JP2007198910A - Distance measuring instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately detect electric pulse signals corresponding to reflected light and reference light. <P>SOLUTION: A received-light signal level adjustment part 18 adjusts at least one or more of an impressed voltage on an LD drive circuit 7, an impressed voltage on a high-voltage power supply 11, and the amplification factor of a variable-gain amplifier 13, so that the amplitude levels of received pulses, corresponding to the reflected light and reference light, reach the minimum amplitude level required in order for the received pulses to be detected by a light receiving part 3, and that their waveforms have substantially the same shape. This optimizes the amplitude level and waveforms of the electric pulse signals corresponding to the reflected light and reference light, respectively, and causes their waveforms to have substantially the same shape, and therefore, the pulse signals, corresponding to the reflected light and reference light, are accurately detected, making it possible to accurately measure the distance to a measuring object. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a distance measuring device that measures the distance to a measurement object by projecting light toward the measurement object and receiving reflected light from the measurement object.

In general, the amount of reflected light from the measurement object varies depending on the distance to the measurement object, the surface state of the measurement object, the material, and the amount of reflected light. From such a background, the conventional distance measuring device arranges a light amount adjusting member in the light emitting unit and the light receiving unit, or controls the light emitting amount of the light emitting unit, thereby measuring the distance to the measuring object and the measuring object. Control is performed so that the amount of reflected light remains constant even if the surface condition, material, amount of reflected light, etc. of the light changes. However, since the electrical pulse signal received by the light receiving unit includes many noise signals in addition to the electrical pulse signal corresponding to the reflected light and the reference light due to disturbances such as light from other than the measurement target, According to the distance measuring apparatus, the measurement error may increase. For this reason, a distance measuring device has been proposed that enables accurate distance measurement even in a situation where a noise signal is included by adjusting the size of the threshold level of the light receiving unit (see Patent Document 2). .
JP-A-5-297140 JP 2000-356777 A

  However, in the method of measuring the distance to the measurement object based on the flight time of the reflected light from the measurement object, the threshold level depends on the waveform of the electric pulse signal to which the threshold level is applied. Only by adjusting the magnitude of, the accuracy of the detection time of each electric pulse signal corresponding to the reflected light or reference light is lowered, and as a result, the distance to the measurement object cannot be measured accurately.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a distance measuring device that measures a distance based on a flight time of light that can accurately detect an electric pulse signal corresponding to reflected light or reference light. Is to provide.

  In order to solve the above problems, the distance measuring device according to the present invention has a minimum amplitude level necessary for detecting the amplitude level of the electric pulse signal corresponding to the reflected light and the reference light, and the waveform is substantially the same shape. At least one of the applied voltage of the driving unit, the applied voltage of the voltage applying unit, and the amplification factor of the amplifying unit is adjusted.

  According to the distance measuring device of the present invention, the amplitude level and waveform of the electric pulse signal corresponding to each of the reflected light and the reference light are optimized and have substantially the same shape, so that the electric pulse corresponding to the reflected light and the reference light. It is possible to accurately detect the signal and accurately measure the distance to the measurement object.

  Hereinafter, the configuration and operation of a distance measuring apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings.

[Configuration of distance measuring device]
As shown in FIG. 1, a distance measuring apparatus 1 according to an embodiment of the present invention emits light toward a measurement target, a reflected light from the measurement target, and the light source 2. The light receiving unit 3 that detects the reference light and the calculation unit 4 that calculates and displays the distance to the measurement object based on the detection timing difference between the reflected light and the reference light in the light receiving unit 3 are provided as main components.

  The light source unit 2 is output from a laser diode (LD) 6 that projects pulsed light having a pulse width of about 10 [ns] toward a measurement object via a light projecting lens 5 and a calculation unit 4. An LD driving circuit 7 that drives the LD 6 by applying a voltage to the LD 6 according to the LD driving signal, an optical fiber 8 that branches to the light receiving unit 3 side using the light transmitted by the LD 6 as reference light, and the light that has reached from the outside of the apparatus And a light receiving lens 9 for condensing light.

  The light receiving unit 3 applies a voltage to the APD 10 in accordance with an avalanche photodiode (APD) 10 that receives the light collected by the light receiving lens 9 and the reference light output from the optical fiber 8 and a high-voltage control signal output from the DAC 20. The high voltage power supply 11 that drives the APD 10 when applied, the transimpedance amplifier 12 that photoelectrically converts the light pulse signal (light reception signal) received by the APD 10 into an electrical pulse signal (hereinafter referred to as reception pulse), and the CPU 19 output A variable gain amplifier 13 for adjusting the amplitude level of the received pulse output from the trans-pin impedance amplifier 12 according to the gain control signal, and the amplitude of the received pulse output from the variable gain amplifier 13 according to the threshold level control signal output from the DAC 20. Level and threshold level Comparator 14 for detecting a received pulse corresponding to the reflected light and reference light by comparing, and a level converter 15 and a flip-flop 16,.

