Abstract:
A rangefinder apparatus includes an infrared light-emitting diode for projecting light toward a range-finding object; a position sensitive device for detecting projected light reflected from the range-finding object and outputting a signal according to a position at which the reflected light is detected; and arithmetic circuit for carrying out an arithmetic operation according to the signal from the photosensitive device and outputting a signal corresponding to a distance to the range-finding object; an integrating circuit for integrating the signal from the arithmetic circuit by repeatedly discharging an integrating capacitor with an integrating period in response to the signal from the arithmetic circuit, to output a signal corresponding to a result of the integration produced by charging the integrating capacitor; a CPU for detecting the distance to the range-finding object according to the signal from the integrating circuit; a battery for supplying a power source voltage; and a step-up regulator for raising the power source voltage of the battery through an oscillating action and outputting the raised voltage to the position sensitive device, arithmetic circuit, and the like, wherein the integrating period of the integrating circuit is prevented from being a constant period.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a rangefinder apparatus used in a camera or the like. 
     2. Related Background Art 
     In an autofocus mechanism (AF mechanism) of a camera or the like, a rangefinder apparatus for measuring the distance to an object by a trigonometric system is used in general. In this rangefinder apparatus, a light-emitting device projects an infrared ray toward the object, a light-receiving device receives reflected light of the ray and outputs a signal according to a position at which the light is received, and a signal processing circuit or the like measures the distance to the object according to this signal. 
     In the rangefinder apparatus, since a predetermined power source voltage is necessary for actuating the signal processing circuit and the like, the voltage of the battery contained in the camera is raised by a step-up regulator, and thus raised voltage is supplied to the signal processing circuit and the like. 
     SUMMARY OF THE INVENTION 
     However, the above-mentioned rangefinder apparatus has a problem that it may fail to obtain accurate range-finding results. 
     Therefore, it is an object of the present invention to resolve this problem and provide a range finder apparatus which can carry out accurate range-finding. 
     In order to achieve this object, the rangefinder apparatus in accordance with one aspect of the present invention comprises light-emitting means for projecting a ray toward a range-finding object; light-receiving means for receiving reflected light of the ray projected from the light-emitting means to the range-finding object and outputting a signal according to a position at which the light is received; arithmetic means for carrying out an arithmetic operation according to the signal from the light-receiving means and outputting a signal corresponding to a distance to the range-finding object; integrating means for integrating the signal from the arithmetic means by discharging or charging an integrating capacitor a plurality of times with a predetermined period in response to the signal from the arithmetic means, so as to output a signal corresponding to a result of the integration; detecting means for detecting the distance to the range-finding object according to the signal from the integrating means; a battery for supplying a power source voltage; and step-up means for raising the power source voltage of the battery through an oscillating action and outputting thus raised voltage; wherein the raised voltage is supplied to at least one of the light-emitting means, light-receiving means, arithmetic means, integrating means, and detecting means; and wherein the predetermined period of the integrating means is kept from being a constant period. 
     The rangefinder apparatus in accordance with another aspect of the present invention comprises light-emitting means for projecting a ray toward a range-finding object; light-receiving means for receiving reflected light of the ray projected from the light-emitting means to the range-finding object and outputting a signal according to a position at which the light is received; arithmetic means for carrying out an arithmetic operation according to the signal from the light-receiving means and outputting a signal corresponding to a distance to the range-finding object; integrating means for integrating the signal from the arithmetic means by discharging or charging an integrating capacitor a plurality of times with a predetermined period in response to the signal from the arithmetic means, so as to output a signal corresponding to a result of the integration; detecting means for detecting the distance to the range-finding object according to the signal from the integrating means; a battery for supplying a power source voltage; and step-up means for raising the power source voltage of the battery through an oscillating action and outputting thus raised voltage; wherein the raised voltage is supplied to at least one of the light-emitting means, light-receiving means, arithmetic means, integrating means, and detecting means; and wherein the predetermined period of the integrating means is asynchronous to an oscillating period of the step-up means. 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention. 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an explanatory view of the rangefinder apparatus in accordance with a first embodiment; 
     FIG. 2 is an explanatory view of an integrating circuit; 
     FIG. 3 is an explanatory chart of an action of the integrating circuit; 
     FIG. 4 is a chart showing the control signal  41  outputted from the CPU  19  to the driver  1 , the control signal  42  outputted from the CPU  19  to the integrating circuit  16 ; 
     FIG. 5A is a chart showing an input signal to the integrating circuit  16  in the rangefinder apparatus  1  in accordance with the above-mentioned embodiment; 
     FIG. 5B is a chart showing an output voltage of a step-up regulator  32  in the rangefinder apparatus  1  in accordance with the above-mentioned embodiment; 
     FIG. 6A is a chart showing an input signal to an integrating circuit in a rangefinder apparatus on which the rangefinder apparatus  1  in accordance with the above-mentioned embodiment is based; 
     FIG. 6B is a chart showing an output voltage of a step-up regulator in the rangefinder apparatus on which the rangefinder apparatus  1  in accordance with the above-mentioned embodiment is based; 
     FIG. 7 is a chart showing range-finding results of the rangefinder apparatus in accordance with the first embodiment; 
     FIG. 8 is a chart showing range-finding results of the rangefinder apparatus on which the present invention is based; and 
     FIG. 9 is an explanatory chart of the rangefinder apparatus in accordance with a second embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following, embodiments of the present invention will be explained with reference to the accompanying drawings. Constituents identical to each other among the drawings will be referred to with numerals or letters identical to each other without their overlapping explanations repeated. Also, dimensional ratios in the drawings do not always match those explained. 
