WO2005046955A2

WO2005046955A2 - Injection unit with nozzle application by pressure

Info

Publication number: WO2005046955A2
Application number: PCT/CH2004/000666
Authority: WO
Inventors: Bruno Stillhard; Ronald Siegrist
Original assignee: Procontrol Ag
Priority date: 2003-11-14
Filing date: 2004-11-04
Publication date: 2005-05-26
Also published as: DE112004002065D2; DE20319386U1; WO2005046955A3; CH697087A5; DE112004002065B4

Abstract

The invention relates to an injection unit for injection molding machines, which comprises an electric motor for the controlled application of nozzles and displacement of the unit. Two parallel hydraulic cylinder are activated by an electromotive hydrostatic transmission associated with the two cylinders for the controlled application of nozzles and displacement of the unit. An accumulator, especially a low-pressure accumulator, remains permanently connected for the low-pressure side during operation.

Description

Injection unit with nozzle pressure

Technical field

The invention relates to an injection unit with an electric motor for controlled nozzle pressure and unit displacement for injection molding machines.

State of the art

With regard to the function of the injection unit, a distinction must be made between the nozzle pressure and the unit displacement. Moving the unit requires a few millimeters in the event of a short lift or a relatively large distance for service work up to 40 cm displacement. Because the injection unit is supported on flawless bearings, the shift can be carried out quickly and with little force. With the function of the pressure two requirements have to be met:

- During the injection cycle, the injection nozzle must always be pressed close to the corresponding part of the mold.

- The contact pressure must be so great that with the strongly changing melt pressure of e.g. From 200 bar to over 2000 bar there is no gap opening through which melt can escape. A permanent seal must be guaranteed in every situation.

Many suggestions for the two functions of the injection unit have already been made, mostly with regard to special aspects. The movement of the unit and the nozzle pressure were not a particular mechanical engineering problem as long as both functions were purely hydraulic, which were fed by a central pressure oil supply and controlled via valves. The use of electric motor drives resulted in a completely new situation. An electric motor must be designed or selected differently, depending on whether, for example, small forces with a large displacement path or large forces with almost no displacement path are required. EP-PS 328 671 proposed a compression spring or a whole for an electrically driven injection molding machine Spring system between the drive and the sliding mechanism. To apply the actual nozzle contact pressure, an additional deflection of up to several millimeters is accepted, which has to be compensated for by appropriate control and regulation corrections via the drive motor. The spring package makes the whole system springy, which on the one hand brings advantages, but on the other hand results in an enormous complication in terms of control technology. In terms of process technology, the nozzle must be held close to the injection opening. The later EP-PS No. 422 224 tries to remedy this disadvantage by additionally force sensors or. Stretch marks can be used in the area of the injection unit. A certain nozzle contact force is specified and then by comparison or. a target-actual deviation of the measured force and the predetermined force of the drive motor is regulated. Although the mere control technology could be simplified here, the entire system remains complex, can be susceptible to faults and is particularly complex in terms of construction.

With DE 195 80 020, the applicant tried to achieve a shock-free application in electrically driven injection molding machines and set itself the task of looking for a new solution which avoids the disadvantages described above and nevertheless allows a real optimization of the entire process of nozzle application in electrically driven injection molding machines , The goal was in particular a structurally and tax technically simple solution.

As a procedural solution, DE 195 80 020 proposes that after spraying the spray nozzle is clamped to the mold and then the nozzle contact pressure is set spring-free depending on the spraying force or the pressure of the spray compound. According to the device, it is proposed that a) the spray nozzle can be clamped between the fixed mold half and the injection unit via tie rods or columns and b) the overdrive is designed to be spring-free by an electromotive drive for generating the nozzle contact force, with c) control means for the position of the nozzle contact force depending on the injection force or the injection pressure are provided.

The nozzle contact pressure is set as a function of the injection force or the pressure of the injection compound by means of appropriate control means. This creates a constant balance of contact pressure and the opening force from the pressure with a selectable preload. The power consumption of the drive motor could be greatly reduced compared to older solutions and with a more structural one Design, the regular effort can be significantly reduced. The solution was successfully put into practice, but with the disadvantage of a considerable amount of effort for the mechanical transmission part.

The new invention was based on the object of simplifying the overdrive part in the case of an electric motor drive and making it cheaper to manufacture.

Presentation of the invention

The solution according to the invention is characterized in that two hydraulic cylinders arranged in parallel can be activated by means of a hydrostatic transmission driven by an electric motor and assigned to the two cylinders, a rechargeable battery remaining switched on permanently for the low-pressure side of the hydraulic cylinder during operation.

