DE10335313B4 - Force sensor, force sensor unit, elongate device and method for detecting a force - Google Patents

Abstract

Sensor for detecting a force (F) acting on an elongate device, in particular an elongate medical device, such as a catheter, with a non-negligible force component in the longitudinal direction of the elongated device, comprising: - a force transducer (3) for the force to be detected; a terminal for attaching the sensor (1) to the elongated device, - at least one Lichteinkoppelbereich, which at least one light in the sensor (1) einkopoppeln optical waveguide (11) is optically connectable, - a light intensity modulator having a pre-definable intensity of the in the Sensor (1) einkoppelbaren light (21) in accordance with the force on the force transducer (3) acting force (F) modulated, and - at least one Lichtauskoppelbereich, through which the light (21) of modulated intensity in at least one light guide (11) can be coupled out, characterized characterized in that a reflector with a we at least one Lichtauskoppelbereich (17) associated reflection surface (15) is provided, which can change their reflection properties depending on the force to be detected (F), preferably in particular irreversible or reversible and deformed depending on the force to be detected (F) deform, especially enlarge and and / or downsize, in which an uneven reflection surface (15) is provided, to which the force (F) acting on the force transducer (3) can act such that the degree of unevenness changes depending on the force (F) and one with the at least one Lichtauskoppelbereich (17) optically connected region of the reflection surface (15) expands and / or limited.

Description

The invention relates to a force sensor, a force sensor unit, an elongate device and a method for detecting a force.

A particular application of this invention relates to the catheter technique, which is defined by an elongated means for at least partially introducing it into an organism through a body orifice. These elongated devices are mainly used in minimally invasive surgery on especially human bodies. So that during the invasion of the elongated device no body vessels are injured by the proximal tip of the elongated device to be operated manually by the attending physician, the physician necessarily orientates himself by what forces are communicated to him at a handle of the elongated device. Because of the friction and the inserted in the course of the invasion of the catheter into the body continuously increasing catheter mass gives the treating physician notified to the handle a barely usable information about the actually occurring at the catheter tip resistance. In order for the treating physician to be able to communicate the correct actuating force to the handle of the catheter, an extraordinarily rich amount of experience in the operation of catheters is required.

From the DE 103 03 270 A1 a catheter arrangement is known in which the force acting on the catheter tip during insertion force is measured by a force sensor. The corresponding measured quantity is communicated tactfully to the physician via a haptic handle. In this way, the discovery of, for example, vein branches or perforations on the cardiac septum is made easier for an inexperienced doctor. An electrodynamic drive device for generating the haptic force prestressing using the force representing the force at the tip is known from US Pat DE 103 19 081 A1 known. Both of the aforementioned documents are intended to be incorporated herein by reference, particularly with regard to the sensors for detecting the forces at the tip of the elongate device and the evaluation of the measured signals.

According to the US Pat. No. 6,221,023 B1 For example, a force sensor is provided at the tip of catheters based on a resistive function operation. The force introduced into the sensor is picked up by a resistance bridge circuit. The sensor must be connected via several lines, in particular for the supply of electrical energy and for signal transmission to an external evaluation unit, wherein the laying of at least one cable requires a large space along the catheter. The design of this sensor is complicated due to the large number of parts, and the associated high manufacturing costs make the known sensor, in particular for catheters due to their preferred disposable property unsuitable. In addition, the miniaturization of the electrically operated force sensor, in particular below a catheter diameter of less than 3 mm, if at all, can be realized only with an extremely high design effort. Furthermore, an electrical force sensor is susceptible to interference with respect to electromagnetic radiation of a magnetic resonance tomograph, which vulnerabilities are to be eliminated in particular in medical technology.

The DE 44 10 463 A1 discloses a fiber optic sensor with two optical fibers, of which an optical fiber is connected to a light source. The ends of the two optical fibers are opposite to a mirrored end of a bending beam, which is clamped quasi-fixed in a capsule housing. The position of the mirrored end is measured by the reflection of the end of the bending beam. The ratio of the light components reflected in the two ends of the optical waveguides results in an evaluation independent of absolute intensity measurements. This fiber-optic sensor is not suitable for use with a catheter insofar as forces can be detected transversely to the longitudinal extension of the optical waveguide with the sensor only. Furthermore, the disclosed sensor structure is not suitable for miniaturization of elongated devices with lateral dimensions of less than 3 mm.

