EP1664704A1

EP1664704A1 - Force transducer

Info

Publication number: EP1664704A1
Application number: EP04765375A
Authority: EP
Inventors: Bruno Starek; Helmut Purner; Franz Vekörrer
Original assignee: Occluscan AG
Current assignee: Occluscan AG
Priority date: 2003-09-18
Filing date: 2004-09-17
Publication date: 2006-06-07
Also published as: US7121148B2; AU2004274637A1; NO20061654L; US20070039394A1; CN1882825B; CA2538950A1; WO2005029025A1; EP1516595A1; JP2007514130A; US20050115330A1; US7401526B2; CN1882825A

Abstract

The invention relates to a force transducer, comprising an oscillator (1), with an inductance (2), formed by a primary winding and a measuring transducer (11), with a secondary winding (30), electrically-connected to the measuring transducer (11) and arranged with a transformer coupling to the inductance (2) of the oscillator (1). On exertion of a force on the measuring transducer (11), the impedance of the measuring transducer (11) is altered, along with the load in the inductively-coupled secondary winding (30). The resulting frequency change in the oscillator (1) is determined by means of an analytical circuit (14) which is proportional to the force acting on the measuring transducer (11).

Description

Force transducer

The invention relates to a transducer for determining physical or mechanical quantities. For the purposes of the invention, force encompasses all variables that can be defined by force, such as pressure, acceleration, torsion, etc. According to the invention, the temperature can also be determined in connection with the use according to the invention of a measurement sensor with pyroelectric properties.

Numerous transducers for determining physical or mechanical quantities are known. Depending on the ^'measuring principle the forces are recorded such transducer by influencing the inductance, capacitance or resistance, said further parasitic influences can be due to the respective measured variable, the measurement principle, is how not dealt with below.

The known transducers are usually very complicated, both electronically and mechanically, and are therefore of expensive construction and, as a result, are very susceptible to faults. In most cases, a mechanically complex and therefore expensive force transmission element is provided as the sensor, which is sometimes not suitable for thin sensors.

From DE 37 35 657 AI is a device for measuring the expansion of full bodies, especially internal ones Strain processes known, wherein an inductance is introduced into the solid body during the manufacturing process, and the change in inductance determines the measure of the stretch. The construction of this measuring device is very complex and complex and cannot be used for small or thin sensors. Another disadvantage is the lack of flexibility in changing the location of the sensor. There is also a galvanic coupling, which can lead to interference.

From DE 44 20 691 Cl a force measuring cell is known which has an elastically deformable force transducer for absorbing the weight force and an inductor arranged adjacent to it, whereby the eddy current effect is used due to the sensor arrangement. The disadvantages mentioned are also present here.

The present invention has the great advantage that, in combination with inductive, capacitive and / or ohmic sensors, the measurements can be carried out in the low-resistance range, for example 1 ohm. As a result, interference is better avoided in relation to the measuring ranges of the known measuring transducers, and no costly building constructions are necessary to comply with safety regulations. Furthermore, the invention has the advantage that its special designs are suitable for very thin sensors, for example a thickness of less than 20 my in the measuring area, and that the measuring sensor can, in principle, be positioned without complex measures.

The galvanic isolation of the transducer from the oscillator circuit also prevents interference on the oscillator. In particular, the invention is very well suited for the use of transducers under harsh conditions such as dirt, moisture, etc.

According to the invention, when the physical or mechanical variable acts on the transducer, the impedance changes, which in turn changes the load in the secondary winding that is electrically (conductively) connected to the transducer and that is coupled to the inductance of the oscillator in a transformer arrangement is changed. As a result of this change in the impedance or the load, the ■ frequency of the oscillator becomes proportional to the physically acting variable. (e.g. force) changes and this frequency change is evaluated and recorded as an electrical measured variable.

In many applications, transducers with piezo sensors are used to measure physical and mechanical variables such as force, pressure, torsion, acceleration, temperature, etc.

Piezo sensors, however, have the known disadvantage that they require an electronic voltage amplifier with a very high-resistance input resistor with high-quality insulation or a so-called charge amplifier for the measurement value acquisition. Such electrometer or charge amplifiers are, on the one hand, very complicated to construct and therefore expensive to manufacture, and on the other hand, these amplifiers offer further sources of possible interference.

Another known disadvantage of piezo sensors is that, due to the principle, no static loads can be detected with these. Transducers from EP 04 59 069 AI are indeed Carrying out only "quasi-static" measurements with piezo sensors is known, but such transducers in turn require an expensive and complex charge amplifier with corresponding insulation resistances.

The advantage of the invention is the use of a force transducer according to the invention with a piezoelectric or piezoresistive transducer, the electrodes of which are electrically connected to the secondary winding of the inductor of the oscillator. When force acts on the piezoelectric or piezoresistive transducer, the capacitance or resistance, and thereby the impedance of the transducer, is changed. This change in impedance causes a change in the load in the secondary winding and, via the transformer coupling, leads to a change in the frequency of the oscillator. By means of this measuring principle according to the invention, a charge or electrometer amplifier is no longer required and static measurements are also possible.

