Aiming at the problem of the malfunction of knitting machines caused by the unstable operation of the piezoelectric needle selector during the jacquard process, a state detection scheme for the piezoelectric needle selector that integrates the sensor and drive function co-located is proposed. The motion state of bimorph piezoelectric cantilever beam and its bi-directional piezoelectric effect in the jacquard process of piezoelectric needle selector are analyzed. Electrical and dynamic models were established for the electrical characteristics inside the bimorph piezoelectric cantilever beam and the dynamic characteristics of the cutter head and baffle of the needle selector. The signal detection circuit is designed to realize the real-time detection of the piezoelectric needle selector state by analyzing the time domain and frequency domain characteristics of the electrical signal. The results show that in the normal working state of the piezoelectric needle selector, the internal electric signal of the piezoelectric driver has two characteristic frequencies, which are between 155 and 180 and between 1630 and 1670 Hz, and the time for the piece to swing to the limit position is relatively long under abnormal working conditions.

In this study, a dual-piezoelectric energy harvesting system with contact and non-contact characteristics was driven by a cantilever beam. The harvester performance of the multipoint energy harvesting system driven by cantilever-beam vibration was designed, detailed analysis and optimization strategies were developed, and its application in the security field was successfully demonstrated. Herein, we provide theoretical guidance for the design of the dual-piezoelectric energy harvesting. We designed and fabricated a prototype of the dual-piezoelectric energy harvesting. A test system was designed and constructed. The relationships among the distance and frequency of the two piezoelectric acquisition mechanisms and the open-circuit voltage were investigated. Additionally, the effects of different loads on the output power were examined. The peak power reached 10.12 mW under a gravitational acceleration of 1g. The analysis indicated that the dual-piezoelectric energy harvest device has a higher energy harvest efficiency than the singlepiezoelectric energy harvest device. Owing to the multipoint harvest strategy, even if a generator suddenly deteriorates or fails, the entire system can maintain a certain power output, which is more commercially feasible. The results of this study indicate that the output of the piezoelectric energy harvesting is stable and reliable and that the output energy satisfies the requirements for a safety warning device.

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