BACKGROUND

The invention relates to a tire building machine and a method for forming a tire layer, in particular a breaker ply.

Figure 1 shows a spool with a stock roll of a continuous strip of rubber material that is used in the manufacture of a breaker ply for tires. The rubber material of the continuous strip has the tendency to sag during storage, in particular during the first few minutes after the continuous strip has been wound onto the spool, while the material is still viscous. The sagging causes the continuous strip to widen at the bottom and to narrow at the top by as much as three millimeters. Furthermore, the top of the stock roll tends to be a few centimeters closer to the center of the spool than the bottom of the stock roll. During unwinding of the continuous strip, a width variation can be detected with an amplitude period that substantially corresponds to the circumference of the stock roll, as shown in the graph of figure 2. The continuous strip is used for forming a breaker ply on top of a conveyor. When stitching the subsequent members of the continuous strip for the formation of a breaker ply, the aforementioned width variations cause the following problems .

In a case where the second member is getting wider than the first member, as shown in figures 3A-C, the second member contacts the first member early at the splice gap measuring unit. Both members are held stationary for stitching, while the splice is still open. Such a splice can be characterized as a V-shaped splice. After stitching, the gap is forcibly closed (if at all possible), thereby causing the leading tip of the second member to be joined at an inward position with respect to the desired outer longitudinal edge of the breaker ply.

In a case where the second member is getting narrower than the first member, as shown in figures 4A-D, the second member contacts the first member early at the end opposite to the splice gap measuring unit. The resulting splice can be characterized as an A-shaped splice. The splice gap measuring unit has not yet detected a closing of the gap and will continue to move both together until they meet at the position of the splice gap measuring unit. This causes deformation and tension in the rubber material of both members. Depending on the tackiness of the rubber material, either the trailing end of the first member shifts inwards with respect to the desired outer longitudinal edge of the breaker ply (figure 4C) , or the leading end of the second member shifts outward with respect to the desired outer longitudinal edge of the breaker ply (figure 4D) .

In any of the above cases, the stitching has the undesirable outcome that the longitudinal edge of the breaker ply contains irregularities at the splices between subsequent members of the continuous strip. An example of such irregularities is known as a 'dog ear' or a 'splice offset ' .

Various solutions are known in which tire layers or tire layer members are manipulated after they have been fed onto a conveyor.

For example, WO 2012/139556 Al discloses two conveyor belts, wherein a strip is transferred from one conveyor belt to the other. The downstream conveyor belt is laterally movable with respect to the upstream conveyor belt. A camera is used to detect and compare the trailing tip to the leading tip and to adjust the position of the trailing tip to an optimal value. The strip is subsequently supplied to a drum for application. WO 2012/13556 Al relates to the already finished tire layer and its correct application to a drum. WO 2012/13556 Al does not relate to the process of forming a tire layer out of subsequent members of a continuous strip through stitching.

EP 2 535 175 Al discloses an apparatus for manufacturing ply material, in which cut pieces are transported in a transport direction on a conveyor. Prior to splicing, the relative positions of the cut pieces are measured on the conveyor. EP 2 535 175 Al proposes to use various clamp and attracting devices to lift one of the cut pieces from the conveyor and positioned it in a splice position above another one of the cut pieces.

DE 10 2006 018 642 Al discloses an apparatus for measuring the leading edge of a strip when it passes over a gap between two subsequent conveyors. One of the conveyors is movable in a direction perpendicular to the transport direction to adjust the position of the strip as it is transferred from one conveyor to the other.

DE 43 09 013 Al discloses an apparatus for splicing strips which are transported on a conveyor in a transport direction until a sensor detects an edge of the leading end. The leading tip is then clamped by a clamping device and transported further in the transport direction while another part of the strip is held fixed by another clamping device. Another sensor is used to detect when the leading tip is in the desired position.

US 2003/0141021 Al, US 4,832,780 A, US

2005/0000626 Al and US 5,720,837 A all disclose solutions relating to the manipulation of strips that have been fully placed onto conveyors. Once on the conveyor, the strips are not easily manipulated and additional means are required to effectuate the manipulation.

It is an object of the present invention to provide a tire building machine and a method for forming a longitudinal tire layer, in particular a breaker ply, in which the negative effects of width variations in the continuous strip on the quality of the tire layer can be reduced .

