Method and apparatus for determining slipping in a nip roller

#1. Field of the Invention

#The present invention relates generally to web printing presses and more particularly to a method and apparatus for determining the presence of slipping of a driven nip roller in a web printing press.

#2. Background Information

#The present invention is elaborated upon below with reference to the drawings, in which:

#FIG. 1 shows a schematic diagram of an embodiment of an apparatus for determining a presence of a slipping driven nip roller of a nip in a web printing press, using a change in tension difference;

#FIG. 2 shows a graph of the difference in tension across a nip in a web printing press as a function of a velocity of a nip roller; and

#FIG. 1 shows a schematic diagram of an apparatus for determining a presence of a slipping driven nip roller in a web printing press 10. Web 12 is moved by driven nips 22, 28 and 34 in the direction indicated by arrow 14. Nips 22, 28 and 34 are formed by nip rollers 20 and 24, 26 and 30, and 32 and 36, respectively. Nips 22, 28 and 34 are designed to be non-slip nips. Nip rollers 22 and 24, 26 and 30, and 32 and 36 rotate as indicated by arrows 27. Nip rollers 20, 26 and 32 are non-slip driven nip rollers driven by nip roller drivers 38, 40 and 39, respectively. Nip roller drivers 38, 40 and 39 may be, for example, electric motors, or other type of suitable drivers. Upstream web span 16 is formed between nips 22 and 28, while downstream web span 18 is formed between nips 28 and 34. The discussion below focuses on nip 28 and associated nip roller 26 and driver 40, but a similar discussion could apply to nips 22 and 34, depending on the configuration of printing press 10.

#Upstream from nip 28, tension sensor 44 provides tension signal 45, which is proportional to the tension in upstream web span 16, to processor 50. Downstream from nip 28, tension sensor 46 provides tension signal 47, which is proportional to the tension in downstream web span 18, to processor 50. Tension sensors 44 and 46 may each be, for example, a transducer, or other type of device for sensing the tension in a web span. Processor 50 exchanges information 42, including nip roller driver speed information, with nip roller driver 40, and sends slip status indication signal 62 to slip indication device 60.

#Processor 50 systematically causes the speed of nip roller driver 40 to be increased and/or decreased relative to a nominal driver speed corresponding to the nominal, or command, press speed. The systematic speed changing may be in accordance with a predetermined algorithm, for example. Using tension sensors 44 and 46, processor 50 monitors the change in web span tension across nip 28 corresponding to each increase and decrease in the speed of nip roller driver 40. Processor 50 uses this data to determine the relationship, especially the linearity and slope of the relationship, of the tension difference between upstream web span 16 and downstream web span 18 to the speed of nip roller driver 40 using known mathematical techniques. Processor 50 may be a microprocessor, for example, or other processing device. Processor 50 interacts with tension control system 52. Alternatively, processor 50 may be integrated into tension control system 52. Tension control system 52 controls the tension in web spans 16 and 18, and may include, for example, a proportional plus integral tension controller.