Showing papers on "Dynamic Vibration Absorber published in 1998"

A Nonlinear Vibration Absorber for Flexible Structures

Abstract: An approach for implementing an active nonlinear vibration absorber for flexible structures is presented. The technique exploits the saturation phenomenon exhibited by multidegree-of-freedom systems with quadratic nonlinearities possessing two-to-one autoparametric resonances. The strategy consists of introducing second-order controllers and coupling each of them with the plant through a sensor and an actuator, where both the feedback and control signals are quadratic. Once the structure is forced near its resonances, the oscillatory response is suppressed through the saturation phenomenon. We present theoretical and experimental results of the application of the proposed vibration absorber. The structure consists of a cantilever beam, the feedback signal is generated by a strain gage, and the actuation is achieved through piezoceramic patches. The equations of motion are developed and analyzed through perturbation techniques and numerical simulation. Then, the strategy is tested by assembling the controllers in electronic components and suppressing the vibrations of the first and second modes of two beams.

Vibration control apparatus and method for calender rolls and the like

Abstract: A vibration control apparatus (20, etc.) and method for a calender (18, etc.) for controlling vibration between two or more rolls (ex. 22, 24, etc.) which controls vibration induced thickness variations in a medium (27) exiting from the nip. The apparatus (20, etc.) includes a frame (19, etc.), a first and second rolls (22, 24, etc.) mounted relative to the frame, and a force generator (32, etc.), such as an electro-mechanical active actuator, servo-hydraulic actuator, controllable semi-active damper, Active Vibration Absorber (AVA), or Adaptive Tuned Vibration Absorber (ATVA), provides cancelling forces to control vibration between the first and second roll (22, 24, etc.) thereby, controlling such vibration induced thickness variations in the medium (27). Preferably, the apparatus includes at least one sensor (ex. 42, 42', 42', 42''', etc.) for providing a signal representative of a vibration condition of at least one of the first or second roll (22, 24, etc.), and preferably both, and a digital controller (50, etc.) for processing the signal representative of said vibration condition preferably according to a feed-forward-type control and providing a control signal to a force generator (32, etc.). Vertical and/or lateral vibration of the rolls (22, 24, etc.) may be controlled simultaneously. Likewise, fundamental vibrational frequencies and their harmonics may be controlled individually, or in combination.

Apparatus and method for controlling damping force characteristic of vehicular shock absorber

Abstract: A damping force characteristic variable type shock absorber which takes a mode of operation into a first mode, a second mode, a third mode, and a fourth mode is connected to a damping force characteristic basic mode switching block and a damping force characteristic special mode switching block. This first mode is such that when the vehicular vertical direction determined by the vehicular vertical behavior determinator is upward, an extension phase provides a relatively high damping force characteristic and a compression phase provides a relatively low damping force characteristic. The second mode is such that when the vehicular vertical direction determined by the vehicular vertical behavior determinator is downward, the extension phase provides a relatively low damping force characteristic and the compression phase provides a relatively highly damping force characteristic. The third mode is such that when the vehicular vertical behavior determinator is neither upward nor downward, both of extension and compression phases provide the relatively low damping force characteristics. The fourth mode is such that when a predetermined condition of a vehicular motion is satisfied, the damping force characteristics in both extension and compression phases are relatively high.

Adaptive tuned vibration absorber, system utilizing same and method of controlling vibration therewith

Abstract: A flex-plate tuned vibration absorber (35) including a tuned mass (43) flexibly suspended by one or more flex plates (58). In one aspect the Tunable Vibration Absorber (TVA) (35) is adaptive in that the position of the mass is adaptively moveable with respect to its initial position, thereby effectuating a change in the TVA's resonant frequency. In one embodiment, the tuned mass (43) moves along a rigid frame (53). In another, movement of the mass (43) statistically stresses a preferably disc-shaped flexible plate (58) thereby changing its stiffness. Preferably, a reducer (78) gears down the speed of the motor (64). In another aspect, a TVA system includes a base sensor (40) providing a base vibration signal, a mass sensor (38) for providing a vibration signal of the tuned mass (43), and an electronic controller (42) for generating a control signal to the TVA (35). The TVA finds application for absorbing vibration in vibrating structures, such as in aircraft.

