WO2019151911A1

WO2019151911A1 - Method and device for controlling position of a tool

Info

Publication number: WO2019151911A1
Application number: PCT/SE2018/050078
Authority: WO
Inventors: Magnus STJERNBERG
Original assignee: Stjernberg Automation Ab
Priority date: 2018-02-01
Filing date: 2018-02-01
Publication date: 2019-08-08
Also published as: CN112004634A

Abstract

The present invention relates a method and system (10) comprising: a laser beam source (11) configured to generate a laser beam (111); an illuminator (13) configured to generate a projection (20) on a surface (19); an image recorder (12) configured to receive an image of said projection (20) and a controller (17). The system (10) further comprises an image processing unit configured to process the image of said projection (20) and the controller is configured to control a position of the laser beam on the surface (19) with respect to the result of image processing.

Description

METHOD AND DEVICE FOR CONTROLLING POSITION OF A TOOL

TECHNICAL FIELD

The present invention relates to a method and device for aiding guidance of a tool in general and controlling a laser beam position in the tool in particular.

BACKGROUND

Generally, the surface of an article may be welded, coated and/or alloyed by the simultaneous and cooperative operation of a laser beam and deposited powder material. Presently, systems exist that employ a laser source and focusing apparatus, with a powder delivery apparatus provided as part of an integral package. The laser beam melts a relatively small area at the surface of the article, and a controlled volume of alloying particles are delivered into the melt pool via the powder flow stream.

In additive manufacturing, i.e. solid freeform fabrication or 3D printing, three-dimensional objects are built-up from raw material, such as powders in a series of two-dimensional layers or cross-sections.

According to some methods layers are produced by melting or softening material, for example, selective laser melting (SLM) or direct metal laser sintering (DMLS), selective laser sintering (SLS), fused deposition modeling (FDM), while others cure liquid materials using different technologies, e.g., stereolithography (SLA).

Additionally, there is sintering, a process of fusing small grains, for example, powders, to create objects. Sintering usually involves heating a powder, e.g. using laser beam. When a powdered material is heated to a sufficient temperature in a sintering process, the atoms in the powder particles diffuse across the boundaries of the particles, fusing the particles together to form a solid piece. In contrast to melting, the powder used in sintering need not reach a liquid phase as the sintering temperature does not have to reach the melting point of the material, sintering is often used for materials with high melting points such as tungsten and molybdenum. Both sintering and melting can be used in additive manufacturing. Selective laser melting (SLM) is used for additive manufacturing of metals or metal alloys, which have a discrete melting temperature and undergo melting during the SLM process.

In all above processes, the position of the nozzle and laser beam with respect to the receiving substrate is very important and crucial to obtain a satisfying result.

SUMMARY

Thus, there is a need for a fast and accurate system for determining position of two objects with respect to each other generally and position of a laser beam and material feed in particular. Especially, there is a need for accurate positioning of a laser beam- nozzle combination with respect to a receiving surface.

