Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
  • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
  • G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
  • G01D5/14—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage
  • G01D5/24—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying capacitance
  • G01D5/241—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying capacitance by relative movement of capacitor electrodes
  • G01D5/2412—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying capacitance by relative movement of capacitor electrodes by varying overlap
  • G01D5/2415—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying capacitance by relative movement of capacitor electrodes by varying overlap adapted for encoders

Definitions

• the invention relates to a device for capacitive position detection of a target object according to the preamble of claim 1.
• the invention relates to a sensor arrangement for capacitive position detection of a target object according to the preamble of claim 12 and a method for capacitive position detection of a target object according to the preamble of claim 17.
• a generic device has a plurality of capacitive probes which are arranged distributed over a detection area in which a position of the target object is to be detected.
• a generic sensor arrangement for capacitive position detection of a target object has a plurality of capacitive probes, which are arranged in a first area, in particular on one side, of a carrier distributed over a detection area in which a position of the target object is to be detectable.
• a plurality of capacitive probes are arranged over a detection area in which a position of the target object is to be detected.
• the capacitances or changes in capacitance of the probes to the environment in dependence on the position or a change in position of the target object or variables derived therefrom serve as measured variables.
• target object can be interpreted very broadly. These can be discrete objects as well as substances, i.e. especially fluids, such as liquids and gases as well as bulk goods.
• target object and object are also used synonymously.
• position with regard to fluids and bulk materials should also be understood to mean their distribution or expansion.
• a generic device is described in ' DE 198 51 213 Cl.
• a plurality of capacitor coatings are applied to a flexible film.
• the film is bent into a desired shape, for example a U or S shape, and used to detect fluids, that is to say liquid or gaseous media.
• a capacitance which is changed by the dielectric properties of the medium to be detected and brought into the vicinity of the respective probe serves as the measurement variable.
• a capacitive proximity switch is disclosed in DE 196 23 969 AI.
• DE 195 03 203 AI describes a capacitive sensor in which a position of an object or a mass distribution can be determined by measuring a displacement current.
• a matrix of capacitive position sensors is disclosed in EP 0 609 021 A2.
• the subject of US Pat. No. 5,136,286 is a device for the capacitive determination of the orientation of a measuring device pointer. Shaped electrodes are used in a special way.
• a device for capacitive monitoring of the composition of a sample, e.g. B. from Blister packs for pharmaceuticals are described in EP 0 302 727 A2.
• Inductive methods and devices are also known in the field of position detection of a target object. Devices of this type are used in a large number of industrial processes in the field of automation. There are also numerous possible applications in the field of automotive technology.
• DE 102 04 453 AI describes an analog inductive displacement transducer with which a relative displacement between a vehicle seat and a motor vehicle body can be determined.
• the measurement principle is the change in magnetic induction caused by a relative displacement of a test body made of a material with high magnetic permeability.
• linear displacement measuring systems are also known in which a tilted longitudinal coil, an inductive displacement sensor with magnetic coupling or an inductive displacement sensor consisting of many individual coils is used.
• a tilted longitudinal coil an inductive displacement sensor with magnetic coupling or an inductive displacement sensor consisting of many individual coils is used.
• the respective detection signals have a comparatively large distance dependency and therefore only limited distances can be monitored.
• ferromagnetic objects or objects can often be detected. This. is undesirable because of the mechanical sensitivity of ferromagnetic objects.
• solutions with a large number of individual coils enable the monitoring of a very large area in principle. But there to . To avoid crosstalk of the signals of the individual coils, each individual coil is subjected to a different frequency, these solutions are associated with a high level of circuitry and equipment.
• the object of the invention is to specify a device, a probe arrangement and a method for capacitive position detection of a target object, with which a target object can be recorded with a high degree of accuracy over a distance of any length.
• the device and the probe arrangement should also be structurally simple to implement.
• the object is achieved by the probe arrangement having the features of claim 11 and by the method having the features of claim 16.
• the generic device according to the invention is characterized in that the probes are each connected to a voltage source via coupling capacitances and can be supplied with a supply voltage and that an evaluation device connected to the probes is provided with which the probe signals form an output signal which is a measure of the position of the target object to be captured is processable.
• the sensor arrangement of the type described above is further developed according to the invention in that at least one coupling electrode is formed in a second region, in particular on an opposite side, or within the carrier, in order to form coupling capacitances via which a supply voltage can be coupled to the probes is provided and that the carrier for forming a coupling layer is at least partially formed from a dielectric material.
