Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1197Z20
The present invention relates to an actuator for
a dosing pump, especially for a paint dosing machine,
comprising
- a grab engaging the piston of the dosing pump,
and
- a power-driven transfer means for transferring
the grab between two extreme positions in which the
piston of the dosing pump is located in a position
corresponding to an empty pump and a position corres-
ponding to a full pump.
When toning paint specific quantities of one or
more toners must be added to the basic paint. The toner
quantities to be dosed must be very precise in order to
obtain a satisfactory toning precision. secause toners
are used as strong concentrates and the smallest toner
dose therefore is very small, a high precision in the
operation of the dos ng pump is required, especially
when dosing small doses. When dosing toner, toner is
sucked by means of the dosing pump from a toner con-
tainer into the pump by displacing the piston over a
distance corresponding to the quantity of said dose,
whereafter the sucked dose is through a nozzle pressed
into a paint can. When the dose is very small, the
movement of the piston is correspondingly very small.
To produce such a small movement with a sufficient
precision has, however, been difficult when using the
present dosing d~vices.
It is previously known to fasten the grap engag-
ing the piston of the dosing pump in a vertical belt
or screw which is moved by means of an electric motor.
However, such a belt or screw drive requires a preci-
sion motor and a precision belt or screw. A step motor
offers the possibility to transfer the grap relatively
precisely but has a limited number of steps so that one
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step corresponds to the smallest dosable toner unit.
In a belt drive operation the movement of the grap is
distributed in equally large movement intervals from
one extreme position to another.
When small toner doses are concerned corres-
ponding to only or a few steps of the step motor, a
faulty movement of the step motor corresponding to one
step, i.e. the displacement of the grab one dosing unit
too little or too much, results in a proportionally
considerabl~ bigger faulty toning with respect to the
movement interval corresponding to a precise toner dose
than when larger toner doses are concerned, which
correspond to several steps of the step motor. Although
the precision in movement of the step motor and the
grap is equal in the entire range of movement of the grab,
the toning precision is, because of the foregoing, con-
siderably poorer in the beginning of the range of movement.
The object of the present invention is to pro-
vide an actuator which eliminates the above mentioned
disadvantage and permits to achieve a high toning
precision also in the beginning of the range of move-
ment of the grab. This object is achieved with the
actuator according to the invention which is charac-
terized in that
- the transfer means comprises a crank mechanism
including a crank driven by means of a power element
and a transfer element provided with a grab and connect-
ed to said crank, and
- the crank is arranged to be located at its
dead point with respect to the transfer movement of the
grab at least when the grab is located in the extreme
position corresponding to an empty pump.
The invention is based on the idea that the
range of movement of the power element required for
small toner doses for transferring the grap over a
distance corresponding to one dose is enlarged as com-
11~7;~
pared to the ranye of movement of the power elementrequired for larger doses. When using an e]ectric
motor as power element, this means that the range of
movement of the motor is enlarged per toner unit in
the beginning of the range of movement of the grab,
whereby the share of any faulty movement of a range of
movement corresponding to a full dose is reduced and
the precision of the toner dose is in a corresponding
manner increased. This can be simply realized by means
of a crank mechanism by utilizing the fact that the
relatively wide range of movement of the crank at the
dead point of the crank causes a relatively small
movement only in the grab. Thus, the wider range of
movement of the crank results in a more precise dis-
tance of movement of the grab and, in a corresponding
manner, the toning precision is substantially improved.
When using larger toner doses, the distance of movement
of the grab is more inaccurate due to the smaller range
of movement of the crank but the absolute toning preci-
sion remains the same as when using small toner doses.
In this way, a higher toning precision is achieved
also when using small toner doses without requiring a
precision mctor. Instead of an electric motor, a hand
crank can be used as power element because such a wide
setting area is obtained for dosing small toner doses
that the setting scale for the hand crank will be
sufficiently clear for a precise visual setting. In
the same way as in a motor drive, a small faulty
movement of the hand crank does not substantially re-
duce the toning precision even when using small ~oner
doses.