SUMMARY OF THE INVENTION

According to a first aspect, the invention provides a tire building machine for forming a tire layer, in particular a breaker ply, with a longitudinal direction and reinforcement cords extending under an oblique cord angle with respect to the longitudinal direction of the breaker ply, wherein the tire building machine comprises:

- a conveyor which is arranged for transporting the tire layer in a transport direction with its longitudinal direction parallel to the transport direction;

- a feeding device with a retainer for retaining subsequent lengths of a continuous strip with longitudinal reinforcement cords and a drive for driving the retainer with a length of the continuous strip retained thereto over a feeding stroke that crosses with the transport direction at an oblique angle;

- a cutting device for cutting off, after completion of the feeding stroke, a length of the continuous strip to form a tire layer member;

wherein the conveyor is arranged for advancing the cut-off tire layer member in the transport direction over a distance that allows for a subsequent length of the continuous strip to be fed by the feeding device over the feeding stroke alongside the cut-off tire layer member in the transport direction;

wherein the tire building machine further comprises

- a stitching device for stitching, after completion of the feeding stroke of the subsequent length of the continuous strip, a leading edge of the subsequent length of the continuous strip to a trailing edge of the cut-off tire layer member in the transport direction;

- a measuring device for obtaining measuring signals indicative of the mutual parallelism of the leading edge of the subsequent length of the continuous strip and the trailing edge of the cut-off member, during the feeding stroke and prior to the stitching; and

- a control system that is operationally coupled to both the measuring device and the feeding device,

wherein the drive is arranged for adjusting the feeding direction of the retainer during the feeding stroke, wherein the control system is arranged for processing the measuring signals and, after completion of a first part of the feeding stroke, sending drive signals to the drive of the feeding device based on the measuring signals to adjust the feeding stroke of the retainer from a first feeding direction to a second, different feeding direction to improve the mutual parallelism of the leading edge of the subsequent length of the continuous strip and the trailing edge of the cut-off member.

None of the publications as mentioned in the background of the invention disclose adjusting a feeding direction during a feeding stroke that crosses with the transport direction of the conveyor at an oblique angle. By adjusting the feeding direction from the first feeding direction to the second feeding direction during the feeding stroke, a misalignment between the leading edge and the trailing edge can be at least partially compensated prior to the subsequent length of the continuous strip being fed fully alongside the cut-off member, thereby at least partially reducing the negative effects of the width variation in the continuous strip on the tire layer.

In an embodiment the first feeding direction is arranged to be parallel to the oblique cord angle. The lengths of the continuous strip can thus be fed parallel to the oblique cord angle. In particular, as the continuous strip is provided with longitudinal reinforcement cords, the reinforcement cords can extend parallel to the oblique cord angle when feeding in the first feeding direction.

In an embodiment the control system is arranged for sending the drive signals for the second part in a range from forty to ninety percent of the feeding stroke, and preferably in a range of fifty to eighty percent of the feeding stroke. In said range, the second part of the feeding stroke can be of sufficient length to at least partially compensate for the width variations.

In an embodiment the measuring device is arranged for obtaining the measuring signals after at least eighty percent, preferably after at least ninety percent and most preferably after the entire first part of the feeding stroke has been completed. In said range, a substantial part of the first part of the feeding stroke has been completed, such that the measuring device can obtain an accurate measurement of the mutual parallelism along the part of the leading edge of the continuous strip that has already been fed alongside the trailing edge of the tire layer .

In an embodiment the measuring device comprises a first sensor and a second sensor, wherein the first sensor is arranged for measuring and sending a signal indicative of a first gap between the cut-off tire layer member and the subsequent length of the continuous strip at a first measuring position at the beginning of the feeding stroke and a second sensor that is arranged for measuring and sending a signal indicative of a second gap between the cut-off tire layer member and the subsequent length of the continuous strip at a second measuring position further downstream along the feeding stroke. The gaps are an indication of the distance between the tire layer and the continuous strip at the respective measuring positions, from which, assuming that the leading edge and the trailing edge are substantially linear, the mutual parallelism of the leading edge and the trailing edge can be derived. In an embodiment the control system is arranged for determining the difference between the gaps based on the measurement signals from the first sensor and second sensor, wherein, when the first gap is smaller than the second gap, the control system is arranged for adjusting the first feeding direction to the second feeding direction over an angle towards the transport direction, and wherein, when the first gap is greater than the second gap, the control system is arranged for adjusting the first feeding direction to the second feeding direction over an angle away from the transport direction. By adjusting the feeding direction in the aforementioned directions, a slight tilting of the leading edge, and in particular the leading tip, towards or away from the trailing edge of the tire layer can be achieved, thereby improving the mutual parallelism .

In an embodiment the drive is arranged for driving the retainer in a feeding direction with an adjustable vector component in the longitudinal direction of the tire layer and an adjustable vector component perpendicular to the longitudinal direction of the tire layer, wherein adjusting the feeding direction from the first feeding direction to the second feeding direction involves adjusting at least the adjustable vector component in the longitudinal direction of the tire layer. The drive can thus be used to control the vector components individually, to move the retainer in any direction which is a sum of both vector components.

