JP2004108395A - Ball screw - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ball screw capable of suppressing dynamic torque variation generated at the ball passing periods of the ball screw resulting from a ball clogging phenomenon in the circulation part. <P>SOLUTION: The ball screw is structured so that a plurality of balls 3 are placed in a runway 6 formed between a screw groove 4 in a screw shaft 1 and a screw groove 5 in a nut 2 and has the circulation part 7 whose two ends are in communication with the screw groove 5 in the nut 2 and so that the balls in the runway circulate, wherein resilient pieces 9 are interposed between the balls 3 in such a way that at least one resilient piece 9 is positioned in the circulation part 7 in any operating condition. The spring constant in the ball incoming/outgoing direction of the circulation part mechanism system S including the balls 3 in the circulation part 7, the resilient pieces 9, and a passage constituent part 10 is made ranging between 0.4-180 N/mm. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a ball screw used for various devices.
[0002]
[Prior art]
Ball screws are devices that can convert rotary motion into linear motion with high efficiency, and realize precise positioning in linear motion. Table screws for machine tools, replacement parts for hydraulic and pneumatic actuators, steering devices for automobiles Etc. are used.
Ball screws require stable dynamic torque characteristics in order to achieve precise positioning and high efficiency. This fluctuation of the dynamic torque causes a load fluctuation in the motor driving the ball screw, thereby lowering the efficiency and increasing the number of accumulated pulses in response to the motor command, thereby deteriorating the positioning accuracy.
Further, in the case of a ball screw used for a power steering of an automobile, an operating characteristic at the time of operating a steering wheel, which is felt by a driver, is called a feeling characteristic. With respect to the operating characteristics, when the output of the motor for driving the ball screw changes, the change is transmitted to the handle portion, giving the driver a feeling of discomfort and anxiety. Therefore, a ball screw with as small an operating change as possible is required.
[0003]
One of the factors that hinder stable dynamic torque in a ball screw is dynamic torque fluctuation due to a relative slip phenomenon that occurs between balls on a rolling surface of a screw shaft and a nut. Various ball screws have been proposed in which the variation factor is improved (for example, Patent Documents 1 to 4).
[0004]
[Patent Document 1]
JP-A-56-116951
[Patent Document 2]
JP 2000-120825 A
[Patent Document 3]
JP 2000-199556 A
[Patent Document 4]
JP-A-13-254802
[0005]
[Problems to be solved by the invention]
Each of these proposals aims to eliminate the above-mentioned fluctuation factors of dynamic torque, but as a result of tests and considerations, it has been found that there are other fluctuation factors of dynamic torque. Neither of the above proposals has attempted to eliminate the cause.
That is, the following two factors hinder stable dynamic torque characteristics.
▲ 1 ▼. Dynamic torque fluctuation due to relative slip phenomenon occurring between balls on the rolling surface of the screw shaft and nut.
▲ 2 ▼. Dynamic torque fluctuation generated in the ball passage cycle due to the ball clogging phenomenon in the ball circulation section.
The above factors (2). In particular, when an eccentric load such as a moment load or a radial load is applied due to misalignment between the screw shaft of the ball screw and the nut, etc. In some cases, the ball narrowed so as to cause the ball to be elastically deformed, and periodic dynamic torque fluctuation was likely to occur.
[0006]
Each of the above proposed examples has the above two factors (1). One of the factors out of (2) [1]. Can be eliminated, but other factors (2). Is not taken into consideration, and dynamic torque fluctuations that occur in the ball passage cycle due to the ball clogging phenomenon in the ball circulation section cannot be suppressed. Therefore, it is considered that it is difficult to obtain a satisfactory ball screw with respect to the improvement of the positioning accuracy and efficiency of the ball screw and the stabilization of the driving torque. The above factors (2). No effective plan to improve this has been proposed at present.
[0007]
An object of the present invention is to provide a ball screw capable of suppressing dynamic torque fluctuation generated in a ball passage cycle of a ball screw caused by a ball clogging phenomenon in a circulation portion.
