WO2013124720A1

WO2013124720A1 - Improvements relating to plasma cutters

Info

Publication number: WO2013124720A1
Application number: PCT/IB2013/000189
Authority: WO
Inventors: Ian Thomas CHRISTIANSEN; Michael George REITER
Original assignee: Mi Industries Pty Ltd
Priority date: 2012-02-13
Filing date: 2013-02-13
Publication date: 2013-08-29

Abstract

A plasma cutting table assembly comprising: a platform, a top carriage assembly adapted to support above the platform and a plasma cutting torch directed downwards towards the platform, a first track assembly engaged with and supporting the top carriage assembly wherein each end of the first track assembly being supported from a respective side carriage assembly, a first said side carriage assembly engaged with and supported from a second track assembly mounted below said platform and aligned at right angles to the first track assembly, and the second said side carriage assembly engaged with and supported from a third track assembly mounted below said platform and aligned parallel to the second track assembly.

Description

Improvements Relating to Plasma Cutters

Technical Field This invention concerns computer numerical controlled (CNC) plasma cutting machines. Plasma cutting is a process used to cut steel and other materials using a plasma torch. In the process a gas stream is blown at high speed from a nozzle and at the same time an electric arc is formed through the gas from the nozzle to the surface being cut, turning some of the gas to plasma. The heat of the plasma is sufficient to melt the material being cut and its velocity blows the molten material away from the cut.

Background Much effort has been put into developing relatively small CNC plasma cutting machines. Plasma torches have been developed with smaller nozzles and a thinner plasma arc which has allowed improved precision on plasma cut edges. Smaller plasma cutting tables have also been developed which are significantly less expensive than earlier generation models. However a disadvantage of the smaller, lighter units to date has been a tendency for less accuracy due to a reduced rigidity.

Plasma cutters produce an intense light which has a high ultraviolet component which therefore requires shielding to protect the eyes of personnel in the vicinity. Such shields have traditionally been awkward to fit and adjust, restrict physical access to the region being cut, and restrict visibility during set up.

An aim of the present invention is to provide a plasma cutting table assembly and a method of operating plasma cutting tables which overcome, or at least reduces, these difficulties. Summary of Invention

Accordingly, in one aspect the invention provides a plasma cutting table assembly comprising:

- a platform,

- a top carriage assembly adapted to support above the platform a plasma cutting torch directed downwards towards the platform,

- a first track assembly engaged with and supporting the top carriage assembly, each end of the first track assembly being supported from a respective side carriage assembly,

- a first said side carriage assembly engaged with and supported from a second track assembly mounted below said platform and aligned at right angles to the first track assembly, and

- the second said side carriage assembly engaged with and supported from a third track assembly mounted below said platform and aligned parallel to the second track assembly.

In another aspect the invention provides a method of operating a plasma cutting apparatus, said apparatus comprising:

- a platform,

- a first said side carriage assembly engaged with and supported from a second track assembly mounted below said platform and aligned at right angles to the first track assembly,

- the second said side carriage assembly engaged with and supported from a third track assembly mounted below said platform and aligned parallel to the second track assembly, and - a controller means,

wherein a controller means controls movement of the cutting torch by controlling movement of the top carriage assembly along the first track assembly, movement of the first side carriage assembly along the second track assembly and movement of the second side carriage assembly along the third track assembly.

Brief Description of Drawings

In order that the invention may be more fully understood there will now be described, by way of example only, preferred embodiments and other elements of the invention with reference to the accompanying drawings where:

Figure 1 is a view of a plasma cutting table assembly according to a first embodiment of the invention;

Figure 2 is an exploded view (less some fastener components) of the cutting table assembly shown in Figure 1 ;

Figure 3 is an isometric view of a side carriage assembly, two of which can be seen in Figure 2 (with each being a mirror image of the other);

Figures 4, 5 and 6 are back, side and front views of the side carriage assembly shown in Figure 3;

Figure 7 is an exploded view (less some fastener components) of the side carriage assembly shown in Figure 3;

Figure 8 is a view of a drive assembly which can be seen in Figure 7;

Figure 9 is another view of the drive assembly shown in Figure 8;

Figure 10 is an exploded view of the drive assembly shown in Figure 8, less some fastener components;

Figure 11 is a side view of the side carriage assembly shown in Figure 3 together with the carriage track assembly with which it is engaged;

