Evaluation of dehydration loss and investigation of its effect on bending response of segmented IPMC actuators

Efforts were made to estimate and analyze the effect of dehydration on the bending response of segmented ionic polymer-metal composite(IPMC)actuators.An experiment was conducted with an IPMC actuator to study the variation of bending characteristics with input voltage.Based on the experimental data,the Cobb-Douglas production method was used to obtain the dehydration factor in terms of input voltage and time.The motion of the patches was restricted to planar in two dimensions.A single-patch IPMC actuator was then modeled following the Euler-Bernoulli approach incorporating loss due to dehydration.A forward kinematics model for the segmented actuators was formulated after constituting the homogeneous coordinate transformation matrix,assuming it is a serial link multi-degree of freedom manipulator.An energy-based dynamic model of the patches was derived using the Lagrange principle.Simulations were performed for single and two segmented IPMC patches to demonstrate the bending response for various input voltages.The results demonstrate the gradual reduction of bending response of an actuator owing to moisture loss.

Motion equations of hemispherical resonator and analysis of frequency split caused by slight mass non-uniformity

The mass non-uniformity of hemispherical resonator is one of reasons for frequency split,and frequency split can cause gyroscope to drift.Therefore,it is of great significance to analyze the relationship between mass non-uniformity and frequency split,which can provide a theoretical basis for mass balance of imperfect resonator.The starting point of error mechanism analysis for gyroscope is the motion equations of resonator.Firstly,based on the Kirchhoff-Love hypothesis in the elastic thin shell theory,the geometric deformation equations of resonator are deduced.Secondly,the deformation energy equation of resonator is derived according to the vibration mode and relationship between the stress and strain of hemispherical thin shell.Thirdly,the kinetic energy equation of resonator is deduced by the Coriolis theorem.Finally,the motion equations of resonator are established by the Lagrange mechanics principle.The theoretical values of precession factor and natural frequency are calculated by the motion equations,which are substantially consistent with the ones by the finite element method and practical measurement,the errors are within a reasonable range.Simultaneously,the varying trend of natural frequency with respect to the geometrical and physical parameters of resonator by the motion equations is consistent with that by the finite element analysis.The above conclusions prove the correctness and rationality of motion equations.Similarly,the motion equations of resonator with mass non-uniformity are established by the same modeling method in case of ignoring the input angular rate and damping,and the state equations with respect to the velocity and displacement of vibration system are derived,then twonatural frequencies are solved by the characteristic equation.It is concluded that one of reasons for frequency split is the 4 th harmonic of mass non-uniformity,and thus much attention should be paid to minimizing the 4 th harmonic of mass non-uniformity in the course of mass balancing for imperfect resonator.