JP2014100864A - Electrically-driven injection unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrically-driven injection unit without increase in the size of a ball screw and cost.SOLUTION: A ball screw 20 which an electrically-driven injection unit 1 has includes: a screw shaft 21 that penetrates a front plate 40 and a bearing housing 30; and a nut 22 that is fixed to a rear part of the bearing housing 30. In the bearing housing 30, a thinned part 50 that comparts the bearing housing 30 into a nut region 30A in which the nut 22 is located, and that extends in a direction that crosses a screw 11, and a body area 30B that performs cantilever support of the nut region 30A at an outer peripheral side of the bearing housing 30 is formed.

Description

  The present invention relates to an electric injection apparatus that drives a screw back and forth with a motor and a ball screw.

The electric injection apparatus uses a motor as a drive source for driving the screw back and forth, and includes a ball screw that converts a rotational motion by the motor into a linear motion.
The base end side of the cylinder and screw is supported by a support device 80 shown in FIG. The support device 80 includes a front plate 81 whose position is fixed, and a bearing housing 82 that is provided behind the front plate 81 and is close to or separated from the front plate 81. A cylinder 83 is fixed to the front plate 81, and a screw 84 is fixed to the bearing housing 82 in the thrust direction by a built-in bearing.

A pair of ball screws 90 are provided symmetrically across the axis of the screw 84 at positions near the outer periphery of the front plate 81 and the bearing housing 82. Each screw shaft 91 of the ball screw 90 passes through the front plate 81 and the bearing housing 82 along the screw 84. A servo motor 94 for driving a ball screw is connected to the end of the screw shaft 91. The screw shaft 91 is supported by a bearing 93 provided on the front plate 81. A nut 92 provided on the screw shaft 91 is fixed to the bearing housing 82.
At the time of injection, the screw shaft 91 is rotated at a high speed by the servo motor 94, and the bearing housing 82 fixed to the nut 92 is advanced at a stroke. Thereby, the resin between the cylinder 83 fixed to the central portion of the front plate 81 and the screw 84 fixed to the central portion of the bearing housing 82 is pressurized and injected into the mold.

JP 2003-14072 A

When the screw 84 is advanced to inject the resin into the mold, a large force (injection load) that presses the bearing housing 82 is required. Therefore, the load of the ball screw 90 is applied at the position of the nut 92 that presses the bearing housing 82. Become big.
Moreover, due to the reaction force of the pressurized resin, a force X1 is applied to the center portion of the front plate 81 and the bearing housing 82 so as to push them apart. Both ends of the outer periphery of the front plate 81 and the bearing housing 82 are constrained by the force to spread. Due to the bending moment generated thereby, the front plate 81 and the bearing housing 82 are bent in a direction in which the central portions of the front plate 81 and the bearing housing 82 are separated from each other, as shown by a one-dot chain line in FIG. Along with this, a bending moment is also generated in the ball screw 90 fixed to the bearing housing 82. An arrow (X2) in FIG. 5 indicates the reaction force of the screw shaft 91 that is pulled between the front plate 81 and the bearing housing 82 by the reaction force X1.
When a bending moment is generated in the ball screw as described above, the stress of the ball screw increases because bending stress and shear stress are added to the injection load. In order to ensure the life of the ball screw, the specifications of the ball screw are determined based on the maximum stress at the time of injection, so that the ball screw becomes large. Since such a large ball screw cannot be selected from commercially available standard products, the cost increases.

  Based on the problems described above, an object of the present invention is to provide an electric injection device that can reduce the cost by avoiding an increase in the size of a ball screw.

The electric injection device of the present invention includes a cylinder and a screw, a first support to which the screw is fixed, a second support to which the cylinder is fixed, a motor that is a driving source for driving the screw back and forth, and a motor. A ball screw that converts rotational motion into linear motion and moves the first support back and forth.
The ball screw includes a second support and a screw shaft that penetrates the first support along the screw, and a nut that is provided on the screw shaft and is fixed to the rear portion of the first support.
And the present invention is a nut region where the nut is located in the first support body and extends in a direction intersecting the screw, a main body region that cantilever-supports the nut region on the outer peripheral side of the first support body, In addition, a lightening portion for partitioning the first support is formed.

