Abstract:
A device for measuring the spring rate of a golf ball is disclosed. The device receives a golf ball between a first anvil and a second anvil. A force gauge is provided on one anvil. A displacer is provided on another anvil. Each anvil defines a ball receiving depression that is larger than the dimples of the golf ball to be measured for negating measurement effects due to golf ball dimples when measurement of the golf ball is conducted. The displacement an anvil is determined. From the force data and displacement data, a spring rate of the golf ball can be calculated and a compression scale value may be calculate and displayed on the device for informing a golfer that is operating the hand held device.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of U.S. Provisional Patent Application No. 61/459,060, entitled “GOLF BALL COMPRESSION TESTER,” filed Dec. 6, 2010, the contents of which are hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a device that is used to find a “compression rating” of a golf ball. More particularly, the invention relates to a portable handheld device that may be used to find a compression rating of a golf ball by a golfer while golfing on a golf course. 
     BACKGROUND OF THE INVENTION 
     Golf balls are manufactured having a variety of properties for appealing to a wide range of golfers. One characteristic of a golf ball is the “compression rating” or compression scale value. The compression rating, at one time in the past, was a measurement of how tightly the rubber threads of the ball were wound around a core of the ball. The tighter the rubber threads, the high the compression rating or the higher the hardness of the ball. Modern manufacturing techniques have replaced the winding of rubber threads with solid rubber, thereby necessitating a way to relate the familiar compression rating of wound balls to solid balls. Some golf ball manufacturers have stopped using the compression rating altogether. Consequently, golfers may benefit from a way to measure a ball to determine what the compression rating of a ball is. 
     Generally, golf balls having a lower compression rating are favored by golfers having a slower swing speed, while golf balls having a higher compression rating are favored by golfers having a faster swing speed. Golf balls are available in a variety of compression ratings, most commonly designated by a compression scale that is expressed in a value that ranges from 50 to 120. Low compression balls, e.g., balls having a compression rating of 70 or below, rebound off the club head differently than high compression balls, e.g., ball having compression ratings of 100 or above. Medium compression balls, e.g., balls having a compression rating of approximately 90, rebound differently than high or low compression rated balls. Knowing the characteristics of the golf ball will allow a golfer to choose the ball that best matches his swinging speed. 
     SUMMARY OF THE INVENTION 
     A device is provided for measuring the compression rating of a golf ball. The device has a housing that defines a ball receiving receptacle for receiving a golf ball. A first anvil and a second anvil are mounted in the housing for receiving the golf ball there between. A force gauge is provided that is in communication with one of the first anvil and the second anvil, preferably with the upper anvil. A displacer, such as a threaded rod, is in communication with one of the first anvil and the second anvil, preferably with the lower anvil. 
     The first anvil defines a first ball receiving surface that defines a first ball receiving depression. The second anvil defines a second ball receiving surface that defines a second ball receiving depression. The first ball receiving depression and the second ball receiving depression are larger than the dimples of the golf ball to be measured for negating measurement effects due to golf ball dimples when measurement of the golf ball is conducted. The displacement of one of the first anvil and the second anvil, preferably the lower anvil, is determined. From the force data and displacement data, a spring rate of the golf ball can be determined and a compression scale value displayed on the device for informing a golfer that is operating the hand held device. 
     In use, a golf ball is located between the first anvil and the second anvil in depressions defined by the anvil surfaces. The golf ball is compressed by displacing one of the first anvil and the second anvil, preferably the lower anvil, to produce a deflection of the golf ball. A displacement of the one of the first anvil and the second anvil, preferably the lower anvil, is determined and communicated to a processor. A force delivered to the one of the first anvil and the second anvil, preferably the upper anvil, as a result of compressing the golf ball is determined. The force is communicated to the processor. The spring rate is calculated by the processor by dividing the force by the deflection of the golf ball. The spring rate is then converted to a compression scale value, e.g., 50 to 120, and is then displayed on a display screen for viewing by a golfer. 
