EP2633340A2

EP2633340A2 - Sensor apparatus, in particular metal sensor, with a field-compensated magnetic field sensor

Info

Publication number: EP2633340A2
Application number: EP11761560.9A
Authority: EP
Inventors: Reiner Krapf; Tobias Zibold; Andrej Albrecht
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2010-10-28
Filing date: 2011-09-21
Publication date: 2013-09-04
Also published as: US20130300401A1; WO2012055641A3; CN103154775A; WO2012055641A2; DE102010043078A1

Abstract

The invention relates to a sensor apparatus, in particular a metal sensor, having at least two coils and a magnetic field sensor, in which the arrangement of coils and magnetic sensor with respect to one another and/or the number of coil turns and/or the winding sense of the coils and/or the coil current is/are selected in such a manner that the magnetic field generated by the coils approximately disappears at the location of the magnetic field sensor. The invention also relates to a method for detecting objects, in particular a method for finding metal objects, using at least two coils and a magnetic field sensor, in particular an AMR, GMR or Hall sensor, in which the arrangement of the coils and the magnetic sensor with respect to one another and/or the number of coil turns and/or the winding sense of the coils and/or the coil current is/are selected in such a manner that the magnetic field generated by the coils approximately disappears at the location of the magnetic field sensor.

Description

Description title

Sensor device, in particular metal sensor, with field compensated magnetic field sensor

The invention relates to a sensor device and a method for localization of objects enclosed in a medium, in particular metallic objects, according to the preamble of claim 1 and claim 15. In addition, the invention describes a tool device, in particular a measuring device, for example a hand-held locating device with Such a sensor device for carrying out the method according to claim 15.

State of the art

For detection of objects enclosed in a medium, such as, for example, a wall, a ceiling or a floor, such as, for example, electrical lines, water pipes, pipes, metal stands, locating devices have been used for some time. Among other things, inductive devices, i. Devices that one

Create magnetic field, which is disturbed by the enclosed in a medium, metallic objects, use.

Such a system is known from DE 10 2004 011 285 AI.

State of the art in the field of metal sensors for finding metallic objects, such as reinforcing bars, pipes or cables, in walls or floors are coil-based metal sensors. These are available in different versions: (i) field-compensated, (ii) differential, (iii) field-compensated and differential. The object of the invention is the improvement of metal sensors for finding metallic objects in walls and floors in terms of miniaturization, integration and performance.

Disclosure of the invention

A core of the invention is a metal sensor for detecting metallic objects in walls and floors, which combines the advantages of field compensated, differential, coil-based sensors and the additional advantages of special magnetic field sensors, especially low-cost Hall sensors, but also AMR / GMR based magnetometers and SQU IDS, makes use of. (AMR sensor: anisotropic magneto-resistive sensor; GMR sensor: giant magneto-resistive sensor; SQUID: superconducting quantum interference device)

Advantages of this og. Magnetic field sensors are the compact size, high sensitivity, in particular a sensitivity to local magnetic field changes instead of changes in the magnetic flux through larger areas. This results in immediate advantages for the metal sensor: compact size, since the sensors themselves are small and, for example, small (print) coils sufficient to generate sufficiently large fields (because of the high sensitivity), integration of several individual sensors, resulting in advantageous properties such as Possibility of position / depth estimation up to a pictorial resolution of the objects to be detected.

For this purpose, the invention proposes a system of transmitting coils and magnetic field sensors. The sensor device according to the invention for the localization of objects enclosed in a medium, in particular for the detection of metallic objects, has an arrangement with at least two coils and a magnetic field sensor, wherein the arrangement of coils and magnetic sensor to each other and / or the number of coil turns and / or the sense of winding the coil and / or the coil current is / are selected such that the magnetic field generated by the coils at the location of the magnetic field sensor approximately disappears.

