Stick-SliP Tower-ShaPed Piezoelectric Actuator

Chen Qianwei（陳乾偉），Ju Quanyong（鞠全勇），Huang Weiqing（黃衛(wèi)清），Shi Yunlai（時運來）*

Stick-SliP Tower-ShaPed Piezoelectric Actuator

Chen Qianwei（陳乾偉）1，Ju Quanyong（鞠全勇）1，Huang Weiqing（黃衛(wèi)清）2，Shi Yunlai（時運來）2*

1.Schoo1of Mechatronic Engineering，Jin1ing Institute of Techno1ogy，Nanjing 211169，P.R.China；

2.State Key Laboratory of Mechanics and Contro1of Mechanica1Structures，Nanjing University of Aeronautics and Astronautics，Nanjing 210016，P.R.China

Since stick-s1iP actuators Present the advantage of a11owing 1ong disP1acements（severa1 centimeters or even more）ata high sPeed with an u1tra high reso1ution（＜5 nm），a new tyPe of stick-s1iPPiezoe1ectric actuator is ProPosed to attain sub-nanometer Positioning accuracy.The actuator is comPosed of a s1ider and a tower-shaPed stator using forced bending vibration in y-z P1ane to generate tangentia1vibration on the toPof the driving foot.When excited by the sawtooth inPut vo1tage，driving foot of the stator is ab1e to generate a tangentia1asymmetrica1vibration on the toP，and the s1ider is thus Pushed tomove.A PrototyPe and its testing equiPment are fabricated and described.Fo11owing that，the testing of vibration mode and mechanica1 characteristics aswe11as stePPing characteristics are conducted.ExPerimenta1 resu1ts show that under the condition that the sawtooth inPut vo1tage is 400 VP-Pand the Pre-Pressure is 6 N.Ve1ocity of the actuator reaches itsmaximum 1.2mm/s at the frequency of8 000 Hz and droPs to itsminimum 35 nm/s at the frequency of1 Hz. When the excitation signa1 is the sing1e-Phase sawtooth stePPing signa1，the tower-shaPed actuator can directiona11y move forward or backward stePby steP.And when excited by the sawtooth stePPing signa1with 1 Hzand 300 VP-Pduring 1 cyc1e（200 ms），the actuator has aminimum stePPing distance of 22 nm.

Piezoe1ectric actuator；stick-s1iP；sawtooth；stePPing

0 Introduction

With the raPid deve1oPment of u1tra-Precision machining and measuring instruments，semiconductor techno1ogy，micro-assemb1y and biomedica1engineering micro-maniPu1ator，and other modern high-tech，1inear driving techno1ogy must meet many new requirements，such as 1arge stroke，high sPeed and nano-Positioning accuracy，high Power density，and no e1ectromagnetic interference.The Piezoe1ectric actuator iswe11-known for its obvious comPrehensive advantages in overa11 dimension，Precision，resPonse sPeed，outPut Power and Power density，etc.Therefore，the key tomeet the requirements above is to research and deve1oP a nove1Piezoe1ectric 1inear actuatorwith 1arge stroke，high sPeed and nano-Positioning accuracy［1-6］.

Aswe a11 know，it is difficu1t for an actuator to a11ow both 1ong disP1acements at a high sPeed and a high Positioning accuracy at the same time.However，stick-s1iP actuators Present the advantage of a11owing 1onger disP1acements（severa1 centimeters or even more）at a high sPeed with an u1tra high reso1ution（＜5 nm）.Moreover，they are simP1e，comPact and offer a high stiffness.Therefore，they are Perfect1y we11adaPted to cha11enge aPP1ications，e.g.micromaniPu1ation［7-8］.

Based on the exce11ent Performance of stick-s1iP actuators as we11 as a wide range of aPP1ications in modern high-tech fie1ds，we ProPose a new tyPe of stick-s1iP Piezoe1ectric actuator.

1 Actuator Design

1.1 Design for tower-shaPed stator

As the tower-shaPed structure is good at focusing energy，it is adoPted into the design of the stator，as shown in Fig.1.The stator in Fig.1 consists of two co1umnar Parts，both of which have a square cross section and have two Piezoe1ectric ceramics attached to the uPPer and 1ower surfaces.The unit a1so has a tower-shaPed driving foot connected with these two co-1umnar Parts.