For these reasons a system is provided comprising: a laser beam source configured to generate a laser beam; an illuminator configured to generate a projection on a surface, an image recorder configured to receive an image of said projection; and a controller. The system further comprises an image processing unit configured to process the image of said projection. The controller is configured to control a position of the laser beam on the surface with respect to the result of the image processing. The system may further comprise a nozzle. In one embodiment, the nozzle is a tubular body with open ends and the laser beam passes through the tubular body. The image recorder may record the image of the projection through said tubular body. The system may further comprise optical elements for focusing laser beam. In one embodiment, the system further comprises optical elements for focusing reflection from the projection. In one embodiment, the laser beam passes through the illuminator. In one embodiment, the illuminator is arranged around the nozzle. The illuminator may be arranged to generate a concentric geometries. The illuminator may comprise a number of light emitting elements controlled by the controller. The illuminator may emit light in visible and/or invisible spectrum. The nozzle may comprise an inner surface portion and a confronting outer surface portion, spaced slightly from each other and cooperating to form an annular conical passage through which a powder material is delivered to an outlet opening. The system may be arranged to be displaced vertically and/or horizontally with respect to a substrate. The laser beam source may be the illuminator. The invention also relates to a method of guiding a body. The method comprising the steps of: generating an illuminated projection; recoding an image of the projections; processing the recorded image; and guiding the body with respect to information from image processing result. The method may further comprise executing one or several methods of: thresholding, blob analysis and image detection; object- and particle- detection algorithms; non-adaptive method include nearest neighbour, bilinear, and smooth-hue transition; adaptive method using edge sensing or variable gradient algorithms to perform the interpolation function; secure image signature; deferred image transport; or Resolution Proportional Digital Zoom (RPDZ). The projection may be a number of concentric circles. A number of fixed parameters may be used for determining deviations, said parameters comprising one or several of: diameter (d1 ) of a circular projection, radius (a) from a center to an inner circle, radius (a+b) from a center to a middle circle; radius (a+b+c) from a center to an outer circle, thickness of a line, circularity of the projection, brightness or intensity, line continuity, Bayer interpolation, flat-field correction, bad-pixel correction, image rotation, scaling and cropping. The method may further comprise continuous image processing, which computes a distance (r1 , r2) from a center point to an edge of visible parts and possible angels, and computes a position of the center point relative the edge and a corner. The body may be a nozzle.

The invention also relates to a computer-readable storage medium storing instructions that when executed by a computer cause the computer to perform a method for using a computer system to guide a body, the method comprising: generating an illuminated projection; recoding an image of the projections; processing the recorded image; and guiding the body with respect to information from image processing result.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is made to the attached drawings, wherein elements having the same reference number designation may represent like elements throughout.

Fig. 1 is a diagram of an exemplary embodiment of a system in which methods described herein may be implemented;

Fig. 2 is a flow diagram illustrating exemplary processing by the system of Fig. 1 ; Figs. 3A-3D illustrate schematic views of generated image projections used for measurement according to one embodiment of the invention;

Fig. 4 is an embodiment illustrating edge detection principles according to one embodiment of the invention;

Fig. 5 is a schematic illustration of one projection with fixed parameters, according to present invention;

Fig. 6 is another schematic illustration of one projection with computation parameters;

Fig. 7 is an embodiment illustrating groove detection principles according to one embodiment of the invention; and

Fig. 8 schematically illustrates one embodiment of a controller of the invention.

DETAILED DESCRIPTION

The following detailed description refers to the accompanying drawings. The same reference numbers in different drawings may identify the same or similar elements.

The system 10 of the invention according to one embodiment is illustrated schematically in Fig. 1 . The system 10, according to this embodiment, comprises a laser source 1 1 , an image recorder 12, a nozzle 13, optical elements (141 , 142, 143, 144), an illuminator 16 and a controller 17.

The laser source 1 1 may be any suitable high power laser capable of melting the fed material. The laser source radiates a laser beam 1 1 1 .

The image recorder 12 may be a camera, for still or moving images operating within visible, UV light, IR light, etc. The image captured by the camera 12 may be processed in the cameras control unit (not shown) or the signal representing the captured image may be provided to the controller 17 for further processing. The nozzle 13, which generally is circular in transverse cross-section, is a tube at the rear and a conical tip 131 at the front end. The nozzle is hollow and form a longitudinally extending beam passage for a laser beam 1 1 1 emitted by the source 1 1.

In one embodiment the conical tip 131 may be constructed of copper and may be removably secured to the front of the nozzle 13. In one embodiment, the conical tip may be adjustable radially, i.e. the size of the passage 132 can be adjusted.

An inner surface portion of the nozzle 13 and a confronting outer surface portion at the nozzle are spaced slightly from each other and cooperate to form an annular conical passage 133 through which (metal) powder 181 is delivered to outlet opening 132. Such powder enters passage 133 through a container 18. The powder may be carried by an inert gas flowing downward in conical passage. In one embodiment, the outlet or entire of passages 133 may be adjustable to control feed volume of the powder material.

