Shedding of shuttle and shuttless technology
- 1. High Speed Shedding Dr Manjunath Burji
- 2. High Speed Shedding Mechanism Shedding Object • Achieved by lowering & lifting the heald frames or warp ends according to the requirement of design. Condition for good shedding • Produce clear shed. • Produce shed of minimum height. • Should impart a smooth movement of the HF with minimum vibration.
- 3. • Should help to achieve higher speeds. • Should help to change design easily. • Should be less expensive.
- 4. Classification of shedding • Tappet/cam shedding. • Dobby shedding. • Jacquard shedding. Tappet shedding • Negative • Positive No heald reversing motion. Positive grooved cam shedding. Positive conjugate or matched cam shedding.
- 5. Limitation of Tappet Shedding • Pattern changes are difficult. • Limited to 8-10 shafts used for 8 or 10 picks/repeat. • Each cam design for a particular lifting plan 3/1 or 2/2 twill. • Rotational speed of shedding cam depends upon pick per cam rotation. • In short cam shedding lacks flexibility in changing lifting plan. • As slope of cam more during change of direction of heald shaft maximum force required by the cam due to slope.
- 6. • No smooth movement. • More vibration. • Clear shed not formed. • Shed height is more, more stress on warps. • Counter gear and cam should be changed when design changes . Limitation of Tappet Shedding
- 8. This type of mechanism is not used much any more. Used in Ruti-c, Highspeed looms. A:Positive Cam Shedding
- 9. Grooved Positive Cam Shedding • Harness are both raised & lowered by the cams. • There are two main types of positive cams. • Grooved Cams. Advantages • Simple. • Slightly expensive. • Easy to maintain. • Less vibration & Smooth movement. Disadvantages • As bowl moves in a groove speed is limited. • Inaccessibility in strap connections to change lift of shafts.
- 11. Matched Positive Cam Shedding • This type of mechanism is common in modern weaving machine. • Current trend is to mount the cam on the floor next to machine. • Automatic harness levelling devices are used in cam shedding to provide even tension on warp yarn during machine stops. • The device also helps with eliminating the startup marks. • Cam mechanism are immersed in the oil bath. • Cams with weave pattern profiles rotate to deliver lifting/ lowering instruction to harness.
- 12. Matched Positive Cam Shedding • A typical cam shedding can handle weave patterns with upto 14 different harness. • Cam shedding mechanisms are relatively simple and inexpensive to design and maintain. • They are more reliable for producing fault free fabric and they do not restrict the weaving machine speed. • Shedding done by pair of conjugate cam ensuring smooth motions for HF. • Cam with zero degree dwell ensures very delicate and smooth movement of HF putting less strain on warp.
- 13. Matched Positive Cam Shedding • Reduced shed height, because of small size of weft carrying element. • Easy accessibility for altering shed height and depth. Advantages • Can work at very high speed (300 to 350 rpm). • Wear & tear less ( oil bath). • Due to rigid linkages, movement of HF smooth. • Use of precision engineering and high grade material to maintain contact of cams and bowls.
- 14. Matched Positive Cam Shedding Disadvantages • Expensive. • Precision settings are required otherwise will lead to costlier breakdown. • Restrict patterning possibilities : time consuming and not practical for frequent pattern changes. • Pitch of cam= 18mm.
- 15. Matched Positive Cam Shedding
- 16. Matched Positive Cam Shedding
- 17. Matched Positive Cam Shedding
- 18. Need for Positive Cam Shedding • Positive cam required for the denser warp and high speed weaving machine. • In high speed weaving machine time available for all the motions is less, controlling the action of heald reversing mechanism in negative tappet shedding precisely & positively is not possible. • It will be no longer possible in negative shedding to keep the connection to HF always taut at all times, & there will be a loss of lift when they are slack.
- 19. Need for Positive Cam Shedding • To change in the amplitude of displacement of heald shaft is difficult in negative tappet shedding as this may disturb the leverage system. • In negative tappet shedding, load on the heald shaft is more. • In wider width loom, control of lift across the fabric width is more difficult. • Simple in construction : easy view. • Easy to maintain : no oil stains. • Less vibrations and smooth movement due to thicker wooden legs.( Sturdy construction)
- 20. Keighley Dobby
- 21. Disadvantages of Mechanical Dobby (Keighley Dobby) • More mechanical parts & linkages. • More wear & tear. • More vibration. • Bottom close shed. • More stress on warp chances of end breaks. • Selection device complicated. • Speed increases load on dobby increases. • Number of heald shaft increases, speed reduction. • Pattern change difficult. More number of lattice. • Negative shedding not suitable for high speed. • Chances of design fault to wrong or loose pegging. • Limitation of speed of selection device.
- 22. Types of Shed
- 23. Rotary Dobby • In order to achieve dobby shedding at faster speeds, new generation rotary dobbies are developed and introduced. • Rotary dobby can allow weaving machine speeds up to 1000-1500 rpm. • The term 'rotary' was chosen because the straightline motion of the healdframes is derived from rotating elements in the dobby.