Since the first support is restrained on the outer peripheral side against the reaction force of the resin at the time of injection, when the bending moment is generated and the first support is bent, the nut area follows the bending of the main body area. Without bending, the direction of narrowing the meat removal part. At that time, since the bending directions of the main body region and the nut region are opposite, the bending on the rear side of the first support body is reduced, so that the bending moment of the ball screw is reduced. In this way, the stress of the ball screw can be suppressed by applying a bending or shearing force by bending the nut region.
Accordingly, since the diameter of the screw shaft and the thickness of the nut are made small, a predetermined life can be secured even with a ball screw having low rigidity. Since such a small ball screw can be selected from commercially available standard products, the component cost of the ball screw can be reduced.

  The thinned portion in the present invention communicates with the first slit extending between the screw and the nut from the rear portion of the first support, and communicates with the first slit within the thickness of the first support. It can be comprised by the 2nd slit extended toward the outer peripheral side of a body.

In the present invention, the first support can be a substantially plate-like member that is erected perpendicular to the axis of the screw. The nut region can be formed to have a substantially rectangular shape having one side along the first slit and the other side along the second slit.
Then, since the nut region can be regarded as a substantially rectangular parallelepiped beam, it becomes easy to control the rigidity of the nut region based on the calculation. By adjusting the rigidity of the nut region so that it bends appropriately, the bending of the rear side of the first support can be reliably reduced, and the stress of the ball screw can be suppressed to a smaller level.

  In the present invention, in order to smoothly move the first support on both sides of the screw, the ball screws are provided on both sides of the axis of the screw, and the thinned portions located around the nuts of the ball screw are arranged on the axis. It can be formed symmetrically on both sides of the.

  According to the electric injection device of the present invention, it is possible to avoid the increase in the size of the ball screw and to reduce the cost.

It is the top view which fractured | ruptured a part of electric injection device concerning the embodiment of the present invention. (A) is a perspective view which shows typically the bearing housing in which a slit is formed. (B) is a top view of a bearing housing. (A) is a top view for demonstrating the behavior of the bearing housing in this embodiment. (B) is a top view for demonstrating the behavior of the bearing housing in a prior art example. It is a graph which shows each deflection amount with the case where a slit is not formed, and this embodiment in which a slit is formed. It is a top view which shows the conventional electric injection apparatus.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
As shown in FIG. 1, the electric injection device 1 of this embodiment includes a cylinder 10, a screw 11 inserted inside the cylinder 10, a motor 12 for rotating the screw 11, and a screw 11 that moves forward and backward. And a pair of ball screws 20 that convert the rotational motion by the servo motor 13 into linear motion, and a support device 3 that supports these components.

A hopper (not shown) is provided at the base end of the cylinder 10. The pellets of thermoplastic resin are supplied into the cylinder 10 through the hopper. The resin pellet is sandwiched between the screw 11 rotated by the motor 12 and the inner wall of the cylinder 10 and sheared. While being plasticized and melted by heat generated by the shearing and heating by the heating means provided on the outer periphery of the cylinder 11, It is sent toward the tip of the cylinder 10. When the servo motor 13 is operated and the screw 11 is advanced by the ball screw 20, the molten resin stored at the tip of the cylinder 10 is injected into a mold (not shown).
Hereinafter, the direction in which the screw 11 advances during injection will be described as the front and the opposite side as the rear.

The support device 3 includes a bearing housing 30 and a front plate 40 provided in front of the bearing housing 30. These are all substantially plate-shaped and are provided in a posture perpendicular to the axis A of the screw 11.
The bearing housing 30 incorporates a bearing (not shown) that rotatably supports the base end side of the screw 11 and fixes the screw 11 in the thrust direction. The base end of the screw 11 is connected to the output shaft of the motor 12.
The bearing housing 30 is moved back and forth while being guided by a guide rod (not shown) provided along the front-rear direction.
In the bearing housing 30, a pair of through holes 31 are formed on both sides (left and right sides) of the screw 11. The screw shaft 21 of the ball screw 20 is inserted through each of the through holes 31.
Both the bearing housing 30 and the front plate 40 are cast.

