Note: Descriptions are shown in the official language in which they were submitted.
2113~71
.
LIQUID DISPENSING APPARATUS
FIELD OF THE INVENTION:
This invention relates to an a~al~us for dispensing minute quantities of
liquid in specific volumes per unit distance and more particularly to controlling
the rate at which such volumes are dispensed depending on the relative motion
s of the dispenser. Specifically, liquid dispensing using syringes is considered.
BACKGROUND OF THE INVENTION:
Dispensing syringes that are used to dispense small quantities of liquids
are used in many industrial applications, such as dispensing glue, paint, printed
10 circuit board m~kin~; material, among other things. Glue may be dispensed onto
containers such as cereal box containers or the like. Paint may be dispensed on
to pressure cast buttons or lapel pins, or in sign m~kin~. Masking material is put
on to lnfini~hed printed circuit boards in the pattern of the required circuit before
an etching solution is introduced thereto. These are only illustrative examples and
several other uses for dispensing syringes exist.
Essentially what happens in the use of a dispensing syringe to dispense a
liquid onto an object, is that the dispensing syringe moves along the object with
the outlet of the dispensing syringe near the object. The amount of liquid that is
required per unit distance along the object is known for any given point along the
20 object. This amount can remain constant for all points along the path of travel
of the dispensing syringe or can vary as necessary. If the amount of liquid to be
laid down is constant for all points along the path, then it can be considered that
the liquid is being laid down at a specific volume per unit distance. Given thisknown rate of volume of liquid per unit distance and the rate of movement of the25 outlet of the dispensing syringe along the object, the rate of dispensing of liquid
from the outlet of the dispensing syringe can be calculated by multiplying thesetwo values. This calculated volume that must be dispensed from the syringe can
be used to calculate the speed of movement of the piston in the syringe as
2113~71
required by dividing the calculated flow rate by the cross-sectional area of thereservoir of the dispensing syringe. Conversely, given this known rate of volumeof liquid per unit distance and the rate of dispensing of the liquid from the
syringe, the necessary rate of movement of the outlet of the dispensing syringe
5 can be calculated, by dividing the rate of dispensing of the liquid from the syringe
by the volume of liquid per unit distance.
Further, the above relationship can also be considered as an equation
wherein the rate of dispensing of the dispensing syringe equals a constant timesthe rate of movement of the outlet of the dispensing syringe, where the constant10 is the amount of volume of liquid per unit distance which is generally known.Often, small amounts or even very small amounts of the liquid must be
dispensed per unit time and it must be dispensed at an accurate rate which is
difficult at small flow rates. There are at least two reasons for this. Firstly, it is
desirable to minimi7P. wastage. Secondly, in some applications such as painting
15 buttons or lapel pins, extreme neatness and accuracy is required.
In order to deposit a known amount of liquid over a given distance of
travel of the outlet of the dispensing syringe, the amount of movement of the
outlet of the dispensing syringe and the amount of liquid dispensed over this
given distance must remain in constant proportion to each other. In order to do
20 this, the rate of change in displacement of the outlet along the workpiece and the
liquid dispensing rate must remain constant, or alternatively the two must each
have the same rate of change. Typically, the rate of dispensing of the liquid from
the dispensing syringe is adjusted, possibly by trial and error, with respect to rate
of movement of the outlet of the dispensing syringe in order to obtain the desired
25 known amount of deposited liquid per unit distance.
In the case where the amount of material required per unit distance is not
constant, it is necessary that the flow rate of the material being dispensed from
the outlet of the dispensing syringe be adjustable directly according to the amount
required, assuming a constant speed of the dispensing syringe across the object.30 Lag in the change of dispensing rate or a change in the dispensing rate to anincorrect amount will cause an improper amount of liquid to be deposited on the
- 2113671
object. Conversely, the rate of movement of the outlet of the dispensing syringeacross may be varied while the rate of dispensing of liquid from the dispensing
syringe rernains constant. It can be seen, therefore, that it is necessary to
consistently and smoothly advance the piston along the cartridge of the dispensing
5 syringe, at a potentially continuously ch~n~:ing speed that changes in proportion
to the amount of liquid per unit length to be deposited on an object and also inproportion to the change in speed of the outlet of the dispensing syringe acrossthe object.
