Coded data generation or conversion – Phase or time of phase change
Reexamination Certificate
1999-12-23
2001-11-27
Young, Brian (Department: 2819)
Coded data generation or conversion
Phase or time of phase change
C341S116000, C318S632000
Reexamination Certificate
active
06323790
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a converter for digitizing the output of a resolver (hereinafter referred to as R/D converter).
2. Description of the Related Art
A resolver is a kind of rotary transformer, and includes two stator windings and one rotor winding. The two stator windings are mechanically disposed at an angle of 90 degrees. The amplitude of a signal obtained by coupling to the stator windings becomes a function of relative position between the position of the rotor (shaft) and the stator. Thus, two kinds of output voltages (S
3
−S
1
, S
4
−S
2
), which are modulated by a sine (sine wave) and a cosine (cosine wave) of a shaft angle and are expressed by the following equations (1) and (2), are obtained from the resolver. Although equation (5) indicates a signal of a resolver format, the signal of the resolver format is based on a signal [output voltages (S
3
−S
1
) and (S
4
−S
2
)] obtained from the resolver output.
S
3
−S
1
=E
0
sin &ohgr;t sin &thgr; (1)
S
4
−S
2
=E
0
sin &ohgr;t cos &thgr; (2)
Where,&thgr; is an axial angle, &ohgr; is an angular velocity corresponding to a rotor excitation frequency (f), and E
0
is an rotor excitation amplitude.
Here, using AD2S90 of Analog Device Company as an example, a conventional resolver digital converter (R/D converter
1
) of a tracking system will be described.
FIG. 13
is a functional block diagram of the AD2S90.
In
FIG. 13
, when a transducer passes through a position equivalent to a least significant bit, the output is renewed by only 1 LSB. Renewal of CLKOUT corresponds to increase of 1 LSB.
When the present word state of an up-down counter
2
is made &phgr;, the output voltage (S
3
−S
1
) is multiplied by cos &phgr; through a sine cosine multiplier
3
, and the output voltage (S
4
−S
2
) is multiplied by sin &phgr;, whereby signals expressed by the following equations (3) and (4) are obtained.
E
0
sin &ohgr;t sin &thgr; cos &phgr; (3)
E
0
sin &ohgr;t cos &thgr; sin &phgr; (4)
The signals expressed by the equations (3) and (4) are subtracted through an error amplifier
4
, whereby a signal expressed by the following equation (5) is obtained.
E
0
sin &ohgr;t (sin &thgr; cos &phgr;−cos &thgr;sin &phgr;)=E
0
sin &ohgr;t sin(&thgr;−&phgr;) (5)
Where, (&thgr;−&phgr;): angular error.
A demodulator circuit
5
and an integrator
6
are connected to an output side of the error amplifier
4
, and a voltage controlled oscillator (VCO)
7
is connected to the demodulator circuit
5
and the integrator
6
. The demodulator circuit
5
, the integrator
6
, and the VCO
7
form a close loop, and operate in such a manner that sin(&thgr;−&phgr;) [see the equation (5)] is made zero. When this operation is realized, the word state &phgr; of the up-down counter
2
connected to the sine cosine multiplier
3
becomes equal to the resolver shaft angle &thgr;.
However, in the foregoing R/D converter
1
of the tracking system shown in
FIG. 13
, attention has not been paid in the following points.
(a) Since it is a kind of PLL control, response speed is low. Particularly, as resolution becomes high, the response speed becomes low.
(b) It is necessary to compensate temperature drift of the analog operating circuit (the sine cosine multiplier
3
, the demodulator circuit
5
, etc.), so that its IC circuit becomes complicated and expensive.
(c) If an interface cable between the resolver (not shown) and the R/D converter
1
becomes long, a phase becomes large because of delay between the excitation sine wave and the sine-wave output and cosine-wave output of the resolver, and an angular error becomes large.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-described circumstances, and an object of the invention is to provide an R/D converter which enables high speed response. Another object of the invention is to eliminate temperature drift compensation and to make an apparatus inexpensive.
According to a first aspect of the invention, an R/D converter comprises a digital signal processing processor to which data obtained through AD conversion of sine-wave output and cosine-wave output of a resolver are inputted, wherein the digital signal processing processor obtains a rotor shaft angle of the resolver through a digital operation on the basis of the digital input data.
According to a second aspect of the invention, in the structure of the first aspect, the R/D converter is characterized in that the digital signal processing processor inputs digital data for an excitation sine wave of the resolver to a DA converter, and the DA converter obtains the excitation sine wave of the resolver on the basis of the input data from the digital signal processing processor.
According to a third aspect of the invention, in the structure of the second aspect, the R/D converter is characterized in that at a specific phase time of the excitation sine wave of the resolver, a sine-wave output signal and a cosine-wave output signal of the resolver are subjected to AD conversion, and the rotor shaft angle of the resolver is calculated.
According to a fourth aspect of the invention, in the structure of any one of the first to third aspects, the R/D converter is characterized in that a quadrant formed by dividing an angular space of the resolver into four equal parts is obtained, the rotor shaft angle of the resolver in the quadrant is obtained on the basis of polarities of the sine-wave output and the cosine-wave output of the resolver, and an initial angle of a rotor shaft angle for calculating VCO is set at the center of each quadrant obtained by dividing into four equal parts.
According to a fifth aspect of the invention, in the structure of the fourth aspect, the R/D converter is characterized in that a sin value corresponding to a difference between the rotor shaft angle of the resolver and an angle corresponding to an address of a sine-wave table is calculated, and an angle of the VCO is increased or decreased on the basis of size relation between the rotor shaft angle of the resolver and the angle of the VCO.
According to a sixth aspect of the invention, in the structure of the fifth aspect, the R/D converter is characterized in that the quadrant is set such that a value in the angular space becomes large from the left to the right, and in the quadrant, if the rotor shaft angle of the resolver exists on the right side as compared with the angle of the VCO, the angle of the VCO is made to increment.
According to a seventh aspect of the invention, in the structure of the fifth aspect, the R/D converter is characterized in that the quadrant is set such that a value in the angular space becomes large from the left to the right, and in the quadrant, if the rotor shaft angle of the resolver exists on the left side as compared with the angle of the VCO, the angle of the VCO is made to decrement.
According to an eighth aspect of the invention, in the structure of any one of the aspects
5
to
7
, the R/D converter is characterized in that an AD conversion value of the sine-wave output of the resolver and a sin value of the angle of the VCO are compared with each other, an address corresponding to an angle of the sine-wave table is increased or decreased by one bit at a time according to the rotor shaft angle in the quadrant, and an angle corresponding to the address is made to approach the rotor shaft angle.
According to a ninth aspect of the invention, in the structure of any one of the fifth to seventh aspects, the R/D converter is characterized in that a rotor angle displacements &Dgr;&thgr; is calculated from AD conversion values of the sine-wave output and the cosine-wave output of the resolver and a sin value and a cos value of the angle of the VCO, and an address corresponding to the angle of the VCO is jumped by a jump amount expressed by &Dgr;&thgr;/K.
REFERENCES:
patent: 4486845 (1984-12-01),
Minebea Co. Ltd.
Nguyen John
Oliff & Berridg,e PLC
Young Brian
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