Study on Positive Let-Off Mechanism



A mechanism controlling the rotation of the beam on a weaving, warp knitting or other fabric is forming machine where the beam is driven mechanically.

  1. Warp beam 
  2. Floating back rest
  3. Feeler 
  4. Spring
  5. Warm 
  6. Ratchet  
  7. Driving rod
  8. Collar
  9. Reciprocating collar
  10. Warm wheel
  11. Large beam wheel
  12. Adjusting rod
The beam turning mechanism is shown in the figure. The beam is driven by ratchet on a short vertical shaft, which also carries the worm, which drives the worm wheel.A pinion on the same shaft as the worm wheel drives the large beam wheel, which is fixed, to one of the beam flanges.

Positive let off motion
Positive let off motion
A pawl operator turns the ratchet wheel by the driving rod, which gets motion of the sley sword. Each time the sley comes forward the oscillating collar is connected to fixed collar & there is engagements of pawl with ratchet.As the tension in the warp sheet is increased, the floating rest will move downwards and the rod carrying the fixed collar will move to the right and the rod R1 will move to move the driving rod to the left.

This will bring the fixed collar to the oscillating collar.As a result, the force of imparted oscillating collar and fixed collar is more. The pawl drives so more ratchet wheel teeth. So the beam motion is more and more warp is withdrawn to the increased tension.


In this mechanism, constant tension can be maintained and any variation in tension can be detected. So it is used in modern power looms


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