Method and arrangement for determining the armature position of an electromagnet

Abstract

The present invention relates to a method and an arrangement for determining the armature (1) position of an electromagnet. In the method the potential differences in the yoke (2) or in the armature (1), generated by a non-homogeneous eddy current distribution in the event of a deflection of the armature (1), are detected to determine the instantaneous armature (1) position relative to a reference position from these potential differences. For this purpose at least one voltage difference is measured between two measuring points on the yoke (2) or armature (1), or between one measuring point on the yoke (2) or armature (1) and a reference potential. The armature (1) position relative to a reference position on the electromagnet is then determined from this voltage difference. The method can be performed cost effectively, and can also easily be applied to existing electromagnets.

Claims

1. A method for determining an armature position of an electromagnet, the method comprising: measuring at least one voltage difference, on a yoke of the electromagnet or on an armature, between two measuring points on the yoke or armature, or between one measuring point on the yoke or armature and a reference potential, via which potential differences in the yoke or armature caused by a deflection of the armature from a null position can be detected, and determining the armature position relative to a reference position on the electromagnet from the measured voltage difference.

2. The method in accordance with claim 1, further comprising: determining the armature position on the basis of a calibration curve or calibration table that has previously been created for the electromagnet.

3. The method in accordance with claim 1, further comprising: determining the armature position on the basis of a dependence, derived from the induction law, of the magnitude of the voltage difference on the armature position relative to the reference position.

4. The method in accordance with claim 1, further comprising: selecting the two measuring points on the yoke or armature, between which the voltage difference is measured, such that they are as far apart from one another as possible.

5. The method in accordance with claim 1, further comprising: measuring a plurality of voltage differences between different measuring points on the yoke or armature in order to determine the armature position.

6. The method in accordance with claim 5, further comprising: measuring at least two voltage differences in each case between the measuring points, which in each case are located on axes that are perpendicular to one another.

7. The method in accordance with claim 1, further comprising: arranging the at least two measuring points on the yoke or armature, between which the voltage difference is measured, asymmetrically on the yoke or armature.

8. The method in accordance with claim 1, further comprising: measuring in addition a coil current of the electromagnet via a measuring shunt, and evaluating the coil current so as to determine positions of the armature that do not cause any potential differences in the yoke.

9. The method in accordance with claim 1, further comprising: measuring the at least one voltage difference via at least one electrical pick-up on the yoke or armature.

10. An arrangement system with an electromagnet, the arrangement system comprising: at least one coil, a yoke, and an armature, which can move relative to the yoke; at least one electrical pick-up attached to the yoke or the armature for measuring a voltage difference between two measuring points, or between one measuring point and a reference potential, via which pick-up electrical contact is made at the measuring points with the yoke or armature; a measuring device connected to the at least one electrical pick-up for measuring the voltage difference; and an evaluation device configured to determine and output an armature position relative to a reference position on the electromagnet based on the measured voltage difference.

11. The arrangement system in accordance with claim 10, further comprising: a plurality of electrical pick-ups for purposes of measuring a plurality of voltage differences are attached to the yoke or the armature, and are in each case connected to the measuring device for measuring the voltage difference, wherein the evaluation device is designed such that it determines and outputs the armature position relative to the reference position from the measured voltage differences.

12. The arrangement system in accordance with claim 11, further comprising: at least two of the electrical pick-ups are attached to the yoke or on the armature such that their measuring points lie on axes at right angles to one another.

13. The arrangement system in accordance with claim 10, wherein the arrangement system has a further measuring device measuring a coil current of the electromagnet, and the evaluation device evaluates the measured coil current for determining positions of the armature that do not cause potential differences on the yoke or armature.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The proposed method and the associated arrangement are explained in more detail in what follows, using two examples of embodiment in conjunction with the figures. Here:

(2) FIG. 1 shows an example of the proposed arrangement with a rotationally symmetric electromagnet, with the armature in the idle position;

(3) FIG. 2 shows the arrangement as in FIG. 1, with the armature in a deflected state;

(4) FIG. 3 shows another example of the proposed arrangement in cross-section, with an electromagnet with a plunger armature;

(5) FIG. 4 shows the arrangement of FIG. 3 in a view from below; and

(6) FIG. 5 shows an example of the measuring and evaluation device of the proposed arrangement.

