Plausibility checking method for additive manufacturing methods

Abstract

The invention relates to a plausibility checking method for rapid prototyping devices, in particular for stereolithography devices. In this connection, input data (14) is checked which is present particularly in the form of graphics data and of which every file renders a layer. Every layer comprises a plurality of pixels. The component to be printed in the respective layer is produced based on output data by the rapid prototyping device. The input data of two consecutive layers is checked and the sum of all pixels to be exposed is determined for every layer. A signal (22) is output in particular as a warning signal (26) when the pixel sum of a following layer is larger than in the previous layer by a predetermined factor.

Claims

1. A plausibility checking method for additive manufacturing devices for producing a component, with input data and output data, comprising providing at least one processor configured to produce the input data as graphics data which is rendered as layers to be printed, respectively, wherein every layer comprises one or more pixels, which correspond to a component region to be printed in a concerned layer, check the input data (14) of at least two consecutive layers and determine for every layer a sum of all the one or more pixels to be exposed, output a signal (22) when the pixel sum of a following layer differs from that of the previous layer at least by a predetermined factor, check any deviation with regard to number of pixels in at least two consecutive layers and output a signal (22) when the deviation changes from a positive deviation into a negative deviation which differs from zero, and generate the output data which controls the additive manufacturing device to produce the component to be printed if no signal is output.

2. The method as claimed in claim 1, wherein the pixel sum is an exposure area, wherein the signal (22) is output when the pixel sum of the following layer is larger at least by the predetermined factor.

3. The method as claimed in claim 1, wherein the signal (22) is output when the sum of all pixels to be exposed of a first layer is zero or smaller than a predetermined value.

4. The method as claimed in claim 1, wherein the method is used with an additive manufacturing device (20) and used with objects printed directly on a platform without a support structure.

5. The method as claimed in claim 1, wherein the difference between the numbers of pixels of at least two consecutive layers is monitored and a signal (22) is output when the difference in percentage terms is larger than a predetermined value, larger than a positive value or smaller than a negative value.

6. The method as claimed in claim 5, wherein the value is an absolute value.

7. The method as claimed in claim 1, wherein an increase and/or decrease in the number of pixels between at least two consecutive layers which have already been checked is considered with regard to a decision if the signal is not output.

8. The method as claimed in claim 1, wherein the signal (22) is displayed on a display device and indicates that a construction error is expected and another orientation of the one or more objects and renewed feeding into the CAM software (12) is recommended.

9. A computer program product comprising program code which is stored on a non-transitory machine-readable medium, the machine-readable medium comprising computer instructions executable by a processor, which computer instructions cause the processor to perform the method as claimed in claim 1, on an additive manufacturing device (20).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages, details and features may be taken from the following descriptions of an exemplary embodiment of the invention in conjunction with the drawings, in which:

(2) FIG. 1 shows a schematic view of the exposed pixels of the layers of an object to be produced, illustrated in different layers, namely the layers 1, 2, 12, 22, 32, 42;

(3) FIG. 2 shows an illustration of the exposed pixels of another object illustrating the layers 3 and 4;

(4) FIG. 3 shows an illustration of the number of pixels of the object according to FIG. 1 over the layers from 0 to 500, namely both with a tilted orientation and a parallel orientation;

(5) FIG. 4 shows an illustration of the first 45 layers in the diagram according to FIG. 3, in turn both with the tilted orientation and the parallel orientation;

(6) FIG. 5 shows an illustration of the increase or decrease in percentage terms of the exposure area from layer to layer, over the first 100 layers, wherein in turn the parallel orientation and the tilted orientation are illustrated;

(7) FIG. 6 shows a schematic illustration of the units for an inventive plausibility checking method;

(8) FIG. 7 shows a schematic illustration of a support structure;

(9) FIG. 8 shows a schematic illustration of a further embodiment of a support structure; and

(10) FIG. 9 shows a schematic illustration of a further embodiment of a support structure.

DETAILED DESCRIPTION

(11) The inventive method is described in more detail on the basis of the Figures, in particular initially of FIGS. 1, 3 and 4.

