Method for referencing a tool in a magnetic levitation system

Abstract

In various embodiments, a method for determining a position of an element of a mechanical system relative to a levitated platform of a magnetic levitation system and / or a workpiece located thereon. The method comprising the following position referencing steps: monitoring at least one parameter of the magnetic levitation system indicative of the position of the levitated platform with respect to the magnetic levitation system, inducing relative movement between the levitated platform and the element of the mechanical system, stopping the relative movement between the levitated platform and the mechanical system when physical contact is established, and determining the position of the element of the mechanical system relative to the levitated platform. The method described herein can be used in additive manufacturing and assembly processes to correct for any misalignment between two independently operating systems.

Description

[0001] METHOD FOR REFERENCING A TOOL IN A MAGNETIC LEVITATION SYSTEM

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] The present application claims the benefit of priority of European Patent Application No. 23195445.4, filed September s, 2023, the content of which is hereby incorporated by reference it its entirety for all purposes.

[0004] FIELD OF THE INVENTION

[0005] The present invention generally relates to the field of automated machine manufacturing and in particular to a method for referencing a tool in a magnetic levitation system.

[0006] BACKGROUND OF THE INVENTION

[0007] Recent advancements in automated manufacturing, particularly in 3D printing, have demonstrated promising potential for producing a wide range of applications, from industrial objects to medical implants. Additive manufacturing, often referred to as 3D printing, encompasses a group of technologies that enable the creation of physical parts or objects through the layer-by-layer addition of materials.

[0008] The manufacturing lines are becoming increasingly complex and involve multiple independently operating systems, each responsible for different stages of the manufacturing process, including 3D printing, milling, and quality control stations. While these systems are typically mechanically operated, such as gantry systems, they may also include nonmechanical systems that utilize levitation technology.

[0009] Magnetic levitation systems comprise stator and mover modules, wherein the interaction between magnetic fields generated by the stator and magnets embedded in the movers enables levitation of the movers above the stator. Each of the movers may be regarded as an independent manufacturing platform. Precise control over the strength and orientation of the magnetic fields allows for stable levitation and frictionless movement of the movers above the stator module. Feedback from magnetic field sensors, such as Hall sensors, enables the control system of the magnetic levitation system to adjust the electric current flowing through the coils in the stator module. By modulating the magnetic field strength and distribution, the control system can counteract external disturbances that may affect the position and orientation of the levitated platform, ensuring stability and controlled movement of the manufacturing platforms throughout the entire manufacturing process.

[0010] When multiple independent manufacturing systems participate in a manufacturing process and interact with an object placed on a levitated manufacturing platform, ensuring correct alignment between the individual machining tools and the object arranged on the levitated platform systems becomes crucial. Modern systems are equipped with position feedback mechanisms that monitor and adjust the relative positions between machining tools and the machined object within the respective system in real-time. However, problems may arise when multiple machining systems are used in combination and interact with an object to be manufactured which is located on a levitated platform. Not only can errors and tolerances of each manufacturing stage agglomerate, but the relative orientation of the manufactured object with respect to the levitated platform can change.

[0011] SUMMARY

[0012] The present invention provides a method which may be used to determine the position of an element of a first mechanical system relative to an element of a second mechanical system. The method may be used in an additive manufacturing or other manufacturing / assembly processes comprising at least one mechanical system, which is a manufacturing / machining system, and a second system, which is a transporting system, preferably a transporting system comprising a magnetic levitation system.

[0013] Accordingly, in various embodiments a method is provided for determining a position of an element of a mechanical system relative to a levitated platform of a magnetic levitation system and / or a workpiece located thereon. In a first step, the method comprises monitoring at least one parameter of the magnetic levitation system indicative of the position of the levitated platform with respect to the magnetic levitation system (in particular with respect to the stator of the magnetic levitation system).

[0014] In a next step, the method comprises inducing relative movement between the levitated platform and the element of the mechanical system. Here, either the element of the mechanical system may be moved towards the levitated platform or vice versa or both the element of the mechanical system and the levitated platform may be moved towards one another.

[0015] In a next step, the method comprises stopping the relative movement between the levitated platform and the mechanical system upon detection of a change of the at least one parameter. Here, a change of the at least one parameter may be only qualified as one when the change of the monitored parameter exceeds a predefined threshold. The predefined threshold may be chosen such that false positives, e.g. induced by noise in the signal, are avoided and a reliable detection is achieved.

