Slurry preparation quality control system based on PLC

Abstract

The invention provides a PLC-based pulp preparation quality control system, and relates to the technical field of papermaking pulp preparation, the system comprises a pulp preparation workshop section and a control device, the pulp preparation workshop section comprises a wet pulp workshop section, an NBKP workshop section, an LBKP workshop section and a mixing box, the output ends of the wet pulp workshop section, the NBKP workshop section and the LBKP workshop section are respectively connected with the mixing box, and the control device is connected with the control device. The control equipment comprises a PLC and a background computer, the PLC is in signal connection with production equipment in the wet pulp working section, the NBKP working section and the LBKP working section, the background computer is in signal connection with the PLC, and the system can automatically adjust operation parameters of the production equipment in the pulp preparing working section based on the pulp forming quality in the pulp preparing process. While the pulping quality is guaranteed, the human input is reduced, the stability and the reliability are realized, and the economic benefit is further improved.

Description

Technical Field

[0001] The invention relates to the technical field of papermaking stock preparation, and in particular to a PLC-based stock preparation quality control system. Background Art

[0002] Papermaking production is divided into two processes: pulp preparation and paper machine. The pulp preparation process is to prepare pulp raw materials for papermaking, and then fully mix various raw materials in a mixing box in a certain proportion according to different paper quality requirements. The pulp preparation process involves a variety of production equipment. In this process, the control of the operating parameters of various production equipment is very important, which will directly affect the quality of pulping and even the final finished paper. At present, in the pulp preparation process, in order to ensure the quality of pulping, the control of the operating parameters of various production equipment often relies on experienced staff, which has high requirements for manpower, and the stability and reliability need to be further improved. Summary of the invention

[0003] In view of this, the purpose of the present invention is to provide a PLC-based stock preparation quality control system to solve the problem that the current stock preparation quality control is too dependent on manpower and has low stability and reliability.

[0004] To achieve the above-mentioned purpose of the invention, the present invention provides a PLC-based slurry preparation quality control system, the system includes a slurry preparation section and a control device, the slurry preparation section includes a wet slurry section, a NBKP section, a LBKP section and a mixing box, the output ends of the wet slurry section, the NBKP section and the LBKP section are respectively connected to the mixing box, the control device includes a PLC controller and a background computer, the PLC controller is respectively connected to the production equipment signals in the wet slurry section, the NBKP section and the LBKP section, the background computer is connected to the PLC controller signal, the PLC controller is used to collect operating parameter data of the production equipment in real time, send the operating parameter data to the background computer, control the production equipment based on the feedback instructions of the background computer, the background computer is used to obtain a slurry quality evaluation result, analyze the slurry quality evaluation result and the real-time collected production equipment operating parameter data, obtain an operating parameter adjustment strategy applied to the production equipment, generate feedback instructions according to the operating parameter adjustment strategy and send them to the PLC controller.

[0005] Furthermore, the wet slurry section includes a slurry storage tower, a pulp squeezer, a high-concentration tank and an intermediate tank which are connected in sequence, and the output end of the intermediate tank is connected to a mixing box.

[0006] Furthermore, the NBKP section includes a conveyor belt, a pulping machine, a discharge trough, a pressure screen, a pulping machine and a post-beating trough which are connected in sequence. The post-beating trough is connected to a mixing box. The conveyor belt in the NBKP section is used to transport the NBKP pulp bag to the pulping machine.

[0007] Furthermore, the LBKP section includes a conveyor belt, a pulping machine, a discharge trough, a pressure screen, a pulping machine and a post-beating trough which are connected in sequence. The post-beating trough is connected to a mixing box. The conveyor belt in the LBKP section is used to transport the LBKP pulp bag to the pulping machine.

[0008] Furthermore, before the background computer obtains the pulping quality evaluation result, the pulping quality is evaluated in multiple dimensions, including the following operations:

[0009] Determine the multi-dimensional quality evaluation index of pulping, determine the correlation between the quality evaluation index of each dimension and the operating parameters of the production equipment, and store the correlation in the background computer;

[0010] The quality of each batch of pulp is evaluated based on multi-dimensional quality evaluation indicators to obtain pulp quality evaluation results of the corresponding batches, and the pulp quality evaluation results are input into the background computer. The pulp quality evaluation results include quality evaluation indicator values ​​of multiple dimensions.

