JP2012068066A - Optical range finder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a multiplication rate of each light receiving element to be maintained constant with high accuracy, to fluctuation of element temperature, in an optical range finder comprising light receiving elements configured to exert a multiplication function through applying bias voltage.SOLUTION: An optical range finder 1 includes and comprises a two-dimensional scan mirror 2, a laser projecting section 3, a laser receiving section 4 equipped with light receiving elements 4b comprising avalanche photodiodes APD, and light projection/reception separator 5. Further, a strip-like reflection board 21 is mounted onto cover glass 7 along a bottom edge of a laser beam scan area SA so as to overlap the laser beam scan area SA. Therefore, so that output of the light receiving elements 4b when reflectance light is received from the reflection board 21 is a target value (prescribed preset value), bias voltage to apply to the light receiving elements 4b is changed.

Description

  The present invention relates to an optical distance measuring device that includes a light receiver having a multiplication effect by applying a bias voltage, and detects light reflected from a measurement object by the light receiver.

Conventionally, as disclosed in Patent Document 1, as an optical distance measuring device, a laser beam is emitted toward a measurement object, a laser beam is emitted, and a laser beam reflected from the measurement object is received. There is an apparatus for measuring a distance to a measurement object by measuring a time difference from the measurement object.
In the optical distance measuring device, an avalanche photodiode APD, which is a light receiving element having a multiplication effect by applying a bias voltage, is used as a light receiver for detecting weak light reflected from a measurement object with high sensitivity. .

Japanese Patent Laid-Open No. 2003-130953

By the way, the multiplication factor of the light-receiving element (avalanche photodiode APD) having a multiplication action varies depending on the element temperature.
For this reason, when the element temperature changes, the output of the light receiving element changes without depending on the reflected light intensity (light quantity), which may cause a deviation in the determination of the light receiving timing and may cause an error in the distance measurement result. .

Therefore, if the bias voltage for making the multiplication factor constant is previously determined for each element temperature and stored in a table, and the bias voltage is determined with reference to the table based on the element temperature at that time, the element temperature changes. However, it is possible to keep the multiplication factor constant.
However, since there is a solid difference in the correlation between the element temperature and the multiplication factor in the light receiving element, it is necessary to prepare the table for each light receiver in order to control the multiplication factor with high accuracy. There is a problem that it is difficult to detect the element temperature correlated with the above with high accuracy.

  The present invention has been made by paying attention to the above-mentioned problems, and it is possible to increase the number of individual light receiving elements with respect to changes in element temperature without preparing a table showing the correlation between bias voltage and element temperature for each light receiving element. An object of the present invention is to provide an optical distance measuring device that can maintain a constant magnification with high accuracy.

  For this reason, the invention according to claim 1 has a multiplication function by applying a bias voltage, a projector that projects measurement light, a scanning device that scans the measurement light toward the measurement object, A light receiver that receives reflected light from the measurement object, and based on the time difference between the light projection timing of the measurement light by the light projector and the light reception timing of the reflected light by the light receiver, In the optical distance measuring device for measuring the distance, a reflection part that reflects the measurement light from the projector toward the light receiver is provided in a part of the scanning area of the measurement light, and the light reflected by the reflection part is provided. Bias voltage changing means for changing the bias voltage is provided so that the output of the light receiver when receiving light has a predetermined set value.

In such a configuration, since the bias voltage is individually changed so that the output of the light receiver becomes a set value (target value) with respect to the reflected light from the reflecting portion, that is, the reflected light with a constant intensity (light quantity), When the output of the light receiver changes due to a change in gain due to temperature change, the bias voltage is changed for each light receiver so that the output becomes a set value, in other words, the gain is constant.
Therefore, even if there is a change in the element temperature and a difference between individual light receivers, the multiplication factor can be kept constant with high accuracy, and high ranging accuracy can be stably obtained.

In the configuration of claim 1, as in claim 2, the bias voltage changing unit is configured to receive the light reflected by the reflection unit based on the arrangement region of the reflection unit in the scanning region. The output can be detected.
In such a configuration, of the reflected light received by the light receiver, the reflected light from the reflecting portion is received when the measurement light scans the region where the reflecting portion is arranged in the scanning region. Or reflected light from the object to be measured based on the arrangement area of the reflection part in the scanning area, and the light receiving device when receiving the reflection light from the reflection part can be distinguished. The output can be detected and used to control the bias voltage.

Also, in the configuration of claim 1 or 2, as in claim 3, the bias voltage changing means detects the output of the light receiver that has received the light reflected by the reflecting portion based on the distance measurement result. be able to.
In such a configuration, since the distance to the reflecting part is known, the reflected light received when the distance measurement result not corresponding to the distance to the reflecting part is obtained is reflected light from the measurement object, and the distance to the reflecting part is The reflected light received when the distance measurement result corresponding to the distance is obtained can be judged as the reflected light from the reflecting part, and the output of the light receiver when the reflected light from the reflecting part is received is detected. Can be used to control the bias voltage.

