JP2006242728A - Range finder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an active range finder which can achieve both maintaining/improving performance of range-finding and increasing the life of the apparatus. <P>SOLUTION: The range finder comprises a light projection part 6 for emitting a light beam toward an object, a light receiving section 7 for receiving a return beam reflected off the object and outputting a detection signal, a operation part 8 for performing distance measurement with respect to the object on the basis of the detection signal, and a control section 9 for controlling the operations of the light projection part 6 and the light receiving section 7. The light projection part 6 includes a light emitting element 1 for emitting a light beam L in response to a driving current Iled and a driving circuit 10 for supplying the light emitting element 1 with the driving current Iled. The control section 9 controls a control circuit 10 of the light projection part 6 to emit light with the level of the driving current Iled gradually switched, monitors the amount of light received of the light receiving section 7 to detect a level suitable for range-finding, and performs range-finding using the driving current Iled with the detected level. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention includes a light projecting unit that projects a light beam onto an object, a light receiving unit that receives a light beam reflected and returned from the object and outputs a detection signal, and the object based on the detection signal. The present invention relates to an optical active distance measuring device including a calculation unit that performs distance measurement and a control unit that controls operations of a light projecting unit and a light receiving unit.

  Optical distance measuring devices are used for various purposes such as automatic focusing of cameras and interpersonal sensors of ticket machines. In particular, an active distance measuring device that projects distance measuring light such as infrared rays onto an object and uses the reflected signal light to determine the distance of the object is widely applied to autofocus of compact cameras, etc. .

  Such an active distance measuring device is basically configured as shown in FIG. In the figure, reference numeral 1 is a light emitting element composed of an infrared light emitting diode (IRled) and the like, and 2 is a light projecting lens for condensing and projecting this light on an object 3. Then, the reflected signal light from the object 3 is received by the light receiving element 5 including the light receiving lens 4 and the light position detecting element (PSD) separated from the light projecting lens 2 by the base line length B, and the light receiving position x is received. If it calculates | requires, the distance L to a target object will be calculated | required by the relationship of L = B * f / x using the focal distance f and the base line length B of the light-receiving lens 4. FIG.

  This method uses a difference in geometric position between the light projecting lens 2 and the light receiving lens 4 and follows the principle of triangulation. The light receiving element 5 made of PSD or the like generates a photocurrent at the light incident position. However, since the conductive portion up to the both end electrodes has a resistance component, the two photocurrent signals I1, I2 are changed according to the light incident position. I2 is output. Thus, the light receiving position x is obtained by calculating the ratio between the two photocurrent signals I1 and I2. For example, x = I1 / (I1 + I2).

Such an active distance measuring device is described in, for example, Patent Documents 1 to 3 below.
Japanese Patent Laid-Open No. 01-199109 JP 08-136247 A Japanese Utility Model Publication No. 05-043110

  For example, an infrared light emitting diode (IRled) is frequently used as the light emitting element of the active distance measuring device. The infrared light emitting diode emits light in accordance with the drive current, and generates light necessary for active distance measurement. The accuracy of active ranging is determined by the signal-to-noise ratio (S / N ratio). In order to increase the S / N ratio and perform stable ranging, it is better that the IRled emission intensity is high. As the emission intensity increases, the amount of light reflected from the object increases, and accurate ranging can be performed without being affected by optical noise such as ambient light or electrical noise. Therefore, from the viewpoint of improving the distance measurement performance, it is preferable to obtain a sufficient light emission intensity by setting the drive current higher. On the other hand, current-driven light-emitting elements such as infrared light-emitting diodes have a property that their lifetime is determined according to the amount of light emission. As the cumulative amount of light emission increases, the luminance decreases and the lifetime becomes shorter. Therefore, from the viewpoint of durability of the distance measuring device, it is preferable to suppress the drive current supplied to the light emitting element as much as possible. As described above, the active distance measuring device is a problem to be solved because the improvement of the distance measuring performance and the life extension of the device are not compatible.

  In view of the above-described problems of the conventional technology, an object of the present invention is to provide an active distance measuring device capable of achieving both maintenance and improvement of distance measuring performance and extending the life of a light emitting element. In order to achieve this purpose, the following measures were taken. That is, the present invention includes a light projecting unit that projects a light beam onto an object, a light receiving unit that receives a light beam reflected and returned from the object and outputs a detection signal, and a detection signal based on the detection signal. A distance measuring device comprising a calculation unit for measuring a distance to an object and a control unit for controlling operations of the light projecting unit and the light receiving unit, wherein the light projecting unit emits a light beam according to a drive current. And a driving circuit that supplies a driving current to the light emitting element, and the control unit controls the driving circuit of the light projecting unit to switch the level of the driving current step by step to perform light projection. And measuring the amount of light received by the light receiving unit to detect a level suitable for distance measurement, and performing distance measurement using the drive current of the detected level.

