Weaving Mechanisms PDF

Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) The Shedding Motion Warp yarns are divided into two layers. Top layer is called top shed line. Bottom layer is called bottom shed line. The gap b/w two layers is called shed....

Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) The Shedding Motion Warp yarns are divided into two layers. Top layer is called top shed line. Bottom layer is called bottom shed line. The gap b/w two layers is called shed. Objectives of the Shedding Motion To raise & lower the healed frames which carry the warp yarns. To make an opening for the passage of picking media. To change the position of warp yarns to interlace the warp & weft as per weave design. Types of the Sheds Different types of shedding mechanisms create four different types of sheds: o Bottom closed shed o Semi open shed o Centre closed shed o Fully open shed Types of the Shedding Mechanisms There are four types of shedding mechanisms as: o Crank shedding o Tappet shedding o Dobby shedding Prepared By: Shakeel Ahmad Paracha Page 1 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) o Jacquard shedding First three shedding mechanisms make use of frames to lift and lower the warp yarns whereas the jacquard shedding mechanism uses individual harness to lift an individual warp yarn. These are the attachments that can be fitted on any loom. Therefore, looms can be classified as: o Crank loom o Tappet loom o Dobby loom o Jacquard loom Positive Shedding Raising & lowering of healed frames is done with the help of Double cams. Negative Shedding Shedding is taken to be negative when the heald frames are either raised or lowered by the mechanism but are returned by the action of some external device, such as springs. Reversing Media The media which brings back the frames in its original position, it may be spring pullies & elastic. Crank Shedding It is the simplest shedding mechanism that can be run at highest loom speed with minimum fabric faults. This mechanism make use of two identical eccentrics/levers placed opposite to each other. This shedding mechanism is suitable only for plain weave. So, this is the major disadvantage of this shedding mechanism that it provides no variety and only plain weave can be made. Prepared By: Shakeel Ahmad Paracha Page 2 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Tappet Shedding It is also a simple shedding mechanism that can be run at highest loom speed with minimum fabric faults. The tappet cam shedding mechanism can handle up to 8 -12 heald frames. This gives the ability to make plain weave, warp rib, weft rib, simple twills, Satin/Sateen and Stripe Satin etc. Tappet cams are used to operate healed frames. Cams are designed according to the type of weave. No. of cams depend upon the weave repeat. e.g., 4 cams for 3/1 twill weave. Tappet cam designed for one weave cannot be used for other weave. Storage of cams is necessary in the mill. Tappet cams are installed on counter shaft or tappet shaft. Tappet shedding mechanism is simple, inexpensive, and easy to maintain and handle. This shedding mechanism does not cause any faults in the fabric because of its simplicity. They also do not impose any limitations on the loom speed. Main disadvantage of this shedding mechanism is that whenever weave design is to be changed, it is necessary to change or at least re-arrange the tappets/cams. Also, if the new weave design has different number of picks per repeat, then gearing to the shaft that drives the tappets must also be changed. Furthermore, tappet cam shedding can only handle square weave designs i.e. only those designs that have same number of ends and picks per repeat. No. of cams for different weaves are as follows: Prepared By: Shakeel Ahmad Paracha Page 3 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) What is a Cam? Cam is a specially designed rotating or sliding piece of metal. Cam is used to convert a rotating motion to a linear reciprocating motion or vice versa. A cam always work in conjunction with a cam follower which helps to transmit the drive. The shape of a cam is specially designed for special purposes. The shape of a cam is different for different weaves. Cam is always given an eccentric motion i.e. its axis of rotation is kept away from the centre. A cam has a flatter portion called base or dwell and a pointed portion called as nose. Tappet cams for shedding motion are designed according to the weave design. For example, for plain weave, cams are designed in pair for two picks per repeat, for 2/1 twill, cams are designed in a group of three i.e. for three picks per repeat and so on. Shedding cams are installed on counter shaft or tappet shaft of the loom. The speed of the tappet or counter shaft must be reduced according to the number of cams installed, e.g., for 3/1 twill the speed of the tappet shaft must be reduced by 1/4 of the main shaft. For 8 thread sateen, the speed must be reduced by 1/8 of the main shaft. Different Cam-Follower Arrangements Construction of a Cam Factors on which construction of tappet cam depends upon: o Type of weave o Dwell period of heald frame o Stroke of heald frame o Dia. of treadle bowl o Nearest point of contact of tappet cam with treadle bowl (the point from where the radius of cam is min. the distance is taken as nearest point). Stroke It is the maximum displacement of healed frame, when it is at its max. position and on its min. position. Prepared By: Shakeel Ahmad Paracha Page 4 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Dwell Period The time for which reed is stationary at rare most position is known as dwell period of reed or the time taken by the heald frame (HF) to come back to its original position. The HF remains stationary in shed opening position and picking media passes through shed. It has direct relation with width of machine and indirect relation with speed of machine. Treadle Bowl Treadle bowl is a kind of lever which moves up and down by the movement of cams. Resultantly, Treadle bowl moves the heald frames up and down. Throw or Lift of a Cam The amount of distance by which a cam is able to lift or displace a heald frame is called as its lift or throw. The lift or throw of a cam is found out as: Repeat Size Limitations of Cams Practically, the cam shedding systems can handle a weave design of 8 - 12 picks per repeat. This is due to the fact that as the number of cams increases, the slope of the cam contour also increases. Consider a 8 cams system for a weave design of 8 picks per repeat. In this case 8 cams will be installed on the counter shaft at an angle of 45° (360/8) from each other. As the number of cams are further increased, the design of the cam would become such that its slope would be further increased. This increases the maximum force acting in the system. Therefore, to produce a vertical force (F) to lift the heald frame, the cam must apply force (R) on the cam follower. As the slope of the cam contour increases (with the increase in the number of cams), the force (R) also increases. To avoid excessive force in the system (to avoid excessive wear and tear) the maximum contour of the cams has to be