|Title of Invention||
"METHOD FOR INJECTION MOULDING AND INJECTION UNIT"
|Abstract||Method for injection moulding of plastic parts with an injection screw (4) driven rotativety and axlalty, whereby the drive for the axial movement takes place with the help of an intermediately connected crank drive (28), characterized in that a double lever mechanism (29) is arranged between the crank drive (28) and Injection screw (4) In such a way, that a preferably etectromotoricaity generated force is introduced computsority coupled by means of the double lever mechanism (29), mainly in axial direction with the lever pair (30,30') with symmetric force effect, into the rear bearing position of the injection screw (4).|
|Full Text||-2-This invention relates to a method for injection moulding and injection unit.
This invention pertains to a method for injection moulding of plastic parts with an injection screw driven rotatory and axially, whereby the drive for the injection displacement Is carried out with the help of an intermediately connected crank drive. The invention further pertains to an injection unit for injection moulding machines, especially with controlled or regulated electromechanical drive for axial movement of the injection screw.
An Injection moulding machine, when considered for main functioning, has three functional groups. At the center is the injection mould. This generally consists of two mould halves. On one side of the injection mould is the drive of automatic opening and closing of the mould halves. On the opposite side, as third group, we find the so-called injection unit. By injectfon unit, we understand here the totality of injection cylinder with heating jacket, injection screw and the drives required for it with the structural joining agents.
In a simplified or shortened way, the individual phases of Injection can be described as follows. Synthetic material is fed into the injectfon cylinder through a tiffing funnel. The raw material Is calculated by the screw movements of the injection screw and moved forwards in the injection cylinder. Due to the rotatory movement of the injection screw, the synthetic material is conveyed more and more to the peak and is primarily melted by the geometry of the screw or by shear heat and comes as molten material In a collection chamber immediately before the nozzle. As approximation values it holds good, that the melting heat Is applied to a large extent in mechanical work between injection screw and cylinder wall and the rest by jacket heating. The molten material get jammed in the collection chamber in case of continued rotation movement of the screw and pushes the injectfon screw backwards in its axis direction due to increase in volume in the collection chamber. If the quantity of fluid
synthetic material required for one shot is ready in the collection chamber, then the screw rotation drive gets stopped. The return flow block brought about at the peak of the screw is closed by means of forward movement. In this way the screw becomes a piston and takes over the function of an injection piston. For injecting the synthetic mass into the mould, a hydraulic mechanism comes into play, which is referred to below also as piston drive. The piston drive pushes the entire screw forward in a purely axial movement. The injection screw, now purely working as piston, sprays the molten material through the nozzle at pressures of up to 2000 bar into the cavities. The injection is understood in two phases. The first phase is the actual filling. The required pressure towards the end of the filling phase could increase to the already mentioned 2000 bar. The filling is followed by the phase of post-pressure, whereby the end pressure of the filling phase is approx. retained.
In practice, depending on the area of application, two methods have got established. In the packing industry, the topmost maxim is a maximum possible number of pieces per unit of time, so that in this way the cheapest parts like yoghurt cups, confectionery packing etc. can be produced. Special capping methods are used, so that the nozzle along with the injection unit can be moved away from the mould immediately after every shot and the flowing out of the molten material into the free air can nevertheless be prevented. For ensuring very high quality specifications for technical applications, say for production of toothed wheels with the highest degree of precision, the nozzle is left against the mould, so that the solidifying synthetic material in the runner can have its effect without any kind of damage like nozzle-wear. Here the injection unit should not be pushed between two cycles. Theoretically, the collection chamber can be designed very long. The length of the screw or the length of the screw paths is decisive for preparation of the molten material. The effective length however gets that much smaller, the longer the collection chamber is before the screw peak. As a basic rule, the collection chamber is designed sufficiently big, so that the maximum portion to be spread can be produced with a single stroke and the described spraying cycle can be utilised. From experience it holds good, that the displacement path of the screw should be maximum three times its diameter, so that the melting quality is guaranteed through the entire dosaging process. For a given screw geometry, thereby the maximum injectable portion is still restricted. For all smaller parts the screw stroke is correspondingly made smaller. One get two obligatory movement functions: - Rotatory screw drive and
Axial movement of the plasticizing screw.