• the invention proposes that the probes are each supplied with a supply voltage via coupling capacitances and that the probe signals processed with the aid of an evaluation device to form an output signal which is a measure of the position of the target object to be detected.
• a first core idea of the present invention can be considered to couple a supply voltage, for example an AC voltage, to the plurality of capacitive probes via coupling capacitances.
• a further basic idea of the present invention with regard to the probe arrangement is to design this probe arrangement in a very compact manner on a carrier in which a plurality of probes are arranged in a first region and in which, spaced apart from the first region, in a second region at least one coupling electrode is provided to form the coupling capacitances with the probes.
• the probes and the coupling electrodes can be provided either directly on the outside of the carrier, which is at least partially made of a dielectric material, or in the interior thereof.
• the first essential advantage of the invention can be seen that the position of any metallic or non-metallic object can be detected, since in any case a change in the capacitance of the probes to the environment is brought about.
• the arrangement of the probes for example along a path, can in principle be of any length and take any shape. For example, straight, i.e. linear paths, circular or zigzag paths are possible, as are flat, i.e. two-dimensional, or also spatial, i.e. three-dimensional, arranged probe configurations.
• any topologies for the probes are therefore possible, in particular also concentric, right-angled and matrix or array-like arrangements. Basically, all "uneven” technically producible topologies are possible.
• the device according to the invention and the method according to the invention not only discrete objects and objects to be detected, but also fluids, that is to say liquids and gases, and bulk goods can be detected independently of the respective material.
• robust metallic targets can also be detected, which is significant for numerous applications.
• the position detection system which in principle is contactless, is that the device, the probe arrangement and the method can each be implemented with little design effort.
• the evaluation device always uses the probe signals, for example the probe voltages, to determine the position of the target object to be detected.
• error quantities which act on all probes, ie all channels, at the same time no longer have any influence on the evaluation.
• error variables include temperature effects as well as electrical disturbances, for example due to electrical fields during welding or radio interference voltages, and effects which result from the dependence of the probe signals on the respective distances of the object.
• the material of the target object to be detected affects the capacities of all probes in the same way, so that the result of the evaluation is independent of the material of the target object to be detected.
• the target object or the object itself can consist of metal, plastic, glass, ceramic, paper, wood, in principle, therefore, of any material. If the object to be detected is made of a conductive material, proof can also be provided regardless of whether the object is grounded or not.
• the invention has particularly important practical applications for all linear displacement measurements, for displacement or angle measurements in power clamps and for level measurements of liquids and bulk materials, directly or through a container wall.
• the coupling capacitances and the capacitances of the probes to the environment which vary due to the variable position of the target object to be detected, each form capacitive voltage dividers.
• the capacitive probes which can also be referred to as measuring probes, are not fed directly, but a voltage divider is built up via the coupling capacitance or the coupling capacitances and the measuring capacitance or the measuring capacitances.
• coupling capacitance is also understood to mean a capacitance whose coupling is changed by the approach of an object
• the term “coupling capacitance” is understood here as “coupling-in” capacitance. This is the capacitance through which the AC voltage is injected onto the measuring probe.
• the capacitance fed directly from the generator that is to say the coupling capacitance
• the probe arrangement according to the invention can be implemented with discrete capacitors.
• the following capacity is only changed in the present invention by the approach of an object. Such a follow-up capacity is not available in the prior art.
• the respective probe voltages are evaluated as probe signals.
• the ratio of the probe capacitance to the coupling capacitance is essentially included in the measured signal.
• At least one probe arrangement according to the invention is provided.
• the probe arrangement according to the invention not only the probes and the coupling capacitances can be realized in a particularly compact and simple manner. They also allow a very high variability in the arrangement of the probes.
• the carrier can be designed as a printed circuit board, so that the highly developed printed circuit board technology can be used for production.
• the shape and size of the probes are arbitrary, with plate-like electrodes being preferably provided, for example on a printed circuit board. Depending on the desired spatial resolution and sensitivity of the probes, their area can range from a few square millimeters to a few square centimeters and above. In particular, it is expedient to select the shape and size of the probes with a view to the target object to be detected.
• the carrier is designed as a flexible printed circuit board.