Figure 12 is a rear view of the arrangement shown in Figure 1 1 ;

Figure 13 is a section view through the line A- A shown in in Figure 11;

Figure 14 is an enlargement of portion of Figure 13;

Figure 15 is a view of portion of the table in Figure 1 when in use where a shield has been added around the cutting region; Figure 16 is a view as in Figure 15 but with the shield tilted upwards from its lowered position in Figure 15; and

Figure 17 is a side view of some of the components in Figure 16. Description of Embodiments

The plasma cutting table assembly 6 shown in the Figures has a tub assembly 12 containing a work platform 14 formed by an array of metal plates 16 aligned vertically and spaced apart with their edges upwards. The tub 12 contains water the top surface of which is a little below the top edge of the metal plates 16. The water contains suitable chemical additives to resist corrosion of the metal components and also inhibit growth of biological materials. In use of the cutting table, metal plate to be cut is laid on the platform 14. The tub assembly 12 is mounted on a base frame assembly 18 comprising four legs 7, 8, 9 and 10 fitted with height-adjustable feet 22. Fastened to the top of the legs 7 and 8 is a side carriage track assembly 24. A corresponding side carriage track assembly 25 is fastened in mirror image on the opposite side of the base frame assembly 18 to the top of the legs 9 and 10. Each side carriage track assembly 24 and 25 extends horizontally from the front 17 to the back 19 of the base frame assembly 18.

The side carriage track assembly 24 comprises a side carriage support rail 28 formed from an elongate length of an extruded aluminium profile 29 with two steel rods 20 and 21 recessed into its upper and lower faces respectively and running for substantially the full length of the profile 29. As best seen in Figure 14, the profile 29 has a generally square form but with numerous channels formed into the external faces of the profile to provide five mounting slots 81 to 85. An elongate hardened steel toothed rack 30 is attached to the profile 29 along the length of the side carriage support rail 28. The teeth on the rack 30 are pointing down. The attachment is by means of screws 31 through the rack 30 and engaged with nuts 43 held captive within mounting slot 85 (as seen in Figure 14) at multiple points along the length of the rack 30. The slots 81 to 85 all have two opposed lateral recesses 86 to accommodate nuts (eg. nut 43) and a deep recess 87 to centre, but not threadedly engage, the tip of a screw (eg. screw 31).

Associated with the side carriage track assembly 24 is a side carriage assembly 26 which is engaged with and supported by the side carriage track assembl .

Extending across and above the platform 14 is a top carriage track assembly 32 comprising a top carriage support rail 34, including a length of the same aluminium profile 29 as that used for the side carriage support rail 28, together with an elongate rack portion 36 fastened longitudinally to the top carriage support rail in a similar manner to that described above in relation to the rack 30.

Each end of the top carriage track assembly is attached by bolts through holes 38 in a flange 40 on the top of each respective side carriage assembly 26 and 27.

One of the side carriage assemblies 26 has a controller assembly 42 attached on a side face of the side carriage assembly. This contains a display 43 and the electronics whereby the operation of the cutter is controlled. The top carriage assembly 44 is engaged with the top carriage track assembly 32 and moves backwards and forwards across the top carriage track assembly under control of the controller assembly 42.

The side carriage assembly 26 comprises a carriage body 46 to which is attached a drive assembly 48. The drive assembly 48 comprises an electric motor 50 with a spur gear 52 on its shaft. The motor is rigidly fastened to a drive support plate 54 which is in turn rigidly fastened to the carriage body 46. The drive support plate 54 carries, on the opposite side to the motor, rollers 55 and 56 which engage respectively with the steel rods 20 and 21 on the side carriage support rail 28 while the gear 52 engages with the rack 30. The rollers thus function as track bearings which bear onto the rods. The carriage body 46 is hollow and, while it is formed from sheet metal, all the edges are either folded or continuously welded and all the corners are complete so that it forms a very rigid structure which does not flex to any significant extent during operation of the plasma cutter. This rigidity contributes substantially to the high accuracy achieved by the cutter.

The electric motor 50 is a stepper motor which allows for accurate control of small increments of each revolution of the gear 52. The motor 50 fits into the carriage body 46 from where it is accessible via the removable carriage cover 58. The motor 50 can thus be removed without disturbing the location of the rollers 56 with the steel rods 20 and 21.