minimized. This is only possible with low number of cams. Prepared By: Shakeel Ahmad Paracha Page 5 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Therefore, in actual practice, it is not feasible to have more than 8 - 12 cams installed on counter shaft. Types of Tappet Shedding There are two types of Tappet Shedding. o Negative Tappet Shedding o Positive Tappet Shedding Negative Shedding Shedding is taken to be negative when the heald frames are either raised or lowered by the mechanism but are returned by the action of some external device, such as springs. Positive Shedding Healed frames are raised & lowered by double cams. Reversing Media The media which brings back the frames in its original position, it may be spring, pullies, & elastic etc. Negative Tappet Shedding Definition Healed frames are lowered by single cams & raised by reversing media (springs, reversing pulley and elastic material). Drive It gets drive from bottom shaft. Working Principle The rotary motion of tappet cams is converted into up & down motion of healed frames. Construction Treadle Lever: One end of treadle lever is fulcrum at point “F” while the other end is connected to the bottom of the healed frames through connecting rod. Treadle Roller or Bowl: Fixed at the treadle lever. Tappet Cam: Fixed on the bottom shaft. Healed Frames: These are tied at top by means of cords or leather strap: strap is passing on the reversing pulley. Prepared By: Shakeel Ahmad Paracha Page 6 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Working When the bottom shaft revolves, the tappet cams fixed on it also revolves in the same direction. The tappets are adjusted at definite angles on the bottom shaft. Suppose tappet/cam “A” is pressing the treadle lever “D” through treadle roller “R”, the heald frame connected to the treadle lever “D” will come down & the second frame will go up due to reversing mechanism. The warp yarns passing through 1st heald frame will form bottom shed line & warp yarns passing through 2nd frame will form top shed line. The weft yarn will pass through the shed at that time. The treadle lever “E” will be pressed by 2nd tappet “B” & the heald frame connected to the treadle lever “E” will move downward. The 1st frame will move up due to the reversing mechanism. In this way, shedding will continue. Reversing Motion on Negative Shedding Positive Tappet Shedding Definition That type of tappet shedding in which healed frames are raised & lowered by double cams (matched cam or conjugate cams). Prepared By: Shakeel Ahmad Paracha Page 7 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Drive It gets drive from tappet shaft. Working Principle The rotary motion of the double cams is converted into up & down motion of the healed frames. Construction Double Cams: Double cams are fitted on the tappet shaft. Treadle Lever: Treadle lever has fulcrum point at F1, upper part of it is connected with fork lever & lower part has contact with the double cams through treadle rollers. Link Rods: One end of it is connected to fork lever & other end with the top of driving rod. Driving Rod: It is fulcrum at F2 & lower end of it is connected to bottom of heald frame through harness lever, T-lever & connecting levers. Lock Screw: It is used to connect link rod. Clamp Screw: It is used for the adjustment of fork lever by moving it up and down. Working When tappet shaft is revolving, the double cams are also revolving. Heald Frame moves downward Suppose the lower cam “A” is pressing the lower treadle roller “E” the treadle lever will move toward the loom side. The upper portion of it will move away the loom direction. The link rod & upper of driving rod will also move in the same direction. The lower portion of the driving rod will move toward the loom side & the heald frame will be lowered through harness lever, T-lever & connecting levers. Heald Frames moves upward Suppose the upper cam “B” is pressing the upper treadle roller “D”, the top of the treadle lever will move towards the loom direction. The link rods & upper of driving rod will also move in the same direction. The lower portion of the driving rod will move away the loom side & the heald frame will move upward through harness lever, T-lever & connecting levers. Prepared By: Shakeel Ahmad Paracha Page 8 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Shed Settings Shed Opening If we move the fork lever upward with clamp screw the opening will increase & vice versa. Shed Height If we increase the length of link rods by lock screw, the height will increase & vice versa. Prepared By: Shakeel Ahmad Paracha Page 9 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Dobby Shedding Dobby shedding is a versatile method of creating a shed and is most commonly designed to handle 12, 16, 20, 24, 28 and up to 32 heald frames. More sophisticated weaves can be woven using dobby shedding mechanism. The dobbies are always mounted in bottom position, except in water jet looms, where the dobbies are mounted in upper position to avoid contact with water. Dobby shedding has virtually no limit to the number of picks per repeat. Therefore, dobby shedding is very suitable to produce fancy weave designs like stripes, checks, geometrical patterns, borders. Dobby shedding mechanism is more complicated than crank or cam systems. They also have a higher initial and maintenance cost. Due to the complexity, dobby shedding is more liable to produce fabric faults as compared to crank or cam shedding systems. Dobby shedding looms also run slower as compared to crank and tappet/cam shedding. The main advantages of the dobby shedding system are: o Variety of weave designs can be produced. o Can handle unlimited picks per repeat of the weave design. o The change over of the weave design on the loom is much easier than cam shedding. o Settings are also easier and convenient. Classification of Dobby Shedding Dobby shedding mechanisms can be classified on various grounds. Mainly they can be classified according to the: o Working Principle o Drive o Performance o Method of Weave Selection According to Working Principle According to the working principles the dobbies can be classified as: o Lever Operated or Reciprocating Dobby o Rotary Dobby In lever operated dobbies movement of the heald frames is controlled through rods and rocker levers. Whereas rotary dobbies attain the raising and lowering of the heald frame through rotating components. According to Drive According to the drive dobbies can be of two types: o Negative Dobbies o Positive Dobbies In negative dobbies, heald frames are lifted by dobby mechanism while the lowering of frame is achieved due to springs. Prepared By: Shakeel Ahmad Paracha Page 10 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) In positive dobbies, both raising and lowering of heald frames is obtained directly by the dobby mechanism. According to Performance or Lift According to the performance or speed of the dobbies, they are classified as: o Single Lift Dobbies o Double Lift Dobbies Old dobbies were designed as single lift dobbies which were slow. Nowadays, all modern dobbies are designed as double lift and they can run at faster