JPH0781563B2 - Linear actuator - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear actuator using a pneumatic cylinder, and in particular, a piston and a movable member such as a table are connected through a slit-shaped opening formed in the cylinder. The present invention relates to a linear actuator of a type.

[Prior Art] A linear actuator that uses the reciprocating motion of a piston with compressed air has advantages such as a higher feed speed and less noise generation. Particularly, a linear actuator is better than a slit-shaped opening formed in a cylinder. A linear actuator of a type that uses a so-called rodless cylinder to drive a movable member such as a table, which has a piston that moves in the cylinder with its head protruding, is generally compared to one that uses a pneumatic cylinder. It can be installed in a small space and is widely used in various machinery.

Conventionally, as a linear actuator using this type of rodless cylinder, as shown in FIG. 19, an air cylinder body a, a piston member b reciprocating in the air cylinder body a by compressed air, and the air cylinder A pair of linear guide means c arranged on both end surfaces of the outer wall of the cylinder body a in parallel with the movement direction of the piston member b, a table d moving along the linear guide means c, and the table d.
And a connecting means e for interlocking the piston member b are proposed (Japanese Patent Laid-Open No. 61-290214).

[Problems to be Solved by the Invention] By the way, when a table moving mechanism is configured by a linear guide means (bearing) of a type utilizing rolling motion of a rolling element, for example, a cross roller guide or a linear sliding bearing, In order to obtain highly accurate table movement and high rigidity against external force, it is common to apply a preload to the rolling elements. There are various methods for applying this preload depending on the configuration and shape of the linear guide means, but in the case of a linear sliding bearing or a cross roller guide of the type that mainly rolls on the side surface of the way, it is usually the 19th. As shown in the figure, a roller guide mounted on the table d side is provided with a pressure bolt f penetrating the sleeve portion that hangs from the end on the table d side (a slide base in the case of a linear sliding bearing).
This pressing bolt f applies a preload to the rolling element g by pressing it toward a roller guide (a raceway base in a linear sliding bearing) attached to the fixed portion a side of the bed or the like.

However, when this preloading method is applied to the above-described conventional linear actuator, the following problems occur. That is, the linear guide means c is the air cylinder body a.
Since the linear guide means c is pressed by the pressing bolt f, the pressing force also acts on the slit-shaped opening formed in the air cylinder body a, and the linear guide means c is placed on the table d position. A compressive force acts on the corresponding opening, and the air cylinder body a
The expansion force due to the compressed air inside acts on the slit-shaped opening, and as a result, the compression force and the expansion force are repeatedly applied to the slit-shaped opening by the movement of the table d. Therefore, there is a problem that metal fatigue easily occurs in the air cylinder body a and durability performance is significantly deteriorated.

As a solution to such a problem, as shown in FIG. 20, it is proposed to provide a base member h for disposing the linear guide means c outside the air cylinder body a. According to this linear actuator, the linear guide means c is a member separate from the air cylinder body a and is a base member h.
On the other hand, since the side surface of the air cylinder body a is not in contact with the base member h, the pressing force when the preload is applied to the linear guide means c by the pressing bolt f acts on the air cylinder body a. Therefore, the problem of deterioration of durability as described above does not occur.

However, the linear actuator in the second proposal has new problems such as deterioration in productivity and increase in cost due to increase in the number of parts because of the necessity of newly providing the base member h.

The present invention has been made in view of the above problems, and an object thereof is to prevent the rodless cylinder from being adversely affected by application of preload to the linear guide means.
Moreover, it is to provide a linear actuator having a small number of parts and good productivity.

[Means for Solving the Problems] In order to achieve the above object, the linear actuator according to claim 1 and claim 2 is an air cylinder body having slits formed along the longitudinal direction, and an air cylinder from the slits. A piston member having a head portion protruding outside the main body and reciprocating in the air cylinder main body by compressed air; and a movable member engaged with the head portion of the piston member and reciprocating in conjunction with the piston member. A linear actuator having a pair of bearings disposed on both shoulders of the air cylinder body and linearly guiding the movable member, wherein the bearings are formed in a substantially rectangular cross section, and one side surface faces downward. The ball rolling groove which inclines upward and the ball rolling groove which inclines upward are provided on the other side surface along the longitudinal direction, respectively. And a pair of sleeves that hang from both ends of the horizontal part, and one of the sleeves has a load ball that inclines upward relative to the downward ball rolling surface of the track. A load area having a groove is formed in the other sleeve part, and a load area having a load ball groove that inclines downward facing the upward ball rolling surface of the raceway is formed, and both ends of this load area communicate with each other. A no-load region that is connected to form an endless track is formed in each sleeve, and a slide base that moves along the above-mentioned track base, and a load ball groove and a track of the slide base that circulates in the above endless track It consists of a number of balls that apply a load between the ball rolling groove of the base,
When the movable member is fixed to the slide base using the connecting bolt, the sleeve portion having the upward load ball groove is drawn to the movable member side more than the sleeve portion having the downward load ball groove. Is characterized by applying a preload to the ball.

