JPH0623597B2 - Rotation-linear motion converter - Google Patents

Description

TECHNICAL FIELD The present invention relates to a rotation-linear motion conversion device, that is, a device for converting a rotational driving force into a linear motion, and has a smooth surface. The present invention relates to a rotation-linear motion conversion device of a type in which a female screw body is externally fitted to a shaft to be paired with each other and a pair of screws are frictionally engaged with each other via a rolling element.

[Prior Art and its Problems] A so-called linear drive device that converts rotational force into linear power is
It is widely used as a drive device for beds in machine tools. A so-called ball screw is a typical linear drive device of this type, and is used as a feeding device in many fields.

Generally, a ball screw has a shaft (1) as shown in FIG.
It is constructed by externally inserting the female screw body (2) into the screw groove (21), (21) formed in them and press-fitting a large number of steel balls (30), (30). The shaft body (1) and the female screw body (2) are made to mate with each other through the balls (30), (30). A return passage (4) is provided on the outer peripheral portion of the female screw body between the start end and the end of the above-mentioned thread grooves (21), (21). ), The steel balls (30), (30) that have escaped from the end portions of the thread grooves (21), (21) are guided to the starting end portions thereof.

In this case, when the shaft body (1) is driven to rotate,
Steel balls (30), (30) are rolling while screw groove (21) Return path
(4) Since it circulates with the screw groove (21), the driving frictional resistance is smaller than that of the feed screw type using a simple screw pair action.

Therefore, the conversion efficiency between the rotational force and the linear moving force is high, and a sufficient linear driving force can be generated with a light rotational force.

However, in this conventional ball screw, the thread groove (21) must be formed in the shaft body (1), which is expensive.

As a solution to the above problem, a linear drive device of the type in which the thread groove (21) is not formed in both the shaft body (1) and the female screw (2) has already been proposed as Japanese Patent Application No. 63-200944. .

This type of linear drive system has a shaft body as shown in FIG.
The outer peripheral surface of (1) is made smooth, and the thread groove (21) is provided only on the inner peripheral surface of the female screw body (2). Steel balls (30), (30) are interposed between the surface and the surface in a sandwiched state.

In this type, since the rolling elements (3), (3) are continuous along the thread groove (21), the contact point between the rolling element (3) and the surface of the shaft body (1) is the thread groove (21). It will be continuous on the screw pair trajectory,
Moreover, the rolling direction of each rolling element (3) at each point is relatively along the thread groove (21). Therefore, when the shaft body (1) is driven to rotate, its torque is transmitted to the rolling elements (3) from a large number of consecutive contacts, and the torque is transmitted by the screw pairs of the rolling elements (3), (3) and the screw groove (21). The linear movement force of the female screw body (2) is converted, and the female screw body (2) is linearly driven.

However, in this type, from the shaft body (1) to the female screw body
A large force cannot be transmitted to (2). That is, there is a problem that the female screw body (2) cannot be applied with a large straightening force.

This is for the following reason. In other words, in this type, when the slip occurs between the shaft body (1) and the steel balls (30), (30), it becomes impossible to convert the rotational force rectilinear force. It is determined by the frictional resistance between the body (1) and the steel balls (30), (30), and this frictional resistance is the thread groove (21),
It is determined by the pressure contact force applied to the steel balls (30), (30) from the wall surface of (21) and the friction coefficient of this portion, and even when a large movement resistance is applied to the female screw body (2), the pressure contact force is This is because it does not exceed the preset pressure contact force. That is, the frictional resistance based on the preset pressure contact force only acts as the upper limit value of the slip prevention force.

Therefore, when the thrust applied to the female screw body (2) by the shaft body (1) is set to a large value, the frictional force acts between the shaft body (1) and the steel balls (30), (30). However, slippage will occur despite the presence of this, and as a result, from the shaft body (1) to the female screw body.
A large force cannot be transmitted to (2).

[Technical Problem] In the present invention, in the rotation-linear motion conversion mechanism, the entire structure is simplified and can be manufactured at low cost, and the linear movement force of the female screw body (2) can be increased. The technical problem is to enable transmission with a configuration in which no thread groove is formed on the surface of the shaft and to increase the frictional resistance between the shaft (1) and the rolling elements (3), (3). To do.