The new invention takes advantage of the fact that the basic components for hydraulic systems e.g. Hydraulic cylinders and battery accumulators are manufactured in large numbers and can therefore be used very cheaply as market products. Compared to DE 195 80 020, the structural outlay can be greatly reduced in terms of cost. Another very great advantage is that the central strength of a hydraulic drive is used, namely the structurally arbitrary distancing of the supply of oil quantity and oil pressure from the consumer point. The hydrostatic transmission can e.g. be arranged below the injection unit, so that better access can be created for the central functions of the injection unit, for the low pressure side, i.e. for the function of the unit displacement, a battery is proposed which consumes very little energy due to the mere pendulum movement of the hydraulic medium on the low pressure side , The large forces for pressing are applied according to the invention by an electric motor.

The new solution allows two particularly advantageous solutions. According to a first solution, the hydrostatic transmission has a working cylinder and an AC servomotor for driving it. The working cylinder and the servo motor are advantageously arranged below the injection unit, so that the accessibility of the injection unit and the drive of the plasticizing screws get maximum accessibility, as was possible with purely hydraulically driven machines. The working cylinder preferably has at least one double active cross section on with respect to a single hydrozyinder. This creates approximately the same distance for the working cylinder and the two hydraulic cylinders. It is also proposed that the working cylinder piston rod can be driven by an AC servo motor via pinion and rack or a threaded spindle or a ball or roller spindle. The space available below the injection unit in many cases allows the piston rod of the working cylinder to be designed to be about twice as long as that of the hydraulic cylinder.

According to a second embodiment, it is proposed that the hydrostatic transmission have a fixed pump, the fixed pump preferably being able to be driven by a servo motor. In special cases, a displacement measuring system can be arranged in the area of the moving parts of the hydraulic cylinder for controlling / regulating the servo motor. In most cases, however, it is sufficient to use the path signal derived from the AC servo motor. The control of the contact pressure can be derived from the torque signal of the AC servo motor.

Brief description of the invention

The invention will now be explained with the aid of a few exemplary embodiments

Details explained. FIG. 1 shows an exemplary embodiment of the first solution with a hydrostatic transmission and an electric motor-driven working cylinder; Figure 2 is a plan view according to arrow II of Figure 1 and shows the parallel arrangement of two hydraulic cylinders; FIG. 3 shows an exemplary embodiment of the second solution with a fixed pump for the hydraulic cylinders driven by a servomotor; 4 shows an embodiment with a crank drive for the implementation of the rotary electric motor drives in a linear drive for the piston rod.

Ways and implementation of the invention

In the following, reference is made to FIGS. 1 and 2. The injection unit 1 is only shown in outline and essentially consists of a carrier block 2, a plasticizer 3 (FIG. 2) with the drive means 4 for the axial and rotary movement of a plasticizing screw 5, which is in an injection cylinder 6 is arranged. The axial and rotary drive is not the subject of the present invention. The injection unit 1 is shown on the right in FIGS. 1 and 2 and a mold part 7 with a correspondingly fixed mold carrier plate 8 on the left side of the figure. The injection unit 10 has a plasticizing screw 5 and a nozzle tip 9, which bears against the corresponding opening of the molded part 7. The injection unit 10 is firmly connected to the mold carrier plate via two symmetrically arranged hydraulic cylinders 1 1, 1 1 'via anchors 1 2 and 1 3 or 1 2' and 1 3 '. A piston rod 14 and a piston 15 are each arranged in the hydraulic cylinders 11, 11 '. Xv indicates the maximum travel distance that is possible by moving the hydraulic piston 15 into the other end position. This route is mainly required for service work as well as the installation and removal of the spray assembly and can be up to 40 cm and more between the mold carrier plate and the injection unit. In FIG. 1, the machine stand 16 is indicated, which carries the mold carrier plate 8. On the opposite side, the injection unit 1 is symbolically mounted on the machine stand 16 on rollers 17. The injection unit 1 can move cyclically by a few millimeters during normal spraying work, to limit the nozzle tip 9 accordingly, lift it cyclically from the molded part and put it back on. The anchors 1 2 and 13 are designed such that lateral deflection forces are compensated, for example by rod ends. Each of the hydraulic cylinders 11, 11 'has on the end side A a pressure medium connection 18 and a connecting line 19 which is connected directly to the corresponding end side A of a pressure generator 20 via a pressure medium connection 21.

The opposite end side B of the hydraulic cylinder also has a pressure medium connection 22, which is connected via a connecting line 23 to a pressure medium connection 24 on the end side B of the working piston 25. In the connecting line 23, a low pressure act 26 is constantly connected.

