Thursday, March 18, 2021

Positive tappet shedding mechanism, structure and working

 

Conventional positive tappet shedding mechanism:


Structure of conventional positive tappet shedding mechanism

The whole mechanism can be divided into two parts:

Tappets and tappet levers:


The tappet C is fastened on the tappet shaft A. 

The tappet shaft receives rotatory motion from the bottom shaft.
 
The bottom shaft transfers motion to the tappet shaft at a right angle.

Two bevel gears having equal teeth are used in this motion transfer. 
The tappet lever  E is fulcrummed at fulcrum point F.  

A bowl D. is mounted at the top end of the tappet lever. 

The bowl gets free on its pivot. The bowl rests in the tappet track B. 
The lower end of the tappet lever gets connected to under motion through commenting rod G.

Under motion: 

It is a mechanism that consist of different shapes and size of connecting rods and levers there are two L shape levers used.

 One L-shaped lever is mounted on the right side and the other L shape lever is mounted on the left side of the loom. 

These L shape levers are fulcrummed at fulcrum points F.

 One end of these levers is connected to the tappet lever through connecting rods. 

The other ends of these L shape levers are connected to Heald shaft I through connecting rods.

The position tappet shedding mechanism raises and lowers the Heald shafts itself.

This kind of shedding mechanism doesn't require reversing motion. 
The load getting applied on the tappet during the lifting of the heald shaft is reduced. 

Better shed settings result in a positive tappet shedding mechanism.  This mechanism helps to make even shed.

The r.p.m. of the loom is also increased. The tappets are mounted at one side of the loom. 




Working principle of conventional positive tappet shedding mechanism:

In the above schematic diagram, the initial heald shaft position is the down position. 

When the tappet C rotates with the tappet shaft A in the anti-clockwise direction, the bowl D mounted at the top end of tappet lever E follows the tappet track B.   

Since the tappet lever is fulcrummed at point F so that the lower end of the tappet lever receives oscillating motion when the bowl follows the tappet track or we can say in other words that the lower end of the tappet lever receives a partial rotatory motion( angular motion).

 This lower end of the tappet lever gets connected to two L shape levers with the help of connecting rods G. 

The oscillating lower end of the tappet lever imparts partial angular motion to the L shape levers. These L shape levers are connected to the heald shaft I through connecting rods. 

When the L shape levers make a partial angular motion at their fulcrum, the ends of L shape levers connected to the healed shaft help to lift up the healed. 

Thus the healed shaft makes up and down movement. 

This tappet is a double-acting tappet so that two times shed formation takes place when the tappet makes one complete revolution.

High-speed positive tappet shedding mechanism:


This positive tappet shedding is a highly efficient shedding mechanism.  Very high loom speed is achieved in this positive shedding mechanism. 

Structure of high-speed positive tappet shedding mechanism:

This mechanism can be divided into two parts:

1 - Cams and cam levers

2 - Under motion mechanism:

Cams and cam  levers:

Cam B is fastened on cam shaft A. 

The cam shaft receives rotatory motion at the right angle from the bottom shaft. 

The cam shaft and bottom shaft are connected with each other through bevel gears.
 
Two cams are used for one heald shaft. Both the cams are placed one over another as shown in the below picture and are connected to each other by rivets. 

A cam lever C gets fulcrummed at point F. Two cam followers D are also mounted on the cam lever. 

The cam followers touch their respective cams. 

You can see clearly that the shaded cam is touching the shaded cam follower and the blank cam is touching the blank cam follower.

These cams get free to rotate at their pivots. The upper end of the cam lever is connected with under motion mechanism through the link I.

Under motion mechanism:

The lever H gets fulcrummed at point F. 

The top end of lever H is connected with cam lever C through the link I.
 
The bottom end of lever H is connected with L -shape levers E through the connecting rod G. 

The L-shape levers are fulcrummed at point F.  

The other end of L-shape levers is connected to the heald shaft J through connecting rods G.


Working principle of high-speed positive tappet shedding mechanism:


The rotating bottom shaft transfers motion to the cam shaft at the right angle through bevel gears.

When the cam shaft rotates, the cam fastened on it also rotates in the same direction.

The blank cam presses the blank follower and the shaded cam presses the shaded follower.

As the blank cam presses the blank follower, the upper end of cam lever C moves in the left direction.

Now the cam lever C pulls the lever H in the left direction through the link.

Since the bottom end of the lever, H is connected with two L- shape levers through connecting rods G so that the bottom end of lever H pushes to the L- shape levers in the right-hand direction.
 
When the bottom end of the L- shape levers moves in the right direction, the other ends of L shape levers help to lift up the heald shaft J through the connecting rod G. 

When the shaded cam presses the shaded follower, the upper end of the cam lever moves in the right direction and the lower end moves to the left direction. 

This reverse motion of the cam lever brings the heald shaft in the bottom position




Please watch the below video in Hindi about positive tappet shedding mechanism:




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