A small linear ultrasonic motor which consists of a piezoelectric ceramic Pb(Zr,Ti)O₃ (PZT) tube (outside diameter 5 mm, inside diameter 3 mm, length 15 mm, acts as stator) and a shaft (acts as slider) has been developed. The outer surface electrode of the PZT tube is divided into 4 parts to excite longitudinal-bending (L₁-B₂) modes, which could be then used to produce linear motion. The motor shows a high power (force) density. It has a no-load speed of 0.14 m/s, a stall force of 0.3 N, and a maximum output power of 9.3 mW under an applied voltage of 100 Vpp. The method for further improving the performance has been discussed. The proposed motor can be further miniaturized because of its simple structure, and it has potential to be applied to medical microrobots, endoscopes, or micro laparoscopic devices, etc.

A control moment gyroscope (CMG) is a key actuator for spacecraft’s attitude and stability control. But there exist micro-vibrations from high-speed flywheel, which will affect the performance of the spacecraft greatly. Due to the unbalanced mass and the supporting structure, the high-speed rotating flywheel could generate disturbance torque, which will be passed to the gimbal to deteriorate the gimbal servo system. At the same time, the rotation of the gimbal will increase the disturbance torque for gyroscopic effect. According to the bearing theory, the stiffness of the bearing is affected by the load that applied on it, which results the influence on the flywheel vibration and the generated disturbance torque. This means that there is a coupling effect in the CMG. In this paper, we focused on this coupling relationship between the flywheel vibration and the gimbal rotation in a single gimbal control moment gyroscope (SGCMG) system. Firstly, a vibration model of the flywheel with variable stiffness supporting is established. And the rotation model of the gimbal is also developed. The flywheel model and the gimbal model are coupled with each other through the variable stiffness supporting and gyroscope effect. Based on the numerical simulations the interactions among the bearing stiffness, the flywheel vibration and the gimbal rotation are analyzed. Finally, experiments are carried out on the prototype. The experimental results have verified the theoretical analysis and the simulations, and which would support the design of high-performance control system.

During the spring of 2008, a chrysanthemum plant showing mild mottle on young leaves was observed in a garden in Beijing, China. After the plant was moved into a greenhouse, symptoms became severe ...