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Claims  |
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I claim:
1. An apparatus for automatically adjusting offset correction values for
current detectors of a digital controller for a servo motor employing the
current detectors, each having an offset value, comprising:
rotation detecting means for receiving both a torque command value and a
electrical angle signal of said servo motor as an input thereto and
detecting that, in one period of an electrical angle, said servo motor
rotates in one direction and a rotational speed thereof is equal to or
lower than a predetermined upper limit set value;
electrical angle detecting mean for detecting, at the time of detection by
said rotation detecting means, a first electrical angle where the torque
command value is maximum and a second electrical angle where the torque
command value is minimum, in the one period of an electrical angle,
respectively;
judgement means for judging whether or not a difference between the first
and second electrical angles detected by said electrical angle detecting
means is 180 degrees; and
correction means for correcting, when said judgement means judges that the
difference between the first and second electrical angles is 180 degrees,
offset correction values for said current detectors in accordance with the
first electrical angle.
2. An apparatus for automatically adjusting offset correction values for
current detectors of a digital controller for a servo motor employing the
current detectors, each having an offset value, comprising:
rotation detecting means for receiving both a three phase feedback a.c.
value and an electrical angle signal of said servo motor as an input
thereto and detecting that, in one period of an electrical angle, said
servo motor rotates in one direction and a rotational speed thereof is
equal to or lower than a predetermined upper limit set value;
electrical angle detecting means for detecting, at the time of detection by
said rotation detecting means, a first electrical angle where a
quadrature-axis current obtained from the three phase feedback a.c. value
of said servo motor is maximum and a second electrical angle where the
quadrature-axis current is minimum, in the one period of an electrical
angle, respectively;
judgement means for judging whether or not a difference between the first
and second electrical angles detected by said electrical angle detecting
means is 180 degrees; and
correction means for correcting, when said judgement means judges that the
difference between the first and second electrical angles is 180 degrees,
offset correction values for said current detectors in accordance with the
first electrical angle.
3. An apparatus according to claim 1, wherein said correction means for
correcting the offset correction values for said current detectors
comprises:
electrical angle existing range judging means for judging in which one of
eight division ranges obtained by dividing an electrical angle of 360
degrees the first electrical angle exists; and
offset correction value outputting means having adjustment values for the
offset correction values, which are set in accordance with the eight
division ranges, and serving to add the adjustment values for the offset
correction values corresponding to the division range, in which the first
electrical angle exists, to the respective offset correction values to
update the offset correction values and to output the resultant values.
4. An apparatus according to claim 2, wherein said correction means for
correcting the offset correction values for said current detectors
comprises:
electrical angle existing range judging means for judging in which one of
eight division ranges obtained by dividing an electrical angle of 360
degrees the first electrical angle exists; and
offset correction value outputting means having adjustment values for the
offset correction values, which are set in accordance with the eight
division ranges, and serving to add the adjustment values for the offset
correction values corresponding to the division range, in which the first
electrical angle exists, to the respective offset correction values to
update the offset correction values and to output the resultant values.
5. An apparatus according to claim 1, wherein said correction means for
correcting the offset correction values for said current detectors
comprises:
electrical angle existing range judging means for judging in which one of
four division ranges obtained by dividing an electrical angle of 360
degrees the first electrical angle exists; and
offset correction value outputting means having adjustment values for the
offset correction values, which are set in accordance with the four
division ranges, and serving to add the adjustment values for the offset
correction values corresponding to the division range, in which the first
electrical angle exists, to the respective offset correction values to
update the offset correction values and to output the resultant values.
6. An apparatus according to claim 2, wherein said correction means for
correcting the offset correction values for said current detectors
comprises:
electrical angle existing range judging means for judging in which one of
four division ranges obtained by dividing an electrical angle of 360
degrees the first electrical angle exists; and
offset correction value outputting means having adjustment values for the
offset correction values, which are set in accordance with the four
division ranges, and serving to add the adjustment values for the offset
correction values corresponding to the division range, in which the first
electrical angle exists, to the respective offset correction values to
update the offset correction values and to output the resultant values.
