Coating product application installation and method for controlling such an installation

Abstract

This coating product application system (I) includes a print head (10) equipped with several nozzles (12), each controlled by a valve (14) supplied by a product source (32). A product accumulator (100), installed on a product circulation circuit (C), includes a deformable or movable wall (102) that at least partially delimits a first variable-volume chamber (C102) supplied with coating product and a second variable-volume chamber (C104) supplied with gas, under a predetermined pressure equal to the nominal operating pressure of the print head (10). The first variable-volume chamber (C102) is supplied or purged with coating product due to a difference between an instantaneous ejection flow rate (Q10) of coating product from the print head (10) and a supply flow rate (Q32) to the print head from the source (32).A control unit (130) adjusts a setpoint value (S130) for the operation of the source (32) as a function of the difference between the instantaneous ejection flow rate and the supply flow rate, in a direction of reducing this difference.

Description

[0001] The present invention relates to a coating product application installation which comprises a print head equipped with several nozzles and supplied by a source of coating product.

[0002] In this type of equipment, each nozzle defines a coating product discharge orifice with a small diameter, in the order of 100 to 300 micrometers (µm). Each nozzle is controlled by a valve, itself supplied by the coating product source. The operation of a print head requires high precision in controlling the pressure of the coating product supplied to the print head. This is especially true if the product is viscous, for example with a dynamic viscosity between 50 and 300 milliPascal.seconds (mPa.s).

[0003] In a coating product application installation with a print head, the potentially viscous coating product must be supplied to the various nozzles with a given supply pressure, for example, equal to 2 bar. In practice, in the case where the nominal coating product supply pressure of the print head is equal to 2 bar, if this pressure is higher than 2.1 bar, there is a risk of creating a parasitic paint cloud, known as "overspray". Conversely, if the supply pressure is lower than 1.9 bar, the instantaneous flow rate of coating product in one or more nozzles may not allow the formation of a continuous or quasi-continuous stream at the nozzle outlet. This is why the desired precision in the coating product supply pressure, at the inlet of a print head, is of the order of 100 millibars (mbar).However, this supply pressure depends on the instantaneous flow rate of coating product in the print head.

[0004] The instantaneous flow of coating material through the various nozzle orifices of the print head results from the opening / closing of the valves that control these different nozzles and which have a response time of the order of 1 millisecond (ms). In a coating material application installation, a source of coating material is used to supply a print head. This source of coating material can be a pressurized coating material tank or a piston tank controlled by an electric motor or other equipment. In all cases, the response time of such equipment is of the order of 500 ms.

[0005] On the other hand, the supply of a print head with coating product, from a source of coating product, takes place through a pipe which can have a length of several meters, for example if the print head is arranged at the end of the arm of a multi-axis robot, while the print source is arranged at the foot of this robot. This pipe induces regular pressure losses, due to its length and its diameter, as well as singular pressure losses, due to the valves, filters and / or elbows arranged along the length of this pipe.

[0006] For all these reasons, the inlet pressure of a printhead is relatively difficult to manage based solely on means of controlling the coating product source.

[0007] A known solution in the field of ink application consists of continuously circulating a relatively high flow rate of coating product and taking a flow rate of around 10% of this relatively high flow rate to supply nozzles of a print head. This induces a continuous circulation of the ink which is not transposable to the application of a paint-type coating product because the shear due to the repeated circulation of the coating product would risk damaging the paint. In addition, a significant flow rate of coating product would have to be brought to the print head, for example equal to 2 liters per minute (l / min) so that 10% of this flow rate represents approximately 200 ml / min. Bringing 2 l / min of coating product to the end of a robot arm turns out to be, in practice, very complicated.

[0008] Another solution which seems obvious but poses integration difficulties because it is bulky, consists of integrating a pressurized product tank or a motorized tank in the immediate vicinity of the print head, or even integrated into the head.

[0009] It is also known from US-A-2019 / 0337001 to provide a coating product control with two print heads, namely a print head used to apply a coating product and a print head arranged on an exhaust pipe. Provision is made to close one of the print nozzles of the exhaust print head when a print nozzle of the print head used to apply the coating product is opened, and vice versa, which makes it possible to use a quasi-constant flow rate of coating product. This leads to a high consumption of coating product, with significant consequences in terms of reprocessing and cost.

[0010] On the other hand, EP-A-2574471 discloses an ink application installation in which a print head is supplied from a reservoir, through a pump and a sub-reservoir equipped with a flexible wall. The operation of the pump is adjusted according to a pressure in a passage provided between the sub-reservoir and the print head, which does not allow the flow of ink actually ejected by the print head to be taken into account.

[0011] It is these drawbacks that the invention more particularly intends to remedy by proposing a new installation for applying coating product in which a supply pressure of a printing head with coating product can be precisely controlled, taking into account the respective response times of the valves of the printing head and of the control members of a source of coating product.

[0012] To this end, the invention relates to a coating product application installation comprising a print head equipped with several nozzles and supplied by a source of coating product, each nozzle being controlled by a valve supplied by the source of coating product. According to the invention, the installation comprises a coating product accumulator installed on a coating product circulation circuit, which passes through the print head, this accumulator comprising a deformable or movable wall delimiting at least in part a first chamber of variable volume supplied with coating product and a second chamber of variable volume supplied with gas under a predetermined pressure. The predetermined supply pressure of the second variable volume chamber is equal to a nominal operating pressure of the print head.The first variable volume chamber is supplied or purged with coating product due to a difference between an instantaneous ejection flow rate of coating product by the print head and a supply flow rate of the print head from the coating product source. The installation comprises means for detecting a difference between the instantaneous ejection flow rate and the supply flow rate. The installation further comprises a control unit configured to adjust an operating setpoint value of the coating product source as a function of the difference between the instantaneous ejection flow rate and the supply flow rate, in a direction of reducing this difference between the flow rates.