The pressure generator 20 essentially consists of a working cylinder 27 with a working piston 28 which is connected directly to an electromotive drive 30 via a piston rod 29. The electric motor drive 30 has an AC servo motor 31, which is only indicated by broken lines, and a reduction gear 32, which engage in a single or double rack 34 via two pinions 33. The toothed rack 34 is an extension of the piston rod 29. The AC servo motor 31 thus drives the working piston 28 directly via the overdrive means shown, and generates the pressure or quantity of the hydraulic medium required for the function of the nozzle pressure and the displacement of the unit. To drive away the injection unit 1, the AC servo motor 31 is activated in such a way that the rack 34 is shifted to the left in the direction of the arrow 40. The hydraulic oil 41 is pumped according to arrow 43 via the pressure medium connection 24 and the connecting line 23 into the rear pressure chamber 42. The result is that the entire injection unit moves to the right according to arrow 45 as long as the AC servo motor 31 remains activated. The movement can be between a few millimeters and 40 cm. Analogously, hydraulic medium 41 flows from the front pressure chamber 46 via the pressure medium connection 18, the connecting line 19 and the pressure medium connection 21 into the front pressure chamber 47 of the working cylinder 27. The injection unit is started up in the opposite direction. The pressing takes place only after the start-up movement has been completed. The piston rod 29 is pressed with maximum engine force in the direction of the arrow 50, so that with the corresponding maximum hydraulic pressure in the front pressure chamber 46 of the hydraulic cylinder 1 1, 1 1 'the required contact pressure is applied as long as necessary. The low pressure battery ensures a constant back pressure.

FIG. 3 shows an exemplary embodiment of the solution with a fixed pump 60 which is driven by an AC servo motor 31. A clutch 61 is located between the AC servo motor 31 and the fixed pump 60. The AC servo motor has power electronics 62 and an internal control unit 63, which is connected to a machine controller 64. The fixed pump 60 has an intake port 65 and an outlet port 66. Depending on the direction of rotation of the fixed pump 60, a start-up or an exit movement is triggered on the injection unit. Arrow 67 shows the movement for starting and pressing. If the oil pump direction of the fix pump is reversed, a drive-away movement is triggered. By means of the corresponding direction of rotation of the AC servo motor 32 and the application of the appropriate torque or oil delivery pressure, the function for moving the injection unit and the nozzle pressure are carried out analogously to the solution according to FIGS. 1 and 2 on the basis of the control commands entered. For an exact positioning, the solution according to FIG. 3 additionally has a displacement measuring system 70 which detects the movement of an extension 71 of the piston rod of the hydraulic cylinder and feeds it to the control unit 63 as a displacement signal.

With the new solution, the torque is adapted to the power required for pressing. This is done by a control system via which the contact pressure of the nozzle is dependent on, for example, the pressure in the injection cylinder is specified. The battery has the great advantage that it can be used to create a closed system. Errors from different cylinders or from thermal expansion, for example, can be reduced to a minimum with the basic pressure in the system. The pump is also sucked in under pressure. The battery has no energy storage function. The battery has a mere tank function. Errors in the hydraulic system (e.g. the pump, leaks because seals only work properly under pressure) can be avoided. The retraction of the unit is supported.

FIG. 4 shows another interesting embodiment with a crank drive 70 for converting the rotary electromotive drives into a linear drive for the piston rod 29. With this solution too, the hydrostatic drive can be arranged, for example, in the lower region of the machine stand 16. In the example 4 shown, the linear movement of the injection screw is also activated via a crank mechanism 71 and an electric motor 72. The rotary movement of the injection screw takes place via an electric motor 73 and a gear 74.

Claims

claims

1.Injection unit with an electric motor for controlled nozzle pressure and unit displacement for injection molding machines, characterized in that two hydraulic cylinders arranged in parallel can be activated by means of an electromotive driven hydrostatic transmission for the controlled nozzle pressure and unit displacement associated with the two cylinders, with a battery for the low pressure side in working mode in particular, a low-pressure battery remains permanently switched on.

2. Injection unit according to claim 1, characterized in that the hydrostatic transmission has a working cylinder and an AC servo motor for driving it.

3. Injection unit according to claim 2, characterized in that the working cylinder has a piston with an approximately double cross-section in relation to a hydraulic cylinder.

4. Injection unit according to claim 2 or 3, characterized in that the working cylinder piston rod can be driven via pinion and single or double toothed rack or a threaded spindle or a ball or roller spindle or a crank mechanism.

5. Injection unit according to claim 1, characterized in that the hydrostatic transmission has a fixed pump.

6. Injection unit according to claim 5, characterized in that the fixed pump can be driven by a servo motor.

7. Injection unit according to claim 5 or 6, characterized in that a displacement measuring system is arranged in the area of the moving parts of the hydraulic cylinder, displacement control / regulation of the servo motor.

8. Injection unit according to claim 7, characterized in that the displacement measuring system has an extension of the piston rod of a hydraulic cylinder.

9. Injection unit according to one of claims 1 to 8, characterized in that the two hydraulic cylinders with the plasticizing screw are in a common plane and the hydrostatic transmission is arranged below the injection unit, in particular in the area of the machine frame.

10. Injection unit according to one of claims 1 to 9, characterized in that the control / regulation of the nozzle pressure and the unit displacement takes place entirely via sensor signals from the AC servo motor.