Tire structural member fabricating method and apparatus for carrying out the same

A tire structural member fabricating method fabricates a tire structural member by successively and contiguously attaching strips 1 to the convex outer surface having an outwardly convex cross section of a forming drum 11 by a strip feed device 21 such that the strips 1 extend obliquely to the center axis C of the forming drum 11. The strip feed device 21 moves parallel to the center axis C of the forming drum 11 at a fixed speed V and feeds strips 1 successively onto the outer surface of the forming drum 11. A controller 40 controls the rotation of the forming drum 11 such that the angular velocity ω of the forming drum 11 varies gradually.

TECHNICAL FIELD

The present invention relates to a tire structural member fabricating method that attaches a plurality of strips successively to the outer surface of a forming drum such that the strips extend obliquely to the axis of the forming drum and to an apparatus for carrying out the tire structural member fabricating method.

BACKGROUND ART

Tire structural members fabricated by a tire structural member fabricating method of this kind include a belt member in the form of a cord-reinforced bias sheet. A belt fabricating method disclosed in JP 2001-88225 A forms a belt sheet on a cylindrical drum.

The belt sheet fabricating method disclosed in JP 2001-88225 A delivers strips successively onto a cylindrical drum rotating at a fixed angular velocity by moving a strip feed device at a fixed speed parallel to the axis of the cylindrical drum to attach the strips to the outer surface of the cylindrical drum obliquely to the axis of the cylindrical drum.

As shown inFIG. 8-1, a cylindrical belt structure01having a cylindrical shape is formed by thus successively attaching the strips to the cylindrical drum in a circumferential arrangement.

A convex cylindrical belt structure02having an outer surface of an outwardly convex cross section as shown inFIG. 8-2is formed by shaping the cylindrical belt sheet01. As shown inFIG. 8-2, stitchers05are pressed against end parts of the cylindrical belt sheet01so as to reduce the diameter of the end parts to form the convex cylindrical belt structure02of a shape conforming to the shape of the outer surface of a green tire.

The thus contracted end parts of the convex cylindrical belt structure02are creased and the thickness of the end parts varies along the circumference of the convex cylindrical belt structure02.

The belt sheet fabricating method disclosed in JP 2001-88225 A attaches the strips to the cylindrical drum. If a convex cylindrical drum having a convex outer surface is used instead of the cylindrical drum, a convex cylindrical belt structure similar to the convex cylindrical belt structure02shown inFIG. 8-2can be formed.

In a convex cylindrical drum having a curved outer surface of an outward convex cross section, the diameter of a middle part is greater than that of end parts. Therefore, when a predetermined number of strips are attached successively to the convex cylindrical drum such that middle parts of the strips are in properly adjoining disposition, end parts of the strips are overlapped.

When a predetermined number of strips are attached successively to the convex cylindrical drum such that end parts of the strips are in properly adjoining disposition, gaps are formed between adjacent middle parts of the strips. In either case, a tire structural member having a uniform quality cannot be formed.

The present invention has been made in view of such problems and it is therefore an object of the present invention to provide a tire structural member fabricating method capable of fabricating a tire structural member of a uniform quality by successively arranging a plurality of strips so that adjacent strips are in properly adjoining disposition, and to provide an apparatus for carrying out the method.

DISCLOSURE OF THE INVENTION

The present invention provides a tire structural member fabricating method, which fabricates a tire structural member by successively and contiguously attaching strips to a convex outer surface having an outwardly convex cross section of a forming drum by a strip feed device such that the strips extend obliquely to a center axis of the forming drum, the method comprising the steps of: continuously attaching strips to the convex outer surface of the forming drum by successively feeding strips onto the convex outer surface by the strip feed device, while the strip feed device is being moved parallel to the center axis of the forming drum relative to the forming drum at a fixed speed and while the forming drum is being rotated about the center axis thereof; and controlling the rotation of the forming drum such that the angular velocity of the forming drum varies gradually from a minimum angular velocity at a moment a leading end of the strip is attached to the convex outer surface of the forming drum to a maximum angular velocity at a moment the strip is attached to a middle part of the convex outer surface of the forming drum and from the maximum angular velocity to a minimum angular velocity at a moment a trailing end of the strip is attached to the convex outer surface of the forming drum, the minimum angular velocity at the moment the trailing end is attached being equal to the minimum angular velocity at the moment the leading end is attached.

