3D measurement system

Abstract

To provide a three-dimensional measurement system which can shorten the time for measuring a three-dimensional shape.SOLUTION: The three-dimensional measurement system comprises: a projector 20; a projection control unit 11 that projects a first projection pattern whose on-time ratio changes in one direction in sine wave form to a measurement object 5; an event camera 30; a first on-time ratio determination unit 12 that determines, for each pixel, a first on-time ratio that can be determined on the basis of the event data outputted by the event camera 30 when the projector 20 is projecting the first projection pattern; a second on-time ratio determination unit 13 that determines, for each pixel, a second on-time ratio that constitutes a second on-time ratio waveform which is different in phase from a first on-time ratio waveform by other than 180 degrees; a phase calculation unit 15 that calculates a phase for the plurality of pixels of the event camera, on the basis of the first and second on-time ratios where an offset component is eliminated; and a coordinate determination unit 16 that calculates three-dimensional coordinates per pixel on the basis of the calculated phase.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This invention relates to a three-dimensional measurement system that measures the three-dimensional shape of an object using a phase shift method. [Background technology]

[0002] As disclosed in Patent Document 1, a system using the phase shift method is known as a three-dimensional measurement system for measuring the three-dimensional shape of a measurement object. The phase shift method is a technique for performing triangulation by projecting multiple phase-shifted stripe pattern images. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-67644 Summary of the Invention [Problem to be solved by the invention]

[0004] As disclosed in Patent Document 1, three-dimensional measurement techniques using the phase shifting method generally use an equation that includes three unknowns: phase, brightness amplitude, and background brightness. Because there are three unknowns, measuring a three-dimensional shape requires at least three or more stripe patterns with different initial phases projected and time to capture images with each stripe pattern image projected. Therefore, it is desirable to shorten the time required to measure a three-dimensional shape.

[0005] The present disclosure has been made based on this situation, and an object thereof is to provide a three-dimensional measurement system that can shorten the time required to measure a three-dimensional shape. [Means for solving the problem]

[0006] The above object is achieved by the combination of features recited in the independent claims, and the subclaims define further advantageous specific examples. The reference numerals in parentheses in the claims correspond to specific aspects described in the following embodiments as one aspect, and do not limit the technical scope of the disclosure.

[0007] One disclosure relating to a three-dimensional measurement system for achieving the above object is: A three-dimensional measurement system using a phase shifting method, A projector (20); a projection control unit (11) that controls the projector to project a first projection pattern onto a measurement object (5), the first projection pattern being a projection pattern in which the on-time ratio per unit time varies sinusoidally in one direction; an event camera (30) having a plurality of pixels, a range including a measurement target being an imaging range, and a pixel that detects a luminance change in the imaging range outputs event data indicating that a luminance change has occurred; a first on-time ratio determination unit (12) that determines, for each pixel, a first on-time ratio that can be determined based on event data output by the event camera when the projector is projecting the first projection pattern; a second on-time ratio determination unit (13) that determines, for each pixel, a second on-time ratio constituting a second on-time ratio waveform that is out of phase with a first on-time ratio waveform that indicates a change in the first on-time ratio relative to a change in position in one direction by a predetermined phase difference other than 180 degrees; an offset removal unit that generates a first on-time ratio waveform and a second on-time ratio waveform from which an offset has been removed, from the first on-time ratio waveform and the second on-time ratio waveform; a phase calculation unit (15) that calculates phases for a plurality of pixels of the event camera based on the first on-time ratio and the second on-time ratio from which the offset component has been removed; and a coordinate determination unit (16) that calculates three-dimensional coordinates for each pixel based on the phase calculated by the phase calculation unit.

[0008] Unlike this three-dimensional measurement system, when a stripe pattern image in which brightness is varied sinusoidally in one direction is projected onto a measurement object, it is necessary to detect the brightness of the projected stripe pattern, so a frame-based camera is used. When a stripe pattern image in which brightness is varied sinusoidally in one direction is captured with a frame-based camera, the amplitude of the brightness values ​​that can be detected by the frame-based camera changes depending on the color of the object onto which the stripe pattern image is projected. Therefore, the amplitude of the image captured by the frame-based camera is not constant.

