JPH0357346B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ball screw unit for limited sliding in which a steel ball is inserted between a screw shaft and a nut so that they roll, and the nut is controlled by a differential screw mechanism for slow and rapid feeding. It is characterized by being carried out using

Conventionally, when moving cutting tools, work tables, workpieces, etc. at slow or rapid speeds, mechanical speed changes have been achieved using a combination of a conical wheel and a pulley or gears, or in a gear device. There are devices that change the diameter ratio or make them differential, and devices that allow the relationship between the driving and driven wheels to be changed in the friction transmission device, but all of them require a considerable amount of space due to the complexity of the mechanism. Not only does this have the disadvantage of increasing the size of the entire machine, but it is also difficult to perform highly accurate feeding operations due to the large load.

Therefore, an object of the present invention is to form two thread grooves separated in the axial direction with a lead difference on a single shaft, and to form a nut that is screwed into these thread grooves via a large number of balls. One of the nuts is fixed in the axial direction and movable in the rotational direction, and the rotation of the nut is selectively allowed or prevented when the shaft rotates, so that the other nut can be moved slightly or rapidly in the axial direction. The object of the present invention is to provide a compact ball screw unit for fine movement and rapid movement, which has a simple structure and high feeding accuracy.

In the present invention, the term "ball screw" refers to a device in which steel balls are inserted between the screw shaft and the nut so that they roll, and in particular, the relative linear motion between the screw shaft and the nut is controlled within a certain range. This invention relates to a ball screw for limited sliding.

Further, among ball screws, a "non-movable ball screw" refers to one in which the nut can rotate relative to each other by rotation of the screw shaft, but cannot perform relative linear motion.

Furthermore, in the present invention, the term "lead" refers to a "screw shaft" that is fitted into each other via a large number of balls.
This refers to the straight-line movement distance that the nut moves relatively in the axial direction.

Furthermore, in the present invention, "ball spline" refers to a device in which a large number of balls are interposed between the spline shaft and the outer cylinder, allowing the spline shaft to move freely in the axial direction and transmitting the rotational torque of the outer cylinder to the spline shaft. refers to something that can be done.

The structure of the present invention will be explained below based on the illustrated embodiment. FIGS. 1 and 2 show a ball screw unit according to the present invention, and in the drawings, reference numeral 1 indicates a non-movable ball in the middle. A single shaft with a screw A and a movable ball screw B and a ball spline C at the end is shown. Therefore, to explain in detail the non-movable ball screw A and the movable ball screw B formed on the shaft 1, a predetermined interval 2 is provided in the middle of the single shaft, and the first screw shaft 3 is on the right side and the first screw shaft 3 on the left side. A second screw shaft 4 is provided, and these first and second screw shafts 3, 4
are provided with spiral thread grooves 5 and 6 for rolling of the balls, respectively. The thread groove 5 of the first screw shaft 3 and the thread groove 6 of the second screw shaft 4 are the same as those of the first screw shaft 3.
A lead difference is provided such that the lead of the second screw shaft 4 is larger than that of the second screw shaft 4.

Reference numerals 7 and 7' denote a single cylindrical nut fixed in the axial direction and rotatable in the rotational direction, which is screwed onto the first screw shaft 3 and the second screw shaft 4 through balls. , 7' are also provided with a spiral thread groove 8 for rolling the balls, which corresponds to the thread grooves 5, 6 of the first screw shaft and the second screw shaft. Here, the thread grooves 8, 8 on the nut side are
As clearly shown in Figure A, the pitch P ₁ between the thread grooves on the center side of the nut is the same as the pitch P ₂ between the other thread grooves,
It is larger than P ₃ and has the relationship of P ₁ = P ₂ + α or P ₁ = P ₃ + α. Therefore _{, the} load balls _{X 1} ...
Each will receive preload toward the outside of the nut. In addition, on the contrary, the pitch P ₁ is made smaller than the pitches P ₂ and P ₃ on both sides, and P ₁ = P ₂ - α or P ₁ =
By establishing the relationship P ₃ −α, the left loaded ball X ₁ ...X ₅ and the right loaded ball Y ₁ ...
...Y ₆ can also be preloaded in the compression direction toward the inside of the nut.

