Abstract:
A printing mail processing apparatus has an apparatus housing with a cassette bay therein, for removably receiving an exchangeable cassette. The cassette bay is closed by a cassette flap that has a finger on an underside thereof that interacts with a sensor. The sensor can detect, before exchange of a cassette that flap position for which a cassette extraction is possible. A microprocessor is connected to the sensor and uses the signal from the sensor to detect the position of the cassette flap. Given a closed cassette flap, the microprocessor causes voltage to be supplied to a chip reader unit mounted in the cassette bay. Given an opened cassette flap, the microprocessor causes voltage to be disconnected from the chip reader unit before each cassette exchange.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention concerns a cassette acceptance device with the capability to recognize the state of the cover of the cassette opening or bay in a printing mail processing apparatus or a similar printing billing or mail processing apparatus. 
   2. Description of the Prior Art 
   Conventional thermotransfer franking machines of the type T1000 and Optimal commercially available from Francotyp Postalia &amp; Co. KG do not have piracy protection for consumable material, i.e. an ink ribbon in a cassette. By means of an encoder, a microprocessor controller allows an ink ribbon conveyor to establish that an encoder disc is fastened on the same axle as a friction wheel, and the latter is likewise rotated. When the flap of the cassette bay is opened, a simple mechanism is activated and the friction wheel is raised from the ink ribbon of the cassette, which allows the cassette to be removed without causing damage. The operation of the machine is interrupted given a faulty ink ribbon transport. 
   The arrangement of a switch on the security housing of a franking machine is known from EP 1300807 A2; for different reasons, namely for protection for an operator so that if fingers of the operator are inserted into an opening of the franking machine, such as Ultimail®, also available from Francotyp Postalia &amp; Co. KG, they are not crushed by the transverse movement of the printing carriage. This solution is only suitable for inkjet printing franking machines, particularly for exchange of ink cartridges via the opening that can be sealed by a flap. The flap is equipped with a stop that, upon opening of the flap, activates a switch inside the security housing, causing current supply to a motor of the transverse movement mechanism of the printing module to be interrupted. Adoption of this solution for thermotransfer franking machines with ink ribbon cassettes is not possible without difficulty since there no movement of the printing module nor an exchange of an ink cartridge. Moreover, recently mail carrier regulating authorities have begun to require a higher printing quality that is supported by piracy protection measures from the franking machine manufacturer (such as a chip applied on the consumable material). 
   DE 199 58 946 A1 discloses a thermotransfer franking machine with a microcomputer to which a contact or sensors is/are applied in order to indirectly establish the presence of exchanged consumable material based on a physical characteristic by means of an evaluation (implemented by the microprocessor) of measured sensor data and stored operating data. If a chip with identifying data is not arranged on the cassette, a chip card (provided for this purpose) must then be inserted into a slot of a chip card reader in order to read the identifying data. The exchange is thus permitted only some time later. Moreover, exactly where the sensors are arranged and which of these are used for evaluation is dependent on the franking machine type, because usually already-present sensors are used that do not specifically detect an exchange of consumable material. 
   A detector is known from DE 199 58 941 A1 that also reliably detects the removal or exchange of consumable material when the apparatus is deactivated and is not supplied with system voltage. For this purpose, the detector uses a typical lithium battery that supplies a memory with a memory-retention voltage. There is no discussion, however, as to exactly where the sensor is arranged relative to the cassette. According to one variant, piracy protection is possible for thermotransfer cassettes in the form of an electronically-programmable chip, but this presumes a precise alignment of the cassette with the chip relative to a reading unit (chip reader) and the application of a contact force on order to securely read the data. Given the use of a chip for the purpose of piracy protection, in operation an electrical voltage is applied across the chip. This document does not address preventing removal or circumvention of the cassette during the operating state, such that access to the activated reading unit is possible. Such an access would at least lead to operational interferences or to manipulation or even to destruction of the chip. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a cassette acceptance device for an ink ribbon cassette that is equipped with an electronically-programmable chip in order to provide a piracy protection, which can be used in a thermotransfer franking machine that is equipped to prevent the measures for piracy protection from being penetrated or attacked. A further object is to fashion a cassette bay in order to ensure the contacting of the chip during the operation. A correct alignment of the cassette relative to the chip reading unit and the application of a contact force on the chip contacts should ensue in an optimally simple and reliable manner. The shape of the cassette flap should contribute to the alignment of the cassette and state recognition of the flap position. It is a further object to design the protection against external access to the chip reading unit during the operating state in a manner that allows detection of the operating state in connection with the piracy protection. 
