JP2009222674A - Reflection-type photoelectric switch and object detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-accuracy reflection-type photoelectric switch, utilizing a simple and low-cost constitution, by utilizing self-adopted type laser measuring instrument. <P>SOLUTION: This reflection-type photoelectric switch includes a semiconductor laser 1, detecting means (photodiode 2, current-voltage conversion amplifier 5) for detecting electric signal which includes interferential waveform, caused by self-combined effect between laser beam radiated from the semiconductor laser 1 and return light from an object 10; and distance determination processing means (filter part 6, digital part 7, determination part 8) for determining as to whether the distance to the object 10 is farther from or nearer to than reference range, based on information of the interferential waveform. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a reflection type photoelectric switch, and more particularly to a reflection type photoelectric switch and an object detection method for detecting whether the distance to an object is far or close to a predetermined reference distance.

  Conventionally, as one of the reflection type photoelectric switches, a distance setting reflection type (Background Suppression, hereinafter abbreviated as BGS) photoelectric switch for detecting whether the distance from the photoelectric switch to an object is greater than or close to a predetermined reference distance has been proposed. Known (for example, refer to Patent Document 1 and Patent Document 2). According to such a BGS photoelectric switch, only an object can be detected without detecting the background.

  On the other hand, a laser measuring instrument using interference (self-coupling effect) in the semiconductor laser between the output light of the laser and the return light from the measurement object has been proposed as a distance meter using the interference of light by the laser ( For example, refer nonpatent literature 1, nonpatent literature 2, and nonpatent literature 3). FIG. 14 shows a composite resonator model of an FP type (Fabry-Perot type) semiconductor laser. In FIG. 14, 101 is a semiconductor laser, 102 is a wall opening of a semiconductor crystal, 103 is a photodiode, and 104 is an object to be measured.

When the oscillation wavelength of the laser is λ and the distance from the wall open surface 102 closer to the measurement target 104 to the measurement target 104 is L, the return light from the measurement target 104 and the resonator 101 are satisfied when the following resonance condition is satisfied. The inner laser beams strengthen each other, 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 measurement object 104 is very weak, because the apparent reflectance in the resonator 101 of the semiconductor laser increases, causing an amplification effect.

  Since the semiconductor laser emits laser beams having different frequencies according to the magnitude of the injection current, an external modulator is not required when modulating the oscillation frequency, and direct modulation is possible by the injection current. FIG. 15 is a diagram showing the relationship between the oscillation wavelength and the output waveform of the photodiode 103 when the oscillation wavelength of the semiconductor laser 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 resonator 101 becomes 0 ° (the same phase), and the return light and the resonator 101 When L = qλ / 2 + λ / 4, the phase difference becomes 180 ° (opposite phase), and the return light and the laser light in the resonator 101 are the weakest. Therefore, when the oscillation wavelength of the semiconductor laser is changed, a place where the laser output becomes strong and a place where the laser output becomes weak appear alternately, and the laser output at this time is detected by the photodiode 103 provided in the resonator 101. As shown in FIG. 15, a step-like waveform having a constant period is obtained. Such a waveform is generally called an interference fringe.

  Each stepped waveform, that is, each interference fringe is called a mode pop pulse (hereinafter referred to as MHP). MHP is a phenomenon different from the mode hopping phenomenon. For example, if the number of MHPs is 10 when the distance to the measurement object 104 is L1, the number of MHPs is 5 at half the distance L2. That is, when the oscillation wavelength of the semiconductor laser is changed for a certain time, the number of MHPs changes in proportion to the measurement distance. Therefore, if the MHP is detected by the photodiode 103 and the frequency of the MHP is measured, the distance can be easily measured.

  A BGS photoelectric switch can be realized by using the self-coupled laser measuring instrument as described above. The BGS photoelectric switch may be turned on / off based on whether the object is at a short distance or a long distance compared to a predetermined reference distance. Therefore, when a self-coupled laser measuring instrument is used as a BGS photoelectric switch, whether the average period of the measured MHP is longer or shorter than the known reference period of the MHP when the object is at the reference distance. Can be determined. When the average period of the measured MHP is longer than the known period of the MHP when the object is at the position of the reference distance, it is determined that the object exists at a shorter distance than the reference distance, and the measurement is performed. When the MHP cycle is short, it is determined to be off because the object is located farther than the reference distance.

JP 63-102135 A Japanese Unexamined Patent Publication No. 63-187237 Tadashi Ueda, Satoshi Yamada, Susumu Shito, “Distance Meter Using Self-Coupling Effect of Semiconductor Laser”, Proceedings of the 1994 Tokai Branch Joint Conference of Electrical Engineering Society, 1994 Satoshi Yamada, Susumu Shito, Norio Tsuda, Tadashi Ueda, “Study on a small rangefinder using the self-coupling effect of a semiconductor laser”, Aichi Institute of Technology research report, No. 31 B, p. 35-42, 1996 Guido Giuliani, Michele Norgia, Silvano Donati and Thierry Bosch, “Laser diode self-mixing technique for sensing applications”, JOURNAL OF OPTICS A: PURE AND APPLIED OPTICS, p. 283-294, 2002