Drive clamp plates 60 are also positioned within the carriage body so that the relatively thin metal of the carriage body 46 is clamped between the drive support plate 54 and the drive clamp plates 60 to improve rigidity.

The upper rollers 55 are spaced from the drive support plate 54 by adjustable cam bearings 57 which allow for the rollers to be aligned accurately with each other. The ends of the axles 53 of the rollers 55 above the rack 30 are supported against each other by an upper anti-torsion plate 66 while the axles 53 of the rollers 56 below the rack 30 are supported against each other by a lower anti -torsion plate 68 which also acts as a sensor plate. While the upper anti-torsion plate 66 provides a means to support the ends of the axles of the upper rollers, the anti-torsion and sensor plate 68 provides that support function for the lower rollers 56 and, in addition, includes two sensors 70 and 72.

The first sensor 70 is an electronic limit stop which provides an indication to the controller assembly when the drive assembly reaches a predetermined maximum allowable point on the carriage track assembly. The first sensor 70 on the side carriage assembly 26 signals to stop both side carriage assemblies when the extreme position is detected at one end of the work platform 14 whereas the first sensor 70 on the side carriage assembly 27 signals to stop both side carriage assemblies when the extreme position is reached at the other end of the work platform 14.

The second sensor 72 is a high accuracy sensor for establishing a zero reference point for the individual carriage assembly. Each side carriage assembly has its own sensor 72 so each side carriage assembly is independently calibrated to its home position.

Each rack 30 and 36 faces downwards from its respective support rail 34 and 28. This reduces the possibility of foreign material falling onto the rack and thus disturbing the accuracy of the positioning of the respective carriage assemblies.

Figures 15 to 17 show the operation of a shield around the cutting region. The top carriage assembly 44 includes a plasma torch 73 which in use is raised and lowered vertically by means of a torch lifter 74 screwed to the front of the top carriage cabinet 75. A motor (not shown) causes the torch lifter rail 76 to raise and lower through the lifter housing 71 as indicated by the arrows A and A' in Figure 17.

A shield support bracket 77 is rigidly connected to the bottom of the rail 76 and the torch lifting frame 78 is pivoted on a pivot pin 79 so it can tilt from horizontal (shown in Figure 15) upward through about 60° (shown in Figure 16) as indicated by the arrows B and B' in Figure 17.

The lifting frame 78 is D-shaped in plan view and suspended from its curved edge are two layers of shield material 80 which is conveniently UV-protective flame-retardant flexible PVC sheeting of the type commonly used for screws on steel welding booths. The shield material forms a shield 88. The sheeting has slits 89 rising vertically from the bottom of the shield 88. The slits in one layer of the material are offset from those in the other layer in order to prevent UV escape through the slits. A lifting pin 90 through the frame 78 is spaced forward of the pivot pin 79 and a flexible lift wire 91 connects the pivot pin 79 to a lift/lower motor 92 which can be activated to lift an lower the frame 78. By this arrangement the plasma torch 73 can be raised or lowered on the torch lifter rail without disturbing the adjustment of the shield 88 relative to the torch 73.

Whilst the above description includes the preferred embodiments of the invention, it is to be understood that many variations, alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the essential features or the spirit or ambit of the invention. It will be also understood that where the word "comprise", and variations such as "comprises" and "comprising", are used in this specification, unless the context requires otherwise such use is intended to imply the inclusion of a stated feature or features but is not to be taken as excluding the presence of other feature or features.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that such prior art forms part of the common general knowledge in Australia.

Claims

1. A plasma cutting table assembly comprising:

- a platform,

2. A plasma cutting table assembly according to claim 1 wherein each said side carriage assembly comprises a cabinet in which all edges of the cabinet have all walls fixed and joined at fixed edges.

3. A plasma cutting table assembly according to any one of the previous claims wherein a shield surrounding the cutting tip of the plasma torch may be tilted by an actuation motor.

4. A method of operating a plasma cutting apparatus, said apparatus comprising:

- a platform,

- a first track assembly engaged with and supporting the top carriage assembly, each end of the first track assembly being supported from a respective side carriage assembly, - a first said side carriage assembly engaged with and supported from a second track assembly mounted below said platform and aligned at right angles to the first track assembly,

- the second said side carriage assembly engaged with and supported from a third track assembly mounted below said platform and aligned parallel to the second track assembly, and

- a controller means,