One side of the front plate 40 faces the bearing housing 30 and is installed on the floor or the like so as not to move. An insertion hole 41 into which the cylinder 10 is inserted is formed in the front plate 40 so as to penetrate in the thickness direction. The cylinder 10 inserted into the insertion hole 41 is fixed to the front plate 40 by shrink fitting or the like.
The front plate 40 incorporates a bearing 42 that supports the screw shaft 21 of the ball screw 20. The bearings 42 are provided on both the left and right sides of the insertion hole 41.
The bearing 42 is an angular ball bearing and applies a large axial load from the rear to the front during injection in addition to the radial load. In this embodiment, it is comprised so that the axial load from the front to the back may also be loaded by combining several single row angular contact ball bearings.

The ball screw 20 includes a screw shaft 21 and a nut 22. Note that illustration of a ball sealed between the nut 22 and the screw shaft 21 and a tube for circulating the ball is omitted.
The screw shaft 21 extends in parallel with the screw 11, and a screw having a length sufficient for the advance / retreat stroke of the screw 11 is formed on the outer periphery. The above-described bearing 42 supports the front side of the screw shaft 21 on which no screw is formed, and is fixed to the front surface of the front plate 40 by a fixture 43. The front end of the screw shaft 21 is connected to the servo motor 13 via a speed reducer.

The nut 22 has a cylindrical part 221 in which a screw is formed on the inner peripheral side, and a flange 222 formed integrally on one end side of the cylindrical part 221.
The cylindrical portion 221 is screwed to the screw shaft 21 by an inner peripheral screw.
The flange 222 has an outer diameter larger than the opening diameter of the through hole 31.
The nut 22 is inserted into the through hole 31 of the bearing housing 30 from the rear side, and the flange 222 is fastened to the rear surface of the bearing housing 30 by a plurality of bolts (not shown), thereby being fixed to the bearing housing 30. . The rear surface of the bearing housing 30 is referred to as a nut fixing surface 33.
Since the axial length of the cylindrical portion 221 is shorter than the thickness of the bearing housing 30, the tip 221 </ b> A of the cylindrical portion 221 is located within the thickness of the bearing housing 30.
The screw shaft 21 and the nut 22 receive a large load based on the injection load. In order to allow the load, the diameter of the screw shaft 21, the thickness of the nut 22, the length of the nut 22, and the like are determined based on the rolling pressure resistance of the ball sandwiched between the screw shaft 21 and the nut 22. Yes.

The present embodiment is characterized in that a lightening portion 50 (space) is formed so as to surround a pair of nuts 22 fixed to the bearing housing 30. The pair of lightening portions 50 are formed symmetrically with respect to the axis A of the screw 11.
As shown in FIG. 2, each thinned portion 50 is formed with a first slit 51 formed from the start end portion 511 located on the nut fixing surface 33 of the bearing housing 30 to the middle of the thickness of the bearing housing 30 toward the front. And a second portion formed with a predetermined length from the start end portion 521 connected to the terminal end portion 512 of the first slit 51 within the wall thickness of the bearing housing 30 toward the outer peripheral portion 32 on the side of the bearing housing 30. It comprises a slit 52.

The first slit 51 extends between the screw 11 and the nut 22 in parallel with the screw 11 to a position exceeding the tip 221 </ b> A of the nut 22.
The second slit 52 is located on the front side of the nut 22 and extends in a direction orthogonal to the first slit 51 to a position exceeding the cylindrical portion 221 of the nut 22. Meat remains between the end portion 522 and the outer peripheral portion 32 of the second slit 52.
The first slit 51 is formed with a constant width W1 and a constant depth D1 over the entire height of the bearing housing 30. Similarly, the second slit 52 is formed with a constant width W2 and a constant depth D2 over the entire height of the bearing housing 30.

