CN1200171A - Device and process for determining film thickness and pattern register in cells plated on inductive debit cards - Google Patents

Abstract

A device for determining the thickness of conductive metal patterns plated on insulating surfaces, such as credit cells in prepaid telephone debit cards, comprising a plurality of sensing modules equal in number to the credit cells in said cards, each module consisting of an oscillator (30) wherein the inductance is provided by a pair of collinear sensing coils (24a, 24b), aligned with the true position of its relative credit cell (25), the output (26) of said sensing assembly being connected to the input of an A/D converter (40) whose output is connected to computing means (11, 21) provided with memory means. Said oscillators are enabled by turns, the output voltage being converted to a numeric value. The converter parameters are adjusted for each sensing module according to coefficients stored in said memory, to compensate for component variations, sensing coil position and so on. The resultant numeric value is processed by the computing means according to a transfer curve (53) which is specific for each sensing module, so as to furnish the film thickness. Said coefficients and transfer curves are previously determined for each one of the positions in the cell array by means of individual calibration, using standard cards of known metal film thickness.

Description

Apparatus and method for determining film thickness and graphic registration in a payment unit coated on an inductive debit card

The present invention relates to the determination of the thickness of a conductive metal layer deposited on an insulating surface, and more particularly to the use in documents such as PI (BR) 7804885, PI (BR) 9201380-5 and PI (BR) 9304503 incorporated herein by reference - Measurement of the thickness of the metal film in the production of the payment unit above the inductive debit card described in 4.

Methods for measuring the thickness of metal layers based on X-ray diffraction are well known, but the expense and time required for these methods limit their use to high-precision measurements in the laboratory.

Furthermore, none of the currently known methods adequately detect registration errors that occur during card production, ie the misalignment of the metal payment element pattern applied to the card with its edge.

In view of the above, the main object of the present invention is to provide a device capable of quickly and effectively measuring the thickness of the metal film with the lowest error margin and low cost.

A further object is to detect misalignment during coating of the payment units, ie a mismatch between the actual position of those payment units and their ideal position relative to the edge of the card, which misalignment reflects that the card is unusable.

The present invention achieves the above objects by means of a device comprising a sensing assembly consisting of a plurality of sensing modules, each module comprising an oscillator, the inductance of which is determined by the Provided by sensing coils aligned in correct position, each sensor is individually energized one at a time by pulses from computing means controlling the process, the oscillator output voltage is coupled to means for converting it into a digital value, which is then determined by the The computing means processes the coefficients stored in the memory means to report the thickness of the metal layer.

According to another feature of the present invention, said coefficient is determined in advance for each position in the payment unit array in an individual calibration manner using a standard card with known metal film thickness.

According to yet another feature of the invention, sensors are provided placed outside the matrix of payment units, making it possible to measure registration errors within the pattern of applied payment units.

According to yet another feature of the invention, the device can check all the payment units in the card as a whole, thus being able to reject cards in which one or more payment units are exposed due to manufacturing defects.

The above features and other aspects and advantages of the present invention will become more apparent by describing specific embodiments shown in the accompanying drawings (by way of example but not limitation), in which:

Fig. 1 shows the connection block diagram of the test device and its external control equipment such as PC compatible microcomputer built according to the principle of the present invention;

Figure 2 shows a more detailed view of a device proposed according to the invention;

Figure 3 illustrates a calibration curve for one sensing module, showing the elements that allow the conversion of measured voltage values into metal layer thicknesses according to the invention;

Figure 4 illustrates the principle of detecting misalignment according to the invention.

Referring now in more detail to the block diagram in Figure 1, the proposed apparatus 20 comprises the following components:

The control panel 21 is CPU-A/D, including microcontroller, analog/digital converter (A/D), memory and accessories;

Decoder card CE022, including an address decoder that controls the operation of each oscillator in the sensor matrix through a separate line 23;

The sensing assembly 27 includes a plurality of sensing modules that are the same as the number of payment units in the card, and each module includes a pair of collinear sensing coils 24a-24b in addition to the oscillator. The end forms a slot for receiving the payment unit 25, the width of the slot being slightly greater than the thickness of the card to allow for occasional inconsistencies.

Still according to FIG. 1 , the device 20 is connected to a PC microcomputer 11 controlling the measurement process through a serial communication line 46 using a standardized protocol such as RS232.

Referring now to FIG. 2, it can be seen that the sensing assembly 27 includes a plurality of test blocks 30, each test block including a Colpitts oscillator, wherein the coils forming the oscillator loop are the inductive sensors 24a and 24b. This oscillator has the property of producing an AC signal with an amplitude proportional to the load on the inductive coil. Considering that the load varies with the properties of the metal layer (thickness, conductivity) and the state of the payment unit (open or short circuit), for known alloys it follows that the signal amplitude between the leads of the sensing coil is related to the metal The thickness of the film is inversely proportional.

Transistors 31 in all oscillators are normally off and oscillation is initiated solely by component CEO 22 by means of a positive voltage pulse 32 applied to the base of the transistor via one of the lines in group 23. The duration 33 of this pulse is significantly longer than the time necessary for the oscillator to reach steady state operation, which eliminates the effects of any possible transients. Part of the oscillating voltage appearing at the collector of transistor 31 is rectified by diode 34 and filtered by capacitor 35, with the result that a reasonably good rectangular pulse 36 of duration equal to the above-mentioned command pulse 32 is obtained.

The amplitude of pulse 36 is much greater than the maximum voltage that can be applied to A/D converter 40 . To this end, a zener diode 37 is used in series with the input of the converter to subtract a constant voltage from said pulse 36, resulting in a pulse 38 of lower amplitude which is fed to the input of said converter 40, Used to convert to a numeric value.

Said delivery is carried out by a numerically controlled potentiometer 39 whose value is adjusted by the CPU 21 by applying a signal to the control terminal 39'. Since there are differences between the components of each oscillator, and the oscillation voltage is affected by the position of the sensing coils in the array (more or less from the edge, etc.), this adjustment needs to be done individually for each test module 30 . The data used to adjust this potentiometer is determined in advance during calibration of the device using a standard card of known thickness and stored in the CPU's memory (not shown).

The control potentiometers 41 and 42 are fine-tuned with the control signal from the CPU in the same way, and the adjustment system is specially carried out for each of the 104 sensing modules: the first adjusts the full range of the A/D converter, and the second is The converter establishes the lowest voltage signal (zero voltage, corresponding to the thickest metal film). As previously mentioned, control potentiometer 39 limits the maximum voltage value applied to the input of the converter.

After those potentiometers are adjusted correctly, the output of the converter will be equal to zero for the thickest metal layer seen earlier, and equal to 255 for the thinnest film expected during manufacture of the debit card. To provide a proportional relationship between the digital value and the metal film thickness (E), the output of the converter 40 is processed by the CPU 21 to generate a 255 complement of the output.

After this step, in case several locations are programmed to be tested, the CPU sends to the CEO 23 the address of the next location to be tested. The digital value is transmitted via serial interface 45 and line 46 to microcomputer 11 (shown in FIG. 1 ), which processes the result to report the actual thickness of the metal layer.

Calculation of this thickness is carried out by means of the transfer curve of each test module (as already said, the transfer curve depends on the properties of the element and the position of the sensor in the matrix). Thus, each of the 104 modules in this example has a transfer curve that can be approximated by one or more straight line segments. FIG. 3 illustrates the approximation of this curve by a line segment 53 defined by two coefficients, the linear coefficient b and the angular coefficient m. Therefore, for each position in the matrix, the thickness will be calculated by the expression E=(VN*m)+b, where VN is the numerical value sent to the CPU.

As mentioned earlier, the characteristic curve of each test module can be approximated more precisely by 2, 3 or more straight line segments, each with a specific angle factor (m1, m2, etc.) and a specific The linear coefficients (b1, b2, etc.) are defined. Clearly, in these cases, the formula for calculating the film thickness will be much more complex than that used for approximation by a single line segment.

Once the thickness values of one or more payment units in the card have been calculated, these values can be stored, printed, transmitted to other devices, etc., or even (when the thickness values exceed the tolerance limits) used to trigger an alarm for rejecting the card etc. In the event that the payment unit breaks due to a manufacturing defect, this fact will be interpreted by the device as "insufficient thickness" causing the card to be rejected.

In addition to thickness determination, the proposed device also allows the determination of occasionally occurring alignment errors. For this purpose, a non-metallic window is provided on the card, said window (rectangular or square) being located in the coated area outside the array of payment cells. The inductive sensor pack is similarly equipped with an additional test module, the coil of which is placed in line with said window.

