Printer carriage alignment for periodic ink replenishment from off-carriage ink supply

A technique for aligning a carriage holding a pen in a printing machine including a carriage axis assembly having a motor drive system for moving the carriage along a carriage axis, a carriage position sensor, and a refill station disposed along the axis. A carriage alignment position at which the pen septum is aligned with the refill valve is determined, by (i) actuating the motor drive system to move the carriage in a first direction along the carriage axis to a first end of carriage travel along the carriage axis, (ii) sensing the position of the carriage at the first end of carriage travel, and storing the sensed first end position, (iii) actuating the motor drive system to move the carriage in a second direction along the carriage axis until the carriage runs into contact with a refill stopper surface of the refill station, (iv) determining a refill stopper carriage position at which the carriage runs into the refill stopper surface, and (v) determining the alignment position from the refill stopper carriage position. The carriage is moved along the carriage axis during printing operations and dispenses droplets of liquid ink from the printhead onto a print medium. A refill operation is conducted by moving the carriage to the alignment position, engaging the pen septum and the refill valve, passing ink through the refill valve and the pen septum, and disengaging the refill valve from the pen septum.

TECHNICAL FIELD OF THE INVENTION 
This invention relates to ink-jet printers/plotters, and more particularly 
to techniques for periodic ink replenishment of printheads at a refill 
station. 
BACKGROUND OF THE INVENTION 
A printing system is described in the commonly assigned patent application 
entitled "CONTINUOUS REFILL OF SPRING BAG RESERVOIR IN AN INK-JET SWATH 
PRINTER/PLOTTER," Ser. No. 08/454,975, filed May 31, 1995, (the '975 
application) which employs off-carriage ink reservoirs connected to 
on-carriage print cartridges through flexible tubing. The off-carriage 
reservoirs continuously replenish the supply of ink in the internal 
reservoirs of the on-carriage print cartridges, and maintain the back 
pressure in a range which results in high print quality. While this system 
has many advantages, there are some applications in which the relatively 
permanent connection of the off-carriage and on-carriage reservoirs via 
tubing is undesirable. 
A new ink delivery system (IDS) for printer/plotters has been developed, 
wherein the on-carriage spring reservoir of the print cartridge is only 
intermittently connected to the off-carriage reservoir to "take a gulp" 
and is then disconnected from the off-carriage reservoir. No tubing 
permanently connecting the on-carriage and off-carriage elements is 
needed. The above-referenced related applications describe certain 
features of this new ink delivery system and the refill station. 
SUMMARY OF THE INVENTION 
In accordance with an aspect of the invention, a method is described for 
aligning a carriage holding a pen in a printing machine including a 
carriage axis assembly including the carriage, a motor drive system for 
moving the carriage along a carriage axis, a carriage position sensor, and 
a refill station disposed along the axis. One embodiment of the method 
includes the steps of: 
determining a carriage alignment position of the carriage alignment method 
at which the pen septum is aligned with the refill valve during an 
alignment process, the alignment process including (i) actuating the motor 
drive system to move the carriage in a first direction along the carriage 
axis to a first end of carriage travel along the carriage axis, (ii) 
sensing the position of the carriage at the first end of carriage travel, 
and storing the sensed first end position, (iii) actuating the motor drive 
system to move the carriage in a second direction along the carriage axis 
until the carriage runs into contact with a refill stopper surface of the 
refill station, (iv) determining a refill stopper carriage position at 
which the carriage runs into the refill stopper surface, and (v) 
determining the alignment position from the refill stopper carriage 
position; 
moving the carriage along the carriage axis during printing operations and 
dispensing droplets of liquid ink from the printhead onto a print medium; 
and 
conducting a refill operation by moving the carriage to the alignment 
position, engaging the pen septum and the refill valve to provide a fluid 
path through the refill valve and the pen septum, passing ink through the 
refill valve and the pen septum to refill the pen, and disengaging the 
refill valve from the pen septum.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
An exemplary application for the invention is in a swath plotter/printer 
for large format printing (LFP) applications. FIG. 1 is a perspective view 
of a thermal ink-jet large format printer/plotter 50. The printer/plotter 
50 includes a housing 52 mounted on a stand 54 with left and right covers 
56 and 58. A carriage assembly 60 is adapted for reciprocal motion along a 
carriage slide rod. A print medium such as paper is positioned along a 
media axis by a media axis drive mechanism (not shown). As is common in 
the art, the media drive axis is denoted as the `x` axis, the carriage 
scan axis is denoted as the `y` axis, and the `z` axis is oriented 
vertically. 
FIG. 3 is a top view diagrammatic depiction of the carriage assembly 60, 
and the refill station. The carriage assembly 60 slides on slider rods 
94A, 94B. The position of the carriage assembly 60 along a horizontal or 
carriage scan axis is determined by a carriage positioning mechanism with 
respect to an encoder strip 92. The carriage positioning mechanism 
includes a carriage position motor 404 (FIG. 12) which drives a belt 96 
attached to the carriage assembly. The position of the carriage assembly 
along the scan axis is determined precisely by the use of the encoder 
strip. An optical encoder 406 (FIG. 12) is disposed on the carriage 
assembly and provides carriage position signals which are utilized to 
achieve optimal image registration and precise carriage positioning. 
Additional details of a suitable carriage positioning apparatus are given 
in the above-referenced '975 application. 
