采用压电蜂鸣器设计和启用压电离合器 【中文6190字】【PDF+中文WORD】

采用压电蜂鸣器设计和启用压电离合器 【中文6190字】【PDF+中文WORD】,中文6190字,PDF+中文WORD,采用,压电,蜂鸣器,设计,启用,离合器,中文,6190,PDF,WORD 【中文6190字】 采用压电蜂鸣器设计和启用压电离合器 摘要 本文开发了一种新型的压电离合器机构，包括驾驶驱动件和从动件，并研究了离合器机构的离合性能。每个部分都是基于一个薄盘压电蜂鸣器作用下耦合模式的摩擦件和一个在非耦合模式的机械振动机构。首先表达出离合器机构和它的实验装置，即一个电力传输系统。然后，操作原则，用于分离的两个相对表面上的逆压电效应和超声悬浮声明，并用于引入观察该压电蜂鸣器的振动模式的碳粉末的成像方法。此外，一个DC / AC谐振逆变器，用于将直流电源的正弦源施加以激励压电蜂鸣器构成。最后，对转速和电气条件，以及与改变状态的转速的瞬 态响应之间的关系进行了研究。 关键词：压电式离合器；压电式蜂鸣器；振动模式；压电效应。 1．介绍 传统的离合器，其中包括电磁离合器，齿轮离合器，摩擦离合器，超越离合器和离心离合器，通常用于启动或停止机械加载，甚至控机械的转速加载中电力传输系统。电磁离合器用于一些磁性粉末具有磁通联系。由激励线圈包围需要传递转矩从磁化后，开端到从动端发送的转矩近似正比于磁场或磁化电流。每个电磁离合器在相同的速度或可控制的速度差下能够连接的驱动和从动件。不幸的是，任何电磁离合器有其固有的缺点，如大的电磁干扰（EMI），这是不利在免费的EMI的地点运行，如医院或精密实验室的离合器[1-4]。对于齿轮离合器，如突起齿轮或键内置在驱动和从动件。由主动和从动之间速度的大小所不相同，以避免过度的冲击或损坏被测的耦合齿轮离合器和非耦合模式[5-8]。为摩擦离合器，主动和从动构件相互连接并互相摩擦，从而使驱动件来驱动从动构件。他们迅速通过一个小的冲击力还是有点震动连接或分离。但是，磨料滑移的部件的接触是由一个重负载，缩短离合材料的耐久性或保持经常的保养[9-11]。对于超速离合器，一个超越离合器包括棘轮，棘爪，旋转缸和楔形块。其施工简便，是离合器用其所述驱动扭矩或运动传递到的从动结束在单向方向。但在一个相当庞大的规模，并在瞬间产生的巨响中从耦合到非耦合，由于成员矩模式限制，这种类型的机制只能适用于中低速和非精密机器[12,13]。 离心离合器，如果其驾驶所需的速度达到驱动的接触，从动部件会通过一个分离离心力的作用自动连接。则该离合器具有相当笨重的机构[14,15]。在解决对于上述传统的离合器问题上，对于超声波离合器驱动力控制设备与被动力反馈控制已经发展[16]。而且，超声波离合器，包括两个超声波换能器机械振动器，用于控制驱动之间的接触或非接触[17]。 基于上述情况，本文开发了一种新的压电离合器机构，包括两个薄盘压电蜂鸣器机械振动器和摩擦件，以减少离合机构，取消了电磁干扰的影响，从耦合瞬态冲击非耦合模式，并控制由驱动传递到从动端的功率。 2．机制设计 如图1. 压电离合器机构包含一个驱动件和一个从动件，其中每个都包含薄盘压电式蜂鸣器（TE41208-26，Seahorn公司，台北，台湾），驱动或从动轴，一个塑料固定器和两个电线。压电式蜂鸣器包括一个压电陶瓷盘（直径，24.8毫米;厚度0.1毫米），镍合金盘（直径41.0毫米;厚度0.1毫米）和镀银电极（直径，24.8毫米;厚度0.02毫米） 图1.压电式离合器机构 如图所示。2.压电陶瓷盘有极化方向和厚度方向。压电的质量蜂鸣器是约1.5g。用于电驱动器，电正弦波源通过镍合金盘和镀银电极提供给压电，如图2所示。3. 在离合器机构的组装中，导电抽头是附着在塑料固定器的外部。该从动轴驱动的轴对齐。压电式蜂鸣器由粘胶在一个节圆固定在塑料固定器的边缘的镍合金盘上的振动模式。对于电线，1被安装在镀银电极驱动轴之间，而另一个被安装导电水龙头及镍合金磁盘之间。图 4. 电力传输系统包括离合器机构，电气控制系统，2预压控制器，两个塑料接头，及其他。电气控制系统包括一个AC电源系统中两个开关S1和S2中，两个导电的水龙头，碳刷，和一个原基地。本系统是用来控制电驱动条件成员，并确定耦合的或非耦合离合器机构的模式。每个预紧控制器包含不锈钢弹簧，两个金属垫圈和一个线性轴承，当垫圈安装在弹簧的两端，并且该轴承是需要支持和引导驱动或从动沿着所述离合器机构的中心轴线。该控制器提供预加载力来驱动或从动构件，以确保其相对表面彼此连接在耦合模式。提供的规格弹簧，塑性系数为约1.15克/厘米，长度为大约18毫米，直径约为4毫米。因此，在对向面接触的预加载力约0.46克。在塑料接头的连接时，其中一个所述驱动轴与电动机之间连接的轴，另一个是从动轴和一个之间连接的负载轴。 图2压电蜂鸣器结构 图3压电蜂鸣器驱动 图4电力传输系统 图5逆压电效应 图 6近场声悬浮 图7碳粉成像方法原理：（a）粉末运动（b）电荷分布 图 8振动模式模式：（a）前视图模式;（b）背面视图模式 3．工作原理 离合器机构的非耦合模式是基于近场声悬浮[18〜20]，这是造成逆压电效应。称为逆压电效应，压电元件的形状由一个正延伸直流驱动电压和一个负的直流驱动电压，如图5中所示。关于声悬浮，一个对象，具有一个平面和刚性底部暂停。上述一个使用辐射的压电振子的辐射表面在物体的底部，以及一个压力Π（kgw/m2）活塞状声波发生在磁悬浮之间的空间对象和所述辐射表面，如在图6中描绘。通常，在悬浮高度比波长小得多的声波。 图9前视图模式的三维视角 这个高度h（M），表示由其中a0是振动振幅（米），ρa为声密度中等（kg/m3的）,ca是介质的声速（m/s），以及γ是比热比[21]。 用公式。 （1），该与振动振幅悬浮高度增加，如果参数如ρA，CA，γ和Π是恒定的。此外，的离合器机构的结果的非耦合模式在很大程度上从声悬浮，使从动轴停止，但是驱动轴仍然在旋转。 图10原理振动模式 图11交流供电系统 图12速度测量系统 图 13速度与在76.0千赫的频率的直流输入电压 图 14 在不同电压下的速度与频率的关系：（a）Vdc =1，2，3V;（b）Vdc =4，5，6V;（c）Vdc =7，8，9V;（d）Vdc =10，11，12V 从图1和4所示，构件被布置成一个公共的旋转轴，是在第一状态下相互接触，如果成员都在低压电蜂鸣器低交流电源供电，这些成员是进一步移动到第二状态，从而在驱动件被断开使用强大的辐射压力从动件字段压电蜂鸣器的面对的表面上，如果一个或两个成员在压电蜂鸣器被通到高压AC电源。如果必要时，两个成员可以互换彼此。然后，对接触面构件紧密耦合在一起而没有电激励压电蜂鸣器，以便得到一个事实，即驱动部件驱动所述从动构件，这些表面还阻隔了断开的成员，从而停止从动构件，但仍然旋转的驱动部件，如一个或两个压电蜂鸣器由高AC电激励电源。 4．机械分析 振动的电模式通电压电蜂鸣器是由一个碳-粉末观察成像方法，以阐明之间的断线面向构件的表面。操作该成像方法中，首先，一些碳的粉末在两侧均匀地扩展的压电式蜂鸣器。然后，该粉末从移动环路中的轴对称弯曲振动的节点压电蜂鸣器，如图所示.7（a），直到露出振动模式的后电接通。由于正电荷和负电荷由残余电场引起的振动，其模式仍保持在两侧压电蜂鸣器，如图所示.7（b）所示，。此外，该振动模式的图案在压电蜂鸣器的两侧被描绘在图8（a）及（b）如果在压电蜂鸣器通过通电正弦波源，涉及5V的幅度和73.25 kHz的频率。在图案，深色区域代表振动模式的节点，并且明亮区域表示的环振动模式。从图9所示，第一结圈，φN1的直径是约5.9毫米，所述第二直径节圆，φN2，是约14.0毫米，直径第三个节点的圆，φn3，是约21.2毫米。例如一个薄盘压电蜂鸣器是一个薄盘的下面，一个二维（2D）的波动方程压电元件，定义如下 这里，u是振幅，r是半径，θ是几何角，c为声速，T是横张力，ρ为质量密度。因此，c为常数如果T和ρ是恒定的。变量θ为进一步与由式得出。 （2）由于给压电蜂鸣器的轴向对称模式。因此，二维波动方程的解包含零级的任期第一种贝塞尔函数J0和欧拉函数的一个术语ejωt如果压电蜂鸣器是由一个电正弦电源激励。 该解决方案表示机械振动是由以下表示，Am进行振动的振幅，k是波数，λ为波长，ω是角频率。示意性的振动模式的示意图显示于图10。此外， φn1 : φn2 : φn3 = α01: α02: α03, 通过计算：α01∼=2.4,α02∼=5.6, 和α03∼=8.6，在α01，α02和α03是：零阶第一的贝塞尔函数的第二和第三零J0，分别为[23]。这一发现表明，式（3）可用于分析所述压电陶瓷的振动行为的一部分。因此，轴向对称弯曲振动模式几乎主宰了压电振动行为在自由边界条件蜂鸣器因为直径φ2大大超过了在压电陶瓷的厚度t2的磁盘[24]。此外，φ2/t2=248，由φ9=24.8毫米计算，并且T2= 0.1毫米。 5.实验装置 用于产生电的正弦交流电源系统源在压电蜂鸣器的输入端子示出图. 11。这个系统包括一个DC / AC谐振逆变器，一个驱动和隔离电路，直流电源（LPS305，美国依赖公司，EI的Monte，CA）和一个函数发生器（FG506，美国依赖公司，EI的Monte，CA）中的谐振坦克由一个串联电感LF（〜=的64ΔH）和一个平行电容Cf（〜=0.1uF）。