Common Handloom product
Chapter 4: Design and Development of Semi-Automatic Handloom
4.3 Sub-system Design
146 Figure 4.1: Metallic mechanism in wooden sley in fly-shuttle handloom
147 i. Treadle and top roller reversing motion.
ii. Jack and lam tie-up iii. Dobby
iv. Jacquard
v. Tappet shedding
Out of the above five mechanisms, the Jacquard type of shedding was accepted since these are suitable for structural designs and ornamental fabrics. The Dobby type of shedding is discarded as the jacquard type can perform a similar function. This attachment does not justify inclusion in a semi-automatic handloom as part of automation. However, being part of the handloom is essential as an additional device for ornamentation in fabrics.
In the case of the Jack and lam arrangement, it is the slow-acting mechanism. Since a semi- automatic handloom is productive, including Jack and lam will reduce the speed and productivity of the loom. Therefore, it is discarded. It exists in Shanti loom along with jacquard mounting provision.
Adding a tappet requires a secondary bottom shaft and reduction gearing in the Tappet mechanism. This mechanism will make the loom either operable as a pedal loom or has to be operated only with the hand (like Banarasi semi-automatic handloom), rendering either of the limb (upper or lower) useless in operating the loom. It will result in fatigue only in one limb.
Also, the versatility of the loom for weaving designed fabric is lost.
Compared to all the other mechanisms, the first one is a manually operated treadle, and the top roller reversing motion is best suited for semi-automatic handloom design and adopted for this. Jacquard type of shedding is also kept as an attachment for ornamentation.
The treadle has been modified to provide a better ergonomic working posture.
4.3.2 Picking mechanism - shuttle propulsion
The second sub-system of a loom is picking, i.e., passing the weft yarn between the open warp shed. In the case of primitive looms, it is done by hand and is also known as a throw shuttle. However, our concern is only with the fly shuttle picking mechanism; hence we need to consider the method of shuttle propulsion. For this, there are several options available and studied as follows.
i. Manual shuttle propulsion is usually found in handlooms with overhead rope tying.
ii. Burmese type of shuttle propulsion.
iii. Mechanized automatic cone type of over-pick mechanism.
iv. Mechanized automatic lever type of under-pick mechanism.
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148 v. Mechanized automatic cone under-pick mechanism.
Manual shuttle propulsion, commonly used in handloom, needs an overhead structure for the tie-up. Also, the degree of automation will be low with this type of shuttle propulsion since shedding is already left manual. This type of picking also demands more synchronous movement from the weaver and is more straining on the part of the weaver. Based on all the above, this type of shuttle propulsion is discarded.
The second type of shuttle propulsion used in Burmese type semi-automatic handloom is most suitable since it uses the motion of the sley for propelling the shuttle across the shed. It is also appropriate from the point of view of utilizing the existing parts like spindles and pickers. It also discards overhead structures required by the previous type of shuttle propulsion, which helps keep the structure light. Based on all these evaluations, this type of shuttle propulsion is selected.
The other three types of shuttle propulsion mechanisms iii, iv, and v need a bottom shaft fitted with reduction gearing and tappet mechanisms. This mechanism also requires higher energy for operation and is therefore discarded for the semi-automatic type of loom design.
Another disadvantage is cost, which will be very high compared to other types.
4.3.3 Beat-up mechanism
The third sub-system of a loom is the beat-up mechanism. This system assists in bringing the last weft to the fall of the cloth by beating up the same. All looms use a reed mounted on the sley race and are reciprocated to and fro for beat-up except primitive handloom. The sweep of sley is not restricted in a conventional loom other than the fall of the cloth and heald. Also, the sley is hung overhead for swinging.
Controlling the sweep of the sley is necessary to obtain uniform beating force repeatedly and produce quality material without pick spacing variations through an automatic take-up mechanism. Also, the sley needs to be underhung to minimize vibration and keep the light structure of the handloom.
Based on the above analysis, in the present design case, the sley is selected for underhung, and its sweep is restricted by using a crankshaft. The flywheel-type crankshaft aims to restrict the sweep of the sley rather than conservation of momentum. The flywheel should be neither too heavy nor too light to solve the purpose.