<< Regarding the Invention of the First Claim >> [Technical Means] The technical means of the present invention taken to solve the above-mentioned technical problem is "a shaft body having a smooth surface without screw grooves.
A female screw body (2) equipped with a screw shaft (21) is externally fitted to (1), and a large number of rolling elements (3) and (3) are housed in the thread groove (21). The shaft body (1) and the female screw body (2) are paired with each other via (3) and (3), and the rolling body (2) that has escaped from the end of the screw groove (21) is inserted into the female screw body (2). Form a return passage (4) that guides 3) and (3) to the starting end of the screw groove (21), and make the cross section of the screw groove (21) into a chevron or arc shape, and in the cross section of the screw groove (21). Rolling element
The inclination angle of the tangent line at the contact point with (3) with respect to the axis of the shaft body (1) is set to 40 degrees or less. "

[Operation] The above technical means operates as follows.

When the shaft (1) is driven to rotate, like the previously proposed one,
The rolling elements (3), (3) that are in contact with the shaft body (1) roll while pressing the wall of the thread groove (21) of the female screw body (2) while rolling. (2) and the pair of screws through the rolling elements (3) and (3). At this time, movement resistance in the opposite direction to the advancing direction is generated in the female screw body (2), and the resistance force in the axial direction acts so as to move the rolling elements (3), (3) in the same direction. However, the angle of the tangent line between the cross section of the thread groove (21) and the rolling element (3) is set so as to have a small inclination angle with respect to the axis lines of the female screw body and the shaft body. ), (3) by the axial movement force, these rolling elements slightly roll in the direction of entering into the wedge-shaped space formed by one slope of the thread groove and the surface of the shaft (1). As a result, the pressing force acting on the rolling elements (3), (3) becomes larger than that in the initial state. Thus, the female screw body (2)
When the movement resistance force acts on, the pressure contact force of the rolling elements (3), (3) increases as the resistance force increases, and the friction resistance increases accordingly. A so-called self-locking action will occur. Then, when the movement resistance of the female screw body (2) becomes larger than the limit value of the frictional resistance, slippage occurs between the shaft body (1) and the rolling elements (3), (3). .

[Effects] The present invention having the above-described configuration has the following unique effects.

As the movement resistance acting on the female screw body (2) increases, the frictional force between the shaft body (1) and the steel balls (30), (30) increases, and a so-called self-locking function is exerted. That is, since a frictional resistance equal to or greater than the frictional resistance applied to the portion in advance can be generated, the linear movement force of the female screw body (2) can be set large.

Since it is not necessary to configure the wall of the screw groove (21) to have an elastic restoring force, the rigidity of the female screw body (2) can be improved, and the durability of the linear moving body can be improved accordingly.

<< Regarding the Invention of the Second Claim >> The invention of the second claim achieves the object of the invention of the first claim by specifying the shape of the thread groove (21) of the female screw body (2) and the female screw. It seeks to improve the range of movement of the body (2).

The configuration specified for this purpose is that "the thread groove (21) has a mountain-shaped cross section and the apex angle is set to 140 to 160 degrees".

In the case of using the screw groove (21) with the above configuration, the rolling element (3)
There are two contact points between the inner peripheral surface of the screw groove (21) and the inner peripheral surface of the screw groove (21), and the pressure contact force acts on these contact portions. Therefore, when movement resistance occurs in the female screw body (2), the rolling element (3) slightly moves so as to bite into the wedge-shaped space (the space formed between the shaft surface and the inner circumferential surface of the thread groove). When moved, the balance of the pressure contact forces acting on the rolling elements (3) at the two contact points changes. That is,
The contact pressure on the bite side is large, and the contact force on the contact on the opposite side is small compared to this.

As described above, when the female screw body (2) has a movement resistance, the pressure contact forces from the two contact points always act on the rolling element (3) on the side of the screw groove (21). Even if a large movement resistance occurs in the body (2), the female screw body (2) and rolling element
The position relative to (3) does not change significantly, and
(2) will be accurately paired with the shaft (1) through the rolling element (3).

Therefore, the accuracy of movement of the one member in the axial direction due to the relative rotation between the shaft body (1) and the female screw body (2) is improved.