Further, in the linear actuator according to a third aspect of the present invention, the bearings arranged on both shoulders of the air cylinder body have ball rolling grooves inclined on the left and right side surfaces upward or downward, respectively along the longitudinal direction. A raceway provided on both shoulders of the air cylinder body, a load area having a load ball groove facing the ball rolling groove, and a no-load area connecting both ends of the load area to each other. A slide table equipped with an endless track, which moves along the above-mentioned raceway, and a large number of which circulate in the above-mentioned non-raceway and apply a load between the load ball groove of the slide table and the ball rolling groove of the raceway. A preload is applied to the ball by making the diameter of the ball larger than the gap between the loaded ball groove and the ball rolling groove.

In such technical means, if the air cylinder main body is provided with a cylinder in which a piston reciprocates, and has a mounting surface for disposing the track of the linear guide means on both shoulders, The shape and configuration of the structure may be changed as appropriate.

The piston member reciprocates in the cylinder by air pressure acting on both ends of the piston member, and a head projecting to the outside of the air cylinder body through a slit formed in the air cylinder body is engageable with the movable member. As long as it is a material, the configuration and shape of the material may be appropriately changed.

Further, the raceway according to claim 1 and claim 2 has a ball rolling groove inclined upward and a ball rolling groove inclined downward, and the sliding base and the movable member are fastened with a coupling bolt. If the moment load generated when
The shape and the inclination angle of the ball rolling groove may be appropriately changed in design.

Further, if the slide table has a load ball groove facing the ball rolling groove of the track table and is provided with an endless track through which the balls circulate, the structure and the like of the slide table may be changed as appropriate. As a method of forming a no-load area that constitutes a ball endless track, a no-load transfer track is formed by forming a no-load rolling hole in the slide base or by a ball cage that is externally attached to the slide base. It does not matter if you select and design things appropriately.

Further, as a method of applying a preload to the balls of the bearing, when fixing the sliding base and the movable member with a coupling bolt, the sleeve portion of the sliding base having an upward load ball groove formed is directed downward. If the load ball groove is drawn to the movable member side more than the other sleeve part formed, thereby generating a moment load between the slide base and the raceway, the top surface of the slide base should be horizontal. A method of forming it slightly inclined or a method of interposing a wedge-shaped member between the upper surface of the slide base and the lower surface of the movable member may be selected as appropriate, but there is no need to provide a special structure or member. From the viewpoint of flexibly responding to different preload values depending on the intended use of the movable member, a shim having a thickness corresponding to the preload value is provided between one end of the sliding base in the width direction and the movable member. It is preferable to interpose and preload the ball.

Further, as the ball rolling groove of the raceway and the load ball groove of the sliding table according to claim 3, the inclination angle is determined so that the sliding table can load in four directions, and the large diameter If the ball is elastically deformed when it is fed into the load range of the slide table, and its restoration is impeded, and if preload is applied to the ball, change the inclination angle, groove shape, etc. of the design as appropriate. It doesn't matter. Further, as the ball diameter at this time, the amount of preload may be appropriately selected depending on the precision and rigidity required for the movement of the movable member.

[Operation] The piston receives the pressure of compressed air and reciprocates in the air cylinder body. In addition, the movable member is installed on a slide table that moves along the track provided in the main body of the air cylinder and engages with the piston head, so that the movable member moves on the track according to the reciprocating motion of the piston. Move back and forth. In the invention according to claim 1 and claim 2, since the load ball groove is formed in the sliding base so that a moment load can be applied, a slight moment load is applied between the sliding base and the rail. Therefore, it is possible to apply a preload to the balls rolling in the load region simply by fastening the slide base to the movable member so that the acting force due to the application of the preload does not act in the direction of narrowing the slit of the air cylinder body.

