Patent Publication Number: US-2007107848-A1

Title: Device to apply rubber tape

Description:
The present invention relates to a device to apply a rubber tape to a surface of a rotating object, e.g. a drum for building a tire rubber component.  
      A method for manufacturing a pneumatic tire which utilizes a rubber component formed by overlap winding a narrow thin raw rubber tape in stead of a relatively wide thick raw rubber strip, has been proposed, for example, as disclosed in Japanese Patent application No. 2000-94542.  
      In order to make such method fit for practical use, tire manufactures makes strenuous efforts in recent years.  
      To realize an efficient production lines, such a narrow thin raw rubber tape has to be wound quickly and exactly.  
      If as shown in  FIG. 9 , the distance (ds) between a let-off roller (a 1 ) at the downstream end of a tape applicator (a) and the surface (cs) of the object (c) is large, it is very difficult to wind exactly. If the winding speed is increased, the thin tape (b) tends to flutter. This also makes it difficult to wind exactly.  
      On the other hand, as shown in  FIG. 7 , in the case of a motorcycle tire T, when compared with the passenger car tires, light truck tires and the like, the tread rubber TR is remarkably curved. When making such a curved tread rubber TR by winding a thin rubber tape, due to the inclination of the surface of the object, as shown in  FIG. 9 , the torsional deformation of the tape existing between the downstream end and the surface becomes large.  
      If the above-mentioned distance is large, the tape can flexibly withstand such deformation. But, if the distance is made small to wind exactly and quickly, the tape tends to locally irregularly elongate. As a result, very small gaps or cavities tend to occur between the windings of the tape. Further, if the winding speed is increased to improve the production efficiency, the raw thin rubber tape becomes liable to break at worst due to the torsional deformation.  
      In addition, a rubber component, e.g. the above-mentioned tread rubber and the like usually has a variable thickness. Such a variable thickness can be achieved by varying the overlap width between the adjacent windings of the rubber tape. Accordingly, the inclination of the surface on which the tape is to be wound is varied with the progress of the winding operation.  
      Therefore, it is very important for obtaining the desired thickness variation, namely, the desired cross sectional shape of the rubber component that the direction of the rubber tape being let off from the tape applicator towards the surface on which the tape is to be wound (hereinafter the “let-off direction”) can be adjusted with respect to the inclination of the surface.  
      An object of the present invention is therefore to provide a device to apply a rubber tape, which can let off the rubber tape at a position near the surface of the object and in a let-off direction suitable for the inclination of the surface of the object so that the tape winding speed can be increased, and the rubber tape can be wound into the target cross sectional shape as exactly as possible without causing defects such as cavities between the windings.  
      According to the present invention, a device to apply a rubber tape to a surface of a rotating object, comprises:  
      a conveyer belt for conveying the rubber tape;  
      a let-off roller as the most downstream side roller on which the conveyer belt runs and from which the rubber tape is let off towards the object;  
      a traverser to move the let-off roller in an X-axis direction which is parallel to the rotational axis of the object;  
      a radial shifter to move the let-off roller in a Y-axis direction which is perpendicular to the X-axis direction;  
      a tilter to turn the rotational axis of the let-off roller around a reference axis which is parallel to a Z-axis direction perpendicular to the X-axis direction and Y-axis direction;  
      the conveyer belt provided with a substantially straight part extending for a certain distance from the let-off roller to the upstream side thereof at a substantially constant inclination angle theta of more than 0 but not more than 70 degrees with respect to a reference plane including the rotational axis of the let-off roller and the rotational axis of the object. 
    
    
      An embodiment of the present invention will now be described in detail in conjunction with the accompanying drawings.  
       FIG. 1  is a schematic perspective view of a device to apply a rubber tape according to the present invention.  
       FIG. 2  is a side view of the rubber tape applying device.  
       FIG. 3  is a side view of an apparatus for making a tread assembly for a motorcycle pneumatic tire in which the rubber tape applying device is incorporated.  
       FIG. 4  is a diagram for explaining motions of the let-off roller when viewed from above the drum.  
       FIG. 5  is a diagram for explaining unfavorable turning motion of the let-off roller.  
       FIG. 6  is a side view for explaining the tape guiding direction of the applicator.  
