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Power Amplifier Providing Low Power Dissipation in a Variable Speed Reel to Reel Tape Transport

IP.com Disclosure Number: IPCOM000080621D
Original Publication Date: 1974-Jan-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 3 page(s) / 51K

Publishing Venue

IBM

Related People

Buhler, OR: AUTHOR

Abstract

This power amplifier selectively energizes a motor from either a T or an H transistor network, as a function of the motor voltage, to thereby optimize motor performance and power dissipation. This power amplifier finds particular utility when used to energize the direct-current reel motors of the reel-to-reel magnetic tape unit shown in Fig. 1.

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Power Amplifier Providing Low Power Dissipation in a Variable Speed Reel to Reel Tape Transport

This power amplifier selectively energizes a motor from either a T or an H transistor network, as a function of the motor voltage, to thereby optimize motor performance and power dissipation. This power amplifier finds particular utility when used to energize the direct-current reel motors of the reel-to-reel magnetic tape unit shown in Fig. 1.

The effective diameter of reels 10 and 11 varies in an inverse fashion as the tape leaves one reel and accumulates on the other. A taut length of tape 12 extends between the reels as it passes over two air bearings or rollers 13 and through tape processing station 14. Each of the reels is connected to a DC motor 15 and 16. The tape extending between the two reels is maintained under constant tension by a motor energization network, not shown. Generally, this network controls the relative magnitudes of the motor armature currents. For example, a constant-current difference is maintained, including, if desired, correction for the changing reel radius.

Motor speed, and thus tape speed, is controlled by two substantially identical servo networks 17, one of which is shown in Fig. 2.

Motor armature 18 is connected to be reversibly energized by H network transistors 19-22 or by T network transistors 19 and 21. When the armature is connected to the H network, the maximum possible armature voltage is approximately 2Vcc and a high tape speed such as 240 inches per second (ips) can be achieved. In this mode of operation the system power dissipation is equal to 2VccI, where I is the motor current. When the armature is connected to the T network, the maximum possible armature voltage is Vcc and a low tape speed of 2 ips can be achieved. In this mode of operation the system power dissipation is equal to VccI.

Input terminals 23 and 24 selectively receive tape motion command voltages, as shown, in order to provide forward (FWD), backward (BKWD), low or high- speed tape movement.

With zero input to terminals 23 and 24, transistors 19 and 21 are controlled by driver 25 such that the voltage level at each of the two armature terminals is approximately zero. Thus, the motor is deenergized.

So long as the voltage across the motor...