Dispensing syringes are often used in hand controlled situations wherein
10 a stylus is hand drawn by an operator along grooves in a template. The outlet of
the dispensing syringe follows the same pattern across an object. Inevitably, the
speed of the stylus within the groove of the template varies due to the nature of
the operator. Again, it is necessary to vary the rate at which the liquid is being
dispensed from the outlet of the dispensing syringe, and therefore also the speed
15 of the piston in the cartridge of the dispensing syringe, proportionally with the
change in speed of the stylus in the grooves of the template.
Another problem associated with depositing a known amount of liquid per
unit distance along an object is that many dispensing syringes are used in
conjunction with a two degree of freedom (two independent axes of motion)
20 robotic table, commonly known as an X-Y table. In such a robotic table, either
the table or the dispensing syringe is independently driven in each of two
mutually perpendicular directions (the X-axis and Y-axis of Cartesian co-
ordinates). In any event, the table and the dispensing syringe are moved with
respect to each other. Typically, the two drive means that are used to drive the25 table or the dispensing syringe with respect to the other in each of the X and Y
axes run at constant speeds. The movement in each of the X and Y axes is
independent from each other and the resulting speed of the table is the vectorial
sum of the two speeds in each of the mutually perpendicular axes. This vectorialsum can be calculated by using the equation SPEED = ((SPEED IN "X"
30 DIRECTION)2 + (SPEED IN "Y" DIRECTION)2) /~. Therefore, in order to move
the table and the dispensing syringe with respect to one another in a path that is
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at an angle to the X and Y axes, the speed of the dispensing syringe is greater
than the speed along either of the X and Y axes.
In order to accommodate such a change in speed of the dispensing syringe
the rate at which the liquid is dispensed from the dispensing syringe must increase
correspondingly, so that the ratio of the speed of the dispensing syringe to the rate
of liquid dispensed therefrom remains constant, with this constant being the
amount of liquid required per unit distance. It is therefore necessary to changethe speed of the piston within the cartridge of the dispensing syringe
proportionally to any change in relative speed of the outlet of the dispensing
syringe across the object, which relative speed can be calculated as discussed
prevlously.
It is also possible to use a dispensing syringe in conjunction with a three
degree of freedom (three independent axes of motion) robotic table, commonly
known as an X-Y-Z table. In such a robotic table, the table is independently
driven in each of three mutually perpendicular directions (the X axis, the Y axis
and the Z axis of Cartesian co-ordinates). As in the above described X-Y table,
the speed of the outlet of the dispensing syringe across an object on the X-Y-Z
table can be calculated by using the equation SPEED = ((SPEED IN "X"
DIRECTION)2 + (SPEED IN "Y" DIRECTION)2 + (SPEED IN "Z"
DIRECTION)2) /2. Typically, a separate drive means would be used to drive the
table or dispensing syringe with respect to each other in each of the X, Y and Zaxes, thereby causing the need for the vectorial sum of the speed in each of these
axes to be calculated to obtain the relative speed of the outlet of the dispensing
syringe with respect to the object on the X-Y-Z table.
BRIEF DESCRIPTION OF THE DRAWINGS:
Embodiments of the present invention will be described hereafter, and
reference will be made to the prior art, all by way of the accompanying drawings,
in which:
Figure 1 is a sectional view of a prior art mech~ni~m;
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Figure 2 is an isometric view of the dispensing syringe of the present
invention in place on a robotic "X-Y-Z" table;
Figure 3is an isometric view of a piston retracting means employed within
the present invention;
Figure 4 is a cross-sectional view from the side, of the piston retracting
means of Figure 3; and
Figure 5 is an isometric view similar to Figure 3 but of an alternative
embodiment of the present invention.
PRIOR ART:
The known prior art is typified by a dispensing syringe as shown in Figure
1. The dispensing syringe 10 has an outlet 11, a cartridge 12 and a piston 13
within the cartridge. This piston 13 is pneumatically powered by way of air
injected into the cartridge through an air line 14 as indicated by arrow 15. Theair line 14 is connected to a controllable source of compressed air. The cartridge
12 contains a supply of liquid 16. In some prior art units the source of air mayalso allow for the supply of a low pl`eS~ e vacuum to the dispensing syringe in
order to draw the piston 13 back. In use, the piston 13 is advanced toward the
opening 11 by allowing the flow of pressurized air from the air line 14. The flow
2 0 of pressurized air is started and stopped, as required. However, it is very difficult,
if not virtually impossible, to advance the piston 13 a required amount by
increasing the air pressure in the air line 14, or even by timing the permitted air
flow, because the air in the air line pressurizes, and thus changes its volume.
