Dobby loom
From Wikipedia, the free encyclopedia
A Dobby Loom is a loom in which each shaft can be selected without using treadles. A dobby loom is an alternative to a treadle loom. Each of them is a floor loom in which each of the warp threads on the loom is attached to a single shaft using a device called a heddle. A shaft is sometimes knows as a harness, but this terminology is becoming obsolete among active weavers. Each shaft controls a set of threads. Raising or lowering several shafts at the same time gives a huge variety of possible sheds through which the shuttle containing the weft thread can be thrown.
A manual dobby uses a chain of bars or lags each of which has pegs inserted. The pegs select the shafts to be moved. A computer assisted dobby loom uses a set of solenoids or other electronic devices to select the shafts. Activation of these solenoids is under the control of computer program. In either case the selected shafts are lifted or sunk by either legpower on a dobby pedal or electric or other power sources.
On a treadle loom, each foot-operated treadle is connected by a linkage called a tie-up to one or more shafts. More than one treadle can operate a single shaft. The tie-up consists of cords or similar mechanical linkages tying the treadles to the lams that actual lift or lower the shaft.
On treadle operated looms, the number of sheds is limited by the number of treadles available. An eight shaft loom can create 254 different sheds. There are actually 256 possibilities which is 2 to the eight power, but having all threads up or all threads down isn't very useful. However, most eight shaft floor looms have only ten and twelve treadles due to space limitations. This limits the weaver to ten to twelve distinct sheds. It is possible to use both feet to get more sheds., but that is rarely done in practice. It is even possible to change tie-ups in the middle of weaving a cloth but this is a tedious and error prone process so this too is rarely done.
With a dobby loom, all 254 possibilities are available at any time. This vastly increases the number of cloth designs available to the weaver. The advantage of a dobby loom becomes even more pronounced on looms with 12 shafts (4094 possible sheds), 16 shafts (65,534 possible sheds), or more. It reaches it's peak on a Jacquard loom in which each thread is individually controlled.
Another advantage to a dobby loom is the ability to handle much longer sequences in the pattern. A weaver working on a treadled loom must remember the entire sequence of treadlings that make up the pattern, and must keep track of where they are in the sequence at all times. Getting lost or making a mistake can ruin the cloth being woven. On a manual dobby the sequence that makes up the pattern is represented by the chain of dobby bars. The length of the sequence is limited by the length of the dobby chain. This can easily be several hundred dobby bars, although an average dobby chain will have approximately fifty bars. A computer controlled loom can handle sequences that are virtually unlimited. Many newer cloth design techniques such as network drafting are practical only on computer-control dobby looms.
A Jacquard loom is an example of an adaptation from a dobby loom. A Jacquard device mounted atop a loom will lift the individual heddles and warp threads. The individual heddles and warp threads can be controlled by a computer or a series of punched cards which select them to rise or fall. Power is usually supplied to the loom to move the many heddles involved. Jacquard weaving can be used to produce some quite intricate patterns.
