Sheet feeding apparatus and facsimile system having same

The present invention relates to a facsimile system comprising a reader for reading an original sheet, a recorder for recording an image on a recording sheet, a stepping motor for feeding at least one of the sheets, a drive means for generating a signal by which the stepping motor is driven repeatedly with predetermined excitation modes, and a discrimination means for discriminating an excited phase of the stepping motor. The power down signal is generated when the discrimination means discriminates the fact that the excited phase of the stepping motor is a second phase.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a sheet feeding apparatus for feeding a 
sheet by driving a sheet feeding mechanism by means of a stepping motor, 
and a facsimile system having such sheet feeding apparatus. 
2. Related Background Art 
FIG. 1 shows a schematic construction of a facsimile system wherein a 
recording sheet 60 comprised of a heat-sensitive paper which is colored 
when heat is applied thereto is fed from a sheet roll 61 of a continuous 
long sheet material housed in a roll holder 62. An image is recorded on 
the recording sheet 60 in a recording portion 63, and the recorded sheet 
is cut from the remaining sheet 60 by means of a cutter 64 and then is 
ejected or discharged by ejecting rollers 65 out of the system. Further, 
in an original reading portion 66, original sheets stacked on an upper 
cover are separated one by one by means of separating rollers 6a, and the 
separated original is moved at a constant speed by means of a feed roller 
6b. Meanwhile, a light source 6c illuminates the original, and the 
reflected light from the original is sent to a photoelectric converter 
element 6f through a mirror 6d and a lens 6e, so that the original 
information is converted to an electric signal which is to be sent to the 
predetermined recording portion 63 or a memory (not shown). 
Now, a recording operation performed in the recording portion 63 will be 
explained. The recording portion 63 includes a line-type recording head 
which comprises a plurality of heating elements selectively heated in 
response to an image signal and which is urged, by means of a bias spring 
69, against a platen roller 67 acting as feeding means for the recording 
sheet 60. By rotating the platen 67 in a direction shown by an arrow a 
through a movement transmission system (not shown) by means of a motor 69, 
the recording sheet 60 is fed, and the image is thermally recorded on the 
recording sheet 60 by heating the recording head 68 in response to the 
image signal. 
On the other hand, a side wall 70 which separates or partitions the roll 
holder 62 from the recording portion 63 is designed to have a height of 
about 1/2 of a maximum permissible diameter of the sheet roll, and a space 
71 is provided between the side wall 70 and the platen roller 67. The 
space 71 serves to create a gentle slack in the leading portion of the 
recording sheet 60 when the leading edge of the recording sheet 60 is 
returned from a cutting position of the cutter 64 to a position where the 
leading edge of the sheet is pinched or nipped between the platen roller 
67 and the recording head 68. To this end, the space 71 has a width 
(between the sheet roll and the platen roller) to an extent that the 
recording sheet 60 is not bent at an acute angle when the sheet is 
slackened. Incidentally, the recording sheet 60 is guided toward the 
recording portion 63 by means of a guide member 72. 
A recent facsimile system has transmission-reception function through 
memory means of large capacity, and includes multiple address function, 
repeater function, confidential function or the like to improve the 
operability and efficiency thereof. To achieve this, techniques regarding 
the high speed reading of the original and/or the high speed recording 
have been required, and, particularly, a method for driving motors such as 
a motor for feeding the original and a motor for feeding the recording 
sheet have been called to account. 
Now, FIG. 2 shows, in a conventional facsimile system, a damping amount of 
a four phase unipolar stepping motor for rotatingly driving the platen 
roller 67 in the recording portion 63 or the feed roller 6b in the 
original reading portion 66, during first phase excitation and second 
phase excitation thereof, when such stepping motor is driven at a low 
speed with 1-2 phase excitation. FIG. 3 shows a displacement amount of the 
feed roller 6b, when the stepping motor of FIG. 2 is driven at a low speed 
with 1-2 phase excitation. 
