GB2582764A

GB2582764A - Direct part marking

Info

Publication number: GB2582764A
Application number: GB1904530.1A
Authority: GB
Inventors: Ahearne Eamonn
Original assignee: University College Dublin
Current assignee: University College Dublin
Priority date: 2019-04-01
Filing date: 2019-04-01
Publication date: 2020-10-07
Also published as: GB201904530D0

Abstract

A direct part marking system 10 utilises a hardened multi-faceted indenter tip to produce one or more indentations (I, Fig.3) in a surface S such that the geometry of the indentations reflects light having a substantially normal angle of incidence relative to the surrounding surface with a non-normal angle of reflection to create a contrasted area with respect to the surface surrounding the indentation. The part marking system comprises an indenter 12 having a longitudinal axis LL; an actuator 22 operable to effect reversible displacement of the indenter in a primary direction along the longitudinal axis into and out of contact with a surface in order to produce an indentation in the surface; wherein the indenter comprises a polyhedral tip 16 defined by a plurality of faces 20 oriented and having a surface finish to produce a specular faceted indentation. Also provided is a method of marking a surface which includes displacing a polyhedral tip of an indenter in a primary direction into the surface to create at least one specular faceted indentation. The indenter tip may have four faces, be a square based pyramid or a Vickers® indenter. The actuator may be piezoelectric or a CNC machine.

Description

Intellectual Property Office Application No. GII1904530.1 RTM Date:27 February 2020 The following terms are registered trade marks and should be read as such wherever they occur in this document: Vickers Intellectual Property Office is an operating name of the Patent Office www.gov.uk /ipo

DIRECT PART MARKING

Field of the invention

The present invention relates to a direct park marking system and method, and in particular a direct part marking system designed to impart specific surface characteristics to the generated symbol elements of a two dimensional bar code or other data matrix in order to significantly enhance the readability of such codes on metal, plastic or other parts, including automated reading by scanners utilising image analysis software.

Background of the invention

Manufacturers of various components, in particular high value metal or plastic components, for example surgical or medical implants or other components, have a need to reliably and robustly mark such components for various purposes.

For example such marking can be utilised to providing a unique device identifier in order to meet the US Food and Drug Administration requirements for unique device identification of medical devices. This identifier must be capable of allowing identification of the device throughout the distribution process or supply chain to provide traceability, and most preferably by electronic tracking systems, many of which use optical scanning systems for reading the device identifier. This also allows parts to be correctly identified to ensure the appropriate part or device is used for a particular procedure, while also ensuring a robust recall procedure can be implemented if required.

There are a number of established methods for providing such direct part marking, for example micro-machining subtractive processes including laser micro-machining, engraving, scribing and dot-peening. These subtractive processes can give rise to a number of issues, in particular degradation of the surface finish and integrity, including the generation of sources of brittle fractures, fatigue and environmental corrosion and a resultant reduction in the longevity of the part or component.

It is therefore an object of the present invention to address the above mentioned issues of existing 35 part marking processes and systems.

Summary of the invention

According to a first aspect of the present invention there is provided a part marking system comprising an indenter having a longitudinal axis; an actuator operable to effect reversible displacement of the indenter in a primary direction along the longitudinal axis into and out of contact with a surface in order to produce an indentation in the surface; wherein the indenter comprises a polyhedral tip defined by a plurality of faces oriented and having a surface finish to produce a specular faceted indentation whose geometry reflects light having a substantially normal angle of 5 incidence to the surface with a non normal angle of reflection to create an area of contrast with the light reflected from the surface surround the indentation.

Preferably, the indenter tip comprises four faces.

Preferably, the indenter tip comprises a square based pyramid.

Preferably, opposed faces of the indenter tip define an internal angle in the range of 90° to 170°, more preferably in the range of 110° to 150°, and most preferably 136°.

Preferably, the indenter tip comprises a Vickers indenter.

Preferably, the indenter tip is at least partially comprised of a material selected from one of natural or synthetic diamond, single crystal or polycrystalline cubic boron nitride and tungsten carbide.

Preferably, the actuator comprises a piezo electric actuator.

Preferably, the actuator comprises an in line force sensor.

Preferably, the part marking system comprises a computer controller arranged to effect operation of 25 the actuator.

Preferably, the actuator comprises a CNC machine.

Preferably, the CNC machine comprises a multi axis CNC machine.

Preferably, the actuator is operable to produce a pattern of indentations in the surface.

