Patent Application
20160054120
This disclosure relates generally to scanning measurement systems. More specifically, this disclosure relates to automated cross direction alignment of upper and lower scanning heads based on measurement of sensor sensitivity.
Sheets or other webs of material are used in a variety of industries and in a variety of ways. These materials can include paper, multi-layer paperboard, and other products manufactured or processed in long webs. As a particular example, long sheets of paper can be manufactured and collected in reels.
It is often necessary or desirable to measure one or more properties of a web of material as the web is being manufactured or processed. Adjustments can then be made to the manufacturing or processing system to ensure that the properties stay within desired ranges. Measurements are often taken using one or more scanning heads that move back and forth across the width of the web.
This disclosure provides automated cross direction alignment of upper and lower scanning heads based on measurement of sensor sensitivity.
In a first embodiment, a method includes moving a first sensor assembly to a plurality of cross direction positions relative to a second sensor assembly, where the first and second sensor assemblies are configured to move in the cross direction relative to a web of material. The method also includes, for each of the plurality of cross direction positions, determining a sensor value associated with a sensor source disposed at the second sensor assembly as measured by a sensor receiver disposed at the first sensor assembly. The method further includes determining a starting alignment position of the first sensor assembly to be a first cross direction position where a difference between the sensor value at the first cross direction position and a corresponding sensor value at one or more adjacent cross direction positions is a minimum.
In a second embodiment, an apparatus includes a first sensor assembly configured to move in a cross direction relative to a web of material. The first sensor assembly includes at least one controller and a sensor receiver configured to receive and measure emissions from a sensor source disposed at a second sensor assembly. The at least one controller is configured to control a motor that is configured to move the first sensor assembly to a plurality of cross direction positions relative to the second sensor assembly. The at least one controller is also configured to determine, for each of the plurality of cross direction positions, a sensor value associated with the sensor source as measured by the sensor receiver. The at least one controller is further configured to determine a starting alignment position of the first sensor assembly to be a first cross direction position where a difference between the sensor value at the first cross direction position and a corresponding sensor value at one or more adjacent cross direction positions is a minimum.
In a third embodiment, a system includes a first sensor assembly and a second sensor assembly. The first sensor assembly is configured to be disposed on a first side of a web of material and to move in a cross direction relative to the web. The second sensor assembly is configured to be disposed on a second side of the web opposite the first side and to move in the cross direction. The first sensor assembly is configured to move to a plurality of cross direction positions relative to the second sensor assembly. The first sensor assembly is also configured, for each of the plurality of cross direction positions, to determine a sensor value associated with a sensor source disposed at the second sensor assembly as measured by a sensor receiver disposed at the first sensor assembly. The first sensor assembly is further configured to determine a starting alignment position of the first sensor assembly to be a first cross direction position where a difference between the sensor value at the first cross direction position and a corresponding sensor value at one or more adjacent cross direction positions is a minimum.
In a fourth embodiment, a non-transitory computer readable medium embodies a computer program. The computer program includes computer readable program code for moving a first sensor assembly to a plurality of cross direction positions relative to a second sensor assembly, where the first and second sensor assemblies are configured to move in the cross direction relative to a web of material. The computer program also includes computer readable program code for determining, for each of the plurality of cross direction positions, a sensor value associated with a sensor source disposed at the second sensor assembly as measured by a sensor receiver disposed at the first sensor assembly. The computer program further includes computer readable program code for determining a starting alignment position of the first sensor assembly to be a first cross direction position where a difference between the sensor value at the first cross direction position and a corresponding sensor value at one or more adjacent cross direction positions is a minimum.
Other technical features may be readily apparent to one skilled in the art from the following figures, descriptions, and claims.
For a more complete understanding of this disclosure, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which:
Scanning systems for sheet- or other web-related processes often use translating scanning heads that house sensors and move back and forth across each side of the web. In some systems, the sensors can be arranged such that a source device and a receiver device are located on opposite sides of the web. The location of the receiver device relative to the source device can have an impact on measured signals, which can cause errors in sensor measurements. In many cases, alignment features on the scanning heads are used to center the sensors relative to each other.
