Motor control apparatus equipped with a controller for controlling rotational position of motor

In a motor control apparatus for controlling a rotational position of a motor, a rotation detector detects the rotational position of the motor, and outputs first and second detection signals having phases corresponding to a detected rotational position of the motor and different from each other, and a position detecting circuit detects a rotational position in a unit which is less than one cycle of the first and second detection signals based on the first and second detection signals, and outputs a rotational position signal representing a detected rotational position. Further, a motor controller compares the rotational position signal with a reference position signal representing a reference rotational position of the motor to obtain a position error, and controls the rotational position of the motor so that the position error is minimized.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a motor control apparatus for use in 
motors such as a brush-equipped DC motor, a brushless motor, or the like, 
and in particular, to a motor control apparatus equipped with a controller 
for controlling a rotational position of a motor so that a positional 
error is minimized by comparing a rotational position signal with a 
reference position signal, with higher-resolution position control and 
speed control. 
2. Description of the Prior Art 
In recent years, office automation equipment such as copying machines, 
printers or the like have been advancing toward digitization, higher 
definitions, and coloring. With this trend, motors used in this equipment 
have been increasingly required to be capable of high-resolution, 
high-precision rotational position control as well as high-precision speed 
control over a wide range of rotational speed. 
An example of the motor control apparatus according to the prior art is 
described below with reference to the accompanying drawings. 
A prior art example is described, for example, in the Japanese Patent 
Examined Publication (Koukoku) No. Showa 63-10668. FIG. 11 is a schematic 
block diagram of this conventional motor control apparatus. 
Referring to FIG. 11, reference numeral 31 denotes a motor, and 32 denotes 
a speed generator for generating a signal representing a rotational speed 
of the motor 31. Denoted by 33 is an FG signal generating circuit 
(frequency signal generating circuit) for generating a rotational speed 
signal (FG signal) having a period corresponding to a rotational speed of 
the motor 31. A reference speed signal generator 100 generates a reference 
speed signal having a predetermined constant period or frequency 
corresponding to the FG signal, and outputs the reference speed signal to 
the speed control circuit 34. The above-mentioned rotational speed signal 
is compared with the reference speed signal from the reference speed 
signal generator 100 by the speed control circuit 34, and a resulting 
speed error signal is fed to a driving circuit 36 via a D/A converter 35. 
In this way, the rotational speed of the motor 31 is controlled so as to 
be constant. 
However, the conventional motor control apparatus shown as above has had 
the following problems. 
In the conventional motor control apparatus shown in FIG. 11, because the 
frequency of an output signal of the speed generator 32 decreases during a 
low-speed rotation, the control rate decreases, and then, it is often 
difficult to implement a stable speed control. Also, it is impossible to 
implement a motor rotational position control when the motor is stepped. 
As a motor which can control the rotational position, stepping motors have 
been available conventionally. As is well known to those skilled in the 
art, in particular when the stepping motor is rotated at a low speed, the 
stepping motor would show significant rotational variations. Therefore, in 
the case where rotation control for variations in low-speed rotation is 
required, there has been a need for additionally providing a fly wheel 
having a larger inertia. 
Also for stepping motors, it would be necessary to keep a continuous flow 
of a rather large driving current through driving coils for the purpose of 
retaining the stop position. This would pose problems in terms of heat 
generation and power consumption as well. 
SUMMARY OF THE INVENTION 
An essential object of the present invention is therefore to provide a 
motor control apparatus capable of performing a rotational position 
control with a higher resolution and a higher precision over a wide range 
of speed. 
Another object of the present invention is therefore to provide a motor 
control apparatus capable of performing a rotational position control and 
a speed control with a higher resolution and a higher precision over a 
wide range of speed. 
In order to achieve the above-mentioned objectiven, according to one aspect 
of the present invention, there is provided a motor control apparatus for 
controlling a rotational position of a motor, the apparatus including: 
a rotation detector for detecting the rotational position of the motor, and 
outputting first and second detection signals having phases corresponding 
to a detected rotational position of the motor and different from each 
other; 
a position detector for detecting a rotational position in a unit finer 
which is less than one cycle of the first and second detection signals 
based on the first and second detection signals outputted from the 
rotation detector, and outputting a rotational position signal 
representing a detected rotational position; and 
a motor controller for comparing the rotational position signal outputted 
from the position detector with a reference position signal representing a 
reference rotational position of the motor to obtain a position error, and 
controlling the rotational position of the motor so that the position 
error is minimized. 
According to another aspect of the present invention, there is provided a 
motor control apparatus for controlling a rotational position and a 
rotation speed of a motor, the apparatus including: 
a rotation detector for detecting the rotational position of the motor, and 
outputting first and second detection signals having phases corresponding 
to a detected rotational position of the motor and different from each 
other; 
a position detector for detecting a rotational position in a unit which is 
less than one cycle of the first and second detection signals based on the 
first and second detection signals outputted from rotation detector, and 
outputting a rotational position signal representing a detected rotational 
position; 
a frequency generator means for generating and outputting a rotation speed 
signal corresponding to the rotation speed of the motor based on either 
one of the first and second detection signals outputted from the rotation 
detector; 
position controller for detecting a position error between a reference 
position signal representing a reference position of the motor and the 
rotational position signal outputted from the position detector, and 
generating and outputting a position control signal representing a 
detected position error; 
a speed controller means for detecting a speed error between a reference 
speed signal representing a reference speed of the motor and the rotation 
speed signal outputted from the frequency signal generator, and generating 
and outputting a speed control signal representing a detected speed error; 
a mixer for adding the position control signal outputted from the position 
controller and the speed control signal outputted from the speed 
controller, and outputting a sum signal representing a sum of an addition 
result; and 
a motor controller means for controlling the rotational position and the 
rotation speed of the motor based on the sum signal outputted from the 
mixer so that the position error and the speed error are minimized, 
respectively. 
According to a further aspect of the present invention, there is provided a 
motor control apparatus for controlling a rotational position and a 
rotation speed of a motor, the apparatus including: 
a rotation detector for detecting the rotational position of the motor, and 
outputting first and second detection signals having phases corresponding 
to a detected rotational position of the motor and different from each 
other; 
a position detector means for detecting a rotational position in a unit 
which is less than one cycle of the first and second detection signals 
based on the first and second detection signals outputted from the 
rotation detector, and outputting a rotational position signal 
representing a detected rotational position; 
a frequency signal generator means for generating and outputting a rotation 
speed signal corresponding to the rotation speed of the motor based on 
both of the first and second detection signals outputted from the rotation 
detector; 
a position controller for detecting a position error between a reference 
position signal representing a reference position of the motor and the 
rotational position signal outputted from the position detector, and 
generating and outputting a position control signal representing a 
detected position error; 
a speed controller means for detecting a speed error between a reference 
speed signal representing a reference speed of the motor and the rotation 
speed signal outputted from the frequency signal generator, and generating 
and outputting a speed control signal representing a detected speed error; 
a mixer for adding up the position control signal outputted from the 
position controller and the speed control signal outputted from the speed 
controller, and outputting a sum signal representing a sum of an addition 
result; and 
a motor controller means for controlling the rotational position and the 
rotation speed of the motor based on the sum signal outputted from the 
mixing means so that the position error and the speed error are minimized, 
respectively. 
