Abstract:
A tachograph has a cubic housing and a printing device having a thermal print head, a feed roller driven by a drive mechanism and a carrier movable out of the housing to reload a ribbon which forms a stock of printing material. Locking means lock and unlock the carrier in a closed position in the housing. A latch element is mounted rotatably on the carrier and subjected to an action of a tension spring. A snap-in hook of the latch element is associated with a snap-in member in a fixed position. An actuating arm is formed with the latch element, and a pushbutton is configured to be in operative connection with the actuating arm and mounted displaceably on the carrier. A fixed stop associated with the actuating arm disengages the latch element from the snap-in member when the pushbutton is actuated, and displaces the carrier in a direction of an insertion position when the actuating arm is supported on the stop.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application is a continuation of international application number PCT/DE03/00983, filed on Mar. 25, 2003, which designates the United States of America, and further claims priority of German patent application number DE 10215122.9, filed on Apr. 5, 2002, the both of which are herein incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     The invention relates to a tachograph having a cubic housing and a printing device, which has a thermal print head, a feed roller which is driven by a drive mechanism, and a carrier which can be moved out of the housing and is used for reloading a ribbon which forms the stock of printing material, and further having means for locking and unlocking the carrier in its closed position in the housing of the tachograph.  
         [0003]     Tachographs which are not designed for the use of record charts as recording media, but rather in which the driving and working time data determined are stored in suitably designed bulk memories, require suitable printing devices for documentation in the form of a visually readable document. These devices have to be arranged inside the tachographs since there is generally not enough space in a driver&#39;s cab of a commercial vehicle for the installation of an independent printer which corresponds with the tachograph. If a tachograph of this type is equipped with a printing device which, contrary to the use of plug-in, card-like printing substrates, envisages a printing principle with strip-like or ribbon-like printing material, it is necessary for the printing device in question to be loaded with the stock of printing material and for the starting section of the printing material to be moved into the printing position.  
         [0004]     One problem is, however, that tachographs are generally designed as built-in appliances and are therefore fitted with a flush front wall so that access for reloading the stock of printing material is only possible from the front side using a carrier which can be displaced in the manner of a drawer or can be pivoted open/folded open on the front side. In this case, in the area in which a tachograph is used, in which considerable vibration and shock loads occur, the locking and unlocking means assigned to the carrier are of crucial importance.  
         [0005]     DE-U 29720521 discloses a tachograph, in which a drawer-like carrier is provided for holding the entire printing device and is assigned a bistable snap-in mechanism. In the event of printing material having to be refilled, the carrier is unlocked by actuation of the front panel of the carrier, which panel serves as a pushbutton, and, when the front panel is released, is displaced into the insertion position. Apart from the outlay and an unreliable performance in respect of security against shocks because of the not inconsiderable mass of the carrier, the bistable snap-in mechanism requires the carrier to be able to be moved in the locked state, in the direction of the rear wall of the housing of the tachograph, which makes sealing of the front panel with respect to the front wall of the tachograph considerably more difficult in the locked state of the carrier.  
         [0006]     The same applies to a printing device described in DE-U 29920901, in which a thermal print head is arranged in a fixed position in the housing of the tachograph and the feed roller mounted in the carrier has to be brought into operative connection again with the thermal print head when the carrier is closed after each insertion of a ribbon. In such a printing device, the relatively high press-on force of the thermal print head obstructs the ability of the carrier to move, and so the snap-in mechanism has to be equipped with an extremely strong ejection spring or the carrier has to be pulled out by hand after being unlocked, which, apart from being disadvantageous to handle, requires esthetically unfavorable gripping means to be provided on the front panel of the carrier.  
       SUMMARY OF THE INVENTION  
       [0007]     An object of the present invention is to provide for a printing device of the generic type used in a tachograph having functionally reliable locking means which can be handled in a simple manner in respect of being unlocked and which meet the requirements of mass production by means of simple components which can easily be fitted.  
         [0008]     In one embodiment, the invention provides for at least one latch element which is subjected to the action of a spring to be provided, for the latch element to be mounted rotatably on the carrier, for a snap-in hook of the latch element to be assigned a snap-in member in a fixed position, for an actuating arm to be formed integrally with the latch element, for a pushbutton which can be brought into operative connection with the actuating arm to be mounted displaceably on the carrier, and for a positionally fixed stop which is assigned to the actuating arm to be provided in such a manner that, when the pushbutton is actuated, the latch element is disengaged from the snap-in member and, by the actuating arm being supported on the stop, the support is displaced in the direction of the insertion position.  
