JP4525253B2 - Optical sensor and distance measuring method - Google Patents

Description

  The present invention relates to a technique for measuring the presence / absence, distance, and the like of an object using light.

  Conventionally, a distance measuring apparatus using an optical pulse is known. For example, in a time-of-flight (TOF) measurement type optical sensor, a distance is measured from a time until a light pulse is reflected by an object and returned (see Patent Documents 1 to 5).

In a TOF measurement type optical sensor, a light pulse having a minimum time width is usually used to increase the distance resolution. On the reception side, the received light pulse is expanded in time axis by so-called equivalent sampling to ensure reception sensitivity. In addition, a method of reducing the influence of noise and improving accuracy by sampling and averaging the same point a plurality of times is often used. In particular, when a low-speed light-emitting device such as an LED is used, since the rising edge of the pulse is dull, it is effective to improve the S / N ratio by averaging.
JP-A-2-228579 JP-A-5-172945 Japanese Patent Application Laid-Open No. 5-223828 JP-A-6-258432 Japanese Patent Laid-Open No. 5-288515

  However, when equivalent sampling or averaging is performed, an improvement in accuracy can be achieved, but there is a problem that the responsiveness is lowered. For example, when the optical pulse is irradiated at 10 MHz and the time base extension of 10,000 times and the average of 1000 points are performed, the responsiveness (measurement time) is reduced to 1 sec.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical sensor and a distance measuring method that achieve both good accuracy and responsiveness.

  In order to achieve the above object, in the present invention, a reference distance as a reference for measurement is set, and it is determined whether the distance to the object is closer or farther than the reference distance. With such a determination process, it is possible to obtain a determination result with sufficient accuracy without sampling the entire received light signal in detail. Therefore, the number of samplings can be greatly reduced and the measurement time can be shortened.

  It is also preferable to measure the distance to the object by repeating the above determination process while switching the reference distance in steps to narrow down the object existing area. According to such distance measurement processing, it is possible to perform distance measurement with a significantly smaller number of samplings compared to a conventional optical sensor.

  Specifically, it is preferable to employ the following configuration.

In the first aspect of the present invention, a light emitting means for irradiating a light pulse, a light receiving means for receiving light, a sampling means for sampling a received light signal obtained from the light receiving means, a processing means for processing the sampled signal, In the optical sensor, a reference distance as a measurement reference is set in advance, and the light emitting means irradiates a light pulse having a pulse width longer than time t (where t = 2 × reference distance / light speed). The sampling means samples the received light signal at a timing (hereinafter referred to as a reference distance timing) after the elapse of time t from the irradiation time of the light pulse, and the processing means determines whether the level of the sampled signal exceeds a threshold value. No, it is determined whether the distance to the object is closer or farther than the reference distance.

  Since the pulse width of the light pulse is longer than the time t, the received light pulse is always observed at the reference distance timing when an object is present near the reference distance. On the other hand, if there is an object farther than the reference distance (if there is no object within the measurable range, it is assumed that the object is at infinity), no received pulse is observed at the reference distance timing. . Therefore, it is possible to accurately determine the relative positional relationship between the object and the reference distance only by sampling the received light signal at the reference distance timing. The number of times of sampling may be one time or a plurality of times.

  In the second aspect of the present invention, the light emitting means for irradiating the light pulse, the light receiving means for receiving the light, and the maximum level of the received light signal obtained from the light receiving means are held, and the held maximum level is set as the maximum value signal. A reference distance that is a reference for measurement is preset in an optical sensor including a maximum value holding unit that outputs a signal, a sampling unit that samples a maximum value signal, and a processing unit that processes the sampled signal. The sampling means samples the maximum value signal at the timing after the time t (where t = 2 × reference distance / light velocity) has elapsed from the irradiation time of the light pulse, and the processing means determines that the level of the sampled signal has a threshold value. Whether the distance to the object is closer or farther than the reference distance is determined based on whether or not the distance is exceeded.

  According to this configuration, after the light reception pulse appears, a signal in which the peak level is maintained can be obtained. That is, even when the pulse width is shorter than time t, a signal having substantially the same waveform as the light reception signal in the first mode can be obtained. Accordingly, regardless of the pulse width of the light pulse, it is possible to determine the distance of the object with respect to the reference distance only by sampling at the reference distance timing, as in the first mode. If a light pulse having a short pulse width is used, the irradiation time of the light pulse can be reduced, so that power consumption can be reduced.

  Here, it is also preferable to provide an adjusting means for adjusting the level of the received light signal or the threshold so that the ratio between the peak level of the received light pulse and the threshold is substantially constant. Various configurations of the adjusting means are conceivable. For example, when adjusting the level of the light receiving signal, an AGC (auto gain control) may be provided after the light receiving means. Further, when the threshold level is adjusted, the peak level of the light reception signal (light reception pulse) is temporarily held and the threshold value is set to a predetermined ratio of the peak level. By adjusting the ratio between the peak level and the threshold value by the adjusting means in this way, the accuracy of threshold value determination can be kept substantially constant.

  In the third aspect of the present invention, a light emitting means for irradiating a light pulse, a light receiving means for receiving light, a sampling means for sampling a received light signal obtained from the light receiving means, a processing means for processing the sampled signal, In the optical sensor, a reference distance as a measurement reference is set in advance, the light emitting means repeatedly irradiates light pulses at a constant period, and the sampling means detects sampling leakage of the received light pulse portion. By gradually delaying the sampling timing in each cycle at a rough interval that does not occur, the time axis of the received light signal is extended, and the processing means has a peak of the time axis extension waveform from the irradiation time of the optical pulse to the time. The distance to the object is the reference depending on whether it appears after the corresponding timing after elapse of t (where t = 2 × reference distance / light speed) Determines whether near or far than away.

According to this configuration, the determination process can be performed with a significantly smaller number of samplings than the conventional equivalent sampling, and the measurement time can be shortened. The third mode is also effective when an optical pulse having a pulse width shorter than the time t is used, as in the second mode.

