Patent ID: 7549370

Claim:
An active vibration attenuation cylinder unit, for a fibre web machine comprising: a cylindrical frame part, having a cylinder part and a cylinder head defining a piston space therebetween, the piston space having a first piston space of cylindrical shape having a first cylindrical height, and a first cross section area, and a second piston rod space of cylindrical shape having a second cross section area less than the first cross section area; a piston unit formed of a cylindrical piston part having a lower surface and an upper annular surface surrounding a cylindrical piston rod joined to the piston part, the piston part having a second height of less than the first cylindrical height of the first piston space, the piston unit mounted in the piston space for linear movement, with the piston part mounted for motion in the first piston space, together with the piston rod which is mounted for motion in the second piston rod space; a container of pressurized fluid medium; and a plurality of valves having response times of about 2 kHz connected between the container of pressurized fluid medium and feed channels, the valves and the feed channels spaced about the cylindrical frame part, the feed channels connected to the piston space at an upper annular surface overlying the upper annular surface of the piston part surrounding the cylindrical piston rod, and the feed channels connected at a lower surface underlying the lower surface of the cylindrical piston part so that actuation of the valves causes the piston unit to oscillate.