[0011] Furthermore, the background computer specifically includes:

[0012] An evaluation and analysis module is used to analyze the pulping quality evaluation results, determine whether the quality evaluation index values ​​of each dimension meet the quality requirements of the corresponding type of pulping according to the pulping type, and screen out the quality evaluation index values ​​that do not meet the quality requirements;

[0013] A joint analysis module is used to input the corresponding type of pulping quality standard index values, quality evaluation index values ​​that do not meet quality requirements, and production equipment operation parameter data into the parameter prediction model for processing to obtain predicted operation parameter data;

[0014] A strategy generation module is used to generate an operating parameter adjustment strategy set based on the predicted operating parameter data and the production equipment operating parameter data uploaded by the PLC controller, wherein the operating parameter adjustment strategy set includes at least one operating parameter adjustment strategy, and the operating parameter adjustment strategy includes the adjustment value of the operating parameter of the production equipment, the adjustment effective time point and the adjustment recovery time point.

[0015] Furthermore, the background computer specifically includes:

[0016] A conflict analysis module, used to determine whether there are conflicting operating parameter adjustment strategies in the operating parameter adjustment strategies when generating an operating parameter adjustment strategy set;

[0017] The priority calculation module is used to compare the weights of conflicting operating parameter adjustment strategies, sort the execution priorities of the operating parameter adjustment strategies in descending order of weight, and filter out the operating parameter adjustment strategies that are not of the highest priority.

[0018] Furthermore, the background computer further includes a weight calculation module, and the weight calculation module is used to perform the following operations:

[0019] Calculate a class of weights for the operation parameter adjustment strategy;

[0020] Calculate the second-class weights of the operation parameter adjustment strategy;

[0021] Based on the first-class weight and the second-class weight of the same operating parameter adjustment strategy, the comprehensive weight is calculated, and the calculation result of the comprehensive weight is used as the final weight of the operating parameter adjustment strategy.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention provides a PLC-based pulp preparation quality control system, which monitors the production equipment in the pulp preparation section and collects its operating parameter data through a PLC controller, and simultaneously obtains the pulping quality evaluation result through a background computer, analyzes the pulping quality evaluation result and the operating parameter data of the production equipment collected in real time, obtains the operating parameter adjustment strategy applied to the production equipment, and generates feedback instructions according to the operating parameter adjustment strategy and sends them to the PLC controller, so that the system can automatically adjust the operating parameters of the production equipment in the pulp preparation section based on the pulping quality during the pulp preparation process, thereby reducing manpower input while ensuring the pulping quality, and having stability and reliability, thereby improving economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only preferred embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0025] Figure 1 It is a schematic diagram of the overall structure of a PLC-based stock preparation quality control system provided in an embodiment of the present invention.

[0026] Figure 2 It is a schematic diagram of the overall structure of the slurry preparation section provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The enumerated embodiments are only used to explain the present invention and are not used to limit the scope of the present invention.

[0028] Reference Figure 1 and Figure 2This embodiment provides a PLC-based stock preparation quality control system, the system includes a stock preparation section and a control device, the stock preparation section includes a wet stock section, an NBKP section, an LBKP section and a mixing box, the output ends of the wet stock section, the NBKP section and the LBKP section are respectively connected to the mixing box. The control device includes a PLC controller and a background computer, the PLC controller is respectively connected to the production equipment signals in the wet stock section, the NBKP section and the LBKP section, and the background computer is connected to the PLC controller signal.

[0029] Generally speaking, wet pulp is pulp with a dryness of about 35% to 55%. The wet pulp section is used to dehydrate and squeeze the stored pulp to form wet pulp and transport it to a mixing box. As a possible implementation, the wet pulp section includes a pulp storage tower, a pulping machine, a high-concentration tank and an intermediate tank connected in sequence, and the output end of the intermediate tank is connected to the mixing box. The pulp storage tower is used to store pulp, and the pulp in the pulp storage tower is transmitted to the pulping machine through a pipeline. The pulping machine can be a double-roll pulping machine. After the pulp enters the pulping machine, a pressure difference is generated inside the pulping machine. The pulp enters the pressing area and the dehydration area for dehydration and squeezing, forming a pulp layer on the roller surface. The pulp concentration reaches 20% to 30%. The pulp is broken up and sent out by a crushing screw, and is transmitted to the mixing box after passing through the high-concentration tank and the intermediate tank in sequence.

