Prediction of dilution in GMA and UGMA stainless steel single layer cladding using response surface methodology

Abstract

This paper describes the use of a variant of GMAW process named as UGMAW (universal gas metal arc welding) process for single layer stainless steel cladding, which makes use of a specially designed torch to preheat the filler wire, using an auxiliary welding power source, before its emergence from the torch. The experimental work undertaken was that of single layer cladding of 12 mm thick low carbon steel with the austenitic stainless steel 316L solid filler wire of 1·14 mm diameter. Dependence of dilution was investigated using four factor five level central composite rotatable design to develop relationship for predicting dilution, which enables to quantify the direct and interactive effects of four numerical factors, namely, wire feed rate, open circuit voltage (OCV), welding speed, electrode stickout and one categorical factor, preheat current. External preheating of the filler wire in UGMAW process resulted in greater contribution of arc energy by resistive heating owing to which significant drop in the main welding current and hence low dilution values were observed. Numerical optimisation was carried out and the optimal solutions generated indicate that for same levels of dilution, higher deposition rates are achievable in UGMAW process, thus making it a good choice for low cost surfacing applications.     

Adaptive dynamic walking of a quadruped robot using a neural system model

We are trying to induce a quadruped robot to walk dynamically on irregular terrain by using a neural system model. In this paper, we integrate several reflexes, such as a stretch reflex, a vestibulospinal reflex and extensor/flexor reflexes, into a central pattern generator (CPG). We try to realize adaptive walking up and down a slope of 12°, walking over an obstacle 3 cm in height, and walking on terrain undulation consisting of bumps 3 cm in height with fixed parameters of CPGs and reflexes. The success in walking on such irregular terrain in spite of stumbling and landing on obstacles shows that the control method using a neural system model proposed in this study has the ability for autonomous adaptation to unknown irregular terrain. In order to clarify the role of a CPG, we investigate the relation between parameters of a CPG and the mechanical system by simulations and experiments. CPGs can generate stable walking suitable for the mechanical system by receiving inhibitory input as sensory feedback and generate adaptive walking on irregular terrain by receiving excitatory input as sensory feedback. MPEG footage of these experiments can be seen at: http://www.kimura.is.uec.ac.jp.     

Simulating Adaptive Human Bipedal Locomotion Based on Phase Resetting Using Foot-Contact Information

Humans generate bipedal walking by cooperatively manipulating their complicated and redundant musculoskeletal systems to produce adaptive behaviors in diverse environments. To elucidate the mechanisms that generate adaptive human bipedal locomotion, we conduct numerical simulations based on a musculoskeletal model and a locomotor controller constructed from anatomical and physiological findings. In particular, we focus on the adaptive mechanism using phase resetting based on the foot-contact information that modulates the walking behavior. For that purpose, we first reconstruct walking behavior from the measured kinematic data. Next, we examine the roles of phase resetting on the generation of stable locomotion by disturbing the walking model. Our results indicate that phase resetting increases the robustness of the walking behavior against perturbations, suggesting that this mechanism contributes to the generation of adaptive human bipedal locomotion.     

Joining phenomena during friction stage of A7075-T6 aluminium alloy friction weld

Abstract

This paper describes the effect of friction welding conditions on joining phenomena during the friction stage of type 7075-T6 aluminium alloy (A7075) friction welds. The friction torque had wear and seizure stages until the initial peak torque when A7075 was welded under high friction speed and low friction pressure, i.e. 27 · 5 rev s^?1 and 30 MPa. Initial seizure and joining began at the central region (centre axis) of the welded interface, and extended towards the peripheral region (outer surface). On the other hand, when A7075 was welded under high friction speed and high friction pressure, i.e. 27 · 5 rev s^?1 and 90 MPa, almost no wear stage existed before the initial peak torque. Initial seizure and joining began at the peripheral region of the welded interface and extended towards the central region. Then, the friction torque reached an initial peak torque when the welded interface was joined completely and upsetting of both base metals started. As a conclusion, the joining mechanism of A7075 friction welding was similar to that of low carbon steel.     

