Abstract:
A dynamic calibrator in an tire uniformity machine for testing a tire having a chuck assembly for receiving and chucking a tire load cell in sensing relation therewith, the load cell transmitting sensed information to a controller, the dynamic calibrator including a rotatable calibration wheel coupled to the chuck assembly; a motor assembly operatively coupled to the wheel to cause rotation thereof; and a wheel velocity sensing assembly.

Description:
RELATED PATENT APPLICATIONS 
   None. 
   BACKGROUND OF THE INVENTION 
   Tire uniformity machines are commonly used to test tires by rotating them at various speeds and measuring the characteristics of the tires and ensure that they are constructed within quality standards. To do this, the tire uniformity machine receives a tire, chucks the tire on a rotating spindle, and, after pressurizing the tire and causing it to rotate, brings a loadwheel into contact with the tire to simulate a road surface and measure the forces generated by the tire. Measurements are also taken at the spindle, and, to that end, the spindle is provided with one or more load cells. It will be appreciated that these load cells are very sensitive and can be affected during shipping or other handling such that the load cell does not generate accurate readings. To ensure that the load cell reads accurately, it is desirable to calibrate the load cell after shipping or other handling. Presently, it is necessary to disassemble the spindle and manually inspect the load cell to ensure that it is in condition to take proper measurements. 
   It will be appreciated that most users are reluctant to perform this task each time the tire uniformity machine is moved. Due to this reluctance, the load cell in the machine may generate inaccurate readings that can skew other measurements made by the tire uniformity machine. As a result, the machine may not provide accurate repeatable output. 
   SUMMARY OF THE INVENTION 
   It is, therefore, one aspect of the present invention to provide a means of obtaining repeatable output from the tire uniformity machine. 
   It is another aspect of the present invention to provide a more convenient means of calibrating a spindle load cell in a tire uniformity machine. 
   In general, the present invention provides a dynamic calibrator in a tire uniformity machine for testing a tire having a chuck assembly for receiving and chucking a tire and a load cell in sensing relation therewith, the load cell transmitting sensed information to a controller, the dynamic calibrator including a rotatable calibration wheel coupled to the chuck assembly, a motor assembly operatively coupled to the wheel to cause rotation thereof, and a wheel velocity sensing assembly. 
   The present invention further provides a dynamic calibrator in a tire uniformity machine for testing a tire having a chuck assembly for receiving and chucking a tire, a load cell in sensing relation with the chuck assembly, the load cell transmitting sensed information to a controller, the dynamic calibrator including a framework attachable to the chuck assembly, a wheel rotatably supported by the framework, a weight releasably attached to a point on the wheel, a motor assembly operative with the wheel to cause rotation thereof, and a velocity sensor measuring a velocity of the calibration wheel, the velocity sensor being in communication with the controller, whereby the wheel is rotated by the motor assembly at a velocity with the weight attached to generate a force measured by the load cell. 
   The present invention further provides a method for calibrating the load cell in a tire uniformity machine having a chucking assembly for receiving and chucking a tire to be tested, a motor assembly capable of rotating the chuck assembly and a load wheel assembly, at least one load cell associated with the tire uniformity machine measuring forces generated by the tire during testing, the method including providing a dynamic calibrator that includes a wheel, coupling the dynamic calibrator to the chucking assembly, rotating the wheel at a known velocity, and recording output values from the load cell. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a top plan view of a tire uniformity machine according to the concepts of the present invention. 
       FIG. 2  is a partially sectioned front plan view of a tire uniformity machine with a dynamic calibrator according to the present invention. 
       FIG. 3  is a partially sectional side elevational view depicting a dynamic calibrator according to the present invention mounted on a spindle in a tire uniformity machine similar to that depicted in  FIG. 1 . 
       FIG. 4  is a bottom elevational view of a dynamic calibrator according to the present invention depicted with weights attached to its circumference. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A tire uniformity machine, generally indicated by the numeral  10  in the FIGURES, generally includes, as best shown in  FIG. 2 , vertical side frame members  11 , a generally horizontal top frame member  12 , and generally horizontal bottom frame members  13  to form a framework F for the machine  10 , creating generally a box-like structure within which a tire T is received and tested. 
   As best shown in  FIG. 1 , tire T may be delivered into the framework F of the machine  10 , and removed therefrom after testing, as by a conveyer, generally referred to by the numeral  15 . Conveyer  15  may include a plurality of rollers  16  rotatably supported between parallel side members  17  forming a roller bed. The side members  17  of conveyer  15  and side members  11  of machine  10  are generally spaced to an extent such that they are capable of receiving tires of significantly varying diameter. Once the tire T is brought within the framework F of the machine  10 , the tire T is chucked and prepared for testing. 
