JP5723517B2 - Optical distance measuring device - Google Patents

Description

  The present invention relates to an optical distance measuring device that detects light reflected from an object to be measured by a photodetector having a multiplication effect by applying a bias voltage.

  Conventionally, as disclosed in Patent Document 1, as an optical distance measuring device, laser light is emitted toward a measurement object, the timing at which the laser light is emitted, and the laser light reflected from the measurement object is received. An apparatus for measuring a distance to a measurement object by measuring a time difference from timing is known. In the optical distance measuring device, a photodetector (avalanche photodiode APD) having a multiplication effect by applying a bias voltage is used as a photodetector for detecting weak light reflected from a measurement object with high sensitivity. It has been.

Japanese Patent Laid-Open No. 2003-130953

  By the way, since the multiplication factor in the photodetector (avalanche photodiode APD) changes depending on the element temperature, when the change in the element temperature occurs, the output level of the photodetector changes without depending on the reflected light intensity, As a result, the light reception determination timing may be shifted, resulting in a measurement error. Here, for example, a correlation between the element temperature and the bias voltage for making the multiplication factor constant is tabulated in advance, and the bias voltage corresponding to the element temperature at that time is determined with reference to the table. For example, the multiplication factor can be stabilized.

  However, since the correlation between the element temperature and the multiplication factor is different for each photodetector, if the bias voltage is set based on a common table, the multiplication factor cannot be stabilized accurately, and light detection is performed. It is necessary to set the table for each device. In addition, it is difficult to detect the element temperature correlated with the multiplication factor with high accuracy, and the bias voltage is set to be deviated from an appropriate value due to the detection error of the element temperature, and the multiplication factor is changed.

  The present invention has been made paying attention to the above-mentioned problems, and can accurately stabilize the multiplication factor of the photodetector with respect to changes in the element temperature, thereby stabilizing the high ranging accuracy. It is an object of the present invention to provide an optical distance measuring device that can be maintained.

For this reason, the invention according to claim 1 has a multiplication function by applying a bias voltage, and a ranging photodetector that receives reflected light from the measurement object, and light directed toward the measurement object. A light source for distance measurement that radiates periodically, and a light detector for light emission monitoring , and splits light emitted from the light source for distance measurement into light and monitor light that are projected toward the measurement object; The monitor light is branched and received by the distance measuring light detector and the light emission monitor light detector, and the output of the distance measuring light detector that receives the reflected light and the monitor light is output to the light emission monitor. The light detection for distance measurement is separated into the detection output of the monitor light and the detection output of the reflected light based on the emission timing of the distance measurement light source detected based on the detection output of the monitor light of the optical detector for detection. The monitor light detection output of the detector and the light emission monitor photodetector The ratio of the detection output of the serial monitor light is to change the bias voltage of the distance measuring light detector so that the target value.

In such a configuration, the light emission monitor light detector and the distance measuring light detector both detect the light emitted from the distance measuring light source, so the difference in output between the two detectors is the distance measuring light detector. The ratio of the detection output indicates the multiplication factor in the photo detector for distance measurement. Therefore, the multiplication factor is corrected by correcting the bias voltage based on the ratio of the detection output. Can be stabilized. Furthermore, in the above configuration, it is possible to correct the bias voltage to an appropriate value without requiring a dedicated light source for emitting the reference light.

In the configuration of the first aspect , as in the second aspect , the intensity of light emitted from the distance measuring light source can be adjusted to be constant. In this case, if the intensity of the light emitted from the distance measuring light source changes, the change in the detection output due to the change in the light intensity is erroneously detected as a change in the multiplication factor due to the temperature change. The intensity of the light emitted from the light source is adjusted to be constant, and the detection output of the ranging light detector does not change with the change in the intensity of the light emitted from the ranging light source. Make it fluctuate.

In the configuration of claim 2 , as in claim 3 , the driving signal of the distance measuring light source can be corrected so that the intensity of light detected by the light emission monitor photodetector is constant.

  According to such an optical distance measuring device, it is possible to correct the bias voltage to obtain a desired multiplication factor under the temperature condition without using the detection result of the element temperature. The multiplication factor in the photodetector can be stabilized and high ranging accuracy can be maintained.

