APPARATUS FOR CONTROLLING PAPER STOCK REFINERS
United States Patent 3610541
In apparatus for refining paper stock, one beater element is both rotated and longitudinally positioned with respect to a stationary second element, a drive motor causing the rotation and a control motor the positioning. In order to maintain the power consumption of the drive motor relatively constant, a first signal is produced which is representative of the actual work performed within the refiner. This signal is compared with a desired set point signal. Any difference therebetween is forwarded to a deadbanded delta T controller that produces an output signal whenever the error is above or below the selected deadband limits. This signal is then compared with a signal representing the actual electric power being utilized by the drive motor for the refiner and any difference therebetween is forwarded to a deadbanded power controller of the pulse duration type which then delivers to the control motor pulses having a duration in accordance with the magnitude of the last-mentioned error, doing so only when the error is above or below the dead zone limits adopted for the power controller.
US Patent References:
Control apparatus for pulp refiners
Irwin - January 1955 - 2699095
Automatic crusher
Patterson - February 1963 - 3078051
Material working apparatus
McMahon - March 1967 - 3309031
Control apparatus for pulp refiners
Irwin - January 1955 - 2699095
Automatic crusher
Patterson - February 1963 - 3078051
Material working apparatus
McMahon - March 1967 - 3309031
Application Number:
04/872145
Publication Date:
10/05/1971
Filing Date:
10/29/1969
View Patent Images:
Export Citation:
Assignee:
Beloit Corporation (Beloit, WI)
Primary Class:
International Classes:
B02C25/00; D21D1/00; B02C7/14; B02C7/06; B02C25/00
Field of Search:
241/37
Primary Examiner:
Kelly, Donald G.
Claims:
What is claimed
1. Apparatus for refining paper stock comprising a pair of relatively rotatable and axially movable refining elements, a drive motor for relatively rotating said elements, a control motor for axially shifting one of said elements with respect to the other, a first control loop including a transmitter for providing a signal which is a measure of the amount of work being performed by said elements while refining said stock, comparator means for comparing said work signal with a set point signal indicative of a desired rate of refining work and a deadbanded controller responsive to any difference between said signals for providing a second set point signal which is indicative of a desired amount of power to be used by said drive motor, and a second control loop including a transmitter for providing a signal which is a measure of the amount of power being used by said drive motor, comparator means for comparing said power signal with said second set point signal, and a deadbanded pulse duration controller connected to said last-mentioned comparator means and to said control motor for providing pulses to said control motor having a duration in accordance with the difference between said work signal and said second set point signal, whereby said control motor shifts said refining elements with respect to each other so as to provide a spacing between said refining elements such that the amount of power called for by said second set point signal is maintained within predetermined limits.
2. Apparatus for refining paper stock comprising a pair of relatively rotatable and axially movable refining elements, an electric drive motor for relatively rotating said elements, an electric control motor for axially shifting one of said elements with respect to the other, means providing a signal which is a measure of the amount of work being performed by said elements while refining said stock, first comparator means for comparing said work signal with a set point indicative of a desired refining work rate to provide an error signal in accordance with any difference between said work signal and said set point, a deadband controller connnected to said first comparator means for producing a second set point in accordance with the value of said error signal, means for providing a signal which is a measure of the amount of electric power being used by said drive motor, second comparator means for comparing said power signal with said second set point to provide a second error signal in accordance with any difference therebetween, and a deadbanded pulse duration controller connected to said second comparator means and to said control motor having a duration in accordance with the value of said second error signal.
3. Apparatus for refining paper stock as set forth in Claim 2 in which said first controller is a proportional-integral-derivative controller.
