Abstract:
A rundown detector system for controlling operation of the cylinder of a circular knitting machine includes a photoelectric circuit, including fiber optic means and a sensor for sensing predetermined extended periods of low reflected light level and emitting signals to a logic circuit. The logic circuit includes a timer and counting mechanism for stopping rotation of the machine cylinder if a predetermined number of signals are emitted to the logic circuit within a predetermined time period. The timer mechanism also prevents stopping of the machine cylinder, upon start-up of the machine, until a predetermined amount of knit fabric absent of defects has moved past the sensor.

Description:
BACKGROUND, BRIEF SUMMARY AND OBJECTS OF THE INVENTION 
     This invention relates to a detector system for knitting machines and more particularly to sensor employed in manufacturing operations to detect defects in knitting fabric. 
     There is a variety of devices available for use on circular knitting machines to reduce the occurrence of fabric defects such as yarn breaks, holes in the fabric, runs in the fabric, etc. 
     Normally the instruments for assuring better quality knitted fabric consist of devices which sense yarn breakage in its passage from a yarn supply to the knitting elements of the circular knitting machine, and devices for sensing fabric condition between the knitting elements and the fabric take-down assembly. 
     One of the more commonly used detectors is an electrical device for stopping operation of the knitting machine when a yarn breaks or runs out. 
     Devices for detecting holes and runs in fabric also are commonly used for automatically stopping operation of the machine. These may be in the form of mechanical fingers or electronic devices for optical scanning of the fabric to locate defects. However, as in the case of rundown detectors, the prior art forms have certain disadvantages. For example, such devices do not have the ability to detect good fabric from bad fabric. Sometimes in oiling the knitting machines, oil may cause streaks on the fabric, thus giving false signals of a run in the fabric. Once the machine has been restarted, the system of the present invention prevents the rundown detector from stopping the machine again until a prescribed amount of faultless fabric has been sensed by the rundown detector. 
     A primary object of the invention is the provision of a new and improved fault detection system for knitting machines. 
     Another object of the invention is to provide a novel rundown detector which substantially eliminates the stopping of the machine due to false signals and deactivates the machine only in the event of an actual rundown defect in the fabric. 
     It is another object of the invention to provide a rundown detector which incorporates a fiber optic means and a floating head for sensing the condition of the fabric. 
     A further object of the invention is to provide a kntting machine incorporating a system for deactivating the machine upon detection of a rundown, a yarn break, or occurrence of an opening in the fabric. 
     Still another object of the invention is a fault detection system which is reliable in operation and which may be economically applied to existing knitting machines. 
     Other objects and advantages of the invention will become apparent when considered in view of the following detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a fragmentary, perspective view of a conventional circular knitting machine having the fault detection system of the present invention applied thereto; 
     FIG. 2 is a schematic block diagram of the system including the circuitry for controlling the machine; 
     FIG. 3 is a block diagram of various components of the system including an enlarged schematic diagram of the logic circuitry of FIG. 2; 
     FIG. 4 is a perspective view of the sensor head of the rundown detector; 
     FIG. 5 is a schematic electrical diagram of various components of the photoelectric amplifier circuit; and 
     FIG. 6 is a diagram of voltage wave forms illustrating operation of the circuit of FIG. 5. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a conventional circular knitting machine 10 having an electrical stop motion is provided with the fault detection system 12 (FIG. 2) of the present invention which includes various devices for reducing the occurrence of defects in the fabric being knit. The system includes a conventional yarn break or runout detector 14, a conventional mechanism 16 for detecting holes in the knit fabric or pressoffs, and a device 18 for detecting runs in the fabric. 
     The rundown detector 18 includes a floating sensor head 20, positioned at a selected point or location, having a guide member 22 which engages the inner portion of the knit tube, as shown by FIG. 1. Upon rotation of the knit fabric tube 24 in the direction of the arrow A, FIG. 1, the sensor head 20 is in contact with the fabric immediately below the knitting elements. The head 20 includes an elongated aperture 26, FIG. 4, which may be, for example, 1/16&#34; wide and 1/2&#34; long, and is secured to an arm 28 which, in turn, is pivotably supported upon a bracket 30. Spring 32 serves to provide a counterbalancing effect on the arm 28 and head 20 so that the head is in light, floating contact with the fabric 24. 
     The detector 18, which optically checks for continuous stitch formation, will not stop the machine 10 except when a rundown is sensed. As long as yarns forming the stiches are intact, light from a photoelectric amplifier circuit 34 is continuously transmitted along a fiber optic tube 36 and through the aperture 26 of the sensor head 20, in engagement with the rotating fabric tube 24, and is reflected off the knitted fabric and back to the photoelectric amplifier circuit 34 via the aperture 26 and the fiber optic tube 38. Alternating periods of relatively high and low reflected light levels are transmitted to the circuit 34 due to alternate peaks and valleys of the knit fabric. When a predetermined, extended period of low reflected light is detected by circuit 34 due to occurrence of a run, an output signal is generated and directed along line 40 to the logic circuit 42. 
     Referrings to FIGS. 5 and 6, the photoelectric circuit 34 operates by sensing peaks P and valleys V in the surface texture of the knit fabric 24 and emitting a signal when the space between two adjacent peaks is longer than normal, as at V-2. 
