Device, method and system for determining the velocity or acceleration of an electrically conductive object

Abstract

The invention relates to a device (20) and a method for determining the speed or acceleration of an electrically conductive object (4, 4c) along a predetermined direction of movement (X), the device comprising: at least four magnets (1, 1b) for generating an external magnetic field (1a), wherein two first magnets (1) are arranged spaced apart in the direction of movement (X) with opposite polarity, and a first sensor (3) is arranged between the two first magnets with a measuring axis (Y) perpendicular to the direction of movement, and two second magnets (1b) are arranged spaced apart in the direction of movement with opposite polarity, and a second sensor (3a) is arranged between the two second magnets with a measuring axis perpendicular to the direction of movement, wherein the first and second magnets or the first and second sensors are arranged along an axis (Z) respectively, which extends perpendicular to the direction of movement (X) and the measuring axis (Y). The speed or acceleration of the object (4, 4c) is formed from the difference of a first and a second measuring signal, which respectively detect an internal magnetic field caused by eddy currents in the object, whereby changes in the distance between the sensor and the measured object and the influence of the external magnetic field can be compensated.

Description

Technical Field

[0001] The invention relates to a device and a method for determining the speed or acceleration of an electrically conductive object along a predetermined direction of movement. The invention also relates to a system having an electrically conductive object and such a device. Background Art

[0002] Such devices are also called Ferraris sensors and typically include a magnet, with the aid of which an external magnetic field is generated, which extends in a field direction perpendicular to the direction of movement of the object. The external magnetic field induces eddy currents in the moving, electrically conductive object, which generate an internal magnetic field that is directed in the opposite direction to the external magnetic field. The magnetic flux density of the internal magnetic field is proportional to the speed of the object. With the aid of the sensor, the magnetic flux density or its changes can be detected and the speed or acceleration of the object can be inferred therefrom.

[0003] An exemplary device for determining the acceleration of an electrically conductive object is described in EP 1 395 836 B1. In the device, a plurality of sensors configured as detector coils and a plurality of magnets are arranged alternately side by side in the direction of movement. The known device is very suitable for detecting the movement of non-magnetized objects. However, it has been found to be disadvantageous that in applications where the electrically conductive object is formed of a magnetizable material or has a magnetization that is optionally variable, it is impossible to reliably determine the acceleration. This is because changes in the distance between the moving object and the sensor and changes in the magnetization of the object cause changes in the measurement signal of the detector coil, which exceed the magnitude of the changes caused by the movement of the object. This therefore affects the measurement quality. Summary of the invention

[0004] Against this background, the object is to make it possible to determine the velocity or acceleration of an electrically conductive, in particular magnetizable, object with increased reliability.

[0005] The object is achieved by a device for determining the speed or acceleration of an electrically conductive object along a predetermined direction of movement, the device comprising:

[0006] - at least two first magnets, for respectively generating an external magnetic field perpendicular to the direction of movement, and

[0007] at least one first sensor for detecting an internal magnetic field caused by eddy currents in the object, wherein a measuring axis of the first sensor extends perpendicularly to the direction of movement, and at least two first magnets and at least one first sensor are arranged spaced apart from one another in the direction of movement, wherein each first sensor is arranged between two first magnets,

[0008] at least two second magnets for respectively generating an external magnetic field perpendicular to the direction of movement, wherein the second magnets are respectively arranged on a common magnet axis with one of the at least two first magnets, the common magnet axis being arranged perpendicular to the measuring axis and perpendicular to the direction of movement, and wherein the first magnet and the second magnet on this common magnet axis are polarized oppositely,

[0009] at least one second sensor for detecting an internal magnetic field caused by eddy currents in the object, said second sensor being arranged together with the first sensor on a common sensor axis parallel to the magnet axis, wherein a measuring axis of the second sensor is arranged parallel to the measuring axis of the first sensor, wherein in each case one second sensor is arranged between two second magnets, and

[0010] - an evaluation device for determining a velocity or an acceleration of an object based on an internal magnetic field detected by the first sensor and the second sensor, in that the evaluation device is configured to receive a first measurement signal from the first sensor and a second measurement signal from the second sensor and to form a difference between the first measurement signal and the second measurement signal for determining the velocity or the acceleration.

