Dust-proof structure for a linear motion actuator

A linear motion actuator of the present invention is provided with a casing including slits extending axially, a carriage being axially movable along guide rails within the casing, the carriage including driven member mounting portions protruded outside through the slits for mounting a driven member, a plurality of seal bands fastened to the driven member mounting portions of the carriage for sealing openings of the slits regardless of the location of the carriage when the seal bands are moved along the slits, and a driving device for driving the carriage to move along the guide rails. The linear motion actuator with a dust-proof function has no need of passing the seal bands through the carriage, so that the carriage have a solid and simple structure of high rigidity without the abnormal shifting motion of the seal bands.

BACKGROUND OF THE INVENTION 
The present invention relates to improvements over the dust-proof structure 
for a linear motion actuator with a carriage which is provided in a 
casing, and is linearly moved in an axial direction. 
In general, a linear motion actuator is provided with a type as shown in 
FIGS. 6 and 7. A pair of parallel linear guides are disposed on an 
elongated base 101. A carriage 105 is fastened to a slider 104, which 
linearly moves along the guide rail 103. The carriage 105 is coupled with 
a ball nut 107 of a ball-and-screw mechanism 106 as a rotation-linear 
converting mechanism. An AC servo motor 108 drives a ball-screw shaft 109 
to rotate. With rotation of the ball-screw shaft, the carriage 105 is 
linearly moved along the guide rail 103 in the axial direction. A 
workpiece W is fastened onto the driven member mounting portion 110 
located on both sides of the carriage 105, by means of screws. The 
accurate linear motion and the accurate positioning of the work can be 
carried out repeatedly. 
The actuator is covered with side covers 111, an upper cover 112, an end 
cover 113, and the like, for the purposes of improving appearance and 
protecting the inner accurate parts, such as the linear guides 102 and the 
ball-and-screw mechanism 106, from incoming dust. 
The driven member mounting portion 110 of the carriage 105 must be exposed 
to, so slits are formed between each side cover and the upper cover 112. 
The slits axially extend over the entire range of the movement of the 
carriage 105. The slits S allows dust to enter the inside of the casing. 
In this respect, the dust-proof measure is imperfect. 
A linear motion actuator of the type in which the slits covering the 
carriage movement range are covered with a movable belt is disclosed in 
Unexamined Japanese Utility Model Publication No. Hei. 4-60642. As shown 
in FIGS. 8 and 9, a carriage 121 is axially slidable within a cylinder 
tube 120 with an axially elongated slit S formed in one side (upper 
surface) thereof. The carriage 121 is coupled with a ball nut 124 
receiving a screw shaft 123 of the ball-and-screw mechanism 122, and is 
linearly moved in the axial direction by an AC servo motor 125. 
A table body 126 is protrudes above the carriage 121, and is exposed over 
the cylinder tube 120 through the slit S. An upper surface of the table 
body 126 serves as a driven member mounting portion 128 with bolt holes 
127 at the four corners. 
A shaft receiving hole 130 through which the screw shaft 123 passes is 
formed in the carriage 121, as shown in FIG. 9. A nut receiving space 131 
for receiving the ball nut 124 is formed in the middle of the shaft 
receiving hole 130. A square groove 131a is formed in the ceiling wall of 
those walls defining the nut receiving space 131. The bottom of the nut 
receiving space 131 is open. A ball nut 124 with a square stopper 132 is 
placed in the nut receiving space 131 in a state that the protrusion 132 
is fit to the groove 131a. 
The carriage 121 having two downward extending slopes is shaped like V in 
cross section. A slider member (not shown) is secured to the bottom edges 
of the slopes of the carriage 121. In this state, the carriage 121 is 
disposed within the cylinder tube 120 shaped like a diamond in cross 
section. 
The table body 126 which protrudes over the carriage 121 has a band 
receiving hole 136 through which the seal band 135 passes. The band 
receiving hole 136 has a gently upward curved band guide face 137, and 
opens downward. The opening of the band receiving hole is longitudinally 
elongated in the lower side of the table body. The seal band 135 made of a 
thin steel band is inserted into the band receiving hole 136 from the 
opening. 
After the carriage 121 is assembled into the cylinder tube 120, the slit S 
of the upper surface of the cylinder tube 120 is covered with the seal 
band 135. A strip like rubber magnet is attached to the edge of the slit 
S. The seal band 135 is magnetically attracted by the magnet rubber, 
thereby improving the sealing performance by the seal band. The ends of 
the seal band 135 are secured to the end cap 140 and the head cap 141. The 
mid portion of the seal band 135 is located on the curved band guide face 
137 of the carriage 121. 