speeds. Single Lift Dobbies In single lift dobbies the mechanism performs the functions once in every pick cycle to open a shed and to return the frame to its original position. Such a mechanism produces either a center closed or bottom closed shed. The single lift dobbies are given their drive from the main shaft and therefore have less time to perform their tasks. Due to the above reason, the single lift dobbies can only run at speed of 160 to 180 ppm. Double Lift Dobbies All latest dobbies are double acting in its drive. Here the cycle of dobby mechanism completes every two picks. The elements of dobby work after every two picks but the shed opening is achieved in every pick cycle. Most of the operations in double lift doubles occur at half the speed of the loom. An open shed is formed, and unnecessary wasted movements are eliminated. These dobbies are suitable for high speed looms. According to Method of Weave Selection Based on the method of selection of weave designs, dobbies are classified as: o Mechanical Dobbies Chain Lattice with Pegs Continuous Pattern Card o Electronic Dobbies Prepared By: Shakeel Ahmad Paracha Page 11 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Principle of Dobby Shedding Mechanism Every dobby shedding mechanism consists of three principle mechanisms: o Drive Mechanism o Selection Mechanism o Lifting Mechanism A permanent drive from either the main or bottom shaft either operates reciprocating knives (in lever dobbies) or operates rotary components/cams (in rotary dobbies). The selection mechanism i.e. whether to lift a heald frame on a particular pick or not comes from the punched card, pegged lattice or electronic means. The selection mechanism checks the weave design information and transmits the necessary motion from the drive mechanism to the lifting mechanism. The lifting mechanism operates the lifting and lowering of the heald frames. Single Lift Negative (SLN) Dobby Fig. (a) Fig. (b) Keighley Double Lift Negative (KDLN) Dobby The basic mechanism of all modern double lift negative dobbies are derived from the Keighley dobby. Keighley dobby has two working knives, two hooks and two feelers for each heald frame. Both are placed opposite to each other and completes one reciprocation after every two picks. This mechanism selects two picks at a time from the lag, i.e., the lattice moves after every two picks. A simple line diagram of the Keighley dobby is given below: Prepared By: Shakeel Ahmad Paracha Page 12 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) As far as the selection mechanism is concerned, following four possibilities exist: Case 1: No pegs for both the Feelers (F1 & F2) Case 2: Peg for Feeler (F1) & no peg for Feeler (F2) Case 3: No peg for Feeler (F1) & peg for Feeler (F2) Case 4: Pegs for both the Feelers (F1 & F2) Based on the above four cases, the drive of the knives is transmitted to the frames accordingly. Case 1: No pegs for both the Feelers (F1 & F2) When there are no pegs for both the feelers (F1 & F2) then the heald frame will remain down on the two consecutive picks. Because: o The knives K1 and K2 will miss the hooks H1 and H2 on the first and second pick respectively and will pass beneath the hooks H1 and H2 giving no motion to the heald frame i.e., the heald frame will be kept down. Case 2: Peg for Feeler (F1) & no peg for Feeler (F2) When there is a peg for the feeler F1 & no peg for the feeler F2 then the heald frame will be up on the first pick and heald frame will be down on the second pick. Because: o On the first pick, the knife K1 will catch the hook H1 to up the heald frame and the knife K2 will miss the hook H2. Prepared By: Shakeel Ahmad Paracha Page 13 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) o On the second pick, both the knives K1 and K2 will miss the hooks H1 and H2 respectively and will pass beneath the hooks H1 and H2 giving no motion to the heald frame i.e., the heald frame will be kept down. Case 3: No peg for Feeler (F1) & peg for Feeler (F2) When there is no peg for feeler F1 & peg for feeler F2 then the heald frame will be down on the first pick and heald frame will be up on the second pick. Because: o On the first pick, both the knives K1 and K2 will miss the hooks H1 and H2 respectively and will pass beneath the hooks H1 and H2 giving no motion to the heald frames i.e., the heald frames will be lowered. o On the second pick, the knife K1 will miss the hook H1 and knife K2 will catch hook H2 to up the heald frame. Case 4: Pegs for both the Feelers (F1 & F2) When there are pegs for both the feelers (F1 & F2) then the heald frame will remain up on the two consecutive picks. Because: o On the first pick, the knife K1 will catch the hook H1 to up the heald frame and the knife K2 will miss the hook H2. o On the second pick, the knife K1 will miss the hook H1 and the knife K2 will catch the hook H2 to up the heald frame. Pegging of Lattice for Dobby Shedding Prepared By: Shakeel Ahmad Paracha Page 14 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Positive Dobby Shedding The positive dobbies have the ability to move the heald frames in both directions. Thus, positive dobbies eliminate the use of spring reversing motion. The positive dobbies have more control of the shedding mechanism and can run safely at higher speeds as compared to negative dobbies. Knowles dobby is one of the earliest types of positive rotary dobby mechanism. The Knowles dobby is single acting or single lift i.e. it performs shedding mechanism after every pick and has become completely obsolete now. Knowles Single Lift Positive (KSLP) Dobby In Knowles dobby both the top and the bottom of the heald frame are connected to the jack with the help of suitable lever arrangement. The jack is also connected to the centre of the vibrator gear by means of a connector or lever. For each heald frame, there is a separate vibrator gear. Two cylinders C1 and C2 are placed just below and above the vibrator gear respectively. Both the cylinders C1 and C2 are extended to the full width of the dobby and they work for all vibrator gears of the heald frames. Both the cylinder gears C1 and C2 have teeth on only half of their circumference, while the other half of the circumference is left blank. The cylinder C1 is rotated in the clockwise direction, while the cylinder C2 is driven in the counter clockwise direction. Both these cylinder gears complete one revolution after every pick. The circumference of the vibrator gear is also not fully covered with teeth. A blank surface of 1 tooth is left on one side while a blank surface of 3 teeth is left on the other side. Initial Position of Gears At the initial position the vibrator gear is kept down. The position of the vibrator gear is such that one tooth gap is at the top while 3 teeth gap is at the bottom. At this position, the Cylinder gear C1 is unable to give drive to the vibrator gear because of the 3 teeth gap. The decision of whether to lift a frame or not comes from the selection mechanism. Prepared By: Shakeel Ahmad Paracha Page 15 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) The selection mechanism comprises of a pattern lattice which