The block diagram which shows the optical ranging apparatus of 1st Embodiment of this invention. The figure which shows the correlation with element temperature and a multiplication factor when a bias voltage is made constant in the photodetector for distance measurement (avalanche photodiode APD) of 1st Embodiment same as the above. The figure which shows the bias voltage for making a multiplication constant constant for every element temperature in the photodetector for distance measurement (avalanche photodiode APD) of 1st Embodiment same as the above. The flowchart which shows the flow of the correction process of the bias voltage in 1st Embodiment same as the above. The block diagram which shows the optical ranging apparatus of 2nd Embodiment of this invention. The block diagram which shows the optical ranging apparatus of 3rd Embodiment of this invention. The flowchart which shows the flow of the correction process of the bias voltage in 3rd Embodiment same as the above. The figure which shows the time division multiplexing system as an example of the separation method of the detection output in 3rd Embodiment same as the above. The figure which shows the frequency division multiplexing system as an example of the separation method of the detection output in 3rd Embodiment same as the above.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a first embodiment of an optical distance measuring device according to the present invention. An optical distance measuring device 1 shown in FIG. 1 includes a distance measuring light source (semiconductor laser) 2 and a distance measuring light detector (light receiving element) 4 for detecting laser light reflected from the measurement object 3. This is an apparatus for measuring the distance to the measurement object 3 based on the time difference between the emission timing of the laser beam toward the measurement object 3 and the light reception timing of the distance measuring photodetector 4.

  The laser light periodically emitted from the distance measuring light source 2 passes through a light projection optical system (including a lens / scanner) 5 and then branches in two directions by a beam splitter 6, and one (probe light). Is projected toward the measurement object 3 and the other (monitor light) is incident on the beam splitter 7. One of the laser beams branched in two directions by the beam splitter 7 is received by a light emission monitor optical detector (light receiving element) 9 via a light emission monitor optical system 8.

  The light emission monitor photodetector 9 includes a photodiode PD which is a photoelectric device having a photovoltaic effect, and generates a voltage corresponding to the intensity of received laser light as a detection output. The timing at which the laser light is detected by the light emission monitor photodetector 9 is determined as the laser light emission timing toward the measurement object 3, and a time-measurement start pulse is generated based on the determination. On the other hand, the laser beam reflected by the measurement object 3 is received by the distance measuring photodetector 4 through the light receiving optical system 10.

  The distance measuring photodetector 4 includes an avalanche photodiode APD having a multiplication effect by applying a bias voltage, and detects a voltage corresponding to the intensity of the laser beam (probe light) reflected by the measuring object 3. Occurs as output. Then, when the ranging light detector (APD) 4 detects the laser light reflected by the measuring object 3, a time stop pulse is generated at this light reception timing, and the time from the time start pulse to the time stop pulse is Measured as a time difference between the emission timing of the laser beam toward the measurement object 3 and the reception timing of the reflected light in the distance measuring photodetector (APD) 4, and based on the time and the propagation speed of the laser beam The distance to the measurement object (object to be measured) 3 is detected.

  One of the laser beams branched by the beam splitter 7 is received by the light emission monitor photodetector 9 as described above, and the other is reflected by the reflection mirror 11 and enters the light receiving optical system 10. The light is received by a ranging photodetector (APD) 4. That is, the distance measuring light detector (APD) 4 has a constant intensity of laser light emitted from the distance measuring light source 2 by the beam splitters 6 and 7 and the reflecting mirror 11 at a constant flight time (flight distance). The laser beam directly received and reflected by the measuring object 3 is received.

  Here, the intensity of the laser beam reflected by the measuring object 3 and received by the distance measuring photodetector (APD) 4 becomes weaker as the distance to the measuring object 3 becomes longer, and this weak reflected light. Therefore, as described above, the avalanche photodiode APD having a multiplication action by applying a bias voltage is used as the light receiving element constituting the distance measuring photodetector 4 as described above. .

  However, when a constant bias voltage is applied to the avalanche photodiode APD, as shown in FIG. 2, the multiplication factor changes according to the element temperature at that time. FIG. 2 shows an example of the correlation between the element temperature and the multiplication factor of the avalanche photodiode APD when the bias voltage is constant, and shows the characteristic that the multiplication factor decreases as the element temperature increases. When the gain of the avalanche photodiode APD changes due to the temperature change, and the magnitude of the output voltage of the ranging photodetector (APD) 4 changes, for example, the light reception timing based on the comparison between the output voltage and the threshold value. When detecting the light, the detected light reception timing is deviated, and the distance measurement results vary.

