Abstract:
A hand-held compression-tester for golf balls applies a biasing force to the golf-ball, loads it, and then releases the load so that only the biasing force remains. Based on the evolution of a loading curve during these intervals, the compression-tester estimates a compression value.

Description:
RELATED APPLICATIONS 
       [0001]    This is a continuation of U.S. application Ser. No. 15/081,209, filed on Mar. 25, 2016, which is a continuation-in-part of international application PCT/US2014/057447, filed on Sep. 25, 2014, which claims the benefit of the Feb. 26, 2014 priority date of U.S. Provisional Application 61/944,813 and the Sep. 25, 2013 priority date of U.S. Provisional Application 61/882,051, the contents of all of which are herein incorporated by reference. 
     
    
     FIELD OF INVENTION 
       [0002]    The invention generally relates to golf, and in particular, to golf-balls. 
       BACKGROUND 
       [0003]    Golfing is a sport of increasing popularity among people of all ages. With the increase in popularity, golfers are continually striving to improve their game. Advancements in golf instruction, golf analytics, golf clubs, and golf-balls all aid this endeavor. 
         [0004]    Proper golf-ball selection paired with a player&#39;s abilities can lead to improved golfing satisfaction and performance. An important property of a golf-ball is its compressions value. 
         [0005]    Golf-ball manufacturers offer a range of golf-ball compression values. However, these compression values change with time. Such changes arise from many causes, including exposure to air, immersion in water, and temperature changes. 
         [0006]    Golf-balls are frequently stored in golf bags that are kept in trunks of hot cars. In many cases, golf-balls are recovered from water hazards. As a result, variation of a golf-ball&#39;s compressibility can be considerable. This variation of compression can have adverse effects on a golf-ball&#39;s performance, and ultimately, on the golfer&#39;s game. 
       SUMMARY 
       [0007]    The invention is based on the recognition that a more accurate for measurement of golf-ball compression is a dynamic measurement that evaluates the evolution of force during a measurement interval to estimate the compression value of a golf-ball. Because modern golf-balls are elastomers, the force compressing a ball to a fixed deflection varies over time. The present invention uses the varying force over the measuring interval to get an improved force value with only a modest deflection. Since only a modest deflection is needed, the forces required to test the golf-ball are lower. In fact, they are low enough to enable the device to be operated with one hand. 
         [0008]    The present invention is directed to a golf-ball compression measurement apparatus. The apparatus includes an opening sized to receive a golf-ball. The opening is formed by a support structure and a beam. Upon receipt of the golf-ball, the golf-ball is compressed for the first time. The force exerted upon the beam over time by the compressed ball is proportional to a modulus, and thus the compression value. The force of the compressed golf-ball, which is different for different hardness of golf-balls, is measured by a strain gauge attached to the beam. A time series of force reading is stored in the computing device. This time series is then used as a basis for fitting a curve. Subsequent calculations then extract a single force that can be used as a basis for evaluating compression values. The ball is further compressed by a predetermined distance, again the force time series collected and a second curve is fit. The second single force point is chosen and knowing the deflections built into the devise a compression value is calculated and then displayed. 
         [0009]    In effect, the measurement algorithm described above provides a dynamic model of the golf-ball as a spring and damper system. The benefit of compressing the golf-ball by a predetermined distance is that an accurate compression value can be calculated without having to measure the distance that the device has traveled. 
         [0010]    In one aspect, the invention features a hand-held golf-ball compression meter. Such golf-ball compression meter includes a housing having a wall forming a circular opening on a first side thereof that has a circumference sized to receive a golf ball, an actuator configured to apply a first force to a golf ball, and an internal support structure that transmits a second force to a load beam coupled to a strain gauge. The compression meter also includes a computing system that receives, from the load beam, a load signal indicative of the second force. The computing system, obtains the load signal, a time series of force values and derives, from that time series, a golf-ball compression value and displays information indicative of that value on a display. 
         [0011]    In some embodiments, the internal support structure comprises first and second golf-ball retainers that face each other and that define between them a space for positioning the golf-ball for measurement of the compression value thereof. 
         [0012]    In other embodiments, the internal support structure comprises a compression pin positioned on a shim above the strain-gauge load beam. 
