JP2017032547A - Laser distance meter false detection suppression circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a false detection suppression circuit for a laser distance meter that prevents false detection in a close distance range arising from mist, rain, window surface contamination of a cover or like, and can resolve false report factors.SOLUTION: A false detection suppression circuit 10 for a laser distance meter 110 in which a light reception output from a light reception element 118 at which each reflection light due to reflection of pulse laser light emitted by a light emitting element 112 by at least one or more objects arrives and a threshold remain inputted into a comparator CMP and which acquires distance information to the object on the basis of a time from an emission start time of the pulse laser light to an output start time of the comparator CMP, comprises: a time counting unit 20a that counts time duration from the emission start time of the pulse laser light; and a setting change unit 20b that changes at least one of an amplification rate on a light reception output side of the comparator CMP and the threshold in accordance with a time count value in the time duration.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a TOF (Time Of Flight) type laser distance meter that uses reflection of pulsed laser light, and in particular, prevents false detection in a short range due to fog, rain, cover window dirt, etc. as much as possible. The present invention relates to a false detection suppression circuit for a laser distance meter.

  The present inventor shall eliminate as much as possible the adverse effects of laser light during outdoor bad weather, etc., and perform accurate detection of intruders etc. regardless of the installation location and weather conditions, and prevent false detection as much as possible. The laser area sensor which can do is already proposed (refer patent document 1).

  Among the inventions disclosed in Patent Document 1, a third embodiment that emphasizes measures against dense fog is described with reference to FIGS. 6 (a) to 6 (f). In the third embodiment, pulsed laser light is emitted, and time information until each reflected light from at least one object existing in the direction returns is obtained to obtain distance information to the object. In addition, a second laser distance meter that obtains light reception level information of the reflected light and time width information of the reflected light on the time axis, a scanning mechanism unit that changes a measurement direction by the second laser distance meter, and this scanning By periodically performing measurement with the second laser rangefinder while changing the measurement direction by the mechanism unit, a detection area is formed, and distance information, light reception level information, and time width information for each measurement direction in the detection area are obtained. The information acquisition unit acquired in time series and the distance information and light reception level information acquired by this information acquisition unit for each measurement cycle are measured adjacent to the measurement direction. When a discontinuous change exceeding a predetermined level occurs when compared with the distance information in the direction and the light reception level information, the distance information corresponding to the discontinuous change in the measurement direction of the measurement period is removed. 2 information correction function, and distance information, light reception level information and time width information acquired by the information acquisition unit for each measurement period, distance information, light reception level information and time width in a plurality of measurement directions adjacent to the measurement direction If the measurement direction range in which the amount of change between adjacent measurement directions is all within a predetermined degree when compared with the information is referred to as a detection angle width, the received light level information corresponding to the specific distance information in the measurement direction, the time A third information supplement that removes the specific distance information in the measurement direction of the measurement cycle when the width information and the detection angle width satisfy a predetermined relationship. An information correction unit that performs correction according to functions, and a portion that is estimated to correspond to the human body from the distance information corrected by the information correction unit, and moves the extracted portion in time series A human body determination unit that determines whether or not the human body is based on a situation, and a human body detection signal output unit that outputs a human body detection signal when the human body determination unit determines that a human body exists. It is characterized by.

  The inventor has also proposed a laser scan sensor that can maintain the reliability of detection of an intruder as much as possible even when the cover of the light receiving unit is dirty (see Patent Document 2).

