2008 NOV 3 - (VerticalNews.com) -- "This paper presents a dispersion movement design for a multi-agent team inspired by the behavior of creatures. The goal of the dispersion algorithm is to maintain the communication network between agents and to enlarge the coverage area as widely as possible," investigators in Taipei, Taiwan report.

  "The communication density, or the number of communication links, is the only information needed. A dispatch rule for releasing agents at a base station is also designed based on the dispersion algorithm. The proposed algorithms have been extensively tested by software simulation. Statistics concerning the coverage area, network partition rate, and spending time are analyzed to verify the feasibility and advantages of the algorithms," wrote Y.L. Jian and colleagues, National Taiwan University ...read more

  2008 SEP 29 - (VerticalNews.com) -- "This paper presents the sliding-mode control of a three-degrees-of-freedom nanopositioner (Z, theta(x), theta(y)). This nanopositioner is actuated by piezoelectric actuators," scientists writing in the Asian Journal of Control report.

  "Capacitive gap sensors are used for position feedback. In order to design the feedback controller, the open-loop characteristics of this nanopositioner are investigated. Based on the results of the investigation, each pair of piezoelectric actuators and corresponding gap sensors is treated as an independent system and modeled as a first-order linear model Coupled with hysteresis. When the model is identified and the hysteresis nonlinearity is linearized, a linear system model With uncertainty is used to design the controller. When designing the controller, the sliding-mode disturbance (uncertainty) estimation and compensation scheme is used. The Structure Of the proposed controller is similar to that of a proportional integral derivative controller. Thus, it can be easily implemented," wrote J.C. Shen and colleagues ...read more

  2008 SEP 15 - (VerticalNews.com) -- "Nanomanipulation with atomic force microscopes (AFMs) for nanoparticles with overall sizes on the order of 10 nm has been hampered in the past by the large spatial uncertainties encountered in tip positioning. This paper addresses the compensation of nonlinear effects of creep and hysteresis on the piezo scanners which drive most AFMs," scientists in the United States report.

  "Creep and hysteresis are modeled as the superposition of fundamental operators, and their inverse model is obtained by using the inversion properties of the Prandtl-Ishlinskii operator. Identification of the parameters in the forward model is achieved by a novel method that uses the topography of the sample and does not require position sensors. The identified parameters are used to compute the inverse model, which in turn serves to drive the AFM in an open-loop, feed-forward scheme. Experimental results show that this approach effectively reduces the spatial uncertainties associated with creep and hysteresis, and supports automated, computer-controlled manipulation operations that otherwise would fail. Note to Practitioners-Manipulation at the nanoscale by using AFMs as sensory robots is well established in research laboratories, and has great potential as a process for prototyping nanodevices and systems, for repairing structures built by other means, and for small batch manufacturing by using multitip arrays. However, precise (to similar to 1 nm, say) AFM nanomanipulation is currently very labor intensive, primarily because of the uncertainty in the position of the AFM tip relative to the sample being manipulated. Positional errors are due to thermal drift and various nonlinearities exhibited by the piezoelectric scanners used by most AFMs. This paper describes a technique for compensating creep and hysteresis, which, after drift, are the major causes of spatial uncertainty in AFMs. The compensator introduced here has been tested experimentally and shown to reduce creep and hysteresis effects by more than an order of magnitude," wrote B. Mokaberi and colleagues ...read more