For example, in application for packing parts, an additional movement is used for the movement of nozzle towards the mould and away from the mould. This third movement function is realized by displacement of the entire injection unit. For the sake of definition, the conveying direction of the screw and accordingly the nozzle is referred to as front; the opposite side, more concretely the support side, is referred to as back. With respect to the three drives of the injection unit, one almost compulsorify gets the following requirements:
- the unit drive for the nozzle preparation (if required) downwards;
- the axial drives of the plastictzing screw backwards;
- rotatory drive of the plasticizing screw upwards or sideways.
This concept has established itself over decades In thousands of variations. As driving agents, the piston drive has to be designed hydraulically, the rotatory drive elecfro-motoricalty and the unit drive hydraulicalfy or pneumatically. The specific advantages of different drive forms are utilized. In case of hydraulic or pneumatic cylinders, a linear movement and the maximum possible linear displacement force is generated without deformation. In electromotoric drives, on the other hand, a rotatory force is generated and is available as such with corresponding gear step-down, adapted to the diameter of plasticizing.
A different method was followed in EP 451294. For the injection movement of the screw, a pure crank drive with a crank between a fixed plate and a plate which can be moved towards and away from It, is suggested; one crank is foreseen for converting a forward and a backward rotation of the drive shaft into a two and fro movement of the invention conveying screw. The drive or over drive for the axial movement of the injection screw, with respect to the use of a crank drive, is directly utilized as impact force between a fixed place and the conveyor screw. This gives still greater disadvantages with respect to the requirement of a short machine. The crank drive along with the fixed plate Is fitted at the back and is situated even behind the not shown rotatory drive or the plasticizing screw. Such
a solution is meaningful only for a very small machine. A further disadvantage arises from the direct intermediate switching of a crank drive between a screw and the fixed plate. The forced intervention of the one crank takes place on the conveyor screw at a significantly great angle to the axis of the Injection screw. To avoid corresponding side forces on the lower jacket surface of the injection cylinder, it is suggested as a variant, to move the injection screw over a longitudinally placed additional pressure plate arranged in between. However, this solution thereby becomes longer. It is however true that it can almost not be surpassed, from the point of view of manufacturing cost for the suggested crank overdrive alone. The cheaper price according to the lessons of EP 451294 must however be paid for, due to the two significant disadvantages for machine extension and necessity of compensating of said forces. According to the lessons of EP 451294, the rotation angle range of the drive shaft or the working range of the crank during forward and backward rotation is restricted by corresponding design of the control device. The working range of the crank should not contain upper and lower dead centers of the crank, and surrounding regions, with respect to the upper and lower dead centers, should nor have a range of about 30°.
The document WO97/34757 suggests a toggle mechanism, which is directly leaning against the ptastlcizlng screw, and thus allows force transmission with an optimum force ratio, the structural concept foresees an intermediate lever, which is driven by a crank and a butt strap. The intermediate lever itself is designed as a two-arm lever, which in the center, by means of a mentioned joint, moves the plastlcfzing screw. The advantage of this solution lies in the fact, that the force transmission takes place from behind directly into the axis of the conveying screw by means of pressing or impacting, and avoids larger side-forces, as compared to EP 0451294. The positioning of the drives and overdrives is disadvantageous. JP-PS 4122618, JP-PS2227230 and EP-PS 1091744 all have a common concept. The drive lever is driven by a crank, is supported somewhat in the center and acts with the upper lever end directly in the axis direction
against the conveying screw as an impact or thrust movement. All three suggested solutions are seized by the disadvantage of large structural length.
SUMMARY OF THE INVENTION:
It Is the task of this Invention to find an optimum solution with respect to the control and regulating-technical control of the entire spraying cycle, i.e. the process-technical side and
especially on the basis of structural and force-related requirements: Of a short, if possible electrically driveable machine; of avoiding side forces on the injection screw; and of the best possible positioning of the drive and overdrive mechanism.
The method as per the invention has the special feature, that between crank drive and injection screw, a double lever mechanism is arranged in such away that a preferably electro-mechanically generated force is guided through the double lever mechanism in a compulsively coupled manner, mainly in axial direction with the lever pair with symmetric force intervention, into the rear support position of the injection screw.
