HYBRID INJECTION MOLDING MACHINE

MACHINE DE MOULAGE PAR INJECTION HYBRIDE

English Abstract

An electro-mechanical drive apparatus uses a single variable speed motor (20),
two one-way clutches (42, 66), and a hydraulic
accumulator (48) to provide both hydraulic power for the linear motion axes
and rotation of the plasticizing screw (14) in an injection
molding machine. When engaged, the first one-way clutch (42) couples the drive
motor (20) to the pump stack (26), while the second
one-way clutch (66) couples the motor (20) to the feed screw (14). During
rotation of the drive motor (20) in a forward direction, (a) the
first one-way clutch (42) engages, rotating the shaft of the hydraulic pump
stack (26) to power the machines hydraulic systems and charge
the accumulator (48); and (b) the second one-way clutch slips. When the drive
motor (20) is rotated in a reverse direction, (a) the second
one-way clutch (66) engages, rotating the feed screw (14), and (b) the first
one-way clutch (42) slips. Preferably, the drive apparatus is
associated with a double shaft motor (20) mounted adjacent separate drive
couplings for the feed screw (14) and hydraulic pump stack (26).

French Abstract

Cette invention concerne un appareil d'entraînement électromécanique qui comprend un seul moteur électrique à vitesse variable (20), deux embrayages unidirectionnels (42, 66), ainsi qu'un accumulateur hydraulique (48) qui va fournir la force hydraulique nécessaire aux axes de déplacement linéaires et à la rotation de la vis de plastification (14) dans une machine de moulage par injection. Lorsqu'ils sont actionnés, le premier embrayage unidirectionnel (42) couple le moteur d'entraînement (20) à la cuve (26) de la pompe, tandis que le second embrayage unidirectionnel (66) couple le moteur (20) à la vis d'alimentation (14). Lorsque le moteur d'entraînement (20) tourne en avant, (a) le premier embrayage unidirectionnel (42) s'enclenche et fait tourner l'arbre de la cuve (26) de la pompe hydraulique afin d'entraîner les systèmes hydrauliques des machines et de charger l'accumulateur (48), tandis que (b) le second embrayage unidirectionnel tourne à vide. Lorsque le moteur d'entraînement (20) tourne en arrière, (a) le second embrayage unidirectionnel (66) s'enclenche et fait tourner la vis d'alimentation (14), tandis que (b) le premier embrayage unidirectionnel (42) tourne à vide. L'appareil d'entraînement est de préférence associé à un moteur (20) à deux arbres qui est monté à proximité de couplages d'entraînement distincts pour la vis d'alimentation (14) et la cuve (26) de la pompe hydraulique.

Claims

CLAIMS:
1. An injection molding machine comprising a hydraulically operated clamping
system, an injection unit including a feed screw capable of rotational and
translational
movement within a barrel, a hydraulic pump, a variable speed electric drive
motor,
characterized in that the injection molding machine further includes
transmission means
for alternately transmitting power from the drive motor to (a) rotate the feed
screw and (b)
activate the hydraulic pump, such that operation of the drive motor in a first
direction
rotates the feed screw to plasticize material in the barrel of the injection
unit and
operation of the drive motor in an opposite direction activates the hydraulic
pump to
enable operation of the clamping system and translational movement of the feed
screw
within the barrel of the injection unit.
2. The injection molding machine of claim 1 wherein the transmission means
comprises:
(a) a first one-way clutch interposed between the drive motor and the
hydraulic
pump, and
(b) a second one-way clutch interposed between the drive motor and the feed
screw,
such that when the drive motor is operated in the first direction,
(i) the second one-way clutch is engaged, rotating the feed screw, and
(ii) the first one-way clutch slips; and
when the drive motor is operated in the opposite direction,
(iii) the first one-way clutch is engaged to operate the hydraulic pump
thereby generating hydraulic power to operate the clamping system and initiate
translational movement of the feed screw, and
(iv) the second one-way clutch slips.
3. A molding machine having a hydraulically operated clamping system, an
injection
unit including a feed screw rotatably and translatably carried in a barrel, a
hydraulic
pump, a variable speed electric drive motor, characterized in that the
injection molding
machine further includes transmission means for alternately transmitting power
from the
drive motor to the feed screw and hydraulic pump, the transmission means
comprising:
(a) a first one-way clutch interposed between the drive motor and the
hydraulic
pump,
7

