WO1998008070A1

WO1998008070A1 - Method of balance screening a pneumatic tire with a tire uniformity machine

Info

Publication number: WO1998008070A1
Application number: PCT/US1996/013706
Authority: WO
Inventors: William Frank Dunn; Joshua Michael Hofmann; John Michael Maloney; George Jeffrey Lipczynski
Original assignee: The Goodyear Tire & Rubber Company
Priority date: 1996-08-23
Filing date: 1996-08-23
Publication date: 1998-02-26

Abstract

A method for checking the balance of a pneumatic tire mounted in a tire uniformity machine is disclosed. Radial and lateral sensors mounted to a tire uniformity machine measure radial and lateral run-out of a tire inflated to a low pressure when the tire is rotated at both low and high speeds of rotation. The resulting signals being outputted by the radial and lateral sensors are converted to radial and a lateral deflection waveforms. These deflection waveforms are compared with empirical data which correlates deflection to imbalance force to determine whether the tires have acceptable imbalance. Tires found to have acceptable imbalance are marked for further balance testing and correction.

Description

METHOD OF BALANCE SCREENING A PNEUMATIC TIRE WITH A TIRE UNIFORMITY MACHINE

FIELD OF THE INVENTION

This invention relates to the field of pneumatic tire balancing, and more particularly, to a method for balance screening pneumatic tires using a tire uniformity machine.

BACKGROUND OF THE INVENTION

In the art of manufacturing pneumatic tires, rubber flow in the mold or minor differences in the dimensions of the belts, beads, liners, treads, plies of rubberized cords, etc., sometimes cause non-uniformities in the final tire. When non-uniformities are of sufficient magnitude, they will cause a tire to be imbalanced. Regardless of its cause, when the imbalance exceeds an acceptable maximum amount, the ride of the vehicle to which such an imbalanced tire is mounted will be adversely affected. Essentially, two separate physical phenomena contribute to the imbalance of a tire, static imbalance and couple imbalance. Static imbalance is the result of net centrifugal forces created by non-niformities in the distribution of tire mass about the rotational axis of the tire. Non-uniformity of tire mass distribution is caused by manufacturing variations which create tire imbalance. As an element of tire mass rotates about an axis, centrifugal force is experienced by the element, which tends to push it away from the center of rotation, the magnitude of this centrifugal force being:

F = m x ω² x r wherein = mass of the element, ω = rotational velocity, and r = radius of the circle of rotation. If the mass of the tire is distributed equally about the center of rotation, the centrifugal force on each of the elements of tire mass would be negated by an equal and opposite force acting upon an element of tire mass located on the opposite side of the center of rotation, and thus no net centrifugal force would act upon the tire during rotation. However, when the distribution of tire mass is nonuniform, so that there are elements of greater mass or elements located at greater radial distance from the center of rotation, the centrifugal force on these elements is not canceled by the opposing force acting on the element of tire mass located on the opposite side of the center of rotation. In such cases, the tire experiences a net centrifugal force acting through the element of either greater tire mass or located at a greater distance from the center of rotation. These net centrifugal forces cause the circumferential tread to deflect radially outward at these elements, and thus the tire distorts, resulting in static imbalance about the center of rotation. Couple imbalance is caused by the above described mass distribution non-uniformities, or mass imbalances, about the radius of the tire which create net moments about an axis in a plane which is through the centerline of the tread radius and perpendicular to the axis of rotation of the tire. The magnitude of such a moment equals the net force acting on the mass non- uniformity, or the imbalance force, multiplied by the distance of the mass non-uniformity from the centerline of the tread (and thus the axis located in the plane through the tread centerline) . This moment can be expressed as: M = F x d = (m x ω² x r) x d wherein variables m, ω, and r are the properties described above and d = distance between the mass non-uniformity and the centerline of the tread. The effect of such moments is that the tire tends to wobble along its axis of rotation. Couple imbalance is usually caused by two "heavy spots" about the circumference of the tire, located 180° apart about the axis of rotation and in separate planes, the planes being parallel and equally spaced from the plane through the centerline of the tread. Such pairs of heavy spots often occur because rubber flow in the mold during tire production causes off register molding of the tire. The combined effect of the static imbalance and the couple imbalance is referred to as the dynamic imbalance of a tire, which is the total imbalance experienced by a rotating tire. As static imbalance and couple imbalance are two distinct and mutually independent physical phenomena, the dynamic behavior of a rotating tire can be analyzed by overlaying the effect of static imbalance on the effect of couple imbalance. Virtually all tires have some differences in the distribution of the tire mass which causes dynamic imbalance to be present, but the imbalance will be negligible, or at least acceptable, in a well- made tire.