Since the angular velocity of the forming drum is increased gradually from the minimum angular velocity at the moment the leading edge is attached to the convex outer surface of the forming roller to the maximum angular velocity at the moment a middle part of the strip is attached to the convex outer surface of the forming roller and from the maximum angular velocity to the minimum angular velocity at the moment the trailing end of the strip is attached to the convex outer surface of the forming drum when the strip feed device moving at the fixed speed relative to the forming drum along the center axis of the forming drum feeds strips successively, the inclination of the strip to the center axis of the forming drum increases gradually from one of the opposite ends of the forming drum toward the middle of the convex outer surface and decreases gradually from the middle part of the convex outer surface toward the other end of the forming drum.

Consequently, the width of the strip attached to the convex outer surface of the forming drum in a plane perpendicular to the center axis of the forming drum increases gradually from one of the opposite ends of the forming drum toward the middle of the convex outer surface and decreases gradually from the middle part of the convex outer surface toward the other end of the forming drum. Thus, a tire structural member having a fixed thickness can be fabricated by successively attaching the predetermined number of the strips to the convex outer surface of the forming drum such that adjacent strips are in proper adjoining disposition and any gap is not formed between middle parts of the adjacent strips. The tire structural member having a fixed thickness improves the quality of a tire.

In the tire structural member fabricating method according to the present invention, the step of controlling the rotation of the forming drum controls the rotation of the forming roller so that the forming drum rotates at angular velocity ω meeting relation expressed by:

tan-1⁡(r⁢⁢ωV)=cos-1⁡(nw2⁢π⁢⁢r)
where w is a width of the strips, n is the number of the strips, V is the fixed speed of the strip feed device, and r is the radius of the convex outer surface of the forming drum as a function of a distance along the center axis of the forming drum by which the strip feed device travels.

Since a middle part of the convex outer surface of the forming drum bulges outward, the radius r of the convex outer surface increases from the minimum radius at one of the opposite ends of the forming drum toward the maximum radius at the middle of the convex outer surface and decreases from the maximum radius to the minimum radius toward the other end. The inclination θ of the strip to the center axis of the forming drum is a function of axial distance; that is, the inclination θ increases from a minimum inclination at one of the opposite ends of the convex outer surface to a maximum inclination at the middle of the convex outer surface and decreases from the maximum inclination to the minimum inclination toward the other end.

Suppose that the strip is inclined at an inclination θ on a circle at an axial distance. Then, the length of the strip on the circle is w/cos θ. Therefore, n times the length is equal to 2πr, namely, the circumference of the convex outer surface. Therefore, n(w/cos θ)=2πr and cos θ=nw/2πr.

When the strip is attached at an inclination θ to the circle, the axial speed is V and the circumferential speed is rω. Therefore tan θ=rω/V. Therefore,

When the forming drum is rotated at the angular velocity ω meeting the foregoing equation, the strips are attached to the enter convex outer surface of the forming drum such that the end parts of the strips do not overlap and any gap is formed between the middle parts of adjacent strips. Thus a tire structural member having a fixed thickness can be fabricated.

Typically, each of the strips may have opposite oblique ends inclined at an angle of cos−1(nw/2πr0), where r0is the radius of the opposite ends of the forming drum, to a direction in which the strip is fed.

Since the opposite ends of the strip are attached to the opposite ends of the forming drum, respectively, the strips can be attached in a smooth circular arc to the forming drum with opposite end parts of the strips properly arranged.

To carry out the tire structural member fabricating method of the present invention, the present invention provides a tire structural member fabricating apparatus comprising: a forming drum having a convex outer surface having an outwardly convex cross section and supported for rotation about a center axis thereof; a drum driving device for rotating the forming drum; a strip feed device for successively feeding strips and successively attaching the strips to the forming drum such that the strips are arranged successively and contiguously in a circumferential direction and are extended obliquely to the center axis of the forming drum; and a moving device for moving the strip feed device parallel to the center axis of the forming drum; wherein the moving device includes a strip feed device driving motor for moving the strip feed device at a fixed speed, the drum driving device includes a drum driving motor, a controller connected to the strip feed device driving motor and the drum driving motor, the controller controlling the strip feed device driving motor and the drum driving motor such that angular velocity of the forming drum varies gradually from a minimum angular velocity at a moment a leading end of the strip is attached to the convex outer surface of the forming drum to a maximum angular velocity at a moment the strip is attached to a middle part of the convex outer surface of the forming drum and from the maximum angular velocity to a minimum angular velocity at a moment a trailing end of the strip is attached to the convex outer surface of the forming drum, the minimum angular velocity at the moment the trailing end is attached being equal to the minimum angular velocity at the moment the leading end is attached.

In the tire structural member fabricating apparatus of the present invention, the controller controls rotation of the forming drum so that the forming drum rotates at angular velocity ω meeting relation expressed by:

tan-1⁡(r⁢⁢ωV)=cos-1⁡(nw2⁢π⁢⁢r)
where w is a width of the strips, n is the number of the strips, V is the fixed speed of the strip feed device and r is the radius of the convex outer surface of the forming drum as a function of distance along the center axis of the forming drum by which the strip feed device travels.

