Cutting machine with overview camera

Abstract

A cutting machine for cutting a flat surface having a graphical design with optical registration features is disclosed. The cutting machine includes a working surface for receiving at least one object, a first camera unit arranged so that the field of vision encompasses the whole working surface, a working group above the working surface, and at least one cutting device for cutting the at least one object. A computing unit with a circuit and program code for controlling the cutting machine includes a storage unit, a circuit and program code for evaluating images of the first camera unit to identify registration features of the at least one object in an image of the first camera unit, and being designed to define a cutting path for the cutting device according to at least one stored instruction and based on positions of the registration features in the image.

Claims

1. A cutting machine for cutting objects which have a flat surface, wherein the flat surface has a graphical design with optical register features, the cutting machine comprising: a working surface configured to receive at least one object, a first camera unit, which is arranged relative to the working surface in such a way that a field of vision of the first camera unit comprises the entire working surface, a working group, which is arranged movably above the working surface and has at least one cutting device as a tool of the cutting machine, the at least one cutting device cutting the at least one object, a computing unit with a circuit and program code for controlling the cutting machine, the computing unit comprising a memory unit for storing instructions for the cutting of certain objects, wherein the computing unit has the circuit and program code analyze images of the first camera unit and is configured to recognize register features of the at least one object in an image of the first camera unit, and is configured to define a cutting path for the cutting device in accordance with at least one stored instruction and based on positions of the register features in the image, wherein an instruction for cutting a specific object comprises information regarding an anticipated position of the specific object on the working surface, wherein the computing unit is configured to derive anticipated positions of register features based on the anticipated position of the at least one object, and wherein the computing unit is configured to define, in the image of the first camera unit, areas around the anticipated positions as regions of interest, beyond which no register features are searched for.

2. The cutting machine according to claim 1, wherein the first camera unit is configured to show only one partial area or a plurality of partial areas comprising the areas defined as regions of interest.

3. The cutting machine according to claim 1, wherein the first camera unit has a zoom function and is configured to zoom in on a partial area.

4. The cutting machine according to claim 1, wherein the computing unit is configured to analyse, in a partial area, at least one area defined as regions of interest.

5. The cutting machine according to claim 1, wherein the register features are register marks which are configured specifically for use with the cutting machine so as to make a position and orientation of the object relative to the working surface detectable, wherein the computing unit is configured to recognize the register marks on the flat surface of the at least one object in the image of the first camera unit, and to define the cutting path based on positions of the register marks.

6. The cutting machine according to claim 5, wherein the register marks comprise edges of the object.

7. The cutting machine according to claim 1, wherein the computing unit is configured to select an instruction based on recognized register features.

8. A computer program product with program code, which is stored on a machine-readable carrier, for controlling the cutting machine according to claim 1, wherein the program code is executable on the computing unit of the cutting machine and, upon execution, performs the following: retrieving information regarding an anticipated position of the at least one object on the working surface; deriving anticipated positions of register features based on the anticipated position of the at least one object; recording an image of the working surface; recognizing the register features of the at least one object in the image, wherein areas are defined around the anticipated positions as regions of interest, beyond which no register features are searched for in the image; associating the at least one object with at least one stored instruction; defining at least one cutting path based on the instruction and positions of the register features in the image; and controlling a cutting device for cutting the at least one object along the at least one cutting path.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The cutting machine according to the invention will be described in greater detail hereinafter purely by way of example on the basis of specific exemplary embodiments shown schematically in the drawings, wherein further advantages of the invention will also be discussed. The drawings specifically show:

(2) FIG. 1 a generic cutting machine with an overview camera;

(3) FIG. 2a-c an image of the overview camera, on the basis of cutting contours derived from the image and a cutting path of the cutting device defined on the basis of the image;

(4) FIG. 3 an exemplary embodiment of a cutting machine according to the first aspect of the invention;

(5) FIG. 4 an exemplary embodiment of a cutting machine according to the second aspect of the invention;

(6) FIG. 5 distortions in an image of the overview camera;

(7) FIG. 6 shadowing in an image of the overview camera;

(8) FIG. 7 an exemplary embodiment of the cutting machine according to the fourth aspect of the invention;

(9) FIG. 8 the working group of the cutting machine from FIG. 7 from above;

(10) FIG. 9-b two exemplary embodiments of the cutting machine according to the fifth aspect of the invention; and

(11) FIG. 10a-b areas defined as region of interest in accordance with the sixth aspect of the invention.