  As described above, a BGS photoelectric switch can be realized by using a self-coupled laser measuring instrument. However, simply determining the average period of MHP and comparing it with the reference period results in poor determination accuracy. Therefore, using the method proposed by the inventor in Japanese Patent Application No. 2007-015020, the frequency distribution of the MHP period is obtained, the representative value of the distribution such as the median or the mode is obtained, and the representative value of the distribution of this period If the distance to the object is calculated based on the frequency distribution of the period and the calculated distance is compared with the reference distance, the determination accuracy can be improved. However, such a method requires a memory and a computer, and there is a problem that the cost of the BGS photoelectric switch increases.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to realize a highly accurate reflective photoelectric switch with a simple and inexpensive configuration using a self-coupled laser measuring instrument.

The reflection type photoelectric switch according to the present invention includes an interference waveform generated by a self-coupling effect of a semiconductor laser that emits laser light, and the laser light emitted from the semiconductor laser and return light from an object existing in front of the semiconductor laser. Detecting means for detecting an electrical signal including: a distance determination processing means for determining whether the distance to the object is far from or close to a predetermined reference distance from information on the interference waveform included in the output signal of the detecting means; It is characterized by providing.
Further, in one configuration example of the reflective photoelectric switch of the present invention, the distance determination processing unit is configured to detect the interference unit when the period of the interference waveform when the object is at the reference distance is a reference period. Counting means for counting the number of the interference waveforms included in the output signal by dividing the number into the number of interference waveforms having a period longer than the reference period and the number of interference waveforms having a period shorter than the reference period; When the number of interference waveforms is larger than the number of interference waveforms having a short period, it is determined that the object is present at a shorter distance than the reference distance, and the number of interference waveforms having a short period is an interference waveform having a long period. And determining means for determining that the object is located at a distance farther than the reference distance when the number of objects is greater than the number.
Further, in one configuration example of the reflective photoelectric switch of the present invention, the distance determination processing unit is configured such that when a half cycle of the interference waveform when the object is at the reference distance is a reference half cycle, Counting means for counting the number of the interference waveforms included in the output signal of the detection means by dividing into the number of interference waveforms having a half cycle longer than the reference half cycle and the number of interference waveforms having a half cycle shorter than the reference half cycle. When the number of interference waveforms having a long half cycle is greater than the number of interference waveforms having a short half cycle, it is determined that the object is present at a shorter distance than the reference distance, and the interference waveform having a short half cycle is And a determination means for determining that the object exists at a distance farther than the reference distance when the number of interference waveforms is larger than the number of interference waveforms having a long half cycle.

Further, in one configuration example of the reflective photoelectric switch of the present invention, the counting means includes a rising edge detecting means for detecting the rising edge of the interference waveform, and a time measurement for measuring a time from the rising edge of the interference waveform to the next rising edge. And when the time from the rising edge of the interference waveform to the next rising edge is longer than the reference period, the number of interference waveforms having a longer period than the reference period is increased, and from the rising edge of the interference waveform to the next rising edge. When the time is shorter than the reference period, the comparison means is configured to increase the number of interference waveforms having a period shorter than the reference period.
Further, in one configuration example of the reflective photoelectric switch of the present invention, the counting means includes a fall detection means for detecting a fall of the interference waveform, and a time from the fall of the interference waveform to the next fall. When the time measurement means for measuring and the time from the fall of the interference waveform to the next fall are longer than the reference period, the number of interference waveforms having a period longer than the reference period is increased, and the interference waveform When the time from the fall to the next fall is shorter than the reference period, the comparison means is configured to increase the number of interference waveforms having a period shorter than the reference period.

Further, in one configuration example of the reflective photoelectric switch of the present invention, the counting means includes a rising edge detecting means for detecting a rising edge of the interference waveform, a falling edge detecting means for detecting a falling edge of the interference waveform, and the interference. First time measuring means for measuring a first time from the rising edge of the waveform to the next rising edge, and second time measuring means for measuring a second time from the falling edge of the interference waveform to the next falling edge If the first time is longer than the reference period or the second time is longer than the reference period, the number of interference waveforms having a period longer than the reference period is increased, When the time is shorter than the reference period, or when the second time is shorter than the reference period, the comparison means increases the number of interference waveforms whose period is shorter than the reference period. The one in which the features.
Further, in one configuration example of the reflective photoelectric switch of the present invention, the counting means includes a rising edge detecting means for detecting a rising edge of the interference waveform, a falling edge detecting means for detecting a falling edge of the interference waveform, and the interference. A first time measuring means for measuring a first time from the rising edge of the waveform to the next falling edge; and a second time measuring means for measuring a second time from the falling edge of the interference waveform to the next rising edge. And when the first time is longer than the reference half cycle or the second time is longer than the reference half cycle, the number of interference waveforms having a half cycle longer than the reference half cycle is increased, When the first time is shorter than the reference half cycle or when the second time is shorter than the reference half cycle, the comparison increases the number of interference waveforms whose half cycle is shorter than the reference half cycle. And it is characterized in that comprising the stages.