According to a still further aspect of the present invention, there is 
provided a motor control apparatus for controlling either one of a 
rotational position and a rotation speed of a motor, the apparatus 
including: 
a rotation detector for detecting the rotational position of the motor, and 
outputting first and second detection signals having phases corresponding 
to a detected rotational position of the motor and different from each 
other; 
a position detector for detecting a rotational position in a unit which is 
less than one cycle of the first and second detection signals based on the 
first and second detection signals outputted from the rotation detector, 
and outputting a rotational position signal representing a detected 
rotational position; 
a frequency signal generator means for generating and outputting a rotation 
speed signal corresponding to the rotation speed of the motor based on 
either one of the first and second detection signals outputted from the 
rotation detector; 
a position controller for detecting a position error between a reference 
position signal representing a reference position of the motor and the 
rotational position signal outputted from the position detector, and 
generating and outputting a position control signal representing a 
detected position error; 
a speed controller for detecting a speed error between a reference speed 
signal representing a reference speed of the motor and the rotation speed 
signal outputted from the frequency signal generator, and generating and 
outputting a speed control signal representing a detected speed error; 
a switch for switching over between the position control signal outputted 
from the position controller and the speed control signal outputted from 
the speed controller so as to select either one of the position control 
signal and the speed control signal in accordance with the rotation speed 
of the motor represented by the rotation speed signal outputted from the 
frequency signal generator, and outputting a selected control signal; and 
a motor controller for controlling either one of the rotational position 
and the rotation speed of the motor based on the selected control signal 
outputted from the switch so that either one of the position error and the 
speed error are minimized, respectively. 
According to a still more further aspect of the present invention, there is 
provided a motor control apparatus for controlling either one of a 
rotational position and a rotation speed of a motor, the apparatus 
including: 
a rotation detector for detecting the rotational position of the motor, and 
outputting first and second detection signals having phases corresponding 
to a detected rotational position of the motor and different from each 
other; 
a position detector for detecting a rotational position in a unit which is 
less than one cycle of the first and second detection signals based on the 
first and second detection signals outputted from the rotation detector, 
and outputting a rotational position signal representing a detected 
rotational position; 
a frequency signal generator for generating and outputting a rotation speed 
signal corresponding to the rotation speed of the motor based on either 
one of the first and second detection signals outputted from the rotation 
detector; 
a position controller for detecting a position error between a reference 
position signal representing a reference position of the motor and the 
rotational position signal outputted from the position detector, and 
generating and outputting a position control signal representing a 
detected position error; 
a speed controller for detecting a speed error between a reference speed 
signal representing a reference speed of the motor and the rotation speed 
signal outputted from the frequency signal generator, and generating and 
outputting a speed control signal representing a detected speed error; 
a switch for switching over between the position control signal outputted 
from the position controller and the speed control signal outputted from 
the speed controller so as to select either one of the position control 
signal and the speed control signal in accordance with the rotation speed 
of the motor represented by the reference speed signal, and outputting a 
selected control signal; and 
a motor controller means for controlling either one of the rotational 
position and the rotation speed of the motor based on the selected control 
signal outputted from the switch so that either one of the position error 
and the speed error are minimized, respectively. 
In the above-mentioned motor control apparatus, the position detector 
preferably comprises: 
a carrier signal generator for generating and outputting first and second 
carrier signals having frequencies higher than those of the first and 
second detection signals and having phases different from each other by a 
predetermined angle; 
a modulator means for modulating the first and second carrier signals 
outputted from the carrier signal generator according to the first and 
second detection signals, respectively, and outputting modulated first and 
second carrier signals; 
an adder for adding up the modulated first and second carrier signals 
outputted from the modulator, and outputting a sum signal of an addition 
result; and 
a phase detector for comparing a phase of the sum signal outputted from the 
adder means with a phase of either one of the first and second carrier 
signals outputted from the carrier signal generator, and detecting a phase 
representing the rotational position of the motor. 
In the above-mentioned motor control apparatus, the position detector also 
preferably comprises: 
a first inverter for inverting the first detection signal outputted from 
the rotation detector, and outputting an inverted first detection signal; 
a second inverter means for inverting the second detection signal outputted 
from the rotation detector, and outputting an inverted second detection 
signal; 
a switch switching signal generator for generating first, second, third and 
fourth switch switching signals at predetermined timings, respectively; 
a first switch including first and second switches, the first switcher 
switching over the first switch between the first detection signal 
outputted from the rotation detector and the inverted first detection 
signal outputted from the first inverter so as to select one of the first 
detection signal and the inverted first detection signal in accordance 
with the first switch switching signal outputted from the switch switching 
signal generator, outputting a selected first signal, switching over the 
second switch to divide and output a voltage of the selected first signal 
into voltages of a plurality of n steps in a voltage-dividing ratio which 
is changed in accordance with the third switch switching signal outputted 
from the switch switching signal generator so as to select one of divided 
voltages, and outputting a selected second signal; 
a second switcher including third and fourth switches, said second switcher 
switching over the third switch between the second detection signal 
outputted from the rotation detector and the inverted second detection 
signal outputted from the second inverter so as to select one of the 
second detection signal and the inverted second detection signal in 
accordance with the second switch switching signal outputted from the 
switch switching signal generator, outputting a selected third signal, 
switching over the fourth switch to divide and output a voltage of the 
selected third signal into voltages of a plurality of n steps in a 
voltage-dividing ratio which is changed in accordance with the fourth 
switch switching signal outputted from the switch switching signal 
generator so as to select one of divided voltages, and outputting a 
selected fourth signal; 
an adder for adding up the selected second signal outputted from the first 
switcher and the selected fourth signal outputted from said second 
switcher, and outputting a sum signal of an addition result; and 
a phase detector means for detecting a phase representing the rotational 
position of the motor based on the sum signal outputted from the adder 
with reference to either one of the first and second switch switching 
signals, and outputting a phase detection signal representing a detected 
phase, 
wherein the first and second switchers switch over the first, second, third 
and fourth switches in voltage-dividing ratios predetermined based on a 
predetermined trigonometric function so that harmonic components of the 
selected second signal outputted from the first switcher become smaller 
and harmonic components of the selected fourth signal outputted from the 
second switcher become smaller. 
In the above-mentioned motor control apparatus, the position detecting 
means also preferably comprises: 
a first invertor for inverting the first detection signal outputted from 
the rotation detector, and outputting an inverted first detection signal; 
a second inverter for inverting the second detection signal outputted from 
the rotation detector, and outputting an inverted second detection signal; 
a switch switching signal generator for generating first and second switch 
switching signals at predetermined timings, respectively; 
a first switcher including a first switch, the first switcher switching 
over the first switch to divide and output a voltage provided between the 
first detection signal and the inverted first detection signal into 
voltages of a plurality of 2n steps in a voltage-dividing ratio which is 
changed in accordance with the first switch switching signal outputted 
from the switch switching signal generator so as to select one of divided 
voltages, and outputting a selected first signal; 
a second switcher including a second switch, the second switcher switching 
over the second switch to divide and output a voltage provided between the 
second detection signal and the inverted second detection signal into 
voltages of a plurality of 2n steps in a voltage-dividing ratio which is 
changed in accordance with the second switch switching signal outputted 
from the switch switching signal generator so as to select one of divided 
voltages, and outputting a selected second signal; 
an adder for adding up the selected first signal outputted from the first 
switcher and the selected second signal outputted from the second 
switcher, and outputting a sum signal of an addition result; and 
a phase detector means for detecting a phase representing the rotational 
position of the motor based on the sum signal outputted from the adder 
with reference to either one of the first and second switch switching 
signals, and outputting a phase detection signal representing a detected 
phase, 
wherein the first and second switchers switch over the first and second 
switches in voltage-dividing ratios predetermined based on a predetermined 
trigonometric function so that harmonic components of the selected first 
signal outputted from the first switcher means become smaller and harmonic 
components of the selected second signal outputted from said second 
switcher become smaller. 
In the above-mentioned motor control apparatus, the motor is preferably a 
brush-equipped DC motor. 
In the above-mentioned motor control apparatus, the motor is alternatively 
and preferably a brushless motor. 