Reference numeral 9 indicates the base end 1 on both end faces of the nuts 7, 7'.
This nut extension part 9 is a cylindrical nut extension part which is integrally locked with the shaft 1 and whose bent end 11 on the opposite side is fitted into the thread grooves 5 and 6 of the shaft 1 all around. The distance is set to be longer than about 1/2 of the axial length of 7 and 7'. Since the nut extensions 9 are provided on the nuts 7 and 7'',
The number of turns of the ball can be set to be greater than the axial length of the nuts 7, 7'. Note that the relative moving distance of the screw shafts 3, 4 or the nuts 7, 7' is the range up to the point where the bent end 11 of the nut extension 9 and the end of the retainer 12 (described later) come into contact with each other, that is, in the illustrated embodiment. , is limited to a distance corresponding to five turns of the ball (see Figure 1). Here, the length of the nut extension part 9 is set to be greater than at least about 1/2 of the axial length of the nuts 7, 7', and the screw shaft 3, 4 or the nuts 7, 7' relative to each other, as shown in FIG.
This is to obtain a maximum stroke of 7'. As shown in FIG. 2A, the width _h1 between the inner circumferential surface of the nut extension 9 and the threads of the screw shafts 3 and 4, and the width between the bottom of the nut side thread groove 8 and the screw shafts 3 and 4. The width diameter h ₂ between the threads is the same dimension, that is, the groove bottom of the nut side thread groove 8 is in contact with the inner circumferential surface of the nut extension part 9 and is on the extension line of the tangent line H parallel to the screw shafts 3 and 4, so the thread The balls rolling in the threaded grooves 5 and 6 of the shafts 3 and 4 are fitted into the threaded grooves 8 on the nut side, and the load is transferred from the load area by simply contacting the inner circumferential surface of the nut extension 9. Rolling transition to no-load area,
Alternatively, the rolling transition in the opposite direction can be smoothly performed. In this case, as shown in FIG. 2B, the no-load ball in the no-load area makes three-point contact with both sides of the thread grooves 5 and 6 on the screw shaft side and the inner circumferential surface of the nut extension 9. Since it is supported at three points, the alignment and circulation movement of the ball is not impaired. Furthermore, since the bent tip 11 is closely fitted into the thread grooves 5 and 6 by a single spiral crest formed on its inner circumference, the internal space of the nut extension 9 is completely isolated from the outside. be done.

Reference numeral 12 denotes a cylindrical retainer that is inserted between the first screw shaft 3 and the nut 7, and the second screw shaft 4 and the nut 7'. A large number of balls rolling between the thread grooves 8 on the corresponding nut side are held in the ball hole 13, and the balls can freely rotate within the ball hole 13. The relative motion among the retainer 12, shaft 1, and nuts 7, 7' is in the following relationship. In other words, Natsuto 7,
When the shaft 1 is rotated with 7' fixed in the rotational and axial directions, the retainer 12 moves in the axial direction together with the shaft 1. On the other hand, if the shaft 1 is fixed in the axial direction and the nuts 7 and 7' are fixed in the rotational direction at the same time, then the shaft 1 is rotated.
The retainer 12 will move in the axial direction together with the nuts 7, 7'. In short, the retainer 12 moves linearly together with the shaft 1 or the nut 7, 7', which is a member that moves in the axial direction.

Reference numeral 14 denotes an angular contact ball bearing attached to the upper surface of the nut 7 on the first screw shaft side, and constitutes a front-to-back combination or a back-to-back combination in a rolling bearing. As clearly shown in FIG. 3, this ball bearing 14 is constructed by inserting balls between an outer ring and an inner ring, and the outer ring 15 has a fixing flange 1 on its upper surface.
6, and at the same time, a branch ridge 18 with ball grooves 17, 17 formed on both sides for ball storage.
is located at the center of the bottom surface. On the other hand, the inner ring is formed by a combination of a nut 7 screwed onto the first screw shaft 3 and an annular ring 19 provided on the left upper surface of the nut. Ball grooves 20, 20 corresponding to the ball grooves 17, 17 of the outer ring are provided in the portion.
Reference numeral 21 denotes a pressing member, such as a double nut, which applies a pressing force in the preload direction to the annular ring 19, and is attached to the upper surface of the left end of the nut 7. By pressing the annular ring 19 toward the ball side using the pressing member 21, a preload can be applied to the ball inserted between the outer ring and the inner ring. Therefore, in this embodiment, the preload can be easily adjusted by simply operating the pressing member.