[0009] In contrast, in this three-dimensional measurement system, the projector projects a first projection pattern, in which the on time ratio per unit time varies sinusoidally in one direction, onto the object to be measured, and is equipped with an event camera as a camera for capturing the projection pattern.

[0010] The event camera is a camera that detects changes in brightness, but does not detect the magnitude of brightness. Therefore, the event data output by the event camera is not affected by differences in the reflectivity of the object onto which the projection pattern is projected. Therefore, the offset of the first on-time ratio that can be determined based on the event data output by the event camera when the projector is projecting the first projection pattern is constant regardless of the pixel.

[0011] If the offset is constant, it can be easily removed from the first on-time ratio and the second on-time ratio. Therefore, the offset can also be removed from the equation for calculating the phase based on the first on-time ratio and the second on-time ratio. If the offset can be removed from the equation for calculating the phase, one unknown is eliminated, and the number of projection patterns projected to calculate the unknown can be reduced. Reducing the number of projection patterns can shorten the time required to measure the three-dimensional shape. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing the configuration of a three-dimensional measurement system 1 according to an embodiment. [Figure 2]FIG. 3 is a block diagram showing operations performed by a control device. [Figure 3] 3A and 3B are diagrams illustrating projection patterns projected by a projector. [Figure 4] FIG. 4 is a diagram showing a three-dimensional measurement process executed by the control device. [Figure 5] FIG. 10 is a diagram conceptually showing the results of frequency analysis of a first on-time ratio waveform. [Figure 6] FIG. 10 is a diagram conceptually showing a first on-time ratio waveform from which an offset has been removed. [Figure 7] FIG. 1 is a diagram showing Equation 1 for calculating a phase θ. [Figure 8] FIG. 1 shows the equations used in the derivation of Equation 1. [Figure 9] 10 is a graph showing the relationship between the phase θ and the height coordinate zm. [Figure 10] FIG. 2 is a diagram for explaining a method for calculating horizontal coordinates (xm, ym). [Figure 11] FIG. 10 is a diagram showing a three-dimensional measurement process executed by the control device 10 in the second embodiment. [Figure 12] FIG. 10 is a diagram showing a three-dimensional measurement process executed by the control device 10 in the third embodiment. [Figure 13] FIG. 10 is a diagram showing an equation for calculating a central difference. [Figure 14] 10A and 10B are diagrams illustrating projection patterns created by changing the number of on / off times. DETAILED DESCRIPTION OF THE INVENTION

[0013] First Embodiment Hereinafter, embodiments will be described with reference to the drawings. FIG. 1 is a diagram showing the configuration of a three-dimensional measurement system 1 according to a first embodiment. The three-dimensional measurement system 1 includes a control device 10, a projector 20, and an event camera 30. The three-dimensional measurement system 1 measures the three-dimensional shape of a measurement object 5 placed on a workbench 2 using a phase shift method. The top surface of the workbench 2 is flat, and the measurement object 5 is positioned at any position on the workbench 2. The three-dimensional measurement system 1 is used, for example, as the eyes of a robot when the robot is made to perform picking, assembly work, product inspection, etc.

[0014] The control device 10 can be realized by a configuration including at least one processor. For example, the control device 10 can be realized by a computer including a processor, nonvolatile memory, RAM, I / O, and a bus line connecting these components. The nonvolatile memory stores a program for operating a general-purpose computer as the control device 10 of this embodiment.

[0015] The processor executes a three-dimensional measurement program stored in the non-volatile memory while utilizing the temporary storage function of the RAM. As a result, the control device 10 operates as a projection control unit 11, a first on-time ratio determination unit 12, a second on-time ratio determination unit 13, an offset removal unit 14, a phase calculation unit 15, and a coordinate determination unit 16 shown in Fig. 2. The control device 10 executing the operations shown in Fig. 2 means that a three-dimensional measurement method corresponding to the three-dimensional measurement program is executed. The operation of each unit shown in Fig. 2 will be explained using the flowchart shown in Fig. 4.

