JP2004309440A - Device for detecting center of beam - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device for detecting the center of a light (laser) beam, which can accurately detect the center of the beam, even when there is widening of the beam. <P>SOLUTION: In the device, a photodetector section 31 where 50 photodetectors are arranged in a direction 4 (Fig.1) in which a level measurement is carried out, receives the laser beam from a rotating laser level 1 (Fig.1), and 50 received signals are input to a microprocessor 46 in parallel via respective 50 comparators 44. The received signals, having a signal level higher than the decision threshold are input to the microprocessor 46 as H-level signals. The microprocessor 46 calculates a photodetector position as the center of a beam Bc, which represents the middle of element numbers corresponding to the upper and the lower ends of the input signals. When the laser beam is to be received by all the photodetectors on the photodetector section 31, the microprocessor 46 changes the decision threshold of the comparators 44 so as to be raised by each prescribed value X. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a detection device that detects the center of an emitted light beam.
[0002]
[Prior art]
2. Description of the Related Art In the field of surveying, a level detecting device that receives a scanning laser beam and detects a scanning position thereof is known (see Patent Document 1). The level detection device receives light (scanning laser light) from a rotating laser level that emits a rotating laser beam, and detects a level (high level) in a direction substantially perpendicular to a plane formed by the laser beam. Specifically, the laser beam is received, the center position of the received beam is detected, and the level of the light surface generated by the trajectory of the laser beam is obtained based on the detected position. Since the laser beam usually has a beam spread, the center in the thickness direction of the surface generated by the beam trajectory is detected. In the device of Patent Document 1, a signal proportional to the area of the light receiving element hit by the laser beam is output from the light receiving unit, and the center position of the laser beam is calculated by processing this signal.
[0003]
[Patent Document 1]
JP-A-7-270160
[Problems to be solved by the invention]
Generally, a laser beam emitted from a rotating laser level has a larger beam spread as the distance from the laser level increases. Therefore, when the distance between the rotating laser level and the level detecting device is long (for example, several hundred meters), all of the light receiving elements of the level detecting device are included in the laser beam width. The apparatus disclosed in Patent Document 1 determines the center position on the assumption that there is an area where the laser beam hits the light receiving element and an area where the laser beam does not hit the light receiving element. Can not.
[0005]
SUMMARY OF THE INVENTION The present invention provides a beam center detecting device that correctly detects the center of a light (laser) beam even when the light beam spreads.
[0006]
[Means for Solving the Problems]
The present invention is applied to a beam center detection device that detects the center of a light beam. A light receiving unit having a sensor array in which a plurality of sensors are arranged in one direction; and a determining unit for determining whether a light receiving signal output from the light receiving unit corresponding to the plurality of sensors is equal to or greater than a determination threshold, At least two light reception signals corresponding to the two sensors located at both ends of the sensor row are less than the determination threshold, and at least one of the light reception signals corresponding to other sensors except the two sensors located at both ends is equal to or greater than the determination threshold, Threshold changing means for changing the determination threshold so as to be determined by the determination means, and center detection means for detecting the center based on the array position of the sensor corresponding to the light receiving signal determined to be equal to or greater than the determination threshold by the determination means. It is characterized by having.
The determination means may be constituted by a comparison circuit, and in this case, the threshold value changing means may be constituted so as to change the comparison reference signal level of the comparison circuit.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings by taking as an example a displacement surveying system using a rotating laser level and a level detector used for surveying.
FIG. 1 is an overall configuration diagram of a displacement measurement system using a beam center detection device according to an embodiment of the present invention. In FIG. 1, the displacement measurement system includes a rotating laser level 1 and a beam center detecting device 3. The rotating laser level 1 includes a laser light source unit that emits a laser beam in a horizontal direction. The laser light source unit is configured to be rotatable about a vertical axis as a rotation axis, and its rotation speed is, for example, 600 rpm (= 10 rpm). A laser light source or a part of an optical system for projecting a laser emits a laser beam while rotating, so that the trajectory 11 of the laser beam from the rotating laser level 1 forms a light plane 2.