The laser scan sensor includes a housing in which an opening is formed, a cover that is disposed so as to cover the opening, and that is capable of transmitting laser light. The laser scan sensor is disposed inside the housing, and passes through the cover. A laser light emitting unit that emits laser light to the outside of the laser and a laser light receiving unit that receives the laser light and outputs a signal corresponding to the amount of light received, and at least one laser light emitted from the laser light emitting unit Measurement is performed by measuring the time taken for each reflected light to return due to being reflected by the object to obtain distance information to each object, and also obtaining light reception level information for each reflected light. A laser distance meter, a scanning mechanism for changing the measurement direction by the laser distance meter, and the distance information and the distance by the laser distance meter while changing the measurement direction by the scanning mechanism. And periodically obtaining the light reception level information to form a detection area, and an information acquisition unit for acquiring the distance information and the light reception level information for each measurement direction in the detection area in time series, Of the distance information for each measurement direction acquired by the information acquisition unit, a storage unit for storing the distance information corresponding to the farthest distance side for each measurement direction, and the distance information closer to the closer side than a predetermined distance A determination unit that determines whether or not a state in which a measurement direction corresponding to the light reception level is equal to or greater than a predetermined threshold occupies a predetermined ratio or more of all measurement directions continues for a predetermined time or more, and a determination result of the determination unit And a warning output control unit that outputs a warning signal according to the measurement method, wherein the predetermined threshold value that is compared with the received light level in the determination unit is stored in the storage unit. It is characterized in that the change on the basis of the distance information for each.

Japanese Patent No. 5092076 Japanese Patent No. 5439684

  When dense fog is generated, much smaller water droplets are floating in the air than in the case of raindrops and snow. The pulse laser beam is diffusely reflected. As the light reception signal waveform, for example, pulses P71 to P74 shown in FIGS. 6A to 6F of Patent Document 1 are fluctuating in places where the respective light reception levels are low compared to other reflections. A shape with a wide pulse time width on the time axis appears in a shape that continues for a relatively long time. In the adjacent measurement directions, pulses having substantially the same shape exist, and substantially similar pulse states exist over a continuous wide range of angles.

  On the other hand, when dirt is attached to the outside of the light receiving unit cover of the laser rangefinder, all of the laser light emitted from the light emitting element does not pass through the cover, and some of it is slightly reflected by the dirt. The reflected light may reach the light receiving element. Even if only a small part of the laser beam is reflected, since the distance to the cover is a short distance, the light receiving level of the reflected light can be a non-negligible magnitude. For example, like the waveform Wx shown in FIGS. 5A to 5C of Patent Document 2, a relatively low mountain-shaped pulse waveform corresponding to the short distance side (left side) appears.

  In these prior arts, in most cases, fog or dirt on the cover is determined in accordance with the light reception level of the reflected light.

  However, for example, when cover dirt and fog are simultaneously present in a specific measurement direction, even if there is a human body, the third signal is generated on the time axis, and it is extremely difficult to distinguish between cover dirt and fog and the human body. Complicated processing has become a factor that hinders human body detection accuracy.

  In view of such a problem of the prior art, the object of the present invention is to prevent false detection factors by preventing false detection in a short range due to fog, rain, cover window dirt, etc. An object of the present invention is to provide a false detection suppression circuit for a laser distance meter.

In order to achieve the above object, the false detection suppression circuit of the present invention includes a light reception output and a threshold value from a light receiving element to which each reflected light arrives when pulse laser light emitted from the light emitting element is reflected by at least one object. Are input to the comparator, and a false detection suppression circuit for a laser distance meter that obtains distance information to the object based on a time from the start of emission of the pulsed laser light to the start of output of the comparator A timing unit that counts an elapsed time from the start of emission of the pulsed laser light, and at least the amplification factor on the light reception output side of the comparator and the threshold value according to the timing value in the timing unit And a setting changing unit for changing one of them.

  Here, the setting change unit may decrease the amplification factor or increase the threshold value while the time measurement value is equal to or less than a predetermined value. Furthermore, the setting change unit may decrease the amplification factor stepwise or increase the threshold stepwise according to the time value while the time value is equal to or less than a predetermined value. . Alternatively, the setting change unit may continuously decrease the amplification factor or continuously increase the threshold according to the time value while the time value is equal to or less than a predetermined value. .

  According to the erroneous detection suppressing circuit having such a configuration, since the false detection in the short-distance area caused by fog or the like is prevented, the identification process between the fog and the human body on the short-distance side becomes unnecessary, and the entire distance It is possible to simplify the human body discrimination process.

  According to the erroneous detection suppressing circuit of the present invention, it is possible to prevent erroneous detection in a short-range area due to fog or the like, and it is unnecessary to perform identification processing between the fog and the human body on the short-range side. The determination process can be simplified.