An object in the area of the magnetic field generated by the coils (= "primary field") generates a "secondary field". This secondary field can then according to the invention be measured by a magnetic field sensor. The compensation of the primary field at the location of the magnetic field sensor achievable in this arrangement is very advantageous for the use of magnetic field sensors for the detection of metallic / magnetizable objects) since too high magnetic fields would bring the magnetic field sensor out of its working range. However, high magnetic fields are necessary in the measurement in order to generate sufficiently high magnetic fields at the location of the object, so that the resulting secondary fields at the location of the sensor are still sufficiently high. The device according to the invention makes it possible advantageously to minimize the primary field or even to make it disappear, but that induced by the primary field

Secondary field of an object to be detected is sufficiently large to be detected with a magnetic field sensor.

Another advantage of the compensation of the primary field is that the ratio of object-conditioned signal (signal resulting from secondary field) to basic signal

(Signal resulting from primary field) is improved by several orders of magnitude.

The described system of transmitting coils and magnetic field sensor can be realized in an advantageous manner with a drive according to the push-pull regulator principle. Advantages of the push-pull controller are the high dynamics over a large field range and the high signal-to-noise ratio due to the advantageous use of a synchronous demodulator.

When using print coils, the secondary fields are very small (typically a few 10 nT). Therefore, the high-sensitivity AMR / GMR magnetic sensors are particularly suitable for such an embodiment while Hall sensors are less suitable in this case.

The use of periodic excitation fields is advantageous since the object-related portion of the received signal can then be very well separated from interference and noise (e.g., with a synchronous demodulator) due to its frequency.

Further advantages of the sensor device according to the invention will become apparent from the dependent claims, the following embodiment, as well as the drawings and the associated description. drawing

In the drawing, an embodiment of the sensor device according to the invention is shown, which will be explained in more detail in the following description. The figures of the drawing, the description and the claims contain numerous features in combination. A person skilled in the art will also consider these features individually and combine them into other or more meaningful combinations.

It shows:

Figure 1 shows a typical arrangement of an inventive

Sensor device in a highly schematic representation,

2a, 2b, the calculated magnetic field of two coils of the sensor device in a graphical representation,

3a, 3b, the calculated magnetic field of the coils of the invention

Sensor device in two orthogonal directions,

4a, 4b show the calculated z component of the primary magnetic field of two coils of the sensor device, as well as the secondary magnetic field generated by an object, in an overview (2a), as well as in a detailed representation (2b),

FIG. 5 control of the sensor device according to the invention by means of a push-pull controller,

Figure 6 shows an embodiment of an inventive tool in the form of a tracking device. Description of an embodiment

FIG. 1 shows a possible embodiment of a device according to the invention

Sensor device 10 in a schematic representation.

The arrangement of a sensor device according to the invention shown by way of example in FIG. 1 has two coils ("outer coil 12", "inner coil 14"), which are used in space for a periodically changing quasi-stationary one

Magnetic field (in particular a dipole field) to produce (see also, for example, Figure 2). A magnetic field sensor 16, which may be formed, for example, as a Hall sensor, an AMR or GMR sensor or else as a SQUID, is used to measure a magnetic field, which is generated in particular by an object to be detected. The arrangement of

Coils and the sensor to each other, and number of turns, sense of winding, and coil current of the coils are inventively chosen such that the magnetic field generated by the coils at the location of the magnetic field sensor (and ideally only there) approximately (and ideally exactly) disappears, i. becomes zero, so at the location of the magnetic field sensor field compensation takes place. (See also, for example, the calculated fields in Figure 3). An ideal field compensation, in which the magnetic field of the coils in the mathematical sense to zero, is hardly realizable from a practical point of view. This is to be expressed by the term "approximate" disappears, the rest and so-called "dirt effects", the absolute

Elimination of the magnetic field in the last consequence, fall under the approximate compensation.

The two coils 12, 14 of the sensor device in the embodiment of Figure 1 are concentric with each other in a common plane, in particular on a common circuit board 18 is formed.

For two in a plane arranged, concentric coils with opposite sense of winding, the magnetic field disappears at the midpoint of the two coils - if they are traversed by the same current - under the

Condition:. N / d = N '/ d' (I)

N: number of turns of the outer coil, d: diameter of the outer coil,

N ': number of turns of the inner coil, d': diameter of the inner coil.

