Printer having printhead angulator assembly

A printer assembly for printing on a supply of media traveling in a media direction. The printer generally includes a platen assembly, a print head assembly and a pivot member. The pivot member provides for pivoting of the print head assembly relative to the platen assembly to adjust for variations in the media as it passes therebetween. Advantageously, the pivot member may be supported directly by the platen assembly, such as by bearing supports of the platen assembly, to reduce positioning error from intervening components. Preferably, the pivot member is positioned upstream of the print head assembly. Also, a pair of pivot members may each be supported at the ends of an angulation arm which is coupled to the print head assembly for angulation in the media direction but is uncoupled in the cross-media direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to printers and more particularly print head assemblies of printers.

2. Description of Related Art

Controlling printing quality often requires proper, accurate registration between a print head and the underlying printer media. Such registration can be difficult to maintain with variations in printer media, including the thickness of the printer ribbon and printer label or paper stock.

A conventional printer10, such as shown inFIGS. 1 and 2, typically includes a printer frame11supporting a media supply12, a ribbon supply13, a platen assembly17and a print head assembly14. The media supply can include a compartment15of paper, labels or other media, that is in a positioned generally above and upstream (with respect to movement of the media) of the print head assembly14. The ribbon supply13includes a supply spool24that supplies a printer ribbon extending through the print head assembly14and onto a takeup spool16. Both of the spools14,24are rotatably supported by the printer frame11. The platen assembly17includes a platen roller18that is rotatably supported by the printer frame11subjacent the print head assembly14.

As shown inFIG. 2, the print head assembly14of the conventional printer10includes a print head ceramic base19, an aluminum heat sink20and a pressure spring21. The ceramic base19includes a print line which is a heating element that is selectively heated to pass ink from a ribbon or to directly thermal print onto the paper, label or other printable media. Supporting the print head ceramic base19is the heat sink20which itself is supported by a bracket22. Ends of the bracket are rotatably supported by the printer frame11, thereby allowing rotation of the heat sink20and the print head ceramic base19relative to the platen roller18.

The print head assembly14of the conventional printer10also includes the pressure spring21that has a V-shape, as shown inFIGS. 1 and 2. The ends of the V-shape are supported by the printer frame11proximate ends of the rotatably supported bracket22and the pressure spring21extends downward onto a middle line of the bracket. In particular, the center of the V-shape has a line of contact due to the spring21being constructed of a ribbon of sheet metal that exerts a torque to control angulation as well as a downward bias on the bracket22. These biases help to maintain contact of the ceramic base19and its print line with the ribbon and printer media passing between it and the platen roller18.

Although helping the ceramic base19to maintain contact with the printer media and platen roller18, the V-shaped pressure spring can interfere with passage of the media. Also, improvements in the ability of the print head assembly14to track the media are always desired.

Therefore, it would be advantageous to have a printer assembly that provides clearance for passage of media in a printer but still follows the media with accuracy for overall improved printing capability.

DETAILED DESCRIPTION OF THE INVENTION

The above needs are met and other advantages achieved by a printer assembly for printing on a supply of media traveling in a media direction of the present invention. The printer generally includes a platen assembly, a print head assembly and a pivot member. The pivot member provides for pivoting of the print head assembly relative to the platen assembly to adjust for variations in the media as it passes therebetween. Advantageously, the pivot member may be supported directly by the platen assembly, such as by bearing supports of the platen assembly, to reduce positioning error from intervening components. Preferably, the pivot member is positioned upstream of the print head assembly. Also, a pair of pivot members may each be supported at the ends of an angulation arm which is coupled to the print head assembly for angulation in the media direction but is uncoupled in the cross-media direction.

In one embodiment, the present invention includes a printer assembly for printing on a supply of media traveling in a media direction. The print head assembly includes a platen assembly configured to support the media. A print head assembly including a print line configured to print on the media as it passes between the print line and the platen. A biasing device of the printer assembly is configured to bias the print head assembly against the media supported by the platen. At least one pivot member is coupled to the print head assembly and pivotally supported relative to the print assembly. In this manner, the print line pivots about the pivot member in the media direction as the media travels between the print head assembly and the platen so as to adjust to variations in the media.