BEST MODE FOR CARRYING OUT THE INVENTION

A tire structural member fabricating method in a preferred embodiment according to the present invention fabricates a belt sheet3, namely, a tire structural member, by successively and contiguously attaching a plurality of strips1to the convex outer surface having a bulging middle part of a forming drum11so that the strips1extend obliquely to the center axis of the forming drum11.

FIGS. 1 to 3show schematic views of a tire structural member fabricating apparatus10for carrying out the tire structural member fabricating method.

The forming drum11has a convex outer surface having an outwardly convex cross section. A peripheral surface of the forming drum11has thereon a plurality of electromagnets12arranged along the circumference of the forming drum11. A servomotor13drives the forming cylinder11through a belt14to rotate the forming roller11about its center axis C.

A strip attaching device21is disposed obliquely above the forming drum11to attach strips1to the forming drum11. A pair of rails23is extended parallel to the center axis C of the forming drum11on a base22. A long sliding support plate25is supported on sliders24that slide along the rails23. The sliding support plate25moves horizontally parallel to the center axis C along the rails23. A threaded shaft26is engaged in a nut27attached to the sliding support plate25. A servomotor28drives the threaded shaft26for rotation through a belt29to move the sliding support plate25parallel to the center axis C.

The sliding support plate25has its length in left-to-right direction as viewed inFIG. 1and slopes down forward, i.e., toward the left as viewed inFIG. 1, so that the front end of the sliding support plate25is at a level lower than that of the back end of the same. The sliding support plate25is supported to be slidable parallel to the center axis C, while maintaining an attitude inclined at an angle θ0(to be referred to later) to the center axis C of the forming drum11.

A feed plate30is placed longitudinally on the sliding support plate25. Carrier rollers31for carrying strips1in the direction of the arrow A are supported on the feed plate30. Guide rollers32are arranged along the right and the left side of the feed plate30.

The feed plate30, similarly to the sliding support plate25, is extended at the angle θ0to the center axis C of the forming drum11. The carrier rollers31and the guide rollers32are arranged on and along a path inclined at the angle θ0to the center axis C.

The strip1to be fed and attached to the forming drum11by the feed plate30is a member obtained by obliquely cutting a long belt of a width w formed by coating a plurality of steel cords2with rubber in a predetermined length, as shown inFIG. 5. The strip1has oblique ends inclined at the angle θ0to its side edges.

The strips1delivered onto the carrier rollers31of the feed plate30are guided by the guide rollers32and are carried in the direction of the arrow A by the rotating carrier rollers31. The strips11are fed successively from the front end (the left end as viewed inFIG. 1) of the feed plate30onto the top of the forming drum11so that their leading ends come into contact first with the forming drum11as shown inFIG. 2.

The electromagnet12attracts the leading end part of the strip1to the outer surface of the forming drum11to pull down the strip1from the feed table30. As shown inFIG. 3, the sliding support plate25supporting the feed plate30moves parallel to the center axis C of the forming drum11while the strip1is pulled and the forming drum11rotates.

In a state where the leading end part of the strip1is attached to the forming drum11, the strip1is fed to the forming drum11so that the longitudinal center axis thereof extends at the angle θ0to the center axis C of the forming drum11. Consequently, the strip1is attached to the outer surface of the forming drum11with the leading edge la thereof extending parallel to an end surface of the forming drum11as shown inFIG. 2, while the strip1is oriented at the angle θ0to the center axis C.

The forming drum11is rotated at an angular velocity ω and the feed plate30is moved parallel to the center axis C of the forming drum11at a speed V. Consequently, the strips1successively fed by the feed plate30are attached obliquely to the outer surface of the forming drum1as shown inFIG. 3.

The foregoing strip attaching cycle is repeated to attach a predetermined number of the strips1contiguously to the outer surface of the forming drum11to form a tire structural member3having an outwardly convex cross section as shown inFIG. 4.

The tire structural member fabricating apparatus10of the present invention is provided with a controller40. The controller40controls the two servomotors13and28. The controller40controls the servomotor28so that the strip feed plate30is moved at the fixed speed V. The controller40controls the servomotor13so that the forming drum11is rotated at the variable angular velocity ω in the following manner.

The controller40controls the servomotor13such that the angular velocity ω of the forming drum11varies gradually from a minimum angular velocity at a moment the leading end1aof the strip1is attached to the outer surface of the forming drum11to a maximum angular velocity at a moment the strip1is attached to a middle part of the outer surface of the forming drum11and from the maximum angular velocity to a minimum angular velocity at a moment the trailing end1bof the strip1is attached to the outer surface of the forming drum11. The minimum angular velocity at the moment the trailing end1bof the strip1is attached is equal to the minimum angular velocity at the moment the leading end1ais.