The new method allows for a large number of further advantageous extensions, especially an optimum utilisation of all significant advantages of a crank drive. The crank drive is particularly preferred for movable run-up of the extreme positions between both dead centres. In very many applications it is advantageous, if the crank drive approaches the front dead centre for each spraying cycle, irrespective of the spraying quantity. It is further suggested to lay down the switchover point for filling on post-pressure in the range of 20 to 40°, preferably in the range of approx. 30° before the front dead centre position of the crank drive. It has been seen that in the front region, in the vicinity of the dead centre, the motor does not have to generate any torque or almost no power. The post-pressure range, especially for an optimum control of a mass cushion, thus becomes much more comfortable and with micro-movements and if required, with support of various characteristics. According to a further advantageous extension of the method, the axial movement can be fixed by the front dead centre of the crank movement. The effective stroke path depends on the part size to be sprayed. In the front region, approx. 30° are utilised for the post-pressure phase, and in the rear region up to 30° can be utilised for a pressure release. In the rear region, the additional movement in the region of the screw return draw after plasticizing yields a pressure release for the mass. For the filling process there remains an angle region of 100 to 140° as maximum path stretch for the largest part to be sprayed. All advantages of crank drive can thereby be utilised to the maximum.
The injection unit as per the invention has the special feature, that the injection unit has a double lever mechanism with lever pair, compulsorily coupled in the region of the rear
support position of the injection screw, with a mainly axial and symmetrical force effect in the injection screw axis, for axia! movement of the injection screw.
The usual practice since decades used the model of direct pressing or impacting of the conveyor screw from behind in axis direction, for generating the extremely high spraying forces during injection and post-pressure. The lever mechanism according to the new invention solution grips on to the rear support position of the injection screw and preferably stretches in the direction of the screw conveyance, i.e. forwards. The new solution has the immediately apparent disadvantage, that several individual parts are required for the lever mechanism. As against this, there are however many important advantages, namely.
a real shortening of the entire machine; an ideal force transmission, especially in combination with application of tensile force,
while using an eccentric drive and crank drive over a pair of levers;
a compact assembly group which forms the injection unit,
an optimum force guidance, as will be explained below;
- furthermore, ideal prerequisites for using the very advantageous servo drives, at least for axial and radial drive of the injection screw.
For special advantageous extensions of the device, reference is made to the claims 4 to 10. The double lever mechanism is provided with a draw lever position which stretches in the direction of the screw conveyance, in the front portion leaning against a vertical swivel arm and connected through it to an electromechanical drive. The drive is provided with a crank overdrive or eccentric overdrive, which is arranged between the draw lever mechanism and a controllable or regulatable drive motor The drive can be designed as servo motor. The entire mechanism is designed in such a way, that the maximum deflection movement of the crank overdrive or eccentric overdrive conforms to the maximum stroke of the injection conveying screw. The decisive advantage of the new concept lies, on the one hand, in the possibility of optimum positioning of all mechanical components, however mainly also in the form of lesser utilised space within the machine stand, than before. On the other hand however, the introduction of a lever mechanism between the injection screw and the crank drive or eccentric drive allows the utilisation of all classical advantages of a crank drive without its disadvantages. Advantageous is an ideal force-path graph for the injection phase. Possible side forces on the injection screw are ruled out due to the parallel force introduction. Depending on the size of the machine, even a single draw lever can be used. In case of a pair of levers, one gets an ideal, symmetric force intervention, especially when the lever pair along with the axis of the injection screw lies in a common plane. The functioning of the injection screw is not impaired in any way, as the lever pair is guided sideways, with a distance and parallel to the spraying cylinder. Ideally, the swivel arms form an angle of approx. 90° with the draw levers, so that the entire swivel movement of the joint lies approx. in the mentioned common plane. The swivel arms are directly supported on a base plate of the unit in a swivelable manner, whereby they are hinged at its upper arm portion to a side lever and at its lower arm portion with the drive. The swivel arm is supported swivellable against the base plate, which also supports the spraying cylinders in a fixed manner. In this way, the enormous forces for the injection pressure can be closed on the shortest path within the unit. Closing of the forces on the shortest path allows, as a rule, a light construction, whereby the necessity of more individual parts, as mentioned above, gets compensated. According to the new solution it is further suggested that the drive for the axial movement be designed as servo motor with gear and be arranged fixed in the unit lower portion.