The object detection method of the present invention includes an oscillation procedure for operating a semiconductor laser by supplying a drive current to the semiconductor laser, a laser beam emitted from the semiconductor laser, and an object existing in front of the semiconductor laser. Based on a detection procedure for detecting an electrical signal including an interference waveform caused by a self-coupling effect with return light, and information on the interference waveform included in the output signal obtained by this detection procedure, the distance to the object is a predetermined reference. A distance determination processing procedure for determining whether the distance is farther or closer than the distance.
Further, in one configuration example of the object detection method of the present invention, the distance determination processing procedure is performed when the period of the interference waveform when the object is at the position of the reference distance is a reference period. A counting procedure for counting the number of interference waveforms included in the obtained output signal by dividing the number into a number of interference waveforms having a period longer than the reference period and a number of interference waveforms having a period shorter than the reference period; When the number of long interference waveforms is larger than the number of interference waveforms having a short period, it is determined that the object is present at a shorter distance than the reference distance, and the number of interference waveforms having a short period is the long period. It is characterized by comprising a determination procedure for determining that the object exists at a distance farther than the reference distance when the number is larger than the number of interference waveforms.
Further, in one configuration example of the object detection method of the present invention, the distance determination processing procedure is performed when the half cycle of the interference waveform when the object is at the reference distance is set as a reference half cycle. The number of the interference waveforms included in the output signal obtained in the procedure is divided into the number of interference waveforms whose half cycle is longer than the reference half cycle and the number of interference waveforms whose half cycle is shorter than the reference half cycle. When the number of interference waveforms having a long half cycle is greater than the number of interference waveforms having a short half cycle, it is determined that the object is present at a shorter distance than the reference distance, and the half cycle is short. When the number of interference waveforms is larger than the number of interference waveforms having a long half cycle, the determination procedure is such that the object is determined to exist at a distance farther than the reference distance.

  According to the present invention, it is possible to realize an accurate reflective photoelectric switch with a simple and inexpensive configuration using a self-coupled laser measuring instrument.

  In the present invention, the counting means includes a rising edge detecting means for detecting the rising edge of the interference waveform, a time measuring means for measuring the time from the rising edge of the interference waveform to the next rising edge, and from the rising edge of the interference waveform to the next rising edge. If the time is longer than the reference period, increase the number of interference waveforms with a longer period than the reference period, and if the time from the rise of the interference waveform to the next rise is shorter than the reference period, the period is longer than the reference period. By using the comparison means for increasing the number of short interference waveforms, it is only necessary to detect the rise of the interference waveform and compare the lengths of the periods, so that the counting means can be realized with a simple structure.

  In the present invention, the counting means includes a falling detection means for detecting the falling edge of the interference waveform, a time measuring means for measuring the time from the falling edge of the interference waveform to the next falling edge, and the falling edge of the interference waveform. If the time from one to the next fall is longer than the reference period, increase the number of interference waveforms with a longer period than the reference period, and the time from the fall of the interference waveform to the next fall is shorter than the reference period In this case, the counting means can be configured simply by detecting the falling edge of the interference waveform and comparing the length of the period by configuring the comparing means to increase the number of interference waveforms whose period is shorter than the reference period. Can be realized.

  In the present invention, the counting means includes a rise detection means for detecting the rise of the interference waveform, a fall detection means for detecting the fall of the interference waveform, and a first time from the rise of the interference waveform to the next rise. A first time measuring means for measuring the time, a second time measuring means for measuring a second time from the fall of the interference waveform to the next fall, and the first time being longer than the reference period, or When the second time is longer than the reference period, the number of interference waveforms having a longer period than the reference period is increased, and when the first time is shorter than the reference period or when the second time is shorter than the reference period The counter means can be realized with a simple structure by comprising the comparing means for increasing the number of interference waveforms having a shorter period than the reference period. In the present invention, the counting accuracy can be improved, and the accuracy of determining the distance of the object can be improved. In the present invention, the influence of the transient response of the oscillation waveform of the semiconductor laser on the counting result can be reduced, and the influence of the DC bias of the interference waveform can be eliminated.

  In the present invention, the counting means includes a rising edge detecting means for detecting the rising edge of the interference waveform, a falling edge detecting means for detecting the falling edge of the interference waveform, and a first time from the rising edge of the interference waveform to the next falling edge. A first time measuring means for measuring time, a second time measuring means for measuring a second time from the fall of the interference waveform to the next rise, and the first time being longer than a reference half cycle Alternatively, when the second time is longer than the reference half cycle, the number of interference waveforms having a half cycle longer than the reference half cycle is increased, and when the first time is shorter than the reference half cycle or the second time is set as the reference When the period is shorter than the half cycle, the counting unit can be realized with a simple configuration by including the comparison unit that increases the number of interference waveforms whose half cycle is shorter than the reference half cycle. In the present invention, the counting accuracy can be improved, and the accuracy of determining the distance of the object can be improved.