谐振逆变器包含一个全桥菜刀有四个MOSFET器件（IRF840，Unitrode公司公司，达拉斯，德克萨斯州）中，谐振回路和等效电路 压电蜂鸣器。MOSFET器件被控制由四个矩形触发信号VGS1 - VGS4，分别是从驱动和隔离电路产生并由函数。脉冲宽度调制控制信号VPWM作为驱动和隔离电路的输入信号从函数发生器产生。因此，振幅正弦源是由直流电源控制，并且正弦信号源的频率是由功能控制发电机。从图12，一个速度测量系统，包括两个数字光学转速计（RM-1501，PROVA公司，台北，台湾）和两个光反射，是量度在构件的轴的旋转速度。每个反射器是附着在该驱动的塑料固定器的外侧。 6.结果与讨论 根据图4，在驱动压电蜂鸣器构件是通过在正弦电源电激励76.0千赫，它是谐振频率相同的频率使用不同的电压，从而控制压电蜂鸣器由图11中所示的直流电源。电源正弦振幅约与DC增加输入电压，如果驱动频率是恒定的。从图13的驱动速度指示驱动轴的速度几乎等于驱动速度指示所述从动轴的速度为离合器机构的联接方式，如果一个低直流输入电压（≤7V）被提供。每个速度从20变23 RPS。在这里，RPS表示每秒改变。此外，该行驶速度可达29 RPS和驱动速度下降为离合器机构的非耦合模式零，如果高直流输入电压（≥8V）被提供。因此，如果驱动频率是恒定的，函数从耦合到非耦合方式的离合器机构通过增加直流输入电压或振幅增强正弦源的。 图15 使用VDC =12V和驱动速度的测量瞬态响应F =变化在不同条件下76.0千赫：（a）从所述非接触联系方式;（b）从接触到非接触模式 然后，均对速度的驱动频率的影响。从图14（a）-（d）中，主动和从动速度几乎不受驱动频率从70到80千赫和驱动速度大致相当于从动速度为耦合方式，如果提供一个低的直流输入电压（≤7V）。每个速度从20到23 RPS不同。但这些速度高度都是受到频率，如果提供一个较高的直流输入电压（≥8V）。例如，驱动速度约等于驱动速度的耦合方式低频（≤73.0千赫）或高频（≥78.5千赫）。每个速度仍是从20至23 RPS不同。值得注意的是，驱动速度大大下降到零，并且行驶速度是略微达因换29 RPS在76.0千赫的频率从耦合到非耦合模式，如果一个高的直流输入电压（≥11 V）被提供。因此，离合器机构可以用于控制驱动部的速度变化，如果压电式蜂鸣器在驱动或从驱动构件被电压击中，在不同电压下压电式蜂鸣器适用于76.0千赫附近的共振频率的频率。 关于驱动速度的瞬态响应，响应时间（〜= 1.5秒，如图15（a））的条件下从所述非接触式稍微接触模式变化的速度超过（〜= 0.9秒，如图所示。图15（b））的条件下从接触到非接触方式发生变化。从图15（a）和（b）所示，非接触模式的驱动速度是零，并且，所述接触模式的是在约22 RPS稳定状态时，离合器的蜂鸣器中的通电由驱动电压来驱动（即VDC =12V），并且通过通电频率（即F =76.0千赫）来测量驱动速度间接和迷你直流电机的稳定结果（TS10SA，东元电机股份有限公司，香港，中国）具备25mm长度，20.1毫米宽度和高度15.1毫米播放发电或连接到一个沿对准轴线与从动轴的感测作用端部。为直流电动机，规格的端电压几乎等于所产生的电压，，如果直流马达起着发电机的作用，该电压是线性增加下加快作业转速。同时，一端电压之间的线性关系的斜率的旋转速度是约6.8毫伏/ RPS。从测得的结果，150mV，在直流电动机的端子电压约表示22 RPS的离合器从动速度。 图16 摩擦时间响应中的部件相面对的表面 基于上述结果，对摩擦时间的响应结果，进行了相对表面的讨论。从图16面对的表面彼此充分接触，并且驱动轴和从动轴是静止的点（一）如果在使用驱动器的条件下，其公式为VM = Vdc = 0V。然后，在相对的表面仍然完全相互接触，并且静摩擦力，fs的，相面对的表面之间从零增大到最大静摩擦力， FS ，最大，在路径（二）驱动器的条件，包括虚拟机≤ 3V和VDC = 0V ，使用。此外，相面对的表面是由点彼此接触，并且最大静摩擦力是下到动摩擦，FK，在路径（三）驱动器的条件，包括VM = 3V和VDC ≤ 7V ，使用。此外，面对的表面不接触彼此，并且动摩擦几乎是恒定的在之间的空间利用强大的超声波悬浮面对表面的路径（ IV ）如果驱动条件，包括VM = 3V和伏≥ 8V。所示的临界点在图16的顶部表示的最大摩擦会因摩擦测量装置或估计测试仪适用于找到堆焊静态或动态摩擦成员在今后的离合器机构面。 7.结论 薄盘压电式蜂鸣器成功地用作耦合方式中的摩擦元件或机械在驱动或从动件的耦合模式中振动。如果必要，两个构件可以彼此互换。这里，驱动部件被连接到一个驱动马达和所述驱动构件被连接到机械负载。从测量的结果中，在面向构件的表面被紧紧地连接在一起，用于创建的耦合模式。如果所有压电蜂鸣器没有电气由交流电力通电，这些面也相互分离。在制造非耦合模式下，如果一个或两个压电蜂鸣器完全由高AC功率电激励。因此，根据非耦合模式驱动轴来驱动从动轴的耦合模式下，驱动部件仍然旋转，从动轴停止。 参考文献 [1] J.P. Yonnet, S. Hemmerlin, E. Rulliere, G. Lemarquand, Analytical calculation of permanent magnet couplings, IEEE Trans. Magn. 29 (1993)2932–2934. [2] M.H. Nagrial, Design optimization of magnetic couplings using high energy magnets, Electr. Mach. Power Syst. 21 (1993) 115–126. [3] J.F. Charpentier, G. Lemarquand, Optimal design of air-gap synchronous permanent magnet couplings, IEEE Trans. Magn. 35 (1999) 1037–1046. [4] D. Albertz, S. Dappen, G. Henneberger, Calculation of the induced currents and forces for a hybrid magnetic levitation system, IEEE Trans. Magn. 33 (1997) 1263–1266. [5] L. Glielmo, L. Iannelli, V. Vacca, F. Vasca, Gearshift control for automated manual transmissions, IEEE/ASME Trans. Mechatronics 11 (2006) 17–26. [6] M. Pettersson, L. Nielsen, Gear shifting by engine control, IEEE Trans. Contr. Syst. Technol. 8 (2000) 495–507. [7] G.-J. Cheon, Nonlinear behavior analysis of spur gear pairs with a one-way clutch, Sound Vib. 304 (2007) 18–30. [8] S. Theodossiades, O. Tangasawi, H. Rahnejat, Gear teeth impacts in hydrodynamic conjunctions promoting idle gear rattle, Sound Vib. 303 (2007)632–658. [9] D.K.Swanson,W.J. Books,Torque feedback control of dry friction clutches for a dissipative passive haptic interface, in: Proc. IEEE Int. Conf. Contr. Appl., vol. 1, 2000, pp. 736–741. [10] W. Ost, B.P. De, J. Degrieck, The tribological behaviour of paper friction plates for wet clutch application investigated on SAE#II and pin-on-disk test rigs, Wear 249 (2001) 361–371. [11] P. Nyman, R. M¨aki, R. Olsson, B. Ganemi, Influence of surface topography on friction characteristics in wet clutch applications,Wear 261 (2006) 46–52. [12] K. Liu, E. Bamba, Analytical model of sliding friction in an overrunning clutch, Tribol. Int. 38 (2005) 