Method and apparatus of measuring a gap between a first and second roll

1. A method of measuring a gap between a first and second roll, wherein the method comprises the steps of:

providing a first and second roll having parallel axes of rotation, the first roll having a first position and the second roll having a second position, the first roll having a first surface and the second roll having a second surface;

defining a gap between the first and second roll which meets a target distance between the first and second roll to allow a web material to pass through the gap;

providing at least a first non-contacting measuring device and which measures a first distance from the first non-contacting measuring device to the first surface to infer the position of the first roll;

inferring the gap between the first and second roll from the inferred position of the first roll;

passing the web material between said first and second surfaces for a resulting transformation; and

wherein the first non-contacting measuring device is selected from the group consisting of an inductive sensor, a capacitance sensor, an Eddy-current sensor, a laser triangulation displacement sensor, a confocal-chromatic sensor and combinations thereof.

2. The method according to claim 1 wherein the first and/or second roll are subjected to a thermal expansion or a thermal contraction during use.

3. The method according to claim 1 wherein the method further comprises the step of:

detecting the wear of the first roll by using the first non-contacting measuring device, and/or

detecting the wear of the second roll by using a second non-contacting measuring device.

4. The method according to claim 1 wherein the method further comprises the steps of:

comparing the gap to a target distance for the gap by using a controller;

repositioning the first and/or second roll such that the gap meets the target distance of the gap.

5. The method according to claim 4 wherein the first and second surfaces are smooth, and wherein the target distance is the distance between the smooth surfaces of the first and second roll, the target distance being from 1 to 20 μm.

6. The method according to claim 4 wherein the first surface has a plurality of protuberances extending outwardly therefrom, each protuberance having an upper edge, wherein the second surface is smooth and wherein the target distance is the distance between the upper edge of the uppermost protuberance of the first roll and the smooth surface of the second roll, the target distance being from 0 to 20 μm.

7. The method according to claim 4 wherein the first and second surfaces have a plurality of protuberances extending outwardly from the surface of each first and second roll, each protuberance having an upper edge, and wherein the target distance is the distance between the upper edge of the uppermost protuberance of the first or second roll and the surface of the respective first or second roll, and wherein the target distance is from 0 to 20 μm.

8. The method according to claim 4 wherein the first and/or second roll are repositioned such that the gap between the first and second roll is within the target distance, wherein repositioning is made by using an actuator which is selected from the group consisting of an electromechanical actuator, a pneumatic actuator, a hydraulic actuator, a linear actuator and combinations thereof.

9. A method of measuring a gap between a first and second roll, wherein the method comprises the steps of:

providing a first and second roll having parallel axes of rotation, the first roll having a first position and the second roll having a second position, the first roll having a first surface and the second roll having a second surface;

defining a gap between the first and second roll which meets a target distance between the first and second roll to allow a web material to pass through the gap;

providing at least a first non-contacting measuring device and which measures a first distance from the first non-contacting measuring device to the first surface to infer the position of the first roll;

providing at least a second non-contacting measuring device and which measures a second distance from the second non-contacting measuring device to the second roll to infer the position of the second roll;

inferring the gap between the first and second roll from the inferred positions of the first and second roll;

passing the web material between said first and second surfaces for a resulting transformation; and

wherein the first and second non-contacting measuring device are selected from the group consisting of an inductive sensor, a capacitance sensor, an Eddy-current sensor, a laser triangulation displacement sensor, a confocal-chromatic sensor and combinations thereof.

10. The method according to claim 9 wherein the first and/or second roll are subjected to a thermal expansion or a thermal contraction during use.

11. The method according to claim 9 wherein the method further comprises the step of:

detecting the wear of the first roll by using the first non-contacting measuring device, and/or

detecting the wear of the second roll by using the second non-contacting measuring device.

12. The method according to claim 9 wherein the method further comprises the steps of:

comparing the gap to a target distance for the gap by using a controller;

repositioning the first and/or second roll such that the gap meets the target distance of the gap.

13. The method according to claim 12 wherein the first and second surfaces are smooth, and wherein the target distance is the distance between the smooth surfaces of the first and second roll, the target distance being from 1 to 20 μm.

14. The method according to claim 12 wherein the first roll has a plurality of protuberances extending outwardly from the first surface, each protuberance having an upper edge, wherein the second surface is smooth and wherein the target distance is the distance between the upper edge of the uppermost protuberance of the first roll and the smooth surface of the second roll, the target distance being from 0 to 20 μm.

15. The method according to claim 12 wherein the first and second surfaces each have a plurality of protuberances extending outwardly therefrom, each protuberance having an upper edge, and wherein the target distance is the distance between the upper edge of the uppermost protuberance of the first or second roll and the surface of the respective first or second roll, and wherein the target distance is from 0 to 20 μm.

16. The method according to claim 12 wherein the first and/or second roll are repositioned such that the gap between the first and second roll is within the target distance, wherein repositioning is made by using an actuator which is selected from the group consisting of an electromechanical actuator, a pneumatic actuator, a hydraulic actuator, a linear actuator and combinations thereof.