Preferably, the part marking system is operable to encode secondary information within the indentation or pattern of indentations.

Preferably, the actuator is operable to effect displacement of the indenter tip in a secondary direction.

Preferably, the indenter tip comprises an indicia formed on or in at least one face.

Preferably, the part marking system comprises a vision system comprising a light source arrange to direct light substantially normally to the surface and a detector arranged to detect light from the light source that has been reflected from the surface.

A method of directly marking a surface comprising the steps of displacing a polyhedral tip of an indenter in a primary direction into the surface such as to create at least one specular faceted indentation having geometry which reflects light having a substantially normal angle of incidence relative to the surrounding surface with a non normal angle of reflection to create a contrasted area with respect to the surface surrounding the indentation.

Preferably, the method comprises mounting the indenter to a CNC machine; and using computer control to effect the displacement of the indenter tip into the surface to form the at least one indentation.

Preferably, the method comprises forming an array or pattern of indentations in the surface.

Preferably, the method comprises displacing the indenter by means of a piezo electric actuator.

Preferably, the method comprises displacing the indenter in a secondary direction in order to encode 20 secondary information within the at least one indentation.

Brief description of the drawings

The present invention will now be described with reference to the accompanying drawings, in which: Figure 1 illustrates a schematic side elevation of a direct part marking system according to an embodiment of the present invention, forming an indentation in a part; Figure 2 illustrates a schematic plan view from beneath of an indenter forming part of the direct part marking system illustrated in Figure 1; Figure 3 illustrates a schematic representation of a part in which an indentation has been produced by means of the direct part marking system and method of the invention; and Figure 4 illustrates a plan view of a part in which an array of indentations have been produced by means of the direct part marking system and method of the invention such as to produce a machine readable pattern on the surface of the part.

Detailed description of the drawings

Referring now to the accompanying drawings there is illustrated a direct part marking system, generally indicated as 10, for particular use in producing one or more indentations I in the surface S of a part P, in particular metal or plastic parts, and for example medical implants, medical devices or the like in order to permit identification, traceability, etc. Referring in particular to Figure 4, by producing an organised array of the indentations I in the surface S it is possible to produce a pattern or data matrix on the surface S of the part P, which can then be read for identification purposes, preferably be means of a conventional sensing device such as a standard charged coupled device (CCD) two-dimensional barcode reader or any other suitable vision or imaging system, and/or by human visual inspection.

As will be described in detail hereinafter the system 10 of the invention is operable to produce areas of high contrast between the light reflected off the unmarked area of the surface S surrounding the indentations I relative to darker regions arising from the deflection of light by the indentations I as hereinafter described. This high contrast between the marked and unmarked regions of the surface significantly increase the readability of the pattern of indentations I. In the embodiment illustrated the part marking system 10 of the invention comprises an indenter 12 having a spindle 14 (shown partially in Figure 1) which terminates at a lower end in a polyhedral tip 16. Although the tip 16 may be of a large number of shapes and geometries, in the preferred embodiment illustrated the tip 16 is in the form of a square-based pyramid. The tip 16 thus defines an apex 18 which is common to four polygonal faces 20 of the tip 16. At least the tip16 of the indenter 12 is formed from a material having a high hardness, for example natural or synthetic diamond, single or polycrystalline cubic boron nitride, tungsten carbide or any other suitable material or combination of materials. The particular material may also be chosen to suit the material of the part P to be marked. Each of the faces 20 are polished or otherwise finished in order to micro-form a specular finish on the corresponding facets of the indentation I such as to maximise reflected incident light as hereinafter described. In a particularly preferred embodiment the indenter 12 is a conventional Vickers indenter which ensures high quality due to the standardisation of production of same and reduces the cost of manufacture of the part marking system 10.

