Tham khảo tài liệu 'business process improvement_5', kỹ thuật - công nghệ, điện - điện tử phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | . Central Composite Designs CCD Comparison of the 3 central composite designs The diagrams in Figure illustrate the three types of central composite designs for two factors. Note that the CCC explores the largest process space and the CCI explores the smallest process space. Both the CCC and CCI are rotatable designs but the CCF is not. In the CCC design the design points describe a circle circumscribed about the factorial square. For three factors the CCC design points describe a sphere around the factorial cube. Determining Ct in Central Composite Designs The value of is chosen to maintain rotatability To maintain rotatability the value of Ct depends on the number of experimental runs in the factorial portion of the central composite design a number of factorial runs If the factorial is a full factorial then a 21 However the factorial portion can also be a fractional factorial design of resolution V. Table illustrates some typical values of Ct as a function of the number of factors. Values of Ct depending on the number of factors in the factorial part of the design TABLE Determining Ct for Rotatability Number of Factorial Scaled Value for Ct Factors Portion Relative to 1 2 22 22 4 3 23 23 4 4 24 24 4 5 25-1 24 4 5 25 25 4 6 26-1 25 4 6 26 26 4 http div898 handbook pri section3 4 of 5 5 1 2006 10 30 40 AM . Central Composite Designs CCD Orthogonal blocking The value of Cm also depends on whether or not the design is orthogonally blocked. That is the question is whether or not the design is divided into blocks such that the block effects do not affect the estimates of the coefficients in the 2nd order model. Example of both rotatability and orthogonal blocking for two factors Under some circumstances the value of 1 allows simultaneous rotatability and orthogonality. One such example for k 2 is shown below BLOCK X1 X2 1 -1 -1 1 1 -1 1 -1 1 1 1 1 1 0 0 1 0 0 2 .