  Therefore, in the first embodiment, as described above, the laser light emitted from the distance measurement light source 2 is directly applied to the distance measurement photodetector (APD) 4 by the beam splitters 6 and 7 and the reflection mirror 11. The output of the distance measuring light detector (APD) 4 at this time and the output of the light emission monitoring light detector (PD) 9 that directly receives the laser light emitted from the distance measuring light source 2 at this time. To obtain the multiplication factor of the ranging photodetector (APD) 4 and correct the bias voltage of the avalanche photodiode APD so that the multiplication factor becomes a target value (bias voltage correction means). ).

  That is, the laser light emitted from the distance measuring light source 2 is received by the distance measuring light detector (APD) 4 as reference light having a constant intensity via the beam splitters 6 and 7 and the reflecting mirror 11. The distance measuring light source 2, the beam splitters 6, 7 and the reflection mirror 11 constitute reference light monitoring means for allowing the distance measuring light detector (APD) 4 to receive reference light having a constant intensity.

  As a configuration (bias voltage correcting means) for correcting the bias voltage, an output voltage Vx of the distance measuring photodetector (APD) 4 and an output voltage Vo of the light emission monitoring photodetector (PD) 9 are used. A ratio calculator 12 for calculating a ratio (multiplier) Mx, a target value storage unit 13 for storing a target value M of the ratio (multiplier) Mx, and a ratio (multiplier) Mx calculated by the ratio calculator 12 The comparison unit 14 compares the target value M stored in the target value storage unit 13 and outputs a bias voltage increase / decrease request signal (error signal), and the increase / decrease of the bias voltage output from the comparison unit 14 And a bias circuit 15 for changing a bias voltage applied to the distance measuring photodetector (APD) 4 based on a request signal. As the target value M, it is preferable to set a value that maximizes the SN ratio in the ranging photodetector (APD) 4.

  The distance measuring light detector (APD) 4 is guided by the beam splitters 6, 7 and the reflection mirror 11, and the laser light (reference light) emitted from the distance measuring light source 2 and the measurement object 3. The laser light (measurement light) reflected from the laser beam is received, but the laser light directly guided by the beam splitters 6 and 7 and the reflection mirror 11 has a timing earlier than the laser light reflected from the measurement object 3. Then, the light is received by the ranging light detector (APD) 4 and is received by the ranging light detector (APD) 4 after a predetermined time from the radiation timing.

  For this reason, whether the output voltage of the photo detector for distance measurement (APD) 4 is an output obtained by detecting the laser light (reference light) guided by the beam splitters 6 and 7 and the reflection mirror 11, from the measurement object 3. Whether the reflected laser beam is detected or not can be determined based on the time difference from the radiation timing. Accordingly, the ratio calculation unit 12 uses the output voltage Vx obtained by detecting the laser light (reference light) guided by the beam splitters 6 and 7 and the reflection mirror 11 from the output voltage of the ranging photodetector (APD) 4. Extraction is performed, and the ratio between the output voltage Vx and the output voltage Vo of the light emission monitor photodetector (PD) 9 is calculated. Since the output voltage Vx is a value obtained by detecting laser light (reference light) having a constant intensity, the output voltage Vx is a constant value if the multiplication factor of the avalanche photodiode APD is constant.

  The output voltage Vx of the distance measuring photodetector (APD) 4 is higher than the output voltage Vo of the light emission monitoring photodetector (PD) 9 due to the high light receiving sensitivity due to the internal multiplication effect of the avalanche photodiode APD. The ratio Mx = Vx / Vo of the two is the light receiving sensitivity of the distance measuring photodetector (APD) 4 when the light receiving sensitivity of the light emission monitoring photodetector (PD) 9 is used as a reference, in other words, the measurement. This indicates the multiplication factor Mx of the distance photodetector (APD) 4. Since the multiplication factor Mx of the distance measuring photodetector (APD) 4 changes according to the change in element temperature, the target multiplication factor M stored in the target value storage unit 13 and the output voltage The comparison unit 14 compares the multiplication factor Mx obtained as a ratio.

  As shown in FIG. 2, for example, when the element temperature of the ranging photodetector (APD) 4 rises with a constant bias voltage, the multiplication factor Mx decreases, and the multiplication factor Mx increases the bias voltage. It increases by doing. Therefore, in order to suppress the decrease in the multiplication factor Mx due to the increase in the element temperature and maintain the multiplication factor Mx in the vicinity of the target value M, as shown in FIG. 3, the bias voltage is increased and changed with the increase in the element temperature. Conversely, the bias voltage may be decreased and changed with respect to an increase in the multiplication factor Mx due to a decrease in the element temperature.