     First Embodiment 
     FIG. 1 shows the schematic configuration of the rangefinder apparatus in accordance with this embodiment. 
     The rangefinder apparatus  1  in accordance with this embodiment is used in an autofocus type camera, and comprises, as shown in FIG. 1, an infrared light-emitting diode (hereinafter referred to as “IRED”)  10  and a position sensing device (hereinafter referred to as “PSD”)  12 . The IRED  10  emits light, by way of an action of a driver  11 , according to a control signal of a microcomputer (hereinafter referred to as “CPU”)  19 . The PSD  12  is a light-receiving means which receives the infrared ray emitted from the IRED  10  and then reflected by an object. Employed as the PSD  12 , for example, is a photodiode which outputs currents as being distributed between two electrodes according to the position where the infrared ray is received. 
     Also, the rangefinder apparatus  1  is provided with an autofocus integrated circuit (hereinafter referred to as “AFIC”)  20 . The AFIC  20  is a circuit which outputs, according to the signal current outputted from the PSD  12 , a distance signal corresponding to the distance to the object. The AFIC  20  comprises a first signal processing circuit  13 , a second signal processing circuit  14 , an arithmetic circuit  15 , and an integrating circuit  16 . The first signal processing circuit  13  and the second signal processing circuit  14  process signal currents I 1  and I 2  outputted from the PSD  12 , respectively. According to the respective signals outputted from the signal processing circuits  13  and  14 , the arithmetic circuit  15  computes and outputs the information concerning the distance to the object. 
     The integrating circuit  16  integrates the output from the arithmetic circuit  15 . Since errors may occur in the range-finding relied on a single light-emitting operation of the IRED  10 , a plurality of light-emitting operations are carried out, so as to yield a plurality of items of distance information, and these plurality of distance information items are integrated by the integrating circuit  16 , so as to output thus integrated information as distance data. 
     The rangefinder apparatus  1  is provided with a CPU  19 . The CPU  19  controls the whole rangefinder apparatus  1 . The CPU  19  is provided with a unit  19   a  that detects, according to the output from the AFIC  20 , the distance to the object. The CPU  19  controls a lens driving circuit  17  so as to move a photographic lens  18  to an in-focus position. Also, the rangefinder apparatus  1  is provided with a battery  31 . The battery  31  is used for supplying a power source voltage to various components of the rangefinder apparatus  1 . Employed as the battery  31 , for example, is a battery contained in a camera. The output voltage V 1  of the battery  31  is supplied to the driver  11  and is used as the power source voltage therefor. 
     A step-up regulator  32  is connected to the battery  31 . The step-up regulator  32  receives the output voltage V 1  of the battery  31  and outputs a raised voltage V 2  which is higher than the output voltage V 1 . Employed as the step-up regulator  32  is a switching regulator having an oscillating circuit therewithin. The raised voltage V 2  outputted from the step-up regulator  32  is supplied to the PSD  12 , a lens driving control circuit  17   a , the CPU  19 , and the AFIC  20 , so as to be used as the power source voltage for each component. 
     The integrating circuit will now be explained in detail. 