In an alternative embodiment the retainer is arranged for retaining only a part of the subsequent length of the continuous strip at or near the leading end thereof with respect to the transport direction. The alternative retainer allows for adjusting only a part of the subsequent length of the continuous strip, while the remainder of the continuous strip may be retained substantially in place.

In an embodiment thereof the feeding device comprises a supporting body to which the retainer is coupled so as to be movable relative to the supporting body in the longitudinal direction of the tire layer, wherein the drive comprises a primary actuator for driving the supporting body, together with the retainer in the first feeding direction, wherein the drive comprises a secondary actuator for driving the movement of the retainer with respect to the supporting body in the longitudinal direction of the tire layer. The sum of the movement of the supporting body in the first feeding direction and the relative movement of the alternative retainer in the longitudinal direction of the tire layer may result in a movement of the alternative retainer in the second feeding direction .

In a further embodiment thereof the supporting body is provided with additional retaining elements for retaining another part of the continuous strip with respect to the part retained by the retainer. Thus, the supporting body can prevent that the compensation of the leading edge of the continuous strip affects the trailing edge of said continuous strip, thereby preventing accumulation of the compensations during the feeding of subsequent lengths of the continuous strip.

In an embodiment the reinforcement cords are made of metal, wherein the retainer is provided with a plurality of magnets for attracting and retaining the reinforcement cords .

According to a second aspect, the invention provides a Method for forming a longitudinal tire layer, in particular a breaker ply, with a longitudinal direction and reinforcement cords extending under an oblique cord angle with respect to the longitudinal direction of the breaker ply wherein the method comprises the steps of:

- subsequently feeding lengths of a continuous strip with longitudinal reinforcement cords over a feeding stroke that crosses with the transport direction at an oblique angle;

- cutting off, after completion of the feeding stroke, a length of the continuous strip to form a tire layer member;

- advancing the cut-off tire layer member in the transport direction over a distance that allows for a subsequent length of the continuous strip to be fed over the feeding stroke alongside the cut-off tire layer member in the transport direction;

- stitching, after completion of the feeding stroke of the subsequent length of the continuous strip, a leading edge of the subsequent length of the continuous strip to a trailing edge of the cut-off tire layer member in the transport direction;

- obtaining measuring signals indicative of the mutual parallelism of the leading edge of the subsequent length of the continuous strip and the trailing edge of the cut-off member, during the feeding stroke and prior to the stitching; and

- during the feeding stroke adjusting, after completion of a first part of the feeding stroke, the feeding stroke based on the measuring signals from the a first feeding direction to a second, different feeding direction to improve the mutual parallelism of the leading edge of the subsequent length of the continuous strip and the trailing edge of the cut-off member.

None of the publications as mentioned in the background of the invention disclose adjusting a feeding direction during a feeding stroke that crosses with the transport direction of the conveyor at an oblique angle. By adjusting the feeding direction from the first feeding direction to the second feeding direction during the feeding stroke, a misalignment between the leading edge and the trailing edge can be at least partially compensated prior to the subsequent length of the continuous strip being fed fully alongside the cut-off member, thereby at least partially reducing the negative effects of the width variation in the continuous strip on the tire layer.

In an embodiment the first feeding direction is parallel to the oblique cord angle. The lengths of the continuous strip can thus be fed parallel to the oblique cord angle. In particular, as the continuous strip is provided with longitudinal reinforcement cords, the reinforcement cords can extend parallel to the oblique cord angle when feeding in the first feeding direction.

In an embodiment in the second part starts in a range from forty to ninety percent of the feeding stroke, and preferably in a range of fifty to eighty percent of the feeding stroke. In said range, the second part of the feeding stroke can be of sufficient length to at least partially compensate for the width variations.

In an embodiment the measuring signals are obtained after at least eighty percent, preferably after at least ninety percent and most preferably after the entire first part of the feeding stroke has been completed. In said range, a substantial part of the first part of the feeding stroke has been completed, such that the measuring device can obtain an accurate measurement of the mutual parallelism along the part of the leading edge of the continuous strip that has already been fed alongside the trailing edge of the tire layer.

In an embodiment obtaining the measuring signal comprises the steps of measuring a first gap between the cut-off tire layer member and the subsequent length of the continuous strip at a first measuring position at the beginning of the feeding stroke and measuring a second gap between the cut-off tire layer member and the subsequent length of the continuous strip at a second measuring position further downstream along the feeding stroke. The gaps are an indication of the distance between the tire layer and the continuous strip at the respective measuring positions, from which, assuming that the leading edge and the trailing edge are substantially linear, the mutual parallelism of the leading edge and the trailing edge can be derived.

