Patent Description:
The manufacture of treads for vehicle tires is typically made with extruders. Treads are also conventionally formed of several layers of material, which may be made of different materials in order to provide the desired performance. It is important that each tread layer have a uniform and consistent thickness for tire uniformity and performance. It is known to use radar technology for tread layer thickness measurements during tread manufacture. This technology, however, has significant limitations when a tread layer contains one or more conductive compounds that have a low electrical resistivity. Such materials absorb radiation from the radar technology, and the measurement of the conductive tread layer becomes problematic or impossible. It is thus desired to have a method and an apparatus that overcome this limitation.

<CIT> describes a method in accordance with the preamble of claim <NUM>.

The invention relates to a method of accordance with claim <NUM> and to an apparatus in accordance with claim <NUM>.

The invention provides in a first preferred aspect a method of measuring a thickness of a tire tread comprising the steps of: providing a tire tread, wherein the tire tread has a first tread layer formed of a conductive compound and a second tread layer formed of a non-conductive compound; continuously conveying the tire tread with a first sensor and a second sensor arranged above and below the tire tread, respectively, wherein the first and second sensors are configured for emitting first and second radiation beams, respectively, into the tire tread and receiving from the first radiation beam a first reflected radiation beam from a surface of the first tread layer and determining a first distance d1, receiving from the second radiation beam a second reflected radiation beam from an interface of the first and second tread layers and determining a second distance d2, and receiving from the second radiation beam a third reflected radiation beam from a surface of the second tread layer and determining a third distance d3, and wherein the first and second sensors are connected together at a fixed height D; and carrying out a continuous material thickness measurement of the first and second tread layers by emitting the first and second radiation beams by the first and second sensors, respectively, receiving the first, second, and third reflected radiation beams, and then determining a thickness d4 of the first tread layer by subtracting distances d1, d2, and d3 from the fixed height D.

The invention provides in a second preferred aspect an apparatus for measuring a depth of each tread layer of a tire tread having at least two tread layers comprising: a bridge table having an upper surface for conveying the tire tread thereon and a plurality of support legs to support the bridge table, a first sensor and a second sensor, wherein the first sensor is connected to a step motor mounted to an upper rail located above the upper surface of the bridge table for translating the first sensor across a width of the upper surface of the bridge table, wherein the first sensor is rigidly connected to the second sensor by a translating support frame, and wherein the translating support frame and the second sensor translate with the first sensor.

The invention thus allows a continuous on-site monitoring of extruded tread layers.

"Ply" means a continuous layer of rubber-coated parallel cords.

"Radial" and "radially" mean directions radially toward or away from an axis of rotation of a tire.

<FIG> illustrates a measurement system <NUM> for measuring a thickness of each layer of a tire tread or a tire component, such as a sidewall or ply composite, wherein each layer may be made of a different compound. A typical tire tread is formed of different layers of compounds to provide a desired rolling resistance and other performance characteristics.

<FIG> illustrates a typical tire tread having a base tread layer <NUM> formed of a base tread compound, a middle tread layer <NUM> formed of a first tread compound, and an outer tread layer <NUM> formed of a second tread compound. The base tread compound, the first tread compound, and the second tread compound are each electrically non-conductive.

As shown in <FIG>, a terahertz (THz) sensor <NUM> may be arranged above (or below) the tire tread to measure a thickness of each tread layer <NUM>, <NUM>, <NUM>. The terahertz sensor <NUM> has a radiation source for emitting continuous electromagnetic radiation beams or pulses in a THz frequency range. For the sake of simplicity, in the remaining disclosure, the term "beam" shall be inclusive of a beam or a pulse. The terahertz sensor <NUM> preferably continuously emits a high frequency incident radiation beam <NUM> that travels through the air and the tread layers <NUM>, <NUM>, <NUM>. The incident radiation beam <NUM> is in a frequency range of <NUM> to <NUM> THz, and more preferably in a frequency range of <NUM> to <NUM>. A reflection of the incident radiation beam occurs at a radially outer surface <NUM> of the outer tread layer <NUM>, at an interface <NUM> between the outer and middle tread layers <NUM>, <NUM>, at an interface <NUM> between the middle and base tread layers <NUM>, <NUM>, and at a radially inner surface <NUM> of the base tread layer <NUM>. Thus, the incident radiation beam <NUM> is reflected from the radially outer surface <NUM> of the outer tread layer <NUM> and is shown as a reflected radiation beam <NUM>. Likewise, the incident radiation beam <NUM> is reflected from the interface <NUM> between the outer and middle tread layers <NUM>, <NUM> and is shown as a reflected radiation beam <NUM>. Also, the incident radiation beam <NUM> is reflected from the interface <NUM> between the middle and base tread layers <NUM>, <NUM> and is shown as reflected radiation beam <NUM>. Lastly, the incident radiation beam <NUM> is reflected from the radially inner surface <NUM> of the base tread layer <NUM> and is shown as reflected radiation beam <NUM>.

