JP2015224660A - Ball screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ball screw for allowing quick determination of whether abnormality occurs inside or not without the need for installing other components than indispensable components for the ball screw, and wirings.SOLUTION: A ball screw 10 includes a screw shaft 1, a nut 2, a plurality of balls 3, and a circulation component 4. A spiral groove 11 of the screw shaft 1 and a spiral groove 21 of the nut 2 form a rolling path where the balls 3 roll in loaded conditions. The circulation component 4 is a component which has a ball return path 45 formed in the nut 2 to return the balls 3 from the end point to the start point of the rolling path. The balls 3 are arranged in the rolling path and in the ball return path 45. The circulation component 4 has a body part 41 arranged on the outer periphery side of the nut 2, and a pair of leg parts 42 inserted into a set of two circulation holes 23 passing through the nut 2 in the radial direction. At the front end of each of the leg parts 42, a tongue 42a is formed. The circulation component 4 is formed of a resin composition containing inorganic pigment whose color is reversibly changed with temperature, and synthetic resin.

Description

  The present invention relates to a ball screw.

The ball screw has a screw shaft, a nut, and a plurality of balls. In the ball screw, the axial dimension of the screw shaft is longer than the axial dimension of the nut, and the screw shaft passes through the nut. A rolling path on which the ball rolls in a loaded state is formed by the spiral groove of the screw shaft and the spiral groove of the nut. The nut has a ball return path for returning the ball from the end point of the rolling path to the start point. The balls are disposed in the rolling path and the ball return path. The nut and the screw shaft move relative to each other via a ball that rolls in a rolling state in the rolling path.
Examples of the part (circulation part) that forms the ball return path in the nut include a part that has a main body and a leg part and is used by inserting the leg part into a hole that penetrates the nut in the radial direction. Specifically, a synthetic resin circulating part composed of a metal return tube and two divided bodies divided along a line indicating the moving direction of the ball can be mentioned. Moreover, the part which comprises a ball | bowl return path with the hole penetrated to the axial direction of a nut can also be illustrated. Specifically, an end deflector and an end cap are mentioned.

Each of the circulating parts has a tongue for lifting the ball from the rolling path into the ball return path at the end of the rolling path and for guiding the ball from the ball return path to the rolling path at the start point. A tongue is arrange | positioned in a rolling path, and the front-end | tip part of a tongue is arrange | positioned in the spiral groove of a screw shaft. The ball in the rolling path is picked up on the ball return path after colliding with the tongue.
Seals that close the gap between the screw shaft and the nut are attached to both ends of the ball screw nut in the axial direction. The base of the seal is fixed to the nut, and the lip of the seal is in contact with the spiral groove of the screw shaft.

With respect to such a ball screw, methods for detecting abnormalities such as seizure, wear, and damage have been proposed. For example, Patent Document 1 describes that a strain gauge is provided in a circulating part, and vibrations and collision forces generated when a rolling element collides with the circulating part are measured to detect an abnormality in the ball screw.
Patent Document 2 discloses a conventional thermolabel for detecting the temperature of an inner ring, an outer ring, a tapered roller or the like (bearing part) in order to prevent damage to a tapered roller or the like of a sealed rolling bearing device for a railway vehicle axle. Is attached to a front lid, a cage or a bearing box, and an abnormal temperature rise inside the rolling bearing is detected due to discoloration of the thermo label.

Also, because the thermo label is affixed at a position away from the bearing parts and because the thermo label is exposed to the outside, it is cooled while the vehicle is running. It is described that it cannot be said that the temperature rise can be detected sufficiently.
Therefore, in the invention described in Patent Document 2, “temperature detection means for detecting the temperature inside the rolling bearing filled with lubricant and transferring heat toward the outside of the rolling bearing” and “the temperature detection means” And a display means for displaying the temperature of the heat transmitted from the temperature detecting means is provided in the sealed type rolling bearing device.
Thereby, in the invention described in Patent Document 2, the filled lubricant becomes substantially equal to the temperature of the inner ring, the temperature of this lubricant is detected by the temperature detecting means, and the detected temperature is installed outside. Since it is displayed on the displayed display means, it is described that an abnormal temperature rise inside the rolling bearing can be reliably detected and seizure can be prevented.

