Printing apparatus

3

printhead operation when the printhead is not in contact with the print medium.

In accordance with this feature, a slight delay or dwell is established between the deactivation of the printhead and its actual movement away from the 5 platen roller. With the preferred arrangement, the printhead is deactivated prior to separation from the platen roller. In the illustrated embodiment, this feature is provided by a second cam which is driven concurrently with the cam used to separate the printhead from the 10 platen. The second cam activates a printhead disabling element such as an on/off switch. In order to insure deactivation of the printhead before separation of the printhead from the platen roller, the cam driving the switch is advanced so that the switch is actuated prior 15 to actuation of the head separating mechanism by the first cam.

According to another embodiment of the invention, the printhead includes a simple but effective stripping mechanism for automatically separating pressure sensi- 20 tive or adhesive labels from their backing or carrier after being printed. In the preferred and illustrated construction, the label and carrier are conveyed between the platen roller and printhead. A stripper plate is posi- 2J tioned immediately downstream of the print station and is preferably located parallel to and immediately adjacent, the platen roller. In normal operation, as the label leaves the printing station, it tends to travel along a feed path located in a plane substantially tangent to a print- jQ ing line defined between the printhead and the platen roller. When stripping of the backing is desired, the backing is directed along a path that diverges substantially from the feed path of the label. In the preferred arrangement, the backing is conveyed over the stripper 35 plate and then directed rearwardly so that it follows the contour and contacts a portion of the periphery of the platen roller. In effect, the backing is "wrapped" around a substantial portion of the platen.

In order to achieve this feature, the backing is caused 4q to travel around the platen roller by a stripper assist bar which is defined by a post or shaft disposed immediately adjacent the platen roller, but spaced therefrom, and having an axis substantially parallel to the axis of the platen roller. In the preferred arrangement, the stripper 45 assist bar is located such that the backing is wrapped around at least 90° of the platen roller periphery. In the illustrated embodiment the stripper assist bar is located in the range of 180°-270° from the print line as measured in the direction of rotation of the platen roller. 50

With the disclosed arrangement, the backing is in frictional engagement with a substantial portion of the platen roller. The platen roller is normally driven in order to feed the label and carrier past the printhead. The frictional engagement between the backing and the 55 platen roller is used to drive the backing and hence facilitates separation of the label from the backing. With the illustrated construction, separate gripper drive rollers or a capstan drive are obviated. The platen roller itself in cooperation with the stripper assist bar provides 60 the necessary tension that is needed to pull the backing onto the takeup reel after separation from the label.

In accordance with a feature of the invention, the stripper assist bar forms part of an assembly that is pivotally mounted for movement between an operative and 65 a retracted position. When separation of the label and backing is not desired, the stripper assist bar may be retracted and the backing or carrier strip is allowed to

4

proceed along the label feed plane and thus remain with the label for separation at a later time.

According to still another feature of the invention, an adjustable detented guide is located immediately upstream from the platen roller. In the preferred construction, the guide comprises a shaft slidably mounting a collar. The collar is movable to any one of a plurality of detented positions on the shaft in order to accommodate a variety of label or print medium widths. When changing label sizes, the collar is simply moved to the detented position corresponding to the width of the print medium being loaded into the printing mechanism.

The disclosed printing apparatus, although simple in construction, is capable of high quality images which are necessary in bar code applications. In addition, a simplified stripping mechanism is provided which eliminates the need for separate drive elements to effect stripping of the backing from the labels.

Additional features of the invention will become apparent and a fuller understanding obtained by reading the following detailed description made in connection with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side elevational view, shown somewhat schematically, of the overall construction of a printing apparatus made in accordance with a preferred embodiment of the invention;

FIG. 2 is an enlarged, fragmentary view, partially in section, of the apparatus shown in FIG. 1;

FIG. 3 is a perspective view of a printhead constructed in accordance with a preferred embodiment of the invention;

FIG. 4 is another perspective view of the printhead shown in FIG. 3;

FIG. 5 is a side elevational view of a cam arrangement forming part of the invention; and,

FIG. 6 is a side elevational view of a detented guide mechanism forming part of the print apparatus shown in FIG. 1.

