Abstract:
A transistor logic device uses a signal from a transducer responsive to the centrifugal force experienced in or near the strike zone of a baseball bat during the swing to digitally process and numerically display numerals representative of the maximum centrifugal force experienced during the swing. Knowledge of the maximum force during the swing is useful on a comparative basis in improving batting performance and the speed of the swing can be computed or the displayed numbers can be converted into numbers revealing swing speed in miles per hour or other units. The use of digital data, dealt with digitally, and displayed digitally simplifies, and reduces the cost and size of the apparatus to allow it to be integrated within an actual baseball bat.

Description:
BACKGROUND 
     A number of sports depend upon skillful swinging of a bat, stick, club, racket, or other implement to drive a ball or other object. Perfection of the needed skill requires development of reproducible physical characteristics of the swing. The swing characteristics of path, speed, and power must be optimized and regularized to achieve a reliable, competitive athletic performance level. Training benefits from the ability to discern which factors require improvement, to what extent, and whether or not improvement is being accomplished. The ability to measure parameters related to the several factors of the swing characteristics provides the ability to gauge comparative improvement in relative terms as well as the ability to establish norms or goals in absolute terms. 
     Bringing a cylindrical bat into proper contact with a baseball traveling along an unpredictable path at speeds approaching 90 miles per hour requires a remarkable combination of eye, body, and mind coordination. The manifold factors of stance, grip, the motions of arms, legs, feet, head, and torso, and ball path estimation all are essential elements of the swing. They contribute in cumulative fashion to the result of a good hit. 
     The speed of the swing of the bat is determinative of two important variables; (1) the force imparted to the ball, and (2) the time available to the batter to decide whether or not to swing. An increase in swing speed desirably increases both variables. Assuming that other factors are fixed, a higher swing speed will result in a higher hit ball speed. A higher swing speed allows the swing to be initiated later in time, thereby increasing the time for decision. 
     It should be noted that for a baseball bat swing, it is desirable to minimize the time elapsed between the start (decision to swing) and ball contact, thereby desirably delaying the point in time at which the decision to swing is made. This is in contrast to other sports, such as golf, where the ball is stationary and the need to decide whether or not to swing is absent. In golf, the sector of the swing arch which requires the maximum velocity is that just prior to impact. The time elapsed between the start of the swing of the club and ball contact is, therefore, less important than in baseball. 
     In the past, swing speed was largely a matter of subjective opinion or feel. The inability conveniently to measure swing speed made it difficult to judge whether or not a refinement or modification in a batter&#39;s technique consistently resulted in a higher swing speed. While the desirability of some kind of measurement was appreciated, the means suggested have been cumbersome, applicable only to simulated clubs or bats, delayed in presentation until long after the event, or more theoretical than practical. 
     The present invention is concerned with the practical acquisition, processing, and presentation of data related to the speed of swing of an athletic implement such as a baseball bat actually used to hit balls and the method and apparatus for doing so. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In accordance with the present invention a numerical display related to the maximum swing speed is provided which is available immediately upon the swing of the bat. A transducer to provide data related to swing speed, a data processor, a digital display, and enabling circuitry are incorporated within the body of a baseball bat or other sports implement. Transistor-Transistor Logic (TTL) is employed wherein the information is digital (pulse counts), is dealt with digitally, and is displayed digitally. The digital treatment employed helps to minimize the size and cost of the device and to provide a unit small enough to be suitable for embedding within the physical confines of a baseball bat. 
     According to the present invention, the variable sensed and utilized is the maximum centrifugal force experienced by the transducer during the swing of the bat. While, in the context of the somewhat different problem of a golf club swing, an accelerometer has been suggested to be used to provide a signal related to linear acceleration experienced at the club head and that signal elsewhere integrated electrically to provide a signal related to linear velocity (See Evans U.S. Pat. No. 3,270,564 for example), the result is an approximation based upon hidden assumptions and delayed long in time. A far more accurate measure of the batter&#39;s performance is provided by direct sensing of centrifugal force. The maximum force which the batter delivers to the bat is the parameter most revealing of the performance of the batter. 
     While the measure of centrifugal force is the most meaningful parameter, the units of the measure are not units familiar to most batters. Rather than deal with actual force units, the invention contemplates display of a digit pair which represents, in unitless relative terms, the maximum force experienced by the transducer during the swing. 
     The digital output may be converted into, and displayed in the familiar units of speed in miles per hour. The maximum centrifugal force can be converted by computation into terms of swing speed using assumed dimensions for a normal batter&#39;s swing radius, or more accurately can be computed for a particular batter by utilizing a program containing factors descriptive of the dimensions of the particular batter&#39;s swing radius. These factors easily can be approximated closely by knowing only the height of the batter, the grip to strike zone distance, and the size of the bat. 
     The centrifugal force is sensed by a spring biased potentiometer actuated by a mass moved outwardly by the force. The force sensing potentiometer can be a conventional analog potentiometer device, or can be a discrete step (commutator) device in which a slider sequentially establishes communication with a series of discrete spots, as for example a multi-pole sliding switch. 
     A constant rate first clock provides pulses to a binary coded decimal (BCD) counter. A variable rate second clock having a variable frequency of pulses determined by the output signal of the force sensing potentiometer is connected to a gate at the input of counters which ultimately provide an output to a digital display which reflects the relative maximum force of the swing. Additional circuitry eliminates readings below a preselected threshold minimum, captures and selects the maximum value for the purpose of display, may convert the force equivalent digital information into velocity units for display and resets the device. 
    