In many systems, upper and lower sensor heads are mechanically coupled to a belt system mounted to a frame and end supports and are driven by a single motor. In these systems, alignment of the sensors in the scanning direction is determined by the accuracy of the belt tooth structure in the drive system. In other systems, upper and lower sensor heads are mechanically uncoupled and are driven independently with separate motors. In those systems, alignment of the sensors may be achieved electronically, such as via one or more position sensors and positional control algorithms.
Sensors are often designed to have a low sensitivity to displacement when they are centered directly opposite from each other. Manufacturing variations in the sensors and variations in mounting the sensors may result in the location of lowest displacement sensitivity being off-center. Stated another way, even though sensor heads may be in perfect or near-perfect alignment, the sensors themselves may still be out of alignment due to manufacturing and installation differences. Confirming and measuring source-to-receiver alignment by manually moving sensor heads relative to each other is a time consuming and error prone process.
Embodiments of this disclosure solve the problem of sensor alignment by measuring sensor sensitivity in an off-sheet alignment calibration process. This alignment calibration process can be performed automatically prior to scanning, such as on a periodic basis, or as part of a diagnostic or maintenance routine to measure sensitivities.
In this example, the web 102 is transported through this portion of the system 100 using two pairs of rollers 104a-104b and 106a-106b. For example, the roller pair 104a-104b can pull the web 102 from a previous stage of a web-manufacturing or web-processing system. Also, the roller pair 106a-106b can feed the web 102 into a subsequent stage of the web-manufacturing or web-processing system. The roller pairs 104a-104b and 106a-106b move the web 102 in a direction referred to as the “machine direction” (MD).
Two or more scanning sensor assemblies 108-110 are positioned between the roller pairs 104a-104b and 106a-106b. Each scanning sensor assembly 108-110 includes one or more sensors capable of measuring at least one characteristic of the web 102. For example, the scanning sensor assemblies 108-110 could include sensors for measuring the moisture, caliper, anisotropy, basis weight, color, gloss, sheen, haze, surface features (such as roughness, topography, or orientation distributions of surface features), or any other or additional characteristic(s) of the web 102. In general, a characteristic of the web 102 can vary along the length of the web 102 (in the “machine direction”) and/or across the width of the web 102 (in a “cross direction” or “CD”). Each scanning sensor assembly 108-110 includes any suitable structure or structures for measuring or detecting one or more characteristics of a web. Each sensor assembly 108-110 is configured to move back and forth (in the cross direction) across the web 102 in order to measure one or more characteristics across the width of the web 102.
Each scanning sensor assembly 108-110 can communicate wirelessly or over a wired connection with an external device or system, such as a computing device that collects measurement data from the scanning sensor assemblies 108-110. For example, each scanning sensor assembly 108-110 could communicate with an external device or system to synchronize a clock of that sensor assembly 108-110 with the clock of the external device or system.
Unlike scanner systems in which different assemblies are mechanically coupled to maintain alignment, the scanning sensor assemblies 108-110 are not mechanically coupled and are independently moveable. However, there are many instances in which it is desirable for the scanning sensor assemblies 108-110 to maintain alignment with each other as the sensor assemblies 108-110 move. In some embodiments, the sensor assembly 108 can be a master sensor assembly, and the sensor assembly 110 can be a follower sensor assembly (or vice versa). The master sensor assembly moves back and forth across all or a portion of the width of the web 102 according to a sensor assembly motion profile. The follower sensor assembly follows the movement of the master sensor assembly in order to maintain alignment with the master sensor assembly. In accordance with this disclosure, an off-sheet alignment calibration process can be performed using the sensor assemblies 108-110 to fine tune the alignment of the sensors as described in greater detail below.
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Various mechanisms can be used to move the carriages 204a-204b along the tracks 202a-202b or to position the sensor assemblies 108-110 at particular locations along the tracks 202a-202b. For example, each carriage 204a-204b could include a respective motor 206a-206b that moves the carriage 204a-204b along its track 202a-202b. As another example, external motors 208a-208b could move belts 209a-209b that are physically connected to the carriages 204a-204b, where the belts 209a-209b move the carriages 204a-204b along the tracks 202a-202b. Any other suitable mechanism for moving each carriage 204a-204b along its track 202a-202b could be used.