DETAILED DESCRIPTION

(12) FIG. 1 shows a generic cutting machine 1. As a flat-bed cutting machine, it has a table with a flat working surface 10, on which there are placed, by way of example, two objects 40, 40′ to be cut.

(13) Above the working surface 10 there is arranged a working group 12 with a cutting tool 15, in particular a blade. The working group 12 is displaceable two-dimensionally relative to the working surface 10 in a motorised manner so as to be able to approach any point of the working surface 10. To this end, the working group 12 is mounted movably in the X direction on a beam 13, which is in turn mounted movably in the Y direction on the table.

(14) A camera unit (overview camera 20) is arranged above the working surface 10 so that images of the entire working surface 10 can be recorded.

(15) In particular, the cutting machine 1 may also have a cutting tool 15 driven in oscillation and/or may be designed for cutting multi-walled composite plates, as described for example in EP 2 894 014 B1.

(16) The cutting machine 1 additionally has a computing unit 30. As shown here, the computing unit may be embodied as an external computer, which has a data connection to the machine 1, or may be integrated in the form of an internal control unit into the machine 1 itself. The overview camera 20 is designed to provide data of recorded images to the computing unit 30 for analysis.

(17) The computing unit 30 comprises a processor with computing capacity and algorithms for controlling the cutting machine 1 in accordance with a provided cutting instruction. The computing unit 30 additionally has a data memory for storing the cutting instructions and possibly further data.

(18) As a starting position, one or more of the objects 40, 40′ to be cut are placed on the working surface 10. It is either known precisely with which instruction or which instructions the objects 40, 40′ placed on the working surface 10 are associated, or it is at least known from which collection of instructions this instruction or these instructions originate.

(19) An image of the entire working region is recorded by means of the overview camera 20, and the position of the cutting contours is determined on the basis of this image. This is achieved by detection of register features in the graphical surface of the objects and also by detection of the position of said register features. The register features are stored as part of the instruction data in the relevant instruction and may be present either in the form of general features of the graphical design, or, advantageously, as register marks provided specifically for registration. This is known from the prior art.

(20) If the corresponding instruction is not yet known, the corresponding instruction may be determined initially with the aid of these markings and position thereof. If there are a plurality of instructions, all corresponding instructions are determined. The position of the cutting contours on the working surface is then determined via the object positions and the relative position of the cutting contours in the instruction data. This is shown by way of example in FIGS. 2a-c.

(21) FIG. 2a shows an image 50 recorded by the overview camera 20 of the cutting machine 1 from FIG. 1. The image region comprises the entire working region of the cutting machine, inclusive of the working surface 10, on which two objects 40, 40′ to be cut are situated. The working group 12 can be seen at the upper edge of the image and is preferably moved to the edge of the working region in order to record the image. The objects to be cut in this example are sheets 40, 40′ (for example made of paper, cardboard or plastic) and each have a graphical design 44, 44′ with patterns and/or inscriptions on their side facing the camera. In the shown example the graphical design in one case is a pattern in the shape of a crescent moon 41 and in the other case is a heart-shaped pattern 41′. In addition, a number of register marks 42 on each of the sheets 40, 40′ are shown. Register marks 42 may be in particular geometric figures, for example circular points of a certain diameter, as shown here.

(22) FIG. 2b shows the cutting contours 45, 45′ of the sheets 40, 40′ to be cut. The shapes of the cutting contours 45, 45′ and the relative positions thereof on each of the sheets 40, 40′ are stored in instructions. Together with the image 50 from FIG. 2a, a position of the cutting contours 45, 45′ on the working surface may be determined.

(23) On the basis of the image 50 from FIG. 2a, the corresponding instruction optionally also can be associated with the relevant sheet 40, 40′ by the control unit.

(24) FIG. 2c illustrates, by way of example, a movement path for the cutting tool of the machine generated on the basis of the determined positions of the cutting contours 45, 45′. Here, the working group is moved relative to the working surface in such a way that the cutting tool is moved firstly from its original position 152 a first cutting path (dashed line 151). The cutting tool is then brought, for example lowered, into a cutting position and cuts the object along the cutting path (solid line 152.

(25) FIG. 3 shows an exemplary embodiment of a cutting machine 1, which has a plurality of reference marks 25 corresponding to the first aspect of the present invention, which reference marks are arranged in the field of vision of the overview camera 20 and fixedly in relation to the working surface 10. In the shown example six reference marks 25 are distributed around the edge of the working surface. The reference marks 25 may be identified in the images of the overview camera 20, and their position in the image may be compared with their known defined positions relative to the working surface 10. The computing unit 30 (shown here integrated in the machine) is thus able to determine positions of objects 40, 40′ on the working surface 10 or positions of referencing features on the objects 40, 40′, in each case with greater accuracy, on the basis of the positions of the reference marks 25.

