[0002] Paint toning machines have been applied widely and for long in the toning of paint with a toning paste, i. e. when small amounts of strong toning pastes are fed into a container containing basic paint, thus providing a paint with a desired tone. There are conventionally two types of paint toning machines. In one type of machines, the containers for toning paste, or at least piston pumps connected thereto, are arranged in a circle, so that when the circle of piston pumps is rotated, a desired feeding pump can be placed above the container for basic paint for feeding paste thereto. Such a paint toning machine is called a carousel-type machine. In such a machine each toning paste must be fed separately, which makes the feeding process slow, particularly if it is necessary, as usual, to mix several types of toning paste with the basic paint. The carousel-type structure also limits the size of the containers for toning paste both due to its outer dimensions and its weight, since the containers in the carousel-type machine are usually supported on a rotating base together with the feeding pumps.

[0003] In the other type of paint toning machines, the containers for toning paste are positioned in an array with fixed positions typically in a rectangular shape, and the piston rods of the piston pumps provided in connection with the containers are connected to a common driving mechanism, which enables the piston rods of all the piston pumps to be lifted or lowered simultaneously. This significantly accelerates the feeding, since several different toning pastes can now be administered simultaneously.

However, a problem with such a machine is that the driving mechanism for the piston rods of the piston pumps operates nonlinearly as a result of the use of lever arms in the mechanism for moving the piston rods. This means in practice that the speed of rotation of the motor that drives the lifting gear for the piston rods of the piston pumps is nonlinearly proportional to the movement of the piston rods of the pumps. Therefore each amount to be fed

requires determination of specific pulse numbers or speeds of rotations of the driving motor, such as a servomotor, which are not linearly dependent on the respective amount to be fed. Another problem with such a paint toning machine is that the driving motor should be rather powerful and have a great motor torque, since all the piston pumps must always be used simultaneously.

Such a machine does not typically comprise coupling or other arrangements for disconnecting the piston pumps from the driving mechanism when they are not needed. Furthermore, such continuous operation, which can even be unnecessary, also means that the machine and the pumps thereof wear more rapidly.

SUMMARY OF THE INVENTION [0004] An objective of the present invention is thus to provide a new type of paint toning machine, where the feeding can be carried out rapidly, efficiently and accurately, but with a low-power driving motor. Another object is to provide a paint toning machine whose basic structure hardly limits the size of the containers for toning paste in the machine or the number of the different paints to be fed. This is achieved with a paint toning machine according to the invention, which is characterized in that the driving means comprise a device for changing the rotary motion of the shaft driven by the servomotor in different directions of rotation into linear motion moving the piston rod of the piston pump in opposite directions, and a coupling for selectively coupling the piston rod of the piston pump and the shaft driven by the servomotor into engagement via said changing device.

[0005] A basic idea of the paint toning machine according to the invention is to use a rotating shaft whose rotary motion in opposite directions is converted by a suitable changing mechanism into reciprocating linear motion, which is connected to drive the piston pumps of the paint toning machine.

Since only a small amount of power is required for such a use, one driving shaft can drive a plurality of piston pumps. Furthermore, an essential advantage of the structure is that each step or revolution of the driving motor corresponds to an equal movement of the piston rod regardless of the original position of the rod at the beginning of the movement.

[0006] In a preferred embodiment of the invention, the device for changing the rotary motion of the shaft driven by the servomotor into reciprocating motion of the piston rod comprises a gearwheel arranged on the

shaft driven by the servomotor, and toothing, provided in the piston rod of the piston pump, which can be arranged to engage the teeth of the gearwheel. In another preferred embodiment, the device for changing the rotary motion of the shaft driven by the servomotor into reciprocating motion of the piston rod comprises a spring band or some other corresponding flexible element, which is incompressible in its longitudinal direction, which is connected to the piston rod and arranged to be wound around or unwound from a ring provided around the shaft driven by the servomotor and possibly coupled to be rotated together with the shaft by means of the aforementioned coupling, depending on the direction of rotation of the shaft driven by the servomotor.