This measuring arrangement offers for all piezoelectric transducers such as quartz, piezoceramic, piezopolymers, e.g. PVDF and its copolymers, polymers with piezo particles or piezo fibers, piezo foams, ferroelectric materials, etc., but also for piezoresistive transducers, such as silicon, the advantages mentioned.

When using a piezoelectric transducer with pyroelectric properties, a change in the polarization of the piezoelectric material of the transducer is brought about by changes in temperature, which in turn can be detected by the electrodes and, as described above, measured as a frequency change in the oscillator. As a result, the transducer also enables the determination of temperatures. By means of a force transducer according to the invention, the vehicle tire pressure and the vehicle tire temperature can be measured simultaneously, for example in a very simple and inexpensive manner.

Of course, the measuring force transducer according to the invention can also be used to determine the acceleration with a measuring sensor with piezoelectric properties in combination with a seismic mass.

A transducer having piezoelectric, piezoresistive or pyroelectric properties is preferred when using the ^"arranged connected secondary winding around a soft magnetic ring core, for example of ferrite, in transformer coupling. As a result, stray losses are of 'magnetic field largely avoided and there is ^an'" with this electrically ideal "coupling.

For areas of application where very thin or three-dimensional sensors are required, such as also in dental applications, the preferred sensor according to the invention is a piezo film (PVDF and its copolymers) with a thickness of less than 80 my, preferably less than 30 my, or a liquid PVDF -Copolymer lacquer is used, which can be cast or sprayed very thinly.

The advantages mentioned can also be achieved for transducers which are formed from piezo foams or so-called ferroelectrets.

To determine the occlusion contact between two bodies pressed against one another, for example in dentistry, discolouring or discoloring foils are used, in which the Contact between the upper and lower jaw teeth leads to discoloration of the film, but also to the contact points on the teeth. Furthermore, the film can have a color layer with a dye enclosed in capsules. Depending on the compressive force acting on the ink layer, a different number of capsules is broken up and a different amount of dye is released. Such foils, however, do not allow the strength of the compressive force, in particular the occlusion pressure between teeth, to be precisely determined.

Electrical pressure sensors are therefore also known for determining occlusion pressure. According to DE 31 17 284 AI, US 4,521,186 and EP 0 379 524 B1 sensors are used which consist of two layers each provided with conductor tracks, between which a resistance layer is provided. When pressure acts on the bite section of the sensor, the resistance between the conductor tracks of the two layers is changed, and this change is recorded as a measured variable.

The known sensors are relatively complicated in structure and handling, so that they could not prevail over the conventional occlusion contact foils with discoloration. In addition, the known sensors have a relatively thick bite section, which affects the accuracy of the occlusion measurement. In addition, the two layers must be electrically contacted with the conductor tracks for supplying the input and output signals. Since the bite section has to be changed for each patient for hygienic reasons, this is associated with additional effort. Essentially the same disadvantages have occlusion pressure sensors that are based on the piezo effect (eg US Pat. No. 4,592,727). In addition, the known piezo sensors have the disadvantage that they are susceptible to failure in adverse environmental conditions (such as water, dirt, oil etc.) due to the required amplifier with a high-impedance input resistance. DE 197 05 569 Cl turns away from the electrical sensors in the bite area and instead proposes an occlusion force transmission with a pressure fluid.

It is also an object of the invention to provide a simply constructed device for the precise determination of the pressure between two _. pressed bodies, in particular the dental contact pressure, to provide, for example, in the area of application _. Dentistry can be handled similarly to the previous occlusion film with discoloration, and in particular requires no electrical contact in the bite area.

A device according to the invention makes it possible in particular to determine the dental contact pressure that occurs between the teeth when an upper and a lower jaw are bitten. This dental contact pressure measurement also enables the distance between the pressed teeth to be determined.

According to the invention, an oscillator with at least one inductor is provided for determining an acting physical or mechanical force. Instead of an oscillator, two or more oscillators can also be provided, for example a measuring and a reference oscillator. The difference in frequency between the two Oscillators can be audibly displayed, for example, according to the so-called beat sum principle.

The oscillator for use in accordance with the invention has a specific natural frequency which can be, for example, in the range between 10 kHz and 1 GHz. The oscillator can be a self-oscillating oscillator, or can be excited by a vibration generator.

In principle, any known LC oscillator, such as a Meissner, Hartley or Colpitts oscillator, can be used, and RL and quartz generators can also be used. However, oscillators are preferably used which are provided with inverters, in particular Schmitt trigger inverters, NAND and / or NOR gates. These oscillators are interesting because they have a very simple and inexpensive structure. A circuit has been found to be particularly suitable which uses a frequency-determining inductance as a transconductance between input and output in the inverter circuit.

The inductance is preferably formed from a primary winding with a soft magnetic core, preferably from a rod or toroidal core made of ferrite, but in principle an air coil is also suitable for the measuring principle according to the invention. A ring core has the advantage that the magnetic scattering of the inductance is reduced compared to a rod core and the transformer coupling is thereby improved. This improves the frequency change in the oscillator.

