The Research Of Dynamic Characteristics On Electromechanical Actuator Servo Mechanism

With the rapid development of the electrical technolongy and the improvedelectronic equipment, the property of the servo motor was greatly improved. As aresult, electronmechanical actuator servo mechanism was widely uesed in a varietyof fields, instead of the traditional air-powered servo and hydraulic servomechanism. At present, most of the research work forcused on the design of thecontrol system and strategy, however, quite a limited work had been done about thedynamic characteristics of the servo mechanism. Therefor based on thethree-dimensional model of the electromechanical actuator servo mechanism, thisarticle did some analysis on the kinematics characteristics of the servo mechanismby the way of Rigid Body Dynamics firstly, then did some further work about thestatic stiffness characteristics and dynamic stiffness characteristics of the parts ofthe servo mechanism under the condition of elastic bodies, on the other hand, thearticle also made some primary discussion on the kinematics of planetary rollerscrew particularly.First of all, it did some special research work on the kinematics characteristicsof the planetary roller screw, which work as the core part of the servo mechanism. Itset up the simplied three-dimensional model of the planetary roller screw andcalculated the stiffness of planetary roller screw from two aspects, including theaxial and circuferential movement. For the axial movement, it transform theplanetary roller screw into a special spring network diagram by the way of directstiffness method. Through the transformation, the various stiffness of the threadcontact can be equivalent to the stiffness of the spring, hence it show the derivationprocess from the axial force to the displacement of the spring node, which can beused to calculate the axial deformantion of the whole roller screw mechanism andcompared with the result of the finite element method analysis, to verafy theexactness of the derivation process. Further more, for the circuferential movement,it gave the influence rules about the rorsional rigidity of the planetary roller screwcaused by the preload force and the axial load on the screw.What’s more, it built the whole three-dimensional model of theelectromechanical actuator servo mechanism, and analyzed the kinematiccharacteristics of the servo mechanism from the aspect of Rigid Body Dynamicsunder the condition of the no elastic assumption. As a result, it gave the motions ofthe motor shaft, upper lug, rocker, wing and the down lug and meanwhile did someforce analysis on the wing, the down lug desk and the bindiny mechanism between the upper lug and the rocker, finally showed us the reaction force and the reactiontorque.Based on the kinematic result of the servo mechanism, taking the elasticity ofthe part into consideration, it did some calculation on the static stiffness of thedifferent part of the servo mechanism, including the shaft-key-screw system, guidemechanism and the joint of between the thread of the upper lug, especially paiedmuch attention on the influence of the clearence and pre-angle on the static stiffnessof the parts. For the next step, it calculated the dynamic stiffness characteristics ofthe part of the servo mechansim and gave the former three modal as well as thenatural frequency, along with the influence of the clearence on the dynamic stiffness.It concluded that the interference had a great influence on the stiffness of theshaft-key-screw system, during a small range, as the interference increases, thestiffness got promoted while out of the small range the interference can’t increasethe stiffness notablely. On the other hand,the clearence had a small influence on thestiffness, which was the same as the pre-angle’s influence on the guide mechanism.At last,the load made a great difference on the dynamic stiffness.