Low friction carrier systems are desirable in printers to allow high speed locating of print heads. In addition, it is desirable to include damping elements to eliminate positioning errors induced by vibrations from operation of the printer motor.
Some previous carrier systems have comprised sleeve bearings which were positioned around supporting shaft and coupled to a carrier. These systems required lubrication of the bar from time to time. This servicing requirements was indesirable since this presented extra maintenance costs and was inconvenient for the user. Sleeve bearing systems of this type require very strict manufacturing tolerances, particularly of the shaft surface, since minor variations either cause a sloppy fit, print errors, or binding of the bearing and shaft.
Other systems have used sealed bearings mounted on pivot arms and held in contact with a supporting bar by helical springs. These systems have the disadvantage that that the pivot arms may require some form of lubrication during the life of the product. Also, the helical springs used are expensive and the tension they provide is not uniform. Assembly procedures for these systems are cumbersome and time consuming. Since the accuracy of carrier registration degrades significantly if the predetermined rigidity is not maintained, all springs used must provide tension in a predetermined range.
The preferred embodiment of the present invention provides a low friction carrier suspension system having optional damping elements. Preload tension of the bearings is provided by a leaf spring coupling one or more of the roller bearings to the carrier. Preload tension is accurately determined by the opening defined by the bearings, and the thickness of the leaf spring material. Different weight carriers which present various inertial loadings can be accommodated by varying the thickness of the leaf spring material.
Some previous printers have attempted to provide damping of unwanted oscillations by electronic circuits coupled to the motor. In the preferred embodiment, mechanical damping elements are mounted on leaf spring material and ensure rapid settling at the target position.