According to the invention, the secondary winding of the inductor is electrically conductively connected to the sensor. The sensor has ohmic and / or capacitive and / or inductive properties. When force is exerted on the measuring sensor, the (transition) resistance and / or the capacitance and / or permeability and thereby the impedance of the same is changed, depending on the design of the measuring sensor. This change in impedance influences / changes the load in the secondary winding arranged in a transformer coupling for inductance and thereby changes the frequency of the oscillator. This frequency change, which is proportional to the force acting, is evaluated in the evaluation circuit.

According to the invention, the force can be determined numerically by units of measurement or, for example, also as a relative measurement not related to units. .The determination of the force is particularly important in dental applications for determining the dental contact pressure or the "chewing pressure and the occlusion". a distance determining • between the mutually gesp essten bodies or zwischen'- ^{possible, "the} teeth.

Although an embodiment according to the invention is intended in particular for determining the contact pressure occurring between teeth, it can generally be used for determining the pressure between two bodies pressed against one another.

Through a special design of the measuring area of a measuring strip used (elevations / depressions with intersecting tips), the user can also slide the teeth i.e. determine an additional dynamic movement to the side.

The sensor can be, for example, an electrically conductive film or an electrically conductive against the wire. Furthermore, the sensor can be formed, for example, from a piezoplate in which the electrodes are electrically connected to the secondary winding and which can be arranged in a transformer coupling around the induction coil. In a preferred variant, the transducer is made in one piece with the secondary winding as a simple film for dental use and is wound as a measuring strip at least once around the inactivity of the oscillator, which is preferably located in a thin, rod-shaped housing. When the teeth grit, the measuring areas of the measuring strip lying between them touch and the contact resistance is changed, which leads to a frequency change of the oscillator via the transformer coupling.

The secondary winding or the one-piece measuring strip is wound at least once around the * inductance of the oscillator. If they are wrapped around the inductor several times, the measuring effect is enhanced.

In general, in the case of the invention, the measuring range or the sensitivity of the measurement can be matched to the respective application area via the transmission ratio of primary winding and secondary winding.

The sensor can also be formed from a material with electrically conductive properties, which is provided with an electrically insulating layer at least in the pressure-absorbing area of the bodies pressed against one another. This electrically insulating layer can be formed, for example, by an electrically insulating plastic or, for example, also by a metal oxide. This electrically insulating layer can when pressure is exerted on the bodies pressed against each other in the area of the contact surfaces, so that the contact resistance is influenced. As a result, the device according to the invention can be matched to the measurement ranges required in the most varied of application areas by selecting the thickness of the electrically insulating layer of the measurement sensor.

In a preferred embodiment, the electrically conductive sensor is made of aluminum and has a natural aluminum oxide layer or an anodized layer in at least one measuring area.

However, the sensor does not need to have an electrically insulating layer that can be destroyed by pressure. Rather, it is possible to use a transducer made of electrically conductive material, the contact resistance of which> changes when the two bodies or teeth are pressed together, for example in the order of 0.1 mQ to 100 Ω, in order to bring about a frequency shift of the oscillator.

If the dental contact pressure is determined, the electrically conductive film can be designed, for example, as a measuring strip. Furthermore, the measuring strip can be formed by a film made of an electrically conductive material and, for example, its inside can be provided with an electrically insulating layer. The electrically conductive material is in particular a metallic material, for example an aluminum or copper material, that is to say aluminum or an aluminum alloy or copper or a copper alloy. Instead of a metal foil, however, an electrically conductive plastic foil can also be used, for example. The electrically insulating layer of the The measuring strip can be a metal oxide or a piezo layer, for example. It is understood that if an electrically insulating layer is present, it only has to be provided in that area of the measuring strip that lies between the bodies or teeth pressed against one another. The measuring strip can also be provided with an electrically insulating layer on the outside.

The sensor can also be formed from an electrically conductive material and an electrically insulating material with ferroelectric properties, for example from an electrically insulating layer with ferroelectric properties. Piezoelectric materials are preferably used for this. Due to the high dielectric constant of these materials _, Transducer an additional capacitive load, - di, e leads to a frequency change - of the oscillator. The dielectric constant is influenced by changing the pressure between the pressed bodies.

Another advantage of the device according to the invention is that when a piezo element is used as part of the sensor, no amplifier is required for this, since this is coupled to the sensor electronics as a low-resistance capacitive load. This enables the pressure between two bodies pressed against one another to be determined even under adverse environmental conditions, in particular in the humid environment of dentistry.

The sensor, in particular the film or the measuring strip, can also be made of a ferromagnetic material, in particular a ferromagnetic material with magneto- elastic properties are formed. So amorphous alloys, so-called metallic glass, have proven to be suitable. Materials with magnetoelastic properties are characterized by the fact that their permeability changes under mechanical stress. By using materials with ferromagnetic properties, an improvement of the measurement effect is made possible by a stronger influence on the inductance.

