JP2007121116A - Optical distance measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a TOP type optical distance measuring device capable of performing distance measurement with high accuracy even under environment having especially high background light in the outdoor or the like. <P>SOLUTION: A transmitter 1 comprises a light emitting element 4 for emitting a light signal synchronized with a modulating signal having a predetermined repeat frequency, and a modulating signal generator 5 for outputting the modulating signal to the light emitting element 4. A receiver 2 comprises a light receiving element 6 for receiving a light beam 11 reflected by a measured object 12 and converting it to an electric signal, a switch 7 for receiving a signal from the modulating signal generator 5 and changing the electric signal from the light receiving element 6 to two routes at a predetermined timing, and first and second accumulation sections 8a and 8b for accumulating electric signals in two routes changed with the switch 7. A signal processing section 3 comprises a differential arithmetic section 9 for performing differential operation of the electric signals accumulated by the first and second accumulation sections 8a and 8b, and a distance determining section 10 for determining distance to the measured object 12 based on the differential arithmetic result of the differential arithmetic section 9. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical distance measuring device, and more specifically, detects a distance to a measurement object by measuring a travel time from when light is emitted until it is reflected by the measurement object and detected by a light receiving element. In particular, it is suitable for use in electronic equipment such as a personal robot that needs to detect an obstacle, a non-contact switch without a mechanical contact, and a non-contact control device.

2. Description of the Related Art Conventionally, a so-called TOF (Time Of Flight) method for measuring a light round-trip time and calculating a distance to a measurement object is widely known as a distance measurement technique. In this method, since the speed of light c is known as 3.0 × 10 ⁸ [m / sec], the distance L to the object is calculated by the following (Expression 1) by measuring the round-trip time Δt. Is to be calculated.

  Various specific signal processing methods of the TOF method have been proposed. For example, in Patent Document 1 (Japanese Patent Laid-Open No. 6-18665), a start pulse (synchronized with a light emitting element) is used as a start signal, and a stop pulse (light reception signal) is used. The charge continues to be accumulated (or discharged) in the integrator until the light is detected, and the round trip time of light is detected from the increase (decrease) amount. A similar measurement method for measuring the time between the start pulse and the stop pulse is, for example, as shown in Patent Document 2 (Japanese Patent Laid-Open No. 7-294642). There are some which obtain the round trip time by measuring the number of pulses until a pulse is detected.

  However, in any of these methods, the signal detected by the light receiving element is converted into a pulse (voltage) signal, and signal processing is performed in such a manner that time information is given to the pulse waveform. In general, the measurement object is not specified, the dynamic range of the amount of reflected light from them is very large, and the noise component due to background light such as natural light is often larger. Under such circumstances, it is very difficult to appropriately extract the signal light pulse light by removing the background light noise. In addition, the voltage waveform easily causes phase delay due to the influence of environment (mainly temperature), etc., so the variation on the time axis becomes very large and some kind of correction means is required, so even in that case the circuit configuration is very complicated As a result, the manufacturing cost increases.

  On the other hand, R. Miyagawa et al. Used a photogate structure with a general CCD structure for the distance measurement sensor, and processed the photocurrent before voltage conversion of the received light signal to measure the distance. A method for obtaining information has been announced (for example, see Non-Patent Document 1).

  FIG. 12 shows a schematic cross-sectional view of the structure of the distance measuring sensor announced, and FIG. 13 shows a timing chart for explaining the operation of the method.

  In FIG. 12, 101 is a P-type semiconductor substrate, 102 is an n-type semiconductor layer forming a light receiving portion, and 103 and 104 are n-type semiconductor layers corresponding to Ach and Bch charge storage portions, respectively. Reference numerals 105 and 106 denote switches having a MOS structure. The n-type semiconductor layers 102 and 103 and the switch 105 form a switching MOS transistor. Similarly, the n-type semiconductor layers 102 and 104 and the switch 106 form a switching MOS transistor. is doing.

As shown in FIG. 13, the light emitting element irradiates the object with light according to the timing of FIG. The optical signal reflected by the object is detected by the light receiving portion formed by the n-type semiconductor layers 101 and 102 shown in FIG. 12, and becomes a light receiving signal as shown in FIG. At this time, the phase relationship between the light emission signal in FIG. 13 (a) and the light reception signal in FIG. 13 (b) is such that the light reception signal is delayed by the time (t ₁ ) during which the light travels back and forth the distance to the measurement object. Here, the Ach gate (GA) is turned on in synchronization with the light emission signal, and the Bch gate (GB) is turned on at the same time as the Ach is turned off. At this time, the duration of the on the respective gate signal (GA, GB) is the same as the duration t ₀ of the emission signal.

By performing the switching operation at such timing, the charge corresponding to (t ₀ -tl) shown in FIG. 13 (e) is accumulated in the Ach charge accumulation unit (103), and the Bch charge accumulation unit In (104), a charge corresponding to (tl) is accumulated. By repeating this operation a plurality of times and accumulating signals to increase signal components and then reading out the signals of both channels, for example, the ratio of both signals can be calculated to measure the distance to the object. . According to this technique, information on the amount of phase delay corresponding to the round trip time of light is processed as accumulated charge amount (intensity). There is no need to consider. For this reason, it is possible to measure a stable distance.

  In a general environment, there is some background light such as sunlight and lighting (fluorescent lamps, etc.). When background light is present, the received light signal waveform is superimposed on the background light. The modulation frequency of background light varies from DC (sunlight) to several tens of kilohertz (inverter lamps), but is at most a kilohertz level in a general living environment. On the other hand, since the TOF method is a delay time measurement using the speed of light, its frequency is high, and it is common to use a level of several tens of MHz. For this reason, the frequency of the background light is sufficiently lower than the pulse waveform of the received light signal, and can be regarded as DC within one period of the pulse waveform.

FIG. 14 shows a timing chart when there is background light. FIG. 14 (e), the as shown in FIG. 14 (f), Ach, since the amount of charge stored in Bch has increased by the amount of the duration of the on-gate, the delay time t _l using these I can't ask for it.

  In order to solve such a problem, in Patent Document 3 (Japanese Patent Laid-Open No. 2004-294420), in addition to the structure similar to the above, another charge storage region is provided, and only background light is monitored in the third time zone. Thus, only the reflected signal is extracted from the outputs of Ach and Bch.

FIG. 15 shows the timing chart. As shown in FIG. 15, a switching MOS transistor that turns on the gate of Cch with the same pulse width following Ach and Bch is provided around the light receiving section (not shown). Since there is no reflected signal light during this time period, charges due to background light alone are accumulated, and the background light intensity is monitored. From these three accumulated carriers (intensities), the following (Equation 2) can be used to determine the distance to the object even in an environment with background light.

The background light as described above reaches, for example, several hundred thousand lux under outdoor sunlight, and has a brightness of several thousand lux even in a relatively bright indoor such as an office. Due to such strong background light, for example, when a normal photodiode is used as the light receiving element, it can be easily calculated that it is generally on the order of mA although it depends on the optical system and its light receiving area. On the other hand, the amount of light reflected and returned from the object greatly depends on the state of reflection on the surface of the object and the distance to the object. Even if mW) is used, if there is a distance of several meters to the object, the amount of light incident on the light receiving element may be reduced to about nW. Under such an environment, the SN ratio of the charges accumulated in the charge accumulation units (103, 104) in FIG. 12 is very low, and a very small signal component exists in most noise components. The capacity of the charge storage unit (103, 104) with respect to the charge is finite, and the lower the S / N ratio, the greater the error in the measurement distance.
Japanese Patent Laid-Open No. 6-18665 Japanese Patent Laid-Open No. 7-294642 JP 2004-294420 A "CCD-Based Range-Finding Senseor" by Ryohei Miyagawa and Takeo Kanada, IEEE Transactions on Electron Devices), Vol. 44 (Vol.44), No. 10 (No. 10), October 1997 (October, 1997), p1648-1652

  SUMMARY OF THE INVENTION An object of the present invention is to provide a TOF type optical distance measuring device capable of measuring a distance with high accuracy even in an environment with strong background light such as outdoors.

In order to achieve the above object, an optical distance measuring device of the present invention comprises:
An optical distance measuring device that detects a distance to the measurement object by measuring a travel time from transmission of light to reception of light reflected by the measurement object,
A light emitting element that emits an optical signal synchronized with a modulation signal having a predetermined repetition frequency;
A light receiving element that reflects the optical signal from the light emitting element on the object to be measured, receives the reflected optical signal, and converts it into an electrical signal;
A switch for switching the electrical signal from the light receiving element to at least two paths at a predetermined timing;
An accumulation / differential operation unit for accumulating the electric signals switched by the switch, and for performing a differential operation of the accumulated electric signals;
And a distance determination unit that determines a distance to the measurement object based on a differential calculation result of the accumulation / differential calculation unit.