  The arithmetic unit 4 calculates a detection timing difference between reception pulses corresponding to the reflected light and the reference light output from the flip-flop 16 and outputs the difference to the CPU 19, and at the same time, the LD drive circuit 7 according to the LD drive signal generated by the CPU 19. And a light receiving signal level adjusting unit 18 for controlling the applied voltage of the LD driving circuit 7, the applied voltage of the high voltage power supply 11, the amplification factor of the variable gain amplifier 13, and the threshold level of the flip-flop 16. The signal level adjusting unit 18 calculates and displays the distance to the measurement object based on the detection timing difference between the received light corresponding to the reflected light and the reference light output from the CPLD 17 and displays the applied voltage of the LD driving circuit 7. LD drive signal to control, high voltage control signal to control applied voltage of high voltage power supply 11, variable gain amplifier The CPU 19 generates a gain control signal for controlling the amplification factor 3 and a threshold level control signal for controlling the threshold level of the flip-flop 16, and the high-voltage power supply 11 and the flip-flop according to the high-voltage control signal and the threshold level control signal generated by the CPU 19. And a DAC 20 for controlling the controller 16.

  In the present embodiment, the high voltage control signal has a set value of 0 to 255. When the set value is 0, the applied voltage of the high voltage power supply 11 is the maximum value within the adjustment range, and the set value is 255. In other words, the applied voltage of the high-voltage power supply 11 becomes the minimum value within the adjustment range. The threshold level setting value has a range of 0 to 3.3 [V] and is divided into 256 from 0 to 255. The smaller the setting value, the higher the threshold level. The gain of the variable gain amplifier 13 has set values of 4, 8, and 50 times, and the initial value is set to 8 times.

[Flow of distance measurement processing]
The distance measuring device 1 having the above configuration detects the received pulse corresponding to the reflected light and the reference light, and measures the distance to the measurement object by executing the distance measuring process described below. Hereinafter, with reference to the flowchart shown in FIG. 2, the operation of the distance measuring apparatus 1 when executing this distance measuring process will be described.

  The flowchart shown in FIG. 2 starts in response to a trigger signal for starting the distance measurement of the distance measuring device 1, and the distance measurement process proceeds to the process of step S1.

  In the process of step S1, the CPU 19 performs the initial setting process of the control signal, the high voltage control signal (setting value 255 (0xFF)) that minimizes the applied voltage of the high voltage power supply 11 within the adjustment range, and the gain of the variable gain amplifier 13 Generates and outputs a gain control signal for multiplying. In addition, by minimizing the applied voltage of the high voltage power supply 11 within the adjustment range, a voltage exceeding the allowable range of the APD 10 is applied, or the APD 10 is destroyed by setting the maximum voltage before adjustment. Can be prevented. Thereby, the process of step S1 is completed and a distance measurement process progresses to the process of step S2.

  In the process of step S2, the CPU 19 controls the voltage applied to the APD 10 so that the received pulse can be detected even when the received pulse corresponding to the reflected light and the reference light is not detected (the LD 6 is turned off). A high voltage control signal is output to the high voltage power supply 11 via the DAC 20. The details of the high voltage adjustment processing will be described later with reference to the flowchart shown in FIG. Thereby, the process of step S2 is completed, and the distance measurement process proceeds to the process of step S3.

  In the process of step S3, the CPU 19 adjusts the voltage applied to the APD 10 to a voltage at which the received pulse corresponding to the reflected light or the reference light cannot be detected with the voltage applied to the APD 10 set in the high voltage adjustment process as a reference ( Light intensity adjustment process). Details of this light amount adjustment processing will be described later with reference to a flowchart shown in FIG. Thereby, the process of step S3 is completed and the distance measurement process proceeds to the process of step S4.

  In the process of step S4, the CPLD 19 determines whether or not a reception pulse corresponding to the reflected light or the reference light has been detected. If the received pulse is not detected as a result of the determination, the CPU 19 executes a gain adjustment process for adjusting the gain of the variable gain amplifier 13 as the process of step S5, and then changes the distance measurement process to the process of step S6. Proceed. Details of this gain adjustment processing will be described later with reference to a flowchart shown in FIG. On the other hand, when the reception pulse is detected, the CPU 19 advances the distance measurement process from the process of step S4 to the process of step S6.

