JP6952570B2 - Screw device that can detect preload - Google Patents

Description

The present invention relates to a screw device capable of detecting a preload by interposing a shim for applying a preload between two nuts.

The screw device includes a screw shaft, a nut, and a plurality of rolling elements such as balls interposed between the screw shaft and the nut. When either the screw shaft or the nut is rotated, the other moves linearly. The screwing device is used as a mechanical element that converts rotation into linear motion or linear motion into rotation. Since the rolling element rolls while the screw shaft rotates, the frictional resistance can be reduced and the efficiency can be improved.

As a conventional screwing device, a double nut screwing device in which a shim is interposed between two nuts to apply a preload is known. The shim is sandwiched between two nuts and compressed. The two nuts are non-rotatably connected to each other by a key as a connecting part. By connecting the two nuts in a non-rotatable manner, the shim can be kept compressed by the two nuts. Preload is applied to the two nuts by the reaction force from the shim so as to eliminate the axial gap. By applying the preload, the rigidity and positioning accuracy of the screw device can be improved.

As a screw device capable of detecting preload, Patent Document 1 describes that the axial end faces of two nuts face each other, a convex portion is provided on one end face of the two nuts, and the convex portion is accommodated on the other end face. A screw device provided with a recess is disclosed. Preload is applied by pushing the convex portion in the circumferential direction with a set screw and shifting the axial phase of one nut with respect to the other nut. There is no shim between the two nuts, and a force sensor is sandwiched between the two nuts. With this force sensor, it is possible to detect the axial preload acting on the two nuts.

Japanese Unexamined Patent Publication No. 2016-223493

When the screw device is used for a long period of time, the rolling element, the screw shaft, and the nut are worn, and the preload applied to the two nuts is reduced, which reduces the positioning accuracy and rigidity of the screw device. If the preload can be detected, the screw device can be replaced before the positioning accuracy and rigidity are reduced. However, the conventional screw device with a shim interposed therebetween has a problem that it is difficult to detect the preload. This is because even if a force sensor (for example, a strain gauge) that detects an axial force is attached to the outer surface of the shim, the amount of axial strain of the shim is small, so that the output of the force sensor is small. Therefore, there are problems that the output of the force sensor is easily affected by noise and the measured function of the force sensor is low.

In the screw device described in Patent Document 1, since the force sensor is sandwiched between the two nuts, the output of the force sensor can be increased. However, since no shim is interposed between the two nuts, there are problems that the preload is not stable and the rigidity of the nuts is low.

Therefore, an object of the present invention is to provide a screw device capable of detecting a preload in a screw device in which a shim is interposed between two nuts.

In order to solve the above problems, one aspect of the present invention includes a screw shaft having a spiral outer surface groove and two nuts assembled to the screw shaft and having a spiral inner surface groove facing the outer surface groove. A plurality of rolling elements interposed between the outer groove of the screw shaft and the inner groove of each of the two nuts, a shim sandwiched between the two nuts and compressed, and the two nuts. A connecting portion that is connected to each other so as not to rotate relative to each other, and a force sensor for detecting a preload are provided. It is a screw device capable of detecting preload that attaches the force sensor to the outer surface.

According to the present invention, the rigidity of the outer surface of the shim in the vicinity of the hole can be locally reduced while maintaining the rigidity of the entire shim to some extent. Since the force sensor is attached to the outer surface of the shim whose rigidity is locally lowered, the output of the force sensor can be increased, and preload detection with higher resolution can be performed. Further, since a rotational force acts on the connecting portion, by separating the hole from the connecting portion, it is possible to prevent the force sensor from superimposing on the preload and detecting the rotational force, and the preload can be clearly detected. ..

It is an exploded perspective view of the screw device which can detect the preload of the 1st Embodiment of this invention. It is a side view of the screw device which can detect the preload of the 1st Embodiment. It is an exploded perspective view of the nut of the screw device which can detect the preload of the first embodiment. It is a perspective view of the shim of the screw device which can detect the preload of the first embodiment. It is a VV line arrow view of FIG. It is a schematic side view of the screw device which can detect the preload of the 1st Embodiment. It is a perspective view of the shim of the screw device which can detect the preload of the 2nd Embodiment of this invention. It is a partial side view of the shim of the screw device which can detect the preload of the 2nd Embodiment. It is an exploded perspective view of the screw device which can detect the preload of the 3rd Embodiment of this invention. It is a figure which shows the result of FEM analysis. It is a graph which shows the test result.

