Research On Ultrasonic Motion Control Mechanism With Screw Structure And Its Application In Pneumatic System

The pneumatic technology utilizing compressed air has an extensive applicationin industrial manufacture. Due to the high compressibility and nonlinearity ofcompressed air, the low positioning accuracy and stick-slip motion under low velocityare caused to pneumatic system. And the applications of pneumatic technology arerestricted. Aiming at this problem, a type ultrasonic unlocking and velocity controlmechanism with screw structure named ultrasonic motion control mechanism (forshort UMCM in this paper) based on novel working principle is proposed. TheUMCM is used in pneumatic system and the performance of position and velocitycontrol is to be improved.The principles of ultrasonic driving and friction reduction effect induced byultrasonic vibrations are analysed, and the foundations of UMCM conception both intheory and experiment are established. The UMCM is comprised by an ultrasonicactuator and screw output shaft. Utilizing the friction reduction effect and ultrasonicdriving, the friction coefficient between the ultrasonic actuator and screw output shaftis reduced and a movement trend between each other is produced. The screw lockingand unlocking statuses of UMCM are transformed and the velocity is controlled.The concepts of friction coefficient remainder rate, rate of screw pitch todiameter, and judging coefficient are defined. The influence of these parameters onthe statuses of locking and unlocking are discussed. It is indicated that when thejudging coefficient is over1, the unlocking status of UMCM can be gained. It is infavour of unlocking design foe UMCM by choosing the larger rate of screw pitch todiameter, and decreasing the friction coefficient remainder rate. A mathematicalmodel of voltage-velocity control characteristics for UMCM is established and thefeatures such as large bearing capacity, output velocity linear control are obtained.Considering the influence of rotary inertia and shear deformation, an amendedformula used for calculating the resonant frequency of bending vibration mode beamis deduced. The range of using for beam calculated by the amended formula isextended. The theoretical result is confirmed both by finite element simulation andexperiment method. Based on the amended formula, a mathematical model ofresonant characteristics curve used for describing the inherent characteristics ofbending beam is founded. A theoretical basis employing for the investigation ofultrasonic actuator utilizing bending vibration mode can be afforded.The exciting mode of PZT plates in plate-attached bending ultrasonic actuator isanalysed theoretically, and the influence of disposition and length of PZT plates on the ultrasonic actuator output performance are researched. The logical dispositionlocation of PZT plates is at the centre wave loop of bending vibration. And the lengthof PZT plates should not be larger than the distance between the two vibration nodes.The simulation confirmation is accomplished to theoretical results by finite elementmethod. A reference for bending ultrasonic actuator design is provided.Two prototypes of UMCM utilizing different structures and exciting modes aredeveloped. One prototype of one wavelength driving mode is adopted with a brasshollow square column structure, and has a weight of24g. The length, width and innerdiameter of this prototype are20mm,8mm, and M4mm, respectively. The otherprototype of three wavelength driving mode is adopted. The latter has a weight of206g, and a hollow steel tube structure with twelve planes is used. The length, width andinner diameter are36mm,46mm, and Tr38mm, respectively.The concepts of steady velocity, inflection load and rate of mass load to selfweight are defined, and an experimental research of UMCM under mass load iscarried out. The transform functions of locking and unlocking with screw structurecan be achieved for the two prototypes. The exciting frequency of one wavelengthUMCM is49.30kHz, and a rate of mass load to self weight is more than30:1underan exciting voltage effective value of7V can be gained. The exciting frequency ofthree wavelength UMCM is42.90kHz, and a rate of mass load to self weight is morethan80:1under an exciting voltage effective value of14V can be gained.The three wavelength UMCM is applied in pneumatic control system, and anovel pneumatic control system with UMCM is achieved. The characteristics such asposition and velocity control of this novel pneumatic control system are tested. It isindicated that the position and velocity control functions of this system can beachieved by controlling UMCM. Compared to the positioning method by mechanicallocking in traditional pneumatic system, a higher positioning accuracy can beobtained in the novel pneumatic control system. The output velocity of the novelsystem can be controlled linearly by exciting voltage, and has an independence onflow of pneumatic circuit. So, the interference immunity is improved and this novelpneumatic system can be applied specially in the occasion of low velocity control.