BEST MODE FOR CARRYING OUT INVENTION

FIG. 1 illustrates the overall construction of a printing apparatus constructed in accordance with a preferred embodiment of the invention. The apparatus includes a printing unit or station indicated generally by the reference character 10 and a print medium supply indicated generally by the reference character 12. In the illustrated embodiment, the apparatus also includes a takeup mechanism indicated generally by the reference character 14 which is used when the printing apparatus is printing labels that are to be stripped from a backing material immediately after printing.

The printing mechanism 10 is operative to imprint or image a print medium 16 which is supplied in continuous form and fed from a supply reel or spool 18. The print medium may be a paper tape, continuous pressure sensitive labels or other suitable print material. A tensioning arm 17 is provided to maintain tension in the medium.

The invention will be described in connection with a thermal printing process. It should be understood, however, that at least some of the aspects of the invention are useable with reclaimed matrix printers, electrostatic printers, etc.

As seen in FIGS. 1 and 2, the print unit 10 includes a printhead 20 including a portion positioned immediately and in close proximity with a platen roller 22. The print 5

medium is fed from the spool 18 and between the printhead 20 and the platen roller 22. In the preferred embodiment, the platen roller is driven by a motor (not shown) and pulls the print medium 16 through the print unit. A print line 24 is defined between the printhead 20 5 and the platen roller 22 and is the position where imaging of the print medium occurs.

The printhead 20 is of conventional construction and although it may be of an electrostatic variety, in the illustrated embodiment, it is a thermal printhead and is 10 available from the ROHM Corporation. As is known, regions defined by thermal elements are selectively energized to selectively heat corresponding regions on the print medium as it moves past the printhead 20. The regions on the print medium that are heated darken to 15 produce an image.

The printhead 20 is supported in predetermined alignment with the platen roller by a frame structure indicated generally by the reference character 30. As seen in FIGS. 1 and 2, the printhead 20 is pivotally hung 20 from a U-shaped channel 32 having downwardly depending flanges 32a, 32b (see also FIGS. 3 and 4). In particular, the printhead includes a support bracket 34 which includes a pair of upstanding, parallel lugs 36 spaced apart on either side of the channel flanges 32c, 25 32b. A pivot pin 38 extends through the lugs 36 and the downwardly depending flanges 32a, 32b of the channel 32. With the disclosed mounting, the printhead 20 "floats" with respect to the platen roller 22. As indicated above, in order to produce high quality images, it 30 is imperative that contact pressure between the printhead 20 and the print medium 16 (along the print line 24) be substantially uniform across the width of the print medium. The pivotal mounting of the printhead 20 enables the printhead 20 to accommodate slight mis- 35 alignments between the platen roller 22 and the printhead 20 as well as the thickness variations in the print medium so that uniform contact is maintained.

As seen in FIG. 3 and 4, the pivot pin 38 is located substantially centrally with respect to a transverse di- 40 mension of the print head 20. An axis 40 of the pivot pin 38 is substantially transverse to a rotating axis 41 of the platen roller 22, but in the preferred embodiment, the axes 40, 41 of the pivot 38 and the roller 22 do not intersect. 45

The printhead 20 is movable towards and away from the platen roller 22 and it is spring biased towards the platen roller. To achieve this feature, the printhead 20 is movable about a second axis 43 which is transverse to the axis 40 of the first pivot. Referring also to FIGS. 2 50 and 3, the channel 32 is mounted to and depends downwardly from a hinge plate 42. A pair of flanges 42a (shown best in FIGS. 3 and 4) depend downwardly from opposite sides of the hinge support plate 42. The flanges defined aligned apertures 46 which defined the 55 transverse pivot axis 43 for the printhead 20. The hinge support plate is mounted between print unit end plates 48,50 which include aligned apertures. The end plate 50 is shown partially in phantom in FIG. 1 only. The position of the endplate aperture aligned with the associated 60 aperture 46 in the flange 42a is indicated by the reference character 54 in FIG. 1 only. The aperture in the endplate 48 is not shown.

The hinge support plate is pivotally supported between the end plates 48, 50 by a shaft 56 which extends 65 through the apertures 46, 54. The shaft 56 is easily removed from the print apparatus to release and dismount the hinge support plate 42 from the print mechanism

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enabling the printhead 20 to be easily removed and serviced.