4. Apparatus for refining paper stock comprising a par of relatively rotatable and axially movable refining elements, a drive motor for relatively rotating said elements, a control motor for axially shifting one of said elements with respect to the other, a first comparator having a pair of input lines, one of said input lines having a set point signal impressed thereon which is a measure of a desired amount of work to be performed by said refining elements, means connected to the other of said input lines for supplying a signal which is a measure of the amount of work being performed by said elements while refining said stock, said first comparator having an output line, a deadbanded controller connected to said output line for providing a second set point signal which is indicative of a desired amount of work to be performed by said refining elements, a second comparator having a pair of input lines, one of the input lines for said second comparator being connected to said deadbanded controller, means connected to the other input line for said second comparator for supplying a signal which is a measure of the power used by said drive motor, said second comparator having an output line, a deadbanded pulse duration controller connected to the output line for said second comparator and connected to said control motor for supplying energizing pulses to said control motor having a duration in accordance with the difference between the value of said power signal and the value of said second set point signal.
1. Apparatus for refining paper stock comprising a pair of relatively rotatable and axially movable refining elements, a drive motor for relatively rotating said elements, a control motor for axially shifting one of said elements with respect to the other, a first control loop including a transmitter for providing a signal which is a measure of the amount of work being performed by said elements while refining said stock, comparator means for comparing said work signal with a set point signal indicative of a desired rate of refining work and a deadbanded controller responsive to any difference between said signals for providing a second set point signal which is indicative of a desired amount of power to be used by said drive motor, and a second control loop including a transmitter for providing a signal which is a measure of the amount of power being used by said drive motor, comparator means for comparing said power signal with said second set point signal, and a deadbanded pulse duration controller connected to said last-mentioned comparator means and to said control motor for providing pulses to said control motor having a duration in accordance with the difference between said work signal and said second set point signal, whereby said control motor shifts said refining elements with respect to each other so as to provide a spacing between said refining elements such that the amount of power called for by said second set point signal is maintained within predetermined limits.
2. Apparatus for refining paper stock comprising a pair of relatively rotatable and axially movable refining elements, an electric drive motor for relatively rotating said elements, an electric control motor for axially shifting one of said elements with respect to the other, means providing a signal which is a measure of the amount of work being performed by said elements while refining said stock, first comparator means for comparing said work signal with a set point indicative of a desired refining work rate to provide an error signal in accordance with any difference between said work signal and said set point, a deadband controller connnected to said first comparator means for producing a second set point in accordance with the value of said error signal, means for providing a signal which is a measure of the amount of electric power being used by said drive motor, second comparator means for comparing said power signal with said second set point to provide a second error signal in accordance with any difference therebetween, and a deadbanded pulse duration controller connected to said second comparator means and to said control motor having a duration in accordance with the value of said second error signal.
3. Apparatus for refining paper stock as set forth in Claim 2 in which said first controller is a proportional-integral-derivative controller.
4. Apparatus for refining paper stock comprising a par of relatively rotatable and axially movable refining elements, a drive motor for relatively rotating said elements, a control motor for axially shifting one of said elements with respect to the other, a first comparator having a pair of input lines, one of said input lines having a set point signal impressed thereon which is a measure of a desired amount of work to be performed by said refining elements, means connected to the other of said input lines for supplying a signal which is a measure of the amount of work being performed by said elements while refining said stock, said first comparator having an output line, a deadbanded controller connected to said output line for providing a second set point signal which is indicative of a desired amount of work to be performed by said refining elements, a second comparator having a pair of input lines, one of the input lines for said second comparator being connected to said deadbanded controller, means connected to the other input line for said second comparator for supplying a signal which is a measure of the power used by said drive motor, said second comparator having an output line, a deadbanded pulse duration controller connected to the output line for said second comparator and connected to said control motor for supplying energizing pulses to said control motor having a duration in accordance with the difference between the value of said power signal and the value of said second set point signal.
Description:
BACKGROUND OF THE INVENTION
1. 1. Field of the Invention
This invention relates generally to apparatus for refining paper stock, and pertains more particularly to a control system for positioning one movable refining element with respect to a stationary refining element in order to maintain the power requirements of the refiner relatively constant.
