Deqing Mei

Active vibration isolation of a micro-manufacturing platform based on a neural network

Abstract A bionics mechanics-based structure model is constructed for the vibration isolation of a micro-manufacturing platform. The developed active vibration isolation system consists of a micro-manufacturing platform, strongly magnetostrictive actuators, air springs, a pedestal and a rubber layer. The actuators and air springs are arranged in parallel. A controller based on a three-layer neural network is applied to realize high performance in isolating complex micro-vibration. The absolute acceleration of the micro-manufacturing platform is used as the performance index of vibration control. The performance of the control system is tested by numerical simulation. The simulation results show that the active vibration isolation system has good isolation performance against floor disturbance and direct disturbance acting on the micro-manufacturing platform in all of the frequency range.

Acoustic radiation torque on an irregularly shaped scatterer in an arbitrary sound field

To eliminate the limitation of the conventional acoustic radiation torque theory, which is only applicable to a disklike scatterer in a plane sound field, a new theory is established to calculate the radiation torque on any irregularly shaped scatterer in any arbitrary sound field. First, with the aid of the conservation law of angular momentum, the acoustic radiation torque is expressed as the angular momentum flux through a spherical surface with the center at the scatterers centroid. Second, the velocity potential of the scattered field is derived, taking into account the influences of the translational and rotational movements of the scatterer induced by the first order stress of the incident sound field. Finally, a general calculating formula of the acoustic radiation torque is achieved. For a disklike scatterer in a plane sound filed, results from the above formula are well identical with those conventional formulas. By studying the case of a semicircular cylinder scatterer in a standing-wave sound field, it is found that for an irregularly shaped scatterer its rotation velocity is normally nonzero and the radiation torque changes with the spatial attitude.

Acoustic Softening and Hardening of Aluminum in High-Frequency Vibration-Assisted Micro/Meso Forming

A hybrid micro/meso forming assisted by high-frequency vibration was experimentally investigated by upsetting aluminum. Experiments with various vibration amplitudes and durations were conducted. The high-frequency vibration resulted in both acoustic softening and hardening behavior. Results showed that the overall forming stress reduced by 30% when a transverse vibration of 9.3 kHz was applied, but the stress recovered once the vibration stopped. On the other hand, a hardening behavior was observed during the vibration and resulted in a permanent hardening of the material even after the vibration had stopped. The effects of acoustic softening and hardening were coupled during the vibration-assisted upsetting. It was found that larger vibration amplitude led to a more significant acoustic softening and hardening. The findings of this study provided a basis to understand the underlying mechanisms of vibration-assisted forming.

A Friction Evaluation Method Based on Barrel Compression Test

To further understand the tribological performance in metal forming, it is critical to accurately evaluate the friction between tool and workpiece. However, the unclear contact conditions at the interfaces and the complex mechanisms of the tribology lead to challenges to assess friction in metal forming processes. In this study, a friction evaluation method by the barrel compression test and its principle model were proposed based on the theoretical analysis and the numerical simulations. Besides the friction factor at the die–specimen interfaces and the initial aspect ratio of the specimen, the strain hardening exponent of the specimen was found to affect the barreling profiles based on the theoretical analysis. Furthermore, the effects of the three influencing factors, including the friction factor at the interfaces, the initial aspect ratio and the strain hardening exponent of the specimen, on the defined barreling factor were numerically analyzed by the finite element method. A predictive model of the barreling factor accounting for these three factors was developed. A friction evaluation method, proposed based on this model, was implemented by various cylinder compression experiments of CuZn40 brass. The method proposed in this study provided a convenient means to identify the contact friction in metal forming processes.

Micro Pin Extrusion of Metallic Materials Assisted by Ultrasonic Vibration

Micro extrusion is an economically competitive process to fabricate micro metallic parts. However, fabrication of extremely small geometric features leads to challenges in tool wear due to localized high stress and friction increase at the interface. This study focuses on micro pin extrusion of aluminum with assistance of ultrasonic vibration. Experiments were conducted with and without ultrasound using magnetostrictive actuator. Load-displacement curves from the experiments showed a load reduction when ultrasonic vibration was applied. Experiments of ultrasonic micro pin extrusion with two configurations were performed. The load reduction behaviors at off-resonance and in-resonance conditions were compared. The reduction can be explained by stress superposition of ultrasonic vibration.Copyright

An analytical model for studying the structural effects and optimization of a capacitive tactile sensor array