The terahertz sensor <NUM> includes a receiving device for receiving the reflected radiation beams <NUM>, <NUM>, <NUM>, <NUM>, wherein a distance from the radially outer surface <NUM> of the outer tread layer <NUM>, the tread interfaces <NUM>, <NUM>, and the radially inner surface <NUM> of the base tread layer <NUM> to the terahertz sensor <NUM>, respectively, is measured. The thicknesses of each tread layer <NUM>, <NUM>, <NUM> can then be calculated.

The receiving device of the terahertz sensor <NUM> that receives each reflected radiation beam <NUM>, <NUM>, <NUM>, <NUM> records data in a time domain format or in a frequency domain format. A time between reflections is a time of flight, or TOF, and is used to calculate a thickness of a tread layer. The equation to calculate a thickness of a tread layer is: <MAT> wherein c is the speed of light, and RI is the refractive index of each tread layer.

<FIG> illustrates a measurement system <NUM> for measuring a thickness of each layer of a tire tread similar to that of <FIG>, but which includes a tire tread having an outer tread layer <NUM> formed of an electrically conductive compound, or having a volume resistivity of less than <NUM> E <NUM> Ohm*cm, as determined using a Keithley Resistivity Chamber. As shown in <FIG>, the terahertz sensor <NUM> emits the incident radiation beam <NUM>, which travels through the air, a radially outer surface <NUM> of the outer tread layer <NUM>, the outer tread layer <NUM>, the middle tread layer <NUM>, and the base tread layer <NUM>. The incident radiation beam <NUM> is reflected from a radially outer surface <NUM> of the outer tread layer <NUM> and is shown as the reflected radiation beam <NUM>. The reflected radiation beam <NUM> is then received by the receiving device of the terahertz sensor <NUM>. However, because the tread has a conductive outer tread layer <NUM>, the reflected radiation beams <NUM>, <NUM>, <NUM> are absorbed by the outer tread layer <NUM>. The reflected radiation beams <NUM>, <NUM>, <NUM> are thus not received by the receiving device of the terahertz sensor <NUM>. As a result, a distance from the terahertz sensor <NUM> to the other surface and interfaces <NUM>, <NUM>, <NUM> cannot be determined, and ultimately, a thickness of tread layers <NUM>, <NUM>, <NUM>. In order to overcome this problem, the following method and apparatus may be utilized.

<FIG> illustrates a method of a double sided, differential measurement using a dual sensor measurement system <NUM> to determine a thickness of each layer of a tire tread or a tire component having a conductive outer layer.

Specifically, as shown in <FIG>, a tire tread includes an outer tread layer <NUM> formed of a conductive compound, or a layer having low emissivity, a middle tread layer <NUM> formed of a non-conductive compound, and a base tread layer <NUM> formed of a non-conductive compound. An upper terahertz sensor <NUM> has a radiation source for emitting continuous electromagnetic radiation beams in a THz frequency range. The upper terahertz sensor <NUM> emits an incident radiation beam or pulse <NUM> that travels through the air, the outer tread layer <NUM>, the middle tread layer <NUM>, and the base tread layer <NUM>. The incident radiation beam <NUM> is reflected from a radially outer surface <NUM> of the outer tread layer <NUM> and is shown as a reflected radiation beam <NUM>. The reflected radiation beam <NUM> is received by a receiving device of the upper terahertz sensor <NUM> and a distance d11 between the upper terahertz sensor <NUM> and the radially outer surface <NUM> is determined.

