Abstract:
An apparatus for facilitating calibration of sensors embedded within an object includes: a foundation; a force generator mounted on the foundation configured to generate a force in a first direction; a load cell connected with the force generator that detects the magnitude of force applied by the force generator; a roller mounting assembly pivotally interconnected with the foundation and pivotable about a first axis of rotation, the first axis of rotation being generally perpendicular to the first direction; and a roller rotatably mounted on the roller mounting assembly for rotation about a second axis of rotation, the second axis of rotation being generally perpendicular to the first direction, the roller protruding in the first direction sufficiently to apply a force to the object. This apparatus can enable force applied to the sensor to be calibrated with sensor output.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to the measurement of properties of industrial roll covers and other objects, and more particularly to the calibration of measurement devices used for such measurement.  
         BACKGROUND OF THE INVENTION  
         [0002]    Cylindrical rolls are utilized in a number of industrial applications, especially those relating to papermaking. Such rolls are typically employed in demanding environments in which they can be exposed to high dynamic loads and temperatures and aggressive or corrosive chemical agents. As an example, in a typical paper mill, rolls are used not only for transporting a fibrous web sheet between processing stations, but also, in the case of press section and calender rolls, for processing the web sheet itself into paper.  
           [0003]    Typically rolls used in papermaking are constructed with the location within the papermaking machine in mind, as rolls residing in different positions within the papermaking machines are required to perform different functions. Because papermaking rolls can have many different performance demands, and because replacing an entire metallic roll can be quite expensive, many papermaking rolls include a polymeric cover that surrounds the circumferential surface of a typically metallic core. By varying the material employed in the cover, the cover designer can provide the roll with different performance characteristics as the papermaking application demands. Also, repairing, regrinding or replacing a cover over a metallic roll can be considerably less expensive than the replacement of an entire metallic roll. Exemplary polymeric materials for covers include natural rubber, synthetic rubbers such as neoprene, styrene-butadiene (SBR), nitrile rubber, chlorosulfonated polyethylene (“CSPE”—also known under the trade name HYPALON® from DuPont), EDPM (the name given to an ethylene-propylene terpolymer formed of ethylene-propylene diene monomer), polyurethane, thermoset composites, and thermoplastic composites.  
           [0004]    In many instances, the roll cover will include at least two distinct layers: a base layer that overlies the core and provides a bond thereto; and a topstock layer that overlies and bonds to the base layer and serves the outer surface of the roll (some rolls will also include an intermediate “tie-in” layer sandwiched by the base and top stock layers). The layers for these materials are typically selected to provide the cover with a prescribed set of physical properties for operation. These can include the requisite strength, elastic modulus, and resistance to elevated temperature, water and harsh chemicals to withstand the papermaking environment. In addition, covers are typically designed to have a predetermined surface hardness that is appropriate for the process they are to perform, and they typically require that the paper sheet “release” from the cover without damage to the paper sheet. Also, in order to be economical, the cover should be abrasion- and wear-resistant.  
           [0005]    Some rolls are present as “nip” rolls, wherein two or more rolls are positioned such that they form a “nip” through which a web can pass. Such rolls are often found, for example, in the press section of a papermaking machine. The rolls press against the web at a prescribed pressure in order to advance processing. However, in some instances the rolls can apply pressure unevenly on the web. Uneven pressure application can result from many circumstances, including (a) the cover of one or more rolls being slightly “out of round”, (b) one roll being mounted so that its axis is not parallel to that of its mating roll, or (c) increased localized wear on one of the roll covers. Irrespective of the cause of the uneven pressure, its presence can negatively impact processing of the web, and can in extreme instances harm the cover or even cause it to fracture.  
           [0006]    Some systems for attempting to detect the pressure at different locations within a roll or roll cover are available. One system includes a flexible strip on which are mounted multiple pressure sensors that can be placed between the rolls and provide pressure readings (see, e.g. U.S. Pat. No. 5,953,230 to Moore). Another system employs sensors that are embedded in the roll cover itself and provide signals to an external processor (see, e.g., U.S. Pat. No. 5,699,729 to Moschel et al.).  