[0030] The NBKP section is used to convert the NBKP dry pulp in the NBKP pulp bag into wet pulp, and then transfer it to the mixing box after impurity separation and beating. NBKP (Needle Bleaching Kraft Pulp) is a long fiber, which is used to provide physical properties of paper, such as strength and stiffness. As a possible implementation, the NBKP section includes a conveyor belt, a pulping machine, a discharge trough, a pressure screen, a pulping machine and a post-beating trough connected in sequence, and the post-beating trough is connected to the mixing box. The conveyor belt in the NBKP section is used to transport the NBKP pulp bag to the pulping machine. Among them, the conveyor belt is used to transport the NBKP pulp bag to the pulping machine. At the pulping machine, the rotation of the turntable generates a huge vortex, which causes the pulp obtained through the NBKP pulp bag to be subjected to strong impact and hydraulic shearing, and to the mechanical action of the blade and the mutual friction of the pulp, so that the pulp fibers are dispersed, and the broken pulp is discharged from the discharge port through the screen plate under the turntable, thereby converting the dry pulp into wet pulp, and the wet pulp enters the discharge trough. The wet pulp in the discharge trough is further transmitted to the pressure screen, and the pressure screen uses the difference in size between the impurities and the pulp fibers to separate the impurities in the wet pulp, and the wet pulp separated by impurities is further transmitted to the pulper. The pulper is used for pulping operations, also known as beating and refining. It mainly changes the fiber morphology through the friction between the pulper turntable and the fixed plate and the mutual friction between the fibers, so that the pulp obtains certain characteristics to ensure that the finished paper can meet the expected quality requirements. The pulp after beating in the NBKP section is finally transmitted to the mixing box through the post-beating trough.

[0031] The LBKP section is used to convert the LBKP dry pulp in the LBKP pulp bag into wet pulp, and then transfer it to the mixing box after impurity separation and pulping. In some possible implementations, the equipment included in the LBKP section is the same as that of the NBKP section, and the process is basically the same. The working principle is not repeated here. The main difference between the two is that the conveyor belt in the LBKP section transfers the LBKP pulp bag to the pulping machine for subsequent processing. LBKP (Leaf Bleaching Kraft Pulp) is short fiber. In toilet paper, short fiber provides the need for paper feel.

[0032] Finally, the pulp transmitted from the wet pulp section, NBKP section and LBKP section is mixed in the mixing box to obtain pulp, which will then enter the paper machine section to produce paper rolls.

[0033] In this embodiment, the PLC controller is respectively connected to the production equipment signals in the wet pulp section, the NBKP section, and the LBKP section, and the production equipment includes but is not limited to a pulp squeezer, a conveyor belt, a pulping machine, a discharge chute, a pressure screen, a pulping machine, and valves in the pipelines connecting the various equipment. The PLC controller is used to collect the operating parameter data of the production equipment in real time, and send the operating parameter data to the background computer, and control the production equipment based on the feedback instructions of the background computer.

[0034] The background computer is used to obtain pulping quality evaluation results, analyze the pulping quality evaluation results and real-time collected production equipment operating parameter data, obtain the operating parameter adjustment strategy applied to the production equipment, generate feedback instructions according to the operating parameter adjustment strategy and send them to the PLC controller.

[0035] The system provided in this embodiment collects the operating parameter data of each production equipment in real time through the PLC controller in the pulp preparation process and sends it to the background computer. The background computer simultaneously obtains the quality evaluation results of the pulp produced by the pulp preparation section under the control of the collected operating parameter data, analyzes the pulp quality evaluation results and the real-time collected production equipment operating parameter data, obtains the operating parameter adjustment strategy applied to the production equipment, generates feedback instructions according to the operating parameter adjustment strategy and sends them to the PLC controller, and the PLC controller adjusts the operating parameters of the production equipment in the pulp preparation section according to the feedback instructions, thereby regulating the production equipment in the pulp preparation section through feedback adjustment, ensuring that the quality of the pulp meets the requirements while reducing human intervention, thereby improving economic benefits.

