DEVICE AND METHOD FOR MEASURING THE CURING PROCESS OF A CURABLE MATERIAL BY MEANS OF DIELECTRIC SPECTROSCOPY

Abstract

The invention relates to a device (10) and method for measuring the curing process of a curable material by means of dielectric spectroscopy, said device comprising: a mobile transmission unit (12) having a sensor (14) for making contact with a sample of the curable material, and a receiving unit (18), which is physically separate from the transmission unit (12), is configured to communicate wirelessly with the transmission unit (12) and contains an analysis device (22). The sensor (14) is formed on a sensor board (44) that is adapted to be detachably connected to the transmission unit, and the analysis device (22) of the receiving unit (18) is designed to determine, on the basis of frequency changes detected during a measurement process, at least three states: a first state of decreasing frequency which corresponds to the sample of the uncured material being applied to the sensor (14), a second state of a substantially constant first frequency which corresponds to a completed application of the sample of the uncured organic material to the sensor (14), and a third state of a substantially constant second frequency which corresponds to a desired curing state of the curable material being reached, wherein the constant second frequency is higher than the constant first frequency.

Claims

1. A device for measuring a curing process of a curable material by dielectric spectroscopy, the device comprising: a mobile transmission unit including a sensor configured to contact a sample of the curable material, wherein the sensor is configured to inject a signal in the form of an alternating electric field with a predetermined frequency into the sample, and a receiving unit physically separate from the transmission unit and configured to communicate wirelessly with the transmission unit, the receiving unit including an analysis device configured to detect changes in the predetermined frequency that occur in the course of a measurement process, wherein the sensor is formed on a sensor circuit board configured to be detachably connected to the transmission unit, wherein the analysis device is configured to determine, on the basis of frequency changes detected during the measurement process, at least three states; (i) a first state of decreasing frequency corresponding to the sample of the curable material, in an uncured state, being applied to the sensor, (ii) a second state of a substantially constant first frequency corresponding to a completed application of the sample of curable material, in the uncured state, to the sensor, and (iii) a third state of a substantially constant second frequency corresponding to a desired curing state of the curable material being reached, wherein the constant second frequency is higher than the constant first frequency, and wherein the receiving unit has a display device for displaying the at least three states, and the device is configured to initiate, once determination of the second state has taken place, the curing process of the curable material.

2. The device according to claim 1, wherein the sensor is part of a resonant circuit containing a capacitor, the resonant circuit exhibiting the frequency change detected during the measurement process.

3. The device according to claim 1, wherein the sensor is a capacitor.

4. The device according to claim 3, wherein the sensor has two cooperative comb electrodes defining a sensor surface.

5. The device according to claim 4, wherein the two cooperative comb electrodes are formed on an upper side of the sensor circuit board.

6. The device according to claim 1, wherein the sensor circuit board has a temperature sensor associated with the sensor, wherein the temperature sensor is located on a rear side of the sensor circuit board.

7. The device according to claim 1, wherein the transmission unit has a UV sensor configured to detect UV irradiation of the sample of the curable material.

8. The device according to claim 1, wherein the display device comprises three LEDs for displaying the at least three states.

9. The device according to claim 1, wherein the receiving unit has at least one relay connected to the analysis device, the at least one relay configured to control a system component depending on at least one of the at least three determined states.

10. A method for measuring a curing process of a curable material by dielectric spectroscopy, the method comprising: injecting with a sensor a signal in the form of an alternating electric field with a predetermined frequency into a sample of the curable material, determining a first state of decreasing frequency resulting from the sample of the curable material, in an uncured state, being applied to lth sensor, determining a second state of a substantially constant first frequency resulting from completed application of the sample of the curable material, in the uncured state, to the sensor, initiating, when the second state has been determined, a curing reaction of the curable material, determining a third state of a substantially constant second frequency resulting from a desired curing state of the curable material being reached, wherein the constant second frequency is higher than the constant first frequency, and displaying each of the first, second and third states upon a respective determination thereof.

