Abstrict A viscosity control (10 200) is disclosed which employs a turbine
flow meter (52). A pump (18) provides for a flow of solution through
a conduit at a relatively constant pressure. The flow rate of the
solution through the conduit thus varies depending on the viscosity
of the solution. The turbine of the flow meter rotates at an angular
velocity related to the flow rate. The rotational velocity of the
turbine is sensed. When the turbine speed decreases as viscosity
increases to a set maximum viscosity, the control supplies solvent
to the solution to decrease the viscosity.
Claims What is claimed is:
1. An apparatus for maintaining the viscosity of a solution in
a desired viscosity range by providing solvent to the solution,
the solution being formed of a material and solvent and the solution
being stored in a supply tank, comprising:
means for defining a flow path for flow of solution along the flow
path;
pump means for pumping the solution along the flow path at a relatively
constant pressure so that the flow rate of the solution varies with
viscosity, said pump means pumping solution from the supply tank
along the flow path;
a turbine flow meter having a turbine in the flow path with the
turbine speed determined by the flow rate of solution in the flow
path;
a positive displacement pump for pumping solvent from a solvent
supply to the solution;
means for sensing the turbine speed and for activating the positive
displacement pump to add solvent to the solution when the turbine
speed sensed falls below a set speed, indicating the viscosity of
the solution is outside the desired range; and
means for sensing the level of solution in the supply tank and
adding material to the supply tank when the level sensed falls below
a minimum level.
2. The apparatus of claim 1 wherein said flow path means further
includes a flow restriction in the flow path downstream of the turbine
to maintain said relatively constant pressure.
3. The apparatus of claim 1 further comprising means for adjustably
setting the set turbine speed resulting in inflow of solvent to
the solution.
4. The apparatus of claim 1 wherein said sensing means adds solvent
to the solution for a predetermined time interval.
5. The apparatus of claim 1 wherein said flow path means defines
a conduit, said pump means pumping the solution through the conduit
at the predetermined pressure, a tee being provided in the conduit
to supply a predetermined rate of solution to a device, with the
excess solution returing to the supply tank.
6. An apparatus for maintaining the viscosity of an ink solution
within a desired viscosity range by providing solvent to the ink
solution, a supply tank containing the ink solution, an ink supply
and solvent supply also being provided, comprising:
a conduit defining a flow path;
a pump for pumping ink solution from the supply tank through the
flow path in the conduit at a relatively constant pressure;
a turbine flow meter having a turbine positioned in the flow path
within the conduit, the speed of rotation of the turbine being porportional
to the flow rate of ink solution through the conduit;
means for drawing off a selected quantity of ink solution downstream
of the turbine within the flow path of the conduit for delivery
to a printing machine, the excess ink solution being returned to
the supply tank;
means for sensing the rotational velocity of the turbine and transforming
the velocity sensed to a voltage;
a set point controller having a volt meter for indicating the voltage
sensed by said turbine speed sensing means and a variable set point
voltage, said controller being activated when the voltage corresponding
to the turbine speed is not exceeding the set voltage;
a solvent supply path for providing solvent from the solvent supply
to the inlet of the pump through a solenoid operated on/off valve;
a timer for opening the solenoid valve to provide solvent from
the supply to the inlet of the pump when the set point controller
is activated, said timer maintaining the solenoid open for a first
predetermined time period and then shutting the valve, said timer
reopening the valve after a second predetermined time interval and
cycling the solenoid valve between open and closed positions until
the set point controller is deactivated;
an ink level sensor mounted in the supply tank for sensing a decrease
of ink solution level below a desired minimum level; and
an ink supply path for providing ink from the ink supply to the
inlet of the pump, said path having a solenoid operated on/off valve
activated by said ink level sensor to provide ink from the ink supply
to the supply tank when the sensor senses the ink solution level
below the desired minimum level.
7. An apparatus for maintaining the viscosity of a material and
solvent solution in a desired viscoity range by adding solvent to
the solution, said solution being stored in a supply tank, comprising:
means for defining a flow path for flow of solution along the flow
path;
pump means for pumping the solution along the flow path at a relatively
constant pressure so that the flow rate of the solution varies with
viscosity, said pump means pumping solution from the supply tank
along the flow path;
a turbine flow meter having a turbine in the flow path with the
turbine speed determined by the flow rate of solution in the flow
path;
means for sensing the turbine speed to generate a signal relating
to viscosity;
a positive displacement pump for pumping solvent from a solvent
supply to the solution;
means for activating said positive displacement pump to add solvent
when a predetermined viscosity signal is generated indicating the
need for additional solvent in the solution; and
means for sensing the level of solution in the supply tank and
adding material to the supply tank when the level sensed falls below
a minimum level.
8. The apparatus of claim 7 wherein said flow path means further
includes a flow restriction in the flow path downstream of the turbine
to maintain said relatively constant pressure.
