JPS6082913A - Active type range finder - Google Patents

Abstract

PURPOSE:To measure easily a distance, and also to make a device small-sized by discriminating whether a signal light quantity which is made incident to only the first photodetecting means is above a prescribed threshold level or not, and the polarity in difference of a signal light quantity of the second photodetecting means. CONSTITUTION:A center position of a photodetecting lens 4, a point where the center of a projected luminous flux forms an image on an object whose distance is measured S, the center position of a photodetecting lens 5, a point where a straight line which passes through a position (c) and is parallel to a straight line (a) (b) crosses a plane containing a photodetecting surface of photodetectors 1, 2, and a point where a part of reflected light from the object whose distance is measured S passes through the center position (c) and forms an image on the photodetecting surface of the photodetectors 1, 2 are denoted as (a), (b), (c), (d) and (e), respectively. In this case, a triangle (a), (b) and (c) and a triangle (d), (c) and (e) become similar, therefore, if the length of a segment (a) (c) and (c) (d) is known, the length of the straight line (a) (b), namely, a distance to the object whose distance is measured S can be known by a position of (e).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an active distance measuring device used in, for example, a camera, which projects a luminous flux onto an object and measures the distance to the object using the reflected light.

In conventional so-called active distance measuring devices, a method of projecting a beam of light onto an object to be measured and measuring the distance by determining the absolute amount of reflected light is disclosed in Japanese Patent Application Laid-open No. 56-121019 and Japanese Patent Application Laid-open No. 56-1989.
It has been proposed in Publication No. 130608 and the like. According to this method, since the reflected light amount value basically depends on the reflectance of the object to be measured, even if measures are taken to reduce this dependence on the reflectance using the baseline effect, etc., for a predetermined distance of 1 set the point,
Rather than that, it is possible to realize an extremely simple type of distance measuring device that can measure either the near side or the far side. However, this method requires multiple thresholds for determining the absolute amount of reflected light to obtain distance resolution capability for more points. Because of the reflectance dependence of each switching setting point, it is not possible to take sufficient measures to reduce reflectance dependence such as This is the result.

By the way, using multiple light receiving elements with different viewing fields,
There are methods for measuring the distance by determining the ratio of the signals obtained, and for determining the extent to which the emitted and received images overlap by making mechanical or electrical movements on the emitter or receiver side that correspond to the distance. Various distance measurement methods have also been proposed. However, these methods require large-scale circuits and occupy space, making it difficult to perform distance measurement using relatively simple decomposition of a small number of zones when the focal length of the photographing lens is short or the F-number is large. However, in a satisfactory optical system, even if the distance measurement accuracy is better than the above-mentioned method of determining an absolute quantity, there are disadvantages in that it is significantly more expensive and larger.

In view of the above-mentioned drawbacks, an object of the present invention is to provide an active distance measuring device that is relatively simple and satisfies distance measuring capability such as discriminating between three distance zones, and that can be obtained on a small scale and at low cost as a whole. Our goal is to provide the following.

The gist of the present invention for achieving the above first objective is to arrange a light projecting section and a light receiving section apart from each other by a predetermined baseline length, and to project light from the light projecting section onto an object to be measured. In the distance measuring device in which the light receiving section detects reflected light as signal light, the light receiving section has first and second light receiving means in the baseline direction, and the first and second light receiving means are arranged in the base direction.
It is determined whether the amount of signal light incident only on the first light receiving means is equal to or higher than a certain threshold value, and the polarity of the difference in the amount of signal light between the first light receiving means and the second light receiving means is determined. This is an active distance measuring device characterized by obtaining distance information to an object to be measured.

In the present invention, the first and second light-receiving means are light-receiving elements such as wrinkle-contoured photodiodes, and each outputs an output signal corresponding to the amount of incident signal light. Now, the amount of signal light incident on the first light receiving means is due to the reflected light flux that moves on the base line depending on the position of the object to be ranged, but by measuring the amount of light, the position of the object to be ranged can be measured. It will be possible. Here, if a threshold value corresponding to the distance switching point is provided, by detecting whether the amount of incident signal light is greater than this value, based on this distance, it is possible to determine whether the object to be measured is at the far point or nearby. It is possible to know whether the object is located at a point, that is, the distance zone in which the object to be measured exists. Note that the correspondence between this threshold value and the position of the distance-measuring object will change slightly depending on the reflectance of the distance-measuring object, but this can be kept within an allowable range.

