JP4144610B2 - Ball screw device and electric injection molding machine - Google Patents

Description

  The present invention relates to a ball screw device that converts rotational motion into linear motion or converts linear motion into rotational motion, and an electric injection molding machine incorporating the ball screw device, and more particularly to a ball screw used for high load applications. This relates to the improvement of durability.

The screw shaft and ball nut in the ball screw device are connected via a plurality of balls circulating in the ball screw groove, and the screw shaft rotates relative to the ball nut with a relatively small driving force. Convert motion to linear motion.
In a general ball screw device, assuming that all the balls in the ball screw groove are equally loaded, the ball screw groove of the ball screw shaft and the ball screw groove of the ball nut are respectively in the same lead. And it is processed so that it may become the same effective diameter.

  However, when a large axial load is applied to the ball nut from the mounting member for attaching the ball nut, the ball nut itself elastically deforms in the axial direction, so that the load distribution on the ball in the ball nut changes along the axial direction. Thus, a large load is applied to the balls located in some of the ball screw groove portions. This leads to a shortening of the life of the ball screw device, and it is necessary to perform a safety design in accordance with the portion where the large load is applied.

  That is, as a conventional countermeasure, in order to suppress the elastic deformation of the ball nut, the outer diameter of the ball nut is increased to increase its cross-sectional area, or a material having a large elastic coefficient is used. Alternatively, it is conceivable to increase the diameter of the balls or increase the number of balls. However, these measures increase the size of the ball nut and the like, increasing the size of the entire ball screw device, and increasing the manufacturing cost and weight.

As a technique for improving the life of the ball screw device while avoiding an increase in the size of the entire ball screw device, there are those disclosed in Patent Document 1 and Patent Document 2. These are processed so that the effective diameter and lead of the ball screw groove are different along the axial direction in consideration of the elastic deformation of the ball nut, and the load is uniformly supported by the balls in all the screw groove portions of the ball screw groove. It is what you want to do.
JP-A-6-300107 JP-A-6-300108

However, even if the technique described in Patent Document 2 is adopted, there is a problem that it is necessary to process the ball screw groove in the axial direction to have a different diameter, which makes it difficult to process and increases costs. is there.
The present invention has been made paying attention to the above-described problems, and with a simple configuration, the load distribution of each ball in the ball nut can be made uniform in the axial direction to improve the life of the ball screw device. It is an object of the present invention to provide a ball screw device that can be used and an electric injection molding machine incorporating the ball screw device.

As described above, conventionally, when a large axial load is applied to the ball nut, the load distribution to the ball in the ball nut changes in the axial direction due to elastic deformation of the ball nut itself in the axial direction. However, there is a lack of consideration for the effects of elastic deformation of the screw shaft.
In view of the above, the present invention considers the influence of the elastic deformation of the screw shaft as well as the elastic deformation of the ball nut side with respect to a large axial load. Taneji without employing a hand stage of correction and the like of the groove (without cost), by identifying the working portion position of the axial load applied to the ball nut, the axial direction of the ball nut This invention is intended to make the ball load distribution uniform.

That is, in order to solve the above-mentioned problem, the invention described in claim 1 of the present invention has a screw shaft having a ball screw groove on the outer surface and a ball screw groove facing the ball screw groove of the screw shaft on the inner surface. At least one ball nut, a spiral passage formed by the ball screw groove of the ball nut and the ball screw groove of the screw shaft, a number of balls circulating in the spiral passage, and the number of balls In the ball screw device, the screw shaft receives the input axial load mainly on one end side in the axial direction.
The ball nut has an axial load acting portion that receives an axial load from a mounting member to which the ball nut is attached, on an axial end side that is distal from an axial end that mainly receives an axial load of the screw shaft. The ball screw device is characterized in that the ratio of the longitudinal sectional area of the ball nut to the longitudinal sectional area of the screw shaft is 0.5 or more and 2 or less .

Here, the portion of the screw shaft that receives the input axial load mainly on one end side in the axial direction is, for example, the position of the support portion when the screw shaft is cantilevered.
Further, the axial load acting portion in the ball nut is usually a mounting portion position where a mounting member connected to the ball nut is mounted.
In the present invention, when the screw shaft is configured to receive the axial load transmitted from the ball nut mainly on one end side in the axial direction, such as when the screw shaft is cantilevered, When a large axial load acts on the ball nut from the mounting member, not only the ball nut has an influence on the load distribution due to the elastic deformation of the screw shaft, but rather it is perpendicular to the screw shaft direction rather than the ball nut. This is based on the knowledge that the elastic deformation of the screw shaft having a small vertical cross-sectional area (hereinafter simply referred to as a vertical cross-sectional area) has a great influence on the load distribution in the axial direction.

