Pump synchronization in an ink jet system printer

An ink jet system printer of the charge amplitude controlling type includes a reciprocating printer head and a constant flow rate plunger pump. An actual printing operation is conducted while the printer head is driven to travel forward, and the constant flow rate plunger pump is energized to develop the ink liquid when the printer head is driven to travel backward. A pressure accumulator of a small capacity is disposed between the constant flow rate plunger pump and the printer head for minimizing the pressure pulsation created by the constant flow rate plunger pump.

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 wherein a printer 
head is driven to reciprocate across the printing region. 
In the conventional ink jet system printer of the charge amplitude 
controlling type, a constant pressure ink liquid supply pump is employed, 
wherein the mass of the ink droplets and the velocity of the ink droplets 
emitted from a nozzle are variable depending on the ink characteristics 
such as the viscosity. These variations will provide a distortion on the 
printed character. Recently it has been proposed to employ a constant flow 
rate ink liquid supply pump in order to compensate for the ambience 
temperature variation. A typical constant flow rate pump and operation 
modes thereof are described in copending application Ser. No. 70,639 (DOS 
2,934,947), now U.S. Pat. No. 4,278,984 issued July 14, 1981, entitled, 
"CONSTANT FLOW RATE LIQUID SUPPLY PUMP", filed on Aug. 28, 1979 by 
Masafumi Matsumoto and Matahira Kotani and assigned to the same assignee 
as the present application, or Ser. No. 97,389 (DOS No. 2,948,131), now 
U.S. Pat. No. 4,263,602 issued Apr. 21, 1981, entitled "CONSTANT FLOW RATE 
LIQUID SUPPLY PUMP", filed on Nov. 26, 1979 by Masafumi Matsumoto and 
Matahira Kotani and assigned to the same assignee as the present 
application. 
However, the above-mentioned constant flow rate ink liquid supply pump 
cannot ensure stable ink droplet formation when the ambience temperature 
is rapidly changed. Moreover, the stable ink droplet formation is not 
expected when the last printing operation is terminated at, for example, 
40.degree. C. and the present printing operation is initiated at, for 
example, 5.degree. C. This is mainly caused by a pressure accumulator 
which is required for removing the pressure pulsation. When the pressure 
accumulator has a small capacity, the pressure pulsation cannot be 
removed. When the pressure accumulator has a large capacity, the system 
cannot respond to the rapid temperature variation. 
Accordingly, an 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 which has a reciprocating printer head. 
Another object of the present invention is to provide an ink liquid supply 
system including a constant flow rate liquid supply pump and a small 
capacity pressure accumulator. 
Still another object of the present invention is to provide a control 
system for correlating the pump drive with the printer head movement 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, an ink liquid supply system includes a constant flow rate ink 
liquid supply pump and a pressure accumulator of a small capacity for 
removing the pressure pulsation created by the constant flow rate ink 
liquid supply pump. The drive timing of the constant flow rate ink liquid 
supply pump is synchronized with the drive timing of a printer head which 
is driven to reciprocate across the printing region. More specifically, 
the initiation of the driving of the constant flow rate ink liquid supply 
pump is effected when the printer head is located at a position not 
effective for the actual printing, for examples, the left-most home 
position of the printer head.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 schematically shows a printer head drive mechanism in an ink jet 
system printer of the charge amplitude controlling type. 
A printer head 10 is slidably mounted on guide rails 12, and driven to 
travel along a print receiving paper 14. A drive mechanism comprises a 
pulse motor 16 (or a DC servomotor) and a drive wire 18 (or a belt) 
extended between pulleys 20, a tension pulley 22 and the pulse motor 16. 
The drive wire 18 is fixed to the printer head 10 at a desired position, 
thereby reciprocating the printer head 10 across a print region AB by 
forwardly or reversely rotating the pulse motor 16 (or the DC servomotor). 
FIG. 2 schematically shows an embodiment of the printer head 10 and an ink 
liquid supply system of the present invention. 
The printer head 10 comprises a nozzle 24 for emitting an ink liquid 
supplied from the ink liquid supply system. An electromechanical 
transducer 26 is attached to the nozzle 24 to vibrate the nozzle 24 at a 
given frequency, thereby forming ink droplets 28 at the given frequency. 
The thus formed ink droplets 28 are selectively charged through the use of 
a charging tunnel 30 in accordance with a print information signal. A 
sensing electrode 32 is disposed in front of the charging tunnel 30 to 
detect whether the ink droplets 28 are accurately charged. An output 
signal of the sensing electrode 32 is used for synchronizing the 
application of the charging signal to the charging tunnel 30 with the 
droplet formation rhythm as is well known in the art. 
