Apparatus to actuate injection element

Details Apparatus to actuate injection element Apparatus to actuate injection element

1999-04-14

2002-07-02

Davis, Robert (Department: 1722)

Plastic and nonmetallic article shaping or treating: processes

Mechanical shaping or molding to form or reform shaped article

Shaping against forming surface

C264S328500, C264S238000, C425S557000, C425S561000

Reexamination Certificate

active

06413465

ABSTRACT:

BACKGROUND OF THE INVENTION
Conventional injection systems operate either through spindle systems or through hydraulic drives. Known injection molding apparatuses for this purpose typically have a hydraulic piston-cylinder system in axial connection with a plasticizer screw. The piston-cylinder system is used to drive the plasticizer screw forward. As a result, plastic melt or the like is injected into an injection molding tool.
Electrically-driven systems, for example, have spindles that are connected to servomotors. The spindles are moved axially through the motion of the servomotors. Their motion is transferred to an injection screw. The motion of the injection screw can thus be controlled precisely, thereby allowing precise regulation of the injected volume of melt.
Recently, the demand for dimensionally small injection-molded parts has increased. Common examples of such parts include micro-mechanical components (e.g., micro gear wheels for watches), medical-technical hardware, and optoelectronic elements (e.g., parts for optical waveguides).
SUMMARY OF THE INVENTION
One of problem that arises in connection with the production of these small parts is that the injection screw must execute very small and precisely-controlled displacements, in order to inject the desired quantity of melt into the mold. This motion must take place in a very short time. Otherwise there is a risk that the small quantity of plasticized melt will “freeze.”
The inherent dynamics of hydraulic drives and also of servodrives does not make it possible to achieve the necessary precision of the injection motion of the male mold in the short time that is available.
The present invention is directed to an apparatus to actuate an injection element and a male mold, by which it is possible to execute very small and reproducible displacements in a very short time. Further, the apparatus is able to approach the switchover point from the injection process to the holding-pressure process, and thus to initiate the holding pressure phase in high dynamics with time and path precision. That is, the switchover point is reached precisely, without any “overshoot” of the injection element.
In general, according to one aspect, the invention features an actuation element that has a tappet, which is guided on a crank plate. The crank plate is turned with positional accuracy by a controlled or regulated servomotor.
In specific embodiments, for the return stroke of the injection element, a second tappet is present, which is actuated by a second crank plate. As an alternative, for the return stroke of the injection element, a contour is milled into the crank plate, within which the tappet is subject to restricted guidance.
The design given here makes it possible for an injection element to achieve an exactly predetermined stroke reproducibly in a very short time and arbitrarily often.
The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.


REFERENCES:
patent: 4315726 (1982-02-01), Semerdjiev et al.
patent: 4449915 (1984-05-01), van den Brink
patent: 5925295 (1999-07-01), Nakamura et al.
patent: 4-122618 (1992-04-01), None

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