Self-generated Vibration Research Articles

Vibration Viscosity Sensor for Engine Oil Monitoring Using Metal Matrix Piezoelectric Composite.

Lubricants such as engine oil play an important role in preventing machine wear and damage. Monitoring the deterioration of lubricating oils is a significant technical issue in machine maintenance. In this study, a sensor for monitoring engine oil viscosity was developed using a metal-core piezoelectric fiber/aluminum composite. This composite is a piezoelectric ceramic that is reinforced by a metal matrix; it is expected to be utilized in harsh environments such as the inside of an engine. An active type measurement method was employed to monitor variations in the viscosity of glycerin solution as a model liquid. In this method, a self-generated vibration is correlated to the viscosity of a liquid by measuring the damped vibration amplitude and the variation in the resonance frequency. The results showed that the vibration had a high sensitivity to the liquid viscosity; further, it was observed that the shift in resonance frequency correlated to a wider range of measurable viscosity. Both measured parameters indicate that the metal-core piezoelectric fiber/aluminum composite is a viable sensor for engine oil monitoring.

Chatter Identification of Face Milling Operation via Time-Frequency and Fourier Analysis

Chatter is generally defined as self-generated vibrations from the interaction between tool and workpiece. It is the most critical vibration in machining operations and can decrease the surface quality and cause the premature tool wear. Chatter creates erroneous vibrations on the workpiece surface. However, even though the spatial response of chatter is still bounded, its frequency response would become unstably broadband, emitting high-pitched sounds. The deterioration in both time and frequency domains implies that chatter is a route-to-chaos process. To capture the time-frequency characteristics of chatter, instantaneous frequency is applied to extract the relevant force vibration of machining chatter, and the energy ratio approach is used to develop a discrete stability lobe diagram of a face-milling operation. The proposed method is validated by measuring the surface roughness of the workpiece.

Tool Wear and Vibrations Generated When Turning High-chromium White Cast Iron with pCBN Tools

Dynamic behavior and stability of system ‘tool-workpiece’ when machining HCCI with pCBN tools are determined by the processes which occur in cutting zone. The cutting process is characterized by formation of tool protection layer (TPL) on the chip contact area but its stability depends on the workpiece material composition, tool material and cutting conditions. The higher content of Si in the HCCI promotes the TPL formation and its stability. The presence and stability of TPL, besides the cutting edge protection, provides the system with additional damping resulting in the suppression of vibrations. A low Si content and low cutting speed leads to increase of cutting forces that in turn causes the self-generated vibration occurrence.

Extension of the destabilization paradox to limit cycle amplitudes for a nonlinear self-excited system subject to gyroscopic and circulatory actions

This study aims at clarifying the phenomenological roots of an acoustical disturbance known as “clutch squeal noise”. A nonlinear two-degrees-of-freedom model is introduced in order to illustrate some basic phenomena leading to self-generated vibrations. The damping of the system as well as both circulatory and gyroscopic actions are included in order to highlight their respective influence and the destabilization paradox. Results are obtained on the stability range of the equilibrium, the nature of the Hopf bifurcation, the limit cycle branches and their stability. A dynamic extension of the destabilization paradox is proposed and some non-periodic behaviours are identified too.

Analysis of Whole-Body Vibration During Manual Wheelchair Propulsion: A Comparison of Seat Cushions and Back Supports for Individuals Without a Disability

Whole-body vibration exposure has been found to be detrimental to the health of humans owing to effects such as degraded comfort, disc degeneration, and lower back pain. The purpose of this study was to determine if selected seat cushions and back supports minimize the transmission of vibrations during manual wheelchair propulsion. Ten unimpaired participants traversed an activities of daily living course using four seat cushions and four back supports. Vibrations were measured using triaxial accelerometers. The time domain and frequency domain transmissibility was used to determine if differences exist among seat cushions and back supports. Differences were found among the four seat cushions and four back supports. Seat cushion and back support manufacturers should concentrate on single-event shocks and repeated shocks, as opposed to oscillatory motions and self-generated vibrations, because the vibrations generated by these events tend to reside in the range of frequencies most sensitive to humans. Vibrations in this range of frequencies have the greatest effect on the transmission of whole-body vibration during manual wheelchair propulsion. Differences among the seat cushions and back supports appear to be due to the seat cushion/back support design and postural support. From a clinical perspective, the time domain transmissibility best describes the transmission of whole-body vibration.

Autoparametric optical drive for micromechanical oscillators

Self-generated vibration of a disk-shaped, single-crystal silicon micromechanical oscillator was observed when the power of a continuous wave laser, focused on the periphery of the disk exceeded a threshold of a few hundred μW. With the laser power set to just below the self-generation threshold, the quality factor for driven oscillations increases by an order of magnitude from Q=10 000 to Qenh=110 000. Laser heating-induced thermal stress modulates the effective spring constant via the motion of the disk within the interference pattern of incident and reflected laser beams and provides a mechanism for parametric amplification and self-excitation. Light sources of different wavelengths facilitate both amplification and damping.

Low frequency self-generated vibration during ambulation in normal men

An assessment was made of the upper body low frequency steady-state vibration in five normal male subjects during level walking in a straight line. Speed of progression ranged from 0.99 to 2.35 m/s. Through a stereophotogrammetric technique, a three-dimensional measurement of the linear displacement of the longitudinal axis of the trunk and head was done. The relevant accelerations were obtained by double differentiation and described both in the time and frequency domains. The data were compared with those available on the biodynamic properties of body tissues and on the subjective response of humans to externally generated whole-body vibration. The comparison yielded a consistent indication of the characteristics of the vibration stimulus to which the human body may be adapted. As walking speed approached its maximum, the vertical acceleration spectrum increased in magnitude and shifted critically close to frequencies at which body organs are known to undergo resonance. A coordinated movement of the trunk with respect to the pelvis helped to reduce to a minimum the value of the acceleration to which the head was submitted in the antero-posterior direction and to shift the relevant spectrum towards the lower frequencies.

Stability criterion for stick-slip motion using a discontinuous dynamic friction model

An analysis of stick-slip stability is presented using a discontinuous friction model which consists of a negative damping action for the slip acceleration phase and a constant frictional resistance for the slip deceleration phase. Limiting conditions for stability due to a positive viscous damping action are defined, where transition from self-generated vibrations to smooth sliding occurs. The implications of the theory are discussed for the design and analysis of equipment subject to such vibrations.