It will however be appreciated that the number of faces 20 forming the tip 16 may be varied, and in addition the exact geometry and materials selected for the tip 16 may be altered, in or der to optimise the indenter 12 and in particular the tip 16 to suit the particular material forming the part P to be marked. The internal angle between opposed pairs of the faces 20 is preferably in the range of between 90 degrees and 170 degrees, more preferably between 110 degrees and 150 degrees, and most preferably approximately 136 degrees. Again it will be appreciated that this included angle may be optimised for the particular material forming the part P, with due regard to the surface integrity where large internal angles are preferred in order to minimise any "barrelling" or "pin cushioning" and to optimise the positive compressive stress in the surface S at the site of the indentation I. In order to effect displacement of the indenter 12 into contact with the surface S the park marking system 10 comprises an actuator 22 which may be of any suitable configuration, and may for example be a mechanical, hydraulic, pneumatic, or electrical actuator or the like. In the preferred embodiment described and shown the actuator 22 comprises a piezo electric actuator coupled to the spindle 14 of the indenter 12 and operable to effect displacement of the indenter 12 in a primary direction parallel to a longitudinal axis LL of the spindle 14, as indicated by the bi-directional arrow shown in Figure 1. The piezo electric actuator 22 allows ease of indentation of multiple materials given the high force capacity and high precision of such piezo electric actuators, thereby facilitating direct park marking with a wide range of materials of the part P and indentation sizes. High indentations speeds are also possible via the use of the piezo electric actuator 22, which is particularly relevant in the automation of part marking according to the system and method of the invention.

The piezo electric actuator 22 is therefore preferably operated under computer control and may also incorporate or be in communication with an inline force sensor (not shown) in order to enable detection of the initial contact of the apex 18 with the surface S of the part P, in addition to allowing precision feedback control during the generation of the one or more indentations I. This feedback control permits improved precision and tolerances on varying surface levels and/or surface curvatures of the part P to be marked, for example a ball shaped hip replacement component or the like. The actuator 22 and indenter 12 are preferably incorporated into a CNC machine (not shown), most preferably in a multi-axis CNC machine, allowing for precise control and permitting the production of an array A of the indentations I in order to create patterns in the surface S of the part P which may then be machine readable by means of, for example, the above mentioned two-dimensional barcode reader. It will of course be appreciated by a person of skill in the art that the array A shown in Figure 4 is for illustrative purposes only, and the indentations I may be arranged in any other form or pattern or groups of patterns.

The use of a CNC machine allows the pattern or array of indentations Ito be precisely located such as to represent two-dimensional barcode data matrices and/or text characters on a wide range of surface shapes and curvatures by closely positioned control in each axis of the machine, synchronised with the control of the indentation I at the programmed position, for example to give precise depth and/or other dimensions to the indentations I. The CNC machine utilised in the part marking system 10 of the invention should be designed for minimised backlash and high overall loop stiffness such that the work piece or part P to be marked can be fixed to a bed of the machine to form a high stiffness loop.

In use the actuator 22 and indenter 12 are suitably mounted to the multi-axis CNC machine and the part P to be marked is secured in a suitable tool holder (not shown) or the like provided on the CNC machine. The pattern or array A of indentations Ito be produced is programmed into the CNC machine and the actuator 22 is then computer controlled to displaced the tip 16 against the surface S in order to deform the material and create the indentation I, the facets of which are created and deformed by the faces 20 of the tip 16 to have a micro-formed specular surface which maximises reflection of incident light. The indenter 12 is preferably displaced linearly from a position above the surface S, along a primary path parallel to a longitudinal axis of the spindle 14, and into contact with the surface S. The use of computer control and force feedback control allows precise control of the depth of the indention I, and thus the geometry of each of the facets of the indentation in order to achieve particular reflectivity.

Once the indentation I is formed to the correct depth and dimensions, the actuator 22 reverses the displacement of the spindle 14 along the primary direction or axis in order to draw the tip 16 back out of contact with the surface S, before the part P and indenter 12 undergo relative movement to position the tip 16 above the next site at which the next indentation I is to be formed. The actuator 22 again displaces the indenter 12 towards the surface S until the tip 16 contacts the part P and further displacement of the indenter 12 creates the next indentation I. This process is repeated until the programmed array A or pattern is formed in the surface S of the part P. In order to read the encoded pattern or array A formed in the surface S the part F' may be scanned with a conventional device such as a barcode reader (not shown) or the like. Such readers will generally comprise a light source (not shown) operable to direct light towards the surface S, and preferably in a direction normal thereto. The surface S surrounding each of the indentations I is relatively planar and will therefore tend to reflect the light directly back towards the barcode reader (not shown) or the like, where it is collected by a suitable sensor or receiver (not shown). However, due to the angular geometry of the indentations I, in particular the angles at which the facets of the indentations I formed by the faces 20 are disposed, in addition to the specular finish created on each of these facets, a substantial portion of the light incident on the or each of the indentations I will be reflected at an angle away from the surface S and thus away from the sensor of the barcode reader (not shown), thereby effectively producing a darkened or contrasted region or area corresponding to each indentation I, which contrasts highly with the effected light from the surrounding surface S, as determined or seen by the barcode reader or other vision system. The high contrast between the indentations I and the surrounding surface S allows the data matrix or set of characters formed by the array A of indentations Ito be quickly and easily read by the two dimensional barcode reader or the like.