    
     THE DRAWINGS 
     FIG. 1 is a logic block diagram showing the basic units of the data processing aspects of the invention; 
     FIG. 2 is a view perspective of the apparatus of the present invention as installed in a baseball bat; and 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     According to the present invention, the speed of a batter&#39;s swing is ascertained, processed and displayed by transistor logic and display circuitry integral with an actual baseball bat. The speed of the swing is measured by utilizing a variable resistance having a magnitude dependent upon the centrifugal force experienced by the bat in or near the strike zone of the bat. A transducer comprising a spring biased mass and a potentiometer having a resistance value related to the displacement of the spring biased mass is employed to provide the input variable to the logic circuitry. The centrifugal force experienced is the most significant parameter of the batter&#39;s swing performance which readily can be measured. That force is convertible into the more easily understood units of miles per hour by knowing or assuming constants related to the batter&#39;s physique. 
     In the transducer employed in the present invention, the centrifugal force (F c ) acts upon a restoration spring associated with the potentiometer in the bat to provide a displacement (x) to change the potentiometer resistance in relation to the displacement. 
     
         F.sub.c =kx 
    
     Centrifugal force is determined by: ##EQU1## 
     In the subject environment, the mass (m) acting against the transducer spring and the radius to the transducer (r) are constants in the centrifugal force equation. Linear velocity (v) and angular velocity () are variables. Simplifying by eliminating constants: 
     