  According to the optical distance measuring device having the above-described configuration, each electrical signal switched at a predetermined timing is accumulated, and a differential operation of the accumulated electrical signal is performed, so that noise components such as background light are appropriately generated. Removed. Thus, only the signal component accumulated as a differential calculation result is extracted. The distance can be calculated with high accuracy by detecting the travel time of the light from the object to be measured by the distance determination unit from the result of the accumulation operation until the signal component has a sufficient magnitude.

In addition, the optical distance measuring device of one embodiment,
The accumulation / differential calculation unit has an integrator using a capacitance element,
The electrical signal is accumulated by the integrator.

  According to the optical distance measuring device of the above embodiment, since a capacitance element which is a general passive element is used for the accumulation / differential calculation unit, a special circuit element is not required on the light receiving side. The light receiving side can be configured using.

In addition, the optical distance measuring device of one embodiment,
The switch switches between the first route and the second route,
The integrator of the accumulation / differential operation unit is a first integrator connected to the first path and a second integrator connected to the second path,
The accumulation / differential operation unit performs a differential operation between the output of the first integrator and the output of the second integrator.

  According to the optical distance measuring device of the above embodiment, since the accumulation / differential calculation unit performs differential calculation of the outputs of the first integrator and the second integrator, the simplest circuit configuration can be obtained. .

  Further, the optical distance measuring device of one embodiment is characterized in that the capacitance values of the capacitance elements used in the first integrator and the second integrator are substantially the same.

  According to the optical distance measuring device of the above embodiment, since the capacitance values of the capacitance elements of the first integrator and the second integrator are the same, the subsequent differential calculation can be executed easily and with high accuracy. it can.

  In one embodiment, at least the light receiving element, the first integrator, and the second integrator are fabricated on the same semiconductor substrate.

  According to the optical distance measuring device of the above embodiment, since at least the first integrator and the second integrator are fabricated on the same semiconductor substrate, the characteristics of the first and second integrators are ideally equalized. Since the error between the first and second integrators can be reduced, the distance can be measured with high accuracy.

In addition, the optical distance measuring device of one embodiment,
The optical distance measuring device according to claim 1.
The accumulation / differential calculation unit has an integrator using a capacitance element,
A differential operation is performed while accumulating the electrical signal by the integrator.

  According to the optical distance measuring device of the above embodiment, in the integrator using the capacitance element of the accumulation / differential calculation unit, signal accumulation is performed while differentially calculating an electric signal including the background light component and the signal light component. Therefore, the number of parts can be reduced, and the storage means is not saturated with background light components even in a large background light environment such as outdoors.

  In one embodiment, the optical distance measuring device switches the photocurrent detected by the light receiving element by the switch, and inputs the photocurrent to the input terminal of the integrator of the accumulation / differential calculation unit. The differential operation is performed by reversing the direction in which the current flows.

  According to the optical distance measuring device of the above embodiment, the effect of differential calculation is obtained by inverting the direction of the current applied to the integrator of the accumulation / differential calculation unit at a predetermined timing by switching the switch. be able to. Thereby, it is possible to accumulate the signal component of the calculation result while performing the differential calculation with one integrator.

In addition, the optical distance measuring device of one embodiment,
The light receiving element is a first light receiving element having a cathode connected to a power source and a second light receiving element having an anode connected to a reference potential.
The switch connects the anode of the first light receiving element to the input terminal of the integrator of the storage / differential operation unit at the predetermined timing, and connects the cathode of the second light receiving element to the storage / differential. It connects to the input terminal of the said integrator of a calculating part, It is characterized by the above-mentioned.

  According to the optical distance measuring device of the above embodiment, since the switch is switched to the anode of the first light receiving element and the cathode of the second light receiving element at a predetermined timing, the direction of the current that effectively acts on the integrator is changed. Can be reversed.

  The optical distance measuring device according to an embodiment is characterized in that the first light receiving element and the second light receiving element have the same structure and the same size.

  According to the optical distance measuring device of the above embodiment, since the first light receiving element and the second light receiving element have the same structure and the same size, their output characteristics are the same, and the error of the current applied to the integrator is reduced. Can be reduced.

  The optical distance measuring device according to an embodiment is characterized in that at least the first light receiving element and the second light receiving element are formed on the same semiconductor substrate.

  According to the optical distance measuring device of the above embodiment, since the first light receiving element and the second light receiving element are fabricated on the same semiconductor substrate, an error in output characteristics between the first and second light receiving elements is ignored. In addition, since the first and second light receiving elements can be disposed adjacent to each other in the vicinity of the poles, it is possible to eliminate uneven irradiation of the optical signal between the first and second light receiving elements. Thereby, it is possible to measure the distance with high accuracy.

In addition, the optical distance measuring device of one embodiment,
A discharge-type first current mirror circuit that generates two currents of the same magnitude as the current flowing through the light receiving element;
A suction type second current mirror circuit that receives one of the two currents generated by the first current mirror circuit and generates a current of the same magnitude as the current;
The switch inputs the other of the currents generated by the first current mirror circuit to the input terminal of the integrator at the predetermined timing, or the current generated by the second current mirror circuit is It is characterized by switching whether to input to the input terminal of the integrator.

  According to the optical distance measuring device of the above embodiment, the same current is generated by the first and second current mirror circuits for the photocurrent generated by the light receiving element, so that the number of light receiving elements and integrators is 1 respectively. As a result, the number of components can be reduced, and errors due to characteristic differences between the light receiving elements and between the integrators can be eliminated.

In addition, the optical distance measuring device of one embodiment,
A constant current source;
A discharge-type first current mirror circuit that generates two currents having the same magnitude as the current flowing through the constant current source;
A suction-type second current mirror circuit that generates two currents of the same magnitude as the current flowing through the constant current source;
The anode of the first light receiving element is connected to one output side terminal of the first current mirror circuit, the cathode of the first light receiving element is connected to the other output side terminal of the first current mirror circuit,
The switch inputs one output side terminal of the first current mirror circuit to the input terminal of the integrator and connects the other output side terminal of the first current mirror circuit to a resistive load at the predetermined timing. Or switching between whether one output side terminal of the first current mirror circuit is connected to a resistive load by inputting the other output side terminal of the first current mirror circuit to the input terminal of the integrator. It is characterized by.

  According to the optical distance measuring device of the above embodiment, the light receiving element is connected between two paths through which the same constant current as the constant current source flows, and the amount of change corresponding to the photocurrent can be extracted. Since the input impedance of the element is reduced, a high-speed response is possible. In addition, since there are two paths through which the same constant current as the constant current source flows, one output side terminal of the first current mirror circuit is made the input terminal of the integrator at a predetermined timing by the switch. Input and connect the other output side terminal of the first current mirror circuit to the resistive load, or input the other output side terminal of the first current mirror circuit to the input terminal of the integrator and input the first current mirror circuit The direction of the current applied to the integrator can be reversed by switching whether one of the output side terminals is connected to the resistive load.

In addition, the optical distance measuring device of one embodiment,
The switch is a first switch and a second switch,
The accumulation / differential calculation unit includes a first accumulation unit and a second accumulation unit,
The light receiving element and the first switch and the second switch are disposed adjacent to each other,
The first storage unit is disposed adjacent to the first switch,
The second storage unit is disposed adjacent to the second switch,
The accumulation / differential calculation unit performs differential calculation of signals accumulated in the first accumulation unit and the second accumulation unit,
At least the light receiving element, the first switch, the second switch, the first accumulation unit, and the second accumulation unit are manufactured on the same semiconductor substrate.

  According to the optical distance measuring device of the above embodiment, the first and second switches are disposed adjacent to the light receiving element, and the first and second storage units are disposed adjacent to the first and second switches. Since these can be manufactured on the same semiconductor substrate, they can be integrated and configured, so that the size can be easily reduced and the manufacturing cost can be reduced. Further, the light receiving element and the storage / differential calculation unit (differential calculation, signal storage) can be configured by one.

  In one embodiment, the optical distance measuring device is configured such that the light receiving element, the first switch, the second switch, the first accumulation unit, and the second accumulation unit are left and right with respect to a center line of the light reception element. It is symmetric.

  According to the optical distance measuring device of the above embodiment, since the light receiving element, the first and second switches, and the first and second accumulating portions are symmetrical with respect to the central axis of the light receiving element, the first accumulation is performed. Since the charges are accumulated in the first and second accumulators without being biased, the distance measurement accuracy is improved and the background light can be effectively removed by the differential calculation.

  An optical distance measuring device according to an embodiment includes two units each including the light receiving element, the switch, and the accumulation / differential calculation unit.

  According to the optical distance measuring device of the above embodiment, it is possible to remove the influence of the received light intensity from the measurement object by providing two sets of units each having the light receiving element, the switch, and the accumulation / differential calculation unit. It is possible to measure the distance accurately.

In addition, the optical distance measuring device of one embodiment,
Two of the units are the first unit and the second unit,
The distance determination unit calculates a ratio between the output of the first unit and the output of the second unit, and determines a distance to the measurement object based on the ratio.

  According to the optical distance measuring device of the above embodiment, since the distance is determined by calculating the ratio of the outputs of the first and second units, the influence of background light can be removed, and the received light intensity from the measurement object can be reduced. Normalization is possible, and accurate distance measurement is possible.