  In the ball nut, the acting portion of the axial load has the largest load on the ball, and the load on the ball decreases as the distance from the acting portion increases. In view of the fact that the load on the ball receiving the directional load is the largest and the load on the ball decreases as the distance from the receiving side increases, the axial load application positions of the ball nut and screw shaft are opposite in the axial direction. By arranging so as to be on the side, the influence of the elastic deformation of the ball nut and the influence of the elastic deformation of the screw shaft tend to cancel each other and balance. As a result, the load distribution of the ball along the axial direction is made uniform.

  At this time, by making the longitudinal sectional area of the ball nut relatively close to the longitudinal sectional area of the screw shaft, that is, by making the longitudinal sectional area of the ball nut and the longitudinal sectional area of the screw shaft equal or substantially equal, And the elastic deformation of the screw shaft become more symmetric when viewed from the respective load application points in the axial direction, so that the effect of the elastic deformation of the ball nut and the effect of the elastic deformation of the screw shaft are further offset. Further, the uniform load distribution due to elastic deformation is promoted. As a result, a ball screw device that can withstand a high load with a more compact ball nut can be configured.

Here, as an invention of Reference 2, a ball screw device includes a screw shaft having a ball screw groove on an outer surface, at least one ball nut having an inner surface having a ball screw groove facing the ball screw groove of the screw shaft, A spiral passage formed by the ball screw groove of the ball nut and the ball screw groove of the screw shaft, a number of balls circulating in the spiral passage, and a return path of the number of balls. The screw shaft is a ball screw device that receives an input axial load mainly on one end side in the axial direction.
The main load direction of all the balls in the spiral passage is set to the same direction with respect to an external load, and the axial direction of the axial load acting portion of the ball nut that receives the axial load from the mounting member to which the ball nut is attached The positions may be the positions where the balls in the spiral passage are respectively present on both sides in the axial direction of the axial load acting portion.

The axial position of the axial load acting portion is preferably at or near the axial center of the ball nut.
The greatest cause of load distribution in the axial direction is due to the elastic deformation of the ball nut and screw shaft members themselves in the axial direction. The magnitude of the member deformation is determined by the length to the ball position in the spiral passage farthest from the axial load acting portion, and the longer the length, the larger the member deformation.

  Therefore, when the axial load acting portion is located at the axial end of the ball nut, the length that determines the member deformation substantially corresponds to the entire length of the ball nut, and the influence of the member deformation increases accordingly. However, even in this case, by adopting the invention of claim 1 above, that is, in a direction in which the deformation of the shaft and the nut is opposite, the load distribution of the ball along the axial direction is made uniform as a result.

  On the other hand, in the invention of Reference 2, if the axial load acting part is set at the central part of the ball nut, for example, the distance to the ball in the spiral passage farthest from the axial load acting part is about half. As for the load distribution of the ball along the axial direction, the effect is almost the same as when the axial length of the ball nut is halved, thereby reducing the amount of elastic deformation in the axial direction. It can be expected to improve the load distribution.

  In other words, according to the invention according to Reference 2, the axial load acting portion is the boundary, and the position closer to the axial one end portion mainly receiving the axial load of the screw shaft than the position of the axial load acting portion (close With the same action as in claim 1, the load distribution of the balls along the axial direction is made uniform, and at the same time, from the axial load acting part to the balls in the spiral passage farthest As the distance becomes shorter than that of the first aspect, the amount of elastic deformation becomes smaller, and the load distribution of the ball along the axial direction becomes more uniform.

  Further, on the side farther from the axial one end portion (the portion at the distal end) that mainly receives the axial load of the screw shaft than the position of the axial load acting portion, the above-mentioned conventional example is formally Although the structure is the same, the amount of elastic deformation is suppressed to the extent that the distance from the axial load acting portion to the ball in the farthest spiral passage is shortened, and at the same time, the axial load acting on the axial load acting portion. Since the axial load applied to the distal portion is small, the far portion is divided by the proximal portion and the distal portion with the axial load acting portion as a boundary. Even in the portion at the upper position, the load distribution of the balls along the axial direction is made uniform.

As described in the operation of the first aspect, it is preferable that the longitudinal sectional area of the ball nut portion on the proximal side is equal to or substantially equal to the longitudinal sectional area of the screw shaft.
Here, the reason that “the main load direction of all the balls in the spiral passage is set to the same direction with respect to the external load” is as follows.
That is, in the case where the main load direction with respect to the external load of the two groups of balls existing on both sides in the axial direction is set opposite to each other across the axial load acting portion in the balls in the spiral passage, (Refer to FIG. 11 and FIG. 12) The axial load is mainly borne only by one ball group on both sides in the axial direction across the axial load acting portion depending on the direction of the axial load. This is because the load distribution in the axial direction that is borne by the two sets of balls on both sides in the axial direction across the action part is greatly unbalanced, and it is difficult to make the load distribution of the balls uniform in the entire axial direction. .