7. An apparatus for automatically adjusting offset correction values for
current detectors of a digital controller for a servo motor employing the
current detectors, each having an offset value, comprising:
rotation detecting means for receiving both a torque command value and an
electrical angle signal of said servo motor as an input thereto and
detecting that, in one period of an electrical angle, said servo motor
rotates in one direction and a rotational speed thereof is equal to or
lower than a predetermined upper limit set value;
torque/electrical angle detecting means for detecting, at the time of
detection by said rotation detecting means, a maximum value of the torque
command value, a first electrical angle at the time of obtaining the
maximum torque command value, a minimum value of the torque command value,
and a second electrical angle at the time of obtaining the minimum torque
command value, in the one period of the electrical angle, respectively;
judgement means for judging whether or not a difference between the first
and second electrical angles detected by said torque/electrical angle
detecting means is 180 degrees; and
correction means for correcting, when said judgement means judges that the
difference between the first and second electrical angles is 180 degrees,
offset correction values for said current detectors in accordance with the
first electrical angle and a difference between the maximum torque command
value and the minimum torque command value.
8. An apparatus according to claim 5, wherein said correction means for
correcting the offset correction values for said current detectors
comprises:
electrical angle existing range judging means for judging in which one of
four division ranges obtained by dividing an electrical angle of 360
degrees the first electrical angle exists; and
offset correction value outputting means having adjustment values for the
offset correction values, which are set in accordance with the four
division ranges and a difference between the maximum torque command value
and the minimum torque command value, and serving to add the adjustment
values for the offset correction values corresponding to the division
range in which the first electrical angle exists and the difference
between the maximum torque command value and the minimum torque command
value to the respective offset correction values to update the offset
correction value and to output the resultant values. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for automatically adjusting
offset correction values for current detectors in a digital controller for
a servo motor for use in a high precision NC system, robot, etc.
Heretofore, in a digital control apparatus for a servo motor for use in a
high precision NC system, robot, etc., in the case where a current
detector composed of an analog circuit is used as current detecting means,
correction of an offset of an output of the current detector is carried
out. That is, when turning on a power source, an output voltage of the
current detector, which is detected while the servo motor is stopped, is
set as an offset correction value, and the offset correction value which
has been set upon turning on the power source is not updated while the
motor is in operation.
However, in the above-mentioned prior art apparatus, there arises a problem
that, when an error occurs between an actual offset value and the offset
correction value, which has been set when turning on the power source, due
to a change of an ambient temperature, a temperature rise in component
elements of the current detector and the like while operating the servo
motor for a long period of time, a ripple having the same period as that
of an electrical angle is generated in the torque of the servo motor.
SUMMARY OF THE INVENTION
The present invention was made in order to solve the above-mentioned
problem, and an object of the present invention is to provide an apparatus
for automatically adjusting offset correction values for current detectors
which is capable of judging occurrence of correction errors of offset
correction values due to a temperature rise in component elements in the
current detectors on the basis of a ripple of the quadratureaxis current
value which is obtained by subjecting a ripple of a torque command value
for the servo motor or a three phase feedback a.c. value to three
phase/two phase conversion, and which is capable of automatically carrying
out the correction of the offset correction values even when the servo
motor is in operation, thereby preventing generation of the ripple of the
torque of the servo motor.
In order to attain the above-mentioned object, a first aspect of the
present invention provides an apparatus for automatically adjusting offset
correction values for current detectors of a digital controller for a
servo motor employing the current detectors, each having an offset value,
which comprises: rotation detecting means for receiving both a torque
command value and an electrical angle signal of the servo motor as its
input and detecting that, in one period of an electrical angle, the servo
motor rotates in one direction and its rotational speed is equal to or
lower than a predetermined upper limit set value; electrical angle
detecting means for detecting, at the time of detection by the rotation
detecting means, a first electrical angle where the torque command value
is maximum and a second electrical angle where the torque command value is
minimum, in one period of an electrical angle, respectively; judgement
means for judging whether or not a difference between the first and second
electrical angles detected by the electrical angle detecting means is 180
degrees; and correction means for correcting, when the judgement means
judges that the difference between the first and second electrical angles
is 180 degrees, offset correction values for the current detectors in
accordance with the first electrical angle.