[0013] By virtue of the invention, the accumulator can be sized so that the deformation or displacement of its wall allows a sufficient volume of coating product to be stored to compensate for a variation in pressure of the coating product at the inlet of the print head, during the response time of the source of coating product. The invention also makes it possible to take into account possible variations in pressure losses in a supply line connecting the source of coating product to the print head. Since the second variable volume chamber is supplied with a pressure equal to the nominal operating pressure of the print head and taking into account the deformable or mobile nature of the wall, it can be assumed that the pressure in the first variable volume chamber is equal to the nominal operating pressure of the print head.In addition, the control unit can control the coating product source according to the difference between the instantaneous ejection flow rate and the feed flow rate in an optimized manner, reducing this difference, which automatically adapts the coating product flow rate delivered by the source to the flow rate actually ejected by the print head.

[0014] According to the advantageous but not obligatory aspects of the invention, such an installation may incorporate one or more of the following characteristics taken in any technically admissible combination: The means for detecting the difference between the instantaneous ejection flow rate and the feed flow rate comprise a sensor, configured to detect a deformation or a displacement of the wall of the accumulator, while the control unit is configured to adjust the operating setpoint value of the coating product source, according to an output signal from the sensor. The position sensor is of the inductive, capacitive, optical type or constituted by a probe. The means for detecting the difference between the instantaneous ejection flow rate and the feed flow rate comprise a first unit for determining the instantaneous ejection flow rate, a second unit for determining the feed flow rate and a control unit is configured to adjust the operating setpoint value according to a difference between the instantaneous ejection flow rate determined by the first unit and the feed flow rate determined by the second unit.The wall is elastically deformable under normal operating conditions of the installation while, preferably, the wall carries an element whose position is detectable by the sensor. The deformable wall of the accumulator is housed in a rigid casing, while the first variable volume chamber is defined inside the deformable wall, while the second variable volume chamber is defined between the deformable wall and the rigid casing, or vice versa. The deformable wall is sleeve-shaped and extends between a first coating product inlet orifice in the accumulator and a second coating product outlet orifice from the accumulator. The wall is a movable piston which separates the two variable volume chambers.The maximum deformation of the deformable wall or the displacement stroke of the movable piston is compatible with a variation in the volume of the first variable volume chamber equal to the sum of the maximum flow rates of the nozzles of the print head multiplied by the response time of the coating product source. The second variable volume chamber is provided with an outlet opening and the second variable volume chamber is supplied with a permanent circulation of gas, between a supply line and its outlet opening. The accumulator is installed, in the circuit, downstream of the print head. The accumulator is installed, in the circuit, upstream of the print head.

[0015] According to another aspect, the invention relates to a first method for controlling an installation as mentioned above, this method comprising at least steps consisting of: a) deducing from a deformation or a displacement of the wall information on the direction of change in the size of an internal volume of the first variable volume chamber of the accumulator; b) if the information deduced in step a) corresponds to an increase in the internal volume, adjusting downwards the operating setpoint value of the source of coating product; and c) if the information deduced in step a) corresponds to a decrease in the internal volume, adjusting upwards the operating setpoint value of the source of coating product.

[0016] Advantageously, the operating setpoint is a control pressure of a pressure tank, a displacement speed of a piston of a piston tank or a rotation speed of a volumetric pump.

[0017] According to yet another aspect, the invention relates to a second method for controlling an installation as mentioned above, this method comprising at least steps consisting of: a') calculating a difference between the instantaneous flow rate of coating product through the print head and the flow rate of supply of coating product to the print head; b') if the difference calculated in step a') is positive, adjusting upwards a set value of flow rate of supply of coating product to the print head; and c') if the difference calculated in step a') is negative, adjusting downwards a set value of flow rate of supply of coating product to the print head.

[0018] The invention will be better understood and other advantages thereof will appear more clearly in the light of the following description of three embodiments of an installation and a method in accordance with its principle, given solely by way of example and with reference to the appended drawings in which: [ Fig.1 ] There figure 1 is a schematic representation of the principle of an installation for applying a coating product in accordance with the invention; [ Fig.2 ] There figure 2 is a fluid and electrical diagram of the installation of the figure 1 ; [ Fig.3 ] There figure 3 is a diagram analogous to the figure 2 , for an installation in accordance with a second embodiment of the invention; and [ Fig.4 ] There figure 4 is a diagram analogous to the figure 2 , for an installation in accordance with a third embodiment of the invention.

[0019] On the figures 2 And 3, thick solid lines are used to represent coating product circulation lines, thick dotted lines are used to represent solvent or cleaning product circulation lines, thin solid lines are used to represent air circulation lines and thick center lines are used to represent electrical conductors for electrical signal circulation.

[0020] Installation I represented at figures 1 And 2 is intended for the application of paint to objects O which, in the example of the figures, are motor vehicle bodies. More specifically, in this example, the installation I aims to enable the creation of a band B of contrasting color, for example black, on the roof of a body.

[0021] Alternatively, the objects to be coated may be parts of a motor vehicle body, for example bumpers or, more generally, any object that can be coated, for example a part of an aircraft fuselage or a household appliance body, these examples not being limiting.

[0022] Furthermore, the coating product applied with installation I of the invention does not necessarily constitute a contrasting color band.

[0023] This coating product can be a paint, a primer or a varnish or a water-soluble or solvent-based base, a two-component coating. In particular, its dynamic viscosity can be between 50 and 300 mPa.s.

[0024] The installation I comprises a conveyor 2 intended to move the objects O along a conveyor axis X2 perpendicular to the plane of the figure 1 .

