Printer with pressure control

Abstract: A printing apparatus for printing designs, halftones, alphanumeric and other printed matter on a sheet material comprising: a printing head (60) controlled by input signals to generate printed matter on sheet material during a printing operation, a printing platen (58) positioned to support sheet material relative to the printing head (60) during a printing operation and drive means (70) for moving the sheet material on the printing platen relative to the printing head during a printing operation. An adjustable pressure generator (130) is connected to the printing head (60) and the printing platen (58) for producing pressure between the printing head and the sheet material during a printing operation. A controlled motor (138) is connected with the adjustable pressure generator (130) for adjusting the pressure generator and setting the pressure between the printing head (60) and the sheet material (S).

Description: This invention relates to a printing apparatus for printing designs, halftones, alphanumeric and other printed matter on a sheet material comprising: a printing head controlled by input signals to generate printed matter on sheet material during a printing operation, a printing platen positioned to support sheet material relative to the printing head during a printing operation, drive means for moving the sheet material on the printing platen relative to the printing head during a printing operation, a movable member connected to the printing head and the printing platen for producing pressure between the printing head and the sheet material during a printing operation, and a controlled motor connected with the movable member for setting the pressure between the printing head and the sheet material. A printing apparatus of this kind is described in WO-A-92 17341. It comprises a pressure control mechanism which allows the printing pressure between the printing head and the printing platen to be regulated and allows the printing head to be lifted away from the printing platen. This pressure control mechanism is, however, of complicated structure and has limitations with respect to the preciseness of pressure setting. This document is the basis for the preamble of claim 1. The demand for signs and other sheet material products with multicolored or enhanced graphic images is enormous. While multicolor printing is well known in the art and producing multicolored or enhanced signs by cutting graphic images in sheet material is also well known, a merger of these arts has not been previously employed to produce enhanced graphic images. Furthermore, the convenience, flexibility and speed of producing signs and other graphic images from computer data bases offers significant advantages and substantial opportunity for improvement. In a thermal printer cooperating with a donor web bearing a printing dye or ink that is transferred to the sheet material by the head during a printing operation, the donor web is moved relative to the head along with the material receiving the printed image so that a printing ink is transferred to the material in accordance with the stored data. Especially in this procedure it is important that the pressure between the printing head and the printing platen can be regulated as exactly as possible by means of a simple mechanism. The problem to be solved by the invention is to provide a mechanism meeting this demand. The invention solves this problem by the features of the independent claim. Advantageous further developments are described in the subclaims. In a printing apparatus according to the invention the rotary cam is engaged by a cam follower to control the printing pressure through the support frame. As the cam is rotated, the cam follower rises and releases the printing pressure. Additionally, the exit point at the periphery of the rotary cam allows the cam follower to be disengaged from the cam so that the entire support frame along with the printing head can be pivoted away from the printing platen. The pressure applied between the printing head and sheet material may be regulated as well as the spacing between the head and material so that a donor web carrying the printing ink moves with the material during printing and is disengaged from the material for slewing during non-printing phases of the operation. As a result of the invention, signs, characters, designs and other graphic images can be produced in multiple colors or halftones and with other printing features which significantly enhance the images. The invention will now be further described with reference to the drawings wherein Fig. 1 is a schematic diagram illustrating a system for printing and cutting signs and other graphic products. Fig 2. is a three dimensional halftone image of the letter "R". Fig. 3 is a three dimensional image of the letters "AR". Fig. 4 shows one embodiment of a thermal printer that may be utilized in the present invention. Fig. 5 is a