US Patent 6,775,588
Fault
Tolerance
in
FastFetch
Many companies classify their picking operation as "mission
critical", meaning that if the system fails they can't ship
products, and if they can't ship products, their business might
experience significant losses or fail. During the design of
the FastFetch system the team continually asked the question, "What
will our fall back process be if this system component fails?".
The following paragraphs discuss how these questions were answered
with FastFetch's tolerance to failure with its
"
design.
Failure of a Light Module
The controller on a bay (and on a cart) continually all light modules connected to the controller, even during periods when no picking is occurring. If a light module fails, the controller or transceiver connected to the light module will not receive a response when polling and will store an error message in non-volatile memory until a PDA or Tabet PC next communicates with the controller or transceiver. One of the first messages sent from the controller or transceiver to the PDA or Tablet PC when it arrives will be the error message reporting the light module failure. After receiving the error message the PDA or Tablet PC will report the failure to the Optimizer PC that will in turn notify all other PDAs or Tablet PCs on carts to avoid using that light module and notify a maintenance person (via email, text message or report) so repairs can be initiated. If picking (or putting if on the cart) is required from the location adjacent to the failed light module, the PDA or Tablet PC will automatically command the picker to retreve (or put) products using voice commands and bar code scanning, just as if the location had no light module. This procedure ensures a "fail soft" response to light module failure. Once the light module has been replaced and the new light module tested, the maintenance person's PDA or Tabet PC will notify the Optimizer PC that the light module is now back in service so all PDAS or Tablet PCs on carts can begin using the light module for subsequent picking.
Failure of a Cart Transceiver
When the PDA or Tablet PC first begins to run the FastFetch application, it first polls the cart transceiver to determine the its status. If the PDA or Tablet PC receives no response after several polls, it assumes the transceiver is not connected or has failed, reports the problem to the picker with a voice message and sends an error message to the Optimizer PC for maintenance notification and reporting. The PDA or Tablet PC will then automatically revert to a non-lighted picking mode, and rather than requiring the picker to touch a flashing LED on the light module when placing items onto the cart, the PDA or Tablet PC will use voice commands and require the picker to scan a cart location bar code. If the cart transceiver fails during picking the PDA or Tablet PC detects the problem in a similar way and takes the same "fail soft" action.
Failure of a Bay Controller
If the picker arrives at a bay and the PDA or Tablet PC doesn't say "STOP", the picker can safely assume the bay controller has failed. In this case, the picker pushes a button labeled "Pick Bay Manually" on the PDA or Tabet PC display to request bar code scanned picking at the bay. The PDA or Tablet PC will then report the failure to the Optimizer PC that will in turn notify all other PDAs or Tablet PC on carts to avoid using that light module and notify a maintenance person (via email, text message or report) so repairs can be initiated. The "Pick Bay Manually" request forces the operator to pick all required items from the bay using voice commands and bar code scanning - in the same way as any bay location without a light module. Consequently, FastFetch employs a "fail soft" solution to bay controller problems.