Abstract:
In an injection molding machine the injection molding unit and the mold closing unit are at least are at least partially operated by electrical drives in form of a linear motor. The rotor and the stator have cylindrical surfaces which are arranged concentrically. The stator windings are symmetrical to the motion axis of the linear motor. Several equally acting first cylindrical surfaces are interleaved with a corresponding number of equally acting other cylindrical surfaces and are respectively operated together for operative connection. This results in a linear motor that is able to provide the advance forces required for injection molding.

Description:
FIELD OF THE INVENTION 
     The invention relates to an injection molding machine and, more particularly, to an injection molding machine for processing plastics materials and other plasticisable compounds including at least partially electrically operated driving units to operate the machine. 
     DESCRIPTION OF THE RELATED ART 
     A linear motor, which is used as the driving unit and is provided with a rotor and stator, is known for plastics material molding machines from DE-T2 37 82 817, which corresponds to EP 0 280 743 B1, and JP-A 63-1516, rotor and stator having cylindrical surfaces which are in operative connection with one another. These surfaces permit the magnetic face, which is needed for the required advancing forces, to be suitably incorporated in the drive axis. If stator windings are symmetrically disposed in accordance with DE-A 44 45 283, the relatively high bearing forces caused by the magnetism are mutually excluded. However, even there, mention is constantly made in the description of only one primary part and one secondary part, which parts co-operate accordingly with one another. If FIG. 3 there is additionally considered, it becomes apparent that the internally situated pipe is merely a carrier pipe which, just like the externally situated pipe, is neither a stator nor a rotor. When such a linear motor is used, there is a simultaneous saving in the complex converting means, which are susceptible to wear and serve to convert a rotary movement into a linear movement, such as, for example, a transmission mechanism, a spindle, levers and toothed rods (cf also EP-A 744 815), but the forces, which are required for a plastics material injection molding machine, cannot yet be applied,therefore to a sufficient extent. 
     Electrical driving units are also often used in conjunction with injection molding machines. thus, for example, it is known from EP 0 662 382 to stack together various hollow-shaft motors inside the injection molding unit to inject the plasticised compound into the injection mould and to fit the nozzle onto the injection mould. However, it is necessary for such purpose, and time-consuming, to convert the rotary movements, produced by the hollow-shaft motors, into translatory movements. However, since all of the shafts or axis for the injection molding machine are translatory shafts with the exception of the feed screw for metering the material to be plasticised, the use of such hollow-shaft motors is only recommended to a limited extent. 
     From handling techniques and medical techniques, linear motors are known which, however, do not have sufficient advancing forces, so that the linear motors, which are mainly fitted in a flat manner, are not suitable for use in an injection molding machine. (Company brochure entitled “New linear Motors and its applications” produced by the company called Fanuc, published in FANUC Tech. Rev. 112, pp. 25-36 (December, 1998); specification sheet linear motors entitled Lin.Mot P belonging to Sulzer Electronics AG, Zurich.) 
     SUMMARY OF THE INVENTION 
     The present invention provides a linear motor for an injection molding machine, which motor can also apply the advancing forces required for an injection molding machine. 
     An injection molding machine for processing plastics materials and plasticisable materials of the present invention includes an injection molding unit and a mould closing unit, which are operated at least partially by an electric driving unit including at least one linear motor, which has a rotor with magnets, disposed along a first cylindrical surface, and a stator with stator windings disposed along a second cylindrical surface, the first and second cylindrical surfaces of stator and rotor being concentrically disposed, and the stator windings being substantially symmetrical relative to an axis of movement of the linear motor. Additionally, a plurality of identically acting first surfaces are stacked with a corresponding number of identically acting second surfaces, the first and/or second surfaces each being operable jointly in operative connection. 
     In consequence, various cylindrical faces can be stacked one inside the other so that a plurality of identically acting magnetic faces are produced which contribute towards increasing the advancing forces up to a range which is required for plastics material injection molding machines, e.g. for applying the closing force. The alleged disadvantage is tolerated in such case, i.e. that the linear motor can tilt more easily so that greater demands for precision are to be made on the means for guiding the parts of the linear motor. However, this is compensated for again by the more compact construction which can be achieved. 