PATHS TO EMBODIMENT OF THE INVENTION

(7) The proposed method and the associated arrangement are explained once again in conjunction with FIGS. 1 and 2, on the basis of an example of a rotationally symmetrical electromagnet. Here FIG. 1 shows a plan view of the electromagnet 1 in the upper part of the figure, in which the resting armature 1 can be seen. The yoke 2 located under the armature, and the coil 3, are also indicated in this part of the figure. In the lower part of FIG. 1, the said electromagnet is again shown, this time in cross-section, wherein the direction of the magnetic field H.sub.ind generated by the current flowing through coil 3 is also indicated by the circulating arrows. In FIG. 1, the armature 1 is in the idle state in which the magnetic circuit is closed by the armature. There is therefore no displacement of the armature relative to the yoke 2, the armature 1 is located in a null setting or null position. In this state, a homogeneous distribution of the eddy currents in the yoke 2 can be assumed.

(8) In this example, two voltage differences u.sub.y and u.sub.x are measured, in each case between two measuring points on the yoke 2. In this example, the axes of the two measuring points in each case are at right angles to one another, in one case parallel to the x-axis, and in the other case parallel to the y-axis, as shown in FIG. 1. The evaluation device is not shown in either this figure or the following FIGS. 2 to 4.

(9) The voltage difference u.sub.x and the voltage difference u.sub.y are both zero in the case of the homogeneous distribution of the eddy currents in the yoke, since there is no potential difference present. If the armature 1 is now displaced from the null position by Δx and/or Δy, as shown in FIG. 2, this results in a non-homogeneous distribution of the eddy currents and thus in a potential difference in the yoke 2. The voltage differences u.sub.x or u.sub.y are no longer equal to zero. By evaluating the amplitudes of these voltage differences, the precise armature position 1 relative to the yoke 2 in the x and y directions can then be determined.

(10) With this electromagnet, a displacement in the z-direction can only be detected by measuring the voltage differences if there is at the same time a displacement in the x-direction, in the y-direction, or in the x- and y-directions. Such a displacement in the z-direction has the same effect on the amplitude of u.sub.x and u.sub.y.

(11) If, however, a displacement occurs solely in the z-direction, this cannot be detected via the voltage differences u.sub.x and u.sub.y. If the displacement is solely in the z-direction, the distribution of the eddy currents remains homogeneous. There are a number of possible options for determining a displacement of the armature in the z-direction alone. One possibility is to undertake additionally an evaluation of the coil current by way of a measuring shunt, as is of known prior art. Another possibility consists in making a number of asymmetrical electrical contacts on the circumference of the yoke, which enables the detection of the armature in the z-direction. The possibility of detecting the armature position in the z-direction also exists by making electrical contacts on the armature in a skilled manner.

(12) The measurement and evaluation for both variants, that is to say, based solely on the voltage differences, or in combination with the detection of the coil current, can be carried out with equipment that is of known prior art. To this end FIG. 5 shows an example of a measurement and evaluation circuit. The power supply 4 generates a time-varying current and/or voltage, which is fed into the coil of the electromagnet 5. The voltage differences u.sub.x, u.sub.y and u.sub.z are converted into signals u′.sub.x, u′.sub.y and u′.sub.z by differential amplifiers 6. Here the voltage differences u.sub.x and u.sub.y between the electrical pick-ups on the yoke of the electromagnet 5 are measured, the voltage difference u.sub.z results from the measurement of the coil current via a measuring shunt (R.sub.meas). The signals u′.sub.x, u′.sub.y and u′.sub.z are then processed by analogue-to-digital converters 7 and forwarded to a microprocessor 8. The microprocessor 8 evaluates the signals, and transmits the result to an I/O-interface 9 to output the armature position determined.

(13) FIG. 3 shows an example of a further design of the proposed arrangement, with an electromagnet that has a plunger armature. On the left-hand side of FIG. 3 can be seen the yoke 2 with the coil 3, in which is arranged the plunger 1. The detection of the armature position in the z-direction takes place by measuring the voltage difference u.sub.z at the two measuring points indicated on the left-hand side of the figure. An armature tilt is measured by measuring u.sub.x and u.sub.y between the measuring points indicated on the right-hand side of FIG. 3, In this part of the figure, only one of the two pairs of measuring points can be discerned, since the second pair of measuring points lies in the plane at right angles to the plane of the figure. This can be seen in FIG. 4, which shows the said arrangement once again in a view from below. By means of an asymmetrical arrangement of the measuring points for the measurement of u.sub.x or u.sub.y, in which, for example, the two measuring points for the measurement of the voltage difference on the right-hand side of FIG. 3 are not at the same axial height, the armature position in the z-direction can also be determined by measuring the voltage difference.

REFERENCE LIST

(14) 1 Yoke 2 Armature 3 Call 4 Power supply 5 Electromagnet 6 Differential amplifier 7 Analogue-digital converter 8 Microprocessor 9 I/O-interface