The measuring sensor, which is preferably designed as a measuring strip, can consist of several layers which alternately consist of an electrically conductive and an electrically insulating material. In such a measuring strip, the layers of electrically conductive material form a plurality of windings which can be activated one after the other in parallel with the pressure acting on the bodies pressed against one another. This enables different measuring and proportional ranges through the number or the selection of the layer materials.

Furthermore, depending on the area of application, the application of further functional layers to the electrically conductive film or to the measuring strip is provided. It is thus possible to apply discolouring or discolouring layers to the external measuring areas, which enable the dentist to determine the contact points of the touching teeth in addition to the dental contact pressure.

Furthermore, it is advantageous to stabilize an approximately 5 my to 10 my thick aluminum foil with an applied plastic layer. This can be done not only on the outside, but also on the inside, but the measuring area (bite area) must remain free of the plastic layer. The plastic has the advantage that it avoids undesired early contacts on the inside of the measuring strip, and furthermore it gives a measuring strip provided with elevations and depressions a desired reversibility of the measurement-receiving areas, as a result of which a more dynamic measurement is possible.

The line-shaped elevations and depressions are preferably arranged at an angle of 45 degrees to the longitudinal direction of the measuring groove. This ensures that the peaks of the ridges intersect at an angle of 90 degrees when collapsed. As a result, the measuring strip is less expensive to manufacture.

The elevations and depressions of the measuring strip are preferably produced by the embossing process.

The transducer can be provided with a self-adhesive layer for 'attachment to the housing ^{' of} the oscillator, for example. It is also possible to provide the measuring strip with a spring clip in order to attach it to the housing. It is also possible to mount the oscillator To be carried out in such a way that the sensor can be attached to it mechanically, for example with an open sleeve or a spring clip similar to a ballpoint pen.

There are numerous other ways to detachably connect the sensor and the housing. For example, openings can be provided on or in the housing through which the sensor, which is designed, for example, as a measuring strip, is inserted or threaded. The sensor can also be applied to an electrically insulating material. The material can be, for example, paper, silk or a plastic, in particular an elastic plastic. The plastic is preferably such that the sensor can be cleaned by sterilization.

The sensor is formed, for example, by a metal foil. For example, noble metals, such as gold or silver, which can also be used on an insulating substrate, e.g. can be applied by vapor deposition.

A measuring strip made of an aluminum material has proven to be particularly advantageous. which is 'p' passivated on the inside with an aluminum oxide layer. The thickness of the aluminum oxide layer can be optimized by anodizing the aluminum strip. The measuring strip has a thickness of, - preferably less than ^: 2-00 "<^' μτn, in particular less than 100 .μm. If the measuring strip is bitten, the electrically insulating layer can be destroyed at the occlusion points. once the measuring strip has been wrapped around the induction coil, another winding around the induction coil which detunes the oscillator. This winding influences the inductance in a transformer coupling and changes the frequency of the oscillator when force is applied. The frequency change caused by the detuning can change cause both an increase and a decrease in the natural frequency of the oscillator, depending on the electromagnetic conditions in the frequency-determining resonant circuit and the choice of the operating point.

Instead of or in addition to the inductive load caused in this way, the frequency change can also be tive and / or ohmic load can be caused. The winding formed by destroying the insulating layer has an ohmic resistance which depends, among other things, on the mechanical contacting at the occlusion points.

Furthermore, in the measuring strip wound around the induction coil, the two end sections of the measuring strip, on which the pressure to be determined acts, that is to say which is bitten, lie with their inner sides on top of one another with the electrically insulating or dielectric layer. So that the gauges at the same time forms a capacitance, which leads to a frequency change, depending on how bite when the thickness of the dielectric layer _t and thus the distance change of the electrically conductive Folienendabschnitte of the strip and the dielectric constant.

The evaluation circuit of the device according to the invention can be a phase lock loop (PLL) circuit and / or for example a PC to which the output signals of the oscillator or the PLL circuit are supplied.

The oscillator can be arranged in a housing with a sleeve-shaped section around which the measuring strip is wound. The oscillator is preferably connected wirelessly to the evaluation circuit. To measure the dental contact pressure, only the measuring strip needs to be looped around the sleeve-shaped, for example pencil-sized housing, whereupon the patient bites on the end sections of the measuring strip wound around the housing of the oscillator. Of course, the sensor or the film or the measuring strip can also be connected to the oscillator and / or evaluation circuit via a cable. The measuring strip according to the invention preferably has a thickness and flexibility corresponding to a conventional occlusion film with discoloration. On the outside, it can also be provided with a coating for recording the occlusion points by discoloration or discoloration in order to obtain further measurement data.

The output signals of the evaluation circuit can, for example, be stored in a memory and / or fed to a display. The display can be formed, for example, by a bar made of light-emitting diodes.

There. the device according to the invention operates in the low-resistance range, it is affected by galvanic effects, e.g. can occur in saliva, not influenced. As a result, in order to comply with the electronic safety regulations, it is also possible to construct the electronics in a favorable manner

A preferred embodiment of the measuring strip has an electrically conductive layer in the measuring areas. This homogenizes the contact resistance of the measuring ranges and improves the characteristics by means of a more constant measuring signal. Furthermore, e.g. a conductive gel has the advantage that it forms an adhesion of the measuring area, so that the end sections of the measuring strip are fixed to each other and this simplifies handling for the dentist.

