Injection molding machine

Principal parts of an injection molding machine (1) are formed by joining a stationary platen (3), moving platen (4), mold clamping mechanism section (7), and rear platen (5) in the order named, the stationary platen (3) and the rear platen (5) are connected by means of tie bars (2), and the moving platen (4) is actuated by means of the mold clamping mechanism section (7) that is provided between the rear platen (5) and the moving platen (4). Guide rods (9) are arranged protruding from that surface of the moving platen (4) which is opposite from the surface on which a stationary-side is mounted, whereby a crosshead (10) is guided in sliding motion. Further, the guide rods (9) are caused to penetrate and project from the rear platen (5), and an injection unit (8) is fixed to their respective distal ends. A slide guide for the crosshead (10) and a support guide for the injection unit (8) are formed integrally with each other, whereby the number of components used and the manufacturing cost are reduced.

TECHNICAL FIELD 
The present invention relates to an improvement of an injection molding 
machine. 
BACKGROUND ART 
Horizontal injection molding machines comprise a mold clamping unit and an 
injection unit that are arranged in the horizontal direction on a base, 
and is constructed in the following manner, as shown in FIG. 30A, for 
example. 
A mold clamping unit 96 is composed of a stationary platen 3, moving platen 
4, rear platen 5, mold clamping mechanism TG, etc. The stationary platen 3 
is fixed to a base BS, and is coupled to the rear platen 5 by means of tie 
bars 2. The moving platen 4 is located between the stationary platen 3 and 
the rear platen 5, and the tie bars 2 are passed individually through 
holes that are formed in the moving platen 4. The mold clamping mechanism 
TG is located between the rear platen 5 and the moving platen 4, and a 
crosshead 10 moves straight toward the stationary platen 3, thereby 
carrying out mold closing operation, as a ball screw BT rotates. Molds 
(stationary mold SM and moving mold MM) are fixed to the stationary platen 
3 and the moving platen 4, respectively. 
An injection unit 8 is provided on the side of the stationary platen 3 
which is remoter from the moving platen 4. When it is moved toward the 
moving platen 4 by means of a ball screw & nut (nozzle-touch mechanism) 
NT, a nozzle 12 of an injection cylinder 11 projects through a through 
hole TH in the central portion of the stationary platen 3, and comes into 
contact with the stationary-side mold SM. 
The injection molding machines described above require use of guide rods 
(not shown) for assisting the crosshead 10 in rectilinear movement. On the 
other hand, the injection unit 8 itself is mounted on the base BS of the 
injection molding machine by means of exclusive guide rods (not shown), 
such as linear motion guides, and is moved toward or away from the 
stationary platen 3. Thus, the guide rods for the crosshead 10 are 
arranged independently of the guide rods for the injection unit 8, in the 
mold clamping mechanism section. 
Vertical injection molding machines comprises a mold clamping unit and an 
injection unit that are arranged in the vertical direction. Some of them 
have the same basic construction as the aforementioned horizontal 
injection molding machines. As shown in FIG. 30B, however, a vertical 
injection molding machine disclosed in Japanese Patent Publication, KOKAI 
No. 8-52756, has the following configuration. A moving platen 4 and a rear 
platen 5 are arranged above and below a stationary platen 3, respectively, 
that is fixed to a machine frame FR, and they are coupled by means of tie 
bars 2 that penetrate the stationary platen 3. 
Molds (stationary mold SM and moving mold MM) are mounted on the stationary 
platen 3 and the moving platen 4. An injection unit 8 is located above the 
moving platen 4 (on the side remoter from the stationary platen 3), and is 
moved toward the moving platen 4 by means of a ball screw & nut 
(nozzle-touch mechanism) NT, whereupon a nozzle 12 of an injection 
cylinder 11 projects through a through hole TH in the central portion of 
the moving platen 4, and comes into contact with the moving-side mold MM. 
A mold clamping mechanism TG is located between the stationary platen 3 
and the rear platen 5, and a crosshead 10 is moved straight toward the 
stationary platen 3 by means of a ball screw BT. 
The aforementioned vertical injection molding machine, which uses a 
toggle-type mold clamping mechanism, also require use of guide rods (not 
shown) for assisting the crosshead 10 in rectilinear movement. On the 
other hand, the injection unit 8 is guided by exclusive guide rods (not 
shown) set up on the moving platen 4 as it moves toward or away from the 
stationary platen 3. Thus, the guide rods for the crosshead 10 are 
arranged, independently of the guide rods for the injection unit 8, in the 
mold clamping mechanism section. 
Both the horizontal injection molding machine of FIG. 30A and the vertical 
injection molding machine of FIG. 30B are subject to the following 
problems. 
(a) The overall length is equal to the sum of the length of the injection 
unit 8 and the length of the mold clamping unit 96, so that it is 
considerably long. 
