GB2074928A - Device for translating motion in one direction into proportional motion in the same direction - Google Patents

Abstract

A hydraulic device is provided for translating a motion vector into a proportional motion vector the device comprising at least two parallel hydraulic cylinders the adjacent ends of which are interconnected, the cylinders having oppositely acting pistons therein, piston rods extending out of the cylinders. If the end of one piston rod is fixed, opposite action of the pistons will move the cylinders at half the speed of the end of the other piston rod if the bores of the cylinder are uniform. The device is useful for a three-mold block injection molding apparatus, one piston rod being attached to a fixed mold portion, the cylinders to a central movable mold portion and the other piston rod to another movable mold portion. When the movable mold portion is moved the central mold portion is moved in the same direction as the movable mold portion but at half its speed and by half the amount.

Description

SPECIFICATION Device for translating motion in one direction into proportional motion in the same direction This invention relates to a device for translating a motion vector into a proportionately related motion vector and to the use of such a device as a mold centering device in injection molding machines.

Injection molding machines may be of the type comprising three mold portions, i.e. a first fixed mold portion, a second movable mold portion and a third central mold portion between the first and second mold portions. At least one cavity mold is defined between the first and central mold portions and at least one other cavity mold is defined between the second and central mold portions. The second mold portion is usually operated by a ram to move it in a linear manner towards and away from the fixed first mold portion. The central mold portion moves with the second mold portion but at half the speed so that the mold portions are relatively displaceable between two positions. One of these positions is a mold closed postion in which all the mold portions are sandwiched together to close the cavity between both the first and central portions and second and central portions.The other of these positions is a mold open position in which there is a gap between the first and central mold portions and a similar gap between the second and central mold portions, i.e. the second mold portion is twice as far from the first mold portion as is the central portion. Normally stripper plates are provided to abut each of the first and second mold portions. These stripper plates can be moved a short distance away from the mold portions in the mold open position to strip molded articles from the cavities.

It will be appreciated that to achieve accurate molding technique a very high degree of accuracy is called for in centering the mold portions, both in alignment and coincidence of the mold closed position of both cavities.

Various techniques have been adopted in the past in attempts to achieve the high degree of accuracy in centering the mold portions. One such technique comprises the use of a pinioned wheel on the central mold portion and two rack members running in opposite directions on said wheel one of the rack members being secured to the fixed first mold portion and one to the movable second mold portion. Such a racking mechanism does achieve both the necessary half speed method of the central mold portion with respect to the second mold portion and the alignment of mold portions. However, the arrangement suffers from the disadvantages firstly, that it is subject to wear and the movement becomes imprecise as wear on the pinions and racks increases, the secondly, should the mold portions jam the rack members are inflexible and will break easily.

Other more sophisticated arrangements have been produced as, for example, that disclosed in Canadian Patent No. 970917 to Husky Manufacturing and Tool Works Ltd.

It is an object of the invention to provide an arrangement for accurate centering of the mold portions into an injection molding machine. A further object of the invention is to provide a device for translating a motion vector into a proportionately related motion vector.

According to the invention is provided a device for translating a motion vector into a proportionally related motion vector comprising: A unit comprising at least two parallel hydraulic cylinders including end walls; A piston having a piston rod in each of said cylinders, said pistons operable in parallel opposite directions and dividing each said cylinder into first and second chambers, each piston rod extending through one of said end walls; hydraulic sealing means in said end walls about said piston rods; passage means communicating said first chamber of each of said cylinders with said second chamber of the other said cylinder; Whereby when one member of the group consisting of said piston rods or said unit is displaced relative to another member of said group then the pistons operate oppositely within said cylinders by displacement of hydraulic fluid through said passage means between each of said first and second chambers to proportionately translate the displacement to the third member of the group.

Also according to the invention is provided, in an injection molding machine, the combination a first stationary mold portion, a second movable mold portion and a third central movable mold portion, at least a first mold cavity being defined between the first mold portion and the central mold portion and at least a second mold cavity being defined between the second mold portion and the central mold portion, said mold portions being relatively displaceable between a mold closed position in which both first and second mold cavities are closed and a mold open position in which both first and second mold cavities are open; means for imparting linear motion to said second mold portion; first unloading means for said first mold portion and second unloading means for said second mold portion said first and second unloading means being movable with respect to their respective mold portions to dislodge an article mold therein; and a device for translating a motion vector into a proportionally related motion vector comprising a unit secured to said central mold portion and comprising at least two hydraulic cylinders of uniform bore and including end walls, said cylinders being parallel to each other and to the direction of movement of said second mold portion; a piston having a piston rod in each of said cylinders, said pistons operable in parallel opposite directions and dividing each cylinder into first and second chambers; said piston rods extending through said end walls and secured one to said first mold portion and the other to the second mold portion; hydraulic sealing means in said end walls about said piston rods; passage means communicating said first chamber of each of said cylinders with said second chamber of the other cylinder, whereby when said second mold portion is displaced then the pistons operate oppositely within said cylinders by displacement of hydraulic fluid through said passage means between said first and second chambers to move said central mold portion at half the speed and in the same direction as the second mold portion.