The AC servo motor 125 is turned forwardly or reversely, so that the screw 
shaft 123 is driven. Then, the ball nut 124 is moved forward or backward. 
In turn, the carriage 121 is moved forward or backward while being guided 
by the cylinder tube 120. The workpiece mounted on the driven member 
mounting portion 128 of the table body 126 is axially moved and stopped at 
a desired position. 
At this time, the seal band 135 prevents dust from entering through the 
slit S of the cylinder tube 120. The table body 126 moves forward while 
pushing upward with the curved surface of the band guide face 137. 
The conventional dust proof structure of the type in which the slit S of 
the cylinder tube 120 is sealed with the seal band 135 has a high dust 
proofing capability, but has the following problems. 
(1) Since the seal band 135 is passed within the carriage 121, the carriage 
structure is complicated, and it is impossible to increase the rigidity of 
the carriage 121. 
(2) The band receiving hole 136 extends longitudinally to pass through the 
central portion of the table body 126 of the carriage 121. The bolt holes 
127 cannot be located in the central part of the driven member mounting 
portion 128 which is advantageous in securing a high rigidity. 
Accordingly, the bolt holes 127 must be located at the four corners of the 
driven member mounting portion 128. This results in increasing the size of 
the carriage 121. 
In the case of a large linear motion actuator which transports a heavy 
workpiece, a high rigidity is essential in order to move the work at a 
high speed and to position it accurately. The carriage of the linear 
motion actuator is a member which couples the linear guides with the 
workpiece. Therefore, the carriage is the most important component in 
determining the rigidity of the linear motion actuator. The structure 
which is not capable of increasing the rigidity is not suitable for a 
large actuator. 
SUMMARY OF THE INVENTION 
The present invention has been made in view of the above circumstances and 
has an object to provide a dust-proof structure for a linear motion 
actuator in which seal bands for sealing the slits allowing the carriage 
to axially move are mounted outside the carriage, and the seal bands and 
the carriage are axially movable in a cooperative manner, whereby the 
dust-proof structure is simplified. 
To achieve the above object, there is provided a linear motion actuator 
having a casing, linear guides located within the casing, a carriage 
axially movable with the assistance of the linear guides within the 
casing, a driving device for axially moving the carriage through a 
ball-and-screw mechanism, and slits elongating in the direction of the 
movement of the carriage being formed in one of the sides of the casing, 
the carriage including driven member mounting portions protruding above 
the casing. In the linear motion actuator thus constructed, pulleys are 
disposed on both ends of the casing as axially viewed. Further, one end of 
the seal band is fastened to one end of the carriage, while the other end 
thereof is fastened to the other end of the carriage in such a way that it 
passes the pulleys, is turned back at one end of the casing, reaches the 
other end of the casing, passes the pulleys, and is turned back thereat, 
thereby forming a loop of the movable seal band. The slits are sealed with 
the looped seal band. 
The casing body is formed by an extrusion mold. An axially extending 
through hole or groove is formed in the extrusion mold. The lower part of 
the looped seal band passes through the through hole or groove. 
Grooves may be formed in the end faces of the portions of the casing. The 
grooves receive the side edge of the seal band, respectively. 
A guide plate is mounted on the lower part of the looped seal band, which 
passes through the through hole or groove of the casing body. 
The lower side of the cover covering the upper side of the casing includes 
a pair of L-shaped extensions. Sound absorbing material is placed within a 
space formed by the extensions. 
Thus, in the dust-proof structure for a linear motion actuator, the pulleys 
are provided on both ends of the casing as axially viewed. The seal band 
is looped in a manner that the seal band is fastened at one end to one end 
of the carriage, and the other end is turned back. The looped seal band 
circulates, together with the carriage reciprocatively moving linearly in 
the axial direction, thereby sealing the slits therewith. Accordingly, 
there is no need of passing the seal band through the carriage. The 
carriage may have a solid and simple structure of high rigidity. The size 
reduction of the linear motion actuator is easy. 
By passing the lower part of the looped seal band through the through hole 
or groove of the casing, the high rigidity and the light weight can both 
be realized. The hollowed structure is well utilized. 
Where the grooves receiving the side edges of the seal band are formed in 
the end faces of the portions of the casing, which define each slit, the 
sealing by the seal band is enhanced, and the abnormal shifting motion of 
the seal band can be minimized. Further, the dust-proof and suppression of 
noise leakage characteristics are enchanced. 
With use of the guide plate to the lower part of the looped seal band, a 
stable movement of the seal band is secured even if the seal band is long 
for a large linear motion actuator. 