  Therefore, when the comparison unit 14 determines that the multiplication factor Mx at that time is lower than the target value M, the comparison unit 14 outputs a multiplication factor increase request signal (bias voltage increase request signal) to the bias circuit 15. Conversely, when it is determined that the multiplication factor Mx at that time is higher than the target value M, a multiplication factor reduction request signal (bias voltage reduction request signal) is output to the bias circuit 15, and If it is determined that the multiplication factor Mx at this time substantially matches the target value M, a multiplication factor maintenance request signal (bias voltage maintenance request signal) is output to the bias circuit 15.

  When the bias circuit 15 receives the multiplication factor increase request signal (bias voltage increase request signal), the bias circuit 15 performs a process of increasing and changing the bias voltage by a fixed value, and the multiplication factor reduction request signal (bias voltage decrease request). Signal), the bias voltage is decreased and changed by a certain value. Further, when a multiplication factor maintenance request signal (bias voltage maintenance request signal) is received, the bias voltage is set to the current value. To maintain. In response to an increase / decrease request signal for the multiplication factor (bias voltage), the increase / decrease of the bias voltage is repeated every time the output voltage Vx is detected, that is, each time the laser light is emitted from the distance measuring light source 2. When the magnification Mx substantially coincides with the target value M, the change of the bias voltage is stopped and the bias voltage is kept constant.

  Note that the detection of the multiplication factor Mx and the change of the bias voltage need not be performed every time the laser light is emitted from the distance measuring light source 2. In addition, the larger the deviation between the multiplication factor Mx and the target value M, the larger the change width of the bias voltage per one time, or the shorter the update period of the bias voltage. The constant value for increasing / decreasing the bias voltage is set in advance as a value that changes the multiplication factor within the allowable variation width, and if it is within the allowable variation width, a request to maintain the bias voltage is generated. It is preferable that the multiplication factor is determined to prevent the multiplication factor from hunting near the target value.

  FIG. 4 is a flowchart showing the flow of the bias voltage correction process. First, when laser light is emitted from the distance measuring light source 2 (step S101), the laser light is received by the light emission monitor photodetector (PD) 9 by the beam splitters 6 and 7, and the detection output of the laser light is output. Vo is obtained (step S102). The laser light emitted from the distance measuring light source 2 is also received by the distance measuring light detector (APD) 4 by the beam splitters 6 and 7 and the reflecting mirror 11, and is detected at a higher level by the APD multiplication function. An output Vx is obtained (step S103).

  The ratio between the detection output Vo and the detection output Vx is the light reception sensitivity (multiplier) of the distance measurement photodetector (APD) 4 based on the light reception sensitivity of the light emission monitor photodetector (PD) 9. Therefore, the ratio (multiplier) Mx = Vx / Vo is calculated (step S104). Next, the ratio (multiplier) Mx and the target value M are compared (step S105). If the ratio (multiplier) Mx is smaller than the target value M, the distance measuring photodetector (APD) 4 The bias voltage is increased and corrected (step S106).

  On the other hand, if the ratio (multiplier) Mx is equal to or greater than the target value M, it is determined whether the ratio (multiplier) Mx is larger than the target value M (step S107), and the ratio (multiplier) Mx is determined. If it is larger than the target value M, the bias voltage of the distance measuring photodetector (APD) 4 is decreased and corrected (step S108). If it is determined that the ratio (multiplier) Mx is not equal to or greater than the target value M and the ratio (multiplier) Mx substantially matches the target value M, the bias voltage at that time is maintained (step). S109).

  According to the first embodiment, the change in the multiplication factor due to the change in the element temperature of the ranging photodetector (APD) 4 is corrected by correcting the bias voltage based on the detection result of the actual multiplication factor Mx. It can be suppressed and the multiplication factor can be stabilized in the vicinity of the target value, so that high ranging accuracy can be stably maintained. Further, the correction of the bias voltage is performed individually for each optical distance measuring device 1 (for each distance measuring light detector (APD) 4), and therefore, due to characteristic variations of the distance measuring light detector (APD) 4. Variations in multiplication factor are also corrected. Further, since the bias temperature is not corrected by detecting the element temperature of the distance measuring photodetector (APD) 4, it is not necessary to tabulate the correlation between the element temperature and the bias voltage in advance. The bias voltage is not erroneously corrected by the temperature detection error, and is not corrected to a multiplication factor different from the target (predetermined value).