A preferred embodiment of the measuring strip has a film composite which has an insulating layer (preferably a polymer or an adhesive layer) on the inside, followed by the electrically conductive layer, and subsequently a stabilizing layer (preferably a polymer), at least the measurement-receiving areas being provided with elevations and depressions in such a way that their tips overlap when the measurement strip is folded up during the actual measurement.

The measuring strip as a composite preferably has a maximum thickness of 15 μm, so that the measurement-receiving area, when folded, reaches a maximum thickness of 30 μm.

Such a measuring strip according to the invention has the advantage that it adapts to the three-dimensional shape of the teeth during the measurement and that there is no blocking effect which hinders the final bite. This enables dental contact pressure measurement or chewing pressure measurement in the natural position of the teeth.

Preferably, for easier handling, the measuring strip or a measuring sensor is already incorporated into a part (cap, sleeve) that can be plugged onto the inductor or can be attached to it with an adhesive layer.

The force transducer according to the invention, together with the use of a measuring strip on which a spacer is attached to at least one measuring area, enables the user in dentistry to determine the preparation height of a tooth to be prepared or to detect a drop below the required preparation height in a targeted manner , For the production of dentures such as crowns, bridges, implant abutment structures, etc., a certain minimum thickness of the denture is required depending on the type of construction (all-ceramic, metal-ceramic, polymer, etc.). For example, a crown made of all-ceramic is said to be in the area that the antagonist opposite, reach a minimum thickness of 1.5 mm to 2 mm to be able to withstand the mechanical influences when chewing. If this minimum thickness is undershot, there is a risk of the dentures being destroyed when biting. Even for dentures with a metal framework, a certain minimum height is required, which in this case primarily serves aesthetics, since the dental technician has to apply several veneer layers to the metal framework, which forms a dark core, in order to achieve a natural appearance of the artificial tooth. On the other hand, the dentist should only remove the absolutely necessary natural tooth substance when preparing the tooth, in order not to permanently damage it, despite the required minimum heights. In the usual inspection of the preparation, the dentist cannot, in many cases, precisely recognize whether he has reached the minimum height in all areas of the prepared tooth due to the invisibility with a closed dentition. When using the invention, he places the measuring strip with the spacer on the tooth to be prepared with the dentition open. When biting, the preferably flexible or rubber-elastic material is compressed, since the spacer has a thickness or height which is above the required minimum height. Where the greatest compression is present, the most pressure is exerted on the measuring strip. This enables the measurement or definition of the smallest distance between the prepared tooth and the antagonist.

The invention is explained in more detail below by way of example with reference to the drawing. In it show:

Figure 1 shows an embodiment of the circuit of the device according to the invention; FIG. 2 shows various characteristic curves of the frequency change when the force acting on the measuring strip / sensor;

3 shows a perspective view of a measuring strip wound around the housing of the oscillator;

FIG. 4 schematically shows the occlusion pressure before and after a dental filling;

FIG. 5 shows a secondary measurement winding with a piezo element wound around the housing of the oscillator in a perspective representation;

FIG. 6 shows the perspective illustration of the oscillator for a measurement sensor for determining the tooth occlusion, the dental contact pressure and / or the chewing force;

FIG. 7 shows a perspective illustration of the part of the oscillator according to FIG. 6 with the primary winding and a plug-on element which can be plugged onto the force transducer, with a measuring strip applied thereon;

FIG. 8 shows a longitudinal section through a measuring strip according to another embodiment;

FIG. 9 top view of the inside of an opened measuring strip with elevations and depressions;

FIG. 10 shows a longitudinal section through the measuring strip according to FIG. 9; FIG. 11 shows a plan view of the measuring strip according to FIG. 9 wound around the oscillator and FIG. 10 after wrapping around the oscillator;

FIG. 12 shows a plan view of the inside of an opened measuring strip with elevations and depressions according to another embodiment;

FIG. 13 shows a longitudinal section through the measuring strip according to FIG. 12;

FIG. 14 shows a cross section through the lower region of the measuring strip according to FIG. 12;

FIG. 15 shows a perspective view of the end sections of the measuring strip after wrapping the oscillator;

Figure 16 is an enlarged view of the cross section of the measuring strip according to Figure 9 to Figure 11;

FIG. 17 shows a longitudinal section through a measuring strip wound around an oscillator with a spacer made of compressible material; and

18 shows a schematic view of the measuring strip according to FIG. 17 between two opposing teeth in the final bite.

According to FIG. 1, the oscillator 1 has a self-oscillating oscillating circuit with an inductor 2 in the form of an induction coil, several capacitors 3, 4, 5, two ohmic resistors 6, 7 and two Schmitt trigger inverters 8, 9 for forming the output signals. The two Schmitt Trigger inverters 8, 9 are supplied with a low-voltage source (not shown), for example 5 V (eg battery or battery).