It is sectional drawing which shows schematic structure of the laser rangefinder 110 to which the fog detection prevention circuit 10 which concerns on 1st Embodiment of this invention is applied. 2 is a block diagram showing an electrical schematic configuration of a laser distance meter 110. FIG. 1 is a schematic configuration diagram of a fog detection preventing circuit 10. FIG. FIG. 4A is a time chart illustrating a case where fog is present on the short distance side and a human body is present on the long distance side. FIG. 4A is a diagram illustrating a light projection waveform, and FIG. 4B is fog detection. FIG. 4C is a diagram showing a threshold value, a light reception waveform, and a comparator output when the prevention circuit 10 is not operating, and FIG. 4C is a diagram showing a threshold value, a light reception waveform, and a comparator output when the fog detection prevention circuit 10 is operating. FIG. 5A is a time chart illustrating a case where fog and a human body are present on the short distance side, and another human body is also present on the long distance side, and FIG. FIG. 5B is a diagram illustrating the threshold value, the light reception waveform, and the comparator output when the fog detection prevention circuit 10 is not operating, and FIG. 5C illustrates the threshold value, the light reception waveform, and the comparator output when the fog detection prevention circuit 10 is operating. FIG. It is a schematic block diagram of 10 A of fog detection prevention circuits which concern on 2nd Embodiment of this invention.

  Hereinafter, as an embodiment of the present invention, a fog detection preventing circuit, which is a specific example of an erroneous detection suppressing circuit, will be described with reference to the drawings.

<First Embodiment>
FIG. 1 is a cross-sectional view showing a schematic configuration of a laser rangefinder 110 to which a fog detection preventing circuit 10 according to a first embodiment of the present invention is applied. FIG. 2 is a block diagram showing a schematic electrical configuration of the laser distance meter 110. FIG. 3 is a schematic configuration diagram of the fog detection preventing circuit 10.

  As shown in FIG. 1, the laser distance meter 110 includes a laser light emitting unit 111 having a laser light emitting element 112 and a laser light receiving unit 115 having a light receiving lens 117 and a light receiving element 118. The laser distance meter 110 is disposed inside a housing 101 having an opening, and the opening is covered with a lens cover 116 that can transmit laser light.

In the laser distance meter 110, the pulsed laser light emitted from the laser light emitting element 112 of the laser light emitting unit 111 passes through the lens cover 116 and reaches an object such as a human body existing outside the housing 101. Part of the laser light reflected by the object returns toward the laser distance meter 110, passes through the lens cover 116, passes through the light receiving lens 117, and reaches the light receiving element 118. Then, distance data to an object such as a human body is acquired by precisely measuring a minute time from when the pulsed laser light is emitted from the laser light emitting element 112 until the reflected light reaches the light receiving element 118. Further, the received light level data indicating the intensity of the reflected light may be acquired together. If there are a plurality of objects in the direction in which the laser light is emitted, distance data (and light reception level data) is acquired for each object.

  Examples of the laser light emitting element 112 in the laser light emitting unit 111 include a semiconductor laser diode (LD). Examples of the light receiving element 118 include an avalanche photodiode (APD). For example, it is desirable to provide a dedicated hardware circuit or the like for the drive control of the light emitting element, the time measurement until the reflected light returns, and the acquisition and recording of the received light level of the reflected light. It is not limited. As a general feature of laser rangefinders, precise distance measurement is possible up to a very long distance, for example, it is possible to measure even at long distances of up to several tens of meters in some cases. is there.

  As shown in FIG. 1, a scanning mechanism 120 mechanically coupled to at least a part of the laser distance meter 110 may be provided so that the measurement direction (angle) of the laser distance meter 110 can be changed. The scanning mechanism 120 can be rotated by incorporating a motor (not shown) or the like. For example, a configuration in which only the optical system portion of the laser distance meter 110 is rotated is conceivable, but a configuration in which the entire laser distance meter 110 is rotated may be used, or other configurations may be used. By rotating the scanning mechanism 120 in a predetermined direction at a constant speed, the measurement direction by the laser distance meter 110 can be changed in conjunction with the rotation.

