Inking system with saturation control means for multi-pen recorders

An ink priming system for a multi-pen recorder of the gravity-fed capillary tube type comprises a gas manifold common to all of the ink bottles individually provided for each channel of the recorder. Individual control valves may be selectively actuated by the operator to prime each pen. When the control valve is closed, the gas pressure is bled off so that the inking system thereafter acts as a normal gravity-fed capillary tube system. A non-clogging inking system is provided by utilizing a short length of flexible thin walled tubing to supply ink to the movable recording pen. The length of this tubing is sufficiently short that evaporation of the ink solvent through the walls of the tube is accompanied by diffusion of the dye back to the ink bottle so that the concentration of dye in the ink at the end of the tube adjacent the recording pen does not exceed saturation value during prolonged periods of non-use of the recorder.

The present invention relates to multi-pen recorders, and, more 
particularly, to a new and improved inking system for multi-pen recorders 
of the gravity-fed capillary type. 
While various types of pressurized inking systems have been heretofore 
proposed in which the ink to a number of recorder pens is continuously 
pressurized, these systems have suffered from the disadvantage that the 
ink pen nib or tip must be pressed against the chart paper with a 
substantial force to prevent leakage from the pen tip due to the pressure 
exerted on the ink supply. This increased pressure increases the friction 
between the pen tip and the chart paper which not only reduces the 
lifetime of the pen tip but also slows down the pen's response time and 
increases the overall hysteresis of the system. Higher driving power which 
is required to obtain acceptable response times also requires a more 
powerful pen servo motor with a suitable feedback system. 
As a result of these disadvantages many multi-pen recorders of the present 
day are of the gravity-fed capillary tube type and employ separate ink 
bottles for each pen. However, in these gravity-fed multi-pen systems some 
form of priming means is required for each ink supply to establish the 
initial flow of ink to each pen tip or to force ink through the tube in 
the event it becomes clogged. Previously, a rubber bulb, piston and 
cylinder, or bellows type arrangement has been used on the ink bottle cap 
of each of the ink bottles in a multi-pen gravity-fed capillary type 
recording system. In these arrangements it was easy for the ink bottle to 
become jostled and ink would get into the bulb or pump and then onto the 
user's hands. Also, with the pump located on the ink bottle cap there was 
little room left for a large ink tube since these ink bottle caps are of 
relatively small dimensions. Accordingly a relatively small diameter 
flexible tube is usually employed to connect the ink bottle cap with the 
pen which is mounted on the servo motor, these tubes being customarily 15 
or 20 cm in length. These flexible tubes are usually made of a plastic 
material, which is quite permeable to the solvents in the ink solution. 
With such a length of thin-walled, small diameter tubing, after a few 
weeks of non-use of the inking system the dye in the ink would precipitate 
out and clog the tube. 
Examples of various types of prior art inking systems for recorders are 
shown in the following patents: Hand U.S. Pat. No. 1,849,084; Bowditch 
U.S. Pat. No. 2,727,802; Cannon U.S. Pat. No. 2,800,385; Holloway U.S. 
Pat. No. 2,820,689; Dressel U.S. Pat. No. 2,821,919; Summers, Jr., et al. 
U.S. Pat. No. 3,046,556; Winston U.S. Pat. No. 3,060,429; Gill, Jr., et 
al. U.S. Pat. No. 3,185,991; Sihvonen U.S. Pat. No. 3,247,519; Behmoras et 
al. U.S. Pat. No. 3,299,436; Hartai U.S. Pat. No. 3,355,424; Schweitzer 
U.S. Pat. No. 3,341,860; Sanderson et al. U.S. Pat. No. 3,371,350; Abrams 
et al. U.S. Pat. No. 3,614,940; Skafvenstedt et al. U.S. Pat. No. 
4,053,901; and Brown Jr. U.S. Pat. RE. No. 25,692. The following patents 
are also cited as having general relevance to the present invention: 
Carter U.S. Pat. No. 626,750; England U.S. Pat. No. 1,907,763; Miller U.S. 
Pat. No. 2,769,573; Marwell et al. U.S. Pat. No. 3,208,639; and Kirch U.S. 
Pat. No. 3,418,054. 