On the other hand, by setting the main load direction of all balls in the spiral passage to the same direction with respect to the external load, the main load direction of all balls in the spiral passage becomes the same direction with respect to the axial load. In other words, it is possible to prevent a significant imbalance such that the ratio of the sharing with respect to the axial load that is borne by the two sets of balls on both sides in the axial direction across the axial load acting portion is prevented, and the above action is effectively performed. Demonstrated.
In order to set the main load direction of all the balls in the spiral passage to the same direction with respect to the external load, for example, the preload direction is set to the same direction on both axial sides of the axial load acting portion. Or set to a state in which no preload is applied (see FIGS. 13 and 14).

Next, with respect to the configuration described in the invention of Reference 2, the invention of Reference 3 mainly uses the axial load of the screw shaft for each of the cross-sectional areas on both sides in the axial direction across the axial load acting portion of the ball nut. The longitudinal cross-sectional area on the distal side is larger than the longitudinal cross-sectional area on the proximal side from the one axial end portion to be received.
According to the present invention, the longitudinal cross-sectional area of both sides of the axial load acting portion in the ball nut is changed to balance the entire load on the ball along the axial direction, thereby further along the axial direction. It is possible to improve the uniform load distribution of the balls.

  That is, when the configuration according to Reference 2 is adopted, for example, if the longitudinal cross-sectional area of the ball nut along the axial direction is uniform, one end in the axial direction that mainly receives the axial load of the screw shaft at the boundary of the axial load acting portion. The load on the ball at the distal portion is generally smaller than that near the portion (proximal portion) (see, for example, FIG. 8). On the other hand, as in the invention of Reference 3, by setting the longitudinal cross-sectional area of the ball nut portion on the distal side to be larger than the longitudinal cross-sectional area of the ball nut on the proximal side, Since the amount of elastic deformation is kept small, the load on the ball at the distal portion increases as a whole, and the load on the ball at the proximal portion decreases as a whole, and further along the axial direction. The load distribution of the balls can be made uniform.

Next, the invention described in claim 2 provides an electric injection molding machine using the ball screw device described in claim 1.
Ball screw devices such as those described above are usually very large loads by converting the rotational force of the motor into axial thrust when the injection molding machine, punching press, and various jacks that are driven by a hydraulic cylinder are driven by an electric motor. It is suitable for application to the place which receives.
In particular, it is suitable for use in an injection molding machine driven by an electric motor. By using the ball screw device according to claim 1 as in the present invention, the life of the ball screw device is increased without increasing the size and weight. -Durability is improved and the life of the injection molding machine is improved.

As described above, when the ball screw device of the present invention is adopted, the load distribution of the ball is reduced by reversing the tendency of the influence on the load distribution in the axial direction due to the elastic deformation of the screw shaft and the ball nut. As a result, the size of the maximum ball load with respect to the external force can be kept small, so that there is an effect that the durability can be easily improved in a high load use environment.
In addition, by making the longitudinal cross-sectional areas of the screw shaft and the ball nut substantially the same and aligning the amount of elastic deformation of both, the ball load distribution may be balanced to improve the durability.
Further, when the invention according to claim 2 is adopted, there is an effect that it is possible to provide an electric injection molding machine suitable for high load use without increasing the cost.

Next, a first embodiment of the present invention will be described with reference to the drawings.
The basic configuration of the ball screw device according to the present invention is the same as that of a general ball screw device. As shown in FIGS. 1 and 2, the screw shaft 1 having a ball screw groove 1d on the outer surface, and the screw shaft 1 It comprises at least one ball nut 2 having a ball screw groove 2d facing the ball screw groove 1d on its inner surface, and is formed by the ball screw groove 2d of the ball nut 2 and the ball screw groove 1d of the screw shaft 1. A number of balls 9 can circulate while rolling in the spiral path, and a return path 2e is provided for returning the ball that has moved to one axial end of the spiral path to the other axial end.

The screw shaft 1 has a cantilever support structure, and one end 1a in the axial direction is rotatably supported by the support unit 3. The support bearing of the ball screw by the support unit 3 is composed of, for example, a thrust angular ball bearing. The support unit 3 is fixed to the fixing member 4.
A pulley 5 is attached to one end of the screw shaft 1 in the axial direction. By rotating the pulley 5, the screw shaft 1 rotates and the ball nut 2 moves linearly. A stopper 6 is attached to the other axial end 1b of the screw shaft 1 to prevent the ball nut 2 from coming off from the other axial end 1b.

