Light line triangulation apparatus

Abstract

The present invention relates to a light line triangulation apparatus with a measurement space for receiving a measurement object, a light projector, adapted to project a light line into the measurement space and/or onto the measurement object, an imager for detecting the light line in the measurement space, wherein the imager comprises imaging pixels arranged in a plurality of columns and rows. The apparatus of the invention is characterized in that the imager comprises multiple identical sets of polarization filters, wherein each set of polarization filters comprises at least two polarization filters with different polarization directions, wherein a respective polarization filter covers one of the columns.

Claims

1. A light line triangulation apparatus with a measurement space for receiving a measurement object, a light projector, adapted to project a light line (18) into the measurement space and/or onto the measurement object an imager for detecting the light line in the measurement space, wherein the imager comprises imaging pixels arranged in a plurality of columns and rows, wherein the imager comprises multiple identical sets (36) of polarization filters, wherein each set of polarization filters comprises at least two polarization filters (34) with different polarization directions, wherein polarization filters with the same polarization filter characteristics cover respective ones of complete columns of pixels, and wherein light from the light line incident on the imager forms a straight image line on the imaging pixels, if no measurement object is present, wherein the image line is peipendicular to the direction defined by the columns.

2. The light line triangulation apparatus of claim 1, wherein each set of polarization filters comprises exactly four polarization filters having different polarization directions.

3. The light line triangulation apparatus of claim 1, wherein the polarization filters have a linear polarization, wherein the polarization direction of at least two polarization filters covering adjacent columns differs by an angle of 45°.

4. The light line triangulation apparatus of claim 1, further comprising an evaluation unit adapted to combine pixel values of at least two pixels of different columns in order to detect the position of the light line.

5. The light line triangulation apparatus of claim 4, wherein the evaluation unit is adapted to combine pixel values of four pixels of different columns in order to detect the position of the light line.

6. The light line triangulation apparatus of claim 4, wherein the evaluation unit is adapted to subtract pixel values of different pixels that are covered by two different polarization filters having a difference in polarization direction of 90°.

7. The light line triangulation apparatus of claim 6, wherein the evaluation unit is adapted to perform the subtraction of the pixel values within a moving window that is moved stepwise over the pixels of the imager.

8. The light line triangulation apparatus of at claim 1, further comprising a transport mechanism which is adapted to move the measurement object relative to the light line in a measurement direction.

9. The light line triangulation apparatus of claim 1, wherein the light projector comprises a laser source, the laser source projecting the light line, wherein the light line.

10. The light line triangulation apparatus of claim 9, wherein the light line is formed by uniformly polarized light.

11. The light line triangulation apparatus of claim 1, wherein at least some of the polarization filters (34) are directly bonded onto the imaging pixels.

12. The light line triangulation apparatus of claim 1, further comprising an evaluation unit adapted to determine height of different portions of the measurement object based on the deformation of the light line.

13. A method of detecting height of different portions of a measurement object using light line triangulation, the method comprising: projecting a light line into a measurement space and/or onto a measurement object, detecting the light line with an imager, wherein the imager comprises multiple identical sets of polarization filters, wherein each set of polarization filters comprises at least two polarization filters with different polarization directions and polarization filters with the same polarization filter characteristics respective ones of complete columns of pixels, wherein light from the light line incident on the imager forms a straight image line on the imaging pixels, if no measurement object is present, wherein the image line is perpendicular to the direction defined by the columns, detecting the height of different portions of the measurement object is detected based on a deformation of the light line and based on polarization information.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described as an example with reference to the Figures.

(2) FIG. 1 shows an overview of a light line triangulation apparatus;

(3) FIG. 2 shows an image sensor of an imager in a top view;

(4) FIG. 3 shows the image sensor in a side section view;

(5) FIG. 4 shows the intensities detected for different polarization directions;

(6) FIG. 5 shows a result map for Stokes vector S1; and

(7) FIG. 6 shows a result map for Stokes vector S2.

DETAILED DESCRIPTION

(8) FIG. 1 shows a light line triangulation apparatus 10 which comprises a measurement space formed by the space above a conveyor belt 12. A measurement object in the form of a car 14 is placed on the conveyor belt 12 and is moved in a measurement direction M.

(9) A light projector 16 comprising a laser source (not shown) projects a light line 18 onto the conveyor belt 12.

(10) The light line 18 is monitored by an imager 20, the imager 20 comprises a lens 22 and is coupled to an evaluation unit 24.

(11) The imager 20 is arranged distant from the light projector 16, wherein an angle α of around 45° is formed between the light projector 16 and the imager 20 at the light line 18.