Where the lower side of the cover covering the upper side of the casing 
includes a pair of L-shaped extensions, and sound absorbing material is 
placed within a space formed by the extensions, the rigidity of the cover 
is increased and the noise proof performance is improved.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A first embodiment of a linear motion actuator according to the present 
invention will be described with reference to FIGS. 1 through 4. 
FIG. 1 is a cross sectional view showing a first embodiment of a linear 
motion actuator of the present invention; 
FIG. 2 is a longitudinal sectional view taken on line II--II in FIG. 1; 
FIG. 3 is a longitudinal sectional view taken on line III--III in FIG. 1; 
and 
FIG. 4 is a front view, partially broken away, showing a linear guide of 
the linear motion actuator. 
In the linear motion actuator of the first embodiment, a pair of linear 
guides 10 are provided within a casing 1 elongated in the axial direction 
of the actuator. A carriage 20 is provided so as to move freely in the 
axial direction along the linear guides 10. 
A driving device 40 is provided which drives the carriage 20 through a 
ball-and-screw mechanism 30 to axially move at a specified speed to a 
specified position. 
A pair of slits S, extending in the moving direction of the carriage 20, 
are formed in the top surface of the casing 1. Each carriage 20 includes a 
driven member mounting portion 24a protruded out of the casing 1 through 
the corresponding slit S. 
The dust-proof structure of the linear motion actuator is described below. 
Pulleys 50 are located at both ends of the casing 1 (as viewed in the axial 
direction), respectively. A seal band 60 has one end fastened to one end 
of the carriage 20. The other end of the seal band 60 is turned up at one 
end of the casing 1 through the pulley 50. The other end of the seal band 
60 is further turned up at the other end of the casing 1 through another 
pulley 50, so that the other end of the seal band 60 is fastened to the 
other end of the carriage 20, whereby forming a movable loop of the seal 
band 60. The slits S are sealed by the movable loop of the seal band 60. 
The construction of the linear motion actuator will be described in more 
detail below. 
The casing 1 is made up of a casing body 2, a couple of side covers 3 and 
3, an upper cover 4, an end cover 5, including a bearing, for closing one 
end of the casing 1, and a motor bracket 6, including a bearing, for 
closing the other end thereof. 
In the first embodiment, the casing body 2, is extruded of aluminum. The 
casing body 2 has an opening of the top thereof. A satisfactory rigidity 
is required for the bottom of the casing body 2; otherwise it is deformed 
by a load, thereby deteriorating the accuracy of the transportation by the 
linear motion actuator. In the first embodiment, the thick part of the 
bottom of the casing body 2 contains a plurality of through holes that are 
axially extended. By providing these through holes, a satisfactory 
rigidity and a reduction of weight are both secured. 
Elongated sunken parts 8, extending over the entire length of the casing 
body 2, are formed in the locations of the base of the casing body 2, 
which are closer to the right and left sides thereof and symmetrical with 
respect to the center of the actuator when viewed in cross section. Guide 
rails 11 of the linear guide 10, respectively, are set in the sunken parts 
8 and fastened thereto by bolts (not shown). Sliders 12 are slidably 
mounted on the guide rails 11, respectively. In the first embodiment, a 
couple of sliders 12 are mounted on each rail 11. 
The structure of the linear guide 10 will briefly be described below. As 
illustrated in an enlarged manner in FIG. 4, each of guide rails 11 is 
substantially square in cross section. Ball rolling grooves 13 which are, 
axially elongated, are formed in the upper parts of both sides of the 
guide rail 11. 
Each of the sliders 12, shaped like an inverted U in cross section, 
consists of a horizontal portion 14 and leg portions 15 downward extended 
from both ends of the horizontal portion 14. Ball bearing grooves 16 are 
formed at the locations of the inner walls of the right and left leg 
portions 15, which respectively confront with the ball rolling grooves 13 
of the guide rails 11. Circulating paths 17, communicating with the ball 
rolling grooves 13 and 16, are formed in the leg portions 15. A plurality 
of balls 18, held by a holder 19, are inserted, in a rollable manner, in 
the rolling paths defined by the ball bearing grooves 13 and 16, and the 
circulating path 17. A plurality of holes 11a for rail mounting are formed 
at proper intervals in each rail 11. Threaded holes 12a for receiving 
bolts are formed at the four corners of the upper surface of each slider 
12. 
The carriage 20 includes a head plate 21 and a vertical portion 22 downward 
extended from the bottom surface of the head plate 21. The width of the 
head plate 21 is slightly shorter than the width of the inside of the 
casing 1, and the length thereof is nearly equal to the total length of 
the two sliders 12 longitudinally arrayed. Both sides of the head plate 21 
are placed on the upper surfaces of the right and left sliders 12 of the 
linear guide 10, and fastened thereto by means of bolts 27 screwed into 
the threaded holes 12a. In this way, the carriage 20 is axially slidably 
supported by the four sliders 12 within the casing 1. 
