Rotary dobby is a type of positive dobby which has been mainly used with rapier and projectile weaving machines. In recent years, manufacturers have demonstrated their rotary dobbies at the international exhibitions, running at speeds up to 1000 rpm. This makes it possible to employ a rotary dobby on high speed air jet and water jet weaving machines. Today, it is a dominant type of dobby in industry that can be used on all types of weaving machines.Material published on the rotary dobby is limited and mainly explains the system and principle of operation and written generally by the rotary dobby manufacturers [1, 2]. Eren et al. compared heald frame motion characteristics generated by rotary dobby and crank and cam shedding motions [3]. No other publication has been found on the theory of rotary dobby in the literature. This paper presents a kinematic design and analysis method explaining the theory of a rotary dobby system. Heald frame displacement, velocity and acceleration curves were obtained and the rotary dobby mechanism parameters affecting heald frame motion are discussed. Principle of Operation of a Rotary DobbyPrinciple of a rotary dobby is based on an eccentric mechanism shown in Figure 1(a). There is a ball bearing between the links 2 and 3. The link 2 is an eccentric, as its center of rotation (A 0 ) is different from its geometrical center 1 (A). Because of this, when the link 2 rotates, for example in counter clockwise direction, its motion is transmitted to the link 4 by the link 3. During one revolution of the link 2, the link 4 swings between its limit positions. When A 0 , A and B are on the same line and A 0 A and AB are extended, the link 4 reaches its most forward position. When A 0 A and AB are folded on top of each other, the rearmost position of the link 4 is reached. The motion of the link 4 is transmitted to the heald frame by motion transmission mechanism shown in Figure 1(b). The most forward position of the link 4 corresponds to the lower position and the rearmost position of the link 4 corresponds to the higher position of a heald frame. The eccentric mechanism with this construction generates a heald frame motion only for plain weave. To convert it to a rotary dobby mechanism, it is necessary to include the necessary means to get the link 4 (hence the heald frame) dwelt at its most forward and the rearmost positions as many loom revolutions as required by the weave.Abstract In this study, a mechanism model is introduced then kinematic design and analysis equations are presented for a rotary dobby. Heald frame motion curve is obtained and analyzed. Mechanism parameters affecting heald frame motion are discussed. It is shown that heald frame motion characteristics were mainly determined by the design of modulator mechanism. Eccentric mechanism of a rotary dobby also had a significant effect on heald frame motion.
PurposeThe purpose of this paper is to investigate warp and weft crimp distribution over the fabric width and how it is influenced by warp tension distribution over the warp width.Design/methodology/approachAn experimental design in this research includes air jet loom, tension sensor, inductive sensor and personal computer.FindingsIt is found that warp crimp in the fabric on the loom is higher in the edge zones than the middle of the fabric and warp crimp in the middle is higher than warp crimp in edge zones of the grey fabric. Weft crimp in the edge zones is higher than in the middle of the grey fabric. The reason behind warp tension and warp and weft crimp variations over fabric width is that weft yarn slips towards inside fabric at selvedges and gets relaxed during beat up.Originality/valueIt is proved that reducing weft yarn slip and therefore weft yarn relaxation during beat up will reduce warp tension and warp and weft crimp variations and improve the uniformity of fabric properties over the fabric width.
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