[0011] In the device according to the invention, an external magnetic field is generated by means of a first and a second magnet, which can induce eddy currents in a moving object. Since the first and second magnets are arranged on a common magnet axis and the first and second sensors are arranged on a common sensor axis, it is possible to compensate for the influence of the external magnetic field, i.e. the pre-magnetization of the object to be measured, in the evaluation device. Likewise, it is possible to compensate for changes in the spacing between the moving object and the sensor. The first sensor and the second sensor detect the same external magnetic field. Since the first magnet and the second magnet are oppositely polarized, the magnets induce eddy currents of opposite directions in the moving object. The internal magnetic field caused by the eddy currents has the same magnitude, but is oppositely oriented. The sensor therefore also detects an internal magnetic field of opposite polarity in addition to the external magnetic field. Since the external magnetic field measured by the first and second sensors is the same, it is possible to compensate for the influence of the external magnetic field by means of the evaluation device. Likewise, it is possible to compensate for changes in the spacing between the object and the two sensors. Therefore, it is possible to achieve increased reliability when determining the speed or acceleration.

[0012] According to the design solution of the present invention, the evaluation device is configured to receive a first measurement signal of a first sensor and a second measurement signal of a second sensor, and to form a difference between the first measurement signal and the second measurement signal for determining the speed or acceleration. By taking the difference, the influence of an external magnetic field on the measurement, i.e., the influence of a pre-magnetization of the object to be measured or a change in the distance between the object and the device on the measurement, can be eliminated. From the taking the difference, a difference value can be obtained, which corresponds to twice the magnitude of the measurement signal. The difference value is essentially related to the speed or acceleration of the moving object.

[0013] Preferably, the first magnet and / or the second magnet are designed as permanent magnets, thereby enabling a compact design of the device. Alternatively, it is preferred that the first magnet and / or the second magnet are designed as electromagnets, so that the external magnetic field generated by the corresponding magnets can be adjusted. A plurality of first magnets and a plurality of second magnets are provided, wherein the first magnets are preferably designed identically and the second magnets are preferably designed identically. Preferably, the plurality of first magnets are arranged along the direction of movement so that adjacent first magnets have opposite polarizations. The plurality of second magnets are advantageously arranged along the direction of movement so that adjacent second magnets have opposite polarizations.

[0014] According to an advantageous design, at least one first sensor and / or at least one second sensor is a Hall sensor. A measurement signal, in particular a Hall voltage, can be obtained by the Hall sensor, which is proportional to the magnetic flux density of the measured magnetic field. The magnetic flux density is proportional to the speed of the moving object, so that the evaluation device can determine the speed based on the measurement signal of the Hall sensor. An alternative, advantageous design proposes that at least one first sensor and / or at least one second sensor is a measuring coil. The measuring coil can generate a measurement signal, in particular an induced voltage, which is proportional to the change in the speed of the moving object, that is, the acceleration of the object. If a plurality of first sensors and / or a plurality of second sensors are provided, the first sensors are preferably constructed identically and / or the second sensors are constructed identically. Preferably, the plurality of first sensors are arranged along the direction of movement so that a first magnet is respectively arranged between two adjacent first sensors. Correspondingly, it is preferred that the plurality of second sensors are arranged along the direction of movement so that a second magnet is respectively present between two adjacent second sensors.

[0015] According to an advantageous design, a plurality of first magnets and a plurality of first sensors are arranged alternately spaced apart from each other along the direction of motion, and a plurality of second magnets and a plurality of second sensors are arranged alternately spaced apart from each other along the direction of motion. In this way, a device can be formed that can determine the linear motion of an object along the direction of motion on a preset path section. Preferably, adjacent first magnets are respectively arranged so that they are oppositely polarized. It is also preferred that adjacent second magnets are respectively arranged so that they are oppositely polarized.

