JP5534555B2 - Screw jack - Google Patents

Description

  The present invention relates to a screw jack using a ball screw.

  Screw jacks are widely used in various factory facilities as a kind of linear actuator. The screw jack is characterized in that it is compact and can easily realize a large operating force as compared with the pneumatic actuator, and the operation sound is low. Another feature is that it is not necessary to prepare a separate hydraulic unit unlike a hydraulic actuator. On the other hand, since the screw jack has a structure that converts a rotational operation into a linear operation, it has been recognized that the screw jack is not suitable for applications requiring high-speed operation or high-frequency operation.

  By the way, manufacturing facilities such as a semiconductor manufacturing apparatus and a liquid crystal display device tend to increase in size, and in order to reduce manufacturing costs, applications requiring high-speed operation and high-frequency operation for linear actuators are increasing. For example, a high-speed and high-frequency operation of 70% duty (operation time + ratio of operation time to pause time) may be required at a speed of 20 m / min. Here, in an electric screw jack that drives a trapezoidal screw by a worm gear that is most common as a screw jack, it is difficult to realize high-speed and high-frequency operation. A screw jack that drives a ball screw by a bevel gear is applied to an application that requires such high-speed and high-frequency operation.

  However, in a screw jack that drives a ball screw by a bevel gear, high-speed operation can be realized relatively easily, but if a high-frequency operation is performed, the problem that the ball screw nut is overheated due to heat loss becomes obvious. become. The problem of overheating of the ball screw nut has been regarded as a problem in machine tools that require precise positioning. Various countermeasures have been proposed as countermeasures against overheating. For example, there is a ball screw having a hollow structure to flow a cooling medium through the hollow portion to prevent overheating (see Patent Documents 1 and 2). Some ball screw nuts have an axial cooling hole, and a cooling medium is passed through the cooling hole to prevent overheating (see Patent Documents 3 and 4).

JP 2000-18364 A JP 2002-113638 A Japanese Patent Laid-Open No. 2000-24876 JP 2004-169743 A

  Although all of the countermeasures against overheating shown in the above-mentioned patent documents exhibit an excellent cooling effect, a cooling hole for flowing a cooling medium to either the ball screw shaft or the ball screw nut is indispensable, and is produced in large quantities. There is a problem that an inexpensive ball screw unit cannot be employed. In the evaluation of merchantability, the manufacturing cost is the largest evaluation item, and the fact that a specially processed ball screw unit has to be adopted significantly reduces the merchantability. SUMMARY OF THE INVENTION An object of the present invention is to provide a screw jack excellent in merchantability that can be operated without overheating even at high speed and high frequency operation, while adopting a mass-produced and inexpensive ball screw unit.

The invention according to claim 1 includes a drive sleeve coupled to a bevel gear and pivotally supported in a housing, a ball screw nut fixed to the drive sleeve, and a ball screw shaft screwed to the ball screw nut. In the screw jack, a nut protection cylinder is attached to the upper part of the housing, a screw shaft cover is attached to the top plate of the nut protection cylinder, and the inside of the screw shaft cover and the inside of the nut protection cylinder communicate with each other to allow free air. The screw jack is characterized in that an air hole is provided in a side surface base portion of the nut protection cylinder.

  The invention described in claim 2 is the screw jack according to claim 1, wherein a filter is provided in the air hole.

  According to a third aspect of the present invention, in the screw jack according to the first or second aspect, the nut protection cylinder and the screw shaft cover are integrated.

  According to the first aspect of the present invention, the air inside the nut protection cylinder and the air outside the nut protection cylinder are exchanged by the reciprocating motion of the ball screw shaft, thereby cooling the ball screw nut. Therefore, it is possible to realize a screw jack excellent in commerciality that can be operated without overheating of the ball screw nut even when a high-speed and high-frequency operation is performed while employing a mass-produced and inexpensive ball screw unit.

  According to the invention described in claim 2, by providing the filter in the air hole, it is possible to prevent the dust and the like from entering the nut protection cylinder by the filter even in an installation environment where the dust and the like are large. Therefore, the screw jack can be stably operated.

  According to the invention described in claim 3, the number of components is reduced by integrating the nut protection cylinder and the screw shaft cover, and a screw jack excellent in mass productivity and low in manufacturing cost can be realized.

It is a longitudinal cross-sectional view which shows the Example of the screw jack which concerns on this invention.

