Device for advancing printable material in a printing means

Abstract: The device (10) is provided with a supply drum (24) for printable material (34) which, by a transport means (42), is supplied step-wise to a printing means (14). The supply drum (24) and the transport means (42) have separate drive means which are controlled by a control unit. Between the supply drum (24) and the transport means (42), there is arranged a first guidance roll (66), resting on the printable material (34) and keeping it tensioned. A loop (90) of printable material is formed in the area of the first guidance roll (66). When the supply drum (24) is driven while the transport means (42) is switched off, the length of the loop (90) increases. The position of the first guidance roll (66) - and thus the length of the loop (90) - is detected by a sensor. When the sensor is actuated, the loop (90) has a predetermined minimum length. Then, while the drive means of the supply drum (24) is switched off, the transport means (42) is driven for advancing the printable material (34) by the predetermined advancing distance. Subsequently, while the printable material (34) is stopped, a printing process is performed in the printing means (14).

Description: The invention is directed to a device for advancing printable material in a printing means, having a supply drum for the printable material and a driven transport means for advancing the printable material to the printing means and for forwarding the printable material after the printing process. Such devices are used for all types of printers, particularly for automatically operating laser printers for printing onto labels or the like. In most cases, the printable material is a strip provided on a supply drum. A motor-driven transport means advances the strip of printable material to the printing means where the printing process is performed. After the strip of printable material has been printed on, the strip is advanced to a further processing station, e.g. a cutting device or a winding drum. From DE-A-31 52 105, there is known a device of the mentioned type wherein a traction drive, arranged in the printing means, continuously advances the printable material (in this case, an endless paper tape). A driven take-off roll serves for unwinding the paper from a supply drum. In the area between said take-off roll and the traction drive, the paper tape loosely sags in a loop-like manner, the extent of sagging being detected by a sensor. Downstream of the traction drive, there is arranged a winding station including a winding drum. Said winding drum, too, has a drive of its own. Also between the traction drive and the winding station, the printed paper tape loosely sags, and the extent of sagging is detected by a sensor. In this known device, the paper is moved forward continuously while being printed. During operation of the device, all of the three drives means, i.e. for the take-off roll, the traction drive and the winding station, are activated, resulting in relatively high energy consumption. When the paper is unwound from the supply drum, the supply drum has to be slowed down in order to prevent uncontrolled rotation of the supply drum and to keep the paper tape between the supply drum and the take-off roll tensioned. It is the object of the invention to provide a device of the above-mentioned type which comsumes relatively little energy during operation. In order to solve said object, it is provided according to the invention that, in the area between the supply drum - being provided with a separate drive - and the transport means, there is provided a first guidance roll pressing against the printable material with a pressing force and keeping the printable material tensioned, that a first position detecting sensor is provided for detecting whether the first guidance roll is within a desired position range in which the length of the portion of printable material extending between the first guidance roll and the transport means equals or exceeds a predetermined minimum length, and that the supply-drum drive and the transport means are intermittently driven by an electronic control unit which, for advancing the printable material by a predetermined advancing distance, first drives the supply-drum drive without driving the transport means, until the first guidance roll is within its desired position range, and, when receiving a signal from the first sensor indicating that the desired position range has been reached, drives the transport means according to the predetermined advancing distance without driving the supply-drum drive, the printing process being performed after completion of the advance movement and while the printable material is stopped. In the device of the invention, the printable material, normally provided as a strip, is moved discontinuously. The printable material is supplied stepwise to the printing means by portions. Each of said portions, before being further advanced, is written on, printed on, or provided with information in some other manner. The supply drum is provided with a separate drive, which drive acts immediately on the supply drum for rotating same. Between the supply drum and the transport means, there is provided a first guidance roll pressing against the strip of printable material and keeping it tensioned. Upon rotation of the supply drum, printable material is supplied. Since, at this time, the transport means is not driven, i.e. is in the switched off-state, this printable material is fed to the area between the supply drum and the transport means. The first guidance roll, being subjected to a force for pressing against the strip of printable material, is moved corresponding to this force, all the time abutting the strip of printable material and keeping it tensioned also while further printable material is supplied from the supply drum. To this purpose, the first guidance roll is adapted both to