In the above-mentioned motor control apparatus, the rotation detector 
preferably comprises: 
a permanent magnet magnetized so as to have multi-poles, the permanent 
magnet rotating integrally with the motor; and 
a magneto-electric conversion element disposed close to the permanent 
magnet so as to be electromagnetically coupled with a magnetic field of 
the permanent magnet, the magneto-electric conversion element converting a 
change in a magnetic field of the permanent magnet corresponding to the 
rotational position of the motor into an electrical signal corresponding 
to the rotational position of the motor. 
In the first aspect of the present invention, with the above-mentioned 
constitution, there is provided a position detector for detecting a 
rotational position in a unit which is less than one cycle of the output 
signals from the rotation detector which outputs first and second 
detection signals having phases corresponding to the rotational position 
of the motor and different from each other. Then, the signal derived from 
the position detector is taken as a rotational position signal, and the 
motor is controlled based on a positional error between the rotational 
position signal, which is given in a unit obtained by dividing one cycle 
of the first and second detection signals into a plurality of n steps for 
every infinitesimal time interval, and the reference position signal. 
Thus, high-resolution, high-precision rotational position control can be 
accomplished. 
Further, in the second and third aspects of the present invention, the 
position control signal outputted from the position controller and the 
speed control signal outputted from the speed controller are mixed or 
added together with each other, or switched over therebetween. Thus, not 
only high-precision halt control but also high-precision rotational speed 
control over a wide range of speed including a low-speed rotation is 
enabled. 
In the first to third aspects of the present invention, the output signal 
from the adder can be approximated to be a sine waveform, so that harmonic 
components can be reduced. Thus, any shift of positional information due 
to harmonic components can be prevented, and high-precision rotational 
position detection and rotational position control can be enabled.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Preferred embodiments according to the present invention will be described 
below with reference to the attached drawings. 
A motor control apparatus of a first preferred embodiment according to the 
present invention is described below with reference to the accompanying 
drawings. 
FIG. 1 is a schematic block diagram showing the first preferred embodiment 
of the motor control apparatus according to the present invention. 
Referring to FIG. 1, reference numeral 1 denotes a motor, and 2 denotes a 
rotation detector. The rotation detector 2 outputs first and second 
position detection signals MR1 and MR2 each having phases which correspond 
to a rotational angular position of the motor 1, and which are different 
from each other by 90.degree.. In the present preferred embodiment, the 
position detection signal MR1 has a phase of cos.theta., and the signal 
has a phase of sin.theta.. The position detection signals MR1 and MR2 are 
generated so as to have a frequency of, for example, 512 waves per 
rotation of the motor 1. 
A block 3 enclosed by broken lines is a position detecting circuit for 
outputting a rotational position signal for one rotation. The position 
detecting circuit 3 contains an interpolation processing circuit 4 
(enclosed by broken line 4) for dividing one cycle of the position 
detection signals MR1 and MR2 into signals each having finer or 
infinitesimal time intervals or periods and generating and outputting a 
signal representing a detailed rotation position of the motor 1. The 
position detecting circuit 3 is an essential important component of the 
present invention. 
Next, the position detecting circuit 3 and the interpolation processing 
circuit 4 are described in more detail. 
Reference numerals 41 and 42 denote amplifiers for amplifying the first and 
second position detection signals MR1 and MR2, respectively. Each of 
reference numerals 43 and 44 denotes a multiplier block, and 47 denotes a 
carrier signal generating circuit for generating carrier signals each 
having a frequency (for example, several tens kHz to several hundreds kHz) 
sufficiently higher than those of the position detection signals MR1 and 
MR2, and each having phases different from each other by 90.degree.. The 
multiplier blocks 43 and 44 multiply the position detection signals 
amplified by the amplifiers 41 and 42, respectively, by the carrier 
signals from the carrier signal generating circuit 47, so that the carrier 
signals are modulated according to the position detection signals MR1 and 
MR2, respectively. In other words, the carrier signal generating circuit 
47 generates two-phase carrier signals whose phases are different from 
each other by 90.degree.. If one of the carrier signals is +sin.omega.t 
(.omega.: angular velocity, t: time), then another carrier signal is 
cos.omega.t or -cos.omega.t (here the former is used for description). 
One multiplier block 43 multiplies the position detection signal MR1 of one 
phase (cos.theta.) by one carrier signal (+sin.omega.t), while another 
multiplier block 44 multiplies the position detection signal MR2 of the 
other phase (sin.theta.) by the other carrier signal (+cos.omega.t). 
Respective output signals (+sin.omega.t.multidot.cos.theta.) and 
(+cos.omega.t.multidot.sin.theta.) from the multiplier blocks 43 and 44 
are applied to an adder 50, and then, the output signals are added up, so 
that an addition result of sin(.omega.t+.theta.) is obtained. 
The added-up signal outputted from the adder 50 is inputted to a low-pass 
filter 45 for removing a high-frequency component, in which unnecessary 
high-frequency components are removed therefrom. The low-pass filtered 
signal is then inputted to a waveform shaping circuit 46 which shapes the 
waveform of the inputted signal into a rectangular wave, and an output 
signal from the waveform shaping circuit 46 is inputted to a phase 
detector 52. 
The phase detector 52 performs a phase comparison between the output signal 
sin(.omega.t+.theta.) outputted from the waveform shaping circuit 46 and 
the output signal sin.omega.t outputted from the carrier signal generating 
circuit 47, and detects a phase .theta.. Alternatively, the phase detector 
52 may perform a phase comparison between the output signal 
sin(.omega.t+.theta.) outputted from the waveform shaping circuit 46 and 
the output signal cos.omega.t outputted from the carrier signal generating 
circuit 47, and detects a phase .theta.. 
More specifically, as shown in FIGS. 2A and 2B, the waveforms of the sine 
signals sin(.omega.t+.theta.) and sin.omega.t are shaped into rectangular 
waves having the same peak-to-peak values, respectively, and the signals 
are compared with each other in a form of rectangular wave, where .theta. 
is extracted as the pulse width of the rectangular wave and is converted 
into a digital signal through an A/D conversion. Next a rotational 
position detecting circuit 5 including the phase detector 52 will be 
described in detail. 
The rotational position detecting circuit 5 performs the phase comparison 
and a carry and cancellation process, and outputs the result thereof as 
rotational position data of, for example, 16 bits. 
Now assume that the rotation detector 2 outputs 512 waves of the output 
signal MR1 or MR2 per rotation, and further divides one wave of the 
position detection signals MR1 or MR2 by 128. The format of the 16-bit 
position data assumes that more significant 9 bits are assigned to 512 
waves of the position detection signal MR1 or MR2, while less significant 
7 bits are assigned to the position data of 128 divisions of one wave of 
the position detection signals MR1 or MR2. Further, the most significant 2 
bits out of the less significant 7 bits are used as carry and cancellation 
data. 
For example, the rotational position detecting circuit 5 and the carrier 
signal generating circuit 47 are digital circuits. 7-bit phase data 
representing a rotational phase from the phase detector 52 is inputted to 
both of a latch 105 and a carry and cancellation pulse generator 102, and 
then, the carry and cancellation pulse generator 102 generates a carry 
pulse or a carry cancellation pulse (up/down pulse) based on the more 
significant two bits among the 7-bit phase data from the phase detector 
52, and outputs the up/down pulse to the up/down counter 103. When the 
more significant two bits change from "11" to "00", then the up pulse is 
inputted to the up/down counter 103, the up/down counter 103 increments 
the counter value thereof by one. On the other hand, when the more 
significant two bits change from "00" to "11", then the down pulse is 
inputted to the up/down counter 103, the up/down counter 103 decrements 
the counter value thereof by one. The count value of 9 bits outputted from 
the up/down counter 103 is inputted to a latch 104. The latches 105 and 
104 latch the inputted less significant 7-bit data and the more 
significant 9-bit data at periodical simultaneous timings, and then, 
output the rotational position signal having a 16-bit position data 
representing a rotational position of the motor 1 to the position control 
circuit 6. 