2. Description of the Prior Art
U.S. Pat. No. 3,309,031 granted Mar. 14, 1967 to Richard F. McMahon et al. for MATERIAL WORKING APPARATUS, is owned by the assignee of the present invention. The control system described and claimed in said patent has functioned admirably well. As a matter of fact, in a sense it has been too perfect because it has been extremely sensitive to both electric power changes also to the temperature changes due to an increase or decrease of the actual work performed on the fluid stock. Also, the alluded to system has been vulnerable to vibration, particularly with respect to the delta T transmitter utilized therein, and this has resulted in some failures. Also, when a failure has occurred, the prior art system has not lent itself readily to manual operation.
SUMMARY OF THE INVENTION
Accordingly, the present invention has for a general object to provide a control system for paper stock-refining apparatus that will be sufficiently precise for the control of the consistency of the stock being processed in order to produce a paper of the appropriate grade, yet which system will be sufficiently insensitive so that constant adjustments or corrections of the axially movable refining element are not being made. In other words, the present invention has for an aim the provision of a practical system for the refining of paper stock which will meet the standards expected of it and which will also result in a relatively uniform power consumption. Consequently, it is within the pruview of the present invention to provide a control system of the envisaged type that will be exceedingly rugged, long lasting, and which will result in a minimum amount of failures.
Briefly, the invention includes two controllers, both of which have dead bands that avoid unnecessary control action. More specifically, the first controller operates when there is a sufficient difference between the signal derived from the actual work being performed within the refiner and a set point indicative of the desired amount of power that should be utilized by the refiner. When the first controller receives a difference signal of sufficient value, it acts to provide a modified or changed set point which is compared with a signal representative of the actual power being consumed by the refiner. The second controller, which is also deadbanded, acts to correctly position the movable beater element within the refiner so as to maintain uniformity of power consumption and also to maintain the desired degree of consistency of the paper stock.
BRIEF DESCRIPTION OF THE DRAWING
The single FIGURE presented for illustrating the invention constitutes a block diagram of the electrical features with the refining apparatus being set forth diagrammatically.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The refiner selected to illustrate the invention has been designated in its entirety by the reference numeral 10. In this regard, the refiner 10 is of the disc variety and therefore includes a stationary beater or refining element 12 and a rotary auxiliary beater or refining element 14. However, the invention is susceptible to use in a Jordan refiner in which a rotatable conical plug is moved axially with relation to the shell complementally enclosing same.
As depicted, the refiner 10 is the present situation has a drive shaft 16 connected with the rotary element 14 and it is through the agency of an electric motor 18 that the shaft 16 is rotated so as to in turn rotate the element 14. In said McMahon et al. patent, a pneumatic motor has been illustrated for the purpose of moving the rotary element with respect to the stationary element. It is contemplated that when practicing the present invention that an electric motor will be utilized. In this regard, the control motor labeled 20 could take the form of the electric motor illustrated in U.S. Pat. No. 1,933,814 issued on Nov. 7, 1933 to Darcy E. Lewellen et al. for STOCK CONSISTENCY CONTROL. In said Lewellen et al. patent. The motor rotates a screw thread that in turn positions the conical plug of the Jordan refiner there shown.
As herein shown, the stock enters the refiner 10 through an inlet 22 and is discharged through an outlet 24. Corresponding to the arrangement used in said McMahon et al. patent, there is an input temperature-measuring element 26 and an output temperature-measuring element 28. A delta T transmitter 30 converts the signals provided by the elements 26 and 28 to a signal having a value proportional to the temperature difference sensed by these elements 26, 28. Since the difference in temperature between the inlet 22 and the outlet 24 is representative of the actual work performed by the refining elements 12 and 14, the signal forwarded by the transmitter 30 will be indicative of the amount of mechanical energy absorbed by the stock as it is being processed within the refiner 10.
