Method of Operating an Off-LIne Finishing Device for Fiber Webs, in Particular an Off-Line Slitter-Winder for Winding Fiber Webs

• US 20200130976A1
• Filed: 10/24/2019
• Published: 04/30/2020
• Est. Priority Date: 10/24/2018
• Status: Active Grant

• Current Assignee: Valmet Technologies OY
• Original Assignee: Valmet Technologies OY
• Inventors: Paanasalo, Jari
• Granted Patent: US 11,142,422 B2
• Time in Patent Office: Days
• CPC Class Codes: B65H 18/08 Web-winding mechanisms
• CPC Class Codes: B65H 2220/01 indicating an entity as a function of which control, adjustment or change is performed, i.e. input
• CPC Class Codes: B65H 2220/02 indicating an entity which is controlled, adjusted or changed by a control process, i.e. output
• CPC Class Codes: B65H 23/185 motor-controlled
• CPC Class Codes: B65H 2301/4148 slitting
• CPC Class Codes: B65H 2511/14 Diameter, e.g. of roll or package
• CPC Class Codes: B65H 2513/11 angular
• CPC Class Codes: B65H 2513/20 Acceleration or deceleration
• CPC Class Codes: B65H 2557/24 Calculating methods; Mathematic models
• CPC Class Codes: B65H 26/025 responsive to web breakage
• CPC Class Codes: B65H 2601/525 Cost of application or use, e.g. energy, consumable
• CPC Class Codes: B65H 2601/60 Miscellaneous
• CPC Class Codes: B65H 2801/84 Paper-making machines

Abstract

A method of operating an off-line finishing device for fiber webs, in particular an off-line slitter-winder for winding fiber webs, wherein in operating the off-line device the running speed is automatically optimized to minimize cost of web breaks. The method considers the costs associated with a web break during unwinding in addition to the cost benefit of maximizing web unwind speed so as to maximize machine utilization. The method determines an optimal web break stopping time in a web break situation and how often a web break is predicted. Automatic optimization incorporates limitations including the maximum rotation speed of the parent roll, the maximum speed of the fiber web being unwound, the maximum positive torque which can be applied to the parent roll to accelerate the parent roll to a rotation rate which produces a desired web speed, and maximum braking torque.

Claims

1. A method of operating an off-line finishing device for fiber webs, having an unwinder and a parent roll mounted thereto, the parent roll having a fiber web with a fiber web length, the unwinder having at least one torque drive motor for controlling an unwind velocity of the parent roll, and at least one torque brake, wherein said at least one torque brake comprises at least one of said torque drive motor and a mechanical brake, the at least one torque brake having a selected braking torque, the method comprising the steps of:

unwinding the fiber web from the parent roll;

continuously calculating an inertia of the parent roll as the parent roll is unwound;

continuously calculating a maximum deceleration of the parent roll by dividing the selected braking torque by the inertia; and

controlling the unwind velocity of the parent roll so that said calculated maximum deceleration will bring the parent roll to a stop in no more than a selected time.

3. The method of claim 1 wherein the off-line finishing device is a slitter winder, and further comprising:

collecting continuously data relating to frequency of occurrence of web breaks per parent roll and determining probability of occurrence of a web break during the unwinding of a fiber web from the parent roll;

determining a cost function for the unwinding of the parent roll as a function of time;

determining a cost function for a web break as a function of the selected time and the probability of occurrence of a web break during the unwinding of a fiber web from the parent roll;

setting the selected time to a time interval which minimizes the total cost of unwinding a fiber web from the parent roll; and

slitting and winding the fiber web length into customer rolls.

2. The method of claim further comprising:

collecting continuously data relating to frequency of occurrence of web breaks per parent roll and determining probability of occurrence of a web break during the unwinding of a fiber web from the parent roll;

determining a cost function for the unwind of the parent roll as a function of time;

determining a cost function for a web break as a function of the selected time and the probability of occurrence of a web break during the unwinding of a fiber web from the parent roll; and

setting the selected time to a time interval which minimizes the total cost of unwinding a fiber web from the parent roll.

4. A method of operating an off-line slitter winder finishing device for fiber webs, having an unwinder and a parent roll mounted thereto, the parent roll having a fiber web with a fiber web length, the unwinder having a maximum web speed, and at least one torque drive motor for controlling an unwind velocity of the parent roll, and at least one torque brake, wherein said at least one torque brake comprises at least one of said torque drive motor and a mechanical brake, the at least one torque brake having a selected braking torque, the method comprising the steps of:

using a model of the off-line slitter winder finishing device for fiber webs to pre-calculate a limit of a web break stopping time required by the selected braking torque in relation to the parent roll inertia and web unwind speed and how much setting a maximum web break stopping time decreases capacity of the finishing device for fiber webs by decreasing average web unwind speed;

collecting continuously data relating to frequency of occurrence of web breaks per parent roll to determining probability of occurrence of a web break;

calculating expected value of capacity loss based on the determined probability of occurrence of a web break and the web break stopping a time; and

while the web unwind speed is lower than maximum running speed, adjusting the maximum web break stopping time and thus the web unwind speed such that the expected value of capacity loss is minimized, wherein the expected value of capacity loss is continuously adjusted as the probability of occurrence of a web break is updated.

5. A method of operating an off-line finishing device for fiber webs, the device having an unwinder and a parent roll mounted thereto, the unwinder having a torque drive and a torque break, the method comprising:

selecting a maximum web speed for unwinding the fiber web;

determining a web break frequency based on a history for a selected number of parent rolls which have been unwound most recently, by dividing the number of web breaks by the number of the selected number of parent rolls which have been unwound;

defining a web break cost as a function of rotation a selected stop time of the parent roll;

defining a cost of incremental increased time to unwind the parent roll caused by reducing web speed below the maximum web speed to achieve the selected stop time of the parent roll, until the parent roll decrease in inertia is such that the parent roll can stop in the selected time at maximum web speed;

minimizing a total cost, due to web breaks and cost of increased time to unwind the parent roll do to unwinding at less than the selected maximum web speed by choice of the selected stop time of the parent roll.

6. The method of claim 6 wherein web break cost is a function of one half of the velocity at break, times the selected stop time of the parent roll plus a fixed cost corresponding to a web break at zero web speed.

7. The method of claim 7 wherein the cost of increased time to unwind the parent roll is a function of an allocation of total cost of operating cost of the off-line finishing device for fiber webs in a time basis.

8. The method of claim 7 wherein the time to stop rotation of the parent roll is determined based on a self-learning algorithm using multiple data instances selected from at least one of:

an occurrence of web breaks, total time to unwinder and the parent rolls in the off-line finishing device for fiber webs, cost of web breaks, total cost of processing the parent rolls in the off-line finishing device, and stop time of the parent roll following a web break.