11. The method according to claim 10, further comprising measuring a frequency of the alternating electric field in the form of oscillation periods or pulses per fixed unit of time.

12. The method according to claim 10, wherein the sensor is arranged on a sensor circuit board, the method further comprising, prior to application of the sample of curable material, in the uncured state, to the sensor, calibrating the sensor to an initial value of the frequency of the alternating electric field such that the sensor of each of a plurality of different sensor circuit boards usable with the method is calibrated to an identical initial value of the frequency of the alternating electric field.

13. The method according to claim 10, further comprising measuring a duration of irradiation of the sample of the curable material with UV light.

14. The method according to claim 10, further comprising measuring the temperature of the sample of the curable material during a duration of the injection of the signal of the alternating electric field into the sample of curable material.

15. The method according to claim 10, wherein the sensor is provided in the form of a capacitor, and the capacitor is part of a resonant circuit, the method further comprising measuring a frequency change of the sensor to determine the first, second and third states.

Description

[0041] An exemplary embodiment of an inventive device and an inventive method are explained in greater detail below on the basis of the enclosed schematic figures. These show:

[0042] FIG. 1 a spatial representation of an embodiment of an inventive device with a receiving unit and a transmission unit obliquely from the front and above,

[0043] FIG. 2 a view of the inventive device corresponding to the view from FIG. 1 obliquely from behind and above,

[0044] FIG. 3a a sensor circuit board from above,

[0045] FIG. 3b the sensor circuit board from FIG. 3a from below, and

[0046] FIG. 4 a measuring curve created during a measurement of the curing process of a curable material by means of the inventive device and on which an application of the inventive method is based.

[0047] FIGS. 1 and 2 show a device generally designated 10 for measuring the curing process of a curable material by means of dielectric spectroscopy. The device 10 comprises a mobile transmission unit 12 with a sensor 14, which is designed to inject a signal in the form of an alternating electromagnetic field with a predetermined frequency into a sample of the curable material. So that the sensor 14 can inject the alternating electric field into the sample, sample material is applied to a sensor surface 16, which is round here, of the sensor 14.

[0048] The device 10 further comprises a receiving unit 18, here with a cuboid housing 20, which unit is physically separate from the transmission unit 12, can communicate wirelessly with the transmission unit 12, and contains in the housing 20 an analysis device 22 indicated by dashed lines (only shown in FIG. 1), which detects frequency changes occurring in the course of a measurement process.

[0049] Arranged on a front side 24 of the housing 20 are a power supply connection 26, a control connection 28 and a data communication connection 30. All connections 26, 28, 30 are depicted purely symbolically. For example, the data communication connection 30 can be designed as a USB port, so that the receiving unit 18 can be connected by means of a USB cable (not depicted) to a monitor and/or computer (not depicted). The power supply connection 26 can be implemented as a socket for receiving a power cable of a power unit, not depicted. The control connection 28 can be a socket into which a control cable (not depicted) fits, which connects the receiving unit 18 to a system component to be controlled.

[0050] The receiving unit 18 has on an upper side 32 of the housing 20 a display device 34, which consists in the exemplary embodiment shown of three LEDs 36, 38 and 40 and the function of which will be explained in greater detail later.

[0051] The mobile transmission unit 12 consists of a likewise cuboid housing 42 here and a sensor circuit board 44, which is rectangular here and carries the sensor 14 with its sensor surface 16 and which in the exemplary embodiment shown is designed as a printed circuit board and can be inserted into a slot 48 formed on the front side 46 of the housing 42. Arranged centrally above the slot 48 on the front side 46 of the housing 42 is a UV sensor 50, which can detect UV light that reaches the sensor surface 16 and thus sample material located on the sensor surface 16.