[0016] Finally, the method comprises determining the position of the element of the mechanical system relative to the levitated platform and / or the workpiece located thereon based on a stop position of the element and / or a stop position of the levitated platform. The present invention relates to a manufacturing method that utilizes two independent systems: a mechanical / machining system and a transport system in the form of a magnetic levitation system. The magnetic levitation comprises at least one levitated platform with a workpiece located thereon and operates according to the principles described above. The workpiece may include an object that is being manufactured, or a part to be assembled to another part. The element of the mechanical system may refer to a tool or any other element of the mechanical system which interacts with the workpiece located on the levitated platform during the manufacturing / machining process.

[0017] According to the invention, monitored movement of entities of the two systems (i.e. tool of the mechanical system or levitated platform of the magnetic levitation system) relative to one another is used to determine the position of the entity of one of the systems within the coordinate system of the other system. Preferably, the magnetic field generated by the magnetic levitation system is used as the sensing field as it may indicate a position in which the entities of both systems contact one another. Physical contact between the entities inherently exerts a force on the entities which, in particular, results in a change of the force acting on the magnetic levitation platform. The point in space or the location at which physical contact between the entities takes place corresponds to the stop position and may be used to reference the location of the entity of one system within the coordinate system of the other system.

[0018] By monitoring the at least one parameter of the magnetic levitation system, the position of the levitated platform relative to the stator may be tracked. When inducing relative movement between the levitated platform and the element of the mechanical system, the changes in the at least one parameter which is being monitored are indicative of a physical contact between entities of the two systems. The relative movement of the two systems is stopped as soon as a change is detected in the at least one monitored parameter. Based on the stop position, the relative position of the element of the mechanical system relative to the levitated platform or - if the position of the workpiece on the levitated platform and its form is known - the workpiece located thereon may be determined. Once the position of the entity of one system has been referenced in the coordinate system of the other system, movement of the entity of one system in the coordinate system of the other system is known from the positional data provided by the other system. The positional data of both systems may be cross-referenced to increase accuracy of the alignment and to detect misalignments.

[0019] For the purpose of the present method, a mechanical system and a magnetically levitated system are used. The mechanical system may comprise any mechanical / machining system, such as a conventional gantry system or robot arm-based system which is movable in at least one axis. The magnetic levitation system, as describe above, may comprise a stator with planar motor arrangement and a levitated platform comprising permanent magnets. Preferably, multiple levitated platforms may be operated by the magnetic levitation system.

[0020] Overall, owing to its fast moving speed, fast response rate and high precision, the magnetic levitation system as used in the context of the method according to various embodiments described herein may be particularly useful for the manufacturing / assembly of different parts, wherein multiple levitated platforms are operated on a stator defining a manufacturing / assembly surface, wherein each levitated platform carries its own individual workpiece to be manufactured / assembled.

[0021] According to various embodiments of the method the element may be fixedly attached to the mechanical system. In other words, movement of the element within the mechanical system may be inferred from positional data of the mechanical system.

[0022] According to various embodiments of the method the element may be movable along at least one axis by means of the mechanical system. Preferably, the element of the mechanical system may be movable in at least three directions and even more preferably the system may offer six degrees of freedom (6DOF). The mechanical system may comprise a gantry-based system or a system using a robotic arm to move the element through space.

[0023] According to various embodiments of the method the monitored parameter may comprise a current provided to the magnetic levitation system to maintain the levitated platform in levitation and / or a current induced in a magnetic sensor provided in the magnetic levitation system. For this purpose, the magnitude of electric current needed to generate the magnetic force by the stator module of the magnetic levitation system to keep the platform levitated at a predetermined distance above the stator module may be used as a reference value. From the change of the magnetic force needed to maintain the platform in levitation at the same position or to maintain continuous movement of the platform and the, the forces acting on the levitated platform may be determined. Thus, changes of the electric current flowing through electromagnets of the stator module (controlled by the control loop of the magnetic levitation system) may be used to determine physical interaction points of the two systems, i.e. the stop positions. A current induced in the magnetic sensor as referred to above may be, for example, an electric current induced in Hall sensors distributed throughout the stator of the magnetic levitation system.