JP 2013-200032 A JP 11-287251 A

Among the above-described background arts, the method using a thermo label and the method for detecting the temperature of a lubricant have room for improvement in that an abnormal temperature rise inside can be detected quickly. In the method using a strain gauge, there is a problem that it takes time to install the strain gauge and wiring.
An object of the present invention is to provide a ball screw that can quickly determine whether or not an abnormality has occurred inside without installing components or wiring other than components essential to the ball screw.

In order to solve the above problems, a ball screw according to one embodiment of the present invention is characterized by having the following configurations (1) to (3).
(1) It has a screw shaft, a nut, a plurality of balls, and a circulating part. The axial dimension of the screw shaft is longer than the axial dimension of the nut, and the screw shaft passes through the nut. A rolling path on which the ball rolls in a loaded state is formed by the spiral groove of the screw shaft and the spiral groove of the nut. The circulating part is a part that forms a ball return path in the nut for returning the ball from the end point of the rolling path to the start point. The balls are arranged in the rolling path and the ball return path. The nut and the screw shaft move relative to each other via a ball that rolls in a rolling state in the rolling path.
(2) The circulation component has a main body portion arranged on the outer peripheral side of the nut and a pair of leg portions inserted into a set of two circulation holes penetrating the nut in the radial direction. A tongue is formed at the tip of the leg, and the tongue is disposed in the rolling path.

(3) The circulating component is formed of a resin composition containing an inorganic pigment that changes color reversibly with temperature and a synthetic resin.
The ball screw of this aspect can have at least one of the following configurations (4) and (5).
(4) The circulating component is composed of two divided bodies divided along a line indicating the moving direction of the ball. The divided body is obtained by injection-molding a resin composition containing an inorganic pigment that reversibly discolors depending on temperature and a synthetic resin.
(5) It has a heat insulating cover that covers a portion of the circulating component that is disposed outside the nut. The heat insulating cover is a cover made of a material having low thermal conductivity (for example, 0.20 W / mK or less), and has a transparency that can identify the color of the circulating component.

As described above, in the ball screw, when the ball is scooped up from the end point of the rolling path into the ball return path, it collides with the tongue of the circulating component. Therefore, the ball is the part that has the largest momentum and the largest calorific value among the parts constituting the ball screw.
If there is an abnormality such as peeling on the screw shaft spiral groove, nut spiral groove, or ball surface, the ball momentum will be greater than if no abnormality has occurred, so the ball temperature will also be abnormal. It will be higher than if it did not occur. When the ball having such a high temperature passes through the circulating component, the ball raises the temperature of the circulating component. In the ball screw of this aspect, the circulating component is formed of a resin composition containing an inorganic pigment that reversibly discolors with temperature and a synthetic resin, so the color of the circulating component varies with the temperature of the circulating component. Changes.
Therefore, in the ball screw of this aspect, it is possible to quickly determine whether or not an abnormality has occurred inside by looking at the color of the circulating component during operation.
Further, when the ball screw of this aspect has the configuration (5), it is possible to prevent the color of the circulating component from being changed by the influence of the temperature outside the ball screw.

  ADVANTAGE OF THE INVENTION According to this invention, the ball screw which can determine immediately whether abnormality has generate | occur | produced is provided, without installing components and wiring other than a component essential to a ball screw.

It is a top view which shows the ball screw of 1st Embodiment. It is A arrow directional view of FIG. It is a figure explaining the ball screw of 1st Embodiment, Comprising: The cross section of a nut is shown, A screw shaft is not made into a cross section, It is a figure which shows a circulation part in the cross section along a division line. It is a perspective view which shows the circulation component which comprises the ball screw of 1st Embodiment and 2nd Embodiment. It is a figure which shows the division body which comprises the circulation component of FIG. It is a top view which shows the ball screw of 2nd Embodiment. It is A arrow directional view of FIG. It is a figure explaining the ball screw of 2nd Embodiment, Comprising: The cross section of a nut is shown, A screw shaft is not made into a cross section, It is a figure which shows a circulation component in the cross section along a division line.

Hereinafter, although embodiment of this invention is described, this invention is not limited to embodiment shown below.
[First Embodiment]
The ball screw 10 of 1st Embodiment has the screw shaft 1, the nut 2, the ball | bowl 3, the circulation component 4, the attachment component 5, and the volt | bolt 6 as shown in FIGS. The axial dimension of the screw shaft 1 is longer than the axial dimension of the nut 2, and the screw shaft 1 passes through the nut 2. The spiral groove 11 of the screw shaft 1 and the spiral groove 21 of the nut 2 form a rolling path on which the ball 3 rolls in a loaded state. The circulating component 4 is a component that forms a ball return path 45, and the ball 3 is disposed in the rolling path and the ball return path 45.

