Duplex/simplex printer

This invention relates to electrostatic printing devices and more particularly to duplex printing. A duplex/simplex printer for producing toner particle images on opposite sides of a substrate during a duplex mode or producing toner particle images on one side of the substrate during a simplex mode including: means for forming a first toner particle image on an imaging member with toner particles electrostatically charged to a first polarity; an image conditioner, being enable only during the duplex mode, for reversing the charge polarity of the particles of the first toner particle image on the imaging member; an intermediate member for receiving of the first toner particle image during the duplex mode; a bias transfer roll, positioned opposed from the imaging member with the intermediate member therebetween, for transferring the first image to the intermediate member by moving the intermediate member and the imaging member past the bias transfer roll being charged at the first polarity during the duplex mode, the duplex mode includes the forming means forming a second toner particle image on the imaging member with toner particles electrostatically charged to the first polarity and means for feeding a substrate between the intermediate member and the imaging member and a controller reversing the charge polarity of the bias transfer roll to a second polarity thereby simultaneously transfer charged particles of the first and second images to opposite sides of the substrate during the duplex mode.