be rotated about its axis of rotation and to be displaced in a direction perpendicular to its axis of rotation. As soon as the first guidance roll, during rotation of the supply drum, is within a desired position range to be detected by the position detecting sensor, the drive for the supply drum is switched off by the control unit. At the same time, the transport means is driven for advancing the strip of material to the printing means. Thus, while the transport means is driven, the portion of the printable material on which printing has been performed during the previous printing process is moved away from the printing means, and, simultaneously, a new portion of the printable material is supplied to the printing means for printing. Since the drive for the supply drum is switched off while the transport means is driven, the guidance roll moves against the pressing force and, also in this case, is in permanent abutment with the strip of printable material and keeps it tensioned. Therefore, the area between the supply drum and the transport means is used like an intermediate storage means, printable material first being supplied thereto from the supply drum and then being removed therefrom by the transport means. By the first guidance roll, the printable material in the area between the transport means and the supply drum is kept tensioned. In the device of the invention, the supply-drum drive and the transport means are driven individually and sequentially by the control unit. Thus, the control unit controls only one drive at a time, i.e. either the drive for the supply drum or the drive for the transport means. Thereby, energy consumption of the device of the invention is reduced. This individual driving of said drive means also yields the advantage that the loads to be switched by the control unit are smaller. For this reason, less power-consuming components can be used in the control unit or at least in those of its electronical units which supply the drive means with electric power. If the first guidance roll is already or still in its desired position range, the control unit, for advancing the printable material by the predetermined advancing distance, immediately drives the transport means without previously driving the supply-drum drive. If the first guidance roll is within the first position range, a certain minimum quantity of printable material is kept available between the supply drum and the transport means. This minimum quantity corresponds to the maximum possible quantity to be advanced in the device of the invention. Only if this minimum quantity of printable material is not available anymore in said intermediate storage area between the supply drum and the transport means, i.e. if the first guidance roll is outside its desired position range (which is detected by the first sensor), the supply-drum drive and, only subsequently, the transport means are driven for advancing the printable material. As mentioned above, the first guidance roll primarily serves for tensioning the printable material arriving between the supply drum and the printing means. This is specifically advantageous for the printing process because printable material, when being tensioned, can be printed on more exactly than when being untensioned or "loose". Another function of the first guidance roll, i.e. allowing detection of the accumulated (minimum) quantity of printable material on the basis of the position of the guidance roll, can also be fulfilled by a sensor detecting the extent of sagging of a loop of printable material between the supply drum and the transport means. In this case, the tension is applied in another manner and by another means onto the presently printed portion of printable material. For the sequential driving of the centrally controlled drive means of the supply drum and the printing means, the first guidance roll is not absolutely required. It merely facilitates reliable detection of the printable material kept available in the loop and supports the tensioning of the strip of printable material, which in turn contributes to a more reliable operation of the device of the invention. Advantageously, the first guidance roll bears against the strip of printable material by its own weight. To this purpose, the first guidance roll, by both ends of its axis of rotation, is guided in preferably vertical longitudinal holes or guiding grooves. The first sensor, for instance, checks a portion of one of said longitudinal holes or of said guiding grooves and thus detects whether the guidance roll is in its desired position range. The first guidance roll is preferably supported between two arms for rotation about a horizontal axis. For moving the first guidance roll in a direction perpendicular to the axis of rotation, the two arms are supported to be swiveled about a swivel axis and carry a second guidance roll to be swiveled about said swivel axis. The strip of printable material coming from the supply drum is guided about the second guidance roll. The second guidance roll is undisplaceable except for being rotatable, so that the first guidance roll is supplied with printable material always from the same location, namely via the second guidance roll. If the device is provided with said second guidance roll while the remaining constructional dimensions thereof are the same, the intermediate storage means takes up more printable material than without the second guidance roll. Preferably, the first sensor detects the position of the first guidance roll on the basis of the swiveling position of the arms. The first sensor is actuated as soon as the arms holding the first guidance roll are within a predetermined range of swiveling positions wherein the first guidance roll is in its desired position range. If two guidance rolls are provided, the strip of printable material is advantageously guided in opposite directions about the first and second guidance