   The above object is achieved in accordance with the present invention by a cassette acceptance device for use with a printing mail processing apparatus having an apparatus housing with an exteriorly accessible cassette bay therein, closeable by a flap, the device including a sensor disposed to interact with a flap finger at an underside of the flap to detect, before exchange of a cassette with respect to the cassette bay, that flap position for which a cassette extraction is possible, and a microprocessor connected to the sensor that detects the position of the cassette flap dependent on the signal from the sensor. The microprocessor, given a closed cassette flap indicated by the sensor signal, causing voltage to be supplied to a chip reader unit mounted in the cassette bay and, given an open cassette flap indicated by the sensor signal, causing the voltage to be disconnected from the chip reader unit before each cassette exchange. 
   For a cassette bay that is sealed by a flap, in accordance with the invention the cassette acceptance mechanism has a sensor that can detect the flap position before the exchange in which a cassette removal is possible. After the exchange and closing of the flap, parameter, usage and operating data stored via the chip attached to the cassette are read in a known manner. A mechanism is provided in the area of the sensor carrier, this mechanism translating the opening of the cassette flap into a movement of a sensor activation element. A sensor carrier supports the sensor and is integrally molded on one of the sides of the shaped cassette bay part above this part. The mechanism is fastened on a chassis such that it can move opposite to an elastic force. A microprocessor is operationally connected with the sensor and detects the position of the cassette flap by means of the sensor and in cooperation with the mechanism. The microprocessor is programmed to enable voltage supply from the microprocessor to the chip reader unit only when the cassette flap is closed. Given a closed cassette flap, external access to the chip reader unit is not possible. By means of mechanical elements of the flap and/or the shape of the cassette bay part, the cassette is pressed into a position in which a locking element acts on an edge of the cassette by means of a pressure element so that a secure electrical contacting of the chip with the chip reader unit exists. By means of the arranged locking element, the cassette is brought into a precise position relative to the chip reader unit and a force sufficient for a secure electrical contacting is thereby applied. Moreover, mechanical guide elements for alignment of the cassette relative to the chip reader unit in connection with the application of a contact force are used in the cassette bay. On its underside, the cassette bay has at least one flap finger and at least one elevation that are disposed between both flap arms with support pins. The elevation is fashioned so that the cassette is forced into the closed flap position in the locking position. Upon opening of the cassette flap, external access to the chip reader unit is prevented until a sensor signal is switched via the activation element upon triggering of the sensor and the voltage supply of the chip reader unit is deactivated. Access to and extraction of the cassette are therefore possible only when the voltage supply of the chip reader unit has been deactivated. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a thermotransfer franking machine with the flap of the cassette bay in place in accordance with the invention. 
       FIG. 2  is a plan view of the thermotransfer franking machine of  FIG. 1  without the cassette flap in place. 
       FIG. 3  is a view of the cassette flap from below. 
       FIG. 4  is a perspective view of a thermotransfer franking machine of  FIG. 1  with the cassette flap opened. 
       FIG. 5   a  is a perspective view of the shaped cassette bay part from the front and lower right in accordance with the invention. 
       FIG. 5   b  is a rear view of the shaped cassette bay part in accordance with the invention. 
       FIG. 6  is a detail of the mechanism to the left, next to the cassette bay in accordance with the invention. 
       FIG. 7  shows sensor for detecting the cassette flap position or encoder position in accordance with the invention. 
       FIG. 8   a  is a front view of the slider shown in  FIG. 5   b.    
       FIG. 8   b  is a side view of the slider shown in  FIG. 5   b.    
       FIG. 9  is a thermotransfer ink ribbon cassette with a chip in a perspective view from the rear and above left, suitable for use in the inventive thermotransfer franking machine in accordance with the invention. 
       FIG. 10  is a perspective view of the feed table and chassis of the thermotransfer franking machine in accordance with the invention. 
       FIG. 11  is a perspective view of the encoder wheel mounting in accordance with the invention. 