(12) When the measurement object, i.e. the car 14, is moved along the measurement direction M and reaches the light line 18, the light line 18 is deformed. The deformation of the light line 18 is then detected by the imager 20. From the detected deformation of the light line, a contour 26 of the car 14 can be determined. The contour 26 is shown on the right-hand side of FIG. 1. As the car 14 moves along the measurement direction M, a plurality of contours 26 can be determined. These contours 26 can be stitched together to form a 3D-model 28 of the car 14.

(13) FIG. 2 shows an image sensor 30 of the imager 20. The image sensor 30 comprises a plurality of pixels 32 (FIG. 3) which are arranged in columns C and rows R. Arranged on the image sensor 30 are polarization filters 34 which are each covering a complete column C of pixels 32.

(14) In case no measurement object is present, then the light line 18 is projected onto the image sensor 30 as a straight line that follows one of the rows R and is thus perpendicular to the direction of the columns C.

(15) In the present example, four different polarization filters 34 are used, wherein a first polarization filter 34a has a polarization direction of 0°, a second polarization filter 34b has a polarization direction of 45°, a third polarization filter 34c has a polarization direction of 90° and a fourth polarization filter 34d has a polarization direction of 135°. The four polarization filters 34a, 34b, 34c, 34d form a filter set 36. Multiple filter sets 36 are arranged over the whole image sensor 30. Thereby, the filter set 36 described above is repeated multiple times.

(16) FIG. 3 shows a sectional view of the image sensor 30. FIG. 3 shows multiple pixels 32 of different columns C but of the same row R, wherein the different polarization filters 34 are bonded onto the pixels 32.

(17) FIGS. 4 to 6 show the results yielded during operation. The results are coded in greyscale to indicate intensity values or calculated values. In the example of FIGS. 4 to 6 a cuboid 44 having a V-shaped groove 46 was used as a measurement object. The polarization of the laser source was aligned to 0°.

(18) It is to be noted that in the V-shaped groove 46 unwanted direct reflections occur. In contrast, the remaining form of the cuboid 44 usually produces “scattered light”, i.e. diffuse reflections that are desired. Also, the V-shaped groove 46 may reflect the light from the light projector 16 onto further parts of the cuboid 44 or onto further parts of the V-shaped groove 46, which may then lead to an unwanted “displacement” of the light line 18 (from the point of view of the imager 20). However, this displacement can be detected using the polarization directions, as described herein.

(19) FIG. 4 shows the resulting intensity values (i.e. pixel values) of pixels that are covered with a polarization filter having a polarization direction of 0°, 45°, 90° and 135°, respectively. In other words, FIG. 4 shows a 0°-map, a 45°-map, a 90°-map and a 135°-map. It can be seen, that e.g. the pixel intensities of 0° mostly show only the V-shaped groove 46, thus the unwanted direct reflections.

(20) In contrast, the intensities for pixels covered with a 90° polarization filter 34 show both the V-shaped groove 46 as well as the cuboid 44 form.

(21) In order to be able to distinguish between the unwanted direct reflections and the desired diffuse reflections the Stokes vectors S1 and S2 are calculated, wherein S1=I0−I90 and S2=I45−I135.

(22) FIG. 5 shows the result map for Stokes vector S1 (S1-map) and FIG. 6 shows the result map for Stokes vector S2 (S2-map). It is apparent that in FIG. 6 the differences between the V-shaped groove 46 and the cuboid 44 form cannot be clearly determined as all resulting values are positive and in the range of >150. However, the result map for S1 shown in FIG. 5 clearly distinguishes the unwanted direct reflections 40 and the desired diffuse reflections 42. Both can be distinguished since the direct reflections 40 comprise values of approximately above 150 and the diffuse reflections 42 comprise values of approximately below −150.

(23) It can thus be seen that the use of the polarization filters 34 allows clearly distinguishing unwanted direct reflections 40 from desired diffuse reflections 42. Thereby the form of the cuboid 44 can be correctly identified.

REFERENCE NUMERAL LIST

(24) 10 light line triangulation apparatus

(25) 12 conveyor belt

(26) 14 car

(27) 16 light projector

(28) 18 light line

(29) 20 imager

(30) 22 lens

(31) 24 evaluation unit

(32) 26 contour

(33) 28 3D-model

(34) 30 image sensor

(35) 32 pixel

(36) 34 polarization filter

(37) 36 filter set

(38) 38 result map

(39) 40 direct reflection

(40) 42 diffuse reflection

(41) 44 cuboid

(42) 46 V-shaped groove

(43) M measurement direction

(44) C column

(45) R row

(46) α angle