  Preferably, the control unit switches the level of the drive current stepwise from a high level to a low level. Further, the drive circuit selectively combines the plurality of constant current sources that output constant currents of different levels and the plurality of constant current sources in accordance with the control from the control unit, so that the level is stepwise. Switch means for generating a current to be switched between and amplifying means for amplifying the generated current and supplying it to the light emitting element as a drive current. For example, the amplification means comprises a current mirror circuit.

  According to the present invention, the active distance measuring device controls the light projecting unit to switch the drive current level stepwise from, for example, a high level to a low level to perform light projection, and monitor the amount of light received by the light receiving unit. Then, a level suitable for distance measurement is detected, and distance measurement is performed using a drive current of a level corresponding to the detected level. In the present invention, when the amount of received light reaches a level suitable for distance measurement, the level of the drive current is fixed to suppress the amount of light emission. By saving unnecessary light emission, the life of the light emitting element can be extended. In addition, reducing the drive current leads to saving of power consumption. On the other hand, the amount of received light is controlled so as to be at a level suitable for distance measurement according to the state of the object for distance measurement. Thereby, there is no possibility that the distance measurement performance is impaired. As described above, it is possible to obtain an active distance measuring device that achieves both long life of the light emitting element and maintenance of distance measuring performance.

  In the present invention, in particular, the level of the drive current is switched stepwise (digitally) to perform projection, and the amount of light received by the light receiving unit is monitored to detect a level suitable for distance measurement. In contrast, for example, light is projected while continuously sweeping the drive current from a low level to a high level (analogly sweeping), and the amount of light received by the light receiving unit is monitored to a level suitable for distance measurement. A configuration is also conceivable in which the drive current sweep is stopped when the distance is reached and distance measurement is performed. In the case of the analog method, since it is necessary to hold and fix the drive current when the amount of received light reaches a level suitable for distance measurement, a sample hold circuit must be incorporated separately, which makes the circuit configuration complicated and accurate. Becomes worse. On the other hand, the present invention adopts a digital switching system, whereby the circuit configuration is simplified and the accuracy is improved.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, in order to clarify the background of the present invention, a constant voltage driving type active distance measuring device will be described as a reference example with reference to FIG. As shown in the figure, the distance measuring device includes a light projecting unit 6, a light receiving unit 7, a calculation circuit 8 that forms a calculation unit, and a sequencer 9 that forms a control unit. The light projecting unit 6 projects a light beam onto the object. The light receiving unit 7 receives the light beam reflected and returned from the object and outputs detection signals I1 and I2. The arithmetic circuit 8 measures the distance to the object based on the detection signals I1 and I2. Specifically, distance measurement data is obtained by performing a ratio calculation of the detection signals I1 and I2. The distance measurement data is once sample-held by the sample hold circuit 12, and then output to an external device via the amplifier A3. The sequencer 9 controls the operations of the light projecting unit 6 and the light receiving unit 7.

  The light projecting unit 6 includes a light emitting element 1 that emits a light beam in response to a driving current Iled, and a driving circuit 10 that supplies the driving current Iled to the light emitting element 1. For example, an infrared light emitting diode can be used as the light emitting element 1. The drive circuit 10 includes a load resistor Rled connected to the cathode of the two-terminal light emitting element 1 and a drive transistor Tr. The base of the drive transistor Tr is connected to the sequencer 9, the collector is connected to one end of the load resistor Rled, and the emitter is grounded. The drive circuit 10 further includes a constant voltage circuit composed of an amplifier A and a transistor Tr1. One input terminal of the two-terminal amplifier A (op-amp) is connected to the sequencer 9 and is supplied with a constant voltage Vled. The other input terminal of the amplifier A is connected to the anode of the two-terminal light emitting device 1. The output terminal of the amplifier A is connected to the base of the transistor Tr1. The emitter of the transistor Tr1 is connected to the power supply Vcc, and the collector is connected to the anode of the light emitting element 1.

  The constant voltage circuit composed of the amplifier A and the transistor Tr1 applies a constant voltage Vled equal to the control voltage Vled supplied from the sequencer 9 to the anode of the light emitting element 1 and drives it at a constant voltage. Specifically, if the voltage drop of the light emitting element 1 is Vf and the voltage drop of the drive transistor Tr is Vtr, the drive current Iled is given by (Vled−Vf−Vtr) / Rled. Actually, when the sequencer 9 applies a control pulse to the base of the drive transistor Tr, the drive transistor Tr becomes conductive, and the drive current Iled flows through the light emitting element 1, and as a result, the luminance L corresponds to the control voltage Vled. The light emitting element 1 emits light. As described above, the conventional active distance measuring device always determines the light emission luminance L with the constant control voltage Vled regardless of the condition of the object.

  The light receiving unit 7 includes a light receiving element 5 made of, for example, PSD and amplifiers A1 and A2 connected to both ends thereof. One amplifier A <b> 1 amplifies the light reception current output from one end of the light receiving element 5 and supplies the detection current I <b> 1 to the arithmetic circuit 8. The other amplifier A2 amplifies the light reception current output from the other electrode of the light receiving element 5 and supplies the detection current I2 to the arithmetic circuit 8 side. A steady current drawing circuit (DCC) is connected between the input and output of each amplifier A1, A2. The steady current extraction circuit DCC is controlled by the sequencer 9 so that a steady current component (DC component) caused by ambient light or the like is extracted from the received light current and only the signal component can be supplied to the arithmetic circuit 8 side.