[0008]
[Means for Solving the Problems]
In the ball screw of the present invention, mutually facing screw grooves are formed on an outer diameter surface of a screw shaft and an inner diameter surface of a nut loosely fitted on the outer periphery of the screw shaft, and a screw groove of the screw shaft and a screw groove of the nut are formed. A plurality of balls are interposed in the rolling path formed between the nuts, and the nut has a circulating portion for circulating the balls of the rolling path with both ends communicating with the screw grooves of the nut, and the circulating portion is circulated by the rolling path and the circulating portion. The ball screw having the path formed has the following configuration. That is, the elastic body is interposed between the balls so that at least one elastic body is located in the circulating portion in an arbitrary operation state. In the circulating unit configuration system including the ball in the circulating unit, the elastic body, and the path component of the circulating unit, the spring constant of the ball in and out direction acting between the ball at one end of the circulating unit and the ball at the other end is 0.4 N / Mm to 180 N / mm.
A more preferable range of the spring constant is in a range of 5 N / mm to 100 N / mm, and further preferably, 15 N / mm to 40 N / mm.
The present invention considers the causes and reasons for the periodic fluctuation of the driving torque, and determines and sets an appropriate spring constant for suppressing the fluctuation. Considering the behavior in the circulation section, when the first ball in the circulation section is pushed by the back ball and comes out on the rolling path, it is caught between the screw shaft and the thread groove rolling surface of the nut, and the external load is As a result, the resistance of the extrusion is generated, so that a ball clogging force is generated in the circulation portion. This clogging force is eliminated by the elastic deformation of the elastic body interposed between the balls in the circulation portion, and the ball clogging phenomenon is prevented. In this case, it was found that whether or not the elimination of the clogging force is satisfactorily performed depends on the ease of elastic deformation of the entire circulating portion. According to the test, when the spring constant of the entire circulating portion is in the range of 0.4 N / mm to 180 N / mm, it is found that the ball clogging is eliminated and the dynamic torque fluctuation generated in the ball passage cycle is suppressed. If this spring constant exceeds 180 N / mm, elastic deformation is unlikely to occur, and it is insufficient to suppress dynamic torque fluctuation by elastic deformation. On the other hand, if the spring constant is less than 0.4 N / mm, the function as the elastic body cannot be obtained, and it becomes insufficient to suppress the dynamic torque fluctuation.
[0009]
The spring constant of the entire circulating portion is a spring constant in the circulating portion constituting system including the ball in the circulating portion, the elastic body, and the path component of the circulating portion, and between the ball at one end of the circulating portion and the ball at the other end. It is the spring constant of the elasticity of the acting ball in and out direction. The spring constant is set according to the length of the circulating portion so that the entire spring constant of the circulating portion constituting system is within the above range.
When the path component of the circulating unit can be regarded as a rigid body, the range of the above-mentioned spring constant is the range of the spring constant constituted by the system of the elastic body and the ball in the circulating unit. If the path component has an elasticity that substantially affects the path cross section, the path bending, and the expansion / contraction, the elastic deformation of the path component cannot be ignored.
[0010]
The elastic body may be entirely interposed between the balls. That is, one ball may be interposed at one ratio. The elastic body may be interposed between the balls at a ratio of one to the plurality of balls. When all the elastic bodies are interposed between the balls, the elastic bodies can also serve as means for reducing the friction between the balls. When the ratio is one for a plurality of balls, the length occupied by the elastic body in the orbital path can be reduced as compared with the case where all the balls are interposed, so that the number of balls to be loaded can be increased, Load capacity can be increased.
[0011]
The shape of the elastic body is, for example, a substantially disk shape, a ring shape, or a ball shape. The outer diameter of the elastic body is smaller than the ball. When the elastic body has a substantially disk shape, ring shape, or ball shape, it is prevented that the elastic body is caught on the inner surface of the path by the circulation portion or the like. In particular, in the case of a ball shape, there is no risk of clogging due to falling. In the case of a substantially disk-like or ring-like shape, the elastic body becomes thin, so that the interposition of the elastic body can reduce the decrease in the number of balls that receive a load, thereby reducing the load capacity.
