JP4887803B2 - Distance measuring device - Google Patents

Description

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

Conventionally, in order to prevent the distance to the measurement object from being accurately measured due to the influence of noise light, light reception that receives an optical signal after a certain time has elapsed after projecting light toward the measurement object A distance measuring device that sets time and sets a gate section so that only reflected light can be received is known (see Patent Documents 1 and 2).
Japanese Patent Laid-Open No. 11-325823 JP 2003-75534 A

  However, since the conventional distance measuring device is configured to generate a gate signal for setting a gate interval based on the output signal from the amplifier at the final stage and the output signal from the amplifier immediately before, the light receiving signal The reflected light cannot be detected depending on the output signal level of the amplifier, such as when the received light signal cannot be detected unless the received light signal is amplified by a plurality of stages of amplifiers.

  Further, according to the conventional distance measuring device, since the gate signal is generated at a preset time, the gate signal may not be able to respond when the distance to the measurement object changes. In order to solve such a problem, it is conceivable to set the width of the gate section wide, but when the gate section is set wide, noise light is easily detected. The distance may be measured incorrectly.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a distance measuring device capable of accurately separating an electric pulse signal corresponding to reflected light and reference light and noise light. There is to do.

  In order to solve the above problem, the distance measuring device according to the present invention assumes a detection time at which an electric pulse signal corresponding to reflected light and reference light is detected before starting measurement of the distance to the measurement object. When measuring the distance to the object to be measured, set a gate section that can detect the electric pulse signal only at the time near the assumed detection time, and set the electric pulse signal that can be detected by the set gate section. Limit and measure the distance to the measurement object.

  According to the distance measuring device of the present invention, the electric pulse signal can be detected only in the section including the time when the electric pulse signal corresponding to the reflected light and the reference light is detected, so that the electric pulse corresponding to the reflected light and the reference light is detected. The signal and noise light can be accurately separated.

  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 collecting 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. A high-voltage power supply 11 that drives the APD 10 by applying, a transimpedance amplifier 12 that photoelectrically converts an optical signal (light reception signal) received by the APD 10 into an electric pulse signal (hereinafter referred to as a reception pulse), and output from the CPU 19 A variable gain amplifier 13 that adjusts the amplitude level of the reception pulse output from the trans-pin impedance amplifier 12 according to the gain control signal, and an amplitude level of the reception pulse that is output from the variable gain amplifier 13 according to the threshold level control signal output from the DAC 20 And the threshold level And a comparator 14, the level converter 15 and a flip-flop 16, which detects the received pulse corresponding to the reflected light and reference light by.

  The arithmetic unit 4 includes a CPLD 17, a CPU 18, and a DAC 19. The CPLD 17 outputs a detection timing difference between reception pulses corresponding to the reflected light and the reference light output from the flip-flop 16 and controls the applied voltage of the LD drive circuit 7 according to the LD drive signal generated by the CPU 18. Further, the CPLD 17 has a configuration as shown in FIG. 2, sets a gate section that can receive a received pulse in accordance with a gate control signal output from the CPU 18, and reflects reflected light detected in the set gate section. A timing difference between reception pulses corresponding to the reference light is output. The detailed operation of the CPLD 17 will be described later.

  The CPU 18 calculates the distance to the measurement object according to the detection timing of the received pulse corresponding to the reflected light and the reference light output from the CPLD 17. Further, the CPU 18 controls an LD drive signal for controlling the applied voltage of the LD drive circuit 7, a high voltage control signal for controlling the applied voltage of the high voltage power supply 11, a gain control signal for controlling the gain of the variable gain amplifier 13, and the flip-flop 16. A threshold level control signal for controlling the threshold level of the signal is generated. The DAC 19 controls the high voltage power supply 11 and the flip-flop 16 in accordance with the high voltage control signal and the threshold level control signal generated by the CPU 18.

[Flow of distance measurement processing]
As described in the prior art, various noise signals are detected from when light is projected toward the measurement object until reception pulses corresponding to the reflected light and the reference light are detected (FIG. 3). reference). If the noise signal is erroneously recognized as a reception pulse corresponding to the reflected light and the reference light before detecting the reception pulse corresponding to the reflected light and the reference light, the distance to the measurement object is erroneously measured. End up. Therefore, the distance measuring apparatus 1 performs the distance measuring process shown below to accurately separate the received pulse and the noise signal corresponding to the reflected light and the reference light regardless of the level of the received pulse, and to measure Measure the distance to the object. Hereinafter, with reference to the flowchart shown in FIG. 4, the operation of the distance measuring device 1 when executing this distance measuring process will be described.