     FIG. 2 shows the electric configuration of the integrating circuit  16 . As shown in FIG. 2, the integrating circuit  16  is equipped with a switch  3   a  which is connected to an output terminal of the arithmetic circuit  15 . Connected to the other end of the switch  3   a  is an external integrating capacitor  2 . Also connected to the other end of the switch  3   a  are a constant current source  4 , by way of a switch  3   b , and an operational amplifier  5  for charging the integrating capacitor  2 . Connected to the “−” input terminal of the operational amplifier  5  is one end of a switch  6 , whereas the output terminal of the operational amplifier  5  is connected to the other end of the switch  6 . A reference power source  7  is connected to the “+” input terminal of the operational amplifier  5 . The switches  3   a ,  3   b , and  6  are controlled by the CPU  19 . 
     FIG. 3 is an explanatory chart of an operation of the integrating circuit, showing an integrating capacitor control signal  31 , a switch  6  control signal  32 , and a switch  3   b  control signal  33 . 
     In the integrating circuit  16 , when the main power for the camera is turned on, and the release button is “half-pushed,” then a control signal from the CPU  19  turns on the switch  6 , so as to charge the integrating capacitor  2 . Consequently, as schematically shown in FIG. 3, the integrating capacitor  2  is charged until it attains a reference voltage (V REF ) given by the reference power source  7 . After the charging, the switch  6  is turned off and held in this state. 
     Thereafter, an infrared ray is emitted from the IRED  10  in a pulsing fashion, and the switch  3   a  is turned on/off in synchronization with a time which is about half the light-emitting width thereof. As a result, the respective outputs from the arithmetic circuit  15  corresponding to the individual infrared light emissions are successively fed into the integrating capacitor  2 . The outputs from the arithmetic circuit  15  are fed into the integrating capacitor  2  as negative voltages, whereby, as shown in FIG. 3, the charging voltage of the integrating capacitor  2  is reduced stepwise by the amount of voltage corresponding to a distance (first integration T 1 ). 
     After the negative voltages are inputted (discharge) by a predetermined number of (e.g., 256) pulse emissions, the switch  3   b  is turned on by a control signal of the CPU  19 . As a consequence, the integrating capacitor  2  is charged at a constant speed determined by the rating of the constant current source  4  (second integration T 2 ). When the voltage of the integrating capacitor  2  returns to the reference voltage (V REF ) upon this charging, the CPU  19  turns off the switch  3   b , thereby stopping the charging of the integrating capacitor  2 . 
     A terminal  2   a  of the integrating capacitor  2  is connected to the CPU  19  by way of a comparator  8 , and the CPU  19  can carry out measurement only during the time when the comparator output is HIGH, thus being able to measure the time required for the second integration. Since the charging speed is constant due to the constant current source  4 , the sum of signal voltages fed into the integrating capacitor  2  in a single range-finding operation, i.e., the distance to the object, can be determined from the time T 2  required for the second integration. 
     Thereafter, in the case where the release button is completely pushed, the CPU  19  controls the lens driving circuit  17  according to the determined distance, thereby causing the taking lens  18  to carry out an appropriate focusing action. 
     Control signals of the CPU  19  will now be explained in detail. 
     FIG. 4 is a chart showing the control signal  41  outputted from the CPU  19  to the driver  11 , the control signal  42  outputted from the CPU  19  to the integrating circuit  16 . In FIG. 4, the ordinate and abscissa indicate voltage and time. As shown, the control signal  41 , pulses are continuously fed into the driver  11 , and the driver  11  is actuated in response thereto, so that the IRED  10  emits light in a pulsing fashion. As a consequence, the IRED  10  emits light a plurality of times with predetermined periods, whereas the light-emitting periods are not a constant period. For example, each light-emitting time t 0  is set to a constant time, whereas extinction times t 1 , t 2 , t 3 , . . . between the light-emitting times t 0  are set to times different from each other, so as to keep the light-emitting periods of the IRED  10  from becoming constant. 
     Also, as shown, the control signal  42 , the integration (discharge) of the integrating capacitor  2  is effected a plurality of times with predetermined periods, whereas the integrating periods are not a constant period. For example, the integrating periods are synchronized with the light-emitting periods of the IRED  10 , each integrating time t 10  is set to a constant time, and non-integrating times t 11 , t 12 , t 13 , . . . between the integrating times t 10  are set to times different from each other, so as to keep the integrating periods from becoming constant. 
