Abstract
In this work we propose a novel method for impact position estimation during baseball batting, which is independent of impact intensity, i.e., force-irrelevant. In our experiments, we mount a piezoelectric vibration sensor on the knob of a wooden bat to record: (1) 3600 vibration signals (waveforms) from ball–bat impacts in the static experiment—30 impacts from each of 40 positions (distributed 1–40 cm from the end of the barrel) and 3 intensities (drop heights at 75, 100, and 125 cm, resp.), and (2) 45 vibration signals from actual battings by three baseball players in the dynamic experiment. The results show that the peak amplitude of the signal in the time domain, and the peaks of the first, second, and third eigenfrequencies (EFs) of the bat all increase with the impact intensity. However, the ratios of peaks at these three EFs (1st/2nd, 2nd/3rd, and 1st/3rd) hardly change with the impact intensity, and the observation is consistent for both the static and dynamic experiments across all impact positions. In conclusion, we have observed that the ratios of peaks at the first three EFs are a force-irrelevant feature, which can be used to estimate the impact position in baseball batting.
Highlights
In baseball batting, the impact position of the ball on the bat is one of the key factors related to batting performance [1,2] and injury [3]
In another work [5], the sweet spot of a wooden baseball bat is represented by an impact zone of only about 3 cm long, where the force and the impulse transmitted to the hands are both minimized [5]
Osawa, Tanaka, Yanai and Sano [14] used the vibration signal retrieved from polyvinylidene difluoride (PVDF) films on the knob of the bat, and estimated the impact positions by calculating the peak amplitude of the filtered signal within the 80–300 Hz band
Summary
The impact position of the ball on the bat is one of the key factors related to batting performance [1,2] and injury [3]. Osawa, Tanaka, Yanai and Sano [14] used the vibration signal retrieved from polyvinylidene difluoride (PVDF) films on the knob of the bat, and estimated the impact positions by calculating the peak amplitude of the filtered signal within the 80–300 Hz band In their static experiment, they collected five measurement data (i.e., 5 impacts) from each of the nine positions (distributed 1–40 cm from the end of the barrel, with a stride of 5 cm) and two intensities (drop heights at 1 and 1.5 m, respectively). The vibration signal features taken are the peak amplitude of the time-domain signal, the peaks at the first three EFs in frequency domain, as well as the ratios of peaks at first three EFs. We perform a series of static and dynamic experiments, and show that the ratios of peaks at the first three EFs in the frequency domain are a force-irrelevant feature, which can be used to estimate the impact position in baseball batting
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