The pivot member may be supported directly by the platen assembly. For example, the print head assembly may be elongated and have a pair of opposite ends each supporting one of the pivot members. A pair of bearing supports rotatably support ends of the platen wherein each of the pivot members is supported by a respective one of the bearing supports. In this manner, the platen is configured to rotate on an axis and the pivot members are supported by a surface fixed relative to the axis.

In another aspect, the pivot members may be supported at ends of an angulation arm and the angulation arm is coupled to the print head assembly for pivoting in the media direction, but is uncoupled with respect to pivoting of the print head assembly across the media direction. For example, the angulation arm may have a coupling positioned midway between its ends that couples it to the print head assembly. The coupling may be a single post extending generally in the media direction from the angulation arm into an opening defined in the print head assembly, or vice versa. This allows the print head to follow the media in the cross-media direction.

The pivot member preferably defines a pivot surface approximating a point. For example, the pivot member may include a cone with a pointed free end defining a pivot surface. These cone pivot members can be supported at the ends of the angulation arm.

Portions of a printer30of one embodiment of the present invention are shown inFIG. 3. The printer30includes, generally, a media supply31, a ribbon supply32, a platen assembly33and a print head assembly34. As will be described below, the print head assembly34includes a pair of pivot points35that accurately facilitate angulation of a print line relative to the media and platen assembly33.

It should be noted that although the illustrated printer30prints using a ribbon and thermal print head, the invention could be useful in any type of printer wherein a printer head needs to follow printer media, such as thermal transfer printing or a direct thermal printing on heat-sensitive media.

The media supply31, as shown inFIG. 3, includes a media supply receptacle36that is positioned upstream (relative to media flow) and that is configured to hold media such as a supply of labels, cards or paper. Generally, the media supply receptacle36is accessible upon opening of a lid or cover of the printer30and, for example, can rotatably support a media supply roll. The media extends from the media supply receptacle36toward the print head assembly34. It should be noted that the media supply31of the printer30of the present invention can be varied widely with the type of media, how the media is stored and how it is supplied and still be within the purview of the present invention. It should be noted that the present invention may be especially advantageously employed, however, for media that has varying thicknesses or inconsistencies such as label stock with embedded RFID tags.

The ribbon supply32includes a ribbon supply frame37, a ribbon supply spool38, a ribbon take-up spool39and a ribbon guide structure40. The ribbon supply frame37includes two spaced walls positioned on opposite sides of the media supply path. Generally, each of the spaced walls includes two lobes41that extend upward away from the media path. A furthest upstream pair of the lobes spaced across the media supply path rotatably support the ribbon supply spool38. Further downstream, and approximately above the print head assembly34, a second spaced pair of lobes41rotatably supports the ribbon take-up spool39.

Also supported by the ribbon supply frame37is the ribbon guide structure40which extends between the walls of the supply frame and has an edge positioned downstream and adjacent the ribbon take-up spool39, as shown inFIG. 3. This edge helps the guide structure guide a ribbon passing onto the ribbon take-up spool39. Generally, the ribbon guide structure40can be shaped and positioned as desired, such as at turns in the ribbon path, to ensure protected flow of the ribbon from the ribbon supply spool38to the ribbon take-up spool39. Extending downward toward the media feed path from the ribbon guide structure40are a plurality of spring compression members58that have generally rectangular shapes and interact with the print head assembly34as described below.

Parts of the ribbon supply frame37could also be considered to be ribbon guide structure40and vice versa. Regardless, it should be noted that the ribbon supply32could have different configurations for supplying ribbon, or not be present at all where a ribbon supply is not required, and still be within the purview of the present invention. Further, the ribbon supply32might even include thermal transfer ribbon supply features when the print head assembly of the present invention is used in a thermal transfer printer.

The platen assembly33, as shown inFIG. 3, is positioned below the print head assembly34on the other side of the ribbon and printer media path. The platen assembly includes a platen roller42and a pair of bearing supports43, as shown inFIGS. 4,5and6. The platen roller42has a support portion45with cylindrical shape that extends cross the media travel path and subjacent the print head assembly34so as to support the printer media and ribbon media therefore.

The support portion45preferably has an outer surface configured to grip and move the printer media past the print head assembly34. A shaft44of the platen roller42has a relatively smaller cylindrical diameter than the support portion45and extends from ends of the support portion. The ends of the shaft44extend through the pair of bearing supports43and into a lower frame46of the printer30where they are rotatably mounted, as shown inFIG. 3. One of the ends of the shaft44typically includes a gear that is driven by a motor assembly to advance the media past the print head assembly34.