  In the third aspect, when the peak of the time-axis expanded waveform appears in the vicinity of the corresponding timing after the time t has elapsed from the irradiation time of the light pulse, the sampling means It is preferable that the received light signal is further sampled at the timing, and the processing means also uses the sampled signal for the determination process.

  That is, when the object is far away from the reference distance and the near / far determination is easy, the determination process is quickly performed only by sweeping roughly. On the other hand, when the object is present in the vicinity of the reference distance and it is difficult to determine the perspective, detailed sampling is performed to improve the determination accuracy. Thereby, both responsiveness and accuracy can be achieved.

  Further, when a peak is observed in the middle of the time axis extension, it is preferable that the light emitting means stops the irradiation of the light pulse until the next measurement period. Further, the sampling process may be stopped. Thus, by omitting unnecessary pulse irradiation and processing, power consumption can be reduced.

  The irradiation time of the light emitting means can be obtained from, for example, a transmission clock that determines the light irradiation timing. Alternatively, it is preferable that the apparatus further includes a second light receiving unit that directly receives light emitted from the light emitting unit, and the sampling unit sets the time when the second light receiving unit receives the light pulse as the irradiation time of the light emitting unit. is there. According to the latter configuration, since the actual irradiation time can be accurately obtained, the accuracy of the determination process is improved.

  In the fourth aspect of the present invention, light emitting means for irradiating light modulated into a sine wave or rectangular wave, light receiving means for receiving light, sampling means for sampling a light reception signal obtained from the light receiving means, and sampling In the optical sensor provided with the processing means for processing the signal, a reference distance as a measurement reference is set in advance, and the light emitting means is twice the time t (where t = 2 × reference distance / speed of light). Irradiates a sine wave or rectangular wave having a longer period, the light receiving means cuts the DC component of the received light signal, and the sampling means is after a time t has elapsed from the time corresponding to the vibration center of the sine wave or rectangular wave. The received light signal is sampled at the timing, and the processing means determines whether the distance to the object is closer or farther than the reference distance based on the polarity of the sampled signal.

  When the half-cycle of the sine wave or rectangular wave is longer than the time t when the sine wave or rectangular wave reciprocates the reference distance, the signal level sampled at the reference distance timing is when the distance to the object matches the reference distance The polarity is reversed depending on whether it is nearer or farther than the reference distance. Therefore, it is possible to accurately determine the relative positional relationship between the object and the reference distance only by sampling the received light signal at the reference distance timing.

  In addition, since the determination can be made based on whether the polarity of the signal is positive or negative, the determination variation is smaller than the threshold determination. Furthermore, since a sine wave or a rectangular wave is used, there is an advantage that noise can be effectively removed by band cutting.

  The “time corresponding to the center of vibration of a sine wave or a rectangular wave” refers to a time when the intensity of light emitted from the light emitting means is (maximum value−minimum value) / 2. Alternatively, it can be said that when the DC component of the sine wave or rectangular wave of the light emitted from the light emitting means is cut, the signal crosses zero. This time can be estimated from the content of modulation control of the light emitting means, for example. Alternatively, a second light receiving unit that directly receives the light emitted from the light emitting unit and cuts the DC component of the received light signal is provided, and the sampling unit sets the time when the output signal of the second light receiving unit zero-crosses. It is also preferable to set the time corresponding to the vibration center.

  The sampling means is preferably composed of a plurality of sampling means whose sampling timings are shifted by a minute time, and it is also preferable that the same received light signal is sampled by the plurality of sampling means and these signals are averaged.

  Thereby, it is possible to obtain a signal having a good S / N ratio by eliminating the influence of noise. In addition, since a plurality of points are sampled from the same received light signal, the responsiveness is not lowered.

  It is also preferable to further include reference distance setting means for setting the reference distance. Various configurations of the reference distance setting means are conceivable. For example, the user may be able to manually set the reference distance. Alternatively, it is also preferable that the optical sensor itself measures the distance to the installed object and automatically sets the measured distance as the reference distance.

  As described above, according to the optical sensor of the present invention, it is possible to accurately determine whether an object is present nearer or farther than the reference distance. If this determination processing function is used, the distance to the object can be measured as follows.

  For example, after setting the reference distance so as to divide the measurement target range into two areas, it is determined whether the object exists in the area closer to or far from the reference distance, and the object on the side where the object exists What is necessary is just to measure the distance to an object by setting an area | region to a new measuring object range, and repeating the said process in multiple times, and narrowing down the existing area | region of an object.

  According to such a configuration, distance measurement can be performed with high accuracy with a significantly smaller number of samplings than in the conventional method.

  In the narrowing-down process, it is preferable to increase the accuracy of the determination process according to the progress of the narrowing down. In other words, the determination accuracy is lowered at the initial stage of narrowing down the measurement target range, and the determination accuracy is increased as the narrowing down of the measurement target range proceeds. Thereby, both speeding up of processing and improvement of ranging accuracy can be achieved.

  In addition to the optical sensor having the above-described configuration, the phase difference method, the triangulation method, the PN code method, and the like, as long as it has a function capable of determining whether the distance to the object is closer or farther than the reference distance. The distance measuring method according to the present invention can be applied to any type of optical sensor.

  The present invention can be understood as an optical sensor or an optical distance measuring device having at least a part of the above means. The present invention can also be understood as an object distance determination method or a distance measurement method including at least a part of the above processing, or a program for realizing the method. Each of the above means and processes can be combined with each other as much as possible to constitute the present invention.

  According to the present invention, since the presence / absence or distance of an object can be measured with high accuracy with a small number of samplings, it is possible to achieve both good accuracy and responsiveness.

  Exemplary embodiments of the present invention will be described in detail below with reference to the drawings.

<First Embodiment>
(Hardware configuration)
An optical sensor according to a first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram illustrating a hardware configuration of the photosensor according to the first embodiment.

  This optical sensor is used to check whether an object is present in an area closer than a set reference distance, whether an object is present in an area farther than a reference distance, This is a sensor that detects whether an object is present. As an application of such an optical sensor, for example, detection of an article conveyed on a belt conveyor, detection of a vehicle passing through a gate, and the like are assumed. That is, it is used in a situation where it is sufficient to detect the presence / absence of an object within a limited range in which the movement path and existence area of the object to be detected are determined to some extent.

