Distance measuring device

Abstract

To provide a distance measuring device capable of improving measurement accuracy while suppressing memory size. [Solution] The distance measuring device comprises a light emitting element 11, a light receiving element 21, an AD converter 35, a plurality of memories 41, 46 having different memory sizes and storing sampling data output from the AD converter, and a distance calculator 51, wherein the total number of addresses in each of the plurality of memories is an integer multiple of the difference in the number of addresses between the plurality of memories, and each of the plurality of memories is divided into blocks of the same size as the difference, and the address of the memory in which a specific light receiving signal is stored is identified by combining the blocks of different memories.

Description

Technical Field

[0001] The present invention relates to a distance measuring device that irradiates a measurement object with pulsed light and measures the distance to the measurement object based on the round-trip time of the pulsed light.

Background Art

[0002] In Patent Document 1, pulsed light obtained by pulsing a signal of a predetermined frequency is used to emit ranging light from a light emitting element as pulsed light, and reflected ranging light reflected by a measurement object is received by a light receiving element, and based on the received signal output from the light receiving element, a light wave distance meter that measures the distance to the measurement object is known. When the light wave distance meter described in Patent Document 1 performs long-distance measurement, distance measurement is performed based on the round-trip time (delay time) of the pulsed light (TOF: Time of Flight).

[0003] For example, in a distance measuring device using the TOF (Time of Flight) principle like the light wave distance meter described in Patent Document 1, generally, the waveform of the pulsed light reflected by the measurement object and returned is sampled by an AD converter, and the sampling data output from the AD converter is stored in a memory. Sampling by the AD converter starts simultaneously with the emission of light from the light emitting element and ends when a time longer than the time corresponding to the maximum measurement distance set as the specification of the distance measuring device has elapsed. Therefore, in order to store all the sampling data output from the AD converter in the memory, the memory size needs to be larger than the value obtained by dividing the maximum measurement distance by the sampling interval (distance conversion value). The sampling interval is a value obtained by converting the sampling rate (Hz) to distance using the speed of the ranging light (pulsed light) (3×10 8 m / s).

[0004] In distance measuring devices that use pulse signals to measure the distance to an object, improvement in measurement accuracy (distance calculation accuracy) is desired. Means of improving distance calculation accuracy include, for example, increasing the sampling interval or narrowing the pulse width. A smaller sampling interval allows for more detailed storage of the waveform shape of the pulse light reflected back from the object. As a result, distance calculation accuracy improves. However, a smaller sampling interval poses the problem of requiring a larger memory size.

[0005] Furthermore, narrowing the pulse width reduces the range of pulse fluctuations, thereby improving the accuracy of distance calculations. In recent years, it has become possible to generate pulsed light with pulse widths of, for example, less than 1 nanosecond. However, narrowing the pulse width presents the problem of requiring a larger memory size. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2016-161411 [Overview of the project] [Problems that the invention aims to solve]

[0007] The present invention was made to solve the aforementioned problems and aims to provide a distance measuring device that can improve measurement accuracy while reducing memory size. [Means for solving the problem]

[0008] The present invention provides a distance measuring device that measures the distance to an object to be measured by irradiating the object with distance measuring light as pulsed light and measuring the distance to the object based on the round-trip time of the pulsed light, comprising: a light-emitting element that emits the distance measuring light as pulsed light; a light-receiving element that receives reflected distance measuring light reflected by the object to be measured and outputs a light-receiving signal corresponding to the reflected distance measuring light; an AD converter that converts the light-receiving signal output from the light-receiving element from an analog signal to a digital signal; a plurality of memories having different memory sizes and storing sampling data output from the AD converter; and a distance calculator that calculates the distance based on the sampling data stored in the plurality of memories, wherein the total number of addresses of each of the plurality of memories is an integer multiple of the difference in the number of addresses of the plurality of memories, and the integer multiples of the plurality of memories are different, and each of the plurality of memories has the same magnitude as the difference. Consists of multiple addresses The memory is divided into blocks, and the combination of these blocks is different from the other memory. and using the address of any of the aforementioned memories , configured to identify the address of the memory in which a specific light-receiving signal is stored, The control unit further comprises a control unit that simultaneously stores the same sampling data sequentially from the first address of each of the multiple memories, and when the sampling data has been stored up to the last address of each of the multiple memories, returns to the first address and overwrites the sampling data from the first address, and during the overwrite, performs control to add the sampling data already stored in the memory and the sampling data to be newly stored in the memory, wherein the control unit identifies the address where the pulse data of the received light signal is stored based on the combination of the blocks of the multiple memories where the sampling data of the received light signal is stored from the start of emission of the pulse light until a time equal to or greater than the time corresponding to the maximum measurement distance has elapsed, The distance measuring device is characterized in that the distance calculator calculates the distance based on the address where the sampling data of the received light signal is stored, and when the sampling data of multiple received light signals from multiple objects to be measured are stored redundantly in the same block of one memory, the distance calculator measures the distance to each of the multiple objects to be measured by referring to the multiple sampling data recorded in different blocks of other memories.

[0009] According to the distance measuring device of the present invention, the AD converter converts the received light signal output from the photodetector from an analog signal to a digital signal and outputs sampling data, which is then stored in multiple memories. The multiple memories have different memory sizes. The distance calculator then calculates the distance based on the sampling data stored in the multiple memories. Here, since the multiple memories have different memory sizes and the sampling data is stored in multiple memories, the distance calculator can calculate the distance to the object to be measured based on the address of the memory where the pulse data of the received light signal is stored. Therefore, each memory does not necessarily have to have the memory size required to store the sampling data for the maximum measurement distance. For example, the memory size of each memory may be smaller than the memory size required to store the sampling data for the maximum measurement distance. Furthermore, by making the sampling interval finer or narrowing the width of the pulsed light (pulse width), more sampling data can be stored in multiple memories with smaller memory sizes. This makes it possible to improve measurement accuracy while keeping the memory size down. Furthermore, according to the distance measuring device of the present invention, even if each memory does not have the memory size necessary to store the sampling data for the maximum measurement distance, the control unit stores the same sampling data simultaneously in multiple memories sequentially from the first address of each memory. Once the sampling data has been stored up to the last address of each memory, the control unit returns to the first address and overwrites the sampling data from the first address. When performing this overwrite, the control unit executes a control to add the sampling data already stored in the memory to the sampling data to be newly stored in the memory. Therefore, each time the sampling data is overwritten by returning to the first address, the sampling data to be newly stored in each memory address is accumulated with the sampling data already stored in each memory address. The distance calculator then calculates the distance to the object to be measured based on the sampling data accumulated in each memory address within a time period longer than the time corresponding to the maximum measurement distance. Therefore, even if each memory does not have the memory size necessary to store the sampling data for the maximum measurement distance, the distance calculator can calculate longer distances to the object to be measured with higher accuracy based on the address of the memory where the pulse data of the received light signal is stored. This allows for improved measurement accuracy and maximum measurement distance while keeping memory size down. Furthermore, according to the distance measuring device of the present invention, the value obtained by subtracting the DC component from the sampling data output from the AD converter is stored in memory. Therefore, even when the control unit performs control to add sampling data already stored in memory with sampling data to be newly stored in memory, it is possible to suppress the memory from becoming saturated due to the increase in the addition result. This makes it possible to improve measurement accuracy while further reducing the memory size. Furthermore, according to the distance measuring device of the present invention, the control unit identifies the address of the memory where the pulse data of the received light signal is stored, based on a combination of blocks of multiple memories where the pulse data of the received light signal is stored. Therefore, even if each memory does not have the memory size necessary to store the sampling data for the maximum measurement distance, the control unit can identify the address of the memory where the pulse data of the received light signal is stored. The distance calculator then calculates the distance based on the address of the memory where the pulse data of the received light signal is stored. This makes it possible to improve measurement accuracy while more reliably reducing the memory size.