may have riser for every respective heald frame. In case of a riser, the heald frame will be lifted up and will remain up until it needs to be lowered. If there is no riser present, the heald frame will go down and remain down until it needs to be lifted. Therefore, this shedding mechanism produces a fully open shed and wasted movements are avoided. Case 1 – When riser is not present When there is no riser on the lattice for a frame, the position of the vibrator gear will remain down and therefore the frame will also remain down. This position is maintained for as many No. of picks as required. Case 2 – When riser is present When there is riser for a frame, the vibrator gear will be lifted. The Cylinder Gear C2 will now be able to mesh with one tooth gap and will move the vibrator gear in clockwise direction. This will cause the frame to move up. The frame will be kept lifted as long as there is a riser and will only go down when no riser is available for that frame. Prepared By: Shakeel Ahmad Paracha Page 16 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Method of Weave Selection The method of weave selection in earlier dobbies used wooden lattice where the signal to lift the heald frame is given by using peg or riser. The above design was improved and signal to lift the heald frame was designed using a continuous punched paper, where a punch hole for a heald frame enable lifting. The continuous paper was later replaced with continuous plastics sheet. In the latest electronic dobbies, solenoids are used and there is no physical method of weave selection. The decision of whether to lift the frame or not is electronically fed to the loom. The solenoids control the lifting of individual frames. Punched Paper/Plastic Method of Selection The selection needles n1 & n2 feels the presence of the hole on the paper for hooks H1 & H2. The needle n1 or n2 falls if there is a hole for them. When this happens, the supplementary knives k1 or k2 is able to move the rod r1 or r2 away from the path of lifting block b1 or b2. Therefore, the hook H1 or H2 remains down and its corresponding knife K1 or K2 is able to lift the corresponding heald frame. This method of selection is more accurate as compared to pegged lattice and with the help of a punching machine the punched paper pattern also takes very less time to prepare. Prepared By: Shakeel Ahmad Paracha Page 17 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Hattersley Double Lift Positive (HDLP) Dobby The double lift positive dobbies that work on the principle of reciprocating knives are classified as Hattersley dobbies. The Hattersley dobbies are very similar to the Keighly dobbies that are also reciprocating type but are double lift negative type. Since there are no return springs present, the knives and the baulk should be rigidly attached to the heald frames to achieve both upward and downward motions. The working principle of double lift Hattersley dobby is shown in the figure below: Prepared By: Shakeel Ahmad Paracha Page 18 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Hattersley dobby Hattersley dobby Here two push bars B1 & B2 are rigidly attached to the knives K1 & K2 and reciprocates along with these knives respectively. Two stop bars S1 & S2 are also provided for the baulk opposite to push bars B1 & B2 respectively. Two locking bars L1 & L2 are also provided for Hooks H1 & H2 respectively. As the knife returns after displacing a hook, its baulk bar pushes the corresponding end of the baulk against its stop bar (S1 or S2). The appropriate lock bar L1 or L2 will hold the bottom of the baulk against its stop bar S1 or S2 and will prevent the frame to go down until the time of next weave selection comes. The locking bars can only engage or disengage at the time of weave selection. Prepared By: Shakeel Ahmad Paracha Page 19 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Rotary Dobby Today, the reciprocating dobbies are only manufactured on positive double lift principle. The highest speed possible to achieve by this method is 500 rpm. In order to achieve dobby shedding at faster speeds, next generation Rotary Dobby is developed. The rotary dobby can run at loom speed of 1000 to 1500 rpm. The term Rotary is used because instead of using reciprocating knives, rotary elements in the dobby shedding are used to lift the heald frames. The rotary dobbies have a cam unit built into the dobby mechanism. Each cam unit is only 12 mm wide and controls one heald frame. The cam unit consists of crank disc that contains: o The cam Itself o Ball bearings for free rotation of cam o Coupling ring o Moveable key Both the cam and the coupling ring fixed to it freely rotates. Rotary Dobby - Selection Mechanism The moveable key attached to the connecting rod is moved by a ratchet placed outside the cam. The ratchet is controlled according to the weave design. When the frame is to be lifted, the ratchet moves the moveable key into a position where it engages with the coupling ring. Therefore, the rotation of the cam and coupling ring is transferred to the connecting rod and ultimately to the jack and the frame is lifted. Prepared By: Shakeel Ahmad Paracha Page 20 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Electronic Rotary Dobby In electronic dobbies the movement of the ratchet instead of a mechanical mean, is achieved electronically using solenoids or electromagnets. Each unit has its own solenoid. If the frame is to be lifted, the electromagnet or solenoid is charged with current which attracts the ratchet so that key could be engaged. Electronic dobby uses a computer to feed the required lifting order of the weave design. The microprocessor of the dobby reads the design and passes signal to their respective solenoids to either lift the frame or not. Prepared By: Shakeel Ahmad Paracha Page 21 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) What is Jacquard Shedding? Jacquard shedding mechanism was invented by a French Silk weaver Joseph Marie Jacquard in 1801. Other types of shedding mechanism used for creation of shed are: o Crank shedding o Tappet shedding o Dobby shedding The above listed shedding motions rely on the use of heald frames to create a shed. Whereas in jacquard shedding instead of heald frames, number of harnesses are used. Each end is passed through an individual harness eye whose lifting and lowering is individually controlled by jacquard shedding mechanism. So, by eliminating the frames and using individual harnesses, the capacity of jacquard shedding motion is increased considerably. The capacity of latest electronic shedding motion has reached up to 25,000 hooks or ends per repeat. The Jacquard Harness System The jacquard shedding mechanism is suspended from the ceiling and is placed above the loom. The jacquard shedding mechanism is connected to the loom through the jacquard harness system. The jacquard harness is the system of cords, heald eyes and lingoes that transmit the movement of the jacquard hooks to the individual warp yarn. At about one metre below the jacquard mechanism, a comber board is placed. The harnesses after passing through the comber board comes straight