High-accuracy measurement of force affects real-time control and process adjustment of industrial production. Piezoelectric sensor can be applied to measure force with the characteristics of high frequency and stiffness, great dynamic response and resistance to harsh conditions. As an important part of test, calibration determines sensitivity coefficient which directly affects test accuracy. To improve the calibration accuracy of offset loading force for multisensor piezoelectric dynamometer, a novel calibration method using sensor sensitivity difference is proposed in this paper. The calibration experiments of four sensors are performed to obtain the axial sensitivities and the force-to-electricity conversion coefficients. The multiple loading-point (MLP) calibration experiments of dynamometer are carried out, and the calibration results prove that the sensitivity difference of four sensors is the main reason affecting the calibration accuracy. The sensitivity difference calibration method (SDCM) is applied to the MLP calibration experiments, and the results show that the average resultant force deviations are reduced from 418.79 N (8.38% full scare (FS) to 24.16 N (0.61% FS) under a loading force of 5000 N, which proves high accuracy and reliability of SDCM. The calibration method will provide guidance for improving the calibration accuracy of dynamometer.

The accuracy of piezoelectric test system has a direct influence on the accuracy of the vector force detection. Piezoelectric sensor parameters are obtained by calibration system calibrated through orthogonal calibration method. Accuracy of the application of field test lacks the corresponding theoretical basis, resulting in test system test accuracy is questioned. In this paper, piezoelectric force test system is used as the research object. In order to verify accuracy of piezoelectric test system through calibration of orthogonal calibration method, a variable angle deflection loading device was designed. An incremental calibration method for thrust test is put forward by applying vector force at different angles. Based on vector force coordinate transformation matrix, a deflection load test and analysis model are established. The vector force coordinates transformation matrix is used to calculate the experimental data obtained from the deviation angle test system, and the deviation of the vector force value is obtained. Finally, the accuracy, effectiveness and rationality of piezoelectric test system through the orthogonal calibration method are verified.

Five-axis machine with rotary-tilting spindle head (RTSH) is always used for sculptured surface machining, and the tool-tip dynamics in various machining postures along the tool path directly affect the machining accuracy and stability. To rapidly evaluate the tool-tip dynamics at different postures during the structural design of tool-spindle-spindle head (TSSH) assembly, this paper proposes a coupled dynamic model of tool-spindle-bearing system (TSBS) and RTSH. The model is a rigid-flexible multibody dynamic model with 36 degrees-of-freedom (DOFs), where in the rotary shaft, swivel shaft and housing are treated as rigid bodies; the tool, tool holder, and spindle shaft are modeled by reduced beams; the bearings and flexible joints are modeled as spring-damping elements. The fully Cartesian coordinates and Lagrangian method are employed to deduce a general parametric dynamic equation. The analytical method for calculating the contact stiffness of bearings and flexible joints is systematically presented, including tool-holder joint, holder-spindle joint, spindle bearings, hirth coupling, and the bearings and locking joints of rotary and swivel shafts. The model is verified by the frequency response functions (FRFs) testing and modal testing at different postures. The experimental results show that the proposed model can be used for accurate and efficient evaluation of the tool-tip FRFs, natural frequencies and mode shapes of TSSH at an arbitrary posture.

A general calibration method of cutter runout and specific cutting force coefficients (SCFCs) for flat-end cutter is proposed in this paper, and a high accuracy of cutting force prediction during peripheral milling is established. In the paper, the cutter runout, the bottom-edge cutting effect, and the actual feedrate with limitation during large tool path curvature are concerned comprehensively. First, based on the trochoid motion, a tooth trajectory model is built up and an analytical instantaneous uncut chip thickness (IUCT) model is put forward for describing the cutter/workpiece engagement (CWE). Second, a noncontact identification method for cutter runout including offset and inclination is given, which constructs an objective function by using the cutting radius relative variation between adjacent teeth, and identifies through a numerical optimization method. Thirdly, with consideration of bottom-edge cutting effect, the paper details a three-step calibration procedure for SCFCs based on an enhanced thin-plate milling experiment. Finally, a series of milling tests are performed to verify the effectiveness of the proposed method. The results show that the approach is suitable for both constant and nonconstant pitch cutter, and the generalization has been proved. Moreover, the paper points out that the cutter runout has a strong spindle speed-dependent effect, the milling force in cutter axis direction exists a switch-direction phenomenon, and the actual feedrate will be limited by large tool path curvature. All of them should be considered for obtaining an accurate milling force prediction.

Plasma is a host of numerous analytes such as proteins, metabolites, circulating nucleic acids (CNAs), and pathogens, and it contains massive information about the functioning of the whole body, which is of great importance for the clinical diagnosis. Plasma needs to be completely cell-free for effective detection of these analytes. The key process of plasma extraction is to eliminate the contamination from blood cells. Centrifugation, a golden standard method for blood separation, is generally lab-intensive, time consuming, and even dangerous to some extent, and needs to be operated by well-trained staffs. Membrane filtration can filter cells very effectively according to its pore size, but it is prone to clogging by dense particle concentration and suffers from limited capacity of filtration. Frequent rinse is lab-intensive and undesirable. In this work, we proposed and fabricated an integrated microfluidic device that combined particle inertial focusing and membrane filter for high efficient blood plasma separation. The integrated microfluidic device was evaluated by the diluted (×1/10, ×1/20) whole blood, and the quality of the extracted blood plasma was measured and compared with that from the standard centrifugation. We found that the quality of the extracted blood plasma from the proposed device can be equivalent to that from the standard centrifugation. This study demonstrates a significant progress toward the practical application of inertial microfluidics with membrane filter for high-throughput and highly efficient blood plasma extraction.

