Installation for application of coating product, and method for controlling such installation

Abstract

To provide an installation for application of a coating product, and a method for controlling the installation.SOLUTION: An installation I comprises a print head 10 with a plurality of nozzles 12 each controlled by a valve 14 supplied by a product source 32. A product accumulator 100, mounted on a product circulation circuit C, comprises a first chamber C102 of variable volume supplied by a coating product, and a second chamber C104 of variable volume supplied by gas, under a predetermined pressure equal to a nominal operating pressure of the print head. The first chamber is supplied by or purged of the coating product because of a difference between an instantaneous coating product ejection flow rate Q10 from the print head and a supply flow rate Q32 to the print head from the source. A control unit 130 adjusts an operation setpoint value S130 of the source as a function of the difference between the instantaneous ejection flow rate and the supply flow rate so as to reduce this difference.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an installation for the application of a coating product, comprising a printhead equipped with a plurality of nozzles and supplied by a source of coating product. [Background technology]

[0002] In such equipment, each nozzle defines a coating product discharge orifice having a small diameter of 100 to 300 micrometers (μm). Each nozzle is controlled by a valve, which in turn is fed by a supply of coating product. Operation of the printhead requires a high degree of precision in controlling the pressure of the coating product delivered to the printhead. This is particularly necessary for viscous products, such as those having a kinematic viscosity of 50 to 300 millipascal-seconds (mPa·s).

[0003] In equipment for applying coating products with a printhead, the coating product, which may be viscous, must be supplied to individual nozzles at a given pressure, for example, 2 bar. In practice, if the nominal pressure of the coating product supply to the printhead is 2 bar, there is a risk of overspray if this pressure is greater than 2.1 bar. On the other hand, if the supply pressure is less than 1.9 bar, the instantaneous flow rate of the coating product at one or more nozzles may not allow for the formation of a continuous or quasi-continuous net at the nozzle outlet. This is why an accuracy of the order of 100 millibars (mbar) is required for the coating product supply pressure at the inlet to the printhead. However, this supply pressure depends on the instantaneous flow rate of the coating product at the printhead.

[0004] The instantaneous flow rate of coating product through the various orifices in the nozzles of the printhead results from the opening and closing of valves that control these valves and have a response time of approximately 1 millisecond (ms). In equipment for applying coating product, a coating product supply is used to supply the printhead. This coating product supply may consist of a pressurized coating product tank or a tank with a piston driven by an electric motor or other device. In either case, the response time of such a device is approximately 500 ms.

[0005] On the other hand, the supply of coating product from the coating product source to the print head is through a line that can be several meters long - for example, if the print head is located at the end of the arm of a multi-axis robot, the printing source is located on the leg of the robot - this line causes periodic pressure losses due to its length and diameter, and significant pressure losses due to valves, filters and / or elbows located along the length of this line.

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

[0007] A known solution in the field of ink application involves continuously circulating a relatively large flow rate of coating product and then supplying the nozzles of a printhead with a flow rate of approximately 10% of this relatively large flow rate. This results in a continuous circulation of ink that is not transportable for use in coating products such as paints, because the shear caused by the repeated circulation of the coating product risks degrading the paint. In addition, a large flow rate of coating product, for example, a flow rate equivalent to 2 liters per minute (L / min), should be supplied to the printhead, and 10% of this flow rate represents approximately 200 mL / min. In practice, it is very difficult to deliver a coating product at 2 L / min to the end of a robotic arm.

[0008] One alternative solution, which may seem obvious but is difficult to implement due to the large volume required, is to incorporate a pressurized product tank or tank with a motor either close to the printhead or into the head.

[0009] Furthermore, from US patent application 2019 / 0337001 it is known to provide control of the coating product by means of two printheads, one used to apply the coating product and one arranged in the discharge line. If one of the print nozzles of the discharge printhead is closed while the print nozzles of the printhead used to apply the coating product are open, or vice versa, it may be possible to use a quasi-constant flow rate. This results in a large consumption of the coating product, with significant implications in terms of reprocessing and costs.

[0010] On the other hand, EP 2 574 471 A1 discloses an ink application system in which the printhead is supplied from the reservoir through a flexible-walled sub-reservoir and a pump, the operation of which is regulated according to the pressure in the passage between the sub-reservoir and the printhead, without taking into account the ink flow rate actually emitted by the printhead.