<Regarding the invention of claim 3> The invention of claim 3 is to achieve the same object as the invention of claim 1 and to further improve the so-called self-locking function. The configuration specified in 1. is that "the cross-sectional shape of the screw groove (21) is an arc, and the curvature of this arc is set sufficiently smaller than the curvature of the cross section of the rolling pair (3)".

With the screw groove (21) of this configuration, the tangent line at the contact point between the rolling element and the screw groove (21) in the initial state is the shaft body.
When the female screw body (2) is parallel to (1) and movement resistance occurs,
When the rolling element (3) slightly moves between the rolling element (3) and the female threaded body (2), the contact moves with this rolling, and the tangent angle gradually increases. Therefore, the rolling element (3) with respect to the screw groove (21) is larger than that in which the tangent angle is set in advance.
Makes it easy to roll slightly in the axial direction, and the self-locking function described above improves accordingly.

[Embodiment] Hereinafter, the first to third embodiments of the present invention will be described with reference to Figs.
Description will be made with reference to FIG.

FIG. 1 shows a linear drive device constructed by using the rotation-linear conversion device of the embodiments of the first and second aspects of the invention.

As shown in FIG. 1, the moving body (D) is fitted and fixed on the female screw body (2) of the rotation-linear conversion device of the present invention, and is arranged in parallel with the shaft body (1) of the ball screw. The guide shaft (G) provided also slidably penetrates through the moving body (D), and the shaft body (1)
The guide shaft (G) is supported at both ends, and the output shaft of the motor (M) as a drive source is connected to the shaft body (1).

In the above-mentioned rotation-linear conversion device, as shown in FIGS. 2 and 3, the surface of the shaft body (1) is made smooth and the thread groove (21) is formed on the shaft body (1). The inserted female screw body (2) is externally attached, and a retainer is installed between the female screw body (2) and the shaft body (1).
With the retainer (9) interposed, the rolling elements (3), (3) and the corresponding steel balls (3
It is designed to hold 0) and (30) in a rollable state.

As shown in FIGS. 2 and 6, the female screw body (2) described above is formed into a cylindrical body having a flange at one end, and has a thread groove (21) at a predetermined pitch on its inner peripheral surface. ) Is engraved, and the cross section of this thread groove (21) has a thread angle of 120
It is set to be in the range of 160 to 160 degrees. The guide groove (90) formed on the retainer (9), which will be described later,
Opening (90), (9
0) has been formed.

The retainer (9) is, as shown in FIGS. 2 and 4,
It is formed in a cylindrical shape and has a pair of guide grooves (90), (90) of the same shape that penetrates from the outer peripheral surface to the inner peripheral surface and is excavated in a spiral shape for 1.5 rounds. The arrangement posture of the whole lecture is set to be the same, and the positions of the starting end and the ending of the guide groove are positioned in the directions opposite to each other in the cross section of the retainer (9), and as shown in FIG. The end face of the terminal portion is inclined so that the inclination direction is tangential to the axis of the screw groove (21). The guide groove
(90) and (90) are set to the same pitch as the above-mentioned thread groove (21), and as shown in FIG. 6, project on the inner peripheral side end of the retainer (9) on the side wall of the thread groove (21). Articles (90) and (90) are projected to face each other. The retainer is attached to the inner peripheral surface of the female screw body (2).

Also, a female screw body that coincides with the start end and the end of the guide groove.
Make the openings (90) and (90) of (2) open in the tangential direction to the axis of the thread groove (21) in the same way as the both end faces of the guide groove (90), and make the female screw body (2) As shown in FIGS. 2 and 3, a return cover (8) is attached and fixed to the outer peripheral surface of the cover so as to cover the opening (90), (90).
On the inner surface of (8), as shown in Fig. 5, guide grooves (80), (8
0) is formed, and both ends of this guide groove are connected to each guide groove (90),
The beginning and end of (90) are aligned.