As seen in FIG. 2, in this stepping motor, the damping occurs when the 
first excitation is changed to the second excitation by trigger. 
Consequently, the movement of the feed roller 6b becomes non-uniform or 
uneven, as shown in FIG. 3, and, thus the original will be fed unevenly 
due to the trigger. Further, since the feed roller 6b rotates only in one 
direction, when a considerable backlash occurs in the motor as shown in 
FIG. 2, a maximum displacement ("P" in FIGS. 2 and 3) of the motor in a 
positive direction (upward direction in FIGS. 2 and 3) leads to the 
rotational amount of the feed roller 6b in FIG. 3 just as it is, thus 
resulting in the error of reading in the positive direction. 
FIG. 4 shows a displacement amount of the platen roller 67 when it is 
driven at a low speed with 1-2 phase excitation in the case where the 
stepping motor having the feature shown in FIG. 2 is adopted to the 
driving mechanism for driving the platen roller 67 in the recording 
portion 63, and FIG. 5 shows an example of an image reproduced or recorded 
when the wholly black image signal is transmitted or received in the 
above-mentioned condition. 
As apparent from FIG. 5, while a wholly black image signal is transmitted 
or received, the recorded image will nevertheless include white stripes 
due to the uneven feeding of the original and recording sheet for the 
above-mentioned reasons. 
FIG. 6A shows current values of phase A and phase B in each quadrant when 
the stepping motor is driven with micro-steps, FIG. 6B shows a phase A 
current value, and FIG. 6C shows a phase B current value. FIGS. 7 and 8 
show an example of a construction of PM-type stepping motor. The stepping 
motor includes a stator 80 and a rotor 81 which is spaced apart from the 
stator by a distance l. FIG. 7 shows a condition that the motor is stopped 
in a second phase (A, BX=N, AX, B=S) and FIG. 8 shows a condition that the 
rotor is stopped in a first phase (A=N, AX, B, BX=S). Here, S and N are 
polarities of a magnetic pole. 
As mentioned regarding the above conventional facsimile system, a holding 
torque of the stepping motor when it is driven with first phase excitation 
differs from that when driven with second phase excitation. That is to 
say, when the stepping motor is driven with the second phase excitation, 
the rotor is shifted with strong force, whereas, when the stepping motor 
is driven with the first phase excitation, the rotor is shifted with weak 
force. Consequently, the vibration of the stepping motor is increased, 
generating the uneven rotation of the motor, thus forming the white 
stripes in the recorded image as shown in FIG. 5. This phenomenon will be 
emphasized when the stepping motor is rotated at a low speed i.e., in a 
high quality image mode (fine mode). 
In order to solve such problem, a technique wherein a sheet feed for single 
scanning line is effected through two steps of the stepping motor has been 
proposed, for example, as disclosed in the Japanese Patent Publication No. 
62-37866. According to this conventional technique, since sub-scanning 
drive is effected on the basis of a unit which corresponds to the sum of 
the moved distance of the rotor when the stepping motor is driven with the 
first phase excitation and the moved distance of the rotor when the 
stepping motor is driven with the second phase excitation, dispersion in 
distances between the scanning lines can be eliminated. 
However, in the fine mode of a facsimile system, since delicate control is 
required, it is necessary to perform the sheet feed for a single scanning 
line through a single step of the stepping motor. In such a case, there 
will arise a problem wherein the holding torque of the stepping motor, 
when it is driven with first phase excitation, differs from that when 
driven with second phase excitation. 
Further, in order to solve the above-mentioned problem, there has been 
proposed a micro-step drive technique that, when the sum of the current 
vectors exists on a circle as shown in FIG. 6A, necessary micro-steps are 
sought by decomposing the full-step (when the electric phase angle is 
90.degree.), and a single step of the stepping motor is decomposed into a 
given number of micro-steps. According to this drive technique, the 
vibration of the stepping motor can be reduced, whereby the original and 
the recording sheet can be uniformly fed. However, since D/A converters, 
special control circuits and the like are required to realize this 
technique, the system was expensive and was large-sized. 