[0008]
The beam center detecting device 3 receives a laser beam from the rotating laser level 1 and detects the center of the beam in the vertical direction. Since the laser beam is emitted while the rotating laser level 1 is rotating at 10 rps, the beam center detecting device 3 receives the laser beam every 0.1 sec. The beam center detecting device 3 is arranged in a direction perpendicular to the light plane 2 and measures the level (level height) of the light plane 2 in the vertical direction. In FIG. 1, the level measurement direction 4 corresponds to the vertical direction.
[0009]
FIG. 2 is an enlarged view of the beam center detecting device 3 when the distance between the rotating laser level 1 and the beam center detecting device 3 is short (for example, 10 m) and the beam spread at the position of the beam center detecting device 3 is not large. It is. 2, the beam center detecting device 3 includes a light receiving element unit 31, a measurement result display unit 32, and various switches 33. The light receiving element unit 31 is configured to have a light receiving surface that is longer in the vertical direction than in the horizontal direction in FIG. 2, corresponding to the level measurement direction 4 in FIG. Since the beam spread is not large, the width of the trajectory 11A of the rotating laser beam is narrower than the vertical light receiving range of the light receiving element unit 31. Therefore, each of the upper end and the lower end of the trajectory 11A exists within the light receiving range of the light receiving element unit 31.
[0010]
The measurement result display unit 32 displays a measurement result such as the center position of the laser beam received by the light receiving element unit 31. The various switches 33 are operation members for performing power ON / OFF of the beam center detection device 3, measurement accuracy setting operation, and the like.
[0011]
The operation of detecting the center position of the laser beam will be described with reference to the block diagram of the beam center detecting device 3 (FIG. 3). The light receiving element section 31 is configured by a light receiving element group in which N light receiving elements such as photodiodes are arranged at predetermined intervals (for example, at a pitch of 1 mm). The arrangement direction of the light receiving elements corresponds to the level measurement direction 4 (FIG. 1). In FIG. 1, light receiving element No. The light receiving element Nos. N are arranged. Each light receiving element of the light receiving element section 31 is configured to individually output a light receiving signal (photocurrent) when receiving a laser beam.
[0012]
The light receiving signal from each light receiving element is converted into a voltage signal by the load resistor 41. This voltage signal is input to the amplifier 43 after the DC component is removed by the capacitor 42. The capacitance of the capacitor 42 is set in advance so as to pass the above-described light receiving signal at intervals of 0.1 sec (that is, a frequency of 10 Hz) and block low-frequency components having a frequency of less than 10 Hz. The amplifier 43 amplifies the input light receiving signal and outputs the amplified light receiving signal to the comparator 44.
[0013]
The comparator 44 outputs an H level signal when the input signal voltage is higher than the determination threshold, and outputs an L level signal when the input signal voltage is equal to or lower than the determination threshold. The determination threshold is set by the microprocessor 46. That is, the microprocessor 46 sets data indicating the determination threshold, and the D / A converter 51 generates a voltage signal according to the set data. The comparator 44 uses the voltage signal generated by the D / A converter 51 as a comparison signal (determination threshold). By providing the comparator 44, erroneous detection due to disturbance light, noise, or the like can be avoided.
[0014]
Although not shown in FIG. 3, N load resistors 41, capacitors 42, amplifiers 43, and comparators 44 are provided for each light receiving element. The amplification factors of the N amplifiers 43 are respectively adjusted such that when the light of the same intensity is incident on each light receiving element, the signal level output from each amplifier matches. The comparison signal from the D / A converter 51 is commonly provided to the N comparators 44.