The thus charged ink droplets 28 are deflected while they pass through a 
constant high voltage electric field established by a pair of deflection 
electrodes 34 and 36 in accordance with charge amplitudes carried thereon. 
Deflected ink droplets 28a are directed to the record receiving paper 14 
which is supported by a platen 38. Ink droplets 28b not contributing to 
the actual printing operation are not charged and they are directed to a 
beam gutter 40 for recirculation purposes. 
The above-mentioned nozzle 24, the electromechanical transducer 26, the 
charging tunnel 30, the sensing electrode 32, the deflection electrodes 34 
and 36, and the beam gutter 40 are incorporated in the printer head 10 
which is slidably mounted on the guide rails 12. The deflection caused by 
the deflection electrodes 34 and 36 is effected in the vertical direction, 
and the printer head 10 is driven to travel in the lateral direction, 
whereby desired patterns are formed on the record receiving paper 14 in 
the dot matrix fashion. 
The ink liquid collected by the beam gutter 40 is returned to the ink 
liquid supply system through a conduit 42. The thus returned ink liquid is 
introduced into a constant flow rate pump, which regulates the ink liquid 
at a fixed flow rate to be fed to the nozzle 24 through a conduit 44. The 
constant flow rate ink liquid is strictly required to ensure accurate 
printing and stabilize the droplet formation. 
The constant flow rate pump mainly comprises two coaxial cylinder blocks 46 
and 48, two coaxial pistons 50 and 52, and a diaphragm 54 interposed 
between the pistons 50 and 52. A first pressure chamber 56 is defined by 
the cylinder block 46 and the piston 50. A second pressure chamber 58 is 
defined by the cylinder block 46, the piston 50, and the diaphragm 54. 
Pressure in the chambers 56 and 58 is varied in response to the 
reciprocating movement of the coaxial pistons 50 and 52, and the diaphragm 
54. 
More specifically, the diaphragm 54 is supported by a reinforcing member 
60, and secured to the piston 52 through the use of the piston 50 and the 
reinforcing member 60. The periphery of the diaphragm 54 is fixed between 
the cylinder blocks 46 and 48. When the piston 52 is driven to 
reciprocate, the diaphragm 54 and the piston 50 are moved in unison with 
the movement of the piston 52. 
The piston 52 is connected to a plunger 62 which is associated with a DC 
solenoid 64. The DC solenoid 64 creates the rightward movement of the 
piston 52. A spring 66 is disposed between the cylinder block 48 and a 
flange portion of the piston 52 to provide the leftward movement of the 
piston 52. An adjusting screw 68 is provided for adjusting the stroke 
length of the plunger 62. That is, the adjusting screw 68 is used for 
adjusting the flow rate of the ink liquid developed from the constant flow 
rate pump. The flow rate can alternatively be modified by changing the 
frequency of an activating signal to be applied to the DC solenoid. The 
second pressure chamber 58 is communicated to the conduit 42 via an inlet 
valve 70 in order to introduce the ink liquid collected by the beam putter 
40. The thus introduced ink liquid is returned to a recovering tank 72 
through an outlet valve 74 and a conduit 76. The recovering tank 72 stores 
the collected, returned ink liquid and a fresh ink liquid supplied from an 
ink liquid reservoir 78 including an ink liquid cartridge 80. A filter 82 
is disposed in the recovering tank 72. The ink liquid stored in the 
recovering tank 72 is supplied to the first pressure chamber 56 through a 
conduit 84 and an inlet valve 86. 
An outlet valve 88 is provided for the first pressure chamber 56 to develop 
an ink liquid of a constant flow rate toward a pressure accumulator 90. 
The pressure accumulator 90 comprises a cylinder 92, a resilient member 
94, for example, a bellows or a diaphragm, a cap 96, and a spring 98. The 
periphery of the resilient member 94 is secured to the cylinder 92, and 
the resilient member 94 is biased downward through the use of the spring 
98 and the cap 96. The pressure accumulator 90 functions to absorb the 
pressure pulsation. The ink liquid of a constant flow rate, which does not 
include pulsation, derived from the pressure accumulator 90 is supplied to 
the nozzle 24 through a filter 100, an electromagnetic valve 102, and the 
conduit 44. 
