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  Tire manufacturing method for improving the uniformity of a tireUSPTO Application #: 20060231191Title: Tire manufacturing method for improving the uniformity of a tire Abstract: A tire manufacturing method includes a method for optimizing the uniformity of a tire by reducing the after cure radial force variation. The after cure radial force variation vector is modeled as a vector sum of each of the vectors representing contributions arising from the tire building steps—the “tire room effect vector” and a vector representing contributions arising from the vulcanization and uniformity measurement steps—the “curing room effect vector.” In further detail, both the tire room and curing room effect vectors can be further decomposed into sub-vectors representing each radial force variation contribution for which a measurable indicator is available. For a series of tires, the method obtains such measurements as the before cure radial runout (RRO) at one or more stages of the building sequence, measurements of loading angles on the tire building equipment, and measurements made during vulcanization process. (end of abstract) Agent: Michelin North America, Inc. Intellectual Property Department - Greenville, SC, US Inventors: William David Mawby, George Phillips O'Brien, Eugene Marshall Persyn, James Michael Traylor USPTO Applicaton #: 20060231191 - Class: 156110100 (USPTO) Related Patent Categories: Adhesive Bonding And Miscellaneous Chemical Manufacture, Methods, Surface Bonding And/or Assembly Therefor, Making Flexible Or Resilient Toroidal Shape; E.g., Tire, Inner Tube, Etc. The Patent Description & Claims data below is from USPTO Patent Application 20060231191. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE [0001] This application is a continuation of previously filed PCT application "Tire Manufacturing Method for Improving the Uniformity of a Tire", assigned PCT/US2004/039021, filed Nov. 19, 2004, which is a continuation-in-part of PCT application "Tire Manufacturing Method for Improving the Uniformity of a Tire", assigned PCT/IB2003/006462, filed Nov. 21, 2003. BACKGROUND OF THE INVENTION [0002] The present invention relates to a manufacturing method for tires, more specifically a method for improving the uniformity of a tire by reducing the after cure radial force variation. In a tire, and more precisely, a radial tire, the after cure radial force variation (RFV) can be affected by many variables introduced from the process of assembly of the green (uncured) tire and during curing of the tire. When the radial force variation in a cured tire exceeds acceptable limits, the result may be unwanted vibrations affecting the ride and handling of the vehicle. For these reasons, tire manufacturers strive to minimize the level of radial force variation in the tires delivered to their customers. [0003] A well-known and commonly practiced method to improve the after cure RFV is to grind the tread surface of the tire in the zones corresponding to excess radial force. This method is effective, but has the drawback of creating an undesirable surface appearance and of removing wearable tread rubber from the product. In addition, this method requires an extra manufacturing step and uses expensive equipment. Alternatively, the after cure RFV may be improved by the method described in U.S. Pat. No. 5,365,781 where the sidewalls of the cured tire are physically deformed in a controlled manner in response to a measured uniformity characteristic. This method eliminates the undesirable removal of tread rubber, but still requires an extra manufacturing step and high-cost equipment. [0004] An alternative to after cure correction of RFV is to treat the sources of RFV in the tire before cure. For example, it is well known in the tire industry to stagger the starting points of the various tire products during the assembly process, followed by observing the effect on after cure RFV. These data are then used to specify an optimum arrangement of product start points for each of the tire building steps according to the configuration that best minimizes after cure RFV. Another approach is disclosed in U.S. Pat. No. 5,882,452 where the before cure radial runout (RRO) of the tire is measured, followed by a process of clamping and reshaping the uncured tire to a more circular form. [0005] Still another approach to a manufacturing method for improved uniformity involves a method where the factors relating to tire building and tire curing that contribute to after cure RRO or RFV are offset relative to a measured before cure RRO. An example of a typical method is given in Japanese Patent Application JP-1-145135. In these methods a sample group of tires, usually four, are placed in a given curing mold with each tire rotated an equal angular increment. The angular increment is measured between a reference location on the tire, such as a product joint, relative to a fixed location on the curing mold. Next, the tires are vulcanized and their composite RFV waveforms recorded. The term "composite waveform" means the raw waveform as recorded from the measuring device. The waveforms are then averaged by superposition of each of the recorded waveforms upon the others. Superposition is a point by point averaging of the recorded waveforms accomplished by overlaying the measured composite waveform from each tire. The effects of the vulcanization are assumed to cancel, leaving only a "formation" factor related to the building of the tire. In like manner, another set of sample tires is vulcanized in a curing mold and their