[First Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a BGS photoelectric switch according to a first embodiment of the present invention.
The BGS photoelectric switch in FIG. 1 collects and emits a semiconductor laser 1 that emits laser light, a photodiode 2 that converts the optical output of the semiconductor laser 1 into an electrical signal, and the light from the semiconductor laser 1. A lens 3 that collects the return light from the object 10 and makes it incident on the semiconductor laser 1, a laser driver 4 that drives the semiconductor laser 1, and a current-voltage conversion that converts the output current of the photodiode 2 into a voltage and amplifies it. The amplifying unit 5, the filter unit 6 that removes the carrier wave from the output voltage of the current-voltage conversion amplifying unit 5, the counting unit 7 that counts the number of MHPs included in the output voltage of the filter unit 6, and the counting result of the counting unit 7 Determination unit 8 that determines whether the object 10 is closer or far than a predetermined reference distance, and a display unit 9 that displays the determination result of the determination unit 8.

The photodiode 2 and the current-voltage conversion amplification unit 5 constitute a detection unit, and the filter unit 6, the counting unit 7, and the determination unit 8 constitute a distance determination processing unit.
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 the change over 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 Tt is the period of the triangular wave. In the present embodiment, the maximum value λb of the oscillation wavelength and the minimum value λa of the oscillation wavelength are always constant, and the difference λb−λa is also always constant.

  Laser light emitted from the semiconductor laser 1 is collected by the lens 3 and enters the object 10. The light reflected by the object 10 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 amplification unit 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.

  The counting unit 7 has a period longer than the number of MHPs included in the output voltage of the filter unit 6, in particular, a known period of the MHP when the object 10 is at a predetermined reference distance (hereinafter referred to as a reference period Th). The number of long MHPs Nlong and the number of MHPs Nshort having a shorter period than the reference period Th are counted for each of the first oscillation period P1 and the second oscillation period P2.

  When the distance per MHP is 0.5 mm, the reference distance is 200 mm, and the frequency of the triangular wave is 1 kHz, the number of MHPs to be measured is the distance [mm] /0.5 [mm] from the object 10. Therefore, when the object 10 is at a position away from the BGS photoelectric switch by the reference distance, the number of MHPs is 200 [mm] /0.5 [mm] = 400 [pieces]. At this time, the reference period Th of MHP is 1 / (1000 × 2) /400=1.25 [μ seconds]. When the distance to the object 10 is longer than the reference distance, the MHP cycle is shorter than the reference cycle Th = 1.25 [μsec], and when the distance to the object 10 is shorter than the reference distance, the MHP cycle is It becomes longer than the reference cycle Th = 1.25 [μ seconds].

  When the object 10 is present at a position closer than the reference distance, the distribution of the MHP cycle shifts to a longer side than the reference cycle Th as shown by a distribution 40 in FIG. On the other hand, when the object 10 exists at a position farther than the reference distance, the distribution of the MHP cycle shifts to a shorter one than the reference cycle Th as shown by a distribution 41 in FIG.

  The determination unit 8 determines whether the object 10 is closer or farther than the reference distance from the counting result of the counting unit 7. That is, the determination unit 8 compares the number Nlong of MHPs having a longer period than the reference period Th with the number Nshort of MHPs having a shorter period than the reference period Th, and if Nlong> Nshort is satisfied, the object 10 has the reference distance. If Nlong <Nshort is satisfied, it is determined that the object 10 exists at a distance farther than the reference distance.

The determination unit 8 performs the determination as described above for each counting period (each of the first oscillation period P1 and the second oscillation period P2 in the present embodiment) in which the counting unit 7 counts the number of MHPs.
The display unit 9 displays the determination result of the determination unit 8.

  As described above, in the present embodiment, by comparing the number Nlong of MHP having a longer period than the reference period Th with the number Nshort of MHP having a shorter period than the reference period Th, the BGS photoelectric switch to the object 10 is compared. Can be determined whether or not the distance (more precisely, the distance from the semiconductor laser 1 to the object 10) is far from or close to the reference distance, so that a highly accurate BGS photoelectric switch can be realized with a simple and inexpensive configuration. it can.

Note that the counting unit 7 and the determination unit 8 may be realized by a computer including a CPU, a storage device and an interface, and a program stored in the storage device, or may be realized by hardware.
In the present embodiment, the number Nlong of MHPs having a longer period than the reference period Th is compared with the number Nshort of MHPs having a shorter period than the reference period Th, but the half period Th / 2 of the reference period ( Hereinafter, the number of MHPs whose half cycle is longer than the reference half cycle Th / 2 may be compared with the number of MHPs whose half cycle is shorter than the reference half cycle Th / 2. The case of using the reference half cycle Th / 2 will be described later.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. In the present embodiment, the counting unit 7 of the first embodiment will be described more specifically. FIG. 5 is a block diagram showing the configuration of the counting unit of the BGS photoelectric switch according to the second embodiment of the present invention.
The counting unit 7 of the present embodiment includes a rising detection unit 70, a falling detection unit 71, time measurement units 72 and 73, and a comparison unit 74.

