Patent GB-918551-A (GB)
Title: Electrostatic incremental drive
IPC: G11B15/20
Filed: 1959-12-31
Abstract: 918,551. Gearing for stopping and starting machinery; slip couplings. INTERNATIONAL BUSINESS MACHINES CORPORATION. Dec. 31, 1959 [Dec. 31, 1958 (3)], No. 44445/59. Class 80 (2). [Also in Groups XXXIV, XXXV, XXXVI and XL (c)] An electrostatic drive for magnetic tape recording apparatus has a driving shaft adapted for continuous rotation, a friction coupling between the driving shaft and associated rings being caused to slip when one or other of a number of brake bands is applied by a suitable potential to semi-conducting material carried by and encircling the rings, mechanical lostmotion means permitting a limited rotation of a member driving the tape after energization of a selected brake band. In one form, a driving shaft 11, Fig. 1, carries rigidly a hub 12, Fig. 2, within which are mounted friction shoes 20 of a conducting material, such as graphite, biased radially outwards by springs 19 to engage the inner peripheries of three rings 15 ... 17. Each of the rings carries a band 21 ... 23 of semi-conducting material, which may comprise a compound of natural or synthetic rubber, a filler such as asbestos, conductive particles such as carbon black and a phenolic resin. The ring 15 is integral with a sleeve 15c surrounded by and drivingly engaging the magnetic recording tape T. The slip coupling shoes 20 drive the rings 15.. 17 unless a potential is applied selectively to one or other of three spring steel bands 25 ... 27 surrounding the bands of semi-conducting material. The ring 15 is provided with an axial projection 15p engaging with slight lost motion in a recess 16b in the ring 16, and the latter has an axial projection 16p engaging with considerably greater lost motion in a similar recess in the ring 17. When two switches S, S1 are positioned as shown, the spring steel brake band 25 holds the ring 15 stationary. By moving the switch S to its second position, the potential is no longer applied to the brake band 25, which accordingly is released, but is instead applied to the brake band 26, which then holds the ring 16 stationary. The slip coupling and the shaft 11 are then able to drive the ring 15 a limited amount to take up the lost motion between the axial projection 15p and the recess 16b. The driven ring 15, and the tape T, then come to rest again. On restoring the switch S to the position shown, the potential is once more applied to the brake band 25, to hold the ring 15 stationary. By flipping the switch S back-and-forth, the tape T can be advanced step-by-step, information being fed thereon at each step. When the desired information has been fed on to the tape, a gap may be made before a further set of information is applied, by moving the switch S1 from the position shown to apply the brake band 27 and hold the ring 17 stationary. The relatively large amount of lost motion between the axial projection 16p on the ring 16 and the recess in the ring 17 allows the ring 15 to rotate a larger amount before it is again brought to rest. A mohair brush 33 cleans the surface of the semi-conducting material. In a modified form, a driving shaft 56, Fig. 4, carries a hub 53 provided with spring friction shoes 57 engaging the inside of a single driven sleeve 51 which directly drives the recording tape T and also carries a ring 52 of semi-conducting material. Two spring steel brake bands 53, 54 surrounding the semiconducting material are secured at one end by springs 61, 62 to a support 60, and at the other end by springs 63, 64 to the same support, lugs 65, 66 on the latter engaging with lost motion holes 53a, 54a in the brake bands. A potential is applied alternatively to the two brake bands 53, 54, application of a potential to, e.g. the brake band 54, causing the latter to grip the ring 52 of semi-conducting material, the rotating drive shaft 56 acting through the slip coupling comprised by the shoes 57 to turn the sleeve 51 and take with it the brake band until the spring 64 has been so extended that the bottom of the hole 54a engages the axial projection 66. During this process, the tape T is driven, until rotation of the sleeve 51 is arrested. A potential is then applied to the brake band 53, and the potential applied to the brake band 54 is switched off. Accordingly the latter is released. while the former brake band 53 is applied. As the slip coupling takes up drive, the brake band 53 is similarly turned until the bottom of its hole 53a engages the axial projection 65, so that the tape T is again moved a further step onwards. A mohair or similar brush 33a cleans the surface of the semi-conducting material. In the form shown, alternative energization of the two brake bands 53, 54 is effected by supplying positive pulses of current at 61<SP>1</SP> to a circuit containing two gas tubes 40<SP>1</SP>, 41<SP>1</SP> which are alternatively operative to supply current to opposite sides of a condenser 60<SP>1</SP>, clamping diodes 66<SP>1</SP> preventing excessive fall of potential of the tube anodes when discharging. The circuit through the clutch bands is completed to earth through a brush 13b. In a modification, Fig. 3 (not shown), energization of the brake bands is effected through manual operation of a switch. In another modification, a driving shaft 111, Fig. 5, drives through slipping friction shoes 119 to rings 115 ... 118, of which the latter drives the tape T and lies between the two rings 116, 117 which are alternatively held by single actuation of a switch S, thereby permitting immediate stepping forward of the tape for each single movement of the switch. In a further modification of this construction, Figs. 6, 7 (not shown), both ends of the brake bands are secured to the support by springs, but a reversible locking device is provided for securing one end or other of each band rigidly in place. In this form, the shaft 111 is driven in either direction through a reversible electric motor, a two-speed gear providing for rapid drive of the shaft 111 when it is desired to re-wind the tape. The control lever of the two-speed gear and a switch S1 are interconnected for simultaneous operation. The tape T is held against the ring 117 by a pair of spring-biased rollers.