US3498339A - Fail safe warp stop circuit - Google Patents

Description

March 3,1970 c. H. DAvis ET Al. 3,498,339

FAIL SAFE WARPv STOP CIRCUIT Filed Aug. 30, less 'Wv-- IO In co IO N g N 5 N I v in n N g .3 N

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' A TORNEY United States Patent 3,498,339 FAIL SAFE WARP STOP CIRCUIT Charles H. Davis, Greenville, S.C., and Warren A. Barber, Martinsville, and Daniel H. Lambros, Dover, NJ., assignors to The Singer Company, New York, N.Y., a corporation of New Jersey Filed Aug. 30, 1968, Ser. No. 756,451 Int. Cl. D03d 45/10, 49/08 US. Cl. 139-336 3 Claims ABSTRACT OF THE DISCLOSURE A circuit is disclosed controlling the energization of the solenoid for actuating the conventional power stop motion of a loom in the event either of power failure or of breakage of warp threads. The circuit is energized from an A.C. source through a switch actuated by moving the loom shipper handle to normal run position. A first controlled rectifier (SCR) supplied by A.C. is triggered into conduction to energize the solenoid responsively to the switch closure. A second SCR supplied by DC. and normally non-conducting is triggered into latched conduction by actuation of the conventional warp-break drop wires and shunts current away from the gate of the first SCR which stops conducting at first zero anode current to deenergize the solenoid and shut down the loom in conventional manner. The second SCR distinguishes between actual war-p breakage and normal transient waving or jiggling of the drop wires by a time delay in the gate circuit. When once fired, the second SCR remains in latched conduction due to the D.C. anode voltage until the shipper is knocked to stop position, which resets the entire circuit.

BACKGROUND OF THE INVENTION -Prior art devices are known for stopping looms responsively to broken warp threads. Typical of these devices is that shown and described in the Sepavich et al. US. Patent No. 2,436,023 wherein a solenoid is energized by falling drop wires which close a contact responsively to broken warp threads and cause a thyratron to conduct and energize the solenoid which controls the stop motion. Diificulties have been experienced by this type of control, which, due to its critical voltage sensitivity, may give an erroneous indication of warp breakage responsively to normal jiggling or waving of the warp threads and thus shuts down the loom unnecessarily and results in lost production. Furthermore, these prior art systems do not inherently provide for safe shut down in case of power failure and this function is generally provided by separate circuitry, which adds to the cost.

SUMMARY OF THE INVENTION It is a general object of this invention to provide a circuit for controlling the energization of the solenoid of a solenoid-actuated power stop motion of a loom responsively to warp breakage which circuit overcomes the difiiculties of the prior art devices noted above.

It is a further object of this invention to provide, in the same circuit used for warp breakage shut down, automatic shutdown in the event of power failure or of failure of the solenoid winding itself.

In attaining the object of this invention, the solenoid is normally energized and is deenergized responsively to warp breakage or power failure to actuate the stop motion. Normal energization is maintained through a first SCR operated on A.C. anode voltage. A second SCR, operatedon D.C. anode voltage, provides when triggered by a falling drop wire, a shunt path for diverting the gate current away from the first SCR causing it to block and to de- 3,498,339 Patented Mar. 3, 1970 DESCRIPTION OF THE INVENTION The single figure of the drawing is a wiring diagram of the circuit of this invention applied to a conventional mechanical stop motion indicated schematically.

Referring now to the figure, a conventional shipper handle 10 which is shown in off position, may be moved in the direct-ion of the arrow shown to start the loom for normal running. A loom shaft 11 provided with a cam 12 in conventional manner operates a knockoff mechanism indicated schematically as 13 when the high point of cam 12 engages a push rod .14 to actuate rod 15 which returns the shipper handle to 01$ position and shuts down the loom. The function of the knockoif mechanism 13, which is conventional, is to provide engagement or disengagement of the rods 14 and 15 responsively to the actuation of the armature 16 of solenoid -17 through mechanical link 18. That is to say, when the solenoid 17 is deenergized, the rods 14 and 15 are connected mechanically by actuation of link 18 so that motion imparted to rod 14 by cam 12 in a predetermined position of shaft 11 will actuate the shipper handle 10 to off position and shut down the loom. When, however, the solenoid '17 is deenergized, the link 18 moves to disconnect rod 14 from 15 and no motion can be transmitted therebet-ween and the loom remains in operation. This type of solenoid actuated knockofi mechanism is well known in the art and may, for example, be the same as that shown and described in the above noted Sepavich et al. U .S. Patent No. 2,436,022 and forms no part of this invention which is concemed with a circuit for controlling the energization of the solenoid 17. This circuit will now be described.

A switch 19 actuated by shipper handle 10 through link 20 closes responsively to initial movement of shipper handle 10 to start position to supply voltage to lines 21-22 from a suitable source 8-8 of low A.C. voltage. A first controlled rectifier (SCR) 23 has its anode 24 and cathode 25 connected in series with the solenoid 17 across lines 21-22. A conventional free wheeling diode 26 is connected in shunt with the solenoid 17 and provides a path for solenoid current caused by magnetic field collapse during the alternate half cycles whenSCR 23 cannot conduct.

A diode 27 and a filter capacitor 28 supply a source of D.C. voltage maintained across the capacitor 28. A second SCR 29 has its anode 30 and cathode 31 connected in series with resistance 32 across the D.C. voltage as shown.