187–194. [13] K. Liu, E. Bamba, Frictional dynamics of the overrunning clutch for pulse-continuously variable speed transmissions: rolling friction,Wear 217 (1998) 208–214. [14] A.M. Yarunov, O.V. Naumova, N.A. Zolotukhina, Synthesis of electromechanical perforators with impact energy accumulators by elastic and centrifugal forces, in: Proc. Korea–Russia Int. Symp. Sci. Technol., vol. 2, 2000, pp. 300–302. [15] S. Hyun, C. Kim, J.H. Son, S.H. Shin, Y.S. Kim, An efficient shape optimization method based on FEM and B-spline curves and shaping atorque converter clutch disk, Finite Elem. Anal. Des. 40 (2004) 1803–1815. [16] T. Koyama, K. Takemura, T. Maeno, Development of an ultrasonic clutch for multi-fingered exoskeleton haptic device using passive force feedback for dexterous teleoperation, in: Proc. IEEE/RSJ Int. Intell. Robot. Syst.,vol. 3, 2003, pp. 2229–2234. [17] K.-T. Chang, A novel ultrasonic clutch using near-field acoustic levitation, Ultrasonics 43 (2004) 49–55. [18] S. Ueha, Y. Hashimoto, Y. Koike, Ultrasonic actuators using near-field acoustic levitation, in: Proc. IEEE Ultrason. Symp., vol. 1, 1998, pp.661–666. [19] T. Otsuka, K. Higuchi, K. Seya, Consideration of sample dimension for ultrasonic levitation, in: Proc. IEEE Ultrason. Symp., vol. 3, 1990, pp.1271–1274. [20] J. Hu, K. Nakamura, S. Ueha, An analysis of a non-contact motor with an ultrasonically levitated rotor, Ultrasonics 35 (1997) 459–467. [21] B. Chu, R.E. Apfel, Acoustic radiation pressure produced by a beam of sound, J. Acoust. Soc. Am. 72 (1982) 1673–1687. [22] K.-T. Chang, M. Ouyang, Rotary ultrasonic motor driven by a diskshaped ultrasonic actuator, IEEE Trans. Ind. Electron. 53 (2006) 831–837. [23] P.V. O’Neil, Advanced Engineering Mathematics, Central Book Company, Taipei, 1983, p. 302. [24] T. Ikeda, Fundamentals of Piezoelectricity, Oxford University Press, New York, 1990. 传记 Kuo-Tsai Changwas born in Taiwan, ROC, in 1964. He received theMSdegree from the Department of Electrical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan, ROC, in 1991, and received the PhD degree from the Department of Engineering and System Science, National Tsing Hua University, Hsinchu, Taiwan, ROC, in 1992. From 2002 to 2006, he was an associate professor in the Department of Electrical Engineering, National United University (NUU), Miaoli, Taiwan, ROC. Since 2006, he has been a professor in the Department of Electrical Engineering at the NUU. His research interests are in the areas of piezoelectric applications, ultrasonic motors and power electronics. Hsuang-Chang Chiang was born in Taiwan, ROC, in 1965. He received the BS and PhD degrees from the Department of Electrical Engineering, National Tsing Hua University, Hsinchu, Taiwan, ROC, in 1987 and 1994, respectively. From 1995 to 2001, he was an associate professor in the Department of Electrical Engineering, National United University (NUU), Miaoli, Taiwan, ROC. Since 2001, he has been a professor in the Department of Electrical Engineering at the NUU. His research interests are in the areas of power electronics, control systems and motor drives. Chun-Wei Lee was born in Taiwan, ROC, in 1982. He received the BS degree from the Department of Electrical Engineering, Ching Yun University, Chung Li, Taiwan, ROC, in 2005, and received the MS degree from the Department of Electrical Engineering, National United University, Miaoli, Taiwan, ROC, in 2007. His research interests are in the areas of control systems and piezoelectric applications. Available online at Sensors and Actuators A 141(2008)515522Design and implementation of a piezoelectric clutch mechanismusing piezoelectric buzzersKuo-Tsai Chang,Hsuang-Chang Chiang,Chun-Wei LeeDepartment of Electrical Engineering,National United University,1,Lien Da,Kungching Li,Miaoli 36003,Taiwan,ROCReceived 20 December 2006;received in revised form 10 July 2007;accepted 3 October 2007Available