| Besides being needed to complete stretch function,a deployable mechanism is expected to rotate the deployed mechanism on special occasions.This paper proposes the principle design of a rotatable and deployable sleeve mechanism.And the primary coverage of this paper is the design of the actuator used in this mechanism.Taking advantage of piezoelectric ultrasonic motors’ merits of high momentum density,high positional accuracy and self-locking when power off,a two-DOF piezoelectric ultrasonic motor was designed to work as the actuator.Referring to the different features of existing piezoelectric ultrasonic motor and the needs of deployable mechanisms,the two-DOF piezoelectric ultrasonic motor was designed to work by the hybrids of vibration modes at first and the preliminary design of the rotatable and deployable sleeve mechanism with its actuator was proposed.Next,based on the preliminary design,the piezoelectric ultrasonic motor was designed to be a sandwich-type one with single diriving foot and fixed by two its sides.By theoretical derivation,one even order longitudinal vibration mode and two odd order bening vibration modes were selected as the piezoelectric ultrasonic motor’s hybrid modes.Then the structure of piezoelectric ultrasonic motor was proposed including the positions and polarization directions of piezoelectric ceramic pieces.A set of piezoelectric ceramic pieces were designed to used to excite both longitudinal and bending vibration of the proposed motor,which enabled the proposed motor realize 2-DOF actuations by its ‘a single beam’ structure.This paper also analyzes the piezoelectric ultrasonic motor’s actuating principle by stating the process of its driving foot moving as elliptical trajectories.Then,based on the structure and actuating principle of the piezoelectric ultra sonic motor,this paper proposes the design of the rotatable and deployable sleeve mechanism.Through modal analysis of its preliminary model in FEM software,the hybird modes of the proposed motor were designed as one secord order longitudinal and two orthogonal fifth order bending vibration.Then,the resonance frequencies of these three working modes were tuned closed by designing the parameter of its structure.By transient analysis,the piezoelectric ultrasonic motor’s working principle was verified prior;then,the piezoelectric ultrasonic motor’s stopping features was analyzed and the used time from its working steady state to stationary state was obtained;the relation between the phase of excitation signal and the elliptical trajectories of piezoel ectric ultrasonic motor’s driving foot was also analyzed and the piezoelectric ultrasonic motor was verified to be able to driving spiral movement.The prototype of the proposed piezoelectric ultrasonic motor was fabricated.Then,the impendance test and mode shape test were executed to obtain the differences between this prototype and its FEM model.A test bench was assembled to test the output characteristics of the piezoelectric ultrasonic motor in two DOFs respectively.The impact of excitation signals’ frequency and voltage on the output velocity was tested.Next,the relation between the piezoelectric ultrasonic motor’s transient output velocity and output force under different preloads were tested.The proposed motor could also executed step drive.Thus,the output step-lengths were tested with the different amounts and voltages of the impulse excitation signals.Finally,the prototype of the rotatable and deployable sleeve mechanism was fabricated and the output charateristics of the piezoelectric ultrasonic motor with different phases of excitation signals were tested in this mechanism.The results indicate that the proposed motor’s maximal output force is 24 N,maximal output is 572 mm/s,and the minimal step-lengths are both 2 μm in two DOFs.The proposed motor was verified to realize the 2-DOF actuation of the rotatable and deployable sleeve mechanism including the linear,rotary and spiral movement of the inner sleeve. |
PDF Full Text Request