The bearing housing 30 is partitioned by the first slit 51 and the second slit 52 into a nut region 30A where the nut 22 is located and a main body region 30B larger than the nut region 30A. 2A, the nut region 30A extends in a direction intersecting the axis A of the screw 11, and includes a short side along the first slit 51 and a long side along the second slit 52. It can be regarded as a beam having a rectangular shape. The nut region 30A is cantilevered by the main body region 30B at a fixed end 30C located on the outer peripheral portion 32 side of the bearing housing 30.
Although the method for forming the lightening portion 50 is arbitrary, in this embodiment, the bearing housing 30 is cast using a mold manufactured in a shape having the lightening portion 50. In addition, after shaping | molding the bearing housing 30, the thickness reduction part 50 can also be formed by cutting.

At the time of injection, the screw shaft 21 is driven at a high speed by the servo motor 13 and the bearing housing 30 is advanced through the nut 22. Thereby, the pressure of the resin between the cylinder 10 fixed to the front plate 40 and the screw 11 fixed to the bearing housing 30 rapidly increases, and the resin is injected into the mold. At this time, a large load is applied to the position of the nut 22 of the ball screw 20.
The behavior of the conventional bearing housing 82 at this time will be described with reference to FIG.
The bearing housing 82 receives a reaction force X1 of the pressurized resin. Since both the left and right sides of the bearing housing 82 are restrained by the ball screw 20 against the reaction force X1, a reaction force X2 in the pulling direction acts on the screw shaft 21. A bending moment with respect to the direction connecting 32 is generated. Then, the bearing housing 82 bends in a direction in which the central portion 35 protrudes rearward of the outer peripheral portions 32 and 32 as indicated by a one-dot chain line in the upper half of FIG. Thereby, the nut fixing surface 33 is inclined.
Since a bending moment is also generated in the ball screw 20 fixed to the bearing housing 82 on the rear side, the stress of the ball screw 20 at the time of injection increases.

As described above, the bending moment is generated in the ball screw 20 due to the deflection of the bearing housing 30. In order to reduce the bending of the bearing housing 30, the thickness of the bearing housing 30 may be increased, but this is difficult because of an increase in weight and cost.
Therefore, in the present embodiment, the above-described thinned portion 50 is formed in the bearing housing 30. When the thinned portion 50 is formed, the rigidity of the bearing housing 30 is reduced, and thus the amount of bending is increased. However, as will be described below, the bending moment of the ball screw 20 is reduced by bending the nut region 30A formed by the thinned portion 50.

With reference to Fig.3 (a), the behavior of the bearing housing 30 of this embodiment is demonstrated.
Since the bearing housing 30 is restrained laterally against the reaction force X1 of the resin at the time of injection, when the bending moment is generated and the bearing housing 30 bends, the nut region 30A of the bearing housing 30 50 is separated from the main body region 30B, and does not follow the deflection of the main body region 30B. The nut region 30 </ b> A bends in the direction of narrowing the second slit 52. Then, on one side of the axis A (see the upper half of FIG. 3A), the main body region 30B bends counterclockwise in the figure, whereas the nut region 30A rotates clockwise with the fixed end 30C as a fulcrum. Turn to. As a result, the bending of the rear side of the bearing housing 30 is reduced. As a result, the bending moment of the ball screw 20 is reduced, so that the nut 22 and the screw shaft 21 are kept substantially horizontal. Thereby, the stress of the ball screw 20 can be suppressed.
Although illustration is omitted, the bending of the lower half of the bearing housing 30 also appears symmetrically with the upper half (see FIG. 5), and the same operation as described above occurs when the nut region 30A below the drawing is bent. .