Further, in order to attain the abovementioned object, a second aspect of
the present invention provides an apparatus for automatically adjusting
offset correction values for current detectors of a digital controller for
a servo motor employing the current detectors, each having an offset
value, which comprises: rotation detecting means for receiving both a
three phase feedback a.c. value and an electrical angle signal of the
servo motor as its input and detecting that, in one period of an
electrical angle, the servo motor rotates in one direction and its
rotational speed is equal to or lower than a predetermined upper limit set
value; electrical angle detecting means for detecting, at the time of
detection by the rotation detecting means, a first electrical angle where
a quadrature-axis current obtained from the three phase feedback a.c.
value of the servo motor is maximum and a second electrical angle where
the quadrature-axis current value is minimum, in the one period of an
electrical angle, respectively; judgement means for judging whether or not
a difference between the first and second electrical angles detected by
the electrical angle detecting means is 180 degrees; and correction means
for correcting, when the judgement means judges that the difference
between the first and second electrical angles is 180 degrees, offset
correction values for the current detectors in accordance with the first
electrical angle.
Further in the first or second aspect of the present invention, the
correction means for correcting the offset correction values for the
current detectors according to a third aspect of the present invention
comprises: electrical angle existing range judging means for judging in
which one of eight division ranges obtained by dividing an electrical
angle of 360 degrees the first electrical angle exists; and offset
correction value outputting means having adjustment values for the offset
correction values, which are set in accordance with the eight division
ranges, and serving to add the adjustment values for the offset correction
values corresponding to the division range, in which the first electrical
angle exists, to the respective offset correction values to update the
offset correction values and output the resultant values.
Further in the first or second aspect of the present invention, the
correction means for correcting offset correction values for the current
detectors according to a fourth aspect of the present invention comprises:
electrical angle existing range judging means for judging in which one of
four division ranges obtained by dividing an electrical angle of 360
degrees the first electrical angle exists; and offset correction value
outputting means having adjustment values for the offset correction
values, which are set in accordance with the four division ranges, and
serving to add the adjustment values for the offset correction values
corresponding to the division range, in which the first electrical angle
exists, to the respective offset correction values to update the offset
correction values and output the resultant values.
Further, a fifth aspect of the present invention provides an apparatus for
automatically adjusting offset correction values for current detectors of
a digital controller for a servo motor employing the current detectors,
each having an offset value, which comprises: rotation detecting means for
receiving both a torque command value and an electrical angle signal of
the servo motor as its input and detecting that, in one period of an
electrical angle, the servo motor rotates in one direction and its
rotational speed is equal to or lower than a predetermined upper limit set
value; torque/electrical angle detecting means for detecting, at the time
of detection by the rotation detecting means, a maximum value of the
torque command value, a first electrical angle at the time of obtaining
the maximum torque command value, a minimum value of the torque command
value, and a second electrical angle at the time of obtaining the minimum
torque command value, in the one period of the electrical angle,
respectively; judgement means for judging whether or not a difference
between the first and second electrical angles detected by the
torque/electrical angle detecting means is 180 degrees; and correction
means for correcting, when the judgement means judges that the difference
between the first and second electrical angles is 180 degrees, offset
correction values for the current detectors in accordance with the first
electrical angle and a difference between the maximum torque command value
and the minimum torque command value.
Further in the fifth aspect of the present invention, the correction means
for correcting offset correction values for the current detectors
according to a sixth aspect of the present invention comprises: electrical
angle existing range judging means for judging in which one of four
division ranges obtained by dividing an electrical angle of 360 degrees
the first electrical angle exists; and offset correction value outputting
means having adjustment values for the offset correction values, which are
set in accordance with the four division ranges and a difference between
the maximum torque command value and the minimum torque command value, and
serving to add the adjustment values for the offset correction values
corresponding to the division range, in which the first electrical angle
exists, and the difference between the maximum torque command value and
the minimum torque command value to the respective offset correction
values to update the offset correction values and output the resultant
values.
By virtue of the first aspect of the present invention, even if correction
errors occur in the offset correction values due to a change of an ambient
temperature and the like while the servo motor is in operation, the
occurrence of the correction errors of the offset correction values due to
a temperature rise in the current detectors is judged on the basis of a
ripple of the torque command value for the servo motor, and in accordance
with the electrical angle where the torque command value becomes maximum
in one period of an electrical angle, the offset correction values for the
current detectors are corrected, so that, even while the servo motor is in
operation, correction of the offset correction values is automatically
performed, and therefore it is possible to prevent generation of a ripple
of the torque of the servo motor and also to suppress deterioration of
control performance such as an increase of a speed ripple.
