JP4875342B2 - Ball screw, injection molding machine - Google Patents

Description

  The present invention relates to a ball screw and an injection molding machine.

  In various apparatuses and devices, a ball screw is used as a drive source for performing a linear operation. In this ball screw, thread grooves are formed in both the threaded rod and the nut, and the ball is sandwiched between the threaded groove of the threaded rod and the threaded groove of the nut. The rod and nut can rotate relative to each other. Then, one of the two members to be moved relative to each other is supported by the screw rod, the other is fixed to the nut, the screw rod is rotated by a rotational drive source such as a motor, and the screw rod is moved forward and backward relative to the nut. Thus, the two members are moved relative to each other.

Such a ball screw is used as a drive source of an injection screw of an injection molding machine, for example.
The injection screw melts the resin and extrudes it into the mold of an injection molding machine. The screw body that rotates the resin that is put into the cylinder from the base end side of the screw body while rotating the screw body in the cylinder. It is moved to the tip side of the screw body while melting. Then, with the molten resin accumulated in the resin reservoir formed between the tip of the screw body and the cylinder, the screw body is advanced with respect to the cylinder, so that the molten resin is removed from the injection port formed in the cylinder. Extrude.
At this time, a ball screw is used as a drive source for advancing the screw body relative to the cylinder (see, for example, Patent Document 1).

Japanese Patent Laying-Open No. 2003-240099 (FIG. 9)

At the time of injection, a reaction force corresponding to the injection pressure acts on the ball screw. At this time, if there is an error between the lead dimension of the thread groove formed on the screw rod and the lead dimension of the thread groove formed on the nut, an excessive force acts on the ball sandwiched between them, and the ball Or, it affects the durability of the thread groove and also affects the operating conditions (load conditions) of the injection molding machine. For this reason, it is necessary to form the lead dimensions with high accuracy.
However, forming the lead dimensions of the threaded rod and nut groove of the ball screw with high accuracy leads directly to an increase in the cost of the ball screw.
Such a problem is common in the case of a ball screw used in a high-load operating environment in which a reaction force from a driven object is large.
The present invention has been made on the basis of such a technical problem. A ball screw capable of preventing an excessive surface pressure from acting on a ball or a screw groove even when operated at a high load is produced at a low cost. The purpose is to provide in.

For this purpose, the ball screw of the present invention includes a screw rod having a thread groove formed on the outer peripheral surface, a nut member having the screw rod inserted therein and a thread groove formed on the inner peripheral surface, and a screw of the screw rod. A ball screw having a plurality of balls interposed between the groove and the screw groove of the nut member, and when the driven object is driven by relatively moving the screw rod and the nut member in the axial direction of the screw rod. A deviation absorbing portion that absorbs a deviation generated between the thread groove of the screw rod and the thread groove of the nut member due to the reaction force transmitted from the object to be driven, and a tube for circulating the ball is formed on the nut member; As a deviation absorbing part, the nut member is eccentric to the side opposite to the side where the plurality of tubes are provided with respect to the threaded rod. It is provided .
As such a deviation absorbing portion, it is possible to adopt a configuration in which a slit extending in parallel with the screw groove is formed in at least one of the rising portion of the screw groove of the screw rod and the rising portion of the screw groove of the nut member. Due to the slit, the rigidity of the rising part of the thread groove of the threaded rod and the rising part of the thread groove of the nut member is reduced, and the reaction force transmitted from the driven object causes a deviation between the thread groove of the threaded rod and the thread groove of the nut member. When the rising portion of the thread groove of the screw rod and the rising portion of the thread groove of the nut member are elastically deformed, this deviation can be absorbed.
Further, as the deviation absorbing portion, at least one of the screw groove of the screw rod and the screw groove of the nut member, a step portion extending in parallel with the screw groove may be formed at the bottom of the screw groove. Also by this, the deviation can be absorbed by elastically deforming the rising part of the thread groove of the screw rod and the rising part of the screw groove of the nut member.
Further, the deviation absorbing portion can be formed such that the outer diameter of the nut member gradually decreases from one side to the other side along the axial direction of the screw rod. If it does in this way, rigidity will become low in the side where the outside diameter of a nut member is small, ie, the side where the thickness of a nut member is small. When a deviation occurs in the screw groove of the screw rod and the screw groove of the nut member due to the reaction force transmitted from the drive object, a force in the tensile direction or the compression direction acts on each of the screw rod and the nut member due to the deviation. The greater the deviation, the greater the force. By reducing the outer diameter of the nut member on the side where a large force acts, the smaller the outer diameter of the nut member, the larger the elastic deformation in the axial direction of the screw rod. Thereby, the deviation can be absorbed.

