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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]

Chatter vibration is apt to occur when machining thin-walled parts with insufficient rigidity. The harmful excitation of periodical cutting forces can be mitigated by enhancing the dynamic stiffness or increasing the damping of the part. A composite viscous damper including air damping and eddy current damping is designed, which can be attached on the thin-walled part by the vacuum. Based on the formulations of air damping and eddy current damping, the optimal equivalent viscous damping is derived for achieving the maximum critical depth of cut. Furthermore, the geometries of the damper are determined for damping a specific thin-walled part after investigating its relationship with viscous damping. The modal test indicates that the damper can suppress multiple modes of the cylindrical thin-walled part, and the amplitude of the first mode of the frequency response function (FRF) is reduced by 57%. The composite viscous damper is applied to suppress the chatter and resonant vibration of the thin-walled part during machining. Milling tests demonstrate that the machining vibration is reduced by 55% and 76% after employing single damper and four dampers, respectively. [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]

As a kind of ubiquitous energy in natural environment, environmental vibration has the characteristics of random amplitude, direction reciprocating, and low frequency. Firstly, an electromagnetic energy harvester using mechanical rectifier is designed, which can rectify the environmental vibration into one-way rotation of the shaft to realize the output of the direct current electric energy. Secondly, the dynamical model of the energy harvester is built and its output characteristics are derived; and the voltage output characteristics under different vibration amplitudes, frequencies and load resistance conditions are numerically analyzed. Finally, the experimental tests on the output characteristics of the energy harvester under determined vibration input are conducted. The results show that this device can transfer the environmental vibration into continuous direct current electric energy output, and the amplitude, frequency and load resistance all have effects on the output voltage of the harvester. When the vibration amplitude is 50 mm, the frequency is 0.8 Hz, and the load resistance is 100 Ω, the peak value of the output voltage is 14.2 V and the instantaneous power can reach 2 W. [ABSTRACT FROM AUTHOR]

Passive control has been effective in damping the machining vibration of thin-walled parts. However, physical addition onto the part causes the dynamics change and limits the engagement of cutting tool, especially in the application of multi-axis machining. Utilizing the non-contact eddy current damping, a two-degree-of-freedom apparatus is designed after experimental investigation into the magnet combination, magnetic flux density and magnetic flux mode on damping behaviors on a specifically designed platform. The apparatus is set up by mounting on the stationary spindle head of a five-axis CNC machine tool. The included neodymium magnets, and then the induced eddy current damping force are able to follow the feeding cutter through the control of two servo motors, keeping out of touch with the thin-walled part to be damped. As the damping force is able to resist the vibration of the machining point induced by the cutting force directly, it allows the design with less volume and mass (i.e. magnets and conductors). In the end, hammer tests are performed to verify the additional damping ratio imposed by the apparatus. Three-axis milling tests of a thin-walled frame are carried out to validate the damping of the apparatus, and five-axis milling tests of thin-walled blade type part are conducted to demonstrate its controllable damping and adaptability to complex tool path. [ABSTRACT FROM AUTHOR]

Thin-walled workpieces are largely manufactured in the aerospace industry. The manufacturing process has been a problem due to its flexibility, and chatter vibrations are apt to occur, which restricts the machining efficiency and quality. A vibration suppression device for thin-walled workpieces is presented based on the electromagnetic induction principle, which utilizes machining vibrations to generate resistant force on the workpiece. The formulated force varies with the workpiece vibration velocity, but in an opposite direction. Excitation tests using the electromagnetic shaker illustrate that the device is effective in vibration attenuation. Finally, machining tests are carried out with applications to two thin-walled structures for further verification. The machining vibrations and surface quality demonstrate the damping promotion of the workpiece assembly, and milling stability limit is increased by more than twofold. [ABSTRACT FROM AUTHOR]

• A coaxial mechanical motion rectifier with function of increasing transmission ratio. • A variable inertia flywheel for extending overrunning phase. • Dynamics modeling of mechanical motion rectifier considering overrunning phase. • Establishment of angular velocity of the generator with variable inertia flywheel. • Max efficiency of 51.54% in lab and max power of 3.35 W in ocean. The wave energy harvester has been employed to power marine devices. For the wave energy harvester based on mechanical motion rectifier, the output power and efficiency are limited due to low inertia-damping ratio and perpendicular motion transformation. A coaxial mechanical motion rectifier with the function of increasing transmission ratio is designed based on a planetary gear train and four one-way clutches, and the input and output shafts are arranged coaxially. A variable inertia flywheel is incorporated in the wave energy harvester to extend the overrunning phase by slowing down the velocity attenuation of the generator. The wheel in variable inertia flywheel is reduced to four cantilever sliders to decrease the starting torque. The dynamics model of the wave energy harvester considering the meshing and overrunning phases is investigated due to the introduction of variable inertia flywheel. The input force and output voltage are simulated with sinusoidal displacement input after obtaining the angular velocity of generator with variable inertia flywheel. A maximum efficiency of 51.54% and average output power of 1.17 W on Instron machine are achieved, while a maximum output power of 3.35 W in ocean tests is obtained. The experiments verify that the design of coaxial mechanical motion rectifier and variable inertia flywheel is beneficial to improving the output power and efficiency. [ABSTRACT FROM AUTHOR]