           [0007]    Systems that employ embedded sensors can be particularly desirable, as they can be monitored easily, even during operation of the roll. Of course, it is important that the embedded sensors be accurate as they detect their particular property of interest. Calibration of the sensors is typically recommended and/or required, as the sensor output can vary due to differences in manufacturing, orientation, and the thickness of the material that covers the sensor. As such, a device and/or method that facilitates calibration of embedded sensors would be desirable.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention is directed to an apparatus and method for calibrating covered rolls having embedded sensors. As a first aspect, the invention includes an apparatus for facilitating calibration of sensors embedded within an object, comprising: a foundation; a force generator mounted on the foundation configured to generate a force in a first direction; a load cell connected with the force generator that detects the magnitude of force applied by the force generator; a roller mounting assembly pivotally interconnected with the foundation and pivotable about a first axis of rotation, the first axis of rotation being generally perpendicular to the first direction; and a roller rotatably mounted on the roller mounting assembly for rotation about a second axis of rotation, the second axis of rotation being generally perpendicular to the first direction, the roller protruding in the first direction sufficiently to apply a force to the object. This apparatus can enable force applied to the sensor to be calibrated with sensor output.  
           [0009]    In some embodiments, two force generators (preferably inflatable air bags) and two load cells are employed. Also, in some embodiments, the apparatus includes a temperature sensor that can detect the temperature of the roller or the object. Such detection can indicate when the object has reached a temperature equilibrium, which can improve the accuracy of calibration.  
           [0010]    As a second aspect, the invention is directed to a method of calibrating an object with embedded sensors. The method begins with the provision of an object with sensors embedded therein and an apparatus as described above. The method continues with the actuation of the force generator to apply a force to the object through the roller. Next, the force generated by the force generator with the load cell is measured, with the output from the sensor responsive to the force applied to the object by the roller also being measured. These previous three steps are repeated for different forces of differing magnitude to correlate pressure input with sensor output.  
           [0011]    In some embodiments, the object is a covered roll, and the object is rotating during application of the force. Some embodiments comprise the monitoring of the temperature of the roller or the object in order to detect when temperature equilibrium is reached; this monitoring typically occurs after to the application of force to the object. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0012]    [0012]FIG. 1 is a perspective view of an apparatus for calibrating sensors embedded in a covered roll according to embodiments of the present invention.  
         [0013]    [0013]FIG. 2 is a side view of the apparatus of FIG. 1.  
         [0014]    [0014]FIG. 3 is a side view of another embodiment of an apparatus for calibrating sensors embedded in a covered roll according to embodiments of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]    The present invention will now be described more fully hereinafter, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, like numbers refer to like elements throughout. Thicknesses and dimensions of some components may be exaggerated for clarity.  
         [0016]    Referring now to the drawings, a calibrating apparatus, designated broadly at  10 , is shown in FIGS. 1 and 2. The calibrating apparatus  10  can be mounted on a lathe L or another rotary device, such as a grinder or the like, that is typically employed to carry out operations on the surface of a covered roll R. The locations, positions and movements of certain components of the apparatus  10  will be described hereinafter by reference to their positions relative to other components thereof. As used herein, “forward” and derivatives thereof and “front” and derivatives thereof refer to the direction defined by a vector parallel to a surface underlying the apparatus  10  and extending from the apparatus  10  toward the roll R. The terms “rear,” “rearward,” and derivatives thereof refer to the direction opposite the forward direction; i.e., the direction defined by a vector extending parallel to the underlying surface from the roll R toward the apparatus  10 . Together, the forward and rearward directions form the “longitudinal” directions of the apparatus  10 . The terms “lateral,” “outer,” and derivatives thereof refer to the directions defined by vectors originating at a vertical longitudinal plane bisecting the apparatus  10  and extending parallel to the underlying surface and perpendicular to the forward direction. The terms “inward,” “inner,” “inboard,” and derivatives thereof refer to the directions that are opposite the lateral directions; i.e., the directions defined by vectors originating at the lateral edges of the apparatus  10  and extending toward the aforementioned bisecting plane. Together, the inward and lateral directions form the “transverse” directions of the apparatus  10 .  
         [0017]    The apparatus  10  includes a generally horizontal foundation  12  that is mounted to the compound of the lathe (i.e., that portion of the lathe on which cutting tools are mounted). The foundation  12  includes a generally horizontal base plate  13  and a generally vertical airbag mounting member  16 , which is fixed to and rises upwardly from the front edge of the base plate  13 . Two triangular supports  14   a ,  14   b  are fixed to the upper surface of the base plate  13  and the rear surface of the airbag mounting member  16 . The foundation  12  also includes a spanning member  36  that extends forwardly from the front surface of the airbag mounting member  16 , and further includes a hinge mounting plate  38  that is fixed to the front edge of the spanning member  36  and extends downwardly therefrom.  