When the plunger 62 is driven to travel rightward by the DC solenoid 64, 
the pistons 52 and 50 and the diaphragm 54 travel rightward. The plunger 
activation is controlled by a solenoid driver 104 which is controlled by a 
control system 106. 
At this moment, the pressure in the first pressure chamber 56 is increased, 
whereby the ball valve in the outlet valve 88 is pushed upward against the 
spring to develop the ink liquid toward the pressure accumulator 90. At 
the same time, the pressure in the second pressure chamber 58 is also 
increased, and the ball valve in the outlet valve 74 is pushed leftward in 
FIG. 2 against the spring to develop the ink liquid toward the recovering 
tank 72 through the conduit 76. 
When the plunger 62 has been shifted right by a predetermined length, the 
DC solenoid 64 is deenergized. Then, the pistons 52 and 50, and the 
plunger 62 are moved leftward due to the retaining strength of the spring 
66 till the plunger 62 contacts the tip end of the adjusting screw 68. 
While the pistons 52 and 50, and the diaphragm 54 travel leftward, a 
negative pressure is created in the first pressure chamber 56, whereby the 
ball valve in the inlet valve 86 is pushed upward against the spring to 
introduce the ink liquid from the recovering tank 72 through the conduit 
84. The ink liquid amount introduced from the recovering tank 72 and 
supplied to the nozzle 24 is determined by the shift length of the piston 
50 and its reciprocating frequency. At the same time, the negative 
pressure is also created in the second pressure chamber 58, whereby the 
ball valve in the inlet valve 70 is pushed upward against the spring to 
introduce the waste ink liquid collected by the beam gutter 40 through the 
conduit 42. 
The above-mentioned operation is repeated to supply the ink liquid at a 
constant flow rate to the nozzle 24, and to effectively recover the ink 
liquid not contributing to the actual printing operation. 
As already discussed above, the pressure accumulator 90 is provided for 
removing the pressure pulsation created by the constant flow rate pump. 
The capacity of the pressure accumulator 90 greatly influences the 
remaining strength of the pressure pulsation and the transient 
characteristics when the ink liquid pressure changes. When the capacity of 
the pressure accumulator 90 is selected to be considerably large, the 
pressure pulsation can be satisfactorily removed, but the response time 
becomes considerably long. That is, the ink liquid supply system will 
never return to a normal operation mode in a short time when the ambience 
temperature suddenly changes. 
FIG. 5 shows pressure versus response time characteristics of an ink liquid 
supply system employing the pressure accumulator 90. When the pressure 
accumulator 90 has a large capacity (shown by a curve I), a considerably 
long period is required for changing the ink liquid pressure from P.sub.1 
to P.sub.2. If the pressure accumulator 90 of a small capacity (shown by a 
curve III) is employed, only a short period is required for changing the 
ink liquid pressure from P.sub.1 to P.sub.2. 
The present invention is to provide an ink liquid supply system which 
employs the pressure accumulator 90 of small capacity. To eliminate the 
print distortion caused by the pressure pulsation, a printer head driver 
108 is controlled by the control system 106 in such a manner that the 
plunger activation is synchronized with the printer head drive. 
Deflection amount y of the ink droplet 28a can be expressed as follows when 
the air resistance is neglected. 
##EQU1## 
where: m is mass of the ink droplet 28a; 
v is the velocity of the ink droplet 28a; 
q is the charge amount of the ink droplet 28a; 
E is the strength of the deflection electric field; 
l is the length of the deflection electrode 34 as shown in FIG. 2; and 
L is the distance between the print receiving paper 14 and the deflection 
electrode 34 as shown in FIG. 2. 
The deflection amount y must be held constant to ensure a clean printing. 
When the ink jet system printer of the charge amplitude controlling type 
is used as a recorder in a facsimile system, three rows are usually 
printed at the same time as shown in FIG. 3. If the deflection amount 
becomes small, there will be produced an undersirable clearance between 
print bands B.sub.1, B.sub.2, . . . , B.sub.N. If the deflection amount 
becomes large, the ink droplets may overlap each other at the boundary 
between the print bands B.sub.1, B.sub.2, . . . , B.sub.N. 
In the above-mentioned equation, the deflection electric field E, the 
length l and the distance L can be maintained stationary without regard to 
the variation of the ambience condition. However, the mass m, the velocity 
v and the charge amount q are difficult to hold stationary when the 
ambience condition varies. 