FIG. 6 is a diagram for explaining the operation of the counting unit 7 of the present embodiment, and is a diagram schematically showing the output voltage waveform of the filter unit 6, that is, the MHP waveform. In FIG. 6, H1 is a threshold value for detecting the rising edge of MHP, and H2 is a threshold value for detecting the falling edge of MHP.
The rise detection unit 70 detects the rise of the MHP by comparing the output voltage of the filter unit 6 with the threshold value H1. The time measuring unit 72 measures the time tu from the rise of the MHP to the next rise based on the detection result of the rise detection unit 70. The time measurement unit 72 performs such measurement every time the rising edge of MHP is detected.

  On the other hand, the fall detection unit 71 detects the fall of MHP by comparing the output voltage of the filter unit 6 with the threshold value H2. The time measuring unit 73 measures the time tdd from the falling edge of MHP to the next falling edge based on the detection result of the falling edge detecting unit 71. The time measurement unit 73 performs such measurement every time a falling edge of MHP is detected.

  The comparison unit 74 compares the time tu from the rising edge of MHP to the next rising edge with the reference period Th described above. If the time tuu is longer than the reference period Th, the number Nlong of MHPs having a longer period than the reference period Th. When the time tuu is shorter than the reference period Th, the number Nshort of MHPs whose period is shorter than the reference period Th is increased by one. The comparison unit 74 performs such counting every time the time tuu is measured.

  Or the comparison part 74 may measure as follows using time tdd from the fall of MHP to the next fall. That is, the comparison unit 74 compares the time tdd from the falling edge of MHP to the next falling edge with the reference period Th, and when the time tdd is longer than the reference period Th, the MHP whose period is longer than the reference period Th. When the number Nlong is increased by 1 and the time tdd is shorter than the reference period Th, the number Nshort of MHPs having a period shorter than the reference period Th is increased by 1. The comparison unit 74 performs such counting every time the time tdd is measured.

  As described above, the counting unit 7 of the present embodiment can count the number Nlong of MHPs having a period longer than the reference period Th and the number Nshort of MHPs having a period shorter than the reference period Th. As described in the first embodiment, the counting unit 7 counts MHP for each counting period (each of the first oscillation period P1 and the second oscillation period P2).

When the comparison unit 74 uses the time tuu, the falling detection unit 71 and the time measurement unit 73 are not essential components. Further, when the comparison unit 74 uses the time tdd, the rising detection unit 70 and the time measurement unit 72 are not essential components.
Other configurations of the BGS photoelectric switch are as described in the first embodiment.

In the present embodiment, it is only necessary to detect the rising edge (or falling edge) of MHP and compare the lengths of the periods, so that the counting unit 7 can be realized with a simple configuration.
However, this embodiment has the following problems. The problem is that in the case of a self-coupled laser measuring instrument used as a BGS photoelectric switch, the oscillation wavelength of the semiconductor laser 1 is changed into a triangular wave shape, and therefore the influence of the transient response at the apex of the triangular wave cannot be completely eliminated. This is not possible, and the MHP cycle may be measured to be longer or shorter than actual, so that an error occurs in the counting result, and as a result, an error may occur in the determination of the perspective of the object 10.

  That is, the filter unit 6 removes the oscillation waveform (carrier wave) of the semiconductor laser 1 from the output voltage waveform (modulated wave) of the current-voltage conversion amplification unit 5 and extracts the MHP waveform as shown in FIG. However, at this time, a spike-like transient response waveform appears at the apex of the triangular wave in the output of the filter unit 6. This transient response waveform causes an error in the measurement of the MHP cycle.

  This problem will be described with reference to FIG. In the example of FIG. 7, the point PE indicates the timing of the maximum value of the triangular wave. As shown in FIG. 3B, at the timing of the maximum value of the triangular wave, downward spike noise is generated at the output of the filter unit 6, so that the waveform of MHP is dragged toward the lower voltage as shown in FIG. It becomes. Therefore, the time tu from the rise of the MHP to the next rise is shorter than the original value, and the time tdd from the fall of the MHP to the next fall is longer than the original value. Such a problem can be improved by performing the operation of the counting unit 7 and the determining unit 8 for one period of the triangular wave. However, when the DC bias exists in the MHP, the transient response of the timing of the maximum value of the triangular wave is obtained. The effect remains because the response is different from the transient response of the minimum value of the triangular wave.

[Third Embodiment]
Next, a third embodiment of the present invention will be described. In the present embodiment, the case where the reference half cycle Th / 2 is used in the BGS photoelectric switch of the first embodiment will be described. FIG. 8 is a block diagram showing the configuration of the counting unit of the BGS photoelectric switch according to the third embodiment of the present invention.
The counting unit 7 according to the present embodiment includes a rising detection unit 70, a falling detection unit 71, time measurement units 75 and 76, and a comparison unit 77.

FIG. 9 is a diagram for explaining the operation of the counting unit 7 of the present embodiment, and schematically shows the output voltage waveform of the filter unit 6, that is, the MHP waveform.
The operations of the rise detection unit 70 and the fall detection unit 71 are the same as those in the second embodiment.

The time measuring unit 75 measures a time tud from the rising edge of the MHP to the next falling edge based on the detection results of the rising edge detecting section 70 and the falling edge detecting section 71. The time measuring unit 75 performs such measurement every time the rising and falling edges of MHP are detected.
On the other hand, the time measurement unit 76 measures the time tdu from the fall of MHP to the next rise based on the detection results of the rise detection unit 70 and the fall detection unit 71. The time measuring unit 76 performs such measurement every time the falling and rising edges of MHP are detected.