In an embodiment the method comprises the step of determining the difference between the gaps based on the measuring signals, wherein, when the first gap is smaller than the second gap, the first feeding direction is adjusted to the second feeding direction over an angle towards the transport direction, and wherein, when the first gap is greater than the second gap, the first feeding direction is adjusted to the second feeding direction over an angle away from the transport direction. By adjusting the feeding direction in the aforementioned directions, a slight tilting of the leading edge, and in particular the leading tip, towards or away from the trailing edge of the tire layer can be achieved, thereby improving the mutual parallelism .

According to a third aspect, the invention provides a tire building machine for forming a tire layer, in particular a breaker ply, wherein the tire layer, during its formation, is arranged with its longitudinal direction in a transport direction, wherein the tire building machine comprises :

- a feeding device with a retainer for retaining and feeding subsequent lengths of a continuous strip with longitudinally extending reinforcement cords over a feeding stroke that crosses with the longitudinal direction of the tire layer, wherein the feeding device is provided with a drive for driving the retainer in a first feeding direction in which the reinforcement cords extend under an oblique cord angle with respect to the longitudinal direction of the tire layer;

- a cutting device for cutting off, after completion of the feeding stroke, a length of the continuous strip along a cutting line at a tire layer width to form a tire layer member;

- a conveyor for advancing the cut-off tire layer member in the transport direction parallel to the longitudinal direction of the tire layer over a distance that allows for a subsequent length of the continuous strip to be fed by the feeding device over the feeding stroke alongside the cut-off tire layer member;

- a stitching device for stitching, after completion of the feeding stroke of the subsequent length of the continuous strip, a leading edge of the subsequent length of the continuous strip to a trailing edge of the cut-off tire layer member in the transport direction;

- a measuring device for obtaining measuring signals indicative of the mutual parallelism of the leading edge of the subsequent length of the continuous strip and the trailing edge of the cut-off member, during the feeding stroke and prior to the stitching; and

- a control system that is operationally coupled to both the measuring device and the feeding device,

wherein the drive is arranged for adjusting the feeding direction of the retainer, wherein the control system is arranged for processing the measuring signals and, after completion of a first part of the feeding stroke, sending drive signals to the drive of the feeding device based on the measuring signals to adjust the feeding direction of the retainer from the first feeding direction to a second, different feeding direction to improve the mutual parallelism of the leading edge of the subsequent length of the continuous strip and the trailing edge of the cut-off member.

According to a fourth aspect, the invention provides a method for forming a longitudinal tire layer, in particular a breaker ply, wherein the tire layer, during its formation, is arranged with its longitudinal direction in a transport direction, wherein the method comprises the steps of :

- feeding subsequent lengths of a continuous strip with longitudinally extending reinforcement cords over a feeding stroke that crosses with the longitudinal direction of the tire layer in a first feeding direction in which the reinforcement cords extend under an oblique cord angle with respect to the longitudinal direction of the tire layer;

- cutting off, after completion of the feeding stroke, a length of the continuous strip along a cutting line at a tire layer width to form a tire layer member;

- advancing the cut-off tire layer member in the transport direction parallel to the longitudinal direction of the tire layer over a distance that allows for a subsequent length of the continuous strip to be fed over the feeding stroke alongside the cut-off tire layer member;

- stitching, after completion of the feeding stroke of the subsequent length of the continuous strip, a leading edge of the subsequent length of the continuous strip to a trailing edge of the cut-off tire layer member in the transport direction;

- obtaining measuring signals indicative of the mutual parallelism of the leading edge of the subsequent length of the continuous strip and the trailing edge of the cut-off member, during the feeding stroke and prior to the stitching; and

- adjusting, after completion of a first part of the feeding stroke, the feeding direction based on the measuring signals from the first feeding direction to a second, different feeding direction to improve the mutual parallelism of the leading edge of the subsequent length of the continuous strip and the trailing edge of the cut-off member .

The various aspects and features described and shown in the specification can be applied, individually, wherever possible. These individual aspects, in particular the aspects and features described in the attached dependent claims, can be made subject of divisional patent applications .