  By the way, when the laser light emitted from the ranging light source 2 is directly received by the ranging photodetector (APD) 4 as the reference light and the bias voltage is corrected from the output at that time, the ranging light is used. If the intensity of the laser light emitted from the light source 2 is required to be a known constant intensity, and the light intensity varies due to product variations of the distance measuring light source 2, the accuracy of correcting the bias voltage decreases. Therefore, in order to maintain the correction accuracy of the bias voltage, it is preferable to add a circuit for controlling the intensity of the laser light emitted from the distance measuring light source 2 to a constant value as in the second embodiment shown in FIG.

  In FIG. 5 showing the second embodiment, the same elements as those in FIG. 1 of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. In the second embodiment shown in FIG. 5, a drive current control circuit 21 (light intensity adjusting means) that controls the drive current of the distance measuring light source 2 based on the detection output of the light emission monitor photodetector (PD) 9. It is configured with.

  Then, the drive current control circuit 21 is configured so that the detection output of the light emission monitor photodetector (PD) 9 is lower than the reference output corresponding to the reference intensity of the laser light and is emitted from the distance measuring light source 2. When the light intensity is weaker than the reference intensity, the drive current is increased and changed by a predetermined value. Conversely, the detection output of the light emission monitor photodetector (PD) 9 corresponds to the reference intensity of the laser beam. If the intensity of the laser light emitted from the ranging light source 2 is higher than the reference intensity, the drive current is decreased and changed by a predetermined value, and the light emission monitoring photodetector When the detection output of (PD) 9 substantially matches the reference output corresponding to the reference intensity of the laser beam, the drive current at that time is maintained.

  According to the second embodiment, the variation in the intensity of the laser light emitted from the distance measuring light source 2 is suppressed, so that the distance measuring light detector (APD) 4 stably receives the laser light having a constant intensity. Accordingly, the actual multiplication factor of the ranging photodetector (APD) 4 can be obtained with high accuracy. Accordingly, by correcting the bias voltage based on the detected actual multiplication factor, the actual multiplication factor Mx of the distance measuring photodetector (APD) 4 can be brought close to the target value M with high accuracy.

  In the first and second embodiments, the output voltage Vx of the ranging photo detector (APD) 4 when the laser beam emitted from the ranging light source 2 is directly received is set to a desired multiplication factor. By correcting the bias voltage so that the target output voltage Vxt can be matched, the multiplication factor of the distance measuring photodetector (APD) 4 can be corrected to the expected value. Further, a second light source (multiplication monitor light source) for detecting the multiplication factor is provided separately from the distance measuring light source 2, and the laser light emitted from the second light source is used as a reference light for distance measurement. The light can be received by the photodetector (APD) 4 and the bias voltage can be corrected based on the detection output at that time.

  FIG. 6 shows a third embodiment including the second light source. The same elements as those in FIG. 1 of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. In FIG. 6, a monitor light source (semiconductor laser) 31 is provided as the second light source (multiplier monitor light source), and laser light (reference light) having a constant intensity emitted from the monitor light source 31 is used for monitoring. The light is incident on the reflecting mirror 33 via the optical system 32, and the reflected light from the reflecting mirror 33 is received by the distance measuring photodetector (APD) 4 via the light receiving optical system 10. That is, the monitoring light source 31, the monitoring optical system 32, the reflection mirror 33, and the light receiving optical system 10 constitute reference light monitoring means for allowing the ranging light detector (APD) 4 to receive reference light having a constant intensity. The

  The laser light emitted from the distance measuring light source 2 is branched by the beam splitter 6 as in the first and second embodiments, one is emitted toward the measuring object 3, and the other is the reflecting mirror. After being reflected at 39, the laser light received by the light emission monitor optical detector (light receiving element) 9 via the light emission monitor optical system 8 and emitted from the distance measuring light source 2 is directly (measurement object 3 Without being reflected by the distance measuring photodetector (APD) 4.