In the present invention, the nuts member, the tube is formed for circulating the balls. As the deviation absorbing portion, the plurality of tubes are formed side by side on one side of the axis of the screw rod, so that the nut member has the axis of the screw rod sandwiched on the side of the nut member. Compared to the opposite side, the rigidity is low. The number of balls sandwiched between the thread groove of the threaded rod and the thread groove of the nut member is smaller on the side where the tube is formed than on the opposite side where the axis of the threaded rod is sandwiched. Less. This is because, on the side where the tube is formed, a part of the ball exists in the tube and is not sandwiched between the screw groove of the screw rod and the screw groove of the nut member.
Since the ball located on the side where the tube is formed has a small number of balls, the load acting on each ball is larger than the opposite side, but the rigidity of the nut member is reduced by the tube. Yes. For this reason, when the reaction force transmitted from the object to be driven causes a deviation in the thread groove of the screw rod and the screw groove of the nut member, a force in the tension direction or the compression direction acts on each of the screw rod and the nut member due to the deviation. The nut member is greatly elastically deformed on the side where the tube is formed and the rigidity is low, whereby the load acting on each ball is reduced. As a result, the deviation can be absorbed as a whole.

Nuts member relative to the threaded rod, by the side of a plurality of tubes are provided arranged eccentrically to the opposite side, the nut member is made thinner on the side where the wall thickness plurality of tubes are provided The rigidity on the side where the tube is formed is further reduced. As a result, the above effect becomes more remarkable.

The injection molding machine of the present invention is an injection in which a mold that forms a molded body of a predetermined shape and a resin that is a raw material of the molded body are melted in a cylinder, and the resin is injected into the mold by a screw that moves forward and backward in the cylinder. A screw and a ball screw that relatively moves the cylinder and the screw back and forth. The ball screw drives the injection screw by relatively moving the screw rod and the nut member constituting the ball screw in the axial direction of the screw rod. And a deviation absorbing portion that absorbs a deviation generated in the thread groove of the screw rod and the thread groove of the nut member by a reaction force transmitted from the driving object, and a tube for circulating the ball is formed on the nut member, As a deviation absorbing part, the tube is formed side by side on the axis of the screw rod, and the nut member is the side on which the plurality of tubes are provided with respect to the screw rod. And it is provided eccentrically on the contralateral.

In such an injection molding machine, as the deviation absorbing portion, a slit extending in parallel with the screw groove can be formed in at least one of the rising portion of the screw groove of the screw rod and the rising portion of the screw groove of the nut member. .
Further, the outer diameter of the nut member can be formed so as to gradually decrease from one side to the other side along the axial direction of the screw rod.

The injection molding machine of the present invention is an injection in which a mold that forms a molded body of a predetermined shape and a resin that is a raw material of the molded body are melted in a cylinder, and the resin is injected into the mold by a screw that moves forward and backward in the cylinder. A screw and a screw rod connected to one of the cylinder and the screw, a nut member connected to the other of the cylinder and the screw, a screw groove of the screw rod, and a screw groove of the nut member to relatively advance and retract the cylinder and the screw; A ball screw having a plurality of balls interposed therebetween, and a plurality of tubes for circulating the balls are formed in the nut member, and the plurality of tubes are arranged on one side across the axis of the screw rod. side by side are formed, nuts are to threaded rod, the side provided with a plurality of tubes may also be characterized in that is provided eccentrically on the opposite side.
Further, when a plurality of ball screws are arranged around the injection screw, the screw of the injection screw and the screw rod or nut member of each ball screw are connected so as to operate integrally by the housing. At this time, the nut member is preferably provided such that the tube faces the injection screw. This is because the outer peripheral portion of the housing is deformed to the opposite side to the reaction force due to the reaction force from the injection screw, and this deformation causes a large deviation on the side of the nut member facing the injection screw. By arranging the tube toward the injection screw, the nut member is easily deformed on the side where a large deviation occurs, and the deviation can be effectively absorbed.