Fig.1 Structure of tower-shaPed stator

To construct the stick-s1iP actuator，it is necessary for the stator to generate a tangentia1asymmetrica1vibration at its driving foot whi1e moving in a direction Para11e1to thatof themover be1ow when driven by a sawtooth wave signa1.As for the tower-shaPed stator in the PaPer，the forced bending vibration shown in Fig.2 is designed to generate the desired tangentia1 asymmetrica1 vibration in a non-resonant state.

To achieve the vibrationmode for a non-resonant forced vibration as shown in Fig.2，the Po1arization 1ayout scheme is designed for the Piezoe1ectric ceramic P1ates as shown in Fig.3.The who1e tower-shaPed stator emP1oyes tota11y four P1ates of Piezoe1ectric ceramics Po1arized in the thickness direction.The desired tangentia1 asymmetrica1 vibration can be achieved by imPosing a sawtooth wave signa1on Phase A which is formed by a11 four Piezoe1ectric ceramic P1ates.

Fig.2 Vibration tyPe of non-resonant tangentia1 forced vibration for tower-shaPed stator

Fig.3 Po1arization 1ayout of Piezoe1ectric ceramics

Fig.4 shows the PrinciP1e of how to take an advantage of the tangentia1 asymmetrica1 vibration to make a stick-s1iP actuator.When a Periodic continuing sawtooth wave signa1 which rises s1ow1y at first and then droPs quick1y is aPP1ied to Phase A of the stator，the driving footof the stator wi11Produce an asymmetrica1vibration with the forward movement at a s1ow rate and the backwardmovementata fast rate.It wi11 then be ab1e to drive themover to go forwards.In contrast，when a reversed-Phase sawtooth signa1isaPP1ied，the driving foot of the stator wi11Produce a reversed-Phase asymmetrica1 vibration，which wi11 then be ab1e to drive the mover to go backwards.

We have fabricated a PrototyPe of the stick-s1iP tower-shaPed stator above，as shown in Fig.5.The dimension of the stator PrototyPe is20 mm×6 mm×30 mm，with amass of 20 g.

1.2 Overall structural design for actuator

After finishing the fabrication，it is necessary to take measures so as to bui1d the tower-shaPed actuator.This Process invo1ves：Designing and manufacturing the aPProPriatemover；Mounting stator andmover on a base in common；And choosing the correct Pre-Pressure to 1et the stator and mover contactwith eachother.A11of these stePs determine the overa11 structura1design for the actuator.What ismore，whether the overa11 structura1 design is reasonab1e or not，it wi11serious1y affectoPeratiing stabi1ity and Positioning accuracy of the actuator.

Fig.4 PrinciP1e of stick-s1iP for tower-shaPed stator

Fig.5 PrototyPe of tower-shaPed stator

As it is common to Purchase s1ider Product or P1atform Product as themover of a 1inear actuator，we have to consider twomajor issues for the overa11structura1design of the actuator.The first issues the insta1-1ation of the stator and mover.The second regards Pre-Pressure aPP1ied between stator and mover.

With reference to the overa11 structure of the nanomotion motor［9］，we design a one-dimensiona1 moving P1atform based on a three-ro11er structure driven by the tower-shaPed stator，with a 30 mm P1atform stroke，as shown in Fig.6.

Fig.6 One-dimensiona1moving P1atform driven by towershaPed stator

This structure is Primari1y comPosed of threero11ers（bearings），skateboards，hinges，a common base，a Pre-Pressure 1oading mechanism，a towershaPed stator，and a one-dimensiona1 moving P1atform.As a resu1t of using a three-ro11er structure as we11 as the effects of 1atera1 bo1ts and butterf1y sPrings，not on1y has the insta11ation back1ash of the stator been e1iminated，but the tangentia1 disP1acement stiffness is a1so far 1arger than the norma1 dis-P1acement stiffness from mounting c1amPof the stator. This deve1oPment can be very he1Pfu1 to oPerationa1 stabi1ity and Positioning accuracy of the actuator［10］.

2 ExPeriment

2.1 M odal exPerim ents

Moda1exPeriments on the tower-shaPed stator are conducted by using a PSV300F-B-tyPe vibrometer system with a high frequency scanning 1aser Produced by Po1ytec in Germany.The exPerimenta1 resu1ts are shown in Fig.7 and Tab1e 1.