     Although it is known, in prior art, which forces are required for an injection molding machine to produce molded parts, only circular arrangements were proposed there, the rotor and stator having concentric surfaces, since the person skilled in the art has probably concluded therefrom, incorrectly, that a corresponding alternative arrangement cannot be achieved to a suitable extent. In order to operate the surfaces jointly in operative connection with one another in fact, said surfaces have to be worked with appropriate precision. In such case, the precision required for the operation of the linear motor increases exponentially with an increasing spacing from the central line of the cylindrical surfaces so that the linear motor can tilt more easily, the greater this spacing is, more especially when the linear motor is to be kept short in order to achieve as compact a construction of the entire injection molding machine as possible. This is further emphasized by the high temperatures which occur at high forces. This may probably also be the reason why, despite their advantages, linear motors have not yet been successful in the field of plastics material injection molding machines, since hitherto the corresponding forces could still not be applied. 
     Cooling ducts may be disposed in the cylindrical walls of the stator, so that the heating, caused by the current, can be reliably dissipated. The cooling medium used therefor can, at the same time, be used to control the temperature of other component parts in the injection molding machine. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     The invention is explained hereinafter with reference to a plurality of embodiments which are illustrated in the accompanying Figures. In the drawing: 
     FIG. 1 illustrates an injection molding unit moved onto the stationary mould carrier of a mould closing unit; 
     FIG. 2 is a horizontal sectional view through the injection molding unit in the region of carrier block and injection bridge; 
     FIG. 2 a  is a sectional view taken along the line  2   a — 2   a  of FIG. 2; 
     FIG. 3 is a sectional view according to FIG. 2 of an alternative embodiment; 
     FIG. 4 illustrates an enlarged portion taken from FIG. 3 in the region of the injection bridge; 
     FIG. 5 is a side elevational view of a mould closing unit, which is shown partially in section; 
     FIG. 6 illustrates an enlarged portion taken from FIG. 5 in the region of the movable mould carrier; 
     FIG. 7 is a side elevational view, shown partially in section, of a 5-point toggle lever of a mould closing unit; 
     FIG. 8 is an enlarged view of one of the two 5-point toggle levers according to FIG. 7; 
     FIG. 9 illustrates a mould closing unit having a Y-shaped toggle lever; 
     FIG.  10 . illustrates the enlarged Y-shaped toggle lever; 
     FIG. 11 is a horizontal sectional view through an injection molding unit in the region of the carrier block and injection bridge in an alternative embodiment; 
     FIG. 12 is a side elevational view, shown partially in section, of a mould closing unit of the pulling type; 
     FIGS. 13 and 14 are views according to FIG. 11 of injection molding units in two additional embodiments; and 
     FIG. 15 illustrates an injection molding unit provided with a closure nozzle. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The invention is now explained more fully, by way of example, with reference to the accompanying drawings. However, the embodiments are only examples which are not to restrict the inventive concept to one specific arrangement. 
     FIG. 1 illustrates initially the injection molding unit of an injection molding machine for processing plastics materials and other plasticisable compounds, such as, for example, ceramic or metallic pulverulent compounds. A plasticising cylinder P is accommodated in the injection molding unit on a carrier block  52 . The plasticisable compound is plasticised in the plasticising cylinder and injected into an injection mould M via a nozzle  21 . For such purpose, the nozzle  21  penetrates the stationary mould carrier  14 . The front portion of the injection molding unit S is supported on the machine base  51  via a supporting member  22  and guided and supported on the machine base via a guiding element  53 . In order to fit the nozzle  21  onto the injection mould M, and to remove such if necessary, nozzle driving units  50  are provided which are hydraulically configured in FIG.  2 . The cylinders of the hydraulic nozzle driving unit  50  form, with the carrier block  52  and a closure  54 , a rigid frame which is guided on guide bars  20 . The guiding element  53  is guided on the cylinders of the nozzle drive  50 . 