4 and 5 show other embodiments of applying preload to a ball bearing, and in FIG. 4, a nut 7a serving as an inner ring screwed onto the first screw shaft 3 is shown. At the center of the upper surface, a branch ridge 18a with ball grooves 20a, 20a formed on both sides is provided, while the outer ring is of a split type, and the bottom surface of each pair of outer rings 15a, 15a is are ball grooves 20a, 20a on the nut side.
Ball grooves 17a, 17a corresponding to these are formed. By fitting a spacer _S1 between the pair of outer rings 15a and 15a, the balls inserted between the ball grooves 15a and 17a on each outer ring side and the nut side are pulled in the pulling direction (the balls separate from each other). A preload can be applied in the direction of compression (direction in which the balls approach each other) or in the compression direction (direction in which the balls approach each other). Next, in Figure 5,
A recess is formed in the upper surface of the nut 7b screwed onto the first screw shaft 3, and ball grooves 20b, 20b are provided at both corners of the recess. On the other hand, ball grooves 17b, 17b corresponding to the ball grooves 20b, 20b on the nut side are formed on the bottom surface of each pair of outer rings 15b, 25b. Therefore, the corresponding ball grooves 15b and 20 on the outer ring side and the nut side
After putting the ball between b, each outer ring 15b, 15b
By fitting the spacer S ₂ in between, a preload can be applied to the ball as well. Note that R ₁ , R ₂
is an annular ring that rotatably holds the ball within the ball hole. In this embodiment, since a spacer is provided between a pair of balls arranged in an annular shape to apply preload, there is an advantage that the preload can be finely adjusted.

6 and 7 show a ball spline C that applies torque to the shaft 1, and a ball spline C that applies torque to the shaft 1.
Reference numeral 2 denotes an outer cylinder, and on the inner diameter of the outer cylinder are a no-load ball guide groove 23 extending in the axial direction and having a deep depth from the inner diameter, and a load ball for torque transmission that is slightly shallower in depth than the no-load ball guide groove 23. Guide grooves 24 are formed alternately in the circumferential direction. Both corners of the torque transmission load ball guide groove 24 are rounded so as to form ball transfer surfaces. 25 is the first screw shaft 3
This is a spline shaft formed at the end of the shaft 1 with a predetermined interval 26 between the shaft 1 and the shaft. It is made into an R shape so that it can be formed. This spline shaft 25 is attached to the outer cylinder 2 so that its spline 27 corresponds to the center of each load ball guide groove 23 on the outer cylinder side.
2 and is positioned. Reference numeral 28 denotes a retainer assembled between the outer cylinder 22 and the spline shaft 25, which holds load balls and non-load balls of the outer cylinder that are in the load ball guide groove 24 of the outer cylinder and abut against the spline shaft 25 to transmit torque. A ball groove 2 that aligns and circulates unloaded balls in the guide groove 23 that do not contribute to torque transmission in the axial direction.
It has 9,30. Note that the loaded balls and non-loaded balls are exactly the same ball, and are given different names depending on whether or not they directly contribute to torque transmission as they circulate in the external guide groove and ball groove of the cage. It's just a thing.

The operation of the ball screw unit of the present invention having the above configuration will be explained with reference to FIG. 8. The shaft 1 in FIG. 8 is rotatably and slidably supported on a bearing (not shown) on the left side as viewed in the figure. On the right side, a ball spline is rotatably and slidably held by an annular body 31 with a handle 31a via an outer cylinder 22. Further, among the ball screws, the non-movable ball screw A fixes its ball bearing 14 to the frame or housing 32, and at the same time operatively connects the nut 7 to an appropriate switching means to selectively fix the nut. Or held in a rotatable state. The above switching means includes a rotating member 33 that rotates integrally with the outer cylinder 22 of the ball spline C, and a flange 33 of the rotating member.
a transmission member 34 interposed between the flange 16 of the ball bearing and in face-to-face contact with both flanges 33a and 16;
and a knock pin 35 for selectively transmitting rotational torque from the ball spline C to the transmission member 34, and the transmission member 34 of the switching means and the nut 7 are fixedly connected by bolts or the like.

