Zhidong Wang

Approach in Assisting a Sit-to-Stand Movement Using Robotic Walking Support System

This paper presents an approach in assisting a sit-to-stand movement using a robotic walking support system. In general, robotic walking support system is used to provide walking stability. We will extend its function to assist a user in executing a sit-to-stand movement. The first approach would be called passive support. In this approach, the support system would be stationary as the user execute the sit-to-stand movement. The knee torque would be determined and this would be compared to a sit-to-stand movement without support. The second approach would be called active support and the knee torque would be supported. A motion control algorithm would be proposed such that the support system will move based on the supporting torque. The actual experimentation on both approaches in assisting a sit-to-stand movement will be presented. The experimental result on active support shows the validity of the proposed motion control algorithm

Modeling and analyzing nano-particle pushing with an AFM by using nano-hand strategy

One of the major limitations for Atomic Force Microscopy (AFM) based nanoparticle pushing is that AFM only has one sharp tip as the end-effector. The interaction force between the nanoparticle and the tip is applied through a single point, which often leads the AFM tip to slip-away from the nanoparticle due to their small touch area. Then several minutes is needed to relocate the missed nanoparticle by a new image scan. Moreover, if the nanoparticle is very soft, the sharp tip may damage the particle instead of pushing it away due to the cutting effect of the sharp tip. In this paper, a nano-hand strategy is proposed to resolve this problem. Based on the theoretical analysis to the behavior model of nanoparticle, the pushing points, pushing step-length and pushing speed of AFM tip are planned artfully, through which a multi-tip manipulation effect can be imitated with a single tip. The nanoparticle is pushed as by a virtual nano-hand during manipulation,. In this way, the slip-away problem due to single AFM tip pushing can be get rid of efficiently. The simulation and experiments results show the increased effectiveness of AFM based nanomanipulation.

Wearable antigravity muscle support system utilizing human body dynamics

In this research, we have developed a wearable antigravity muscle support system, which assists daily activities of physically weak persons by reducing the load to the lower extremities. Many activities of a human being are performed smartly by cooperating motions of different body parts to reduce loads. In this paper, we propose a dynamics-based support concept based on the posture and motion of the user, and analyses of humans smart motion in order to assist the user smartly and naturally by the wearable support system. Based on the proposed concept, a dynamics-based control algorithm for devices without using biological signals is implemented. Experimental results illustrate the validity of the proposed system.

A probabilistic approach for on-line positioning in nano manipulations

Nanomanipulation and nanoassembly using atom force microscopy (AFM) is a potential and promising technology for nanomanufacturing. Precise position of the tip of AFM is important to increase the accuracy and efficiency on fabricate complex nanostructures. However at the nano-scale, it is difficult to acquire the tip position expressed by the coordinate in real time due to PZT nonlinearity and thermal drift through the general measure. In this paper, a probabilistic approach incorporating a Kalman filter based localization algorithm is introduced into the on-line estimation of the tip position expressed by probability distribution known as probability density function. A probabilistic motion model of AFM tip is introduced that consists of a PZT dynamic model based on the Prandtl-Ishlinskii (PI) model, and motion error distribution obtained from calibration experiments. An observation model by using a local scanning algorithm is proposed and the change of uncertainty distribution on scanning landmarks, e.g. nano-particles, near the target position is analyzed. Some experiment results are included for showing the motion error distribution and a simulation result is presented to illustrate the validity of the proposed method.

Stable Nanomanipulation Using Atomic Force Microscopy: A virtual nanohand for a robotic nanomanipulation system.

Atomic force microscopy (AFM) has become a promising tool for not only imaging and measuring matter at the nanoscale [1] but also manipulating and fabricating nano-objects [2], [3]. AFM offers multiple working modes for sensing and actuating with one versatile probe. It can easily switch between scanning and manipulating a nano-object either in an ambient atmosphere or in a liquid environment [4]. One of the important nanoparticle manipulations is the nanoparticle transfer, in which two movements of grasping and transferring are involved. Although the two movements are directly in conflict with the single probe-based mechanism, an AFM-based robotic nanomanipulation system with a virtual nanohand has been developed to solve the conflicting issue of movements. In this article, we show how an AFM-based virtual nanohand is designed to grasp and transfer a nanoparticle at the nanometer scale stably, efficiently, and effectively.