Moreover, in the structure of Claims 1-3, like Claim 4, the said reflection part can be made into the reflecting plate arrange | positioned in the said scanning area | region.
In such a configuration, when the reflecting plate is arranged in the scanning region, the reflected light with a constant intensity (light quantity) can be stably received by the light receiver, and the light reflected by the reflecting plate is received. The bias voltage is changed so that the output of the optical receiver becomes the set value, in other words, the multiplication factor is constant.

In the configuration of claim 4, as in claim 5, radiation of the measurement light toward the measurement object and reception of reflected light from the measurement object are performed via a transparent plate, and the transparent plate The reflection plate can be attached to.
In such a configuration, in an optical distance measuring device that radiates measurement light and receives reflected light through a transparent plate such as a cover glass attached to the window of the housing, the reflective plate is attached to the transparent plate, The bias voltage is changed based on the output when the light receiver receives the reflected light from the provided reflector.

Further, in the configuration of claims 1 to 3, as in claim 6, radiation of the measurement light toward the measurement object and reception of reflected light from the measurement object are performed via a transparent plate, A part of the transparent plate can be used as the reflecting portion.
In such a configuration, in the optical distance measuring device that radiates measurement light and receives reflected light through a transparent plate such as a cover glass attached to the window portion of the housing, the measurement light is reflected by a part of the transparent plate, The light reflected from the transparent plate is received by the light receiver, and the bias voltage is changed based on the output of the light receiver when the light reflected from the transparent plate is received.

In the configuration of claim 6, as in claim 7, the transparent plate is formed in a shape bent so as to be convex toward the projector in the scanning area, and the vicinity of the apex of the transparent plate is It can be a reflection part.
In such a configuration, the transparent plate is formed in a bent shape so as to be convex toward the projector in the scanning region, thereby preventing reflected light from the plane of the transparent plate from entering the visual field of the light receiver. In addition, it is possible to reduce the noise caused by the reflected light from the transparent plate mixed with the reflected light from the measurement object, while the reflected light from the transparent plate can enter the field of view of the receiver near the top of the transparent plate. The bias voltage is changed so that the output of the light receiver that receives the light reflected in the vicinity becomes the set value.

In the configuration of claims 1 to 7, as in claim 8, the bias voltage changing means sets the bias voltage to an initial value until the scanning amplitude by the scanning device reaches a set value from the start of scanning. After the scanning amplitude reaches the set value, the bias voltage is set to the initial value according to a deviation between the output of the light receiver that has received the light reflected by the reflecting unit and the set value. Can be changed step by step.
In such a configuration, immediately after the scanning of the measurement light is started and the scanning amplitude does not reach the set value, the output when the reflected light from the reflecting portion is received cannot be accurately monitored. Until the scanning is performed, the initial value is maintained without changing the bias voltage, and when scanning is performed with the expected amplitude, the bias based on the output when the reflected light from the reflecting portion is received The voltage change is started, and the bias voltage is changed stepwise from the initial value.

In the configuration of claims 1 to 8, as in claim 9, the bias voltage changing means obtains an average value for the output of the light receiver that has received the light reflected by the reflecting portion, and the average value is obtained. Based on this, the bias voltage can be changed.
In such a configuration, the average value is obtained for the output of the light receiver that has received the light reflected by the reflecting portion, thereby smoothing the output variation and changing the bias voltage based on the average output level.

Further, in the configuration according to any one of claims 1 to 9, as in claim 10, the deviation between the output of the light receiver that has received the light reflected by the reflecting portion and the set value is an allowable error. The bias voltage can be changed when exceeding.
In such a configuration, if the deviation between the output of the light receiver that has received the light reflected by the reflecting portion and the set value is within an allowable error and the output of the light receiver substantially matches the set value, the bias voltage is adjusted accordingly. When the deviation exceeds the allowable error, the bias is changed to correct the multiplication factor, thereby converging the deviation within the allowable error.

Moreover, in the structure of Claims 1-10, like Claim 11, the reflectance in the said reflection part may be set to the value which does not saturate the output of the said light receiver which received the light which the said reflection part reflected. it can.
In such a configuration, since the reflecting portion is arranged at a position closer to the projector than the object to be measured, the intensity (light quantity) of the reflected light at the reflecting portion is high, and the light receiving device when the reflected light from the reflecting portion is received. If the output saturates, it becomes unclear whether the bias voltage is excessive or insufficient. Therefore, when the reflected light from the reflector is received, the reflectivity of the reflector is lowered so that the output of the receiver is not saturated. Suppress.

  According to such an optical distance measuring device, without preparing a bias voltage table for each photoreceiver, the gain of the photoreceiver can be accurately and constantly maintained with respect to changes in element temperature and individual differences in the photoreceiver, High ranging accuracy can be obtained stably.

