FRICTION DEVICE PREFERABLY FOR TYPEWRITER/PRINTER RIBBONS

Abstract: A friction device, preferably for printer/typewriter ribbons, intended to provide engagement between a drive means (3) and a medium which is to be advanced by the drive means. A counter pressure roller (4) is arranged with a flexible shaft (8) which is mounted at a distance from the driving surface of the drive means (3) which is less than the radius of the counter pressure roller (4).

Description: FRICTION DEVICE PREFERABLY FOR TYPEWRITER/PRINTER RIBBONS. TECHNICAL FIELD The invention relates to a friction device, preferably in typewriter/printer ribbons for providing engagement between a drive means and a medium which is to be advanced with the aid of the drive means, the friction means including a counter pressure roller. BACKGROUND ART In advancing ribbons in printers and typewriters the ribbon is pulled by a drive means past the printing location. The drive means co-acts with the printing means of the printer such that for each character that is written the ribbon is pulled forward a given length corresponding to a type width plus margin. In order that the ribbon will not slip on engagement with the drive means, there is arranged a counter pressure roller which engages with spring bias against the drive wheel of the drive means. It is important here that the counter pressure roller engages against the drive wheel with the same pressure along its entire axial length. Otherwise, a transverse force may affect the movement of the ribbon such as to cause incorrect collection of used ribbon, with a breakdown as a result. DISCLOSURE OF INVENTION The object of the invention is to solve the above-mentioned problem in a simple and cheap way, by mounting the counter pressure roller on a flexible shaft, the force required for bending the shaft being taken up by the drive roller. BRIEF DESCRPTION OF DRAWING The drawing illustrates schematically in a side view the parts of a printer/ typewriter ribbon cassette which are of interest for the invention. The cassette is represented by two end walls 1, 2 between which there are arranged a drive wheel 3 and a counter pressure roller 4. The drive wheel 3, which has a cylindrical surface with a surface coating of a friction material, e.g. hard rubber, is mounted with the aid of two pins 5, 6 in the end walls 1 and 2. The pin 6 is provided with a groove 7 at its free end for co-action with a projection on a pin in a drive means associated with the writer for driving the ribbon (not illustrated in the Figure). As with the drive wheel 3, the counter pressure roller 4 has a cylindrical surface of friction material, and through the roller there is an axial hole co- acting with a helix spring 8 with a running fit. Co-axial recesses 9 and 10 are arranged in the respective end portion of the roller 4. The end walls 1 and 2 are provided with projections 11 for axial guidance of the drive wheel 3 and counter pressure roller 4. Holes 13, 14 are arranged in the end walls for mounting the drive wheel shaft pins 5, 6 and holes 15, 16 for mounting the helix spring 8. The centre-to-centre distance between said holes 13-15 and 14-16 is somewhat less than the sum of the radii of the drive wheel and counter pressure roller. This results in that the helix spring 8, constituting the shaft to the counter pressure roller 4, is subjected to bending in its parts which are not radially retained, as will be seen from the drawing.

Claims: C L A I M S 1 Friction device preferably for printer/typewriter ribbons, for providing engagement between a drive means and a medium which is to be advanced by said drive means, the friction device including a counter pressure roller, characterized in that the shaft of the counter pressure roller is flexible and mounted at a distance from the driving surface of the drive means which is less than the radius of the counter pressure roller. 2 Friction device as claimed in claim 1, characterized in that the shaft comprises a helix spring.

Inventors: HENRIKSSON BENGT-AOKE, HENRIKSSON, BENGT-AOKE
Applicants: ERICSSON TELEFON AB L M, TELEFONAKTIEBOLAGET L M ERICSSON
Application year: 1986
Main classification: B41J33
IPC codes: B41J33, B65H20