  As shown in FIG. 1, the optical sensor includes a transmission clock generation unit 1, a pulse generation unit 2, a drive circuit 3, a light emitting element 4, a light receiving element 5, an amplifier 6, a delay time generator 7, a timing pulse generation unit 8, and a sampling. A holding unit 9, a comparator 10, a threshold generator 11, and a microcontroller 12 are included.

  The transmission clock generation unit 1 is a circuit that generates a transmission clock signal. This transmission clock signal is input to the pulse generator 2 and used as a reference clock signal for generating an irradiation light pulse. The transmission clock signal is also input to the delay time generator 7.

The pulse generator 2 is a circuit that converts a transmission clock signal into a pulse signal having a predetermined width. In the present embodiment, a pulse signal having a pulse width equal to the time T expressed by the following equation is generated.
T = 2 × Lmax / c
Lmax: Measurable range (distance) of the optical sensor
c: speed of light

  The drive circuit 3 is a circuit that drives the light emitting element 4 by modulating the current based on the pulse signal and supplying the current to the light emitting element 4.

  The light emitting element 4 is an element that converts electrical energy into light energy and emits a light pulse into space. As the light emitting element 4, a device such as an LED or a laser diode can be used, but an LED is employed in the present embodiment.

  The light receiving element 5 is an element that converts light energy into electric energy, and can be configured by a device such as a photodiode. The light reception signal output from the light receiving element 5 is converted and amplified into a voltage waveform by the amplifier 6 and output to the sampling hold unit 9.

  In the present embodiment, the light emitting element 4 corresponds to the light emitting means of the present invention, and the light receiving element 5 and the amplifier 6 correspond to the light receiving means of the present invention.

The delay time generator 7 is a circuit that generates a delay signal having a predetermined delay time t1 with respect to the transmission clock signal (corresponding to the irradiation time of the light pulse). The delay time t1 is expressed by the following formula.
t1 = 2 × L / c
L: Reference distance, L <Lmax

  The reference distance L is a distance that serves as a measurement reference, and is a parameter that is preset when the product is manufactured or is manually set before the measurement. However, the internal holding format of this parameter does not need to be a distance value, and may be held as a time converted value or a value in a unique format. The reference distance L is smaller than the measurable distance Lmax of the optical sensor.

  The timing pulse generator 8 is a circuit that generates a sampling pulse based on the delay signal input from the delay time generator 7. Here, a sampling pulse that appears after the elapse of time t1 from the irradiation time of the light pulse is generated.

  The sampling hold unit 9 is a sampling unit that samples (samples) the received light signal according to the sampling pulse input from the timing pulse generation unit 8. The sampled signal is input to the comparator 10.

  The comparator 10 is a circuit that compares the level of the sampled signal with the threshold value input from the threshold value generator 11. The comparison result signal is input to the microcontroller 12.

  The microcontroller 12 is a circuit composed of an A / D converter, a D / A converter, a CPU, a memory, and the like, and can execute various digital signal processing according to a program stored in the memory. In the present embodiment, the comparator 10, the threshold generator 11 and the microcontroller 12 correspond to the processing means of the present invention.

(Perspective judgment processing)
Next, the perspective determination process in the optical sensor having the above configuration will be described.

  First, in synchronization with the transmission clock signal generated by the transmission clock generator 1, a light pulse having a width T is emitted from the light emitting element 4. When an object exists within the measurable range, the light pulse is reflected by the object, and the reflected light is received by the light receiving element 5. The output (light reception signal) of the light receiving element 5 is amplified by the amplifier 6 and then input to the sampling hold unit 9.

  FIG. 2 shows the waveforms of the irradiation light pulse and the light reception signal. When the distance to the object is equal to the reference distance L, as shown in FIG. 2A, the light reception signal is received at a timing after the time t1 has elapsed from the pulse irradiation time (hereinafter referred to as “reference distance timing t1”). A rise appears. When the distance to the object is shorter than the reference distance L, the received light pulse arrives before the reference distance timing t1, as shown in FIG. Since the pulse width T of the optical pulse satisfies the relationship of T> t1, in this case, the received light pulse is always observed at the reference distance timing t1. On the other hand, when the distance to the object is longer than the reference distance L, as shown in FIG. 2C, the received light pulse is not returned (not observed) at the reference distance timing t1.

  In other words, when the light reception signal level at the reference distance timing t1 is LOW (part other than the light reception pulse), the object is farther than the reference distance L and the light reception signal level is HI (light reception pulse part). It can be said that the object is closer than the reference distance L.

  The perspective determination process of the present embodiment uses this characteristic. That is, the received light signal is sampled at only one point of the reference distance timing t 1 by the sampling hold unit 9, the level of the sampled signal is compared with the threshold value by the comparator 10, and the result is passed to the microcontroller 12. The microcontroller 12 determines whether the distance to the object is closer or farther than the reference distance L depending on whether the signal level exceeds a threshold value.

According to such determination processing, the relative positional relationship between the object and the reference distance L can be determined with high accuracy by sampling only one point. This eliminates the need to sample the entire received light signal in detail (expand the time axis) and check the waveform, and can significantly improve the response compared to the conventional method. Note that the sampling at the reference distance timing t1 may be executed only once, but is preferably executed a plurality of times and averaged. By taking the average, noise can be reduced and the accuracy of the perspective determination process can be improved.

<Variation 1 of the first embodiment>
FIG. 3 shows a first modification of the photosensor according to the first embodiment. While the threshold is fixed in the first embodiment, in the first modification, the threshold level is adjusted so that the ratio between the peak level of the received light pulse and the threshold is substantially constant.

  Generally, the intensity of light received by the light receiving element 5 varies depending on the distance to the object and the state of the reflecting surface of the object. Therefore, as shown in FIG. 4A, the case where the received light signal intensity (level) is high and the case where it is low may result in different threshold determination results even if sampling is performed at the same timing. In the first modification, in order to improve this point, the threshold level is dynamically changed.