  The flowchart shown in FIG. 4 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 18 sets the set values of the respective units in the distance measuring device 1 to initial values. 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 DAC 18 controls the voltage applied to the APD 10 to a voltage at which the light can be detected even when the CPU 18 does not detect the received pulse corresponding to the reflected light and the reference light (the LD 6 is turned off). A high-voltage control signal is output to the high-voltage power supply 11 via 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 18 adjusts the applied voltage to the APD 10 up to a voltage at which the APD 10 cannot detect light with reference to the applied voltage to the APD 10 set in the process of step S2. 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 17 sets a gate interval for enabling detection of the received pulse according to the gate control signal output from the CPU 18 for each of the reflected light and the reference light (gate setting process). Details of the gate setting process will be described later. Thereby, the process of step S4 is completed and the distance measurement process proceeds to the process of step S5.

  In the process of step S5, the CPLD 17 outputs the detection timing difference of the received pulse corresponding to the reflected light and the reference light detected in the gate interval set by the process of step S4, and the CPU 18 is output from the CPLD 17. The distance to the measurement object is calculated based on the detection timing difference. Thereby, the process of step S5 is completed and a series of distance measurement processes are complete | finished.

[Gate setting process]
Next, the operation of the distance measuring device 1 when executing the gate setting process in step S4 will be described with reference to the flowchart shown in FIG.

  The flowchart shown in FIG. 5 starts when the process of step S3 is completed, and the gate setting process proceeds to the process of step S11.

  In the process of step S11, the CPLD 17 sets the set values of the gate control signal and the gate 1 control signal (described later in detail) to initial values. Thereby, the process of step S11 is completed and the gate setting process proceeds to the process of step S12.

  In the process of step S12, the CPLD 17 sets the start timing of the gate signal that defines the gate section according to the gate control signal output from the CPU 18. In this embodiment, the gate control signal has a value of 1 to 15, and when the set value is 0, the gate signal is activated in synchronization with the timing when the LD 6 projects light, and the set value is In the case of 15, the gate signal is activated 180 (= 15 × 20) [nS] after the LD 6 projects light. Thereby, the process of step S12 is completed, and the gate setting process proceeds to the process of step S13.

  In the process of step S <b> 13, the CPU 18 emits light from the LD 6 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 S13 is completed, and the gate setting process proceeds to the process of step S14.

In the process of step S14, the CPLD 17 determines whether or not a reception pulse corresponding to the reflected light and the reference light has been detected within a predetermined time. As a result of the determination, if the received pulse corresponding to the reflected light and the reference light is not detected within the predetermined time, CPLD17 advances the gate setting process to the process of step S 15. On the other hand, when the reception pulse corresponding to the reflected light and the reference light is detected within a predetermined time, the CPLD 17 advances the gate setting process to the process of step S18.

In the process of step S15, the CPU 18 determines whether or not the set value of the gate control signal is 1. If the set value is 1 as a result of the determination, the CPU 18 sets the current set value as the final set value of the gate control signal as the process of step S16, and then ends the series of gate setting processes. On the other hand, if the set value is not 1, the CPU 18 sets a value obtained by subtracting 2 from the current set value as the process of step S17 as the final set value of the gate control signal, and then ends the series of gate setting processes. To do.

  In the process of step S18, the CPU 18 increments the set value of the gate control signal by one. Thereby, the process of step S18 is completed, and the gate setting process proceeds to the process of step S19.

  In the process of step S19, the CPU 18 determines whether or not the set value of the gate control signal is 15 or less. If it is determined that the set value is 15 or less, the CPU 18 returns the gate setting process to the process of step S12. On the other hand, if the set value is not 15 or less, the CPU 18 sets a value obtained by subtracting 3 from the current set value as the process of step S20 as the final set value of the gate control signal, and then performs a series of gate setting processes. finish.

〔Concrete example〕
Finally, with reference to FIG. 6, the operation of the CPLD 17 when detecting the reception pulse corresponding to the reflected light and the reference light in accordance with the gate interval set by the above-described gate setting process will be described. The example shown in FIG. 6 is the operation of the CPLD 17 when the set value of the gate control signal is 1.

  When the LD drive signal rises at time t1 shown in FIG. 6A, the gate 1 loops the clock signal (loop clock) through n flip-flops, and the counter is turned on every time the clock signal is looped. By receiving the counter clock signal (see FIG. 6B) output from the (n-1) th flip-flop, the number of loops of the loop clock is monitored. Thereafter, the counter starts the gate 1 control signal that allows detection of the received pulse at the timing (time t2 shown in FIG. 6B) when the loop clock loop count becomes the same as the set value of the gate control signal. The gate 1 control signal falls at the timing (time t3 shown in FIG. 6B) when the loop clock loop count becomes equal to or greater than the set value of the gate control signal. Then, the gate 2 calculates the logical product of the gate 1 control signal and the reception pulse, and notifies the CPU 18 of the rise time of the logical sum signal (time t4 shown in FIG. 6 (e)) as the reception pulse detection timing. .

