linear function determining circuit 7b, and a quadratic function determining circuit 7c in order to determine a speed change. It includes a distance prediction calculation circuit 8 for predicting the subject distance at the time (at the start of exposure), and a control circuit 9 for controlling them.

[Problems to be Solved by the Invention] The above-described conventional speed detection device is effective when the distance measurement time is so small that it can be ignored and there is no error in the distance measurement result.

However, in practice, these must be considered, and there are the following disadvantages. That is, a complicated circuit is required to strictly obtain the order of the function of the movement speed of the subject 1 from the distance data, which is expensive.
In addition, when a software operation is performed using a one-chip microcomputer (for example, a CPU) or the like, the operation time cannot be ignored and the speed of an object moving at a high speed such as an automobile is detected. It becomes impossible.

For these reasons, what is required in the speed detection device is a distance measurement device that has a very small distance measurement error and that can perform a distance measurement operation at a high speed. However, noise always exists in electronic circuits, and it is not easy to create an ideal distance measuring device.

On the other hand, the applicant of the present application has already proposed (for example, see Japanese Patent Application Laid-Open No. 63-132110) realizing high-precision autofocus by a noise canceling effect by integration. However, the distance measurement method that emits IRED repeatedly as in this proposal still has a long time lag, and is not suitable for a speed detection device.

Therefore, it was expected that it would be very difficult to measure the distance with high accuracy and with a short time lag, and to detect the speed of the subject in the same way as in the related art.

According to the present invention, since the distance measuring apparatus always has a distance measuring error and a time lag, and it takes time to read and calculate a distance measuring result, the moving speed of a subject is detected with high accuracy and at high speed. It is possible to detect a moving speed of a subject with high accuracy and high speed, and to provide a moving speed detecting device for a subject which can be realized with a relatively simple configuration. It is intended to be.

[Means for Solving the Problems] In order to achieve the above object, in the subject moving speed detecting device of the present invention, a light projecting means for projecting light to the subject and a light projecting means for projecting light from the projecting means are provided. A distance measuring unit that receives reflected light from the subject and outputs a value that depends on the subject distance; a light projecting control unit that repeats the light projecting of the light projecting unit a plurality of times at predetermined time intervals; An integrating means for integrating the output of the distance measuring means every time the light emitting means emits light, and an optical axis direction of the light emitting means based on a result of integration by the integrating means and an output of the distance measuring means. And speed calculation means for calculating the moving speed of the subject with respect to.

[Operation] According to the present invention, the moving speed of a subject can be obtained from the integration result and the distance measurement result of a plurality of distance measurement operations by the above-described means. The processing can be performed by

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a schematic configuration of a subject moving speed detecting apparatus according to the present invention.

That is, the CPU 11 controls the entire device, and the CPU 11 includes a driver 13 and a distance calculation circuit (AF).
Circuit) 14 and an integrating circuit 15 are connected.

The driver 13 drives an infrared light emitting diode (IRED) 12a included in the distance measuring optical system 12, and causes the IRED 12a to emit light a plurality of times at the same time interval under the control of the CPU 11.

The distance measuring optical system 12 condenses the IRED 12a, the light projecting lens 12b that projects light (infrared light signal) from the IRED 12a toward the subject 10, and the reflected light from the subject 10. It comprises a light receiving lens 12c and a light position detecting element (PSD) 12d that generates signal currents I ₁ and I ₂ according to the incident position of the reflected signal light condensed by the light receiving lens 12c.

The distance calculation circuit 14 calculates the distance 1 to the subject 10 by calculating the output signal of the PSD 12d based on the projection of the light from the IRED 12a in an analog manner.

The integration circuit 15 integrates the distance measurement results in the distance calculation circuit 14 sequentially.

The CPU 11 controls the drive timing of the driver 13 and the distance calculation circuit 14, and, based on the distance measurement result (ln) in the distance calculation circuit 14 and the integration result (V _OUT ) in the integration circuit 15 with respect to the optical axis direction of the subject 10. The moving speed is calculated.

FIG. 2 shows an example of the integration result in the integration circuit 15.

Here, the vertical axis indicates the subject distance (l), the horizontal axis indicates time (t), and the straight line (l (t)) indicates that the subject 10 moves at a constant speed.

In the second diagram (a), time 0, t, 2t, 3t, represent each distance measurement result of 4t as _{l 1, l 2, l 3} , l 4, l 5 , respectively, there is no error in the measurement result The case is shown as an example.

The integration result in this case is the total area of the hatched portions shown, that is, the sum (S ₁ + S ₀ ) of the upper right hatched portion S ₁ and the lower right hatched portion S ₀ .