       FIG. 12  is a side view of the feed table and chassis of the thermotransfer franking machine in accordance with the invention. 
       FIG. 13  is a front view of the feed table and chassis of the thermotransfer franking machine in accordance with the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows a perspective view of a thermotransfer franking machine  1  from the front and upper right. The thermotransfer franking machine  1  is equipped on its right side  7  and on its upper part  10  with a flap  5  for the cassette bay of the franking machine  1 , and on its left side with a weighing plate  2  of a scale component. All housing parts are manufactured, for example, from colored plastic. The transport of mail pieces to and from the franking machine  1  ensues on the feed table  4  of the franking machine on the front side of the franking machine  1 , from the left side and to the right side  7 . 
     FIG. 2  shows a plan view of a thermotransfer franking machine without the flap. The flap was removed on the front side of the upper part  10 . Parts that are covered in  FIG. 1  are thereby visible, such as: the left external housing wall  3  near the cassette bay on the left side near the weighing plate  2  and the covering  30  for a left-side cassette acceptance mechanism; the thermotransfer ink ribbon cassette  8  with a locking element  11  for precise positioning of the cassette  8  in a locked position, and with a pressure element  12  for the cassette  8  for applying a contact force; the thermotransfer print head  9 ; the covering  60  for a right-side mechanism of the cassette acceptance and the right external housing wall  6  near the cassette bay on the right side  7  of the franking machine. The left-side covering  30  and the right-side covering  60  respectively have slit-shaped openings  31  and  61  for the left and for the right flap arms of the flap  5  (not shown), respectively. A damping element  59  for braking the flap opening speed of the cassette flap is mounted on the cover  30  for the left-side of the cassette acceptance mechanism. External access to the chip reader unit is thereby prevented for a sufficiently-long time and the voltage supply of the chip reader unit can be deactivated in this time period. The aforementioned parts—except for the locking element  11  and the pressure element  12 —are connected with the upper part  10  and belong to the upper housing shell. The feed table  4  belongs to the lower housing shell of the thermotransfer franking machine. Both the upper housing shell and the lower housing shell can be manufactured by injection molding. 
     FIG. 3  shows a view of the cassette flap  5  from below. In a depression  56 , the cassette flap  5  has a cavity  57 , corresponding to the size of the pressure element  12 , which exerts a pressure force on the chip (not visible). A flap finger  53  and projections  541 ,  542  are arranged between the two flap arms  51  and  52 . The left flap arm  52  is fashioned as a gearwheel segment in order to interact with the gearwheel of the damping element (not shown). Bearing pins  511 ,  521  for a connection (not shown, but rotatable on the axle  55 ) with the upper housing shell are respectively integrally molded on the flap arms  51  and  52 . A spring  58  that produces a resilient and elastic force counter to the closing of the flap  5  is arranged at one of the bearing pins  511 . The cassette flap  5  likewise can be manufactured by injection molding. In the event that the ink ribbon cassette  8  has not been correctly inserted by the operator, the projections  511 ,  542  on the underside of the cassette flap  5  force the ink ribbon cassette  8  into the locked position, at the latest upon closing of the cassette flap  5 . 
     FIG. 4  shows a perspective view from the front and above right of a thermotransfer franking machine  1  with flap  5  opened. The flap  5  is shown opened in the direction toward the upper part  10 . The flap  5  has flap arms  51 ,  52  arranged on both sides of its underside. The right external housing wall  6  on the cassette bay merges on the right side  7  into the right side wall of the upper shielding element of the franking machine, and into the right cover  60 . A first step  62  (aligned as above) is provided that corresponds to the flap shape on its underside. The left external housing wall  3  on the cassette bay merges into the upper shell of the franking machine and into the left cover  30 . A second step  32  (aligned as above) is provided that corresponds to the flap shape on its underside and accommodates the damping element  59  thereon. The damping element  59  is formed of a braking drum and a gearwheel that is engaged with the gearwheel segment of the left flap arm  52 . Upon closing of the flap, the arms  51 ,  52  of the cassette flap  5  respectively dip into the corresponding slit-shaped openings  31  and  61  in the steps  32  and  62  of the left and right covers  30  and  60 . On its underside, the flap  5  has a flap finger  53  serving as an activation element for a mechanism that acts on a sensor (not visible) that detects the state of the flap  5 . A disconnection of the supply voltage already ensues upon lifting off the front flap edge by a few millimeters (approximately 10 to 20 mm travel), i.e. before an access to the chip reader unit or, respectively, the extraction of the cassette  8  is possible. A correctly-placed ink ribbon cassette  8  is precisely arranged by a locking element  11  resiliently mounted on the shaped cassette bay part  17 . The ink ribbon cassette  8  is held in a locking position by the pressure element  12 , the pressure element  12  being arranged at the tip of the locked element  11  (not visible) and a positive application of a sufficient contact force on the chip of the ink ribbon cassette  8  is effected. 
