Coded data generation or conversion – Phase or time of phase change – Synchro or resolver signal
Reexamination Certificate
2001-09-25
2003-08-19
Williams, Howard L. (Department: 2819)
Coded data generation or conversion
Phase or time of phase change
Synchro or resolver signal
C341S111000
Reexamination Certificate
active
06608573
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an automatic resolution changing method and circuit for use in digital conversion of two-phase sinusoidal wave signals and, more particularly, to an automatic resolution changing method and circuit for use in digital conversion of two-phase sinusoidal wave signals, which provides high resolution during the low speed rotation of, for example, a resolver rotor or an encoder shaft, and which provides high followability during the high speed rotation thereof.
2. Description of the Related Art
Hitherto, conventional methods have been performed in conventional digital conversion circuits, as illustrated in
FIG. 3
, for digital conversion of, for instance, two-phase sinusoidal wave signals. That is, in
FIG. 3
, reference numeral
1
designates a first multiplying D/A converter for multiplying an output of a COS ROM
2
, to which an angular output (&phgr;) of a known resolver (not shown) is fed back and inputted, by a sinusoidal component sin &thgr;·sin &ohgr;t of a resolver signal and for outputting a result of the multiplication, that is, sin &thgr;·cos &phgr;·sin &ohgr;t as a first converter output. Incidentally, “sin &ohgr;t” denotes an excitation signal for the resolver.
Similarly, a second multiplying D/A converter
3
is operative to multiply an output of a SIN ROM
4
, to which an angular output (&phgr;) of the resolver is fed back and inputted, by a cosinusoidal component cos &thgr;·sin &ohgr;t of a resolver signal and for outputting a result of the multiplication, that is, cos &thgr;·sin &phgr;·sin &ohgr;t as a second converter output.
A phase sensitive detection circuit
5
is connected to an output terminal of both the first multiplying D/A converter
1
and the second multiplying D/A converter
3
. A signal representing a value obtained by subtracting the second converter output cos &thgr;·sin &phgr;·sin &ohgr;t of the second multiplying D/A converter
3
from the first converter output sin &thgr;·cos &phgr;·sin &ohgr;t of the first multiplying D/A converter
1
is inputted to the phase sensitive detection circuit
5
, which then outputs a control residual &egr;. Incidentally, &egr;=sin &thgr;·cos &phgr;−cos &thgr;·sin &phgr;=sin(&thgr;−&phgr;).
The control residual &egr; is inputted to a compensator
6
, from which an angular velocity d&phgr;/dt (=&phgr;dot) is then outputted. This compensator
6
is designed according to the characteristics of a counter
7
in the subsequent stage. For example, when the counter
7
has a first-order integral element, it is sufficient that a feedback control system is constituted in such a way as to have PI (Proportional+Integral) control elements, which include a first order lag filter, to thereby control the counter
7
stably with high accuracy at high speeds.
The angular velocity d&phgr;/dt (=&phgr;dot) is inputted to the counter
7
, which is a plant, and then integrated therein and subsequently, outputted as a digital angular output &phgr; (that is, an output counter value).
Incidentally, in the present specification, the angular velocity d&phgr;/dt and rotation angle are assumed to be expressed in electrical angles.
The conventional conversion circuit is configured as described above, and thus has the following drawbacks. That is, although the enhancement of resolution during the low speed rotation of, for example, a resolver rotor or of an encoder shaft, and the improvement of followability during the high speed rotation thereof are required of the aforementioned tracking system, which is a closed loop negative feedback circuit, for digital conversion of a resolver signal, the resolution with respect to the rotation angle is inversely proportional to the follow-up speed. Moreover, the range of the follow-up speed is uniquely determined according to the conversion performance of the circuit, so that the circuit is forced to be used within an allowable range of the follow-up speed. Thus, it is difficult to manage both the high resolution during the low speed rotation of, for example, a resolver rotor and the high followability during the high speed rotation thereof.
Further, the conventional conversion circuit has such a drawback not only in the case of applying this conventional conversion circuit to a resolver but the case of applying this conventional conversion circuit to an angular signal outputted by an encoder. That is, such a signal outputted from the encoder has no excitation component. The block configuration of the digital conversion circuit for digital conversion of an angular signal outputted from an encoder is obtained by removing the sin &ohgr;t component of each of the signals and by omitting the phase sensitive detection circuit
5
therein. However, in such digital conversion circuit for digital conversion of angular signals outputted from an encoder, an angular velocity d&phgr;/dt (=&phgr;dot) outputted from the compensator
6
is integrated in the counter
7
, and subsequently, the result of the integration is outputted as a digital angular output &phgr;. Therefore, the conversion circuit has a drawback similar to the aforementioned in the case of the circuit for digital conversion of a resolver signal.
The present invention was developed to eliminate the aforementioned drawbacks. Accordingly, an object of the present invention is to provide an automatic resolution changing method for use in digital conversion of two-phase sinusoidal wave signals, which provides high resolution during the low speed rotation of a resolver rotor or of an encoder shaft, and which provides high followability during the high speed rotation thereof.
SUMMARY OF THE INVENTION
To achieve the foregoing object, according to an aspect of the present invention, there is provided an automatic resolution changing method for use in a high-precision digital conversion of two-phase sinusoidal wave signals. This automatic resolution changing method comprises the steps of detecting a two-phase-sinusoidal-wave-like A-phase output and a two-phase-sinusoidal-wave-like B-phase output, which are outputted based on the rotation of a rotor with respect to a stator, integrating an angular velocity of the rotor on the basis of the control residual obtained from the two-phase sinusoidal wave signals in a counter, performing digital conversion of the rotation angle (&thgr;) of the rotor with respect to the stator, and outputting a result of the digital conversion. Further, when the result of the digital conversion is outputted, in the case where the angular velocity is equal to or higher than a first percentage of a follow-up speed at a current resolution of the counter, the resolution of the counter is reduced, while in the case where the angular velocity is equal to or lower than a second percentage of the follow-up speed at the current resolution of the counter, the resolution of the counter is increased. Thus, the present invention can provide a method of performing digital conversion of two-phase sinusoidal wave signals.
Further, in the case of an embodiment of this automatic resolution changing method for use in a high-precision digital conversion of two-phase sinusoidal wave signals, when the resolution of the counter is reduced, the resolution thereof is reduced by 1 bit. Moreover, when the resolution of the counter is increased, the resolution thereof is increased by 1 bit. Thus, the present invention can provide a method of performing digital conversion of two-phase sinusoidal wave signals, which provides good followability.
Moreover, in the case of an embodiment of this automatic resolution changing method for use in a high-precision digital conversion of two-phase sinusoidal wave signals, the above first percentage is 87.5%, and the second percentage is 37.5%. Thus, the present invention can provide a method of performing digital conversion of two-phase sinusoidal wave signals, which provides high followability.
Furthermore, according to another aspect of the present invention, there is provided an
Sughrue & Mion, PLLC
Tamagawa Seiki Kabushiki Kaisha
Williams Howard L.
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