         [0009]     One advantageous development of the invention is that latch elements are provided on both sides of the carrier, and that the latch elements are fastened on a shaft which is mounted in the carrier, that a pin is fastened to the actuating arm, that the pushbutton is provided with a sloping plane which is assigned to the pin, that at least one latch element is assigned a switch indicating the closed position of the carrier, and that a spring-mounted push-in member which preferably interacts with the rear wall of the tachograph is arranged on the carrier.  
         [0010]     A preferred exemplary embodiment of the invention makes provision, in conjunction with a printing device, in which the thermal print head which is subjected to the action of a spring is mounted pivotably in a bearing bridge fastened to the cover plate of the housing of the tachograph and the feed roller and the drive mechanism are assigned to the carrier, with, in the closed position of the carrier, the feed roller being supported under the thermal print head, which rests resiliently on it, on retaining arms formed the bearing bridge, that the snap-in members assigned to the latch elements, and stops are arranged or formed on the limbs of the bearing bridge.  
         [0011]     The preferred exemplary embodiment can furthermore be developed by the fact that the bearing bushings of the feed roller, which bushings are arranged in the framework of the drive mechanism, are assigned wedge surfaces and snap-in lugs formed on the retaining arms, and in that the guide of the carrier has a play corresponding to the travel of the snap-in lugs.  
         [0012]     It is also conceivable that, in the case of a printing device according to the preferred exemplary embodiment, holders are formed for the bearing bushings of the feed roller in the bearing bridge in such a manner that, in interaction with the thermal print head resting resiliently on the feed roller, a play-free snap-in connection is provided for the feed roller and therefore for the carrier, and the latch elements are not absolutely necessary. This means that only the unlocking means have to be provided in order, when the pushbutton is actuated, to lift the bearing bushings out of the holders and to displace the carrier in the direction of the insertion position, with a push-in device which is provided in the rear space of the carrier displacing the carrier into a gripping position after the pushbutton is released. If a push-in device is not provided, then the unlocked carrier can be pulled out of the tachograph into the insertion position by means of gripping means formed in a suitable manner on the front panel.  
         [0013]     Further advantageous refinements of the invention emerge from the following description and the attached drawings. Apart from the fact that it achieves the set object in a satisfactory manner, the invention provides the advantage of being able to be used both in a structural concept, in which the entire printing device is assigned to the carrier, in which case suitable measures for forming the stops and snap-in members have to be taken in the housing of the tachograph in question, and also in the preferred exemplary embodiment which envisages the thermal print head and feed roller being separated in the event of a ribbon being reloaded. Furthermore, in the case of the preferred exemplary embodiment, the latch elements are used for exactly aligning the feed roller with the thermal element strip.  
         [0014]     The invention provides a particular effect by virtue of the fact that, when the carrier is locked by means of the pushbutton mounted in the front panel, the latch elements are pivoted and then, by the actuating arms being supported on the stops, a deflection of force causes the carrier to be displaced in the direction of the insertion position, so that, on the one hand, when the pushbutton is released, re-locking is prevented and, on the other hand, the frictional connection between the thermal print head and the feed roller is released, if appropriate with a pressure point caused by snap-in lugs being overcome. In this case, the actuation of the pushbutton by hand and the pivoting of the latch elements over a sloping plane permit a relatively strong tension spring which acts on the latch elements, and therefore enable a sufficiently high security against shocks.  
