Distance measuring device and distance measuring method
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- OMRON CORP
- Filing Date
- 2022-04-01
- Publication Date
- 2026-08-04
AI Technical Summary
【0026】 本発明によれば、TOF(Time of Flight)方式を用いた距離測定装置を用いて、より精度よく、対象物の位置を測定することが可能となる。
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention relates to a distance measuring device that measures the distance to an object using the TOF (Time Of Flight) method, and a distance measuring method.
Background Art
[0002] There is known a distance measuring device using the TOF (Time of Flight) method that measures the distance to an object that reflects light by using the time from when light is projected until the reflected light with respect to the light is received (see, for example, Patent Document 1). Then, by projecting laser light while rotating a laser light source around an axis in the vertical direction, laser light is projected in various directions on a horizontal plane, and by detecting the reflected light, a scanning type distance measuring device that detects the presence or intrusion of an object in a wide area around is known.
[0003] In these scanning type distance measuring devices, there are cases where laser light is projected through a window portion (window part) of a case in which a laser light source, a rotation mechanism, a light receiving element, etc. are stored, and the reflected light is received. In such a case, a part of the laser light projected from the laser light source is reflected by the window portion, and when the light receiving element detects the reflected light from the window portion, the accuracy of distance measurement to the object may decrease.
Prior Art Documents
Patent Documents
[0004]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0005] This invention has been made in view of the above circumstances, and its objective is to provide a technology that enables more accurate measurement of the position of an object using a distance measuring device employing the Time of Flight (TOF) method. [Means for solving the problem]
[0006] To achieve the aforementioned objectives, this disclosure adopts the following configuration: A light source that emits pulsed detection light, A light receiving unit receives reflected light from an object that detects the light and outputs a signal corresponding to the received light intensity. A distance calculation unit calculates the distance to the object based on the emission time of the detected light and the reception time of the reflected light obtained from the signal output by the light receiving unit, A distance measuring device comprising a window portion positioned between the light source and the object, and capable of transmitting the detected light, A peak value detection unit detects the peak value of the signal output by the light receiving unit, A peak width derivation unit derives a predetermined peak width or a value related to the peak width in time before and after the peak value of the signal output by the light receiving unit, based on the peak value detected by the peak value detection unit. A fall-end detection unit detects a predetermined fall-end time after the peak value of the signal output by the light-receiving unit, A light reception time calculation unit calculates the light reception time of the reflected light based on the peak width or a value related to the peak width derived by the peak width derivation unit and the fall time detected by the fall time detection unit. This distance measuring device is characterized by having the following features.
[0007] In this disclosure, as described above, the peak value detection unit in the distance measuring device detects the peak value of the signal output by the light receiving unit. Then, the peak width derivation unit derives the peak width of the peak related to the peak value or a value related to the peak width (hereinafter also referred to as "peak width, etc.") based on the peak value. In addition, in this disclosure, the fall time detection unit detects the fall time of the peak. Then, the light reception time calculation unit calculates the light reception time of the reflected light using the fall time of the peak and the peak width, etc. Note that the value related to the peak width mentioned above includes half the peak width, or a value obtained as a result of calculations such as multiplying the peak width by a coefficient or adding a constant to it.
[0008] In the distance measuring device described herein, the detection light emitted from the light source is reflected not only from the object but also from the window portion. The peak waveform of the received light intensity of the reflected light from the object is disturbed by the reflected light from the window portion, and as a result, the detection accuracy of the received light time of the reflected light from the object decreases. More specifically, since the window portion is located closer to the light source than the object, the waveform of the peak of the received light intensity of the reflected light from the object is disturbed, especially the waveform before the peak.
[0009] In contrast, this disclosure detects the peak value (intensity value) of the received intensity of reflected light from the object, and derives the peak width, etc., from this peak intensity value. Then, the reflected light reception time, which is the time of the peak of the received intensity of the reflected light from the object, is calculated from the fall time of the received intensity of the reflected light from the object and the peak width, etc. This makes it possible to determine the peak time of the reflected light intensity, i.e., the reflected light reception time, without using the rise time, etc., before the peak in the peak waveform of the received intensity of the reflected light. Therefore, the influence of reflected light from the window can be eliminated, and the reception time of the reflected light from the object can be determined with greater accuracy. As a result, it is possible to improve the accuracy of measuring the distance to the object.
[0010] Furthermore, this disclosure further includes a peak time detection unit that detects the peak time from a predetermined rise time and fall time at the peak of the signal output by the light receiving unit. If the peak time detected by the peak time detection unit is longer than a predetermined first threshold, the light reception time calculation unit may calculate the light reception time of the reflected light based on the peak time detected by the peak time detection unit.