[0016] A DLP (registered trademark) projector can be used for the projector 20. A DLP projector is equipped with a DMD (Digital Mirror Device) element. The DMD element is an element in which minute mirrors, each corresponding to a pixel of the image to be projected, are arranged in an array. The DMD element can change the angle of each mirror between an on angle, which projects light to the outside, and an off angle, which does not project light to the outside. Therefore, a DLP projector can adjust the on / off time for each pixel.

[0017] The projector 20 is controlled by the control device 10 to project a projection pattern in which the on time ratio per unit time varies sinusoidally in one direction onto the measurement object 5. In this embodiment, the one direction is the x direction.

[0018] FIG. 3 is a diagram illustrating a projection pattern projected by the projector 20. FIG. 3 shows the change in on-time relative to the change in pixel position in the x direction, which is an example of one direction, with the y coordinate of the projector 20 fixed at an arbitrary coordinate. As shown in FIG. 3, the projection pattern is a pattern in which the on-time changes sinusoidally relative to the change in x pixel position. The sine wave here does not specify the position where the phase θ is 0 degrees. Therefore, the sine wave can also be referred to as a cosine wave.

[0019] For any y coordinate, the on-time of the projection pattern changes in the same way as the x-pixel position changes. The on-time on the vertical axis is the time that the light is continuously on within a unit time. The unit time is, for example, 255 ms. The color of the light projected from each pixel of the projector 20 during the on-time is a single color. The single color used in the projection pattern can be any color, such as red, green, or blue. The light intensity of the on-portion of the projection pattern needs only to be at a level that allows the event camera 30 to detect on / off.

[0020] The event camera 30 has multiple pixels arranged in a two-dimensional array. In the event camera 30, a pixel that detects a brightness change asynchronously outputs event data including two-dimensional data that can identify the position of that pixel. The event data includes the two-dimensional data, the time when the brightness change occurred, and the sign of the brightness change.

[0021] The position of the event camera 30 is fixed so that the shooting range is an area including the measurement target object 5. The distance between the projector 20 and the event camera 30 is measured in advance.

[0022] [Three-dimensional measurement processing] Next, the three-dimensional measurement process executed by the control device 10 will be described with reference to Fig. 4. The control device 10 executes this three-dimensional measurement process to measure the three-dimensional shape of the measurement object 5. The three-dimensional measurement process is started, for example, when the user performs a predetermined start operation.

[0023] Steps S11 and S12 are executed by the projection control unit 11. In step S11, the projector 20 is controlled to project a first projection pattern. In this state, the event camera 30 is caused to capture an image of the measurement target 5. The first projection pattern is a pattern in which the on-time changes sinusoidally with respect to the change in pixel position in one direction, the x-direction.

[0024] In S12, the projector 20 is controlled to project the second projection pattern. In addition, in this state, the event camera 30 is caused to capture an image of the measurement target 5. The second projection pattern is a projection pattern having a phase θ different from that of the first projection pattern. The phase θ is the phase of the sine wave indicated by the projection pattern shown in FIG. 3. The phase difference δ between the phase θ1 of the first projection pattern and the phase θ2 of the second projection pattern is set to a value other than 0 degrees or 180 degrees. For example, the phase difference δ is 90 degrees. The reason for setting a value other than 0 degrees or 180 degrees is that the phase θ is calculated using Equation 1, which will be described later.

[0025] S13 is executed by the first on-time ratio determination unit 12. Note that S13 may be executed before S12. In S13, an on-time ratio is determined for each pixel of the event camera 30 based on event data output by the event camera 30 when the projector 20 is projecting the first projection pattern. The on-time ratio determined here is referred to as the first on-time ratio. The on-time ratio is the ratio of the time that a part of the projection pattern corresponding to each pixel of the event camera 30 is on relative to a unit time. The event data includes the time when a luminance change occurred and the sign of the luminance change. Therefore, it is possible to calculate the time that a part of the projection pattern corresponding to each pixel of the event camera 30 is on from the event data. The unit time ratio can be calculated by dividing this time by the unit time.

