Error recovery in a cartridge handling system

Abstract

Disclosed is an optical disk handling system, called an autochanger, having two control systems to provide the six motions necessary to move optical disk cartridges from storage holding cells to an optical drive. Whenever the mechanisms are being moved, the control systems monitor the progress of the movement, and should the control system detect an error conditon, a state update flag is changed to prevent further updates of the state of the system. With state updates disabled, the control system will stop all mechanisms and prevent further movement of the mechanisms. When the operation appears complete, an error recovery software function is called. When the error recovery software detects that the state update flag is in an error condition, error recovery is initiated. After the mechanism's state has been established, error recovery movement is started, based on the operation that was being performed at the time of the error, and the state of the machine at the time of the error. The type operation being performed is saved in non-volatile memory, so that the type of operation will be saved should electrical power fail during the operation. Therefore, after power is restored, power fail error recovery can perform error recovery based on the type of operation being attempted at the time power was lost.