JP2008256050A - Resin nut, and sliding screw device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resin nut reducing partial wear of a screw thread and extending the service life even under a high surface pressure condition, and also to provide a sliding screw device using the nut. <P>SOLUTION: The resin nut 3 is screwed with a screw shaft 1 and is axially moved relatively with the screw shaft 1. The Young's modulus of resin material forming the resin nut is a value approximately uniformize contact pressure distribution in an axial direction in contact faces of the nut and the screw shaft when the load is applied to the nut in an axial cross-section of the nut, and the contact pressure distribution is acquired by heat transmission-structure interaction analysis by a finite element method using two-dimensional axisymmetric model of the nut. The Young's modulus forming the resin nut is 2.48 GPa-5 GPa at 25°C. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a resin nut and a sliding screw device using the same, and in particular, the Young's modulus of a resin material constituting the nut can be set to a maximum value of a contact pressure on a screw contact surface based on a structural analysis. The present invention relates to a resin nut and a sliding screw device using the same.

  A slide screw device that converts rotational motion into linear motion has the advantage that it can be designed more compactly than a ball screw device. Sliding screw devices using nuts often attach driven bodies such as moving tables that rotate the screw shaft and transmit linear driving force to the flanges of the nuts. It is used a lot. Among them, sliding screw devices using resin nuts have recently been used for optical measuring equipment, semiconductor manufacturing equipment, medical equipment, etc., and specifications and characteristics according to each equipment have been required. Yes.

  As a resin nut for a sliding screw device, the whole is formed of a resin by cutting or injection molding, and a thermoplastic polyimide resin is used as a resin for forming this nut (see Patent Document 1), polyphenylene sulfide resin (Refer to Patent Document 2), and polyphenylene sulfide resin blended with tetrafluoroethylene resin or organic resin powder not melted at high temperature (refer to Patent Document 3).

However, since the screw nut is likely to be unevenly worn and the positioning accuracy is lowered, the resin nut cannot be extended in life under high surface pressure conditions. Also, when trying to prevent such uneven wear from the material surface, in the sliding screw device, many conditions such as load load and frictional heat generation must be taken into account, and the optimum physical properties are selected experimentally. It was difficult.
JP-A-6-193701 JP 2001-116102 A JP 2003-239932 A

  The present invention has been made in order to cope with such problems, and can reduce uneven wear of a thread and has a long life even under high surface pressure conditions, and uses the nut. An object of the present invention is to provide a sliding screw device.

  The resin nut of the present invention is a resin nut that is screwed onto the screw shaft and moves relative to the screw shaft in the axial direction, and the Young's modulus of the resin material forming the resin nut is that of the resin nut. In the axial cross section, the contact pressure distribution in the axial direction on the contact surface between the resin nut and the screw shaft when a load is applied to the resin nut is a value that can be made substantially uniform. It is obtained by analysis by a finite element method using a two-dimensional axisymmetric model of a resin nut.

  In the analysis by the finite element method, the temperature distribution inside the screw shaft and the resin nut during the sliding between the screw shaft and the resin nut is obtained, and then the temperature distribution and a predetermined load are constrained. It is a heat transfer-structure coupled analysis that analyzes the contact pressure distribution as a condition.

  The maximum value of the contact pressure in the contact pressure distribution is less than 12 MPa.

  The resin material forming the resin nut has a Young's modulus of 2.48 GPa to 5 GPa at 25 ° C.

  The resin nut is characterized in that a flange is formed.

  The sliding screw device of the present invention is a sliding screw device in which a nut is screwed onto a screw shaft and the nut is moved relative to the screw shaft in the axial direction, and the nut is the resin nut of the present invention. Features.

The resin nut of the present invention accurately determines the Young's modulus of the nut resin material by the heat transfer-structure coupled analysis by the finite element method using a predetermined model, and accurately determines the contact pressure distribution with the screw shaft that the nut thread receives. Since the contact pressure distribution is set to a value that can be made substantially uniform based on the analysis result, uneven wear of the thread is reduced even under high surface pressure conditions, and the life of the nut can be extended.
For example, by setting the Young's modulus of the resin material forming the resin nut to 2.48 GPa to 5 GPa, the maximum value of the contact pressure in the contact pressure distribution can be less than 12 MPa, which is the upper limit of the load resistance of the sliding screw device. Pulling up and extending the life under high surface pressure conditions.

  The sliding screw device of the present invention is a sliding screw device in which a nut is screwed onto a screw shaft and the nut is moved relative to the screw shaft in the axial direction, and the maximum value of the contact pressure in the contact pressure distribution is a predetermined value or less. Since the above resin nut with less uneven wear of the thread is used, the service life is long under high surface pressure conditions.