     Light from the source 35 is conducted along fibers within a tube 36 and directed onto the moving fabric 24. A portion of the light is reflected from the cloth, directed along tube 38 and detected by a photocell 37. The signal is amplified in such a way that valleys in the fabric (relatively low reflected light) are represented by positive peaks in a voltage wave form at the output of amplifier 39. Peaks in the fabric (high reflected light) cause negative voltage valleys in the output waveform (I. of FIG. 6) of the amplifier. 
     The amplifier 39 is connected to a voltage integrator 41 which produces a &#34;ramp&#34; output (II. of FIG. 6). Since the ramp builds at a nearly linear slope rate, while the input voltage is positive, the maximum voltage of the ramp depends upon the length of time the input voltage is positive. The maximum ramp voltage, therefore, depends on the length or width of the valley in the fabric. 
     The integrator output feeds into a comparator 43 along with a fixed reference voltage to which the ramp voltage is compared. When the ramp voltage exceeds the reference voltage, caused by a rundown, the comparator provides an output which triggers a one-shot output 45. 
     The signal is fed simultaneously to a shift register 44 and a timer 46 which form part of the logic circuit. The timer 46 enables the shift register 44 to operate to count a predetermined number of additional signals generated along line 40 from the photoelectric circuit 34, one signal being generated each time the fault or defect in the fabric rotates past the sensor head 20. After the shift register receives a predetermined number of signals within a prescribed period determined by the timer 46 which is sufficient to determine that the fault being detected is a rundown, the knitting machine electric stop motion 50 is activated to stop the drive to cylinder of machine 10. If the prescribed number of signals is not received during the prescribed time period, the logic circuit 42 will reset itself without stopping the machine. For the stop motion 50 to stop the machine, a signal must be received from the shift register 44 through line 54 and a signal must be directed from switch 60 along the line 62 to the AND circuit 64. The switch 60 senses when the machine 10 is running. Whenever signals appear at the same time along lines 54 and 62 the AND circuit 64 produces an output signal which through triac 52 in line 66 activates the electric stop motion 50 either directly or indirectly to stop operation of the machine. The stop motion, when activated, deactivates the main motor, not shown, which drives the knitting machine. 
     When a signal from the shift register 44 is directed to the AND circuit 64, the latch 68, provided to store information, also activates the rundown indicator light 70 which signals to an operator the particular reason for the machine shutdown. The main warning light 72 also will be on indicating to an operator that the machine needs attention. If the machine is stopped by an operator, no indicator lights will be on. 
     After the operator has corrected the problem, and the machine restarted, rundown indicator light 70 will go off. However, the main warning light will remain on until the rundown detector 18 has &#34;seen&#34; a predetermined number of revolutions of faultless fabric 24. During this time the machine cannot be stopped due to signals generated by the photoelectric circuit 34. 
     Restarting of the machine activates a lockout timer 76 through switch 60. The lockout timer 76 is activated for a prescribed period of time which would permit a predetermined number of revolutions of the fabric tube 24 being knit, for example, five revolutions of the tube. If the rundown detector 18 does not sense a fault in the fabric during this time and the fabric is &#34;verified&#34; to be &#34;good,&#34; the timer 76 will time out and the main warning light 72 will be turned off. 
     Occasionally when a machine has been stopped for oiling of various components, oil streaks will get onto the fabric which will give fault signals to the rundown detector 18 when the machine is restarted. Upon restarting the machine the lockout timer 76 also is activated. If, before timer 76 times out, the detector 18 senses an oil streak and a signal is emitted by the photoelectric circuit 34, the signal is directed along line 80 to restart the lockout timer 76. The lockout timer 76, which is also connected to the shift register 44 and timer 46, prevents the shift register from sending a signal to stop the motion until the timer 76 times out without receiving a signal from the photoelectric circuit 34. The timer 76 may stay on indefinitely as long as signals are generated by the circuit 34, before the timer 76 can time out. If the oil streaks move below the sensor head 20, and a signal is not received from circuit 34 before the timer 76 times out, the fabric is verified to be good and deactivation of the timer 76 turns off the warning light 72. 
     The yarn break detector 14, as shown schematically on FIG. 1, is of a conventional type. For example, the detector may include a spring biased guide arm for selectively activating a switch. The yarn tension normally maintains the arm in an inoperative position, and when the yarn breaks or runs out the arm is biased to operate a switch. While one detector 14 has been shown, it is to be understood that detectors may be provided for each yarn fed to the knitting elements. 
     Upon activation of a detector 14, a signal is sent simultaneously to the logic circuit 42 along line 94 and to the electric stop motion 50 aloong line 96, which stops the machine. The latch 68 of the logic circuit activates the yarn break indicator light 88 and the main warning light 72. 
     The hole detector mechanism 16, which is operated upon the occurrence of a hole or pressoff, also is of a conventional type. The detector may consist of a spring loaded plunger which normally engages the knit fabric tube. Upon the occurrence of a hole the plunger contacts metal at the back of the fabric tube which sends a signal simultaneously along line 98 to the logic circuit 42 and along line 100 to the electric stop motion 50 to stop the machine and activate warning line 72 and the hole detector light 90.