[0011] As described above, in the distance measuring device according to this disclosure, the window is positioned between the light source and the object. Therefore, if the object is located at a sufficiently far distance from the window, the output signal of the light receiving unit due to reflected light from the window does not affect the output signal of the light receiving unit due to reflected light from the object. Accordingly, this disclosure further includes a peak time detection unit that detects the peak time from a predetermined rise time and fall time at the peak of the signal output by the light receiving unit. If the peak time detected by the peak time detection unit is longer than a predetermined first threshold, the light receiving time calculation unit calculates the light receiving time of the reflected light using the peak time detected by the peak time detection unit.
[0012] According to this, if the object is located sufficiently far from the window and the output signal of the light receiving unit due to reflected light from the window does not affect the output signal of the light receiving unit due to reflected light from the object, the method for determining the reception time of the reflected light can be changed. Specifically, instead of determining the reception time of the reflected light from the object using the peak width and fall time, the reception time of the reflected light from the object can be directly determined from the peak time detected by the peak time detection unit using the rise time and fall time.
[0013] As a result, the process of determining the reception time of reflected light from the peak width and fall time can be performed only when the influence of reflected light from the window area affects the measurement result, and In outdoor conditions, conventional distance measurement methods can be used. The predetermined first threshold is the peak time at which the peak time detection unit can determine that the output signal of the light receiving unit due to reflected light from the window does not affect the output signal of the light receiving unit due to reflected light from the object, if the peak time detected by the peak time detection unit is later than this threshold. This first threshold is determined in advance experimentally or theoretically based on calculations.
[0014] Furthermore, this disclosure further includes an output unit that outputs the distance to the object calculated by the distance calculation unit, If the peak value detected by the peak value detection unit is less than or equal to a predetermined second threshold, the output unit may choose not to output the distance to the object.
[0015] In distance measuring devices, for a single emission of detection light, a peak due to reflected light from the window and a peak due to reflected light from the object are detected separately. In such cases, since the reflectivity of the window is usually low, the peak due to reflected light from the window is often smaller than the peak due to reflected light from the object. Therefore, in this disclosure, if the peak value detected by the peak value detection unit is less than or equal to a predetermined second threshold, the peak is determined to be the peak due to reflected light from the window, and the output unit does not output the distance to the object.
[0016] This prevents the output unit from outputting the distance to an object even when there is no object, based on the reflected light from the window. Here, "the output unit does not output the distance to an object" means that the output signal from the light receiving unit based on the reflected light from the window is ignored, the time of reception of the reflected light is not calculated, the time of reception of the reflected light is calculated but the distance to the object is not calculated, and the distance to the object is calculated but not output.
[0017] In addition, in the present disclosure, the peak width derivation unit may derive, by reading from a table storing the relationship between the peak value and the peak width or a value related to the peak width, the peak width or a value related to the peak width corresponding to the peak value.
[0018] According to this, it is possible to derive the peak width or a value related to the peak width by using information measured or calculated in advance with high precision, and it becomes possible to obtain information such as the peak width more accurately or quickly.
[0019] In addition, in the present disclosure, the peak width may be the time difference between a predetermined rise time before the peak value and the fall time. Here, in a conventional distance measuring device, in many cases, the rise time and the fall time of the peak waveform of the reflected light from the object are measured, and the median value thereof is used as the peak time. Therefore, in the present disclosure, if the peak width is set as the time difference between the predetermined rise time and the fall time, the fall time without the influence of the reflected light from the window portion and the peak width obtained based on the relationship between the peak value and the peak width prepared in advance are used to calculate the peak time having the same definition as in the conventional case, and the light reception time of the reflected light can be calculated. For example, the rise time may be obtained by subtracting the peak width from the fall time, and the median value of the rise time and the fall time may be used as the peak time as in the conventional case, or the time obtained by subtracting half of the peak width from the fall time may be used as the peak time.
[0020] In addition, the present disclosure includes a light source that emits pulsed detection light, a light reception unit that receives the reflected light of the detection light from the object and outputs a signal according to the light reception intensity, a distance calculation unit that calculates the distance to the object based on the emission time of the detection light and the light reception time of the reflected light obtained from the signal output by the light reception unit, and a window unit that is disposed between the light source and the object and is capable of transmitting the detection light. The distance measurement method in the distance measuring device thus provided is A peak value detection step of detecting a peak value of a signal output by the light receiving unit; A peak width derivation step of deriving a predetermined peak width or a value related to the peak width before and after the peak value of the signal output by the light receiving unit in terms of time based on the peak value detected in the peak value detection step; A fall part detection step of detecting a predetermined fall time after the peak value of the signal output by the light receiving unit; A light reception time calculation step of calculating the light reception time of the reflected light based on the peak width or the value related to the peak width derived in the peak width derivation step and the fall time detected in the fall part detection step; A distance measurement method characterized by comprising the above steps may be provided.