Scanning sensor heads 210a-210b are connected to the carriages 204a-204b. Each sensor head 210a-210b respectively includes at least one web sensor 212a-212b that captures measurements associated with the web 102. Each sensor head 210a-210b includes any suitable structure for carrying one or more sensors. Each web sensor 212a-212b includes any suitable structure for capturing measurements associated with one or more characteristics of a web. The web sensors 212a-212b may represent a contact sensor that takes measurements of a web via contact with the web or a non-contact sensor that takes measurements of a web without contacting the web.
In many systems, a web sensor 212a-212b could include a source element mounted on one of the sensor heads 210a-210b and a receiver element mounted on the other of the sensor heads 210a-210b. The web sensor 212a could represent the source element, and the web sensor 212b could represent the receiver element (or vice versa). In some embodiments, the source element may be an emitter of nuclear radiation, infrared light, visible light, a magnetic field, or any other suitable type of emission. Similarly, the receiver element may be a receiver or detector configured to receive and measure nuclear radiation, infrared light, visible light, a magnetic field, or any other suitable type of emission. As particular examples, the receiver may be an ion chamber, a light detector, or a camera.
Each sensor head 210a-210b also respectively includes at least one position sensor element 214a-214b for capturing relative or absolute “cross direction” positional information of that sensor head 210a-210b for use in aligning the sensor assemblies 108-110. Each position sensor element 214a-214b includes any suitable structure for capturing positional information of a corresponding sensor head relative to the web 102 or another calibrated reference point (such as a linear scale) or for determining a difference in cross direction position of the follower sensor assembly 110 relative to the master sensor assembly 108.
Power can be provided to each sensor head 210a-210b in any suitable manner. For example, each sensor head 210a-210b could be coupled to one or more cables that provide power to that sensor head. As another example, each carriage 204a-204b could ride on one or more cables or rails used to supply power to the associated sensor head 210a-210b. Each sensor head 210a-210b could further include an internal power supply, such as a battery or an inductive coil used to receive power wirelessly. Each sensor head 210a-210b could be powered in any other or additional manner.
In this example, each sensor head 210a-210b can send sensor measurement data to an external controller 216. The controller 216 could use the measurement data in any suitable manner. For example, the controller 216 could use the measurement data to generate CD profiles of the web 102. The controller 216 could then use the CD profiles to determine how to adjust operation of the system 100. The controller 216 could also use the CD profiles or the measurement data to support monitoring applications, process historian applications, or other process control-related applications.
The controller 216 includes any suitable structure(s) for receiving sensor measurement data, such as one or more computing devices. In particular embodiments, the controller 216 includes one or more processing devices 218, such as one or more microprocessors, microcontrollers, digital signal processors, field programmable gate arrays, or application specific integrated circuits. The controller 216 also includes one or more memories 220, such as one or more volatile and/or non-volatile storage devices, configured to store instructions and data used, generated, or collected by the processing device(s) 218. In addition, the controller 216 includes one or more interfaces 222 for communicating with external devices or systems, such as one or more wired interfaces (like an Ethernet interface) or one or more wireless interfaces (like a radio frequency transceiver). The controller 216 could represent all or part of a centralized control system or part of a distributed control system. In particular embodiments, the controller 216 includes a measurement subsystem (MSS), which interacts with the sensor assemblies 108-110 to obtain and process measurements of the web 102. The processed measurements can then be provided to other components of the controller 216.
Each sensor head 210a-210b and the controller 216 can communicate wirelessly or via a wired connection. In the embodiment shown in
The scanning sensor assemblies 108-110 operate in order to maintain alignment between the sensor heads 210a-210b. For example, the carriage 204a of the master sensor assembly 108 can move back and forth along the track 202a according to a motion profile (thereby moving the sensor head 210a). At the same time, the carriage 204b of the follower sensor assembly 110 can follow the movement of the master sensor assembly 108 so that the sensor heads 210a-210b maintain substantially the same cross direction location or a substantially fixed offset that does not change with movement. Note that the term “alignment” here refers to a desired relationship between sensor heads, including situations where the sensor heads have substantially the same cross direction position and situations where the sensor heads have a desired amount of offset in their cross direction positions.