There may be some loss of accuracy due to friction of the piston 13 within the
cartridge 12, and also due to the viscosity of the fluid 16 within the reservoir 12,
but these are not serious problems and may be calibrated or adjusted for.
In order to overcome the problem of inaccurate dispensing, it has been
found that using a positive mechanical linkage between the piston and a driving
means produces a means of more accurately dispensing a known amount of liquid
per unit time from the dispensing syringe. Such types of mechanical linkages aretaught by the following prior art patents.
2113671
U.S. Patent 4,731,058 to DOAN, issued March 15, 1988, discloses a drug
delivery system wherein a syringe including a plunger is placed within a chassis.
A motor drives a lead screw through a gear arrangement. A drive nut and the
free end of the plunger are arranged such that rotational movement of the lead
5 screw moves the drive nut and thereby moves the plunger to dispense the contents
of the syringe. A switch arrangement causes the motor to stop if excessive
reservoir back pressure caused by occlusion, plunger assembly friction, a depleted
reservoir, and the like, is realized. This patent teaches the use of an electricmotor and direct mechanical drive including a rotating drive shaft, further coupled
10 with a threaded member that engages a plunger on a standard syringe, to drive the
plunger with respect to the syringe and dispense the contents of the syringe.
U.S. Patent 4,848,606 to TAGUCHI et al, issued July 18, 1989, discloses
an appalalus for dispensing a predetermined volume of paste-like fluid. The
inventive device disclosed in this patent has a motor that turns a shaft that has a
screw thread thereon. A nozzle holder moves up and down the threaded portion
of shaft. This controls the Z-axis position of the nozzle. The dispensing is
controlled in a similar manner, with a motor driving a shaft that has a threadedportion thereon. A piston driving device is driven up and down the shaft as the
shaft rotates. The piston driving device is coupled to the piston that is operatively
20 engaged within a nozzle. Vertical movement of the piston allows for controlled
dispensing of liquid from the nozzle. This patent teaches direct mechanical
coupling between the rotating motor and the piston or plunger of a dispenser.
What is not taught in the above discussed two patents is that there is no
direct rotation of the shaft that is directly connected to the piston of the syringe.
25 Direct rotation of the shaft that moves the piston of the syringe is, however,
taught in U.S. Patent 5,027,984 to GAKHAR et al, issued July 2, 1991, and in
U.S. Patent 3,984,033 to GROTH et al, issued October 5, 1976, among others.
In U.S. Patent 5,027,984 to GAKHAR et al, a cocking gun attachment is
disclosed wherein a portable electric screwdriver can be used to rotate a threaded
30 shaft to push a piston. Two arms are held to preclude rotation of the entire unit
- 211~671
with respect to the rotating threaded shaft, thereby causing advancement of the
rotating shaft and the piston with respect to the receptacle of the cocking gun.U.S. Patent 3,984,033 to GROTH et al discloses an electric gun for
dispensing of comestibles, such as cookie dough, wherein an electric motor drives
a threaded piston rod by way of a set of gears. The threaded piston rod is
threadably engaged in a thrusting face so as to cause the thrusting face to advance
forwardly as the threaded piston rod rotates.
What is not disclosed in these patents is the direct connection of a threaded
piston shaft to a piston that is upwardly retained internally within a syringe and
that actually makes contact with the contents of the syringe. Such direct
connection is disclosed in U.S. Patent 5,022,563 to MARCHITTO et al, issued
June 11, 1991. In this patent a dispenser-gun assembly for viscous fluids and a
dispenser therefor is disclosed, wherein a threaded rod is attached to a drive
plunger element that is operatively retained within the tubular cylindrical chamber.
A ratchet mechanism including an advancing mechanism with a trigger portion
and a pawl member attached thereto, advance the drive plunger rod by way of
grasping the trigger portion and moving it towards the handle portion.
What is not disclosed in the prior art is the use of a dispensing syringe in
conjunction with a two degree of movement robotic table, and further having the
2 o advancement of the piston within the cartridge of the dispensing syringe
proportionally controlled to the speed of movement of the outlet of the dispensing
syringe with respect to an object on such a robotic table.