(b) The guide rods are needed to assist the crosshead 10 of the toggle-type 
mold clamping mechanism in rectilinear movement. Also, these guide rods 
are mounted in the mold clamping mechanism section. Since the guide rods 
for assisting the injection unit 96 in rectilinear movement are provided 
on the base BS of the injection molding machine or set up on the side of 
the moving platen 4 remoter from the mold clamping unit, however, the 
guide rods for the crosshead 10 cannot play the part of the guide rods for 
the injection unit 96. 
An example that deals with the aforesaid problem (a) is disclosed in 
Japanese Patent Publication, KOKAI No. 8-57896. According to this prior 
art, the overall length of the injection molding machine is made shorter 
than the sum of the length of the injection unit 8 and the length of the 
mold clamping unit 96. Referring now to FIGS. 31A and 31B, this 
arrangement will be described. 
FIG. 31A is a general view of a horizontal injection molding machine, in 
which a moving platen 4 and a rear platen 5 are arranged on one and the 
other sides, respectively, of a stationary platen 3 that is fixed to a 
machine frame FR, and the moving platen 4 and the rear platen 5 are 
coupled by means of tie bars 2 that penetrate the stationary platen 3. 
Molds (stationary mold SM and moving mold MM) are fixed to the stationary 
platen 3 and the moving platen 4. An injection unit 8 is located on that 
side of the rear platen 5 remoter from the moving platen 4, and is moved 
straight toward the stationary platen 3 through a center hole 32 in the 
rear platen 5 by means of a ball screw & nut (nozzle-touch mechanism) NT. 
A nozzle 12 of an injection cylinder 11 projects through a through hole 33 
in the central portion of the stationary platen 3, and comes into contact 
with the stationary-side mold SM. 
As shown in FIG. 31B, a mold clamping mechanism TG is located between the 
rear platen 5 and the stationary platen 3, and a crosshead 10 (or a ball 
nut that replaces the crosshead) moves straight toward the stationary 
platen 3 as a ball screw BT rotates. 
According to the prior art (FIG. 31A) disclosed in KOKAI No. 8-57896, as is 
evident from comparison between FIGS. 31A and 30A, the overall length of 
the injection molding machine is so short that the aforesaid problem (a) 
is solved. However, the aforesaid problem (b) is left unsolved. Thus, 
according to this prior art, the guide rods (not shown) are needed to 
assist the crosshead 10 (or the ball nut that replaces it). Since these 
guide rods cannot play the parts of any other members, however, a number 
of pieces of parts have to be provided. 
According to this prior art, as shown in FIG. 31A, moreover, both the mold 
clamping mechanism TG and the injection cylinder 11 are located between 
the rear platen 5 and the stationary platen 3, so that the construction of 
the mold clamping mechanism TG is subject to restrictions. 
This is because a plurality of links 88 must be arranged so as to surround 
the injection cylinder 11 in the center. In consequence, the ball screw 
BT, the crosshead 10 (or the ball nut that replaces it), and a coupling 
link for connecting each link 88 and the crosshead 10 must be provided for 
each of the links 88 so that the links 88 can bend and stretch separately, 
as shown in FIG. 31B. Also, there is a problem such that a strong bending 
moment acts on the ball screws BT that are in engagement with the 
crossheads 10 when the toggle links 88 are locked up. 
DISCLOSURE OF THE INVENTION 
The object of the present invention is to provide an injection molding 
machine with a reduced overall length, in which guide rods for guiding a 
crosshead of a mold clamping mechanism section are used also as guide rods 
for guiding an injection unit, whereby the number of components therein is 
reduced. 
In order to achieve the above object, an injection molding machine 
according to the present invention comprises: a stationary platen fixed to 
a machine frame of the injection molding machine; a rear platen fixed to 
the respective one ends of a plurality of tie bars, the respective other 
ends of the tie bars being fixed to the stationary platen; a moving platen 
arranged between the stationary platen and the rear platen with the tie 
bars passing through the through holes formed on the moving platen for the 
passage of the tie bars; an injection unit arranged on the side of the 
rear platen not opposed to the moving platen and fixed to the respective 
one ends of guide rods, the respective other ends of the guide rods being 
fixed to the surface of the moving platen on which a moving mold is not to 
be mounted; a moving mold and a stationary mold which are mounted opposite 
on the moving platen and the stationary platen, respectively; and a 
toggle-type mold clamping mechanism arranged between the rear platen and 
the moving platen and is provided with a crosshead having through holes 
formed for the passage of the guide rods, with the guide rods passing 
through the through holes. An injection cylinder of the injection unit 
passes through hole formed in the center of the rear platen, a gap formed 
in the center of the mold clamping mechanism, and a through hole formed in 
the center of the moving platen; the crosshead moves in a straight line, 
guided by the guide rods, when the crosshead is driven, so that the moving 
platen and the injection unit, coupled to the moving platen by means of 
the guide rods, moves toward or away from the stationary platen. 