The printer 50 has four ink-jet print cartridges 70, 72, 74, and 76 that 
store ink of different colors, e.g., yellow, cyan, magenta and black ink, 
respectively, in internal spring-bag reservoirs. As the carriage assembly 
60 translates relative to the medium along the y axis, selected nozzles in 
the ink-jet cartridges are activated and ink is applied to the medium. 
The carriage assembly 60 positions the print cartridges 70-76, and holds 
the circuitry required for interface to the heater circuits in the 
cartridges. The carriage assembly includes a carriage 62 adapted for the 
reciprocal motion on the front and rear sliders 92A, 92B. The cartridges 
are secured in a closely packed arrangement, and may each be selectively 
removed from the carriage for replacement with a fresh pen. The carriage 
includes a pair of opposed side walls, and spaced short interior walls, 
which define cartridge compartments. The carriage walls are fabricated of 
a rigid engineering plastic. The print heads of the cartridges are exposed 
through openings in the cartridge compartments facing the print medium. 
As mentioned above, full color printing and plotting requires that the 
colors from the individual cartridges be applied to the media. This causes 
depletion of ink from the internal cartridge reservoirs. The printer 50 
includes four take-a-gulp IDSs to meet the ink delivery demands of the 
printing system. Each IDS includes three components, an off-carriage ink 
reservoir, an on-carriage print cartridge, and a print head cleaner. The 
ink reservoir includes a bag holding 370 ml of ink, with a short tube and 
refill valve attached. Details of a ink reservoir bag structure suitable 
for the purpose are given in co-pending application Ser. No. 08/805,860 
filed Mar. 3, 1997, SE-EFFICIENT ENCLOSURE SHAPE FOR NESTING TOGETHER A 
PLURALITY OF REPLACEABLE INK SUPPLY BAGS, by Erich Coiner et al. These 
reservoirs are fitted on the left-hand side of the printer (behind the 
door of the left housing 58) and the valves attach to a valve holder arm 
170, also behind the left door, as will be described below. The print 
cartridge in this exemplary embodiment includes a 300-nozzle, 600 dpi 
printhead, with an orifice through which it is refilled. The head cleaner 
(not shown) includes a spittoon for catching ink used when servicing and 
calibrating the printheads, a wiper used to wipe the face of the 
printhead, and a cap (used to protect the printhead when it is not in 
use). These three components together comprise the IDS for a given color 
and are replaced as a set by the user. 
The proper location of each component is preferably identified by color. 
Matching the color on the replaced component with that on the frame that 
accepts that component will ensure the proper location of that component. 
All three components will be in the same order, with, in an exemplary 
embodiment, the yellow component to the far left, the cyan component in 
the center-left position, the magenta component in the center-right 
position and the black component in the far-right position. 
The ink delivery systems are take-a-gulp ink refill systems. The system 
refills all four print cartridges 70-76 simultaneously when any one of the 
print cartridge internal reservoir's ink volume has dropped below a 
threshold value. A refill sequence is initiated immediately after 
completion of the print that caused the print cartridge reservoir ink 
volume to drop below the threshold and thus a print should never be 
interrupted for refilling (except when doing a long-axis print that uses 
more than 15.5 ccs of ink of any color). 
The '975 application describes a negative pressure, spring-bag print 
cartridge which is adapted for continuous refilling. FIGS. 4-8 show an 
ink-jet print cartridge 100, similar to the cartridges described in the 
'975 application, but which is adapted for intermittent refilling by 
addition of a self-sealing refill port in the grip handle of the 
cartridge. The cartridge 100 illustrates the cartridges 70-76 of the 
system of FIG. 1. The cartridge 100 includes a housing 102 which encloses 
an internal reservoir 104 for storing ink. A printhead 106 with ink-jet 
nozzles is mounted to the housing. The printhead receives ink from the 
reservoir 104 and ejects ink droplets while the cartridge scans back and 
forth along a print carriage during a printing operation. A protruding 
grip 108 extends from the housing enabling convenient installation and 
removal from a print carriage within an ink-jet printer. The grip is 
formed on an external surface of the housing. 
FIGS. 5-8 show additional detail of the grip 108. The grip includes two 
connectors 110, 112 on opposing sides of a cylindrical port 114 which 
communicates with the reservoir 104. The port is sealed by a septum 116 
formed of an elastomeric material. The septum 116 has a small opening 118 
formed therein. The grip with its port 114 is designed to intermittently 
engage with a needle valve structure 120 connected via a tube 122 to an 
off-carriage ink reservoir such as one of the reservoirs 80-86 of the 
system of FIG. 1. FIG. 5 shows the valve structure 120 adjacent but not 
engaged with the port 116. FIG. 6 shows the valve structure 120 fully 
engaged with the port. As shown in FIG. 6, the structure 120 includes 
hollow needle 122 with a closed distal end, but with a plurality of 
openings 124 formed therein adjacent the end. A sliding valve humidor 128 
tightly fits about the needle, and is biased by a spring 126 to a valve 
closed position shown in FIG. 5. When the structure 120 is forced against 
the port 116, the humidor is pressed up the length of the needle, allowing 
the needle tip to slide into the port opening 118, as shown in FIG. 6. In 
this position, ink can flow through the needle openings 124 between the 
reservoir 104 and the tube 130. Thus, with the cartridge 100 connected to 
an off-carriage ink reservoir via a valve structure such as 120, a fluid 
path is established between the print cartridge and the off-carriage 
reservoir. Ink can flow between the off-carriage ink reservoir to the 
cartridge reservoir 104. When the structure 120 is moved away from the 
handle 108, the valve structure 120 automatically closes as a result of 
the spring 126 acting on the humidor 128. The opening 118 will close as 
well due to the elasticity of the material 116, thereby providing a 
self-sealing refill port for the print cartridge. 
