Line printer character chain lubricating device

A low cost line printer character chain lubricating device that provides an accurate amount of lubricant between a line printer character chain and the hard, smooth support surface about which the chain rotates. The lubricating device is located in a depression in the hard, smooth support surface and includes a piece of flexible, abrasion-resistant, microporous nitrile rubber that is impregnated with lubricating oil. The nitrile rubber has a smooth convex arcuate surface for contacting the character chain. A bracket semipermanently mounts the nitrile rubber in the depression in the support surface such that the convex arcuate surface of the nitrile rubber contacts the side of the character chain that normally contacts the hard, smooth support surface as the chain rotates. Depressions in the nitrile rubber beside the arcuate surface serve as charging reservoirs for the lubricating oil. As the line printer character chain rotates and contacts the arcuate surface of the nitrile rubber, the lubricating device provides oil on a need only basis such that an accurate amount of oil is automatically maintained between the chain and the hard, smooth support surface. The size of the micropores in the nitrile rubber, in relation to the lubricating oil used, controls the desired level of lubrication.

BACKGROUND OF THE INVENTION 
This invention relates in general to impact line printers that have a 
character chain printing mechanism that rotates on a hard support surface 
and more particularly to the lubrication of such a line printer character 
chain mechanism. 
Impact line printers may print utilizing a rotating chain that has raised 
linguistic characters, such as alphanumerics, on the exposed exterior 
surface thereof. For example, in such a printer the character chain may be 
rotated at a high speed and hammers may be selectively actuated in a 
properly timed manner to impact selected areas of the paper (or another 
record medium) such that the paper impacts with a ribbon which then 
impacts upon the raised linguistic characters on the character chain of 
the line printer as the characters are in motion. A 1500 line per minute 
printer may have a character chain that moves at a velocity of 210 inches 
per second. The chain must move over a hard, smooth support surface such 
that the chain is firmly supported when impacted. The support surface must 
also be hard and smooth so that it will not significantly wear down over 
time and so that the chain will remain taut for proper operation. 
Commonly, both the character chain and the support surface are made of 
hardened steel. 
Experience has shown that such line printer character chains must be 
lubricated for proper operation. However, if too little lubricant is 
provided between the line printer character chain and the hard support 
surface, the surfaces will heat up and seize together. On the other hand, 
if too much lubricant is provided between the line printer character chain 
and the hard support surface, the lubricant will get on the other parts of 
the line printer, the paper being printed by the line printer, and/or the 
characters on the chain to cause smudging of the printing. 
A known printer character chain lubricating device has an oil reservoir 
from which oil is dropped at intervals (provided by an electronic timer) 
upon a felt wick. The oil passes down the wick, one end of which is 
located under a nylon wear surface which contacts the chains surface. Two 
little holes in the nylon surface permit the oil from the wick to be 
pumped onto the surface of the nylon in contact with the chain as the 
chain passes thereover. Such a system is rather expensive, does not 
necessarily dispense the proper amount of oil needed, and in general is 
not as reliable as is desired. 
Thus, a line printer character chain lubricating device that provides a 
precise amount of lubricant on a need only basis would be very desirable. 
Such a device of course must also be inexpensive, reliable and require 
little maintenance and downtime. 
SUMMARY OF THE INVENTION 
The present invention provides a lubricating device that precisely supplies 
only the desired amount of lubricant between a line printer character 
chain and the hard support surface about which the character chain is 
rotated. The character chain lubricating device is located in a depression 
in the hard support surface and includes a piece of flexible, microporous, 
polymeric material that is impregnated with a liquid lubricant that is 
chemically non-reactive to the polymeric material. Means are provided for 
semipermanently mounting the polymeric material in the depression in the 
support surface so that a portion of the polymeric material is in contact 
with the character chain as it passes thereby in rotation. As the chain 
rotates, the microporous polymeric material maintains a desired amount of 
lubricant between the hard support surface and the side of the character 
chain normally in contact with the hard support surface. 