   A chip reader unit (covered) is arranged in an opening on the rear housing wall  173  of the cassette bay  17 . The cassette bay is laterally bordered on both sides by a right inner housing wall  171  and a left inner housing wall  172 . The left inner housing wall  172  has an opening  18  for the friction wheel  38 , which is raised from the ink ribbon cassette in the representation according to  FIG. 4 , i.e. given an opened flap  5 . 
     FIG. 5   a  is a perspective view of the shaped cassette bay part from the front lower right. Respective mechanisms located under the cover and steps of the upper housing shell rest (in a manner not shown) on the chassis between the left and right inner housing walls  172  and  171  and the left and right outer housing walls on the shaped cassette bay part  17 , while the associated sensors rest on respective integrally-molded sensor carriers  174  and  175 . The sensor  36  for detection of the cassette flap state/encoder position rests on the external sensor carrier  174  of the shaped cassette bay part  17 , the sensor carrier  174  being integrally-molded on the left inner housing wall  172 . The inner space (cassette bay) of the shaped cassette bay part  17  is bordered by the right inner housing wall  171 , the left inner housing wall  172  and the rear housing wall  173 . A molding  1731  on the edge between the left inner housing wall  172  and the inside of the rear housing wall  173  forms an outer wall of a channel  1734  for a slider  43  (shown in other figures), of which only its top slope  434  is visible in  FIG. 5   b . A quadrilateral opening  1732  in the rear housing wall  173  accommodates the chip reader unit  14 . A circular opening  1733  in the rear housing wall  173  is provided for the winding mandrel of the cassette coil (not shown). The left inner housing wall  172  has an opening  18  and a lateral guide  1721  for correct positioning of the cassette upon insertion. The right inner housing wall  171  likewise has a lateral guide. An upper housing wall  176  likewise has guides  1761 ,  1762  as positioning aids. The upper housing wall  176  laterally merges into the left and right inner housing wall and to the rear into the rear housing wall  173  and not only stabilizes the cassette bay but also carries integrally-molded fasteners (obscured in  FIG. 5   b ) for the elastic locking element  11 , on the free ends of which the pressure element  12  is integrally molded. A frame  177  (protruding into the inner space of the cassette bay) for the print head is integrally-molded on the lower end of the rear housing wall  173  in the middle thereof. The space enclosed by the lateral integrally-molded sensor carriers  174  and  175  is sealed from below by base plates  178 ,  179 , which are respectively integrally-molded on the rear housing wall  173  between the left and right inner housing walls  172  and  171 . For low-friction mail piece transport, it is advantageous for the base plate  178  to gently rise outwardly relative to the feed table  4 . Downstream in terms of mail flow, the base plate  178  terminates in a thickened edge  1781  before the frame  177  for the print head. For ejection of the mail pieces, it is advantageous for the base plate  179  to begin with a thickening  1791  after the frame  177 , the thickening  1791  accommodating non-actuated rollers  1792  and  1793  and supporting them such that they can rotate. 