FIGS. 4-8 illustrate a locking structure 172 for releasably locking the 
valve 120 into the valve holder arm 170 at socket 174. The structure 172 
has locking surfaces 172B (FIG. 5) which engage against the outer housing 
of the valve body 120A. The structure is biased into the lock position by 
integral spring member 172A (FIGS. 7 and 8). By exerting force on 172 at 
point 170C (FIGS. 7 and 8) the spring is compressed, moving surface 172B 
out of engagement with the valve body, and permitting the valve to be 
pulled out of the refill arm socket 174. This releasing lock structure 
enables the valve and reservoir to be replaced quickly as a unit. 
The print cartridges 70-76 in this exemplary embodiment each comprise a 
single chamber body that utilizes a negative pressure spring-bag ink 
delivery system, more particularly described in the '975 application. 
The off-carriage ink reservoirs 80-86 are placed on a variable height 
refill platform 150, which can place the off-carriage reservoirs at an up 
position. At this position, with increased pressure head at the reservoir 
due to its elevated position, the print cartridge reservoir will refill. 
To prevent a print cartridge vacuum pressure which is too low to provide 
high quality printing, the position of the off-carriage reservoir is 
subsequently lowered with respect to the printhead nozzles, allowing a 
small amount of ink, e.g. on the order of 1-3 cc of ink in an exemplary 
embodiment, to flow from the print cartridge reservoir 104 back through 
the refill tube 130 into the off-carriage reservoir. The refill valve 
structure 120 can then be disconnected from the cartridge refill port, and 
the printing system can proceed with printing operations with a print 
cartridge that has been refilled with ink. 
The variable height refill platform 150 ensures that each off-carriage 
reservoir bag can be virtually depleted of ink, by moving the bag higher 
in relation to the printhead nozzles to increase the pressure head, thus 
maximizing the pressure differential that drives the flow in ink into the 
cartridges. 
In the exemplary system of FIG. 1, the refill platform 150 is in the left 
housing 56 of the printer 50 as shown in FIG. 2. A cam system 180 is 
employed to raise and lower the platform. A stepper motor 188 drives a 
gear train 190 to actuate the cam system. 
The four off-carriage ink reservoirs 80-86 are supported on the platform 
150. Short flexible tubes 150, 152, 154 and 156 connect between ports 
80A-86A of corresponding reservoirs 80-86 and needle valve structures 160, 
162, 164 and 166 supported at a valve holder arm 170. These needle valve 
structures each correspond to the valve structure 120 of FIGS. 4-8. 
The refill platform 150 is an elevator that holds the four reservoirs and 
can be moved up and down by the stepper motor drive. 
To perform a refill the carriage assembly 60 is moved to the refill station 
where the four off-carriage reservoirs 80-86 are connected to the 
corresponding print cartridges 70-76 via the shut-off valves 160-166. The 
above referenced pending application, U.S. application Ser. No. 
08/810,840, filed Mar. 3, 1997 PRINTING SYSTEM WITH SINGLE ON/OFF CONTROL 
VALVE FOR PERIODIC INK REPLENISHMENT OF PRINTHEAD, by Max S. Gunther et 
al., provides additional details of the shut-off valves. Another form of 
shut-off valving suitable for the purpose is described in the above 
referenced pending application, U.S. application Ser. No. 08/726,587, 
filed Oct. 7, 1996, INKJET CARTRIDGE FILL PORT ADAPTER, Robert J. Katon et 
al. The connection of the reservoirs is accomplished by turning a stepper 
motor 200 that advances a valve support arm 202 that rotates on axle 209, 
and on which the valve structures and valve holder structure 170 are 
mounted, as shown in FIGS. 3 and 10-11. A system suitable for moving the 
valves into and out of engagement with the refill ports is more fully 
described below. While the valves are engaged in the refill ports of the 
print cartridges, ink is pulled into the print cartridge reservoir due to 
the slight vacuum pressure (back pressure) in it. 
The entire sequence of the refill operation can be performed relatively 
quickly, e.g. an estimated total time for the refill operation of 180 
seconds for this exemplary embodiment. This is a relatively short time 
period for the refill. Another advantage is that the refill can be 
performed without the need to remove and replace the print cartridges from 
the carriage, thus further contributing to the efficiency of the refill 
process. Yet another advantage is that all of the print cartridges are 
simultaneously replenished with ink during the refilling process, without 
removing the print cartridges from the carriage. 
FIG. 12 is a simplified functional block diagram showing the system 
controller 400 and various elements of the drive and control system. The 
controller 400 provides firing impulses to the firing chamber resistors of 
the printhead 106, and counts the number of drops fired for each color. 
The controller controls the carriage stepper drive motor 404, receiving 
carriage position data from a carriage encoder sensor 406. The controller 
also issues drive signals to the platform motor 188 and refill motor 200, 
receiving platform and valve position data from encoders 408 and 402. 