The constant flow rate ink liquid supply pump employed in the present ink 
liquid supply system functions to vary the pressure in the pressure 
accumulator 90 when the viscosity of the ink liquid is varied due to 
temperature variations, whereby the flow rate Q is held stationary. FIG. 4 
shows pressure versus ambience temperature characteristics and flow rate 
versus ambience temperature characteristics of the constant flow rate 
pump. Accordingly, if the constant flow rate pump is employed, the above 
discussed mass m, velocity v and charge amount q can be held substantially 
stationary even when the ambient temperature varies. 
However, the constant flow rate characteristics cannot be expected when, 
for example, the last printing operation is terminated at a temperature 
40.degree. C. and a pressure P.sub.1, and the present printing operation 
is initiated at a temperature 5.degree. C. A predetermined time period is 
required for changing the pressure to a normal pressure P.sub.2. Until the 
pressure reaches the normal pressure P.sub.2, the flow amount becomes 
smaller than the constant value, and therefore, the deflection amount y 
becomes larger than a predetermined value. As already discussed above, the 
predetermined time period required for changing the pressure to the normal 
pressure P.sub.2 can be minimized when the pressure accumulator 90 has a 
small capacity. 
Our experience revealed that a clean printing can be ensured when the 
pressure pulsation (ripple) is held smaller than 1.5%. FIG. 6(A) shows a 
print-out sample where the pressure pulsation is held at zero. FIG. 6(B) 
shows a distorted print-out sample where a considerable pressure pulsation 
remains. However, if the distorted portion is controlled to occur at a 
predetermined position, the actual print-out can be made clean as shown in 
FIG. 6(C). 
The present invention is to minimize the above-mentioned time period 
required for reaching the normal operation pressure. The pressure 
accumulator 90 does not have a large capacity. Accordingly, the print 
distortion caused by the pressure pulsation cannot be neglected, but a 
control system is provided to locate the distorted portion at a 
predetermined position on the actual print-out, thereby making clean the 
actual print-out. 
Operation modes of the ink jet system printer of the present invention will 
be described, in detail, with reference to FIGS. 7(A) through 7(E). 
When a drive synchronization signal S.sub.y (shown in FIG. 7(B)) is applied 
from the control system 106 to the printer head driver 108, an 
acceleration command is applied to the pulse motor 16. The pulse motor 16 
is gradually accelerated forward through the use of a slewing frequency 
signal during a period of time T.sub.a. When the pulse motor 16 reaches a 
preselected rotating velocity, the constant speed rotation is maintained 
for a period of time T.sub.t as shown in FIG. 7(C). Thereafter, the 
slewing frequency signal is applied to the pulse motor 16 to gradually 
decelerate the rotation during a period T.sub.a. The pulse motor 16 is 
held stationary for a period T.sub.S, thereby completing the forward drive 
operation (T.sub.f). At the trailing edge of the next appearing drive 
synchronization signal S.sub.y, the pulse motor 16 initiates the reverse 
drive operation (T.sub.r). In this way, one cycle reciprocation is 
completed to conduct one band printing. The above-mentioned operation is 
repeated to conduct the printing for the print bands B.sub.1, B.sub.2, . . 
. , B.sub.N. 
FIG. 7(A) shows the print timing. The actual printing operation is 
conducted at a period shown by the hatched portion. That is, the actual 
printing operation is conducted while the printer head is driven to travel 
forward at the constant speed. FIG. 7(D) shows a solenoid activation 
signal developed from the solenoid driver 104. The solenoid 64 is 
energized at a period of time T.sub.1 which is initiated at the trailing 
edge of the drive synchronization signal S.sub.y for performing the 
reverse rotation of the pulse motor 16. That is, the first pressure 
chamber 56 of the constant flow rate pump conducts the liquid developing 
operation while the printer head is driven to travel backward during which 
the actual printing operation is not conducted. More specifically, the 
first pressure chamber 56 develops the ink liquid toward the nozzle 24 at 
the period T.sub.1, and introduces the ink liquid from the recovering tank 
72 at a period T.sub.2. FIG. 7(E) shows an ink liquid pressure developed 
from the pressure accumulator 90 and applied to the nozzle 24. The 
constant flow rate pump creates the pressure pulsation .DELTA.P(.DELTA.Q) 
around 6%. However, in the actual printing period T.sub.e, the pressure 
pulsation .DELTA.P' is below 1.5%. Therefore, a clean printing is 
expected. In FIG. 6(C), the actual printing is conducted at a section 
a.sub.2, and the actual printing is not conducted at a section a.sub.1. 
The invention being thus described, it will be obvious that the same may be 
varied in many ways. Such variations are not to be regarded 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.