![]() Displacing these high-stiffness flexures in order to install and preload the piezoelectric stack actuator is a difficult task. For high-speed nanopositioning applications, stiff flexures are often used to achieve high mechanical bandwidth. ![]() Flexures have been used to provide preload and guide the motion of piezoelectric stack actuators. A common practice to avoid such damage is to mechanically preload the piezoelectric stack to compensate for excessive tensile load. When driving the actuator at high speeds, the high inertial (tensile) force due to the effective mass of nanopositioning system could damage the actuator ( Chaplya et al., 2006 Koruza et al., 2015). An inevitable drawback of piezoelectric stack actuators is that there are highly vulnerable to tensile and lateral forces ( Fleming and Leang, 2014). The estimated total displacement of actuator is Δ l = NVd 33, where N is the number of piezoelectric layers, V is the driving voltage, and d 33 is the piezoelectric coefficient. ![]() All piezoelectric layers are poled in the direction of their thickness. There are bonded mechanically in series, and connected electrically in parallel as shown in Figure 2. These actuators are constructed by bonding multiple layers of piezoelectric material together. Piezoelectric stack actuators have been widely used in high-speed nanopositioning due to its ability to provide ultra-fast responses, fine movement, and high pushing force ( Physik Instrumente, 2016). All the above advantages enable the design of compact, light, and fast nanopositioners that capable of providing smooth and repeatable motion to fulfill the requirement of nanoscale applications. As a result, the overall mass of flexure-guided nanopositioner is significantly reduced compared to its rigid-link counterparts. Flexure-guided mechanisms can be machined from a monolithic (single piece) material via wire electrical-discharge-machining (wire-EDM) and no assembly of links and joints is required. The absence of moving and sliding joints provides a considerable advantage to eliminate problems due to wear, backlash, friction, and the need for lubrication. Flexures replace traditional joints, such as bearings and rollers, in rigid-link mechanisms. Example of a flexure-guided nanopositioner is shown in Figure 1. Flexure-guided systems exploit the advantages of compliant mechanisms ( Howell, 2001 Lobontiu et al., 2001 Lobontiu and Garcia, 2003 Yong et al., 2008), where a flexible element acts like a linear spring and deforms elastically to offer repeatable and accurate fine motions ( Lobontiu, 2003, 2015 Yong et al., 2012). Nanopositioners with the ability to provide sub-nanometer resolution and high-speed motion have became a vital component in applications, such as scanning probe microscopy ( Schitter et al., 2007 Ando, 2012 Yong and Moheimani, 2015 Yong and Fleming, 2016), alignment of fiber optics ( Wang et al., 2007), nano-indentation ( Bhushan, 1999 Miyahara et al., 1999), nano-fabrication ( Wiesauer and Springholz, 2000 Vicary and Miles, 2009), cavity ring-down spectroscopy in optical applications ( Berden et al., 2000 Debecker et al., 2005), micro-gripper ( Noveanu et al., 2015 Xu, 2015 Liu and Xu, 2016), and beam steering systems ( Gorman et al., 2003).įlexures have played an important role in high-speed nanopositioning systems. The ever-increasing demand for high speed and high precision in nanotechnology applications has increased the use of nanopositioning systems in the field. This article surveys key challenges in existing preload techniques in the context of high-speed nanopositioning designs, and explores how these challenges can be overcome. To protect the piezoelectric actuator, preload is often applied to compensate for these inertial forces. During high-speed operations, excessive inertia force due to the effective mass of nanopositioning system could potentially damage the actuator. However, these actuators are highly sensitive to tensile and lateral forces. High-speed nanopositioning devices are commonly driven by compact and stiff piezoelectric stack actuators. These systems are capable of providing motions with sub-nanometer resolution over a positioning bandwidth of a few kilohertz or more. Recent development in high-speed nanotechnology applications, such as scanning probe microscopy and nanofabrication, has increased interest on the advancement of high-bandwidth flexure-guided nanopositioning systems.
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