side elevation view of the thermal printer in Fig. 4 with portions broken away to show the internal structure. Fig. 6 is an enlarged fragmentary view of the printer as shown in Fig. 5 and shows the drive mechanism for moving a strip of sheet material relative to the print head. Fig. 7 is an enlarged fragmentary view of the printer similar to Fig. 6 and shows the print head, roller platen and sheet material detector. Fig. 8 is a fragmentary front view showing the support structure and drive mechanism for the roller platen and drive sprockets. Fig. 9 is another side elevation view showing the cassette supporting the donor web with the printing ink and the code reader before reading the code for the donor web. Fig. 10 is a fragmentary view similar to Fig. 9 after a code reading. Fig. 11 is a schematic diagram illustrating the components that are responsible for controlling the various functions of the thermal printer in response to the coding on a donor web cassette. Fig. 1 illustrates a microprocessor based system, generally designated 10, having apparatus for making signs, characters, designs and other graphic products with enhancements provided by the addition of color, halftones and other printed features. For example, the letter "R" shown in Fig. 2 has printed halftone characteristics which imbue the letter with a three dimensional character. Such printed enhancements of the letter are quite distinctive and when such letters are cut along the peripheral edges C from a sheet material such as a vinyl sheet which can withstand weather, wear, abuse and other hazards rather well, a very attractive sign or other graphic product is generated. Similarly, the letters "AR" shown in Fig. 3 can be prepared in two dimensional form on a single sheet of vinyl or other material with a three dimensional character by using different colors for the face of the letters and the shadow or third dimension. The system disclosed in Fig. 1 enables a graphic product to be created and produced with enhancements from a data base on which both the printed and cut features of the product are commonly based. To produce a graphic product with enhancements, the system 10 includes a digitizer 12 or other data input device which supplies a microprocessor based or other computer 14 with machine readable data defining at least the peripheral edges of the graphic product and possibly internal edges as well. The computer 14 displays the machine readable data defining the edges as an image on the screen 15. Then printed enhancements from the special enhancement programs in memory 16 printing designs are added within the edges of the displayed image with the aid of the computer as the operator or composer desires. All the edge and enhancement features are then referenced to one another in a common data base. For example, the enhancement features may include special programs that allow halftone images such as the halftone features shown in Fig. 2 to be added within the peripheral edges of the pattern P. Alternatively, the memory 16 may include an entire font of halftone or otherwise enhanced characters including the edge data, in which case the data input to the computer 14 for the purposes of preparing a final product may be selected entirely from the memory. Still further, the digitizer may serve as the sole input device and may provide the critical data points defining the peripheral edges to be cut as well as the edges of the printing as in the enhanced letters "AR" shown in Fig. 3. Still other data sources may be utilized to supply the computer 14 with an infinite variety of graphic images with enhancements that can be produced by the system 10. From the data defining the enhanced graphic product, the computer 14 generates at least one printing program for operating a printer 20 that prepares one portion of the enhanced graphic product, and a cutting program that operates a cutter 22 and prepares the remaining portion of the product. Additional printing programs may also be generated, for example, to prepare additional printed material in different colors. Each program is stored in a memory 24, and when the product is to be produced, a controller 26 reads the programs and operates the printer 20 and cutter 22 respectively. For example, to create the graphic image of the letters "AR" in Fig. 3, the outline of the letters and the shadow of the third dimension are printed by the printer 20 on a sheet material, such as a vinyl secured by a pressure sensitive adhesive on a releasable backing material. One such vinyl is sold by the Assignee of this application under the trademark SCOTCHCAL of 3M Company. The printer prints the outline of the letters and third dimension in black or another color contrasting with the basic color or colors of the vinyl material. The printed sheet of vinyl on the releasable backing material is then mounted in the cutter 22 and the controller 26 cuts the vinyl only along the peripheral edges C of the image and