Further, as shown in FIGS. 7 and 8, since the holding torque is 
proportional to the total value of the exciting currents flowing in the 
stator of the stepping motor, when it is assumed that the current flow in 
the first phase excitation is "1", the current flow in the second phase 
excitation will be .sqroot.2 (=1/.sqroot.2 +1/.sqroot.2). Consequently, 
the holding torque was increased accordingly, with the result that the 
vibration of and the uneven rotation of the stepping motor was not 
effectively eliminated even by the above-mentioned drive technique. 
In order to solve this problem, a technique that the motor currents in the 
first and second phase excitations for a stepping motor are controlled to 
reduce or eliminate the difference between the torque generated in the 
first phase excitation and the torque generated in the second phase 
excitation has been proposed, for example, in the U.S. Pat. No. 4,642,544 
or in the U.S. Ser. No. 148,690, now U.S. Pat. No. 4,857,817. In both 
cases, however, such proposal relates to the stepping motor alone and does 
not relate to the sheet feeding apparatus or the facsimile system at all. 
In addition, the latter proposes a technique that the current is changed 
by a resistor and the former proposes a technique that the current is 
controlled by controlling the duty of pulses; thus, these techniques made 
the construction complicated. 
Furthermore, in the conventional facsimile systems, there was a further 
problem that, since the cutter for cutting the recorded sheet was normally 
driven by the stepping motor, noise was generated during the cutting 
operation of the recording sheet. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to eliminate the above drawbacks, 
i.e., to perform the reading of the original and the reproduction of the 
original image with high quality by suppressing fluctuation of the holding 
torque generated in the phase excitation by altering or changing the 
winding current per one phase according to an excited condition of each 
phase. 
Other objects of the present invention will be apparent from the following 
explanation regarding embodiments of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will now be explained in connection with a preferred 
embodiment thereof with reference to the accompanying drawings. 
FIG. 9 shows a schematic construction of a motor controlling portion in a 
sheet feeding apparatus according to the present invention. 
The motor controlling portion comprises a register 10 for storing a 
frequency dividing ratio in a counter 13, a register 11 for storing data 
of the presence of current control and presence of power down (i.e., 
normal mode or power down mode) of a driving current of a motor, and a 
register 12 for storing an exciting output, rotation direction and serial 
driving stepping number per one trigger, regarding the motor. The counter 
13 executes the frequency dividing of the inputted block signal 14 as 
indicated by the register 10, and the frequency divided clock signal acts 
as a driving clock signal for the motor. A counter driver 15 controls the 
driving of a counter 17 and receives a frequency dividing clock signal 19 
from the counter, a trigger signal 16 and a busy signal 18 from the 
counter 17. If the counter driver circuit 15 receives the trigger signal 
16 when the counter 17 is not being driven, it outputs a trigger signal 20 
to the counter 17. The counter 17 begins to operate when it receives the 
trigger signal 20, and sends, to an exciting output circuit 21, pulses by 
the stepping number indicated by the register 12. 
The exciting output circuit 21 outputs exciting signals 22.about.24 on the 
basis of conditions of the register 12 and of the counter 17, thereby 
driving a motor driving circuit 25. The motor driving circuit 25 receives 
the exciting signals 22.about.24. The received exciting signals are 
decoded by a decoder 25-1 and are output from the circuit 25 as four phase 
motor exciting signals A, B, AX and BX. A power down indicating circuit 26 
outputs a power down signal 33 when an indicating signal 27 from the 
register 11 indicates the presence of the current control and the motor 
current is set to the normal mode. 
The trigger signal 16 instructs the initiation of operation of the motor. 