According to the present invention, slide guiding for the crosshead of the 
mold clamping mechanism section and support of the injection unit can be 
achieved simultaneously by using a single guide rod, so that exclusive 
guides need not be provided for supporting the crosshead and the injection 
unit. Thus, the number of components used and the manufacturing cost of 
the injection molding machine can be reduced. 
Since mold clamping and mold opening operations are carried out by means of 
a plurality of toggle links that are connected to the single crosshead, 
moreover, a force from the crosshead links that acts during the mold 
clamping operation is canceled in the crosshead, and stable mold clamping 
and mold opening operations can be carried out without any undue bending 
moments acting on ball screws for driving the crosshead or the guide rods.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring first to FIGS. 1 to 17, a first embodiment of the present 
invention will be described. 
Referring to FIGS. 1 and 2, an arrangement of principal parts of a vertical 
injection molding machine 1 according to the first embodiment will be 
described. 
A mold clamping mechanism section 7 of the vertical injection molding 
machine 1 uses three tie bars 2 that are arranged at regular intervals on 
the circumference of a circle around an axis C--C. A stationary platen 3 
is coupled to the respective lower ends of these tie bars 2, and a rear 
platen 5 to the upper ends. Thus, the space between the stationary platen 
3 and the rear platen 5 is kept constant. A moving platen 4 is arranged 
between the stationary platen 3 and the rear platen 5. The moving platen 4 
is formed with through holes that have a diameter large enough to allow 
free passage of the tie bars 2. The tie bars 2 penetrate these through 
holes, individually, for sliding motion. The stationary platen 3, moving 
platen 4 and rear platen 5 have a form of an equilateral triangle with the 
vertexes thereof cut off, each. FIG. 3 shows the form of the stationary 
platen 3. 
Arranged between the rear platen 5 and the moving platen 4, moreover, is a 
mold clamping mechanism section 7 that includes toggle links 6. As the 
mold clamping mechanism section 7 is actuated (toggle links 6 bend or 
stretch), the moving platen 4 moves toward or away from the stationary 
platen 3. In FIGS. 1 and 2, the portion on the left-hand side of the axis 
C--C represents a state in which the moving platen 4 is situated remote 
from the stationary platen 3, while the right-hand side portion represents 
a state in which the moving platen 4 is situated nearest to the stationary 
platen 3. 
The moving platen 4 is fitted with a moving mold (not shown) on that 
surface thereof which faces the stationary platen 3, and the stationary 
platen 3 is fitted with a stationary mold (not shown) on that surface 
thereof which faces the moving platen 4. A mold thickness adjusting 
mechanism 14 (mentioned later) is provided on the side of the stationary 
platen 3. 
As shown FIG. 1, three guide rods 9 are set up individually on air 
cylinders 13 (mentioned later) on the upper surface (on the side remoter 
from the stationary platen 3) of the moving platen 4. These guide rods 9 
are arranged at regular intervals on the circumference of a circle around 
the axis C--C, and as shown in FIG. 5, are arranged nearer to the center 
(axis C--C) than the tie bars 2. The guide rods 9 penetrate a crosshead 10 
that constitutes part of the mold clamping mechanism section 7, and 
further penetrate the rear platen 5 so as to project above it, having 
their respective upper end portions fixed to an injection unit 8 that is 
provided with an injection cylinder 11. Thus, the moving platen 4 and the 
injection cylinder 11 are coupled to each other by means of the guide rods 
9, and the injection cylinder 11 is provided on the upper side of the rear 
platen 5 (the side not opposed to the moving platen 4). 
When its axis is in line with the axis C--C of the injection molding 
machine, the injection cylinder 11 penetrates a through hole 32 bored in 
the central portion of the rear platen 5, a through hole 43 bored in the 
central portion of the crosshead 10, and a through hole 33 bored in the 
central portion of the moving platen 4. 
The crosshead 10 of the mold clamping mechanism section 7 is guided for 
up-and-down motion (motion in the mold opening or closing direction) by 
the guide rods 9. When the crosshead 10 is actuated (mentioned later), the 
mold clamping mechanism section 7 operates so that the distance between 
the rear platen 5 and the moving platen 4 changes. Thus, the moving platen 
4 moves in the direction of the axis C--C. When the moving platen 4 moves, 
the injection cylinder 11, which is coupled to the moving platen 4 by 
means of the guide rods 9, also moves at the same time without changing 
its position relative to the moving platen 4. 
As the moving platen 4, having the moving-side mold (not shown) fixed 
thereon, moves in the mold clamping direction, therefore, the injection 
cylinder 11 moves integrally with the moving-side mold, and the distal end 
of a nozzle 12 is kept in contact with a sprue of the moving-side mold 
that is mounted on the moving platen 4. Thus, a nozzle-touch state is 
maintained. 