During the mode of operation, the nozzle is injected with a high-power laser beam passing through the nozzle 13, and one or more powdered materials, e.g. carried by gas, in order to achieve, after melting the materials, a layer of surface coating 191 on the workpiece 19. Consequently, the nozzle has a structure allowing the free passage of the laser beam and the supply of materials in powder form peripherally.

The optical elements comprise a first focusing lens 141 , a second focusing lens 142 and a third focusing 143, and a two-way mirror 144. The number and function of the optical elements may vary with respect to function of the system.

The laser beam 1 1 1 , radiated from the laser source 1 1 , passes through the third focusing lens 143, which focus the beam onto the mirror 144. The reflected beam from the mirror 144 passes through the second focusing lens 142 and passes through the narrow end of conical tip 131 and exits through outlet opening 132 to impinge on upper surface of a workpiece 19 that is disposed in front of and in close proximity to exit opening 132. In a manner known to the art, during welding or cladding, for example, this laser beam heats a localized portion of surface of the workpiece 19 to form a shallow puddle of molten material. The camera“sees” the surface of the workpiece 19 through the mirror and the nozzles inner tubular passage, i.e. reflections 121 from the surface of the workpiece 19 are focused through second lens 142, pass through the two-way mirror 144 and focused through the first lens 141 onto the image sensor (not shown) of the camera 12.

Each lens may be individually adjusted vertically (lenses 141 and 142) or horizontally (lens 143) to focus the laser beam or reflections. In this case one or several motors (not shown) may cooperate with the lenses for displacing them vertically and/or horizontally. The mirror 144 may be rotatably adjusted to adjust the laser beam’s projection.

The illuminator 16 may comprise a number of light emitting elements 161 , such as Light Emitting Diodes (LEDs), for emitting light 162 in visible or invisible light spectrum. In this example, the illuminator 16 is configured as a collar around the body of the nozzle 13 comprising three rows of LEDs. In the present example the emitted light forms three concentric light circles (e.g. as illustrated in Fig. 3A) concentric with the focal point of the laser beam 1 1 1. The shapes 20 of the light generated by means of the elements 161 , are within the visible sight of the camera 12 concentric with the laser impinge point on the workpiece. This means that the illuminator may generate shapes with maximum size of the opening 134 of the nozzle 13, which is the maximum view sight for the camera with respect to the opening 132.

Clearly, the circular shape of the projection 20 can be varied depending on the application and needs. In one embodiment, the illuminator 16 may be connected to the controller 17 to control the illuminator to generate different forms or shapes, with different intensities, colors, etc.

The light emitting elements 161 may also comprise laser diodes. In one embodiment a second laser source may be used as illuminator. In yet another embodiment, an additional laser source may be situated in same position as laser source 1 1 or the camera or any other suitable position that can generate projections. In one embodiment the laser source 1 1 may be use as illumination source.

Fig. 8 is a diagram of an exemplary controller 17 in which methods and systems described herein may be implemented. The controller 17 may include a bus 171 , a processor 172, a memory 173, a read only memory (ROM) 174, a storage device 175, an input device 176, an output device 177, and a communication interface 178. Bus 171 permits communication among the components of the controller. The controller 17 may also include one or more power supplies (not shown). One skilled in the art would recognize that controller 17 may be configured in a number of other ways and may include other or different elements.

Processor 172 may include any type of processor or microprocessor that interprets and executes instructions. The processor 172 may also include logic that is able to decode media files, such as audio files, video files, multimedia files, image files, video games, etc., and generate output to, for example, a speaker, a display, etc. Memory 130 may include a random access memory (RAM) or another dynamic storage device that stores information and instructions for execution by the processor 172. Memory 130 may also be used to store temporary variables or other intermediate information during execution of instructions by the processor 172.

