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114 Yung-Chieh Hung and Yeh-Liang HsuFig. 5 Functional model for US Patent 6,918,449between the elements of the core techniques.Figure 5 shows the functional model of US Patent69,18,449. A rectangle in Fig. 5 represents a ‘systemcomponent’, which is the basic element constitutinga system or a product. A hexagon represents a ‘supersystem’, which is an essential factor that will influencecomponents of the system. An ellipse representsa ‘target’, which is the acceptor of the majorfunction in the engineering system. A solid linerepresents relational actions linking the variouscomponents.In the original design, the motor, the driveshaft,the output shaft, the magnetic hammer, and themagnetic anvil are the five important system componentsfor generating impact torque, which is themajor function (or primary useful function) of themagnetic impact tool. The output shaft is also necessaryto tighten or loosen screws. The other twocomponents, the magnetic bypass device and thechanging device, are the auxiliary elements toprovide the function of adjusting the value of impacttorque.3.2 Apply the approaches of design-aroundReferring to Fig. 1, there are two possible designaroundapproaches. In this section, the approach of‘eliminating one or more elements of a claimedsystem’ is used.As discussed earlier, the application of the conceptof ‘ideality’ in TRIZ can reduce the number ofelements in the system to lower product cost andenhance product benefits. Commercial softwareTechOptimizer 4.0 from Invention Machine Corporation[7] was used to ‘trim’ the original functionmodel and generate a new design concept to achievethe goal of ideality.Trimming is a method for improving systemsbased upon the elimination of components that areproblematic, costly, or unessential in the system. Inthis research, after value analysis on the functionalmodel for US Patent 6,918,449, the changing devicewas chosen to be eliminated. Without the changingdevice, the bypass device cannot work by itself andshould also be eliminated. The simplified functionalmodel is shown in Fig. 6. The dotted squares anddotted lines are the components and the relationalactions to be trimmed respectively. In addition,some relational actions from the original designmay be eliminated or transferred as a result of reconfiguringthe system.3.3 Formulate the new design problemWithout the changing device and the bypass device,the impact torque cannot be adjusted and the wholefunction of the magnetic impact tool deteriorates.Therefore, the useful functions of the eliminatedcomponents have to be redistributed. As shown inFig. 6, the function ‘change magnetic flux’ originallyprovided by the changing device and the bypassdevice will be provided by the magnetic anvil. TwoProc. IMechE Vol. 221 Part B: J. Engineering Manufacture JEM667 Ó IMechE 2007