Printing device with adjustable printing head gap

Details Printing device with adjustable printing head gap Printing device with adjustable printing head gap

1993-02-10

1994-11-01

Wiecking, David A.

Typewriting machines

Including adjustment for optimum printing plane

400 56, 400 57, 400 59, B41J 25308

Patent

active

053602765

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to a printing device and, in particular, a printer having a frame, an abutment retained therein for supporting a recording medium, a print head which is mounted on the frame so aa to be movable relative to the abutment in the direction of the print lines, an actuating drive for setting the print head distance relative to the abutment, and a pressing element which is fixed to the frame, presses the recording medium onto the abutment and can be deflected substantially perpendicular to the surface of the abutment in accordance with the thickness of the recording medium.
2. Description of the Related Art
U.S. Pat. No. 4,676,675 discloses an apparatus for adjusting the portion of a print head in a matrix printer in which a sensor intended for resting on the surface of the recording medium is arranged on the print head carrier. The print head carrier can be adjusted with the aid of an eccentric adjusting mechanism toward and away from the abutment. To determine the thickness of the recording medium, the latter is first drawn into the printing position. The print head carrier is then moved into a reference position which is located furthest away from the abutment and is determined by means of a light barrier. The distance of the sensor surface from the abutment in this reference position is stipulated and known. The print head carrier is subsequently moved toward the abutment until the sensor rests with a particular contact pressure on the surface of the recording medium which has in the meantime been drawn in, the path covered up to this point being measured by means of a counter. Subsequently, this measured route is subtracted from the previously known reference route in the arithmetic unit. The difference corresponds to the thickness of the recording medium. On the basis of the value thus determined for the thickness of the recording medium, the print head carrier is then moved away from the abutment again until the desired distance between the print head and the surface of the recording medium has been set.
The method described above is relatively cumbersome and complex. A further disadvantage in this solution is that the calculation of the thickness and thus also the setting of the head distance can only take place when the recording medium is already in the printing position. This leads to a considerable loss of time. Furthermore, the distance between the abutment and the sensor must not be greater than the distance between the abutment and the print head. On the other hand, however, it must not be substantially smaller either since it would otherwise not be possible to set the distance between the surface of the recording medium and the print head to a desired value. This requires not only a relatively precise adjustment of the sensor relative to the print head, but can also cause difficulties when paper of a different thickness is drawn in.
In order to eliminate the disadvantages described above, it has already been proposed in an apparatus of the type known from U.S. Pat. No. 4,676,675 to arrange a sensor ahead of the printing position--seen in the drawing--in direction of the recording medium--on a part which is fixed to the printer frame relative to the abutment in such a way that, when the recording medium has not yet been drawn in, it rests on the abutment and can be deflected or deformed by the recording medium being drawn in, the deflection or deformation of the sensor being converted into a proportional electrical parameter. The sensor proposed in this solution comprises movable parts which become soiled due to the unavoidably occurring paper dust and can thus become jammed. Furthermore, these mechanical parts would have to be adjusted.
The document German Published Application 26 08 301 C 2 furthermore discloses an apparatus for controlling the distance of a print head from a recording medium, in which a sensor in the form of a two-armed lever is mounted so as to be pivotable on the print head carrier or the print head c

REFERENCES:
patent: 4676675 (1987-06-01), Suzuki et al.
patent: 4943174 (1990-07-01), Eicher
patent: 4974974 (1990-12-01), Yoshida et al.
patent: 5087135 (1992-02-01), Tew et al.
patent: 5193918 (1993-03-01), Lohrmann et al.
"Dynamic Head To Platen Gap Measuring Tool" by Gianmoena et al, IBM Technical Disclosure Bulletin vol. 25, No. 10, Mar. 1983, p. 5176.

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