초록 ▼

Paper and continuous web scanners operate at varying and high temperature conditions. Regulating the temperature within the measurement gap between dual scanner heads during measurement and calibration modes of operation by employing air wipe and sheet guide temperature control assures consistent an

Paper and continuous web scanners operate at varying and high temperature conditions. Regulating the temperature within the measurement gap between dual scanner heads during measurement and calibration modes of operation by employing air wipe and sheet guide temperature control assures consistent and accuracy sensor measurements of sheet characteristics. Air wipes blow pre-heated air into the measurement and the sheet guides are heated. The air temperature fluctuations that otherwise caused significant adverse effects on the sensors that measure, for example, the basis weight, ash content, and thickness of the moving sheet, are eliminated.

대표청구항 ▼

1. A system for controlling the temperature in a measurement gap adapted to accommodate a continuous web, having a first side and a second side, that travels in a downstream direction, which comprises: (a) a first sensor head disposed adjacent to a first side of the web, the first sensor head includ

1. A system for controlling the temperature in a measurement gap adapted to accommodate a continuous web, having a first side and a second side, that travels in a downstream direction, which comprises: (a) a first sensor head disposed adjacent to a first side of the web, the first sensor head including: a first operative surface facing the first side of the web;means for heating the first operative surface; andmeans for measuring the temperature of the first operative surface;(b) a second sensor head disposed adjacent to a second side of the web, the second sensor head including: a second operative surface facing the second side of the web, wherein the first operative surface and the second operative surface define the measurement gap through which the continuous web travels, and wherein the measurement gap has a web entry end and a web exit end that is downstream from the web entry end;means for heating the second operative surface; andmeans for measuring the temperature of the second operative surface;(c) temperature sensor to detect the ambient temperature within the measurement gap and that generates signals representative of the ambient temperature;(d) means for supplying a heated gas at the web entry end such that the heated gas flows continuously into the measurement gap via the web entry end and out of the measurement gap through the web exit end;(e) computing means in communication with the temperature sensor to process the signals to generate a gap temperature profile and that stores a predetermined desired gap temperature profile; and(f) control means in communication with the computing means for controlling the temperature of the heated gas that is supplied, the means for heating the first operative surface, and the means for heating the second operative surface to correct for deviation from the desired gap temperature profile. 2. The system of claim 1 wherein the means for heating the first operative surface comprises a plurality of first heating devices incorporated in the first operative surface and the means for heating the second operative surface comprises a plurality of second heating devices incorporated in the second operative surface and wherein the control means regulates the amount energy generated by the first and second heating devices and the of temperature of the heated gas. 3. The system of claim 1 wherein the means for supplying a heated gas at the web entry comprises a source of heated gas and a first nozzle that directs a stream of heated gas toward the first side of the web and a second nozzle that directs a stream of heated gas toward the second side of the web. 4. The system of claim 1 wherein at least one of the first sensor head or second sensor head includes a sensor that measures one or more characteristics of the continuous web and the controller means maintains the temperature in the vicinity of the sensor within a defined range regardless of whether the continuous web is moving within the measurement gap or not. 5. The system of claim 1 wherein the control means regulates a first control loop when the measurement gap is in an on sheet mode with the continuous web traveling therein and regulates a second control loop when the measurement gap is in an of sheet mode without the continuous web traveling therein. 6. A control system to regulate the ambient temperature of a measurement gap adjacent a target area within a dual head scanner having at least one sensor for continuous on-line measurement of one or more characteristics of a moving sheet, wherein the dual head scanner includes a first head having a first plate and a second head having a second plate, wherein the at least one sensor is mounted in either the first head or second head or in both, and wherein the first plate and second plate define a measurement gap through which the sheet travels, the control system comprising: means for heating the first plate that includes a first associated adjustable actuator that regulates the temperature of the first plate;means for heating the second plate that includes a second associated adjustable actuator that regulates the temperature of the second plate;means for injecting a heated gas at a web entry end of the measurement gap, such that the heated