Further, the ball nut 2 is provided with a flange portion 7 a on the axial end side distal to the support unit 3, and the flange portion 7 a constitutes an attachment portion 7 to which the attachment member 8 is attached. And the attachment member 8 slid with respect to the said attachment part 7 is bolted. This mounting portion 7 constitutes an axial load acting portion.
In the ball screw device having the above configuration, as shown in FIG. 3A, when an axial load F1 is applied from the mounting member 8 to the mounting portion 7 of the ball nut 2, the shaft from the ball nut 2 to the screw shaft 1 is The directional load is transmitted, and an axial load F2 in the opposite direction is generated as a reaction force at the axial one end 1a on the fixed side.

At this time, assuming that the screw shaft 1 is a rigid body as in the prior art and considering the elastic deformation of the ball nut 2, the load distribution of the ball along the axial direction is as shown in FIG. The load becomes the largest at the position of the portion 7 and gradually decreases toward the other end (support unit 3 side).
On the other hand, when the ball nut 2 is assumed to be a rigid body and the elastic deformation of the screw shaft 1 is taken into consideration, the load distribution of the ball along the axial direction is as shown in FIG. The load is greatest at the axial end 1a of the shaft 1 and gradually decreases toward the other end (the mounting portion 7 of the ball nut 2).

  Actually, both the ball nut 2 and the screw shaft 1 are elastically deformed in the axial direction. Therefore, when the elastic displacement of both 1 and 2 is taken into consideration, the load distribution of the ball as shown in FIG. That is, in this embodiment, the mounting portion 7 of the ball nut 2 is provided at a position distal to the support unit 3 so that the load application position of the ball nut 2 and the load application side of the screw shaft 1 are opposite to each other. Since the load distribution along the axial direction is relatively large at both ends and relatively small at the center, the difference between the maximum value and the minimum value is small. That is, the load on the ball is made uniform.

  Here, unlike the present invention, as shown in FIG. 4A, a mounting portion 7 of the ball nut 2 is provided at a position proximal to the support unit 3, and the load acting position and shaft of the ball nut 2 are provided. When the load acting side is the same side, assuming that the screw shaft 1 is a rigid body and considering the elastic deformation of the ball nut 2, the load distribution of the ball is expressed as shown in FIG. The load becomes the largest at the attachment portion 7 and gradually decreases toward the other end (on the other end 1b side in the axial direction of the screw shaft). Further, when the ball nut 2 is assumed to be a rigid body and the elastic deformation of the screw shaft 1 is considered, the load distribution of the ball is expressed on the support unit 3 side (in the axial direction of the screw shaft 1 as shown in FIG. 4C). The load is greatest at one end 1a side, and gradually decreases toward the other end (on the other axial end 1b side of the screw shaft). Therefore, considering the elastic deformation of both 1 and 2, as shown in FIG. 4D, the difference between the maximum value and the minimum value of the ball load becomes extremely large.

  Basically, if both the screw shaft 1 and the ball nut 2 are rigid bodies, such a problem does not occur. However, if a large axial load is received in a practically limited space, the screw shaft 1 and the ball nut inevitably. The nut 2 also elastically deforms in the axial direction, and as a result, the axial distribution of the ball load is generated as described above. Naturally, it is presumed that the portion with the largest ball load is the hardest portion in terms of durability, and damage starts from that portion.

In order to reduce the load on individual balls, ball screws tend to be designed to increase the number of load balls by increasing the number of turns and the number of rows of spiral passages in order to reduce the load on each ball. As a result, the length of the ball nut 2 becomes longer, and the influence of the elastic deformation of the ball nut 2 and the screw shaft 1 tends to be further ignored. On the other hand, in the ball screw device according to the present invention, only by specifying the position of the mounting portion 7 of the ball nut 2 in relation to the support unit 3, the elastic deformation of the screw shaft 1 and the ball nut 2 is performed. The adverse effects are greatly reduced, leading to an improvement in the durability and life of the ball screw device.
That is, the present invention is an effective technique that is more effective as it becomes a ball nut device for high load applications.

