JP2006308357A - Optical distance measuring device and electronic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive optical distance measuring device having a small size and small power consumption, and an electronic device having the optical distance measuring device. <P>SOLUTION: A light emission signal A is generated by an oscillator 1, and the generated light emission signal A is transmitted to a light emitting element 2, and light is emitted from the light emitting element 2 synchronously with the light emission signal A. The light emitted from the light emitting element 2 and reflected by a detection object 13 enters a light receiving element 3, and is converted into a current signal and changed into a light reception signal B. The light reception signal B is converted into a voltage signal by a preamplifier 4, and enters a mixer part 7. The light emission signal A is input directly into the mixer part 7 from the oscillator 1, and synthesized with the light reception signal B by logic operation. A composite signal C from the mixer part 7 is converted into an integral signal D proportional to the distance by an integrator 11, and the distance to the detection object is calculated by a determination part 12. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical distance measuring device, and in particular, the detection of the above-mentioned obstacle of an electronic device that needs to detect the obstacle, such as a personal robot, a non-contact switch without a mechanical contact, or a non-contact control device. The present invention relates to an optical distance measuring device that is suitable for use. The present invention also relates to an electronic apparatus, and more particularly to an electronic apparatus that needs to detect an obstacle, such as a personal robot, a non-contact switch without a mechanical contact, or a non-contact control device.

  Methods for measuring the distance to an object using light can be broadly classified into two types: a triangulation method and a time of flight (TOF) method. (Here, the TOF method includes in principle all methods for measuring the round-trip time of light.) The former shows how the light intensity center of gravity on the light receiving surface of reflected light changes depending on the distance to the object to be detected. This is a detection method using a position detection element (PSD).

  Hereinafter, the former triangulation method will be briefly described with reference to FIG.

  In FIG. 17, point A is a point on the optical axis of light emitted from the light emitting element 101, point B is a reflection point of light emitted from the light emitting element 101 on the detected object 103, and point C is reflected light. The point on the axis is located at the center of the light receiving lens 104. Point D is a point moved from the point C on the surface of the light receiving element 102 in parallel with the optical axis AB, and point E is the center of gravity of the amount of light incident on the light receiving element 102 with the reflected optical axis. Further, x is the distance DE from the point D to the point E, y is the length of the side AB, d is the length of the side CD, and l is the length of the side AC.

Light is emitted from the light emitting element 101 to irradiate the detected object 103, and the reflected light reflected by the detected object 103 is condensed on the light receiving element (PSD) 102 by the light receiving lens 104. Then, the light receiving element 102 detects x, which is the distance from the point D to the point E. Finally, since the triangle ABC and the triangle DCE are in a similar relationship, y, which is a detection distance, is derived using the following equation (1) established between x and y.

  In the above triangulation system, as shown in the equation (1), y is inversely proportional to x. Therefore, as the detection distance y increases, x decreases, and the position detection element (PSD) 102. There is a problem in that the resolution is deteriorated because the resolution is constant. That is, the triangulation method has a problem that the resolution is not linear with respect to the detection distance y, and the resolution is lowered when it is desired to detect a far distance. Further, in order to detect a distant distance, it is necessary to increase l and d, and there is a problem that the size of the optical distance measuring device increases.

  On the other hand, the latter TOF method is a method that can avoid the problem that the resolution is low and the problem that the optical distance measuring device is large.

That is, in the latter TOF method, in order to measure the time from when light is emitted until it is reflected back to the object to be detected, y is the detection distance from the light emitting element to the object to be detected, c is the speed of light, and Δt Is the time from when light is emitted until it is reflected by the object to be detected and returned, the detection distance y can be obtained from the following equation (2).

  Therefore, in the TOF method, as shown in the equation (2), y and Δt are in a proportional relationship, and the resolution with respect to the distance is theoretically uniform. Therefore, the uniform resolution from a short distance to a long distance. Can be earned. In addition, since it is not necessary to increase the size according to the measurement distance, the optical distance measuring device can be made compact.

  Conventionally, as an optical distance measuring device adopting the TOF method, a light emitting element emits light in synchronization with a clock pulse, and the emitted pulsed light is reflected by a detection object until detected by the light receiving element. In some cases, the distance is calculated by counting the clock pulses between them with a counter.

Specifically, this optical distance measuring device obtains the detection distance y from the following equation (3), where c is the speed of light, n is the number of clock pulses counted by the counter, and T is the period of the clock pulse. It is like that.

  Here, in this method, since the measurement distance is an integral multiple of the frequency of the clock pulse, the distance resolution is determined by the clock frequency, and there is a problem that a high-speed pulse signal is required to obtain high resolution. For example, when it is desired to set the resolution to 10 cm, if y = 10 cm and n = 1 in the equation (3), T = 0.67 nsec, and a high-frequency pulse signal of 1.5 GHz and its high-frequency signal processing circuit are required. End up. However, since such high-frequency signal processing circuit components are generally expensive, there is a problem that the price of the device itself is increased.

  An example of a TOF optical distance measuring device that can avoid such a problem is disclosed in, for example, Japanese Patent Laid-Open No. 7-294642 (Patent Document 1). This TOF optical distance measuring device is characterized in that the distance resolution can be increased without using a high-frequency signal.

  FIG. 18 is a diagram showing a timing chart of the optical distance measuring device.

As shown in FIG. 18, n counter clock signals whose phases are shifted by 2π / n are generated, a counter is provided for each clock signal, and counting is performed until a stop signal (light reception signal) is detected. Up. Since the pulse count value of each counter has the above phase relationship, the number of pulse counts differs depending on the counter. Some counters count as N pulses, and the remaining counters count as (N + 1) pulses. Here, when the number of counters counted as N pulses is m and the number of counters counted as (N + 1) pulses is (n−m), the average n of the number of counts is calculated using the following equation (4). .

  By substituting this into the above equation (3), the distance resolution can be improved n times without increasing the clock frequency.

As another TOF optical distance measuring device, there is a device that detects a signal detected by a light receiving element with a delay by a round trip time of light between objects to be detected. In this method, for example, when a sine wave is used as the light emission signal, the delay time is expressed as a phase delay from the light emission signal in the light reception signal, and by comparing the phase of the light emission signal and the light reception signal, the delay time is It is possible to detect the distance. Specifically, assuming that E0 and E1 are amplitudes and f is a modulation frequency, the light emission signal and the light reception signal are represented by the following equations (5A) and (5B). From this, the detection distance y can be measured by comparing the phases of the light emission signal and the light reception signal.

  However, since the speed of light is about 3.0e8 [m / s], for example, when detecting a distance within 1 m, the maximum delay time is 6.7 [ns], and this delay time is the phase delay. In this case, a high-frequency signal must be used so that the frequency f in the equation (5) has a period of the same level as this delay time (6.7 ns). That is, in order to detect the phase of such a high frequency signal, there is a problem that a detection means having a very high speed response is required.

  An example of a TOF optical distance measuring device that can avoid the problem of requiring a detection means having a very fast response is described in, for example, Japanese Patent Application Laid-Open No. 2004-32682 (Patent Document 2). There is an optical distance measuring device of the TOF method.

  FIG. 19 and FIG. 20 are diagrams for explaining the TOF optical distance measuring device of Patent Document 2, and are diagrams for explaining a phase difference detection method by beatdown of the TOF distance measuring device. is there.

  In the TOF type distance measuring device, as shown in FIG. 19, the signal detected by the light receiving element and the local oscillation signal having a frequency slightly lower (or higher) are mixed to correspond to the frequency difference between the two signals. A beat signal having an envelope to be generated is generated. Since the phase of this beat signal preserves the phase information of the received light signal, as shown in FIG. 20, the signal intensity at the four points of the envelope is detected by an integrator to form a low frequency signal that forms the envelope. The phase information of the signal can be extracted. For example, if the frequency shift applied by the frequency converter is 1/1000, the time axis will be expanded 1000 times, so the maximum delay time for detecting a distance within 1 m is 6.7 μs, and detection is performed. It can be done easily.

  However, the above-described pulse count method has a problem that the higher the distance detection accuracy, the more the number of oscillators and the number of counters increase, and the circuit becomes large and expensive. . Furthermore, since each clock signal is independent of the light emission signal, there is a problem that detection accuracy is greatly influenced by noise such as jitter. For example, when trying to obtain a resolution of 10 cm as described above, even if 100 pulses and counters are used, the frequency of each pulse can be reduced to 1/100, but it must be delayed by 0.67 ns between each pulse. Therefore, there is a problem that it is difficult to perform accurate measurement.