The perspective view which shows the scanning system of the laser beam in the optical distance measuring device of embodiment of this invention System block diagram of an optical distance measuring device according to an embodiment of the present invention The flowchart which shows the flow of the change process of the bias voltage in the optical distance measuring device of embodiment of this invention. The figure which shows the reflective characteristic of a laser beam when the vertex of the bent part of a cover glass is made into the reflection part in the optical distance measuring device of embodiment of this invention. The figure which shows the arrangement pattern of a reflection part in the case of using the vertex of the bending part of a cover glass as a reflection part in the optical distance measuring device of embodiment of this invention. The figure which shows the reflection characteristic in the vertex vicinity in case the vertex of the bending part of a cover glass is made into a reflection part in the optical distance measuring device of embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a perspective view showing an optical system of an optical distance measuring device 1 according to the present invention. The optical distance measuring device 1 includes a two-dimensional scanning mirror (scanner, scanning device) 2, a laser projector (projector) 3. The laser light receiving section (light receiver) 4 and the light projecting / receiving separator 5 are configured to project the laser light (measurement light) toward the measurement object and receive the reflected light from the measurement object. It is made through a cover glass 7 which is a transparent plate attached to a light projecting / receiving window 6 opened in a housing (not shown).
The cover glass 7 is formed of a glass plate, and the cover glass 7 is curved or a flat cover glass 7 so that the laser light reflected by the cover glass 7 does not enter the field of view of the laser light receiving unit 4. Are attached so as to cross the optical axis at an angle.

The optical distance measuring device 1 includes a timing table that determines the coordinates and time at which the laser light is to be projected, emits the laser light according to this timing table, and directs it toward the measurement object from the laser projector 3. The distance to the measurement object is calculated based on the time difference between the laser light emission timing and the light reception timing at which the laser light receiving unit 4 receives the reflected light from the measurement object and the propagation speed of the laser light.
That is, the optical distance measuring device 1 is a device that measures the distance to the measurement object by the optical pulse time-of-flight measurement method.
Note that the optical distance measuring device 1 can be configured to output an image (ranging image data) obtained by performing color coding for each pixel according to the length of the distance measurement result.

FIG. 2 is a block diagram showing details of the system configuration of the optical distance measuring device 1.
The laser projector 3 includes a laser element 3a and a projecting optical system 3b, and drives and controls the laser element 3a based on a laser emission timing control signal to emit laser light (pulse light) as measurement light. Laser light emitted from the laser element 3a is emitted through the light projecting optical system 3b, passes through the light projecting / receiving light separator 5, is reflected by the two-dimensional scanning mirror 2, and passes through the cover glass 7 to be measured. Radiated towards an object.

Here, when the two-dimensional scanning mirror 2 vibrates two-dimensionally, the reflected light from the two-dimensional scanning mirror 2 is scanned in a two-dimensional region, and thereby the measurement object is scanned two-dimensionally with laser light. The The scanning of the laser beam by the two-dimensional scanning mirror 2 is a raster scan or a Lissajous scan. However, a system in which a laser beam is scanned two-dimensionally by a laser beam by combining two one-dimensional scanning devices (scanning mirrors) may be used.
The laser light transmitted through the cover glass 7 and emitted toward the measurement object is reflected by the measurement object, and this reflected laser light is transmitted through the cover glass 7 and reflected by the two-dimensional scanning mirror 2. Then, it is reflected by the light projecting / receiving separator 5 and received by the laser light receiving unit 4.

The laser light receiving unit 4 includes a light receiving optical system 4a, a light receiving element 4b, a preamplifier 4c, and a bias circuit 4d.
The laser light reflected by the light projecting / receiving separator 5 is collected by the light receiving optical system 4a and received by the light receiving element 4b, and the light receiving element 4b corresponds to the intensity (light quantity) of the laser light reflected by the measurement object. The generated voltage is generated as a detection output.

The light receiving element 4b is an avalanche photodiode APD that has a multiplication action by applying a bias voltage, and the bias circuit 4d applies a bias voltage to the avalanche photodiode APD.
The output signal (analog signal) of the light receiving element 4b indicating the intensity (light quantity) of the reflected light from the measurement object is amplified by the preamplifier 4c, and the amplified signal is converted into a digital signal by the A / D converter 10. The analog signal output from the preamplifier 4 c and the digital signal output from the A / D converter 10 are output to the distance measuring unit 11.

The distance measuring unit 11 generates a time stop pulse based on an output signal (analog signal) of the light receiving element 4b, measures a time difference from a time start pulse generated by a light emission monitor unit (not shown) to the time stop pulse, The distance to the measurement object is calculated from this time difference.
The digital signal output from the A / D converter 10, that is, the intensity (light quantity) data of the reflected light is used by the distance measuring unit 11 to select the detection method of the laser light irradiation timing and light reception timing.

In the present embodiment, the bias voltage applied by the bias circuit 4d is controlled in order to make the multiplication factor of the light receiving element (avalanche photodiode APD) 4b constant.
In order to control the bias voltage, as shown in FIGS. 1 and 2, a strip-shaped reflector 21 is attached to the cover glass 7 so as to overlap the scanning area SA along the lower end of the laser beam scanning area SA. .
When a laser beam is projected when the scanning timing comes to the position of the reflecting plate 21, the laser beam is reflected by the reflecting plate 21, and the reflected light from the reflecting plate 21 is transmitted to the laser light receiving unit 4 (light receiving element 4b). It is designed to receive light.