[0012]
The material of the elastic body is, for example, a thermoplastic elastomer. When the thermoplastic elastomer is used, it is easy to set the spring constant in the range of 0.4 N / mm to 180 N / mm.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
A first embodiment of the present invention will be described with reference to FIGS. In the ball screw, screw grooves 4 and 5 corresponding to each other are formed on the outer diameter surface of the screw shaft 1 and the inner diameter surface of the nut 2 loosely fitted on the outer periphery of the screw shaft 1. A plurality of balls 3 are interposed in a spiral rolling path 6 formed between the balls. The nut 2 has a circulating portion 7 in which both ends communicate with the thread groove 5 to circulate the balls 3 of the rolling path 6, and the rolling path 6 and the circulating portion 7 form a circuit path 8. The orbital path 8 may be one turn of the spiral of the screw grooves 4 and 5 or may be a plurality of turns. In this embodiment, the number of turns is two or more. Further, the number of the orbiting path 8 may be one or plural in one ball screw. In this embodiment, two circulating portions 7 are provided in the nut 2 to form two circulating paths 8. The circulation part 7 is formed by a path component 10 composed of a return tube attached to the nut 2.
[0014]
In the ball screw having this configuration, an elastic body 9 is interposed between adjacent balls 3. The elastic body 9 is arranged such that at least one elastic body 9 is located in the circulation section 7 in an arbitrary operation state of the ball screw. That is, at least one elastic body 9 is always present in the circulation portion 7 regardless of the operation state. The elastic body 9 may be interposed between the balls 3 at a ratio of one to the plurality of balls 3 or may be interposed between all the balls 3. In this embodiment, as shown in FIG. 2, one elastic body 9 is interposed between a plurality of balls 3. As shown in the figure, a plurality of (for example, 3 to 5) elastic bodies 9 may be always interposed in the circulation section 7. In FIG. 2, hatching attached to the elastic body 9 is for making the arrangement easy to see, and does not show a cross section.
The spring constant of the elastic body 9 is in the following range over the entire path of the circulation section 7. That is, the ball 3 at one end of the circulating unit 7 in the circulating unit configuration system S including the ball 3 in the circulating unit 7, the elastic body 9, and the path component 10 of the circulating unit 7. _A And ball 3 at the other end _B Is set in the range of 0.4 N / mm to 180 N / mm. For example, as shown in FIG. 12, the other end of the circulation portion 7 is closed, and the ball 3 at one end is closed. _A Is set so that the value obtained when the spring constant in the circulating section 7 is measured in a state in which a pushing force is applied by a load applying means (not shown) to the above range. Ball 3 _A The load acting on the ball 3 _A Is measured by the dial gauge 15.
[0015]
When the path component 10 of the circulating unit 7 can be regarded as a rigid body, the spring constant of the circulating unit constituting system S is the spring constant of the system of each elastic body 9 and the ball 3 in the circulating unit 7. When the path component 10 has elasticity that affects the cross-sectional area and the like in the path, the elastic deformation of the path component 10 also affects the spring constant. The spring constant is set according to the length of the circulating portion 7 so that the entire spring constant of the circulating portion constituting system S falls within the above range.
In this embodiment, the shape of the elastic body 9 is substantially disc-shaped and ring-shaped, but may be various shapes such as ball-shaped. However, the outer diameter of the elastic body 9 is smaller than the outer diameter of the ball 3. The specific shape of the elastic body 9 will be described later. The material of the elastic body 9 is, for example, a thermoplastic elastomer, such as a polyester elastomer.
[0016]
The operation and effect of the ball screw having the above configuration will be described together with the results of tests and verifications in comparison with the conventional ball screw.
FIG. 14 shows a test apparatus. In this test apparatus, a nut 2 of a ball screw A to be tested is fixed to a nut rotation stopper 31 and a screw 32 is rotated by a motor 32 to measure a dynamic torque and the like of the nut 2. An output shaft of the motor 32 is connected via a coupling 35 to a drive shaft 34 rotatably supported by a bracket 33 via a bearing (not shown), and a ball screw coupled to the drive shaft 34 by a flange 36. One end of the screw shaft 1 of the ball screw A is connected and fixed to the fixed bush 37. The other end of the screw shaft 1 is rotatably supported by another bracket 38. A strain gauge 39 is attached to the nut rotation stopper 31, and the dynamic torque acting on the nut 2 is detected via the distortion gauge 39 by the distortion of the nut rotation stopper 31. The output of the strain gauge 39 is taken out via a bridge box and an amplifier (neither is shown) and recorded by the recorder 42. Further, a strain gauge 43 is attached to the path component 10 composed of the return tube of the ball screw A, and the stress generated in the tube that is the path component 10 is detected by the recorder 42 based on the voltage value. The strain gauge 43 of the tube is attached as shown in an enlarged manner in FIGS. Although not shown in FIG. 1, the path component 10 formed of a tube is fixed to the nut 2 by a fixing component 11.