[0010] In the distance measuring device according to the present invention, preferably, The combination of the aforementioned blocks is divided into patterns, and the address of the memory in which the pulse data of the received light signal is stored is calculated. It is characterized by the following: [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a distance measuring device that can improve the measurement accuracy while suppressing the memory size.

Brief Description of the Drawings

[0015] [Figure 1] It is a schematic diagram showing the distance measuring optical system of the distance measuring device according to the embodiment of the present invention. [Figure 2] It is a schematic diagram showing the arithmetic processing unit of the distance measuring device according to the present embodiment. [Figure 3] It is a timing chart showing the light emission signal and the light reception signal of the distance measuring device according to the present embodiment. [Figure 4] It is a schematic diagram exemplifying the memory size of the memory of the present embodiment. [Figure 5] It is a schematic diagram exemplifying the state in which the memory of the present embodiment is divided into blocks. [Figure 6] It is a schematic diagram exemplifying the relationship between the pulse data of the light reception signal and the blocks of the memory. [Figure 7] It is a schematic diagram exemplifying the combination of the blocks of the memory in which the pulse data of the light reception signal is stored. [Figure 8] It is a schematic diagram exemplifying another relationship between the pulse data of the light reception signal and the blocks of the memory. [Figure 9] It is a flowchart showing a specific example in which the distance measuring device according to the present embodiment calculates the distance to the measurement object. [Figure 10] It is a flowchart showing a specific example in which the distance measuring device according to the present embodiment calculates the distance to the measurement object. [Figure 11] It is a schematic diagram exemplifying the relationship between the pulse data of the light reception signal and the blocks of the memory. [Figure 12] It is a schematic diagram exemplifying the combination of the blocks of the memory in which the pulse data of the light reception signal is stored. [Figure 13] It is a flowchart showing a third specific example in which the distance measuring device according to the present embodiment calculates the distance to the measurement object. [Figure 14] It is a flowchart showing a third specific example in which the distance measuring device according to the present embodiment calculates the distance to the measurement object.

Mode for Carrying Out the Invention

[0016] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. The embodiments described below are preferred specific examples of the present invention, and various technically preferable limitations are imposed. However, the scope of the present invention is not limited to these aspects unless there is a description to specifically limit the present invention in the following description. Also, in each drawing, the same reference numerals are assigned to the same components, and detailed descriptions are omitted as appropriate.

[0017] FIG. 1 is a schematic diagram showing a ranging optical system of a distance measuring device according to an embodiment of the present invention. As shown in FIG. 1, the ranging optical system 1 includes an emission optical system 2, a light receiving optical system 3, and an aiming optical system 4. In FIG. 1, for convenience of explanation, the measurement object 5 is shown as a prism which is a retroreflector. However, the measurement object 5 is not limited to a prism. Also, the ranging optical system 1 shown in FIG. 1 is an example of the ranging optical system of the distance measuring device according to the present embodiment. That is, the ranging optical system of the distance measuring device according to the present embodiment is not limited to the ranging optical system 1 shown in FIG. 1.

[0018] The ranging optical system 1 has a ranging optical axis 6 directed toward the measurement object 5. The emission optical system 2 has an emission optical axis 7. The light receiving optical system 3 has a light receiving optical axis 8. The aiming optical system 4 has an aiming optical axis 9. A light-emitting element 11, a focusing lens 12, a half-mirror 13, and deflection mirrors 15 and 16 are provided on the emission optical axis 7. The range-measuring light passing through the emission optical axis 7 is deflected by the deflection mirrors 15 and 16 and aligns with the range-measuring optical axis 6. The light-emitting element 11 is, for example, a laser diode, a pulsed laser diode, or a pulsed fiber diode, and emits the range-measuring light as pulsed light based on a pulsed signal (pulse signal). The waveform shape of the pulse signal is not particularly limited and may be a square wave pulse signal or a triangular wave pulse signal.

[0019] An objective lens 17 and a dichroic mirror 18 are provided on the rangefinder optical axis 6. The dichroic mirror 18 transmits visible light and reflects rangefinder light. The portion of the rangefinder optical axis 6 that has passed through the dichroic mirror 18 becomes the sighting optical axis 9. An eyepiece lens 19 is provided on the sighting optical axis 9.

[0020] The objective lens 17, dichroic mirror 18, and eyepiece 19, etc., constitute the sighting optical system 4. The condensing lens 12, half mirror 13, deflection mirrors 15 and 16, and objective lens 17, etc., constitute the exit optical system 2.

[0021] The portion of the distance measuring optical axis 6 reflected by the dichroic mirror 18 becomes the light receiving optical axis 8. A light intensity adjuster 14 and a light receiving element 21 are provided on the light receiving optical axis 8. For example, a photodiode or an avalanche photodiode (APD) can be used as the light receiving element 21. The objective lens 17, dichroic mirror 18, and light intensity adjuster 14, etc., constitute the light receiving optical system 3.

[0022] The reflected optical axis of the half-mirror 13 is guided to the photodetector 21 via the reflector 22 as the internal reference optical axis 23. The half-mirror 13 and the reflector 22 constitute the internal reference optical system 24. The light-emitting element 11 and the photodetector 21 are each electrically connected to the arithmetic processing unit 27.

[0023] Optical path switches 25 are provided on the output optical axis 7 and the internal reference optical axis 23. The optical path switches 25 selectively block or open the output optical axis 7 and the internal reference optical axis 23. The optical path switches 25 to switch between a state in which the distance measuring light transmitted through the half mirror 13 is emitted toward the object to be measured 5, and a state in which a portion of the distance measuring light reflected by the half mirror 13 is emitted toward the internal reference optical system 24.

[0024] Next, we will explain the operation of the distance measuring optical system 1. The distance measuring light 28, emitted as pulsed light from the light-emitting element 11 and converted into a parallel beam by the focusing lens 12, passes through the center of the objective lens 17 and is emitted towards the object to be measured 5.