         F.sub.c ≈v.sup.2 ≈ω.sup.2 
    
     The actual linear speed of the bat at the radius of the transducer can be calculated using: ##EQU2## 
     Turning now to FIG. 1, operation of the device is illustrated with reference to a logic block diagram. 
     CLOCK 1 is an oscillator having an output of pulses at a predetermined, fixed frequency. The output pulses are processed in the BCD COUNTER, a binary to decimal (BCD) converting counter the output of which is input to a SAMPLE RATE LOGIC device which produces signals used in conjunction with other circuitry to produce control signals. 
     A second clock oscillator (CLOCK 2) produces clock pulses at a variable rate which depends upon the variable resistance of the TRANSDUCER POTENTIOMETER of the centrifugal force measuring transducer in the baseball bat. The pulse from CLOCK 2 are input to a COUNTER GATE. When a control signal from the SAMPLE RATE LOGIC device is received at the other input of the COUNTER GATE, the pulses from CLOCK 2 are input to COUNTER, a cascaded pair of decimal counters which are provided with a pre-loaded count of 75 by an output of the SAMPLE RATE LOGIC device. When enabled, the COUNTER counts CLOCK 2 pulses in excess of 75. If, during the sample period, CLOCK 2 yields a sufficient count, the COUNTER will exceed 99 and overflow, thus producing a ROLL signal. 
     If a ROLL signal occurs during a valid sampling period, a VALID COUNT signal is produced which sets a flip-flop in the COUNT TRANSFER LOGIC device to enable the possibility of updating the DISPLAY. 
     A MEMORY LATCH device retains the previous highest count for display by the LED DISPLAY device. The COMPARATOR compares the latest count with the stored count, and, only if the latest count is higher, the new count is transferred to the MEMORY LATCH device to replace the prior count. 
     The LED DISPLAY may be a conventional light emitting diode device (LED) or a liquid crystal display (LCD) to produce a numeric decimal display of the count retained by the MEMORY LATCH device. To conserve power, the LED DISPLAY is stroboscopically pulsed. A RESET device clears the MEMORY LATCH device whenever a reset signal is received. 
     The entire apparatus or device easily is formed on a small printed circuit board using Transistor Transistor Logic (TTL) integrated circuits of the 74LS (low power Schottky) family. The assembly can be encapsulated in resin such as a silicone elastomer and implanted in a relatively small bore or excavation in a baseball bat. A small battery is required for circuit and display power and may be replaceable or rechargeable. 
     DESCRIPTION OF A PREFERRED EMBODIMENT 
     FIG. 2 illustrates a conventional wooden baseball bat having the device of the present invention integrated with it by excavation of a suitably shaped cavity 20 into which the device 10 is embedded. A cover plate 12 restores the exterior shape of the bat. A digital decimal display 14 provides the numerical value related to the measured swing. A switch 16 enables the circuit and a battery 18 powers it and the display 14. 
     Referring again to FIG. 1, the invention is shown as a logic block diagram. 
     CLOCK 1 and CLOCK 2 are halves of a dual pulse generating oscillator (U01) such as a 556 device. The CLOCK 1 oscillator section is provided with conventional external enabling circuitry including a trimpot for fine adjustment of clock frequency. The other half of the dual oscillator is used for CLOCK 2. The external enabling circuitry for CLOCK 2 includes the variable resistance of a force transducer, the TRANSDUCER POTENTIOMETER (R03), a 1/4 watt 10K Ω potentiometer. The variable resistance is used in an RC circuit to vary the frequency of pulses from CLOCK 2 in relation to the resistance of the TRANSDUCER POTENTIOMETER (R03), which resistance is representative of the displacement by centrifugal force experienced by the associated mass as the bat is swung. A suitable potentiometer is Maurey Instrument Corporation Number M 1326-1-103, 10K Ω. 
     The constant frequency pulses from CLOCK 1 are converted from binary to decimal in a BCD COUNTER (U03) such as a 74LS190 device. The four binary signal outputs representative of decimals 0-9 are directed to a SAMPLE RATE LOGIC device (U02) which comprises three of the four NOR gate portions of a 74LS02 device. 
     One signal output of the SAMPLE RATE LOGIC device is one input to the COUNTER GATE (U04) which comprises one NAND gate portion of a 74LS00. The function is to provide signals indicative of a fixed interval of a specific number of pulses, conveniently ten pulses. The other signal input to the COUNTER GATE is the pulses (variable in rate) from CLOCK 2. The output of the COUNTER GATE, when enabled during the fixed interval, is the train of pulses of CLOCK 2 during a valid count interval. These signal pulses are counted in the COUNTER. The COUNTER is a cascaded pair (U05 and U07) of 74LS190 decimal counters arranged to count up to decimal 99 and, upon the next pulse, then to overflow or roll over to output a ROLL signal. The COUNTER is preloaded with decimal 75 by the SAMPLE RATE LOGIC device to prevent counting below the threshold of 75. This avoids useless counting. The count signal representing the present count is directed to the COMPARATOR (U08) and U10) and to the MEMORY LATCH. The ROLL signal is directed to a COUNT TRANSFER LOGIC device (U02, U04, U06). 
     The COMPARATOR device comprises a pair of 74LS85 devices (U08 for the most significant digit and U10 for the least significant digit) for each of the two digits of the LED DISPLAY. The pair of devices in the COMPARATOR are connected to compare the prior count information stored in the MEMORY LATCH (which information represents the decimal numerals displayed at the LED DISPLAY) with the present or current count information from the COUNTER. If the current count is a valid count (meaning a count great enough to cause a ROLL signal), and if the current count is numerically greater than the count information stored in the MEMORY LATCH (the prior count), then the current count information is directed to the COUNT TRANSFER LOGIC device. 
     The COUNT TRANSFER LOGIC device is a combination of one NOR gate of a 74LS02 (U02); one NAND gate of a 74LS00 (U04); and a flip-flop of a 74LS85 (U-6). The function of the COUNT TRANSFER LOGIC device is to receive an enabling signal from the SAMPLE RATE LOGIC device once for every tens count cycle of the BCD to establish each counting interval; a signal from the counter representing the present or current count if a valid count (a count with a ROLL signal); and an enabling signal from the COMPARATOR if the current count is greater than the prior count stored in the MEMORY LATCH. If all conditions are met, then the COUNT TRANSFER LOGIC device transfers the new count to the MEMORY LATCH to replace (update) the count stored in the MEMORY LATCH and thereby the digits displayed by the LED DISPLAY. The LED DISPLAY comprises a pair of octal LED display panels (U12 and U13) and a pair of digital to octal drivers (U11 and U14) which are 74LS47 devices. The decimal numerals displayed by the LED DISPLAY is related to, but not necessarily numerically identical with, the count. A reset clears the memory latch. 
     In operation, every BCD count cycle (10 pulses of CLOCK 1) starts a sampling period or fixed interval for pulses from CLOCK 2. As the bat swing occurs, numerous sampling periods of CLOCK 2 pulses occur sequentially. The pulse rate of CLOCK 2 depends upon the centrifugal force experimented at the TRANSDUCER POTENTIOMETER. The count of CLOCK 2 pulses in each fixed interval or sample period is compared with the prior count of the previous sample period and, if greater, is forwarded to the octal drivers to update the decimal numerals displayed by the LED DISPLAY. Uselessly low counts are ignored. 
     The unitless digits of the decimal numerical display can be converted into bat speed by looking up the displayed number in a table such as TABLE I, below, suitable for the particular batter. 
     The radius (r) is the batter&#39;s swing radius which can be provided from a table conveniently based upon the observation that a person&#39;s arm reach is related to standing height. An exemplary table is provided below for a batter 70 inches tall: 
     