  The light receiving element 5 on the light receiving unit 7 side outputs detection signals I1 and I2 corresponding to the light receiving position of the light reflected from the object to the arithmetic circuit 8 side. The arithmetic circuit 8 calculates the ratio of the detection signals I1 and I2 to obtain distance measurement data. At this stage, the sequencer 9 controls the opening and closing of the switch SW1, and samples and holds the distance measurement data in the sample and hold circuit 12. The distance measurement data sampled and held is output to the main body of the apparatus via the amplifier A3.

  FIG. 2 is a circuit diagram showing another reference example of the active distance measuring device. The active distance measuring device shown in FIG. 1 employs constant voltage drive, whereas the reference example shown in FIG. 2 employs constant current drive. The light receiving unit 7, the calculation unit 8, the sequencer 9, and the sample hold circuit 12 are the same as those in the reference example of FIG. 1, but the configuration of the light projecting unit 6 is different.

  As shown in the figure, the light projecting unit 6 includes a light emitting element 1 that emits a light beam in accordance with the driving current Iled, and a driving circuit 10 that supplies the driving current Iled to the light emitting element 1. The light emitting element 1 is a two-terminal device such as an infrared LED. The drive circuit 10 includes a 2-input 1-output type amplifier (op-amp) A, a drive transistor Tr, and a load resistor Rled. The collector of the driving transistor Tr is connected to the cathode of the two-terminal light emitting element 1. The anode is connected to the power source Vcc. The emitter of the drive transistor Tr is grounded via the load resistor Rled. The base of the drive transistor Tr is connected to the output terminal of the amplifier A. One input terminal of the amplifier A is connected to the sequencer 9 and receives a control pulse. This control pulse has a voltage of Vled and a time width of Ton. The other input terminal of the amplifier A is connected to the emitter of the drive transistor Tr. With this configuration, the drive circuit 10 is a constant current source for the light emitting element 1. In response to the control pulse supplied from the sequencer 9, the drive circuit 10 causes a constant current Iled expressed by Iled = Vled / Rled to flow through the light emitting element 1 for a predetermined light emission time Ton. The light emitting element 1 emits light with a luminance corresponding to a constant driving current Iled.

  The distance measuring device according to the reference example shown in FIGS. 1 and 2 uses a two-terminal device such as an infrared LED as a light emitting element. As is well known, the luminance of an LED decreases due to the amount of light emission and the time of light emission, and its lifetime is limited. The lifetime of the LED is significantly affected by various parameters such as light emission current, temperature, light emission time, and repetitive light emission interval, and its durability is limited.

  In a conventional distance measuring device, the life required by the application is first determined. A predetermined light emission current level and light emission time are determined so as to satisfy the required life or durability. Naturally, setting the light emission current level lower and setting the light emission time shorter leads to longer life.

  On the other hand, the active distance measuring device has a higher S / N ratio and higher basic distance measuring performance as the difference in intensity between ambient light (noise) and light emission (signal) increases. Therefore, from the viewpoint of ranging performance, it is preferable that the driving current is set as high as possible to increase the amount of light emission, and it is possible to accurately measure an object at a long distance and low reflectance. As described above, the improvement in durability performance and the improvement in basic ranging performance are in a mutually contradictory relationship. In reality, the amount of light emission is determined by the durability performance required for the product, and ingenuity is devised to improve the accuracy as much as possible. For example, distance measurement is repeated on the same object within an allowable range, and the obtained result is averaged to obtain final distance data.

  In the conventional active distance measuring device shown in FIGS. 1 and 2, the light emission intensity and the light emission time are fixedly set in advance, and distance measurement is performed regardless of the state of the object. However, in the actual distance measurement, the distance of the object changes, and the surface reflectance also changes. For example, if it is assumed that the object is positioned in the front and back in the range of 0.5 to 3 m and the surface reflectance varies between 9 and 72%, the object having the distance of 3 m and the reflectance of 9% is the most received light amount. Less. On the other hand, the amount of light received by an object at a position of 0.5 m and a surface reflectance of 72% is 288 times that of the previous example. This ratio is obtained by light quantity simulation. In other words, the light emission amount required under the best condition may be 1 / 288th of the light emission amount required under the worst condition. For example, when measuring a target with a distance of 3 m and a surface reflectance of 9%, when a driving current of 1 A is required, an object with a surface reflectance of 0.5 m and a reflectance of 72% is about 3.5 mA. The light emission current is good.

  For example, when the driving current is set to 1 A in the active distance measuring device shown in FIG. 2, an object having a distance of 3 m and a surface reflectance of 9% has an appropriate light emission amount, whereas the surface reflectance is 0.5 m. In the case of a 72% target, light emission corresponding to the drive current of 1A-3.5 mA = 996.5 mA becomes unnecessary. Due to this loss, the durability of the active distance measuring device cannot be improved.