Each of the bearing supports43, which may also be considered part of the print head assembly34, have an overall semicircular disc shape defining a central opening47, a heat sink support surface48, a pivot support surface49, a downstream notch50and a frame snap51.

The central opening47allows passage of the shaft44of the platen roller42therethrough and into the lower frame46of the printer30. In addition, the central opening47may also be configured to receive a bearing for rotatably supporting the shaft44. The bearing supports, as shown inFIG. 3, are positioned in notches defined in the lower frame46wherein the ends of the shaft44extend away from the support portion45of the platen roller42, through openings defined in the lower frame46and into the central opening47in each of the bearing supports43.

The frame snap51is positioned upstream and defines a notch configured to grip a portion of the lower frame46of the printer30. This connection inhibits rotational motion of the bearing supports43with respect to the lower frame46. In addition, the frame snap51is positioned at the end of an arc-shaped arm that is free to flex under the forces of the passing media and movement of the platen roller42. This facilitates the angulation of the print head54during printing.

The heat sink support surface48is defined by a flange positioned downstream and extending from a top edge of the bearing supports43. This flange extends generally perpendicularly away from the media path and the heat sink support surface48accordingly extends at a right angle to the top edge of the bearing supports43. The pivot support surface49extends parallel to the top edge and generally parallel to the media supply path. A plateau of each of the bearing supports34defines the pivot support surface49at a position upstream of the heat sink support surface48.

As will be shown below, the bearing supports43, and their respective heat sink and pivot support surfaces48,49provide direct or near-direct reference points for the angulation of the print head. This is in contrast to conventional printers in which the angulation of the print head relative to the platen is controlled by several components, or there are several intervening components (e.g., V-shaped pressure spring21, heat sink20, bracket22and printer frame11) between it and the platen.

The print head assembly34includes a spring housing52, a heat sink53, a print head54and an angulation arm55, as shown inFIGS. 3-6. The spring housing has an elongate rectangular shape and extends across the media feed path so that its ends are over the bearing supports43. Defined along the length of the spring housing52are a plurality of spring receptacles56. The spring receptacles56have top openings extending away from the media feed path wherein each of the spring receptacles is configured to receive one of a plurality of coil springs57, as shown inFIG. 5. In addition, the spring receptacles56are spaced and shaped to correspond to the rectangular spring compression members58which extend into the receptacles from the ribbon guide structure40fixed to the printer frame. In this manner, a downward bias is exerted on the print head assembly34to help it to follow the surface of the media as it passes thereunder.

Although there are five springs57in the illustrated embodiment, this number may vary, such as by using more springs for a greater cumulative bias, or allowing the use of lesser-biased springs, or less springs for less bias. The use of coil springs is advantageous in that they are generally more cost effective than other springs, such as the V-shaped spring23, but other types of springs could also be employed, such as leaf springs, as long as some bias is imparted on the print head54in the direction of the printer media. The use of less expensive springs is facilitated by the pivoting action of the print head assembly34of the present invention which does not require any precisely defined spring behavior to cause angulation.

The spring housing52also includes a post59that ends in a flange60. The post has a cylindrical shape and extends upstream, generally parallel with the path of the media and from a center position on the spring housing52. The post59provides a rotatable mounting for the angulation arm55, as shown inFIGS. 4 and 5. The flange60at the end of the post59holds the angulation arm55on the post59by abutting an upstream surface of the angulation arm55. This mounting uncouples movement of the angulation arm55and the spring housing52across the media path but, due to the orientation of the post59and the flange60, couples rotation or tilt in the direction of the media. Generally, the cross media direction rotation is controlled by the bias of the coil springs57and contact with the platen44which provides the most direct feedback on side-to-side positioning.

The heat sink53also extends across the media path to the top edges of the two bearing supports43. The heat sink53is preferably constructed by extrusion and has various structures that advantageously eliminate the need for an intervening bracket between the print head54and the media and platen assembly33. The illustrated heat sink53, for example, includes a base wall61, an upstream wall62, a downstream wall63and a bull nose64that all extend continuously along its length, due to its extruded manufacture. Notably, however, the heat sink53could also be constructed using other methods and still have similar structural characteristics. Preferably, the heat sink is made of a metal or other material that conducts heat away from the print head54and this function is facilitated by the aforementioned wall structure.