[0025] The installation I also comprises a print head 10 mounted at the end of the arm 22 of a multi-axis robot 20 arranged in the vicinity of the conveyor 2. The print head 10 is supplied with coating product to be applied from a supply module 30 which comprises a source of coating product to be applied formed here by a pressure tank 32.

[0026] The module 30 is connected to the print head 10 by a supply line 40 which circulates inside the multi-axis robot 20, in particular inside its arm 22.

[0027] The module 30 comprises a piloted solenoid valve 34 connected, on the upstream side, to a source of pressurized air which delivers air with a pressure equal to 6 bars. On the downstream side, the solenoid valve 34 is connected to the internal volume V32 of the pressure tank 32. A pressure gauge 38 makes it possible to know the pressure of the air delivered by the solenoid valve 34.

[0028] An upstream end 42 of the supply line 40 plunges into the pressure tank. A first cut-off valve 43 and a first filter 44 are arranged on the line 40, in its upstream part, inside the supply module 30.

[0029] A downstream end of the supply line 40 is connected to the print head 10 which is therefore supplied with coating product from the source of coating product, through the line 40. The pressure of the coating product at the inlet of the print head depends on the pressure of the coating product supplied by the pressure tank and the pressure losses in the supply line, which can vary depending on the position of the arm 22.

[0030] A control module 50 is arranged near the print head 10, for example in the arm 22 of the multi-axis robot 20. By "near" is meant that the supply module is located less than one meter, preferably less than 50 cm, more preferably less than 20 cm, from the print head. The supply line 40 passes through the control module 50. At this module 50, the line 40 is equipped with a second cut-off valve 45 and a second filter 47.

[0031] For example, the first filter 44 may be configured to retain elements whose maximum dimension is greater than 40 µm, while the second filter 47 is configured to retain elements whose maximum dimension is greater than 20 µm.

[0032] A second pipe 60, for supplying the print head 10 with solvent or cleaning product, is connected to the pipe 40, downstream of the second cut-off valve 45. This pipe 60 is itself equipped with a third cut-off valve 62 and connected to a source of solvent (not shown), which may be a reservoir or a closed-loop circulation circuit, sometimes called “circulating”.

[0033] The print head 10 is equipped with several nozzles 12, each of which is configured to deliver a jet J12 of coating product to be applied to an object O.

[0034] Each nozzle 12 defines a coating product discharge orifice, not shown, whose diameter is of the order of 100 to 300 µm. Each nozzle 12 is controlled by a valve 14 which is itself supplied with coating product via the pipe 40. The valves 14 may be of the type known from EP-A-2442983 or from US-B-9638350, the technical teaching of which is incorporated into the present application, by reference.

[0035] The valves 14 are controlled electrically or pneumatically, in a manner known per se.

[0036] A third evacuation pipe 70 connects the print head 10 to a purge 80. The upstream end 72 of the pipe 70 is connected to the print head 10, while its downstream end 76 opens onto the purge 80. A fourth cut-off valve 74 is mounted on the pipe 70.

[0037] Lines 40 and 70 together constitute a circuit C which connects the coating product source 32 to the purge 80 and which passes through the print head 10.

[0038] A fourth pipe 90 connects a source 96 of pressurized air to the print head 10, being controlled by a solenoid valve 94 equipped with a pressure gauge 98. A pressure sensor 92 is arranged on the pipe 90 and makes it possible to control the pressure supplying the print head 10 with pressurized air, with a predetermined pressure, for example equal to 2 bars. This pressurized air makes it possible to supply the nozzle opening actuators.

[0039] An accumulator 100 is arranged on the pipe 70, i.e. downstream of the print head 10 in the direction of circulation of the coating product between the coating product source 32 and the purge 80. The accumulator 100 is therefore installed on the circuit C.

[0040] This accumulator 100 comprises a deformable wall 102 and a rigid casing 104 which surrounds the deformable wall.

[0041] On the one hand, the deformable wall 102 defines an internal chamber C102 supplied with coating product exiting the print head 10. Given the deformable nature of the wall 102, the internal chamber C102 is of variable volume.

[0042] We note respectively Q10 the instantaneous flow rate of ejection of coating product by the print head 12, Q32 the flow rate of supply of the print head by the pressure tank 32 and Q'10 the flow rate of supply of the accumulator 100 by the print head.

[0043] We have the relationship: Q32 = Q10 + Q ′ 10

[0044] This can be expressed as follows: Q ′ 10 = Q32 − Q10

[0045] It follows from equation 2 that the flow rate Q'10 can be positive or negative. If the flow rate Q10 is strictly less than the flow rate Q32, the flow rate Q'10 is positive and the variable volume chamber C102 is gradually supplied with coating product. If the flow rate Q10 is strictly greater than the flow rate Q32, the flow rate Q'10 is negative and the variable volume chamber C102 is gradually purged of the coating product it contains.

[0046] On the other hand, a peripheral chamber C104 is defined around the deformable wall 102, inside the rigid envelope 104. Given the deformable nature of the wall 102, the peripheral chamber C104 is also of variable volume.

[0047] By deformable, it is meant that the wall 102 is elastically deformable, under the effect of a difference in fluid pressure between the variable volume chambers C102 and C104, under normal conditions of use of the installation I, in particular in terms of temperature and pressure of the coating product.

[0048] Here, the deformable wall 102 is sleeve-shaped and extends between a first inlet orifice 106 for the coating product coming from the print head 10 into the internal chamber C102, i.e. into the accumulator 100, and a second orifice 108 for discharging the coating product from the accumulator 100, in the direction of the purge 80.

[0049] A pressure sensor 78 makes it possible to detect the pressure of the coating product in the portion of the pipe 70 connecting the print head 10 and the accumulator 100.

