JP2000102956A - Screw position takeout mechanism of injection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To greatly improve the accuracy of positioning control by a method wherein by applying a preload to a bearing part, the fluctuation of a stroke indicating bar can be limited, and even in a high speed injection device, the stroke indicating bar accurately shows the position of a screw. SOLUTION: Inner rings 16a, 17a of single row angular ball bearings 16, 17 are fitted on a sleeve 13 so as to face in opposite directions, while a position takeout arm 18 is fitted on each of the outer rings 16b, 17b of the bearings 16, 17. The sleeve 13, in such conditions, is fixed to a piston rod 21 by means of a plurality of bolts 22 each provided with a hexagonal hole. When being clamped by the bolts 22, the inner rings 16a, 17a are brought into a close contact with each other so as to cause a preload.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw position extracting mechanism suitable for a high-speed injection device.

[0002]

2. Description of the Related Art For example, in FIG. 1 of JP-A-7-47581, "Hydraulic control circuit for injection molding machine", reference numeral 11 denotes a heating cylinder, and 14 denotes a screw (screw.
Here, it is described as a screw. ), 16 are pistons,
Reference numeral 18 denotes an oil motor, and 46 denotes a speed detecting unit. In the plasticizing and measuring step, the screw 14 is rotated by the oil motor 18 to store the resin material in the heating cylinder 11. Retreats, the retreat distance is monitored by the speed detection unit 46, and in the next injection step, the resin material is injected from the injection nozzle 12 by advancing the piston 16 at high speed by hydraulic pressure. The control of the transfer speed of the piston 16) is performed based on a detection signal of the speed detection unit 46.

As described above, directly monitoring the position of the screw 14 is extremely important in the injection molding process.
By the way, as is apparent from FIG. 1 of the publication, the screw 14 moves linearly by the action of the piston 16 and also rotates by the action of the oil motor 18. Therefore, in order to take out the position of the screw 14, a mechanism described in the following figure is required.

FIG. 6 is a diagram showing the principle of a conventional typical screw position extracting mechanism.
0, the holding ring 102 is fitted to the rear end of the screw 101, and the holding ring 102 is fixed to the tip of the piston rod 103, so that the screw 101 is connected to the piston rod 103 and the holding ring 102 has a single row deep groove. The inner ring 106 of the ball bearing 105 is fitted, the position extracting arm 108 is fitted to the outer ring 107 of the single row deep groove ball bearing 105, and the stroke indicating rod 1 of the position extracting arm 108
09 faces the position sensor 111.

Since the single row deep groove ball bearing 105 is interposed, even if the screw 101 rotates, the position taking arm 1
08 can be non-rotating, the stroke indicator rod 10
9 can be simply moved linearly right and left in the figure.

[0006]

The conventional injection speed is 30.
It was about 0 mm / sec. When this was increased to 1000 to 1300 mm / sec in response to a recent demand for higher speeds, the screw 101 was slightly "jerky".
It was found to exhibit the following behavior.

Therefore, the present inventors examined the dynamic characteristics of the screw and the injection speed in the actual machine. FIGS. 7A and 7B
Is a graph of conventional screw position and injection speed.
In (a), the horizontal axis indicates time, and the vertical axis indicates the screw position. The screw starts to advance from the point P1, and thereafter, the curve is steered finely. That is, a large number of decelerations or stops were recognized during the movement. (B) shows the time on the horizontal axis and the injection speed on the vertical axis. A deceleration phenomenon had occurred. In addition, at least two speed-up phenomena were observed in the deceleration range after the point P2. Now we can see the jerky behavior on the graph, but we need to take countermeasures.

[0008]

Means for Solving the Problems Incidentally, reference numeral 46 in FIG. 1 of the gazette described in the section of the prior art has been described as a speed detecting section. That is, reference numeral 46 denotes a screw position detector, which is read as a speed. If the speed is smaller than a predetermined value, the piston speed is increased, and if the speed is larger than a predetermined value, the piston speed is reduced. The feedback control is performed based on the position information of the screw.

Therefore, the present inventors have considered that the stroke indicating rod 109 in FIG. 6 may not transmit the true position of the screw 101. FIG. 8 is a diagram for estimating a conventional problem. If the stroke indicating rod 109, which should be at the position indicated by the solid line, is shifted to the position of the stroke indicating bar 109B indicated by the imaginary line, the control unit 112 obtains It is determined that 101 has advanced too much (or the speed is too high), and a command is issued to the hydraulic control unit 113 to slow down the movement of the piston 114. In the case of the stroke indicating rod 109C shown by an imaginary line, the reverse is true.
In this way, the stroke indicator rod 109 serving as a control reference is used.
Swings like 109B or 109C, the piston 114 directly affected by the influence decelerates or stops during forward movement, and the trouble shown in the above graph occurs.