In short, in the non-movable ball screw A, the ball bearing 14 is fixed in both the axial direction and the rotational direction. On the other hand, the nut 7 is fixed in the axial direction, but alternatively fixed or rotatable in the rotational direction. On the other hand, the movable ball screw B has its nut 7' fixed to a work table or the like 36, and as a result, the nut 7' is held fixed in the rotational direction but movable in the axial direction. . Further, the lead L ₁ of the first screw shaft 3 is larger than the lead L ₂ of the second screw shaft 4.

Under the above conditions, we will explain the slow feed of the work table 36 fixed to the nut 7' on the movable ball screw B in the left direction in the figure.
As shown in FIG. 8, when the nut 7 on the non-movable ball screw side is fixed in the rotational direction, clockwise (clockwise) rotational torque is transmitted from the handle 31a to the spline shaft 25 via the outer cylinder 22. , the shaft 1 is also rotated in the same direction, and thereby the first screw shaft 3 and the second screw shaft 4 formed on the shaft 1 are also rotated clockwise. Here, the tip of the dowel pin 35 has advanced only to the contact surface between the housing 33a of the rotating member 33 and the transmission member 34, and has not fit into the hole 34a of the transmission member 34.
The flange 33a of the rotating member simply slides on the contact surface of the transmission member 34, and the rotational torque from the ball spline C side is not transmitted to the transmission member 34. Therefore, since the nut 7 screwed onto the first screw shaft 3 is fixed in both the rotational direction and the axial direction, it is guided by the thread groove 8 on the nut side and the shaft 1 has a leftward The screw feeding action is activated, and as a result, the shaft 1 is moved forward to the left. On the other hand, since the nut 7' screwed onto the second screw shaft 4 is fixed only in the rotational direction and is slidable in the axial direction, the rotation of the second screw shaft 4 as the shaft rotates, It is guided by the thread groove 6 of the second screw shaft and retreated (apparently displaced) to the right. In other words, the first screw shaft 3 and the lead L ₁ are set larger than the lead L ₂ of the second screw shaft 4, so for example
When L ₁ =10 mm and L ₂ =9 mm, the work table 36 fixed to the nut 7' on the second screw shaft is fed at a slow speed with a lead difference, that is, L ₁ -L ₂ =1 mm.

Next, fast forwarding of the work table 36 to the right in the figure will be explained. As shown in FIG.
The rotary member 33 and the conductive member 34 are fitted into the hole 34a so as to rotate integrally. When a clockwise rotational torque is applied to the spline shaft 25 in such a state, the first screw shaft 3 and the second screw shaft 4 of the shaft 1 are also rotated in the same direction. in this case,
Since the transmission member 34 fixedly connected to the nut 7 is in a state where it can rotate integrally with the rotation member 33, the rotational torque from the ball spline C is transferred to the nut 7 side via the rotation member 33 and the transmission member 34. It will be transmitted at a constant velocity. As a result, the nut 7 on the first screw shaft 3 rotates clockwise together with the first screw shaft 3, and therefore the shaft 1
Since there is no screw feeding action, the shaft simply rotates in a fixed position. On the other hand, the second
The work table 36 fixed to the nut 7' on the screw shaft 4 is guided by the thread groove 6 of the second screw shaft and rapidly moved to the right by the lead _L2 of the second screw shaft. Next, fine movement feed to the right in the figure will be explained.

First, when a counterclockwise (left rotation) rotational torque is transmitted to the spline shaft 25 through the outer cylinder 22 of the handle with the nut fixed in the rotational direction,
The shaft 1 is also rotated in the same left rotation direction, thereby causing the first threaded shaft 3 and the second threaded shaft formed on the shaft 1 to
The screw shaft 4 also rotates counterclockwise. Here, the tip of the knock pin 35 is connected to the housing 3 of the rotating member 33.
3a and the transmission member 34, and does not fit into the hole 34a of the transmission member 34, the flange 33a of the rotating member simply slides on the contact surface of the transmission member 34, and the ball The rotational torque from the spline C side is not transmitted to the transmission member 34.

