Constant flow rate liquid supply pump

An ink liquid supply system for an ink jet system printer comprising an ink liquid reservoir for containing ink liquid therein, and a constant flow rate pump for supplying the ink liquid to a nozzle. The constant flow rate pump comprises a first chamber for introducing an ink liquid collected by a beam gutter of the ink jet system printer and for returning the ink liquid to the ink liquid reservoir. The constant flow rate pump further comprises a second chamber for introducing the ink liquid from the ink liquid reservoir and for developing the ink liquid to the nozzle. The first and second chambers include a coaxial piston disposed therein for varying the pressure created in the first and second chambers.

BACKGROUND AND SUMMARY OF THE INVENTION 
The present invention relates to an ink liquid supply system for an ink jet 
system printer of the charge amplitude controlling type and, more 
particularly, to a constant flow rate pump for use in the ink liquid 
supply system. 
A constant flow rate ink liquid supply pump is essential and required in an 
ink jet system printer of the charge amplitude controlling type to ensure 
an accurate printing. The constant flow rate pump is effective not only to 
stabilize the ink liquid speed emitted from a nozzle but also to maintain 
the ink viscosity at a fixed value. 
Accordingly, an object of the present invention is to provide a constant 
flow rate pump for use in an ink liquid supply system of an ink jet system 
printer of the charge amplitude controlling type. 
Another object of the present invention is to provide a constant flow rate 
pump which is small in size. 
Still another object of the present invention is to provide a small pump 
which integrally includes a pressure chamber for supplying the ink liquid 
to a nozzle and another pressure chamber for introducing waste ink liquid 
from a beam gutter of the ink jet system printer of the charge amplitude 
controlling type. 
Yet another object of the present invention is to provide a novel ink 
liquid supply system in an ink jet system printer of the charge amplitude 
controlling type. 
Other objects and further scope of applicability of the present invention 
will become apparent from the detailed description given hereinafter. It 
should be understood, however, that the detailed description and specific 
examples, while indicating preferred embodiments of the invention, are 
given by way of illustration only, since various changes and modifications 
within the spirit and scope of the invention will become apparent to those 
skilled in the art from this detailed description. 
To achieve the above objects, pursuant to an embodiment of the present 
invention, a pump integrally includes three pressure chambers, which are 
divided by bellows and a three staged piston. The first pressure chamber 
functions to introduce the waste ink liquid collected by a beam gutter of 
the ink jet system printer of the charge amplitude controlling type. The 
second pressure chamber introduces the ink liquid from an ink liquid 
reservoir, and the third pressure chamber develops the ink liquid toward a 
nozzle of the ink jet system printer of the charge amplitude controlling 
type. 
In a preferred form, a pressure accumulator is disposed between the outlet 
of the second pressure chamber and the inlet of the third pressure chamber 
in order to always maintain the pressure in the third pressure chamber 
higher than that in the second pressure chamber.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows an ink jet system printer embodying the present invention. 
The ink jet system printer mainly comprises a print forming section and an 
ink liquid supply system. 
The print forming section of an ink jet system printer of the charge 
amplitude controlling type comprises a nozzle 1 for emitting an ink liquid 
supplied from the ink liquid supply system through an electromagnetic 
valve 11. An electromechanical transducer 2 is attached to the nozzle 1 to 
vibrate the nozzle 1 at a given frequency, thereby forming ink droplets 4 
at the given frequency. The thus formed ink droplets 4, which are emitted 
from the nozzle 1, are charged through the use of a charging electrode 3 
in accordance with a print information signal. The thus charged ink 
droplets 4 are deflected while they pass through a constant high voltage 
electric field established by a pair of deflection electrodes 5 in 
accordance with charge amplitudes carried thereon, and directed to a 
record receiving paper 6. Ink droplets 4' not contributing to the actual 
print operation are not charged and are directed to a beam gutter 7 for 
recirculation purposes. 
The above-mentioned nozzle 1, electromechanical transducer 2, charging 
electrode 3, deflection electrodes 5 and beam gutter 7 are mounted on a 
carriage 8 (shown by broken lines), which is driven to reciprocate along 
slidable shafts 9 in the lateral direction. That is, the deflection caused 
by the deflection electrodes 5 is effected in the vertical direction, and 
the carriage 8 is driven to travel in the lateral direction, whereby 
desired patterns are formed on the record receiving paper 6 in the dot 
matrix fashion. 
The ink liquid collected by the beam gutter 7 is returned to the ink liquid 
supply system through a conduit 10. The thus returned ink liquid is 
introduced into a constant flow rate pump, which develops the ink liquid 
of a fixed flow rate and a fixed viscosity to be applied to the nozzle 1 
through a conduit 12 and the electromagnetic valve 11. The constant flow 
rate and constant viscosity ink liquid is highly required to ensure 
accurate printing or to stabilize the droplet formation. 