In the example shown in FIGS. 1 and 2, the reflecting plate 21 as the reflecting portion is a strip-shaped member extending over the entire scanning width along the lower end of the laser beam scanning area SA. The position to be provided is not limited to the lower end of the scanning area SA, and the reflecting plate 21 may be arranged at any one of the upper end, the left end, and the right end, and among the upper end, the lower end, the left end, and the right end. You may arrange | position the reflecting plate 21 in multiple places.
Further, the reflecting plate 21 may be disposed at at least one of the four corners of the laser beam scanning area SA, and the shape of the reflecting plate 21 is not limited to a strip shape (rectangle).
In other words, the reflection plate 21 may be disposed in the laser beam scanning area SA at a position where the laser beam is projected. However, since the region where the reflecting plate 21 is provided cannot be measured without laser light being projected toward the measurement object located outside the cover glass 7, it is preferable to arrange the region on the periphery of the scanning region SA. .

Furthermore, if the reflecting plate 21 is attached to the inner side surface of the cover glass 7, the reflecting plate 21 can be easily provided. However, the attachment position of the reflecting plate 21 is not limited to the cover glass 7, but two-dimensional. It can be fixed between the scanning mirror 2 and the cover glass 7 using a stay or the like.
However, it is preferable that the reflecting plate 21 is installed in the apparatus housing inside the cover glass 7. If the reflecting plate 21 is installed in the device casing inside the cover glass 7, it can be avoided that the laser light projected toward the reflecting plate 21 is reflected by other obstacles, and the scanning amplitude and light emission timing can be reduced. If the scanning is performed with the desired value, the laser light receiving unit 4 can surely receive the reflected light from the reflecting plate 21.

Then, the bias circuit 4d includes a light receiving element (avalanche photo) so that the output of the laser light receiving unit 4 (light receiving element 4b) when receiving the laser light reflected by the reflecting plate 21 becomes a predetermined set value (target value). The bias voltage applied to the diode APD) 4b is changed.
Here, among the outputs of the laser light receiving unit 4 (light receiving element 4b), the output when the laser beam reflected by the reflecting plate 21 is received can be determined from the region where the reflecting plate 21 is arranged in the scanning region. It can be presumed that the output in the region (scanning point) where 21 is placed is the output when the laser beam reflected by the reflecting plate 21 is received.

In addition, since the laser beam is reflected by the reflecting plate 21 before being irradiated on the measurement object, and the distance to the reflecting plate 21 is known, the measurement result of the known distance is obtained. The output can be estimated to be an output when the reflected light from the reflecting plate 21 is received.
Furthermore, when the output is in the area where the reflecting plate 21 is arranged and the distance measurement result corresponds to the distance to the reflecting plate 21, it is determined that the output is when the reflected light from the reflecting plate 21 is received. can do.

The reflecting plate 21 is disposed at a short distance from the laser light receiving unit 4. If the reflectance of the laser beam on the reflecting surface is high, the light receiving element (when receiving the reflected light from the reflecting plate 21) The output of the avalanche photodiode APD) 4b is saturated, and it cannot be determined from the output whether the multiplication factor of the light receiving element 4b is higher than the set value.
Therefore, the reflection surface of the reflection plate 21 is made black, for example, so that the reflectance is set so as not to saturate the output of the laser light receiving unit 4 (light reception element 4b) when the reflected light from the reflection plate 21 is received. It is.

As a processing block for changing the bias voltage, an average value calculating unit 12, a target setting unit 13, a deviation calculating unit 14, an adjusting unit 15, and a bias voltage changing unit (bias voltage changing means) 16 are provided.
The average value calculation unit 12 calculates an average value in a plurality of frames n for a signal indicating the intensity (light quantity) of the laser light reflected by the reflecting plate 21 among the digital signals output from the A / D converter 10.

The target setting unit 13 stores in advance a target value of the output of the light receiving element (avalanche photodiode APD) 4b when the laser beam reflected by the reflecting plate 21 is received, and this target value (set value) is calculated as a deviation calculating unit 14. Output to.
The deviation calculation unit 14 is a deviation between the target value (set value) output from the target setting unit 13 and the average value calculated by the average value calculation unit 12, that is, the light reception when the laser beam reflected by the reflecting plate 21 is received. An error with respect to the target value of the output of the element (avalanche photodiode APD) 4b is calculated.

The adjustment unit 15 inputs the deviation (error) calculated by the deviation calculation unit 14 and makes the output of the light receiving element (avalanche photodiode APD) 4b close to the target value when the laser beam reflected by the reflecting plate 21 is received. Set the change (correction value) of the bias voltage.
The bias voltage changing unit 16 changes the bias voltage applied to the light receiving element (avalanche photodiode APD) 4b by the bias circuit 4d according to the change set by the adjusting unit 15.
The bias voltage changing unit 16 can be configured by a D / A converter or a variable resistor.