  FIG. 3 is a circuit diagram showing a prototype of a distance measuring device on which the present invention is based. For easy understanding, portions corresponding to those of the active distance measuring device according to the reference example shown in FIGS. 1 and 2 are denoted by corresponding reference numerals. As shown in the figure, this active distance measuring device receives a light beam 6 reflected from the object and outputs detection signals I1 and I2 by projecting a light beam to the object. A light receiving unit 7, a calculation circuit (calculation unit) 8 that measures a distance to an object based on the detection signals I 1 and I 2, and a sequencer (control unit) 9 that controls operations of the light projecting unit 6 and the light receiving unit 7. It consists of

  The light projecting unit 6 includes a light emitting element 1 made of an LED or the like and a drive circuit 10. The anode of the two-terminal light emitting element 1 is connected to the power supply Vcc, and the cathode is connected to the drive circuit 10. The drive circuit 10 includes a 2-input 1-output type amplifier (op-amp) A, a drive transistor Tr, and a load resistor Rled. The collector of the drive transistor Tr is connected to the cathode of the light emitting element 1, and the emitter is grounded via the load resistor Rled. The base of the transistor Tr is connected to the output terminal of the amplifier A. A control voltage Vswp is applied to one input terminal (hereinafter referred to as an input node in this specification) of the amplifier A, and the other input terminal is connected to the emitter of the transistor Tr. As a result, the drive circuit 10 passes a drive current Iled defined by Iled = Vswp / Rled to the light emitting element 1. As a result, the light emitting element 1 emits light with a luminance L corresponding to the control voltage Vswp.

  A constant current source i, a load capacitor C, and a switch SW are connected to the input node and are a part of the drive circuit 10. The constant current source i is connected between the power supply Vcc and the input node. The load capacitor C is connected between the input node and the ground line. The switch SW is also connected between the input node and the ground line. The opening / closing of the switch SW is controlled by a control pulse supplied from the sequencer 9.

  The light receiving unit 7 includes a light receiving element 5 and a pair of amplifiers A1 and A2. The light receiving element 5 is composed of, for example, a position detecting element (PSD), and outputs an optical signal corresponding to the light receiving position of the light returned from the object from a pair of electrodes. The amplifiers A1 and A2 amplify optical signals output from both electrodes of the light receiving element 5, and output the amplified signals to the arithmetic circuit 8 side as detection signals I1 and I2. A DCC for extracting a steady component is connected between the input / output terminals of the amplifiers A1 and A2.

  The arithmetic circuit 8 calculates the ratio of the detection signals I1 and I2 output from the light receiving unit 7 to obtain distance measurement data. The distance measurement data is sampled and held by the sample and hold circuit 12 and then output to the apparatus main body via the amplifier A3.

  The sequencer 9 supplies the above-described control pulse to the light projecting unit 6 side, and includes a pair of external comparators C1 and C2. The detection current I1 is supplied from the light receiving unit 7 side to the positive input terminal of the comparator C1, and a predetermined reference voltage Vref is supplied from the sequencer 9 side to the other input terminal. The output terminal of the comparator C1 is connected to the sequencer 9. Similarly, a detection current I2 is supplied to the positive input terminal of the comparator C2 from the light receiving unit 7 side, a predetermined reference voltage Vref is supplied to the negative input terminal from the sequencer 9 side, and an output terminal is connected to the sequencer 9. . In such a configuration, the control unit composed of the sequencer 9 and the pair of comparators C1, C2, etc. controls the drive circuit 10 of the light projecting unit 6 and projects the light while sweeping the drive current Iled from the low level to the high level. The amount of light received by the light receiving unit 7 is monitored, and when the level reaches a level suitable for distance measurement, the sweep of the drive current Iled is stopped to perform distance measurement, and the switch SW1 of the sample hold circuit 12 is controlled. Confirm the distance measurement result.

  FIG. 4 is a timing chart for explaining the operation of the prototype distance measuring device shown in FIG. In the standby period T0, the switch SW is in the on state and the input node is grounded, so that Vswp is at the zero level. Therefore, since the drive current Iled does not flow, the light emission intensity L is also zero. Further, since the light receiving unit 7 side does not receive any light from the object, there is no output from the comparator C1 or C2. Subsequently, when ranging starts at timing T1, the sequencer 9 outputs a control pulse to turn the switch SW from on to off. As a result, the current supplied from the constant current source i starts to be charged into the load capacitor C, and the potential Vswp of the input node rises linearly from the low level to the high level. Along with this, the drive current expressed by Iled = Vswp / Rled is swept from the low level to the high level, and as a result, the emission intensity L gradually increases. In accordance with this, the amount of light received on the light receiving unit 7 side also increases.

