Patent Application
20060056575
This application claims the priorities of German Utility Model application Serial No 203 20 021.7 filed Dec. 24, 2003, German Utility Model application Serial No 20 2004 000 413.5 filed Jan. 13, 2004 and German Utility Model application Serial No 20 2004 002 273.7 filed Feb. 13, 2004, the subject-matter of which is incorporated herein by reference.
The invention concerns a position detector for countingly detecting translatory and/or rotational movements, preferably in a predetermined direction, which can be autonomous insofar as it can carry out at least the required counting and storage operations independently of an external power source.
For that purpose a position detector can comprise a sensor portion including at least one permanent magnet which serves as an exciter magnet and which moves with the body whose movements are to be counted, that is to say for example with a rotating shaft or a reciprocating machine carriage, in which respect it is generally fixed directly to that body or is coupled thereto in such a way that it reflects the movement thereof.
In addition the sensor portion of the position detector has a ‘ferromagnetic element’ which is referred to in that fashion herein and which comprises a combination of hard-magnetic and/or soft-magnetic components which, upon the application of an external magnetic field of given magnitude, by virtue of an abrupt change in its consistency (for example switching and/or alignment of a large number of the Weiss domains present therein) and/or geometry (change in position of ferromagnetic components in space), result in an abrupt change in the magnetic flux and thus in a corresponding voltage pulse of given power in a coil surrounding same. The abrupt change in the ferromagnetic element is therefore described by an abrupt switching of the Weiss domains or by an abrupt change in reluctance.
A particular configuration of the first-mentioned group are pulse and Wiegand wires which do not make use of any macroscopic mechanical effect in production of the above-mentioned voltage pulses.
A representative of the second group in which mechanical macroscopic effects—here storage of the subsequently produced electrical energy in a spring—are used are magnetic reed contacts, as are set forth in U.S. Pat. No. 6,628,741. Major disadvantages precisely of that specific structure are mechanical fatigue and uncontrolled bouncing of the contacts as well as the slight measuring effect. A minimal solution which is optimum in terms of cost is scarcely to be achieved in that respect.
EP 0 658 745 A2 discloses a position sensor in which the ferromagnetic element comprises a rotatably mounted permanent magnet and an iron core, to which the rotatably mounted permanent magnet ‘holds on’ until the magnetic repulsion force which the approaching exciter magnet exerts thereon becomes so great that it overcomes the holding force between the iron core and the rotatably mounted permanent magnet and the latter abruptly rotates about its axis. That causes an abrupt change in the position of the Weiss domains and therewith the magnetic flux which passes through an induction coil wound on the iron core (large dΦ/dt), and a usable voltage pulse is induced in that coil.
What is common to all those solutions is that the respectively induced voltage pulse not only serves as a signal pulse to be counted, but it can also be used for the power supply for at least a part of the electronic system arranged downstream of the sensor portion, so that the system is capable, without an external supply of electrical energy, of executing the counting and storage operations required for detecting the movement to be monitored, that is to say for example for counting the revolutions of a shaft or the reciprocating movements of a carriage and storing the count value obtained in that situation so that such value is available for an external user.
An object of the invention is to design a position detector for detecting a rotational and/or translatory movement, which can be implemented at a low level of technical and cost expenditure.
A further object of the invention is to provide a position sensor having an energy consumption which is as low as reasonably possible and of a minimal structural size.
According to the invention there is provided a position detector which for countingly detecting rotational and/or translatory movements in preferably a predeterminable direction comprising at least one exciter magnet, a single ferromagnetic element, and at least one induction coil associated with the ferromagnetic element, wherein the movement to be, detected is represented by a relative movement between the exciter magnet and the ferromagnetic element and the energy which is taken from the kinetic energy of the movement to be detected during the approach as between those two elements and accumulated by means of the ferromagnetic element is abruptly liberated upon the attainment of a given relative position and thus a given magnetic field strength and a voltage pulse is produced by the sudden change in the magnetic flux in the induction coil. The detector further includes as an electronic system at least one rectifier circuit for rectifying voltage pulses of the induction coil, at least one capacitor which can be charged up by voltage pulses in the same direction, at least one comparator circuit which produces a pulse recognition signal upon the occurrence of a voltage pulse to be counted, a non-volatile counting and memory circuit which is formed by a register, in the form of a memory, of a counter and executes a counting and storage operation for each pulse recognition signal, wherein the electrical energy stored in the capacitor serves for the power supply at least of the non-volatile counting and memory circuit, a data read circuit which serves for further processing and output of the data stored in the non-volatile counting and memory circuit to an external user, and a control circuit which prevents interference with the counting and storage operation by operation of the data read circuit and vice-versa.