At this time, attention is directed to a first summing junction or comparator circuit 32 having a first input terminal 32a, a second input terminal 32b and an output terminal 32c. The input terminal 32 a carries a set point signal representing a desired amount of work that is to be performed within the refiner 10, whereas the signal representing the actual amount of work performed within the refiner 10 is derived from the transmitter 30 and is delivered via the input terminal 32b. The comparator 32 senses any algebraic difference between the signals applied to the terminals 32a, 32 b and the difference appears as an error signal at the output terminal 32 c.
The output terminal 32 c is connected to a delta T controller 34 having a suitable dead band or dead zone so that it only operates to provide a corrective output signal when the error signal from the comparator 32 is above or below prescribed limits. In addition to being deadbanded, the controller is preferably a proportional-plus-derivative type which supplies an output signal that is a linear combination of the error signal from the comparator 32, and the time-rate-of-change of such error signal and the time integral thereof. Controllers of this type are commonly known as PID controllers. The point to bear in mind is that there is no change in the normal or base level of the output signal from the controller 34 until the error signal from the comparator 32 has exceeded the predetermined limits that are selected. It is within the dead zone that the controller 34 has no effect and no adjustment is made as explained below.
A second summing junction or comparator circuit 36 has a pair of input terminals 36a, 36b and an output terminal 36c. The input terminal 36a is connected directly to the controller 34 so as to deliver the output signal from said controller 34 to the comparator circuit 36. The input terminal 36b, however, is connected directly to a power transmitter 38 of the wattmeter type which provides a signal which is a measure of the instantaneous power being consumed by the motor 18. Hence, any difference between the signal from the controller 34 and the signal from the transmitter 38 appears as an error signal that is fed from the terminal 36c to a power controller 40 that is also deadbanded and is of the pulse duration type so that pulses are produced which have a width or span in accordance with the value of the error signal derived from the comparator circuit 36.
It is the pulse signal from the controller 40 that is employed for energizing the control motor 20 to position or space the movable refining element 14 with respect to the stationary refining element 12. Here again, it will be appreciated that there will be no signal available for energizing the motor 20 until the error signal from the comparator circuit 36 has exceeded prescribed limits. Thus, not only must the controller 34 first receive a signal outside of the limits imposed on it, but after such a condition has arisen, the controller 40 then must likewise receive a signal outside of its limits.
Having presented the foregoing information, the operation of the disclosed system has already been for all intents and purposes explained. However, a brief review should be of assistance in appreciating the benefits to be derived therefrom. With a given spacing between the elements 12, 14 of the refiner 10 and a specified flow of fluid stock therethrough, there will be a temperature rise existing between the inlet 22 and the outlet 24. The transmitter 30 determines its output signal on the basis of this difference and the signal is compared with the desired set point signal supplied at the comparator 32 via its terminal 32 a. If the resulting error signal is above or below selected limits, then the controller 34 outputs a signal to the comparator circuit 36 which output signal is immediately compared with the signal derived from the power transmitter 38. If this error signal is above or below prescribed limits, then the controller 36 provides an output signal which is employed for operating the control motor 20 to initiate a shift of the longitudinally or axially movable element 14. If the fiber content of the flow into the refiner 10 through the inlet 22 has increased in relation to the liquid content, then the load imposed upon the drive motor 18 will be increased and this dictates that the element 14 should be moved further away from the element 12. However, there is not the continual shifting back and forth of the element 14 with respect to the element 12 because of the dead zones incorporated into the operation of the controllers 34 and 40. The same action transpires if the consistency of the fluid stock decreases, for then the power consumed by
It will be understood that first and second control loops are established. The first such loop includes the delta T transmitter 30, the comparator circuit 32 and the controller 34. The second such loop includes the power transmitter 38, the comparator circuit 36 and the controller 40. The final control element, of course, is the positioning motor 20.