The constant flow rate pump comprises three coaxial cylinders 13, 14 and 
15, and three bellows 19, 20 and 21, which, in combination, determine 
three pressure chambers 16, 17 and 18. The pressure in each pressure 
chamber is varied by shifting the bellows 19, 20 and 21 along the axis of 
the cylinder. More specifically, the bellows 19 has a wider diameter than 
the bellows 20, which has a wider diameter than the bellows 21. The outer 
periphery of the bellows 19 is fixed between the cylinder 13 and a bearing 
supporter 29. The inner periphery of the bellows 19 is fixed to an end of 
a piston 22. The outer periphery of the bellows 20 is held between the 
cylinder 13 and cylinder 14, and the inner periphery thereof is secured to 
an end of a piston 23. The outer periphery of the bellows 21 is supported 
by the cylinders 14 and 15, and the inner periphery thereof is fixed to an 
end of a piston 24 through the use of a fixing cap and a screw 25. The 
pistons 22, 23 and 24 are coaxially connected to each other with the 
intervention of fixing caps and the inner peripheries of the bellows 19 
and 20. The piston 22 has a wider diameter than the piston 23, which, in 
turn, has a wider diameter than the piston 24. 
An eccentric cam 27 connected to a driven source (not shown), and a roller 
26 are provided to shift the piston 22 in the direction shown by arrows A 
and B. A spring 28 is fixed to the other end of the piston 22 to bias the 
roller 26 into contact with the eccentric cam 27. When the piston 22 is 
reciprocated, the pistons 23 and 24 are also reciprocated in unison with 
the piston 22 and, therefore, the bellows 19, 20 and 21 perform the 
rolling movement. This creates the variation of the pressure in each 
pressure chamber 16, 17 and 18. 
The piston 22 is slidably supported by a bearing 30, which is secured to 
the bearing supporter 29. The stroke value of the pistons 22, 23 and 24 is 
adjustable through the use of a flow rate adjusting screw 31 coupled to an 
opening of the bearing supporter 29. That is, the flow rate is 
controllable through the use of the flow rate adjusting screw 31. 
An inlet valve 32 is provided in the cylinder 13 to communicate the 
pressure chamber 16 with the conduit 10 connected to the beam gutter 7. An 
outlet valve 33 is also provided in the cylinder 13 for communicating the 
pressure chamber 16 to a subtank 35 through a conduit 34. The subtank 35 
receives the collected ink liquid through the conduit 34, and a new ink 
liquid contained in an ink cartridge 36 through a switching 
electromagnetic valve 38. The subtank 35 is constructed so that a constant 
amount of ink liquid is always contained therein. 
An ink solvent cartridge 37 contains a solvent, which is selectively 
applied to the subtank 35 through the switching electromagnetic valve 38. 
A filter 39 is disposed in the subtank 35. The ink liquid contained in the 
subtank 35 is introduced into the pressure chamber 17 through the filter 
39, a conduit 40 and an inlet valve 41. 
The pressure chamber 17 is also connected to a pressure accumulator 43 via 
an outlet valve 42. The pressure accumulator 43 comprises a cylinder 44, a 
bellows 45 of which the outer periphery is fixed to the cylinder 44, and a 
spring 47 for depressing the bellows 45 downward via a cap 46. The 
cylinder 44 is provided with an outlet valve 48, which is connected to the 
subtank 35 through a conduit 49. 
A conduit 52 is formed in the cylinder 44 and in another cylinder 51 in 
order to communicate the pressure-accumulator 43 with the pressure chamber 
18 through an inlet valve 50 formed in the cylinder 15. The pressure 
chamber 18 is also communicated with another pressure accumulator 54 via 
an outlet valve 53 formed in the cylinder 15. The pressure accumulator 54 
comprises the cylinder 51, a bellows 55 disposed in the cylinder 51, the 
outer periphery of the bellows 55 being fixed to the cylinder 51, and a 
spring 57 for depressing the bellows 55 downward via a cap 56. 
A pole 58 is fixed to the cap 56 in such a manner that the pole 58 extends 
upward through the cylinder 51. The end of the pole 58 is associated with 
an actuator 60 of a microswitch 59. The microswitch 59 is associated with 
a valve drive circuit 61 for selectively switching the electromagnetic 
valve 38. As already discussed above, the switching electromagnetic valve 
38 functions to selectively supply the subtank 35 with the new ink liquid 
contained in the ink cartridge 36 and the solvent contained in the ink 
solvent cartridge 37, thereby maintaining the ink viscosity at a constant 
value. 
The pressure accumulator 54 is connected to the conduit 12 through a filter 
62. The above-mentioned inlet or outlet valves comprise a ball valve, a 
valve seat and a spring for depressing the ball valve against the valve 
seat, respectively. 
When the eccentric cam 27 is driven to rotate, the piston 22 is 
reciprocated. At the same time, the pistons 23 and 24 are reciprocated, 
whereby the ink liquid of the constant flow rate is emitted from the 
nozzle 1. The ink liquid collected by the beam gutter 7 is introduced into 
the pressure chamber 16 when the piston 22 is driven to travel in the 
direction shown by the arrow B. This is because the pressure in the 
pressure chamber 16 is reduced when the piston 22 travels in the direction 
shown by the arrow B due to the diameter difference between the bellows 19 
and 20. The ink liquid introduced into the pressure chamber 16 is supplied 
to the subtank 35 when the piston 22 traveles in the direction shown by 
the arrow A, because the pressure in the pressure chamber 16 is increased. 