  Here, in the configuration of the above embodiment, the operation when the vertical cross-sectional area of the screw shaft 1 and the vertical cross-sectional area of the ball nut 2 are made equal will be described. As shown in FIGS. The load is balanced to the left and right by increasing the axial ends at the same level, and the maximum load on the ball can be suppressed. On the other hand, for example, when the vertical cross-sectional area of the ball nut 2 is made larger than the vertical cross-sectional area of the screw shaft 1 as in the conventional case, a left-right difference occurs, and the load acting side of the screw shaft 1 (the side opposite to the mounting portion 7). That is, the maximum load on the ball is increased on the support unit side, which is disadvantageous compared to the case where the vertical cross-sectional area of the screw shaft 1 and the vertical cross-sectional area of the ball nut 2 are equal. The difference in load distribution between FIGS. 5A and 5B is obtained by changing the vertical cross-sectional areas of the screw shaft 1 and the ball nut 2. That is, FIG. 5B shows a case where the vertical cross-sectional area of both is reduced, and FIG. 5A shows a case where the vertical cross-sectional area of both is increased. That is, it is understood that the larger the longitudinal cross-sectional area, the more effective. When the screw shaft 1 and the ball nut 2 are compared, the longitudinal cross-sectional area of the screw shaft 1 on the inner side inevitably tends to be smaller than the vertical cross-sectional area of the ball nut 2. In order to effectively suppress the influence of the elastic deformation, it is desirable that each of the vertical cross-sectional areas is as large as possible. Therefore, it is preferable to increase the vertical cross-sectional area of the screw shaft 1 to be approximately equal to the vertical cross-sectional area of the ball nut 2. Further, the maximum value of the longitudinal sectional area ratio is preferably approximately 2 or less as a range in which the influence of the ball load can be balanced to some extent due to the elastic deformation of the screw shaft 1 and the ball nut 2.

Next, a second embodiment will be described with reference to the drawings. The same parts as those in the first embodiment will be described with the same reference numerals.
The basic configuration of the ball screw device of this embodiment is the same as that of the first embodiment as shown in FIG. That is, it is composed of a screw shaft 1 having a ball screw groove 1d on the outer surface and a ball nut 2 having a ball screw groove on the inner surface facing the ball screw groove 1d of the screw shaft 1, In addition, a large number of balls can circulate while rolling in a spiral passage formed by the ball screw groove 1d of the screw shaft 1 and the balls moved to one end in the axial direction of the spiral passage can be moved in the axial direction. A return path (not shown) for returning to the end is provided.

  The screw shaft 1 has a cantilever support structure, and one end 1a in the axial direction is rotatably supported by the support unit 3. The support bearing of the ball screw by the support unit 3 is composed of, for example, a thrust angular ball bearing. The support unit 3 is fixed to the fixing member 4. A pulley 5 is attached to one end of the screw shaft 1 in the axial direction. By rotating the pulley 5, the screw shaft 1 rotates and the ball nut 2 moves linearly. A stopper 6 is attached to the other axial end 1b of the screw shaft 1 to prevent the ball nut 2 from coming off from the other axial end 1b.

The ball nut 2 is configured by a flange-matched tundum nut structure in which a flange portion 7a is provided at the center, and the flange portion 7a located at the axial center portion of the ball nut 2 forms a mounting portion 7, and the mounting portion A mounting member 8 to be slid with respect to 7 is bolted and attached. The mounting portion 7 constitutes an axial load acting portion.
Here, by providing the mounting portion 7 constituting the axial load acting portion at the axial center portion of the ball nut 2, the axial portion of the mounting portion 7 in the spiral passage where the axial load is loaded is provided on both sides in the axial direction. The ball will be located.
In the following description, the ball nut portion closer to the support unit 3 across the mounting portion 7 is referred to as a proximal ball nut 2A, and the ball nut portion farther from the support unit 3 is referred to as a distal ball. This is called nut 2B.

  Here, conventionally, there is a ball screw having a flange-matching double nut structure in which the flange portion 7a is disposed in the center portion in the axial direction of the ball nut 2. With this ball screw, the flange portion 7a is connected to the shaft of the ball nut 2. The purpose of arranging in the center of the direction is to apply a preload to the balls in the spiral passage by sandwiching a spacer 20 or the like between the flange portions 7a as shown in FIGS. That is, in the conventional ball screw shown in FIG. 11, a tensile preload is applied by inserting a spacer 20 thicker than the screw pitch, and the proximal ball nut 2A and the distal ball nut 2B sandwiching the flange portion 7a. As a result, the main load direction of the ball with respect to the external load is set to the opposite direction between the proximal ball nut 2A and the distal ball nut 2B. Further, in the conventional ball screw shown in FIG. 12, a compression preload is applied by inserting a spacer 20 thinner than the screw pitch, and a proximal ball nut 2A and a distal ball nut 2B sandwiching the flange portion 7a. As a result, the main load direction of the ball with respect to the external load is set to the opposite direction between the proximal ball nut 2A and the distal ball nut 2B. As described above, in the conventional ball nut, the main load direction of the ball in the spiral path with respect to the external load is opposite to the flange portion 7a even when the flange portion 7a is disposed in the central portion of the ball nut 2 in the axial direction. It is a direction and is outside the scope of the present embodiment (out of range).

