Motor control method and apparatus

A motor control method and apparatus in which when a motor rotating at prescribed RPM is to be stopped, a reverse maximum voltage is applied to the motor to rotate it in a reverse direction. Upon reversal of the direction of rotation of the motor, the reverse maximum voltage is cut off to stop the rotation of the motor in a shortest period of time.

BACKGROUND OF THE INVENTION 
The present invention relates to a motor control method and apparatus, and 
more particularly to a method of and an apparatus for controlling a 
secondary scanning motor employed in a radiation image information readout 
device, a radiation image information recording device, a facsimile 
machine, or the like for reading or recording image and character 
information. 
There have been developed radiation image information readout devices for 
reading radiation image information recorded on an image information 
carrier such as a stimulable phosphor sheet. 
When a certain phosphor is exposed to a radiation such as X-rays, 
.alpha.-rays, .beta.-rays, .gamma.-rays, ultraviolet rays, or electron 
beams, the phosphor stores a part of the energy of the radiation. When the 
phosphor exposed to the radiation is exposed to stimulating rays such as 
visible light, the phosphor emits light in proportion to the stored energy 
of the radiation. The phosphor exhibiting such a property is referred to 
as a "stimulable phosphor". 
The applicant has proposed radiation image readout systems employing a 
sheet of such a stimulable phosphor. The radiation image of an object such 
as a human body is recorded on the stimulable phosphor sheet, and then the 
stimulable phosphor sheet is exposed to stimulating light for emitting 
light therefrom which is read by a photoelectric transducer as an electric 
signal that is utilized for various diagnostic purposes. See for example 
U.S. Pat. Nos. 4,258,264, 4,276,473, and 4,315,318. 
In one of the radiation image readout systems, the stimulable phosphor 
sheet is fed by a sheet feeder at a constant speed during which time the 
sheet is scanned with stimulating light one-dimensionally in a direction 
normal to the direction of feed of the sheet. The light emitted from the 
sheet upon exposure to the stimulating light is photoelectrically read to 
produce radiation image information in the form of an electric signal. 
More specifically, the stimulable phosphor sheet is mechanically fed in one 
direction for secondary scanning thereof, while at the same time a light 
beam such as a laser beam is swept one-dimensionally over the sheet in the 
direction perpendicularly to the sheet feeding direction for primary 
scanning of the sheet. Therefore, the stimulable phosphor sheet is scanned 
two-dimensionally. The light emitted from the stimulable phosphor sheet is 
detected on a time series basis by a light detector such as a 
photomultiplier to produce image information. 
For improving the readout accuracy, it has been proposed to make a 
mechanical improvement for feeding the stimulable phosphor sheet at a 
constant speed. In addition, it has also been proposed to feed the 
stimulable phosphor sheet in one direction for reading the radiation image 
in a pre-reading mode, and then feed the stimulable phosphor sheet in the 
opposite direction to read the radiation image in a main reading mode. 
Various readout conditions in the main reading mode can be established on 
the basis of information attained in the pre-reading mode. 
The stimulable phosphor sheet is actually fed on an endless feed belt. 
Since it is necessary to keep the same laser beam scanning position in the 
pre-reading and main reading modes, the endless feed belt comprises a 
perforated endless belt and a suction box is disposed below the endless 
belt for attracting the stimulable phosphor sheet to the endless belt to 
maintain the sheet and the endless belt in the same relative position. 
To utilize the effective area of the stimulable phosphor sheet to the 
maximum extent, radiation image information is recorded on the sheet as 
fully over its length in the direction of feed thereof as possible. It is 
therefore preferable for the secondary scanning motor to be rotatable 
selectively in one direction or the other at a constant speed and also to 
be able to stop its rotation within a minimum period of time after 
application of a stop signal to the motor, so that the recorded 
information can be read to a maximum extent and free of distortions from 
the stimulable phosphor sheet. 
