JP2011117860A - Body detection sensor and method of body detection - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sensor with enhanced body detection accuracy. <P>SOLUTION: This body detection sensor includes: a semiconductor laser 1 radiating laser light; a photodiode 2 for detecting an electric signal including an interference waveform caused by a self-coupling effect between the laser light radiated from the semiconductor laser 1 and return light thereof, and a current-voltage converter/amplifier 5; a signal extractor 7 for measuring the cycle of the interference waveform included in an output signal of the converter/amplifier 5; and a body detector 8 for detecting the existence of a body 11 emerging in the radiating direction of the laser light or detecting a change in motion of the body 11 existing in the radiating direction of the laser light from an initial state, based on a measurement result of the signal extractor 7. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an object detection sensor and an object for detecting presence / absence of an object in the laser light emission direction and a change in the movement of an object from information on interference caused by a self-coupling effect between a laser beam emitted from a semiconductor laser and its return light It relates to a detection method.

  Conventionally, a self-coupling type laser measuring instrument using interference (self-coupling effect) inside a semiconductor laser between a laser beam and a return beam from a measurement object has a problem that it takes time to detect an object. Therefore, the inventor has proposed an object detection sensor capable of detecting an object at high speed (see Patent Document 1). FIG. 18 is a block diagram showing a configuration of the object detection sensor disclosed in Patent Document 1. In FIG.

  The object detection sensor in FIG. 18 condenses light from a semiconductor laser 201 that emits laser light, a photodiode 202 that is a light receiver that converts the optical output of the semiconductor laser 201 into an electrical signal, and the semiconductor laser 201. The lens 203 that radiates and collects the return light from the object 212 and enters the semiconductor laser 201, the laser driver 204 that drives the semiconductor laser 201, and the output current of the photodiode 202 are converted into voltage and amplified. A current-voltage conversion amplifier 205, a filter circuit 206 for removing a carrier wave from the output voltage of the current-voltage conversion amplifier 205, and a mode hop pulse (hereinafter referred to as MHP) which is a self-coupled signal included in the output voltage of the filter circuit 206. The counting device 207 for counting the number, the distance from the object 212 based on the number of MHPs, and the object 21 A speed arithmetic unit 208 for calculating a, a display device 209 for displaying the calculation result of the arithmetic unit 208, and an object detection apparatus 211 to detect whether an object 212 is present in the radial direction of the semiconductor laser 201.

  The object detection device 211 detects the period of the MHP, and determines that the object 212 exists in the laser light emission direction when the MHP having a period different from the period of the MHP by the stationary reflecting wall surface 210 satisfies a predetermined condition. To do. More specifically, the object detection device 211 measures the MHP period during the counting period for counting the number of MHPs every time MHP is input, and the frequency of the MHP period during the counting period is determined from the measurement result of this period. A distribution is created, a representative value T0 of the distribution of the MHP period is calculated from the frequency distribution, and the representative value T0 calculated in the counting period one cycle before the laser beam is compared with the detection period in the current counting period. When the number N of MHPs whose period is longer than a predetermined number of times of the representative value T0 is obtained, and the ratio N / Nall of the number N to the total number Nall of MHPs whose period is measured during the detection period is equal to or greater than a predetermined threshold value. , It is determined that the object 212 exists in the laser light emission direction.

JP 2009-092461 A

  According to the object detection sensor disclosed in Patent Document 1, an object can be detected at a higher speed than a self-coupled laser measuring instrument. However, the object detection sensor disclosed in Patent Document 1 has a problem in that the accuracy of object detection is low because there is an error in the MHP cycle.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an object detection method capable of improving the accuracy of object detection.

  The object detection sensor of the present invention includes at least one of a semiconductor laser that emits laser light, a first oscillation period in which the oscillation wavelength continuously increases monotonously, and a second oscillation period in which the oscillation wavelength continuously decreases monotonously. Oscillating wavelength modulating means for operating the semiconductor laser such that the laser beam is repeatedly present, and detecting means for detecting an electric signal including an interference waveform caused by a self-coupling effect between the laser light emitted from the semiconductor laser and its return light A signal extraction unit that measures the period of the interference waveform included in the output signal of the detection unit every time an interference waveform is input; a storage unit that stores a measurement result of the signal extraction unit; and a storage unit that stores the measurement result When the period of one interference waveform is the period of interest, the representative value of the distribution of the periods of the plurality of interference waveforms measured immediately before the period of interest and stored in the storage means Representative value calculation means for calculating a representative value of the distribution of the periods of the plurality of interference waveforms measured immediately after the attention period and stored in the storage means; and the attention period as a period of the interference waveform to be corrected, Period correction means for correcting the period of the interference waveform to be corrected by comparing the period of the interference waveform to be corrected and the two representative values, and updating the period stored in the storage means according to the result of the correction By comparing the threshold value based on the representative value T1 with the representative value T2, where T1 is the smaller of the two representative values calculated by the representative value calculating means, and T2 is the larger one, the laser is compared with the representative value T2. Object detection means for detecting the presence of an object appearing in the light emission direction or detecting a change in the movement of the object existing in the laser light emission direction from an initial state, The representative value of the distribution of the maximum value is the moving average value, the average value, the maximum value, the minimum value, the mode value, the median value, or the product of the class value and the frequency obtained from the frequency distribution of the period of the interference waveform. It is one of the following class values.

  The object detection sensor of the present invention includes a semiconductor laser that emits laser light, a first oscillation period in which the oscillation wavelength continuously increases monotonously, and a second oscillation period in which the oscillation wavelength continuously decreases monotonously. Oscillation wavelength modulation means for operating the semiconductor laser so that at least one of them repeatedly exists, and detection for detecting an electrical signal including an interference waveform caused by a self-coupling effect between the laser light emitted from the semiconductor laser and its return light Means, signal extraction means for measuring the period of the interference waveform included in the output signal of the detection means every time the interference waveform is input, storage means for storing the measurement result of the signal extraction means, and storage means When the period of one interference waveform stored in is used as the period of interest, the distribution of the periods of the plurality of interference waveforms measured immediately after this period of interest and stored in the storage means Representative value calculating means for calculating a table value, and the period of interest as the period of the interference waveform to be corrected, and the interference waveform predefined from the period of the interference waveform to be corrected and the initial value of the distance from the semiconductor laser The period of the interference waveform to be corrected is corrected by comparing the representative value of the period distribution and the representative value calculated by the representative value calculating means, and the period stored in the storage means is corrected according to the result of the correction. The threshold correction unit based on the representative value T1 and the representative value when the smaller one of the pre-defined representative value and the representative value calculated by the representative value calculating means is T1 and the larger one is T2. By comparing with the value T2, the presence of an object appearing in the laser light emission direction is detected, or a change in the motion of the object existing in the laser light emission direction from the initial state is detected. A representative value of the period distribution of the interference waveform is a moving average value, an average value, a maximum value, a minimum value, a mode value, a median value, or a frequency distribution of the period of the interference waveform. The obtained product is one of the class values that maximizes the product of the class value and the frequency.

