AXIOMATIC DESIGN IN SOFTWARE DESIGN FOR SIX SIGMA (DFSS) - Software Design for Six-Sigma: A Roadmap for Excellence - page 337

A case study is presented in Hintersteiner and Nain, (2000) and is reproduced
here. In this study, axiom 1 was applied for hardware and software systems to
the design of a photolithography tool manufactured by SVG Lithography Systems,
Inc(Wilton, CT). The system uses one 6 degrees of freedom (DOF) robot to move
wafers between different wafer processing areas in a work cell as well as moving the
wafers into and out of the system. A second robot also is used in a similar fashion for
transporting reticles (i.e., wafer field masks). The example outlines the design of the
robot calibration routine for these robots. This routine is responsible for initializing
and calibrating the robot with respect to the discrete locations in each work cell.
Constraints imposed on the design of the robot calibration routine include the
use of a standard robot accessory (a teaching pendant with display, known as the
metacarpal-phalangeal [MCP] joint control pad) for the user interface, speed and
trajectory limitations, restrictions on robot motions at each discrete location in the
work cell, and implied constraints for minimizing the necessary time required to
calibrate the locations. Efforts were made early on in the design process to establish
and reconcile the functional requirements dictated by various departments, including
engineering, assembly, field servicing, and so on. For example, requirements from
engineering emerged from the design of the work cell itself, whereas field service
requirements focused more on ease of use and maintaining a short learning curve.
The top-level decomposition is shown in (13.4). The programs are the blocks of
code that perform the value-added functions of selecting the locations (DP1), moving
the robot between locations (DP2), calibrating the locations (DP3), and recording the
locations (DP4). The only interface defined here is the user interface (DP5), which
displays information gathered by and given to the user during different phases of
the calibration. The control logic is DP6. The support programs (DP7) constitute the
elements required to maintain the continuity thread between the various programs
and the control logic. These include global variables, continuous error recovery logic,
library functions, and so forth.
The corresponding design matrix, shown in (13.4) indicates that the robot cali-
bration routine is a decoupled design. The off-diagonal “X” terms indicate that, for
example, the locations to be calibrated must be established before the motion to the
locations and the calibration and recording routines for those locations are designed.
This has ramifications not only for how the programs interact, but also for the user
interface.
⎧
⎨
⎩

⎫
⎬
⎭

⎧
⎨
⎩

⎫
⎬
⎭

⎡
⎣

⎤
⎦

FR1: Select locations
FR2: Move robot
FR3: Calibrate location
FR4: Record location
FR5: Provide user interface
FR6: Control processes
FR7: Integrate and support

X000000
XX 00000
X 0 X 0000
XXXX 000
XXXXX 00
XXXXXX 0
XXXXXXX

DP1: Location selection list
DP2: Robot motion algorithm
DP3: Calibration algorithm
DP4: Record algorithm
DP5: MCP interface
DP6: Control logic diagram
DP7: Support programs

=

(13.4)
Similarities between the information exchanged with the user for each program
give rise to the creation of basic building blocks for developing the interface. Although
not shown here, the decomposition has been performed to the low-level design for