   In that regard, the upper frame members  12  carry a chuck assembly, which may be divided into upper and lower assemblies, the orientation of which is flexible, for example, a first chuck assembly, generally referred to by the numeral  20 , and second chuck assembly  90  shown in  FIG. 2 , may form the overall chuck assembly. First chuck assembly generally includes a chuck  21  and a spindle  22 . The spindle  22  may be made hollow defining a passage for transporting air to and from the tire T to maintain proper inflation thereof. To that end, a union  26  may be rotatably coupled to one end of spindle  22  such that the spindle  22  may rotate within union  26  facilitating delivery of air to the tire T, from an air supply  28  ( FIGS. 1 and 2 ), during rotation of the upper chuck assembly  20 . 
   The chuck assembly  20  may be driven by a motor assembly, generally indicated by the numeral  30 , or, as shown, motor assembly  30  may drive the load wheel as described more completely below. Motor assembly  30  is supported on framework F and may be secured by bolts (not shown). A housing, generally referred to by the numeral  40 , surrounds motor  31  to protect the motor  31  from any debris. 
   A second chuck assembly  90 , ( FIG. 2 ) is shown mounted on upper frame member  12  and is at least partially supported on a shaft  91  which is attached to an actuator assembly  92 . Actuator assembly  92  is operable to raise and lower the chuck assembly  90 . In other words, the actuator assembly  92  may axially move the second chuck assembly  90  toward or away from the first chuck assembly  30 . In this way, the tire T can be chucked between the first and second chuck assemblies  20 ,  90  for testing purposes. 
   Second chuck assembly  90  is freely rotatable, and rotates under torque generated by the load wheel assembly  120 , described below, acting through the chucked tire T. 
   When a tire is received within the machine  10 , the second chuck assembly  90  may be moved axially to chuck the tire T between the first and second chuck assemblies  20 ,  90  in preparation for testing. It will be appreciated that when the second chuck assembly  90  is in its retracted position, the tire T may be moved into registry with the second chuck  90  along conveyor  15 . At this point, the second chuck assembly  90  is urged axially toward the tire T so that the tire T engages the first chuck assembly  20  to firmly seat the tire T. The tire T is then inflated to the desired inflation pressure by air directed from supply  28  through union  26 . Once inflated, the tire T is rotated and a load wheel, described below, is moved into engagement with the tire T to perform testing thereon. 
   A load wheel assembly, generally indicated by the numeral  120 , is also provided and is carried by a carriage, generally referred to by the numeral  121 , which may be mounted on the frame F. The load wheel assembly  120  includes a load wheel  122  rotatably mounted on a spindle  123  located on carriage  121 . The spindle  123  has associated with it one or more load cells which are used to measure certain characteristics of the tire T, as will be explained. The carriage  121  is movable toward and away from the tire T under the power of a load wheel motor assembly, generally indicated by the numeral  125 . 
   During operation, tire T is brought into the tire uniformity machine  10  along conveyor  15 . Once the tire T is in registry with the chuck assembly  20 , 90 , the tire T is chucked and the load wheel,  122  is brought in to contact with the tire T. Motor assembly  30  drives spindle  123  to rotate load wheel  122 , such that, when load wheel  122  is in contact with the tire T, the load wheel  122  causes the tire to rotate on chuck assembly  20 . Load cells associated with the load wheel  122  measure forces transmitted from the tire T to the load wheel  122  and relay this information to a controller C. These forces, along with other measurements made by the tire uniformity machine  10 , allow controller C to assess the characteristics of the tire T and make corrections, as necessary. 
   In some tire uniformity machines, as shown in  FIG. 3 , a load cell  130  may be associated with the chuck assembly  20 ,  90 . In this configuration, the load cell  130  associated with the chuck assembly  20 ,  90  may measure the characteristics of the tire T. 
   Since accurate testing depends on the ability of load cell  130  to provide accurate and consistent readings of the forces at the tire T, calibration of the load cell  130  may be necessary from time to time. A dynamic calibrator, generally referred to by the numeral  200  in the accompanying FIGURES, is provided to perform calibration of the load cell  130 . The calibrator  200  may be mounted on the chuck assembly  20  facilitating its use in the field, as well as, during assembly and installation of the tire uniformity machine  10 . Such attachment, also, eliminates the need to disassemble the chuck assembly  20 . 