The line printer character chain lubricating device according to the 
present invention automatically provides lubricant only when needed such 
that a desired level of lubricant is maintained between the character 
chain and the hard support surface. Thus, if the desired level of 
lubricant already exists between the chain and the support surface, no 
further lubricant is automatically provided; but if the desired level of 
lubricant does not exist between the chain and the support surface, then 
lubricant is automatically provided as the chain passes over the polymeric 
material. The desired level of lubricant is provided by appropriately 
selecting the pore size of the microporous, polymeric material with 
respect to the nature of the lubricating liquid used. For example, in the 
preferred embodiment, the microporous, polymeric material is nitrile 
rubber, the lubricating liquid is Shell Lubricating Oil No. 32, and the 
micropores are on the average approximately 20 microns in diameter. 
The present invention is reliable and long lasting. For example, in a 1500 
line per minute printer having a character chain moving at 210 inches per 
second and having approximately three quarter inch links, the flexible 
polymeric material will be contacted by a link almost one million separate 
times per hour of operation. A piece of nitrile rubber polymeric material 
of the preferred embodiment has been operated for several hundred hours 
without showing appreciable wear (abrasion resistant) or surface glazing 
(burnishing). It is anticipated that in normal usage, a lubricating device 
according to the present invention should have its charging reservoirs 
filled with lubricating liquid at regular intervals (such as once a month) 
and can be routinely replaced at longer regular intervals (such as once 
every several months). Thus, the present invention is reliable, 
inexpensive, easily replaceable during routine maintenance, and accurately 
maintains the desired amount of lubricant between the hard support surface 
and the side of the character chain that normally contacts the hard 
support surface.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 shows a line printer character chain mechanism 10 in front view. The 
mechanism 10 includes a casting 11 that has a hard, smooth support surface 
12 about which the character chain 13, formed by individual links 14, is 
rotated. In a 1500 line per minute printer, a character chain may rotate 
at a linear rate of 210 inches per second. Shown below the mechanism 10, 
in cross section, are an inked ribbon 20, a piece of paper 21 to be 
printed on and a bank of hammers 22 with some individual hammers of the 
bank represented at 23. The hammers may be solenoid actuated and there is 
a hammer for each column to be printed on the paper. As the character 
chain 13 rotates at a constant velocity, the hammers 23 are selectively 
actuated to impact the adjacent paper and drive it against the character 
chain with the inked ribbon 20 therebetween to print the desired 
characters on the paper. Located in a depression 23 in the hard, support 
surface 12 is a lubricating device 30 formed by a bracket 31 that holds a 
piece of microporous, polymeric material 32. The material 32 contacts the 
side of the links 14 that normally contacts the support surface as the 
links rotate to provide lubrication. 
Referring to FIGS. 1 through 5, the support surface 12 is smooth and is 
provided by hardened steel. The chain must move over such a hard, smooth 
support surface such that the chain is firmly supported when impacted. 
FIG. 5 shows how the chain links are supported when impacted in more 
detail. The support surface must also be hard and smooth so that it will 
not wear down over time such that the character chain will remain taut on 
the surface for proper operation. 
The character chain 13 is formed by links 14 which are mounted on a grooved 
belt 40. The links and belt rotate about the hard, smooth support surface 
12. The support surface is hard and smooth because the chain must move at 
high speed and yet be fully supported when the links are impacted via the 
hammers. The chain is mounted taut by initially adjusting the eccentric 
41. The chain is directly driven in rotation by engaging the teeth 42 of 
the links 14 with a mating stationary rotating gear at a location not 
shown (on the back of FIG. 1). 
The links 14 have flat surfaces 43 for contacting the support surface 12 
during linear travel (including when the links are impacted via the 
hammers) and a slightly rounded portion 44 for supporting the links as 
they turn the corner at 45 or 46. As the links go around the corners at 45 
and 46, the link portions 50, which interlock with the grooved belt 40, 
mate with non-driving, freely rotating gears at each corner to keep the 
chain in proper alignment on the hard, smooth support surface 12. 
FIG. 5 shows a partial, sectional perspective view (upside down from FIG. 
1) of a link 14 when it is in the printing position on the character chain 
mechanism. The link 14 rides on the hard, smooth support surface 12 and 
guide plates 51 and 52 cover most of the link 14. The links each have an 
elevated portion 54 which extends between and beyond the plates 51 and 52. 