[0025] The distance measuring light reflected from the object to be measured 5 enters the objective lens 17 as reflected distance measuring light 28', is focused by the objective lens 17, reflected by the dichroic mirror 18, and after the light intensity is adjusted by the light intensity adjuster 14, it enters the light receiving element 21. The light receiving element 21 outputs a received signal 29 corresponding to the received reflected distance measuring light 28'.

[0026] A portion of the distance-measuring light 28 (internal reference light 28") emitted from the light-emitting element 11 is reflected by the half-mirror 13. When the internal reference optical axis 23 is opened by switching the optical path of the optical path switcher 25, the internal reference light 28'' enters the photodetector 21 via the internal reference optical system 24. The photodetector 21 outputs a received signal corresponding to the received internal reference light 28''. The processing of the received signal when the photodetector 21 receives reflected distance-measuring light 28' is the same as the processing of the received signal when the photodetector 21 receives internal reference light 28''. Therefore, in this embodiment, the processing of the received signal of reflected distance-measuring light 28' will be explained as an example.

[0027] The visible light entering through the objective lens 17 passes through the dichroic mirror 18 and is focused by the eyepiece lens 19. The surveyor can sight the object to be measured 5 using the visible light entering through the eyepiece lens 19.

[0028] Next, the calculation processing unit 27 of the distance measuring device according to this embodiment will be described. Figure 2 is a schematic diagram showing the calculation processing unit of the distance measuring device according to this embodiment. Figure 3 is a timing chart showing the light emission signal and light reception signal of the distance measuring device according to this embodiment. The timing chart shown in the upper part of Figure 3 is a timing chart showing the generation timing of the pulse signal (light emission signal) output from the driver 33. In other words, the timing chart shown in the upper part of Figure 3 is a timing chart showing the light emission timing of the light-emitting element 11. The timing chart shown in the lower part of Figure 3 is a timing chart showing the generation timing of the light-receiving signal output from the light-receiving element 21.

[0029] The arithmetic processing unit 27 of this embodiment includes an FPGA (Field Programmable Gate Array) 31, a driver 33, an amplifier 34, an AD converter 35, an oscillator 36, and a processing unit 52. The processing unit 52 can be, for example, a CPU (Central Processing Unit) or a DSP (Digital Signal Processor).

[0030] FPGA31 includes a control unit 32, a register 37, a first selector 38, a first adder 39, a first memory 41, a first address counter 42, a first pulse detector 43, a second selector 44, a second adder 45, a second memory 46, a second address counter 47, a second pulse detector 48, a precision distance calculator 49, and a coarse distance calculator 51. Note that FPGA31 may be a known microcomputer. The coarse distance calculator 51 in this embodiment is an example of the "distance calculator" of the present invention.

[0031] As shown in Figure 2, the FPGA 31 of this embodiment has multiple memories. The number of memories is not limited to two, but may be three or more. For the sake of explanation, in this embodiment, we will take the case where the FPGA 31 has two memories (first memory 41 and second memory 46) as an example. The memory size of the first memory 41 is different from the memory size of the second memory 46. That is, the first memory 41 and the second memory 46 have different memory sizes. The memory sizes of the first memory 41 and the second memory 46 may be smaller than the memory size required to store the sampling data of the maximum measurement distance set as the specification of the distance measuring device according to this embodiment.

[0032] The control unit 32 outputs a pulse signal having a predetermined frequency to the driver 33 based on the signals output from the AD converter 35 and the oscillator 36. The oscillator 36 can be, for example, a temperature-compensated crystal oscillator (TCXO). The driver 33 drives the light-emitting element 11 based on the pulse signal output from the control unit 32 and emits the distance measuring light 28 as pulsed light at predetermined time intervals.

[0033] In other words, as shown in the timing chart in the upper part of Figure 3, the light-emitting element 11 emits distance-measuring light 28 as pulsed light at predetermined time intervals based on the pulse signal (light emission signal) output from the driver 33. The light-emitting element 11 emits distance-measuring light 28 at predetermined time intervals until a time equivalent to the maximum measurement distance has elapsed, at which point the emission of distance-measuring light 28 is terminated. Note that in Figure 3, for the sake of explanation, only the timing of the first pulse signal output from the driver 33 after the start of light emission is shown.

[0034] The distance measuring light 28 (i.e., reflected distance measuring light 28') reflected by the object to be measured 5 enters the photodetector 21 as pulsed light. The photodetector 21 then outputs a received signal 29 corresponding to the received reflected distance measuring light 28'. Therefore, as shown in the timing chart in the lower part of Figure 3, the received signal 29 from the photodetector 21 is a pulsed output. Note that in Figure 3, for the sake of explanation, only the timing of the first output of the received signal 29 from the photodetector 21 after the start of light emission is shown. As shown in Figure 3, a delay time td occurs between the received signal and the emitted signal, corresponding to the straight-line distance between the distance measuring device and the object to be measured 5.

[0035] The light-receiving signal 29 output from the light-receiving element 21 is amplified by the amplifier 34. The signal amplified by the amplifier 34 is input to the AD converter 35. The AD converter 35 converts the light-receiving signal output from the light-receiving element 21 and amplified by the amplifier 34 from an analog signal to a digital signal and outputs it as sampled data. Sampling by the AD converter 35 starts simultaneously with the emission of light from the light-emitting element 11 and ends after a time equivalent to the maximum measurement distance has elapsed.

[0036] The sampled data output from the AD converter is stored in the first memory 41 via register 37 and the first adder 39, and also in the second memory 46 via register 37 and the second adder 45. In other words, each of the first memory 41 and the second memory 46 stores the sampled data output from the AD converter. At this time, the first memory 41 and the second memory 46 simultaneously store the same sampled data.

[0037] Register 37 functions, for example, as a latch circuit and holds predetermined information. Register 37 is a flip-flop that latches digital data as sampled data output from the AD converter, and can reliably capture data that is input at high speed. The control unit 32 may control register 37 and input the value obtained by subtracting the DC component from the sampled data output from the AD converter 35 to the first adder 39 and the second adder 45. In this case, the value obtained by subtracting the DC component from the sampled data output from the AD converter 35 is stored in the first memory 41 and the second memory 46, respectively.

[0038] The first adder 39 adds the sampling data already stored in the first memory 41 to the sampling data to be newly stored in the first memory 41. In this specification, "sampling data to be newly stored" corresponds to the sampling data output from the AD converter. That is, when sampling data is first stored from the first address of the first memory 41 to the last address of the first memory 41, the first selector 38 outputs "0" based on the control signal transmitted from the control unit 32. On the other hand, when sampling data has been stored from the first address of the first memory 41 to the last address of the first memory 41 and is overwritten by returning to the first address, the first selector 38 outputs the sampling data already stored in the first memory 41 based on the control signal transmitted from the control unit 32. Therefore, each time the sampling data is overwritten by returning to the first address of the first memory 41, the sampling data to be newly stored at the address of the first memory 41 is accumulated with the sampling data already stored at the address of the first memory 41.

[0039] In this specification, "first stored" means that the data is stored for the first time during the process of measuring the distance to any object 5, and does not mean that the data is stored for the first time after the distance measuring device according to this embodiment has come into use.

