Technical Field

The present invention relates to thermal printers. More particularly, the present invention relates to printers which utilize a thermal transfer ribbon for effecting printing on record media by transfer of thermal material initiated from heating of printing elements on the thermal print head.

Background Art

In the field of thermal printers/ a print head having a plurality of printing elements is positioned adjacent paper or like record media and the printing elements are heated to an elevated temperature sufficient for effecting printing of characters on the paper. Printing is effected by transferring material in the form of ink from a thermal transfer ribbon, upon heating of the printing elements, onto the paper. The heating of the printing elements which are in contact with the thermal transfer ribbon during the actual printing operation cause the ribbon to be partially fused or bonded with the paper and to interfere with the freedom of advancement of the paper and the ribbon in a subsequent printing operation. It is therefore necessary to separate or strip the ribbon from the paper after each printing operation in one or another direction.

In the case of a thermal transfer printer which utilizes a thermal print head having a plurality of printing elements disposed in both horizontal and vertical directions on the print head substrate, stripping or separating the ribbon from the paper is possible only after printing one complete line of characters, rather than after each dot row, or after printing several characters. In the case of a thermal

printer which utilizes a print head having a plurality of printing elements disposed in a vertical or aligned direction on the print head substrate, stripping of the ribbon from the paper is possible only after printing a complete line of characters due mainly to the closeness of the printed dots making up the character.

The print head is shuttled or moved in transverse direction with each set of vertical elements printing on integral number of characters to complete the print line. In the case of a print head having five banks or sets of print elements, each bank or set prints eight characters for a total of up to 40 characters along a print line. After printing of a line of characters is completed, the ribbon must be stripped from the paper prior to printing the next line. It is noted that the ribbon is oriented in a generally horizontal direction while the paper is oriented and displaced in a vertical direction.

Various ways have been proposed for effecting separation of a ribbon from the paper after printing. Thus, for example, U.S. Patent No. 4,396,308 discloses an arrangement in which the ribbon is pulled away from the paper after printing. U.S. Patent No. 4,458,253 discloses a thermal printing apparatus in which a ribbon is movable relative to the paper by an eccentric to move the ribbon into and out of contact with the paper.

U.S. Patent No. 4,509,060 discloses a thf-rmal transfer system in which an ink sheet is separated from a record sheet after printing by a separator member which pierces the ink sheet and pushes the underlying recording sheet away from the ink sheet. In a prior art arrangement referred to in this patent a stationary pawl or like separating member is positioned between the ink sheet and the paper and is effective in forcibly separating the ink

sheet from the paper as the two are moved together in one direction.

If the principle of a stationary separating member were applied to a thermal printer in which a ribbon is moved in one direction, usually in a horizontal direction, and the paper is moved in another direction, perpendicular thereto, the paper would have to be over-indexed to achieve separation and then retracted to accept printing of the next line. Such arrangement would disadvantageously effect the speed of printing.

Disclosure of the Invention

It is an object of the present invention to provide a thermal printer which operates in compact areas, operates at higher speeds and in which separation is effected in an assured manner.

Thus, according to the invention, there is provided a thermal printer having a print head operably associated with a transfer medium for transferring images in the form of a line of printing onto a record medium in a printing operation, said printer including separating means for separating the transfer medium from the record medium subsequent to a printing operation, characterized in that said separating means include a stripping member positioned prior to the printing operation in a first position between portions of said transfer medium and said record medium spaced from said line of printing, and characterized by actuating means operable, following a printing operation, to move said stripping member from said first position to a second position so as to separate said transfer medium from said record medium in the region of said line of printing, and thereafter return said stripping member to said first position prior to a further printing operation.

Stripping or separating the thermal transfer ribbon from the paper may be accomplished according to the invention by different arrangements and means. A stripper blade may be mounted to one of several parts of the printer and then actuated to separate the ribbon from the paper after printing. The blade may be of stainless steel material and include a beveled edge for effecting the separating or stripping action. The blade may be of plastics materials, such as Mylar (Registered Trade Mark) .

