More Precise Nanopositioning with Intelligent Damping Methods
If a piezo actuator is controlled by a brief voltage pulse, in order to, for example, move the attached mirror to a new position, the piezo crystal expands within a specific rise time. In the process of moving, a damped vibration around the controlled position will be triggered. This phenomenon is, physically speaking, natural and must therefore be taken into account when operating the actuator. Slower control leads to smaller oscillation amplitude, though it increases the time to reach the desired position. On the other hand, shortening the triggering pulse leads to further increase of excited oscillation, but not to a shortening of the rise time.
One cannot completely eliminate this natural oscillation. When talking about positioning accuracies in the nanometer range it must therefore be evaluated critically. It is thus the goal of piezosystem jena to achieve the tolerance band during positioning as quickly as possible and thereby minimize the oscillation of the actuator. This is where damping comes into play. At piezosystem jena, various possibilities have been tested to reduce the natural oscillation of a system through systematic damping measures.
Damping with Electrical Components
The mechanical oscillations of an actuator also cause the electric energy to oscillate. Hence, one possibility of damping is the transfer of excess energy from the piezo actuator to other electrical components. This also leads to a damping of the mechanical oscillations. With this procedure, piezosystem jena was able to achieve promising damping results. Because electrical properties rather than mechanical controls are decisive here; even extremely high peak oscillation values can be reduced quickly.
In an open loop test with a PX200 (Image 1), was well as in a closed loop test with a MIPOS500SG (Image 2) by piezosystem jena, the actuators achieved the targeted tolerance range significantly more quickly – in part, up to 50 percent!
Insertion of Damping Materials
With this process, flexible damping materials are integrated at neuralgic points of the actuator in order to damp unwanted oscillations caused by the actuator itself. The position and form of the respective damper is fitted to each component and optimized for the customer’s application. In tests, peak oscillation values were significantly damped. In addition, extreme oscillations transferred from the structure onto the actuator can be quickly compensated by well positioned dampers (Image 3).
Damping via Surface Friction
The introduction of sources of friction is also an effective method of reducing oscillations and achieving a quicker settling time – whether the oscillations are caused by the movement or externally induced. At specific points along the motion axis special friction surfaces are installed in the actuator. The principle works in a similar manner to a classic brake, in the way it is employed, e.g. in vehicles. The energy of the vibration is transformed into frictional heat and thus dampens the natural oscillation.
As mentioned before, there are also external factors that transfer undesired energy onto the actuator and thus lead to vibrations. The structure, or rather the device in which the actuator is integrated, is the most frequent cause of disturbances. Specially damped actuators can help to reduce even these oscillations. Unfortunately, miracles cannot be performed in this respect: a violently vibrating or extremely weak structure even a perfect actuator cannot position within the nanometer range.
Individual Solutions are Key!
Intelligent damping solutions can drastically reduce the influence of internal oscillations and external vibrations. Therefore, even during preliminary stages of development of nanopositioning systems, it is important to know the specific operating environment of the piezo actuator. This way, the manufacturer can develop a tailor-made positioning solution with the highest possible precision – as piezosystem jena has been doing for years.
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