METHOD FOR DETERMINING THE POSITION OF A WORKPIECE IN AN ORTHONORAL REFERENCE POINT BASED ON THE STRUCTURE OF A NUMERICALLY CONTROLLED MACHINE TOOL

Description

Technical field of the invention

[0001] The invention falls within the field of numerically controlled machine tools, and in particular accessories and tooling for numerically controlled machine tools.

[0002] More specifically, the invention relates to a method for determining a workpiece origin position in a numerically controlled machine tool, and a system for implementing said method. Technological background

[0003] A numerically controlled machine tool, referred to as a "machine tool" hereafter, is a machine adapted to control the movement of a tool based on instructions from a control unit, typically a computer, to perform operations on a workpiece fixed within the machine tool's enclosure. These operations may consist of material removal, such as machining or polishing, assembly operations, such as welding or bonding, or any other operation that can be performed by the action of a tool on a workpiece.

[0004] Instructions are transmitted in the form of a computer program. The tool's movement is performed from a starting position at a point on the tool intended to act on the workpiece. This starting position is commonly called the "program origin" and is characterized by coordinates in a standardized orthonormal coordinate system based on the machine's structure. The program origin is defined by an operator.

[0005] The movement of the tool is determined according to the position of the part within said structure, this position being characterized by coordinates of a point called "part origin".

[0006] In order to perform operations on the part that meet high precision requirements, it is necessary to know precisely the position of the program origin and the part origin relative to each other.

[0007] To this end, solutions have been developed using optical sensors placed within machine tool enclosures and adapted to identify the position in space of the workpiece origin, and in particular the position of a reference object on the workpiece defining the workpiece origin, for example, an end of an edge, the center of a hole, etc. These optical sensors communicate the position of the workpiece origin thus measured to the control unit, and the toolpath can be determined from the program origin and the workpiece origin with high precision.

[0008] To identify the position of a reference object, optical sensors rely on contrast differences in an acquired image of the part. More specifically, a contrast difference is determined between a foreground surface, for example, defined by one face of the part, and a background surface, for example, defined by a second face of the part or a face of a support structure. This contrast difference is caused, for example, by a difference in material, surface finish, etc., between the foreground and background surfaces.

[0009] However, these optical sensors have limitations, as they may fail to recognize certain reference objects under specific circumstances. Indeed, when the foreground and background have insufficient contrast to be distinguished by the optical sensors, the latter are likely to produce erroneous measurements. These erroneous measurements can lead to the production of parts that do not meet manufacturing requirements, and therefore can cause significant quality problems. US 2008 / 239326 A1 describes a method for determining the position of a part according to the preamble of claim 1.

[0010] The present invention proposes to solve this drawback and therefore aims to ensure the accuracy of the identification of the part origin position in all circumstances, and thus aims to guarantee compliance with the quality requirements of the parts produced following this identification. Summary of the invention

[0011] The invention solves the aforementioned drawbacks by proposing a solution enabling the identification of the position of a part origin under all circumstances.

[0012] To this end, the invention relates to a method for determining the position of a part in an orthonormal frame based on a structure of a numerically controlled machine tool in order to determine the trajectory of a tool for carrying out an operation on said part.

[0013] The process includes the following steps: holding the part in position on a support fixed in an enclosure of said machine tool, so as to arrange a through hole in the part opposite a through orifice in the support, said hole opening entirely into said orifice, illumination by a light source, so as to emit light radiation from the support, towards an optical measuring device arranged in the enclosure of the machine tool, through the hole and the orifice, reading of the part by the optical measuring device, so that the latter determines the position of said part in the orthonormal frame.

[0014] Advantageously, the process includes, before the lighting stage, a stage of integrating the light source within the support.

[0015] In particular embodiments, the invention may further comprise one or more of the following features, taken individually or in all technically possible combinations.

[0016] In particular implementation modes, the step of integrating the light source within the support is followed by a step of electrically connecting the light source by an electrical connection module arranged within the machine tool enclosure.

[0017] In particular modes of implementation, the hole in the part is arranged coaxially with a through hole formed by the orifice of the support.

[0018] According to another aspect, the present invention also relates to a system for implementing the process described above.

[0019] The system comprises a part with a through hole extending from an outer face of the part to an inner face of the part, and a support with a through orifice extending from an outer face of the support. The part is fixed to the support such that its inner face is aligned with the outer face of the support and the through hole opens entirely into the orifice. The system further comprises a light source fixed to the support so as to emit light through the through hole and orifice to an optical measuring device.

[0020] In particular embodiments, the orifice is constituted by a hole with which the through hole of the part is arranged coaxially.

[0021] In particular embodiments, the light source is removable from the support.

[0022] In particular embodiments, the light source is arranged in a cavity in the support into which the orifice opens.

