Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2002-08-02
2003-09-16
Nguyen, Lamson (Department: 2861)
Incremental printing of symbolic information
Ink jet
Controller
C347S037000
Reexamination Certificate
active
06619778
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a technology for controlling an operation of a carriage motor in a printer.
2. Description of the Related Art
An ink jet printer is provided with a carriage having a print head, a carriage motor for moving the carriage, and a drive control device for controlling the carriage motor.
FIG. 6
is a block view showing the structure of a conventional drive control device. The drive control device has a control circuit
300
, a drive circuit
320
and a carriage motor
330
. The carriage motor
330
is provided with an encoder
332
for detecting the current speed V
c
of the carriage.
FIGS.
7
(
a
) and
7
(
b
) show output signals from the encoder
332
(hereinafter, referred to as an “encoder output signals”). A typical encoder output signal includes an A phase signal and a B phase signal. The direction of rotation (forward and reverse) of the carriage motor
330
is determined in response to the phaseal relationship of the A phase signal and the B phase signal. For example, if the A phase signal is rising while the B phase signal is at the L level, forward rotation is determined (FIG.
7
(
a
)), and if the A phase signal is rising while the B phase signal is at the H level, reverse rotation is determined (FIG.
7
(
b
)). The position of the carriage is determined in response to the direction of rotation of the carriage motor
330
and the number of pulses in the encoder output signal. Also, the current speed V
c
of the carriage is determined as a value proportional to the inverse of the cycle T
en
of the encoder output signal, that is, Vc=(k/T
en
), where k is a constant.
The control circuit
300
includes a subtractor
302
for obtaining a differential &Dgr;V between a target speed V
t
and current speed V
c
, a proportional element
304
, an integral element
306
, a derivative element
308
and an adder
310
. The three operation elements
304
,
306
and
308
output operation results in response to the speed differential &Dgr;V, and the operation results are then summed by the adder
310
. A summed result &Sgr;Q is supplied to the drive circuit
320
as a control signal. The drive circuit
320
supplies a drive signal S
dr
in response to the control signal &Sgr;Q to the carriage motor
330
.
The control circuit
300
having PID control functions can control the speed and position of the carriage motor
330
with high precision. Due to various reasons, however, so-called hunting may occur.
FIGS.
8
(A) and
8
(B) show the hunting occurred in the speed V and the speed differential &Dgr;V. The abscissa in FIG.
8
(A) is the position (or time) and the ordinate is the speed V. The ordinate in FIG.
8
(B) is the speed differential &Dgr;V. The target speed V
t
is set beforehand in response to the difference between the target position and the current position of the carriage. In the example of FIG.
8
(B), hunting occurs such that the speed differential &Dgr;V fluctuates both positively and negatively. The cause of such hunting is, for example, that the cycle T
en
of the encoder output signal is unstable when the motor
330
begins to move, resulting in instability of the measured value of the current speed V
c
(=k/T
en
).
In a printer wherein ink is ejected from a print head with a carriage, printing is carried out by ejecting ink from the print head while the carriage is moving at a constant speed. Suppression of hunting and precise control of the speed of the carriage are thus strongly desired in such a printer.
SUMMARY OF THE INVENTION
Accordingly, an object thereof to provide a technology for improving the precision of speed control of the carriage in a printer.
In order to attain the above object of the present invention, there is provided a printer comprising a carriage having a print head; a carriage motor for moving the carriage; and a drive control device for controlling operation of the carriage motor. The drive control device includes: a drive circuit for driving the carriage motor; a detector for detecting a current speed of the carriage; a target speed generator for generating a target speed for the carriage; and a control section for generating a control signal supplied to the drive circuit in response to the target speed and the current speed of the carriage. The control section includes a plurality of operation elements including a proportional element and an integral element; a control signal generator for summing operation results from the plurality of operation elements to generate the control signal; and a speed differential generator for generating a speed differential to be inputted to the plurality of operation elements in response to the target speed and the current speed of the carriage. The speed differential generator generates the speed differential having a smaller range of change than an actual differential between the target speed and the current speed during a predetermined period immediately after the carriage begins to move, and supplies the speed differential to the plurality of operation elements.
The speed differential generator may generate the speed differential showing a predetermined pattern of change during the predetermined period.
In one embodiment, the speed differential generator generates the speed differential which maintains a constant value during the predetermined period.
In another embodiment, the speed differential generator generates the speed differential such that it monotonously decreases during the predetermined period.
The speed differential generator may use an actual differential between the target speed and the actual speed as the speed differential after the predetermined period.
These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with the accompanying drawings.
REFERENCES:
patent: 6040670 (2000-03-01), Kaneko et al.
patent: 6189993 (2001-02-01), Mantell
Nguyen Lamson
Seiko Epson Corporation
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