An advantage of a Mylar blade is realized by reason of the inherent characteristics of the material to exhibit certain static electric properties which are created when the ribbon and the paper are moved relative to the blade. Since a thermal transfer ribbon provides very little structural rigidity due to the material utilized and to the ribbon thickness, support of the ribbon in the vertical direction is advantageous in that ribbon buckling and curline are minimized. The static properties of the Mylar material of the blade serve to aid in the support of the ribbon in its positioning past the printing station.

Another arrangement uses a wire which is mounted to the printer and is interposed between the ribbon and paper. Such wire arrangements may take the form of a preferomed wire, as a leaf spring, the form of a wire material that assumes an arc or curve when the actuation force is reversed, or the form of a wire that takes advantage of the motion of the paper to aid in returning the wire to its arcuate position. In certain of the separating or stripping arrangements, the paper is usually moved upward a great distance than the height of one print line in order to create blank space between print lines. The additional paper movement, -after completion of the stripping action, can aid in repositioning of the wire.

A preferred arrangement of separating or stripping mechanism includes the use of a formed stripper blade which is attached to the print head carriage. A small formed metal blade is secured to the stripper blade and is designed to have a spring or like resilient characteristic to aid in separating or stripping the ribbon from the paper. This means for actuating the stripper blade includes a cam arrangement that is coupled with the print head carriage drive mechanism so as to have the actions synchronized during the printing operation.

Brief Description of the Drawing

Embodiment of the present invention will now be described, with reference to the accompanying drawings, in which:

Figs. 1A and IB are face views of types of thermal print heads showing banks of printing elements and wherein separation of the ribbon from the paper is an essential operation;

Figs. 2A-2D show successive steps in one arrangement of ribbon separation which uses a beveled blade;

Figs. 3A and 3B show the two steps in an arrangement using a separation or stripping wire;

Fig. 4 is a perspective view of an arrangement for actuating a separating or stripping wire;

Figs. 5A and 5B are a perspective view and a side view of another arrangement for actuating a separating or stripping wire;

Fig. 6 is a perspective view of a portion of a printer incorporating ribbon stripping mechanism;

Fig. 7 is a perspective view of a portion of a printer incorporating another type of ribbon stripping mechanism;

Fig. 8A is a diagrammatic view of a ribbon stripper blade associated with a print head as generally configured and as shown in Fig. IB;

Fig. 8B is a side view of a portion of a printer showing a preferred arrangement of the ribbon stripping mechanism;

Figs. 9A and 9B show front and side elevational views of a preferred ribbon stripping member;

Fig. 10A shows another arrangement of means for actuating the ribbon stripping mechanism;

Fig. 10B shows a profile of a cam for use in the mechanism of Fig. 10A;

Fig. IOC shows a detail of the ribbon stripping actuating member in Fig. 10A; and

Figs. 11A and 11B show a perspective view and a side elevational view of another arrangement of the ribbon separating mechanism.

Best Mode for Carrying Out the Invention

Referring now to Figs. 1A and IB there are illustrated face views of two print heads of the types commonly used in thermal printing operation. The print head in Fig. 1A includes a substrate 52 which has five banks, overall indicated as 54, of print elements 56, with each bank 54A, 54B, 54C, 54D and 54E containing seven print elements. The printing speed with such an arrangement is increased by increasing the number of print elements 56 on the substrate 52 thereby increasing the speed by a factor of several times and still maintaining a relatively low cost print head. The five banks (54A-54E) of print elements 56 are arranged and fabricated on one substrate material, and for a thick film type thermal print head which predominantly uses silk screen processes for fabrication, the number of print elements can be increased, say to the 35 shown.

without incurring substantial increases in print head cost. The thermal print elements 56 are connected by respective conductor runs 55 to connector pads (not shown) . A common conductor 57 is provided to complete the circuitry for the print elements 56.