rolls. This means that the strip of printable material follows an S-shaped course in the area of the two guidance rolls. Preferably, when starting the device of the invention, a check-up is performed for examining whether the printable material has been inserted correctly in the device. After the device has been switched on, the drive means for the supply drum is driven, while the transport means is in the switched-off state, until the first guidance roll is in its desired position range, which is indicated by the first position detecting sensor. If the sensor has not been actuated within a predetermined length of time, the control unit outputs a signal indicating a malfunction. This signal indicates that the position detecting sensor is defect; then, the drive for the supply drum is switched off. If said sensor has responded, the transport means is driven for a predetermined second period of time, or - when using a stepper motor - is actuated by a predetermined number of pulses, with the supply-drum drive being not driven. If the sensor, until lapse of this second period of time or until the end of the driving of the stepper motor by the last pulse, does not emit a signal indicating that the first guidance roll has left the desired position range, this means that the guidance roll has not been moved out of its position by the printable material advanced by the transport means, which normally is the case if the strip of printable material is correctly guided about the first guidance roll (the second period of time is set accordingly). Also in this respect, the control unit outputs a signal indicating a malfunction which, in this case, signals that the printable material has not been correctly guided about the first guidance roll. As far as, upon switch-on of the device of the invention, the first guidance roll is already in its desired position range and, thus, the first sensor responds, driving of the transport means as mentioned above is immediately started while the supply-drum drive is switched off. In an advantageous embodiment of the invention, the transport means is provided with a rotatable drive roll and a pressing roll pressing thereagainst and being rotatable about its axis. Between these rolls, the printable material is guided and is moved forward through friction. The thus designed transport means is quite simple in construction. This transport means is also adapted for advancing strips of printable material having no perforated longitudinal edge portions, whereas perforations are positively required if transport is performed by a traction drive. Thus, the strip of printable material is easier in manufacture. Printable material having perforated longitudinal edge portions has the disadvantage that the edge portion must be removed after printing on the printable material, necessiting additional work. Advantageously, the pressing roll presses on the drive roll or, resp. the interposed printable material with its own weight only. To this end, the pressing roll is guided to be displaced in a radial direction relative to the drive roll, e.g. in vertical longitudinal holes. By mounting the pressing roll in this manner, insertion of the strip of printable material prior to starting the device of the invention is facilitated. In a further advantageous embodiment of the invention, the supply drum is rotated by a direct-current motor and the drive roll of the transport means is driven by a stepper motor, the supply drum and the drive roll being preferably rotated via intermediate transmissions. Said stepper motor allows advancing the strip of printable material by almost exactly the predetermined advancing distance, particularly if the stepper motor can be driven by steps of less than 1 mm. Advantageously, the printing means is arranged between the transport means and the supply drum or the guidance roll, resp. Since the guidance roll keeps the printable material tensioned, also the strip of printable material in the area of the printing means is tensioned accordingly, having a favorable effect during marking or printing, resp. Particularly when using a laser write head, it is necessitated, for correct printing, that the printable material extends in a plane. In a still further embodiment of the invention, it is provided that the printable material leaving the printing means and being forwarded by the transport means is received and wound up by a winding drum provided with a separate drive to be driven by the control unit. By being wound up, the printable material is arranged for easy handling also after printing. Between the transport means and the winding drum, a third guidance roll is arranged which, as is the case with the first guidance roll, presses against the strip of printable material with a pressing force, preferably with its own weight, for keeping it tensioned. This has a positive effect on the winding process and the winding coil. Basically, the specific support of the third guidance roll is of minor relevance as long as it is safeguarded that the third guidance roll is in permanent abutment with the strip of printable material. Namely, also the area between the transport means and the winding drum acts as a (second) intermediate storage means. Already printed printable material is supplied to this intermediate storage means by the transport means while the drive of the winding drum is switched oft. Then, printable material is removed therefrom while the winding drum is rotated and the transport means is switched off. The displacement action of the third guidance roll in perpendicular direction to the axis of roatation thereof should be guaranteed so that the guidance roll can always exert tension onto the printable material. Advantageously, the third guidance roll is supported - in the manner of the first guidance roll - between two arms adapted for swiveling. The axis of rotation of the drive roll of the transport means coincides with the