| 摘要 |
<p>In order to provide an ink level detecting unit of an ink jet recording apparatus, which detects surely residual vibration by resonance with a medium such as ink coming into contact with a vibration element without receiving influences such as noise, thereby to heighten ink detection accuracy and reliability, there are provided a piezoelectric element 12 provided in an ink tank 11, an excitation pulse generating part 13 for applying an excitation pulse to the piezoelectric element 12, a sensor 14 which detects a frequency of a counter electromotive force waveform from the piezoelectric element 12 based on residual vibration by resonance with a medium in the ink tank 11, and a judgment part 15 which judges the existence of ink on the basis of the detected frequency. The sensor 14 has two band pass filters 22A and 22B which cause only waveforms in the predetermined frequency bands that have been previously assumed according to ink presence and ink absence to pass; and a frequency measuring part 150 which binarizes the counter electromotive force waveform, counts the number of pulses of the binarized counter electromotive force waveform, counts time from the predetermined number-th pulse to the predetermined number of pulse, and detects a frequency of the counter electromotive force waveform on the basis of this time. <IMAGE></p> |