In the prior art [H. Emanuelsson, et al., "Initial Experiences With a Miniaturized Pressure Transducer During Coronary Angioplasty", Catheterization and Cardiovascular Diagnosis 24 (1991), pp. 137-143] discloses a fiber optic pressure sensor suitable for integration into guidewires having a diameter of 0.36 mm is suitable and used to measure blood pressure. It can be determined with this sensor, a pressure lateral, but not a force perpendicular to the axis of a guide wire, which is why this sensor is not suitable for detecting the feed / contact force.

Frequently, phase-sensitive evaluation methods are also used in the measuring head in which distances of reflecting surfaces in the range of the wavelength of the light used are modulated. Due to the small modulation paths, these methods are very sensitive to thermal expansion of the construction materials and have high assembly costs due to extremely small manufacturing tolerances. In addition to the very exact installation is always a robust frame for holding the reflective surface necessary. This is for measuring a pressure that is always evenly distributed and perpendicular to a surface, not detrimental. For a force measurement, however, a sturdy frame forms a force shunt which directs an unpredictable portion of the measuring force past the sensor, thus preventing accurate force measurement. Advantageously, therefore, a sensor can be used, which provides large deformations, the force completely absorbs, converts an axial force into a determinable output and is inexpensive to produce.

From the DE 100 55 629 A1 For example, a fiber optic sensor is known which makes pressure on its surfaces measurable by the birefringence properties altered by pressure. The sensor consists of a sandwich of two polarizing filters with liquid crystal trapped therebetween. By varying the polarization position, the intensity of the reflected light changes and thus enables a measurement of an applied pressure or a force. The change in the birefringence properties is correlated not only with the pressure but also with the temperature and must be compensated.

From the US 5 987 995 A a fiber optic pressure sensor is known, with the help of a lever mechanism blood pressure can be measured with a medical instrument. Here, the blood pressure can act on a membrane via a lateral opening, which in turn is connected to a lever, which in turn reflects the light fed in by a fiber differently. Here, the fiber is concentrically fastened in a holder to which the reflection arm is attached. In the chamber in which the light intensity is modulated, a back pressure is to be provided, which allows a pressure measurement. The structure is relatively expensive and requires compliance with small assembly or manufacturing tolerances, whereby the structure is more expensive in contrast to the proposed invention. The structure is not suitable to measure an axially applied force approximately error-free.

From the US 2002/0162399 A1 a pressure sensor is known in which a membrane is connected via a rigid edge structure, to the center of which a rigid light reflector is again attached. This structure is not usable without additional adapters for force measurement due to the rigid frame. Furthermore, the very sensitive interference method for evaluating the phase position of the light is evaluated, which makes temperature compensation difficult or necessary and, as described, due to the necessary small tolerances high production costs.

In the DE 691 06 367 T2 discloses a fiber optic pressure sensor comprising an elastic deformation body having one or more inclusions. The elastic housing allows in addition to a pressure measurement and a force measurement in the axial direction of the elongated device. The inclusions are moved due to the mechanical size force or pressure relative to the fiber surface, out of the light, and also enters again. The sensor is essentially based on the distance modulation of the reflective particles with respect to the light exit surface. Depending on the distribution of the density and the position of the reflective particles, the sensor is differently sensitive to forces and pressures and, prior to being passed on to the customer, certainly requires a precise, complex calibration. Due to the proposed structure, the operating principle is based on distance modulation of reflective particles that are located at a certain distance from the light exit. This modulation does not usually provide the degree of modulation, which can be achieved by changing the curvature with the associated better focusing of the light, which disadvantageously decreases the signal / noise ratio, and thus increases even the smallest detectable measuring unit. A stronger modulation by a direct modulation by curvature of the reflection or the light exit surface in direct contact with the reflection body to increase the degree of modulation is not provided.

From the US 4599908 a fiber-optic pressure sensor is known, which has an optical path through the sensor cell, which is narrowed by the mechanical measurement variable and thus leads to the modulation of the luminous flux. Difficult in the production of this sensor in the micro-scale is a defined hole production, through which the light can pass defined. Laterally acting forces in this sensor certainly lead to the displacement of the surfaces and thus to the closing of the channels and thus to a false measurement of the force.