  On the other hand, in the ball screw which is the object of the present embodiment, the main load direction of the ball in the spiral passage with respect to the external load is set so as to be all the same direction on both axial sides of the flange portion 7a. . That is, when an axial load is input, the ratio of the axial load sharing between the proximal ball nut 2A and the distal ball nut 2B across the mounting portion 7 is set to be substantially equal.

  In order to set all the main load directions of the balls in the spiral passage with respect to the external load to the same direction, for example, as shown in FIG. 13, a ball (oversize ball) slightly larger than the space of the ball screw groove is used. This can be achieved by bringing the ball into contact with four points to apply a preload, or adopting a configuration in which no preload is applied as shown in FIG. Here, although a single nut structure is illustrated in FIGS. 13 and 14, a tandem nut structure may be used, and a spacer may not be interposed between the opposing flange portions 7a. When inserting a spacer, a spacer having a thickness equal to the screw pitch may be inserted.

Next, the operation and the like will be described.
In the ball screw device having the above-described configuration, as shown in FIG. 8A, when an axial load F1 is applied from the mounting member 8 to the mounting portion 7 of the ball nut 2, the shaft is moved from the ball nut 2 to the screw shaft 1. The directional load is transmitted, and an axial load F2 in the opposite direction is generated as a reaction force at the axial one end 1a on the fixed side.

At this time, assuming that the screw shaft 1 is a rigid body as in the prior art and considering the elastic deformation of the ball nut 2, the load distribution of the ball along the axial direction is as shown in FIG. The load becomes largest at the position of, and gradually decreases from the position toward both sides in the axial direction.
On the other hand, when the ball nut 2 is assumed to be a rigid body and the elastic deformation of the screw shaft 1 is taken into consideration, the load distribution of the ball along the axial direction is as shown in FIG. At the one end 1a side in the axial direction), the load becomes the largest and gradually decreases in the direction away from the support unit 3.

Actually, since both the ball nut 2 and the screw shaft 1 are elastically deformed in the axial direction, the ball load distribution as shown in FIG.
That is, on the proximal ball nut 2A side, as in the first embodiment, the axial load distribution state at the ball nut 2 and the axial load distribution state at the screw shaft 1 are opposite to each other. The load distribution along the axial direction is a distribution in which both ends are relatively large and the central portion is relatively small, but the difference between the maximum value and the minimum value is small. That is, the load on the ball is made uniform. In particular, when a ball screw having the same load capacity as that of the first embodiment is used, the load on the ball is made more uniform than that of the first embodiment by the length of the proximal ball nut portion in the axial direction. ing.

  On the distal ball nut 2B side, although the axial load distribution state at the ball nut 2 and the axial load distribution state at the screw shaft 1 coincide, the axial load applied is small and the axial direction Since the length is short, the load difference (difference between the maximum value and the minimum value) at both ends in the load distribution along the axial direction is small, and the load on the ball is uniform in the ball nut 2 as a whole.

Thus, similarly to the first embodiment, in the ball screw device of the present embodiment, the screw shaft 1 and the ball are identified only by specifying the position of the mounting portion 7 of the ball nut 2 in relation to the support unit 3. The adverse effect due to the elastic deformation of the nut 2 is greatly reduced, leading to an improvement in durability and life of the ball screw device.
That is, this embodiment is an effective technique that is more effective as it becomes a ball nut device for high load applications.

In particular, since the mounting portion 7 is provided at the central portion in the axial direction of the ball nut, the mounting portion position of the mounting member 8 is equal to the amount of the mounting portion 7 being moved to the center while achieving uniform load distribution of the balls. By approaching the support unit 3 (on the screw shaft fixing side), the entire ball nut device can be made more compact than the first embodiment.
Here, a flange-matched tandem nut structure has been described as an example of the ball nut 2, but the configuration of the ball nut 2 is not limited to this. A single nut can provide the same function.

Further, in the ball nut 2, the outer diameters of the proximal ball nut 2A and the distal ball nut 2B are equal, that is, the longitudinal sectional areas of both nuts 2A and 2B are equal. If both nuts 2A and 2B are made equal, manufacturing blanks, jigs, and the like can be made common, which facilitates manufacturing.
At this time, if the vertical cross-sectional area of the screw shaft 1 and the vertical cross-sectional area of the ball nut 2 are equal, on the proximal ball nut 2A side, the load on the ball becomes the same size at both axial ends. Can be balanced, and the maximum load on the ball can be suppressed.

