Printer

Details Printer Printer

2001-03-15

2002-08-13

Hirshfeld, Andrew H. (Department: 2854)

Typewriting machines

Including adjustment for optimum printing plane

Responsive to thickness of record-medium

C400S055000, C400S058000

Reexamination Certificate

active

06431771

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dot impact line printer and, particularly, to a technique for regulating a distance between a printing head and a printing sheet.
2. Description of Related Art
In a dot impact line printer, printing is performed by a printing head with needles. The needles impact a surface of a printing sheet, which is supported by a platen, through an ink ribbon so as to form dots in the printing sheet. The depth at which the needles penetrate the pointing sheet is determined by input character information. Printing depth and the ink contrast becomes deeper by making the stroke of the printing head needles longer and paler by making the stroke shorter. Therefore, for constant printing, it is necessary to make the stroke distance constant, that is, to maintain a constant distance between the printing head and the printing sheet. The distance between the printing head and a platen will be referred to as “platen gap”, hereinafter.
FIG. 1
shows a construction of a main portion of a conventional dot impact line printer. As shown in
FIG. 1
, the distance between printing mechanism
19
and platen
3
is regulated by rotating ball screws
53
and
54
by platen driven portions
50
and
51
. Guide rails
60
and
61
are used to move the platen
3
in parallel precisely. Further, in order to move platen
3
in parallel precisely, platen driving portions
50
and
51
are synchronized with each other by drive synchronizer
52
.
FIGS. 2 and 3
show a procedure for detecting a thickness of a printing sheet of a conventional dot impact line printer. As shown in
FIG. 2
, it is possible to detect the printing sheet thickness by urging printing sheet thickness sensor
55
against sensor support
20
through printing sheet
40
. As shown in
FIG. 3
, platen
3
is moved to a predetermined position according to the thickness of the printing sheet thus detected.
An automatic sheet thickness detection mechanism disclosed in, for example, Japanese Patent Application Laid-open No. H6-055784 comprises a platen, which is moved from an initial position toward the side of a printing mechanism by an elevator mechanism using a lead screw to regulate a platen gap, a sheet thickness detection sensor fixed to the platen to determine the platen gap, a detection rod engaged with the sheet thickness detection sensor and in contact with a printing sheet to move according to the thickness of the printing sheet and a home position sensor for detecting the initial position of the platen. The platen is moved in parallel toward the side of the printing mechanism until the sheet thickness detection sensor operated by the movement of the detection rod corresponding to the sheet thickness is returned to an idle state.
A sheet thickness regulation mechanism disclosed in, for example, Japanese Patent Application Laid-open No. H2-258380 comprises a manual switch for manually selecting between an automatic setting mode and a selective setting mode, a switch for selecting a platen gap suitable for special sheets having partially different sheet thickness and a memory for storing data corresponding to the appropriate platen gaps for the special sheets.
As shown in
FIG. 1
, it is necessary to synchronize platen driving portion
51
provided in one end of platen
3
with platen driving portion
51
provided in the other end thereof with high precision. Further, it is necessary that ball screws
53
and
54
have substantially the same operating characteristics and the regulations thereof must be performed frequently.
That is, in order to move the long platen in parallel precisely by the elevator mechanism using such as lead screw, a complicated guide structure and a synchronizing structure for synchronizing both ends of the platen are necessary. Further, a large amount of regulation is necessary even after an assembling of the mechanisms.
As shown in
FIGS. 4 and 5
, which show problems related to conventional sheet thickness detection, it si impossible to set appropriate platen gaps for sheets having partially different thicknesses. For example, if a label sheet having four rounded corners is different in thickness between a label sheet portion and a peeling portion thereof, sheet thickness detection sensor
55
detects the thickness of the peeling sheet portion as shown in FIG.
4
. When the position of platen
3
is set according to the detection data as shown in
FIG. 5
, it is necessary, in order to maintain speed in printing on the label portion, to maintain a response frequency of the printing mechanism. The response frequency depends upon a specific vibration frequency of the printing mechanism, the platen gap and a rebound coefficient of the sheet, etc. The rebound coefficient depends upon the thickness of the printing sheet and the number of sheets to be printed, etc. It is usual that the rebound coefficient is inversely proportional to the thickness of the printing sheet and, with the same platen gap, the response frequency of the printing mechanism becomes lower when the thickness of the printing sheet is increased. Therefore, the platen gap [becomes] will not be appropriate for the printing speed. In such case, it is usual that an operator confirms the thickness of the printing sheet at a printing position and instructs a change of the thickness of the sheet, which is automatically detected by the printing device.
Further, such printing device is usually requested to maintain the response frequency in order to maintain the printing speed. Since the response frequency depends upon a specific vibration frequency of the printing mechanism, the platen gap and a rebound coefficient of the sheet, etc., and the rebound coefficient depends upon the thickness of the printing sheet and the number of sheets to be printed, etc., and since the rebound coefficient is inversely proportional to the thickness of the printing sheet and, with the same platen gap, the response frequency of the printing mechanism becomes lower when the thickness of the printing sheet increased, there is a limit to the printing speed. However, there is no particular prior art considering this problem.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a printer having a platen gap setting mechanism with a simple construction and high precision. Another object of the present invention is to provide a printer capable of setting an appropriate platen gap corresponding to a printing sheet having partially different thicknesses.
According to the first aspect of the present invention, a printer includes a printing head, and a platen arranged with a gap with respect to the printing head. The platen is pivotally coupled to a support to move towards and away from a printing path, a detector for detecting a thickness of a printing sheet, and an actuator for pivoting the platen about an axis of the support as a function of the detected thickness of the printing sheet. The support has a shaft provided in parallel to the platen and a frame rotatably supported by the shaft at two points, for supporting a center shaft of the platen at two points. As a result, an angle of the platen with respect to the shaft of the frame is easily regulated.
That is, in the printer of the present invention, the platen is mounted on the shaft, which is rotatable together with the frame. Therefore, it is possible to regulate the platen gap by the rotation of the frame about that shaft.
Thus, it is possible to remove the complicated platen driving portions at both ends of the platen, the guide rails and the drive synchronization portion, which are indispensable in the conventional printer.
It is preferable that the printing sheet feeder preferably includes means for automatically moving the sheet position detected by the detector for detecting the thickness of the printing sheet to the printing position.
That is, the printer of the present invention detects the thickness of the printing sheet at a first printing position. Therefore, it is possible to set a correct platen gap e

Affiliated with

Also associated with

Rating

Printer does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Printer, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Printer will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2936872