FURBY, David (165 Whalans Road, Greystanes, New South Wales 2145, AU)
WILSON, Neil (69-71 Clapham Road, Sefton, New South Wales 2162, AU)
FURBY, David (165 Whalans Road, Greystanes, New South Wales 2145, AU)
| Claims 1. An apparatus for exerting a holding pressure on mould dies, the apparatus including an actuating means which is located adjacent to a deformation means, the actuating means being * driven by a driving means, wherein during an operation of the apparatus the driving means exerts the holding pressure on the mould dies through the deformation means, and in doing so causes a deformation of the deformation means so as to indicate the holding pressure being exerted onto the mould dies. 2. The apparatus of claim 1 Wherein there is included a displacement sensing means for sensing the deformation, to indicate the holding pressure. 3. The apparatus of claim 2 wherein the actuating means is a ball screw interacting with a ball nut, the ball nut being driven by the motor means. 4. The apparatus of claim 1 or 2 wherein the deformation sensed is amplified by an amplification means. 5. The apparatus of claim 4, wherein the amplification means comprises a lever that is pivoted about the deformation means, the displacement sensing means being adapted to sense a displacement of a free end of the lever. 6. The apparatus of any one of claims 1 to 5, wherein the deformation means is elastic. 7. The apparatus of claim 6, wherein the deformation means is one of a polymeric pad, a spring arrangement, and a disk spring arrangement. 8. An injection or dosing apparatus including a chamber and piston assembly which includes a piston that is adapted to move into a chamber which holds a first flowable material, the chamber being located within an extent of a mixer, wherein when the piston moves into the chamber, the chamber dispenses the first flowable material into the mixer. 9. The apparatus of claim 8, wherein the chamber and piston assembly includes at least another piston that is adapted to move into a corresponding chamber 10. The apparatus of claim 9, further including at least one other chamber and piston assembly that has one or more pistons adapted to move into one or more respective chambers. 11. The apparatus of claim 10, wherein the chamber assemblies are interchangeable with each other. 12. The apparatus of any one of claims 9 to 11, wherein the chamber and piston assemblies are driven by separate motive means or a single motive means. 13. The apparatus of claim 12, wherein the motive means is a toothed belt and pulleys arrangement, or gears. 14. The apparatus of claims 8 or 9, wherein the chamber and piston assembly is formed in a block. 15. The apparatus of claim 11 , wherein the chamber and piston assembly communicates with the mixer via internal passage ways through the block. 16. The apparatus of claims 8 or 9, wherein the chamber and piston assembly connects to an actuator for the chamber and piston assembly by a ready release mechanism. 17. The apparatus of any one of claims 8 to 16, further comprising a canister that contains a reservoir for the first flowable material, the container including a flowable material cavity and an air cavity with a flexible diaphragm therebetween, the diaphragm having two or more membranes. 18. An injection or dosing apparatus including at least a first chamber and piston assembly which includes a piston adapted to move into a corresponding chamber for delivering a flowable material, wherein the assembly is engaged to a supporting means for the apparatus via a releasable holding mechanism, and the chamber and/or the piston can be decoupled from the supporting means. 19. The apparatus of claim 18, wherein the releasable holding mechanism includes a mount which receives a portion of said piston in a direction which is perpendicular to the direction of motion of said piston in said chamber. 20. The apparatus of claims 18 or 19, further comprising said releasable holding mechanism includes a member having a channel or recess which extend in a first direction and a bight through a wall defining said channel or recess to receive a portion of said piston. 21. The apparatus of any one of claims 18 to 20, wherein the portion of said piston to be held in said releasable holding mechanism includes a turned down portion having shoulders adjacent thereto. |
Field of the invention
[001] The present invention relates to an injection and dosing apparatus for use with injection moulding systems.
Background of the invention
[002] Silicone rubber or other elastomeric products are produced using injection moulding systems. A typical mould includes two or more mould dies, which need to be held together against the pressure created by the injected mixture, to avoid a leakage of the silicone mixture injected between the mould dies. Prior art injection moulding systems require hydraulic systems to apply this holding pressure.
[003] Any reference herein to known prior art does not, unless the contrary indication appears, constitute an admission that such prior art is commonly known by those skilled in the art to which the invention relates, at the priority date of this application.