[0036] As a possible implementation method, before the background computer obtains the pulping quality evaluation result, it is necessary to perform a multi-dimensional evaluation on the pulping quality, which specifically includes the following operations:

[0037] S101, determining multi-dimensional quality evaluation indicators of pulping, and determining the correlation between the quality evaluation indicators of each dimension and the operating parameters of the production equipment, and storing the correlation in the background computer.

[0038] Exemplarily, before evaluating the quality of the pulp, a quality evaluation index system for the pulp must first be constructed. In this embodiment, the quality evaluation index system for the pulp includes multi-dimensional quality evaluation indicators, such as fiber purity, whiteness, moisture content, impurity content, physical properties, etc. These quality evaluation indicators evaluate the quality of the pulp from different dimensions. Each quality evaluation indicator is associated with at least one production equipment operating parameter, indicating that the production equipment operating parameter associated with it will have a significant impact on the quality evaluation indicator.

[0039] S102, evaluating the quality of each batch of pulp based on multi-dimensional quality evaluation indicators, obtaining pulp quality evaluation results of the corresponding batches, and inputting the pulp quality evaluation results into a background computer, wherein the pulp quality evaluation results include quality evaluation indicator values ​​of multiple dimensions.

[0040] Exemplarily, the quality of each batch of pulp is evaluated based on multi-dimensional quality evaluation indicators. The pulp quality can be evaluated by relevant experts based on the quality evaluation indicator system, or the pulp can be tested by professional testing equipment to obtain the corresponding quality evaluation index value, or the pulp quality evaluation result can be obtained by combining expert evaluation + equipment testing. This implementation mode does not make specific limitations on this.

[0041] On the basis of the above-mentioned implementation mode, the background computer specifically includes an evaluation and analysis module, a joint analysis module and a strategy generation module.

[0042] The evaluation and analysis module is used to analyze the pulping quality evaluation results, determine whether the quality evaluation index values ​​of each dimension meet the quality requirements of the corresponding type of pulping according to the pulping type, and screen out the quality evaluation index values ​​that do not meet the quality requirements. The quality evaluation index values ​​that do not meet the quality requirements are quality evaluation index values ​​that are lower than the quality standard index values ​​of the corresponding dimensions.

[0043] The joint analysis module is used to input the corresponding type of pulp quality standard index value, the quality evaluation index value that does not meet the quality requirements and the production equipment operation parameter data into the parameter prediction model for processing to obtain the predicted operation parameter data. The production equipment operation parameters input into the parameter prediction model are the operation parameter data used by the production equipment in the pulp preparation section when producing the pulp corresponding to the quality evaluation index value.

[0044] The parameter prediction model is a model obtained by pre-training a basic neural network based on pulping quality standard index values ​​of different sample types, quality evaluation index values ​​of samples that do not meet quality requirements, and sample production equipment operation parameter data. The basic neural network can be an MPL feedforward neural network, a long short-term memory network, or a recurrent neural network, etc. This embodiment does not make specific limitations on this.

[0045] The strategy generation module is used to generate an operation parameter adjustment strategy set according to the predicted operation parameter data and the production equipment operation parameter data uploaded by the PLC controller. The operation parameter adjustment strategy set includes at least one operation parameter adjustment strategy, and the operation parameter adjustment strategy includes the adjustment value of the operation parameter of the production equipment, the adjustment effective time point and the adjustment recovery time point. The adjustment effective time point indicates when the operation parameter adjustment strategy takes effect; the adjustment recovery time point indicates when the operation parameter adjustment strategy is restored to the default value or revoked.