The electronic system defined therein includes the minimal circuitry configuration which is required for counting movement processes such as for example revolutions of a shaft or reciprocating movements of a carriage or the like and storing the respectively ascertained count value, without in that respect being reliant on an external power supply. Provided for those functions are in particular the at least one rectifier circuit, the at least one capacitor, the at least one comparator circuit and the non-volatile counting and memory circuit. As the count values ascertained must be made available to a user, the arrangement further includes a data read circuit and a control circuit, wherein the latter provides for trouble-free implementation of the counting and storage operations on the one hand and the reading operations on the other hand, in respect of which the data read circuit takes over the respectively present count value in order to make it available to a user, optionally in processed form.
A particularly preferred feature according to the invention provides that the components and circuit units belonging to the electronic system are combined in an IC component to afford an integrated circuit so that the entire position detector then consists of only three units, namely the exciter magnet, the ferromagnetic element with induction coil wound thereon and the IC component.
Transfer of the stored data to a user can be effected in two fundamentally different ways:
a) The reading operations (in each case: adoption of the counter condition contained in the non-volatile counting and memory circuit by the data read circuit and subsequent data transfer) are initiated by inquiry signals sent by the user and which can occur at any moment in time, thus constituting asynchronous operation.
b) The reading operations are controlled by the electronic system of the position detector itself so that there cannot be any conflict with the counting and storage operations which can occur at any moments in time, but at time intervals which are not less than a minimum value by virtue of the movement to be monitored, thus constituting synchronised operation.
In case a) the control circuit provides inter alia that, when a reading operation is initiated and takes place, the occurrence of a voltage pulse to be counted initially does not trigger any counting and storage operation but is in intermediate storage until the reading operation is concluded in order then to provide for counting of the event which has been placed in intermediate storage, and storage of the new count value, so that no count errors occur.
As the user, by virtue of his inquiry signal, must be able to initiate a reading operation even when no voltage pulse to be counted has occurred for a prolonged period of time so that the capacitor cannot provide any electrical energy, circuit components which are required for the reading operation are supplied with external electrical energy at least for the period of time which is required for that purpose.
The variant a) requires the following conditions to be met:
the data read circuit, after the occurrence of an inquiry signal, accesses the counting and storage circuit with a certain dead or delay time which is longer than the time required for a counting and storage operation;
the energy stored in the at least one capacitor, in spite of inevitable leakage currents, is kept at such a high level thereby at least for the duration of the period of time required for a reading operation, that a counting event which has been in intermediate storage can still be surely processed although the energy supply from the exterior is switched off again at the end of the reading operation; and
the time between two counting and storage operations is greater than the sum of the times which are required for a counting and storage operation and data transmission.
In case b) those conditions do not have to be met as the electronic system of the position detector can always establish whether precisely no counting and storage operation is taking place and whether there is sufficient energy taken from the movement to be monitored and stored in electrical form in order to be able to execute a reading operation. Here therefore it is possible to construct a position detector which is completely autonomous in operation, that is to say which is entirely independent of an external source of electrical energy.
If the energy required for the reading operation is high, because for example data transfer to the user is to be effected by means of a transmitter by radio, it is possible to provide a further capacitor which for example is charged with a plurality of voltage pulses which come from the induction coil and whose polarity is opposite to the polarity of the pulses to be counted, until sufficient electrical energy is available.
These and further advantageous features of a position detector according to the invention are set forth in the appendant claims.
Further objects, features and advantages of the invention will be apparent from the description hereinafter by way of example of preferred embodiments thereof.