swiveling axis so that the arms are articulated to the axis of rotation of the drive roll in a simple constructional manner. In the area between the transport means and the winding drum, a second position detecting sensor is arranged for detecting whether the third guidance roll is within a specific position range. This position range is provided such that the length of the portion of printable material extending between the transport means and the winding drum is equal to or smaller than a predetermined maximum length. After a printing process has been performed and after the printable material has been wound onto the winding drum, the third guidance roll remains in this desired position range until completion of the next printing process. If the third guidance roll is arranged on the arms articulated about the axis of rotation of the drive roll of the transport means, the desired position range of the third guidance roll is advantageously monitored by detection of the swiveling position of the arms through the second position detection sensor. Also while the printable material is wound onto the winding drum, the drive means - in coordination with the drive means for the supply drum and the transport means - is driven in such a manner that only one drive is in the switched-on state at a time, i.e. there are never driven two or more drive means at the same time. Preferably, this is performed in that the control unit, while the supply drum and the winding drum are switched off, drives the transport means for supplying a new strip of printable material to the printing means and simultaneously moving the already printed strip of printable material away from the printing means towards the winding drum (i.e. feeding the strip to the second intermediate storage means downstream of the transport means). Depending on the length of the advancing distance, the third guidance roll leaves its desired position range during this process. Subsequently, however, the third guidance roll is returned to this desired position range. To this purpose, the drive means for the winding drum is driven while the transport means (and the supply-drum drive) is switched off, so that printed printable material is moved out of the second intermediate storage means and the third guidance roll is displaced because no new printable material is supplied to the second intermediate storage means. If the advancing distance is so short that the third guidance roll remains in its desired position range while the transport means is driven and the drive for the winding drum is switched off, the winding drum is not driven by the control unit after the transport means has been switched off. Thus, it is safeguarded that only one of the three drive means is driven at a time, whereby the energy consumption of the device is reduced by about 50 % and less power-demanding components can be used. Also when using a winding drum, it is checked, after the device has been switched on, whether the printable material in the area between the transport means and the winding drum is correctly guided about the third guidance roll. To achieve this, it is provided that the control unit, after the transport means has been switched off, drives the winding-drum drive for a predetermined period of time and outputs a signal indicating a malfunction if, until lapse of the time period, the second position detecting sensor has not outputted a signal indicating that the third guidance roll has reached its desired position range. This signal is to indicate that the printable material is not guided around the third guidance roll because, otherwise, the guidance roll would have to be displaced into its desired position range. A third sensor is provided for detecting whether printable material has been inserted into the device at all. In an advantageous embodiment of the invention, it is provided - instead of using the winding drum und the third guidance roll - that the printed strips of printable material coming from the transport means are fed to a cutting device for sequentially cutting the strip of printable material corresponding to the printed areas and for depositing the cut strip portions in a storage container or, resp. feeding them to said container. The device of the invention is particularly suited for printing means for automatically producing labels of different sizes on a strip of printable material. In the device of the invention, the advancing distance is variable so that also portions of printable material of different lengths can be printed. Between the supply drum and the transport means and between the transport means and the winding drum (if provided), the respective strip of printable material is guided in the manner of a loop. However, in these areas, the strip of printable material does not loosely sag but is kept tensioned by the first or the third guidance roll, resp. Due to the loop-like guidance of the strip of printable material, the effect of an intermediate storage area is obtained. These intermediate storage areas, however, are not provided for keeping printable material available in case that the transport means temporarily advances the printable material faster than printable material is delivered from the supply drum; namely, the device of the invention does not work in continuous operation. Instead, it is the function of the intermediate storage areas to guarantee that the transport means can advance printable material when the supply drum is not rotated, and to allow printable material to be wound onto the winding drum when the transport means is not driven. The fact that the different drive means are driven sequentially and individually reduces the energy consumption of the device. Unless the drive motors for the supply drum, the transport means and the winding drum (if provided) are driven, they are switched off or are blocked via an intermediate transmission. Thus, it is precluded that