Fig. IB is a different arrangement of a print head having a substrate 58 which has five banks, overall indicated as 60, of print elements 62, with each bank 60A, 60B, 60C, 60D and 60E containing seven print elements in aligned vertical manner. The vertical alignment of the seven print elements 62 provides for printing a seven high dot matrix character in each pass of the print head in the printing operation. The thermal print elements 62 are connected by respective conductor runs 64 to connector pads (not shown). A common conductor run 66 is provided to complete the circuitry for each print element 62.

In the case of a thermal transfer printer utilizing a thermal print head having a plurality of print elements disposed both horizontally and vertically on a substrate, as shown in Fig. 1A, stripping of the ribbon from the paper is possible only after printing one complete line oof characters, rather than after printing each dot row or after printing several characters. In this case, the print head is shuttled or moved about one-half inch in the transverse direction, with each set of vertical print elements printing an integral number of characters to complete the print line. For example, each of the five banks of print elements prints eight characters, for a total of up to 40 characters in the print line. Affter printing, a complete stripping of the ribbon from the paper is required before the succeeding line can be printed. It is noted that the ribbon is horizontally oriented while the paper is oriented and is displaced in the vertical direction. In order to

print the subsequent line, the used ribbon must be taken up or indexed out of the printing position and new ribbon must be positioned over the next print line location.

Figs. 2A-2D illustrate, in diagrammatic form, the successive steps in an arrangement in which the ribbon is separated from the paper in a thermal printer by a stationary stripping member. The several figures show a platen 70, paper 72 positioned against the face of the platen, a ribbon 74 disposed against the paper, and a print head 76 positioned in printing and non-printing positions and supported from a carriage 78. A stripper blade 80 is positioned and interposed between the ribbon 74 and the paper 72 for separating the ribbon therefrom after the printing operation. The stripper blade 80 has a beveled tip 82 for precise separation of the ribbon 74 from the paper 72. The stripper blade may be attached, for example, to the front of the ribbon cassette.

Fig. 2A shows the arrangement of the parts in the printing position wherein the platen gap is closed and wherein the lower edge 84 of the ribbon 74 is about level with the lower side 86 of the platen 70. Fig.. 2B shows the parts in a non-printing position wherein the platen gap is open and the ribbon 74 and the paper 72 are being advanced upwardly in the direction of the arrows 88 and 90, and as clearly shown by the position of the lower edge 84 of the ribbon 74. During such upward movement, the ribbon 74 and the paper 72 encounter the beveled edge 82 of the stripper blade 80 which separates the ribbon from the paper. Fig. 2C shows the ribbon 74 moving downwardly in the direction of the arrow 92 and returning to the printing position as the ribbon is being indexed in a horizontal direction. In this manner, the ribbon is moved and indexed so that new ribbon is in position for the next line of printing, as illustrated in Fig.

2D. It is seen that due to the relative position of the print elements, as 56 and 62 (Figs. 1A and IB), the stripper blade 80 must be positioned in proximity to the uppermost dots of each printed character, but not interfere with printing thereof. Therefore, the blade thickness must be held at a minimum, however consistent with the required stiffness and structural integrity.

It should be clear that in this arrangement the paper must be over-indexed or moved vertically upwards a distance ensuring complete separation of the ribbon from the paper, and then retracted downwards, while the ribbon 74 is being indexed generally in the horizontal direction.

Figs. 3A and 3B illustrate an embodiment according to the invention showing a printer including the platen 70, the paper 72 positioned against the face of the platen, the ribbon 74 disposed against the paper, and the print head 76 positioned in printing and non-printing positions and supported by the carriage 78. In this embodiment, the ribbon stripping device is a wire 98 of a diameter of approximately 0.127 mm. The wire 98 may be secured at one end thereof to a side of the ribbon cassette or to a side frame of the printer and the other end may be connected to actuating mechanism, later described. The wire 98 forms an arc above the zone or area of printing during the printing cycle. After the printing cycle or during non-printing operations, the wire 98 is pulled taut by mechanical actuating mechanism to straighten the wire toward a horizontal position and to effect separation of the ribbon 74 from the paper 72. The action of the actuating mechanism, combined with the upward motion of the ribbon 74 and of the paper 72, in the direction of the arrows 88, 90, as the paper is indexed to the next position for a printing cycle, strips the ribbon 74

from the paper 72. After the stripping operation, the mechanical actuating mechanism releases the tension on the wire 98, thereby permitting it to return to the unstrained or arcuate position.