AFM tip on-line positioning by using the landmark in nano-manipulation

AFM has been proved to be a powerful nano-manipulation tool taking advantage of its ultra high resolution and precision. However the large spatial uncertainties associated with AFM tip positioning dual to the PZT nonlinearity and thermal drift are still challenging problems, which hinders its wide application especially in building complex structures In this paper, a probabilistic approach combined with the Kalman filter based localization algorithm is proposed to improve the accuracy of the tip positioning in the task space coordinate frame. A motion model based on the Prandtl-Ishlinskii (PI) model is established, the distribution of model error is statistically obtained through the experimental calibration process. In addition, to further reduce the tip position uncertainties, an environment measurement models is developed through sensing the landmark intermittently with local scanning method during manipulation. Both the simulations results and experimental results are presented to demonstrate the validity of the proposed method.

Modeling and analyzing nano-rod pushing with an AFM

In developing nano-devices and nano-structures, traditional methodologies on MEMS meet the difficulty from the scale restriction. With the strategy of objects assembly, using AFM to handle nano-rods and other nano-objects is considered as an important and high potential technology in constructing nano-structures. However most of AFM only has one tip as the end effector and cannot control both translational and rotational motions during manipulation, this makes it be difficult to realize posture controllable manipulation especially in nano environment. In this paper, the behavior of nano-rod under pushing is theoretically analyzed and modeled. Viscous friction is incorporated in the model and the two situations that the pivot of the nanorod is either inside or outside the rod are addressed. By modeling, the pivot can be determined at each manipulation in real time, and the pushing points can be planned to realize posture controllable manipulation by using nano-hand strategy which is inspired by stable pushing theory of object manipulation in macro world, and to improve the reliability and the precision of manipulation.

Atomic force microscope deposition method for nano-lines

Nano-devices have many potential applications. However, how to connect the nano-components is a problem during fabrication of nano-devices. This paper introduces a nano-line deposition method with atomic force microscope(AFM). This method is expected to be used as a nano-welding technique, which can improve the physical and electrical connections between the various components of nano-devices. With this method, nano-lines can be deposited continuously, rather than depositing a row of nano-dots to form a nano-line. The method comprises two features. One is current-induced deposition rather than voltage. Experiments show that current-induced method can fabricate more continuous and smoother nano-lines than voltage-induced method.The other is a simple tip-substrate distance control means. AFM deposition is based on field emission theory, so tip-substrate distance is an important factor for field emission. A simple tip-substrate distance control means is introduced in this paper, which makes the deposition process easier.

Spatial Manipulation and Assembly of Nanoparticles by Atomic Force Microscopy Tip-Induced Dielectrophoresis

In this article, we present a novel method of spatial manipulation and assembly of nanoparticles via atomic force microscopy tip-induced dielectrophoresis (AFM-DEP). This method combines the high-accuracy positioning of AFM with the parallel manipulation of DEP. A spatially nonuniform electric field is induced by applying an alternating current (AC) voltage between the conductive AFM probe and an indium tin oxide glass substrate. The AFM probe acted as a movable DEP tweezer for nanomanipulation and assembly of nanoparticles. The mechanism of AFM-DEP was analyzed by numerical simulation. The effects of solution depth, gap distance, AC voltage, solution concentration, and duration time were experimentally studied and optimized. Arrays of 200 nm polystyrene nanoparticles were assembled into various nanostructures, including lines, ellipsoids, and arrays of dots. The sizes and shapes of the assembled structures were controllable. It was thus demonstrated that AFM-DEP is a flexible and powerful tool for nanomanipulation.

A rapid and automated relocation method of an AFM probe for high-resolution imaging.

The atomic force microscope (AFM) is one of the most powerful tools for high-resolution imaging and high-precision positioning for nanomanipulation. The selection of the scanning area of the AFM depends on the use of the optical microscope. However, the resolution of an optical microscope is generally no larger than 200 nm owing to wavelength limitations of visible light. Taking into consideration the two determinants of relocation-relative angular rotation and positional offset between the AFM probe and nano target-it is therefore extremely challenging to precisely relocate the AFM probe to the initial scan/manipulation area for the same nano target after the AFM probe has been replaced, or after the sample has been moved. In this paper, we investigate a rapid automated relocation method for the nano target of an AFM using a coordinate transformation. The relocation process is both simple and rapid; moreover, multiple nano targets can be relocated by only identifying a pair of reference points. It possesses a centimeter-scale location range and nano-scale precision. The main advantages of this method are that it overcomes the limitations associated with the resolution of optical microscopes, and that it is label-free on the target areas, which means that it does not require the use of special artificial markers on the target sample areas. Relocation experiments using nanospheres, DNA, SWCNTs, and nano patterns amply demonstrate the practicality and efficiency of the proposed method, which provides technical support for mass nanomanipulation and detection based on AFM for multiple nano targets that are widely distributed in a large area.