The reference numeral 28 designates a latch signal for latching data 30 
representing the frequency dividing ratio in the register 10, 29 
designates a latch signal for latching data 30 representing the serial 
driving stepping number and rotation direction of the motor in the 
register 12, 31 designates a clear signal for clearing the registers 
10.about.12, and 32 designates a latch signal for latching information 
such as the power down mode and the like in the register 11. These signals 
are outputted from a CPU 411 shown in FIG. 12. 
The power down signal 33 is outputted when the motor is to be driven in the 
power down mode (where the current values of the windings of the motor is 
decreased by 50% or more, or less of those in the normal mode). The 
reference numeral 34 designates a busy signal showing a condition that the 
motor is being rotated. 
FIG. 10 is a block diagram showing a schematic construction of a reading 
portion or reader 404 (FIG. 12) in the facsimile system. 
The reader comprises a reading motor control circuit 40 including the 
circuits and the like shown in FIG. 9, a four phase unipolar stepping 
motor for feeding an original to be read, and a motor driving circuit 45 
which receives an exciting signal 35 for each phase and other various 
signals from the reading motor control circuit 40 and drives the stepping 
motor with chopper drive. The motor driving circuit 45 can also drive the 
stepping motor with the current value (flowing in the windings of the 
stepping motor 41) of, for example, 1/2 of the current value in the normal 
mode. The reader further includes a stabilizer 42 for suppressing 
variation of luminance of a light 43 illuminating the original to 
stabilize the luminance of the light 43, and an image sensor 44 for 
reading the original image and for photoelectrically converting it. 
FIG. 11 is a block diagram showing a schematic construction of a recording 
portion or recorder 405 (FIG. 12) for recording the image on the recording 
sheet. The recorder comprises a recording motor control circuit 46 which 
controls the operation of a motor 47 for feeding the recording sheet and 
which has similar elements shown in FIG. 9, a motor driving circuit 45 
having the same construction of the motor driving circuit of FIG. 10, a 
four phase unipolar stepping motor 47 for feeding the recording sheet, a 
thermal head 49 comprising a thermal line head for recording the image on 
the recording sheet on the basis of image information, and a head driver 
48 for driving the thermal head 49. 
FIG. 12 is a block diagram showing a schematic construction of a facsimile 
system according to an embodiment of the present invention. 
The facsimile system comprises a modem 400, a line control unit (NCU) 401, 
a modem control circuit 402 for controlling the modem 400, a telephone 
403, the reader 404 shown in FIG. 10, the recorder 405 shown in FIG. 11, 
sensor and the like 406 for detecting the presence of the recording sheet 
and of the original, a width of the recording sheet and the like, a 
speaker 407 for generating an error sound, monitor sound of the line and 
the like, an operation panel 408 including operation keys, displayers and 
the like, a ROM 409 for storing a control program of the CPU 411 and 
various data, a RAM 410 which is used as a work area of the CPU 411 and 
which can temporarily store the original image data, received image data 
and the like, and the above-mentioned CPU 411 including, for example, a 
microcomputer, various control circuits and the like for controlling the 
whole system. 
FIG. 13 is a flow chart showing an initial setting process for the motor 
control circuit 40 or 46 shown in FIG. 9 or FIG. 10. A program for 
executing this process is stored in the ROM 409. 
In FIG. 13, first of all, the data for setting the motor driving frequency 
is written in the register 10 in a step Sl. In this way, the frequency 
dividing ratio of the clock signal 14 effected in the counter 13 is 
determined. Next, in a step S2, information regarding the presense of the 
current control, the presence of the power down of the driving current of 
the motor and the like are set in the register 11. In step S3, the 
information regarding the stepping number of the motor enable or disenable 
of the exciting output, normal or reverse of the rotation direction of the 
motor are set in the register 12. Incidentally, the latchings or settings 
of the various data in these registers can be effected by outputting the 
data corresponding to the data bath 30 and by latching the data in the 
desired registers by means of the corresponding latch signal. 