[0050] The peripheral chamber C104 is supplied with pressurized air through a fifth pipe 110 equipped with a piloted solenoid valve 114, the upstream side of which is connected to a source 116 of pressurized air and which is associated with a pressure gauge 118. P104 denotes the pressure supplying the chamber C104 with pressurized air, which is determined by the elements 110 to 118. The supply pressure P104 is equal to the nominal operating pressure of the print head 10, namely the pressure that the coating product must have at the inlet of the print head. In particular, the supply pressure P104 of the peripheral chamber C104 with air is equal to the nominal pressure supplying the valves 14 with coating product.

[0051] Advantageously, and according to a non-represented aspect of the invention, the peripheral chamber C104 comprises an outlet opening putting the peripheral chamber C104 into fluid communication with an exhaust, or directly with the environment of the print head, so as to establish a permanent circulation of air flow in the chamber C104 between the pipe 110 and this outlet opening. This makes it possible to ensure in the external chamber C104 a pressure at a constant value P104, even during variations in the volume of the internal chamber C102. This makes it possible to overcome the constraints of regulating the pressure supply to the external chamber C104, which would cause the accumulator 100 to lose response time and performance. Thanks to this permanent circulation at a set pressure, the pressure in the peripheral chamber C104 is constant without response time, and the pressure regulation performance at the nozzles is greatly improved.

[0052] A sensor 120 is connected to the accumulator 100 and configured to detect a deformation of the deformable wall 102. A deformation of the wall 102 corresponds to a situation where the flow rates Q10 and Q32 are different. Thus, the sensor 120 is a means of detecting a difference between these flow rates.

[0053] For example, the sensor 120 may be an inductive sensor that comprises an inductive cell 122 capable of detecting the position of a metal element 124 mounted on a portion of the deformable wall 102. The inductive sensor 120 emits an oscillating electromagnetic field that allows the metal element to induce eddy currents in response that are detected by the sensor. Thus, the sensor 120 is a position sensor of the portion of the deformable wall 102 that carries the element 124. In this case, the metal element 124 also belongs to the means for detecting a difference between the flow rates Q10 and Q32.

[0054] Alternatively, the sensor 120 is an optical sensor, for example a laser sensor which measures the distance between the deformable wall 102 and the sensor 120, which makes it possible to deduce therefrom the variations in volume of the internal chamber C102. In this variant, the external wall 104 may be transparent if the sensor is placed outside the external wall. Alternatively, the sensor 120 is another type of optical sensor, for example a camera which measures by image analysis the deformation of the wall, which makes it possible to deduce therefrom the variations in volume of the internal chamber C102.

[0055] According to another variant, the sensor 120 is a capacitive sensor which has the advantage of not requiring a metallic mass on the deformable wall 102.

[0056] According to yet another variant, the sensor 120 is a feeler which comprises a rod bearing against the deformable wall. This type of sensor does not require a metal mass on the deformable wall 102. The rod of the feeler is advantageously coupled to a linear potentiometer.

[0057] The electrical output signal S120 of the sensor 120 is supplied, via a first electrical conductor 126, directly or indirectly to an electronic control unit 130 which itself controls, directly or indirectly by means of an electrical signal S130, the solenoid valve 34. The electronic control unit 130 is preferably integrated in the supply module. The control signal S130 is supplied, via a second electrical conductor 136, to the solenoid valve 34 and includes a pressure setpoint value for the pressure tank 32, in other words a setpoint value for the pressure of the coating product at the outlet of the pressure tank.

[0058] Thus, the value of the air supply pressure setpoint of the pressure tank 32 is adjusted by the electronic control unit 130 as a function, in particular, of the output signal S120 of the sensor 120 which constitutes a member for determining the difference between the instantaneous ejection flow rate Q10 and the supply flow rate Q32.

[0059] The position of the accumulator 100, as close as possible to the print head 10, makes it possible to issue a command to correct the pressure of the pressure tank 32 which depends less on the state parameters of the system, such as the temperature, the viscosity of the coating product, the pressure losses in the supply line than if this accumulator were far from the print head. Indeed, during a variation in pressure in the print head, the internal chamber C102 changes volume to reach a state of equilibrium depending on the supply pressure of the peripheral chamber C104. The sensor 120 then measures the deformation of the internal chamber C102.

[0060] In response, the electronic control unit 130 emits a pressure correction signal, by increasing or reducing the supply pressure of the pipe 40, depending on the volume of the deformable chamber C102, while the pressure in the print head is always the same, regardless of the system state parameters. This makes it possible in particular to limit the need to use numerous system state sensors, and numerous calculation steps in order to adapt the supply pressure setpoint value according to these different state parameters. The structure of the system is greatly simplified, the energy consumption is also reduced, and this increases the reliability of the performance of the control loop.

[0061] By measuring the position of the metallic element 124, the cell 122 of the sensor 120 detects a deformation of the deformable wall 102 of the accumulator 100.

[0062] After a possible calibration, the detected position of the metallic element 124 makes it possible to know or estimate the volume of the chamber C102.

[0063] The sensor 120 makes it possible, in particular, to know the direction of movement of the metal element 124, that is to say to detect when it moves away from or when it approaches the cell 122, according to a direction of translation of the metal element 124. A variation in this position of the metal element according to the direction of translation corresponds to a deformation of the deformable wall 102.

[0064] We assume that the cut-off valve 74 is closed.

[0065] If the metal element 124 moves closer to the cell 122, this means that the volume of the internal chamber C102 increases, i.e., the coating product tends to accumulate in this chamber C102. On the contrary, if the metal element 124 moves away from the cell 122, this means that the volume of the chamber C102 decreases and the coating product tends to flow from the internal chamber C102 to the valves 14 of the print head 10.