In one configuration example of the object detection sensor according to the present invention, when the period correction unit is Tx = T1 + α · (T2−T1) (0 ≦ α ≦ 1), the period of the interference waveform to be corrected is If it is less than a predetermined number k times Tx (k is a positive value less than 1), the interference waveform after correcting the period obtained by combining the period of the interference waveform to be corrected and the period of the next measured interference waveform And the period of the interference waveform to be corrected is not less than (m-0.5) times Tx and less than (m + 0.5) times Tx. (M is a natural number greater than or equal to 2), the period obtained by equally dividing the period of the interference waveform to be corrected into m equals the period after correction, and there are m waveforms with the period after correction. Is.
Further, in one configuration example of the object detection sensor of the present invention, the object determination means satisfies Th1 ≦ T2 ≦ Th2 when the threshold value based on the representative value T1 is Th1, Th2 (Th1 <Th2). In this case, it is determined that there is no object in the laser light emission direction, and when Th1> T2 or T2> Th2 is satisfied, it is determined that an object exists in the laser light emission direction. .
Further, in one configuration example of the object detection sensor of the present invention, the object determination unit sets an initial state when the object is stationary in the laser light emission direction, and sets a threshold value based on the representative value T1 to Th1. , Th2 (Th1 <Th2), when Th1 ≦ T2 ≦ Th2 is satisfied, it is determined that the object existing in the laser light emission direction is not moving, and Th1> T2 or T2> Th2 is satisfied. It is determined that an object existing in the laser light emission direction has moved.

Further, in one configuration example of the object detection sensor according to the present invention, the threshold values Th1 and Th2 are set as Th1 = aT1, Th2 = bT1 (0.5 ≦ a <1, 1 <b ≦ 1.5). Threshold setting means for setting is provided.
Further, in one configuration example of the object detection sensor of the present invention, when the minimum value is Tmin and the maximum value is Tmax in the period of the interference waveform corrected by the period correction unit, the threshold values Th1 and Th2 Is provided with threshold value setting means for setting Th1 = T1−Tmin and Th2 = T1 + Tmax.
Further, in one configuration example of the object detection sensor of the present invention, when the variance value of the period of the interference waveform corrected by the period correction unit is σ ² , the threshold values Th1 and Th2 are set as Th1 = T1. Threshold value setting means for setting −Aσ ² , Th2 = T1 + Aσ ² (A is a positive real number) is provided.

Further, in one configuration example of the object detection sensor of the present invention, the object determination means uses a reflection wall surface facing the semiconductor laser across a space where the object is to enter as a reference surface, and the reference surface and the semiconductor laser. When T2 ≦ Th2 is established, it is determined that no object is present in the laser light emission direction, and when T2> Th2 is established, the laser light It is determined that an object is present in the radiation direction.
Further, in one configuration example of the object detection sensor of the present invention, the object determination unit is based on any one of the inner surface and the outer surface of the transparent cover that protects the semiconductor laser, which has not been subjected to antireflection treatment. When detecting whether or not an object is present in front of the reference surface as a surface, if Th1 ≦ T2 is satisfied, it is determined that no object is present in front of the reference surface, and Th1> T2 is satisfied, It is determined that an object is present in front of the reference plane.

  Further, the object detection method of the present invention is such that at least one of the first oscillation period in which the oscillation wavelength continuously increases monotonically and the second oscillation period in which the oscillation wavelength continuously decreases monotonously exists repeatedly. An oscillation procedure for operating the laser, a detection procedure for detecting an electric signal including an interference waveform caused by a self-coupling effect between the laser light emitted from the semiconductor laser and its return light, and an output signal obtained by this detection procedure A signal extraction procedure for measuring the period of the interference waveform included in each time an interference waveform is input, a storage procedure for storing the measurement result of this signal extraction procedure in the storage means, and one stored in the storage means When the period of the interference waveform is the period of interest, a representative value of the distribution of the periods of the plurality of interference waveforms measured immediately before the period of interest and stored in the storage means and immediately after the period of interest A representative value calculation procedure for calculating a representative value of a distribution of periods of a plurality of interference waveforms measured and stored in the storage means, and the period of interest is a period of the interference waveform to be corrected, and the interference waveform of the correction object A cycle correction procedure for correcting the cycle of the interference waveform to be corrected by comparing the cycle with the two representative values, and updating the cycle stored in the storage unit according to the result of the correction, and the representative value calculation When the smaller one of the two representative values calculated in the procedure is T1, and the larger one is T2, the threshold value based on the representative value T1 is compared with the representative value T2, thereby appearing in the laser light emission direction. An object determination procedure for detecting the presence of the detected object or detecting a change in the motion of the object existing in the laser light emission direction from the initial state, and the representative value of the distribution of the period of the interference waveform is shifted. The average value, the average value, the maximum value, the minimum value, the mode value, the median value, or the class value obtained from the frequency distribution of the period of the interference waveform is the class value that maximizes the product of the class value and the frequency. It is characterized by this.

  Further, the object detection method of the present invention is such that at least one of the first oscillation period in which the oscillation wavelength continuously increases monotonically and the second oscillation period in which the oscillation wavelength continuously decreases monotonously exists repeatedly. An oscillation procedure for operating the laser, a detection procedure for detecting an electric signal including an interference waveform caused by a self-coupling effect between the laser light emitted from the semiconductor laser and its return light, and an output signal obtained by this detection procedure A signal extraction procedure for measuring the period of the interference waveform included in each time an interference waveform is input, a storage procedure for storing the measurement result of this signal extraction procedure in the storage means, and one stored in the storage means When the period of the interference waveform is the period of interest, a representative value calculating unit that calculates the representative value of the distribution of the periods of the plurality of interference waveforms measured immediately after the period of interest and stored in the storage means. The period of interest is the period of the interference waveform to be corrected, the period of the interference waveform to be corrected, the representative value of the period distribution of the interference waveform defined in advance from the initial value of the distance to the semiconductor laser, and the A period correction procedure for correcting the period of the interference waveform to be corrected by comparing with the representative value calculated in the representative value calculation procedure, and updating the period stored in the storage unit according to a result of the correction; By comparing the threshold value based on the representative value T1 with the representative value T2, where T1 is the smaller of the specified representative value and the representative value calculated in the representative value calculation procedure, and T2 is the larger one, Detecting the presence of an object appearing in the laser light emission direction, or detecting a change in motion of an object existing in the laser light emission direction from an initial state, and an object determination procedure, Typical values of the distribution of the period of the interference waveform are moving average value, average value, maximum value, minimum value, mode value, median value, or class value and frequency obtained from the frequency distribution of the period of the interference waveform. It is one of the class values that maximizes the product of.

  According to the present invention, since the error in the period of the interference waveform is corrected, the accuracy of object detection can be improved.

  Further, in the present invention, by defining in advance a representative value of the period distribution of one interference waveform from the initial value of the distance to the semiconductor laser, it is not necessary to calculate two representative values, and the representative value is set to 1. Therefore, it is possible to detect an object or a change in motion of an object in a shorter time than a conventional object detection sensor.