In addition, the optical distance measuring device of one embodiment,
Two of the units are the first unit and the second unit,
When the switching time of the first unit is T, the switching time of the second unit is 2T or more.

  According to the optical distance measuring device of the above embodiment, since the switching time of the second unit is twice or more that of the first unit, the second unit can detect the intensity of light received from the measurement object. Can be effectively normalized by the received light intensity, and an accurate distance measurement can be performed.

  In the optical distance measuring device according to an embodiment, the switching signal for driving the switch changes between a first accumulation time zone that is driven at a switching time T and a second accumulation time zone that is driven at a switching time of 2T or more. It is characterized by.

  According to the optical distance measuring device of the above embodiment, by operating at switching time T and 2T or longer, the result measured at switching time T is held, and then the result measured at switching time 2T is measured with the same element. . Since the distance can be calculated from these two results, it is not necessary to use two units, and the apparatus can be miniaturized.

  The optical distance measuring device according to one embodiment is characterized in that the modulation signal is a pulse wave.

  According to the optical distance measuring device of the above embodiment, since the modulation signal is a pulse wave, the resolution can be made constant over the entire distance measuring range.

In addition, the optical distance measuring device of one embodiment,
The switching times of the first unit and the second unit are substantially the same,
The modulation signal includes a sine wave signal.

  According to the optical distance measuring device of the above embodiment, since the modulation signal is a sine wave and the switching times of the first and second units are substantially the same, the background light can be effectively removed, and the light reception signal Therefore, accurate distance measurement can be performed.

In addition, the optical distance measuring device of one embodiment,
Two of the units are the first unit and the second unit,
The accumulation / differential operation units of the first and second units each have an integrator using a capacitance element,
The capacitance value of the capacitance element used for the integrator of the storage / differential operation unit of the first unit is substantially the same as the capacitance value of the capacitance element used for the integrator of the storage / differential operation unit of the second unit. It is characterized by being.

  According to the optical distance measuring device of the above embodiment, since the capacitance elements constituting the integrator of the first unit and the second unit have substantially the same capacitance value, the received light intensity can be normalized effectively.

Also, in the optical distance measuring device of one embodiment, two of the above units are a first unit and a second unit,
The first unit and the second unit are manufactured on the same semiconductor substrate.

  According to the optical distance measuring device of the above embodiment, since the first unit and the second unit are fabricated on the same semiconductor substrate, the difference between the elements constituting the first and second units is eliminated. Therefore, it is possible to effectively remove the influence of the background light and to measure the distance with high accuracy.

  In one embodiment of the optical distance measuring device, the light emitting element is a light emitting diode.

  According to the optical distance measuring device of the above embodiment, since the light emitting element is a light emitting diode, an optical distance measuring device capable of measuring a distance with high accuracy even in an environment with strong background light can be realized.

  In one embodiment of the optical distance measuring device, the light emitting element is a laser diode.

  According to the optical distance measuring device of the above-described embodiment, since the light emitting element is a laser diode, it is possible to irradiate light with a high energy density to a farther measurement object, so that the measurable range of distance can be increased. Can be enlarged.

  An optical distance measuring device according to an embodiment includes a scanning mechanism that scans a light beam emitted from the light emitting element.

  According to the optical distance measuring device of the above embodiment, since the scanning mechanism for the light beam emitted from the light emitting element is provided, it is possible to measure the distance to a wide range of objects, and the optical distance measuring device according to the present invention. The application range of can be expanded.

  As is clear from the above, according to the optical distance measuring device of the present invention, since the storage unit does not saturate with noise components even in an environment where the background light is very strong such as outdoors, it is possible to obtain sufficient signal components. It is possible to detect the travel time of light and calculate the distance with high accuracy.

  The optical distance measuring device of the present invention will be described in detail below with reference to the illustrated embodiments.

(First embodiment)
FIG. 1 is a block diagram of the optical distance measuring device according to the first embodiment of the present invention, and FIG. 2 is a timing chart showing the operation of the optical distance measuring device. An outline of the optical distance measuring device of the present invention will be described with reference to FIGS.

  As shown in FIG. 1, this optical distance measuring device receives a light beam 11 reflected by the measurement object 12 and a transmitter 1 that emits a light beam 11 as an optical signal to the measurement object 12. And a signal processing unit 3 for processing a signal from the receiver 2.

  The transmitter 1 includes a light emitting element 4 that emits an optical signal synchronized with a modulation signal having a predetermined repetition frequency, and a modulation signal generator 5 that outputs the modulation signal to the light emitting element 4.

The receiver 2 receives the light beam 11 reflected by the measurement object 12 and converts it into an electrical signal, and receives a signal from the modulation signal generator 5. The switch 7 switches the electrical signal of the two paths to the two paths at a predetermined timing, and the first and second storage units 8a and 8b that store the electrical signals of the two paths switched by the switch 7, respectively. . The switch 7 receives the switching signals SW _A and SW _B from the modulation signal generator 5 and performs a switching operation.

  The signal processing unit 3 includes a differential calculation unit 9 that performs a differential calculation of the electrical signals stored in the first and second storage units 8a and 8b, and a differential calculation result of the differential calculation unit 9. And a distance determination unit 10 that determines the distance to the measurement object 12 based on the above.

  The first and second accumulators 8a and 8b and the differential operation unit 9 constitute an accumulation / differential operation unit.

As shown in FIG. 1, a light beam 11 is emitted from a light emitting element 4 toward a measurement object 12 in synchronization with a signal from a modulation signal generator 5. Here, the light emission signal (modulation signal) is a pulse wave having a constant repetition frequency with a pulse width t ₀ as shown in FIG. However, the modulation signal is not limited to a pulse wave, and any function can be obtained as long as it has a shape that can be expressed as a time function, such as a triangular wave, a sawtooth wave, or a sine wave. Details of each modulation signal other than the pulse wave will be described later.

As shown in FIG. 2B, the light beam 11 reflected by the measurement object 12 is phase-delayed from the modulation signal by the time (t ₁ ) when the light beam 11 reciprocates the distance to the measurement object 12. It is detected by the light receiving element 6. Here, Ip represents the received light signal intensity due to the reflected light, and Ib represents the noise intensity due to the background light. Now, when the range that can be measured is 7.5 m, it can be easily calculated that the pulse width needs 50 nsec from (Equation 1). Furthermore, since the background light is at most about several tens of kHz, its period is about several tens of μsec, which is sufficiently large for the pulse width of 50 nsec. Therefore, as shown in FIG. Can be considered.

Thereafter, the path of the received light signal is switched by the switch 7 at the timing of the switching signals SW _A and SW _B (shown in FIGS. 2C and 2D). A first accumulation unit 8a is provided in the switched first route (Ach). Like the Ach signal shown in FIG. 2 (e), per period of the modulation signal,
(Ip (t ₀ −t _l ) + Ib · t ₀ )
Is stored in the first storage section 8a. Further, the second path (Bch) includes a second storage unit 8b. Like the Bch signal shown in FIG.
(Ip · t _l + Ib · t ₀ )
Is stored in the second storage unit 8b.

The outputs of the first and second accumulating units 8a and 8b are respectively input to the signal processing unit 3, and the difference is calculated by the differential operation unit 9. The differential signal after the differential calculation can be expressed by the following (Equation 3) using the number of integrations N.

From the above, the background light is completely removed after the differential calculation, and the number of integrations N may be set so that the signal amount is sufficient. Therefore, the distance determination unit 10 calculates the time t from (Equation 3). _A distance value can be obtained by calculating 1 and substituting it into (Equation 1).

  However, the distance can be measured using (Equation 3) when the received light signal intensity Ip is known. For example, the transmitter and the receiver are opposed to each other, and the light energy is obtained by using coherent light such as a laser as the light emitting element. This is limited to the case where a measurement system that directly receives light without dispersing the light is used. In such a case, since the emission energy and the light reception energy are equal, the distance can be measured using (Equation 3) by measuring the light reception signal intensity Ip in advance. As described above, the distance can be obtained using only (Equation 3) only in a specific case. In a general distance measuring device, the transmitter and the receiver are arranged at the same position, and the reflected light from the measurement object is obtained. Most applications detect and measure the time that light travels back and forth the distance to the measurement object.

  Therefore, by providing two sets of units each having the receiver 2 and the differential operation unit 9, it is possible to detect the reflected light from the measurement object and measure the distance. Details will be described below.

(Second embodiment)
FIG. 3 is a block diagram of an optical distance measuring device according to a second embodiment of the present invention, and FIG. 4 is a timing chart showing its operation. The outline of the optical distance measuring device of the present invention will be described with reference to FIGS. In FIG. 3, the same components as those in FIG. 1 are denoted by the same reference numerals.

  As shown in FIG. 3, the optical distance measuring device receives a light beam 11 reflected by the measurement object 12 and a transmitter 1 that emits a light beam 11 as an optical signal to the measurement object 12. And a signal processing unit 3 for processing a signal from the receiver 2.