  Further, since the reflectance of the object to be detected varies, it is necessary to adjust the amplification degree of the light receiving circuit on the assumption that the amount of received light detected by the light receiving element has a very wide dynamic range. Here, in order to perform phase detection using the beat signal described above, it is necessary to correctly display the envelope waveform as shown in FIG. 20, but generally the swing width of an operational amplifier or the like is about 10 to several tens V at most. On the other hand, the dynamic range of the received light amount is much larger than this, and there is a problem that an adjustment circuit for the amplification degree corresponding to the received light amount is required.

  Furthermore, when the reflectance of the detected object is low or when the detected object is at a long distance, the amount of received light itself becomes small. In such a case, it is necessary to take measures to increase the light emission amount, increase the amplification degree, or increase the sensitivity of the light receiving element. Increasing the amount of light emission can be realized by increasing the output of the light emitting elements or increasing the number of light emitting elements. However, as shown in FIG. 20, the TOF optical distance measuring device detects a beat signal. Therefore, the light emitting element must be continuously driven, and there is a problem that current consumption of the light emitting element increases.

  Even if the energy use efficiency is increased by using the light emitting element as a laser diode, the laser light is a point light source, and therefore the amount of light that satisfies the safety standard (for example, JIS standard class 1 in Japan) For example, even if invisible light such as infrared light is used, the allowable amount for continuous light irradiation is 1 mW or less. As described above, the conventional apparatus has a problem that there are many limitations on increasing the light emission amount, which is not practical.

  Also, when increasing the amplification factor of the light receiving unit, it is essential to keep the noise of the circuit low. The frequency of the high-frequency component of the beat signal corresponds to the detectable distance. For example, when detecting 1 m, a sine wave having a period of 6.7 ns is required. This requires a high frequency of 150 MHz. In general, amplifiers have a trade-off relationship between bandwidth and amplification, and the amplification cannot be increased as the frequency increases, so it is difficult to amplify weak high-frequency light. .

Further, when the sensitivity of the light receiving element is increased, there is a problem that the price and size increase as described below. The most common photodiode as a light receiving element is inexpensive, but the sensitivity is about 0.2 to 0.5 A / W depending on the wavelength. In contrast, an avalanche photodiode has a sensitivity that is about 100 times greater than that of a photodiode, but has a problem that a high bias is required and current consumption is large. Furthermore, since sensitivity variation due to temperature is large, there are many cases where temperature control is required by Peltier or the like, and there is a problem that the price and size further increase. In addition, since the photomultiplier tube is very large and expensive, there is a problem that it is difficult to make the photomultiplier tube compact.
Japanese Patent Laid-Open No. 7-294642 JP 2004-32682 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide an optical distance measuring device that is inexpensive, small and consumes less power, and an electronic apparatus having the optical distance measuring device.

In order to solve the above problems, the optical distance measuring device of the present invention is
An oscillator,
A light emitting element that emits outgoing light toward an object to be detected based on a signal from the oscillator;
A light receiving element that receives reflected light from the detected portion of the emitted light; and
A logical operation is performed on the signal from the oscillator and the signal representing the reflected light from the light receiving element to obtain a primary signal having a certain relationship with the distance between the light emitting element and the detected object. A logical operation unit to output;
A calculation unit that receives the primary signal from the logic operation unit and calculates the distance.

  According to the present invention, the logical operation unit performs a logical operation on the signal from the oscillator and the signal from the light receiving element to generate a primary signal having a certain relationship with the distance. Thereafter, since the calculation unit calculates the distance based on the primary signal, the distance can be measured with high accuracy.

  In one embodiment, the signal from the oscillator is a rectangular pulse wave.

  According to the embodiment, since the signal from the oscillator is a rectangular pulse wave, the signal output from the light receiving element can be a substantially rectangular pulse wave. Therefore, the rise time and fall time of the signal output from the light receiving element can be made extremely short, and high-precision distance measurement can be realized.

  In the optical distance measuring device according to one embodiment, the logical operation unit includes a logical product operation circuit or a negative logical operation circuit.

  According to the embodiment, since the logical operation unit is composed of a logical product operation circuit (AND circuit) or a negative logical operation circuit (NAND circuit), the signal from the oscillator and the light emitting element to the detected object. It is possible to extract only the overlapping portion on the time axis with the signal from the light receiving element that is phase-delayed by the reciprocating distance, and it is possible to easily create a signal including accurate information on the distance to the object to be detected. .

  In one embodiment of the optical distance measuring device, the logical operation unit is composed of an exclusive OR operation circuit.

  According to the embodiment, since the logical operation unit is composed of an exclusive OR operation circuit (EXOR circuit), the phase is delayed by a round-trip distance from the signal from the oscillator to the detected object from the light emitting element. From the signal from the light receiving element, a signal including information on the distance to the detected object corresponding to the delay amount can be generated with high accuracy and easily.

  In one embodiment of the optical distance measuring device, the logical operation unit is an analog multiplier.

  According to the embodiment, since the logic operation unit is composed of an analog multiplier, a signal from the oscillator and a signal from the light receiving element delayed in phase by a round trip distance from the light emitting element to the detected object Thus, only overlapping portions on the time axis can be extracted, and a signal including accurate information on the distance to the object to be detected can be easily created.

  An optical distance measuring device according to an embodiment includes an amplifier connected between the light receiving element and the logical operation unit.

  According to the above embodiment, even when the amount of reflected light from the object to be detected is low, the signal intensity of the signal from the light receiving element can be amplified to a level at which the operation of the logic operation unit can be performed. Therefore, even when the reflectance of the detected object is low or when the detected object exists far away, the distance to the detected object can be measured.

  In one embodiment, the amplifier has an automatic gain adjustment function in which the amplifier controls the output signal intensity of the amplifier to be constant.

  According to the embodiment, since the amplifier has an automatic gain adjustment function (AGC function), the waveform of the received light signal can be made constant. Therefore, when the signal from the light receiving element is calculated by the logic operation unit, an error caused by the rise time of the signal from the light receiving element can be reduced.

  In the optical distance measuring device according to an embodiment, when the amplification degree of the amplifier is α, the input signal strength of the amplifier is Vin [V], and the output signal strength of the amplifier is Vout [V], Vout < α × Vin.

  According to the embodiment, the amplification degree α of the amplifier satisfies Vout <α × Vin, and the output signal strength of the amplifier exceeds the output possible range of the amplifier, so that the amplifier is in a saturated state. Therefore, errors due to the rise time of the received light signal can be reduced.

In one embodiment of the optical distance measuring device, the signal from the oscillator is a rectangular pulse wave, the rising time of the received light signal is tr [μs], and the high-frequency cutoff frequency of the amplifier is f _c [MHz]. when the a tr <0.35 / _{f c.}

According to the embodiment, the rise time tr of a pulse wave because satisfy tr <0.35 / f _c, the rise time of the output signal of the amplifier is dominant in amplifier, due to the rise time of the light receiving signal The error can be reduced.

In one embodiment of the optical distance measuring device, the signal from the oscillator is a rectangular pulse wave, the rising time of the received light signal is tr [μs], the slew rate of the amplifier is SR [V / μs], When the saturation voltage (voltage saturation level) of the amplifier is V _max [V], tr <V _max / SR.

  According to the embodiment, since the slew rate SR of the amplifier satisfies tr <Vmax / SR, the rise time of the output signal of the amplifier is dominant to the amplifier, and errors due to the rise time of the received light signal are reduced. I can do things.

Further, in the optical distance measuring device according to an embodiment, the maximum detection distance that can be calculated by the calculating unit is y _max [m], the pulse width of the rectangular pulse wave is tw [s], and the speed of light is c [m / s. ], Tw> 2y _max / c.

According to the above embodiment, since tw> 2y _max / c, the signal from the oscillator and the signal from the light receiving element always have an overlapping region on the time axis. Therefore, the logic operation unit can easily and accurately generate a signal including information on the distance to the detected object.

  The optical distance measuring device according to an embodiment is connected between the amplifier and the logic operation unit, and signals to the logic operation unit only when the intensity of the signal from the amplifier is greater than a predetermined value. Is provided.

