汽车覆盖件成形过程数值模拟研究

本文介绍汽车覆盖件成形过程有限元模拟两个软件ＩＴＡＳ—３Ｄ和ＤＹＮＡＭＩＣ的最新研究成果，基本原理和有关接触搜索、摩擦和拉伸筋模型等关键技术。并有两个应用实例     

Microstructural and textural evolution during large strain hot rolling (LSR) of Mg–Al (AZ31) alloy

Abstract

Grain refinement has been achieved through large strain rolling (LSR) in Mg AZ31 alloy. The evolution of microstructure and texture has been found to be dependent on the amount of reduction. After the critical amount of reduction, grain refinement proceeds through continuous dynamic recrystallisation (CDRX).     

Dynamic Young's modulus and glass transition temperature of selected tropical wood species

Abstract

Dynamic Young's modulus (E _d) of selected tropical wood species, namely Dyera polyphylla, Endospermum diadenum, Cratoxylum arborecens, Alstonia pneumatophora, Macaranga gigantea and Commersonia bartramia, used for the study was measured using the free–free flexural vibration method. Young's modulus from three point bending (E _3pb) and compression parallel to grain (E _cp) was also studied. The results show that the relationship between E _d and E _3pb for all wood species is very significant with the mean value of E _d consistently larger than or sometime equal to E _3pb. Surprisingly, the relationship between E _d and E _cp is not significant except for Alstonia pneumatophora. The dynamic mechanical thermal properties were also investigated using the dynamic mechanical thermal analyser (DMTA). The results showed that the storage modulus of the wood species at –90°C is in the range of 1·48–4·09 GPa with a glass transition temperature ranging from 50 to 70°C.     

Dynamic simulation of cooling stack and cooling circuit for converter gas cooling

Abstract

A dynamic simulation programme for the recooling circuit of converter gas cooling systems has been developed to assist in the design of new plant and efforts to increase the production capacity of existing plant. A suitable choice of independent variables (enthalpy h and pressure p) allows clear mathematical modelling and enhances the numeric performance of the model. The results have been verified by comparison with the operational data from existing steel plants. This simulation programme offers steelmakers the following advantages when seeking an increase in production: recalibration of existing systems and determination of maximum allowable heat input to the cooling circuit; proposals for modification of existing systems to increase the allowable heat input under constraints for optimal investment cost and installation downtime; design of new, low investment cost cooling systems tailored for existing plant infrastructure and local market conditions.     

14—EQUIVALENT TWISTS IN TYRE CORDS

This paper describes an empirical method for choosing a twist level for a new tyre cord that will ‘match’ the twist in an existing successful cord, i.e., one that will give the same twist angle. The technique is based on published cord geometry and is shown to give reliable results. No knowledge of densities or packing factors is required, and the results are independent of the number of yarns in the cord. The method offers the possibility of calculating twist angles and related properties for cords at any twist once a sufficiently reliable value of one cord constant has been determined. A table of matched twists calculated in this way is given.     

A Framework for Automatic Generation of a Contact State Graph for Robotic Assembly

Dynamic manipulation of an active object is introduced as a general model of hopping and juggling tasks. In this setting, juggling and hopping are two extreme cases of this general model. Behavioral resemblance of these two tasks is afterwards extended to a detailed mathematical analogy between them. Then the analogy is exploited to develop a unified and abstract planning framework for juggling and hopping. To this end, dynamic manipulation of an active object is decomposed into three distinct phases and two transitions: Carry I, Free flight and Carry II phases. These phases are analogous to Lift off, Free flight and Touch down in hopping. In the next step, a mathematical model for each phase is developed. It is shown that dynamic grasp (in Carry phases of juggling) and foot stability (in Support phases of hopping) conditions share similar sets of dynamic equations. Accordingly, Lift off/Release and Touch down/Catch conditions in hopping/juggling are derived. It is shown that analogous strategies can be developed for Lift off and Release. The analogy is held for Touch down and Catch conditions as well. It is discussed that in the planning framework the initial and the goal configurations of the three phases are set in a model-based and forward manner. To do so, Touch down/Landing time, Free flight duration and robot/object maneuvers during Free flight are used as free parameters for planning in order to ensure foot stability in hopping and dynamic grasp in juggling along with other constraints.     

Three-Dimensional Path Planning of a Climbing Robot Using Mixed Integer Linear Programming

The City-Climber robot is a novel wall-climbing robot developed at The City College of New York that has the capability to move on floors, climb walls, walk on ceilings and transit between them. In this paper, we first develop the dynamic model of the City-Climber robot when it travel on different surfaces, i.e., floors, walls and ceilings, respectively. Then, we present a path planning method for the City-Climber robot using mixed integer linear programming (MILP) in three-dimensional (3-D) building environments that consist of objects with primitive geometrical shapes. MILP provides an optimization framework that can directly incorporate dynamic constraints with logical constraints such as obstacle avoidance and waypoint selection. In order to use MILP to solve the obstacle avoidance problem, we simplify and decouple the robot dynamic model into a linear system by introducing a restricting admissible controller. The decoupled model and obstacle can be rewritten as a linear program with mixed-integer linear constraints that account for the collision avoidance. A key benefit of this approach is that the path optimization can be readily solved using the AMPL and CPLEX optimization software with a MATLAB interface. Simulation results show that the framework of MILP is well suited for path planning and obstacle avoidance problems for the wall-climbing robot in 3-D environments.     

Observer-Based Dynamic Control of an Underactuated Hand

The purpose of this paper was to construct a velocity observer based on the dynamic model and realize accurate dynamic curve and force control. Curve fitting with the observer obtained precise velocity signals. Compared with PID and factored moment methods, it decreased the fitting errors a lot and achieved ideal results. Compensated with the inverse dynamic equation, the force-based impedance control with the observer could not only realize accurate force tracking, but achieve finger dynamic control by the combination of curve fitting and force tracking. Furthermore, a static grasp model was established for appropriate force distribution. The finger could grasp slippery, fragile, comparatively heavy and large objects like an egg with only base joint torque and position sensors, which illustrated that the hand could accomplish difficult tasks by using the static grasp model and dynamic control.     

Object Category Acquisition by Dynamic Touch

The acquisition of object categories which underlie the human lexicon is a prerequisite for domestic robots to communicate with users in a human-like manner. The theory of J. J. Gibson inspires the approach to obtain shared categories through interaction with the shared environment, where explorative behaviors of infants play the role of obtaining distinctive features of objects to shape their categories. Although several existing studies have reproduced the exploratory behaviors of infants by robots to investigate their roles in acquiring such categories, those active categorization methods utilized static touches and the recognition tended to fail by changes of contact conditions. This paper introduces another possible approach to object categorization — object category acquisition by dynamic touch. Dynamic touch (e.g., shaking) provides the agent with the information of the whole object to enable quick and robust recognition. The amplitude spectrum of auditory data which humans obtain during shaking is found to be an effective feature for identifying the object categories of differing dynamics, e.g., rigid objects, paper materials and bottles of water, even though the objects within each category vary in size, shape, amount and contact conditions. Experimental results are given to show the validity of the proposed method and future issues are discussed.     

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.