Next, when this reflected light beam is projected onto the first light receiving means and the second light receiving means arranged above the baseline, the amount of signal light becomes equal to the first and second light receiving means. The position of the object to be measured is one point.

Extremely accurate, independent of reflectance.

Therefore, by determining the polarity of the difference in the amount of signal light received by the first and second light receiving means, it is possible to know whether the position of the object to be measured is farther or closer than this one point.

Now, assuming that the light receiving means consists of only two, the first and second light receiving means, the amount of signal light received by the first light receiving means is equal to the signal received by the first distance switching point and the first and second light receiving means. Since the second distance switching point is determined by the polarity of the difference in light amount, it is possible to determine three distance zones: the near point, the midpoint, and the far point.

The present invention will be explained in detail below based on illustrated embodiments.

"Figures 1 and 2 are principle explanatory diagrams, Figure 3 is a block circuit configuration diagram, Figure 4 is a timing chart of signals output from the circuit in Figure 3, and Figure 5 is the circuit in Figure 3. The signal waveform diagram in the figure and FIG. 6 are concrete block circuit configuration diagrams of the synchronous detection circuit included in FIG. 3.

In the 19th (a), 1.2 is a light-receiving element made of a silicon photodiode or the like, and 3 is a light-emitting element arranged at a predetermined interval from the light-receiving element 1.2 and emits near-infrared light. The luminous flux emitted from the light emitting element 3 is projected onto the object S to be measured via the light projecting lens 4, and the reflected light is incident on the light receiving elements J and 2 via the light receiving lens 5. There is.

Here, the center position of the light emitting lens 4 is a, the point where the center of the emitted light beam forms an image on the object S to be measured is b, and the center position of the light receiving lens 5 is C1. A point d is a point where a straight line parallel to the straight line ab intersects with a plane including the light receiving surface of the light receiving element 1.2. If the point of image formation on the light-receiving surface of 2 is e, triangle abc and triangle dce are similar, so if the lengths of line segments aC and cd are known, the length of line ab is determined by the position of e, That is, the distance to the distance-measuring object S can be known.

Next, in FIG. 1(b), the light beam projected by the light emitting element 3 passes through the light projection lens 4 and is reflected on the object S to be measured. The photodetector 1.2
This is a model showing the relationship between the light receiving elements 1 and 2 when images are formed on the top, and the image S' shown by diagonal lines. ■
The state represents when equal amounts of images are generated on the light receiving elements 1 and 2, and in the present invention, by detecting this state, first, the switching distance of one point is determined. According to this method, the light receiving element 1.
Since this is based on the concept of ratio in which one element receives 1/2 of the total amount received by S, errors due to changes in the reflectance of the object to be measured S will not be reduced in principle.

Furthermore, in order to determine another switching distance, the absolute value of the signal amount is detected using only one light receiving element, and distance measurement is performed by determining whether or not it is greater than a predetermined value. However, as mentioned above, in this method, the switching distance tends to depend on the reflectance of the object to be measured S, so in order to obtain an acceptable distance measurement accuracy, the setting of the switching point and the m-section of the optical system are determined using known methods. It is desirable to do this in various ways. Specific examples of these various methods include:
By adjusting the focus of the light emitting element 3 or (and) the light receiving element 1.2 to obtain a clear image in front of the switching point, the amount of reflected light from a distant object to be measured can be adjusted to the square of the distance. A method that not only attenuates inversely proportionally but also attenuates due to the effect of blur, or a method that uses a light emitting element as small as possible compared to the base line length, or Japanese Patent Application Laid-Open No. 57-5911
Examples include devising the setting of the intersection of the light emitting axis and the light receiving axis, as seen in Publication No. 2. By using these methods alone or in combination, it is not necessarily difficult to keep the dependence of one switching distance on the reflectance of the object to be measured within an allowable range.

Figures 2 (a), (b), and (c) show the distance and reflectance of the object to be measured when the three zones of near point, midpoint, and far point are identified in the conventional example and the present invention. FIG. Figure 2 (a) is an extension of the conventional example in which the two boundaries have reflectance dependence, while in (b) there is no reflectance dependence at the boundary between the periapsis and the midpoint, and the midpoint This is a case in which care is taken to minimize the reflectance dependence of the boundary between and the far point. (c) shows a case in which care is taken so that the boundary between the midpoint and the far point has no dependence on reflectance, and the boundary between the near point and the far point has less dependence on reflectance. In other words, by introducing a method that eliminates the reflectance dependence of one boundary line, the degree of latitude in setting the three best in-focus points increases, and the second
This means that it is possible to obtain much better distance measurement resolution than in the case shown in FIG.