Roof Isolation System to Reduce the Seismic Response of Buildings: A Preliminary Assessment

Abstract: A roof isolation system is proposed as a means to reduce the detrimental effect of earthquakes in buildings. This roof isolation system entails the insertion of flexible laminated rubber bearings between a building's roof and the columns that support it, and the addition of viscous dampers connected between the roof and the rest of the building. The properties and dimensions of the rubber bearings and viscous dampers are selected in a way that makes the roof, bearings, and dampers form a highly damped vibration absorber. Presented also is a comparative study with a simple five‐story steel building under a strong earthquake ground motion that is carried out to assess the effectiveness of the proposed system. In this comparative study, it is found that the roof isolation scheme reduces the floor displacements and interstory drifts of the analyzed building by as much as 83 percent. On the basis of these results and in view of its simplicity, it is concluded that the proposed roof isolation system ha...

Isolated hand-held vibrating device

Abstract: An isolator for use in a hand-held vibrating device for providing optimum vibration isolation by utilizing elastomeric sections. Six embodiments are shown which utilize elastomer sections to enhance vibration isolation along an axial direction of vibration. A first embodiment includes a frustoconical section, while the second employs a W-shaped buckling element. A third embodiment includes use of a tuned fluid inertia which is tuned to substantially coincide with a predominant operating frequency of the vibrating device and produces forces to substantially reduce the vibration transmission, while three other embodiments employ metallic buckling springs. Another embodiment employs a tuned vibration absorber and still another combines a tuned mass with a buckling column.

Hollow drive shaft with integrated vibration absorber

Abstract: The invention relates to a drive shaft with an integrated vibration absorber. The aim of the invention is to reduce effectively, in a targeted manner and by simple means, excessive vibration in a drive shaft embodied as a hollow shaft (8) by acting on the vibration maximum (antinode). A vibration absorber (2) positioned inside the hollow shaft (8) consists of a damping mass (absorber mass) (4) and an elastic coupling element (6). The absorber mass (4), which is actively connected to the inner wall of the hollow shaft (8) via the elastic coupling (6), is rotationally and axially symmetrical and at its centre has a necking (12) for receiving the elastic coupling element (6). The invention also relates to the use of said drive shaft as a drive shaft (8) (hollow shaft) mounted transversally in the vehicle and as a drive shaft (8) mounted longitudinally in the vehicle (cardan shaft embodied as hollow shaft).

Vibration and Noise Control of the Fuselage via Dynamic Absorbers

Abstract: A closed, elastic cylindrical shell is used as a simple model of the aircraft’s fuselage. For reducing the vibration of the fuselage and the subsequent interior sound pressure due to the propellers, several dynamic absorbers are attached to the shell. In the paper, we analytically derive the vibration and the interior sound pressure of the shell by employing the techniques of subsystem synthesis and modal expansion where the external distributed pressures are chosen according to experimental data of an actual aircraft. The absorbers are successful for attenuating the vibration and the noise. The effects of altering various parameters of the shell, the external pressures, and the absorbers, are also studied and discussed. Finally, some general guidelines of absorber design for vibration and noise control of the fuselage are presented.

High bandwidth tunability in a smart vibration absorber

Abstract: The theory of an electrically tunable Terfenol-D vibration absorber is developed in this paper. An overview of mangetostriction including discussion of the (Delta) E effect is presented. Experimental results showing agreement with prior art are included that demonstrate electrical control of a magnetostrictive actuator resonant frequency by varying the resonance between 1275 Hz and 1725 Hz. The tunability of the transducer resonant frequency is then implemented to achieve high bandwidth tunability in the performance of a Terfenol-D vibration absorber.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Beam-type dynamic vibration absorber comprised of free-free beam. technical note

Abstract: This note presents a new beam-type vibration absorber having a suppressing effect on several vibration modes of beams. An approximate tuning method of the beam-type dynamic absorber is proposed, in which application is made of the tuning conditions of an absorber in the two-degrees-of-freedom system. Numerical investigations have shown the approximate tuning method to be useful and have demonstrated the effectiveness of the beam-type dynamic vibration absorber. This new absorber will be used for the deck type of steel bridge without an intermediate sway bracing, which has a space under the deck whereby this beam-type dynamic absorber may be attached.

