Reducing SU-8 hygroscopic swelling by ultrasonic treatment

The volume expansion of SU-8 resist brings serious dimensional errors to electroformed structures.Two approaches have been proposed to reduce resist distortions during electroforming:electroforming at room temperature and adding auxiliary features for mask patterns.However,the former method induces higher internal stresses in the electroformed metal layers.And the latter method makes it difficult to predict the expansion behaviors of the resists.In the paper,the thermal expansion of the SU-8 mould is calculated by ANSYS firstly,and the lower thermal expansion value indicates that hygroscopic swelling plays a leading role in SU-8 mould distortions.An original technique is presented to reduce SU-8 hygroscopic swelling by ultrasonic treatment.The dimensional errors of the electroformed structure fabricated on the ultrasonic treatment mould are 50% lower than the one without ultrasonic treatment.Simulation of hygroscopic swelling is conducted by finite element analysis,and the results indicate that the hygroscopic strain ε of SU-8 after electroforming is declined from 6.8% to 3.1% because of ultrasonic.The measurements show that ultrasonic treatment increased the water contact angle of cured SU-8 from 70.8?to 74.9?.Based on these results,the mechanism of ultrasonic effect on hygroscopic swelling is proposed from the view of ultrasonic vibration decreasing the number of hydroxyl groups in SU-8.The research presents a novel method to improve the precisions of electroformed structures.It has no influence on the internal stresses of final structures and does not increase the complexities of mask layouts.

Methods for the Construction and Realization of a Humanoid Robot's Simulation Platform

This paper proposes a method of humanoid robot data structure definition based on the characteristics of a graph with tree structure. It applies the depth-first search algorithm to traverse and uses screw theory and chain of multiplication to describe the robot＇s postures. The platform references zero moment point theory as the stability constraint of the robot＇s dynamic walking and plans the gaits accordingly, h also realizes the visualization of motion control. This study provides superior means and methods to the evolution of a humanoid robot.

Microfluidic separation of particles by synergistic effect of geometry-induced hydrodynamics and magnetic field

Microfluidic combined with magnetic field have been demonstrated to be the promising solutions for fast and low-damage particles separation.However,the difficulties in the precise layout of magnets and accurate prediction of particle trajectories lead to under and over separation of target particles.A novel particle separation lab-on-chip(LOC)prototype integrated with microstructures and micropolar arrays is designed and characterized.Meanwhile,a numerical model for the separation of magnetic particles by the synergistic effect of geometry-induced hydrodynamics and magnetic field is constructed.The effect of geometry and magnetic field layout on particle deflection is systematically analyzed to implement accurate prediction of particle trajectories.It is found that the separation efficiency of magnetic particles increased from 50.2%to 91.7%and decreased from 88.6%to 85.7%in the range of depth factors from 15µm to 27µm and width factors from 30µm to 60µm,respectively.In particular,the combined effect of the offset distance of permanent magnets and the distance from the main flow channel exhibits a significant difference from the conventional perception.Finally,the developed LOC prototype was generalized for extension to arbitrary systems.This work provides a new insight and robust method for the microfluidic separation of magnetic particles.

Control theorem of a universal uniform-rotating magnetic vector for capsule robot in curved environment

For realizing non-contact steering swimming of a capsule robot in curved environment filled with viscous liquid,based on spatial orthogonal superposition theorem of alternating magnetic vectors,an innovative physical method is proposed,which employs three-axis orthogonal square Helmholtz coils fed with three phase sine currents to create a universal uniform magnetic spin vector as energy source.According to the antiphase sine current superposition theorem generalized in this paper,an effective control method for successively adjusting the orientation and the rotating direction of the universal magnetic spin vector is proposed.For validating its feasibility and controllability,three-axis Helmholtz coils,power source and an innovative capsule robot prototype were manufactured,experiments were conducted in both spiral pipe and animal intestine.It was demonstrated that the orientation and the rotational direction of the universal uniform-magnetic spin vector can be adjusted successively through digital control and steering swimming of the capsule robot in spiral intestine can be achieved successfully.The breakthrough of the universal rotating uniform-magnetic vector will push forward the development of modern physics and biomedical

Dynamic characteristics of an intestine capsule robot with variable diameter

This paper proposes an intestine capsule robot with variable diameter. It is driven by external rotating magnetic field and has the function of automatic radial clearance compensation. An external magnetic field generating device and a capsule robot with variable diameter are developed. Radial dynamic balance equation and kinematics equation of the capsule robot traveling inside flexible elasto-wall environment are established, and dynamic characteristics of the capsule robot inside flexible elasto-wall pipe and rigid wall pipe environments are analyzed and compared. Simulations and experiment results show that its dynamic characteristics in both pipes are almost the same. Under the action of radial clearance compensation, fluid dynamic pressure around outer surface of the capsule robot and its propulsion, as well as its adaptability to diameter change range, are significantly improved. Its propulsion and moving speed are controlled by adjusting rotating angular speed of the rotating magnetic field. This innovative capsule robot with radial clearance compensation has a promising prospect for inside intricate gastrointestinal (GI) tract in non-invasive therapy applications.

