Application of Genetic Algorithms for biped robot gait synthesis optimization during walking and going up-stairs

Selecting an appropriate gait can reduce consumed energy by a biped robot. In this paper, a Genetic Algorithm gait synthesis method is proposed, which generates the angle trajectories based on the minimum consumed energy and minimum torque change. The gait synthesis is considered for two cases: walking and going up-stairs. The proposed method can be applied for a wide range of step lengths and step times during walking; or step lengths, stair heights and step times for going up-stairs. The angle trajectories are generated without neglecting the stability of the biped robot. The angle trajectories can be generated for other tasks to be performed by the biped robot, like going down-stairs, overcoming obstacles, etc. In order to verify the effectiveness of the proposed method, the results for minimum consumed energy and minimum torque change are compared. A Radial Basis Function Neural Network is considered for the real-time application. Simulations are realized based upon the parameters of the 'Bonten-Maru I'humanoid robot, which is under development in our laboratory. The evaluation by simulations shows that the proposed method has a good performance.     

Abnormal transient phenomena in the continuous casting process: Part 1

Abstract

This paper is the first of a series of two describing online monitoring of the continuous casting machine and the abnormal transient phenomena observed. The present paper, Part 1, pays attention to assessment of the friction between the billet and mould based upon the cam rod force and the electric current intensity of the mould oscillation motor. Information relating to casting parameters before 58 breakouts has been obtained with a monitoring computing program. Almost 40% of the breakouts could have been forecast through assessment of the billet-mould friction force before the breakouts. Transient phenomena in the withdrawal machine have been detected. The jerking of the strand is related to high billet-mould friction; however, other parameters such as the billet cutoff unit and roller bed design also have some effects on this transient phenomenon. Some mechanisms influencing the jerking of the strand are proposed.     

Determination of Structural Damping and Optimal Vibration Control of an Adhesively-Bonded Double Containment Cantilever Joint

In this study, the loss factors of an adhesively-bonded double containment cantilever joint were determined for different plate and support lengths. The response of the adhesive joint subjected to a transverse excitation force was measured with a contactless eddy-current sensor and the first bending natural frequency was determined using the Fast Fourier Transform method. The loss factor was calculated using the half-power bandwidth method based on the power spectrum of the joint vibration. After an excitation force was applied to the joint, the damped free vibration analysis was carried out using the finite element method and its measured loss factor. The transverse vibration attenuation was actively controlled with different numbers of actuators located on the top surface of the plate. The optimal control of the vibration attenuation was achieved based on a performance index by considering the strain energy, the kinetic energy, the work done on the adhesive joint by the actuators as well as the vibration attenuation time. Genetic Algorithm was implemented to this optimization problem in which the optimal control force histories, the optimal locations and the optimal numbers of the actuators were searched. Eight actuators exhibited the best control force history minimizing the performance index to 3.34 × 10^–2. Thus, the attenuation time was reduced from 16 s to 0.15 s and the absolute displacement was decreased from 13.1 mm to 17.15 × 10^–3 mm for 0.15 s. In addition, the modal strain energy and kinetic energy were found to be at lowest levels. As the actuator number was increased only a minor decrease in the performance index was observed after four actuators.     

FUZZY GLOBAL SLIDING MODE CONTROL BASED ON GENETIC ALGORITHM AND ITS APPLICATION FOR FLIGHT SIMULATOR SERVO SYSTEM

To alleviate the chattering problem, a new type of fuzzy global sliding mode controller (FGSMC) is presented. In this controller, the switching gain is estimated by fuzzy logic system based on the reachable conditions of sliding mode controller(SMC), and genetic algorithm (GA) is used to optimize scaling factor of the switching gain, thus the switch chattering of SMC can be alleviated. Moreover, global sliding mode is realized by designing an exponential dynamic sliding surface. Simulation and real-time application for flight simulator servo system with Lugre friction are given to indicate that the proposed controller can guarantee high robust performance all the time and can alleviate chattering phenomenon effectively.     

Photographic Procedure for Complex Chart Visual Interpretation Records*

Comparison of complicated chart records is not an easy task, even if great trouble is taken to produce transparent film copies dye-toned to contrasting colours. The lines may cross and re-cross so frequently that the sequence of events is difficult to see. In suchcases superimposition of above-the-line and below-the-line silhouettes is helpful, since it permits both the sign and the magnitude of the error at any point to be readily seen. Photographic procedures are described for making such silhouettes from commercially available materials.     

