Servo-driven clamping unit for use in injection molding machine

Details Servo-driven clamping unit for use in injection molding machine Servo-driven clamping unit for use in injection molding machine

2002-01-14

2004-06-22

Mackey, James P. (Department: 1722)

Plastic article or earthenware shaping or treating: apparatus

Female mold and charger to supply fluent stock under...

With means to close mold

C425S451600

Reexamination Certificate

active

06752619

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to servo-driven clamping units for use in injection molding machines, and more particularly, to a servo-driven clamping unit for use in an injection molding machine, which can facilitate precise positioning control of mold clamping, so as to improve stability and reliability for proceeding an injection molding process.
BACKGROUND OF INVENTION
Generally, a conventional injection molding machine adopts a hydraulic clamping mechanism for performing mold-opening and mold-closing operations, and is mainly composed of a machine base, a clamping unit, an injection unit and a hydraulic electric control system.
FIG. 1
illustrates a conventional clamping unit
1
, comprising: a front platen
3
; a rear platen
4
; a plurality of tie bars
2
symmetrically positioned and mounted in parallel to corners of the platens
3
,
4
respectively; a movable platen
5
movably sleeved about the tie bars
2
between the front platen
3
and the rear platen
4
; a hydraulic cylinder
6
mounted on the rear platen
4
, for providing power to drive the movable platen
5
to move forward and in reverse along the tie bars
2
; and a set of toggle linkage mechanisms
7
for interconnecting the rear platen
4
and the movable platen
5
, and driven by the hydraulic cylinder
6
for inducing the back and forth movement of the movable platen
5
. This conventional injection molding machine, however, is endowed with quite a few of drawbacks. First, the hydraulic clamping mechanism is not sensitive enough, thereby making the use of the hydraulic cylinder
6
for operating mold-opening or mold-clamping, not able to achieve high accuracy in mold positioning control. Further, hydraulic transmission may be affected by many factors. For example, variation of temperature or humidity in a working environment influences viscosity of hydraulic oil and frictional resistance of oil movement in the hydraulic cylinder
6
; therefore, in practice, the hydraulic clamping mechanism is often defective with time-ineffective and energy-consuming problems. Moreover, the hydraulic cylinder
6
acting as a power source for mold clamping operation, is formed with a guide rod connected to one end of a connector device
8
, whereas the other end of the connector device
8
is pivotally coupled to the toggle linkage mechanism
7
. However, during element assemblage, a piston ring in the hydraulic cylinder
6
can bear with a certain extent of flexibility, thereby making the hydraulic cylinder
6
not possibly made in perfect association with the connector device
8
; this therefore degrades the dimensional accuracy of fabricated products. In addition, this hydraulic system cannot efficiently control the entire progress of moving the guide rod of the hydraulic cylinder
6
, so that precise positional control during mold-clamping operation is not possibly achieved by using the hydraulic system.
U.S. Pat. No. 4,642,044 discloses a conventional servo-driven clamping unit
1
′ for use in an injection molding machine disclosed, so as to solve the foregoing problem of positioning control, as shown in FIG.
2
. The clamping unit
1
′ adopts a servo-motor
9
to drive mold-opening and mold-closing operations, wherein the servomotor
9
is mounted on a rear platen
4
′, and turns to generated torque force that is transmitted through a shaft connector
10
associated with the servo-motor
9
, an idler gear
11
and a follower gear
12
engaged with the idler. When the follower gear
12
is driven to rotate, a ball screw
14
coupled to the follower gear
12
by means of a guide device
13
can be induced to move forward and backward along a horizontal direction, allowing the torque force to be converted into axial pushing force. The ball screw
14
is further connected to a toggle linkage mechanism
7
′ by means of a connector device
8
′, wherein the toggle linkage mechanism
7
′ interconnects the rear platen
4
′ and a movable platen
5
′. When the ball screw
14
moves forward, the toggle linkage mechanism
7
′ is driven by the connector device
8
′ to move the movable platen
5
′ forward along tie bars
2
′ and toward a front platen
3
′, until mold halves being coupled together, so that mold-clamping operation is completed, and the servo-motor
9
stops operating at this time. For opening the mold halves, the servo-motor
9
turns at an opposite direction, allowing the ball screw
14
to move backward and generate a backward pulling force to move the movable platen
5
′ away from the front platen
3
′, so that the coupled mold halves can be separated apart from each other, and mold-opening operation is accomplished.
However, the foregoing servo-driven clamping unit
1
′ has the following drawbacks. First, power transmission through the idler gear
11
and the follower gear
12
cannot be perfectly performed due to dimensional errors made during gear fabrication; this undesirably results in energy loss and also inaccuracy of positioning control during mold-clamping operation. And, the gear transmission system is further defective for noise production, frequent requirement of element lubrication, and reduction in usage lifetime of elements. Moreover, the ball screw
14
is assembled with the connected device
8
′ by means of screws, and thereby easily applies unbalanced force to the connected device
8
′; this may lead to rotational deviation of the ball screw
14
and detrimentally affect lifetime of the ball screw
14
. Furthermore, two ends of the ball screw
14
are not balanced supported by only one guide device
13
, and thus rigidity and stability of the ball screw
14
are not strong enough in operation, which in turn deteriorates the accuracy of positioning control during mold-clamping. In addition, the toggle linkage mechanism
7
′ used in the conventional servo-driven clamping unit
1
′ is relatively complicated in structure; this increases complexity in fabrication, and also makes the mold-opening or mold-clamping operation not time-effective to implement.
SUMMARY OF THE INVENTION
A primary objective of the present invention is to provide a servo-driven clamping unit for use in an injection molding machine, in which internal elements of the clamping unit are precisely engaged with each other for accurate power transmission and mold-clamping positioning.
Another objective of the invention is to provide a servo-driven clamping unit for use in an injection molding machine, in which two ends of a ball screw are well supported by bearing devices, allowing the ball screw to be accurately assembled in the clamping unit, so as to improve rigidity and stability of the ball screw in operation.
A further objective of the invention is to provide a servo-driven clamping unit for use in an injection molding machine, in which a toggle linkage mechanism is structurally simplified in element linkage, so as to enhance mold-clamping force.
In accordance with the foregoing and other objectives, the present invention proposes a servo-driven clamping unit for use in an injection molding machine, comprising: a plurality of tie bars symmetrically positioned and mounted in parallel to corners of a front platen and a rear platen; a movable platen movably sleeved about the tie bars and positioned between the front and rear platens; a servo-motor mounted on the rear platen, for providing power for operating the clamping unit; a belt-gear mechanism associated with the servo-motor, for transmitting torque force and turning speed provided from the servo-motor; a ball screw transmission mechanism including a ball screw and a guide device connected to the belt-gear mechanism, for converting the torque force transmitted from the belt-gear mechanism into axial pushing force, wherein the guide device is formed with a threaded hole for allowing the ball screw to be inserted through the threaded hole; a toggle linkage mechanism for interconnecting the rear platen and the movable platen, and bear

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