According to a very special advantageous extension, the injection unit is designed with movable base support as complete unit integrally with the electromechanical drive for the conveyor screw, and can be moved to and fro like a carriage. For mounting the spraying pressure, the conveyor screw is preferably drawn over its rear rest position with a pair of levers on the base plate, in the manner of a draw carriage in conveying direction. This design concept allows the entire drive unit for the draw lever pair to be built in under the base piate, and joined fixed with it. In the upper part of the drawing agent, the inner space remains free for the spraying cylinder. On shifting the unit for the to arid fro movement of the nozzle, the entire injection unit is moved. For the motoric driving agents, a continuous crank drive shaft, common for both levers of the lever pair, is foreseen. This allows a symmetric drive and overdrive for both sides of the injection screw. From this we get a further very important aspect, namely the symmetry of forces on the one hand, especially also the symmetry of the most important space-requiring parts of the entire injection moulding machine. As an extension of the new solution method, the injection unit can be produced as a compact assembly group. A drive housing is placed directly below the base plate. A new concept however allows a great freedom for the choice and exact arrangement of the motoric driving agents. The new solution can be applied for the most varied kinds of Injection moulding machines, e.g. machines specialized for CD. The new concept is further ideal for a very economic fabrication, namely production of the assembly group. The corresponding advantages become particularly pronounced when the assembly group contains almost all important components ready for production, which is necessary for the functioning of the injection unit. In this way, assembly costs can be saved. It Is possible to arrange a part of the local electronic mechanism or control, e.g. the power electronics directly under the injection unit, e.g. in the lower portion.
The invention further relates to the application of the Injection unit as per claim 3, with a double lever pair which forms an impact anchor with the rest position (12c).
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
The invention Is now explained In more details on the basis of a few design
examples. The following are shown:
Flg.1 The classical type of the Injection side of an injection moulding machine
with hydraulic drive for the injection movement;
Fig.2 A solution of the state-of-the-art technology with three eietro-motoric drives
Fig.3 An example for the new solution as per the invention;
Fig.4 The main elements for the drive and overdrive for the injection movement;
Fig.5 A diagram for the most important parameters during an injection phase;
Figs.6a-6c three different positions of a crank drive and lever mechanism;
Fig.7a Figure 3 in enlarged scale;
Fig.7b Figure 4a in a perspective representation, with pair-wise draw levers;
Fig.8a A view with part cut out for the movement of the components towards one
Fig.8b A section IIXb - HXb of fig. 8c;
Fig.8c A frontal view of the injection unit according to arrow IIXc of Tig. 8a;
Fig.9a A section of the drive side for the injection movement;
Fig.9b A view from top according to arrow IXb of fig. 9a;
Fig.10 An injection unit with control/regulation concept;
Figs.11a and 11b An example for both screw movements (forward run and
backward run) from dead center to dead center;
Figs. 12a- 12c Different dispositions for the lever mechanism.
Figures 1 and 2 show two typical solutions as per the state-of-the-art technology: fig. 1a hydraulic solution and fig. 2 a so-called electrical solution. In fig. 1 however, only the axial movement over a hydraulic piston is activated. Already
since a long time the necessity of a shorter machine is known. Both examples do not conform to this necessity.
Fig. 1 shows schematically a school example of the state-of-the-art technology for the spraying side of Injection moulding machine. The heart piece is the injection cylinder 1, into which raw material 3 is fed mostly in granular form through a filling funnel 2. In the injection cylinder 1, there is a conveyor screw or an Injection screw 4, which is supported on the right side at a rest position. The rotatory movement of the injection screw is generated by a toothed wheel 6, and the injection movement as piston drive is generated by a hydraulic piston 7, which is movable in a hydraulic cylinder 8 by a certain axial displacement SpW. The mass SpW depends on the desired quantity for injecting a part or the corresponding quantity for multiple moulds. The "periphery" required for the hydraulic system is only indicated by the reference symbol 9. Absolutely on the left side, the injection cylinder 1 ends with a nozzle 10, through which the molten plastic mass 11 is injected into the cavities of the mould. The injection cylinder 1 is surrounded with hot packs 12. With the mass data SpH the maximum possible injection stroke is denoted. The technology of the injection process is presumed as
- 13 -
known. Interesting is also the mass data Nsch,, with which the effective length of the injection screw is denoted. On the right side of the picture, the excess length of the machine is given as U. This indicates that the hydraulic drive side takes a significantly great length, by which the machine is extended by the hydraulic system, kept ready at the back.
