nanoLINE: sophisticated propulsion technology on piezo-basis

Positioning precisely like a microscope

The different positioning tasks are quit various. IEF-Werner in Furtwangen, Germany has been concerned with this topic for over 30 years and already developed various solutions that are suitable for series production. But greater challenges still arise when the client demands: “… but it has to be microscopically precise!”

Furtwangen, 19.08.2015 – Particular factors are crucial for highest precision in mechanical engineering. On the one hand there is the selection of the right drive components. On the other hand a large “know-how” in the production of precision parts is required, as for example in guidelines or slides. But still, the most important factor is to have innovative ideas, especially if the task is to reduce friction. These factors are all unified in the so-called nanoLINE-technology developed by IEF-Werner GmbH in Furtwangen. Drive concepts on basis of the nanoLINE technology are suited to assemble smallest components, which require highest precision in assembling. Fundamentally, they contain the combination of two technologies, namely the piezo ceramic actuator and the aerostatic bearing. A piezo actuator is an engine with extraordinary features concerning positioning accuracy, dynamics and force development. Air bearings are bearings, in which the two components that are moved towards each other are separated by an extremely thin layer of air, produced by compressed air. This makes frictionless movement possible. Another feature of the air bearing is the avoidance of the Stick-Slip-effect. This effect describes backsliding of surfaces moving against each other. This backsliding makes it difficult to position the drive components, especially if the positioning task is situated in the micrometre area.

The combination of these different technologies results in a robust and reliable product. It is able to position accurately on 0.001 millimetres repetitively. These features render the nanoLINE-drive component quit suitable as a standard in micro assembly technology. The compact construction form allows solutions for so-called desktop-factories. Here the challenge is to accommodate a great number of production tasks in localized manner. This can lead to a disadvantage: as the more technology is accommodated in small space, the more restricted becomes its accessibility. In particular, if the operator has to be protected of the mechanics of the machine by a cover or safety components. Access leads in most cases to downtime of the machine. Here at the latest another advantage of the piezo drives becomes important. Piezo drives are very dynamic, but produce only small forces. Hence, machines equipped with piezo drives do not need any kind of cover or costly safety parts.

A classic example

One of the most common production and assembly systems in assembly technology are the so-called Pick & Place systems. A Pick & Place system generally consists of several linear axes, which are combined with a rotation movement to begin with. In a Pick & Place system based on the nanoLINE technology of IEF-Werner, all axes are moved by fast piezo actuators. Equipped like this it is possible to lift parts between 40 and 500 grams and transport those with a velocity of up to 200mm/s. The whole process has a repetitive accuracy of < 1 µm. Speed, radius of motion and turning movement of conventional Pick & Place systems – also robots belong to this category – must be observed constantly as soon as the danger zone is intervened in the process. This is demanded by common guidelines and norms as for example by the European norm EN62061 (functional safety) and EN61800-5-2 (safety functions of electric drive systems). Only if all regulations are satisfied strictly, people are permitted to work in immediate proximity to this kind of system. In a modern and flexible production surrounding it can barely be avoided that human and machine work next to each other closely. With the aid of the nanoLINE technology by IEF-Werner it is possible to conduct assembly and transport procedures, while operators are working in close proximity to the assembly system. The operator is even able to interfere with the assembly or transport process at any time without putting himself at risk. As soon as for example a gripper is fastened, the respective axis stands immediately still, until it is released by the operator. Subsequently the interrupted process can be continued, because the axis recognizes its position at any times. This is provided by the incorporated absolute encoder.

Positioning with special demands

An additional area where the nanoLINE technology can be used is as positioning unit of silicon wafers. These are barely automatable due to large production tolerances. The wafer positioning unit by IEF-Werner is part of a complete system and serves to position silicon wafers with an external diameter of 300 mm. The discrepancy of the external diameter of up to 0,2 mm is due to manufacturing tolerances. A robot deposits the wafer on the rotation unit. Now the wafer is moved into the machining position, by moving up the entire rotation unit with the wafer along a guide. In the machining position the wafer is turned by the rotation unit several times. Here absolute run-out accuracy is required. For this purpose the rotation unit is equipped with an air bearing, which enables the unit to reach ideal concentricity properties. This is made possible by decoupling all mechanic conjunctions with compressed air. This is how manufacturing tolerances do not influence the concentricity quality anymore. The rotation unit is driven by a piezo actuator. The actuator is fastened externally on the air bearing and touches the rotation unit almost effortless on a tiny spot. This contact area is enough to set the rotation unit into motion. During this rotation the wafer is measured by a high precision image processing system. Afterwards the wafer is removed by the robot.

With the aid of piezo actuators uncommon concepts are realisable. The most important advantages of the nanoLINE technologies are the kinetic energies, which are harmless for humans as well as the precise positioning. These advantages restrict the payload, the weight of the parts which can be handled respectively. Nevertheless the nanoLINE drive components are broadly applicable, especially if high precision and maximum repetitive accuracy in the area of micro production are at issue.