In the US Pat. No. 3,580,082 A fiber-optic pressure sensor is presented whose output signal is modulated by a membrane whose center is located at a defined distance above the light exit surface of an optical fiber. In this case, in turn, the membrane is supported by a stable frame, which leads to errors in a full-surface force coupling due to a force shunt.

It is an object of the invention to provide a sensor of simple construction, which can be integrated into elongate devices of less than 3 mm diameter, in particular 0.33 mm (1 French), and can detect forces which at least partially on the elongate device in the longitudinal direction attack. Here, a full-surface force coupling should lead to accurate measurement results, the degree of modulation should be significantly higher than that of simple distance modulation, lateral forces should not lead to excessive incorrect measurements and the sensor should be able to be manufactured inexpensively.

This object is solved by the features of patent claim 1. Thereafter, the sensor according to the invention is adapted to detect a force acting on an elongate device, in particular an elongate medical device, such as a catheter or guidewire, which force may have a non-negligible force component in the longitudinal direction of the elongate device. The sensor according to the invention has a force transducer on which at least the essential part of the force to be detected can be introduced either via the elongate device or directly into the sensor. According to the invention, the sensor should be such that it can be attached to the elongate device and, in particular, can be retrofitted to already existing elongate devices. According to the invention, the sensor has at least one light coupling region, at which light can enter the sensor, in particular at a predetermined, known intensity. The Lichteinkoppelbereich is optically connected to at least one optical waveguide, which connection in the interior of the sensor or outside can be realized, wherein the optical waveguide is preferably connected outside the sensor to a light source. The sensor according to the invention has a light intensity modulator which modulates the previously determined intensity of the light which can be coupled into the sensor as a function of the force which is introduced into the sensor via the force transducer, that is to say it changes as a function of the force. The sensor according to the invention has a light coupling-out region, which at the same time can also form the light coupling region and via which the light of modulated intensity can be coupled out into at least one light guide. In this case, the same light guide can be used, which is already used for coupling the light into the sensor. The modulated or unmodulated light intensity can be evaluated by a particularly sensor-external evaluation unit, which can determine the amount of force to be determined by using a proportional ratio between the intensity change and the force.

• – mit dem erfindungsgemäße Sensor besteht die Möglichkeit, eine Kraftsensorik in langgestreckten Einrichtungen zu integrieren, welche eine laterale Erstreckung oder einen Durchmesser von weniger als 3 mm, insbesondere 0,33 mm (1 French), aufweisen;
• – der erfindungsgemäße Sensor ist wegen der geringen Teileanzahl für eine Massenproduktion geeignet;
• – der einfache Aufbau des erfindungsgemäßen Sensor erfüllt ohne weiteres die hohen Anforderung der Hygiene in der Medizintechnik;
• – mit dem erfindungsgemäßen Sensor können aufgrund der Nutzung der sensiblen Lichtintensitätsmeßgröße sehr genaue Kraftbetrags- und/oder Kraftwirkungsmessungen erreicht werden; und
• – der erfindungsgemäße Sensor verzichtet auf elektrische Leitungen, die insbesondere bei einem Einsatz von einem Magnetresonanztomographen wegen der dabei auftretenden elektromagnetischen Wechselfeldern die Meßergebnisse verfälschend beeinflussen können.

The sensor according to the invention offers the following advantages over the known force sensors mentioned above:

• - With the sensor according to the invention it is possible to integrate a force sensor in elongate devices, which have a lateral extent or a diameter of less than 3 mm, in particular 0.33 mm (1 French);
• - The sensor according to the invention is suitable because of the small number of parts for mass production;
• - The simple construction of the sensor according to the invention readily meets the high requirement of hygiene in medical technology;
• - Due to the use of the sensitive Lichtintensitätsmeßgröße very accurate Kraftbetrags- and / or force measurements can be achieved with the sensor according to the invention; and
• - The sensor according to the invention dispenses with electrical lines, which can affect the measurement results in particular when using a magnetic resonance imaging because of the electromagnetic alternating fields occurring in the process.

