Information
-
Patent Grant
-
6350021
-
Patent Number
6,350,021
-
Date Filed
Monday, March 29, 199925 years ago
-
Date Issued
Tuesday, February 26, 200222 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
- Bootzin; Joel H.
- Piper Marbury Rudnick & Wolfe
-
CPC
-
US Classifications
Field of Search
US
- 347 68
- 347 69
- 347 70
- 347 71
- 347 72
- 347 50
- 347 40
- 347 20
- 347 54
- 347 78
- 399 261
- 361 700
- 029 8901
-
International Classifications
-
Abstract
An ink jet printing system comprising a droplet generator (5), a supply tank (3), supply transfer means for driving the ink from said tank to said generator and means for measuring the flow rate of the stream of ink droplets by monitoring the change of ink level in said tank, said system including a bleed connection (19) from the generator to the tank in closed circuit with said tank. An ink jet printing system comprising means for using measurements of the rate of change of liquid level in an ink supply tank to provide an indication that there has been a fault in the system. An ink jet printing system comprising a holding tank (101) for receiving liquid issued from the ink jet generator during preparation of the system.
Description
This invention relates to an ink jet printing system.
U.S. Pat. No. 4,555,712 discloses an ink jet printing system comprising: a droplet generator for generating a stream of ink droplets; a supply tank for supplying ink to the generator; a pressure source for applying pressure to the ink in the supply tank to force it to the droplet generator; a gutter for collecting ink droplets not used in printing; a return tank for receiving the ink collected in the gutter; and a pump for pumping ink from the return tank to the supply tank. The printing system further comprises a measurement system for measuring the flow rate of the steam of ink droplets generated by the generator by monitoring the change of ink level in the supply tank when ink is not being pumped from the return tank to the supply tank.
In ink jet printing it is known to increase the rate of flow of ink to a droplet generator without increasing the flow rate of the stream(s) of ink droplets generated by the generator, by providing a bleed connection from the droplet generator. An example of this is disclosed in U.S. Pat. No. 4,555,709.
Ink jet printing systems are cleaned before, after, and, when required, during use by flushing with ink solvent. Solvent flushes out of the droplet generator of the system via its droplet forming nozzle(s). It is known to supply this solvent to the tank which directly supplies the droplet generator during printing, resulting in an undesirable dilution of the printing ink. Solvent is also flushed out of the droplet generator via its bleed outlet, if it has one. It is known to dump this solvent, which wastes solvent, is environmentally unfriendly, and labour intensive in that the dumping is required to be carried out.
According to a first aspect of the present invention there is provided an ink jet printing system comprising: a droplet generator for generating at least one stream of ink droplets; a supply tank for supplying ink to said generator; supply transfer means for driving the ink from said tank to said generator; and measurement means for measuring the flow rate of the stream(s) of ink droplets generated by said generator by monitoring the change of ink level in said tank, said system including a bleed connection from said generator to said tank in closed circuit with said tank, the presence of said bleed connection thereby increasing the rate of flow of ink from said tank to said generator without affecting the measurement by said measurement means of the flow rate of the stream(s) of ink droplets generated by said generator.
According to a second aspect of the present invention there is provided an ink jet printing system comprising: a droplet generator for generating at least one stream of ink droplets; a supply tank for supplying ink to said generator; supply transfer means for driving the ink from said tank to said generator; a holding tank for receiving liquid issued by said generator during preparation of the system for subsequent printing, said holding tank being connected to said supply tank for the supply of said liquid to the supply tank during said subsequent printing; and means for determining during said subsequent printing the times at which the composition of the ink supplied to said generator is such that it is appropriate to use the liquid contained in said holding tank.
According to a third aspect of the present invention there is provided an ink jet printing system comprising: a tank for holding a liquid for use in the operation of said system; a multi-level or continuous level sensor for measuring the rate of change of liquid level in said tank during said operation; and means for using this measurement to provide an indication that there has been a fault in said system.
An ink jet printing system in accordance with the present invention will now be described, by way of example, with reference to the accompanying drawings in which:
FIG. 1
is a block schematic diagram of the system;
FIG. 2
shows a development of the system of
FIG. 1
; and
FIG. 3
shows a modification to the system of FIG.
2
.