(b) a second one-way clutch interposed between the drive motor and the feed
screw,
such that when the drive motor is operated in a first direction,
(i) the second one-way clutch is engaged, rotating the feed screw, and
(ii) the first one-way clutch slips; and
when the drive motor is operated in an opposite direction,
(iii) the first one-way clutch is engaged to operate the hydraulic pump,
thereby generating power to operate the clamping system and initiate
translational
movement of the feed screw, and
(iv) the second one-way clutch slips.
8

Description

CA 02345949 2001-07-09
HYBRID INJECTION MOLDING MACHINE
Technical Field
The present invention relates generally to injection molding machines and,
more
particularly, to an injection molding machine that uses a single electric
motor to rotate the
feed screw and, alternatively, drive a hydraulic pump stack.
Background Art
The injection unit of a typical injection molding machine provides essentially
two
functions during the course of a normal cycle of operation; namely, injection
and
extruder. The injection function occurs when the feed screw is moved forward
linearly
(without rotation) to force plastic melt into the mold. The extruder function
is
accomplished when the feed screw is rotated to plasticize additional material
for the next
shot. As the feed screw is rotated during the extruder function, the plastic
melt is
gradually forced past the end of the screw, creating a pressure or force to
move the
screw rearward to its pre-injection position as the melt accumulates.
Both the injection and extruder functions require an associated drive
apparatus in
the injection unit. In prior art hydraulic machines, the movement for the
injection function
is typically performed by a hydraulic cylinder, while the rotation of the feed
screw for
extruder run is normally accomplished by a hydraulic motor. More recently,
electric
motors combined with mechanical systems have been used as the direct power
source in
the injection unit. Some of the prior art electric systems have used separate
motors for
each function; i.e., one motor for rotating the feed screw and a second motor
in
combination with a mechanism, such as a ball screw, to convert rotary motion
into the
linear movement required for injection. Other prior art "hybrid" machines have
used an
electric motor to rotate the feed screw with the remaining functions of the
machine being
hydraulically driven, with power provided by an electric motor diving one or
more
hydraulic pumps.
While the "hybrid" machine incorporates some of the advantages of both
electric
(better control of screw rotation) and hydraulic (lower overall cost)
machines, there
remains room for improvement. In particular, there is potential for a more
economical
system since there is excess capacity in the electric motor that rotates the
screw. This
motor is only used during the portion of the cycle where the thermoplastic
material is