[0016] Preferably, at least two first magnets, at least one first sensor, at least two second magnets and at least one second sensor are arranged on a common scanning head. It is therefore possible that the device is designed as a prefabricated assembly that can be installed as a whole into a system, such as a machine tool.

[0017] A further subject matter of the invention is a system having an electrically conductive object and an apparatus as described above for determining a speed or an acceleration of the electrically conductive object along a predetermined direction of movement.

[0018] The same advantages as described in conjunction with the device for determining a velocity or acceleration can be achieved in the system.

[0019] The movable object has the function of an eddy current in the system, in which eddy currents are induced by the external magnetic field of the first and second magnets. The object can itself be the object to be monitored or can be fixed to the object to be monitored, for example a non-conductive object. Such an object can be a rotatably arranged shaft, a rotatably arranged machine shaft, a rotatable part of a support, a movable part of a linear guide. Alternatively, it is possible that the object is an electrically conductive raw material or semi-finished product, for example a plate, a tube or a rod.

[0020] According to an advantageous embodiment of the system, the object is magnetized. The object can be designed as a permanent magnet or can be held and magnetized by a movable magnet clamping mechanism, in particular a magnet chuck or a magnet clamping plate. The device for determining the speed or acceleration can achieve compensation of the external magnetic field required for clamping by the magnet clamping mechanism.

[0021] Preferably, the object of the system is arranged to be linearly movable. Alternatively, it is preferred that the object is arranged to be rotatable, ie, can be set in rotation. In this case, the device can be fixedly arranged for determining the speed or acceleration, so that the speed or acceleration of the relative movement of the object relative to the device can be determined.

[0022] Another subject matter of the present invention is a method for determining a speed or acceleration of an electrically conductive object along a predetermined direction of movement by means of the device according to the invention, wherein

[0023] - generating an external magnetic field perpendicular to the direction of movement by means of at least two first magnets,

[0024] - detecting an internal magnetic field caused by eddy currents in the object by means of at least one first sensor,

[0025] - generating an external magnetic field perpendicular to the direction of movement by means of at least two second magnets, respectively, and

[0026] - detecting an internal magnetic field caused by eddy currents in the object in a field direction by means of at least one second sensor, and

[0027] The speed or acceleration of an object is determined by means of an evaluation device based on an internal magnetic field detected by a first sensor and a second sensor in that, according to the method according to the invention, a first measurement signal of the first sensor and a second measurement signal of the second sensor are received by means of the evaluation device and a difference between the first measurement signal and the second measurement signal is formed for determining the speed or acceleration, wherein the determined speed or acceleration is independent of the distance and / or the premagnetization of the object.

[0028] The same advantages as described in connection with the device for determining velocity or acceleration can be achieved in this method. As already explained in connection with the corresponding advantageous embodiments of the device, the influence of external magnetic fields on the measurement or the influence of distance changes on the measurement can be eliminated by the difference formation.

[0029] Alternatively or additionally, in the system and / or the method, the advantageous features and embodiments described in conjunction with the device for determining a velocity or an acceleration of an electrically conductive object may also be used individually or in combination. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Further details and advantages of the invention are explained below with reference to the exemplary embodiments shown in the drawings. It is shown in the drawings:

[0031] Figure 1 A schematic cross-sectional view showing a first embodiment of a system according to the invention;

[0032] Figure 2 Show according to Figure 1 A schematic top view of a system of FIG. 1 , wherein the object is shown in perspective;

[0033] Figure 3 A schematic cross-sectional view showing a second embodiment of a system according to the invention;

[0034] Figure 4 Show according to Figure 3 A schematic top view of a system of FIG. 1 , wherein the object is shown in perspective;

[0035] Figure 5 Show according to Figure 3and 4 A variation of the system; and

[0036] Figure 6 A block diagram is shown for illustrating an evaluation device, which can be used according to Figure 1-5 used in the system. DETAILED DESCRIPTION

[0037] Figure 1 and 2 The view in shows a first embodiment of a system according to the invention, which comprises an electrically conductive object 4 and a device 20 for determining the speed or acceleration of the object 4 along a preset direction of movement X. The object 4 can be, for example, a raw material or a semi-finished product of a production process, which moves linearly, for example, when it is transported to a machine tool not shown in the figure. Alternatively, the object 4 can be arranged on an object that can move linearly. The object 4 can be made of metal, for example, aluminum, copper, iron, steel, in particular chrome steel. In addition, the object 4 can be magnetized, for example, by a magnetic clamping mechanism that can move together with the object 4, in particular a magnetic chuck or a magnetic clamping plate, which holds the object 4.