online 16 October 2007AbstractThis paper develops a novel piezoelectric clutch mechanism,including a driving member and a driven member,and investigates the clutchingperformance of the clutch mechanism.Each member is based on a thin-disk piezoelectric buzzer as a frictional member under coupling mode and amechanical vibrator under non-coupling mode.In doing so,the clutch mechanism and its experimental set-up namely a power transmission systemare first expressed.Then,operating principles such as inverse piezoelectric effect and ultrasonic levitation for separating two facing surfaces of themembers are stated,and a carbon-powder imaging method for observing the vibration mode of the piezoelectric buzzer is introduced.Moreover,a DC/AC resonant inverter for converting a DC source to a sinusoidal source applied to energize the piezoelectric buzzer is constructed.Finally,relationships between rotational speeds and electrical conditions as well as the transient response of the rotation speed with the condition of changeare investigated.2007 Elsevier B.V.All rights reserved.Keywords:Piezoelectric clutch;Piezoelectric buzzer;Vibration mode;Piezoelectric effect1.IntroductionConventional clutches,including electromagnetic clutches,gear clutches,friction clutches,overrunning clutches and cen-trifugalclutches,areusuallyappliedtostartorstopamechanicalload,and even to control a revolving speed of the mechanicalload in power transmission systems.For the electromagneticclutches,some magnetic powders with magnetic flux linkagesenclosed by an exciting coil are needed to transmit the torquefromthedrivingtodrivenendaftermagnetization.Thetransmit-ted torque is approximately proportional to the magnetic fieldor magnetization current.Each electromagnetic clutch is capa-ble of connecting the driving and driven members at the samespeedorundercontrollablespeeddifference.Unfortunately,anyelectromagnetic clutch has its inherent shortcoming such as agreat electromagnetic interference(EMI),which is unfavorableat free-of-EMI sites such as hospitals or precision laboratories,during the running of the clutch 14.Corresponding author.Tel.:+886 37 381372;fax:+886 37 327887.E-mail address:ktchangnuu.edu.tw(K.-T.Chang).For the gear clutches,protrusions such as gear teeth or keysare built in the driving and driven members.The differencebetween the driving and driven speeds is small in order to avoidan excessive impact or damaging the gear clutches under cou-pling and non-coupling modes 58.For the friction clutches,the driving and driven members are connected with each otherusing frictions,which enable the driving member to drive thedriven member indeed.They are promptly connected or sep-arated by a small impact force or a little vibration.However,an abrasive slip at the contact of the members is caused by aheavy load to shorten the durability of the clutching materialsor maintain the members frequently 911.For the overrun-ning clutches,an overrunning clutch comprises ratchet wheels,ratchet pawls,rotary cylinders and wedge blocks.This clutch isused to transmit the torque or motion from the driving to drivenend in one-way direction.In spite of its simple construction,a considerably bulky size and a loud noise arising at the tran-sientmomentofthemembersfromthecouplingtonon-couplingmode restrict this type of mechanism can only applicable forlow-speed and non-precision machines 12,13.For the centrifugal clutches,the contact of the driving anddriven members is automatically connected or separated by acentrifugal force if the desired speed at the driving or driven0924-4247/$see front matter 2007 Elsevier B.V.All rights reserved.doi:10.1016/j.sna.2007.10.018516K.