and parallel on the loom. Prepared By: Shakeel Ahmad Paracha Page 22 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) The Capacity of Jacquard The capacity of jacquard to handle ends per repeat depends upon the number of hooks present in it. The jacquard mechanism is composed of number of hooks placed in rows. The total jacquard capacity is found out by: Jacquard capacity = Number of hooks in one row x Number of rows The hooks are moved up and down according to the weave design. Since, harnesses are attached to these hooks, so they also move up and down with the hook. For example, if 8 hooks are placed in one row and there are 50 such rows then the total capacity of jacquard would be 400 (8 x 50) as shown below: Jacquard Card Punching The jacquard cards are carried by the cylinder which presents one card to the needles after every pick. So, the number of cards required for a particular weave design must be equal to number of picks per repeat of the design. The size and the number of holes that any jacquard card can have depends upon the jacquard capacity. For example, for 400 (8 x 50) capacity jacquard there would also be 400 needles placed in the order of 8 x 50 corresponding to positions of hooks as shown below: Prepared By: Shakeel Ahmad Paracha Page 23 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) The number of cards that make up one repeat are laced together to form a loop which is repeated again and again throughout the weaving process. Consider a portion of the weave design for which the cards have to be punched. Number of Harnesses per Hook To each hook of the jacquard shedding mechanism several harnesses are attached. The number of harnesses to be attached to each hook depends upon: o The ends per repeat of the weave design o Total ends present in the fabric o Jacquard capacity Example 1 How many harnesses will be attached to each hook if the capacity of jacquard is 400 (8 x 50) and the fabric being produced completes on 400 ends per repeat. The total ends in the fabric are 1600. o Solution ▪ Ends per repeat = 400 ▪ Jacquard capacity = 400 ▪ Total ends = 1600 ▪ Harnesses per hook =? Number of repeats handled by jacquard = Jacquard capacity/(Ends per repeat Number of repeats handled by jacquard = 400/400 = 1 Utilized jacquard capacity = Number of repeats handled by jacquard x Ends per repeat Utilized jacquard capacity = 1 x 400 = 400 Harnesses per hook = Total ends/Utilized jacquard capacity Harnesses per hook = 1600/400 = 4 Prepared By: Shakeel Ahmad Paracha Page 24 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Example 2 A fabric design completing on 200 ends and 400 picks per repeat is to be produced on a jacquard of 600 capacity (12 x 50). The width of the fabric is 60" and has 60 ends and picks per inch. How many harnesses will be attached to each hook? o Solution ▪ Ends per repeat = 200 ▪ Ends per inch = 60 ▪ Width = 60" ▪ jacquard capacity = 600 ▪ Harnesses per hook =? ▪ Total ends = Ends per inch x Width = 60 x 60 = 3600 Number of repeats handled by jacquard = Jacquard capacity/(Ends per repeat) Number of repeats handled by jacquard = 600/200 = 3 Utilized jacquard capacity = Number of repeats handled by jacquard x Ends per repeat Utilized jacquard capacity = 3 x 200 = 600 Harnesses per hook = Total ends/Utilized jacquard capacity Harnesses per hook = 3600/600 = 6 Example 3 A weave completing on 150 x 300 threads is to be produced on a jacquard having capacity of 400 (10 x 40). Calculate the size of the repeat in inches and harnesses per hook. The fabric is woven at a width of 50" with 60 ends and 60 picks per inch. o Solution ▪ Ends per repeat = 150 ▪ Picks per repeat = 300 ▪ Fabric width = 50" ▪ Ends per inch = 60 ▪ Picks per inch = 60 Prepared By: Shakeel Ahmad Paracha Page 25 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) ▪ Harnesses per hook =? ▪ Jacquard capacity = 10 x 40 = 400 ▪ Total ends = 60 x 50 = 3000 Number of repeats handled by jacquard = Jacquard capacity/(Ends per repeat) Number of repeats handled by jacquard = 400/150 Number of repeats handled by jacquard = 2.66 or 2 Utilized jacquard capacity = Number of repeats handled by jacquard x Ends per repeat Utilized jacquard capacity = 2 x 150 = 300 Harnesses per hook= Total ends/Utilized jacquard capacity Harnesses per hook= 3000/300 = 10 Width of repeat = (Ends per repeat)/(Ends per inch) Width of repeat = 150/60 = 2.5" Height of repeat = (Picks per repeat)/(Picks per inch) Height of repeat = 300/60 = 5" Casting Out In case of shedding mechanisms other than jacquard, the warp thread density can be controlled by changing the reed count and reed plan. However, since every jacquard has a specific harness density i.e., number of harnesses per inch, therefore the maximum ends per inch achievable on the loom is equal to the harness density. There is no possibility of having ends per inch greater than harness density, however, by the process of casting out, warp thread density less than harness density can be obtained. Example 1 Show a casting out plan for obtaining a warp thread density of 30 ends per inch if the harness density of the jacquard is 40. The capacity of the jacquard is 400 (8 x 50). Also, show the effective and remaining jacquard capacity after casting out. o Solution ▪ Harness density = 40 Harnesses per inch ▪ Ends per inch required = 30 ▪ Jacquard capacity = 400 Casting out plan = (Ends per inch required)/Harness density Casting out plan = 30/40 = 3/4 (3 out of 4 hooks utilized) Effective jacquard capacity = Jacquard capacity x Casting out plan (utilized hooks) Effective jacquard capacity = 400 x 3/4 = 300 hooks Remaining jacquard capacity = Jacquard capacity x Casting out plan (remaining hooks) Remaining jacquard capacity = 400 x 1/4 = 100 hooks Prepared By: Shakeel Ahmad Paracha Page 26 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Example 2 The harness density of a jacquard having a capacity of 400 (8 x 50) is 80. If 40 ends per inch are required in the fabric, show the necessary casting out. Also, calculate the effective and remaining capacity after casting out. o Solution ▪ Harness density = 80 Harnesses per inch ▪ Ends per inch required = 40 ▪ Jacquard capacity = 400 Casting out plan = (Ends per inch required)/Harness density Casting out plan = 40/80 = 1/2 (1 out of 2 hooks utilized) Effective jacquard capacity = Jacquard capacity x Casting out plan (utilized hooks) Effective jacquard capacity = 400 x 1/2 = 200 Remaining jacquard capacity = Jacquard capacity x Casting out plan (remaining hooks) Remaining jacquard capacity = 400 x 1/2 = 200 Prepared By: Shakeel Ahmad Paracha Page 27 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Prepared By: Shakeel Ahmad Paracha Page 28 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Example 3 The harness density of a jacquard is 100. If 70 ends per inch are required in the fabric, show the necessary casting out. Also, calculate the effective and remaining capacity after casting out if the capacity of the jacquard is 600 (10 x 60). o Solution ▪ Harness density = 100 Harnesses per inch ▪ Ends per inch required = 70 ▪ Jacquard capacity = 600 Casting out plan = (Ends per inch required)/Harness