any internal edges in accordance with the cutting program in the memory 24. By utilizing a printing program and cutting program which have a common data base for defining both the peripheral edges to be cut as well as the printed material, the printing and cutting operations on the sheet of vinyl material are coordinated. After weeding to remove unwanted vinyl material within or around the image, the vinyl forming the enhanced graphic image is lifted from the underlying backing material and is attached to a sign board, window or other object. It is generally preferable, but not essential, to carry out the printing operation in the printer 20 before the sheet material is cut by the cutter 22. With a separate printer and cutter it is also essential that the graphic image that is printed on the vinyl be registered in the cutter with the printing program origin and the cutting program origin coincident. In this manner the lines of cut and the printed portion of the image maintain the correspondence established by the common data base. This registration can be accomplished by printing an origin point on the vinyl along with the printed portion of the image and then optically aligning the origin point with a reference position for the material in the cutter 22. If the printing and cutting operations are carried out by a single machine or a machine having a common drive mechanism for positioning the vinyl relative to a printing head and a cutting head, then the origin point or other reference can be eliminated. One embodiment of a printer for accomplishing the printing operation disclosed in Fig. 1 is illustrated in Fig. 4. The printer 40 utilizes a set of sprockets to engage corresponding feed holes extending along each longitudinal edge of a strip S of the sheet material from which the graphic product is prepared, and correspondingly the cutter 22 has a set of sprockets to engage the same series of feed holes during the cutting operation. In this manner the registration of the cut edges of the graphic with the printed image is insured in the longitudinal direction. Since the graphic image is absolutely fixed both transversely and longitudinally on the strip S relative to the feed holes, the feed holes become a proper reference for the image in both the printing and cutting operations. Alternatively, the printer can prepare a positional reference track T on the print-receiving surface of the sheet material to establish a known positional relationship between the printed image on the strip S and the strip itself. The cutting operation is then carried out by the cutter after the printing operation, and the cutter reads the positional reference track on the sheet material in order to coordinate the position of the material and the cutting tool with the printed material. As shown in Fig. 4 the strip S is supplied in a roll which is supported on a platform 42 at the back side of the printer and is fed over a guide roller 44 before it enters the housing 46 of the printer. After the strip passes through the printer where the printing operation takes place, it is discharged freely at the front side of the machine or may be retrieved on a take-up reel if desired. Although the printer 40 is connected for controlling the printing operation to the controller 26 in Fig. 1, the printer includes a control panel 48 on the housing 46 to stop and start printing operations. Additionally the control panel 48 includes controls for slewing the strip S independently of the printing operation and other controls for operating the printer as will become more apparent hereafter. The upper portion of the printer 40 has a cover 50 with a handle 52 that can be opened and closed in order to expose the internal structure of the printer as shown more particularly in Figs. 5-10. Within the printer 40, the strip S passes over a roller platen 58 relative to a thermal print head 60 which is pressed downwardly onto the strip of material and generally establishes a linear zone of contact between the material and the platen. In one embodiment the strip of vinyl sheet material is 38 cm (15") wide and a hard rubber sleeve on the roller platen as well as the print head are approximately 30,5 cm (12") wide. Thus a marginal edge portion of the strip overlaps the rubber sleeve 59 of the roller platen at each end as indicated in Fig. 8. A drive sprocket 62, having a set of sprocket pins engages a series of feed holes along the one marginal edge of the strip S, and a similar drive sprocket 64 having sprocket pins engages a series of feed holes along the opposite marginal edge of the strip. As shown in Figs. 6 and 8, the drive sprockets 62,64 are fixedly mounted to a drive shaft 66. The drive shaft is rotatably mounted within the housing 46 of the printer and is driven from a step motor 70 by a series of drive gears 72,74, toothed drive pulleys 76,78 and a toothed drive belt 80. In addition the roller platen 58 which is also rotatably mounted within the