         [0015]     It is furthermore advantageous that, after the carrier is unlocked and after the pushbutton is released, the push-in device assigned to the carrier is used to displace the carrier into a gripping position. In this case, the compression spring assigned to the push-in device is dimensioned in such a manner that it overcomes at least the friction of the carrier in its guide and therefore only an insignificant amount of force is required in addition to the effort necessary during the closing of the carrier to pivot the latch elements and raise the thermal print head when bringing the feed carrier into the printing position. The closed position of the carrier is signaled by means of switches assigned directly to the latch elements. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0016]     The invention will be explained in greater detail below with reference to drawings, in which:  
         [0017]      FIG. 1  shows a perspective of a tachograph equipped with a printing device of the generic type,  
         [0018]      FIG. 2  shows a partial side view of the tachograph according to  FIG. 1  provided with cut-open sections, in the insertion position of the carrier,  
         [0019]      FIG. 3  shows a shortened side view of the tachograph according to  FIG. 1 , which is provided with cut-open sections, in the closed position of the carrier, and  
         [0020]      FIG. 4  shows a plan view of the push-in device, which is assigned to the carrier, in accordance with the arrow direction X in  FIG. 1 , with the cover plate cut open.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     The tachograph  1  which is illustrated by  FIG. 1  has a built-in housing part  2  and a front panel  3  fastened to the latter. The built-in housing part  2  comprises a cover part  4  and a bottom part  5 , side walls  6  and  7  and also a rear wall  8  being integrally formed on the cover part  4 . Limbs overlapping the side walls  6 ,  7  and the rear wall  8  are integrally formed on the bottom part  5  and on them latches, two  9  and  10  of which can be seen in  FIG. 1 , are formed. When the cover part  4  and base part  5  are joined together, said latches can be brought into engagement in a bayonet-like manner with tabs  11  and  12  which are formed on the side walls  6 ,  7 . U-shaped components  13 , the limbs of which are designed as resilient claws  14  and  15 , are fastened on both side walls  6 ,  7  for the purpose of fastening the tachograph  1  in a built-in compartment or in a suitable opening, for example in a dashboard. A depression provided in the cover panel  17  for a nameplate is referred to by  16 . A window cutout  18  through which the read-out of a display  19  can be read is provided in the front panel  3  in a manner known per se. Furthermore, pushbuttons  20 ,  21 ,  22  and  23  which are used, on the one hand, for logging on the driver and passenger and, on the other hand, for releasing personal data cards assigned to the particular driver and front passenger, reach through the front panel  3 . Guide slots  25  and  26  which are formed in a bead-shaped projection  24  and are countersunk in a funnel-shaped manner are used for introducing the data cards into the reading/writing assemblies located in the built-in housing part  2 . Recesses of the bead-shaped projection  24 , one of which is referred to by  27 , are used for grip when removing the data cards.  
         [0022]     As shown in  FIG. 1 , the printing device assigned to the tachograph  1  is in a state in which a carrier  28  is located in the insertion position, which is defined by a stop, with regard to the ribbon  29  which is to be reloaded from time to time and forms the stock of printing material. Said ribbon is accommodated in a trough  30  formed in a suitable manner in a carrier  28  which can be displaced in a drawer-like manner in the tachograph  1 . Cheeks  31  and  32  integrally formed on this carrier  28  are used for guiding the carrier  28  in guide rails  33  and  34  formed or fitted, on the one hand, on the side wall  6  and, on the other hand, on a stabilizing structural part provided in the built-in housing part  2 . A front wall of the carrier  28  is referred to by  35  and is designed in conjunction with an indentation (not referred to specifically), which is also suitable for providing a seal and is in the front panel  3 , in such a manner that it is fitted flush into the outer contours of the front panel  3 . A pushbutton  36  which is led out of the front wall  35  is used to trigger printing. By means of a rocker switch  37  which is likewise arranged on the carrier  28 , different functions and data memories can be selected and, for example in conjunction with the pushbuttons used for logging on the drivers, the working time data of the drivers can be interrogated.  
         [0023]     A further pushbutton  38  which is guided in the front wall  35  is used for unlocking the carrier  28  in the event of printing material having to be refilled. A tear-off comb which is formed on the front wall  35  and is used for severing a printed document is referred to by  39 . As  FIG. 1  shows, an elastomeric feed roller  41  which is connected to a shaft  40  and is used for advancing the printing material is mounted on the carrier  28 . That is to say, a framework  42  is fastened on the carrier  28  and bearing bushings, which are assigned to the shaft  40  and one of which is referred to by  45 , are secured in the limbs  43  and  44  of said framework. Directing disks  46  and  47  which are formed integrally on the bearing bushings  45  are used for axially aligning the shaft  40  when bringing the feed roller  41  into the printing position with the thermal printing head  48 , part of which is illustrated in  FIGS. 2 and 3 . Furthermore, the framework  42  is used for the mounting of the drive mechanism which drives the shaft  40 , i.e., a motor and a gear mechanism which is required between its motor shaft and the shaft  40  and which is assigned a covering  49  integrally formed on the front wall  35 . Latch elements which are arranged in a rotationally fixed manner on a shaft  52  mounted in the framework  42  are referred to by  50  and  51  and their function will be explained in greater detail below. A pin which is referred to by  53  and is fastened to the latch element  51  is assigned to the pushbutton  38 .  
