Dobby is one of the shedding devices that are used for shedding in weaving machines and provide the movement of frames for this purpose. Among the shed opening systems in weaving machines, the dobby shed opening system gives more movement to the frame than the eccentric system.
This number is generally limited to 32, but according to special needs this number reduces the efficiency of the machine up to 48 frames. The number of frames is determined in the construction of the dobby mechanism. Framed dobbies working in different numbers can be produced according to the needs of the market and economy. The pattern type and motif size that can be obtained in dobby weaving machines is limited by the number of frames that can be attached to the machine.
We can classify dobby systems in terms of their structures and working principles as follows:
>>>> Closed mouth dobbies: In this machine, after the weft is opened, the weft is thrown and the weft is closed before the tambourine moves to compress the weft into the fabric. After the muzzle is closed, the weft is compressed by the tambourine.
>>>> Dobby with open mouth: In these machines, after the shed is opened and the weft is thrown, the dobby shed does not close while the weft is approached to the fabric surface by the stencil. After the weft is fully approached to the fabric surface, the new nozzle is opened without closing.
>>>> Top shed dobby: In these machines, the dobby can only lift the frame.
>>>> Full mouth dobbies: Both up and down movement can be given in these machines. This mouthpiece is formed by lowering some of the frames up and some of them down.
>>>> Single stroke dobbies: The blade that gives movement to the frame legs and sinkers is unique. The fact that this blade is single ensures that only the upper nozzle is opened in the machine. At the same time, the speed of the machine is low.
>>>> Double stroke dobbies: In these dobbies, the blades that move the frame legs and sinkers are double. There are two knives called upper knife and lower knife in dobby. Having two blades ensures both full nozzle opening and high efficiency of the machine.
Although the basic principles of dobby machines are the same, they are classified according to their control systems and motion transmissions.
>>>> Negative action dobbies: It is the system that only allows the frames to be lifted up at the time of operation. The back movement of the frames is carried out by springs. Due to its simple structure, it is a system with a wide area of use.
>>>> Positive action dobbies: It performs both the upward movement and the reverse movement of the weaving frames. It is a dobby system generally used for weaving heavy fabrics.
Dobby machines; It takes its movement from the crankshaft with the help of chain or from the engine with the help of belts. Dobby machines driven by the crankshaft are used more often.
Each frame is connected to 1 dobby legs that can move around the 2st axis with thongs and iron bars. The notched part on the top of the feet is used to adjust the nozzle height. There is one dobby stand for each frame. The connection piece (3) is connected axially to the dobby legs. Parts 4a and 4b are fitted with hooks 5a and 5b. The hooks can move up and down on axes 4a and 4b. The described assembly is available for each frame separately. The weight of the frames and the retraction device always pull points 4a and 4b towards points 6a and 6b. Beneath the hooks are two blades 7a and 7b.
The other ends of these blades are connected to the 8-center lever. A 9 arm is attached to one end of this lever, and the other end of this arm takes action over the eccentric shaft and ensures that the tine movement and the mouthpiece formation work in harmony. The hooks are attached to the sinkers 10 by rods 10a and 11b. The sinkers are movable on the 12th axis. There are two rods and two sinkers for each frame.
The patterning laths (14) are on the log (15). The log rotates a certain amount in each revolution of the machine and provides the movement of the laths for the next shed. Dobby nails are attached to the holes on the dobby strips. These nailed nails lift the sinkers up. In the figure, it is seen that the lower blade has moved to the right and the lower hook attached to it has moved to the right. The point 4b has moved away from the constant 13b, and the connection piece no. 3 has pulled the dobby legs to the right, causing the frames to rise.
In the second weft, the movement sequence is on the upper blade. Two things can happen here. The frame will go down or maintain its above state relative to the weave.
If there is no nail in the lath that hits the bottom of the sinker (ie the hole is left empty), the part of the sinker on the right side of the 12th axis will go down, and the part on the other side of the axis will go up. Thus, the rod that rests on the sinker will also rise, pulling the hook away from the blade. For this reason, the upper hook will not match the movement of the blade that will move to the right and the frame will go down while point 4a is moving to the left.
If there is a nail in the lath on the bar below the sinker, the right side of the sinker will remain up and the other portion will stay down. So the frame will not move. Therefore, the Hatersley dobby works on the open mouth principle.
The figure above shows the endless cardboard attached to the dobby assembly controlled by the punched cardboard. It is the dobby assembly that has the most common usage area. Its working principle is the same as the pattern slat dobby assembly described above. However, here the patterns are read not through nails driven into the laths, but through the holes drilled on the cardboard.