As noted above, sensors can become misaligned during use due to a variety of factors, such as manufacturing and installation differences or position tracking errors during movement. For example,
Various techniques may be used by the follower sensor assembly 110 to improve or maintain the desired alignment with the master sensor assembly 108 while a scan operation is in progress. Some of these alignment techniques rely on an assumption that the sensor assemblies 108-110, the sensor heads 210a-210b, or the sensors 212a-212b are in alignment at a static predefined “zero starting point” or baseline before a scan operation occurs. That is, in order for the follower sensor assembly 110 to improve or maintain the desired alignment with the master sensor assembly 108 during a scan, the follower sensor assembly 110 calibrates alignment of the sensors 212a-212b before the scan to account for any constant offset error 240.
In accordance with this disclosure, alignment of the web sensors 212a-212b may be calibrated before a scan by measuring sensor sensitivity across a range of deliberate misalignments. For example, one or more components of the scanning sensor assemblies 108-110 (such as the web sensors 212a-212b, the position sensors 214a-214b, and the controller 216) may be used in an alignment calibration process before a scanning process is performed. The alignment calibration process is described in greater detail below.
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As described above, the sensor head 210b includes at least one web sensor 212b and at least one position sensor element 214b. The sensor head 210b also includes a power supply/receiver 304, which provides operating power to the sensor head 210b. For example, the power supply/receiver 304 could receive AC or DC power from an external source, and the power supply/receiver 304 could convert the incoming power into a form suitable for use in the sensor head 210b. The power supply/receiver 304 includes any suitable structure(s) for providing operating power to the sensor head 210b, such as an AC/DC or DC/DC power converter. The power supply/receiver 304 may also include a battery, capacitor, or other power storage device.
A controller 306 controls the overall operation of the sensor head 210b. For example, the controller 306 could receive measurements associated with one or more characteristics of the web 102 from the web sensor 212b. The controller 306 could also receive positional measurements associated with the position of the sensor head 210b from the position sensor element 214b. The positional measurements could correlate the position of the sensor head 210b with respect to another sensor head or with respect to the web 102 or a reference point. The controller 306 could further control the transmission of this data to the controller 216 or other destination(s). The controller 306 includes any suitable processing or control device(s), such as one or more microprocessors, microcontrollers, digital signal processors, field programmable gate arrays, or application specific integrated circuits. Note that the controller 306 could also be implemented as multiple devices.
A motor controller 308 can be used to control the operation of one or more motors, such as one or more of the motors 206a-206b, 208a-208b. For example, the motor controller 308 could generate and output pulse width modulation (PWM) or other control signals for adjusting the direction and speed of the motor 206b. The direction and speed could be controlled based on input from the controller 306. The motor controller 308 includes any suitable structure for controlling operation of a motor.
A wireless transceiver 310 is coupled to the antenna(s) 224b. The wireless transceiver 310 facilitates the wireless transmission and reception of data, such as by transmitting web measurements, positional measurements, and related data to the controller 216 and receiving commands from the controller 216. The wireless transceiver 310 includes any suitable structure for generating signals for wireless transmission and/or for processing signals received wirelessly. In particular embodiments, the wireless transceiver 310 represents a radio frequency (RF) transceiver. Note that the transceiver 310 could be implemented using a transmitter and a separate receiver.
Although
The method 400 for alignment calibration can be performed “off-web” (meaning without using a web being manufactured or processed), such as during a maintenance period or cycle. As a particular example, the method 400 could be performed when part or all of a sensor (such as one of the web sensors 212a-212b) is replaced, repaired, or otherwise adjusted with respect to its corresponding sensor head. The method 400 can be performed with no sheet between the web sensors 212a-212b or with a “dummy” sheet having known properties between the web sensors 212a-212b.
