JP6952569B2 - 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 non-rotatably connected to each other and a force sensor for detecting a preload, and at least one of the two nuts, a contact surface with the shim, and / or the two of the shim. A recess is provided on the contact surface of at least one of the nuts so as to reduce the contact area away from the connecting portion, and on the outer surface of the shim and / or at least one outer surface of the two nuts in the vicinity of the recess. It is a screw device capable of detecting preload to which the force sensor is attached.

According to the present invention, since a recess is provided on the contact surface between the nut and the shim so as to reduce the contact area, the stress (stress = force / contact area) expressed by the force / contact area is locally increased. Can be done. The output of the force sensor can be increased by attaching the force sensor to the outer surface of the shim and / or the outer surface of the nut where the stress is increased in the vicinity of the recess. Further, since a rotational force acts on the connecting portion, by separating the concave portion 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. FIG. 2 is a view taken along the line IV-IV in FIG. 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 schematic side view of the screw device which can detect the preload of the 1st Embodiment. It is an exploded perspective view of the screw device which can detect the preload of the 2nd 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 9a and 9b 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 facing the nut 2 is not provided with a recess.

The recess 12 includes a bottom surface 12b and a side wall 12a. In this embodiment, the recess 12 is formed in a substantially arc shape and opens to the inner and outer surfaces of the nut 2 in the axial direction (see also FIG. 4). The recess 12 forms a thin portion 14 having a reduced thickness in the radial direction on the outer peripheral side of the contact surface 11.

As shown in FIG. 2, a recess 15 is also provided on the other end face 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. Similarly, a recess 17 (see FIG. 1) is also provided on the contact surface 16 of the nut 3 with the shim 4. A recess 18 (see FIG. 3) is also provided on the other end face 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. Keys 25 and 26 (see FIG. 1) 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. 1, the shim 4 is sandwiched between two nuts 2 and 3. The outer diameter of the shim 4 is smaller than the outer diameter of the nuts 2 and 3 (see 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. 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. The inner surface of the split shim 4a is formed in a semi-cylindrical shape. 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. The inner surface of the split shim 4b is formed in a semi-cylindrical shape. It is also possible to configure the shim 4 from a single component without dividing it.

As shown in the axial view of the shim 4 in FIG. 4, since the recess 12 is provided on the contact surface of the nut 2, the contact area between the nut 2 and the shim 4 is reduced by the area of the recess 12. The contact area between the nut 2 and the shim 4 is shown by diagonal lines.

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

As shown in FIG. 5, the shim 4 is sandwiched between two nuts 2 and 3 and compressed. The force sensor 31 detects an axial force, that is, a preload. 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. 4, in the axial view of the nut, the first fan-shaped virtual region of the nut 2 defined by the sensitive portions 31a and 31b of the force sensor 31 (the fan-shaped region of the central angle θ1 surrounded by the alternate long and short dash line, the following θ1) is included in the second fan-shaped virtual region of the nut 2 defined by the recess 12 (the fan-shaped region having a central angle θ2 surrounded by the alternate long and short dash line, hereinafter referred to as θ2). Here, the first fan-shaped virtual region θ1 is a line L1 connecting the virtual axis C of the nut 2 and one end of the sensitive portions 31a and 31b in the circumferential direction, and a circle of the virtual axis C and the sensitive portions 31a and 31b. It is a fan-shaped region defined by a line L2 connecting the other ends in the circumferential direction and having a central angle of less than 180 degrees. The second fan-shaped virtual region θ2 is defined by a line L3 connecting the virtual axis C and one end of the concave portion 12 in the circumferential direction, and a line L4 connecting the virtual axis C and the other end of the concave portion 12 in the circumferential direction. At the same time, it is a fan-shaped region with a central angle of less than 180 degrees.