[0052] To be able to operate the transmission unit 12 independently of mains power, located in the housing 42 of the transmission unit 12 is a rechargeable battery (not shown), which supplies the power required for operating the transmission unit 12. The rechargeable battery can be a lithium-ion battery, for example, or also one or more so-called supercaps. To be able to charge the battery located in the housing 42, a charging connection socket 54 is provided on the rear side 52 of the housing 42 (see FIG. 2), which socket can be connected by way of a suitable connection cable (not shown) to a charging socket 58 provided on the rear side 56 of the housing 20 of the receiving unit 18. When the transmission unit 12 is connected to the receiving unit 18 using the sockets 54 and 58 to charge the battery of the transmission unit 12, the charge state of the battery can be monitored by means of a three-stage charge state display 60 here, which is present on the upper side 32 of the housing 20 of the receiving unit 18. In addition, an identically or similarly implemented charge state display can also be present on the housing 42 of the transmission unit 12 (not depicted), so as to be able to check the charge state of the battery of the transmission unit 12 even in a state in which the transmission unit 12 is not connected to the receiving unit 18 for charging.

[0053] Also located on the rear side 52 of the housing 42 is a switch 62, which is used to turn the transmission unit 12 on and off.

[0054] The sensor circuit board 44 is now described in greater detail with reference to FIGS. 3a and 3b, wherein FIG. 3a shows an upper side 64 and FIG. 3b a lower or rear side 66 of the sensor circuit board 44.

[0055] As is evident from FIG. 3a, located on the upper side 64 of the sensor circuit board 44 are two comb electrodes 68 and 70 formed from printed electrical conductors, which are arranged engaging in one another so that their teeth 72 and 74 alternately follow one another with a small spacing between one another. The two comb electrodes 68, 70 are represented purely symbolically in FIG. 3a and in reality completely fill the sensor surface 16. The form and arrangement of the comb electrodes 68, 70 is thus definitive for the sensor surface 16, which is round here and the outer edge 76 of which is positioned so that the comb electrodes 68, 70 are located precisely within the sensor surface 16. Each comb electrode 68, 70 is connected by way of a conductor 78, 80 to an electric contact field 82, 84 in each case on the upper side 64, which field is formed on the left-hand short side of the sensor circuit board 44 in FIG. 3a.

[0056] Also located on the upper side 64 of the sensor circuit board 44 is an aerial 86, which is implemented as a meander-shaped electrical conductor and connected to an electric contact field 88. The aerial 86 is used for wireless communication between the transmission unit 12 and the receiving unit 18.

[0057] On the lower side 66, depicted in FIG. 3b, of the sensor circuit board 44, a temperature sensor 90 is located in a region of the sensor circuit board overlaid by the sensor surface 16 and is in contact via conductors 92, 94 and 96 with electric contact fields 98, 100 on the lower side 66 and with an electric contact field 104 on the upper side 64 of the sensor circuit board 44 by way of a through contact or via 102. The temperature sensor 90 can be a thermistor of the type Pt100, for example, and serves to measure the temperature of the sample material during the measurement of a curing process of a curable material located on the sensor surface 16 as a sample.

[0058] Also arranged on the lower side 66 of the sensor circuit board 44 is an integrated circuit 106, which is connected electrically conductively via conductors to the contact field 98 (by way of two vias 108 and 110) and to other contact fields 112, 114, 116 and 118 and serves inter alia to calibrate the predetermined frequency that the sensor 14 is to inject in the form of an alternating electromagnetic field into a sample material located on the sensor surface 16. It can thus be guaranteed by means of the integrated circuit 106 that each sensor circuit board 44 injects a desired identical predetermined frequency into a sample, so that a plurality of measurements carried out using different sensor circuit boards 44 are comparable with one another. The sensor circuit board 44 can be switched on and off via the contact fields 112 and 118. The integrated circuit board 106 can also be used to identify each sensor circuit board 44 without risk of confusion, for example by means of an identification code contained in the integrated circuit 106 or programmed into it.

[0059] The previously described electric contact fields on the upper side 64 and lower side 66 of the sensor circuit board 44 serve to produce an electrically conductive connection between the sensor circuit board 44 and the transmission unit 12 when the sensor circuit board 44 is plugged into the housing 42 through the slot 48. Located in the housing 42 are corresponding mating contacts, not shown here, which interact with the contact fields of the sensor circuit board when the sensor circuit board 44 is in the plugged-in state.

