SLAY RECIPROCATION IN A WEAVING LOOM
Shuttle projection cannot be understood without considering the motion of the slay during shuttle traverse, the shuttle moving in a complex path in all three coordinates. In some shuttle less weaving machines the weft is inserted across a stationary picking track and this complication is avoided. It has been standard practice to drive the slay by a four bar chain arrangement with varying degrees of eccentricity. In some designs the crank centre is located on a horizontal line passing through the slay sword pin with the slay on front centre, but where a longer dwell has to be provided for the purpose of facilitating shuttle traverse, the crank centre is located below the horizontal and the ratio of crank radius to connecting rod length is increased. A similar result is achieved on the early.Somet flexible rapier weaving machine by adding a constrain to the crank pin in the form of a bell crank lever pivoted on the loom frame.
With true reciprocation:
ƒ=ω2r (cosθ +B cos 2 θ + C cos 4θ……n cos nθ)
When r is the crank radius, θ is the angle between the crank and horizontal, l is the length of the connecting rod and n=l/r
The maximum and minimum approximate values are
ƒm =v2/r(1±r/l)
In a loom with a slay mass of 107kg,a speed of 220ppm,distance from rocker shaft centre to slay sword pin centre 0.72 m,radius of gyration of slay mass about the swing rail 0.61m,crank radius 7.6cm and crank arm length 21.6 cm.
Maximum accelerating force when θ=0 and cosθ=1.i.e. at front centre.
F=W/g×v2/r (1+r/l) =427 kgf
The minimum accelerating force at back centre when θ=1800 is 205kgf.These forces set up vibrations, the first harmonic at a frequency of 3.66HZ.If accelerating forces are to be reduced by increasing n,this could be achieved by retaining r at 0.07m and increasing l to 0.30m,thus increasing n from 2.84 to 3.94.This reduces the maximum accelerating force at front centre from 427 to 394kg,a reduction of approximately 8%.The sourer 100 cm 100 W loom has the lowest value of n and the highest value of eccentricity i.e. its reciprocal at 2.38 and 0.42 respectively.
Attempts have been made at partial balance of then reciprocating forces. If a 60% balance is so to be achieved under for the situation under consideration, the partial balance torque would be:
Wrb=0.6(107×0.076)
=4.88 kg.m
As species restricted the balance weight centre of gravity could not be located at a radius much greater than (rn=0.15m), which would require an impractical corresponding balance weight mass of 32.5kg.As shuttle loom speed have rarely exceeded 250 rev/min the advantage of partial balance has not been great.Picanol claimed to have reduced vibration on their model MDC by balancing the primary drive with a fly wheel running at 4.3 times the speed of the loom.
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