Further, in the invention according to claim 3, since the sliding base can load loads in four directions perpendicular to the longitudinal direction of the raceway base, it has a large diameter larger than the gap between the ball rolling groove and the loaded ball groove. A preload can be applied to the ball by feeding the large diameter ball into the load range of the slide table, and it is not necessary to apply an external force for applying the preload to the bearing.

[Examples] Hereinafter, the linear actuator of the present invention will be described in detail with reference to the accompanying drawings.

First Embodiment FIGS. 1 to 14 show a linear actuator according to the inventions of claims 1 and 2, and an air cylinder body 1 arranged in a fixed portion such as a bed, and an air cylinder. A piston member 2 that reciprocates in the air cylinder body 1 by compressed air sent into the body 1, a pair of raceways 3 arranged on both shoulders of the air cylinder body 1, and slides on the raceway 3. A pair of bearings including a sliding base 4 and a table 5 installed between the sliding bases.

First, the air cylinder body 1 is formed by extruding aluminum and has a substantially rectangular cross-section. The air cylinder body 1 has an air cylinder 12 provided with a slit 11 along the axial direction at the substantially center thereof and both side surfaces. A mounting surface 13 for mounting the track way 3 is formed on the upper shoulder. A through hole 14 for disposing a nut 32 with which the fixing bolt 31 of the track 3 is engaged is formed below the mounting surface 13.
On the other hand, a hollow portion 15 is formed around the air cylinder 12 in order to reduce the weight of the main body. Reference numeral 16 is a magnet attached to the table 5.
It is a detector for detecting the position of 51.

On the other hand, the piston member 2 has piston packings 21 at the front and rear ends and reciprocates in the air cylinder 12, and the inside of the air cylinder 12 via a slit 11 formed in the air cylinder 12. A piston yoke 24 that is disposed over the outside of the air cylinder body 1 and that engages with the central portion of the piston axle 22 in the longitudinal direction by a fixing bolt 23 to transmit the output acting on the piston axle 22 to the outside. A piston mount 25 that connects the piston yoke 24 and the table 5 is formed.

Next, the relationship between the operation of the piston member 2 and the seal mechanism that prevents air leakage from the slit 11 provided in the air cylinder 12 will be described. The slit 11 of the air cylinder 12 is provided with an inner seal band 26 for sealing air leakage on the inside thereof and an outer seal band 27 for preventing dust from entering from the outside on the outside thereof. In the piston member, the bands 26 and 27 are located in the concave groove formed in the piston yoke 24, as shown in FIGS. Then, when compressed air is supplied into the air cylinder 12 and the piston axle 22 starts to move, the inner seal band 26 and the outer seal band 27 are pushed by the piston yoke 24 and are separated by the slit 11.
After being peeled off and passing through the piston yoke 24, it again sticks to the slit 11, and the inside of the slit 11 is sealed by air pressure. Reference numeral 28 is an outer seal band
It is a scraper for removing dust adhering to 27.

Next, the bearing that linearly guides the table will be described.

As shown in FIGS. 3 to 14, the bearing of the present embodiment has a cross section in which a horizontal portion 4a and sleeve portions 4b and 4c hanging from both ends thereof are formed and a concave portion which is opened obliquely downward is formed. A substantially inverted L-shaped slide base 4, a pair of lids 6 attached to the front and rear end faces of the slide base 4 in the longitudinal direction, and the sleeve portions 4b, 4c.
Between the slide table 4 and the ball holding plate 7 attached to the lower end of the slide table, the track table 3 whose cross-sectional shape of at least the upper part is substantially the same as the concave shape of the slide table 4, and the slide table 4 and the track table 3. It is composed of a large number of balls 8 for applying a load.