A resin nut and a sliding screw device using the same according to the present invention will be described with reference to FIGS. FIG. 1 is a perspective view of a sliding screw device, and FIG. 2 is an axial sectional view of a resin nut.
The sliding screw device 2 includes a screw shaft 1 and a resin nut 3 that is screwed into the screw groove of the screw shaft 1 and moves while sliding on the screw shaft 1. It is converted into a linear motion of the resin nut 3. In addition, it is also possible to apply a linear motion to the screw shaft 1 by rotating the resin nut 3 at the same position. The resin nut 3 is molded by injection molding of a resin composition.

As shown in FIG. 2, a female screw 3 a that is screwed to the screw shaft 1 (see FIG. 1) is formed on the inner diameter surface of the resin nut 3. A driven body such as a moving table is attached to the flange 4 of the resin nut 3.
The internal thread 3a on the inner diameter surface of the resin nut 3 is formed by a mold during injection molding. The internal thread 3a can also be formed by machining after injection molding, and the shape of the thread is not particularly limited, and may be any shape such as a trapezoid, a gothic arc, a triangle, and a rectangle.

  As described above, the resin nut has a problem in that the screw thread is likely to be unevenly worn and the positioning accuracy is lowered. In order to investigate the cause of this uneven wear, structural analysis was performed by the finite element method using a two-dimensional axisymmetric model of the nut. It was found that the axial contact pressure distribution was uneven in proportion to the wear amount. On the other hand, as a result of various examinations and analyzes on the influence of the nut material, when the Young's modulus (tensile modulus) of the material is too large or too small, the contact pressure distribution on the screw contact surface is biased, and the contact pressure The maximum value (maximum contact pressure) is increased, but it has been found that by making it within a predetermined range, it is possible to bias the distribution and reduce the maximum contact pressure. The resin nut of the present invention is characterized in the manufacturing process of determining the Young's modulus of the nut material to be used based on the structural analysis.

The Young's modulus of the resin material for forming the resin nut 3 is the difference between the resin nut and the screw shaft when a load is applied to the resin nut in the axial cross section of the resin nut 3 (see FIG. 2). Any value can be used as long as the contact pressure distribution in the axial direction on the contact surface can be made substantially uniform.
In the present invention, the contact pressure distribution is a distribution in which the contact pressure (peak value) of the friction contact surface that is the same as the number of pitches in an arbitrary axial section of the resin nut 3 is viewed in the axial direction. The distribution being substantially uniform means that the distribution of the contact pressure (peak value) on each contact surface is small and substantially uniform.
In the present invention, the term “substantially uniform” means that, in the contact pressure distribution, the ratio between the minimum value (excluding non-contact) and the maximum value of the contact pressure (peak value) at each contact surface is 10 or less.

Further, the Young's modulus of the resin material for forming the resin nut 3 is preferably a value at which the maximum value of the contact pressure is less than 12 MPa in the contact pressure distribution. The range of such Young's modulus is 2.48 GPa to 5 GPa at 25 ° C. If the Young's modulus is less than 2.48 GPa and exceeds 5 GPa, the contact pressure distribution is biased and the maximum value of the contact pressure is 12 MPa or more.
In the present invention, the Young's modulus of the resin material is a value obtained by a tensile test using a test piece made of a resin composition alone or a resin composition containing an additive as required. The Young's modulus is measured at several points within the operating temperature range of the nut, and the temperature dependence is taken into consideration in the analysis. At the time of nut production, Young's modulus is adjusted by selecting a resin and blending an additive.

  Examples of the resin composition for forming the resin nut 3 include thermoplastic polyimide resins, polyether ether ketone resins, polyphenylene sulfide (PPS) resins, polyamideimide resins, phenol resins, and blends thereof. As a main component, a resin composition containing about 10 to 40 vol% of tetrafluoroethylene (PTFE) resin can be mentioned. The PPS resin includes a cross-linked type, a semi-cross-linked type, a linear type, a branched type, and the like depending on the cross-linked state of the molecule, and any of them can be used, or a blend of these may be used.

  As the resin as the main component, a PPS resin is preferable. By using a PPS resin as the main component, a resin nut can be obtained at a low cost and sufficiently practical, with a wide operating temperature range (sliding portion temperature of −5 ° C. to 150 ° C.). Moreover, since the PPS resin is excellent in chemical resistance, it can be used even in an environment such as water or chemicals. Further, by blending PTFE resin with PPS resin, stable low friction characteristics can be obtained, there is no noise, the starting friction coefficient is lowered, and the wear resistance is improved.

  Additives to be blended include colorants such as carbon powder, iron oxide, and titanium oxide, thermal conductivity improvers such as graphite, metal powder, metal oxide powder, and carbon powder, and glass fiber, carbon fiber, aramid fiber, Abrasion resistance improving materials such as whiskers can be mentioned.