(12) In FIG. 1, six different images of exposed pixels are illustrated corresponding to the respective layers 1, 2, 12, 22, 32 and 42. They form the graphics data and have each been produced by means of the CAM software.

(13) According to FIG. 1, the layer 0001.png is free from exposed pixels.

(14) This may basically also be taken from FIG. 4. There, the solid gray curve shows a small value close to zero or possibly exactly zero in layer no. 1, referred to as Slice Number 1 therein.

(15) In FIGS. 3 and 4, the total number of the exposed pixels is plotted as “total area [pixel]” above the number of the respective layer (“slice number”). The respective curves for a correct orientation and for an incorrect orientation are plotted, in FIG. 3 the total area with parallel orientation (“total area, parallel orientation”) as a thick black line and in FIG. 4 as a black line with circles, and in both FIGS. 3 and 4 the curve in case of an incorrect orientation as a gray line, referred to as “total area non-parallel orientation”.

(16) In FIG. 3, the total number of layers is plotted on the axis of abscissas, i.e. 500, while the scale in FIG. 4 is selected such that only the layers 1 to 45 are plotted.

(17) In the exemplary case, the layer thickness of every layer is 50 μm, wherein it is to be understood that the method may be applied analogously with any layer thickness.

(18) Even if no pixels are to be seen in “0001.png” of FIG. 1, 10 pixels are present indeed. In the consecutive layer, referred to as layer “0002.png” herein, the total number of pixels is 8726.

(19) Now, the inventive plausibility checking method checks the ratio of the exposed pixels between consecutive layers, in this case the layers “0001.png” and “0002.png”. Accordingly, the ratio is 827.6:1, calculated from the pixel numbers 8726 and 10.

(20) In any case, it is considerably larger than a predetermined value which is set to the factor 2 herein, and a signal is output inventively which indicates a case of error. In this case, there is a construction error as the 3D object was tilted accidentally in the CAD processing such that it does not bear against the zero level or base with a planar exterior surface but only with the mentioned 10 pixels.

(21) Now, the further check is described herein even if the inventive method already now causes the print job to be interrupted and asks the user to correct the orientation of the one or more objects in the CAM software.

(22) If the number of pixels of the first layer is smaller than a predetermined value, e.g. 100, an additional error message may be output if necessary, e.g. also to the effect that planar contact with the zero level of the installation space is not given.

(23) However, it is apparent from FIG. 3 and FIG. 4 that, in case of a parallel orientation, the number of pixels to be exposed in the first 45 layers is almost 1.8 million. This orientation is a buildable orientation; the CAM software has realized the parallel orientation in correspondence with the user input.

(24) Layer 3 corresponding to “0003.png” has a pixel number of 24565. Here, in turn, the quotient would be calculated from the number of exposed pixels of the layers 3 and 2, and a value would result which amounts to approximately 3 and is larger than 2 in any case.

(25) Here, too, an error would be indicated if the error inquiry got through to that point.

(26) The layers 12, corresponding to “0012.png”, 22, corresponding to “0022.png”, 32, corresponding to “0032.png” and 42, corresponding to “0042.png” are also illustrated herein as is apparent from FIG. 1 and show that the construction area increases considerably corresponding to the number of the exposed pixels. However, the relative increase in the number of pixels per layer is below the factor 2, wherein the increase in pixels decreases increasingly strongly relatively, when viewed over 10 layers.

(27) According to the invention, it is favorable when the relative increase in the number of pixels is checked. This is apparent from FIG. 5. The type of curves corresponds to the curves from FIGS. 3 and 4. The delta, i.e. the difference in the total area, is referred to as “delta total area”, respectively, i.e. the increase or decrease in the number of exposed pixels compared to that of the previous layer.

(28) If you consider the error case initially, it is apparent from FIG. 4 that the number of pixels differs from zero in case of layer 3 and only decreases in case of layer 4, and again differs from zero in case of layer 5.