The refill mechanism provides a concern during start up of the printer. 
Suppose that the power is inadvertently shut off during a refill and that 
the valves are still engaged in the printheads. It is prudent to assume 
that the valves will be engaged in the print cartridges for a long time. 
This implies that, upon startup and initialization, the carriage cannot be 
immediately moved, since the valves may still be engaged, and serious 
damage could occur. Additionally, since the print cartridges are assumed 
to be very full, since the machine has sat with valves engaged for a long 
time and the platform has not been moved down, the refill cycle needs to 
be completed by moving the platform down to remove ink and set the 
printhead back pressure. Thus, during startup, (1) the platform is moved 
to the down position to set the back pressure, then (2) the valves are 
disengaged. Lastly, refill servicing should be performed to ensure print 
cartridge health. 
Carriage Alignment Technique 
The plotter includes apparatus that provides motion to the ink-jet pens and 
locates them in order to provide good image quality. This apparatus 
includes the Y or carriage axis drive system and the carriage assembly, 
shown in the isometric view of FIG. 13 of the carriage axis assembly 450. 
The Y drive system provides an accurate motion to the carriage, in 
position and speed, and is robust against perturbations. The motion is 
provided by a motor-belt-tensioner system, held at each end of the 
carriage slider rods. The motor 404 is mounted at the left end of the 
assembly 450, to the left holder bracket 410. The left and right holder 
brackets 410, 412 is attached to the carriage slider rods 94A, 94B. The 
drive belt 96 is driven by the motor 404, and is reeved about pulleys (not 
shown) mounted in the holder brackets. The carriage 60 is secured to the 
drive belt 96, so that rotational motor movement is translated into linear 
motion of the carriage along the slider rods. 
The system 50 also includes a machine chassis (not shown), which in an 
exemplary embodiment is an aluminum extrusion which is located under the 
slider rods 94A, 94B and between machine side plates (not shown), which 
provide stiffness to the carriage path in order to avoid deformations due 
to the weight of machine components or to other forces. The chassis also 
holds structural components of the machine. 
The carriage motion speed and position are read by an optical encoder 
sensor 406, sensing lines on a linear encoder strip 92 attached to the 
plastic holder brackets 410, 412, and loaded with leaf springs. A suitable 
encoder system is described in U.S. Pat. No. 5,276,970, CODESTRIP IN A 
LARGE-FORMAT, IMAGE-RELATED DEVICE, the entire contents of which are 
incorporated herein by this reference. Electrical signals to and from the 
carriage are supported by a trailing cable, which leads to the machine 
controller 400. 
The carriage 60 holds the removable pens 70-76 in stalls, and provides a 
correct position of the pens 70-76 in space, i.e. relative to each other 
and to the paper or print medium. 
The carriage motion apparatus is susceptible to positioning errors due to 
dimensional tolerances. The encoder 92 has a very good resolution in 
position, referred to the side ends of the carriage path, which are sensed 
during initialization. However, any part attached to the machine side 
plates (e.g. side plate 602, FIG. 19) such as the refill station 600, or 
to the machine chassis have this reference through several parts that can 
add significant dimensional tolerances. These tolerances stack up, and 
depend not only on variability between machines, but also during machine 
life due to thermal effects, transportation shocks and the like. A 
refill-station-carriage alignment technique in accordance with an aspect 
of the invention reduces the effect of the stack of tolerances and 
variations during machine life, and achieves a very accurate positioning 
between the pen septum and the corresponding refill valve. 
In an exemplary embodiment, the alignment technique refers the carriage 60 
directly to the refill station (600), providing a travel stopper for the 
carriage directly on the refill station, and reducing to a minimum the 
number of parts involved in the tolerance stack. Physically this stopper 
includes two surfaces, one located on the carriage and the other located 
on the refill station, that bump against each other during an 
initialization sequence. 
The travel stoppers are shown in FIGS. 14-20. FIG. 14 is a expanded scale, 
partially broken-away view of the area noted in circle 14 in FIG. 13, and 
shows the carriage right side stopper surface 414, located on the carriage 
60 directly adjacent the front slider rod 94A. The right holder stopper 
surface 416 is shown in the isometric view of FIG. 15, and more clearly in 
the expanded scale, partially broken-away view of FIG. 16. As the carriage 
60 is driven to the right side, the respective right stopper surfaces 414 
and 416 will come into contact. In this exemplary embodiment, the stopper 
surface 414 is a surface feature of the carriage 60, which is a molded 
plastic part fabricated of PPS with 15% carbon fiber, and the stopper 
surface 416 is a surface feature of the right holder 412, which also is a 
molded plastic part, fabricated of polycarbonate with 40% glass fiber. 
FIGS. 17-18 show the left, refill, side stopper surface 418 on the carriage 
60. FIG. 17 is an isometric view of the carriage 60, with FIG. 18 an 
expanded scale view of the area noted as area 18 in FIG. 17. FIGS. 19-20 
show the refill station stopper surface 420. The left side stopper surface 
418 is a surface feature of the carriage; the refill station stopper 
surface 420 is a surface feature of the frame 630. As the carriage 60 is 
driven to the left side to the refill station, the respective stopper 
surfaces 418, 420 will come into contact. 
The voltage applied to the Y axis motor 404 is controlled by a 
microprocessor controller 400, to control the speed and position of the 
carriage. This motor control is accomplished through a closed servo loop, 
with the feedback given by the carriage encoder 406 and encoder strip 92. 
