Fault-signal generators and methods for resolver systems

Details Fault-signal generators and methods for resolver systems Fault-signal generators and methods for resolver systems

2000-11-16

2002-07-30

Tokar, Michael (Department: 2819)

Coded data generation or conversion

Phase or time of phase change

Synchro or resolver signal

C324S076110, C324S076520, C324S076770, C340S008100

Reexamination Certificate

active

06426712

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to resolver systems and, more particularly, to resolver-to-digital converters (RDCs) for these systems.
2. Description of the Related Art
FIG. 1
illustrates a conventional resolver system
20
that includes a resolver
22
and an RDC
24
. The resolver
22
has a rotor
26
that rotates in a stator
28
and is coupled to a rotatable member
30
whose angular position is defined by an angle &thgr;. A rotor winding
32
is carried on the rotor
26
and is excited by a carrier signal
34
(typically a sinusoid having a frequency that is generally in the range of 2-20 KHz) from a carrier signal generator
36
. In addition, first and second stator windings
40
and
42
are carried on the stator
28
.
In response to the carrier signal
34
in the rotor winding
32
, sense signals are magnetically coupled into the stator windings
40
and
42
as they rotate with the rotatable member
30
. The amplitudes of the sense signals change as the relationships between the stator windings and the rotor winding change with variations in the angle &thgr;. The stator windings
40
and
42
are electrically offset from each other by an offset angle. This offset angle is typically 90° so that the sense signals are generally in quadrature.
In a quadrature relationship, the rotor windings
40
and
42
provide sense signals A
1
sin &thgr; and A
2
cos &thgr; to the RDC
24
wherein the sense signals are modulated onto the carrier signal
34
. The RDC
24
receives the sense signals A
1
sin &thgr; and A
2
cos &thgr; and the carrier signal
34
and generates a digital estimate &phgr; of the angle &thgr; of the rotatable member
30
. Typically, RDCs also provide an analog estimate &phgr; of the velocity of the rotatable member
30
.
Resolver systems are used in a variety of applications (e.g., automotive motion sensing and control, automotive motor control, industrial and servo motor control, encoder emulation and factory automation) for providing an estimate &phgr; of a position angle &thgr; of rotatable members (e.g., vehicle steering wheels, aircraft control structures, robot arms, gyroscope members, machine tools and scanned antennas) over a wide range of member velocities (e.g., 0-1 Khz).
In these applications, the resolver
22
of
FIG. 1
may be located at a substantial distance from the RDC
24
and, accordingly, the sense signals A
1
sin &thgr; and A
2
cos &thgr; are typically coupled through transmission lines (e.g. twisted pairs)
44
. However, the length, position, environment (e.g., vibration) and physical state (e.g., worn or crimped) of the cables or the physical state of the resolver (e.g., inoperative) may cause the sense amplitudes A
1
and A
2
to vary significantly from their nominal value A
nom
(or, in the extreme, cause a complete loss of sense signals). If the variation is excessive, the accuracy of the digital estimate &phgr; may be degraded to a level at which it should not be relied on by circuits or systems that receive it.
It has been proposed, for example, that the orientation of a vehicle's front wheels be controlled in response to a resolver system that provides an estimate &phgr; of the angle &thgr; of the vehicle's steering wheel. If the accuracy of the estimate &phgr; has been degraded for any reason, it is imperative for safety that the coupling between the steering wheel position and the steering actuator be immediately replaced with a backup system.
It is desirable, therefore, that a resolver system include a reliable fault detection system that can provide meaningful fault signals S
fault
(provided from the RDC
24
in FIG.
1
). Although some conventional resolver systems have included fault detection systems, their performance parameters (e.g., sensitivity, accuracy and response time) have typically lacked the ability to detect out-of-specification conditions and this ability is critical in many modern applications of resolver systems.
SUMMARY OF THE INVENTION
The present invention is directed to resolver systems that generate an estimate &phgr; of a rotatable member's position angle &thgr; and provide fault signals which monitor the reliability and accuracy of the estimate.
Fault signals of the invention are derived from a monitor signal which multiplies resolver and estimate signals to derive information on the absolute and relative levels of resolver sense signals. At least one fault signal is derived from a loop error signal of the system servo loop. These fault signals report on, for example, mismatched sense signals, out-of-range sense signals and loss of position tracking to thereby enhance accuracy and safety in various resolver applications.
The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.


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