With reference to FIG. 4, the effect | action by the above-mentioned thinning part 50 is confirmed.
FIG. 4 shows the amount of deflection of the bearing housing 30 that changes in accordance with the distance from the axis A of the screw 11.
When the lightening part 50 is not formed, as shown by the alternate long and short dash line, the deflection amount draws a uniform increasing curve from the front side to the rear side.
On the other hand, when the thinned portion 50 is formed, as shown by the solid line, the amount of bending increases due to a decrease in rigidity (see the portion (1) in the graph), but bending occurs due to the bending of the nut region 30A. As a result, the amount of deflection is substantially constant in the range where the nut 22 is located ((2) in the graph). Thus, the stress of the ball screw 20 can be suppressed by applying a bending or shearing force by the bending of the nut region 30A.
According to this embodiment, as described above, since the stress of the ball screw 20 is suppressed by bending the nut region 30A of the bearing housing 30, the diameter of the screw shaft 21 and the thickness of the nut 22 are reduced. Therefore, a predetermined life can be secured even with the ball screw 20 having low rigidity. If it is such a small size, the ball screw 20 can be selected from commercially available standard products, so that the component cost of the ball screw 20 can be reduced.

  The first slit 51 and the second slit 52 are not necessarily formed from the upper surface to the lower surface of the bearing housing 30. Assuming that the region including the portion into which the screw 11 is inserted and the portion into which the ball screw 20 is inserted (through hole 31) is the main body of the bearing housing 30, the first slit 51 and the first slit 51 extend across the entire height of the main body. Two slits 52 are formed. However, for example, when a leg portion is provided below the main body, the first slit 51 and the second slit 52 are not formed, and a slit is horizontally inserted to divide the leg portion from the main body. Good. As a result, each of the main body region 30B and the nut region 30A in the main body of the bearing housing 30 bends without being constrained by the legs, so that the bearing housing 30 behaves in the same manner as described above, and the stress of the ball screw 20 is suppressed. It is done.

The first slit 51 and the second slit 52 may have any form as long as a cantilever-shaped nut region 30A that can be bent in a direction opposite to the bending direction of the main body region 30B can be formed.
The corner portion where the first slit 51 and the second slit 52 communicate with each other does not have to be L-shaped bent in a plan view as described above, and may be chamfered in a planar shape or a curved shape. Or the 1st slit 51 and the 2nd slit 52 whole may be formed in planar view C-shape (or circular arc shape). Thus, if the 1st slit 51 and the 2nd slit 52 are made into the shape which continued smoothly, the flow of the stress of the center part periphery of the main body area | region 30B will become good, and the rigidity of the main body area | region 30B will improve. Thereby, since the bending of the main body region 30B is reduced, the bending moment of the ball screw 20 is reduced.

The depth D1 of the first slit 51 and the depth D2 of the second slit 52 are each arbitrarily determined. Depending on the depth D1 of the first slit 51, the area of the cross section of the nut region 30A is determined. Further, the length of the nut region 30A is determined according to the depth D2 of the second slit 52. The depths D1 and D2 can be set based on the rigidity of the nut region 30A based on them and the rigidity of the main body region 30B.
Here, if the depth D2 of the second slit 52 is too large, the nut region 30A bends excessively due to a decrease in rigidity, so that the stress of the ball screw 20 cannot be applied. If the depth D2 of the second slit 52 is too small, the nut region 30A cannot be bent enough to reduce the bending of the rear side of the bearing housing 30 due to the increase in rigidity.
The width W1 of the first slit 51 and the width W2 of the second slit 52 are also arbitrarily determined.
The widths W1 and W2 and the depths D1 and D2 are not necessarily constant in the height direction of the bearing housing 30.
A simulation program can be used to set the widths W1 and W2 and the depths D1 and D2.