  As is clear from the above description, in the distance measuring apparatus 1 according to the embodiment of the present invention, before the measurement of the distance to the measurement object is started, the CPU 18 receives a reception pulse corresponding to the reflected light and the reference light. When measuring the distance to the object to be measured assuming the detected time, a gate interval is set so that the received pulse can be detected only in the vicinity of the assumed time, and detected by the CPLD 17 by the set gate interval. Since the received pulse is limited, the received pulse corresponding to the reflected light and the reference light can be accurately separated from the noise light, and accurate distance measurement can be performed.

In the distance measuring apparatus 1 according to the embodiment of the present invention, the CPU 18 sets the detection level of the reflected light and the reference light to the detection level when measuring the distance to the measurement object, and the LD 6 sends out the light. When a gate signal having a predetermined pulse width is activated after a predetermined time has elapsed, the received pulse detected while the gate signal is activated is used as a received pulse of reflected light and reference light, and the gate signal is activated The gate signal activation time is delayed by a predetermined time from the light transmission time of the LD 6 until the reception pulse is not detected at a predetermined time, and the gate signal activation time one or more times before the gate signal activation time at which the reception pulse is no longer detected is the gate signal. since set as start time, the state of the measuring object, the circuit state, to fine-tune the start time of the gate section in accordance with the measurement distance, be performed more accurate distance measurement That.

  As mentioned above, although the embodiment to which the invention made by the present inventors was applied has been described, the present invention is not limited by the description and the drawings that form part of the disclosure of the present invention according to this embodiment. For example, the gate section of the CPLD 17 may be variably set externally or via the CPU 18. According to such a configuration, when the gate interval such as when the measurement distance is a fixed value can be set in advance, the gate interval can be set without performing unnecessary processing. Further, it is desirable that the gate section for the reference light is started at the shortest timing or the longest timing from the time when the LD 6 transmits the light. According to such a configuration, since the detection time of the reference light is a specified time, it is possible to perform distance measurement with minimum processing without adding unnecessary processing. Further, the CPU 18 may execute the distance to the measurement object a plurality of times before starting the measurement of the distance to the measurement object, and set the gate section during the execution of the plurality of processes. According to such a configuration, the heat generation state of the CPU 18 can be kept constant, the processing of the CPU 18 can be stabilized, and unnecessary processing can be minimized, so that the distance measurement processing can be stabilized. The gate section can be optimized according to the distance to the measurement object. Further, the CPLD 17 and the CPU 18 may be integrally configured. As described above, it is a matter of course that all other embodiments, examples, operation techniques, and the like made by those skilled in the art based on the above embodiments are 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 block diagram which shows the internal structure of CPLD shown in FIG. It is a figure for demonstrating a noise signal being detected after projecting light toward a measuring object until it detects the received pulse corresponding to reflected light and reference light. 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 gate setting process shown in FIG. FIG. 3 is a timing chart for explaining the operation of the CPLD shown in FIG. 2.

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: CPU
19: DAC

Claims (3)

A light source unit that emits pulsed light toward the measurement object;
A branching unit that branches the light transmitted 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 light receiving unit that converts the reflected light and the reference light into an electrical pulse signal;
An amplifying unit for amplifying the electric pulse signal converted 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;
Before starting the measurement of the distance to the object to be measured, the pulsed light is transmitted and the reference light is transmitted, and further, the detection unit generates electricity corresponding to the reflected light and the reference light. When receiving a pulse signal and setting a gate interval based on the time when this electrical pulse signal is received, and then measuring the distance to the measurement object, the time zone set as the gate interval, A control unit for setting an electric pulse signal as a detectable time zone;
Have
The control unit sets an applied voltage for determining a detection level of the light receiving element so that light is not detected when the light source unit is turned off.
Further, when the received pulse is detected within a predetermined time after irradiating light at a predetermined time interval set in time series and irradiating light at the current time, the next time Repeat the process of irradiating light with
A distance measuring device characterized in that the gate section is set with a gate start time as a time earlier than a light irradiation time when a received pulse is not detected within a predetermined time. The distance measuring device according to claim 1,
The distance measuring device according to claim 1, wherein the gate section can be variably set externally or via a calculation unit . The distance measuring device according to claim 1,
The distance measuring device, wherein the control unit is formed integrally with the calculation unit .

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