It is an object, therefore, of the present invention to provide a new and 
improved ink priming system for a multi-pen recorder of the gravity-fed 
capillary tube type wherein one or more of the above discussed 
disadvantages of prior art arrangement is eliminated. 
It is another object of the present invention to provide a new and improved 
ink priming system for a multi-pen recorder wherein means are provided for 
selectively supplying gas under pressure to any one of the ink reservoirs 
associated with each recording pen of the recorder. 
It is a further object of the present invention to provide a new and 
improved ink priming system for a multi-pen recorder wherein a manifold 
common to the recording pens is provided to which gas under pressure is 
supplied and individual control valves are provided for selectively 
supplying gas from the manifold to the ink bottle associated with a 
particular recording pen so as to prime this pen. 
It is another object of the present invention to provide a new and improved 
non-clogging inking system for use in a recorder wherein the ink, which 
comprises dye in a suitable solvent, is connected to the moveable recorder 
pen element through a flexible tubular member which is permeable to the 
ink and has a length such that the concentration of the dye in the ink at 
the end of the tubular member which is connected to the recorder pen does 
not exceed its saturation value. 
It is a further object of the present invention to provide a new and 
improved non-clogging inking system for use in a recorder or the like, 
wherein a flexible tube is employed to connect the ink supply with the 
recorder pen, said tube being sufficiently short that evaporation of the 
ink solvent through the walls of the tube is accompanied by diffusion of 
dye back to the ink supply so the concentration of dye in the ink at the 
end of the tubular member near the recorder pen does not exceed 
saturation. 
Briefly considered, the present invention relates to an ink priming system 
for a multi-pen recorder of the gravity-fed capillary tube type in which 
individual ink bottles are provided for each recorder pen. A gas manifold, 
common to all of the ink bottles, is connected to each of the ink bottles 
through a suitable control valve so that gas which is supplied to the 
manifold under pressure may be selectively applied to any ink bottle to 
force ink from that bottle out of the corresponding pen to prime it. As 
soon as the recording pen is primed and the control valve is released, the 
gas pressure is bled off so that the system thereafter acts as a normal 
gravity-fed capillary tube recording system. Therefore, during normal 
usage of the recording pen the ink is not pressurized and hence the pen 
nib may press relatively lightly on the chart paper and may be driven by a 
relatively low powered pen motor as compared to conventional pressurized 
inking systems. 
In accordance with the further aspect of the invention, a non-clogging 
inking system is provided for each recorder pen by utilizing a short 
length of flexible thin walled tubing to supply ink to the moveable 
recording pen element. The length of this permeable, thin walled tube is 
sufficiently short that evaporation of the ink solution through the walls 
of the tube is accompanied by diffusion of the dye back to the ink bottle 
so that the concentration of dye in the ink at the end of the tubular 
member which is connected to the recorder pen does not exceed saturation 
value. As a result, the recorder pen may remain motionless for long 
periods of time without causing precipitation of the dye and clogging of 
either the tubular member or the recorder pen.

Referring now to the drawings, the ink priming system of the present 
invention is therein illustrated with one channel of the multi-pen 
recorder system being shown in detail. More particularly, the capillary 
tube pen element 10, which comprises a metal tube having an extremely 
small diameter hole therethrough, is provided with a nib portion 12 which 
is adapted to engage the chart paper. The recording element 10 is mounted 
in a light-weight metal frame 14 which is secured to a suitable 
galvanometer type pen motor (not shown) so that the element 10 is rotated 
about the axis 15 in accordance with a given input signal, as will be 
readily understood by those skilled in the art. An ink bottle 16 is 
provided for each channel of the multi-pen recorder, and the ink 18 within 
the bottle 16 is normally supplied through the metal tube 20, which is 
mounted in the cap portion 22, a relatively large diameter thick-walled 
tubing section 24 and a relatively short, small diameter thin-walled 
tubing section 26 to the downwardly extending rear end portion 28 of the 
recording pen element 10. 