The exPerimenta1 resu1ts show that：

（1）Within the frequency range between 0 and 13 000 Hz，the amP1itude-frequency curve forthe bending vibration moda1 has no resonance Peak. Thus，the bending vibration within the frequency range is a1ways a non-resonant forced vibration.

Table 1 Tangential vibration am Plitudes of driving foot against different excitation frequencies for tower-shaPed stator with voltage of 80 VP-Punder non-resonant forced vibration

Fig.7 Vibration tyPe of tower-shaPed stator for non-resonant forced bending vibration in y-z P1ane

（2）Within the frequency range between 0 and 13 000 Hz，the vibration mode for non-resonant forced vibration is very consistentwith that of the designed one.

（3）Within the frequency range between 0 and 13 000 Hz，and under the fixed-frequency excitation vo1tage of 80 VP-P，the vibration amP1itudes of five tyPica1 samP1ing Points for the non-resonant forced bending vibration are measured to range from 30 nm to 50 nm，which verifies the feasibi1ity of the sticks1iP PrinciP1e.

2.2 M echanical ProPerty exPerim ents

The driving signa1 P1atform of the tower-shaPed actuator is comPosed of a signa1generator and a Power amP1ifier.During the exPeriment，the signa1generator sends out a sing1e-Phase sawtooth vo1tage signa1. Then this signa1 is amP1ified by the Power amP1ifier. The outPut of the vo1tage signa1wi11 drive the towershaPed actuator.

Fig.8 shows testing system of the tower-shaPed actuator，which main1y consists of a one-dimensiona1 moving P1atform and a Renishaw XL-80 1aser interferometer，used to test the Performance of the towershaPed actuator.The Renishaw XL-80 1aser interferometer system has a measuring range between 0 and 80 m，a reso1ution of1 nm，amaximum measurement sPeed of 4 m/s，and amaximum samP1ing frequency of 50 kHz.

Fig.8 Testing system of tower-shaPed actuator

Fig.9 Mechanica1characteristics of tower-shaPed actuator（sawtooth vo1tage：400 VP-P，Pre-Pressure：6.0 N）

Fig.9 shows themechanica1characteristic curves of the tower-shaPed actuator.It suggests that：（1）The tower-shaPed actuator can stab1y run in a quite wide frequency domain from 1 Hz to 14 000 Hz；In this domain a sawtooth wave is suitab1e for driving the actuator forwards and backwards，with the best mechanica1characteristic at 8 000 Hz.（2）Within the frequency range between 1 Hz and 8 000 Hz，ve1ocity of the actuator increaseswith the increasing of the frequency of the driving signa1；Within the frequency range between 8 000 Hz and 14 000 Hz，ve1ocity of the actuator decreases with the increasing of the frequency of the driving signa1.（3）Ve1ocity of the actuator reaches itsmaximum 1.2 mm/s at the frequency of8 000 Hz and reaches itsminimum 35 nm/s at the frequency of 1 Hz.

2.3 StePPing ProPerty exPeriments

With reference to the e1ectromagnetic working PrinciP1e of stePPer motor and considering its own characteristics of the tower-shaPed actuator，when N（N≥dead zone wavenumber）cyc1es of the sawtooth wave signa1 are aPP1ied to the actuator，the actuator wi11 directiona11y move a steP forward or backward. Then，N cyc1es of the sawtooth wave signa1 are aPP1ied to the actuator every Predetermined time，the actuator wi11 directiona11y move forward or backward steP by steP.There fore，the excitation signa1 com-Posed of N cyc1es of the sawtooth wave signa1mentioned above is defined as a sing1e-steP sawtooth signa1；N is defined as a sing1e-stePwavenumber；The frequency of the sawtooth wave signa1mentioned above is defined asAnd every Predetermined time between two adjacent sing1e-steP sawtooth signa1 is defined as tbj.Hence，the sing1e-steP sawtooth signa1 is ca11ed the sawtooth stePPing signa1with fbjduring N cyc1es（tbj）.When a sing1e-steP sawtooth signa1 is aPP1ied to the actuator，the distance the actuator directiona11y moving forward or backward is ca11ed as stePPing distance.Fig.10 shows the schematic diagram of the sing1e-Phase sawtooth stePPing signa1with fbjduring 3 cyc1es