[0026] The change in the first on-time ratio relative to the change in x pixels can also be determined by calculating the first on-time ratio for each pixel of the event camera 30. The waveform showing the change in the first on-time ratio relative to the change in x pixels is referred to as the first on-time ratio waveform.

[0027] S14 is executed by the second on-time ratio determination unit 13. In S14, the on-time ratio is determined for each pixel of the event camera 30 based on the event data output by the event camera 30 when the projector 20 is projecting the second projection pattern. The on-time ratio determined here is referred to as the second on-time ratio. By calculating the second on-time ratio for each pixel of the event camera 30, the change in the second on-time ratio relative to the change in x pixels can also be determined. The waveform showing the change in the second on-time ratio relative to the change in x pixels is referred to as the second on-time ratio waveform.

[0028] The next steps S15 and S16 are performed by the offset removal unit 14. Both the first on-time ratio waveform and the second on-time ratio waveform have an offset. In S15, the offset of the first on-time ratio waveform and the second on-time ratio waveform is calculated. The offset can be calculated by performing frequency analysis on the first on-time ratio waveform or the second on-time ratio waveform. The first on-time ratio waveform and the second on-time ratio waveform have different phases θ but the same offset. Therefore, frequency analysis needs to be performed on only either the first on-time ratio waveform or the second on-time ratio waveform.

[0029] Figure 5 conceptually shows the results of frequency analysis of the first on-time ratio waveform. As shown in Figure 5, when the first on-time ratio waveform is frequency analyzed, a zeroth-order spectrum is observed at a frequency lower than the frequency of the first on-time ratio waveform. This frequency is the offset component. Note that Figure 5 is a conceptual diagram, and the frequency components that indicate the three-dimensional shape and frequency components caused by noise are omitted.

[0030] In S16, the offset calculated in S15 is removed from each of the first on-time ratio waveform and the second on-time ratio waveform. Figure 6 conceptually shows the first on-time ratio waveform with the offset removed. The first on-time ratio waveform after the offset has been removed can be expressed as I1 = A cos θ, where I1 is the first on-time ratio after the offset has been removed, A is the amplitude of the waveform, and θ is the phase of the waveform.

[0031] Step S17 is executed by the phase calculation unit 15. In step S17, the phase θ is calculated for each pixel (x, y) of the event camera 30. The phase θ for each pixel (x, y) of the event camera 30 is calculated using equation 1 shown in FIG. 7. In equation 1, I1 is the first on-time ratio after offset removal for the pixel (x, y). I2 is the second on-time ratio after offset removal for the pixel (x, y). δ is the phase difference between the first on-time ratio waveform and the second on-time ratio waveform. Therefore, the value of the variable on the right side of equation 1 can be determined for each pixel (x, y). Therefore, the phase θ can be calculated for each pixel (x, y) of the event camera 30 from equation 1. While a general phase shift method uses brightness, this embodiment uses the first on-time ratios I1 and I2. The first and second on-time ratios can be considered substitute values ​​for brightness.

[0032] Figure 8 shows the derivation process of Equation 1. Equation 2 is an equation that shows the first on-time ratio waveform after offset removal. Equation 3 is an equation that shows the second on-time ratio waveform after offset removal. By dividing both sides of Equation 3 by Equation 2, it can be transformed into Equation 4. Transforming Equation 4 gives Equation 5. Transforming Equation 5 further gives Equation 6. Transforming Equation 6 gives Equation 1.

[0033] S18 and S19 are executed by the coordinate determination unit 16. In S18, the height coordinate z of the coordinate measurement point P is calculated from the phase θ of each pixel (x, y) calculated in S17. m The coordinate measurement point P is a point on the surface of the measurement object 5 or the work table 2.