  The transmitter 1 includes a light emitting element 4 that emits an optical signal synchronized with a modulation signal having a predetermined repetition frequency, and a modulation signal generator 5 that outputs the modulation signal to the light emitting element 4.

  The receiver 2 receives the light beam 11 reflected from the measurement object 12 and converts the light beam 11 into electric signals, and the signals from the modulation signal generator 5. The first and second switches 7A and 7B that switch the electrical signals from the first and second light receiving elements 6A and 6B at a predetermined timing, and the electrical signals of the two paths switched by the first switch 7A are received. The first and second accumulators 8a and 8b for accumulating, respectively, and the third and fourth accumulators 8c and 8d for accumulating electric signals of the two paths switched by the second switch 7B, respectively. Yes. The first and second switches 7 </ b> A and 7 </ b> B perform a switching operation by switching signals SW <b> 1 to SW <b> 4 from the modulation signal generator 5.

  The signal processing unit 3 includes a first differential operation unit 9A that performs a differential operation of the electrical signals accumulated by the first and second accumulation units 8a and 8b, and third and fourth accumulation units 8c, A second differential operation unit 9B that performs a differential operation of the electrical signal accumulated by 8d, and the measurement object 12 based on the differential operation results of the first and second differential operation units 9A and 9B. A distance determination unit 10 for determining the distance.

  The first to fourth accumulation units 8a, 8b, 8c, 8d and the first and second differential operation units 9A, 9B constitute an accumulation / differential operation unit. Here, the first light receiving element 6A, the first switch 7A, the first and second storage units 8a and 8b, and the first differential operation unit 9A constitute a first unit, and the second light receiving element 6B and the second switch 7B, the third and fourth accumulation units 8c and 8d, and the second differential operation unit 9B constitute a second unit.

となる。 As shown in FIG. 3, the light beam 11 reflected by the measurement object 12 is detected by the first light receiving element 6a and the second light receiving element 6b. For the first and second paths of the first unit indicated by the reference number “A” in FIG. 3, as shown in FIG. 4 (a) to FIG. 4 (f), FIG. Processing is performed in the same manner as the timing shown in FIG. Therefore, the output of the first unit to the (first and second routes) path is the same as in (Equation 3),

It becomes.

On the other hand, for the first and second paths of the second unit indicated by the sub-number “B” of the reference number, FIG. 4 (a), FIG. 4 (b), FIG. at the timing of the 4 (j) are shown as light emitting signal (shown in FIG. 4 (g) and FIG. 4 (h)) (FIG. 4 (shown in a)) the switching signal SW3 of the pulse width 2t ₀ synchronized with, SW4 The path is switched by the switch 7b. The first path (Cch) of the switched second unit is provided with a third accumulation unit 8c, as shown in FIG.
Ip (t ₀ ) + Ib · 2t ₀
Is stored in the third storage unit 8c. Further, the second path (Dch) of the second unit is provided with a fourth accumulation unit 8d, and as shown in FIG.
Ib ・ 2t ₀
Is stored in the fourth storage unit 8d.

The outputs of the third and fourth accumulators 8c and 8d are input to the signal processor 3, and the difference is calculated by the differential calculator 9. The signal after the differential operation can be expressed by the following (Equation 5).

As described above, the switching time t ₀ is known as the differential calculation result of the second unit path by setting the switching time to be twice or more the path of the first unit with respect to the path of the second unit. The shape depends on the reflected light intensity Ip.

Assuming that the first differential signal is S ₁ and the second differential signal is S ₂ , the distance (L) to the measurement object 12 is the ratio S ₁ / S ₂ of both differential calculation results in the distance determination unit 10. Can be detected by taking

となり、次の(式６)が導き出され、距離(Ｌ)は検出することができる。

That is,
S ₁ / S ₂ = N · Ip (t ₀ −2t _l ) / N · Ip (t ₀ ) = (t ₀ −2t _l ) / t ₀

Then, the following (Expression 6) is derived, and the distance (L) can be detected.

Here, the switching time of the path of the second unit is set to 2t ₀ as shown in FIG. 4 for simplicity, but if the path of the second unit is not less than twice the path of the first unit in particular, the entire reflected signal light is the second unit. Since it is included in one route, the same effect can be obtained. However, when it is longer than twice, the amount of charge accumulated by the background light only increases, and as shown in FIG. 4, it is most preferable when it is twice the switching time of the path of the first unit.

  In the second embodiment described above, the first switching signal shown in FIGS. 4 (c) and 4 (d) and the second switching signal shown in FIGS. 4 (g) and 4 (h) are used. Was driving another unit, but in a single unit configuration, the first switching signal in the first accumulation time zone and the second switching signal in the second accumulation time zone are measured with a time difference. However, the same effect can be obtained. In this case, there is no difference in which of the first and second switching signals is calculated first, and the first measurement result is held using a memory or sample hold circuit and then measured with another switching signal. The distance value can be obtained by performing a predetermined calculation using the obtained result.

  In FIG. 4, the pulse wave is used as the modulation signal applied to the light emitting element. This is because when the modulation signal is a pulse wave, the light reception waveform also becomes a pulse wave, and when the reflected signal light is received, the same light reception intensity (a constant value) is maintained. Therefore, the accumulated amount of each signal is the distance to the measurement object 12 (L). Therefore, it has linearity (linearity) over the entire range. Thereby, the resolution can be made constant over the entire distance measurement range. On the other hand, when a triangular wave or a sawtooth wave is used for the modulation signal, the received light waveform is a linear function of time, and the accumulated amount is a quadratic function. It is preferable to appropriately use these according to the application.

  According to the optical distance measuring device, two sets of units each having a light receiving element, a switch, and an accumulation / differential calculation unit are provided, and the influence of the light receiving intensity from the measurement object 12 can be removed. Accurate distance measurement is possible.

  Further, since the distance is determined by calculating the ratio of the outputs of the first and second units, the influence of the background light can be removed, the received light intensity from the measurement object 12 can be normalized, and the accurate distance Can be measured.

(Third embodiment)
Next, FIG. 5 shows a block diagram showing the configuration of the optical distance measuring device of the third embodiment of the present invention when the modulation signal is a sine wave, and FIG. 6 shows a timing chart thereof. In FIG. 5, the same components as those in FIG. 1 are denoted by the same reference numerals.

  As shown in FIG. 5, this optical distance measuring device receives a light beam 11 reflected by the measurement object 12 and a transmitter 1 that emits a light beam 11 as an optical signal to the measurement object 12. And a signal processing unit 3 for processing a signal from the receiver 2.

  The transmitter 1 includes a light emitting element 4 that emits an optical signal synchronized with a modulation signal having a predetermined repetition frequency, and a modulation signal generator 5 that outputs the modulation signal to the light emitting element 4.

The receiver 2 receives the light beam 11 reflected by the measurement object 12 and converts it into an electrical signal, and receives a signal from the modulation signal generator 5. Switch 7 for switching the electrical signal of the four paths at a predetermined timing, and first to fourth accumulation units 8a, 8b, 8c, 8d for accumulating the electrical signals of the four paths switched by the switch 7, respectively. Have. The switch 7 performs a switching operation according to the switching signals SW _{A to} SW _D from the modulation signal generator 5.

  The signal processing unit 3 includes a first differential operation unit 9A that performs a differential operation of the electrical signals accumulated by the first and third accumulation units 8a and 8c, and a second and fourth accumulation unit 8b, A second differential operation unit 9B that performs a differential operation of the electrical signal accumulated by 8d, and the measurement object 12 based on the differential operation results of the first and second differential operation units 9A and 9B. A distance determination unit 10 for determining the distance.

  The first to fourth accumulation units 8a, 8b, 8c, 8d and the first and second differential operation units 9A, 9B constitute an accumulation / differential operation unit.

Emission signal of the light emitting element 4 (modulation signal) is oscillated at a period 4t ₀ as shown in FIG. 6 (a), the light receiving signal, to the object of measurement 12 as shown in FIG. 6 (b) The light is detected by the light receiving element 6 with a phase delay of the distance (L) by the time t ₁ when the light reciprocates. The signals detected by the light receiving element 6 are switched to four paths by the switch 7 at the timing of the switching signals SW _{A to} SW _D (shown in FIGS. 6C to 6F), and the first to fourth accumulations are performed. Stored in the units 8a, 8b, 8c and 8d, respectively. Here, the durations of the four switching signals SW _{A to} SW _D shown in FIGS. 6C to 6F are arbitrary times within a quarter period (t ₀ ) of the sine wave of the modulation signal. .

Of the signals accumulated in the first to fourth accumulation units 8a, 8b, 8c, and 8d after being divided into four, the first difference between the signal of the first accumulation unit 8a and the signal of the third accumulation unit 8c. The differential calculation is performed by the dynamic calculation unit 9A, and the differential calculation is performed by the second differential calculation unit 9B on the signal of the second storage unit 8b and the signal of the fourth storage unit 8d. After the differential calculation by the first and second differential operation units 9A and 9B, there are storage units (not shown), and signals are stored a plurality of times. By performing the following processing on the accumulated differential signals in the distance determination unit 10, the phase of the received light signal can be obtained, and the object to be measured is determined by the phase difference from the modulation signal (shown in FIG. 6 (a)). The distance (L) up to 12 can be detected by the following (Equation 7).