It is a block diagram which shows the structure of the object detection sensor which concerns on the 1st Embodiment of this invention. It is a figure which shows one example of the time change of the oscillation wavelength of the semiconductor laser in the 1st Embodiment of this invention. It is a wave form diagram showing typically the output voltage waveform of the current-voltage conversion amplification part in the 1st embodiment of the present invention, and the output voltage waveform of a filter part. It is a figure for demonstrating a mode hop pulse. It is a figure which shows the relationship between the oscillation wavelength of a semiconductor laser, and the output waveform of a photodiode. It is a figure for demonstrating operation | movement of the signal extraction part in the 1st Embodiment of this invention. It is a block diagram which shows the structure of the object detection part in the 1st Embodiment of this invention. It is a figure for demonstrating operation | movement of the period correction | amendment part in the 1st Embodiment of this invention. It is a figure for demonstrating the correction principle of the measurement result of the signal extraction part in the 1st Embodiment of this invention. It is a figure which shows frequency distribution of the period of a mode hop pulse. It is a figure which shows the change of the distance with an object in case the object is moving at constant velocity. It is a figure which shows the frequency distribution of the period of a mode hop pulse in case an object is moving at constant velocity. It is a figure which shows the change of the distance with an object in case the speed of an object is changing, and the change of the speed of an object. It is a figure which shows the frequency distribution of the period of a mode hop pulse when the speed of an object is changing. It is a figure which shows the principal part schematic structure of the incident / exit part of the semiconductor laser which concerns on the 3rd Embodiment of this invention. It is a figure which shows the example of the time change of the oscillation wavelength of the semiconductor laser in the 4th Embodiment of this invention. It is a block diagram which shows the structure of the object detection sensor which concerns on the 6th Embodiment of this invention. It is a block diagram which shows the structure of the conventional object detection sensor.

[First Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the object detection sensor according to the first embodiment of the present invention. 1 includes a semiconductor laser 1 that emits laser light, a photodiode 2 that converts the light output of the semiconductor laser 1 into an electrical signal, and collects and emits light from the semiconductor laser 1, The lens 3 that collects the return light from the reflecting wall surface 10 or the object 11 and makes it incident on the semiconductor laser 1, the laser driver 4 that serves as an oscillation wavelength modulation means for driving the semiconductor laser 1, and the output current of the photodiode 2 A current-voltage conversion amplification unit 5 that converts and amplifies the signal, a filter unit 6 that removes a carrier wave from the output voltage of the current-voltage conversion amplification unit 5, and an MHP that is a self-coupled signal included in the output voltage of the filter unit 6 The signal extraction unit 7 that measures the period of the laser beam and the presence of the object 11 that appears in the laser beam emission direction, or the object 1 that exists in the laser beam emission direction from the initial state. Having an object detection unit 8 for detecting a change in the movement, and a display unit 9 for displaying the detection result of the object detection unit 8.

  The photodiode 2 and the current-voltage conversion amplification unit 5 constitute detection means. Hereinafter, for ease of explanation, it is assumed that a semiconductor laser 1 of a type that does not have a mode hopping phenomenon (VCSEL type, DFB laser type) is used.

  The laser driver 4 supplies a triangular wave drive current that repeatedly increases and decreases at a constant change rate with respect to time to the semiconductor laser 1 as an injection current. As a result, the semiconductor laser 1 has a first oscillation period in which the oscillation wavelength continuously increases at a constant change rate in proportion to the magnitude of the injection current, and a first oscillation period in which the oscillation wavelength continuously decreases at a constant change rate. It is driven to alternately repeat the two oscillation periods. FIG. 2 is a diagram showing a change with time of the oscillation wavelength of the semiconductor laser 1. In FIG. 2, P1 is the first oscillation period, P2 is the second oscillation period, λa is the minimum value of the oscillation wavelength in each period, λb is the maximum value of the oscillation wavelength in each period, and Tcar is the period of the triangular wave. In the present embodiment, the rate of change of the oscillation wavelength of the semiconductor laser 1 needs to be constant.

  The laser light emitted from the semiconductor laser 1 is collected by the lens 3 and enters the reflecting wall surface 10 when the object 11 does not exist in the laser light emission direction, and enters the object 11 when the object 11 exists. The light reflected by the reflecting wall surface 10 or the object 11 is collected by the lens 3 and enters the semiconductor laser 1. However, condensing by the lens 3 is not essential. The photodiode 2 is disposed in the semiconductor laser 1 or in the vicinity thereof, and converts the optical output of the semiconductor laser 1 into a current. The current-voltage conversion amplifier 5 converts the output current of the photodiode 2 into a voltage and amplifies it.

  The filter unit 6 has a function of extracting a superimposed signal from the modulated wave. FIG. 3A is a diagram schematically illustrating an output voltage waveform of the current-voltage conversion amplification unit 5, and FIG. 3B is a diagram schematically illustrating an output voltage waveform of the filter unit 6. In these figures, the oscillation waveform (carrier wave) of the semiconductor laser 1 in FIG. 2 is removed from the waveform (modulation wave) in FIG. 3A corresponding to the output of the photodiode 2, and the MHP in FIG. A process of extracting a waveform (interference waveform) is shown.

Next, the signal extraction unit 7 measures the period of MHP included in the output voltage of the filter unit 6 every time MHP is generated. Here, the MHP that is a self-coupled signal will be described. As shown in FIG. 4, when the distance from the mirror layer 1013 to the object 11 is L and the oscillation wavelength of the laser is λ, the return light from the object 11 and the optical resonance of the semiconductor laser 1 are satisfied when the following resonance conditions are satisfied. The laser light in the chamber strengthens and the laser output increases slightly.
L = qλ / 2 (1)
In Formula (1), q is an integer. This phenomenon can be sufficiently observed even if the scattered light from the object 11 is very weak, because the apparent reflectance in the resonator of the semiconductor laser 1 increases, causing an amplification effect. In FIG. 4, reference numeral 1019 denotes a dielectric multilayer film to be a mirror.

  FIG. 5 is a diagram showing the relationship between the oscillation wavelength and the output waveform of the photodiode 2 when the oscillation wavelength of the semiconductor laser 1 is changed at a certain rate. When L = qλ / 2 shown in Expression (1) is satisfied, the phase difference between the return light and the laser light in the optical resonator becomes 0 ° (the same phase), and the return light and the optical resonator The laser beam is the most intense, and when L = qλ / 2 + λ / 4, the phase difference is 180 ° (reverse phase), and the return light and the laser beam in the optical resonator are most weakened. Therefore, when the oscillation wavelength of the semiconductor laser 1 is changed, a place where the laser output becomes strong and a place where the laser output becomes weak alternately appear repeatedly. When the laser output at this time is detected by the photodiode 2, as shown in FIG. A stepped waveform with a constant period can be obtained. Such a waveform is generally called an interference fringe. Each stepped waveform, that is, each interference fringe is MHP. As described above, when the oscillation wavelength of the semiconductor laser 1 is changed for a certain period of time, the number of MHPs changes in proportion to the measurement distance.

  6 (A) to 6 (D) are diagrams for explaining the operation of the signal extraction unit 7. FIG. 6 (A) schematically shows the waveform of the output voltage of the filter unit 6, that is, the waveform of MHP. FIG. 6B shows a waveform obtained by binarizing MHP, FIG. 6C shows a sampling clock input to the signal extraction unit 7, and FIG. 6D shows FIG. It is a figure which shows the measurement result of the signal extraction part 7 corresponding to).