Summary of the invention
[004] The present invention provides an apparatus for exerting a holding pressure onto mould dies, the apparatus including an actuating means which is located adjacent to a deformation means, the actuating means being driven by a driving means, wherein during an operation of the apparatus the driving means exerts the holding pressure on the mould dies through the deformation means, and in doing so causes a deformation of the deformation means so as to indicate the holding pressure being exerted onto the mould dies.
[005] The apparatus can also include a displacement sensing means for sensing the deformation, to indicate the holding pressure.
[006] The actuating means can be a ball screw interacting with a, ball nut, the ball nut being driven by a motor means.
[007] The deformation sensed can be amplified by an amplification means.
[008] The amplification means can include a lever that is pivoted in response to the deformation of the deformation means, the displacement sensing means being adapted to sense a displacement of a free end of the lever.
[009] The deformation means can be elastic. [010] The deformation means can be one of a polymeric pad, a spring arrangement, and a disk spring arrangement.
[011] The present invention also provides an injection or dosing apparatus including a chamber and piston assembly which includes a piston that is adapted to move into a chamber which holds a first flowable material, the chamber being located within an extent of a mixer, wherein when the piston moves into the chamber, the chamber dispenses the first flowable material into the mixer.
[012] The chamber and piston assembly can include at least another piston that is adapted to move into a corresponding chamber
[013] The apparatus can further include at least one other chamber and piston assembly that has one or more pistons adapted to move into one or more respective chambers.
[014] The chamber assemblies can be interchangeable with each other.
[015] The chamber and piston assemblies can be driven by separate motive means or a single motive means.
[016] The motive means can be a toothed belt and pulleys arrangement, or gears.
[017] The chamber and piston assembly can be formed in a block.
[018] The chamber and piston assembly can communicate with the mixer via internal passage ways through the block.
[019] The chamber and piston assembly can connect to an actuator for the chamber and piston assembly by a releasable holding mechanism.
[020] The apparatus can also include a canister that contains a reservoir for the first flowable material, the container including a flowable material cavity and an air cavity with a flexible diaphragm between them, the diaphragm can have two or more membranes.
[021] The present invention further provides an injection or dosing apparatus including at least a first chamber and piston assembly which includes a piston adapted to move into a corresponding chamber for delivering a flowable material, wherein the assembly is engaged to a supporting means for the apparatus via a releasable holding mechanism, and the chamber and or the piston can be decoupled from the supporting means. [022] The releasable holding mechanism can include a mount which receives a portion of the piston in a direction which is perpendicular to the direction of motion of the piston in the chamber.
[023] The releasable holding mechanism can include a member having a channel or recess which extends in a first direction and a bight through a wall defining the channel or recess to receive a portion of the piston. .
[024] The portion of the piston to be held in the releasable holding mechanism includes a turned down portion having shoulders adjacent thereto.
Brief description of the drawings
[025] An embodiment or embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
[026] Figure 1 illustrates a sectional plan view through an injection moulding system which includes a mixer;
[027] Figure 2A illustrates an exploded sectional side view the valve block and the piston and chamber assembly;
[028] Figure 2B illustrates an exploded plan view the valve block and the piston and chamber assembly of Figure 2A;
[029] Figure 3A illustrates a side assembled view of the components illustrated in
Figure 2 A and 2B;
[030] Figure 3B illustrates a plan assembled view of the components illustrated in
Figure 2A and 2B;
[031] Figure 4 illustrates a front elevation view of the injection moulding system of
Figure 1 in connection with the component containers, the elevation view being taken from the direction marked by II;
[032] Figure 5 illustrates in a side cross sectional view showing the component canister and a mixer, the cross sectional view being taken along the line marked ΙΙΙ-ΠΙ in Figure 4;
[033] Figure 6 illustrates, in a cross sectional view taken along ΠΙ-ΙΙΙ, the actuating assembly in more detail;
[034] Figure 7 illustrates a cross sectional side view of the a press assembly for use with the injection moulding system; [035] Figure 8 illustrates a side view of an alternative press assembly;
[036] Figure 9A illustrates in plan view showing in more detail the press assembly illustrated in Figure 8;
[037] Figure 9B illustrates in side elevation view the press assembly illustrated in
Figure 8;
[038] Figure 10A illustrates in plan view an anti-torsion structure for the shaft in the press assembly;
[039] Figure 10B illustrates in side elevation view the structure shown in Figure 10A;
[040] Figure 10C illustrates in end elevation view the structure shown in Figure 1 OA;
[041] Figure 11 illustrates a sectional plan through an injection moulding system, where the chamber and piston assemblies and the mixer are driven by the same source;
[042] Figure 12 illustrates a sectional plan through a further injection moulding system, where the system is driven via gears or direct drives.
