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
2002-04-04
2004-11-09
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
C425S149000
Reexamination Certificate
active
06814558
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
1. Field of the Invention
The present invention relates to a ball screw nut support device for converting rotational motion into linear motion or a ball screw nut support device for inversely converting linear motion into rotational motion, and an injection molding machine incorporating the ball screw nut support device. More particularly, it relates to a support construction for a plurality of ball screw nuts that individually support a load in the one-side direction of a ball screw used for injection, mold opening/closing, mold clamping, and linear driving of an ejector etc. in an electric injection molding machine.
2. Description of Related Art
Conventionally, as a driving source for a straight movement axis of an injection molding machine, oil pressure has mainly been used. In recent years, however, electrical drive has often been used because of its advantage that the work environment is improved, the electric energy efficiency is increased, and the control of the velocity, position, and the like of a working portion is facilitated. Specifically, as a driving source for injection drive of an injection screw, platen movement of mold clamping device, mold clamping, and linear movement of the ejector etc., an electric servomotor and a ball screw construction having the highest mechanical efficiency for converting the rotation of the motor into linear drive have been used.
Some electric injection driving unit for the conventional injection molding machine has one or two drive motors. In the case where one drive motor is provided, a pair of screws and nuts for converting the rotation into linear motion are provided symmetrically on both sides of the injection screw to balance the driving force, and the power is transmitted by a toothed belt for transmission or a gear train (for example, see an injection device of an injection molding machine disclosed in Japanese Patent Publication No. 8-9184 (No. 9184/1996)).
Although the above-described conventional electric injection driving unit has no problem when being used for a small-sized injection molding machine, when being used for an injection molding machine of a middle or larger size, a pressure required for injection at the time of injection is very high, so that a specially designed motor is needed to deliver high torque, and therefore it has a problem in that not only the cost is high but also the arrangement balance at the time of mounting of injection molding machine is bad.
In the injection drive of injection molding machine, when molten resin stored at the tip end of the injection screw is pushed rapidly into a mold cavity by advancing the injection screw, the injection screw requires a great pushing force. Therefore, when a ball screw is used for injection drive, the load is high in the one-side direction of straight reciprocating drive caused by the ball screw, so that the allowable maximum loading force of the ball screw is selected so as to correspond to the pushing force at the time of injection drive. Also, the loading force of ball screw is calculated by the pressure withstanding the rolling of a ball held between a screw groove and a ball nut groove, and the loading capacity in designing is calculated assuming that an even pressure is applied to working balls on the working spiral of screw.
In the case where a ball screw is used for the injection drive of a small-sized injection molding machine, even if a ball screw of a size having a loading capacity corresponding to the driving force of ball screw or a ball screw of a size exceeding the loading capacity is selected, the ball screw can be selected from commercially available standard sizes, so that the cost of ball screw device scarcely poses a problem. However, when the injection pressure increases in an injection molding machine of a middle or larger size, the size of ball screw becomes out-of-standard, so that the cost presents a big problem, and thus limit design is required.
When a high tensile force is applied in the axial direction of a ball screw shaft, the ball screw shaft elongates in its portion between a bearing on the fixed side and a ball nut, and the ball nut is also elongated or contracted by the axial force. Therefore, the screw pitch on the screw side of ball screw shifts from that on the ball nut side thereof, and thus the pressure received by the ball changes depending on the axial position.
FIG. 18
shows a conventional ball screw device disclosed in Japanese Patent Provisional Publication No. 2000-108175 (No. 108175/2000). This ball screw device is constructed so that a ball screw shaft
010
is rotated by being driven on the left-hand fixed side, not shown, and is restrained axially by a strong thrust bearing, so that a moving frame
06
connected to an injection screw by a ball screw of the ball screw shaft
010
is pushed by a ball screw nut
011
and thereby is moved in the injection direction indicated by an arrow mark. Reference numeral
59
denotes a flange-shaped pressure sensor (load cell).
In the construction of this ball screw device, as shown in a schematic view of FIG.
19
-(I) and a characteristic graph of FIG.
19
-(II) showing load as a function of axial nut width, the load received by a ball increases toward the working end of the ball nut
011
. Since the capacity of a ball screw
050
increases, even if the length of the ball nut
011
is increased, deformation is greater at the end of the nut
011
, and a tendency for the load at the working end to increase cannot be avoided. Reference numeral
04
denotes a fixed-side member that pivotally supports the ball screw shaft
010
via a bearing.
A ball screw device for injection drive of injection molding machine, which has been disclosed in Japanese Patent Provisional Publication No. 2000-185339 (No. 185339/2000), is constructed as described below. As shown in
FIG. 20
, a plurality of ball nuts
052
,
053
, which fit on a ball screw shaft
051
driven by an electric motor, are disposed in series on one ball screw shaft, and fluid pressure cylinders
054
and
055
for transmitting a thrust from the ball nuts
052
and
053
to a movable member
060
of an electric injection molding machine are connected to the ball nuts
052
and
053
, respectively. Further, the cylinder chambers of the fluid pressure cylinders
054
and
055
are connected to each other by a communicating tube
056
. In this ball screw device, a load applied to the ball screw shaft
051
is distributed evenly to the ball nuts
052
,
053
so that the service life of the ball screw shaft
051
is prolonged.
As explained in the above-described conventional example, if an attempt is made to increase the length of the ball nut to obtain a ball screw nut of high load, the deformation in the end portion of nut increases, so that the load on the working end side tends to increase more and more. Also, the ball screw device constructed so that a plurality of ball nuts are threadedly engaged with the ball screw shaft in series, a working body is connected to each of the ball nuts via the fluid pressure cylinder, and the cylinder chambers of the fluid pressure cylinders are connected to each other by the communicating tube is capable of evenly distributing a load applied to the nut. In this ball screw device, however, the fluid may leak from the fluid pressure cylinder, or the position of ball nut may be changed by the compression of oil due to pipe volume, so that the injection screw may be incapable of keeping the proper positions of injection start and end.
OBJECT AND SUMMARY OF THE INVENTION
An object of the present invention is to provide a ball screw device in which an even load is applied to each of a plurality of ball screw nuts without a change of attachment position of the ball screw nut with respect to a working body. Also, another object of the present invention is to provide a ball screw device in which a plurality of ball screw nuts can share a heavy load of a ball screw shaft without a change of attachment position of the ball screw nut with respe
Ishiwada Takeshi
Kohno Kazukiyo
Kubota Koji
Yamamoto Yoshito
Heitbrink Tim
Mitsubishi Heavy Industries Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
LandOfFree
Ball screw device and injection molding machine... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Ball screw device and injection molding machine..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ball screw device and injection molding machine... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3297954