In the system, the pattern is read through the needles connected to the sinkers. The needles fall into the holes opened on the cardboard in accordance with the knitting, activating the sinkers and from there the system.
Preparation of Dobby Carton
After the dobby plan of the weave or pattern to be woven is prepared, mechanically controlled dobbies are also drilled into the pattern cardboards or attached to the pattern bars by nailing or relaying in order to make it able to control the dobby machine.
Dobby cartons are in the form of tape. It is available in strips of various sizes and made of various durable materials. It is used as much as the desired report length and the last two ends are combined into an endless strip. According to the drawn dobby plan, the drilling of the cardboards is started from right to left, and the rotation of the dobby cardboards in the pattern log of the dobby is clockwise.
In addition to the main weave of the fabric to be woven, an edge weave is given so that the edge of the fabric can be smooth. The warp threads that will form the edge threads may be more taut or loose. This causes defects in the fabric. In order to prevent mistakes, a mesh is selected and used according to the tension of the edge.
The dobby plan is coded so that the knitted fabric can be woven. Coding is done by reading from right to left, starting from the top line. In the dobby plan, the lower numbers represent the frame numbers, and the upper numbers represent the key numbers of the cardboard punching machine. This number change is due to the fact that the first frame is accepted as the frame away from the edge, in other words, from the fabric. In punching machines, the frame closest to the fabric was accepted as the first frame and numbered. There is a problem in this application. In my cardboard punches, the edge knitting should always be pierced on the edge of the cardboard.
The coded weave is punched into the pattern cardboard by a tool similar to a typewriter.
The numbers in the first row are pierced by pressing the white keys, and the numbers in the second row are pierced by pressing the red keys. After a row is pierced in the cardboard, the arm of the tool is pulled down and the next two weft movements are drilled.
In order to ensure that the dobby machines are controlled according to the desired weave and pattern, the dobby plan leading to the preparation of the pattern cartons or pattern chains used in mechanical dobbies should be prepared. With the dobby plan of the weaves in weaving, the movement of the frames on the weaving machine can be detected. The drawing and dobby plans of the twill weave given in the figure have been drawn.
According to the dobby plan, frames 1, 1 and 4 will be lifted while the 5st weft is being thrown. Frames 2, 1 and 2 will be lifted up while the 5nd weft is being thrown. This continues until the 5th weft and a report is completed. The repetition of this report continues throughout the weaving process. After the dobby plan of the weave or pattern to be woven is prepared, it must be transferred to the dobby machine. In mechanically controlled dobbies, it must be transferred by drilling on the pattern cartons or by attaching nails or relays to the pattern bars. Pattern cartons are generally used in mechanically controlled dobbies.
The number of frames required for the fabric to be woven is determined by looking at the dobby plan. This number should not exceed the frame capacity of our weaving machine. If this number exceeds, we should direct the desired weave to the jacquard system, which has a higher capacity than the dobby system.
The number of frames required for the knitting done above is 5. In other words, this weave can be woven in an eccentric or dobby system if desired. It is the preparation of dobby cardboards from the dobby plan of the weave and applying them to the filled points on the dobby plank as holes in the cardboard.
Dobby cartons are in pieces or in bands. It is used as much as the desired report length and the last two ends are combined into an endless strip.
According to the drawn dobby plan, the drilling of the cartons is started from right to left. The rotation of the dobby cardboards in the pattern log on the dobby is clockwise. The process to be done at this stage is to puncture the cardboard. This drilling process can be done with mechanically controlled tools of various structures or electronically controlled devices.
In the dobby plan, it is seen that the dobby cardboard is prepared by drilling in order to control the frames that need to be lifted in each weft according to the weft order. Generally, in patterns with small weft patterns, since a small number of cardboards will cause a problem to rotate on the pattern log, the cardboard sequence is repeated by repeating. Thus, the dobby system works more comfortably.
In weaving machines in electronically controlled dobbies Instead of cards or chains in mechanical dobbies, there are magnetic control sticks. Magnetic blocks work in conjunction with electronic pattern memory or direct microprocessor unit. Pattern information is sent directly to the magnetic bar as electrical signals. When the claw enters the space on the receiving disk, the receiving disk is rotated by the main shaft. With the rotation of the receiving disk, motion transmission to the frames begins. Frames maintain their condition when the tab does not go into the notch. Electronically controlled dobbies have a microprocessor control device. All movements are controlled by this remote control.