In addition to encoding this primary information into the surface S of the part P, the park marking system 10 and method of the invention may be utilised to encode secondary information into one or more of the indentations I, for example by displacing the indenter 12 in a secondary direction during and/or after displacement in the primary direction, which can be readily achieved in particular when utilising a multi-axis CNC machine. For example, a displacement of +/-10% from a nominal position along one axis could represent a covert 0 or 1 respectively. This encoding could also be achieved by varying the depth of any one or more of the indentations I by, for example, +/-10% while having no significant impact on the readability of the indentations I. Additionally or alternatively an indicia could be formed on or in one or more faces 20 of the indenter 12 in order to produce a negative of that indicia in one or more of the facets of the indentation I. Such indicia could be used for example 5 as a forensic and counterfeiting measure.

It will therefore be appreciated that the direct park marking system 10 and method of the invention provides a relatively simple yet robust means of direct park marking a surface, and does not involve the removal of material and/or chemical or phase changes on the surface, unlike many conventional 10 solutions for direct park marking. The indentations I produced in the surface S of the part P provide a high contrast with the surrounding surface when viewed using a conventional vision system such as a barcode reader, greatly improving the readability of the data matrix formed by the indentations.

Claims

Claims 1. A part marking system comprising an indenter having a longitudinal axis; an actuator operable to effect reversible displacement of the indenter in a primary direction along the longitudinal axis into and out of contact with a surface in order to produce an indentation in the surface; wherein the indenter comprises a polyhedral tip defined by a plurality of faces oriented and having a surface finish to produce a specular faceted indentation whose geometry reflects light having a substantially normal angle of incidence to the surface with a non normal angle of reflection to create an area of contrast with the light reflected from the surface surround the indentation.
2. The part marking system of claim 1 in which the indenter tip comprises four faces.
3. The part marking system of claim 1 or 2 in which the indenter tip comprises a square based pyramid.
4. The part marking system of any preceding claim in which opposed faces of the indenter tip define an internal angle in the range of 90° to 170°, more preferably in the range of 110° to 150°, and most preferably 136°.
5. The part marking system of any preceding claim in which the indenter tip comprises a Vickers indenter.
6. The part marking system of any preceding claim in which the indenter tip is at least partially comprised of a material selected from one of natural or synthetic diamond, single crystal or polycrystalline cubic boron nitride and tungsten carbide.7 The part marking system of any preceding claim in which the actuator comprises a piezo electric actuator.
7. The part marking system of any preceding claim in which the actuator comprises an in line force sensor.
8. The part marking system of any preceding claim comprising a computer controller arranged to effect operation of the actuator.
9. The part marking system of any preceding claim in which the actuator comprises a CNC machine.
10. The part marking system of claim 10 in which the CNC machine comprises a multi axis CNC machine.
11. The part marking system of any preceding claim in which the actuator is operable to produce a pattern of indentations in the surface.
12. The part marking system of any preceding claim in which the system is operable to encode secondary information within the indentation or pattern of indentations.
13. The part marking system of any preceding claim in which the actuator is operable to effect displacement of the indenter tip in a secondary direction.
14. The part marking system of any preceding claim in which the indenter tip comprises an indicia formed on or in at least one face.
15. The part marking system of any preceding claim comprising a vision system comprising a light source arrange to direct light substantially normally to the surface and a detector arranged to detect light from the light source that has been reflected from the surface.
16. A method of directly marking a surface comprising the steps of displacing a polyhedral tip of an indenter in a primary direction into the surface such as to create at least one specular faceted indentation having geometry which reflects light having a substantially normal angle of incidence relative to the surrounding surface with a non normal angle of reflection to create a contrasted area with respect to the surface surrounding the indentation.
17. The method of claim 16 comprising mounting the indenter to a CNC machine; and using computer control to effect the displacement of the indenter tip into the surface to form the at least one indentation.
18. The method of claim 16 or 17 comprising forming an array or pattern of indentations in the surface.
19. The method of any of claims 16 to 18 comprising displacing the indenter by means of a piezo electric actuator.
20. The method of any of claims 16 to 19 comprising displacing the indenter in a secondary direction in order to encode secondary information within the at least one indentation.