In the usual tire manufacturing process, tires are placed first in a tire uniformity machine to correct force variations and then placed in a tire balancing machine to check for unacceptable imbalance. Sufficiently large non-uniformities in a tire will cause, besides imbalance as outlined above, force variations on a surface, such as a road, against which the tires roll. These force variations produce vibrational and acoustical disturbances in the vehicle upon which the tires are mounted, and when such variations exceed an acceptable maximum level, the ride of a vehicle utilizing such tires will be adversely affected.

Consequently, there have been a number of methods developed to correct excessive force variations by removal of rubber from the shoulders and/or the central region of the tire tread by means such as grinding. Most of these correction methods include the steps of indexing the tire tread into a series of circumferential increments and obtaining a series of force measurements representative of the force exerted by the tire as these increments contact a surface. This data is then interpreted and rubber is removed from the tire tread in a pattern generated by this interpretation.

Force variation correction methods are commonly performed with a tire uniformity machine (TUM) , which includes an assembly for rotating a test tire against the surface of a freely rotating loading wheel. In such an arrangement, the loading wheel is moved in a manner dependent on the forces exerted by the rotating tire and those forces are measured by appropriately placed measuring devices. When a tire being tested yields less than acceptable results, shoulder and center rib grinders are used to remove a small amount of the tire tread at precisely the location of non-uniformities detected by the measuring devices. As the tire is rotated, it is measured and ground simultaneously. In a sophisticated tire uniformity machine, such as a Model No. D70LTX available from the Akron Standard Co. of Akron Ohio, the force measurements are interpreted by a computer and rubber is removed from the tire tread using grinders controlled by the computer. Examples of machines utilizing these methods are disclosed in U.S. Patent Nos . 3,739,533, 3,946,527, 4,914,869, and 5,263,284. Once a tire undergoes correction for force variations in a TUM, it is common manufacturing practice to place the tire in a tire balance machine to measure the amount of imbalance of the tire. In the prior art, these balance machines were dedicated to checking the imbalance of a tire and performed no other task. Typically, the tires would be mounted on a rim in a manner similar to that of the tire uniformity machine, inflated to a particular pressure, and the static and couple imbalances checked by one of a variety of well-known methods. In present, state-of- the-art tire manufacturing processes, a large percentage of the tires checked have acceptable amounts of imbalance. Given this percentage of acceptably balanced tires, the present method of manufacturing tires, in which balance checking requires mounting and inflating the tires on a balance machine separate from the tire uniformity machine, is a time-consuming and expensive process. Limiting balance checking to only tires in which the balance is questionable would save time, energy, and cost due to the elimination of the necessity of this manufacturing operation for the majority of tires produced.

Nothing in the prior art, suggests the combination of method steps and component elements arranged and configured for both correcting for excessive force variation and checking for imbalance on a single machine.

It is an object of the present invention to provide a method for balance checking pneumatic tires in a tire uniformity machines to obviate the problems and limitations of the prior art methods of balance checking. Other objects of this invention will be apparent from the following description and claims.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a method of evaluating the amount of imbalance of a pneumatic tire on existing tire uniformity machines adapted for this procedure subsequent to evaluating and correcting for any force variations. A tire uniformity machine is modified by the addition of a radial run-out sensor and a lateral run-out sensor which are connected to the existing computer of the tire uniformity machine. These sensors are preferably non-contact, capacitive or laser sensors which measure the deflection of a rotating tire resulting from static and dynamic imbalance forces. After any necessary corrective grinding is completed, the tire is deflated to a pressure sufficient only to maintain tire shape. The tire is then rotated at a first rotational speed on the tire uniformity machine, which is relatively low, and the radial runout and lateral run-out are measured for one revolution of the tire. These low-speed measurements are sent to the computer controlling the tire uniformity machine. The tire is then accelerated to a second rotational speed, which is relatively high, and the radial run-out and lateral run-out are again measured for one revolution of the tire and these high-speed measurements are also sent to the computer controlling the tire uniformity machine. The computer then subtracts the low-speed waveforms from the high speed waves forms to achieve radial and lateral deflection universal charge waveforms. The computer next compares the deflection waveforms to empirically derive correlation data to determine the static and couple imbalances acting on the tire. Tires with unacceptable balance are marked for further balance checking and tires which are marked acceptable undergo any other necessary processing. BRIEF DESCRIPTION OF THE DRAWINGS