[0040] The second adder 45 adds the sampling data already stored in the second memory 46 to the sampling data to be newly stored in the second memory 46. That is, when sampling data is first stored from the first address to the last address of the second memory 46, the second selector 44 outputs "0" based on the control signal transmitted from the control unit 32. On the other hand, when sampling data is stored from the first address to the last address of the second memory 46 and then returned to the first address to overwrite the data, the second selector 44 outputs the sampling data already stored in the second memory 46 based on the control signal transmitted from the control unit 32. Therefore, each time the sampling data is overwritten by returning to the first address of the second memory 46, the sampling data to be newly stored at the address of the second memory 46 is accumulated on the sampling data already stored at the address of the second memory 46.

[0041] The first address counter 42 calculates the address of the first memory 41 based on the control signal transmitted from the control unit 32, and outputs the calculation result to the first memory 41 and the first pulse detector 43. The second address counter 47 calculates the address of the second memory 46 based on the control signal transmitted from the control unit 32, and outputs the calculation result to the second memory 46 and the second pulse detector 48.

[0042] The first pulse detector 43 detects pulse data of the received light signal based on the sampling data stored in the first memory 41 and outputs it to the precision distance calculator 49 and the coarse distance calculator 51. The second pulse detector 48 detects pulse data of the received light signal based on the sampling data stored in the second memory 46 and outputs it to the rough distance calculator 51.

[0043] The rough distance calculator 51 calculates the rough distance to the object to be measured 5 based on the pulse data of the received light signals output from the first pulse detector 43 and the second pulse detector 48. That is, the rough distance calculator 51 calculates the rough distance to the object to be measured 5 based on the sampling data stored in the first memory 41 and the second memory 46. Specifically, the rough distance calculator 51 calculates the distance between the distance measuring device and the object to be measured 5 based on the delay time td shown in Figure 3 (TOF: Time of Flight). At this time, the rough distance calculator 51 subtracts the rough distance calculated from the received light signal of the internal reference light 28'' from the rough distance calculated from the received light signal of the reflected ranging light 28'. In this way, the rough distance calculator 51 can eliminate the effects of temperature drift, etc., of the electrical circuit, the arithmetic processing unit 27 by finding the difference between the rough distance calculated from the reflected ranging light 28' and the rough distance calculated from the internal reference light 28''. The rough distance calculator 51 then outputs a signal related to the calculation result of the rough distance to the processing unit 52.

[0044] The precision distance calculator 49 calculates a precision distance less than or equal to the sampling interval based on the pulse data of the received light signal output from the first pulse detector 43. For example, the precision distance calculator 49 calculates the precision distance using the Fourier transform. At this time, the precision distance calculator 49 subtracts the precision distance calculated from the received light signal of the internal reference light 28'' from the precision distance calculated from the received light signal of the reflected ranging light 28'. In this way, the precision distance calculator 49 can eliminate the effects of temperature drift, etc., of the electrical circuit, the arithmetic processing unit 27 by finding the difference between the precision distance calculated from the reflected ranging light 28' and the precision distance calculated from the internal reference light 28''. The precision distance calculator 49 then outputs a signal related to the calculation result of the precision distance to the processing unit 52.

[0045] The processing unit 52 adds the rough distance value output from the rough distance calculator 51 and the precise distance value output from the precise distance calculator 49 to perform a calculation to determine the distance from the distance measuring device to the object to be measured 5.

[0046] As mentioned above, sampling by the AD converter 35 starts simultaneously with the emission of light from the light-emitting element 11 and ends after a time equal to or greater than the time corresponding to the maximum measurement distance. Therefore, in the comparative example where only one memory is provided to store the sampling data, the memory size must be larger than the value obtained by dividing the maximum measurement distance by the sampling interval (distance equivalent value) in order to store all of the sampling data output from the AD converter in the memory. The sampling interval is the speed of the distance measuring light (pulsed light) (3 × 10⁻¹⁰ 8 This value is obtained by converting the sampling rate (Hz) using m / s into distance. In distance measuring devices that measure the distance to an object using pulse signals, there is a desire to improve the measurement accuracy (distance calculation accuracy), but there is a problem that improving the distance calculation accuracy requires a larger memory size.

[0047] In contrast, the distance measuring device according to this embodiment is equipped with multiple memories. The multiple memories have different sizes from each other. In the example of the arithmetic processing unit 27 shown in Figure 2, the FPGA 31 has two memories (first memory 41 and second memory 46). The first memory 41 and the second memory 46 have different sizes from each other. The rough distance calculator 51 then calculates the rough distance to the object to be measured 5 based on the sampling data stored in the first memory 41 and the second memory 46.

[0048] Since the first memory 41 and the second memory 46 have different memory sizes, and the sampling data output from the AD converter 35 is stored in the first memory 41 and the second memory 46, the coarse distance calculator 51 can calculate the distance to the object to be measured 5 based on the addresses of the first memory 41 and the second memory 46 in which the pulse data of the received light signal is stored. Therefore, each of the first memory 41 and the second memory 46 does not necessarily have to have the memory size required to store the sampling data for the maximum measurement distance. For example, the memory size of each of the first memory 41 and the second memory 46 may be smaller than the memory size required to store the sampling data for the maximum measurement distance. Furthermore, by making the sampling interval finer or narrowing the width of the pulsed light (pulse width), more sampling data can be stored in the first memory 41 and the second memory 46 with smaller memory sizes. This makes it possible to improve measurement accuracy while keeping the memory size down.

[0049] Furthermore, if the memory sizes of the first memory 41 and the second memory 46 are smaller than the memory size required to store sampling data for the maximum measurement distance, it is possible to improve measurement accuracy while more reliably reducing the memory size. In addition, if the memory sizes of the first memory 41 and the second memory 46 are smaller than the memory size required to store sampling data for the maximum measurement distance, it is possible to achieve lower power consumption, miniaturization, and reduced heat dissipation of the distance measuring device.

[0050] Next, a first specific example of how the distance measuring device according to this embodiment calculates the distance to the object to be measured will be described with reference to the drawings. Figure 4 is a schematic diagram illustrating the memory size of the memory in this embodiment. Figure 5 is a schematic diagram illustrating the memory of this embodiment divided into blocks. Figure 6 is a schematic diagram illustrating the relationship between the pulse data of the received light signal and the memory blocks. Figure 7 is a schematic diagram illustrating a combination of memory blocks in which the pulse data of the received light signal is stored. Figure 8 is a schematic diagram illustrating another relationship between the pulse data of the received light signal and the memory blocks. Figures 9 and 10 are flowcharts illustrating a first specific example of how the distance measuring device according to this embodiment calculates the distance to the object to be measured.

[0051] Note that the timing charts shown in the upper part of Figures 6 and 8 correspond to the timing chart shown in the upper part of Figure 3. The timing charts shown in the middle part of Figures 6 and 8 correspond to the timing chart shown in the lower part of Figure 3. The timing charts shown in the lower part of Figures 6 and 8 are schematic diagrams illustrating combinations of multiple memory blocks.