Figure 4 shows the principle of alignment error determination. Considering one edge 61 of the window 60, three possible approximate positions of the inductive sensor core can be seen. In Fig. 4-a, the core 62 is placed entirely on the uncoated area, so the current induced in the metal layer is the lowest; therefore the voltage on the oscillator terminals will be the largest. Figure 4-b shows a position where the core 63 is partly on the coated area and partly on the window; in this case some load will be generated; therefore the oscillation amplitude will be smaller than above. Finally, in Fig. 4-c, the core 64 rests entirely on the metallized area. The oscillator coil is most heavily loaded; thus the oscillating voltage is minimal.

By proper selection of the size and position of the window and the position of the corresponding inductive sensor, it is possible to detect both longitudinal and transverse deviations of the metal pattern coated on the card as well as the rotation of the pattern relative to the axis of the card.

Obviously, the voltage value detected by the sensor will vary according to the thickness of the metal layer on the card, so there needs to be an appropriate software to interpret the value provided by the alignment sensor.

As before, the maximum and minimum acceptable measurement levels must be determined in advance using standard cards with known misalignment. These values are stored in the memory of the computer to be able to reject those cards whose registration error exceeds the allowable deviation from the correct position.

Although the present invention has been described on the basis of specific embodiments, it is obvious that various variations and modifications can be introduced without departing from the scope of the inventive concept. Thus, for example, as long as sufficient memory is available and all necessary software is installed, all data processing can be done by the CPU 21 of the device, thereby eliminating the need to use the microcomputer 11.

Furthermore, while this description illustrates an apparatus for testing cards with 104 units (100 payment units and 4 units for location/validity), it goes without saying that the principles of the invention are equally applicable to cards with any number of units The card can even be used to measure the thickness of continuous metal layers coated on insulating materials.

Claims (8)

1. Device for determining film thickness and graphic alignment in payment units coated on inductive debit cards, characterized in that it comprises a sensor module consisting of a number of sensing modules equal to the number of payment units in said card Sensing assembly (27), each module comprising an oscillator (30) in which the inductance is provided by a pair of collinear coils (24a, 24b), the longitudinal axis of which is aligned with the corresponding payment unit (25) Position alignment, the output (26) of the sensing assembly is connected to the input of an A/D converter (40), the output of the converter is connected to a device equipped with software for thickness calculation and with each independent Computing means (11, 21) for storing means of data related to the sensing module. 2. The device for measuring film thickness and graphic alignment in a payment unit coated on an inductive debit card as claimed in claim 1, characterized in that the graphic alignment is passed through sensing coils (62, 63, 64 ) is checked by an additional sensing module placed outside the area of the payment cell array. 3. Device for determining film thickness and pattern alignment in payment elements coated on inductive debit cards as claimed in claim 1, characterized in that each of said sensing modules comprises a Colpitts oscillator device. 4. The device for measuring film thickness and pattern alignment in a payment unit coated on an inductive debit card according to claim 1, characterized in that at the output of the sensing assembly (27) and A/ A Zener diode (37) is inserted between the input terminals of the D-converter (40). 5. The device for measuring film thickness and pattern alignment in payment units coated on inductive debit cards as claimed in claim 1, characterized in that a digital control potentiometer (39) is connected to said A/ The input path of the D-converter (40), wherein the control terminal (39') of the potentiometer is connected to the computing means (21). 6. The device for determining the film thickness and pattern alignment in the payment unit coated on the inductive debit card as claimed in claim 1, characterized in that the numerically controlled potentiometer (41, 42) is connected to the A/D converter The fact of the full scale and zero voltage terminals of the potentiometer, wherein said potentiometer control terminals (41', 42') are connected to said computing means (21). 7. Method for determining film thickness and graphic alignment in payment units coated on inductive debit cards, characterized in that: • select at least one location within the array of payment cells to be tested; - read the relevant coefficients of the test modules corresponding to the selected positions from the memory of the computing means (11, 21); By feeding the control signal generated by the CPU (21) to the control terminal (39) of the digitally controlled potentiometer (39, 41, 42) connected to the signal input terminal, full scale and zero voltage terminal of the A/D converter (40) respectively ', 41', 42') to preset the converter, the control signal is derived from the coefficients. - Calculation of the film thickness by processing the digital values delivered from the A/D converter to the computing means (21, 11) according to a transfer curve related to the position within the array and the metal alloy from which the film is made. 8. The method for determining the film thickness and pattern alignment in a payment unit coated on an inductive debit card as claimed in claim 7, characterized in that all the The values of the coefficients and the conversion curves are determined in advance by measuring on a standard card with known metal film thickness.

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