SUM~ARY OF THE INVENTION:
A liquid dispensing apparatus for use in conjunction with a two axis of
movement robotic table adapted to hold a workpiece in a given position, with theworkpiece having a receiving surface for receiving liquid dispersed from said
liquid dispensing apparatus, for accurately dispensing known volumes of liquid
onto the receiving surface, is disclosed. The apparatus comprises a cartridge
having a longitudinal axis and defining a reservoir for cont~ining an amount of
liquid therein, the cartridge having an outlet of known cross sectional area. A
- 2113671
piston is positioned within the cartridge and is adapted for translational movement
therewithin along the longitudinal axis. The displacement of the piston within the
cartridge, with respect to the outlet, defines the volume of the reservoir. There
- is a driving means for effecting translational movement of the piston with respect
5 to the cartridge so as to cause a change in the volume of the reservoir, and acontrol means for operating the driving means. An interconnection means having
a threaded portion thereon mechanically interconnects the piston and the drivingmeans, such that the driving means may rotatably drive the piston within the
cartridge. A first retaining means retains the interconnection means in threadably
10 - engaged relation thereto. A second retaining means retains the interconnection
means in freely rotatable non-threaded relation thereto. One of the first and
second retaining means is securely connected to the piston and the other of the
first and second retaining means is securely connected to the cartridge. The
interconnection means is longitudinally rigid between the first retaining means and
15 the second retaining means thereby to preclude unwanted relative movement along
the longitudinal axis of the piston with respect to the cartridge. When the piston
is advanced towards the outlet by way of a known degree of rotation of the
interconnection means, the piston advances along the cartridge by a known
amount to thereby dispense a known volume of the liquid from the reservoir
2 o through the outlet. The rate of liquid dispensing from the reservoir is
substantially proportional to the relative speed of the outlet with respect to the
workpiece, in a direction substantially perpendicular to the receiving surface of
the workpiece.
At the end of each piston advancement that disperses liquid from said
25 reservoir through said outlet, a piston retracting means is selectively actuated so
as to slightly retract the piston a minor amount within the cartridge.
In a further embodiment of the present invention, a liquid dispensing
apparatus adapted to accurately dispense known volumes of liquid onto the
receiving surface a workpiece is disclosed. The apparatus comprises a cartridge
30 having a longitudinal axis and defining a reservoir for containing an amount of
liquid therein. The cartridge has an outlet of known cross sectional area and an
-- 2113671
inlet for allowing the liquid to be deposited into the cartridge. A piston is
positioned within the cartridge and is adapted for translational movement
therewithin along the longitudinal axis. The displacement of the piston within the
cartridge, with respect to the outlet, defines the volume of the reservoir. There
iS also provided a driving means for effecting translational movement of the
piston with respect to the cartridge so as to cause a change in the volume of the
reservoir, and control means for operating the driving means. There is an
interconnection means for mechanically interconnecting the piston and the
driving means, such that the driving means may rotatably drive the piston withinthe cartridge, the interconnection means having a threaded portion thereon. A
first retaining means retains the interconnection means in threadably engaged
relation thereto. A second retaining means retains the interconnection means in
freely rotatable substantially non-ksm~l~t~ble relation thereto. A feedback loopmeans indicates the relative position of the outlet of the dispensing syringe with
respect to a datum point. One of the first and second retaining means is securely
connected to the piston and the other of the first and second retaining means issecurely connected to the cartridge. The interconnection means is longitudinallyrigid between the first retaining means and the second retaining means thereby to
preclude unwanted relative movement along the longitudinal axis of the piston
with respect to the cartridge. When the piston is advanced towards the outlet byway of a known degree of rotation of the interconnection means, the piston
advances along the cartridge by a known amount to thereby dispense a known
volume of the liquid from the reservoir through the outlet. The rate of liquid
dispensing from the reservoir is substantially proportional to the relative speed of
the outlet with respect to the workpiece, in a direction substantially perpendicular
to the receiving surface of the workpiece. The rate of liquid dispensing is
controlled by feedback signals from the feedback loop.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:
Reference will now be made to Figure 2 which shows the liquid dispensing
appaldl~ls 20 of the present invention mounted on an X-Y-Z robotic table 22,
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more specifically on the fixed table 23. The liquid dispensing apparatus 20 is
disposed over and generally manipulated over the surface of a workpiece 24,
which is received on and supported by the table member 23 of the robotic table
22. Liquid from the liquid dispensing apparatus 20 is deposited onto the
receiving surface 26 of the workpiece 24 as the liquid dispensing apparatus 20 is
moved around the workpiece 24, and is resultingly moved around the table
member 23, in a manner that will now be described.