The structure, operation, and advantages of the presently preferred embodiment of the invention will become further apparent upon consideration of the following description taken in conjunction with the accompanying drawings, wherein: Fig. 1 is a schematic illustration of a force variation machine adapted for balance checking tires with a tire mounted thereon in accordance with the invention;

Figs. 2A and 2B, collectively Fig. 2, are detailed views of a radial run-out sensor as positioned for static imbalance evaluation;

Figs. 3A and 3B, collectively Fig. 3, are detailed views of a lateral run-out sensor as positioned for couple imbalance evaluation;

Fig. 4 illustrates a flow diagram of the operation of the referenced invention;

Fig. 5 is a chart of radial high speed and low speed waveforms of an example tire balance check to illustrate the method of the present invention; and

Fig. 6 is a chart of radial deflection waveform and static imbalance force waveform, of the example tire balance check to illustrate the method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

Referring to Figs. 1 and 2, there is illustrated a typical tire uniformity machine (TUM) 10, also known as a force variation machine (FVM) , adapted for balance screening a tire 12 mounted within the machine. Tire 12 is typically a pneumatic tire having a circumferential tire tread 13, with top and bottom shoulder regions and a central region between the top and bottom shoulder regions, and sidewalls 15A,15B. The tire 12 can be mounted on a rim 14 secured to a tire spindle 16 and inflated to a desired pressure. A variable speed motor 17, shown with phantom lines, rotates the tire spindle 16 and rim 14. The tire 12 can be placed under load by a load wheel 18, which is rotatably supported on a spindle 20 extending through the load wheel. During the testing of the tire for non-uniformities, the load wheel 18 is pressed against the tire to load the inflated tire with a specified force (for example, 600 to 1900 lb) to simulate road conditions and against which the tread of the tire rotates. Bearing blocks (not shown) are mounted to a carriage (not shown) which supports the ends of the spindle 20 and are moved by conventional means, such as an electric motor (not shown) operating through a ball-and-screw connection, to move the load wheel 18 into and out of engagement with the tire 12. A shoulder grinding assembly 24 is located substantially 180° with respect to tire 12 from load wheel 18. The shoulder grinding assembly 24 includes substantially identical top and bottom shoulder grinders (only 24A is illustrated and described) , which include grinding wheels that are powered by motors and are independently moved into and out of engagement with the shoulder regions of tire 12. As shown, the top shoulder grinder 24A, including a grinding wheel 26A powered by a motor 28A, can be moved into and out of engagement with the shoulder portions of tire 12 by any conventional means, such as hydraulic servo devices (not shown) . A center grinder assembly 30 is located adjacent wheel 12 approximately 90° counter-clockwise about tire 12 from load wheel 18. The center grinder assembly 30 has a grinding wheel.32 that is powered by a motor 34 and is moved into and out of engagement with the central region of the tread of tire 12 by conventional means, such as with an hydraulic servo device (not shown) .

Conventional radial and lateral load cells 36 and 38 are mounted on spindle 20 with load wheel 18 suspended therebetween. The radial and lateral load cells 36,38 are typically used to measure the lateral and radial forces transmitted from the tire 12 as it rotates against the load wheel 18. Each of the load cells 36,38 includes a lateral load cell section conventionally used to measure the lateral force exerted by the tire 12 against load wheel 18 in a direction parallel to the axis of rotation extending about which the load wheel rotates. The load cells 36,38 also include a radial load cell section conventionally used to measure the radial force at the point of intersection of the tire 12 and the load wheel 18 exerted by the tire 12 against the load wheel 18 and through spindle 20 about which the load wheel rotates . Voltage signals, proportionate to the magnitude of the radial and lateral forces, are generated by load cells 36,38 and inputted through lines 42 and 44, respectively, into an electric signal conditioner 40, which converts the force measurement voltage signals generated by the load cells 36,38 into signals which can be inputted to and stored in a computer 45. The electric signal conditioner 40 includes radial top and lateral top amplifiers (not shown) connected by line 44 to load cell 38 and radial bottom and lateral bottom amplifiers (not shown) connected by line 42 to load cell 36.