It is within the scope of the present invention to use several wire configurations for effecting separating or stripping of the ribbon 74 from the paper 72. A first arrangement uses a preformed or preset wire, similar in shape to a leaf spring, and wherein the wire returns to its unstrained position when not actuated or worked. A second arrangement may use a wire of an appropriate material that forms the arcuate shape when the actuation force is reversed to provide a stripping action similar to that accomplished in the first wire arrangement. A third arrangement, with the wire stripper, takes advantage of the motion of the paper (upward) to aid in returning the wire to its arcuate form and position. In the latter case, the paper is moved upwardly a greater distance than the height of one print line (generally about 28-30 percent greater) in order to create blank space between print lines, such additional paper movement, after stripping of the ribbon from the paper, being an aid in the repositioning of the wire to its arcuate form.

Fig. 4 shows mechanical actuating apparatus for causing a wire 100 to be moved in the manner of straightening thereof for stripping the ribbon from the paper. In this arrangement, the wire 100 is preformed and is attached at one end 102 to a left side frame 104 of the printer and extends through an opening 106 in a right side frame 108 and is connected to an actuating lever 110 pivoted on a pin 112. A solenoid 114 is actuated to move the plunger 116 thereof in the direction of the arrow 118 to cause pivoting or swinging of the lever 110 on the pin 112 and to move the lever 110 and the wire 100 to the

respective phantom-line positions. In this manner, the preformed wire 100 is straightened into a tensioned condition to effect stripping of the ribbon from the paper in a simultaneous motion of wire and paper movement. It is seen that the wire 100 in a tensioned or taut condition is adjacent an upper edge 120 of a print head 122 and the wire is above the edge 120 when in an arcuate position which allows movement of the print head during the printing cycle.

Figs. 5A and 5B are a perspective view and a side elevational view, partly in section, of actuating apparatus for a stripping wire 152, the wire being secured at the ends thereof to a right hand swingable member 154 and a left hand swingable member 156. The members 154 and 156 are connected at respective ends 162 and 164 thereof by means of a rod 158 and are suitably supported on a pivot line 160. A solenoid 166 includes a plunger 168 which is coupled in suitable manner to one end 162 of the swingable member 154 and, upon actuation of such solenoid, causes swinging of the stripping mechanism.

Fig. 5B shows the platen 70, the paper 72 positioned against the paper, and the print head 76 positioned in non-printing position and supported by the carriage 78. The ribbon 74 and the paper 72 are shown moving in the direction of the arrows 88 and 90 while the member 156 is being swung in a counterclock¬ wise direction, as indicated by the arrow 170, upon movement of the plunger 168 of solenoid 166 in the direction of the arrow 172. It is seen that this arrangement utilizes a taut wire implementation of the stripping mechanism wherein the wire support members 154 and 156 are actuated by the solenoid 166 as required after printing each line. The wire 152 is displaced in the direction opposite the direction of movement of the ribbon 74 and the paper 72 so that the combined actions occur simultaneously and effect stripping of the ribbon from the paper.

Fig. 6 illustrates another arrangement of ribbon stripping mechanism associated with a portion of a printer 174 that includes a thermal print head 176 supported from and carried by a print head assembly 178. The print head assembly 178 carries and supports both the print head 176 and a flat ribbon¬ like cable 180 for supplying current and heat for thermal printing. The print head 176 includes a substrate which carries a plurality of conductor runs 182 connected to print elements 184. A thermal transfer ribbon 186 is directed in a path past the print head 176 and a ribbon stripping member 188 formed in the shape of an inverted ϋ is suitably supported from and carried by the print head carriage assembly 178.