Mould powder consumption of continuous casting operations

Abstract

Mould powder consumption is an important parameter in continuous casting. Previous investigations, involving regression analysis or estimation of powder consumption, have identified the factors controlling powder consumption. However, those data were obtained for casting speeds less than 2 m min ^-1, and some relate to speeds less than 1 m min ^-1. Sumitomo Metal Industries has developed a medium thick high speed continuous casting operation for speeds between 2 and a maximum of 8 m min ^-1. Some of the powder consumption data obtained using the new process could not be explained on the basis of the former investigations: these data are discussed in the present report. The conclusions drawn are: (i) gravity is the main driving force for inflow of liquid powder between mould wall and solidified shell; (ii) to increase the powder consumption per unit strand surface area for speeds of ~8 m min ^-1 is difficult; and (iii) a powder consumption of under 0·1 kg m ^-2 is sufficient when casting at 8 m min ^-1.     

Fine tuning straightening process using genetic algorithms and finite element methods

Abstract

The process of straightening steel sections is used not only to actually straighten the product but also to reduce its internal residual stresses. Fine tuning this process within an industrial plant is complicated because of the time needed for conducting the tests and the difficulties in measuring the final residual stresses. This paper presents a methodology based on genetic algorithms and finite element analysis that seeks the best position of the rollers to produce a straightened product with the minimum amount of residual stresses. The process consists of simulating multiple roller positions using a previously validated finite element model and analysing the resulting residual stresses. Genetic programming is used to choose the best solutions that will give rise to the next generation of individuals. For several generations, the system combines a series of optimum solutions in which residual solutions are minimised. The best solutions obtained enable the rollers to be positioned in a way that guarantees a good end quality for the product.     

Application of a Genetic Algorithm Associated With Adhesive Joint Analysis to the IC Chip Pick-up Process

In the condition investigated here, a concentrated force is applied to both IC chip and blue tape bonded by an adhesive under pin–pin boundary conditions. The experimental results show that even though IC chips of 0.1 mm thickness are subjected to a concentrated force of 4.8 N, they cannot be fully separated from the blue tape and fail easily during the pick-up process. However, when IC chips of 0.34 mm thickness are subjected to a concentrated force of only 3.5 N, they can be fully separated from the blue tape without breakage. These two experimental findings are then explored analytically by applying the C++ program of the genetic algorithm associated with adhesively bonded joint analysis to the IC chip pick-up process. In accordance with the experimental results, the results for the 0.1 mm thick IC chips reveal no solutions for the material properties or adhesive thickness to satisfy the conditions of the IC chip successful pick-up process, although those for the 0.34 mm thick IC chips show solutions for the values of both the elastic modulus and the adhesive layer's thickness. As regards the easy failure of IC chips with 0.1 mm thickness, if the blue tape's mechanical properties are appropriately chosen and then used in this process and its elastic modulus is greater than one-tenth that of the IC chips, the probability of the IC chips being fully separated from the blue tape can be expected to increase.     

Mechanical characteristics of resistance multispot welded joints

Abstract

In the present study, three-dimensional thermal elastoplastic analysis has been carried out in order to clarify the mechanical phenomena of the thermal elastoplastic behaviour of multispot welded joints. As the shape of multispot welded joints is not axisymmetrical, unlike single spot welded joints, the solution domain for simulation should be three-dimensional. Therefore, the present study first developed three-dimensional heat conduction and thermal elastoplastic programs using the isoparametric finite element method. Second, from the results analysed by the developed programs, thermal and mechanical characteristics and their production mechanisms on single and multispot welded joints were clarified. Moreover, effects of pitch length on the temperature distribution, welding residual stresses and plastic strain of multispot welded joints were evaluated, indicating that a pitch of 30 mm was more advantageous compared to a pitch of 15 mm.     

Development of efficient numerical heat transfer model coupled with genetic algorithm based optimisation for prediction of process variables in GTA spot welding

Abstract

Although numerical heat transfer models based on conduction mode of heat transfer have become a strong basis for the quantitative analysis of fusion welding, they still find limited use in actual design for three primary reasons. First, these traditional models consider a volumetric heat source term, which ironically requires a-priori knowledge of the final weld pool dimensions. Second, the numerical models need confident values of a few parameters, e.g. arc efficiency and arc radius, which are usually uncertain and requires many trial and error simulations to realise their suitable values. Third, these models are rarely attempted for the prediction of possible weld conditions for a requisite or target weld dimensions, which is of paramount interest in design for welding. The present work attempts to circumvent these issues by linking a genetic algorithm (GA) based global optimisation scheme with a finite element based three-dimensional numerical heat transfer model. The numerical model includes a volumetric heat source that adapts itself to the computed weld pool geometry at any instant. The GA module identifies the optimum values of a set of uncertain parameters needed for the reliable modelling calculations and next, identifies the suitable values of the process variables, e.g. weld current, for a target weld dimension. In each case, the GA module guides the numerical model to compute weld dimensions for a given set of inputs, traces the sensitivity of the error in prediction on the inputs being optimised, updates them accordingly and reuses the numerical model to finally obtain their optimised values. The complete integrated model is validated with a number of experimental results in gas tungsten arc spot welding processes.