ROM 173 may include a conventional ROM device and/or another static storage device that stores static information and instructions for processor 172. Storage device 175 may include a magnetic disk or optical disk and its corresponding drive and/or some other type of magnetic or optical recording medium and its corresponding drive for storing information and instructions. The storage device 175 may also include a flash memory (e.g., an electrically erasable programmable read only memory (EEPROM)) device for storing information and instructions.

Input device 176 may include one or more conventional mechanisms that permit a user to input information to the controller 17, such as a keyboard, a keypad, a directional pad, a mouse, a pen, voice recognition, a touch-screen and/or biometric mechanisms, etc.

Output device 177 may include one or more conventional mechanisms that output information to the user, including a display, a printer, one or more speakers, etc.

Communication interface 178 may include any transceiver-like mechanism that enables controller 17 to communicate with other devices and/or systems. For example, communication interface 178 may include a modem or an Ethernet interface to a LAN. Alternatively, or additionally, communication interface 178 may include other mechanisms for communicating via a network, such as a wireless network. For example, communication interface may include a radio frequency (RF) transmitter and receiver and one or more antennas for transmitting and receiving RF data.

According to one exemplary implementation, controller 17 may perform various processes in response to processor 172 executing sequences of instructions contained in memory 173. Such instructions may be read into memory 173 from another computer-readable medium, such as storage device 175, or from a separate device via communication interface 180. It should be understood that a computer-readable medium may include one or more memory devices or carrier waves. Execution of the sequences of instructions contained in memory 173 causes processor 172 to perform the acts that will be described hereafter. In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions to implement aspects consistent with the invention. Thus, the invention is not limited to any specific combination of hardware circuitry and software.

The entire system 10 may be arranged movable with respect to the workpiece 19; it can move in X, Y (perpendicular to plane of the drawing) and Z directions, i.e. vertically and horizontally.

The main object of the invention is to aid guiding and positioning of the nozzle 13 and laser beam with respect to the workpiece vertically and/or horizontally: The camera 12 is configured to record image(s) from the illuminated shapes (projection). The recorded image signal is processed in the camera or provided to the controller 17 via interface 178 to process the recorded image signal and analyse the images to determine parameters relevant to position and/or distance of the nozzle to the workpiece 19.

Fig. 2 illustrates exemplary steps of a method according to the invention:

1 ) Process starts;

2) Illuminator 16 illuminates the surface of the workpiece 19 with a proper shape(s);

3) The image recorder 12 captures image of the illuminated area;

4) The image is processed in the image processor in the camera and/or in the

controller 17. The image processing function processes the image to detect the illuminated concentric circles (according to this example); 5) The controller 17 determines deviations in the image, such as one or more of: size of the circles, distance between circles, deviations in form of one or several circles, light intensity, colour, etc.;

6) The controller 17 adjusts the tool (i.e. combination of the laser beam and nozzle) with respect to the determined deviations. The adjustment may comprise vertical distance of the nozzle to the workpiece; X and Y positions of the nozzle with respect to the workpiece, laser power, tilting angel, etc.,

7) The process continues until the operation is stopped 8).

Figs 3A-3D illustrate examples of projections 20 on the surface of the workpiece from the light sources 161 , in this case comprising concentric circles 21 , 22 and 23.

In Fig. 3A, the rings are distanced. The size of the rings and distance between the rings may be interpreted as (in this case) too long distance between the nozzle 13 and the workpiece 19.

In Fig. 3B the size of the rings and distance between rings may be interpreted as in focus, i.e. correct position.

In Fig. 3C, the size of the rings and the distance between rings may be interpreted as too short distance between the nozzle 13 and the workpiece 19.

In Fig. 3D, the circles are partly invisible which means that there may be a level difference or an edge in the workpiece.

Thus, with multiple rings (or other suitable shapes) of different diameters, it is possible to detect geometries, edges and the like irrespective of how the tool is oriented or moving.