で表される。同様に、積分値Ｂは、

ここで、ｔ₁＝ｔ₀＋π／4＝ｔ₀＋π／(2ω)であるから、

で表される。また、積分値Ｃは、

ここで、ｔ₂＝ｔ₀＋π／2＝ｔ₀＋π／ωであるから、

で表される。また、積分値Ｄは、

ここで、ｔ₃＝ｔ₀＋3π／2＝ｔ₀＋3π／(2ω)であるから、

で表される。したがって、

となり、これより、

となり、

が得られる。
ｔ₀のときの発光波形の出力が、
ωｔ₀＋ψ＝ｎ・２π／ω (ただしｎ＝０,１,２,…)
となるように、ｔ₀とψとの関係を固定すると、

となり、特にψ＝０とするとき、

となり、(式１)におけるΔｔは、

で表され、これを式１に代入することにより(式７)が導かれる。 The derivation process of (Equation 7) will be described below.
The light emission waveform and light reception waveform are arbitrary sine wave functions g (t), f (t),
g (t) = c · exp {j (ωt + ψ)} + d
f (t) = a · exp {j (ωt + φ)} + b
In this case, the phase difference between the light emission waveform and the light reception waveform can be expressed by φ−ψ. In order to obtain this, the following calculation is performed.
In the received light waveform represented by the function f (t), A is the first interval, B is the second interval, C is the third interval, and D is the integration value of the fourth interval. It is assumed that the first section to the fourth section are out of phase by 90 degrees. Then, the integral value A is

It is represented by Similarly, the integral value B is

Here, since t ₁ = t ₀ + π / 4 = t ₀ + π / (2ω),

It is represented by The integral value C is

Here, since t ₂ = t ₀ + π / 2 = t ₀ + π / ω,

It is represented by The integral value D is

Here, since t ₃ = t ₀ + 3π / 2 = t ₀ + 3π / (2ω),

It is represented by Therefore,

And from this,

And

Is obtained.
The output of the emission waveform at t ₀ is
ωt ₀ + ψ = n · 2π / ω (where n = 0, 1, 2,...)
If the relationship between t ₀ and ψ is fixed so that

Especially when ψ = 0,

And Δt in (Equation 1) is

(Equation 7) is derived by substituting this into Equation 1.

  When a sine wave is used for the modulation signal, the light receiving element 6, the switch 7 for switching to the first to fourth accumulation units 8a, 8b, 8c, and 8d with four switching signals shifted in phase by 90 degrees and the first accumulation unit 8a And a differential calculation unit of the third storage unit 8c and a differential calculation unit of the second storage unit 8b and the fourth storage unit 8d, and a single light receiving element 6 obtains a measurement value necessary for calculating the distance. be able to. Although FIG. 6 shows an example of sinusoidal modulation as a continuous wave, the same effect can be obtained by modulating a light emission signal with a sinusoidal wave having one or more cycles generated intermittently.

となり、同様に(式７)を書き換えかえると、

となる。 Further, the signals S ₁ , S ₂ , S _{A to} S _D shown in the above (Equation 6) and (Equation 7) are expressed as charge amounts. Generally, when a signal is detected, it is converted into a voltage and read. The stored charge amount Q is between the capacitance C and the potential V.
Q = CV ......... (Formula 8)
The relationship holds. Therefore, the signal amounts indicated by S ₁ , S ₂ , S _{A to} S _D in (Expression 6) and (Expression 7) are as follows when handled as potentials.
V = Q / C = S / C (Equation 9)
When (Equation 6) is rewritten using this (Equation 9),

Similarly, when (Equation 7) is rewritten,

It becomes.

Here, C ₁ and C ₂ are capacitances of capacitance elements provided after differential calculation of the path of the first unit and the path of the second unit, respectively. As shown in (Equation 10) and (Equation 11), when the capacitance values of both capacitance elements are equal, the capacitance values are normalized and do not affect the calculation result.

  Moreover, since it is preferable that the first unit and the second unit have the same characteristics, it is preferable that the first unit and the second unit are integrated on the same semiconductor substrate.

  According to the optical distance measuring device having the above configuration, since background light such as outdoors does not saturate with a noise component even in a very strong environment, the light travel time is detected from a sufficient signal component, and high accuracy is achieved. It is possible to perform a simple distance calculation.

  The signal processing method and the outline of the configuration for removing the influence of background light have been described above. Specific examples of each configuration will be described in detail according to the following fourth to eighth embodiments.

(Fourth embodiment)
FIG. 7 is a circuit configuration diagram of an optical distance measuring device according to a fourth embodiment of the present invention. The configuration of the fourth embodiment of the present invention will be described with reference to FIG. FIG. 7 shows a part of the receiver 2 and the signal processing unit 3 shown in FIGS. 1, 3 and 5, and the light receiving element 6 and the first and second storage units 8a and 8b and the difference between them. The dynamic calculation unit 9 represents “1 unit”. The optical distance measuring device is configured using one or two of the configurations in FIG. 7 (first unit and second unit). Hereinafter, although the same effect as in FIG. 7 is described, different configurations will be described in the respective embodiments. However, they can be used in combination so that the above-described functions can be realized. The description of this combination is omitted in the following embodiments.

  As shown in FIG. 7, the cathode of the light receiving element 6 whose anode is connected to the ground is connected to the input terminal of the switch 7. One output terminal of the switch 7 is connected to an inverting input terminal of an operational amplifier (hereinafter referred to as an operational amplifier) 13a, and a capacitance element 14a is connected between the output terminal and the inverting input terminal of the operational amplifier 13a. The other output terminal of the switch 7 is connected to the inverting input terminal of the operational amplifier 13b, and the capacitance element 14b is connected between the output terminal and the inverting input terminal of the operational amplifier 13b. The non-inverting input terminals of the operational amplifiers 13a and 13b are connected to the reference potential Vs. The output terminals of the operational amplifiers 13 a and 13 b are connected to the differential operation unit 9, and the output voltage Vo is output from the output terminal of the differential operation unit 9.

  In FIG. 7, the optical signal detected by the light receiving element 6 is switched between the first path and the second path by the switch 7 at the timing shown in FIGS. Here, the upper side of FIG. 7 is a first path, and the lower side is a second path. In both paths, an integrator composed of operational amplifiers 13a and 13b and capacitance elements 14a and 14b is configured, and a signal detected by the light receiving element 6 is accumulated. This integrator is the first and second accumulators 8a and 8b shown in FIGS. The first and second accumulators 8a and 8b accumulate signals for a predetermined number of times over a plurality of periods of the modulation signal. The first and second accumulators 8a and 8b input a signal represented by (Equation 3) and the like to the differential operation unit 9.

  By configuring the integrator using the capacitance elements 14a and 14b as the storage unit, it is possible to easily configure a high-speed response integrator, and it is possible to appropriately store the distributed charges.

となる。(式１２Ａ),(式１２Ｂ)に示すように、第１,第２積分器(８a,８b)を構成するキャパシタンス素子１４a,１４bの容量値が異なると、差動演算結果は一定のオフセットをもつようになる。差動演算の結果を用いて距離を判定するため、オフセット電位の存在は誤差を生む要因となり好ましくない。 The input to the integrator is a current (charge amount), but the output is a voltage, and the differential operation unit 9 is also configured as a voltage process. Therefore, the equation (8) as a reference, the first integrator capacitance element values of the capacitance elements 14a of (8a) and C _1, the second integrator capacitance element value of the capacitance element 14b of (8b) C ₂ Then, taking the timing of FIG. 2 as an example, the output of the first and second integrators (8a, 8b) is

It becomes. As shown in (Expression 12A) and (Expression 12B), if the capacitance values of the capacitance elements 14a and 14b constituting the first and second integrators (8a and 8b) are different, the differential calculation result has a certain offset. It will have. Since the distance is determined using the result of the differential operation, the presence of the offset potential is not preferable because it causes an error.

と表すことができ、(式３)の出力と等価となる。同様に、スイッチングのタイミングを図４や図６のように変更することにより、図７の構成を用いてそれぞれの効果を得ることが可能であるが、説明は重複するので省略する。以後の各実施形態においても同様にそれぞれの構成でスイッチングのタイミングを変更することによりそれぞれの差動演算結果が得られることは明らかであり、以後の実施形態においてこの説明は省略する。 For this reason, the capacitance elements 14a and 14b constituting the first and second integrators (8a and 8b) have the same capacitance value. Furthermore, since the characteristic deviation between the two integrators also causes an error, the error due to the characteristic difference can be reduced ideally by being manufactured with the same structure on the same semiconductor substrate. At this time, since C ₁ = C ₂ , the output voltage Vo in FIG.