The printhead 20 is resiliently biased towards contact with the platen roller 22 by a tension spring 58 which acts between the hinge plate 42 and the print mechanism frame. In particular, a downwardly extending post 60 is fastened to the underside of the hinge plate 42. An arm 70 extends rightwardly (as viewed in Figures 1 and 2) from the base of the post and defines a cam follower for a cam 72. The tension spring 58 extends from the end of the arm 70 to a pin-like element 74 or screw fastened to the end plate 50. The cam 72 is eccentrically fixed to a shaft 76 by a set screw 77. One end of the shaft 76 is attached to an operating handle 80 (shown in FIG. 1 only). Rotation of the operating handle 80 rotates the cam. The cam includes a high point or lobe 72a. When the lobe 72a contacts the arm 70, the arm 70 is driven downwardly causing the hinge plate 42 to rotate clockwise about the axis 43, raising the printhead 20 with respect to the platen roller 22. The printhead is normally raised in order to facilitate loading of the print medium through the print mechanism, i.e., to enable the print medium to be threaded between the printhead 20 and the platen roller 22. After the print medium is loaded, the operating handle 80 is reverse rotated enabling the spring 58 to raise the arm 70 thus pivoting the hinge plate 42 counterclockwise and moving the printhead 20 into contact with the print medium 16 located between itself and the platen roller 22. The spring 58 applies a resilient bias so that the printhead is urged into contact by a predetermined force determined by the spring tension. It should be noted here, that as the printhead 20 is lowered, the pivot 38 allows the printhead 20 to rock (about the axis 40) in order to provide a uniform contact force across the print line 24.

In accordance with a feature of the invention, the position of the printhead 20 relative to the platen roller 22 is monitored by a sensor which in the illustrated embodiment comprises a switch 100 (shown in FIGS. 1 and 5). The switch is mounted to the end plate 50 and includes a switch arm 100a which may include a roller 104. A cam 110 associated with the switch is rotatable with the printhead separation cam 72 described above. In the illustrated embodiment, both cams 72, 110 are secured to the shaft 76 such that rotation of the operating lever 80 produces concurrent rotation of both cams. The purpose of the switch is to deactivate the printhead 20 when it is not in contact with the print medium. When the printhead 20 is of the thermal variety, it is imperative that it not be energized unless it is in contact with the print medium. When the printhead 20 is not in contact with the print medium, the energy generated by the printing elements in the printhead will not dissipate. This undissipated energy could damage the printhead.

In accordance with this feature, the cams 72, 110 are designed and selected such that the sensor 100 deactivates or disables the printhead 20 prior to any movement in the head 20 away from the platen roller 22. In the illustrated embodiment, this is achieved by advancing the cam 110 so that when the operating lever 80 is rotated, the sensor cam 110 moves the switch arm 100a prior to the head separating cam 72 producing movement in the printhead arm 70. Although various methods for achieving this relationship can be used, in the illustrated embodiment the sensor cam is "advanced" with respect to the separation cam, so that its high point (indicated by the reference character 112) immediately actuates the switch 100 when the lever 80 is rotated 7

clockwise. The separation cam 72 does not produce any substantial movement in the printhead 20 until the operating lever 80 is rotated further.

Returning to FIGS. 1 and 2, the print unit 10 can imprint or image a variety of print medium 16 including 5 paper tape and adhesive labels carried on a continuous backing or carrier strip. When adhesive labels are being imprinted, the print mechanism 10 can be operated in two different modes. In one mode, the label and associated carrier are conveyed past the printhead 20 and 10 both travel along a path indicated by the reference character 200, i.e., in a plane substantially tangent to the Printline 24. In this so-called "batch" mode, the label remains fixed to the carrier as it is discharged from the print station. ^

In a second mode of operation, the printhead 20 automatically strips a backing 16' from the label as the label leaves the print station. In the strip mode, the label proceeds along substantially the same path 200 as previously described for the batch mode, while the backing 20 material 16' is partially "wrapped" around the stripper plate 210, the platen roller 22, and the stripper assist bar 220, and wound onto the take up spool 206. Unlike the prior art, however, separate gripper rollers are not 25 needed to strip the backing from the label. According to this embodiment of the invention, the platen roller 22 is used to provide the requisite driving or pulling force for the backing material.