The slide table 4 is made of a hardenable steel material or the like having a rigidity, and as shown in FIGS. 6 and 7, the concave portion thereof has a shape that widens obliquely downward. The sleeve portion 4b forming the recess has a load region having a load ball groove 41 having an arcuate cross section which is inclined upward on the inner surface side thereof.
42 is formed over the entire length in the longitudinal direction, while the other sleeve portion 4c has a load region 44 having a load ball groove 43 with an arcuate section inwardly slanting downward on its inner surface side in the same manner as the entire length in the longitudinal direction. It is formed over. Also, in each of the sleeve portions 4b, 4c,
An unloaded ball hole 45 is formed at a position adjacent to the load areas 42, 44 along the lengthwise direction of the sleeve portions 4b, 4c. Reference numeral 46 is a lid attachment hole into which a hexagon socket head bolt 61 as shown in FIG. 5 is screwed when attaching the lid 6 to the front and rear end surfaces of the slide base 4 in the longitudinal direction. Reference numeral 47 is a mounting hole into which the coupling bolt 51 is screwed when the table 5 is mounted on the upper surface of the slide base 4.

Further, the lid body 6 is made of a rigid hard synthetic resin, and as shown in FIGS. 10 and 11, the lid body 6 is
Guide grooves of substantially arc shape corresponding to the load areas 42 and 44 and the unloaded ball holes 45 formed on the sleeves 4b and 4c of the slide base 4 when the slide base 4 is attached to the front and rear end surfaces of the slide base 4. 61 are formed,
By inserting a semicircular guide piece 62 into the guide groove 61, a ball turning circuit 63 for connecting and connecting the load regions 42, 44 and the unloaded ball hole 45 is configured, and the load regions 42, 44 or Each ball 8 rolling in the unloaded ball hole 45 is turned by the ball turning circuit 63 and guided to the unloaded ball hole 45 or the unloaded balls 42, 44. Further, a taper-shaped projection 64 is provided at one end of the guide groove 61 located on the load regions 42, 44 side when mounted on the slide base 4 so as to roll the load regions 42, 44. The ball 8 that has run is smoothly picked up in the ball turning circuit 63, and the ball 8 is smoothly sent from the ball turning circuit 63 to the load regions 42 and 44. Further, the lid 6 is provided with the hexagon socket head cap bolt.
A through hole 65 through which 61 passes is provided, and a convex portion 66 that fits into a concave groove formed on the slide base 4 side is provided around the through hole 65 on the inner surface of the lid body 6. Slide each lid 6 to the slide base 4
The respective lid bodies 6 can be easily positioned when they are attached to the front and rear end surfaces.

Furthermore, the ball holding plates 7a and 7b are shown in FIG.
As shown in FIG. 4, a steel plate or the like having rigidity is formed by press forming, and a through hole 72 through which a mounting screw 71 screwed into the lower surface of each sleeve portion 4b, 4c of the slide base 4 is formed is formed. .
When each ball holding plate 7a, 7b is attached to the sleeve portion of the slide base 4, one side end 73 along the lengthwise direction projects into a recess formed on the lower surface side of the slide base 4, The opening width of the load regions 42, 44 in which the ball 8 rolls is formed smaller than the diameter of the ball 8 to prevent the ball 8 from falling off when the slide base 4 is removed from the track base 3. .

On the other hand, as shown in FIGS. 8 and 9, the trackway 3 has a rectangular cross section in which one side surface is cut out in a trapezoidal shape, and the trapezoidal cutout 33 slides on the downward inclined surface. Sleeve part
A ball rolling groove 34 facing the loaded ball groove 41 formed on the inner surface side of 4b is formed, while a shoulder above the side surface on the opposite side is formed on the inner surface side of the slide base sleeve portion 4c. Load ball groove
A ball rolling groove 35 facing the surface 43 is formed. Further, a mounting hole 36, through which a fixing bolt 31 screwed to the air cylinder body 1 penetrates, is provided at the center of the way 3 perpendicularly to the upper surface of the way 3 and at appropriate intervals in the longitudinal direction of the way 3. Have been drilled.

In assembling the linear actuator of the present embodiment configured as described above, first, after mounting the raceway base 3 on the mounting reference surface 13 of the air cylinder body 1, the sleeve 4b is placed outside and the sliding base 4 is mounted. The table 5 is assembled to the raceway 3, and the table 5 is connected to the upper surface of the sliding table 4 with the connecting bolts 51, while the piston mount 25 is engaged with the lower surface side of the central portion of the table 5, and finally the air cylinder body 1 is attached to the bracket 17. A supply pipe connected to a pressure control means (not shown) with a supply valve and a discharge valve (not shown) for compressed air, which are fixed to each other by bolts via a fixing portion and are provided at both ends of the air cylinder body 1 respectively. And an exhaust pipe (not shown) are connected.