During normal operation of the recording channel, the space 30 above the 
ink 18 in the bottle 16 is not pressurized and hence the recording system 
acts as a conventional gravity-fed capillary type system. However, in 
accordance with the present invention, a pressurized ink priming system is 
provided for each of the channels of the multi-pen recorder. More 
particularly, a suitable gas, such as carbon dioxide, is stored in liquid 
form in a relatively large disposable bottle 32, the liquid carbon dioxide 
in the bottle 32 being at a relatively high pressure such as 845 psig. A 
bottle hold and puncturing device 34 is employed to hold the bottle 32 and 
supplies carbon dioxide through the tube 36, a manifold valve 38, and the 
tubing 40 to a pressure regulator 42 which reduces the pressure of carbon 
dioxide from the bottle 32 to a pressure in the range of from 4 to 10 
psig. While other hydrocarbons or halocarbons are available with a lower 
vapor pressure, which will require a less rugged container 32 and a 
simpler pressure regulator 42 than when carbon dioxide is employed, carbon 
dioxide is preferred as a suitable gas from both a fire hazard and an 
environmental hazard standpoint. A spare carbon dioxide bottle 44 is 
mounted in the bottle holding and puncturing device 46 and may be 
selectively utilized in place of the bottle 32 by suitable actuation of 
the manifold valve 38. 
The output of the regulator 42 is supplied through a three-way valve 48 to 
a gas manifold 50 which is common to all of the recording channels of the 
multi-pen recorder. More particularly, the manifold 50 comprises a central 
chamber 52 which extends longitudinally along the length of the manifold 
50 and is connected to the valve 48 through the conduit 54. A series of 
control valves indicated generally at 56 are mounted in the top wall of 
the manifold 50 and individually communicate with the chamber 52 through 
the vertical bores 58. Each of these control valves is actuated by means 
of a depressible top member 60. A flexible tube 62 is employed to 
interconnect a metal sleeve 64, which is mounted in the cap 60, and a 
metal sleeve 66, which is mounted in the ink bottle cap portion 22, the 
sleeve 66 communicating with the space 30 within the ink bottle 16 through 
the conduit 68 formed in the cap 22. The cap portion 22 is provided with 
an outwardly extending flange portion 70 which fits within and is engaged 
by the top wall of an outer cap member 72, a sealing washer 74 being 
provided on the flange 70 which seals the inner cap member 22 to the upper 
end of the screw thread portion of the ink bottle 16 so that a pressure 
seal is provided between the bottle 16 and the cap member 22. 
Considering now in more detail the control valve 56, this valve is of the 
so-called tank valve construction and is similar to a conventional 
automotive tire valve. More particularly, the valve 56 comprises an outer 
housing 76 the bottom end of which is threaded into the bore 58, the 
washer 78 and sealing ring 80 being provided to maintain a tight seal 
between the housing 76 and the manifold 50. A two-piece valve core 82 is 
threaded into the upper end of the housing 76 so that a tight seal is 
effected between the valve core seal 84 and the housing 76. A valve core 
pin 86 is slidably mounted in the valve core 82 and carries a valve seat 
seal 88 which is normally biased upwardly into engagement with the bottom 
end of the valve core 82 by means of the coil spring 90. The depressible 
cap member 60 is provided with a downwardly extending pin 92 in the top 
wall thereof so that when the cap 60 is depressed the valve core pin 86 is 
engaged and depressed and the control valve 56 is opened. As the cap 60 is 
depressed a sealing member 94 which is mounted in the cap 60 is moved 
downwardly into engagement with the upper end of the housing 76 to prevent 
gas supplied to the manifold 52 from escaping to the atmosphere. 
Accordingly, when the cap 60 is depressed the pressurized carbon dioxide 
in the manifold 52 is supplied through the valve 56 and the tubing 62 to 
the space 30 in the top of the ink bottle 16. As a result, the ink 18 is 
forced outwardly through the tubes 20, 24 and 26 and into the recording 
pen element 10 so that the recording pen tip 12 is primed. 
The cap 60 is depressed by the operator only for a sufficient time to 
establish the desired capillary ink flow between the bottle 16 and the pen 
tip 12 after which the cap 60 is released. Normally, the cap member 60 is 
positioned by means of the spring 90 with the sealing member 94 spaced 
above the upper end of the housing 76. When the cap 60 is released after 
an ink priming operation the pressure established in the space 30 of the 
ink bottle 16 and the spring 90 cooperate to lift the cap 60 so that the 
pressurized carbon dioxide in the space 30 is bled off through the space 
between the outer threads 96 on the upper end of the housing 76 and the 
inner wall of the cap member 60. 
