Search

A piezoelectric vibration sensing system (PVSS) was devised in this study and employed for the purpose of vibration sensing in machining. The system comprises three primary components, wherein the sensor is utilized for the collection and conversion of energy, subsequently transmitting it to the data acquisition card (DAC) via a low-noise cable. The crux of the entire system lies in the upper computer-based control application, which facilitates the transmission of instructions to the DAC for data acquisition and transmission. The integration of Wi-Fi data transfer capability between the DAC and the computer serves to eliminate the principal issue associated with employing the sensor as a voltage source. The sensitivity of the designed device was calibrated utilizing commercial accelerometers, while an aluminum workpiece was fabricated to conduct vibration and machining tests in order to verify the performance of the PVSS. The shaker excitation experiment yielded a peak voltage of 0.05 mV, thereby substantiating that the PVSS can more accurately discern the natural frequency of the workpiece below 5000 Hz compared to commercial accelerometers. The experiments verify that the devised PVSS can precisely measure vibrations during the milling process, and can be implemented for the purpose of detecting machining stability. [ABSTRACT FROM AUTHOR]

The energy harvester has been employed to transform mechanical vibration into electrical power in the field of road transportation. An electromagnetic energy harvester for bicycle application to recycle low-frequency vibration is proposed. The input of up-down motion is transformed into bidirectional rotation by the transmission part, and then translated into unidirectional rotation by the rotating motion rectifier. The rectifier outputs rotation to the generator, and the electrical energy generated can be stored in super capacity at the charging mode or light up the LED at the discharging mode. Lab experiments are conducted to test the proposed harvester on Instron servo-hydraulic machine. A power of 0.491 W and a total efficiency of 52.8% are achieved with sinusoidal displacement inputs from 1.0 Hz to 2.5 Hz and external resistors from 50 Ω to 200 Ω. Field tests of applying the harvester onto the bicycle are carried out and a power of 0.313 W is obtained when riding through the speed bump. Above tests demonstrate potential applications of the harvester in self-powered devices. • A harvester for low-frequency vibration is proposed and applied onto the bicycle. • Mechanism of the harvester is designed by ball screw and rotating motion rectifier. • Engagement and disengagement periods of the rectifier are investigated. • The harvester can achieve a power of 0.491 W and a total efficiency of 52.8%. [ABSTRACT FROM AUTHOR]

Highlights • A general design routine for multi-DOF TMD is proposed. • The multi-DOF TMD is designed via the graphical approach. • Frequencies of the TMD are formulated analytically. • A three-DOF TMD is implemented for damping single mode. Abstract The multi-degree-of-freedom (MDOF) tuned mass damper (TMD) has demonstrated a more effective performance than single-DOF and multiple SDOF TMDs. For a damping mass in the space, there are maximum six DOFs; however, only along the vibration direction of the main structure can the motion of the TMD be utilized to control the vibration mode. Therefore, the maximum available DOFs of a TMD for mitigating single translational mode are three (i.e. one translational DOF and two rotational DOFs). A general routine of suppressing single vibration mode by multi-DOF TMD is presented, especially, a three-DOF TMD is used for example. Based on the non-dimensional dynamic model, the design parameters of the TMD are optimized via the simulated annealing algorithm according to the H∞ criterion. The graphical approach is utilized to design the configuration of the TMD with prescribed DOFs. Stiffness and natural frequencies are formulated analytically by the compliance matrix method, based on which the dimensions of the TMD are determined. It is demonstrated that the SDOF and two-DOF TMDs are special cases of the three-DOF TMD from the point of mathematical modeling, numerical optimization and design methodology. Theoretical formulation is verified by conducting hammer tests on the TMD under various geometry configurations. After employing the three-DOF TMD, 86.5% reduction of the amplitude of the frequency response function (FRF) of an I-shaped part is achieved, which shows 29.5% improvement than previous two-DOF TMD. [ABSTRACT FROM AUTHOR]