  The detection output Vx of the distance measuring photodetector (APD) 4 is output to the comparison unit 34. The comparison unit 34 compares the target value Vxt set by the target value setting unit 36 with the actual detection output Vx. Is done. The target value Vxt is a detection output obtained at a desired multiplication factor when a laser beam (reference light) having a constant intensity emitted from the monitor light source 31 is received.

  When it is determined that the actual detection output Vx is lower than the target value Vxt and the multiplication factor at the distance measuring photodetector (APD) 4 is lower than the expected value (target value), the comparison unit 34. Outputs a bias voltage increase request signal (multiplier increase request signal), and conversely, the actual detection output Vx is higher than the target value Vxt, and the multiplication factor in the distance measuring photodetector (APD) 4 is increased. Is determined to be higher than the expected value (target value), the comparison unit 34 outputs a bias voltage reduction request signal (multiplication factor reduction request signal), and the actual detection output Vx is further set to the target value. If it substantially matches the value Vxt, a bias voltage maintenance request signal (multiplier maintenance request signal) is output.

  When the bias circuit 35 to which the request signal from the comparison unit 34 is input, when the bias voltage increase request signal is received, the bias voltage is increased and changed by a certain value, and the bias voltage decrease request signal is received. In this case, a process for decreasing and changing the bias voltage by a predetermined value is performed, and when the bias voltage maintenance request signal is received, the bias voltage is maintained at the current value.

  The flowchart in FIG. 7 shows the flow of bias voltage correction processing in the third embodiment including the monitor light source 31. First, when laser light is emitted from the monitor light source 31 (step S201), the laser light passes through the monitor optical system 32, the reflection mirror 33, and the light receiving optical system 10, and the distance measuring photodetector (APD). ) 4 and the detection output Vx of the laser beam from the monitor light source 31 is obtained (step S202). On the other hand, when the distance measuring photodetector (APD) 4 receives the laser light from the monitor light source 31, a detection output obtained at a desired multiplication factor is set as the target value Vxt (step S1). S203).

  Then, the laser beam detection output Vx from the monitor light source 31 is compared with the target value Vxt (step S204), and if the actual detection output Vx is smaller than the target value Vxt, the ranging light The bias voltage of the detector (APD) 4 is increased and corrected (step S205). On the other hand, when the actual detection output Vx is equal to or greater than the target value Vxt, it is determined whether or not the actual detection output Vx is larger than the target value Vxt (step S206), and the actual detection output Vx is the target value Vxt. If it is larger, the bias voltage of the distance measuring photodetector (APD) 4 is corrected to decrease (step S207). If the actual detection output Vx substantially matches the target value Vxt, the bias voltage at that time is maintained (step S208).

  With the bias voltage correction control, the detection output Vx of the ranging light detector (APD) 4 when the laser light (reference light) emitted from the monitor light source (semiconductor laser) 31 is received becomes the target value Vxt. The bias voltage is corrected so as to approach, and as a result, the multiplication factor in the distance measuring photodetector (APD) 4 is corrected to an initial value (target value). Therefore, similarly to the first and second embodiments, the light receiving timing can be detected with high accuracy based on the detection output Vx of the distance measuring photodetector (APD) 4, and thus high distance measurement. Accuracy can be maintained.

  Further, since the monitor light source 31 is provided separately from the distance measuring light source 2, the intensity of the reference light used to detect the multiplication factor of the distance measuring photodetector (APD) 4 is increased regardless of the distance measuring operation. The value can be set to an optimum value for detecting the magnification, and the reference light can be received by the distance measuring photodetector (APD) 4 at a timing separate from the radiation of the laser light for distance measurement. it can. However, in the third embodiment, it is necessary to separate the detection output Vx that has received the laser light from the ranging light source 2 and the detection output Vx that has received the laser light from the monitoring light source 31.

  FIG. 8 shows the separation method, in which the laser light emitted from the distance measuring light source 2 is reflected by the measuring object 3 and is received by the distance measuring photodetector (APD) 4. The period from the end of the period to the beginning of the next ranging period is set as a monitoring period in which the ranging light detector (APD) 4 receives the laser light emitted from the monitoring light source 31. Then, the laser light emitted from the monitoring light source 31 in the monitoring period is periodically received from the monitoring light source 31 in synchronization with the monitoring period so that the distance measuring photodetector (APD) 4 receives the laser light. Emits light.