In order to retain the cap 60 loosely on the upper end of the valve 56, a 
threaded insert 98 is secured in the bottom end of the cap 60. Initially, 
the cap 60 is assembled on the upper end of the valve 56 by threading the 
insert 98 over the outer threaded portion 96 on the housing 76 so that the 
cap 60 is loosely retained on the upper end of the valve 56. The tubing 62 
may then be connected to the corresponding ink bottle 16. 
In order to prevent the leakage of carbon dioxide from the manifold 52 
during periods when no recorder pen is being primed, the control valves 56 
are preferably of the tank valve type manufactured by the Schrader Div. of 
Scovill Mfg. Co. which have a leakage rate of less than one nanoliter per 
second. Since the rest of the ink priming system is only pressurized 
intermittedly, the corresponding seals do not have to have such a low 
leakage rate. 
Considering now the operation of the ink priming system of the present 
invention, during periods when the ink priming system is not required, the 
three-way valve 48 may be moved to the position in which the output of the 
regulator 42 is blocked so as to discontinue the supply of pressurized 
carbon dioxide to the manifold chamber 52. This minimizes the chance that 
one of the control valves 56 may accidently leak and vent all of the 
carbon dioxide in the bottle 32 to the atmosphere. However, when the ink 
priming system is to be used, the three-way valve 48 is turned to the 
position in which the output of the regulator 42 is supplied through the 
conduit 54 to the manifold chamber 52. When the operator desires to prime 
a particular one of the recording pens 10, he depresses the corresponding 
one of the cap members 60 so that the associated control valve 56 is 
opened and carbon dioxide under pressure is supplied to the ink bottle 16 
and a flow of ink is established over the above described path to the pen 
tip 12. In this connection it will be understood that the conduit 54 may 
be relatively long so that the carbon dioxide bottles 32, 44, pressure 
regulator 42, and valves 38, 48 may be positioned in a remote place while 
the manifold 50 is positioned relatively close to the row of ink bottles 
16. Preferably the conduit 54 is made of nylon which is not as permeable 
to carbon dioxide as other plastic materials. In accordance with a further 
aspect of the invention, the manifold 50 is provided with one or two 
auxiliary control valves 56a in addition to the control valves required 
for each of the ink bottles 16 associated with each recording pen of the 
multi-pen recorder. These auxiliary control valves may be employed to 
flush out any one of the recording pens 10 or to blow ink out of the pens. 
More particularly, the auxiliary control valve may be connected to a 
bottle 16 which is filled with a suitable solvent rather than the ink 18. 
The output tube 24a (FIG. 3), which is connected to the bottle of solvent, 
is then connected to an elbow block indicated generally at 100 which may 
be of the type shown and described in detail in my co-pending application 
Ser. No. 867,201, filed Jan. 5, 1978, which is assigned to the same 
assignee as the present invention. The elbow block 100 is provided with a 
vertically extending opening 102 in the top wall thereof into which the 
pen nib 12 may be tightly inserted. The opening 102 is connected to the 
end of the tube 24a through the conduit 104 and a metal tube 106 which 
extends out of the block 100. When the auxiliary valve 56a is opened the 
solvent in the associated bottle 16 is forced through the tube 24a and the 
conduits 104 and 102 in the block 100 into the end of pen tip 12 so that 
solvent is fed in the reverse direction through the recording pen 10 and 
its associated tubing elements 26 and 24 so as to flush out these elements 
and remove any precipitated dye and/or the like which may remain therein. 
In this connection it will be understood that the ink bottle 16 is removed 
from the associated recording pen 10 when such a flushing operation is 
performed. In the alternative, the bottle associated with one of the 
auxiliary valves 56a may contain air, in which case ink may be blown from 
a selected one of the recording pens 10 by placing the pen tip 12 in the 
opening 102 and opening the corresponding auxiliary control valve 56a. 
When the valve 56a is opened carbon dioxide under pressure is forced into 
the bottle of air so that air under pressure is applied to the pen tip 12 
and forces the ink in a reverse direction back through the recording pen 
10 and the tubes 26 and 24. Such flushing or flowing of air into the 
recording pens may be utilized, for example, to prepare the recorder for 
storage, or the like. 