When the carriage stops due to some reason, and the controller 400 is 
still ordering a movement, the controller 400 knows that the carriage is 
stopped through the feedback given by the encoder 406, and increases the 
voltage applied to the motor continuously, i.e., the controller increases 
the force applied to the carriage, until the carriage moves again or the 
voltage applied to the motor 404 reaches some established or fixed limit. 
As will be described below, there are two motor voltage limits of interest 
to this invention, a high voltage limit and a low voltage limit, which are 
used to sense the location of the stoppers. 
The alignment technique includes an algorithm which uses values determined 
during the initialization sequence and a constant stored in the memory of 
the machine during the machine assembly process. In a general sense, the 
algorithm includes the following steps. Initialization commences when 
power to the machine is switched on. The carriage 60 is driven by the 
Y-axis motor drive system to make bumping contacts, i.e. "bumps," at both 
sides of its path, assigning to the right side the position value 0, and 
to the left side the position value read from the encoder that corresponds 
to the full length of the carriage path. The bumps are made in two 
sequences on each side. A strong bump is made by applying a high voltage 
limit to the motor 404 to overcome any relatively high friction caused by 
dust or dirty sliders, or by the media cutter (not shown) being out of its 
position. The cutter is disposed at the left (refill) side of the carriage 
assembly, and is parked at a refill stop position. However, if someone or 
something moves it out of its position, the carriage must move it to its 
parked position during initialization, using a high motor 404 drive 
voltage, since the cutter has relatively high friction. The position of 
the heavy bump stop is read by the encoder and stored in memory. Once the 
carriage path is clean, i.e. after the strong bump, another bump, a fine 
or light bump is made by applying a low voltage limit. The position of the 
fine bump is read by the encoder and stored in memory. The second bump 
contact is sensed using the fine motor voltage limit in order to avoid any 
deformation or movement of any part, and the position of the fine bump is 
used to refer all positions of the printer/plotter. However, as a 
protection against malfunction, if the difference in position between the 
strong bump position and the fine bump position is bigger than a limit 
threshold value, the machine gives a system error notification to the 
customer. 
At the right side, the bump contact is made against the holder 412 which is 
solidly fixed to the slider rods 94A, 94B, and is given the reference 
value of 0. At the left side, at the refill station, the "LEFT STOP 
POSITION" is given by a stopper referenced to the refill station and not 
to the left holder. The right reference position, set to a 0 value, is 
used to refer several items on the machine, including the service station 
location, the paper edge detection, platen roller angular position mark. 
Once the machine is initialized, the controller knows the position of the 
refill mechanism, and is able to refer to any feature of it with very 
small error. The alignment between the pen septums and the refill valves 
is given by a constant distance K1 stored in the machine memory during 
assembly. This constant is the distance between the "LEFT STOP POSITION" 
and the "ALIGNMENT POSITION." Thus, each time the carriage is driven to 
the refill station, it will be positioned at the "LEFT STOP POSITION" 
minus K1. If the machine during its life changes this "LEFT STOP POSITION" 
because of thermal effects, shock during transportation or other 
perturbation, the system is able to align with accuracy because the refill 
position sensed during each initialization upon power up. 
An exemplary embodiment of the alignment algorithm 500 is shown in the flow 
diagrams of FIGS. 21A-21B. The algorithm commences upon powering the 
machine up, at 502. An initial parameter set is read by the algorithm at 
504, setting the voltage equal to 0, and the values of the high voltage 
limit and the fine voltage limit. The right side strong bump movement is 
carried out by steps 506-508, with the controller 400 determining the 
position of the carriage, i.e. "position 1," when the carriage has been 
stopped, and the motor voltage reaches the high voltage limit. Position 1 
is read and stored in the machine memory, and the motor 404 voltage set to 
0 at step 510. 
At step 512, the algorithm reads a distance parameter value, and at step 
514, starting from the right stop position, the carriage is moved left an 
amount equal to the distance parameter value. Now the right side fine bump 
takes place, in steps 516-518. The motor 404 is controlled to move the 
carriage to the right, until the carriage contacts the stopper, and the 
motor voltage reaches the fine voltage limit. The position of the carriage 
60 at this point, the right stop position, is read, and the voltage is set 
to 0 at step 520. At step 524, the algorithm reads an error parameter 
value. At step 526, the magnitude of the position 1 stored value minus the 
stored value for the right stop position is compared to the error value. 
If the magnitude is not less than the error, a system error is declared at 
528, and the machine operator is notified by an error message, e.g. on the 
machine display. If the magnitude is less than the error, then the right 
stop position is set to 0, and the motor voltage is set to 0 at step 530. 
Next, the left side strong bump is carried out at steps 532-534, with the 
carriage being moved to the left side, until the left stopper is contacted 
and the high motor voltage limit is reached. At 536, the encoder position 
is read at position 2, and the motor voltage is set to 0. The carriage is 
then moved right (step 538) by the distance input at step 512. The left 
fine bump is then carried out at steps 540-542. When the carriage is 
stopped by contact with the left stopper, and the motor drive voltage 
reaches the fine voltage limit, the LEFT STOP POSITION value is read by 
the encoder, and the motor voltage set to 0 at step 544. The error 
parameter value is then compared to the magnitude of the position 2 value 
minus the left stop position, and if the magnitude is not less than or 
equal to the error, a system error is declared at 548. If the magnitude is 
less than the error value, the algorithm reads a constant K1 at 550, and 
at step 552, sets the alignment position to LEFT STOP POSITION-K1. The 
algorithm is then completed until the next time the machine is powered up. 