The present inventors have studied the structure of the single-row deep groove ball bearing 105 in order to clarify the above estimation. FIG.
(A), (b) is a structural diagram and an action diagram of a single row deep groove ball bearing conventionally adopted. As shown in (a), the single-row deep groove ball bearing 105 has balls (steel balls) 116... Interposed between an inner ring 106 and an outer ring 107 (holding tools are not shown), and has an internal clearance. Has a gap P called. This gap P
There are grades of C2, normal, C3, C4, and C5 specified by JIS B 1520 (Radial internal clearance of rolling bearings). If the nominal diameter of the bearing is 100 mm and C3 class, the clearance is 30 to 58 μm. Become.

The inner clearance tends to increase in diameter when the inner ring 106 is fitted to the shaft, and the outer ring 107 tends to reduce in diameter when fitted to the bearing housing. It is something to keep. If the internal clearance is not expected, an excessive pressing force acts on the ball 116, and the life is shortened. Due to the internal clearance, there is a possibility that the outer ring 107 is inclined to the angle θ with respect to the inner ring 106 as shown in FIG. This was found to be the cause of the above-mentioned problem. Therefore, it suffices that the outer ring 107 does not tilt with respect to the inner ring 106.

More specifically, in the first aspect of the present invention, the screw is housed in the heating cylinder so as to be rotatable and movable in the axial direction.
It is a screw type injection device that turns the screw by rotating means in the measuring process and moves the screw in the injection process,
In a screw position taking-out mechanism that measures the axial position of the screw by mounting a stroke indicating rod to the rear end of the screw or a shaft member connected to the rear end via a bearing part and monitoring the indicating rod, the bearing part is A single row radial bearing having a contact angle capable of applying a pressurization, or a double row radial bearing applied with a pressurization.

[0013] By applying a pressure to the bearing portion, the deflection of the stroke indicating rod can be suppressed. As a result, even in a high-speed injection device, the stroke indicating rod accurately indicates the position of the screw, and the accuracy of the position control can be dramatically improved.

According to a second aspect of the present invention, the single row radial bearing is a single row angular contact ball bearing. Single row angular contact ball bearings are widely available on the market and are inexpensive.
Therefore, by adopting a single row angular contact ball bearing,
An increase in the cost of the injection device can be suppressed.

[0015]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a principle view of a screw position extracting mechanism (first embodiment) according to the present invention. A screw position extracting mechanism 10 includes a shaft member 12 (in this example, a shaft member 12 connected to a rear end of a screw 11). This is a combination of the sleeve 13 and the holding ring 14.)
Bearing 15 (in this example, single row angular contact ball bearing 16,
17 are combined back to back. ), The position pick-up arm 18 is attached.
This is a mechanism for measuring the axial position of the screw 11 by extending the stroke indicating rod 19 to the side and causing the stroke indicating rod 19 to face the position sensor 20. The configuration of the shaft member 12 is arbitrary. Furthermore, the bearing member 15 may be directly fitted to the rear end of the screw 11 without the bearing member 12.

An example of the order of assembling the above components will be described.
The inner races 16a, 17a of the single row angular contact ball bearings 16, 17 are fitted to the sleeve 13 in a back-to-back state. The sleeve 13 is fixed to the piston rod 21 with a plurality of hexagon socket head bolts 22. As will be described in detail with reference to the next drawing, when tightening with the bolt 22, the inner rings 16a and 17a come into close contact with each other and pressurize.

On the other hand, a retaining ring 14 is fixed to the rear end of the screw 11, and the retaining ring 14 is fixed to the sleeve 13 with a plurality of hexagon socket head bolts 23, so that a screw position extracting mechanism is provided. 10 is an assembly completion. However, this assembling order is an example, and the order may be changed. In addition, 25, 2
5 is an oil seal and 26 is an end plate.

FIGS. 2 (a) and 2 (b) are structural views and action diagrams (first embodiment) of a single-row angular contact ball bearing employed in the present invention. (A) shows two single-row angular contact ball bearings 16, 17;
FIG. 5 is an enlarged view of a main part of the single row angular contact ball bearing 16 on the left.
Is that the inner ring 16a is δ relative to the outer ring 16b in the free state.
Only at the left side of the figure, a gap 29 is generated between the outer ring 16b and the ball 28, for example. This gap is due to the internal clearance adopted for the JIS bearing. The right single-row angular contact ball bearing 17 is a so-called opposite of the left single-row angular contact ball bearing 16 and is free from the outer race 17b with respect to the inner race 17a.
Has a structure shifted by δ to the right of the figure.
For example, a gap 29 is generated between the outer ring 17b and the ball 28.