  An embodiment of a screw jack 1 according to the present invention will be described with reference to FIG. FIG. 1 is a longitudinal sectional view of a screw jack 1 according to the present invention, and shows a state in which the screw jack 1 is placed. The housing 2 includes three parts: a body housing 3, a lower end cap 4, and an upper end cap 5.

  A lower end cap 4 is attached to the lower surface of the body housing 3, and an upper end cap 5 is attached to the upper surface thereof. The lower and upper surfaces of the body housing 3 and the attachment surfaces of the lower end cap 4 and the upper end cap 5 are finished to be smooth so that the lubricating oil can be sealed. An input cartridge 7 that pivotally supports a bevel pinion 6 that is an input shaft is mounted on one side surface of the body housing 3. The mounting surfaces of the body housing 3 and the input cartridge 7 are also finished smoothly so that the lubricating oil can be sealed.

  A through hole 8 is provided at the center of the lower end cap 4, and a protrusion 9 is provided concentrically with the through hole on the lower surface of the lower end cap 4. The protrusion 9 facilitates positioning work when the screw jack 1 is installed on the object. An oil seal 12 is disposed between the inner peripheral surface of the lower end cap 4 and the outer peripheral surface of the drive sleeve 11.

  A through hole 13 is also provided at the center of the upper end cap 5, and the drive sleeve 11 can extend upward from the through hole. An oil seal 14 is disposed between the inner peripheral surface of the upper end cap 5 and the outer peripheral surface of the drive sleeve 11.

  A bevel gear 15 is coupled to the outer peripheral surface of the cylindrical drive sleeve 11 using a key (not shown), and the tooth portion of the bevel gear 15 is engaged with the tooth portion of the bevel pinion 6. A lower bearing 16 and an upper bearing 17 are disposed on both ends of the outer peripheral surface of the drive sleeve 11 with the bevel gear 15 interposed therebetween.

  Further, the drive sleeve 11 incorporates a seal member 18 below the upper bearing 17, and the lip portion 19 of the seal member 18 has a sealing structure in contact with the lower end surface of the upper end cap 5. . Therefore, the upper bearing 17 is isolated from the inside of the body housing 3, and the bevel gear 15 can be oil-lubricated while the upper bearing 17 can be grease-lubricated. Thus, the bevel gear and the upper bearing can be reliably lubricated.

  A ball screw nut 21 is fixed to the upper inner peripheral surface of the drive sleeve 11. Specifically, the male screw of the ball screw nut 21 is screwed into the female screw 22 provided on the upper inner peripheral surface of the drive sleeve 11, and is securely fixed using a screw or the like (not shown) as a locking stopper. .

  A ball screw shaft 23 is screwed onto the inner peripheral surface of the ball screw nut 21 via a ball.

  Since the screw jack 1 according to the present invention is required to operate at high speed, a high lead type is preferable as the ball screw unit. However, even a high lead ball screw unit capable of high-speed operation does not require a cooling hole in the ball screw nut 21, and a mass-produced inexpensive ball screw unit can be used.

  A nut protection cylinder 24 is attached to the upper surface of the upper end cap 5. The nut protection cylinder 24 has a mounting flange 25 at the bottom of the cylinder, and a screw shaft cover 27 is attached to the top plate 26 at the top of the cylinder. An air hole 28 is provided in the side base of the nut protection cylinder 24. The air hole 28 has a function as a through hole for air inside and outside separated by the nut protection cylinder 24, and the cross-sectional shape of the air hole 28 is not limited to a circular shape. Further, a filter (not shown) is attached to the air hole 28 as necessary. By providing a filter in the air hole 28, it is possible to prevent dust and the like from entering the inside of the nut protection cylinder 24 even in an installation environment where there is much dust and the like.

  The screw shaft cover 27 is made of resin in order to reduce the weight, but even if it is a screw jack with the same load capacity, the stroke length of the screw shaft extends over a wide range depending on the specifications. The three parts of the attachment part 29, the cylinder part 30, and the cap part 31 are joined without being manufactured as a molded product. By adopting such a configuration, it is possible to use the same member for the attachment portion 29 and the cap portion 31 among the three members even when the stroke lengths of the screw shafts are greatly different.

  In the embodiment shown in FIG. 1, the nut protection cylinder 24 and the screw shaft cover 27 are separate parts. However, in the case of a specification for mass-producing screw jacks having the same stroke length, the nut protection cylinder 24 and the screw shaft cover 27 Can also be integrated. As a result, the number of components is reduced, and a screw jack with a low manufacturing cost can be realized.