In
Referring generally to the drawing, all the illustrated embodiments include at least one exciter magnet 2 which is connected to a component or body whose movement is to be monitored, in such a way that it performs that movement to be monitored with the body or it represents such movement. In that respect the exciter magnet 2 periodically approaches a ferromagnetic element which is shown in
In the embodiment illustrated in
After the production of such a voltage pulse the sensor wire and the magnetic field passing therethrough are then identically polarised, that is to say the sensor wire is biased in a direction opposite to its previous polarisation direction p, so that, without further measures, when the first exciter magnet 2 next moves past the sensor wire 6, at most an improvement in the bias effect would be achieved, which is only linked to the induction of a weak voltage pulse (attenuated pulse). Therefore the embodiment illustrated in
What is essential in the embodiment shown in
In comparison, in the embodiment illustrated in
In the embodiment shown in
In
In the embodiment illustrated in
In the embodiment illustrated in
In all these embodiments the exciter magnet 2 can be both of a circular and also a square or other rectangular cross-section in order to focus the magnetic flux lines issuing therefrom in such a way that they pass through or act on the ferromagnetic element in the optimum manner.
All circuit units are disposed in an IC component 20 indicated by a broken line.
More specifically the IC component 20 includes a comparator circuit 22, a rectifier circuit 24, a voltage limiting circuit 26, a capacitor 28, a control circuit 30, a non-volatile memory and counting circuit 32, a data read circuit 34 and two diodes 36 and 37.
The voltage pulses coming from the terminals 8 of the induction coil 7 are fed to the IC component 20 by way of its input terminals 39, 40 of which the former is connected to the ground line 41 passing therethroughwhile the other is connected to the rectifier circuit 24.
The rectifier circuit 24 is identified by the symbol for a diode and in the simplest case can consist of a single diode which is of such a polarity that it transmits either only voltage pulses of negative amplitude or, as shown in
As a comparatively high voltage is dropped at a diode in the forward direction, the rectifier circuit 24 used is preferably a switching transistor with a substantially lower forward voltage, being controlled in such a way that it transmits voltage pulses of a predetermined polarity coming from the induction coil 7, blocks voltage pulses of the opposite polarity, and in addition prevents discharge of the downstream-connected capacitor 28 by way of the induction coil 7.
Alternatively the rectifier circuit 24 can also be formed by a Grätz bridge, which affords the advantage that the capacitor 28 can be charged by all voltage pulses delivered by the induction coil 7 and counted and stored each half revolution.
In order to trigger a counting and storage operation only when the capacitor has been charged to the required extent, the attainment of a suitable voltage level is the subject of inquiry by means of the comparator circuit 22.
In a first variant the comparator circuit 22 is connected by way of a line 43 to the input terminal 39 at which the voltage pulses coming from the induction coil appear. In that case, it produces a pulse recognition signal which leads to a counting and storage operation, for example when the amplitude of such a voltage pulse, after passing through a positive maximum value, passes downwardly through a predeterminable level, as that is an indication that the capacitor 28 is charged to its maximum. In that way generally only voltage pulses of one polarity (here: positive polarity) and thus entire revolutions or complete reciprocating movements are counted. It is advantageous with this arrangement that each one to be counted can be detected independently of the charge condition of the capacitor 28, which the latter has immediately prior to the occurrence of that voltage pulse.
In a second variant the comparator circuit 22 is connected to the output of the rectifier circuit 24 by way of a line 44, that is to say it queries the voltage at the capacitor and produces a pulse recognition signal leading to a counting and storage operation when the absolute value of that voltage, which rises upon the occurrence of a voltage pulse, exceeds a predeterminable level in an upward direction. That level is so selected that it is just below the maximum value which is predetermined by the voltage limiting circuit 26, and the fact that it is exceeded therefore also indicates that the capacitor 28 is at maximum charge (soon). In the case of this variant, it is necessary to provide that the voltage at the capacitor 22 has fallen below the above-discussed level, prior to the occurrence of a voltage pulse to be counted. In this case therefore the arrangement will only use one half-wave rectifier circuit 24 and the capacitance of the capacitor 28 and the maximum value which is predetermined by the voltage limiting circuit 26 will be so matched to the electrical current requirement of the circuit units to be supplied from the capacitor 28 that the capacitor 28 is sufficiently discharged after the complete execution of a counting and storage operation. Alternatively or supplemental thereto, a controllable switch, for example in the form of a switching transistor, can be provided in parallel with the capacitor 28; closure of that switch provides that the capacitor 28 is necessarily completely discharged after the conclusion of each counting and storage operation.
In order to make it clear that, of the two lines 43, 44, there is only ever one that is present, they are illustrated by dash-dotted and dashed lines respectively.
