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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a motor drive control apparatus and
relates more particularly to a motor drive control apparatus suitable for
use in a rotation polyhedral mirror drive control apparatus for an optical
scanning apparatus utilized for a laser printer, a facsimile apparatus, a
copying machine, a display apparatus, etc.
2. Description of the Related Art
In recent years, as environmental problems have been closed up, energy
saving, ecology and recycling have come to be talked about as
countermeasures for solving these problems. For this purpose, various
kinds of regulations have been made at present. An optical scanning unit
using such a rotation polyhedral mirror as a polygon mirror is not an
exception in the discussion of such environmental problems, and various
countermeasures have been made to the drive control of an optical
deflector of this unit in relation to energy saving.
An optical deflector of the conventional optical scanning unit has problems
of noise, a rise in temperature and the useful life of the optical
deflector because a rotation polyhedral mirror is driven to rotate at a
high speed. As one of countermeasures for solving these problems, there
has been employed a system for stopping the rotation of a motor for
driving the rotation polyhedral mirror, constituting the optical
deflector, during a standby time of the optical scanning unit, not during
a printing operation period thereof.
If non-contact dynamic pressure bearings are used for the bearings of a
motor that drives the rotation polyhedral mirror to rotate, the bearings
are brought into contact with each other when the number of revolution of
the motor is decreased as at the time of stopping the rotation of the
motor. Therefore, it is not so desirable to stop the rotation of the
motor. Thus, there is employed a system for rotating the motor during a
standby time of the optical scanning unit at a smaller number of
revolution than the number of revolution at the time of the print
operation. As detailed countermeasures for this, the number of the
revolution of the motor is controlled to be low by dividing the frequency
of an oscillation output of an oscillation circuit acting as a number of
revolution command by a circuit inside the optical defector. Alternately,
the motor is driven to rotate at a number of revolution which does not
cause the dynamic pressure bearings to be brought into contact with each
other by setting the driving voltage of the motor itself of the rotation
polyhedral mirror at a lower level than the driving voltage during the
printing operation, as described in the Japanese Patent Application
Laid-open Publication No. 4-107520.
Further, the above-described system for stopping the rotation of the motor
or for driving the motor at a low number of revolution during the standby
time of the optical scanning unit has, on the other hand, a problem that
the starting time of the motor becomes longer. As countermeasures for
solving this problem, there has been proposed a technique for increasing
the driving voltage of the motor at the motor starting time and then
returning the voltage to the original or ordinary driving voltage after a
lapse of a predetermined time, as described in the Japanese Patent
Application Laid-open Publication No. 61-112580. There has also been
proposed another technique for driving the motor at a maximum voltage of a
driving power source at the time of starting the motor and then gradually
lowering the voltage to a normal motor driving voltage after a pulse
interval obtained by an optical synchronization detector for a deflected
laser beam has become a predetermined period, as described in the Japanese
Patent Application Laid-open Publication No. 61-261716.
However, when the system is employed in which the motor for driving the
rotation polyhedral mirror to rotate as an optical deflector is rotated at
a low driving voltage during the standby time of the optical scanning
unit, a certain level of driving voltage is necessary in order to stably
rotate the motor. For this purpose, the voltage needs to be set at a
voltage slightly higher than the minimum driving voltage. Accordingly,
although it is possible to drive the motor for driving the rotation
polyhedral mirror to rotate at a lower driving voltage, this set voltage
which is slightly higher than the minimum driving voltage means a waste of
power.
Further, the rotation polyhedral mirrors have variations in their
individual manufacturing precision. Therefore, if the driving voltage of
the motor is set at a constant value, there is a possibility that some of
the rotation polyhedral mirrors do not have a stable rotation.
Further, if the dynamic pressure bearings are used for the bearings of the
motor as in the case of the optical deflector unit described in the
Japanese Patent Application Laid-open Publication No. 4-107520, depending
on the variations of the manufacturing precision of the rotation
polyhedral mirrors, the bearings are always in contact with each other
during the standby time so that the optical deflector may be damaged.
Further, according to the technique described in the Japanese Patent
Application Laid-open Publication No. 61-261716, in the case of detecting
the number of revolution of the motor by turning on a laser light source,
it is at least necessary to keep the laser light source on during the
detection operation of the number of revolution. This has a problem of
lowering the life of the laser light source as compared with the case of
carrying out the detection of the number of revolution of the motor
without keeping the laser light source on.
