Distance measurement device

Abstract: A distance measurement device comprises a plurality of light emitting devices for projecting lights to an object for measuring distance, a plurality of photo-sensing devices provided one for each of said light emitting devices such that reflected projection images of the projection lights of said light emitting devices are focused thereto, at least one of said photo-sensing devices being arranged at such an optical position that a reflected projection image of the object due to one of said light emitting devices other than that associated with said one photo-sensing device is focused thereto under a far near distance photographing condition, and selection means for selecting a combination of said photo-sensing device arranged at said optical position and one of said light emitting devices which is not associated with said photo-sensing device to produce distance information in the far near distance photographing condition.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an active type distance measurement device for measuring distances to a plurality of distance measurement view fields to be used in a camera having an auto-focusing function. Related Background Art Document US-A-4 943 824 discloses a device for measuring an object distance used in a camera, wherein the object distance of a focus adjusting condition is measured in a plurality of distance measuring areas in the photographing scene. In particular, a plurality of light emitting devices in the form of a light emitting diode and a slit plate in combination with a light projecting lens is provided. The slit plate comprises a plurality of slits by means of which a plurality of light beams can be projected to an object for measuring the distance between the object and the camera, thereby performing the distance measurement of the object of each light projection axis provided by the light emitting diode and the slit plate. Specifically, the reflected light of the slit bundles of light beams projected on the object along each light projection axis passes a light receiving lens and is directed on a light receiving device comprising a plurality of particular light receiving elements. The electric currents output by each light receiving element corresponds to the light incident position and a distance calculation circuit calculates each object distance based on the detected electric currents. The calculated object distance based on a relationship between the corresponding light emitting devices and the associated photo-sensing devices is then used for also determining, whether the object is located at a distance which is nearer than the usual distance range. In general, the detection results are used for controlling and adapting the camera system to the detected object distance. Furthermore, in prior art distance measurement devices having a plurality of distance measurement view fields as shown in Fig. 8, light projected from a plurality of light emitting devices 1, 2 and 3 are projected to objects 5, 6 and 7 through a projection lens 4 and the lights reflected by the objects 5, 6 and 7 are focused on a plurality of two-split silicon photo-cells (SPC) through a focusing lens 8. Numeral 12 denotes a camera body which includes the distance measurement device. The two-split SPC's 9, 10 and 11 are formed by SPC's 9F, 10F and 11F which are closer to the light emitting devices and SPC's 9N, 10N and 11N on the opposite side, as shown in Fig. 9A, projection light images on the two-split SPC's when distances to the objects are 6 meters, 1.2 meters and 0.6 meter, respectively, are shown by 9B, 10B and 11B in Fig. 9B and 9C, 10C and 11C in Fig. 9C, and ratios of light images on 9F and 9N, 10F and 10N, and 11F and 11N are calculated to determine the distances to the objects 5, 6 and 7. However, in the prior art camera, when the object is far near such as at approximately 0.2 meter, a center of gravity of the projected image is actually moved to a near end as shown by 10E in Fig. 10, but because of large defocusing of the image, a ratio of the incident lights to 10F and 10N on the two-split SPC 10 is apparently closer to the far end than that of the projected image 10D obtained when the distance is 0.6 meter, and an error in the distance measurement appears. In a camera having distance measurement view field rather than a plurality of distance measurement view fields, a sensor for measuring a far near distance may be separately provided. However, in the camera for measuring the distances to the plurality of view fields, there is no space to separately arrange a sensor for measuring the far near distance because the two-split SPC 11 is located adjacent to the two-split SPC 10. Even if there is a space, another sensor and an associated circuit are required in a large scale circuit required for the measurement of the distances to the plurality of view fields. SUMMARY OF THE INVENTION It is an object of the present invention to provide a distance measurement device which solves the problems encountered in the prior art and enables the measurement of a far near distance without requiring a separate optical system. According to the present invention this object is accomplished by a distance measuring apparatus according to the accompanying claims. The present invention accordingly provides means for selecting a combination other than a normal combination of light emitting/photo-sensing devices in the distance measurement device having a plurality of distance measurement view fields by a combination of a plurality of light projection/sensing elements so that an object at a far near distance is measured by the presence or absence of the sensed light outputs. