Mechanical Warp Stop Motion
There are two types of mechanical warp stop motion-
· Vibrator bar type
· Castellated bar type
Vibrator bar type:
The vibrator or oscillating bar type warp stop motions were previously being used on almost all types of looms. Now-a-days, these warp stop motions are being superseded by castellated bar type because of the following disadvantages:
· Open type drop wires cannot be used and hence pinning at the loom is consequently not possible.
· Maximum four banks can be used.
· Shaking movement due to the oscillating bar disturbs the lower edges of the drop wires thus causing them prone to jump and unnecessary friction is created between the yarn and the drop wires.
Working principle:
The eccentric A fitted on the bottom shaft B rocks the vibrating bar to and fro through the fork lever D, connecting rod E, oscillating shaft F. The fork lever D and the rod E are connected through a spring G so that the motion imparted to the vibrator bar is a negative one.
The two sides of the vibrating bar have five vertical serrations. On each side of the vibrating bar there is a fixed bar H having vertical serrations on the inner side. The drop wires I are supported by the warp threads. For each bank there is a bar J with smooth rounded edges which pass through the slots of the drop wires. These bars are stationary and serve the purpose of holding the drop wires in the event of an end breakage.
Under normal working conditions, the bottom ends of the drop wires are clear of the path of the oscillating bar which makes to and fro movement between the fixed bars during the one complete revolutions of bottom shaft. This movement gives complete up and down movement to the hitter through L-shaped link L, connecting rod M, cross lever N, and knock off rod O. K mounted on the knock off rod escapes the striker P on the sley every time the later comes forward. However, whenever a drop wire falls down on the drop wire bar due to a warp breakage, the path of the vibrating bar is obstructed; serrations of these drop wires prevent them to slip off and turn over. When its movement is obstructed the hitter K is in the middle of its path, the striker P on the sley hits the hitter as the sley moves forward. The hitter is pressed back resulting in the release of the starting handle from the knotch.
Castellated bar:
The mechanism consists of a slide A, slider bar B, the slide oscillating device and the knock off device. All these parts are illustrated in figure. The slide is placed into the groove of the slider bar which is secured firmly at both ends at the side brackets. The top of each bar is castellated. The number of bars used depends upon the density of warp (10-12 drop pins per cm. on each bar). Normally four bars are used.
The warp threads are drawn through the drop pins, heald eyes and reed dents at the same time in the preparatory department. When the warp beam is taken to the loom for gaiting of warp, the drop pins are threaded on to the slide bars. Then the slides are coupled to the mechanism by a pin passing through the holes C and the slots D. The slider bars are held firm in their end frames by bolts passed through the holes. The whole unit is placed behind the heald frames.
The warp tension has to be adjusted in order to keep the drop pin clear of the slides. When a warp thread breaks, the corresponding drop pin falls down in to the moving cut out of the slider. The free movement of slide A is arrested as the drop pin comes against the rigid cut put of the slide bar B and the knock off mechanism is actuated and the loom stops.
The slide A moves forward and backward by means of an eccentric in the driving box. The slide A is connected to the forked bracket which is attached to a tubular lever G fulcrummed at O. The lever G is oscillated by a cam coupling H. A small shaft S inside the drawing box consists of a chain driven wheel I, a double sided cam J and the cam coupling H. The motion to the shaft S is given from the crank shaft through a chain and chain wheel I. In the hollow part of the tubular lever G a spring loaded finger K passes through. The finger K during its oscillation above the double sided cam J clears the flat sides of the cam with each complete movement.
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If a slide is locked by a falling drop pin, the free motion of the lever G is arrested with a finger K positioning immediately above the cam J. The continuously rotating cam J with the projecting part lifts the finger K which in turn lifts the knock off lever L. The lever L is connected to a knock off finger M by means of a cable. When the lever is raised by the finger K, the cable pulls the knock off finger M in front of the striker N which finally knocks off the starting handle.
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