         [0018]    Those skilled in this art will recognize that the foundation  12  may take other configurations. For example, the dimensions and thicknesses of the illustrated components may vary, two or more of the components may be formed as unitary members or as separate components, or the base plate  13  may be configured to attach to a device other than a rotary device. In any event, the foundation should be shaped to provide suitable mounting locations for the other components of the apparatus  10 , and should be formed of a material (such as steel) that is sufficiently strong and rigid to withstand the rigors of operation.  
         [0019]    Referring again to FIGS. 1 and 2, two airbags  20   a ,  20   b  are mounted to the front surface of the airbag mounting member  16  via necks  18 . The airbags  20   a ,  20   b  are mounted in transverse alignment on the airbag mounting member  16 . The airbags  20   a ,  20   b  (typically formed of rubber) are inflatable and are connected to a pneumatic pressure source (not shown). Upon inflation, the airbags  20   a ,  20   b  exert a force/pressure onto components to which they are connected.  
         [0020]    Those skilled in this art will recognize that the invention may utilize alternative configurations to generate force or pressure. For example, in some embodiments, only one airbag may be employed. In other embodiments, other force generators, such as hydraulic systems, mechanical systems, electromagnetic systems, and the like, may also be employed to generate force/pressure for the apparatus  10 .  
         [0021]    Referring still to FIGS. 1 and 2, two load cells  24   a ,  24   b  are attached to respective load cell plates  23  (only one of which is illustrated herein) via threaded shafts  23   a ,  23   b . The load cell plates  23  are in turn attached to necks  22   b  of the airbags  20   a ,  20   b . The load cells  24   a ,  24   b  are of conventional construction and need not be described in detail herein. The load cells  24   a ,  24   b  are configured to measure a load applied in the longitudinal direction by the airbags  20   a ,  20   b . A preferred load cell is the SWP-5K-4 model, available from Transducer Techniques (Temecula, Calif.). Other force measuring devices may be substituted for the load cells  24   a ,  24   b.    
         [0022]    Referring once more to FIGS. 1 and 2, a roller mounting assembly  26  is attached to the forward ends of the load cells  24   a ,  24   b . The roller mounting assembly  26  includes a bearing mounting plate  27  that extends downwardly to a pivotal interconnection with the lower end of the hinge mounting plate  38  via a hinge  40 , such that the bearing mounting plate  27  is free to pivot about a transverse axis of rotation A 1 . It is preferred that the hinge  40  have very precise tolerances and that it be able to withstand very high loads (as much as 4,000 lb. or more) applied perpendicularly to the axis A 1 .  
         [0023]    Referring still again to FIGS. 1 and 2, the roller mounting assembly  26  also includes two roller bearings  28   a ,  28   b  that are mounted onto the front surface of the bearing mounting plate  27  via screws or other fasteners. A flange  32  is fixed (typically via threaded fasteners) to the lower portion of the front surface of the bearing mounting plate  27 . Two set screws  34  (only one is shown herein in FIG. 2) extend upwardly through the flange  32  and contact the lower edges of the roller bearings  28   a ,  28   b.    
         [0024]    Referring once again to FIGS. 1 and 2, a roller  30  is rotatably mounted in the roller bearings  28   a ,  28   b  for rotation about a transverse axis of rotation A 2 . The roller  30  may take any number of forms, but is preferably formed of a material (such as steel) that is uncovered or covered with cover that has a hardness of at least 3 P&amp;J. Also, the roller  30  may be of any desired length and diameter, but is preferably between about 2 and 5 inches in length and 3 and 8 inches in diameter.  
         [0025]    Mounting and operation of the apparatus  10  begins with the mounting of a covered roll R in which sensors have been embedded onto a rotary device, such as the aforementioned lathe or grinder, that is ordinarily employed to perform operations on such a roll. The sensors can be any type of sensor that detects pressure applied thereto or stress/strain induced therein; exemplary sensors include optical, piezoelectric, and piezoresistive sensors. An exemplary optical sensor is disclosed in U.S. patent application Ser. No. 09/489,768, the disclosure of which is hereby incorporated herein in its entirety. The cover of the roll R is typically a polymeric material such as rubber, polyurethane, epoxy, blends, mixtures and combinations thereof, and the sensors are typically embedded below the surface of the cover. In some embodiments, after the roll R is mounted onto the rotary device, the axial locations of the sensors are marked to facilitate positioning of the apparatus  10 .  