The liquid dispensing apparatus 20 is securely attached to and supported
by a base member 21 where it is received and securely retained in an opening 25
therein. The base member 21 is vertically slidably engaged for movement in the
X direction 30 in a pair of track members 27 on a vertical support member 28.
The base member 21 is driven in the Z direction 34 along the track members 27
of vertical support member 28 by an internal drive motor (not shown), which may
be driven at various speeds.
The vertical support member 28 is in turn slidably supported on a
horizontal support bar 31 for movement in the X direction 30 along the horizontal
support bar 31. The vertical support member 28 is driven along the horizontal
support bar 31 by motor 36 which turns a threaded member (not shown) that is
internally disposed within the horizontal support bar 31. A co-operating threaded
receiving member (not shown), which is rigidly attached to the vertical support
member 28 is threadably engaged on the threaded member within the horizontal
support bar 31, and is driven thereby.
The horizontal support bar 31 is rigidly attached to a pair of brace
members 33, which are each in turn supported on horizontal guide rails 35. The
brace members 33 are adapted to move along the horizontal guides rails 35 in theY direction 32. A motor (not shown) similar to motor 36 drives the brace
members 33 along the horizontal guide rails 35.
It can be seen that the speed of the liquid dispensing apparatus 20 with
respect to the fixed table member 23, and therefore with respect to the workpiece
24, is the vectorial sum of the relative speed of the base member 21 with respect
to the vertical support member 28, the relative speed of the vertical support
`- 2113~1
member 28 with respect to the horizontal support bar 31, and the relative
horizontal speed of the brace members 33 with respect to the horizontal guide
rails 35 and can be calculated by the equation SPEED = ((SPEED IN "X"
DIRECTION)2 + (SPEED IN "Y" DIRECTION)2) h.
The liquid dispensing apparatus 20 comprises a cartridge 40 having a
longitudinal axis "L". A reservoir 42 is defined within the cartridge 40. The
reservoir 42 contains an amount of liquid 44 therein. Thè cartridge 40 has an
outlet 46 at the lower end 48 thereof, with the outlet 46 having a known cross-
sectional area. The reservoir 42 also has a known cross-sectional area and the
o ratio of the cross-sectional area of the outlet 46 to the cross-sectional area of the
reservoir 42 can readily be calculated. At the top end of the cartridge 40 is a
flange 41 and an opening 43 for receiving the piston 50 therein. The cartridge
40 is preferably part of a standard "off-the-shelf" dispensing syringe.
It can be seen that the liquid dispensing a~palalus 20 is ultimately driven
in each of the "X" direction 30, "Y" direction 32, and "Z" direction 34
independently of the other two directions. Resultingly, as movement in each of
these directions stops or starts, or even changes, the actual speed of the outlet 46
of the cartridge 40 with respect to the receiving surface 26 of the workpiece 24will change. Correspondingly, it is necessary to change the amount of liquid 44
that is dispensed through the outlet 46 to correspond with the change in relative
speed of the outlet 46 with respect to the receiving surface 26 of the workpiece24.
This is accomplished through a control means 74 which controls the speed
of the electric motor 62 proportionally to the vectorially calculated relative speed
of the outlet 46 of the cartridge 40 with respect to the receiving surface 26 of the
workpiece 24.
Within the cartridge 40 is a piston 50 that is adapted for translational
movement within the cartridge 40 along the longitudinal axis "L". The piston 50
defines the upper limit of the reservoir 42, and thus the displacement of the piston
50 within the cartridge 40 with respect to the outlet 46 defines the volume of the
reservoir 42.
-- 211 3~71
12
The translational movement of the piston 50 within the cartridge 40 is
effected by a driving means 60, which comprises an electric motor 62. The
electric motor 62 is physically connected to the cartridge 40 by way of a plate
member 64 that is rigidly attached to the base of the electric motor 62. The plate
5 member 64 is slidably but non-rotatably engaged with a pair of vertically
displaced guide members 66, which are rigidly attached at their bottom ends 67
to an attachment member 68. The attachment member 68 has a pair of opposed
curved end portions 69 and a central portion 70 joining the opposed curved end
portions 69. Together, the central portion 70 and the opposed curved end portions
o 69 form a channel 71, which is adapted to receive the flange 41 of the cartridge
40 in tight frictional engagement therein. The cartridge 40 is merely rotated toinsert the two opposed portions of the flange 41 into the channel 71.