Strictly speaking, for the above relationship (I), the respective coil diameter must be large relative to the pitch of the individual coil turns in the coil.

An advantage of using two coils with opposite sense of winding is in particular that one can connect the coils in series.

In the embodiment of Figure 1, the coils are formed as a print coil on the circuit board 18. In alternative embodiments, it is also possible to use conventional coils, more than two coils and, in particular, not concentrically arranged coils.

Thus, it is also possible that the transmitter coils are adjacent to each other and / or overlap, for example. However, a core of the invention is always to mount the magnetic field sensor in a range disappearing coil magnetic field.

With a suitable coil arrangement, number of turns and winding sense, it is possible to electrically connect the coils in series. They are then flowed through by the same current and changes in this current, which are generated for example by temperature or other environmental influences, do not affect the field compensation at the location of the magnetic field sensor in an advantageous manner.

In the center, ie in the center of the circular coils 12, 14, a magnetic field sensor 16 in the embodiment of a GMR sensor is arranged in the embodiment of FIG. Alternative magnetic field sensors are also possible. An object in the region of the magnetic field generated by the coils 12, 14 (= "primary field") generates a "secondary field". This secondary field is then measured according to the invention by the magnetic field sensor 16. In this way, an object can be detected. (See also Figure 4)

The preferred direction of the sensor, that is, the direction to the magnetic fields must be parallel to be measured by the sensor with maximum sensitivity, in a planar, concentric coil assembly with magnetic field sensor in the coil center, as shown in Figure 1, in the normal direction of the coil plane demonstrate.

The compensation of the primary field at the location of the magnetic field sensor 16 is advantageous for the use of a magnetic field sensor in this application (detection of metallic / magnetizable objects), since too high magnetic fields bring the sensor 16 out of its working range. However, high magnetic fields are necessary to generate sufficiently high magnetic fields at the location of the object, so that the resulting secondary fields at the location of the sensor 16 are still sufficiently high. Another advantage of the compensation of the primary field is that the ratio of object-related signal (signal resulting from secondary field) to basic signal (signal resulting from primary field) is improved by several orders of magnitude.

When optimizing the diameters of the coils of the sensor arrangement according to the invention, two opposing effects have to be considered:

(1) The dipole character of the total field is more pronounced when the inner coil has the smallest possible diameter in relation to the outer coil.

The diameter of the inner coil is substantially limited by the size of the magnetic field sensor and is thus at a minimum value of about 5 mm

(2) However, the smaller the ratio of the coil diameters of the smaller the magnetic field gradient in the region of the zero point of the field the value one. This reduces the requirements for the positioning accuracy of the magnetic field sensor.

Figures 2a and 2b show the calculated magnetic field of two print coils (outer coil with 4 turns, radius 2 cm), inner coil (1 turn, radius 0.5 cm) in the x-z plane. The magnetic field is rotationally symmetric about the z-axis. The left-hand figure 2a shows the dipole-shaped field in the outer region, the right-hand figure 2b shows the compensation of the fields generated by the two coils in the region of the inner coil.

In addition to the dipole arrangements described here, quadrupole arrangements are also conceivable which operate on the same principle.

Figures 3a and 3b show calculated magnitudes of the magnetic field of the outer coil (A), the outer and inner coils (B). The curves show that the magnetic field of the outer and inner coil disappears together at the origin (so-called "field compensation") .The outdoor field is almost unaffected by the compensation, which is important to ensure the same sensor range without the additional compensation coil in Shape of the inner coil would be achieved.

Figure 4 shows the z-component of the primary (C) and secondary magnetic field (D) along the z-axis. (Figure 4b shows a detail in the immediate vicinity of the zero point, compare the respective scales). The source of the secondary field in this simulation is an iron sphere (with relative magnetic permeability μ = 1000 and diameter 1 cm) located on the z-axis 5 cm away from the sensor. Calculated is the case for small frequencies of the excitation field (ω 0). It should be noted that without the inner compensation coil, the sensor field in the origin / zero point would have the value 1, ie a factor of 10,000 would be greater than the object field.