Therefore, since the nut 7 screwed onto the first screw shaft 3 is fixed in both the rotational direction and the axial direction, the shaft 1 guided in the thread groove 8 on the nut side has a right As a result, the shaft 1 is advanced to the right with the lead _L1 .

On the other hand, the nut 7' screwed onto the second screw shaft 4
is fixed only in the rotational direction and is slidable in the axial direction, so as the second screw shaft 4 rotates with the rotation of the shaft 1, it is guided by the thread groove 6 of the second screw shaft and rotates to the left. It is also caused to retreat (apparent displacement) with the lead L ₂ in the direction. Then, the first screw shaft 3
The lead L ₁ of is set larger than the lead L ₂ of the second screw shaft 4, so for example, L ₁ = 10 mm, L ₂ =
9 mm, the work table 36 fixed to the nut 7' on the second screw shaft has a lead difference, that is, L ₁
Even if -L ₂ = 1 mm, it will result in slight movement feed to the right.

Next, fast forwarding of the work table 36 to the left in the figure will be explained.

As shown in FIG. 9, the dowel pin 35 is pressed so that its tip is inserted into the hole 34a of the transmission member 34, so that the rotating member 33 and the transmission member 34 are rotated integrally.

When a counterclockwise rotational torque is applied to the spline shaft 25 in this state, the first screw shaft 3 and the second screw shaft 4 of the shaft 1 are also rotated in the same direction. In this case, the transmission member 3 fixedly connected to the nut 7
4 is in a state where it can rotate integrally with the rotating member 33, the rotational torque from the ball spline C is transmitted to the nut 7 side at a constant velocity via the rotating member 33 and the transmission member 34. the result,
Since the shaft 1 rotates counterclockwise together with the first screw shaft 3, and therefore no screw feeding action is applied to the shaft 1, the shaft 1 merely rotates at a fixed position. On the other hand, the work table 36 fixed to the nut 7' on the second screw shaft 4 is
It is guided by the thread groove 6 of the screw shaft 4 and is rapidly moved to the left by the lead L of the second screw shaft ₂ .

By the way, the nuts 7, 7' of the present invention are integrally provided with nut extensions 9, 9 on both sides thereof, so that the first screw shaft 3 of the shaft is not connected to the fixed nut 7 during slow feeding. When the shaft 1 and the second screw shaft are moved in the axial direction relative to each other, or when the nut 7' on the second screw shaft is moved in the axial direction relative to the second screw shaft 4 rotating in a fixed position during rapid traverse, the shaft 1 and the second screw shaft The distance of movement of the nut 7' is limited to the range in which the bent tips 11, 11 of the nut extensions and the end of the retainer 12 on the shaft come into contact.

As described above, according to the present invention, the first and second helical thread grooves having a lead difference are spaced apart in the axial direction on a single shaft that is rotatably and movably provided in the axial direction. a first nut screwed into the first thread groove through a plurality of balls, the first nut being fixed in the rotational direction and movable in the axial direction;
Further, a second nut screwed into the second thread groove through a number of balls is fixed in the axial direction and movable in the rotational direction, and the rotation of the second nut is selectively controlled by a switching means. By allowing or blocking the rotation of the second nut when the shaft rotates, the first nut can be moved slightly or rapidly in the axial direction. Compared to systems in which the feed amount is changed and adjusted using various transmission devices, the structure is simpler and the whole can be made more compact. Furthermore, since a large number of balls are interposed between the first and second nuts and the shaft, sliding resistance etc. are extremely small during relative rotation and axial movement between them, making the relative movement nimble and highly accurate. Therefore, the feeding accuracy can be significantly improved.

Furthermore, if the pitch between the thread grooves in the central part of each of the first and second nuts is made different from the pitch between the other thread grooves of the nuts, the balls interposed between the nuts and the shaft can be It is possible to apply a preload of At the same time, it is possible to improve follow-up when changing the direction of rotation of the shaft and switching the feed direction.This can further improve feed accuracy, that is, positioning accuracy, and reduce rattling, etc. As a result, abnormal wear does not occur, so its life can be significantly extended. In particular, we used so-called finite stroke type ball nuts, which hold the balls in a retainer so that they can roll freely, as the first and second nuts, so there is no resistance when the balls circulate like in infinite circulation type ball nuts, and the nuts are light and nimble. It is possible to ensure accurate movement, and it is possible to achieve high speed and high precision.