         [0013]    Also among the embodiments are those in which the computing system causes the display to indicate the compression value using both textual information and graphic information. 
         [0014]    In still other embodiments, the golf-ball compression meter comprises a communication interface for transmitting data to an external receiver. 
         [0015]    Also among the embodiments are those that have a linkage that causes the compression meter to transition between a first state in which the compression meter applies a first force to the golf ball and a second state in which the compression meter applies a second force to the golf ball. 
         [0016]    In another aspect, the invention features a method for measuring a compression value of a golf-ball by imposing a first force to cause the golf-ball to transition into a first loaded state, imposing a second force that, when added to the first force, causes the golf-ball to transition into a second state, releasing the second force, thereby permitting the golf-ball to transition back to the first state, measuring a time-varying load on the golf-ball during the transition back to the first state, and based at least in part on the time-varying load, estimating the compression value. 
         [0017]    Practices of the invention include those in which measuring a time-varying load comprises causing the golf-ball to engage a load-beam of a strain-gauge, and providing an output of the strain-gauge to a processing system, those in which estimating the compression value comprises fitting a curve through the time-varying load and basing the estimate at least in part on a point on the fitted curve, and those in which estimating the compression value comprises fitting a curve through the time-varying load and basing the estimate at least in part on first and second points on the fitted curve. 
         [0018]    In some practices, the first point is on a loading portion of the curve and the second point is on a recovery portion of the curve. 
         [0019]    These and other features of the invention will be apparent from the following detailed description and the accompanying drawings, in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is an isometric view of a golf-ball compression meter; 
           [0021]      FIG. 2  shows internal components of the compression meter shown in  FIG. 1 . 
           [0022]      FIG. 3  shows a close-up of a portion of the internal components shown in  FIG. 2 ; 
           [0023]      FIG. 4  shows a method for estimating compression value; 
           [0024]      FIG. 5  shows a load curve; 
           [0025]      FIG. 6  shows an actuator in the disengaged position 
           [0026]      FIG. 7  shows an actuator in the engaged position 
           [0027]      FIG. 8  shows an isometric view of an alternative embodiment of a golf-ball compression meter; 
           [0028]      FIG. 9  is a cross-section of the compression meter shown in  FIG. 8 ; 
           [0029]      FIG. 10  is a flow-chart of a method for calculating a compression value using the compression meter in  FIG. 8 ; 
           [0030]      FIG. 11  shows a cross-section of a housing prior to the loading phase shown in  FIG. 5 ; and 
           [0031]      FIG. 12  shows a cross-section of the housing in the loading phase shown in  FIG. 5 . 
           [0032]      FIG. 13  shows the rubber or elastomeric ring that surrounds the release button. 
           [0033]      FIG. 14  shows a textured region that enhances the grip and identifies the finger position that facilitates pressing the release button. 
           [0034]      FIG. 15  shows details of snap clips that provide support in keeping the two halves of the housing together under load. 
           [0035]      FIG. 16  shows fiducials used to visually align a golf-ball for insertion into the compression meter. 
       
    
    
     DETAILED DESCRIPTION 
       [0036]    As shown in  FIG. 1 , an exemplary golf-ball compression meter  8  includes a housing  10  sized to be easily held by a player&#39;s hand. The housing  10  can made of any of a variety of materials, including metal, carbon, glass-fiber composites, plastic, or combinations thereof. 
         [0037]    The housing  10  includes a display  16  on a top section  18  thereof. Examples of a display  16  include those that have a light-emitting diode display (LED) and those that have a liquid-crystal display (LCD). 
         [0038]    A hole  12  extends through the housing  10  from a front side  11  to a rear side  13  thereof. The front  11  side has a front opening  14  adapted to receive a golf-ball  21 . The rear side  13  has a corresponding rear opening  15  whose circumference is less than that of the front opening  14 . The smaller circumference of the rear opening  15  prevents a golf-ball that has pressed through the front opening  14  from falling out of the housing  10  through the rear opening  15 . The rear opening  15  also provides a convenient place for a user to push against a golf-ball to eject it. 
         [0039]    The rear opening&#39;s smaller circumference is sized to enable proper positioning of a golf-ball  21  between an upper ball-retainer  20  and a lower ball-retainer  22 . The upper ball-retainer  20  and the lower ball-retainer  22  are positioned above and below the front opening  14  respectively. 