At this time, in the linear actuator of the present embodiment, the load ball grooves 41, 43 formed on the slide base 4 and the ball rolling grooves 34, 35 formed on the raceway 3 are arranged from the sleeve portion 4b side to the sleeve portion 4b. It is arranged so that a moment load acting counterclockwise on the 4c side can be applied. Therefore, when the sliding table 4 is attached to the table 5, if the connecting bolt 51 is fastened by inserting the shim 9 between the upper surface of the sliding table 4 above the sleeve portion 4c and the lower surface of the table 5, the upward load ball The one sleeve portion 4b having the groove 41 formed therein is attracted to the table 5 side more than the other sleeve portion 4c having the downward load ball groove 43 formed therein, and a moment load corresponding to the thickness of the shim 9 is applied to the slide base. A preload is applied to the ball 8 which is generated between the rail 4 and the track 3 and which is loaded between them.

Therefore, when a preload is applied to the ball 8, only a moment load acts on the raceway 3, and an acting force acts on the air cylinder body 1 in which the raceway 3 is arranged in a direction to narrow the slit 11. Moreover, the slits 11 formed in the air cylinder body 1 are not deformed due to the preload applied to the balls 8.

◎ Second Embodiment FIGS. 15 to 18 show an embodiment of the linear actuator in the invention according to claim 3, and Table 5
The linear actuator is substantially the same as the linear actuator according to the first embodiment except that the bearing that linearly guides is changed.

In this embodiment, as shown in FIG. 16, the bearing slide base 4 includes a horizontal portion 4a and left and right sleeve portions 4 which hang down from both ends thereof.
It has b and 4c and is formed in a substantially inverted C shape in cross section, and has a concave portion on the lower surface, and the upper surface along the longitudinal direction on the lower surface side of the horizontal portion 4a and the inner surface side of the left and right sleeve portions 4b and 4c respectively. The load areas of the endless track and the lower endless track are formed, and a load ball groove on which the balls 8 roll is formed in this load area. Also, the left and right sleeves 4
Unloaded ball holes 45 corresponding to the load areas of the upper and lower endless tracks are formed in b and 4c.

In addition, the raceway 3 has a cross-sectional shape in which both side surfaces of the rectangle are cut out in a trapezoidal shape and both left and right shoulders are cut out. It becomes the lower ball rolling groove 34 corresponding to the lower endless track provided on the inner surface side, while the upward sloping surface of both shoulder notches has the sliding base horizontal portion 4a.
Is the upper ball rolling groove 35 corresponding to the upper endless track provided on the lower surface side. Further, a mounting hole 36 through which a fixing bolt 31 for fixing the raceway 3 to the air cylinder body 1 penetrates is provided at the center of the raceway 3 perpendicularly to the top surface of the raceway 3 and in the longitudinal direction of the raceway 3. Are provided at appropriate intervals.

Further, at each end of the sliding base 4 in the longitudinal direction, as in the first embodiment, a ball which is connected to the load area formed on the sliding base 4 and the corresponding unloaded ball hole 45 is connected. A ball retainer, to which a lid 6 having a swirl circuit is attached, and on the inner surface side of each sleeve 4b, 4c, a long hole through which a ball 8 projects is formed to form a load area in cooperation with a load ball groove. 7 is incorporated.

The bearing of this embodiment configured as described above is arranged so that the contact angles of the balls 8 contacting the slide base 4 and the drive base 3 can be applied with loads in four directions orthogonal to the longitudinal direction of the track base 3. Therefore, when a ball 8 having a diameter larger than the gap between the loaded ball groove and the ball rolling groove is fed into the load area, the ball 8 is elastically deformed and its restoration is hindered, and the ball 8 is Preload is applied to.

Therefore, in applying the preload to the balls 8, it is not necessary to apply any external force to the slide base 4 or the raceway 3, and the action based on the preload is exerted on the air cylinder body 1 on which the raceway 3 is arranged. There is no such thing.

[Advantages of the Invention] As described above, according to the linear actuator of the present invention, the action of applying a preload to the balls rolling in the load region of the slide base does not affect the air cylinder body. In addition, the durability of the air cylinder body can be maintained even when the bearing for guiding the table is directly arranged on the air cylinder body, and the base for arranging the bearing is provided on the air cylinder body. Since it is not necessary to provide it separately, it is possible to improve productivity and reduce costs.