density Casting out plan = 70/100 = 7/10 (7 out of 10 hooks utilized) Effective jacquard capacity = Jacquard capacity x Casting out plan (utilized hooks) Effective jacquard capacity = 600 x 7/10 = 420 Remaining jacquard capacity = Jacquard capacity x Casting out plan (remaining hooks) Remaining jacquard capacity = 600 x 3/10 = 180 Prepared By: Shakeel Ahmad Paracha Page 29 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Classification of Jacquard Shedding Various jacquard shedding systems that are presently being used can be classified according to the following basis: o According to lift o According to pitch o According to selection of weave design o According to cylinders According to Lift The jacquard shedding mechanism according to the lift can be classified as: o Single lift jacquard o Double lift jacquard The single lift or single acting jacquards work after every pick cycle and are slower in operation. Whereas, the double lift or double acting jacquards work after every two picks and are used for higher speed looms. According to Pitch The term pitch refers to the distance between the centres of two consecutive needles. According to pitch, jacquards are classified as: o Coarse pitch jacquard o Fine pitch jacquard If the needles are coarse then the pitch will be high, and less number of needles can be accommodated in a given area and vice versa. The coarse pitch jacquard also known as English jacquards, because of coarse needles have a limited capacity. The common sizes of coarse pitch jacquard are 200, 400, 600, and 800. The fine pitch jacquard is also called as French pitch or Continental pitch jacquard. These are modern types of jacquards that were originated in France and has the capability to make a fully open shed. The most popular fine pitch jacquards are the Verdol and Vincenzi jacquards. The typical sizes of the fine pitch jacquard are 880 or 1320 (Vincenzi) and 896 or 1344 (Verdol). According to Selection of Weave Design According to the selection method of weave design, jacquards are of the following two types: o Mechanical jacquards ▪ Punched card type ▪ Continuous paper type o Electronic jacquards The mechanical jacquards have a mechanical means of selecting the weave design, whereas, in electronic jacquards, the selection is done electronically without the need of any punched or continuous paper. The earliest form of the mechanical jacquards made use of punched pattern card. Each card represents one pick. Several cards are joined to form a loop. Prepared By: Shakeel Ahmad Paracha Page 30 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) The punched cards are mounted on a cylinder which intermittently rotates after one or two pick cycles. The punched card was then replaced by an endless plastic paper. This paper also has holes punched into its surface according to the weave design. The paper has the advantage that it is lighter, stronger and consumes less space. The most modern form of the jacquard is the electronic jacquard in which no paper or card is used. The lifting order is fed to the loom by a computer electronically. The movement of the hooks in electronic jacquards is done by using solenoids. As the solenoid is charged, it becomes an electromagnet which attracts the hook up and hence the end is lifted. As the solenoid is discharged, the hook is released, and the end is moved down. According to Cylinders According to the number of cylinders used in jacquard shedding mechanism, jacquards are classified as: o Single cylinder jacquards o Double cylinder jacquards The single cylinder jacquards have only one operating cylinders, whereas, double cylinder jacquards have two cylinders available i.e. one for the odd picks and other for even pick. Prepared By: Shakeel Ahmad Paracha Page 31 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Principle of Jacquard Shedding Mechanism [Single Lift Single Cylinder (SLSC) Jacquards] The jacquard shedding mechanism can be easily understood by studying the very basic single lift negative shedding mechanism. Being single lift, all working parts of the shedding mechanism complete its cycle once in every pick. Being negative in action, the lifting of harness is achieved through the jacquard hooks while the lowering is done by virtue of dead weights attached to the harness. The single lift jacquard has one needle and one hook for each end in the repeat. Each needle is kinked or curved around the vertical hook to the movement of each hook. Each hook is connected to each harness after passing through a grate. On the left side of each needle a spring is provided that pushes the needles on the right side. The right side of the needles touch the pattern card that is mounted on the cylinder. The pattern card has holes punched according to the weave design. The punching of the card is done for each pick in the repeat. The cards are laced together to form a continuous chain. The cylinder moves by one card after every pick. For each row of hooks, one row of lifting knifes is provided. For 400 capacity jacquards (8 x 50), there would be 8 rows of knives provided on the griffe. All the knives are fixed in a frame called as griffe. The griffe reciprocates once after every pick and is normally driven from crank shaft. The single lift, single cylinder produces a bottom closed shed. The single lift negative shedding mechanism is shown in the figure below: Fig. (1) Prepared By: Shakeel Ahmad Paracha Page 32 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Fig. (2) Fig. (3) Prepared By: Shakeel Ahmad Paracha Page 33 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Fig. (4) Fig. (5) Prepared By: Shakeel Ahmad Paracha Page 34 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Fig. (6) Fig. (7) Prepared By: Shakeel Ahmad Paracha Page 35 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Fig. (8) Fig. (9) Prepared By: Shakeel Ahmad Paracha Page 36 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Fig. (10) Fig. (11) Prepared By: Shakeel Ahmad Paracha Page 37 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Fig. (12) Fig. (13) Prepared By: Shakeel Ahmad Paracha Page 38 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Fig. (14) Fig. (15) Prepared By: Shakeel Ahmad Paracha Page 39 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Fig. (16) Double Lift, Single Cylinder Jacquard (DLSC) The double lift jacquards have twice the number of hooks than its needles. For example, a 400 needle jacquard will have 800 hooks. Each needle in this case controls two hooks and both of these hooks control lifting of a single end depending of the weave design. The pair of hooks is connected to one neck-cord/warp end. One hook (odd numbered) controls the neck-cord/warp end in the odd picks and the other hook (even numbered) controls the neck-cord/warp ends in the even picks. The double lift, single cylinder jacquard has two sets of knives, each set placed on a separate griffe. The first set of knives controls the odd hooks and the second set controls the even hooks. The two sets of knives are operated in the alternate order, one set is rising while the other is descending at the same time. The two griffes