-T.Chang et al./Sensors and Actuators A 141(2008)515522Fig.1.Piezoelectric clutch mechanism.end is arrived.But this clutch has a considerably bulky mecha-nism 14,15.To mitigate or solve the aforementioned problemsregarding the above conventional clutches,an ultrasonic clutchfor a driving power control of multi-fingered exoskeleton hapticdevice with passive force feedback control has been developed16.And,an ultrasonic clutch,including two ultrasonic trans-ducers as mechanical vibrators and frictional members as well,for controlling the contact or non-contact between the drivingand driven shafts has been investigated 17.These ultrasonicclutches are heavy and bulky.Based on the above,this paper develops a novelpiezoelectricclutchmechanism,includingtwothin-diskpiezoelectricbuzzersas mechanical vibrators and frictional members as well,to min-imize the clutch mechanism,cancel the EMI effect,decline theimpact of the members at the transient state from the couplingto non-coupling mode,and control the power transmitted fromthe driving to driven end.2.Mechanism designFrom Fig.1,the piezoelectric clutch mechanism containsa driving member and a driven member,each of which con-tains a thin-disk piezoelectric buzzer(TE41208-26,SeahornInc.,Taipei,Taiwan),a driving or driven shaft,a plastic fixer,aFig.2.Structure of piezoelectric buzzer.Fig.3.Electrical drive of piezoelectric buzzer.conductive tap and two electric wires.The piezoelectric buzzercomprises a piezoceramic disk(diameter,24.8mm;thickness,0.1mm),a nickel-alloy disk(diameter,41.0mm;thickness,0.1mm)and a silvering electrode(diameter,24.8mm;thick-ness,0.02mm),as shown in Fig.2.The piezoceramic disk has apolingdirectionatitsthicknessdirection.Themassofthepiezo-electric buzzer is approximately 1.5g.For the electrical drive,an electrical sinusoidal source is supplied to the piezoelectricbuzzer via the nickel-alloy disk and the silvering electrode,asdepicted in Fig.3.Intheassemblyoftheclutchmechanism,theconductivetapisadheredtotheoutsideoftheplasticfixer.Theaxisofthedrivingshaft is aligned that of the driven shaft.The piezoelectric buzzerisfixedtotheedgeoftheplasticfixerbyviscoseatanodalcircleof the vibration mode on the nickel-alloy disk.For the electricwires,one is mounted between the driving(driven)shaft andthe silvering electrode,and the other is mounted between theconductive tap and the nickel-alloy disk.Fig.4.Power transmission system.K.-T.Chang et al./Sensors and Actuators A 141(2008)515522517Fig.5.Inverse piezoelectric effect.Fig.6.Near-field acoustic levitation.From Fig.4,the power transmission system comprises theclutchmechanism,anelectricalcontrolsystem,twopreloadcon-trollers,two plastic couplings,and others.The electrical controlsystem includes an AC power supply system,two switches S1and S2,two conductive taps,four carbon brushes,and a sourcebase.This system is used to control electrical drive conditionsof the members and determine the coupling or non-couplingmode of the clutch mechanism.Each preload controller con-tains a stainless spring,two metal washers,and a linear bearing,where the washers are mounted at both ends of the spring,andthe bearing is needed to support and guide the driving or drivenshaft along a center line of the clutch mechanism.This con-troller provides a preload force to the driving or driven memberFig.7.Principle of carbon-powder imaging method:(a)movement of powders;(b)distribution of electrical charges.Fig.8.Patternsofvibrationmode:(a)front-viewpattern;(b)back-viewpattern.soastoensurethatfacingsurfacesofthemembersareconnectedwith each other under coupling mode.For specifications of thespring,the plastic coefficient is about 1.15g/cm,the length isapproximately18mm,andthediameterisapproximately4mm.Thus,the preload force on the contact of the facing surfacesis approximately 0.46g.In the connection of the plastic cou-plings,one is linked between the driving shaft and a motorshaft,and the other is linked between the driven shaft and aload shaft.3.Operating principleThe non-coupling mode of the clutch mechanism is basedon near-field acoustic levitation 1820,which is caused byinverse piezoelectric effect.For the inverse piezoelectric effect,518K.