  The comparison unit 77 compares the time tud from the rise of the MHP to the next fall and the time tdu from the fall of the MHP to the next rise with the reference half cycle Th / 2, and the time tud is the reference half cycle Th / 2. Or longer than the reference half cycle Th / 2, the number Nlong of MHPs having a longer half cycle than the reference half cycle Th / 2 is increased by 1, and the time tud is greater than the reference half cycle Th / 2. If the time tdu is shorter than the reference half cycle Th / 2, the number Nshort of MHPs whose half cycle is shorter than the reference half cycle Th / 2 is increased by one. The comparison unit 77 performs such a count every time either the time tud or tdu is measured.

  As described above, the counting unit 7 of the present embodiment calculates the number Nlong of MHPs having a half cycle longer than the reference half cycle Th / 2 and the number Nshort of MHPs having a half cycle shorter than the reference half cycle Th / 2. Can count. As described in the first embodiment, the counting unit 7 counts MHP for each counting period (each of the first oscillation period P1 and the second oscillation period P2).

In the case of the present embodiment, the determination unit 8 compares the number Nlong of MHPs whose half cycle is longer than the reference half cycle Th / 2 with the number Nshort of MHPs whose half cycle is shorter than the reference half cycle Th / 2. When Nlong> Nshort is satisfied, it is determined that the object 10 is present at a shorter distance than the reference distance. When Nlong <Nshort is satisfied, it is determined that the object 10 is present at a distance longer than the reference distance.
Other configurations of the BGS photoelectric switch are as described in the first embodiment.

In this embodiment, in addition to the effect of the second embodiment, the count value is doubled, so that the counting accuracy can be improved, and as a result, the accuracy of determining the distance of the object 10 can be improved. it can.
However, this embodiment has the following problems. The problem is that it becomes difficult to determine the distance of the object 10 when a DC bias exists in the MHP.

  This problem will be described with reference to FIGS. The example of FIG. 10 shows an example in which the average voltage of MHP is higher than the originally assumed value due to the DC bias. As shown in FIG. 10, when a DC bias exists in MHP, MHP is not correctly divided into ½ at the rise and fall, so the time tud from the rise of MHP to the next fall becomes longer than the original value. The time tdu from the fall of MHP to the next rise is longer than the original value.

  For this reason, the distribution of the half-cycle of MHP is a superposition of two normal distributions that are line-symmetric with respect to the reference half-cycle Th / 2 as shown in FIG. That is, the number Nlong of MHPs whose half cycle is longer than the reference half cycle Th / 2 and the number Nshort of MHPs whose half cycle is shorter than the reference half cycle Th / 2 are substantially the same. Therefore, an error occurs in the MHP counting result, and it is difficult to correctly determine the perspective of the object 10 by erroneously determining that Nlong> Nshort, or in some cases, erroneously determining that Nlong <Nshort.

[Fourth Embodiment]
Next, a fourth embodiment of the present invention will be described. In the present embodiment, the counting unit 7 of the first embodiment will be described more specifically. The configuration of the counting unit 7 of the present embodiment is the same as that of the second embodiment, and will be described using the reference numerals in FIG.
The operations of the rise detection unit 70, the fall detection unit 71, and the time measurement units 72 and 73 are the same as those in the second embodiment.

  The comparison unit 74 of the present embodiment compares the time tu from the rising edge of MHP to the next rising edge and the time tdd from the falling edge of MHP to the next falling edge with the reference period Th, and the time tuu is the reference period. When longer than Th or when the time tdd is longer than the reference period Th, the number Nlong of MHPs having a longer period than the reference period Th is increased by 1, and when the time tuu is shorter than the reference period Th or when the time tdd is the reference period If it is shorter than Th, the number Nshort of MHPs whose cycle is shorter than the reference cycle Th is increased by one. The comparison unit 74 performs such counting every time one of the times tuu and tdd is measured.

As described above, the counting unit 7 of the present embodiment can count the number Nlong of MHPs having a period longer than the reference period Th and the number Nshort of MHPs having a period shorter than the reference period Th. As described in the first embodiment, the counting unit 7 counts MHP for each counting period (each of the first oscillation period P1 and the second oscillation period P2).
Other configurations of the BGS photoelectric switch are as described in the first embodiment.

  In the present embodiment, in addition to the effects of the third embodiment, the influence of the transient response of the apex of the triangular wave on the counting result can be reduced, and the problem described in the second embodiment is solved. be able to.

  As described with reference to FIG. 7, at the timing of the apex of the triangular wave, MHP has a waveform that is dragged to a lower voltage, so the time tu from the rise of MHP to the next rise becomes shorter than the original value, and MHP The time tdd from the fall of one to the next fall becomes longer than the original value.