  In the process of step S6, the CPU 19 determines whether or not the minimum amplitude level necessary for detecting the amplitude level of the reception pulse corresponding to the reflected light and the reference light and the waveforms have substantially the same shape. . As a result of the determination, if the amplitude level of the received pulse corresponding to the reflected light and the reference light is detected and the waveform is not substantially the same shape, the CPU 19 performs a distance measurement process. The process returns to step S2. On the other hand, when the amplitude level of the received pulse corresponding to the reflected light and the reference light is detected and the waveform has substantially the same shape, the CPU 19 performs a distance measurement process in step S7. Proceed to the process.

  In the process of step S7, the CPU 19 detects the received pulse by setting the threshold level to a value lower than the previous threshold level, and reaches the measurement object according to the detection timing difference of the received pulse corresponding to the reflected light and the reference light. Measure and display the distance. Thereby, the process of step S7 is completed and a series of distance measurement processes are complete | finished.

[High voltage adjustment processing]
Next, with reference to the flowchart shown in FIG. 3, the operation of the distance measuring apparatus 1 when executing the high voltage adjustment process in step S2 will be described.

  In the flowchart shown in FIG. 3, the minimum amplitude level necessary for detecting the amplitude level of the received pulse corresponding to the reflected light and the reference light in the processing of step S1 is completed. In addition, the process starts when it is determined that the waveforms are not substantially the same shape, and the high voltage adjustment process proceeds to the process of step S11. This high voltage adjustment process is performed for each of the received pulses corresponding to the reflected light and the reference light.

  In the process of step S11, the CPU 19 generates a threshold level control signal for setting the threshold level of the flip-flop 16 to the maximum value (0.0 [V]) so that the received pulse cannot be detected, and the generated threshold level control. The signal is output to the flip-flop 16 through the DAC 20. Thereby, the process of step S11 is completed, and the high voltage adjustment process proceeds to the process of step S12.

  In the process of step S <b> 12, the CPU 19 increases the applied voltage of the high voltage power supply 11 by reducing the set value of the high voltage control signal output to the high voltage power supply 11 by one. Note that the CPU 19 performs the first high voltage adjustment process such as reducing the set value of the high voltage control signal by 3 if the high voltage adjustment process is the first time, and reducing the set value of the high voltage control signal by 1 if the second time. Depending on whether or not, the adjustment amount of the set value of the high voltage control signal may be changed. According to such processing, the adjustment time can be shortened, and the adjustment accuracy can be improved by performing fine adjustment. Thereby, the process of step S12 is completed, and the high voltage adjustment process proceeds to the process of step S13.

  In the process of step S13, the CPU 19 determines whether the set value of the high voltage control signal is 0, in other words, whether the applied voltage of the high voltage power supply 11 is the maximum value within the adjustment range. If the set value of the high-voltage control signal is 0 as a result of determination, the CPU 19 determines that the applied voltage of the high-voltage power supply 11 cannot be adjusted within the adjustment range, and the set value of the high-voltage control signal is processed as step S14. Is fixed to an arbitrary value (for example, 255), and then a series of high voltage adjustment processing is terminated. According to such processing, even when the applied voltage of the high-voltage power supply 11 cannot be adjusted, the amplitude level of the reception pulse corresponding to the reflected light and the reference light is set to an amplitude level that is highly likely to be measured. It is possible to optimize the initial voltage when adjusting the applied voltage of the high-voltage power supply 11 to a voltage at which the received pulse cannot be detected. On the other hand, when the set value of the high voltage control signal is not 0, the CPU 19 advances the high voltage adjustment process to the process of step S15.

  In the process of step S15, the CPU 19 lowers the threshold level of the flip-flop 16 so that the threshold level of the flip-flop 16 becomes 1.5 [V], in other words, the threshold level control capable of detecting the received pulse. A signal is generated, and the generated threshold level control signal is output to the flip-flop 16 via the DAC 20. Thereby, the process of step S15 is completed, and the high voltage adjustment process proceeds to the process of step S16.

  In the process of step S16, the CPLD 17 determines whether or not a reception pulse has been detected. If the received pulse is not detected as a result of the determination, the CPLD 17 returns the high voltage adjustment process to the process of step 11. On the other hand, when the reception pulse is detected, the CPLD 17 advances the high voltage adjustment process to the process of step S17.