     In order to inject plasticised material into the injection mould, an injection unit E is provided. When the injection unit is actuated, the injection bridge  23  and, hence, the feed screw is axially moved. The injection bridge  23  carries the metering motor  28 , by means of which a feeding means 15 —a feed screw in the embodiment—can be rotated. While the metering motor  28  has to produce a rotary movement to rotate the feeding means 15 , translatory movements are required to drive the nozzle and for injection purposes. A linear motor is used as the electrical driving units for these translatory movements, and it includes a rotor having magnets disposed along a first cylindrical surface  11 . The linear motor also has a stator with stator windings  26  disposed along an additional cylindrical surface  12 . The cylindrical surfaces  11  and of the stator and rotor are concentrically disposed, so that the magnetic face, which is required to produce suitable advancing forces for movements in the injection molding machine, can be increased. So that the relatively high bearing forces are eliminated, not only are the circular surfaces provided; additionally the stator windings  26  and preferably also the magnets  25  of the stator are disposed symmetrically relative to the axis of movement a—a of the linear motor. FIG. 2 a  illustrates the circular surfaces and shows the application of corresponding forces on the basis of the force density which can be achieved at these faces. 
     In all of the embodiments, what is to be understood by the term surfaces is both the external surface of a cylinder and the internal surface of a pipe; in both cases, cylindrical surfaces  11  and  12  are involved. The magnets  25  may be permanent magnets, but they may also be separately excited coils having an iron core. Furthermore, the driving unit may be operated in a controlled or regulated manner, that is to say, for example, it can be operated as a servomotor over a regulating path. 
     In the case of the injection molding units illustrated in FIGS. 1 and 4, the linear motors of the injection unit are so disposed that the axis of movement a—a of the linear motor is, at the same time, the injection axis s—s of the injection molding unit S. When transferred to the mould closing unit shown in FIGS. 5-8 (see below), the axis of movement a—a of the linear motor is, at the same time, the axis of symmetry s—s of the mould closing unit F. For simplification purposes, the same identification s—s is used in both cases, and also, moreover, the reference numerals in the drawings are so selected that identically acting parts are provided with identical reference numerals. 
     To produce the necessary advancing forces, the cylindrical faces are disposed in a stacked manner. FIGS. 2 and 2 a  illustrate how a plurality of identically acting first surfaces  11  are stacked with a corresponding number of additional surfaces  12  for the injection movement. A cylinder  60  is supported on the closure  54 , which is moved jointly with the carrier block  52  via the nozzle driving unit  50  as a consequence of the connection, and it has identically acting surfaces on its inside and on its outside. It may be open to question whether these surfaces are initial surfaces of the rotor or additional surfaces of the stator. In the embodiment, the surfaces of the cylinder  60  are first surfaces of the rotor. These surfaces are formed by identically acting additional or first surfaces of two concentric cylinders  70  and  71 . When viewed externally, the impression is given that piston rod and cylinder of a piston-cylinder-unit would extend into one another. The surfaces are so disposed that the internal surface of the external cylinder  70  co-operates with the outside of the cylinder  60 , and the external surface of the internal cylinder  71  co-operates with the inside of the cylinder  60 . A greater advancing force than was usual hitherto can be produced by this stacking arrangement. 
     In order to protect the linear motor from contamination and, if necessary, to produce a chamber which can be provided with a suitable lubricant, an additional cylinder  17  moves jointly with the cylinder  60  and is, in this respect, just like the cylinder  60  connected to the closure  54 . This cylinder  17  overlaps the linear motor and has, at its front end on the left of FIG. 2, a mounting  18  which cooperates with a bearing face  19  of the cylinder  70 . The parts of the linear motors are guided towards one another via mounting  18  and bearing face  19 , and, in consequence, the parts of the injection molding machine are centered in order to ensure a precision which is required to produce high-quality parts. At the same time, the mounting  18  and bearing face  19  act in a sealing manner. 
     If the stator windings of the concentric cylinders  70  and  71  are energized, an advancing movement results in co-ordination with the magnet of the cylinder  60 . While the cylinder  60  remains in an unchanged manner, the concentric cylinders  70  and  71  are moved jointly with the injection bridge  23 . FIG. 3 illustrates an alternative embodiment of the injection molding unit S, where cylinder  60  and concentric cylinders  70  and  71  have been reversed. The cylinder  60 , with which the cylinders  70  and  71  co-operate, is mounted on the carrier block  52 , said cylinders now being a component part of the injection bridge  23 . The reversal necessitates a reversal of rotor and stator. If, in the first embodiment, the cylinder  60  was the rotor, then it is now the stator. The injection bridge  23  also slides here on the cylinders of the hydraulic nozzle driving unit, but a frame, which reinforces the injection molding unit S per se, is not provided as in the first case. The additional cylinder  17  supports the linear motor by means of mounting  18  and in co-operation with the bearing face  19 . 