Computer 45, conventionally programmed to determine the conicity, lateral force values, radial run-out, and radial force values of the tire 12, and to control the corrective grinding action to take, as discussed in U.S. Patent Application Serial No. 08/534,089, entitled METHOD OF CORRECTING CONICITY, RADIAL RUN OUT, AND FORCE VARIATIONS IN A PNEUMATIC TIRE, assigned to the Goodyear Tire & Rubber Company, the assignee of the present invention, and incorporated in its entirety by reference herein is connected to the shoulder grinding assembly 24 and to the center grinder assembly 26 to position and operate the grinding assemblies, as required.

The present invention measures and analyzes the radial and lateral deflections of a tire rotating at a first, lower speed, and then at a second, higher speed, in tire uniformity machine 10 to determine the imbalance forces acting on the tire. In particular, the invention is directed towards the addition of two sensors 46,48 to the standard tire uniformity machine 10 described above. The first sensor 46 is a no-contact capacitive probe or laser type device mounted so as to enable measurement of radial run-out of a tire 12 mounted on a machine 10. The second sensor 48 is a no-contact capacitive probe 48 or laser type device mounted to enable measurement of lateral run-out, of a tire 12 mounted in the machine 10. The two probes 46,48 are connected via an electrical signal conditioner 47 to the existing computer 45 of tire uniformity machine 10 to which the probes 46,48 send run-out data for analysis of the imbalance of the tire after the machine has completed any necessary corrective tire uniformity grinding of the tire and before the tire is removed from the machine .

To provide a tire uniformity machine 10 with the capability of balance checking, a radial run-out sensor 46 and a lateral run-out sensor 48 are mounted to the standard machine described above and connected through electrical cables 52 and 56, respectively, an electrical signal conditioner 47 which converts the measured voltage signals generated by sensors 46 and 48 into signals which are then inputted into computer 45. Referring to Figs. 1 and 2, a radial run-out sensor 46 is preferably movably mounted (not shown) to machine 10 in a manner which enables sensing face 47 of sensor 46 to be located at a fixed position in near proximity to the center of circumferential tread 13 of tire 12 and also enables adjustment of the location of sensing face 47 to allow for balance checking of tires of different diameters. In the preferred embodiment, radial run-out sensor 46 is a commercially available no-contact capacitive probe or laser type as a no-contact probe is most desirable for the high operating speeds preferred. However, it is within the scope of the present invention to use other means for radial run-out sensor 46, such as a mechanical contact probe, in which case radial run-out sensor 46 would be mounted to tire uniformity machine 10 in a manner which enabled sensing face 47 to physically contact a circumferential tread 13 of tire 12 during balance checking.

Radial run-out sensor 46 senses a target area 50, see Fig. 2A, on the center of circumferential tread 13 of tire 12 as the circumferential tread rotates past the fixed position of the radial run-out sensor. The radial run-out sensor 46 measures the distance R between the sensing face 47 and the target area 50 on circumferential tread 13. Target area 50 is preferably a circular area which is sufficiently large so as not to be affected by the height differences of the tread pattern. Radial run-out sensor 46 generates voltage signals which are proportional to distance R, which are sent from the radial runout sensor through electrical cable 52 to electrical signal conditioner 47 and then to computer 45. The radial run-out is measured at low speed to quantify the tire run-out . When there is static imbalance in the tire 12, the resulting deflections of circumferential tread 13 caused by the net centrifugal forces acting on the tread wall will cause variations in the run-out waveform during a revolution of tire 12. The resulting variations of the run-out waveform, are determined (preferably by the computer 45) .