Next, in the block circuit of FIG. 3, the drive circuit 10 for the light emitting element 3 can perform modulation drive using a signal B such as a constant voltage or constant current by a known means, so a detailed explanation thereof will be omitted. First, at the start of distance measurement, the switching member 11
transitions from closed to open state, resistor 12 and capacitor 1
3, the signal A that is the output of the inverter 14 becomes the old gh level signal (hereinafter referred to as H
) to a Low level signal (hereinafter referred to as "low level signal"). In addition, S, R of RS flip-flops 15 to 17
The terminal outputs Q and its inverted output Q by H.
The T flip-flops 18 and 19, the D flip-flops 20 and 21, and the frequency divider 22 are each cleared manually by C.
It is assumed that the circuit is reset by changing L to H, outputs Q, sets its inverted output Q to H, and is triggered by the rising edge of the clock input from L to H. While the signal A is H, each of the flip-flops 15 to 21 and the frequency divider 22 is initialized with its Q output set to L and its output set to H.

Meanwhile, each AND gate 23~ except for AND gate 29
The output of 35 is L because at least one input is L.

When the signal A becomes L, each of the flip-flops 15 to 21 and the frequency divider 22 are released from their reset states, and the Q output of the T flip-flop 19 divides the clock of the oscillator 36 by 1/2.
The light emitting element 3 starts blinking by the driving circuit 10 which outputs a signal B whose frequency is divided by 4 and turns on when the signal B is H and turns off when the signal B is L. At the same time, as shown in the timing chart of FIG. 84, signals C and D, which are the outputs of AND gates 27 and 28, send sampling control signals to a synchronous detection circuit 37, which will be described in detail later, to start synchronous detection. At this time, the Q output of the frequency divider 22 is L, and D
The signal E, which is the Q output of the flip-flop 20, is L, and the signal F, which is the Q output of the D flip-flop 20, is also L.
is H, so the analog switch 38 is open and the switch 39 is closed. These analog switches 38.
The gate 39 is set to a closed state 8 (conductive state i) by setting the gate to H using logic signals E and F, and is set to an open state (non-conducting state) by setting the gate to l.

The light receiving element 1 is connected between the non-inverting and inverting inputs of the operational amplifier 40, and closing the analog switch 39 prevents mutual interference such as leakage of photocurrent from the light receiving element 2 to the light receiving element 1 side. This is to form a closed loop in the light receiving element 2 to prevent this. After a predetermined period of time determined by the number of stages of the frequency divider 22 has elapsed, the Q output of the frequency divider 22 becomes H, the Q output becomes L, and further delayed by one cycle of the signal B, the D
The signal E, which is the Q output of the flip-flop 20, becomes H, and the signal F, which is the Q output, becomes L. Therefore, at the timing shown in FIG. 4, the signal G, which is the output of the AND gate 34, becomes H for a predetermined period of time.

On the other hand, the potential of the output of the synchronous detection circuit 37 increases in a positive direction from the reference potential v2 according to the amount of signal received by the light receiving element 1. When no signal is detected by the light-receiving element l, that is, in the state I in FIG. 1(b), theoretically V2 should be output as the output of the synchronous detection circuit 37, but in reality The signal contains the offset of the synchronous detection circuit 37 and noise. Wait until the output of the synchronous detection circuit 37 stabilizes, that is, wait a predetermined time determined by the number of stages of the frequency divider 22, and when the signal G becomes H, the output of the synchronous detection circuit 37 turns off the light receiving element 1. Detect whether there is a signal condition and how much signal there is. Therefore, as shown in FIG.
A comparison is made with v4 which is the potential of V2+β which is higher than v3. If the output of the synchronous detection circuit 37 exceeds v4,
The output of the comparator 42 is H, and when the signal G is H, the signal of the AND gate 23 is H, and the Q output of the RS flip-flop 15 is latched at H. If the output of the synchronous detection circuit 37 exceeds v3, the output of the comparator 41 is H, and when the signal G is H, the output of the AND gate 24 is H, and the Q output of the RS flip-flop 16 is H.
latched to.