tensile forces can cause unintended and uncontrolled advancing of the printable material while the drive motors are not driven. An embodiment of the invention will be explained in more detail hereunder with reference to the Figures. Fig. 1 is a perspective side view of the device, Fig. 2 is a plan view of the device according to Fig. 1, and Figs. 3 to 5 are side views of the device according to Fig. 1 in different operating conditions of the device. Figs. 1 and 2 show a perspective side view and a plan view of a device 10 for the discontinuous advance of printable material in a printing means. The device 10 can be roughly divided into three sections, i.e. a supply station 12, the printing means 14 proper and a winding station 16. The device 10 shown in the Figures forms part of a fully automated printing system using a laser write head 18 for printing onto the printable material, the laser write head 18 being shown only by the chain-dotted lines in Fig. 3. For the sake of clarity and for the better understanding of the invention as such, the other components of the printing system are neither shown in the Figures nor described here in greater detail. The device 10 is provided with a base plate 20 being, for instance, part of a frame or intermediate bottom of a housing accommodating the printing system. A vertical plate 22, also forming part of the housing, extends perpendicular to base plate 20. In the area of the supply station 12, the vertical plate 22 holds a rotatably supported supply drum 24. The axis 26 of supply drum 24 is rotated by the drive shaft 28 of a direct-current motor 30. By means of a holding bracket 32, motor 30 is fastened to the side of vertical plate 22 averted from supply drum 24. A strip 34 of printable material is held on supply drum 24. For adapting the supply drum to strips of printable material having different widths, the supply drum 24 has its axis 26 provided with two disks 36, one of them being displaceable and adapted to be fixedly connected to axis 26 by a locking screw 38. The strip 34 of printable material is a laser-sensitive film material consisting substantially of two layers arranged on top of each other. The upper layer, facing the laser write head 18, evaporates when the laser beam impinges thereon, thus exposing the lower layer arranged thereunder. This lower layer differs in color from the upper layer so that an image is generated on the printable material. The printing means 14 is arranged adjacent to the supply station 12 for the printable material 34,. The printing means 14 is provided with an even plate 40, with the laser write head 18 arranged thereabove as shown in Fig. 3. During the printing process, the strip 34 of printable material lies on said even plate 40 and is written on by the laser beam 19 of the laser write head 18. On the side of printing means 14 facing away from supply station 12, a transport means 42 is arranged for advancing the strip 34 of printable material in advancing direction (arrow 44). The transport means 42 has a rotatable drive roll 46 which is arranged next to plate 40 of printing means 14 at the side of plate 40 averted from supply station 12. The drive roll 46 is rotatably supported by the vertical plate 22 and a plate 48 extending in parallel thereto and carrying the plate 40 of printing means 14. The surface of plate 40 extends tangentially to drive roll 46. The axis 49 of drive roll 46 is driven by a stepper motor 52 and via a driving belt 50. Above drive roll 46, there is arranged a rotatably supported pressing roll 53 extending in parallel to drive roll 46 and having its axis 54 guided in vertical longitudinal holes 56 in plate 48 and vertical plate 22. Pressing roll 53 presses with its own weight against drive roll 46. The printable material 34, if inserted in the device, passes between drive roll 46 and pressing roll 53 so that the strip 34 of printable material is advanced through friction when drive roll 46 is rotated. To this purpose, the peripheral surface of drive roll 46 is provided with a suitable material. The winding station 16 is arranged downstream of the transport means 42 as seen in advancing direction 44. Winding station 16 consists of a winding drum 58 of a design similar to supply drum 24. The axis 60 of winding drum 58 is rotated by the drive shaft 62 of a direct-current motor 64. The direct-current motor 64 is supported in the same manner at the rear side of vertical plate 22 as the direct-current motor 30 for supply drum 24. Since the arrangement of winding drum 58 and the drive thereof are similar to the arrangement and the drive of supply drum 24, no detailed description of the winding station 16 will be given here. The first guidance roll 66 is arranged in the area between the supply station 12 and the printing means 14, being supported for free rotation by two arms 68. The arms 68 are supported to be swiveled about a swivel axis 70 being parallel to the horizontal rotational axis of the first guidance roll 66. Particularly, the arms 68, by their ends facing the first guidance roll 66, are articulated to the rotational axis of a second guidance roll 72. The rotational axis of said second guidance roll 72 is rotatably supported by the vertical plate 22 and a vertical support 74 resting on base plate 20. The first and second guidance rolls 66 and 72 extend in parallel to the supply drum 58. The strip 34 of printable material is guided about the first two guidance rolls 66,72, following an S-shaped path and being in abutment to the peripheral portion of the first guidance roll 66 facing base plate 20. From this area, the strip 34 of printable material runs over plate 40 of printing means 14 and into the gap between drive roll 46 and pressing roll 53 of transport means 42 where it is held by clamping action. Thus, between supply drum 24 and transport means 42, the strip 34 of printable material is guided in the manner of a sagging loop. In this