[0021] In addition, the present disclosure includes a peak time detection step of detecting a peak time of a signal output by the light receiving unit; When the peak time detected in the peak time detection step is longer than a predetermined first threshold value, in the light reception time calculation step, the light reception time of the reflected light is calculated based on the peak time detected in the peak time detection step. The above distance measurement method may be provided.
[0022] In addition, the present disclosure further includes an output step of outputting the distance to the object calculated by the distance calculation unit; When the peak value detected in the peak value detection step is less than or equal to a predetermined second threshold value, in the output step, the distance to the object is not output. The above distance measurement method may be provided.
[0023] In addition, in the peak width derivation step of the present disclosure, a value related to the peak width or the peak width corresponding to the peak value is read from a table storing the relationship between the peak value and the peak width or the value related to the peak width, and is derived. The above distance measurement method may be provided.
[0024] Furthermore, the present disclosure may also describe the above-described distance measurement method, characterized in that the peak width is the time difference between a predetermined rise time and a predetermined fall time prior to the peak value.
[0025] Furthermore, each of the above configurations and processes can be combined with each other to constitute the present invention, provided that no technical inconsistencies arise. [Effects of the Invention]
[0026] According to the present invention, it is possible to measure the position of an object with greater accuracy using a distance measuring device that employs the Time of Flight (TOF) method. [Brief explanation of the drawing]
[0027] [Figure 1] This is a schematic diagram of a laser scanner according to an embodiment of the present invention. [Figure 2] This is a schematic diagram of the internal structure of a laser scanner according to an embodiment of the present invention. [Figure 3] This is a functional block diagram of the control unit according to an embodiment of the present invention. [Figure 4] This figure shows an example of the relationship between the signal intensity of reflected light and time according to an embodiment of the present invention. [Figure 5] This figure illustrates the effect of window reflected light on the signal intensity of the reflected light according to the present invention. [Figure 6] This figure illustrates a method for calculating peak time according to an embodiment of the present invention. [Figure 7] This figure shows an example of the relationship between peak intensity and pulse width according to an embodiment of the present invention. [Figure 8] This figure shows the types of relationships between the signal intensity of reflected light and distance according to embodiments of the present invention. [Figure 9] This is a flowchart of the distance measurement process according to an embodiment of the present invention. [Modes for carrying out the invention]
[0028] <Examples of application> As shown in Figure 1, a laser scanner 1, which is an example of an object to which the present invention is applied, detects when an obstacle such as a person (hereinafter also referred to as an object) approaches its vicinity. The side surface of the light-emitting / receiving unit 3 of the laser scanner 1 forms a window and is made of a material that can transmit detection light and reflected light from the object. From the light-emitting / receiving unit 3, pulsed detection light is emitted onto the scanning surface 3b toward the radially outward direction of the light-emitting / receiving unit 3. This detection light is emitted over a wide angular range while rotating in the circumferential direction of the light-emitting / receiving unit 3. When this rotating detection light is irradiated onto an object, the presence of the object and its distance from the laser scanner 1 are detected by detecting the reflected light.
[0029] As shown in Figure 2, the laser scanner 1 is equipped with a laser light source 33 and a mirror 32 as light sources that emit detection light. A rotary actuator 20 is coupled to the laser light source 33 and the mirror 32 via a shaft 31. This rotary actuator 20 rotates based on command signals from the control unit 22. As the rotary actuator 20 rotates, the laser light source 33 and the mirror 32 rotate around the rotation axis AX1. At that time, the laser light source 33 intermittently emits light, irradiating the scanning surface 3b with pulsed detection light L1 while rotating.
[0030] The reflected light, after being irradiated onto the target object ob and reflected back, passes through the window section 3a again and enters the interior of the light-emitting / receiving section 3, is reflected by the mirror 32, passes through the optical system 34, and is then received by the light-receiving element 35. The distance to the target object ob is calculated from the time of flight (TOF) from the time the laser light source 33 irradiates the detection light L1 until the reflected light L3 is detected.
[0031] Here, when pulsed detection light L1 is irradiated from the laser light source 33, a portion of it is reflected by the window portion 3a and becomes window-reflected light L2, which is detected by the light-receiving element 35. However, the detection of this window-reflected light L2 may reduce the accuracy of distance measurement to the object ob.
[0032] As shown in Figure 5, when the distance to the object ob is short, the output signal of the light-receiving element 35 due to reflected light L3 from the object ob (dotted line) and the output signal due to window reflected light L2 (dashed line) may overlap in time. In this case, the output signal of the light-receiving element 35 becomes the sum of the output signals of reflected light L3 from the object ob and window reflected light L2, and the rise time changes from t1 to t1'. As a result, the detected peak time is also shifted forward from tp to tp', which reduces the detection accuracy of the peak time of reflected light L3 from the object ob.