Next, when the signal E changes from L to H1 and the signal F changes from H to L, the analog switch 38 is closed, the analog switch 39 is opened, and the light receiving elements 1 and 2 are connected between the positive and negative inputs of the operational amplifier 40. Connected. however,
The anode and cathode directions of the light receiving element 1.2 are opposite to each other. Due to the feedback impedance of the operational amplifier 40, the resistors 43 to 45, and the capacitor 46, the difference in photocurrent flowing through the light receiving element 1.2 is outputted from the operational amplifier 40 as a voltage added to the reference voltage v1. Therefore, in the cases of ■ and H in FIG. 1(a), the output of the synchronous detection circuit 37 is on the negative side of the reference voltage V2, does not change in the case of ■, and is positive in the cases of ■ and ■. output to the side. That is, when the signal amount is greater in the light receiving element 2 than in the light receiving element 1, a negative potential is applied to the reference voltage V2, in the opposite case, a positive potential is applied, and when the signal amount is the same, a zero potential is applied to the reference voltage V2.

Wait a predetermined period of time until the output of the synchronous detection circuit 37 becomes stable, and as shown in the timing chart of FIG.
When becomes H, the output of the synchronous detection circuit 37 and the reference potential v3 are compared by the comparator 41, and if the output exceeds V3, that is, if the signal of the output is larger than that of the light receiving element 2, the output of the comparator 41 becomes H, and gate 25
The output of the RS flip-flop 17 becomes H, the Q output of the RS flip-flop 17 is latched to H, and the Q output is latched to L. When the output of the synchronous detection circuit 37 is lower than the reference voltage v3, that is, when the signal of the light receiving element 1 is greater than or equal to the signal of the second signal, the output of the comparator 41 is L, and the output of the AND gate 25 is L. , the Q output of the RS flip-flop 17 remains at L, and the Q output remains at H.

Next, when the Q output of the D flip-flop 21, that is, the signal J becomes H, the output of the RS flip-flop 15.16 causes the outputs of the AND gates 32, 33 and 26, that is, the signal, to have ranging information in 1 to 3. Output. Also, the Q output of the flip-flop 21 changes to L, the output of the AND gate 31 remains L, the signal J is latched to H, and the output of the OR gate 47 also becomes H, so the flip-flop 18
.about.20 and the frequency divider 22 are reset, the signals B-E, G, and ■ remain at L, and the signal F remains at H. To perform distance measurement, the switching member 11 is closed, and after each circuit is reset, the switching member 11 is opened again, and the above operation is repeated.

FIG. 6 is a block circuit diagram of the synchronous detection circuit 37. As mentioned above, for example, using the signal B shown in FIG. 4, the light is turned on when it is H and turned off when it is L. The element drive circuit 10 modulates and projects near-infrared light from the light emitting element 3 onto the object S to be measured. The reflected light is transmitted to light receiving element 1 or 2.
receives the light and transmits the photocurrent to an operational amplifier 40 and a resistor 43 to
The feedback circuit formed by 45 and capacitor 46 converts it into a voltage signal, but this feedback circuit is given a frequency characteristic, and the current/voltage conversion efficiency is lowered at low frequencies, so that the signal B etc. High efficiency in the frequency domain,
This prevents the influence of external light such as direct light on distance measurement and saturation of the output of the operational amplifier 40.

From the output signal of the operational amplifier 40, the bypass filter 51
The high frequency components including this modulation frequency are passed through, and the low frequency components are attenuated and then amplified by the amplifier 51. From the output signal, the signal C7D shown in FIG. 3 synchronized with the frequency of the signal B is used, that is, when the light emitting element 3 is on, the signal C1 is turned off. Holding. After passing the output of the sample hold circuit 53, that is, the signal when the light emitting element 3 is turned on, through the buffer circuit 54, the inverter circuit 55 converts the signal to the calculation reference potential v.
A summing amplifier 57 adds and amplifies the output inverted with respect to 2 and the output of one of the sample-and-hold circuits 52, that is, the signal of the buffer circuit 56 which is the light-off signal. Thereby, the difference in the input to the light receiving elements 1 and 2 when the light emitting element 3 is turned on and when the light is turned off can be obtained. however,
The summing amplifier 57 is an inverting amplifier, and its output is used as the output of the synchronous detection circuit 37 after attenuating high frequency components by a low-pass filter 58 .

Now, the relationship between the information latched in the RS flip-flops 15 to 17 and the distance measurement zone is, for example, in the state shown in FIG. When the output 2 is H, it is the middle point, and when the output of the AND gate 26 is 3, it is the far point. In other words,
The combination is as follows.