Which is equivalent to the output of (Equation 3). Similarly, by changing the switching timing as shown in FIG. 4 and FIG. 6, it is possible to obtain the respective effects using the configuration of FIG. Similarly, in each of the subsequent embodiments, it is obvious that each differential operation result can be obtained by changing the switching timing in each configuration. This description is omitted in the following embodiments.

  In the configuration of the fourth embodiment, the charges accumulated in each integrator are accumulated simultaneously by the signal light and the background light. For this reason, in an environment where the background light is strong, the differential calculation result is not affected by the background light, but the output of the integrator is greatly affected by the background light. That is, the magnitude of the output of the differential calculation unit 9 is greatly influenced by the intensity of the background light, and it is necessary to increase the capacitance value of the capacitance element used for the integrator. If the capacitance value is increased, the integrator As a result, it is difficult to increase the accuracy of distance measurement. A configuration for solving such a problem will be described in the following embodiments.

(Fifth embodiment)
FIG. 8 is a circuit configuration diagram of an optical distance measuring device according to a fifth embodiment of the present invention. The configuration of the fifth embodiment of the present invention will be described with reference to FIG.

  As shown in FIG. 8, the anode of the first light receiving element 26A having the cathode supplied with the power supply voltage Vcc is connected to one input terminal of the switch 27, and the cathode of the second light receiving element 26B having the anode connected to the ground. Is connected to the other input terminal of the switch 27. One output terminal of the switch 27 is connected to the inverting input terminal of the operational amplifier 21, and the capacitance element 22 is connected between the output terminal of the operational amplifier 21 and the inverting input terminal. The non-inverting input terminal of the operational amplifier 21 is connected to the reference potential Vs. The output voltage Vo is output from the output terminal of the operational amplifier 21.

と表すことができる。図２,図４,図６においてスイッチ２７が各端子に接続する持続時間(ｔ_０)は同じであるため、(式１５)は以下のように書き直すことができる。

In FIG. 8, the upper side is the first light receiving element 26A, and the lower side is the second light receiving element 26B. The signal light is evenly irradiated onto the light receiving surfaces of the first and second light receiving elements 26A and 26B by an appropriate optical system. The switch 27 is switched to the anode of the first light receiving element 26A and the cathode of the second light receiving element 26B at the timings shown in FIGS. The photocurrent of the light receiving element selected by the switch 27 is accumulated in an integrator having the same configuration as in the fourth embodiment. Here, since the switch 27 is switched to the anode terminal of the first light receiving element 26A and the cathode terminal of the second light receiving element 26B, the switch 27 is connected to the first light receiving element 26A side as shown in FIG. when it is, photocurrent I ₁ acts in a direction flowing into the integrator, and when the switch 27 is connected to the second light receiving element 26B side, the photocurrent I ₂ is applied in a direction flowing out from the integrator To do. Since the first and second light receiving elements 26A and 26B are evenly irradiated with the reflected light, the first and second light receiving elements 26A and 26B have the same photocurrent value, and the magnitude Ip is used as follows. Can be expressed as
I ₁ = Ip · f (t) (Equation 14A)
I ₂ = Ip · g (t) ……… (Formula 14B)
Here, f (t) and g (t) represent the waveforms (time functions) of I ₁ and I ₂ , respectively.
Therefore, the output (Vo) of the integrator is

It can be expressed as. In FIGS. 2, 4, and 6, since the duration (t ₀ ) during which the switch 27 is connected to each terminal is the same, (Equation 15) can be rewritten as follows.

  As described above, according to the optical distance measuring device of the fifth embodiment, the integrator (21, 22) using the capacitance element 22 performs the differential operation while accumulating the electric signals of the two paths. Since the number of parts can be reduced and the error of the differential calculation can be eliminated ideally, the distance can be measured with higher accuracy.

  Further, by switching the switch 27, the effect of differential calculation can be obtained by inverting the direction of the current applied to the integrators (21, 22) at a predetermined timing. In addition, the signal component of the calculation result can be accumulated.

  In the configuration of FIG. 8, the direction of the photocurrent applied to the integrator is reversed by switching, so that the differential calculation is realized with one integrator, and the capacitance difference and the characteristic difference of the integrator are ideal. Therefore, it can be set to 0.

(Sixth embodiment)
FIG. 9 is a circuit configuration diagram of an optical distance measuring device according to the sixth embodiment of the present invention. The configuration of the sixth embodiment of the present invention will be described with reference to FIG. Here, the first current mirror circuit 33a is a discharge type current mirror circuit including one input side terminal and two output side terminals through which a current having the same value as the current flowing through the input side terminal flows. The second current mirror circuit 33b is a suction type current mirror circuit including one input side terminal and one output side terminal through which a current having the same value as the current flowing through the input side terminal flows.

  As shown in FIG. 9, the cathode of the light receiving element 36 having the anode connected to the ground is connected to the input side terminal of the first current mirror circuit 33a. One output side terminal of the first current mirror circuit 33a is connected to the input side terminal of the second current mirror circuit 33b, and the other output side terminal of the first current mirror circuit 33a is connected to one input terminal of the switch 37. The other input terminal of the switch 37 is connected to the output side terminal of the second current mirror circuit 33b. The output terminal of the switch 37 is connected to the inverting input terminal of the operational amplifier 31, and the capacitance element 32 is connected between the output terminal of the operational amplifier 31 and the inverting input terminal. The non-inverting input terminal of the operational amplifier 31 is connected to the reference potential Vs. The output voltage Vo is output from the output terminal of the operational amplifier 31.

9, the photocurrent I ₁ detected by the light receiving element 36 is a current signal I ₁ having the same current value by the first current mirror circuit 33a of the discharge type two produce. One flows I ₁ into _one terminal of the switch 37, the other flows directly into the suction type second current mirror circuit 33 b, and the second current mirror circuit 33 _b sucks I ₂ from the switch 37. First, second current mirror circuit 33a, since the replicating optical current magnitude of I ₁ and I ₂ in 33b is the same (Ip), the current to be applied to the integrator as shown from the switch 37 Since the direction can be reversed, the output (Vo) of the integrator can be expressed as (Equation 16) as in the fifth embodiment.

  As described above, according to the optical distance measuring device of the sixth embodiment, the integrator (31, 32) using the capacitance element 32 performs the differential operation while accumulating the electric signals of the two paths. Since the number of parts can be reduced and the error of the differential calculation can be eliminated ideally, the distance can be measured with higher accuracy.

  Further, by switching the switch 37, the effect of differential operation can be obtained by inverting the direction of the current applied to the integrators (31, 32) at a predetermined timing. In addition, the signal component of the calculation result can be accumulated.

  In this sixth embodiment, since only one integrator and one light receiving element are used, the characteristic difference between the two integrators related to the fourth embodiment, the irradiation unevenness between the two light receiving elements related to the fifth embodiment, etc. The output difference due to can be ideally zero.

(Seventh embodiment)
FIG. 10A is a circuit configuration diagram of an optical distance measuring device according to a seventh embodiment of the present invention. The configuration of the seventh embodiment of the present invention will be described with reference to FIG. 10A. Here, the first current mirror circuit 43a is a discharge type current mirror circuit including one input side terminal and two output side terminals through which a current having the same value as the current flowing through the input side terminal flows. The second current mirror circuit 43b is a suction-type current mirror circuit including one input side terminal and two output side terminals through which a current having the same value as the current flowing through the input side terminal flows.

  As shown in FIG. 10A, the negative side of the constant current source 44 is connected to the input side terminal of the first current mirror circuit 43a, and the positive side of the constant current source 44 is connected to the input side terminal of the second current mirror circuit 43b. ing. The cathode of the light receiving element 46 is connected to one output side terminal of the first current mirror circuit 43a, and one output side terminal of the first current mirror circuit 43a is connected to the other output side of the second current mirror circuit 43b. Connected to the terminal. The anode of the light receiving element 46 is connected to one output side terminal of the second current mirror circuit 43b, and one terminal of the second current mirror circuit 43b is connected to the other output side terminal of the first current mirror circuit 43a. is doing. The first output terminal 48a connected to the other output side terminal of the first current mirror circuit 43a is connected to one input terminal of each of the switches 47a and 47b. A second output terminal 48b connected to one output side terminal of the first current mirror circuit 43a is connected to the other input terminal of each switch 47a, 47b. The output terminal of the switch 47a is connected to the inverting input terminal of the operational amplifier 41, and the capacitance element 42 is connected between the output terminal of the operational amplifier 41 and the inverting input terminal. The non-inverting input terminal of the operational amplifier 41 is connected to the reference potential Vs. The output voltage Vo is output from the output terminal of the operational amplifier 41.

In FIG. 10A, the constant current source 44 supplies a constant DC current I ₀ , and this current I ₀ is input to the discharge-type first current mirror circuit 43 a and the suction-type second current mirror circuit 43 b, respectively. Further, the first and second output terminals 48a and 48b respectively connected to the output side terminals of the first current mirror circuit 43a are connected to the integrators (41, 42) in the subsequent stage by the switch 47a (see FIG. 2). , See FIG. 4 and FIG. A first path is between the other output side terminal of the first current mirror circuit 43a and one output side terminal of the second current mirror circuit 43b, and the first output side terminal of the first current mirror circuit 43a The second path is between the other output side terminal of the two current mirror circuit 43b.