Usually, the speed v can be obtained as follows: v = Δl / Δt (1) Therefore, the speed v of the subject 10 moving at a constant speed in the time width 4t can be calculated by the following relationship: v∝S ₁ / 4t (2).

At this time, the value of S ₁ is the integration result (S ₁ + S ₀₎ and although the value of S ₀ can not be determined to be determined, the value of S _{0 is, S 0 = l 5 × 4t} ... (3) It can be obtained by the relationship.

Thus, the moving speed v of the subject 10 is calculated as
It can be obtained according to the last distance measurement result and the time width of the distance measurement.

FIG. 2 (b) shows an example in which the distance measurement results l' ₁ , l' ₂ , l' ₃ , l' ₄ , l' ₅ at time 0, t, 2t, 3t, 4t vary. Is shown.

As described above, when the variation is considered to occur randomly, the integration result S ′ _{1 is obtained} by the integration effect.
+ S ' ₀ is almost equal to S ₁ + S _{0 in} FIG. 4 (a). Therefore, even in the case where there is variation in the distance measurement results for each time, according to the relationship of the above equation (2), extremely high-accuracy speed detection is possible.

Here, the case where the number of times of distance measurement (l ₅ ) is 5 has been described as an example, but the present invention is not limited to this, and it goes without saying that the effect increases as the number of times increases.

Further, in order to predict the location l _A of the object 10 based on the speed obtained v and the last measurement result l _B after a predetermined time t _A is determined by the calculation of _{l A = l B + v ·} t A Since various methods are already known, the description here is omitted.

FIG. 3 shows details of the configuration of the optical system 12 for distance measurement.

The distance measuring optical system 12 constitutes a known one-point distance measuring device, and is a so-called active method of projecting AF light onto the subject 10.

Now, when the IRED 12a emits light, the light becomes AF light and is projected on the subject 10 via the light projecting lens 12d. Then, the AF light is reflected by the subject 10, and is condensed via the light receiving lens 12c to be formed as an image on the PSD 12d.

In this case, the incident position x of the reflected light is expressed as a function of the subject distance l as shown by the following equation according to the principle of triangulation.

Here, S is the distance between the principal points (base line length) between the light projecting lens 12b and the light receiving lens 12c, f is the distance from the light receiving lens 12c, and the PSD 12d is arranged at this position. .

The PSD 12d outputs two current signals I ₁ and I _{2 that} are functions of the incident position x. The total signal photocurrent and Ip _0, PSD12d
Assuming that the length of tp is tp, l can be expressed as in the following equation.

Here, a is the emission center of the IRED 12a and the projection lens 12b.
When a line parallel to the line connecting the principal points is extended from the principal point of the light receiving lens 12c, the point that crosses the PSD 12d from the PSD 12d
Is the length up to the end on the IRED12a side.

FIG. 4 shows the integration circuit 15 based on the output signals I ₁ and I ₂ of the PSD 12d.
2 shows a specific circuit configuration for integrating distance information.

In FIG. 4, reference numerals 21 and 22 denote output amplifiers I ₁ and I ₂ of the PSD 12 d generated in response to the light emission of the IRED 12 a with low input impedance and amplify them.
Is a compression diode for compressing only the amplified currents I ₁ and I ₂ .

Reference numerals 25 and 26 denote buffers for guiding the compression voltage of the compression diodes 23 and 24 to a differential operation circuit 30 including NPN transistors 27 and 28 and a current source 29.

Here, the operation of the differential operation circuit 27 will be described using symbols in the drawing. Holds. Is is the transistor 27,2
8 and a reverse saturation current of the diode 23, 24, V _T is the thermal voltage.

Further, the current Ia and the current Ib are calculated from the above equations (8), (9), and (10) from the relationship of Ia + Ib = I ₀₁ (10). The relationship holds.

Therefore, from the above equations (7) and (11), And a signal current Ia proportional to the reciprocal of the subject distance 1 is obtained.

Further, 31 in the figure is a current source, and a current Ic flowing by the current source 31 is: Has the relationship Therefore, the current Ix flowing through the compression diode 32 is Becomes

On the other hand, a current Id is supplied to the compression diode 33 by the current source 34, and the compression voltage of the compression diodes 32, 33 is supplied to the respective buffers 35, 36 via the buffers 35, 36, respectively. Entered into 38 respectively.

Therefore, this NPN transistor 39,40 and current source
Note that the output current Il of the differential operation circuit 37 composed of 41 now has a voltage generated by the compression diodes 32 and 33 on the power supply side reference. Becomes Therefore, from the above equation (14), the current Il is Which is obtained as a current signal proportional to the subject distance l.

