Patent GB-803730-A (GB)
Title: Improvements relating to conveyors
Inventor: LLOYD JOHN DALE
IPC: B65G23/00
Filed: 1955-02-12
Abstract: 803,730. Endless belt conveyers. MAVOR & COULSON, Ltd. Feb. 12, 1955, No. 4233/55. Class 78 (1). In a belt conveyer the portion of the belt having the greatest tension is engaged by a pulley mounted on a movable support and acted on by a yielding force opposing the tension, movement of the pulley as a result of the belt tension being communicated to a device for stopping the driving motor of the conveyer which has three operative positions, i.e. a notension position, a running-tension position, and an excessive-tension position, the device comprising two switches both of which must be actuated to stop the drive, one switch being actuated directly by excessive tension while the other is actuated after a delay long enough to prevent the excessive tension occurring during starting of the conveyer from causing premature operation of the stopping device. As shown, a belt conveyer driven on its lower run has the stretch 16 of the belt passing to the drive unit engaged by a pulley 32 carried between the ends of a pair of depending arms 25 pivoted at 28 to brackets 29. An arcuate slot 36 in each bracket 29 determines the limits of movement of the roller axle 32A about the pivots 28. One arm 25 has a second arm 26 associated with it which has a slotted pivotal connection at its outer end with a lever 27 pivoted at 27A producing a magnified deflection of a plate 31 acting on lever 24 of a control box 22. When the conveyer is running pulley 32 is swung upwards by the tension force acting on arrow A against the weight of the roller acting along arrow C on the opposite side of the line B joining pivot 28 and axle 32A, to an extent proportional to the tension. Lever 24 is mounted on a shaft 45 in box 22 and is held against plate 31 by a spring 48A. A shaft 46 mounted on a plate 47 carrying self-closing micro-switches 41, 42 is coupled to shaft 45. When shaft 45 turns owing to increase of tension in the belt a cam 51 secured to shaft 46 is turned towards microswitch 42 to open its contacts at a predetermined tension, this switching off the drive to the conveyer if the contacts of micro-switch 41 are also open. The latter contacts are adapted to be open during normal running but closed during starting by the operation of a timer 57 consisting of a rod 59, a pulling force on which operates an escapement to allow it to be withdrawn slowly. The pulling force is provided by a spring 63. When the belt is at rest shaft 46 is turned back to engage a grub screw 55 with one end of a slot 54 in a sleeve 53 carrying an arm 62 which through a buffer member 60 depresses rod 59, this movement not being transmitted to the escapement. A cam member 52 on sleeve 53 is simultaneously moved away from microswitch 41 to allow its contacts to close. Upon starting of the belt shaft 56 is turned forwards to release the sleeve 53 and allow cam member 52 to be slowly turned back by the spring 63 acting on the escapement to re-open microswitch 41, after the initial surge in the conveyer belt, which temporarily opens micro-switch 42, has died away. Specification 803,729, [Group XXXVII], is referred to.