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The control precision of gimbal system for a Control Moment Gyro(CMG) is a main factor affecting the output torque accuracy of the CMG.Generally,a harmonic driver a harmonic driver is adopted to improve the dynamic response ability of the gimbal system,however,the induced mechanical resonance seriously reduces the control precision of the gimbal system.In order to eliminate the resonance and satisfy the control precision of the gimbal system,a kinetic model was set up.A proper damping ratio was chosen to design the dominating poles according to the demands of gimbal system for dynamic performance.The zeroes induced by a controller were calculated to be equal to the poles induced by mechanical resonance,so that the mechanical resonance was eliminated.Simulation and experiment results show that the proposed method eliminates the gimbal resonance of the CMG,and the control precision of 0.175 rad/s is 0.002.When the gimbal system tracks a 0.175 sin(2πt) rad/s sine given velocity,the relative amplitude error is 3.28% and the phase error is 0.13 rad.The control performance satisfies the demands of CMG for high output torque precision very well.

A CMOS full differential interface circuit with low noise and high linearity was presented for closed-loop capacitive micro-accelerometers.Based on switched-capacitor detection,the circuit was designed to improve its linearity by a 0.5 μm n-well CMOS process technology.The simulation result shows that the proposed two-path feedback structure provides a good system linearity of 0.01%.The optimized designed PID controller was added into the system,which decreases the stabilization error effectively,increases the system responding speed by 31%,and the linearity by 66.7%.With a ±5 V supply and a sampling frequency of 64 kHz,the circuit can offer the equivalent input noise in 8 μg·Hz-1 2,system sensitivity in 1.22 V/g,system linearity in 0.03%,and the work range in ±2 g.These results prove that this circuit is suitable for applications of high performance micro-accelerometers to seism detection,oil exploration,etc..

To overcome the influence of the nonlinear friction on the gimbal servo-system of a double gimbal control moment gyro with harmonic drivers,the methods of modeling and compensation of the nonlinear friction are proposed.Firstly,the relationships between the nonlinear friction torque and the angle acceleration of a gimbal motor and the friction torque and the current of the gimbal motor are deduced according to the mathematical model of gimbal servo-system.Then,based on the angle position measured by encoders,the angle velocities of the motor and loader sides are calculated and an angle acceleration estimator is designed to estimate the angle accelerations of the motor and loader sides.Furthermore,the nonlinear friction torque is calculated and modeled as the Coulomb,viscous and Stribeck friction model.Finally,a feedforward compensation controller based on the model is designed to restrain the nonlinear friction and to improve the control precision.Experimental results indicate that compared with those of the conventional PID control method,the peak-peak value of angle velocity error curve has decreased by 28.2% and the mean squared error decreased by 25.7% after the feedforward compensation controller is added.It concludes that the feedforward compensation controller decreases the angle velocity error caused by nonlinear friction and improves the control precision of the servo-system.

To improve the efficiency of energy harvesting, this paper presents a tri-stable energy harvesting device, which can realize inter-well oscillation at low-frequency base excitation and obtain a high harvesting efficiency by tri-stable coherence resonance. First, the model of a magnetic coupling tri-stable piezoelectric energy harvester is established and the corresponding equations are derived. The formula for the magnetic repulsion force between three magnets is given. Then, the dynamic responses of a system subject to harmonic excitation and Gaussian white noise excitation are explored by a numerical method and validated by experiments. Compared with a bi-stable energy harvester, the threshold for inter-well oscillation to occur can be moved forward to the low frequency, and the tri-stable device can create a dense high output voltage and power at the low intensity of stochastic excitation. Results show that for a definite deterministic or stochastic excitation, the system can be optimally designed such that it increases the frequency bandwidth and achieves a high energy harvesting efficiency at coherence resonance.