Active Vibration Isolation for a Long Range Scanning Tunneling Microscope (original) (raw)
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Sensors and Actuators A: Physical, 2005
Active vibration isolation is gaining increased attention in the ultra high precision applications to effectively treat the unavoidable ground vibration. The use of active vibration isolation is now being explored for the Molecular Measuring Machine (M 3) at the National Institute of Standards and Technology to improve its imaging resolution. The M 3 system uses a Mallock suspension to establish a non-rotation constraint to the stage motion. The vibration isolation system has to work within the Mallock geometry. The system is also a six-input-six-output system; therefore, a clever design is needed to maximize the controller performance while limiting it to within the stability range. The control algorithm adopted uses discrete sliding mode control, taking advantage of its easy computer implementation and its robust high performance properties. The experimental results show that the controller is effective over the operating frequency band and is superior to the conventional lead-lag type controller.
Vibration isolation analysis for a scanning tunneling microscope
Review of Scientific Instruments, 1992
We analyze the efficiency of a vibration isolation system (VIS) for a scanning tunneling microscope as a function of the different parameters involved. The VIS consists of a stack of several metallic plates, separated by rubber elements with known properties. We show three-dimensional graphs obtained for different values of parameters such as rigidity (spring) constant (K), damping constant (C), mass (M), and the number of stages (n). Analyzing the K dependence of the position of the main peaks, we find a parabolic behavior when the damping constant is small, with a slight deviation for larger values.
Modelling and Control Techniques of an Active Vibration Isolation System
2004
In the field of high-resolution measurement and manufacturing, effective anti-vibration measures are required to obtain precise and repeatable results. This is particularly true for experiments or processes where the typical amplitudes of the ambient vibration and the dimensions of the investigated or manufactured structures fall in the same range, e.g. submicron semiconductor production, holographic interferometry, confocal optical imaging, and scanning probe microscopy. In the active vibration isolation system examined, signals are acquired by extremely sensitive vibration detectors, and the vibration is reduced using either local analog feedback control or digital model-based control to drive electrodynamic actuators. This papers deals with the modelling and control techniques of such an active vibration isolation system. The modelling, parameter identification, and model updating procedure are described. The experimental setup for testing such an antivibration system is describe...
Vibration isolation for scanning tunneling microscopy
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1987
Vibration isolation technology for scanning tunneling microscopy (STM) to suppress the external mechanical perturbation down to a subatomic scale is described. The system is simplified into two subsystems, a tunneling assembly and a supporting table. Each of them has its own mechanical eigenfrequency. The principle of the isolation exists in making the two eigenfrequencies very different from each other. A theory of isolation developed is based on a model of multiply coupled oscillators with damping. Experimental results of the isolation characteristics for the two types of isolators constructed, one consisting of two-stage coil springs and the other of multiply stacked metal plates with rubber pieces among them, are well explained by the theory. STM images of graphite are obtained by using these isolators combined with various tunneling assemblies. Thereby the basis for design of the isolators is clarified.
Active isolation of vibration with adaptive structures
The Journal of the Acoustical Society of America, 1994
The problem of actively isolating the periodic vibrations of a rigid machine mounted on a supporting flexible structure is usually approached by applying the active inputs in parallel or series with the passive inputs. This has a number of disadvantages which are related to the development of a high power, compact yet stiff/active isolation unit. In this experimental work, a new approach in which the receiving structure is considered to have adaptive properties is studied. The aim is to control the transmitted vibrations by distributed arrays of piezoelectric transducers bonded to the receiving structure. The experimental rig consists of a rigid thick plate (the machine) supported at the corners by four elastic springs mounted on a thin clamped-free elastic steel plate (the receiving structure). The thick plate is driven by a harmonic force input. Response in the receiving panel is measured with a scanning laser vibrometer. Active inputs to the receiving structure are induced by three pairs of piezoceramic actuators bonded to the surface and configured to induce bending. The error sensors consist of up to two polyvinylidene fluoride (PVDF) strips attached to the panel surface in various positions. The control approach uses a two channel feedforward adaptive LMS algorithm implemented on a TMS320C25. The results show that the first three modes of the system can be controlled efficiently when driven "on resonance," thus effectively isolating the vibrating structure from the "machine" raft input. However, when the system is driven "off resonance," the vibrations of the receiving structure proved more difficult to reduce effectively. The paper presents vibration distribution of the receiving plate with and without control for a number of input frequencies as well as a variety of control transducer configurations.
Active vibration isolation of multi-degree of freedom systems
1997
One of the principal objectives of vibration isolation technology is to isolate sensitive equipment from a vibrating structure or to isolate the structure from an uncertain exogenous disturbance source. In this paper a dynamic observer-based active isolator is proposed that guarantees closed-loop asymptotic stability and disturbance decoupling between the vibrating structure and isolated structure. The proposed active isolator is applied to a uniaxial vibrational system and compared to an optimal linear-quadratic design
Smart Materials and Structures, 2007
An original control approach for robust vibration isolation is introduced in this paper. Two feedback signals, the relative displacement and the transmitted force between the sensitive element and its disturbing support, are employed in a so-called mixed control design. This strategy is used to perform control in the case of protection of electronic components, such as frequency generators, vibrating gyroscopes and certain accelerometers, essential to the operation of electronic cards. The simplicity of the control law allows us to tune the parameters of the controller with a very simple optimization process.
Magnetic and Elastomeric Damping Effects on the Vibration Amplitude of a Vibration Isolation System
SAMPE 2020 | Virtual Series
This technical paper describes the design and experimental process for a single-stage multi-degreeof-freedom vibration isolation system for a scanning tunneling microscope. The mathematical model used for the mass-spring system analysis will be presented, along with various design iterations for the mass-spring system and the frame. Based on the mathematical model, a MATLAB script is developed to study hundreds of springs available online so that a spring that satisfies important specifications can be chosen. Finite Element software is used to investigate the natural frequencies of the frames, which will assist the frame's design selection. Throughout the design process, magnetic and elastomeric damping methods are actively considered to simplify the design due to tight constrain of the vacuum chamber.
Active and Passive disturbance isolation for high accuracy control systems
2013
Micro-vibrations are a major contributor to the performances of an increasing number of Earth Observation and space science missions as line of sight stability requirements get tighter with increasing resolution and longer instruments integration time. These mission performances are sensitive to the presence of disturbance sources such as wheels, cryocoolers and solar array drive mechanisms. Astrium is currently managing microvibrations attenuation by implementing elastomer-based isolators set at the reaction wheels interface without locking devices. This flight-proven passive solution guarantees good rejection performances at high frequencies in line with current mission requirements. However, such systems cannot offer by nature high isolation capability at low frequencies, which could reveal insufficient for future demanding Earth and Science Observation programmes. This paper presents the work done in the frame of an ESA study on the design of mixed passive and active solutions o...