[0017]
FIG. 16 shows a result of measuring dynamic torque fluctuation caused by a ball clogging phenomenon in a conventional ball screw using the above-described test apparatus. FIG. 1A shows a case of a normal ball screw (all ball specification) in which no inclusions such as spacers and elastic bodies are interposed between the balls. FIG. 2B shows a case where a spacer ball is interposed between the balls, and FIG. 2C shows a case where a resin spacer is interposed between the balls. As can be seen from FIG. 9A, in the case of a normal ball screw having a total ball specification, the fluctuation of the dynamic torque coincides with the ball passage period. Even if a spacer ball was used (FIG. 16 (B)) or a spacer formed of resin was inserted between the balls (FIG. 16 (B)), no improvement was obtained.
FIG. 16A shows the measurement results of the tube distortion amount together with the dynamic torque fluctuation. This indicates that the dynamic torque fluctuation is synchronized with the stress generated in the tube and the passage period of the ball. This confirmed that the ball was clogged in the tube when the dynamic torque was increased.
[0018]
The ball clogging phenomenon will be described based on the measurement results with reference to FIG. The ball 3 on the rolling path 6 is in an elastically deformed state because it receives an external load. On the other hand, the ball 3 in the circulation portion 7 is not deformed because it is not subjected to an external load. The ball 3 in the circulation section 7 does not enter the rolling path 6 unless pushed out by the ball 3 coming from behind.
Therefore, in order for the ball 3 to enter the rolling path 6 from the circulation portion 7 and revolve along the rolling surface, the following three steps are required.
▲ 1 ▼. It is pushed out by the ball 3 coming from behind. (FIG. 17A).
▲ 2 ▼. The pushed ball 3 is elastically deformed by receiving an external load by being sandwiched between the screw groove rolling surfaces of the shaft and the nut. (FIG. 17 (B)).
(3). The elastically deformed ball receives rotation from the rotating rolling surface and revolves along the rolling surface. (FIG. 17C).
[0019]
Here, the ball A (3) trying to enter the rolling path 6 does not move between the above (1) and (2). However, the ball B (3) coming from behind as in (2) tries to push out the ball A, so that the ball is clogged in the circulation portion 7. Subsequently, in (3), the ball that has entered the rolling path 6 starts rotating, so that the ball clogging is released. Since the above phenomenon occurs continuously, dynamic torque fluctuation occurs in the ball passing cycle.
In particular, when an eccentric load such as a moment load or a radial load is applied between the screw shaft 1 and the nut 2 of the ball screw due to misalignment or the like, the screw shaft and the nut rolling surface near the entrance and exit of the ball circulating portion 7 make the ball 3 It can be understood from the fact that the dynamic torque may be narrowed so as to elastically deform, and thus a periodic dynamic torque fluctuation is likely to occur.
[0020]
Therefore, the dynamic torque fluctuation generated in the ball passing cycle cannot be solved by inserting spacer balls or spacers between the load balls and eliminating friction between adjacent balls on the rolling surface. That is, it was found that the effect was not exhibited by the improvement in the rolling surface where the ball was subjected to the external load.
[0021]
From the above results, as an example of a method for eliminating the above-mentioned ball clogging force in a region where the ball 3 is not elastically deformed by an external load, an elastic member is provided between the balls 3 in the circulating portion 7 excluding the screw shaft and the nut rolling surface. 9 was inserted, and the means for eliminating the ball clogging force generated in the circulation section 7 was evaluated.
The basic structure and the measurement results are shown in FIGS. This basic structure is such that one coil spring having a free length L is interposed between the balls 3 in the circulating portion 7 as the elastic member 9, and the ball screw is driven within a range where the elastic member 9 does not come off from the circulating portion 7. did. The behavior in that case is shown.