The term "mold portion" is defined herein as either a mold block itself or a part of the machine carrying a mold block.

The device used in the present invention has all the advantages of the rack and pinion device of the prior art especially that motion imparted to the second mold portion in a straight line direction from a ram is transmitted to the device which acts directly in the same direction. There is no need for articulated linkages providing stresses in other directions on connections to the mold portions.

Moreover fine adjustment of the exact location of the mold portions with respect to the piston rods is very easy. The device also has advantages over all previous systems in that it provides immediate response to movement of the second mold portion without mechanical backlash and is very smooth in operation, some cushioning effect being obtained due to the hydraulic fluid. A safety valve may be provided for the hydraulic cylinders so that if a mold should jam or there be some mechanical breakdown of the molding operation, the device will release the safety valve before breaking or otherwise failing. Maintenance of the device is simple in that it can be easily removed from and be secured to the molding machine. The device does not suffer from the disadvantages of excessive wear or heat production.

Fig. 1 is a perspective view of a motion translation device according to the invention having one side broken away to show the interior of the device; Fig. 2 is a side-elevational view of a portion of an injection molding machine embodying a motion translation device depicted in Fig. 1, the machine being in the mold closed position; Fig. 3 is another side elevational view of the machine of Fig. 2 in the mold open position; Fig. 4 is a view of an enlargement of pait of the machine of Fig. 2 in the mold closed position the motion translation device being shown in section to show the interior of the cylinder unit; Fig. 5 is another view of the enlargement of Fig. 4 in the molds being between the closed and fully open position;; Fig. 6 is a view of a detail of Figs. 2-5 in the stripper plate closed position showing one means of operating a stripper plate according to the invention; and Fig. 7 is a view similar to that of Fig. 6 in the stripper plate open position.

An injection molding machine according to the invention comprises a fixed first platen 1, a movable second platen 2 and a movable third central platen 3 comprising platen halves 31 and 33. The second platen 2 is under the control of a reciprocating ram 4. The second platen 2 and third platen 3 slide on tie bars 5 through their upper parts, the tie bars 5 extending from the machine frame (not shown) and the fixed platen 1. The second platen 2 slides on tie bars 6 through its lower part. The tie bar 6 extends between the machine frame and fixed platen 1. The platens 1 2 and 3 may be rectangular e.g. square, with the tie bars 5, 6 disposed near their corners. Fixed platen 1 is rigid with the injection apparatus for injecting plastic, an injection nozzle 7 being shown schematically.From fixed platen 1 injected plastic is conveyed by conventional means (not illustrated) to the central third platen parts 31,32 from which it is distributed conventionally. A stationary first mold portion is mounted on fixed platen 1. A second mold portion 12 is mounted on movable second platen 2 to move with it. Another mold portion comprising two mold halves 33, 34 mounted respectively on platen parts 31,32. The mold portion 1 and mold half 33 define at least one mold cavity between them and similarly mold portion 12 and mold half 34 define at least one mold cavity between them. A set of, say, four guide pins 8 on each mold portion 11, 12 support stripper plates 1 3, 14 respectively which stripper plates 13, 14 are each axially slidable within limits with reference to the respective mold portions 11,12.

The mold portions 11, 12 and mold halves 33, 34 are aligned and guided by means of hydraulic device 50 so illustrated along in Fig. 1. The hydraulic device also controls and defines the proportional displacements between the platens 1,2 carrying mold portions 11, 12 and the central platen 3 carrying mold halves 33, 34. Hydraulic device 50 comprises two parallel hydraulic cylinders 51 and 52 of uniform bore in a single cylinder block having end walls 53, 54, 55 and 56.

The end walls 53 and 55 are formed from a single metal plate 57 closing two adjacent ends of cylinders 51 and 52. Similarly, end walls 54 and 56 are formed by a single metal plate 58 closing the other two adjacent ends of cylinders 51 and 52. Pistons 61,62 are slidable within the cylinders 51, 52 respectively and each piston 61, 62 is provided with a hydraulic o-seal 63, 64 respectively. Thus piston 61 divides the space within cylinder 51 into a first chamber 65 and a second chamber 66 which vary in size according to the position of piston 61. Similarly piston 62 divides cylinder 52 into a first chamber 67 and a second chamber 68 which vary according to the position of piston 62. The first chamber 65 of cylinder 51 communicates with second chamber 68 of cylinder 52 by a passage 71 which is formed partly in that part of the cylinder block between the cylinders 51,52 and partly in the end walls.