The electric motor 62, which is the driving means for effecting
translational movement of the piston 50 with respect to the cartridge 40, is
15 mechanically inter-connected to the piston 50 by way of an interconnection means
80, which is preferably a threaded rod 82. The threaded rod 82 is securely
attached to the rotating drive shaft (not shown) of the electric motor 62 so that as
the drive shaft rotates the threaded rod 82 rotates correspondingly. The threaded
rod 82 is rotatably attached to the piston 50 such that there is no relative
20 translational movement along the longitudinal axis "L" between the piston 50 and
the threaded rod 82. The threaded rod 82 is received within the attachment
member 68 by a first retaining means 90 that retains the threaded rod 82 in
threadably engaged relation thereto.
The electric motor is a stepping motor, controlled by the control means 74
25 -- which is typically a microcomputer which issues a series of clocked pulses to
the electric motor. This permits the motor to be driven a very specific number
of steps, whereby the advance of the piston 50 is controlled. It is also possible
to drive the motor backwards, to effect a back pull on the piston, depending on
the manner of its mounting to the threaded rod. The electric motor 62 may also
30 be a DC motor, or its system may be in a servo-motor arrangement.
2113~71
As the electric motor 62 rotates the threaded rod 82, the threaded rod 82
moves translationally along the longitudinal axis "L" with respect to the first
ret~ining means 90. Correspondingly, the piston 50 is moved translationally along
the longitudinal axis "L" so as to advance within the cartridge 40 toward the
5 outlet 46. It can be seen that in order for this to occur, the electric motor 62 and
the plate member 64 must also move downwardly with the threaded rod 82 along
the vertically displaced guide members 66.
A second retaining means, which is actually the internal bearings of the
electric motor 62, retains the threaded rod 82 in freely rotatable substantially non-
10 tr~nsl~t~ble relation. In this manner, rotation of the threaded rod 82 does notcause translation of the threaded rod 62 along its length, which is along the
longitudinal axis "A", which in turn allows the rotation of the threaded rod 82 to
tr~n~l~t~bly move the piston 50 with respect to the cartridge 40, because the
cartridge 40 is substantially rigidly connected to the electric motor 62 by way of
15 vertically displaced guide members 66 and plate member 64.
The first retaining means 90 will now be discussed in greater detail with
reference to Figures 3 and 4. The first retaining means 90 comprises a force
transmitting member 92 that is threadably engaged on the threaded rod 82 and a
nut 91 that is threadably engaged on the force transmitting member 92. The nut
20 91 acts as a stop means for stopping the downward vertical movement of the plate
member 64 along the threaded rod 82. The first retaining means 90 also
comprises a stop means 94 that is connected in non-rotatable relation to the
attachment member 68, and is thereby also connected in non-rotatable relation tothe cartridge 40. The force transmitting member 92 and the stop means 94 are
25 rotatably moveable with respect to each other between a first relative position, as
indicated by arrow "A" and a second relative position as indicated by arrow "B",with the first and second relative positions are defined by a lot 97 in the force
transmitting member 92. A spring means 98 is connected between the force
transmitting member 92 and the stop means 94 at pins 99. A machine screw 96,
30 which passes through the slot 97 and is threadably engaged in the stop means 94
limits such relative movement of the force transmitting member 92 and the stop
2113671
14
means 94 between the first relative position and the second relative position bycontacting the first 97a and second 97b ends of the slot 97. Further, the machine
screw 96 can be used to force opposing surfaces 93, 9S of the force transmittingmember 92 and stop means 94 respectively into frictional engagement with one
s another so as to limit the relative speed of rotational travel of the force
transmitting member 92 and stop means 94 between the first relative position andsecond relative position, and also to thereby limit the impact of the machine screw
96 at the first end 97a of the slot 97.
