Pasomphone Hemthavy’s research while affiliated with Tokyo Institute of Technology and other places

This paper describes the development of bipolar electrostatic chucks with a compliant beam-array structure using abrasive water jet technology. The chucks are cut out from 3D-printed composite-laminated plates and the attractive forces that they generate are measured. Their performance is compared with electrostatic chucks (ESCs) made using a 3D-printing method developed by previous research. The ESCs fabricated using the proposed method have better beam tips with straight corners and flat contact surfaces. Moreover, when comparing the percentage of the attractive force (per unit area) of a stacked device to a single module, the water jet ESCs perform better (77.2%) than the 3D-printed ESCs (57.8%). The higher performance is mainly because the proposed method has excellent fabrication repeatability, which allows the beam tips of a stacked device to have an aligned height. This fabrication method is expected to contribute to the mass production of ESCs.Graphical abstract

This technical paper demonstrates the influence of the probe-tip surface smoothness of a bipolar electrostatic chuck (ESC) on electrostatic force. ESC, which has a silicon-based beam-array microstructure, aims to pick and place a dielectric object with a curved surface owing to the compliance of its elastically deformable beams. The ESC was fabricated using a lithography technique, specifically deep reactive ion etching (DRIE), to smooth the surface of the beam tip. The surface roughness of the beam tips was observed using a field-emission scanning electron microscope (FE-SEM), and the adhesional force was experimentally evaluated. The results show that by the smoothing process, the adhesional force per unit area is significantly increased compared to the previous study reported by Choi (one of the authors). This suggests that the proposed bipolar ESC device has great potential for use in various industries.

This study proposes and verifies bipolar electrostatic grippers stacking 3D-printed-layered modules consisting of arrays of elastically deformable bipolar beams. The influence of the mechanical compliance of grippers on the attractive force that it generates is clarified by comparing two types of modules having either high or low mechanical compliances. Experiments measured the attractive force of the gripper and demonstrated the pick-and-place performance of a thin film. The results show that mechanical compliance plays an important role in mitigating the attractive force decrease in stacking modules. The grippers’ ability for thin film handling is demonstrated by observing pick-and-place behaviours of the proposed bipolar electrostatic grippers.

Based on a theory of sessile drop in gravity, a method to evaluate surface tension is proposed, and its applicability is discussed. All of parameters are theoretically normalized. Although it is impossible to obtain analytic solution of the surface profile of the sessile drop, it is possible in an extreme condition of large volume. A universal parameter which determines the volume of liquid is derived in a normalized form. The large volume condition is theoretically defined using the parameter. Under the large volume approximation, an equation is derived which gives the surface tension from a height and an angle of the drop surface. In order to discuss applicability of the approximation, numerical calculation is carried out. It is found that the surface tension can be obtained with a tolerance less than 16%, if we measure the height of the sessile drop and the contact angle, under the large volume approximation. This method proposed in the present study is beneficial for the estimation of wettability of liquid using sessile drop.

There has been much research offering theoretical explanations of rolling behavior considering the effect of adhesion, which is essential when the object is small. However, there has been a shortage of experimental verifications because objects are too small to manipulate and observe directly. This study measured the moment and observed the contact area before, during, and after rolling with an experimental setup on a relatively large scale. The experiment setup consisted of two glass cylinders which were placed in between two PDMS blocks. This paper reports three main findings: the results suggest that viscosity influences the transition of states of the contact. The critical rolling resistance is dependent on the radius of the cylinders and the applied weight to the cylinders. The results support the theoretical expectation of the value of a critical rolling resistance, which is the product of the radius of the cylinders and the work of adhesion. This study offers experimental foundations to develop theories of rolling of micro-cylinders.

A 3D-printed-layered structure for forming the compliant bipolar electrostatic gripper is proposed. A prototype gripper module, which consists of an array of elastically deformable bipolar micro-probes, is fabricated using a conventional 3D printer. Experiments are conducted to examine the attractive force and the pick-and-place performance of the prototype. Experimental results show that the prototype module can generate the maximum attractive pressure of 87.1 Pa, which can pick and hold a piece of xerographic paper of 31.2 mg successfully. The effects of residual charges and the probe-tips flattening process on the attractive force are also discussed.

This paper proposes a contact model between a rigid sphere and an elastic plane covered with a thin liquid film. The elastic contact is determined by Johnson–Kendall–Roberts theory, which deals with the energy equilibrium of elastic and interfacial energies. In elastic contact under presence of thin liquid film, the energy needed to separate the two bodies is defined as the summation of the interfacial energy among the sphere, liquid, and plane. Capillary force affects the two bodies because a liquid bridge is formed between them. Shape of the liquid bridge, assumed by the Clark’s toroidal approximation, determines the capillary force. The hysteresis of the liquid contact angles and that of the liquid volume between loading and unloading processes are considered. In loading process, the liquid film is squeezed out from the contact area and accumulates at the contact edge with increasing the liquid contact angles. In unloading process, the accumulated liquid is dragged to the contact edge, and the contact angles decrease. An irreversible force curve is obtained from these two hystereses, and the effect of liquid bridge is discussed based on the calculated results. In addition, the adhesion-hysteresis mechanisms caused by the capillary force are discussed.

This paper proposes an analytical model for the Boussinesq problem between a tilted rigid punch and an elastic half space to enable the analysis of elastic deformations inside and outside a contact area. Inside the contact area, two types of pressure distributions are applied: one generates a flat elastic deformation, and the other produces a tilted elastic deformation. The projection of this elastic deformation varies depending on the observed horizontal direction because the elastic deformation is non-axisymmetric. To calculate integrals for the non-axisymmetric elastic deformation, we use the polar coordinate system with two angular coordinates, which can enable the calculation of an integral at any arbitrary point. The proposed model can obtain the relationship between the pressure distribution and the elastic deformations inside and outside a contact area from any arbitrary direction. In addition, the normal load and torque applied inside the contact area are obtained, and these parameters are normalized using the contact radius and the elastic modulus. At the zero-pressure point around the contact edge, the elastic deformation is smooth.

In this study, we fabricated a bipolar electrostatic chuck having hairy silicon-based microstructure with smooth contact surface by lithography technology. Using DRIE, we succeeded in creating electrostatic chuck structure with high surface accuracy. We deserved the surface of tips observation with FE-SEM , and evaluated the performance by force curve measurement. The state of detachment could be detected by monitoring the transition of force-displacement in force curve measurement .As a result, compared to previous research, the adhesion per unit area greatly improved. Additionally, we obtained guidelines for further improvement in performance.