  According to the embodiment, since the output of the amplifier is input to the logic operation unit via the logic buffer operation unit, when the light amount of the received light signal is small and the output of the amplifier is less than the threshold value of the logic buffer unit, the logic buffer The calculation unit does not output a signal and measurement is impossible. Therefore, since the measurement is not performed when the output of the amplifier is equal to or less than the threshold value of the logical buffer calculation unit and the error is large, the error due to the rise time of the signal from the light receiving element can be reduced.

  The optical distance measuring device according to an embodiment includes a phase adjustment connected between at least one of the light receiving element and the logic operation unit and between the oscillator and the logic operation unit. A part.

  Since the signal from the light receiving element is input to the logic operation unit via, for example, an amplifier or a logic buffer operation unit, a phase delay occurs in each circuit unit input to the logic operation unit. According to the embodiment, since the phase adjustment unit is provided, the phase adjustment unit can cancel the effect of the phase delay, and the distance to the object to be detected can be accurately measured. When the light receiving element outputs a pulse wave signal, the distance detectable by the pulse width of the pulse wave can be maximized.

  In the optical distance measuring device according to an embodiment, the calculation unit includes an integrator.

  According to the above embodiment, since the calculation unit has an integrator, the output of the logic operation unit including distance information can be appropriately converted into a signal having a signal intensity corresponding to the distance, and the distance determination in the subsequent stage can be performed. Processing can be facilitated.

  Moreover, in the optical distance measuring device according to an embodiment, the primary signal is a signal having a period, and the integrator integrates a plurality of periods of the primary signal.

  In general, the output signal of the logic operation unit includes noise such as jitter, and if the distance is calculated in one cycle of the signal output from the logic operation unit, the error becomes large.

  According to the embodiment, since the integrator integrates a plurality of periods of the signal output from the logic operation unit, the noise can be averaged and a distance measurement error can be reduced.

  Further, in the optical distance measuring device according to one embodiment, the oscillator oscillates a signal having a period, receives the signal having the period from the oscillator, and a time corresponding to a plurality of periods of the signal is one period. A frequency division unit that outputs a signal having a period corresponding to time, the signal from the frequency division unit, and the primary signal from the logic operation unit, and the plurality of periods for integration by the integrator. The switch part which controls this.

  According to the embodiment, the switch unit can synchronize a specific phase point of the signal having the period from the oscillator with respect to each of the integration start time and the integration end time, It is possible to prevent the integration period from varying.

  Further, in the optical distance measuring device according to one embodiment, the signal output by the frequency divider is a rectangular pulse wave, and the integrator is provided every half cycle of the signal output by the frequency divider. Repeat integration and reset.

  According to the embodiment, the integrator repeats integration and reset every half cycle of the signal output from the frequency divider, and thus can measure a continuous distance.

  The optical distance measuring device according to an embodiment includes a determination unit that is connected to the output side of the integrator and determines the distance based on a minimum value or a maximum value of an integration signal output from the integrator. Prepare.

  According to the embodiment, since the determination unit determines the distance based on the minimum value or the maximum value of the integrated signal output from the integrator, the distance can be accurately determined.

  In one embodiment, the integrator outputs an integrated signal having a period, and the determination unit determines the distance based on a moving average of the integrated signal having the period.

  The moving average (countable average) is a technique for improving the S / N ratio of a periodic signal by mixing periodic signals in accordance with the period.

  According to the embodiment, the determination unit determines the distance based on the moving average of the output of the integrator, so that the noise included in the integration signal can be removed, and the error in distance measurement is reduced. can do.

  In the optical distance measuring device according to one embodiment, the calculation unit includes a low-pass filter.

  According to the embodiment, since the calculation unit has a low-pass filter, the output of the logic operation unit including the distance information can be appropriately converted into a signal having a signal strength corresponding to the distance, and the distance determination in the subsequent stage can be performed. Processing can be facilitated.

  In one embodiment, the light emitting element is a laser diode.

  According to the above embodiment, since the light emitting element is a laser diode (LD), the light emitted from the light emitting element can be ideally collimated, and can be detected by a far object. In contrast, light irradiation can be performed at a high energy density. Accordingly, the distance can be measured even for a far object to be detected.

  In one embodiment, the light-emitting element is a light-emitting diode.

  According to the said embodiment, since a light emitting element is a light emitting diode (LED), safety to eyes is also high and manufacturing cost can be reduced further.

  Moreover, the optical distance measuring device of one Embodiment is provided with the wavelength filter which restrict | limits the range of the wavelength of the light which injects into the light-receiving surface of the said light receiving element.

  When an LD or LED is used as the light emitting element, the wavelength of light emitted from the light emitting element is single.

  According to the embodiment, since the wavelength filter that limits the wavelength range of the light incident on the light receiving surface of the light receiving element is provided, light having a wavelength other than the signal light incident as disturbance light in the use environment is removed by the wavelength filter. The noise light component can be removed. Therefore, highly accurate measurement can be performed.

  In one embodiment of the optical distance measuring device, the oscillator repeatedly outputs an on and off signal, and the light emitting element emits light only when an on signal is received from the oscillator.

  According to the embodiment, the oscillator outputs the ON and OFF signals periodically and repeatedly, and the light emitting element emits light only when receiving the ON signal from the oscillator. Noise information other than distance information included in the output signal of the unit can be minimized, and highly accurate distance measurement can be performed.

  The optical distance measuring device according to an embodiment may be configured such that the light receiving element does not receive light from the light emitting element based on the signal intensity of the signal output when the light receiving element receives light from the light emitting element. A subtraction signal generation unit that generates a subtraction signal obtained by subtracting the signal strength of the output signal is provided, and the logical operation unit receives the subtraction signal from the subtraction signal unit.

  According to the embodiment, when the light receiving element does not receive light from the light emitting element, only disturbance light is incident on the light receiving element and detected, and when the light receiving element receives light from the light emitting element. The disturbance light and the signal light are incident on the light receiving element. Therefore, subtracting the output signal when the light receiving element does not receive the light from the light emitting element from the output signal when the light receiving element receives the light from the light emitting element, extracts only the component of the signal light it can.

  In one embodiment, the light receiving element is an avalanche photodiode (APD).

  According to the above embodiment, since the light receiving element is an APD, the sensitivity of photocurrent conversion is high, and the photocurrent can be amplified and output, so that the amplification factor of the subsequent amplifier or the like can be lowered. Therefore, noise can be reduced, and highly accurate distance measurement can be performed.

  In one embodiment of the optical distance measuring device, the light receiving element is a photodiode.

  According to the embodiment, since the light receiving element is a relatively inexpensive photodiode (PD), the manufacturing cost can be reduced.

  An optical distance measuring device according to an embodiment includes a preamplifier that is connected between the photodiode and the logic operation unit, and that converts a current signal output from the photodiode into a voltage signal. The photodiode and the preamplifier are formed on the same semiconductor substrate.

  According to the embodiment, since the photodiode and the preamplifier that converts the output current into a voltage signal are formed in the same semiconductor substrate, the distance that the current signal transmits through the wiring can be remarkably shortened. Therefore, noise applied to the wiring can be reduced.

  The optical distance measuring device according to an embodiment includes an amplifier connected between the preamplifier and the logic operation unit, and the photodiode, the preamplifier, the amplifier, and the logic operation unit are the same. It is formed on a semiconductor substrate.

  According to the embodiment, since the photodiode, the preamplifier, the amplifier, and the logical operation unit are formed on the same semiconductor substrate, it is possible to reduce noise caused by the wiring connecting the components. In addition, the circuit area of the entire signal processing circuit can be reduced, and the manufacturing cost can be significantly reduced.

  An optical distance measuring device according to an embodiment includes a preamplifier that is connected between the photodiode and the logic operation unit, and that converts a current signal output from the photodiode into a voltage signal, and the preamplifier. And an amplifier connected between the logic operation unit, the preamplifier, the amplifier, and the logic operation unit are formed on a first semiconductor substrate, while the photodiode is a second semiconductor It is formed on a substrate.

  Since the spot diameter of the signal light on the light receiving surface of the light receiving element varies depending on the distance of the object to be detected, the size of the light receiving area of the light receiving element needs to be a certain area or more to increase the amount of light received as much as possible. In general, a photodiode can be manufactured at a low cost with fewer manufacturing steps than a signal processing circuit portion. Therefore, the manufacturing cost can be reduced by forming only the photodiode that requires an area on another substrate in a separate process.

