The present invention relates to compounds of formula wherein R1, R2, R3, R4, X, W, m and n are as defined hereinabove. A commutator is employed for fractionally sampling, or distributing, signals from, or to, a multiple channel polyphase filter. A negative pressure component placed in the pocket space creates a pressure difference over the drying wire and the web for attaching the web to the drying wire so the cross-direction shrinkage of the web is controllable. The securing member has a second fixing portion corresponding to the first fixing portion. A center, in a direction of rotation of the pressing roller, of a contact part of the fixed member that is in contact with the pressing roller through the belt member resides at a position that is displaced toward an entrance side of the fixing part with respect to a center of rotation of the pressing roller. Preferably two target connectors are provided, and are movably supported by the frame.