[0046] It can be seen that in this embodiment, the background computer discovers the quality evaluation index value that does not meet the quality requirements through the evaluation and analysis module, and processes it with the corresponding type of pulping quality standard index value and the production equipment operation parameter data input parameter prediction model to obtain predicted operation parameter data. The strategy generation module is used to generate an operation parameter adjustment strategy set according to the predicted operation parameter data and the production equipment operation parameter data uploaded by the PLC controller, so that the background computer can automatically generate corresponding feedback instructions based on the operation parameter adjustment strategy set, thereby controlling the corresponding production equipment to adjust the operation parameters through the PLC controller according to the feedback instructions, so as to improve the pulping quality so that it can meet the quality requirements and improve the stability and reliability of pulp production.

[0047] As a possible implementation, the background computer specifically further includes a conflict analysis module and a priority calculation module.

[0048] The conflict analysis module is used to determine whether there are conflicting operating parameter adjustment policies in the operating parameter adjustment policies when generating the operating parameter adjustment policy set.

[0049] For example, when one operating parameter adjustment strategy requires increasing the opening of valve A, while another operating parameter adjustment strategy requires decreasing the opening of valve A, and the effective time periods of the two operating parameter adjustment strategies are the same or overlap, it is determined that the two operating parameter adjustment strategies conflict.

[0050] The priority calculation module is used to compare the weights of conflicting operating parameter adjustment strategies, sort the execution priorities of the operating parameter adjustment strategies in descending order of weight, and filter out operating parameter adjustment strategies that are not of the highest priority.

[0051] It can be seen that in this implementation, after the background computer generates an operating parameter adjustment strategy set, before further generating feedback instructions based on the operating parameter adjustment strategy set, it detects the conflicting strategies in the operating parameter adjustment strategy set. When conflicting strategies are found, their respective priorities are sorted by comparing the weights of the conflicting strategies, and the operating parameter adjustment strategies that are not of the highest priority are further filtered out, and the operating parameter adjustment strategies of the highest priority are retained, so as to avoid conflicting and contradictory adjustment strategies in the strategy set, which may cause the system to fail to execute instructions correctly.

[0052] Based on the above implementation, the background computer further includes a weight calculation module, which is used to perform the following operations:

[0053] S201. Calculate a type of weight of an operation parameter adjustment strategy.

[0054] For example, the weights of the operation parameter adjustment strategy can be calculated by constructing an evaluation index judgment matrix using the AHP method according to the pulping quality evaluation index system, and then normalizing the evaluation index judgment matrix using the square root method to obtain a weight. At the same time, the consistency test can be further performed to determine whether the constructed matrix has logical errors.

[0055] S202: Calculate the second-class weights of the operation parameter adjustment strategy.

[0056] The second type of weights for calculating the operating parameter adjustment strategy can be: construct a pulping quality evaluation matrix according to the quality evaluation index values ​​of each dimension in the pulping quality evaluation index system, the pulping quality evaluation matrix has i rows and j columns, i is the number of dimensions of the pulping quality evaluation index system, j is the number of indicators in each dimension, and the nth element in the mth row represents the value of the nth indicator in the mth dimension. Then, each indicator value is processed positively and negatively, and the difference and conflict of the indicator are calculated. The difference is used to characterize the difference between the indicator values ​​determined by different methods when the indicator values ​​are determined by various methods such as expert evaluation and equipment testing. The greater the difference, the higher the weight assigned. Conflict is used to characterize the correlation between different indicators. The stronger the correlation, the weaker the conflict, and the corresponding weight is reduced. Then, the information amount of the indicator is calculated based on the difference and conflict of the indicator, and finally the second weight is calculated using the indicator information amount.

[0057] S203. Calculate the comprehensive weight based on the first-class weight and the second-class weight of the same operating parameter adjustment strategy, and use the calculation result of the comprehensive weight as the final weight of the operating parameter adjustment strategy.

[0058] Exemplarily, the final weight is calculated as follows:

[0059]

[0060] In the formula, w i represents the final weight of the i-th quality evaluation performance indicator, fw i represents the first weight of the i-th key performance indicator, sw i represents the second weight of the i-th key performance indicator.