  In the switching state of the switches 47a and 47b shown in FIG. 10A, when the first output terminal 48a is connected to the integrator (41, 42), the second output terminal 48b has a resistance R as an example of a load resistance. Is connected to the reference potential Vs through the ground and grounded. Conversely, in the switching state of the switches 47a and 47b shown in FIG. 10B, when the second output terminal 48b is connected to the integrator (41, 42), the first output terminal 48a is connected to the reference potential via the resistor R. Connected to Vs and grounded. The configuration of the integrators (41, 42) at the subsequent stage is the same as that in the previous first to sixth embodiments.

Since both the first path and the second path are directly connected by a current mirror circuit, the photocurrent generated by the light receiving element 46 is supplied to the first and second output terminals 48a and 48b as a current difference from the constant current source 44. appear. For example, in the switching state of the switches 47a and 47b shown in FIG. 10A, when the photocurrent Ip is generated by the light receiving element 46, I ₀ flows out from one output side terminal of the first current mirror circuit 43a to the first path. current is separated by Ip at the cathode of the light receiving element 46, (I ₀ -Ip) is directed to the other output terminal of the second current mirror circuit 43b. However, since the input terminal of the second current mirror circuit 43b is connected to the constant current source 44, the current I ₀ is always sucked into the other output terminal of the second current mirror circuit 43b. A current corresponding to the photocurrent Ip flows through the two output terminals 48b and the resistor R. Similarly, the current flowing out from the other output side terminal of the first current mirror circuit 43a to the second path by I ₀ is separated by I p at the first output terminal 48a, and (I ₀ -I p) becomes the second current. While going to one output side terminal of the mirror circuit 43b, a current corresponding to the photocurrent Ip flows out to the inverting input terminal side of the operational amplifier 41 through the first output terminal 48a.

Conversely, the switch 47a shown in FIG. 10B, when you switch 47b, the light receiving element 46 when the light current Ip is generated, in one first path from the output terminal of the first current mirror circuit 43a only I ₀ The flowing current is separated by Ip at the cathode of the light receiving element 46, and (I ₀ -Ip) is directed to the other output side terminal of the second current mirror circuit 43b. However, since the input terminal of the second current mirror circuit 43b is connected to the constant current source 44, the current I ₀ is always sucked into the other output terminal of the second current mirror circuit 43b. A current corresponding to the photocurrent Ip flows from the inverting input terminal side of the operational amplifier 41 through the two output terminal 48b. Similarly, the current flowing out from the other output side terminal of the first current mirror circuit 43a to the second path by I ₀ is separated by I p at the first output terminal 48a, and (I ₀ -I p) becomes the second current. The current corresponding to the photocurrent Ip flows out through the first output terminal 48a and the resistor R while going to one output side terminal of the mirror circuit 43b.

  In this way, since the direction of the current applied to the integrator (41, 42) can be reversed by the timing of the switches 47a, 17b, the output (Vo) of the integrator is the fifth embodiment, the sixth embodiment. It can express as (Formula 16) similarly.

  As described above, according to the optical distance measuring device of the seventh embodiment, the integrator (41, 42) using the capacitance element 42 performs the differential operation while accumulating the electric signals of the two paths. Since the number of parts can be reduced and the error of the differential calculation can be ideally eliminated, the distance can be measured with higher accuracy.

  Further, by switching the switches 47a and 17b, the direction of the current applied to the integrator (41, 42) can be reversed at a predetermined timing, so that the effect of differential operation can be obtained. The signal component of the calculation result can be accumulated while performing the dynamic calculation.

In the seventh embodiment, the same effect as in the sixth embodiment can be obtained, and the current of I ₀ always flows from the constant current source 44, and the input impedance of the light receiving element 46 can be lowered. Therefore, a high-speed response is possible compared to the sixth embodiment. For this reason, ranging accuracy can be remarkably improved.

(Eighth embodiment)
FIG. 11 is a cross-sectional view of the main part of the receiver of the optical distance measuring device according to the seventh embodiment of the present invention. The configuration of the eighth embodiment of the present invention will be described with reference to FIG.

  In FIG. 11A, a part surrounded by a dotted line is a main part of a receiver having the functions of a light receiving element, a switch, and an accumulating part. On the P-type semiconductor substrate 58, a light receiving part 56 as an example of the light receiving element. The first N-type diffusion layer is formed, and the second N-type diffusion layers serving as the first and second storage portions 50a and 50b are formed on both sides of the light receiving portion 56 with a predetermined interval therebetween. Further, between the light receiving unit 56 and the first storage unit 50a and between the light receiving unit 56 and the second storage unit 50b, an example of the first and second switches is formed on the P-type semiconductor substrate 58 by a gate oxide film and an electrode. Gates 51a and 51b are formed. The light receiving unit 56, the storage units 50a and 50b, and the gates 51a and 51b are symmetrical with respect to the center line CL of the light receiving unit 19. Furthermore, it is also targeted for a plane perpendicular to the paper surface including the center line CL.

  In addition, there is a differential operation unit 59 subsequent to the first and second storage units 50a and 50b made of the second N-type diffusion layer, and the difference between the signals detected by the first and second storage units 50a and 50b is output. (Vo). The first and second storage units 50a and 50b and the differential operation unit 59 constitute an accumulation / differential operation unit.

  FIG. 11B shows a potential distribution along the XIB-XIB line in FIG. In FIG. 11 (b), hν represents the energy of one photon (h is Planck's constant, and ν is the frequency of light).

  As shown in FIG. 11 (b), by applying a potential to the gate 51a, the potential below the gate 51a rises, and the optical carriers in the light receiving section 56 move to the left side in the figure along the potential step, and are most potential. Is accumulated in the first accumulation unit 50a, which is a high accumulation unit. The gates 51a and 51b correspond to the switches described with reference to FIGS. 2, 4, and 6. By appropriately switching the gates 51a and 51b at these timings, optical carriers are transferred to the first and second storage units 50a and 50b. Sorted. Thus, the carriers stored in the first and second storage units 50a and 50 are detected as potentials corresponding to the stored charge amounts as shown in (Equation 8), where C is the storage capacity. Then, the differential calculation unit 59 represents the differential calculation result of the potential corresponding to the charge amount stored in the first and second storage units 50a and 50b by (Expression 4), (Expression 5), and the like. Output in the form. Since the subsequent processing is as described above, it is omitted here. The first and second accumulators 50a and 50b have the same effect as the integrator.

  Here, since the optical carriers generated in the light receiving unit 56 are distributed to the left and right by the gates 51a and 51b, if the carrier generated in the light receiving unit 56 is biased, (Expression 3), (Expression 4), (Expression 5) ) Change in the first term and the second term, and the background light component cannot be properly removed and the distance is erroneously detected. For this reason, the light receiving unit 56, the first and second accumulating units 50a and 50b, and the gates 51a and 51b are symmetrical so that the optical carriers generated in the light receiving unit 56 are equally distributed to the left and right.

  According to the optical distance measuring device of the eighth embodiment, the light receiving unit 56, the gates 51a and 51b, and the first and second storage units 50a and 50b are symmetrical with respect to the central axis of the light receiving element. Since charges are accumulated in the first and second accumulators 50a and 50b without deviation, the distance measurement accuracy is improved and background light can be effectively removed by differential calculation.

  In the above first to eighth embodiments, as described above, in order to have a cm level resolution in a range of several meters as an optical distance measuring device, a response of several tens of nsec level as a modulation signal, that is, a response of MHz or more. There is a need for a light emitting device having LEDs and LDs are capable of such a high-speed response, and can be manufactured in a small size and at a low cost, so that they are suitable as light emitting elements for the optical distance measuring device of the present invention. LED (light emitting diode) is suitable for relatively short distance applications because its luminous flux diverges, and LD (laser diode) can emit collimated light, and can irradiate a measurement object at a high energy density and far away. It is suitable for long-distance use, but is not limited to this segregation. In order to improve the SN even in the optical distance measuring device with the background light countermeasures as described above, it is better that the signal light is as strong as possible when used outdoors during the day, and the LD is also used for short distance applications. It may be preferable.

  Furthermore, by using a scanning mechanism that scans the light beam emitted from the light emitting element in one dimension, a two-dimensional image can be obtained using the scanning angle and the measured distance value. Similarly, a three-dimensional distance image can be obtained by using a scanning mechanism that scans a light beam two-dimensionally.