[0034] Height coordinate z m is the distance from the plane including the projector 20 and the event camera 30 to the object. m is the phase θ and height coordinate z shown in Figure 9. m 9 is determined using a graph showing the relationship between the coordinates of the projector 20, the coordinates of the event camera 30, the height coordinate z m, which can be created if the length of one period of the projection pattern on the reference plane is known. The reference plane is parallel to the projection plane, which is the surface of the work table 2, and the distance to the projector 20 and the event camera 30 is z m This is the surface where

[0035] If the projector 20 and the event camera 30 are fixed, the coordinates of the projector 20 and the event camera 30 become known. m is the value to be given. Furthermore, the height coordinate z m Once this is determined, the length of one period of the projection pattern on the reference plane is also determined. Therefore, the graph shown in FIG. 9 can be obtained in advance.

[0036] The graph shown in FIG. 9 is obtained in advance, and in S18, the phase θ calculated in S17 is applied to the graph shown in FIG. 9 obtained in advance, and the height coordinate z of each coordinate measurement point P is calculated. m If it is not clear which period the phase θ is in, the height coordinate z m However, the height coordinate z at a coordinate measurement point P cannot be determined. m is the height coordinate z of the coordinate measurement point P adjacent to the coordinate measurement point P. m Therefore, even if it is not clear which period the phase θ is in, it is possible to measure the three-dimensional shape of the measurement target 5. m is known, so the height coordinate z of the work table 2 m By comparing with the height coordinate z of coordinate measurement point P, m may be determined.

[0037] In S19, the height coordinate z in S18 m For the coordinate measurement point P, the horizontal coordinate (x m , y m The height coordinate z m is associated with the pixel (x, y). Once the pixel (x, y) is determined, the direction (α x , α y) is determined. x As shown in FIG. 10, x is the direction from the event camera 30 to the coordinate measurement point P. m z m z in the plane m is the angle between the axis. y Although not shown in FIG. 10, α y is the direction from the event camera 30 to the coordinate measurement point P, m z m z in the plane m As can be seen from Figure 10, the horizontal coordinate (x m , y m ) is the height coordinate z m and α m , α y can be calculated by geometric calculation.

[0038] By performing the processes from S17 to S19 for each pixel (x, y), the three-dimensional coordinates of the measurement object 5 can be determined.

[0039] Summary of the first embodiment In the three-dimensional measurement system 1 of this embodiment described above, the projector 20 projects a first projection pattern and a second projection pattern, the on-time ratio per unit time of which varies sinusoidally in the x direction, onto the measurement object 5. The three-dimensional measurement system 1 also includes an event camera 30 as a camera for capturing images of the projection patterns.

[0040] The event data output by the event camera 30 is not affected by differences in the reflectance of the object onto which the projection pattern is projected. Therefore, the offset of the first on-time ratio that can be determined based on the event data output by the event camera 30 when the projector 20 is projecting the first projection pattern is constant regardless of the pixel.

[0041] If the offset is constant, it can be easily removed from the first on-time ratio and the second on-time ratio. Therefore, the offset can also be removed from Equation 1, which calculates the phase θ based on the first on-time ratio and the second on-time ratio. If the offset can be removed from Equation 1, which calculates the phase θ, one unknown is eliminated, so the number of projection patterns projected to calculate the unknown can be reduced. Reducing the number of projection patterns projected can shorten the time required to measure the three-dimensional shape.

[0042] In this three-dimensional measurement system 1, the projector 20 not only projects a first projection pattern but also projects a second projection pattern. The second projection pattern is a pattern whose phase θ differs from that of the first projection pattern by a phase difference δ. The second on-time ratio determiner 13 generates a second on-time ratio waveform based on the event data output by the event camera 30 when the projector 20 is projecting the second projection pattern (S14).

[0043] The second on-time ratio waveform generated in this manner has the same offset component as the first on-time ratio waveform. Therefore, offset removal unit 14 removes the same offset component from the first on-time ratio waveform and the second on-time ratio waveform (S16). Because it is only necessary to remove the same offset component from the two waveforms, processing is simpler than when different offset components are removed from the two waveforms.