Fig. 2 shows a further example of the state-of-the-art technology. It relates to an excerpt (8) A of the Japanese patent document 62-248615. In the schematically shown solution, the electro- motoric drives are also similarly interesting. The entire injection unit is moved with the help of a motor 20 for the to and fro guiding of the nozzle 10 on to the injection mould. The motor 21 drives the toothed wheels 6' for the rotatory movement of the conveyor screw and the motor 22 drives the toothed wheels 23 and 24 for the piston movement of the injection screw 4. The movement transmission can take place with the help of a shaft 25 or spherical spindle 26. What stands out in the second example is asimilarly significant overlength 0, which is required by the electro-motoric drive and overdrive agents for the axial movement of the conveyor screw 4 alone. On the basis of only two examples as shown in fig. 1 and fig. 2, it has to be concluded that an electro-motoric overdrive is of no use with respect to the machine length.
Fig. 3 now shows with a new solution example as per the invention, that the machine length can be restricted with the rear end E. With U = 0 it is indicated that with the new solution with drives and overdrives, no additional length is required. The reason for this is, that according to the new solution, a double lever mechanism or draw lever mechanism 29 of the drive and overdrive agents stretches against the machine interior. The injection screw 4 is moved forwards with a drawing force Z acting from outside, for the injection phase. Both the main elements for the double lever mechanism are draw lever 30 and swivel arm 31. The swivel arm 31 is activated below by a connecting rod 32 and a crank drive 28 with eccentric 33. The eccentric 33 is driven by a servo motor with gear. The draw lever 30 grips on to the rear rest position or the bearing housing and stretches in the direction SF of the screw conveyance, i.e. forwards, so that the drawing effect is brought about.
Fig. 4 shows a slightly modified example of fig. 3, however reduced to a sketch model. In fig. 3, the draw lever 30 and the connecting rod 37 are on the same side, directed towards right in the picture. In fig. 4, on the other hand, the connecting rod 32 is arranged in the opposite direction. From this we obtain, that a draw force Z'- which is generated by the draw lever 30,
is caused below fey an impact force on the connecting rod 32. Apart from the different rotation direction, this does not make any difference for the crank drive as far as the type of force effect on the bearing point 34 is concerned. In fig. 4, schematically a crank drive is shown instead of a classical eccentric drive as in fig. 3. An important statement in fig. 4 emerges from the three drawn in positions, namely a front dead centre position 14, a back dead centre position 15, a front switchover point 16 from filling to post-pressure, as well as a rear switchover point 17 for pressure release. The extreme positions between both the dead centres are shown, which have to be traversed only for the biggest possible injection part. For reducing stroke (Sp.H), for smaller parts, the rear switchover point 17 compulsorily shifts forwards (arrow 18). The entire working range is then lesser than 180°. We get three angle regionsa , ß and ð. Thereby a and ß are in the magnitude range of approx. 20 to 40°, selected according to the component size. The angle 5, on the other hand, is laid down by the size of the component to be injected and the corresponding design of the entire unit. One gets an additional variable from the screw diameter.
Fig. 5 shows in a simulation image with definite, pre-selected process magnitudes, and shows the emerging parameters for an injection phase with run-up of the front dead centre vicinity. Only the dashed-dotted line should be emphasised, which gives the motor torque, and also the crossed line which gives the motor rotation speed. The region B shows the region of high motor torque. A denotes the increasing motor rotation speed with an actual peak at the end of A. This means that the motor is taxed at its peak capacity at the end of the region A or B. In the transition from B to C both, torque as well as rotation, collapse. This conforms to the front switchover point 16 in fig. 4. This enables that the drive motor can be overloaded in a clearly restricted time span of lesser than 100 msec, and allows selection of a smaller drive motor.