• a flexible circuit board can in principle be brought into any desired shape, so that any three-dimensional. Areas can be monitored. For example, the position of a lever that moves on a circular or spherical segment can be monitored.
• a film can also be used as the carrier, in which the corresponding metallic structures are applied, for example vapor-deposited, using a suitable mask.
• the probe arrangement can therefore be constructed in one piece as a coherent dielectric metallized on both sides or as an interrupted dielectric metallized on both sides with distributed capacitances.
• a certain freedom of design with regard to three-dimensional areas to be monitored can also be achieved by using several probe arrangements according to the invention, in which a conventional printed circuit board is used as the carrier. Separate circuit boards can also be an advantage to compensate for any mechanical stresses or temperature fluctuations.
• the coupling electrode can be divided into a plurality of individual electrodes. This can be useful if different coupling potentials are to be applied to the individual coupling capacities.
• the coupling electrode is designed as a continuous potential area. This is particularly important since, in the case of the capacitive position detection system proposed here, in contrast to an inductive detection system with a number of coils, the individual capacitances do not have to be subjected to different frequencies.
• the continuous coupling electrode thus serves as a common base, which can be supplied with a supply voltage, in particular an AC voltage. Compared to an inductive system, the required electronics are therefore much easier to implement.
• the probe arrangement according to the invention can be used particularly advantageously if parts on the carrier additionally ner evaluation electronics, ie parts of the evaluation device, are arranged. In this way, very compact structures are possible.
• the probes and the coupling electrodes can be arranged inside the carrier.
• the probes and the coupling electrodes are arranged directly on the outside of the carrier.
• An arrangement of the coupling electrodes within the carrier can be preferred if further metal layers are provided on or in the carrier for shielding or for receiving further circuit components.
• the coupling capacitors can also be at least partially designed as discrete capacitors. This can be advantageous, for example, if individual probes have to be positioned differently for different applications.
• the accuracy of the evaluation and thus of the position verification can be increased overall if at least one of the probes is designed and / or used as a reference probe.
• This can in particular be an inactive measuring probe, i.e. a probe that is positioned so that the target object to be detected never reaches its detection area.
• the signal of an active measuring probe can also be used as a reference if it is ensured that the object to be detected is not in the detection area of this probe at the time in question.
• the voltage amplitudes of the other amplitudes can then be compared, for example.
• the measuring electrodes or measuring probes have the same or at least a similar shape and / or area as the reference electrode or the reference electrodes.
• the evaluation of the respective Signals with regard to position determination are then particularly simple.
• the evaluation device has a rectifier at least for each probe.
• the evaluation unit expediently has a central processing unit.
• this can also be a circuit made up of analog components, for example an operational amplifier circuit.
• a microprocessor is preferably used for this.
• at least one analog-digital converter is then also provided for digitizing the analog measurement signals.
• a large number of analog-digital converters can be dispensed with and instead one or more multiplexers can be provided in the evaluation device, via which or via which the probe signals from at least two probes can be fed to the central processing unit, for example to the microprocessor are.
• each channel can of course also be equipped independently with a rectifier, any processing electronics and an analog-digital converter.
• the probe voltages there is the greatest possible freedom.
• the differences between the individual signal voltages can be evaluated, for example.
• the quotients of a plurality of voltage amplitudes are formed for evaluation. In this way, undesired interference effects that act in the same way on all probes, such as temperature and electrical interference fields, can also be eliminated.
• the speed of the signal processing can be increased if the evaluation device has a signal processor for preprocessing the analog probe signals.
• Figure 1 is a schematic representation of a first embodiment of a device according to the invention.
• FIG. 2 shows a schematic partial view of a second exemplary embodiment of a device according to the invention
• FIG. 3 shows a schematic partial view of a third exemplary embodiment of the device according to the invention.
• FIG. 5 shows a diagram in which the signal voltage of three probes is plotted as a function of the fill level of a liquid or bulk material to be detected
• FIG. 6 shows a first exemplary embodiment of a probe arrangement according to the invention
• FIG. 7 shows a second exemplary embodiment of a probe arrangement according to the invention
• Fig. 8 shows a third embodiment of a probe arrangement according to the invention
• FIG. 1 A first exemplary embodiment of a device 10 according to the invention is shown schematically in FIG. 1.
• the device 10 generally consists of a plurality, i.e. at least two capacitive measuring plates or probes 20, 30, 40.
• an AC voltage is coupled as a supply voltage from a voltage source 14 to the probes 20, 30, 40.