  In the process of step S17, the CPU 19 determines whether or not the detection of the received pulse has been confirmed once. If the result of determination is that it has been confirmed once, the CPU 19 ends the series of high voltage adjustment processing. On the other hand, if it has not been confirmed once, the CPU 19 advances the high voltage adjustment process to the process of step S18.

  In the process of step S18, the CPU 19 sets that the detection of the received pulse has been confirmed once, for example, by incrementing the value of the program counter by one. By executing the confirmation process a plurality of times in this way, it is possible to prevent erroneous detection of a received pulse due to noise light and perform accurate voltage adjustment. Thereby, the process of step S18 is completed and the high voltage adjustment process proceeds to the process of step S19.

  In the process of step S19, the CPU 19 determines whether or not the amount of change in the set value of the high voltage control signal is 3 or more. If the amount of change in the set value of the high voltage control signal is 3 or more as a result of the determination, the CPU 19 advances the high voltage adjustment process to the process of step S21. On the other hand, when the variation amount of the set value of the high voltage control signal is not 3 or more, the CPU 19 advances the high voltage adjustment process to the process of step S20.

  In the process of step S <b> 20, the CPU 19 generates a high voltage control signal obtained by incrementing the set value by 1 from the current set value, and outputs the generated high voltage control signal to the high voltage power supply 11 via the DAC 20. Thereby, the process of step S20 is completed and the high voltage adjustment process returns to the process of step S11.

  In the process of step S <b> 21, the CPU 19 generates a high voltage control signal obtained by multiplying the current set value by three, and outputs the generated high voltage control signal to the high voltage power supply 11 via the DAC 20. Thereby, the process of step S21 is completed and the high voltage adjustment process returns to the process of step S11.

[Light intensity adjustment processing]
Next, with reference to the flowchart shown in FIG. 4, the operation of the distance measuring apparatus 1 when executing the light amount adjustment processing in step S3 will be described.

  The flowchart shown in FIG. 4 starts when the process of step S2 is completed, and the light amount adjustment process proceeds to the process of step S31. This high voltage adjustment process is performed for each of the received pulses corresponding to the reflected light and the reference light.

  In the process of step S31, the CPU 19 sets which of the reflected light and the reference light the light intensity adjustment is for. Thereby, the process of step S31 is completed, and the light amount adjustment process proceeds to the process of step S32.

  In the process of step S32, the CPU 19 sets the threshold level of the flip-flop 16 to 1.2 [V], generates a threshold level control signal capable of detecting the received pulse, and flips the generated threshold level control signal via the DAC 20 Output to the group 16. Note that the CPU 19 sets the variable gain such that the threshold level is 1.0 [V] when the gain of the variable gain amplifier 13 is 50 times, and the threshold level is 1.2 [V] when the gain is not 50 times. The threshold level value may be adjusted according to the amplification factor of the amplifier 13. According to such processing, the influence of the noise signal can be reduced and the SN ratio can be improved. Thereby, the process of step S32 is completed, and the light amount adjustment process proceeds to the process of step S33.

  In the process of step S33, the CPU 19 controls the LD 6 so as to project light toward the measurement object by outputting an LD drive signal to the LD drive circuit 7 via the CPLD 17. Thereby, the process of step S33 is completed, and the light amount adjustment process proceeds to the process of step S34.

  In the process of step S34, the CPU 19 determines whether or not a reception pulse is detected. If the received pulse is not detected as a result of the determination, the CPU 19 advances the light amount adjustment process to the process of step 38. On the other hand, when the reception pulse is detected, the CPU 19 advances the light amount adjustment process to the process of step S35.

  In the process of step S35, the CPU 19 determines whether or not the set value of the high voltage control signal is 255 or less, in other words, whether or not the applied voltage of the high voltage power supply 11 is the minimum value within the adjustment range. If it is determined that the set value of the high voltage control signal is 255 or less, the CPU 19 decreases the applied voltage to the APD 10 by incrementing the set value of the high voltage control signal by 1 as a process of step S36. Then, the light amount adjustment process is returned to the process of step S33. On the other hand, when the set value of the high voltage control signal is 255, the CPU 19 determines that the light quantity is excessive, and after performing error setting (error setting 2) as the process in step S37, the light quantity adjustment process is performed in step S50. Proceed to In the process of step S36, the CPU 19 reduces the set value of the high voltage control signal by 3 if the light intensity adjustment process is the first time, and decreases the set value of the high voltage control signal by 1 if the light intensity adjustment process is the second time. You may make it change the adjustment amount of the setting value of a high voltage | pressure control signal according to whether the adjustment process is the 1st time. According to such processing, the adjustment time can be shortened, and the adjustment accuracy can be improved by performing fine adjustment.