area, however, the strip 34 of printable material is kept tensioned because, with the arms 68 being in a swiveled position, the first guidance roll 66 lies on the strip 34 of printable material while keeping the strip tensiond by its own weight. The swiveling position of the arms 68 and thus the vertical distance of the first guidance roll 66 from the base plate is detected by a first position detecting sensor 76 (cf. Figs. 2 and 3). The first position detecting sensor 76 is arranged at the vertical plate 22, namely in the swiveling range of the arms 68. The sensor 76 consists of a light-emitting and a light-receiving element. When the arm 68 enters the sensor area, the light-receiving element receives the light emitted by the light-emitting element due to reflection by that arm 68 which is arranged closer to vertical plate 22. Lateral shielding plates 78 are arranged on arm 68. As long as said shielding plates 78 are in a position in front of sensor 76, the light-receiving element of the sensor receives light so that the sensor is actuated. Thus, when sensor 76 is actuated, the first guidance roll 66 is within a defined first desired position range. As soon as the first guidance roll 66 enters this position range or, resp. moves out of this position range, this is detected by the first sensor 76. In said desired position range, a certain length of printable material is arranged between the second guidance roll 72 and the plate 40, i.e the portion of the strip of printable material within this area has a certain minimum length. Between printing means 14 and winding station 16, there is arranged a third guidance roll 80 which - similar to the first guidance roll 66 - is supported by two arms 82 for free rotation. Said arms 82 are articulated at the axis of rotation 49 of drive roll 46. The printable material 34 is guided about the drive roll 46 and the third guidance roll 80, following an S-shaped path and being in abutment to the peripheral portion of the third guidance roll 80 facing base plate 20. Due to the swiveled arrangement of the arms 82, the third guidance roll 80 lies on the strip 34 of printable material and keeps it tensioned in the area between transport means 42 and winding drum 58. The swiveling position of the arms 82 is detected by a second position detecting sensor 84 (cf. Figs. 2 and 3), being arranged slightly below the level of the drive roll 46 and operating according to the same priciple as the first position detecting sensor 76. The arm 82 being closer to vertical plate 22 has a lateral shielding plate 86 attached thereto, shielding the second sensor 84 in dependence of the swiveling position of arms 82. Thus, the second position detecting sensor 84 serves for monitoring a (second) desired position range of the third guidance roll 80. As long as the third guidance roll 80 is within this desired position range, the portion of the strip 34 of printable material between transport means 42 and winding drum 58 has specific maximum length. A third sensor 88 is arranged above plate 40 of printing means 14 for detecting whether or not printable material is present on plate 40. The operation of device 10 will be described herunder with reference to Figs. 3 to 5. The motors 30, 52 and 64 for the supply drum 24, the drive roll 46 of transport means 42 and the winding drum 58 are driven by a central electronical control unit, e.g. a microcomputer. Said control unit receives the output signals of the three sensors 76, 84 and 88 and is connected to the laser write head 18. The central control unit, being omitted in the Figures for reasons of clarity, controls the whole process performed by the device 10 and the printing system to which device 10 belongs. As to the driving of the motors, the decisive aspect consists in operating only one motor at a time, i.e. never supplying driving energy to several of these motors at the same time. After the printing system has been switched on, the control unit first interrogates the third sensor 88 for checking whether printable material has been inserted into device 10. If this is not the case, the control unit outputs a signal indicating a malfunction and being used for generating an optical or acoustic signal "Insert printable material". After printable material has been inserted, the contol unit checks whether the printable material is correctly guided about the guidance rolls. To this purpose, the motor 30 for the supply drum 24 is driven while motors 52 and 64 are not driven. Thereby, supply drum 24 is rotated and printable material is wound off. This printable material is supplied to the area between supply station 12 and printing means 14 or transport means 42. Since this printable material is not further transported (the transport means being not driven at this time), the loop of printable material in the area of the first guidance roll 66 is enlarged and, as a result, the arms 68 are swiveled downwardly. When the first position detection sensor 76 is actuated, i.e. when it is detected that the first guidance roll 66 is within its first desired position range, the direct-current motor 30 for supply drum 24 is switched off by the control unit. If the first sensor 76 is not actuated within a predetermined first period of time, the control unit emits a signal indicating that the first sensor 76 is defect. On the condition that the first sensor 76 has responded, i.e. has been actuated, the stepper motor 52 of transport means 42 is switched on while the motors for the two drums are switched off. The driving of motor 52 is kept up for a specific number of pulses, i.e. the transport means 42 advances the strip 34 of printable material for a predetermined maximum distance corresponding to the number of pulses or steps. This advancing distance is such that, if the strip 34 of printable material has been correctly guided about the first guidance roll 66 from below, the arms 68 or the plates 78, resp. have moved out