[0033] In contrast, in this embodiment, t2 is detected as the falling edge time of the output signal of the photodetector 35 due to reflected light, and the peak value of the intensity of the output signal of the photodetector 35 is determined. The relationship between the peak value and peak width of the output signal of the photodetector 35 when there is no window reflected light L2 is stored in advance as a table, and the peak width W is determined from the peak value IP. The peak time tp2 is calculated by performing the calculation tp2 = t2 - W / 2 from the falling edge t2 and the peak width W. This makes it possible to eliminate the influence of window reflected light L2.
[0034] Embodiments of the present invention will be described below with reference to the drawings. However, each of the following examples is not specified. Unless otherwise specified, the listed components are not intended to limit the scope of this invention to those components alone.
[0035] <Examples> Figure 1 shows a laser scanner 1, which is an example of an object to which the invention disclosed herein applies. Figure 1(a) is a front view of the laser scanner 1, and Figure 1(b) is a top view. The laser scanner 1 is a device for safety control, such as detecting when an obstacle (hereinafter also referred to as an object) such as a person approaches and stopping dangerous equipment when it gets too close. As shown in Figure 1(b), the laser scanner 1 has a sensor unit 2 and an I / O unit 4, and becomes operational when the I / O unit 4 is connected to the sensor unit 2. The I / O unit 4 is provided with an information terminal 4a for sending and receiving control signals and detection signals to and from the outside, and a power terminal 4b for power supply. The distance to the object measured by the laser scanner 1 is output through the information terminal 4a.
[0036] The sensor unit 2 is equipped with a light-emitting and receiving unit 3. The light-emitting and receiving unit 3 has a roughly cylindrical shape, and its sides have a tapered shape that decreases in diameter towards the bottom. The sides of the light-emitting and receiving unit 3 also form a window portion 3a, which is made of a material that can transmit detection light and reflected light from the object. As shown in Figure 1(a), detection light is emitted from the light-emitting and receiving unit 3 toward the radially outward direction of the unit on the scanning surface 3b, which is a horizontal plane. As shown in Figure 1(b), this detection light is emitted at predetermined angles over a wide angular range while rotating in the circumferential direction of the light-emitting and receiving unit 3. When this rotating detection light irradiates an object, the presence of the object and its distance from the laser scanner 1 are detected by detecting the reflected light. Strictly speaking, this distance from the laser scanner 1 may be the distance from the rotation axis AX1 or the distance from the laser light source 33.
[0037] Figure 2 shows a schematic diagram of the internal structure of the laser scanner 1. Inside the laser scanner 1 is a laser light source 33, which serves as a light source for emitting detection light. A mirror 32 is attached to the laser light source 33 to change the direction of reflected light L3 from the object ob. A rotary actuator 20, such as a stepping motor, is connected to the laser light source 33 and the mirror 32 via a shaft 31. This rotary actuator 20 rotates based on command signals from the measurement control unit 22a (described later) in the control unit 22. This control unit 22 has a hardware configuration equivalent to or partially that of a normal PC, which includes a calculation unit, a storage unit, a communication unit (none of which are shown), etc., and may be located inside the sensor unit 2 or configured using an external PC.
[0038] As the rotary actuator 20 rotates, the laser light source 33 and mirror 32 rotate around the rotation axis AX1. When the laser light source 33 emits light, it is possible to irradiate the scanning surface 3b with a pulsed detection light L1 while it rotates. Furthermore, the shaft 31 of the rotary actuator 20 is equipped with an encoder 21, which measures the rotation angle and transmits it to the control unit 22. This encoder 21 makes it possible to obtain information about the direction of the object ob, and also allows the laser light source 33 and mirror 32 to rotate at a desired constant speed.
[0039] The reflected light, after being irradiated onto the target object ob and reflected back, passes through the window section 3a again and enters the interior of the light-emitting / receiving section 3, is reflected by the mirror 32, passes through the optical system 34, and is then received by the light-receiving element 35. In this light-receiving element 35, the intensity of the reflected light is converted into an electrical signal and transmitted to the measurement control unit 22a (described later) in the control unit 22. This control unit 22 measures the time of flight (TOF) from the time the laser light source 3 emits pulsed light L1 until the reflected light L3 is detected, and calculates the distance to the target object ob from this time of flight. The starting point of the time of flight (emission time) is, as described above, the time the laser light source 3 emits pulsed light. The time taken for the laser light source 3 to emit light, or the time taken for the input signal for emission to be applied to the laser light source 3, may be detected optically or electrically. Alternatively, a simulated object may be placed inside the device, and the time taken for the reflected light emitted from the laser light source 3 and reflected from the simulated object to be received may be used as the emission time. By doing so, error factors such as delays in the drive circuit of the laser light source 3 can be corrected.