[0052] First, as shown in Figure 4, a first memory 41 and a second memory 46, each having a different memory size, are prepared (step S11 in Figure 9). As mentioned earlier regarding Figure 2, the number of memories is not limited to two, but may be three or more. For the sake of explanation, in this specific example, we will use the case where two memories (first memory 41 and second memory 46) are used.

[0053] In this specific example, the number of addresses in the first memory 41 is 10240. The addresses in the first memory 41 range from 0 to 10239, from the first address to the last address. The number of addresses in the second memory 46 is 8192. The addresses in the second memory 46 range from 0 to 8191, from the first address to the last address. The difference between the number of addresses in the first memory 41 and the number of addresses in the second memory 46 is d (=2048) (Step S11 in Figure 9).

[0054] Assuming that the quantization decomposition of the AD converter 35 is constant, the number of addresses in each memory is equivalent to the memory size of each memory. Also, assuming that the quantization decomposition of the AD converter 35 is constant, the difference in addresses between multiple memories is equivalent to the difference in memory sizes between those memories. Therefore, in this specific example, we will explain by assuming that the number of addresses in each memory is equivalent to the memory size of each memory, and that the difference in addresses between multiple memories is equivalent to the difference in memory sizes between those memories.

[0055] In this specific example, the number of addresses in the first memory 41 and the second memory 46 are integer multiples of the difference d between the number of addresses in the first memory 41 and the number of addresses in the second memory 46. That is, the number of addresses in the first memory 41 (10240) is 5 times the difference d (2048). The number of addresses in the second memory 46 (8192) is 4 times the difference d (2048). Note that the number of addresses in the first memory 41 (10240) and the number of addresses in the second memory 46 (8192) do not necessarily have to be integer multiples of the difference d (2048).

[0056] Next, as shown in Figure 5, the first memory 41 and the second memory 46 are each divided into blocks according to the magnitude of the difference in the number of addresses d (step S12 in Figure 9). In this specific example, the number of addresses in the first memory 41 is 5 times the difference in the number of addresses d, so the first memory 41 is divided into 5 blocks X0 to X4. Also, the number of addresses in the second memory 46 is 4 times the difference in the number of addresses d, so the second memory 46 is divided into 4 blocks Y0 to Y3.

[0057] Note that the size of each block does not have to be equal to the difference d in the number of addresses. Also, the size of each block may differ between the first memory 41 and the second memory 46. In this specific example, we will explain using the case where the size of each block is equal to the difference d in the number of addresses.

[0058] In this specific example, the number of addresses in each block X0-X4 and Y0-Y3 is the difference d between the number of addresses. For example, if the sampling rate of the AD converter 35 is 500MHz, the sampling interval (distance equivalent) is 300mm. Therefore, the difference d (2048) between the number of addresses in this specific example corresponds to a distance of 300 × 2048 = 614400mm (614.4m).

[0059] The address of block X0 is 0~d-1 (0~2047). The address of block X1 is d~2d-1 (2048~4095). The address of block X2 is 2d~3d-1 (4096~6143). The address of block X3 is 3d~4d-1 (6144~8191). The address of block X4 is 4d~5d-1 (8192~10239).

[0060] Furthermore, the address of block Y0 is 0~d-1 (0~2047). The address of block Y1 is d~2d-1 (2048~4095). The address of block Y2 is 2d~3d-1 (4096~6143). The address of block Y3 is 3d~4d-1 (6144~8191).

[0061] Next, simultaneously with the emission of light from the light-emitting element 11, the AD converter 35 starts sampling the received light signal (step S13 in Figure 9). Then, the control unit 32 simultaneously stores the same sampled data output from the AD converter 35 into the first memory 41 and the second memory 46, starting from the first address of each (step S14 in Figure 9). That is, the control unit 32 stores the sampled data output from the AD converter 35 into the first memory 41, starting from the first address (0) and moving toward the last address (10239). The control unit 32 also stores the sampled data output from the AD converter 35 into the second memory 46, starting from the first address (0) and moving toward the last address (8191).

[0062] Next, when the sampled data is stored up to the last address (8191) of the second memory 46, the entirety of the second memory 46 is used. Similarly, when the sampled data is stored up to the last address (10239) of the first memory 41, the entirety of the first memory 41 is used. Therefore, the control unit 32 determines whether the sampled data output from the AD converter 35 has been stored sequentially up to the last addresses of the first memory 41 and the second memory 46, respectively (step S15 in Figure 9).

[0063] If the sampling data has not been stored up to the last address (8191) of the second memory 46 (step S15: NO in Figure 9), the control unit 32 continues to store the sampling data output from the AD converter 35 sequentially from the first address (0) of the second memory 46 toward the last address (8191) of the second memory 46 (step S14 in Figure 9).

[0064] On the other hand, if the sampling data has been stored up to the last address (8191) of the second memory 46 (step S15 in Figure 9: YES), as shown in Figure 6, the control unit 32 returns to the first address (0) of the second memory 46 and overwrites the sampling data output from the AD converter 35 sequentially from the first address (0) of the second memory 46 to the last address (8191) of the second memory 46 (step S16 in Figure 10). During this overwriting, the control unit 32 adds the sampling data already stored in the second memory 46 and the sampling data to be newly stored in the second memory 46, and stores the result of this addition in the second memory 46 (step S16 in Figure 10).

[0065] In other words, when the sampling data is first stored from the first address (0) to the last address (8191) of the second memory 46 (during the "first cycle" storage shown in Figure 6), the second selector 44 outputs "0" based on the control signal transmitted from the control unit 32. On the other hand, when the sampling data is stored from the first address (0) to the last address (8191) of the second memory 46 and then overwritten back to the first address (0) (during the "second cycle" and subsequent cycles shown in Figure 6), the second selector 44 outputs the sampling data already stored in the second memory 46 based on the control signal transmitted from the control unit 32. Therefore, from the second cycle onward, each time the sampling data is overwritten, the new sampling data to be stored at the address of the second memory 46 is accumulated on the sampling data already stored at the address of the second memory 46.

[0066] During this overwrite operation, the control unit 32 may input the value obtained by subtracting the DC component from the sampling data output from the AD converter 35 to the first adder 39 and the second adder 45, and store it in the first memory 41 and the second memory 46, respectively. In this case, the value obtained by subtracting the DC component from the sampling data output from the AD converter 35 is stored in the first memory 41 and the second memory 46, respectively. This prevents the second memory 46 from becoming saturated due to an increase in the sum of the sampling data, even when the sampling data already stored in the second memory 46 and the sampling data to be newly stored in the second memory 46 are added and stored in the second memory 46.

[0067] Figure 6 shows how the control unit 32 overwrites the sampling data already stored in the first memory 41 and the second memory 46 by adding the newly added sampling data to be stored in each of the first memory 41 and the second memory 46. The control described above for step S14 (step S15:NO in Figure 10) following step S15 in Figure 10, and the control described above for step S16 in Figure 10, are also performed for the first memory 41.