The procedure for obtaining the contact pressure distribution by the finite element method will be described below. As analysis means by the finite element method, existing analysis software or the like can be used. The analysis results and the like shown in the following examples are the results of using analysis software “ANSYS” version 8.0 manufactured by Ansys, USA.
Analysis was performed using a two-dimensional axially symmetric model (symmetrical with respect to the y-axis in the figure) as shown in FIG. The simplified model is because the nut structure is substantially axisymmetric and the calculation time can be shortened. Although it is simplified, there are structural parts that are slightly different from the actual ones, but it is difficult to consider that they are elements that have a great influence on the overall structure. Moreover, in fact, frictional heat is generated on the contact surface by rotating, but the rotation cannot be considered because the model is two-dimensional. Therefore, the frictional surface was analyzed by calculating the frictional heat generated by rotational friction and setting the heat supply to the contact surface in the form of heat flux.

In a sliding screw device using a resin nut, the load applied when the nut breaks is often lower than the load assumed from the material strength alone. This is because thermal expansion occurs in the resin due to the temperature distribution due to frictional heat generation, and the characteristics of the contact between the screw shaft and the nut are born, and the contact form creates a bias in the temperature and contact pressure of the friction surface. It is considered that the breakage occurs even under load.
Therefore, in the present invention, in the analysis by the finite element method, first, the temperature distribution inside the nut or the like when sliding between the screw shaft and the nut is obtained by heat transfer analysis, and then the temperature load caused by the temperature is determined by structural analysis. The contact pressure distribution is obtained from a predetermined load, and a heat transfer-structure coupled analysis is performed in consideration of the influence of heat.

[Heat transfer analysis]
The above analysis is an analysis in a static state in which an analysis assuming that the nut actually slides on the screw shaft cannot be performed. For this reason, frictional heat is applied to the friction surface. However, if the analysis is performed as it is, the analysis is performed under such a condition that the nut slides at the position where the screw shaft is fixed. Therefore, in the model, only the contact part where the nut and screw shaft do not move continues to rise in temperature, and the resulting temperature distribution when the heat inflow from the friction surface and the heat outflow from the heat transfer surface are in equilibrium. Only a part of the temperature is much higher than the actual temperature. On the other hand, according to an actual machine or the like, when the nut of the slide screw device is slid and moved over a certain distance, the heat inflow and heat outflow are considered to be in equilibrium, and the temperature of both the nut and screw shaft converges. In the structural analysis, the temperature distribution of the nut and screw shaft in this temperature equilibrium state is also used.
Therefore, as a heat transfer analysis procedure, first, the temperature of the screw shaft is derived, and then the temperature distribution of the nut is also determined using the temperature of the screw shaft.

[Structural analysis]
Next, in the structural analysis, the temperature distribution as a result of the above heat transfer analysis and other conditions such as loads are input as constraint conditions for the analysis. FIG. 4 shows the condition setting. (1) First, the temperature distribution of the screw shaft and nut obtained from the heat transfer analysis is read as the condition setting for the structural analysis, and is loaded on the model as the temperature constraint condition.
(2) In addition to the heat generated by friction, a load is applied by a driven body such as a moving table. Therefore, in addition to the temperature load of (1), as shown in FIG. To load.
(3) Input the above two loads, and execute the analysis by adding a constraint condition to the lower part of the screw shaft so that rigid body motion does not occur. As a result, it is possible to observe a structural change in which the influence of the thermal expansion of the material due to the temperature distribution and the influence of the surface pressure load are combined.

The contact pressure distribution generated between the nut and the screw shaft under the following conditions was determined by a heat transfer-structure coupled analysis consisting of the above heat transfer analysis and structural analysis using a two-dimensional axisymmetric model.
The screw shaft was a stainless steel 30 degree trapezoidal screw made of austenitic stainless steel SUS303, with a crest diameter of 12.0 mm, a trough diameter of 9.5 mm, and a pitch of 2.0 mm.
The resin nut was made of PPS resin and had a valley diameter of 12.5 mm, a crest diameter of 10.0 mm, and a pitch of 2 mm. The moving stroke of the nut is 300mm. The external dimensions were analyzed using the shape shown in FIG. The shape of the contact portion with the screw shaft is the same as that of the screw shaft, and is a 30 degree trapezoidal screw that is easy to form. The physical properties of SUS303 and PPS resin are shown in Table 1 below. In the analysis, the temperature dependence of the Young's modulus and the directionality of the thermal expansion coefficient were considered.

