Plastic article or earthenware shaping or treating: apparatus – Control means responsive to or actuated by means sensing or... – Feed control of material en route to shaping area
Reexamination Certificate
2002-09-13
2004-10-12
Heitbrink, Tim (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Control means responsive to or actuated by means sensing or...
Feed control of material en route to shaping area
C425S567000, C425S574000
Reexamination Certificate
active
06802703
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-335450, filed Oct. 31, 2001, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an injection unit of an electric injection molding machine, which is used to plasticize raw material resin and fill dies with the plasticized resin and, particularly, to the construction of a drive mechanism to advance a screw in a heating barrel.
2. Description of the Related Art
The construction of an injection unit in a conventional electric injection molding machine is described, for example, in Jpn. Pat. Appln. KOKAI Publication No. 10-286848 or Published Japanese Patent No. 2631521.
FIG. 2
shows, as an example of the construction of a conventional injection unit, the construction described in the Jpn. Pat. Appln. KOKAI Publication No. 10-286848. This injection unit comprises a heating barrel
1
, a screw
2
, a front plate
3
, a rear plate
4
, an intermediate plate
6
, etc.
The heating barrel
1
is, on the leading end thereof (the left side in the drawing), connected to the rear surface of dies (not shown) through a nozzle (not shown). The screw
2
is incorporated in the heating barrel
1
. The tail end of the heating barrel
1
is supported by the middle of the front plate
3
. Behind the front plate
3
is arranged the rear plate
4
opposite to the front plate
3
. Four tie bars
5
span the space between the front plate
3
and the rear plate
4
, which are connected to each other through these tie bars
5
.
Between the front plate
3
and the rear plate
4
is arranged the intermediate plate
6
. Through holes are provided at four corners of the peripheral edge portion of the intermediate plate
6
, and the tie bars
5
pass through these through holes. The intermediate plate
6
can move in a back-and-forth direction (a left-and-right direction in the figure) while being guided by the tie bars
5
.
A bearing
7
is built in the middle of the intermediate plate
6
and the tail end of the screw
2
is supported by this bearing
7
. Furthermore, a servomotor
9
for charging is placed on the intermediate plate
6
. A pulley
8
is attached to the tail end portion of the screw
2
. This pulley
8
is connected to the rotating shaft of the servomotor
9
through a timing belt.
Nuts
32
of ball screws are fixed in two places of the peripheral edge portion of the rear surface of the intermediate plate
6
. Bearings
34
are built in two places of the peripheral edge portion of the rear plate
4
, and the threaded rods
31
of the ball screws are supported by these bearings
34
. The tail end portion of the threaded rod
31
of each ball screw protrudes from the rear surface of the rear plate
4
and a pulley
36
is attached to this portion. These pulleys
36
are connected to a servomotor for injection (not shown) through a timing belt. Moreover, in this example, a pressure sensor
35
to detect a reaction force that acts on the screw
2
during injection is attached to the middle of the rear surface of the intermediate plate
6
.
In the injection unit, by rotating the screw
2
by use of the servomotor
9
, a raw material resin is introduced into the heating barrel
1
and melted. Also, the molten resin is injected from the heating barrel
1
into the dies by driving the intermediate plate
6
by means of the ball screws
30
thereby to advance the screw
2
in the heating barrel
1
.
In a case where, as in the example, the nut
32
of the ball screw is attached to the rear surface of the intermediate plate
6
, the length of the nut
32
has a direct effect on the total length of the injection unit. That is, when the length of the nut
32
is increased, the total length of the injection unit also increases by this amount.
Incidentally, in an injection unit of an electric injection molding machine, high response is required during the control of the advance speed of the screw
2
. Therefore, it is necessary to minimize the inertia of an axial driving mechanism of the screw
2
(generally, ball screws
30
are used as in the example). For this purpose, it is desirable to use ball screws of the smallest possible diameter.
On the other hand, in order to withstand the thrust during injection, it is necessary to increase the number of balls that transmit force between the threaded rod and the nut. In order to increase the number of balls, it is necessary to increase the number of turns and the number of rows. However, if this is carried out, the length of the nut increases. In order to shorten the length of the nut, it is necessary to increase the number of balls per perimeter by increasing the diameter of the threaded rod. However, if this is carried out, the inertia increases and the response during the acceleration and deceleration of the screw becomes worse.
Furthermore, in a case where, as in the example, means for detecting the back pressure of the screw
2
(the pressure sensor
35
) is provided in addition to the ball screws
30
for the axial driving of the screw
2
, it is impossible to individually detect the load of each of the ball screws
30
. For this reason, when an excessive force acts on one ball screw, it is impossible to detect the abnormality and the ball screw may be broken early. Incidentally, in the described Published Japanese Patent No. 2631521, this problem is solved by inserting back-pressure detection means in the connection between the nut of each ball screw and the intermediate plate.
When the axial driving mechanism of the screw
2
is constituted by a plurality of ball screws
30
, the axis of the screw
2
and the axis of each of the ball screws
30
are not on the same straight line, as shown in
FIG. 3
, and therefore bending moment acts on the intermediate plate
6
, thereby generating deflection. Because this bending moment acts on the ball screws
30
as a lateral load, an excessive force acts on the balls kept between the nut
32
and the threaded rod
31
, shortening the life of the ball screws
30
.
To solve this problem, it is conceivable to decrease the amount of deformation of the intermediate plate
6
by increasing the rigidity of the intermediate plate. However, if the thickness of the intermediate plate
6
is increased, the total length of the injection unit also increases by this amount.
BRIEF SUMMARY OF THE INVENTION
The present invention was made in view of the problems with the injection unit of a conventional injection molding machine. The object of the invention is to provide an injection unit which enables the total length of the unit to be shortened, is excellent in response during the control of the advance speed of a screw, and has a long life of an axial driving mechanism of the screw.
The injection unit of an electric injection molding machine of the invention comprises: a heating barrel having a nozzle at the leading end thereof; a screw, the leading end side of which being incorporated in the heating barrel; a front plate supporting the tail end of the heating barrel; a rear plate arranged behind the front plate opposite to the front plate; tie bars spanning a space between the front plate and the rear plate and connecting both together; an intermediate plate arranged between the front plate and the rear plate, moving along the tie bars in a back-and-forth direction and rotatably supporting a vicinity of the tail end of the screw; a rotationally driving mechanism mounted to the intermediate plate and configured to rotate the screw; and ball screws mounted to the rear plate and configured to drive the intermediate plate in a back-and-forth direction. In this injection unit of an electric injection molding machine, the nut of each of said ball screws is rotatably attached to said rear plate, through holes are formed in said intermediate plate, the leading end portion of the threaded rod of each of said ball screws and the leading end portion of the nut are inserted in ea
Kasai Toshihiro
Kawai Junsuke
Kobayashi Kazuhito
Nishizawa Makoto
Heitbrink Tim
Pillsbury & Winthrop LLP
Toshiba Machine Co. Ltd.
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