The strip1attached to the outer surface of the forming drum11is deformed when the angular velocity ω of the forming drum11is varied as mentioned above.FIG. 6is a development of the thus deformed strip1on a plane.

InFIG. 6, the leading end la of the deformed strip1is aligned with the Y-axis (X=0) and the middle of the leading end1ais on the origin of the X-Y coordinate system.

The horizontal distance between the leading end1aand the trailing end1bof the strip1is D. The trailing end1bextends along a line parallel with the Y-axis and crossing the X-axis at X=D, and X=D/2 is the abscissa of the center of the strip1.

Suppose that a part of the outer surface of the forming drum1at a distance x (X=x) along the center axis C (X-axis) of the forming drum11from the leading end la of the strip1on the Y-axis (X=0) has a radius r and the forming drum11is rotating at an angular velocity ω at a moment the strip1is attached to the same part of the outer surface of the forming drum11. Then, the speed dY/dt (t represents time) along the Y-axis of the strip1at X=x is equal to the circumferential speed rω of the same part of the outer surface of the forming drum11, and the speed dX/dt along the X-axis of the strip1at X=x is equal to the fixed speed V.

Therefore, the gradient dY/dX of the vector sum of the speeds dY/dt and dX/dt is rω/V. Therefore,

The angle θ is the inclination of the strip1to the center axis C (X-axis) at a point X=x. Therefore, the length along the Y-axis at the point X=x is w/cos θ.

The circumference of a circle on the outer surface of the forming drum11at X=x is 2πr. Therefore, n(w/cos ω) is 2πr when n strips1are attached to the outer surface of the forming drum11so that the strips1are arranged in properly adjoining disposition without forming any gap between adjacent strips1at the point X=x. Therefore, the strips1are properly arranged when a condition expressed by Expression (2) is satisfied.

θ in Expression (1) and θ in Expression (2) are same. Therefore, from Expressions (1) and (2),

A tire structural member of a fixed thickness can be formed by thus attaching the n strips1to the outer surface of the forming drum11in the range of 0≦X≦D so that the strips1are arranged in proper adjoining disposition without forming any gap between adjacent strips1when the angular velocity ω of the forming drum11is controlled so as to meet a condition expressed by Expression (3) when the strip1is being attached to a part at the point X=x of the outer surface of the forming drum11.

The following equation is obtained by substituting Expressions (1) and (2) into an equation: tan2θ=1/cos2θ−1

(r⁢⁢ωV)2=(2⁢π⁢⁢rnw)2-1
Expression (4) is obtained by rearranging this equation.

A condition expressed by Expression (4) is the same as that expressed by Expression (3). Therefore, the angular velocity ω of the forming drum11may be controlled so as to meet the condition expressed by Expression (4).

FIG. 7is a graph showing a cross section of the outer surface of the forming drum11on an orthogonal coordinate system.

InFIG. 7, distance x along the center axis C of the forming drum is measured on the horizontal axis and radius r of the outer surface of the forming drum11is measured on the vertical axis. The radius r is a function of x, namely, r=f(x).

Suppose that the radius of the opposite ends respectively at x=0 and x=D of the forming drum11to which the strip1is attached is r0. Then, f(0)=f(D)=r0. The radius of a circle on the outer surface of the forming drum11at x=D/2 is a maximum radius f(D/2).

The feed plate30move in a direction parallel to the X-axis at the fixed speed V. Therefore, the feed plate30that started attaching a strip1to a part at x=0 of the forming drum11at t=0 attaches the strip1to a part at x=Vt at t=t.

Therefore, the radius r of the outer surface of the forming drum11can be expressed by: r=f(Vt), namely, a function of time.

Expression (5) is obtained by substituting r=f(Vt) into Expression (4).

Thus, the angular velocity ω can be expressed by a function of time t.

The controller40controls the servomotor13to rotate the forming drum11at the angular velocity ω calculated by using Expression (5). Consequently, the n strips1can be successively attached to the outer surface of the forming drum11in a proper arrangement to form a high-quality tire structural member of a fixed thickness.

Suppose that the opposite ends at X=0 and X=D of the forming drum11have a radius r0. Then, it is known from Expression (2) that the strips1can be attached to the forming drum11so that the opposite ends of the strips1are properly arranged on the opposite ends of the forming drum11when the leading end1aand the trailing end1bof each strip1are cut so as to slope at an angle meeting an equation: cos θ0=nw/2πr0to the side edge of the strip1.