Accordingly, as the motor 1 rotates, the less significant 7 bits change, 
for example, as 0000000, 0000001, 0000010, . . . , and a carry occurs when 
the more significant 2 bits out of the less significant 7 bits have 
changed from 11 to 00 with an overflow. 
As a result, the least significant bit of the more significant 9 bits 
changes from 0 to 1, where the processing moves to the next one wave of 
the position detection signal MR1 or MR2. By repeating this process, data 
of all 16 bits changes every infinitesimal or minute rotational angle in 
response to the rotational angle of the motor 1. Thus, upon completion of 
one rotation of the motor 1, data of all 16 bits return to all 0's of the 
initial value from a state of all 1's. 
On the other hand, in the case of reverse rotation of the motor 1, it is 
assumed that a carry cancellation occurs when the more significant 2 bits 
out of the less significant 7 bits have changed from 00 to 11. 
By executing the above operation, positions within one rotation can be 
divided into 16-bit data, that is, 65536 data. 
A reference position signal generator 101 generates a reference position 
signal representing a reference rotational position data and having data 
which is incremented by one at a predetermined constant time interval 
every 1/2.sup.16 of one rotation of the motor 1, and outputs the reference 
position signal to the position control circuit 6. It is noted that the 
reference position signal should be fed as a sufficiently high-resolution 
high-precision signal matching the trend toward higher-resolution, 
higher-precision position detection signals (which is applicable to the 
reference speed signals and the like in the later-described preferred 
embodiments). 
The position control circuit 6 compares the reference position signal from 
the reference position signal generator 101 with the rotational position 
signal outputted from the position detecting circuit 3, and outputs a 
position control signal corresponding to a resulting positional error of a 
difference therebetween. The position control signal is inputted to a 
driving circuit 8 via a D/A converter 7. Then the motor 1 is controlled in 
rotational position so that the resulting rotational position error is 
minimized as close to zero as possible. 
As to the signal processing from the position control circuit 6 to the D/A 
converter 7 to the driving circuit 8, there may be some routes, along 
which the positional error signal is passed to the driving circuit 8 
through a digital filter, an amplifier, and a D/A converter 7, or along 
which the positional error signal is passed through a D/A converter 7 and 
then, in an analog form, through a filter and an amplifier so as to be 
inputted to the driving circuit 8, and so forth. 
As shown above, in the motor control apparatus according to the present 
invention, one wave of the output signal of the rotation detector 2 is 
divided into a plurality of phases by the interpolation processing circuit 
4, every infinitesimal time interval, and a resulting divided signal is 
taken as a rotational position signal. This makes it possible to implement 
rotational position control of high resolution and high positional 
precision. 
FIG. 3 is a schematic block diagram showing a second preferred embodiment 
of the motor control apparatus according to the present invention. In FIG. 
3, the same components as those of the preferred embodiment of FIG. 1 are 
designated by the same reference numerals in principle and their 
description is omitted. 
Referring to FIG. 3, reference numeral 9 denotes an FG signal generating 
circuit for generating a rotational speed signal (FG signal) having a 
frequency corresponding to a rotational speed, based on an exclusive Or 
calculation result between both of two-phase position detection signals 
(referred to as two-phase signals hereinafter) MR1 and MR2 whose phases 
are different from each other by 90.degree. in response to the rotational 
position of the motor 1. The FG signal generating circuit 9 may generate 
the rotational speed signal or FG signal based on either one of the 
two-phase signals MR1 and MR2. 
A reference speed signal generator 100 generates a reference speed signal 
having a predetermined constant period or frequency corresponding to the 
FG signal, and outputs the reference speed signal to a speed control 
circuit 12 and an integrator 10. The integrator 10 integrates in time the 
reference speed signal from the reference signal generator 100, and then, 
outputs an integrated signal, namely, a reference position signal to a 
position control circuit 11. 
The speed control circuit 12 compares the reference speed signal from the 
reference speed signal generator 100 and the rotational speed signal or FG 
signal from the FG signal generating circuit 9 with each other so as to 
generate a control signal corresponding to a resulting speed error of a 
speed difference therebetween. 
On the other hand, the position control circuit 11, which has a 
constitution similar to that of FIG. 1, compares the reference position 
signal, which is obtained from the reference speed signal via the 
integrator 10, with the rotational position signal outputted from the 
position detecting circuit 3, and generates a control signal corresponding 
to a resulting positional error of a difference therebetween. The speed 
control signal corresponding to the speed error and the position control 
signal corresponding to the positional error are mixed so as to be added 
together by a mixing circuit 13 of an adder. The output signal from the 
mixing circuit 13 is inputted to the driving circuit 8 via the D/A 
converter 7. Thus, in the motor 1, the rotational position and the 
rotational speed thereof are controlled so that the positional error and 
the speed error are minimized, respectively, as close to zero as possible. 
As shown above, in the second preferred embodiment according to the present 
invention, with the use of the control signal obtained by adding up the 
speed control signal corresponding to the speed error and the position 
control signal corresponding to the positional error, controlling the halt 
position and enhancing the rotational speed precision at a certain 
constant rotational speed are achieved. 
When the position detecting circuit 3 detects the rotational position by 
the above-mentioned interpolating detection, enough of a higher resolution 
can be attained for a range of the low-speed rotation to implement stable 
control. Further, as the motor 1 comes to a higher-speed rotation, the 
frequency of the interpolating detection becomes higher, and this requires 
a higher speed processing. However, since the processing naturally has a 
limit speed, there is such a possibility that some error may occur. 
In the second preferred embodiment of FIG. 3, the speed control circuit 12 
may be changed to a speed and phase control circuit, in which the 
frequency and phase components of the reference speed signal and the 
frequency and phase components of the FG signal are compared with each 
other, respectively, so that signals of a speed error and a phase error 
can be outputted to the mixing circuit 13. 
FIG. 14 shows a motor control apparatus of a modified embodiment of the 
second preferred embodiment shown in FIG. 3. Differences between the 
preferred embodiments shown in FIGS. 3 and 14 will be described 
hereinafter. 
Referring to FIG. 14, the motor control apparatus of the modified second 
preferred embodiment further comprises an additional speed control circuit 
17, a switch 18, and a switching controller 19. The speed control circuit 
17 differentiates the rotational position signal outputted from the 
position detecting circuit 3 to obtain a rotation speed signal, compares 
the reference speed signal from the reference speed signal generator 100 
with the rotation signal obtained through the differential to generate a 
control signal representing a speed error of a difference therebetween, 
and then, outputs the control signal through the switch 18 to the mixing 
circuit 13. 
On the other hand, the speed control circuit 12 outputs the control signal 
through the switch 18 to the mixing circuit 13. The switching operation of 
the switch 18 is controlled by the switching controller 19 in accordance 
with the speed represented by the reference speed signal. 
When the speed of the reference speed signal is equal to or lower than a 
predetermined threshold speed, the switching controller 19 controls the 
switch 18 so that the control signal from the speed control circuit 17 is 
outputted through the switch 18 to the mixing circuit 13. On the other 
hand, when the speed of the reference speed signal is higher than the 
predetermined threshold speed, the switching controller 19 controls the 
switch 18 so that the control signal from the speed control circuit 12 is 
outputted through the switch 18 to the mixing circuit 13. 
Therefore, in the case of the low rotation speed of the motor 1, namely, 
even when the FG signal outputted from the FG signal generating circuit 9 
has a low frequency, in a manner similar to that of the first preferred 
embodiment according to the present invention, the control of the 
rotational position and the control for the halt position can be 
performed. Further, in the case of a higher rotation speed, since the 
control signal from the speed control circuit 12 has noise components 
smaller than those of the control signal from the speed control circuit 
17, the precision for the variation in the rotation speed can be improved. 