  Specifically, as shown in FIG. 3, in addition to the configuration of the first embodiment, a peak detection circuit 13 and a voltage divider 14 are provided. These circuits correspond to the adjusting means of the present invention. The peak detection circuit 13 is a circuit that detects the peak level (that is, the maximum voltage of the light reception pulse portion included in the light reception signal) from the light reception signal input from the amplifier 6, and the voltage divider 14 is provided from the peak detection circuit 13. This circuit divides the input peak level into a predetermined ratio. In this embodiment, the voltage divider 14 that divides the pressure by 50% is used.

  In the above configuration, at the first measurement, the peak level of the received light signal is acquired and 50% of the peak level is set in the comparator 10 as a threshold value. In the second and subsequent measurements, as in the first embodiment, one-point sampling is performed at the reference distance timing t1, the level of the sampled signal is compared with a threshold value, and the distance of the object is determined.

  As a result, as shown in FIG. 4B, the same threshold determination result can be obtained if the distance to the object is the same regardless of the intensity of the received light signal, and the accuracy and reliability of the determination process are improved. To do.

<Modification 2 of the first embodiment>
FIG. 5 shows a second modification of the photosensor according to the first embodiment. In the first modification, the threshold level is adjusted. In the second modification, the level of the received light signal is adjusted. The targeted effect is the same as in the first modification.

  Specifically, as shown in FIG. 5, an AGC amplifier 15 is provided instead of the amplifier 6 of the first embodiment. The AGC amplifier 15 is a circuit that automatically adjusts the amplification factor so that the peak level of the received light signal is constant. This AGC amplifier 15 corresponds to the adjusting means of the present invention.

  According to this configuration, the peak level of the received light signal to be sampled is substantially constant regardless of the distance to the object and the state of the reflecting surface of the object. Therefore, even if a fixed threshold is used, the same determination result can be obtained if the distance to the object is the same, and the accuracy and reliability of the determination process are improved.

<Modification 3 of the first embodiment>
In the first embodiment, the irradiation time of the light pulse is obtained from the transmission clock signal. However, since there is a certain time delay until the output signal of the transmission clock generator 1 reaches the light emitting element 4, strictly speaking, there is a slight difference between the transmission clock signal and the irradiation time of the optical pulse. Arise. Further, the amount of deviation varies depending on the temperature characteristics of the circuit. Therefore, it can be said that it is preferable to compensate for time delay and temperature characteristics by devising a circuit configuration on the transmission side or providing a temperature compensation circuit.

  On the other hand, the modification 3 employs a configuration in which the light pulse emitted from the light emitting element is directly received and the light reception time is used as the light pulse irradiation time. Specifically, as shown in FIG. 6, in addition to the configuration of the first embodiment, a light receiving element 16 and an amplifier 17 are provided. The light receiving element 16 is disposed in the vicinity of the light emitting element 4 so that the light irradiated from the light emitting element 4 can be directly received. These light receiving element 16 and amplifier 17 correspond to the second light receiving means of the present invention.

  In the above configuration, when a light pulse is emitted from the light emitting element 4, the light is simultaneously received by the light receiving element 16. The received light pulse is amplified by the amplifier 17 and then input to the delay time generator 7. The delay time generator 7 generates a delay signal having a predetermined delay time t 1 with respect to the received light pulse, and inputs the delay signal to the timing pulse generator 8. Other operations are the same as those in the first embodiment.

  According to such a configuration, the actual pulse irradiation time can be obtained accurately, so that the accuracy of the determination process is improved. In addition, there is no need to add a temperature compensation circuit or the like, which is advantageous in terms of cost.

<Modification 4 of the first embodiment>
FIG. 7 shows a fourth modification of the photosensor according to the first embodiment. This modification 4 is characterized in that a plurality of sampling hold units are provided in parallel.

  As a hardware configuration, three sampling hold units 9a, 9b, and 9c are arranged in parallel in the subsequent stage of the amplifier 6, and two minute time delay units 18a and 18b are provided in series in the subsequent stage of the timing pulse generating unit 8. While the sampling pulse from the timing pulse generator 8 is input as it is to the first sampling hold unit 9a, the sampling pulse delayed by the time Δt is input to the second sampling hold unit 9b, A sampling pulse delayed by time Δt × 2 is input to the sampling hold unit 9c. In this modification, the comparator and the threshold generator are eliminated, and the outputs of the sampling hold units 9a, 9b, 9c are directly passed to the microcontroller 12.

  In the above configuration, the light reception signal of the light receiving element 5 is amplified and then input to the three sampling hold units 9a, 9b, and 9c simultaneously. On the other hand, the timing pulse generator 8 supplies a sampling pulse delayed by time t1−Δt from the pulse irradiation time. Then, as shown in FIG. 8, the sampling hold units 9a, 9b, and 9c sample the same received light signal at timings “t1−Δt”, “t1”, and “t + Δt”, respectively. The three signals sampled in this way are A / D converted by the microcontroller 12 and averaged by digital signal processing. Then, the average value is compared with the threshold value, and the relative positional relationship between the object and the reference distance L is determined.

  According to such a configuration, it is possible to obtain a signal with a good S / N ratio by eliminating the influence of noise. In addition, since a plurality of points are sampled from the same received light signal, the responsiveness is not lowered.

<Other Modifications of First Embodiment>
In addition, it is also preferable to combine each structure of the modifications 1-4 mentioned above. As an example, FIG. 9 shows a configuration of an optical sensor in which the second modification and the third modification are combined. With such a configuration, the determination accuracy can be further improved.

It is also preferable to improve accuracy by repeating sampling at the reference distance timing t1 a plurality of times and taking an average of these signals. Even if such an average process is performed, sufficient response can be obtained as compared with the conventional method.

<Second Embodiment>
Next, a second embodiment of the present invention will be described. In the first embodiment, an optical pulse longer than the time t1 is used, whereas in the second embodiment, an optical pulse having a pulse width shorter than the time t1 (for example, a minimum time width) is used.

  When such an optical pulse with a short pulse width is used, the distance of the object cannot be determined by the same method as in the first embodiment. This is because if the distance to the object is shorter than the reference distance L, the received light pulse may pass before the reference distance timing t1 (see FIG. 10A), and one-point sampling at the reference distance timing t1. This is because it cannot be distinguished from the case where the distance to the object is longer than the reference distance L (see FIG. 10B).