According to this embodiment, as described above, the guide rods 9 for 
supporting the injection unit 8 on the moving platen 4 to keep the 
distance between the injection unit 8 and the moving platen 4 constant 
serve also as guide rods for guiding the crosshead 10 of the mold clamping 
mechanism section 7 in rectilinear movement. Thus, the number of 
components used can be reduced. 
As shown in FIG. 1, moreover, the guide rods 9 are fixed to the moving 
platen 4 by means of the air cylinders 13, individually. By causing these 
three air cylinders 13 synchronously to project, therefore, the nozzle 12 
can be separated as required from the sprue of the moving-side mold so 
that it can carry out sprue-break operation. A drive mechanism for moving 
the guide rods 9 up and down may be formed of a rectilinear motion 
mechanism that comprises ball screws, ball nuts, etc., as well as of the 
air cylinders 13. 
The following is a description of arrangements of various parts, such as 
the mold thickness adjusting mechanism, mold clamping mechanism section 7, 
etc., which constitute the vertical injection molding machine 1 according 
to the first embodiment. 
[Mold Thickness Adjusting Mechanism] 
As shown in FIG. 1, a broadened rectangular stopper portion 15 is provided 
integrally on the upper end of each of the three tie bars 2. As shown in 
FIG. 7, each stopper portion 15 is fixed to the rear platen 5 by means of 
bolts that penetrate its four corners, individually. As a result, the rear 
platen 5 is fixed to the tie bars 2 so as to keep a fixed distance from 
the stationary platen 3. In order to regulate the distance between the 
stationary platen 3 and the rear platen 5 based on the mold thickness, 
therefore, it is necessary to adjust the amount of plunge of the lower end 
portions of the tie bars 2 with respect to the stationary platen 3. The 
mold thickness adjusting mechanism 14 for carrying out this adjustment is 
provided on the side of the stationary platen 3. 
As shown in FIG. 1, the lower end portion of each tie bar 2 projects 
downward through the stationary platen 3, and an external thread portion 
cut in the lower end portion of each tie bar 2 is screwed in a die height 
adjusting nut 17 that is mounted on the lower surface side of the 
stationary platen 3 (on the side remoter from the moving platen 4) so as 
to be rotatable and immovable in the axial direction. Since a peripheral 
wall is formed integrally on the outer peripheral portion of the lower 
surface of the stationary platen 3 to form a cup-shaped base, machine 
elements such as the die height adjusting nut 17 never interfere with the 
floor surface. As shown in FIG. 4, moreover, an external gear 18 in the 
form of a circular ring internally touching a thread portion cut in the 
outer peripheral portion of each die height adjusting nut 17 is rotatably 
held on the lower surface of the stationary platen 3 by means of four 
rollers 19, and is rotated by a die height adjusting motor 20 fixed to a 
side of the peripheral wall of the stationary platen 3, through an 
intermediate gear 21. 
When the die height adjusting motor 20 is actuated, the intermediate gear 
21 and the external gear 18 rotate, and moreover, the three die height 
adjusting nuts 17 in contact with the external gear 18 rotate all together 
in the same direction. Thus, all the three tie bars 2 that are screwed 
individually in the die height adjusting nuts 17 synchronously project 
upward or recede downward together from the stationary platen 3, whereby 
the distance between the stationary platen 3 and the rear platen 5, that 
is, the mold thickness, is adjusted. Alternatively, the external gear 18 
(FIG. 4) may be replaced with a pulley of the same diameter such that the 
power of the die height adjusting motor 20 can be transmitted by means of 
a timing belt. If a peripheral groove having a depth greater than the 
thickness of the timing belt is formed in the thickness-direction central 
portion of the outer peripheral portion of the pulley, the timing belt can 
be prevented from interfering with the die height adjusting nuts 17. 
[Ejector Mechanism] 
As shown in FIGS. 1 and 4, an ejector mechanism 22, along with the mold 
thickness adjusting mechanism 14, is provided on the surface of the 
stationary platen 3 which is opposite from the side on which the 
stationary mold is mounted. 
The ejector mechanism 22 is composed of ball screws 24 mounted on the 
aforesaid surface of the stationary platen 3 by means of bearings 23 so as 
to be rotatable and immovable in the axial direction, pulleys 25 fixed 
integrally on the respective proximal portions of the ball screws 24, ball 
nuts 26 in mesh with the ball screws 24, individually, an ejector plate 27 
having the ball nuts 26 fixed integrally thereon, an ejector rod 28 set up 
integrally on the central portion of the ejector plate 27 and penetrating 
a hole in the central portion of the stationary platen 3, plate guides 29 
set up on the lower surface of the stationary platen 3 and penetrating the 
ejector plate 27, etc. 
