GB2114680A

GB2114680A - Actuator for a dosing pump

Info

Publication number: GB2114680A
Application number: GB08302262A
Authority: GB
Inventors: Pentti Airaksinen
Original assignee: W Rosenlew Oy AB
Current assignee: W Rosenlew Oy AB
Priority date: 1982-02-10
Filing date: 1983-01-27
Publication date: 1983-08-24
Also published as: DK50683A; NO830428L; SE8300581D0; IT8319492A0; IT1161573B; CA1197220A; DE3302836A1; GB8302262D0; FR2521226A1; AU1075083A; JPS58151519A; FI820432L; SE8300581L; DK50683D0

Abstract

An actuator for a dosing pump, especially, for a paint toning machine, comprising a grab (11) displacing the piston (7) of the dosing pump (2) and a crank lever system for transferring the grab between two extreme positions in which the piston of the dosing pump is located in a position (I) corresponding to an empty pump and in a position corresponding to a full pump. The crank lever system comprises a crank (9) driven by a power element (14) and a connecting rod (10) provided with a grab, the crank being 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 (I) corresponding to an empty pump so that the wide range of movement (???) of the crank produces only a small transfer movement (H) of the grab. <IMAGE>

Description

SPECIFICATION Actuator for a dosing pump, especially for a paint dosing machine The present invention relates to an actuator for a dosing pump, especially for a paint dosing machine, comprising - agrab engaging the piston of the dosing pump, and - apower-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 corresponding 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.

Because toners are used as strong concentrates and the smallest toner dose therefore is very small, a high precision in the operation of the dosing pump is required, especially when dosing small doses. When dosing toner, toner is sucked by means of the dosing pump from a toner container 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 devices.

It is previously known to fasten the grab engaging 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 precision motor and a precision belt or screw. A step motor offers the possibility to transfer the grab relatively precisely but has a limited number of steps so that one step corresponds to the smallest dosable toner unit. In a belt drive operation the movement of the grab is distributed in equally large movement intervals from one extreme position to another.

When small toner doses are concerned corresponding 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 considerably 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 grab is equal in the entire range of movement of the grab, the toning precision is, because of the foregoing, considerably poorer in the beginning of the range of movement.

The object of the present invention is to provide an actuator which eliminates the above mentioned disadvantage and permits to achieve a high toning precision also in the beginning of the range of movement of the grab. This object is achieved with the actuator according to the invention which is characterized 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 connected 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 grab over a distance dorresponding to one dose is enlarged as compared to the range of movement of the power element required for larger doses. When using an electric 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 distance 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 precision 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 motor.

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 reduce the toning precision even when using small toner 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, Figures 2, 3 and 4 illustrate on an enlarged scale a motor-driven embodiment of an actuator according to the invention in the lower dead point position, central position and upper dead point position, respectively, 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 rotatably mounted in a machine frame 8 and is articulated to a connecting rod 10 connected at its upper end to a grab 11 slidably mounted on a vertical guide 1 2. 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 ll of its path of movement where it has displaced the piston rod to the uppermost position, as shown in Figure 4.

The 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 iargest 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 movement a of the crank causes only a reiatively 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 range 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 substantially 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 1 5, Fig. 5, can be used as power element for the crank. The setting scale 1 6 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 required 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.

The drawing and the description associated therewith are only intended to illustrate the idea of the invention. In its details, the actoator 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 1 5 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 connecting rod with a slide structure, in which the slide 1 7 is fastened to the grab and the outer end of the crank 9 is mounted on horizontal guides 1 8 in the slide, as illustrated in Figure 6. The slide is vertically movable on the guide 12.

Claims

1. An actuator for a dosing pump, especially for a paint toning machine, comprising -a a grab (11) engaging the piston (7) of the dosing pump, and - apower-driven transfer means for transferring the grab between two extreme positions (I, II) in which the piston of the dosing pump is located in a position corresponding to an empty pump and a position corresponding to a full pump, characterized in that - the transfer means comprises a crank mechanism (9,10; 9, including a crank (9) driven by means of a power element (14; 15) and a transfer element (10; 17) provided with a grab (11) and connected to said crank, and - the crank (9) 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 (I) corresponding to an empty pump.

2. An actuator according to claim 1, characterized in that the transfer element comprises a connecting rod (10) rotatably connected to the outer end of the crank (9).

3. An actuator according to claim 2, characterized in that the grab (11) in the connecting rod (10) is mounted for movement along a guide (12) parallel to the movement of the piston (7).

4. An actuator according to claim 1, characterized in that the transfer element comprises a slide (17) in which the outer end of the crank (9) is movably mounted on a guide (18) and which is mounted for movement along a vertical guide (12).

5. An actuator according to any of the claims 1 to 4, characterized in that power element rotating the crank (9) comprises an electric motor (14).

6. An actuator according to any of the claims 1 to 4, characterized in that the power element rotating the crank (9) comprises a hand crank (15).

7. An actuator according to any of the preceding claims, characterized in that the crank (9) is arranged to be located at its second dead point with respect to the transfer movement of the grab ( 1 1 ) when the grab is located in the extreme position (II) corresponding to a full pump (2).