Referring to Figs. 1 and 3, a lateral run-out sensor 48 is preferably movably mounted (not shown) to machine 10 in a manner which enables sensing face 49 of sensor 48 to be located at a fixed position in near proximity to one sidewall 15, preferably 15A, of tire 12 and also enables adjustment of the location of sensing face 49 to allow for balance checking of tires of different widths. In the preferred embodiment, lateral run-out sensor 48 is a commercially available no-contact capacitive probe, or laser type, as a no-contact probe is most desirable for the high operating speeds preferred. However, it is within the scope of the present invention to use other means for lateral run-out sensor 48, such as a mechanical contact probe, in which case lateral run-out senor 48 would be mounted to tire uniformity machine 10 in a manner which enabled sensing face 49 to physically contact a sidewall 15 of tire 12 during balance checking. Lateral run-out sensor 48 senses a target area 54 on the outer surface of centerwall 15 of a tire 12 as the centerwall rotates past the fixed position of lateral run-out sensor for low speed and high speed measurements. The lateral run-out sensor 48 measures the lateral run-out waveform between the sensing face 49 and the target area 54 on the outer surface of sidewall 15.

Lateral run-out sensor 48 generates voltage signals which are proportional to the lateral run-out variation and which are sent from the lateral run-out sensor through electrical cable 56 to electrical signal conditioner 47 and then to computer 45. The lateral run-out is measured at low speed to quantify tire lateral run-out. When there is couple imbalance in the tire 12, the resulting "wobble" or motion of tire 12 along its axis of rotation, will cause variations in distance L during a revolution of tire 12. The resulting variations of the lateral run-out waveform, are determined (preferably by the computer 45) .

To enable the tire uniformity machine 10 to measure the amount of static imbalance force or couple imbalance moment acting on a tire, the computer 45 must be able to correlate the measured radial deflection D_R to the static imbalance force and to correlate the measured lateral deflection D to the couple imbalance moment. The radial deflection D_R and the lateral deflection D_L are proportional to static imbalance force and couple imbalance moment, respectively, by different factors. Furthermore, the correlation between the each type of deflection and the imbalance force or moment which causes it will be different for tires of different sizes, geometries, material properties, etc. Therefore, there is a first factor correlating radial deflection to static imbalance force, and a second factor correlating lateral deflection to couple imbalance moment, for each size tire within each class of tire. Once all these correlation factors are determined and stored within computer 45, tire uniformity machine 10 can then balance check any desired tire by the method outlined later in this specification.

To determine these correlation factors, a series of tests are conducted for each size tire within each class of tire for which it is desired to be balance screened on the particular machine. For a particular size tire of a particular class, a perfectly balanced tire 12 undergoes a series of trials to correlate both the radial run-out sensor 46 and lateral run-out sensor 48 for that particular type of tire. To correlate the radial run-out sensor 46, a number of trials are conducted wherein, for each trial, a load of known weight is attached at a known location on the centerline of circumferential tread 13, the tire is rotated and the distance R at that location is measured with the radial run-out sensor. Then, the distance R measured when the load is attached is subtracted from a reference distance R₀ measured without the load (thus when the tire was balanced) to achieve the radial deflection D_R caused by the known load. The static imbalance force caused by the known load is easily calculated by the method using the formula F = m x ω² x r as discussed in the Background of the Invention. Therefore, a factor which correlates a measured deflection to an amount of static imbalance force is now known, the static force-radial deflection correlation factor F_CF. To ensure accuracy of the empirically derived correlation factor F_CF, a number of tests should be conducted for each tire type in which in which the load is incrementally increased or decreased for each test run, which results in a corresponding increase or decrease in the amount of radial deflection D_R measured. Then, the static force-radial deflection correlation factor F_CF for that type of tire would be the average of all the empirically derived correlation factors F_CF, which should be approximately the same from each test. However, because of the phenomena by which the rubber experiences "growth" at high rotational speeds, a correlation factor derived at a low speed would overestimate the imbalance force at high speed because some of the measured change in radial distance R will be caused by this rubber growth in addition to the deflection due to static imbalance force. Therefore, the basic test procedure outlined above should be conducted at the desired operational high rotation resulting in a correlation factor which is necessarily smaller then one determined at a low rotational speed (i.e., a load will cause greater measured deflection at high speed due to the effect of rubber growth) . The static force-radial deflection correlation factor F_CF is then stored in the computer 45 for each type of tire 12 to enable the computation of the static imbalance forces acting upon a tire being tested by measuring the radial deflections D_R about, the circumference of the tire. In the usual case, the static force- radial deflection correlation factor F_CF will be expressed as a number of ounces of static imbalance force per so many thousands of an inch of radial deflection.