[0066] Normally, the pressure of the coating product at the outlet of the print head 10, as detected by the pressure sensor 78, does not vary. It is the variations in the volume of the internal chamber C102 which accommodate the variations in the flow rate of coating product in the print head, following the sequential openings and closings of the valves 14. The pressure of coating product in the internal chamber C102 is equal to the air pressure in the peripheral chamber C104, since the deformable wall ensures a pressure balance between the chambers C102 and C104. In the example of the figures, if the supply pressure of the peripheral chamber is 2 bar, the pressure of the coating product in the internal chamber is also 2 bar.If coating material from the print head accumulates in the internal chamber C102, this tends to move the metal element 124 closer to the cell 122, which is detected by the sensor 120 and transmitted to the electronic control unit 130 within the signal S120. Conversely, if coating material flows from the internal chamber C102 towards the print head, this causes the metal element 124 to move away from the cell 122, which is detected by the sensor 120 and transmitted to the electronic control unit 130 within the signal S120.

[0067] The pressure sensor 78 can be used to detect a drift in the pressure in the first variable volume chamber C102 and signal such a drift to the control unit 130, by a connection not shown. For example, if a large quantity of coating product reaches the first variable volume chamber C102, to the point that the deformable wall 102 abuts the rigid wall 104, it is no longer possible for the first variable volume chamber C102 to absorb more coating product and the pressure detected by the sensor 78 tends to increase and diverge from the desired nominal value, P104. This can be considered a fault. Conversely, if the pressure detected by the sensor 78 decreases from the desired nominal value P104, a fault is also identified.

[0068] The sensor 120 has a relatively low response time, compared to the response time of the supply module 30, more particularly of the pressure tank 32. For example, in the case of an inductive sensor, the response time of the sensor 120 may be of the order of a microsecond, for example between 1 and 100 µs, whereas the response time of the supply module 30, therefore of the source of coating product formed by the pressure tank 32, is of the order of 500 ms.

[0069] The internal volume of the internal chamber C102 varies according to the selective openings / closings of the valves 14, with a period of the order of 1 millisecond for a valve. In practice, the print head comprises several valves, for example between 40 and 100, and the pressure variations due to the openings and closings of each of these valves appear at periods independent of each other, and can cause pressure variations at a frequency of up to 60 kHz. Indeed, the opening of a valve 14 has the effect of circulating the coating product through the nozzle 12 associated with this valve, including reducing the pressure of the coating product upstream of this nozzle.

[0070] Furthermore, a synergistic effect is observed thanks to the simultaneous presence of nozzle actuators 14 pneumatically supplied by the third source 96 and the regulation of product supply pressure by means of an accumulator 100 according to the invention. Indeed, the pressure regulation performance of the accumulator 100 makes it possible to correct the response time defects of the paint supply, which makes it possible to avoid too great an imbalance in pressure between the coating product in the nozzles and the supply pressure of the nozzle opening and closing actuators. This excessive imbalance would hinder the closing of the nozzles and could lead to leaks, poor cutting of the deposited drops, and greatly degrade the printing performance.It would then be necessary to control the air supply pressure regulation of the nozzle actuators, which would introduce an additional response time, and which would make the operation of the print head much more delicate. The invention makes it possible, in particular, to avoid these problems.

[0071] Furthermore, the movements of the robot tend to vary the pressure losses in the supply line 40. These different pressure variations result in movements of the metal element 124 towards / away from the cell 122, which is integrated into the signal S120 and processed by a microprocessor 132 of the electronic control unit 130 to be integrated into the signal S130. Given the respective response times of the sensor 120 and the supply module 30, the taking into account by the microcontroller 132 of the control unit 130 of the output signal S120 from the sensor 120 does not disturb the control of the module 30 by the unit 130.

[0072] On the other hand, the accumulator 100 is advantageously configured so that the maximum deformation of its deformable wall 102 is compatible with a variation in the volume of the internal chamber C102 equal to the sum of the maximum flow rates of the nozzles 12 of the print head 10 multiplied by the response time of the pressure reservoir 32. Thus, the internal chamber C102 of the accumulator 100 makes it possible to accommodate variations in the flow rate of coating product applied by the print head 10, depending on the selective opening of the valves 14, without significant variation in the pressure P102 in the internal chamber C102, this pressure remaining equal to the pressure P104 in the peripheral chamber C104, which is set at a predetermined value by the elements 110 to 118, as explained above. In other words, assuming that hysteresis is negligible, the values ​​of pressures P102 and P104 are constant and equal.

[0073] Under these conditions, the accumulator 100 makes it possible to temporarily accommodate coating product, when the first variable volume chamber C102 is supplied with coating product, or to expel a certain quantity of coating product, when the first variable volume chamber is purged with coating product, during the phases of adaptation of a pressure setpoint value of the pressure tank 32, while this internal chamber C102 remains at a constant pressure P102, which makes it possible to maintain the supply pressure of the nozzles 14 at this value. Indeed, by neglecting the pressure losses in the section of pipe 70 located between the elements 10 and 100, the pressure at the outlet of the print head 10 at the upstream end 72 of the pipe 70 is maintained equal to the pressure P102.This pressure at the outlet of the print head is equal to the pressure in a supply channel for the valves 14 arranged within the print head 10. The valves 14 are therefore supplied with a pressure which can be considered constant and equal to the pressure P102 or P104.

[0074] In a variant not shown of the first embodiment, the electronic control unit 130 is integrated into an automaton which controls the solenoid valve 34. The electronic control unit then does not increase the cost of the installation I.

[0075] In the second and third embodiments of the invention shown in figures 3 And 4, elements similar to those of the first embodiment bear the same references. If an element is shown in these figures without being mentioned in the description, it is the element bearing the same reference in the first embodiment. If an element is mentioned in the description with a reference number, without being identified by this number in these figures, it corresponds to the element bearing the same reference in the first embodiment.

[0076] The following describes mainly what distinguishes these second and third embodiments from the first embodiment.

