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Tachless Reel Assessment Test for Tape Drive

IP.com Disclosure Number: IPCOM000047472D
Original Publication Date: 1983-Nov-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 3 page(s) / 58K

Publishing Venue

IBM

Related People

Danielsen, KD: AUTHOR [+3]

Abstract

The rotational inertia of a reel of tape placed in a tape drive can be determined by using the voltage-current relationship of the motor that is used to rotate the reel. The rotational inertia of the reel needs to be determined such that proper current can be applied to the motors for further testing such as for interlayer slip of the layers of the tape on the reel and to provide the correct power to the motor on the initial threading operation as the tape is passed from the supply reel to the take-up reel mounted in the tape drive. Reel-to-reel tape drives have no mechanical buffering such as vacuum columns or dancer arms. The magnetic tape is passed directly between a supply reel and a take-up reel.

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Tachless Reel Assessment Test for Tape Drive

The rotational inertia of a reel of tape placed in a tape drive can be determined by using the voltage-current relationship of the motor that is used to rotate the reel. The rotational inertia of the reel needs to be determined such that proper current can be applied to the motors for further testing such as for interlayer slip of the layers of the tape on the reel and to provide the correct power to the motor on the initial threading operation as the tape is passed from the supply reel to the take-up reel mounted in the tape drive. Reel-to-reel tape drives have no mechanical buffering such as vacuum columns or dancer arms. The magnetic tape is passed directly between a supply reel and a take-up reel. The reel-to-reel servo system assumes that each reel of tape has a known rotational inertia and that the tape wound around each of the reels is at the correct tension. Thus the rotational inertia of the reel of tape must be known to provide a proper power to the motors driving the reels. The drive must discriminate between different reel sizes, that is, different amounts of tape wound onto the reels, and determine the tension conditions of the windings before a threading operation. Previously, a tachometer mounted on the supply reel motor supplied this information. To determine the rotational inertia of the reel of tape and thereby determine the length of the tape wound on the reel without external programming, an initial constant current or voltage pulse is applied to the motor, rotating the supply reel in the unwind direction. The differential voltage or current profile will vary according to the inertia of the reel. The inertia of the reels determines the length of the tape placed on the reels. The sequence for determining the inertia is shown in Fig. 1. In Fig. 1, the first step shown is that the reel is engaged to the clutch for rotating the reel. A timer is then loaded which supplies the power to the reel motor for a limited period of time. The next step shows that the power is applied in the forward direction to the motor to unwind the tape from the reel. This power is applied for a very short period of time as determined by the timer. After this time, the differential voltage profile is sensed if a constant current pulse is applied to the motor or the current profile is sensed if a constant voltage pulse is applied to the motor. The profile varies according to the inertia of the reel and the tape. This profile is then used to set a flag which determines the size of the reel an...