         [0024]     It can be gathered from the partial side view of the tachograph  1  shown in  FIG. 2  that the pin  53  interacts with a sloping plane  54  which is formed on the pushbutton  38 , which is guided and supported in a suitable manner in the front wall  35 . In addition, a cut-open section A in the cheek  31  shows a tension spring  55  which is assigned to the latch elements  50 ,  51  and is fitted, on the one hand, on a hook  56  fixed on the framework and, on the other hand, on an angled lever  57  of the latch element  51 . A latch which is formed in each case on the latch elements  50 ,  51  and is provided with a snap-in hook  59  is referred to by  58 . An actuating arm which is likewise integrally formed on the two latch elements  50 ,  51  and on which a sliding surface  61  is formed is represented by  60 . A cut-open section B of the side wall  6 , front panel  3  and component  13  and a further cut-open section C of the cheek  31  of the carrier  28  permit a view of a limb  62  of a bearing bridge  63  which is fastened to the cover panel  17 .  
         [0025]     Studs  64 ,  65 ,  66  and  67  which are pressed into the cover plate  17  and disks which are pressed onto the latter and two of which are illustrated in  FIG. 2  and are referred to by  68  and  69  are used for the fastening of the bearing bridge  63 . The bearing bridge  63  is used, on the one hand, for mounting the thermal print head  48 , the pivot axis of which is referred to by  70 , and, on the other hand, for securing the feed roller  41  when the latter is in the printing position. In the insertion position of the carrier  28  that is illustrated in  FIG. 2 , the print head carrier  71  bears under the action of a spring (not illustrated) against a stop (likewise not illustrated) which is formed on the bearing bridge  63 . In the printing position of the carrier  28  according to  FIG. 3 , the print head carrier  71  is raised against the cover panel  17  and the thermal element strip  72  which is fastened to the print head carrier  71  is in operative connection with the feed roller  41  and with the printing substrate  73  which is situated between the feed roller  41  and the thermal element strip  72  and runs off from the ribbon  29 . It can furthermore be gathered from  FIG. 2  that switches  74 , bolts  75  and tabs  76  which are assigned to the latch elements  50 ,  51  are fitted or formed in pairs on the identically designed limbs  62  of the bearing bridge  63 . In addition, retaining arms  79  which are assigned to the feed roller  41  and are provided with wedge surfaces  77  and snap-in lugs  78  are integrally formed on the limbs  62 . Instead of the cylindrical bolts  75 , fingers provided with a ramp may also be formed directly out of the limbs  62 , which produces a greater security against shocks with a smaller outlay.  
         [0026]     The shortened side view of  FIG. 3  shows in the closed position of the carrier  28 , in which the feed roller  41  or the bearing bushings  45  of the shaft  40  of the feed roller  41  are held on the retaining arms  79  of the bearing bridge  63 , in which case the retaining arms  79  engage between the limbs  43 ,  44  of the framework  42  and the directing disks  46 ,  47  formed on the bearing bushings  45 , firstly, by means of cut-open sections D of the side wall  6  and component  13  and also E of the front panel  3 , the allocation of the structural elements situated in the carrier  28  to the structural elements arranged in a fixed position in the built-in housing part  2  in the closed position of the carrier  28 , and, secondly, by means of a cut-open section F of the cover part  4 , a section of the carrier  28  and of the push-in device  80  assigned to the latter, in accordance with the section line G in  FIG. 4 . It can be seen here that the latches  58  engage by means of the snap-in hooks  59  under the action of the tension spring  55  behind the bolts  75 , which are provided in snap-in members, and at the same time are in operative connection to the switches  74 . In addition, a compression spring  81  of the push-in device  80  acts on the snap-in hooks  59 .  FIG. 3  shows that, in the closed position of the carrier  28 , there is a distance a between the sliding surfaces  61  of the actuating arms  60  and the tabs  76  serving as stops. A threaded stud which is attached to the rear wall  8  and is used for aligning the tachograph  1  when it is inserted is referred to by  82 .  