[0044] The offset removal unit 14 calculates an offset from the generated first on-time ratio waveform or the second on-time ratio waveform (S15). Because the offset is calculated from the actually generated waveform, even if the offset differs for each three-dimensional measurement system 1 due to individual differences in the projector 20, the offset can be removed from the first on-time ratio waveform and the second on-time ratio waveform with high accuracy.

[0045] Second Embodiment Next, a second embodiment will be described. In the following description of the second embodiment, elements having the same reference numerals as those used previously are the same as those in the previous embodiments unless otherwise specified. Furthermore, when only a portion of the configuration is described, the previously described embodiment can be applied to the other portions of the configuration.

[0046] FIG. 11 shows the three-dimensional measurement process executed by the control device 10 in the second embodiment. FIG. 11 shows the process executed instead of FIG. 4. In FIG. 11, S13-1, S14-1, and S16-1 are executed instead of S13, S14, and S16 in FIG. 4. Also, S15, which calculates the offset, is not executed. Instead, the offset is determined in advance based on measurements or the like and stored in a predetermined storage unit of the control device 10.

[0047] In S13-1, similar to S13, the first on-time ratio determiner 12 determines the first on-time ratio for each pixel included in the event camera 30 based on the event data output by the event camera 30 while the projector 20 is projecting the first projection pattern. In S13, the first on-time ratio waveform was also determined, but in S13-1, the first on-time ratio waveform is not determined.

[0048] In S14-1, similar to S14, the second on-time ratio determiner 13 determines the second on-time ratio for each pixel included in the event camera 30 based on the event data output by the event camera 30 while the projector 20 is projecting the second projection pattern. However, unlike S14, the second on-time waveform is not determined.

[0049] After S14-1 is executed, S16-1 is executed. In S16-1, the offset removal unit 14 removes the offset by subtracting a pre-stored offset from the first on-time ratio and the second on-time ratio of each pixel determined in S13-1 and S14-1. Thereafter, S17 and subsequent steps are executed, as in the first embodiment.

[0050] In the second embodiment, the offsets are stored in advance, eliminating the need for offset calculation processing, and therefore the time required to measure the three-dimensional shape can be further reduced compared to the first embodiment.

[0051] Third Embodiment Fig. 12 shows three-dimensional measurement processing executed by the control device 10 in the third embodiment. Fig. 12 shows processing executed in place of Fig. 4. Fig. 12 executes S14-2, S15-2, and S16-2 in place of S14, S15, and S16 in Fig. 4.

[0052] In the three-dimensional measurement process shown in FIG. 12, step S12 of projecting and capturing the second projection pattern is not executed. Even without executing step S12, the second on-time ratio waveform can be generated by step S14-2. Step S14-2 is executed by the second on-time ratio determination unit 13. In step S14-2, the first on-time ratio waveform generated in step S13 is first differentiated to calculate the second on-time ratio waveform. The first differentiation results in a waveform with a phase θ shifted by 90 degrees. Therefore, the waveform obtained by first differentiating the first on-time ratio waveform can be used as the second on-time ratio waveform.

[0053] The first derivative can be calculated using central differencing. The formula for central differencing is shown in Figure 13. With central differencing, three pixels of data are required to calculate one derivative value. However, the center of the three pixels of data is not used in the calculation.

[0054] In S15-2, the offset of the first on-time ratio waveform is calculated. Unlike S15-2, the second on-time ratio waveform is not used, and the offset is calculated by frequency analysis of the first on-time ratio waveform. The reason the second on-time ratio waveform is not used is because the second on-time ratio waveform is generated by differentiating the first on-time ratio waveform, and the offset is removed by differentiation.

[0055] In S16-2, the offset calculated in S15-2 is removed from the first on-time ratio waveform. Thereafter, S17 and subsequent steps are executed in the same manner as in the first embodiment.

[0056] In this third embodiment, the second on-time ratio waveform is generated by first-order differentiation of the first on-time ratio waveform. Therefore, there is no need to project a second projection pattern. In addition, when the second on-time ratio waveform is generated in this manner, the second on-time ratio waveform is a waveform from which the offset has been removed, so there is no need for a separate process to remove the offset.