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A PLC-based stock preparation quality control system, characterized in that: The system includes a slurry preparation section and a control device. The slurry preparation section includes a wet slurry section, an NBKP section, an LBKP section and a mixing box. The output ends of the wet slurry section, the NBKP section and the LBKP section are respectively connected to the mixing box. The control device includes a PLC controller and a background computer. The PLC controller is respectively connected to the production equipment signals in the wet slurry section, the NBKP section and the LBKP section. The background computer is connected to the PLC controller signal. The PLC controller is used to collect operating parameter data of the production equipment in real time, send the operating parameter data to the background computer, control the production equipment based on the feedback instructions of the background computer, and the background computer is used to obtain a slurry quality evaluation result, analyze the slurry quality evaluation result and the real-time collected production equipment operating parameter data, obtain an operating parameter adjustment strategy applied to the production equipment, generate a feedback instruction according to the operating parameter adjustment strategy and send it to the PLC controller.

2. A PLC-based stock preparation quality control system according to claim 1, characterized in that: The wet slurry section comprises a slurry storage tower, a slurry press, a high-concentration tank and an intermediate tank which are connected in sequence, and the output end of the intermediate tank is connected to a mixing box.

3. A PLC-based stock preparation quality control system according to claim 1, characterized in that: The NBKP section includes a conveyor belt, a pulping machine, a discharge trough, a pressure screen, a pulping machine and a post-beating trough connected in sequence. The post-beating trough is connected to a mixing box. The conveyor belt in the NBKP section is used to transport the NBKP pulp bag to the pulping machine.

4. A PLC-based stock preparation quality control system according to claim 1, characterized in that: The LBKP section includes a conveyor belt, a pulping machine, a discharge trough, a pressure screen, a pulping machine and a post-beating trough connected in sequence. The post-beating trough is connected to a mixing box. The conveyor belt in the LBKP section is used to transport the LBKP pulp bag to the pulping machine.

5. The PLC-based stock preparation quality control system according to claim 1, characterized in that: Before the back-end computer obtains the pulp quality evaluation results, the pulp quality is evaluated in multiple dimensions. The following operations are included: Determine the multi-dimensional quality evaluation index of pulping, determine the correlation between the quality evaluation index of each dimension and the operating parameters of the production equipment, and store the correlation in the background computer; The quality of each batch of pulp is evaluated based on multi-dimensional quality evaluation indicators to obtain pulp quality evaluation results of the corresponding batches, and the pulp quality evaluation results are input into the background computer. The pulp quality evaluation results include quality evaluation indicator values ​​of multiple dimensions.

6. A PLC-based stock preparation quality control system according to claim 5, characterized in that: The background computer specifically includes: An evaluation and analysis module is used to analyze the pulping quality evaluation results, determine whether the quality evaluation index values ​​of each dimension meet the quality requirements of the corresponding type of pulping according to the pulping type, and screen out the quality evaluation index values ​​that do not meet the quality requirements; A joint analysis module is used to input the corresponding type of pulping quality standard index values, quality evaluation index values ​​that do not meet quality requirements, and production equipment operation parameter data into the parameter prediction model for processing to obtain predicted operation parameter data; A strategy generation module is used to generate an operating parameter adjustment strategy set based on the predicted operating parameter data and the production equipment operating parameter data uploaded by the PLC controller, wherein the operating parameter adjustment strategy set includes at least one operating parameter adjustment strategy, and the operating parameter adjustment strategy includes the adjustment value of the operating parameter of the production equipment, the adjustment effective time point and the adjustment recovery time point.

7. A PLC-based stock preparation quality control system according to claim 6, characterized in that: The background computer specifically includes: A conflict analysis module, used to determine whether there are conflicting operating parameter adjustment strategies in the operating parameter adjustment strategies when generating an operating parameter adjustment strategy set; The priority calculation module is used to compare the weights of conflicting operating parameter adjustment strategies, sort the execution priorities of the operating parameter adjustment strategies in descending order of weight, and filter out the operating parameter adjustment strategies that are not of the highest priority.

8. A PLC-based stock preparation quality control system according to claim 7, characterized in that: The background computer further includes a weight calculation module, which is used to perform the following operations: Calculate a class of weights for the operation parameter adjustment strategy; Calculate the second-class weights of the operation parameter adjustment strategy; Based on the first-class weight and the second-class weight of the same operating parameter adjustment strategy, the comprehensive weight is calculated, and the calculation result of the comprehensive weight is used as the final weight of the operating parameter adjustment strategy.

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