(26) It is also possible to verify a correct orientation of the overview camera 20 relative to the working surface 10, and to correct the orientation as necessary, on the basis of the positions of the reference marks 25 in the image of the overview camera 20.

(27) FIG. 4 shows a cutting machine 1, on the working surface 10 of which there are placed two objects 40, 40′ of different material thickness. The first object 40 has a greater material thickness and is made for example of a multi-layer cardboard or a composite plate. As a result of the position of the overview camera 20, there are distortions in the images recorded by said overview camera, and these distortions increase with greater proximity to the edges of the image. However, in the case of a negligible material thickness (for example in the case of paper), as is the case here with the second object 40′, due to the planar surface of the working surface 10 there are no problems encountered when recognising objects 40, 40′ or their position on the working surface 10.

(28) The distortions become relevant, however, with increasing material thickness and increasing eccentricity in the positioning of the object relative to the camera position. This is illustrated in FIG. 5. This shows the object features 44, 44′ of the two objects from FIG. 4 recognised in the image of the camera. Whereas the features 44′ of the thin object 40′ made of paper are presumed to be in their correct position, the presumed positions of the features 44 of the thick object 40, which on account of the greater material thickness are situated in a plane distanced further from the working surface 10 than the features 44′ of the thin object 40′, deviate more greatly from their actual positions with increasing distance from the camera position 21. The reference marks 42 in the image of the camera are thus each shown further away from the image centre (dashed circles 49) than they are actually situated.

(29) On the one hand, this may mean that the object 40 either is not recognised at all on the basis of the image of the overview camera 20, or is even mistaken for another object and is thus cut incorrectly. On the other hand, it is possible that the object 40 is correctly recognised, but, since the positions of the reference features have been deduced incorrectly, an imprecise to completely incorrect cutting path is calculated. In this case the object 40 is also cut incorrectly.

(30) This problem is solved in accordance with the second aspect of the present invention in that information regarding the material thickness of the object 40 to be cut is provided to the control unit 30. The material thickness may be determined beforehand by a camera, specified by a user, or also provided as part of the instruction, for example.

(31) A deviating distortion in the image of the overview camera 20 may be excluded by means of the information regarding the material thickness, whereby an exact recognition and determination of the position of the object 40 and its register features is made possible.

(32) Alternatively, the overview camera 20 may be designed to be automatically height-adjustable and may be displaced in the Z direction depending on the material thickness, whereby the distance to the object surface and therefore the focus remain constant independently of the particular material thickness.

(33) FIG. 6 shows an image 50 of the working surface 10 recorded by the overview camera 20. The working surface 10 is partially in a shadow 70. This may be the result of direct solar radiation, for example, such that the working group 12 casts a shadow 70 over the working surface 10, as in this example. The object 40 to be cut is situated partially in the shadow 70 and partially in the brightly lit area of the working surface 10.

(34) A disadvantage may therefore be that not all contours of the register features are detected with sufficient precision in the image 50 of the overview camera. In accordance with the third aspect of the invention the camera therefore detects an HDR (=high dynamic range) image of the working surface 10, so as to ensure a sufficiently high contrast both in dark and light areas for determination of the position of the register marks 42 in the image 50.

(35) Various methods are known for recording HDR images. For example, two images of different exposure time recorded directly one after the other may be superimposed. Alternatively, just one image is recorded, wherein the overview camera is designed to select the exposure time for each pixel or for certain pixel areas depending on the brightness of the particular imaging region.

(36) A recording of a plurality of images of the same scene may be used advantageously—also with uniform exposure—in order to reduce artefacts and image noise and thus in order to more accurately determine contours, so as to enable a more accurate and quicker determination of the position of the register marks 42 in the image 50. Pixels at the edge regions of the register marks 42 for example may be assigned a brightness value averaged from values of the plurality of images.

(37) In accordance with the fourth aspect of the invention shown in FIGS. 7 and 8, the cutting machine 1 has a further camera 60 in addition to the overview camera 20. This second camera is likewise oriented towards the working surface 10. It has a clearly smaller recording region 62 than the overview camera 20, but is arranged movably relative to the working surface 10, so that preferably images of the entire working surface 10 can be recorded. The second camera 60 is preferably mounted movably as a beam camera on the same beam 13 as the working group 12. In particular, it may be embodied as part of this working group 12. FIGS. 7 and 8 by way of example show a corresponding embodiment of the cutting machine 1.