In addition to the functions which have already been described hereinbefore, the voltage limiting circuit 26 which is identified by the symbol for a Zener diode performs the task of limiting the charging voltage of the capacitor 28 to a value which is non-critical in particular for the non-volatile counting and memory circuit 32 which is preferably in the form of a FRAM circuit. Admittedly those circuits are not immediately destroyed by excessively high supply voltages, but nonetheless their service life can be considerably curtailed by over-voltages.
In situations of use in which a particularly long service life does not play a part, the voltage limiting circuit 26 can also be omitted from the first variant in which the comparator circuit is connected to the input terminal 39 by way of the line 43.
A FRAM counting and memory circuit is advantageous for the reason that on the one hand it requires very little energy for a counting and storage operation while on the other hand it permits between 1012 and 1013 storage cycles. Therefore each individual voltage pulse can be not only counted but also immediately stored. When using a memory circuit technology whose service life is limited to a substantially lower number of storage cycles, in contrast the counting operations would have to be separated from the storage operations. In addition so much energy would have to be made available to each voltage pulse that a volatile counter could be supplied from the capacitor without losing its count value, even when prolonged time intervals are involved (for example in the region of 1 second) between successive voltage pulses. If with that technology the voltage pulses to be counted occur in succession at relatively small time intervals because the movement to be monitored takes place relatively quickly again, they must in fact be counted individually, but the count value must then be stored in the non-volatile memory only when the capacitor threatens to lose the required supply voltage in relation to a movement which again becomes slower, because of the related prolonged absence of a further count pulse. If therefore for example the capacitor at each voltage pulse has so much energy that on statistical average it is only every 100 voltage pulses that there occurs such a long pulse space that the supply voltage threatens to drop away excessively greatly, the number of the storage operations is only one hundredth of the number of the voltage pulses to be counted, whereby the total service life of the non-volatile memory is correspondingly prolonged.
In other words: the very long service life of the FRAM circuits makes it possible not only to count each individual voltage pulse but also to store the respectively associated count value immediately and, because of the low energy demand involved, to use sensor arrangements which for each voltage pulse supply comparatively little electrical energy as no pulse spaces have to be bridged over.
The capacitor 28 serves as an energy storage means which, after the occurrence of a voltage pulse to be counted, supplies both the control circuit 30 and in particular also the non-volatile counting and memory circuit 32 with electrical energy until the latter is certain to have processed that voltage pulse so that the position detector operates autonomously in respect of the counting and storage operations and is not reliant on an external voltage supply.
In the embodiment shown in
As there is the possibility that, prior to a time at which the inquiry signal is applied, no further counting operation has occurred for a prolonged period of time, and the capacitor 28 can thus not provide electrical energy, an external power supply to be applied to the terminals 48, 49 is required for the control circuit 30 and the data read circuit 34. The diode 37 provides that the capacitor 28 does not in any event serve as a power source for the data read circuit 34 while the diode 36 prevents the capacitor 28 being charged up by virtue of the application of the external power supply or a defective counting and storage operation being triggered in the counting and memory circuit.
A reading operation is initiated by a read signal which is fed from the input 50 of the IC component 20 by way of the line 51 to the control circuit 30 and the data read circuit 34. If an I2C interface is used as the data read circuit 34, after the occurrence of a read signal it delays its access, by way of the line 46, to the counting and memory circuit 32 as standard by a fixed period of time, which is symbolically indicated in
The data line 54 can also be part of a bus line or can be replaced by a radio connection between a transmitter (not shown) contained in the data read circuit 34 and a receiver to be found at the user. As generally a plurality of position detectors each having a respective transmitter are associated with a receiver, as is the case for example in the centralised detection of revolutions of water or gas meters or the like, each position detector must transmit not only the respective counter condition but also identification data which are stored in relation thereto and which clearly identify it, to the central user. Upon initiation of the system those characteristic data and an output counter condition can be read into the counting and memory circuit 32 by the data read circuit 34. That is symbolically indicated by the arrow 53 pointing in the opposite direction, in the data line 52.
The task of the control circuit 30 is to prevent mutual interference upon temporal coincidence as between a counting and storage operation on the one hand and a reading operation on the other hand since, as mentioned, those two kinds of event can occur totally independently of each other at any time.