Referring to
FIG. 1
, a supply pump
1
pumps ink from a supply tank
3
to the droplet generator
5
of a printhead
7
. Droplet generator
5
generates a plurality of streams of ink droplets
9
, and a gutter
11
of the printhead
7
collects ink droplets not used in printing. A vacuum source
13
draws ink collected in gutter
11
to a return tank
15
. A bleed connection
19
continuously bleeds ink from generator
5
to supply tank
3
.
In the printing system the flow rate of the streams of ink droplets
9
is measured as follows. Ink level sensors
23
,
25
are located respectively at levels A and B of supply tank
3
. A central control system
21
measures the time it takes for the ink to fall from level A to level B. This provides a measure of the flow rate of the streams of ink droplets
9
. In this connection it is to be appreciated that, since all the ink which leaves generator
5
via bleed connection
19
returns directly to supply tank
3
, the loss of ink via bleed connection
19
will have no nett effect on the using up of ink in supply tank
3
. Hence, the time taken for the ink level to drop from A to B provides an accurate measure of the flow rate of the streams of ink droplets
9
generated by generator
5
. In other words, since supply tank
3
, droplet generator
5
, and bleed connection
19
are in closed circuit, the rate of drop of ink level in supply tank
3
is an accurate representation of the flow rate of the streams of ink droplets
9
generated by generator
5
.
A transfer pump
17
pumps ink from return tank
15
via a non-return valve
45
to supply tank
3
. When the ink level in supply tank
3
falls below level B, control system
21
starts pump
17
. When the ink level in supply tank
3
rises above level A, control system
21
stops pump
17
. The flow rate measurement of the previous paragraph is made by control system
21
when ink is not being pumped from return tank
15
to supply tank
3
.
For accurate printing the velocity of the streams of ink droplets
9
is maintained at a constant value. This is achieved by means of central control system
21
which maintains constant the composition, temperature, and pressure of the ink in droplet generator
5
.
The composition is maintained as follows. To replace ink used up in printing, an ink level sensor
27
is located at a top-up level in return tank
15
. When the level of the ink in tank
15
drops below the top-up level, control system
21
opens valves
29
and
31
to reservoirs
33
and
35
respectively. Reservoir
33
contains the same ink as supplied to generator
5
but with a slightly lower proportion of ink solvent therein so that it is slightly more viscous. Reservoir
35
contains ink solvent. Vacuum source
13
draws into return tank
15
ink and ink solvent from reservoirs
33
,
35
. Control system
21
keeps open valves
29
and
31
for relative periods such that an ink of the same viscosity as that supplied to generator
5
resides in return tank
15
, i.e. the aforementioned slightly lower proportion of ink solvent in the ink of reservoir
33
is offset by the ink solvent drawn from reservoir
35
. To replace ink solvent which has evaporated in the course of printing or which has been added in the course of printing as a consequence of cleaning the printhead
7
with solvent, the flow rate measurement made using level sensors
23
,
25
is used by control system
21
to determine whether to add ink solvent from reservoir
35
or thicker ink from reservoir
33
. If the flow rate measurement made is less than the desired flow rate, the assumption is that ink solvent has been lost through evaporation, and hence control system
21
opens valve
31
so that ink solvent is drawn into return tank
15
. If the flow rate measurement made is greater than the desired flow rate, the assumption is that ink solvent has been added through cleaning, and hence control system
21
opens valve
29
so that thicker ink is drawn into return tank
15
. Of course, any error in the relative mixing to replace ink used up in printing, i.e. the relative mixing of ink and ink solvent from reservoirs
33
,
35
, will be corrected for by control system
21
in response to the flow rate measurements made using level sensors
23
,
25
.
Central control system
21
maintains the temperature constant using a temperature sensor
37
to sense the temperature of the ink in generator
5
, and a heater
39
and cooler
41
located in the ink supply path from supply pump
1
to generator
5
. In dependence on the temperature sensed, operation of heater
39
and cooler
41
is controlled so that the desired ink temperature in generator
5
is maintained. In this connection it is to be appreciated that, since the presence of bleed connection
19
increases the ink flow rate to generator
5
, it enhances temperature control, since there is less time between heater/cooler
39
/
41
and generator
5
during which cooling of the ink can occur.
Central control system
21
maintains the pressure constant using a pressure sensor
43
to sense the pressure of the ink in generator
5
. In dependence on the pressure sensed, the speed of supply pump
1
is adjusted so that the desired ink pressure in generator
5
is maintained.