Furthermore, the angle formed by the first slit 51 and the second slit 52 is not limited to a right angle and is arbitrary. For example, the second slit 52 can be inclined with respect to the first slit 51 so that the end portion 522 of the second slit 52 is positioned in front of the start end 521. Due to the second slit 52, the width (the dimension in the front-rear direction) of the nut region 30A is thicker than the main body region 30B on the outer peripheral portion 32 side, and the width of the main body region 30B is thicker than the nut region 30A on the axis A side. . Thereby, in the nut region 30A, the rigidity on the base end side is increased, and therefore the load that can be received by the bending of the nut region 30A is increased. On the other hand, in the main body region 30 </ b> B, since the rigidity of the central portion 35 where the bending moment is maximized is increased, the bending is smaller than the configuration in which the second slit 52 is orthogonal to the first slit 51. Thereby, the bending moment of the ball screw 20 becomes smaller.
According to the above configuration, the stress on the ball screw 20 can be further reduced by the synergistic effect of increasing the rigidity of the base end side of the nut region 30A and increasing the rigidity of the central portion 35 of the main body region 30B.
The first slit 51 does not necessarily have to be parallel to the axis A of the screw 11 and can be inclined with respect to the axis A.

  By the way, the same thinning part as the above can be formed also in the front plate 40. In that case, what is necessary is just to form a 1st slit and a 2nd slit so that the bearing 42 fixed to the front surface of the front plate 40 and the fixing tool 43 may be enclosed. Accordingly, the bending moment of the ball screw 20 due to the bending of the front plate 40 symmetrically with the bearing housing 30 as shown in FIG. 5 can be reduced, so that the stress on the front side of the ball screw 20 can also be reduced.

In the present invention, the number of ball screws 20 is arbitrary. One ball screw 20 may be used as long as the balance when the screw 11 is advanced and retracted can be maintained.
In the above embodiment, the pair of ball screws 20 are provided on the left and right sides of the support device 3, but the pair of ball screws 20 may be provided on the upper and lower sides of the support device 3. In this case, the first slit 51 and the second slit 52 can be formed so as to surround the nut 22 fixed to each of the upper and lower outer peripheral portions 32 of the bearing housing 30.
Alternatively, a total of four ball screws 20 can be provided on each of the left and right sides and the upper and lower sides of the support device 3.
Furthermore, as long as the bearing housing 30 is partitioned into the nut region 30A and the main body region 30B, the lightening portion does not necessarily have to be in the form of a slit.

  Unless deviating from the gist of the present invention, the above-described configuration can be selected or changed to another configuration as appropriate.

DESCRIPTION OF SYMBOLS 1 Electric injection apparatus 3 Support apparatus 10 Cylinder 11 Screw 12 Motor 13 Servo motor (drive source)
20 Ball screw 21 Screw shaft 22 Nut 30 Bearing housing (first support)
30A Nut region 30B Main body region 30C Fixed end 31 Through hole 32 Outer peripheral part 33 Nut fixing surface (rear part)
35 Center 40 Front plate (second support)
41 Insertion hole 42 Bearing 43 Fixing tool 50 Thickening part 51 1st slit 52 2nd slit 221 Tube part 221A Tip 222 Flange A Axis W1, W2 Width D1, D2 Depth

Claims (4)

Cylinders and screws,
A first support to which the screw is fixed;
A second support to which the cylinder is fixed;
A motor that is a drive source for driving the screw back and forth;
A ball screw that converts rotational motion by the motor into linear motion and moves the first support back and forth, and
The ball screw has a screw shaft that penetrates the second support and the first support along the screw, and a nut that is provided on the screw shaft and is fixed to a rear portion of the first support. ,
In the first support,
The first support is partitioned into a nut region where the nut is located and extending in a direction intersecting the screw, and a main body region that cantilever-supports the nut region on the outer peripheral side of the first support. For the purpose of forming a lightening part,
An electric injection device characterized by that. The meat extraction part is
A first slit extending between the screw and the nut from the rear portion of the first support;
A second slit that communicates with the first slit within the thickness of the first support and extends toward the outer peripheral side of the first support.
The electric injection device according to claim 1. The first support is a substantially plate-like member that is erected perpendicular to the axis of the screw,
The nut region has a substantially rectangular shape having one side along the first slit and the other side along the second slit.
The electric injection device according to claim 2. The ball screw is provided on both sides of the screw axis,
The thinned portions located around the nut of each of the ball screws are formed symmetrically on both sides of the axis.
The electric injection device according to any one of claims 1 to 3.

Images