  An electronic apparatus according to the present invention includes the optical distance measuring device according to the present invention.

  According to the present invention, the distance to the detected part can be measured with high accuracy. In addition, the function of the electronic device can be controlled based on the highly accurate distance to the detected part.

  According to the optical distance measuring device of the present invention, the distance to the object to be detected is measured directly using the signal from the oscillator and the signal from the light receiving element. Can be measured. Further, a simple signal processing circuit configuration can be obtained, and the manufacturing cost can be significantly reduced, and the size can be significantly reduced.

  Hereinafter, the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 is a block diagram of an optical distance measuring device according to a first embodiment of the present invention.

  As shown in FIG. 1, the optical distance measuring device includes an oscillator 1, a light emitting element 2, a light receiving element 3, a preamplifier 4, a mixer unit 7 that is a logical operation unit, a first switch 8, Two switches 9, an integrator 11, and a determination unit 12 are provided. The integrator 11 and the determination unit 12 constitute a calculation unit 10.

  A light emission signal A is generated by the oscillator 1, the generated light emission signal A is sent to the light emitting element 2, and light is emitted from the light emitting element 2 in synchronization with the light emission signal A. The light emitted from the light emitting element 2 and reflected by the detected object 13 enters the light receiving element 3 and is converted into an electric signal, which becomes a light receiving signal B. Thereafter, the light reception signal B is converted into a current signal by the preamplifier 4 and input to the mixer unit 7. Further, the light emission signal A is directly input from the oscillator 1 to the mixer unit 7 and synthesized with the light reception signal B.

  The mixer unit 7 includes a logical product operation circuit (AND circuit), an exclusive logical sum circuit (EXOR circuit), a negative logical product operation circuit (NAND circuit), an analog multiplier, or the like. The composite signal C, which is the primary signal output from the mixer unit 7, reflects the distance to the detected object 13 and is constant with respect to the distance between the light emitting element 2 and the detected object 13. Have a relationship. The calculation of the distance to the detected object 13 will be described later. The synthesized signal C of the mixer unit 7 is converted into an integrated signal D proportional to the distance by the integrator 11, and the distance to the detected object is calculated by the determination unit 12.

  FIG. 2 is a waveform diagram showing a timing chart of each circuit unit of the optical distance measuring device according to the first embodiment.

  The principle of distance detection will be described below with reference to FIG. A shown in FIG. 2 is a light emission signal. As shown in FIG. 2, the light emission signal A is a rectangular pulse wave having a constant pulse width and a repetition frequency. The light emission signal may be any wave as long as the composite signal C of the mixer unit 7 can be expressed as a function relating to the distance y from the light emitting element 2 to the detected object 13, such as a triangular wave, a sawtooth wave, or a sine wave. It may be a wave of shape. As in the first embodiment, when the light emission signal A is a rectangular wave, the integral signal D of the calculation unit that determines the distance y has linearity with respect to y, and is most preferable. The waveform of the light emission signal A is the same in all the embodiments described below, and hence the description of the light emission signal A will be omitted hereinafter.

  B shown in FIG. 2 is a light reception signal output by the preamplifier 4 that has received a signal output by the light receiving element 3 that has received the reflected light from the object 13 to be detected. The light reception signal B is a voltage signal. The time Δt shown in FIG. 2 corresponds to the time required for the light to travel back and forth the distance y to the detected object 13. The light reception signal B is delayed from the light emission signal A by a phase corresponding to the time Δt.

Here, since there is some distance between the light emitting element 2 and the light receiving element 3 as shown in FIG. 1, the distance that the light reciprocates is as shown by the block arrow in FIG. This is the hypotenuse length of the isosceles triangle formed by the reflection point on the detection object 13, which is different from y shown in FIG. However, since the distance between the light emitting element 2 and the light receiving element 3 is actually very small with respect to the distance y to be detected in most cases, the distance that the light reciprocates can be approximated to 2y. (6).

C shown in FIG. 2 is a synthesized signal synthesized by the mixer unit 7. Here, in the example shown in FIG. 2, a digital logical product operation circuit (AND circuit) or an analog multiplier is used as the calculation function of the mixer unit 7. The light emission signal A and the light reception signal B are multiplied. That is, as shown in FIG. 2, the synthesized signal C extracts an overlapping region of both signals on the time axis. This overlap width td changes according to the distance y to the detected object 13, and is expressed by the following equation (7).

D shown in FIG. 2 is an integration signal that is an output of the integrator 11. FIG. 3 is a diagram illustrating an example of the configuration of the switches 8 and 9 and the integrator 11. In FIG. 3, the integrator 11 includes an operational amplifier 18, an integration resistor 15 having a resistance value R0, and an integration capacitor 16 having a capacitance C0 as a negative feedback connection. The composite signal C output from the mixer unit 7 is input to the integrator via the first switch 8. Further, a structure in which the second switch 9 and the reset resistor 17 having a resistance value R1 are connected in series is connected in parallel with the integrating capacitor 16. ON / OFF of the first switch 8 is controlled based on the light emission signal A from the oscillator 1. Further, the light emission signal A is input to the second switch 9 via a logic negation operation circuit (NOT circuit) 14, and ON / OFF is controlled based on a signal from the logic negation operation circuit 14. During the time tw of the light emission signal A, the first switch 8 is turned on and at the same time the second switch 9 is turned off, so that charges are accumulated in the integration capacitor 16 according to the following equation (8). ing.

  Here, V represents the pulse height of the synthesized signal C, and V0 represents the integrated signal D. The signal intensity is 0 when the light emission signal A is at the low level, and the signal intensity is 0 when the light reception signal B is also at the low level. At this time, the signal intensity of the low level of the combined signal C is also 0, and the integrator performs integration for the high level time of the combined signal C. Therefore, the signal to be integrated after being reset by the second switch 9 is not input. For this reason, the integral signal D can be expressed as in equation (8).

  As is apparent from the equation (8), the output signal intensity V0 is a function (linear function) of y. The slope of the linear function is constant, and the resolution is constant regardless of the distance y to the detected object 13. Here, the resistance value of the integration resistor 15 and the capacitance of the integration capacitor 16 are selected so that the operational amplifier 18 is not saturated as a result of integration of the maximum integration time tw. The charge accumulated in the integration capacitor 16 until the time tw is such that when the light emission signal A is turned off, the first switch 8 is turned off and the second switch 9 is turned on. Discharging occurs with a time constant based on 16 capacities. When the light emission signal A is turned on again, charges are accumulated in the capacitor C0 of the integrating capacitor 16, and the same operation is repeated. In the first embodiment, the time constant composed of the resistance value R1 of the reset resistor 17 and the capacitance C0 of the integration capacitor 16 sufficiently discharges the charge accumulated in the integration capacitor 16 while the light emission signal A is OFF. Is set to a value that can be

  The integration signal D repeatedly output in this way is input to the determination unit 12. In the case of the integrator 11 that outputs the signal indicated by D in FIG. 2 and is represented by the configuration of FIG. 3, the determination unit 12 detects the minimum value and uses the equation (8) to calculate the distance y. And the distance to the detected object 13 is detected. Here, as the configuration of the integrator 11, the first switch 8, and the second switch 9, the configuration shown in FIG. 3 is shown as an example, but the configurations of the integrator, the first switch, and the second switch are shown in FIG. However, the configuration of the integrator and the first and second switches may be any configuration as long as the configuration changes according to the pulse width td of the composite signal C. Of course. For example, although not described in detail, the second switch is controlled in the same manner as described above, but the ON / OFF of the first switch is controlled by the composite signal C, and an arbitrary DC potential is applied to the integrated signal. good.

As described above, in the first embodiment, the overlapping area of the light emission signal A and the light reception signal B is extracted to detect the distance y to the detected object 13. Therefore, the pulse width tw of the light emission signal A needs to satisfy the following formula (9) with respect to the maximum detection distance y _max .

  Note that equation (9) holds true for all subsequent embodiments, but will be omitted in the following embodiments.

  In the above description, the function of the mixer unit 7 having an AND circuit and an analog multiplier has been described as an example. However, the configuration of the mixer unit is not limited to this. The mixer unit may be any arithmetic unit as long as the output can be expressed as a function of Δt, such as an exclusive OR operation circuit (EXOR circuit) or a logical NOT product operation circuit (NAND circuit). Of course.