  As shown in FIG. 2, in addition to the laser light emitting element 112 and the light receiving element 118 described above, the laser rangefinder 110 has a first input terminal IN1 for inputting a light receiving output from the light receiving element 118 and a second input terminal for control. Fog detection prevention circuit 10 having IN2 and output terminal OUT for outputting the comparison result, control output terminal to laser light emitting element 112, control output terminal to fog detection prevention circuit 10, and output terminal OUT of fog detection prevention circuit 10 And a control arithmetic unit 20 having a timer 20a and a setting changing unit 20b.

  The control arithmetic unit 20 may also be used as a control unit for controlling other functions of the laser distance meter 110, an arithmetic control unit for controlling the entire apparatus including the scan mechanism 120, and the like.

  As shown in FIG. 3, the fog detection preventing circuit 10 has a comparator CMP therein, and its output is connected to the output terminal OUT. One of the input terminals of the comparator CMP is connected to the first input terminal IN1, and the light reception output from the light receiving element 118 is input thereto. The other input terminal of the comparator CMP is connected to a connection point between a resistor R2 (5.6 kΩ) and a resistor R3 (220Ω) connected in series between 3.3 V and the ground GND. Acts as a threshold in the comparator CMP. This connection point is further connected to the second input terminal IN2 via a resistor R1 (1.2 kΩ).

With such an internal configuration of the fog detection preventing circuit 10, the light receiving output from the light receiving element 118 is compared with the threshold value in the comparator CMP, and if the light receiving output is larger, the HIGH level is output from the output terminal OUT. For example, the LOW level is output from the output terminal OUT. The threshold value input to the comparator CMP can be changed by an input to the second input terminal IN2, and is about 600 mV when the input is at the HIGH level and about 100 mV when the input is at the LOW level.

  FIG. 4 is a time chart illustrating a case where fog is present on the short distance side and a human body is present on the long distance side, and FIG. 4 (a) is a diagram illustrating a light projection waveform, and FIG. ) Is a diagram showing the threshold value, light reception waveform and comparator output when the fog detection prevention circuit 10 is not operating, and FIG. 4C is a diagram showing the threshold value, light reception waveform and comparator output when the fog detection prevention circuit 10 is operating. It is.

  As shown in FIG. 4A, pulsed laser light is emitted according to the light projection waveform P1 output from the control arithmetic unit 20 to the laser light emitting element 112.

  When the fog detection prevention circuit 10 is not in operation, as shown in FIG. 4B, a low and wide mountain waveform WF corresponding to fog appears on the short distance side on the time axis, and on the long distance side. A high and narrow mountain waveform WH1 corresponding to the human body appears. Since the input from the control arithmetic unit 20 to the second input terminal IN2 of the fog detection preventing circuit 10 remains at the LOW level, the threshold value input to the comparator CMP remains at about 100 mV. For this reason, in the output of the comparator CMP, a wide pulse waveform PF corresponding to fog appears on the short distance side on the time axis, and a narrow pulse waveform PH1 corresponding to the human body appears on the long distance side. .

  On the other hand, during the operation of the fog detection preventing circuit 10, as shown in FIG. 4C, the fog calculation preventing circuit 10 is supplied from the control arithmetic unit 20 for a predetermined period T1 from the rising of the light projection waveform P1. Since the input to the second input terminal IN2 is changed to the HIGH level, the threshold value input to the comparator CMP also increases to about 600 mV. Therefore, in the output of the comparator CMP, the pulse waveform PF corresponding to the fog does not appear on the short distance side on the time axis, and only the narrow pulse waveform PH1 corresponding to the human body appears on the long distance side.

  Here, the predetermined period T1 is determined so as to increase the threshold value input to the comparator CMP within a range up to about 4 m (or about 3 to 5 m) in terms of distance. This is because the reflected light caused by fog is relatively strong and may cause false detection up to about 4 m.

  As shown in FIG. 1, in the TOF laser rangefinder 110 in which the laser light emitting unit 111 and the laser light receiving unit 115 are independently arranged, light is projected and received in a short range where fog can be detected. The axes do not overlap, and a constant distance is maintained. As a result, the light reception level when fog is detected is below a relatively low constant level, and the light reception level can be further reduced by using an aspheric lens for the light projecting lens or the light receiving lens 117. Further, it is known that the reflection level of the human body in the short distance region is higher than that of the fog, and the simple configuration described above can eliminate the influence of the fog without degrading the detection performance for the human body.