Detailed description of the embodiment or embodiments
[043] The applicant has developed an injection moulding system which is described and illustrated in PCT/AU2009/000787 (WO2009/152578). Reference is made to that application, its description and illustrations and the contents of which is incorporated herein in its entirety.
[044] As shown in Figures 1, 2A, 2B, 3 A, and 3B, a dosing and injection moulding system 10 includes a combined first chamber and piston assembly 12 (comprising two chambers with respective pistons), a second chamber and piston assembly 14, a mixer 16 having communication with the chamber and piston assemblies 12 and 14, and a servo drive or motor 18 to drive assembly 12. A servo drive or motor means 19 drives assembly 14. Various types of mixers 16 can be used. For instance, a cavity transfer mixer, a shear mixer, or other types of mixers can be used.
[045] The mixer 16 is located generally between the assemblies 12, 14. The assemblies and the mixer 16 are positioned so that the assemblies 12, 14 are generally located adjacent to and within the extent of the mixer 16. This configuration helps ensure a close proximity between the assemblies 12 and 14 and the mixer 16, and thus the passageways between these devices have their length kept to a minimum. As will be described in more detail later, it will be appreciated that in some embodiments, the second chamber and piston assembly 14 can be combined with assembly 12. Alternatively there can be a further assembly that is separate to assemblies 12, 14. Alternatively, the system 10 can have either one of the assemblies 12 or 14 only.
[046] Each chamber and piston assembly will generally be located within the extent of the mixer. When any part of the chamber and piston assembly or the mixer needs to be replaced, any residual material or components that remain between the chambers 42 and 43 and mixer 16 is often wasted, therefore a reduced distance between the chambers 42 and 43 and the mixer 16 results into a reduced amount of wastage of the materials or components needed in injection moulding.
[047] Motive power is delivered to the chamber and piston assemblies 12 and 14, to move the pistons into the chambers, via two motor means 18 and 19 which drives the screws 34 and 35 respectively. In Figure 1, the motor means 18 which drives ball screw 34 for the combined first chamber and piston assembly 12 also drives the mixer 16. A toothed drive pulley 58 is mounted on the output shaft 60 of the motor means 18. The driver pulley 58 drives driven pulleys 62 and 64, respectively mounted around the ball screw 34 and onto the mixer 16 drive input shaft, by way of a toothed belt 66. A similar driven pulley and toothed belt arrangement is provided for the other motor means 19 to independently drive the ball screw 35 for the second chamber and piston assembly 14.
[048] The two chambers 42 are held by a stationary chamber support block 44, and the other chamber 43 is held by its own stationary chamber support block 45. Each chamber support block 44, 45 is secured to a respective valve block 46 and 47. An O-ring seal is provided at the end of each chamber between the chamber support block 44 and 45 and its respective valve block 46 and 47 to avoid inadvertent leakage of the viscous material out of the chambers 42 and 43. ,
[049] As illustrated in Figures 2A, 2B, 3A and 3B, the piston support 39 can be a coupling, such as a claw coupling 38, via which the piston 41 engages the ball screw 35. The piston 41 has a narrowed neck (or 'turned down portion') 13 which is located adjacent to a head portion 15. The neck 13 is received by a channel or recess 53 in the claw coupling. The head portion 15 is received by detent formed by a U-shaped bight 37 that is formed through the wall defining the channel 53. The bight 37 receives the head portion 15 in a direction that is perpendicular to the direction of the piston's motion in its respective chamber. The shoulder formed between the head 15 and the neck portion 13 is held within the claw coupling 38 and prevents inadvertent removal of the piston 41 from the coupling 39 during its operation. The coupling 39 is in turn attached to the terminus of ball screw 34. This coupling arrangement provides a relatively easy to use 'ready release system', in that the coupling allows ready disengagement of the piston 41 from the ball screw 35. A similar arrangement is provided for the dual piston arrangement of assembly 12 and its ball screw 34. A similar claw coupling 38 can be used as the piston support 38 within assembly 12, except that the claw coupling 38 would have two bights to accommodate the two pistons 40.