[0040] Figure 3 shows a detailed functional block diagram of the control unit 22. The control unit 22 is equipped with a measurement control unit 22a that issues control commands for scanning the transmitted and detected light and receives the output signal from the light receiving element 35. It is also equipped with a distance calculation unit 22b that calculates the distance to the object ob based on the output signal from the light receiving element 35, and an output unit 22c that outputs the distance calculated by the distance calculation unit 22b.
[0041] Furthermore, the distance calculation unit 22b is provided with a peak value detection unit 220 that detects the peak value of the output signal of the light-receiving element 35, and a peak width derivation unit 221 that derives the peak width W of the output signal of the light-receiving element 35 from the peak value of the output signal of the light-receiving element 35. In addition, a fall time detection unit 222 that detects the fall time of the peak of the output signal of the light-receiving element 35 is provided, and a light-receiving time calculation unit 224 that calculates the light-receiving time of reflected light based on the above-mentioned peak width W and the fall time. Furthermore, separate from the above method, a peak time detection unit 223 is provided that detects the time of the peak from the rise time and fall time of the peak.
[0042] Here, as described above, when pulsed detection light L1 is emitted from the laser light source 33, a portion of it is reflected by the window portion 3a and becomes window reflected light L2, which is detected by the light receiving element 35. The detection of this window reflected light L2 may reduce the accuracy of distance measurement to the object ob. This point will be explained below.
[0043] As described above, in the laser scanner 1, pulsed detection light L1 is emitted from the laser light source 33, reflected light L3 from the object ob is detected, and the distance to the object ob is calculated by measuring the time between these two points. Therefore, it is necessary to accurately detect the time at which the reflected light L3 is received by the photodetector 35. In the laser scanner 1, the time at which the pulsed reflected light L3 is received is obtained by detecting the time tp at which the peak of the output signal from the photodetector 35 is detected, as shown in Figure 4. In practice, the time at which the output signal is at a fixed ratio (e.g., half value) of the peak value before and after the peak of the output signal from the photodetector 35 is determined as the rise time t1 and fall time t2, respectively, and the peak time tp is set to the midpoint between the rise time t1 and the fall time t2, and the peak time tp is calculated as the time at which the reflected light L3 is received.
[0044] Figure 5 shows the effect of window reflected light L2. In Figure 5, the signal strength due to reflected light L3 from the object ob is shown by a dashed line, and the signal strength due to window reflected light L2 is shown by a dashed line. The signal strength of the sum of reflected light L3 and window reflected light L2 is shown by a solid line. As shown in Figure 5, when the distance to the object ob is short, the output signal from reflected light L3 from the object ob and the output signal from window reflected light L2 may overlap in time. In that case, the output signal of the photodetector 35 becomes the sum of the output signals of reflected light L3 from the object ob and window reflected light L2, and the rising edge waveform changes in particular, and the rising edge time changes from t1 to t1'. As a result, the peak time is also shifted forward from tp to tp' when calculated, so the detection accuracy of the peak time of the output signal from reflected light L3 from the object ob decreases.
[0045] In contrast, in this embodiment, as shown in Figure 6, we focused on the fact that, in the sum of the output signals from reflected light L3 from the object ob and window reflected light L2, the peak time changes significantly compared to the output signal from reflected light L3, but the peak intensity changes almost none. Then, for the reflected light, t2 is detected as the falling time of the output signal of the photodetector 35, and the peak intensity IP of the output signal of the photodetector 35 is determined. The relationship between the peak intensity IP and peak width W of the detected signal of the photodetector 35 is stored in advance as a table, and the peak The peak width W is determined from the intensity IP, and the peak time tp2 is calculated by performing the following calculation: tp2 = t2 - W / 2 using the fall time t2 and the peak width W. This makes it possible to eliminate the influence of window reflected light L2 on the output signal due to reflected light L3 from the object ob. The process for calculating the peak time tp2 shown in Figure 6 is also referred to as the peak intensity reference process. Furthermore, the table storing the relationship between the peak intensity IP and peak width W of the detection signal of the photodetector 35 is also referred to as the peak intensity / peak width relationship table.
[0046] Figure 7 shows an example of the relationship between peak intensity IP and peak width W. In the region where the peak intensity IP is relatively small, the peak width W does not change much even if the peak intensity IP changes. However, in the region where the peak intensity IP is larger than a certain level, the peak width W increases sharply as the peak intensity IP increases. In this embodiment, this relationship between peak intensity IP and peak width W is put into a table and stored in the memory unit (not shown) of the control unit 22. However, in this disclosure, it is not necessarily required to put the relationship between peak intensity IP and peak width W into a table and store it. The curve shown in Figure 7 may be approximated and defined using a polynomial, exponential function, etc., and the peak width W may be calculated from the peak intensity IP using the defined approximation formula.