To calibrate the lateral run-out sensor 48, the same basic procedure is used, except that two loads are added for each test, which are located 180° from each other as measured about the circumference of the tire and located equidistant from, and on opposite sides of, the tire tread centerline. The result of a series of these tests will be a couple moment -lateral deflection correlation factor M_CF for each type of tire 12 by which the lateral deflections D_L measured during a revolution of a tire being tested can be used to determine the couple imbalance moments acting upon the tire. In the usual case, each couple moment-lateral deflection correlation factor M_CF will be expressed as a number of in-ounces of couple imbalance moment per so many thousands of an inch of lateral deflection. It must be noted that these factors only determine the net moment at an angular location on the circumference of the tire. As a smaller mass non-uniformity at two inches from tread centerline can cause the same moment as a larger mass non-uniformity at one inch from tread centerline, both non-uniformities are indistinguishable from each other by the method of the present invention. The routine for balance screening a pneumatic tire mounted on a tire uniformity machine 10 is shown in the flow diagram of Fig. 4. First, a tire which has undergone any necessary grinding in the tire uniformity process is completely deflated from the pressure required for the correction process or deflated to an internal pressure sufficient only to maintain the shape of the tire. The tire 12 will still be fully centered about the rim of the tire uniformity machine 10, but the low pressure will allow the tire to react to the imbalance forces. Next, the tire is brought to a designated low rotational speed, most preferably about 60 rpm. Then, the radial run-out sensor 46 measures the radial distances R about the circumferential tread 13, and the lateral run-out sensor 48 measures the lateral distances L about a sidewall 15, for one revolution of tire 12. Referring to Figs. 5 and 6, the voltage signal generated by the measurement of the radial distance R is sent to computer 45 via electrical signal conditioner 47 and stored as a low speed radial distance waveform 60 and the voltage signal generated by the measurement of the lateral distance L is sent to the computer and stored as a low speed lateral distance waveform 62. Fig. 5 is an illustration of the radial run-out waveforms 60, 64 which would be generated by a computer of a tire uniformity machine according to the present invention when a tire with several mass non-uniformities on the tire are balance screened. The example shown in Fig. 5 has the mass non-uniformities located at about 180° and 270°. Although the tire has some imbalance forces present at the low rotational speed, the amount of the imbalance forces and moments should not be large enough to cause radial or lateral deflections, respectively, sufficient to be detectable by the radial and lateral run-out sensors 46 and 48, respectively. Therefore, each low speed waveform 60 and 62 is essentially a reference baseline which indicates the inherent run-outs of the tire and measures the actual dimensions about the tread and sidewalls.

Next, the tire is accelerated to a high speed, most typically about 400 rpm. Then, the radial run-out sensor 46 once again measures the radial distance R about the circumferential tread 13, and the lateral run-out sensor 48 again measures the lateral distance L about a sidewall 15, for one revolution of tire 12. Referring to Fig. 5, the voltage signal generated by this second measurement of the radial distance R is sent to the computer and stored as a high speed radial distance waveform 64 and the voltage signal generated by the second measurement of the lateral distance L is sent to the computer and stored as a high speed lateral distance waveform 66 (not shown) . As the centrifugal forces are proportional to the square of the angular velocity (using the formula F = m x ω² x r as discussed in the Background of the Invention) , the imbalance forces and moments present at the high rotational speed are significantly greater than at the low rotational speed, and thus even small mass distribution non-uniformities will generate enough static imbalance force and couple imbalance moment to cause measurable radial and lateral deflections.