Hereinafter, a screw device capable of detecting preload (hereinafter, simply referred to as a screw device) according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. However, the screwing device of the present invention can be embodied in various forms, and is not limited to the embodiments described in the present specification. The present embodiment is provided with the intention of allowing those skilled in the art to fully understand the scope of the invention by making sufficient disclosure of the specification.
(First Embodiment)

FIG. 1 shows an exploded perspective view of the screw device according to the first embodiment of the present invention, and FIG. 2 shows a side view. The screw device of the present embodiment is a so-called double nut ball screw, which is a screw shaft 1, two nuts 2 and 3, a shim 4 sandwiched between two nuts 2 and 3, and a screw shaft 1 and two nuts 2. , 3 Each of the balls 5 and 6 is provided as a rolling element.

A spiral outer surface groove 1a is formed on the outer surface of the screw shaft 1. Balls 5 and 6 roll in the outer groove 1a. The cross-sectional shape of the outer surface groove 1a is a Gothic arch or a circular arc.

Two nuts 2 and 3 are assembled to the screw shaft 1. The nuts 2 and 3 have a substantially cylindrical shape. Inner surface grooves 2a and 3a facing the outer surface groove 1a of the screw shaft 1 are formed on the inner surface of the nuts 2 and 3. The cross-sectional shape of the inner grooves 2a and 3a is a Gothic arch or a circular arc. One nut 3 is provided with a flange 3b for attaching to a mating component. The other nut 2 is not provided with a flange.

As shown in FIG. 2, a spiral passage 7 is formed between the outer surface groove 1a of the screw shaft 1 and the inner surface groove 2a of the nut 2. Balls 5 (see FIG. 1) are arranged in this passage 7. The nut 2 is provided with a return path 8 connected to one end and the other end of the passage 7 so that the ball 5 can circulate. In FIG. 2, the center lines of the spiral passage 7 and the return path 8 are shown by alternate long and short dash lines. In this embodiment, the return path 8 is composed of a through hole 8a provided in the nut 2 and a pair of turning paths 8b connecting the through hole 8a and the passage 7. The turning path 8b is formed in the circulation portions 9a and 9b attached to the axial end faces of the nut 2. The circulation portions 9a and 9b scoop up the ball 5 rolling in the passage 7 from the outer surface groove 1a of the screw shaft 1 and guide it to the through hole 8a. The ball 5 that has passed through the through hole 8a is returned to the passage 7 again from the circulation portions 9b and 9a on the opposite side. Similarly, the nut 3 is formed with a passage 7, a through hole 8a, and a turning path 8b. Since these configurations are the same, the same reference numerals are given and the description thereof will be omitted.

As shown in the exploded perspective view of the nuts 2 and 3 in FIG. 3, the axial end surface of the nut 2, that is, the contact surface 11 of the nut 2 with the shim 4 is formed in a substantially annular shape. The substantially annular contact surface 11 is provided with a recess 12 into which the circulation portion 9a is inserted (see FIG. 1). The contact surface 13 of the shim 4 with the nut 2 is a flat surface.

As shown in FIG. 2, a recess 15 into which the circulation portion 9b is inserted is also provided on the other end surface of the nut 2 in the axial direction. The shape of the recess 15 is the same as the shape of the recess 12 when the nut 2 is rotated 180 degrees around an axis perpendicular to the paper surface of FIG. The contact surface 16 of the nut 3 with the shim 4 is also provided with a recess 17 (see FIG. 1) into which the circulation portion 9b is inserted. Further, a recess 18 (see FIG. 3) into which the circulation portion 9a is inserted is also provided on the other end surface of the nut 3 in the axial direction.