As analysis conditions, 1200 N was applied as a load at the position shown in FIG. 4 in the axially downward direction to the nut, and the rotational speed of the screw shaft was set to 100 rpm. The ambient temperature is 30 ° C.
Further, in the heat transfer analysis, it is necessary to input the heat transfer coefficient as a value representing the magnitude of heat transfer between each material and the atmospheric fluid as a technical coefficient in addition to the physical property values of each material. . Regarding this value, a clear one was not obtained, and a provisional value was entered. Since the heat transfer coefficient between the solid surface and the natural convection air is about 10 ⁰ to 10 ¹ strong W / m ² / K, the distance between SUS and air was 15 W / m ² / K. The value between PPS and air was considered to be smaller than that between SUS and air, and the value between PPS and air was given by 5 W / m ² / K.
The set values used in the heat transfer analysis are shown in Table 2 below.

FIG. 6 shows a result of contact pressure distribution generated between the nut and the screw shaft obtained by the above analysis.
FIG. 6 shows the contact pressure distribution with the coordinate axis (x-axis) taken along the groove from the top of the nut and the pressure along the coordinate (y-axis). In FIG. 6, since the distance along the groove is divided by the distance corresponding to one pitch, the x axis is increased by one at one pitch. Further, as shown in FIG. 6, there are 12 pitches of the analysis condition nuts, so that there are 12 contact pressure peaks.
As shown in Fig. 6, in the case of the Young's modulus shown in Table 1, the ratio between the minimum value (excluding non-contact) and the maximum value of the contact pressure is almost equal to 10 or less, and the maximum contact pressure is also less than 12 MPa. You can see that.

Next, in Table 1, the Young's modulus of the resin material was changed and other conditions were similarly analyzed, and the Young's modulus dependence of the maximum contact pressure was examined. The results are shown in Table 3 and FIG. The change ratio of Young's modulus with respect to temperature was the same as in Table 1.

  As shown in Table 3 and FIG. 7, when the Young's modulus of the resin material exceeds 5 GPa, the maximum contact pressure gradually increases to 12 MPa or more. When the Young's modulus of the resin material is less than 2.48 GPa, the maximum contact pressure suddenly increases and exceeds 12 MPa.

When the contact pressure increases, external force is received in a large proportion in the vicinity of the contact surface, and it is considered that the possibility of stress concentration leading to fracture increases. In addition, uneven wear of threads occurs. Therefore, when a predetermined load is applied, by using a sliding screw structure / material that can make the resulting contact pressure distribution as uniform as possible, the stress concentration and the increase in the value associated with the increase in contact pressure can be reduced. it is conceivable that.
In the resin nut of the present invention, the Young's modulus of the nut material is made from 2.48 GPa to 5 GPa based on the above analysis, so that the contact pressure distribution is substantially uniform and the maximum contact pressure is reduced, and the load resistance of the sliding screw device is reduced. The upper limit is increased and the life is extended under high surface pressure conditions.

  Since the resin nut and the sliding screw device of the present invention can reduce uneven wear of the screw thread and have a long life even under high surface pressure conditions, various devices such as an optical measuring instrument, a semiconductor manufacturing device, a medical device, etc. Etc. can be suitably used.

The perspective view of the slide screw apparatus using the resin-made nuts of this invention is shown. It is an axial sectional view of the resin nut of the present invention. It is a figure which shows the two-dimensional axisymmetric model used by analysis. It is a figure which shows the example of a condition setting. It is a figure which shows the setting of analysis conditions (dimension etc.). It is a figure which shows the analysis result of contact pressure distribution. It is a figure which shows the Young's modulus dependence of the maximum contact pressure.

Explanation of symbols

1 Screw shaft 2 Sliding screw device 3 Plastic nut 4 Flange

Claims (6)

A resin nut that is screwed onto the screw shaft and moves relative to the screw shaft in the axial direction,
The Young's modulus of the resin material forming the resin nut is an axial direction at the contact surface between the resin nut and the screw shaft when a load is applied to the resin nut in the axial section of the resin nut. The contact pressure distribution of
The resin-made nut, wherein the contact pressure is obtained by analysis by a finite element method using a two-dimensional axisymmetric model of the resin-made nut.   In the analysis by the finite element method, the temperature distribution inside the screw shaft and the resin nut during sliding between the screw shaft and the resin nut is obtained, and then the temperature distribution and a predetermined load are constrained. The resin nut according to claim 1, wherein the resin nut is a heat transfer-structure coupled analysis for analyzing the contact pressure as a condition.   The resin nut according to claim 1 or 2, wherein a maximum value of the contact pressure in the contact pressure distribution is less than 12 MPa.   4. The resin nut according to claim 1, wherein a Young's modulus of a resin material forming the resin nut is 2.48 GPa to 5 GPa at 25 ° C. 5.   The resin nut according to any one of claims 1 to 4, wherein a flange is formed on the resin nut.   A sliding screw device for screwing a nut onto a screw shaft and moving the nut relative to the screw shaft in the axial direction, wherein the nut is a resin nut according to any one of claims 1 to 5. A sliding screw device characterized by that.