For the purpose of this application, an electrically non-conductive compound means a compound having a volume resistivity of at least <NUM><NUM> Ohm*cm, as determined using a Keithley Resistivity Chamber.

For the purpose of this application, an electrically conductive compound means a compound having a volume resistivity of less than <NUM><NUM> Ohm*cm, as determined using a Keithley Resistivity Chamber, preferably less than <NUM><NUM> Ohm*cm.

The incident radiation beam <NUM> is also reflected from an interface <NUM> between the outer tread layer <NUM> and the middle tread layer <NUM>, an interface <NUM> between the middle tread layer <NUM> and the base tread layer <NUM>, and a radially inner surface <NUM> of the base tread layer <NUM>. However, each of these reflected radiation beams is absorbed by the conductive outer tread layer <NUM>. As a result, a distance between the upper terahertz sensor <NUM> and each interface and surface <NUM>, <NUM>, <NUM> cannot be determined, and ultimately, a thickness d12 of the outer tread layer <NUM>.

In order to determine the thickness d12 of the outer tread layer <NUM>, a lower terahertz sensor <NUM> is used in conjunction with the upper terahertz sensor <NUM>. The lower terahertz sensor <NUM> also has a radiation source for emitting continuous electromagnetic radiation beams in a THz frequency range. The lower sensor <NUM> emits an incident radiation beam or pulse <NUM> that travels through the air, the radially inner surface <NUM> of the base tread layer <NUM>, and each tread layer <NUM>, <NUM>, <NUM>. The incident radiation beam <NUM> is reflected from the radially outer surface <NUM> of the outer tread layer <NUM>, however, it is absorbed by the conductive outer tread layer <NUM>. Because the tread layers <NUM> and <NUM> are non-conductive, reflections of the incident radiation beam <NUM> are possible with respect to tread layers <NUM> and <NUM>. The incident radiation beam <NUM> is reflected from the radially inner surface <NUM> of the base tread layer <NUM> and is shown as a reflected radiation beam <NUM>. The reflected radiation beam <NUM> is received by a receiving device of the lower terahertz sensor <NUM> and a distance d21 between the lower terahertz sensor <NUM> and the radially inner surface <NUM> is determined. Also, the incident radiation beam <NUM> is reflected from the interface <NUM> of the middle tread layer <NUM> and the base tread layer <NUM> and is shown as a reflected radiation beam <NUM>. The reflected radiation beam <NUM> is received by the receiving device of the lower terahertz sensor <NUM> and a distance d22 between the lower terahertz sensor <NUM> and the interface <NUM> of the middle tread layer <NUM> and the base tread layer <NUM> is determined. Additionally, the incident radiation beam <NUM> is reflected from the interface <NUM> of the middle tread layer <NUM> and the outer tread layer <NUM> and is shown as a reflected radiation beam <NUM>. The reflected radiation beam <NUM> is received by the receiving device of the lower terahertz sensor <NUM> and a distance d23 between the lower terahertz sensor <NUM> and the interface <NUM> of the middle tread layer <NUM> and the outer tread layer <NUM> is determined.

The thickness d12 of the outer tread layer <NUM> can then be determined as follows: <MAT> wherein D is the fixed distance or height between the sensors.

<FIG> illustrates a typical scenario when a continuous measurement system <NUM> may be utilized. A tire tread or tire component <NUM> is continuously formed by an extrusion system <NUM> and then continuously conveyed on a conveyor belt system <NUM> to the continuous measurement system <NUM>.

As shown in <FIG>, a continuous measurement system <NUM> includes a bridge table <NUM> having an upper surface <NUM> for supporting a tire tread or a tire component <NUM>. The bridge table <NUM> includes a plurality of support legs <NUM>. The measurement system <NUM> further includes an upper terahertz sensor <NUM> and a lower terahertz sensor <NUM>. The upper terahertz sensor <NUM> is mounted to a step motor <NUM>. The step motor <NUM> is optionally mounted on a C-frame or an upper rail <NUM> located above the upper surface <NUM> of the bridge table <NUM>. In an example including the optional upper rail <NUM>, the upper rail <NUM> is mounted across a width of the bridge table <NUM>, and thus perpendicular to a longitudinal axis of the bridge table <NUM>. The upper terahertz sensor <NUM> can thus translate across the width of the bridge table <NUM>, and thus a width of the tire tread or tire component <NUM>, by the step motor <NUM> to take continuous depth measurements of each surface and interface of each layer of the tire tread or the tire component <NUM>.