In this case, the guide groove (80) and the opening (99) constitute the return passage (4) described above, and the spiral groove formed by the guide groove (90) and the screw groove (21). The space of is continuous in a loop through the openings (90), (90) of the female screw (2) and the guide groove (80), and a large number of spheres (30), (30) in this loop-shaped space. Are accommodated, and these assemblies become linear moving bodies. When this linear moving body is fitted onto the shaft body (1), one of the spheres (30), (30) exposed from between the ridges (91), (91) of the guide grooves (90), (90) is exposed. The part is pressed against the surface of the shaft body (1). Therefore, when the shaft (1) is driven to rotate,
Steel ball (30, (30) is the thread groove (21) of the shaft body (1) and the female screw body (2).
It is circulated through the space formed by the guide groove (90) and the screw groove (21) and the opening (99) and the guide groove (80) while being pinched between the female screw body (2). ) Threads (21)
These spheres roll when they are located between the shaft and the shaft (1). Then, during this rolling, the rotational force of the shaft body (1) is converted into the traveling force of the linear moving body by the above-mentioned action, and at the same time, the so-called self-locking function described above is exhibited.

In the above example, the spherical bodies (30), (30) are guide grooves.
It is housed in (90), (90) and is maintained in a state in which it is prevented from falling off from the retainer (9) by the ridges (90), (90). Therefore, as described above, a large number of steel balls (30), (30) movably accommodated in the assembly of the female screw body (2), the retainer (9) and the return cover (8) are included in the assembly. Never fall out of. Further, when the linear drive device is assembled and disassembled, the linear moving body can be handled as a unit, which improves productivity of the linear drive device and simplifies disassembly and repair.

In the above embodiment, the thread groove (21) of the female screw body (2) is
The thread angle is set in the range of 140 degrees to 160 degrees, but more preferably, the thread angle is 150 degrees to 16 degrees.
Set it to 0 degrees. In principle, the larger the vertical angle, the larger the maximum linear movement force, but the screw groove (21)
Becomes shallower and problems such as processing accuracy occur.

Next, the embodiment shown in FIG. 7 is an embodiment of the invention of the above-mentioned third claim, in which the cross section of the screw groove (21) is formed into an arc, and this radius of curvature is the radius of the sphere. It is set about 2.5 times.

Also in the case of this embodiment, the maximum linear moving force becomes larger as the radius of curvature of the screw groove (21) becomes layered, as in the case of the first embodiment, but the screw groove (21) becomes larger as the curvature deformation half-open becomes larger.
The depth becomes extremely shallow, which causes problems such as processing accuracy. Practically, the radius of curvature of the thread groove cross section is preferably about 1.5 to 3 times the radius of curvature of the steel ball.

The following modifications are possible in each of the above embodiments.

． Deformation in which the cross-sectional shape of the screw groove (21) is an arc shape consisting of a quadratic curve other than an arc, and in this case, a rolling element
Deformation with two points of contact with (3).

． Deformation in which the sphere (30) is a rolling element such as a cylindrical body.

． Change of other parts to publicly known configuration or main configuration.

[Brief description of drawings]

FIG. 1 is an explanatory view of a linear drive device constructed by using the rotation-straight translation device of the embodiment of the present invention, and FIGS. 2 to 6 are first views.
FIG. 7 is an explanatory view of a rotation-straightening conversion device according to an embodiment of the present invention, and FIG. 7 is an explanatory view of essential parts of an embodiment of the invention according to the first and third claims, FIG. FIG. 9 is an explanatory view of a conventional rotation-to-straight conversion device. In the figure, (1) ... shaft body (2) ... female screw body (3) ... rolling element (4) ... return passage (21) …… Screw groove

Claims (3)

[Claims] 1. A female screw body (2) having a thread groove (21) is externally fitted to a shaft body (1) having a smooth surface having no thread groove, and a large number of the thread bodies are formed in the thread groove (21). Housing the rolling elements (3), (3) of the shaft body (1) and the female screw body through the rolling elements (3), (3).
(2) and the screw pair, and screw groove (21) in the female screw body (2).
Form a return passage (4) that guides the rolling elements (3), (3) that have escaped from the end of the to the starting end of the screw groove (21), and make the cross section of the screw groove (21) into a chevron or arc shape. A rotation-linear motion conversion device in which an inclination angle of a tangent line at a point of contact with the rolling element (3) in the cross section of the thread groove (21) with respect to the axis of the shaft (1) is set to 40 degrees or less. 2. The rotation-linear motion conversion device according to claim 1, wherein the thread groove (21) has a mountain-shaped cross section and the apex angle is set to 140 to 160 degrees. 3. The rotation-straightening according to claim 1, wherein the cross-sectional shape of the thread groove (21) is an arc, and the curvature of this arc is set sufficiently smaller than the curvature of the cross section of the rolling element (3). Motion converter.