  Therefore, in the present embodiment, as shown in FIG. 11, a peak holding circuit 20 as a maximum value holding means is added to the subsequent stage of the amplifier 6. The peak holding circuit 20 holds the maximum level of the received light signal and outputs the held maximum level as a maximum value signal. The holding value of the peak holding circuit 20 is reset for each measurement cycle by a signal from the pulse generator 2.

  According to this configuration, as shown in FIG. 12, after the light reception pulse appears, a signal whose peak level is held is input to the sampling hold unit 9. Since this maximum value signal is a signal having substantially the same waveform as the light receiving signal in the first embodiment, whether the distance to the object is closer than the reference distance L only by observing the signal level at the reference distance timing t1. You can determine how far away.

  Therefore, also in this embodiment, there can exist the same effect as 1st Embodiment. In addition, since the irradiation time of the light pulse can be significantly reduced, the power consumption of the optical sensor can be reduced. In the case of the present embodiment as well, the accuracy and reliability of the determination process can be further improved by performing modifications according to the modification of the first embodiment.

<Third Embodiment>
Next, a third embodiment of the present invention will be described. In the present embodiment, an optical pulse having a pulse width shorter than the time t1 (for example, a minimum time width) is used. In the second embodiment, the received light signal is converted by the maximum value holding means. Is different in that perspective is determined by extending the time axis at rough intervals.

  As the hardware configuration of the optical sensor, as shown in FIG. 13, a voltage-delay time converter 30 is provided instead of the delay time generator 7 of the first embodiment, and a sawtooth wave generation unit 31 and a constant voltage generation unit are provided. 32 is added.

  The sawtooth wave generator 31 is a circuit that outputs a linearly increasing voltage, and its slope is variable. The constant voltage generator 32 is a circuit that outputs a constant voltage. The output voltage of the constant voltage generator 32 is set to a value corresponding to the reference distance L. The voltage-delay time converter 30 is a circuit that generates a delay signal proportional to the input voltage. That is, the voltage input from the sawtooth wave generator 31 is converted into a delay signal whose delay time gradually increases, while the voltage input from the constant voltage generator 32 has a constant delay time t1. Converted to a delayed signal.

  The perspective determination process in the optical sensor having the above configuration is performed as follows.

First, light pulses having a minimum time width are repeatedly emitted from the light emitting element 4 at a constant period synchronized with the transmission clock signal. The light pulse reflected by the object is received by the light receiving element 5, amplified, and sequentially input to the sampling hold unit 9.

  On the other hand, the voltage-delay time converter 30 generates a delay signal based on the output voltage from the sawtooth generator 31 and supplies it to the timing pulse generator 8. Therefore, as the sampling pulse, a signal is generated so that the sampling timing in each cycle is gradually delayed.

  The delay interval here may be considerably coarser than the interval in normal equivalent sampling, and at least it is sufficient if it is an interval that does not cause sampling leakage in the received light pulse portion. For example, an interval of about half to a quarter of the pulse width is sufficient.

  The sampling and holding unit 9 samples the light reception signal of each cycle according to the sampling pulse, and performs time axis expansion of the light reception signal. Then, the microcontroller 12 indicates that the peak of the time-axis expansion waveform appears after the reference distance timing (actually the time t1 ′ corresponding to the reference distance timing t1) because it is necessary to consider the expansion rate of the time-axis expansion. Whether or not the distance to the object is closer or longer than the reference distance L.

  At this time, if it is found that the peak of the time-axis expanded waveform is clearly separated from the reference distance timing t1 ′, the determination result is output at this point and the processing ends. However, if a peak appears in the vicinity of the reference distance timing t1 ', more detailed sampling is performed.

  Specifically, the voltage input to the voltage-delay time converter 30 is switched to that of the constant voltage generation unit 32, and the sampling hold unit 9 performs sampling at the reference distance timing t1. Then, sampling is performed a plurality of times at the timing, the obtained signals are integrated and averaged, and detailed perspective determination is performed.

  According to the present embodiment described above, the determination process can be performed with a significantly smaller number of samplings than the conventional equivalent sampling, and the measurement time can be shortened. In addition, when the object is far away from the reference distance L and the determination of perspective is easy, the determination process is performed quickly only by sweeping roughly, while the object exists in the vicinity of the reference distance L and the determination of perspective is performed. If difficult, detailed sampling is performed to improve the determination accuracy, so that both responsiveness and determination accuracy can be achieved. In addition, since the irradiation time of the light pulse can be significantly reduced, the power consumption of the optical sensor can be reduced.

<Modification 1 of 3rd Embodiment>
FIG. 14 is a diagram for explaining Modification Example 1 of the optical sensor according to the third embodiment, and shows waveforms of an irradiation light pulse, a light reception signal, a sampling pulse, and a time axis extension wave.

  In the first modification, the microcontroller 12 sequentially monitors the time axis expansion waveform, and if a peak (light reception pulse portion) is observed during the time axis expansion, the pulse generation unit 2 and the timing pulse generation unit A stop signal is sent to 8 to stop the light pulse irradiation and the sampling process until the next measurement period.

  By such control, useless pulse irradiation and processing can be omitted, and power consumption can be reduced.

<Modification 2 of 3rd Embodiment>
In the configuration described above, the reference distance L is manually set at the time of product manufacture or measurement. However, in the second modification, the reference distance L is automatically set by the teaching function. The hardware configuration is the same as that of FIG.

  At the time of teaching, the optical sensor and the measurement target object are arranged in the same positional relationship as at the time of measurement, and a teaching button (not shown) of the optical sensor is pressed. At the time of teaching, the optical sensor operates as a distance measuring sensor of a general time-of-flight measurement method.