of the area of the first sensor 76. Should sensor 76 remain actuated until the end of the pulse driving of stepper motor 52, the control unit generates an output signal indicating that the printable material is not correctly guided about the first guidance roll 66. As soon as the first sensor 76 is switched off during the pulse driving, the stepper motor 52 is stopped. At the same time, the direct-current motor 64 for winding drum 58 is driven for checking whether the third guidance roll 80 lies on the strip 34 of printable material. To this purpose, motor 64 is driven for a predetermined third period of time; if the second position detecting sensor 84 is not actuated within this third period of time, it has to be assumed that the strip 34 of printable material is not guided about the third guidance roll 80. In this case, the control unit emits a corresponding output signal indicating this malfunction. When the strip 34 of printable material is to be advanced to undergo printing, the control process for device 10 is as follows: Upon receipt of an instruction signal for advancing the strip 34 of printable material by a predetermined advancing distance (this information being provided as a string of data or the like), it is first checked by the first sensor 76 whether the first guidance roll 66 is within its (first) desired position range. If this is not the case (Fig. 3), the control unit immediately drives the stepper motor 52 for transport means 42; namely, the control unit emits a number of driving pulses corresponding to the advance by the predetermined advancing distance. The maximum advancing distance is determined by the supply of printable material which in turn is determined by the length of loop 90 and by the distance between the second guidance roll 72 and the edge of plate 40 of printing means 14 facing guidance roll 72. Based on the maximum allowable advancing distance for an advancing step, it is possible to determine the maximum angle between arms 68 and vertical support 74 still allowing a sufficient quantity of printable material to be kept available by the resulting loop 90. Thus, if the first sensor 76 is actuated, this means that enough printable material is kept available by loop 90 so that transport means 42 can be driven immediately for advacing the printable material by the predetermined advancing distance. Since, at this time, supply drum 24 is not rotated, loop 90 becomes shorter. As a result, the arms 68 are swiveled upwardly and the vertical distance between first guidance roll 66 and base plate 20 is enlarged, i.e. guidance roll 66 is raised. This situation is shown in the left area of Fig. 4. Since winding drum 58 is not rotated while transport means 42 is driven, the loop 92 of printable material between transport means 42 and winding station 16 becomes larger, which is shown in the right area of Fig. 4. For winding up the printable material having been printed on during a (or the) previous printing process and being advanced by transport means 42, motor 64 of winding drum 58 is driven while stepper motor 52 is switched off; accordingly, winding drum 58 is rotated. At the same moment when the second sensor 84 is actuated, direct-current motor 64 is switched off so that device 10 is in the operating condition shown in Fig. 5. In this operating condition, all of the drives of device 10 are switched off. After stepper motor 52 has been switched off, laser write head 18 is driven for printing onto the strip 34 of printable material in the area of printing means 14. During the printing process, strip 34 is not advanced; instead, laser write head 18 is moved over plate 40 by suitable drive means (not shown) for writing onto strip 34 within the portion thereof extending through printing means 14. After completion of the printing process, device 10 is in the operating condition shown in Fig. 5. If, in this operating condition of device 10, the printable material is to be advanced by a further advancing distance, the control unit first interrogates the first sensor 76 to check whether the first guidance roll 66 is within its desired position range wherein loop 90 has a predetermined minimum length. Since this is not the case in the situation shown in Fig. 5, motor 30 for supply drum 24 is driven so that printable material is wound off supply drum 24. Accordingly, loop 90 becomes larger and arms 68 are swiveled downwardly. When the first sensor 76 is covered by the plates 78, it is actuated and emits a corresponding signal to the control unit which then switches off direct-current motor 30. In order to keep the first sensor 76 actuated also if the arms 68 are swiveled past the sensor, the plates 78 extend to both sides of that arm 68 which is arranged immediately adjacent vertical plate 22. As soon as the first sensor 76 is actuated, i.e. is switched on, it is safeguarded that loop 90 has the predetermined minimum length. Now, the operating condition of device 10 is as shown in Fig. 3 and the further driving process is performed in the manner described above. If device 10 is in the operating condition according to Fig. 5 at the beginning of an advancing movement, it is not absolutely required that the arms 68 are brought into the position shown in Fig. 3 by rotating supply drum 24. If, for instance, the exact swiveling position of arms 68 is detected by an angle detector, it is possible to calculate the length of loop 90 and - based on the distance of the second guidance roll 72 to plate 40 of printing means 14 - the supply of printable material stored by loop 90. Then, it is checked on the basis of the predetermined advancing distance whether the supply of printable material stored in loop 90 is sufficient for the advance. If this is the case, transport means 42 is driven immediately. This manner of proceeding is advantageous particularly if the printable material is to be advanced by a relatively short advancing distance each time.