As shown in FIG. 1, the end face of the nut 2 on the opposite side of the shim 4 is closed by the ring-shaped cap 21. Similarly, the end face of the nut 3 on the opposite side of the shim 4 is also closed with the ring-shaped cap 22. The caps 21 and 22 are attached to the nuts 2 and 3 by a fastening member such as a screw.

As shown in FIG. 2, in the present embodiment, the phases of the through holes 8a of the two nuts 2 and 3 in the circumferential direction are matched. In the side view of FIG. 2, the circulation portion 9a of one adjacent nut 2 and the circulation portion 9b of the other nut 3 are staggered, that is, the circulation portion 9a of one nut 2 is mainly below the through hole 8a. The circulation portion 9b of the other nut 3 is arranged mainly above the through hole 8a.

As shown in FIG. 3, key grooves 23 and 24 are formed on the outer surface of the facing ends of the nuts 2 and 3. As shown in FIG. 1, the keys 25 and 26 as connecting portions for connecting the two nuts 2 and 3 so as not to rotate relative to each other are fitted in the key grooves 23 and 24. The shim 4 is also formed with a key groove 27 into which the keys 25 and 26 are fitted.

As shown in FIG. 4, the shim 4 has a ring shape and includes a pair of arc-shaped divided shims 4a and 4b having a central angle of approximately 180 degrees. The outer diameter of the shim 4 is smaller than the outer diameter of the nuts 2 and 3 (see FIG. 5). A key groove 27 into which the keys 25 and 26 are fitted is formed in the central portion of the outer surface of the divided shims 4a and 4b in the circumferential direction. A pair of flat surfaces P1-1 and P1-2 are formed on both sides of the key groove 27 of the dividing shim 4a in the circumferential direction. A pair of flat surfaces P2-1 and P2-2 are formed on both sides of the key groove 27 of the dividing shim 4b in the circumferential direction. It is also possible to configure the shim 4 from a single component without dividing it.

Each of the divided shims 4a, 4b is provided with a plurality of axial holes 32a, 32b, 32c extending in the axial direction of the shim 4. Specifically, a plurality of, for example, three holes 32a, 32b. 32c is provided. The holes 32a, 32b, 32c penetrate from one end surface to the other end surface of the shim 4 in the axial direction. The holes 32a, 32b, 32c are cylindrical.

As shown in the axial view of the shim 4 in FIG. 5, a force sensor 31 is attached to the outer surface of the shim 4 in the vicinity of the holes 32a, 32b, 32c. Specifically, the force sensor 31 is attached to one of the two flat surfaces P2-1 and P2-2 of the split shim 4b, P2-1. The flat surface P2-1 is in the vicinity of the recess 17 of the nut 3. As shown by the alternate long and short dash line in the figure, the force sensor 31'can be attached to the flat surface P1-1 of the split shim 4a. As shown in FIG. 1, the flat surface P1-1 is in the vicinity of the recess 12 of the nut 2. The force sensor 31 is attached to the flat surface P2-1 by an adhesive. If the force sensor 31 is attached to the flat surface P2-1, it is possible to prevent stress from being generated in the force sensor 31.

As shown in FIG. 6, the force sensor 31 is, for example, a strain gauge, and includes a resin base 31c and sensitive portions 31a and 31b embedded in the resin base 31c to measure the strain of the shim 4. Lead wires (not shown) are connected to the sensitive units 31a and 31b. The sensitive units 31a and 31b include a first sensitive unit 31a that detects an axial force and a second sensitive unit 31b that detects a circumferential force. By measuring the difference between the axial force and the circumferential force, the axial force generated due to thermal expansion can be canceled.

As shown in FIG. 5, in the axial view of the shim 4, the holes 32a, 32b, 32c are arranged substantially parallel to the flat surface P2-1 at a substantially constant depth h from the flat surface P2-1. The width W1 of the sensitive portions 31a, 31b of the force sensor 31 is smaller than the width W2 of the region of the holes 32a, 32b, 32c on the back of the force sensor 31. Further, the width W1 of the sensitive portions 31a and 31b of the force sensor 31 is larger than the diameter d of the holes 32a, 32b and 32c. The diameters d of the holes 32a, 32b, and 32c are substantially the same.

