Patent Application
20140142739
The following generally relates to controlling web forming processes, which, generally, are processes which include creation of loosely held together sheet structure or flat sheets, e.g., by the laying down of fibers. While the present invention can be applied to a variety of web forming processes (e.g., paper, plastic, fabric, etc.), it will be described herein with particular reference to a paper machine.
In paper manufacturing, local regions of stagnant peaks and valleys can lead to poor roll quality like ridge formation or baggy (stretchy) rolls as product is accumulated onto a steel spool to form the roll. A typical roll can grow to several meters in diameter. Poor roll quality defect is the result of localized compounding of a stagnant peak and valley pattern during the course of building the roll. As the roll grows in diameter, the pattern compounds, causing the peak to increase in height and causing the valley to form a larger depression. As a result of the defect, ridges form in the roll. Even more, once the roll exceeds a given diameter, sheet stretching exists, which causes a roll to become “baggy.” Baggy rolls can result in costly problems such as line breaks or printing defects.
To improve roll quality, mechanical (side to side) oscillations of the sheet forming table or reel spool to distribute any stagnant peaks and valleys over a cross-directional region, preventing layering in the same spot. However, this mechanical approach requires special machinery to be added to a paper machine, which may not be possible due to space or cost constraints. Without a mechanical device, human operators must be relied upon to continuously make adjustments with limited success.
Uniformity of a property of a web of sheet material can be specified as variations in two perpendicular directions: the machine direction (MD), which is in the direction of web movement during production, and the cross-machine direction (CD), which is perpendicular to the MD. Different sets of actuators are used to control the variations in each direction. CD variations appear in measurements known as CD profiles and are typically controlled by an array of actuators located side-by-side and across the web width.
Aspects of the application address the above matters, and others.
In one aspect, an initial setpoint determiner that determines an initial setpoint for controlling an industrial process based on a sensed signal indicative of a characteristic of an output generated by the industrial process, a setpoint adjuster that periodically determines an adjustment signal based on local regional error characteristics of the output generated by the industrial process, and a final setpoint determiner that determines a final setpoint signal that controls the industrial process based on the initial setpoint and the adjustment signal.
In another aspect, a method determining an initial setpoint for controlling an industrial process based on a sensed signal indicative of a characteristic of an output generated by the industrial process, periodically determining an adjustment signal based on local regional error characteristics of the output generated by the industrial process, determining a final setpoint signal that controls the industrial process based on the initial setpoint and the adjustment signal.
In another aspect, a computer readable storage medium is encoded with computer executable instructions, which, when executed by a processor, causes the processor to: determine an initial setpoint for controlling an industrial process based on a sensed signal indicative of a characteristic of an output generated by the industrial process, periodically determine an adjustment signal based on local regional error characteristics of the output generated by the industrial process, and determine a final setpoint signal that controls the industrial process based on the initial setpoint and the adjustment signal.
The present application is illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements and in which:
The control signal generator 103 comprises an initial setpoint determiner 105, a setpoint adjuster 106, and a final setpoint determiner 107. The initial setpoint determiner 105 monitors properties of the paper making machine 102 and generates an initial control signal that includes an initial setpoint based at least on the monitored properties. The setpoint adjuster 106 generates an adjustment signal, which, as described in greater detail below, is based on at least one of the monitored properties in an identified local region and the initial control signal.
The final setpoint determiner 107 generates a final setpoint to control the machine 102 based on the initial control signal and the adjustment signal. Generally, the adjustment signal temporarily perturbs the initial setpoint so as to mitigate undesired characteristics (e.g., peaks and/or valleys) in the paper making process. This may result in enhancement of the structural integrity of a paper and/or paper roll under construction. For example, peaks and valleys in a roll under construction may be reduced relative to not employing the adjustment signal from the adjusted setpoint determiner 106.
The illustrated paper making machine 102 includes a wire section 110, a press section 112, and a dryer section 114 with a midsection broken away to indicate that other web processing components, such as a sizing section, additional dryer sections and/or other components may be included. The wire section 110 comprises a wire belt 116 wound around a drive roller 118 and a plurality of guide rollers 120 arranged relative to the drive roller 118. The drive roller 118 is driven so that an upper side of the wire belt 116 moves in a machine direction (MD). A headbox 122 receives pulp slurry (e.g., paper stock) that is discharged through a slice lip 124, which is controlled using a plurality of CD actuators 126 (e.g., slice screws). Dilution valves can also be used onto the upper side of the wire belt 116. The pulp slurry is drained of water on the wire belt 116 to form a web 128 of paper.