[0077] In the second embodiment, the source of coating product is a reservoir 32 comprising a piston 33 whose movement is controlled by an electric motor 34 driven by an electronic control unit 130, by means of a control signal S130. More precisely, the motor 34 comprises a control card 35, most often called a “variator”, which receives operating instructions or setpoints from the electronic control unit 130, these setpoints including in particular a value of the speed of movement of the piston 33 or a value of the rotation speed of the motor 34, which is uniquely linked to the flow rate Q32 of coating product delivered by the reservoir 32 to the pipe 40, which is the flow rate for supplying the print head 10 with coating product.

[0078] A supply line 40 connects a supply module 30, which includes the piston reservoir 32, to a print head 10 equipped with nozzles 12 and valves 14. The line 40 extends between an upstream end 42 connected to the piston reservoir 32 and a downstream end 46 connected to the print head 10. A first cut-off valve 43, a first filter 44, a second filter 47 and a second cut-off valve 45 are mounted in series on the line 40.

[0079] Solvent or cleaning agent is supplied to the print head 10 by means of a second line 60 controlled by a third shut-off valve 62.

[0080] A third line 70 connects the print head 10 to a purge 80 and is equipped with a fourth cut-off valve 74.

[0081] An accumulator 100 is mounted on the pipe 40, upstream of its second end 46 and comprises, as in the first embodiment, a deformable wall 102 and a rigid casing 104. Thus the accumulator is mounted upstream of the print head in the circuit C which connects the source of coating product 32 to the purge 80. An internal chamber C102 and a peripheral chamber C104, both of variable volume, are defined in the accumulator 100, as in the first embodiment. A sensor 120 makes it possible to detect a deformation of the deformable wall 102 and delivers to the electronic control unit 130 a signal S120 representative of the detected deformation, therefore of a possible difference between the flow rates Q10 and Q32.

[0082] A pressure sensor 78 makes it possible to know the pressure in the pipe 40, upstream of the accumulator 100. Alternatively, the pressure sensor 78 is installed on the line connecting the accumulator 100 to the print head 10 and makes it possible to know the pressure in the pipe 40, downstream of the accumulator 100.

[0083] A fourth pipe 90 supplies the valves 14 with pressurized air, from a source 96, being controlled by a solenoid valve 94 associated with a pressure gauge 98. A pressure sensor 92 makes it possible to know the pressure in the pipe 90. The supply pressure of the valves 14 via the pipe 90 is considered here to be constant and equal to 2 bars, for example.

[0084] A fifth pipe 110 connects a source 116 of pressurized air to the peripheral chamber C104, through a solenoid valve 114 associated with a pressure gauge 118. The supply pressure of the valves 14 via the pipe 90 is also considered here to be constant and equal to 2 bars, for example. Advantageously, the supply pressure of the peripheral chamber C104 with pressurized air is equal to the nominal supply pressure of the printing head 10 with coating product.

[0085] First and second electrical conductors 126 and 136 are used to carry signals S120 and S130, as in the first embodiment.

[0086] The operation of the installation I according to this second embodiment is comparable to that of the first embodiment. In particular, the electrical output signal from the sensor 120 is processed by a microprocessor 132 of the electronic control unit 130 to adjust the electrical signal S130 for controlling the electric motor 34 taking into account a possible deformation of the deformable wall 102 corresponding to an increase or a decrease in the quantity of coating product present in the internal chamber C102.

[0087] The sensor 120 of this second embodiment may be of the same type or of a different type than that of the first embodiment.

[0088] Whether in the first or in the second embodiment, a method for controlling the installation I may comprise the following steps: a) deducing from a deformation or a displacement of the wall 102 information on the direction of change in the size of the internal volume of the variable volume chamber C102; b) if the information deduced in step a) corresponds to an increase in the internal volume, adjusting downwards the operating setpoint value of the coating product source 32, which is part of the electrical control signal S130; and c) if the information deduced in step a) corresponds to a decrease in the internal volume, adjusting upwards the operating setpoint value of the coating product source 32.

[0089] Regardless of the embodiment, the sensor may be an inductive sensor, as explained with reference to the first embodiment. Alternatively, it may be a capacitive sensor, an optical sensor, or a feeler. Other types of sensor are conceivable.

[0090] Regardless of the embodiment, the functions of the internal chamber C102 and peripheral chamber C104 can be reversed compared to the example in the figures. In other words, the peripheral chamber C104 can be connected to the print head and supplied with coating product, while the internal chamber is supplied with pressurized air.

[0091] The invention is not limited to the case where the deformable wall 102 forms a sleeve which completely surrounds the internal chamber C102. In particular, the deformable wall 102 may only partially delimit the internal chamber C102, the latter being moreover defined by a rigid wall, as is the case for the peripheral chamber C104 in the examples.

[0092] In a variant shown in figure 4 , compatible with all embodiments of the invention, the accumulator 100 has a substantially spherical or cylindrical outer wall 104 defining an internal volume, and the deformable wall 102 is positioned so as to divide the volume defined by the outer wall 104 into a first chamber C102 and a second chamber C104, one being in fluid communication with the print head, the other being supplied with pilot air by the pressurized air source 116. During pressure balancing, the deformable wall 102 deforms, and the sensor 120 measures this deformation.

[0093] According to another variant not shown of the first and second embodiments, the deformable wall 102 can be replaced by a piston, which is a rigid part. In other words, the wall which separates the variable volume chambers C102 and C104 is a piston, which makes it possible to improve the accuracy of the measurement carried out using the sensor 120 because the variation in volume and the displacement of the piston are linear. Such an approach requires establishing a seal between the two variable volume chambers C102, C104, which is not necessary with a deformable wall. In this case, the translational movements of the piston make it possible to balance the pressures P102 and P104 prevailing respectively in the two chambers C102 and C104.