[050] As the pistons 40 and 41 are plunged into the respective chambers 42 and 43 the contents of the chambers 42 and 43 are each separately dispensed, under pressure, to three mixer inlet passages 48 located in valve blocks 46 and 47. There can be one way valves 50 and 51 located in the valve blocks 46 and 47 which control the flow of the material from the chambers 42 and 43 to the mixer 16, and prevent any back flow of the material.
[051] By passing the dispensed material through ports in the valve and mixer blocks, instead of using hoses, there should result a minimisation of wasted material over the life of the injection moulding machine. Hoses also run the risk of bursting or working loose without notice and thus this risk is reduced. The decreased use of hoses in the system also makes the system safer, with less entanglement as there e would otherwise have been there due to the presence of hoses.
[052] The mixer inlets 48 allow the component to be fed via separate passages into the mixer 16. The mixer 16 is enclosed in a water cooled jacket 54, for example an aluminium water cooled jacket. In the mixer 16 the flowable materials are mixed to form an injectable material. The mixture exits from the mixer 16 through a nozzle 56. The water cooled jacket 54 for the mixer 16 and the water cooled nozzle 56 keep the mixing mixed components in the mixer 16 cool, to counteract any excess heat that can be produced because of, for instance, the shear forces present in a shear mixer. The excess heat can otherwise cause the components to prematurely set.
[053] As described above a separate feed tube between the mixer inlet 48 and the mixer
16 is provided for each material. That is, each chamber 42 or 43 dispenses its content to a dedicated port, so that the various components do not contact each other until they are sent to the mixer 16. This is illustrated in Figure 4, where the chambers 42 and 43 are shown to dispense their content through separate feed tubes 82, 84, 86, to the mixer 16. Figures 1, 2A and 2B also show that the feed tubes 82, 84, 86, deliver the components to generally the same area within the mixer 16. However, depending on the chemical nature of the components used in the mixture, the system can have fewer feed tubes. For instance, if the components dispensed by the chambers 42 in the first assembly 12 can be premixed without setting and creating blockage, the chambers 42 can dispense into the same feed tube. [054] Figure 4 illustrates a front elevation view of the aforementioned parts of the injection moulding system 10, and also containers (or "canisters") 72, 74, 76 which supply the materials to be mixed. The motor means 18 and 19, chamber and piston assemblies 12 and 14, and the mixer 16 are enclosed within a machine guard 70 which covers these machine parts. The containers 72, 74, 76 are located external to the machine guard 70 for convenient replacement or refilling. Each container outlet 78 is adapted to pass through the guard 70 and inject the content of the container towards the appropriate chamber 42 or 43.
[055] As illustrated in Figure 4, the container outlet 78 is fitted through the machine guard 70, and is received by a fitting 80. The fitting 80 is a 'plug-in' fitting 80 that allows the outlet 78 to be plugged into the appropriate receptacle to connect to the corresponding chamber assembly 12 or 14, or a particular chamber of the chamber assembly 12. Such a 'plug-in' fitting can utilise quick release mechanisms such as bayonets or other similar fittings, with the proviso of having to provide adequate sealing between the components of the containers and the receptacles at the guard 70.
[056] The contents of the containers are forced under pressure out of the containers and are directed towards the valve blocks 46, 47 in Figure 1, and the flow of the contents into the chambers 42 and 43 can be controlled by one way valves located in the valve blocks. From the chambers 42 and 43, the flowable materials are fed to the mixer 16 via the mixer inlets (or "feed tubes") 82, 84, 86, which are ported through the blocks (including valve blocks 46 and 47).
[057] The configuration of the injection moulding system 10, as described above, allows for a modular construction and assembly for the various parts. For instance, each of the product containers can be removed, replaced, and reconnected to the machine guard. Also, the chamber and piston assemblies 12 and 14 can readily be detached from the system and reattached in any order (e.g. interchanged from respective original positions). If for any reason a chamber assembly needs to be removed (e.g. to be replaced, cleaned, or repaired), the pistons are retracted from the chambers by the ball screw 34, and then the chamber assembly can then be removed from its respective valve block. By detaching the piston support 38 from the bearing block 32, the piston 40 can then be removed for e.g. cleaning, fitting, or replacement.