[0015]
Output signals (light receiving signals) of the N comparators 44 are input to the microprocessor 46 in parallel. The microprocessor 46 constantly monitors the light receiving signal while the power switch of the beam center detecting device 3 is ON. The microprocessor 46 determines the position of the light receiving element located at the center of the array among the plurality of light receiving elements corresponding to the plurality of comparators 44 that output the H-level signal as the center position of the laser beam received by the light receiving element unit 31. And
[0016]
For example, when the distance between the rotating laser level 1 and the beam center detecting device 3 is 10 m and the number N of light receiving elements of the light receiving element unit 31 is 50, the above-described determination threshold is set to a high level signal by receiving a laser beam. It is preferable that the number of comparators 44 to be output is set to be about ten. That is, the width of the trajectory 11A of the laser beam corresponds to 10 light receiving elements.
[0017]
FIG. 4 is a diagram illustrating a relationship between the light receiving element group of the light receiving element unit 31, the output signal distribution curve 61 of the amplifier 43, and the determination threshold (reference level 62A) of the comparator 44. Generally, the laser beam emitted from the rotating laser level 1 has the maximum optical power at the center of the beam, and the optical power decreases as approaching the periphery of the beam. Accordingly, the output signal distribution curve 61 of the amplifier 43 becomes maximum at the point P corresponding to the center Bc of the laser beam, and decreases as the distance from the beam center Bc increases and decreases. The signal whose H level is input to the microprocessor 46 is a light receiving signal corresponding to a portion of the output signal distribution curve 61 that exceeds the reference level 62A. In FIG. 4, the light receiving element corresponding to the light receiving signal whose H level is input to the microprocessor 46 is shown in black. The microprocessor 46 regards the black portion of the light receiving element 31 as the laser beam width, and calculates the center position of the laser beam from the upper end position and the lower end position.
[0018]
When the microprocessor 46 outputs an instruction to display the calculation result on the liquid crystal display unit 47, the measurement result is displayed on the measurement result display unit 32 (FIG. 2). As the measurement result, for example, an arrow mark indicating the direction in which the center of the beam is located is displayed. In addition to the arrow mark, a display for changing a display color or a blinking speed may be performed. The external output communication line 48 is used to send a signal indicating a measurement result to an external device.
[0019]
FIG. 5 is an enlarged view of the beam center detecting device 3 when the distance between the rotating laser level 1 and the beam center detecting device 3 is long (for example, 500 m) and the beam spread at the position of the beam center detecting device 3 is large. is there. In FIG. 5, since the beam spread is large, the width of the trajectory 11B of the rotating laser beam is wider than the vertical light receiving range of the light receiving element unit 31. Therefore, each of the upper end and the lower end of the trajectory 11B is outside the light receiving range of the light receiving element unit 31, and the laser beam is received by all the light receiving elements of the light receiving element unit 31.
[0020]
Conventionally, when the spread of the laser beam is larger than the light receiving element portion 31, the beam center cannot be detected. The present invention is characterized by the operation when the beam spread occurs as described above.
[0021]
FIG. 6 is a diagram illustrating a relationship between the light receiving element group of the light receiving element unit 31 when the beam spread is large, the output signal distribution curve 66 of the amplifier 43, and the determination threshold (reference level 62A) of the comparator 44. Since the laser beam is received by all of the light receiving elements of the light receiving element section 31, the entire output signal distribution curve 66 exceeds the reference level 62A. In such a case, the microprocessor 46 changes the determination threshold of the comparator 44 to a higher value.
[0022]
FIG. 7 is a diagram showing the relationship between the light receiving element group of the light receiving element unit 31 after the change of the determination threshold, the output signal distribution curve 66 of the amplifier 43, and the determination threshold (reference level 62B) of the comparator 44. A light receiving signal corresponding to a portion exceeding the reference level 62B in the output signal distribution curve 66 is input to the microprocessor 46 as an H level. The microprocessor 46 regards the black portion of the light receiving element 31 as the laser beam width, and calculates the center position of the laser beam from the upper end position and the lower end position.