  In the process of step S38, the CPU 19 determines whether or not the set value of the high voltage control signal is the same as the set value after completion of the high voltage adjustment process. If the set values are the same as a result of the determination, the CPU 19 advances the light amount adjustment process to the process of step S44. On the other hand, if the set values are not the same, the CPU 19 advances the light amount adjustment process to the process of step S39. If the set values are the same and the adjustment is performed for the first time, it is considered that the amount of light is too small. Therefore, the CPU 19 advances the light amount adjustment process to the process of step S45, and in steps S44 and S46 to 48 described later. Processing may be omitted.

  In the process of step S39, the CPU 19 determines whether or not the detection of the received pulse has been confirmed once. And as a result of discrimination | determination, when confirmed once, CPU19 advances a light quantity adjustment process to the process of step S49. On the other hand, if it has not been confirmed once, the CPU 19 advances the light amount adjustment process to the process of step S40.

  In the processing of step S40, the CPU 19 sets that the first confirmation has been made by incrementing the value of the program counter by one. By executing the confirmation process a plurality of times as described above, it is possible to prevent erroneous detection of the received pulse corresponding to the reflected light and the reference light due to the noise light, and to perform accurate voltage adjustment. Thereby, the process of step S40 is completed, and the light amount adjustment process proceeds to the process of step S41.

  In the process of step S41, the CPU 19 determines whether or not the amount of change in the set value of the high voltage control signal is 3 or more. If the amount of change in the set value of the high voltage control signal is 3 or more as a result of the determination, the CPU 19 advances the light amount adjustment process to the process of step S43. On the other hand, when the amount of change in the set value of the high voltage control signal is not 3 or more, the CPU 19 advances the light amount adjustment process to the process of step S42.

  In the process of step S <b> 42, the CPU 19 generates a high voltage control signal in which the setting value is reduced by 1 from the current setting value, and outputs the generated high voltage control signal to the high voltage power supply 11 via the DAC 20. Thereby, the process of step S42 is completed, and the light amount adjustment process returns to the process of step S33.

  In the process of step S43, the CPU 19 generates a high voltage control signal in which the setting value is reduced by 3 from the current setting value, and outputs the generated high voltage control signal to the high voltage power source 11 via the DAC 20. Thereby, the process of step S43 is completed, and the light amount adjustment process returns to the process of step S33.

  In the process of step S44, the CPU 19 determines whether or not it is the first light amount adjustment process. If it is the first light amount adjustment process as a result of the determination, the CPU 19 determines that the light amount is in an excessively small state, sets the error (error setting 1) as the process in step S45, and then performs the light amount adjustment process in step S50. Proceed to processing. On the other hand, if it is not the first light amount adjustment process, the CPU 19 advances the light amount adjustment process to step S46.

  In the process of step S46, the CPU 19 generates and generates a threshold level control signal that lowers the threshold level of the flip-flop 16 to 1.3 [V], in other words, the threshold level is lowered by the process of step S32. The threshold level control signal is output to the flip-flop 16 via the DAC 20. According to such processing, it is possible to prevent the reception pulse corresponding to the reflected light and the reference light from being originally detected due to the influence of noise and disturbance light, but not to be detected. The applied voltage can be adjusted accurately. Thereby, the process of step S46 is completed, and the light amount adjustment process proceeds to the process of step S47.

  In the process of step S47, the CPU 19 controls the LD 6 to project light toward the measurement object by outputting an LD drive signal to the LD drive circuit 7 via the CPLD 17. Thereby, the process of step S47 is completed, and the light amount adjustment process proceeds to the process of step S48.

  In the process of step S48, the CPU 19 determines whether or not a reception pulse is detected. If the received pulse is not detected as a result of the determination, the CPU 19 advances the light amount adjustment process to the process of step 45. On the other hand, when the reception pulse is detected, the CPU 19 advances the light amount adjustment process to the process of step S49.

  In the process of step S49, the CPU 19 determines the applied voltage of the high-voltage power supply 11 when measuring the distance to the measurement object as the current set value. Thereby, the process of step S49 is completed, and the light amount adjustment process proceeds to the process of step S50.

  In the process of step S50, the CPU 19 determines whether or not the setting of the applied voltage of the high-voltage power supply 11 when measuring the distance to the measurement object is completed. If the setting is not completed as a result of the determination, the CPU 19 returns the light amount adjustment process to the process of step S31. On the other hand, when the setting is completed, the CPU 19 ends the series of light amount adjustment processing.