A recess 22 is formed in a part of the outer peripheral surface of the nut 2. On the outer flat surface 22 a of the nut 2, which is the bottom surface of the recess 22, a pair of circulation holes 23 that penetrate the nut 2 in the radial direction and a female screw 24 that meshes with the male screw of the bolt 6 are formed.
As shown in FIG. 4, the circulation component 4 includes a main body portion 41 disposed on the outer peripheral side of the nut 2 and a pair of leg portions 42 inserted into the circulation hole 23. The circulating component 4 is composed of two divided bodies that are divided along a line L indicating the moving direction of the ball 3.

As shown in FIG. 5, the divided body 40 of the circulation component 4 includes a main body 410 and a pair of legs 420, and a groove 450 corresponding to the ball return path 45 is formed therein. A tongue 42 a is formed at the tip of one leg 420. The lower surface (surface on which the leg portion 42 extends) 41 b of the main body 41 is a surface that is brought into contact with the outer flat surface 22 a of the nut 2. An inner boundary portion 44 between the main body portion 41 and the leg portion 42 of the circulation component 4 is formed in a round shape, and an escape portion for escaping this portion is formed at the opening end of the circulation hole 23 of the nut 2.
The divided body 40 of the circulating component 4 is formed of a resin composition containing vanadium zirconium yellow powder (an inorganic pigment that changes color reversibly with temperature) and a synthetic resin. Therefore, the color of the circulating component 4 changes according to the temperature at that time.
The divided body 40 is manufactured by the following method (production method 1), for example.

<Production method 1>
The pellet of polyacetal resin, calcium carbonate powder and vanadium zirconium yellow powder are put into a biaxial kneading extruder so that the mass ratio of polyacetal: calcium carbonate: vanadium zirconium yellow = 100: 15: 10 is obtained. Is operated at a kneading and melting temperature of 200 to 230 ° C. to obtain compound pellets. Next, the obtained pellets are put into a hopper of an injection molding machine to which a mold corresponding to the divided body is attached, and injection molding is performed under normal injection molding conditions of polyacetal resin.
The divided body 40 manufactured by the manufacturing method 1 becomes yellow at less than 60 ° C. and becomes orange at 60 ° C. or more.
The attachment component 5 includes a recess 51 into which the main body 41 of the circulation component 4 is fitted, a recess 52 in which the head of the bolt 6 is disposed, and a through hole 53 that penetrates the bottom of the recess 52.

The circulating component 4 is assembled by joining two identical divided bodies 40 shown in FIG. 5, and a ball return path 45 including two grooves 450 is formed inside the circulating component 4.
When attaching the circulating component 4 to the nut 2, first, each leg portion 42 is inserted into each circulation hole 23 of the nut 2, and the tip end portion of the tongue 42 a is disposed in the spiral groove 11 of the screw shaft 1. The main body 41 is disposed on the outer flat surface 22a. Next, the mounting part 5 is fitted to the main body 41 with the recess 51 facing the outer flat surface 22 a, the bolt 6 is passed through the through hole 53 of the recess 52, and the male screw of the bolt 6 is engaged with the female screw 24 of the nut 2.

In the ball screw of the first embodiment, the ball 3 whose temperature is high collides with the tongue 42 a of the circulation component 4 and enters the ball return path 45, and passes through the circulation component 4. The temperature of the becomes higher. The color of the circulating component 4 changes as described above according to the temperature at that time. When an abnormality occurs inside the ball screw, the temperature of the ball 3 is 80 ° C. or higher, and the temperature of the circulating component 4 is 60 ° C. or higher. Along with this, the temperature of the circulating component 4 changes from yellow to orange.
Therefore, according to the ball screw of the first embodiment, it is possible to quickly determine whether or not an abnormality has occurred inside by looking at the color of the circulating component 4 during operation.
If the circulating part 4 is hidden while the ball screw is incorporated in the machine, the ball can be changed by changing the color of the circulating part 4 by providing a mechanism such as providing a window through which a part of the circulating part 4 can be seen. Abnormalities inside the screw can be detected. Further, in a life test or the like performed in a state where the circulating component 4 is visible, it can be easily confirmed whether or not an abnormality has occurred inside the ball screw.

