Electricity: measuring and testing – Magnetic – Displacement
Patent
1995-09-29
1998-02-24
Strecker, Gerard R.
Electricity: measuring and testing
Magnetic
Displacement
123414, 324103P, 324166, 3242072, 327 62, G01B 730, G01D 514, H03K 512, G01P 344
Patent
active
057214867
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention concerns a method of and a device for determining the position of a rotating shaft. A cogwheel rotates in front of a Hall generator and a magnet at a specific angular speed w. The wheel's cogs produce variations in the magnet's flux density B over time. The Hall generator detects the variations and emits a proportional signal B(t). The instantaneous position of the shaft is calculated from the signal.
A method of this genus is known from the German Patent No. 3,220,896. A sensor measures the variations over time t of a magnetic flux density B produced by a segmented wheel of ferromagnetic sheet rotating in front of a Hall generator. Downstream of the Hall generator is a processor with a component that differentiates a signal B(t) and emits a result B'(t). Result B'(t) is employed only to control a gate that in turn controls a counter. The number of pulses is associated with the length of the segments. The differentiated signal accordingly only controls a gate. Cog shape is not precisely correlated with the resulting curve.
Positioning a differentiating circuit comprising two Hall generators in front of a rotating cogwheel with a permanent magnet is known from the German Patent No. 4,209,212. The cogwheel is specifically segmented to produce phase-shifted signals in the generators. At least two cogs must accordingly be scanned to determine the position of the wheel. The wheel must rotate rapidly. Cog shape is not directly associated with the shape of a curve.
The French Patent No. 2,571,134, finally, describes a device with a cogwheel and a Hall generator within the wheel's range. The magnet's flux density B is measured as the wheel rotates. Although the flux is basically sinusoidal, it has an anomaly in the gaps between the cogs. Variations in the anomaly are mathematically processed. There is no precise correlation between the positions of cogs and a signal curve.
SUMMARY OF THE INVENTION
The principal object of the present invention is accordingly a method of, and a device for determining the position of a rotating shaft whereby a curve is generated that precisely represents the position of the edges of cogs and accordingly allows precise determination of the position of the rotating shaft. This object, as well as other objects which will become apparent from the discussion that follows, are achieved, in accordance with the present invention, by providing a wheel that rotates at a specific angular speed w between a Hall generator and a magnet, wherein the wheel is provided with cogs (Z) that have an ascending edge (ZFA) and a descending edge (ZFF) and produce variations in the magnet's flux density (B) over time, wherein the Hall generator detects these variations and emits a proportional signal B(t), and wherein the signal is converted in a differentiator into a differentiated signal (SMP1). According to the invention, the maxima (SMP1.sub.max) and minima (SMP1.sub.min) of the differentiated signal are identified and a digital output (AS) is derived from it. The transitions from the low level (ASL) to the high level (ASH) of the digital output represent the maxima and the transitions from the high level to the low level represent the minima of the differentiated signal.
The present invention exploits the awareness that it is the edges of the cogs that produce the widest variation in magnetic flux density per unit of time as the wheel rotates. This parameter is independent of the absolute value of the flux and is accordingly unaffected by temperature or operating distance or by tolerances in the Hall generator.
The method in accordance with the present invention accordingly allows the construction of an analog Hall generator that can obtain highly precise digital signals from practically any type of wheel. The instantaneous position of a cog can be precisely detected and the corresponding position of a camshaft, crankshaft, or similar component can accordingly be determined just as precisely.
A rectangular measurement-point signal can be constructed f
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AB Elektronik GmbH
Strecker Gerard R.
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