The lower terahertz sensor <NUM> is fixedly connected to the upper terahertz sensor <NUM> via a translating support frame <NUM> so that the upper and lower terahertz sensors <NUM>, <NUM> maintain a fixed height apart from each other of a distance D and move in sync together. The upper and lower terahertz sensors <NUM>, <NUM> are mounted to the translating support frame <NUM>. The translating support frame <NUM> has an upper frame member <NUM> connected to the upper terahertz sensor <NUM>, a lower frame member <NUM> connected to the lower terahertz sensor <NUM>, and two opposed side members <NUM>, <NUM> that are rigidly connected to the upper and lower frame members <NUM>, <NUM>. The translating support frame <NUM> has an open interior or window <NUM> that is positioned around a portion of the bridge table <NUM> to allow the tire tread or tire component <NUM> to freely pass through the window <NUM> while the upper and lower sensors <NUM>, <NUM> take measurements. The translating support frame <NUM> and upper and lower terahertz sensors <NUM>, <NUM> translate in unison by the step motor <NUM>. The lower terahertz sensor <NUM> is optionally connected to the lower support rail <NUM> by a support member <NUM> to provide stability.

Each terahertz sensor <NUM>, <NUM> has a adiation source for emitting electromagnetic radiation beams or pulses in a THz frequency range and a receiving device for receiving a reflected radiation by a layer of the tire tread or the tire component <NUM>. The electromagnetic radiation beams or pulses are in the terahertz frequency range of <NUM> to <NUM> THz, and more preferably in a frequency range of <NUM> to <NUM>.

<FIG> illustrates a method of a double sided, differential measurement using a dual sensor system <NUM> that is similar to the method shown in <FIG>. <FIG> shows a tire tread having a non-conductive outer tread cap layer <NUM>, an optional non-conductive inner tread cap layer <NUM>, a conductive base tread layer <NUM>, and an optional conductive cushion gum layer <NUM>. Because the tread <NUM> includes the conductive base tread layer <NUM> and the optional conductive cushion gum layer <NUM>, a dual sensor measurement system <NUM> having an upper sensor <NUM> and a lower sensor <NUM> is needed to determine a thickness of the tread layers <NUM>, <NUM>, <NUM>, <NUM>.

In some examples, the lower sensor <NUM> may be a lower frequency sensor. The lower sensor <NUM> measures a depth of the conductive base tread layer <NUM> and a depth of the optional conductive cushion gum layer <NUM>. If a lower frequency sensor is used, a preferred frequency range is <NUM> to <NUM>. A pulsed terahertz radar may also be used for the lower sensor <NUM>. The pulsed sensor may have a frequency range of <NUM> to <NUM> THz or <NUM> to <NUM>.

In examples where the optional cushion gum layer <NUM> is not included, the lower sensor <NUM> emits an incident radiation beam <NUM> that travels through the air, a radially inner surface <NUM> of the base tread layer <NUM>, and the base tread layer <NUM>. The incident radiation beam <NUM> is reflected from the radially inner surface <NUM> of the base tread layer <NUM> and is shown as a reflected radiation beam <NUM>. The reflected radiation beam <NUM> is received by a receiving device of the lower sensor <NUM> and a distance between the lower sensor <NUM> and the radially inner surface <NUM> of the base tread layer <NUM> is determined.

In examples where the optional cushion gum layer <NUM> is included, the lower sensor <NUM> emits an incident radiation beam <NUM> that travels through the air, a radially inner surface <NUM> of the cushion gum layer <NUM>, the cushion gum layer <NUM>, and the base tread layer <NUM>. The incident radiation beam <NUM> is reflected from the radially inner surface <NUM> of the cushion gum layer <NUM> and is shown as a reflected radiation beam <NUM>. The reflected radiation beam <NUM> is received by the receiving device of the lower sensor <NUM> and a distance between the lower sensor <NUM> and the radially inner surface <NUM> of the cushion gum layer <NUM> is determined.