  On the other hand, in the example of FIG. 12, the point PE indicates the timing of the minimum value of the triangular wave. As shown in FIG. 3B, at the timing of the minimum value of the triangular wave, upward spike noise occurs at the output of the filter unit 6, so that the waveform of MHP is dragged to the higher voltage as shown in FIG. It becomes. Therefore, the time tu from the rise of the MHP to the next rise is longer than the original value, and the time tdd from the fall of the MHP to the next fall is shorter than the original value.

  7 and 12, the number of MHPs whose period is longer than the original value due to the influence of the transient response is equal to the number of MHPs whose period is shorter than the original value. Therefore, the number Nlong of MHPs having a longer period than the reference period Th and the number Nshort of MHPs having a shorter period than the reference period Th both increase or decrease by the same number. And the influence of the transient response of the apex of the triangular wave on the counting result can be reduced.

  In the case of the present embodiment, even when a DC bias exists in the MHP, the time tu from the rise of the MHP to the next rise and the time tdd from the fall of the MHP to the next fall do not change. The influence of the DC bias can be eliminated, and the problem described in the third embodiment can be solved.

[Fifth Embodiment]
In the first to fourth embodiments, the MHP waveform is extracted from the output signal of the photodiode that is the light receiver. However, it is also possible to extract the MHP waveform without using the photodiode. FIG. 13 is a block diagram showing a configuration of a BGS photoelectric switch according to the fifth embodiment of the present invention. The same reference numerals are given to the same configurations as those in FIG. The BGS photoelectric switch of this embodiment uses a voltage detection unit 11 instead of the photodiode 2 and the current-voltage conversion amplification unit 5 of the first to fourth embodiments.

  The voltage detector 11 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 10, 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.

Similar to the first to fourth embodiments, the filter unit 6 has a function of extracting a superimposed signal from the modulated wave, and extracts an MHP waveform from the output voltage of the voltage detection unit 11.
The operations of the semiconductor laser 1, the laser driver 4, the counting unit 7, the determination unit 8, and the display unit 9 are the same as those in the first to fourth embodiments.

  Thus, in this embodiment, the MHP waveform can be extracted without using a photodiode, and the parts of the BGS photoelectric switch can be reduced as compared with the first to fourth embodiments. The cost of the photoelectric switch can be reduced.

  The present invention can be applied to a reflective photoelectric switch.

It is a block diagram which shows the structure of the BGS photoelectric switch 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 which shows the relationship between the distance of an object and the frequency distribution of the period of a mode pop pulse in the 1st Embodiment of this invention. It is a block diagram which shows the structure of the counting part of the BGS photoelectric switch which concerns on the 2nd Embodiment of this invention. It is a waveform diagram which shows typically the output voltage waveform of the filter part in the 2nd Embodiment of this invention. It is a wave form diagram which shows typically the output voltage waveform of the filter part in the timing of the maximum value of a triangular wave. It is a block diagram which shows the structure of the counting part of the BGS photoelectric switch which concerns on the 3rd Embodiment of this invention. It is a waveform diagram which shows typically the output voltage waveform of the filter part in the 3rd Embodiment of this invention. It is a wave form diagram for demonstrating the problem of the counting part of the BGS photoelectric switch which concerns on the 3rd Embodiment of this invention. It is a figure which shows the example of the frequency distribution of the half period of a mode pop pulse in case the DC bias exists in a mode pop pulse in the 3rd Embodiment of this invention. It is a wave form diagram which shows typically the output voltage waveform of the filter part in the timing of the minimum value of a triangular wave. It is a block diagram which shows the structure of the BGS photoelectric switch which concerns on the 5th Embodiment of this invention. It is a figure which shows the compound resonator model of the semiconductor laser in the conventional laser measuring device. It is a figure which shows the relationship between the oscillation wavelength of a semiconductor laser, and the output waveform of a built-in photodiode.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 2 ... Photodiode, 3 ... Lens, 4 ... Laser driver, 5 ... Current-voltage conversion amplification part, 6 ... Filter part, 7 ... Counting part, 8 ... Determination part, 9 ... Display part, 10 ... Object 11... Voltage detector 70. Rising detector 71 71 Falling detector 72, 73, 75, 76 Time measuring unit 74, 77 Comparison unit.

Claims (10)