FIG. 22 is a simplified flow diagram generally illustrating the operation 
of the machine 50 and its use of the carriage alignment algorithm. When 
power is applied to the machine, an initialization sequence is conducted 
(580), to initialize various system parameters. Next, the carriage 
alignment algorithm (500) is performed, to determine the carriage 
alignment position to be used during refill operations. Under control of 
the system controller 400, the machine performs ink-jet printing 
operations at 582, wherein the carriage is driven along the scan axis, and 
liquid ink droplets are ejected to produce a desired image on a medium 
surface. The medium is advanced to position the medium for successive 
carriage printing swaths. Upon completion of the printing operations, or 
under circumstances determined by the controller 400, a refill operation 
(584) will be conducted to replenish the ink supply carried on the 
carriage by the pens 70-76. This refill operation includes the steps of 
positioning the carriage at the alignment position determined during the 
algorithm 500, engaging the refill valves with the pen septums, passing 
ink through the refill valves and the pen septums into the pens, and 
disengaging the refill valves and the pen septums. Additional printing 
operations can now be performed. 
Carriage Clamping and Pen Septum/Refill Valve Engagement 
After the carriage 60 has been aligned at the refill station 600 for a 
refill operation, the carriage is clamped in position, and the refill 
valves are moved into engagement with the respective pen septums. The risk 
of a pen movement relative to the carriage during the clamping engagement 
process is relatively high, since the force applied to the pens can be 
relatively high, e.g. about 2 kg per pen, with four pens mounted in the 
carriage. The consequence of a pen movement is a loss in print quality. It 
would therefore be advantageous to provide a mechanism of clamping the 
carriage which would balance the forces such that the net resultant is 
zero. To achieve this goal, the refill station includes a mechanism that 
clamps the carriage and allows the clamping and engagement forces to 
travel from the septum surface up through the clamping features in the 
carriage, and so avoid any displacement between the carriage and the 
slider rods, this being the area with a greater risk of movement due to 
clearances. The refill station in this exemplary embodiment clamps the 
carriage at four points. Theoretically the carriage should be clamped in 
only three points instead of four points in order to avoid being redundant 
in the number of support points, but the shape of the carriage suggests 
that it is much easier to clamp it in four points due to the carriage's 
symmetry. In order to avoid any kind of twist in the carriage, due to the 
four contact points, the clamp is made flexible. The refill mechanism 
includes two hinges. The first hinge is about a main shaft, with the 
station frame and the valve holder mounted for independent rotation. The 
second hinge is between the frame and the clamp. The clamping and 
actuation mechanism is described with respect to FIGS. 23-32. 
FIG. 23 is an isometric, partially exploded view of the refill station 600 
and the left side of the carriage axis assembly. FIG. 24 is a reverse 
direction isometric view of the refill station 600 in isolation. The 
refill station has a fixed support bracket 220 which is secured to the 
machine chassis. Additional support is provided by a bridge 614 which 
receives fasteners 616A-616C through holes 614A-614C for insertion in 
bores formed in the end of the left (motor) holder bracket 410 (which is 
referenced to the slider rods 94A, 94B) and in the main axle 204. The 
bridge 614 increases the stiffness of the carriage axis assembly, and 
provides an accurate link between the slider rods and the refill station 
(through main axle 204) in order to achieve a better alignment between the 
refill valves and the pens. 
The refill station 600 includes a frame 620, shown in isolation in the 
isometric view of FIG. 25, and a valve holder 202 shown in isolation in 
the isometric view of FIG. 26. The frame 620 and the valve holder 202 are 
each mounted for rotation about the main axle 204. The frame 620 includes 
a refill mechanism lid 622 to which the motor 200 is mounted. The frame 
includes a spaced first pair of struts 622A and 622B which have shaft 
openings 624A, 624B respectively formed therein for receiving therethrough 
the main shaft 204 along a first hinge axis 610. The frame further 
includes a spaced second pair of struts 622C, 622D which have respective 
shaft openings 624C, 624D formed therein for receiving hinge pins 626A, 
626B along a second hinge axis 612. The frame is thus mounted for hinging 
rotation about the main shaft 204, and the motor 200 and its gear train 
230 are carried with the frame 620. 
The motor gear train is shown in FIGS. 24 and 29, and includes the motor 
spur gear 232 mounted on the motor shaft, gear 234 which meshes with gear 
232, gear 236 which meshes with gear 238, which is mounted on a drive axle 
222, and pinion gears 210A, 212B which mesh with the valve holder gear 
racks 212A, 212B. 
FIG. 26 shows the valve holder 202, which includes the gear racks 212A, 
212B extending from a main body portion 202A. Extending from one end of 
the main body portion are a pair of struts 202B, 202C which have 
respective shaft openings 202D, 202E formed therein for receiving 
therethrough the main shaft 202 along the first hinge axis 610. The valve 
holder is sized so that the struts 202B, 202C fit on the shaft 202 between 
the struts 622A, 622B of the frame 620 when assembled into the refill 
station. Extending from a second end of the body portion 202A is a valve 
holder portion 170, which has defined therein a plurality of apertures 
202G-202J for receiving the valves 160-166 (FIG. 2) connected to 
respective supplemental ink supplies. These apertures are aligned in a row 
which is parallel to the second hinge axis 612. 
