Indentation marking apparatus

Abstract: An indentation marking head (20) for creating indented indicia in a workpiece comprises a substantially planar disk (10) which bears around its periphery a plurality of slugs (21) which are appropriately contoured to create the indicia when impressed against the workpiece. The disk has a continuous circumference and is resiliently deformable from its planar configuration to allow a slug to be impressed against a workpiece located next to a principal surface of the disk (10).

Description: The present invention relates to indentation marking apparatus, especially to an indentation marking head for creating indented indicia in a workpiece. For example, the indicia can be created in metal and plastic surfaces of pieces and can correspond to identification codes or other information that are to be marked in the workpiece. EP-A-91579 discloses a marking machine which includes a typewheel which has a central wheel section and a number of discrete, radial spring arms emanating from the central wheel section. Each spring arm carries at its free end a die corresponding to a character. The typewheel is mounted for rotation on a spindle, and a work surface is presented to the dies. The dies are caused to impact the work surface by the action of a cam. The spring arms are only supported where they join the central wheel section and so repeated impacts can lead to fatigue of the spring arms resulting in their deformation and possible eventual fracture, limiting the useful life of the typewheel. DE-3610665 describes a typewheel for an embossing machine. The typewheel is disc shaped and has a number of separate tongues extending radially from a securing ring. The free ends of the tongues have a type holder inserted carrying a type on a lower face for embossing an article. A flexible rubber coating is applied to and connects the tongues together to reduce vibrations in the tongues and mechanical stresses in the typewheel. The present invention provides an indentation marking head for creating indented indicia in a workpiece, in which slugs bearing contours corresponding to the markings to be made in the workpiece are arranged around the periphery of a disk which has a continuous circumference. Accordingly, in one aspect, the invention provides an indentation marking head for creating indented indicia in a workpiece, comprising a substantially planar disk which bears around its periphery a plurality of slugs which are appropriately contoured to create the indicia when impressed against the workpiece, the disk having a continuous circumference and being resiliently deformable from its planar configuration to allow a slug to be impressed against a workpiece located next to a principal surface of the disk. The marking head of the present invention has the advantage that the likelihood of irreparable deformation of the support for individual slugs is reduced compared with existing print heads such as disclosed in EP-A-91579. The support provided by a disk with a continuous circumference can be considerably greater than when the slugs are provided on individually deformable fingers. This allows individual slugs to be deformed repeatedly with reduced risk of permanent damage to the support, enabling prolonged use of the disk. This facilitates handling of the disk when it is being installed in a marking machine since the disk is less susceptible to damage when being so manipulated. The reduced likelihood of permanent deformation of individual fingers of the support means that there is reduced likelihood of inadvertent contact between a workpiece and a slug support, which can lead to undesirable marking of the workpiece (especially scratching), or wear of the slug, or both. It has also found that support of slugs on a disk with a continuous circumference leads to reduced vibration of the slugs as a result of movement into contact with and away from a workpiece: slugs mounted on individual deformable fingers can tend to vibrate, especially in the plane of the disk, leading to possible misalignment of indicia on the workpiece. Generally, all the slugs are mounted on the same face of the resilient disc. Preferably, the angular spacing between adjacent slugs is substantially constant around the disk. The spacing will be selected to ensure that adjacent slugs can be differentiated adequately when the disk is deformed to cause a selected slug to indent a workpiece. Generally, the spacing between the slugs will be kept to a minimum consistent with this requirement, to allow the maximum number of slugs to be accommodated on a disk. The flexibility of the disk can be adjusted by selective removal of material, for example by locally reducing the thickness of the disk or by making holes in the disk. Generally however the thickness of the disk is substantially constant over its area. The material of the disk will be selected according factors including its desired flexibility, the weight of the slugs, and the intended distance between the slugs and the workpiece. The disk might be formed from a metal or a polymeric material. A particular preferred material is a steel which has been suitable treated to render it resiliently deformable. Preferably, the thickness of the disk is less than about 0.5 mm, more preferably less than about 0.1 mm, especially less than about 0.05 mm. Preferably, the marking head comprises a disk with openings in it and a plurality of slugs which have been fixed in respective openings. This has the advantage of facilitating manufacture of the marking head and can allow usable slugs to be salvaged from a damaged marking head. Furthermore, the marking head can in some circumstances be repaired by replacement of worn slugs. The use of a disk which has a continuous circumference can facilitate that repair since the greater mechanical integrity of the disk enables it to tolerate the thermal or mechanical process steps involved in the repair. Techniques for fixing the slugs in the openings in the marking head including mechanical fixing or by bonding, or by a combination of these techniques. Bonding techniques include for example use of adhesives and soldering and