The sensor or sensor 11 is designed as a one-piece measuring strip and has at least one winding, which, as shown schematically in FIG. 1, forms a secondary winding 30 in a transformer coupling to the inductor 2. Furthermore, a further secondary winding 12 with an ohmic resistor 13 or another load is arranged in a transformer circuit with the inductor 2. With the additional secondary winding 12, the characteristic curve of the frequency change when a force is exerted on the measurement sensor 11 can be optimized.

The inductor 2 can also be designed as a differential transformer or differential coil. This embodiment is particularly advantageous if, as mentioned above, two or more oscillators are provided. A differential coil is present when the winding 12 is omitted in FIG. 1. In contrast, the winding 12 is present in the differential transformer and is arranged symmetrically to the primary winding 2.

The measuring strip can also be formed by a sensor 11, which is connected to the secondary winding 30 via electrical lines. As shown in FIG. 1, the two lines can be connected via a resistor 29. Such a resistor is advantageous if the measurement sensor 11 has inductive or capacitive, including piezoelectric or piezoresistive properties. FIG. 2 shows five different measurement characteristic curves A, B, C, D and E, whereby the characteristic curve A is largely unusable, while the characteristic curve B has a long proportional range, the characteristic curve C has a shorter proportional range and the characteristic curve D has two proportional ranges. The characteristic curve E shows an increase in the oscillator frequency with an increase in the measuring force.

The output signals of the inverter 9 are fed to the evaluation circuit 14, which can be formed, for example, by a PLL circuit, ie a circuit which compares the input frequency with an internal frequency, and generates an output signal 15 if there is a frequency difference. While a digital output signal is generated by the Schmitt trigger inverter 9 for signal extraction, an analog output signal is formed by the PLL circuit. This can to a not shown analog digital converter _j ei domestic digital signal ^converted! and stored in a memory module, not shown, and displayed on a light-emitting diode bar, also not shown. For example, three to ten memory modules can be present, so that three to ten measurements can be displayed in succession on three to ten light bars. This representation allows the dentist to measure the bite force and the tooth spacing several times before, during and after the dental work to be carried out.

According to Figure 3, the oscillator 1 (Figure 1) is arranged in a sleeve-shaped, approximately pencil-sized housing 16. As indicated by the arrow 10, the oscillator is connected wirelessly to the evaluation circuit 14 (FIG. 1).

In FIG. 3, the measuring strip 11 is wound around the housing 16 in the area of the induction coil 2 (FIG. 1). Its end sections 17, 18 thus form superimposed flags. The measuring strip 11, which has a width corresponding approximately to a tooth, consists for example of an aluminum foil which is provided on its inside 19 with an insulating aluminum oxide layer. To measure the occlusion pressure, bite on the superimposed flags 17, 18. As a result, the aluminum oxide layer is destroyed at the occlusion point 20, or its layer thickness is at least reduced in such a way that a closed, electrically conductive turn is formed which changes the inductance and thus the frequency of the oscillator 1 (FIG. 1). To increase the measuring effect, the measuring strip 11 can also be wound several times around the housing. The measuring strip can also consist of a metal foil without an insulating layer. The contact resistance between the flags 17, 18 then depends on the occlusion pressure.

If according to FIG: 4, the patient, for example, ''^'' is eIHE filling in the occluding with the maxillary tooth 21 lower teeth 22, the occlusion pressure is in accordance with (I) measured before the filling for reference and stored Then, the tooth 22 is shown in (II). Provide the filling 23 and sand the filling (III) until the reference occlusion pressure is the same as before the filling (I). When inserting dentures such as crowns, bridges, etc., it has proven to be advantageous if the Pressure or the distance between the adjacent teeth of the denture before, during and after insertion is determined in a reference measurement.

In FIG. 5, secondary winding 30 is wound several times around housing 16 in the area of induction coil 2 (FIG. 1). The two feed lines 26 of the secondary winding 30 are with the two piezo electrodes 27 of the piezo element 24 connected. By exerting pressure on the occlusion site 20, the piezo element 24 is influenced as previously described, thereby detuning the oscillator and thus making it possible to determine the occlusion pressure.

According to FIG. 6 and FIG. 7, the oscillator 1 has a handle 31 with a switch 32 for operating the oscillator and a tapered section 33, in which the inductor 2 is arranged, as indicated by dashed lines in FIG. The oscillator 1 is received by a charging station 34, which is inductively coupled to the oscillator 1.

As can be seen from FIG. 7, the measuring strip or measuring sensor 11 can be provided on a plug-on element 35, which e.g. in the form of a sleeve or a cap can be plugged onto the tapered section 33 with the inductor 2. The sensor 11 can be attached to the plug-on element 35 e.g. be adhesively attachable.

