Secondary Motions of Loom: Types, Mechanism and Working Principle
Sinha Islam Ayon
Dept. of Textile Engineering,
BGMEA University of Fashion and Technology
Loom is very important part for weaving process. It has three types of motions: primary motion, secondary motion and auxiliary motion. This motion is the most necessary for any loom to produce fabric, without these motions weaving is not possible. The fundamental motion of a loom is called primary motion. After primary motion most important motion is secondary motion. If weaving is to be continuous then these mechanisms are essential. Actually, the loom motions which help to weave a fabric continuously are called secondary loom motions. Though the fabric can be woven without these motions, but you can’t keep the weaving process continue without secondary motions of loom. So it’s very important for loom.
Secondary Motions of Loom:
There are two types of secondary motion of loom. They are:
- Take-up motion
- Let-off motion
A. Take Up Motion
The take up motion is to draw a fabric to the cloth roller regularly and withdraws the cloth from the weaving area at a regular or constant rate so as to give the required pick-spacing (in picks/inch or picks/cm) and then winds it on to a cloth roller. Take up motion determines the number of ends and picks per centimeter or inch.
The main part of this mechanism is the take up rollers, which draws the cloth at the regular rate, and the number of picks per inch decides this rate. The take up roller is covered with emery cloth or hard rubber depends on the type of cloth woven. The drive to the take up roller is by a train of gear wheels put into motion straightly from the main shaft.
Classification of take up motion:
Take up motion can be classified in many ways. They are:
According to drive:
- Negative take up
- Positive take up
According to motion of the cloth/rate of take up:
According to drive given to the cloth roller:
- Direct drive
- Indirect drive
According to number of gear train:
According to brand name:
According to drive
a. Negative take up motion:
The word ‘negative’ justify the take up motion that no positive or direct motion is imparted to the take-up roller to wind up the woven cloth. It is the motion in which the take up roller is rotated by means of a weight or spring, the roller only rotates when the force applied by the weight or spring is greater than the warp lay tension in the fabric. In this way, the motion of the rocking shaft actuates a system of levelers and ratchet a ratchet-pawl mechanism, favored by gravity aided movement of dead –weighted which in turns, transmits the rotational motion to take up roller through a worm and worm-wheel.
The backward motion of the slay or backward sewing of the rocking shaft (R) keeps the weights raised by a lever (L), thus system stay inactive while forward motion of it sets free the weight system yet motion of the wheel trains remains balanced with warp tension till impulsive blow of it during beat-up brings the tension of the woven cloth to zero. Weights going down with gravity make the pawl (P) to jump retaining pawl (P), comes into play to prevent further rotation of gear trains. With little control over uniform take up or pick spacing, system is only suitable for course fabric.
b. Positive take up motion:
In positive take up motion gets transmitted to take up roller directly through gear train. The different types of positive take up discussed below.
Five wheel take-up mechanism:
The process of withdrawing fabric from weaving zone at a regular rate and then winding the woven cloth on the cloth roller with the continuous progress of weaving is called take up motion. For doing these work two types of mechanism is used. One is 5-wheel mechanism and another is 7-wheel mechanism. Actually, 5-wheel take up mechanism is used in case of jute weaving.
A = Rachet wheel =50-60T
B = Change wheel =1/4
C = Stud wheel = 100-120T
D = Stud pinion = 12-18T
E = Take up wheel = 60-100T
F = Take up roller = 15-16″ (circum)
G = Finger
H = Take up lever
M = Pushing pawl
N = Rotating catch
- The beam wheel E is set screwed on the beam shaft and its teeth engaged those of stud pinion D which is linked with stud wheel C.
- The stud pinion and stud wheel work loosely upon a stud in a slotted bracket, the slot is concentric with the cloth beam F.
- In this positive take up motion is primarily imparted from the sley sword. The finger enters into the slot of the take up lever H, which is fulcrumed at I.
- A swinging motion is given to the sley sword and this will cause the paw M to drive the ratchet wheel A and set the train of wheels in motion.