Further, if the motor is driven to rotate at a low driving voltage which
merely does not cause the bearings to be in contact with each other as
shown in Japanese Patent Application Laid-open Publication No. 4-107520,
there is a problem that a PLL (Phase Locked Loop) control can not be
applied for the number of revolution control and thus it is difficult to
detect the normal or steady rotation mode.
Furthermore, when there is a large manufacturing error in the rotation
polyhedral mirrors as the optical deflectors due to the variations of
their manufacturing precision, the rotation of the rotation polyhedral
mirrors becomes unstable and thus the number of revolution becomes
unstable. Therefore, it becomes difficult to detect the number of
revolution in this case. Also, the number of revolution can not be
detected if, for example, a galling is caused in the bearings for some
reason, which may result in a damaging of the optical deflector.
SUMMARY OF THE INVENTION
The present invention has been made in the light of the above-described
situation, and it is a first object of the present invention to provide a
motor drive control apparatus which can drive a motor at a driving voltage
in the vicinity of a minimum level at which the PLL control can be carried
out.
It is a second object of the present invention to provide a motor drive
control apparatus which can drive a motor in a driving current in the
vicinity of a minimum level at which the PLL control can be carried out.
In order to achieve the first object of the present invention, according to
a first aspect of the present invention, there is provided a motor drive
control apparatus, comprising: a number of revolution setting unit for
outputting a number of revolution command signal for setting a number of
revolution of the motor; a driving means for driving a motor to rotate at
a predetermined number of revolution based on the number of revolution
command signal output from the number of revolution setting means; a
number of revolution detecting unit for detecting a number of revolution
of the motor; a driving voltage adjusting means for adjusting a level of a
driving voltage of the motor supplied to the driving means; a PLL control
means for comparing a phase of a number of revolution command signal
output from the number of revolution setting unit with a phase of a number
of revolution detection signal output from the number of revolution
detecting means and for controlling the number of revolution of the motor
so that the difference between both the phases falls within a
predetermined range of value; and a voltage control means for instructing
the driving voltage adjusting means to adjust the driving voltage of the
motor at a value in the vicinity of a minimum level at which the PLL
control can be carried out.
Further, according to a second aspect of the present invention, in the
motor drive control apparatus of the above-described first aspect of the
present invention, the voltage control means is so structured to instruct
the driving voltage adjusting means that the driving voltage of the motor
is increased at the time of starting the rotation of the motor, that the
driving voltage is reduced at a point of time when the difference between
the phase of a number of revolution command signal output from the number
of revolution setting means and the phase of a number of revolution
detection signal output from the number of revolution detecting means has
fallen within the predetermined range of value, that the driving voltage
is increased gradually at a point of time when the difference between the
phase of a number of revolution command signal output from the number of
revolution setting means and the phase of a number of revolution detection
signal output from the number of revolution detecting means has exceeded
the predetermined range of value and a phase locked state has been
canceled, and that the level of the driving voltage is maintained at a
point of time when the difference between both the phases has fallen
within the predetermined range of value again and the phases have been in
a locked state.
Further, according to a third aspect of the present invention, in the motor
drive control apparatus of the above-described first aspect of the present
invention, the voltage control means is so structured to instruct the
driving voltage adjusting means such that, at the time when the motor
shifts its operation from the normal or steady operation mode to a
predetermined low-speed operation mode, the driving voltage of the motor
is reduced from the normal operation mode at a point of time when the
number of revolution of the motor has reached a preset number of
revolution of the predetermined low-speed operation mode, the driving
voltage is increased gradually at a point of time when the difference
between the phase of the number of revolution command signal output from
the number of revolution setting means and the phase of the number of
revolution detection signal output from the number of revolution detecting
means has exceeded the predetermined range of value and the phase locked
state has been canceled, and the level of the driving voltage is
maintained at a point of time when the difference between both the phases
has fallen within the predetermined range of value and the phases have
been in the locked state.
According to the motor drive control apparatus having the above-described
structure, the number of revolution setting means outputs the number of
revolution command signal for setting the number of revolution of the
motor, and the driving means drives the motor to rotate at the
predetermined number of revolution based on the number of revolution
command signal output from the number of revolution setting means.