  First, the signal extraction unit 7 determines that the output voltage of the filter unit 6 shown in FIG. 6A is high level when the output voltage of the filter unit 6 rises to a threshold value TH1 or more, and the output voltage of the filter unit 6 decreases. When the threshold value TH2 (TH2 <TH1) or less is determined, the output of the filter unit 6 is binarized by determining the low level. The signal extraction unit 7 measures the binarized MHP rising edge period (that is, the MHP period) every time the rising edge occurs. At this time, the signal extraction unit 7 measures the MHP cycle with the sampling clock cycle shown in FIG. 6C as one unit. In the example of FIG. 6D, the signal extraction unit 7 sequentially measures Tα, Tβ, and Tγ as the MHP cycle. As is apparent from FIGS. 6C and 6D, the sizes of the periods Tα, Tβ, and Tγ are 5 [samplings], 4 [samplings], and 2 [samplings], respectively. The frequency of the sampling clock is assumed to be sufficiently higher than the highest frequency that MHP can take.

  Next, the object detection unit 8 detects whether or not the object 11 exists in the laser light emission direction based on the measurement result of the signal extraction unit 7. FIG. 7 is a block diagram showing a configuration of the object detection unit 8. The object detection unit 8 includes a storage unit 80, a representative value calculation unit 81, a period correction unit 82, an object determination unit 83, and a threshold setting unit 84. In the present embodiment, a case where a moving average value is used as a representative value of the distribution of MHP cycles is described, but the present invention is not limited to this. The case where a representative value other than the moving average value is used will be described later.

  The storage unit 80 stores the measurement result of the signal extraction unit 7. When the MHP cycle measured at a time prior to the current time stored in the storage unit 80 is set as an attention cycle, the representative value calculation unit 81 has a predetermined number of MHP cycles measured immediately before the attention cycle. The moving average value TA and the moving average value TB of a predetermined number of MHP cycles measured immediately after the period of interest are calculated. Each time a new measurement result is output from the signal extraction unit 7 and stored in the storage unit 80, the representative value calculation unit 81 sets a new measurement result as a new attention once compared to the current attention period for which the moving average value has been calculated. As a cycle, the moving average values TA and TB are calculated. The calculation result of the representative value calculation unit 81 is stored in the storage unit 80.

  The period correction unit 82 sets the target period as the MHP period to be corrected, and compares the moving average values TA and TB calculated by the representative value calculation unit 81 with the MHP period to be corrected, thereby correcting the MHP to be corrected. Correct the period. The period correction unit 82 performs this correction every time a new measurement result is output from the signal extraction unit 7 and stored in the storage unit 80. FIGS. 8A to 8D are diagrams for explaining the operation of the period correction unit 82.

  The period correcting unit 82 sets T1 as the smaller one of the two moving average values TA and TB calculated by the representative value calculating unit 81, T2 as the larger one, and Tx = T1 + α · (T2−T1) (0 ≦ When α ≦ 1) and the period T of the MHP to be corrected is less than k · Tx as shown in FIG. 8A (k is a positive value less than 1), correction is performed as shown in FIG. A period obtained by combining the period M of the target MHP and the period Tnext of the next measured MHP is defined as a corrected MHP period T ′, and a waveform obtained by combining the periods is defined as one waveform.

  Further, the period correction unit 82, when the period T of the MHP to be corrected is (m−0.5) · Tx or more and less than (m + 0.5) · Tx (m is a natural number of 2 or more), It is assumed that a period obtained by dividing the MHP period T into m equal parts is a period after correction, and there are m waveforms with the period after correction. The example of FIG. 8C is a case where m = 2 and the period T of the correction target MHP is 1.5 Tx or more and less than 2.5 Tx. In this case, as shown in FIG. Is divided into two equal parts, Tdiv1 and Tdiv2.

  The period correction unit 82 updates the measurement result of the signal extraction unit 7 stored in the storage unit 80 according to the correction result. Therefore, in the example shown in FIGS. 8A and 8B, the two measurement results of the signal extraction unit 7 are combined into one, and FIGS. In the example shown in (D), one measurement result of the signal extraction unit 7 is divided into two. Also, the MHP cycle measured before the MHP cycle to be corrected has already been corrected by the cycle correction unit 82. That is, the moving average value TA calculated by the representative value calculation unit 81 is calculated from the corrected measurement result. The period correction unit 82 performs the correction process as described above each time a new measurement result is output from the signal extraction unit 7 and stored in the storage unit 80.

  FIG. 9 is a diagram for explaining the principle of correcting the measurement result of the signal extraction unit 7, and schematically showing the waveform of the output voltage of the filter unit 6, that is, the waveform of MHP. However, in order to simplify the explanation, the principle here explains the case where the object 11 is stationary or the case where the center of vibration of the object 11 does not change. A reference period T0 is used instead of the average values T1 and T2. The reference period T0 is a moving average of the MHP period when the object 11 is stationary, the MHP period at the calculated distance, or a fixed number of MHP periods measured immediately before period correction by the period correction unit 82. One of the values. The principle of period correction when the object 11 moves will be described later.

The period of MHP differs depending on the distance to the object 11, but if the distance to the object 11 is unchanged, the MHP appears in the same period. However, due to noise, the MHP waveform may be missing or a waveform that should not be counted as a signal may be generated, resulting in an error in the MHP cycle.
When signal loss occurs, the MHP cycle Tw at the location where the loss occurs is approximately twice the original cycle. That is, when the MHP cycle is approximately twice or more the reference cycle T0, it can be determined that the signal is missing. Therefore, the signal loss can be corrected by dividing the period Tw into two equal parts.

  Further, the MHP cycle Ts at the location where noise is counted is approximately 0.5 times the original cycle. That is, when the MHP cycle is less than about 0.5 times the reference cycle T0, it can be determined that the signals are excessively counted. Therefore, by adding the period Ts and the next measured period Tnext, it is possible to correct erroneously counted noise.

  The above is the basic principle of MHP cycle correction. Instead of setting the threshold value for determining the period Tw that the signal is considered to be missing to a value that is twice the reference period T0, the threshold value is 1.5 times (the actual use in this embodiment is (m−0.5 )), And 1.5 (when m = 2, the reason) is disclosed in Japanese Patent Laid-Open No. 2009-47676. The principle described in Japanese Patent Application Laid-Open No. 2009-47676 is a principle for correcting the measurement result of MHP. The period T of MHP and the count result N are expressed as follows: M is the number of sampling clocks per half cycle of the triangular wave. Since T = M / N and M is a constant value, the threshold value for determining the cycle Tw in which the signal is considered to be missing is the reference cycle T0 as in the case of correcting the count result N. It can be seen that it may be 1.5 times the value.

  Next, the principle of period correction when the object 11 moves will be described. The frequency of MHP can be represented by the sum of a frequency proportional to the distance to the object 11 (the period at this time is the reference period T0) and a frequency proportional to the speed of the object 11. When the MHP cycle is T in the state where the object 11 is present, the probability distribution of the individual MHP cycles varies due to noise or the like, and is generally a normal distribution centered on T. Therefore, when the object 11 is stationary, the probability distribution of each MHP cycle is also a normal distribution centered on the reference cycle T0, and the frequency distribution of the MHP cycle during the stationary period is shown in FIG. As described above, a normal distribution centered on the reference period T0 is obtained.