  According to the present invention, when a deviation occurs between the thread groove of the threaded rod and the thread groove of the nut member due to the reaction force transmitted from the driven object when the ball screw is operated, a part of the threaded rod or nut member is formed. It is possible to absorb the deviation by elastically deforming. This makes it possible to prevent an excessive surface pressure from acting on the ball and the thread groove even when operated with a high load. Furthermore, this makes it possible to reduce the processing accuracy of the thread grooves of the ball screw and the nut member as compared with the prior art, thereby reducing the manufacturing cost and reducing the cost.

[First embodiment]
Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
As shown in FIG. 1, the injection molding machine 10 includes an injection unit 20 that melts and injects a resin, and a molding unit 30 that molds the resin injected from the injection unit 20.
Among these, the molding unit 30 includes a mold (not shown) for forming a molded product having a predetermined shape, and a mold opening / closing mechanism (not shown) for opening / closing and clamping the mold. Yes.

  The injection unit 20 includes a hopper 21 that is charged with a pellet-like or powdered resin that is a raw material, an injection screw (driving object) 22 that melts the resin charged from the hopper 21 and injects the resin into the molding unit 30, and an injection And a drive mechanism 23 for driving the screw 22.

The injection screw 22 includes a cylindrical cylinder 24 and a screw body 25.
The cylinder 24 has an inlet from the hopper 21 at one end and an inlet through which the resin is injected into a mold (not shown) at the other end. The cylinder 24 is attached and fixed to a front plate 41 fixed to the base 40.
The screw body 25 is rotatably supported by a bare housing (housing) 42 via a bearing or the like. The bare housing 42 is supported on the base 40 via a slide rail 43, and is thereby movable forward and backward in the axial direction of the screw body 25.

The drive mechanism 23 is mainly composed of a ball screw 50 and a motor 51 that drives the ball screw 50.
The screw rod 52 of the ball screw 50 is disposed with its axial direction parallel to the screw body 25 of the injection screw 22, and is supported on the front plate 41 in a freely rotatable state via a bearing or the like, and a motor 51. Is rotated around its axis.
On the other hand, the nut member 53 of the ball screw 50 is fixed to the bare housing 42.

As shown in FIG. 2, thread grooves 54 and 55 are formed in the threaded rod 52 and the nut member 53, respectively. A plurality of thread grooves 54 and 55 are formed between the thread groove 54 of the threaded rod 52 and the thread groove 55 of the nut member 53. Ball 56 is sandwiched. By these balls 56, the screw rod 52 and the nut member 53 are not in direct contact with each other.
As shown in FIG. 3, such ball screws 50 are arranged at the four corners of a rectangular front plate 41, for example, and the injection screw 22 is located at the center thereof.

  In the ball screw 50, when the screw rod 52 is rotated by the motor 51, the screw rod 52 and the nut member 53 engaged with each other via the ball 56 relatively move in the direction along the axis of the screw rod 52. As a result, the bare housing 42 and the front plate 41 are driven toward and away from each other, and the screw main body 25 provided in the bare housing 42 moves forward and backward with respect to the cylinder 24.

In the present embodiment, the ball screw 50 has the following configuration.
That is, as shown in FIG. 2, a slit (deviation absorbing portion) 60 extending in parallel with each other is formed between the screw grooves 54 and 55 adjacent to each other in both the screw rod 52 and the nut member 53. -ing By forming the slit 60, the rigidity of the rising portions 54a and 55a of the thread grooves 54 and 55 is lowered.
When the injection screw 22 is operated by operating the ball screw 50, the screw body 25 receives a reaction force due to the pressure of the molten resin in the resin reservoir formed at the tip of the cylinder 24, and this is received by the ball housing 42 through the bare housing 42. It is transmitted to the screw 50. Then, a tensile force or a compressive force in the axial direction of the screw rod 52 acts on the screw rod 52 and the nut member 53 of the ball screw 50, and an error in the lead dimension of the screw groove 54 of the screw rod 52 and the screw of the nut member 53. Due to the difference in lead dimensional error of the groove 55, a deviation occurs between the screw rod 52 and the nut member 53. This deviation increases toward the downstream side in the force transmission direction in the case of a tensile force and toward the upstream side in the case of a compressive force, and via the ball 56, the rising portion 54 a of the screw groove 54 of the screw rod 52 and the screw of the nut member 53. A surface pressure corresponding to the amount of deviation acts between the rising portion 55 a of the groove 55. When this surface pressure is applied, the rising portions 54a and 55a are elastically deformed by the slit 60, so that the surface pressure can be relaxed and the deviation can be absorbed.