• Updated tuning methodology of vibration absorber to improve the machining stability. • Stability pocket relocation to maximize critical cutting depth at specified speed. • Design of stability pocket considering robustness of cutting parameter selection. • Fast and accurate identification of chatter stability boundary. • Two-dimensional chatter stability optimization and milling cutter application. The Equal Real Troughs optimization criterion of vibration absorber improves unconditionally stable cutting depth of single-dimensional chatter vibration. However, the stability pockets within the lobes are decreased after tuning, which therefore causes the machining efficiency reduction at certain spindle speed. Noting that the spindle speed is preferred as a constant in the workshop once the assembly of machine tool/cutter/workpiece are determined, an updated optimization methodology is proposed to maximize the critical cutting depth within specified spindle speed range by utilizing the lobing effect. The optimization routine is formulated based on the boundary identification of stability lobe diagram (SLD), which is derived by the Zero-Order Analytical (ZOA) solution. The tuning methodology is validated on the design of vibration absorber in order to raise the machining stability of slender milling/turning cutter with large length-diameter ratio. The updated methodology enables the stability lobes relocation of single/two-dimensional chatter vibration for achieving higher critical cutting depth at specified spindle speed, and assures the stability width assignable considering the robustness of cutting parameter selection. [ABSTRACT FROM AUTHOR]

The cutting efficiency and surface quality in the machining of compliant workpieces have been severely affected by machining vibration. As industrial workpieces are most likely to have multiple flexible modes due to its complex geometry and each mode can only be damped by a single vibration mode of a tuned mass damper (TMD), a two-degree-of-freedom (DOF) magnetic TMD (MTMD) is designed for damping the vibration of aluminum thin-frame workpiece with multiple modes. The natural frequencies of the MTMD are designed to be adjustable as evidenced by hammer tests and are tuned to coincide with the modes of the workpiece. Eddy current damping is incorporated for promoting damping by utilizing the relative motion between the mass block and magnets inside the MTMD. Frequency response functions demonstrate that the MTMD is effective in attenuating the amplitude of the first and second modes by 21.6 and 12.1 dB. Milling tests are finally carried out to validate its effectiveness. [ABSTRACT FROM AUTHOR]

Machining vibrations are harmful to workpiece surface quality and tool life, especially for thin-walled parts. A lightweight damping device is proposed by utilizing eddy current damping, and it can be easily attached onto the workpiece surface by glue. The cylindrical device is mainly composed of a magnet, an aluminum cylindrical conductor, and two springs. An induced repulsive force due to the machining vibration is generated and transmitted to the workpiece and then contributed to the vibration attenuation. Dynamic response evaluation on a cantilever beam by hammer tests demonstrates that the device is able to damp vibration mode and the effect of additive mass on the beam dynamics is investigated by roving the attaching point. Moreover, the device is applied to damp multiple modes and attenuate machining vibration of a thin-walled frame. Machining tests under different configurations of cutting parameters are carried out, and its effectiveness of wide band and adaptability to the varying machining processes are validated. [ABSTRACT FROM AUTHOR]

The tuned mass damper (TMD) has been applied to the machining vibration control widely, and it is categorized into several groups depending on the available degrees of freedom (DOF). Previous works have been mostly focused on the application of single-DOF TMD, but it is revealed that the damping performance could be further promoted by multiple-DOFs TMD. A two-DOF TMD for the milling vibration mitigation is investigated. The TMD possessing translation and rotation motion is designed with tunable stiffness and damping, and the design parameters are optimized numerically based on the H ∞ criterion. The TMD is implemented on a workpiece fixture with single dominant mode, and the experimentally tuned frequency response function (FRF) has 80.8 percent reduction on the amplitude of the flexible mode. Spindle speeds corresponding to the resonance and chatter vibrations are selected for the machining tests. The measured vibrations and surface quality validate the improvement of the machining stability by the TMD, and the critical depth of cut is increased at least two folds. [ABSTRACT FROM AUTHOR]