In the embodiment according to FIG. 8, the measuring strip 11, which is wound around the inductor 2, is constructed from a plurality of functional layers 36 to 41. The outermost layer 36, which is provided at the two end sections of the measuring tire 11, is formed by a discoloring and / or discoloring material in order to determine the tooth contact points. The adjoining layer 37 constitutes an electrically insulating and stabilizing carrier layer, preferably made of a plastic, for the adjoining, electrically conductive layer 38, which consists for example of a metal such as aluminum. A further electrically insulating layer 39, for example made of plastic, is arranged on the inside of the layer 38, but does not cover the measurement-receiving areas at the two ends of the measuring strip 11. The layer on the measuring areas 40 on the inside of the measuring strip is formed by an electrically conductive and deformable material, for example a gel. Furthermore, an adhesive layer is applied to the inside of the measuring strip, which ends in front of the two measuring areas 40 and which serves to fasten the measuring strip 11 to the plug-on element 35 or directly to the tapered area 33 of the oscillator.

In the embodiment according to FIG. 9 to FIG. 11, the measuring strip 11 has elevations 43 and depressions 44 which run alternately and linearly parallel next to one another. The linear elevations 43 and depressions 44 are arranged obliquely to the longitudinal axis of the measuring strip 11.

As shown in FIG. 11, the elevations 43 and depressions 44 intersect on the ones lying one on top of the other. measuring areas of the end portions of the measuring strip 11 when it is wound around the oscillator portion 33.

If the measuring strip 11 or measuring transducer consists of an electrically conductive material, the intersecting tips 45 of the elevations 43 (FIG. 16) form electrical contact surfaces, the size of which increases when the measuring-recording regions of the measuring strip 11 are pressed together. By increasing or reducing the contact area, the electrical contact resistance of the measuring strip 11 is correspondingly reduced or increased.

The angle alpha which the tips 45 assume can be, for example, 120 degrees, as shown in FIG. The distance a from a tip 45 to the next tip 45 is preferably less than 0.5 mm. FIG. 12 to FIG. 14 show another embodiment of the measuring strip 11 or of the measuring sensor, which differs from the embodiment according to FIG. 9 to FIG. 11 essentially in that the elevations 43 and depressions 44 only in the measuring areas 46 and 47 at the end sections of the measuring strip 11 are provided and extend transversely in one region 46 and longitudinally to the measuring strip 11 in the other region 47. As can be seen from FIG. 15, the tips 45 of the ridges intersect at an angle of 90 degrees.

17 has a spacer 48 made of a compressible material, which is formed for example by a rubber-elastic plastic, at least on an outer side of the measuring area.

FIG. 18 shows the sensor according to FIG. 17 in the event of a final bite between a prepared tooth 51 and the opposite tooth 52 in the event of a final bite. It can be seen that the measurement sensor 11 adapts to the shape of the tooth 52. The prepared tooth 51 also compresses the spacer 48. As a result, the spacer 48 is pressed against the sensor 11, with a different pressure, depending on the compression. As can be seen from FIG. 18, a greater pressure is exerted at A by the spacer 48 on the section of the measuring areas 46, 47 arranged there than at B. The thickness of the spacer 48 can be selected such that the distance A can be determined , This is possible in that the compressible material of the spacer 48 from a certain thickness increases significantly the pressure on the measuring areas 46, 47 and thus to a Frequency change of the oscillator 1 leads. This enables the user to determine, for example in area A, whether he has reached the preparation height required for the tooth replacement to be formed when preparing a tooth.

Claims

claims

1. force transducer, characterized by at least one oscillator (1) with at least one inductance (2) formed by a primary winding and at least one transducer (11) with a secondary winding (30) which is electrically conductively connected to the transducer (11) and which to the inductance (2) of the oscillator (1) is arranged in a transformer coupling, the impedance of the measuring sensor (11) and the load of the inductively-iv-coupled secondary winding (30) changing when a force acts on the measuring sensor (11), and an evaluation circuit (14) for determining the resulting change in frequency of the oscillator (1), which is proportional to the force acting on the sensor (11).

2. Force transducer according to claim 1, characterized in that the oscillator (1) has at least one capacitance (3, 4, 5) and / or at least one resistor (6, 7) and / or at least one further inductor.

3. Force transducer according to claim 1, characterized in that the oscillator (1) is wirelessly connected to the evaluation circuit (14).

4. Force transducer according to claim 1, characterized in that the inductance (2) of the oscillator (1) has a soft magnetic core, preferably a rod or toroidal core made of ferrite.

5. Force transducer according to claim 1, characterized in that the inductance (2) is associated with a further secondary winding (12) with a load (13) for optimizing the measurement characteristic (A, B, C, D, E).

6. Force transducer according to claim 1, characterized in that the transducer (11) and the secondary winding (30) electrically connected to it are electrically isolated from the circuit of the oscillator (1).

7. Force transducer according to claim 1, characterized in that the transducer (11) has inductive properties and / or capacitive properties, 'and / or ohmic properties.

8. force transducer according to claim 7, characterized in that the transducer (11) has ferroelectric properties.

9. force transducer according to claim 7, characterized in that the transducer (11) has piezoelectric and / or piezoresisitve properties.

10. Force transducer according to claim 7, characterized in that the sensor (11) has pyroelectric properties.

11. Force transducer according to claim 7, characterized in that the transducer (11) has ferromagnetic properties.

12. Force transducer according to claim 11, characterized in that the transducer (11) has ferroelastic or magnetoelastic properties.