A bias stabilizing resistance 33 is connected in shunt with cathode 25 and gate 34 of the first SCR 25. A shunt path across cathode 25 and gate 34 is also formed by the series connection of resistance 35, anode 30 and cathode 31 of SCR 29.

A resistance 36 and capacitor 37 are each connected across the cathode 31 and gate 38 of the second SCR 29.

The switch 39 closes automatically in response to breakage of a warp thread but can be made operative to close in response to any loom malfunction to signal a loom shut down. In a preferred embodiment, the switch will take the form of drop wire contacts which are in common use on looms to detect warp thread breakage.

It will be seen that closure of switch 39 provides a path through diode 40 and resistance 41 for flow of unidirectional current into the gate 38 of SCR 29. A resistance 42 shunts the series combination of diode 40, resistance 41 and capacitor 37.

The operation of this circuit will now be described.

Under normal operation, the shipper handle when moved in the start direction indicated by the arrow, actuates a linkage whereby the drive clutch connects the loom to the drive motor in a conventional manner. Initial movement of the shipper handle 10 will close switch 19 applying A.C. voltage from a source S-S to lines 21-22. Providing drop wire switch 39 is open, SCR 23 will conduct every half cycle applying half-wave current through the solenoid 17, which will actuate armature 16 and through link 18 will disable the stop motion mechanism 13 as described above. Armature 16 will be held in this position as long as SCR 23 remains conductive assisted by the current averaging effect of the diode 26. SCR 23 is turned on every half cycle by positive triggering current supplied to the gate 34 by the diode 27 through resistances 32 and 35. This represents the normal running condition for the loom.

Now, in the event of a broken warp thread, switch 39 will close, applying current rectified by diode 40 through resistance 41 to the gate of SCR 29 (which was hitherto off) and turning it on. It will be noted that any short or momentary duration of closure of switch 39 caused by normal Waving or jiggling of drop wires will not fire SCR 29. This is so because the current flow into the gate 38 is controlled by the rate at which capacitor 37 can be charged through the resistance 41. Thus values of resistance 41 and capacitor 37 can be chosen so that switch 39 must remain closed a predetermined minimum time before SCR 29 can be turned on and this provides means for discriminating between a real thread break and normal jiggling of the drop wires. However, when once fired, the SCR 29 latches into conduction because of the D.C. anode current supplied by diode 27 and remains so until the shipper handle and linkage disengages the loom from its driving source.

When SCR 29 conducts, current formerly supplied to gate 34 through resistance 35 is now shunted through the anode 30 and cathode 31 of the now conducting SCR 29 causing SCR 23 to stop conducting at the next zero anode current. The solenoid 17 is deenergized and the armature 16, being spring and/or gravity loaded, returns to its former position and, in so doing, moves the link 18 to enable the knockoff mechanism to return the shipper handle to off position on the next actuation of rod 14 by cam 12 and thus shut down the loom. After the broken warp thread is fixed, the switch 39 will be opened and the circuit will 'be restored to the condition found at the beginning of this operation.

It will be noted that, in this circuit, any failure resulting in deenergizing the solenoid 17 will shut down the loom. This includes failure of the solenoid winding itself as Well as failure in the power supply S-S. This function is inherent and does not require any additional circuitry.

The use of one controlled rectifier operating on A.C. anode voltage to supply the current for the solenoid, with a second controlled rectifier operating on D.C. anode voltage for controlling the turn off of gate current to the first rectifier, when combined with a time delay circuit for the gate of the second rectifier represents a unique circuit for attaining the desired objects of this invention.

Having thus described the invention, it will be seen that changes and modifications may be made therein by those skilled in the art without departing from the spirit and scope of the invention and no limitation thereof is intended with respect to the details disclosed.

Having thus set forth the nature of this invention, what is claimed herein is:

1. In a warp stop system for a loom having a knockoff device rendered effective by a solenoid to cause the shipper handle to stop the loom when actuated by a moving part of the loom, a circuit for controlling the energization of the solenoid from an A.C. voltage source comprising:

(a) a first controlled rectifier,

(b) first switch means actuated by the shipper handle to connect said first rectifier in series with said solenoid across said A.C. voltage source,

(c) means for supplying a fixed gating signal to said first rectifier sufiicient to cause it normally to conduct,

(d) means deriving a D.C. voltage from said A.C. voltage source,

(e) a second controlled rectifier having its anodecathode voltage supplied by said D.C. voltage,

(f) means connecting the second rectifier to provide a low impedance path shunting the gate and cathode of the first rectifier when the second rectifier is conducting,

(g) second switch means operative responsively to loom malfunction to supply gate current to said second rectifier, and

(h) means for delaying the firing of said second rectifier until said switch means has been closed for a predetermined minimum time.

2. A circuit according to claim 1 wherein the firing delay means (11) includes:

(a) a diode and a resistance connected in series with the second switch means and with the gate and cathode of the second rectifier across the A.C. source, and

(b) a' capacitor connected between the gate and the cathode of the second rectifier.

3. A circuit according to claim 1 wherein the means ((1) deriving a D.C. voltage from said A.C voltage source includes:

(a) a diode which also supplies the gating signal for the first rectifier.

References Cited UNITED STATES PATENTS HENRY S. JAUDON, Primary Examiner US. Cl. X.R. 139-353

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