  Here, consider a case where the object 11 is moving at a constant speed as shown in FIG. In the self-coupled laser sensor, the change in the MHP period due to the change in the distance to the object 11 is very small as compared with the change rate of the MHP frequency due to the change in the speed of the object 11. For this reason, the probability distribution of the period of each MHP is centered on a value T whose period has changed from T0 corresponding to the average distance to the object 11 by the magnitude of the velocity at both point A and point B in FIG. Therefore, the frequency distribution of the MHP period during the period from point A to point B is also a normal distribution centered on T (FIG. 12).

  Next, consider the case where the speed of the object 11 is changing as shown in FIGS. 13 (A) and 13 (B). Here, for the sake of simplicity, a polygonal line motion is considered. That is, the distance L to the object 11 is simplified to the distance LA in the period A and the distance LB in the period B. Similarly, the speed V of the object 11 is simplified to the speed VA in the period A and the speed VB in the period B. When the motion of the object 11 is simplified in this way, the frequency distribution of the MHP cycle is as shown in FIG. In FIG. 14, TA is a period of MHP corresponding to the average speed of the object 11 in the period A, and TB is a period of MHP corresponding to the average speed of the object 11 in the period B.

  If the speed change of the object 11 changes smoothly, the speed of the object 11 at time t in FIGS. 13 (A) and 13 (B) is between the speeds VA and VB. Is also between the periods TA and TB. If the period of MHP at this time is TX, the probability distribution of the period of MHP when a signal is lost and two MHPs become one is considered to be a normal distribution centered on 2TX. Further, when the MHP of the period TX is divided into two by noise, the two probability distributions of MHP are symmetrical with 0.5 TX as an axis. Therefore, when considering period correction of TX, which is considered to be a value between TA and TB, it is appropriate to perform period correction based on the moving average value of TA and TB instead of the reference period T0. The above is the principle of MHP cycle correction when the object 11 moves.

  Next, the object determination unit 83 sets the smaller one of the two moving average values TA and TB calculated by the representative value calculation unit 81 to T1, and sets the larger one to T2, and sets the threshold based on T1 to Th1, Th2 (Th1 When <Th2) is satisfied, if Th1 ≦ T2 ≦ Th2 is satisfied, it is determined that the object 11 does not exist in the laser beam emission direction. Further, when Th1> T2 or T2> Th2 is satisfied, the object determination unit 83 determines that the object 11 that did not exist in the initial state exists in the laser light emission direction. However, this determination assumes that the object 11 is not present between the stationary reflecting wall surface 10 and the semiconductor laser 1, and assumes that the object 11 enters the space between the reflecting wall surface 10 and the semiconductor laser 1. is doing.

The threshold value setting unit 84 sets the threshold values Th1 and Th2 as in the following equation before the determination process by the object determination unit 83.
Th1 = aT1 (2)
Th2 = bT1 (3)
The coefficients a and b are predetermined constants that satisfy 0.5 ≦ a <1 and 1 <b ≦ 1.5. The threshold value setting unit 84 performs such threshold value setting processing every time the moving average value is calculated by the representative value calculation unit 81.

When the case where the object 11 is stationary in the laser beam emission direction is set to the initial state, the determination by the object determination unit 83 is as follows. That is, when Th1 ≦ T2 ≦ Th2 is satisfied, the object determination unit 83 determines that the object 11 existing in the laser light emission direction is not moving from the initial state, and when Th1> T2 or T2> Th2 is satisfied. It is determined that the object 11 has moved.
The object determination unit 83 performs the determination process as described above every time a measurement result is output from the signal extraction unit 7. The display unit 9 displays the determination result of the object determination unit 83.

  As described above, according to the present embodiment, unlike the object detection sensor disclosed in Patent Document 1, it is not necessary to create a frequency distribution of the MHP period. Therefore, the memory of the object detection sensor disclosed in Patent Document 1 It is possible to realize object detection or detection of object motion change with a memory having a smaller storage capacity. Further, the two moving average values TA and TB can be calculated in a shorter time than the time required to create the frequency distribution of the MHP cycle. Therefore, in this embodiment, it is possible to detect an object or a change in motion of an object in a shorter time than the object detection sensor disclosed in Patent Document 1. Further, in the present embodiment, since the error of the MHP cycle is corrected, the accuracy of object detection can be improved.

  In the case of detecting whether or not the object 11 is present between the reflecting wall surface 10 and the semiconductor laser 1 using the reflecting wall surface 10 as a reference surface for object detection, the determination can be made using only the threshold Th2. Good. That is, the object determination unit 83 determines that the object 11 does not exist in the laser light emission direction when T2 ≦ Th2 is satisfied, and that the object 11 exists in the laser light emission direction when T2> Th2 is satisfied. judge.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. In the present embodiment, another method for setting threshold values Th1 and Th2 for object detection will be described. Also in the present embodiment, since the configuration of the object detection sensor is the same as that of the first embodiment, description will be made using the reference numerals in FIGS.

When the threshold value setting unit 84 of the present embodiment sets Tmin as the minimum value among the measurement results of the signal extraction unit 7 corrected by the period correction unit 82 and Tmax as the maximum value among the corrected measurement results, The threshold values Th1 and Th2 are set as follows.
Th1 = T1-Tmin (4)
Th2 = T1 + Tmax (5)
The threshold value setting unit 84 performs the above threshold value setting process every time the measurement result of the signal extraction unit 7 is corrected by the period correction unit 82.

Alternatively, the threshold value setting unit 84 sets the threshold values Th1 and Th2 as follows when the variance of the measurement result of the signal extraction unit 7 corrected by the period correction unit 82 is σ ^2. Also good.
Th1 = T1-Aσ ² (6)
Th2 = T1 + Aσ ² (7)
In Expressions (6) and (7), A is a predetermined positive real number, for example, 3.

The object determination unit 83 performs the determination process as described in the first embodiment using the threshold values Th1 and Th2 set by the threshold setting unit 84.
Other configurations of the object detection sensor are as described in the first embodiment. Thus, in this embodiment, the threshold values Th1 and Th2 for object detection can be automatically set to appropriate values.

[Third Embodiment]
In the first and second embodiments, the reflection wall surface 10 is used as a reference surface for object detection. However, antireflection processing is performed only on one surface of a transparent body that forms a laser beam incident / exit portion from the semiconductor laser 1. The surface of the transparent body that is not subjected to the antireflection treatment may be used as a reference surface for object detection. FIG. 15 is a diagram showing a schematic configuration of a main part of an input / output unit of a semiconductor laser according to a third embodiment of the present invention. The same components as those in FIG. The major difference between the present embodiment and the first embodiment is that there is no reflecting wall surface and the object detection processing of the object detection unit 8 is different.

In FIG. 15, 130 is a sealed case for housing the semiconductor laser 1, 131 is a transparent cover (transparent body) such as glass provided on the front surface of the semiconductor laser 1 to protect the semiconductor laser 1, and 132 is on the surface of the transparent cover 131. An antireflection film (AR coating) is provided.
The transparent cover 131 is provided by being fitted into the window portion of the sealed case 130. Then, the semiconductor laser 1 is assembled in the sealed case 130 with the laser light incident / exit surface as the front surface facing the transparent cover 131.