As shown in FIG. 4, the ejector plate 27 has a substantially square 
external shape, and the ball screws 24 and the plate guides 29 are 
arranged in two sets in positions on diagonal lines corresponding to the 
four corners of the square. A timing belt 30, which is driven by means of 
an ejector servomotor 31, is passed around the pulleys 25 on the 
individual ball screws 24. As the ejector servomotor 31 rotates, the two 
ball screws 24 synchronously rotate in the same direction. As a result, 
the ejector plate 27, which has the ball nuts 26 fixed integrally thereon, 
moves toward or away from the stationary platen 3 along the two plate 
guides 29, and the ejector rod 28, which is fixed to the ejector plate 27, 
projects or recedes from that surface of the stationary platen 3 on which 
the stationary-side mold is mounted, thus moving in the mold clamping or 
mold opening direction, and drives an ejector pin of the stationary mold 
(not shown). 
[Moving Platen] 
As shown in FIGS. 5 and 6, the moving platen 4 fitted on which a moving 
mold is mounted, like the stationary platen 3 (FIG. 3), has a form of an 
equilateral triangle with the vertexes cut off. A through hole 33 is bored 
in its central portion, through which the injection cylinder 11 is passed. 
Through holes in which the tie bars 2 are slidingly fitted are provided 
individually in three spots on the outer peripheral portion corresponding 
to the vertexes of the equilateral triangle. 
As shown in FIG. 5, moreover, the three guide rods 9, which are situated 
inside the tie bars 2 corresponding thereto in position, are set up on the 
upper surface (the surface on which a moving mold is not to be mounted) of 
the moving platen 4 by means of the air cylinders 13, individually. 
Further, a staple 35 for pivotally mounting a first link 34, which 
constitutes part of each toggle link 6, is fixed on the portion of the 
upper surface of the moving platen 4 which is situated between each two 
adjacent tie bars 2. As shown in FIG. 5, the first link 34 is bifurcated 
at its end portion, and the staple 35 is provided with three projections 
that pivotally support the first link 34 so as to hold the bifurcated 
portion between them. The first link 34 rocks in the diametrical direction 
of the through hole 33. 
[Rear Platen] 
As shown in FIGS. 7 and 8, the rear platen 5, like the moving platen 4 and 
the stationary platen 3, has a form of an equilateral triangle with the 
vertexes cut off. A through hole 32 is bored in its central portion, 
through which the injection cylinder 11 is passed. As shown in FIG. 7, 
moreover, the stopper portions 15 on the respective end portions of the 
tie bars 2 are fixed with bolts individually at three spots on the outer 
periphery of the upper surface (surface not opposed to the moving platen 
4) of the rear platen 5. Further, through holes for the passage of the 
guide rods 9 are bored through the portions of the rear platen 5 which are 
situated nearer to the through hole 32 than the positions in which the 
stopper portions 15 are fixed. 
As shown in FIG. 8, a staple 39 for pivotally mounting a second link 38, 
which constitutes part of each toggle link 6, is fixed on the portion of 
the lower surface of the rear platen 5 which is situated between each two 
adjacent tie bars 2. An end portion of the bifurcated second link 38 is 
pivotally attached to the staple 39. As shown in FIG. 2, the other end 
portion of the second link 38 is pivotally attached to the first link 34. 
[Mold Clamping Mechanism Section] 
In the injection molding machine according to this embodiment, as mentioned 
before, the injection cylinder 11 penetrates the center of the mold 
clamping mechanism section. Unlike the conventional toggle-type mold 
clamping mechanism, the mold clamping mechanism section 7 cannot be 
designed so that the ball screws and the like for driving the crosshead 10 
are arranged penetrating its center. 
To cope with this problem, according to the present embodiment, bearings 36 
(FIG. 1) are embedded individually in three positions on the outer 
periphery of the rear platen 5 outside the positions in which the tie bars 
2 penetrate the rear platen 5. Ball screws 37 for driving the crosshead 10 
are supported individually by means of the bearings 36 so as to be 
rotatable and immovable in the axial direction. A pulley 46 is fixed to 
the upper end of each ball screw 37. As shown in FIG. 7, a timing belt 48 
is passed around the pulleys 46 and a servomotor 47 for mold clamping so 
that the three ball screws 37 synchronously rotate in the same direction 
as the servomotor 47 for mold clamping rotates. Reference numeral 49 
denotes a small pulley for regulating the path of travel of the timing 
belt 48. 
As shown in FIGS. 8 and 9, the crosshead 10 is formed of a sheet of a 
substantially Y-shaped plate. More specifically, it has a form such that 
three arm portions protrude radially from its central portion at intervals 
of 120.degree. between them. Each arm portion is formed with a through 
hole 41 through which a tie bar 2 passes and a through hole 42 through 
which a rod 9 passes. Integrally embedded in the extreme end portion of 
each arm portion, moreover, is a ball nut 40 to mate with each 
corresponding ball screw 37. The crosshead 10 is guided mainly by the 
guide rods 9 in movement in the direction of the axis C--C. 
