Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2002-05-08
2003-04-29
Nguyen, Thinh (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C400S322000
Reexamination Certificate
active
06554395
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The technical field of this invention is servo control and more particularly control of print head position and velocity during printing.
BACKGROUND OF THE INVENTION
Ink jet printing requires careful control of the print head speed during a printing pass across the paper. It is generally desirable to have a constant print head velocity during printing. This involves four phases of print head drive control. In a first phase the print head is held in position beyond the beginning of the print swath. In a second phase the print head is accelerated up to the desired print velocity. During the third phase the velocity is regulated to be constant during actual printing. In the fourth phase after passing the end of the print swath, the print head is decelerated to a stop. In order to increase the printer throughput, it is common to limit the print head carriage travel to less than the entire page width for lines that do not require printing across the entire page width. This could occur for text at the end of a paragraph. Following this deceleration, the controller returns to the first phase where it holds print head position.
FIG. 1
illustrates the print head control in accordance with the prior art. Print head control system
100
includes printer engine
110
, interface circuits
120
and microprocessor controller
130
. Printer engine
110
includes print head
101
, drive motor
102
, drive belt
103
, pulley
104
and linear position encoder strip
105
. Print head
101
includes the mechanisms for producing ink droplets for application to the page being printed. These mechanisms are conventional, not a part of this invention and will not be described in detail. Drive motor
102
receives drive signals v
M1
and v
M2
and moves belt
103
accordingly. Belt
103
is continuous and wraps around pulley
104
. Print head
101
is attached to belt
103
and moves when belt
103
moves. Pulses from linear position encoder strip
105
are detected by a quadrature pulse encoder which generates two signals CH_A and CH_B which are 90° out of phase. This position sensing system is known in the art, is not a part of this invention and will not be described in further detail.
Interface circuits
120
include quadrature pulse encoder (QEP) decoder/counter
121
, digital to analog converter
123
and motor drive circuit
125
. Quadrature pulse encoder decoder/counter
121
receives the two signals CH_A and CH_B and produces a counter value x indicative of the position of print head
101
. The relative phase of the two signals CH_A and CH_B provide an indication of the direction of motion and the number of pulses indicates that amount of travel. Special purpose circuits to embody quadrature pulse encoder decoder/counter
121
are known in the art. A Hewlett-Packard HP-2020 decoder integrated circuit is widely used for this purpose. Digital to analog converter (DAC)
123
receives a digital current command signal i
cmd
from microprocessor controller
130
and converts this into an analog signal driving motor drive circuit
125
. Digital to analog converter
123
and motor drive circuit
125
operate to supply electrical power to motor
102
to achieve the desired motion of print head
101
. Motor drive circuit
125
is constructed to be compatible with motor
102
to effect control of the position and velocity of print head
101
.
Microprocessor controller
130
includes command generator (Cmd Gen)
131
, summing junction
132
, proportional-integral-derivative (PID) controller
133
, velocity estimator
134
and mode switch
135
. The name microprocessor controller implies that this function is embodied by a programmed microprocessor. Though illustrated as separate components, it is known in the art to embody the control illustrated in
FIG. 1
via discrete equations performed by a programmed microprocessor. Microprocessor controller
130
receives the print head position signal x and produces a digital current command signal i
cmd
for control of the position and velocity of print head
101
. Command generator
131
generates a command signal r corresponding to the desired print head movement. This will be further described below. Summing junction
132
forms an error signal e between this command signal r and a feedback signal from QEP decoder/counter
121
. This error signal e is subject to a proportional-integral-derivative controller
133
. Proportional-integral-derivative control is well known in the art. Proportional-integral-derivative controller
133
calculates the sum of three terms from the error signal. A proportional term is proportional to the error signal e. An integral term is a time sum of the error signal e. Lastly, a derivative term is the rate of change of the error signal e. The sum of these three terms is the current command signal i
cmd
.
Microprocessor controller
130
operates in two modes as selected by mode switch
135
. In a velocity mode velocity estimator
134
forms a velocity estimate v
est
of the print head
101
velocity from the position signal x. Summing junction
132
subtracts this velocity estimate v
est
as selected by mode switch
134
from the command signal r. In a position mode, mode switch
135
selects the position signal x. Summing junction
132
subtracts the position signal x from the command signal r.
FIG. 2
illustrated the typical operation of prior art print head control system
100
. The Y-axis of
FIG. 2
a
is r, from command generator
131
. The Y-axis of
FIG. 2
b
is x, the print head position from QEP decoder/counter
121
.
FIGS. 2
a
and
2
b
have aligned X-axes in time t. During time interval t
1
microprocessor controller
130
is in position mode and mode switch
135
selects position signal x from QEP decoder/counter
121
. Command generator
131
generates command signal r corresponding to the desired print head position. For the sake of this example, assume that the desired position is near the leftmost limit of print head
101
travel beyond the printable portion of the page. Proportional-integral-derivative controller
133
produces a current command signal i
cmd
which results in print head
101
reaching the commanded position. At that time the error signal e is zero and no further movement takes place.
During time interval t
2
microprocessor controller
130
is in an acceleration phase. Mode switch
135
selects the velocity estimate v
est
from velocity estimator
134
. Command generator
131
generates the command signal r corresponding to the desired velocity. As illustrated in
FIG. 2
a
, the command signal r increases during time interval t
2
corresponding to the desired acceleration.
FIG. 2
b
shows a corresponding change in the position signal x. The rate of acceleration commanded during time interval t
2
is selected to reach the desired velocity for printing when the edge of the printable area is reached.
During time interval t
3
the printing takes place. Microprocessor controller
131
is in the velocity mode and commands a constant velocity. Proportional-integral-derivative controller
133
produces a current command signal i
cmd
to achieve this desired constant velocity.
FIG. 2
b
illustrates linear change in the position signal x with respect to time.
During time interval t
4
microprocessor controller
130
is in a deceleration phase. Command generator
131
generates a command signal r corresponding to decreasing velocity, eventually reaching a zero velocity. In this example, this deceleration phase stops print head
101
at the end of the current print line. This is not necessarily the end of the printable part of the page.
FIG. 2
b
shows slowing of the rate of change of the position signal x to zero at the end of time interval t
4
.
Time interval t
5
is another hold position interval. Mode switch
135
selects the position signal x and command generator
131
produces the command signal r corresponding to the desires hold position. In this example the desired position during time interval t
5
is at the far right, the opposite end of the range of travel of pr
Cole Charles P.
Fedigan Stephen J.
Brady III W. James
Huffman Julian D.
Marshall, Jr. Robert D.
Nguyen Thinh
Telecky , Jr. Frederick J.
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