     An object of this invention is to provide a hand-held device that will measure the spring rate of a golf ball to a very high degree of accuracy and repeatability. 
     A further object of this invention is to provide a way to relate a measured spring rate of a golf ball to a compression scale value that a majority of people familiar to the game of golf have used and understood for many years. 
     A further object of the invention is to display a compression scale value so a person familiar with the game of golf will be able to relate a golf ball hardness to a performance of the ball and to performance of the golfer. 
     A further object of this invention is to provide a measuring tool that is compact and lightweight enough to be carried while playing a game of golf. 
     A further object of this invention is to provide a device that measures the spring rate of a golf ball to a set of absolute standards. 
     A further object of the invention is to measure the spring rate of a golf ball to such a high degree of accuracy that the device of the invention can be used to check the quality of manufacturing of the golf ball and verify that the ball meets an advertised compression rating. 
     A further object of this invention is to provide a device that can verify that a golf ball meets or exceeds compression rating standards that have been established by organizations such as the Professional Golf Association, hereafter known as the “PGA”. 
     A further object of this invention is to measure the spring rate of a golf ball without causing damage to the golf ball, such as causing the ball to be out of roundness or marking the surface of the ball. 
     A further object of this invention is to related how a temperature of a ball can change the compression scale value of the ball. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects of this invention will become more fully apparent from the following detailed description of an embodiment of the invention and from the accompanying drawings, in which: 
         FIG. 1  is an isometric view of a golf ball compression tester device of the invention. 
         FIG. 2  is an isometric partial cut-away view showing the internal mechanics of the golf ball compression tester of  FIG. 1 . 
         FIG. 3  is a schematic view of one embodiment of sensing components of the device of  FIG. 1 . 
         FIG. 4  is an isometric view of the device of  FIG. 1  showing a recessed area of a lower anvil provided for “dimple negation”. 
         FIG. 5  is an isometric view of the force sensing assembly of the device of  FIG. 1 . 
         FIG. 6  is an isometric view of the force sensing assembly of the device of  FIG. 1  showing an exploded view of the parts within. 
         FIG. 7  is a cross-sectional isometric view of the device of  FIG. 1  taken along lines  7 - 7  of  FIG. 1  showing one embodiment of a golf ball guide that stops the ball in the correct location for centering the ball within anvils for testing. 
         FIG. 8  is a graphical representation of force v. deflection data generated during testing to determining spring rate of golf balls. 
         FIG. 9  is an exploded view of a display assembly of the device of  FIG. 1 . 
         FIG. 10  shows a comparison between two golf balls having different sizes and different configurations of dimples. 
         FIG. 11  is a graphical representation that shows correlation between a compression scale and a measured spring rate. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the figures, shown is a golf ball compression testing device, designated generally  10 . Device  10  includes a housing  12  that defines a ball receiving receptacle  14  for receiving a golf ball  16  to be tested. Device  10  includes a force gauge assembly  18  located in housing  12 . Force gauge assembly  18  includes an upper anvil  20  ( FIGS. 1, 4, 5 ) secured in an upper anvil housing  22  by retaining ring  23 . Housing  22  preferably has a hexagonal shape for preventing rotation, but other shapes may also be utilized. Upper anvil  20  defines an upper ball receiving surface  24  on a lower side that defines an upper depression  26  having a diameter  27 . Upper anvil  20  defines a protuberance  28  on an upper surface that selectively communicates with beam  30  of a tension measuring device  32  ( FIGS. 2, 4, 5 ), e.g., a strain gauge, for measuring a force applied by protuberance  28  of upper anvil  20 . Strain gauges are useful to get very high degrees of accuracy and repeatability for measuring applied forces without also requiring a significant ball deflection due to forces that would complicate the measurement taken. 
     Force gauge assembly  18  additionally includes a lower anvil  36 . Lower anvil  36  defines internal threads  38 . Lower anvil  36  is preferably hexagonally shaped to prevent rotation when handle  58  is rotated to compress ball  16 , as will be explained below. Lower anvil  36  has an upper surface that defines a lower ball receiving surface  40 . Lower ball receiving surface  40  defines a lower depression  42  having a diameter  43 . Lower anvil  36  may have a lower surface that communicates with thrust member  44 , as shown in  FIG. 2 . 