4, the rising portions 54a and 55a are obtained when the width dimension of the slit 60 and the contact angle α of the ball 56 with respect to the thread grooves 54 and 55 are changed with respect to the thread grooves 54 and 55 having the same lead dimensions. The rigidity ratio is shown. The larger the width dimension of the slit 60, the lower the rigidity of the rising portions 54a and 55a, and the easier it is to elastically deform. Further, as the contact angle α of the ball 56 increases, the ball 56 comes into contact with the leading end sides of the rising portions 54a and 55a, so that the rigidity of the rising portions 54a and 55a is reduced and is easily elastically deformed. For this reason, in order to increase the elastic deformation of the rising portions 54a and 55a and increase the deviation absorbing ability, it is preferable to increase the width of the slit 60 and the contact angle α of the ball 56 as much as possible.
FIG. 5 shows the relationship between the rigidity of the rising portions 54 a and 55 a and the surface pressure by the ball 56. As can be seen from FIG. 5, reducing the rigidity of the rising portions 54 a and 55 a is effective in reducing the surface pressure by the ball 56.

  In view of the action of the slit 60, it is preferable to make the depth of the slit 60 as large as possible. However, if the slit 60 is made too deep, the strength in the axial direction of the screw rod 52 and the nut member 53 is lowered. . For this reason, the depth of the slit 60 is the difference between the lead dimension error of the screw groove 54 of the screw rod 52 and the lead dimension error of the screw groove 55 of the nut member 53, that is, the rising portion 54 a of the screw groove 54 of the screw rod 52. Although it may be set as appropriate according to the magnitude of the surface pressure acting between the rising portion 55a of the thread groove 55 of the nut member 53, the depth is equal to or less than the depth of the thread grooves 54, 55. Is preferred. Moreover, in order to prevent surface pressure concentration on the bottom of the slit 60 when elastically deformed, it is preferable that the bottom of the slit 60 has an R shape.

  In addition to this, in order to reduce the rigidity of the rising portions 54a and 55a and facilitate elastic deformation, a step extending in parallel to the screw grooves 54 and 55 at the bottom of the screw grooves 54 and 55 as shown in FIG. The parts (deviation absorbing parts) 61, 62, etc. may be formed.

  By forming the slit 60 in this way, the deviation generated between the screw rod 52 and the nut member 53 can be absorbed. Therefore, the screw of the screw rod 52 can be compared with the case where the slit 60 is not formed. It becomes possible to reduce the accuracy of the lead dimension of the groove 54 and the thread groove 55 of the nut member 53. As a result, the manufacturing cost of the screw rod 52 and the nut member 53, that is, the ball screw 50 can be reduced.

[Second Embodiment]
Next, a second embodiment of the present invention will be described.
Here, since the overall configuration of the injection molding machine 10 can be the same as that of the first embodiment, only the characteristic configuration will be described in the following description, and the other portions will be described. Omitted.
As shown in FIG. 7A, in the injection molding machine 10 of the second embodiment, instead of providing the slit 60, the nut member 53 of the ball screw 50 has a tapered shape, and the screw rod 52 The thickness t of the nut member 53 in the direction orthogonal to the axis, that is, in the radial direction is gradually changed from the one end 53b side to the other end 53c side of the nut member 53 along the axial direction of the screw rod 52. At this time, the surface pressure is increased by the deviation generated between the thread groove 54 of the threaded rod 52 and the thread groove 55 of the nut member 53 on the one end 53b side and the other end 53c side, as shown in FIG. It is preferable to reduce the thickness of the nut member 53 toward this side.