FIG. 4 is a schematic block diagram showing a third preferred embodiment of 
the motor control apparatus according to the present invention, in which 
the occurrence of a detection limit speed for a range of high-speed 
rotation can be avoided. In FIG. 4, the same components as those of the 
preferred embodiments of FIGS. 1 and 3 are designated by the same 
reference numerals in principle and their description is omitted. 
Referring to FIG. 4, reference numeral 15 denotes a speed and phase control 
circuit, which compares a rotational speed signal outputted from the FG 
signal generating circuit 9 with a reference speed signal from the 
reference speed signal generator 100, and then, generates a control signal 
corresponding to a frequency error of a frequency difference therebetween 
and a phase error of a phase difference therebetween. On the other hand, 
reference numeral 14 denotes a position control circuit, similar to those 
designated by reference numerals 6 and 11 respectively shown in FIGS. 1 
and 3, which compares a reference position signal from the reference 
position signal generator 101 and a rotational position signal outputted 
from the position detecting circuit 3 with each other, and then, generates 
a control signal corresponding to a resulting positional error of a 
difference therebetween. 
Reference numeral 16 denotes a control signal switching circuit, which 
switches over between the control signal outputted from the position 
control circuit 14 and the control signal outputted from the speed and 
phase control circuit 15, according to a rotational state or a rotational 
speed of the motor 1. The switching over operation of the switching 
circuit 16 is controlled by a switching controller 200 in accordance with 
the FG signal outputted from the FG signal generating circuit 9. The 
above-mentioned switching operation is implemented in principle by an 
automatic switching operation, but may also be implemented by a manual 
switching operation. 
The output signal from the switching circuit 16 is inputted to the driving 
circuit 8 via the D/A converter 7, and then, either the rotational 
position or the rotational speed of the motor 1 is controlled in 
accordance with a driving control signal outputted from the driving 
circuit 8. 
An operation of the motor control apparatus with the above-mentioned 
constitution will be described. 
In the stages of start to a low-speed rotation having a rotational speed up 
to a predetermined reference rotational speed, the switching circuit 16 is 
switched over to the control signal derived from the position control 
circuit 14, in which state the rise of the number of revolutions is 
effected in accompaniment by the high-resolution position detection 
implemented by the interpolating detection continued from the start time. 
Thus, even at a timing when the predetermined reference number of 
revolutions or the predetermined reference rotational speed is reached, 
stable motor control can be achieved through the high-resolution 
rotational position control. 
In order to obtain a middle-speed rotation, in a manner similar to that of 
the low-speed rotation, the switching circuit 16 is switched over to the 
control signal derived from the position control circuit 14 for the start 
time, in which state the rise of the number of revolutions is effected in 
accompaniment by the high-resolution position detection implemented by the 
interpolating detection. Then, at a timing when the predetermined 
reference rotational speed is reached, the switching circuit 16 is 
switched over to the control signal derived from the speed and phase 
control circuit 15, and then, stable rotational speed control can be 
achieved. 
Further, in order to obtain a high-speed rotation, in a manner similar to 
that of the low-speed rotation, the rise of the number of revolutions is 
effected in accompaniment by the high-resolution position detection 
implemented by the interpolating detection for the start time. With the 
rotational speed is increased, and when the interpolating detection 
becomes a processing of high-frequency range until the interpolating 
detection enters such a high-frequency range so as to reach the detection 
limit speed, then the switching circuit 16 is switched over to the control 
signal derived from the speed and phase control circuit 15, and then, any 
misdetection due to the detection limit can be eliminated, and also, the 
rotational speed can be maintained. In addition, since the motor 1 is 
controlled by the rotational position control during the acceleration 
stage from the start time, the rotational position precision can also be 
maintained. 
As shown above, in the third preferred embodiment according to the present 
invention, controlling the switching over operation among the speed error 
signal, the phase error signal and the positional error signal, depending 
on which is preferred, the enhancement of rotational position precision or 
the enhancement of rotational speed precision of the motor 1, namely, 
according to the rotational speed of the motor 1 is achieved. Accordingly, 
stable motor control with a higher precision can be performed in a wider 
speed range. 
FIG. 12 shows a modified third preferred embodiment of the motor control 
apparatus which is modified from that shown in FIG. 4. As shown in FIG. 
12, the switching over operation of the switching circuit 16 may be 
controlled by the switching controller 200, depending on the rotational 
speed of the motor 1 to be controlled, in accordance with the reference 
speed signal outputted from the reference speed signal. 
Depending on the circumstances, it may be arranged that the motor control 
apparatus of the second preferred embodiment and the motor control 
apparatus of the third preferred embodiment are provided in combination, 
in which both of (a) the mixed motor control system for effecting the 
position control, and the speed and phase control and (b) the switching 
control system for effecting switching between the position control, and 
the speed and phase control are used in combination so that the two 
systems can be selectively switched over, thus, this makes it possible to 
switch over among three types of controls comprising (a) the position 
control, (b) the speed control (or speed and phase control), and (c) the 
mixed control of position control and speed control (or speed and phase 
control). With this arrangement, various kinds of controls can be 
performed according to the type and rotational state of the motor 1 to be 
controlled. 
Now preferred embodiments of the interpolation processing circuit 4 
included in the position detecting circuit 3 of the preferred embodiments 
according to the present invention shown in FIGS. 1, 3, and 4 will be 
described in detail. 
The conventional interpolation processing circuit is exemplified by one as 
described in the Japanese Patent Laid-Open Publication No. Heisei 
2-248816. With this arrangement, however, there would be some cases where 
the output signal from the mixer contains such a large amount of 
unnecessary high-frequency components, and unnecessary components which 
have failed to be removed by the filter appear as a deterioration in 
positional information, and then, this requires further improvement in 
order to achieve the high-precision position control. 
FIG. 5 is a circuit diagram of a preferred embodiment of the interpolation 
processing circuit 4 of the motor control apparatus according to the 
present invention, which has been adapted to more practical use with the 
aim of improving those problems. 
Referring to FIG. 5, reference numeral 301 denotes a rotation detector, 
which outputs two-phase signals MR1 and MR2 each having a phases which 
correspond to a rotational position of the motor 1 and which are different 
from each other by 90.degree.. Reference numerals 302 and 303 denote 
amplifiers for amplifying two-phase signals MR1 and MR2 from the rotation 
detector 301, respectively. 
Reference numerals 304 and 305 denote first and second voltage-dividing 
ratio switching circuits, respectively, for dividing the voltages of the 
output signals MR1 and MR2 through the amplifiers 302 and 303 from the 
rotation detector 301, into voltages according to pre-programmed 
voltage-dividing ratios at respective predetermined timings. Each of the 
first and second voltage-dividing ratio switching circuits 304 and 305 
divides the voltage or the inverted voltage (inverted by each of inverting 
buffers 121 and 125) of each of the output signals MR1 and MR2 amplified 
by the amplifiers 302 and 303 after being outputted from the rotation 
detector 301, into voltages of a plurality of n steps (where n is an 
integer equal to or larger than 2, and n=8 in the present preferred 
embodiment), in accordance with switch switching signals Sa, Sb, Sc and Sd 
generated by and outputted from a switch switching signal generating 
circuit 110. 
The switching operation is effected every minute or infinitesimal time 
interval which is obtained by dividing one cycle of the carrier signals 
described in FIG. 1 into a plurality of n infinitesimal time intervals, 
where n=16, for example. This will be described later with reference to 
FIG. 6. 
The first voltage-dividing ratio switching circuit 304 comprises a 
non-inverting buffer 120, an inverting buffer 121, a two-contact type 
analog switch 122 for selecting one of the output signals from the two 
buffers 120 and 121, and a four-contact type analog switch 123 having a 
resistance voltage divider for switching the voltage-dividing ratio in 
four steps. The switch 123 has voltage-dividing resistors R1 to R4 for 
voltage division in four steps, where the resistance values of the 
resistors are selected so that the voltage of the output signals from the 
switch 122 is divided at ratios predetermined based on a trigonometric 
function as will be described later. The switching operation of the 
voltage-dividing ratio by the first voltage-dividing ratio switching 
circuit 304 is executed in accordance with the switch switching signals Sa 
and Sc. 