     Here, “constant period” means that the time from when the integrating capacitor  2  starts an integration to when it starts the next integration is always constant, or the time from when the IRED  10  starts a light emission to when it starts the next light emission is always constant. As a consequence, “not a constant period” also includes a case where, for example, a reference non-integrating time (reference time) is set in the control signal of the integrating capacitor  2 , a predetermined time is sequentially added to or subtracted from the reference time every time an integration is carried out, so as to yield a non-integrating time, and the non-integrating time is returned to the reference time after a predetermined number of integrating operations are carried out. 
     When the integrating periods of the integrating capacitor  2  are thus kept from being constant, the integrating periods and the oscillating period of the step-up regulator  32  can be prevented from being synchronized with each other. As a consequence, even in the case where a ripple is generated as a noise in the raised voltage outputted by the step-up regulator  32 , whereby the output signal of the PSD  12 , first signal processing circuit  13 , or second signal processing circuit fluctuates or generates a noise in the output thereof under the influence of the ripple, influences exerted on the range-finding results are reduced, thus enabling accurate range-finding. 
     Specific range-finding results obtained by the rangefinder apparatus  1  will now be explained. 
     FIG. 5A is a chart showing an input signal to the integrating circuit  16  in the rangefinder apparatus  1  in accordance with this embodiment, whereas FIG. 5B is a chart showing an output voltage of the step-up regulator  32  in the rangefinder apparatus  1  in accordance with this embodiment. FIG. 6A is a chart showing an input signal to an integrating circuit in a rangefinder apparatus on which the rangefinder apparatus  1  in accordance with the above-mentioned embodiment is based, whereas FIG. 6B is a chart showing an output voltage of a step-up regulator in the rangefinder apparatus on which the rangefinder apparatus  1  in accordance with the above-mentioned embodiment is based. In each of FIGS. 5A,  5 B,  6 A, and  6 B, the abscissa indicates time, 0.1 ms per scale. In each of FIGS. 5A and 6A, the ordinate indicates voltage value, 0.2 V per scale. In each of FIGS. 5B and 6B, the ordinate indicates the voltage value of AC component, 50 mV per scale. Here, times P 1  to P 4  in one chart correspond to those in the other charts. 
     In the output voltage of the step-up regulator  32  in the rangefinder apparatus  1  in accordance with this embodiment, as shown in FIG. 5B, a ripple corresponding to its oscillating period is generated, whereby the voltage fluctuates with a substantially constant period. In FIG. 5A, on the other hand, the non-integrating time (time in which the pulse waveform is LOW) of the range finder apparatus  1  is set such that, with the reference time being 340 μs, the non-integrating time is increased by 4 μs every time when integrated until it reaches 368 μs, at which it is returned to 340 μs again. As a consequence, the oscillating period of the step-up regulator  32  and the integrating period of the integrating capacitor  2  are not synchronized with each other. 
     As shown in FIG. 6B, a ripple is also generated in the output voltage of the step-up regulator, according to its oscillating period, in the rangefinder apparatus on which the rangefinder apparatus  1  in accordance with this embodiment is based. In FIG. 6A, on the other hand, the non-integrating time (time in which the pulse waveform is LOW) of the rangefinder apparatus is fixedly set to 354 μs. As a consequence, a period which is six times the oscillating period is in synchronization with the integrating period of the integrating capacitor  2 . 
     FIG. 7 shows range-finding results of the rangefinder apparatus  1  in accordance with this embodiment. FIG. 8 shows range-finding results of the rangefinder apparatus on which the rangefinder apparatus  1  in accordance with this embodiment is based. The range-finding results in FIGS. 7 and 8 are those obtained when range-finding operations were carried out 20 times for each distance while the distance to the object was changed stepwise. In each of FIGS. 7 and 8, the ordinate indicates the value of distance signal obtained as being computed by the CPU, whereas the abscissa indicates the distance to the object. Also, in each of FIGS. 7 and 8, the solid line, symbol X, downward triangle, and upward triangle indicate the designed value (theoretical value), average value of 20 range-finding operations at each distance, permissible upper limit at each distance, and permissible lower limit at each distance, respectively. 