  FIG. 5 is a time chart illustrating a case where fog and a human body are present on the short distance side and another human body is also present on the long distance side, and FIG. 5A is a diagram illustrating a light projection waveform. FIG. 5B is a diagram showing a threshold value, a light reception waveform and a comparator output when the fog detection prevention circuit 10 is not operated. FIG. 5C is a diagram showing a threshold value, a light reception waveform and a comparator output when the fog detection prevention circuit 10 is operated. It is a figure which shows a comparator output.

  As shown in FIG. 5A, the pulse laser beam is emitted in the same manner as in FIG. 4A according to the projection waveform P1 output from the control arithmetic unit 20 to the laser light emitting element 112.

When the fog detection preventing circuit 10 is not in operation, as shown in FIG. 5B, the low and wide mountain-shaped waveform WF corresponding to the fog on the short distance side on the time axis and the high and wide corresponding to the human body. Narrow Yamagata waveform WH2
And a high and narrow mountain waveform WH1 corresponding to the human body appear on the far side. Since the input from the control arithmetic unit 20 to the second input terminal IN2 of the fog detection preventing circuit 10 remains at the LOW level, the threshold value input to the comparator CMP remains at about 100 mV. Since the chevron waveform WF is wider than the chevron waveform WH2, a pulse waveform PF having a wide width corresponding to fog appears on the short-distance side on the time axis in the output of the comparator CMP, as in FIG. 4B. At the same time, a narrow pulse waveform PH1 corresponding to the human body appears on the far side. That is, on the short distance side, the human body cannot be detected due to fog.

  On the other hand, during the operation of the fog detection preventing circuit 10, as shown in FIG. 5C, the fog calculation preventing circuit 10 is supplied from the control arithmetic unit 20 for a predetermined period T1 from the rising of the projection waveform P1. Since the input to the second input terminal IN2 is changed to the HIGH level, the threshold value input to the comparator CMP also increases to about 600 mV. Therefore, in the output of the comparator CMP, a pulse waveform PH2 corresponding to the human body appears on the short distance side on the time axis, and a narrow pulse waveform PH1 corresponding to the human body appears on the long distance side. That is, even on the short distance side, it is possible to accurately detect the human body by preventing erroneous detection due to fog.

  According to the configuration of the first embodiment described above, by adding the fog detection preventing circuit 10 having a relatively simple configuration to the laser distance meter 110, the fog on the short distance side is erroneously detected and the output of the comparator CMP is output. Can be prevented from appearing. This eliminates the need for the identification process between the fog and the human body on the short distance side, and simplifies the human body identification process over the entire distance.

  Further, by adding the fog detection preventing circuit 10 to the control arithmetic circuit of the conventional TOF type laser distance meter, the detection signal itself due to reflection from fog or window surface is removed, and the control arithmetic circuit is applied to the human body. Focus on processing the corresponding detection signal. As a result, the load on the detection process is reduced, so that even a CPU with a low processing capability is expected to improve detection capability beyond a certain level. Further, it is possible to substantially eliminate the restriction for detecting the fog and the human body separately, and the human body detection performance at a short distance in a bad environment state where the fog is generated can be greatly improved.

Second Embodiment
FIG. 6 is an overview configuration diagram of a fog detection preventing circuit 10A according to the second embodiment of the present invention. Since the second embodiment is the same as the first embodiment described with reference to FIG. 3 except for the points described below, the same reference numerals will be given to the same components, and the main differences will be described. Will be described.

  As shown in FIG. 6, the fog detection preventing circuit 10A has a comparator CMP therein, and its output is connected to the output terminal OUT. One of the input terminals of the comparator CMP is between a resistor R5 (50Ω) and a resistor R6 (50Ω) connected in series between the first input terminal IN1 to which the light receiving output from the light receiving element 118 is input and the ground GND. The connection point is further connected to the drain of the FET whose gate is connected to the second input terminal IN2 through the resistor R4 (1 kΩ) and whose source is grounded. The other input terminal of the comparator CMP is connected to a connection point between a resistor R7 (10.5 kΩ) and a resistor R8 (330Ω) connected in series between 3.3 V and the ground GND. Acts as a threshold in the comparator CMP.

