Patent Application
20100019581
This applications claims priority from German patent application serial no. 10 2008 040 668.6 filed Jul. 24, 2008.
The invention concerns a method for controlling an electromagnet.
In the context of the present invention, an electromagnet to be controlled comprises a yoke and an armature, with an induction coil associated with the yoke in order to induce a magnetic flux in the electromagnet. By virtue of the magnetic flux, a magnetic force can be exerted on the armature of the electromagnet, for example so as to attract the armature more strongly or less so and thereby establish a relative position between the armature and the yoke. In practice, the procedure for controlling an electromagnet of this type is that with the help of a separate sensor, for example a Hall sensor or a measurement coil, an actual value of the magnetic flux through the electromagnet is determined. This actual value determined with the help of the separate sensor is compared with a nominal value, and if a difference is found between the actual and the nominal values, the electromagnet is adjusted on the basis of the difference so as to bring the actual value closer to the nominal value. The use of separate sensors, however, add complexity and is expensive. A method for controlling an electromagnet is therefore needed, which does not require additional sensors.
Starting from that situation, the present invention addresses the problem of providing a new type of method for controlling an electromagnet.
According to a first aspect of the invention, this problem is solved by a method for regulating the magnetic flux through an electromagnet. In this case, from an electric voltage applied to an induction coil and determined by an appropriate measurement method, and from an electric current flowing through the induction coil and also determined by an appropriate measurement method, an actual value of the magnetic flux is calculated, the actual value so determined is compared with a predetermined nominal value, and as a function of the difference between the actual and nominal values, the voltage applied to the induction coil and/or the electric current flowing through the induction coil is/are adapted so as to bring the actual value of the magnetic flux closer to its nominal value.
According to a second aspect of the invention, the problem is solved by a method for regulating the magnetic force of an electromagnet. In this case, from an electric voltage applied to an induction coil and determined by an appropriate measurement method, and from an electric current flowing through the induction coil and also determined by an appropriate measurement method, an actual value of the magnetic force is calculated, the actual value so determined is compared with a predetermined nominal value, and as a function of the difference between the actual and nominal values, the voltage applied to the induction coil and/or the electric current flowing through the induction coil is/are adapted so as to bring the actual value of the magnetic force closer to its nominal value.
According to a third aspect of the invention, the problem is solved by a method for regulating the relative position between the yoke and the armature of the electromagnet. In this case, from an electric voltage applied to an induction coil and determined by an appropriate measurement method, and from an electric current flowing through the induction coil and also determined by an appropriate measurement method, an actual value of the relative position calculated, the actual value so determined is compared with a predetermined nominal value, and as a function of the difference between the said actual and nominal values, the voltage applied to the induction coil and/or the electric current flowing through the induction coil is/are adapted so as to bring the actual value of the relative position closer to its nominal value.
In all the methods according to the invention, the electromagnet is regulated without the use of additional sensors. By measuring the current flowing through the induction coil and the voltage applied to the induction coil, an actual value of the magnetic flux and/or of the magnetic force and/or of the relative position between the yoke and the armature of the electromagnet can be determined. Since the determination of this actual value does not involve the use of additional sensors, complexity and costs can be reduced. Furthermore, the number of possible sources of error is reduced.
Preferred further developments of the invention emerge from the subordinate claims and the description presented below. Example embodiments of the invention, to which it is not limited, are explained in greater detail with reference to the drawing, which shows:
The invention concerns a method for controlling an electromagnet, such that as shown in
Since the induction coil 12 is carrying an electric current i, a magnetic flux φ is induced in the electromagnet, namely in its yoke 10, due to which a magnetic force F can be exerted on the armature 11 in order to establish a relative position between the yoke 10 and armature 11.
To control such an electromagnet, in the sense of the present invention it is proposed that from the electric voltage U and from the electric current i flowing through the induction coil and also determined by an appropriate measurement method, an actual value of the magnetic flux is calculated. In this case the magnetic flux is calculated in accordance with the following equation:
where φ is the magnetic flux, U is the electric voltage applied to the induction coil and determined by an appropriate measurement method, i is the electric current flowing through the induction coil and also determined by an appropriate measurement method, R is the predetermined electrical resistance of the electromagnet, and w is the predetermined number of turns of the induction coil.
The actual value of the magnetic flux determined from the above equation is then compared with a specified nominal value, and as a function of the difference between the actual and nominal values the voltage U applied across the induction coil, and hence the electric current i flowing through the induction coil are adapted in such manner that the actual value of the magnetic flux approaches its nominal value.
From the above, computationally determined actual value of the magnetic flux, the magnetic force acting on the armature 11 can be calculated using the following equation:
where F is the magnetic force, μ0 is the specified permeability of vacuum, and A is the predetermined active attraction force area of the electromagnet.
From the above formula, in addition or alternatively to the actual value of the magnetic flux an actual value for the magnetic force can be calculated, so as then to compare the actual magnetic force value with a corresponding, specified nominal value and, as a function of a difference between the actual and nominal values, to adapt the voltage U applied across the induction coil 12, and hence the electric current i flowing through the induction coil in such manner that the actual value of the magnetic force approaches its nominal value.
According to an advantageous further development, from the actual value of the magnetic flux or from the actual value of the magnetic force an actual value of a relative position between the yoke 10 and the armature 11 of the electromagnet can be calculated. For this, the actual value of the relative position as a function of the actual value of the magnetic flux or of the magnetic force is determined from a characteristic performance curve of the electromagnet. The actual value so determined is then again compared with a corresponding nominal value, and as a function of the difference between the actual and nominal values the voltage U applied across the induction coil 12, and hence the electric current i flowing through the induction coil are adapted in such manner that the actual value of the relative position approaches its nominal value.
With the method according to the invention, various control parameters of an electromagnet can accordingly be adjusted, namely the magnetic flux and/or the magnetic force and/or the relative position between the yoke and the armature of the electromagnet.
The method according to the invention can be applied without any additional sensors, and thus allows an electromagnet to be controlled in a simple and inexpensive manner.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2008 040 668.6 | Jul 2008 | DE | national |
