Electric injection molding machine

Details Electric injection molding machine Electric injection molding machine

2001-02-14

2003-03-11

Heitbrink, Tim (Department: 1722)

Plastic article or earthenware shaping or treating: apparatus

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

C425S572000

Reexamination Certificate

active

06530774

ABSTRACT:

DESCRIPTION OF THE INVENTION
Field of the Invention
The invention relates to an electric injection molding machine. It relates especially to a transmission mechanism that transmits rotation of a motor to a screw shaft in the electric injection molding machine.
BACKGROUND OF THE INVENTION
In an injection molding machine, resin heated and melted in a heating cylinder is injected into a cavity of a mold apparatus under high pressure so that the cavity is filled with the molten resin. The molten resin is then cooled and solidified so as to obtain a molded article.
The injection molding machine includes a mold clamping apparatus and an injection apparatus. The mold clamping apparatus is provided with a stationary platen, a movable platen and a mold clamping cylinder. The movable platen is advanced and retracted by the mold clamping cylinder, to thereby perform mold closing, mold clamping and mold opening.
The injection apparatus includes a heating cylinder for heating and melting resin supplied from a hopper, and an injection nozzle for injecting the molten resin. A screw is disposed inside the heating cylinder so that the screw can be rotated about an axis and can be advanced and retracted, i.e. moved rectilinearly along the axis of rotation. The screw is advanced so as to inject the molten resin, and retracted so as to meter the molten resin.
There has been provided an electric injection molding machine in which an electric motor is used to advance and retract the screw.
FIG. 1
is a schematic view of a conventional electric injection molding machine. In
FIG. 1
, a screw
101
is disposed inside a heating cylinder
100
so that the screw
101
can be rotated and can be advanced and retracted (i.e. moved leftward and rightward in FIG.
1
). The rear end (rightward end in
FIG. 1
) of the screw
101
is fixed to a bearing box
109
. At the rear (rightward in
FIG. 1
) of the heating cylinder
100
, a drive section
102
is disposed for rotating, advancing and retracting the screw
101
. The drive section
102
includes a frame
103
, a metering motor
104
disposed movably forward and backward (leftward and rightward in
FIG. 1
) relative to the frame
103
, and an injection motor
105
fixed to the frame
103
.
A guide bar
106
is disposed on the frame
103
so that the guide bar
106
extends parallel with the screw
101
. A support plate
107
is slidably disposed relative to the guide bar
106
. The metering motor
104
is fixed to the support plate
107
. Therefore, the metering motor
104
is moved forward and backward (leftward and rightward in
FIG. 1
) along the guide bar
106
.
A drive-side pulley
108
is fixed to the output shaft of the metering motor
104
. A driven-side pulley
110
is fixed around the outer surface of the bearing box
109
. A timing belt
111
is extended between and wound around the drive-side pulley
108
and the driven-side pulley
110
. The drive-side pulley
108
, the driven-side pulley
110
and the timing belt
111
constitute the rotation transmission mechanism that connects the bearing box
109
and the metering motor
104
.
In an injection stage, when the injection motor
105
is driven, the rotation of the injection motor
105
is transmitted to a ball screw shaft
112
. Since a ball nut
113
is fixed to the frame
103
, the ball screw shaft
112
is advanced while being rotated, so that the screw
101
is also advanced.
In this conventional injection molding machine, the metering motor
104
, the support plate
107
and the bearing box
109
are moved by the advancing and retracting motion of the ball screw shaft
112
. Therefore, mechanical vibration is increased in the injection stage since the mass of the moved portion is large. Meeting a predetermined injection speed is also delayed. Moreover, the reliability of electric wires to supply electricity to the metering motor
104
is deteriorated since the metering motor
104
is moved.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an electric injection molding machine that can decrease mechanical vibration in the injection stage.
Another object of the invention is to provide an electric injection molding machine that can meet a predetermined injection speed rapidly.
A further object of the invention is to provide an electric injection molding machine that has the high reliability of electric wires to supply electricity to the metering motor.
To achieve the above object, an electric injection molding machine is provided and has a mechanical frame comprising a front plate and a rear plate, a heating cylinder fixed to the front plate, a screw disposed inside the heating cylinder so that the screw can be rotated about and can be advanced and retracted along an axis, a ball screw shaft which is disposed along the axis and which advances and retracts a screw shaft, a metering motor fixed to the front plate, and a rotation transmission mechanism which transmits rotation of the metering motor to the screw shaft. The rotation transmission mechanism is supported by the front plate and slidably engaged with the ball screw shaft along the axis.
The electric injection molding machine according to the invention further includes the heating cylinder fixed to a front portion of the front plate, the front plate having a cavity inside thereof, and the rotation transmission mechanism disposed inside the cavity.
The rotation transmission mechanism further includes a hollow shaft driven by the metering motor, a gear train which connects the hollow shaft to an output shaft of the metering motor, a screw support plate fixed to a rear end of the screw shaft, a bearing holder connected with the screw support plate and rotatably connected with a front end of the ball screw shaft, first spline cogs formed on an inner cylindrical surface of the hollow shaft, and second spline cogs formed on the bearing holder and slidably engaged with the first spline cogs along the axis.
Consequently, since the metering motor and the hollow shaft are not moved by the advancing and retracting motion of the ball screw shaft, the mass of the moved portion is small so that mechanical vibration is decreased in the injection stage. A predetermined injection speed is also met rapidly. Moreover, the reliability of electric wires to supply electricity to the metering motor is improved.
The above and further objects and novel features of the invention will more fully appear from the following detailed description when the same is read in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are for purpose of illustration only and are not intended as a definition of the limits of the invention.


REFERENCES:
patent: 5129808 (1992-07-01), Watanabe et al.
patent: 5679384 (1997-10-01), Emoto
patent: 5747076 (1998-05-01), Jaroschek et al.
patent: 6227839 (2001-05-01), Yoshida et al.
patent: 547950 (1929-11-01), None
patent: 0 350 872 (1990-01-01), None
patent: 0 743 167 (1996-11-01), None
patent: 0 882 564 (1998-12-01), None

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