[Second Embodiment]
The ball screw 10 of 2nd Embodiment has the screw shaft 1, the nut 2, the ball | bowl 3, the circulation component 4, the transparent coating | coated component 7, and the volt | bolt 6 as shown in FIGS. That is, the ball screw 10 of the second embodiment has a covering component 7 that also serves as an attachment component of the circulation component 4 instead of the attachment component 5 of the ball screw 10 of the first embodiment. The rest is the same as the ball screw 10 of the first embodiment.
The covering component 7 includes an attachment portion 71 having a recess 71 a into which the main body portion 41 of the circulation component 4 is fitted, and a cover portion 72. The attachment portion 71 has a recess 71b in which the head of the bolt 6 is disposed and a through hole 71c that passes through the bottom of the recess 71b. The cover portion 72 is a thin-walled portion that covers a portion of the main body portion 41 that is detached from the attachment portion 71, and has a recess that is continuous with the recess 71 a of the attachment portion 71. The covering component 7 covers all of the portion of the circulating component 4 protruding from the nut 2 by the concave portion 71 b of the attachment portion 71 and the cover portion 72.

The covering component 7 corresponds to a heat insulating cover and is obtained, for example, by injection molding a polyethylene terephthalate (PET) resin.
When attaching the circulation component 4 to the nut 2, first, each leg portion 42 is inserted into each circulation hole 23 of the nut 2, and the main body portion 41 is disposed on the outer flat surface 22 a of the nut 2. Next, the main body 41 is covered with the concave portion 71a of the mounting portion 71 and the cover portion 72 with the concave portion 71a of the covering component 7 facing the outer flat surface 22a, and the bolt 6 is passed through the through hole 71c of the concave portion 71b. Is engaged with the female screw 24 of the nut 2.

In the ball screw of the second embodiment, the temperature of the circulating component 4 also increases as the ball 3 whose temperature is high passes through the circulating component 4. The color of the circulating component 4 changes as described above according to the temperature at that time. When an abnormality occurs inside the ball screw, the temperature of the ball 3 is 80 ° C. or higher, and the temperature of the circulating component 4 is 60 ° C. or higher. Along with this, the temperature of the circulating component 4 changes from yellow to orange.
Further, since the entire portion of the circulating component 4 protruding from the nut 2 is covered by the concave portion 71b and the cover portion 72 of the covering component (heat insulating cover) 7, the temperature of the circulating component 4 is the temperature outside the ball screw. It is prevented from changing under the influence of

Therefore, according to the ball screw of the second embodiment, it is possible to quickly determine whether or not an abnormality has occurred inside by looking at the color of the circulating component 4 through the covering component 7 during operation. Moreover, the abnormality detection accuracy in a high temperature use environment is higher than that of the ball screw of the first embodiment.
The ball screw of the second embodiment is a covered part in which a heat insulating cover that covers all portions of the circulating part 4 protruding from the nut and an attachment part for fixing the circulating part 4 to the nut 2 are integrated. 7, the heat insulating cover and the mounting part may be separate parts.
Moreover, the division body 40 of the circulating component 4 constituting the ball screw of the first embodiment and the second embodiment can be manufactured by the following manufacturing method 2 instead of the manufacturing method 1 described above.

<Production method 2>
First, FEP (tetrafluoroethylene-hexafluoropropylene copolymer) resin pellets, calcium carbonate powder and vanadium zirconium yellow powder are fed into a biaxial kneading extruder at a mass ratio of FEP: calcium carbonate: vanadium zirconium yellow = 100: 15:10, and the biaxial kneading extruder is operated at a kneading and melting temperature of 210 to 230 ° C. to obtain compound pellets.
Next, the obtained compound pellets, polyacetal resin pellets, and cross-linking agent (morpholine disulfide) are compounded in a pressure ratio such that compound: polyacetal: cross-linking agent = 90: 100: 10. The FEP and the polyacetal are cross-linked by holding for 40 minutes at a temperature of 120 to 170 ° C. and a pressure of 10.13 MPa to 30.4 MPa. Next, a resin obtained by crosslinking FEP and polyacetal is put into a granulation extruder to obtain crosslinked resin pellets.

Next, the obtained pellets of the crosslinked resin are put into a hopper of an injection molding machine to which a mold corresponding to the divided body is attached, and the material temperature is 210 to 230 ° C., the mold temperature is 50 ° C., and the injection pressure is 98 MPa. Perform injection molding under conditions.
The divided body 40 manufactured by the manufacturing method 2 becomes yellow at less than 60 ° C. and becomes orange at 60 ° C. or more.
Since the circulating component 4 made of the divided body 40 obtained by the manufacturing method 2 is made of a synthetic resin in which a polyacetal resin and FEP that is a fluororesin are crosslinked, the polyacetal resin-made divided body 40 obtained by the manufacturing method 1 is used. The wear resistance is higher than that of the circulating component 4.