Further, the through hole 43 through which the injection cylinder 11 passes 
is bored in the central portion of the crosshead 10. As shown in FIG. 9, 
moreover, a staple 45 for pivotally mounting one end of a crosshead link 
44 (FIG. 2) is fixed to the portion of the outer peripheral portion of the 
central portion of the crosshead 10 which is situated between each two 
adjacent arm portions. As shown in FIG. 2, the other end of each crosshead 
link 44 is pivotally mounted on the central portion of its corresponding 
second link 38. 
Thus, when the servomotor 47 for mold clamping is driven to rotate the 
three ball screws 37 (FIG. 1) synchronously, thereby feeding the crosshead 
10 toward the rear platen 5, the second links 38 and the first links 34, 
which constitute the toggle links 6, bend to carry out mold opening 
operation (state on the left-hand side of the dashed line of FIGS. 1 and 
2). When the crosshead 10 is fed away from the rear platen 5, in contrast 
with this, the second links 38 and the first links 34 stretch, thereby 
carrying out mold clamping operation (state on the right-hand side of the 
dashed line of FIGS. 1 and 2). 
When locking up the mold is completed, strong forces from the second links 
38 and the first links 34 act so as to push in the crosshead links 44. The 
staples 45 (FIG. 9) that support the crosshead links 44 are fixed to the 
crosshead 10 formed of a Y-shaped plate, arranged circumferentially at 
regular intervals around the axis C--C, so that forces to press the 
crosshead links 44 are perfectly balanced as an internal stress of the 
crosshead 10. In this case, unlike the prior art case (example disclosed 
in KOKAI No. 8-57896) shown in FIGS. 31A and 31B, therefore, no 
substantial forces externally act so as to drive out the crosshead 10 
sideways, and there act neither bending moments on the ball screws 37 that 
are connected to the crosshead 10 nor forces to press the through holes 41 
and 42 of the crosshead 10 against the guide rods 9. 
[Injection Unit] 
As shown in FIG. 14 the injection unit 8, which is fixed to the respective 
distal ends of the guide rods 9 projecting upward from the rear platen 5, 
is composed of a front plate 50, pusher plate 51, rear plate 52, tie rods 
53, etc., in general. 
As shown in FIG. 10, the front plate 50 has a shape obtained by 
concentrically joining together two equilateral triangles of the same 
shape with an angular shift of 60.degree.. As shown in FIGS. 10 and 15, 
those three spots on the outer peripheral portion which correspond 
individually to the vertexes of one of the equilateral triangles are fixed 
individually to the respective distal ends of the guide rods 9. As shown 
in FIG. 14, the three tie rods 53 are set up integrally by means of bolts 
or the like on those three spots on the outer peripheral portion which 
correspond individually to the vertexes of the other equilateral triangle. 
As shown in FIG. 11, moreover, a water jacket (not shown) and a mounting 
portion 54 for mounting the injection cylinder 11 are provided on the 
lower surface (surface opposed to the rear platen) of the front plate 50, 
and a through hole 56 to be penetrated by an injection screw 55 is bored 
through the center of the front plate 50. 
As shown in FIGS. 12 and 13, the pusher plate 51 has substantially the same 
external shape as the one equilateral triangle that constitutes the front 
plate 50. Through holes to be penetrated by the tie rods 53 are bored in 
positions corresponding individually to the vertexes of the equilateral 
triangular shape of the pusher plate 51, and a bush 57 (FIG. 4) is fitted 
in the inner peripheral surface of each through hole. 
As shown in FIGS. 16 and 17, the rear plate 52 also has substantially the 
same external shape as that of the pusher plate 51. The rear plate 52 is 
fixed to the respective end portions of the tie rods 53 by means of bolts 
or the like. 
As shown in FIG. 14, an injection pulley 59 and an injection ball screw 60 
are fixed to a sleeve 61, which is fitted in a large-diameter through hole 
58 formed in the central portion of the pusher plate 51 by means of two 
bearings so as to be rotatable and immovable in the axial direction. A 
screw fixing sleeve 63, having a screw rotating pulley 62 fixed integrally 
thereon, is attached to the inside of the sleeve 61 by means of four 
bearings so as to be rotatable and immovable in the axial direction. 
Further, the injection screw 55 is removably fitted into a hole 64 formed 
in the lower end of the screw fixing sleeve 63, by means of a split ring 
or the like which serves as a key or cotter. 
