EP3741468B1

EP3741468B1 - Apparatus and method for weighing the paint applied to a panel

Info

Publication number: EP3741468B1
Application number: EP20175889.3A
Authority: EP
Inventors: Fabrizio Filippini; Roberto Sorbini
Original assignee: Cefla SCARL
Current assignee: Cefla SCARL
Priority date: 2019-05-23
Filing date: 2020-05-21
Publication date: 2025-11-05
Anticipated expiration: 2040-05-21
Also published as: EP3741468A1

Description

The present invention relates to an apparatus and a method to detect the quantity of paint applied to a product, preferably a mainly flat panel.
A mainly flat panel means a panel wherein two of the three dimensions are much larger than the third dimension. Typically, the measures of such panels range 300x300x18 mm to 1250x2400x30 mm.
In the art, applying paint to such panels using apparatuses that spray or apply paint through a roller is known. Applying paint with the aim of ennobling the basic panel is also known; the panel can be made of a low quality material like plywood or MDF, while when painted it can look made of solid wood, even of a precious wood essence like e.g. durmast.
It is apparent that the quality of the finished product depends on the thickness of the applied paint: the thicker the paint layer, the more the paint can mask possible defects of the basic material.
With the aim of monitoring the industrial process of panel finishing, too, detecting the thickness of the paint applied to a given panel is desirable.
As of today, this detection is manually made, by weighing on a scale a test panel before and after paint application, which is a cumbersome and complex process, as can be inferred from the following description.
Generally, the process for monitoring the quantity of paint applied to a panel comprises the following steps:

1. The painting process starts with a basic adjustment of the apparatus due to the human operator's experience;
2. Alternatively to the preceding point, when the paint applying apparatus is provided with an automatic positioning system and a system for the recall of previously saved working programs, a working program is recalled, which comprises all the necessary parameters;
3. A test panel of known dimension is used, generally a tenth of square meter in order to facilitate calculation; the panel must have the same features in terms of paint absorption as the panels that are painted in the painting line;
4. The test panel is weighed on an at least decimal precision scale;
5. The test panel is painted;
6. The test panel is weighed on the scale quoted at point 4;
7. The weight of the applied paint by square meter is calculated by difference;
8. If necessary, the applied paint is adjusted and the check procedure (points 3-7) is repeated until the target is reached;
9. Periodically, the check of the paint applied is repeated, at least every 30 minutes, on each apparatus of the painting line.

Although the weighing method is quite complex, it is nonetheless easier than the direct measuring of the thickness of the applied film, which is extremely difficult to perform.
Typically, an apparatus for applying paint on products using the roller technology is provided with a conveying system, on which panels to be painted are laying. The panels are brought near the application head, made of two rollers: a first chromed dosing roller and a second rubber applying roller. The paint is withdrawn from a tank through a pump, and conveyed to a tank formed by said pair of rollers, which are pressurized.
The transposition of the paint from the applying roller onto the panel occurs through pressure. The quantity of paint is adjusted through the variation of the pressure applied by the dosing roller on the applying roller.
Advantageously, a load cell system can be used, measuring the thrust force of the dosing roller into the applying roller. In this way, an indication exactly proportional to the variation of the applied paint weight is obtained.
One of the documents disclosing systems to monitor the thickness of a layer of paint applied to a product is KR20170053901A of Daewoo Shipbuilding & Marine . It discloses a device and a method to evaluate the transfer efficiency of a spray-painting apparatus. Said apparatus comprises a weight measuring sensor, capable of measuring the variation of weight of the paint in a storage container. The method comprises the following steps: applying a paint coating to a test part according to a condition of spray painting to be evaluated; measuring a weight variation of the paint after the spray application; calculating the volume of the paint used for the application based on a weight variation of the paint and the density of the paint; drying the painted sample measuring the thickness of a dried paint film applied to the sample; inversely calculating the volume of a wet paint film before being dried considering a solid rate of the paint, and calculating the transfer efficiency of the paint based on the volume of the wet paint film and the volume of the paint used for the application.
Another document is CN108704800 of Jiangsu Zhongyue Coating Equipment CO LTD. The weight of the paint required for each spray is pre-set by a controller; a weight sensor detects the weight of the paint in a first barrel in real time; the controller receives the weight parameter sent by the weight sensor, and compares the weight before and after spraying. If the weight difference is lower than the pre-set value, the controller opens a first solenoid valve; if it is higher, the controller reduces the opening of said solenoid valve, adjusting the quantity of applied paint.
JP2001-038273 (Dainippon Ink & Chemicals) discloses an apparatus and a method for applying paint to panels by means of rollers comprising:

a transport device of the said panels preferably in the form of a closed belt conveyor;
a pair of rollers, a first dosing roller and a second applicator roller, for applying the said paint to said panels;
a control unit able to detect and to process the parameters coming from the detection system of the said apparatus;
a paint tank;
a detection bar for detecting the dimensions of the said panels while they are passing.

