Coded data generation or conversion – Phase or time of phase change – Synchro or resolver signal
Reexamination Certificate
1998-07-08
2001-02-13
Williams, Howard L. (Department: 2819)
Coded data generation or conversion
Phase or time of phase change
Synchro or resolver signal
C341S111000
Reexamination Certificate
active
06188341
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an interpolation circuit for interpolating detection signals from an encoder for to thereby detect rotational angles or positions on a straight line.
BACKGROUND ART
In a detecting device for detecting positions of a table and a motor of a machine tool of an NC apparatus, a rotary-type pulse encoder attached to the motor shaft or the like and a linear-type pulse encoder attached to a worktable or the like are known as means for detecting the movement and moving speed of a moving body. As the moving body moves, these encoders generate an A-phase signal, a sine-wave signal (Ksin &thgr;), and a B-phase sine-wave signal (Ksin(&thgr;±&pgr;/2)), which has a phase difference of 90° from the A-phase signal, and obtains angle data (&thgr;) by carrying out interpolative computation with use of these two sine-wave signals, thereby improving the resolution for the position and speed.
There are known methods for this interpolation technique, including a method in which a converter circuit for sine- and cosine-wave signals from a signal source is composed of a plurality of resistors and comparator arrays. In another method based on the interpolation circuit configuration shown in
FIG. 15
, a sine-wave signal V
A
and a cosine-wave signal V
B
are inputted to the interpolative computation unit
2
after being A/D-converted by unit of A/D converters
1
a
and
2
a
, respectively, and the interpolative computation unit
2
computes tan
−1
(V
A
/V
B
) to obtain angle data &thgr;. The computation of this inverse transform of a tangent can be carried out by using a calculation process based on a Taylor expansion, for example.
An interpolation circuit used for a conventional encoder carries out interpolative computation on the assumption that it receives an A-phase signal (sine-wave signal) and a B-phase signal (cosine-wave signal) that are equal in amplitude K and have a phase difference of &pgr;/2.
In general, however, A- and B-phase signals that are inputted to an encoder do not always have an accurate phase difference of &pgr;/2, and are not always equal in amplitude. In other words, the phase difference between the two signals may be deviated from &pgr;/2 or the amplitude ratio may be deviated from 1.
If interpolative computation is carried out with use of these deviated signals, the obtained angle &thgr; may possibly be subject to an interpolation error attributable to the deviation.
Conventionally, therefore, this interpolation error is removed by a method in which an analog regulator circuit is provided in front of A/D converters so that the amplitude ratio between the A- and B-phase signals inputted to the analog regulator circuit can be adjusted to 1 or that phase difference between the A- and B-phase signals can be adjusted to &pgr;/2.
However, the removal of the interpolation error by means of the analog regulator circuit requires a complicated circuit configuration. Since the regulator circuit is an analog circuit, moreover, it is necessary to adjust the regulator circuit itself.
DISCLOSURE OF THE INVENTION
The object of the present invention is to provide an interpolation circuit for an encoder, in which interpolation data cleared of an interpolation error that is attributable to signal deviations can be obtained by correcting interpolation data, which is obtained by interpolative computation, without adjusting input signals.
In order to achieve the above object, an encoder interpolation circuit according to the present invention comprises:
interpolative computation means for receiving two encoder signals of difference phases, carrying out interpolative computation for these signals and outputting interpolation angle data, correction data forming means for obtaining and outputting correction data corresponding to a combination of a detected deviation of the two encoder signals from a normal waveform and the interpolation angle data outputted from the interpolative computation means; and corrective computation means for correcting the interpolation angle data outputted from the interpolative computation means with the correction data outputted from the correction data forming means and outputting corrected interpolation angle data.
Preferably, the deviation of the two encoder signals is the ratio of the amplitude of one sine-wave encoder signal to the amplitude of the other sine-wave encoder signal.
Preferably, the deviation of the two encoder signals is a phase error as the difference between the predetermined a phase difference between two encoder signals and an actual phase difference between the two encoder signals.
Preferably, the correction data forming means forms the correction data by substituting an output of the interpolative computation means and a detected phase error, as a deviation of the two encoder signals, individually for variables in a computational expression for obtaining preset correction data and operating the computational expression.
Preferably, the correction data forming means is previously stored with the value of correction data for a combination of the output of the interpolative computation means and the output of the correction data forming means, and the correction data forming means receives the output of the interpolative computation means and the output of the correction data forming means and outputs the correction data corresponding to the combination of these outputs.
Preferably, the correction data stored in the correction data forming means can be fetched with an address which represents a combination of the output of the interpolative computation means and the output of the correction data forming means.
Further preferably, the correction data forming means is stored with a data table so that corresponding data can be fetched with an address which represents a combination of angle data in a limited range and a detected signal deviation, and the correction data forming means includes means for receiving the detected deviation of the two encoder signals and the output of the interpolative computation means, and determining an address based on the deviation and the output, and means for forming the correction data by accessing said data table to fetch the corresponding data with the determined address and processing the fetched data.
According to the present invention, interpolation data cleared of an interpolation error that is attributable to signal deviations can be obtained by correcting interpolation data, which is obtained by interpolative computation, without adjusting input signals.
REFERENCES:
patent: 5625310 (1997-04-01), Takeishi
patent: 5677686 (1997-10-01), Kachi et al.
patent: 5786781 (1998-07-01), Taniguchi et al.
patent: 44 43 898 (1996-06-01), None
patent: 0 599 175 (1994-06-01), None
patent: 0 669 517 (1995-08-01), None
patent: 3-31720 (1991-02-01), None
patent: 3-223621 (1991-10-01), None
patent: 5-231879 (1993-09-01), None
patent: 7-174586 (1995-07-01), None
patent: 7-198417 (1995-08-01), None
patent: 7-218288 (1995-08-01), None
patent: 8-122097 (1996-05-01), None
patent: 8-145719 (1996-06-01), None
Institute of Electrical and Electronics Engineers: “A Method of Improving the Resolution and Accuracy of Rotary Encoders Using Code Compensation Technique” Instrumentation and Measurement Technology Conference, US, New York, IEEE, vol. Conf. 8, p. 183-184.
Inoue Tadashi
Taniguchi Mitsuyuki
Fanuc Ltd.
Staas & Halsey , LLP
Williams Howard L.
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