Since the intensity (light quantity) of the laser beam reflected by the reflecting plate 21 is constant, as described above, the output of the light receiving element (avalanche photodiode APD) 4b when receiving the laser beam reflected by the reflecting plate 21 is the target. Changing the bias voltage to have a value makes the multiplication factor (the gain of the output level with respect to the incident light amount) constant of the light receiving element (avalanche photodiode APD) 4b.
Therefore, when the multiplication factor changes due to the change in the element temperature of the light receiving element 4b, the bias voltage is changed to keep the multiplication factor constant, and the fluctuation of the output level due to the change of the element temperature can be suppressed.

Further, even when the correlation between the element temperature and the multiplication factor varies among the individual light receiving elements 4b, the output when the laser beam having a constant intensity (light quantity) reflected by the reflecting plate 21 is received becomes the target value (set value). If the bias voltage is corrected so that the correlation between the reflected light intensity (light quantity) and the output is made constant, it is possible to suppress the fluctuation of the output level due to the variation.
If the output level with respect to the reflected light intensity (light quantity) can be made constant, it is possible to suppress the occurrence of deviation in the determination of the light reception timing, so that high ranging accuracy can be stably obtained with respect to changes in element temperature and element variations. be able to.

In the following, the above-described bias voltage changing process will be described in more detail with reference to the flowchart of FIG.
When the optical distance measuring device is activated in step S101, first, in step S102, the bias voltage applied to the light receiving element (avalanche photodiode APD) 4b is set to the standard value V0.
The standard value V0 is previously adapted as a value at which the output of the light receiving element (avalanche photodiode APD) 4b becomes a set value (design value) at the standard temperature.

In step S103, the temporary operation is started in a state where the bias voltage applied to the light receiving element (avalanche photodiode APD) 4b is set to the standard value V0.
In step S104, scanning of laser light by the two-dimensional scanning mirror 2 and control of laser emission timing are started.
The two-dimensional scanning mirror 2 includes a vibration sensor (strain gauge, piezoresistive element, etc.) that detects the vibration of the mirror, and in laser beam scanning control, according to the mirror vibration detected based on the output of the vibration sensor. The amount of operation of the mirror driving means is feedback controlled.

In step S105, whether or not the scanning amplitude of the laser beam by the two-dimensional scanning mirror 2 and the laser emission timing have reached the target values, that is, the intended scanning region SA is scanned with the laser beam at the intended emission timing. It is determined whether or not scanning has started.
When the scanning amplitude of the laser beam by the two-dimensional scanning mirror 2 and the laser emission timing do not reach the target values, the process returns to step S104, the scanning of the laser beam by the two-dimensional scanning mirror 2, and the laser emission. Continue timing control.

On the other hand, when the scanning amplitude of the laser beam by the two-dimensional scanning mirror 2 and the laser emission timing reach the target values, the process proceeds to step S106, and feedback control of the bias voltage applied to the light receiving element (avalanche photodiode APD) 4b is started. To do.
In step S107, a target value E0 of the output E (detected light amount) of the laser light receiving unit 4 when the laser light reflected from the reflecting plate 21 is received is set, and a deviation ΔE between the target value E0 and the actual output E is set. An allowable error ε that is an allowable value is set. The target value E0 and the allowable error ε are values stored in advance, but may be arbitrarily changed.

In step S108, the standard value V0 of the bias voltage used in the temporary operation is set to the initial value of the bias voltage V1 in the feedback control.
In step S109, a control step ΔV when changing the bias voltage by feedback control, that is, a change width of the bias voltage per cycle is set.
In step S110, distance measurement data for each scanning point (pixel) obtained by two-dimensionally scanning laser light is acquired.

In step S111, whether or not the acquired distance measurement data is data obtained at a scanning point (pixel) in the arrangement area of the reflection plate 21, in other words, it is assumed that the reflected light from the reflection plate 21 is received. It is determined whether or not the distance measurement data is obtained within a preset area.
And it is not the data obtained by the scanning point (pixel) in the arrangement | positioning area | region of the reflecting plate 21, but the distance measurement data obtained by the area | region (outside the arrangement | positioning area | region of the reflecting plate 21) which the cover glass 7 permeate | transmits a laser beam. If it judges, it will return to step S110.

On the other hand, when the distance measurement data at the scanning point (pixel) in the arrangement area of the reflection plate 21 is obtained, the process proceeds to step S112, and the distance measurement data is a value substantially corresponding to the distance to the reflection plate 21. Judge whether there is.
Since the distance to the reflecting plate 21 is not changed and is a known value, if the distance measuring data is a result of receiving the reflected light from the reflecting plate 21, the distance measuring data is the reflecting plate 21. If it is deviated from the distance to the reflecting plate 21, it can be determined that it is not distance measurement data as a result of receiving the reflected light from the reflecting plate 21.

