Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1998-11-25
2001-04-03
Tamai, Karl E. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S156030, C324S207200
Reexamination Certificate
active
06211588
ABSTRACT:
FIELD OF THE INVENTION
The present invention refers to a brushless electromotor comprising a rotor having a permanently magnetized propulsion magnetization zone with at least one pair of magnetic poles, and a stationary coil assembly with at least one stator coil, said rotor being rotationally movable by the magnetic fields of said stator coils.
BACKGROUND OF THE INVENTION
Brushless D.C. motors essentially comprise a rotor in the form of a multipolar permanent magnet. The rotor is rotated by electronic commutation of the current in the stator coils. For this control of the current in the stator coils it is necessary to determine the position of the rotor as precisely as possible: the more precisely the position of the rotor is known, the more precisely the total field of the stator coils may be adjusted for a smooth operation resp. the position of the rotor may be regulated e.g. if an actuator is concerned.
A known measuring method of the rotor position is to arrange Hall elements in the area of the rotor, i.e. usually near its circumference, an electric parameter of which varies in function of a magnetic field, e.g. the Hall voltage or the resistance. Unless it is provided with the magnetization for the propulsion of the rotor anyway, the area of the rotor which travels past the Hall elements receives a particular magnetization whose division and position exactly corresponds to the magnetization which serves for the propulsion.
The disadvantage of the known embodiment is that the Hall elements must be adjusted very precisely in order to obtain an optimum commutation of the stator coil current. Since the Hall elements are discrete components, each Hall element generally has to be mounted and adjusted individually. Altogether, this results in a relatively complicated construction, a laborious adjustment and high requirements with respect to the positioning precision.
According to FR-A-2 155 303, the axle e.g. of a motor is provided with a magnet assembly, and a quantitative detection of the rotation of the axle in fractions of turns is effected by means of a magnet sensor which scans the magnet assembly. In one embodiment, the magnet assembly essentially consists of two annular magnets which are disposed at a certain distance from each other and comprise a number of axial magnetizations. The disposition of the two magnets is such that an annular zone with an axial magnetic field of changing polarity is formed in the gap between the magnets while the field lines are almost parallel at the center of the gap. The multiple sensor disposed in this gap responds when a respective threshold of every sensor is exceeded or not attained, whence the position of the magnet assembly is deduced. The construction of the magnet assembly results in relatively high field intensities and sharp transitions between the different magnetization zones. The number of sensors is chosen such that the series of sensors is shorter than a complete magnetization zone.
This disposition requires an additional, special measuring magnet, and on account of the construction size, the overall conception requires magnetic field sensors in the form of discrete components. An integration of the Hall elements on a chip is not mentioned either.
EP-A-0 590 222 describes a linear position detector which comprises a number of Hall elements which are integrated in a semiconductor chip. The two respective adjacent Hall elements are determined between which the magnetic induction generated e.g. by a magnet which is displaceably arranged above the sensor passes through zero. The resolution of this detector corresponds to the distance between two Hall elements. If used for the detection of an arcuate movement, at least the problem of the tangential positioning error remains unsolved, and the increased requirements for a continuous and ungradated detection of the rotational position of the rotor of a D.C. motor for the generation of a continuous stator coil current are not mentioned.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a brushless electromotor comprising a rotational position sensor which allows a more economical overall motor manufacture.
Another object is to design the detection device in such a manner as to allow an increased arithmetic resolution of the rotational position detection.
At least one of the mentioned objects is attained by an electromotor wherein a permanently magnetized measuring magnetization zone is provided on the rotor and a sensor is disposed in the range of the magnetic field of said measuring magnetization zone, said sensor comprising an arrangement of at least five elements which are sensitive to the magnetic field and are integrated on a semiconductor chip in a straight or curved row essentially, and which cover more than one period of the measuring magnetization, so that the position of the rotor can be determined with high precision from the output signal of said field-sensitive elements, which is generated by the action of the magnetic field of the measuring magnetization zone, by numeric correlation of the measuring signals with a predetermined reference curve corresponding to one or several period(s). Further preferred embodiments of such an electromotor are described herein.
In the D.C. motor of the invention, the magnetization zone which serves for the measurement of the rotor positions is disposed very close to the rotational axis of the rotor. Furthermore, this magnetization zone is essentially annular in shape, and its magnetization is preferably parallel to the rotational axis. Thus, the position of the rotor may be detected by a number of Hall elements which are preferably disposed on a circle arc section and which may be integrated in an economical manner on a semiconductor chip due to the small spatial dimension of the measuring magnetization zone. According to presently used chip sizes, the arc length on which the Hall elements used for the measurement are formed is smaller than 5 mm and preferably 3 mm at the most. However, greater arc lengths are not completely excluded, but in the case of an integration on a single chip, this would be increasingly uneconomical.
In order to avoid complicated adjustments particularly in the tangential direction in spite of the small dimensions and the strong curvature of the measuring arrangement, a greater number of Hall elements than necessary for the measurement is generally provided. The tangential displacement can be realized by the selection of a group of Hall elements from the number of available Hall elements. If integrated on a chip, redundant Hall elements can be provided economically as well.
Preferentially, the arcuate line on which the Hall elements are disposed on the chip may have a smaller curvature than the desired measuring line in the measuring magnetization zone. As the measuring magnetization poles become very narrow near the axle, the available magnetic field intensity is also strongly reduced, especially at a distance of the Hall elements resp. of the chip from the measuring magnetization surface in the millimeter range. This again results in increased requirements with respect to the positioning precision, which can be fulfilled by the redundant measuring elements in a surprisingly effective manner, however.
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Patent Abstracts of Japan, vol. 013, No. 383 (E-811), Aug. 24, 1989 & JP 01 133594 A (Secoh Giken. Inc.), May 25, 1989.
Patent Abstracts of Japan, vol. 097, No. 10, Oct. 31, 1997 & JP 09 163706 A (Sharp Corp), Jun. 20, 1997.
Foley & Lardner
Saia-Burgess Electronics AG
Tamai Karl E.
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