[0038] The device 20 is designed according to the type of Ferraris sensor and comprises a plurality of first magnets 1 which are arranged spaced apart from one another along a direction of movement X. The first magnets 1 are designed as permanent magnets. Adjacent first magnets 1 each have opposite polarizations, so that a plurality of external magnetic fields 1a are generated parallel and antiparallel to a field direction Y which is arranged perpendicular to the direction of movement X. A first sensor 3 is arranged between two adjacent first magnetic fields 1, by means of which an internal magnetic field 8 is detected, which is generated by eddy currents 6 induced in the object 4. The internal magnetic field 8 is measured by the sensor 3 along a measuring axis 5 in Figure 1 and extends parallel to the field direction Y.

[0039] In order to be able to determine the speed or acceleration of the object 4 with increased reliability, the device 20 additionally has a second magnet 1b and a second sensor 3a. According to this embodiment, the second magnet 1b is designed as a permanent magnet. The second magnet 1b is arranged together with the first magnet 1 on a common magnet axis 12, which extends along an arrangement direction Z, which is arranged perpendicular to the field direction Y and perpendicular to the direction of movement X. In addition, the first magnet 1 and the second magnet 1b, which are arranged on the same magnet axis 12, are polarized oppositely. The second magnet 1b therefore also generates an external magnetic field 8 perpendicular to the direction of movement X, wherein it is respectively antiparallel to the external magnetic field of the corresponding first magnet 1 arranged on the same magnet axis 12. The second sensor 3a is arranged together with the first sensor 3 on a common sensor axis 9, which extends parallel to the magnet axis 12. The measuring axis of the second sensor 3a extends parallel to the measuring axis 5 of the first sensor 3, so that the internal magnetic field 8 caused by the eddy currents 6 in the object 4 can also be detected by the second sensor 3a. The magnet axis 12 extends parallel to an arrangement direction Z which is arranged perpendicular to the movement direction X and perpendicular to the field direction Y.

[0040] Another component of the device 20 is an evaluation device 11 for determining the velocity or acceleration of the object 4 from the internal magnetic field 8 detected by the first sensor 3 and the second sensor 3a. Figure 2 The evaluation device 11 schematically shown in FIG. Figure 2 The signal lines (not shown) are connected to the first sensor 3 and the second sensor 3a. In this regard, the measurement signals of the first and second sensors 3, 3a are provided to the evaluation device 11 for processing. In this regard, the sensors 3, 3a each detect a measurement signal which is proportional to the magnetic flux density of the measured magnetic field, i.e., for example, in the case of the configuration as Hall sensors 3, 3a, the evaluation device 11 can determine the speed of the moving object 4. As long as, for example, when the sensors 3, 3a are configured as measuring coils, the sensors 3, 3a each detect a measurement signal which is proportional to the change in the speed of the moving object, the evaluation device 11 can determine the acceleration of the moving object 4.

[0041] In the device 20 , the first and second magnets 1 , 1 a and the first and second sensors 3 , 3 a are arranged on a common scanning head 2 . Alternatively, the evaluation device 11 can also be designed as part of the scanning head 2 .