     Bottom plate  46  is affixed to a lower end of housing  12 . Bottom plate  46  defines central orifice  48 . A displacement mechanism, such as threaded rod  50 , extends through central orifice  48  of bottom plate  46 . Threaded rod  50  defines an upper threaded end  52  that is threadably received within internal threads  38  of lower anvil  36 . Upper threaded end  52  of threaded rod  50  may contact a lower surface of thrust member  44  ( FIG. 2 ). Upper threaded end  52  preferably defines left handed Acme threads having a known thread pitch. The thread pitch is a trade-off between the number of turns required to make a measurement and the amount of torque required to turn the handle to make a measurement. The preferred thread pitch is 1/16 inch. Threaded rod  50  additionally defines a downwardly facing shoulder  54  ( FIGS. 2, 3 ). Threaded rod  50  has a lower end  56  that extends outwardly from bottom plate  46 . 
     Handle  58  is affixed to lower end  56  of threaded rod  50  for rotating threaded rod  50  to induce axial displacement of lower anvil  36 . Thrust bearing  60  surrounds threaded rod  50  and is located between downwardly facing shoulder  54  and an upper surface of bottom plate  46 . Thrust bearing  60  is provided to take the force applied against ball  16 . Thrust bearing  60  decreases the torque needed to rotate handle  14  to compress ball  16  with lower anvil  36 . Alternatively, threaded rod  58  may be rotated by a motor (not shown). 
     Encoder wheel  62  is located between an upper surface of thrust bearing  60  and downwardly facing shoulder  54  of threaded rod  50 . Encoder wheel  62  is provided to mechanically or electrically track a number of rotations of threaded rod  50 . The rotation tracking is converted into deflection by using a relationship of threads or threaded end  52  to a reading from encoder wheel  62 . Encoder wheel  62  may be optical, magnetic, or use other means of tracking a number of rotations of threaded rod  50 . Alternatively, deflection may be sensed by a deflection gauge  63 . In a preferred embodiment, maximum deflection is 0.140″, although other ranges may be used. 
     Processor  64  is provided within housing  12  and communicates with encoder wheel  62  for converting the number of rotations of threaded rod  50  and the known thread pitch into a measurement of axial displacement of lower anvil  36 . Alternatively, processor  64  communicates with deflection gauge  63  ( FIG. 3 ). Processor  64  is additionally in communication with tension measuring device  32 . Switch  65  is also in communication with processor  64  and may be manual or automatic as is discussed below. 
     A display assembly  66  ( FIG. 9 ) is provided in housing  12 . Display assembly  66  includes front bezel  67 , display panel  68 , such as an LCD, processor  64  and a zebra strip  69  interposed between processor  64  and display panel  68 . A back bezel  70  engages a rear surface of housing  12  and receives battery door  71  for securing a power supply, such as a lithium battery  72 , in display assembly  66 . 
     Because anvils  20  and  36  define depressions  26  and  42 , respectively, different golf ball types may be accommodated. For example,  FIG. 9  shows two different golf balls  73  and  74  having two different size dimples,  75  and  76 . Additionally, space between the dimples is smaller for ball  73 . Further, golf ball dimple variations exist when balls are made with more than one size of dimple on the same ball. The purpose of depressions  26  and  42  is to form a “dimple negation” feature. 
