Near-Field Electrospinning with Close-Loop Motor Control for Manufacturing Polyvinylidene Fluoride Fibers.

In this study, we report a close-loop motor control for a cylindrical collector to obtain continuous and uniform polyvinylidene fluoride (PVDF) piezoelectric fiber arrays using near-field electrospinning (NFES). The as-spun PVDF piezoelectric nanofibers were laid on the top of parallel electrodes to generate current and voltage signals by means of mechanical energy of low-frequency vibrations being converting to electrical energy. The PVDF fibers can be used as a flexible sensing device, such as a smart fabric, owing to their excellent voltage response. A PVDF fiber with continuous and uniform diameter is expected to have stable energy conversion for achieving higher electrical current and voltage signals. To ensure the quality of the production process, a closeloop system for motor speed control was designed to improve on the disadvantages of open-loop systems, such as sensitivity to disturbances and inability to compensate for these disturbances automatically. Transient response and steady-state error can be controlled more conveniently and accurately. The experimental scheme was designed using Taguchi Methods. A mixed solution of 18 wt% PVDF was placed in a metal needle injector and driven by a syringe pump at 0.2, 0.4, and 0.8 ml/h feeding rates. The needles with 0.2, 0.25, and 0.33 mm diameters were subjected to 13k, 15k, and 17k high voltages with a gap of 1 mm between the metal needle and the cylindrical collectors (electrical fields: E =1.3 × 10⁷, 1.5 × 10⁷, and 1.7 × 10⁷ V/m, respectively). The metal needle travelled in the axial direction of the cylindrical collectors at120, 160, and 200 mm/min, respectively. The cylindrical collector motor operated with six different speeds in the range of 900-1900 rpm. With the motor speed control system, about I_p-p = 8.8 × 10^-7 A (I_max = -5.0 × 10^-7 A) and V_p-p = 0.22 V (V_max = -0.12 V) were obtained from the PVDF piezoelectric fiber array, which is obviously better than its counterpart of about I_p-p = 3.2 × 10^-7 A (I_max = -2.1× 10^-7 A) and V_p-p = 0.17 V (V_max = -0.10 V) with the open-loop system. [ABSTRACT FROM AUTHOR]