Towards zero-defect inkjet printing via piezo self-sensing signals

초록

Piezo self-sensing has attracted significant interest for inkjet monitoring due to its ability to rapidly assess the jetting status of multiple nozzles using the piezo actuator itself as a sensor, eliminating the need for additional hardware. However, simultaneous use of piezo elements for both actuation and sensing presents challenges, as the differing electrical requirements often lead to weak sensing signals, limiting the detection of subtle jetting anomalies. To address this issue, we propose an impedance modifier circuit based on bidirectional diodes connected to the driver output. This circuit provides low output impedance during actuation and high output impedance immediately after, thereby enhancing the sensing signal without affecting jetting performance. The method is scalable and compatible with multi-head systems. To validate its feasibility, we developed a real-time monitoring system capable of simultaneously evaluating two inkjet heads. In experiments involving approximately 3000 cases of both intentional and unintentional jetting failures, the system accurately classified all events-distinguishing not only between normal and faulty nozzles but also identifying specific failure modes. Furthermore, a printing test using a 360 DPI bitmap image (1024 x 500 pixels) confirmed the method's effectiveness, achieving defect-free printing through automatic selection of functional nozzles via piezo self-sensing.

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