     FIG. 5   b  shows a rear view of the shaped cassette bay part with a channel-shaped molding  1734  on its outer wall  1730 . The channel  1734  centrally has a guide channel  1734  for the rail  432  and a catch or dog  4331  on the front side of the slider  43 . In the shown position, a force can be exerted by the pressure spring  44  on the mechanism (encoder wheel mounting, not shown) via the slider  43 . The mechanism can move across the slider  43  by virtues of a first force F 1  acting on the slider  43 . A pressure spring  44  is arranged on the slider  43  so that the pressure spring  44  relaxes and the first elastic force F 1  is effectively exerted on the mechanism when opening of the cassette flap  5  ensues. The slider  43  is movably arranged between the shaped cassette bay part  17  and the chassis in the channel  1734  of the shaped cassette bay part  17  and, in the representation according to  FIG. 5   b , is shifted upwardly. Upon activation the top slope  434  proceeds counter to the dynamic effect (force action) of the pressure spring  44 . The slider  43  has an actuation slope  437  for the mechanism (located under the cover and steps of the upper housing shell) that is supported on the chassis. Operation thereof is initiated by a change of the cassette flap position (stable), detected by the sensor  36  that rests on the sensor carrier  174  of the shaped cassette bay part  17 . The sensor carrier  174  is externally integrally-molded on the left inner housing wall  172  and has a sensor activation lever  361  that is brought into engagement with the mechanism. The other sensor carrier  175  of the shaped cassette bay part  17  likewise can have a sensor in order to detect the ejection of mail pieces. The back side  1730  of the rear housing wall  173  of the shaped cassette bay part  17  has a fastener  1763  for the locking element  11  resiliently mounted on the upper housing wall  176 . The back side  1730  of the rear housing wall  173  of the shaped cassette bay part  17  shows the circular opening  1733  passing through it and a circuit board  13 , which enables the electrical connection and mechanical fastening of the chip reading unit. The shaped cassette bay part  17  can be manufactured by injection-molding. 
     FIG. 6  shows details of the mechanism that is arranged to the left, next to the cassette bay under the left cover  30 . The mechanism has an encoder wheel mounting that is fastened on the chassis such that it can rotate around a rotation axle  39 . The slider  43  is forcibly connected with the encoder wheel mounting, which can move counter to a second resilient force. Given an opened flap  5 , the slider  43  between the chassis (not shown) and outer channel wall  1731  thus serves for force transfer to the encoder wheel mounting, which has a rocker  333  mounted such that it can rotate on the axle  39 , the axle  39  being oriented transverse to the mail piece transport direction. Given a closed cassette flap (not shown), a force F is exerted on the top slope  434  of the slider  43  by the flap finger  53 . The slider  43  is therefore shifted downwardly (as shown in the representation according to  FIG. 6 ) and thus can exert no force on the encoder wheel mounting. A tension spring  37  is fastened on the shaped cassette bay part  17  near the left outer housing wall and engages the encoder wheel mounting  33  so that the tension spring  37  is tensed when the cassette flap  5  is opened, so a second resilient force F 2  is effectively exerted on the mechanism. The sensor actuation element itself has a spring and, in this exemplary embodiment, is formed as a sensor actuation lever  361  mounted such that it can resiliently rotate. Due to the force effect of the tension spring  37 , a crank disk  3347  on the end of a fourth rocker  334  of the encoder wheel mounting is raised relative to the level of the feed table  4 , thereby activating the sensor actuation lever  361 . The sensor actuation lever  361  thereby performs a rotational movement around an axle  360 , and a vane  362  integrally-molded on another end of the sensor actuation lever  361  projects from the detection region of the sensor electronic of the sensor electronic housing  363 . At the same time, a friction wheel  38  is pushed through an opening  18  in the left inner housing wall  172  and through a lateral window opening of the ink ribbon cassette onto the ink ribbon. The friction wheel  38  is rigidly coupled with an encoder wheel (not shown) via a common bolt  34  supported in at least one rocker  333 . When the ink ribbon is advanced (due to a printing event), this leads to a rotation movement that is transferred to the encoder wheel and is detected by an encoder (not shown). 
   A sensor  36  for detection of the position of the cassette flap  5  (i.e., the encoder position) is shown in perspective view, from the front and upper right, in  FIG. 7 . A spring  364  holds the sensor actuation lever  361  in the shown position when it is not activated. This is the case when the cassette flap  5  is opened. The spring  364  is designed, for example, as a torsion spring with one spring leg situated in a hole  3611  of the sensor actuation lever  361  and the other spring leg resting on a sensor electronics housing  363 . The sensor electronic  5  includes, for example, a light barrier that (in the shown position) is interrupted by the vane  362  integrally molded on the lever  361 . For example, a sensor of the type Photointerrupter LG-413L from the company Kodenshi Corp. can be used. Given suitable dimensions of the encoder wheel mounting  33 , the friction wheel  38  performs a sufficiently-large pivot movement that also actuates the sensor actuation lever  361 , due to its lever length between its axle  360  and its outermost end. 
