The present invention relates to a new and improved construction of thread braking mechanism.
In its more particular aspects, the present invention relates to a new and improved construction of thread braking mechanism comprising two rollers or rolls which are substantially axially parallel arranged and freely rotatably journaled in a housing. These two rollers define therebetween a clamping bite or gap through which a thread or the like extends and which drives the two rollers while being drawn through the clamping bite. A first one of the two rollers constitutes a stationary roller and a second one of the two rollers is substantially axially parallel displaceable relative to the first stationary roller and can be resiliently pressed thereagainst with an adjustable bias or force. The thread braking mechanism further comprises a rapid braking device by means of which the adjusted bias is suddenly increased in order to initiate a rapid braking operation.
Thread braking mechanisms of this kind are known, for example, from German Patent Publication Nos. 2,531,971, 2,349,334 and 2,534,364. During operation thereof a continuous braking action on the thread is caused by the pressing work which has to be performed during the continuous deformation by the thread of a rubber-elastic covering which is present on at least one of the two rollers while the thread, which is intended to be braked, is approximately vertically drawn through the clamping bite or gap between the two rollers and thereby drives these two rollers.
Such thread braking mechanisms are predominantly employed, one for each thread, in combination with warp creels in which a multitude of threads or the like, while running off the creel, is intended to be braked without wear between their associated bobbins and a winding machine like, for example, a warping or beam warping machine. Generally, the pressure at which the displaceable second roller is pressed against the stationary first roller can be increased or decreased, and thus the braking action can be intensified or reduced in common for all of the thread braking mechanisms by central adjusting means.
At the high winding rates of modern equipment the relatively small rollers in such thread braking mechanisms attain very high velocities. When the equipment or installation is suddenly stopped or shut down, for example, in the case of a thread rupture or when encountering an emergency braking operation, these rollers still continue to run for a short period of time. There thus results a sagging of the threads, and thus, the danger of entanglements in the thread field which cause further thread ruptures or longer shut-down times and diminish the quality of the produced goods.
In order to counter this danger it is known to provide an additional rapid thread braking device which is activated within a short period of time when the machine is suddenly brought to a standstill and which additionally brakes the two rollers. German Patent Publication No. 2,531,971 discloses such a rapid braking device. In this device a compression spring generates the bias for the pair of rollers during normal operation and is rapidly and additionally tensioned by means of a piston-cylinder drive. A rapid braking of the rollers which are now pressed against each other at a significantly increased force and thus a rapid standstill of the rollers and of the thread are thereby achieved.
The known mechanism proposes to use the same spring for generating the bias of the rollers which has to be very finely adjusted as well as, by additionally tensioning the spring, for generating a stopping force which is appreciably massively increased as rapidly as possible above the aforementioned bias. Such use of the same spring for these two purposes is afflicted with considerable disadvantages. In the known mechanism the use of a compression spring which has a very small spring rate or constant is recommended in order to be able to sufficiently precisely uniformly adjust for all thread braking mechanisms even the smallest pressures desired during operation and acting between the two rollers without there becoming effective manufacturing tolerances. In correspondence therewith such a spring requires long displacement paths for achieving the additional stopping force required for the rapid braking operation. As is well known, the spatial conditions in the region of the thread braking mechanisms of a warp creel are very limited and these are undesired the presence of members or parts which impair the optical control of such locations. Furthermore, long displacement paths require correspondingly longer periods of time which, in turn, results in expensive constructions in order that the stopping force may become effective within the desired very small period of time. This is required because the standstill of the rollers should coincide with the standstill of the remaining equipment or installation, particularly of the winding machine. In this context it should be considered that, without further influence, the run-out of the rollers will be extensive at low thread tension, however, will be small at great thread tension.