Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
1998-12-23
2001-03-13
Strecker, Gerard (Department: 2856)
Electricity: measuring and testing
Magnetic
Displacement
C324S207250, C073S862331
Reexamination Certificate
active
06201389
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention has to do with a device for determining the position and/or torsion of rotating shafts.
A rotary angle sensor for determining the position of rotating shafts is known from the international patent publication No. WO 92/107,22. A bipolar-radially magnetized annular magnet is placed on the shaft, which is enclosed by a stator. Two oppositely-placed air gaps are built into the stator. A Hall element is placed in one of the air gaps.
If the annular magnet rotates in the stator, the Hall element records only one Hall voltage curve in dependence on the position angle, which curve runs similar to a sine wave. If the shaft turns by 360°, it is thus only possible to measure in the linear area of a quadrant, or only from 0° to 90°. The rounded and flattened parts of the Hall voltage curve are unsuited for measurement purposes. In fact, if the linear area in the first quadrant from 0° to 90° is followed by another in the third quadrant from 180 to 270°, then this, by reason of the intermediate rounded and offset parts, cannot be used for measurement of a position within a full turn.
A rotary angle sensor is known from the international patent publication No. WO 95 14 911 A1. It consists of a stationary and a rotating component. The stationary component has two crescent-shaped stator component elements, which are arrayed to be opposite while retaining a spacer recess. The rotating component is an annular magnetic element which is retained by a magnet mounting unit, which is connected to a shaft.
The disadvantage is that only one Hall element is placed in the spacer recess. This makes it possible to determine only one shaft setting between 0° and 90°.
A measuring device for determining torsion of a rotating shaft is known from the German patent No. DE 42 31 646 A1. However, here two annular bodies are placed onto the shaft. The bodies are kept on the shaft by intermediate rings and equipped with teeth, between which there are gaps. By means of a plastic ring, an additional body with teeth is attached, so that an air gap results. An annular yoke is placed about the body, so that four coils are embedded in annular fashion. Projections form an additional air gap. A source of alternating current is applied to the coils, and thus an alternating magnetic field is induced. Torsion in the shaft causes a displacement of the two measuring units from each other. The resulting change of voltage in the pickup coils is therefore a measurable value.
A device to measure torsion and/or relative angular movement is described in the German patent No. DE 42 32 993 A1. In it, on one side of a first coil arrangement, a first and second annular element, shaped like pineapple or orange slices, are placed at different widths and at equal intervals. On one of the lateral surfaces of a second coil arrangement, third, fourth and fifth similarly-shaped annular segments are attached. This device measures two straight-running curves whose output signals are 0 in the crossing point, which corresponds to a torsion or angular motion.
Finally, an arrangement for determining torsion, torsion moment and/or rotary angle of at least two shafts that are connected with each other is known from the German patent No. DE 42 32 994 A1. In this patent, in the area where the two shafts are connected, there are two coil devices, which retain an air gap. The device operates according to the transformer principle. However, it only detects voltages that occur with a change in rotary angle and are dependent with that change in rotary angle.
SUMMARY OF THE INVENTION
Proceeding from a rotary angle sensor with a Hall IC element of the type known from the international patent publication No. WO 92/10772 A1, the objective of the invention is to improve the measurement options, particularly in the entire angular range from 0° to 360°. Additionally, the torsion of at least one of the rotating shafts should be able to be determined.
These objects, as well as other objects which will become apparent from the discussion that follows, are achieved, in a device for determining the position and/or torsion of a rotating shaft according to the invention by providing at least one radial-bipolar annular magnet element connected with the shaft and at least one stator element, made of a magnetoconductive material, surrounding the annular magnet element. At least three air gaps are located in the stator element, displaced one from the other at an equal angle (5). Two Hall IC elements, each of which is disposed in two adjacent air gaps, are connected to an evaluation unit which detects a Hall IC voltage curve, assigns a flux-voltage value to a position angle on the Hall IC voltage curves and calculates the de facto position angle and produces an output signal representing the position angle.
The advantages achieved with the invention are particular in that two Hall IC voltage curves are measured. Using this rotary angle sensor, it is possible to record positions of the shaft between 0° and 360°. Thus, the measurement options are multiplied by comparison with known rotary angle sensors.
Two rotary angle sensors of the type described above, according to the invention, can be placed next to each other on the shaft, thus forming a torsion sensor.
This torsion sensor is thus characterized by the following features:
a first and a second bipolar-radial annular magnet element is placed on at least one shaft,
each annular magnet is surrounded by a stator element, in which at least three air gaps are situated, displaced by the same angle, and
a Hall IC element is placed in each of the neighboring air gaps of each stator element.
The fact that two rotary angle sensors are placed on one shaft allows not only the position of the rotating shaft, but also its torsion to be determined. The torsion, or a torque moment generated, is determined by the varying current -voltage values within the Hall IC voltage curves, and issued as output. Placing two rotary angle sensors on one shaft also has the advantage that if one sensor fails, the second continues to operate precisely. Additionally, the two sensors can be used to mutually check each other's functions.
The two Hall IC elements that are placed in a stator element can be connected to an evaluation unit which
records a measured Hall IC voltage curve from each Hall IC element,
assigns each recorded current-voltage value to a position angle on the Hall IC voltage curves, and
from the position angles assigned to the current-voltage value, calculates the actual position angle, and issues it as an output signal.
Accordingly, the evaluation unit that operates in this way makes it possible to use one Hall IC voltage curve as the measurement curve and the second Hall IC voltage curve as a decision curve. Additionally, this evaluation unit makes it possible alternately to switch to the linear portions of each of the Hall IC voltage curves, so that between 0° and 360°, operations can always be conducted in a straight-running curve area. By this means, it is possible to achieve not merely a 360° measurement, but a 360° measurement with very high precision. The evaluation unit can be configured as a microcomputer or a user-computer switching circuit, also called a UCSC. It should have at least a computer (central processing unit) which is linked with a memory unit. On the input side of the computer, two analog-to-digital converters are placed which are parallel to each other. On the output side, an analog or a digital output signal appears. The analog signal can be given by a digital-to-analog converter, which is connected with the computer on the output side. If a CAN-BUS interface is connected with the computer, the digital output signal appears. In each case, one of the Hall IC elements is connected with one of the two analog-to-digital converters. The output signal appears at the digital-to-analog converter. In place of a digital computer, an analog computer can be provided, which is then able to be linked only with the memory unit. The computer permits the values determined to be evaluate
Apel Peter
Wilczek Klaus
AB Eletronik GmbH
Milde Hoffberg & Macklin, LLP
Strecker Gerard
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