Similarly passage 72 is provided communicating between first chamber 67 of cylinder 52 and second chamber 66 of cylinder 51. The passages 71, 72 are provided for the flow of hydraulic fluid between the cylinder chambers so that where either piston 61,62 is displaced within its respective cylinder hydraulic fluid flows from the chamber which is being decreased in size into the communicating chamber of the other cylinder moving the piston therein in an equal and opposite direction. If the bores of the cylinders are not uniform the movement of the pistons will be opposite but not equal. The pistons 61, 62 are provided with piston rods 73, 74 extending out from the end walls 53 and 56 respectively. Seals 75 and 76 are provided around the rods against leakage of hydraulic fluid from the cylinders 51,52.

One example of using the hydraulic device 50 to translate one motion vector into another proportional motion vector will now be described.

The piston rod 74 may be secured, for example, at a threaded bolt portion 77 to the stationary first mold portion 11 of the above described injection molding machine. The threaded bolt 30 portion 77 suitably engages with a nut portion 87 mounted on the first mold portion 11. A locking nut 97 is provided to lock the position of bolt portion 77 and nut portion 88.

The cylinder block of device 50 is secured to the third platen 3 by bolts 91, 92 so that the cylinders 51. 52 and piston rods 73, 74 are parallel with the tie bars 5 and 6. By means of adjustment at bolt portion 77 and nut portion 87 the piston 62 can be positioned in cylinder 52 so that second chamber 68 is at its smallest size when first mold portion 11 and mold half 33 are in the mold closed position.

The piston rod 73 is secured at a threaded bolt portion 78 to the movable second mold portion 12 at nut portion 88 using locking nut 98 in a similar manner to that in which threaded bolt portion 77 is secured to first mold portion 11. Adjustment of the position of the piston 61 in cylinder 51 is similar to that for piston 62 in cylinder 52. It should be noted that it is not necessary to calculate the precise adjustment for each piston and cylinder combination independently. Once one piston has been accurately positioned, the position of the other piston is fixed in relation thereto by securing one nut position on its bolt portion. It is then only necessary to secure the other nut portion at a similar point or the other bolt position.

Thereafter, when the movable second mold portion 12 moves actuated by ram 4 from open position or partly open position (Fig.3) to the closed position (Fig. 4), the piston 61 moves to the right forcing hydraulic fluid from second chamber 66 of cylinder 51 into first chamber 67 of cylinder 52 thereby relatively displacing piston 62 to the left. Since piston 62 is secured to stationary first mold position 1, it does not actually move and the relative displacement is achieved by movement of platen 3 to the right. It can be seen that due to the opposed relative displacements of pistons 61 and 62 any movement of mold portion 12 in either direction results in a movement in the same direction but at half the speed and in half the amount of platen 3. If the bores of cylinders 51 and 52 are not uniform this proportion will be different.

The device 50 may be located at any location where it does not impede operation of the injection molding machine. Preferably, two devices 50 are located on opposite sides of the molding machine.

A further feature of the invention concerns the action of the stripper plates 1 3, 14. The pistons 61 and 62 of the hydraulic device 50 are provided with further piston rods 83 and 84 extending from end walls 54 and 55 respectively. Seals 93 and 94 are provided to prevent leakage of hydraulic fluid around piston rods 83 and 84 at the end walls 54 and 55. The protruding ends of piston rods 83 and 84 can be left free or they may be provided with means to operate stripper plates 13 and 14 respectively. When such means to operate the stripper plates is provided it is suitably as illustrated in Fig. 6 and Fig. 7. The piston rod 83 is slidably mounted on stripper plate 13 at a bearing 101. A stop 102 is also provided on piston rod 83.

As piston 61 comes towards the end of its leftward travel in opening the mold portions stop 102 acts against bearing 101 whereby piston rod 83 is no longer permitted to slide in bearing 101 and acts to move stripper plate 13 to move it away from stationary first mold portion 11.

The stripper plate may be returned to abut the mold portion 13 by any suitable conventional means (not illustrated), for example, by springs or pneumatically.

The mounting and operation of piston rod 84 with respect to stripper plate 14 and moveable second mold portion 12 is exactly similar to that described for piston rod 83.

Claims (14)

1. A device for translating a motion vector into a proportionally related motion vector comprising: a unit comprising at least two parallel hydraulic cylinders including end walls; a piston having a piston rod in each of said cylinders, said pistons operable in parallel opposite directions and dividing each said cylinder into first and second chambers; each piston rod extending through one of said end walls; hydraulic sealing means in said end walls about said piston rods; passage means communicating said first chamber of each of said cylinders with said second chamber of the other said cylinder, whereby when one member of the group consisting of said piston rods or said unit is displaced relative to another member of said group the pistons operate oppositely within said cylinders by displacement of hydraulic fluid through said passage means between each of said first and second chambers to proportionately translate the displacement to the third member of the group.

