METHOD FOR OPERATING AN INJECTION MOULDING MACHINE

Abstract

A method is described for operating an injection moulding machine, which has one or more movable machine parts which can be moved by suitable drives along specifiable travelling distances. Movement of a movable machine part is repeated cyclically. In order to reduce the movement times of the movable machine parts to a minimum, provision is made for one or more of the movable machine parts to successively reduce the power reserves of one or more of the drives associated with a movable machine part, until a specifiable minimum of power reserve is reached, wherein the minimum can be zero. In each cycle, the power reserve of the drive or drives is determined and is successively reduced, in particular from cycle to cycle. A movable platen, an ejector, a core puller, a plasticizing screw and/or an injection piston can be provided as movable machine part.

Claims

1.-20. (canceled)

21. A method for operating an injection moulding machine including one or more movable machine parts, comprising: determining and successively reducing a power reserve of a drive operably connected to a movable platen until reaching a specified minimum of the power reserve for the drive as the movable platen, which has fastened thereto a moulding part of an injection moulding tool and is moved cyclically and repeatedly along a specified traveling distance toward and away from a fixed platen between a closing position and an opening position of the injection molding tool, has reached an end position or an opening position; defining the specified traveling distance on the basis of a course of a desired speed of the movable platen; successively altering the desired speed according to the available power reserves by successively reducing a travel time for covering the specified traveling distance so as to reduce a movement time of the movable platen, sufficient for each case of application of a clamping unit of the injection moulding machine; and defining each case of application by a particular weight of the injection moulding tool or of the moulding part of the injection moulding tool and by a particular travelling distance for the moulding part.

22. The method of claim 21, wherein the specified minimum is close to zero.

23. The method of claim 21, wherein the specified minimum is less than 10% of a maximum available power.

24. The method of claim 21, wherein the specified minimum is less than 5% of the maximum available power.

25. The method of claim 21, wherein the specified minimum is equal to zero.

26. The method of claim 21, wherein the power reserve of the drive is determined and successively reduced in each cycle.

27. The method of claim 21, wherein the power reserve of the drive is determined and successively reduced from cycle to cycle.

28. The method of claim 21, further comprising continuously measuring a physical parameter as a measuring value during movement of the movable platen along the specified traveling distance for determining the power of the drive.

29. The method of claim 28, wherein plural physical parameters are continuously measured in short time intervals for achieving a plurality of measurement values.

30. The method of claim 28, further comprising: evaluating the measuring value at the end of the traveling distance; and calculating the power reserve for the movement along the traveling distance; and executing the movement in a later cycle by reducing the power or providing a greater power for moving the movable platen.

31. The method of claim 30, wherein the later cycle is a next cycle.

32. The method of claim 21, wherein the power reserve is reduced until a maximum available power of the drive is chosen for moving the machine part.

33. The method of claim 21, further comprising measuring a current intensity and a rotation speed of the drive.

34. The method of claim 21, further comprising: measuring a pressure in a cylinder chamber of the drive; and measuring a travelling speed of a piston or of a piston rod in relation to the cylinder chamber.

35. The method of claim 21, further comprising altering the desired speed from a cycle to cycle.

36. The method of claim 21, further comprising: processing the desired speed to a position setpoint; and executing a position regulation of the movable platen in response to the position setpoint.

37. The method of claim 21, wherein the power reserve of the drive connected to the movable platen is determined, when the movable platen has reached a particular state.

38. The method of claim 21, further comprising: operably connecting a plurality of drives to the movable platen; determining the power reserve of each of the drives independently of one another; and successively reducing the power reserves of the drives.

39. The method of claim 38, further comprising defining for each of the drives a same minimum power reserve.

40. The method of claim 38, further comprising defining individually for each of the drives a distinct individual minimum of the power reserve.

41. The method of claim 21, further comprising: operably connecting a plurality of drives to the movable platen; determining the power reserve of each of the drives independently of one another; forming a total the individual power reserves of the drives; and successively reducing the total of the power reserves of the drives. until a specifiable minimum has been reached in relation to the total of the power reserves.

Description

[0021] The invention is to be described in further detail below with the aid of example embodiments and with reference to FIGS. 1 to 4. There are shown:

[0022] FIG. 1: a diagrammatic illustration of an electric injection moulding machine with an electric drive

[0023] FIG. 2: a diagrammatic illustration of a hydraulic injection moulding machine with a hydraulic drive

[0024] FIG. 3: a flow chart for the method according to the invention

[0025] FIG. 4a, 4b: different movement profiles for different power reserves with illustration of the respective desired speed value course in FIG. 4a and illustration of the respective position setpoint course in FIG. 4b.