- Ratchet wheel is moved the distance of one tooth by the oscillating pawl for every pick.
- Thus motion is transferred to the cloth roller from the ratchet wheel by means of five wheels.
Seven wheel take up mechanism:
Take-up is to draw a fabric to the cloth roller regularly. Texture of a fabric largely depends upon the number of ends and picks per centimeter or inch. This motion determines the number of picks of weft per inch or centimeter and contributes to the uniform texture of the fabric. It is the work of the weaver for accurately fixing the position of the fell of the cloth before starting a loom.
This positive take-up mechanism consists of seven wheels. These are:
- Standard wheel,
- Change pinion,
- Stud pinion,
- Stud wheel,
- Swing pinion and
- Take-up roller wheel.
Actually, the motion is primarily imparted from the sleysword. The sleysword is connected to the slay that gets motion from crank shaft and the crank shaft gets motion from motor by gearing. At the bottom of sleysword a connecting rod is connected which passes the motion to monkey tail.
The monkey tail is fulcrum with two pawls: the upper is holding pawl and lower is pulling pawl. These two pawls are mounted easily to the ratchet wheel which is connected with the standard wheel by shaft. Over the standard wheel the change pinion is geared. The change pinion is connected with the stud pinion by shaft and the stud wheel is geared with the stud pinion upon it. The swing pinion is connected with the stud wheel and the cloth take-up roller wheel is geared with the swing pinion.
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The cylinder upon which the woven fabric is wound, is connected with this wheel by shaft. Now when the sley moves one time after one pick insertion the connecting rod pass this motion to the monkey tail and as the pawls are fulcrum with monkey tail they get downward motion. By using this downward motion the pushing pawl pulls the ratchet wheel one time and the holding pawl holds the ratchet in this position. Finally the cloth roller gets the motion by gear train and thus fabric is wound on cloth roller continuously with the weaving of fabric.
Advantages of 7 take-up wheel over 5 wheel take-up mechanism:
- It can give a larger number of picks per inch in cloth from a little stock of wheels by changing two wheels in the train,
- It can give even a fraction of a pick per inch in cloth.
- The number of teeth in the change wheel and the number of picks per quarter-inch has been simplified.
B. Let Off Motion
Let-off motion is a secondary loom motion. The main objectives of let off motion are to release the warp after beating of every inserted pick and to regulate the warp tension. The motion which delivers the warp yarns from the warp beam at the required rate that a suitable constant tension by unwinding it from a flanged bobbin called let off motion. When the fabric weaving remains continue, the take-up motion pulls the woven fabric continuously to maintain the fell of the cloth position.
Functions of let off motion:
- To maintain or control the necessary tension upon the warp.
- To unwind and deliver the necessary amount of warp sheet from the warp beam with the simultaneous and continuously to take up motion.
- To impact the no of picks per unit space in a fabric being subsidiary to take up motion.
Conditions of good let off motion:
A good let off motion must possess certain features which are given below:
- Uniform and equal tension upon the warp.
- Provision to regulate decreasing diameter of warp on the beam during weaving.
- Arrangement for taking the warp back.
- It should also be sensitive to any little variation in the diameter of the weft yarn and tension upon the warp.
Types of let off motion:
- Positive let off motion.
- Semi-positive let off motion.
- Negative let off motion.
Difference between positive and negative let off motion:
Let-off motion is classified as negative and positive let-off. In case of negative let-off warp is pulled from the warp beam against a slipping-friction system. For positive let-off system, warp beam is rotated at a controlled rate in order to maintain constant warp tension. Positive let off motion. 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.
- Warp beam
- Floating back rest
- Driving rod
- Reciprocating collar
- Warm wheel
- Large beam wheel
Positive let off mechanism:
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, and 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.
A pawl operator turns the ratchet wheel by the driving rod that gets motion of the sley sword. Each time the sley moves forward the oscillating collar is connected to fixed collar and 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 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.
Semi-positive let off motion:
The delivery of warp is controlled in such way that an adjustment can be made to maintain tension or path length by slippage. Some jobs are done manually and come mechanically.