[0068] Next, the control unit 32 determines whether a time equivalent to the maximum measurement distance has elapsed since the start of light emission from the light-emitting element 11 (step S17 in Figure 10). If a time equivalent to the maximum measurement distance has not elapsed (step S17: NO in Figure 10), the control unit 32 continues to perform the control described above with respect to step S16 in Figure 10.

[0069] On the other hand, if a time equivalent to the maximum measurement distance has elapsed (step S17 in Figure 10: YES), the control unit 32 stops the emission of light from the light-emitting element 11 and stops sampling of the received signal by the AD converter 35, and determines the combination of blocks in the first memory 41 and the second memory 46 in which the pulse data of the received signal is stored (step S18 in Figure 10).

[0070] In the example shown in Figure 6, the pulse data of the received light signal is stored in block X2 of the third cycle of the first memory 41 and in block Y0 of the fourth cycle of the second memory 46. Therefore, as shown in Figure 7, the combination of blocks in the first memory 41 and the second memory 46 in which the pulse data of the received light signal is stored is "first memory 41: block X2 - second memory 46: block Y0". As shown in Figure 6, there is only one combination of blocks in the first memory 41 and the second memory 46 from the start of light emission of the light-emitting element 11 until a time equivalent to the maximum measurement distance has elapsed.

[0071] In the distance measuring device according to this embodiment, it is desirable to appropriately adjust the memory size (or number of addresses) of the first memory 41, the memory size (or number of addresses) of the second memory 46, and the difference between the memory size of the first memory 41 and the memory size of the second memory 46 (or the difference in the number of addresses d) so that there is only one combination of blocks in the first memory 41 and blocks in the second memory 46 from the start of light emission of the light-emitting element 11 until a time equivalent to or greater than the time corresponding to the maximum measurement distance has elapsed.

[0072] Next, the control unit 32 controls the first address counter 42 and calculates the address of the first memory 41 where the pulse data of the received light signal is stored, based on the combination of the blocks of the first memory 41 where the pulse data of the received light signal is stored and the blocks of the second memory 46 (step S19 in Figure 10). For example, in this specific example, the address of the beginning of block X2 in the third cycle of the first memory 41 is (5 × d) × (3 - 1) + (2 × d) = 5 × 2048 × 2 + 2 × 2048 = 24576. The control unit 32 may also control the second address counter 47 and calculate the address of the second memory 46 where the pulse data of the received light signal is stored. The address of the beginning of block Y0 in the fourth cycle of the second memory 46 is the same as the address of the beginning of block X2 in the third cycle of the first memory 41.

[0073] In this way, the control unit 32 can identify the address of the memory where the pulse data of the received light signal is stored by using multiple memories having different smaller memory sizes. The rough distance calculator 51 then calculates the rough distance to the object to be measured 5 based on the address where the pulse data of the received light signal is stored (step S19 in Figure 10). In other words, the rough distance calculator 51 calculates the rough distance to the object to be measured 5 based on the sampling data accumulated in the memory address until a time equal to or greater than the time corresponding to the maximum measurement distance has elapsed. For example, the rough distance calculator 51 calculates the rough distance to the object to be measured 5 by calculating the product of the address of the memory where the pulse data of the received light signal is stored and the sampling interval (distance equivalent value).

[0074] As shown in Figure 8, the control unit 32 may also divide the combinations of blocks in the first memory 41 and the blocks in the second memory 46 into patterns and calculate the address of the memory where the pulse data of the received light signal is stored (step S19 in Figure 10).

[0075] In other words, in the specific example shown in Figure 8, the first pattern is one in which the blocks of the first memory 41 and the blocks of the second memory 46 are the same pattern. If the pulse data of the received light signal is present in the first pattern, the control unit 32 uses the address of either the first memory 41 or the second memory 46 as is and calculates the address in which the pulse data of the received light signal is stored.

[0076] The second pattern is a combination of block X4 in the first memory 41 and block Y0 in the second memory 46. If the pulse data of the received light signal exists in the second pattern, the control unit 32 adopts the address of the first memory 41 and calculates the address where the pulse data of the received light signal is stored.

[0077] The third pattern is a combination of blocks X0 to X2 of the first memory 41 and blocks Y1 to Y3 of the second memory 46. If the pulse data of the received light signal exists in the third pattern, the control unit 32 uses an address obtained by adding the address of the first memory 41 and the memory size of the first memory 41 (in this specific example, the number of addresses: 10240) to calculate the address where the pulse data of the received light signal is stored.

[0078] The fourth pattern is a combination of blocks X3 to X4 of the first memory 41 and blocks Y0 to Y1 of the second memory 46. If the pulse data of the received light signal exists in the fourth pattern, the control unit 32 uses an address obtained by adding the address of the first memory 41 and the memory size of the first memory 41 (number of addresses in this specific example: 10240) to calculate the address where the pulse data of the received light signal is stored.

[0079] The fifth pattern is a combination of blocks X0 to X1 in the first memory 41 and blocks Y2 to Y3 in the second memory 46. If the pulse data of the received light signal exists in the fifth pattern, the control unit 32 uses an address obtained by adding the address of the first memory 41 and twice the memory size of the first memory 41 (in this specific example, the number of addresses: 10240) to calculate the address where the pulse data of the received light signal is stored.

[0080] The sixth pattern is a combination of blocks X2 to X4 of the first memory 41 and blocks Y0 to Y2 of the second memory 46. If the pulse data of the received light signal exists in the sixth pattern, the control unit 32 uses an address obtained by adding the address of the first memory 41 and twice the memory size of the first memory 41 (in this specific example, the number of addresses: 10240) to calculate the address where the pulse data of the received light signal is stored.

[0081] As shown in Figure 8, the control unit 32 can also identify the address of the memory where the pulse data of the received light signal is stored by using multiple memories with different smaller memory sizes. Then, the rough distance calculator 51 calculates the rough distance to the object to be measured 5 based on the address where the pulse data of the received light signal is stored (step S19 in Figure 10).

[0082] Next, the precision distance calculator 49 calculates the precision distance less than or equal to the sampling interval using the Fourier transform (step S21 in Figure 10). Known calculation methods can be used for calculating the precision distance using the Fourier transform. The precision distance calculator 49 may also calculate the precision distance using methods other than the Fourier transform.

[0083] Next, the processing unit 52 adds the rough distance value calculated by the rough distance calculator 51 and the precise distance value calculated by the precision distance calculator 49 to determine the distance from the distance measuring device to the object to be measured 5 (step S22 in Figure 10).