As shown in FIGS. 12, 13 and 15, an injection servomotor 65 and a metering 
motor 66 are fixed to the outer peripheral portion of the pusher plate 51 
so that the injection pulley 59 and screw rotating pulley 62 can be 
rotated independently of each other by the individual motors with the aid 
of timing belts 67 and 68. 
As shown in FIG. 14, the sleeve 61 and the screw fixing sleeve 63 are 
independently attached to the pusher plate 51 for rotation without being 
associated with each other. When only the metering motor 66 is rotated 
with the injection servomotor 65 stopped, therefore, the screw fixing 
sleeve 63 and the injection screw 55 attached thereto rotate without 
moving in the axial direction. Also, the ball screw 60 fixed to the sleeve 
61 is screwed in a ball nut 69 that is fixed to the rear plate 52. When 
only the injection servomotor 65 is rotated with the metering motor 66 
stopped, therefore, the pusher plate 51 itself is axially fed by the 
rotatory motion of the ball screw 60, so that the pusher plate 51 moves 
toward or away from the rear plate 52, and the injection screw 55 moves 
integrally with various members attached to the pusher plate 51 in the 
axial direction. 
Since the ball nut 69 that supports the ball screw 60 is attached to the 
rear plate 52 through a ring-shaped load cell 70 (FIG. 14) that is formed 
of a magnetostrictive material, axial forces acting on the ball screw 60, 
that is, injection pressure, dwell pressure, and back pressure, can be 
detected by means of this load cell 70. 
According to this embodiment, as shown in FIG. 1, the guide rods 9 are 
mounted inside a circle that passes through the three tie bars 2, and the 
ball screws 37 are arranged outside the circle. In contrast with this, the 
guide rods 9 may be mounted outside the circle that passes through the 
three tie bars 2. In this case, the ball screws 37 are arranged inside the 
circle. 
Referring now to FIGS. 18 to 29, a second embodiment of the present 
invention and modifications of some elements thereof will be described. 
Referring first to FIGS. 18 and 19, an arrangement of principal parts of a 
vertical injection molding machine 71 according to the second embodiment 
will be described. 
Since the principal parts of this vertical injection molding machine 71, 
including a stationary platen 72, rear platen 74, moving platen 73, 
injection unit 81, mold clamping mechanism section 79, mold thickness 
adjusting mechanism 77, etc., are arranged in the same manner as their 
corresponding elements according to the first embodiment described before, 
a detailed description of those parts is omitted. In FIG. 18, the portion 
on the left-hand side of the axis C--C represents a state in which the 
moving platen 73 is situated remote from the stationary platen 72, while 
the right-hand side portion represents a state in which the moving platen 
73 is situated nearest to the stationary platen 72. 
The tie bars 2 used in the first embodiment are three in number, but, in 
the present embodiment, four tie bars 75 are used. As shown in FIGS. 20, 
21 and 23, therefore, the stationary platen 72, moving platen 73, and rear 
platen 74 have a rectangular external shape. FIG. 18 is a sectional view 
taken along line R--R of FIG. 20, and FIG. 19 is a sectional view taken 
along line P--P of FIG. 20. As shown in FIG. 20, moreover, the mold 
thickness adjusting mechanism 77 is constructed in the same manner as the 
mold thickness adjusting mechanism 14 according to the first embodiment 
except that it is provided with four tie bars 75 and four die height 
adjusting nuts 76. Also, the ejector mechanism 78 has the same 
construction as the ejector mechanism 22 according to the first embodiment 
does. 
The elements of the vertical injection molding machine 71 according to this 
second embodiment which are structurally different from their counterparts 
according to the first embodiment are mounting structures for the mold 
clamping mechanism section 79 and guide rods 82 for guiding a crosshead 80 
and an injection unit 81. The following is a description of these points. 
[Mold Clamping Mechanism Section] 
As shown in FIGS. 18 and 23, two ball screws 83 of the mold clamping 
mechanism section 79 are attached to the rear platen 74, in positions on 
either side of a center through hole to be penetrated by an injection 
cylinder, so as to be rotatable and immovable in the axial direction. 
These ball screws 83 are synchronously rotated by means of a timing belt 
85 as a servomotor 84 (FIG. 23) for mold clamping, fixed to one side of 
the rear plate 74, is driven. A small pulley 90 is means for regulating 
the path of travel of the timing belt 85. 
As shown in FIG. 18, ball nuts 86 to mate with the ball screws 83 are fixed 
to the crosshead 80. When the two ball screw 83 rotate synchronously, 
therefore, the crosshead 80 moves toward the rear platen 74 or away from 
the rear platen 74. As the crosshead 80 moves in this manner, the moving 
platen 73 is moved by means of crosshead links 87 and toggle links 88, 
whereupon mold clamping and mold opening operations are carried out. 