[0042] exist Figure 3 and 4The figure in FIG. 1 shows a second embodiment of the system according to the invention, which has an electrically conductive object 4c and a device 20 for determining the speed or acceleration of the object 4c along a predetermined direction of movement X. In contrast to the first embodiment, the object 4c is rotatably mounted, for example in a rotatable chuck, in particular a magnetic chuck. The device 20 comprises a scanning head 2, which is coupled to a scanning device according to Figure 1 and 2 The scanning head 2 has, in contrast, exactly one first sensor 3 and a second sensor 3a, which are arranged on a common sensor axis 9. Furthermore, the scanning head 2 comprises exactly two first magnets 1 of opposite polarity and exactly two second magnets 1b of opposite polarity. The direction of movement X runs tangentially to the direction of rotation of the object 4c in the region of the measuring axis 5 of the first sensor 3. The first sensor 3 and the second sensor 3a are arranged along the direction of movement X between the first and second magnets 1, 1b.

[0043] In addition, refer to Figure 1 and 2 An implementation scheme of the first embodiment is shown in FIG.

[0044] exist Figure 5 2 shows a variant of the second embodiment, in which the device 20 has two scanning strips 10, 10a, which are assembled to form a scanning head. The first scanning strip 10 comprises a first magnet 1 and a first sensor 3. The second scanning strip 10a comprises a second magnet 1b and a second sensor 3a. The scanning strips 10, 10a are arranged parallel to each other and extend in the direction of movement X of the object to be detected.

[0045] Figure 6 A schematic diagram of an evaluation device 11 is shown, which can be used in the above-mentioned device 20. The evaluation device 11 is fed with measurement signals of one or more first sensors 3 and one or more second sensors 3a. The measurement signals can be measurement signals which are proportional to the speed of the object 4, 4c or proportional to the acceleration of the object 4, 4c. The evaluation device 11 is configured to receive a first measurement signal of the first sensor 3 and a second measurement signal of the second sensor 3a and to form a difference between the first measurement signal and the second measurement signal. The influence of external magnetic fields on the result is eliminated by the difference calculation and an output signal W is obtained, which corresponds to twice the magnitude of the measurement signal and is only related to the speed of the object.

[0046] The above-mentioned system has a device 20 for determining the speed or acceleration of an electrically conductive object 4, 4c along a predetermined direction of movement X, the device comprising a first magnet 1 for generating an external magnetic field 1a perpendicular to the direction of movement X and at least one first sensor 3 for detecting an internal magnetic field 8 caused by eddy currents 6 in the object 4, 4c, wherein a measuring axis 5 of the first sensor 3 extends perpendicular to the direction of movement X and the first magnet 1 and the first sensor 3 are arranged spaced apart from each other along the direction of movement X. Other components of the device are: at least one second magnet 1b for generating an external magnetic field 1a perpendicular to the direction of movement X, the second magnet being arranged together with the first magnet 1 on a common magnet axis 12, the magnet axis being arranged perpendicular to the measuring axis 5 and perpendicular to the direction of movement X, the first magnet 1 and the second magnet 1b being polarized in opposite directions; and at least one second sensor 3a for detecting an internal magnetic field 8 caused by eddy currents 6 in the object 4, 4c, the second sensor being arranged together with the first sensor 1 on a common sensor axis 9 parallel to the magnet axis 12, wherein a measuring axis 5' of the second sensor 3a is arranged parallel to the measuring axis 5 of the first sensor 3. Furthermore, the device 20 comprises an evaluation device 11 for determining the velocity or acceleration of the object 4 , 4 c from the internal magnetic field detected by the first sensor 3 and the second sensor 3 a .

[0047] Description of Reference Numerals

[0048] 1 Magnet

[0049] 1a External magnetic field

[0050] 1b Magnet

[0051] 2 Scanning head

[0052] 3 Sensors

[0053] 3a Sensor

[0054] 4 Objects

[0055] 4c Object

[0056] 5,5' measuring axis

[0057] 6 Eddy Current

[0058] 7. Arrange the axis

[0059] 8 Internal magnetic field

[0060] 9 Sensor axis

[0061] 10 Scan Bar

[0062] 10a Scanning bar

[0063] 11 Evaluation Units

[0064] 12 Magnet axis

[0065] W Output signal

[0066] X direction of movement

[0067] Y field direction

[0068] Z layout direction.