         [0040]    Within the housing  10  is a load beam  24  fitted with a strain gauge  25 , which can also be seen in more detail in  FIG. 3 . Also within the housing  10  is an internal support structure that provides an interface between the golf-ball and the load beam  24 . In some embodiments, the internal support structure takes the form of a compression pin  26  that sits between the lower ball-retainer  22  and on a shim  27  supported by the load beam  24 . 
         [0041]    A computing system  28  links to the display  16  and to the load beam  24  using suitable wiring. A power supply  29  provides power for both the computing system  28  and the display  16 . In one embodiment, the power supply  29  is a replaceable battery. In a typical embodiment, the computing system  28  includes a processor and a memory. In some embodiments, the computing system  28  is configured for data exchange. In these embodiments, the computing system  28  further includes a Universal Serial Bus (USB) port, Blue Tooth, and/or a WiFi adapter to facilitate data exchange. The exchanged data may then be used to track compression values of golf-balls from a particular manufacturer, from different manufacturers, and/or over periods of time. The compression value can also be provided to a second device, such as a smart phone, a GPS devices and/or another data receivers. As a result becomes possible to conveniently compression numbers of golf-balls from a particular manufacturer, from different manufacturers, and/or over periods of time. 
         [0042]    In a preferred embodiment, the front section of the housing  10  has a 1.70″ diameter opening that accepts a standard size golf-ball and a 1.375″ opening on the rear section of the housing  10  that centers the golf-ball above the compression pin  26 . The radius of the lower ball-retainer  22  is greater than that of the ball&#39;s diameter. This ensures that the internal support structure can transfer the entire compressive load to the load beam  24 . 
         [0043]    As shown in  FIG. 4 , a method of determining golf-ball compression includes receiving a golf-ball through the front opening  14  in the housing  10  so that the load beam  24  can support it (step  30 ), and positioning the received golf-ball over the internal support structure and the strain gauge load beam  24  with a second opening in the housing  10  (step  32 ). This is followed by determining a compression value of the golf-ball from a resulting compressing of the golf-ball in the first opening (step  34 ) and displaying the compression value on the display  16  (step  36 ). 
         [0044]    In general, numeric compression values would vary noticeably depending on the orientation in which the ball is inserted into the compression meter  8 . Therefore, to avoid confusion, it is preferable to quantize the compression value before display into one of several ranges and to simply identify range of values on the display  16 . Thus, instead of displaying an actual numerical value, the display  16  displays a range in which the numerical value falls. 
         [0045]    The display can communicate these ranges in any of several ways. For instance, the display can display words, such as “very soft,” “soft,” “medium,” “firm”” or “very firm.” 
         [0046]    In another embodiment, the display communicates the ranges as different colors. For example, black may indicate high compression value and a red may indicate lower compression. 
         [0047]    In another embodiment, the display communicates the ranges using a gradient scale in which a number of illuminated bars indicate the ball&#39;s hardness. 
         [0048]    Compression value is related to the ratio of compressive stress to compressive strain, which is sometimes referred to as the golf-ball&#39;s modulus. Compressive stress is the compressive force divided by the area of the sample. Compressive strain is the change in length from the uncompressed state to the compressed state divided by the uncompressed length. 
         [0049]    The compression meter  8  operates by applying a first load to the golf-ball, thus causing it to transition into a biased state, adding a second load to the first load, thus causing the golf-ball to transition into a loaded state, and then releasing the second load, thus causing the golf-ball to revert back to its biased state. 
         [0050]    Referring to  FIG. 5 , the foregoing procedure results in a load signal  37  having a biasing phase  38 , a loading phase  40 , and a recovery phase  42 . The illustrated load signal  37  is obtained as a time series. Thus, in  FIG. 5 , the horizontal axis is time and the vertical axis is a measure of load.  FIG. 5  thus shows a time series of load values. 
         [0051]    The biasing phase  38  begins when the user inserts the golf-ball into the hole  12 . This places the golf-ball into the biased state in which its diameter is reduced to the first diameter. As is apparent from  FIG. 10 , there is a relatively low load that settles into equilibrium. 