In this arrangement wherein the structural integrity of the ribbon must be maintained, the ribbon 186 is moved generally horizontally, albeit at an angle of about ten degrees, past the printing station and is indexed in a direction about ninety degrees displaced from the direction of paper movement. In this embodiment of the several elements shown in Fig. 6 and allowing for such ribbon angle of about ten degrees, the ribbon 186 is not indexed the full width of the print line after each printing operation, so that the used portion of the ribbon remains in proximity with the paper for several subsequent print lines after printing each line.

The disclosed stripping technique involves movement of the paper relative to the ribbon wherein during the stripping operation the paper is normally indexed one print line (9 dot rows or 3.43 mm). It has been found in the implementation of the ribbon stripping mechanism that due to the proximity of the stripper blade 190 to the print head 176, the paper indexing distance is not sufficient to produce a complete separation of the ribbon 186 from the paper.

In operation and to ensure complete separation of the ribbon, the paper is over-indexed or moved vertically upward a distance equal to 18 dot rows and then retracted 9 dot rows downward while the ribbon 186 is being indexed generally in the horizontal direction. This arrangement ensures complete separation of ribbon from paper and represents a stripping method that is highly reliable. The operations of stripping and forward paper indexing occur simultaneously and the operations of ribbon indexing and paper retraction (reverse indexing) also occur simultaneously, all during the time available for returning the print head during the non-printing cycle.

In the arrangement of Fig. 6, a combination of the lateral motion of the stripping member 188 which is carried by the print head carriage 178 during the printing and the return cycles in the directions of the arrow 192, together with pivotal motion of the stripping member 188 and of the carriage 178 away from the paper during the return cycle of the print head carriage, and the vertical motion of the paper, effect separation of the ribbon from the paper. Therefore, the stripping action begins as the print head pressure is being released and continues as the blade 190 moves from right to left (return cycle) and as the paper is advanced or indexed upward. In Fig. 6, of course, it is seen that there may be some difficulty or complication when loading and threading the ribbon 186 in the printer.

Fig. 7 illustrates a variation or modification of the Fig. 6 arrangement wherein a portion of the printer 174 includes the print head 176 supported from and carried by the print head carriage assembly 178. The assembly 178 carries and supports both the print head 176 and the ribbon cable 180, the print head including the conductor runs 182 connected to the print elements 184. The ribbon 186 is directed

in an angled path past the print head 176 and a ribbon stripping member 194 is suitably supported from and carried by the carriage 178. The stripping member 194 includes a support arm 196 at each end thereof (only one shown) for attaching to the carriage 178, and such member is formed in the shape of an inverted U in one plane, substantially parallel to the plane of the print head 176. The stripping operation is essentially the same as that described for Fig. 6.

Fig. 8A and 8B show another arrangement of ribbon stripping mechanism supported by a carriage 198 that carries a print head 200 adjacent a ribbon 202 and paper 204. The stripping mechanism 206 is generally V-shaped and shown in more detail in Figs. 9A and 9B. Fig. 8A shows the print head 200 with five banks 208 of print elements as arranged and shown in detail in Fig. IB. The stripping mechanism 206 comprises a top elongated portion 210 and right and left downwardly extending frontal side portions 212 and 214 and formed as a V-shaped configuration with right and left upwardly extending rearward side portions 216 and 218. The side portions 216 and 218 are connected by a lip 220 extending therebetween which is structured in a turned over manner for support of the stripping mechanism 206 on the print head carriage 198. The stripping mechanism 206 includes a stripping element 222 which assumes the shape of an elongated blade having a lower angled portion 224 and attached, as by bonding, to the top portion 210 of the stripping mechanism.

The design and shape of the stripping mechanism 206 permits spring loading the stripping blade 222 so that when the carriage 198. with the print head 200 pivots to open the platen gap or to release the pressure of the print head from the paper, in an arrangement similar to the pivoting motion explained for Figs. 6 and 7, the blade 222 separates the paper

204 by pushing the paper away from the ribbon 202. The V-shaped member 206 is made of 0.3 mm thick stainless steel and the blade 222 is made of 0.05 mm thick stainless steel. The blade 222 effects the initial separation of the ribbon 202 from the paper 204 and the member 206 provides the strength and rigidity for completing the separation.