Orthogonal transformation operation theorem of a spatial universal uniform rotating magnetic field and its application in capsule endoscopy

According to the anti-phase sine current superposition theorem, the orientation, the magnetic flux density, the angular speed and the rotational direction of the spatial universal rotating magnetic field (SURMF) can be controlled within the tri-axial orthogonal square Helmholtz coils (TOSHC). Nevertheless, three coupling direction angles of the normal vector of the SURMF in the Descartes coordinate system cannot be separately controlled, thus the adjustment of the orientation of the SURMF is difficult and the flexibility of the robotic posture control is restricted. For the dimension reduction and the decoupling of control variables, the orthogonal transformation operation theorem of the SURMF is proposed based on two independent rotation angular variables, which employs azimuth and altitude angles as two variables of the three-phase sine current superposition formula derived by the orthogonal rotation inverse transformation. Then the unique control rules of the orientation and the rotational direction of the SURMF are generalized in each spatial quadrant, thus the scanning of the normal vector of the SURMF along the horizontal or vertical direction can be achieved through changing only one variable, which simplifies the control process of the orientation of the SURMF greatly. To validate its feasibility and maneuverability, experiments were conducted in the animal intestine utilizing the innovative dual hemisphere capsule robot (DHCR) with active and passive modes. It was demonstrated that the posture adjustment and the steering rolling locomotion of the DHCR can be realized through single variable control, thus the orthogonal transformation operation theorem makes the control of the orientation of the SURMF convenient and flexible significantly. This breakthrough will lay a foundation for the human-machine interaction control of the SURMF.

Study on the Hydrophobic Property of Shark-Skin-Inspired Micro-Riblets

This paper aims to characterize the hydrophobic property of shark-skin-inspired riblets with potential engineering appli- cations. Based on the hydrophobic theory, a new hydrophobic model which is consistent with the special structure of shark-skin-inspired micro-riblets was proposed. Then, the contact angles of different droplets were measured by optical contact angle measuring device on the shark-skin-inspired micro-riblets and the smooth surface, respectively. The results show that the surface of micro-riblets possesses obvious hydrophobicity, and the actual contact angles of different droplets residing on the riblets decrease with the increase in the droplet volume. According to the new hydrophobic model and the measurement of contact angle, it was found that the arrangement and structure of the shark-skin-inspired micro-riblets significantly affect the surface hydrophobic property. Using the new hydrophobic model, the prediction error of contact angle can be less than 3% compared with the measured one. The research on hydrophobic property of biomimetic micro-riblets is proved to be necessary and important to well explain drag reduction and microbe-resistant property of micro-riblets.

Surface shape control of the workpiece in a double-spindle triple-workstation wafer grinder

Double-spindle triple-workstation（DSTW） ultra precision grinders are mainly used in production lines for manufacturing and back thinning large diameter（≥300 mm） silicon wafers for integrated circuits.It is important, but insufficiently studied,to control the wafer shape ground on a DSTW grinder by adjusting the inclination angles of the spindles and work tables.In this paper,the requirements of the inclination angle adjustment of the grinding spindles and work tables in DSTW wafer grinders are analyzed.A reasonable configuration of the grinding spindles and work tables in DSTW wafer grinders are proposed.Based on the proposed configuration,an adjustment method of the inclination angle of grinding spindles and work tables for DSTW wafer grinders is put forward. The mathematical models of wafer shape with the adjustment amount of inclination angles for both fine and rough grinding spindles are derived.The proposed grinder configuration and adjustment method will provide helpful instruction for DSTW wafer grinder design.

Self-centering characteristics of a petal-shaped capsule robot

Based on the multiple wedge effects, a petal-shaped capsule robot(PCR) is proposed, and the self-centering phenomenon of the PCR is discovered. For investigating the self-centering characteristics, an innovative concept of the instantaneous fluid membrane(FM) thickness, along with the dynamic FM thickness, is proposed; thus a dynamic FM thickness model and a hydrodynamic pressure(HP) model are derived when the PCR axis deviates from the pipe axis under the effect of gravity. A kinematics equation during suspending process in the vertical direction and a swimming kinematics equation in axial direction are derived respectively. Four capsule robots with different eccentricities of the tiles were manufactured and tested, the theoretical and experimental results show that the HP gradient is a fundamental reason for the self-centering phenomenon. The PCR with the self-centering ability can directly avoid the contact with the bottom of the gastrointestinal(GI) tract, achieving the excellent obstacle surmounting ability in the GI complex environment with the less twisted impact on the GI tract, which has a promising application prospect in the GI diagnosis.

Effects of the reciprocating parameters of the carrier on material removal rate and non-uniformity in CMP

Based on the Preston equation, the mathematical model of the material removal rate （MRR）, aiming at a line-orbit chemical mechanical polisher, is established. The MRR and the material removal non-uniformity （MRNU） are numerically calculated by MATLAB, and the effects of the reciprocating parameters on the MRR and the MRNU are discussed. It is shown that the smaller the inclination angle and the larger the amplitude, the higher the MRR and the lower the MRNU. The reciprocating speed of the carrier plays a minor role to improve the MRR and decrease the MRNU. The results provide a guide for the design of a polisher and the determination of a process in line-orbit chemical mechanical polishing.

Special issue： Near-net shaping technology

Near-net shaping is an efficient, economical and environmentally-friendly approach to manufacture products which are very close to the final shape, reducing the need for surface finishing. It has become more and more important to use raw materials and energy in an optimal way. Near-net shaping technology has attracted increasing attention in both academic and industrial communities, especially in China, because China has become the world＇s largest regional market for main material forming methods, such as casting, forging and injection molding. The main objective of this special issue in Frontiers of Mechanical Engineering is to bring together the leading ideas, experience and research results of academic scientists and researchers on various aspects of near-net shaping technology. This special issue contains eleven papers contributed by prestigious experts from different countries, including four reviews and seven research articles. These papers cover a broad area of the near-net shaping technology,