[0094] When the wall 102 is deformable, it may be made of elastomer, for example FKM (fluorocarbons) or FFKM (perfluoroelastomers) or any other elastically deformable material such as rubber, possibly with a tetrafluoroethylene coating to ensure the chemical resistance of the rubber to coating products.

[0095] In the third embodiment shown in the figure 4 , the variable volume chambers C102 and C104 are separated by a wall 102 which deforms, in the event of a transient pressure difference between these chambers, which has the effect that the pressures P102 in the chamber C102, P104 in the chamber C104 balance out as soon as an imbalance occurs. Unlike the first and second embodiments and the variant with piston mentioned above, the position of the wall 102 is not detected by a sensor of the type of sensor 120.

[0096] In this third embodiment, the instantaneous flow rate Q10 of coating product ejection by the print head is determined. This can be done by assuming that the size and / or mass of the coating product droplets exiting the nozzles 12 are known, by measurement or after calibration. As a non-limiting example, a control unit 121 integrated into the print head 10 can be used to determine the number of openings / closings of the valves 14 over a given period of time. By assuming that each opening / closing releases a droplet, the number of droplets ejected over the period, therefore the flow rate Q10, is known. The control unit does not have to count the number of openings / closings because it is known from the control signal received by the control unit 121.This number is transmitted to the electronic control unit 130 within an output signal S121 of the control unit 121, which passes through an electrical conductor 126. The microprocessor 132 is then able to calculate the instantaneous flow rate Q10.

[0097] Alternatively, the instantaneous flow rate Q10 is calculated in the control unit and transmitted to the electronic control unit within the signal S121.

[0098] Alternatively, the control unit 121 can be replaced by another device for determining the instantaneous flow rate Q10, by direct or indirect measurement.

[0099] On the other hand, the flow rate Q32 of the tank 32, which is the theoretical flow rate of supply of the printing head 10 with coating product, is calculated by the control card 35, as a function of the speed of movement of the piston 33, which is linked unequivocally to the speed of rotation of the motor 34.

[0100] On the other hand, the electronic control unit 130 receives a signal S35 from the electronic card 35 of the electric motor 34 which includes the flow rate Q32.

[0101] The electronic units 35, 121 or equivalents make it possible to detect when the flow rates Q10 and Q32 are different. They therefore constitute means for detecting the difference between the instantaneous ejection flow rate Q10 and the feed flow rate Q32.

[0102] It is then possible for the microprocessor 132 to compare the flow rates Q10 and Q32 and to regulate the flow rate Q32 to adjust it to the flow rate Q10. In other words, the microprocessor 132 can calculate a difference between the flow rates Q10 and Q32. If the flow rate Q10 is strictly greater than the flow rate Q32, the electronic control unit 130 controls the motor 34 by increasing the set value of the flow rate Q32. If the flow rate Q10 is strictly less than the flow rate Q32, the electronic control unit 130 controls the motor 34 by decreasing the set value of the flow rate Q32.

[0103] Thus, particularly in the case of a 30 feed module with motor / piston or a gear pump, i.e. in the case of volume dosing, it is possible to regulate the feed flow rate Q32 as a function of the instantaneous flow rate Q10 of the print head which operates at constant pressure.

[0104] In this third embodiment, the accumulator 100 is used only to absorb, in other words to compensate for, the transient variations in flow rate and pressure, while the regulation is carried out by the control unit 130, on the basis of the cumulative volume deviations of ejection Q10 and supply Q32.

[0105] This third embodiment requires knowing the size and / or mass of the droplets to determine the instantaneous volume Q10, therefore the difference between the flow rates Q10 and Q32 to be compensated by the accumulator 100. Knowing the size of the drops is more complicated than measuring a displacement as in the first and second embodiments but remains feasible because this size or this mass can be determined optically, using a device which makes it possible to measure the drops before application, or by measuring the total quantity with each coating product.

[0106] In this third embodiment, the pressure sensor 78 operates as in the first embodiment, which is all the more important since the deformations of the deformable wall are not detected, in the absence of a sensor 120.

[0107] As a variant of this third embodiment, the flow rate Q32 is calculated in the control unit 130.

[0108] In the variant of the first and second embodiments where the wall 102 is replaced by a piston and / or in the third embodiment, it is advantageously provided that the maximum stroke of the piston is compatible with a variation in the volume of the first variable volume chamber C102 equal to the sum of the maximum flow rates of the nozzles 12 of the print head 10 multiplied by the response time of the source 32 of coating product.

[0109] Alternatively, in the second and third embodiments, the electronic control unit 130 and the control card 35 are combined into a single electronic device, advantageously integrated into the motor 34. In this case, the signal S120 or S121 is supplied directly to the motor and the operating setpoint value of the motor is generated within this electronic device.

[0110] Alternatively, and regardless of the embodiment, the source of coating product may be different from the examples shown in the figures with reference 32. It may for example be a gear pump, a pressure regulator supplied at a pressure higher than the supply pressure of the print head, which regulates the supply pressure of the line 40.

[0111] The value of the pilot pressure P104 can be, for example, of the order of 2 bars, and can be adjusted according to the viscoelastic properties of the coating product, the temperature, and the system state parameters.

[0112] Alternatively, the pressurized air sources 36, 96 and 116 may be combined into a single common pressurized air source.

[0113] Alternatively, at least one of the signals S120, S121 and S130 is transmitted by a wireless channel.

[0114] According to another variant of the invention, also not shown, the circuit C is a closed loop for circulation of the coating product, with return of the coating product from the outlet orifice 108 of the first variable volume chamber C102 to the reservoir 32.