[058] The above described system 10 is suitable for mixing and injecting a silicone based mixture composed of three different materials so as to produce a foamed silicone product. It can be modified to output mixtures made of four or more components. For instance the second chamber and piston assembly 14 can be modified so that it is similar to the first chamber and piston assembly 12, and outputs two different ingredients into mixer 16. Conversely the second chamber and piston assembly 14 can be removed if only two different flowable components are needed to form the mixture. Of course, the system can be used with only one chamber and one piston, if the different components can be premixed and injected into the mould cavity directly.
[059] If required, the first and second chamber and piston assemblies 12 and 14 can have, in each, any appropriate or required number of chambers and pistons. For example, if desired, the assembly 14 and its associated motor means 19 can be removed or otherwise not provided. Instead, 3 or 4 component chambers and respective pistons can be provided in the assembly 12. In this arrangement the amount of component dispensed can be controlled by the size (volume) of the respective chambers, with all chambers dispensing fully after each full stroke. The amount of components dispensed can alternatively be controlled by controlling via electronic means or valves, the amount of component which passes into the respective chambers from the reservoirs or containers of the components.
[060] Figures 5 and 6 further illustrate in more detail each container and its connection to its corresponding chamber. The construction of each container is similar to that disclosed in the applicant's co-pending application PCT/AU2009/000787 (WO2009/152578).
[061] The container 72 can be protected and/or insulated by a protective sleeve 73, such as a Kevlar sleeve. A flexible diaphragm 90 separates the container into a product cavity 100 in which the material for forming the mixture is contained, and an air cavity 96. The container has a vacuum priming port 94 through which a vacuum or negative pressure can be applied to the air cavity 96. Pressurised or regulated air can then be injected into the air cavity 96 via an air inlet 98. The pressured air can be supplied from, for instance, a pressurised air canister or a compressor which is located within the confines of the machine embodying the system 10, or a separate compressor system. The air cavity 96 expands when pressurised air enters the cavity 96. As it expands, the air cavity 96 pushes the flexible diaphragm 90, which carries the container outlet 78, into the product cavity 100. The resulting change in pressure in the product cavity 100 causes the flowable material to exit out of the container via the container outlet 78, and flow toward the valve block 46, where the corresponding one way valve directs the product into the corresponding chamber.
[062] The flexible diaphragm 90 can comprise multiple layers of membranes. Should a first membrane (the membrane that is immediately adjacent to the product cavity 100) be stretched beyond its elastic limit and burst, the remaining membrane or membranes keep the product from leaking into the air cavity 96. The more membranes there are in the flexible diaphragm 90, the less likely the product will leak into the air cavity 96, but the stiffer the diaphragm 90 will be. Therefore the appropriate number of membranes in the diaphragm will depend on a balance of these two factors.
[063] As illustrated in Figures 5 and 6, the piston 40 rigidly connects to a piston support
38 that is actuated by a threaded ball screw 34. The threaded ball screw 34 passes through a ball nut 36 that is rotatably mounted in a bearing block 32, the ball nut 36 being rotatable with respect to the ball screw 34. The translational movement of the ball screw 34 is guided by a pair of guide rods 33 (or "anti rotation rods").
[064] The ball screw 34 or 35 is rigidly connected to a torque bar 31 that extends between the pair of guide rods 33. This connection can be achieved by, for instance, welding. Alternatively, the ball screw 34 or 35 can extend through a hole in the torque bar 31, to be secured to the torque bar by a cap and bolt arrangement as shown. The torque bar 31 slides along the guide rods 30, with appropriate friction reducing means 49 such as linear motion bearings to reduce friction between the torque bar 31 and the guide rods 33.
[065] The piston support is shown here as a claw coupling 38. The piston 40 in this embodiment engages the coupling 38, and extends through the coupling 38, the coupling 38 being attached to the terminus of the ball screw 34. The piston 41 is thus releasably attached to the ball screw 34.
[066] The motor means 18 (shown in Figure 1) causes the pulley 62, and in turn the ball nut 36, to rotate. As a result of the guide rods 33 and the torque bar 31, the ball screw 34 is prevented from rotating in response to the torque generated by the ball nut 36. Whereas the ball nut 36 rotates inside the bearing block 32 (shown in Figure 1), the rotation being facilitated by bearings such as angular contact thrust bearings 55, the ball screw 34 translates in the direction defined by the guide rods 33 (i.e. move away or toward the chamber and piston assembly 12). An inboard movement of the ball screw '34 acts on the piston support block 38, and pushes the piston 40 to move toward and into the chamber 42, thereby causing the content of the chamber 42 to be dispensed. Conversely, when the motor means 18 drives the ball screw 34 in the . opposition direction, the ball screw 34 translates in an outboard direction and causes the piston 40 to retract from the chamber 42, allowing the chamber 42 to refill.