[0084] In this specific example, the control unit 32 stores the same sampling data simultaneously in the first memory 41 and the second memory 46, starting from the first address of each. Once the sampling data has been stored up to the last address of the first memory 41 and the second memory 46, it returns to the first address and overwrites the sampling data from the first address. When performing this overwrite, the control unit 32 executes a control that adds the sampling data already stored in each memory 41 and 46 to the sampling data to be newly stored in each memory 41 and 46. Therefore, each time the control unit returns to the first address and overwrites the sampling data, the sampling data to be newly stored in each memory 41 and 46 is accumulated on the sampling data already stored in each memory 41 and 46. The rough distance calculator 51 then calculates the rough distance to the object to be measured 5 based on the sampling data accumulated in each memory 41 and 46 until a time equal to or greater than the time corresponding to the maximum measurement distance has elapsed. Therefore, even if each memory 41, 46 does not have the memory size necessary to store sampling data for the maximum measurement distance, the rough distance calculator 51 can calculate the longer rough distance to the object to be measured 5 with higher accuracy based on the address of the memory where the pulse data of the received light signal is stored. This makes it possible to improve measurement accuracy and the maximum measurement distance while keeping the memory size down.

[0085] Furthermore, the control unit 32 identifies the address of the memory where the pulse data of the received light signal is stored, based on the combination of blocks in the first memory 41 and the second memory 46 where the pulse data of the received light signal is stored. Therefore, even if each memory 41 and 46 does not have the memory size necessary to store the sampling data for the maximum measurement distance, the control unit 32 can identify the address of the memory where the pulse data of the received light signal is stored. Then, the rough distance calculator 51 calculates the rough distance based on the address of the memory where the pulse data of the received light signal is stored. This makes it possible to improve measurement accuracy while more reliably reducing the memory size.

[0086] Furthermore, if the value obtained by subtracting the DC component from the sampling data output from the AD converter 35 is stored in the first memory 41 and the second memory 46, respectively, it is possible to prevent the first memory 41 and the second memory 46 from becoming saturated due to the increasing sum of the results. This makes it possible to further reduce the memory size while improving measurement accuracy.

[0087] In this specific example, we have explained the case where there is only one pulse data for the received light signal, but there may be multiple pulse data for the received light signal. For example, there may be a first pulse data for the received light signal from an object 5 (e.g., a tree) that is relatively close to the distance measuring device, and a second pulse data for the received light signal from an object 5 (e.g., a cliff) that is relatively far from the distance measuring device. Even when there are multiple pulse data for the received light signals, the control unit 32 can identify the memory address where each of the multiple pulse data for the received light signals is stored based on the combination of blocks in the first memory 41 and the second memory 46 in which each of the multiple pulse data for the received light signals is stored. A detailed explanation of this will be given later.

[0088] Furthermore, in this specific example, if the pulse data of the received light signal spans adjacent blocks in the first memory 41 and adjacent blocks in the second memory 46, the control unit 32 may estimate the apparent address in the first memory 41 and the second memory 46 by using the pulse data before and after the block that the pulse data of the received light signal spans.

[0089] Next, a second and third specific example of how the distance measuring device according to this embodiment calculates the distance to the object to be measured will be described with reference to the drawings. In cases where the components of the distance measuring devices in the second and third specific examples are the same as those of the distance measuring device in the first specific example described above with respect to Figures 4 to 10, redundant explanations will be omitted as appropriate, and the following explanation will focus on the differences.

[0090] Figure 11 is a schematic diagram illustrating the relationship between the pulse data of the received light signal and the memory blocks. Figure 12 is a schematic diagram illustrating a combination of memory blocks in which pulse data of a received light signal is stored. Note that the timing chart shown in the upper part of Figure 11 corresponds to the timing chart shown in the upper part of Figure 3. The timing chart shown in the middle part of Figure 11 corresponds to the timing chart shown in the lower part of Figure 3. The timing chart shown in the lower part of Figure 11 is a schematic diagram illustrating combinations of multiple memory blocks.

[0091] The second specific example explains the case where pulse data of multiple received light signals exists. Specifically, as shown in Figure 11, it explains the case where pulse data of the first received light signal exists due to the first object to be measured, and pulse data of the second received light signal exists due to the second object to be measured. Between the first received light signal and the emitted light signal, a first delay time td1 occurs, corresponding to the straight-line distance between the distance measuring device and the first object to be measured. Also, between the second received light signal and the emitted light signal, a second delay time td2 occurs, corresponding to the straight-line distance between the distance measuring device and the second object to be measured. The process by which the distance measuring device in this specific example calculates the distance to the object to be measured is the same as the flowchart shown in Figures 9 and 10.

[0092] In the example shown in Figure 11, the pulse data of the first received light signal is stored in block X2 of the second cycle of the first memory 41 and in block Y3 of the second cycle of the second memory 46. Similarly, the pulse data of the second received light signal is stored in block X2 of the third cycle of the first memory 41 and in block Y0 of the fourth cycle of the second memory 46. Therefore, as shown in Figure 12, the combination of blocks in the first memory 41 and the second memory 46 in which the pulse data of the first received light signal is stored is "First memory 41: block X2 - Second memory 46: block Y3". Also, the combination of blocks in the first memory 41 and the second memory 46 in which the pulse data of the second received light signal is stored is "First memory 41: block X2 - Second memory 46: block Y0".

[0093] In this way, even if blocks storing pulse data for multiple light-receiving signals overlap in either the first memory 41 or the second memory 46 (first memory 41 in this example), it is possible to confirm that pulse data for multiple light-receiving signals exists in the other of the first memory 41 or the second memory 46 (second memory 46 in this example). The control unit 32 then controls the address counter (second address counter 47 in this example) of the memory that has confirmed the pulse data for multiple light-receiving signals (second memory 46 in this example) or the memory with a larger number of pulse data for light-receiving signals (second memory 46 in this example), and calculates multiple addresses of the memory (second memory 46 in this example) that stores the pulse data for multiple light-receiving signals.

[0094] According to this specific example, even if blocks containing pulse data of multiple light-receiving signals overlap in either the first memory 41 or the second memory 46, the control unit 32 can identify multiple addresses of the memory containing the pulse data of multiple light-receiving signals by using multiple memories with different but smaller memory sizes and by referring to the memory that has confirmed the pulse data of multiple light-receiving signals (the memory with a larger number of pulse data of light-receiving signals). Then, the rough distance calculator 51 can calculate the rough distance to the first and second measurement targets based on the multiple addresses containing the pulse data of multiple light-receiving signals.

[0095] Figures 13 and 14 are flowcharts illustrating a third specific example in which the distance measuring device according to this embodiment calculates the distance to the object to be measured. The third specific example describes the case where the reflectance of the object to be measured 5 is relatively low. In other words, this specific example describes the case where the signal-to-noise ratio (SNR) of the received signal 29 corresponding to the reflected distance measuring light 28' is relatively low. Examples of cases where the reflectance of the object to be measured 5 is relatively low include long-distance measurements that do not use a prism, which is a retroreflector, and cases where the angle of incidence of the distance measuring light 28 to the object to be measured 5 is relatively small. A specific example of long-distance measurements that do not use a prism, which is a retroreflector, is, for example, when non-prism measurement (distance measurement without using a prism, which is a retroreflector) is performed on a building, which is the object to be measured 5, located about several kilometers away from the distance measuring device. A specific example of a case where the angle of incidence of the distance measuring light 28 to the object to be measured 5 is relatively small is, for example, when distance measurement is performed on a manhole cover, which is the object to be measured 5, located about several tens of meters away from the distance measuring device.

