Piezo elements and actuators

It is no trivial matter to automatically and accurately dose tiny quantities or volumes in the microliter or even nanoliter range, especially since the demands placed on the components are constantly increasing as miniaturization moves on. The devices of choice are micro-dosing pumps, also known as micro-dispensers. They act as displacement pumps, i.e. they supply defined volumes per stroke or per time interval, allowing for very accurate dosing. An important requirement for this is the choice of the appropriate pump drive, however. Piezo elements and piezo actuators are ideally suited for this task; they generate the linear motions required in a very precise and direct way and can also be perfectly matched to the relevant application environment. Versatile Power Packs
Piezoelectric materials can be used in the manufacture of powerful drive solutions (Fig. 1) which are ideally suited for use in micro-dosing pumps: They provide (high) speeds and operate with short response times, thus allowing high pumping frequencies and flow rates. The variable strokes and high stiffness allow to precisely control the dosing processes, and the durability of piezoelectric drive solutions is convincing. Since they are very compact and require little power they can also be used in drives for mobile devices or lab-on-a-chip technology. Furthermore, piezo actuators are maintenance-free, because they have no moving parts in the conventional sense. PI Ceramic, Lederhose, (see text box) offers a wide range of piezoelectric components in a wide variety of shapes, standard as well as custom-made, and also piezo actuators with and without preloading in different sizes (Fig. 2) to suit almost every application. Piezo Actuators for Micro-Diaphragm Pumps ...
In micro-diaphragm pumps the transported medium is separated from the drive by a diaphragm (Fig. 3). The drive therefore cannot exert any adverse effects on the media pumped. Highly dynamic disk-shaped piezo elements make a miniaturized drive for this type of pump. High delivery rates can thus be realized by varying the switching frequencies or the amplitude of the piezo displacement. The micro-diaphragm pumps which are often used for dosing applications are suitable for both liquids and gases. Possible uses range from laboratory technology and medical engineering, chemistry and pharmaceutical applications to mechanical engineering. Compact piezo-driven diaphragm pumps here can accurately dose the lubricants and coolants required "on the spot", for example, and thus usually make it possible to reduce consumption. ... for Peristaltic Pumps ...
Peristaltic pumps are ideal in cases where liquids or gases are to be dosed not only accurately, but at the same time as evenly and with as little pulsing as possible. The external mechanical deformation of the tubing forces the medium to be transported through a tube. Peristaltic pumps can be easily sterilized, are non-contact in operation, and can be operated without valves. The pumping direction is determined by the control of the individual actuators. Peristaltic pumps can be found in laboratory technologies, as well as the dosing of industrial adhesives or soldering fluxes, and most infusion pumps also operate according to this principle. Figure 4 shows a peristaltic pump with mounted piezo elements. The drive element consists of flat piezo bender elements, compact piezo chip actuators or piezo stack actuators, depending on the power and size requirements. Bender actuators are suitable mainly for applications with low backpressure and for liquids with low viscosity; they convince by virtue of the small amount of mounting space they require and are thus easily integrated into the pumps. Piezo actuators allow more viscous substances to be processed but more space is required for the drive. … for Micro-Dosing Valves
It is often difficult to clearly distinguish micro-dosing valves from micropumps, because both are involved in the dosing. In valve applications (Fig. 5) the forces required are usually higher. Micro-dosing valves achieve flow rates up to tens of liters per minute for highly accurate individual and bulk dosing of gases or liquids in the microliter and nanoliter range. The dosing frequencies here are usually in the kilohertz range, with low switching times of the piezo actuators being in the millisecond to microsecond range. A variety of piezo components are used in the micro-dosing valves; e.g. piezo tubes are used for drop-on-demand methods in ink jet printers. Miniaturized valves for nanoliter dosing tasks are produced using piezo disks, for example, which are also used for lab-on-a-chip applications. Piezo actuators, which generate more force, can be used for valves where space is no issue, as can piezo drives with leverage. These are suitable for larger drop sizes – depending on the material properties (Fig.6). Similar applications can also be found in the industrial sector for the fine-dosing of soldering fluxes, oils, greases, adhesives etc. PI Ceramic, a subsidiary of Physik Instrumente, develops and manufactures piezoceramic materials which are used in today’s high-tech markets. In addition to the broad spectrum of standard products, a top priority is the realization of custom-engineered solutions.