brazing. Mechanical techniques include for example press fitting and the use of clamping fixtures such as circlips. A particularly preferred material for the disk is a hardened and tempered steel in which openings have been created by a cutting process, for example by a laser cutting process. The steel can be tempered again after the laser cutting process to ensure that it is not hardened locally in the region of the openings. The disk will usually be substantially circular so that it can be rotated to present indicia sequentially to a workpiece that is moved below it. The radial distance from the axis of rotation of the disk to the slugs will generally be at least about 4 cm, more preferably at least about 6 cm. The radial distance will generally be less than about 15 cm, more preferably less than about 12 cm. A larger disk may be used if required, for example to accommodate large slugs. The marking head of the invention can be used to create a variety of indicia on a workpiece. The indicia might include for example alphanumeric characters and machine readable indicia such as bar code markings. The workpiece in which the indicia are created can have a hard surface which is relatively resistant to impact marking. The surface might be provided by a material such as a metal, including steels, aluminium, copper and so on. The surface of the workpiece might also be provided by a polymeric material. The slugs may be made from hardened and tempered tool steel and from wear resistant alloys such as those made by powder metallurgy. Tungsten carbide can be appropriate for applications where wear resistance is required. In another aspect, the invention provides a marking machine which comprises a support for a workpiece to be marked, a marking head of the type discussed above, means for rotating the disk to present different ones of the slugs to the workpiece, and means for deforming the disk from its planar configuration to cause individual ones of the slugs to contact the workpiece to mark an indicium in the workpiece. In a preferred arrangement, the support is preferably arranged so that the disk is deformed to cause the slug to contact the workpiece through a distance of not more than about 5 mm, preferably not more than about 4 mm. Preferably the deformation will be arranged to be at least about 1 mm, more preferably at least about 2 mm. Preferably one or both of the deformation means and rotating means is manually and/or automatically operable. The automatic operation of the machine may be controlled by electronic control circuitry which may be interfaced with a computer to control the automatic operation of the machine. The impact means can be actuated manually, hydraulically, pneumatically, electrically, mechanically, or by a combination of any of these techniques. For example, the impact means can be actuated by means of a cam and appropriate cam follower such as that disclosed in EP-A-91579. A preferred drive means for the impact means operates electromagnetically. The rotating means and carriage means can be moved by a stepper motor, belts and pulleys, chains and toothed wheels or a motor and gear wheels. The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a plan view of a resilient disk for use as part of the present invention; Figure 2 is a plan view of an indent marking head according to the present invention; Figure 3 is a side view of a section through an indent marking head according to the present invention; Figure 4 is a plan view of an indent marking machine using the indent marking head of Figures 2 and 3; and Figure 5 is a side view of the indent marking machine shown in Figure 4. Referring to the drawings, Figure 1 shows a resilient disk 10 which has a continuous circumference so that the extreme edge of the disk is unbroken. The disk 10 has a central mounting aperture 11 and a plurality of holes 12 located around its periphery, generally towards its edge. The holes 12 are positioned so that each hole is equally distant from its two nearest neighbours. As any pair of neighbouring holes subtend the same angle at the centre of the disk, the angular spacing between the holes can be considered to be substantially constant. Typically the disk has a diameter of 120 mm and, when intended for marking small indicia, has 40 holes at 9° pitch. Typically the resilient disk is made from hardened and tempered tool steel with thickness about 0.03 mm. These parameters have been found to produce a disk having the desired properties which allow it to obviate the disadvantages of the typewheel used previously. Figures 2 and 3 show an indent marking head 20 which includes the resilient disk 10 shown in Figure 1, with a number of slugs 21 mounted on the resilient disk. Each slug is a discrete member having a rear mounting side 22 and a forward side 23 bearing a raised contour 24. The raised contour is in the shape of an indicium and the slug acts as a die to indent the surface of the work piece with the shape corresponding to the contour. The indicia on the slugs might be for example text characters, numerals, symbols and machine readable marks (such as bar codes). The contours may be, but are not limited to, continuous lines, broken lines or in the form of a dot matrix. The resilient disk is made from hardened and tempered steel and the holes are cut in it by means of a programmed laser beam. The bur material around the holes can be metallurgically altered (especially hardened) by the laser cutting. The bur material is removed and the disk can be tempered to remove hardening effects. The disk can then be cleaned by vapour blasting. Typically, the slugs are made from hardened and tempered tool steel but may be made from tungsten carbide to make them more durable. The contours are produced by engraving the forward side and spigots extend from the rear mounting side. The slugs are mounted on the resilient disk by placing the spigots in the holes cut in the resilient disk. The use of holes and spigots helps to increase the accuracy with which the slugs are positioned on the resilient disk. The slugs are then secured in place. The slugs may be secured by soldering, brazing, cementing or any other