Optimal impedance control based on body inertia for a hydraulically driven hexapod robot walking on uneven and extremely soft terrain

This paper presents the implementation of impedance control for a hydraulically driven hexapod robot named COMET‐IV, which can walk on uneven and extremely soft terrain. To achieve the dynamic behavior of the hexapod robot, changes in center of mass and body attitude must be taken into consideration during the walking periods. Indirect force control via impedance control is used to address these issues. Two different impedance control schemes are developed and implemented: single‐leg impedance control and center of mass‐‐based impedance control. In the case of single‐leg impedance control, we derive the necessary impedance and adjust parameters (mass, damping, and stiffness) according to the robot legs' configuration. For center of mass–based impedance control, we use the sum of the forces of the support legs as a control input (represented by the body's current center of mass) for the derived impedance control and adjust parameters based on the robot body's configuration. The virtual forces from the robot body's moment of inertia are adapted to achieve optimal control via a linear quadratic regulator method for the proposed indirect attitude control. In addition, a compliant switching mechanism is designed to ensure that the implementation of the controller is applicable to the tripod sequences of force‐based walking modules. Evaluation and verification tests were conducted in the laboratory and the actual field with uneven terrain and extremely soft surfaces. © 2011 Wiley Periodicals, Inc.     

Molecular cloning and characterization of a thermostable α-amylase exhibiting an unusually high activity

An α-amylase gene was cloned from the thermophilic bacterium Bacillus subtilis isolated from Indonesian oil palm shell waste. The gene expressed an extracellular enzyme. Optimal hydrolysis conditions for the enzyme were 70°C and pH 6.0. The specific activity of the enzyme was 16.0 kU per mg of protein, which was higher than for other thermostable amylases. Hydrolytic products of the enzyme using starch and glycogen were mainly maltohexaose and maltopentaose. The enzyme had a K _m value of 0.099 mg/mL for amylopectin, more than 10 times lower than for amylose. The catalytic efficiency of the enzyme using amylopectin was 39,200 mL/mg·s and was 3,270 mL/mg·s using amylose. The enzyme liquefied corn starch at pH 5.0, which was successfully converted to glucose using commercial glucoamylase and pullulanase without pH adjustment. The enzyme has advantages for industrial applications.     

Hiding data: a high-capacity distortionless approach

The widespread use of 3D models has become an interest in steganography. In this paper, we present a novel data hiding method for 3D models. Based on the representation information, the key idea is to consider the vertex index as a message block. A message consists of three types of message blocks, namely, unique, repeated and 1-bit or 0-bit repetitions blocks. Three embedding methods, namely, vertex index embedding (VIE), dynamic-length bit-string mapping (DBM), and repeated bits embedding (RBE), each best for a respective type of message block are devised. All message vertices are then arranged in the light of proposed vertex order and output as the stego-model. The message block is extracted from the vertex of the stego-model by the order of vertex sequence and its index in the ordered vertex list. While integrating the proposed methods our scheme gains high capacity compared to existing techniques while preserving reasonable robustness. In addition, our method is efficient, 25 times faster than previous techniques. With high capacity, several novel applications like content annotation for large documents, 3D meta model for related resources, etc., becomes possible, making the 3D model as an excellent data container.     

Continuous monitoring of SF/sub 6/ degradation in high voltage switchgear using Raman scattering

In high voltage SF/sub 6/ insulated switchgear, the level of SF/sub 6/ concentration needs to be monitored regularly because of its degradation by switching arcs and on-going partial discharges or coronas. In the work reported here, measurements of SF/sub 6/ dissociation rate following 75 /spl mu/A positive and negative coronas have been made using a mass spectrometer and Raman spectroscopy. The two sets of data correlate well, the rates of degradation of SF/sub 6/ and production of gaseous by-products being shown to be proportional to the charge transported by the corona. SF/sub 6/ provides a particularly strong Raman signal at 773.5 cm/sup -1/, and the results demonstrate the feasibility of using Raman scattering to monitor SF/sub 6/ degradation in high-voltage switchgear.     

Label‐QoS switching protocol for quality of service assurance in dynamic swarm robot local network

This paper presents the modeling and analysis of a proposed label–quality of service (QoS) switching protocol for heterogeneous robot in a swarm. Establishing the data communication and network in multirobot task allocation is an important aspect in robot collaboration. Instead of passing the data through the cloud network, each robot can be configured as a node in its swarm for intercommunication. This research was conducted to model and propose aggregation and classification methods in a swarm robot network inspired from multiprotocol label switching, namely, label‐QoS switching protocol. Each packet of data is forwarded with a proposed 2‐side label values that are concerned with addressing and QoS. This proposed protocol was applied in each of the node's routing, and it was set up with forwarding information table. The simulation and analysis were conducted in 2 situations: (1) with a constant n–label switch mobile robot and a number of packet data increasing with time and (2) with a constant number of packet and varying n–label switch mobile robot by time. With reference to the network parameter performances, it shows that the anomaly treatment by the proposed protocol is able to prioritize the data forwarding between the robots at the edge of the swarm with class of service although the robot community at the center is increasing or getting crowded.     

Isothermal Drying of Pore Networks: Influence of Friction for Different Pore Structures

An existing network model for isothermal drying of capillary porous media is extended to account for viscosity in the liquid phase so that it is no longer restricted to structures with large pores. Modeling challenges and solution methods are presented in detail. The model is compared with a bundle of capillaries model of drying. Finally, simulation results for two-dimensional pore networks with mono-modal and bimodal pore structure are shown and discussed.     

A Screening method for total oxalate determination in plant material by gas chromatography

Oxalates in plant material can be methylated directly to from dimethyl oxalate. After addition of water and chloroform, the volatile compoun is extracted into the organic phase and analysed quantitatively by gas chromatography. Some forms of oxalates are difficult to methylise, and this is apparent when 20% boron trifluoride-methanol is used as the methylating reagent. The use of 7% hydrochloric acid-methanol improved methylation, but the best result was obtained by repacing the acid catalyst with sulphuric acid and increasing the acid concentration up to 30%. Using this reagent, recovery from spiked samples was satisfactory (ranging from 92 to 105%), and precision of the method was good (Relative Standard Deviation (RSD) 1.3% at a total oxalate content of 1.95%).     

Isothermal Drying of Pore Networks: Influence of Friction for Different Pore Structures

An existing network model for isothermal drying of capillary porous media is extended to account for viscosity in the liquid phase so that it is no longer restricted to structures with large pores. Modeling challenges and solution methods are presented in detail. The model is compared with a bundle of capillaries model of drying. Finally, simulation results for two-dimensional pore networks with mono-modal and bimodal pore structure are shown and discussed.     

Synthesis and Optimization of 2-ethylhexyl Ester as Base Oil for Drilling Fluid Formulation

A stable ester was synthesized to overcome the ester hydrolysis problem during the drilling of oil or gas wells using a conventional ester-based drilling fluid. The thermal and hydrolytic stability of the produced ester was high owing to the transesterification method employed in this study. The reaction was performed using 2-ethylhexanol and methyl laureate esters in the presence of sodium methoxide as a catalyst. In order to obtain the optimum synthesis conditions, a response surface methodology (RSM) was appraised based on the central composite design (CCD). The optimum conditions were determined as follows: 0.6 wt.% catalyst, 70°C reaction temperature, 1:1.5 molar ratio, and 11.5 min of reaction time. The results of 77 wt.% 2-ethylhexyl ester (2-EH) illustrated a high agreement between the experimental and RSM models. The reaction product contained 77 wt.% 2-EH and 23% 2-ethylhexanol. The kinematic viscosity was 5 mm²/s at 40°C and 1.5 mm²/sec at 100°C; the specific gravity was 0.854, flash point was 170°C, and pour point was ?7°C. The produced product showed similar properties to the available commercial product. However, it was observed that the mud formulation using the synthesized base oil had superior rheological properties at 121°C.