Keighley double acting negative dobby l Structure and working

Keighly double-acting negative dobby mechanism, structure, and working:

- Keighley dobby is a double lift negative dobby.

- When the loom makes two revolutions of the crankshaft,  this dobby makes one revolution. 

- The loom rpm gets increased if the loom is equipped with a double-acting dobby.

- This is a very simple dobby mechanism.

Structure of Keighley dobby:

The T-shape lever I is mounted on the dobby shaft O. This T- shape lever gets freely mounted on the dobby shaft. An upper knife A is mounted on the X-side of the T-shape lever I. The lower knife B is mounted on the Y-side of the T- shape lever. These knives are pivoted and get free to make free partial angular displacement. The upper hook C rests upon the upper connecting rod E and the lower hook D rests upon the lower connecting rod F. These hooks are connected with jack lever H through the link. The jack lever gets fulcrummed at point O. The heald shaft J is connected with the jack lever through two leather straps L. One spiral spring K gets mounted at each side of the heald shaft. The lower ends of the springs are connected with the side frame. Two feelers are mounted under the upper and lower connecting rods. The lower connecting rod rests upon the feeler S and the upper connecting rod rests upon the feeler T. A pattern cylinder G is mounted under the feeler. The lattice is mounted over the pattern cylinder G. The peg R is inserted in the hole of the legs Q. An L-shape crank N is fastened on the bottom shaft P. The T-shape lever I and L-shape crank N are connected to each other with the help of connecting rod M.

Working principle of Keighley dobby:

When the L-shape crank mounted on the bottom shaft rotates, it transfers motion to the T-shape lever I. The T-shape lever I makes a reciprocating motion when the L-shape crank rotates. The pattern cylinder G rotates with the help of a ratchet wheel and pawl. The peg R mounted on the leg Q presses the corresponding feeler S and T. As one end of the feeler goes upward, the other end of the feeler comes downward at the same time. The bottom end of either the upper or lower connecting rod comes downward. Since the upper and lower hooks rest upon corresponding connecting rods so that the hook falls on the knife while the corresponding connecting rod comes downward. Now the reciprocating knives pull the hook toward the right-hand side. The hook pulls to the jack lever and the heald shaft goes upward with the jack lever. In this way, the heald shaft makes up and down movement. The pulling spring helps to bring the heald shaft in a lower position.

Please click on the below video link to watch the full topic in Hindi:

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