[067] A similar arrangement is provided for the other chamber and piston assembly 14, whereby a ball screw attachment block is also slidably mounted on a pair of guide rods. The ball screw attachment block rigidly carries the ball screw 34 for the chamber and piston assembly 14. [068] As will be appreciated the pistons 40 and 41 travel into the chambers 42 and 43 by such a distance that, for example, one shot of the flowable components will be dispensed from each chamber 42. Each chamber 42 can hold exactly one shot of the component needed, or alternatively can be sized to hold multiple shots of the components. For instance the chambers 42, 43 can be made to hold three shots of the material, and the motor means 18 and 19 can be subject to programmable control so that they cause the pistons 40 and 41 to move into the chamber 42 and 43 to displace 1 , 2, or 3 shots of the material.
[069] The parts of the system 10 which include the chamber and piston assemblies and the mixer as described above are collectively referred to as the dosing assembly. The following describes those parts of the system 10 which apply a holding pressure to keep the mould dies together while the mixture is being injected into the dies.
[070] Figure 7 illustrates a press assembly 120 which is employed in the injection moulding system 10, to exert a holding pressure on the mould dies or on any bolsters (or "platens") that carry the mould dies. The mixer's output nozzle 56 injects the mixture into a cavity located between the mould dies (not shown in this figure) which can be attached to bolsters 131, 132. The fixed bolster 131 is positioned adjacent to and lies against a manifold block 130 which supports the mixer 16. The manifold block 130 is water cooled. The moving bolster 132 is coaxial with the fixed bolster 131 and is adapted for translation toward the fixed bolster 131 by being mounted on horizontal rails and is connected to a ball screw shaft 140 for motive power. In embodiments where the mould dies are not attached to bolsters, the mould dies themselves are coaxially mounted on the shaft 140.
[071] . The ball screw shaft 140 is driven by a motor means 142 such as a servo motor. A ball nut 144 (driven preferably via a belt by motor 142) is rotatable relative to the shaft 140, and is mounted to a brace 145. The ball screw shaft 140 is prevented from rotating by a shaft stabiliser 141, or by its connection to the mounting to the moveable bolster 132. The shaft stabiliser 141 can be made to move between guide rods (similar to the arrangement provided for the ball screws 34 used in the chamber and piston assemblies 12, 14), or is otherwise rotationally restrained to prevent the shaft 140 from rotating due to the torque produced by the motor means 142 and exerted on the ball nut 144. Thus only the ball nut 144 rotates, and the shaft 140 translates. Rotation of the ball nut 144 in one direction causes the shaft 140 to move the moving bolster 132 towards the fixed bolster/131. Eventually the movement of the shaft 140 causes the bolsters 131 and 132 to meet each other and thus close the two mould dies, with an appropriate pressure. The mixer-driving motor 18 then drives the mixer 16 to produce the mixture. The nozzle 56 then injects the mixture into the cavity between the mould dies. The motor 18 (or 19) for the chamber and piston assembly 12 (or 14) now drives in the other direction, withdrawing the pistons from the chambers and allowing the product container to refill the chambers.
[072] The pressure exerted onto the mould dies (due to the mixture being injected between the dies) tends to push the mould dies apart. To prevent the mould dies from separating, the motor 142 continues to cause the shaft 140 to push the bolsters 131, 132 together. The pressure needed to hold the mould dies together is referred to as the 'holding pressure' . The shaft 140 in this sense is an actuator for actuating the moving bolster 132. To measure the holding pressure thus exerted on the bolsters 131, 132 by the torque of the motor 142, a deformation means 146 such as a polyurethane pad (or a bed of springs, or Bellville washers (disk springs)) is provided between the shaft 140 and the moving bolster 132.
[073] The deformation means 146 can be made from a range of alternative materials, or composite materials or by different arrangements, providing the elasticity of the material is maintained and its spring constant is known regardless of the amount of its deformation (or deflection) by compressive forces. A deformation means having a substantially unvarying spring constant in the deformation range caused by the type of compressive forces applied in the injection moulding system is preferred. However, if the spring constant varies, the variation can be accounted for by a control system. For instance, given that the control system has access to data regarding the relationship between the spring constant and the deformation, once the amount of deformation is measured, the control system can perform an integration operation to calculate the accumulative force that would have been needed in order to achieve the amount of measured deformation. It is also preferred that the deformation means allows a control system or an operator to calibrate the holding pressure against the amount of deformation in the deformation means.