-T.Chang et al./Sensors and Actuators A 141(2008)515522Fig.9.Dimensional view of the front-view pattern.the shape of a piezoelectric element extends by a positiveDC driving voltage,and contracts by a negative DC driv-ing voltage,as shown in Fig.5.For the acoustic levitation,an object with a planar-and-rigid bottom suspends above aradiation surface of a piezoelectric vibrator using a radia-tion pressure (kgw/m2)on the bottom of the object,and apiston-like acoustic wave occurs in the space between the lev-itation object and the radiation surface,as depicted in Fig.6.Generally,the levitation height is much less than the wave-length of the acoustic wave.This height,h(m),is expressedbyh=a0?1+4ac2a(1)where a0is the vibration amplitude(m),ais the sound den-sity of medium(kg/m3),cais the sound velocity of medium(m/s),and is the specific heat ratio 21.Using Eq.(1),thelevitation height increases with the vibration amplitude if theparameters such as a,ca,and are constant.Additionally,the non-coupling mode of the clutch mechanism results largelyfromtheacousticlevitationsothatthedrivenshaftalmoststops,but the driving shaft still rotates.From Figs.1 and 4,the members are arranged to rotate abouta common axis of rotation to be in contact with each other in aFig.10.Schematic vibration mode.Fig.11.AC power supply system.Fig.12.Speed measuring system.first state if both piezoelectric buzzers in the members are elec-trically energized by low AC power.These members are furthermovedintoasecondstatewherebythedrivingmemberisdiscon-nectedfromthedrivenmemberusingastrongradiationpressurefield on the facing surface of the piezoelectric buzzer if one ortwo piezoelectric buzzers in the members are electrically ener-gizedbyhighACpower.Bothmembersmaybeinterchangeablewith one another,if necessary.Then,the contact surfaces of themembers are tightly coupled together without electrically ener-gizing the piezoelectric buzzers,so as to get the fact that thedriving member drives the driven member.These surfaces arealso separated for disconnecting the members,so as to stop thedriven member,but still rotate the driving member,if one ortwo piezoelectric buzzers are electrically energized by high ACpower.Fig.13.Speeds vs.DC input voltage at the frequency of 76.0kHz.K.-T.Chang et al./Sensors and Actuators A 141(2008)515522519Fig.14.Speeds vs.frequency under different voltages:(a)Vdc=1,2,3V;(b)Vdc=4,5,6V;(c)Vdc=7,8,9V;(d)Vdc=10,11,12V.4.Mechanical analysisAsreferringtoRef.22,thevibrationmodeoftheelectricallyenergized piezoelectric buzzer is observed by a carbon-powderimagingmethodsoastoelucidatethedisconnectionbetweenthefacingsurfacesofthemembers.Tooperatetheimagingmethod,some carbon powders are first uniformly spread on both sidesof the piezoelectric buzzer.Then,the powders are moving fromthe loops to nodes in the axialsymmetrical flexural vibration ofthe piezoelectric buzzer,as shown in Fig.7(a),until revealinga pattern of the vibration mode after electrically turning on.The pattern of the vibration mode still holds on both sides ofthe piezoelectric buzzer due to positive and negative chargescaused by a residual electric field Er,as shown in Fig.7(b),afterelectricallyturningoff.Moreover,patternsofthevibrationmodeat both sides of the piezoelectric buzzer are depicted in Fig.8(a)and(b)if the piezoelectric buzzer is electrically energized byan electrical sine source,involving the amplitude of 5V andthe frequency of 73.25kHz.In the patterns,dark areas indicatenodes of the vibration mode,and bright areas indicate loops ofthe vibration mode.From Fig.9,the diameter of the first nodalcircle,n1,is approximately 5.9mm,the diameter of the secondnodal circle,n2,is approximately 14.0mm,and the diameterof the third nodal circle,n3,is approximately 21.2mm.Next,a two-dimensional(2D)wave equation of a thin-diskpiezoelectric element such as a thin-disk piezoelectric buzzer isdefined as follows2u(r,t)=1c22t2u(r,t)(2)wherec=?THere,u is the vibration amplitude,r is the radius,and is thegeometrical angle;c is the sound velocity,T is the horizontaltension,and is the mass density.Thus,c is constant if T and areconstant.ThevariableisfurtherwithdrawnfromEq.