Weft-bar (set mark) prevention system for a loom

A weft-bar prevention system for a loom in which warp threads let-off from warp beams are guided to a cloth fell under an appropriate warp tension by the aid of an elastically supported guide member which comprises:

• (a) a color-divided disc connected to a drive shaft of a loom for rotating in synchronization with the movement of the loom, one flat surface of which is divided into two different colored ranges respectively indicative of a closed-shed angular range and an open-shed angular range;
• (b) an optical sensor disposed facing one of the two different colored ranges, said optical sensor including a light-emitting section and a light-receiving section for outputting two angular range signals indicative of the closed-shed angular range and the open-shed angular range, respectively, according to the magnitude of the light emitted therefrom, reflected from said color-divided disc, and received thereby;
• (c) a selector connected to said optical sensor for selecting one of a closed-shed warp tension signal and an open-shed warp tension signal in accordance with the two angular range signals from said optical sensor and outputting signals corresponding thereto;
• (d) a bistable multivibrator connected to said selector, said multivibrator being set via said selector to output a timing signal when said optical sensor is activated;
• (e) an actuator driver connected to said bistable multivibrator and said selector for outputting one of a closed-shed warp tension signal and an open-shed warp tension signal only while said bistable multivibrator is outputting a timing signal;
• (f) a high-pressure governor for producing a predetermined high-pressure air source;
• (g) a low-pressure governor for producing a predetermined low-pressure air source;
• (h) a high-pressure electromagnetic valve pneumatically connected to said high-pressure governor for supplying the high-pressure air source in response to the closed-shed warp tension signal from said actuator driver;
• (i) a low-pressure electromagnetic valve pneumatically connected to said low-pressure governor for supplying the high-pressure air source in response to the open-shed warp tension signal from said actuator driver;
• (j) a three-way electromagnetic valve pneumatically connected to said two high- and low-pressure electromagnetic valves and a source of atmospheric pressure, said three-way valve being pneumatically connected to said high- and low-pressure electromagnetic valves in response to the timing signal from said bistable multivibrator and released to atmospheric pressure when said bistable multivibrator outputs no signal;
• and
• (k) an air cylinder pneumatically connected to said three-way electromagnetic valve for moving the guide member in such a direction that warp thread tension is increased to a degree determined by high-pressure air introduced thereinto when the timing signal from said bistable multivibrator is applied to said three-way electromagnetic valve and when the closed-shed warp tension signal is applied to said high-pressure electromagnetic valve to supply high-pressure air thereinto;
• and to a degree determined by low-pressure air introduced thereinto when the timing signal from said bistable multivibrator is applied to said three-way electromagnetic valve and when the open-shed warp tension signal is applied to said low-pressure electromagnetic valve to supply a low-pressure air thereinto.

A weft-bar prevention system for a loom in which warp threads let-off from warp beams are guided to a cloth fell under an appropriate warp tension by the aid of an elastically supported guide member which comprises:

• (a) a color-divided disc connected to a drive shaft of a loom for rotating in synchronization with the movement of the loom, one flat surface of which is divided into two different colored ranges respectively indicative of a closed-shed angular range and an open-shed angular range;
• (b) an optical sensor disposed facing one of the two different colored ranges, said optical sensor including a light-emitting section and a light-receiving section for outputting two angular range signals indicative of the closed-shed angular range and the open-shed angular range, respectively, according to the magnitude of the light emitted thereform, reflected from said color-divided disc, and received thereby;
• (c) a selector connected to said optical sensor for selecting one of a closed-shed warp tension signal and an open-shed warp tension signal in accordance with the two angular range signals from said optical sensor and outputting signals corresponding thereto;
• (d) a bistable multivibrator connected to said selector, said multivibrator being set via said selector to output a timing signal when said optical sensor is activated;
• (e) an actuator driver connected to said bistable multivibrator and said selector for outputting one of a closed-shed warp tension signal and an open-shed warp tension signal only while said bistable multivibrator is outputting a timing signal;
• (f) tension-applying means for applying an additional tension to the warp threads;
• (g) a pressure governor for producing a pressurized air source;
• (h) a three-way electromagnetic valve pneumatically connected to said pressure governor in response to the timing signal from said bistable multivibrator and released to atmospheric pressure when no timing signal is outputted from said bistable multivibrator;
• (i) an air cylinder pneumatically connected to said three-way electromagnetic valve for moving said tension-applying means in such a direction that warp thread tension is increased when the timing signal from said bistable multivibrator is applied to said three-way electromagnetic valve to introduce pressured air thereinto, said air cylinder releasing said tension-applying means when the timing signal is not applied to said three-way electromagnetic valve;
• and
• (j) an actuator mechanically engaged with said tension-applying means for releasing said tension-applying means to a greater-tension position when the timing signal from said bistable multivibrator is applied to said three-way electromagnetic valve to introduce pressurized air thereinto and when the closed-shed warp tension signal is applied to said actuator drive to deenergize said actuator;
• and for urging said tension-applying means to a smaller-tension position when the timing signal from said bistable multivibrator is applied to said three-way electromagnetic valve to introduce pressurized air thereinto and when the open-shed warp tension signal is applied to said actuator driver to energize said actuator.

A method of preventing weft-bar in a loom caused when a loom is started, which comprises the following steps of:

• (a) detecting whether the loom is started within a closed-shed range of loom movement or in an open-shed range of loom movement;
• (b) outputting a closed-shed warp tension signal when the loom is started from the closed-shed range and an open-shed warp tension signal when the loom is started from the open-shed range;
• (c) determining at least one initial cycle during which warp tension is controlled after the loom has been started and outputting a timing signal for determined at least one initial cycle;
• (d) increasing the warp tension to a greater degree in response to the closed-shed warp tension signal and to the timing signal;
• (e) increasing the warp tension to a smaller degree in response to the open-shed warp tension signal and to the timing signal;
• and
• (f) not increasing the warp tension after the determined at least one initial cycle,
• whereby additional tensions are applied to the warp threads according to the angular ranges of the loom for at least one initial cycle after the loom has been started.