Further, the number of revolution detecting means detects the number of
revolution of the motor, and the driving voltage adjusting means adjusts
the level of the motor driving voltage supplied to the driving means.
Further, the PLL control means compares the phase of the number of
revolution command signal output from the number of revolution setting
means with the phase of the number of revolution detection signal output
from the number of revolution detecting means and controls the number of
revolution of the motor so that the difference between both the phases
falls within the predetermined range of value. The voltage control means
instructs the driving voltage adjusting means to adjust the driving
voltage of the motor at a value in the vicinity of the minimum level at
which the PLL control can be carried out.
According to the first to third aspects of the present invention, it
becomes possible to carry out a stable drive control of the motor for all
operation modes in the vicinity of a controllable minimum driving voltage,
so that it is possible to prevent a rotation failure due to variations of
motors or an increase in power consumption.
In order to achieve the second object of the present invention, according
to a fourth aspect of the present invention, there is provided a motor
drive control apparatus, comprising: a number of revolution setting unit
for outputting a number of revolution command signal for setting a number
of revolution of a motor; a driving means for driving the motor to rotate
at a predetermined number of revolution based on the number of revolution
command signal output from the number of revolution setting means; a
number of revolution detecting means for detecting the number of
revolution of the motor; a driving current adjusting means for adjusting a
level of a driving current of the motor supplied to the driving means; a
PLL control means for comparing a phase of a number of revolution command
signal output from the number of revolution setting means with a phase of
a number of revolution detection signal output from the number of
revolution detecting means and for controlling the number of revolution of
the motor so that the difference between both the phases falls within a
predetermined range of value; and a current control means for instructing
the driving current adjusting means to adjust the driving current of the
motor at a value in the vicinity of a minimum level at which a PLL control
can be carried out.
Further, according to a fifth aspect of the present invention, in the motor
drive control apparatus of the above-described fourth aspect of the
present invention, the current control means is so structured to instruct
the driving current adjusting means that the driving current of the motor
is increased at the time of starting the motor, that the driving current
is reduced at a point of time when the difference between the phase of the
number of revolution command signal output from the number of revolution
setting means and the phase of a number of revolution detection signal
output from the number of revolution detecting means has fallen within the
predetermined range of value, that the driving current is increased
gradually at a point of time when the difference between the phase of the
number of revolution command signal output from the number of revolution
setting means and the phase of the number of revolution detection signal
output from the number of revolution detecting means has exceeded the
predetermined range of value and a phase locked state has been canceled,
and that the level of the driving current is maintained at a point of time
when the difference between both the phases has fallen within the
predetermined range of value again and the phases have been in a locked
state.
Further, according to a sixth aspect of the present invention, in the motor
drive control apparatus of the above-described fourth aspect of the
present invention, the current control means is so structured to instruct
the driving current adjusting means that, at the time when the motor
shifts its operation from a steady operation mode to a predetermined
low-speed operation mode, the driving current of the motor is reduced from
the steady operation mode at a point of time when the number of revolution
of the motor has reached a preset number of revolution of the
predetermined low-speed mode, that the driving current is increased
gradually at a point of time when the difference between the phase of the
number of revolution command signal output from the number of revolution
setting means and the phase of a number of revolution detection signal
output from the number of revolution detecting means has exceeded the
predetermined range of value and a phase locked state has been canceled,
and that the level of the driving current is maintained at a point of time
when the difference between both the phases has fallen within the
predetermined range of value and the phases have been in a locked state.
According to the motor drive control apparatus having the above-described
structure, the number of revolution setting means outputs a number of
revolution command signal for setting the number of revolution of the
motor, and the driving means drives the motor to rotate at the
predetermined number of revolution based on the number of revolution
command signal output from the number of revolution setting means.
Further, the number of revolution detecting means detects the number of
revolution of the motor, and the driving current adjusting means adjusts
the level of the motor driving current supplied to the driving means.
Further, the PLL control means compares the phase of the number of
revolution command signal output from the number of revolution setting
means with the phase of the number of revolution detection signal output
from the number of revolution detecting means and controls the number of
revolution of the motor so that the difference between both the phases
falls within the predetermined range of value. The current control means
instructs the driving current adjusting means to adjust the driving
current of the motor at a value in the vicinity of the minimum level at
which the PLL control can be carried out.