  At timing T2, the levels of the detection currents I1 and I2 corresponding to the amount of received light exceed the preset reference voltage Vref. This reference voltage Vref is set in advance on the sequencer 9 side so that the amount of received light is in a range suitable for distance measurement. When the levels of the detection signals I1 and I2 exceed Vref, the outputs of the comparators C1 and C2 are inverted from the low level to the high level. In response to this, the sequencer 9 releases the control pulse, and the switch SW is turned on from off. Since the input node is grounded by the switch SW, Vswp suddenly falls to zero level. Therefore, the emission intensity L is also zero. In practice, the necessary distance data can be obtained by measuring the distance while maintaining the emission intensity L at the stage of the timing T2. After that, the sequencer 9 releases the control pulse and turns off the light emitting element.

  As is clear from the above description, the voltage Vswp is swept in an expanded manner with time at the light emission start timing T1. For example, the corresponding drive current Iled is swept so as to change from 0 mA to 1.2 A. At the same time, the amount of reflected light returning to the light receiving unit 7 is monitored by the comparators C1 and C2, and when the amount of light received is sufficient as the amount of light for distance measurement, the sweep is stopped and light emission is ended. The received light amount monitoring on the light receiving unit 7 side makes a determination by monitoring the detection currents I1 and I2 and both are equal to or higher than the reference voltage Vref. Alternatively, I1 + I2 representing the total light amount of the light receiving element 5 may be monitored with a single comparator. Further, Vref for determining the level for determination may be appropriately corrected according to ambient brightness, temperature, and the like.

  The prototype distance measuring device shown in FIG. 3 obtains a level suitable for distance measurement while continuously sweeping the drive current Iled, and performs actual distance measurement by holding and fixing this level. Since it is a so-called analog system, the drive circuit 10 needs a sample hold circuit including a capacitor C and a switch SW in order to hold and fix a drive current suitable for distance measurement. In addition, the driving current cannot be accurately controlled because of the analog method. Accordingly, the present invention provides an improved digital type distance measuring device by improving the analog type prototype. FIG. 5 is a circuit diagram showing an embodiment of an active distance measuring device according to the present invention. In order to facilitate understanding, parts corresponding to those of the analog type active distance measuring device shown in FIG. 3 are denoted by corresponding reference numerals. As shown in the figure, the digital active distance measuring device includes a light projecting unit 6 for projecting a light beam onto an object, and a detection signal I1, I2 by receiving the light beam reflected and returned from the object. , A calculation circuit (calculation unit) 8 for measuring the distance to the object based on the detection signals I1 and I2, and a sequencer (control unit) for controlling the operations of the light projecting unit 6 and the light receiving unit 7. ) 9.

  The light projecting unit 6 includes a light emitting element 1 made of an LED or the like and a drive circuit 10. The anode of the two-terminal light emitting element 1 is connected to the power supply Vcc, and the cathode is connected to the drive circuit 10. The drive circuit 10 includes a 2-input 1-output type amplifier (op-amp) A, a drive transistor Tr, and a load resistor Rled. The collector of the drive transistor Tr is connected to the cathode of the light emitting element 1, and the emitter is grounded via the load resistor Rled. The base of the transistor Tr is connected to the output terminal of the amplifier A. A control voltage that changes stepwise is applied to one input terminal (input node) of the amplifier A, and the other input terminal is connected to the emitter of the transistor Tr.

  The drive circuit 10 further includes a plurality of constant current sources 14, switch means 15, and a resistor R. In this embodiment, five constant current sources 14 are used to supply constant currents i, 2i, 4i, 8i, and 16i, respectively. The switch means 15 comprises five switches, each connected between the corresponding constant current source and the input node of the amplifier A. The resistor R is also connected between the input node and the ground potential. The switch means 15 composed of five switches selectively combines the five constant current sources 14 in accordance with control from the sequencer 9 to generate a step current Istp whose level is switched in steps from i to 31i. This step current Istp flows through the resistor R to the ground line. Therefore, the voltage appearing at both ends of the resistor R is represented by R · Istp = R · ni (n is 1 to 31). This voltage R · ni is applied to the input node of the amplifier A as a control voltage. The amplifier A performs an amplification operation so that Vled = Iled · Rled is equal to the control voltage R · ni. Therefore, from Iled · Rled = R · ni, Iled = R · ni / Rled. Since n changes stepwise from 1 to 31, the level of the drive current Iled amplified by the gain R / Rled also changes stepwise from 1 to 31. As described above, the drive circuit 10 causes the light-emitting element 1 to pass the drive current Iled defined by Iled = R · ni / Rled. As a result, the light emitting element 1 emits light with a luminance that changes stepwise according to Iled.

  The light receiving unit 7 includes a light receiving element 5 and a pair of amplifiers A1 and A2. The light receiving element 5 is composed of, for example, a two-part SPD, and outputs an optical signal corresponding to the light receiving position of the light returned from the object from a pair of electrodes. The amplifiers A1 and A2 amplify optical signals output from the respective electrodes of the light receiving element 5, and output the amplified signals as detection signals I1 and I2 to the arithmetic circuit 8 side. A DCC for extracting a steady component is connected between the input / output terminals of the amplifiers A1 and A2.

  The arithmetic circuit 8 calculates the difference between the detection signals I1 and I2 output from the light receiving unit 7 to obtain distance measurement data. The distance measurement data is sampled and held by the sample and hold circuit 12 and then output to the apparatus main body via the amplifier A3.