Near point: the signal from the light receiving element l is greater than the predetermined value v4,
and is larger than the signal from the light receiving element 2.

Midpoint: When the signal from the light receiving element 1 is smaller than the predetermined value V4 but larger than the no-signal level v3 and larger than the signal from the light receiving element 2.

Far point: When the signal from light receiving element 2 is greater than the signal from light receiving element 1, or when there is no signal from both light receiving elements.

As shown in the examples in Figures 1 and 3, the light receiving element 1 is viewed from the near side and the light receiving element 2 is viewed from the far side, and the boundary between the near point and the midpoint is defined as the absolute amount of the signal obtained by the light receiving element 1. In this case, the light receiving element 1 is viewed from the far side and the light receiving element 2 is viewed from the near side, and the boundary between the near point and the midpoint is viewed from the light receiving element 1.2. Distance measurement can also be carried out in the state shown in Fig. 2(b), in which the boundary between the midpoint and the far point is determined based on the absolute amount of signal obtained by the light-receiving element 1. It can be easily accomplished.

In addition, in this example, the absolute amount of one light receiving element and the difference between the two light receiving elements were processed in time series, but each light receiving element 1
．． 2 may be provided with a signal processing circuit, respectively, to determine the absolute amount and the difference at the same time, and the scope of the present invention is not limited to this embodiment. Furthermore, it is also easy to change the order of time-series processing to first look at the difference between two light-receiving elements, and then look at the amount of signal incident on a single light-receiving element later.

As explained above, the active distance measuring device according to the present invention not only determines the absolute amount of signals obtained by the light-receiving element, but also adds the concept of the ratio of 1/2 the amount of the signals obtained. At the same time, it is possible to configure a simple distance measuring device on a small scale, and at the same time, the number of post-processing circuits can be reduced to one system due to difference calculation and time-series processing by switching the connection of light receiving elements, and it is possible to reduce the number of processing circuits for multiple systems. This method has the advantage that it is not necessary to consider variations in characteristics of each processing circuit, which are problematic when calculating each output.

[Brief explanation of the drawing]

Figures 1 (a) and (b) are explanatory diagrams of the distance measurement principle used in the present invention, and Figures 2 (a), (b), and (c) are distance measurement characteristics of the embodiment of the present invention and the conventional example. FIG. 3 is a circuit configuration diagram of an embodiment of the active distance measuring device according to the present invention, FIG. 4 is a timing chart of signals output from the circuit shown in FIG. 3, and FIG. is a signal waveform diagram in the circuit diagram of FIG. 3, and FIG. 6 is a block circuit configuration diagram of the synchronous detection circuit in FIG. 3. 1.2 is a light receiving element, 3 is a light emitting element, 4 is a light projecting lens, 5 is a light receiving lens, 10 is a light emitting element drive circuit, 11 is a switching member, 15 to 21 are flip-flops, 22
1 is a frequency divider, 23 to 35 are AND gates, 37 is a synchronous detection circuit, 38 and 39 are analog switches, 40 is an operational amplifier, 41 and 42 are comparators, and 47 is an OR gate. Patent applicant: Canon Co., Ltd. Figure 1: V mouth weight - 5' Figure 2

Claims (1)

[Claims] 1. A light projector and a light receiver are arranged at a predetermined baseline length,
In the distance measuring device in which the light receiving unit detects reflected light of the light projected from the light projecting unit on the object to be measured as signal light, the light receiving unit includes first and second light receiving means in the baseline direction. and determines whether the amount of signal light incident only on the first light receiving means is greater than or equal to a certain threshold, and the polarity of the difference in the amount of signal light between the first light receiving means and the second light receiving means. An active distance measuring device characterized in that distance information to the object to be measured is obtained by determining the distance. 2. The method according to claim 1, wherein the determination of the amount of signal light incident only on the first light receiving means and the polarity determination of the difference in the amount of signal light of the first and second light receiving means are performed in a time series manner. Active ranging device. 3. The active measurement method according to claim 2, comprising means for performing the time-series determination at a predetermined timing within a predetermined time allotted to each, and means for latching the result. range device. 4. A claim in which the polarity of the difference in the amount of signal light between the first and second light receiving means can be determined by connecting the first light receiving means and the second light receiving means in antiparallel. The active distance measuring device according to item 2.