[0023] In particular embodiments, the system includes an electrical connection module configured to supply the light source with electricity when the support is fixed to a structural element of the machine tool.

[0024] In particular embodiments, the light source includes a diffusion element for diffusing light through the hole and the orifice. Brief description of the figures

[0025] Other features and advantages of the invention will become apparent from the following detailed description, given by way of non-limiting example, with reference to the accompanying drawings in which: there figure 1schematically represents an enclosure of a numerically controlled machine tool in which is illustrated a system for implementing the process according to the invention, and a detailed view of a part of the system.

[0026] Note that the figures are not necessarily drawn to scale for reasons of clarity. Detailed description of the invention

[0027] The present invention relates to a method for determining the position of a part 100, and more specifically of a reference object of said part 100, in an orthonormal coordinate system based on the structure of a machine tool. Determining the position of a reference object of said part 100 makes it possible to determine the trajectory of a tool 20 for performing an operation on said part 100.

[0028] The present invention also relates to a system 10 for implementing this method.

[0029] In examples of implementation of the present invention, the operation to be carried out on the part 100 may consist of a material removal, for example machining, polishing, etc., assembly operations, such as welding, gluing, etc., or any operation in which a tool 20 is moved along a predetermined path to act on a part 100. This part 100 may be formed from a raw part, a semi-finished part, etc.

[0030] Furthermore, it should be noted that not all the components of a machine tool are described in this text, as they are well known to those skilled in the art.

[0031] The method according to the present invention comprises a first step consisting of holding the workpiece 100 in position, on which the machine tool 20 is intended to perform an operation. Holding the workpiece 100 in position consists of eliminating all of its degrees of freedom.

[0032] This part 100 is held in position on a support 110 fixed in an enclosure of said machine tool, so as to arrange a through hole 101 in the part 100 opposite a through orifice 111 in the support 110. Advantageously, the hole 101 opens entirely into said orifice 111, that is to say, the entire surface of its cross-section opens into said orifice 111.

[0033] As shown by figure 1 , the hole 101 extends from an external face 102 of the part 100 to an internal face 103 of the part 100. The term "hole" in this text defines a cylindrical opening, preferably with a circular cross-section.

[0034] In the implementation example shown on the figure 1The part 100 is fixed to the support 110 so that its inner face 103 is arranged to rest against an outer face 112 of said support 110. The part 100 is fixed to the support 110 by any appropriate means within the reach of a person skilled in the art, so as to ensure that it is held in position.

[0035] Furthermore, the opening 111 extends from the outer face 112 of the support 110. Preferably, the opening 111 is a hole with which the hole 101 of the part 100 is coaxially aligned. This feature allows for precise alignment of the part 100 with respect to the support 110.

[0036] The support 110 may consist of a structural element 30 of the machine tool, such as a table, or may consist of an added device, fixed on the structural element 30 of the machine tool in a manner appropriate to the reach of a person skilled in the art.

[0037] In the example shown on the figure 1The support 110 is an added device fixed against the structural element 30 of the machine tool, by an internal face 113. The part 100 can be fixed to the added device upstream, that is to say before the latter is fixed to the structural element 30 of the machine tool, or can be fixed to the added device once the latter has been fixed to the structural element 30.

[0038] The process also includes a step of illumination by a light source 120, so as to emit light radiation from the support 110, towards an optical measuring device 40 arranged within the machine tool enclosure, through the hole 101 and the orifice 111. The light radiation is schematically represented by arrows in the detailed view of the figure 1 .

[0039] The optical measuring device 40 is configured to acquire, along a given optical axis, for example perpendicular to the outer face 102 of the part 100, an image of the part 100 fixed on the support 110, and is configured to identify at least one reference object of the part 100, such as an edge or points of said part 100. Based on this reference object, the trajectory of the tool 20 is determined by a control unit to perform operations on the part 100. In the preferred embodiment of the present invention, as shown in the figure 1 , the reference object of the part is the center of hole 101.

[0040] Such an optical measuring device is known to those skilled in the art. Therefore, it is not described in detail in this text.

[0041] Following the lighting step, the process according to the invention includes a step of reading the part 100 by the optical measuring device 40, so that the latter determines the position of said part 100 in the orthonormal frame, on the basis of the recognition of the reference object of the part 100.

[0042] Thus, the position of part 100 relative to tool 20, and more precisely relative to the position of a point on tool 20, is determined accurately and reliably. Indeed, thanks to the illumination step, and in particular thanks to the direction and orientation of the light emission, the reference object of part 100, and more specifically hole 101, is easily identifiable because it is highlighted by backlighting.

[0043] Thus, hole 101 can be precisely identified and the position of its center can be precisely determined. Consequently, the movement of tool 20 to perform operations on part 100 is carried out precisely relative to the position of the center of hole 101.