FIG. 14 shows a data construction of the register 10, where the information 
for setting or determining the motor driving frequency (frequency dividing 
ratio) is stored. 
FIG. 15 shows a data construction of the register 11, which indicates that, 
when MSB is "0", the current of the motor flows in the normal mode and, 
when the MSB is "1", the current of the motor flows in the power down 
mode, and that, when LSB is "1", the current control is indicated or 
instructed. 
FIG. 16 shows a data construction of the register 12, which indicates that, 
when the MSB is "1", the exciting output is enable and, when the MSB is 
"0", the exciting output is disenable and that, when a sixth bit is "1", 
the rotation direction of the motor is normal and, and the sixth bit is 
"0" the rotation direction of the motor is reverse. Bits 0.about.5 
indicate the stepping number of the motor serially rotated by a single 
trigger output. 
FIG. 17 is a flow chart showing outputting operation of the trigger signal 
16 outputted to the respective motor control circuits of the reader 404 
and the recorder 405 of the CPU 411. In this example, the busy signal 34 
from each motor control circuit is inputted, and the motor driving trigger 
signal 16 is outputted when the corresponding motor is not driven. 
FIG. 18 is a timing chart showing an example of the current control in the 
motor control circuit 40 or 46 of the facsimile system according to the 
embodiment of the present invention. In this example, the register 10 is 
set to "5", the register 11 is set to "1" and the register 12 is set to 
"C7H" (H shows a six-decimal number). 
The clock signal 19 is a signal obtained by frequency-dividing the clock 
signal 14 into five by means of the counter 13 in correspondence to the 
value "5" of the register 10. The reference numeral 500 designates a 
condition that the excitation becomes enable by setting the value "C7H" in 
the register 12. Since the LSB of the register 11 is "1", the current 
control is in a high level ("1"). 
The reference numeral 501 shows an inputted timing of the trigger signal 
16, from where the motor drive is started. A, AX, B and BX show exciting 
signals of the four phase motor. In this case, when the motor is excited 
with two phases, i.e., when either of A and AX phase signals and either of 
B and BX phase signals are simultaneously in the high level, the power 
down signal 33 becomes the high level, thus reducing the value of the 
current flowing the windings of the motor to about 1/2. In this way, in 
both the first phase excitation and second phase excitation, the values of 
the current flowing the windings of the motor will be substantially the 
same. 
This power down signal 33 is output from the aforementioned power down 
indicating circuit 26, which circuit receives a value LSB (DA) of the 
inputting signal of the decoders 25-1 and controls to output the power 
down signal 33 when this value is "1" (high level). 
FIG. 19 shows a relation between the excitation condition of the motor and 
the displacement amount of the motor corresponding thereto, when the above 
current control is executed. As seen in FIG. 19, the motor is driven to 
have the same displacement amounts in both first and second phase 
excitations. 
FIG. 20 is a timing chart showing the current values flowing in the 
windings of the motor, where iA, iAX, iB and iBX show the current value 
flowing the respective windings. In this way, by reducing the current 
values flowing the respective windings in the second phase excitation by 
about 1/2, the phase current flows along a square as shown in FIG. 21A, 
thus keeping the total current value to substantially constant. 
FIG. 22 shows a relation between the torque and the speed of the stepping 
motor, and FIG. 23 shows a flow chart for a motor controlling process in 
the original reading operation in a facsimile system according to another 
embodiment of the present invention. 
In general, a stepping motor used as the aforementioned reading motor has a 
pull-in torque which decreases as the driving frequency thereof increases. 
A ratio of such reduction in the pull-in torque when the current flowing 
the windings of the stepping motor is controlled differs from that when 
the current is controlled. More particularly, the torque when the current 
is controlled will more decrease than that when the current control is not 
effected. 
Thus, the case where the above-mentioned current control is executed to 
rotate the motor at a high speed will now be considered. 