{1 ▼ '. Ball A (3) is pushed out by ball B (3) coming from behind. (FIG. 18A).
(2) '. The extruded ball A (3) is elastically deformed by receiving an external load by being sandwiched between the screw shaft rolling surfaces of the screw shaft 1 and the nut 2. At this time, a ball clogging force is generated in the circulation portion 7, but the ball clogging force is eliminated by the elastic displacement of the elastic member 9 (here, a coil spring having a free length L) inserted between the balls 3. (L ′ <L) (FIG. 18B).
(3) '. The elastically deformed ball A (3) receives a rotation force from the rotating rolling surface and revolves along the rolling surface by itself. Due to the movement of the ball A (3), the coil spring (elastic body 9) elastically displaced in (2) 'returns to the original length L. (FIG. 18C).
[0022]
As shown in FIG. 19, in the ball screw using this structure in the circulation portion 7, it was confirmed that dynamic torque fluctuation did not occur in the ball passage cycle, and it was found that the above idea was correct. According to the above results, in order to eliminate the ball clogging generated in the ball circulating portion 7, the elastic body 9 is provided between the balls 3, thereby suppressing the dynamic torque fluctuation generated in the ball passage cycle caused by the ball clogging. It can be seen that a ball screw is obtained.
This structure is applicable to all ball screws having the circulating portion 7, and the circulating method is not limited. Further, the present invention can be applied to a ball screw using the above-described spacer ball.
[0023]
Next, the disk-shaped elastic body 9 as shown in FIG. 3 was evaluated in the same manner as described above using a ball screw inserted between the balls 3 in the circulation portion 7. Further, the case where the ratio of the elastic body 7 inserted between the balls 3 was changed was also performed. The results are shown in FIGS.
According to this result, even in the structure in which the above-mentioned substantially disk-shaped elastic body 9 is interposed, there is no dynamic torque fluctuation generated in the ball passage period. From this, it was confirmed that the structure in which the elastic body 9 was interposed between the balls 3 satisfies the basic performance as in the above-described basic structure.
For example, if the reciprocating operation of the nut 2 is in a very short swinging operation, that is, if the ball 3 hardly revolves and the elastic body 9 is always arranged in the circulating portion 7, this elasticity is similar to the basic structure. Even one arrangement of the body 9 can satisfy the function.
Further, in the operating state of the ball screw, after the nut 2 is moved for a long distance, the above-described swing operation may be performed at a certain place.
In this case, the above function can be satisfied by inserting the elastic member 9 between the balls 3 incorporated in the ball screw at such a ratio that at least one elastic member 9 always exists in the circulation portion 7.
In this structure, when the elastic body enters the rolling surface, there is no functional problem even if the balls 3 come into direct contact with each other as shown in FIG.
[0024]
Next, for the purpose of grasping the amount of elasticity required in the circulating portion 7, the ratio of the elastic body 9 interposed between the balls 3 in the circulating portion 7 is changed so that the plurality of balls 3 and the elastic body 9 The spring constant in the configured system S of the entire circulating section was measured. In addition, the measurement was performed in the same manner while changing the material. FIG. 13 shows the outline of the measurement and the measurement results.
Thus, even if the number of interposed elastic members 9 and the material thereof are variously changed, the spring constant of the entire system S in the circulating portion including the plurality of balls 3 in the circulating portion 7 and the inserted elastic members 9 is 0.4 N / mm. It was found that the dynamic torque fluctuation occurring at the ball interval period can be suppressed when the speed is up to 180 N / mm.
[0025]
The elastic body 9 used here is a polyester-based elastomer material, but is a thermoplastic elastomer, and if it is a material having good moldability such as a styrene-based, olefin-based, polyurethane-based, PVC-based, or polyamide-based material, It is possible to satisfy the spring constant, and these may be used.
The shape and material of the elastic body 9 to be inserted between the balls 3 are not limited as long as the elastic body 9 satisfies the spring constant of the system S of the entire circulating portion.
In addition, the length of the circulating portion differs depending on the specifications of the ball screw and the circulating method, so that the number of balls arranged in the circulating portion differs. The above spring constant can be realized by adjusting the number of.