[0057] Furthermore, for the first on-time ratio waveform, an offset is calculated from the generated first on-time ratio waveform (S15-2), and the offset is removed from the first on-time ratio waveform. Thus, the offset can be removed from the first on-time ratio waveform with high accuracy.

[0058] Although the embodiments have been described above, the disclosed technology is not limited to the above-described embodiments, and the following modifications are also included in the scope of the disclosure. Furthermore, various modifications other than those described below can be made without departing from the spirit of the invention.

[0059] <Variation 1> In the embodiment, the projection pattern is a pattern in which the ON time during which the light is continuously ON within a unit time is changed in a sinusoidal manner in the x direction. However, instead of being continuously ON, the projection pattern may be a pattern in which the ON time is set to a time that is sufficiently shorter than the unit time, and the number of ON / OFF times within the unit time is changed in a sinusoidal manner in the x direction, as shown in Fig. 14 .

[0060] <Variation 2> In the embodiment, the first derivative is calculated by central difference, but the first derivative may be calculated by forward difference or backward difference. [Explanation of symbols]

[0061] 1: Three-dimensional measurement system 2: Work table 5: Measurement object 10: Control device 11: Projection control unit 12: First on-time ratio determination unit 13: Second on-time ratio determination unit 14: Offset removal unit 15: Phase calculation unit 16: Coordinate determination unit 20: Projector 30: Event camera

Claims

1. A three-dimensional measurement system using a phase shift method, comprising: A projector (20); a projection control unit (11) that controls the projector to project a first projection pattern onto a measurement object (5), the first projection pattern being a projection pattern in which the on-time ratio per unit time varies sinusoidally in one direction; an event camera (30) having a plurality of pixels, a range including the measurement object as a photographing range, and a pixel that detects a luminance change in the photographing range outputs event data indicating that a luminance change has occurred; a first on-time ratio determination unit (12) that determines, for each pixel, a first on-time ratio that can be determined based on the event data output by the event camera when the projector is projecting the first projection pattern; a second on-time ratio determining unit (13) that determines, for each pixel, a second on-time ratio constituting a second on-time ratio waveform that is out of phase with a predetermined phase difference other than 180 degrees from a first on-time ratio waveform that indicates a change in the first on-time ratio with respect to a change in the position in one direction; an offset removal unit that generates the first on-time ratio waveform and the second on-time ratio waveform from which an offset has been removed, from the first on-time ratio waveform and the second on-time ratio waveform; a phase calculation unit (15) that calculates phases for the plurality of pixels of the event camera based on the first on-time ratio and the second on-time ratio from which the offset component has been removed; and a coordinate determination unit (16) that calculates three-dimensional coordinates for each pixel based on the phase calculated by the phase calculation unit.

2. 2. The three-dimensional measurement system according to claim 1, the projection control unit sequentially projects the first projection pattern and a second projection pattern, the second projection pattern having a phase different from that of the first projection pattern by the phase difference, onto the measurement object; the second on-time ratio determination unit determines the second on-time ratio for each pixel based on the event data output by the event camera when the projector is projecting the second projection pattern; The three-dimensional measurement system includes an offset removal unit (14) that removes the same offset from the first on-time ratio and the second on-time ratio.

3. 3. The three-dimensional measurement system according to claim 2, the offset removal unit calculates an offset from the first on-time ratio waveform or the second on-time ratio waveform, and removes the calculated offset from the first on-time ratio waveform and the second on-time ratio waveform.

4. 2. The three-dimensional measurement system according to claim 1, The second on-time ratio determination unit calculates the second on-time ratio by first-order differentiating the first on-time ratio waveform.

5. 5. The three-dimensional measurement system according to claim 4, A three-dimensional measurement system comprising an offset removal unit (14) that calculates an offset from the first on-time ratio waveform and removes the calculated offset from the first on-time ratio waveform.

Images