   A front view of the slider  43  is shown in  FIG. 8   a  and a side view is shown in  FIG. 8   b . The slider  43  enables the pivot motion and, given opening of the flap  5 , serves for force transfer to the encoder wheel mounting. A pressure spring  44  shifts the slider  43  upwardly with a predetermined force and thereby slides the axle  34  of the encoder wheel mounting  33  into an elongated (oblong or slotted) hole of the chassis  40 , causing the encoder position to change to such a degree that the friction wheel  38  is no longer in contact with the cassette ink ribbon. Given an opened cassette flap  5 , no force F is exerted on the top slope  434  of the slider planar body by the flap finger  53 . The slider planar body  431  has a flat, smooth back side and at least one rail  432  for guidance to its front side, which is integrally molded running in the movement direction. A second, narrow guide rail  4311  can be integrally molded on the front side of the slider planar body  431 . Its upper end is bordered by the top slope  434  and its lower end is bordered by a hollow cylinder that is integrally molded so as to curve forward. The wall  436  of the hollow cylinder has a fastening opening  438  for a pressure spring  44 . Given an opened cassette flap  5 , either a top  435  of the hollow cylinder or an actuation slope  437  of the slider planar body can come into engagement with at least one part of the mechanism located behind the left cover  30  of the upper housing shell. Between its middle and its lower end, the slider planar body  431  has a tuning fork-shaped opening  439  for a snap-in spring part  433  in the middle of the tuning fork-shaped opening  439 . The snap-in spring part  433  is directed with its nose  4331  in the guide groove  1735  and prevents removal of the slider  43  from the channel in the mounted state (as is shown in  FIG. 5   b ). 
   A thermotransfer ink ribbon cassette with chip is shown in  FIG. 9  in perspective view from the rear upper left. The thermotransfer ink ribbon is visible in a lower first opening  88  and in a second opening  85  of the left side wall  83  of the housing of the thermotransfer ink ribbon cassette. The chip  81  (for example a conventional type SEL 4442 from Siemens AG) is centrally mounted near the upper edge of upper cassette wall  82  and the rear cassette wall  84 . The latter has a height H=55 mm and a maximal length L=10.2 mm in the region of the lower first opening  88  up to the upper edge. A circular opening  86  is incorporated into the one half of the rear cassette wall  84  for a winding mandrel (not shown). The other half abuts the left side wall  83  of the housing. 
   A perspective view from the front left and above of the feed table and of the chassis of the franking machine is shown in  FIG. 10 . The perspective view also shows the relative position of mechanical and electrical components for the feed table  4  and for the chassis  40 . These components (such as the locking element  11  with the pressure element  12 , the circuit board  13  with the chip reader unit  14 , the rollers  1792  and  1793  (participating in an un-actuated manner in the ejection), the sensor  36  and the slider  43 ) are all mounted on the shaped cassette bay part shown in  FIGS. 5   a  and  5   b . The position of the locking element  11  with the pressure element  12  relative to the thermotransfer print head  9  corresponds to the necessary separation resulting from the height H of the cassette  8 . The thermotransfer print head  9  is fastened on the chassis  40  and protrudes into the mail transport path. 
   The slider  43  is arranged between the chassis  40  and the shaped cassette bay part, upstream (in terms of the mail flow) from the thermotransfer print head  9 . A mechanism is arranged upstream (in terms of the mail flow) from the slider  43  and fastened on the chassis  40  such that it can rotate around a rotation axis  39 . The mechanism has an oblong guide opening  46  introduced into the chassis  40  for the axle  34 , for the encoder wheel  35  and the friction wheel  38 , an encoder wheel mounting  33  that has a nose  3336  for fastening one end of a tension spring (not shown) and a separation element  47  that has a neck  471  with head  472  for fastening to the other end of the tension spring (not shown). The force effect of the tension spring (not shown) effects the support (shown in  FIG. 10 ) of the axle  34  on one end in the oblong guide opening  46 . The actuation slope  437  of the slider  43  abuts the axle  34  in order to be able to shift the bolt  34  into the oblong guide opening  46  when the cassette flap  5  is opened. The force effect of the pressure spring (not shown) of the slider is stronger than that of the tension spring and causes (in a manner not shown) the bolt  34  to be positioned at the other end in the oblong guide opening  46 . The pressure spring is tensed upon closing of the cassette flap  5 , in that its finger  53  presses on the top slope  434  (as has already been explained using  FIG. 8   b ). 