Now, if it is assumed that the pull-in torque of the order of 400 
gf.multidot.cm is required in the normal mode. In this case, when it is 
desired that the motor having the feature shown in FIG. 22 is rotated at 
800 pps, there arises a problem that the motor can be rotated if the 
above-mentioned current control is not executed, but cannot be rotated if 
the current control is executed. 
Generally, in a facsimile system, when the original image to be transmitted 
is read, the motor is being rotated at a low speed in consideration of the 
sensitivity of the photoelectric converter element (image sensor), the 
transmitting speed and the like. On the other hand, for the purposes other 
than such reading operation of the original and the photoelectric 
converting operation, such as for the purpose of ejecting the transmitted 
original the motor is rotated at a higher speed to shorten the working 
time. 
The original reading control sequence shown in the flow chart of FIG. 23 
can meet with such requirements. 
More particularly, in a step S10, the rotation speed of the original 
feeding motor is set to 800 pps, and in a step Sll non-current control 
mode is set. Then, in steps S12.about.S15, the original is fed to the 
reading position at a speed of 800 pps, and in a step S16 the rotation 
speed of the motor is decreased to 400 pps immediately before the reading 
of the original is initiated. Then, in a step S17, the current control 
mode is set, thus performing the reading operation of the original to be 
transmitted, while executing above-mentioned current control at a low 
speed (steps S18.about.S20). 
In a step S21, the rotation speed of the motor is returned to 800 pps again 
when the reading operation of the original is completed, and in a step S22 
the current control is inhibited, thus ejecting the original at a higher 
speed (steps S23.about.S25). 
Incidentally, this sequence can be applied to the recording sheet feeding 
motor in the recoder in the same manner. In this case, the motor can be 
rotated at a low speed while exciting the current control, for example 
when the image is being recorded on the recording sheet through the 
thermal head, and can be rotated at a higher speed without the current 
control to feed the recording sheet at a high speed, when the recording 
sheet is fed to the recording position and/or when the recorded sheet is 
ejected. 
In the above embodiment, an example of the PM-type stepping motor is used. 
However, even if a stepping motor in which a distance between magnetics 
arranged on a stator and rotor thereof can be changed in accordance with 
the change in the excited phases is used for reading the original, 
recording the image and cutting the recording sheet, by changing the 
current flowing in the windings of the motor in accordance with the change 
in the excited phases, the holding torque of the motor can be kept 
constant. 
As mentioned above, according to this embodiment, by controlling the value 
of the current flowing in the windings of the stepping motor in 
correspondence to the conditions of the phase excitation of the motor, the 
stepping motor can be smoothly and uniformly rotated whereby the recording 
sheet and the original can be fed at a constant or even speed. 
Further, by applying the above-mentioned sheet feeding apparatus to the 
facsimile system, the reading of the original and the recording of the 
image to be reproduced can be performed with high quality. In addition, by 
applying such sheet feeding apparatus to the driving circuits for driving 
the sheet cutting motor and the like, the cutting noise of the recording 
sheet can be reduced. 
Furthermore, since the damping amount of the motor is reduced, the noise in 
the whole sheet feeding apparatus can also be reduced. In addition, since 
the current control is not executed when the sheet is to be fed at a high 
speed, but is executed when the sheet is to be fed at a low speed, the 
feeding error of the sheet can be eliminated and the working speed of the 
whole apparatus can be increased. 
In this way, according to the present invention, by suppressing the 
fluctuation in the holding torque due to the phase excitation of the 
motor, the vibration of the stepping motor can be reduced. 
Further, by suppressing the fluctuation in the holding torques due to the 
phase excitation of the stepping motors in the reader and the recorder of 
the facsimile system, the reading of the original and the recording of the 
image to be reproduced can be performed with high quality. In addition, 
according to the present invention, the cutting noise generated in the 
sheet cutting operation can be reduced.