2. A device as claimed in claim 1 in which the unit comprises two cylinders having uniform bores.

3. A device as claimed in claim 1 or 2 in which the unit is provided with means to release hydraulic fluid if the pressure rises above a prechosen valve.

4. A device as claimed in claim 1, claim 2 or claim 3 in which said unit comprises cylinders bored in a single cylinder block.

5. A device as claimed in claim 1, claim 2 or claim 3 in which the piston rods extend from opposing end walls of said cylinders.

6. A device as claimed in claim 1, claim 2, or claim 3 in which further piston rods extend through the others of the end walls, these being hydraulic sealing means in said other end walls about said further piston rods.

7. In an injection molding machine, the combination of a first stationary mold portion, a second movable mold portion and a third central movable mold portion, at least a first mold cavity being defined between the first mold portion and the central mold portion and at least a second mold cavity being defined between the second mold portion and the central mold portion, said mold portions being relatively displaceable between a mold closed position in which both first and second mold cavities are closed and a mold open position in which both first and second mold cavities are open; means for imparting linear motion to said second mold portion; first unloading means for said first mold portion and second unloading means for said second mold portion said first and second unloading means being movable with respect to their respective mold portions to dislodge an article molded therein; and a device for translating a motion vector into a proportionally related motion vector comprising a unit secured to said central molded portion and comprising at least two hydraulic cylinders of uniform bore and including end walls, said cylinders being parallel to each other and to the direction of movement of said second mold portion; a piston having a piston rod in each of said cylinders, said pistons operable in parallel opposite directions and dividing each cylinder into first and second chambers; said piston rods extending through said end walls and secured one to said first mold portion and the other to the second mold portion; hydraulic sealing means in said end walls about said piston rods; passage means communicating said first chambers of each of said cylinders with said second chamber of the other cylinder, whereby when said second mold portion is displaced then the pistons operate oppositely within said cylinders by displacement of hydraulic fluid through said passage means between said first and second chambers to move said central mold portion at half the speed and in the same direction as the second mold portion.

8. The combination as claimed in claim 6 in which at least two of said motion translating devices are performed.

9. The combination as claimed in claim 7 in which further piston rods are provided extending through opposite to the piston the others of the end walls these being hydraulic sealing means in said end walls about said further piston rods.

10. The combination as claimed in claim 9 in which means for operating said first unloading means is provided on one of said further piston rods and means for operating said second unloading means is provided on the other of said further piston rods.

11. The combination as claimed in claim 10 in which said first and second unloading means comprises a first stripper plate movable into and out of abutment with the first mold portions and said second unloading means comprises a second stripper plate movable into and out of abutment with the second mold portion and said means in operating said first and second unloading means comprises means on each of said stripper plates for slidingly engaging said respective further piston rods and stop means located at pre-choseri corresponding points on the further piston rods for engaging said stripper plates and moving them with said further piston rods out of abutment with their respective mold portions.

12. The combination as claimed in claim 11 in which each stripper plate is spring biased towards abutment with the respective mold portion.

13. In an injection molding machine, in combination, a first stationary mold portion, a second movable mold portion and a third central movable mold portion, at least a first mold cavity being defined between the first mold portion and the central mold portion and at least a second mold cavity being defined between the second mold portion and the central mold portion said mold portions being relatively displaceable between a mold closed position in which both first and second mold cavities are closed and a mold open position in which both first and second mold cavities are open; means for imparting linear motion to said second mold portion; first unloading means for said first mold portion and second unloading means for said second mold portion said first and second unloading means being movable with respect to their respective mold portions to dislodge an article molded therein; and hydraulic means acting linearly in a direction the same as or parallel to the linear motion of the second mold portion, whereby when said second mold portion is displaced then the central third mold portion moves in the same direction at half the speed.

14. A combination as claimed in claim 13 in which said hydraulic means also acts to operate the first and second unloading means.

1 5. A device for translating a motion vector into a proportionally related motion vector comprising, a unit comprising at least two parallel fluid operable cylinders including end walls; a piston having a piston rod in each of said cylinders said pistons operable in parallel opposite directions and dividing each said cylinder into first and second chambers; each piston rod extending through one of said end walls; passage means communicating said first chamber of each of said cylinders with said second chamber of the other said cylinder, whereby when one member of the group consisting of said piston rods or said unit is displaced relative to another member of said group the pistons operate oppositely within said cylinders by displacement of fluid through said passage means between each of said first and second chambers to proportionately translate the displacement to the third member of the group.