 The warp threads are separated by the heddles into two or more groups, each controlled and automatically drawn up and down by the motion of the heddles.In the case of small patterns the movement of the heddles is controlled by "cams" which move up the heddles by means of a frame called a harness; in larger patterns the heddles are controlled by a dobby mechanism, where the healds are raised according to pegs inserted into a revolving drum.Where a complex design is required, the healds are raised by harness cords attached to a Jacquard machine.