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a block diagram of a distance measurement device in accordance with the present invention, Fig. 2 shows a circuit diagram of drive means of Fig. 1, Fig. 3 shows a circuit diagram of switching means of Fig. 1, Fig. 4 shows a block diagram of distance calculation means of Fig. 1, Fig. 5 shows a circuit diagram of output level discrimination means of Fig. 4, Fig. 6 shows a circuit diagram of integration level discrimination means of Fig. 4, Fig. 7 shows a circuit diagram of light emitting/photo-sensing device combination selection means of Fig. 1, Fig. 8 shows light paths of a distance measurement device having a plurality of distance measurement view fields, Figs. 9A, 9B, 9C and 9D show projected images on photo-sensing devices on the plurality of distance measurement view fields, and Fig. 10 shows a center projection image at a near distance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 best illustrates a feature of the present invention. In Fig. 1, numerals 1, 2 and 3 denote light emitting devices such as infrared light emitting diodes, numerals 9, 10 and 11 denote photo-sensing devices such as two-split SPC's, numerals 13, 14 and 15 denote drive means controlled by control signals T1, T2 and T3 from-distance measurement control means 22 to be described later for causing the light emitting devices 1, 2 and 3 to emit lights, numerals 16, 17 and 18 switching means controlled by control signals R1, R2 and R3 from the distance measurement control means 22 for switching the outputs of the photo-sensing devices 9, 10 and 11, numeral 19 denotes distance calculation means for producing distance information such as a magnitude of the photo-sensed output and a distance signal, numeral 20 denotes light emitting/photo-sensing device combination selection means which selects a combination of light emitting devices and the photo-sensing devices in accordance with a distance measurement sequence for producing the control signals T1, T2 and T3, and R1, R2 and R3, numeral 21 denotes distance information evaluation means which evaluates the distance information from the distance calculation means 19 in accordance with the distance measurement sequence to produce a distance measurement output, and numeral 22 denotes distance measurement control means including the light emitting/photo-sensing device combination selection means 20 and the distance information evaluation means for controlling the distance measurement sequence. Fig. 2 shows a circuit diagram of the drive means 13 of Fig. 1. In Fig. 2, numeral 23 denotes a resistor for limiting a current, numeral 24 denotes a transistor for driving the light emitting device 1, numeral 25 denotes a resistor for limiting a current, and numeral 26 denotes an AND gate which receives the control signal T1 and a light emission timing signal IRON from a timing circuit (not shown) in the distance measurement control means 22. When the control signal T1 is at an H-level, the light emitting device 1 is caused to emit a light by the transistor 24 in accordance with the light emission timing signal IRON. Other drive means 14 and 15 are of the same configuration. Fig. 3 shows a circuit diagram of the switching means 16 of Fig. 1. In Fig. 3, numeral 27 denotes an inverter which receives the control signal R1, and ASW1, ASW2, ASW3 and ASW4 denote analog switches. When the control signal R1 is at the H-level, the output of the inverter 27 is at an L-Level so that the switches ASW1 and ASW2 are turned on and the switches ASW3 and ASW4 are turned off. Thus, the outputs 9F and 9N of the photo-sensing device 9 are supplied to the distance calculation means 19. When the control signal R1 is at the L-level, the output of the inverter 27 is at the H-level and the switches ASW1 and ASW2 are turned off while the switches ASW3 and ASW4 are turned on. Thus, the outputs 9F and 9N of the photo-sensing device 9 are connected to a reference voltage VREF. Fig. 4 shows a block diagram of the distance calculation means 19 of Fig. 1. In Fig. 4, numeral 28 denotes single/sum selection means for selecting one or sum of sensor outputs from the switching means 16, 17 and 18, numeral 29 denote current-voltage conversion means for converting an output