By virtue of the second aspect of the present invention, even if correction
errors occur in the offset correction values due to a change of an ambient
temperature and the like while the servo motor is in operation, the
occurrence of the correction errors of the offset correction values due to
a temperature rise in the current detectors is judged on the basis of a
ripple of the quadrature-axis current value which is obtained from a
feedback current value for the servo motor, and, in accordance with the
electrical angle where the quadrature-axis current value becomes maximum
in one period of an electrical angle, the offset correction values for the
current detectors are corrected, so that, even while the servo motor is in
operation, correction of the offset correction values is automatically
performed, and therefore it is possible to prevent generation of a ripple
of the torque of the servo motor and also to suppress deterioration of
control performance such as an increase of a speed ripple.
By virtue of the fifth aspect of the present invention, even if correction
errors occur in the offset correction values due to a change of an ambient
temperature and the like while the servo motor is in operation, the
occurrence of the correction errors of the offset correction values due to
a temperature rise in the current detectors is judged on the basis of a
ripple of the torque command value, and, in accordance with the electrical
angle, where the torque command value becomes maximum, and a difference
between the maximum torque command value and the minimum torque command
value, which have been obtained in one period of an electrical angle of
the servo motor driving current, respectively, the offset correction
values for the current detectors are corrected, so that, even while the
servo motor is in operation, correction of the offset correction values is
automatically performed, and therefore it is possible to prevent
generation of a ripple of the torque of the servo motor and also to
suppress deterioration of control performance such as an increase of a
speed ripple.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing a digital controller for a servo motor
having an apparatus for automatically adjusting offset correction values
for current detectors of a first embodiment of the present invention;
FIG. 2 is a block diagram showing an internal structure of the apparatus
for automatically adjusting offset correction values shown in FIG. 1;
FIG. 3 is a flow chart showing the processing operation performed in the
apparatus for automatically adjusting offset correction values shown in
FIG. 2;
FIGS. 4A and 4B are respectively a diagram showing the values of an
electrical angle fl, the signs of plus and minus of offset correction
errors dIu and dIv and the magnitude relation therebetween in the first
and third embodiments of the present invention, and a diagram showing
adjustment values for an offset correction value cl of phase U and an
offset correction value c2 of phase V in the first and third embodiment of
the present invention;
FIGS. 5A and 5B are respectively a diagram showing the values of an
electrical angle fl, the signs of plus and minus of offset correction
errors dIu and dIv and the magnitude relation therebetween in the second
and third embodiments of the present invention, and a diagram showing
adjustment values for an offset correction value cl of phase U and an
offset correction value c2 of phase V in the second and third embodiment
of the present invention;
FIG. 6 is a block diagram showing a digital controller for a servo motor
having an apparatus for automatically adjusting offset correction values
for current detectors of a third embodiment of the present invention;
FIG. 7 is a block diagram showing an internal structure of the apparatus
for automatically adjusting offset correction values shown in FIG. 6;
FIG. 8 is a flow chart showing the processing operation performed in the
apparatus for automatically adjusting offset correction values shown in
FIG. 6;
FIG. 9 is a block diagram showing a digital controller for a servo motor
having an apparatus for automatically adjusting offset correction values
for current detectors of a fourth embodiment of the present invention;
FIG. 10 is a block diagram showing an internal structure of the apparatus
for automatically adjusting offset correction values shown in FIG. 9;
FIG. 11 is a flow chart showing the processing operation performed in the
apparatus for automatically adjusting offset correction values shown in
FIG. 9; and
FIGS. 12A and 12B are respectively a diagram showing the values of an
electrical angle f1 and the signs of plus and minus of offset correction
errors dIu and dIv in the fourth embodiment of the present invention, and
a diagram showing adjustment values for the offset correction value cl of
phase U and the offset correction value c2 of phase V in the fourth
embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The preferred embodiments of the present invention will hereinafter be
described with reference to the accompanying drawings.