If the period of time required for the motor to stop its rotation after the 
stop signal has been applied thereto is short, the motor can quickly be 
brought into a standby condition in preparation for a next information 
readout cycle. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a motor control method 
and apparatus capable of shortening the period of time as much as possible 
which is required for the motor to bring its rotation to an end after 
application of a stop signal thereto. 
Another object of the present invention is to provide a method of 
controlling a motor to stop its rotation when the motor is driven to 
rotate at a speed of rotation dependent on a speed command signal, 
comprising the steps of applying a signal indicative of a reverse maximum 
speed to the motor from the time a rotation stop command is applied, 
thereafter detecting the direction of rotation of the motor, and applying 
a signal indicative of a substantially zero speed to the motor from the 
time a reversal of the direction of rotation of the motor is detected. 
Still another object of the present invention is to provide an apparatus 
for controlling a motor, comprising a motor, direction detecting means for 
detecting the direction of rotation of the motor, speed indicating (motor 
rotating) means for rotating the motor at a prescribed speed, rotation 
stop means for cutting off an output signal applied by the speed 
indicating means to the motor, reverse maximum speed indicating means for 
issuing a signal to rotate the motor at a maximum speed in a reverse 
direction which is opposite to the direction in which the motor is rotated 
by the speed indicating means, and a selector circuit responsive to an 
output signal from the rotation stop means for effecting switching from 
the signal of the speed indicating means to the signal of the reverse 
maximum speed indicating means for application to the motor. 
The above and other objects, features and advantages of the present 
invention will become more apparent from the following description when 
taken in conjunction with the accompanying drawings in which a preferred 
embodiment of the present invention is shown by way of illustrative 
example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
As shown in FIG. 1, a radiation image information readout device in which 
the present invention can be incorporated includes a stimulable phosphor 
sheet 2 serving as a recording medium on which a radiation image is 
recorded. Upon exposure to stimulating light in the form of a laser beam 
emitted from a laser beam source 14, the stimulable phosphor sheet 2 emits 
light which is photoelectrically read to obtain the radiation image 
information recorded on the sheet 2. The stimulable phosphor sheet 2 is 
fed in a secondary scanning direction indicated by the arrow A by an 
endless belt 8 trained around a roller 6 driven by a motor 4. The belt 8 
comprises a perforated suction belt having a plurality of holes defined 
therein, and a suction device 12 is disposed between the upper and lower 
runs of the belt 8. When the suction device 12 is actuated, the holes of 
the belt 8 communicate with the suction port (not shown) of the suction 
device 12 to draw air inwardly through the belt holes into the suction 
device 12 for thereby positioning the stimulable phosphor sheet 2 on the 
belt 8 without slippage thereon. 
The roller 6 is connected coaxially to a rotary encoder 10 serving as a 
distance detecting means for detecting the distance which the stimulable 
phosphor sheet 2 is fed. 
The laser beam source 14 serving as a stimulating light source preferably 
comprises an He - Ne laser. The laser beam emitted from the laser beam 
source 14 is directed to a galvanometer mirror 16 which scans the laser 
beam in a main scanning direction indicated by the arrow B. The stimulable 
phosphor sheet 12 irradiated with the laser beam emits light commensurate 
with the image information recorded on the sheet 12. The light emitted 
from the sheet 12 is led by a light guide 18 to a photomultiplier 20 which 
converts the detected light into an electric signal that is displayed on a 
CRT or the like. 
FIG. 2 shows an electric circuit incorporated in the radiation image 
information readout device. The rotary encoder 10 generates output pulses 
P dependent on the RPM of the motor 4 through an output terminal connected 
to the input terminal of a counter 22. The counter 22 counts the output 
pulses P from the rotary encoder 10. 
The counter 22 has an output terminal coupled to a speed computing unit 26 
which computes the speed of movement of the suction belt 8, i.e., the 
speed of travel of the stimulable phosphor sheet 2 based on the count 
output from the counter 22 and reference clock pulses generated by a 
reference clock pulse generator 24. The speed computing unit 26 is 
arranged to detect a change in the count of the counter 22 between 
reference clock pulses as a speed signal. This is because the output 
pulses P from the rotary encoder 10 correspond to the rotation of the 
motor 4, and hence the count of the counter 22 corresponds to the distance 
which the stimulable phosphor sheet 2 is fed. 