In examples where there the optional inner tread cap layer <NUM> is not included, the lower sensor emits an incident radiation beam <NUM> that travels through the air, the radially inner surface <NUM> of the optional cushion gum layer <NUM> (if included), the optional cushion gum layer <NUM> (if included), and the base tread layer <NUM>. The incident radiation beam <NUM> from the lower sensor <NUM> is reflected from an interface <NUM> of the base tread layer <NUM> and the outer tread layer <NUM> and is shown as a reflected radiation beam <NUM>. The reflected radiation beam <NUM> is received by the receiving device of the lower sensor <NUM> and a distance between the lower sensor <NUM> and the interface <NUM> of the base tread layer <NUM> and the outer tread layer <NUM> is determined.

Additionally, in examples where the optional inner tread cap layer <NUM> is included, the lower sensor emits an incident radiation beam <NUM> that travels through the air, the radially inner surface <NUM> of the optional cushion gum layer <NUM> (if included), the optional cushion gum layer <NUM> (if included), and the base tread layer <NUM>. The incident radiation beam <NUM> from the lower sensor <NUM> is reflected from an interface <NUM> of the base tread layer <NUM> and the inner tread cap layer <NUM> and is shown as a reflected radiation beam <NUM>. These measurements may be used to determine a thickness of each conductive tread layer <NUM>, <NUM>.

In some examples, the upper sensor <NUM> may be the same as the lower sensor <NUM>. In other examples, a frequency modulated continuous wave (FMCW) terahertz radar is used for the upper sensor <NUM>, which measures the non-conductive outer tread cap layer <NUM> and the optional non-conductive inner tread cap layer <NUM>. The FMCW frequency may be in a range of <NUM> to <NUM> with a bandwidth of <NUM>. When a FMCW radar is used, a distance to each interface or layer is given by: <MAT> where.

In examples where the optional inner tread cap layer <NUM> is not included, the upper sensor <NUM> emits an incident radiation beam <NUM> that travels through the air, the radially outer surface <NUM> of the outer tread cap layer <NUM>, and the outer tread cap layer <NUM>. The incident radiation beam <NUM> is reflected from the radially outer surface <NUM> of the outer tread cap layer <NUM> and is shown as a reflected radiation beam <NUM>. The incident radiation beam <NUM> is also reflected from an interface <NUM> of the outer tread cap layer <NUM> and the base tread layer <NUM> and is shown as a reflected radiation beam <NUM>. The reflected radiation beams <NUM>, <NUM> are received by a receiving device of the upper sensor <NUM> and distances between the upper sensor <NUM> and the radially outer surface <NUM> of the outer tread cap layer <NUM> and the upper sensor <NUM> and the interface <NUM> of the outer tread cap layer <NUM> and the base tread layer <NUM> are determined.

In examples where the optional inner tread cap layer <NUM> is included, the upper sensor <NUM> emits an incident radiation beam <NUM> that travels through the air, the radially outer surface <NUM> of the outer tread cap layer <NUM>, the outer tread cap layer <NUM>, and the inner tread cap layer <NUM>. The incident radiation beam <NUM> is reflected from the interface <NUM> of the outer tread cap layer <NUM> and the inner tread cap layer <NUM> and is shown as a reflected radiation beam <NUM>. Additionally, the incident radiation beam <NUM> is reflected from an interface <NUM> of the inner tread cap layer <NUM> and the base tread layer <NUM> and is shown as a reflected radiation beam <NUM>. These measurements may be used to determine a thickness of each tread layer <NUM>, <NUM>.

In cases where it is difficult to see an interface of the tread layers due to small differences in refractive index RI of less than <NUM>%, it is possible to better "see" an interface by using the upper and lower sensors <NUM>, <NUM>, and then superimposing spectra data collected from the upper and lower sensors <NUM>, <NUM>.

