Suction roll for conveying a flexible strip

A roll body has inside a plurality of suction holes extending along the axis of the roll body such that the suction holes make a concentric circle within the roll body and has a large number of pores connecting each suction hole with the circumferential surface of the roll body. A shaft protrudes from the roll body at one side, and the shaft is covered with a housing. The housing is connected with a vacuum suction device, and the air pressure in the housing is negative. In the housing, ends at one side of the suction holes reach the circumferential surface of the shaft, and a belt is wound around the shaft. While the roll body is rotating to convey a strip wound therearound, the belt wound around the shaft opens the ends of suction holes which communicate with pores being in contact with the strip and closes the ends of suction holes which communicate with pores being out of contact with the strip.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a suction roll for conveying in one 
direction a strip of flexible material such as a strip of paper, a resin 
film or a strip of sheet metal. 
2. Description of Related Art 
Conventionally, a suction roll for conveying a strip of flexible material 
has many pores on its circumference, and the pores are connected with a 
vacuum suction device such as a blower. While the air pressures in the 
pores are negative, the circumference of the suction roll holds the strip 
of flexible material. 
Practically, only about a half of the circumference of the suction roll is 
in contact with the strip of flexible material, and the other half does 
not contribute to the suction of the strip. The pores on the latter half 
of the circumference are open to the outside, and the vacuum suction 
device takes in air through these pores. This lowers the efficiency of the 
vacuum suction device, thereby requiring a large-sized apparatus. 
It is a conventional way of solving this problem that the half of the 
circumference of the suction roll which is out of contact with the strip 
is covered with a resin seal. In this way, however, the following problems 
occur: (1) even if a material which has a high abrasion resistance is used 
for the seal, the seal is abraded easily because of its function and must 
be exchanged frequently; (2) because dust is caused by the abrasion of the 
seal, the suction roller is not suitable for use in a clean room; (3) 
because the seal covers a large part (about the half) of the suction roll, 
a large power is required to rotate the suction roll; (4) processing of 
the surface of the seal which will be in contact with the suction roll and 
regulation of the pressure of the seal on the suction roll are difficult; 
and (5) because the seal cannot seal the pores perfectly, it is impossible 
to completely prevent the vacuum suction device from taking in air through 
the pores. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a suction roll which does 
not allow a vacuum suction device to take in air through pores without a 
seal and has a high suction efficiency. 
In order to attain the object, a suction roll according to the present 
invention has in a roll body, a plurality of suction holes extending in a 
direction of the axis of the roll body such that the suction holes make a 
concentric circle in the roll body, and a large number of pores connecting 
each suction hole with a circumferential surface of the roll body, and the 
suction holes are connected with and cut off from a negative pressure side 
by opening/closing means. The opening/closing means operates in accordance 
with rotation of the roll body to connect suction holes which communicate 
with pores that are in contact with a conveyed strip with the negative 
pressure source and to cut off suction holes which communicate with pores 
that are out of contact with the strip from the negative pressure source. 
As the roll body is rotating, the pores which are in contact with the strip 
are changing in the rotating direction. The opening/closing means operates 
in accordance with the change of the pores. The opening/closing means 
connects a suction hole communicating with pores which have come into 
contact with the strip with the negative pressure side, and thereby, the 
strip receive suction from the pores. On the other hand, the 
opening/closing means cuts off a suction hole communicating with pores 
which have separated from the strip from the negative pressure side. With 
this structure, the negative pressure side is never connected with pores 
which are open to the outside and therefore never takes in air. 
Consequently, the efficiency of the vacuum suction device is improved, and 
the problems caused by using a seal can be avoided.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Some exemplary suction rolls according to the present invention are 
hereinafter described with reference to the accompanying drawings. 
First Embodiment: see FIGS. 1-4 
A suction roll 1 according to the present invention comprises a roll body 2 
in the center, shafts 3 and 4 which protrude from the roll body 2 at both 
sides, housings 11 and 21 which cover the shafts 3 and 4 respectively, and 
endless belts 15 and 25 which are provided in the housings 11 and 21 
respectively. 
In the roll body 2, a plurality of suction holes 5 are made such that each 
suction hole 5 extends along the axis of the roll body 2 and that the 
suction holes 5 make a concentric circle of the roll body 2. Each of the 
suction holes 5 is connected with the circumferential surface of the roll 
body 2 by a large number of pores 6. A rotating force is transmitted to 
the suction roll 1 through either the shaft 3 or the shaft 4, and the 
suction roll 1 rotates in a direction indicated with arrow X at a constant 
speed. A flexible strip 30 to be conveyed is wound around the roll body 2, 
and as the suction roll 1 is rotating, the strip 30 is turned and 
conveyed. 