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be elucidated on the basis of an exemplary embodiment shown in the attached schematic drawings, in which:

figure 1 shows a spool with a stock roll of a continuous strip that has been sagging during storage;

figure 2 shows a graphical representation of the width variation in the continuous strip according to figure 1 as a result of sagging during storage;

figures 3A-3C show the subsequent steps of a known method for stitching members of a breaker ply in a case where the second member is wider than the first member ;

figure 4A-4D show the subsequent steps of a known method for stitching members of a breaker ply in a case where the second member is narrower than the first member;

figure 5 shows a top view of the breaker ply and the continuous strip, supplemented with the parameters for calculating the difference in cord length in the continuous strip as a result of a width variation;

figures 6A-6C show a tire building machine and subsequent steps of a method for stitching members of a breaker ply according to a first embodiment of the invention, in a case where the second member is wider than the first member;

figures 7A-7C show the tire building machine and subsequent steps of an alternative method for stitching members of a breaker ply according to a first embodiment of the invention, in a case where the second member is narrower than the first member; and

figure 8 shows an alternative tire building machine for performing the subsequent steps of the methods according to figures 6A-C and figures 7A-C.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 shows a spool 1 for use in a tire building machine according to the invention. The spool 1 is provided with a winding axis or rotational axis S around which a continuous strip 2 has been wound to form a stock roll 3. The stock roll 3 is stored on the spool 1 for later use in a method for forming a tire layer, in particular a breaker ply 4, as shown in figure 5, figures 6A-6C and 7A- 7C.

The continuous strip 2 is created by continuously extruding or calandering a band of elastomeric or rubber material with a preset strip width Wl while embedding a plurality of mutually parallel, longitudinal reinforcement cords. During storage, the stock roll 3 has the tendency to sag with respect to the spool 1 upon which it is supported. Sagging particularly becomes an issue when the rubber material has a low viscosity. In the example as shown in figure 1, the sagging has been schematically exaggerated. The dashed lines indicate the theoretical contour of the stock roll 3 without sagging. The solid lines show the sagged contour, which is wider by a first width variation Al at the bottom and narrower by a second width variation A2 at the top. The width variations Al, A2 can be in a range up to three millimeters, or even exceeding three millimeters. Furthermore, it can be observed that the top of the stock roll 3 is a few centimeters closer to the rotational axis S of the spool 1 than the bottom of the stock roll 3. During unwinding of the continuous strip 2, width variations Al, A2 can be observed. As shown in figure 2, the width W varies of the length L of the unwound continuous strip 2 by an amplitude that substantially corresponds to the circumference of the stock roll 1.

Figure 5, figures 6A-C and figures 7A-C show the continuous strip 2 and the breaker ply 4 in the tire building machine according to the invention. The tire building machine comprises a feeding device 5, a stitching device 6, a cutting device 7, a conveyor 8 and a measuring device 9 which will be discussed in more detail hereafter.

In figure 5, the situation is shown in which the continuous strip 2 is unwound and supplied alongside the breaker ply 4. The breaker ply 4 is placed on the conveyor 8, which is arranged for advancing or transporting the breaker ply 4 in a transport direction T. The breaker ply 4 has a first longitudinal edge El and a second longitudinal edge E2 which are substantially parallel, and which define the width W2 of the breaker ply 4. The breaker ply 4 has a longitudinal direction parallel to the longitudinal edges El, E2 and parallel to the transport direction T. The breaker ply 4 is provided with a trailing edge 40 with respect to the transport direction T. The trailing edge 40 meets the second longitudinal edge E2 under a sharp angle to form a trailing tip 42 which faces the continuous strip 2.

The continuous strip 2 is fed over a feeding stroke towards the breaker ply 4 in a first feeding direction Fl onto a cutting table 71 of the cutting device 7. The feeding stroke crosses or intersects with the longitudinal direction and/or the transport direction T of the breaker ply 4. The continuous strip 2 comprises the aforementioned band 20 of rubber material and the embedded metal (steel) reinforcement cords 21 (only partially shown) , extending in the longitudinal direction of the continuous strip 2, substantially parallel to the first feeding direction Fl. The continuous strip 2 has a downstream end 22 with respect to the first feeding direction Fl. The downstream end 22 has been cut by a cutter 70 (schematically depicted as scissors, but in practice usually a disc shaped cutter or a guillotine) along a cutting line C under a so called oblique 'breaker angle' Bl with respect to the first feeding direction Fl . The continuous strip 2 comprises a first longitudinal edge and a second longitudinal edge which, downstream of the cutting line C, form a leading edge 23 and a trailing edge 24, respectively, of the continuous strip 2 in the transport direction T. The leading edge 23 and the downstream end 22 meet under a sharp angle to form a triangular leading tip 25 that faces the breaker ply 4. As shown in figure 5, the continuous strip 2 has been fed onto a cutting table 5 of a cutting device (not shown in its entirety) , alongside the trailing edge 40 of the breaker ply 4, such that a length of the continuous strip 2 completely fills the width W2 between the longitudinal edges El, E2 of the breaker ply 4. After the leading edge 23 of the length has been stitched to the trailing edge 40 of the breaker ply 4, the length may be cut off from the continuous strip 2 to form a cut-off, rhomboid shaped tire layer member. The breaker ply 4 is formed by subsequently stitching and cutting off of such tire layer members of the continuous strip 2. The resulting breaker ply 4 contains reinforcement cords 21 extending under a so called oblique 'cord angle', with respect to the transport direction T of the breaker ply 4, parallel to the breaker angle Bl.