As shown in FIG. 5, 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 recess 12 is provided on the contact surface 11 of the nut 2 with the shim 4 so as to reduce the contact area, the stress (stress = force / contact area) expressed by the force / contact area can be locally increased. can. By attaching the force sensor 31 to the outer surface of the shim 4 having increased stress near the recess 12, the output of the force sensor 31 can be increased. Further, since a rotational force acts on the keys 25 and 26, by separating the recess 12 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, and clear the preload. Can be detected.

According to the FEM analysis and test results of the screw device (details will be described later), it was found that a large stress is generated in a wider area on the outer surface of the shim 4 having no recess than the outer surface of the nut 2 having the recess 12. rice field. By attaching the force sensor 31 to the outer surface of the shim 4, the output of the force sensor 31 can be made larger than when it is attached to the outer surface of the nut 2.

In the axial view of the nut 2, the first fan-shaped virtual area θ1 of the nut 2 defined by the sensitive portions 31a and 31b of the force sensor 31 is included in the second fan-shaped virtual area θ2 of the nut 2 defined by the recess 12. Therefore, the stress can be increased over the entire range of the sensitive portions 31a and 31b of the force sensor 31, and the output of the force sensor 31 can be further increased.

Since the outer diameter of the shim 4 is made smaller than the outer diameter of the nut 2, the stress acting on the outer surface of the shim 4 can be made larger. On the contrary, if the outer diameter of the shim 4 is made larger than the outer diameter of the nut 2, the stress acting on the inside of the shim 4 can be increased, but the stress acting on the outer surface of the shim 4 cannot be increased.

Since the recess 12 is a recess 12 for the circulation portion 9a for circulating the ball 5, the area of the recess 12 can be increased, and the stress acting on the outer surface of the shim 4 can be further increased.

Since the shim 4 is divided into two and the keys 25 and 26 are fitted to the pair of divided shims 4a and 4b, respectively, it is easier to assemble than when the shim 4 is formed into a ring shape, and the pair of divided shims 4a from the keys 25 and 26 , 4b can reduce the rotational force acting on it.

Since the force sensor 31 includes a first sensitive portion 31a for detecting the axial force of the shim 4 and a second sensitive portion 31b for detecting the circumferential force of the shim 4, the axial force and the circumferential direction are provided. The difference from the force can be measured, and the axial force generated due to thermal expansion can be canceled.
(Second Embodiment)

FIG. 6 shows an exploded perspective view of the screw device according to the second embodiment of the present invention. The screw device of the second embodiment also intervenes 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 ball 5 is circulated by using the circulation portion 9a fitted in the recess 12 of the contact surface 11 of the nut 2, but in the second embodiment, for example, two return pipes 42a are used to circulate the ball. 5 is circulated. 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 of the nut 42, and the other end of the return pipe 42a is connected to the other end of the inner groove 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 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. Similarly, the return pipe 43a is attached to the nut 43.

The contact surface 44 of the nut 42 with the shim 4 is provided with a recess 45 similar to the recess 12 of the screw device of the first embodiment. The circulation portion is not inserted into the recess 45, and the inside of the recess 45 is hollow. By providing the recess 45 on the contact surface 44 of the nut 42 with the shim 4, the output of the force sensor 31 attached to the outer surface of the shim 4 can be increased as in the screw device of the first embodiment.

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 recess is provided on the contact surface of the nut with the shim, but a recess may be provided on the contact surface of the shim with the nut.

In the above embodiment, the force sensor is attached to the outer surface of the shim, but since a large stress is also generated on the outer surface of the nut near the recess, the force sensor can be attached to the outer surface of the nut (Examples described later). reference). When attaching the force sensor to the outer surface of the nut, attach the force sensor to the shim side of the spiral passage between the outer groove of the screw shaft and the inner groove of the nut.

In the above 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, but the sensitive portion of the force sensor. However, it is also possible to provide only the first sensitive portion for detecting the axial force and to provide the force sensor for detecting the circumferential force on another flat surface.

Using the nuts 2 and 3 shown in FIG. 1, the stress acting on the nuts 2 and 3 and the shim 4 when a compressive force was applied was analyzed by FEM. The result of FEM analysis is shown in FIG.