In accordance with a further aspect of the invention, a hand pump indicated 
generally at 110 is provided which may be used to pressurize the manifold 
chamber 52 during periods when no carbon dioxide bottle 32 is used. More 
particularly, the pump 110 comprises a rubber bulb 112 with check valves 
114 and 118 at either end thereof. The check valve 114 is connected to one 
end of a long tube 116 the other end of which is connected to the 
three-way valve 48. In the third position of the valve 48 the tube 116 is 
connected to the tube 54 which communicates with the manifold chamber 52. 
When the bulb 112 is squeezed air pressure up to approximately 10 psig can 
be built up in the manifold chamber 52 and is prevented from escaping by 
means of the check valve 114. After a suitable pressure has been 
established in the manifold chamber 52, any one of the control valves 56 
may be opened by depressing the cap 60 and air under pressure will be 
supplied to the space 30 above the ink reservoir 18 so that the 
corresponding pen 10 is primed in the manner described in detail here 
before. 
In accordance with a further aspect of the invention, the hand pump 110 may 
be disconnected from the end of the tube 116 and the check valve 118 in 
the other end of the bulk 112 may be connected to the tube 116. If the 
tube 112 is then squeezed and released, a vacuum is established in the 
manifold chamber 52 as the squeezed bulb 112 expands. A vacuum of 
approximately -1.5 psig may be established with such an arrangement. After 
a vacuum of this level has been established in the manifold chamber 52, 
depression of any one of the cap members 60 causes the corresponding 
control valve 56 to open so that the vacuum in the manifold 52 may be used 
to draw ink out of the corresponding recorder pen 10 and into the ink 
bottle 16. Such an arrangement may be employed in place of the above 
described elbow block arrangement to remove ink from the recording pen 10. 
In accordance with a further important aspect of the invention, the tube 24 
which is connected at its upper end to the right angle end portion 120 of 
the tube 20 has a relatively large inner diameter and has relatively thick 
walls so that the solvent which is present in the ink 18 cannot readily 
evaporate through the walls of the tubing section 24. Preferably the 
tubing 24 is made of polyvinyl chloride or ethylene vinyl acetate, has an 
inside diameter of 0.62 inches and an outside diameter of 0.125 inches and 
may have an inner lining of polyethylene to reduce evaporation. The tubing 
section 26 is of relatively small inner diameter so it can fit over the 
capillary tube end portion 28 of the recorder pen 10 and is also flexible 
enough so it does not restrict movement of the recorder pen during a 
recording operation. Preferably, the tubing section 26 is also made of 
polyvinyl chloride and has an inner diameter of 0.023 inches and an outer 
diameter of 0.046 inches. 
In prior art arrangements a tube of the dimensions of the tubing section 26 
was connected all the way from the ink bottle 16 to the end portion 28 of 
the recording pen 10, a distance in some instances of from 15 to 20 
centimeters. Such a small diameter tubing was required in prior art 
arrangements when a rubber bulb was used on the ink bottle cap to prime 
the recording pens. I have found that when such a long length of small 
tubing 26 is employed substantial evaporation of the ink solvent occurs 
through the relatively thin, permeable walls of the tubing when the 
recorder is not in use and the pen tip 12 is not moving. Since the 
evaporated solvent had to be replaced by drawing ink from the ink bottle, 
a relatively large ink current is established, which moves on the order of 
10 mm per day, this ink current leaving the ink bottle and moving down the 
tubing to replace the evaporated solvent. When additional ink is thus 
drawn out of the ink bottle and into the small diameter tubing the 
concentration of dye in the tubing is increased and will reach saturation 
value, at which point the dye will precipitate out and clog the tubing 
unless some of the dye can diffuse back into the ink bottle. However, I 
have also found that the dye can diffuse out of such a small diameter 
tubing at only a rate of approximately 1 mm per day. This means that after 
a short period of non-use of the inking system the dye will exceed 
saturation value and will precipitate out and clog a length of tubing in 
the order of 15 to 20 cm. 