housing 46 is driven from the drive shaft 66 by means of drive pulleys 82,84 and an O-ring drive belt 86 at one end of the platen and drive pulleys 88,90 and an O-ring drive belt 92 at the opposite end of the platen. The gears, pulleys and toothed drive belt 80 ensure that the strip S of sheet material is precisely positioned on the roller platen and control the speed at which the strip S moves through the printer. The drive pulleys 82,84, 88,90 are selected to establish a peripheral speed of the roller platen 58 that is slightly higher than the peripheral speed of the drive sprocket 62 and 64 to augment the feeding of the strip S past the print head 60. Since the drive sprockets positively engage the strip and control the speed of the strip, the O-ring drive belts 86,92 must allow limited slip. As shown most clearly in Fig. 6 a pair of curved, sheet metal plates 94,96 guide the strip S of sheet material circumaxially onto and off of the roller platen 58 and the cylindrical surfaces of the sprockets 62,64 in a U-shaped feed path. The cylindrical surfaces of the sprockets lie in a cylindrical plane which is much larger in diameter than the cylindrical, strip-engaging surface of the roller platen 58 and is tangential to the cylindrical surface. Preferably the cylindrical surface of the platen is formed by a hard rubber sleeve which improves the frictional engagement of the platen with the releasable backing material of the strip. To keep the strip S fully engaged with approximately 180° of the sprockets 62,64, a pair of holddown bails 98 straddle the pins of each sprocket. The bails are pivotally suspended from the housing 46 on pins 100 as indicated in Fig. 9 so that the bails can be lifted away from the sprockets and allow a strip of sheet material to be mounted on and removed from the sprockets and roller platen 58. Over-center springs 102 assist in holding the bails downwardly on the strip and also permit lifting the bails away from the sprockets during installation or removal of a strip. In addition a pair of holddown rollers 104,106 in Fig. 6 extend between the bails 98 at the supply and discharge points from the roller platen. Thus, the series of feed holes along each edge of the strip S are threaded onto the sprockets 62 and 64 by lifting the bails, and are held firmly engaged with the sprockets and the roller platen by lowering the bails. The thermal print head 60 is mounted in an upper support frame 110 that is pivotally mounted on an axle 112 at the back side of the housing 46 as shown in Figs. 5, 6 and 9. In Fig. 9 the support frame is shown in phantom at a partially elevated position. The actual suspension of the thermal print head 60 from the support frame 110 is illustrated in detail in Fig. 7. A suspension plate 114 is connected with the frame 110 by means of a series of bolts 116 which are secured to the plate 114 and slideably received within the frame 110 so that the plate 114 together with the print head 60 can move vertically in Fig. 7 relative to the support frame. Surrounding each of the sliding bolts 116 and interposed between the frame 110 and plate 114 is a coil spring 117 (Fig.7) which applies pressure downwardly to the plate 114 and presses the print head 60 against the strip S of sheet material and the roller platen 58 along a line of contact. The print head 60 has a plurality of heating elements distributed evenly along the head from one end of the roller platen 58 to the other, and the heating elements are densely packed along the line of contact preferably with a density of 118 elements per cm (300 elements per inch). One such a head is made by Kyocera Industrial Ceramics, Inc. of Kyoto, Japan. In addition to supporting the thermal print head 60, the mounting plate 114 also serves as a heat sink for the heat generated in the print head and supports a pair of dancer rolls 118,120 which guide a web or foil W over the head. The web bears a heat sensitive printing ink or printing dye in black, white or other colors on the surface of the web facing the strip S of sheet material. The web W bearing the printing ink is interposed between the print head 60 and the strip S of sheet material, and when the heating elements of the head 60 are selectively energized, the portion of the ink immediately under a heating element is released from the web and transferred to the sheet material. With high density heating elements, graphic images of high resolution are thus created on the strip of sheet material. The excitation of the heating elements is, of course, controlled in accordance with the program of printed material that is read by the controller 26 from memory 24 in Fig. 1. The web W of printing ink has a width substantially equal to that of the print head and is moved synchronously with the strip of sheet material relative to the head by virtue of the pressure applied between the print head and the roller platen 58. As the web W moves, a pair of static suppression brushes 122,124 