In the above description the velocity of the streams of ink droplets
9
is maintained constant by maintaining constant each of the composition, temperature, and pressure of the ink in droplet generator
5
. It is to be appreciated that this velocity maintenance could also be achieved by allowing each of the composition, temperature, and pressure to vary within predefined limits, but to control this variation such that the result of the combination of all three parameters always results in the same desired velocity of the streams of ink droplets
9
. The requirement is that the three parameters are controlled such that the velocity is maintained constant.
It is also to be appreciated that the ink held in reservoir
33
need not be thicker than that supplied to generator
5
, but could be of the same consistency. In this case, when the ink level in return tank
15
drops below the top-up level, only ink from reservoir
33
is supplied to return tank
15
. When ink solvent is lost through evaporation, as before, valve
31
is opened to supply ink solvent from reservoir
35
. When ink solvent is added in cleaning, ink from reservoir
33
is supplied.
It is further to be appreciated that supply pump
1
could be replaced by a pressure source which applies pressure to the ink in supply tank
3
to force it out and around to generator
5
. In this case a pump would be required in bleed connection
19
.
The sensing of ink level in tanks
3
,
15
could be achieved, not by means of sensors
23
,
25
,
27
located at fixed positions within tanks
3
,
15
, but by one sensor in each tank
3
,
15
which floats on the surface of the ink and therefore changes level therewith.
Referring to
FIG. 2
, in the development a holding tank
101
, various valves
103
,
105
,
107
,
109
,
111
,
113
,
115
,
117
,
119
,
121
, and a flush path
123
, have been added to the system of FIG.
1
.
During normal operation of the system, i.e. during printing by the system as described with reference to
FIG. 1
, control system
21
opens valves
103
,
109
,
117
and
119
, and closes valves
105
,
107
,
115
,
121
and
111
. Thus, as described with reference to FIG.
1
: ink in gutter
11
is drawn into return tank
15
by vacuum source
13
; ink is continuously bled from droplet generator
5
to supply tank
3
via connection
19
; and ink is pumped by supply pump
1
from supply tank
3
to droplet generator
5
via heater
39
and cooler
41
.
Prior to printing by the system during start-up of the system, control system
21
opens valves
105
,
107
,
115
and
121
, closes valves
103
,
109
,
117
,
119
and
111
, and switches valve
113
to connect to vacuum source
13
—valve
113
may be switched to connect holding tank
101
to either source
13
or atmospheric pressure. Supply pump
1
pumps ink solvent from reservoir
35
around flush path
123
to generator
5
. The ink solvent which collects in gutter
11
is drawn into holding tank
101
by vacuum source
13
. Solvent is also drawn by source
13
into holding tank
101
from bleed connection
19
. Thus, following start-up, ink solvent used to flush clean the system resides in holding tank
101
.
The same procedure is followed to flush clean the system during shut-down following printing. Thus, again the ink solvent used resides in holding tank
101
.
Blockage may occur of the droplet forming nozzles of generator
5
. This blockage may be removed by manually spraying onto the nozzles ink solvent, closing valve
109
, opening valve
107
, and switching valve
113
to vacuum source
13
. Source
13
draws the ink solvent through the nozzles into generator
5
unblocking the nozzles, and then via bleed connection
19
and valve
107
to holding tank
101
. Thus, the used ink solvent again resides in holding tank
101
. Valves
115
,
117
,
119
,
121
are closed during the operation so that printhead
7
may be switched to vacuum.
Since each of the cleaning processes of the previous three paragraphs results in a liquid comprising predominantly ink solvent residing in holding tank
101
, this liquid may be used in printing by the system in place of the ink solvent in reservoir
35
. For example, if the flow rate measurement made using level sensors
23
,
25
is below that desired, liquid from holding tank
101
may be supplied to return tank
15
instead of ink solvent from reservoir
35
. The liquid is supplied by switching valve
113
to atmospheric pressure, and opening valve
111
so that vacuum source
13
draws the liquid from holding tank
101
to return tank
15
.