Figures 6a and 6c show three different positions of lever mechanism and crank drive. The disposition somewhat conforms to fig. 3 with both-sided draw effect on the swivel arm. Fig. 6a gives a rear dead centre position 15, as well as a rear switchover point 16 with included angle a. The maximum injection stroke is denoted by SpH Fig. 6b shows a further interesting aspect, namely the lever lengths a. Apparently, by choosing the corresponding lengths, e.g. oc/5 at the eccentric, an additional advantage can be achieved. The maximum possible crank path of the relatively small eccentric has a relatively small arc movement of the
bearing position 36, and hence a relatively small deflection from a parallel level HE as consequence. Fig. 6c shows the opposite extreme position, namely the front switchover point 16 and the front dead centre 14 with angel p. The mass X indicates that the stroke path in the region of the angles a and p is very small and moves towards zero, the closer the eccentric comes to the dead centre position.
Fig. 7a is shown physically, and not only schematically as figures 1 and 2. The schematic representation does give a good impression of the inter-dependability of the individual components, e.g. all drives. From the schematic depiction, it is not possible to identify where the machine parts are actually mounted. Fig. 7a shows clearly that the new solution gives a compact assembly group for an entire injection unit 35. This aspect is further strengthened with a perspective according to fig. 7b. Fig. 7b additionally shows a preferred extension, in which the draw lever is designed as lever pair 30, 30' and accordingly, the swivel arms are designed double as 31, 31'. The draw forces Z, Z1 are not only halved, but also work symmetrically with respect to the axis X. In fig. 7b the effective lines corresponding to the draw forces Z, Z' and the corresponding axial pressure P on the injection mass are drawn. All three lie on a common plane HE. Fig. 7a shows fig. 3 in enlarged scale. The entire lever mechanism 29 depicts a multiple joint. A joint 36 here, as connection of a draw lever 30 and swivel arm 31, and a joint 37, as connection between swivel arm 31 and connecting rod 32, are, considered in the picture plane, free or yield a deflection in a circular movement. The swivel arm 31 has a purely rotating axis 38 which is supported on a base plate 40 of the injection unit 35. The levers 30 are connected to the bearing point 34 by bearing studs 39. The draw forces Z, Z' are generated by the drive agents through the connecting rod 32 as Zx and yield a reaction force PR which somewhat conforms to the pressure force P on the conveyor screw 4. The screw cylinder 13, on its part, is screwed fixed along with the rear housing part 41 to the base plate 40 or the cowl 40' of the base plate 40, so that the major share of the pressure force P is again balanced with the reaction force PR through the injection cylinder 1. However, there remains a difference, i.e. the force which is obtained from the free flowing through cross-section of the nozzle 10. This can be compensated, as explained later, by the adjusting agents of the entire unit. The base plate 40 is extended downwards with a drive box 42, 42'. A drive motor, e.g. a servomotor 43, can be flanged on with gear 44.
From fig. 8a, one can structurally identify the relationship between the injection movement of the injection screw 4 relative to the base plate 40, and the unit displacement relative to the machine bed 55. In fig. 8a, both the most important parallel movement planes 50 and 51 are also marked with two thick, drawn out lines. The injection screw 4 can be shifted to and fro horizontally against the base plate 40 by a slide shoe rail and guide rail 52, as indicated by the arrow 53. As already described, this movement is attained by a swivel movement of the swivel arm 31 as shown by arrow 54. The fixed machine bed is denoted by the reference sign 55, on which a guide rail 56 is fixed. The base plate 40 has on each side two slide shoes 57, which are horizontally shiftable on the guide rails 56. As the shifting forces, arrow 58, for the entire injection unit 35 is significantly smaller as compared to the maximum pressure forces for the injection screw, there is a greater selection possibility for the choice of driving agents for the unit displacement. One can, for example, use electro-motoric drive motor or even a pneumatic cylinder. Fig. 8b is a section IIXb - IIXb of fig. 8c and is placed in the central portion over the width k through the injection screw.
