Vibration control apparatus and method for calender rolls and the like

An apparatus for calendering a medium, comprising:

• (a) a frame,
• (b) at least two calender rolls rotatably mounted relative to said frame and located adjacent to one another so as to form at least one nip and,
• (c) at least one reference sensor for providing at least one reference signal synchronized with a rotational speed of at least one of said at least two calender rolls,
• (d) at least one error sensor for providing at least one error signal correlated to relative vibration between at least two of said at least two calender rolls,
• (e) a controller for processing said at least one error and reference signals and producing at least one control signal, and
• (f) at least one controllable force generator responsive to said at least one control signal for providing at least one control force to control dynamic vibration between said at least two calender rolls to control vibration induced thickness variations in said medium.

An apparatus for calendering a medium, comprising:

• (a) a calender frame,
• (b) a first calender roll supported for rotatable movement relative to said frame,
• (c) a second calender roll also supported for rotatable movement relative to said frame, said second calender roll being mounted so as to form a nip between said first and second calender rolls which receives the medium,
• (d) error sensor means for deriving a first error signal correlated to vertical vibration between said first and second calender rolls and a second error signal correlated to lateral vibration between said first and second calender rolls,
• (e) reference sensor means for deriving a reference signal correlated to a rotational speed of at least one of said first and second calender rolls,
• (f) a controller for processing said error signal correlated to said vertical and lateral vibration and said reference signal and producing a control signal, and
• (g) controllable force generator means responsive to said control signal for providing both vertical and lateral dynamic forces to control both vertical and lateral dynamic vibration between said first and second calender rolls thereby controlling thickness variations in the medium resulting from relative vibration between said first and second calender rolls.

A method of controlling the thickness of a calendered medium, comprising the steps of:

• (a) feeding a medium between a nip formed between two calender rolls,
• (b) generating from a reference sensor a reference signal correlated to rotational speed of at least one of said two calender rolls,
• (c) generating from at least one error sensor an error signal representative of residual vibration between said two calender rolls,
• (d) processing said reference signal and said error signal within a controller to produce a control signal, and
• (e) controlling a force generator responsive to said control signal for providing force to control dynamic vibration between said two calender rolls to control thickness variations within said medium.