[0023]
The flow of the process of calculating the beam center in the beam center detecting device 3 described above will be described with reference to the flowchart of FIG. The processing shown in FIG. 8 is repeatedly performed by the microprocessor 46 while the power of the beam center detecting device 3 is ON.
[0024]
In step S11 of FIG. 8, the microprocessor 46 sets a determination threshold value for the comparator 44, and proceeds to step S12. When the microprocessor 46 outputs data indicating the determination threshold to the D / A converter 51, the D / A converter 51 outputs a comparison signal corresponding to the data. When the previous determination threshold value is stored in the microprocessor 46, the stored determination threshold value is used. If the previous determination threshold value is not stored in the microprocessor 46 immediately after the power is turned on, a predetermined initial value is used. The initial value is a value corresponding to the reference level 62A.
[0025]
In step S12, the microprocessor 46 determines whether or not the light receiving signals input from the N comparators 44 include an H level signal. The microprocessor 46 makes an affirmative decision in step S12 when an H-level signal is included and proceeds to step S13, and makes a negative decision in step S12 when an H-level signal is not included, and performs the processing shown in FIG. To end. The case where the determination in step S12 is negative is a case where the laser beam from the rotating laser level 1 does not hit the light receiving element unit 31 of the beam center detecting device 3.
[0026]
In step S13, the microprocessor 46 determines whether all of the light receiving signals input from the N comparators 44 are at the H level. The microprocessor 46 makes an affirmative decision in step S13 when all are H-level signals and proceeds to step S18, and makes a negative decision in step S13 when an L-level signal is included and proceeds to step S14. When the process proceeds to step S18, the state is as shown in FIG.
[0027]
In step S14, the microprocessor 46 sets the light receiving element No. It is determined whether the light receiving signal input from the comparator 44 corresponding to 1 is at the H level. The microprocessor 46 makes an affirmative decision in step S14 when an H-level signal is input, and proceeds to step S19, and makes a negative decision in step S14 when an L-level signal is input, and proceeds to step S15. . The case of proceeding to step S19 is a case where the laser beam from the rotating laser level 1 is deflected toward the upper side of the light receiving element unit 31.
[0028]
In step S15, the microprocessor 46 sets the light receiving element No. It is determined whether the light receiving signal input from the comparator 44 corresponding to 50 is at the H level. The microprocessor 46 makes an affirmative determination in step S15 when an H-level signal is input and proceeds to step S19, and makes a negative determination in step S15 when an L-level signal is input and proceeds to step S16. . The case of proceeding to step S19 is a case where the laser beam from the rotating laser level 1 is deflected to the lower side of the light receiving element unit 31.
[0029]
In step S16, the microprocessor 46 calculates the center C = (D + U) / 2. Here, D is the light receiving element number at the lower end where the H level signal is input. U is the upper end light receiving element number to which the H level signal is input. The microprocessor 46 sets the array position of the light receiving elements corresponding to the element number C as the laser beam center Bc. After calculating the laser beam center Bc, the microprocessor 46 instructs the liquid crystal display unit 47 to display the calculation result, and proceeds to step S17.
[0030]
In step S17, the microprocessor 46 stores the set determination threshold value in the memory in the microprocessor 46, and ends the processing in FIG.
[0031]
In step S18, the microprocessor 46 sets the comparator 44 to increase the current determination threshold by a predetermined value X, and returns to step S13. Thereby, the determination threshold is increased so that the determination threshold approaches a value corresponding to the reference level 62B. The predetermined value X may not be a value that increases the determination threshold from the reference level 62A to the reference level 62B in one determination threshold change process. That is, the predetermined value X may be set so as to gradually increase the determination threshold while repeating the processing of step S13 and step S18.
[0032]
In step S19, the microprocessor 46 sets the comparator 44 to increase the current determination threshold by a predetermined value X / 2, and returns to step S14. Thereby, the determination threshold is increased so that the determination threshold approaches a value corresponding to the reference level 62B. In step S19, since the signal from one of the upper end (element number 1) and the lower end (element number 50) of the light receiving element unit 31 is at the L level, the change width (X / 2) is half that of step S18. The determination threshold is gradually increased.