[0047] Figure 8 shows the types of relationships between the window reflected light L2, the characteristics of the reflected light L3 from the object ob, and the influence of the reflected light L3 on the output signal from the window reflected light L2. In Figure 8, the horizontal axis is the distance from the rotation axis AX1 of the laser scanner 1, not time. In this disclosure, for example, the distance to the object ob is calculated by multiplying the speed of light by half the flight time from the emission of the pulsed detection light L1 to the reception of the reflected light L3, so a similar explanation is possible even if time is converted to distance. Figure 8(a) shows the case where the intensity of the output signal due to the window reflected light L2 is low and the object ob is sufficiently far away. In this case, the window reflected light L2 is not detected because the intensity of the output signal is low in the first place, and it does not affect the output signal due to the reflected light L3 from the object ob, so the window reflected light L2 is ignored.
[0048] Next, Figure 8(b) shows the case where the intensity of the output signal from the window reflected light L2 is relatively high and the object ob is sufficiently far away. In this case, the window reflected light L2 is detected by the photodetector 35, but because the output signal from the window reflected light L2 and the output signal from the reflected light L3 from the object ob are sufficiently far apart, the output signal from the window reflected light L2 does not affect the output signal from the reflected light L3 from the object ob. Figure 8(c) shows the case where the intensity of the output signal from the window reflected light L2 is somewhat high and the object ob is close. In this case, the output signal from the window reflected light L2 partially overlaps with the output signal from the reflected light L3 from the object ob, which affects the detection of the peak position of the output signal from the reflected light L3 from the object ob. In this case, peak intensity reference processing as explained using Figure 6 is necessary.
[0049] Figure 9 shows a flowchart of the process related to measuring the distance of the object ob in this embodiment. This flowchart represents the flow for one scan of the laser scanner 1, which is operated by executing a program stored in the memory unit (not shown) of the control unit 22. By repeatedly operating this flowchart, it is possible to constantly detect the approach of the object ob.
[0050] When this flow is executed, first, in step S101, a scan is started based on a command from the measurement control unit 22a of the control unit 22. This starts a scan in which the laser scanner 1 rotates the laser inspection light L1 on the scanning surface by a predetermined angle (for example, 270 degrees) around the rotation axis AX1. In step S102, pulsed detection light L1 is emitted from the laser light source 33 and light is projected. Then, in step S103, the reflected light reflected by the object ob or the window part 3a is received by the light receiving element 35.
[0051] Next, in step S104, the control unit 22 samples the output signal of the light-receiving element 35 for each distance during the time period from light emission to light reception, and converts it into digital data. More specifically, the relationship between the output signal from the light-receiving element 35 and time is proportionally converted into the relationship between the output signal and distance, and then converted into digital data. Then, in step S105, the peak time detection unit 223 detects the rising edge position P1 and falling edge position P2 of the obtained output signal, and calculates the peak position PP1.
[0052] In step S106, it is determined whether the distance to the peak position PP1 is greater than or equal to a predetermined first threshold. If it is determined that the distance to the peak position PP1 is greater than the first threshold (YES in step S106), the object ob is sufficiently far away, and therefore the peak of the output signal at peak position PP1 is not the peak of the output signal due to window reflected light L2 or the peak of the output signal due to reflected light L3 influenced by window reflected light L2, so the process proceeds to step S108. On the other hand, if it is determined in step S106 that the distance to the peak position PP1 is less than or equal to the first threshold (NO in step S106), it is determined that the peak of the output signal at peak position PP1 may be the peak of the output signal due to window reflected light L2 or the peak of the output signal due to reflected light L3 influenced by window reflected light L2, so the process proceeds to step S107.
[0053] In step S108, the distance to the peak position PP1 is used as the distance to the object ob. On the other hand, in step S107, it is determined whether the peak intensity of the output signal at peak position PP1 is greater than the second threshold. If it is determined that the peak intensity of the output signal at peak position PP1 is greater than the second threshold (YES in step S107), the obtained peak is determined to be the peak of the output signal due to reflected light L3 from the object ob, which is affected by the window reflected light L2, and the process proceeds to step S109. On the other hand, if it is determined in step S107 that the peak intensity of the output signal at peak position PP1 is less than or equal to the second threshold (NO in step S107), the obtained peak is determined to be the peak of the output signal due to the window reflected light L2, and the process proceeds to step S110.
[0054] In step S109, the peak intensity criterion processing described above is performed. More specifically, the peak value detection unit 220 detects the intensity of the output signal at the peak (peak intensity IP), and the peak width derivation unit 221 reads out the value of the peak width W as time corresponding to the peak intensity IP from the peak intensity peak width relationship table described above. In addition, the fall time detection unit 222 detects the fall time t2 at the peak. Then, the peak width W as time is converted to a peak width W2 as distance, and the fall time t2 at the peak is converted to a fall position P2 as distance.