current of the single/sum selection means 28 to a voltage, numeral 30 denotes an AC amplifier for amplifying an AC signal component due to flashing of the light emitting devices 1, 2 and 3 while blocking a DC component of the output of the current-voltage conversion means 29, numeral 31 denotes an inverting amplifier for inverting the output of the AC amplifier 30, numeral 32 denotes synchronous integration means for selectively integrating the outputs of the AC amplifier 30 and the inverting amplifier 31 in synchronism with the flashing of the light emitting devices 1, 2 and 3, numeral 33 denotes output level discrimination means for comparing the output of the AC amplifier 30 with a predetermined level and outputting a signal to the distance information evaluation means 21, and numeral 34 denotes integration level discrimination means for comparing the integration of the synchronous integration means 32 with a predetermined level and outputting a signal to the distance information evaluation means 21. The distance measurement by the single/sum selection means 28, the current-voltage conversion means 29, the AC amplifier 30, the inverting amplifier 31 and the synchronous integration means 32 is done in the manner described in Japanese Laid-Open Patent Application No. 60-19116. Fig. 5 shows a circuit diagram of the output level discrimination means 33 of Fig. 4. In Fig. 5, numerals 35 and 36 denote resistors for dividing the reference voltage VREF, and numeral 37 denotes a comparator for comparing the output of the AC amplifier 30 with the voltage divided by the resistors 35 and 36 and outputting a comparison result to the distance information evaluation means 21. When the photo-sensed output is large, the output of the comparator is at the H-level so that the gain of the AC amplifier 30 is reduced as required. Fig. 6 shows a circuit diagram of the integration level discrimination means 34 of Fig. 4. In Fig. 6, numerals 38 and 39 denote resistors for dividing the reference voltage VREF, numeral 40 denotes a comparator for comparing the output of the synchronous integration means 32 with the reference voltage VREF and outputting a comparison result to the distance information evaluation means 21, and numeral 41 denotes a comparator for comparing the output of the synchronous integration means 32 with the voltage divided by the resistors 38 and 39 outputting a comparison result to the distance information evaluation means 21. If the output of the comparator 41 is at the L-level after one of the sensed output has been integrated by the synchronous integration means 32 for a predetermined period, it means that the sensed output is low and the distance information evaluation means 21 receives no sensed output. When the output of the comparator 41 is at the H-level, the synchronous integration means reverse-integrates both sensed outputs, and when the integrated value exceeds the reference voltage VREF, the output of the comparator 40 changes from the H-level to the L-level. The distance information evaluation means 21 calculates the distance based on the time required for the level change. Fig. 7 shows a circuit diagram of the light emitting/photo-sensing device combination selection means 20 of Fig. 1. In Fig. 7, numerals 42 and 43 denote OR gates which output the control signals T1 and R1 for selecting the combination of the light emitting device 1 and the photo-sensing device 9 by a signal STEP1 from a timing circuit (not shown) of the distance measurement control means 22, output the control signals T2 and R2 for selecting the combination of the light emitting device 2 and the photo-sensing device 10 through the OR gate 42 by a signal STEP2, output the control signals T3 and R3 for selecting the combination of the light emitting device 3 and the photo-sensing device 11 through the OR gate 43 by a signal STEP3, and output the control signals T2 and R3 for selecting the combination of the light emitting device 2 and the photo-sensing device 11 through the OR gates 42 and 43 by a signal STEP4. In accordance with the above configuration, the distance information for the object in the normal distance range is produced in STEP1, STEP2 and STEP3 under the control of the distance measurement control means 22. On the other hand, in STEP4, the combination of the light emitting device 2 and the photo-sensing device 11 is selected. Thus, for the object which is in the normal distance range, there is no projected image from the light emitting device 2 on the photo-sensing device 11 as shown in Figs. 9B, 9C and 9D and the output from the output level discrimination means 33 is at the L-level. However, when the object is at far near distance, a portion of the projected image is on the photo-sensing device 11 as shown in Fig. 10 and the output of the output level discrimination means 33 is at the H-level because of a short distance. Thus, the distance information evaluation means 21 can discriminate whether the object is in the normal