This paper presents an analytical model to study the structural effects of a capacitive tactile sensor array on its capacitance changes and sensitivities. The tactile sensor array has 8 × 8 sensor units, and each unit utilizes the truncated polydimethylsiloxane (PDMS) pyramid array structure as the dielectric layer to enhance the sensing performance. To predict the capacitance changes of the sensor unit, it is simplified into a two-layered structure: upper polyethylene terephthalate (PET) film and bottom truncated PDMS pyramid array. The upper PET is modeled by a displacement field function, while each of the truncated pyramids is analyzed to obtain its stress–strain relation. Using the Ritz method, the displacement field functions are solved. The deformation of the upper electrodes and the capacitance changes of the sensor unit can then be calculated. Using the developed model, the structural effects of the truncated PDMS pyramid array and the PDMS bump on the capacitance changes and sensitivities are studied. To achieve the largest capacitance changes, the dimensions have been optimized for the sensor unit. To verify the developed model, we have fabricated the sensor array, and the average sensitivities of the sensor unit to the x-, y-, and z-axes force are 0.49, 0.50, and 0.32% mN−1, respectively, while the model predicted values are 0.54, 0.54, and 0.35% mN−1. Results demonstrate that the developed model can accurately predict the sensing performance of the sensor array and could be utilized for structural optimization.

A flexible tactile sensor array based on pressure conductive rubber for three-axis force and slip detection

This paper presents a novel flexible tactile sensor array with the capabilities to measure three-dimensional (3D) forces and slip occurrence by using the INASTAMOR pressure conductive rubber as the sensing material. The tactile sensor array has 3 × 3(= 9) sensing units, and each unit has a three-layered structure: bottom electrode, middle conductive rubber chips, and top PDMS bump. The structural design, 3D force and slip detection principles, fabrication process of this sensor array are presented. The fabricated sensor array has a spatial resolution of 7 mm. 3D force measurement and slip detection performances of this sensor array are characterized experimentally. Results demonstrated that the sensor array can measure 3D forces. The full-scale range and sensitivities of force measurements for x-, y- and z-axes are 5 N, 5 N, 20 N and 0.65 V/N, 0.67 V/N, 0.23 V/N, respectively. Results also showed the sensor array could detect slipping by using the discrete wavelet transform (DWT) to analyze the measured force data. Thus, the proposed flexible tactile sensor array could be applied to robot hand grasping application that requires slip detection and 3D contact force measurement.

Experimental Study of High-Frequency Vibration Assisted Micro/Mesoscale Forming of Metallic Materials

Micro/mesoscale forming is a promising technology for mass production of miniature metallic parts. However, fabrication of micro/mesoscale features leads to challenges due to the friction increase at the interface and tool wear from highly localized stress. In this study, the use of high-frequency vibration for potential application in micro/mesoscale forming has been investigated. A versatile experimental setup based on a magnetostrictive (Terfenol-D) actuator was built. Vibration assisted micro/mesoscale upsetting, pin extrusion and cup extrusion were conducted to understand the effects of workpiece size, excitation frequency, and the contact condition. Results showed a change in load reduction behavior that was dependent on the excitation frequency and the contact condition. The load reduction exhibited in this study can be explained by a combination of stress superposition and friction reduction. It was found that a higher excitation frequency and a less complicated die-specimen interface were more likely to result in a friction reduction by highfrequency vibration. Disciplines Manufacturing | Metallurgy Comments This article is from Journal of Manufacturing Science and Engineering 133 (2011): 1, doi:10.1115/1.4004612. Posted with permission. Authors Zhehe Yao, Gap-Yong Kim, LeAnn E. Faidley, Qingze Zou, Deqing Mei, and Zichen Chen This article is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/me_pubs/117

Design of a Wearable Thermoelectric Generator for Harvesting Human Body Energy

This paper presents the design and fabrication of a wearable thermoelectric generator (TEG) with high power density for harvesting the human body heat energy. The proposed TEG was fabricated using a flexible printed circuit board (FPCB) as the substrate. The P-type and N-type thermoelectric blocks were made of Bi2Te3-based thermoelectric material and welded on the FPCB, and they were surrounded by the soft PDMS material. The prototyped TEG consisted of 18 thermocouples, which was connected by FPCB and silver paste over an area of 42 × 30 mm2. The fabricated TEG could generate a voltage of 48 mV for a temperature difference of 12 K. Then, the TEG was mounted onto the human wrist skin to harvest the human body heat energy. Results showed that the measured output power was 130.6 nW at ambient temperature of 25 °C. Thus, the developed TEG has the potential for human body heat energy harvesting and utilized for the development of wearable self-powered mobile devices.

A flexible capacitive tactile sensor array with high scanning speed for distributed contact force measurements

This paper presents an 8×8 (=64) capacitive tactile sensor array with integrated four capacitance-digital-converter (CDC) scanning circuit for three-axis force measurement. For the structural design of the sensor array, the upper and lower electrodes generate four capacitors in one sensing unit and decompose the contact force into three-axis force components. To enhance the flexibility, a thinner PDMS bump (0.5 mm) and truncated pyramid dielectric layer with finer dimensions are utilized. To increase the scanning speed, we divide the sensor array into four regions and using four CDC circuits to simultaneously measure the capacitance changes of these regions. The sensor array is mounted onto a hand finger for grasping of a paper cup. Results showed that the sensor array can detect the distributed contact force at high scanning speed, thus could be utilized in robotic grasping applications.