• Capacities 24, 34, 44 arise between the individual probes 20, 30, 40 and an object 12 to be detected as the target object. Capacities are shown in Fig. 1 in the manner of an equivalent circuit diagram.
• the coupling capacitances 22, 32, 42 also do not necessarily have to be discrete capacitors.
• the probes 20, 30, 40 are also each connected to an evaluation device 50, which is explained in more detail below with reference to FIGS. 2 and 3.
• the evaluation device 50 evaluates the probe voltages of the probes 20, 30, 40 and generates an output signal 52 depending on the position of the object 12 relative to the probes 20, 30, 40.
• a grounded object 12 is assumed for simplification.
• the reference potential of the voltage source 14 is also earth.
• the coupling capacitance 22 and the capacitance 24 form a capacitive voltage divider with the probe voltage as the center voltage.
• the probe voltage U 2u results from the injected voltage U 0 ' , the value C 22 of the coupling capacitance 22 and the value C 24 of the capacitance 24: And correspondingly for the further probes 30, 40.
• the probe voltages of the various probes 20, 30, 40 are therefore dependent on the position of the object 12, the probe that indicates the lowest level that the object 12 is closest to. Since an alternating voltage is applied to the coupling capacitances 22, 32, 42 by the voltage source 14, an alternating voltage is also present at the probes 20, 30, 40, which is processed with the aid of the evaluation device 50.
• each object 12 to be detected has a parasitic capacitance.
• the capacitance of one of the probes 20, 30, 40 to earth is formed by the series connection of the capacitance of the probe to the object 12 and the parasitic capacitance of the object 12 to the earth potential.
• the capacitance of the probe against an earthed object is greater than the capacitance of the probe against an ungrounded object due to this series connection. For this' reason 12 changes an ungrounded object, the probe voltages less than a grounded object 12th
• the arrow 18 in FIG. 1 indicates a displacement of the object 12 within the detection area 16.
• the evaluation circuit 50 always uses a plurality of probe voltages to determine the position of the object 12. Defects such as temperature, electrical interference due to welding fields or radio interference voltages and the distance of the object 12 to the probes 20, 30, 40, which act on all channels simultaneously, can be eliminated in this way.
• the result of the evaluation is also • independent of the material of the object 12.
• the parasitic capacitance of a non-grounded object 12 is the same for all probes 20, 30, 40, the result of the evaluation is also independent of the grounding of the object.
• FIGS. 2 and 3 Two examples of the design of the evaluation device 50 in detail are shown in FIGS. 2 and 3. Equivalent components are identified by the same reference numerals.
• the probe voltage of the probes 20, 30, 40 is first applied to a rectifier 26, 36, 46.
• the rectified signals are then fed to a microprocessor 54 via a multiplexer 56 and an analog-digital converter 58.
• the microprocessor 54 calculates an output signal depending on the position of the object 12 from the digitized signals and outputs this signal to the output 52.
• a large number of expensive analog-digital converters can be dispensed with.
• a separate analog-to-digital converter 28, 38, 48 is provided for each probe channel.
• the probe voltages of the probes 2Q, 30, 40 can therefore in principle be evaluated independently of a sampling frequency of a multiple.
• the coupling capacitances 22, 32, 42 of the device 10 shown in FIG. 1 can in principle be designed as discrete capacitors 23, 33, 43, as is shown schematically in FIG. 9. This variant is particularly useful when the positioning of one or more probes is to be changed, for example to monitor different areas or paths.
• the probes 20, 30, 40 are arranged linearly in an area 16 to be monitored.
• a probe arrangement 60 according to the invention is used particularly advantageously for positioning the probes 20, 30, 40.
• the first example of a probe arrangement 60 according to the invention shown in FIG. 6 is made from a circuit board coated on both sides.
• the probes 20, 30, 40 are formed from the printed circuit board coating on a first side 71 of the printed circuit board functioning as carrier 70. These individual probes 20, 30, 40 may have in principle any 'shapes, in particular different sizes.
• a continuous coupling electrode 80 for forming the coupling capacitances 22, 32, 42 is formed on the opposite outside 73 of the carrier 70. This coupling electrode 80, which basically performs the function of a capacitor plate and in the end to 'arrival of the AC generator is used is also referred to as a base point.
• connection to the supply voltage can also be relatively high-resistance, for example ohmic resistances of up to 1 megohm are possible here.