  Due to the nut member 53 having such a shape, the distribution of rigidity of the nut member 53 differs in the axial direction of the screw rod 52. When a surface pressure corresponding to the amount of deviation acts between the screw groove 54 of the screw rod 52 and the screw groove 55 of the nut member 53 due to the deviation generated between the screw rod 52 and the nut member 53. The nut member 53 is more elastically deformed as the rigidity is lower, that is, the deviation is larger. The elastic deformation of the nut member 53 exhibits a large surface pressure relaxation effect at a portion where the surface pressure is particularly high, absorbs the deviation, and makes it possible to equalize the load applied to the ball 56.

  Even with such a configuration, it is possible to obtain the same effects as those of the first embodiment.

[Third embodiment]
Next, a third embodiment of the present invention will be described.
Here, the entire configuration of the injection molding machine 10 can be the same as that of the first embodiment, and therefore, only the characteristic configuration will be described in the following description, and the other portions will be described. Omitted.
As shown in FIG. 8, the nut member 53 of the ball screw 50 is provided with a tube 70 for circulating the ball 56. While the ball 56 rolls between the screw groove 54 of the screw rod 52 and the screw groove 55 of the nut member 53, the ball 56 spirals along the screw grooves 54 and 55 (for example, 0.5 around the screw rod 52). Rotation, or 1.5 rotations), then returns to the original position through the tube 70 and circulates.
As shown in FIG. 9, the ball screw 50 has a plurality of sets of circulation paths of the balls 56 by such tubes 70. In such a ball screw 50, a plurality of sets of tubes 70 are provided as deviation absorbing portions arranged on one side with respect to the central axis of the nut member 53. Further, the nut member 53 is formed with a through hole 71 having a thread groove 55 as a deviation absorbing portion eccentric to the side where the tube 70 is provided with respect to the central axis of the nut member 53.

In this manner, the nut member 53 is thin on the side where the tube 70 is provided and thick on the opposite side while being attached to the screw rod 52. Therefore, the rigidity of the nut member 53 is small on the side where the tube 70 is provided and large on the opposite side.
Further, in the nut member 53, since there is a ball 56 existing in the tube 70, it exists between the screw groove 54 of the screw rod 52 and the screw groove 55 of the nut member 53 on the side where the tube 70 is provided. The number of balls 56 to be played is small, and on the opposite side, the number of balls 56 existing between the thread groove 54 of the screw rod 52 and the thread groove 55 of the nut member 53 is large.
Therefore, due to the deviation generated between the screw rod 52 and the nut member 53, a surface pressure corresponding to the amount of deviation acts between the screw groove 54 of the screw rod 52 and the screw groove 55 of the nut member 53. In some cases, the nut member 53 is greatly elastically deformed on the tube 70 side having low rigidity. Further, since the number of balls 56 is smaller on the tube 70 side, the load acting on each ball 56 is equalized between the tube 70 side and the opposite side. Accordingly, it is possible to prevent an excessive load / surface pressure from acting on the ball 56 and the thread grooves 54 and 55 at a specific portion where the deviation becomes large. As a result, even by such a method, the deviation generated between the screw rod 52 and the nut member 53 is absorbed, and the lead dimension accuracy of the screw groove 54 of the screw rod 52 and the screw groove 55 of the nut member 53 is lowered. As a result, the manufacturing cost of the ball screw 50 can be reduced.

[Fourth embodiment]
Next, a fourth embodiment of the present invention will be described.
Here, the entire configuration of the injection molding machine 10 can be the same as that of the first embodiment, and therefore, only the characteristic configuration will be described in the following description, and the other portions will be described. Omitted.
As shown in FIG. 10, in the fourth embodiment, a plurality of tubes 80 are provided on one side of the nut member 53 as in the third embodiment. The side on which these tubes 80 are provided is arranged as a deviation absorbing portion so as to face the injection screw 22 on the center side of the bare housing 42. At this time, in the nut member 53, the thread groove 55 is not eccentric.

As shown in FIG. 3, when the molten resin is pushed out by the injection screw 22, the pressure of the molten resin contributes as a reaction force, and the central portion of the bare housing 42 is separated from the distal end portion of the injection screw 22. Deform in the direction. On the other hand, the outer peripheral portion of the bare housing 42 is deformed so as to be pulled toward the front plate 41 by the ball screw 50.
Thus, the ball screw 50 has not only a tensile load in the axial direction toward the front plate 41 but also a radial load toward the center of the bare housing 42 to which the injection screw 22 is assembled, and the bending direction of the bare housing 42. Therefore, the surface pressure distribution of the ball screw 50 has a surface pressure acting on the ball 56 and the thread grooves 54 and 55, compared to the case where only a simple axial tensile load acts. To increase.

