Tags
Vibration Isolation, Actuators
Reference
(Shingo Ito & Georg Schitter, 2016)
Author(s)
Ito, S., & Schitter, G.
Year
2016

Classification of high-precision actuators

Table 1: Zero/Low and High stiffness actuators
Categories Pros Cons
Zero stiffness No vibration transmission Large and Heavy
Low stiffness High vibration isolation Typically for low load
High Stiffness High control bandwidth High vibration transmission

Time Delay of Piezoelectric Electronics

In this paper, the piezoelectric actuator/electronics adds a time delay which is much higher than the time delay added by the voice coil/electronics.

Definition of low-stiffness and high-stiffness actuator

  • Low Stiffness actuator is defined as the ones where the transmissibility stays below 0dB at all frequency
  • High Stiffness actuator is defined as the ones where the transmissibility goes above 0dB at some frequency

Figure 1: Definition of low-stiffness and high-stiffness actuator

Figure 1: Definition of low-stiffness and high-stiffness actuator

Low-Stiffness / High-Stiffness characteristics

  • The low stiffness actuators achieve smooth transition from active isolation to passive isolation.
  • The high stiffness actuators can have a gap between the passive and active isolation vibration where the vibrations are amplified in a certain frequency band.

Controller Design

Figure 2: Obtained transmissibility

Figure 2: Obtained transmissibility

Discussion

The stiffness requirement for low-stiffness actuators can be rephrased in the frequency domain as: “the cross-over frequency of the sensitivity function of the feedback system must be larger than \(\sqrt{2} \omega_r\) with \(\omega_r\) is the resonant frequency of the uncontrolled system”.

In practice, this is difficult to achieve with piezoelectric actuators as their first resonant frequency \(\omega_r\) is too close to other resonant frequencies to ensure close-loop stability. In contrast, the frequency band between the first and the other resonances of Lorentz actuators can be broad by design making them more suitable to construct a low-stiffness actuators.

Bibliography

Ito, S., & Schitter, G., Comparison and classification of high-precision actuators based on stiffness influencing vibration isolation, IEEE/ASME Transactions on Mechatronics, 21(2), 1169–1178 (2016). http://dx.doi.org/10.1109/tmech.2015.2478658 ↩