An elongated sunken part 23 is formed at the central part of the upper 
surface of the head plate 21 of the carriage 20, while extending over the 
entire length of the head plate 21. Two elongated protruded portions 24, 
upward protruded from the head plate 21 of the carriage 20, are located on 
both sides of the sunken part 23. The protruded portions 24 extend over 
the entire length of the head plate 21 of the carriage 20. The upper 
surfaces of the protruded portions 24 are slightly higher than the upper 
cover 4, and serve as the driven member mounting portions 24a. Stepped 
portions 24b, stepped down from the driven member mounting portions 24a, 
are formed at both ends of each of the protruded portions 24 when viewed 
in the longitudinal direction. 
The protruded portions 24 are located just above the right and left guide 
rails 11 of the linear guide 10. That is, the driven member mounting 
portions 24a of the carriage 20 are located on the axial lines of the 
linear guide 10 where are the best locations for securing a rigidity. With 
this layout of the protruded portions 24, the reduced thickness of the 
head plate 21 of the carriage 20 can be used. 
The ball-and-screw mechanism 30 includes a ball-screw shaft 31 and a 
ball-screw nut 32. The ball-screw shaft 31, of which the outer surface is 
helically threaded, is supported at one end by the end cover 5, and at the 
other end by the motor bracket 6. More exactly, one end of the ball-screw 
shaft 31 is received by the bearing of the end cover 5, while the other 
end thereof is received by the bearing of the motor bracket 6. The 
ball-screw shaft 31 is located at the central part of the casing 1 when 
viewed in the width direction of the casing, while extending in parallel 
with the guide rails 11 of the linear guide 10. The end portion of the 
ball-screw shaft 31, supported by the motor bracket 6, protrudes out of 
the motor bracket 6 and coupled with the output shaft of driving device 
40, such as a drive motor. 
The ball-screw nut 32 has a helical thread on the inner surface thereof, 
which confront with the helical thread of the ball-screw shaft 31. The 
ball-screw nut 32 engage the ball-screw shaft 31 to allow a plurality of 
balls to roll between the confronting helical threads of them. The 
ball-screw nut 32 is of the end-cap circulating type in which ball 
circulating members (end caps) 35 are removably coupled with both ends of 
the nut. A ball return path as an axially extending through-hole is formed 
in the thick part of the nut body. A curved path, formed in the end face 
of the end cap 35 where is in contact with the nut body, communicates with 
the confronting helical threads and the return path. 
With rotation of the ball-screw shaft 31 relative to the ball-screw nut 32, 
steel balls forwardly roll within the helical space defined by the 
confronting helical threads of the ball-screw shaft 31 and the ball-screw 
nut 32. The balls emanate the helical space, travel through the curved 
path of the end cap 35 and the return path of the nut body and returns to 
the original position. 
The ball-screw nut 32 may be of the tube circulating type or the piece 
type, in place of the end-cap circulating type. 
In the ball-screw nut 32 of the tube circulating type, a ball circulating 
path shaped like U is assembled into the upper portion of the nut body. 
The balls roll forward within the helical space defined by the confronting 
helical threads, and pulled into the ball circulating tube. The balls 
forwarded through the tube ride over the land of the ball-screw shaft 31, 
and return to the helical space. In this way, the balls circulate through 
the path endlessly. 
In the ball-screw nut 32 of the piece type, a piece with a circulating 
groove is embedded into the thick part of the nut body. The balls are 
forwarded through the circulating groove of the piece, and ride over the 
land of the ball-screw shaft 31, and return to the helical space. 
An AC servo motor as the driving device 40 is firmly mounted on the outer 
surface of the motor bracket 6. The output shaft of the AC servo motor 40 
is coupled, through a coupling 39, with the ball-screw shaft 31 rotatably 
supported by the bearing within the casing 1. 
The ball-screw nut 32, which engages the ball-screw shaft 31 through the 
balls, is embedded into and secured to the vertical portion 22 of the 
carriage 20, whereby the carriage 20 is coupled with the ball-and-screw 
mechanism 30. 
When the ball-and-screw mechanism 30 is operated by the driving device 40, 
the carriage 20 must be moved in the axial direction in connection with 
the ball-screw nut 32. To this end, the slit S is formed between each side 
cover 3 and the upper cover 4. Thus, a couple of slits S are provided 
respectively in association with the couple of protruded portions 24. 
The side covers 3 and the upper cover 4, which define the slits, are both 
extruded of aluminum. The thick end faces, confronting with each other, 
have guide grooves 3a and 4a as a guiding device for the seal band. 