As described in the third embodiment, the nut member 53 has the tube 80 provided on one side so that the number of balls 56 engaged between the screw rod 52 and the nut member 53 is opposite to the tube 80 side. Less than.
By directing the nut member 53 such that the side on which the tube 80 is provided to the center side of the bare housing 42, the screw 56 and the ball 56 that meshes with the nut member 53 are weakly engaged on the tube 80 side and are opposite to each other. Since the engagement becomes stronger on the side, the acting load on the ball 56 arranged on the tube 80 side, which originally has a small number of balls and tends to increase the surface pressure, is reduced, and the acting load on the ball 56 is increased on the opposite side.

  As a result, the loads acting on the individual balls 56 on the side opposite to the tube 80 side are equalized, and an excessive load / surface pressure is applied to the balls 56 and the thread grooves 54 and 55 at a specific portion where the deviation becomes large. It becomes possible to prevent it from acting. As a result, even by such a method, the deviation generated between the screw rod 52 and the nut member 53 is absorbed, and the lead dimension accuracy of the screw groove 54 of the screw rod 52 and the screw groove 55 of the nut member 53 is lowered. Thus, the manufacturing cost of the ball screw 50 can be reduced.

FIG. 11 shows the change in the maximum surface pressure acting on the thread grooves 54 and 55 when such a ball screw 50 is arranged with the direction of the tube 80 of the nut member 53 being changed. Here, the bare housing 42 has a rectangular shape, and the ball screw 50 is provided such that the axis line is located at an equal distance from the corner of the bare housing 42 in the height direction and the width direction.
Then, in the ball screw 50 located at the upper left as viewed from the injection screw 22 side, the surface pressure at the position where the ball 56 is in contact with the ball screw 50 when the molten resin is about to be pushed out by the injection screw 22 is obtained. Examined.
At this time, the tube 80 is upward (“U” in FIG. 11), downward (“D” in FIG. 11), right (“R” in FIG. 11), and left (“L” in FIG. 11). When it is changed, it can be seen that the surface pressure varies depending on the orientation, and further, it can be seen that the surface pressure decreases by directing the tube 80 downward and rightward, that is, toward the injection screw 22 side.
Therefore, the change in the maximum surface pressure acting on the thread grooves 54 and 55 when the direction of the tube 80 was varied by 15 ° was examined. As a result, as shown in FIG. 12, it was confirmed that the surface pressure was reduced by positioning the tube 80 toward the injection screw 22 side.

  In each of the above embodiments, when an excessive load / surface pressure is applied, the screw rod 52 or the nut member 53 itself is elastically deformed to suppress / equalize the surface pressure. In addition to this, when an excessive load or surface pressure is applied, at least one of the screw rod 52 and the nut member 53 is extended or shortened by an external force exerted by various devices such as a hydraulic cylinder, so that the load / surface pressure is increased. It is also possible to adopt a configuration that reduces this.

Moreover, in each said embodiment, although the structure of the injection molding machine 10 was shown, it is good also as what kind of structure except the part used as the principal part of this invention.
Furthermore, a plurality of the configurations shown in the first to fourth embodiments may be used in an appropriate combination.
In addition to this, as long as it does not deviate from the gist of the present invention, the configuration described in the above embodiment can be selected or changed to another configuration as appropriate.