(29) This is expressed in the gray curve according to FIG. 5 wherein the delta is negative in case of layer 4 as there is a decrease in the number of pixels between layer 3 and layer 4.

(30) Ultimately, the gray curve according to FIG. 5 is the differential of the gray curve from FIG. 4.

(31) The black curve in FIG. 5 shows the deviation, i.e. the delta, of the black curve from FIG. 4 in the non-error case. The first 100 layers are plotted on a secondary axis or secondary abscissas in high resolution on the right-hand side.

(32) As is apparent, the delta is small from layer to layer, less than +/−0.4%, i.e. it amounts to less than 0.4%.

(33) The following table represents the delta for the layers 1 to 10 numerically; accordingly, layer 2 is assigned the value of 87160%, approximately corresponding to the factor of 872.6 according to the above description.

(34) TABLE-US-00001 TABLE Delta of the pixels available in the image relative to the number of pixels in the previous image, in percent. Delta total area [%], Delta total area [%], slice parallel orientation = non-parallel orientation = number = Delta total area compared to Delta total area compared to layer previous layer, previous layer, number in %, parallel orientation in %, tilted orientation 1 2 0.00 87160.00 3 0.00 181.52 4 0.00 −64.46 5 0.00 181.39 6 0.00 80.03 7 0.00 54.88 8 0.00 40.33 9 0.00 34.33 10 0.00 28.96 11 0.00 24.66 12 0.00 21.08 13 0.00 18.23 14 0.00 16.31 15 0.00 14.34 16 0.00 13.11 17 0.00 11.80 18 0.00 10.83 19 0.00 9.88 20 0.00 9.32

(35) It is to be understood that the threshold value starting from which a signal may be output is adjustable to a large extent. The delta decreases when the layer number increases corresponding to the course of the gray curve in the FIGS. 4 and 5.

(36) It is apparent from FIG. 2 how a building job for objects with support structures is checked according to a further configuration of the invention. Here, the layers 3 and 4 corresponding to “0003.png” and “0004.png” are illustrated. Comparison of both exposure images reveals that a new component region or island 10 emerges in layer 4. However, in this exemplary embodiment the ratio of exposed pixels would not be such that an error signal according to the above check would be output. However, the non-connected component region or island 10 is realized as a new area in free space, and respective layer development would cause a new object to be created without connection to the construction platform and the rest of the object which would accordingly be able to possibly move freely in the print fluid or which would be attached to a wrong position possibly.

(37) This error case is also covered inventively, and it is recommended to the user to insert a support structure in the CAM software for the non-connected component region 10 or else to realign the component correspondingly.

(38) A diagram is apparent from FIG. 6 which is to symbolize the individual steps and units for the inventive method. A CAM software module 12 produces the input data 14, which is supplied to a plausibility checking module 16, via user intervention. The plausibility checking module 16 outputs output data 18 which serves as data which is fed to the stereolithography device 20.

(39) However, the output data 18 is only output directly if the plausibility check was successful, i.e. no signal was output. Transmission of output data is stopped until the user has noticed the warning message and has enabled further processing or follows the warning message.

(40) The signal 22 is output when either the number of exposed pixels between consecutive layers differs by less than a predetermined value or a comparison of consecutive layers reveals that a new island 10 has emerged in the respective considered layer compared to the previous layer.

(41) Such a comparison may be realized by means of a standard image processing algorithm.

(42) In the exemplary embodiment illustrated, the signal 22 is fed to the CAM device, and additionally a display device 24 is activated via a warning signal 26, said display device indicating to the user not to release the building job.

(43) Even if only a display device 24 is illustrated in FIG. 6, it is to be understood that bidirectional communication with the plausibility checking module 16 is possible herein to the effect that then the user decides how to proceed further with the building job in the plausibility checking module 16.

(44) For instance, corresponding to the recommendation the user will then cancel and delete the building job and resort to the CAM software module 12 again to carry out the necessary corrections therein.

(45) It is to be understood that the then corrected building job is fed to the plausibility checking module 16 again such that the plausibility check may be performed several times also cyclically until an adequate building job is provided which is fed to the stereolithography device 20 by means of the output data 18.