[0055] Then, based on the peak width W2 value and the falling edge position P2, the peak position PP2 is calculated using the formula PP2 = P2 - W2 / 2 and adopted as the distance to the object ob. Meanwhile, in step S110, the obtained peak is judged to be the peak of the output signal due to the window reflected light L2 and is ignored. When the processing of steps S108, S109, or S110 is completed, the process proceeds to step S111. In step S111, it is determined whether the acquisition of the distances of all peaks obtained by the projection in step S102 and the reception in step S103 has been completed. If it is determined that the acquisition of the distances of all peaks (all object obs) has been completed, the process proceeds to step S112. On the other hand, if it is determined that the acquisition of the distances of all peaks has not been completed, the process proceeds to step S106 to acquire the distance of the next peak.
[0056] In step S112, it is determined whether or not the entire scan angle has been completed. In this embodiment, the laser scanner 1 performs light emission and reception for each scan angle θ, and since light emission and reception occur approximately 500 to 5000 times in one scan, the distance to the object ob is obtained for all scan angles θ. If it is determined in step S112 that the acquisition of the distance to the object ob for all scan angles has been completed, the process proceeds to step S113, and one scan is completed. On the other hand, if it is determined that all scan angles have not been completed, the process returns to step S102, the detection light L1 is emitted again from the laser light source 33, and the process from step S102 onwards is repeated.
[0057] In the flow chart of Figure 9, during the processing flow related to distance measurement, time information is converted into distance information, and both peak positions PP1 and PP2 are calculated as the positions of the object ob. However, in step S108, the peak time tp1 of the time information is calculated, and in step S109, the peak time tp2 of the time information is calculated, and the light reception time calculation unit 224 may calculate the light reception time at the light receiving element 35. Then, after the processing for one scan is completed in S113, the peak times tp1 and tp2 are converted into distance information and calculated as the positions of the object ob. In any case, the results of the flow chart of Figure 9 are output by the output unit 22c as the calculation results by the distance calculation unit 22b.
[0058] In the processing flow for distance measurement shown in Figure 9, if the peak distance is greater than the first threshold in S106, the peak position PP1 detected by the peak time detection unit 223 is used in S108. However, it is also acceptable to use the peak position PP2 calculated by the peak intensity criterion processing, regardless of the peak distance.
[0059] In the above embodiment, the peak intensity IP was obtained by sampling the output signal of the photodetector 35, and the fall time t2 was determined as the time after the peak of the output signal of the photodetector 35 when the output signal becomes a fixed ratio (e.g., half value) of the peak intensity IP value. In this disclosure, the fall time t2 (fall position P2) may also be obtained by taking the second derivative of the curve of the output signal of the photodetector 35. Alternatively, the peak intensity IP and fall time t2 (fall position P2) may be obtained by model fitting from multiple data on the falling side of the peak in the curve of the output signal of the photodetector 35. For example, the peak intensity IP and fall time t2 (fall position P2) can also be obtained by model fitting a quadratic or cubic function from the data of three points on the falling side of the peak. Furthermore, in this disclosure, the peak time tp2 (peak position PP2) itself may be obtained by model fitting from multiple data on the falling side of the peak in the curve of the output signal of the photodetector 35.
[0060] In order to allow for comparison between the constituent elements of the present invention and the configurations of the embodiments, the constituent elements of the present invention are noted below with reference numerals in the drawings. <Note 1> A light source (33) that emits pulsed detection light, A light receiving unit (35) receives the reflected light from the object that detects the light and outputs a signal corresponding to the received light intensity, A distance calculation unit (22b) calculates the distance to the object based on the emission time of the detected light and the reception time of the reflected light obtained from the signal output by the light receiving unit, A distance measuring device (1) comprising a window portion (3a) positioned between the light source and the object, which is capable of transmitting the detected light, A peak value detection unit (220) detects the peak value of the signal output by the light receiving unit, A peak width derivation unit (221) derives a predetermined peak width or a value related to the peak width in time before and after the peak value of the signal output by the light receiving unit, based on the peak value detected by the peak value detection unit, The light receiving unit detects a predetermined falling time after the peak value of the signal it outputs. The decrease time detection unit (222) and A light reception time calculation unit (224) calculates the light reception time of the reflected light based on the peak width or a value related to the peak width derived by the peak width derivation unit and the fall time detected by the fall time detection unit, A distance measuring device (1) characterized by comprising the following: <Note 6> A light source (33) that emits pulsed detection light, A light receiving unit (35) receives the reflected light from the object that detects the light and outputs a signal corresponding to the received light intensity, A distance calculation unit (22b) calculates the distance to the object based on the emission time of the detected light and the reception time of the reflected light obtained from the signal output by the light receiving unit, A distance measuring method in a distance measuring device (1) comprising a window portion (3a) positioned between the light source and the object, which is capable of transmitting the detected light, A peak value detection step (step S109) in which the peak value of the signal output by the light receiving unit is detected, A peak width derivation step (step S109) is performed to derive a predetermined peak width or a value related to the peak width in the time period before and after the peak value of the signal output by the light receiving unit, based on the peak value detected in the peak value detection step, A fall time detection step (step S109) is performed to detect a predetermined fall time after the peak value of the signal output by the light receiving unit, A light reception time calculation step (step S109) calculates the light reception time of the reflected light using the peak width or a value related to the peak width derived in the peak width derivation step and the fall time detected in the fall time detection step, A distance measurement method characterized by having the following features. [Explanation of symbols]
