Abstract:
A method and device whereby green tire components are on-line controlled as to quality, dimensions and structure by means of electric resistance measurements.

Description:
The present invention relates to a method of on-line controlling tire manufacturing components. 
     More specifically, the present invention relates to a method of on-line controlling the quality, dimensions and structure of green road vehicle tire components. 
     BACKGROUND OF THE INVENTION 
     In the road vehicle tire manufacturing industry, green components are first produced in forming devices and then processed and assembled into tires, which are then cured in respective molds. 
     To ensure conformance of the tires to given specifications, the green components from the forming devices are normally on-line quality controlled to ensure the respective mixes are as required, i.e. are such as to impart the required physical characteristics to the components. As it is processed and fed to the tire assembly machine, each component normally also undergoes various other on-line controls: identification control to identify and ensure the component being supplied is the one actually required; quality control to ensure given physical characteristics (elasticity, hardness, etc.) of the component; dimensional control to ensure the shape and dimensions of the component and/or the shape, dimensions and location of part of the component are as required; and structural control to ensure a given distribution of material within the component (no porosity, etc.). 
     On known tire manufacturing lines, all these controls are performed using various types of equipment normally comprising laser beam devices (such as the one described in U.S. Pat. No. 5537207) and optical and continuous weighing devices, all of which are capable of controlling dimensional characteristics, but not material quality. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a method of on-line controlling tire manufacturing components, designed to eliminate the aforementioned drawbacks. 
     According to the present invention, there is provided a method of on-line controlling tire manufacturing components, whereby at least two distinct points of a said component are placed in contact with respective terminals having different electric potentials to generate an electric current between said two points; said electric current being measured to determine the value of an electric resistance of said component between said two points; and said electric resistance value being compared with at least one reference value. 
     When the two points, for example, are located a given distance apart, it is possible to determine the electric resistance value of the material of which the component is made, and, by comparing this value with a number of reference values (specific to the material), to determine the type of component and the percentages and dispersion of carbon black and carbon aggregates within the material. 
     When controlling, for example, a component, the specific electric resistance of the material of which is known by being determined beforehand using the above method, it is possible, by determining, again using the above method, the electric resistance between two given points on the component, and comparing the resistance value with a number of reference values, to determine fairly accurately the distance between the two contact points (thus enabling dimensional control of the component) and also the presence of any air pockets and/or porosity between the two points and within the component. 
     Finally, when the component being checked contains, for example, portions with specific characteristics, e.g. highly electrically conductive portions for grounding static, determining the electric resistance between specific points on the component provides for determining the presence or absence and the extension of the portion in question. 
     In each case, given a specific tolerance range about each reference value, comparing the measured resistance value with the reference value or values therefore provides for determining acceptance or rejection of the component, and whether any intervention is required on the production line. 
     In other words, the above method provides for performing a sort of tire production line check-up by means of controls which may be all or for the most part resistive, i.e. mostly of the same type, and wherein all the controls of the same type may possibly be performed using one control device. 
     The present invention also relates to a device for on-line controlling tire manufacturing components. 
     According to the present invention, there is provided a device for on-line controlling tire manufacturing components, the device comprising at least two terminals which are placed in contact with respective distinct points of a said component; an electric circuit connecting said terminals to each other; a voltage source located along said circuit to maintain said two terminals at different electric potentials; current-measuring means located along said circuit to determine the value of an electric resistance of said component between said points; and comparing means connected to said current-measuring means to compare said electric resistance value with at least one reference value. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: 
     FIG. 1 shows a circuit diagram of a device in accordance with the present invention, for controlling a tire manufacturing line; 
     FIG. 2 shows a circuit diagram of a variation of a control station of the FIG. 1 device; 
     FIG. 3 shows a schematic lateral elevation of a particular embodiment of the FIG. 2 control station; 
     FIG. 4 shows a circuit diagram of the FIG. 3 control station; 
     FIG. 5 shows a schematic, larger-scale, partially sectioned view in perspective of a detail in FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Number  1  in FIG. 1 indicates as a whole a control device for a line  2  for producing and assembling components T from which to produce green tires (not shown). (In the example shown, the components considered, which may also be preassembled, are, purely by way of example, three in number and indicated T 1 , T 2 , T 3 ). 
     Line  2  extends through a number of control stations S (in the example shown, control stations S are one for each component T and indicated S 1 , S 2 , S 3 , though, in actual fact, a given component may undergo two or more controls in a number of stations S coinciding spatially with one another); and control device  1  comprises a measuring unit  3  for measuring the electric resistance between two terminals indicated V and C. 