As shown in FIG. 6, the shim 4 is sandwiched between two nuts 2 and 3 and compressed. Axial preload is applied to the two nuts 2 and 3 by the reaction force from the shim 4. The preload is detected by the force sensor 31. The force sensor 31 is connected to an amplifier board (not shown). The amplifier board outputs output data obtained by digitizing a voltage signal. The output data is input to a failure diagnosis system (not shown). The failure diagnosis system can judge the failure by comparing the output data of the force sensor 31 with a predetermined threshold value, can machine-learn the output data of the force sensor 31 to judge the failure, and can judge the failure. It is also possible to determine a failure by deep learning the output data of 31 using artificial intelligence. It is also possible to introduce IoT and transmit the output data of the force sensor 31 to the cloud via an internet line by a transmitter.

The effect of the screw device of this embodiment will be described below.

Since the holes 32a, 32b, 32c are provided in the shim 4 apart from the keys 25 and 26, the flat surface P2-1 of the shim 4 in the vicinity of the holes 32a, 32b, 32c while maintaining the rigidity of the entire shim 4 to some extent. The rigidity can be reduced locally. Since the force sensor 31 is attached to the flat surface P2-1 whose rigidity is locally lowered, the output of the force sensor 31 can be increased, and preload detection with higher resolution can be performed. Further, since the rotational force acts on the keys 25 and 26, by separating the holes 32a, 32b and 32c from the keys 25 and 26, it is possible to prevent the force sensor 31 from superimposing on the preload and detecting the rotational force. , Preload can be detected clearly.

Since the holes 32a, 32b, and 32c extend in the axial direction of the shim 4, it is possible to prevent the axial rigidity of the entire shim 4 related to the preload from being lowered. Further, since the holes 32a, 32b, and 32c do not appear on the outer surface of the shim 4, it is easy to secure a mounting space for the force sensor 31 on the outer surface of the shim 4.

Since the recess 17 is provided in the contact surface 16 of the nut 3 with the shim 4, the stress (stress = force / contact area) expressed by the force / contact area can be increased. By attaching the force sensor 31 to the flat surface P2-1 of the shim 4 having increased stress near the recess 17 of the nut 3, the output of the force sensor 31 can be increased.

Since the shim 4 is divided into two and holes 32a, 32b, 32c are provided in the pair of divided shims 4a, 4b, respectively, the rigidity of the shim 4 can be made substantially uniform in the circumferential direction.
(Second Embodiment)

FIG. 7 shows the shim 33 of the screw device of the second embodiment of the present invention. Since the configurations of the screw shaft 1 and the two nuts 2 and 3 are the same as those in the first embodiment, the illustration is omitted.

As shown in FIG. 7, the shim 33 of the second embodiment includes a pair of arcuate split shims 33a and 33b having a central angle of approximately 180 degrees, similarly to the shim 4 of the first embodiment. A key groove 34 into which the keys 25 and 26 are fitted is formed in the central portion of the outer surface of the divided shims 33a and 33b in the circumferential direction. A pair of flat surfaces P1-1 and P1-2 are formed on both sides of the key groove 34 of the dividing shim 33a in the circumferential direction. A pair of flat surfaces P2-1 and P2-2 are formed on both sides of the key groove 34 of the dividing shim 33b in the circumferential direction.

Each of the divided shims 33a, 33b is provided with a plurality of right-angled holes 35a, 35b, 35c extending in the perpendicular direction to the flat surfaces P1-1, P1-2, P2-1, P2-2 of the shim 33. In this embodiment, a plurality of holes 35a, 35b, 35c, for example, three holes 35a, 35b, 35c are provided on the flat surfaces P1-1, P1-2, P2-1, P2-2 of the divided shims 33a, 33b. The holes 35a, 35b, and 35c are arranged in the directions perpendicular to the axis of the shim 33 on the flat surfaces P1-1, P1-2, P2-1, and P2-2. The diameters of the holes 35a, 35b and 35c are substantially the same. The holes 35a, 35b, 35c penetrate from the outer surface to the inner surface of the shim 33. The holes 35a, 35b, 35c are cylindrical.