(46) Exemplary support structures 30 for clarification of the invention are illustrated in FIG. 7. They extend between the base or zero level 32 and the object 34.

(47) A first support bar 36, a second support bar 38 and a support branch 40 are illustrated exemplarily. They are provided virtually, i.e. as input data 14, for the plausibility checking module 16.

(48) Every support structure 30 is sliced, i.e. consists of layers, in the exemplary case having a layer thickness of 50 μm.

(49) The support bar has 36300 layers, i.e. a length of 15 mm, from the base 32 to the branch 40.

(50) In case of the print material used, it may have this length without a crossbar being necessary, and may then offer the desired support.

(51) The length of the bar 36 between the branch 40 and the object 34 amounts to 250 layers or 12.5 mm.

(52) The cross-sectional area 42 or the number of pixels per layer amounts to approximately 450, with a deviation range of +/−50, for the bar, both below and above the branch. This corresponds to a diameter of approximately 1.2 mm.

(53) For the bar 38, the pixel number per layer also amounts to between 400 and 500.

(54) However, as it is not supported laterally by a branch, the unsupported length is considerably larger than for bar 36 and amounts to 600 layers or 30 mm.

(55) This length is too large to still allow for reliable support.

(56) According to the invention, an error signal is thus output for the bar 38. Due to the branch 40 or else due to the object 34, the number of pixels per layer changes significantly for bar 36 when viewed over 400 layers but remains within 400 to 500 for bar 38.

(57) In this exemplary embodiment the number of consecutive layers for which no increase in area is required to prevent the signal amounts to 400. The predetermined measure of the increase in area—and thus of the increase in the number of pixels—amounts to 50%.

(58) At the branch at layer 300 the number of pixels increases to 750 for bar 36. This is sufficient to prevent the error case and thus the signal—even if at layer 400, i.e. after the branch, the number of pixels is smaller than 500 again.

(59) However, at layer 400 of bar 38 the number of pixels is still less than 500—i.e. across its entire length up to this point—such that the signal is triggered thereat.

(60) It is to be understood that the indicated values are only exemplary and may be adapted to the requirements to a large extent depending on the print material.

(61) In FIG. 8, a different support structure compared to the embodiment in FIG. 7 is illustrated. Here, the support bars 36 are considerably shorter and have a ratio of height to diameter 42 of approximately 6:1.

(62) In case of this ratio, the bars 36 are considered to be stable such that no signal 22 is output.

(63) However, the bar 38 has a height to diameter ratio (HDV) of approximately 25:1.

(64) This is too much for sufficient stability especially as there is no lateral support or branch. An error signal is output.

(65) In FIG. 9, the bars 36 have almost the same length as bar 38 from FIG. 8. They have a height to diameter ratio of approximately 20:1, which would be too much without support.

(66) However, already in the lower third of their height they branch out into struts 44 which have a laterally supporting effect. As a result, the error case is prevented particularly as the self-supporting length of the bars 36 in FIG. 9 is only up to a HDV of approximately 5:1.

(67) In this respect, it is crucial for error prevention if the self-supporting, i.e. branchless length of a support bar has a HDV of more than a predetermined measure, here e.g. 8:1.

(68) This may be detected by the number of layers compared to the area of the support structure (=number of pixels).

(69) It is to be understood that the third dimension has to be considered in fact, too, even if 2D structures are illustrated herein.

(70) It should be further understood that the predetermined measures, values, ratios, and any other value or number discussed herein are not limited to the values set forth but may vary depending on the specific job or building structure that is being manufactured.

(71) Functions of the printing system described hereinabove may be controlled through instructions executed by a computer-based control system. A control system suitable for use with embodiments described hereinabove may include, for example, one or more processors connected to a communication bus, one or more volatile memories 56 m (e.g., random access memory—RAM) or non-volatile memories (e.g., Flash memory). A secondary memory (e.g., a hard disk drive, a removable storage drive, and/or removable memory chip such as an EPROM, PROM or Flash memory) may be used for storing data, computer programs or other instructions, to be loaded into the computer system.