     Measuring unit  3 —for example, a commercially marketed HEWLETT PACKARD HP4439B measuring unit—comprises a voltage source  4  (for generating an adjustable constant direct voltage) having a grounded first terminal and a second terminal connected to terminal V; and an ammeter  5  having a first terminal connected to terminal C and a grounded second terminal. 
     Ammeter  5  is connected (in known manner not shown) to voltage source  4  to determine the voltage value applied to terminal V with respect to the ground potential, and so calculate the resistance value between terminals V and C by applying Ohm&#39;s law (R=V/I). Ammeter  5  also provides for controlling voltage source  4  in known manner, to vary the voltage applied to terminal V with respect to the ground voltage as a function of the resistance between terminals V and C, and so keep the current value within the instrument reading range. Measuring unit  3  is thus able to measure widely differing resistance values (within a measuring range of 1 to 10 16  Ohms) while maintaining a relatively high degree of precision. 
     Each control station S comprises a pair of terminals—in particular, an input terminal A and an output terminal B—which have respective terminals  6  and  7  connectable electrically to distinct points of relative component T. Control device  1  comprises two switches  8  and  9  (preferably known and electronically controlled) connected to terminals V and C respectively, and for selectively connecting each pair of terminals A and B to measuring unit  3 . 
     Finally, control device  1  comprises a known comparator  10  for comparing a resistance value, measured by ammeter  5 , with one or more reference values; and a processor  11  which dialogs with comparator  10  to supply comparator  10  with the reference value (stored in a nonvolatile memory and established on the basis of calibration readings of specimen components) and receive back the measured and reference value comparison result. 
     Processor  11  is connected to and supplies a control unit  12  of line  2  with commands as a function of the result of said comparison (or the results of a number of comparisons). More specifically, processor  11  supplies control unit  12  with a command to reject component T, a command to stop operation and request the presence of an operator, or a command to vary the parameters of the operations performed on line  2 . 
     Control stations S are arranged in series along production line  2 , and each control a particular characteristic of a respective component T by measuring the electric resistance between two given points of the component T. To measure the resistance between two given points of a component T at a control station S, terminals  6  and  7  of station S are connected—as described later on—to the given points of component T and, at the same time, switches  8  and  9  are operated to connect the pair of terminals A and B of station S to terminals V and C of measuring unit  3 . 
     By way of example, at control station S 1 , respective terminals  6  and  7  are connectable to given points located a given distance apart on the same surface, preferably the upper surface, of a respective component T. On the basis of the resistance value measured between the two points, processor  11  is able to determine the resistivity value or specific electric resistance of the material of component T, and, by comparing this value with a number of reference values, to determine the type of component in question and the percentages and dispersion of carbon black and carbon aggregates within the material. 
     By way of a further example, at control station S 2 , respective terminals  6  and  7  are connectable to given points on different surfaces of a respective component T; and, from the resistance value measured between the two given points, and the specific electric resistance value of the material of component T (measured at the previous control station S 1 ), processor  11  is able to determine the distance between the two contact points (thus enabling dimensional control of the component) and, by comparison with reference values, the presence of any air pockets and/or porosity between the two given points and within component T. 
     By way of yet a further example, at control station S 3 , respective terminals  6  and  7  are connectable to given points on opposite surfaces—in particular, on a top and bottom surface—of a respective component T; and, on the basis of the resistance value measured between the two given points, processor  11  is able to determine whether component T contains portions with specific characteristics, e.g. highly electrically conductive portions within or on the surface of substantially insulating or semiconducting materials for grounding static. 
     In an alternative embodiment not shown, at least one of control stations S 1 , S 2 , S 3  is replaced by a control station (not shown) having three pairs of terminals  6  and  7 , and which, when supplied with a component T, successively performs the above three measurements by operating switches  8  and  9 , or may perform only one or two of the above measurements, depending on the type of component T. 
     In the FIG. 2 embodiment, control stations S 1 , S 2 , S 3  are replaced by one control station S 4  having three different terminals  6  connected to respective terminals A connectable to terminal V of measuring unit  3  by switch  8 , and one terminal  7  permanently connected to terminal C of measuring unit  3 . When supplied with a component T, control station S 4  successively performs the above three measurements by appropriately operating switch  8 , or may perform only one or two of the above measurements, depending on the type of component T. 
     In the embodiment shown in FIGS. 3-5, control device  1  comprises one control station S 5  in which two different measurements may be performed on a respective component T, in particular a continuous strip of extruded green tread. 