[0115] According to another variant of the invention, also not shown, the coating product reservoir 32 is included in the print head 10 or arranged in the immediate vicinity of this head, downstream of the second filter 47. In this case, the influence of the pressure losses in the arm 22 of the robot 20 is minimized.

[0116] According to another variant of the invention, not shown, the source of coating product is a volumetric pump. In this case, the operating setpoint value delivered by the electronic control unit is a rotation speed value of this pump.

[0117] According to a variant applicable to all embodiments, the second variable volume chamber C104 can be supplied with a pressurized gas other than air, for example nitrogen.

[0118] The embodiments and variants envisaged above may be combined with each other within the scope of the appended claims.

Claims

1. An installation (I) for the application of a coating product comprising a print head (10) equipped with a plurality of nozzles (12) and supplied by a source (32) of coating product, each nozzle being controlled by a valve (14) supplied by the source of coating product, characterized in that - the installation comprises a coating product accumulator (100) installed on a circuit (C) for the circulation of the coating product, which passes through the print head (10); - the accumulator comprises a deformable or movable wall (102) delimiting, at least in part, a first chamber (C102) of variable volume supplied with coating product and a second chamber (C104) of variable volume supplied with gas, under a predetermined pressure (P104); - the predetermined pressure (P104) for supplying the second chamber (C104) of variable volume is equal to a nominal operating pressure of the print head (10); - the first chamber (C102) of variable volume is supplied or purged with coating product due to a difference between an instantaneous coating product ejection rate (Q10) from the print head (10) and a supply rate (Q32) to the print head from the coating product source (32); - the system comprises means (120, 124; 121, 35) for detecting a difference between the instantaneous ejection rate (Q10) and the supply rate (Q32); and - the installation comprises a control unit (130) configured to adjust an operating setpoint value (S130) of the coating product source (32) as a function of the difference between the instantaneous ejection flow rate (Q10) and the supply flow rate (Q32), in a direction to reduce this difference between the flow rates.

2. The installation according to claim 1, characterized in that the means for detecting the difference between the instantaneous ejection flow rate (Q10) and the supply flow rate (Q32) comprises a sensor (120), configured to detect a deformation or a displacement of the wall of the accumulator, and in that the control unit (130) is configured to adjust the setpoint value (S130) for operation of the source (32) of the coating product, as a function of an output signal (S120) of the sensor.

3. The installation according to claim 2, characterized in that the sensor (120) is of the inductive, capacitive, optical or probe type.

4. The installation according to claim 1, characterized in that the means for detecting the difference between the instantaneous ejection flow rate (Q10) and the supply flow rate (Q32) comprising a first unit (121) for determining the instantaneous ejection flow rate (Q10) and a second unit (35) for determining the supply flow rate (Q32) and in that the control unit (130) is configured to adjust the operating setpoint value as a function of a difference between the instantaneous ejection flow rate (Q10) determined by the first unit and the supply flow rate (Q32) determined by the second unit.

5. The installation according to one of the preceding claims, characterized in that the wall (102) is elastically deformable under the normal operating conditions of the installation (I) and in that, preferably, the wall carries an element (124) the position of which can be detected by the sensor (120).

6. The installation according to claim 5, characterized in that the deformable wall (102) of the accumulator (100) is housed in a rigid shell (104), in that the first chamber (C102) of variable volume is defined inside the deformable wall, in that the second chamber (C104) of variable volume is defined between the deformable wall and the rigid shell, or vice versa.

7. The installation according to any of claims 5 and 6, characterized in that the deformable wall (102) is in the shape of a sleeve and extends between a first port (104) for entry of coating product into the accumulator (100) and a second port (108) for discharge of coating product from the accumulator.

8. The installation according to any one of claims 1 to 4, characterized in that the wall is a movable piston that separates the two chambers (C102, C104) of variable volume.

9. The installation according to one of claims 5 to 8, characterized in that the maximum deformation of the deformable wall (102) or the displacement stroke of the movable piston is compatible with a variation in the volume of the first chamber (C102) of variable volume equal to the sum of the maximum flow rates of the nozzles (12) of the print head (10) multiplied by the response time of the coating product source (32).

10. The installation according to any one of the preceding claims, characterized in that the second chamber (C104) of variable volume is provided with an outlet opening and in that the second chamber of variable volume is supplied with a permanent gas flow, between a supply line (110) and its outlet opening.

11. The installation according to one of the preceding claims, characterized in that the accumulator (100) is installed, in the circuit (C), downstream of the print head (10).

12. The installation according to one of claims 1 to 11, characterized in that the accumulator (100) is installed, in the circuit (C), downstream of the print head (10).

13. A method for controlling a coating product application installation (I) according to claim 2, characterized in that it comprises at least steps consisting in: a) deducing from a deformation or a displacement of the wall (102) information on the direction of evolution of the size of an inner volume of the first chamber (C102) of variable volume of the accumulator (100) ; b) if the information deduced in step a) corresponds to an increase in the inner volume, adjusting the value of the operating setpoint (S130) of the coating product source (32) downward; and c) if the information deduced in step a) corresponds to a decrease in the inner volume, adjusting the value of the operating setpoint (S130) upward.

14. The method according to claim 13, characterized in that the operating setpoint is a control pressure of a pressurized tank (32), a displacement speed of a piston (33) of a tank equipped with a piston, or a rotational speed of a volume pump.

15. The method for controlling an installation (I) for application of a coating product according to claim 4, characterized in that it comprises at least steps consisting in: a') calculating a difference between the instantaneous flow rate (Q10) of coating product through the print head (10) and the flow rate (Q32) of coating product supplied to the print head ; b') if the difference calculated in step a') is positive, adjusting upward a coating product feed rate setpoint (Q32) of the print head; and c') if the difference calculated in step a') is negative, adjusting downward a coating product feed rate setpoint (Q32) of the print head.

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