respective RFV waveforms are obtained. The respective waveforms are again averaged by superposition, this time with the staring points of the waveforms offset by the respective angular increments for each tire. In this manner, the effects of tire building are assumed to cancel, leaving only a "vulcanization factor." Finally, the average waveforms corresponding to the formation factor and the vulcanization factor are superimposed. The superimposed waveforms are offset relative to each other in an attempt to align the respective maximum of one waveform with the minimum of the other waveform. The angular offset thus determined is then transposed to the curing mold. When uncured tires arrive at the mold, each tire is placed in the mold at the predetermined offset angle. In this manner, the formation and vulcanization contributions to after cure RFV are said to be minimized. A major drawback to this method is its assumption that the formation and vulcanization contributions to after cure RFV are equivalent for each tire. In particular, the factors contributing to the formation factor can vary considerably during a manufacturing run. In fact, these methods contain contradictory assumptions. The methodology used to determine the vulcanization factor relies on an assumption that the step of rotation of the tires in the curing mold cancels the tire building (or formation) effects. This assumption is valid only when the contribution of before cure RRO is consistent from one tire to the next tire, without random contributions. If this assumption is true, then the subsequent method for determination of the formation factor will produce a trivial result. [0006] Further improvements have been proposed in Japanese Patent Application JP-6-182903 and in U.S. Pat. No. 6,514,441. In these references, methods similar to those discussed above are used to determine formation and vulcanization factor waveforms. However, these methods add to these factors an approximate contribution of the before cure RRO to the after cure RFV. The two methods treat the measured before cure RRO somewhat differently. The method disclosed in reference JP-6-198203 optimizes RRO effects whereas the method disclosed in U.S. Pat. No. 6,514,441 estimates RFV effects by application of a constant stiffness scaling factor to the RRO waveform to estimate an effective RFV. Both these methods continue to rely on the previously described process of overlapping or superpositioning of the respective waveforms in an attempt to optimize after cure RFV. [0007] The most important shortcoming of all the above methods is their reliance of superpositioning or overlapping of the respective waveforms. It is well known in the tire industry that the vehicle response to non-uniformity of RFV is more significant in the lower order harmonics, for example harmonics one through five. Since, the above methods use composite waveforms including all harmonics, these methods fail to optimize the RFV harmonics to which the vehicle is most sensitive. In addition, a method that attempts to optimize uniformity using the composite waveforms can be shown, in some instances, to produce after cure RFV that actually increases the contribution of the important lower order harmonics. In this instance, the tire can cause more vehicle vibration problems than if the process were not optimized at all. Therefore, a manufacturing method that can optimize specific harmonics and that is free of the aforementioned assumptions for determining the effects of tire formation and tire vulcanization would be capable of producing tires of consistently improved uniformity. SUMMARY OF THE INVENTION [0008] In view of the above background, the present invention provides a tire manufacturing method that can effectively reduce the after cure radial force variation (RFV) of each tire produced. The method of the present invention operates to optimize each harmonic of RFV. A composite RFV signal, such as those described above, is a scalar quantity that is the variation of the tire's radial force at each angular position around the tire from the average radial force corresponding to the vertical load applied to the tire. When this composite is decomposed into its respective harmonic components, each harmonic of RFV can be expressed in polar coordinates as an after cure RFV vector. This vector has a magnitude equal to the peak-to-peak magnitude of the force variation of the respective harmonic and an azimuth equal to the angular difference between the measuring reference point and the point of maximum RFV. [0009] The method of the present invention provides a significant improvement over previous methods by employing a vectorial representation of the several factors that contribute to the measured after cure RFV for a tire produced by a given process. The after cure RFV vector is modeled as a vector sum of each of the vectors representing RFV contributions arising from the tire building steps--the "tire room effect vector" and a vector representing RFV contributions arising from the vulcanization and uniformity measurement steps--the "curing room effect vector." In further detail, both the tire room and curing room vectors can be further decomposed into sub-vectors representing each RFV contribution for which a measurable indicator is available. For a series of tires, the method obtains such measurements as the before cure radial runout (RRO) at one or more stages of the building sequence, measurements of loading angles on the tire building equipment, and measurements made during vulcanization process. After vulcanization, the tires are mounted on