According to the fourth to sixth aspects of the present invention, it
becomes possible to carry out a stable drive control of the motor in all
operation modes in the vicinity of a controllable minimum driving current,
so that it is possible to prevent a rotational failure due to variations
of motors or an increase in power consumption.
Further, according to the first to sixth aspects of the present invention,
since a required number of revolution of the motor is set within the PLL
controllable range in controlling the drive of the motor, this number of
revolution can bear sufficiently in actual use.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram for showing a configuration of a first embodiment
of a rotation polyhedral mirror drive control apparatus for an optical
scanning apparatus to which the present invention is applied.
FIG. 2 is a block diagram for showing a schematic configuration of a PLL
control circuit for the rotation polyhedral mirror drive control device
shown in FIG. 1.
FIG. 3 is a time chart for explaining the operation of the rotation
polyhedral mirror drive control device shown in FIG. 1.
FIG. 4 is a block diagram for showing a configuration of a second
embodiment of a rotation polyhedral mirror drive control apparatus for an
optical scanning apparatus to which the present invention is applied.
FIG. 5 is a time chart for explaining the operation of the rotation
polyhedral mirror drive control device shown in FIG. 4.
FIG. 6 is an explanatory diagram for showing a schematic configuration of
the optical scanning device relating to the embodiments of the present
invention to be used for a laser printer or the like.
FIG. 7 is an explanatory diagram for showing a detailed configuration of
the optical scanning apparatus in FIG. 6.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiments of the present invention will be explained below with reference
to the drawings. FIG. 6 shows a schematic configuration of an optical
scanning apparatus to be used for a laser printer, a laser copying
machine, etc. relating to the embodiment of the present invention. In FIG.
6, a photosensitive body 1 is charged by a charging device for
transferring 2. The charged photosensitive body 1 has a characteristic
that when it receives light, the potential of the light receiving portion
of the charged photosensitive body 1 is lowered. By utilizing this
characteristic of the photosensitive body 1, a laser beam is irradiated by
a scanning optical device 3 onto a portion of the photosensitive body 1
where a toner is to be adhered. The scanning optical body 3 is structured
to include a rotation polyhedral mirror 13 and a cylinder mirror 15. The
rotation polyhedral mirror 13 is fixed to the axis of rotation of a motor
9, and the motor 9 is driven by a rotation polyhedral mirror drive control
device 17.
A detailed configuration of the scanning optical device 3 is shown in FIG.
7. Referring to this drawing, the scanning optical device 3 has a laser
diode 10, a collimator lens 11, a cylinder lens 12, the rotation
polyhedral mirror 13, a f.multidot..theta. lens system 14, a cylinder
mirror 15 and a synchronization sensor 16. A laser beam emitted from the
laser diode 10 reaches the rotation polyhedral mirror 13 through the
collimator lens 11 and the cylinder lens 12. The rotation polyhedral
mirror 13 is a polygonal pillar body having a plurality of mirror surfaces
or facets on the side surfaces and this is driven to rotate at a high
speed by the motor 9. By the deflection function of the rotation
polyhedral mirror 13, the laser beam obtains a reflection angle and scans
on the photosensitive body 1 through the f.multidot..theta. lens system 14
and the cylinder mirror 15.
When a laser beam is irradiated onto the surface of the photosensitive body
1 by the scanning optical device 3, a toner is adhered by a developer 5 to
only a portion of this surface where the potential has changed. The toner
is transferred to an image bearing member 6 such as a sheet of paper by
the transfer charging device 2, and is then fused on the image bearing
member 6 by a fixing device 7. The toner which remains on the surface of
the photosensitive body 1 is removed by a cleaner 8, and thereafter the
photosensitive body 1 is charged again and is exposed with a laser beam
emitted from the scanning optical device 3.
FIG. 1 shows a configuration of the rotation polyhedral mirror drive
control apparatus for an optical scanning apparatus relating to a first
embodiment of the present invention. Referring to this drawing, the
rotation polyhedral mirror drive control device has an external processing
circuit section 20 for controlling a motor circuit section 30 and the
motor circuit section 30 for directly contributing to the drive control of
a driving motor that rotates the rotation polyhedral mirror of an optical
deflector.