9. The apparatus of claim 7 further comprising means for adjustable
setting the predetermined viscosity signal resulting in inflow of
solvent to the solution.
10. The apparatus of claim 7 wherein said activating means adds
solvent to the solution for a predetermined time interval.
11. The apparatus for claim 7 wherein said flow path means defines
a conduit, said pump means pumping the solution through the conduit
at the relatively constant pressure, a tee being provided in the
conduit to supply a predetermined rate of solution to a device,
with the excess solution returning to the supply tank.
12. The apparatus of claim 7 wherein said means for adding material
includes a positive displacement pump to supply material to the
supply tank.
13. An apparatus for maintaining the viscosity of an ink solution
within a desired viscosity range by providing solvent to the ink
solution, a supply tank containing the ink solution, an ink supply
and solvent supply also being provided, comprising;
a conduit defining a flow path;
a pump for pumping ink solution from the supply tank through the
flow path in the conduit at a relatively constant pressure;
a turbine flow meter having a turbine positioned in the flow path
within the conduit, the speed of rotation of the turbine being proportional
to the flow rate of ink solution through the conduit;
means for drawing off a selected quantity of ink solution downstream
of the turbine within the flow path of the conduit for delivery
to a printing machine, the excess ink solution being returned to
the supply tank;
means for sensing the rotational velocity of the turbine and transforming
the velocity sensed to a voltage;
a set point controller having a volt meter for indicating the voltage
sensed by said turbine speed sensing means and a variable set point
voltage, said controller being activated when the voltage corresponding
to the turbine speed is not exceeding the set voltage;
a solvent supply path for providing solvent from the solvent supply
to the inlet of the pump through operation of a positive displacement
pump;
a timer for activating the positive displacement pump to provide
solvent from the supply to the inlet of the pump when the set point
controller is activated, said timer maintaining the positive displacement
pump activated for a first predetermined time period and then deactivating
the positive displacement pump, said timer reactivating the positive
displacement pump after a second predetermined time interval and
cycling the positive displacement pump between activation and deactivation
unless the set point controller is deactivated;
an ink level sensor mounted in the supply tank for sensing a decrease
of ink solution level below a desired minimum level; and
an ink supply path for providing ink from the ink supply to the
inlet of the pump, said path having a second positive displacement
pump activated by said ink level sensor to provide ink from the
ink supply to the supply tank when the sensor senses the ink solution
level below the desired minimum level.
Description TECHNICAL FIELD
This invention relates to the printing industry, in particular
to a control system for maintaining the viscosity of an ink solution
in a desired range by selective addition of a solvent.
BACKGROUND OF THE INVENTION
The typical inks used in the flexographic printing industry must
be mixed with a solvent, such as alcohol or water, to form a usable
ink solution with an acceptable viscosity. Because the solvents
are so volatile, evaporating to the atmosphere, solvent must be
continuously added to the ink solution to maintain the desired viscosity.
Different control apparatus have been developed in an attempt to
maintain a solution at a desired viscosity. U.S. Pat. No. 3557817
issued on Jan. 26 1971 to Edwin H. Royse discloses one apparatus
for mixing fluids of different specific gravity to maintain a solution
with the desired properties. U.S. Pat. No. 3848618 issued Nov.
19 1974 to Edwin H. Royse discloses another device for mixing fluids
of different specific gravities to maintain a solution of desired
properties.
While the devices previously designed, including those disclosed
in the patents above, are satisfactory in many aspects, a need still
exists for an improved control system for maintaining the viscosity
of an ink solution within the desired range. A critical consideration
is the difficulty in maintaining such a control system. A complex
and multicomponent system can often require excessive time for cleaning
and maintenance, compromising the very purpose for the control system
to eliminate labor intensive maintenance.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, an apparatus
is provided for maintaining the viscosity of an ink solution within
a desired viscosity range by providing solvent to the solution.
The apparatus includes structure for defining a flow path for flow
of ink solution along the flow path. Pump structure is provided
for pumping the ink solution along the flow path at a relatively
constant pressure so that the flow rate of the ink solution varies
with the viscosity of the ink solution. A turbine flow meter is
provided which has a turbine in the flow path. The turbine speed
varies with the flow rate of the ink solution along the flow path.
Structure is also provided for sensing the turbine speed and for
adding solvent to the ink solution when the turbine speed sensed
indicates the viscosity is outside the desired range.
In accordance with another aspect of the present invention, a flow
restriction is placed within the flow path downstream of the turbine
to maintain the relatively constant pressure. In accordance with
another aspect of the present invention, the ink solution is stored
in a supply tank. The pump structure pumps ink solution from the
supply tank through the flow path. Structure is provided for sensing
the level of ink solution in the supply tank and adding ink to the
supply tank when the level falls below a minimum level. In accordance
with yet another aspect of the present invention, structure is provided
for adjustably setting the predetermined speed of the turbine which
initiates solvent input.
BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the present invention and
for further advantages thereof, reference is now made to the following
Description taken in conjunction with the accompanying Drawings,
wherein:
FIG. 1 is a schematic view of a first embodiment of the present
invention; and
FIG. 2 is a schematic view of a second embodiment of the present
invention.
DETAILED DESCRIPTION
With reference now to the accompanying FIG. 1 a viscosity control
10 is illustrated for controlling the viscosity of an ink solution
12 by periodically adding a solvent, typically alcohol or water.
The ink solution 12 is stored in a supply tank 14 for eventual
supply to an ink pan (not shown) which is part of the actual printing
machine. With many solvents, including alcohol, the ratio of ink
and solvent will be a nonstable ratio because the solvent will evaporate.
As the solvent evaporates, the viscosity of the ink solution increases.
If solvent is not added on a periodic basis, the viscosity of the
ink solution may become too high for proper operation of the printing
press.
A pump assembly 16 is associated with the supply tank 14. The assembly
16 includes a centrifugal pump 18 set within the supply tank 14
below the desired minimum ink level 20. A motor 22 drives a centrifugal
pump through a motor shaft (not shown) contained within a fluid
housing 24 extending into the ink solution to the pump. The pump
is operated and draws ink solution from supply tank 14 into an inlet
and pumps the ink solution from the pump to outlet pipe 26 extending
from the supply tank 14. Outlet pipe 26 leads to a pair of 90.degree.
elbows 28 and 30. An on/off valve 32 is connected to elbow 30. A
nipple 34 extends from the on/off valve to a tee 36. Another branch
of the tee connects to a U-shaped pipe 38. A second tee 40 is secured
to the U-shaped pipe 38. A restrictor section 42 having a restriction
orifice 44 is connected to one leg of tee 40. A return pipe 46 is
connected to section 44 downstream of orifice 44 which ends in the
ink solution within the supply tank 14. Thus, a continuous recirculating
flow path is defined through these elements whereby the pump pumps
the ink solution from the supply tank about the circuit to return
to the supply tank. The actual ink solution delivered to the ink
pan is drawn off from the third port of tee 40 through an on/off
valve 48 and pipe 50 to the ink pan (not shown).
The third port of tee 36 is employed to mount a turbine flow meter
52. Meter 52 includes a turbine 54 which is mounted in the flow
path through the tee 36 so that ink solution pumped through the
tee will spin the turbine about its rotational axis 56. The angular
velocity of rotation of the turbine 54 about axis 56 will be a function
of the flow rate of ink solution through the tee 36.
Preferably, the turbine flow meter 52 is of a type using a magnetic
pick-up to generate an electrical signal of a frequency related
to the speed of rotation of the turbine 54. The electrical signal
is transferred through signal wires 58 to a frequency transmitter
60. Frequency transmitter 60 is powered from power supply 88 and
acts to transform the frequency signal to a voltage related to the
frequency.
The voltage signal from transmitter 60 is transmitted through signal
connection 62 to a set point controller 64. The voltage generated
by the transmitter 60 deflects an instrument needle 66 within the
controller. When the turbine speed is zero, no voltage is transmitted
by transmitter 60 to the controller 64 and the instrument needle
66 falls to the zero position on the scale 68. As the turbine speed
increases, the voltage from transmitter 60 to controller 64 will
increase, deflecting the needle 66 upscale.
The controller also contains a set point needle 70 which can be
adjustably set on scale 68 by a set point control 72. When the needle
66 is at the same point or downscale of the set point needle 70
a contact is closed within the controller to close a circuit 73
extending from controller 64 to a timer 74.
When the circuit to the timer 74 is closed, the timer will activate
a solenoid valve 76 through control lines 78 to permit solvent to
flow from a solvent supply source (not shown) into the supply tank.
The solvent passes into a tee 80 and from there into an inlet tube
82 connected to the suction side of the pump 18. A suction is created
by the pump within the inlet pipe 82 which causes solvent to flow
from the supply into the pump when the solenoid valve is opened.
The timer 74 is set to maintain the solenoid valve in the open
position only for a predetermined increment of time. The timer then
permits the solenoid valve 76 to close. If sufficient solvent has
been added to reduce the viscosity, and thus increase the speed
of turbine 54 so that the needle 66 reads upscale of set point needle
70 no additional solvent will be needed. However, if insufficient
solvent has been provided in the first cycle, the timer will reopen
the solenoid valve 76 after a second predetermined time increment
has elapsed and will continue the cycle until sufficient solvent
has been added to decrease the viscosity until the ink solution
viscosity is in the desired viscosity range.