Embodiment 1
FIG. 1 is a block diagram showing a digital controller for a servo motor
including an apparatus for automatically adjusting offset correction
values for current detectors of a first embodiment of the present
invention. In the digital controller shown in FIG. 1, an adder 1 to which
a speed command value a is input is connected to both a sine-wave table 3
and an apparatus 4 for automatically adjusting offset correction values
through a speed control unit 2. Thus, a torque command value b output by
the speed control unit 2 is input to both the sine-wave table 3 and the
automatic offset correction value adjusting apparatus 4. An output
terminal of the automatic offset correction value adjusting apparatus 4
and an output terminal of a current detector 5 of phase U having an offset
value are connected to an adder 6, so that an offset correction value cl
of phase U output by the automatic offset correction value adjusting
apparatus 4 and a detected current value d1 of phase U having an offset
value output by the current detector 5 are input to the adder 6. The adder
6 and the sine-wave table 3 are connected to an adder 7 so that a current
command value el of phase U output by the sine-wave table 3 and a feedback
current value g1 of phase U output by the adder 6 are input to the adder
7. The adder 7 is connected to a servo motor 10 through a proportional
element 8 and a servo amplifier 9. The above-mentioned current detector 5
of phase U is provided between the servo amplifier 9 and the servo motor
10. Further, an output terminal of the automatic offset correction value
adjusting apparatus 4 and an output terminal of a current detector 11 of
phase V having an offset value are connected to an adder 12 so that an
offset correction value c2 of phase V output by the automatic offset
correction value adjusting apparatus 4 and a detected current value d2 of
phase V having an offset value output by the current detector 11 are input
to the adder 12. The adder 12 and the sine-wave table 3 are connected to
an adder 13 so that a current command value e2 of phase V output by the
sine-wave table 3 and a feedback current g2 of phase V output by the adder
12 are input to the adder 13. The adder 13 is connected to the servo motor
10 through a proportional element 14 and the servo amplifier 9. The
current detector 11 of phase V is provided between the servo amplifier 9
and the servo motor 10. In addition, the adders 7 and 13 are connected to
the servo motor 10 through an adder 15, a proportional element 16 and the
servo amplifier 9.
Further, the servo motor 10 is connected to an encoder 17 which is
connected to both the automatic offset correction value adjusting
apparatus 4 and the sine-wave table 3 through a position counter 18 so
that an electrical angle signal f of the servo motor 10 output by the
position counter 18 is input to both the automatic offset correction value
adjusting apparatus 4 and the sine-wave table 3. Further, the encoder 17
is connected to the adder 1 through a speed detector 19 so that a speed
feedback value h output by the speed detector 19 is input to the adder 1.
FIG. 2 is a block diagram showing an internal structure of the automatic
offset correction value adjusting apparatus 4 shown in FIG. 1. In FIG. 2,
means 21 for setting a speed control processing cycle receives both a
torque command value b and an electrical angle signal f of the servo motor
10 as its input, and passes both the torque command value b and the
electrical angle signal f therethrough and also sets a speed control
processing cycle on the basis of a speed control processing return flag so
that the processing proceeds to a next speed control processing cycle.
Means 22 for detecting rotation of the servo motor 10, to which the speed
control processing cycle setting means 21 is connected, receives both the
torque command value b and the electrical angle signal f as its input and
detects that the rotational direction is the same as that in the last
speed control processing cycle and the rotational speed is equal to or
lower than a predetermined upper limit set value so that a difference in
phase between the torque of the servo motor 10 and the torque command
value b does not raise a problem. Means 26 for detecting an electrical
angle, to which the rotation detecting means 22 is connected, receives
both the torque command value b and the electrical angle signal f as its
input. The electrical angle detecting means 26 is constituted by means 23
for detecting a maximum value which operates to store an electrical angle
as a first electrical angle f1 when the torque command value b is maximum,
means 24 for detecting a minimum value which operates to store an
electrical angle as a second electrical angle f2 when the torque command
value b is minimum, and an electrical angle counter 25 which operates to
count an electrical angle signal f and to output a speed control
processing return flag to the speed control processing cycle setting means
21, if the lapse of one period of the electrical angle is not detected,
and this electrical angle detecting means 26 operates at the time of
detection by the rotation detecting means 22. A judgement means 27, to
which the electrical angle detecting means 26 is connected, judges whether
or not a difference between the first and second electrical angles f1 and
f2 detected by the electrical angle detecting means 26 is 180 degrees.
Means 28 for judging an electrical angle existing range, to which the
judgement means 27 is connected, judges, when the judgement means 27
judges that a difference between the first and second electrical angles f1
and f2 is 180 degrees, in which one of eight division ranges obtained by
dividing the electrical angle of 360 degrees the first electrical angle f1
exists. Means 29 for outputting offset correction values, to which the
electrical angle existing range judging means 28 is connected, has
adjustment values for the offset correction values which were set in
accordance with the eight division ranges. With this structure, the offset
correction value outputting means 29 operates to add the adjustment values
for the offset correction values corresponding to the division ranges, in
which the first electrical angle f1 exists, to the offset correction
values, respectively, to thereby update the offset correction values and
to output the resultant values as offset correction values cl and c2. The
electrical angle existing range judging means 28 and the offset correction
value outputting means 29 constitute correction means 30, so that offset
correction values for the current detectors 5 and 11 shown in FIG. 1 are
corrected in accordance with the first electrical angle fl.