         [0052]    The loading phase  40  begins when the user activates the actuator, thus squeezing the golf-ball into the loaded state. This results in a much higher load that likewise settles into equilibrium. 
         [0053]    The recovery phase  42  begins when the user releases the force that caused the ball to be in the loaded state. As a result, the ball is free to revert to the biased state. 
         [0054]    As can be seen in  FIG. 5 , curve fitting a times series promotes precision by smoothing out the irregularities in the many individual data points. The improved load-reading precision also allows lower forces to be applied to the golf-ball and more accurate compression values to be determined using the two fixed deflections. The lower forces, coupled with the mechanical advantage of the linkages discussed below enable one handed operation of the compression meter. 
         [0055]      FIG. 5  also shows why using the force time series data from the unloading portion of the curve to select the low load point is advantageous. In the initial loading of the ball in the very first fraction of a second that the ball is compressed, it goes through an initial reduction in the required force and then very shortly the force value increases. At that point the force decays slightly before starting to increase again. Upon increasing the force to the higher level, the force again decays a small amount. One embodiment is to use the force value at the end of the high load time series before it starts to increase. This embodiment uses the beginning of the unloading low load force time series as the selected low force as this curve is well behaved without the abrupt changes in force seen during the initial low loading. 
         [0056]    In operation, the user presses the golf-ball by hand through the front opening  14  so that it rests on top of the compression pin  26 , which itself is on the shim  27  supported by the strain gauge&#39;s load beam  24 . This compresses the golf-ball in the process, thus placing it in its biased state. The biased golf-ball now exerts a force on the load beam  24 . This force is proportional to the modulus of the golf-ball, and thus the compression value. 
         [0057]    The load beam  24  provides the strain gauge  25  with a basis for measuring this force. The strain gauge  25  provides its measurement to the computing system  28 , which calculates an appropriate value to show on the display  16 . 
         [0058]    Preferably, the golf-ball is compressed with minimal or no rotation, as would occur if one were using a screw or a similar device. 
         [0059]    The measuring system uses a strain gauge  25  to measure the force used to compress the golf-ball. The internal support structure controls golf-ball placement within the housing  10  and prevents unnecessary golf-ball movement. 
         [0060]      FIG. 6  shows an embodiment in which an actuator comprises a lever arm  502  having a cam  506  on a distal end thereof. When the user moves the lever arm  502 , the cam  506  causes an upper compression pin  504  to exert a first force on the golf-ball. This causes the golf-ball to transition into its loaded state. 
         [0061]    The golf-ball rests on a lower compression pin  26 , which rests on a shim  27  that ultimately transmits a second force to the load beam  24  of the strain gauge  25 . The strain gauge  25  provides a load signal  37  indicative of the load on the golf-ball to the computing system  28 . 
         [0062]    In  FIG. 6 , the lever arm  502  is in a disengaged position. In this position, the golf-ball  21  is biased as a result of being within a space that has a first diameter D 1  that is slightly smaller than the nominal diameter D 0  of the golf-ball  21 . This places the golf-ball  21  in an initial state in which it experiences a load associated with the difference between the nominal diameter and the first diameter. By subjecting each golf-ball to a constant bias prior to the actual measurement of compression value, the compression meter  8  tends to eliminate errors caused by variations in golf-balls. This tends to promote accuracy. 
         [0063]    In  FIG. 7 , the lever arm  502  has been moved into an engaged position. This results in application of a force that causes the golf-ball  21  to deform until it reaches a second diameter D 2 . At this point, the golf-ball  21  is in its loaded state. This force is maintained until the golf-ball  21  reaches an equilibrium final state. When this force is released, the golf-ball  21  begins the process of recovery to its biased state. 
         [0064]    During the loading phase  40 , the lever arm  502  deforms the golf-ball. This requires work, which is manifested in an increase in the internal energy of the golf-ball  21 . In the recovery portion, the golf-ball  21  releases the internal energy as it recovers its original shape. The rate at which the golf-ball  21  releases this internal energy provides information on its compression value. From the point of view of the computing system  28 , the rate at which this energy is released can be derived by analysis of a time series showing the evolution of this load signal  37  over time. This time series thus contains important information concerning the properties of the golf-ball  21 . 