[0044] The light source 120 is fixed within the support 110 during an integration step carried out before the lighting step. The integration step is followed by a connection step in which the light source 120 is connected by an electrical connection module 50 arranged within the machine tool enclosure and connected to a power supply.

[0045] The connection module 50 is fixed to the structural element 30 of the machine tool and is connected to a power source. In the example shown on the figure 1in which the support 110 is an added device, the connection is made when the latter is fixed on the structural element 30 of the machine tool, for example by establishing contact between connectors of the connection module 50 with terminals of the light source 120 previously fixed within the support 110.

[0046] The light source 120 may include a lighting module (not shown in the figure) coupled to a diffuser, for example made of plastic, designed to diffusely reflect the light emitted by the lighting module so that the luminance is uniform. This feature helps to ensure high accuracy when identifying the position of part 100, as it prevents potential reflection phenomena that could distort the measurements.

[0047] Advantageously, the light source 120 can be removable from the support 110, so that it can be removed after operations have been carried out on the part 100 or for maintenance operations.

[0048] In the preferred embodiment of the invention, the light source 120 is arranged in a cavity 114 of the support 110 into which the orifice 111 opens. The cavity 114 is therefore adapted to receive the light source 120, and more specifically, the diffuser.

[0049] As shown by figure 1 , cavity 114 has an opening leading to a side of support 110 allowing the light source 120 to be engaged easily and quickly, and possibly to be removed.

[0050] Advantageously, in an example of implementation not shown in the figure, the support 110 can hold in position several parts 100 each having a hole 101 opening into the orifice 111 or into an associated orifice 111, each hole 101 constituting a reference object of a part 100.

[0051] The present invention finds advantageous application in the field of micromechanics and in particular in the field of watchmaking.

[0052] In particular, the tool 20 can be formed by a cutting tool designed to remove material from the part 100, the latter being formed by a needle. More specifically, the present invention can be implemented to create a gouge on the head of the needle, concentric with the hole 101.

[0053] It goes without saying that the invention is not limited to this application and that it could be implemented in any field in which operations must be carried out on parts by a tool of a machine tool.

Claims

1. Method for determining the position of a part (100) in an orthonormal frame of reference based on a structure of a numerically controlled machine tool in order to determine the trajectory of a tool (20) for performing an operation on said part (100), the method including the steps of: - holding the part (100) in position on a fixed carrier (110) inside an enclosure of said machine tool, so as to arrange a through-hole (101) comprised in the part (100) such that it faces a through-orifice (111) comprised in the carrier (110), said hole (101) opening out in its entirety inside said orifice (111), - illuminating, using a light source (120), so as to emit light radiation from the carrier (110) towards an optical measuring instrument (40) arranged inside the enclosure of the machine tool, through the hole (101) and the orifice (111), - reading the part (100) using the optical measuring instrument (40) so as to determine the position of said part (100) in the orthonormal frame of reference; said method being characterised in that it includes, before the illumination step, a step of integrating the light source (120) into the carrier (110).

2. Method according to claim 1, wherein the step of integrating the light source (120) into the carrier (110) is followed by a step of electrically connecting the light source (120) by an electrical connection module (50) arranged in the enclosure of the machine tool.

3. Method according to one of claims 1 to 2, wherein the hole (101) in the part (100) is arranged coaxially with a through-hole constituted by the orifice (111) in the carrier (110).

4. System (10) for implementing the method according to one of claims 1 to 3, characterised in that it includes a part (100) comprising a through-hole (101) extending from an outer face (102) of the part (100) to an inner face (103) of the part (100), a carrier (110) comprising a through-orifice (111) extending from an outer face (112) of the carrier (110), the part (100) being fixed to the carrier (110) such that its inner face (103) is arranged against the outer face (112) of said carrier (110) and such that the hole (101) opens out in its entirety inside said orifice (111), the system (10) further including a light source (120) fixed into the carrier (110) so as to emit light radiation through said hole (101) and orifice (111) to an optical measuring instrument (40).

5. System (10) according to claim 4, wherein the orifice (111) is constituted by a hole (101) with which the through-hole (101) in the part (100) is coaxially arranged.

6. System (10) according to one of claims 4 or 5, wherein the light source (120) can be removed from the carrier (110).

7. System (10) according to one of claims 4 to 6, wherein the light source (120) is arranged in a cavity (114) in the carrier (110) into which the orifice (111) opens out.

8. System (10) according to one of claims 4 to 7, comprising an electrical connection module (50) configured to power the light source (120) with electricity when the carrier (110) is fixed to a structural element (30) of the machine tool.

9. System (10) according to one of claims 4 to 8, wherein the light source (120) includes a diffusing element for diffusing the light through the hole (101) and the orifice (111).