     According to FIG. 3, the stator windings  26  can be divided into a plurality of separate electrical switching zones along their axis of movement a—a. The entire range of movement is shown by the range D. During displacement, all of the switching zones A, B and C are involved during the injection operation, above all towards the end, in order to permit the required forces to be applied with the participation of all of the switching zones. However, as soon as a specific zone is no longer in operative connection with the surfaces of the rotor by means of its face, the zones which are no longer required can be switched-off to save energy. 
     Cooling ducts  27 , which lie behind or adjacent the stator windings  26  when viewed from the magnets  25 , are associated with said stator windings in the cylindrical walls of the stator, so that the heating, caused by the current, can be reliably dissipated. The cooling medium employed may be used at the same time to control the temperature of other component parts in the injection molding machine. 
     The enlarged portion according to FIG. 4 shows that the magnets  25  are also attached to the walls of the cylinders  70  and  71 . The magnets are provided with the identifications for their north-south (N-S) poles. The stator windings  26 , however, are identified with U-V. The injection bridge, which is substantially formed by the concentric cylinders  70  and  71 , has sufficient space in its center, that is to say in the center of the cylinder  71 , to support the metering motor  28  as well as the locking arrangement for the feeding means 15 . 
     The linear motor, as an electrical driving unit, may also be employed for other assemblies of the injection molding machine. It is possible, more especially, to provide the translatory shafts with linear motors. On the injection molding side, such shafts are the driving unit for fitting the nozzle  21  onto the injection mould as well as the already explained injection means E or the actuating mechanism for a closure nozzle V (FIG.  15 ). On the side of the mould closing unit F, this is, for example, the closure mechanism for moving the movable mould carrier  13  towards and away from the stationary mould carrier  14 , which may apply the closing force if necessary. If the mould closing unit is constructed so that the closing mechanism only accomplishes the mould closing movement, while the closing force is applied by a separate arrangement, this separate arrangement may be provided with a linear motor. On the mould closing side, an ejector unit  16  or a core puller unit K (FIG. 5) on the injection mould M may also be provided with a linear motor. 
     FIG. 5 illustrates a mould closing unit F, wherein the movable mould carrier  13  is moved along guide bars  56  by means of the closing mechanism. During displacement, the injection mould M is alternately closed and opened. The closing mechanism is supported on a supporting element  57 . FIG. 6 illustrates an enlarged portion of FIG. 5 in the region of the movable mould carrier. A comparable construction, such as was previously the case with the injection molding unit, is also apparent here. A cylinder  60 , with an inside and an outside, is the rotor with the magnet  25 . The movable mould carrier, however, carries the concentric cylinders  70  and  71  as the stator. The cylinder  60  and the additional cylinder  17  are mounted on the supporting element  57 , said additional cylinder being mounted and guided on the bearing face  19  here also with the mounting  18 . In the embodiment, therefore, relatively large cylinders are also stacked inside one another here. Sufficient space is available in the interior of the cylinder  71  to accommodate an ejector unit  16 , which is also actuated as a linear motor. An extremely short structural design is therefore produced. 
     If desirable, however, a plurality of individual cylinders may also be stacked around the closing axis s—s and/or disposed concentrically, which cylinders are then operated identically in this respect. 