As shown in
While the sensor assembly 108 (and the web sensor source 212a) remains in the starting position, the sensor assembly 110 (and the web sensor receiver 212b) moves to a plurality of cross direction positions relative to the sensor assembly 108 at step 404. Each cross direction position of the sensor assembly 110 relative to the sensor assembly 108 can be pre-determined or measured upon arrival of the sensor assembly 110 at the position (such as by using one or more position sensors 214a-214b). The multiple cross direction positions can span a range covering both sides of the estimated position of the center line of the web sensor 212a (such as a range spanning from 10 mm to the left of the web sensor 212a to 10 mm to the right of the web sensor 212a). The multiple cross direction positions can be evenly spaced, such as every 1 mm. However, the cross direction positions may be unevenly spaced or may be randomly or semi-randomly selected.
At step 406, at each of the cross direction positions, the web sensor 212a is activated, and the intensity of a signal from the web sensor 212a is measured at the web sensor 212b. For comparison purposes, the intensity of the signal emitted from the web sensor 212a could be the same for each position; however, differences in alignment at the multiple positions cause different measurements at the web sensor 212b. The measurement of the signal intensity at each cross direction position is recorded along with the corresponding cross direction position.
At step 408, a controller (such as the controller 216 or the controller 306) correlates the signal intensity measurements and the cross direction positions to mathematically determine a receiver measurement versus cross direction position profile. The profile could have any suitable form that associates receiver measurements and cross direction positions.
At step 410, the controller identifies a cross direction position where the web sensor 212b is least sensitive to changes in the cross direction position. For example, in
Based on the data plot 501 shown in
For many sensors, the point of best alignment coincides with the largest measurement of signal intensity, such as at the data point 500a in
Similar to the profile plot 501 in
Using the method 400 as described above, the optimum alignment point between upper and lower sensor heads can be determined automatically to reduce cross direction alignment errors rather than relying on a visual or mechanical alignment of external enclosures. In systems where head-to-head alignment sensors are available (such as the position sensors 214a-214b), such alignment sensors can be used in a feedback loop during scanning to maintain an alignment set point. If no position sensor is available, motor encoder or stepper motor steps from the drive can be used to offset the heads prior to scanning.
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In some embodiments, various functions described above are implemented or supported by a computer program that is formed from computer readable program code and that is embodied in a computer readable medium. The phrase “computer readable program code” includes any type of computer code, including source code, object code, and executable code. The phrase “computer readable medium” includes any type of medium capable of being accessed by a computer, such as read only memory (ROM), random access memory (RAM), a hard disk drive, a compact disc (CD), a digital video disc (DVD), or any other type of memory. A “non-transitory” computer readable medium excludes wired, wireless, optical, or other communication links that transport transitory electrical or other signals. A non-transitory computer readable medium includes media where data can be permanently stored and media where data can be stored and later overwritten, such as a rewritable optical disc or an erasable memory device.
It may be advantageous to set forth definitions of certain words and phrases used throughout this patent document. The terms “application” and “program” refer to one or more computer programs, software components, sets of instructions, procedures, functions, objects, classes, instances, related data, or a portion thereof adapted for implementation in a suitable computer code (including source code, object code, or executable code). The terms “transmit” and “receive,” as well as derivatives thereof, encompass both direct and indirect communication. The terms “include” and “comprise,” as well as derivatives thereof; mean inclusion without limitation. The term “or” is inclusive, meaning and/or. The phrase “associated with,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, have a relationship to or with, or the like. The phrase “at least one of,” when used with a list of items, means that different combinations of one or more of the listed items may be used, and only one item in the list may be needed. For example, “at least one of: A, B, and C” includes any of the following combinations: A, B, C, A and B, A and C, B and C, and A and B and C.
While this disclosure has described certain embodiments and generally associated methods, alterations and permutations of these embodiments and methods will be apparent to those skilled in the art. Accordingly, the above description of example embodiments does not define or constrain this disclosure. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of this disclosure, as defined by the following claims.
