This paper proposes an improved evolutionary algorithm with parallel evaluation strategy (EAPES) for solving constrained multi-objective optimization problems (CMOPs) efficiently. EAPES stores feasible solutions and infeasible solution separately in different populations, and evaluates infeasible solutions in an unusual manner, such that not only feasible solutions but also useful infeasible solutions will be used as parents to reproduce the populations for the next generation. The EAPES proposed in this paper ranks infeasible solutions based on the scalarizing function named constrained penalty-based boundary intersection (C-PBI), which is determined by objective function values and a total constraint violation value. Then, this paper investigates the performance of the C-PBI-based EAPES to search for Pareto-optimal solutions compared to the non-dominated sorting genetic algorithm II (NSGA-II) and the previous EAPES without using C-PBI. The C-PBI-based EAPES with a well-tuned parameter is most capable to explore Pareto-optimal solutions with good diversity, spread, and convergence to the true Pareto front. The C-PBI-based EAPES assigns bad rank to the infeasible solutions that are expected away from an unknown Pareto front, and does not store such solutions. Thus the C-PBI-based EAPES exhibits a higher searching capability than the previous EAPES by evaluating infeasible solutions in an appropriate balance between objective functions and total constraint violation.
Nonlinear friction is the main stabilization error source of missile’s seeker. In this paper, the frictional torque of a gimbaled-mirror seeker under changing environment temperature is analyzed. The torque is consisted of rolling friction due to elastic hysteresis, sliding friction due to pivoting and friction torque due to lubricant viscosity. Based on the theory of thermo-elasticity, axial and radial coupling thermal deformation between precision bearing and its installation structure are both included in the analysis model. Coupling deformation dramatically changes the actual contact angle and axial force of bearing, which consequently change the value of frictional torque. Temperature effect on viscosity of lubricant is also studied and improved Walther Equation is used to fit the viscosity- temperature relationship of lubricant. A measure system based on electrical measure method was established and temperature test chamber was used to simulate the temperature changing. Experiment results have shown that this model is accurate for friction torque calculation of gimbaled seeker under changing environment temperature.
An attempt of experiment / simulation integrated design optimization is performed for the blade airfoil shape of a vertical axis wind turbine. A variable fidelity Kriging surrogate model approach is utilized in this integrated design optimization, in which a surrogate model is constructed from both high-fidelity and low-fidelity sample points information. In this research, the high and low fidelity performance functions are respectively defined from experimental and numerical evaluation methods. In the numerical evaluation method, 2D steady computational fluid dynamics (CFD) simulations are performed for the evaluation of an airfoil shape. An optimal airfoil shape is explored on the accurate variable fidelity surrogate model which is constructed in 9 design variables space representing various blade airfoil shapes. The validity and effectiveness of the present integrated design optimization are discussed by comparing with another approximate optimal airfoil shape which is obtained only by CFD computations. The optimal design obtained by the developed approach showed 8% larger performance value in the experimental evaluation compared with the approximate optimal design. More efficient shape optimization can be realized by including the low-fidelity information, whose functional trends are utilized to construct accurate surrogate models.
Computer-Aided Process Planning (CAPP) systems have become essential in manufacturing environments to integrate the information between CAD and CAM systems, and to automatically generate the NC code from the CAD model. Though the future of these systems seems to belong to the use of Artificial Intelligence to create knowledge-based algorithms which emulate human decisions, the CAPP systems based on feature recognition and model matching, which use databases of previously known mechanical components to generate new process plans, are also a very interesting option due to their accuracy and smaller development costs. Many researchers have proposed different kind of feature recognition algorithms before. However, these algorithms are usually application-dependent and require external codes to identify the features of wireframe models. This paper proposes a new methodology for shape recognition and model matching stages which improves the accuracy of the recognition tasks, uses solid models instead of wireframe models and can be successfully applied to any kind of part. The methodology is based on an original coding system that links the geometric information extracted from the CAD model with the features of the part by means of an identification sequence which is detailed in the text. Also, a score system has been created for the model matching stage. The obtained results show that the system presents high accuracy in shape recognition, feature identification and model matching tasks, even when the analyzed part is similar to the ones in the database. In addition, quantitative geometric data is also extracted from the CAD model on behalf of future steps of the CAPP system, such as the NC code generation stage. In contrast to other systems, this methodology can be easily applied to the industry since it makes use of the CAD model only.