[0026]
Next, various specific examples of the elastic body 9 interposed between the balls 3 will be described. In the example of FIG. 3, the elastic body 9 has a substantially disk shape, and the ball contact surfaces 9a on both sides thereof have a concave shape. The elastic body 9 has a ring shape with an end having a central hole 9b. The ball contact surfaces 9a on both sides of the elastic body 9 have a compound conical surface shape in which a contact surface inner diameter portion 9aa and a contact portion outer diameter portion 9ab formed of conical surfaces having different center angles are connected. More specifically, the contact surface inner diameter portion 9aa has a spherical surface portion 9ac having a diameter substantially equal to the ball diameter R as a ball contact portion, as shown in FIG.
When the elastic body 9 has a substantially disc shape, instead of the ball contact surfaces 9a on both sides having the above-mentioned composite cone shape, the elastic body 9 has a single cone shape or a slightly larger diameter than the ball diameter. May be used. Further, the ball contact surfaces 9a on both sides may have a Gothic arch-shaped cross-sectional shape composed of two arcs having different centers of curvature.
[0027]
When the elastic body 9 is formed in a ring shape such as the above-mentioned substantially disc-shaped hole, the shape of the elastic body 9 is such that the balls 3 on both sides do not contact each other as shown in FIG. Is preferred. When the ball 3 is on the rolling path 6, even if the balls 3 on both sides of the elastic body 9 are in contact with each other as shown in FIG. It is preferable to prevent the balls 3 on both sides from contacting each other as shown in FIG.
[0028]
Further, the elastic body 9 does not necessarily have to have elasticity as a whole, but may have elasticity in the ball arranging direction interposed between the balls 3. For example, the elastic body 9 may have a composite shape in which the intermediate member 9A is sandwiched between the ball contact members 9B on both sides as in the example of FIG. 5, and only the intermediate member 9A may have elasticity. With such a composite shape, the ball contact members 9B on both sides can be selected from those having a low coefficient of friction and those having good wear resistance.
When the elastic body 9 is formed into a ring having ends, a spring washer may be used. For example, both ends 9d and 9e may be displaced in the axial direction from each other as shown in FIG. Further, as shown in FIG. 7, a circumferential gap d between both ends 9d and 9e may be a bending allowance.
As shown in FIG. 8, the elastic body 9 may have a ball shape.
[0029]
In the above-described embodiment, the circulation portion 7 has a return tube type. However, the present invention may be applied to an internal circulation type in addition to the external circulation type represented by the return tube, regardless of the ball circulation type. can do. The external circulation system is a system in which the ball 3 is circulated outside the main body of the nut 2, and there is a guide plate system in which a circulation portion 7 is formed in a guide plate 25 as shown in FIG. . The internal circulation system is a system in which the ball 3 is circulated inside the main body of the nut 2, and as a representative example, a top system in which the circulation unit 7 is formed by a top 26 as shown in FIG. There is an end cap type in which the circulation portion 7 is formed by an end cap 27. The present invention can be applied to each of these circulation types.
[0030]
In the present invention, when the elastic body 9 is interposed for each of the plurality of balls 3, an interposing member such as a spacer ball or a spacer having no elasticity may be interposed between other balls. This interposed member is used for reducing the friction between balls in the rolling path 6.
Further, in the present invention, the elastic body 9 in the circulating unit 7 is interposed, but even without the elastic body 9, the path component 10 of the circulating unit 7 and the component for fixing the path component 10 are included. It is also possible to eliminate the ball clogging force generated in the circulating unit 7 by giving a spring property somewhere in the system.
[0031]
【The invention's effect】
The ball screw according to the present invention includes an elastic body interposed between the balls so that at least one elastic body is located in the circulating portion in an arbitrary operation state, and a path configuration of the ball, the elastic body, and the circulating portion in the circulating portion. Since the spring constant of the elasticity acting between the ball at one end and the ball at the other end of the circulating portion in the circulating portion configuration system including the components is set in the range of 0.4 N / mm to 180 N / mm, the balls in the circulating portion Fluctuations in dynamic torque that occur in the ball passing cycle of the ball screw due to the clogging phenomenon can be suppressed. Therefore, the positioning accuracy and efficiency of the ball screw are improved, and the driving torque is stabilized. Further, when this ball screw is applied to a ball screw for an automobile typified by an electric power steering, an operation characteristic called a feeling characteristic accompanying a periodic dynamic torque fluctuation is improved.