The upper cover 4 includes L-shaped extensions 4b and 4b in the central 
portion thereof. The extensions 4b extend over the entire length of the 
upper cover 4. The end faces of the extensions 4b and 4b confront with 
each other, with a space therebetween being corresponding to the width of 
the ball-screw nut 32. A space defined by the extension 4b and 4b and the 
underside of the upper cover 4 is filled with sound absorbing material 70, 
such as sponge. 
A permanent magnet (not shown), for example, is secured to the underside of 
the carriage 20. An proximity switch, such as a Hall effect element, 
facing the permanent magnet, is mounted on the inner surface of the casing 
body 2. The original position of the carriage 20 in the linear motion 
axial direction is detected by the proximity switch and the permanent 
magnet. The AC servo motor 40 is controlled by the detected original 
position signal, thereby accurately positioning the linearly driven 
carriage 20. 
A contact position detector (not shown), such as a limit switch, which is 
used for preventing an overrun of the carriage 20, may be provided at the 
end of the casing 1. In this case, the lead wire of the limit switch may 
be put in a groove 2A, formed in the outer surface of the casing body 2, 
so as not interfere with other members. 
In the linear motion actuator thus constructed, the casing 1 has a 
substantially closed structure except for the slits S. These slits S are 
closed by the seal band 60. With this construction, the linear motion 
actuator is protected from dust. 
The slit structures of the linear motion actuator will be described below. 
Since the slit structures of the right and left slits S are substantially 
the same, the slit structure of one of these slits will be described. 
The pulleys 50 are provided at the four corners of the casing 1 (FIGS. 2 
and 1). The pulley 50a at the upper corner of the motor bracket 6 is 
provided at the location on the line extended from the slit S. The pulley 
50b at the lower corner of the motor bracket 6 is provided right under the 
pulley 50a. The pulley 50c at the upper corner of the end cover 5 is 
provided at the location on the line extended from the slit S. The pulley 
50d at the lower corner of the end cover 5 is provided right under the 
pulley 50c. 
The seal band 60 which is put on the four pulleys 50 is a flat sail cloth 
band containing polyurethane. One end of the seal band 60 is fastened to 
the stepped portion 24b formed at one end of the carriage 20, by means of 
set screws 61. The other end of the seal band 60 is fastened to the 
stepped portion 24b formed at the other end of the carriage 20, by means 
of set screws 61. Thus, the seal band 60 forms a loop extending from one 
end of the carriage 20 to the other end thereof through a route connecting 
pulleys 50a, 50b, 50c, and 50d. 
The side edges of the seal band 60 are inserted into the guide groove 3a of 
the end face of the side cover 3 and the guide groove 4a of the end face 
of the upper cover 4, respectively. With this structure, the sealing 
effect by the seal band 60 is enhanced, and the seal band 60 is guided 
without being shifted sideways. The lower portion of the loop of the seal 
band 60, which ranges from the pulley 50b at the lower corner of the motor 
bracket 6 to the pulley 50d at the lower corner of the end cover 5, pass 
through a through-hole 7a located right under the guide rail 11, which is 
one of the plurality of through-holes 7 longitudinally passing through the 
casing body 2. A rectangular guide plate 63 is fastened to the location of 
the middle of the loop of the seal band 60, viz., a position right under 
the carriage 20 when the carriage passes the middle of the casing 1 when 
viewed axially. A gap is present between each side of the guide plate 63 
and the corresponding inner wall of the through-hole 7a, whereby the seal 
band 60 is prevented from being shifted sideways. 
After the carriage 20 is assembled to the sliders 12 of the linear guide 
10, the ends of the seal band 60 are fastened to the stepped portions 24b 
of the carriage 20, whereby forming the loop of the seal band 60. 
Thereafter, the side covers 3 and the upper cover 4 are set to the casing 
body. 
A workpiece (not shown) as a driven member, is firmly secured by bolts onto 
a pair of the driven member mounting portions 24a of the carriage 20, 
which protrude above the upper cover 4 of the casing 1. 
It is assumed now that the carriage 20 stops at a position close to the 
motor bracket 6. 
Under this condition, the AC servo motor 40 is forwardly turned. With the 
forward turn of the driving device 40, the ball-screw shaft 31 of the 
ball-and-screw mechanism 30 is forwardly turned. The rotary force of the 
ball-screw shaft 31 is transmitted to the ball-screw nut 32 by the balls 
33, which are inserted between the helical thread 31a of the ball-screw 
shaft 31 and the helical thread 32a of the ball-screw nut 32. By the 
rotary force, the ball-screw nut 32 moves axially, so that the carriage 20 
secured to the ball-screw nut 32 moves also axially. 