  Here, when the mixer section is a NAND circuit, the combined waveform C is a waveform in which ON and OFF are reversed in FIG. From this, when detecting a time width similar to that of the first embodiment, an OFF time width may be detected instead of detecting the ON time width td. In this case, of course, the ON time width may be detected instead of the OFF time width.

  FIG. 4 is a waveform diagram showing a timing chart of each circuit unit when the mixer unit, which is the logical operation unit shown in FIGS. 1 and 3, is configured by an EXOR circuit.

  As shown in FIG. 4, the EXOR of the light reception waveform B and the light emission signal A, which is phase-delayed by a time corresponding to the light round trip time Δt, is calculated, and the light emission signal A is used to pass through the integrator 11 having the configuration shown in FIG. Thus, the integrated signal becomes a waveform integrated for the time of Δt as shown in D of FIG. Here, the minimum value of the integration signal D is obtained by a value in which the integration interval is td → Δt in the equation (8). Here, the conditions of the integrating resistor 15 having a resistance value R0, the integrating capacitor 16 having a capacitance C0, and the reset resistor 17 having a resistance value R1 are the same as described above, and thus description thereof is omitted.

  FIG. 5 is a block diagram of an optical distance measuring device according to a modification of the first embodiment. The optical distance measuring device shown in FIG. 5 is different from the optical distance measuring device of the first embodiment in that an amplifier 19 is connected between the preamplifier 4 and the mixer unit 7.

  There are various types of objects 13 to be detected, and their reflectances are also various. In addition, since the distance y to the detected object 13 is various, generally, the dynamic range of the light amount detected by the light receiving element 3 is wide. When the reflectance of the detected object 13 is small or the distance y is large, there is a problem that the output signal of the preamplifier 4 is sufficiently small and the mixer unit 7 cannot perform the calculation. However, in the embodiment of the modification shown in FIG. 5, the amplifier 19 is connected to the subsequent stage of the preamplifier 4 shown in FIG. 5, so that the signal intensity can be increased to a level that can be calculated by the mixer unit 7.

  Further, if the signal strength is low even if the amplifier 19 is used, it is preferable to connect a logic buffer operation unit (not shown in FIG. 5) downstream of the amplifier 19. In this way, when the amount of light received is equal to or less than the threshold value of the logical buffer calculation unit, the signal input to the mixer unit 7 is always OFF, and as a result, the output of the mixer unit 7 is always OFF. In this way, it is possible to determine that measurement is impossible, and it is possible to prevent erroneous detection of distance when the amount of received light is insufficient.

  When the logical buffer arithmetic unit as described above is used, it is possible to prevent a large erroneous detection, but it is impossible to completely eliminate the malfunction. Ideally, it is desirable that the amplifier 19 has an automatic gain control function (Auto Gain Control: AGC function) for controlling the output signal strength to a constant level. In general, the pulse signal of the oscillator 1 has a certain time to transit from the Low level to the High level. In general, the rise (fall) time of this pulse is defined as the time when the pulse height is 10% to 90%. The light reception signal detected by the light receiving element also has a rise time defined in the same manner. However, since the detection target 13 is various as described above, and the distance y to the detection target 13 is also various, the light reception signal. There are various levels.

  Now, consider a case where the output of the amplifier 19 having a constant amplification degree is three patterns of V0, V1, and V2 shown in FIG. In FIG. 6, Vth is a threshold level of the mixer unit 7 in the subsequent stage. Since the expression (9) is established, when the light reception signal B rises, the light emission signal A is always at a high level, and the rise of the output of the mixer unit 7 is such that the light reception signal B crosses Vth in FIG. Decide on the point to be

  As shown in FIG. 6, when the signal intensity is the maximum V0, the rising edge of the composite signal C is time t0, when it is V1, it is t1, and when it is V2, it is t2. Thus, the distance detected by the received light signal intensity varies. Therefore, in order to make the output signal strength constant, the amplifier 19 is provided with an AGC function having a feedback function. In this way, for example, in FIG. 6, all the signal intensities can be adjusted to V1, so that erroneous detection of the detection distance based on the received light signal intensity can be prevented.

  In general, the AGC function is to perform an operation on the signal intensity after amplification and increase or decrease the amplification degree α, so that the measurement accuracy can be made very high, while not only the time required for the measurement is increased. Also, the circuit configuration becomes complicated, and the distance measuring device becomes somewhat expensive.

  Therefore, the output signal intensity of the amplifier 19 is set to have an amplification degree α that is larger than the maximum value of the voltage display range of the amplifier when the minimum light quantity is satisfied among the specifications of the distance measuring device. In this way, as will be described below with reference to FIG. 7, the error can be reduced by the amplifier 19 having a simple configuration having a constant amplification degree.

  In FIG. 7, Vmax [V] is the maximum value of the voltage display range of the amplifier 19, Vth [V] is the threshold value of the mixer unit 7 as in FIG. 6, Vout [V] is the output signal strength of the amplifier, and Vin [V] V] indicates the output signal intensity of the preamplifier 4. When the amplification degree α is small and α × Vin is smaller than Vmax (dotted line waveform in FIG. 7), the rising time of the composite signal C is t2. From this, the erroneous detection range of the distance is the rise time t0 or more and t2 or less of the combined signal C when the amount of received light is the maximum. If the degree of amplification α satisfies Vout <α × Vin, the output signal strength of the amplifier exceeds the possible output range of the amplifier, and is in a saturated state. Therefore, errors due to the rise time of the signal from the light receiving element 3 can be reduced.

  On the other hand, even when the amount of received light is at the lowest level, when the output signal of the amplifier 19 is set to be equal to or greater than the maximum value of the voltage display range of the amplifier as shown by a one-dot broken line, the erroneous detection range is from t0 to t1. Thus, the range of erroneous detection of distance can be reduced.

The amplifier 19 has a band (high frequency cut-off frequency) f _c [MHz], so that a signal having a frequency higher than fc does not pass. Further, the rise time tr [μs] of the amplifier 19 satisfies the following expression (10) which is a well-known relationship due to the relationship with the time constant of the amplifier and the like.

As shown in FIG. 8, the light-receiving signal having a rise time tr is limited to the rise time by the bandwidth f _c of the amplifier 19, a waveform determined by the bandwidth of the amplifier 19 shown by the solid line in FIG. 8 is output. Here, as described with reference to FIG. 7, the output signal intensity has reached the saturation level of the amplifier 19, and therefore does not become smaller than the slope of the solid line in FIG. 8. That is, the rising time of the composite signal C does not vary regardless of the amount of received light, and the distance can be detected with high accuracy.

Such an amplifier has a slew rate value indicating the performance of the rising speed of the pulse signal. This slew rate is generally a value indicating how many V can be increased per “1 μs” and is expressed by “V / μs”. Here, as described with reference to FIG. 7, since the output signal of the amplifier is at the saturation level, when the level is Vmax as shown in FIG. 9, the pulse rise time limited by the amplifier is the slew rate value SR. Can be expressed as Vmax / SR. Here, when there is a relationship of the following equation (11) between the light emission signal A and the slew rate of the amplifier 19,

  As shown in FIG. 9, the received light signal having the rise time tr is limited to the rise time by the slew rate SR of the amplifier 19, and a waveform determined by the slew rate of the amplifier 19 indicated by the solid line in FIG. As described above, the rising time of the composite signal C does not vary regardless of the amount of received light, and the distance can be detected with high accuracy.

  As described above, the amplification factor α is selected so that the output signal level of the amplifier 19 becomes the saturation level of the amplifier even at the minimum light amount specified by the distance measuring device, and the rising time tr of the received light signal and the band of the amplifier 19 are selected. And the slew rate are designed to satisfy the expressions (10) and (11), respectively, even when the dynamic range of the amount of light received from the detection target 13 is wide, there is almost no error in the measurement distance. A highly accurate distance can be detected.

  By the way, in an arithmetic circuit such as an amplifier, the phase is delayed by a certain amount between the input signal and the output signal. Originally, when the distance y is 0, the light emission signal A and the light reception signal B completely coincide with each other, but both signals are shifted due to this phase delay. Since this initial phase shift is a time that cannot be used for measuring the distance within the pulse width tw, the light is completely wasted, and wasted energy is consumed.