  First, light pulses having a minimum time width are repeatedly emitted from the light emitting element 4 at a constant period synchronized with the transmission clock signal. The light pulse reflected by the object is received by the light receiving element 5, amplified, and sequentially input to the sampling hold unit 9. On the other hand, the voltage-delay time converter 30 generates a delay signal based on the output voltage from the sawtooth generator 31 and supplies it to the timing pulse generator 8. At this time, by making the slope of the output voltage in the sawtooth generator 31 smaller than the slope at the time of measurement (during perspective determination processing) described above, the delay interval is made finer and a detailed time axis expanded waveform is acquired. .

  Then, the time at which the rise of the time axis expansion waveform exceeds the threshold is specified, and the flight time of the optical pulse is calculated. The distance to the object is the value of half the flight time multiplied by the speed of light.

  The microcontroller 12 sets the distance measured in this way in the constant voltage generation unit 32. At the time of measurement (during distance determination processing), this set value is used as the reference distance L.

  With the above configuration, the reference distance L can be automatically set, and the operability of the optical sensor is improved.

  Note that the same configuration as the teaching function can be applied to the photosensors of the first and second embodiments. Also in the case of the third embodiment, the accuracy and reliability of the determination process can be further improved by performing a modification according to the modification of the first embodiment.

<Fourth embodiment>
Next, a fourth embodiment of the present invention will be described. In the first to third embodiments, an optical pulse is used, whereas in the fourth embodiment, light modulated into a rectangular wave (also referred to as a square wave) is used.

  As shown in FIG. 15, the hardware configuration of the optical sensor is such that a DC cut unit 40 is added after the light receiving element 5 in the configuration of the first embodiment, and a band pass filter 41 is added after the amplifier 6. is there. A comparator and threshold generator are not required.

  The DC cut unit 40 is a circuit that sets a ground potential at the center between the maximum value and the minimum value of the received light signal intensity by cutting the DC component of the received light signal. The bandpass filter 41 is a circuit for shaping a rectangular wave into a sine wave and removing noise by cutting unnecessary bands. The band pass filter 41 may be provided in front of the amplifier 6.

  The perspective determination process in the optical sensor having the above configuration is performed as follows.

  The pulse generator 2 generates a pulse signal based on the transmission clock signal. Irradiation light is emitted from the light emitting element 4 in accordance with this pulse signal. At this time, a rectangular wave as shown in FIG. 16A is obtained by setting the duty ratio of the pulse signal to 50%. The pulse width of the pulse signal is set so that the period of the rectangular wave is longer than twice the time t1. However, time t1 is the time (t1 = L / c) when the rectangular wave reciprocates the reference distance L.

  When an object exists in the measurable range, the irradiated light is reflected by the object, and the reflected light is received by the light receiving element 5. The output (light reception signal) of the light receiving element 5 is DC cut by the DC cut unit 40 and amplified by the amplifier 6. The waveform of the received light signal after DC cut and amplification is shown in FIG. Thereafter, by passing through the band-pass filter 41, a sine wave as shown in FIG. 16C is obtained.

  In the present embodiment, the time after the elapse of time t1 from the time corresponding to the vibration center of the irradiation light (rectangular wave) is set as the reference distance timing t1, and the received light signal is sampled at the reference distance timing t1. The level of the received light signal at the reference distance timing t1 becomes zero when the distance to the object is equal to the reference distance L, becomes positive when the distance is close, and becomes negative when the distance is far. That is, the relative positional relationship between the object and the reference distance L can be determined by examining the polarity of the signal level at the reference distance timing t1.

  Therefore, in the perspective determination process of this embodiment, the light receiving signal is sampled at only one point of the reference distance timing t 1 by the sampling hold unit 9 and the signal is input to the microcontroller 12. The microcontroller 12 determines whether the polarity of the signal is positive or negative and whether the distance to the object is closer or longer than the reference distance L.

  According to such determination processing, the relative positional relationship between the object and the reference distance L can be determined with high accuracy by sampling at one point, and the responsiveness can be significantly improved as compared with the conventional method. In addition, since the determination can be made based on whether the polarity of the signal is positive or negative, the determination variation is smaller than the threshold determination. Furthermore, since a sine wave or a rectangular wave is used, there is an advantage that noise can be effectively removed by band cutting. Since the white noise level is proportional to the root of the spectrum bandwidth, an improvement in the S / N ratio can be expected by narrowing the signal band.

  Note that although rectangular wave irradiation light is used here, similar effects can be obtained by using irradiation light modulated into a sine wave. In addition, it is also preferable to combine the configurations of the above-described embodiments and modifications thereof with those of the present embodiment.

<Fifth Embodiment>
According to the perspective determination processing in the first to fourth embodiments, it is possible to accurately determine whether an object is present nearer or farther than the reference distance L. In the fifth embodiment of the present invention, the distance to the object is measured using such a distance determination processing function of the optical sensor.

  Hereinafter, with reference to FIG. 17 and FIG. 18, the processing flow of the distance measuring method will be described in detail. Here, the processing when the photosensor of the first embodiment is used is illustrated.

  First, in step S1, the microcontroller 12 initializes the value of the measurement target range. For example, when the measurable range Lmax of the optical sensor is 10 meters, the initial value of the measurement target range is set to “0 to 10 meters”.

  In step S2, the microcontroller 12 sets the reference distance L1 so as to divide the measurement target range into two regions. For example, if the measurement target range is “0 to 10 meters”, “5 meters”, which is a half of the range, is set as the reference distance L1.

In step S3, sampling is performed at the reference distance timing t1 corresponding to the reference distance L1 set in step S2, and the region closer to and far from the reference distance L1 is compared by comparing the level of the sampled signal with a threshold value. It is determined in which of the objects the object exists. In the example of FIG. 18A, a determination result that an object exists in a region far from the reference distance L1 is obtained.

  In step S4, the microcontroller 12 sets a region on the side where the object exists as a new measurement target range based on the determination result. That is, in the example of FIG. 18A, a range of “5 to 10 meters” is a new measurement target range.

  In step S5, the microcontroller 12 determines whether or not to end the narrowing down.

  When continuing the narrowing down, the processes in steps S2 to S4 are repeated again. That is, “7.5 meters” that bisects the measurement target range “5 to 10 meters” is set as the new reference distance L2, and the reference distance timing t2 corresponding to the reference distance L2 as shown in FIG. The perspective of the object is determined. Based on the determination result, the measurement target range is further narrowed down to “5-7.5 meters”, and as shown in FIG. 18C, the object is related to the reference distance timing t3 corresponding to the reference distance “6.25 meters”. Perspective determination is performed.