(72) For example, computer programs (e.g., computer control logic) may be loaded from the secondary memory into a main memory for execution by one or more processors of the control system. Alternatively or additionally, computer programs may be received via a communication interface. Such computer programs, when executed, enable the computer system to perform certain features of the present invention as discussed herein. In particular, the computer programs, when executed, enable a control processor to perform and/or cause the performance of features of the present invention. Accordingly, such computer programs may implement controllers of the computer system.

(73) Aspects of the invention may be operational with numerous other general purpose or special purpose computing system environments or configurations. Examples of well-known computing systems, environments, and/or configurations that may be suitable for use with the invention include, but are not limited to, personal computers, server computers, hand-held or laptop devices, multiprocessor systems, microprocessor-based systems, set top boxes, programmable consumer electronics, network PCs, minicomputers, mainframe computers, distributed computing environments that include any of the above systems or devices, and the like.

(74) The computing environment may execute computer-executable instructions, such as program modules. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. The invention may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules may be located in both local and remote computer storage media including memory storage devices.

(75) Components of a computer used herein may include, but are not limited to, a processing unit, a system memory, and a system bus that couples various system components including the system memory to the processing unit. The system bus may be any of several types of bus structures including a memory bus or memory controller, a peripheral bus, and a local bus using any of a variety of bus architectures. By way of example, and not limitation, such architectures include Industry Standard Architecture (ISA) bus, Micro Channel Architecture (MCA) bus, Enhanced ISA (EISA) bus, Video Electronics Standards Association (VESA) local bus, and Peripheral Component Interconnect (PCI) bus also known as Mezzanine bus.

(76) The system memory may include computer storage media in the form of volatile and/or nonvolatile memory such as read only memory (ROM) and random access memory (RAM). A basic input/output system (BIOS), containing the basic routines that help to transfer information between elements within computer, such as during start-up, is typically stored in ROM. RAM typically contains data and/or program modules that are immediately accessible to and/or presently being operated on by processing unit.

(77) The drives and their associated computer storage media may provide storage of computer readable instructions, data structures, program modules and other data for the computer. A user may enter commands and information into the computer through input devices such as a keyboard and pointing device, commonly referred to as a mouse, trackball or touch pad. Other input devices (not shown) may include a microphone, joystick, game pad, satellite dish, scanner, or the like. These and other input devices are often connected to the processing unit through a user input interface that is coupled to the system bus, but may be connected by other interface and bus structures, such as a parallel port, game port or a universal serial bus (USB). A monitor or other type of display device is also connected to the system bus via an interface, such as a video interface. In addition to the monitor, computers may also include other peripheral output devices such as speakers and printer, which may be connected through a output peripheral interface.

(78) The computer may operate in a networked environment using logical connections to one or more remote computers, such as a remote computer. The remote computer may be a personal computer, a server, a router, a network PC, a peer device or other common network node, and typically includes many or all of the elements described above relative to the computer. The logical connections may include a local area network (LAN) and a wide area network (WAN), but may also include other networks. Such networking environments are commonplace in offices, enterprise-wide computer networks, intranets and the Internet.

(79) The terms “program” or “software” or “algorithm” are used herein in a generic sense to refer to any type of computer code or set of computer-executable instructions that can be employed to program a computer or other processor to implement various aspects of embodiments as discussed above. Additionally, it should be appreciated that according to one aspect, one or more computer programs that when executed perform methods of the present invention need not reside on a single computer or processor, but may be distributed in a modular fashion among different computers or processors to implement various aspects of the present invention.

(80) An algorithm is herein, and generally, conceived to be a self-consistent sequence of steps leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like.

(81) Any of the following terms such as “sending”, “receiving”, “transmitting”, “forwarding”, “caching”, “causing”, “providing”, “generating”, “adding”, “subtracting”, “removing”, “analyzing”, “determining”, “enabling”, “identifying”, “modifying” or the like, refer to the actions and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (e.g., electronic) quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices.