WO1991006929A1

WO1991006929A1 - Automatic stamp machine

Info

Publication number: WO1991006929A1
Application number: PCT/NL1990/000165
Authority: WO
Inventors: Petrus Johannes De Rijk; Antonius Johannes Montagne
Original assignee: Product Partners
Priority date: 1989-11-01
Filing date: 1990-11-01
Publication date: 1991-05-16
Also published as: AU6740690A; NL8902699A

Abstract

Automatic stamp machine for automatically dispensing value-denominated stamps, provided with a chassis, a drive system with a stepping motor, an optical measuring system for consecutively scanning a progressively moved strip of stamps which are fed from a stamp roll and are each separated from one another by a separating edge and for generating a signal which represents the degree of light attenuation, a processing and control unit for examining the light attenuation signal to determine the separating edge, and a cropping system for cutting off an externally specified number of stamps under the control of the processing and control unit. The optical measuring system is designed to measure the average light attenuation, at least over a portion of the width of the stamp strip, at discrete length intervals with high resolution. The optical measuring system is synchronised with the drive system so that a light measurement takes place for every step of the stepping motor per said length interval. The digitally designed processing and control unit determines the separating edge on the basis of detection criteria and is of self-adjusting design, the stamp parameters such as length and light attenuation and their variation being automatically determined and processed. During an initialisation phase the processing and control unit determines a threshold value for stamp detection by storing a histogram of measured values of light attenuation for a number of stamps in the data memory, the threshold, tr, being calculated as follows: tr = Min + A.(Mod - Min), where Min is the minimum value of the light attenuation found and Mod is the mode found, i.e. the value occurring most, and A is a weighting factor.

Description

Automatic stamp machine.

The invention relates to an automatic stamp machine for automatically dispensing value-denominated stamps, provided with a chassis, a drive system with a stepping motor, an optical measuring system for consecutively scanning a progressively moved strip of stamps which are fed from a stamp roll and are each separated from one another by a separating edge and for generating a signal which represents the degree of light attenuation, a processing and control unit for examining the light attenuation signal to determine the separating edge, and a cropping system for cutting off an externally specified number of stamps under the control of the processing and control unit. Such an automatic stamp machine is disclosed in US Patent Specification 4,637.523-

The automatic machine known from said patent specification is intended to dispense a number of stamps, with the aid of a cropping operation, in response to an externally generated request signal and the device is intended in particular for examining whether or not a blank or imprinted stamp is dispensed as a valid stamp. The said processing and control unit is designed to distinguish blank stamps from printed stamps with the aid of the optical scanning system. The circuit designed for this purpose using analog techniques makes use of only two sharply different detection criteria for the light attenuation signal. The known automatic machine is intended, in particular, for stamps of very defined dimensions. The device is not capable of being able to handle, without separate preset lengths, the various types of value-denominated stamps existing in practice and having a large spread in length and light attenuation. No position information is available either in the processing and control unit and no feedback is possible to another size and light attenuation.

The object of the invention is to eliminate the abovementioned problems and to provide an automatic stamp machine with which many types of value-denominated stamps having a large range of sizes and light attenuation can be examined and dispensed .

According to the invention, this is achieved in an automatic machine of the type mentioned in the introduction in that the optical scanning system is designed to measure the average light attenuation, over at least a portion of the width of the stamp strip, at discrete length intervals with high resolution, the optical measuring system being synchronised with the drive system so that a light measurement takes place for every step of the stepping motor per said length interval, and in that the digitally designed processing and control unit determines the separating edge on the basis of detection criteria and is of self-adjusting design, the stamp parameters such as length and light attenuation and their variation being automatically determined and processed and conse¬ quently, all the stamps encountered in practice can be dispensed by the automatic machine.

US Patent Specification 4,716,799 discloses an automatic stamp machine for issuing admission or lottery tickets of a particular type. The issuing takes place at relatively low issuing speed and the optical system is used solely to know the ticket length. The issuing and fault detection takes place exclusively on the basis of this length information. The specified adaptive operation relates to the mean stamp length, which is a parameter which is not strictly necessary for issuing. On the other hand, the automatic stamp machine according to the application is capable of dispensing value-denominated stamps having a large range of sizes and light attenuation at high speed. The starting point of the present automatic stamp machine is an issuing on the basis of optical detection and fault detection based on length information. The detection parameters are adjusted on the basis of the optical properties, as a result of which a reliable optical detection always takes place. The average stamp length is in fact redundant information and it is used, in addition to the optical information, for fault detection and fault repair. If a fault condition occurs in the automatic stamp machine during issuing, for example as a consequence of altering stamp properties, the automatic machine again carries out the initialisation phase, depending on the type of fault. The parameters of the adaptive measuring system are determined again and the issuing is resumed. To summarise, in the known automatic stamp machine the adaptive operation takes place solely on the basis of the average stamp length, whereas in the case of the automatic stamp machine according to the invention, the adaptive operation takes place on the basis of optical .properties and stamp length. A fundamentally better detection is obtained by a different optical measuring system and an operation which is independent of stamp length as a result of a different mechanical construction. The invention will be explained in greater detail on the basis of exemplary embodiments, with reference to the drawings, in which:

Figure 1 shows an elevation of the one open side of the automatic machine according to the invention; Figure 2 shows an elevation of the other open side of the automatic machine according to the invention;

Figure 3 shows a cross-sectional elevation of the optical system from the automatic machine of Figures 1 and 2;

Figure 4 shows a block diagram of the general principle of the automatic machine according to the invention;

Figure 5 shows a state diagram of the automatic machine according to the invention;

Figure 6 shows an example of the light attenuation profile of a strip of stamps having a high contrast; Figures 7a. b and c show light attenuation profiles and histograms of one and the same strip of stamps A, respectively, in three different automatic machines 1, 2 and 3; and

Figures 8a, b and c show light attenuation profiles and histograms, respectively, of three different strips of stamps B, C and D in the same automatic machine 1.

The device shown in the figures for automatically dispensing value-denominated stamps or, to give it a short name, automatic stamp machine is a combined electronic and mechanical device which is capable of issuing a specified number of value-denominated stamps automatically via remote operation. Value-denominated stamps are understood to mean all the stamps which are supplied on rolls, such as postage stamps, stamps in supermarkets, automatic filling stations, etc. In these cases, the stamps are separated one from another by a separating edge, for example a perforation or special printing such as a transverse line. The automatic stamp machine is filled with one roll of stamps which is transported to the stamp outlet by means of a drive system such as a positioning motor with associated drive roller and pressure roller. Stated briefly, the stamps are scanned by the optical measuring system, the stamps being examined for various properties such as size, light transparency or light attenuation, etc. by the processing and control unit, and a self-adjusting measuring system being obtained by means of feedbacks. This makes it possible to handle different types of stamps, for example with a length of 14-43 πim and a width of 15-30 mm, and with a stamp printing which has to fulfil at least a minimum optical detection criterion. The number of stamps is then counted and, after the specified number has passed, the stamp strip is progressively moved further over a certain distance until the rear separating edge of the last stamp has arrived opposite the cropping system and cropping takes place. As a result of using said cropping system, it is not necessary to pull off and tear off the stamps oneself.

In Figure 1, 1 is the chassis of the automatic stamp machine, 2 is the externally insertable cassette, 3 is the stamp roll, 4 is the stamp roller shaft, 5 is the stamp strip, 6 is a drive roller driven by the stepping motor (not shown) , 7 is a pressure roller, 8 is a leafspring, 9. 10 and 11 are, respectively, the photosensitive cell, a light guide and a prism, 12 and 13 are respectively the upper and lower knife of the cropping system, 14 is a lock for sealing off the cassette holder, and 21 is a stock sensor. Figure 2 shows the other side of the housing. Here 20 is the stepping motor, 21 is the stock sensor, 1 is the light-emitting cell, 22 is the processing and control unit, 23 is a number of display members, 24 is a magnetic coil for the cropping knife, 25 is a supply on-off switch, 26 is an actuating switch, 27 is a mains lead, 28 is a communication port or gateway, 29 is a transformer and 33 is a lock sensor.

Figure 3 shows a cross section of the optical measuring system. This shows clearly how the light beam delivered by the infrared light-emitting cell or LED 15 is deflected towards the stamp strip 5 via the prism 11. The light transmitted through said strip 5 is finally collected via the detection wedge or detection guide 10 by the photosensitive cell or infrared sensitive PIN-diode 9. It is clear that the movement of the stamp strip 5 is directed perpendicularly to the drawing plane of Figure 3-

Figure 4 shows a block diagram of the operation of the automatic stamp machine from Figures 1 to 3- The knife control circuit 31. which receives the cutting command from the processing and control unit 22, delivers a control signal to the electro¬ magnet 24, which moves the movable knife 12. The circuit 31 contains a buffer capacitor from which the energy is obtained for moving the electromagnet 24 and a pulse-width modulation circuit with which the holding force of the magnet is regulated. Shown on either side of the progressively moving stamp strip 5 are the infrared light-emitting cell (LED) 15 and the photosensitive cell or PIN-diode 9- The prism 11 and the light guide or detection wedge 10 are again arranged between them. The cells 15 and 9 are connected respectively to the LED drive circuit and a 10-bit A/D converter in the optical interface 30. The stamp strip 5 originating from the stock roll 3 passes between the prism 11 and the detection wedge 10 and causes a varying light transmission through the optical channel which is dependent on the light attenuation of the stamp strip.

An average measurement is carried out over the width of the stamp strip with the measuring system. The average light transparency or attenuation is measured at discrete length- position intervals and the measurement signal is processed digitally in the processing and control unit. The position of the separating edge is determined with the aid of detection criteria to be explained below. It is consequently possible to count the number of stamps which has been transported and to determine where the exact separating edge is situated, after which a command signal can be delivered for the cropping system. A position window is introduced to take account of the progressive movement, determined by the drive system, of the stamp strip 5 from the measuring system to the cropping system 12, 13.

After every detection of a separating edge, for example the perforations 38, the number of stamps still to be counted is reduced by one. When all the stamps specified have been counted, the last dete^*cted perforation 38 is transported towards the knife system 12, 13 and the stamp strip 5 is cut off. Since a separating edge, such as a perforation, is on average one mm wide, approxi¬ mately three to four measurements will be carried out during the passage of the separating edge, which ensures the accuracy of the cutting action of the knife. After this cutting-off has taken place, the stamp strip is rewound a number of steps from behind the knife. As a result of this, the stamps are again in an optimum position, ready for the subsequent issue. Instructions for issuing stamps are received directly via the communication port 28 from the payment system connected.

The optical measurement is synchronised with the progressive movement of the stamp strip which is brought about by the stepping motor with high resolution, i.e. a very small step. A light measurement takes place at every small step of the stepping motor with the aid of the pulsed light-emitting cell 15- Since the stepping motor 20 has a step angle of, for example, 3-75° and the radius r of the drive roller is, for example, 4.5 mm, a transpor¬ tation distance of X = 2 π r (α/36θ) = 2 π 4.5 (3-75/360) = 0.3 mm will be traversed per step. It will be clear that the stamp strip can be moved progressively either forwards or backwards.

Under the control of the unit 22, the motor control circuit 32 provides the progressive movement, possibly with half-step facility, adjustable minimum speed, acceleration, maximum speed and deceleration of the stamp strip. 7 again indicates the pressure roller and 6 indicates the drive roller driven by the stepping motor 20.

A communication interface 33 for communication to the outside via the communication (RS 232) port 28, a data memory 34, a memory section 36. incorporated in the parameter memory 35. for parameters after manufacture and a memory section 37 for para¬ meters after initialisation are furthermore respectively connected to the processing and control unit 22. The communication interface 33 provides the communication of the automatic stamp machine with the payment system. It contains a communication protocol embodying fault correction and message recognition. Valid messages for the automatic stamp machine are transmitted to the processing and control unit. Automatic stamp machine signals are emitted from the processing and control unit 22 to the issuing system via said communication interface 33-

Extensive procedures for the initialisation of the automatic machine and dealing with faults occurring during issuing make the automatic machine a universal, self-learning system for issuing stamps, which, if provided with a standard RS 232 or current-loop connection, can be connected directly to the payment system. Communication with a payment system takes place, for example, in accordance with the ISO 1745 protocol. The automatic stamp machine is controlled by the processing and control unit 22 with the aid of the state diagram shown in Figure 5- The control signals EC (error code) and MSG (message) shown in said diagram provide for the transition between the various states and stand, respectively, for the error code and the message code.

The "POWER UP" state

After the mains voltage has been switched on (hardware reset), the automatic machine enters the "POWER UP" state. In this state, the parameters present in the non-volatile parameter memory (EEPROM) 36 are checked for their validity. If the parameters are not valid, the parameters are taken over from the program memory. A hardware check is then carried out. If the hardware is not found to be in order, the error code acquires a value which corresponds to the error detected. For an error code of zero, the automatic machine proceeds to the subsequent "INIT" (initialisation) state and for any error code not equal to zero, the automatic machine proceeds to the "ERROR" state.

The "INIT" state

In this state, a check is first of all made on whether there are stamps in the optical transmission channel. If this is the case, they are rewound until the optical transmission channel is transparent. The light attenuation of the transparent optical transmission channel has been measured after manufacture and its value has been stored in the non-volatile parameter memory 36. During rewinding, the measured value of the light attenuation is compared with this stored value. If the feed strip which hangs out of the automatic machine is so long that its rewinding would lead to a paper fault, the automatic machine generates an error code which is not equal to zero and proceeds to the "ERROR" state. If the optical transmission channel is transparent, the rewinding stops and a test of the optical measuring system follows. This test comprises measuring the amount of light which comes from the transparent channel with infrared LED switched on and switched off. If the measured contrast difference is too small to guarantee good operation of the automatic machine, the error code is again made unequal to zero, and the automatic machine again proceeds to the "ERROR" state. If the measured contrast is adequate, the automatic machine starts stamp detection. For this purpose, a number of stamps is first progressively moved out of the automatic machine. Then said stamps are rewound again. During this rewinding, the light attenuation due to the stamps is measured at each step change of the stepping motor (three measurements per mm of stamp). The resolution of the measuring system is 0.1# (range 0 ... 1000; 0 corresponding to minimum light attenuation and 1000 to maximum light attenuation) .

An example of a light attenuation profile of a strip of stamps having high contrast is shown in Figure 6, the light attenuation or "att" (i.e. attenuation) and stamp strip position or "location" being indicated along the vertical and horizontal axis respectively.

Depending on the available memory and the processing speed of the processing and control unit, the data may be stored in the data memory, either in compressed or uncompressed form.

A number of methods of stamp detection are described below, and this is followed by an explanation of the manner in which it is implemented in the automatic stamp machine.

1. The stamp detection during issuing may take place by peak detection carried out on the result of correlating the light attenuation profile of the stamp to be issued with the light transparency profile or light attenuation profile, stored in the memory, of a reference stamp. For this purpose, a measurement of the light attenuation is carried out at every position s_#tep of the motor and the result is added to a buffer which contains a number of positions which is equal to the number of measurement values of the reference step. When this addition takes place, the oldest measurement value is simultaneously removed from the buffer. After every position step, the correlation of the data stored in the buffer and the data of the reference stamp is then calculated. After every positive peak in the correlation result, a stamp is cut off. In order to eliminate the effect of local small maxima, a peak detection is carried out with hysteresis. The maximum is valid only if the subsequent correlation result has a value which is a few units lower. In that case, the light attenuation profile of at least one stamp is stored, for example starting and ending at the apex of the perforation. The length of the stamp is equal to the number of memory locations which is occupied by said profile. Said length may be used for verification purposes during the issuing of stamps. This manner of stamp detection during issuing requires a high processing speed of the processing and control unit. A relatively large data memory (RAM) is also required; stamps 3 cm long require a storage of 90 . 10 = 900 bits. 2. The stamp detection during issuing may also take place by peak detection carried out on the light attenuation profile of the stamp to be issued. Depending on the type of separating edge, special printing or dark line or perforation, a positive or negative peak detection is carried out with associated crossing of a detection threshold. In the case of a perforation, as soon as the light attenuation of the stamp goes below the threshold value, a negative peak detection is therefore carried out on the light attenuation; every minimum measured corresponds to a perforation and therefore with a stamp to be issued. To eliminate the effect of local small minima, a negative peak detection is carried out with hysteresis. The minimum is valid only as a perforation if the subsequent measurement gives a value which is a few units higher. In case 2, a lower processing speed of the control and processing unit than in case 1 is adequate. The amount of data memory (particularly during issuing) can also be appreciably restricted. This is possible because only the threshold value and the stamp length (total, 10 + 8 = 18 bits) have to be stored for the purpose of dispensing.

The threshold value can be obtained in various ways, viz. with the methods a, b and c as discussed below: a. The threshold value is permanently adjusted. In this case, there is no adaptive operation at all of the detection system. Variation in light attenuation of the optical transmission channel due to production spread, and also considerable variation in the light attenuation of the stamps due to difference in printing and paper quality of different stamp types, and also appreciable variation in the amount of ambient light radiated in and effects of ageing, contamination and temperature upon the optical and electronic measuring system give rise to incorrect detection of perforations. Some of these effects can be reduced by carrying out the peak detection under the control of the measured length. For an operation which is still to some extent reliable, adjustment of said threshold value is desirable for every automatic stamp machine. b. The threshold value is determined from a weighted average of the minimum and maximum value of the measured light attenuation of the stamps measured during initialisation. The weighting factor can be fed to the automatic machine as a parameter. The form of the general expression is: tr = Min + A. (Max - Min). Here, tr is the threshold value to be determined, A is the weighting factor, and Max and Min are the maximum and the minimum value respectively of the light attenuation, determined during initialisation, of a number of stamps.

Because the threshold value is always determined during initialisation, the automatic machine adjusts itself depending on the stamp type and is compensated for production spread, ageing and contamination. A disadvantage of this method is that a few high values of the light attenuation, for example due to very heavy printing locally of the stamps, have a considerable effect on the determination of the threshold value. In addition, it is the case that in this method, the weighting factor differs for every automatic stamp machine and stamp type if the optical measuring system is strongly non-linear (due to non-uniform light distribution of the infrared LED and non-uniform distribution of the perforation over the width of the stamp) . Just as under a, this makes adjustment of the automatic stamp machine after produc¬ tion necessary. c. A considerable improvement is possible by not taking a weighted average of the maximum and minimum value of the light attenuation, but a weighted average of the mode (the value occur¬ ring most) and the minimum value of the light attenuation of the stamps measured during initialisation. A few high values, which seldom occur, of the light attenuation now have little effect on the determination of the threshold value. In this case, a histogram of the measured values of the light attenuation is stored in the data memory instead of a complete light attenuation profile of a number of stamps. If no adaptive operation is required during the issuing of the stamps, the histogram is superfluous after initia- lisation and if only the data derived therefrom (the threshold value and the stamp length) need to be known during issuing, said memory becomes free after initialisation for other data (communi¬ cation buffer, temporary storage of variables and the like) . In general, the threshold value can be calculated in this method in accordance with the expression: tr « Min + A. (Mod - Min). Here, Mod is the mode, i.e. the value occurring most, and Min is the minimum value of the light attenuation of the profile measured during initialisation. A is a parameter or weighting factor which can now have the same value for every type of stamp for all the automatic machines and for many different stamp types.

The methods b and c can be implemented with so-called direct and indirect adaptive operation.

Direct adaptive operation is understood to mean that the automatic machine continuously recalculates the detection threshold during issuing. That is to say:

In method b, the detection threshold is determined in accordance with: tr = Min + A. (Max - Min). Here, Min and Max are the average of the measured minimum and maximum values and the light attenuation of a number of stamps. This number may, for example, be equal to the number of stamps measured during the initialisation. In method c, the detection threshold is determined in accordance with: tr = Min + A. (Mod - Min). Here, Min and Mod are the averages of the measured minimum value and of the calculated mode, respecti¬ vely, of the light attenuation of a number of stamps. This number may, for example, be equal to the number of stamps which has been measured during the initialisation phase.

Indirect adaptive operation is understood to mean that the detection threshold has a fixed value during stamp issuing. If an error occurs in the stamp detection, for example stamp too long or stamp too short, a new initialisation phase automatically follows in which the detection threshold and the stamp length are re- measured. In this manner, the automatic stamp machine adapts itself indirectly during issuing to the new optical conditions. The advantage of this implementation over the implementation employing direct adaptive operation is that the issuing speed can be higher and that no memory is necessary during issuing for storing a histogram as referred to under method c.

A very advantageous design of the automatic stamp machine is obtained with the last method. The stamp detection during issuing thus takes place in accordance with 2, while the parameters necessary for the purpose are determined in accordance with method c. The preparation of the histogram and the determination of the threshold value now takes place during the rewinding of the strip of stamps transported outwards for this purpose. During the preparation of the histogram, use is made of a quantised logarithmic distribution. This means that the 1000 values of the light attenuation possibly occurring are divided into a number of groups. For each group, the number of times that a measured value falls into said group is recorded. By now making the groups larger for increasing values of the light attenuation and calculating the threshold in accordance with the abovementioned method, the mode being equal to the highest value belonging to the group with the highest number in which most of the measurement results have finished up, the result is obtained that, for all the attenuation profiles which occur, the threshold value has a value which is greater than the minimum (Mod > Min) and considerably smaller than the maximum, even if all the values (0 ... 1000) occur equally often. The only condition which has to be fulfilled for correct detection is that the perforation in the stamp always has a lower light attenuation value than the printed stamp. In the automatic stamp machine described here, the histogram contains 112 positions in which the attenuation values are stored in accordance with the following table:

Table

If we give each value an equal maximum chance of occurring (255 times in 350 measurements) a total memory capacity of 112 . 8 = 896 bits is required for 350 measurements for the histogram in accordance with the above grouping.

After every measurement of the attenuation of the stamp, the content of the position in the histogram corresponding to the measurement result is incremented. The attenuation is measured after every step of the stepping motor.

After sufficient stamps have been measured and the histogram has been filled, the threshold value can be determined from said histogram.

In the embodiment of the automatic stamp machine described here, the mode is determined from 350 measurement results (a strip of stamps approximately 75 πωi long) in accordance with the method described above. The histogram has 112 positions having a quantised logarithmic distribution, each position with a range of 0-255- In practice, this is found to be amply sufficient for all types of stamps and automatic machines.

Figures 7a, 7b and 7c show a light attenuation profile and a histogram (on the left and right, respectively, in the figure) of stamp B, stamp C and stamp D respectively, all measured in the same automatic stamp machine 1. Figures 8a, 8b and 8c show a light attenuation profile and a histogram (on the left and right, respectively, in the figure) of stamp A in automatic machine 1, automatic machine 2 and automatic machine 3. respectively. The attenuation profiles give the measured light attenuation as a function of the position on the stamp strip. The histograms show the position horizontally and the number of measurement results vertically with a value inside the range of said position. In the profiles, the calculated values of the mode and the detection threshold, tr, and also the measured minimum are indicated by a broken line. The weighting factor A is 0.784 in all cases. This parameter can be adjusted via the communication interface 33-

During the filling of the histogram, a check is also carried out on the contrast of the stamp strip. If said contrast is too low (ratio between maximum and minimum attenuation less than ...) , an error code is used and the automatic machine proceeds to the "ERROR" state. When the entire stamp strip has been rewound, i.e. there is then a transparent optical channel, the determination of the stamp length follows. The first stamp is first of all transported outwards. Although the length of this stamp is measured, it has no effect on the determination of the final stamp length; this is because the first stamp may have been partly torn off. The stamp length of the first stamp is equal to the number of steps that the strip has to be transported until the first perforation has been found. After determining the final stamp length, a determination is made, on the basis of the tolerance permitted thereon, of whether the first stamp is long enough or is too short. In the latter case, the stamp is not counted during issuing. The stamp strip is then transported outwards a further three stamps. The average length is measured over these three stamps. If it is found after checking that the measured length with the specified tolerance parameter is valid, said length is stored and used for checking during stamp issuing. If the length is insufficient or if it exhibits too great a spread over the measured three stamps, an error code ensues and the automatic stamp machine proceeds to the "ERROR" state. The length is valid if: length < maximum permitted length and length < opto-to-knife distance - rewinder distance after cutting + tolerance. If the measured length is sufficient, a check is first of all made on whether the first stamp, whose length is still stored, is within the specifications. If the stamp is too long, the error code FST (First STamp too long) ensues and the automatic machine proceeds to the "ERROR" state. If the stamp is too short, the auto¬ matic machine continues to transport the stamp strip until the first perforation is reached. The short stamp is then issued during the subsequent issuing but not included in the count. After this, and if the measured length of the first stamp is sufficient, the automatic machine is ready for issuing stamps. If the automatic machine has entered the initialisation state while stamps have still to be issued, the desired number of stamps is issued as yet. The number that still has to be issued (= cut off) is stored in the non-volatile parameter memory as parameter STAMPC (stamps to cut) if an error occurs or after the failure of the mains. The value of the STAMPC parameter is then retrieved from the non-volatile parameter memory and compared with zero. If this value is not equal to zero, an OUT message is generated with STAMPC (MSG = OUT, ARG = STAMPC) as argument. With this message, the automatic machine proceeds to the "BUSY" state in which the instruction is carried out.

In the event that the value of the STAMPC parameter is equal to zero after initialisation, the automatic machine proceeds to the "COMMUNICATION" state.

The "COMMUNICATION" state In the communication state, the automatic stamp machine waits for a message from the issuing system or another connected control system such as PC, interface and the like. In addition to the codes which are necessary for communication in accordance with ISO 1745. a message contains a command code (MSG) , possibly with an argument (ARG) and/or a question character (QUERY) . If a commanδ has been received, the automatic machine proceeds to the "BUSY" state in which the command received is carried out. Various commands can be transmitted to the automatic machine in one message. The automatic machine places said commands with associated arguments and queries in a buffer. After carrying out a command, the automatic machine returns to the communication state and the subsequent command is processed.

The "BUSY" state

A description for the "OUT" command which is valid both for direct and indirect adaptive working, follows below. After receiving the "OUT nnn" command, the automatic machine starts to issue stamps. For every step of the stepping motor, a light measurement is carried out. When a perforation is detected, the number of stamps still to be issued (STAMPS) is reduced by one. During this issuing, the number of steps between the perforations is also recorded and compared with the stamp length (LENGTH) determined during the INIT state. As soon as the number of steps in which a perforation is detected is less than the LENGTH-TOL (TOL = permitted tolerance on the detected stamp length) the STS (Stamp Too Short) error code ensues. The automatic machine then proceeds to the "ERROR" state. If the perforation is not found within LENGTH + TOL steps, the STL (Stamp Too Long) error signal ensues. The automatic machine also proceeds to the "ERROR" state in that case. In this way, an error in the paper transport or an unspecified stamp can be detected.

Alternatively, it is also possible to proceed as follows. Since, as stated above, the exact stamp length is measured at the beginning of the stamp strip and is known, the position of the next perforation can be predicted during the progressive movement. If no perforation is then encountered at the predicted position, for example as a consequence of blocked holes, the following actions can take place. The progressive movement of the stamp strip can be stopped, after which an error signal is given. The progressive movement can be continued (PERFO-SKIP) by yet a further stamp length, a check being made on whether a perforation then appears. If the latter is detected, it is assumed that the previous perforation was apparently blocked and the stamp is included in the counting. This means that an error correction takes place. If no perforation is detected, the progressive movement is stopped and the error signal is emitted. Optionally, it is possible to proceed further for a stamp length again. This fault repair mechanism makes it possible to eliminate errors in the stamp manufacture and it is nevertheless possible for satisfactory stamp issuing to take place. The number of perforations acceptable for skipping can be adjusted by the user to zero, one, two, etc.

If a transparent optical channel is measured, the NST (No STamps) error code ensues and the automatic machine proceeds to the "ERROR" state. The error handling associated with these errors is described in the "ERROR" state.

The stamps are cut off if the number counted is equal to the number to be cut off. Said number to be cut off can be adjusted with the CNT nnn (CouNT number) parameter. If CNT = 0, the number to be cut off is made equal to the number to be issued at the start of issuing. If CNT = n, cutting off always takes place after n stamps. For the purpose of cutting off, the last detected perforation is always transported first to the knife. After cutting off, the stamp strip behind the knife is transported backwards a few steps in order to avoid paper faults. This number of steps is always stored so that the measurement of the length of the stamps during issuing is not thereby interfered with. After cutting, the number of stamps still to be cut off is decreased by the number cut off just before that. The new number of stamps still to be issued is then made equal to the new number of stamps still to be cut off. Only if the number of stamps still to be cut off has become equal to zero, does the automatic machine return to the "COMMUNICATION" state if the error code is zero. The "ERROR" state

A description of the handling of faults which have occurred during stamp issuing follows below, both for indirect and for direct adaptive operation. If an error code which is not equal to zero occurs, the automatic machine enters this state. __α audible signal then ensues immediately, the knife 12 is raised, the motor 20 and the infrared LED 15 are switched off and the red stock sensor LED 21 is switched on. After virtually every error, the automatic machine subsequently proceeds to the "COMMUNICATION" state, in which the error code keeps its value. Depending on the value of the error code, some commands will in fact be carried out but others will not. The "OUT nnn" command is carried out only if the error code is zero. In the event that the error code is STS or STL, a single automatic error correction is carried out by the automatic machine. The STS and STL error codes occur only during the issuing of the stamps, in particular if a stamp being too short or a stamp being too long is detected. The automatic error correction thereafter proceeds as follows. The automatic machine rewinds the stamps to the first perforation which is detected. This was the stamp measured last. This perforation is transported to the knife and the stamp strip is cut off. The number of stamps still to be cut off is corrected, the error code is made zero and the automatic machine proceeds to the "INIT" state. If the initialisation proceeds satisfactorily, the remaining stamps are still issued. If the error code was first STS and a stamp being too short (which is now the first stamp) is again detected, this stamp is issued but not included in the count. If the first stamp again appears too long, the automatic machine enters this error state with the FST (First STamp too long) error code. This stamp can be removed by the staff. This stamp must not be issued because the total of the stamps given to the customer becomes too large. For the automatic stamp machine, only the stamps cut off by the automatic machine are considered as issued stamps. If the STS and STL errors were the consequence of a paper fault and said paper fault is not eliminated during initialisation, the automatic machine enters the "ERROR" state, with an error code belonging to this fault.

After the lock of the automatic machine has been opened, the OPN (open) error code overwrites the prevailing error code. When the lock is closed again, the error code again becomes zero and the automatic machine enters the "INIT" state. The opening and closing of the automatic stamp machine can thus be viewed as a reset command.

The "POWER FAIL interrupt", the "SOFTWARE WATCHDOG" and the "LOCK & SWITCH" test.

While the automatic stamp machine is in operation, a test is continuously carried out on the lock (LOCK) and the (optionally present) switch (SWITCH). In the same routine, a so-called "watchdog trigger" is given. The absence of said watchdog trigger implies a fault in the progress of the program. In that case, the automatic machine is restarted (reset) . If the lock is opened, the "OPN" error code ensues and the automatic machine proceeds to the "ERROR" state. This error code overwrites any other error code. If the automatic machine detects that the switch is depressed, a number of stamps is issued. This number can be adjusted with the "MAN" (manual) parameter.

If the automatic machine detects that the mains voltage has failed, the motor and all the LEDs are switched off. Important parameters, including the number of stamps still to be cut off, the total number issued, the subtotal and the stock are then written into the non-volatile parameter memory. After the mains voltage has been restored, the automatic machine enters the "POWER UP" state and after initialisation, the remaining number of stamps still to be cut off is automatically issued. The automatic issuing of stamps can be stopped by opening the lock of the automatic machine and giving a CAN (cancel) instruction. The number of stamps still to be cut off is thereby made zero.

It is obvious that various modifications can be made which fall within the scope of the invention. Thus, an optical detection sensor 21 can be provided which determines the presence of a minimum number of stamps in the cassette. When the stamp roll runs low, this sensor detects that the stock is lower than a prespecified number. The user is then made aware of this. A second check is possible by storing the ntimber of stamps on the full reel beforehand as initial data in the processing and control unit and then subtracting the stamps issued therefrom.

Claims

Claims 1. Automatic stamp machine for automatically dispensing value- denominated stamps, provided with a chassis, a drive system with a stepping motor, an optical measuring system for consecutively scanning a progressively moved strip of stamps which are fed from a stamp roll and are each separated from one another by a separating edge and for generating a signal which represents the degree of light attenuation, a processing and control unit for examining the light attenuation signal to determine the separating edge, and a cropping system for cutting off an externally specified number of stamps under the control of the processing and control unit, characterised in that the optical system is designed to measure the average light attenuation, over at least a portion of the width of the stamp strip, at discrete length intervals with high resolution, the optical measuring system being synchronised with the drive system so that a light measurement takes place for every step of the stepping motor per said length interval, and in that the digitally designed processing and control unit determines the separating edge on the basis of detection criteria and is of self- adjusting design, the stamp parameters such as length and light attenuation and their variation being automatically determined and processed, and consequently, all the stamps encountered in practice can be dispensed by the automatic machine.

2. Automatic stamp machine according to claim 1, characterised in that the processing and control unit is designed to determine a light attenuation profile of every passing stamp, a peak detection being carried out as soon as the light attenuation of the stamp passes a threshold value, the measurement being carried out with hysteresis such that a peak is evaluated as a separating edge if the subsequent measurement has a value which differs by a few units.

3. Automatic stamp machine according to claim 2, characterised in that the separating edge is a perforation, so that during the determination of the light attenuation profile of each passing stamp and if the light attenuation falls below the threshold value during this operation, the processing and control unit carries out a negative peak detection such that the peak is evaluated as a perforation after the subsequent measurement has a value which is a few units higher.

4. Automatic stamp machine according to claim 1, characterised in that the processing and control unit is designed to determine a light attenuation profile of every passing stamp and to compare it in each case with the profile of the light attenuation, stored in a memory, of a reference stamp, the correlation result being evalua¬ ted and every positive peak detection therein being carried out with hysteresis such that a maximum is evaluated as a separating edge if the subsequent correlation result has a value which is a few units lower.

5. Automatic stamp machine according to one of the preceding claims, in which the optical measuring system has a light- emitting cell and a light-sensitive cell between which an optical measuring channel is determined and in which the processing and control unit contains a data memory, characterised in that the processing and control unit is designed such that on placing a stamp roll or on opening or closing the automatic machine, an initialisation phase is carried out in which the stamps are at least rewound until the optical measuring channel is transparent and the value of the light attenuation during the rewinding is compared with the light attenuation of the transparent optical measuring channel originally measured and stored after manufacture, and in which, if the optical measuring channel is transparent, the rewinding is stopped, after which the optical measuring system is tested with switched-on and switched-off light-emitting cell for the amount of light received, an error code being set if the measured contrast difference is too small and the automatic machine starting stamp detection if the contrast difference is adequate, a number of stamps first being moved progressively out of the automatic machine and then being rewound and the light attenuation due to the stamps being measured at every position step during this operation.

6. Automatic stamp machine according to claim 5. characterised in that the processing and control unit is designed to determine a threshold value for the stamp detection during the initialisation phase by storing a profile of the light attenuation for a number of stamps in the data memory, the threshold, tr, being calculated in accordance with: tr = Min + A. (Max - Min), where Min and Max are, respectively, the minium value found and the maximum value found of the light attenuation, and A is a weighting factor.

7. Automatic stamp machine according to claim 5. characterised in that the processing and control unit is designed to determine a threshold value for the stamp detection during the initialisation phase by storing a histogram of measured values of the light attenuation for a number of stamps in the data memory, the threshold, tr, being calculated in accordance with: tr = Min + A. (Mod - Min) , where Min is the minimum value of the light attenuation found and Mod is the mode found, i.e. the value occurring most, and A is a weighting factor.

8. Automatic stamp machine according to claim 5. characterised in that the processing and control unit is designed with direct adaptive operation for recalculating each time a threshold value for the stamp detection during stamp issuing.

9. Automatic stamp machine according to claim 8, characterised in that the processing and control unit each time stores a profile of the light attenuation of a number of stamps in the data memory during stamp issuing and calculates the threshold value, tr, therefrom in accordance with: tr = Min + A. (Max - Min) , where Min and Max are the averages of the measured minimum and maximum value of the light attenuation and A is a weighting factor.

10. Automatic stamp machine according to claim 8, characterised in that the processing and control unit each time stores a histogram, for a number of stamps, of measured values of the light attenuation in the data memory during stamp issuing and calculates the threshold value, tr, therefrom in accordance with: tr = + A. (Mod - Min), where Min and Mod are the averages, respectively, of the measured minimum value and the calculated mode, i.e. the value occurring most, of the light attenuation of the number of stamps and A is a weighting factor.

11. Automatic stamp machine according to claim 5. characterised in that the processing and control unit is designed with indirect adaptive operation, in which a threshold value for the stamp detection and the stamp length are remeasured during the initialisation phase, and the processing and control unit maintains the measured detection threshold and stamp length during stamp issuing, and in which a new initialisation phase ensues if an error occurs in the stamp detection.

12. Automatic stamp machine according to claim 1 in which the specified number of stamps is n and in which the cropping system is provided with a knife member situated transversely to the path of the stamp strip, characterised in that the processing and control unit is designed to set a position window after detecting the n-th perforation which corresponds to the running distance of the stamp strip between measuring system and knife member.

13- Automatic stamp machine according to claim 5. characterised in that the processing and control unit is designed to predict, from the derived fixed stamp length, the position of the next perforation, the progressive movement of the stamp strip being stopped with a subsequent error signal or being continued with an on-going stamp counting if no peak value and therefore no perfora- tion is encountered at the predicted position.

14.Automatic stamp machine according to claim 1, characterised in that the stepping motor has a stepping angle of α = 3-75° and in that the drive roller driven by the stepping motor has a radius of r = 4.5 mm, so that the distance traversed by the stamp strip per step is i = 2 n r.(α/36θ^β) = 0-3 mm.