[Guide Rod] 
The two guide rods 82 are set up on the upper surface (surface opposed to 
the rear platen 74) of the moving platen 73 through air cylinders 89. As 
shown in FIGS. 21 and 23, these guide rods 82 penetrate through holes 
formed in the crosshead 80 and the rear platen 74 so as to project above 
the rear platen 74. As shown in FIG. 19, the injection unit 81 is fixed to 
the respective upper ends of the guide rods 82. 
Mounting positions for the two guide rods 82 on the moving platen 73 are 
selected lest the two guide rods 82 passing through the through holes in 
the rear platen 74 interfere with the ball screw 83 that are attached to 
the rear platen 74. Thus, the two guide rods 82 are arranged substantially 
on a diagonal line of the rectangular shape of the moving platen 73. As 
shown in FIG. 23, therefore, the positions in which the two guide rods 82 
penetrate the rear platen 74 are also situated on a diagonal line of the 
rectangular shape of the rear platen 74. 
As in the first embodiment, the guide rods 82 guide the crosshead 80 in 
sliding motion, the guide rods 82 support the injection unit 81, and 
sprue-break and nozzle-touch operations are carried out as the air 
cylinders 89 project or recede. 
The injection unit 81 differs from the one according to the first 
embodiment in that its front plate, pusher plate, and rear plate have a 
rectangular shape and are connected by means of four tie rods 91. However, 
drive mechanisms for the individual parts are substantially equivalent to 
those of the injection unit 8 according to the first embodiment described 
with reference to FIG. 14. In FIGS. 18 and 24, reference numerals 92 and 
93 denote a metering motor and an injection servomotor, respectively. 
Referring now to FIGS. 25 to 29, modifications of the second embodiment 
will be described. 
[First Modification] 
As shown in FIG. 25, four sets of toggle links 88 are arranged on the upper 
surface (the surface opposed to a rear platen 74) of a moving platen 73. A 
set of double-toggle link is formed from those two sets of toggle links 
88, among these toggle links 88, which are opposed in the direction of the 
short sides of the rectangular shape of the moving platen 73. Thus, two 
sets of double-toggle links are formed from the four sets of toggle links 
88. In order to maintain the balance between each pair of sets of toggle 
links 88, a ball screw 83 for feeding a crosshead 94 is arranged halfway 
between those two sets of toggle links 88. Mounting positions for two 
guide rods 82 on the moving platen 73 are located halfway between those 
two sets of toggle links 88 which are opposed in the direction of the long 
sides of the rectangular shape of the moving platen 73. 
As shown in FIG. 26, the crosshead 94 has a form such that two long arms 
and two short arms protrude from its central portion that has a through 
hole for the passage of an injection cylinder in the center. A ball nut to 
mate with each ball screw 83 is embedded in the extreme end portion of 
each long arm, and staples 95 are provided individually on the left- and 
right-hand outer peripheries of the extreme end portion. Pivotally mounted 
on the staples 95 are crosshead links connected to the paired toggle links 
88. Formed individually in the respective extreme end portions of the 
short arms, moreover, are through holes through which the guide rods 82, 
set up individually on the air cylinders 89 on the upper surface of the 
moving platen 73, are passed, and the crosshead 94 is guided by the guide 
rods 82. 
[Second Modification] 
In the first modification described above, as shown in FIG. 25, the 
mounting positions for the guide rods 82 on the moving platen 73 are 
located halfway between those two sets of toggle links 88 which are 
opposed in the direction of the long sides of the rectangular shape of the 
moving platen 73, so that a line that connects the two guide rods 82 
extends at right angles to a line that connects the two ball screws 83. 
Alternatively, the two guide rods 82 may be mounted on the moving platen 
73 so that the line that connects them is situated on extensions of the 
line that connects the two ball screws 83, as shown in FIG. 27. 
According to this arrangement, the crosshead 94 used in this modification 
has a form such that two long arms protrude from its central portion that 
has a through hole for the passage of an injection cylinder in the center, 
as shown in FIG. 28. A ball nut to mate with each ball screw 83 is 
embedded in the proximal end portion of each arm, and a through hole for 
the passage of each guide rod 82 is formed on the distal end portion. 
[Third Modification] 
In the second modification described above, no interactive forces act 
between one pair of toggle links 88 and the other pair of toggle links 88. 
Accordingly, the crosshead 94 may be divided into two crossheads 94a and 
94b, as shown in 29, instead of being formed integrally in the manner 
shown in FIG. 28. In this case, the ring-shaped central portion that 
connects the two arm portions and allows the passage of the injection 
cylinder can be omitted, so that replacement of the injection cylinder can 
be facilitated. 
Although the first and second embodiments of the vertical injection molding 
machine described above, are vertical injection molding machines, these 
knowledge can be also applied to a horizontal injection molding machine. 
In this case, the same results such as reduction in the number of 
components used and reduction in manufacturing cost as in the case of the 
vertical injection molding machine can be obtained.