That is, the differential operation circuit 37 is a circuit for supplying a current signal corresponding to the subject distance l to the integration circuit 15,
Each time 12a is emitted, the current source 4
When 1 is turned on, the current Il depending on the subject distance l is integrated by the integrating capacitor 45 of the integrating circuit 15.

The integration capacitor 45 is reset by a reset circuit 46 prior to the emission of the IRED 12a.
For this reason, after a series of distance measurement operations, the output terminal
47 shows a signal corresponding to the integrated output indicated by S ₁ + S ₀ in FIG. 2A, or S ′ ₁ + S ′ _{0 in} FIG. 2B.
A signal corresponding to the integration output indicated by.

On the other hand, the differential operation circuit 38 including the NPN transistors 42 and 43 and the current source 44 is a circuit for obtaining the last distance measurement result, that is, the distance measurement result ₁₅ in FIG. of the the current source 44 is turned on at the timing, the current Il ₂ flowing through the resistor 48.

This current Il ₂ is, as in the above equation (16), Satisfying the relationship depending on the subject distance l. Accordingly, the voltage signal output to the output terminal 49, it is possible to detect only the last measurement result l _5.

The voltage signals appearing at the output terminals 47 and 49 are captured by an A / D converter (not shown) built in the CPU 11 shown in FIG.
Is determined.

 That is, from the above equation (16), the current Il is Il = A · l (18) where A is a constant.

The position of the subject 10 l (t), from FIG. _{2, l (t) = l 5} -v (t-t 5) ... (19) ∴Il = A {l 5 -v (t-t 5 )｝ (20) Assuming that the integration time required to integrate this is T, the output voltage V _OUT appearing at the output terminal 47 is Here, B is a constant, and C is the capacity of the integrating capacitor 45.

Thus, the voltage V _OUT at the output terminal 47, i.e. the integrated output obtained by integrating the distance measurement result, information obtained from the output terminal 49, i.e. the last measurement result l _5, the moving velocity v of the object 10 It is possible to calculate (predict) the position of the subject 10 after a predetermined time as well as to obtain the position.

As described above, the moving speed of the subject is obtained using the integration results and the distance measurement results of the plurality of distance measurement operations.

That is, the light emission of IRED and the integration of the distance measurement result based on this light emission are repeated a plurality of times, and the moving speed of the subject is obtained from the integration result obtained by this and the final distance measurement result. In this case, a series of operations such as distance measurement and integration are analog operations that are completed instantaneously, and operations such as A / D conversion and speed detection calculations that require relatively long time are collectively performed after the above-described series of operations. And do it. As a result, it is possible to cancel a distance measurement error that always exists in one distance measurement operation, and to perform high-speed processing. Therefore, high-accuracy and high-speed speed detection can be realized with a simple configuration.

The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the invention.

[Effects of the Invention] As described in detail above, according to the present invention, a ranging error that always exists in one ranging operation can be cancelled, and processing can be performed at high speed. In addition, it is possible to provide a moving speed detecting device for a subject which can detect the moving speed of the subject at high speed and can be realized with a relatively simple configuration.

[Brief description of the drawings]

1 to 4 show an embodiment of the present invention. FIG. 1 is a block diagram schematically showing a configuration of a moving speed detecting device for a subject, and FIG. 2 is an example of an integration result in an integration circuit. FIG. 3 is a configuration diagram showing details of a distance measuring optical system, FIG. 4 is a diagram showing a specific circuit configuration example for integrating distance information, and FIG. It is a block diagram of a speed detection device shown for explaining the problem. 10… Subject, 11… CPU, 12… Distance measuring optical system, 12a…
... IRED, 12d ... PSD, 13 ... Driver, 14 ... Distance calculation circuit, 15 ... Integration circuit, 23,24,32,33 ... Compression diode, 29,31,34,41,44 ... Current Source, 30, 37, 38 ... differential operation circuit, 45 ... integration capacitor, 46 ... reset circuit,
48. Resistance.

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁶ , DB name) G01C 3/00-3/32 G01B 11/00-11/30 G01P 3/36 G02B 7/28-7 / 38 G03B 13/36

Claims (1)

(57) [Claims] 1. A light projecting means for projecting light onto a subject, a distance measuring means for receiving light reflected from the subject by the light projecting means, and outputting a value dependent on the subject distance, Light projection control means for repeating the light projection of the light means a plurality of times at predetermined time intervals, integration means for integrating the output of the distance measuring means each time the light projection means performs light projection, A speed calculating means for calculating a moving speed of the subject in the optical axis direction of the light projecting means from a result of integration by the means and an output of the distance measuring means.