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Error Recovery Procedure for Magnetic Tape Transport Failure

IP.com Disclosure Number: IPCOM000083658D
Original Publication Date: 1975-Jul-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 5 page(s) / 80K

Publishing Venue

IBM

Related People

Cloud, SP: AUTHOR [+3]

Abstract

Shown is a flow chart for control flow in the control unit for a magnetic tape transport. The flow chart might most easily be implemented by use of a programmable logic array. The purpose of the diagrammed control procedure is to control a magnetic tape transport trying to recover from loss of air bearing pressure in the transport, loss of vacuum in the tape vacuum column of the transport, temporary power failure, or other failures in the electromechanical functions of the tape transport controlling the movement of the tape.

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Error Recovery Procedure for Magnetic Tape Transport Failure

Shown is a flow chart for control flow in the control unit for a magnetic tape transport. The flow chart might most easily be implemented by use of a programmable logic array. The purpose of the diagrammed control procedure is to control a magnetic tape transport trying to recover from loss of air bearing pressure in the transport, loss of vacuum in the tape vacuum column of the transport, temporary power failure, or other failures in the electromechanical functions of the tape transport controlling the movement of the tape.

In most of these failures the control unit will revert to a mode of starting to thread tape as if no tape were in the tape path. The first aspect of a start thread condition is to determine if tape threading appears to be normal, or some adverse condition has occurred. One adverse condition is loss of air bearing pressure to mandrel, which provides the air bearings for the tape as it moves along the tape path in the transport. The monitoring of mandrel pressure is in parallel with all other control functions, and thus is done continuously.

The continuous monitoring of air bearing pressure is represented by decision block 10, whose output loops backs upon itself as long as the air bearing pressure is always up. If the air bearing pressure drops, control passes from decision block 10 to decision block 12 to check if there is tape in the thread path. If there is no tape in the thread path (all tape is on the supply spool), control passes to process block 14. At block 14 the spool motor is set to backward spool speed, and the tachometer, which monitors motion of the spool motor, is reset to zero.

Decision block 16 monitors the tachometer count. When the tach count equals M, the control unit is assured that all of the tape is wound on the spool and control passes to process block 18. At process block 18, information is sent back to a central processing unit indicating that the unload is complete and that an error did occur. The unload complete finishes control by the control unit and control is now at the central processing unit.

When the tachometer counter is being monitored for the M count at decision block 16, a "no" condition passes control to the tape in thread path decision block
20. As long as there is no tape in thread path while the spool is rewinding the tape, control flow loops back to the decision block 16 checking for the M count in the tach counter. However, if tape should appear in the thread path while the spool is moving backward attempting to wind tape onto the spool, control passes to decision block 22. This event could occur if the spool had been moving forward pushing tape into the thread path, when the command to turn the spool backward at process block 14 occurred.

It is possible that the forward inertia of the spool could cause the leading edge of the tape to go past the tape in thread path sensor, before the spool motor became act...