Therefore, if the distance measurement data does not substantially match the distance to the reflector 21, it is determined that the distance measurement data is not the distance measurement data as a result of receiving the reflected light from the reflector 21, and the process returns to step S110.
On the other hand, if the distance measurement data substantially matches the distance to the reflecting plate 21, it is determined that the distance measurement data is a result of receiving the reflected light from the reflecting plate 21, and the process proceeds to step S113.

That is, when the distance measurement data obtained at the scanning point in the arrangement area of the reflection plate 21 and the distance measurement data substantially matches the distance to the reflection plate 21, the distance measurement data is It is determined that the reflected light from the reflecting plate 21 is calculated based on the output of the laser receiving unit 4 when the laser receiving unit 4 receives the reflected light.
In other words, when the process proceeds to step S113, the output of the laser light receiving unit 4 when the reflected light from the reflecting plate 21 is received is detected.

Here, whether or not the processing of either step S111 or step S112 is omitted, and the distance measurement data at the scanning point (pixel) in the arrangement area of the reflector 21 is obtained, the process proceeds to step S113. Alternatively, the process may proceed to step S113 when the distance measurement data substantially matches the distance to the reflecting plate 21.
However, if the distance measurement data obtained at the scanning points (pixels) in the arrangement area of the reflection plate 21 and the distance to the reflection plate 21 are substantially the same, the process proceeds to step S113. It can be determined with high accuracy that the distance measurement has been performed based on the output of the laser light receiving unit 4 when the reflected light from the reflecting plate 21 is received.

In step S113, the output E of the laser light receiving unit 4 that is the basis of the distance measurement data, that is, the output E of the laser light receiving unit 4 when the reflected light from the reflecting plate 21 is received is operated with the same bias voltage V1. An average value Ea in a plurality of past frames is calculated.
In step S114, a deviation ΔE (ΔE = Ea−E0) between the average value Ea calculated in step S113 and the target value E0 set in step S107 is calculated.

In step S115, it is determined whether or not the absolute value of the deviation ΔE calculated in step S114 is smaller than the allowable error ε.
When the absolute value of the deviation ΔE is smaller than the allowable error ε, the output E of the laser light receiving unit 4 when receiving the reflected light from the reflecting plate 21 substantially matches the target value E0, and the current bias voltage Since it is not necessary to change V1, the process returns to step S110 without changing the bias voltage V1.

On the other hand, when the absolute value of the deviation ΔE is larger than the allowable error ε, the output E of the laser light receiving unit 4 when the reflected light from the reflecting plate 21 is received is deviated from the target value E0, and the output level thereof is It is determined that there is a possibility that the determination of the light reception timing is caused by the deviation and the distance measurement accuracy is lowered, and the process proceeds to step S116.
That is, the allowable error ε is set as the maximum value of the deviation ΔE within a range in which the distance measurement error caused by the light reception timing judgment shift due to the output level shift does not exceed the allowable range, and the absolute value of the deviation ΔE is the allowable error. If it is smaller than ε, it can be estimated that ranging accuracy is ensured.

After step S116, the output E of the laser light receiving unit 4 when the reflected light from the reflecting plate 21 is received is brought close to the target value E0 by correcting the multiplication factor by changing (correcting) the bias voltage V1.
First, in step S116, whether or not the deviation ΔE is a positive value larger than 0, in other words, the output E of the laser light receiving unit 4 when the reflected light from the reflecting plate 21 is received from the target value E0. Is also determined.

When the deviation ΔE is a positive value larger than 0 and the output E of the laser light receiving unit 4 when receiving the reflected light from the reflecting plate 21 is higher than the target value E0, the step The process proceeds to S117 (bias voltage changing means).
In step S117, the bias voltage V1 is corrected to a value smaller than the previous value by the control step ΔV, and the bias voltage V1 after the correction is applied to the light receiving element (avalanche photodiode APD) 4b.

When the bias voltage V1 applied to the light receiving element (avalanche photodiode APD) 4b is changed to a lower voltage, the multiplication factor in the light receiving element (avalanche photodiode APD) 4b decreases, and laser light having the same intensity (light quantity) is received. The output E at that time will decrease.
Accordingly, if the bias voltage V1 is changed to be lower in a state where the output E of the laser light receiving unit 4 when receiving the reflected light from the reflecting plate 21 is higher than the target value E0, the output E becomes the target value E0. Will approach.

On the other hand, when the deviation ΔE is a negative value smaller than 0 and the output E of the laser light receiving unit 4 when receiving the reflected light from the reflecting plate 21 is lower than the target value E0, the step The process proceeds to S118 (bias voltage changing means).
In step S118, the bias voltage V1 is corrected to a value higher than the previous value by the control step ΔV, and the increased bias voltage V1 is applied to the light receiving element (avalanche photodiode APD) 4b.

When the bias voltage V1 applied to the light receiving element (avalanche photodiode APD) 4b is changed to a higher voltage, the multiplication factor in the light receiving element (avalanche photodiode APD) 4b increases, and laser light of the same intensity (light quantity) is received. Output E will increase.
Accordingly, if the bias voltage V1 is changed to a higher value while the output E of the laser light receiving unit 4 when receiving the reflected light from the reflecting plate 21 is lower than the target value E0, the output E becomes the target value E0. Will approach.