  Thereby, the detection output Vx of the ranging light detector (APD) 4 in the monitoring period is a detection output of the laser light emitted from the monitoring light source 31, and the ranging light in the ranging period is The detection output Vx of the detector (APD) 4 can be distinguished from the detection output of the laser light emitted from the distance measuring light source 2 and reflected by the measurement object 3. That is, the detection output separation method shown in FIG. 8 is a method in which the detection of the laser light reflected by the measurement object 3 and the detection of the laser light emitted from the monitor light source 31 are performed separately in time. In other words, the time division multiplexing system is adopted as the optical multiplexing modulation system.

  Therefore, if the bias voltage is corrected so that the detection output Vx in the monitoring period approaches the target value Vxt, the detection output Vx that has received the laser light (reference light) from the monitor light source 31 is brought close to the target value Vxt. Thus, the multiplication factor of the photo detector for distance measurement (APD) 4 can be maintained near the target value even if there is a temperature change.

  FIG. 9 shows another example of the separation method, in which the laser light from the monitor light source 31 is modulated with a light emission pattern that has no correlation with the light emission pattern of the laser light in the distance measuring light source 2, and the difference in the light emission pattern. In this method, the detection output of the reflected laser beam from the measurement object 3 and the detection output of the laser beam from the monitor light source 31 are separated. Specifically, FIG. 9 shows that each of the light sources 2 for distance measurement and the light source for monitoring 31 emit light periodically at mutually different modulation frequencies, and the fact that the modulation frequency of each light source is different makes each light source (for each frequency). An example of a frequency division multiplexing method for obtaining a detection output (light intensity) of () is shown.

  Further, as a method of obtaining the detection output (light intensity) for each light source by modulation (difference in light emission pattern), the monitor light source 31 is modulated by a random number different from that of the distance measuring light source 2 and the random number code is different. A spread spectrum modulation method that obtains the detection output (light intensity) for each light source by using it can also be adopted.

  The reference light (APD) 4 receives the reference light (the laser light directly guided from the distance measuring light source 2 or the laser light emitted from the monitor light source 31) every time the reference light is received. In addition to obtaining a detection output for the reference light and executing a bias voltage correction process (including a determination of maintaining the current state), the bias voltage correction process is executed at a rate of once for a plurality of times of receiving the reference light. In addition, a plurality of detection outputs obtained by receiving the reference light a plurality of times can be averaged, and the bias voltage can be corrected based on the detection output after the averaging processing.

  In the configuration using the monitor light source 31, the laser light can be emitted from the monitor light source 31 regardless of the distance measuring operation. The monitor light source 31 is caused to emit light at a rate of> 1) or the monitor light source 31 is caused to emit light every predetermined time. From the detection output of the distance measuring photodetector (APD) 4 at that time, The bias voltage can be corrected.

DESCRIPTION OF SYMBOLS 1 Optical ranging device 2 Ranging light source 3 Measuring object 4 Ranging photodetector (avalanche photodiode APD)
5 Projection optics 6, 7 Beam splitter 8 Emission monitor optical system 9 Emission monitor photodetector (photodiode PD)
DESCRIPTION OF SYMBOLS 10 Light reception optical system 11 Reflecting mirror 12 Ratio calculating part 13 Target value memory | storage part 14 Comparison part 15 Bias circuit (bias voltage correction means)
21 Drive current control circuit (light intensity adjustment means)
31 Light source for monitor (light source for multiplication monitor)

Claims (3)

A ranging light detector that has a multiplication effect by applying a bias voltage and receives reflected light from the measurement object; a ranging light source that periodically emits light toward the measurement object; A light emission monitor light detector , branching the light emitted from the distance measuring light source into light projected to the measurement object and monitor light, and branching the monitor light to the distance measuring light The detector and the light emission monitor photodetector receive light, and the output of the ranging light detector that receives the reflected light and the monitor light is output as the detection output of the monitor light of the light emission monitor photodetector. The detection output of the monitor light and the detection output of the reflected light are separated based on the radiation timing of the distance measuring light source detected based on the detection light, and the monitor light detection output and the light emission of the ranging light detector The ratio of the monitor light detector to the monitor light detection output is notable. Wherein changing the bias voltage of the distance measuring light detector so that the value, the optical distance measuring device. The optical distance measuring device according to claim 1 , wherein the intensity of light emitted from the distance measuring light source is adjusted to be constant . 3. The optical distance measuring device according to claim 2 , wherein a driving signal of the distance measuring light source is corrected so that the intensity of light detected by the light emission monitoring light detector is constant .

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