The second voltage-dividing ratio switching circuit 305 comprises a 
non-inverting buffer 124, an inverting buffer 125, a two-contact type 
analog switch 126 for selecting one of the output signals from the two 
buffers 124 and 125, and a four-contact type analog switch 126 having a 
resistance voltage divider for switching the voltage-dividing ratio in 
four steps. The switch 126 has voltage-dividing resistors R1 to R4 for 
voltage division in four steps, where the resistance values of the 
resistors are selected so that the voltage of the output signals from the 
switch 126 is divided at ratios predetermined based on a trigonometric 
function as will be described later. The switching operation of the 
voltage-dividing ratio by the first voltage-dividing ratio switching 
circuit 305 is executed in accordance with the switch switching signals Sb 
and Sd. 
Designated by reference numeral 106 is an adder circuit for performing an 
addition of output signals outputted through resistors R and R from the 
first and second voltage-dividing ratio switching circuits 304 and 305. 
Designated by reference numeral 107 is a low-pass filter for removing 
high-frequency components from an output signal outputted from the adder 
circuit 106. Reference numeral 108 denotes a waveform shaping circuit for 
shaping a signal from which unnecessary components have been removed by 
the low-pass filter 107, into a rectangular wave. Reference numeral 109 
denotes a phase detector which detects the phase .theta. by making a phase 
comparison between the signal outputted from the waveform shaping circuit 
108 and the signal Sa (or Sb in a further preferred embodiment) outputted 
from the switch switching signal generating circuit 110, and then, outputs 
data representing the detected phase .theta. to the latch 105 and the 
carry and cancellation pulse generator 102 shown in FIG. 1. An operation 
of the present interpolation processing circuit 4 shown in FIG. 5 will be 
described below. 
The rotation detector 301 outputs the two-phase signals MR1 and MR2 having 
phases which correspond to the rotational position of the motor 1, and 
which are different from each other by 90.degree.. The amplifiers 302 and 
303 amplify those two-phase signals MR1 and MR2, respectively. The output 
signal from the amplifier 302 is represented by Acos.theta., and the 
output signal from the amplifier 303 is represented by Asin.theta., where 
A is the amplitude of each of the amplified output signals MR1 and MR2 
through the amplifiers 302 and 303 from the rotation detector 301, and 
.theta. is the phase thereof. 
Reference characters Sa, Sb, Sc and Sd represent first, second, third and 
fourth switch switching signals, respectively. The switch switching 
timings shown in FIG. 6 are determined by these switch switching signals 
Sa, Sb, Sc and Sd. 
FIG. 6 shows timings for switching effected by the first and second 
voltage-dividing ratio switching circuits 304 and 305. 
In FIG. 6, it is shown that the switches 122, 123, 126 and 127 are 
connected to switch terminals a, b, c, d, e, f, g, h, i, j, k and l of 
FIG. 5 during the High periods thereof. In FIG. 6, the horizontal axis 
represents the time, where the time interval from T0 to T16 shown in FIG. 
6 is assumed to be one cycle, and the timing of T0 serves as a reference 
timing for phase comparison. 
FIG. 7(a) shows a state in which the first voltage-dividing ratio switching 
circuit 304 switches the voltage-dividing ratio in four steps on the 
output signal from either the non-inverting buffer 120 or the inverting 
buffer 121, in accordance with the switch switching signals Sa and Sc, and 
FIG. 7(a) shows a change in the output signal "ma" voltage-divided at the 
voltage-dividing ratios during one cycle period by the voltage-dividing 
ratio switching circuit 304. The resistance values of R1, R2, R3 and R4 
shown in FIG. 5 are previously determined so that the amplified output 
signal MR1 from the rotation detector 301 is divided into voltages of four 
steps at predetermined ratios predetermined based on a trigonometric 
function. 
The changing waveform voltage-divided at the predetermined voltage-dividing 
ratios shown in FIG. 7(a) corresponds to a stair-shaped waveform resulting 
from digitizing in time one carrier signal sin.omega.t in predetermined 
minute or infinitesimal time intervals (or sampling and holding the same 
carrier signal) which are minute divisions of one cycle of the carrier 
signal. Therefore, the voltage of the amplified output signal 
MR1=Acos.theta. from the rotation detector 301 is divided into the 
voltages of eight steps in the present preferred embodiment according to 
the above-mentioned voltage-dividing ratios, and then, this results in an 
output signal "ma" from the first voltage-dividing ratio switching circuit 
304. In other words, the output signal "ma" from the first 
voltage-dividing ratio switching circuit 304 is the result of such a 
process that the voltage of one detection signal MR1 outputted from the 
rotation detector 301 is divided into voltages of eight steps, using the 
resistors R1 to R4, at the ratios predetermined based on a trigonometric 
function (sin.omega.t), in accordance with the switch switching signals Sa 
and Sc shown in FIG. 5. The output signal "ma" can be approximated to the 
waveform represented by the following equation (1): 
EQU ma=Acos.theta..multidot.sin.omega.t (1) 
where if the period from T0 to T16 shown in FIG. 6 is one cycle, then 
.omega. is the angular frequency and t is the time. In FIG. 7(a), although 
the waveform of "ma" is different from that of sin.omega.t by a change of 
cos.theta., the waveform of "ma" is shown by the change at the 
voltage-dividing ratios predetermined based on sin.omega.t, as an example, 
for a better understanding of the change in the voltage-dividing ratios. 
Further, the plotting of the change in the output signal "ma" due to a 
change in cos.theta. for one cycle period is omitted in FIG. 7(a). 
By the way, the voltage-dividing ratios by the resistors R1, R2, R3 and R4 
are previously determined so as to be equal to the ratios of the voltages 
when the waveform of sin.omega.t is digitized into four time intervals 
each having 22.5 degrees for a quarter of cycle from 0 degree to 90 
degrees and is approximated into a stair-shaped waveform as shown in FIG. 
13, so that the difference or the distortion between the waveform of 
sin.omega.t (or cos.omega.t in a further preferred embodiment) and the 
stair-shaped waveform, namely, harmonic components of the stair-shaped 
waveform becomes smaller or the minimum as small as possible. Concretely 
speaking, as shown in FIG. 13, for example, the signal level of the 
stair-shaped waveform for a phase range from 22.5 degrees to 45 degrees is 
determined so that an area A500 of the sin .theta. waveform hatched from 
the top right toward the bottom left becomes equal to an area A501 of the 
stair-shaped waveform hatched from the top left toward the bottom right. 
In another example, the signal level of the stair-shaped waveform for a 
phase range from 22.5 degrees to 45 degrees may be determined so as to be 
equal to the time average value of the sin .theta. waveform. In a further 
example, the signal level of the stair-shaped waveform for a phase range 
from 22.5 degrees to 45 degrees may be determined so as to be equal to 
half the sum of the maximum and minimum levels of the sin .theta. 
waveform. 
Further, FIG. 7(b) shows a change in the output signal "mb" voltage-divided 
at the voltage-dividing ratios by the voltage-dividing ratio switching 
circuit 305, when the voltage of another detection signal MR2 from the 
rotation detector 301 is divided into voltages of eight steps, so as to be 
approximated to the stair-shaped waveform which is the result of 
digitizing another carrier signal cos.omega.t as in FIG. 7(a). 