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extruded (plasticated) to build the shot. Since the motor and the associated
variable
speed drive have a relatively high cost, it is desirable to maximize the
utilization of this
motor. Furthermore, for the injection molding machines with variable speed
motors
currently available, the motors are either dedicated to specific axes (as with
electro-
mechanical systems), or are applied to standard hydraulic circuits redundantly
so that no
economy of control is gained by the variable speed motor and drive.
Accordingly, it is an object of the present invention to provide a drive
apparatus
that is simple in construction and effectively enables a single variable speed
motor to be
used to provide power for a combination of mechanical and hydraulic machine
elements.
Briefly stated, the present invention is directed to a drive apparatus
including a
variable speed motor, preferably brushless DC, and conventional power
transmission
components to alternately provide (a) rotation of the feed screw in the
injection unit of an
injection molding machine or (b) operation of a hydraulic pump stack in order
to provide
power to the machine's hydraulic system. The drive apparatus further includes
a first
one-way clutch between the motor and the feed screw, and a second one-way
clutch
befinreen the motor and the hydraulic pump stack.
During operation of the most machine functions, the drive motor is rotated in
a
forward (clockwise) direction to rotate the input shaft of the pump stack,
thereby providing
hydraulic power for the operating elements in the various motion axes, such as
clamp
and injection. The hydraulic power from the pump stack is also used to charge
a
hydraulic accumulator, providing a hydraulic power reserve for intervals when
the motor
is not available to drive the pump. More specifically, during forward rotation
of the drive
motor, (a} the first one-way clutch is engaged, rotating the shaft of the pump
stack; and
(b) the second one-way clutch slips.
The motor is rotated in a reverse (counterclockwise) direction to accomplish
the
extruder function, i.e., to rotate the feed screw through a suitable
transmission
mechanism. In particular, during reverse rotation, (a) the second one-way
clutch is
engaged, rotating the feed screw via pulleys and a drive belt at a
predetermined speed to
plasticize material; and (b) the first one-way clutch slips.
The preferred embodiment of the drive apparatus inGudes a double shaft motor
mounted to engage suitable power drive couplings for the feed screw and the
hydraulic
pump stack. Overall, the present invention provides a compact drive system for
a single
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motor to power all machine axes; this improves reliability and allows faster
response over
prior art systems that require a shift mechanism to divert power to the
different axes.
Advantages of the preferred embodiment inGude: better utilization of motor
capacity,
improved energy efficiency, reduced overall machine cost and more accurate
control of
feed screw rotation.
Fig. 1 is a side elevational view of an injection molding machine, including a
drive
apparatus according to the present invention.
1o Fig. 2 is a right end elevational view of the injection molding machine
illustrated in
Fig. 1.
Fig. 3 is a top plan view of the injection molding machine illustrated in Fig.
1.
Fig. 4 is an enlarged, fragmentary side elevational view, partially in
section, taken
along the line 4-4 in Fig. 3.
Fig. 5 is an enlarged, fragmentary view, partially in section, of the drive
apparatus
shown in Fig. 4, with certain parts removed for clarity.
Best Mode for Carn~iLng Out the Invpntinn
The present invention will be described in connection with a typical injection
molding machine 1 that includes a clamping system 2 and an injection unit 10.
As shown
in Fig. 1 and 4, the injection unit 10 is carried by horizontal support rods 4
attached to a
base 8 of the injection molding machine 1. The injection unit 10 is adapted to
move
along the support rods 4 for purposes of positioning, such as making
connection with a
mold (not shown) attached to stationary platen 6.
The primary components of the injection unit 10 include a barrel 12 containing
a
feed screw 14 (Fig. 4) that works to plasticize thermoplastic material that
enters the
barrel 12 through housing 15 from hopper 16. The operative functions of the
injection
molding machine 1, including the injection unit 10, are initiated by a drive
assembly 18.
The drive assembly 18 of injection unit 10 includes an electric drive motor
20, pump drive
coupling 22, extruder drive coupling 24, hydraulic pump stack 26 and support
housing 28,
see Figs. 2 and 4. As will be described in greater detail in the following
paragraphs, the
drive assembly 18 operates to rotate the feed screw 14 to plasticize the
material during
the extruder function, and to generate the hydraulic power required for the
other machine
functions.
3

