Negative Tappet Shedding

negative tappet shedding
Construction: Figure shows a negative tappet shedding mechanism. A pair of tappets A & B is fixed to the bottom shaft C at 180ยบ to each other. Two treadle levers D & E are connected to the loom back-rail by a bracket F. The bracket acts as a fulcrum for the levers. The two treadles have teeth to carry the lamb rods G & H respectively. Two heald shafts J & K are connected to the lamb rods.
A top reversing roller shaft Q carries two rollers of different diameters. The roller of small diameter N is connected to the leather strap L to which the front heald shaft J is connected. The roller P of large diameter is connected to leather strap M to which the back heald shaft K is connected. The tappets A & B touch the anti-friction bowls or followers R & S respectively, which are fixed to the treadle levers. The heald shafts have heald eyes T & U through which the warp threads pass X is the warp sheet & Y is the cloth. The odd ends are passed through one heald shaft while the even ends are passed through the other heald shaft.
Working Principle:
When the bottom shaft is rotated in the clockwise direction as shown in the figure, the tappets are also rotated. The tappet will depress the anti-friction bowl & the treadle. Being fulcrum at one end, the front portion of the treadle moves down. This action is transferred to the lamb rod, the heald shaft & the leather strap. So one heald shaft is lowered & the threads connected to this heald shaft are lowered & form the bottom layer of the shed.
This leather straps attached to the reversing rollers are connected in opposite directions, i.e. when leather strap is pull down, it is unwound from the roller. The shaft therefore rotates in the clockwise direction & the other leather strap is wound on to its roller. The heald shaft is raised & therefore the lamb rod & treadle lever are also raised. The threads connected to the heald shaft are also raised & form the top layer of the shed.
For the next shed, the other tappets works with the other set of bowl, treadle, lamb rod, heald shaft, strap & roller & the other heald shaft is lowered. The first heald shaft is raised by the top reversing rollers, & the positions of the heald shafts are thus interchanged. Thus, for one rotation of the bottom shaft, two sheds are formed.


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