A Study on Computer Aided Optimization Design for the Frame Form Generation of Electric Bicycle

Transcription

1 A Study on Computer Aided Optimization Design for the Frame Form Generation of Electric Bicycle Chih-Fu Wu*, Chun-Yin Wu**, Mu-Lin Lu***,Yu-Mao Lin*** * Tatung University Graduate School of Industrial Design Prof. TAIWAN, wcf@ttu.edu.tw ** Tatung University Graduate School of Mechanical Engineering Prof. TAIWAN, cywu@me.ttu.edu.tw *** Tatung University Graduate School of Industrial Design Graduate Student TAIWAN, g @mail.ttu.edu.tw Abstract: Although the design of an electric bicycle has its demands and advantages among other types of bicycles, it is not popular in the consumer market. The reason could be that the forms of the bicycle designs are not compatible with their revealed values. When designing a bicycle frame, the concepts development process of designers are often limited by the production process, such as the analysis of Ergonomic and the traditional frame form. It is difficult to break through the limitation of the existing bicycle frame forms. The purpose of this study explores the possible variations of frame design of city bicycles. First, the edge boundaries were decided by using the results generated from Ergonomic measurements including weight, pressure, riding posture, and the arrangement of components, such as batteries and motor. After that, the technique of Topology Optimization Design (TOD) including Optimization algorithm, Structural analysis tool, and Topology optimization method was used to help reconstruct the frame forms. Eight different types of representative frame forms were generated based on cluster analysis. After that, these 8 frame forms were mixed together with existing 22 frame forms for another cluster analysis. The result revealed that these 8 frame forms were related to existing frame category and made their own group. Based on the results, the authors demonstrated that it is possible for designers to use computers to facilitate their design work. Furthermore, under the production restriction, the computer still can help stimulate a design s design concepts. Key words: Electric bicycle, Topology Optimization Design, Optimization Algorithm, Topology Optimization Method, Cluster Analysis 1. Introduction Because the blossom of exercising is in vogue nowadays, it is investigated that bicycle is the most popular exercising product. An estimation shows that there are about one billion bicycles in the world, and there are about ninety to one hundred million new bicycles enter the market each year. According to the investigation by Yang [1] et al., the bicycle designers place importance on the place of the battery most, and then the motor, frame form is the last one that designers are concern about. They also cluster frames in exist to investigate the influence of the frame form on image perception. And Wang [2] et al. use Bezier to construct frame forms and then investigate the image perception. Therefore we can see that designers still like to use the frame form in exist to design bicycles.

2 John Chris Jones, 1992[3] bought up that designers were limited by their ideas in mind in concept development process. This study will use CAE to help designers when develop the concepts, in case of the lose of thinking point, and stimulate a design s design concepts. The method also can be used in the field of product design in which needs to concentrate on structure intensity. 2. The Factor of Affecting Frame Form Yang [1] put bicycles into seven kind of groups: mount bike, sport bike, city bike, lady bike, children bike, and folding bike. But not every kind of bicycles can be used for being electric bicycles, as the fig.1 shows, nowadays electric bicycles are designed as the kinds of mount bike, city bike, lady bike, and folding bike. Taiwan Bicycle Industry R&D Center[5] classifies bicycles, and finds out that the frame form of city bike has more different form designs. So we chose city bike to be the research object. The city bike s property is between mount bike and lady bike. The difference is the design of the angle of seat tube and head tube, we can see the handlebar are all straight type, so the reason to affect the posture of riders is the angle of seat tube and head tube. 2.1 Riding Posture Craig [5] has proved that if the body of the bicycle rider tilt forward 15 o can increase 4% vital capacity. It is because tilt forward can remove the weight of the body from chest. Wu [6] et al. used motion system to measure and found that when the frames sizes are different, the riders change their posture a lot, and their body s tilt angle also change a lot. Therefore when riding a bicycle, the human body s posture are related to the sport efficacy of lower limbs. The riding posture will affect the spread of frame loading force. We use motion analysis system to measure the rider s tilt body when they ride city bike, the arms and handlebar s horizontal angle is 46 degree, the body and the seat cushion s horizontal angle is 56 degree. 2.2 The Place of the Loading Force on Frame Edmund R. Burke [7] found that there are five points contact with bicycle when riding a bicycle. These points are two hands, buttocks, and two feet s, as we can see in fig Stepping Force Hontz [8] use EMG to analyze the EMG of the lower lumps muscle, and found out that the motion of stepping on pedal is in order. Groot[9] et al. found that the angle of the seat post has no influence on exerting pressure upon pedal. Cal stone and M. L. Hullt [10] s research that when riding a bicycle at the speed of 10.2km/h and at the stepping 97rpm, the force and torque of step are measured as 475N and 50N at the Z axis and X axis. 3. Structure Optimization Design Structure Optimization Design can develop product form. In this field, it includes Size Optimization Design, Form Optimization Design, and Topology Optimization Design. The tech of Size Optimization Design and Form Optimization Design have been developed leaving out nothing required; however, the traditional Size Optimization Design and Form Optimization Design need to dependent on designer s experiment to give structure s initial form, and the initial form will get different local optimal answer. After Bendsφe Kikuchi [11] brought up that the idea of getting optimal material(optimal material distribution, OMD ), Structure Optimization Design has stride forward to the field of Topology Optimization Design.

