Kinematics of Rotary Dobby and Analysis of Heald Frame Motion in Weaving Process

Abstract

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.

Mathematical Model of Cam Profile Based on Heald Frame Motion Characteristics

“…Due to this construction, the eccentric mechanism generates a heald frame motion only for plain weaving. In order to convert it to a rotary dobby mechanism, it is necessary to include the necessary means to get the lifting arm 15 (hence, the heald frame) dwelt at its forwardmost and rearmost positions as many loom revolutions as required by the weave [3].…”

“…At present, the weaving technology is focused towards higher speeds, higher efficiency, and easier control and operation [1,2]. Eren [3][4][5][6] introduced kinematic models for the motion of rotary dobbies, cranks, and cam shedding mechanisms, and equations governing heald frame motion were derived. In addition, the obtained heald frame motion curves were compared with each other, while the heald frame motion characteristics were mainly determined the design of the modulator mechanism.…”

Design of a new rotary dobby mechanism

“…In recent years it has been observed that the speed of rotary armatures has reached 1000 rpm and above. Thus, it is possible to operate the rotary dobbies at high speeds in air-jet and water-jet weaving machines [10]. Nowadays electronically controlled rotary dobbies are used.…”

Dynamics Analysis of the Rigid‐Flexible Coupling Lifting Comprehensive Mechanism for a Rotary Dobby

“…The slider (5) is hinged with the slide frame (6). The slider frame (6) is driven by the slider (5) to do nonuniform circular motion around the axis of the big disc. The axis of rotation (7) is fixed with the slider frame (6), and it is connected with the eccentric disc (8) through the spline.…”

“…They used the vector triangle method to solve the kinematics of the main drive mechanism; moreover, the dynamic analysis of the mechanism was carried out by using the equivalent simplified model and the test system of the dobby is designed. Eren et al [5] analyzed the kinematics of the rotary dobby; in addition, the influence of mechanism parameters on the motion of the heald frame was mainly discussed.…”