Fig. 4 illustrates exemplary steps of edge detection using a system according to the present invention. Assuming that a system (not shown) according described embodiment used for e.g. one of a cladding, welding, cutting, 3D-printing or like applications, a laser beam 1 1 1 is centered in the concentric circles’ projection above the workpiece 19.

Projections are illustrated in three different positions with three different dotted circles and the arrow shows the direction of the movement of the nozzle. Fig. 5 illustrates a number of parameters which can be fixed and used for determining deviations: these parameters may include diameter of the projection“d1”, radius“a” from center to inner circle, radius“a”+”b” from center to middle circle; radius“a”+”b”+”c” from center to outer circle, thickness of the lines (not shown),“circularity” of the projection, brightness or intensity, line continuity, Bayer interpolation, flat-field correction, bad-pixel correction, image rotation, scaling and cropping, etc.

In one example, shown in fig. 6, the continuous image processing, computes the distance (r1 , r2) from the center point to the edge of the visible parts and possible angels, and computes the position of the center point relative the edge and in case of example of Fig. 4, also the corner.

Examples of other algorithms and methods that can be used are:

^■ Thresholding, blob analysis and image detection;

^■ Object- and particle-detection algorithms;

^■ Non-adaptive methods include nearest neighbour, bilinear, and smooth-hue

transition;

^■ Adaptive methods: can use edge sensing or variable gradient algorithms to

perform the interpolation function;

^■ Secure Image Signature, which places a digital time stamp, frame counter, and trigger counter into every image delivered from the camera in real time. Monitoring the trigger-to-frame counter gives an indication of a missed frame that may be very useful in time- critical systems;

^■ Deferred image transport allows multiple cameras to acquire images

simultaneously and stage the read-out of images in a controlled manner to the PC. This ensures the camera-to-PC bus bandwidths are not exceeded;

^■ Resolution Proportional Digital Zoom (RPDZ) is a post processing algorithm that maintains a constant data rate between a camera and a host computer while digitally modifying (zooming) the camera’s field of view (FOV). This is done by subsampling pixels in the image in a manner proportional to the digital zoom level.

Based on the computed edge detection, the movement of tool relative the edge is controlled and adjusted. Fig. 7 illustrates another schematic example, e.g. in a welding application. In this case a groove 70 is welded. In same way as in the previous example, projections are illustrated in three different positions with three different dotted circles and the arrow shows the direction of the movement of the nozzle. However, in this case the groove 70, its extent and depth is detected by detecting the deviations in the projections during the image processing and the path of the nozzle is controlled.

The processed image may be compared to predetermined threshold values or shapes to determine distance and/or edges.

The method steps may be stored on a computer-readable storage medium as instructions that when executed by a computer cause the computer to perform a method for using a computer system to guide the nozzle.

The various embodiments of the present invention described herein is described in the general context of method steps or processes, which may be implemented in one embodiment by a computer program product, embodied in a computer-readable medium, including computer-executable instructions, such as program code, executed by computers in networked environments. A computer-readable medium may include removable and non-removable storage devices including, but not limited to, Read Only Memory (ROM), Random Access Memory (RAM), compact discs (CDs), digital versatile discs (DVD), etc. Generally, program modules may include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Computer-executable instructions, associated data structures, and program modules represent examples of program code for executing steps of the methods disclosed herein. The particular sequence of such executable instructions or associated data structures represents examples of corresponding acts for implementing the functions described in such steps or processes.

Software and web implementations of various embodiments of the present invention can be accomplished with standard programming techniques with rule-based logic and other logic to accomplish various database searching steps or processes, correlation steps or processes, comparison steps or processes and decision steps or processes. It should be noted that the words "component" and "module," as used herein and in the following claims, is intended to encompass implementations using one or more lines of software code, and/or hardware implementations, and/or equipment for receiving manual inputs.

