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12 Cha p te r F o u r
Manufacturer’s robot cell
11
control software installed
10
Manufacturer’s cell control
software installed
9
8
7
Formal recording
6 of faults started
5
4
3
2
1
0
Jan <–> July AugSept Oct Oct Nov Dec Jan Feb Mar Apr May June
Mechanical Failure Software Failure
1989
FIGURE 4.4 Frequency of software faults.
• Wrong number of hardware units
• Wrong procedures for writing data to hardware
Restriction faults:
• Omission of procedures to prevent invalid input or output of
data
• Wrong limit value for validity check of arguments
Function faults:
• Omission of saving data to global variables
• Unnecessary calling modules
• Wrong limit value for judging whether or not hardware is set
• Reference to undefined local variables
• Omission of loop variable incrementation
• Logic expressions that are always true