[0024] According to various embodiments of the method the element of the mechanical system may comprise a tool of the mechanical system. Examples of the tool of the mechanical system may include tools of additive manufacturing, tools used in dispensing applications, tools used in subtractive manufacturing (milling, turning), tools used for assembly of different pieces, or sensors including optical probes or touch probes. According to various embodiments of the method the tool may comprise an extruder nozzle of a 3D printer. In such an embodiment, the mechanical system may comprise a 3D printer, with the extruder nozzle depositing print material on the levitated platform which corresponds to the print bed. In further related embodiments, the tool may comprise an array of extruder nozzles. Each extruder nozzle may be used to extrude a different print material. The printing operation of the 3D printer may correspond to printing operation of ordinary 3D printers as know from the state of the art, i.e. by printing layer upon layer.

[0025] According to various embodiments of the method, inducing relative movement between the levitated platform and the element of the mechanical system may comprise moving the element by means of the mechanical system towards the levitated platform and / or the workpiece located thereon. Thus, the levitated platform may remain stationary while the element of the mechanical system approaches the levitated platform and / or the workpiece located thereon, acting as a movable probe. As soon as the element of the mechanical system comes into physical contact with the levitated platform or the workpiece located thereon, a change of the electromagnetic force necessary to maintain the platform in levitation at the same height above the stator or at the same position on the stator, or in the electric current induced in the magnetic sensors on the platform is detected.

[0026] According to various embodiments of the method, inducing relative movement between the levitated platform and the element of the mechanical system may comprise moving the levitated platform and / or the workpiece located thereon by means of the levitation system towards the element of the mechanical system. Thus, the element of the mechanical system may remain stationary and act as a stationary probe while the levitated platform moves towards the element.

[0027] According to various embodiments of the method, change of the at least one parameter may include an increase of a current provided to the magnetic levitation system to maintain the levitated platform in levitation and / or a current induced in a magnetic sensor provided in the magnetic levitation system beyond a predefined threshold. Thus, only a change in the monitored parameter that is larger than a predefined threshold may be considered as relevant to define the stop position. It should be noted that the predefined threshold may be chosen such that is well below changes of the signal corresponding to forces acting on the element and / or workpiece which may lead to breaking or deforming thereof.

[0028] According to various embodiments of the method, the step of determining the position of the element of the mechanical system relative to the levitated platform and / or the workpiece located thereon may comprise using the stop position of the mechanical system (i.e. the element thereof) as a reference position for the levitated platform and / or the workpiece located thereon in a coordinate system of the mechanical system, and / or using the stop position of the levitated platform as a reference position for the element of the mechanical system in a coordinate system of the magnetic levitation system.

[0029] According to various embodiments the method may further comprise attaching a referencing tool to the mechanical system in addition to or instead of the tool of the mechanical system, performing the steps for determining the position of the element of a mechanical system relative to the levitated platform and / or a workpiece located thereon with the referencing tool. Thus, the referencing tool could be used to reference the two systems, given the offset or difference of dimensions between the tool and the referencing tool is known. This may be a particularly useful method for fragile tools or tools with geometry inconvenient for the referencing method described herein.

[0030] According to further embodiments the method may include performing the steps for determining the position of the element of a mechanical system relative to the levitated platform and / or a workpiece located thereon with regard to at least one further axis along which the element is movable, wherein the at least one further axis is perpendicular to the axis. In general, the referencing method may be performed along any of the three axes (x, y, z) separately.

[0031] According to further embodiments the method may comprise correcting the position of the element of the mechanical system (within the coordinate system of the magnetic levitation platform) and / or the position of the levitated platform and / or the workpiece located thereon (within the coordinate system of the mechanical system) by a correction distance corresponding to a distance travelled by the element and / or the levitation platform during a response time of a parameter monitoring system of the magnetic levitation system and / or the response time of the overall magnetic levitation system. The purpose of this step is, if deemed necessary, to account for the response time of the hardware used to monitor the parameter which may lead to slight offsets in the stop positions and thus to slight positional errors. The correction may be made by adjusting the position of mentioned components by a specific correction distance, wherein the correction distance is determined based on the distance traveled by the element and / or the levitation platform during the response time of a parameter monitoring system. The response time refers to the time it takes for the monitoring system to detect and respond to changes in the parameters of the magnetic levitation system.