When the ball-screw nut 32 moves, the steel balls roll forward within the 
ball threads, facing each other, of the ball-screw shaft 31 and the 
ball-screw nut 32. Since the ball-and-screw mechanism 30 is of the end-cap 
circulating type, the balls circulate in a manner that after reaching the 
nut end, the balls moves through the curved path of the end cap 35 and the 
return path of the nut body, and returns to the start position. If the 
ball-and-screw mechanism of the tube circulating type, the balls roll one 
or two and half turn through the helical path defined by the coupled 
helical threads, and then are pulled into the ball circulating tube of the 
nut. The balls obliquely ride over the lands of the ball-screw shaft 31 
within the tube, and returns to the helical thread path. This circulation 
of the balls is repeated. 
Thus, a number of steel balls circulate through the helical thread path and 
within the ball-screw nut 32, while rolling. Therefore, continuous 
generation of noise is inevitable in the ball-screw nut 32 of the 
ball-and-screw mechanism 30. The suppression of this noise will be 
described later. 
The carriage 20 is supported at both sides by the sliders 12 of the linear 
guides 10. Accordingly, with the movement of the carriage 20, the sliders 
12 move along the guide rails 11 of the linear guides 10. Thus, the 
carriage 20 is guided along the guide rails 11, with the movement of the 
sliders 12. In this way, the smooth movement of the carriage 20 is 
guaranteed, and an exact linear movement of the workpiece attached to the 
carriage 20 is secured. 
When the sliders 12 move, a number of the steel round bodies 18 roll 
forward within the ball rolling grooves 13 of the guide rails 11 and the 
ball rolling grooves 16 of the sliders 12. The round bodies 18 are turned 
back by way of the curved path provided at one end of each slider 12, pass 
through the circulating paths 17 formed in the leg portions 15 of the 
sliders 12, and reach the other ends of the sliders 12. The round bodies 
18 are turned back again by way of curved paths of the other ends of the 
sliders 12, and return to the coupled the ball rolling grooves 13 and 16. 
In this way, a number of solid steel round bodies 18 circulates within the 
sliders 12 while rolling. Accordingly, a continuous noise is generated 
also in the slider 12 portions of the linear guides 10 when the linear 
motion actuator is operating. 
The noise suppression mechanism for suppressing the continuous noise will 
be described below. 
In the first embodiment, the sound absorbing material 70, mounted on the 
underside of the upper cover 4, is used for suppressing the continuous 
noise generated in the slider 12 portions of the linear guides 10 and the 
ball-screw nut 32 portion of the ball-and-screw mechanism 30. Further, 
noise suppression is ensured by sealing the slits S as the openings of the 
closed casing 1 with the seal bands 60. It is noted that the sound 
absorbing material 70 is disposed right above the ball-screw nut 32 where 
noise generation tends to occur. Because of this feature, the noise 
generated is effectively suppressed. A pair of extensions 4b and 4b, 
shaped like L, elongating over the entire length of the lower surface of 
the upper cover 4, are provided for supporting the sound absorbing 
material 70. Provision of the extensions 4b and 4b increases the rigidity 
of the upper cover 4. 
The carriage 20 is driven by the driving device 40 through the 
ball-and-screw mechanism 30, and moves axially in the casing 1 while being 
guided by the linear guides 10. With the movement of the carriage, the 
protruded portions 24 of the carriage, which bear the work and are 
protruded from the surface of the upper cover 4, move axially within and 
along the slits S. As the protruded portions 24 of the carriage move, the 
looped seal bands 60 fastened at the ends to the protruded portions 24 are 
also turned. When the carriage 20 moves to the right (FIG. 2), for 
example, the seal bands 60 are turned back on the pulleys 50c and 50d, 
disposed in this order in the carriage advancing direction. The seal bands 
60 are turned back again on the pulleys 50b and 50a. In this way, the seal 
bands 60 are turned clockwise in FIG. 2. With the turn of the seal bands 
60, the guide plates 63 mounted on the lower parts of the seal bands 60 
move in the direction opposite to the carriage advancing direction. The 
distance the guide plates 63 move is equal to the stroke length of the 
carriage 20. There is no fear that the guide plates 63 collide with the 
end cover 5 and the motor bracket 6. 
It is noted that the gap present between each the guide plates 63 and the 
inner wall of the through-hole 7a associated therewith is very small. 
Therefore, the looped seal bands 60 can be effectively prevented from 
being shifted sideways. 
