Showing papers on "Active vibration control published in 1984"

Nonlinear natural control of an experimental beam

Abstract: This paper is concerned with an experiment conducted at the NASA Langley Research Center that was designed to control the motion of a beam. The experimental setup consists of a free-free uniform beam acted upon by four electromagnetic force actuators, with the motion being measured by nine displacement sensors. The entire assembly is linked to a digital computer permitting on-line real-time computation of the control forces. The control scheme is based on the independent modal-space control method in conjuction with a nonlinear, on-off control law for the modal forces. The actuator forces are then synthesized from the modal forces by means of a linear transformation, resulting in quantized forces. The sensors' data are processed by modal filters. It is observed that the independent controls are very effective in suppressing the motion of the beam, even though there is about a 50% difference between the actual and the analytically computed natural frequencies.

Vibration type force detector

Abstract: A vibration type force detector in which the vibration string is made of a platinum-based nickel-containing alloy. The magnitude of a force to be detected is obtained through the measurement of a natural vibration frequency of a string vibrating with the force loaded thereto. However, the force detector using a Pt-Ni alloy vibration string based on the invention makes it possible, for the first time, to apply a vibrational type force detector to a precision measurement of force or weight. Measurement with an accuracy of 10-5 is made possible by the present invention.

Vibration wave motor having a vibrator of non-uniform elastic modulus

Abstract: In a vibration wave motor for driving a movable member contacting a vibration member by a travelling vibration wave generated in the vibration member attached to electrostrictive elements, by applying a periodic voltage to the electrostrictive elements. The vibration member is of two-plate structure having a non-uniform elastic modulus in the direction of amplitude of the travelling vibration wave.

Experimental research on flexible beam modal control

Abstract: A hardware experiment has been developed to study the active vibration control (low-authority control) of a clamped-free flexible beam, where the design methodology is based on direct velocity feedback control. The objective of the experiment is to demonstrate and verify the dynamics and advanced control laws as applied to a structural element. Another important feature of the experiment is the feasibility of hardware realization, especially the dedicated noncontacting actuating and sensing method. Sensing is provided by a purely optical displacement sensor, while an electrodynamic force system provides the actuation. Experimental results are compared with numerical simulations of open- and closed-loop performance in both the colocated and noncolocated actuator/sensor positions. In most cases, good agreement is achieved between the experiments and theoretical predictions.

Apparatus for detecting ultrasonic vibration

Abstract: This invention is an apparatus for detecting the vibration of a Langevin type electrostrictive ultrasonic vibrator comprising a system made up of an iron core, a coil and a magnet surrounding but not connected to a magnetic projection attached to the rear end of the vibrator. The vibration of the magnetic projection is detected by the system surrounding it and the resulting induced voltage is fed back to a control to maintain the vibration at the desired resonant frequency.

Controllable vibration damper for vehicles

Abstract: By means of the present application the construction of a controllable vibration damper with electromotive adjustment arranged in the internal chamber of the vibration damper is essentially simplified in that the power supply of the electric motor is formed by vibration damper subassemblies electrically insulated from one another and movable in relation to one another.

Real Time Vibration Control of Rotating Circular Plates by Temperature Control and System Identification

Abstract: A system for real-time control of the transverse vibration of a rotating circular plate, based on a thermal stressing technique and dynamic system identification, is presented in this paper. In this method the plate natural frequency spectrum is modified through the purposeful introduction of thermal membrane stresses. The critical speed is maximized. In effect vibration is controlled through real-time control of the plate design. Evaluations with computer simulation and experimental measurements on a thin circular plate verify the system capability to control transverse vibration in a changing thermal environment.

Studies on the Ring Type Magnetic Ultrasonic Vibration Detector

Abstract: Ring type magnetic ultrasonic vibration detectors suitable for measuring ultrasonic longitudinal vibration systems are proposed and studied. They consist of detecting coils, permanent magnetic thin disks or strips and foam rubber supporters. These detectors are most suitable for measuring high power ultrasonic vibration systems, and have superior linearity and good stability. Output voltage is proportional to vibration velocity or vibration stress amplitude of a vibration system. The position of maximum detector output voltage can be shifted along the vibration system by rearrangement of the detector.

Impact Response of Rotor-bearing System to an Arbitrary Excitation of Pedestals : 2nd Report: Experiments on Rotor Vibration due to Various Types of Excitation

Abstract: Vibration experiments on a rotor-bearing system were systematically executed in four different types of excitation and the results were discussed with respect to non-linear effects of the bearing oil film. Not the obvious non-linearity of the unbalance response, but linearity to a large amplitude was shown by the corresponding alternative force and the static force acting on the rotor itself, and the non-linear solution and the static deflection were compared.

Studies on Ultrasonic Plastic Welding with Two Longitudinal Vibration Systems

Abstract: Ultrasonic plastic welding with two longitudinal vibration systems is proposed and studied. The welding limit of this system may be doubled compared with a conventional ultrasonic welding method with one vibration system. The required vibration velocity of one of vibration systems for welding becomes about half and hence the required power becomes about quarter. The damage of specimen by welding becomes smaller. In the case of thick and large specimen, i.e. transmission welding, and where the vibration frequencies of upper and lower vibration systems are same, the vibration distribution along welding specimen can be changed by controlling the vibration phase difference between upper and lower welding tips. The welding position can be set at a vibration stress maximum position by controlling the vibration phase difference. This method with two vibration systems has various useful features and is effective for plastic welding.

Vibration absorbing article made of shape memory alloy.

Abstract: The invention relates to an article with vibration damping capacity and includes a metal alloy with potential shape memory properties whereby the alloy is in the martensitic state at room temperature or above and absorbs in this state in a durable way at least 10 percent of the imposed vibration energy with a vibration amplitude greater than 10 and smaller than the limit of microplastic deformation.

On a Controlling Method of Amplitude and Frequency of Self-excited Vibration in an Externally Pressurized, Recessed-type Gas Bearing

Abstract: A self-excited vibration induced in an externally pressurized, recessed-type gas bearing is applicable to a pneumatic vibrator. An orifice and a chamber connected to a recess produce a self-excited vibration describing a limit cycle, the amplitude and frequency of which vary with the area of the orifice and the volume of the chamber. In this paper, it is proposed, utilizing such a phenomenon, to provide the recess with an orifice of variable area and a chamber of variable volume as a powerful method to control the amplitude and frequency of the vibration, in addition to the conventional method of changing the supply pressure and the load, and the controlling ability of the proposed method is discussed theoretically and experimentally.