         [0065]    Golf-balls are typically viscoelastic. This means that when the golf-ball is compressed to a fixed distance, its load signal  37  will have an initial maximum load followed by decay over time. To estimate the load, the computing system  28  fits an equation to the decay curve. Suitable equations reply on a log fit or an exponential fit. 
         [0066]    After having estimated an analytic representation of the fitting function, the computing system  28  can either extrapolate to shorter or longer than recorded times (abscissa values) or rely on an abscissa associated with a fixed ordinate as a basis for measurement. This ordinate represents a constant offset from the instant that the initial load is applied. The offset, in the case of the loading phase, should be long enough to allow the golf-ball to reach equilibrium. A suitable offset in many cases is one second after the maximum load. The offset in the case of the recovering bias state is chosen to be very short. Preferably, the offset is much less than 1 second. 
         [0067]      FIG. 5  shows first and second points  44 ,  45  that are used as a basis for estimating compression value. The first point  44  corresponds to a higher load and the second point  45 . In the embodiment describe herein, the time corresponding to the second point  45  comes after the time corresponding to the first point  44 . This is believed to provide a more accurate estimate. However, in principle it is also possible for the second point  45  to come before the first point  44 . 
         [0068]      FIG. 8  is an isometric view of a compression meter  8  having a housing  10  consisting of a ventral half  46  and a dorsal half  48  joined together. A trigger  50  on the ventral half  46  causes a golf-ball to transition from its biased state to its loaded state. A release button  52  on the dorsal half  48  causes the golf-ball to transition from its loaded state back to the biased state. 
         [0069]      FIG. 9  shows a cross-section of the housing  10  in  FIG. 8  in which one can see that when a user squeezes the trigger  50 , it compresses a first spring  54  and moves a first linkage,  56  into engaged position. This, in turn, compresses a leaf spring and a second spring  58 . This causes part of the release button  52  to protrude out of the housing  10  so that the user will later be able to cause the golf-ball to transition back to the biased state. 
         [0070]    The first linkage  56  moves a second linkage  60  into an engaged position. The second linkage  60  then moves a lower anvil  62  into its engaged position. The lower anvil  62  exerts additional force onto the golf-ball, thus placing it into its loaded state. The increase force exerted on the golf-ball is transmitted to an upper anvil  64  and eventually conveyed to a load module  66  that includes the strain gauge  25  and other components described in connection with  FIG. 1-3  for measuring load. The anvils  62 ,  64  can take on a variety of forms, such as a diamond form, a hexagonal form, or an octagonal form. 
         [0071]    Once the user has pressed the trigger  50 , the processing system  28  goes to work recording the load signal  37 . A short time thereafter, the display  16  will instruct the user to press the release button  52 . 
         [0072]    Pressing the release button  52  ends the loading phase  40  by pushing the first and second linkages  56 ,  60  back to the unengaged position and drawing the lower anvil  62  back to the position it was in during the biasing phase  38 . It also returns the trigger  50  back to its original position protruding out from the housing  10  with some help from the first spring  54 . The processor  28  then continues to record the load signal  37 , selects the representative high and low force values at the first and second ordinates  44 ,  45 , and calculates and displays information indicative of the compression value on the display  16 . 
         [0073]    The first and second linkages  56 ,  60  allow multiple diameters to be measured. The opening  12  is slightly smaller than the industry-standard nominal golf-ball diameter of 1.68 inches. Inserting the golf-ball  21  into the opening  12  places the golf ball into a ball chamber that is slightly too small for the golf ball. This compresses the ball and exerts a bias force on the strain gauge  26  beneath the golf-ball  21 . By engaging the linkages  56 ,  60  to a fixed stop, the user reduces size of the ball chamber. This further compresses the golf-ball  21 . Since the two sizes of the ball chamber have been pre-defined, the computing system  28  can calculate the difference between F 1  and F 2  to yield the slope of the load deflection curve. The computing system  28  converts this value to a rating familiar to golfers and displays it on the display  16 . 
         [0074]    Referring now to  FIG. 10  the two-step method carried out by the computing system  28  includes receiving a golf ball into the ball chamber (step  68 ) so that the strain gauge  25  measures a bias force (step  70 ). The user then squeezes the trigger, thus shrinking the ball chamber (step  72 ) and increasing the loading force significantly (step  74 ). After a brief interval, display  16  prompts the user to press the release button. In response, the user presses the release button (step  75 ). The processor then records a time series as the load signal  37  transitions from the loading phase  40  to the recovery phase  42 , where the ball  21  again experiences the same initial bias force F 1 . 