As
a first memory 70 which can be in the form of a flip-flop which is normally reset (logic zero at the Q-output) and which is set by a pulse recognition signal applied to its clock input by way of the line 71 from the comparator circuit 22 so that at its Q-output it outputs a logic one serving as a counting signal level;
a second memory 72 which can be in the form of a flip-flop which is normally reset (logic one at the {overscore (Q)}-output) and is set by an inquiry signal applied to its clock input by way of the line 51 so that at its {overscore (Q)}-output it delivers a logic zero serving as a blocking signal level; and
a blocking circuit 74 which can be in the form of an AND-gate with two inputs of which one is connected to the Q-output of the first memory 70 and the other to the output of an OR-gate 75, of the two inputs of which one is connected to the {overscore (Q)}-output of the second memory 72 and the other is connected to the output of the blocking circuit 74. That output also actuates the one input of an AND-gate 77 directly and the other input of that AND-gate 77 by way of a delay member 78. The blocking circuit 74 transmits a counting signal level coming from the first memory 70 by way of the AND-gate 77 and the line 76 to an edge-sensitive counting input of the counting and memory circuit 32 for triggering a counting and storage operation only when no blocking signal level occurs at its other input.
After termination of the storage operation in the counting and memory circuit 32 the latter on the line 79 applies a reset pulse to the first memory 70 and after termination of data output to the user a reset pulse is applied to the second memory 72 by the data read circuit 34 on the line 80.
The AND-gate 77, the delay member 78 and the OR-gate 75 form a spikes trap and hold circuit which, when a counting signal level and a blocking signal level occur almost at the same time, prevents the appearance of undefined spikes at the input of the counting and memory circuit.
The mode of operation of the control circuit 30 is as follows:
When the comparator circuit delivers a pulse recognition signal on the line 71, the first memory 70 is set.
If the second memory 72 is not set because no immediately preceding inquiry signal was applied by way of the line 51, the logic one at its {overscore (Q)}-output holds the blocking circuit 74 open and the counting signal level which appears at the Q-output of the first memory 70 passes by way of the AND-gate 77, with a very short delay caused by the delay member 78, to the counting and memory circuit 32 and there triggers a counting and storage operation.
If a short time later an inquiry signal occurs on the line 51, the second memory 72 is admittedly set, but the logic zero appearing thereby at its {overscore (Q)}-output remains ineffective as the OR-gate 75 applies the logic one present at the output of the blocking circuit 74 as a counting signal level to the second input of the blocking circuit 74 so that the latter holds itself as long as the first memory 70 is not reset. That inquiry signal which occurs a short time after a pulse recognition signal cannot interfere with the counting and storage operation which is just running since, as already mentioned, the data read circuit 34 accesses the counting and memory circuit 32 with the delay time which is symbolically indicated by the delay member 47 and which is so great that, even with an extremely short spacing between the pulse recognition signal and the subsequent inquiry signal the counting and storage operation is certain to be concluded when access is effected by the data read circuit 34.
If however upon setting of the first memory 70 the second memory 72 is already set because an inquiry signal has occurred prior to the pulse recognition signal, then the logic zero at the {overscore (Q)}-output of the set second memory 72, by way of the OR-gate 75, blocks the blocking circuit 74 and the counting signal level appearing at the Q-output of the first memory 70 remains ineffective until a signal which comes from the data read circuit by way of the line 80 and which indicates successful conclusion of the data read operation resets the second memory 72, whereby the blocking circuit 74 is enabled and the counting signal level which has been put into intermediate storage can trigger a counting and storage operation in the above-described manner.
If a pulse recognition signal occurs at such a short time spacing after an inquiry signal that the signal level at the output of the blocking circuit 74 admittedly still briefly rises, but the OR-gate then nonetheless closes the blocking circuit 74, the spike which is produced as a result is suppressed by the spike trap formed by the delay member 78 and the AND-gate 77.
As the control circuit 30 must then operate both when a voltage pulse to be counted occurs but no external supply voltage is applied to the terminals 48, 49 and also when an inquiry is to be effected without the capacitor 28 supplying an adequate supply voltage, it is connected to the two energy sources, in which respect, as already mentioned, the diodes 36, 37 serve for decoupling purposes.
The electronic processing system shown in
Otherwise the foregoing information set forth in regard to those circuitry configurations with reference to
The essential difference in relation to the above-described embodiment is that here forwarding of the data does not take place in response to an inquiry signal coming from the user, which can occur at any moment in time, but is triggered by the control circuit 30′ by a signal applied to the data read circuit on the line 82 and which is produced in time-displaced relationship relative to the voltage pulses to be counted, in such a way that there cannot be any mutual interference between the counting and storage operation on the one hand and the reading operation on the other hand.