Rotation of the threaded rod 82 in the direction as indicated by arrow "C"
10 causes the force transmitting member 92 to correspondingly rotate in the direction
as indicated by arrow "D", with respect to the stop means 94, thus causing the
slot 97 to rotate such that the machine screw 96 moves within the slot 97 from
the second relative position, as indicated by arrow "B" to the first relative position
as indicated by arrow "A". This also causes the piston to slightly advance within
the cartridge 40. When the threaded rod 82 stops rotating, the spring means 98
causes relative rotation of the force transmitting member 92 with respect to thestop means 94 in the direction as indicated by arrow "E", thus causing the slot 97
to rotate such that the machine screw 96 moves within the slot 97 from the firstrelative position as indicated by arrow "A" to the second relative position as
20 indicated by arrow "B". Resultingly, the piston 50 slightly retracts within the
cartridge 40, so as to withdrawn any liquid 44 that is at the outlet 46 of the
cartridge 40 slightly away from the outlet 46 so as to preclude any dripping of the
- liquid that is immediately at the outlet 46.
In this manner, the above described device, as shown in Figures 3 and 4,
25 is a piston retracting means.
In an alternative embodiment, it is contemplated that the piston S0 could
be retracted very slightly within the cartridge 40 by way of introducing reducedair ples~uie behind the piston S0. The piston S0 could only retract very slightly,
depending on the looseness along the first longitudinal axis "L" of the piston S0
30 with respect to the threaded rod 82.
2113671
In a further alternative embodiment, as shown in Figure 5, an alternative
X-Y-Z robotic table 110 is shown. In this alternative X-Y-Z robotic table 110,
the workpiece 112 is basically cylindrically shaped in the relative movement of
the surface 114 of the workpiece 112 in the "Y" direction 116 is caused by
5 rotation of the workpiece 112 about its longitudinal axis "M". The speed of the
surface 1 14 can be calculated by multiplying the diameter 1 18 of the workpiece112 by the constant Pi. The relative speed of the surface 114 of the workpiece
112 with respect to the outlet 119 of the liquid dispensing apparatus 120.
In an alternative embodiment, it is contemplated that the liquid dispensing
0 apparatus of the present invention be used in a configuration where the dispensing
apparatus is moved about freely over the surface of a workpiece, without having
moved in a predictable, or even pre-programmed manner, such as by an X-Y
robotic table. One type of liquid dispensing apparatus that is moved about freely
in use is a hand held liquid dispensing appald~us. It is common to use a hand
held dispensing appald~us in situations where a human operator's skill is required.
Such situations including the laying down of "paint" on a lapel pin or similar, to
form a pattern thereon. It is important to change the rate of liquid dispensing in
a hand held liquid dispensing apparatus, or any type of liquid dispensing
appal~lus that is moved about freely, so that the amount of liquid dispensed over
20 a given distance of travel of the outlet of the dispensing syringe, remains constant.
Resultingly, it is necessary that the rate of advancement of the piston in the
cartridge change proportionally with respect to the varying rate of change in
displacement of the outlet.
In order to do so, it is necessary to provide feedback regarding the rate of
25 change of displacement of the outlet, to the source of power controlling the rate
of advancement of the piston in the cartridge. The feedback signal provided
essentially indicates the relative position of the outlet of the dispensing syringe
with respect to a datum point, either the previous position of a fixed position,which allows the change in displacement to be calculated. A corresponding
30 proportional change in displacement for the piston can be calculated, and themotor means powering the piston can be controlled accordingly. The feedback
21~3671
16
signal may be a digital signal or an analog signal. Alternatively, an analog
feedback signal that is proportional to the speed of the outlet with respect to the
workpiece can also be used. Such an analog signal is usually with respect to a
zero speed and is typically a zero signal at a zero speed.
In order to obtain information about the physical position of the outlet of
the dispensing syringe, so that a feedb~ck signal can be provided, a mechanism
such as a pantograph structure can be used. A motion transmitting portion of the pantograph structure undergoes a relative physical displacement, corresponding
to the change in position of the outlet of the dispensing syringe in any direction.
This relative physical displacement is transmitted by the motion transmitting
portion of the pantograph structure to a device that converts this relative physical
displacement into an electrical signal. This electrical signal can be either an
analog signal, which represents movement on a continuous basis, or a discrete
digital signal, which represents movement as change and displacement over a
small increment in time. This electrical signal becomes the feedback signal
described above.
Other modifications and alterations may be used in the design and
manufacture of the Liquid Dispensing Apparatus of the present invention without
departing from the spirit and scope of the accompanying claims.