The external processing circuit section 20 has a number of revolution
setting circuit 21, a driving voltage adjusting circuit 22 and a voltage
control circuit 23. The number of revolution setting circuit 21 outputs a
number of revolution command signal for setting a number of revolution of
the motor. By the voltage control circuit 23, the number of revolution
setting circuit 21 is set with a high number of revolution N1 at the time
of starting the optical scanning apparatus or at the printing time, for
example, and set with a low number of revolution N2 at a stand-by time or
at the low-speed operation time such as at the image resolution
change-over time.
The driving voltage adjusting circuit 22 adjusts the level of the motor
driving voltage to be supplied to a motor control circuit 31 of the motor
circuit section 30 under the control of the voltage control circuit 23.
According to the operation mode of the optical scanning apparatus, the
voltage control circuit 23 instructs the number of revolution setting
circuit 21 to change the set number of revolution so that the motor is
driven to rotate at different number of revolutions between the normal or
steady operation time such as at the printing time and the low-speed
operation time such as at the stand-by time or the resolution change-over
time, for example. At the same time, the voltage control circuit 23
instructs the driving voltage adjusting circuit 22 to adjust the motor
driving voltage at a level in the vicinity of a PLL controllable minimum
level based on the phase detection signal output from a PLL control device
or means, to be described later, for showing whether the phase of the
number of revolution detection signal for detecting the number of
revolution of the driving motor is in a locked state or not.
The motor circuit section 30 has the motor control circuit 31, switching
transistors 32, 33, 34, 35, 36 and 37 for controlling to which one of
field coils 38, 39 and 40 of the motor a current is to be supplied, a
crystal oscillator 45 for generating a number of revolution command
signal, a number of revolution detecting circuit 46 for detecting the
number of revolution of the motor, and Hall elements H1, H2 and H3 for
detecting position information of the rotation angle of the motor rotor
and like.
The motor control circuit 31 is structured to include a drive control
section for controlling the current conduction of the field coils 38, 39
and 40 through the switching transistors 32, 33, 34, 35, 36 and 37, and
the PLL control circuit.
The switching transistors 32, 33, 34, 35, 36 and 37 are three-phase bridge
connected to structure a driving circuit, and AC output terminals of this
circuit are connected to one end of the field coils 38, 39 and 40
respectively. The other ends of the field coils 38, 39 and 40 are
connected in common. The commonly connected collectors of the switching
transistors 32, 33 and 34 are connected to a terminal V0 of the motor
control circuit 31, and the commonly connected collectors of the switching
transistors 35, 36 and 37 are grounded. Further, the bases of the
switching transistors 32, 33, 34, 35, 36 and 37 are connected to terminals
01 to 06 of the motor control circuit 31 respectively. The driving voltage
of the motor is applied to the commonly connected collectors of the
switching transistors 32, 33 and 34 from the terminal V0 of the motor
control circuit 31.
The number of revolution detecting circuit 46 is structured to output a
pulse signal of a frequency corresponding to the number of revolution by
detecting a change of magnetism of a permanent magnet fixed to the motor,
for example.
The Hall elements H1, H2 and H3 have their respective terminals 1a, 2a and
3a connected in common, and a power source voltage Vcc is applied to these
terminals through a resistor 44. Terminals 1b, 2b and 3b are grounded by
being connected in common. Thus, a current is always being supplied to
each of the Hall elements H1, H2 and H3. When the rotor of the motor
rotates, each of the Hall elements H1, H2 and H3 detects a magnetic flux
of the permanent magnet fixed to the rotor, and outputs from each of
output terminals 1c, 1d, 2c, 2d, 3c and 3d a voltage of a different
polarity depending on whether the N pole or the S pole of the permanent
magnet passes through the fitting position of each Hall element. The drive
control section receives the output signals of the Hall elements H1, H2
and H3 as the position information of the rotor of the motor and uses this
position information for generating a control signal to determine the
order of the switching of the switching transistors 32, 33, 34, 35, 36 and
37.
A schematic configuration of the PLL control circuit is shown in FIG. 2.
Referring to FIG. 2, the PLL control circuit 60 has a frequency divider
61, a phase comparator 62, a phase lock detecting circuit 63 and an
integrating circuit 64. A frequency dividing ratio is set to the frequency
divider 61 based on a number of revolution command output from the number
of revolution setting circuit 21, and the frequency divider 61 divides the
frequency of an oscillation output from the crystal oscillator 45
according to the number of revolution command.