  In this way, the above process is repeated a plurality of times to narrow down the object existing area gradually, and the narrowing is terminated when the width of the measurement target range becomes narrower than the resolution (step S5; YES).

  In step S6, the microcontroller 12 calculates the distance to the object from the reference distance (or reference distance timing) used in the final perspective determination and the determination result.

According to the present embodiment described above, distance measurement can be performed with high accuracy with a significantly smaller number of samplings than in the conventional method. Specifically, the measurement time reduction effect is at least log ₂ (range / accuracy) times compared to the method of sweeping the entire received signal.

<Modification 1 of 5th Embodiment>
In the fifth embodiment, the measurement target range is narrowed by 1/2 according to the perspective determination result. However, in Modification 1, the new measurement target range is slightly wider in consideration of the accuracy (error) of the perspective determination process. Set.

  For example, as shown in FIG. 19A, when the accuracy of the perspective determination process (determination error range) is 1 meter, an erroneous determination may occur in the range of ± 0.5 meters of the reference distance L. At this time, if it is erroneously determined that the object exists in the far area FA even though the object exists in the area NA closer than the reference distance L, in the process of the fifth embodiment, as shown in FIG. Therefore, a new measurement target range is set in the area FA on the side where no object exists, and the subsequent narrowing process cannot be performed correctly.

  Therefore, in the first modification, when narrowing down the measurement target range, the measurement target range is set slightly wider so that the determination error range is always included in the new measurement target range. Specifically, as shown in FIG. 19C, a determination error range (4.5 to 5.5 meters) is included in an area FA (a range of 5 to 10 meters) where a determination result that an object exists is obtained. The range to which the above range is added is set as a new measurement target range.

  Thereby, even if an erroneous determination occurs, the influence can be avoided, and the ranging accuracy can be improved.

<Modification 2 of Fifth Embodiment>
The accuracy of the perspective determination process is improved by sampling a plurality of times at the reference distance timing and averaging them. Theoretically, if N points are sampled, the size of the determination error range is 1 / √N. Therefore, the possibility of erroneous determination itself can be reduced by increasing the number of sampling points.

  However, if the number of sampling points is increased, the processing time increases accordingly.

  Therefore, it is preferable that the averaging process is not performed in the first half of the narrowing-down that does not require much determination accuracy, or even if it is performed, the number of sampling points is reduced and the number of sampling points is increased in the second half of the narrowing down to increase the accuracy. Thus, by increasing the accuracy of the perspective determination process according to the progress of narrowing down (that is, as the accuracy of distance determination increases), it is possible to achieve both distance measurement accuracy and responsiveness.

  Examples of accuracy setting methods include the number of times of narrowing down, the size (distance) of the measurement target range, or a method of increasing the number of sampling points so as to be roughly proportional to the reference distance, and an appropriate determination error based on the size of the measurement target range. Various methods such as a method for calculating the range are conceivable, and any of them may be adopted. A specific example of the determination error range dynamic setting method will be described below.

  In this example, the size of the determination error range is determined so that the area excluded from the narrowing down range per unit time is maximized.

The size (distance) of the measurement target range in the i-th perspective determination process is defined as LA _i ,
When the size (distance) of the determination error range in the i-th perspective determination process is a _i ,
The size (distance) LA _{i + 1} of the measurement target range in the ( _{i + 1} ) th perspective determination process is expressed by Equation 1.

That is, the area LA _{i− that} is excluded from the narrowing-down range in the i-th perspective determination process can be expressed by Equation 2.

As described above, if N points are sampled, the size of the determination error range is 1 / √N, and therefore the time T _i required for the i-th perspective determination processing satisfies Expression 3.

Therefore, the area excluded from the narrowing range per unit time is expressed by Expression 4.

のときに、式４は最大値をとる。 The first derivative of Equation 4 is 0

In this case, Equation 4 takes the maximum value.

  As described above, at each stage of the perspective determination process, by dynamically setting the determination error range so as to satisfy Equation 5, the area excluded from the narrowing range per unit time is maximized, and the ranging accuracy and responsiveness are maximized. Can be achieved.

<Other Modifications of Fifth Embodiment>
In the fifth embodiment, the narrowing is performed to the range below the resolution. However, if one or more rising points of the pulse waveform are sampled in the middle of the narrowing, the waveform is estimated from that value and exceeds the threshold value. It is also preferable to estimate the time. Thereby, the further improvement of responsiveness can be aimed at.

  Although the case where the photosensor of the first embodiment is used is illustrated here, the same distance measurement process can be performed by any of the photosensors of the second to fourth embodiments. Furthermore, as long as it has a function that can determine whether the distance to the object is closer or farther than the reference distance, it can be any type of optical sensor such as phase difference method, triangulation method, PN code method, etc. Also, the above distance measuring method can be applied.

The block diagram which shows the hardware constitutions of the optical sensor which concerns on 1st Embodiment. The figure which shows the waveform of the irradiation light pulse and light reception signal in 1st Embodiment. The figure which shows the modification 1 of the optical sensor which concerns on 1st Embodiment. The figure explaining the level adjustment of a threshold value. The figure which shows the modification 2 of the optical sensor which concerns on 1st Embodiment. The figure which shows the modification 3 of the optical sensor which concerns on 1st Embodiment. The figure which shows the modification 4 of the optical sensor which concerns on 1st Embodiment. The figure explaining the sampling process in the optical sensor of FIG. The figure which shows the structure which combined the optical sensor of FIG. 5 and FIG. The figure explaining the problem at the time of using an optical pulse with a short pulse width. The block diagram which shows the hardware constitutions of the optical sensor which concerns on 2nd Embodiment. The figure which shows the waveform of the irradiation light pulse and light reception signal in 2nd Embodiment. The block diagram which shows the hardware constitutions of the optical sensor which concerns on 3rd Embodiment. The figure which shows the modification 1 of the optical sensor which concerns on 3rd Embodiment. The block diagram which shows the hardware constitutions of the optical sensor which concerns on 4th Embodiment. The figure which shows the waveform of the irradiation light and light reception signal in 4th Embodiment. The flowchart which shows the flow of a process of the ranging method which concerns on 5th Embodiment. The figure explaining the narrowing-down process in the distance measuring method of FIG. The figure explaining the modification of the distance measuring method which concerns on 5th Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transmission clock generation part 2 Pulse generation part 3 Drive circuit 4 Light emitting element 5 Light receiving element 6 Amplifier 7 Delay time generator 8 Timing pulse generation part 9, 9a, 9b, 9c Sampling hold part 10 Comparator 11 Threshold generator 12 Microcontroller 13 Peak detection circuit 14 Voltage divider 15 AGC amplifier 16 Light receiving element 17 Amplifier 18a, 18b Minute time delay unit 20 Peak holding circuit 30 Voltage-delay time converter 31 Saw wave generation unit 32 Constant voltage generation unit 40 DC cut unit 41 Band pass filter