moves in opposition to each other and completes one reciprocation after every two picks. The cylinder moves intermittently after every pick presenting a new punched card to the needles. Although, the movement of knives is double acting, this type of jacquard cannot be truly classified as double acting shedding mechanism. Because even though the knives work after every two picks cycle, but the cylinder has to move after every pick i.e. its movement is single acting type. Double-lift single-cylinder (DLSC) jacquard is shown in Figure. Prepared By: Shakeel Ahmad Paracha Page 40 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) In this case, one end is controlled by two hooks which are controlled by a single needle. For example, hooks 1 and 2 control the end 1 and hooks 3 and 4 control the end 2. Two sets of knives are used in DLSC jacquard and they move up and down (rise and fall) in complete phase difference i.e. when one set of knives (K1 and K3) attain the highest position, the other set of knives (K2 and K4) attain the lowest position. At the given position, end 1 has been raised as the hook 1 has been lifted by the corresponding knife K1. However, end 2 has not been raised as hook 3 was not caught by the knife K3. In the next pick, end 1 will be lowered as the needle E has been pressed towards the left due to the absence of a hole in the punch card. So, hook 2 has become tilted and it will not be raised by the knife K2 when the latter will rise. Hook 1 will also descend along with knife K1. Thus, the end 1 will be lowered. On the other hand, end 2 will be raised in the next pick as there is a hole in the punch card corresponding to the position of the needle F. So, hook 4 is upright and it will be caught by knife K4 when the latter will move upward. Prepared By: Shakeel Ahmad Paracha Page 41 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) In case of DLSC jacquard, if the loom speed is 300 picks per minute then the cylinder will turn 300 times per minute, but the knives will reciprocate (rise and fall) 150 times per minute. This is the advantage of DLSC jacquard over SLSC jacquard. DLSC jacquard produces semi open shed because if a particular end has to be in raised position for two consecutive picks, it will descend up to the middle point of its vertical path and then move up. This will happen because one of the hooks will descend and the other hook will move up with their respective knives and they will cross at the middle of their vertical path. If the end has to remain in bottom position for two consecutive picks, it will remain at the bottom without any intermediate movement. Double Lift, Double Cylinder jacquard (DLDC) In double lift, double cylinder jacquard, each harness or end is controlled by two needles and two hooks. Therefore a 400 capacity machine will have 800 hooks and 800 needles. Here two cylinders are provided, one carries a pattern card for odd numbered picks and the other cylinder carries a pattern card for even numbered picks. One cylinder is placed on the right side while the other cylinder is placed on the left side. On odd picks, the odd numbered cylinder is presented and on even picks, the even numbered cylinder is presented to the needles. Apart from this, the working is similar to the double lift, single cylinder jacquard. Figure depicts the double-lift double-cylinder (DLDC) jacquard. In case of DLDC jacquard, the number of cylinder rotation or turn and number of reciprocation cycle of knives is half as compared to that of SLSC. In this case, one end is controlled by two hooks as it was in case of DLSC. However, each of the hooks is controlled by separate needles. Hooks 1 and 2 control the end 1 and hooks 3 and 4 control the end 2. Needles 1, 2, 3, and 4 control the hooks 1, 2, 3 and 4 respectively. The two needles (say N1 and N2) corresponding to a particular end (say end 1) are controlled by two cylinders in two picks. One of the needles (N2) is controlled by the right cylinder (cylinder 2) and the other needle (N1) is controlled by the left cylinder (cylinder 1). One cylinder carries the punch cards for even pick numbers like N, N+2, N+4, N+6 and so on. Here N is an even number. Prepared By: Shakeel Ahmad Paracha Page 42 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) The other cylinder carries the punch cards for odd pick numbers like N+1, N+3, N+5 and so on. In one pick, either of the two cylinders performs the selection operation. DLDC jacquard is capable to handle the maximum loom speed (picks per minute) among the three types of jacquards. Figure shows that end 1 is in raised position and end 2 is in lowered position in this current pick. End 1 will continue to be in raised position in the next pick as there is a hole in punch card on cylinder 2 corresponding to the position of needle 2 (N2). So, hook 2 will remain in upright position and thus it will be raised by the knife 2 (K2). On the other hand, end 2 will continue to be in lowered position as it is being tilted by needle 4 (N4) as there is no hole on cylinder 2 corresponding to the position of N4. So, knife 4 (K4) will miss the hook 4 when the former will rise in the next pick. Fine Pitch Jacquards (Special Jacquards) Vincenzi and Verdol are two types of fine pitch Jacquards which were both originated in France. Vincenzi Jacquard uses pattern card or direct method of weave selection. Vincenzi Jacquard has 40 needles per square inch. The standard sizes of Vincenzi Jacquards are 440, 880, 1320, 1760 and so on. Verdol jacquard uses continuous paper and indirect method of weave selection. Verdol jacquard has 80 needles per square inch and exists in sizes of 448, 896, 1344, 1792 and so on. Both these fine pitch Jacquards are much smaller than coarse pitch Jacquards. For example, 1344 capacity Verdol machine is quite smaller than 600 coarse pitch machine. In double lift coarse pitch jacquards each harness is controlled by two separate hooks. Whereas in double lift Vincenzi and Verdol Jacquards, these two hooks are replaced by a specially designed double hook. Prepared By: Shakeel Ahmad Paracha Page 43 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) To avoid excessive needle pressure on the punched card, stop bars are used. In order to keep the lower end of the hook unit straight and vertical, anti-swing bar is used. The Vincenzi Jacquard The Vincenzi Jacquards have been made as: o Single Lift, Single Cylinder (SLSC) o Double Lift, Single Cylinder (DLSC) o Double Lift, Double Cylinder (DLDC) But the most common form of Vincenzi jacquard is in the format of double lift, double cylinder. Being double lift, it will have two sets of knives mounted on separate griffe opposite to each other and makes one complete reciprocation after two picks. A double lift, double cylinder Vincenzi jacquard is shown in the figure below: The cylinder placed on the right works for odd picks i.e., 1, 3, 5…. and the cylinder placed on the left works on even picks i.e., 2, 4, 6…. Initially, the odd cylinder will present a card for 1st pick. If there is a hole for this hook, the Knife K1 will lift the hook H1 in the 1st pick cycle as shown in the figure. In the 2nd next pick