The phase comparator 62 compares the phase of a number of revolution
command signal output from the frequency divider 61 with the phase of a
number of revolution detection signal output from the number of revolution
detecting circuit 46, and outputs a signal corresponding to the phase
difference to the phase lock detecting circuit 63 and the integrating
circuit 64.
The phase lock detecting circuit 63 outputs a phase detection signal LD for
showing whether the phase of the number of revolution detection signal is
in the locked state or not from the result of the comparison between the
phase of the number of revolution command signal and the phase of the
number of revolution detection signal output from the number of revolution
detecting circuit 46.
The integrating circuit 64 integrates the output signals of the phase
comparator 62 and uses the result of the integration for the generation of
a switching control signal to be supplied to each base of the switching
transistors 32, 33, 34, 35, 36 and 37. The output signal of the
integrating circuit 64 is compared with a modulation signal of a
triangular wave or the like by a comparator 51, and a PWM signal is
generated. This PWM signal is supplied to each base of the switching
transistors 32, 33, 34, 35, 36 and 37 from the terminals O1 to O6 of the
motor control circuit 31 in a predetermined order based on the position
information of the rotor of the driving motor obtained from the Hall
elements H1, H2 and H3. As a result, a rotation magnetic field is
generated in the magnetic field coils 38, 39 and 40, and the drive motor
fitted with the rotation polyhedral mirror is driven to rotate.
The operation of the rotation polyhedral mirror drive control unit relating
to the first embodiment of the present invention having the
above-described structure will be explained next with reference to FIG. 3.
At the time of starting the motor, the driving voltage adjusting circuit
22 supplies a voltage Vmax of a maximum level of a driving voltage Vcc to
the motor control circuit 31 under the control of the voltage control
circuit 23 in order to shorten the starting time of the motor. The motor
control circuit 31 applies the voltage Vmax to the commonly connected
collectors of the switching transistors 32, 33 and 34 from the terminal
V0.
On the other hand, a high number of revolution N1 is set to the number of
revolution setting circuit 21 based on an instruction signal of the
voltage control circuit 23, and a number of revolution command is output
from the number of revolution setting circuit 21 to the frequency divider
61 of the motor control circuit 31. By this number of revolution command,
the frequency dividing ratio of the frequency divider 61 is set according
to the number of revolution N1, and the frequency of the oscillation
output of the crystal oscillator 45 is divided. The number of revolution
command output from the frequency divider 61 is changed to a PWM signal
through the phase comparator 62, the integrating circuit 64 and the
comparator 51, and the PWM signal is supplied to each base of the
switching transistors 32, 33, 34, 35, 36 and 37 from the terminals O1 to
O6 of the motor control circuit 31 in a predetermined order based on the
position information of the rotor of the motor obtained from the Hall
elements H1, H2 and H3. As a result, the number of revolution of the motor
increases, and the phase of the number of revolution command signal output
from the frequency divider 61 and the phase of the number of revolution
detection signal output from the number of revolution detecting circuit 46
are compared with each other by the phase comparator 62.
At a point of time when the phase difference has become within a
predetermined range of value, that is, when the detected number of
revolution of the motor has reached the number of revolution N1, the phase
detection signal LD output from the phase lock detecting circuit 63
changes from a high level to a low level, and the phase of the number of
revolution detection signal is locked by the PLL control circuit 60. At
this time, the motor for driving the rotation polyhedral mirror of the
optical deflector to rotate is set to a state of being controlled to
rotate at a constant speed at the number of revolution N1 and at the
driving voltage Vmax.
The voltage control circuit 23 receives the phase detection signal LD, and
at a point of time when this signal has become a low level, the voltage
control circuit 23 outputs an instruction signal for reducing the driving
voltage Vcc to the driving voltage adjusting circuit 22. As a result, the
driving voltage Vcc is reduced gradually from the Vmax level, and when the
driving voltage Vcc has been reduced to the level where Vcc=V2, the motor
becomes no more able to generate a torque for driving the rotation
polyhedral mirror at the number of revolution N1, so that the phase locked
state of the number of revolution detection signal is canceled and the PLL
control can not be carried out. Accordingly, the number of revolution of
the motor is lowered, the difference between the phase of the number of
revolution command signal output from the frequency divider 61 and the
phase of the number of revolution detection signal output from the number
of revolution detecting circuit 46 becomes different for each timing of
comparison, and the phase detection signal LD becomes a high level.
