Precision Controlled Actuation and Vibration Isolation Utilizing Magnetorheological (MR) Fluid Technology

Abstract

Precision controlled vibration isolation utilizing magnetorheological (MR) fluid technology for potential space optical applications, such as surveillance and directed energy, is addressed. This research includes the design, development and preliminary testing of a semiactive, proof-of-concept, MR vibration isolator. Base disturbances designed to produce payload vibration responses were employed in a single degree-of-freedom test apparatus. The MR vibration isolator served as the load-coupling element between the payload and the base disturbance input. The three-parameter isolator consists of two passive spring elements combined with one MR damping element. The MR damper control algorithm uses relative rate between damper cylinder and piston to dynamically vary the effective coefficient of damping. The result of this technology is ability to tune isolation frequency within a given range. Through intelligent modulation of the damping element alone, dynamic changes in both apparent stiffness and damping of the isolator are achieved. For applications where the ability to vary stiffness and damping would improve pointing accuracy and jitter control, this technology holds great appeal.

<title>Survey of state-of-the-art vibration isolation research and technology for space applications</title>

“…3 Vibration control systems can be classified as passive, active, semi-active (adaptive-passive), or hybrid. 5,6 A passive isolator is defined as a compact connection that receives no external energy or information 7,5 and behaves like a low pass filter. 8 The compact connection consists of a resilient stiffness member and an energy dissipation or damping member that either absorbs vibrations or loads the vibrational path.…”

“…2 Advantages of passive systems are simplicity, guaranteed stability, 9 reliability, and no required power. 5 However, passive control has many limitations for vibration isolation in space applications: 1) inability to practically achieve isolation at very low frequencies, 2) trade-off between resonant peak and high-frequency attenuation, 3) trade-off between base motion isolation and disturbance rejection, 4) inability to adapt to changes in structural parameters over time resulting in reduced performance, 5) inability to optimize the design for varying excitation frequencies, 6) may amplify low frequency vibrations, and 7) may require structural off-load mechanisms to survive launch and ground tests. 8,2,10 Active control is a method of loading a vibrational path using force actuators that require external energy and information as inputs.…”

“…6,7 Active isolation has many advantages over passive isolation: 1) it removes trade-offs between low-frequency amplification and high-frequency attenuation, 2) it removes the base motion isolation and disturbance rejection trade, 3) and allows intelligent and a fast response to disturbances. 8,5 The disadvantages of active isolation are: 1) it requires relatively high power, 2) it can create instability in the system, 3) may require complex control laws and components, and 4) failure of the control system results in no isolation at all. 5,2,10 In practice, active isolation and passive isolation are combined into what is sometimes referred to as hybrid isolation.…”

“…8,5 The disadvantages of active isolation are: 1) it requires relatively high power, 2) it can create instability in the system, 3) may require complex control laws and components, and 4) failure of the control system results in no isolation at all. 5,2,10 In practice, active isolation and passive isolation are combined into what is sometimes referred to as hybrid isolation. Advantages of hybrid isolation are it: 1) allows transmissions of static loads through the isolation system, 7 2) reduces the external power required in comparison to a purely active system by reducing the bandwidth needed by the active portion, 2,10 and 3) allows some vibration isolation if the active element fails.…”

“…Advantages of hybrid isolation are it: 1) allows transmissions of static loads through the isolation system, 7 2) reduces the external power required in comparison to a purely active system by reducing the bandwidth needed by the active portion, 2,10 and 3) allows some vibration isolation if the active element fails. 5 Disadvantages are 1) a risk of instability created by the active element 5 and 2) a risk of degradation due to detuning of the passive element.…”