FIG. 1 is a block diagram showing the configuration of the optical distance measuring device according to the first embodiment of the present invention. FIG. 2 is a timing chart showing the operation of the optical distance measuring device. FIG. 3 is a block diagram of an optical distance measuring device according to a second embodiment of the present invention. FIG. 4 is a timing chart showing the operation of the optical distance measuring device. FIG. 5 is a block diagram of an optical distance measuring device according to a third embodiment of the present invention. FIG. 6 is a timing chart showing the operation of the optical distance measuring device. FIG. 7 is a circuit configuration diagram showing a partial configuration of the optical distance measuring device according to the fourth embodiment of the present invention. FIG. 8 is a circuit configuration diagram showing a partial configuration of the optical distance measuring device according to the fifth embodiment of the present invention. FIG. 9 is a circuit configuration diagram showing a partial configuration of the optical distance measuring device according to the sixth embodiment of the present invention. FIG. 10A is a circuit configuration diagram showing a partial configuration of the optical distance measuring device according to the seventh embodiment of the present invention. FIG. 10B is a circuit configuration diagram for explaining the operation of the optical distance measuring device. FIG. 11 (a) is a cross-sectional view of the main part of the receiver of the optical distance measuring device according to the eighth embodiment of the present invention, and FIG. 11 (b) is taken along the line XIB-XIB in FIG. It is a figure which shows potential distribution. FIG. 12 is a schematic cross-sectional view showing a configuration of a main part of a conventional optical distance measuring device. FIG. 13 is a timing chart showing the operation of the optical distance measuring device. FIG. 14 is a timing chart showing the operation of the optical distance measuring device. FIG. 15 is a timing chart showing the operation of the optical distance measuring device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Transmitter 2 ... Receiver 3 ... Signal processing part 4 ... Light emitting element 5 ... Modulation signal generator 6, 26A, 26B, 36, 46 ... Light receiving element 6A ... 1st light receiving element 6B ... 2nd light receiving element 7, 27 , 37, 47a, 47b ... switch 7A ... first switch 7B ... second switch 8a, 50a ... first accumulating unit 8b, 50b ... second accumulating unit 8c ... third accumulating unit 8d ... fourth accumulating unit 9, 59 ... Differential calculation unit 9A ... first differential calculation unit 9B ... second differential calculation unit 10 ... distance determination unit 11 ... light beam 12 ... measurement object 13a, 13b, 21, 31, 41 ... operational amplifiers 14a, 14b, 22 , 32, 42 ... capacitance element 33a 43a ... first current mirror circuit 33b, 43b ... second current mirror circuit 44 ... constant current circuit 48a ... first output terminal 48b ... second output terminal 51a, 51b ... gate 56 ... light receiving part 58 ... P-type semiconductor substrate

Claims (25)

An optical distance measuring device that detects a distance to the measurement object by measuring a travel time from transmission of light to reception of light reflected by the measurement object,
A light emitting element that emits an optical signal synchronized with a modulation signal having a predetermined repetition frequency;
A light receiving element that reflects the optical signal from the light emitting element on the object to be measured, receives the reflected optical signal, and converts it into an electrical signal;
A switch for switching the electrical signal from the light receiving element to at least two paths at a predetermined timing;
An accumulation / differential operation unit for accumulating the electric signals switched by the switch, and for performing a differential operation of the accumulated electric signals;
An optical distance measuring device comprising: a distance determination unit that determines a distance to the measurement object based on a differential calculation result of the accumulation / differential calculation unit. The optical distance measuring device according to claim 1.
The accumulation / differential calculation unit has an integrator using a capacitance element,
An optical distance measuring device which accumulates the electric signal by the integrator. The optical distance measuring device according to claim 2,
The switch switches between the first route and the second route,
The integrator of the accumulation / differential operation unit is a first integrator connected to the first path and a second integrator connected to the second path,
The accumulation / differential calculation unit performs an optical difference calculation between the output of the first integrator and the output of the second integrator. The optical distance measuring device according to claim 3.
An optical distance measuring device characterized in that capacitance values of capacitance elements used in the first integrator and the second integrator are substantially the same. The optical distance measuring device according to claim 3.
An optical distance measuring device, wherein at least the light receiving element, the first integrator, and the second integrator are formed on the same semiconductor substrate. The optical distance measuring device according to claim 1.
The accumulation / differential calculation unit has an integrator using a capacitance element,
An optical distance measuring device that performs differential calculation while accumulating the electrical signal by the integrator. The optical distance measuring device according to claim 6,
The photocurrent detected by the light receiving element is switched by the switch, and the differential calculation is performed by reversing the direction of the photocurrent input to the input terminal of the integrator of the accumulation / differential calculation unit. An optical distance measuring device. The optical distance measuring device according to claim 7,
The light receiving element is a first light receiving element having a cathode connected to a power source and a second light receiving element having an anode connected to a reference potential.
The switch connects the anode of the first light receiving element to the input terminal of the integrator of the storage / differential operation unit at the predetermined timing, and connects the cathode of the second light receiving element to the storage / differential. An optical distance measuring device connected to an input terminal of the integrator of the arithmetic unit. The optical distance measuring device according to claim 8,
The optical distance measuring device, wherein the first light receiving element and the second light receiving element have the same structure and the same size. The optical distance measuring device according to claim 8,
An optical distance measuring device, wherein at least the first light receiving element and the second light receiving element are fabricated on the same semiconductor substrate. The optical distance measuring device according to claim 7,
A discharge-type first current mirror circuit that generates two currents of the same magnitude as the current flowing through the light receiving element;
A suction type second current mirror circuit that receives one of the two currents generated by the first current mirror circuit and generates a current of the same magnitude as the current;
The switch inputs the other of the currents generated by the first current mirror circuit to the input terminal of the integrator at the predetermined timing, or the current generated by the second current mirror circuit is An optical distance measuring device that switches whether to input to an input terminal of an integrator. The optical distance measuring device according to claim 7,
A constant current source;
A discharge-type first current mirror circuit that generates two currents having the same magnitude as the current flowing through the constant current source;
A suction-type second current mirror circuit that generates two currents of the same magnitude as the current flowing through the constant current source;
The anode of the first light receiving element is connected to one output side terminal of the first current mirror circuit, the cathode of the first light receiving element is connected to the other output side terminal of the first current mirror circuit,
The switch inputs one output side terminal of the first current mirror circuit to the input terminal of the integrator and connects the other output side terminal of the first current mirror circuit to a resistive load at the predetermined timing. Or switching between whether one output side terminal of the first current mirror circuit is connected to a resistive load by inputting the other output side terminal of the first current mirror circuit to the input terminal of the integrator. An optical distance measuring device. The optical distance measuring device according to claim 1.
The switch is a first switch and a second switch,
The accumulation / differential calculation unit includes a first accumulation unit and a second accumulation unit,
The light receiving element and the first switch and the second switch are disposed adjacent to each other,
The first storage unit is disposed adjacent to the first switch,
The second storage unit is disposed adjacent to the second switch,
The accumulation / differential calculation unit performs differential calculation of signals accumulated in the first accumulation unit and the second accumulation unit,
At least the light receiving element, the first switch, the second switch, the first accumulation unit, and the second accumulation unit are fabricated on the same semiconductor substrate. The optical distance measuring device according to claim 13,
The optical distance measuring device, wherein the light receiving element, the first switch, the second switch, the first accumulation unit, and the second accumulation unit are symmetrical with respect to a center line of the light receiving element. . The optical distance measuring device according to claim 1.
An optical distance measuring device comprising two units each having the light receiving element, the switch, and the accumulation / differential calculation unit. The optical distance measuring device according to claim 15,
Two of the units are the first unit and the second unit,
The distance determination unit calculates a ratio between the output of the first unit and the output of the second unit, and determines a distance to the measurement object based on the ratio. apparatus. The optical distance measuring device according to claim 15,
Two of the units are the first unit and the second unit,
An optical distance measuring device characterized in that when the switching time of the first unit is T, the switching time of the second unit is 2T or more. The optical distance measuring device according to claim 1.
The optical distance measuring device according to claim 1, wherein the switching signal for driving the switch changes between a first accumulation time zone driven at a switching time T and a second accumulation time zone driven at a switching time 2T or more. The optical distance measuring device according to claim 17,
An optical distance measuring device, wherein the modulation signal is a pulse wave. The optical distance measuring device according to claim 16,
The switching times of the first unit and the second unit are substantially the same,
The optical distance measuring device, wherein the modulation signal includes a sine wave signal. The optical distance measuring device according to claim 15,
Two of the units are the first unit and the second unit,
The accumulation / differential operation units of the first and second units each have an integrator using a capacitance element,
The capacitance value of the capacitance element used for the integrator of the storage / differential operation unit of the first unit is substantially the same as the capacitance value of the capacitance element used for the integrator of the storage / differential operation unit of the second unit. An optical distance measuring device characterized by the above. The optical distance measuring device according to claim 15,
At least two of the units are a first unit and a second unit,
An optical distance measuring device, wherein the first unit and the second unit are fabricated on the same semiconductor substrate. The optical distance measuring device according to any one of claims 1 to 22,
An optical distance measuring device, wherein the light emitting element is a light emitting diode. The optical distance measuring device according to any one of claims 1 to 22,
An optical distance measuring device, wherein the light emitting element is a laser diode. The optical distance measuring device according to any one of claims 1 to 24,
An optical distance measuring device comprising a scanning mechanism for scanning a light beam emitted from the light emitting element.

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