[Gain adjustment processing]
Next, with reference to the flowchart shown in FIG. 5, the operation of the distance measuring apparatus 1 when executing the gain adjustment process in step S5 will be described.

  The flowchart shown in FIG. 5 starts when it is determined that the reception pulse corresponding to the reflected light or the reference light is not detected in the process of step S4, and the gain adjustment process proceeds to the process of step S61. Note that this gain adjustment processing is performed for each of the received pulses corresponding to the reflected light and the reference light.

  In the process of step S61, the CPU 19 determines whether or not the set value of the gain of the variable gain amplifier 13 is 50 times or 4 times. If the result of determination is 50 times or 4 times, the CPU 19 ends the gain adjustment processing. On the other hand, if it is not 50 times or 4 times, the CPU 19 advances the gain adjustment process to the process of step S62.

  In step S62, the CPU 19 determines whether or not error setting 1) has been made in the light amount adjustment processing. If the error setting 1 is determined as a result of the determination, the CPU 19 determines that the received light pulse is not always detected by the high voltage control signal set in the high voltage adjustment process, and the gain adjustment process is performed in step S64. Proceed to the process. On the other hand, when the error setting 1 is not made, the CPU 19 determines that there is an excessive light amount state in which there is no voltage at which the received pulse cannot be detected even if the set value of the high voltage control signal set in the high voltage adjustment process is adjusted. Then, the gain adjustment process proceeds to the process of step S63.

  In the process of step S63, the CPU 19 controls the set value of the gain of the variable gain amplifier 13 to 4 times. Thereby, the process of step S63 is completed and a series of gain adjustment processes are completed.

  In the process of step S64, the CPU 19 determines whether or not the applied voltage of the LD drive circuit 7 has been increased. If the applied voltage of the LD drive circuit 7 has already been increased as a result of the determination, the CPU 19 ends the series of gain adjustment processes after setting the amplification factor of the variable gain amplifier 13 to 50 as the process of step S65. To do. On the other hand, if the applied voltage of the LD drive circuit 7 has not been increased, the CPU 19 performs the processing of step S66 by using the boost power source 21 to increase the LD6 without increasing the amplification factor of the variable gain amplifier 13 as shown in FIG. After the drive voltage is increased, a series of gain adjustment processing is terminated.

  As is clear from the above description, according to the distance measuring apparatus 1 according to the embodiment of the present invention, the received light signal level adjusting unit 18 has the amplitude level of the received pulse corresponding to the reflected light and the reference light at the light receiving unit 3. At least of the applied voltage of the LD drive circuit 7, the applied voltage of the high voltage power supply 11, and the amplification factor of the variable gain amplifier 13 so that the minimum amplitude level necessary for detection and the waveform are substantially the same shape. Adjust one or more. According to such a configuration, the amplitude level and waveform of the electric pulse signal corresponding to each of the reflected light and the reference light are optimized and have substantially the same shape. Therefore, the electric pulse signal corresponding to the reflected light and the reference light. Can be accurately detected, and the distance to the measurement object can be accurately measured.

  Further, according to the distance measuring apparatus 1 according to the embodiment of the present invention, the received light signal level adjusting unit 18 can detect the received pulse even when the received pulse corresponding to the reflected light and the reference light is not detected. Since the applied voltage of the high-voltage power supply 11 is adjusted to a voltage level at which the received pulse corresponding to the reflected light or the reference light cannot be detected after adjusting the applied voltage of the high-voltage power supply 11 to a correct voltage level, the minimum The amplitude level of the received pulse can be set to an optimum value corresponding to the element characteristics of the APD 10 and the ambient state during measurement by the number of parts.

  Further, according to the distance measuring apparatus 1 according to the embodiment of the present invention, the received light signal level adjusting unit 18 sets the amplification factor of the variable gain amplifier 13 to a value different from the initial value, thereby applying the high voltage power supply 11. Since the amplitude level of the received pulse corresponding to the reflected light and the reference light is adjusted within the voltage adjustment range so that the light receiving unit 3 can detect the amplitude level of the received pulse and the waveform has substantially the same shape. Therefore, it is possible to improve the measurement accuracy failure due to the improper adjustment of the applied voltage.

  Further, according to the distance measuring apparatus 1 according to the embodiment of the present invention, the received light signal level adjusting unit 18 changes the applied voltage of the LD drive circuit 7 from the initial value, thereby adjusting the applied voltage of the high-voltage power supply 11. The amplitude level of the received pulse corresponding to the reflected light and the reference light is adjusted so that the minimum amplitude level necessary for the light receiving unit 3 to detect the waveform and the waveform are substantially the same. The waveform of the received pulse can be optimized without being strongly influenced by the gain amplifier 13.