As already discussed, the new ink is supplied from the ink cartridge 36 to 
the subtank 35 to maintain the amount of ink liquid contained in the 
subtank 35 at the constant value. 
The pressure in the pressure chamber 17 is reduced when the pistons 22, 23 
and 24 travel in the direction shown by the arrow B, because the bellows 
20 is larger than the bellows 21. The inlet valve 41 is opened to 
introduce the ink liquid from the subtank 35 to the pressure chamber 17. 
The thus introduced ink liquid does not include any dust and bubbles 
because the filter 39 is disposed in the subtank 35. At this moment, the 
pressure in the pressure chamber 18 is reduced below the pressure in the 
pressure accumulator 43. Therefore, the ink liquid contained in the 
pressure accumulator 43 is introduced into the pressure chamber 18 through 
the inlet valve 50. The introduction of the ink liquid into the pressure 
chamber 18 is effectively conducted. This smooth introduction of the ink 
liquid ensures a constant flow rate ink liquid supply. 
Contrarily, the pressure in the pressure chambers 17 and 18 is increased 
when the pistons 22, 23 and 24 travel in the direction shown by the arrow 
A. The ink liquid in the pressure chamber 17 is developed toward the 
pressure accumulator 43 through the outlet valve 42. The ink liquid in the 
pressure chamber 18 is supplied to the pressure accumulator 54 through the 
outlet valve 53. The ink liquid contained in the pressure accumulator 54 
is fed to the nozzle 1 through the filter 62, where the dust is removed, 
the conduit 12 and the electromagnetic valve 11. 
Therefore, the nozzle 1 emits the ink liquid at a constant flow rate. 
The ink liquid amount developed from the pressure chamber 18 to the 
pressure accumulator 54 is less than that from the pressure chamber 17 to 
the pressure accumulator 43 and, therefore, there is a possibility that 
the pressure in the pressure accumulator 43 or the pressure chamber 17 may 
become greater than that in the pressure chamber 18. In this case, the 
outlet valve 48 is opened when the pressure in the pressure accumulator 43 
becomes greater than a preselected value, whereby the ink liquid contained 
in the pressure accumulator 43 is directed to the subtank 35 through the 
conduit 49. Therefore, when the pistons 22, 23 and 24 travel in the 
direction shown by the arrow A, the pressure in the pressure accumulator 
43 never becomes higher than that in the pressure chamber 18 and the inlet 
valve 50 is not opened. More specifically, the pressure in the pressure 
accumulator 43 is held below the predetermined value to preclude the 
deformation of the bellows 21. As discussed above, the pressure in the 
pressure chamber 18 is always higher than that in the pressure chamber 17 
without regard to the travel direction of the pistons 22, 23 and 24. 
Therefore, the ink liquid supplied through the conduit 12 shows the 
constant flow rate as long as the bellows 21 is not deformed and the cam 
27 is rotated at a constant speed. That is, the ink liquid is emitted from 
the nozzle 1 at the constant flow rate. 
FIG. 2 shows another embodiment of the constant flow rate pump of the 
present invention. 
The constant flow rate pump of FIG. 2 mainly comprises two coaxial pistons 
70 and 71, the piston 70 having a longer diameter than the piston 71, and 
stair shaped coaxial cylinders 74 and 75. An eccentric cam 73 connected to 
a driving source (not shown) and a roller 72 connected to the piston 70 
are provided for reciprocating the pistons 70 and 71. O-shaped rubber 
rings 76 and 77 are secured to the cylinders 74 and 75, respectively, to 
define pressure chambers 78 and 79. An inlet valve 80 is provided for the 
pressure camber 78, and an outlet valve 82 is provided for the pressure 
chamber 78. An inlet valve 81 and an outlet valve 83 are provided for the 
pressure chamber 79. The piston 70 is slidably supported by a bearing 84 
which is secured to a bearing supporter 86. 
The end of the piston 70 is fixed to a spring 85, whereby the roller is 
maintained in contact with the eccentric cam 73. A screw 87 is secured to 
the end of the bearing supporter 86 to adjust the stroke value of the 
pistons 70 and 71. 
The inlet valve 80 is connected to the beam gutter 7 for recovering the 
collected ink liquid, and the outlet valve 82 is connected to the subtank 
35. The inlet valve 81 is connected to the subtank 35 for introducing the 
ink liquid into the pressure chamber 79, and the outlet valve 83 is 
connected to the nozzle 1 through the pressure accumulator, the conduit 12 
and the electromagnetic valve 11. 
The invention being thus described, it will be obvious that the same may be 
varied in many ways. Such variations are not to be ragarded as a departure 
from the spirit and scope of the invention, and all such modifications are 
intended to be included within the scope of the following claims.