[0007] The paint toning machine according to the invention can be made more compact by providing two piston pumps with a single device for changing the rotary motion of the shaft driven by the servomotor in different directions of rotation into linear motion that moves the piston rod of the piston pump in opposite directions. In such a case the two piston pumps form a pair where one pump sucks fluid into itself while the other one forces it out. This compact structure is further improved by an embodiment where the piston pumps of the pair are arranged opposite one another, such that the piston rods thereof are combined into a single rod.

[0008] In order to provide a suitable speed of rotation for the shaft driving the piston pumps, the paint toning machine according to the invention also comprises a reduction gear arranged between the servomotor and the driving shaft of the piston pumps. This reduction gear enables selecting a suitable speed of rotation and good torque for the driving shaft. As stated above, due to the aforementioned structure a single driving shaft can be provided with several mechanisms, which change the rotary motion of the shaft into linear motion moving the piston rod of either a single piston pump or a pair of pumps. In this manner, the desired number of the piston pumps in the paint toning machine can be easily achieved by only one motor where the length of the shaft driven by the motor is increased suitably, such that a required number of changing devices can be connected to the shaft for the specific number of piston pumps needed.

BRIEF DESCRIPTION OF THE DRAWINGS [0009] In the following, the paint toning machine according to the invention will be described in more detail with reference to the accompanying drawing, in which Figure 1 shows schematically an exemplary embodiment of the paint toning machine according to the invention, and Figure 2 shows in more detail a part of the paint toning machine shown in Figure 1.

DETAILED DESCRIPTION OF THE INVENTION [0010] Figure 1 shows schematically the basic structure of an exemplary embodiment of the paint toning machine according to the invention.

This machine usually comprises a servomotor 2, which is able to rotate a driving shaft 5 via a reduction gear 19. In the use according to the invention, the driving shaft 5 is rotated back and forth, and this reciprocating motion is converted into reciprocating linear motion of piston rods of feeding pumps. For the sake of simplicity, Figure 1 only shows two paint containers 11 and 12 in more detail. In the paint toning machine according to the invention, these containers can contain either toning paste or basic paint. The fact that basic paint can also be placed in a container for toning paste is somewhat different from the conventional practice in connection with paint toning machines.

However, the structure of the paint toning machine according to the invention also enables a procedure where the same machine also feeds the basic paint, in which case the process starts with an empty paint container into which the paint is fed.

[0011] The paint containers 11 and 12 are provided with piston pumps 3 and 4 for feeding the paint in the containers 11 and 12. The feeding is controlled by valves 15 to 18. In principle, the feeding takes place such that at the beginning the valve situated between the paint container and the piston pump, i. e. valve 15 or 17, is kept open and the piston pump sucks paint into the pump cylinder. The cylinder is typically filled up and the amount of paint to be fed is adjusted such that first, during the pumping phase, some of the paint in the cylinder is pumped back into the paint container, whereafter the piston rod is stopped. Then the valve to the paint container is closed, and the valve to a feed nozzle 13 or 14, i. e. valve 16 or 18, is opened and the motion of the

piston rod is continued so that the paint remaining in the cylinder of the piston pump can be discharged via the feed nozzle.

10012] In the paint toning machine according to the invention, the driving mechanism for the piston rods 7 of the piston pumps consists of a changing mechanism 10 arranged in connection with the shaft 5 driven by the servomotor 2, the mechanism changing the rotary motion of the driving shaft 5 into axial motion of the piston rod 7. An exemplary embodiment of such a mechanism is shown in Figure 2. In the figure, the piston rod 7 is a gear rack and the element 10 is a gearwheel. When the teeth of the gearwheel engage the gear rack, the gearwheel moves the gear rack with it, thus changing the rotary motion of the gearwheel into linear motion of the gear rack. The example of Figure 2 does not show a coupling 8.

[0013] Another exemplary embodiment of the changing device is an arrangement where the piston rods of the piston pumps are connected to a spring band or some other corresponding flexible element, which is incompressible in its longitudinal direction and is arranged to be wound around or unwound from a ring provided around the shaft driven by the servomotor and possibly connected to be rotated together with the shaft by means of the aforementioned coupling, depending on the direction of rotation of the shaft driven by the servomotor. Different arrangements with toothed belts or chains can also be used as a moving device.