At a point of time when the phase detection signal LD has become a high
level, the voltage control circuit 23 outputs an instruction signal for
increasing the driving voltage Vcc to the driving voltage adjusting
circuit 22. As a result, the driving voltage Vcc increases, and at a point
of time when the driving voltage Vcc has reached a voltage V1 slightly
higher than a voltage V2, the phase difference between the phase of the
number of revolution command signal and the phase of the number of
revolution detection signal becomes within a predetermined range of value.
Accordingly, the phase detection signal LD output from the phase lock
detecting circuit 63 changes from a high level to a low level, and the
phase of the number of revolution detection signal is locked by the PLL
control circuit 60, so that the motor can be controlled to rotate at a
constant speed.
In the manner as described above, the driving voltage Vcc can be adjusted
to a level in the vicinity of a PLL controllable minimum level and the
optical scanning apparatus can carry out a normal or steady operation such
as a printing operation.
Next, at the time when the normal operation mode is shifted to a
predetermined low-speed operation mode such as the standby time or the
resolution change-over time, a number of revolution N2 for the standby
time lower than the number of revolution N1 for the normal operation is
set to the number of revolution setting circuit 21 by an instruction
signal of the voltage control circuit 23. A frequency dividing ratio
corresponding to the number of revolution N2 is set to the frequency
divider 61 by the number of revolution command output from the number of
revolution setting circuit 21, and a number of revolution command signal
of the frequency corresponding to the set number of revolution N2 is
output to the phase comparator 62 from the frequency divider 61. The motor
is driven based on this number of revolution command signal. This number
of revolution decreases gradually from the set number of revolution N1 for
the normal operation. At a point of time when a number of revolution of
the motor detected by the number of revolution detecting circuit 46 has
reached the number of revolution N2, the phase detection signal LD output
from the phase lock detecting circuit 63 changes from a high level to a
low level, and the phase of the number of revolution detection signal
becomes in the locked state by the PLL control circuit 60. At this point
of time, the driving voltage of the motor for driving the rotation
polyhedral mirror of the optical deflector to rotate is V1 which is the
same as that for the normal operation, and the rotation of the motor is
controlled at a constant speed at the number of revolution N2.
The voltage control circuit 23 receives the phase detection signal LD, and
at a point of time when this signal has become a low level, the voltage
control circuit 23 outputs an instruction signal for reducing the driving
voltage Vcc to the driving voltage adjusting circuit 22. As a result, the
driving voltage Vcc is reduced gradually from the V1 level, and when the
driving voltage Vcc has been reduced to the level where Vcc=V4, the motor
becomes no more able to generate a torque for driving the rotation
polyhedral mirror at the number of revolution N2, so that the phase locked
state of the number of revolution detection signal is canceled and the PLL
control can not be carried out. Accordingly, the number of revolution of
the motor is lowered, the difference between the phase of the number of
revolution command signal output from the frequency divider 61 and the
phase of the number of revolution detection signal output from the number
of revolution detecting circuit 46 becomes different for each timing of
comparison, and the phase detection signal LD becomes a high level.
At a point of time when the phase detection signal LD has become a high
level, the voltage control circuit or device 23 outputs an instruction
signal for increasing the driving voltage Vcc to the driving voltage
adjusting circuit 22. As a result, the driving voltage Vcc increases, and
at a point of time when the driving voltage Vcc has reached a voltage V3
slightly higher than a voltage V4, the phase difference between the phase
of the number of revolution command signal and the phase of the number of
revolution detection signal becomes within a predetermined range of value.
Accordingly, the phase detection signal LD output from the phase lock
detecting circuit 63 changes from a high level to a low level, and the
phase of the number of revolution detection signal is locked by the PLL
control circuit 60, so that the motor can be controlled to rotate at a
constant speed.
In the manner as described above, the driving voltage Vcc can be adjusted
to a level in the vicinity of a PLL controllable minimum level and the
optical scanning apparatus becomes in a predetermined low-speed operation
mode such as for the standby time and the resolution change-over time.
According to the first embodime | | |
