Electricity: motive power systems – Positional servo systems
Reexamination Certificate
2000-04-21
2002-10-01
Masih, Karen (Department: 2837)
Electricity: motive power systems
Positional servo systems
C318S254100, C318S132000, C318S434000, C388S805000
Reexamination Certificate
active
06459225
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a servo-control apparatus for motor, servo-controlling a motor by using a DSP as digital control means, and more particularly it relates to a motor servo-control apparatus suitable for controlling a plurality of motors used in an image forming apparatus.
2. Related Background Art
FIGS. 12 and 13
are conventional circuit diagrams for effecting servo-control of a plurality of motors by using a micro computer. Particularly,
FIG. 12
is a block diagram showing an entire circuit in which a plurality of motor units
301
having the same construction are connected to a single micro computer
300
, and
FIG. 13
is a block diagram showing an internal construction of one of the motor units
301
.
Now, the conventional servo-control will be described. In
FIGS. 12 and 13
, there are shown a micro computer
300
, motor units
301
, a control IC
302
, a three-phase motor
303
, three hole sensors
304
for detecting a position of a main pole of a rotor, an FG sensor
305
for detecting a pattern magnetized on the rotor and for outputting 36 pulses per one revolution of the motor, an oscillator
306
, a current detecting resistor
307
, a control portion
308
, a driver portion
309
, an electric current limiter detecting portion
310
, a speed control portion
311
, a frequency divider
312
, an integration amplifier
313
, resistors and capacitors constituting integration filters
314
to
317
, a control signal
318
emitted from the micro computer
300
and adapted to drive/stop the motor, and a ready signal
319
which becomes active when the motor reaches a predetermined revolution number.
Next, an operation of the circuit will be described. When a motor driving command is emitted from the micro computer
300
controlling an image forming apparatus through the signal line
318
, the control portion
308
detects the position of the main pole of the rotor of the motor
303
by the hole sensors
304
and forms a three-phase exciting pattern so as to rotate the motor in a desired direction and sends an exciting signal to the driver portion
309
. On the basis of the exciting signal, the driver portion
309
drives an output transistor (not shown) so that an electric current direction with respect to a coil of the motor is switched to generate desired excitation. On the other hand, when the rotor of the motor
303
is rotated, predetermined pulses are generated by the FG sensor
305
and are sent to the speed control portion
311
. In the speed control portion
311
, a reference clock formed by the oscillator
306
and the frequency divider
312
is compared with the pulse detected by the FG sensor
305
, and the difference therebetween is outputted.
Incidentally, the reference clock is set to obtain a target revolution number (number of revolutions) of the motor. Namely, when the FG sensor outputs 30 pulses per one revolution of the motor, in order to rotate the motor at 600 rpm, the reference clock of 300 Hz (=(600/60)×30) may be given.
The difference with respect to the target speed obtained by the speed control portion
311
is integrated by the integration amplifier
313
, and a result is sent to the driver portion
309
. In this case, gain and a phase compensation value are determined by the resistors and capacitors
314
to
317
. These constants are referred to as servo constants.
Further, in the driver portion
309
for the motor of the conventional image forming apparatus, a transistor of bipolar type is used. Thus, since heat loss of the driver portion is great, a radiator plate is provided. Further, in order to reduce heat generation due to such heat loss as much as possible, the efficiency of the motor must be increased so that the desired power can be obtained with the least electric power. To this end, a brushless motor of the outer rotor type having good efficiency is used.
As mentioned above, in the conventional circuit arrangement, the motor is controlled by sending only stop/start signals to the motor units
301
from the micro computer
300
, and a servo-control loop is formed in each motor unit
301
. The reason for this is that, since the processing ability of the conventional micro computer is limited, servo-control must be effected in each motor unit
301
. As the processing ability of the micro computer or a DSP (digital signal processor) has been improved, servo-control for the motors has been able to be effected by the micro computer or the DSP itself. Further, due to an increase in processing ability of the DSP, a plurality of motors have been able to be servo-controlled independently.
As a result, in place of the above-mentioned conventional circuit arrangement, it has been considered to provide a circuit having motors servo-controlled by the DSP. Such a circuit will be explained herein below.
FIGS. 14 and 15
are views showing such a circuit. Particularly,
FIG. 14
is a block diagram showing an entire circuit in which a plurality of motor units are connected to a single DSP, and
FIG. 15
is a block diagram showing the internal construction of one of the motor units.
In
FIGS. 14 and 15
, there are shown a DSP
501
serving to control six motors
505
, motor units
502
each including a drive circuit, a driver
504
, a three-phase DC brushless motor
505
, a charge pump circuit
401
for generating gate voltage for N-chMOS of the driver
504
, pre-driver circuits
402
to
407
, exciting switching signals
408
to
413
, a current sense signal
414
, hole sensor signals
415
to
417
, an MR sensor signal
418
, hole sensor amplifiers
419
to
421
, an MR sensor amplifier
422
, N-chMOS transistors (driver portions)
515
to
520
, a current detecting resistor
521
, U-phase output
522
connected to a U-phase coil of the motor, V-phase output
523
connected to a V-shape coil, W-phase output
524
connected to a W-phase coil, hole sensors
525
to
527
, an MR sensor
528
, and a serial communication bus
532
for effecting communication with a control CPU (not shown) of the image forming apparatus.
Next, an operation of this servo-control circuit will be described. First of all, when a motor drive command is transmitted from the CPU through the serial communication line
532
, the DSP
501
ascertains the position of the rotor detected by the hole sensors
525
to
527
on the basis of the hole sensor signals
415
to
417
and determines the switching timing so as to obtain the desired rotation and effects control on the basis of the switching signals
408
to
413
to give a desired rotational direction and a desired electric current to the motor.
Namely, the N-chMOS transistors
515
to
520
are switched to give the desired rotational direction, and the N-chMOS transistors
515
,
517
,
519
are PWM-switched to cause the desired electric current to flow into the coil of the motor. In this case, the gate voltages of the N-chMOS transistors
515
,
517
,
519
are increased to Vcc+10V by the charge pump circuit
401
.
For example, when the DSP
501
ascertains the rotor position of the motor on the basis of the hole sensor signals
415
to
417
amplified by the hole sensor amplifiers
419
to
421
and the hole sensors
525
to
527
and switches the direction of the electric current from the U-phase
522
to the W-phase
523
to obtain the desired rotational direction, the pre-drivers
402
to
407
turn ON the N-chMOS transistors
515
,
518
and turn OFF the transistors
516
,
517
,
519
,
520
. As a result, an electric current path extends from Vcc to the current detecting resistor
521
through the transistor
515
, U-phase output
522
, V-phase output
523
and transistor
518
, thereby generating a magnetic force in the desired coil. In this case, the PWM signal given by the DSP
501
is composed or combined with the switching signal
408
, so that the N-chMOS transistor
515
is PWM-controlled by the pre-driver
402
.
Accordingly, ON-duty electric current defined by the PWM signal flows from the U-phase to the V-phase. In this way,
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