Claims: A device for advancing printable material in a printing means, comprising a supply drum (24) for the printable material and a driven transport means (42) for advancing the printable material (34) to the printing means (14) and for further transporting the printable material (34) after the printing process, characterized in that the supply drum (24) is drivable by a separate supply-drum drive (30), that, in the area between the supply drum (24) and the transport means (42), there is provided a first guidance roll (66) pressing against the printable material (34) with a pressing force and keeping the printable material (34) tensioned, that a first position detecting sensor (76) detects whether the first guidance roll (66) is within a desired position range in which the length of the portion of printable material (34) extending between the supply drum (24) and the transport means (42) equals or exceeds a predetermined minimum length, and that a control unit is provided for intermittently driving the supply drum (24) and the transport means (42), which control unit, for advancing the printable material (34) by a predetermined advancing distance, first drives the supply-drum drive (30) without driving the transport means (42), until the first guidance roll (66) is within its desired position range, and, when receiving a signal from the first position detecting sensor (76) indicating that the first guidance roll (66) has reached the desired position range, drives the transport means (42) according to the predetermined advancing distance without driving the supply-drum drive (30), the printing process being performed after completion of the advance movement and while the printable material (34) is stopped. The device according to claim 1, characterized in that, for advancing the printable material (34) by the predetermined advancing distance, the control unit, without driving the supply-drum drive (30) previously, immediately drives the transport means (42) corresponding to said advancing distance without simultaneously driving the supply-drum drive (30) if the first guidance roll (66) is within its desired position range. The device according to claim 1, characterized in that the first guidance roll (66) presses on the printable material (34) with its own weight. The device according to claim 1 or 2, characterized in that the first guidance roll (66) is supported between two arms (68) for rotation about a horizontal axis. The device according to claim 4, characterized in that said arms (68) are supported to be swiveled about a swivel axis (70) and that the two arms (68) carry a second guidance roll (72) to be swiveled about said swivel axis (70) and guiding the printable material (34) supplied from the supply drum (24). The device according to claim 4 or 5, characterized in that the first position detecting sensor (76) is actuated as soon as the arms (68) holding the first guidance roll (66) are within a predetermined range of swiveling positions. The device according to claim 5 or 6, characterized in that the printable material (34) is guided in opposite senses about the first and second guidance rolls (66,72). The device according to any one of claims 1 to 7, characterized in that the control unit, after the device has been switched on and if the first guidance roll (66) is within its desired position range, for a predetermined period of time feeds drive signals to the transport means (42), and that the control unit outputs a signal indicating a malfunction if, until lapse of said period of time, the first position detecting sensor (76) has not outputted a signal indicating that the first guidance roll (66) has left the desired position range. The device according to any one of claims 1 to 8, characterized in that the transport means (42) is provided with a rotatable drive roll (46) and a pressing roll (53) pressing thereagainst and rotatable about its axis, between which rolls (46,53) the printable material (34) is guided and is moved forward through friction. The device according to claim 9, characterized in that the axis of the pressing roll (53) is guided in vertical longitudinal holes (56) and that the pressing roll (53) presses, with its own weight, against the drive roll (46) or the printable material (34), respectively. The device according to any one of claims 1 to 10, characterized in that the supply drum (24) is driven by a direct-current motor (30) and the drive roll (46) is driven by a stepper motor (52). The device according to any one of claims 1 to 11, characterized in that the transport means (42), as seen in the moving direction (44) of the printable material (34), is arranged downstream of the printing means (14). The device according to any one of claims 1 to 12, characterized in that the already printed printable material (34) advanced by the transport means (42) is received by a winding drum (58) provided with a separate drive to be driven by the control unit. The device according to claim 13, characterized in that, between the transport means (42) and the winding drum (58), there is arranged a third guidance roll (80) pressing against the printable material (34) with a pressing force and keeping it tensioned. The device according to claim 14, characterized in that the third guidance roll (80) presses on the printable material (34) with its own weight. The device according to claim 14 or 15, characterized in that the third guidance roll (80) is rotatably supported by arms (82) supported to be swiveled about a horizontal swivel axis. The device according to claim 16, characterized in that the swivel axis of said arms (82) is the rotational axis of the drive roll (46) of the transport means (42). The device according to any one of claim 14 to 17, characterized in that a second position detecting sensor (84) is provided which detects that the third guidance roll (80) is within a desired position range in which the length of the portion of printable material (34) extending between the transport means (42) and the winding drum (58) is equal to or smaller than a predetermined maximum length. The device according to any one of claim 16 to 18, characterized in that the second position detecting sensor (84) is actuated when the arms holding the third guidance roll (80) are within a predetermined range of swiveling positions. The device according to claim 18 or 19, characterized in that the control unit, for winding up the printable material (34) after the latter has been advanced by the advancing distance, without driving the supply-drum drive (30) and without driving the transport means (42), drives the winding-drum drive (64) until the second position detecting sensor (84) emits an output signal indicating that the third guidance roll (80) has reached its desired position range. The device according to any one of claims 18 to 20, characterized in that the control unit, after the device has been switched on and subsequent to the sequential driving of the supply-drum drive (30) and of the transport means (42), drives the winding-drum drive (64) for a predetermined period of time and that the control unit outputs a signal indicating a malfunction if the second position detecting sensor (84) has not outputted a signal indicating that the third guidance roll (80) has reached its desired position range. The device according to any one of claims 1 to 21, characterized in that a third sensor (88) is provided for detecting the presence of printable material (34). The device according to any one of claims 1 to 11, characterized in that, in the moving direction of the printable material (34) downstream of the printing means (14), there is provided a cutting device controlled by the control unit and cutting a portion corresponding to the advancing distance off the printable material (34).

Inventors: GRAESSLE JOSEF, SCHWARZ WERNER, GRAESSLE, JOSEF, SCHWARZ, WERNER, Grässle, Josef
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1991
Main classification: B65H23
IPC codes: B65H23, B65H77