Principles of Operation
Each position in the card corresponds to a "Bolus" hook, which can either be raised or stopped dependent on whether the hole is punched out of the card or the card is solid. The hook raises or lowers the harness, which carries and guides the warp thread so that the weft will either lie above or below it. The sequence of raised and lowered threads is what creates the pattern. Each hook can be connected to a number of threads, allowing more than one repeat of a pattern. A loom with a 400 hook head might have four threads connected to each hook, resulting in a fabric that is 1600 warp ends wide with four repeats of the weave going across.
The term "Jacquard loom" is a misnomer. It is the "Jacquard head" that adapts to a great many dobby looms such as the "Dornier" brand that allow the weaving machine to then create the intricate patterns often seen in Jacquard weaving.
Jacquard looms, whilst relatively common in the textile industry, are not as ubiquitous as dobby looms which are usually faster and much cheaper to operate. However, unlike jacquard looms, they are not capable of producing so many different weaves from one warp. Modern jacquard looms are controlled by computers in place of the original punched cards, and can have thousands of hooks.
The threading of a Jacquard loom is so labor-intensive that many looms are threaded only once. Subsequent warps are then tied in to the existing warp with the help of a knotting robot which ties each new thread on individually. Even for a small loom with only a few thousand warp ends the process of re-threading can take days.
Read more about this topic: Jacquard Loom
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