• the overall circuit structure is therefore very uncritical.
• a coupling layer 72 is also formed by the material of the circuit board 70 between the coupling electrode 80 and the probes 20, 30, 40, which increases the coupling capacitances 22, 32, 42 due to the dielectric properties of the circuit board material.
• the coupling layer 72 can consist of a material with a determinable dielectric, for example of printed circuit board material, plastic, glass, ceramic, air or of a foam.
• FIG. 7 differs from the variant according to FIG. 6 essentially in that only the probes 30, 40 are arranged on a common carrier 70, but the probe 20 is arranged on a separate carrier. Furthermore, the variant in FIG.
• each coupling capacitance 22, 32, 42 can in principle be supplied with a different AC voltage.
• the connections between the coupling electrodes 25, 35, 45 can in turn be relatively high-ohmic.
• FIG. 8 a more complex embodiment is shown in FIG. 8.
• the probes 20, 30, 40 are in turn arranged on the outside 71 of the carrier 70.
• the coupling electrode 80 is arranged in the interior of the carrier 70, which can be a multilayer printed circuit board, for example.
• a further metallic layer 86 is provided above the coupling electrode 80 and can optionally be used to shield the probes from radiation from interference fields.
• An electrical circuit, schematically represented by component 90, is arranged on the side of carrier 70 opposite probes 20, 30, 40.
• coupling capacitances 22, 32, 42 are formed by the probes 20, 30, 40 and the coupling electrode 80, which are increased by the dielectric properties of the coupling layer 42.
• the probes 20, 30, 40 In order to be able to record the movement of an object 12 without gaps, the probes 20, 30, 40 must be arranged relative to one another in such a way that their sensitivity curves overlap at least partially.
• An example of a simple contactless determination of the displacement of an object 12 using a device according to the invention and the method according to the invention is explained with reference to FIG. 4.
• the probe voltage of a total of three probes 20, 30, 40 is plotted there, which are arranged approximately as shown schematically in FIGS. 1 to 3. As can be seen from FIG. 4, the minimum value of the probe voltage of the probe 20 is reached when the probe 20 and the object 12 are exactly opposite one another. If the object 12 moves in the direction of the probe 30, the voltage on the probe 20 increases again and the voltage on the probe 30 decreases accordingly.
• the position of the object 12 can be represented as a function of time.
• FIG. 5 Another application example of the present invention is explained with reference to FIG. 5.
• the probe voltages of the three probes 20, 30, 40 are shown for an application in which the fill level of a liquid or a bulk material is detected as the target object.
• the probes 20, 30, 40 are preferably arranged vertically.
• the capacities of the probes further up to the environment are gradually increased.
• the capacitance values of the probes arranged below remain unchanged due to the liquid or bulk material that is still present there.
• the evaluation of the probe voltages for liquids or bulk goods must therefore be done differently than for an individual object to be verified.
• the minimum value of the probe voltage of the probe 20 is reached when the probe 20 is completely covered by the liquid or the bulk material. If the liquid or bulk solids level continues to increase, the voltage at the probe 30 also decreases and finally drops to the minimum value. In contrast to the application shown in FIG. 4, the probe voltages naturally do not rise again as soon as the corresponding probe is covered by the liquid or the bulk material.
• the present invention proposes a new device, a sensor arrangement and a method for contactless capacitive position detection of an object, which on the one hand enables a particularly precise determination of the position of an object or also of liquids and bulk materials and which on the other hand is constructive, especially in comparison to known ones inductive solutions, is particularly easy to implement.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)
• Electronic Switches (AREA)

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• 2004
  • 2004-04-16 DE DE102004018630A patent/DE102004018630A1/de not_active Ceased
• 2005
  • 2005-03-31 EP EP05716480A patent/EP1735595B1/de not_active Expired - Lifetime
  • 2005-03-31 DE DE502005002502T patent/DE502005002502D1/de not_active Expired - Lifetime
  • 2005-03-31 US US10/599,879 patent/US20070205775A1/en not_active Abandoned
  • 2005-03-31 WO PCT/EP2005/003389 patent/WO2005100924A1/de not_active Ceased
  • 2005-03-31 JP JP2007507692A patent/JP2007533220A/ja active Pending
  • 2005-03-31 AT AT05716480T patent/ATE383567T1/de not_active IP Right Cessation

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