[0033]
When the microprocessor 46 calculates the laser beam center Bc in step S16, an average value of a plurality of detection results may be calculated. As described above, the laser beam is input to the light receiving element unit 31 at intervals of 0.1 sec (10 Hz). Therefore, for example, if the average value of the detection results of five times is obtained to obtain the laser beam center Bc, the display of the liquid crystal display unit 47 can be updated every 0.5 seconds.
[0034]
The beam center detecting device according to the embodiment described above will be summarized.
(1) The determination threshold of the comparator 44 is configured to be variable, and when the laser beam is received by all of the light receiving elements on the light receiving element unit 31 (Yes in step S13), the determination threshold of the comparator 44 is set to a predetermined value X The value is changed to be higher at a time (step S18). Accordingly, even if the laser beam from the rotating laser level 1 spreads, the beam center Bc can be accurately measured without expanding the light receiving range of the light receiving element unit 31 in the level measurement direction 4 (that is, increasing the number of light receiving elements). Can be calculated. This is particularly effective when the distance between the rotating laser level 1 and the beam center detecting device 3 is several hundred meters or more.
[0035]
(2) In addition to the above (1), if a light receiving signal from one of the upper end (element number 1) and the lower end (element number 50) of the light receiving element unit 31 is not input to the microprocessor 46, The judgment threshold value is increased little by little in a half change width (X / 2). This prevents the number of light receiving signals input to the microprocessor 46 after the change of the determination threshold value from suddenly decreasing.
[0036]
(3) The light receiving element section 31 in which N (50 in the above example) light receiving elements are arranged side by side along the level measurement direction 4 (FIG. 1) receives a laser beam from the rotating laser level 1 and outputs N light. Are input in parallel to the microprocessor 46 via the N comparators 44, respectively. The light receiving signal having a signal level higher than the determination threshold is input to the microprocessor 46 as an H level signal. The microprocessor 46 calculates the light receiving element position located at the center of the element numbers (U and D) corresponding to the upper and lower ends of the input signal as the beam center Bc. Thus, the beam center detection device 3 can be obtained with a simple configuration without using a digital peak hold circuit or a high-speed A / D conversion circuit. As a result, the effect of reducing the cost and power consumption of the beam center detecting device 3 can be obtained. When the power consumption is reduced, the continuous use time can be extended when the beam center detection device 3 is driven by a battery.
[0037]
(4) Since the light receiving signal is input to the microprocessor 46 via the comparator 44, a higher judgment threshold value than the light receiving signal due to disturbance light other than the laser beam from the rotating laser level 1 is set in the comparator 44, Signals due to disturbance light and noise can be prevented from being input to the microprocessor 46. As a result, the beam center Bc can be accurately calculated.
[0038]
In the above description, the example in which the process according to FIG. 8 ends when the microprocessor 46 makes a negative determination in step S12 has been described. However, the process may return to step S11.
[0039]
In step S19, the determination threshold value of the comparator 44 is changed by X / 2. However, the change width of the determination threshold value is not limited to X / 2, and may be, for example, X / 4.
[0040]
The above-described D / A converter 51 has been described as an example configured separately from the microprocessor 46. However, when the microprocessor 46 has a built-in D / A conversion circuit, the built-in D / A converter is a D / A converter. It may be used in place of the / A converter 51.
[0041]
In the above-described embodiment, the configuration in which the same number of amplifiers and comparators as the number of the plurality of light receiving elements are provided has been described. Instead, one amplifier and one comparator are provided for each of the plurality of light receiving elements, signals from the plurality of light receiving elements are respectively amplified by the amplifier, and the level of the amplified signal is determined by the comparator. Is also good. The signals from the plurality of light receiving elements are sequentially switched using, for example, a relay circuit or the like.