The sensor according to the invention can detect forces in the amount and / or direction of action in real time and in particular continuously. In particular, the sensor according to the invention is designed to detect a force mainly in the longitudinal direction of the elongate device.

In a preferred embodiment of the invention, a reflector is provided, which has a reflection surface assigned to the at least one light outcoupling region. The reflection surface is designed to be so sensitive to force or pressure that it can change its reflection properties as a function of the load acting on the load cell. Preferably, the initial, unencumbered reflection properties of the reflector automatically restore after the load has been released. In the case of certain disposable products, however, it may be advantageous to dispense with a reversibility of the reflection properties with regard to favorable production costs. Preferably, the reflecting surface changes to a force effect such that it is increased or decreased.

The reflection surface is uneven, in particular curved, designed. Due to the unevenness of the reflection surface, the coupled-in light is reflected more or less strongly. This deterioration or improvement of the reflection properties can be changed by the force input into the force sensor of the sensor in that the degree of unevenness changes accordingly. In the case of a curved reflection surface, it can preferably be flattened or flattened when a force is introduced, as a result of which a higher or lower light intensity can be created at a predetermined point, which is preferably the light outcoupling region of the sensor. In this way, a higher or lower intensity than the predetermined, known initial intensity can be generated, which can be interpreted by the evaluation unit as an increasing or decreasing force on the elongate device.

In a particular further development of the invention, a spherical force transducer is provided, which is designed to be reflective on its side facing the light input and / or light outcoupling region.

In a further development of the invention, the particular uneven reflection surface can be dimensionally stable in such a way that it irreversibly or reversibly expands and / or limits the dimensions of the light outcoupling region. In particular, the material defining the light outcoupling region is softer than the dimensionally stable reflection surface, so that when force is applied to the force transducer of the sensor, the uneven reflection surface in particular engages with the material and the latter is enlarged and / or reduced to a manner impressing the shape of the reflection surface.

With this further development, the number of parts of the sensor is further reduced, because the functions of sub-components of the sensor are taken over with the hardness properties of main components.

Preferably, the light intensity signal emerging from the sensor is evaluated monochromatically and / or over a spectrum.

Furthermore, the invention relates to a sensor unit which has at least one optical waveguide which can be connected or connected to at least one light source, and a sensor according to the invention.

In one development of the invention, the sensor according to the invention is arranged on the end surface of the at least one optical waveguide, wherein preferably the sensor, in particular with its force transducer, can be in direct contact with the at least one optical waveguide.

So that the force can be predeterminedly introduced into the sensor, in particular on the force transducer, according to a specific sensor structure, an adapter can be arranged between the elongate device and the sensor.

In addition, the invention relates to an elongate device, in particular a medical-technical elongated device, such as a catheter, which device has at least one optical waveguide which is connected to at least one light source, and a sensor according to the invention, which is optically connected to the optical waveguide.

In a development of the invention, in the case of the elongate device, the sensor according to the invention or the sensor unit according to the invention is positioned in the region of the distal end of the elongate device, wherein a small distance from the distal end is preferred. The sensor should not be exposed directly to the forces, but the forces should be transmitted via an adapter piece of the elongated device to the sensor or the sensor unit.

In one development of the invention, the at least one optical waveguide extends along the elongate device from the sensor, preferably to an evaluation unit. Preferably, the sensor is attached to at least one guidewire of the elongate device.

In a particular embodiment of the invention, the longitudinal extension of the elongate device is formed essentially exclusively by the at least one optical waveguide. Guide wires are therefore not necessary if a fiber material is selected for the optical waveguide, which has both the corresponding optical properties and the necessary strength and flexibility.

Finally, the invention relates to a method for detecting a force acting on an elongate device. Thereafter, an initial intensity of a photometric quantity is predetermined, the quantity of photometry modulated as a function of the force, the modulated luminous intensity compared with the predetermined initial intensity, and a non-negligible longitudinal force component of the elongate device determined from the ratio of the initial intensity to the modulated intensity.