  FIG. 10 is a block diagram showing an optical distance measuring device of a further modification of the first embodiment that can avoid this. As shown in FIG. 10, by connecting a phase adjustment unit 28 between the oscillator 1 and the mixer unit 7 which is a logic operation unit, the phase shift is the same amount as the phase shift amount delayed in the light receiving system. When the distance y is 0, the light emission signal A and the light reception signal B can be completely matched. An example of such a phase adjustment unit 28 is a logic buffer arithmetic circuit. The phase adjustment unit 28 does not need to be a subsequent stage of the oscillator 1. For example, the phase adjustment unit 28 may be a subsequent stage of the amplifier 19 or a subsequent stage of the preamplifier 4. May be adjusted to be 0. By connecting the phase adjustment unit 28 in this way, the pulse width tw of the light emission signal A can be used without waste as a time width capable of ranging. Therefore, since it is not necessary to increase the pulse width in anticipation of the phase shift, the current consumption of the optical distance measuring device can be reduced.

(Second Embodiment)
FIG. 11 is a block diagram of an optical distance measuring device according to the second embodiment of the present invention.

  The optical distance measuring device according to the second embodiment is different from the first embodiment in that a frequency divider 29 is connected between the oscillator 1 and a node between the first switch 8 and the second switch 9. This is greatly different from the optical distance measuring device in the form.

  In the optical distance measuring device of the second embodiment, the same components as those of the optical distance measuring device of the first embodiment are denoted by the same reference numerals, and description thereof is omitted. Further, in the optical distance measuring device according to the second embodiment, the description of the operations and effects common to the optical distance measuring device according to the first embodiment will be omitted, and the optical distance measurement according to the first embodiment will be omitted. Only configurations, operational effects, and modifications different from those of the apparatus will be described.

  As shown in FIG. 11, the optical distance measuring device includes an oscillator 1, a light emitting element 2, a light receiving element 3, a preamplifier 4, a mixer unit 7, a first switch 8, a second switch 9, An integrator 11, a determination unit 12, an amplifier 15, a buffer unit 26, a phase adjustment unit 28, and a frequency divider 29 that is a frequency division unit are provided.

  The light emission signal of the oscillator 1 is sent to the light emitting element 2, and pulsed light synchronized with the light emitting element 2 is emitted toward the detection target 13, and the reflected light signal is detected by the light receiving element 2. The output signal of the light receiving element 2 passes through the preamplifier 4, the amplifier 15, and the buffer unit 26 in this order, and reaches the mixer unit 7. The mixer unit 7 performs signal processing similar to that of the first embodiment based on the signal from the buffer unit 26 and the signal received from the oscillator 1 via the phase adjustment unit 28.

  The light emission signal of the oscillator 1 is frequency-divided by n by the frequency divider 29 and converted into control signals for the first and second switches 8 and 9. The frequency-divided signal D is input to both the first switch 8 and the second switch 9 to determine the integration calculation and reset timing of the integrator 11. The signal output from the mixer unit 7 is input to the integrator 11 only when the first switch 8 is conductive (only when the first switch 8 is ON), and the integrated signal is input to the determination unit 12. The distance to the detected object 13 is detected from the signal intensity of the integrated signal.

  The second switch 9 is synchronized with the first switch 8, and the second switch 9 is turned off when the first switch 8 is turned on, while the second switch 9 is turned off when the first switch 8 is turned off. The 2 switch 9 is turned on. By controlling the first switch 8 and the second switch 9, integration calculation and reset are repeatedly performed.

  FIG. 12 is a diagram illustrating an example of the configuration of the mixer unit 7, the frequency divider 29, the first switch 8, the second switch 9, and the integrator 11. Hereinafter, switching and integration calculation of the optical distance measuring device according to the second embodiment will be described with reference to FIG.

  The mixer unit 7 continuously inputs the composite signal C correlated with the distance y to the detected object 13 to the first switch 8. Further, from the dividing period 19, a divided signal D obtained by dividing the light emission signal A by n is output. This frequency-divided signal D switches the first switch 8 and at the same time switches the second switch 9 via a logical negation (NOT) 14. In this way, by passing the NOT signal through the frequency division signal D, the first switch 8 and the second switch 9 are caused to perform the switching operation in which conduction and interruption are mutually inverted, and the first switch 8 Is conducted (the first switch 9 is cut off), the integrator 11 integrates the composite signal of the mixer unit 7 by n pulses, while the second switch 9 is conducted (the first switch 8 is turned on). When the signal is cut off, the integrated signal is reset. The first switch 8 and the second switch 9 constitute a switch unit.

  FIG. 13 is a waveform diagram showing a timing chart of each circuit unit of the optical distance measuring device according to the second embodiment.

  In FIG. 13, A indicates a light emission signal, and B indicates a light reception signal. As described in detail so far, the light receiving signal 3 is emitted from the light emitting element 2 in synchronization with the light emitting signal A, and the light receiving signal B is phase-delayed by Δt according to the distance y to the detected object 13. It is to be detected.

  In FIG. 13, C indicates a composite signal by the mixer unit 7. The composite signal C is configured by, for example, a logical product operation circuit (AND circuit) as in the first embodiment. In FIG. 13, D indicates the frequency-divided signal D by the frequency divider 29. FIG. 13 illustrates the case where n = 3 as an example. Of course, in the present invention, n is not limited to 3. The integration calculation described with reference to FIG. 12 is performed using the frequency-divided signal D. In FIG. 13, E indicates an integral signal. As shown in FIG. 13, when the frequency-divided signal D is High and the combined signal C is High, charges are accumulated in the integrating capacitor 16 having the capacitance C0. When the frequency-divided signal D is High and the combined signal C is Low, the previous potential is held. This is repeated n (n is a natural number of 2 or more, n = 3 in this embodiment) steps, and reset when the frequency-divided signal D is switched off. In this way, the integrator 11 integrates a plurality of periods (three periods in this embodiment) of the primary signal from the mixer unit 7. The signal output from the frequency divider 29 is a rectangular pulse wave, and the integrator 11 repeats integration and resetting every half cycle of the signal output from the frequency divider 29.

Here, the integrated signal intensity can be obtained as in the following equation (12) (see equation (8)).

Since the oscillator 1 outputs a repetitive signal, the pulse width and the period are ideally constant, but actually, jitter exists in both the pulse width and the period. Further, since noise is constantly applied in the signal processing circuit, td in the equation (12) has fluctuation due to the synthetic signal C fluctuating at random. The following equation (13) can be adopted as an equation that can reduce the effect of td fluctuation.

  If equation (13) is used to integrate multiple signals, errors due to noise and jitter included in each pulse can be averaged, compared with the case where equation (12) is adopted. Thus, the error can be reduced.

  In the first and second embodiments and the modifications of these embodiments, the determination unit 12 shown in FIGS. 1, 5, 10, and 11 has a function of taking a moving average of the integration signal from the integrator 11. Yes. A noise component is added to the output from the integrator 11. The determination unit 12 detects the distance to the detected object 13 based on the minimum value of the integrated signal (maximum value when the output of the mixer unit 7 is a negative signal), and the integrated signal intensity due to noise is detected. An increase or decrease causes a distance detection error.

  As described above, it is possible to reduce the distance detection error due to such noise by integrating a plurality of signals, but in order to measure the distance with higher accuracy, the determination unit 12 performs the moving average process. To do. If the integrated signal is averaged in this way, the noise component can be smoothed, and the distance can be detected with high accuracy.

(Third embodiment)
FIG. 14 is a block diagram of an optical distance measuring device according to a third embodiment of the present invention.

  In the optical distance measuring device of the third embodiment, the same components as those of the optical distance measuring device of the second embodiment are denoted by the same reference numerals, and the description thereof is omitted. Further, in the optical distance measuring device of the third embodiment, the description of the operations and effects common to those of the optical distance measuring device of the first embodiment will be omitted, and the optical distance measurement of the second embodiment will be omitted. The description of the effects and modifications common to the apparatus is also omitted. In the optical distance measuring device according to the third embodiment, only the configuration, operational effects, and modifications different from those of the optical distance measuring device according to the first and second embodiments will be described.

  As shown in FIG. 14, the optical distance measuring device includes an oscillator 1, a light emitting element 2, a light receiving element 3, a preamplifier 4, a mixer unit 7, a determination unit 12, an amplifier 19, and a buffer unit 26. And a phase adjustment unit 28 and a low-pass filter (LPF) 20. The LPF 20 and the determination unit 12 constitute a calculation unit 40.