- 24. Rotary Dobby (Mechanical) • Lifting of jacks in ordinary lever and cam dobbies is done by simple harmonic motion of knives. • This results in more vibration and wear & tear of the working parts. Hence working at low speeds. • So these dobbies are not suitable for high speed shuttless weaving. • As the modern machines are designed for very high speed is need for dobby mechanism that matches speed of machine. • Therefore Rotary dobby “ Rotary principle” is used.
- 25. Rotary Dobby (Mechanical) • The term “ Rotary dobby” is derived from the fact that rotating cam elements in this new dobby system brings lifting of the healds in the loom. • A load on mechanical dobby increases with increased loom speed, number of HF and lift of HF. Rotary dobby • Selection unit(Reading). • Cam unit for lifting jack.
- 28. Rotary Dobby (Mechanical) • Cam unit: Heart shaped crank disc, cam, coupler ring, ball bearing. • Working Hole in the pattern card. • HF goes to upper position OR remain at same position for consecutive picks. Blank space in the pattern card. • HF goes to bottom position OR remain at same position for consecutive picks.
- 29. Mechanical Selection Disadvantages • A separate card punching activity is required and this is time consuming process. • In the long run, plastic cards may get damaged and lead to wrong selection. • Mechanical selection not reliable for long run. Electronic Dobby overcomes the above disadvantages.
- 33. Electronic Rotary Dobby • It is clear from above sequence by charging electromagnet, HF at top position or move from bottom to top. • If the electromagnet discharged, HF either retained in the bottom shed position of shifted from top to bottom shed position. • Dobby consist of two units, a cam unit and electromagnetic selection control unit. • 180 degree rotation of cam causes lifting or lowering of the heald frame.
- 35. Advantages of Rotary Dobby • The rotary movement of the cam system is converted in to the lifting & lowering movement of the heald frame. Hence this dobby can be run at high speeds and is immensely suitable for modern shuttless loom. • All the functional elements of this dobby are arranged concentrically on a shaft with precision ball bearings, so machine vibration and wear & tear of parts are extremely reduced. • A specially designed transmission key with high rigidity is used for overcoming the strain involved when two machine elements are in simultaneous rotary motion.
- 37. Disadvantages of Mechanical Jacquard • Mechanical jacquard are complicated in their construction, consisting of a large number of relatively delicate parts which are difficult to maintain as well as lubricated. • Mechanical jacquard also consist higher number of mechanical linkages. • Drive given to jacquard from the crankshaft of machine. • Selection mechanism is completely mechanical oriented.
- 38. Disadvantages of Mechanical Jacquard • Generally more the linkages in jacquard, then more will be the problems/ defects in the loom and fabric, such as wear & tear & faulty selection. • Use of more number of mechanical linkages restrict and reduce the speed of the loom. ( Plain loom with mechanical jacquard runs in the speed range of 100-130 rpm). • Also, preparing punched pattern cards and changing design is tedious and time consuming as it is mechanical and makes the system less flexible with respect to design change. • These jacquard cannot run at the speed of present generation looms with 500-1000 rpm. • The power required to drive the mechanical jacquard is more. • Bottom close shed is formed, unnecessary movement of warp.
- 42. Bonas Electronic Jacquard • Solenoids forms the interface between control signal and mechanism. • Lifting hooks. Two spring steel hooks linked by the cord. • Double sets of pulleys. • Oscillating knives. • 22 to 24 V voltage supply. • Jacquard capacity 896, 1344, 1792 & 2688 hooks. • Shed height 50 to 110 mm. • Open shed formation.
- 44. Difference between Electronic Jacquard • Solenoids operates as Staubli: Retaining electromagnet, Bonas: Pull type electromagnet. • Between solenoid & half hook there are Staubli: Mechanical transmission element, Bonas: No mechanical element. • If warp thread remains in upper shed for successive picks it means : Bonas & Staubli: No movement of the hooks, card & pulleys. • A surge of current to the solenoid has effect of : Bonas: Raising of warp, Staubli: Lowering of warp.
- 45. Design Requirement of Electronic Jacquard • The number of functions performed mechanically should be reduced so as to reduce wear and improve selection procedure. Hence to & fro moving pattern cylinder, needles etc should be dispensed with and replaced by a much simpler and reliable selection mechanism. • The mass of remaining mechanical elements eg. Knives & hooks which continually move to & fro and are subjected to constantly repeated high acceleration & deceleration forces, should be reduced. Also the power needed to drive the knives & patterning hooks should be minimized. (Reinforced plastic incorporating carbon fibre).
- 46. Design Requirement of Electronic Jacquard • The system should be extremely flexible with possibility of quicker design changing so as to enable weaver to remain competitive in an everchanging world. • Needs for higher productivity, better quality & greater flexibility. • A modern jacquard of average configuration operating on a high speed weaving machine can involve nearly 700 million selection process in a 8 hour shift.
- 47. Design Requirement of Electronic Jacquard • If the jacquard has to perform error free over long periods, the high performance can be achieved by major changes in its operation. The modification aimed at achieving this are 1. Keeping the movements involved to minimum. 2. Extremely fine tolerance in engineering & fitting. 3. Use of high wear resistant materials. 4. Use of lighter materials like reinforced plastic. 5. Reduced downtime by longer life of components & easy changeover facilities etc…
- 48. Data Transfer & Management