Further advantages, features and characteristics of the invention will become apparent from the following description of preferred embodiments of the invention with reference to the accompanying drawings, in which show

1a a schematic diagram of the sensor according to the invention in a first embodiment, which is shown in an unloaded state;

1b according to the sensor 1a in a loaded condition;

2a a schematic diagram of a second embodiment of the sensor according to the invention, which is shown in an unloaded state;

2 B according to the sensor 2a in a loaded condition;

3 a distal portion of one end of a medical elongate device, such as a catheter.

The in the 1a and 1b illustrated embodiment of the sensor according to the invention 1 includes a force transducer 3 in the execution according to the 1a and 1b a spherical elastic body 5 and / or a housing 7 has, which is formed for example of silicone. For ease of manufacture of the sensor according to the invention, the housing 7 as an encapsulation part around the body 5 formed overflowing. For a fixed mounting coupling of the force transducer to an optical fiber 11 surrounds the housing 7 the end 13 of the optical fiber 11 firmly.

The spherical body 5 has a reflection surface 15 , which is assigned to a Lichtein- and Lichtauskoppelbereich, which are both defined as an intermediate or transition point at the light leaves the optical waveguide and into the body 5 , ie into the sensor.

In the execution according to 1a and 1b lies the spherical body 5 at the end surface 19 of the end 13 of the light guide 11 on, so that in the contact area of the spherical body 5 and the optical fiber 11 a reflection surface 15 , also adjacent to the contact area, in the optical fiber 11 is effective. That through the light guide 11 through light to be coupled 21 , which has an initial intensity, passes through the Lichteinkoppelbereich on the surface 19 directly to the reflection surface 15 of the spherical body 5 , is reflected there and passes through the light extraction area on the surface 19 of the optical fiber 11 again in the latter as a ray of light 23 , the light intensity of a preferably at the end of the light guide 11 arranged monochromatic evaluation unit (not shown) or a spectrum is evaluated.

As in 1a is indicated schematically, only a part of the coupled light on the curved surface 15 of the spherical body 5 reflected so that light returns to the optical fiber again via the light extraction area. The stronger the curvature on the spherical body 5 is formed, the weaker is the reflected light in the optical waveguide 23 , which by the opposite the arrow 21 narrower arrow 23 should be indicated.

It is also conceivable a diametrically the reflection surface 15 opposite reflection surface 25 to provide in a modified version. In this case, the spherical body 5 transparent, so that the coupled light through the light body 5 through at the reflection surface 25 is reflected to partially over the Lichtauskoppelbereich in the optical waveguide 11 to get.

Becomes one substantially along the waveguide 11 directed force F the force transducer 3 communicated as in 1b is shown, so deform both the elastic housing 7 as well as the elastic, spherical body 5 from their substantially spherical initial shape into an egg or ellipsoidal shape as in 1b is indicated. Due to this deformation, the degree of curvature at the reflection surfaces decreases 15 and or 25 so that the effective reflection surface 15 and or 25 increases and that the light extraction area of the sensor 1 associated higher-intensity reflected light into the waveguide 11 can be initiated.

By means of a calibration of the force sensor with regard to the ratio of degree of curvature / force, degree of curvature / effective reflection surface, effective reflection surface / modulated intensity, a quantitative evaluation of the force can take place on the basis of the modulated light intensity.

Should the fiber optic cable 111 Be carried out elastically reversible at its end, any number of power impressions by the sensor of the invention 101 be detected. In the 2a and 2 B an alternative embodiment is shown, wherein for better readability of the figure description for identical and similar components of the inventive sensor of the alternative embodiment, the same reference numerals are used to 100 are increased.

The in 2a and 2 B illustrated inventive sensor 101 is different from the sensor 1 according to the 1a and 1b in that the spherical body 105 is formed of a solid material that is harder than the material of the optical waveguide 111 at the end 113 is. For the case 107 is, as well as in the execution according to the 1a and 1b , an elastic material, such as silicone, used to allow flexible encapsulation and attachment of the force transducer 103 on the optical fiber 111 is ensured.

As in 2 B is shown, the end is 113 of the waveguide 100 due to moving in the longitudinal direction of the optical waveguide 100 acting force F is depressed. Due to the spherical indentation area, the contact area is increased, ergo the reflection surface 115 is increased, resulting in that light with a greater modulated intensity over the light extraction area of the sensor 101 in the optical fiber 111 arrives.