  A light emission signal A from the oscillator 1 and a light reception signal B including a phase delay corresponding to the distance y to the detected object 13 are processed by the mixer unit 7 and output as a composite signal C from the mixer unit 7. As shown in FIG. 14, in the third embodiment, the LPF 20 that is a part of the calculation unit is connected between the mixer unit 7 and the determination unit 12. The output signal of the LPF 20 is processed by the determination unit 12, and the determination unit 12 determines the distance y to the detected object 13.

  FIG. 15 is a waveform diagram illustrating a timing chart of each circuit unit of the optical distance measuring device according to the third embodiment.

The light reception signal B is phase-delayed with respect to the light emission signal A (cycle T) by the traveling time Δt of light corresponding to the distance y to the detected object 13. In the mixer unit 7 (for example, a logical product operator (AND)), both signals are combined into a combined signal C. Here, the synthesized signal C is a rectangular wave having a period T and a pulse width td. If the cut-off frequency of the LPF 20 is sufficiently lowered with respect to the frequency of the composite signal C, only the DC component passes through the LPF 20. Therefore, if the pulse width of the light emission signal A is tw and the signal intensity of the composite signal C is Vin, the LPF 20 The output signal Vout is expressed by the following equation (14) using the equation (7).

  Expression (14) indicates that the distance y to the detected object 13 and the output signal D (Vout) of the LPF 20 are in a proportional relationship. Since the input signal strength (Vin) is known, y can be calculated by detecting Vout. In the present invention, the light emitting element 2 is preferably a laser diode (LD) or a light emitting diode (LED), and is appropriately selected according to the specifications of the distance measuring device. In the case where a beam is irradiated over a wide range at a short distance, an LED having a lower cost than an LD is desirable. In addition, since the light emission of the LED is larger than the light emission point of the LD, the LED has an advantage of higher safety for human eyes than the LD.

  On the other hand, the LD is suitable for detecting an object at a long distance. This is because LD has high collimation characteristics and can collimate the emitted light with an appropriate lens arrangement, so that the light energy is not dispersed by the beam spread as in the case of an LED, and it has a high energy density. This is because an object at a distance can be irradiated. In addition, since the irradiation area can be reduced because the beam does not spread, it is possible to irradiate a long-distance object with a small spot, and it is clear to which part of the detected object the distance is measured. When LD is used, it is necessary to set the duty ratio of the light emission signal A to be sufficiently small in order to ensure safety for the eyes, and classification according to the purpose is required.

  The environment in which the optical distance measuring device is used includes disturbance light having various wavelengths such as sunlight and fluorescent lamps, and the detection of the distance becomes difficult as the ratio (SN ratio) to the reflected signal light intensity decreases. As described above, since the light emitting element 2 is a single wavelength light emitting element such as an LED or an LD, it is preferable that the light incident on the light receiving element 3 is passed through an appropriate wavelength filter.

FIG. 16 is a diagram illustrating a pass band of a wavelength filter for a light emitting element that emits light having a spectrum with λ _C as a center wavelength.

  In FIG. 16, the horizontal axis indicates the wavelength of light, and the vertical axis indicates the intensity of light. Moreover, the curve shown with a dotted line has shown the pass band of the wavelength filter. Most ideal is when the BPF (band pass filter) shown in FIG. 16C is used. This is because the BPF shown in FIG. 16C is set in the passband so as to cover only the wavelength distribution of the light emitting element, and light of other wavelengths does not enter the light receiving element. When the light emitting element is an infrared light emitting element, the wavelength of infrared light is longer than that of visible light. Therefore, in order to remove a visible light component contained in a relatively large amount of sunlight or a fluorescent lamp, FIG. HPF (high pass filter) having a wavelength pass band shown in FIG. When a short wavelength light source is used, an LPF (low pass filter) having a wavelength pass band shown in FIG. 16B can also be used.

  However, although the wavelength filter as described above is effective in reducing the detection ratio of disturbance light, the influence of disturbance light having the same wavelength as that of the light emitting element cannot be eliminated. Generally, there are three types of disturbance light: sunlight (DC), fluorescent lamps (50 Hz, 60 Hz), and inverter lamps (several tens of kHz). The frequency of the light emission signal A shown in FIG. 2 and other timing charts is made sufficiently higher than these frequencies. Further, the oscillator 1 periodically outputs ON and OFF signals so that the light emitting element 2 emits light only when receiving the ON signal from the oscillator 1. Furthermore, the low-level signal intensity of the light reception signal B is stored using a sample hold circuit (a sample hold circuit is an example of a subtraction signal generation unit), and the hold value is subtracted from the light reception signal B. In this way, the influence of disturbance light can be removed.

  This is because the reflected signal and disturbance light are incident on the light receiving element during the time when the light reception signal is ON, and only the disturbance light is incident on the light receiving element during the OFF time period. When the frequency of the light emission signal A is set sufficiently higher than the frequency of the above three types of disturbance light, the noise intensity due to the disturbance light in the time zone when the light reception signal B is ON is the disturbance light noise in the OFF time zone immediately before or immediately after. It can be regarded as almost the same level as strength. Therefore, by subtracting the signal intensity in the OFF time zone from the signal in the ON time zone of the light reception signal B, only the signal component can be extracted effectively.

  Moreover, there is no limitation with respect to the detected object 13, and since various objects are targeted, there may be a case where the amount of received light is sufficiently small. In such a case, it is preferable to employ an avalanche photodiode (APD) as the light receiving element 2 in order to reliably receive a signal. APD has high photosensitivity and is suitable for detecting weak light.

  On the other hand, when the amount of reflected light is sufficiently large, it is preferable to employ a photodiode (PD) as the light receiving element. The photodiode is the most common light receiving element, and can be manufactured at low cost by using a normal semiconductor manufacturing process using Si (silicon). Therefore, the cost of the entire apparatus can be reduced. In addition, by forming the photodiode and the preamplifier on the same semiconductor substrate in the same process, not only can the cost be reduced by integration, but also the wiring length between the photodiode and the preamplifier can be shortened, so that current noise applied to the wiring is reduced. The minimum value can be suppressed. For this reason, highly accurate measurement is realizable. The integration as described above is not limited to a preamplifier, but from a preamplifier to a calculation unit (excluding a determination unit), specifically, a photodiode, a preamplifier, an amplifier, a logical operation unit, an integrator (integrator Alternatively, LPF may be used instead of the same semiconductor substrate. In this case, noise can be minimized and the manufacturing cost for the signal processing IC can be minimized.

  When the amount of reflected light is insufficient or when measuring an object to be detected at a very short distance, it may be necessary to increase the light receiving area of the PD. In general, the structure of a PD on a semiconductor substrate is simpler than that of a signal processing IC section, and the number of processes such as film formation, cleaning, photolithography, and etching required in a semiconductor manufacturing process is small. On the other hand, since the signal processing IC section has a complicated structure such as a transistor, the number of processes as described above is very large, which is more expensive than PD. For this reason, if the area of the PD portion is large, the occupation ratio of the PD portion that can be reduced by using an expensive manufacturing process is high, resulting in an increase in manufacturing cost.

  As a result of comprehensive examination of the manufacturing process to be used, the area of the PD, the performance degradation due to the current noise of the wiring, etc., which increases when the PD and IC are made different substrates, only the photodiode part is manufactured on a separate substrate If manufacturing costs are easier to connect with the wiring section, the PD and IC section (for example, preamplifier, amplifier, logic operation section, integrator (LPF instead of the integrator) may be used) are formed on separate substrates. Of course, it may be.

  The optical distance measuring device as described above can not only accurately measure and display the distance, but also can manufacture the light emitting portion and the light receiving portion close to each other, so that it is compared with the conventional device. The device can be made much smaller. For this reason, the apparatus of the present invention can be mounted not only on a large electronic device but also on a small electronic device. And it is suitable for giving an electronic device a certain function using the measured distance value.

  When the optical distance measuring device according to the present invention is used for an electronic device such as a non-contact switch capable of controlling ON / OFF according to a distance from an obstacle or an obstacle detector, the performance of the electronic device can be improved. At the same time, the electronic device can be made compact.