   A circular opening  48  in the chassis  40  is provided for a winding mandrel (not shown) that is downstream (in terms of the mail flow) from the thermotransfer print head  9 . At the outlet of the mail path, the feed table  4  exhibits a quadrilateral opening  45  that is provide for an actuated ejection roller  15  that faces the un-actuated rollers  1792 ,  1793  of the shaped cassette bay part, these un-actuated rollers  1792 ,  1793  also participating in the ejection of the mail pieces. 
     FIG. 11  shows a perspective view of an encoder wheel mounting from the front and upper left. The first and third rockers  331  and  33  of the encoder wheel mounting  33  exhibit bearing openings  3315  and  3335  for the axle  34  (not shown), via which the encoder wheel  35  (not shown) and the friction wheel  38  (not shown) are rigidly connected with one another. The second and fourth rocker  332  and  334  of the encoder wheel mounting  33  exhibit bearing openings  3325  and  3345  for the rotation axle  39  (shown in a dash-dot manner). One end of the tension spring  37  is connected with an end  3336  of the third rocker  333  of the encoder wheel mounting  33 . A crank disk  3347  is arranged on the end  3346  of the third rocker  334  of the encoder wheel mounting  33  that is facing away from the rotation axle  39 . The first and second rockers  331  and  332  are separated from one another via a connection piece  335 . Connection pieces are likewise integrally molded between the other adjacent rockers. A nose  3317  is integrally molded on the first rocker  331 . 
   A side view of the feed table and chassis of the franking machine in the state of a closed (not shown) flap is shown in  FIG. 12  and a front view is shown in  FIG. 13 . The inventive mechanism includes the separation element  47  fastened on the chassis  40 , the oblong opening (not visible) introduced into the chassis  40  and the encoder wheel mounting  33  that can rotate around a rotation axle  39  fastened on the chassis  40 . This encoder wheel mounting  33  actuates a sensor  36  and supports the axle  34  for the encoder wheel  35  and the friction wheel  38 , whereby the position of the axle  34  is changed by the slider  43  due to the elastic force F 1  of a pressure spring  44  counter to the elastic force F 2  of a stressed tension spring  37  between the separation element  47  (fastened on the chassis  40 ) and the encoder wheel mounting  33  as soon as the flap is opened and the force effect F decreases. When a closing of the cassette flap  5  ensues, the pressure spring  44  is tensed since F 2 &lt;F 1 &lt;F. Via the opening  18 , the friction wheel  38  of the shaped cassette bay part then arrives (in the manner shown in  FIG. 5   a ) at engagement in the inserted cassette with its thermotransfer ink ribbon. 
   The axle  34 , the rotation axle  39 , the separation element  47  and the chassis  40  preferably are produced from metal, and the locking element  11 , the tension spring  37 , the pressure spring  44 , the torsion spring  364  preferably are produced from spring steel. The torsion spring  364  exerts a third force effect F 3  on the crank disk  3347  of the spring-mounted encoder wheel mounting  33  via the sensor actuation lever  361 , with F 3 &lt;F 2 . 
   The encoder wheel mounting  33  can be manufactured from plastic or metal by injection-molding, but the invention is not limited to the shown preferred embodiment. 
   Alternatively, the encoder wheel mounting  33 , the axle  34  and the axle  39  can exhibit a non-linear shape. For example, they can be curved from a wire segment like a paper clip. A hollow shaft attached on the wire segment instead of the axle  34  then bears the encoder wheel  35  and the friction wheel  38 . The arrangement of the tension and/or pressure springs can be modified or omitted. The sensor actuation element is described above as a spring-supported, rotatable sensor actuation lever  361 , but other embodiments are conceivable as long as they are able to detect a rotation movement. For example, a gearwheel engaged with a further gearwheel arranged on the rotation axle  39  can be arranged on the rotation axle  360  at the sensor  36 . The torsion spring  364  can then be omitted. A further slider can serve as the sensor actuation element in a further embodiment variant. 
   Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventor to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of his contribution to the art.