Patent GB-626721-A (GB)
Title: Improvements in and relating to tension control systems
IPC: G11B15/43
Filed: 1946-10-30
Abstract: 626,721. Winding wire &c. BRITISH-THOMSON-HOUSTON CO., Ltd. Oct. 30, 1946, No. 32270. Convention date, Oct. 30, 1945. [Class 120 (ii)] [Also in Groups XVI and XXXVIII] In a recording and reproducing apparatus in which a magnetic strip 1 is driven by a constant speed pulley 6 between reels 2, 3, spring-loaded dancer pulleys 7, 8 are provided between each reel 2, 3 and the driving pulley 6, whereby the tension in the strip 1 each side of the driving pulley 6 varies the ratios of friction-gears, coupling a shaft 18 carrying the driving pulley 6 to the shafts 28, 29 carrying the reels 2. 3 respectively: The shaft 18 is driven by a reversible motor 13 via friction-gearwheels 16, 17 and. is coupled by a belt drive to a layshaft 22 carrying a friction-disc 23, which is coupled to reel 2 by a floating friction-gearing 24, friction-disc 26 and shaft 28, and to reel 3 by a similar gearing 25, disc 27 and shaft 29. The friction-gearing 24 is supported by links 42, 43 and the gearing 25 by links 40, 41. The lower ends of links 41, 43 are connected to a bar 53 which is movable, within limits imposed by arcuate slots 49, 50, by means of a lever 55 under the. control of a knob 12. The lower end of the link 40 is connected to one end of a lever 44 pivoted at a fixed point 46, while the lower end of link 42 is similarly connected to a lever 45 pivoted at a fixed point 47. The shaft 62, which carries dancer pulley 7 on a spring-arm 60, is mounted in fixed bearings and is biassed by a spring 64 to urge the dancer pulley' 7 in an upward direction. Similar provision is made in respect of shaft 63, by a spring 65, to bias the pulley 8 also in an upward direction. The shafts 62, 63 are also provided with eccentric bosses which cause the links 68, 69 connected to the outer ends of levers 45, 44, respectively, to be moved downwardly when the dancer pulleys 7, 8 move upwardly. When the strip 1 is driven in the " FORWARD direction, i.e. when recording or reproducing, the strip 1 passes from reel 2 to reel 3, and the bar 53 rests in the right-hand position as shown in Fig. 1. In the event of the strip between reel 2 and the driving pulley 6 tending to become slack owing to reel 2 revolving too quickly, the dancer pulley 7 moves -upwards, the link' 68 downwards, and the link 42 upwards to lift one end of the gearing 24 about the upper end of link 43. The resulting frictional forces acting in an axial direction on the wheels 34, 35, 36, 37 of the gearing 24 cause a movement to the right to bring the said wheels 34 to 37 into a position more nearly approaching a tangential relationship with the friction-discs 23, 26, resulting in a reduction of gear ratio so that the speed of the reel 2 is reduced. In the event of the strip 1 becoming tensioned owing to the reel 2 revolving too slowly an inverse procedure to that described above, occurs. At the part of the strip 1 between the pulley 6 and the reel 3, an opposite effect is required, i.e. the speed of the reel 3 should be decreased when the tension in the strip 1 increases. This requirement is met when the lower ends of the supported links are closer together at the bottom than at the top, the links 40, 41 being shown in such position in Fig. 1.. When the knob 12 of the reversing switch 14 is set to " REWIND " the bar 53 is moved to the left-hand position. so that the reel 3 is speeded up when the strip 1 tightens over the pulley 8, and the reel 2 is slowed down when the strip tightens over the pulley 7, and vice versa. In operation it is found that, owing to frictional resistances, the part of the strip between the take-up reel and the driving pulley 6 is required to be in greater tension than the part between the take-off reel and the driving pulley. The spring 64 is therefore set with an initial tension greater than that of the spring 65, so that during rewinding from reel 3 to reel 2 extra tension is applied 'to the part of the, strip passing over pulley 7. When the switch-rod 12a is set to " FORWARD," however, an additional spring 92 is brought into tension and adds to the effect of spring 65 so that the combined effect is greater than that of the spring 64, and greater tension is produced in the part of the spring 64, and greater .tension is produced in the part of the strip passing over pulley 8. Level winding on the reels 2, 3 is provided by means of cams 82, 83 and levers 84, 85 which axially oscillate rods 70, 71 supporting guide pulleys 9, 10 respectively. An alternative construction of the variable ratio friction gear is described with reference to Figs. 5 and 6 (not shown).