  The sequencer 9 supplies a control signal for switching and controlling the switch means 15 on the light projecting unit 6 side, and includes a pair of comparators C1 and C2. The detection current I1 is supplied from the light receiving unit 7 side to the positive input terminal of the comparator C1, and a predetermined reference voltage Vref is supplied from the sequencer 9 side to the other input terminal. The output terminal of the comparator C1 is connected to the sequencer 9. Similarly, a detection current I2 is supplied from the light receiving unit 7 side to the positive input terminal of the comparison device C2, a predetermined reference voltage Vref is supplied from the sequencer 9 side to the negative input terminal, and an output terminal is connected to the sequencer 9. . In such a configuration, the control unit including the sequencer 9 and the pair of comparators C1 and C2 controls the drive circuit 10 of the light projecting unit 6 to perform light projection by switching the level of the drive current Iled step by step. At the same time, the amount of light received by the light receiving unit 7 is monitored to detect a level suitable for distance measurement, the distance is measured using the drive current Iled of the detected level, and the switch SW1 of the sample hold circuit 12 is controlled. To confirm the measurement result.

  FIG. 6 is a graph showing the time change of the step current Istp. In this embodiment, the step current Istp is switched stepwise from the high level (31i) to the low level (i). For example, when all five constant current sources 14 are turned on by the sequencer 9, the step current Istp becomes i + 2i + 4i + 8i + 16i = 31i, and the step current Istp = 31i at the maximum level is output. When the constant current source with the smallest output is selected from the five constant current sources 14, the step current Istp = i is obtained, and the current at the minimum level is obtained. In this way, the sequencer 9 appropriately controls the switching means 15 so that the level of the step current Istp decreases stepwise from 31i to i. In response to this, the drive current Iled also changes stepwise from a high level to a low level. At the same time, the amount of reflected light returning to the light receiving unit 7 side is monitored by the comparators C1 and C2, and when the amount of received light that is necessary and sufficient for distance measurement is reached, the drive current is switched stepwise Stop. The amount of received light monitoring on the light receiving unit 7 side is determined by monitoring the detection signals I1 and I2 and both are equal to or higher than the reference voltage Vref. Alternatively, I1 + I2 representing the total light amount of the light receiving element 5 may be monitored with a single comparator. Further, the reference voltage Vref that determines the level for determination may be appropriately corrected according to ambient brightness, temperature, and the like.

  FIG. 7 is a circuit diagram showing another embodiment of the drive circuit 10 included in the light projecting unit 6. In the previous embodiment shown in FIG. The operational current A was used to amplify the step current Istp to obtain the drive current Iled. In this method, a step current Istp is passed through a resistor R, and the voltage drop generated at that time is supplied to the input node of the operational amplifier A. At this time, in order to obtain a resolution of 32 levels, the power supply voltage Vcc applied to one end of the resistor R must be set to be high to some extent. Therefore, in the embodiment shown in FIG. 7, an amplifier circuit is configured by cascading current mirror circuits instead of the operational amplifier. In this way, the power supply voltage Vcc can be lowered. Specifically, the step current Istp generated by the plurality of constant current sources 14 and the switch means 15 is supplied to the base of the drive transistor Tr via the current mirror circuits M1, M2, M3 connected in three stages. To be supplied. For example, the amplification factor of the first stage current mirror circuit M1 is 20: 1. The amplification factor of the second-stage current mirror circuit M2 is set to 10 to 1, for example. The amplification factor of the third-stage current mirror circuit M3 is set to 5: 1. As a result, the step current Istp amplified 1000 times flows to the drive transistor Tr. In this embodiment, the drive circuit 10 of the light projecting unit can be configured purely with a current amplifier circuit.

  FIG. 8 is a circuit diagram showing an embodiment in which the distance measuring device according to the present invention is incorporated in an IC. As shown in the figure, the distance measuring IC includes eight connection terminals. Among these, the external light emitting element 1 is connected to the input terminal IRD. The control terminals CNTR and ADJ receive control signals CNTR and ADJ from the outside, respectively. The output terminal Dout outputs an output signal Dout indicating the distance measurement result to the outside. In the present embodiment, the signal representing the distance measurement result is binary, indicating that the measurement object is located either near or near. The power supply terminal VB supplies a power supply potential VB from the outside. The ground terminal GND is grounded. External capacitors are connected to the remaining terminals OSC. An external resistor is also connected to the terminal Vref.

  The distance measuring IC incorporates a two-part SPD as the light receiving element 5. A built-in head amplifier 11 is connected to the two-split SPD. The head amplifier 11 can be switched between addition (+) and subtraction (−). On the addition side, the signals output from the 2-split SPD are added and amplified. The output result is used for monitoring the amount of received light. On the other hand, the subtraction side obtains the difference between the pair of SPDs and amplifies it. The output result is used for distance measurement. Specifically, it is used for perspective determination of an object. Amplifiers 17 and 18 are connected to the output of the head amplifier 11 in two stages, and a sample hold circuit 12 is connected thereafter. The output from the head amplifier 11 is amplified by the two-stage amplifiers 17 and 18 and then sampled and held by the sample and hold circuit 12. A reference voltage Vref1 is supplied to each of the amplifiers 17 and 18 in order to cancel the background from the received light signal. A comparator C is connected to the sample and hold circuit 12, and the comparison result is output as an internal signal Cout. The comparator C compares the signal held in the sample hold circuit 12 with a predetermined reference voltage Vref2. This comparator C is used for both the received light amount determination and the perspective determination. At that time, the reference voltage Vref2 is appropriately switched.