     The linear motor may also be used for other types of closing mechanisms, though the description of the stacking has been somewhat curtailed hereinafter to achieve a clear description. FIGS. 7 and 8 illustrate a closing mechanism with a multi-point toggle lever, here a 5-point toggle lever. The movable mould carrier is guided on guide bars  56 , and an ejector unit is to be actuated centrally in the movable mould carrier via a linear motor. FIG. 8 illustrates the structure of the 5-point toggle lever  80 . The toggle lever is supported on the supporting element  57  by the pivot joint  84 . It is supported on the movable mould carrier  13  by the pivot joint  86 . The pivot joints  84  and  86  are interconnected via two arms  87  and  88  which, in turn, for their part are pivotally interconnected at the pivot point  85 . A pivot point  83  for a pivotal arm  81  is provided on the arm  87 . Said pivotal arm communicates with the drive at the pivotal point  82 . If the drive is moved linearly along the closing axis, the arm  81  urges the arm  87  in an arc forwardly and then upwardly. The arms  87  and  88  thereby come into an extended position and are prevented from falling-back by automatic locking, supported by the arm  81 . The advantage of this embodiment is that, in the extended position, no force has to be applied to the arm  81  in order to maintain the extended position. This is advantageous since, during the linear movement, the covering of the cylindrical surfaces  11  and  12  also reduces, so that the force, produced by the linear motor, is smaller towards the end of the movement. FIG. 8 also shows that the linear motor for the ejector unit  16  can be guided back into the cylinder of the linear motor of the closing mechanism  0 . 
     An alternative type of closing mechanism is the Y-shaped toggle lever shown in FIGS. 9 and 10, which is otherwise constructed like the previously described mould closing units F. The Y-shaped toggle lever  90  supports the driving unit, in that it suspends said unit in a freely displaceable manner via two pivotal arms  91 . If the rotor  30  is moved, it acts on the pivotal point  93  and brings the arms  92  into the extended position. Here also, a relatively small force is to be applied in the extended position. The rotor  30  may be so configured that, during the application of a small force, it only slightly co-operates with the surfaces of the stator while, during the application of a high force, a total co-operation of the surfaces  11  and  12  is effected. 
     It is thereby indicated that, basically, the cylindrical surfaces can be so disposed that, when a high force has to be applied, a large covering of the surfaces  11  and  12  also exists, so that a high force is produced also as a consequence of a large abutment face. This is explained for an injection molding unit S with reference to FIG.  11 . The linear motor is employed as injection means E, wherein the covering of the cylindrical surfaces  11  and  12  is increasing when the nozzle is fitted onto the injection mould M. This is achieved when the cylinder  60  is supported on the carrier block. Here, the cylinder  60  is the stator. In order to move the injection bridge, the cylinders  70  and  71  are pulled over the cylinder  60  so that, during the injection process, a greater force is produced the further the feed screw is moved in the direction towards the injection mould. In consequence, the injection bridge  23  moves to the left in FIG.  11 . 
     The same principle can also be achieved with the mould closing unit. FIG. 12 illustrates a linear motor as the closing mechanism, the covering of the cylindrical surfaces  11  and  12  increasing during the application of the closing force. A mould closing unit is involved, wherein the movable mould carrier is pulled over the stationary mould carrier  14 . In the embodiment, the bars  56  are not securedly mounted on the stationary mould carrier. They are provided with the first surfaces in this region. If the stator is actuated on the stationary mould carrier, the rotor is pulled into the linear motor, so that a greater covering of the surfaces is produced with an increasing closing movement of the injection mould M, and maximum force is achieved at the end of the mould closing movement. FIG. 12 also shows that the linear motor has its axis of movement a—a coinciding with the central axis of the bar  56 . 
     With an otherwise identical structure as in FIG. 3, FIG. 13 shows that the nozzle driving unit, which was hydraulic in FIG. 3, may also be in the form of a linear motor. In this respect, the bars  20  are provided with magnets, so that they may serve as rotors of the nozzle driving unit N. They co-operate with a stator which slides along the bars  20 . Because of this structure, a corresponding movement along the bars  20  is possible. 
     In an alternative embodiment, FIG. 14 shows that the axis of movement a—a of the linear motor may also coincide with the central axis of the guide bars  20  in the injection molding unit. In this embodiment, a stacking of injection means and nozzle driving unit N around the bars  20  is created. The nozzle driving unit N lies around the bar  20 . The guide bar is the rotor, while a sleeve represents the stator  40 . This sleeve is the stator on the inside and, in turn, is already the rotor with magnets for the injection means E on the outside. In consequence, an additional sleeve is placed around the sleeve as stator  41 , which additional sleeve is, for its part, also the injection bridge  23 . Finally, the injection bridge carries the metering motor  28 . 
     It is self-evident that this description may be subjected to the most varied modifications, changes and adaptations, which range from equivalents to the dependent claims.