Electricity: motive power systems – Positional servo systems
Reexamination Certificate
2002-09-27
2004-11-23
Leykin, Rita (Department: 2837)
Electricity: motive power systems
Positional servo systems
C318S270000, C318S271000, C318S610000, C388S806000
Reexamination Certificate
active
06822411
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for controlling a motor and, more particularly, to control executed when a mechanism is driven using a motor as a power source.
BACKGROUND OF THE INVENTION
Currently, motors are used as power sources of various apparatuses. Especially, many OA devices and home electric appliances use DC motors because they have simple structures, require no maintenance, generate little rotation variation and vibration, and are capable of high-speed operation and accurate control.
In recent years, printers, and especially general commercial printers that are often for home use, are required to have not only higher image quality but also lower operation noise. Noise generated in operation includes that generated in printing and that generated in driving mechanical portions. In inkjet printing apparatuses which have only a few noise sources in printing, noise generated in driving mechanical portions is reduced.
An inkjet printing apparatus has, as its main mechanical portions, a printhead scanning mechanism and a printing medium convey mechanism. Noise is reduced by using a DC motor and linear encoder as a driving means for the printhead scanning mechanism. Today, a DC motor and rotary encoder are also being employed as a driving means for the printing medium convey mechanism in many cases.
From the viewpoint of noise reduction, an effect can be expected when a DC motor is employed. From the viewpoint of accurate printing medium conveyance, more advanced position control is required in addition to a mechanical accuracy.
In an inkjet printing apparatus, the printhead is mounted on a carriage, which is driven by a motor. By way of example, control of the motor can be divided broadly into three control regions, namely an acceleration control region, a constant-velocity control region and a deceleration control region. In general, the printing operation is performed in the constant-velocity control region in order to assure image quality by holding the ink ejection interval constant. Though there are also systems in which printing is carried out also in the acceleration and deceleration control regions in order to raise printing speed, in all cases it is desired that any fluctuation in carriage velocity be made as small as possible during execution of printing. Accordingly, velocity servo control is suited as the feedback control method in the period during which printing is performed, i.e., in the constant-velocity control region. The reason for this is that velocity servo control is feedback control the aim of which is to make the velocity of the controlled system at a certain time coincide with a target velocity.
The specification of Japanese Patent Application Laid-Open No. 2001-63168 describes a motor control apparatus for performing stable control at the timing of a change from velocity control to position control. A conventional example of motor control, inclusive of the content set forth in the above specification, will now be described.
FIG. 4
is a block diagram illustrating the ordinary feedback control procedure of a motor employing velocity servo control. Such velocity servo control is performed by a technique referred to as PID control or classical control. This procedure will now be set forth.
First, a target velocity desired to be imparted to a controlled system is applied in the form of an ideal velocity profile
4001
. The profile provides velocity command values at applicable times. This velocity information changes with the passage of time. Drive is controlled by performing variable-value control with regard to the ideal velocity profile.
In velocity servo control, a PID operation generally is carried out. This is an operation involving a proportionality term P, an integration term I and a differentiation term D. The difference is found between encoder velocity information, which is obtained by encoder velocity information conversion means
4005
based upon information detected by an encoder sensor
4004
, and the velocity command value obtained from the ideal velocity profile
4001
. This numerical value is delivered to a PID arithmetic circuit
4002
as a velocity error, which is the velocity shortfall relative to the target velocity. Through a technique referred to as a PID operation, the PID arithmetic circuit
4002
calculates the energy that is to be applied to a DC motor
4003
at this time. Upon receiving this energy, the motor driver circuit regulates the current value by changing the duty of the applied voltage through, e.g., pulse-width modulation (PWM) control, thereby effecting velocity control by regulating the energy applied to the DC motor
4003
.
The DC motor, which is rotated owing to application of the current value, rotates physically while being influenced by an external disturbance
4006
. The output of the motor is fed back by being sensed by the encoder sensor
4004
.
FIG. 5
is a graph illustrating an example of the relationship between time and both velocity and present position owing to the above-described control. In FIG.
5
, time is plotted along a horizontal axis
5051
, velocity along a vertical axis
5052
on the left side and position along a vertical axis
5053
on the right side.
With regard to position indicated along the vertical axis on the right side, numeral
5043
denotes the position at which printing starts and
5042
the position at which printing ends. The interval between points
5043
and
5042
represents the printing region. Numeral
5041
denotes an arrival position, namely the position eventually reached by rapid deceleration following the end of printing.
With regard to velocity indicated along the vertical axis on the left side, numeral
5031
denotes attainment velocity of the carriage sought in order to implement an ink ejection frequency desirable for printing. Numeral
5032
denotes the initial velocity in the ideal profile.
Further, the ideal velocity profile is indicated at
5001
. This signifies the best velocity profile in which the printing region between the printing starting position
5043
and printing end position
5042
is traversed by the attainment velocity
5031
, with the carriage coming to rest at the arrival position
5041
upon being promptly decelerated. The ideal velocity profile
5001
is composed of an acceleration control region
5011
, an ideal constant-velocity control region
5012
and an ideal deceleration control region
5013
along the time axis.
Numeral
5004
denotes an ideal position profile, which indicates the transition of position in a case where drive is performed in accordance with the ideal velocity profile
5001
. Time that passes through the printing starting position
5043
in the ideal position profile
5004
is an ideal time
5021
for starting printing. This generally indicates the ideal time at which constant-velocity control begins. Similarly, time that passes through the printing end position
5042
in the ideal position profile
5004
is an ideal time
5023
for ending printing. This generally indicates the ideal time at which deceleration control begins.
Numerals
5003
and
5005
denote actual velocity and actual position profiles, respectively. The actual velocity profile
5003
is composed of the acceleration control region
5011
, an actual constant-velocity control region
5014
and an actual deceleration control region
5015
along the time axis.
If variable-value control is applied to the ideal velocity profile
5001
by the velocity servo control described in
FIG. 4
, the actual velocity will always follow up the ideal velocity with a certain delay. This means that even if the ideal time
5021
for starting printing arrives, the attainment velocity
5031
will not be reached and neither will the printing starting position
5043
. The printing starting position
5043
is reached only when the actual time
5022
for starting printing arrives. During travel through the printing region from this point onward, constant-velocity control is required in order to suppress a fluctuation in velocity
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Leykin Rita
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