As shown in the partial side view of the shim 33 in FIG. 8 (side view seen from the direction orthogonal to the flat surface P2-1), the force sensors 36a and 36b are attached to the flat surface P2-1 of the shim 33. Specifically, the force sensors 36a, 36b are attached next to the holes 35a, 35b, 35c in the circumferential direction of the shim 33, and at substantially the same positions as the holes 35a, 35b, 35c in the axial direction of the shim 33. The force sensors 36a and 36b detect an axial force (that is, compression strain). The force sensors 36a and 36b are arranged between the holes 35a and 35b and between the holes 35b and 35c. Further, force sensors 37a and 37b are attached next to the holes 35b in the axial direction. The force sensors 37a and 37b detect the circumferential force (that is, the circumferential distortion) of the shim 33.

According to the screw device of the second embodiment, the following effects are obtained.

Since the holes 35a, 35b, 35c extend in the direction perpendicular to the flat surface P2-1 of the shim 33, the rigidity of the flat surface P2-1 can be reduced. By attaching the force sensors 36a, 36b, 37a, 37b to the flat surface P2-1 having reduced rigidity, the output of the force sensors 36a, 36b, 37a, 37b can be increased.

Since the force sensors 36a, 36b are arranged next to the holes 35a, 35b, 35c in the circumferential direction of the shim 33 and at substantially the same positions as the holes 35a, 35b, 35c in the axial direction of the shim 33, the flat surface P2-1 The force sensors 36a and 36b can be arranged in a portion where the rigidity is particularly reduced (see Examples described later). Therefore, the outputs of the force sensors 36a and 36b that detect the axial force can be increased.

Since the force sensors 36a and 36b for detecting the axial force and the force sensors 37a and 37b for detecting the circumferential force are provided, the difference between the axial force and the circumferential force can be measured, and the heat can be measured. Axial forces generated due to expansion can be canceled.
(Third Embodiment)

FIG. 9 shows an exploded perspective view of the screw device according to the third embodiment of the present invention. The screw device of the third embodiment is also interposed between the screw shaft 1, the two nuts 42, 43, the shim 4 sandwiched between the two nuts 42, 43, and the screw shaft 1 and the two nuts 42, 43. It has balls 5 and 6. Since the configurations of the screw shaft 1, the shim 4, and the balls 5 and 6 are the same as those in the first embodiment, the same reference numerals are given and the description thereof will be omitted.

In the first embodiment, the balls 5 and 6 are circulated by using the circulation portions 9a and 9b that fit into the recesses 12, 15, 17 and 18 on the axial end faces of the nuts 2 and 3, but the second embodiment. In the embodiment, the balls 5 and 6 are circulated by using the return pipes 42a and 43a attached to the nuts 42 and 43. A flattening portion 42b is formed on the outer surface of the nut 42, and a return pipe 42a is attached to the flattening portion 42b. The return pipe 42a is formed in a portal shape by bending both ends. Both ends of the return pipe 42a penetrate the nut 42 in the axial direction. One end of the return pipe 42a is connected to one end of the inner groove 42c of the nut 42, and the other end of the return pipe 42a is connected to the other end of the inner groove 42c of the nut 42. The ball 5 rolling in the spiral passage between the outer surface groove 1a of the screw shaft 1 and the inner surface groove 42c of the nut 42 is scooped up at one end of the return pipe 42a, passes through the return pipe 42a, and then passes through the return pipe 42a. It is returned to the passage again from the other end of the. Similarly, the flattening portion 43b is also formed on the nut 43, and the return pipe 43a is attached to the flattening portion 43b.

The present invention is not limited to being embodied in the above embodiment, and can be changed to other embodiments without changing the gist of the present invention.

In the above embodiment, the hole in the axial direction is a through hole and the hole in the right angle direction is a through hole, but a hole that does not penetrate these holes, that is, a bottomed hole can also be used.

In the first embodiment, the sensitive portion of the force sensor includes a first sensitive portion that detects an axial force and a second sensitive portion that detects a circumferential force. It is also possible that the sensitive portion includes only the first sensitive portion that detects the axial force, and the force sensor that detects the circumferential force is provided on another flat surface.