[0014] The essential feature of the paint toning machine according to the invention is that it comprises for each piston pump a coupling 8 with which the piston rod of the piston pump can be coupled to engage the shaft 5 driven by the servomotor. This coupling can either couple the changing device 10 to rotate with the shaft 5, as shown in the embodiment of Figure 1, or it can couple the piston rod to engage the changing device 10. In the latter case the changing device is naturally connected permanently to rotate with the driving shaft 5.

[0015] In the embodiment of Figure 1, it is possible that the gearwheel 10 shown in Figure 2 is mounted in bearings in the driving shaft 5, and an annular part or coupling element 8, which is provided near the gearwheel 10, is arranged to rotate with the driving shaft. When the coupling element 8 is arranged to engage the gearwheel 10, the wheel is made to rotate with the driving shaft 5. Such an operation is illustrated in the diagram of Figure 1 by means of a solenoid 9, which is activated to press an appropriate

coupling part, such as a pin, of the ring 8 against the gearwheel 10, which then starts to rotate with the ring 8.

[0016] The coupling structure described above is only an exemplary embodiment. A person skilled in the art understands that various types of conventional coupling means that are obvious to those skilled in the art can be applied in a case where the forces that are to be coupled are not great. On the other hand, the coupling device requires that no slipping occurs but coupling leads to an immediate, non-slipping engagement.

[0017] The paint toning machine according to the invention is shown in Figure 1 as further comprising a control unit 6, which can be a general-purpose personal computer provided with suitable software. This control unit 6 controls the servomotor, the coupling 9 and the valves that are necessary for the feeding. Therefore, the feeding amounts of different paints or toning pastes that are required for each different tone of paint are programmed into the computer. As described above, several feeding pumps can be coupled simultaneously to the driving shaft 5, so that they can be used to feed several paints simultaneously. On the other hand, it is clear that when the couplings 8 are open, the piston pump in question does not move.

Therefore the piston pumps which are not intended to move either due to feeding or the agitation of paint in the paint container can be disconnected from the operation of the machine. This helps avoid unnecessary wearing of the machine and the piston pumps thereof.

[0018] As described above, the paint toning machine according to the invention enables feeding large amounts of basic paint together with small amounts of toning paste. This is based on the fact that both the paint containers and the piston pumps connected thereto can be of different sizes.

Therefore the paints that should be fed in large amounts can be placed in larger paint containers and fed by means of larger piston pumps.

[0019] Figure 2 shows in greater detail a unit used in connection with the paint toning machine according to the invention when the piston pumps are operated in pairs. Like reference numerals refer to like parts in Figures 1 and 2, and the denoted parts are also used similarly. Figure 2 illustrates how the rotation of the shaft 5 driven by the servomotor 2 in opposite directions also causes opposite movements in the two piston pumps coupled thereto. When the gearwheel rotated by the driving shaft 5 engages the piston rod of the piston pumps 3 and 4 arranged as a single gear rack 7,

the rotation of the driving shaft 5 in one direction results in a suction phase in one piston pump, and correspondingly the rotation of the shaft in the opposite direction leads to an opposite function in the other piston pump.

[0020] The use of such units as shown in Figure 2 as basic elements of the paint toning machine provides a very compact structure at low costs. On the other hand, it is obvious that with such a structure the paints in the paint containers 11 and 12 cannot be fed simultaneously but only in successive steps. However, in practice this does not significantly slow down the operation of the machine. The tones in the paint containers 11 and 12 can also be selected such that they are contained in the same toning formula as rarely as possible, so that in most cases all the necessary paints can be administered in one go. The movement of the other piston pump in the pair of pumps is also necessary since it can be used in the agitation of the paint in the paint container. This means in practice that paint is first sucked into the piston pump and then forced back to the paint container in order to agitate the paint.

It is necessary to agitate the paints every now and then in order to prevent them from solidifying.

[0021] The paint toning machine according to the invention is described above by means of only a few exemplary embodiments. Therefore it is clear that it can be modified in several manners with respect to mechanics without deviating, however, from the basic idea of the invention and the scope of protection defined in the appended claims.