mounted in the plate 114 wipe the side of the web opposite from the printing ink. With the drive sprockets 62 and 64 having a larger diameter than the roller platen 58, the roller platen defines a relatively thin line of contact with the strip S of sheet material and yet the sprockets can engage an inverted U-shaped segment of the strip which is substantially larger than the segment contacting the hard rubber sleeve of the roller platen. This allows a narrow linear zone of high pressure contact to be made by the strip with the printing head while a dispersed area of contact with the strip is provided for driving the strip. In order to regulate the amount of pressure applied to the web W and strip S by the head and the roller platen, the projecting or cantilevered end of the support frame 110 is moved up and down relative to the platen 58 by a pressure regulating mechanism that is adjusted by the controller 26. The pressure regulating mechanism includes one or more cams 130 shown in Fig. 5 which are rotatably mounted in the housing 46 on a shaft 132. The cam 130 includes a spiral cam slot 134 that is engaged by a cam follower 136 connected to the projecting end of the support frame 110. As the cam 130 is rotated by means of the pressure regulating step motor 138, the cam follower together with the support frame 110 move up and down and the pressure applied to the web W and strip S of sheet material between the print head 60 and roller platen 58 is adjusted through the coil springs 117 (Fig. 7). By controlling the rotation of the cam 130 with the step motor 138, a precise pressure setting can be obtained since the displacement of the support frame is directly proportional to the pressure. The spiral cam slot 134 includes an exit point 140 at the periphery of the cam 130 so that the cam follower and correspondingly the support frame 110 can be lifted completely free of the cam when the cam has rotated to the upright position. The controller 26 may thus regulate the position of the cam to permit or prevent the lifting of the support frame 110 and print head 60 at appropriate times in a printing operation. The pressure regulating mechanism can also be utilized to lift the pressure head out of contact with the strip S and roller platen since the spiral cam slot 134 is comprised by a groove that can both push and pull the cantilevered end of the support frame 110 up and down. Thus, for example, at the end of a printing operation the regulating motor 138 can drive the cam 130 to a position at which there is zero pressure between the print head and the roller platen or the print head can actually be lifted away from the roller platen so that the strip S of sheet material can be slewed back and forth relative to the print head without making contact with the web W of printing ink. The lifting feature of the pressure regulating mechanism is desirable when, for example, multiple colors are printed on the strip S of sheet material in multiple passes of the material over the roller platen relative to the head. Between each pass the web W must be changed or indexed so that printing inks of different colors can be transferred from different webs or different portions of one web onto the same segments of the strip S in overlapping, side-by-side or spaced relationship. The ability to overlap the colors is particularly useful when subtractive inks or color process dyes are employed to mix the colors and obtain still further colors. The pressure regulating step motor 138 may also be adjusted by the controller 26 of Fig. 1 in accordance with other printing parameters of the operation. For example, the texture or character of the printing-receiving surface on the strip S of sheet material may require setting the pressure at a preferred level for ideal transfer of the ink between the web W and the strip S. Other parameters that may effect the desired pressure level include the speed at which the printing operation is carried out, the character or color of the printing ink that is transferred from the web W and the intensity or tone of the printed material desired on the strip. The adjustment of the pressure level can occur prior to or throughout the printing operation in accordance with print characteristics that are stored in the print program or are measured during the printing operation. As indicated above, a printing operation may be carried out to produce printed material in various colors, and generally the entire printing and cutting operation for making a sign or other graphic product is pre-programmed, not only with respect to the design and arrangement of the printed matter within the peripheries of the graphic product, but also the colors of the print and the sheet material on which the print is placed. Accordingly, in order to carry out a printing operation properly, the operator of the printer must install both the strip of sheet material and a cassette that is called for by the program. Additionally, the