(38) In FIG. 7 an exemplary embodiment of the cutting machine 1 is shown, wherein a second camera unit 60 is provided in the working group 12 and is designed to record images in the direction of the working surface 10. Here, the image region 62 of said camera in each position comprises only a small part of the working surface 10. The overview camera 20 is also designed in this embodiment to record images of the entire working surface 10.

(39) In FIG. 8 the working group 12 mounted movably on the beam 13 and comprising the blade 15 and beam camera 60 is shown from above. The position of the relatively high overview camera 20 is also shown. The working group 12 is positioned here in such a way that two register marks 42 of an object 40 to be cut are situated in the field of vision 62 of the beam camera 60.

(40) A detailed image recorded by the beam camera 60 may now be compared with the overall image recorded previously by the overview camera 20. The positions of the register marks 42 may thus be verified or determined relative to the working surface 10. An image is firstly recorded by means of the overview camera 20. By means of this image, relative positions of the register marks 42 are firstly determined, that is to say the arrangement of the register marks relative to one another. One or more registered marks 42 is/are then approached by the beam camera 60, and the position of said register mark(s) is determined with high accuracy.

(41) In order to verify the register mark positions, the positions determined with the overview camera 20 are compared with the positions determined with the beam camera 60.

(42) In order to determine the register mark positions on the working surface 10, the positions of all register marks 42 are determined with high accuracy by transformation of the positions determined in the image of the overview camera 20 by the positions determined in the image of the beam camera 60.

(43) In accordance with the fifth aspect of the invention, such an additional camera 60 may also be used for calibration of the overview camera 20. This is shown in FIGS. 9a and 9b. The cutting machine 1 in this case has a calibration function controlled by the computing unit 30. Within the scope of this function, once started, positions of a plurality of grid points on the entire working surface 10 may be determined fully automatically with high accuracy with the aid of the beam camera 60. To this end, as shown in FIG. 9a, the working surface itself may be embodied as a calibration working surface 18, i.e. may itself comprise the corresponding grid points, or alternatively, as shown in FIG. 9b, a calibration sheet 48 is placed on the working surface 10 for calibration and comprises the grid points.

(44) The positions of the grid points determined by the beam camera 60 are stored as target positions. The same grid points are then recorded by the overview camera 20. With the aid of the target positions and the comparison with the positions of the grid points in the image of the overview camera 20, the overview camera 20 and the beam camera 60 may be calibrated relative to one another. If the beam camera 60 is housed in the same working group 12 as the cutting tool 15, errors in the drive system of the working group 12 may thus also be compensated for, advantageously.

(45) In accordance with the sixth aspect of the invention, an ROI (=region of interest) area may be selected already before the image of the overview camera is recorded and is the only area of interest for the determination of the position of the register features. This is illustrated in FIGS. 10a and 10b.

(46) To this end, cutting instructions are provided, in which specific additional information is stored, which information allows the working surface 10 to be limited to the ROI area. It includes, in particular, anticipated positions of the objects 40, 40′ to be cut and their dimensions. Either just one image of the selected areas is then recorded, or just the corresponding areas of the overall image are analysed. This advantageously saves computing and memory capacity and accelerates the process. In addition, printed images are prevented from being incorrectly misinterpreted as register marks. If just one image of the ROI is recorded by the overview camera, the overview camera may additionally be designed to zoom in on the corresponding area, whereby a higher resolution is achievable.

(47) In FIG. 10a in image 50 of the entire working surface 10 is shown, as has been recorded by the overview camera (see FIG. 2a). On the basis of information regarding the likely position of the objects 40, 40′ on the working surface 10, areas 52 which each comprise an anticipated position of the relevant registered marks 42 are defined by the computing unit. Only in these areas 52 are register marks 42 searched for, and therefore only positions of register marks 42 which also lie in these areas 52 are determined. This advantageously not only spares computing capacity in time, but also prevents misinterpretations of features of the graphical design 41, 41′ as register features.

(48) In FIG. 10b the image 50 of the overview camera from FIG. 10a has been limited to two ROI areas and therefore comprises only the area images 51 and 51′. An object 40, 40′ to be cut is shown at least in part in each area image 51, 51′, and therefore the register marks 42 are visible, so that a cutting path can be generated in each case. Due to the smaller image area which has to be analysed, the relative positions of the register marks 42 may be detected more quickly, thus accelerating the process.

(49) It goes without saying that these described figures schematically show only possible exemplary embodiments. The various approaches may also be combined with one another and with devices or methods from the prior art.