The measurement system <NUM> may further include an electronic control system that is communicatively coupled with the upper and lower sensors <NUM>, <NUM> and a step motor connected to the upper sensor <NUM>. The electronic control system may include a processor and a memory, in combination with a plurality of sensors and actuators, to carry out the various controls described herein. In one example, an evaluation device is included as a module in a control system. Further, the control system may include a display for displaying data regarding a tire generated by the evaluation device. For example, radiation pulses described below may be displayed on the display.

The measurements as described above can be carried out both with a THz pulse or a THz wave, such as a sinusoidal wave, as excitation. In pulse systems, we speak of time domain spectrometers; in wave systems, we speak of frequency domain spectrometers. There are apparatuses that detect both an amplitude and a travel time of a signal, as well as apparatuses that only determine an amplitude.

By Fourier transformation, a measured time signal can be converted to a frequency domain. An amplitude is recovered in the frequency domain in a form of a frequency-dependent amplitude that is in a form of an amplitude spectrum, and a travel time is recovered in a form of a frequency-dependent phase, that is in a form of a phase spectrum. For a spectral analysis, a so-called transfer function can be determined, that is to say, a quotient of a sample spectrum divided by a reference spectrum. From the transfer function, a frequency-dependent refractive index of a rubber sample can be determined. Such parameter is a characteristic material variable for the rubber sample. The refractive index here is a proxy for an optical density or a time delay that the rubber sample caused. If the refractive index is known, one rubber sample measurement is sufficient for a layer thickness determination.

Regarding any of the tire tread or tire component examples explained herein, the tire tread or a tire component is not limited to the layer configurations as described. For example, a tire tread may have a base tread layer and an outer tread layer including both a first outer tread layer compound and a second outer layer tread compound. The first outer tread layer compound and the second outer layer tread compound may be conductive or non-conductive. The first and second outer tread layer compounds may account for portions of an axial width of the outer tread layer, such that the first outer tread layer compound accounts for a first portion of an axial width of the outer tread layer and the second outer tread layer compound accounts for a second portion of the axial width of the outer tread layer. The first and second outer tread layer compounds have an interface wherein the first and second outer tread layer compounds are adjacent.

Claim 1:
A method of measuring a thickness of a tire tread, the method comprising the steps of:
providing a tire tread, wherein the tire tread at least has a first tread layer (<NUM>) formed of a first compound and a second tread layer (<NUM>) formed of a second compound, wherein the electrical conductivity of the first compound is higher than the electrical conductivity of the second compound or wherein the first compound is an electrically conductive compound and the second compound is an electrically non-conductive compound;
continuously conveying the tire tread;
arranging a first terahertz sensor (<NUM>) and a second terahertz sensor (<NUM>) above and below the tire tread, respectively, wherein the first and second terahertz sensors (<NUM>, <NUM>) are configured for emitting first and second radiation beams (<NUM>, <NUM>), respectively, into the tire tread;
receiving from the first radiation beam a first reflected radiation beam (<NUM>) from a surface (<NUM>) of the first tread layer (<NUM>) and determining a first distance (d1);
receiving from the second radiation beam (<NUM>) a second reflected radiation beam (<NUM>) from an interface (<NUM>) of the first and second tread layers (<NUM>, <NUM>) and determining a second distance (d2);
receiving from the second radiation beam (<NUM>) a third reflected radiation beam (<NUM>) from a surface of the second tread layer (<NUM>) and determining a third distance (d3), and
carrying out a material thickness measurement, preferably a continuous, repeated or periodical material thickness measurement during the continuous conveying of the tire tread, of the first and second tread layers (<NUM>, <NUM>) by emitting the first and second radiation beams (<NUM>, <NUM>) by the first and second terahertz sensors (<NUM>, <NUM>), respectively, receiving the first, second, and third reflected radiation beams (<NUM>, <NUM>, <NUM>), characterized in that
the first and second terahertz sensors (<NUM>, <NUM>) are connected together at a fixed sensor distance or sensor height (D) and that the first and second terahertz sensors (<NUM>, <NUM>) are arranged colinear, and in that said carrying out a material thickness measurement determines a thickness (d4) of the first tread layer (<NUM>) using said first, second and third distances (d1, d2, d3) and said fixed sensor distance or sensor height (D).