[074] A positional transducer 148, in this case a linear transducer, senses the amount of deflection in the deformation means 146 due to compression from the motor 142 via the shaft 140. Given the spring constant of the deformation means 146, the area of the pad, and the amount of deflection measured by the positional transducer 148, it is possible to calculate the amount of pressure , exerted on the deformation means 146, and thus the holding pressure exerted to keep the bolsters 131, 132 together, by the motor 142. It will be appreciated that while other devices capable of providing load-position information can be used in place of the position transducer 148, one of the advantages of the preferred system is the ability to simply and cheaply provide an amplification of the deflection and thus a more accurate reading of the pressure applied. Alternative systems can include a load cell or a position sensor.
[075] In injection systems where the holding pressure is applied using a hydraulic system, the pressure applied to the bolsters is readily measured. However, hydraulic systems can be bulky, and if there is a blockage or restriction occurs in the system, a readout of the hydraulic pressure might not be the same as the holding pressure. The provision of the deformation means 146 and the positional transducer 148 allows a motor driven clamping system to replace the hydraulics system, and at the same time allows ready measurement of the holding pressure directly. The space saving thus realised reduces the size of the overall injection moulding system 10.
[076] It will be noted that the deformation means 146 helps the system tolerate misalignment of the mould dies or the bolsters which carry the mould dies. For instance, because of its flexibility, the deformation means 146 can be pressed against, to stabilise, a bolster that is slightly misaligned with respect to its axis of movement (i.e. not substantially perpendicular to the direction of the shaft 140). A load cell or position sensor alone cannot provide this additional advantage.
[077] Figure 8 shows an alternative press assembly 121, where the deformation in the deformation means can be amplified, to increase the accuracy of a readout of the deformation. This amplification can be achieved by an amplification lever or arm 170 that is located adjacent to the deformation means 1 6. The deformation means 146 is mounted between a base 147 that is attached to the moving bolster 132, and a plate 149 that is attached to the shaft 140. The amplification arm 170 is pivotably mounted to a link 1 1 that is rigidly attached to the base 147. The pivot point 172 of the arm 170 is therefore the pivotable connection between the arm 170 and the link 171. An intermediate portion 173 of the arm is attached to the plate 149.
[078] The shaft 140, which carries the plate 149, pushes toward and compresses the deformation means 146. The plate 149 therefore moves with respect to the base 147 when the deformation means 146 is compressed. The end 172 of the arm 170 that is connected to the link 171 does not move with respect to the base 147. However, the intermediate portion 173 of the arm 170 is caused by the translation of the plate 149 to rotate about the pivot point 172. The free end 174 of the amplification arm 170 also rotates about the pivot point 172.
[079] A first end 175 of the transducer 148 is attached to the free end 174 of the amplification arm 170. A second end 177 of the transducer 148 is pivotably attached to a support structure for the transducer. When the free end 174 of the arm 170 rotates about the arm's pivot point 172, the transducer 148 rotates about its second end 177 so as to accommodate the change in the position of the arm 170.
[080] The ratio of the angular movement at the free end 174 to the angular movement at the intermediate portion is the same as the ratio of the entire length of the arm 170 'L' to the distance between the pivot point 172 and the intermediate portion 173, Ή'. By measuring the displacement of the free end 174 of the arm 170, the deformation read by the transducer 1 8 is amplified by a factor of about L H when compared to the actual deformation of the deformation means 146. The location of the 'intermediate portion' 173 (and therefore H) can thus be chosen depending on the desired amplification factor L/H. In the example shown, the amplification factor is roughly 10.
[081] Figures 9A and 9B depict the above described embodiments of the assembly in more detail. As shown in Figure 9A, the movement of the moving bolster 132 is guided by a pair of guide rails 180. The moving bolster 132 can be fitted with a friction reduction arrangement, such as linear bearings 133, which facilitates the travel of the bolster 132 with respect to the guide rails 180. The deformation means 146, sandwiched between a base 182 and an end plate 184, carries the moving bolster 132. The ball screw shaft 140 used to actuate the bolster 132 is rigidly attached to the end plate 184, for example by using an Allen screw.
