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Abstract

An event-driven control system controls movement of a base and carriage of a storage and retrieval machine. The control system is microprocessor-based and includes a motion controller, a machine control task, an input/output interface, an input/output task, and a microprocessor that executes the machine control task and the input/output task. In operation, a plurality of interrupts is issued to the machine control task in response to events which occur in an operating environment of the storage and retrieval machine. To respond to the interrupts, at least one subroutine in response to the reception of each interrupt. The execution of the subroutines controls movement of the base and the carriage of the storage and retrieval machine. Movement of the base and the carriage of the storage and retrieval machine (1) is substantially entirely controlled by issuing and responding to the interrupts as different events occur in the operating environment that cause the interrupts to be issued. As a result, the storage and retrieval machine is controlled in a manner which is substantially free of polling by the machine control task of the input/output interface and the motion controller for status information. Since the control system does not have to constantly monitor the status of input/output information from the input/output interface and the status of motion control information from the motion controller, the efficiency of the control system is greatly improved.

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First Claim