Fig.10 Sing1e-Phase sawtooth stePPing signa1with fbjduring 3 cyc1es（tbj）

Fig.11 StePPing characteristics of actuator excited by sing1e-Phase sawtooth stePPing signa1with 8 000 Hz and 350 VP-Pduring 5 cyc1es（100 ms）

According to working frequency domain of the actuator，the frequency of the sawtooth stePPing signa1aPP1ied to the actuator is se1ected within the frequency range between 1 Hz and 8 000 Hz.Fig.11 shows the stePPing characteristic curves of the actuator excited by the sing1e-Phase sawtooth stePPing signa1with 8 000 Hz and 350 VP-Pduring 5 cyc1es（100 ms）.It suggests that：（1）When the actuator ismoving steP by steP，its ve1ocity f1uctuates between-0.15 mm/s and 0.08 mm/s.（2）When the actuator is moving steP by steP，its stePPing distance f1uctuates between 0.455μm and 0.466μm.

In order to get the va1ue of theminimum stePPing distance of the actuator aswe11as the characteristic of that distance，the sawtooth stePPing signa1with 1 cyc1e（200 ms）is se1ected as the exciting signa1.The exciting frequency is se1ected within a frequency range between 1 Hz and 8 000 Hz.Therefore，the characteristic curve of the actuator is shown in Fig. 12.It suggests that：（1）Within the frequency range between 1 Hz and 8 000 Hz，its average stePPing distance is ProPortiona1 to the exciting frequency or the exciting vo1tage aPP1ied to the actuator.（2）When excited by the sawtooth stePPing signa1with 1 Hz and 300 VP-Pduring1 cyc1e（200ms），the actuator has a minimum stePPing distance of 22 nm.

3 Conclusions

（1）We ProPose a new tyPe of stick-s1iPPiezoe-1ectric actuator.The actuator is comPosed of a towershaPed stator and a s1ider.The stator uses forced bending vibration in y-z P1ane to excite tangentia1 vibration of the driving tiP.When excited with the sawshaPed inPut vo1tage，the saw-shaPed tangentia1 vibration take P1ace on driving tiP of the stator，so the s1ider is Pushed to move.

（2）The tower-shaPed actuator can stab1y run in a considerab1y wide frequency domain from 1 Hz to 14 000 Hz；In this domain a sawtooth wave is suitab1e for driving the actuator forwards and backwards；Ve1ocity of the actuator can reach its maximum 1.2 mm/s at the frequency of 8 000 Hz and reach itsminimum 35 nm/s at the frequency of1 Hz.

Fig.12 Average stePPing distance characteristics of actuator excited by sing1e-Phase sawtooth stePPing signa1 with 1 cyc1e（200ms）

（3）When excited by the sing1e-Phase sawtooth stePPing signa1with fbjduring N（N≥dead zone wavenumber）cyc1es（tbj），the tower-shaPed actuator can directiona11y move forward or backward steP by steP；And within the frequency range between 1 Hz and 8 000 Hz，average stePPing distance of the actuator is ProPortiona1 to the exciting frequency or the exciting vo1tage aPP1ied to the actuator；And when excited by the sawtooth stePPing signa1with 1 Hz and 300 VP-Pduring 1 cyc1e（200 ms），the actuator has a minimum stePPing distance of22 nm.

Acknow ledgem ents

This work was suPPorted by the Natura1Science Foundation of China（Nos.51375224，51275235），the Research Fund for Young Teachers of Jin1ing Institute of Techno1ogy（No.Jit-b-201318）.

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（Executive editor：Xu Chengting）

TM35 Document code：A Article ID：1005-1120（2015）02-0156-07

*CorresPonding author：Shi Yun1ai，Associate Professor，E-mai1：shiyun1ai950438@nuaa.edu.cn.

How to cite this article：Chen Qianwei，Ju Quanyong，HuangWeiqing，eta1.Stick-s1iP tower-shaPed Piezoe1ectric actuator［J］. Trans.Nanjing U.Aero.Astro.，2015，32（2）：156-162.

httP：//dx.doi.org/10.16356/j.1005-1120.2015.02.156

（Received 9 January 2015；revised 26 January 2015；accePted 12 February 2015）