13. Force transducer according to claim 7, characterized in that the transducer (11) is at least partially formed from an electrically conductive material.

14. • __ force transducer according to claim 13, characterized in that the electrically conductive material is a metal, preferably silver, aluminum or copper.

15. Force transducer according to claim 1, characterized in that the oscillator (1) is provided in a housing which has a section (33) with the inductor (2), around which the secondary winding (30) can be arranged.

16. Force transducer according to one of the preceding claims, characterized in that the transducer (11) and the secondary winding (30) are integrally formed.

17. Force transducer according to one of the preceding claims, characterized in that an electrically conductive and integrally formed with the secondary winding (30) transducer (11) with ferromagnetic properties at least partially within the Primary winding of the inductor (2) can be arranged as an inductive core.

18. Force transducer according to one of the preceding claims, characterized in that at least the measuring area of the transducer (11) is designed in the form of a film.

19, force transducer according to claim 18, characterized in that the sheet-shaped measuring sensor (11) consists of an electrically conductive material and / or of a material having magnetoelasti- ^α chen properties.

20. Force transducer according to claim 16 and claim 19, characterized in that the. with the secondary winding (30) formed integrally as a film transducer (11) from a metal, preferably silver, aluminum or copper, or from a metallic glass, and can be wound at least once around the inductor (2).

21. Force transducer according to one of the preceding claims, characterized in that the film-shaped transducer (11) has at least one further layer (36, 37, 39, 40, 41) on the inside and / or on the outside with functional properties.

22. Force transducer according to claim 21, characterized in that the functional layer (36, 37, 39, 40, 41) insulating and / or electrically conductive and / or stabilizing and / or reversible and / or adhesive and / or coloring and / or discoloring and / or has chemically reacting and / or insulating properties that can be destroyed when subjected to force.

23. A force transducer according to claim 21, characterized in that a layer (40) made of an electrically conductive material, preferably an electrically conductive liquid or an electrically conductive gel, in the measurement-receiving areas (46, 47) on the inside of the film-shaped sensor (11) , is applied.

24. Force transducer according to one of the preceding claims, characterized in that the transducer (11) has an electrically insulating layer with ferroelectric and / or piezoelectric properties.

25. Force transducer according to one of the preceding claims, characterized in that a spacer (48) is provided on at least one measuring area (46, 47) of the film-shaped measuring sensor (11).

26. Force transducer according to claim 25, characterized in that the spacer (48) is formed from an elastic and / or a compressible material when subjected to a force.

27. Force transducer according to one of the preceding claims, characterized in that the sensor (11) is designed as a measuring strip.

28. Force transducer according to claim 18, characterized in that the film-shaped transducer (11) has ferroelectric and / or piezoelectric and / or piezoresistive and / or pyroelectric properties.

29. Force transducer according to one of the preceding claims, characterized in that the measurement transducer (11) in at least one measurement-receiving area (46, 47) has elevations (43) and / or depressions (44), which depend on the size of the deform the force transducer (11).

30. Force transducer according to claim 29, characterized in that the elevations (43) and depressions (44) alternate and run parallel to one another in a linear manner.

31. Force transducer according to claim 29 or 30, characterized in that the film-shaped transducer (11) is designed such that the tips (45) of the elevations (43) of one measuring area (46, 47) and the tips (45) of the Cut elevations (43) of the other measuring area (47, 46) lying on them.

32. Force transducer according to claim 31, characterized in that the linearly parallel peaks (45) of the elevations (43) of the two measuring areas (46, 47) at an angle of approximately 70 degrees to 110 degrees, preferably from 80 degrees to 100 degrees, cut.

33. Force measuring transducer according to claim 31, characterized in that the tips (45) of the elevations (43) enclose an angle (alpha) between 100 degrees and 140 degrees, preferably between 110 degrees and 130 degrees and / or the distance (a) from one tip (45) to the next tip (45) is less than 1 mm, preferably less than 0.5 mm.

34. Force transducer according to one of the preceding claims, characterized in that at least one electrically insulating layer and / or at least one electrically conductive layer is designed to be destructible by the action of pressure.

35. Force transducer according to one of the preceding claims, characterized in that the measurement sensor (11) in the measurement-receiving area (46, 47) has a thickness of at most 150 my, preferably at most 100 my.

36. Use of a force transducer according to one of the preceding claims for determining the temperature.

37. Use of a force transducer according to one of the preceding claims for determining the tooth occlusion and / or the dental contact pressure and / or the chewing force.

38. Use of a force transducer according to claim 38, wherein the measurement sensor (11) in the measurement-receiving area (46, 47) has a thickness of at most 30 my, preferably at most 15 my.

39- Use of a force transducer according to claim 37 or 38, characterized in that a measuring sensor (11) is used, the width of which corresponds to the width of the tooth (21, 22) to be measured in the measuring area (46, 47).

40. Use of a force transducer according to one of the preceding claims for determining the preparation height or the preparation depth on a prepared tooth (51).