In accordance with the present invention, the tubing section 26 is made 
relatively short and preferably has a length such that evaporation of the 
ink solvent through the walls of the tubing section 26 is substantially 
balanced by diffusion of dye back into the adjacent end of the tubing 
section 24. As stated heretofore, the tubing 24 has a relatively large 
inner diameter and relatively little evaporation through the thick walls 
thereof so that the concentration of dye in the ink adjacent the tubing 
section 26 is substantially the same as in the bottle 16. The ink bottle 
is thus effectively connected to the end of the short tubing section 26, 
by employing the large diameter tubing 24, so that dye can diffuse out of 
the short length of tubing 26 and maintain the ink below saturation value 
throughout the length of the tubing 26. 
Assuming that evaporation of the ink solvent is uniform along the length of 
the tubing section 26, if the density of the dye divided by the saturation 
density is designated as "rho", the idealized characteristic 120 shown in 
FIG. 4 may be computed for the steady-state or equilibrium condition in 
which the dye concentration is at saturation at the end of the tube 26 
adjacent the recording pen portion 28, i.e., Rho (O)=1.0. In FIG. 4 the 
value "rho(y)" is plotted along the ordinate and y is plotted along the 
abscissa, where y=.sqroot.V/LD.multidot.X. In this formula for y, X is the 
distance from the pen end of the tubing 26, and D is the diffusion 
constant for the particular dye molecules which are used in the ink. The 
quantity L/V for a particular tube can be measured by filling a given 
length of such tubing with water, plugging both ends and measuring the 
time required for all of the water to evaporate out of the tubing i.e., 
the length of tubing divided by the velocity at which ink must enter the 
tubing to keep it full. For example, with a polyvinyl chloride tubing of 
the dimensions given above for the tubing 26, a period of from 15 to 20 
days is required for all of the water to evaporate out of a length of 
tubing 20 cm long. 
The idealized characteristic 120 can be employed to determine the proper 
length of tubing 26 for a particular type of tubing and concentration of 
dye in the ink supply 18. Preferably, the dye in the ink 18 within the 
bottle 16 has a concentration of 50% of its saturation blackness thus 
allowing for a substantial increase in concentration before reaching 
saturation. If the ink 18 has a higher concentration in the bottle 16 the 
trace is not any blacker but there is less change in concentration before 
saturation is reached. On the other hand, if a concentration less than 50% 
is used the trace will become progressively lighter as the concentration 
is reduced. From the characteristic 120 of FIG. 4 a concentration of 0.5 
(50%) gives a value for "y" of 1.1774. The length of tubing 26 which is 
permitted under the ideal conditions of the characteristic 120 may then be 
calculated from the formula X=.sqroot.DL/V.multidot.1.1774. On the other 
hand, if the concentration of the dye in the bottle 26 is 20% (0.2) then 
the length of tubing 26 may be substantially greater corresponding to a 
value of "y" in FIG. 4 of 1.8. The value L/V may be obtained, as discussed 
previously, by measuring the time required to evaporate all of the water 
out of a given length of tubing through the walls thereof. It should be 
emphasized that the characteristic 120 in FIG. 4 is based on the ideal 
situation in which there is equilibrium of the dye concentration 
distribution and corresponds to a condition in which the concentration of 
dye at the pen end of the tubing 26 never exceeds the saturation value of 
1.0. Since it is not necessary to design an inking system with such rigid 
requirements, the length of tubing 26 which is actually used may be 
somewhat longer than that indicated by the characteristic 120 and still 
provide non-clogging of the tubing 26 during periods of non-use of many 
months. For example, with a polyvinyl chloride tubing 26 of the dimensions 
given above, the tubing 26 may have a length of 1.25 inches. 
The end of the tube 26 is conveniently secured within the end of the larger 
tubing 24 by using a suitable glue, such as PVC dissolved in cyclohexanone 
of cyclohexane, or other suitable glue of the type used with PVC plumbing 
fixtures. In this connection it is pointed out that a preferred 
arrangement for supplying ink from the reservoir 18 to the capillary tube 
end portion 28 would be a conduit having a gradually tapered inner 
cross-section. However, such a tapered pipe is quite difficult to 
fabricate on an economical basis. In the alternative, a tapered pipe may 
be approximated by employing several lengths of tubing having increasingly 
larger internal diameters so that a stepped conduit of increasingly larger 
inner diameter is provided in the direction away from the pen portion 28. 
While there have been described what are at present considered to be the 
preferred embodiments of the invention, it will be understood that various 
modifications may be made therein which are within the true spirit and 
scope of the invention.