The function and type of beat-up mechanism
The main function of the beating-up mechanism is to push the weft yarn introduced into the shed to the cloth fell, so that it can be closely interlaced with the warp yarn to form a fabric.
2. Types of beat-up mechanisms
Currently there are three main types of beat-up mechanisms used on various types of shuttleless looms: link beat-up mechanisms, cam beat-up mechanisms and reed beat-up mechanisms.
1. Connecting rod beat-up mechanism
The connecting rod beat-up mechanism uses rods to convert the rotation of the main shaft of the loom into the reciprocating beat-up of the reed. The most widely used is the four-link beat-up mechanism, and there are also six-link beat-up mechanisms based on the four-link. In addition, in order to adapt to certain fabric varieties, there are also some special multi-link beating mechanisms. Here we mainly introduce the four-link beating mechanism. The four-link beating-up mechanism has a simple structure and is easy to manufacture, and is widely used in shuttleless looms.
Figure 1-13 is a casual diagram of the four-bar beat-up mechanism of a certain shuttleless loom. A is the spindle, AB is the crank, BC is the connecting rod (hand), and D is the rocker shaft. Together they form a crank-rocker mechanism. The leisure characteristics of the four-bar linkage beat-up mechanism can be expressed by the leisure of point C. If the extension line C1 C2 connecting the two extreme positions of connecting rod BC passes through the center of the spindle, it is called an axial beating mechanism; otherwise, it is called a non-axial beating mechanism. Weft mechanism. The degree e to which the main axis center deviates from the C1 C2 line is called non-axial deflection. If the spindle center A is located above the C1 C2 line, then e is a positive value and the rear dead center position is less than 180°; otherwise, it is a negative value and the rear dead center is The point position is greater than 180°.
The ratio L/R of the crank AB and the connecting rod BC and the size of the non-axial deflection e all affect the relaxation of point C, that is, the relaxation of the reed. Among them, the main influence is the ratio L/R. According to the size of the ratio L/R, the beat-up mechanism can be divided into long hand-held beat-up mechanism, medium hand-held beat-up mechanism and short hand-held beat-up mechanism.
Generally speaking, L/R>6 is called a long-hand beating mechanism; L/R=3~6 is called a medium-hand beating mechanism; L/R<3 is called a short hand-beating mechanism. According to the linkage mechanism leisure analysis method, the leisure law of point C can be obtained. The shorter the connecting rod BC is, when the crank is near the front dead center (0°), the faster the reed is and the greater the acceleration is, which is conducive to beating up. In addition, the short hand beat-up mechanism agrees with the weft carrier (mainly The spindle angle of the rapier passing through the shed is relatively large, the reed stays relatively long at the rear, and the weft carrier has ample time to pass through the entire shed. Therefore, the short-hand beat-up mechanism is suitable for wide and heavy fabrics. For weaving, such as on an air-jet loom, L/R<2, the grip is quite short. However, the shorter the hand is, the greater the change in the acceleration of the reed will be, which will intensify the vibration of the loom and is not conducive to high speed. It is usually supplemented by a light reed base to adapt to high speed and reduce vibration. Medium and long hand-held beat-up mechanisms are mostly used on light-weight and narrow-width looms.
2. Cam beat-up mechanism
The cam beat-up mechanism uses cams, rotors and other components to transmit the rotation of the main shaft to the reed to complete the beat-up action. The cam beat-up mechanism of shuttleless looms generally adopts a conjugate cam mechanism with separate reed seats. The beat-up push and return strokes are controlled by the main and auxiliary cams respectively. The contour curve of the cam can be completely adjusted according to the leisure of the reed seat. It needs to be designed so that there can be a long resting time of the reed seat for the weft carrier to pass through the shed. These features are suitable for the requirements of the beat-up mechanism that matches the shuttleless weft insertion, so it has become a widely used one on modern shuttleless looms. Beating-up mechanism, projectile shuttle, rapier, air-jet, water-jet and other types of looms are used.