   Dynamic calibrator  200  is generally provided with a framework, generally referred to by the numeral  201 , having a top frame member  202 , a bottom frame member  203  and side frame members  204  which may define a generally box-like structure. It should be noted that references to top or bottom are made to aid the reader in understanding the description, but are not limited as to the particular orientation of elements. A calibration wheel, generally referred to by the numeral  205 , is located within the framework  201  and made rotatable therein. 
   Calibration wheel  205  has a rim  206  radially spaced from the center  207  of the wheel  205  by a spoke-like web  209  extending from a central hub  210 . Hub  210  may be adapted to be received by chuck assembly  20 , and, thus, is provided with an exterior surface  211  suitable for mating with chuck assembly  20 . In the embodiment shown, surface  211  has a frusto-conical shape, which generally conforms to the cavity defined by the cap assembly  141  of chuck assembly  20 . The frusto-conical surface  211  defines a bore  213  for receiving a portion of a shaft  215 , which is rotationally coupled to hub  210 , as by a key  216 . Hub  210  may further define a first recess  217  extending below a plane defined by the end face  219  of hub  210 . As shown, the wall  221  of recess  217  may be generally circular. A washer  222  sized to fit within the confines of wall  221  may be placed adjacent to the floor  223  of recess  217  and axially held by a fastener, which attaches to shaft  215 . 
   The hub  210  may further be provided with a second recess  224  formed axially adjacent the bore  213  and sized to receive a bearing support assembly, generally referred by the numeral  225 . The inner surfaces of second recess  224  may be dimensioned to provide adequate clearance between the hub  210  and bearing support assembly  225  to allow free rotation of the hub  210 . 
   Bearing support assembly  225  defines a central bore  226  for receiving shaft  215  and suitable antifriction bearings  227 , which interrelate with the shaft  215  and allow free rotation thereof. The bearing support assembly  225  has a generally annular wall  228 , which may be sloped or otherwise contoured at the bottom portion  229  of wall  228  to properly align with the interior surfaces of the hub  210 . The lower portion  230  of wall  228  generally extends axially away from the hub  210  toward the bottom frame member  203 . An aperture  231  formed in bottom frame member  203  effects an extension of central bore  226  through the bottom frame member  203  allowing the shaft  215  to extend externally of the framework  201 . A spacer  232  may be fastened to bottom member  203  and define a spacer bore  233  that lies adjacent to and corresponds with the central bore  226 . As necessary, a seal may be provided between these bores  226 ,  233 . 
   A motor assembly, generally indicated by the numeral  235 , may be placed adjacent spacer  233 . The motor assembly  235  generally includes a motor  236  having a motor shaft  237  that extends from at least one end  238  of the motor  236 . As shown in  FIG. 3 , the motor  236  is mounted to the spacer  232  with the motor shaft  237  entering spacer bore  233  where it can be coupled to the shaft  215 . 
   A coupling assembly  240  may be provided to couple motor shaft  237  to shaft  214 , and may include a clamp joined by fasteners, as is common in the art. Once the shafts  215 ,  237  are coupled, the motor assembly  235  may be used to rotate the hub  210  at a known velocity. A stepper motor may be used to rotate hub  210  and provide accurate control of the wheel&#39;s velocity measurement. The motor assembly  235  may be provided with a pickup  239  for sending and receiving velocity control information to controller C. 
   For calibration purposes, the dynamic calibrator  200  is fastened to the chuck assembly  140  as by fasteners  246  attaching the frame  201  to the chuck assembly  140 . The wheel  205  may be rotated at the known velocity and readings from the load cell  130  recorded. To generate a profile, i.e., a record of a number of readings from the load cell  130 , the wheel  205  may be rotated at a number of velocities. Alternatively, for a single velocity, a weight  250  having a known mass, or plurality of weights, are fastened to the wheel as by bolts  251  extending through holes  252  defined within the rim. With the weights  250  attached, the calibration wheel  205  is rotated at a velocity and the output values of the load cells are recorded. By changing the weights  250  and/or changing the wheel velocity, a first test profile is generated by the measurements from the load cell  130  and recorded by the controller C. Consequently, when it becomes necessary to recalibrate the load cells  130 , such as after moving or any other circumstances making calibration desirable, the load cell&#39;s performance may be compared to the first test profile by performing the same procedure to generate a second test profile. If the first and second test profiles do not fall within a tolerable range of each other, adjustments may be made to the load cell  130  to align the first and second test profiles. As will be appreciated, this may require performing the calibration procedure a number of times. 
   While a full and complete description of the invention has been set forth in accordance with the dictates of the patent statutes, it should be understood that modifications can be resorted to without departing from the spirit hereof or the scope of the appended claims.