         [0026]    After the roll R is mounted, the apparatus  10  is mounted onto the rotary device. More specifically, in the illustrated embodiment the base plate  13  is mounted to the compound of the lathe. It is preferred that the mounting be achieved (for example, with slots being present in the base plate  13  or in the compound of the lathe through which bolts are inserted) such that the base plate  13  may be shifted longitudinally (i.e., toward and away from the roll R) to enable the roller  30  to be positioned precisely. Typically, the desired position for the roller  30  is parallel to and nearly touching the roll R. The proximity of the roller  30  to the roll R can be adjusted by sliding the foundation  12  relative to the lathe (i.e., this movement adjusts the roller  30  in the horizontal plane) and checking the position with a nip foil. The roller  30  can be adjusted in the vertical plane by adjustment of the set screws  34 , which can alter the level of the roller bearings  28   a ,  28   b  and, in turn, the orientation of the axis A 2  of the roller  30 ; this alignment can be checked with a level resting on the roller  30 .  
         [0027]    Once positioned, the apparatus  10  can then be used to calibrate the sensors in the roll R. The roll R is rotated about its axis by the lathe (a speed of 45 rpm or greater is typical). The airbags  20   a ,  20   b  are then inflated by the pressure source until the roller  30  is applying a desired load (as measured by the load cell) to the roll R (because the bearing mounting assembly  26  is free to pivot about the hinge  40 , force applied by the airbag  20   a ,  20   b  is transmitted to the roller  30 ). It is preferred that, if multiple airbags (like the airbags  20   a ,  20   b  illustrated herein) are employed, that they be loaded to similar levels. Data regarding sensor output is collected for the measured load. The load is then increased incrementally (typically, three or more different loads are applied, at levels that may vary between about 100 and 1,500 pli), and data collected for each load. The apparatus  10  is then shifted axially (this can usually be accomplished by moving the compound of the lathe along the axis of the roll R) to the next sensor position, and the loading and data collection steps are repeated. From this data, correlations between load and sensor output can be developed that can be employed when collecting and interpreting sensor data on the roll during operation on a paper machine or other mechanical system.  
         [0028]    Another embodiment of an apparatus of the present invention is illustrated in FIG. 3 and designated broadly therein at  10 ′. The apparatus  10 ′ includes the same components as the apparatus  10 , but also includes a thermocouple mounting arm  52  that is attached to the airbag mounting plate  16 ′ and extends forwardly to the roller  30 ′. A thermocouple  50  is attached to the free end of the thermocouple mounting arm  52  and rests upon the roller  30 ′. The thermocouple  50  illustratively and preferably has a concave surface that matches the surface of the roller  30 ′.  
         [0029]    The thermocouple  50  detects the temperature of the surface of the roller  30 ′ during the calibration procedure. The thermocouple  50  may be included on an apparatus of the present invention to address variations in sensor output as a function of load due to temperature. This capability can be useful in that certain sensors provide output based on the strain they experience under load. The strain for a particular sensor is dependent upon the applied load and the modulus of elasticity of the cover material. Because polymeric roll covers are formed of materials for which the modulus of elasticity can vary significantly over the temperatures of operation, the sensor output for a particular load can vary until the cover reaches a temperature equilibrium. One method of detecting temperature equilibrium for the cover is to measure the temperature of the roller  30 ′ (which should, at equilibrium, have essentially the same temperature as the roll R, or have a temperature that can, through empirical testing and/or calibration, be related to the temperature of the roll R) over a period of time under load until the temperature stabilizes. Once the temperature has stabilized, the calibration of the sensors can proceed, and more accurate results can be obtained.  
         [0030]    Those skilled in this art will appreciate that the apparatus  10 ′ may take other configurations. For example, a pyrometer or other temperature sensing device may be employed instead of a thermocouple. Also, the temperature sensing device may be mounted on other locations on the apparatus  10 ′, such as on the bearing mounting plate. Further, the surface of the roll R may be measured directly, or the temperature of either the roller  30 ′ or the roll R may be measured using a non-contact technique (such as an IR-based system).  
         [0031]    The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention.