Impact Analysis of a Dual-Crawler-Driven Robot

This paper presents the impact analysis of a new dual-crawler-driven robot. This dual-crawler-driven robot is realized by connecting rigidly two crawler modules. In this newly proposed crawler module, a planetary gear reducer is deployed as the power transmission device to give two different outputs with just one actuator. Compared with the crawler driven by two actuators, our crawler module driven by one actuator could show good impact absorption when the robot collides with an obstacle due to the fact that there exists an output redundancy in each module. To determine what the advantage of our mechanism to the impact absorption is, impact analysis of the robot is conducted from the external components of the robot to its internal transmission parts while the robot encounters a collision with obstacles. The results of impact effect to the actuators in our mechanism are correspondingly derived in comparison with that in the conventional mechanism where each output is provided by one actuator. Numerical results are used to demonstrate the advantage of our mechanism on impact absorption.     

A geometric constraint-based approach to force and motion coupling between real and virtual mechanisms

This paper presents a new stable controller design for use with a general 6-d.o.f. robotic haptic device. A virtual manipulator concept is developed that couples the haptic device kinematics with the constraints of a simulated manipulator. Using impedance-based constraints, the haptic device is controlled to oppose applied forces in directions orthogonal to the motions of the virtual manipulator. The virtual manipulator kinematics constrains the haptic device motion, allowing motion to simulate specific virtual mechanisms. The implementation is illustrated using experimental simulations.     

Snake-Like Robot for Rescue Operations — Proposal of a Simple Adaptive Mechanism Designed for Ease of Use

Rescue operations are one of most effective applications for robots and various rescue robots operated by rescue staff have been developed. However, in large-scale disasters, there is a significant problem, i.e., a shortage of operators. In this paper, we consider this problem and propose a snake-like rescue robot which is designed for non-professional volunteer operators. To realize the rescue robot simply, we focus on mechanical design, and realize usability by utilizing properties of its body and the real world. Experiments have been carried out to demonstrate the effectiveness of the proposed robot.     

Densi cation and crystallisation behaviour of Si–B–O–N ceramics prepared by hot pressing with organic precursors

Abstract

Powders of Si–B–O–N prepared by organometallic polymeric precursor were hot pressed into ceramics at different temperatures. Experimental results indicated that density of ceramics increased slowly with increasing temperature before 1400°C, and increased rapidly after 1400°C. Density of ceramics sintered at 1600°C was 2.11 g cm^-3, which was the highest in this system. Amorphous silicon oxynitride decomposed when sintered at temperatures higher than 1600°C. Differential scanning calorimetry and X-ray diffraction analyses results showed that the amorphous Si–B–O–N began to crystallise at 1350°C and only h-BN precipitates was detected. Observations using SEM showed that particles precipitated at 1400°C were close to equiaxial crystals, however, particles precipitated at 1600°C were well developed platelets. The growth mechanism of precipitates was step like epitaxial growth. Crystals in ceramics sintered at 1700°C were quite small and adhered by molten silica.     

Evaluation of the polymer-nonpolymer adhesion in particle-filled polymers with the acoustic emission method

The acoustic emission (AE) test was employed to study the debonding of glass beads from a polystyrene (PS) matrix for uniaxially loaded specimens of composites with a different adhesion level between the glass surface and PS. The adhesion was varied by tailoring the interface with endfunctionalized PS or polystyrene-block-poly-(2-vinylpyridine) copolymers adsorbed onto the glass surface. The number of beads was about 30 000 per specimen, which allowed good statistics to be obtained in the experimental data. The number of AE events, the debonding stress, the AE amplitude (AEA) for every signal, and the elongation of the specimen were recorded in the test. The experimental distribution of the number of AE signals per stress unit was fitted with a Weibull function and the maximum of the function was associated with the average debonding stress (ADS). The distribution of AE signals via AEA was also fitted with a Weibull function and the amplitude that corresponded to the maximum of the function was used as a parameter to characterize the AE energy released. All the parameters were used for the analysis of the failure mechanism of the composites. The ADS increases as the interface strength increases. The AEA measurement data usually should be fitted by two Weibull functions with two AEAs of relatively small and large energy (I and II, respectively). Both AEA-I and AEA-II decrease as the adhesion increases. These two maxima are assumed to characterize two different microdefects at the interface. AEA-I is caused by the propagation of the microdefects that were formed at the interface during the material preparation. The dewetting of the glass beads at larger stress affects the AE signals with larger AEA-II. It is suggested that the decrease in AEA with adhesion is caused by the propagation of microdefects towards the matrix. Simultaneous consideration of ADS and AEA allows the interfacial strength and location of the microcracks to be evaluated. The polydispersity of the PS matrix, the duration of sample preparation (melting under pressure), the rate of specimen deformation in the test, and the volume fraction of the filler within the range 2-15 vol.% have very slight effects on the results.     

Hybrid PP–EPR–GF composites. Part II: fracture mechanisms

Abstract

The fracture mechanism of hybrid iPP–EPR–GF composites has been studied by notched Charpy, three- and four-point bending fracture tests. The results of impact tests illustrate that increasing both temperature and EPR/GF ratio increases the impact energy of iPP–EPR–GF. Indeed, with increasing temperature, a brittle, ductile, transition temperature (BDTT) occurs. The results of a three-point bending test show that fracture toughness (K_IC ) can be improved by addition of both GF and EPR. Since the trend in the fracture toughness values is close to what would be expected by the rule of blends, it can be concluded that the use of both GF and EPR has no significant synergistic effect on toughening. The results of a four-point bending test show that craze-like damage appears in front of the pre-crack and its propagation is dictated by the GF and EPR content. Looking in more detail at the damaged zone by means of cross-polarised light microscopy, evidence of birefringence can be revealed. Briefly, the dominant mechanism of fracture in the iPP–EPR–GF system studied in this work can be related to a craze-like type damage, which includes both highly localised dilatational shear bands, due to cavitation of the EPR particles, and some crazing induced by the stress concentration associated with GF.     

Graphite nucleation control in grey cast iron

Abstract

A research programme has been undertaken to achieve a more detailed understanding of graphite nucleation control in grey cast irons, at different sulphur (0˙02–0˙1%), residual aluminium (0˙001–0˙010%) and zirconium (0˙001–0˙015%) levels in iron melts. It was found that three groups of elements are important to sustain a three stage model for the nucleation of graphite in grey irons:

(i) strong deoxidising elements (Al, Zr) to promote early formed very small microinclusions, oxide based, which will act as nucleation sites for later formed complex (Mn,X)S compounds

(ii) Mn and S to sustain MnS type sulphide formation

(iii) inoculating elements (Ca, Sr, etc.) which act in the first stage or/and in the second one of graphite formation, to improve the capability of (Mn,X)S compounds to nucleate graphite.

It was confirmed that 0˙07%S level is beneficial for graphite nucleation in grey irons with a lower incidence of carbides and undercooled graphite, compared to 0˙023%S cast irons. Low residual Al level (0˙001–0˙003%) results in higher chill and more undercooled graphite and lower eutectic cell count, in inoculated irons. A 0˙007–0˙010%Al content in the melt is important to sustain type A graphite nucleation and reduced chill. Not only inoculation but also the preconditioning (Al or/and Zr) of the base iron has a strong beneficial effect on the solidification pattern of cast irons. Both Al and Zr sustain the type A graphite formation with a lower degree of undercooling and free carbides. These elements were associated in a complex alloy (FeSi based), very efficient in preconditioning of grey irons for thin wall castings, at a low addition rate.     

Joint strength and failure mechanism of laser spot weld of mild steel sheets under lap shear loading

Abstract

Ultimate strength and failure mechanism of laser spot welds under lap shear loading were investigated. Optical micrographs of cross-section of spot welds before and after failure were examined to understand the failure behaviour. The experimental results indicate that laser spot welds can fail in two distinct modes, namely interfacial and pullout failure. A failure mechanism which was confirmed by SEM investigations was proposed to describe these two failure modes. According to the experimental observations, a simple stress solution related to the far field load was conducted and the critical weld nugget diameter to ensure pullout failure mode was estimated. The results were compared with the experimental data and also with the test data of resistance spot welds. It was observed that the critical nugget diameter of laser spot welding was larger than that of resistance spot welding due to the different failure location in pullout mode. Furthermore, the effect of welding parameters on joint strength and failure mode was studied.     

Uneven terrain negotiable mobile platform with passively adaptive double tracks and its application to rescue missions

This paper presents the design and integration of ROBHAZ-DT3, a newly developed mobile robot system with a chained double-track mechanism. It is designed to carry out military and civilian missions in various hazardous environments. A passive adaptation mechanism equipped between the front and rear body enables ROBHAZ-DT3 to have good adaptability to uneven terrains, including stairs. The passive adaptation mechanism reduces energy consumption when moving on uneven terrain. It has a simple design and remote control, since no actuators are equipped for adaptation. Based on this new design concept, dynamic analysis and simulations were conducted to verify the mobility of the double-track mechanism, and to obtain significant design parameters such as the optimal track size and allowable attack angle. Also, dynamic effects in vehicle turning were investigated to assess the proper driving torque. Based on this novel mobile mechanism, a rescue version of ROBHAZ-DT3 with appropriate sensors and a semi-autonomous mapping and localization algorithm was developed to participate in the RoboCup 2004 US Open (Urban Search and Rescue Competition). From the various experiments in the realistic arena, we verified that ROBHAZ-DT3 is reliable when traveling over rugged terrain, and that the proposed mapping and localization algorithm are effective in unstructured environments with uneven ground like the rescue area.     

基于PRO/E的薄板长直焊缝自动焊接小车机构设计及运动学仿真研究

薄板长直焊缝焊接是工业焊接技术中的一个技术难点,如何提高焊接质量和焊接效率是其关键.而薄板长直焊缝自动焊接机中的小车机构,又是设计中的重点之一.本文结合薄板长直焊缝自动焊接工艺的特点和要求,应用Pro/E三维数字建模及MECHANISM机构运动学仿真,对自动焊接小车机构进行了优化设计及运动分析与仿真研究.解决了焊接小车机构设计中位移、速度、干涉等不合理现象和优化机构设计方面的技术问题,使焊接小车机构得到了合理的优化,缩短了设计周期,降低了设计成本,提高了设计的可靠性,为复杂运动机构设计与优化提出了一种切实可行的现代设计方法.