     Depressions  26  ( FIG. 5 ) and  42  ( FIG. 4 ), both have diameters  27  and  43 , respectfully. The diameters  27  and  43  are larger than dimples  75 ,  76  of golf balls  73 ,  74 . Preferably, depressions,  26  and  42 , are curved to match the radius of a standard golf ball, i.e., a diameter of 1.680±0.15 inches (42.67 mm) for cradling the ball on at least three points of contact on anvils  20 ,  36 , no matter how the ball is placed between anvils  20 ,  36 . The uncertainty of the measurements of force when flat anvils are used to do the same compression test is negated by dimple negation achieved by providing depressions  26 ,  42  with diameters of  27  and  43  that are larger than the worst case dimple size of a standard golf ball. The dimple negation feature increases the accuracy of measuring the compression rating of a standard golf ball by decreasing the uncertainty of force required to overcome the dimples in the standard golf ball. Dimple negation also allows for less force to be applied against ball  16  to make a measurement of spring rate or by decreasing the uncertainty of the force measurement during an application of low forces. 
     Dimple negation allows for a lower force and increase in accuracy that will not affect the roundness of the ball after testing for spring rate. Golf balls take time to return to their original roundness after being struck by a club or pinched by a compression testing device. Therefore, a lower applied force is desirable. Dimple negation also allows for less effort needed to turn handle  58  to raise lower anvil  36  against ball  16  to compress ball  16  against upper anvil  20  to an amount of force necessary to successfully measure spring rate, i.e., to achieve an amount of force “F 1 ”, as will be explained below. 
     To further increase accuracy and repeatability of the compression test, ball  16  must be accurately placed between anvils  20  and  36 . Taper stops  77 , shown in  FIG. 7 , function to stop ball  16  in the geometric center between the anvils  20  and  36 . 
     In use, golf ball  16  is placed into ball receiving receptacle  14  of device  10 . Taper stops  77  provide a backstop for correctly locating ball  16  between anvils  20  and  36 . Golf ball  16  is secured within the ball receiving receptacle  14  and the force gauge assembly  18  by rotating handle  58 . Rotation of handle  58  rotates threaded rod  50 , which axially displaces lower anvil  36  until golf ball  16  makes contact with upper ball receiving surface  24  of upper anvil  20 . Handle  58  should continue to be rotated until golf ball  16  is secured between upper ball receiving surface  24  of upper anvil  20  and lower ball receiving surface  40  of lower anvil  36 . 
     Device  10  may be turned on via an activation switch  65  or device  10  may be activated by sensing a low force limit, e.g., force F 1  of  FIG. 8 . Once device  10  is turned on, an encoder count of encoder wheel  62  is communicated to processor  64 . At this time, golf ball  16  is compressed by continuing to rotate handle  58  in a first direction to continue to rotate threaded rod  50  for continued axial displacement of lower anvil  36  in an upward direction. The axial displacement of lower anvil  36  produces a corresponding deflection of golf ball  16 . 
     The axial displacement of lower anvil  36  and the corresponding deflection of golf ball  16  is calculated by counting a number of rotations of threaded rod  50  with encoder wheel  62 . With the known thread pitch of threaded rod  50  and the known number of rotations of threaded rod  50 , axial displacement and golf ball deflection may be measured by encoding the rotation of threaded rod  50 . Alternatively, deflection may be calculated by deflection gauge  63  ( FIG. 3 ). 
     As best shown in  FIG. 5 , due to an upward force provided by lower anvil  36 , upper anvil  20  is additionally displaced such that upwardly facing protuberance  28  of upper anvil  20  contacts beam  30  of tension measuring device  32 . Additional compression of golf ball  16  provided by further rotations of handle  58  results in a deflection of beam  30 . Tension measuring device  32  determines a force applied by upwardly facing protuberance  28  against beam  30 . The force measurement, or load information, of tension measuring device  32  is then communicated to processor  64 . Once a force measurement of at least F 2  is communicated to processor  64 , processor  64  then calculates a spring rate of golf ball  16  by dividing the force calculation by the deflection of golf ball  16 . The spring rate of golf ball  16  is then converted by processor  64  to a compression scale value in accordance with the graph of  FIG. 11 . The compression scale value is then displayed on display screen  66 , which alerts a user that further compression, i.e., further rotation of handle  58 , is not required. Encoder wheel  62  or deflection gauge  63  is read to determine if lower anvil  36  is lowered after a period of time, e.g., after 5 seconds. If lower anvil  36  is not reduced, then a user is alerted that the golf ball should be removed, e.g., by flashing display  68  or by other warnings. 