[0026] FIG. 1 shows an embodiment of an electric injection moulding machine with a toggle lever clamping unit. A fixed platen 8E, a movable platen 6E and a support plate 9E are arranged on a machine bed. The support plate 9E is also mounted displaceably on the machine bed for purposes of mould height adjustment. An injection moulding tool 7E comprises mould halves 7Ea and 7Eb, wherein one mould half, namely the movable mould half 7Ea, is fastened on the movable platen SE and the other, fixed mould half 7Eb is fastened on the fixed platen. A toggle lever system 5E is provided between the support plate 9E and the movable platen 6E. An electric motor 4E serves for actuating the toggle lever system. Electromotively driven toggle lever systems are known in various configurations to the specialist in the art, so that no further explanations are necessary here. In particular, the structural details of a toggle lever system and the way in which the electric motor 4E is connected with the toggle lever system with regard to drive are known to the specialist in the art, in order to move it from a folded position, which corresponds to an open position of the clamping unit, into an extended position, which corresponds to a closed position of the clamping unit, and vice versa. A rotary encoder 3E and a current measurement device 10E are provided on the electric motor 4E. The prevailing rotation speed n can be determined via the rotary encoder 3E, the current measurement device 10E measures the prevailing current intensity I. The rotation speed n and the current intensity I are fed to a machine control 1E and are evaluated there, which is described in further detail below in connection with FIG. 3. The electric motor 4E is supplied with control signals from the machine control 1E via a line 2E.

[0027] The hydraulic injection moulding machine shown in FIG. 2 is likewise equipped with a three-plate clamping unit. It comprises a fixed platen 11H with a mould half 10Hb, a movable platen 9H with a movable mould half 10Ha, a support plate 14H and a toggle lever system 8H between support plate and movable platen. The actuation of the toggle lever system 8H takes place by means of a hydraulic cylinder 7H, which is connected by means of suitable hydraulic lines, not illustrated here, with a hydraulic drive 13H, which has a pressure sensor 12H. The supplying of the hydraulic cylinder with a pressure medium, in particular with hydraulic oil, takes place via a proportional valve 5H, which can be actuated by the machine control 1H via a control line 2H. Furthermore, pressure sensors 3H and 4H are provided for the chambers of the hydraulic cylinder lying on both sides of the piston. In addition, a position measurement system 6H is associated with the hydraulic cylinder 7H, in order to be able to measure the travelling distance of the piston and/or of the piston rod and therefore ultimately the travelling distance of the movable platen. Also in the case of hydraulic injection moulding machines, the structural details of a toggle lever system and the way in which the cylinder 7H is connected with the toggle lever system with regard to drive are known to the specialist in the art, so that a more detailed description in this respect is not necessary at this point.

[0028] The method according to the invention is now to be explained in further detail with the aid of FIGS. 3, 4a and 4b. At the start of the loop (reference number or respectively step 0) a particular course of a desired speed value for a particular travelling distance on closing or respectively for a particular stroke of the movable platen is specified, for example the curve v.sub.1 in FIG. 4a. In the example, the stroke or respectively the travelling distance of the movable platen is to be 150 mm. The speed v.sub.1 firstly increases, then it is throttled when the contact of the mould halves of the injection moulding tool is to be expected; thereafter, the locking of the clamping unit takes place with a short acceleration phase, until the speed v.sub.1 at the end of the travelling distance drops down to zero. With the speed course v.sub.1 a position setpoint course results according to the curve S.sub.1 in FIG. 4b. The speed course v.sub.1 and the position course s.sub.1 form together a specified travel profile for the start of the loop 0.

[0029] In the next step (1) a check is undertaken as to whether the clamping unit is to be operated with a different travel profile, for example because a different injection moulding tool with a different travelling distance or respectively with a different stroke is being used. If this is not the case, the clamping movement is started (2), i.e. the movable platen is closed according to the curve v.sub.1. At 1 ms intervals, the measurement (step 3) takes place of the parameters which are required for the calculation of the power reserves. In the case of an electric drive (FIG. 1, reference number 4E), the current intensity I (=measurement for the torque) and the rotation speed n are therefore measured at 1 ms intervals.

[0030] In step 4 a check is carried out as to whether the movement is completed, i.e. whether the clamping unit is closed. As long as the movable platen, and therefore the movable mould half of the injection moulding tool, are being moved, this is of course not yet the case, and the steps 3 and 4 are repeated. Owing to the short scanning time of 1 ms, the steps 3 and 4 are generally repeated several hundred to several thousand times, depending on how many seconds the movable platen requires in order to cover the desired stroke (here 150 mm).