cycle the even cylinder will present the 2nd card. Prepared By: Shakeel Ahmad Paracha Page 44 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) If the harness is to be lifted for 2nd continuous pick, the card will again have a hole for this hook. The knife K1 will now be in upward position while the knife K2 will be in the downward position, the Hook H2 will now engage with knife K2. The knife K1 while moving down will slightly lower the harness but in the meantime, the knife K2 will engage the H2, and the harness will again be lifted up. This creates a semi-open type shed. The cylinders of Vincenzi Jacquards are made in hexagonal shape to facilitate working at high speeds. The Verdol Jacquard The Verdol jacquards are only made in single cylinder format and can either be: o Single lift o Double lift The modern form of mechanical jacquards used nowadays are always contracted in double lift Verdol format. The indirect method of selection used in Verdol jacquard is shown in the figure below: Selection Method of Verdol Jacquard The selecting needle (S) rests on continuous plastic pattern carried by the cylinder. Each of the selection needle (S) is attached to an auxiliary needle (A). A swing board (B), containing Lips (L), while moving towards right could hit or miss the corresponding auxiliary needles. If there is a hole for the needle (S), the corresponding auxiliary needle (A) will fall down and will miss the action of swing board (B). This will keep the hook in line with its corresponding knife. On the other hand, if there is no hole for needle (S), the auxiliary needle (A) will be pushed towards right by the swing board (B) that will push the hook away from the moving knife and the hook will not be lifted. The working principle of a double lift Verdol jacquard is represented in the following figure. Prepared By: Shakeel Ahmad Paracha Page 45 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Double Lift Verdol Jacquard Shedding (DLVJS) Just like the Vincenzi jacquard, the double lift Verdol jacquard instead of having two separate hooks, has one double hook for each harness. Two set of knives placed opposite to each are used for each pair of hooks that complete their reciprocation after two picks. Additionally, at the bottom of each double hook, a supplementary hook (H) is provided. This works in conjunction with supplementary knife carried by the fixed griffe (G). A single cylinder moves after every pick to give selection according to the weave design. Figure (A) shows that the hook has been lifted up. Once lifted, the supplementary hook (H) will be locked over the fixed griffe. Figure (B) shows that the hook will remain lifted if it is required to be lifted for next pick (s) because in the next pick cycle the needle will again have a hole for this hook and will not be pushed towards right. Any harness will therefore remain lifted for the required number of picks and will only come down when required. Therefore, this shedding mechanism produces a fully open shed unlike any other jacquard shedding. Figure (C) shows that here the feeling needle will not have a hole for the next pick cycle. Therefore, the hook will be displaced towards right by the swing board of selection mechanism and will disengage the supplementary hook off the fixed griffe (G). Therefore, as the knife moves down, the harness will lower into the bottom shed position due to dead weight (lingo) or spring attached at the bottom. Figure (D) shows that the harness is in the bottom position and is ready to be lifted as soon as its needle will get a hole and its hook will get in line with its corresponding knife. Prepared By: Shakeel Ahmad Paracha Page 46 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Electronic Jacquard Shedding (EJS) The first ever electronic jacquard was introduced in 1983 at ITMA, Milan, Italy by Bonas. Electronic Jacquards have the capability to connect with computers installed with specialized CAD software for weaving. Intricate woven designs can be formed on such CAD software, which can then be transferred to the electronic jacquard shedding via floppy, USB or network. Electronic jacquard selection mechanism used by Bonas is represented in the following figure: Just like the electronic dobby, electronic jacquard shedding mechanism rely on solenoids (electromagnets) to select whether the particular hook is to be lifted or not. The lifting or driving mechanism is still mechanically carried out using knives as the driving element. Electronic jacquard therefore eliminates the need of any physical medium for the selection of the weave design i.e. punched cards or continuous punched pattern. The lifting order is fed to the loom electronically using computers. As shown in the figure, a double roller or pulley system (a) is used to move the harness up and down. The lower roller is attached to the harness whereas the upper roller is attached to two knives (f) & (g). Both these knives are placed opposite to each other and are double acting. Prepared By: Shakeel Ahmad Paracha Page 47 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Two hooks (b) & (c) are provided that can be driven by the knives (f) & (g) respectively. Two retaining hooks (d) & (e) can catch the hooks (b) & (c) depending upon the weave design. Suppose the initial position is represented by (1). The hook (b) and its knife (f) are in the uppermost position whereas the hook (c) and its knife (g) are in the lowermost position. At this position, the harness is at the bottom position. Suppose the harness is to remain lowered in the next pick, in this case, the right-hand solenoid (H) would be energized so that the retaining hook (d) does not catch hook (b). The knife (g) will now go up taking the hook (c) up as well. At the same time, the knife (f) will go down and the hook (b) will also go down with it. This is shown at point (2). At point 3, the knife (g) and its hook (c) will reach the top while the knife (f) and its hook (b) will reach the bottom position. Ultimately the harness will not move at all and will remain in the bottom position. Suppose the harness is now to be lifted in next pick cycle. In this case, the left side of solenoid (H) will not be energized and the retainer (e) would therefore catch the hook (c). The knife (g) will now go down while the knife (f) will go up. Since the hook (c) is retained by the retainer, the knife (f) while going up will lift up the entire roller assembly, lifting the harness as well. This is shown at point (4). At point 5, the harness is at the top most position as the knife (f) has reached the top along with its hook (b). Suppose the harness is to be remain lifted in the next pick as well. The right-hand side of the solenoid will not be energized so that the retainer (d) could catch the hook (b). The harness will therefore remain lifted as long as required and will only come down when the solenoid is charged just before the next pick cycle so that the retainer could release its corresponding hook. Prepared By: Shakeel Ahmad Paracha Page 48 of 49  Textile Institute of Pakistan, Karachi. TEXT312 (Weaving Mechanisms) Prepared By: Shakeel Ahmad Paracha Page 49 of 49