a uniformity measurement machine and the measured after cure RFV harmonic components are obtained. At this point, none of the coefficients for the magnitude and azimuth of the sub-vector components is known. [0010] The present invention further improves on previously described methods since it does not rely on manipulation of the measured, composite RFV waveforms to estimate the tire room and curing room effects and does not rely on any of the previously described assumptions. The present invention uses the aforementioned measured data as input to a single analysis step. Thus, the coefficients of all the sub-vectors are simultaneously determined. Once these coefficients are known, the tire room effect vector and curing room effect vector are easily calculated. Thereafter, as the individual tires are manufactured, the before cure RRO and other manufacturing data are measured and recorded at one or more steps during the manufacture of the tires. These data are input to the vector model and the magnitude and azimuth of the tire room effect are calculated. Finally, the estimated tire room and curing room effect vectors are used to calculate the angular orientation of the uncured tire in the curing mold that will minimize after cure RFV for that individual tire. In summary, A method for improving the uniformity of a tire comprises the steps of: [0011] (a) Determining a set of vector coefficients for estimating the after cure radial force variation of a tire; [0012] (b) Estimating the after cure uniformity of an individual tire comprising the sub-steps of: [0013] (i) Measuring a before cure radial runout characteristic of said individual tire; [0014] (ii) Choosing a harmonic of radial force variation to be optimized; [0015] (iii) Estimating said after cure uniformity from said vector coefficients; [0016] (c) Aligning said individual tire at a predetermined curing room azimuth angle, loading said individual tire in said curing mold, and curing said tire. [0017] The method of the invention just described further improves on previous methods in its treatment of the factors relating before cure RRO to after cure RFV. It has been found that RRO variations on the before cure tire do not always produce an after cure RFV contribution that is a scalar multiple of the RRO vector either in magnitude or azimuth. Thus, a scalar representation that relies on a simple stiffness factor can lead to erroneous result. [0018] The contribution of green tire RRO to after cure RFV may at least include effects owing to the radial RRO of the green tire carcass, the RRO of the tread and belt assembly, and a certain level of RRO owing to manufacturing tooling effects not accounted for by any of the green tire RRO effects. In the present invention method, the contribution of the green RRO to after cure RFV is modeled as the vector product of a gain vector GC and a green tire RRO vector GR1. The gain vector correctly models the transformation from before cure RRO to after cure RFV. At least one pair of vector coefficients corresponds to the gain vector. [0019] A first part of the green tire vector can be estimated by combining the first harmonic RRO vector of the green carcass, GR1C, with a carcass gain vector, GNC. The vector product of GNC and GR1C is known as the carcass effect vector. This effect may vary from tire to tire. [0020] A second part of the green tire vector may be modeled by combining the first harmonic of the RRO vector of the green tread and belt assembly, GR1T, with a tread and belt assembly gain vector, GNT. The vector product of GNT and GR1T is known as the tread and belt assembly effect vector. This effect may also vary from tire to tire. [0021] A third part of the green tire vector is due to "tooling" effects not captured by GR1C or GR1T. These tooling vectors are constant vectors and whose magnitude is not expected to vary from tire to tire. Examples of the tooling effects are vector components related to tire building apparatus such as the First Stage Building drum vector, the Second Stage Building drum vector, Tread and Belt Assembly Building drum vector, and the Transfer Ring vector. The Intercept vector models any other constant effect not described by any of the previous vectors. [0022] The tooling effects allow an improvement to the accuracy of the model. The measured RRO is the sum of the actual green tire RRO and the RRO of the measuring device upon which the tire is currently mounted, be it building drum or a measurement apparatus. In this improvement of the method, the step of determining a set of vector coefficients further compromises the sub-step of recording a loading angle of a tire carcass on any or a combination of the first stage tire building drum, second stage tire building drum, or transfer ring. Likewise, the step of estimating the after cure uniformity of an individual tire further compromises the sub-step of recording a loading angle of a carcass of an individual tire on the same tooling. [0023] The tooling effects may be manipulated during the tire building steps to minimize further the after cure RFV. This is accomplished by altering the magnitude of the tire room effect vector according to an optimization criterion. This method comprises the steps of: [0024] Determining a set of vector coefficients for estimating the after cure radial force variation of a tire; [0025] (b) Estimating the after cure uniformity of an individual tire comprising the sub-steps of: [0026] (i) Measuring a before cure radial runout characteristic of said individual tire; Continue reading... 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