It will be appreciated from the following that the liquid residing in holding tank
101
may not be predominantly ink solvent. Consider a modification to the system of
FIG. 2
where the temperature control afforded by temperature sensor
37
and heater/cooler
39
/
41
is removed, and the velocity of the streams of ink droplets
9
maintained constant by varying the ink composition to cater for ambient temperature change. If the ambient temperature of the print run prior to a present print run was significantly lower (or higher) than that of the present print run, then the composition of the ink in the system at the start of the present print run will be appreciably thinner (thicker) than that appropriate for the present print run. Thus, the system is initially run prior to printing to feed this thinner (thicker) ink into holding tank
101
. This thinner (thicker) ink may then later during printing be supplied to return tank
15
when appropriate.
It is to be realized that the purpose of holding tank
101
is to receive liquid that issues from droplet generator
5
during preparation of the system for subsequent printing, so that this liquid may then be used later during the subsequent printing when the conditions of the system are such that it is appropriate to use this liquid. In this connection the aforementioned flush cleaning of the system during shut-down can be considered preparation of the system for subsequent printing, since the cleaning takes place so that the system is not ‘dirty’ at the beginning of the next print run.
Referring also to
FIG. 3
, in the modification, level sensors
23
and
25
of supply tank
3
have been replaced by multi-level sensor
201
, and level sensor
27
of return tank
15
has been replaced by multi-level sensor
203
.
A multi-level sensor comprises at least three level sensors, each of which detects whether liquid height is above or below the level at which it is located. Typically, the number of sensors used is such that they may be located with a frequency of one every 5 to 10 mm of tank height.
Utilising the detection provided by multi-level sensors
201
,
203
, central control system
21
is able to determine the rate of fall/rise of liquid level in tanks
3
,
15
respectively. Control sytem
21
monitors the determined rates, and, if either deviates by more than a predetermined amount from its expected value, provides an indication that there has been a fault in the printing system, and further provides an indication of what this fault is.
The following examples illustrate how control system
21
is able to provide an indication of what the fault is that has occurred. In each example: the occurrence of a particular type of fault is first given (i.e. it is first stated how a particular constituent element of the printing system is not operating as it should be); the effect(s) of the fault occurrence is/are then given; and finally the resultant rise/fall rate in supply tank
3
/return tank
15
is given.
If either of valves
117
,
119
is stuck closed, the fall in ink level in supply tank
3
that would normally take place, will not. The ink level will remain the same. Thus, the fall rate in supply tank
3
will be zero. Further, gutter
11
will not be supplying unused ink to return tank
15
. The rise in ink level in return tank
15
that would normally be taking place, will either not occur at all, if top-up via valves
29
,
31
,
111
is not taking place, or will occur more slowly. Thus, the rise rate in return tank
15
will either be zero or relatively low.
If either of valves
115
,
121
is stuck closed during flushing, the rise in liquid level in holding tank
101
that would normally take place, will not. The level will remain the same. Thus, the rise rate in holding tank
101
will be zero.
If valve
103
is stuck closed, the rise in ink level in return tank
15
that would normally be taking place, will either not occur at all, if top-up via valves
29
,
31
,
111
is not taking place, or will occur more slowly. Thus, the rise rate in return tank
15
will either be zero or relatively low.
If either valve
105
or valve
107
is stuck closed during flushing, the rise in liquid level in holding tank
101
that would normally be taking place due to the receipt of liquid via both valves
105
and
107
, will only be taking place due to the receipt of liquid via one valve
105
or
107
, and therefore will take place more slowly. Thus, the rise rate in holding tank
101
will be relatively low.
If valve
45
is stuck closed, the rise in ink level in supply tank
3
that would normally take place when transferring ink from return tank
15
to supply tank
3
, will not take place. This ink level will be falling. Thus, the rise rate in supply tank
3
will be negative. Further, the fall in ink level in return tank
15
that would normally be taking place, will not. This level will be rising. Thus, the fall rate in return tank
15
will be negative.
If any one of valves
29
,
31
,
111
is stuck closed at a time it is instructed to be open, the top-up that would normally be received by return tank
15
via the stuck closed valve
29
or
31
or
111
, will not be received, and hence the rise in ink level in return tank
15
will be slower than expected. Thus, the rise rate in return tank
15
will be relatively low.
If valve
105
is stuck open during printing, the rise in ink level in return tank
15
will occur more slowly than expected. Thus, the rise rate in return tank
15
will be relatively low.