[0096] When the reflectivity of the object to be measured 5 is relatively low, it may not be possible to obtain a received light signal 29 of sufficient magnitude (intensity) for distance calculation with only one flash of light from the light-emitting element 11. To address such distance measurements, there is a method that repeatedly performs the following steps: (1) light emission from the light-emitting element 11, (2) sampling of the received light signal by the AD converter 35, and (3) storage (integration) of the sampled data in memory, integrating the sampled data until the waveform of the pulse signal appears in memory. The purpose of the method of integrating the sampled data is to make the waveform of the pulse signal appear when the signal-to-noise ratio is so low that the received light signal 29 is completely hidden by noise, and to improve the signal-to-noise ratio and thus the accuracy of distance calculation when the shape of the pulse signal waveform can be grasped, but a received light signal 29 of sufficient magnitude for distance calculation cannot be obtained.

[0097] In this method, it is unknown which address in memory the pulse signal waveform will float to until the pulse signal waveform actually floats to memory. Therefore, in this method, the memory generally needs to have a size that can store all of the sampling data for the maximum measurement distance.

[0098] In contrast, in the distance measuring device according to this embodiment, even if each memory 41, 46 does not have the memory size necessary to store sampling data for the maximum measurement distance, the rough distance calculator 51 can calculate the rough distance to the object to be measured 5 based on the address of the memory where the pulse data of the received light signal is stored.

[0099] To explain in detail, first, steps S31 to S37 shown in Figures 13 and 14 are the same as the control described above for steps S11 to S17 in Figures 9 and 10. In step S38 following step S37, the control unit 32 checks the sampling data stored in the first memory 41 or the second memory 46 (step S38 in Figure 14). Next, the control unit 32 determines whether the magnitude of the pulse data of the received light signal based on the sampling data stored in the first memory 41 or the second memory 46 exceeds a predetermined value (step S39 in Figure 14). At this time, if the signal-to-noise ratio is so low that the received light signal is completely hidden by noise, the control unit 32 also checks whether or not there is a pulse signal (step S39 in Figure 14) to bring out the waveform of the pulse signal.

[0100] If the magnitude of the pulse data of the received light signal does not exceed a predetermined value (step S39: NO in Figure 14), the control unit 32 starts sampling the received light signal by the AD converter 35 at the same time as the light-emitting element 11 starts emitting light again (step S33 in Figure 13). On the other hand, if the magnitude of the pulse data of the received light signal exceeds a predetermined value (step S39: YES in Figure 14), the control unit 32 stops the light-emitting element 11 from emitting light and stops sampling the received light signal by the AD converter 35, and determines the combination of blocks in the first memory 41 and the second memory 46 in which the pulse data of the received light signal is stored (step S41 in Figure 14). Steps S42 to S44 shown in Figure 14 are the same as the control described above with respect to steps S19 to S22 in Figure 10.

[0101] In this specific example, when the magnitude of the pulse data of the received light signal, based on the sampling data stored in the first memory 41 or the second memory 46, exceeds a predetermined value, the rough distance calculator 51 calculates the rough distance to the object to be measured 5 based on the address where the pulse data of the received light signal is stored. This makes it possible to improve measurement accuracy and maximum measurement distance while keeping the memory size down, even when the signal-to-noise ratio of the received light signal is relatively low.

[0102] Embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the claims. The configurations of the above embodiments can be partially omitted or combined in any way different from those described above. [Explanation of Symbols]

[0103] 1: Rangefinder optical system, 2: Ejection optical system, 3: Light receiving optical system, 4: Sighting optical system, 5: Object to be measured, 6: Rangefinder optical axis, 7: Ejection optical axis, 8: Light receiving optical axis, 9: Sighting optical axis, 11: Light-emitting element, 12: Focusing lens, 13: Half mirror, 14: Light intensity adjuster, 15: Deflection mirror, 16: Deflection mirror, 17: Objective lens, 18: Dichroic mirror, 19: Eyepiece lens, 21: Light-receiving element, 22: Reflecting mirror, 23: Internal reference optical axis, 24: Internal reference optical system, 25: Optical path switch, 27: Processing unit, 28: Rangefinder light, 28': Reflected rangefinder light, 28”: Internal reference light, 29: Received light signal, 31: FPGA, 32: Control unit, 33: Driver 34: Amplifier, 35: AD converter, 36: Oscillator, 37: Register, 38: First selector, 39: First adder, 41: First memory, 42: First address counter, 43: First pulse detector, 44: Second selector, 45: Second adder, 46: Second memory, 47: Second address counter, 48: Second pulse detector, 49: Precision distance calculator, 51: Coarse distance calculator, 52: Processing unit

Claims

1. A distance measuring device that irradiates an object to be measured with a distance measuring light as pulsed light and measures the distance to the object based on the round-trip time of the pulsed light, A light-emitting element that emits the distance-measuring light as the pulsed light, A light-receiving element that receives reflected distance-measuring light that has been reflected by the object to be measured and outputs a light-receiving signal corresponding to the reflected distance-measuring light, An AD converter that converts the received light signal output from the light receiving element from an analog signal to a digital signal, Multiple memories having different memory sizes and storing the sampling data output from the AD converter, A distance calculator that calculates the distance based on the sampling data stored in the plurality of memories, Equipped with, The total number of addresses for each of the aforementioned multiple memories is an integer multiple of the difference in the number of addresses between the multiple memories, and the integer multiples for each of the multiple memories are different. Each of the aforementioned multiple memories is divided into blocks consisting of multiple addresses of the same size as the difference, The system is configured to identify the address of the memory in which a specific light-receiving signal is stored, using the block combinations of different memories and the address of any of the memories. The control unit further comprises a control unit that simultaneously stores the same sampling data in each of the multiple memories in order from the first address, and when the sampling data has been stored up to the last address of each of the multiple memories, returns to the first address and overwrites the sampling data from the first address, and during the overwrite, performs control to add the sampling data already stored in the memory and the sampling data newly stored in the memory. The control unit identifies the address where the pulse data of the received light signal is stored, based on the combination of blocks in the plurality of memories where the sampling data of the received light signal is stored, from the time when the emission of the pulsed light starts until a time equal to or greater than the time corresponding to the maximum measurement distance has elapsed. The distance calculator calculates the distance based on the address in which the sampling data of the received light signal is stored. A distance measuring device characterized in that, when the sampling data of multiple light-receiving signals from multiple objects to be measured are stored redundantly in the same block of one memory, the distance calculator measures the distance to each of the multiple objects to be measured by referring to the multiple sampling data recorded in different blocks of other memories.

2. The distance measuring device according to claim 1, characterized in that the combination of the blocks is divided into patterns and the address of the memory in which the pulse data of the received light signal is stored is calculated.

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