A Multi-Cellular PZT Actuator/Generator with Tunable Stiffness and Resonant Frequencies

骨骼肌由许多独立的肌纤维组成，每个肌纤维在一个紧凑的身体中有效地产生机械输出。一束肌肉纤维的集体行为表现出独特的特征和功能，这是今天的执行器无法产生的。例如，与传统的电动机不同，肌肉在机械上是灵活的，可以适应负载条件。肌肉可以在很宽的范围内改变有效刚度和输出阻抗。此外，可以从相同的模块，即肌纤维，构建具有广泛大小，功率和自由度范围的各种肌肉。受骨骼肌结构的启发，该项目研究了使用致动器材料的细胞人造肌肉，特别是PZT（锆钛酸铅）。像肌肉纤维一样，PZT细胞单元是一个独立的单元，旨在实现最佳效率和功能。利用有效的挠度，每个PZT细胞可以产生与骨骼肌纤维相当的大位移和力。这样的最佳单元不可避免地要小到驱动大负载。将PZT单元以串联、并联和拮抗的方式排列，一束PZT单元共同表现出单个PZT驱动器无法产生的独特特征和功能。这些包括：A)；可变刚度：打开或关闭单个细胞单元会对多细胞系统的总刚度产生重大变化。B)。量身定制的力-位移特性：通过利用单个单元的ON-OFF非线性和叠加众多非线性函数，我们可以根据任务目标和环境条件定制总体力-位移曲线。这允许我们在执行器级别物理地实现动物运动的“工作循环”特征。C)。可变谐振频率：由于每个单元的挠曲和PZT堆栈的共同作用，多单元PZT驱动器形成了一个质量弹簧系统网络。该多自由度系统具有谐振频率，在谐振频率下，输出位移远大于其静态行程，使得扑动和运行等循环运动非常高效。此外，单个单元的通断开关引起质量分布的变化，从而使谐振频率高度可调。D)。能量收集：新的致动器完全可反向驱动，摩擦可以忽略不计。低摩擦和可调谐的共振能力使多单元阵列能够以最有效的谐振频率捕获能量，以应对环境施加的压力。

A skeletal muscle consists of a number of independent muscle fibers, each producing a mechanical output efficiently in a compact body. Collective behaviors of a bundle of muscle fibers exhibit unique features and functionality that today's actuators are unable to produce. Unlike conventional electric motors, for example, muscles are mechanically flexible and adaptable to load conditions. Muscles can vary effective stiffness and output impedance in a wide range. Furthermore, a variety of muscles having a wide range of size, power, and degrees of freedom can be built from the same module, i.e., the muscle fiber. Inspired by this skeletal muscle architecture, this project investigates cellular artificial muscles using actuator materials, in particular, PZT (Lead Zirconate Titanate). Like a muscle fiber, a PZT cellular unit is an independent unit that is designed for optimal efficiency and functionality. Using an effective flexure, each PZT cell can produce large displacement and force comparable to a skeletal muscle fiber. Such an optimal unit is inevitably small to drive a large load. Arranging the PZT cells in series, parallel, and antagonistic configurations, a bundle of PZT units collectively exhibit unique features and functionality that a single bulk PZT actuator cannot produce. These include: A). Variable stiffness: Switching individual cellular units ON or OFF creates a significant change to the aggregate stiffness of the multi-cellular system. B). Tailored force-displacement characteristics: By exploiting the ON-OFF nonlinearity of individual units and superimposing the multitude of the nonlinear functions, we can tailor the aggregate force-displacement curve to task goals and environment conditions. This allows us to physically implement the "work loop" characteristics of animal motion at the actuator level. C). Variable resonant frequencies: The multi-cellular PZT actuator forms a network of mass-spring systems due to the combined effect of a flexure and PZT stack at each unit. This multi d.o.f. system has resonant frequencies at which the output displacement becomes much larger than its static stroke, making cyclic motion, such as flapping and running, very efficient. Furthermore, ON-OFF switching of individual units causes a change to the mass distribution and thereby makes the resonant frequency highly tunable. D). Energy harvesting: The new actuator is completely backdriveable having negligibly small friction. Low friction and tunable resonance capability enables a multi cell array to capture energy at a resonant frequency that is the most effective for the environmentally imposed forcing.