Beam-Type Dynamic Vibration Absorber Comprised of Free-Free Beam

Abstract: This note presents a new beam-type vibration absorber having a suppressing effect on several vibration modes of beams. An approximate tuning method of the beam-type dynamic absorber is proposed, in which application is made of the tuning conditions of an absorber in the two-degrees-of-freedom system. Numerical investigations have shown the approximate tuning method to be useful and have demonstrated the effectiveness of the beam-type dynamic vibration absorber.

Elastomeric tuned vibration absorber

Abstract: A tuned vibration absorber (40) includes a mounting plate (42) having at least two (46, 56), and alternatively four, mounting holes (46, 50) in spaced relationship from a longitudinal center axis of the plate (42). An elastomeric spring (60) is bonded to the mounting plate (42). A main tuning mass (70) is bonded to the elastomeric spring (60) opposite the mounting plate (42), and fine tuning masses (72) are riveted directly onto the main tuning mass (70). The elastomeric spring (60) and main mass (70) both have a rectangular profile to maintain a low profile height from the mounting plate (42). A cover (50) is formed of a single sheet of metal bent to form a rectangular box with one open side. The cover (50) includes mounting flanges (54) with holes (56) that align with the mounting holes (46) on the mounting plate (42). For mounting the vibration absorber on a stiffening ring (10) of an aircraft frame, a spacing plate (90) is positionable between a portion of the mounting plate (42) and the stiffening rib (10) of an aircraft frame, and adjacent to an overlapping secondary stiffening (14, 16) ring to provide a flat mounting surface.

Electrically-tunable vibration absorbers

Abstract: An ETVA (electrically-tunable vibration absorber) has a vibratable mass with a mechanical spring suspension supplemented by an electromagnetic spring simulation that can be adjusted electrically to vary the self-resonant frequency of the vibratable mass and tune it to a disturbing frequency that is to be suppressed. A flux path from the electromagnet traverses an air gap between a pair of oppositely-facing matching magnetic pole arrays, one of which is attached to the vibratable mass while the other pole array is substantially attached to the object structure that is being treated to suppress vibration. The two interfacing arrays are configured in mirror-image relationship as seen in cross-section, and are held by the spring suspension so as to be mutually aligned under a quiescent condition and to move relative to each other under vibration only in a designated direction so that the gap separation distance remains substantially constant and thus the flux density at the poles remains substantially constant and unmodulated, resulting in high efficiency due to minimal eddy current losses.

Actively tuned solid state piezoelectric vibration absorber

Abstract: A tunable solid state piezoelectric vibration absorber and an active tuning method were developed and demonstrated. A passive vibration absorber generally acts to minimize structural vibration at a specific frequency associated with either a tonal disturbance or the response of a lightly damped structural vibratos mode. Because this frequency is rarely stationary in real applications, damping is usually added to ensure some level of effectiveness over a range of frequencies. Maximum response reductions, however, are achieved only if the absorber is lightly damped and accurately tuned to the frequency of concern. Thus, an actively-tuned vibration absorber should perform better than a passive one and, furthermore, could be made lighter. In its simplest form, a vibration absorber consists of a spring-mass combination. A key feature of the tunable vibration absorber described herein is the use of piezoelectric ceramic elements as part of the device stiffness. The effective stiffnesses of these elements was adjusted electrically, using a passive capacitive shunt circuit, to tune the resonance frequency of the device. The tuning range of the absorber is thus bounded by its short- circuit and open-circuit resonance frequencies. An alternative tuning approach might employ resistive shunting, but this would introduce undesirable damping. Another feature of the device is the ability to use the piezoelectric elements as sensors. A control scheme was developed to estimate the desired tuning frequency from the sensor signals, to determine the appropriate shunt capacitance, and then to provide it. The shunt circuit itself was implemented in ten discrete steps over the tuning range, using a relay-driven parallel capacitor ladder circuit. Experimental results showed a maximum 20 dB, and a 10 dB average improvement in vibration reduction across the tuning range, as compared to a pure passive absorber tuned to the center frequency, with additional benefit extending beyond the tuning range.

