Factory Explorer® v2.4 Technical Alert #21
Throughput Rates and Release Patterns
Summary: Factory Explorer®'s capacity analysis engine is unable to manipulate release rates to meet specified throughput rates when a product specifies a set of release patterns with an overall release rate of zero, and will halt with an internal error. To avoid this problem, do not specify a release pattern where the number of lots per release is always zero. Factory Explorer® v2.5 beta 3 includes a model validation check for this condition.
Details: In a model that specifies throughput rates, Factory Explorer® must perform the capacity analysis calculations twice. First it forces a small but non-zero flow on all release products, and performs the analysis to calculate overall line yields. It then uses line yield information to back-calculate appropriate release rates, and then performs the analysis again with these new release rates. To force non-zero flow on all release products, it manipulates each product's release patterns (if specified) or generates a dummy set of release patterns if none are specified. The manipulation of release patterns involves calculating the release rate for the current set of release patterns, and then multiplying by a ratio to reach the desired release rate. This multiplication cannot work if the current set of release patterns has an overall release rate of zero. An overall release pattern rate of zero can only occur if the number of lots per release is specified as a constant of zero. The current release of Factory Explorer® halts with an internal error at this point, because it cannot perform the release rate manipulation. The error message is "Assertion Failed: old_unit_rate != 0.0, File: C:\fx\PRODUCT.C, Line: 3090". Factory Explorer® v2.5 beta 3 includes a model validation check for this condition, and points out the offending product.
Workaround: To avoid this problem, do not specify release patterns with the number of lots per release set to a constant of zero. If you wish to have a release rate of zero, simply do not specify any release patterns.