Apparatus For Keeping A State Of Tension Constant On A Material Web Which Runs Between Successive Pairs Of Driving Rollers

Abstract

An apparatus for keeping a state of tension constant on a material web which runs between successive pairs of driving rollers includes a torsion bar having a lever extension with a guide roller over which the material is directed. Sensing means are associated with the lever to sense variations of the torsion acting on the bar through the displacement of the lever by the variations in tension of the material which is being fed and this sensing means is connected to electrical control means for varying the speed of one or the other set of rollers or for braking the speed of one of the sets of the rollers in order to vary the tension on the web material which is fed.

Description

SUMMARY OF THE INVENTION

This invention relates in general to web feeding devices, and in particular, to a new and useful apparatus for maintaining a state of tension constant on a material web which runs between successive driving rollers by sensing the tension on the material and by driving the rollers accordingly.

In a known control of the type with which the present invention refers the movements of the scanning means or sensing means are transmitted to a baffle plate and the size of the gap between the baffle plate and an air feed pipe varies in dependence of the scanning roller. The pressure in the air pipe changes to provide a control of the braking element cooperating with the material web in the sense of a tension correction. A disadvantage of such an arrangement is that it is susceptible to trouble and the change over to a different nominal tension value requires complicated and time consuming operations; and, once the values have been selected, their reproducibility cannot be readily ensured. In another known arrangement a scanning roll is pressed elastically against the web. It serves thus to produce the desired tension in the material web between the leading and trailing driving rollers and the tension thus produced is maintained in the range determined by the deflection of a spring system. This known arrangement has the disadvantage that it reacts very slowly and it is insensitive to minor tension variations and therefore, it is only useable to a limited extent for keeping low fabric tensions constant. In addition, the spring system must be set repeatedly and shifted for each desired web tension. In this known arrangement, the reproducibility of the tension values after they have been set is not readily ensured.

An object of the present invention is to provide an apparatus with which practically any fabric tension between successive driving rollers can be produced and maintained in a simple manner and which includes sensing means which react automatically to provide a correction of the tension on the web material being fed to maintain it at a nominal value within minute deviations. The apparatus of the invention ensures that webs to be treated are protected from damages due to different tensions and that the energy expended during the adjustment to achieve a certain desired web tension is reduced while permitting the treatment with the webs with different tensions on one and the same apparatus.

In accordance with the invention, the apparatus includes a scanning roller which is supported on a lever arm which is engaged with a torsion bar such that a certain rotary position of the torsion bar corresponds to each web tension produced by the speed difference of the driving rollers of a forward and trailing roller sets. Such a rotary position can be set as a nominal value so that any deviations from this nominal rotary position, as a result of tension variations which act on the web, may be employed to actuate a control to influence the speed of at least one of the driving roller sets to effect a correction of the tension. With such an arrangement only the effective tension of the material web is measured by the scanning roller. To each nominal tension value of the material web which is to be maintained by a certain speed difference of the driving rollers, there is a corresponding rotary position of the torsion bar and a corresponding inclination of the lever holding the scanning roller. This nominal position can be set by an electrical or mechanical connection to a control element so that the control element will respond instantaneously to influence the speed of one driving roller set and to effect a corrective speed up or slow down of the web material in order to achieve the desired tension on the fabric in accordance with the setting of the torsion bar. The apparatus of the invention permits, with relatively simple means, a reliable control for keeping a certain tension in a material web constant and to immediately correct even minor deviations. The arrangement is such that the nominal tension value can be varied within wide limits and thus the apparatus is adapted to the respective processing conditions of the materials.

Accordingly, it is an object of the invention to provide an improved device for maintaining a uniform or nominal value of tension on a web fed between two sets of feeding rollers which includes a torsion bar having a lever carried thereby which includes a roller at its outer end which is engaged with the web material being fed, the bar being deflectible by the deflection of the lever with the roller, due to variations of web tension, to actuate a speed control mechanism for varying the speed of one of the feed roller sets to maintain the nominal tension value.

A further object of the invention is to provide a device for controlling the tension of a web which is simple in design, rugged in construction, and economical to manufacture.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated and described a preferred embodiment of the invention .

BRIEF DESCRIPTION OF THE DRAWINGS

The only FIGURE of the drawings is a schematic side elevational view of a device for maintaining a fixed tension on a web material which is constructed in accordance with the invention.

GENERAL DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawing in particular, the invention embodied therein comprises apparatus for feeding a material web generally designated 1 with a fixed or nominal tension thereon between two sets of feed rollers 2, 2 and 2', 2'. The web material may be a textile fabric web, a paper web, or a plastic web, for example. Between the two sets of feeding rollers the web is directed as a web loop 3 around fixed deflecting rollers 5, 5' and over a scanning roller 4 which is rotatably supported between the free ends of laterally spaced supporting levers 6, 6 (only one of which is shown). The levers 6,6 are rigidly connected to the respective ends of a torsion bar 7 which is rigidly secured in a stationary; machine part and which will which deflect slightly under torsional loading of the respective lever 6. The suspension for the torsion bar 7 is such that different free spring lengths are possible. The result is a very precise particularly friction free support and guidance of the scanning roller 4 which engages the web material 1. By using a very light weight construction for the scanning roller 4 the system can be made so that it is relatively poor inertially.