Uncertainty is unavoidable in engineering design, which may result in variations in the objective functions and/or constraints. The former may degrade the designed performance while the latter can even change the feasibility of the obtained optimal solutions. Taking uncertainty into consideration, robust optimization (RO) algorithms aim to find optimal solutions that are also insensitive to uncertainty. Uncertainty may include variation in parameters and/or design variables, inaccuracy in simulation models used in design problems, and other possible errors. Most existing RO algorithms only consider uncertainty in parameters, but overlook that in simulation models by assuming that the simulation model used can always provide identical outputs to those of the real physical systems. In this paper, we propose a new RO framework using Gaussian processes, considering not only parameter uncertainty but also uncertainty in simulation models. The consideration of model uncertainty in RO could reduce the risk for the obtained robust optimal designs becoming infeasible even if the parameter uncertainty has been considered. Two test examples with different degrees of complexity are utilized to demonstrate the applicability and effectiveness of our proposed algorithm.

The effects of formalin fixation on bone material properties remain debatable. In this study, we collected 36 fresh-frozen cuboid-shaped cortical specimens from five male bovine femurs and immersed half of the specimens into 4% formalin fixation liquid for 30 days. We then conducted three-point bending tests and used both beam theory method and an optimization method combined with specimen-specific finite element (FE) models to identify material parameters. Through the optimization FE method, the formalin-fixed bones showed a significantly lower Young's modulus (−12%) compared to the fresh-frozen specimens, while no difference was observed using the beam theory method. Meanwhile, both the optimization FE and beam theory methods revealed higher effective failure strains for formalin-fixed bones compared to fresh-frozen ones (52% higher through the optimization FE method and 84% higher through the beam theory method). Hence, we conclude that the formalin fixation has a significant effect on bovine cortical bones at small, elastic, as well as large, plastic deformations.

Parallel kinematic machines (PKMs) have been proposed as an alternative solution for high-speed machining (HSM) tool for several years. However, their dynamic characteristics are still considered an issue for practice application. Considering the three prismatic–revolute–spherical (3-PRS) PKM design as a typical compliant parallel device, this paper applies substructure synthesis strategy to establish an analytical elastodynamic model for the device. The proposed model considers the effects of component compliances and kinematic pair contraints so that it can predict the dynamic characteristics of the 3-PRS PKM. Based on eigenvalue decomposition of the characteristic equations, the natural frequencies and corresponding vibration modes at a typical configuration are analyzed and verified by numerical simulations. With an algorithm of workspace partitions combining with eigenvalue decompositions, the distributions of lower-order natural frequencies throughout the workspace are computed to reveal a strong dependency of dynamic characteristics on mechanism's configurations. In addition, the effects of the radii of the platform and the base along with the cross section of the limb on lower-order natural frequencies are analyzed to provide useful information during the early design stage. At last, frequency response analysis for the tool center point (TCP) is worked out based on the elastodynamic model to provide primary guideline for cutting chatter avoidance.

As a newly invented parallel kinematic machine (PKM), Exechon has attracted intensive attention from both academic and industrial fields due to its conceptual high performance. Nevertheless, the dynamic behaviors of Exechon PKM have not been thoroughly investigated because of its structural and kinematic complexities. To identify the dynamic characteristics of Exechon PKM, an elastodynamic model is proposed with the substructure synthesis technique in this paper. The Exechon PKM is divided into a moving platform subsystem, a fixed base subsystem and three limb subsystems according to its structural features. Differential equations of motion for the limb subsystem are derived through finite element (FE) formulations by modeling the complex limb structure as a spatial beam with corresponding geometric cross sections. Meanwhile, revolute, universal, and spherical joints are simplified into virtual lumped springs associated with equivalent stiffnesses and mass at their geometric centers. Differential equations of motion for the moving platform are derived with Newton's second law after treating the platform as a rigid body due to its comparatively high rigidity. After introducing the deformation compatibility conditions between the platform and the limbs, governing differential equations of motion for Exechon PKM are derived. The solution to characteristic equations leads to natural frequencies and corresponding modal shapes of the PKM at any typical configuration. In order to predict the dynamic behaviors in a quick manner, an algorithm is proposed to numerically compute the distributions of natural frequencies throughout the workspace. Simulation results reveal that the lower natural frequencies are strongly position-dependent and distributed axial-symmetrically due to the structure symmetry of the limbs. At the last stage, a parametric analysis is carried out to identify the effects of structural, dimensional, and stiffness parameters on the system's dynamic characteristics with the purpose of providing useful information for optimal design and performance improvement of the Exechon PKM. The elastodynamic modeling methodology and dynamic analysis procedure can be well extended to other overconstrained PKMs with minor modifications.