The base wall61is planar and extends (except for the tilt when following the media) generally parallel to and in the direction of media flow. The base wall61has an upstream free edge and downstream supports the upstream wall62and downstream wall63that extend perpendicularly therefrom. The walls62,63are spaced apart so as to provide a slot for holding the spring housing52therebetween. In this manner, the spring housing52and the heat sink53are fixed with respect to each other. Extending from the intersection of the downstream wall63and the base wall61is the bull nose64.

The bull nose64, as shown inFIG. 6, has a rounded cross-section and is positioned proximate the media path and the underlying platen roller42. In addition, the bull nose64is configured to extend up and along the heat sink support surface48on the bearing supports43due to the tilt of the print head assembly34and the pressure of the media moving, via rotation of the platen roller42, in the media direction under the print head assembly. The shape of the bull nose64eases the passage of ribbon media over itself and onto the ribbon take-up spool39.

The print head54is positioned at the media interface of the outside surface of the base wall61. The print head includes a burn line that extends across the media path and is controlled and energized by a multiple pin connector65that extends along the base wall61and past the free edge of the base wall in the upstream direction as shown inFIG. 4. The connector is in turn connected to a controller and power supply that enables selective heating of the burn line and printing on the passing media. It should be noted that although a linear, thermal print head54is shown, the present invention may be used with any of a range of print heads, such as ink-jet print heads, wherein the positioning of the print head and its ability to follow the media is important for print quality.

The angulation arm55includes a crossbar66, a pair of legs67and a post grip68, as shown inFIG. 7. The crossbar66extends approximately the width of the media path and supports the legs67at its ends, wherein each of the legs extends in the direction of a respective one of the bearing supports43. The post grip68is defined at the center of the crossbar and includes an opening sized to snap-fit around, but allow rotation relative to, the post59of the spring housing52. As described above, this connection and motion uncouples rotation of the spring housing52and the angulation arm55across the media path.

One of a pair of pivot points35is supported by the end of each of the legs67. The term “pivot point” as used herein refers to a relatively small-area which supports pivoting of the print head assembly34relative to the platen assembly33. For example, as shown inFIG. 6, the pivot points are at the ends of a pair of conical shaped members that come to a point at their free ends. These pivot points35are configured to rest on the pivot support surface49of each of the bearing supports43. They are free to slide and pivot with respect to the bearing supports43as the downstream print head54follows the varying thickness of ribbon and printer media between it and the platen roller42. Advantageously, the common, singular part reference of the bearing supports43and the pivot support surface49reduces the tolerance stack up associated with multiple intervening parts between the print head54and the platen roller42.

During operation of the printer30, the media, such as label or card stock, is dispensed from the media supply receptacle36downstream toward the platen assembly33and the print head assembly34. At the same time, the ribbon media extends off of the ribbon supply spool38toward the platen assembly33and the print head assembly34. The printer ribbon extends over bull nose64of the heat sink53and over the burn line of the print head54and onto the ribbon take-up spool39. The printer media extends over the outer surface of the support portion45of the platen roller42and is urged downstream by the driving of the platen roller. Variations in the printer media and ribbon media urge the print head54, heat sink53and spring housing52toward the spring compression members58, thereby compressing the springs57and angling the print head54to rotate about the pivot points35. The pivot points35tilt and/or slip against the pivot support surface49of the bearing supports43, thereby controlling the amount of tilt with respect to the platen roller42. Thus, a torque resisting the tilt and causing the print head54to follow the media surface is generated and without the use of an expensive custom spring.

In another embodiment, the present invention includes a variation in the bearing supports43, as shown inFIGS. 8,9and10. This embodiment lacks the upper edge of the initially illustrated embodiment but still includes the central opening47, heat sink support surface48and the pivot support surface49.

The present invention has many advantages. The use of the print head locating features, such as the heat sink support surface48and the pivot support surface49, reduces tolerance stack up when compared to conventional printers. The springs need not generate a torque or precise placement and therefore can be less expensive coil springs. The extruded heat sink53has components such as the bull nose64and base wall61supporting the print head54directly, that improves precision location of the print head54and eliminates an intervening bracket.