Dobby loom | Types of dobby loom | Dobby loom mechanism

 

Dobby loom

The dobby loom has a dobby mechanism that is used to program the harness combination for the weaving pattern. It stands for "Draw Boy" which refers to the weaver’s assistant who was used to control the warp thread by pulling the draw thread. The mechanism of dobby replaces the traditional floor loom treadle/lam combination. The performance of multi-harness looms is greatly improved by using a dobby mechanism, as it overcomes the major problems associated with the use of a large number of treadles.

Dobby Loom lets you choose a combination of harnesses for each shade opening. The great advantage of a dobby loom is that it avoids the need and labor of making multiple tie-ups to be placed under a loom. Investing in Dobby weaving ensures many years of comfortable and productive weaving.

Mechanical dobby is a program bar with a peg system. The numbered holes in the program bars match the pair of looms. If you want to raise a harness, you place a peg in the corresponding hole in the program bar. The series of your program bars can be as long as you like; however, if the number of program bars becomes too large, you may want to consider an electronic dobby. Electronic Dobby will give you almost unlimited harness adjustments using computers and software from Fiberworks PCW, Patternland, Weavemaker, Weave It, Weavepoint, or Pro Weave.

Types of dobby loom

A manual dobby uses a series of bars or lags, each of which has pegs inserted to select the shafts to move. A computer-assisted dobby uses a set of solenoids or other electrical devices to select loom shafts. Activation of these solenoids is controlled by a computer program. In both cases, the selected shafts are raised or lowered by the leg power on the dobby pedal or electric or other power sources.

Manual dobby loom

In a treadle loom, each foot-operated treadle is connected by a link called a tie-up with one or more shafts. Multiple treadles can drive a single shaft. The tie-up consists of a rope or similar mechanical connection that binds the treadles to the lam that actually lifts or lowers the shaft.

In treadle-driven looms, the number of sheds is limited by the number of treadles available. An eight-shaft loom can produce 254 different shades. There are actually 256 possibilities which are 2 to 8th power, but not all threads above or all threads below are very useful. Due to space constraints, most eight-shaft floor looms have only ten to twelve footprints. This limits the weaver to ten to twelve distinct sheds. It is possible to use both legs to get more shade, but in practice, this is rarely done. It is even possible to change the tie-up in the middle of the fabric weave but it is a tedious process, so it is rarely done.

With a dobby loom, all 254 possibilities are available at any time. This greatly increases the number of fabric designs available to weavers. The advantage of a dobby loom becomes more pronounced on looms of 12 shafts (4094 possible shades), 16 shafts (65,534 possible shades), or more.

Computer-controlled dobby loom

Computer-controlled dobby loom takes this one step further by replacing mechanical dobby chains with computer-controlled shaft selection. In addition to being able to handle virtually unlimited sequences, shaft sequences are built into computer screens instead of mechanical dobby chains. This allows the loom to load and switch weave drafts in seconds without getting up from the loom. In addition, the computer-generated design process provides the weaver with a more straightforward way of designing the fabric; seeing the pattern on the computer screen is easier than trying to look at Dobby Chain.

Dobby loom mechanism

There are two types of dobby mechanisms. Such as-

i. Negative dobby shedding mechanism

ii. Positive dobby shedding mechanism

Negative dobby shedding mechanism

A climax Dobby is described here to explain the Dobby shading mechanism. The climax dobby is the double lift double jack-lever negative dobby. Here the two jack levers are operated by a single bulk lever. They are joined with a wooden lever and a bulk lever by a link. The double lever is connected to the fulcrum med and S-lever at one point.

A climax Dobby is described here to explain the Dobby shading mechanism. The climax dobby is the double lift double jack-lever negative dobby. Here the two jack levers are operated by a single bulk lever. They are joined with a wooden lever and a bulk lever by a link. The double lever is connected to the fulcrum med and S-lever at one point.

The T-lever is a fulcrum med and it is controlled by an upright shaft and an L-lever. They get speed from motors and machine pulleys. When the filler comes in contact with a peg and when it is not in contact it goes down.

Positive dobby shedding mechanism

In this type of shed, both lifting and lowering of the frame are possible. Lifting occurs through the jack and lever and is reduced by the spring in the tension.

Positive dobby shedding consists of three cylinders, a jack lever, a spring, and a shaft. Of the three cylinders, a shaft is a complete part on one side so that the upper cylinder is counterclockwise and the lower cylinder is counterclockwise. The cylinder is attached to the upper half-toothed disc when the peg or pattern plan is found when the main cylinder moves from the shaft. So that the held frame is at the top, and when the pattern cylinder cannot find a peg, the main cylinder is attached to the bottom half-toothed disc and the spring held holds the frame downwards.