Next, a mechanism for applying suction to the strip 30 is described. 
Each suction hole 5 extends between the shafts 3 and 4, and both end 
portions 5a and 5b thereof are bent to the circumferential surfaces of the 
shafts 3 and 4 respectively. The end portions 5a and 5b are bent in the 
same direction as the pores 6 extend to the circumferential surface of the 
roll body 2. 
The housings 11 and 21 are fixed on a base (not shown) and the shafts 3 and 
4 are fastened to the housing 11 and 21 by bearings 13 and 23 respectively 
such that the shafts 3 and 4 can freely rotate. The housing 11 is 
connected with a vacuum suction device (not shown) through an opening 12, 
and sealed by the bearing 13 and 23 so that the housing 11 serves as a 
negative pressure chamber. The housing 21 is open to the outside through 
an opening 22. 
Further, in the housings 11 and 21, rollers 16 and 26 are rotatably 
fastened respectively. The belt 15 is wound around the roller 16 and the 
shaft 3 such that the belt 15 closes the ends 5a of the suction holes 5. 
Likewise, the belt 25 is wound around the roller 26 and the shaft 4 such 
that the belt 25 closes the ends 5b of the suction holes 5. The winding of 
the belt 15 in the negative pressure side (see FIG. 3) and the winding of 
the belt 25 in the air side (see FIG. 4) are symmetric, and the belts 15 
and 25 rotate with the rotation of the suction roll 1. In the negative 
pressure side, the belt 15 opens the ends 5a of suction holes 5 which 
communicate with pores 6 being in contact with the strip 30 and closes the 
ends 5a of suction holes 5 which communicate with pores 6 being out of 
contact with the strip 30. In the air side, the belt 25 closes the ends 5b 
of the suction holes 5 which communicate with pores 6 being in contact 
with the strip 30 and opens the ends 5b of the suction holes 5 which 
communicate with pores 6 being out of contact with the strip 30. 
In other words, the pores 6 being in contact with the strip 30 are 
connected with suction holes 5 each of which has an end 5a connected with 
the vacuum suction device and another end 5b cut off by the belt 25 from 
the outside. Thereby, the air pressures in these suction holes 5 are kept 
negative, and suction is applied to the strip 30 by the pores 6 upon the 
circumference of the roll body 2. On the other hand, the pores 6 being out 
of contact with the strip 30 are connected with suction holes 5 each of 
which has an end 5b open to the outside and another end 5a cut off by the 
belt 15 from the vacuum suction device. Accordingly, the vacuum suction 
device does not take in air through the latter pores 6, and the vacuum 
suction device can work efficiently. Also, since the pores 6 out of 
contact with the strip 30 are reliably kept open to the outside, the strip 
30 will not coil around the roll body 2 during conveyance even if no 
tension is applied to the strip 30. 
Second Embodiment: See FIG. 5 
In the first embodiment, two belts 15 and 25 for opening and closing the 
ends 5a and 5b of the suction holes 5 are provided. However, the belt 25 
is dispensable. FIG. 5 shows an exemplary structure which can eliminate 
the belt 25. In this case, the ends 5b of the suction holes 5 are all 
closed. 
Third Embodiment: See FIG. 6 
FIG. 6 shows a suction roll which is a third embodiment of the present 
invention. In the third embodiment, porous segments 7 replace the pores 6 
in the first and the second embodiments. The porous segments 7 are 
embedded in a roll body 2' such that each porous segment 7 is connected 
with each suction hole 5'. The segments 7 are sintered products with 
numerous pores or are resin molded products. The other parts of the third 
embodiment are the same as shown in FIGS. 1 through 4 or FIG. 5. A 
sectional view of the suction roll taken by a line III--III in FIG. 6 is 
the same as FIG. 3. 
Other Embodiments 
Although the present invention has been described in connection with the 
preferred embodiments above, it is to be noted that various changes and 
modifications are possible to those who are skilled in the art. Such 
changes and modifications are to be understood as being within the scope 
of the present invention. 
The number of suction holes 5 and the number of pores 6 are arbitrary, but 
a large number of suction holes and pores secure the suction. 
As means of opening and closing the suction holes 5, a mechanical means 
such as electromagnetic valves or mechanical valves operated by a cam can 
be used as well as the belts 15 and 25. In a case of using such valves, 
the valves are opened and closed in accordance with the rotation of the 
roll body.