In the semi positive let off motion, a pushing pawl present in a Rachel wheel Rachel is connected by a shaft in warm C with warm wheel B and warm wheel rotates in clockwise direction. Weight lever is fulcrumed at H and floating back rest K is present downwards and other end of wt. lever is to the pushing pawl.
- Warp beam
- Warm wheel
- Rachet wheel
- Weight lever
- Floating roller
The warp beam is driven through a worm and worm wheel which are turned by a pawl and rachet. When warp tension more the floating back rest is lowered and this causes downward movement of weight lever at the back side and upward movement of connecting rod. The out end of pawl move upwards and other end comes to the contact of rachet teeth and makes rotation of rachet wheel and worm and warm wheel. As worm and worm wheel are on the same shaft. So the warp beam rotates highly and causes let off motion and uniform tension. When warp tension is less. The floating back rest moves upward and this causes downward movement of the out end of the wt lever and the other end of pawl be disengages with rachet teeth and no let off motion.
Negative let off motion
Let-off is to supply warp thread in the weaving zone at a predetermined rate. Negative let-off is a mechanism for controlling the rotation of the beam on a weaving, warp knitting or other fabric forming machine where the beam is pulled round by the warp against a breaking force applied to the beam.
- Warp beam.
- Beam ruffle.
- Machine frame.
- Weight lever.
The warp beam ruffle is wrapped around by chain. The one end of the chain is fixed at the machine frame whereas the other end is connected to fulcrummed device to the weight lever, which is pivoted and a dead weight is placed which can be moved along the length of the weight lever. In this system the tension of the warp is regulated by the friction between chain and the beam ruffle. The friction is controlled by dead weight on the weight lever and the distance of dead weight from the pivot. Heavier the dead weight and longer the distance of it from the pivot lesser the let-off. The warp beam dia softly decreases as weaving proceeds. So it’s necessary to increase the let off rate. If the dead weight is kept on the same place, the let-off rate will stay unchanged. So an experienced worker is required to change the dead weight gradually with the change of the warp beam dia. As a result irregular tension occurs and the rate of yarn breakage may increase.
- Cheap and simple in construction.
- Suitable for light and medium weight of fabrics.
- Easy to maintain.
- Difficulty in taking back the warp beam after picking gout.
- Difficulty in regulating equal tension on the warp.
- The varying tension on warp thread shows dark and light or shady places in the cloth.
- Possibility of thread breakage due to tension variation. As a result, bad quality fabric produced.
Development of let-off motion:
This is a modern type of let off motion in which the weaver’s beam is driven with the help of servo motor, as the beam diameter changes, r.p.m of the beam are controlled through load cell. Take-up which is responsible to draw the fabric from fell of cloth at regular rate (picks/inch) and to wind the cloth on cloth roller. It is synchronized with let off motion. The speed of take up is less than let off motion due to crimp of warp.
The secondary motions facilitate the weaving of fabric in a continuous way. The take-up motion withdraws the cloth from the weaving area at a constant rate so as to give the required pick-spacing and then winds it on to a cloth roller. On the other hand let-off motion delivers the warp to the weaving area at the required rate and at constant tension by unwinding it from the weaver’s beam. The secondary motions are carried out simultaneously. After all this motion is very important for our study because without this motion we can’t think about production from loom.
- Subhankar Maity, Kunal Singha, Mrinal Singha “Recent Developments in Rapier Weaving Machines in Textiles” American Journal of Systems Science 2012; 1(1): 7-16 doi: 10.5923/j.ajss.20120101.02
- Handbook of Weaving by Sabit Adanur
- Weaving: Conversion of Yarn to Fabric by M. H. Mohamed and Peter R. Lord
- Abu Sayed, “What are the primary and secondary motions? Auxiliary functions of weaving process” TextileApex.blogspot.com
- Md Sohanur Rahman Sobuj “Motion of Loom” Textilestudycenter.com
- Saiful Islam “Motions of Loom” Textile-craft.blogspot.com
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Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.