  When laser light is input / output through a transparent body such as glass, the laser light is reflected slightly at the interface between the transparent body and air. In order to prevent such reflection, the surface of the transparent body is exclusively coated with a filler in which a low refractive index material is dispersed to form an antireflection film. Also in the present embodiment, an antireflection film 132 is provided on the surface of the transparent cover 131 in order to suppress unnecessary reflection on the transparent cover 131 serving as the laser light incident / exit surface. Only the antireflection film 132 is provided, and the antireflection film is not formed on the outer surface thereof, so that the laser beam is reflected on the outer surface of the transparent cover 131. A part of the laser light output from the semiconductor laser 1 is reflected by the outer surface of the transparent cover 131 and returned to the semiconductor laser 1.

  Of course, the outer surface of the transparent cover 131 is not subjected to the antireflection treatment, but the semiconductor laser 1 is intentionally subjected to a treatment necessary for obtaining a reflected light having an intensity that causes a self-coupling effect. May be. Specifically, the outer surface of the transparent cover 131 can be mirror-polished, or an optical film having a certain reflectivity can be formed by coating.

  According to the configuration shown in FIG. 15, when the object 11 is not present in the laser light emission direction, a part of the laser light emitted from the semiconductor laser 1 is reflected by the outer surface of the transparent cover 131 and is reflected on the semiconductor laser 1. Will return. As a result, in the semiconductor laser 1, interference due to the self-coupling effect between the output light and the reflected light from the transparent cover 131 occurs.

The object determination unit 83 of the object detection unit 8 may perform determination using only the threshold Th1 when one surface of the transparent cover 131 is used as a reference surface for object detection as in the present embodiment. That is, the object determination unit 83 determines that the object 11 does not exist in the laser light emission direction when Th1 ≦ T2 is satisfied, and that the object 11 exists in the laser light emission direction when Th1> T2 is satisfied. judge.
Other configurations of the object detection sensor are as described in the first and second embodiments.

  As described above, according to the present embodiment, the present invention can be applied even when one surface of the transparent cover 131 is used as a reference surface for object detection, and is the same as in the first and second embodiments. The effect of can be obtained.

[Fourth Embodiment]
Next, a fourth embodiment of the present invention will be described. In the first to third embodiments, the semiconductor laser 1 is oscillated in a triangular wave shape. However, the present invention is not limited to this, and the semiconductor laser 1 may be oscillated in a sawtooth wave shape as shown in FIG. That is, in the present embodiment, the semiconductor laser 1 may be operated so that one of the first oscillation period P1 and the second oscillation period P2 is repeatedly present. Even when the semiconductor laser 1 oscillates in a sawtooth shape as in the present embodiment, the rate of change of the oscillation wavelength of the semiconductor laser 1 needs to be constant. The operation in the first oscillation period P1 or the second oscillation period P2 is the same as in the case of triangular wave oscillation.

  In the first to fourth embodiments, the moving average value is used as the representative value of the distribution of the MHP cycle. However, the present invention is not limited to this, and instead of the moving average value, the average value, the maximum value, The representative value of the minimum value, the mode value, the median value, or the class value obtained from the frequency distribution of the MHP cycle, where the product of the class value and the frequency is maximum (hereinafter referred to as the maximum occupied value). It may be used.

  That is, in the first to fourth embodiments, the representative value calculation unit 81 uses the MHP cycle stored at the time prior to the current time stored in the storage unit 80 as the cycle of interest. An average value, maximum value, minimum value, mode value, median value, or maximum occupied value of a predetermined number of MHP cycles measured immediately before the cycle, and a predetermined number of MHP cycles measured immediately after the target cycle The average value, maximum value, minimum value, mode value, median value, or maximum occupation value may be calculated. Other configurations of the object detection unit 8 may execute the processes described in the first to fourth embodiments using the representative value calculated by the representative value calculation unit 81 instead of the moving average value. Note that the two representative values calculated by the representative value calculation unit 81 need to be representative values of the same type.

[Fifth Embodiment]
Next, a fifth embodiment of the present invention will be described. In the first to fourth embodiments, the representative value calculation unit 81 calculates two representative values, but a fixed value may be used as one representative value. Also in the present embodiment, since the configuration of the object detection sensor is the same as that of the first embodiment, description will be made using the reference numerals in FIGS.

  In the present embodiment, for example, the reflection wall surface 10 is used as a reference surface for object detection, and the distance between the reflection wall surface 10 and the semiconductor laser 1 is set as an initial value of the distance. As described with reference to FIG. 5, the number of MHPs is proportional to the measurement distance. Therefore, when the initial value of the distance is determined, the number of MHPs corresponding to the initial value of the distance can be obtained. And the period of MHP can be calculated | required from the number of MHP per time. The MHP cycle may be set as the initial value of the representative value.

The representative value calculation unit 81 of the present embodiment has a predetermined value measured immediately after the attention period when the MHP period stored at the time before the current time and stored in the storage unit 80 is the attention period. A moving average value, average value, maximum value, minimum value, mode value, median value, or maximum occupation value of a number of MHP cycles may be calculated. Other configurations of the object detection unit 8 are the first to fourth embodiments using the initial value of the representative value defined in advance from the initial value of the distance and the representative value calculated by the representative value calculation unit 81. What is necessary is just to perform the process demonstrated by.
Thus, also in this embodiment, the same effects as those in the first to fourth embodiments can be obtained.

[Sixth Embodiment]
Next, a sixth embodiment of the present invention will be described. In the first to fifth embodiments, the photodiode 2 and the current-voltage conversion amplification unit 5 are used as detection means for detecting an electric signal including an MHP waveform. However, the MHP waveform is not used without using a photodiode. It is also possible to extract. FIG. 17 is a block diagram showing a configuration of an object detection sensor according to the sixth embodiment of the present invention. The same reference numerals are given to the same configurations as those in FIG. The object detection sensor of this embodiment uses a voltage detection unit 12 as detection means instead of the photodiode 2 and the current-voltage conversion amplification unit 5 of the first embodiment.

  The voltage detector 12 detects and amplifies the voltage between the terminals of the semiconductor laser 1, that is, the anode-cathode voltage. When interference occurs between the laser light emitted from the semiconductor laser 1 and the return light from the object 11, an MHP waveform appears in the voltage between the terminals of the semiconductor laser 1. Therefore, it is possible to extract the MHP waveform from the voltage between the terminals of the semiconductor laser 1.

The filter unit 6 removes the carrier wave from the output voltage of the voltage detection unit 12. Other configurations of the object detection sensor are the same as those in the first to fifth embodiments.
Thus, in this embodiment, the MHP waveform can be extracted without using a photodiode, and the number of parts of the object detection sensor can be reduced as compared with the first embodiment. Cost can be reduced. In the present embodiment, since no photodiode is used, the influence of disturbance light can be removed.

  In the first to sixth embodiments, at least the signal extraction unit 7 and the object detection unit 8 are realized by, for example, a computer including a CPU, a memory, and an interface, and a program that controls these hardware resources. it can. The CPU executes the processes described in the first to sixth embodiments in accordance with a program stored in the memory.