Construction and Central Pattern Generator-Based Control of a Flipper-Actuated Turtle-Like Underwater Robot

This paper deals with the construction and control of a turtle-like underwater robot with four mechanical flippers. Each flipper consists of two joints generating a rowing motion by a combination of lead-lag and feathering motions. With cooperative movements of four flippers, the robot can propel and maneuver in any direction without rotation of its main body and execute complicated three-dimensional movements, including ascending, submerging, rolling and hovering. The control architecture is constructed based on a central pattern generator (CPG). A model for a system of coupled nonlinear oscillators is established to construct a CPG and has been successfully applied to the eight-joint turtle-like robot. The CPGs are modeled as nonlinear oscillators for joints and inter-joint coordination is achieved by altering the connection weights between joints. Rowing action can be produced by modulating the control parameters in the CPG model. The CPG-based method performs elegant and smooth transitions between swimming gaits, and enhanced adaptation to the transient perturbations due to nonlinear characteristics. The effectiveness of the proposed method is confirmed via simulations and experimental results.     

Welding current prediction in GMAW and UGMAW processes using response surface methodology

Abstract

Among all process variables in gas metal arc welding (GMAW) process, welding current is the most influential variable affecting heat input and weld quality. Its dependence on other process variables in GMAW and universal gas metal arc welding (UGMAW) processes (which makes use of a specially designed torch to preheat the filler wire independently, before its emergence from the torch) has been investigated using four factor five level central composite rotatable design to develop relationship for predicting welding current, which enables to quantify the direct and interactive effects of four numeric factors, namely wire feedrate, open circuit voltage, welding speed and electrode stickout and one categorical factor preheat current. Mathematical models developed show that welding current increased linearly with increaseing wire feedrate and open circuit voltage, whereas it decreased with increasing electrode stickout and preheat current. Numerical optimisation was carried out, and the optimal solutions generated indicate that under the same input conditions higher deposition rates are achievable in UGMAW process.     

Application of statistical design to optimisation of hardness and hydrogen content of chromium coating under pulse reverse electroplating

Abstract

The optimal plating settings in the pulse reverse electroplating mode for studying the mechanical properties of hard chromium deposits were derived by using experimental strategies including a factorial portion of central composite design and optimum paths coupled with the desirability function. This allows determining of the operating conditions leading to the highest hardness before and after aging and the lowest amount of occluded hydrogen. The morphologies of prepared films were observed by AFM.     

Gait transition for a quadrupedal robot by replacing the gait matrix of a central pattern generator model

The pattern-generator-based approach for legged robot control is inspired by biological neural mechanisms of locomotion, in which a special challenge is gait transition. In this paper we build a holosymmetric central pattern generator model and propose parameter-setting principles for a gait matrix capable of producing typical quadrupedal gaits, and based on them present an approach of directly replacing the gait matrix for gait transition, with a focus on three problems emerging during transition: breakpoint, phase-lock and oscillation-stop. Breakpoints are smoothed by remaining the current outputs during transition, similar to a zero-order holder. Breaking the phase-lock is accomplished by adding a perturbation to the state matrix at the transiting point. An oscillation-stop of less than one period can be ignored. With such treatments, it is proved that gait transitions between any two gaits on a quadrupedal robot can be achieved at arbitrary phase locations in a walk cycle, theoretically and experimentally in part.     

Neurobiological Basis of Controlling Posture and Locomotion

Posture and movements are our only physical means of interacting with the environment. As we express our thoughts and emotions through posture and movements, they indicate our will or intentions. Locomotion is representative of purposeful goal-directed behaviors that are initiated by signals arising from either volitional processing in the cerebral cortex or emotional processing in the limbic system. Regardless of whether the locomotion is volitional or emotional, it is accompanied by automatically controlled movement processes such as the adjustment of postural muscle tone and rhythmic limb movements that are unconsciously executed. Sensori-motor integration at the level of the brainstem and spinal cord plays major roles in this automatic control. Signals processed in the basal ganglia and the cerebellum act on the cerebral cortex, the limbic system and the brainstem so that locomotor behaviors are appropriately and precisely regulated depending on the behavioral context. The purpose of this review is to describe how purposeful locomotor behaviors are initiated, executed and regulated so as to enable locomotive subjects to interact with and adapt to the environment.