  The distance measuring IC has a light emitting element 1 made of an infrared LED or the like externally attached. A built-in drive circuit 10 is connected to the light emitting element 1. The built-in drive circuit 10 selectively combines a plurality of constant current sources 14 that output constant currents of different levels and a plurality of constant current sources 14 to generate a step current Istp whose level is switched stepwise. The switch means 15 and the amplifying means for amplifying the generated step current Istp and supplying it to the light emitting element 1 as the drive current Iled. In this embodiment, the amplifying means is composed of cascaded current mirror circuits.

  The distance measuring IC further includes a control logic circuit as a built-in sequencer 9. This control logic circuit operates in response to the control signals CNTR and ADJ and the internal signal Cout, and outputs an output signal Dout representing the distance measurement result. At that time, the control logic circuit performs addition / subtraction switching with respect to the head amplifier 11. Further, the reference voltage Vref2 is switched for the comparator C as necessary. In addition, stepwise switching control of the drive current (light emission current) is performed on the drive circuit 10. An oscillation circuit OSC is connected to the control logic circuit 9 and supplies an operation clock signal of 10 kHz to 150 kHz. In addition, the distance measuring IC includes a regulator Vreg, and adjusts a power supply voltage VB supplied from the outside via a power supply terminal VB to generate an internal power supply voltage Vcc. In this embodiment, the external power supply voltage VB is 6 to 2.4V. On the other hand, the internal power supply voltage Vcc is adjusted to 2.2V.

  FIG. 9 is a timing chart for explaining the operation of the distance measuring IC shown in FIG. Changes in the external power supply voltage VB, the external control signals CNTR and ADJ, the drive current Iled, the internal signal Cout, and the output signal Dout along the time axis T are shown. The internal signal Cout is parenthesized to distinguish it from the external signal. In addition, an internal reset signal Reset is also shown in the timing chart. The power supply is inserted at timing T0, and the external power supply voltage VB rises. In accordance with this, the output signal Dout and the internal signal Cout are initialized to a high level. When the power is turned on, a power-on reset is performed and the internal reset signal Reset is raised. As a result, the control logic circuit 9 or the like built in the distance measuring IC is reset and enters a standby state. For example, the head amplifier is reset to the addition side.

  Subsequently, when the external control signals CNTR and ADJ rise at timing T1, the operation is started. As the first stage, first, the setting operation of the drive current Iled is performed. Specifically, the drive current Iled is switched stepwise from the high level to the low level from the timing T1 to the timing T4. Correspondingly, the amount of received light decreases step by step. First, the drive current Iled at the maximum level is output between timings T1 and T2. Accordingly, the amount of received light exceeds Vref2 representing an appropriate amount in a normal case, so that the internal signal Cout is switched from the high level to the low level. Thereafter, Iled gradually decreases, but still exceeds an appropriate level, so Cout remains at a low level. Since Iled has reached an appropriate level at time T3, the internal signal Cout is switched from the low level to the high level. At this time, the level of the drive current Iled is set for distance measurement. Thereafter, at timing T4, the control signal ADJ returns from the high level to the low level, and the first stage is completed.

  Subsequently, the second-stage ranging operation is performed after timing T4. At that time, the control logic circuit switches the head amplifier to the subtraction side, and switches the reference voltages Vref1 and Vref2 from detection of received light amount to detection of distance. Subsequently, ranging, specifically, the output of the internal comparison signal Cout is counted while the light emitting element emits light a predetermined number of times (128 in this embodiment) from timing T4 to T5. Cout is a binary signal indicating that the object is at a long distance when it is at a high level and that the object is at a short distance when it is at a low level. If the count result of Cout is low level, for example, 128/2 + 1 times or more, the output signal Dout is set to low level, indicating that the object is at a short distance. This output determination is performed every time the light emission is repeated 128 times. For example, in the first determination from timing T4 to timing T5, it is determined that Dout is at a high level and the object is at a long distance. At the next timing T5-T6, the internal signal Cout fluctuates between the high level and the low level. However, since the count number of the high level is still large, Dout is positioned at the high level. After the next timing T6, the count of Cout is reversed, the number of times of the low level is increased, and Dout is switched from the high level to the low level accordingly. That is, the process after the timing T4 represents a state in which the object is approaching from a distance, and represents that the object has just entered the short distance range from the long distance range at the timing T6.