At this time, the maximum value of the longitudinal cross-sectional area ratio is preferably approximately 2 or less as a range in which the influence of the ball load can be balanced to some extent due to the elastic deformation of the screw shaft 1 and the ball nut 2.
Furthermore, if the longitudinal cross-sectional area of the distal ball nut 2B is set larger than that of the proximal ball nut 2A, the load distribution of the balls in the axial direction can be made more uniform. That is, increasing the longitudinal cross-sectional area on the distal ball nut side increases the axial load borne on the distal ball nut side, lowering the ball load on the proximal ball nut side and reducing the distal ball By increasing the load of the ball on the nut side, the load balance of the entire ball becomes more uniform.

Next, an embodiment in which the ball screw device having the above configuration is adopted in an electric injection molding machine as shown in FIG. 6 will be described. Note that the energy consumption of the electric injection molding machine can be reduced by changing the actuator from the hydraulic cylinder device to the electric motor 19 and the ball screw device A.
In FIG. 6, reference numeral 10 denotes a molding base, reference numeral 11 denotes an injection part, reference numeral 12 denotes a mold holding part, and reference numeral 15 denotes a resin hopper.

And the bracket 17 (attachment member 8) provided in the one end part of the injection machine 16 is attached to the attachment part 7 of the ball nut 2 in the some ball screw apparatus A based on this embodiment, and the said some ball screw The device A is fed in the axial direction.
One end side in the axial direction of the screw shaft 1 of each ball screw device A is fixed to the frame of the injection unit 11 via the support unit 3, and a drive shaft of the electric motor 19 is connected to a pulley provided at the one end in the axial direction. Are connected via the belt 18 so that the driving force from the motor 19 can be transmitted.

In such an injection molding machine, each screw shaft 1 is rotated by driving the electric motor 19, and each ball nut 2 is linearly moved in the axial direction, so that the injection machine 16 is moved in the axial direction to hold the mold. Approach / separate part 12.
Then, by the injection operation, an axial load toward the support unit 3 is input from the injector 16 to each ball nut 2, and the axial load is transmitted to the screw shaft 1, and the screw shaft 1 mainly supports the support unit 3. It will be received at the position of.

  At this time, when the axial load is large, such as a high radiation output, the ball nut 2 and the screw shaft 1 undergo elastic deformation that cannot be ignored. However, as described above, the mounting portion 7 is attached to the support unit 3. In this embodiment set at the distal end, the load distribution of the ball is made uniform, and the adverse effect of the elastic deformation is reduced. Therefore, it can be seen that the ball screw device is suitable for application to an electric injection molding machine.

That is, the ball screw device according to the present embodiment is suitable for high-load applications despite the fact that it does not require an increase in size or special processing, and can be used in an electric injection molding machine without increasing costs. .
In the above description, the case where the device of the first embodiment is adopted as the ball screw device has been described as an example. However, even when the ball screw device of the second embodiment is applied, the same operation and effect are exhibited. To do.

Here, in all the above-described embodiments, the case where the screw shaft 1 rotates to move the ball nut 2 linearly is described as an example, but the present invention is not limited to this. Even when one axial end portion of the ball nut 2 is fixed and a load is input from the position of the screw shaft 1 opposite to the one end portion of the ball nut 2, the same operation and effect as described above are obtained.
In addition to the ball screw device in which the screw shaft 1 rotates and the ball nut 2 moves, the ball nut 2 rotates and the screw shaft 1 moves, and the screw shaft 1 is fixed and the ball nut 2 rotates and moves straight. This is effective for all types of use in which the ball nut 2 is fixed and the screw shaft 1 moves linearly while rotating.

Examples of the operational effects of the above ball screw devices will be described.
As the ball screw device, there are four types of devices shown in FIG. 9, wherein (a) is a device based on the specification based on the first embodiment, and (b) is a device based on the conventional specification for comparison. (C) and (d) are based on the second embodiment, and (d) is a configuration in which the longitudinal cross-sectional area of the distal ball screw 2B is larger than the proximal ball screw 2A based on the invention of Reference 3. It is.

That is, as shown in each drawing of FIG. 9, the internal specifications of each ball screw device are as follows: shaft diameter φ100 of all screw shafts 1, leads 20, ball diameter of balls 15.875, number of circuits in ball nut 2. The 2.5 winding 4 rows are designed in the same way, and only the mounting method, flange position, and nut outer diameter are changed.
And when the ball load distribution inside each ball screw device was calculated. The result shown in FIG. 10 was obtained.

From the results in FIG. 10, even if the load capacity (rated load) determined by the internal specifications of the ball screw device is the same and the axial load applied to it is the same, it depends on the mounting conditions, flange position, and nut outer diameter. It can be seen that the actual internal load distribution varies greatly.
That is, it is understood that the load distribution cannot be made uniform under the conventional apparatus condition (b), but the load distribution can be equalized by using the apparatus condition (a) according to claim 1.