Referring to Figs. 4, 5, and 6, with the four waveforms 60, 62, 64, and 66 stored in the memory of computer 45, the computer then calculates the static imbalance forces and the couple imbalance moments acting on the tire 12. The computer can mathematically operate on the waveforms by subtracting the low speed radial distance waveform 60 from the high speed radial distance waveform 64 to get a radial deflection waveform 68 and subtracting the low speed lateral distance waveform 62 from the high speed lateral distance waveform 66 to get lateral deflection wave form 70. Next, the computer 45 utilizes the static force- radial deflection correlation factor F_CF to convert the radial deflection waveform 68 into a static imbalance waveform 72 and utilizes couple moment-lateral deflection correlation factor M_CF to convert the lateral deflection wave form 70 into a couple imbalance moment waveform 74. Fig. 6 illustrates the radial deflection waveform 68 and the static imbalance force waveform 72 that would be generated by the data of Fig. 5. If the any value of force on the static imbalance waveform 72 or moment on the couple imbalance waveform 74 exceeds a preset limit of acceptable imbalance, the tire is marked by conventional tire marking means with a first mark (not shown) . If all force and moment values on the static and couple imbalance waveforms, respectively, are less than or equal to an acceptable imbalance limit, then the tire 12 is marked by conventional marking means with a second mark (not shown) . Finally, the tire 12 is demounted from the tire uniformity machine 10, and if marked with the first mark, and thus having unacceptable imbalance, it is routed to a balance machine for more extensive balance checking, whereas if the tire is marked with the second mark, it is routed for any other necessary processing. Furthermore, the data from this balance screening process can be stored for other future analysis.

While the invention has been described in combination with embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing teachings. Accordingly, the invention is intended to embrace all such alternatives, modifications and variations as fall within the scope of the appended claims .

Claims

We claim :

1. A method of balance screening a pneumatic tire on a tire uniformity machine comprising the steps of: rotating said tire about a rotational axis of said tire at a first speed; measuring the radial run-out of said tire at said first speed with a radial sensor; inputting a first radial signal from said radial sensor into a computer as a first radial distance waveform; rotating said tire at a second speed; measuring the radial run-out of said tire at said second speed with said radial sensor; inputting a second radial signal from said radial sensor into said computer as a second radial distance waveform; generating a radial deflection waveform corresponding to the difference between said first and second radial distance waveforms; and comparing values of radial deflection represented in said radial deflection waveform with an acceptable value of radial deflection.

2. The method of claim 1 further including the steps of : converting said radial deflection waveform into a static imbalance waveform wherein said values of radial deflection are converted to values of force; and comparing said values of force of said static imbalance waveform to an acceptable value of force.

3. The method of claim 2 further including the step of outputting a first signal whenever one of said values of force of said static imbalance waveform exceeds said acceptable value of force.

4. The method of claim 3 further including the step of outputting a second signal whenever all of said values of force of said static imbalance waveform are less than said acceptable value of force .

5. The method of claim 4 further including the steps of : marking said tire with a first mark when said first signal is outputted; and marking said tire with a second mark when said second signal is outputted.

6. The method of claim 1 further comprising the steps of : measuring the lateral deflection of said tire at said first speed with a lateral sensor; inputting a first lateral signal from said lateral sensor into said computer as a first lateral distance waveform; measuring the lateral deflection of said tire at said second speed with said lateral sensor; inputting a second lateral signal from said lateral sensor into said computer as a second lateral distance waveform; generating a lateral deflection waveform corresponding to the difference between said first and second lateral distance waveforms; and comparing values of said lateral deflection represented in said lateral deflection waveform with acceptable values of deflection.

7. The method of claim 6 further including the steps of: converting said lateral deflection waveform into a couple imbalance waveform wherein said values of lateral deflection are converted to values of moment ,* and comparing said values of moment of said couple imbalance waveform to an acceptable value of moment .

8. The method of claim 7 further including the step of outputting a first signal if any of said values of moment represented in said couple imbalance waveform exceeds said acceptable value of moment.

9. The method of claim 8 further including the step of outputting a second signal if all of said values of moment represented in said couple imbalance waveform are less than or equal to said acceptable value of moment .

10. The method of claim 9 further including the steps of: marking said tire with a first mark when said first signal is outputted; and marking said tire with a second mark if said second signal is outputted.

11. The method of claim 6 further including the step of inflating said tire to an internal pressure sufficent to maintain the shape of said tire prior to said step of rotating said tire at said first rotational speed.

12. The method of claim 6 wherein said step of rotating said tire at a first speed includes the step of rotating said tire at a speed of at least about 60 rpm.

13. The method of claim 12 wherein said step of rotating said tire at a second speed includes the step of rotating said tire at a speed of at least between about 400 rpm.