[Brief description of the drawings]
FIG. 1 is a cutaway side view of a ball screw according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view of the ball screw obliquely broken.
3A is an explanatory view showing a relationship between a cross section of the elastic body and a ball, FIG. 3B is a cross-sectional view of the elastic body, and FIG. 3C is an enlarged view of a portion C in FIG. .
FIG. 4 is an explanatory diagram showing a relationship between various modified examples of an elastic body and balls.
FIG. 5 is a front view and a sectional view showing another modification of the elastic body.
FIG. 6 is a front view and a side view showing still another modified example of the elastic body.
FIG. 7 is a front view, a side view, and a front view showing a further modified example of the elastic body in a state where a gap is opened.
FIG. 8 is an explanatory diagram showing a relationship between a ball and a further modification of the elastic body.
FIG. 9 is a cross-sectional view of a ball screw according to another embodiment of the present invention.
FIG. 10 is a cutaway perspective view of a ball screw according to still another embodiment of the present invention.
FIG. 11 is a sectional view of a ball screw according to still another embodiment of the present invention.
FIG. 12 is an explanatory view showing a test apparatus for measuring a spring constant.
FIG. 13 is a graph of test results showing the stiffness value (spring constant) of the circulating portion constituting system of the ball screw and the quality of dynamic torque change in the case of various materials and the number of elastic bodies.
FIG. 14 is an explanatory diagram of a measuring device for measuring a dynamic torque or the like of a ball screw.
15 (A) is a view showing the XV portion of FIG. 14 in an enlarged manner from below, and FIG. 15 (B) is a diagram further showing a part thereof.
FIGS. 16A to 16C are graphs showing test results of dynamic torque in a case where a normal ball screw and a spacer ball are used and a case where a resin nut is used, respectively.
FIG. 17 is an explanatory view of a conventional ball screw clogging operation.
FIG. 18 is an explanatory diagram of a ball screw clogging eliminating operation according to the embodiment.
FIG. 19 is a graph of a measurement result of the dynamic torque.
FIG. 20A is a cross-sectional view of a ball screw according to still another embodiment of the present invention, and FIG. 20B is an explanatory diagram of a test result of dynamic torque thereof.
FIG. 21 (A) is a sectional view of a ball screw according to still another embodiment of the present invention, and FIG. 21 (B) is an explanatory diagram of a test result of dynamic torque thereof.
[Explanation of symbols]
1: Screw shaft
2 ... nut
3. Ball
4,5 ... thread groove
6 ... Rolling path
7. Circulation section
8 orbiting route
9 ... elastic body
A: Ball screw
S… Circulation system

Claims (5)

Opposite screw grooves are formed on the outer diameter surface of the screw shaft and the inner diameter surface of the nut loosely fitted on the outer periphery of the screw shaft, and a rolling path formed between the screw groove of the screw shaft and the screw groove of the nut. A ball screw having a circulating portion in which a plurality of balls are interposed and both ends of which communicate with the thread groove of the nut to circulate the balls of the rolling path in the nut, and a circular path is formed by the rolling path and the circulating portion. In the above, an elastic body is interposed between the balls such that at least one elastic body is located in the circulating section in an arbitrary operation state, and the ball including the ball in the circulating section, the elastic body, and a path component of the circulating section includes A ball screw characterized in that a spring constant of elasticity in a ball in / out direction acting between a ball at one end and a ball at the other end of the circulation system in the component system is in a range of 0.4 N / mm to 180 N / mm. 2. The ball screw according to claim 1, wherein the elastic body is entirely interposed between the balls. 2. The ball screw according to claim 1, wherein the elastic body is interposed between the balls at a ratio of one to the plurality of balls. The ball screw according to any one of claims 1 to 3, wherein the elastic body has a substantially disk shape, a ring shape, or a ball shape having an outer diameter smaller than that of the ball. 5. The ball screw according to claim 1, wherein the material of the elastic body interposed between the balls is a thermoplastic elastomer.

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