The clamp or cradle 630 is another component of the refill station, and is 
shown in isolation in the isometric view of FIG. 27. The clamp 630 has two 
spaced strut portions 630A, 630B, which are joined by two link portions 
630D, 630E. The clamp ends of the strut portions terminate in hooks 630E, 
630F, which define clamp surfaces 630G, 630H. The link portion 630C 
defines an elongated flat clamp surface 630I. The strut portions have 
formed therein openings 630I, 630H formed therein for receiving hinge pins 
626A, 626B along the second hinge axis 612. The clamp 630 is sized so that 
the struts 622C, 622D fit inside the strut portions 630A, 630B along hinge 
axis 612. The clamp is therefor mounted for rotational movement about the 
second hinge axis 612, within a range of motion. 
It is noted that the valve holder 202 and valve holder portion 170 are 
arranged to position valves held therein along respective valve axes 120A 
(FIG. 29) which intersect the second hinge axis 612. The valves held in 
the holder portion 170 are mounted for rotation about the first hinge axis 
610, on a radius equal to the distance between the first and second hinge 
axes. Further, the valve holder portion 170 supports the valves so that, 
as the valve holder rotates about the first hinge axis 610 during the 
engagement process, the valve rotates as well, with its axis extending 
tangentially to a cylinder centered on the first hinge axis 610, with a 
radius equal to the distance between the two hinge axes. 
The frame 610, valve holder 202 and clamp 630 are each one piece, molded 
plastic parts in this exemplary embodiment. An exemplary material suitable 
for the purpose is polyphenil oximetilene, to which glass fibers are added 
to fabricate the frame and valve holder for added stiffness. No fibers are 
added to this material in the exemplary embodiment to fabricate the clamp 
630, so that the clamp is flexible. 
The carriage 60 is provided with two carriage clamp arms 640A, 640B (FIG. 
13) which provide clamp surfaces 640C, 640D which engage clamp surface 
630I of the refill station 600 during the valve engagement process at the 
refill station. Two additional carriage clamp surfaces 640E, 640F are 
provided on the carriage 60 (FIG. 23) which are also engaged at the same 
time. 
The refill station 600 engages the carriage 60 in the following manner, as 
illustrated in FIGS. 28-32. The carriage is first aligned at the refill 
station along the carriage axis. FIG. 28 is a simplified side view of 
elements of the refill station, with the carriage (partially shown in this 
view) positioned for a refill operation. The frame 620 is not shown in 
FIG. 28. The valve holder 202 and the clamp 630 are illustrated in their 
respective positions prior to commencement of the refill operation. 
FIG. 29 is a broken-away cross-sectional view showing the frame 620 with 
the motor gear train 230, the valve holder 202 and the clamp 630 with the 
carriage in position at the refill station. The carriage is only partially 
shown in FIG. 29. It will be seen that the refill station components 
provide clearances permitting the carriage 60 to be passed along the scan 
axis into the refill station 600. 
With the carriage 60 aligned at the refill position, the motor 200 is 
actuated, turning the pinion gears 212A, 212B through the gear train 230. 
While the valve holder 202 is free to rotate about the first hinge toward 
the pen septums in the initial stage of the process, considerable force is 
required to engage the valves in the pen septums, in this embodiment, 
about 2 Kg per valve, or 8 Kg for the four valves set in the valve holder. 
The clamping of the carriage and the valve engagement will be described as 
separate processes, for purposes of this explanation, although as will be 
discussed below, the two functions will typically occur simultaneously. 
Assume that, in this initial stage, then, the valve holder rack remains 
substantially stationary as the pinion gear rotates, the frame 620 instead 
rotating due to the torque applied by the motor. As the frame 620 rotates 
in a clockwise direction about the first hinge axis 610, the clamp 630 is 
carried by the frame in its movement. As this movement continues, the 
clearances between the clamp 630 and the carriage 60 are taken up, and the 
clamp 630 catches or makes contact with the carriage at the four carriage 
clamp surfaces 640C-640F, as illustrated in FIG. 30. Due to the hinging 
action of the clamp about the second hinge axis 612, the forces applied by 
the clamp on the carriage 60 at clamp surfaces 630G-630J are balanced in 
equilibrium. In the absence of valve engaging forces on the pens held in 
the carriage, these clamp forces will be quite small, and due to friction 
in the mechanism. 
With the clearances between the clamp surfaces and the carriage taken up, 
the torque applied by the pinion gear will be transferred to the valve 
holder gear rack 230, rotating the valve holder counterclockwise about the 
first hinge axis 610. As this rotation of the valve holder continues, the 
valves move on an arc of radius equal to the distance between the two 
hinge axes, into engagement with the pen septums, as illustrated in FIG. 
31. A valve arm encoder 402 provides movement/position information to the 
controller 400 relative to the frame 620, so that the motor 200 is stopped 
at a predetermined position, with the valves in a fully engaged position 
relative to the pen septums. The controller 400 counts the number of steps 
the motor 200 is advanced, from commencement of the movement until the 
motor is stopped as a result of the sensor signal. Now the refill 
operation is conducted, with ink from a supplemental off-carriage 
reservoir being passed through each valve to a corresponding pen septum 
and into the internal pen reservoir. 