In figure 5, the effects of sagging of the stock roll 3 on the characteristics of the continuous strip 2 are shown. LI indicates an optimal cord length of the leading edge 23 of the continuous strip 2 between the first longitudinal edge El and the second longitudinal edge E2 (or the width W2 ) of the breaker ply 4 in case of a continuous strip 2 that has an optimal strip width Wl and an optimal breaker angle Bl . This initial cord length is also representative of the cord length of the reinforcement cords 21 that are embedded in the continuous strip 2. Due to the sagging, the strip width may vary along the longitudinal direction of the continuous strip 2 by a few millimeters in either width direction, as indicated with widening distance Al or narrowing distance A2.

In case of a widening of the continuous strip 2 over the widening distance Al, the breaker angle of the leading edge 23 of the continuous strip 2 with respect to the transport direction T is increased over a first angle difference HI to a second breaker angle B2. As a result, the cord length is reduced by a first cord length difference Dl to a second cord length L2. In case of a narrowing of the continuous strip 2 over the narrowing distance A2, the breaker angle of the leading edge 23 of the continuous strip 2 with respect to the transport direction T is decreased over a second angle difference H2 to a third breaker angle B3. As a result, the cord length is increased by a second cord length difference D2 to a third cord length L3.

The second cord length L2, the third cord length L3, the first cord length difference Dl and the second cord length difference D2 can be calculated as follows:

First, the optimal cord length LI is calculated from the given width W2 of the breaker ply 4 divided by the sinus of the optimal breaker angle Bl. Then, the first angle difference HI or the second angle difference H2 is calculated from the inverse sinus of the value resulting from division of the widening distance Al or the narrowing distance A2, respectively, by the optimal cord length LI. The first angle difference HI or the second angle difference H2 is then subtracted from the optimal breaker angle Bl, to arrive at the second breaker angle B2 or the third breaker angle B3, respectively. The first cord length difference Dl or the second cord length difference D2 can subsequently be calculated by dividing the widening distance Al or the narrowing distance A2, respectively, by the tangent of the second breaker angle B2 or the third breaker angle B3, respectively. Finally, the second cord length L2 can be calculated by substracting the first cord length difference Dl from the optimal cord length LI and the third cord length L3 can be calculated by adding the second cord length difference D2 to the optimal cord length LI .

When such calculations are applied to a width variation by a widening distance Al or a narrowing distance A2 of three millimeters, an optimal breaker angle Bl of twenty degrees and a width W2 of the breaker ply of three hundred millimeters, the resulting cord length differences Dl, D2 are approximately 8 millimeters. Thus, depending on the optimal breaker angle Bl, a width variation Al, A2 of a few millimeters still contributes to a significant cord length difference Dl, D2. When a previously cut-off member of the continuous strip 2 has the optimal cord length LI, and the subsequent length of continuous strip 2 has a non- optimal cord length L2 or L3, the cord length difference Dl, D2 will inevitably cause difficulties in joining the leading edge 23 of the continuous strip 2 with the trailing edge 40 of the breaker ply 4, resulting in open splices, or deformations or rippling of the splice during stitching.

To compensate for the aforementioned effects of sagging of the stock roll 3 on the width Wl of the continuous strip 2, the tire building machine according to the invention is provided with the feeding device 5 and the measuring device 9 which mutually cooperate to compensate for the width variations, as shown in figures 6A-C and 7A- C.

The feeding device 5 is provided with a retainer 50 and a drive 51 for driving the retainer 50. In this exemplary embodiment, the retainer 50 comprises a beam 52 with a plurality of magnets 53 which magnetically attract and retain the metal reinforcement cords 21 in the continuous strip 2. Alternatively, grippers or any other suitable means for retaining the continuous strip 2 may be used. The beam 52 is used to retain the downstream end 22 of the continuous strip 2 and to move it in the feeding direction Fl into a position alongside the breaker ply 4. The drive 51 is a so-called ^y XY drive' which enables controlled movement of the beam 52 with a vector component in an X-direction parallel to the transport direction T and/or a vector component in an Y-direction perpendicular to the transport direction T. The drive 51 of the feeding device 5 is operationally coupled to a control system 54 that is arranged for sending control signals to the drive 51.