FIG. 2B is a view showing how to assemble the two bearings 16 and 17. The inner rings 16 a and 17 a are pressed as indicated by the white arrows to bring them into close contact. As a result, the δ and δ become zero. As a result, the inner ring 16a and the ball 28
Contact at P4, the outer ring 16b and the ball 28 contact at P5,
As a result, the inner ring 16a cannot move in the radial direction with respect to the outer ring 16b. This is one of the actions and effects of applying “pressurization”.

The angle between the line L1 passing through P4 and P5 and the line L2 orthogonal to the axis is called a contact angle β. In the case of a single row deep groove ball bearing, β = 0. The angle β is present (not zero), so that in the left angular ball bearing 16, the inner ring 16a does not move further to the right. Therefore, the angular ball bearing 16 can bear an axial load (axial load) to some extent. The same applies to the right bearing 17. The right bearing 17 prevents the inner ring 17 a from moving to the left.
6 and 17 are back-to-back, resulting in a bearing structure that can withstand both left and right axial loads.

However, since the internal clearance, which should be originally secured, is reduced to almost zero by applying the pressurization, the life of the bearings 16 and 17 is shortened at the cost.
However, these bearings 16 and 17 only support the relatively light position take-out arm 18, and the number of rotations used is low. Accordingly, the service life in practical use is sufficient, and the disadvantages of applying the pres- sure are within an acceptable range.

A two-row outward angular ball in which two rows of balls (or rollers) are arranged between wide inner and outer rings such that the inner ring 16a and the inner ring 17a are integrated and the outer ring 16b and the outer ring 17b are integrated. Bearing (or double-row outward tapered roller bearing)
The same effect can be exerted even if is adopted. These bearings are generally referred to as two-row radial bearings, but it is premised that these two-row radial bearings are pre-pressed.
This is because pressurization cannot be applied later. However, multi-row radial bearings are less versatile than single-row radial bearings and are therefore expensive.

FIGS. 3A and 3B are graphs of the screw position and the injection speed of the present invention. In (a), the horizontal axis indicates time, and the vertical axis indicates the screw position, and the screw starts to advance from point P6. On the way, the curve slightly steers,
Not really harmful. In (b), the horizontal axis is time,
The vertical axis indicates the injection speed, and it was confirmed that the curve was smooth. Such good (a) and (b) were obtained because the problem assumed in FIG. 8 (the phenomenon that the stroke indicating rod 109 swings to 109B and 109C) can be corrected in this embodiment, and FIG. Stroke indicating rod 19 is screw 1
This is because the position of No. 1 was faithfully reproduced.

FIGS. 4 (a) and 4 (b) are structural views and action diagrams (second embodiment) of a single-row angular contact ball bearing employed in the present invention. (A) shows two single-row angular contact ball bearings 36 and 37;
FIG. 3 is an enlarged view of a main part of FIG.
FIG. 2 (a) is the same as FIG. 2 (a) except that the balls 38, 38 are interposed between the inner rings 36a, 37a.
Are not offset from the outer rings 36b, 37b. However, internal gaps 39, 39 exist. These single-row angular contact ball bearings 36, 37 are extremely inexpensive bearings that can be purchased at a cost of about 1/5 to 1/10 of the single-row angular contact ball bearings 16, 17 in FIG.
However, the following benefits are required.

In (b), the left and right outer rings 36b, 37
b, a spacer ring 41 of an appropriate thickness is interposed,
The inner rings 36a and 37a are pushed as indicated by white arrows. Then, the inner races 36a, 37a are shifted by δ, δ with respect to the outer races 36b, 37b, whereby the internal clearance can be made zero.

FIG. 5 is a principle view of a screw position extracting mechanism (second embodiment) according to the present invention. The screw position extracting mechanism 10B includes a shaft member 12 connected to the rear end of the screw 11 and a bearing portion 15 ( In this example, the position extracting arm 18 is mounted via a single-row angular contact ball bearing 36, 37 with a spacer ring 41 interposed therebetween.
9 is a mechanism for measuring the axial position of the screw 11 by extending the side 9 and causing the stroke indicating rod 19 to face the position sensor 20.