Fig. 9a shows the extension of the screw coupling 59 and the bearing 65 arranged behind it with thrust bearings, in order to be able to introduce the rotation movement and the axial movements through the servo drives in each position of the plasticizing screw. The plasticizing screw 4 is coupled with a shaft intermediate piece 60 in a quickly detachable manner. The injection cylinder is connected fixed to the base plate 40 by a jacket part 61 and moves along during the unit displacement for nozzle adjustment. The bearing housing 34 is compactly joined to the plasticizing screw by different bearings 63, 65 in such a way, that the rotating movement of the plasticizing screw 4 is guaranteed, irrespective of the displacement position of the plasticizing screw 4 and bearing housing 34. The drive motor 21 and gear 19 are supported on the bearing housing 34 in such a way, that the rotating drive movement is transmitted on to the shaft intermediate piece 60 or the injection screw. The example in fig. 9a shows a very advantageous transmission through an eccentric shaft 70, which is driven as continuous shaft by a servomotor 43, with the help of an intermediately switched gear. The eccentric shaft 70 transmits along with the eccentric part 71 and bearing 72, the required force on to the connecting rod 32, corresponding to the entire sequence required by the injection cycle, with the help of a control. From the eccentric movement, a swivel movement as shown by the arrow 73 results for the swivel arm 31, which is a counter movement as mirror-image of the movement shown by arrow 54 in fig. 8a. Fig. 9b shows the carriage-like shiftability of the plasticizing screw on rails 52 and the entire injection unit 35 on guide rails 56 in a top
view of the entire injection unit. The guide rails 56 are firmly anchored on the machine bed
Fig. 10 shows an injection unit with the most important components of the control-regulation 80. The movement control takes_place as shown on the basis of an example of servomotor 43, which is designed as a local electronic system 81 as power electronics. From the local electronic system, one can sensor-technically determine with high precision, the position of the rotor and ,by means of the compulsory and possibly clearance-free mechanical coupling with the injection screw, one can determine the path position of the plasticizing screw. In a multiple-parameter regulator 82, on the basis of force sensor 83 and, if required, a pressure sensor P of the fluid molten plastic in the nozzle area, the control commands required for an injection cycle can be determined in real time (real time regulation) with the help of a high capacity computer and given to the servomotor 43. Power electronics, servomotor, mechanical compulsory coupling by an eccentric drive, give a maximum possible control even of micro-movements of the injection screw.
Fig. 1 la shows, as example for a simulation picture, the maximum possible stroke path from dead centre to dead centre and includes the injection phase and the post-pressure phase. For explanation of signs, refer to fig. 5. The data on speed represents possible maximum values. Additionally interesting is the fig. 1 lb, which shows the reverse movement direction, namely plastification, The plasticizing screw can be driven with constant rotation speed or profiled. The volume increase resulting from the conveyance is carried out with controlled pressure by means of the same lever mechanism, possibly without load change on the mechanics and correspondingly controlled return run movement. Considered from the super-ordinate point of view, the injection phase takes place as speed regulation, the post-pressure as pressure regulation. The return draw of the screw again takes playe by means of a speed regulation. Thereby the multiple-parameter regulator allows regulation of several parameters, whereby the parameters form a kind of hood limiting bonnet. Only one parameter is actively regulated at a time, the one that "impacts" at that moment on to the hood restricting bonnet, while in the corresponding time period the other regulator parts are inactive because they are not required at that moment for regulating correction. The possibility of carrying out both movement directions, with inclusion of dead centre areas, with the same regulation or the same regulating algorithms, is very significant.
Figures 12a and I2b show the already described parallel lever mechanism built in two different ways. Common to all solutions is an eccentric shaft 70, from which a lever mechanism is guided up to the bearing housing 34 in a forked manner or as mirror-image on both sides. Both the parallel lever mechanisms are identical and generate a complete symmetry for the force intervention from both sides on to the bearing housing 34. One obtains an ideal force introduction of the lever pairs 30, also because both guide rails 52 and 56 are designed as two parallel pulls, so that one gets a real parallel pull. This results in the maximum possible precision of the path guiding and force guiding between the injection screw 4 and the drive motor or the servomotor 43. The rotation of the one drive shaft of the servomotor is forked up in the eccentric overdrive in a parallel pull, and guided together again asymmetrically only by the bearing position 34. Fig. 12c shows a particularly advantageous application of the injection unit, in which the double lever pair forms an impact anchor with the bearing position.
- 17 - WE CLAIM
1. Method for injection moulding of plastic parts with an injection screw
(4) driven rotativety and axially, whereby the drive for the axial
movement takes place with the help of an intermediately connected
crank drive (28), characterized in that
a double lever mechanism (29) is arranged between the crank drive (28) and injection screw (4) in such a way, that a preferably electro-motorically "generated' force is introduced compulsorily coupled by means of the double lever mechanism (29), mainly in axial direction with the iever pair (30, 3') with symmetric force effect, into the rear bearing position of the injection screw (4).