[0060] The sensor circuit board 44, which is implemented as described as a printed circuit board, can be provided for single use and is then disposed of after carrying out a measurement. It is also possible to reuse a sensor circuit board 44 that has been used once, but it must then be ensured that a sample material applied to the sensor surface 16 can be detached from the sensor surface 16 again without damaging the sensor circuit board 44. This can be achieved, for example, by suitable coating of the sensor surface 16, which either prevents irrevocable adhesion of the sample material applied or is so hard that applied sample material can be scratched off again without damaging the underlying sensor 14.

[0061] In the embodiment described here, the sensor 14 defined by the two cooperative comb electrodes 68, 70 forms a capacitor of an electric resonant circuit, the frequency change of which is detected by the analysis device 22 during the measurement process. The sensor 14 is part of a freely oscillating oscillator circuit here and constitutes the frequency-determining element of the freely oscillating oscillator circuit. The metrological detection of the frequency changes that occur when a curable material to be examined is placed on the sensor surface 16 and then subjected to a curing process is accomplished in the exemplary embodiment shown by means of an ultrafast comparator circuit (not shown), which is known in itself and is located in the transmission unit 12.

[0062] The execution of a measurement of the curing process of a curable material is described in greater detail below with reference to FIG. 4, which shows a measuring curve M such as occurs during a measurement of the curing process of a curable material carried out by means of the device 10. In the diagram according to FIG. 4, the number of oscillation periods per unit of time, described as counts, of said resonant circuit is plotted over the time sequence of the measurement. A measurement begins at time to with an empty sensor 14, i.e., no sample to be examined is located on the sensor surface 16. The number of counts detected by the analysis device 22 has a value c.sub.1 at the beginning, which corresponds to the predetermined frequency of the alternating electromagnetic field present at the sensor 14. This predetermined frequency is dependent on the curable material to be examined and the desired penetration depth of the alternating electromagnetic field into the sample material and can be approx. 9 MHz, for example.

[0063] A sample of the curable material to be examined is then applied to the sensor surface 16. To prevent the applied sample material from spreading beyond the sensor surface 16, the outer edge 76 of the sensor surface 16 can be formed slightly raised. Application of the normally liquid or paste-like sample material to the sensor surface 16 leads to an increase in the dielectric constant of the sensor 14 acting as a capacitor and thus an increase in its capacitance, which in turn brings a fall in the frequency of the resonant circuit. The number of counts detected by the analysis device 22 therefore decreases. In the analysis device 22, two count values c.sub.2 and c.sub.3 are determined, to which c.sub.3<c.sub.2<c.sub.1 applies. It is important here that the value c.sub.2 is sufficiently smaller than the value c.sub.1 and that the interval between c.sub.2 and c.sub.3 is large enough to be able clearly to detect a frequency drop caused by the sample material application. The interval determined along the measuring curve by the values c.sub.2 and c.sub.3 corresponds here to a first state of falling frequency, which corresponds to application of the sample material to the sensor 14. Reaching or passing through this first state is displayed by the display device 34 by illumination of the LED 36, which is a red LED in the exemplary embodiment shown.

[0064] In the course of further application of the sample material to the sensor surface 16, the count value detected by the analysis device 22 falls further until a material-specific layer thickness of the sample material has resulted on the sensor surface 16, after which a further application of sample material no longer leads to a further drop in the count value, as each predetermined frequency can only penetrate up to a certain depth into a sample. Since the interval defined by the values c.sub.2 and c.sub.3 has been exited downwards in the course of further application of the sample material, the red LED 36 is no longer illuminated.

