Device and method for on-line control of the fibre direction of a fibre web

A method for on-line control of the fibre direction of a continuous fibre web in a paper or board machine comprising at least one former including at least one headbox being arranged for delivering a stock, which in the former is formed into said fibre web, though a slice including lips which are movable in relation to each other and define a discharge opening, said method including:

• measuring the fibre direction of the fibre web by means of a fibre direction meter arranged downstream the former;
• calculating and transmitting individual control signals, each being a function of measured fibre direction values, to a predetermined number of actuating members, which are arranged in predetermined positions along the lips for regulating the discharge opening locally as a response to the control signals,
• wherein the improvement comprises:
• identifying an array of fibre direction values, {v1 v2 v3 . . . vN}, of the measured fibre direction values, said fibre direction values of said array originating from positions in the cross direction of the fibre web which correspond to the positions of the actuating members;
• comparing said identified array of fibre direction values with an array of desired fibre direction values, {b1 b2 b3 . . . bN}, by means of calculating an array of error values in accordance with {e1 e2 e3 . . . eN}={b1-v1 b2-v2 b3-v3 . . . bN-vN};
• and
• calculating each of said control signals as a function of a predetermined number of said error values in accordance with
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A device for on-line control of the fibre direction of a continuous fibre web in a paper or board machine, comprising at least one former including at least one headbox being arranged for delivering a stock, which in said former is formed into said fibre web, though a slice including lips which are movable in relation to each other and define a discharge opening, said device comprising:

• a fibre direction meter arranged downstream of the former for measuring the fibre direction of the fibre web;
• a predetermined number of actuating members, which are arranged in predetermined positions along said lips for regulating the discharge opening locally as a response to individual control signals, each being a function of measured fibre direction values;
• a control unit, said fibre direction meter and said actuating members being directly connected to said control unit, said control unit being arranged for receiving the measured fibre direction values from the fibre direction meter, calculating said control signals, and transmitting the control signals to the actuating members;
• the control unit is arranged for identifying an array of fibre direction values, {v1 v2 v3 . . . vN}, of the measured fibre direction values, said fibre direction values of said array originating from positions in the cross direction of the fibre web which correspond to the positions of the actuating members;
• the control unit is arranged for comparing the identified array of fibre direction values with an array of desired fibre direction values {b1 b2 b3 . . . bN} by means of calculating an array of error values, {e1 e2 e3 . . . eN}={b1-v1 b2-v2 b3-v3 . . . bN-vN};
• and
• the control unit is arranged for calculating said control signal for each actuating member as a function of a predetermined number of said error values in accordance with
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• where J is a predetermined integral number and C0 C1 C2 . . . CJ are predetermined constants.