3 Therefore Topology Optimization Design help to improve traditional design, and it includes three modules: Optimization algorithm, Structural analysis tool, and Topology optimization method. 3.1 Optimization Algorithm There are several kinds of Optimization method nowadays. John Holland brought out Genetic Algorithm, and its general idea is like gene in chromosome. Through choosing fitness value randomly to decide appropriate parent, then the parent through the process of reproduction, cossover, and mutation to obtain the better next generation. The parent and next generation mean different arrangement of gene, and after several times of operations, we can switch the arrangement into structure design field to decide the optimal distribution of material. 3.2 Topology Optimization Method Hrennikoff [12] first brought out Finite Element Method which is used to calculate the displacements of each node and the value of stresses of each element in the structure to check the design requirement of allowable displacement or stress. 4. Experiment Method This study first use Topology Optimization to obtain frame forms, and then analyze these frames by using cluster analysis. This step is to prove the structure intensity. After that, do another cluster analysis by mixing the Topology Optimization frames and the city bike frames in exist. 4.1 Defining the Limitation of the Topology Optimization First, define the general city bicycle form, and the material is set as AL6061-T6. This study define the rider s weight to be 980N; the loading of the seat post is %(the proportion of the arm and weight)and then decompose it to horizontal and vertical force; the loading of the head tube is % and also decompose it to horizontal and vertical force, therefore, we define it to be 1960N. (40,83) (620,83) (0,0) Fx=-69.2N Fy=-1960N Fy=-406N Fx=274N (439,-405) (847,-276) Fx=-200N Fig.2 The Initial Design Range Coordinates Fig.3 The Place of the Head Tube, Seat Tube, Chainwheel & Cranksand and Their Loading Force 4.2 Resulting the Topology Optimization Bicycle Frame Form After defining the limitation of the initial design range and loading condition, we execute the Topology Optimization program. This program result about three hundred frame forms. It is because this study will pay attention to the out figure, we invite four subjects who have design background to delete the similar frames and reserve thirty frames. Next we investigate ten subjects, about 24 years old, six males and four females. These ten subjects were requested to see thirty kinds of frames which are shows as gray color on pictures which size are 8cm*6cm. The frame form shows by the Topology Optimization is composed by rectangle elements, so it still need to be embellished. When embellishing the frame form, we need to notice the frame structure element s color. Red indicates the place where the stress is the largest, then is purple, blue shows the finite element which