Considering that humans perform handwriting task with reduced powers by contacting elbow or wrist on a table, it is reasonable to deem that manipulators can save energy and simultaneously accomplish writing tasks precisely like humans by bracing intermediate links such as elbow or wrist. First this paper discusses equation of motion of robot under bracing constraint condition, based on the robot's dynamics with constraint condition including motor dynamics. Then a control method to utilize the constraint dynamics is proposed to control simultaneously bracing force and hand's trajectory in work space. Even though the model used for the simulation analyses is simple four-links manipulator, the simple structure can help understand even more clearly the effects got by bracing part of the manipulator. This paper demonstrates the merits of the strategy to utilize bracing by comparing the contacting motions with non-contacting motions, including ; (1) the energy consumption can be reduced; (2) the hand trajectory tracking becomes accurate; (3) there is an optimum contacting point that minimize the energy consumption on condition that trajectory-tracking task be given to the hand.
This paper will describe and simulate the dynamic response of an innovative suspension system for vehicle seat. In which, the isolated object is supported by a wedge mechanism which comprises a horizontal spring, a roller and a wedge. Besides, the dynamic stiffness of system is corrected by an auxiliary mechanism (AM) including a roller (follower) which always contacts the circular surface of the cam via another horizontal spring. Hence, this seat suspension prototype not only broad the excitation frequency region but also remains the load bearing capacity and is named by “model with AM”. The dynamic stiffness-configurative parameter relationship is presented. Then, a virtual mechanical prototyping model of the system is created by using SOLIDWORKS software. Next, by applying dynamic analysis in COSMOSMotion module of the Solidworks product family, the real behaviour of system is tested and evaluated without using the traditional build-and-test method. With this way, it can increase the quality of product by reducing manufacturing cost and error. The simulation results show that the model with AM outperforms the linear counterpart. Besides, these results furnish a useful insight for the design and manufacture of the seat suspension system for vehicle.
In this study, the cognitive load that occurs in assembly works requiring human-robot collaboration is investigated. It is aimed to detect the effects of the workplaces designed with the approach of extended cognition on cognitive load and gender differences in cognitive load. Two workplace designs were used to investigate the task load that occurs in human-robot collaboration works and the effect of extended cognition on cognitive load. In both designs there was a sedentary workplace and same assembly work which requires human-robot collaboration. Differently, for the experimental group, the manual drawing was integrated to work table to detect the effect of extended cognition. For both groups task load is measured by using NASA-TLX (Task Load Index) method. Experimental results showed that the design with the extended cognition concept helps to reduce mental task load for male participants which is an important issue for yield, work safety, and quality in human-robot collaboration works. Experimental results also showed that there are no significant differences in cognitive load between genders. Unlike other studies, in this paper, human-robot cooperative works are examined according to gender difference with a point of extended cognition. The importance of the workplace design for human-robot interaction is presented.
The goal of this study is to investigate the effect of actuator position on the theoretical energy consumption of an electrically powered bipedal robot. Specifically, the study focuses on the legs of the afore-mentioned robot because their function is limited, as they are primarily used for either locomotion or standing, and thus, this is suitable for optimization. Furthermore, the hip and knee joints constitute the most powerful joints, and thus, these are studied first. A mathematical formulation is adopted to represent the relationship between the actuators and the robots joints. A genetic optimization is used to minimize the energy loss due to motor winding resistance and no-load torque by altering the position of the actuator with respect to the joints. The results indicate that the energy lost during typical motions can be reduced by up to 30% by using bi-articular actuation. Additionally, most benefits can be realized by adding only a bi-articular actuator between the hip roll and knee pitch axes.
A bolter miner is a new type of mining machinery with cutting and anchoring functions. Owing to its structural diversity, the cutting head performance of a bolter miner varies. However, there is still no effective method to evaluate the cutting head performance. Based on multi-aspect factors influencing the cutting head performance, the main factors such as the load fluctuation coefficient, mean torque, and specific energy were taken into account. Combined with the characteristics of multi-criteria decision-making approaches and the superiority of game theory in calculating the weight of the cutting performance indexes, an evaluation method based on the game-theory-extenics model is proposed. In addition, by combining the geological conditions of a particular coalmine, three pick layout schemes for the cutting head are compared, the final one of which was chosen through a performance evaluation. The results were successfully applied to the first shield bolter miner in China, and good results were obtained for engineering application.