         [0075]    Based on the recorded time series, the computing system  28  then calculates a slope based on the points identified by the first and second ordinates  44 ,  45  (step  76 ) and the fixed deflection. The computing system  28  then converts this slope to the corresponding commercial compression rating (step  78 ) and displays information indicative of the compression rating on the display  16  (step  80 ). 
         [0076]    In determining compression value obtained from two points along the load signal  37 , the compression meter  8  calculates a slope, converts it into a form that would be familiar to golfers, and shows the result on the display  16 . An advantage of this method is that one can determined a golf-ball&#39;s compression without having to know its initial diameter. This eliminates error caused by manufacturing variations, as well as size changes resulting from environmental variables, such as temperature. The use of two known positions removes the requirement for measuring displacement. This results in a particularly simple compression meter  8  that avoids the use of complex devices such as linear encoders to determine displacement. 
         [0077]    By obtaining two compression measurements without removing the ball or adjusting its position, the data are collected over the same surface features, thereby negating any dimple effects. Furthermore, when Dl and D 2  are appropriately small, the ball&#39;s load/displacement characteristics are comfortably within the linear region of the curve. Therefore, the device calculates the compression rating in a regime below a golf club strike, producing an accurate and valuable measurement for the golfer, without damaging the ball. 
         [0078]      FIG. 11  shows a cross-section of the housing  10  when the compression meter  8  is in the disengaged position of the biasing phase  38 , in which the linkages  56 ,  60  are positioned to make the low force measurements. To increase the force, the user would grip the device in one hand and use their fingers to squeeze the trigger  50 . 
         [0079]      FIG. 12  shows a cross-section of the compression meter  8  in the loading phase  40  just after the trigger  50  has been squeezed. The trigger  50  provides mechanical advantage and applies a greater force on the first linkage  56  to rotate the second linkage  60 . The second linkage  60  urges the release button  52  out of the housing  10 . The final part of the linkage is the lower anvil  62  which is attached to a distal end of the second linkage  60 . In the loading phase  40 , the lower anvil  62  moves into a position in which it further compresses the golf-ball  21 . 
         [0080]    As shown in  FIG. 13 , a thin ring  84  of rubber or elastomeric material surrounds the release button  52 . This ring  84  provides cushioning when the trigger action engages the linkages and snaps the release button  52  into its out position. It also dampens a great deal of objectionable noise. 
         [0081]    As shown in  FIG. 14 , a textured region  86  distal to the trigger  50  enhances the grip guides the user to the most advantageous location to grip the compression meter  8  to press the release button. 
         [0082]    This compression meter  8  is a precision measuring apparatus. It is therefore important to maintain the integrity of the housing  10  while simultaneously keeping weight to a practical minimum.  FIG. 15  shows details of the design for snap clips  88  that provide additional support in keeping the dorsal and ventral halves  46 ,  48  of the housing  10  together under load. 
         [0083]    In practice, measured compression values are a function of which axis on the ball one applies the compressive force. Thus, if one were to measure a ball&#39;s compression value, and to then remove the ball, rotate it ninety degrees, and re-insert the ball, the second compression value might well be different from the first. 
         [0084]    In recognition of the foregoing phenomenon, when inserting the ball, it is useful to orient the ball in the same manner as it will be oriented when being struck by a club after the measurement. This will ensure that the compression rating accurately represents the feel the golfer can expect upon contact. Some balls have as much as 10% difference between the compression value on one orthogonal axis compared to another.  FIG. 16  shows fiducials  90 ,  92  that can be used to visually align a golf-ball for insertion into the compression meter  8 . 
         [0085]    Other mechanisms can be used to compress the golf-ball. For example, in one embodiment, a closing motion of a clamshell exerts a compression force on the golf-ball. 
         [0086]    A compression meter  8  as described herein thus provides a convenient way to measure the compression of a golf-ball that is also small enough to fit into a golf bag and easy to use. It provides at least a reasonable estimate of that value by measuring deflection or strain and the force required to achieve that deflection.