     Handle  58  may then be rotated in a second direction to lower the lower anvil  36 , thereby eliminating the compression forces on golf ball  16 . Golf ball  16  may then be removed from ball receiving receptacle  14  of device  10 . Processor  64  is preferably shut down after a period of non-use, e.g., after 30 seconds. 
     By using the methods described above, a spring rate and compression scale value may be obtained for a golf ball  16  placed in the ball receiving receptacle  14 . Referring now to  FIG. 8 , shown is a graphical representation of the force v. deflection data from measurements conducted by device  10  of the invention. The x-axis represents a deflection value of golf ball  16 . The y-axis indicates a force value delivered by device  10  to create deflection of ball  16 . High force/deflection curve  100  indicates a spring rate of a golf ball having a high compression scale value. High force/deflection curve  100  is calculated by measuring a first force (F 1 ) required to achieve a first ball deflection (D 1 ) and plotting point  102 . A higher, second force (F 2 ), required to achieve a second ball deflection (D 2 ) is measured and plotted as point  104 . Other data points at deflections between D 1  and D 2  may also be measured and plotted. An example spring rate of a golf ball having a high compression scale value is the change in force divided by the change in deflection, i.e.,
 
Spring Rate=( F 2 −F 1)/( D 2 −D 1)
 
     Still referring to  FIG. 8 , low force/deflection curve  106  indicates a spring rate of a golf ball having a relatively low compression scale value. Curve  106  is calculated by measuring a first force (F 1 ) required to achieve a first ball deflection (D 1 ′) and plotting point  108 . A higher, second force (F 2 ) required to achieve a second ball deflection (D 2 ′) is measured and plotted as point  110 . An example spring rate of a golf ball having a low compression scale value is the change in force divided by the change in deflection, i.e.,
 
Spring Rate=( F 2 −F 1)/( D 2′− D 1′)
 
     The calculated spring rate is converted to a compression scale value in software in the processor  64 . The calculated compression scale value is then displayed on display screen  66 . 
     The measurement of additional balls having a spring rate between the spring rate of a golf ball having a high compression scale value and a golf ball having a low compression scale value will generate additional force/deflection curves, e.g., curves  112 ,  114  and  116 . In all cases, a low application of force, i.e., F 1 , and a high application of force, i.e., F 2 , are applied. The additional force/deflection curves, e.g., curves  112 ,  114  and  116 , are bounded by high compression curve  100  and low compression curve  106 . Therefore, accurate determination of the spring rate is dependent upon taking deflection measurements between deflections D 1  and D 1 ′ at force F 1  and is dependent upon taking deflection measurements between deflections D 2  and D 2 ′ at force F 2 . 
     Force/deflection curves  112 ,  114 , and  116  are generated by measuring ball deflection at various compression forces of golf balls having mid-range compression rates. Lines  100 ,  112 ,  116  and  106  are substantially parallel to one another within the selected force measurement range of F 1  to F 2 . Therefore, measurements taken with the selected force measurement range of F 1  to F 2  provide greater differentiations as compared to measurements taken at lower force ranges, e.g., from 0 to F 1 . Care should be taken to select an upper force F 2  that is less than a force that may permanently change the size of a golf ball. In one embodiment, a mechanical step is provided for preventing an application of force that is greater than 200 lbs. Typically, force F 2  is approximately twice the magnitude of force F 1 . In a preferred embodiment, F 1  has a value of 10 lbs. and F 2  has a value of 130 lbs., although other values may also be used. 
     The device of the invention is, therefore, useful for providing an ability to measure a spring rate of a golf ball and to calculate and display a compression scale value while a golfer is playing a round of golf. 
     Thus, the present invention is well adapted to carry out the objectives and attain the ends and advantages mentioned above as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, numerous changes and modifications will be apparent to those of ordinary skill in the art. Such changes and modifications are encompassed within the spirit of this invention as defined by the claims.