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Referring more particularly to Fig. 5, the drive assembly 18 includes a pump
drive
coupling 22 that connects the motor 20 to the hydraulic pump stack 26. Mounted
on the
shaft 38 of motor 20 are a one-way clutch 42 and two ball bearing assemblies
44, which
collectively serve to support and engage a connector sleeve 40 that attaches
directly to
the shaft 34 of the pump stack 26. As will be more fully described later,
while the motor
20 is capable of rotation in either direction, the one-way clutch 42 acts to
allow rotation of
the pulley 40 in one direction only. In the context of this disclosure, each
element
described as a °one-way clutch° is preferably a mechanical cam
type clutch made to
engage a rotating cylindrical element with a surrounding member for one
direction of
rotation; there is essentially no resistance from the clutch when the element
is rotated in
the opposite direction. Morse Industrial, Emerson Power Transmission Corp. is
a well
known supplier of this type of clutch.
A motor mounting plate 51 connects directly to a support housing 36 and is
configured to travel with the support housing 28 along the guide rods 30. As
shown, the
~ 5 motor 20 sits directly on top of the mounting plate 51.
The drive assembly 18 also includes an extruder drive coupling 24 to connect
the
motor 20 to the feed screw 14. In a manner similar to that described above for
the pump
drive coupling 22, the extruder drive coupling 24 includes a pulley 64 mounted
on motor
shaft 38 through a one-way clutch 66 and bearings 68. A second pulley 72 in
extruder
drive coupling 24 connects to the feed screw 14 and is driven by pulley 64
through a
drive belt 70.
The operation of the drive assembly 18 will now be described. To initiate the
extruder function, motor 20 is activated to rotate in a counterclockwise
direction. This
rotation of motor shaft 38 causes one-way clutch 66 to engage, driving pulley
64 and,
consequently, pulley 72 by virtue of drive belt 70. The rotation of pulley 72
imparts like
rotation to the feed screw 14. As the feed screw 14 is rotated, material
supplied from
hopper 16 feeds through housing 15 and is plasticized within barrel 12. The
rotation of
feed screw 14 also serves to advance material toward the nozzle (discharge)
end of
barrel 12, causing the pressure of the melt to increase at the end of the
screw 14- as the
3o charge of material begins to accumulate. When the pressure of the plastic
melt reaches
a certain level, it will begin to force feed screw 14 rearward, thereby moving
the entire
drive assembly 18 to the rear of injection unit 10. Specifically, the rearward
movement of
feed screw 14 applies a force to housing 36, causing housing 36 to move
likewise to the
rear, carrying motor 20, pump stack 26 and associated drive components.
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The rate of rearward movement of the feed screw 14 can be controlled by the
hydraulic cylinders 46 connected to either side of the housing 36 (see Fig. 1
). The
appropriate valuing of the fluid in the cylinders 46 can slow the rearward
movement (but
not the rotation) of the feed screw 14, thereby increasing the back pressure
of the plastic
melt. Alternatively, the hydraulic cylinders 46 can be used to apply force on
the housing
36 in a way that increases the rate at which the feed screw moves back,
thereby
decreasing the back pressure of the melt.
As the motor 20 rotates in a counterclockwise direction during the extruder
function, the one-way clutch 42 slips on shaft 38 so that no rotational force
is transmitted
to the pump shaft 34. The extrusion function is complete when a sufficient
charge of
plastic melt is accumulated in front of the feed screw 14, as required to fill
the cavity of
the mold mounted on the stationary platen 6.
As soon as the extrusion function is complete, the motor 20 is reversed so
that it
rotates in a clockwise direction; as a result, one-way clutch 42 is engaged on
shaft 38,
rotating connector sleeve 40 and shaft 34 of the hydraulic pump stack 26. The
hydraulic
energy generated by the pump stack 26 is used to operate machine functions
and/or
charge a hydraulic accumulator 48, as determined by the operating sequence of
the
injection molding machine 1. For example, to perform the injection function,
hydraulic
energy is directed via suitable valuing (not shown) to the hydraulic cylinders
46; the
cylinders operate to impart a translational (linear) movement to the feed
screw 14 by
applying a force to the housing 36.
The forward movement of feed screw 14 causes the plastic melt accumulated at
the end of the barrel to be forced out of the barrel and into the mold cavity.
During
injection, a braking motor 50 is energized to impart sufficient force to the
drive belt 70 to
keep the feed screw 14 from rotating in a clockwise direction when the feed
screw 14 is
moved forward to inject the plastic melt. (The force of the plastic melt on
the flight of the
feed screw 14 creates a torque that tends to rotate feed screw 14.) Upon
completion of
the injection function, the cylinders 46 are used to maintain pressure on the
plastic melt
("pack and hold) to ensure that the part is properly formed.
At the beginning of the pack and hold interval, the motor 20 reverses rotation
to
begin another extrusion function as described previously. The accumulator 48
provides
the hydraulic energy required to maintain operation of the cylinders 46 while
the motor 20
is rotating the feed screw. Similarly, the accumulator 48 would provide the
hydraulic
energy to open the mold after pack and hold is complete. Depending on the
duration of
5

CA 02345949 2001-03-29
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the extrusion operation, the hydraulic energy required to operate the eject
system and/or
close the clamp system in preparation for injection, is supplied by the
accumulator 48
and/or pump stack 26 as required by the components of the injection molding
machine 1.
Industrial An~licabilitv
Overall, the present invention provides a compact drive system for a single
motor
to power all machine axes; this improves reliability and allows faster
response over prior
art systems that require a shift mechanism to divert power to the different
axes.
Advantages of the preferred embodiment.include: better utilization of motor
capacity,
improved energy efficiency, reduced overall machine cost and more accurate
control of
feed screw rotation.
While the invention has been illustrated in some detail according to the
preferred
embodiment shown in the accompanying drawings, and while the preferred
embodiment
has been described in some detail, there is no intention to thus limit the
invention to such
detail. On contrary, it is intended to cover all modifications, alterations,
and equivalents
falling within the scope of the appended claims. For example, although the
drive
couplings are generally described as belts and pulleys, other mechanical
couplings, such
as suitable gearing, can be used to perform the same function.
6

Representative Drawing