Thus, the looped seal bands 60 turn in a considerably stable state with the 
movement of the carriage 20, while at the same time seal the slits S, 
which range within the moving range of the driven member mounting portions 
24a of the carriage 20. The sealing is made in a manner that the side 
edges of each seal band 60 are inserted into the guide groove 3a of the 
end face of the side cover 3 and the guide groove 4a of the end face of 
the upper cover 4. Extremely small gaps, shaped like U in cross section, 
defined by the seal bands 60, the side covers 3, and the upper cover 4 
connect the inside and the outside of the casing 1. The inner precise 
parts of the linear motion actuator is reliably protected from fine 
foreign matters, such as dust. Further, the seal bands 60, when turned, 
are not shifted sideways. Furthermore, noise generated in the linear 
guides 10 and the ball-and-screw mechanism 30 can be effectively confined 
within the casing 1. 
The linear motion actuator of the first embodiment is designed for the 
transportation of large and heavy workpieces. To transport such a 
workpiece at high speed and accurately to position it, a high rigidity is 
required for the actuator. Particularly the carriage, which couples the 
work with the linear guides, directly receives the load of the workpiece. 
It is a very important component in determining the rigidity of the linear 
motion actuator. In the first embodiment, special design efforts to 
construct the structure to provide a high rigidity of the linear motion 
actuator are made. 
The first feature to obtain a high rigidity of the linear motion actuator 
is the hollowed structure of the casing body 2 in which many through holes 
7 are formed in the thick part of the bottom of the casing body 2. This 
hollowed structure contributes to reduce the weight of the linear motion 
actuator and to increase the rigidity thereof. 
The second feature is that the driven member mounting portions 24a of the 
carriage 20, which directly receive the load of the workpiece, are located 
just above the guide rails 11 of the linear guides 10. With this feature, 
the heavy workpiece placed on the driven member mounting portions 24a is 
supported on the locations on the axial lines of the linear guides 10 
where provide the most rigidity. The weight reduction by thinning the 
carriage 20 and the substantial increase of the rigidity of the linear 
motion actuator can both be achieved. 
The third feature is that in the dust-proof structure for sealing the slits 
S necessary for the movement of the carriage 20, which are formed in the 
upper surface of the casing 1, the movable bands 60 are used by making 
well use of the through-hole 7a formed in the casing body 2. Specifically, 
the seal bands 60 are looped. One end of each looped seal band is fastened 
to the carriage 20. With the movement of the carriage 20, the looped seal 
bands 60 are circulated through the through-hole 7a. The structure of the 
carriage 20 is much simpler than that of the conventional one. As a 
result, a high rigidity of the carriage 20 is secured, and the size 
reduction of thereof is realized. 
A second embodiment of the linear motion actuator according to the present 
invention will be described with reference to FIG. 5. The dust-proof 
structure in the second embodiment is suitable for a linear motion 
actuator for transporting a driven member of a relatively light weight. 
A casing 1, having one piece construction consisting of the bottom portion, 
side portions, and the upper portion, is formed by extrusion molding. A 
slit S, axially extended, is formed in the upper portion. A shallow sunken 
part 80, axially extended, is formed at the central part of the upper 
surface of the bottom portion. The sunken part 80 serves as a path for the 
seal band 60. A guide rail 11 is disposed on the surface of the bottom 
portion of the casing 1. The guide rail 11 is U-shaped in cross section. 
Ball rolling grooves 13, longitudinally extended, are formed in the inner 
walls, facing each other, of the guide rail 11. The ball-screw nut 32 of a 
ball-and-screw mechanism 30 is axially movably provided in the U-shaped 
guide rail 11. In this case, the ball-screw nut 32 serves also as a slider 
12 of the linear guide 10. 
Ball rolling grooves (not shown) are formed in both sides of the ball-screw 
nut 32, while confronting with the ball rolling grooves 13 of the guide 
rail 11. The ball-screw nut 32 is engaged with the guide rail 11 through a 
plurality of balls which roll along ball rolling paths formed by the ball 
rolling grooves opposite to each other. 
Ball circulating paths as through holes extending in parallel with the 
respective ball rolling paths are formed in the thick parts of the right 
and left sides of the ball-screw nut 32. End caps 32E are fastened to the 
end faces of both ends of the ball-screw nut 32 when longitudinally 
viewed, by means of bolts 32B, respectively. A curved groove is formed in 
each end cap 32E. The curved grooves connect the ball rolling paths and 
the ball circulating paths. The ball rolling paths, the ball circulating 
paths, and the curved grooves cooperate to form a loop of the ball 
circulating path. The ball-screw nut 32 is linearly moved while being 
guided by the guide rail 11. At this time, a plurality of balls roll 
forward within the looped ball circulating path. 