(2)duetotheaxialsymmetricalmodeofthepiezoelectricbuzzer.Thus,the solution of the 2D wave equation contains a term of zero-order first-kind Bessel function J0and a term of Euler functionejtif the piezoelectric buzzer is electrically energized by an520K.-T.Chang et al./Sensors and Actuators A 141(2008)515522electrical sine source.This solution indicating the mechanicalvibration is expressed byu(r,t)=AmJ0(kr)ejt(3)wherek=2=cHere,Amis the vibration amplitude,k is the wave num-ber,is the wavelength,and is the angular frequency.Aschematic diagram of the vibration mode is revealed in Fig.10.Additionally,n1:n2:n3=01:02:03,calculatedby01=2.4,02=5.6,and03=8.6,where 01,02and 03are the first,second and third zeros of zero-order first-kind Bessel func-tion J0,respectively 23.This finding indicates that Eq.(3)is available for analyzing the vibration behavior of the piezo-ceramic part.Therefore,the axialsymmetry flexural vibrationmode almost dominates the vibration behavior of the piezoelec-tricbuzzerunderfreeboundaryconditionsbecausethediameter2greatly exceeds that of the thickness t2in the piezoceramicdisk 24.Also,2/t2=248,calculated by 9=24.8mm,andt2=0.1mm.5.Experimental setupAn AC power supply system for generating an electrical sinesource at input terminals of the piezoelectric buzzer is shownin Fig.11.This system includes a DC/AC resonant inverter,adriven and isolated circuit,a DC power supply(LPS305,Amer-ican Reliance Inc.,EI Monte,CA)and a function generator(FG506,American Reliance Inc.,EI Monte,CA).The resonanttank consists of a series inductance Lf(=64?H)and a parallelcapacitance Cf(=0.1?F).The resonant inverter contains a full-bridge chopper with four MOSFET devices(IRF840,UnitrodeInc.,Dallas,TX),a resonant tank and an equivalent circuit ofthe piezoelectric buzzer.The MOSFET devices are controlledby four rectangular triggering signals vgs1 vgs4,respectively,which are produced from the driven and isolated circuit andcontrolled by the function generator.A pulse width modulationsignal vpwmas an input signal of the driven and isolated circuitis generated from the function generator.Thus,the amplitudeof the sine source is controlled by the DC power supply,andthe frequency of the sine source is controlled by the functiongenerator.From Fig.12,a speed measuring system,includingtwo digital optical tachometers(RM-1501,Prova Inc.,Taipei,Taiwan)and two optical reflectors,is constructed to measurerotational speeds of the shafts in the members.Each reflector isadheredontheoutsideoftheplasticfixerinthedrivingordrivenmember.6.Results and discussionAccording to Fig.4,the piezoelectric buzzer in the drivenmemberiselectricallyenergizedbyelectricalsinesourcesatthesame frequency of 76.0kHz that is the resonance frequency ofthe piezoelectric buzzer using different voltages,which are con-trolledbytheDCpowersupplyshowninFig.11.TheamplitudeFig.15.Measured transient responses of the driven speed using Vdc=12V andf=76.0kHz under different conditions of changes:(a)from the non-contact tocontact modes;(b)from the contact to non-contact modes.of electrical sine source approximately increases with the DCinput voltage if the driving frequency is constant.From Fig.13,the driving speed indicating a speed of the driving shaft almostequals the driven speed indicating a speed of the driven shaftfor the coupling mode of the clutch mechanism if a low DCinput voltage(7V)is supplied.Each speed is varying from 20to 23rps.Here,rps means the revolution per second.Also,thedriving speed is up to 29rps,and the driven speed is down tozeroforthenon-couplingmodeoftheclutchmechanismifahighDC input voltage(8V)is supplied.Therefore,a