gas flows continuously into the measurement gap via the web entry end and out of the gap through a web exit end, and that includes a third adjustable actuator that regulates the flow rate and/or temperature of the heated gas wherein the means for injecting the heated gas comprises at least one nozzle located exterior of the web entry end to supply heated gas into and through the measurement gap;air temperature sensor for measuring the ambient air temperature of the measurement gap adjacent the target area and for generating signals representative of the ambient air temperature;plate temperature sensor for measuring the temperatures of the first and second plates; andcontroller means that is in communication with the air temperature sensor to provide control signals to actuate at least one of the first associated adjustable actuator, the second associated adjustable actuator, and third associated adjustable actuator in order to maintain the temperature of the ambient air temperature of the measurement gap adjacent the target area to within a desired air temperature range and to maintain the first and second plate temperatures within a desired plate temperature range. 7. The control system of claim 6 wherein the means for heating the first plate and the means for heating the second plate are positioned to provide uniform heating along the first and second plate surfaces. 8. The control system of claim 6 wherein the means for injecting a heated gas comprises a source of heated gas and a first nozzle that directs a stream of heated gas toward a first side of the web and a second nozzle that directs a stream of heated gas toward a second side of the web wherein the first and second nozzles are located exterior of the web entry end to supply heated gas into and through the measurement gap. 9. The control system of claim 6 wherein the moving sheet comprises paper and wherein the sheet travels in a machine direction and the dual head scanner moves in a cross direction which is perpendicular to the machine direction. 10. A control system to regulate the ambient temperature of a measurement gap adjacent a target area within a dual head scanner having at least one sensor for continuous on-line measurement of one or more characteristics of a moving sheet, wherein the dual head scanner includes a first head having a first plate and a second head having a second plate, wherein the at least one sensor is mounted in either the first head or second head or in both, and wherein the first plate and second plate define a measurement gap through which the sheet travels, the control system comprising: means for heating the first plate that includes a first associated adjustable actuator that regulates the temperature of the first plate;means for heating the second plate that includes a second associated adjustable actuator that regulates the temperature of the second plate;means for injecting a heated gas at a web entry end of the measurement gap, such that the heated gas flows continuously into the measurement gap via the web entry end and out of the gap through a web exit end, and that includes a third adjustable actuator that regulates the flow rate and/or temperature of the heated;air temperature sensor for measuring the ambient air temperature of the measurement gap adjacent the target area and for generating signals representative of the ambient air temperature,plate temperature sensor for measuring the temperatures of the first and second plates; andcontroller means that is in communication with the air temperature sensor to provide control signals to actuate at least one of the first associated adjustable actuator, the second associated adjustable actuator, and third associated adjustable actuator in order to maintain the temperature of the ambient air temperature of the measurement gap adjacent the target area to within a desired air temperature range and to maintain the first and second plate temperatures within a desired temperature range and wherein the controller means maintains the ambient air temperature in the measurement gap at the air desired temperature range and maintains the first and second plate temperatures within the desired plate temperature range even when a moving sheet is not present in the gap. 11. A control system to regulate the ambient temperature of a measurement cap adjacent a target area within a dual head scanner having at least one sensor for continuous online measurement of one or more characteristics of a moving sheet, wherein the dual head scanner includes a first head having a first plate and a second head having a second plate, wherein the at least one sensor is mounted in either the first head or second head or in both, and wherein the first plate and second plate define a measurement gap through which the sheet travels, the control system comprising: means for heating the first plate that includes a first associated adjustable actuator that regulate the temperature of the first plate;means for heating the second plate that includes a second associated adjustable actuator that regulates the temperature of the second plate;means for injecting a heated gas at a web entry end of the measurement gap, such that the heated gas flows continuously into the measurement gap via the web entry end and out of the cap through a web exit end, and that includes a third adjustable actuator that regulates the flow rate and/or temperature of the heated;air temperature sensor for measuring the ambient air temperature of