distance range or at the far near distance by the output of the output level discrimination means 33 for other combination than the combination of the light emitting device and the photo-sensing device for the normal distance measurement view field. While the input to the distance calculation means is switched in the above embodiment, separate distance calculation means may be provided for each photo-sensing device and the evaluation input to the distance information evaluation means may be switched. While whether the object is at the far near distance or not is determined by the output of the output level discrimination means in the above embodiment, it may be determined by the output of the integration level discrimination means. Further, while whether the object is at the far near distance or not is determined by the combination of the center light emitting device and the left (or right) photo-sensing device in the above embodiment, it may likewise be determined by the combination of the right (or left) light emitting device and the center photo-sensing device. In accordance with the present invention, the object at the far near distance can be detected by changing the combination of the light emitting devices and the photo-sensing device for the plurality of distance measurement view fields. Instead of providing a plurality of light emitting devices, a single light emitting device may be provided and an optical system for splitting a light projection optical axis into a plurality of axes may be arranged in front of the light emitting device. The photo-sensing means may be a single device such as a position sensitive device (PSD) and an output thereof may be used to detect the photo-sensed position. The two-split sensor may be substituted by a PSD.

Claims: A distance measuring apparatus for an autofocus camera for measuring distances within a plurality of distance measurement view fields, said apparatus comprising: light projection means (1 to 3) for projecting light beams in a plurality of directions along plural light projection axes, wherein each axis corresponds to a view field; photo-sensing means (9 to 11) having a plurality of photo-sensing regions, corresponding to each of said light projection axis, wherein a pair composed of each said photo-sensing region and each said light projection axis is optically associated with each other so that reflected light of each said light projection axis is received by said associated photo-sensing region when an object is located at a usual distance range; a processing circuit (22) for calculating in a first processing operation, a distance to said object in each of said distance measurement view fields on the basis of an output signal of the photo-sensing region to said associated light projection axis; characterized in that said reflected light from a predetermined light projection axis is received at a region other than said region which is normally associated with said light projection axis when said object is at nearer distance than said usual distance range; and said processing circuit (22) has switching means (16, 17, 18, 20) for switching to said first processing operation when the distance calculation can be performed by utilizing said normally composed pair, and to a second processing operation in which said output signal of said photo-sensing region is different from said normally associated composed pair of said light projection axis and said photo-sensing region, and said processing circuit (22) is arranged to determine, whether the distance calculation can be performed by utilizing said normally associated composed pair in said second processing operation. An apparatus according to claim 1, characterized in that said photo-sensing means (9 to 11) comprises independent photo-sensing portions for each photo-sensing region. An apparatus according to claim 1, characterized in that said light projection means (1 to 3) are arranged to project light beams, independently in a time division manner, along respective light projection axes, and said processing circuit (22) is arranged to input said output signals of said photo-sensing region which is associated with said respective light projection axis. An apparatus according to claim 1, characterized in that said processing circuit (22) is arranged to judge in said second processing operation, whether said object from which said light is reflected is located at a distance nearer than a predetermined distance. An apparatus according to claim 1 or 4, characterized in that said processing circuit (22) is arranged in a manner so that the determination of said second processing operation is performed independently of said measurement result of the distance calculation.

Inventors: MAEDA KAZUYUKI, TAKA HIDEO, MAEDA, KAZUYUKI, TAKA, HIDEO, Maeda, Kazuyuki, c/o Canon Kabushiki Kaisha, Taka, Hideo, c/o Canon Kabushiki Kaisha
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1992
Main classification: G03B13
IPC codes: G02B7