Further, initialization means 31, to which the rotation detecting means 22,
the judgement means 27 and the offset correction value outputting means 29
are connected, initializes the maximum value and the minimum value of the
torque command value b and the values of the first and second electrical
angles f1 and f2 on the basis of an initialization flag output from one of
the rotation detecting means 22, the judgement means 27 and the offset
correction value outputting means 29, and then outputs a speed control
processing return flag to the speed control processing cycle setting means
21. Besides, at the time of performing initialization of the processing
cycle, setting of initial values of the offset correction values is also
performed in the initialization means 31.
In the automatic offset correction value adjusting apparatus 4 having the
structure as described above, if correction errors have occurred in the
offset correction values of the current detectors 5, 11, a ripple having
the same period as that of the electrical angle is generated in the torque
of the servo motor 10, and there exist a first electrical angle f1 where
the torque command value b is maximum and a second electrical angle f2
where the torque command value b is minimum. In the present embodiment,
automatic adjustment of the offset correction values is performed by
detecting the first electrical angle f1.
FIG. 3 is a flow chart showing the processings performed in the automatic
offset correction value adjusting apparatus 4 shown in FIG. 2. Among the
steps of the processings, Steps S0 and S1 show processing steps of
initialization, and a speed control processing step SV and Steps S2 to S8
show processing step which are executed in a normal operation of the servo
motor 10. As shown in FIG. 3, firstly in Step S0, according to the
above-mentioned prior art, the offset correction values which are
determined at the time of turning on a power supply, are set as initial
values. Then, in Step S1, the maximum value b1 and the minimum value b2 of
the torque command value b and the values of the first and second
electrical angles f1 and f2 are initialized by the initialization means
31.
After a normal operation of the servo motor 10 is started and the speed
control processing step SV has been executed, in Step S2, the rotation
detecting means 22 detects the present rotational direction of the motor
shaft and then compares this rotational direction thus detected with the
rotational direction in the last speed control processing cycle. If the
rotational direction is changed, the processing proceeds to Step 8, where
the maximum value and the minimum value of the torque command value b and
the values of the first and second electrical angles f1 and f2 are
initialized by the initialization means 31, and then the processing
proceeds to a next speed control processing cycle. On the other hand, if
the present rotational direction is the same as that in the last speed
control processing cycle, the processing proceeds to Step S3. In Step S3,
the present rotational speed is detected by the rotation detecting means
22. Then, if the present rotational speed thus detected is equal to or
higher than a predetermined upper limit set value, in the same manner as
that of Step S2, the processing proceeds to Step S8, and the maximum value
and the minimum value of the torque command value b and the values of the
first and second electrical angles f1 and f2 are initialized by the
initialization means 31, and then the processing proceeds to a next speed
control processing cycle. On the other hand, if the rotational speed is
equal to or lower than the predetermined upper limit set value, the
processing proceeds to Step S4. In Step S4, until the time when the
electrical angle counter 25 detects the lapse of one period of the
electrical angle, the torque command value b and the electrical angle
signal f are input to the maximum value detecting means 23 and the minimum
value detecting means 24 once at every speed control processing cycle, and
the value of the electrical angle signal at the time when the torque
command value b measured during one period of the electrical angle becomes
maximum is stored as a first electrical angle f1 in the maximum value
detecting means 23, and the value of the electrical angle signal at the
time when the torque command value b measured during one period of the
electrical angle becomes minimum is stored as a second electrical angle f2
in the minimum value detecting means 24. If the lapse of one period of the
electrical angle is not detected, the processing proceeds to a next speed
control processing cycle. On the other hand, if the lapse of one period of
the electrical angle is detected, the processing proceeds to Step S5. In
Step S5, based on the fact that a torque ripple of the servo motor 10 due
to correction errors of the offset correction values has the same period
as that of the electrical angle, if an absolute value of a difference
between the first and second electrical angles f1 and f2 is not 180
degrees, it is judged by the judgement means 27 that a torque ripple due
to any factor other than corre | | |