       FIG. 7  is a cross sectional view of an exemplary motorcycle tire.  
       FIG. 8  is a diagram for explaining problems in the prior art.  
       FIG. 9  is a perspective view for explaining the prior art. 
    
    
      In the drawings, a device to apply a rubber tape according to the present invention (hereinafter the “tape applying device  1 ”) is a device to feed and apply a long continuous raw rubber tape  3  to a winding surface S of a rotating object  4  and thereby to form windings  5  of the rubber tape  3  around the object  4 .  
      In this embodiment, as shown in  FIG. 3 , the tape applying device  1  is incorporated in an apparatus  100  for making a tread assembly for a motorcycle pneumatic tire T, which apparatus  100  comprises: an extruder  11  for extruding raw rubber in a form of tape  3 ; the tape applying device  1 ; and a profiled drum  6 . Thus, in this embodiment, the above-mentioned rotating object  4  generically means the profiled drum  6  itself and a material previously wound around the drum  6 .  
      Incidentally, as shown in  FIG. 7 , the motorcycle tire T comprises: a tread portion Tt; a pair of axially spaced bead portions Tb each with a bead core Tc therein; a pair of sidewall portions Ts extending between the tread edges TE and the bead portions Tb; a carcass Tp extending between the bead portions Tb; and a tread reinforcing belt  7  disposed radially outside the carcass Tp in the tread portion Tt. The tread portion Tp is curved so that the maximum tire section width lies between the tread edges TE.  
      In this example, the drum  6  has, as shown in  FIG. 1 , an outer circumferential surface S which is curved to accord with the curve of the inner surface of the tire belt  7 , namely, the tread reinforcing cord layer, e.g. band such as jointless spiral band  9 , breaker such as cross-ply breaker  11  and the like. Therefore, the outer diameter of the circumferential surface S of the drum  6  becomes maximum at the center of its width, and the diameter decreases continuously from the center towards each edge of the winding surface S.  
      To the circumferential surface S, the belt  7  is first applied or wound. Then, a raw rubber tape  3  is overlap wound on the belt  7 , whereby the tread rubber TR is formed by the windings of the tape. Thus, a tread assembly of the belt  7  and tread rubber TR is formed on the drum  6 .  
      Incidentally, in order to remove the tread assembly, the drum  6  has a collapsible structure as well known in the art. The drum  6  is rotated by a motor Md controlled by a controller CON.  
      The tape applying device  1  includes an endless conveyer belt J to which the raw rubber tape  3  is adhered with utilizing its tackiness.  
      The conveyer belt J is supported and guided by rollers R and runs between a tape receiving section  14  provided near the extruder  11  and an applicator section  17  provided near the drum  6 .  
      In the tape receiving section  14 , the raw rubber tape  3  extruded from the extruder  11  is adhered onto the conveyer belt J. In the applicator section  17 , the raw rubber tape  3  is separated from the conveyer belt J at the position of the roller R on the most downstream side, and the separated tape  3  transfers to the drum. Between these sections  14  and  17 , an accumulator section  15  is formed.  
      The tape receiving section  14  comprises a transfer roller Ra and a cylinder actuator  18 . The cylinder actuator  18  is controlled by the controller CON in order to move the transfer roller Ra between two positions: a separate position at a small distance from a lower calender roller  11   a  of the rubber extruder  11 ; and a contact position at which the transfer roller Ra can contact with the lower calender roller  11   a.    
      By moving the transfer roller Ra towards the contact position, the raw rubber tape  3  on the lower calender roller  11   a  is adhered to the conveyer belt i running on the transfer roller Ra. After the tape is adhered to the conveyer belt J, the transfer roller Ra returns to the separate position. Thus the tape transfers.  
      The accumulator section  15  comprises: a going-belt accumulator  15 A for the conveyer belt J going from the extruder  11  to the drum  6 ; and a retuning-belt accumulator  15 B for the conveyer belt J retuning from the drum  6  to the extruder  11 . Each accumulator  15 A,  15 B is formed by a festoon of the conveyer belt J as shown in  FIG. 3 .  