It is a figure which shows schematic structure of the injection molding machine in this embodiment. It is a figure which shows the structure of the screw rod of a ball screw, a nut member, and a ball | bowl in 1st embodiment. It is a figure which shows an example of the attachment positional relationship of the injection screw with respect to a bare housing, and a ball screw. It is a figure which shows the relationship between the slit width formed in a screw rod and a nut member, the contact angle of the ball | bowl with respect to a thread groove, and the rigidity ratio of the standing part of a thread groove. It is a figure which shows the relationship between the rigidity ratio of the standing part of a thread groove, and the surface pressure which acts on a ball | bowl. It is a figure which shows the other example of a structure of the screw rod of a ball screw, a nut member, and a ball | bowl. In 2nd embodiment, it is a figure which shows the relationship between the example of the nut member formed in the taper shape, and the surface pressure which acts on the position of a ball | bowl. It is sectional drawing which shows the tube formed in the nut member. In 3rd embodiment, it is a figure which shows the structure of a tube and a nut member. It is a figure which shows the structure of the tube and nut member in 4th embodiment. It is a figure which shows the relationship between the direction of a tube, and the surface pressure which acts on a ball | bowl. It is a figure which shows the relationship between the angle of a tube, and the surface pressure which acts on a ball | bowl.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Injection molding machine, 20 ... Injection part, 22 ... Injection screw (drive object), 23 ... Drive mechanism, 24 ... Cylinder, 25 ... Screw main body, 40 ... Base, 41 ... Front plate, 42 ... Bare housing (housing ), 50 ... Ball screw, 52 ... Screw rod, 53 ... Nut member, 54, 55 ... Screw groove, 54a, 55a ... Rising part, 56 ... Ball, 60 ... Slit (deviation absorbing part), 61, 62 ... Step part (Deviation absorption part), 70, 80 ... tube

Claims (8)

A screw rod having a thread groove formed on the outer peripheral surface;
A nut member in which the screw rod is inserted and a thread groove is formed on the inner peripheral surface;
A plurality of balls interposed between the thread groove of the threaded rod and the thread groove of the nut member,
When the drive object is driven by relatively moving the screw rod and the nut member in the axial direction of the screw rod, the screw groove of the screw rod and the screw of the nut member are driven by a reaction force transmitted from the drive object. With a deviation absorbing part that absorbs deviations that occur between the grooves ,
A tube for circulating the ball is formed in the nut member,
The plurality of tubes are formed side by side on one side across the axis of the screw rod,
The ball screw characterized in that the nut member is eccentrically provided as the deviation absorbing portion on the opposite side to the side on which the plurality of tubes are provided with respect to the screw rod .   As the deviation absorbing portion, a slit extending in parallel with the screw groove is formed in at least one of the rising portion of the screw groove of the screw rod and the rising portion of the screw groove of the nut member. The ball screw according to claim 1.   As the deviation absorbing portion, at least one of the thread groove of the threaded rod and the thread groove of the nut member, a step portion extending in parallel with the thread groove is formed at the bottom of the thread groove. The ball screw according to claim 1 or 2.   2. The deviation absorbing portion is formed such that an outer diameter of the nut member gradually decreases from one side to the other side along the axial direction of the screw rod. 4. The ball screw according to any one of 3. A mold for forming a molded body of a predetermined shape;
An injection screw that melts a resin as a raw material of the molded body in a cylinder and injects the resin into the mold by a screw that advances and retreats in the cylinder;
A ball screw that relatively advances and retracts the cylinder and the screw, and
When the injection screw is driven by relatively moving a screw rod and a nut member constituting the ball screw in the axial direction of the screw rod, the ball screw is driven by a reaction force transmitted from an object to be driven. And a deviation absorbing portion that absorbs a deviation generated in the thread groove of the nut member ,
A tube for circulating the ball is formed in the nut member,
The plurality of tubes are formed side by side on one side across the axis of the screw rod,
The injection molding machine according to claim 1 , wherein the deviation absorbing portion is provided such that the nut member is eccentric with respect to the screw rod on the side opposite to the side on which the plurality of tubes are provided . As the deviation absorbing portion, a slit extending in parallel with the screw groove is formed in at least one of the rising portion of the screw groove of the screw rod and the rising portion of the screw groove of the nut member. The injection molding machine according to claim 5 . As the deviation absorbing portion, the outer diameter of the nut member, characterized in that the are from the axis on one side along the direction of the threaded rod is formed so as to be gradually smaller toward the other side of claim 5 or 6. An injection molding machine according to 6 . A plurality of the ball screws are arranged around the injection screw,
The screw of the injection screw and the screw rod or the nut member of each of the ball screws are connected so as to operate integrally by a housing,
6. The injection molding machine according to claim 5 , wherein the nut member is provided so that the tube faces the injection screw.

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