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149 4.3.4 Take up mechanization
Take up is another sub-system of a loom falling under secondary weaving motions. In the absence of take-up motion, continuous weaving is not possible. Various alternatives were studied and evaluated to adopt an appropriate take-up mechanism for the loom design; the same is mentioned below.
a. Negative manual take-up b. 5-wheel take-up motion c. 7-wheel take-up motion
d. The worm and worm wheel take-up motion.
Since negative take-up motion is unsuitable, it is rejected because it is manual and intermittent for the semi-automatic loom. It also provides no control on weft spacing.
In the case of 5-wheel take-up motion, being positive, automatic, and simple, the reciprocating movement of the sley actuates it. This take-up motion, in conjunction with the take-up guard, provides for different pick spacing and is found suitable for the loom design and adopted.
In the case of the 7-wheel take-up mechanism, it is more complex and will cost much higher. It also requires more energy to operate. Based on these, this mechanism is rejected.
Similarly, the worm and worm wheel take-up mechanism is rejected on the ground that its working is not superior to the 5-wheel take-up motion but needs provision of the shaft at a right angle to the cloth beam, thereby increasing the complexity of the loom.
4.3.5 Let-off mechanism
Let off is another sub-system of the loom and categorized as the second in the secondary weaving motions.
Let off mechanism works in conjunction with the take-up mechanism. The various alternatives available for consideration are
a. Negative let-off mechanism based on chain, lever, and dead weight b. Negative let-off mechanism based on spring-loaded resistance c. Positive let-off mechanism
The negative let-off mechanism is actuated by the tension generated due to the take-up of woven cloth by the positive take-up mechanism. The positive let-off mechanism is independent of the take-up mechanism and is mainly actuated by the reciprocating motion of the sley. It is much more complicated and requires many more different parts. So, It is more
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150 expensive. Since the loom to be designed is to be made simple, low cost, and easily operable and serviceable, the positive let oft mechanism is inappropriate in this context.
The spring-loaded negative let-off mechanism is better in conjunction with an oscillating backrest. It also does not require many parts like chain, lever, dead weight, and frequent adjustment during weaving. Based on the above comparison, the spring-loaded negative let- off mechanism is used in the loom. It has a wooden ruffel secured to the warp beam over which one rope is passed on two grooves, and the end of the rope is loaded with spring, and resistance is generated by loading the spring with the nuts and bolts provided for the purpose.
Wherever take-up mechanisms were introduced without controlled beat-up, results were disastrous.
4.3.6 Oscillating Backrest
The shedding mechanism selected for the loom design is the treadle and top roller reversing mechanism. This type of shedding mechanism produces a center-closed shed, which results in tensioning the warp sheet during shed formation, and once the shed is closed, the warp sheet becomes slack due to tension relaxation. It affects the pick spacing by affecting the beat-up adversely. An oscillating backrest is used to compensate for this disadvantage of center- closed shedding.
In the case of a mechanized power loom, the backrest oscillates through a cam fitted on the crankshaft. However, for simplicity and cost reduction, a spring-loaded oscillating backrest is designed for the loom.
Here during the shedding, the springs of the backrest yield; thus, the extra length of warp is released for shedding, but immediately once the shedding is over and shed closed, the resultant slackness of the warp sheet is removed by the backrest since the springs exert tension on it
4.3.7 Temple motion
Another sub-system of a loom is the temple mechanism. The Temple mechanism is categorized in the third set of weaving motions as tertiary or auxiliary. This category of motion is essential for producing defect-free fabrics. Temple motion assists in weaving fabric of uniform width and unbroken selvedge. In normal handlooms, manual temples are used.
These need a frequent adjustment with the fall of the cloth.
An automatic roller of the ring temple is used in the power loom. Ring temple is expensive and delicate. Therefore, the common roller-type temple is selected for the loom design. Here
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151 two numbers of spiked rollers are used on each side (left and right), and as the cloth is taken up after weaving, the rollers roll to release the woven cloth maintaining uniform width. The selvedge obtained is also unbroken.
These temples can be adjusted for different widths of fabrics and are fitted to the loom with the help of a leaf spring set to provide spring-back action. In case the sley hits the temples, because of the spring back action, the temples will not damage the sley.