This invention relates to a novel gripping apparatus, particularly to that type of a steel-belt gripping apparatus which holds the weft to repeatedly traverse the upper and the lower layers of the warp without incurring any collision against the warp.
Shuttleless looms are usually classified into two types--a jet type and a weft-supplying type. The former is operated with water or air ejection to transfer the weft across the warp, while the latter is provided with a weft gripping device to perform the same function. Traditionally, the weft gripping device used in the latter type of looms includes a weft supplying a fork and a weft transfer hook. As shown in FIG. 1A, with the weft held in position, the weft supplying fork delivers the weft from an open side to a midway point wherefrom the weft is picked up by the weft transfer hook and carried to the other side. The drawbacks of the conventional gripping device are: (1) both the fork and the hook are bulky and heavy, easy to collide with or break the warp; (2) greater driving power is necessary; (3) if the speed of the gripping device is fast, it is easy to break the weft; and (4) the loom adapted to the conventional gripping device is also bulky, and greater installation space is required.
Shown in FIG. 1B is an improved gripping device in which the fork and the hook have been both reduced in size, and in which the fixed weft supplying and transfer mast is replaced with a relatively movable steel belt, main changes in minimizing the physical volume of the entire loom. However, the gripping device is still bulky and the operational speed cannot be fast. Moreover, as the weft supplying action is synchronized with internal weft gripping operation through a pair of parallel installed plates within two bottom sides of the gripping device, the gripping effect is not satisfactory and results in producing longer residual yarn from the weft tailings (the width of the residual yarn is about 40-60 mm). Besides, the operational speed is still slow, and greater power is still required. The main reason for this defect is that the size of the gripping device is too large. Referring to FIGS. 1, 1A, 1B and 1C represent different sizes of the gripping device, and the reference letters denote respectively: u the upper warp layer, d the lower warp layer, h the heald frame, and r the reed. The movement of the gripping device generally follows the back-and-forth motion of the reed's swing while the movement of the upper and lower warp layers is to swing up and down alternatively under the driving force of the heald frame. The gripping device holding the weft travels through the opening of the upper and lower warp layers u and d at each of therir intersections. However, if the size of the gripping device is as large as that shown in FIG. 1A, it must wait until the opening of the upper and lower warp layer is at its maximum so as to effect quick passing with the weft through the opening (as shown in FIG. 1A'). In addition, as the duration of the passing action of the gripping device is very short, the moving speed thereof must be increased. Consequently, owing to the higher tensile force applied by the gripping device, the weft is easily broken. Preferably, if the size of the gripping device is as small as that shown in FIG. 1C, the gripping device can quickly cross the upper and the lower warp layers u and d upon the initial intersection opening (as shown in FIG. 1C') at the time duration of c--c'. Therefore, the gripping device has sufficient time to travel through the two warp layers, and the weaving speed is substantially increased. Above all, weft breaking is greatly minimized. Owing to the small size of the gripping device, it seldom collides with the warp layers, and, therefore, no warp will be caused to break. According to the knowledge of the inventor, the size of the gripping device currently used in the European countries is about the same size as that shown in FIG. 1A, while the size of the gripping device presently in use in the States and in Japan as well as in Taiwan is about the same size as that shown in FIG. 1B. The operating speed of the known gripping device is limited accordingly.
The facts are numerous concerning the bulky size of the conventional gripping device. Except for the fact that a technical breakthrough remains to be made, the most important one is that the gripping elements of the weft supplying fork in the conventional gripping device are usually disposed in the inner portion of the device. In other words, the weft supplying fork must have a weft gripping element for delivering the weft to the hook member, and the weft gripping element must also be a movable part; therefore, if the gripping element is installed in the weft supplying fork, the physical volume of the weft supplying fork will certainly be maximized. Also a weft gripping element internally installed in the weft supplying fork suffers some problems: (1) since the gripping element is arranged within the inner portion of the weft supplying fork, the weft exchange actions of both the weft supplying fork and the weft transfer hook must be synchronized perfectly, otherwise, no exchange action will take place; (2) during the exchange action conducted by the weft transfer hook within the weft supplying fork, the gripping element is easily bumped and damaged; and (3) it is difficult to repair the damaged gripping element.