[0032] According to further embodiments of the method the at least one parameter of the magnetic levitation system is indicative of the orientation of the levitated platform with respect to the magnetic levitation system. The orientation of the levitated platform with respect to the magnetic levitation system refers to the angle between the place of the levitated platform relative to the surface of the stator unit. According to further embodiments the method may comprise determining the position of the workpiece on the levitated platform based on at least one determined position of the element of the mechanical system relative to the workpiece located on the levitated platform, determining, based on the determined position of the workpiece on the levitated platform, an orientation and / or location of the workpiece on the levitated platform, determining an offset between a target position and / or orientation of the workpiece on the levitated platform and the determined position of the workpiece on the levitated platform, adjusting an orientation of the levitated platform to compensate the determined offset of the location of the workpiece on the levitated platform. In this manner, a misalignment of the workpiece, which is fixed to the levitated platform and not movable with respect thereto, on the platform may be compensated for and the movement path of the levitated platform may be also corrected to account for or compensate the misalignment of the workpiece on the levitated platform.

[0033] BRIEF DESCRIPTION OF DRAWINGS

[0034] FIG. 1 shows an embodiment of the tool referencing method for 3D printing according to the invention.

[0035] FIG. 2 shows an exemplary time course of the electromagnetic force exerted by the magnetic levitation system.

[0036] FIG. 3 shows an embodiment of the tool referencing method for assembly according to the invention.

[0037] DETAILED DESCRIPTION

[0038] The following description of the embodiments is merely illustrative in nature and is in no way intended to limit the invention, its application or uses. Additionally, the invention may be practiced according to the claims without some or all of the illustrative information.

[0039] FIG. 1 shows an exemplary scheme 100, which depicts an embodiment of the tool referencing method for 3D printing application. In such an embodiment, the mechanical system comprises a 3D printer wherein the tool located thereon is an extruder 103. The extruder 103 is mounted on a linear drive axis 102, which moves the extruder 103 along the vertical axis, while a magnetically levitated print bed 104 performs horizontal movements at a constant distance above a stator 106 of a magnetic levitation system. The change in relative position of the extruder 103 and the levitated print bed 104 is performed by moving the levitated print bed 104 and the extruder 103 mounted thereon while at least one parameter of the magnetic levitation system is monitored. Upon physical contact between the extruder 103 and the levitated print bed 104 and / or a workpiece 105 located thereon, a feedback system 101 of the 3D printer provides a stop position of the extruder 103 and / or a feedback system of the magnetic levitation system (not explicitly shown) provides a stop position of the levitated print bed 104. By referencing the known stop position of one system, e.g. the extruder 103, in particular its tip, within in the other system, e.g. the magnetic levitation system, the composite system is calibrated. Once the composite system has been calibrated based on the stop positions, the manufacturing process can take place, i.e. the extruder 103 can deposit print material onto the levitated print bed 104, effectively manufacturing the workpiece 105.

[0040] A graph 200 is shown in FIG. 2, which depicts an example parameter reading during the referencing method of the present invention. In the graph 200, a series of data points 201 represents the magnitude of the electromagnetic force Fem, measured in Newton, over time, measured in seconds, wherein the force Fem corresponds to the electromagnetic force exerted to keep the levitated platform at a constant height above the planar motor arrangement or to keep the levitated platform moving at a constant velocity. The stop position, corresponding to the point of physical contact between the two systems and a change of forces acting on the levitated platform, is detected as a change of the electromagnetic force Fem (e.g. magnitude of the electromagnetic force vector), which is indicated in the graph 200 by a shaded area 202. Due to noise in the system, the change of the electromagnetic force which is interpreted as a stop point may need to be larger than a predefined threshold.

[0041] FIG. 3 shows an exemplary scenario 300, which displays an embodiment of the tool referencing method for an assembly application. In this embodiment, a tool 301 is mounted on a mechanical system which is able to move the tool 301 along multiples axes, wherein movement along each axis is supervised by a position feedback system. The tool 301 holds a first workpiece 302, which needs to be assembled to a second workpiece 303 located on a magnetically levitated platform 304. In this example, the magnetically levitated platform 304 is maintained at a constant position above a stator 305. The magnetically levitated platform 304 and the tool 301 of the mechanical system are parts of two independent systems, which need to be calibrated to each other to enable precise assembly of the first workpiece 302 to the second workpiece 303. According to an embodiment of the method for tool referencing as described herein, moving the first workpiece 302 along the z axis (vertically) until it touches the second workpiece 303 (scenario I) results in a change of the electromagnetic force Fem_z, thereby defining the stop position of tool of the mechanical system, wherein the precise coordinates are provided by the position feedback of the z axis. Similarly, the first workpiece 302 can be referenced to the second workpiece 303 along the x axis (scenario II) and y axis (scenario III), wherein the corresponding changes of the electromagnetic force Fem_x and Fem_y, respectively, are observed. In that manner, a precise location / orientation of the second workpiece 303 on the magnetically levitated platform 304 may be determined. This in turn, enables precise manufacturing of an object on the magnetically levitated platform, such as placing the first workpiece 302 exactly on a target spot 306, which comprises an adhesive.