In other words, the output signal "mb" from the second voltage-dividing 
ratio switching circuit 305 is a result of such a process that the voltage 
of the output signal MR2=sin.theta. from the rotation detector 301 is 
divided using the four resistors R1 to R4 at ratios predetermined based on 
a trigonometric function (cos.omega.t) in accordance with the switch 
switching signals Sb and Sd. The output signal "mb" can be approximated to 
the waveform represented by the following equation (2): 
EQU mb=Asin.theta..multidot.cos.omega.t (2) 
In this case also, although the waveform of the output signal "mb" is 
different from that of cos.omega.t by change in sin.theta., FIG. 7(b) 
shows the change in the output signal "mb" voltage-divided at the 
voltage-dividing ratios based on cos.omega.t, for the same reason as that 
of FIG. 7(a). 
As shown above, the first and second voltage-dividing ratio switching 
circuits 304 and 305 operate to process the first and second carrier 
signals sin.omega.t and cos.omega.t, respectively, by dividing and 
digitizing (or sampling and holding) their one cycle into the units of a 
predetermined minute or infinitesimal time interval, and then, the 
digitized first and second carrier signals are multiplied by the detection 
output signals MR1=cos.theta. and MR2=sin.theta., respectively. 
The adder circuit 106 performs an addition of the output signals "ma" and 
"mb" from the first and second voltage-dividing ratio switching circuits 
304 and 305. 
FIG. 7(c) shows the output signal "mc" after the addition by the addition 
circuit 106. The output signal "mc" from the adder circuit 106 is 
expressed by the following equation (3), showing that phase information is 
included therein: 
EQU mc=1/2.multidot.(ma+mb)=1/2.multidot.Asin(.omega.t+.theta.) (3) 
Designated by reference numeral 107 is the low-pass filter for removing 
high-frequency components from an output signal of the adder circuit 106. 
Reference numeral 108 denotes a waveform shaping circuit for shaping a 
signal from which unnecessary components have been removed by the low-pass 
filter 107, into a rectangular wave. 
The phase detector 109 detects the phase .theta. by making a phase 
comparison between a signal containing phase information and outputted 
from the waveform shaping circuit 108 and the switch switching signal Sa 
outputted from the switch switching signal generating circuit 110. 
As seen above, the interpolation processing circuit 4 of the present 
preferred embodiment can approximate to a sine waveform, the output signal 
from the adder circuit 106 is a result of adding up the output signals 
"ma" and "mb" voltage-divided in eight steps for each switching of the 
switches 122 and 123 or 126 and 127 and outputted from the first and 
second voltage-dividing ratio switching circuits 304 and 305. 
Further, by increasing the number of steps of voltage division by the 
voltage-dividing ratio switching circuits 304 and 305, the output signal 
"mc" from the adder circuit 106 can be approximated further to a sine 
wave, and then, the high-frequency components can be decreased. Therefore, 
the phase characteristics of the low-pass filter 107 can be improved so 
that the high-precision rotational position detection can be performed. 
FIG. 8 is a circuit diagram of a second preferred embodiment of the 
interpolation processing circuit 4 of the motor control apparatus 
according to the present invention. 
Referring to FIG. 8, reference numeral 401 denotes a rotation detector, 
which generates and outputs two-phase signals MR1 and MR2 having two 
phases which correspond to a rotational position of the motor 1 and which 
are different from each other by 90.degree.. Reference numerals 402 and 
403 denote amplifiers for amplifying the output signals MR1 and MR2 from 
the rotation detector 401. Reference numerals 404 and 405 denote first and 
second voltage-dividing ratio switching circuits, respectively, which 
divide the voltages of the output signals MR1 and MR2 or the inverted 
signals thereof, which are amplified by the amplifiers 402 and 403 after 
being outputted from the rotation detector 401, into voltages of a 
plurality of n steps (n=8 in the present preferred embodiment) in 
accordance with the switch switching signals Sa to Sd outputted from a 
switch switching signal generating circuit 410, and then, which switch the 
voltages of the output signals MR1 and MR2 or the inverted signals thereof 
in accordance with the switch switching signals Sa to Sd. 
Designated by reference numeral 406 is an adder circuit for performing an 
addition of the output signals from the first and second voltage-dividing 
ratio switching circuit 404 and 405. Designated by reference numeral 407 
is a low-pass filter for removing high-frequency components from the 
output signal from the adder circuit 406. Reference numeral 408 denotes a 
waveform shaping circuit for shaping a signal from which unnecessary 
components have been removed by the low-pass filter 407, into a 
rectangular wave. Reference numeral 409 denotes a phase detector which 
detects the phase .theta. by making a phase comparison between a signal 
outputted from the waveform shaping circuit 408 and a switch switching 
signal Sa (Sb in a further preferred embodiment) outputted from the switch 
switching signal generating circuit 410, and then, outputs data 
representing the detected phase .theta. to the latch 105 and the carry and 
cancellation pulse generator 102 shown in FIG. 1. 
Referring to FIG. 8, the first voltage-dividing ratio switching circuit 404 
comprises a four-contact type analog switch 420, a non-inverting buffer 
421, an inverting buffer 422, and a two-contact type analog switch 423. In 
a manner similar to that of the first voltage-dividing ratio switching 
circuit 404, the second voltage-dividing ratio switching circuit 405 
comprises a four-contact type analog switch 424, a non-inverting buffer 
425, an inverting buffer 426, and a two-contact type analog switch 427. 
The timings of the switch switching signals Sa, Sb, Sc and Sd are the same 
as those of the first preferred embodiment of the interpolation processing 
circuit 4. The output signals "ma" and "mb" from the first and second 
voltage-dividing ratio switching circuits 404 and 405 and the output 
signal "mc" from the adder circuit 406 are the same as those of the first 
preferred embodiment of the interpolation processing circuit 4. As shown 
above, in the present preferred embodiment, detecting the rotational 
position with a higher precision, in a manner similar to that of the first 
preferred embodiment of the interpolation processing circuit 4 is 
achieved. However, as shown in FIG. 8, the non-inverting buffers 421 and 
425 and the inverting buffers 422 and 426 are disposed in succession to 
the four-contact type analog switches 420 and 424 which perform the 
voltage division by the resistors R1 to R4, in which the switching 
operation of the two-contact type analog switches 423 and 427 is performed 
in accordance with the switch switching signals Sa and Sb. 
Therefore, in the first preferred embodiment of the interpolation 
processing circuit 4 shown in FIG. 5, when the turn-on resistances of the 
two-contact type analog switches 122 and 126 are changed, there occur 
differences in amplitude between the respective output signals from the 
first and second voltage-dividing ratio switching circuits 304 and 305. 
This causes such a possibility that the detection precision of rotational 
position may deteriorate. 
In contrast to this, the circuit arrangement of the second preferred 
embodiment of the interpolation processing circuit 4 shown in FIG. 8 
causes such an effect that influences of variations in the turn-on 
resistance values of the analog switches 423 and 427 can be reduced by 
increasing the resistance value of the resistor R of the adder circuit 
406. 
Next, FIG. 9 is a circuit diagram of a third preferred embodiment of the 
interpolation processing circuit 4 of the motor control apparatus 
according to the present invention. 
Referring to FIG. 9, reference numeral 501 denotes a rotation detector, 
which outputs the two phase signals having phases which correspond to a 
rotational position of the motor 1 and which are different from each other 
by 90.degree.. Reference numerals 502 and 503 denote amplifiers for 
amplifying output signal from the rotation detector 501. Reference 
numerals 504 and 505 denote first and second voltage-dividing ratio 
switching circuits, respectively, for dividing the voltages or the 
inverted voltages of the output signals amplified by the amplifiers 502 
and 503 after being outputted from the rotation detector 501, into 
voltages of a plurality of 2n steps (2n=8 in the present preferred 
embodiment) in accordance with the switch switching signals Sa and Sb 
outputted from a switch switching signal generating circuit 510, switching 
the switches 522 and 525 in accordance with the switch switching signals 
Sa and Sb, and outputs switched voltage signals "ma" and "mb". Designated 
by reference numeral 506 is an adder circuit for performing the addition 
of the output signals "ma" and "mb" from the first and second 
voltage-dividing ratio switching circuits 504 and 505. Designated by 
reference numeral 507 is a low-pass filter for removing high-frequency 
components from an output signal of the adder circuit 506. Reference 
numeral 508 denotes a waveform shaping circuit for shaping a signal from 
which unnecessary high-frequency components have been removed by the 
low-pass filter 507, into a rectangular wave. 
