US 5,880,586 AGranted

Apparatus for determining rotational position of a rotatable element without contacting it

AssigneeRobert Bosch GmbH

InventorsAnton Dukart, Hermann Winner, Siegbert Steinlechner, Erich Zabler

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Abstract

The apparatus for determining rotational position of a rotatable element without contacting it includes a sensor device having two Hall or AMR sensor elements for sensing a magnetic field of magnetic field strength (B) generated by or influenced by the rotational position of the rotatable element and for producing output signals according to the magnetic field and thus the rotational position of the rotatable element. In order to easily detect the absolute rotational position of the rotatable element, the sensor device is constructed and positioned with respect to the rotatable element so that in every rotational position the field lines from the rotatable element extend at right angles to the sensor structures defined by the direction of an alternating current in the sensor elements. Using different embodiments of an electronic evaluation circuit, the direction components of the magnetic field are evaluated to determine the rotational position by comparing the input current to one of the sensors and the sum of the output signals of the respective sensor elements. Either sinusoidal or rectangular alternating voltages or direct voltages are input to the sensor elements.

Claims16

Dependent claims

An apparatus for determining rotational position of a rotatable element without contact with the rotatable element, said apparatus comprising

a sensor device having at least two sensor elements for sensing a magnetic field of magnetic field strength (B) generated by the rotatable element or influenced by rotation of the rotatable element and for producing output signals according to said magnetic field, said sensor elements having sensor outputs;
and
evaluation circuit means for evaluating said output signals including
means for supplying said at least two sensor elements with respective alternating currents (I.sub.1, I.sub.2) that are 90.degree. out of phase in accordance with formulae Ia and Ib:
I.sub.1 =Io cos(.omega.t) (Ia)
I.sub.2 =Io sin(.omega.t) (Ib)
to produce respective output voltages (U.sub.H1, U.sub.H2) at said sensor outputs according to formulae IIa and IIb:
U.sub.H1 =C.sub.1 B.sub.1 cos(K.alpha.) I.sub.1 (t) (IIa)
U.sub.H2 =C.sub.2 B.sub.2 sin(K.alpha.) I.sub.2 (t) (IIb)
wherein t is time, .omega. is frequency in reciprocal time units, Io is a constant and is a maximum current value for I.sub.1 and I.sub.2, C.sub.1 =C.sub.2 =C=another constant and B.sub.1 =B.sub.2 =B=an additional constant magnetic field strength value, such that C.sub.1 B.sub.1 and C.sub.2 B.sub.2 are maximum voltage values and are equal, .alpha. is an angle of rotation of the rotatable element and K is a constant such that K.alpha. is the phase factor;
means (23) for summing said output voltages (U.sub.H1, U.sub.H2) to form a sum signal;
and
a phase comparator (25) for producing a rotational position signal proportional to the rotational position of the rotatable element from the sum signal and said alternating current supplied to one of the at least two sensor elements.

10 more elements

An apparatus for determining rotational position of a rotatable element without contact with the rotatable element, said apparatus comprising

a sensor device having two sensor elements (30,31) for sensing a magnetic field of magnetic field strength (B) generated by the rotatable element or influenced by rotation of the rotatable element and for producing sensor output signals according to said magnetic field, said sensor elements having sensor outputs at which said sensor output signals appear;
and
evaluation circuit means for evaluating said output signals including
means (28,29) for triggering said two sensor elements with a direct voltage (V.sub.s) to produce respective output voltages (U.sub.a1,U.sub.a2) at said sensor outputs given by formulae IVa and IVb:
U.sub.a1 (K.alpha.)=C V.sub.s cos(K.alpha.) (IVa)
U.sub.a2 (K.alpha.)=C V.sub.s sin(K.alpha.) (IVb);
wherein is an angle of rotation of the rotatable element, K is constant such that K is the phase factor and C is another constant;
means (51) for amplifying a difference between said respective output voltages (U.sub.a1,U.sub.a2) to form an amplified difference signal, said means for amplifying having respective inputs connected to respective switch terminals;
means (48a, 48b, 50, 49) for periodically alternately switching said respective output voltages (U.sub.a1, U.sub.a2) between said respective switch terminals;
means (52) for filtering the amplified difference signal to form a filtered difference signal;
and
a phase comparator (36) for producing a rotational position signal according to the rotational position of the rotatable element from the filtered difference signal and a switching signal supplied by said means for switching said respective output voltages.

9 more elements

Dependencies are inferred from the claim text.