the measurement gap adjacent the target area and for generating signals representative of the ambient air temperature;plate temperature sensor for measuring the temperatures of the first and second plates; andcontroller means that is in communication with the air temperature sensor to provide control signals to actuate at least one of the first associated adjustable actuator, the second associated adjustable actuator, and third associated adjustable actuator in order to maintain the temperature of the ambient air temperature of the measurement gap adjacent the target area to within a desired air temperature range and to maintain the first and second plate temperatures within a desired plate temperature range and wherein the controller means regulates a first control loop when the dual head scanner is in an on sheet mode with the sheet traveling therein and regulates a second control loop when the dual head scanner is in an off sheet mode without the sheet traveling therein. 12. A method of controlling the ambient temperature within an air gap within a dual head scanner through which a continuous web travels, the air gap being defined by (i) a first head that has a first operative surface that is connected to a first plate actuator for heating the first operative surface and (ii) a second head that has a second operative surface that is connected to a second plate actuator for heating the second operative surface, and wherein the air gap has heated was injected therein at a web entry end from a source of heated gas that is connected to a third air actuator for regulating the flow and/or temperature of the heated gas, the method comprising the steps of: detecting the ambient temperature within the air gap with air sensors positioned on the first operative surface and on the second operative surface and generating air temperature signals indicating the ambient temperature,detecting the plate temperatures of the first and second operative surfaces with plate temperature sensors positioned on the first operative surface and on the second operative surface and generating plate temperature signals indicating the first and second operative surface temperatures;analyzing the air temperature and plate temperature signals and generating target air temperature and target plate temperature set points to be used for heat control during off sheet and on sheet modes of operations, wherein initial target first and second plate temperatures are selected from the steady state temperatures of the first and second plates during on sheet operations and an initial target air gap temperature is selected from the steady state temperature of the air gap during on sheet operations;comparing actual first and second plate temperatures and air gap temperature to the respective target temperatures and generating error information based on the comparison; andsending the error information to either a first or second control loop wherein the first control loop, when active, operates when the dual head scanner is in an on sheet mode and the second control loop, when active, operates when the dual head scanner is in an off sheet mode to allow manipulation of set points of at least one of the first plate actuator, second plate actuator, and third air actuator to correct deviations from a desired air gap temperature profile and wherein the set points for the control loop that is not active are stored as a starting point to enable responsive reaction when the state of operation is switched between the on sheet and off sheet modes of operation. 13. The method of claim 12 wherein the initial target first and second plate temperatures are selected from the steady state temperatures of the first and second plates during on sheet operations with the first and second plate actuators being set to a value of between 10% to 40% of maximum and the initial target air gap temperature is selected front the steady state temperature of the air gap during on sheet operations with the third air actuator power being set to a value between 10% to 40% of maximum. 14. The method of claim 12 wherein the temperature of the first plate and the temperature of the second plate are maintained within the same temperature ranges in both the on sheet and off sheet modes of operation. 15. The method of claim 12 wherein in the on sheet mode of operation a continuous web travels through the air gap as one or more characteristics of the continuous web is measured with one or more sensors that are positioned in the first or second heads. 16. The method of claim 15 further comprising the steps of: removing the continuous web from the air gap; andswitching to the off sheet mode of operation while maintaining the temperature of the first plate and the temperature of the second plate in the same temperature ranges as when the continuous web was within the gap in the on sheet mode of operation. 17. The method of claim 16 wherein the one or more sensors is calibrated in the off sheet mode of operation. 18. The method of claim 12 wherein the continuous web comprises paper. 19. The method of claim 12 wherein heated gas is injected through a first nozzle that directs a stream of heated gas toward a first side of the continuous web and a through a second nozzle that directs a stream of heated gas toward a second side of the continuous web. 20. The method of claim 12 wherein the first plate actuator and the second plate actuator are positioned to provide uniform heating along the first and second plate surfaces.