[0042]
Further, one comparator may be provided for the plurality of light receiving elements and the plurality of amplifiers, and the level of the signal from each amplifier may be determined by the comparator. Switching of signals from a plurality of amplifiers is performed sequentially using, for example, a relay circuit.
[0043]
In the above description, an example in which the comparator 44 is used has been described. However, the present invention can be applied to a case where an A / D conversion circuit is used instead of the comparator 44. In this case, the light receiving signal (digital value) after the A / D conversion is input to the microprocessor 46. The microprocessor 46 regards the input digital value as being a light receiving signal when it is higher than the valid threshold, and does not regard it as a light receiving signal when the input digital value is lower than the valid threshold. This effective threshold value corresponds to the determination threshold value of the comparator 44 described above.
[0044]
In the above description, the Gaussian distribution in which the optical power is maximum at the center of the laser beam and decreases as approaching the periphery of the beam has been described as an example. The present invention can be applied to detection of the center of a beam having a TEM10 mode distribution, for example, in addition to such a distribution.
[0045]
Correspondence between each component in the claims and each component in the embodiment of the invention will be described. For example, the level measurement direction 4 corresponds to one direction. The light receiving means is constituted by, for example, the light receiving element unit 31. The sensor array corresponds to a light receiving element group. The determining means is constituted by, for example, the comparator 44. The threshold changing means is constituted by, for example, the microprocessor 46 and the D / A converter 51. The center detecting means is constituted by, for example, a microprocessor 46. Note that each component is not limited to the above configuration as long as the characteristic functions of the present invention are not impaired.
[0046]
【The invention's effect】
The beam center detecting device according to the present invention can correctly detect the center of a light (laser) beam even when the beam spreads.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of a displacement measurement system using a beam center detection device according to an embodiment of the present invention.
FIG. 2 is an enlarged view of the beam center detecting device when the beam spread is not large.
FIG. 3 is a block diagram of a beam center detection device.
FIG. 4 is a diagram illustrating a relationship between a light receiving element group of a light receiving element unit, an output signal distribution curve of an amplifier, and a determination threshold of a comparator.
FIG. 5 is an enlarged view of the beam center detecting device when the beam spread is large.
FIG. 6 is a diagram illustrating a relationship between a light receiving element group of a light receiving element unit, an output signal distribution curve of an amplifier, and a determination threshold of a comparator.
FIG. 7 is a diagram illustrating a relationship between a light receiving element group of a light receiving element unit, an output signal distribution curve of an amplifier, and a determination threshold of a comparator.
FIG. 8 is a flowchart illustrating a flow of a process of calculating a beam center.
[Explanation of symbols]
1 ... rotating laser level, 2 ... plane of light,
3 ... beam center detection device 4 ... level measurement direction
11 (11A, 11B): trajectory of the beam,
31 ... light receiving element part 32 ... measurement result display part
44: comparator, 46: microprocessor,
51 ... D / A converter

Claims (2)

In a beam center detection device that detects the center of a light beam,
Light receiving means having a sensor row in which a plurality of sensors are arranged in one direction,
Determining means for determining whether or not the light receiving signals respectively output from the light receiving means corresponding to the plurality of sensors are equal to or greater than a determination threshold;
At least two light receiving signals corresponding to two sensors located at both ends of the sensor array are less than the determination threshold, and at least one of light receiving signals corresponding to other sensors except the two sensors located at the both ends is determined. A threshold changing unit that changes the determination threshold so as to be determined by the determination unit,
A beam center detection device, comprising: a center detection unit that detects the center based on an arrangement position of a sensor corresponding to a light reception signal for which a value equal to or greater than the determination threshold is determined by the determination unit. The beam center detection device according to claim 1,
The determination means includes a comparison circuit,
The beam center detecting device, wherein the threshold value changing means changes a comparison reference signal level of the comparison circuit.

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