Xerox Corp yesterday duly launched its new generation of digital copiers, which can be upgraded from stand-alone copiers to a so- called multifunction device that operates on a network and can be used for printing, sending facsimile messages, scanning and copying. The company unveiled the Document Center 220 and 230 with optional facsimile capability, saying they are available now, with networked versions available in the fourth quarter. The other two models, the Document Center 240 and 265 will be available in the second half of 1997. No prices were given, but Xerox admits it has got many things wrong in the past: this time, We are finally letting the market, not our technology, drive us, a chastened Paul Allaire, chief executive told the New York Times.