The speed computing unit 26 has an output terminal connected to one input 
terminal of a comparator 28 with its other input terminal coupled to the 
output terminal of a speed setting unit 30. The comparator 28 therefore 
detects the difference between the preset output from the speed setting 
unit 30 and the output from the speed computing unit 26, and applies the 
differential output to a voltage computing unit 32 which computes a 
voltage commensurate with the differential output and indicative of a 
speed. The speed-indicating (motor rotating) voltage issued from the 
output terminal of the voltage computing unit 32 is applied to a selector 
circuit 34. The selector circuit 34 is connected to the output terminal of 
a reverse maximum speed indicator 36. 
To the selector circuit 34, there are also connected a rotation stop switch 
40 and an output terminal of the rotary encoder 10 which produces an 
output R. The selector circuit 34 is responsive to the output signal from 
a rotation start switch 38 for selecting and issuing out the voltage 
generated by the voltage computing unit 32, and is also responsive to the 
output from the rotation stop switch 40 for selecting and issuing out the 
voltage generated by the reverse maximum speed indicator 36. 
The selector circuit 34 is also arranged such that when the polarity of the 
output R of the rotary encoder 10 is reversed after the output signal has 
been generated by the rotation stop switch 40, the selector circuit 34 
cuts off the voltage from the reverse maximum speed indicator 36. The 
output signal from the selector circuit 34 is amplified by a power 
amplifier 42 and then applied to the motor 4. 
The selector circuit 34 is illustrated in greater detail in FIG. 3. 
The rotation start switch 38 is connected to the SET terminal of a first 
flip-flop 44 with its output terminal connected through a first driver 46 
to a first relay coil 48. The first relay coil 48 serves to open and close 
a first relay contact 50 connected to the output terminal of the voltage 
computing unit 32. The rotation stop switch 40 is connected to the SET 
terminal of a second flip-flop 52 having its output terminal connected 
through a second driver 54 to a second relay coil 58 which opens and 
closes a second relay contact 56. 
The output terminal of the second flip-flop 52 is also connected to one 
input terminal of an AND gate 60, the other input terminal of which is 
supplied with the polarity reverse signal R from the rotary encoder 10. 
The output terminal of the AND gate 60 is coupled to the RESET terminals 
of the flip-flops 44, 52 and also to a third relay coil 64 through a third 
driver 62. The third relay coil 64 serves to open and close a third relay 
contact 66. 
The output terminal of the reverse maximum speed indicator 36 is connected 
to a side b of the second relay contact 56, which is connected to the 
third relay contact 66. The first relay contact 50 is connected to a side 
a of the second relay contact 56. 
Operation of the circuit shown in FIGS. 2 and 3 will be described below. 
When the rotation start switch 38 is turned on instantaneously, it produces 
an output signal to set the first flip-flop 44. The output from the first 
flip-flop 44 then energizes the first relay coil 48 to close the first 
relay contact 50. At this time, the second relay contact 56 is on the side 
a, and the third relay contact 66 is closed. Therefore, the voltage 
computing unit 32 is connected through the relay contacts 50, 56, 66 to 
the power amplifier 42. Stated otherwise, the selector circuit 34 responds 
to the output signal from the rotation start switch 38 to select the 
output voltage from the voltage computing unit 32. The selected output 
voltage is then amplified by the power amplifier 42 and applied to the 
motor 4 to energize the same. The rotation of speed of the motor 4 rotated 
is detected by the rotary encoder 10. The pulsed output P from the rotary 
encoder 10 is counted by the counter 22, the count of which is converted 
by the speed computing unit 26 into a speed signal. The speed signal from 
the speed computing unit 26 is compared by the comparator 28 with the 
speed setting from the speed setting unit 30. The detected differential 
output from the comparator 28 is applied to the voltage computing unit 32 
which issues a speed-indicating voltage representative of the differential 
output. Therefore, the rotation of the motor 4 is controlled so as to be 
equal to the rotation A corresponding to the speed setting of the speed 
setting unit 30 as shown in FIG. 4(a). 