Figs. 10A, 10B and 10C illustrate another arrangement of ribbon stripping or separating mechanism including a stainless steel inverted U- shaped member 226 having a top blade portion 228 and right and left leg portions 230 and 232. A print head 234 is suitably driven in the directions of the arrow 236 an amount shown by the phantom line 238 for printing along the print line 240. A ribbon 242 is disposed at an angle to the print line 240 and driven therepast in indexing manner, and paper 244 is suitably indexed in a direction normal to the print line 240. The member 226 is guided by frame elements 246 and 248 on the right side and elements 250 and 252 on the left side to be moved in a vertical direction as indicated by arrow 254.

A lower rectangular member 256 has angled slots 258 and 260 disposed near the ends thereof for receiving pins 262 and 264 attached as a part of legs 230 and 232, respectively, and operably sliding along the slots as the member 256 is moved in a side-to-side direction. The member 256 is caused to be moved in such direction by means of camming mechanism comprising a cam member 266 (Fig. 10B) having a groove 268 formed therein for receiving a cam follower in the form of a pin 270 attached to the member 256. The cam member 266 is rotated by suitable means through a shaft 272. While only one groove 268 is shown in the cam member 266, a second groove (not shown) may be included for the purpose of driving the print head 234 in the side-to-side direction. The grooves 258 and

260 are cut at 45 degrees so as to provide a vertical displacement of the member 226 equal to the horizontal displacement of the actuating member 256. If a time of 40 milliseconds is permitted for the ribbon stripping operation, the stripping velocity will be 190 mm per second. A vertical displacement of 7.62 mm is preferred to ensure complete stripping of the ribbon 242 from the paper 244 after each line of printed characters.

In the arrangement wherein the cam member 266 includes the groove 268 and also includes another groove (not shown) for driving the print head 234, the action of the print head and of the ribbon stripper are "locked" together. During the printing cycle of the operation (carriage moving left to right) the follower 270 follows a constant radius portion 274 of the groove 268 and there is no displacement of the stripper member 226. During the return cycle of the operation, the pin 270 is guided into the reduced radius portion 276 of the groove 268 and the actuating member 256 is moved to the right, as indicated by the arrow 278, which causes the pins 262 and 264 to move along the slots 258 and 260 and to displace the stripping member 226 downward to separate the ribbon 242 from the paper 244.

Figs. 11A and 11B show another arrangement of a portion of a thermal printer with ribbon stripping mechanism wherein a print head carriage 280 supports and carries a print head 282 and an associated heat sink 284, and such carriage 280 is caused to be moved along a carriage shaft 286 by means of a follower 288 operating in a camming groove (not shown) . The print head 282 is moved along a print line for printing by print elements, as 290, and a ribbon 292 is disposed adjacent the print elements at an angle to the line of printing to make use of a greater area of the ribbon. A stripping blade 294

made of 0.127 mm thick copper is attached to a portion 296 of the carriage 280, the blade extending substantially the width of the carriage 280 and formed to provide three portions. The lower rectangular portion 298 is fixed to the carriage portion 296, the middle portion 300 extends generally vertical, and the upper portion 302 is directed at an angle from the print head 282. The portions 300 and 302 of the stripping blade 294 are effectively spring loaded so as to provide space for the ribbon 292 between the blade and the print head 282. A pair of ribbon cables 304 and 306 provide current to the print head 282.

It is thus seen that herein shown and described is mechanism or apparatus for stripping or separating a thermal transfer ribbon from the paper in thermal printing operations wherein the stripping or separating mechanism includes blades of various configurations or wires formed in a number of ways to perform the stripping or separating operation. The blades or wires are positioned between the paper and the ribbon and engage the facing surfaces thereof and effect stripping of the ribbon from the paper when the blades or wires are actuated by actuating means.