A semiconductor laser that emits laser light;
Detection means for detecting an electrical signal including an interference waveform caused by a self-coupling effect between laser light emitted from the semiconductor laser and return light from an object existing in front of the semiconductor laser;
A reflection type photoelectric switch comprising: distance determination processing means for determining whether the distance to the object is farther or closer than a predetermined reference distance from information on the interference waveform included in an output signal of the detection means; . The reflective photoelectric switch according to claim 1,
The distance determination processing means includes
When the period of the interference waveform when the object is at the reference distance is defined as a reference period, the number of the interference waveforms included in the output signal of the detection means is an interference whose period is longer than the reference period. Counting means for counting the number of waveforms and the number of interference waveforms having a period shorter than the reference period;
When the number of interference waveforms having a long period is greater than the number of interference waveforms having a short period, it is determined that the object is present at a shorter distance than the reference distance, and the number of interference waveforms having a short period is the period. The reflection type photoelectric switch comprising: a determination unit that determines that the object exists at a distance farther than the reference distance when the number of interference waveforms is larger than the number of long interference waveforms. The reflective photoelectric switch according to claim 1,
The distance determination processing means includes
When the half cycle of the interference waveform when the object is at the reference distance is defined as a reference half cycle, the number of the interference waveforms included in the output signal of the detection unit is set to be less than the reference half cycle. Counting means for counting the number of interference waveforms having a long period and the number of interference waveforms having a half period shorter than the reference half period;
When the number of interference waveforms having a long half cycle is greater than the number of interference waveforms having a short half cycle, it is determined that the object is present at a shorter distance than the reference distance, and the number of interference waveforms having a short half cycle is The reflection type photoelectric switch comprising: a determination unit that determines that the object exists at a distance farther than the reference distance when the half cycle is larger than the number of long interference waveforms. The reflective photoelectric switch according to claim 2,
The counting means includes
Rising detection means for detecting the rising of the interference waveform;
Time measuring means for measuring the time from the rise of the interference waveform to the next rise;
When the time from the rise of the interference waveform to the next rise is longer than the reference period, the number of interference waveforms having a period longer than the reference period is increased, and the time from the rise of the interference waveform to the next rise is increased. A reflection type photoelectric switch comprising a comparison means for increasing the number of interference waveforms having a period shorter than the reference period when the period is shorter than the reference period. The reflective photoelectric switch according to claim 2,
The counting means includes
A fall detection means for detecting a fall of the interference waveform;
Time measuring means for measuring the time from the fall of the interference waveform to the next fall;
When the time from the fall of the interference waveform to the next fall is longer than the reference period, the number of interference waveforms having a period longer than the reference period is increased, and the fall of the interference waveform is followed by the next fall. And a comparison means for increasing the number of interference waveforms having a shorter period than the reference period when the time until the reference period is shorter than the reference period. The reflective photoelectric switch according to claim 2,
The counting means includes
Rising detection means for detecting the rising of the interference waveform;
A fall detection means for detecting a fall of the interference waveform;
First time measuring means for measuring a first time from the rise of the interference waveform to the next rise;
Second time measuring means for measuring a second time from the fall of the interference waveform to the next fall;
When the first time is longer than the reference period or when the second time is longer than the reference period, the number of interference waveforms having a longer period than the reference period is increased, and the first time is increased. A reflection type photoelectric device comprising: a comparison unit configured to increase the number of interference waveforms having a shorter period than the reference period when the reference period is shorter or when the second time is shorter than the reference period. switch. The reflective photoelectric switch according to claim 3, wherein
The counting means includes
Rising detection means for detecting the rising of the interference waveform;
A fall detection means for detecting a fall of the interference waveform;
First time measuring means for measuring a first time from the rise of the interference waveform to the next fall;
Second time measuring means for measuring a second time from the fall of the interference waveform to the next rise;
When the first time is longer than the reference half cycle or when the second time is longer than the reference half cycle, the number of interference waveforms having a half cycle longer than the reference half cycle is increased, When the time of 1 is shorter than the reference half cycle or when the second time is shorter than the reference half cycle, the comparison means increases the number of interference waveforms whose half cycle is shorter than the reference half cycle. A reflective photoelectric switch characterized by that. In the object detection method for detecting whether the distance to the object is longer or closer than a predetermined reference distance,
An oscillation procedure for operating the semiconductor laser by supplying a driving current to the semiconductor laser;
A detection procedure for detecting an electrical signal including an interference waveform caused by a self-coupling effect between a laser beam emitted from the semiconductor laser and a return beam from an object existing in front of the semiconductor laser;
A distance determination processing procedure for determining whether the distance to the object is farther or closer than a predetermined reference distance from information on the interference waveform included in the output signal obtained by the detection procedure Detection method. The object detection method according to claim 8.
The distance determination processing procedure includes:
When the period of the interference waveform when the object is at the position of the reference distance is set as a reference period, the number of the interference waveforms included in the output signal obtained by the detection procedure is set to be longer than the reference period. Counting procedure divided into the number of interference waveforms having a long period and the number of interference waveforms having a period shorter than the reference period,
When the number of interference waveforms having a long period is greater than the number of interference waveforms having a short period, it is determined that the object is present at a shorter distance than the reference distance, and the number of interference waveforms having a short period is the period. And a determination procedure for determining that the object exists at a longer distance than the reference distance when the number of interference waveforms is larger than the number of long interference waveforms. The object detection method according to claim 8.
The distance determination processing procedure includes:
When the half cycle of the interference waveform when the object is at the position of the reference distance is defined as a reference half cycle, the number of the interference waveforms included in the output signal obtained by the detection procedure is determined as the reference half cycle. A counting procedure that divides into a number of interference waveforms having a longer half cycle and a number of interference waveforms having a shorter half cycle than the reference half cycle;
When the number of interference waveforms having a long half cycle is greater than the number of interference waveforms having a short half cycle, it is determined that the object is present at a shorter distance than the reference distance, and the number of interference waveforms having a short half cycle is The object detection method comprising: a determination procedure for determining that the object exists at a distance farther than the reference distance when the half cycle is greater than the number of interference waveforms having a long half cycle.

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