Further, (c) and (d) are those in which the mounting portion 7 is installed in the center in the axial direction based on the invention of Reference 2, but (d) dare to change the nut outer diameter on the A side and B side, The longitudinal cross-sectional area on the distal ball nut 2B side is larger than that of the proximal ball nut 2A, and is balanced so that the load on the entire ball becomes more uniform. According to this, even if it compares with (a) based on the said Claim 1, the maximum ball | bowl load is equivalent or less, and there is no inferiority.
Moreover, even if the nut outer diameter is the same on the A side and B side (c), the maximum ball load is slightly less than (a), but clearly compared with the conventional (b) shaft. It can be seen that the load distribution of the balls along the direction is uniform.

It is a figure showing a ball screw device concerning a 1st embodiment of the present invention. It is a figure which shows the structure of the ball screw apparatus main body which concerns on 1st Embodiment of this invention. It is a figure explaining the effect | action and effect of the ball screw apparatus which concerns on 1st Embodiment of this invention, (a) is an action state of an axial load, (b) is a case where a screw shaft is assumed to be a rigid body. (C) shows the load distribution of the ball when the ball nut is assumed to be a rigid body, and (d) shows the load distribution of the ball in consideration of the elastic deformation of the screw shaft and the ball nut. Yes. It is a figure explaining the effect | action and effect of the ball screw apparatus which concerns on a comparative example, (a) is an action state of an axial load, (b) is a load distribution of the ball | bowl when a screw shaft is assumed to be a rigid body, (C) shows the load distribution of the ball when the ball nut is assumed to be a rigid body, and (d) shows the load distribution of the ball in consideration of the elastic deformation of the screw shaft and the ball nut. It is a figure explaining the influence on the load distribution of a ball | bowl by the ratio of the longitudinal cross-sectional area of the screw shaft which concerns on 1st Embodiment of this invention, and the longitudinal cross-sectional area of a ball nut, (a) And (b) is both longitudinal sections This is a case where the areas are equal, and (c) shows a case where the longitudinal sectional area on the ball nut side is relatively large. It is a figure which shows the electric injection molding machine using the ball screw apparatus based on this invention. It is a figure which shows the ball screw apparatus which concerns on 2nd Embodiment. It is a figure explaining the effect | action and effect of the ball screw apparatus which concerns on 2nd Embodiment, (a) is the action state of an axial load, (b) is the load of a ball | bowl when a screw shaft is assumed to be a rigid body. (C) shows the load distribution of the ball when the ball nut is assumed to be a rigid body, and (d) shows the load distribution of the ball in consideration of the elastic deformation of the screw shaft and the ball nut. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure explaining the specification of each ball screw apparatus in an Example, (a) is an example of an apparatus based on Claim 1, (b) is an example of a conventional apparatus for comparison, (c) is a reference 2. (D) shows an example of an apparatus based on the invention of Reference 3, respectively. It is a figure which shows the load distribution of the ball | bowl along the axial direction in each ball screw apparatus in FIG. It is a figure explaining the main load direction of the ball | bowl in a helical channel | path, Comprising: It is a figure which shows the conventional ball screw to which the preload is provided by tension | pulling. It is a figure explaining the main load direction of the ball | bowl in a helical channel | path, Comprising: It is a figure which shows the conventional ball screw to which the preload is provided by compression. It is a figure explaining the main load direction of the ball | bowl in a spiral channel | path, Comprising: It is a figure in case the preload is given to the same direction over the whole axial direction by the oversized ball. It is a figure explaining the main load direction of the ball | bowl in a helical channel | path, Comprising: It is a figure when the preload is not provided.

Explanation of symbols

1 Screw shaft 1a Axial end 1d Ball screw groove 2 Ball nut 2d Ball screw groove 2e Return path 2A Proximal ball nut 2B Distal ball nut 3 Support unit 4 Fixing member 7 Mounting portion 8 Mounting member 9 Ball F1 At mounting portion Acting axial load F2 Reaction force generated on the screw shaft side

Claims (2)

A screw shaft having a ball screw groove on the outer surface, at least one ball nut having a ball screw groove facing the ball screw groove of the screw shaft on the inner surface, the ball screw groove of the ball nut, and the ball screw groove of the screw shaft And a plurality of balls circulating in the spiral passage, and a return path of the plurality of balls. The screw shaft mainly receives an input axial load in the axial direction. In the ball screw device received on one end side,
The ball nut has an axial load acting portion that receives an axial load from a mounting member to which the ball nut is attached, on an axial end side that is distal from an axial end that mainly receives an axial load of the screw shaft. Provided,
A ball screw device , wherein a ratio of a vertical cross-sectional area of a ball nut to a vertical cross-sectional area of a screw shaft is set to 0.5 or more and 2 or less .   An electric injection molding machine using the ball screw device according to claim 1.

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