The stripping mechanism includes a stripper plate 210 3Q which is positioned immediately downstream of the print line 24. The stripper plate is parallel and is located in close proximity to the platen roller 22. When the backing is to be stripped from the label, the backing material 16' is fed over the stripper bar and around the 35 lower periphery of the platen roller 22 as indicated by the reference character 202. In order to urge the material 16' into contact with the lower region of the roller, a stripper assist bar 220 is located next to and spaced slightly from the platen roller 22. In the preferred and 40 illustrated embodiment the stripper assist bar parallels the axis 41 of the roller 22. Preferably, the axis of the stripper assist bar is located at a point that is greater than 180° but less than 300° from the print line as measured in the direction of rotation of the platen roller. 45 With this arrangement, the backing material is in frictional contact with at least a 90° portion of the lower periphery of the platen roller 22 and indicated by the angle 'A'. Since the platen roller 22 is normally driven (in order to drive the print medium past the printhead 50 20, the backing material itself is pulled due to the frictional contact between itself and the lower region of the platen roller.

The stripping operation operates as follows: the label leaving the print station, tends to follow the path indi- 55 cated by the reference character 200. The carrier on the other hand, diverges sharply from this plan as it is fed downwardly over the stripper bar. To further facilitate separation of the backing material from the label, a relatively sharp but rounded, well defined corner 210a 60 is provided at the left edge of the stripper plate 210. The backing material then re-engages the periphery of the roller 22, the arc of contact (angle 'A') being greater than 90°. This contact provides the necessary pulling force on the backing to cause separation from the label. 65 The carrier is then wound onto the take up reel 206. With the disclosed embodiment, the drive for the take up spool is not relied on to produce the required pulling

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force on the backing nor is a separate drive roller necessary.

In order to facilitate loading of the print mechanism when used in this mode, the stripper assist bar 220 is supported by a frame that is pivotally mounted for movement between a loading and a retracted position. In the retracted position, the stripper assist bar 220 is spaced from the platen roller 22. The assembly comprises a pair of parallel arms 224 (only one is shown), the upper ends of which, support the stripper assist bar 220. The lower ends are pivotally mounted to the end plate 48 and a supplemental endplate 225 (a portion of which is shown in phantom in FIG. 2). The supplemental endplate is supported by posts 227a, 2276, 229. The supplemental endplate 225 may be integrally formed with the endplate 50. The frame is rotatable about a pivot axis 230. A locking arrangement including a spring loaded pin 232 is provided to lock the stripper assist bar in its operative position versus the edge 233 of the plate 225.

The mounting of the stripper assist bar allows it to be dropped to a lower position until the carrier is fed between the platen roller 22 and the stripper bar assembly and onto the take up reel. Once threading has been completed, the stripper bar is rotated counterclockwise and locks into the position shown in FIGS. 1 and 2. The pin 232 is engageable with an edge 233 of a locking plate 234 forming part of the supplemental endplate 225.

According to another feature of the invention, an easily adjustable guide 240 is provided immediately upstream of the platen roller 22. Referring in particular to FIG. 6, in the preferred embodiment, the guide 240 comprises the post or shaft 229 mounted between the end plates 48, 225. The shaft mounts a fixed collar 244 on one end, a side surface 244a of which defines a guide surface for the print medium 16. A movable collar 246 is movable along the shaft 229 and also defines a side surface 246a that defines a guide surface for the other side of the print medium.

In the preferred arrangement a plurality of grooves 248 are formed in the shaft 229 which correspond to commonly used print medium widths. A single detent spring coil 249 forming part of the movable guide 246 is engageable with the grooves 248 so that the guide 246 can be easily positioned to define a guideway 250 for the print medium being loaded or changed. As a result, changing print medium sizes is easily accomplished.

This feature in connection with the printhead raising mechanism allows the operator to change the print medium quickly and without substantial machine down time. Changing the size of the print medium does not require readjustment of either the printhead contact pressure or manual adjustments in the feed path.

As indicated above, the printhead 20 must maintain uniform contact with the print medium 16. The floating relationship provided by the pivotal mounting of the printhead 20 allows the printhead to compensate for misalignment between itself and the platen roller or changes in print medium thickness. The disclosed printing mechanism is capable of high quality printing and is especially useful for printing bar code information. Moreover, the mechanism itself is easily maintained and inexpensive to build. The stripping feature is accomplished with less parts than in many prior art devices and therefore reduces the overall cost of the print apparatus.

Although the invention has been disclosed with a certain degree of particularity, it should be understood