In the first embodiment, the shim is provided with a hole in the axial direction, and in the second embodiment, the shim is provided with a hole in the direction perpendicular to the shim, but these can also be used together.

Using the nuts 2 and 3 shown in FIG. 1, the shims 4 and the shims 33 shown in FIG. 7, the stress acting on the shims 4 and 33 when a compressive force of 6000 N was applied was subjected to FEM analysis. The result of FEM analysis is shown in FIG.

FIG. 10 (a) shows a conventional example in which the shim is not provided with a hole, and FIG. 10 (b) shows an invention example (1) (in the first embodiment) in which the shim 4 is provided with axial holes 32a, 32b, 32c. In the shim 4), FIG. 10 (c) is an example of the invention (2) (the shim 33 of the second embodiment) in which the holes 35a, 35b, 35c in the direction perpendicular to the shim 33 are provided.

As shown in FIG. 10B, in the invention example (1), the compression strain is generated over substantially the entire region of the flat surface P2-1 of the shim 4 in which the axial holes 32a, 32b, 32c are present on the back surface. It turned out to be bigger. It can be seen that if the force sensor 31 is attached to the flat surface P2-1, the output of the force sensor 31 can be increased. As shown in FIG. 10 (c), in the invention example (2), a large compressive strain was generated between the hole 35a and the hole 35b and between the hole 35b and the hole 35c. It can be seen that if the force sensors 36a and 36b are attached to this position, the output of the force sensors 36a and 36b can be increased.

FIG. 11 shows the test results when strain gauges are attached to the shims 4 and 33 as force sensors 31, 36a and 36b. The horizontal axis of FIG. 11 is the axial load (kN) applied to the nuts 2 and 3, and the vertical axis of FIG. 11 is the output (V) of the strain gauge. In the invention example (1), the output of the strain gauge could be increased by about 30% as compared with the conventional example. In the invention example (2), the output of the strain gauge could be increased by about 400% as compared with the conventional example.

1 ... screw shaft, 1a ... outer groove, 2,3,42,43 ... nut, 2a, 3a, 42c ... inner groove, 4,33 ... shim, 4a, 4b, 33a, 33b ... split shim, 5,6 ... Ball (rolling body), 25, 26 ... Key (connecting part), 31, 36a, 36b ... Force sensor, 31a ... 1st sensation part (sensing part), 31b ... 2nd sensing part (sensing part) , 32a, 32b, 32c ... Axial holes, 35a, 35b, 35c ... Right-angled holes, P2-1 ... Flat surface of shim (outer surface of shim), W1 ... Width of sensing part of force sensor, W2 ... Width of multiple hole areas

Claims (6)

A screw shaft with a spiral outer groove,
Two nuts assembled to the screw shaft and having a spiral inner groove facing the outer groove,
A plurality of rolling elements interposed between the outer surface groove of the screw shaft and the inner surface groove of each of the two nuts.
A shim that is sandwiched between the two nuts and compressed,
A connecting portion that connects the two nuts so that they cannot rotate relative to each other,
Equipped with a force sensor for detecting preload,
The shim is provided with at least one hole away from the connecting portion.
A preload-detectable screw device that attaches the force sensor to the outer surface of the shim near the hole. The preload-detectable screw device according to claim 1, wherein the hole includes at least one axial hole extending in the axial direction of the shim. The preload detection is possible according to claim 2, wherein the width of the sensitive portion of the force sensor is smaller than the width of the region of the plurality of holes on the back of the force sensor in the axial view of the shim. Screw device. The preload-detectable screw device according to claim 1, wherein the hole comprises at least one right-angled hole extending in the direction perpendicular to the flat surface of the shim to which the force sensor is attached. The preload-detectable screw according to claim 4, wherein the force sensor is mounted next to the hole in the circumferential direction of the shim and at substantially the same position as the hole in the axial direction of the shim. Device. The shim comprises a pair of arcuate split shims.
The screw device capable of detecting preload according to any one of claims 1 to 5, wherein each of the pair of split shims is provided with the hole.

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