The water drained from the pulp slurry to form the web 128 has been referred to as white-water with pulp in a low concentration and is collected under the wire section 110 and recirculated in the paper making machine 102. The web 128 is further drained of water in the press section 112 and is delivered to the dryer section 114. The dryer section 114 comprises a plurality of steam-heated drums 129. The web 128 may be processed by other components in the MD along the process and is ultimately taken up by a web roll 130. A sensor 132 senses characteristics of the web 128. The sensor 132 is located substantially adjacent to the web roll 130. It is noted that one or more other sensors can be used, including a stationary sensor for measuring part or the entire web 128 and that the sensor 132 can be positioned at other locations along the web 128. Other paper making machines are also contemplated herein.
Turning to
As briefly discussed above, the sensor 132 senses process properties of the web 128 (
The initial setpoint determiner 105 includes an error determiner 202 that subtracts the monitored properties signal from a target control signal of a target profile 207, creating an error signal. In one instance, the target control signal represents a preferred state of the at least one sensed property obtained by the sensor 132. The error signal indicates a current state of the paper making machine 102. The initial setpoint determiner 105 also includes a feedback CD control 203 that generates an initial setpoint signal based on the error signal, and makes the initial setpoint signal available to the final setpoint determiner 107. Execution rate of the inner components of the initial setpoint determiner 105 is dictated by availability of the sensed process property from evaluator 201. Typical execution rate is longer than every 20 to 60 seconds, which is the typical scan update time for generating a new sensed process property profile.
The setpoint adjuster 106 includes a local region detector 204. The local region detector 204 evaluates the error signal and the initial setpoint signal, detecting build problems on a sheet as the sheet is being rolled. The detected build problems include, but are not limited to, undesired patterns on the sheet, such as peaks or valleys, which cause non-uniformities in a roll created from the sheet. The detected build problems and an identification of a location of the local region where build problems exist are included in a build signal.
The setpoint adjuster 106 also includes a perturber control 206 that generates a perturbation value based on the build signal and the initial setpoint. The perturbation value, in one instance, simulates the effects of oscillating mechanical devices and ultimately affects the short-term variation of the paper making machine 102. The perturbation value is generated to disrupt or perturb the sheet, which facilitates mitigating defects in the roll under construction.
The final setpoint determiner 107 adds the adjustment signal and the initial setpoint signal to create an adjusted setpoint signal with a final setpoint value. The controller 104 controls production of paper of the paper making machine 102 in accordance with the final setpoint signal.
Next, at
A pattern identifier 302 receives the build signal from the local region detector 204 (
In one instance, the pattern identifier 302 determines a spatial dithering pattern that disperses non-uniformities present in a roll. The spatial dithering pattern introduces, for example, fast CD (profile) changes into the adjustment signal, which facilitates dispersing stagnant peaks and/or valleys in the roll. The pattern identifier 302 selects a pattern that dithers the adjustment signal with an excitation pattern resembling peaks and valleys in the roll. For example, when the local region detector 204 detects drastic peaks and valleys, the pattern identifier 302 may assign a saw tooth pattern (an example of which is discussed below) as the dithering pattern. If the local region detector 204 detects more subtle peaks and valleys in the roll, the pattern identifier 302 may identify a sine wave pattern (an example of which is discussed below) to dither the adjustment signal and disperse imperfections.
The perturbation value (and thus the adjustment signal) is changed incrementally for a given detected pattern. Consequently, the amplitude of the adjustment signal can be increased gradually over time to more aggressively correct any roll defect. Also, the adjustment signal can be region-specific, meaning that the perturbation value can be generated to be incrementally changed for a localized control zone in the region where roll defects are apparent. The incremental changes are added to a sub-part of the target control signal, via the final setpoint determiner 107 (
The perturber enabler 306 generates a perturber enable signal, which determines periods of time when the setpoint adjuster 106 turns spatial dithering on. The perturbation value affects the steady-state performance of the controller 104. If problems develop during a given time window during manufacture of the roll, the perturber enabler 306 activates dithering by outputting the perturber enable signal. In one example, the perturber enabler 306 uses the build signal of the local region detector 204 to determine a probability of the detected region having a build problem. The perturber enabler 306 transmits a perturber disable signal or no signal, disabling dithering during periods of time when problems in the sheet are unlikely to develop. Alternatively, the perturber enabler 306 outputs the perturber enable signal, enabling dithering, when problems are likely to develop.