Reference numeral 509 denotes a phase detector which detects the phase 
.theta., as described with reference to FIG. 5, by making a phase 
comparison between a signal outputted from the waveform shaping circuit 
508 and a switch switching signal Sa (or Sb in a further preferred 
embodiment) outputted from the switch switching signal generating circuit 
510, and then, outputs data representing the detected phase .theta. to the 
latch 105 and the carry and cancellation pulse generator 102 shown in FIG. 
1. 
Referring to FIG. 9, the first voltage-dividing ratio switching circuit 504 
comprises a non-inverting buffer 520, an inverting buffer 521, and an 
eight-contact type analog switch 522. 
In a manner similar to that of the first voltage-dividing ratio switching 
circuit 504, the second voltage-dividing ratio switching circuit 505 
comprises a non-inverting buffer 523, an inverting buffer 524, and an 
eight-contact type analog switch 525. 
FIG. 10 shows the timings at which the first and second voltage-dividing 
ratio switching circuits 504 and 505 perform the switching operation in 
accordance with the switch switching signals Sa and Sb, with the 
arrangement of FIG. 9. 
In FIG. 10, it is shown that the switches 522 and 525 are connected to 
switch terminals a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, and p of 
FIG. 9 during the High periods. In FIG. 10, the horizontal axis represents 
time, where the time interval from T0 to T16 shown in FIG. 10 is assumed 
to be one cycle, and the timing of T0 serves as the reference for phase 
comparison. 
With regard to the resistors R1, R2, R3, R4, R5, R6 and R7 shown in FIG. 9, 
the resistance voltage-dividing ratios are determined so that a sine wave 
type approximation is done in eight steps on the voltages between the 
amplified output signals and the inverted signals thereof of the rotation 
detector 501. Not only the output signals "ma" and "mb" from the first and 
second voltage-dividing ratio switching circuits 504 and 505, but also the 
output signal "mc" from the adder circuit 506 are the same as those of the 
first preferred embodiment of the interpolation processing circuit 4. 
In the circuit arrangement of the third preferred embodiment of the 
interpolation processing circuit 4 shown in FIG. 9, as compared with the 
first preferred embodiment shown in FIG. 5, the two-contact type analog 
switches 122 and 126 of the voltage-dividing ratio switching circuits 304 
and 305 shown in FIG. 5 are not used, so that the possibility of 
deterioration in the detection precision due to variations in their 
turn-on resistances has been eliminated. Thus, the circuit arrangement of 
the third preferred embodiment is advantageous over the first preferred 
embodiment. 
Here is added a description on the controlled motor 1 and the rotation 
detector 2 of the preferred embodiments according to the present invention 
as shown in FIGS. 1, 3 and 4. 
As the controlled motor 1, it is appropriate to use a brush-equipped DC 
motor or a brushless motor. More specifically, when a brush-equipped DC 
motor or a brushless motor is used, the circuit operates so that the 
positional error is minimized as close to zero as possible in the 
operation of halt position control, in which case a motor driving current 
corresponding to a load torque flows. This means that when the load torque 
is smaller, the motor driving current needs only to be a small one 
correspondingly, while when the load torque is larger, a motor driving 
current corresponding to the load torque flows. 
That is, unlike conventional stepping motors, a large driving current does 
not need to flow in order to retain the halt position. This is more 
advantageous in terms of heat generation and power consumption. In the 
circuit operation, the feedback loop is made up so that the so-called 
step-out phenomenon, as would occur to the conventional stepping motors, 
will not occur. 
Further, for the rotation speed control, attaining higher-precision speed 
control with less low-speed variations is achieved. This eliminates the 
need of a fly wheel having a larger inertia which would be required for 
stepping motors. 
Also, the rotation detector 2 can be implemented with a relatively simple 
construction, by making it up from a permanent magnet which is magnetized 
so as to have multi-poles and which rotates integrally with the motor 1, 
and a magneto-electrical conversion element which is located in proximity 
or close to the permanent magnet so as to be electromagnetically coupled 
with the magnetic field of the permanent magnet and which converts a 
change in the magnetic field or magnetic force of the permanent magnet 
into an electrical signal corresponding to a rotational position of the 
motor 1. 
As described hereinabove, the present invention can produce the following 
advantageous effects. 
(a) The motor control apparatus of the present invention is provided with 
the rotation detector which outputs first and second signals having phases 
corresponding to a rotational position of the motor 1 and different from 
each other, and the position detecting circuit including the interpolation 
processing circuit which detects the rotational position in units which 
are less than one cycle of the first and second signals. In this 
arrangement, the reference position signal and the rotational position 
signal outputted by the position detecting circuit are compared with each 
other, and the feedback is applied so that the resulting positional error 
is minimized as close to zero as possible. Since the rotational position 
of the motor 1 is controlled in this way, rotational position control with 
high resolution and high positional precision can be attained. 
(b) The motor control apparatus of the present invention is provided with 
the mixing circuit of the adder circuit which mixes or adds up the 
position control signal outputted from the position control circuit and 
the speed control signal outputted from the speed control circuit. In this 
arrangement, the feedback is applied by the output signal from the mixing 
circuit so that the resulting positional error and the resulting speed 
error are minimized as close to zero as possible, and then, the rotational 
position and rotational speed of the motor 1 are controlled. Thus, 
implementing the control of the halt position and also enhancing the 
rotational precision at the constant rotational speed is achieved. 
(c) The motor control apparatus of the present invention is provided with 
the position control circuit and the speed control circuit. In this 
arrangement, the position control signal and the speed control signal 
outputted from those circuits are switched over depending on a rotational 
state or rotation speed of the motor 1, and the feedback is applied so 
that the resulting positional error or the resulting speed error is 
minimized as close to zero as possible, and then, the rotational position 
or the rotational speed of the motor 1 is controlled. Thus, even in such a 
high-speed region that the detection limit of the interpolation processing 
circuit 4 is reached, maintaining the stable rotational precision without 
any error is achieved. Further, controlling whether the rotational 
position precision or the rotational speed precision is enhanced by the 
switching selection of the switching circuit is also achieved. 
(d) The motor control apparatus of the present invention is provided with 
the first and second voltage-dividing ratio switching circuits for 
dividing the voltages or the inverted voltages of the output signals from 
the rotation detector, into voltages of a plurality of n steps, while 
changing the voltage-dividing ratio. In this case, the detection system is 
of a type for detecting the phase of the signal of the sum of the output 
signals of both the switching circuits is detected. In this arrangement, 
the output signal from the adder circuit can be approximated to a sine 
waveform, so that the low-pass filter characteristic can be improved, and 
the harmonic components can be reduced. Thus, any shift of detected 
position information due to high-frequency components can be prevented, so 
that the detection precision of rotational position can be enhanced. 
Further, the voltage of the first output signal or the inverted output 
signal thereof, as well as a second output signal or the inverted output 
signal thereof, which are outputted from the rotation detector is divided 
into voltages of a plurality of n steps in ratios predetermined based on a 
trigonometric function. Thus, the phase characteristic of the low-pass 
filter can be even more improved so that the rotational position detection 
with even higher precision can be expected. 
Although the present invention has been fully described in connection with 
the preferred embodiments thereof with reference to the accompanying 
drawings, it is to be noted that various changes and modifications are 
apparent to those skilled in the art. Such changes and modifications are 
to be understood as included within the scope of the present invention as 
defined by the appended claims unless they depart therefrom.