As described above, when the bias voltage V1 is decreased or increased by the control step ΔV depending on whether the output E of the laser receiving unit 4 when receiving the reflected light from the reflecting plate 21 is higher or lower than the target value E0, Returning to step S110, the distance data after the change of the bias voltage V1 is acquired.
The bias voltage V1 is repeatedly changed until the absolute value of the deviation ΔE becomes smaller than the allowable error ε. When the absolute value of the deviation ΔE becomes smaller than the allowable error ε, the bias voltage V1 at that time is held.

Accordingly, the temperature of the light receiving element (avalanche photodiode APD) 4b changes to change the multiplication factor. As a result, the output E of the laser light receiving unit 4 when the reflected light from the reflecting plate 21 is received is the target value E0. If it deviates from this, the multiplication factor is kept constant by correcting the bias voltage V1.
Further, even if the correlation between the element temperature and the multiplication factor varies for each light receiving element (avalanche photodiode APD) 4b, the laser light receiving unit when the reflected light from the reflecting plate 21 having a constant intensity (light quantity) is received. Since the bias voltage V1 is changed so that the output E of 4 coincides with the target value E0, the multiplication factor is controlled to be kept constant with respect to changes in element temperature and element variations.

Therefore, without preparing a table showing the correlation between the bias voltage V1 and the element temperature for each light receiving element (avalanche photodiode APD) 4b, the multiplication factor of each laser receiving unit 4 can be accurately adjusted with respect to changes in the element temperature. It can be kept constant, and high ranging accuracy can be obtained stably.
The control step ΔE for determining the change width of the bias voltage V1 is set to a larger value as the absolute value of the deviation ΔE is larger, and the output E of the laser light receiving unit 4 when the reflected light from the reflecting plate 21 is received is the target value E0. If the control step ΔE is changed to a smaller value as the value approaches, the responsiveness of the bias voltage V1 to the change in multiplication factor and the convergence stability can both be achieved.

Further, the bias voltage V1 can be changed by a proportional / integral / derivative operation based on the deviation ΔE.
Moreover, the initial value of the bias voltage when starting the feedback control of the bias voltage V1 can be variably set based on the detected value of the element temperature.
Further, it is preferable that a variable region (upper and lower limit values) of the bias voltage V1 is set in advance and the bias voltage V1 is changed within the variable region. Even if the bias voltage V1 is changed within the variable region, the reflector 21 When the output E of the laser light receiving unit 4 when receiving the reflected light from the laser beam cannot be made sufficiently close to the target value E0, the amount of light emitted from the laser projecting unit (projector) 3 is reduced. Therefore, it is possible to generate a failure detection signal and stop the distance measuring operation.

Furthermore, in the said embodiment, although the reflecting plate 21 was provided as a reflection part which reflects the laser beam scanned with the two-dimensional scanning mirror 2 toward the laser light-receiving part 4, a part of cover glass 7 was used as a reflection part. Can be used.
Embodiment which uses a part of cover glass 7 as a reflection part is described based on FIGS.
As shown in FIG. 4, the cover glass 7 (transparent plate) is formed in a shape bent so as to be convex toward the laser light receiving unit 4 in the scanning region, and the vicinity of the apex 7a of the cover glass 7 is a reflection unit. Used as

The ridge line formed by the apex 7a of the cover glass 7 may extend in the horizontal direction as shown in FIG. 5A, or extend in the vertical direction as shown in FIG. 4B. However, it is preferable that the ridge line passes through the vicinity of the center of the scanning region, and the scanning region is divided into approximately two equal parts vertically or horizontally by the ridge line.
If the ridge line is greatly deviated from the center of the scanning region, one inclined surface becomes long. As a result, the length in the optical axis direction from the vertex 7a to the portion of the cover glass 7 corresponding to the end of the scanning region ( The depth of the cover glass becomes long, and the apparatus becomes large. On the other hand, if the ridge line passes through the approximate center of the scanning region, the depth of the cover glass becomes the shortest, which can contribute to downsizing of the apparatus.

When measuring the distance to the object to be measured, if the laser light reflected by the inner surface of the cover glass 7 enters the field of view of the laser light receiving unit 4, noise will be generated. As shown in FIG. The cover glass 7 has a bent shape that is convex toward the laser light receiving unit 4, and the inner plane of the cover glass 7 is an inclined surface whose distance from the two-dimensional scanning mirror 2 becomes longer as the distance from the vertex 7 a portion increases. Then, the laser light is incident on the inner plane of the cover glass 7 with an incident angle α (α> 0), and as shown in FIG. 4, the laser light can be reflected toward the outside of the scanning region, Noise reduction can be achieved.
On the other hand, in the vicinity of the vertex 7a of the cover glass 7, as shown in FIG. 6, the reflected light from the cover glass 7 can be put into the field of view of the laser light receiving unit 4 by satisfying certain conditions, and the vicinity of the vertex 7a. If the bias voltage V1 is changed so that the output E of the laser light receiving unit 4 when receiving the reflected light at the point coincides with the target value E0, the multiplication factor of the light receiving element (avalanche photodiode APD) 4b can be controlled to be constant. .