With such an internal configuration of the fog detection preventing circuit 10A, the threshold value input to the comparator CMP is fixed to about 100 mV. Instead, the input gain (amplification factor) of the light reception output from the light receiving element 118 to the first input terminal IN1 can be changed by the input to the second input terminal IN2. When the input to the second input terminal IN2 is at the LOW level, the input gain remains substantially 1/1, but when the input to the second input terminal IN2 is at the LOW level, the input gain is about 1/6. Go down.

  According to the configuration of the second embodiment described above, the control arithmetic unit 20 connects the second input terminal IN2 of the fog detection preventing circuit 10A during the predetermined period T1 from the rising time of the projection waveform P1. By changing the input to the HIGH level, it is possible to achieve substantially the same operational effects as in the first embodiment.

<Other embodiments>
In the first embodiment and the second embodiment described above, the input from the control arithmetic unit 20 to the second input terminal IN2 of the fog detection preventing circuit 10A for a predetermined time period T1 from the rising time of the projection waveform P1. Is changed to HIGH level, the threshold value in the comparator CMP or the input gain (amplification factor) on the light receiving output side is discontinuously changed.

  However, for example, a D / A conversion terminal is used for the output from the control arithmetic unit 20, and the program in the control arithmetic unit 20 causes the comparator CMP to perform a predetermined period T1 in the middle of a predetermined period T1 from the rising edge of the projection waveform P1. The threshold value or the input gain (amplification factor) on the light reception output side may be changed stepwise. Alternatively, the threshold value in the comparator CMP or the input gain (amplification factor) on the light reception output side is continuously changed according to the elapsed time from the rising of the light projection waveform P1 until the predetermined period T1 is reached. Also good.

  Further, these changes may be made in an analog manner using a charge / discharge circuit constituted by a CR circuit or the like instead of digitally using the timer 20a of the control arithmetic unit 20.

  It should be noted that the present invention can be implemented in various other forms without departing from the spirit or main features thereof. Therefore, the above-mentioned embodiment is only a mere illustration in all points, and should not be interpreted limitedly. The scope of the present invention is indicated by the claims, and is not restricted by the text of the specification. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

DESCRIPTION OF SYMBOLS 10 Fog detection suppression circuit 10A Fog detection suppression circuit 20 Control arithmetic unit 20a Timer 20b Setting change part 100 Laser scan sensor 101 Case 110 Laser distance meter 111 Laser light emission part 112 Laser light emission element 115 Laser light reception part 116 Lens cover 117 Light reception lens 118 Light receiving element 120 Scan mechanism

Claims (4)

A light receiving output from a light receiving element to which each reflected light arrives due to reflection of pulse laser light emitted from the light emitting element by at least one object and a threshold value are input to a comparator, and light emission of the pulse laser light is performed. A false detection suppression circuit for a laser rangefinder that acquires distance information to the object based on a time from the start to the output start of the comparator,
A time measuring unit for measuring the elapsed time from the start of emission of the pulsed laser light,
A false detection suppression circuit comprising: a setting changing unit that changes at least one of the gain on the light receiving output side of the comparator and the threshold according to a time value in the time measuring unit. In the false detection suppression circuit according to claim 1,
The false detection suppression circuit, wherein the setting change unit lowers the amplification factor or increases the threshold while the measured value is equal to or less than a predetermined value. In the false detection suppression circuit according to claim 2,
The setting change unit is configured to decrease the amplification factor stepwise or increase the threshold stepwise according to the timekeeping value while the timekeeping value is equal to or less than a predetermined value. False detection suppression circuit. In the false detection suppression circuit according to claim 2,
The setting change unit is configured to continuously decrease the amplification factor or continuously increase the threshold according to the time value while the time value is equal to or less than a predetermined value. False detection suppression circuit.

Images