well known technique using an extra material. Alternatively, the slugs may not have a spigot extending from the rear mounting side and the slugs may be mechanically secured to the holes in the resilient disk by press fastening or snap lock fastening. The slugs may also be screwed or bolted to the disk. It is not necessary to provide holes in the disk to receive the slugs, and the slugs may be mounted directly on the surface of the resilient disk using any of the methods mentioned above. Figures 4 and 5 illustrate an indent marking machine, designated generally by reference numeral 30, having an indent marking head 20 as described above. The indent marking machine comprises a base 31 and a support column 32 mounted on the base. There is also provided a carriage 33 mounted on two bearing bars 34, 35 so that the carriage can slide on the bars and move, relative to the base, in an x-direction. A stepper motor 36 drives a worm screw 37 to cause the carriage to move. A further stepper motor 38 drives a further worm screw 39 to cause the carriage to move, relative to the base, in a y-direction. A spindle 40 mounted on bearings (not shown) is located in the carriage and the indent marking head 20 is mounted coaxially on the spindle with the slugs 21 facing downward. A stepper motor 41 is provided to drive the spindle so that the indent marking head can be rotated. A rod 42 actuated by a solenoid 43 is located in the carriage with the rod positioned above a slug. A work piece 44 is positioned between the base 31 and the indent marking head 20. A power supply and electronic circuitry to control the stepper motors and solenoid are also provided but not shown. In operation, a work piece is placed on the base beneath the indent marking head. The carriage is moved so that the work piece can be marked at the correct place. The head is rotated so that the slug bearing the correct indicia is located between the rod and the workpiece, and electrical power is supplied to the solenoid causing the rod to strike the slug on the rear mounting side. The resilient disk deforms and the slug impacts on the surface of the workpiece, indent marking it by virtue of the contour on the forward face of the slug. The rod withdraws back to its initial position in the solenoid, and the resilient disk reforms raising the slug from the surface of the workpiece. If further marks are required, the carriage moves along to a new position and the head is rotated to the next required indicia and the workpiece surface is marked as previously. This process repeats until all the marks required on that surface of the workpiece have been made. Then, either a new surface of the same workpiece or a new workpiece is presented to the marking head and further marking carried out. Conventional apparatus for automatically supplying new work pieces to the machine may be used with it so that the marking of a series of work pieces may be totally automated under the control of a computer running a suitable program. The marking head can be releasably mounted on the spindle so that marking heads having different sizes, or types, of indicia may be easily substituted for the one previously being used. This also helps in replacing slugs bearing frequently used indicia which may have worn out or become damaged. The marking head may be provided with at least one slug which can dot mark the work piece thereby possibly improving the versatility of the indent marking machine as it can both dot markings, possibly in addition to character markings. This can obviate the need to buy both a dot and a character indent marking machine. A suitable dot marking slug might have at least one point, for example of a hard material such as tungsten carbide. The machine may be operated manually, by providing a knob on the spindle, definite indexing of the head position, handles for manually positioning the carriage and having the rod extend through the top of the solenoid so that the rod can be actuated by striking it with a heavy tool. Such a machine is fully portable and particularly useful for taking to manufacturing sites so as to indent mark special components. Various modifications to the machine are also envisaged. Instead of using a solenoid, other impact means may be used such as hydraulic, pneumatic, spring or cam operated. Manual movement of the carriage will be aided by the provision of a ratchet for definite indexing. When stepper motors are used to move the carriage this may be effected by gearing (such as a rack and pinion arrangement) by chains and toothed wheels, by belts and pulleys or by lead screws and nuts.

Claims: An indentation marking head (20) for creating indented indicia in a workpiece, comprising a substantially planar disk (10) which bears around its periphery a plurality of slugs (21) which are appropriately contoured (24) to create the indicia when impressed against the workpiece, the disk having a continuous circumference and being resiliently deformable from its planar configuration to allow a slug to be impressed against a workpiece (44) located next to a principal surface of the disk. A marking head as claimed in claim 1, in which the angular spacing between adjacent slugs is substantially constant around the disk. A marking head as claimed in claim 1 or claim 2, in which the disk is formed from a resiliently deformable metal. A marking head as claimed in any one of claims 1 to 3, in which the thickness of the disk is substantially constant over its area. A marking head as claimed in claim 4, in which the thickness of the disk is less than about 0.05 mm. A marking machine (30) which comprises a support for a workpiece to be marked, a marking head (20) as claimed in any one of claims 1 to 5, means for rotating (40, 41) the disk to present different ones of the slugs (21) to the workpiece (44), and means (42, 43) for deforming the disk from its planar configuration to cause individual ones of the slugs to contact the workpiece to mark an indicium in the workpiece.

Inventors: GODBEHERE EDWARD, GODBEHERE, EDWARD
Applicants: PRYOR EDWARD & SON, EDWARD PRYOR & SON LTD.
Application year: 1997
Main classification: B41J3
IPC codes: B44B5, B41J3