The condition for allowing the reflected light from the cover glass 7 to enter the field of view of the laser light receiving unit 4 is that when the light projection beam is emitted near the vertex 7a of the cover glass 7, a part of the light projection beam is covered. It is a condition that the light is incident at a right angle to the plane of the glass 7. Specifically, the diameter of the projection beam is 2 W, the distance between the scanning base point (two-dimensional scanning mirror 2) and the cover glass 7 is L, It is only necessary to satisfy tan θ1 ≦ w / L, where θ1 is an angle between two planes sandwiching the apex 7a of the vertical plane.
As described above, if a part of the cover glass 7 is used as the reflecting portion, the number of parts can be reduced as compared with the case where the reflecting plate 21 is provided.

Further, since the vertex 7a of the cover glass 7 is located near the center of the scanning region, the laser light receiving unit 4 can receive the reflected light from the vicinity of the vertex 7a as the reflecting portion even if the scanning amplitude slightly varies. Accordingly, the determination of whether or not the scanning amplitude has reached the target in step S105 in the flowchart of FIG. 3 is omitted, and the laser light receiving unit when the reflected light from the reflecting unit is received before the scanning amplitude reaches the target. 4 outputs can be monitored.
The cover glass 7 can be bent into a bellows shape so as to be convex at a plurality of locations, and a plurality of ridge lines can be used as reflecting portions, respectively, and the angle θ1 is gradually increased toward the vertex 7a. It is also possible to form the cover glass 7 so as to be larger, and the cover glass 7 may be curved by continuously changing the angle θ1.

1 Optical distance measuring device 2 Two-dimensional scanning mirror (scanning device)
3 Laser projector (projector)
4 Laser receiver (receiver)
4b Light receiving element (avalanche photodiode APD)
4d Bias circuit 5 Emitter / receiver separator 7 Cover glass (transparent plate)
7a Vertex 11 Distance measurement unit 12 Average value calculation unit 13 Target setting unit 14 Deviation calculation unit 15 Adjustment unit 16 Bias voltage change unit 21 Reflector

Claims (11)

A projector for projecting measurement light;
A scanning device that scans the measurement light toward the measurement object;
Having a multiplication effect by applying a bias voltage, and receiving a reflected light from the measurement object,
In the optical distance measuring device that measures the distance to the measurement object based on the time difference between the light projection timing of the measurement light by the light projector and the light reception timing of the reflected light by the light receiver,
In a part of the scanning region of the measurement light, a reflection unit that reflects the measurement light from the projector toward the light receiver is provided,
An optical distance measuring device comprising bias voltage changing means for changing the bias voltage so that an output of the light receiver when receiving light reflected by the reflecting portion becomes a predetermined set value.   2. The light according to claim 1, wherein the bias voltage changing unit detects an output of the light receiver that has received the light reflected by the reflection unit based on an arrangement region of the reflection unit in the scanning region. Distance measuring device.   3. The optical distance measuring device according to claim 1, wherein the bias voltage changing unit detects an output of the light receiver that has received the light reflected by the reflecting unit based on a distance measurement result. 4.   The optical distance measuring device according to claim 1, wherein the reflection unit is a reflection plate disposed in the scanning region. Radiation of the measurement light toward the measurement object and reception of reflected light from the measurement object are performed through a transparent plate,
The optical distance measuring device according to claim 4, wherein the reflecting plate is attached to the transparent plate. Radiation of the measurement light toward the measurement object and reception of reflected light from the measurement object are performed through a transparent plate,
The optical distance measuring device according to claim 1, wherein a part of the transparent plate is used as the reflecting portion. The transparent plate is formed in a shape that is bent so as to be convex toward the projector in the scanning region,
The optical distance measuring device according to claim 6, wherein a vicinity of an apex of the transparent plate is used as the reflecting portion.   The bias voltage changing unit fixes the bias voltage to an initial value until the scanning amplitude by the scanning device reaches a set value from the start of scanning, and after the scanning amplitude reaches the set value, the bias voltage is changed. The voltage is changed stepwise from the initial value in accordance with a deviation between the output of the light receiver that has received the light reflected by the reflecting portion and the set value. The optical distance measuring device according to claim 1.   9. The bias voltage changing unit according to claim 1, wherein the bias voltage changing unit calculates an average value for the output of the light receiver that has received the light reflected by the reflecting portion, and changes the bias voltage based on the average value. The optical distance measuring device according to any one of the above.   The bias voltage changing unit is configured to change the bias voltage when a deviation between an output of the light receiver that receives light reflected by the reflection unit and the set value exceeds an allowable error. The optical distance measuring device according to any one of 1 to 9.   11. The optical measurement according to claim 1, wherein the reflectance of the reflection unit is set to a value that does not saturate an output of the light receiver that receives light reflected by the reflection unit. Distance device.