The outer ring 36b, the spacer ring 41, and the outer ring 37b are superimposed on each other with the end plate 26 and the bolt 27, and the inner rings 36a, 37a are attached to the sleeve 13
4 (b) can be realized by pressing the bolt with the bolt 22. Although not shown, if a thin shim (spacer shim) is inserted into the right side of the outer ring 37b in the drawing and the right side of the inner ring 37a in the drawing, and the thickness of the thin shim can be changed as necessary, the control of the pressurization is easy. Is preferable.

The structure employing the spacer ring 41 shown in FIG. 5, ie, the structure of the second embodiment, has the advantage that the number of parts is increased, but the bearings 36 and 37 are inexpensive, so that the manufacturing cost can be reduced. There is. The first shown in FIG.
The embodiment uses expensive bearings 16 and 17, but reduces the number of parts. Therefore, the first and second embodiments may be appropriately selected according to necessity.

The "single-row radial bearing having a contact angle capable of applying a pressurized force" described in claim 1 is described in JI.
Counter bore ball bearing of SB 1538, JIS B 15
22 angular ball bearings and JIS B 1534 tapered roller bearings can be employed. Tapered roller bearings have a large rated load but are expensive. In this regard, angular contact ball bearings, especially single row angular contact ball bearings, are large in production, inexpensive and readily available.

[0030]

According to the present invention, the following effects are exhibited by the above configuration. A first aspect of the present invention is a screw position taking-out mechanism that measures a shaft position of a screw by attaching a stroke indicating rod to a rear end of the screw via a bearing section and monitoring the indicating rod. It is characterized by adopting a combination of two single-row radial bearings with a contact angle that can be applied or a two-row radial bearing that has been pressurized. The deflection of the bar can be suppressed. As a result,
Even in a high-speed injection device, the stroke indicating rod accurately indicates the position of the screw, and the accuracy of position control can be dramatically increased.

When two single-row radial bearings are combined as a bearing portion, the assembly is slightly troublesome, but the cost of the bearing can be reduced because the bearing itself is inexpensive. If a two-row radial bearing is used as the bearing part, the bearing will be more expensive than a single-row radial bearing.
The number of assembly steps can be reduced.

According to the second aspect, the single-row radial bearing is a single-row angular ball bearing, and the single-row angular ball bearing is widely available on the market and is inexpensive. Therefore, by adopting the single-row angular contact ball bearing, it is possible to suppress an increase in the cost of the injection device.

[Brief description of the drawings]

FIG. 1 is a principle view of a screw position extracting mechanism according to the present invention (first embodiment).

FIG. 2 is a structural diagram and action diagram of a single-row angular contact ball bearing employed in the present invention (first embodiment).

FIG. 3 is a graph of screw position and injection speed of the present invention.

FIG. 4 is a structural view and action diagram of a single-row angular contact ball bearing employed in the present invention (second embodiment).

FIG. 5 is a principle view of a screw position extracting mechanism according to the present invention (second embodiment).

FIG. 6 is a principle diagram of a conventional representative screw position extracting mechanism.

FIG. 7 is a graph of conventional screw position and injection speed.

FIG. 8 is a diagram of a conventional problem estimation.

FIG. 9 is a structural diagram and action diagram of a conventional single-row deep groove ball bearing.

[Explanation of symbols]

10, 10B ... screw position taking-out mechanism, 11 ... screw, 12 ... shaft member, 13 ... sleeve as shaft member, 14 ... holding ring as shaft member, 15 ... bearing part,
16, 17 ... single row angala ball bearings, 16a, 17a ...
Inner ring, 16b, 17b Outer ring, 18 Position extraction arm, 19 Stroke indicating rod, 20 Position sensor, 28
... Balls, 36, 37 ... Single-row Angara ball bearings, 36a, 3
7a: inner ring, 36b, 37b: outer ring, 38: ball, 41 ...
Spacer ring, β ... contact angle.

Claims (2)

[Claims] 1. A screw type injection device in which a screw is housed in a heating cylinder so as to be rotatable and axially movable, the screw is turned by a rotating means in a plasticizing / metering step, and the screw is moved in an injection step, A screw position take-out mechanism for measuring the axial position of the screw by mounting a stroke indicating rod to a rear end of the screw or a shaft member coupled to the rear end via a bearing portion and monitoring the indicating rod, The part is a combination of two single-row radial bearings having a contact angle capable of applying a pressurization or a double-row radial bearing under a pressurization. . 2. The screw position taking-out mechanism according to claim 1, wherein said single-row radial bearing is a single-row angular ball bearing.