The measuring device 9 is arranged for measuring a first gap Gl between the breaker ply 4 and the continuous strip 2 in a direction parallel to the transport direction T at or near the trailing tip 41 of the breaker ply 4, while simultaneously measuring a second gap G2 between the breaker ply 4 and the continuous strip 2 in a direction parallel to the transport direction T further downstream in the feeding direction Fl . In this particular embodiment, the measuring device 9 comprises a first sensor in the form of a first camera 91 and a second sensor in the form of a second camera 92. The first camera 91 is arranged at or near the trailing tip 41 of the breaker ply 4. The first camera 91 is fixed at said position at or near the trailing tip 41. The second camera 92 is attached to the beam 52 so as to be moveable together with the beam 52. As the beam 52 travels downstream in the feeding direction Fl, the second camera 92 passes the first camera 91 and is able to measure the second gap G2 further downstream in the feeding direction Fl . Alternatively, the second camera 92 may be arranged in a fixed or moveable manner independent of the beam 52. The measuring device 9 is operationally coupled to the control system 54 for sending measuring signals indicative of both gaps Gl, G2 to the control system 54.

The control system 54 is optionally provided with a user control (not shown) that allows for the control system 54 to be switched from 'normal mode' to 'compensation mode'. If the continuous strip 2 on a stock roll 1 appears to have a consistent width Wl, the control system 54 can be set to 'normal mode' and the continuous strip 2 can be moved by the feeding device 5 in a single stroke and in a single feeding direction Fl, parallel to the longitudinal direction of the continuous strip 2, into a position fully alongside the breaker ply 4, such that the length of the continuous strip 2 downstream of the cutting line C completely fills the width W2 of the breaker ply 4. As no compensation is required, this process can be performed in a relatively high pace.

However, if the width Wl of the continuous strip 2 is inconsistent, or if the control system 54 is not provided with a user control, the control system 54 is set to operate in 'compensation mode'. In this mode, the control system 54 controls the drive 51 of the feeding device 5 such that the beam 52 feeds a length of the continuous strip 2 in the feeding direction Fl over a first part of the feeding distance or the feeding stroke in which the continuous strip 2 only partially fills the width W2 of the breaker ply 4. In particular, the first part of the feeding stroke brings the continuous strip 2 at least halfway alongside the breaker ply 4, but not completely alongside the breaker ply 4. As can be observed from figures 6A and 7A, in this example, the feeding of the continuous strip 2 in the first feeding direction Fl is interrupted at a distance H from the first longitudinal edge E2 of the breaker ply 4, at approximately eighty to ninety percent of the width W2 of the breaker ply 4. At this moment, both gaps Gl, G2 are measured and measuring signals indicative of both gaps Gl, G2 are send to the control system 54.

The control system 54 is arranged for receiving and processing the received measuring signals. Based on the measuring signals, the control system 54 determines whether there is a difference between both measured gaps Gl, G2. A difference between the measured gaps Gl, G2 is an indication of a widening or a narrowing of the width Wl of the continuous strip 2. In particular, if the distance between the measuring position of the first gap Gl and the measuring position of the second gap G2 in the initial feeding direction Fl is sufficient, the difference between the measured gaps Gl, G2 can be effectively used as an indicator for the orientation or parallelism of the leading edge 23 of the continuous strip 2 with respect to the trailing edge 40 of the breaker ply 4. For the purpose of the invention, leading edge 23 and the trailing edge 40 are assumed to be substantially linear. If a difference is detected, the control system 54 sends a drive signal to the drive 51 to adjust the first feeding direction Fl to an adjusted or different second feeding direction F2, F3 with different vector components X, Y. The second feeding direction F2, F3 also crosses at an oblique angle to the transport direction T.

In particular, the second feeding direction F2,

F3 is chosen such that, during the remaining, second part of the feeding stroke, the length of the continuous strip 2 downstream of the cutting line C is slightly forced into a direction in which the leading edge 23 of the continuous strip 2 becomes more parallel to the trailing edge 40 of the breaker ply 4. In figure 6A, the situation is shown in which the first gap Gl is smaller than the second gap G2. Accordingly, the second feeding direction F2 is adjusted over an angle towards the transport direction T to compensate. As can be observed in figure 6B, after feeding the continuous strip 2 over the second part of the feeding stroke in the second feeding direction F2, the leading edge 23 of the continuous strip 23 has been slightly tilted towards the transport direction T, such that the breaker angle of the continuous strip 2 is reduced, the cord length is increased and the parallelism between the leading edge 23 of the continuous strip 2 and the trailing edge 40 of the breaker ply 4 is improved. In figure 7A, the situation is shown in which the first gap Gl is greater than the second gap G2. Accordingly, the second feeding direction F3 is adjusted over an angle away from the transport direction T to compensate. As can be observed in figure 7B, after feeding the continuous strip 2 over the second part of the feeding stroke in the second feeding direction F3, the leading edge 23 of the continuous strip 23 has been slightly tilted away from the transport direction T, such that the breaker angle of the continuous strip 2 is increased, the cord length has decreased and the parallelism between the leading edge 23 of the continuous strip 2 and the trailing edge 40 of the breaker ply 4 is improved .

