Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
1999-05-14
2002-09-10
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207250, C324S207240
Reexamination Certificate
active
06448760
ABSTRACT:
BACKGROUND
The invention concerns arrangements for detecting a rotational or translatory movement.
Arrangements are known in which the rotational speed and the rotational direction of a rotary drive are determined by means of two Hall sensors offset from each other by 90°. For these arrangements, a N-S magnetized annular magnet is disposed concentric to the drive axis and nonrotatably connected thereto. During rotation of the annular magnet, the two Hall sensors disposed laterally to the annular magnet are each penetrated by a variable magnetic field. The magnetic field changes appearing on the sensors are converted by means of threshold value switches into two binary pulse sequences offset from each other by 90°. By counting the number of pulses per time unit, the rotational speed of the rotary drive can be determined; and by comparison of the two pulse sequences, the direction of rotation can also be determined.
Disadvantageously, two sensors are necessary in these arrangements for detection of the rotational speed and rotational direction. Because of the need for exact positioning of the two sensors relative to each other and relative to the axis of rotation, expensive construction is associated therewith. Cost-intensive bonding and connection of the two Hall sensors are also necessary.
From DE 42 33 549 Al, a device for detection of the rotational speed and the rotational direction of a rotary drive is known, which has a magnetic signal-generating element nonrotatably connected with the rotary drive. During rotation of the signal-generating element, a rotational direction encoded magnetic field, which is detected by a sensor and fed to an electric evaluation unit, is created. Since during rotation of the signal-generating element, a rotational direction encoded magnetic field is created, only one sensor is necessary for detection of the direction of rotation. Encoding of the direction of rotation occurs, for example, by means of an eccentric rotation of an annular magnet around the axis of the rotary drive or by encoding the magnetic field of the annular magnet.
Disadvantageous in the known device is the fact that encoding of the magnetic field is essential for detection of the direction of rotation. Simple to produce, inexpensive symmetrical annular magnets in concentric arrangement can, consequently, not be used.
From DE 44 23 461 Al, a volumeter for determination of the flow volume of a liquid through a volumeter body is known, wherein a magnet wheel is disposed nonrotatably on a screw rod with which a sensor arrangement with one sensor is associated. During rotation of the magnetic pole shoes of the magnetic wheel, an asymmetric magnetic field which enables detection of the direction of rotation develops on the sensor. With this device, a rotational direction encoded magnetic field is likewise generated.
DE 35 43 603 A1 describes a position detector with a ferromagnetic magnetoresistor unit, which is disposed at an angle relative to a multipolar annular magnet. A sensor to detect the magnetic leakage field of the annular magnet is disposed on the magnetoresistor unit. Because of the inclination of the magnetoresistor unit, the sensor is likewise disposed at an angle; however, it is not described that rotation direction-dependent signals are in any way evaluated.
From DE 41 25 482 A1, a synchro system with an annular magnet and two magnetic field sensor elements disposed offset relative to each other in the circumferential direction of the axis of rotation on a common sensor carrier is known. The two sensor elements are attached with an arrangement of their measurement axes parallel to each other on a mounting surface, which runs obliquely inclined relative to the axis of rotation of the magnetic element.
DE 41 13 880 A1 describes the realization of a fixed predetermined phase angle distance between measurement signals which are shifted by 90° relative to each other. For this, two Hall elements are fixedly mounted on a one-piece sensor carrier, and, in fact, on two mounting surfaces disposed at an angle relative to each other.
From EP 151 002 A2, an arrangement is known whereby the magnetic field generating part is located on the sensor element. A tipping of the sensor element takes place in order to adjust a specific magnetic field on the sensor favorable for measurement, but not for detection of a rotation direction-dependent signal.
The prior art is thus characterized by the fact that for detection of the direction of rotation either two sensors are used or encoding of the magnetic field occurs.
It is further known, for the determination of the speed of a translatory movement between two parts of an aggregate, to provide one aggregate part with a symmetrical magnet extending longitudinally and the other aggregate part with a Hall sensor such that upon relative movement of the aggregate parts, the Hall sensor moves parallel to the magnet and thus the magnetic field lines of the magnet pass through the Hall sensor. Disadvantageously, in such an arrangement it is impossible to also determine the direction of movement between the parts of the aggregate.
SUMMARY OF THE INVENTION
The object of the invention is to provide a simple arrangement for the detection of a rotational or translatory movement between a symmetrically structured magnet and a magnetic sensor element, whereby changes in the magnet's field strength act on the sensor element, for example, a Hall element. The arrangement should ensure reliable detection of rotational or translatory movement with only one sensor element, whereby a reversal of movement should be detectable within one signal period.
The solution according to the invention enables direction encoding with only one sensor element by means of a special alignment of an analog, magnet-sensitive sensor element. The solution according to the invention provides an intentional tipping or shifting of the sensor element in contrast to a transverse orientation of the sensor element relative to the signal-generating element. Thus, altered signals with additional informational value are created, which are used for the reliable detection of the rotational or translatory movement. The sensor element generates signal pulses which have a rising or falling signal waveform between their edges depending on the direction of movement. Upon reversal of the direction of movement, the sign of the signal waveform changes. Thus, a reversal of the direction, in particular, can be evaluated with high accuracy.
Transverse orientation of the sensor element is understood to mean an orientation in which the normal vector of the sensitive surface of the sensor element is perpendicular to the axis of the signal-generating element. A transverse orientation of the sensor element relative to the signal-generating element or its axis is used in all arrangements known in the prior art for detection of a translatory or rotational movement, since in this orientation the active component of the magnetic field and, accordingly, the signal generated, is the greatest. The signal associated with a transverse alignment of the sensor element is, however, not only maximal, but also symmetrical, such that no directional data are included in the signal.
In contrast, the present invention provides that the normal vector of the sensor element is not perpendicular to the axis of the signal-generating element. Thus, with a relative movement between the signal-generating element and the sensor element there is a rise or fall of the magnetic field measured, depending on the direction of movement, and on the strength of the respective transverse component of the vector of the magnetic field applied to the sensor element.
The solution according to the invention enables, in particular, an exact determination of a reversal of direction, since a symmetric signal develops only with a reversal of direction. Because of the deviation of the sensor element from the transverse position, the signal generated during right-hand rotation or left-hand rotation is not symmetric, but rises or falls. This rising or
Juerjens Gerhard
Neumann Jürgen
Brose Fahrzeugteile GmbH & Co. KG Coburg
Christie Parker & Hale LLP
Patidar Jay
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