4 has normal stress. Therefore we can embellish the frame form by the picture resulted from Topology Optimization program. Then follow up the ANSYS to analysis the frames static structures, we use the same structure edge boundaries definitions to observe if the result can fit the intensity design. 4.3 Comparing the Topology Optimization Frame and the City Bicycle Frame in Exist After the stage of the first experiment, we use cluster analysis to sift the representative frames, and mix with the city bicycle frames in exist to do another cluster analysis. We investigate ten subjects, about 26 years old, six males and four females who don t have design background. The subjects compare the similarity by looking at the frame pictures which the size is 8cm*6cm show as gray color. They degree of similarity is 0-10 points, 10 is the most similar one and 0 is not. 5. Result The frame forms composed by rectangle elements were show to the subjects to test the similarity, and then do cluster analysis to group the frames into nine groups. After that, we chose the representative frame for each group, and proceeded the next experiment. Before ANSYS, we analysis the structure by using the same material and edge boundaries. The result shows that this structure s stress (Von Fig.4 Graph of Frame Cluster Analysis Mises) is on the center of chainwheel, the value is N/mm 2, this structure s largest stress is 1013N/mm 2. After cluster analysis, we group the frames into eight groups, and chose the representative frames for each group. Then collect twenty-one frames in exist together with nine Topology Optimization frames. There are thirty frames altogether to do another similarity experiment. In this experiment result, the number 2,21, and 30 frames (Topology Optimization frames)were together with number 22 frame(the frame in exist)which can show that the frame produced by Topology Optimization can be the real frame form. However, in the seventh group, all the frames are produced by Topology Optimization, and the frame form is like mount bicycle, and the eighth group is isolated group. 6. Discussion and Conclusion The seven groups were obtained by Topology Optimization and is an isolated group. The eighth group is also isolated, therefore, the frames in the Fig.5 Pictures we show to the subjects. The left blue rows are representative frames which were produced by Topology Optimization, the gray two rows show the frames which were embellished. Fig.6 The right picture shows the Von Mises, and the left one shows the meshed module

5 seventh and eighth group are not similar. So we can know the Topology Optimization truly can produce new structures, and this result shows the Topology Optimization Design can help stimulate a design s design concepts. This study shows the Topology Optimization program, and it can help designers to develop the concepts, and produce the structure that designers can t think about. The frames produced by the Topology Optimization need to be given initial design range and edge boundaries to construct the Fig.6 The Frame Cluster Analysis Graph(Eight Groups) structures which can be used in reality. And this study also shows the rationality that we can use Topology Optimization on other product design development. Fig.7 The Eighth Group is Isolated Group Fig.8 The Fourth Group Shows the Topology Optimization Frames Were Similar with the Frame in Exist 7. Acknowledge The authors would like to thank the National Science Council of R.O.C for her financial support under contract number NSC E References 1. Li-Hui Yang,A Study on Electric Bicycle Form Image Perception,Tatung University Graduate School of Industrial Design,P41-43(2003) 2. Chung-Hsin Wang,A Study on the Influence of the Features of a Bicycle's Frame Form on the Image perception, National Cheng Kung University Graduate School of Industrial Design,pp18-36(2003) 3. John Chris Jones,Design Method,Taiwan,Lu Her(1970) 4. Hsin-Fu Hwang,A Study on the Deisgn Tendency of Bicycle Form in 1999,Taiwan Bicycle & Healthy Technology R&D Center,pp15-25(2001) 5. Craig Jr. A. B., Effects of Position on Expiratory Reserve Volume of the Lungs, Applied Physiology 15, pp (1990). 6. Shih-Chang Chen,,A Study on Saddle Design for Various Types of Bicycles Based on the Seat Pressure of People with Different Anthropometric Characteristics,Tatung Graduate School of Industrial Design,p30-35 (2001)

6 7. Edmund R. Burke, High-Tech Cycling, Human Kinetic, Houtz S. J. and Fisher F. J., An Anlysis of Muscle action and joint Excurison on a stationary bicycle, J. Bone Jt. Surg, Vol. 41A, pp (1959) 9. G. De Groot, E. Welbergen, L. Clijsen, J. Clarijs, J. Cabri, and J. Antonis, Power, muscular work, and external forces in cycling, Ergonomics, Vol. 37, No. 1, pp (1994) 10. Cal stone and M. L. Hull, The effect of rider weight on rider-induced load during common cycling situation, Journal of Biomechanics, vol.28, No. 4, pp (1995) 11. Bende, M. P. and Kikuchi, N., Generating Optimal Topologies in Structural Design Using a Homogenization Method, Computer Methods in Applied Mechanics and Engineering, 71,pp (1988) 12. Hrennikoff, A., Solution of Problems in Elasticity by the Frame Work Method, Journal of Aeronautical Sciences, Vol. 23, No. 9, pp (Dec.1941) 13. Andreas Rietz, A first laboratory exercise in topology optimization using matlab, Sweden(2000) 1. Pan, Jiung-Cheng,Topology Optimization of the Mountain Bike Frame with Full Suspension,National Taiwan University Graduate School of Mechanical Engineering, pp (1984)