If valve
107
is stuck open during printing, when transfer is not taking place from return tank
15
to supply tank
3
, the fall in ink level in supply tank
3
will occur more quickly than expected. Thus, the fall rate in supply tank
3
will be relatively high. When transfer is taking place, the rise in ink level in supply tank
3
will occur more slowly than expected. Thus the rise rate in supply tank
3
will be relatively low. In both cases, i.e. not during and during transfer, there will be an unexpected rise in the level in holding tank
101
. Thus, the rise rate in holding tank
101
will be positive.
If valve
113
is stuck at vacuum during printing, no top-up from holding tank
101
will be received by return tank
15
when valve
111
is opened. The level in return tank
15
will therefore rise more slowly than expected, and there will be no drop in the level in holding tank
101
. Thus, the rise rate in return tank
15
will be relatively low, and the fall rate in holding tank
101
will be zero.
If valve
45
is stuck open when transfer is not required from return tank
15
to supply tank
3
, there will be back flow due to the action of vacuum source
13
. Hence the level in return tank
15
will be rising more quickly than expected, and the level in supply tank
3
will be falling more quickly than expected. Thus, both the rise rate in return tank
15
and the fall rate in supply tank
3
will be relatively high.
If any one of valves
29
,
31
,
111
is stuck open at a time it is instructed to be closed, a top-up that would not normally be received by return tank
15
at that time, will be received via stuck open valve
29
or
31
or
111
. The level in return tank
15
will therefore rise more quickly than expected. Thus, the rise rate in return tank
15
will be relatively high.
If supply pump
1
fails to operate, the fall in ink level in supply tank
3
that would normally take place, will not. The ink level will remain the same. Thus, the fall rate in supply tank
3
will be zero. Further, gutter
11
will not be supplying unused ink to return tank
15
. The rise in ink level in return tank
15
that would normally be taking place, will either not occur at all, if top-up via valves
29
,
31
,
111
is not taking place, or will occur more slowly. Thus, the rise rate in return tank
15
will either be zero or relatively low.
If transfer pump
17
is worn, both the fall in level in return tank
15
and the rise in level in supply tank
3
, will be slower than expected. Thus, both the fall rate in return tank
15
and the rise rate in supply tank
3
will be relatively low. This change in rate may be used to control the speed of transfer pump
17
.
If transfer pump
17
fails to operate, the level in return tank
15
will be rising rather than falling as expected, and the level in supply tank
3
will be falling rather than rising as expected. Thus, both the fall rate in return tank
15
and the rise rate in supply tank
3
will be negative.
If cooler
41
is frozen, the fall in ink level in supply tank
3
that would normally take place, will not. The level will remain the same. Thus, the fall rate in supply tank
3
will be zero. During transfer form return tank
15
to supply tank
3
, the level in supply tank
3
will rise more quickly than usual. Thus, the rise rate in supply tank
3
will be relatively high. Due to the absence of the supply of unused ink by gutter
11
to return tank
15
, when top-up via valves
29
,
31
,
111
is not taking place, the level in return tank
15
will remain the same, rather than be rising as expected. Thus, the rise rate in return tank
15
will be zero. During transfer from return tank
15
to supply tank
3
, the absence of the supply of unused ink will result in the level in return tank
15
falling more quickly than usual. Thus, the fall rate in return tank
15
will be relatively high.
If gutter
11
is not collecting or is collecting little unused ink, during transfer from return tank
15
to supply tank
3
the level in return tank
15
will fall more quickly than expected. Thus, the fall rate in return tank
15
will be relatively high. When transfer is not taking place, assuming no top-up via valves
29
,
31
,
111
, the level in return tank
15
will either not rise at all or will rise very slowly. Thus, the rise rate in return tank
15
will be zero or relatively very low.
It is to be appreciated that each of multi-level sensors
201
,
203
could be replaced by a continuous level sensor which continuously provides to control system
21
measurement of liquid level.
It is also to be appreciated that the indication of what fault it is that has occurred, provided by control system
21
, may not be definitively determined by the rise/fall rate in supply tank
3
/return tank
15
, but may require the supply to control system
21
of other information regarding the condition of the printing system.