An essential advantage of this concept is that the entire electronic processing system can operate autonomously, that is to say completely independently of an external supply with electrical power.
For that purpose the circuit arrangement includes a further rectifier circuit 24′ which is of such a polarity that, with the voltage pulses which are of a polarity that is opposite to the voltage pulses to be counted, it charges up a further capacitor 28′ whose charging voltage is checked by means of a further comparator circuit 22′. Whenever that charging voltage exceeds a predetermined level the comparator circuit 22′ delivers on the line 71′ a signal to the control circuit 30′ which thereupon, by way of the lines 82, 83, actuates the data read circuit 34′ and the counting and memory circuit 32 respectively for a reading operation by way of a data line 52 and subsequent forwarding of the data on the data line 54.
As the predetermined level of the charging voltage of the further capacitor 28′ can only ever be exceeded when a voltage pulse appears, whose polarity is opposite to the polarity of the voltage pulses to be counted, there cannot be any time conflict between the counting and storage operations on the one hand and the reading operations on the other hand. The control circuit 30′ can therefore be of a substantially simpler construction than was described for the control circuit 30 as, after actuation thereof by the comparator circuit 22′, it only has to provide for the correct temporal sequence of the control signals to the counting and memory circuit 32 and the data inquiry circuit 34′.
If the data inquiry circuit 34′ includes a transmitter which requires substantially more electrical power than is contained in a voltage pulse for forwarding the data to the user, the further capacitor 28′ can be so large that it integrates the charges of a plurality of such pulses. The level interrogated by the comparator circuit 22′ is then so selected that it is exceeded only when the capacitor has been charged up by a correspondingly large number of voltage pulses. In that case the further capacitor 28′ will generally not be contained in the IC component, to which the other parts of the circuitry are preferably combined.
If conversely only very little energy is required by the data read circuit 34′ in order to forward the stored and processed data to the user, the power supply both for the control circuit 30′ and also the data read circuit 34′ can be effected from the capacitor 28. The rectifier 24 is then preferably in the form of a Grätz bridge while the further rectifier 24′, the further capacitor 28′ and the further comparator circuit 22′ can be omitted. The control circuit 30′ can then for example trigger a data read operation without risk of conflict by virtue of delivering a suitable control signal after the execution of each counting and storage operation, while maintaining a safety time interval.
Another possibility provides using two comparators 22 and 22′ which both interrogate the voltage pulses appearing at the inputs 39, 40 so that the one comparator 22 delivers a pulse recognition signal for example upon the occurrence of each positive voltage pulse and the other comparator 22′ delivers a signal triggering a data read operation upon the occurrence of each negative voltage pulse, thereby also avoiding mutual interference.
It should be expressly pointed out that the electronic system of a position detector according to the invention does not necessarily have to be arranged in the immediate proximity of the sensor portion (comprising at least one exciter magnet, a ferromagnetic element and an induction coil). Rather, such a long line can be provided between the terminals 8 of the induction coil 7 and the input terminals 39, 40 of the electronic system that the electronic system is closer to the user than the sensor portion, in which case the data line 54 is then correspondingly short. In this case also the sensor portion and the electronic system form a unitary position detector in accordance with the present invention.
If a further induction coil or for example a Hall probe or a field plate is associated with the ferromagnetic element 6 so that the sensor portion of the position detector according to the invention comprises for example a reed contact arrangement and a Hall probe or another combination of the components just mentioned, the rotational and/or translatory movement can also be countingly detected in both directions.
It will be appreciated that the above-described embodiments of the position detector have been set forth by way of example and illustration of the invention and that further modifications and alterations may be made therein without thereby departing from the scope of the invention.
It will be expressly noted at this juncture that the reference numerals contained in the accompanying claims are included therein solely for greater ease of understanding thereof and in themselves are not intended as limiting the scope of the invention to the structures identified in the foregoing description by the respectively corresponding reference numerals.
| Number | Date | Country | Kind |
|---|---|---|---|
| 203 20 021.7 | Dec 2003 | DE | national |
| 20 2004 000 413.5 | Jan 2004 | DE | national |
| 20 2004 002 273.7 | Feb 2004 | DE | national |