1. 1. Field of the Invention
This invention relates generally to apparatus for refining paper stock, and pertains more particularly to a control system for positioning one movable refining element with respect to a stationary refining element in order to maintain the power requirements of the refiner relatively constant.
2. Description of the Prior Art
U.S. Pat. No. 3,309,031 granted Mar. 14, 1967 to Richard F. McMahon et al. for MATERIAL WORKING APPARATUS, is owned by the assignee of the present invention. The control system described and claimed in said patent has functioned admirably well. As a matter of fact, in a sense it has been too perfect because it has been extremely sensitive to both electric power changes also to the temperature changes due to an increase or decrease of the actual work performed on the fluid stock. Also, the alluded to system has been vulnerable to vibration, particularly with respect to the delta T transmitter utilized therein, and this has resulted in some failures. Also, when a failure has occurred, the prior art system has not lent itself readily to manual operation.
SUMMARY OF THE INVENTION
Accordingly, the present invention has for a general object to provide a control system for paper stock-refining apparatus that will be sufficiently precise for the control of the consistency of the stock being processed in order to produce a paper of the appropriate grade, yet which system will be sufficiently insensitive so that constant adjustments or corrections of the axially movable refining element are not being made. In other words, the present invention has for an aim the provision of a practical system for the refining of paper stock which will meet the standards expected of it and which will also result in a relatively uniform power consumption. Consequently, it is within the pruview of the present invention to provide a control system of the envisaged type that will be exceedingly rugged, long lasting, and which will result in a minimum amount of failures.
Briefly, the invention includes two controllers, both of which have dead bands that avoid unnecessary control action. More specifically, the first controller operates when there is a sufficient difference between the signal derived from the actual work being performed within the refiner and a set point indicative of the desired amount of power that should be utilized by the refiner. When the first controller receives a difference signal of sufficient value, it acts to provide a modified or changed set point which is compared with a signal representative of the actual power being consumed by the refiner. The second controller, which is also deadbanded, acts to correctly position the movable beater element within the refiner so as to maintain uniformity of power consumption and also to maintain the desired degree of consistency of the paper stock.
BRIEF DESCRIPTION OF THE DRAWING
The single FIGURE presented for illustrating the invention constitutes a block diagram of the electrical features with the refining apparatus being set forth diagrammatically.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The refiner selected to illustrate the invention has been designated in its entirety by the reference numeral 10. In this regard, the refiner 10 is of the disc variety and therefore includes a stationary beater or refining element 12 and a rotary auxiliary beater or refining element 14. However, the invention is susceptible to use in a Jordan refiner in which a rotatable conical plug is moved axially with relation to the shell complementally enclosing same.
As depicted, the refiner 10 is the present situation has a drive shaft 16 connected with the rotary element 14 and it is through the agency of an electric motor 18 that the shaft 16 is rotated so as to in turn rotate the element 14. In said McMahon et al. patent, a pneumatic motor has been illustrated for the purpose of moving the rotary element with respect to the stationary element. It is contemplated that when practicing the present invention that an electric motor will be utilized. In this regard, the control motor labeled 20 could take the form of the electric motor illustrated in U.S. Pat. No. 1,933,814 issued on Nov. 7, 1933 to Darcy E. Lewellen et al. for STOCK CONSISTENCY CONTROL. In said Lewellen et al. patent. The motor rotates a screw thread that in turn positions the conical plug of the Jordan refiner there shown.
As herein shown, the stock enters the refiner 10 through an inlet 22 and is discharged through an outlet 24. Corresponding to the arrangement used in said McMahon et al. patent, there is an input temperature-measuring element 26 and an output temperature-measuring element 28. A delta T transmitter 30 converts the signals provided by the elements 26 and 28 to a signal having a value proportional to the temperature difference sensed by these elements 26, 28. Since the difference in temperature between the inlet 22 and the outlet 24 is representative of the actual work performed by the refining elements 12 and 14, the signal forwarded by the transmitter 30 will be indicative of the amount of mechanical energy absorbed by the stock as it is being processed within the refiner 10.