  Next, the operation of the screw jack according to the present invention will be described. A load is connected to the lower end of the ball screw shaft 23 using a metal fitting such as a clevis. A motor is connected to the shaft end of the bevel pinion 6, and the bevel pinion 6 is driven by the motor. When the bevel gear 15 meshed with the bevel pinion 6 rotates, the drive sleeve 11 coupled to the bevel gear 15 and the ball screw nut 21 fixed to the drive sleeve 11 also rotate. Here, if the load side is constrained not to rotate, the rotation of the ball screw shaft 23 is also constrained, so that the ball screw shaft 23 screwed into the ball screw nut 21 performs a linear motion in the axial direction. Become. Such an action is the same as a general screw jack.

  In FIG. 1, when the ball screw shaft 23 moves upward, the space volume inside the screw shaft cover 27 decreases as the volume occupied by the ball screw shaft 23 increases. Further, when the ball screw shaft 23 moves downward, the space volume inside the screw shaft cover 27 increases as the volume occupied by the ball screw shaft 23 decreases. Thus, the reciprocating motion of the ball screw shaft 23 reduces or increases the space volume inside the screw shaft cover 27.

  On the other hand, the space volume inside the nut protection cylinder 24 is not changed by the reciprocating motion of the ball screw shaft 23. Since the volume occupied by the ball screw nut 21 and the ball screw shaft 23 in the nut protection cylinder 24 is unchanged, the space volume in the nut protection cylinder 24 does not change even when the ball screw shaft 23 reciprocates. It should be noted here that the inner diameter of the mounting portion 29 of the screw shaft cover 27 and the top plate 26 of the nut protection cylinder 24 is larger than the outer diameter of the ball screw shaft 23. Therefore, the inside of the screw shaft cover 27 and the inside of the nut protection cylinder 24 are in communication, and air can freely move between the inside of the screw shaft cover 27 and the inside of the nut protection cylinder 24.

  When the ball screw shaft 23 moves up, the air inside the screw shaft cover 27 is pushed out into the nut protection cylinder 24 as the ball screw shaft 23 moves up. As a result, the pressure inside the nut protection cylinder 24 becomes high, and the air inside the nut protection cylinder 24 is discharged from the air hole 28 to the outside. On the other hand, when the ball screw shaft 23 is lowered, air is sucked from the nut protection cylinder 24 into the screw shaft cover 27 as the ball screw shaft 23 is lowered. Then, the pressure inside the nut protection cylinder 24 becomes low, and air is sucked from the outside into the nut protection cylinder 24 through the air hole 28. In this way, by the reciprocating motion of the ball screw shaft 23, air is sucked and exhausted through the air hole 28 between the inside and the outside of the nut protection cylinder 24. In this process, the heat loss at the ball screw nut 21 is cooled by the air flow. Therefore, even if the ball screw unit operates at high speed and with high frequency, the ball screw nut 21 is reliably cooled, and the temperature rise of the ball screw nut 21 can be suppressed. In addition, since the ball screw nut 21 does not require a cooling hole, a mass-produced and inexpensive ball screw unit can be employed, and a screw jack with excellent merchantability can be realized.

  As mentioned above, although this invention was demonstrated based on the Example, this invention is not limited to the Example mentioned above, A various deformation | transformation implementation can be performed. For example, in the above-described embodiment, the normal configuration in which the load is suspended from the lower end of the ball screw shaft 23 has been described. However, a push-up configuration in which the load is connected to the upper end of the ball screw shaft 23 upside down may be used. It is also possible to use the ball screw shaft 23 in a horizontal configuration in which the ball screw shaft 23 is horizontal.

  The screw jack according to the present invention can be widely used in various factory facilities as a kind of linear actuator.

1 Screw jack 2 Housing
11 Drive sleeve
15 Bevel Gear
17 Upper bearing
21 Ball screw nut
23 Ball screw shaft
24 Nut protection cylinder
27 Screw shaft cover
28 Air holes

Claims (3)

In a screw jack having a drive sleeve coupled to a bevel gear and pivotally supported in a housing, a ball screw nut fixed to the drive sleeve, and a ball screw shaft screwed to the ball screw nut,
Attaching a nut protection cylinder to the top of the housing, attaching a screw shaft cover to the top plate of the nut protection cylinder,
The inside of the screw shaft cover and the inside of the nut protection cylinder communicate with each other so that air can freely move,
A screw jack characterized in that an air hole is provided in a side surface base portion of the nut protection cylinder.   The screw jack according to claim 1, wherein a filter is provided in the air hole.   The screw jack according to claim 1 or 2, wherein the nut protection cylinder and the screw shaft cover are integrated.

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