As shown in Figure 1-14, the beat-up conjugate cam is installed in the left and right cam boxes. When the main shaft 1 rotates, the main cam 2 pushes the roller 4 so that the reed base 9 is centered on the rocker shaft 6 Swing counterclockwise to drive reed 8 to beat up. After beating up, the auxiliary cam 3 pushes the roller 11 to make the reed base swing clockwise. When the sword running plate installed on the reed seat is flush with the left and right sword belt guide rails on the fixed frame, the reed seat will stop to facilitate weft insertion and leisure.
The conjugate cam beat-up mechanism has the following characteristics:
(1) The reed holder and the steel reed can remain stationary during weft insertion, and the weft insertion mechanism and the reed holder can be separated to adapt to high speeds.
(2) The reed holder can remain stationary behind the shed for a long time, creating favorable conditions for high speed and wide width. At the same time, it makes full use of the height of the shed and reduces the beating stroke.
(3) The cam, rotor and swing arm are enclosed in the box, which can realize oil bath lubrication. The oil film formed between the leisure pairs can also alleviate the impact between the rotor and cam caused by beating up, and can Make multiple cam boxes work simultaneously.
(4) The cam arrangement and assembly accuracy requirements are very high. The conjugation accuracy between the cam and the rotor should be controlled between 0.02~0.03mm. The cost of the cam beat-up mechanism is relatively high.
(5) The beating cam has a large load, and its pressure angle should not be large. It should generally be less than 30° to reduce impact wear. The pressure angle of the auxiliary cam can be appropriately relaxed.
Generally speaking, the characteristics of the cam beat-up mechanism are that the rest time of the reed base is short, the rest time is long, the acceleration is large, and the mechanism is easy to vibrate. From the perspective of reducing vibration, it is better to have a small stroke of the reed holder. However, when the size of the weft carrier is certain and the stroke of the dent holder is small, the opening stroke will increase, and the difference in stroke between the front and rear heaves will increase. It is also large, which increases the difference in warp tension, causing the warp to break easily, and making the cloth mouth jump up and down. Therefore, the reed seat movement cannot be too small, and it needs to be comprehensively determined based on the weft insertion method, machine speed, weaving technology, etc.
On the other hand, according to the technological characteristics of various fabrics and on the premise of meeting technological needs, design and selection�Appropriate movement of the reed seat
The law of movement is very important. The leisure rules of the dent seat should meet the following points:
(1) The acceleration of the dent seat should change gradually from stationary to leisure and from leisure to stationary, and there should be no sudden changes.
(2) The acceleration of the reed seat at the moment of beating up should ensure that the inertial force of the reed seat is greater than the beating resistance.
(3) During the rest of the time, the acceleration curve should be continuous, the changes should be gentle, and the peak value should be small.
Regarding the above points, a single leisure curve equation cannot meet all the requirements at the same time. Two or three curves are often used to combine them. The more commonly used one is the combined sine and cosine acceleration curve, and the other is the improved trapezoidal acceleration curve.
3. Reed beat-up mechanism
Both the connecting rod beat-up mechanism and the cam beat-up mechanism have reciprocating rest of the reed seat, and their rest stability is poor. In order to adapt to the requirements of high-speed and multi-shed looms, etc. , the circular reed beat-up mechanism appeared. It cancels the reciprocating leisure of the reed seat, and uses the rotating polygonal reed blade to directly push the weft yarn into the fabric mouth, as shown in Figure 1-15.
There are polygonal reed blades 2 arranged on the main shaft 1, and the warp yarns 3 and 4 are embedded in the gaps between adjacent reed blades. When the reed blade rotates with the main shaft, its beating radius will beat the weft yarn 5 Push towards the weaving edge. Its transmission mechanism is simple, its operation is stable, and it is suitable for high-speed operation, but the production cost of special-shaped reed blades is high.
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