The described system of transmitting coil and magnetic field sensor can be controlled very well and advantageously with a push-pull controller 20. Advantages of the push-pull controller are the high dynamics over a large field range as well as the high signal-to-noise ratio by using a synchronous demodulator. FIG. 5 shows an exemplary connection of the coils and of the magnetic sensor in push-pull operation.

In the embodiment according to FIG. 5, the push-pull regulator 20 consists of a signal source 24, controllable amplifiers 26, 28, synchronous demodulator 22 and integrating comparator 30. The controllable amplifiers 26, 28 energize the two transmitting coils 12, 14 with 180 ° phase-shifted, periodically changing Currents of independent amplitude. The transmitting coils (for example outer and inner coils according to FIG. 1) are now wound in such a way that, at least in the absence of metallic / magnetizable objects in the region of the transmitting coil field, they produce - at least at one time - oppositely directed magnetic fields which cancel out at the location of the sensor. The sensor 16 is optionally connected to the synchronous demodulator 22 via an optional amplifier 32. The push-pull control via the integrating comparator 30 controls the amplitudes of the transmitting coil currents by means of the controllable amplifiers 26, 28 in such a way that the magnetic field disappears at the location of the sensor even if a metallic / magnetizable object is present in the region of the transmitting coil field at least at one point in time. This control value changes in the presence of a metallic / magnetizable object and can therefore be used to detect such.

In addition to the system of a sensor device with two coils and a magnetic field sensor shown here, however, systems having more than two coils and / or a plurality of magnetic field sensors are conceivable and also useful.

Thus, in particular, the use of a plurality of "compensation coils" (in the exemplary embodiment, the inner coil 14 for canceling the primary field) at different locations is possible. Sensor systems are possible in which the positions of the plurality of compensation coils are arranged both inside and outside the "outer" transmission coil.

It may also be advantageous to arrange the transmitting coils in different levels.

Also, the use of multiple magnetic field sensors at each of the locations that are held by the respective compensation coil field-free is an advantageous Variant of the sensor device according to the invention. The advantage of this is that you can measure the secondary field (ie, the field generated by an object to be measured) at different locations and thus at least in principle conclusions about object properties, such as the lateral position, the Einschlusstiefe or orientation can draw

6 shows a possible exemplary embodiment of a tool device according to the invention as a measuring device, in the form of a hand-held locating device 86g, which has a sensor device according to the invention. The hand-held device 86g has a locating device 24g with a sensor device 26g according to the invention. The sensor device 26g comprises in the manner already described at least two coils and at least one magnetic field sensor, which are arranged in accordance with the invention and operate according to the inventive method. The locating device 24g further comprises a drive unit 28g, in particular with a push-pull control 20, and an evaluation unit 30g for processing and processing the measurement signals. Thus, in particular, the control signal 32 of the push-pull control 20 (see also FIG. 5) can be used by the evaluation unit 30g in order to characterize an object as detected or not detected. That is, the control signal 32 of the differential mode control of the sensor device according to the invention is used to detect the objects.

The manual positioning device 86g also has rollers 88g with distance measuring means, not shown in more detail, by means of which an operator can move the hand-held device 86g along the medium. On a display 90g of the hand-held location device 86g, the hand-held location device 86g displays detected objects as a function of the traveled path. The displacement sensor allows the assignment of a detection value of the sensor device according to the invention to a spatial position of the measuring device. In particular, the measuring device according to the invention enables the correlated representation of the detection signal and position of enclosed objects via a corresponding output unit, 90g, in particular a graphic display. In simpler embodiments, the displacement sensor can be dispensed with and the detection of an object, for example, only by a light signal and (/ or an acoustic signal to be transmitted. The method according to the invention or a tool device operating according to this method is not limited to the exemplary embodiments illustrated in the figures. In particular, the inventive method is not limited to the

Use of two transmitting coils, in particular second concentrically arranged transmitting coils. Thus, it is also possible that the transmitter coils are adjacent to each other and / or overlap, for example. A core of the invention is to attach the magnetic field sensor in a range disappearing coil magnetic field.