  Further, according to the distance measuring device 1 according to the embodiment of the present invention, the received light signal level adjustment unit 18 adjusts the threshold level used for detection of the received pulse corresponding to the reflected light and the reference light, thereby reflecting the reflected light. Alternatively, the voltage applied to the high-voltage power supply 11 is adjusted to a voltage level at which the received pulse corresponding to the reference light cannot be detected. Therefore, the amplitude level of the electric pulse signal corresponding to each of the reflected light and the reference light is further optimized, Distance can be measured more accurately.

In general, since the response speed tr of the light receiving element (see Equation 1 below) changes according to the applied voltage, a shift (phase shift) occurs in the light reception timing of the reflected light and the reference light according to the applied voltage. Further, when the applied voltage to the light receiving element is 110 [V] or more, this inter-terminal capacitance is generally stabilized, so this phase shift does not occur. Therefore, when the voltage applied to the APD 10 is changed in the high voltage adjustment process described above, a difference occurs in the detection timing of the received pulse corresponding to the reflected light and the reference light as shown in FIG. On the other hand, when the gain of the variable gain amplifier 13 is adjusted as shown in FIG. 8, for example, in the gain adjustment process described above, a difference occurs in the delay time according to the gain, and light projection is performed as shown in FIG. There will be a time difference in the time from light to detection of the received pulse. Therefore, it is desirable to correct the detection timing of the received pulse corresponding to the reflected light and the reference light by executing a correction process described later in the distance measurement process.

  Hereinafter, the operation of the distance measuring apparatus 1 when executing this correction processing will be described with reference to the flowchart shown in FIG.

  The flowchart shown in FIG. 10 is started when the process of step S7 is completed, and the correction process proceeds to the process of step S71.

  In the process of step S71, the CPU 19 reads the voltage applied to the APD 10 when the reception pulse corresponding to the reflected light and the reference light is detected. Thereby, the process of step S71 is completed, and the correction process proceeds to the process of step S72.

  In the process of step S72, the CPU 19 obtains the relationship between the applied voltage to the APD 10 and the correction value of the measurement distance when receiving the reception pulse corresponding to the reflected light and the reference light as shown in FIG. The correction value of the measurement distance corresponding to the applied voltage value read in the process is read. Note that the table shown in FIG. 11 shows that the amount of phase shift is 3.4 degrees when the applied voltage difference to the APD 10 when detecting the received pulse corresponding to the reflected wave and the reference wave is 30 [V] at the maximum. It is created based on the fact that a fluctuation time of 0.031 [nS] corresponding to is generated and a measurement distance error corresponding to a maximum of 4.7 [mm] is generated. Thereby, the process of step S72 is completed, and the correction process proceeds to the process of step S73.

  In the process of step S73, the CPU 19 reads the amplification factor of the variable gain amplifier 13 when the reception pulse corresponding to the reflected light and the reference light is detected. Thereby, the process of step S73 is completed, and the correction process proceeds to the process of step S74.

  In the process of step S74, the amplification factor (A, B, C, D of the variable gain amplifier 13 when the CPU 19 detects the reception pulse corresponding to the reflected light and the reference light as shown in FIG. 12 is shown in FIG. The correction value of the measurement distance corresponding to the amplification factor read in the process of step S74 is read out from the table showing the relationship between the correction values of the measurement distance and the corresponding values A, B, C, and D in the table. Note that the table shown in FIG. 12 shows a delay time time difference corresponding to a measurement distance error of about 2 [mm] when the gain of the variable gain amplifier 13 is 8 times and when the gain is 50 times. It is created based on the possibility that 13 [pS] is generated. Thereby, the process of step S74 is completed, and the correction process proceeds to the process of step S75.

  In the process of step S75, the CPU 19 corrects the distance to the measurement object calculated by the process of step S7 using the correction value read by the processes of steps S72 and S74. Thereby, the process of step S75 is completed and a series of correction processes are completed.

  As mentioned above, although embodiment which applied the invention made by the present inventors was described, this invention is not limited by the description and drawing which make a part of indication of this invention by this embodiment. That is, it should be added that other embodiments, examples, operation techniques, and the like made by those skilled in the art based on the above-described embodiments are all included in the scope of the present invention.