The stimulable phosphor sheet 2 is now fed at a constant speed by the motor 
4 which is controlled to rotate as described above. When the stimulable 
phosphor sheet 2 has reached a prescribed position, a signal is generated 
by a detector (not shown) to actuate the rotation stop switch 40 which 
issues an output signal. The second flip-flop 52 is then set to energize 
the second relay coil 58 to shift the second relay contact 56 from the 
side a to the side b. As a consequence, the output signal from the reverse 
maximum speed indicator 36 is applied via the second and third relay 
contacts 56, 66 to the power amplifier 42, and the output voltage from the 
voltage computing unit 32 is blocked by the second relay contact 56 
against application to the power amplifier 42. Thus, the selector circuit 
34 responds to the output signal from the rotation stop switch 40 to 
select the output voltage from the reverse maximum speed indicator 36, 
rather than the speed-indicating voltage from the voltage computing unit 
32. The selected output voltage is amplified by the power amplifier 42 and 
then applied to the motor 4. If the rotation stop switch 40 generates its 
output signal at a time t.sub.0 (FIG. 4(a)), then the motor 4 is 
controlled from the time t.sub.0 on to rotate at the rotation B 
corresponding to the output voltage from the reverse maximum speed 
indicator 36. Therefore, The rotation of the motor 4 is rapidly reduced 
and the motor 4 is then controlled to rotate in the reverse direction as 
shown in FIG. 4(a). When the rotation of the motor 4 is reversed, the 
polarity of the output R of the rotary encoder 10 is also reversed to 
cause the selector circuit 34 to stop the selection of the output voltage 
from the reverse maximum speed indicator 36. More specifically, when the 
polarity of the output R of the rotary encoder 10 is reversed, the AND 
gate 60 is opened to energize the third relay coil 64 for thereby opening 
the third relay contact 66. Therefore, the output voltage from the reverse 
maximum speed indicator 36 is cut off. As a result, the speed setting for 
the motor 4 is virtually zero, and no voltage is applied to the motor 4. 
The rotation of the motor 4 is stopped at a time t.sub.2 as illustrated in 
FIG. 4(b). 
FIG. 4(b) shows a characteristic curve obtained at the time the voltage 
applied to the motor 4 is cut off simply by a command signal for stopping 
the rotation of the motor 4. In FIG. 4(b), it takes a period of time from 
t.sub.0 to t.sub.1 for the motor 4 to stop its rotation. According to the 
arrangement of the invention, however, the motor 4 can be stopped in the 
time interval from t.sub.0 to t.sub.2 (FIG. 4(a)) which is shorter than 
the time period from t.sub.0 to t.sub.1. 
With the arrangement of the present invention, the voltage representing the 
reverse maximum speed is applied to the motor during the time interval 
from the rotation stop command to the reverse rotation of the motor, so 
that the time required for the motor to stop its rotation is much shorter 
than the conventional time period. 
Where the present invention is incorporated in the system for reading 
radiation image information from the stimulable phosphor sheet, switching 
between the pre-reading mode and the main reading mode can quickly be 
effected, and the stimulable phosphor sheet can be fed at a stable 
secondary scanning speed while it is scanned fully over is image recording 
region. Furthermore, the system can quickly be readied for a next cycle of 
image readout operation. Where the stimulable phosphor sheet is used 
recyclically in a circulatory manner, the cycles of use of the sheet can 
be shortened. 
The principles of the present invention are also applicable to other 
devices such as copying machines, facsimile machines, or the like. 
Although a certain preferred embodiment has been shown and described, it 
should be understood that many changes and modifications may be made 
therein without departing from the scope of the appended claims.