materials on which the printing takes place as well as the donor webs used in the printing process may have different printing characteristics beyond just color which render the materials incompatible or the resulting product inferior unless the printer is controlled and adjusted properly to compensate for the different characteristics. For example, the pressure applied between the donor web and strip of sheet material may need to be adjusted up or down in accordance with the donor web that is being used in a printing operation. Also the speed at which the printing operation is carried out may affect the pressure and vice versa. Furthermore, the excitation of elements in the printing head may need to be modified in accordance with the thermal characteristics of the ink or the speed and the pressure with which the printing operation is carried out. In sum there are a number of variables that require adjustment either prior to or during the printing operation in order to produce a satisfactory graphic product. For the reasons given above, the controller 26 of Fig. 1 shown in greater detail in Fig. 11 has a microprocessor 250 which regulates the operation of the printer 40 to set and adjust various of the operating parameters in a printing operation. The microprocessor responds to a number of inputs including the keyboard 252, the printing and cutting program derived from the memory 24 and a code reader 254 which detects printing characteristics of the web W and printing ink in the cassette 170. From these various inputs, the microprocessor regulates the pressure applied between the printing head 60 and roller platen 58 through the pressure control means 256 including the drive motor 138 and controlling cam 130 of Fig. 5, the speed of printing through the feed driver 258 which regulates the step motor 70 for the roller platen 58 in Fig. 6 and the image intensity through a print head drive 260 which controls the excitation of the heating elements in the print head 60. The setting of the various parameters and regulation during a printing operation is accomplished in conjunction with the display 262. In the event of a fault of the system, any error or detected fault is identified through the display 262 on the printer and if the fault is serious, the microprocessor immediately stops or inhibits printer operation.

Claims: A printing apparatus for printing designs, halftones, alphanumeric and other printed matter on a sheet material (S) comprising: a printing head (60) controlled by input signals to generate printed matter on sheet material (S) during a printing operation, a printing platen (58) positioned to support sheet material (S) relative to the printing head (60) during a printing operation, drive means (70) for moving the sheet material on the printing platen relative to the printing head (60) during a printing operation, a movable member (130) connected to the printing head (60) and the printing platen (58) for producing pressure between the printing head (60) and the sheet material (S) during a printing operation, and a controlled motor (138) connected with the movable member (130) for setting the pressure between the printing head (60) and the sheet material (S), characterized in that said movable member is a rotary cam (130) including a spiral cam slot (134) engaged by a cam follower (136) connected to a pivotable support frame (110) for said printing head (60) and that said cam slot (134) includes an exit point (140) at the periphery of the rotary cam (130). A printing apparatus as defined in claim 1, characterized in that the controlled motor (138) sets the pressure between a zero pressure level at which the sheet material (S) can be slewed freely over the printing platen (58) relative to the printing head (60) without printing on the material (S), and a given pressure level at which the sheet material (S) is pressed against the printing platen (58) by the printing head (60) during printing. A printing apparatus as defined in claim 1 or 2, characterized in that a donor web (W) is disposed adjacent the printing head (60) and bears a printing ink transferred from the web (W) to a sheet material (S) supported by the printing platen (58) during a printing operation, the characteristics of the donor web (W) and the printing ink being known, and that the controlled motor (138) sets the pressure between the printing head (60) and the sheet material (S) at a level dependent upon the known characteristics of the donor web (W) and printing ink.

Inventors: BRANT LISA M, HEVENOR CHARLES M, LOGAN DAVID J, LOOS WILLIAM A, NILAND JAY T, STEMPIEN JOSEPH W, VOELKER MARTIN C, WEBSTER RONALD B, BRANT, LISA M., HEVENOR, CHARLES M., LOGAN, DAVID J., LOOS, WILLIAM A., NILAND, JAY T., STEMPIEN, JOSEPH W., VOELKER, MARTIN C., WEBSTER, RONALD B.
Applicants: GERBER SCIENT PRODUCTS INC, GERBER SCIENTIFIC PRODUCTS, INC.
Application year: 1993
Main classification: B41J25
IPC codes: B41J11, B41J15, B41J17, B41J25, B41J2