function ofthe clutch mechanism from the coupling to non-coupling modeis enhanced by increasing the DC input voltage or the amplitudeof the sine source if the driving frequency is constant.Next,effects of driving frequencies on the speeds are stated.From Fig.14(a)(d),the driving and driven speeds are almostunaffected by driving frequencies from 70 to 80kHz,and thedrivingspeedisapproximatelyequivalenttothedrivenspeedforthe coupling mode if a low DC input voltage(7V)is supplied.Each speed is varying from 20 to 23rps.But these speeds arehighly affected by the frequencies if a high DC input voltageK.-T.Chang et al./Sensors and Actuators A 141(2008)515522521Fig.16.Friction time-response of the facing surfaces in the members.(8V)is supplied.For example,the driving speed approxi-mately equals the driven speed for the coupling mode at thelow frequencies(73.0kHz)or high frequencies(78.5kHz).Each speed is still varying from 20 to 23rps.Notably,the drivenspeed is greatly down to zero,and the driving speed is slightlyup to 29rps at the frequency of 76.0kHz due to the change fromthe coupling to non-coupling mode if a high DC input voltage(11V)is supplied.Therefore,the clutch mechanism can beused for speed variation in the driven part if the piezoelectricbuzzer in the driving or driven member is electrically energizedat the frequency of 76.0kHz near the resonant frequency of thepiezoelectric buzzer under different voltages.Regarding the transient response of the driven speed,theresponse time(=1.5s,as shown in Fig.15(a)under the condi-tion of change from the non-contact to contact modes slightlyexceeds that(=0.9s,as shown in Fig.15(b)under the condi-tion of change from the contact to non-contact modes.FromFig.15(a)and(b),the driven speed of the non-contact mode iszero,and that of the contact mode is approximately 22rps insteady state when one of the buzzers in the clutch is electricallyenergized by the driving voltage(i.e.Vdc=12V)and the opera-tion frequency(i.e.f=76.0kHz).To measure the transient andsteady results of the driven speed indirectly,a mini DC motor(TS10SA,Teco Electric Inc.,Hong Kong,China)with 25mmlength,20.1mm width and 15.1mm height for playing the gen-eratingorsensingroleisconnectedtotheendofthedrivenshaftalong an aligning axis.For specifications of the DC motor,theterminal voltage almost equals the generated voltage which islinearlyincreasedwithrotationalspeedunderopen-circuitoper-ations if the DC motor plays the generating role.Meanwhile,aslope of a linear relationship between the terminal voltage andtherotationalspeedisapproximately6.8mV/rps.Fromthemea-sured results,the terminal voltage of 150mV in the DC motorapproximately indicates the driven speed of 22rps in the clutch.Based on the above results,a friction time-response of thefacing surfaces of the members is discussed.From Fig.16,thefacing surfaces are fully contact with each other,and the drivinganddrivenshaftsarestaticatthepoint(I)ifthedriveconditions,including VM=Vdc=0V,are used.Then,the facing surfacesare still fully contact with each other,and the static friction,fs,between the facing surfaces is increased from zero to themaximum static friction,fs,max,at the path(II)if the drive con-ditions,including VM3V and Vdc=0V,are used.Moreover,the facing surfaces are contact with each other by points,andthe maximum static friction is down to the kinetic friction,fk,at the path(III)if the drive conditions,including VM=3V andVdc7V,areused.Furthermore,thefacingsurfacesarenotcon-tact with each other,and the kinetic friction is almost constantby using a strong ultrasonic levitation in the space between thefacing surfaces at the path(IV)if the drive conditions,includ-ing VM=3V and Vdc8V,are used.The critical point shownin the top of Fig.16 indicating the maximum friction will be522K.-T.Chang et al./Sensors and Actuators A 141(2008)515522measured or estimated by friction measuring devices or