It is a block diagram which shows the structure of the distance measuring device used as embodiment of this invention. It is a flowchart figure which shows the flow of the distance measurement process used as embodiment of this invention. It is a flowchart figure which shows the flow of the high voltage adjustment process shown in FIG. It is a flowchart figure which shows the flow of the light quantity adjustment process shown in FIG. FIG. 3 is a flowchart showing a flow of gain adjustment processing shown in FIG. 2. It is a figure which shows the internal structure of the LD drive circuit shown in FIG. It is a figure for demonstrating the change of the detection timing of the received pulse of reflected light and reference light accompanying the change of the applied voltage to a light receiving element. It is a figure which shows the example of a setting of the gain of a variable gain amplifier. It is a figure for demonstrating the change of the time from the light projection accompanying the change of the gain of a variable gain amplifier to the detection of a received pulse. It is a flowchart figure which shows the flow of the correction process used as embodiment of this invention. The relationship between the applied voltage to APD at the time of detecting the received pulse corresponding to reflected light and reference light, and the correction value of measurement distance is shown. The relationship between the gain of the variable gain amplifier and the correction value of the measurement distance when detecting the reception pulse corresponding to the reflected light and the reference light is shown.

Explanation of symbols

1: Distance measuring device 2: Light source unit 3: Light receiving unit 4: Calculation unit 5: Projection lens 6: Laser diode (LD)
7: LD drive circuit 8: Optical fiber 9: Light receiving lens 10: Avalanche photodiode (APD)
11: high-voltage power supply 12: transimpedance amplifier 13: variable gain amplifier 14: comparator 15: level converter 16: flip-flop 17: CPLD 17
18: Light reception signal level adjustment unit 19: CPU
20: DAC

Claims (6)

A light emitting element that emits pulsed light toward the measurement object;
A driving unit that drives the light emitting element by applying a voltage to the light emitting element; a branching unit that branches light emitted from the light source unit as reference light;
A light receiving element that receives reflected light from the measurement object and reference light branched by the branching unit;
A voltage application unit that drives the light receiving element by applying a voltage to the light receiving element;
A light receiving unit that converts light received by the light receiving element into an electrical pulse signal;
An amplifying unit for amplifying the electric pulse signal generated by the light receiving unit;
A detection unit for detecting an electric pulse signal corresponding to the reflected light and the reference light from the electric pulse signal amplified by the amplification unit;
A calculation unit that calculates a distance from the detection timing difference of the electric pulse signal corresponding to the reflected light and the reference light in the detection unit to the measurement object;
The applied voltage of the drive unit so that the amplitude level of the electrical pulse signal corresponding to the reflected light and the reference light is detected by the detection unit and the waveform has substantially the same shape. And a level adjusting unit that adjusts at least one of an applied voltage of the voltage applying unit and an amplification factor of the amplifying unit. The distance measuring device according to claim 1,
The level adjusting unit adjusts the applied voltage of the voltage applying unit to a voltage level at which the electric pulse signal can be detected even when the electric pulse signal corresponding to the reflected light and the reference light is not detected. A distance measuring device that adjusts the applied voltage of the voltage applying unit to a voltage level at which an electric pulse signal corresponding to reflected light or reference light cannot be detected based on the voltage level. The distance measuring device according to claim 1 or 2,
The level adjusting unit sets an amplification factor of the amplifying unit to a value different from an initial value, so that an electric pulse corresponding to the reflected light and the reference light is within an adjustment range of an applied voltage of the voltage applying unit. A distance measuring device, wherein the amplitude level of the signal is adjusted so that the minimum amplitude level necessary for the detection unit to detect the waveform and the waveforms have substantially the same shape. It is a distance measuring device given in any 1 paragraph among Claims 1 thru / or 3, Comprising:
The level adjustment unit changes an applied voltage of the driving unit from an initial value, thereby adjusting an amplitude level of an electric pulse signal corresponding to the reflected light and the reference light within an adjustment range of an applied voltage of the voltage application unit. Is adjusted so that the waveform has substantially the same shape and the minimum amplitude level necessary for the detection to be detected by the detection unit. It is a distance measuring device given in any 1 paragraph among Claims 1 thru / or 4, Comprising:
The calculation unit takes into account the phase shift caused by changing the applied voltage of the voltage application unit and / or the detection delay time of the electrical signal caused by changing the amplification factor of the amplification unit. A distance measuring device that corrects a distance to an object. It is a distance measuring device given in any 1 paragraph among Claims 1 thru / or 4, Comprising:
The level adjustment unit adjusts a threshold level used for detecting an electric pulse signal corresponding to the reflected light and the reference light, so that the electric pulse signal corresponding to the reflected light or the reference light cannot be detected. A distance measuring device that adjusts an applied voltage of a voltage applying unit.

Images