      In the going-belt accumulator  15 A, the conveyer belt J winds between a series of upper horizontal rollers R 1 U and a series of lower horizontal rollers R 1 L. The upper horizontal rollers R 1 U are mounted on a fixed horizontal beam  19 A of a support frame  19  in a line, whereas the lower upper horizontal rollers R 1 L are mounted on a vertically-movable horizontal frame  19 C in a line.  
      In the retuning-belt accumulator  15 B, similarly, the conveyer belt J winds between a series of upper horizontal rollers R 2 U and a series of lower upper horizontal rollers R 2 L. The upper horizontal rollers R 2 U are mounted on a fixed horizontal beam  19 B of the support frame  19  in a line, whereas the lower upper horizontal rollers R 2 L are mounted on a vertically-movable horizontal frame  19 D in a line.  
      The tape applying device  1  includes: a first motor M 1  to drive the retuning conveyer belt J in sync with the extrusion speed of the tape which is continuously extruded from the extruder  11 ; and a second motor M 2  to drive the going conveyer belt J intermittently, engaging with the intermittent rotation of the drum  6 . The first motor M 1  and second motor M 2  are controlled by the controller CON.  
      By the rotation of driving rollers coupled with the first motor M 1 , the conveyer belt J is took out from the retuning-belt accumulator  15 B, and the extruded rubber tape  3  is adhered thereto. Then, the conveyer belt J with the rubber tape thereon travels into the going-belt accumulator  15 A.  
      During stopping of the rotation of the drum  6 , the conveyer belt J with the rubber tape  3  thereon is accumulated in the going-belt accumulator  15 A, and the conveyer belt J on which the tape is to be adhered is took out from the retuning-belt accumulator  15 B.  
      When the rotation of the drum  6  is started, by the rotation of driving rollers coupled with the second motor M 2 , the conveyer belt J with the rubber tape thereon is took out from the going-belt accumulator  15 A, and the rubber tape  3  is fed to the drum, leaving from the conveyer belt J running on the roller R on the most downstream side (namely, the “let-off roller  16 ”). Then, the conveyer belt J returns to the retuning-belt accumulator  15 B.  
      As shown in  FIG. 1 , the applicator section  17  comprises: (1) a traverser  21  to move the let-off roller  16  in an X-axis direction parallel with the rotational axis (i) of the object  4  or drum  6 ; (2) a radial shifter  22  to move the let-off roller  16  in a Y-axis direction perpendicular to the X-axis direction so as to be able to come close and come away from the object  4 ; and (3) a tilter  23  to turn the let-off roller  16  around a reference axis zi so as to be able to incline towards either side of a reference line xj, wherein the reference line xj is parallel to the X-axis direction, and the reference axis zi is parallel to a Z-axis direction perpendicular to the X-axis direction and the Y-axis direction.  
      The traverser  21  comprises: lateral guide rails  21 A laying in the X-axis direction; and a main carriage  21 B on the lateral guide rails  21 A. The main carriage  21 B is movable in the X-axis direction by a driving mechanism engaged with a motor Mx, utilizing for example a ball screw, gears, power transmission belt and the like. By moving the main carriage  21 B, the let-off roller  16  can traverse the entire width of the drum  6 . The moving speed, moving distance and moving direction of the main carriage  21 B can be completely controlled by controlling the rotation of the motor Mx with the controller CON.  
      The radial shifter  22  comprises: radial guide rails  22 A laying in the Y-axis direction and fixed to the main carriage  21 B; and a sub carriage  22 B on the radial guide rails  22 A. The sub carriage  22 B is movable in the Y-axis direction by a similar driving mechanism engaged with a motor My, utilizing for example a ball screw, gears, power transmission belt and the like. By moving the sub carriage  22 B forwards, the let-off roller  16  approaches the drum  6 . The moving speed, moving distance and moving direction of the sub carriage  22 B relative to the main carriage  21 B can be completely controlled by controlling the rotation of the motor My with the controller CON.  
      The tilter  23  comprises: a support shaft  23 A extending uprightly from the sub carriage  22 B; and a turning bed  23 B supported by the support shaft  23 A turnably around the axis  23   i  of the shaft  23 A. In this example, the axis  23   i  of the support shaft  23 A defines the above-mentioned reference axis zi.  