2. Method as claimed in claim 1, whererin,
the crank drive (28) for run-up of the extreme positions between both dead centers or dead center proximity is movable, and the force is introduced especially as draw force into the rear bearing position, whereby the crank effect or eccentric effect of the correspondingly changed translation into the dead center proximity is compensated or corrected in the control/regulating unit (80), preferably with additional regulating-technical agents like specific pressure characteristics, speed characteristics, moulding-specific characteristics like of mass cushion etc.
3. Injection- unit for injection moulding machines/ particularly with
controlled or regulated electro-mechanical drive for the axial
movement of said injection screw, wherein,
the injection unit (35) has a double lever mechanism (29) compulsorily coupled in the region of the rear bearing position of said injection screw, having a lever pair (30, 30') with a mainly axial and symmetric force effect in the injection screw axis, for the axial movement of said injection screw.
Injection unit as ciaimed in claim 3, wherein,
the electro-mechanicat drive is provided with an eccentric or crank
drive (28) through which the motoric drive is guided on to the lever
mechanism (29) and is preferably designed as double eccentric crank
or double crank, and said lever mechanism is preferably equipped with
a lever pair (30, 30') which stretches parallel to said injection screw
axis, leaning against vertical swivel arms (31, 31') and is connected by
these to the drive,
Injection unit as claimed in one of the claims 3 and 4. wherein,
said (ever pair forms a draw anchor with the bearing position (36),
whereby said draw lever pair, along with the axis of said injection
screw, lies somewhat on a common plain.
Injection unit as claimed in one of the claims 3 to 5, wherein,
the electro-mechanical drive is equipped with a controllable or
reguiatable drive, particularly a servo-motor (4 3), and the maximum
deflection movement of the crank overdrive or eccentric overdrive
corresponds to the maximum stroke of said injection screw, which can
be utilized if required.
Injection unit as ciaimed in one of the claims 3 to 6, wherein,
said swivel arms form an angle of approx. 90° with said lever pair, in
such a way that the swivel movement of the hinged joined lies as far
as possible close to a common plane with the plasticizing screw,
whereby said swivel arms are supported swivelable against a base
plate (40) of the unit, and at the lower arm portion, are hinged with
said eccentric drive or crank drive,
Injection unit as claimed in one of the claims 3 to 7, wherein,
the drive is designed as servomotor (43) with gear, arranged fixed
with the lower part of the unit and is moved along on displacement of the unit, for the to and fro movement of the nozzle, whereby said eccentric drive or crank drive is preferably equipped with a continuous drive shaft, and said fever mechanism is designed symmetric on both sides of said injection screw.
Injection unit, especially as claimed in one of the claims 1 to 8, wherein said injection unit is preferably designed as compact assembly group, with said base plate (40), as complete integral component with said electro-mechanical eccentric drive or crank drive for said injection screw and can be shifted to and fro tike a carriage, and said injection screw can be moved over its rear bearing position with the help of said lever pair, relatively and parallel to the base plate tike a carriage, for the axial movement of the injection screw.
Injection unit as claimed in one of claims 1 to 9, wherein it is locally equipped with control-regulating agents for coordinating all movement functions and the pressure graph of the injection mass, particularly for the working range of the injection screw during the stroke movement for injection and return run movement during plasticizing.
Dated this 5th day of JUNE 2002.
Method for injection moulding of plastic parts with an injection screw (4) driven rotativety and axlalty, whereby the drive for the axial movement takes place with the help of an intermediately connected crank drive (28), characterized in that a double lever mechanism (29) is arranged between the crank drive (28) and Injection screw (4) In such a way, that a preferably etectromotoricaity generated force is introduced computsority coupled by means of the double lever mechanism (29), mainly in axial direction with the lever pair (30,30') with symmetric force effect, into the rear bearing position of the injection screw (4).
|Indian Patent Application Number||IN/PCT/2002/00754/KOL|
|PG Journal Number||24/2007|
|Date of Filing||05-Jun-2002|
|Name of Patentee||NETSTAL-MASCHINEN AG|
|Applicant Address||SWITZERLAND, CH-8725 NAFELS|
|PCT International Classification Number||B09C 45/50|
|PCT International Application Number||PCT/CH00/536|
|PCT International Filing date||2000-10-02|