[Brief description of drawings]

FIG. 1 is a front sectional view showing a first embodiment of a linear actuator according to the present invention, FIG. 2 is a sectional view taken along the line II of FIG. 1, and FIG. 3 is a bearing assembly of a linear actuator according to the first embodiment. FIG. 4 is an enlarged view showing a state, FIGS. 4 and 5 are a plan view and a side view showing a bearing of the linear actuator according to the first embodiment, and FIGS. 6 and 7 are front views showing a sliding base of the bearing. Side views, FIGS. 8 and 9 are perspective views and cross-sectional views showing a bearing rail, and FIGS. 10- (a) and (b) are front views showing a bearing lid and a partial cross-section. A side view and FIG. 11 are shown in FIG. 10- (a).
II-II sectional view, FIG. 12 is a perspective view showing a guide piece fitted to the lid, FIG. 13- (a), (b) and FIG. 14- (a),
(B) is a plan view and a front view showing a ball retainer of a bearing, FIG. 15 is a front sectional view showing a second embodiment of the linear actuator of the present invention, and FIG. 16 is a linear actuator according to the second embodiment. Enlarged view showing the bearing assembly state, FIGS. 17 and 18 are a side view and a plan view showing the bearing of the linear actuator according to the second embodiment, FIG.
19 and 20 are front sectional views showing a conventional linear actuator. [Explanation of symbols] 1: Air cylinder body, 2: Piston member 3: Track, 4: Sliding table 5: Table, 8: Ball 9: Shim

Claims (3)

[Claims] 1. A piston having an air cylinder body having a slit formed along the longitudinal direction and a head portion projecting from the slit to the outside of the air cylinder body, and reciprocating in the air cylinder body by compressed air. A member, a movable member which is engaged with the head of the piston member and reciprocates in conjunction with the piston member, and a pair of bearings which are arranged on both shoulders of the air cylinder body and linearly guide the movable member. In the linear actuator having the above, the bearing is formed in a substantially rectangular cross section, and has a ball rolling groove inclined downward on one side surface and a ball rolling groove inclined upward on the other side surface. Along the lengthwise direction, there are track rails that are placed on both shoulders of the air cylinder body, and a pair of sleeves that hang from both ends of the horizontal section. The load zone has a load ball groove that slopes upwards facing the facing ball rolling surface, and the other side has a load ball groove that slopes downwards facing the upward ball rolling surface of the raceway. A load table having a load zone is formed, and a no-load zone forming an endless track by connecting both ends of the load zone to each other is formed in each sleeve portion, and a slide table that moves along the track table, It is composed of a number of balls that circulate in an endless track and that apply a load between the load ball groove of the slide table and the ball rolling groove of the track table. When fixed to, the sleeve portion having the upward load ball groove formed is drawn to the movable member side more than the sleeve portion having the downward load ball groove formed, thereby preloading the ball. Linear actuator that does. 2. When fixing the movable member to the slide base using a connecting bolt, a shim is interposed between the upper surface of the slide base and the lower surface of the movable member on the side of the sleeve where the downward load ball groove is formed. Disguise,
2. The linear actuator according to claim 1, wherein the sleeve portion having the upward load ball groove is attracted to the movable member side more than the sleeve portion having the downward load ball groove. 3. A piston having an air cylinder body having a slit formed along the longitudinal direction and a head portion projecting from the slit to the outside of the air cylinder body, and reciprocating in the air cylinder body by compressed air. A member, a movable member which is engaged with the head of the piston member and reciprocates in conjunction with the piston member, and a pair of bearings which are arranged on both shoulders of the air cylinder body and linearly guide the movable member. In the linear actuator including the above, the bearing has ball rolling grooves that incline upward or downward on both left and right sides along the longitudinal direction, and is arranged on both shoulders of the air cylinder body. It has an endless track consisting of a way, a load area having a load ball groove facing the ball rolling groove and an unloaded area connecting both ends of this load area. It consists of a slide that moves along the way, and a number of balls that circulate in the above-mentioned endless track and apply a load between the load ball groove of the slide and the ball rolling groove of the way. A linear actuator characterized in that a preload is applied to the ball by making a diameter of the ball larger than a gap between the loaded ball groove and the ball rolling groove.