  As is clear from the above operation, the distance measuring IC of the present invention can extend the life of the infrared LED element without flowing the drive current of the infrared LED element more than necessary, and is an expensive and highly durable special specification. Even if a neutral infrared LED element is not used, a normal inexpensive infrared LED element can be used. In the embodiment of FIG. 8, the control is performed by the logic of the circuit formed as an IC. However, instead of this, the control may be performed by software by the CPU.

  FIG. 10 is a schematic diagram showing an application example of the distance measuring device according to the present invention, which is used as a human detection sensor. As shown in the figure, a urinal 31 provided on the wall surface 32 is connected to a water supply pipe 33 for supplying washing water to the urinal 31 and a water distribution pipe 34 for discharging sewage. An electromagnetic valve 35 is disposed in the middle of the water supply pipe 33. The electromagnetic valve 35 has a coil (not shown) and a valve body provided in the coil, and is closed when the coil is not excited (normal state) to shut off the water supply pipe 33 and open with the excitation of the coil. Thus, on / off control is performed so that the water supply pipe 33 is opened. Then, the washing water is supplied to the urinal 31 through the water supply pipe 33 by the opening operation of the electromagnetic valve 35. The distance measuring device 0 according to the present invention is disposed above the urinal 31 so that the presence or absence of the user of the urinal 31 is detected. The control circuit 37 is a microcomputer having a CPU, ROM, RAM, and the like, and is embedded in the wall surface 32 above the urinal 31. A distance measuring device 0 and an electromagnetic valve 35 are connected to the control circuit 37, and the control circuit 37 inputs a detection result of the distance measuring device 0 and outputs a drive signal to the electromagnetic valve 35 based on the detection result. To do. That is, control is performed so that the washing water flows when the user leaves after entering the predetermined distance range.

  FIG. 11 is a schematic diagram showing another application example of the distance measuring apparatus according to the present invention. FIG. 11 is a perspective view showing an external configuration of an ATM which is one embodiment of an automatic transaction apparatus. This ATM is installed so that at least the front part is exposed to the outdoors, etc. The apparatus main body includes a bill deposit / withdrawal port 41 that can be opened and closed by a shutter, a CRT 42 as a display device for dialog with a user, A key input unit 43, a card mounting unit 44 on which a user authentication card is mounted, a distance measuring device 0 as an interpersonal sensor disposed on the front surface of the apparatus main body, and the like are provided. Is installed. The distance measuring device 0 includes a light projecting unit 6 and a light receiving unit 7. The ATM is placed in a standby state or a power saving state when there is no user. Even in this case, the distance measuring device 0 is in an operating state. When the distance measuring device 0 detects the approach of the user, the ATM returns from the standby state to the operating state.

It is a circuit diagram which shows the reference example of a distance measuring device. It is a circuit diagram which shows the other reference example of a distance measuring device. It is a circuit diagram which shows another reference example of a distance measuring device. It is a timing chart with which it uses for operation | movement description of the reference example shown in FIG. 1 is a circuit diagram showing an embodiment of a distance measuring device according to the present invention. It is a schematic diagram with which it uses for operation | movement description of embodiment shown in FIG. It is a circuit diagram which shows the principal part of other embodiment of the distance measuring device concerning this invention. It is a circuit diagram which shows the Example of the distance measuring device concerning this invention. It is a timing chart with which it uses for operation | movement description of the Example shown in FIG. It is typical sectional drawing which shows one application example of the distance measuring device concerning this invention. It is a typical perspective view which similarly shows the other application example. It is a schematic diagram which shows the principle of the conventional ranging apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 0 ... Distance measuring device, 1 ... Light emitting element, 5 ... Light receiving element, 6 ... Light emitting part, 7 ... Light receiving part, 8 ... Arithmetic circuit, 9 ... Sequencer, DESCRIPTION OF SYMBOLS 10 ... Drive circuit, 14 ... Constant current source, 15 ... Switch means, A ... Amplifier, M ... Current mirror circuit

Claims (4)

A light projecting unit that projects a light beam onto the object, a light receiving unit that receives the light beam reflected and returned from the object and outputs a detection signal, and a measurement to the object based on the detection signal. A distance measuring device comprising a calculation unit that performs distance and a control unit that controls operations of the light projecting unit and the light receiving unit,
The light projecting unit includes a light emitting element that emits a light beam according to a driving current, and a driving circuit that supplies a driving current to the light emitting element,
The control unit controls the driving circuit of the light projecting unit to switch the level of the drive current stepwise to perform light projection, and monitors the amount of light received by the light receiving unit to obtain a level suitable for distance measurement. A distance measuring device that detects and performs distance measurement using a drive current of the detected level.   The distance measuring apparatus according to claim 1, wherein the control unit switches the level of the drive current stepwise from a high level to a low level.   The driving circuit selectively combines the plurality of constant current sources that output constant currents having different levels and the plurality of constant current sources in accordance with control from the control unit, and the levels are stepwise. 2. The distance measuring apparatus according to claim 1, comprising switch means for generating a switching current and amplification means for amplifying the generated current and supplying the generated current to the light emitting element as a drive current.   4. A distance measuring apparatus according to claim 3, wherein said amplifying means comprises a current mirror circuit.

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