[0065] When sufficient sample material has been applied to the sensor surface 16, a second state of a substantially constant first frequency occurs, which corresponds to a completed application of the sample to the sensor 14. In the diagram according to FIG. 4, this second state is defined by an interval, which is determined by the count values c.sub.4 and c.sub.5, wherein c.sub.5<c.sub.4 applies. The values c.sub.4 and c.sub.5 are determined here such that the substantially constant first frequency, which corresponds to a related count value, is located between the values c.sub.4 and c.sub.5. As soon as the count value detected by the analysis device 22 falls below the value c.sub.4, this is classed as reaching the second state and signaled by illumination of the LED 38, which is a yellow LED in the exemplary embodiment shown. As FIG. 4 shows, the measuring curve now runs initially substantially horizontally, i.e., a stationary state is reached, which characterizes the completed application and distribution of the sample material on the sensor surface 16.

[0066] Now the curing process can be initiated. According to the curve reproduced in FIG. 4, this takes place at a time t.sub.1, for example by irradiation of the sensor surface 16 bearing the sample material with UV light. At the beginning of the curing process, on account of the temperature increase produced by the incipient polymerization of the sample material, it can occur that the count value detected by the analysis device 22 still falls slightly (see FIG. 4), because the sample material becomes somewhat more liquid due to the temperature increase and the dipole mobility in the sample material still increases temporarily. The value c.sub.5 co-defining the second state is selected here so that the lowest count value occurring following initiation of the curing process is still located above the value c.sub.5 and thus within the interval defined by the values c.sub.4 and c.sub.5. If a temperature increase of the sample material occurring due to the incipient polymerization should become too great, for example due to irradiation with UV light that is too intensive or too long (or generally expressed, due to too hard an initiation of the curing process), the value would fall below c.sub.5 and this would signal that overheating of the sample material has taken place, which has potentially damaged the sample material irreversibly. Measurement of the time progression is then terminated, which can be displayed by flashing of the yellow LED 38, for example.

[0067] Provided that proper initiation of the curing process has taken place, after any passage through the previously explained local minimum, the measuring curve rises again and once more passes the value c.sub.4, but from below to above this time. In the moment in which the count value detected by the analysis device 22 passes the value c.sub.4 in the direction of rising count values, the previously illuminated yellow LED 38 goes out and at this time t.sub.2 an internal timer (not shown) is started, which is used to determine a later time control interval defined by times t.sub.3 and t.sub.4 in which a desired curing state should have been reached.

[0068] As is evident from FIG. 4, the count value detected by the analysis device 22 rises more or less continuously due to the progressive curing (polymerization) of the sample material until a third state of a substantially constant second frequency is reached, which corresponds to a desired curing state of the curable material. This third state is determined by count values c.sub.6 and c.sub.7, wherein c.sub.6<c.sub.7 applies and wherein c.sub.7<c.sub.1 usually also applies. The substantially constant second frequency corresponds here to a related count value, which is located between c.sub.6 and c.sub.7. As already stated, this third state is advantageously defined not only by the count values c.sub.6 and c.sub.7, but moreover by the time values t.sub.3 and t.sub.4, so that for the third state, the control window B depicted in FIG. 4 results, which is delimited by the count values c.sub.6 and c.sub.7 and the time values t.sub.3 and t.sub.4 and the attainment of which characterizes a completed curing process with a defined curing quality. Reaching the third state is signaled by illumination of the LED 40, which is a green LED in the present exemplary embodiment.

[0069] The described sequence of measurement of the curing process of a curable material gives rise to a number of advantages. For example, initiation of the curing process can be triggered automatically by way of the control connection 28 (by corresponding activation of the UV light source, for example) as soon as the value falls below c4 for the first time. A prerequisite for this is that the value c.sub.4 is located only slightly above the count value that corresponds to the second state of a substantially constant first frequency. It is possible, furthermore, then to terminate an energy supply (heat supply, irradiation, etc.) automatically as soon as the value c.sub.6 has been reached from below. This option naturally only applies to systems in which an energy supply takes place not only for the purpose of initiating the curing process, but also during the curing process. It would also be possible to trigger post-exposure on reaching time t.sub.3 if the value c.sub.6 should not have been reached by this time.

[0070] Another advantage of the sequence described consists in it being the curing progression (polymerization progression) itself that leads to the start of the internal timer. This start is thus independent of preceding time delays, which can occur due to the process of dosing the sample material onto the sensor surface 16, for example.