An ink level sensor 84 is also provided which employs two probes
86 which end at the desired minimum ink level 20 within the supply
tank 14. When the ink solution level is at or above the minimum
level, the probes 86 are surrounded by the ink solution, which permits
a small current to flow between the probes. The power source for
this current flow is the power supply 88. An ink controller 90 is
positioned within the circuit between the power supply and ink level
sensor. If the circuit is open, i.e., by the ink solution falling
below the desired minimum ink level 20 the ink controller will
activate a solenoid valve 92 through circuit 94 to permit ink to
travel from an ink supply (not shown) through the solenoid valve,
tee 80 and into the inlet pipe 82. Again, the pump creates a vacuum
in the inlet pipe 82 which draws in the ink from the supply. Ink
will be added until the ink solution level again rises to the minimum
level 20 which reinstates the current flow through the probes.
As can be understood, the pump 18 provides for circulation of the
ink solution at a relatively constant pressure, assisted by the
restriction orifice 44. With a constant pressure, the flow rate
of the ink solution will vary as the viscosity varies. Typically,
as viscosity increases the flow rate will decrease. The turbine
flow meter 52 functions to measure the flow rate past the turbine
54 and thus also indicates the viscosity of the ink solution. For
a given application, the set point needle 70 can be set by control
72 to provide maintenance of the ink solution viscosity below a
predetermined maximum level.
Preferably, a preheat device 96 is employed to preheat the ink
solution 12 when operation is first initiated. As can be appreciated,
the continuous flow of the ink solution driven by the pump 18 will
provide some frictional heating of the ink solution, which has an
effect on its viscosity. The preheat device 96 is intended to bring
the temperature of the ink solution 12 quickly to the steady state
temperature to allow rapid adjustment of the set point controller.
In one device constructed in accordance with the teachings of the
present invention, a turbine flow meter is employed which has a
flow range of 0.5 to 5 gallons per minute in a flow line of 1/2
inch diameter. The frequency of signals generated by rotation of
the turbine within the turbine flow meter varies from 0 to 500 Hertz,
corresponding to the range of zero flow to maximum flow through
the associated line. The frequency transmitter associated with the
turbine flow meter will convert the signal frequency to a voltage
which varies from 10 millivolts to 500 millivolts related directly
to the signal frequency. The flow meter was manufactured by E. F.
M. Flow Meter Co. of Garland, Tex.
FIG. 2 illustrates a viscosity control 200 forming a second embodiment
of the present invention. A number of elements in control 200 are
identical in function to those in control 10 and these elements
are identified by the same reference numerals.
In viscosity control 200 the signal output from turbine flow meter
52 and ink level sensor 84 feed directly into control module 202
for processing. When additional ink is required, control module
202 will cause positive displacement pump 204 to operate to pump
a desired quantity of ink from the ink supply to supply tank 14.
When a need for additional solvent is sensed, control module 202
will cause positive displacement pump 206 to operate to pump a desired
quantity of solvent from the solvent supply to supply tank 14. Preferably,
pumps 204 and 206 are of the peristaltic type. Pumps 204 and 206
having a pumping capacity of between 6 and 20 gallons/day would
be suitable for the viscosity control 200.
Control module 202 provides a visual display of actual flow viscosity
on scale 208 and of the viscosity set point on scale 210. Adjust
knob 212 provides for adjustment of the setpoint. Switch 214 turns
power on and off to control module 202 and indicator light 216 indicates
the power condition. Switch 218 and indicator light 220 provide
ink level control. Indicator light 222 indicates a balanced ink
solution. Indicator light 224 indicates a caution for abnormal balance
in the ink solution. Indicator light 226 is an alarm for zero flow
conditions in the flow meter, indicating flow blockage.
The control 200 has a strainer in the inlet to pump 18 and a separate
filter 228 in the flow path upstream of turbine flow meter 52. These
filters catch paper lint present in supply tank 14 due to ink pan
return flow to prevent clogging of the meter 52. The meter 52 in
control 200 uses a turbine 54' in the flow path for rotation about
an axis 230 which parallels the flow as the flowing ink solution
impinges on the curved turbine blades on turbine 54'. The rotational
velocity of the turbine 54' is sensed by magnetic pickup.
The flow restrictor section 42 is relocated downstream of the branch
to the ink pan. Also on/off valve 32 is positioned between tee 40
and meter 52.
Though the present invention has been described for use in the
flexographic printing industry with alcohol as the solvent, the
invention can also be used for inks where water forms the solvent
by simply substituting a water source for the alcohol source. Also,
the present invention can be employed with other viscous materials
used in other industries that require the use of solvent.
While several embodiments of the present invention have been described
in detail herein and shown in the accompanying Drawings, it will
be evident that various further modifications and substitutions
of parts and elements are possible without departing from the scope
and spirit of the invention. |