         [0027]     As can be gathered from  FIG. 4 , in particular from the cut-open section H in the cover panel  17 , the push-in device  80  is arranged in a frame  83  of the carrier  28  which is chambered and has struts for stiffening purposes. That is, intersecting arms  87  and  88  are directly and integrally formed on a ram  84 , which is used as a push-in member and has a ram head  85 , and a shank  86  which supports the compression spring  81 . The intersecting arms  87 ,  88  are guided in the frame  83  and are used, in conjunction with a wall (not referred to specifically) of the frame  83 , through which they are guided, to limit the travel of the ram  84 . The installation of the push-in device  80 , which, by the ram head  85  being supported on the rear wall  8  of the tachograph  1  under the action of the compression spring  81 , causes the carrier  28  to be displaced, after being unlocked, into a gripping position, takes place in a simple manner by the fact that, after the compressions spring  81  is placed onto the shank  86 , the push-in device  80  is pushed into the frame  83  and secured on the carrier  28  by means of the intersecting arms  87 ,  88 . Catch elements formed on the carrier  28  serve to secure the intercepting arms  87 ,  88  when the latter come into the retaining position during displacement of the carrier  28 .  
         [0028]     The functioning of the unlocking of the carrier  28  will be summarized once again in brief below. If it can be seen that printing material has to be refilled in the form of a new ribbon  29 , then the carrier  28  is first of all unlocked by actuation of the pushbutton  38 . When the pushbutton  38  is released, the push-in device  80  displaces the carrier into a gripping position. The carrier  28 — the front panel  35  serving as a gripping element—can then be pulled out of the device into the insertion position which is determined by a suitable stop (not illustrated). After a new ribbon  29  is inserted, the carrier  28  can be pushed back into the device by applying pressure to the front panel  35 , in which case the free end of the printing substrate  73  is drawn off from the ribbon  29  to such an extent that it overlaps at least the feed roller  41  before the latch elements  50 ,  51  are snapped into place and the feed roller  41  is brought into the printing position.  
         [0029]     Specifically, there is the following sequence of functions when actuating the pushbutton  38  to unlock the carrier  28 . First, by the pin  53  sliding along the sloping plane  54  of the pushbutton  38 , the latch elements  50 ,  51 , which are fastened on the common shaft  52 , are pivoted in the arrow direction P counter to the action of the tension spring  55  and, as a result, the lock between the bolts  75  and the latching hooks  59  is released. After passing through the distance A, the actuating arms  60  strike against the tabs  76 . In this case, owing to the different distance between the shaft  52  and the points at which the actuating arms  60  strike against the tabs  76 , on the one hand, and between the shaft  52  and the pin  53 , on the other hand, a two-armed lever is produced. The latter causes, by the sliding surfaces  61  of the actuating arms  60  being supported on the positionally fixed tabs  76  on further actuation of the pushbutton  38 , the carrier  28  to be displaced by a deflectional force in the direction of the insertion position. At the same time, the bearing bushings  45  of the shaft  40  of the feed roller  41  are pushed over the snap-in lugs  78 , this presupposing a certain amount of play between the guide rails  33 ,  34  and the cheeks  31 ,  32  of the carrier  28  or a certain pivotability of the feed roller  41  about the driving gearwheel of the drive mechanism, and the feed roller  41  is therefore brought out of frictional connection with the thermal print head  48 .  
         [0030]     In this situation, the push-in device  80 , the entire travel of which is referred to by b in  FIG. 4 , acts in such a manner that the bottom (not illustrated) of a chamber, which is formed on the front wall  35 , serves to guide the pushbutton  38  and through which a shank  91  of the pushbutton  38  reaches, strikes against the pushbutton  38 , which is still being firmly held, and, when the pushbutton  38  is released, the carrier  28  is displaced into the gripping position, in which the intercepting arms  87 ,  88  bear against the frame  83 . In contrast with the design of the pushbutton  38  selected in  FIG. 2 , the pushbutton  38  may also be designed unambiguously, i.e., provided with a shank  91  which has a flat profile and on which the sloping plane  54  is formed on the end side.