Active counter-force control has significant advantages over the more traditional motion based active vibration suppression for isolation of disturbance sources. In this paper, features of four specific actuators, two hybrid isolation struts, and three system level realizations are reviewed with a focus on vibration isolatiodsuppression to reduce cryocooler disturbance forces. All of the discussed hardware and systems are based on electromagnetic reaction mass actuators. Significant vibration reductions can be achieved with such systems. The best measured tonal performance for all three systems discussed exceeds two orders of magnitude (40 dB) of vibration reduction. Control bandwidth can exceed 500 Hz. The necessary actuators are also robust, compact, and lightweight. Two of the systems were realized with miniature actuators weighing 3.8 ounces (107 grams) and 3.12 ounces (88 grams) respectively. Such systems have significant promise for addressing critical vibration isolation needs for upcoming space missions such as SIM, NGST, TPF, SBL, etc., through isolation of onorbit noise sources such as cryocoolers and reaction wheels. They could also be quite useful for terrestrial applications in telecommunication, manufacturing, and semiconductor processing industries.
Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. ABSTRACT1Spacecraft carry instruments and sensors that gather information from distant points, for example, from the Earth's surface several hundred kilometers away. Small vibrations on the spacecraft can reduce instrument effectiveness significantly. Vibration isolation systems are one means of minimizing the jitter of sensitive instruments. This paper describes one such system, the Satellite Ultraquiet Isolation Technology Experiment (SUITE). SUITE is a piezoelectric-based technology demonstration scheduled to fly in 2000 on PICOSat, a microsatellite fabricated by Surrey Satellite Technology, Ltd. Control from the ground station is planned for the first year after launch. SUITE draws on technology from previous research programs as well as a commercial piezoelectric vibration isolation system. The paper details the features of SUITE, with particular emphasis on the active hexapod assembly. A description of the PICOSat spacecraft and the other considerations preceding the development of the flight hardware begins the paper. Experiment goals are listed. The mechanical and electromechanical construction of the SUITE hexapod assembly is described, including the piezoelectric actuators, motion sensors, and electromagnetic actuators. The data control system is also described briefly, including the digital signal processor and spacecraft communication. The main features of the software used for real-time control and the supporting Matlab software used for control system development and data processing are summarized.
Cryocoolers are well known sources of harmonic disturbance forces. In this paper two miniaturized, add-on, vacuum compatible, active vibration control systems for cryocoolers are discussed. The first, called VIS6, is an active/passive isolation hexapod and has control authority in all six degrees of freedom. This capability is desirable when reduction of all cryocooler disturbance loads, including the radial loads, is required. Each of the six identical hexapod struts consists of a miniature moving coil electromagnetic proof mass actuator, custom piezoelectric wafer load cell, viscoelastic passive isolation stage, and axial end flexures. The first five disturbance tones are reduced over a bandwidth of 250 Hz using a filtered-x least mean square algorithm. Load reductions of 30-40 dB were measured both axially and radially. The second system, called VRS1, is a pure active control system designed to reduce axial expander head disturbance loads. It works on the basis of a counter-force developed from an electromagnetic proof mass actuator. Error signals are provided from a commercial accelerometer to a standalone digital signal processor, on which a filtered-x least means square control algorithm is implemented. Over the 500 Hz control bandwidth, the 1 1 disturbance tones were reduced on between 14 to 40 dB.
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