During the second part of the feeding stroke, use is made of the mass of the continuous strip 2 and the friction between the continuous strip 2 and the cutting table 5, which effectively limits the freedom of movement of the continuous strip 2 upstream of the cutting line C with the length of the continuous strip 2 that is located downstream of the cutting line C, and which allows for only this downstream length to be at least partially fed in the adjusted feeding direction F2, F3 during the remaining second part of the stroke. As a result, the difference between the measured gaps Gl, G2 can be reduced.

The drive 51 is subsequently operated to feed the remaining length of the continuous strip 2 in the adjusted second feeding direction F2, F3 over the remaining feeding distance or the remaining second part of the stroke (corresponding to the distance H at which the first part of the feeding stroke was interrupted) into a position in which the length of the continuous strip 2 completely fills the width W2 of the breaker ply 4 or in which the leading edge 23 of the continuous strip 2 is completely alongside the trailing edge 40 of the breaker ply 4.

Logically, one would try to fully compensate the difference between the gaps Gl, G2. However, the feeding of the length of the continuous strip 2 downstream of the cutting line C in the adjusted feeding direction F2, F3 will also have an effect on the trailing edge of the continuous strip (not shown) , which, after stitching of the leading edge 23 to the trailing edge 40 of the breaker ply 4, will become the new trailing edge 40 of the breaker ply 4. Thus, the compensation at the leading edge 23 of the continuous strip 2 could have a cumulative effect for the subsequent compensations of the subsequent lengths of the continuous strip 2. Therefore, to achieve or maintain an optimal compensation throughout the process of forming the breaker ply 4, the compensation of the difference between the gaps Gl, G2 for each individual length of the continuous strip 2 should be achieved only partially, for example in the range of eighty to ninety percent. After the leading edge 23 of the continuous strip 2 has at least partially been aligned with respect to the trailing edge 40 of the breaker ply 4, the conveyor 8 is operated to reverse the breaker ply 4 with respect to the transport direction T into abutment with the continuous strip 2, as shown in figures 6C and 7C, respectively. Subsequently, the stitcher 6, which comprises well-known stitcher wheels, is rolled over the abutting leading edge 23 and trailing edge 40 to join said edges by pressure, thereby forming a high quality splice.

Figure 8 shows an alternative embodiment of the feeding device 105, which is provided with a main supporting body 150, in this example in the form of a beam 152 with a series of magnets 53. The drive comprises a primary actuator 151 for moving the beam 152 in the first feeding direction Fl, parallel to the longitudinal direction of the continuous strip 2. The alternative feeding device 105 is provided with a moveable retainer 155 that is coupled to the beam 152 so as to be movable. The drive is provided with a secondary actuator 156, preferably in the form of a piston or a linear drive, which moves the retainer 155 in a direction X parallel to the longitudinal direction of the breaker ply 4 with respect to the beam 152. The secondary actuator 156 has a neutral or center position, and can be moved with respect to the neutral or center position in the longitudinal direction of the breaker ply 4 in the transport direction T or in a direction opposite to the transport direction T, depending on the required direction of the compensation of the leading edge 23 of the continuous strip 2. Apart from the way the compensation is achieved, the compensation is similar to the compensation as described above in relation to figures 6A-C and 7A-C. A benefit of the movability of the retainer 155 with respect to the main supporting body 150 is that the movable retainer 155 is able to retain, move and compensate the leading edge 23 only, while the trailing edge of the continuous strip 2 (not shown) , is retained in place by the beam 152. Thus, the aforementioned accumulation of the compensation for subsequent lengths of the continuous strip 2 could be reduced.

In summary, the invention relates to a tire building machine and a method for forming a tire layer wherein the tire building machine comprises a feeding device with a retainer for retaining lengths of a continuous strip and a drive for driving the retainer over a feeding stroke that crosses with the transport direction at an oblique angle, wherein the drive is arranged for adjusting the feeding direction during the feeding stroke to improve the mutual parallelism of the leading edge of the subsequent length of the continuous strip and the trailing edge of the cut-off member.

It is to be understood that the above description is included to illustrate the operation of the preferred embodiments and is not meant to limit the scope of the invention. From the above discussion, many variations will be apparent to one skilled in the art that would yet be encompassed by the spirit and scope of the present invention .