The foregoing description of embodiments of the present invention, have been presented for purposes of illustration and description. The foregoing description is not intended to be exhaustive or to limit embodiments of the present invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of various embodiments of the present invention. The

embodiments discussed herein were chosen and described in order to explain the principles and the nature of various embodiments of the present invention and its practical application to enable one skilled in the art to utilize the present invention in various embodiments and with various modifications as are suited to the particular use

contemplated. The features of the embodiments described herein may be combined in all possible combinations of methods, apparatus, modules, systems, and computer program products.

Claims

1. A system (10) comprising:

• a laser beam source (1 1 ) configured to generate a laser beam (1 1 1 );

• an illuminator (13) configured to generate a projection (20) on a surface (19);

• an image recorder (12) configured to receive an image of said projection (20); and

• a controller (17);

characterized in

that the system (10) further comprises an image processing unit configured to process the image of said projection (20); and

that the controller is configured to control a position of the laser beam on the surface (19) with respect to the result of image processing.

2. The system of claim (1 ), wherein the system further comprises a nozzle (13).

3. The system according to any of claims 1 or 2, wherein the nozzle is a tubular body with open ends and the laser beam passes through the tubular body.

4. The system according to any of previous claims, wherein the image recorder records said image of the projection through said tubular body.

5. The system according to any of previous claims, further comprising optical elements for focusing (141 , 143) laser beam (1 1 1 ).

6. The system according to any of previous claims, further comprising optical elements (141 , 142) for focusing reflection (121 ) from projection (20).

7. The system according to any of previous claims, wherein the laser beam passes through the illuminator.

8. The system according to any of claims 2-7, wherein the illuminator is arranged around the nozzle.

9. The system according to any of previous claims, wherein the illuminator is arranged to generate a concentric geometries.

10. The system of claim 8, wherein the illuminator comprises a number of light emitting elements (161 ) controlled by the controller.

1 1 . The system according to any of previous claims, wherein the illuminator emits light in visible and/or invisible spectrum.

12. The system according to any of claims 2-1 1 , wherein the nozzle (13) comprises an inner surface portion and a confronting outer surface portion, spaced slightly from each other and cooperating to form an annular conical passage (133) through which a powder material (181 ) is delivered to an outlet opening (132).

13. The system according to any of previous claims, being arranged to be displaced

vertically and/or horizontally with respect to a substrate.

14. The system according to any of previous claims, wherein the laser beam source is the illuminator.

15. A method of guiding a body (13), the method comprising the steps of:

• generating an illuminated projection;

• recoding an image of the projections;

• processing the recorded image; and

• guiding the body with respect to information from image processing result.

16. The method of claim 15, further executing one or several methods of:

• thresholding, blob analysis and image detection;

• object- and particle-detection algorithms;

• non-adaptive method include nearest neighbour, bilinear, and smooth-hue

transition;

· adaptive method using edge sensing or variable gradient algorithms to perform the interpolation function;

• secure image signature;

• deferred image transport; or

• Resolution Proportional Digital Zoom (RPDZ).

17. The method of claim 15, wherein said projection is a number concentric circles.

18. The method of claim 17, wherein a number of fixed parameters are used for determining deviations, said parameters comprising one or several of: diameter (d1 ) of a circular projection, radius (a) from a center to an inner circle, radius (a+b) from a center to a middle circle; radius (a+b+c) from a center to an outer circle, thickness of a line, circularity of the projection, brightness or intensity, line continuity, Bayer interpolation, flat-field correction, bad-pixel correction, image rotation, scaling and cropping.

19. The method of claim 17, further comprising continuous image processing, which

computes a distance (r1 , r2) from a center point to an edge of visible parts and possible angels, and computes a position of the center point relative the edge and a corner.

20. The method according to any of claims 15-19, wherein said body is a nozzle.

21 . A computer-readable storage medium storing instructions that when executed by a computer cause the computer to perform a method for using a computer system to guide a body, the method comprising:

• generating an illuminated projection;

• recoding an image of the projections;

• processing the recorded image; and

• guiding the body with respect to information from image processing result.