As shown in FIG. 7A, the compressive force is 6000 N. As shown in FIG. 7 (b), the large stress was generated on the outer surface of the shim 4 near the recesses 12 and 17 (see FIG. 1) of the nuts 2 and 3, that is, the flat surfaces P1-1 and P2-. It was 1. Since the recesses 12 and 17 are provided in the two nuts 2 and 3, respectively, there are two places where a large stress is generated. It can be seen that the output of the force sensor 31 can be increased by attaching the force sensor 31 to one of the two flat surfaces P1-1 and P2-1. A large stress was also generated on the outer surface P3 of the nut 2 in the vicinity of the recess 12. It was found that the output of the force sensor 31 can be increased even if the force sensor 31 is attached to this portion. FIG. 7 (c) shows a state in which FIG. 7 (b) is rotated 180 degrees around the axis. It can be seen that a large stress is not generated on the outer surface of the shim 4 away from the recesses 12 and 17, that is, the flat surfaces P1-2 and P2-2.

FIG. 8 shows a test result when a strain gauge is attached to the shim 4 as a force sensor 31. ch1-1 and ch2-1 indicate the output of the strain gauge when the strain gauge is attached to the two flat surfaces P1-1 and P2-1, and ch1-2 and ch2-2 are the two flat surfaces. The output when the strain gauge is attached to P1-2 and P2-2 is shown. The horizontal axis of FIG. 8 is the axial load (kN) applied to the two nuts, and the vertical axis of FIG. 8 is the output (V) of the strain gauge. By attaching the strain gauges to the flat surfaces P1-1 and P2-1, the output of the strain gauges could be doubled compared to the case where the strain gauges were attached to the flat surfaces P1-2 and P2-2. .. Note that a negative strain gauge output means compression strain.

1 ... screw shaft, 1a ... outer groove, 2,3,42,43 ... nut, 2a, 3a ... inner groove, 4 ... shim, 4a, 4b ... split shim, 5,6 ... ball (rolling body), 9a, 9b ... Circulation part, 12 ... Recessed part, 11,44 ... Contact surface, 12,45 ... Recessed part, 25, 26 ... Key (connecting part), 27 ... Key groove, 31 ... Force sensor, 31a ... First sensitive part ( Sensory part), 31b ... Second sensitive part (sensitive part), P1-1 ... Flat surface (outer surface of shim) θ1 ... 1st fan-shaped virtual area, θ2 ... 2nd fan-shaped virtual area

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,
A recess is provided in at least one of the two nuts on the contact surface with the shim and / or on the contact surface of the shim with at least one of the two nuts so as to reduce the contact area away from the connecting portion. Provide,
A preload-detectable screw device that attaches the force sensor to the outer surface of the shim and / or at least one outer surface of the two nuts in the vicinity of the recess. In the axial view of the nut, the first fan-shaped virtual region of the nut defined by the sensitive portion of the force sensor is included in the second fan-shaped virtual region of the nut defined by the recess. The screw device capable of detecting preload according to claim 1. The force sensor is attached to the outer surface of the shim,
The recess is provided on the contact surface of at least one of the two nuts with the shim.
The preload-detectable screw device according to claim 1 or 2, wherein the outer diameter of the shim is smaller than the outer diameter of the two nuts. The screw device capable of detecting preload according to any one of claims 1 to 3, wherein a circulation portion for circulating the rolling element is inserted into the recess. The shim comprises a pair of arcuate split shims.
The preload-detectable screw according to any one of claims 1 to 4, wherein the pair of split shims is formed with a pair of key grooves into which the pair of keys as the connecting portion are fitted. Device. The force sensor includes a first sensitive unit that detects an axial force of the shim and / or the nut, and a second sensitive unit that detects a circumferential force of the shim and / or the nut. The screw device capable of detecting a preload according to any one of claims 1 to 5, wherein the screw device is characterized by the above.

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