  The present invention is applied to a technique for detecting the presence or absence of an object in the direction of laser light emission or a change in the movement of an object from information on interference caused by the self-coupling effect between laser light emitted from a semiconductor laser and its return light. Can do.

  DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 2 ... Photodiode, 3 ... Lens, 4 ... Laser driver, 5 ... Current-voltage conversion amplification part, 6 ... Filter part, 7 ... Signal extraction part, 8 ... Object detection part, 9 ... Display part, DESCRIPTION OF SYMBOLS 10 ... Reflective wall surface, 11 ... Object, 12 ... Voltage detection part, 80 ... Memory | storage part, 81 ... Representative value calculation part, 82 ... Period correction part, 83 ... Object determination part, 84 ... Threshold setting part, 130 ... Sealing Case 131: Transparent cover, 132 ... Antireflection film.

Claims (20)

A semiconductor laser that emits laser light;
Oscillation wavelength modulation means for operating the semiconductor laser so that at least one of a first oscillation period in which the oscillation wavelength continuously increases monotonously and a second oscillation period in which the oscillation wavelength continuously decreases monotonously exists ,
Detecting means for detecting an electric signal including an interference waveform generated by a self-coupling effect between the laser light emitted from the semiconductor laser and its return light;
Signal extraction means for measuring the period of the interference waveform included in the output signal of the detection means every time the interference waveform is input;
Storage means for storing the measurement result of the signal extraction means;
When the period of one interference waveform stored in the storage unit is set as the period of interest, a representative value of the distribution of the periods of the plurality of interference waveforms measured immediately before the period of interest and stored in the storage unit and the period of interest Representative value calculating means for calculating a representative value of the period distribution of the plurality of interference waveforms measured immediately after and stored in the storage means;
The period of interest is set as the period of the interference waveform to be corrected, and the period of the interference waveform to be corrected is compared with the two representative values to correct the period of the interference waveform to be corrected. Period correction means for updating the period stored in the storage means;
When the smaller one of the two representative values calculated by the representative value calculating means is T1, and the larger one is T2, the threshold value based on the representative value T1 is compared with the representative value T2, thereby comparing the laser light. Detecting the presence of an object that has appeared in the radiation direction, or an object determination means for detecting a change in the motion of the object that exists in the laser beam radiation direction from an initial state,
Representative values of the distribution of the period of the interference waveform are a moving average value, an average value, a maximum value, a minimum value, a mode value, a median value, or a class value and a frequency obtained from the frequency distribution of the period of the interference waveform. An object detection sensor characterized in that it is one of the class values with the maximum product. A semiconductor laser that emits laser light;
Oscillation wavelength modulation means for operating the semiconductor laser so that at least one of a first oscillation period in which the oscillation wavelength continuously increases monotonously and a second oscillation period in which the oscillation wavelength continuously decreases monotonously exists ,
Detecting means for detecting an electric signal including an interference waveform generated by a self-coupling effect between the laser light emitted from the semiconductor laser and its return light;
Signal extraction means for measuring the period of the interference waveform included in the output signal of the detection means every time the interference waveform is input;
Storage means for storing the measurement result of the signal extraction means;
When a period of one interference waveform stored in the storage means is an attention period, a representative for calculating a representative value of a distribution of periods of a plurality of interference waveforms measured immediately after the attention period and stored in the storage means A value calculating means;
The period of interest is the period of the interference waveform to be corrected, the period of the interference waveform to be corrected, the representative value of the period distribution of the interference waveform defined in advance from the initial value of the distance to the semiconductor laser, and the representative value A period correcting means for correcting the period of the interference waveform to be corrected by comparing with the representative value calculated by the calculating means, and updating the period stored in the storage means according to the result of the correction;
The threshold value based on the representative value T1 is compared with the representative value T2, where T1 is the smaller of the predefined representative value and the representative value calculated by the representative value calculating means, and T2 is the larger. The object determination means for detecting the presence of an object appearing in the laser light emission direction or detecting a change in the movement of the object existing in the laser light emission direction from an initial state,
Representative values of the distribution of the period of the interference waveform are a moving average value, an average value, a maximum value, a minimum value, a mode value, a median value, or a class value and a frequency obtained from the frequency distribution of the period of the interference waveform. An object detection sensor characterized in that it is one of the class values with the maximum product. The object detection sensor according to claim 1 or 2,
When the period correcting means has Tx = T1 + α · (T2−T1) (0 ≦ α ≦ 1), when the period of the interference waveform to be corrected is less than a predetermined number k times the Tx (k is 1). Less than a positive value), the period obtained by combining the period of the interference waveform to be corrected and the period of the next measured interference waveform is the period of the corrected interference waveform, and the combined waveform is a single waveform. When the period of the interference waveform to be corrected is not less than (m−0.5) times Tx and less than (m + 0.5) times Tx (m is a natural number of 2 or more), An object detection sensor characterized in that a period obtained by dividing the period of the interference waveform into m equal parts is a period after correction, and there are m waveforms after the correction. The object detection sensor according to any one of claims 1 to 3,
When the threshold based on the representative value T1 is Th1, Th2 (Th1 <Th2), and the object determination means satisfies Th1 ≦ T2 ≦ Th2, there is no object in the laser light emission direction. An object detection sensor characterized in that, when Th1> T2 or T2> Th2 holds, it is determined that an object is present in the laser light emission direction. The object detection sensor according to any one of claims 1 to 3,
When the object determination means is in an initial state when the object is stationary in the laser light emission direction and the threshold value based on the representative value T1 is Th1, Th2 (Th1 <Th2), Th1 ≦ T2 When ≦ Th2 is satisfied, it is determined that the object existing in the laser light emission direction is not moving, and when Th1> T2 or T2> Th2 is satisfied, the object existing in the laser light emission direction is moved. An object detection sensor characterized by determining. The object detection sensor according to claim 4 or 5,
Furthermore, threshold value setting means for setting the threshold values Th1 and Th2 as Th1 = aT1 and Th2 = bT1 (0.5 ≦ a <1, 1 <b ≦ 1.5) is provided. Object detection sensor. The object detection sensor according to claim 4 or 5,
Further, when the minimum value of the period of the interference waveform corrected by the period correcting means is Tmin and the maximum value is Tmax, the threshold values Th1 and Th2 are set as Th1 = T1−Tmin and Th2 = T1 + Tmax. An object detection sensor comprising a threshold setting means. The object detection sensor according to claim 4 or 5,
Further, when the dispersion value of the period of the interference waveform corrected by the period correcting means is σ ² , the threshold values Th1 and Th2 are set to Th1 = T1−Aσ ² , Th2 = T1 + Aσ ² (A is a positive real number) ) And a threshold value setting means for setting the object detection sensor. The object detection sensor according to claim 4,
When the object determining means detects whether or not an object exists between the reference surface and the semiconductor laser, with a reflective wall surface facing the semiconductor laser across a space where the object is to enter as a reference surface , T2 ≦ Th2 is satisfied, it is determined that no object is present in the laser light emission direction, and when T2> Th2 is satisfied, it is determined that an object is present in the laser light emission direction. Object detection sensor. The object detection sensor according to claim 4,