Claims

1. A device (20) for determining the speed or acceleration of an electrically conductive object (4, 4c) along a predetermined direction of movement (X), - having at least two first magnets (1) for respectively generating an external magnetic field (1a) perpendicular to the direction of movement (X), and - having at least one first sensor (3) for detecting an internal magnetic field (8) caused by eddy currents (6) in the object (4, 4c), wherein a measuring axis (5) of the first sensor (3) extends perpendicularly to the direction of movement (X), and the at least two first magnets (1) and the at least one first sensor (3) are arranged spaced apart from one another along the direction of movement (X), wherein each first sensor (3) is arranged between two first magnets (1), - having at least two second magnets (1b) for respectively generating an external magnetic field (1a) perpendicular to the direction of movement (X), the at least two second magnets being respectively arranged on a common magnet axis (12) with one of the at least two first magnets (1), the magnet axis being arranged perpendicular to the measuring axis (5) and perpendicular to the direction of movement (X), and wherein the first magnet (1) and the second magnet (1b) on this common magnet axis (12) are polarized in opposite directions, - having at least one second sensor (3a) for detecting an internal magnetic field (8) caused by eddy currents (6) in the object (4, 4c), the second sensor being arranged together with the first sensor (3) on a common sensor axis (9) parallel to the magnet axis (12), wherein the measuring axis (5') of the second sensor (3a) is arranged parallel to the measuring axis (5) of the first sensor (3), wherein each second sensor (3a) is arranged between two second magnets (1b), and - having an evaluation device (11) for determining the speed or acceleration of the object (4, 4c) based on the internal magnetic field (8) detected by the first sensor (3) and the second sensor (3a), in that the evaluation device (11) is set up to receive a first measurement signal of the first sensor (3) and a second measurement signal of the second sensor (3a) and to form a difference between the first measurement signal and the second measurement signal for determining the speed or acceleration.

2. The device according to claim 1, It is characterized in that The first magnet (1) and / or the second magnet (1b) are configured as permanent magnets or electromagnets.

3. The device according to claim 1 or 2, It is characterized in that The at least one first sensor (3) and / or the at least one second sensor (3a) is a Hall sensor or a measuring coil.

4. The device according to claim 1 or 2, It is characterized in that A plurality of first magnets (1) and a plurality of first sensors (3) are arranged alternately and spaced apart from each other along the movement direction (X), and a plurality of second magnets (1b) and a plurality of second sensors (3a) are arranged alternately and spaced apart from each other along the movement direction (X).

5. The device according to claim 1 or 2, It is characterized in that The at least two first magnets (1), the at least one first sensor (3), the at least two second magnets (1b) and the at least one second sensor (3a) are arranged on a common scanning head (2).

6. A system having an electrically conductive object (4, 4c) and a device according to any one of claims 1 to 5 for determining a speed or an acceleration of the electrically conductive object (4, 4c) along a predetermined direction of movement (X).

7. The system according to claim 6, It is characterized in that The object (4, 4c) is magnetized.

8. A method for determining the speed or acceleration of an electrically conductive object (4, 4c) along a predetermined direction of movement (X) by means of a device according to any one of claims 1 to 5, wherein - generating an external magnetic field (1a) perpendicular to the direction of movement (X) by means of at least two first magnets (1), respectively, and - detecting an internal magnetic field (8) caused by eddy currents in the object by means of at least one first sensor (3), and - generating an external magnetic field (1a) perpendicular to the direction of movement (X) by means of at least two second magnets (1b), respectively, and - detecting an internal magnetic field (8) caused by eddy currents in the object (4, 4c) in a field direction (Y) by means of at least one second sensor (3a), and The speed or acceleration of the object (4, 4c) is determined by means of an evaluation device based on an internal magnetic field (8) detected by the first sensor (3) and the second sensor (3a), in that a first measurement signal of the first sensor (3) and a second measurement signal of the second sensor (3a) are received by means of the evaluation device and a difference between the first measurement signal and the second measurement signal is formed for determining the speed or acceleration, wherein the determined speed or acceleration is independent of the distance and / or premagnetization of the object (4, 4c).

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