14. The method of claim 1 further including the steps of : inputting into a signal conditioner a first radial voltage signal from said radial sensor; inputting a first radial signal corresponding to said first radial voltage signal from said signal conditioner into said computer as said first radial distance waveform,- inputting into said signal conditioner a second radial voltage signal from said radial sensor; and inputting a second radial signal corresponding to said second radial voltage signal from said signal conditioner into said computer as said second radial distance waveform.

15. The method of claim 14 wherein: said step of inputting said first and second radial signals with said radial sensor includes inputting said first and second radial signals with a no-contact capacitive probe; and said step of inputting said first and second lateral signals with said lateral sensor includes inputting said first and second lateral signals with a no-contact capacitive probe.

16. A method of balance screening a pneumatic tire on a tire uniformity machine comprising the steps of: rotating said tire at a first speed; generating a first lateral signal at said first speed with a lateral sensor; inputting into a computer said first lateral signal as a low speed lateral distance waveform; rotating said tire at a second speed which is higher than said first speed; generating a second lateral signal at said second speed with said lateral sensor; inputting into said computer said second lateral signal as a high speed lateral distance waveform; generating a lateral deflection waveform corresponding to the difference between said high speed lateral distance waveform and said low speed lateral distance waveform; determining a couple imbalance waveform by converting said lateral deflection waveform to values of moment; and comparing said values of moment of said couple imbalance waveform to an acceptable value of moment .

17. The method of claim 16 further including the step of outputting a first signal if any of said values of moment of said couple imbalance waveform exceeds said acceptable value of moment .

18. The method of claim 17 further including the step of outputting a second signal if all of said values of moment of said couple imbalance waveform are less than or equal to said acceptable value of moment .

19. The method of claim 18 further including the steps of: marking said tire with a first mark when said first signal is outputted; and marking said tire with a second mark when said second signal is outputted.

20. The method of claim 16 further including the step of bringing said tire to an internal pressure sufficient to maintain the shape of said tire prior to said step of rotating said tire at said first rotational speed.

21. The method of claim 16 further including the steps of: inputting into a signal conditioner a first lateral voltage signal; inputting said first lateral signal corresponding to said first lateral voltage signal from said signal conditioner into said computer as said low speed lateral distance waveform; inputting into said signal conditioner a second lateral voltage signal; and inputting said second lateral signal from said signal conditioner into said computer as said high speed lateral distance waveform.

22. The method of claim 16 wherein said step of generating said first lateral signal with said lateral sensor includes generating said first lateral signal with a no-contact capacitive probe .

23. A method of balance screening a pneumatic tire on a tire uniformity machine comprising the steps of: rotating said tire at a first speed; measuring a first radial run-out of said tire at said first speed; rotating said tire at a second speed which is higher than said first speed; measuring a second radial run-out of said tire at said second speed; determining the radial deflection of said tire by calculating the difference between said measured second and said measured first radial run-out; converting said radial deflection of said tire to values of force; and comparing said values of force to an acceptable value of force .

24. The method of claim 23 further comprising the steps of: measuring a first lateral run-out of said tire at said first speed; measuring a second lateral run-out of said tire at said second speed; determining the lateral deflection of said tire by calculating the difference between said measured second lateral run-out and said measured first lateral run-out; converting said lateral deflection to values of moment; and comparing said values of moment to an acceptable value of moment .

25. The method of claim 24 wherein: said step of measuring said first and second radial run-out of said tire includes measuring said radial run-out with a no- contact capacitive probe,* and said step of measuring said first and second lateral run-out of said tire includes measuring said lateral run-out with a no- contact capacitive probe.

26. The method of claim 23 further including the steps of: outputting a first signal if any of said values of force exceed said acceptable value of force; and outputting a second signal if all of said values of force are less than or equal to said acceptable value of force.

27. The method of claim 26 further including the steps of: marking said tire with a first mark whenever said first signal is outputted; and marking said tire with a second mark whenever said second signal is outputted.

28. The method of claim 24 further including the steps of: outputting a third signal if any of said values of moments exceed said acceptable value of moment; and outputting a fourth signal if all of said values of moment are less than or equal to said acceptable value of moment.

29. The method of claim 26 further including the steps of marking said tire with a third mark whenever said third signal is outputted; and marking said tire with a fourth mark whenever said fourth signal is outputted.