[082] As shown in Figure 9B, the press assembly 121 is supported by a frame 186. The fixed bolster 131 and the brace 145 are affixed to the frame 186, as is the motor means 142 for driving the press assembly 121. A pair of tension bars or links 188, each having a boss 153 with an aperture 151 therethrough at each end, provide a tensile resistance to the compressive forces generated to produce the holding pressure on the mould dies. The links 188 mount to, and extend from, a horizontally extending cylindrical spigot 157 which is attached to or formed on either side of the brace 145 (on which is mounted the ball nut 144), across to the a similar cylindrical spigot 157 on the fixed bolster 131. The ball screw shaft 140 is rigidly attached to the plate 184, for example via an Allen screw.
[083] The links 188 can have a series of paired holes 181. Each pair of holes 181 define a position at which the guide rails 180 can be mounted. This helps accommodate mould dies of different sizes or different number of mould dies between the bolsters 131, 132, as is required by the specific injection moulding task. [084] Figures 10A, 10B, and IOC depict the anti-torsion arrangement 190 that is provided to keep the ball screw shaft 140 from rotating when the ball nut 144 is driven to rotate by the motor means. The ball screw shaft 140 is rigidly secured to the shaft stabiliser 141. The shaft stabiliser 141 is movably held between a pair of shaft support rails 192. Linear bearing blocks 194 enable the shaft stabiliser 141 to slide along the shaft support rails 192.
[085] In many applications, relatively large holding pressures need to be applied to the mould dies. As a result the motor means needs to apply a large torque. In the current system 10, to account for the large torque applied by the motor means 142 upon the ball screw shaft 140 and thus upon the shaft stabiliser 141, the shaft stabiliser 141 is further supported by anti-rotation brackets 200. The anti-rotation brackets 200 are located so that they resist the tendency for the shaft stabiliser 141 to rotate when the holding pressure is being applied against the mould dies.
[086] Each anti-rotation bracket 200 has a horizontally arranged first member 202 that runs along each shaft support rail 192. A second member 204 is generally perpendicular to the first member 202. The second member 204 is located against the brace 145 (or "ball nut plate"). A third member 206, which is a reinforcing web, is provided between the first and second members 202 and 204, to help prevent the first and second members of the bracket 200 from buckling due to the torque.
[087] When the ball screw shaft 140 is being retracted away from the mould dies, a substantially smaller torque is applied by the motor means because the motor means no longer needs to output enough torque to apply the holding pressure. Therefore, when the shaft 1 0 is beirig retracted, the shaft stabiliser 141, the linear bearings 194, and the shaft support rails 192 provide a sufficient arrangement to counteract the shaft's tendency to rotate.
[088] In the above, the chamber and piston assemblies 12, 14 are described to be driven by different motors 18, 19, and this allows the assemblies 12, 14 to be independently controlled. However in alternative embodiments, as shown in Figure 11 , the chamber and piston assemblies 12, 14 can be driven by the same motor 18 with a single drive belt. In these cases, the chambers 42, 43 can be sized so that they output their respective component in the correct proportion in relation to each other when they enter the mixer 16.
[089] In another alternative embodiment illustrated in Figure 12, instead of the pulley and belt arrangement shown in Figure 1, gear trains 61, 63 are used to allow the motor to drive the chamber and piston assemblies and the mixer 16. However, if the injection moulding system 10 is intended to be used in a 'clean room' environment (e.g. to make medical products), the meshed gear arrangement is less desirable than the pulley and belt arrangement. The reason for this is that to ensure a smooth operation of the meshed gears, lubricant needs to be added to the gears. As a result, particles of lubricant or oil or metal dust can be ejected by the gears. Even in small amounts these can jeopardise the clean room environment, in which a very low level of foreign particles in the air is tolerated.
[090] Although servo motors have been mentioned as the means which drive the injection system, other motor means can be used. For instance other motor means that can be used include electric motors, AC motors, pneumatic or hydraulics motors or the like.
[091] Where ever it is used, the word "comprising" is to be understood in its "open" sense, that is, in the sense of "including", and thus not limited to its "closed" sense, that is the sense of "consisting only of. A corresponding meaning is to be attributed to the corresponding words "comprise", "comprised" and "comprises" where they appear.
[092] It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text. All of these different combinations constitute various alternative aspects of the invention.
[093] While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, and all modifications which would be obvious to those skilled in the art are therefore intended to be embraced therein.