Whether the object determination means has an object in front of the reference surface with any one of the inner surface and outer surface of the transparent cover protecting the semiconductor laser not subjected to anti-reflection treatment as a reference surface. When detecting whether or not Th1 ≦ T2 holds, it is determined that no object exists in front of the reference plane, and when Th1> T2 holds, it is determined that an object exists in front of the reference plane. A featured object detection sensor. An oscillation procedure for operating the semiconductor laser so that at least one of the first oscillation period in which the oscillation wavelength continuously increases monotonously and the second oscillation period in which the oscillation wavelength continuously decreases monotonously exists;
A detection procedure for detecting an electrical signal including an interference waveform generated by a self-coupling effect between laser light emitted from the semiconductor laser and its return light;
A signal extraction procedure for measuring the period of the interference waveform included in the output signal obtained by the detection procedure every time the interference waveform is input;
A storage procedure for storing the measurement result of the signal extraction procedure in the storage means;
When the period of one interference waveform stored in the storage means is the period of interest, the representative value of the distribution of the periods of the plurality of interference waveforms measured immediately before the period of interest and stored in the storage means and the period of interest A representative value calculation procedure for calculating a representative value of the period distribution of the plurality of interference waveforms measured immediately after and stored in the storage means;
The period of interest is set as the period of the interference waveform to be corrected, and the period of the interference waveform to be corrected is compared with the two representative values to correct the period of the interference waveform to be corrected. A cycle correction procedure for updating the cycle stored in the storage means;
When the smaller one of the two representative values calculated in the representative value calculating procedure is T1 and the larger one is T2, the threshold value based on the representative value T1 is compared with the representative value T2, thereby comparing the laser light. An object determination procedure for detecting the presence of an object that appears in the radiation direction or detecting a change in the motion of an object that exists in the laser beam radiation direction from an initial state;
Representative values of the distribution of the period of the interference waveform are a moving average value, an average value, a maximum value, a minimum value, a mode value, a median value, or a class value and a frequency obtained from the frequency distribution of the period of the interference waveform. An object detection method characterized in that the product value is one of class values that maximizes the product of. An oscillation procedure for operating the semiconductor laser so that at least one of the first oscillation period in which the oscillation wavelength continuously increases monotonously and the second oscillation period in which the oscillation wavelength continuously decreases monotonously exists;
A detection procedure for detecting an electrical signal including an interference waveform generated by a self-coupling effect between laser light emitted from the semiconductor laser and its return light;
A signal extraction procedure for measuring the period of the interference waveform included in the output signal obtained by the detection procedure every time the interference waveform is input;
A storage procedure for storing the measurement result of the signal extraction procedure in the storage means;
When the period of one interference waveform stored in the storage means is an attention period, a representative that calculates a representative value of the distribution of the periods of a plurality of interference waveforms that are measured immediately after the attention period and stored in the storage means Value calculation procedure,
The period of interest is the period of the interference waveform to be corrected, the period of the interference waveform to be corrected, the representative value of the period distribution of the interference waveform defined in advance from the initial value of the distance to the semiconductor laser, and the representative value A period correction procedure for correcting the period of the interference waveform to be corrected by comparing the representative value calculated in the calculation procedure, and updating the period stored in the storage unit according to the result of the correction;
The threshold value based on the representative value T1 is compared with the representative value T2, where T1 is the smaller of the predefined representative value and the representative value calculated in the representative value calculation procedure, and T2 is the larger. By detecting the presence of an object that appears in the laser light emission direction, or an object determination procedure for detecting a change in the motion of an object that exists in the laser light emission direction from an initial state,
Representative values of the distribution of the period of the interference waveform are a moving average value, an average value, a maximum value, a minimum value, a mode value, a median value, or a class value and a frequency obtained from the frequency distribution of the period of the interference waveform. An object detection method characterized in that the product value is one of class values that maximizes the product of. The object detection method according to claim 11 or 12,
When the period correction procedure is Tx = T1 + α · (T2−T1) (0 ≦ α ≦ 1), when the period of the interference waveform to be corrected is less than a predetermined number k times the Tx (k is 1). Less than a positive value), the period obtained by combining the period of the interference waveform to be corrected and the period of the next measured interference waveform is the period of the corrected interference waveform, and the combined waveform is a single waveform. When the period of the interference waveform to be corrected is not less than (m−0.5) times Tx and less than (m + 0.5) times Tx (m is a natural number of 2 or more), An object detection method characterized in that a period obtained by dividing the period of an interference waveform into m equal parts is a period after correction, and there are m waveforms with a period after correction. The object detection method according to any one of claims 11 to 13,
In the object determination procedure, when the threshold value based on the representative value T1 is Th1, Th2 (Th1 <Th2), and Th1 ≦ T2 ≦ Th2 is satisfied, there is no object in the laser light emission direction. An object detection method comprising: determining and determining that an object is present in the laser light emission direction when Th1> T2 or T2> Th2 is satisfied. The object detection method according to any one of claims 11 to 13,
In the object determination procedure, when the object is stationary in the laser light emission direction, the initial state is set, and when the threshold value based on the representative value T1 is Th1, Th2 (Th1 <Th2), Th1 ≦ T2 When ≦ Th2 is satisfied, it is determined that the object existing in the laser light emission direction is not moving, and when Th1> T2 or T2> Th2 is satisfied, the object existing in the laser light emission direction is moved. An object detection method characterized by determining. The object detection method according to claim 14 or 15,
Further, before the object determination procedure, the threshold values Th1 and Th2 are set as Th1 = aT1 and Th2 = bT1 (0.5 ≦ a <1, 1 <b ≦ 1.5). An object detection method comprising a procedure. The object detection method according to claim 14 or 15,
Further, before the object determination procedure, when the minimum value is Tmin and the maximum value is Tmax in the period of the interference waveform corrected by the period correction procedure, the threshold values Th1 and Th2 are set to Th1 = T1−Tmin. , Th2 = T1 + Tmax, a threshold setting procedure for setting the object detection method. The object detection method according to claim 14 or 15,
Further, when the variance of the period of the interference waveform corrected in the period correction procedure is σ ² before the object determination procedure, the threshold values Th1 and Th2 are set to Th1 = T1−Aσ ² and Th2 = T1 + Aσ. ^2. An object detection method comprising a threshold setting procedure for setting ² (A is a positive real number). The object detection method according to claim 14.
When the object determination procedure detects whether an object exists between the reference surface and the semiconductor laser, with a reflective wall surface facing the semiconductor laser sandwiching a space where the object is to enter, as a reference surface , T2 ≦ Th2 is satisfied, it is determined that no object is present in the laser light emission direction, and when T2> Th2 is satisfied, it is determined that an object is present in the laser light emission direction. Object detection method. The object detection method according to claim 14.
Whether the object exists in front of the reference plane, with any one of the inner and outer surfaces of the transparent cover that protects the semiconductor laser not subjected to anti-reflection treatment as a reference plane. When detecting whether or not Th1 ≦ T2 holds, it is determined that no object exists in front of the reference plane, and when Th1> T2 holds, it is determined that an object exists in front of the reference plane. Characteristic object detection method.

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