     In the rangefinder apparatus  1  in accordance with this embodiment, as shown in FIG. 7, the distance signal obtained by range-finding was a value between the permissible upper and lower limits at each distance, whereby data substantially similar to the designed value were obtained as the distance signal. In the rangefinder apparatus on which the rangefinder apparatus  1  is based, by contrast, as shown in FIG. 8, the distance signal was measured greater at each distance and, in particular, it became a value greater than the permissible upper limit at longer distances, thus failing to yield a distance signal corresponding to the distance to the object, whereby it was impossible to carry out accurate range-finding. 
     As explained in the foregoing, since the integrating periods of the integrating circuit  16  are kept from being a constant period, the rangefinder apparatus  1  in accordance with this embodiment can prevent, when a ripple is generated in the raised voltage outputted from the step-up regulator  32 , the period of the ripple and the period of integration from being synchronized with each other. As a consequence, the ripple in the raised voltage can be made less influential in the range-finding results, whereby accurate range-finding can be carried out. 
     The present invention is also applicable to the case where the charging/discharging operations are the reverse of those in the above-mentioned embodiment, i.e., in an integrating circuit in which a plurality of charging operations are carried out so as to increase the charging voltage stepwise and then only a single discharging operation is effected. 
     The distance to the object is obtained on the basis of the time needed in the second integral, while it may also be obtained on the basis of the result of the A/D conversion of the integral voltage value obtained by the first integral, namely, the voltage value which is reduced due to the discharge of integral capacitor or the voltage value which is increased due to the charge of integral capacitor. 
     Though the raised voltage V 2  of the step-up regulator  32  is supplied to the PSD  12 , AFIC  20 , CPU  19 , and the lens driving control circuit  17   a  in this embodiment, the present invention is also applicable to such a case where a step-down regulator is disposed downstream the step-up regulator  32 , so that the output voltage of the step-down regulator is supplied to the PSD  12  and the like. In this case, the voltage in which the regulator ripple is reduced by the step-down regulator can be supplied to individual electronic components such as PSD  12 . 
     Though this embodiment relates to the case where the rangefinder apparatus in accordance with the present invention is applied to an autofocus type camera, the rangefinder apparatus in accordance with the present invention is not limited thereto and may be employed in others such as video camera as long as they have a range-finding function. 
     Second Embodiment 
     Though the rangefinder apparatus  1  in accordance with the first embodiment changes the non-integrating time so as to keep the integrating period from being constant, the rangefinder apparatus in accordance with the present invention is not limited thereto and may make the integrating period asynchronous to the oscillating period of the step-up regulator  32 . 
     FIG. 9 is an explanatory chart of the rangefinder apparatus in accordance with the second embodiment, showing an integrating capacitor control signal  91  and a step-up regulator control signal  92 . For example, letting the integrating period of the integrating capacitor  2  be t 10 +t 11 , and the oscillating period of the step-up regulator  32  be tx, the integrating period t 10 +t 11  of the integrating capacitor  2  is caused to satisfy the relationships of the following expressions (1) and (2) with respect to the oscillating period tx of the step-up regulator  32 : 
     
       
           n·tx≠t   10 + t   11   (1) 
       
     
     
       
           tx≠n ·( t   10 + t   11 )  (2) 
       
     
     where n is an integer. 
     Since the integrating period of the integrating capacitor  2  is thus kept from being synchronized with the oscillating period of the step-up regulator  32 , even in the case where a ripple is generated as a noise in the raised voltage outputted from the step-up regulator  32 , whereby the output signal of the PSD  12 , first signal processing circuit  13 , or second signal processing circuit  14  fluctuates or generates a noise therein under the influence of the ripple, influences exerted on the range-finding results are reduced as in the rangefinder apparatus  1  in accordance with the first embodiment, thus enabling accurate range-finding. 
     Also, in the range finder apparatus in accordance with this embodiment, since the integrating period may be left constant, it becomes easy to control the integrating period. 
     It is particularly effective in the case using a step-up regulator of a type in which, while the oscillating period of the step-up regulator  32  is fixed, its pulse width changes in response to changes in the amount of current supply, i.e., of a fixed frequency type. 
     As explained in the foregoing, the following effects can be obtained by the present invention. 
     Namely, it can prevent, when a ripple is generated in the raised voltage outputted from step-up means, the period of ripple and the period of integration from being synchronized with each other. Therefore, the ripple in the raised voltage can be made less influential in range-finding results, thus enabling accurate range-finding. 
     From the invention thus described, it will be obvious that the invention may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended for inclusion within the scope of the following claims.