At this time, attention is directed to a first summing junction or comparator circuit 32 having a first input terminal 32a, a second input terminal 32b and an output terminal 32c. The input terminal 32 a carries a set point signal representing a desired amount of work that is to be performed within the refiner 10, whereas the signal representing the actual amount of work performed within the refiner 10 is derived from the transmitter 30 and is delivered via the input terminal 32b. The comparator 32 senses any algebraic difference between the signals applied to the terminals 32a, 32 b and the difference appears as an error signal at the output terminal 32 c.
The output terminal 32 c is connected to a delta T controller 34 having a suitable dead band or dead zone so that it only operates to provide a corrective output signal when the error signal from the comparator 32 is above or below prescribed limits. In addition to being deadbanded, the controller is preferably a proportional-plus-derivative type which supplies an output signal that is a linear combination of the error signal from the comparator 32, and the time-rate-of-change of such error signal and the time integral thereof. Controllers of this type are commonly known as PID controllers. The point to bear in mind is that there is no change in the normal or base level of the output signal from the controller 34 until the error signal from the comparator 32 has exceeded the predetermined limits that are selected. It is within the dead zone that the controller 34 has no effect and no adjustment is made as explained below.
A second summing junction or comparator circuit 36 has a pair of input terminals 36a, 36b and an output terminal 36c. The input terminal 36a is connected directly to the controller 34 so as to deliver the output signal from said controller 34 to the comparator circuit 36. The input terminal 36b, however, is connected directly to a power transmitter 38 of the wattmeter type which provides a signal which is a measure of the instantaneous power being consumed by the motor 18. Hence, any difference between the signal from the controller 34 and the signal from the transmitter 38 appears as an error signal that is fed from the terminal 36c to a power controller 40 that is also deadbanded and is of the pulse duration type so that pulses are produced which have a width or span in accordance with the value of the error signal derived from the comparator circuit 36.
It is the pulse signal from the controller 40 that is employed for energizing the control motor 20 to position or space the movable refining element 14 with respect to the stationary refining element 12. Here again, it will be appreciated that there will be no signal available for energizing the motor 20 until the error signal from the comparator circuit 36 has exceeded prescribed limits. Thus, not only must the controller 34 first receive a signal outside of the limits imposed on it, but after such a condition has arisen, the controller 40 then must likewise receive a signal outside of its limits.
Having presented the foregoing information, the operation of the disclosed system has already been for all intents and purposes explained. However, a brief review should be of assistance in appreciating the benefits to be derived therefrom. With a given spacing between the elements 12, 14 of the refiner 10 and a specified flow of fluid stock therethrough, there will be a temperature rise existing between the inlet 22 and the outlet 24. The transmitter 30 determines its output signal on the basis of this difference and the signal is compared with the desired set point signal supplied at the comparator 32 via its terminal 32 a. If the resulting error signal is above or below selected limits, then the controller 34 outputs a signal to the comparator circuit 36 which output signal is immediately compared with the signal derived from the power transmitter 38. If this error signal is above or below prescribed limits, then the controller 36 provides an output signal which is employed for operating the control motor 20 to initiate a shift of the longitudinally or axially movable element 14. If the fiber content of the flow into the refiner 10 through the inlet 22 has increased in relation to the liquid content, then the load imposed upon the drive motor 18 will be increased and this dictates that the element 14 should be moved further away from the element 12. However, there is not the continual shifting back and forth of the element 14 with respect to the element 12 because of the dead zones incorporated into the operation of the controllers 34 and 40. The same action transpires if the consistency of the fluid stock decreases, for then the power consumed by
It will be understood that first and second control loops are established. The first such loop includes the delta T transmitter 30, the comparator circuit 32 and the controller 34. The second such loop includes the power transmitter 38, the comparator circuit 36 and the controller 40. The final control element, of course, is the positioning motor 20.