      The turning bed  23 B is engaged with a motor Mz through a transmission (not shown). The turning speed, turning angle and turning direction of the turning bed  23 B can be completely controlled by controlling the rotation of the motor Mz with the controller CON. Incidentally, the turning angle is detected by an angle sensor such as an encoder or the like and based on the output of the sensor the turning angle is determined by the controller CON.  
      As another alternative arrangement, it is also possible to exchange the positions of the traverser  21  and radial shifter  22 , namely, to arrange the main carriage  21 B above the sub carriage  22 B, and the turning bed  23 B is provided on the carriage  21 B.  
      In the turning bed  23 B in this example, a table-like frame  26  is disposed thereon, and a tape guide  25  is arranged on the frame  26  So as to position at almost same height as the rotational axis the drum. The tape guide  25  in this example comprises: a platy support arm  27  fixed to the top of the table-like frame  26 ; and a plurality of rollers R horizontally mounted on the support arm  27 .  
      The rollers R include: the above-mentioned let-off roller  16  disposed at the front end of the support arm  27 ; and a large-diameter driving roller  28  for driving the conveyer belt J coupled with the above-mentioned second motor M 2 .  
      In this embodiment, the rotational axis  16   i  of the let-off roller  16  is positioned within a standard plane  29  which is a plane  4 S perpendicular to the Z-axis direction and including the rotational axis (i) of the drum  6 . In other words, the plane  4 S (standard plane  29 ) which includes both of the axis  16   i  and the axis (i) is perpendicular to the Z-axis direction. Accordingly, within the standard plane  29 , the notational axis  16   i  of the let-off roller  16  can move in both of the X-axis direction (traverse direction) and the Y-axis direction (back-and-forth direction towards the rotational axis of the drum), and also can turn around the reference axis zi, as shown in  FIG. 4 .  
      The controller CON can control the motions of the traverser  21 , radial shifter  22  and tilter  23  so that the rotational axis  16   i  of the let-off roller  16  becomes substantially parallel with the profile line of the winding surface S which appears in the standard plane  29 , while moving in the X-axis and Y-axis directions.  
      It is preferable that as shown in  FIG. 4 , the reference axis zi passes through the bisecting point P of the width of the let-off roller  16 , more specifically, the bisecting point P of the length of the rotational axis  16   i  of the let-off roller  16 . If the reference axis zi does not pass through the bisecting point P, as shown in  FIG. 5 , errors delta x and delta y of the point P in the X-axis direction and Y-axis direction vary according to the turning angle, and thus it becomes necessary to compute and control the feeding speed of the tape, taking account of the variable errors as the traverser  21  and radial shifter  22  move in the X-axis and Y-axis directions.  
      Here, the let-off roller  16  is wider than the conveyer belt J, and the conveyer belt J is wider than the rubber tape. The diameter of the let-off roller  16  is considerably small when compared with the diameter of the drum. For example, the diameter of the let-off roller  16  is less than 20% of the drum diameter.  
      As shown in  FIG. 2 , the distance L between the winding surface S and the surface of the conveyer belt J on the let-off roller  16  is not more than 20 mm, preferably not more than 15 mm, more preferably not more than 10 mm, but not less than 3 mm, preferably not less than 5 mm, more preferably not less than 7 mm. If the distance L is more than 20 mm, it becomes difficult to control the overlapping width exactly. If the distance L is less than 3.0 mm, disorder such as constriction is liable to occur at the winding start end of the rubber tape  3 .  
      As shown in  FIG. 6 , in a part F before the let-off roller  16 , the going conveyer belt J runs for a certain distance at a constant angle theta with respect to a reference plane K, wherein the reference plane K is a plane including the axis  16   i  of the let-off roller  16  and the rotational axis (i) of the object  4 . Thus, in the vertical plane perpendicular to the rotational axis (i) of the object  4 , the reference plane K is a straight line drawn between the axis  16   i  and axis (i) as shown in  FIG. 3 .  
      By providing this straight part F, the residual stress and strain of the rubber tape can be reduced during running this part F. To derive this effect, it is preferable that the length of this straight part F is about 60 to 100 cm.  