[Materials for circulating parts and insulation cover]
The circulating component constituting the ball screw of the present invention is formed of a resin composition containing an inorganic pigment reversibly discolored by temperature and a synthetic resin.
Examples of synthetic resins that can be used include engineering plastics such as polyacetal, polyamide, and polyetheretherketone. By using a synthetic resin in which a fluororesin is cross-linked to such an engineering plastic, the wear resistance of the circulating component is improved. Examples of the fluororesin to be crosslinked include FEP (tetrafluoroethylene-hexafluoropropylene copolymer), PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), and the like.
The resin composition preferably contains a filler or an acid acceptor.

As fillers, fused silica, crystalline silica, alumina, zircon, calcium silicate, calcium carbonate, potassium titanate, silicon carbide, silicon nitride, aluminum nitride, boron nitride, beryllia, zirconia, fosterite, steatite, spinel, mullite And powders such as titania, or beads, glass fibers and the like obtained by spheroidizing these. Examples of the inorganic filler having a flame retardant effect include aluminum hydroxide, magnesium hydroxide, zinc borate, and zinc molybdate.
Examples of inorganic pigments (temperature indicating materials) that reversibly discolor with temperature include vanadium tin yellow, vanadium zirconium yellow, praseodymium yellow, chromium titanium yellow, antimony yellow, and cadmium yellow.

  Examples of the material of the heat insulating cover that covers the circulating parts include AS (acrylonitrile styrene) resin, PC (polycarbonate) resin, PET (polyethylene terephthalate) resin, PMMA (polymethyl methacrylate) resin, and PS (polystyrene) resin. The thermal conductivity of each resin is 0.15-0.16 W / mK for AS resin, 0.19 for PC resin, 0.14 W / mK for PET resin, 0.02-0.03 W / mK for PMMA resin, The PS resin is 0.10 to 0.14 W / mK.

DESCRIPTION OF SYMBOLS 1 Screw shaft 11 Spiral groove of screw shaft 2 Nut 21 Helical groove of nut 22 Recessed part provided in outer peripheral part of nut 22a Outer flat surface of nut 23 A set of two circulation holes penetrating nut in radial direction 24 Female thread 3 Ball DESCRIPTION OF SYMBOLS 4 Circulating part 40 Divided body of circulating part 41 Main part of circulating part 42 Circulating part leg 42a Circulating part tongue 45 Ball return path 410 Divided body main body 420 Divided body leg part 450 Groove corresponding to ball return path 5 Mounting parts 6 Bolts 7 Covering parts (heat insulation cover)
71 Attached part of the covering part 71a A recessed part for fitting the main part of the circulating part 71b A recessed part for arranging the head of the bolt 71c A through hole 72 A covering part of the covered part 10 Ball screw L A line indicating the moving direction of the ball

Claims (3)

A screw shaft, a nut, a plurality of balls, and a circulation part;
The axial dimension of the screw shaft is longer than the axial dimension of the nut,
The screw shaft passes through the nut;
A rolling path in which the ball rolls in a loaded state is formed by the spiral groove of the screw shaft and the spiral groove of the nut,
The circulating component is a component that forms a ball return path in the nut for returning the ball from the end point of the rolling path to the start point,
The balls are arranged in the rolling path and the ball return path,
The nut and the screw shaft move relative to each other through the ball that rolls in a loaded state in the rolling path,
The circulation component has a main body portion arranged on the outer peripheral side of the nut, and a pair of leg portions inserted into a pair of circulation holes penetrating the nut in a radial direction, A tongue is formed at the tip, and the tongue is disposed in the rolling path.
The circulating part is a ball screw formed of a resin composition containing an inorganic pigment reversibly discolored according to temperature and a synthetic resin. The circulating component is composed of two divided bodies divided along a line indicating the moving direction of the ball,
The ball screw according to claim 1, wherein the divided body is obtained by injection molding a resin composition containing an inorganic pigment reversibly discolored by temperature and a synthetic resin.   The ball screw according to claim 1, further comprising a heat insulating cover that covers a portion of the circulating component that is disposed outside the nut.

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