     As shown in FIG. 3, production line  2  comprises a known extruder  13 , which feeds component T onto a roller conveyor  14  for feeding component T to successive known work stations (not shown) and comprising a number of equally spaced horizontal rollers  15 . Some of rollers  15  are powered (in known manner not shown) to impart a forward movement to component T, while the other rollers  15  are mounted idly to simply support component T. Control station S 5  is located along conveyor  14 , with the electric connections shown in FIG. 4, and the mechanical structure shown schematically in FIG.  5 . 
     As shown in FIG. 4, control station S 5  comprises two terminals  16  and  17  electrically connectable to a top surface  18  of component T; and a terminal  19  defined by a respective idle roller  15  connectable electrically to a bottom surface  20  of component T. 
     Terminal  16  is connected permanently to terminal C of measuring unit  3 ; terminal  17  is connectable selectively to terminal C or V of measuring unit  3  by two known switches  21  and  22 ; and terminal  19  is connectable to terminal V of measuring unit  3  by switch  22 . More specifically, when switches  21  and  22  are set to a first position indicated I in FIG. 4, terminal  17  is connected to terminal V and terminal  19  is disconnected to perform a first resistance measurement of component T between two points on surface  18 ; when switches  21  and  22  are set to a second position indicated II in FIG. 4, terminal  17  is connected to terminal C in parallel with terminal  16 , and terminal  19  is connected to terminal V, to perform a second resistance measurement of component T between a point on surface  18  and a point on surface  20 . 
     The second measurement measures the electric resistance between a point, on bottom surface  20  of component T, contacting terminal  19 , and two points, on top surface  18  of component T, contacting terminals  16  and  17 . In alternative embodiments not shown, the resistance of a component T is measured between a first set of points on the same or different surfaces and contacting first terminals connected in parallel, and a second set of points on the same or different surfaces and contacting second terminals connected in parallel. 
     With reference to FIG. 5, at least the roller  15  defining terminal  19  (and indicated  15   a ) is a metal roller fitted to a respective shaft  23 , the opposite ends of which project outwards of roller  15   a  and engage in rotary manner respective holes formed in two beds  24  (only one shown in FIG. 5) made of electrically insulating material to electrically insulate roller  15   a ; and roller  15   a  is connected electrically by a known sliding contact  25  to a terminal  26  in turn connected to switch  22  by an electric cable  27 . 
     Terminals  16  and  17  are defined by respective rollers  28  made of conducting material, preferably metal, and fitted idly to a support  29 , which comprises a rod  30  maintained by a frame  31  in a horizontal position perpendicular to the traveling direction  32  of component T along roller conveyor  14 . Support  29  also comprises two cylindrical sleeves  33 , each fitted in rotary and axially-sliding manner to rod  30  and having a respective lock sleeve  34 , which is fitted in rotary and axially-sliding manner to rod  30 , is connected in rotary and axially-fixed manner to respective sleeve  33 , and has a respective radial through screw  35  for axially locking lock sleeve  34  along rod  30 . 
     Each sleeve  33  is connected integrally to an end portion  36  of a respective arm  37  extending radially outwards with respect to relative sleeve  33  and comprising a further end portion  38  made of electrically conducting material. End portion  38  is connected integrally to end portion  36 —also made of electrically conducting material—by an intermediate portion  39  made of electrically insulating material, and supports a respective roller  28  in rotary manner by means of a respective transverse shaft  40  parallel to rod  30 . 
     A respective counterweight  41  of given weight is fitted in sliding manner along each arm  37 , comprises a respective lock screw  42  by which it is locked axially to respective arm  37 , and provides for imparting to respective arm  37  a given downward torque about rod  30 . 
     In actual use, rollers  28  are pressed, at constant, adjustable pressure, against top surface  18  of component T by the combined weight of arms  37 , which is mainly due to the mass of counterweights  41 . 
     End portion  38  of each arm  37  is fitted with a terminal  43 , which is connected to measuring unit  3  (terminal  16 ) or to switch  21  (terminal  17 ) by a respective electric cable  44  (shown in FIGS.  3  and  4 ). 
     To ensure a continuous reading, a cylindrical terminal has been found to be most effective, with the lateral surface being brought into contact with component T. For which reason, terminals  16 ,  17 ,  19  in FIGS. 5,  6 ,  7  are advantageously, though not necessarily, defined by cylindrical rollers. 
     In a preferred embodiment not shown, cables  27  and  44  are shielded cables to reduce the effect of electromagnetic noise on the resistance measurements performed by measuring unit  3 .