The predetermined criteria 308 may set the frequency of the dithering pattern. For example, the frequency of a saw tooth dithering pattern (and as a result, the adjustment signal) can be increased by frequency criteria provided by the predetermined criteria 308. The predetermined criteria 308 may dither the adjustment signal at a greater frequency than the initial setpoint determiner 105. As such, process perturbation can be performed at a greater frequency than introducing the frequency before the initial setpoint determiner 105. The identified pattern, perturber enable signal, and the predetermined criteria 308 are used by the perturber waveform generator 310 to generate a waveform (e.g. the adjustment signal). The adjustment signal generated by perturber waveform generator 310 results in more rapid dithering than the execution periods of the initial setpoint determiner 105 would provide without the adjustment signal.
The adjustment signal is output to the final setpoint determiner. The final setpoint determiner 107 is implemented in an open-loop summation point, or feed forward point, to bypass dependency on the initial setpoint determiner 105. Choice of the open-loop summation point also alleviates the need to aggressively tune the initial setpoint determiner 105. Combining the addition of a flipping localized setpoint dithering pattern with the permissive state and a faster setpoint output oscillator, the dithering technique induces a higher level of process perturbation than available methods through feedback control. The final setpoint signal is generated by combining the adjustment signal and the error signal. The final setpoint signal is output by the final setpoint determiner 107 to the controller 104, which can implement the final setpoint signal in the paper making portion 102.
The initial direction of move is determined by de-trending the setpoint shape of the detected local region and comparing the setpoint of the control zone with the maximum deviation from the de-trend shape, as shown in
Dithering of the steady-state setpoint shape with incremental changes is for the purpose of inducing fast changes into the controller 104, and not to drastically interfere with the operation or affect the steady-state performance of the initial setpoint determiner 105. As noted above, the perturber enabler 306 establishes a time window when local identified regions can be dithered with a perturbation value.
Another signal that is analyzed by the perturber enabler 306 to activate dithering is a “run-rest” signal. The run-rest signal is a clocked signal that is synchronized with the start event for building a roll of product. This signal is set false at the start of roll build and is set true after a specified elapsed time from start of roll build. The elapse time from start of roll build can be set to a duration shorter than when roll build quality problems typically develop during a roll build cycle. This signal is AND with the aforementioned signals to allow dithering to run. Finally, perturber enabler 306 monitors a master on/off setpoint dithering signal. The on/off signal allows an individual to completely override the perturber enabler 306. An example of dithering activation is shown in
In the present application, the predetermined criteria 308 can include a frequency of dithering activation that results in dithering greater than once per scan. Accordingly, dithering can be performed, for example, every 5 to 15 seconds, instead of every 30 or 45 seconds, etc. Generally, the initial setpoint determiner 105 can be tuned conservatively to activate once per scan, with the objective of minimizing error in the controlled profiler measurement. If the initial setpoint determiner 105 is tuned too aggressively, over corrections may exist. An example of the final setpoint signal is shown in
It is to be appreciated that the ordering of the acts in the methods described herein is not limiting. As such, other orderings are contemplated herein. In addition, one or more acts may be omitted and/or one or more additional acts may be included.
At 1102, machine properties are sensed. The properties can include, for example, in the pulp and paper industry, at least one of paper weight, paper moisture, caliper profiles, etc. of a sheet being rolled.
At 1104, the properties are compared with a target control signal and an error signal is generated.
At 1106, an initial setpoint signal is generated based on the error signal.
At 1108, an adjustment signal is generated based on the error signal and the initial control signal.
At 1110, a final setpoint signal is generated based on the initial setpoint signal and the adjustment signal.
At 1112, a machine is controlled based on the final setpoint signal.
The above may be implemented by way of computer readable instructions, which when executed by a computer processor(s), cause the processor(s) to carry out the described techniques. In such a case, the instructions are stored in a computer readable storage medium associated with or otherwise accessible to the relevant computer.
Of course, modifications and alterations will occur to others upon reading and understanding the preceding description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