Should the fiber optic cable 111 Be carried out elastically reversible at its end, any number of power impressions by the sensor of the invention 101 be detected.

In 3 is schematically the end area 71 a catheter according to the invention shown, the end of which is slightly curved or hook-shaped, in order to introduce the catheter end more easily in Y-arterial branches can. The sensor according to the invention 1 is not right at the top 73 arranged but at some distance from the top 73 so that an axial force can be forced in the sensor. The top 73 facing area 75 The catheter may include catheter accessories. On the top 73 opposite side 77 of the sensor 1 the at least one optical waveguide (not shown in detail) is provided, wherein the catheter in this section from the sensor to the actuating device can be formed exclusively from an optical waveguide which can have an opaque, organism-compatible outer skin (not shown).

Claims (11)

Sensor for detecting a force (F) acting on an elongated device, in particular an elongate medical device, such as a catheter, with a non-negligible force component in the longitudinal direction of the elongate device, comprising - a force transducer ( 3 ) for the force to be detected, - a connection for attaching the sensor ( 1 ) to the elongated device, - at least one Lichteinkoppelbereich, which with at least one light in the sensor ( 1 ) einkoppelnden optical waveguide ( 11 ) is optically connectable, - a light intensity modulator having a predeterminable intensity of the in the sensor ( 1 ) coupled-in light ( 21 ) according to the on the load cell ( 3 ) modulating force (F), and - at least one Lichtauskoppelbereich, over which the light ( 21 ) modulated intensity in at least one light guide ( 11 ) can be coupled, characterized in that a reflector with a the at least one Lichtauskoppelbereich ( 17 ) associated reflection surface ( 15 ), which can change its reflection properties depending on the force to be detected (F), preferably in particular irreversible or reversible and depending on the force to be detected (F) deform, in particular enlarge and / or reduce, in which an uneven Reflection surface ( 15 ) is provided, to which the on the load cell ( 3 ) acting force (F) can act such that the degree of unevenness changes depending on the force (F) and one with the at least one Lichtauskoppelbereich ( 17 ) optically connected region of the reflection surface ( 15 ) extended and / or limited. Sensor according to Claim 1, in which the in particular spherical load cell ( 3 ) a curved reflection surface ( 15 ) having. Sensor according to claim 1 or 2, which is designed for the continuous real-time detection of forces (F) according to the magnitude and / or direction of action. Sensor unit according to one of claims 1 to 3, in which the sensor ( 1 ) on an end face ( 19 ) of the at least one optical waveguide ( 11 ), in particular the force transducer ( 3 ) in direct contact with the at least one optical waveguide ( 11 ) stands. Sensor unit according to one of claims 1 to 4, in which the sensor ( 1 ) is limited by a flexible and / or deformable, in particular elastic wall material, in particular silicone. Sensor unit according to one of claims 1 to 5, in which an adapter is arranged, which is designed for the predeterminable introduction of the force acting on the elongated device force (F). Elongated device with a sensor according to claims 1 to 6 ( 1 ) for detecting a force acting on the elongated device (F), in particular medically technical elongated device, such as catheters, with at least one optical waveguide ( 11 ), which is connected to at least one light source, and to the sensor ( 1 ) is optically connected. Elongated device according to claim 7, in which the sensor ( 1 ) is disposed in the region of a distal end of the elongate device, in particular at a distance from the distal end. Elongated device according to one of Claims 7 to 8, in which the sensor ( 1 ) is attached to at least one guidewire of the elongated device. Elongated device according to one of Claims 7 to 9, whose longitudinal extension is essentially defined by the at least one optical waveguide ( 11 ) is formed. Method for measuring a sensor formed on an elongate device with a sensor according to claims 1 to 6 ( 1 ), in particular an elongated medical device, such as a catheter, engaging force (F), wherein: an initial intensity of a Lichtmeßgröße is predetermined, the Lichtmeßgröße is modulated in dependence on the force (F), the modulated light intensity is compared with the predetermined initial intensity, and a non-negligible longitudinal force component of the elongate device is determined from the ratio of initial intensity to modulated intensity, with method steps according to the operation of the sensor recited in any one of claims 1 to 6 ( 1 ).

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