                       TABLE I______________________________________    (Batter Height 70 inches)    Bat Speed (mph)DIGITAL  Grip to Ball distance (inches)READING  16      18      20    22    24    26______________________________________ 5       27.4    28.0    28.5  29.1  29.6  30.110       30.4    31.0    3107  32.2  32.8  33.415       33.5    34.1    34.8  35.5  36.1  36.720       36.5    37.3    38.0  38.7  39.4  40.125       39.6    40.4    41.1  41.9  42.7  43.430       42.6    43.4    44.3  45.1  45.9  46.735       45.6    46.5    47.4  48.3  49.2  50.040       48.6    49.6    50.5  51.5  52.4  53.345       51.5    52.6    53.6  54.6  55.6  56.650       54.5    55.6    56.6  57.7  58.7  59.855       57.3    58.5    59.6  60.7  61.8  62.060       60.2    61.4    62.6  63.7  64.9  66.065       62.9    64.2    65.5  66.7  67.9  69.170       65.7    67.0    68.3  69.6  70.8  72.175       68.4    69.8    71.1  72.4  73.8  75.080       71.0    72.5    73.9  75.2  76.6  77.985       73.6    75.1    76.6  78.0  79.4  80.890       76.2    77.7    79.2  80.7  82.1  83.695       78.7    80.2    81.8  83.3  84.8  86.3100      81.1    82.7    84.3  85.9  87.5  89.0______________________________________