[0031] When the movement is completed and the end of the travelling distance is reached (i.e. the moulding tool has covered the desired stroke), in the next step (5) the calculation of the power reserves takes place. For this, firstly the power maximum P.sub.max-current achieved with this movement sequence is determined and compared with the maximum possible or respectively available power P.sub.max-available of the drive. The difference produces the current power reserve P.sub.res. In the case of an electric drive, therefore, the course of the product I (current intensity)n (rotation speed) x torque constant is calculated, and the maximum of this product is determined. By determining the difference with the maximum available or respectively retrievable power of the drive (P.sub.max-availableP.sub.max-current), the remaining power reserve P.sub.res for this clamping travel of the movable platen is obtained. When such a power reserve has been determined, i.e. when reserves P.sub.res are present (step 6), a new travel profile can be determined, i.e. in step 7 a new setpoint calculation takes place for a speed course, taking into consideration the power reserves, and from there a return is made to the start of loop (step 0). The entire calculated power reserves can be taken as basis all at once, or only a portion of the power reserves, for the new setpoint calculation. Preferably, only a portion of the power reserves is used for the new setpoint calculation, so that in the next cycle again a power reserve, which is this time somewhat smaller, is determined. From this power reserve, which is then still available, a portion can again be used for the new setpoint calculation, so that in the next cycle possibly again a power reservethis time even smalleris determined. Therefore, the power reserve can be determined from cycle and cycle and reduced until a specifiable minimum is reached. Preferably, the minimum lies close to or at zero, i.e. in the optimum state practically no more power reserves are available. This means that the maximum available power of the drive is utilized and consequently also the movement time of the movable platen has become minimal.

[0032] Observing the curves v.sub.1 to v.sub.3 or respectively s.sub.1 to s.sub.3 in the travel profiles (see FIGS. 4a, 4b), the first movement of the movable platen in step 5 would produce a power reserve of 30%. At step 7, one could then specify a new desired speed value course according to the curve v.sub.2 and return to the start of the loop (step 0). On renewed reaching of step 5, the calculation would produce a new power reserve P.sub.res of only 20%. The end position 150 mm (i.e. the closed state of the moulding tool) is in this case reached at an earlier point in time (s.sub.2). In step 7 one could now specify a new desired speed value course according to the curve v.sub.3 and return to the start of the loop etc. Depending on the extent to which the power reserves P.sub.res are reduced from cycle to cycle, it is detected earlier or later in step 6 that no more power reserves are available. For the current case of application, the quickest possible movement of the movable platen has been reached. In FIG. 4b it can be seen how through the reduction of the power reserves the reaching of the stroke distance takes place earlier by approximately one tenth of a second (the end shifts in FIG. 4b from right (s.sub.1) to left (s.sub.3). As a result, therefore, the movement time is reduced to a minimum for a particular case of application.

[0033] If a new injection moulding tool is installed at a later time, or another travel profile is specified, the calculation is reset (step 9) and a new optimization algorithm is started.

[0034] The invention can be used both for electric and also for hydraulic drives.

[0035] In the case of an electric drive, the rotation speed and the torque (or respectively the current intensity) are measured as described above, from the product the power is determined and the maximum of the power is determined in a cycle. In the case of a hydraulic drive, the pressure in one of the cylinder chambers, preferably the pressure in both cylinder chambers, the reservoir pressure and the speed of travel of the piston are measured.

[0036] An essential advantage of the invention lies in a shortening of the cycle time and therefore an increase in the machine output. The potential is great especially in small stroke applications, because in these applications, viewed in terms of percentage, a considerable proportion of the cycle time is used for the closing and opening of the tool. In these applications, today the greatest power reserves are present at the drive.

[0037] The invention is not restricted to the moving of the movable platen. In an analogous manner, the moving of an ejector, of a core puller, of a plasticizing screw and/or of an injection piston could also be optimized. Basically, the invention is able to be applied to all movable machine parts which are moved forward and back cyclically along travel distances. Therefore, a handling or robot axis could also be optimized accordingly.

[0038] When the power reserve is determined, as here, is determined with the aid of a measurement parameter, e.g. the motor current or the piston force, in addition temperature-dependent phenomena, such as for example the friction or the oil compressibility, could also be taken into consideration.

[0039] The method according to the invention is not restricted to the operation of injection moulding machines having a toggle lever clamping unit, but rather can be used in all types of clamping units.

LIST OF REFERENCE NUMBERS

Electric Injection Moulding MachineFIG. 1

[0040] 1E machine control with inverter [0041] 2E actuation electric motor [0042] 3E rotary encoder [0043] 4E electric motor [0044] SE toggle lever system [0045] 6E movable platen [0046] 7E injection moulding tool [0047] 7Ea movable mould half [0048] 7Eb fixed mould half [0049] 8E fixed platen [0050] 9E support plate [0051] 10E current measurement device

Hydraulic Injection Moulding MachineFIG. 2

[0052] 1H machine control [0053] 2H actuation proportional valve [0054] 3H pressure sensor chamber A [0055] 4H pressure sensor chamber B [0056] 5H proportional valve [0057] 6H position measurement system hydraulic cylinder [0058] 7H hydraulic cylinder [0059] 8H toggle lever system [0060] 9H movable platen [0061] 10H injection moulding tool [0062] 10Ha movable mould half [0063] 10Hb fixed mould half [0064] 11H nozzle-side platen [0065] 12H pressure sensor hydraulic reservoir [0066] 13H hydraulic drive/hydraulic reservoir [0067] 14H support plate