This apparatus comprising e weighting device, which determines the weight of the entire apparatus, before and after applying the paint to the panels and which is calculates as the value of the reduction in weight of the paint.
JP 2009 233616 (Nisshin Steel Co. Ltd.) discloses a control method for an apparatus comprising rollers for coating metal plates and which is able to prevent the deposition of an anomalous quantity of coating on said plates by means of a feed-back mechanism which determines the quantity of coating deposited on the said plates.
In the art, using detecting bars in order to detect the dimensions of the parts to be painted when passing is known.
A detecting bar typically comprises three basic elements:

A lamp emitting light placed above the panel conveying system and before the applying machine/s, having the same width as the maximal dimension of the panels to be painted;
A bar of photosensors placed under the light emitting lamp, in a suitable position in order to allow the passing of panels between said lamp and photosensor bar, so that said panels darken a number of photosensors equal to their width; generally said photosensor bar is placed between two rollers of the conveying system;
A control and processing system calculating the area of the panel/s when passing according to the work speed and the number of darkened photosensors; the control system sends then the datum to the line controller or to the control unit of the roller applying apparatus.

Finally, it is known that the stability of paint temperature in roller apparatuses is fundamental in order to prevent variations in paint viscosity, that in their turn produce significant variations of the weight of the applied paint.
Aim of the present invention is providing an apparatus and a method for measuring the layer of paint applied to products, which is rapid, automated and cheap.
This object is achieved by an apparatus and a method having the features of the independent claims. Advantageous embodiments and refinements are specified in claims dependent thereon.
The apparatus according to the present invention is defined by claim 1 and comprises a weight sensor applied to a paint tank, from which paint is withdrawn to apply it to said panel. Said sensor allows to evaluate the quantity of paint applied to one or more products. Moreover, said apparatus comprises a sensor capable of measuring the dimension of the panel when passing. Said parameters are sent to a control unit capable of processing them and calculate the quantity of paint applied to panels in the form of weight/surface.
The method according to the present invention is defined by claim 4 and comprises the following steps:

a. Measuring the dimensions of one or more panels before its/their entry into an apparatus for applying paint, preferably a roller apparatus, when passing through a detecting bar provided with a suitable software;
b. Painting said panel/s;
c. Measuring the quantity of paint contained in the paint tank before and after the application of paint to the pre-set number of panels;
d. Through a control unit, periodically dividing the quantity of applied paint detected through the weight measured in the paint tank by the surface on which it was applied, obtaining a parameter expressed in weight/surface (generally g/m²).

A first advantage of the present invention consists in the possibility of automating the process of weighing the paint applied to a panel, which can be performed in the production line, without stopping the production line, without the need for test panels, without dedicating a human operator to this operation.
A second advantage of the present invention consists in the improved control of the industrial process of applying paint through roller technology.
A third advantage comes from the fact that the apparatus to perform said method requires a minimum number of additional components with respect to the known art, which translates into an apparatus with a reasonable cost.
Further advantages and properties of the present invention are disclosed in the following description, in which exemplary embodiments of the present invention are explained in detail on the basis of the drawings:

Figure 1: Axonometric view of an apparatus for applying paint according to the present invention;
Figure 2: View of the paint tank in a lateral and in a front view.

Figure 1 shows an axonometric view of a painting production line 1, comprising a plurality of (not shown) apparatuses, among which there is provided an apparatus 2 for applying paint to products, using the roller technology. The bold arrow shows the feeding direction of the products in the production line.
A panel 4 to be painted is conveyed to said apparatus 2 through a band conveyor 5. Before entering into said apparatus 2, said panel 4 is measured when passing by a detecting bar 3, which detects its top dimensions and sends them to a control unit.
In the apparatus 2, said panel is painted through rollers when passing; the Figure shows a painted panel 4V coming out from said apparatus 2. The roller technology used in this apparatus is known art, and therefore is not described in detail.
Here will suffice to say that the weight of applied paint through a roller apparatus is adjusted by varying the pressure of the dosing roller applied on the applying roller through a suitable slide, and using a manual or motorized jack.
The position of the dosing roller with respect to the applying roller is detected through mechanical or digital position markers, detecting the change of position of the dosing roller in its translational motion toward the applying roller.
Said position can be adjusted through a control unit, when said jacks are provided with a motor; conversely, on the screen of the control unit of the apparatus or of the production line, one can read the applied adjustment.
Advantageously, a load cell system is provided, measuring the thrust force of the dosing roller into the applying roller. In this way, an indication exactly proportional to the variation of the applied paint weight is obtained.
As customary in the known art roller apparatuses, in said apparatus 2 for applying paint through rollers, there is provided a tank containing the paint to be applied.
Figure 2 shows said tank 6 in a side and in a front view. Said tank is provided with a load cell 7, allowing to detect the weight variation due to paint withdrawal. This parameter, too, is sent to said control unit.
The use of a load cell is advantageous in that it allows to obtain the weight in kilograms of the tank containing said paint.
Moreover, said tank is provided with a temperature-adjusting system of the paint contained inside it. E.g., in an embodiment, said paint tank 6 is in the form of a first steel tank contained in a second tank, so that the gap is filled with diathermic oil, which is heated through an electrical resistance controlled by a pyrometer.
The method according to the present invention comprises the following steps:

a. Measuring the dimensions of one or more panels 4 before their entry into an apparatus 2 for applying paint when passing, through said detecting bar 3 provided with a suitable software, said parameter being sent to a control unit;
b. Painting, preferably roller painting, said panels 4;
c. Measuring the quantity of paint contained in said paint tank 6 before and after the painting of the pre-set number of panels; said parameter being sent to the same control unit;
d. Through said (not shown) control unit, periodically dividing the quantity of applied paint detected through paint weighing by the surface on which it was applied, obtaining a parameter expressed in weight/surface (g/m²).

Upstream of said steps, the apparatus 2 for roller painting is adjusted with basic parameters taken from the experience of the human operator, or alternatively, when the painting apparatus is provided with automated positioning and working program recalling systems, recalling a working program containing all the necessary parameters.
Moreover, again upstream of said steps, the temperature of the paint contained inside paint tank 6 is adjusted, in that, as explained, variations of paint viscosity can produce significant variations of the paint weight applied to panel 4.
The software of the control unit can detect the signal coming from said detecting bar 3, and the signal of the weight of the paint contained in said tank 6 detected by said load cell 7, and process said data with the aim of obtaining the datum relative to the quantity of paint applied on panel 4V. Said parameter is shown on a screen 8 of said apparatus 2, or on a different (not shown) screen of said painting line 1.
In an embodiment, said screen can be a touch screen and therefore can be used both to read data, and to input the desired parameters into the painting apparatus 2 (paint temperature, transit speed of panels, quantity of paint to be applied, etc.).
The following is an example of a real situation:

Into said apparatus six big panels (1250x2400 mm) are successively fed;
Each panel is provided of a surface of 3 m²;
For a total of six panels there are provided 18 m² of painted surface;
The consumption of paint is 300 g for each panel;
For the six panels a consumption of 1,800 g of paint is recorded.

Therefore, there is applied 100 g/m² of paint, which is the customary way of indicating the quantity of paint applied on the panel 4V in the art.
It is worthwhile observing that the same method, that is measuring the surface of the panel to be painted, weighing the quantity of paint withdrawn from the paint tank, sending said parameters to a control unit processing them and producing the value of the paint applied in the form of weight/surface, can be applied to an apparatus applying paint with spraying technology.

1: painting production line
2: roller apparatus for applying paint
3: detecting bar
4: panel
5: band conveyor
6: paint tank
7: load cell
8: screen

Claims

Apparatus (2) for applying paint to products, preferably to panels (4), using rollers, comprising at least the following components:
- a device (5) conveying said panels, preferably in the form of a band conveyor;

- a pair of rollers, a first dosing roller and a second applying roller for applying paint to said panels;

- a control unit capable of detecting parameters coming from a detecting system of said apparatus,

- a paint tank (6) containing the paint to be applied and comprising a measuring device, in the form of a load cell (7), capable of detecting the weight variation of the paint contained in said tank;

- a detecting bar (3) for detecting the dimensions of said panels when passing, preferably placed before the entry of said panels into said apparatus (2);
characterized in that it comprises a load cell system measuring the thrust force of the dosing roller into the applying roller providing an indication exactly proportional to the variation of the applied paint weight;
- means capable of maintaining said paint in said tank (6) at a constant temperature.

- the control unit being configured by a software for detecting the signal coming from said detecting bar (3), and the signal of the variation of the weight of the paint contained in said tank 6 detected by said load cell (7) to obtain the quantity of paint applied on said panel.
Apparatus (2) for applying paint to panels (4) using roller technology according to claim 1, further comprising a screen (8) allowing to read the parameters applied to the industrial process of painting panels (4).
Apparatus (2) for applying paint to panels (4) using roller technology according to claim 2, wherein said screen (8) is a touch screen, allowing to input the parameters of the painting process, parameters taken from the group consisting of transit speed of panels (4), adjustment of the quantity of supplied paint, temperature of supplied paint.
Method for detecting the quantity of paint applied to products using the apparatus as in the previous claims,
characterized in that it comprises the following steps:
a. measuring when passing the dimensions of one or more panels (4) through the detecting bar (3) provided with a suitable software, before its/their entry into said apparatus (1), said parameter being sent to the control unit;

b. painting said panel/s (4);

c. measuring the quantity of paint contained in the paint tank (6) before and after the painting of the pre-set number of panels (4); said datum being sent to the same control unit by a weight sensor applied to the paint tank;

d. through said control unit, periodically dividing the quantity of supplied paint detected by the surface on which it was applied, obtaining a parameter expressed in weight/surface,

e. further comprising the following step upstream step a):
adjusting the temperature of the paint applied to said panels (4), by working on the paint tank (6).