A ball-screw shaft 31 is screwed into the ball-screw nut 32, with the balls 
intervening therebetween. The ball-screw shaft 31 is rotatably supported 
through the bearings (not shown) by the end cover and the motor bracket, 
both are not shown, provided at the ends of the casing 1. The ball-screw 
shaft 31 is driven by a drive motor, causing the ball-screw nut 32 to 
linearly move in the axial direction. 
The carriage 20 mounted on the ball-screw nut 32 includes a waist 20A, 
which is narrower than the width of the slit S of the casing 1, and a head 
plate 21 located outside the casing 1. 
In the second embodiment, only one seal band 60 is used in the dust proof 
structure of the linear motion actuator. The ends of the seal band 60 are 
fastened to the end part of the waist 20A of the carriage 20, thereby 
forming a loop of the seal band. 
Four pulleys are provided on both ends of the casing 1, as in the first 
embodiment. The seal band 60 is put on the pulleys. The looped seal band 
60 is turned with the movement of the carriage 20, thereby sealing the 
slit S. The lower part of the band loop is placed within the sunken part 
80 of the upper surface of the bottom portion of the casing 1. The guide 
plates 63, used in the first embodiment, are not used in this second 
embodiment where the casing 1 is short. 
The side edges of the seal band 60 are inserted into the guide grooves 1a 
formed in the end faces of the upper portion of the casing 1, which define 
the slit S. By this construction, a reliable sealing is further secured 
and the seal band is not shifted sideways. A heavy workpiece placed on the 
driven member mounting portions 24a of the carriage 20 is supported on the 
locations on the axial lines of the linear guides 10 which provides the 
most rigidity, as in the first embodiment. Since the through hole 
receiving the seal band 60 is not formed in the carriage 20, the rigidity 
of the linear motion actuator is high. 
In the second embodiment, only one set of the linear guide 10 and the 
ball-and-screw mechanism 30, provided within the casing 1 is used. 
Further, one dust-proof structure containing one seal band 60 and the 
pulleys for supporting the seal band is used. Further, the ball-screw nut 
32 of the ball-and-screw mechanism 30 serves also as the slider. By this 
construction, the resultant linear motion actuator is small in size and 
light in weight. 
In the embodiments as mentioned above, although the seal band 60 which put 
on the four pulleys is a flat sail cloth band containing polyurethane, 
steel or plastic may also be used for the seal band. 
The use of a ventilation device, such as a small blower which is mounted on 
a suitable location, e.g., the motor bracket 6 at the end portion of the 
casing, may increase the inner pressure within the actuator in comparison 
with the pressure outside the actuator so that the air is blown into the 
actuator. In this case, the dust proofing effect is further enhanced. When 
the ventilation device sucks air from the inside of the actuator, a 
negative pressure is created within the actuator. In this case, generation 
of dust such as metal particles, lubricant particles, and the like can be 
suppressed within the actuator. These measures can be realized with a 
reduced amount of air flow since the opening area of the casing is very 
small. 
The ball-screw nut 32 used in the above-mentioned embodiments is square in 
shape, but may be tubular. 
As seen from the foregoing description, the linear motion actuator of the 
present invention is provided with the casing having the slits extending 
axially, the carriage being axially movable along the guide rails within 
the casing, the carriage including the driven member mounting portions 
protruded outside through the slits for mounting the driven member, the 
seal bands fastened to the driven member mounting portions of the carriage 
for sealing the opening of the slit regardless of the location of the 
carriage when the seal band is moved along the slit, and the driving 
device for driving the carriage to move along the guide rails. 
In this linear motion actuator, the seal band is looped in a state that the 
ends of the seal band are respectively located at the front and rear sides 
of the driven member mounting portion when viewed in the axial direction. 
Further, in the linear motion actuator, the side edges of the seal band are 
respectively inserted into the axially elongated grooves formed in the end 
faces of the portions defining the slit, whereby the seal band is smoothly 
movable in the axial direction but is not shifted in the direction 
opposite to the axial direction. 
The seal band is passed through the axially elongated through hole formed 
in the casing, and the seal band is guided through the through hole by the 
guide plate fastened thereto, the guide plate being axially movable. 
The driving device includes the ball-screw shaft axially oriented and the 
ball-screw nut screwed into the ball-screw shaft. The sound absorbing 
material is disposed in the axially extending sunken part formed in the 
location of the casing closer to the ball-screw shaft. 
With such a construction, there is no need of passing the seal band through 
the carriage. Accordingly, the carriage may have a solid and simple 
structure of high rigidity. The size reduction of the linear motion 
actuator is easy, free from the abnormal shifting motion of the seal band. 
Accordingly, the linear motion actuator with a dust-proof function, 
provided by the invention, is small in size, light in weight, and high in 
rigidity.