[0042] Overall, the exemplary scenario 300 illustrated in FIG. 3 may be used to calibrate the composite system, i.e. to determine or verify the position indications of one system within the other system. In a calibrated composite system, the exemplary scenario can be used to determine or verify the location / orientation of a workpiece on the magnetically levitated platform.

Claims

Claims1. Method for determining a position of an element of a mechanical system relative to a levitated platform of a magnetic levitation system and / or a workpiece located thereon, the method comprising the following position referencing steps: monitoring at least one parameter of the magnetic levitation system indicative of the position of the levitated platform with respect to the magnetic levitation system; inducing relative movement between the levitated platform and the element of the mechanical system; stopping the relative movement between the levitated platform and the mechanical system upon detection of a change of the at least one parameter; determining the position of the element of the mechanical system relative to the levitated platform and / or the workpiece located thereon based on a stop position of the element and / or a stop position of the levitated platform.

2. Method of claim 1 , wherein the element is fixedly attached to the mechanical system.

3. Method of claim 1 , wherein the element is movable along at least one axis by means of the mechanical system.

4. Method of any one of claims 1 to 3, wherein the monitored parameter comprises a current provided to the magnetic levitation system to maintain the levitated platform in levitation and / or a current induced in a magnetic sensor provided in the magnetic levitation system.

5. Method of any one of claims 1 to 4, wherein the element of the mechanical system comprises a tool of the mechanical system.

6. Method of claim 5, wherein the tool comprises an extruder nozzle of a 3D printer.

7. Method of any one of claims 1 to 6,wherein inducing relative movement between the levitated platform and the element of the mechanical system comprises moving the element by means of the mechanical system towards the levitated platform and / or the workpiece located thereon.

8. Method of any one of claims 1 to 6, wherein inducing relative movement between the levitated platform and the element of the mechanical system comprises moving the levitated platform and / or the workpiece located thereon by means of the levitation system towards the element of the mechanical system.

9. Method of any one of claims 1 to 8, wherein change of the at least one parameter includes an increase of a current provided to the magnetic levitation system to maintain the levitated platform in levitation and / or a current induced in a magnetic sensor provided in the magnetic levitation system beyond a predefined threshold.

10. Method of any one of claims 1 to 9, wherein the step of determining the position of the element of the mechanical system relative to the levitated platform and / or the workpiece located thereon comprises: using the stop position of the mechanical system as a reference position for the levitated platform and / or the workpiece located thereon in a coordinate system of the mechanical system; and / or using the stop position of the levitated platform as a reference position for the element of the mechanical system in a coordinate system of the magnetic levitation system.11 . Method of any of claims 5 to 10, as long as dependent on claim 5, further comprising: attaching a referencing tool to the mechanical system in addition to or instead of the tool of the mechanical system; performing the steps for determining the position of the element of a mechanical system relative to the levitated platform and / or a workpiece located thereon with the referencing tool.

12. Method of any of claims 1 to 11 , further comprising: performing the steps for determining the position of the element of the mechanical system relative to the levitated platform and / or a workpiece located thereon with regardto at least one further axis along which the element is movable, wherein the at least one further axis is perpendicular to the axis.

13. Method of any one of claims 1 to 12, further comprising: correcting the position of the element of the mechanical system and / or the position of the levitated platform and / or the workpiece located thereon by a correction distance corresponding to a distance travelled by the element and / or the levitation platform during a response time of a parameter monitoring system of the magnetic levitation system and / or the response time of the overall magnetic levitation system.

14. The method of any one of claims 1 to 13, wherein the at least one parameter of the magnetic levitation system is indicative of the orientation of the levitated platform with respect to the magnetic levitation system.

15. Method of any one of claims 1 to 14, further comprising: determining the position of the workpiece on the levitated platform based on at least one determined position of the element of a mechanical system relative to the workpiece located on the levitated platform; determining, based on the determined position of the workpiece on the levitated platform, an orientation and / or location of the workpiece on the levitated platform; determining an offset between a target position and / or orientation of the workpiece on the levitated platform and the determined position of the workpiece on the levitated platform; adjusting an orientation of the levitated platform to compensate the determined offset of the location of the workpiece on the levitated platform.

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