Gun barrel vibration absorber

Abstract: A weapon system includes a gun barrel and a vibration absorber fitted onto a free end of the gun barrel. The vibration absorber includes a compliant energy storage device, such as a spring, and a mass secured to the energy storage device. The potential energy stored in the spring and the kinetic energy stored in the mass inertia are dissipated in part as friction, and re-introduced in part to the gun barrel such that the re-introduced energy is out of phase relative to the gun barrel motion. As a result, the vibration absorber does not totally dissipate the stored energy, but rather reshapes the receptance of the gun system so as to significantly reduce the vibration energy that migrates into the gun structure from known disturbances. This improves the overall accuracy of the gun system. In addition, the vibration absorber reduces the load between the gun barrel and the projectile during launch, thereby reducing the gun barrel muzzle wear and the exit yaw rate of the projectile.

Optimum delayed feedback vibration absorber for MDOF mechanical structures

Abstract: An optimal active vibration absorber is designed for wide band excitations using a delayed partial state feedback. The final structure, named delayed feedback vibration absorber (DFVA), offers the minimum M/sub peak/ for the primary system involved within a given frequency band. A min-max problem is solved. It is shown that, the vibration suppression characteristics can be improved better than 20% over the optimum passive absorber for a typical case. Stability discussions associated with delayed systems are also presented and included in the optimization process.

Adaptively tuned vibration absorber with dual flexures

Abstract: An apparatus for counteracting vibrations includes a housing for attachment to a vibrating member. First and second bodies are connected to the housing by first and second springs, respectively, with a combined stiffness which defines a resonant frequency at which the first and second bodies oscillate with respect to the housing. Each of the first and second springs include a plurality of rods fixedly connected between a pair of rings. A lever engages the first and second bodies to vary a spacing between those bodies when force from an actuator is applied to the lever. The lever action alters the stiffness of the first and second springs which varies the resonant frequency of the vibration absorber.

Pivoting tuned vibration absorber and system utilizing same

Abstract: A tuned vibration absorber and vibration-reduced pipeline system utilizing same The tuned vibration absorber includes a support frame, a tuning mass mounted for pivotal movement relative to the support frame about a pivot; the tuning mass including a lever, and a spring contacting the lever In the vibration-reduced pipeline system, the absorber's support frame is preferably secured atop of the pipeline section, preferably by at least one strap, to absorb vibrations thereof In a preferred aspect, the tuning mass includes an arm extending from the pivot in a first direction and a weight repositionably mounted thereon The lever extends from the arm along a second direction substantially orthogonal to the first direction Preferably the line of action (along A--A) of the spring extends substantially parallel to the first direction An adjuster is provided for readjusting a position of the tuning mass relative to said support frame due to drift in the spring Preferably, the absorber includes pin means, such as a readily removable pin, for quickly disconnecting the spring as well as pin means for limiting deflection of the tuning mass A cover including first and second portions houses the tuning mass and spring

Adaptively tuned vibration absorber for reduction of aircraft cabin noise

Abstract: An aircraft engine is attached to the fuselage by a mounting structure that has a vibration absorbing system which includes first and second sensors to produce signals indicating vibration along two orthogonal axes. A third sensor, such as an accelerometer, is coupled to the mounting structure for sensing vibration of the engine. A tachometer circuit, connected to the third sensor, produces first and second speed signals that indicate the speeds of two rotating spools in the engine. Four vibration absorbers are attached to the engine mounting structure and controllers are provided to dynamically tune the resonant frequency of each vibration absorber in response to a unique combination of one of the two vibration signals and one of the two speed signals. Thus the vibration absorbers reduce the engine spool vibrations that are transmitted through the mounting structure along the two orthogonal axes. The resonant frequency of each absorber is altered to track variation of the vibrations due to changes in engine speed.

Adaptively tuned elastomeric vibration absorber

Abstract: An apparatus for reducing vibration has a mount for attaching to a vibrating body, such as the frame of an aircraft A plate is spaced from the mount with a mass there between A first elastomeric ring is compressed between the mass and the mount, and a second elastomeric ring is compressed between the mass and the plate The rings act as a spring having a stiffness that defines a resonant frequency at which the mass oscillates Vibration in the body is reduced by the mass movement absorbing vibrational energy and the energy absorption is maximized when the mass resonates at the vibration frequency A controller senses body vibration and operates a mechanism that alters the spacing between the mount and the plate thereby adjusting the spring stiffness The stiffness of the spring is changed until the resonant frequency of the mass is tuned to the vibration frequency of the body