[0061] 1. Laser scanner 2. Sensor Unit 3...Light emitter / receiver section 4. I / O Units 20... Rotary actuator 21... Encoder 22.. Control Unit 22a...Measurement and Control Unit 22b...Distance calculation section 22c... Output section 220...Peak value detection unit 221...Peak width derivation section 222... Falling edge time detection unit 223...Peak Time Detection Unit 224... Light reception time calculation unit
Claims
1. A light source that emits pulsed detection light, A light receiving unit receives reflected light from an object that detects the light and outputs a signal corresponding to the received light intensity. A distance calculation unit calculates the distance to the object based on the emission time of the detected light and the reception time of the reflected light obtained from the signal output by the light receiving unit, A distance measuring device comprising a window portion positioned between the light source and the object, and capable of transmitting the detected light, A peak value detection unit detects the peak value of the signal output by the light receiving unit, A peak width derivation unit derives a predetermined peak width or a value related to the peak width in time before and after the peak value of the signal output by the light receiving unit, based on the peak value detected by the peak value detection unit. A fall time detection unit detects a predetermined fall time after the peak value of the signal output by the light receiving unit, A light reception time calculation unit calculates the light reception time of the reflected light based on the peak width or a value related to the peak width derived by the peak width derivation unit and the fall time detected by the fall time detection unit. Equipped with, The light receiving unit further comprises a peak time detection unit that detects the peak time from a predetermined rise time and fall time at the peak of the signal output by the light receiving unit, If the peak time detected by the peak time detection unit is longer than a predetermined first threshold, the light reception time calculation unit calculates the light reception time of the reflected light based on the peak time detected by the peak time detection unit. The window portion is composed of a substantially cylindrical side surface having a tapered shape that decreases in diameter towards the bottom. A distance measuring device characterized in that, due to the rotation of a rotary actuator, the detection light is emitted while rotating in the circumferential direction of the window portion.
2. The system further includes an output unit that outputs the distance to the object calculated by the distance calculation unit, The distance measuring device according to claim 1, characterized in that if the peak value detected by the peak value detection unit is less than or equal to a predetermined second threshold, the output unit does not output the distance to the object.
3. The distance measuring device according to claim 1, characterized in that the peak width derivation unit reads and derives a peak width or a value related to the peak width corresponding to the peak value from a table that stores the relationship between the peak value and the peak width or a value related to the peak width.
4. The distance measuring device according to claim 1, characterized in that the peak width is the time difference between a predetermined rise time and a predetermined fall time prior to the peak value.
5. A light source that emits pulsed detection light, A light receiving unit receives reflected light from an object that detects the light and outputs a signal corresponding to the received light intensity. A distance calculation unit calculates the distance to the object based on the emission time of the detected light and the reception time of the reflected light obtained from the signal output by the light receiving unit, A distance measuring method in a distance measuring device comprising a window portion disposed between the light source and the object, and capable of transmitting the detected light, A peak value detection step for detecting the peak value of the signal output by the light receiving unit, A peak width derivation step, based on the peak value detected in the peak value detection step, derives a predetermined peak width or a value related to the peak width in the time period before and after the peak value of the signal output by the light receiving unit, A fall time detection step for detecting a predetermined fall time after the peak value of the signal output by the light receiving unit, A light reception time calculation step calculates the light reception time of the reflected light using the peak width or a value related to the peak width derived in the peak width derivation step and the fall time detected in the fall time detection step. It has, The system further includes a peak time detection step that detects the peak time from a predetermined rise time and fall time at the peak of the signal output by the light receiving unit, If the peak time detected in the peak time detection step is longer than a predetermined first threshold, the light reception time calculation step calculates the light reception time of the reflected light based on the peak time detected in the peak time detection step. The window portion is composed of a substantially cylindrical side surface having a tapered shape that decreases in diameter towards the bottom. A distance measurement method characterized in that, due to the rotation of a rotary actuator, the detection light is emitted while rotating in the circumferential direction of the window portion.