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A Performance Analysis System for the Sport of Bowling

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Light Level<br />

100<br />

90<br />

80<br />

70<br />

60<br />

50<br />

40<br />

30<br />

20<br />

10<br />

0<br />

Release<br />

Point<br />

-50 0 100 200 300 400 500 600 700 800<br />

Milliseconds (since Release)<br />

Figure 3-2: Raw Data Release Region (800 ms)<br />

By considering <strong>the</strong> nature <strong>of</strong> <strong>the</strong> ideal wave<strong>for</strong>m (an increasing frequency "chirp"), it is<br />

possible to deduce <strong>the</strong> shape <strong>of</strong> <strong>the</strong> frequency spectrum <strong>of</strong> <strong>the</strong> raw data. Since <strong>the</strong> lane is<br />

more heavily oiled near <strong>the</strong> foul line, <strong>the</strong> coefficient <strong>of</strong> friction is lower, and <strong>the</strong> ball will<br />

slide more. This sliding prevents <strong>the</strong> ball's linear momentum from being transferred into<br />

angular momentum, thus maintaining a fairly constant velocity <strong>for</strong> <strong>the</strong> first few<br />

revolutions <strong>of</strong> <strong>the</strong> ball. Thus, a fundamental frequency is established that is close to <strong>the</strong><br />

initial angular velocity at release.<br />

140<br />

120<br />

100<br />

Impact<br />

(Head Pin)<br />

Light Level<br />

80<br />

60<br />

40<br />

20<br />

0<br />

2000<br />

2100 2200 2300 2400 2500 2600 2700 2800<br />

Milliseconds (since Release)<br />

Figure 3-3: Raw Data Impact Region (800 ms)<br />

As <strong>the</strong> ball continues down <strong>the</strong> lane, it eventually gains angular velocity, and this change<br />

will be reflected in additional higher frequency content, albeit with a decreasing<br />

magnitude, in <strong>the</strong> frequency bands immediately adjacent to <strong>the</strong> fundamental frequency.<br />

Due to <strong>the</strong> harmonic content introduced by <strong>the</strong> sharp peaks and multiple local peaks,<br />

<strong>the</strong>re should be additional frequency content at integer multiples <strong>of</strong> <strong>the</strong> fundamental<br />

frequency, appearing as an attenuated "echo" <strong>of</strong> <strong>the</strong> shape <strong>of</strong> <strong>the</strong> frequency content<br />

around <strong>the</strong> fundamental. The characteristic frequency spectrum shape just described is<br />

shown in Figure 3-4.<br />

43

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