Design and verification of a micro piezoelectric motor with energy harvesting characteristic for capsule endoscope

Wireless capsule endoscopy has the distinctive advantage of providing trustworthy results without substantial discomforts to patients. However, lack of capsule active motion control and energy supply have been significant obstacles preventing wider applications of this technology. To overcome these problems, this paper presents a micro piezoelectric motor with energy harvesting feature. The motor is driven by a single-phase voltage and can be used in capsule endoscopy. The stator was constructed by bonding two PZT plates (PZT₁ and PZT₂) onto the adjacent outer surfaces of a metal base. PZT₁ and PZT₂ can both be used to excite the in-plane bending modes of the stator to generate a traveling wave in the stator. The PZT plate supplied with no-exciting voltage source can be used to convert the superfluous vibration energy of stator body into electric energy to power small electronic devices. The elliptical trajectories of points on the stator surface result from a superposition of the two bending modes. The vibration and energy conversion characteristics of the stator were analyzed by using the finite element analysis software ANSYS. The structure parameters of the stator were adjusted until the mode mixture of the stator disappeared. A prototype motor was fabricated and tested to explore its mechanical and electric energy output abilities. The size of the prototype motor is about 9.8×9.2×22.0 mm³. The tested resonance frequencies of the operating modes are 15.305 kHz and 15.815 kHz, respectively. The maximum no-load speed is 85 rpm. The applied single-phase driving voltage is 100 V_o-p (peak voltage) at frequency of 15.54 kHz. The stall torque is 0.98 mN·m, and the maximum output power of the harvesting PZT plate is 127 mW under an optimal equivalent load resistance of 5.16 kΩ.