      In view of smooth transfer and adhesion of the winding start end of the rubber tape to the surface S, the angle theta is preferably not less than 20 degrees, more preferably not less than 30 degrees, but not more than 70 degrees, preferably not more than 60 degrees, more preferably not more than 50 degrees. It is most preferable that the extension T of the straight part F is tangent to the winding surface S and the rubber tape  3  runs along this line, as shown in  FIG. 6 .  
      In this embodiment, a tape cutter  31  is disposed in this straight part F. The tape cutter  31  has a rotary blade of which rotation by a motor Mc is controlled by the controller CON so as to be able to cut the rubber tape on the moving conveyer belt J.  
      Further, the applicator section  17  comprises a presser roller  40 , at least the surface of which is formed by a spongy material which can make elastic deformation easily.  
      The presser roller  40  is rotatably horizontally supported by a holder attached to the end of the rod of a cylinder actuator  41  mounted on the support arm  27 . By activating the cylinder actuator  41  by supplying high-pressure air, the presser roller  40  can press the rubber tape  3  against the winding surface S. The presser roller  40  is used at least at one point when the winding start end of the rubber tape  3  is adhered to the winding surface S. Also, it is possible to use it all the time during winding in order to press the rubber tape  3  against the winding surface S. This cylinder actuator  41  is also controlled by the controller CON.  
      The above-mentioned controller CON is a computer which comprises a central processing unit, memory, input and output devices (such as keyboard, display, printer) and the like as well known in the art. The driving units of the above-mentioned motors Md, M 1 , M 2 , Mx, My, Mz, Mc and actuators  18 ,  41  are connected to the computer through interface adapters. Further, various sensors for detecting the turning angle and position of the let-off roller  16 , and sensors for the rubber tape at various positions and the like are also connected to the computer through interface adapters.  
      Thus, the controller CON can operate the tape applying device  1  according to the program stored in the memory and the outputs of the sensors.  
      Comparison Tests  
      Using the above-mentioned apparatus shown in  FIG. 3 , various tread assembles were made by restricting the motions of the traverser  21 , radial shifter  22  and tilter  23  as shown in Table 1. For example, by restricting the motions of the radial shifter  22  and tilter  23 , the tape applying device  1  can simulate the prior art device shown in  FIGS. 8 and 9 . The tread assembly Ref. 1 was made in this way.  
      In each case, a rubber tape  3  was wound on a belt previously wound on the drum. The width of the winding surface of the drum was 185 mm. The difference (Dc−Ds) between the diameter Dc of the winding surface at the center and the diameter Ds at the edges was 120 mm.  
      using such tread assemblies, motorcycle pneumatic tires (tire size 190/55R17) were made. And the tires were checked for tire uniformity (radial force variation) and defects of the tread rubber (namely, windings of the rubber tape) at the tread surface.  
      (1) Uniformity Test  
      Using a tire tester, the radial force variation RFV (over all) was measured according to the Japanese Automobile Standards Organization JASO-C607, “Testing method for automobile tire uniformity”. In this test, with respect to each test tire, 30 pieces were measured and the average value was obtained. The results are shown in Table 1.  
      (2) Defect in the Tread Surface  
      In this test too, with respect to each test tire, 30 pieces were prepared and visually checked for bareness of rubber (namely, lack of rubber) on the tread surface and evaluated into three ranks A, B and C as follows. The number of tires in each rank was counted. The results are shown in Table 1. 
          A: there was no defect     B: negligible        

      C: unacceptable  
                                                   TABLE 1                                   Ref. 1   Ref. 2   Ex. 1   Ex. 2   Ex. 3   Ex. 4   Ex. 5   Ex. 6                                                                        Let-off roller                                       Traversal motion(X-axis)   yes   yes   yes   yes   yes   yes   yes   yes       Radial motion (Y-axis)   no   no   yes   no   no   yes   no   yes       Turning motion(Z-axis)   no   yes   yes   no   yes   yes   yes   yes       Distance L (mm)   10   10   10   7   15   20   25   10       Use of Presser roller   no   no   no   no   no   no   no   yes       Uniformity (N)   51   48   42   40   41   44   45   38       Defect in tread surface       Rank A   24   26   29   30   30   29   28   30       Rank B   3   3   1   0   0   1   2   0       Rank C   3   1   0   0   0   0   0   0