The invention will be described in more detail
in the following with reference to the accompanying
drawings in which
Figure 1 illustrates schematically the operating
principle of the dosing device of the toning machine,
11972~0
Figures 2, 3 and q illustrate on an enlarged
scale a motor-driven embodiment of an actuator accor-
ding to the invention in the lower dead point position,
central position and upper dead point position, respec-
tively,
Figure 5 shows a hand-operated embodiment of the
actuator, and
Figure 6 shows an alternative embodiment of the
actuator.
A separate dosing pump 2 is installed for each
toner container 1 in the dosing machine. By means of
said pump, toner is dosed through a valve 3 into a
nozzle 4 and further into a paint can 5 to be toned.
A common actuator 6 is installed on the machine frame
for driving the pumps. When toning, said actuator is
transferred to the pump dosing in each particular case
and is brought into engagement with the piston rod 7
of this pump for displacing the piston.
The actuator comprises a crank 9 which is rota-
tably mounted in a machine frame 8 and is articulated
to a connecting rod 10 connected at its upper end to a
grab 11 slideably mounted on a vertical guide 12. To
the crank is fastened a drive pulley 13 rotated by an
electric motor 14. The electric motor is a conventional
micromotor, for example, an automobile windscreen wiper
motor.
The crank and the connecting rod are dimensioned
and arranged so that the crank is located at its lower
dead point when the grab 11 is located at the lower
extreme position of its path of movement where it is
ready to engage the piston rod located at its lowermost
position, as shown in Figure 2, and so that the crank
is located at its upper dead point when the grab 11 is
located in the upper extreme position II of its path
of movement where it has displaced the piston rod to
the uppermost position, as shown in Figure 4. The
li9~Z;~O
quantity of a toner dose to be sucked into the pump
thus depends on the distance over which the piston is
displaced upwards from the lower extreme position of
the piston rod. Of course, the dose is at its largest
when the piston rod is located in the upper extreme
position.
It will be noted that when the crank is located
close to its lower dead point, a relatively large area
of movemento~ o~ the crank causes only a relatively
small lifting movement H for the connecting rod. Thus,
a faulty movement of the crank, i.e. the rotation of
the crank somewhat more or less than the desired
theoretical xange of movement, in which the desired
toner dose is obtained, causes a very small inaccuracy
in the toner dose. As the crank rotates farther away
from the dead point, the ever smaller range of movement
of the crank causes a lifting movement of said size in
the connecting rod whereby a faulty movement of the
crank causes an ever increasing error in the lifting
movement. However, because an ever larger toner dose
is concerned, the inaccuracy in the dose will be sub-
stantially as small as in smaller toner doses, i.e.
the absolute toning precision remains the same in the
entire dosing area of the pump. Thus, a conventional
electric motor can be used as rotary motor for the
crank.
Instead of an electric motor, a hand crank 15,
Fig. 5, can be used as power element for the crank.
The setting scale 1~ which is associated with the
crank and which indicates to which point the crank must
be rotated for sucking into the pump a toner dose re-
quired in each particular case can, in the critical
initial area corresponding to small toner doses, be
provided with a sufficiently rough scale for a quick
and precise visual setting of the crank.
~lg~
The drawing and the description associated
therewi-th are only intended to illustrate the idea of
-the invention. In its details, the actuator according
to the invention may vary considerably within the scope
of the claims. Thus, it is possible to use, instead of
or in addition to the separate hand crank 15 shown in
Figure 5, a hand crank secured directly as an extension
of shaft of the crank 9. Similarly, it is possible
provide the crank mechanism with another structure than
a connecting rod 10, for example, by replacing the
connectiny rod with a slide structure, in which the
slide 17 is fastened to the grab and the outer end of
the crank 9 is mounted on horizontal guides 18 in the
slide, as illustrated in Figure 6. The slide is verti-
cally movable on the guide 12.
