Funding entity CRISA
Dual-piston compressors for Stirling-cycle cryocoolers consists of an expander piston (or master) and a balancer piston (or slave). In normal operation, the former is moved using an electric servomotor commanded by the cold-tip temperature controller while the latter is moved in the opposite direction with a different servomotor to cancel the vibration forces (cased by the master's movement) that would produce an undesirable mechanical vibration of the compressor. The synchronized piston movement described so far, greatly improves the vibration level with respect to the use of a single piston but the problem is still quite important in practical system and further improvement is necessary. Otherwise, the remaining vibration may affect the stability of the platform upon which the compressor is placed and/or may deteriorate the performance of sensitive electronic systems mounted on the same platform.
Although the exact model that relates a compressor-motor movement and the compressor vibration is not fully known at this moment, an active-vibration-control system is going to be investigated in this project.
The available literature shows that compressor vibration can be measured or estimated so that a control algorithm can modify the feeding voltage of the balancer piston of Stirling compressors in order to provide active damping of that vibration. Specialized load-cell-based dynamometers or accelerometers have been proposed to measure compressor-generated vibration.
Several active-vibration-control algorithms will have to be considered in this project. To start with, an algorithm proposed by Astrium/CRISA will be studied in detailed. As shown bellow, the main advantages of this algorithm are that (a) it does not required a detailed model to describe the vibration mechanism and (b) it does not apply a classical closed-loop control system and stability is easily guaranteed. On the other hand, the exact attenuation level of the vibration problem cannot be established easily.
According to the specifications received from Astrium/CRISA, this project comprises the implementation and validation of active-vibration-control algorithms for cryogenic compressors to be proposed in future space missions.
CRISA-VIBRACIONES