By providing the nut extension, it is possible to shorten the length of the first and second nuts while ensuring a predetermined stroke, making it easier to process the first and second nuts with high precision. This makes it possible to further improve feeding accuracy.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention; FIG. 1 is a half-cut vertical front view showing the ball screw unit of the present invention, FIG. 2 is a half-cut vertical front view showing the structure of the ball screw, and FIG. 3 is a ball screw unit. 4 and 5 are half-cut longitudinal sectional front views showing the structure of a non-movable ball screw equipped with a bearing.
The figure is a half-cut vertical front view showing another embodiment of the ball bearing.
FIG. 6 is a cross-sectional side view showing the structure of the ball spline, FIG. 7 is a partially cutaway front view of the same ball spline, FIG. 8 is a longitudinal sectional view showing the ball screw unit of the present invention in use, and FIG. 9 FIG. 2 is a vertical sectional view of a main part showing a switching state of a dowel pin. Explanation of symbols, 1... Shaft, 2, 26... Spacing, 3... First screw shaft, 4... Second screw shaft, 5...
...Thread groove (first screw shaft), 6... Thread groove (second screw shaft), 7... Nut (first screw shaft), 7'... Nut (second screw shaft), 8... Thread groove (Natsuto), 9
... Nut extension part, 10 ... Base end, 11 ... Bent tip, 12, 28 ... Cage, 13 ... Ball hole, 14 ... Ball bearing, 15 ... Outer ring, 16, 33
a...Flange, 17, 20...Ball groove, 18
... Branch ridge, 19 ... Annular ring, 21 ... Pressing member, 22 ... Outer cylinder, 23 ... No-load ball guide groove, 24 ... Load ball guide groove, 25 ... Spline shaft, 27 ... Spline, 29, 30...
Ball groove, 31...ring body, 31a...handle,
32...Housing, 33...Rotating member, 34...
... Transmission member, 34a... Hole of transmission member, 35...
Knock pin, 36...Work table, A...Non-movable ball screw, B...Movable ball screw, C...
Ball spline, L... Length of nut extension,
P ₁ , P ₂ , P ₃ ... Pitch, R ₁ , R ₂ ... Annular ring,
S ₁ , S ₂ ... Maza.

Claims (1)

[Claims] 1. Spiral first and second thread grooves having a lead difference and formed in the same direction are formed apart from each other in the axial direction, and are provided to be rotatable and movable in the axial direction. a single shaft, which is fixed in the rotational direction and movable in the axial direction; and a first nut which is fixed in the axial direction and movable in the rotational direction and is screwed into the second thread groove of the shaft via a number of balls that are rotatably held by a cage and is fixed in the axial direction and movable in the rotational direction. , selectively allowing or blocking the rotation of the first nut, transmitting the rotating torque of the shaft to the first nut when the rotation of the first nut is allowed, and not transmitting the rotating torque of the shaft to the first nut when blocking the rotation. said first and second nuts are each provided with a cylindrical nut extension on both sides thereof, and the relative movement between said first and second nuts and said shaft causes said first and second nuts to switch between said first and second nuts. A ball held in a retainer protruding axially from a side surface of the second nut is brought into contact with the inner periphery of the nut extension to prevent the ball from falling off, and the switching means prevents rotation of the first nut and the shaft. By switching the rotational torque to the first nut to a non-transmitting state and rotating the shaft, the second nut can be tightened even by the lead difference between the first and second thread grooves in which the first nut and the second nut are screwed together. is capable of fine movement in the axial direction, and the switching means allows rotation of the first nut and switches the rotational torque of the shaft to the state of transmitting it to the first nut, so that the first nut is rotated integrally with the shaft. In particular, the ball screw unit for fine movement and rapid traverse allows the second nut to be rapidly traversed in the axial direction using only the lead of the second thread groove into which the second nut is screwed.