Claims (15)

A light emitting means for irradiating a light pulse;
A light receiving means for receiving light;
Sampling means for sampling the received light signal obtained from the light receiving means;
In an optical sensor comprising processing means for processing a sampled signal,
A reference distance is set in advance as a measurement reference.
The light emitting means irradiates a light pulse having a pulse width longer than time t (where t = 2 × reference distance / light speed),
The sampling means samples the received light signal at a timing after the elapse of time t from the irradiation time of the light pulse,
The processing means is an optical sensor that determines whether the distance to an object is closer or farther than the reference distance depending on whether the level of the sampled signal exceeds a threshold value. A light emitting means for irradiating a light pulse;
A light receiving means for receiving light;
Maximum value holding means for holding the maximum level of the received light signal obtained from the light receiving means and outputting the held maximum level as a maximum value signal;
Sampling means for sampling the maximum value signal;
In an optical sensor comprising processing means for processing a sampled signal,
A reference distance is set in advance as a measurement reference.
The sampling means samples the maximum value signal at a timing after the elapse of time t (where t = 2 × reference distance / light speed) from the irradiation time of the light pulse,
The processing means is an optical sensor that determines whether the distance to an object is closer or farther than the reference distance depending on whether the level of the sampled signal exceeds a threshold value. The optical sensor according to claim 1, further comprising an adjusting unit that adjusts the level of the received light signal or the threshold value so that a ratio between the peak level of the received light pulse and the threshold value is substantially constant. A light emitting means for irradiating a light pulse;
A light receiving means for receiving light;
Sampling means for sampling the received light signal obtained from the light receiving means;
In an optical sensor comprising processing means for processing a sampled signal,
A reference distance is set in advance as a measurement reference.
The light emitting means repeatedly irradiates light pulses at a constant period,
The sampling means performs time axis expansion of the received light signal by gradually delaying the sampling timing in each cycle at a rough interval that does not cause sampling leakage of the received light pulse part,
The processing means determines whether or not the peak of the time-axis extended waveform appears after a time t (where t = 2 × reference distance / light speed) has elapsed from the irradiation time of the light pulse, after a corresponding timing. An optical sensor for determining whether is closer or farther than the reference distance. When the peak of the time axis extension waveform appears in the vicinity of the corresponding timing after the elapse of time t from the irradiation time of the light pulse,
The sampling means further samples the received light signal at a timing after the elapse of time t from the irradiation time of the light pulse,
The optical sensor according to claim 4, wherein the processing means also uses the sampled signal for the determination process. 6. The optical sensor according to claim 4, wherein, when a peak is observed in the middle of the time axis extension, the light emitting means stops the irradiation of the light pulse until the next measurement period. A second light receiving means for directly receiving the light emitted from the light emitting means;
The optical sensor according to claim 1, wherein the sampling unit sets a time when the second light receiving unit receives a light pulse as an irradiation time of the light emitting unit. A light emitting means for irradiating light modulated into a sine wave or a rectangular wave;
A light receiving means for receiving light;
Sampling means for sampling the received light signal obtained from the light receiving means;
In an optical sensor comprising processing means for processing a sampled signal,
A reference distance is set in advance as a measurement reference.
The light emitting means irradiates a sine wave or a rectangular wave having a period longer than twice the time t (where t = 2 × reference distance / light speed),
The light receiving means cuts a DC component of the light reception signal,
The sampling means samples the received light signal at a timing after elapse of time t from the time corresponding to the center of vibration of the sine wave or rectangular wave,
The processing means is an optical sensor that determines whether the distance to the object is closer or farther than the reference distance based on the polarity of the sampled signal. A second light receiving means for directly receiving the light emitted from the light emitting means and cutting a DC component of the received light signal;
The optical sensor according to claim 8, wherein the sampling unit sets a time corresponding to the vibration center as a time when the output signal of the second light receiving unit zero-crosses. The sampling means comprises a plurality of sampling means whose sampling timings are shifted by a minute time,
The optical sensor according to claim 1, wherein the same received light signal is sampled by a plurality of sampling means and the signals are averaged. The optical sensor according to claim 1, further comprising reference distance setting means for setting the reference distance. The optical sensor according to any one of claims 1 to 11,
After setting the reference distance so as to divide the measurement target range into two areas, determine whether the object exists in an area closer or farther than the reference distance,
Set the area on the side where the object exists as a new measurement target range,
An optical sensor that measures the distance to an object by narrowing down the region where the object exists by repeating the above process a plurality of times. The optical sensor according to claim 12, wherein the accuracy of the determination process is increased in accordance with the progress of the narrowing down. An optical sensor that can determine whether the distance to an object is closer or farther than the set reference distance.
After setting the reference distance so as to divide the measurement target range into two areas, determine whether the object exists in an area closer or farther than the reference distance,
Set the area on the side where the object exists as a new measurement target range,
A distance measuring method for measuring a distance to an object by repeating the above process a plurality of times to narrow down an object existing area. The distance measuring method according to claim 14, wherein the accuracy of the determination process is increased in accordance with the progress of the narrowing down.

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