In accordance with a feature of the invention, movement of the scanning roller and hence the lever 6 and the deflection of the torsion bar 7 is used to actuate motor speed control means 14 for actuating a driving motor (not shown) connected to a drive shaft 16 and/or a drive shaft 18 for the rollers 2' and 2', respectively. In one embodiment, one of the levers 6 cooperates with a feeler 8 of a transmitter 9 which acts through an amplifier 20 to produce a control signal at the motor speed control 14. In another embodiment the feeler 8 or the lever 6 is connected with an electrical potentiometer 22 which includes amplification means or electrical transformation means for providing a signal to the motor speed control 14 for varying the speed of the shaft 16 and 18 or for providing a braking action on the shafts in accordance with the changes sensed.

The transmitter 9 advantageously is mounted on a plate 10 which is movably arranged in respect to a block 11. By means of a manually operated knob 12 and a threaded spindle carried by the knob the relative position of the feeler 8 in respect to the lever 6 can be varied.

The desired tension or nominal tension of the material web between the driving rollers 2, 2 and 2', 2' is adjusted by a setting of the speed difference in the run of the driving rolls. This nominal tension yields a certain position of the torsion bar 7 and an inclination of the lever 6, and this position is adjusted to achieve a zero tension or nominal tension position. By turning the knob 12 and making a corresponding adjustment of the feeler 8 the inclination of lever 6 associated with a certain web tension can be a nominal value or zero value at which the control element 14 does not respond. Any deflection of the lever 6, 6 from the zero position, however, actuates the feeler 8 and the transmitter 9 and the amplifier 20 and the speed control 14 to change the speed value of the driving rolls 2', 2'. The rolls 2', 2' then drive at either a faster or slower speed to adjust the tension to a desired value until the lever 6 moves back to a zero position and stops the correcting action of the motor speed control 14.

By using a torsion bar 7, practically any force range and any tension stress can be kept constant in the material web 1. For extreme values, it is only necessary to replace the torsion bar 7 by those of stronger or weaker dimensions. In any case the apparatus can be easily and simply adapted to the desired purpose within wide limits since a certain material tension effects in any case a certain deflection of the scanning roller 4 which can be set in a very simple manner as the nominal value for the control element.

A particularly simple operation of the control device is possible by connecting the free end of the torsional bar or one of the torsion bars directly with a rotary potentiometer such as the potentiometer 22. In this arrangement, the zero position is set in the control device which would correspond to the voltage given off by the potentiometer in the position of the setting in which it is put in by the torsion of the torsion bar as a result of the desired fabric stress. Deviation of the fabric stress from the desired nominal tension will effect a shifting of the potentiometer through the deflection of the torsion bar. The control device 14 receives thus a voltage different from the set value and the voltage difference is proportional to the fabric tension difference. With this voltage difference the speed difference of the driving rollers 2', 2' is corrected by a control device.

Claims

What is claimed is

1. An apparatus for monotoring a predetermined tension on a web, comprising a first and a second set of feed rollers disposed in spaced relationship and arranged for feeding the web therebetween, motor speed control means connected to at least one of said first and second sets of feed rollers for driving said set of feed rollers at a speed distinct from that of the other set of feed rollers for imparting a predetermined nominal tension to the web being fed therebetween, a scanning roller located between said first and second sets of feed rollers and arranged in contact with the web being fed therebetween, a lever system connected to said scanning roller and comprising a pair of laterally spaced levers each connected at one end to the opposite ends of said scanning roller and the opposite ends of said levers being rigidly interconnected, a fixed support, a torsion bar positioned on he pivotal axis of said lever system and secured to said fixed support and means engageable with said lever system and connected to said motor speed control means to actuate said motor speed control means in accordance with the deflection translated from said scanning roller to the at least one of said torsion bar and said lever to drive one of said sets of feed rollers at a speed to restore said torsion bar and said lever system to a predetermined nominal setting position.

2. An apparatus, according to claim 1, wherein said torsion bar is of a size selected in accordance with the tension desired and is exchangeable.

3. An apparatus, according to claim 1, wherein said means engageable with at least one of said torsion bar and said lever comprises a potentiometer having a rotary member for setting the voltage difference in accordance with the setting of said torsion bar and/or said lever, said potentiometer being connected to said motor speed control means and providing directly as a control for varying the speed of said driving roller sets.

4. An apparatus, according to claim 1, wherein a feeler arranged in bearing relationship with at least one of said levers and being displaceable by movement of said lever and being connected to said motor speed control means for varying the speed of one of said sets of feed rollers.

5. An apparatus, according to claim 1, wherein a first fixed deflecting roller is located between said first set of feed rollers and said scanning roller, a second fixed deflecting roller located between said second set of feed rollers and said scanning roller, and the axis of said first and second fixed deflecting rollers being located in a plane spaced from the axis of said scanning roller so that the web passing between said first and second sets of feed rollers is guided over said first and second fixed deflecting rollers and said scanning roller for forming a loop in the web.

6. An apparatus, according to claim 5, including a fixed plate positioned adjacent to said lever system, a movable plate mounted on said fixed plate for movement toward and away from at least one of said levers, a transmitter mounted on said movable plate and having a sensing finger extending outwardly therefrom and engaged with said lever and being deflectable by said lever upon movement thereof upon torsioning of said torsion bar, and means connected to said movable plate for adjusting the position of said movable plate with said transmitter and said sensing finger.