This elevated portion has raised characters thereon for impact printing as 
the chain rotates. Thus, only the portion of the links having the raised 
characters is exposed during printing. The plates 51 and 52 guide the 
links while they are in the printing position so that the printing is in a 
straight line. 
FIGS. 2 and 6 show in detail the chain printer lubricating device 30 which 
is mounted in a depression 23 in the hard, smooth support surface 12. A 
metal bracket 31 is permanently mounted by bolts, such as at 60 and 61, or 
other suitable mounting means to the casting 11. A piece of flexible, 
microporous, polymeric material 32, such as nitrile rubber, is located in 
the bracket 31. The flexible material 32 may be bent for insertion into 
the bracket 31. The microporous material has ears 62 on each corner for 
interlocking with the bracket to hold the material 32 in place. The 
microporous material 32 has a raised convex arcuate surface 63 for 
contacting the surface of the links that normally contacts the hard, 
smooth support surface as the links pass thereby. The size of the surface 
area of the material 32 which comes into contact with the chain helps to 
determine the level of lubrication provided. The microporous material has 
hollow depressions 64 on either side of the convex surface 63. Such 
depressions do not extend completely through the material 32 and serve as 
charging reservoirs for lubricating liquid. 
Nitrile rubber microporous material 32 may be formed into an appropriate 
shape by cutting it or perhaps molding it. The nitrile rubber microporous 
material has a surface that is highly abrasion resistant and 
nonburnishing. That is, as the chain rotates at a linear velocity of 210 
inches per second, the raised surface 63 contacts (is hit by) 
approximately one million individual links per hour. It has been found 
that the nitrile rubber microporous pad 32 wears slightly, but is 
generally abrasion resistant and non-burnishing after several hundred 
hours of normal printer operation. The charging reservoirs 64 may be 
filled at normal maintenance intervals (such as once a month) and the 
microporous material replaced at longer intervals (such as every several 
months). The charging reservoir accepts refilling lubricant and the 
lubricant readily diffuses into the microporous material. 
The size of the micropores in the microporous material is selected to 
maintain the desired level of lubricant between the line printer character 
chain and the hard, smooth support surface. Such selection of micropore 
size of course depends on the lubricating liquid used. In general, a 
preferred range of micropores is between 2 microns and 50 microns in 
diameter. In the preferred embodiment, the microporous material is nitrile 
rubber, manufactured by the Micro-Well Division of Monarch Marking which 
is a division of Pitney Bowes under the name Micro-Well, and has 
micropores approximately 20 microns in diameter; and the corresponding 
lubricating liquid is Shell Tellus Lubricating Oil No. 32. 
EXAMPLE 
An example of microporous polymeric material and liquid lubricant according 
to the present invention is provided. The microporous, polymeric material 
(designated 32) can be nitrile rubber manufactured under the name 
Micro-Well and has micropores approximately 20 microns in diameter 
therein. The nitrile rubber may be 3.375 inch (85.7 mm) long and 1.62 inch 
(41.1 mm) wide. The nitrile rubber may have a top flat surface 0.379 inch 
(9.6 mm) above its base with the curved arcuate surface (designated 63) 
extending 0.06 inch (1.5 mm) above such top flat surface. The curved 
arcuate surface may have a radius of curvature of 2.0 inches (50.8 mm). 
The depressions for holding the oil (designated 64) can be located 
equidistant from and on either side of the curved arcuate surface on 1.37 
inch (34.8 mm) centers in the length dimension. Such depressions may be 
0.25 inch (0.64 mm) in the material length dimension, 0.88 inch (22.4 mm) 
in the material width dimension and extend into the material from the top 
flat surface 0.319 inch (8.1 mm). The nitrile rubber may be impregnated 
with, and the depressions may be filled with, Shell Tellus Lubricating Oil 
No. 32. The nitrile rubber may have suitable ears on each corner for 
engaging a mounting bracket to hold the nitrile rubber stationary with 
respect to the hard, smooth support surface. 
The invention has been described in an illustrative manner, and it is to be 
understood that the terminology which has been used is intended to be in 
the nature of words of description rather than of limitation. 
Obviously, many modifications and variations of the present invention are 
possible in light of the above teachings. It is, therefore, to be 
understood that within the scope of the appended claims, the invention may 
be practiced otherwise than as specifically described.