Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting
Reexamination Certificate
2000-07-06
2002-10-22
Heitbrink, Jill L. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
C264S328100, C425S150000, C425S595000
Reexamination Certificate
active
06468449
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a mold clamping apparatus and mold opening control method for injection molding machines. More particularly, the present invention relates to a hybrid mold clamping apparatus and mold opening control method which takes advantage of the structure thereof, whereby the mold opening and closing action is electro-mechanically implemented, and the mold clamping action is hydraulically implemented.
BACKGROUND OF THE INVENTION
As a basic structure for electromechanical mold clamping devices, the mold opening and closing action and the mold clamping action are performed by rotating a ball screw axle using a servo motor, thus moving a movable platen integrally formed with a ball nut which fits onto the ball screw axle. In this type of structure, an extremely large mold-clamping force acts on the ball screw and the ball nut, such that a high-load ball screw is required.
In contrast to this, a mold clamping apparatus has been disclosed in Japanese Patent application H9-29802, in which the mold clamping mechanism is equipped with a mold clamping axle having a trapezoidal screw, angle screw, etc. separate from the ball screw-driven mold opening and closing mechanism, and where the mold clamping force from a hydraulic cylinder operates on the mold clamping axle to clamp a mold. This is a “hybrid” mold clamping apparatus, in which the mold opening and closing mechanism and the mold clamping mechanism are independently constituted. In such a mold clamping apparatus, mold clamping force load will be distributed over an angle screw or trapezoidal screw making surface contact, and no large mold clamping force is loaded on the mold opening and closing ball screw. However, with this type of mold clamping apparatus, the mold clamping axle and the mold clamping nut rub one another during the mold opening and closing operations, whereby frictional resistance is generated between the angle screw, etc. and the nut, whereby drive energy is lost, wear on the screw is created, etc.
Similarly, mold clamping apparatuses into which mold-clamping mechanisms are built around respective multiple tie bars are publicly known through Japanese Utility Model H7-11944 and Japan Patent 2511111 as mold clamping apparatuses in which the mold opening-closing mechanism and the mold clamping mechanism are separately constituted. Such mold clamping mechanisms are equipped with at least a tie bar, a half nut capable of fitting this tie bar, and a mold clamping cylinder which moves the half nut or the tie bar back and forth. When the mold is closed, these half nuts engage the respective tie bar angle screw threads, and the mold clamping cylinder pulls on the tie bar affixed by the half nut to the mold. However, such mold clamping apparatuses have multiple mold clamping mechanisms, and the mold thickness must be adjusted to be equal so that the respective mold clamping mechanisms are equal in order that the respective half nuts equally engage the tie bar angle screw threads during mold clamping. A mold thickness adjustment apparatus which synchronizes and adjusts the mold thickness is therefore required, thus increasing the number of parts in the mold clamping apparatus and requiring more effort for initial assembly adjustment and maintenance of the mold clamping apparatus.
As a partial solution to these problems, the present inventor described in Japanese Patent application H10-108616 for a mold clamping apparatus as shown in FIG.
8
.
The mold clamping mechanism comprises a mold opening and closing screw axle
41
, which is a ball screw, a mold opening and closing nut
42
, which is a ball nut, a mold clamping axle
31
having a movable platen
4
, which are attached or integral pieces. Rotational driving of the mold opening and closing screw axle
41
by a servo motor
11
causes the movable platen
4
to advance and retreat to open and close the mold.
The mold clamping mechanism is also equipped with a mold clamping ram
15
contained in a support platen
3
, having a half nut device
20
attached at its end. During mold clamping operations, a mold clamping ram
51
receives the mold clamping load over the entire surface of the annular convex portion (annular tooth portion) of the mold clamping axle
31
through the half nut
21
of the closed half nut device
20
.
A mold thickness adjustment device
60
comprises a servo motor
61
having a rotary rotary encoder and a brake. A flat gear
65
is rotated by the servo motor causing a cylindrical member
64
to come in and out of contact with the mold clamping ram
51
.
A proximity switch
81
is attached to the front end of the half nut device
20
. Mold thickness adjustment is performed in order to set and adjust the position of the half nut
21
such that the half nut
21
and the mold clamping axle
31
mesh well when the half nut
21
is tightened at the completion of the mold closing operation.
During the mold thickness adjustment, the servo motor
61
advances the cylindrical member
64
. The mold clamping ram
51
which is in contact therewith similarly advances. A proximity switch
81
advances with the half nut device
20
. During this forward advance, the proximity switch
81
detects the position at which the half nut
21
and the mold clamping axle
31
mesh well. That position is set in the injection molding machine control device as the mold thickness adjustment position. During subsequent mold opening and closing operations, the cylindrical member
64
limits the advance and retreat positions of the mold clamping ram
51
, holding the position of the half nut
21
at the mold thickness adjusted position.
In the above-described mold clamping apparatus, the mold opening and closing mechanism and the mold clamping mechanism are coaxially arrayed compactly on the center axis of the mold clamping device. Movement of the movable platen
4
during mold opening and closing is therefore carried out with a high degree of straightness, and the mold clamping force applied during clamping is accurately applied to the center of the movable platen
4
. The half nut
21
is completely open during mold opening and closing operation, so that movement of the movable platen
4
at a high speed and a low frictional resistance is effected without contact between the half nut
21
and the mold clamping axle
31
. Furthermore, the mold thickness adjustment device
60
is compactly arranged on the center axis of the mold clamping device, so that there are few mold clamping device parts. This, of course facilitates assembly adjustment, maintenance, and mold thickness adjustment.
However, in the mold thickness adjustment device
60
, the retracted mold clamping ram
51
is positioned by mechanical contact with the cylindrical member
64
which is held at the mold thickness adjustment position. Thus, the half nut
21
is held in a position at which it meshes with the mold clamping axle
31
. Therefore, the cylindrical member
64
is positioned in the direct vicinity of the rear side of the mold clamping ram
51
at the time of mold clamping. Therefore, if molten resin overfills the die cavity, resulting in an overpack, when the mold clamping ram
51
retracts, it will contact the cylindrical member
64
and be unable to retract further. As a result, as the support platen
3
retreats, a large tension will be imposed on the tie bars
5
. In the worst case, this can cause the tie bars
5
to break. It may also be difficult to remove the overpack state as the half nut many not open.
It is therefore an object of the present invention to provide a mold clamping device which has the basic structure of the single mold opening and closing mechanism and single mold clamping mechanism as described in Japanese Patent Application H10-108618, having an improved mold thickness adjustment mechanism whereby accurate positioning and holding of the platen may be achieved using a simple control device which does not rely on mechanical positioning of a half nut device for mold thickness adjustment positioning during mold opening and closing. It is a fu
Devinsky Paul
Heitbrink Jill L.
McDermott & Will & Emery
Sodick Co. Ltd.
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