Claims
- 1. An ink jet printing system comprising: a droplet generator for generating at least one stream of ink droplets; a supply tank for supplying ink to said generator; supply transfer means for driving the ink from said tank to said generator; and measurement means for measuring the flow rate of the stream(s) of ink droplets generated by said generator by monitoring the change of ink level in said tank, said system including a bleed connection from said generator to said tank in closed circuit with said tank, the presence of said bleed connection thereby increasing the rate of flow of ink from said tank to said generator without affecting the measurement by said measurement means of the flow rate of the stream(s) of ink droplets generated by said generator.
- 2. A system according to claim 1 further comprising: a gutter for collecting ink droplets not used in printing; a return tank for receiving the ink collected in the gutter; and return transfer means for driving ink from said return tank to said supply tank, the flow rate measurements made by monitoring the change of ink level in said supply tank being made when ink is not being driven from the return tank to the supply tank.
- 3. A system according to claim 2 further comprising control means for maintaining substantially constant the velocity of the stream(s) of ink droplets generated by said droplet generator.
- 4. A system according to claim 3 wherein said control means controls the composition, temperature, and pressure of the ink in said droplet generator.
- 5. A system according to claim 4 wherein said control means maintains substantially constant said composition, temperature, and pressure.
- 6. A system according to claim 5 wherein said control means maintains substantially constant said composition by supplying ink solvent and ink to said return tank, the supply being made in dependence on the ink level in said return tank and the flow rate measurement made by monitoring the change of ink level in said supply tank.
- 7. A system according to claim 5 wherein said control means maintains substantially constant said temperature by sensing the temperature of the ink in said droplet generator, and, in response thereto, adjusting the temperature of the ink in the ink path from said supply tank to said droplet generator.
- 8. A system according to claim 5 wherein: said supply transfer means comprises a pump located in the ink path from said supply tank to said droplet generator; and said control means maintains substantially constant said pressure by sensing the pressure of the ink in said generator, and, in response thereto, adjusting the speed of operation of said pump.
- 9. An ink jet printing system comprising: a droplet generator for generating at least one stream of ink droplets; a supply tank for supplying ink to said generator; supply transfer means for driving the ink from said tank to said generator; a holding tank for receiving liquid issued by said generator during preparation of the system for subsequent printing, said holding tank being connected to said supply tank for the supply of said liquid to the supply tank during said subsequent printing; and means for determining during said subsequent printing the times at which the composition of the ink supplied to said generator is such that it is appropriate to use the liquid contained in said holding tank.
- 10. A system according to claim 9 further comprising: a gutter for collecting ink droplets not used in printing; a return tank for receiving the ink collected in the gutter; a reservoir of ink solvent connected to the return tank; a reservoir of ink connected to the return tank; and return transfer means for driving ink from said return tank to said supply tank, said holding tank being connected to said return tank and thereby to said supply tank.
- 11. A system according to claim 10 further comprising: a bleed connection from said generator to said supply tank; and valve means for directing said liquid issued by said generator during preparation from said gutter and said bleed connection to said holding tank.
- 12. A system according to claim 10 wherein: said preparation of the system for subsequent printing comprises flushing with ink solvent, said liquid received by the holding tank thereby comprising predominantly ink solvent; said system further comprises measurement means for measuring the flow rate of the stream(s) of ink droplets generated by said generator by monitoring the change of ink level in said supply tank when ink is not being driven from said return tank to said supply tank; and said holding tank supplies said liquid to said return tank when the flow rate measured by said measurement means is below that desired.
- 13. An ink jet printing system comprising: a tank for holding a liquid for use in the operation of said system; a multi-level or continuous level sensor for measuring the rate of change of liquid level in said tank during said operation, said multi-level sensor comprising at least three level sensors each of which detects whether liquid height is above or below the level at which it is located, said continuous level sensor comprising a sensor which continuously provides measurement of said liquid level; and means for using said measurement of the rate of change of said liquid level in said tank to provide an indication that there has been a fault in said system.
- 14. A system according to claim 13 wherein said means for using also provides an indication of what the fault is that has occurred.
Priority Claims (1)
Number |
Date |
Country |
Kind |
9603813 |
Feb 1996 |
GB |
|
PCT Information
Filing Document |
Filing Date |
Country |
Kind |
PCT/GB97/00487 |
|
WO |
00 |
Publishing Document |
Publishing Date |
Country |
Kind |
WO97/30850 |
8/28/1997 |
WO |
A |
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Number |
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Date |
Kind |
4555709 |
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Nov 1985 |
A |
4827280 |
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May 1989 |
A |
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WO |