Considerable force is exerted by the valves on the pens during the refill 
operation, e.g. 2 Kg per pen, or a total of 8 Kg with four pens in the 
cartridge. The clamping mechanism including the clamp 630 and the second 
hinge about axis 612 exerts clamping forces which balance the large forces 
exerted on the pen septums by the valves. This is illustrated in FIG. 27, 
where the force vectors R, indicating the force applied against the clamp 
surfaces 630G, 630H, 630L, 630K of the clamp 630 by the carriage 60 are 
exactly counterbalanced by the forces 2R applied to the clamp 60 by the 
second hinge pins mounted through the openings 630I, 630J. 
FIG. 32 illustrates the force equilibrium achieved by the clamp in a 
conceptual sense. This is a side view of a simple clamp structure 630', 
mounted for hinging movement about a hinge axis 612'. Also partially shown 
in broken-away form is a carriage 60' which carries a pen with a refill 
port septum (not shown) engaged by a valve (not shown) moving along a 
valve axis 120A, with a force indicated by vector 680 of magnitude F and a 
direction along the valve axis 120A. The clamp surface 630H' makes contact 
against carriage surface 640F', and clamp surface 630K' makes contact 
against clamp surface 640D', exerting forces R.sub.1 and R.sub.2, 
respectively. The resultant of the forces applied to the carriage by the 
clamp and by the valve is effectively zero; the forces are in equilibrium. 
In a general sense, this is shown by the following. The sum of the moments 
about either point 1 or point 2 is 0. Assume that point 1 is a distance a 
from the valve axis 120A, and that point 2 is a distance b from the axis. 
Thus, R.sub.2 (a+b)=-Fa, and R.sub.2 =F(a/(a+b)). Further, R.sub.1 
(a+b)=Fa, and R.sub.1 =F(b/(a+b)). As a result of this force equilibrium, 
even though the force F can be relatively large, e.g. 2 Kg per pen, no 
force is transmitted to the slider rods through the carriage from the 
engagement force. While only two clamp points are shown in FIG. 32, the 
clamping/engagement force equilibrium is achieved with three, four (as 
shown in the exemplary embodiment) or more clamp points. 
All these reactions are independent of the overall clamp deformations. This 
is due to the flexibility of the clamp material and to the flexible shape 
of the clamp 630. The clamp 630 behaves as an isostatic structure instead 
of a hyperstatic one. If the clamp surfaces do not lie on the same plane, 
due to tolerance build-up, the clamp struts and links can flex, taking up 
the tolerances and achieving contact with the respective four contact 
surfaces of the carriage. The top hinge about axis 612 makes the reactions 
independent of the clamp angle or position, allowing wide compliance on 
the carriage clamping. 
As indicated above, once the clearances between the respective clamping 
points on the clamp 630 and the carriage 60 are taken up during initial 
activation of the motor drive, further clamping forces by the clamp on the 
carriage are exerted only in reaction to the valve engagement forces being 
exerted on the pen septums and thus on the carriage (since the pens are 
rigidly mounted in stalls of the carriage). Thus, the balancing clamping 
forces are applied simultaneously with, and in reaction to, the 
significant valve engagement forces. 
Upon completion of the ink refill, the clamping and valve engagement 
process can be reversed to disengage the valves from the pen septums and 
release the carriage clamping. The motor is now driven in the reverse 
direction, i.e. the pinion gears 212A, 212B are driven in the 
counterclockwise direction. The controller 400 will drive the motor 200 in 
the reverse direction by a number of motor steps equal to the number 
counted for the advancing movement, plus a predetermined number of 
additional steps to ensure that all tolerances have been overcome. The 
valves are designed in such a way, with a spring, such that a 
disengagement force is not need to disengage the valves from the pen 
septums. Due to the spring bias, a holding force is applied by the motor 
and rack to hold the valves in engagement, and upon release of the holding 
force, the valves disengage without further externally applied force, 
since the spring assists in the disengagement. With the motor driven in 
the reverse direction, the holding force on the valves is released, and 
the valves will disengage from the pen septums. Torque exerted by the 
motor will be taken up by the frame, which will now rotate 
counterclockwise, carrying the clamp with it and releasing the clamping 
forces applied to the carriage. The clamp defines an end stop surface 630M 
which contacts a corresponding stop surface 410A on the bracket 410 as the 
motor continues its reverse drive, stopping travel of the clamp in the 
counterclockwise direction. 
The refill station 600 provides the advantage of single motor actuation of 
two functions, the clamping of the carriage to the refill station, and the 
engagement of the valves with the pen septums to permit replenishment of 
the pen reservoir. The ability to use a single motor for multiple purposes 
results in reduced cost, complexity, weight, and size, increased 
reliability and simplified control electronics. 
While the clamping mechanism of the disclosed system operates to engage the 
carriage to stabilize the carriage during pen engagement and refilling 
procedures, the pens could be individually engaged by individual clamps 
which operate independently to apply clamping forces to pen surfaces which 
compensate the pen engagement forces. 
It is understood that the above-described embodiments are merely 
illustrative of the possible specific embodiments which may represent 
principles of the present invention. Other arrangements may readily be 
devised in accordance with these principles by those skilled in the art 
without departing from the scope and spirit of the invention.