In addition to the system shown here with two coils but also systems with more than two coils are conceivable and useful. In particular, the use of several "compensation coils" (inner

Coils) in different places possible. Sensor systems are possible in which the positions of the plurality of compensation coils are arranged both inside and outside the "outer" transmission coil. It may also be advantageous to arrange the transmitting coils in different levels.

Also, the use of multiple magnetic field sensors at each of the locations that are kept free of field by the respective compensation coil is an advantageous variant of the sensor device according to the invention. The advantage of this is that you can measure the secondary field (ie, the field generated by an object to be measured) at different locations and thus at least in principle conclusions about object properties, such as the lateral position, the Einschlusstiefe or orientation can draw

Also, the magnetic field could be brought to zero by a shielding device and the magnetic sensor be mounted in the appropriate place.

The tool according to the invention is not limited to a measuring device, in particular a tracking device. Also sawing, grinding or drilling

Tool devices can with the sensor device according to the invention be equipped as it is integrated as in the tool device measuring system or as a tool to be attached to the accessory.

Claims

claims

1. Sensor device (10,26g), in particular metal sensor, with at least two coils (12,14) and a magnetic field sensor (16), characterized in that the arrangement of coils (12,14) and magnetic sensor (16) to each other and / or the number of coil turns and / or the winding sense of the coils and / or the coil current are chosen such that the magnetic field generated by the coils (12,14) at the location of the magnetic field sensor (16) approximately disappears, in particular completely compensated.

2. Sensor device according to claim 1, characterized in that a first, outer coil (12) and a second inner coil (14) are provided, which are in particular arranged concentrically to one another.

3. Sensor device according to claim 1 or 2, characterized in that the magnetic field sensor (16) of the turns of at least one coil (14) is enclosed.

4. Sensor device according to claim 1, 2 or 3, characterized in that the magnetic field sensor (16) in the center of at least one, substantially circular coil (14) is arranged.

5. Sensor device according to one of the preceding claims, characterized in that at least two coils (12,14) and a magnetic field sensor (16) are arranged in a plane.

6. Sensor device according to one of the preceding claims, characterized in that at least two coils (12,14) and a magnetic field sensor (16) on a common printed circuit board (18) are arranged.

7. Sensor device according to one of the preceding claims, characterized in that at least one coil (12,14) is designed as a print coil.

8. Sensor device according to one of the preceding claims, in particular according to claim 6 and / or 7, characterized in that the magnetic field sensor (16) is an AMR sensor.

9. Sensor device according to one of the preceding claims 1 to 7, characterized in that the magnetic field sensor (16) is a GM R sensor.

10. Sensor device according to one of the preceding claims 1 to 7, characterized in that the magnetic field sensor is a Hall sensor.

11. Sensor device according to one of the preceding claims 1 to 7, characterized in that the magnetic field sensor (16) is a SQUID.

12. Sensor device according to one of the preceding claims, characterized in that at least two coils (12, 14) are electrically connected in series.

13. Sensor device according to one of the preceding claims, characterized in that it has a push-pull regulator (20) for controlling the coils (12, 14).

14. Tool, in particular a measuring device (86g) for detecting objects, in particular metallic objects, with at least one sensor device (10,26g) according to at least one of the preceding claims.

15. A method for detecting objects, in particular a method for finding metallic objects, using at least two coils (12, 14) and a magnetic field sensor (16), in particular an AMR, GMR or Hall sensor, wherein the arrangement of Coils (12, 14) and the magnetic sensor (16) to each other and / or the number of coil turns and / or the winding sense of the coils and / or the coil current are selected such that the magnetic field generated by the coils (12, 14) Location of the magnetic field sensor (16) approximately disappears, in particular completely compensated.

16. The method according to claim 15, characterized in that a push-pull regulator (20) controls the amplitudes of the coil currents of the at least two coils by means of controllable amplifier (26, 28) such that at the location of the magnetic sensor (16) - at least at one time - the Magnetic field disappears.

17. The method according to claim 16, characterized in that a control value (34) of the push-pull regulator (20) is used to detect an object, in particular a metallic object.