It is a block diagram of the optical distance measuring device of a 1st embodiment of the present invention. It is a wave form diagram which shows the timing chart of each circuit part of the optical distance measuring device of 1st Embodiment. It is a figure which shows an example of a structure of the switch and integrator which the optical distance measuring device of 1st Embodiment has. It is a wave form diagram which shows the timing chart of each circuit part in case the mixer part of the optical distance measuring device of 1st Embodiment is comprised by the EXOR circuit. It is a block diagram of the optical distance measuring device of the modification of 1st Embodiment. It is a figure explaining the error prevention by an AGC function. It is a figure explaining the error by the amplification degree of an amplifier. It is a figure explaining that the pulse rising speed restriction | limiting by the zone | band of an amplifier reduces distance detection error. It is a figure explaining that the pulse rising speed restriction | limiting by the slew rate of an amplifier reduces a distance error. It is a block diagram which shows the optical distance measuring device of the further modification of 1st Embodiment. It is a block diagram of the optical distance measuring device of a 2nd embodiment of the present invention. It is a figure which shows an example of a structure of a mixer part, a frequency divider, a 1st switch, a 2nd switch, and an integrator. It is a wave form diagram which shows the timing chart of each circuit part of the optical distance measuring device of 2nd Embodiment. It is a block diagram of the optical distance measuring device of 3rd Embodiment of this invention. It is a wave form diagram which shows the timing chart of each circuit part of the optical distance measuring device of 3rd Embodiment. It is a figure explaining the pass band of the wavelength filter with respect to a light emitting element. It is a figure for demonstrating a triangular distance system. It is a figure which shows the timing chart of each circuit part of the conventional optical distance measuring device. It is a figure for demonstrating the conventional optical distance measuring device of a TOF system. It is a figure for demonstrating the conventional optical distance measuring device of a TOF system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Oscillator 2 Light emitting element 3 Light receiving element 4 Preamplifier 7 Mixer part 8 1st switch 9 2nd switch 10,40 Calculation part 11 Integrator 12 Judgment part 13 Detected object 14 Logical negation operation circuit 15 Integration resistance 16 Integration capacity 17 Reset resistance 18 operational amplifier 19 amplifier 20 low pass filter 26 buffer unit 28 phase adjustment unit 29 frequency divider

Claims (31)

An oscillator,
A light emitting element that emits outgoing light toward an object to be detected based on a signal from the oscillator;
A light receiving element that receives reflected light from the detected portion of the emitted light; and
A logical operation is performed on the signal from the oscillator and the signal representing the reflected light from the light receiving element to obtain a primary signal having a certain relationship with the distance between the light emitting element and the detected object. A logical operation unit to output;
An optical distance measuring device comprising: a calculation unit that receives the primary signal from the logic operation unit and calculates the distance. In the optical distance measuring device according to claim 1,
The optical distance measuring device, wherein the signal from the oscillator is a rectangular pulse wave. In the optical distance measuring device according to claim 1,
The optical distance measuring device, wherein the logical operation unit comprises a logical product operation circuit or a negative logical operation circuit. In the optical distance measuring device according to claim 1,
The optical distance measuring device, wherein the logical operation unit is composed of an exclusive OR operation circuit. In the optical distance measuring device according to claim 1,
The optical distance measuring device is characterized in that the logical operation unit comprises an analog multiplier. In the optical distance measuring device according to claim 1,
An optical distance measuring device comprising an amplifier connected between the light receiving element and the logic operation unit. In the optical distance measuring device according to claim 6,
The optical distance measuring apparatus, wherein the amplifier has an automatic gain adjustment function for controlling the output signal intensity of the amplifier to be constant. In the optical distance measuring device according to claim 6,
When the amplification factor of the amplifier is α, the input signal strength of the amplifier is Vin [V], and the output signal strength of the amplifier is Vout [V],
Vout <α × Vin
An optical distance measuring device. The optical distance measuring device according to claim 8,
When the signal from the oscillator is a rectangular pulse wave, the rising time of the received light signal is tr [μs], and the high-frequency cutoff frequency of the amplifier is f _c [MHz],
tr <0.35 / _{f c}
An optical distance measuring device. The optical distance measuring device according to claim 8,
The signal from the oscillator is a rectangular pulse wave, the rising time of the received light signal is tr [μs], the slew rate of the amplifier is SR [V / μs], and the saturation voltage of the amplifier is V _max [V]. When
tr <V _max / SR
An optical distance measuring device. In the optical distance measuring device according to claim 2,
When the maximum detection distance that can be calculated by the calculation unit is y _max [m], the pulse width of the rectangular pulse wave is tw [s], and the speed of light is c [m / s],
tw> 2y _max / c
An optical distance measuring device. In the optical distance measuring device according to claim 6,
A logic buffer operation unit that is connected between the amplifier and the logic operation unit and that outputs a signal to the logic operation unit only when the intensity of the signal from the amplifier is greater than a predetermined value; Optical distance measuring device. In the optical distance measuring device according to claim 1,
An optical distance measuring device comprising: a phase adjusting unit connected between at least one of the light receiving element and the logical operation unit and between the oscillator and the logical operation unit. . In the optical distance measuring device according to claim 1,
The optical distance measuring device, wherein the calculation unit includes an integrator. The optical distance measuring device according to claim 14,
The primary signal is a signal having a period,
The optical distance measuring device, wherein the integrator integrates a plurality of periods of the primary signal. The optical distance measuring device according to claim 15,
The oscillator oscillates a signal having a period,
A frequency divider that receives a signal having the period from the oscillator and outputs a signal having a period corresponding to a period of time of a period of a plurality of periods of the signal;
An optical distance comprising: a switch unit that receives the signal from the frequency dividing unit and the primary signal from the logical operation unit and controls the plurality of cycles integrated by the integrator. measuring device. The optical distance measuring device according to claim 16,
The signal output by the frequency divider is a rectangular pulse wave,
The optical distance measuring device according to claim 1, wherein the integrator repeats integration and resetting every half cycle of the signal output from the frequency divider. The optical distance measuring device according to claim 16,
The calculation unit is connected to the output side of the integrator, and has a determination unit that determines the distance based on the minimum value or the maximum value of the integration signal output from the integrator. measuring device. The optical distance measuring device according to claim 18,
The integrator outputs an integration signal having a period,
The optical distance measuring device, wherein the determination unit determines the distance based on a moving average of an integral signal having the period. The optical distance measuring device according to claim 18,
The optical distance measuring device, wherein the calculation unit includes a low-pass filter. In the optical distance measuring device according to claim 1,
The optical distance measuring device, wherein the light emitting element is a laser diode. In the optical distance measuring device according to claim 1,
The optical distance measuring device, wherein the light emitting element is a light emitting diode. In the optical distance measuring device according to claim 1,
An optical distance measuring device comprising a wavelength filter for limiting a wavelength range of light incident on a light receiving surface of the light receiving element. In the optical distance measuring device according to claim 1,
The optical distance measuring device characterized in that the oscillator periodically outputs an on and off signal, and the light emitting element emits light only when an on signal is received from the oscillator. The optical distance measuring device according to claim 24,
A subtracted signal obtained by subtracting the signal intensity of the signal output when the light receiving element does not receive light from the light emitting element from the signal intensity of the signal output when the light receiving element receives light from the light emitting element. An optical distance measuring device comprising: a subtracting signal generating unit for generating, wherein the logical operation unit receives the subtracting signal from the subtracting signal unit. In the optical distance measuring device according to claim 1,
The optical distance measuring device, wherein the light receiving element is an avalanche photodiode. In the optical distance measuring device according to claim 1,
The optical distance measuring device, wherein the light receiving element is a photodiode. The optical distance measuring device according to claim 27,
A preamplifier connected between the photodiode and the logic operation unit and converting a current signal output from the photodiode into a voltage signal;
The optical distance measuring device, wherein the photodiode and the preamplifier are formed on the same semiconductor substrate. The optical distance measuring device according to claim 28,
An amplifier connected between the preamplifier and the logical operation unit;
The optical distance measuring device, wherein the photodiode, the preamplifier, the amplifier, and the logic operation unit are formed on the same semiconductor substrate. The optical distance measuring device according to claim 27,
A preamplifier connected between the photodiode and the logic operation unit and converting a current signal output from the photodiode into a voltage signal;
An amplifier connected between the preamplifier and the logical operation unit;
The optical distance measuring device according to claim 1, wherein the preamplifier, the amplifier, and the logical operation unit are formed on a first semiconductor substrate, while the photodiode is formed on a second semiconductor substrate.   An electronic apparatus comprising the optical distance measuring device according to claim 1.

Images