[0011] More specifically, the present invention aims to overcome the aforementioned drawbacks by proposing a new installation for the application of a coating product, in which the pressure for supplying the print head with the coating product is precisely controlled taking into account the respective response times of the valves of the print head and of the control elements of the source of coating product. Summary of the Invention

[0012] To this end, the present invention relates to an apparatus for applying a coating product, comprising a printhead provided with a plurality of nozzles and supplied by a coating product supply source, each nozzle being controlled by a valve supplied by the coating product supply source. According to the present invention, the apparatus comprises a coating product accumulator installed in a circulation circuit for the coating product passing through the printhead, the accumulator having a deformable or movable wall at least partially defining a first variable-volume chamber supplied by the coating product and a second variable-volume chamber supplied by gas under a predetermined pressure. The predetermined supply pressure for the second variable-volume chamber is equal to the nominal operating pressure of the printhead. The first variable-volume chamber is supplied with or purged of coating product depending on the difference between the instantaneous coating product discharge flow rate from the printhead and the supply flow rate from the coating product supply source to the printhead. The apparatus comprises means for detecting the difference between the instantaneous discharge flow rate and the supply flow rate. The apparatus further comprises a control unit configured to adjust the operating setpoint of the coating product supply source in response to the difference between the instantaneous discharge flow rate and the supply flow rate in a direction that reduces this flow rate difference.

[0013] The present invention allows the accumulator to be sized so that deformation and displacement of the accumulator walls allow it to store a sufficient volume of coating product to compensate for changes in coating product pressure at the inlet of the printhead during the response time of the coating product source. Furthermore, the present invention allows for consideration of changes in pressure drop that may occur in the supply line connecting the coating product source to the printhead. Because the variable-volume second chamber is supplied with a pressure equal to the nominal operating pressure of the printhead, and taking into account the deformable or movable nature of the walls, the pressure in the variable-volume first chamber can be assumed to be equal to the nominal operating pressure of the printhead. Furthermore, the control unit can control the coating product source in an optimized manner depending on the difference between the instantaneous discharge flow rate and the supply flow rate to reduce this difference, which automatically adapts the coating product flow rate delivered by the source to the flow rate actually discharged by the printhead.

[0014] According to advantageous but non-essential aspects of the invention, such an installation may incorporate one or more of the following characteristics, taken alone or in any technically possible combination: The means for detecting the difference between the instantaneous discharge flow rate and the supply flow rate comprises a sensor configured to detect deformation or displacement of the wall of the accumulator, while the control unit is configured to adjust the operating set point of the coating product supply source in response to the output signal of the sensor. The position sensor is an inductive sensor, a capacitive sensor, an optical sensor or a probe type sensor. The means for detecting the difference between the instantaneous discharge flow rate and the supply flow rate comprises a first unit for determining the instantaneous discharge flow rate and a second unit for determining the supply flow rate, and the control unit is configured to adjust the value of the operating set point in response to the difference between the instantaneous discharge flow rate determined by the first unit and the supply flow rate determined by the second unit. The wall is elastically deformable under nominal operating conditions of the installation, while preferably the wall has an element whose position can be detected by a sensor. The deformable wall of the accumulator is housed in a rigid shell, while a first chamber of variable volume is defined inside the deformable wall, while a second chamber of variable volume is defined between the deformable wall and the rigid shell, or vice versa. A deformable wall is sleeve-shaped and extends between a first coating product inlet port into the accumulator and a second coating product outlet port from the accumulator. The wall is a movable piston that separates two chambers of variable volume. The maximum deformation of the deformable wall or movement of the movable piston corresponds to a change in volume of the variable volume first chamber equal to the sum of the maximum flow rate of the nozzles of the print head multiplied by the response time of the source of coating product. A variable volume second chamber is provided with an outlet opening, and the variable volume second chamber is supplied by a continuous gas flow between the supply line and the outlet opening. An accumulator is located in the circuit downstream from the printhead. An accumulator is placed in the circuit upstream of the printhead.

[0015] According to another aspect, the present invention relates to a first method for controlling an installation as described above, the method comprising the steps of: a) deriving information about the direction of change in size of the inner volume of the first chamber of the variable volume of the accumulator from the deformation or displacement of the wall; b) adjusting the operating set point of the coating product source downward if the information estimated in step a) corresponds to an increase in the internal volume; and c) adjusting the operating set point of the coating product source upward if the information estimated in step a) corresponds to a decrease in the internal volume. At least includes.

[0016] Advantageously, the operating set point is the control pressure of a pressurized tank, the displacement speed of a piston in a chamber having a piston, or the rotation speed of a volumetric pump.

[0017] According to yet another aspect, the present invention relates to a second method for controlling the above-mentioned installation, the method comprising: a') calculating the difference between the instantaneous flow rate of coating product through the print head and the supply flow rate of coating product to the print head; b') if the difference calculated in step a') is positive, setting the coating product supply flow set point to the print head upward; and c') if the difference calculated in step a') is negative, setting the coating product supply flow set point to the print head downward. At least includes.

[0018] The invention will be better understood and other advantages of the invention will become more apparent in the light of the following description of three embodiments of an apparatus and method according to the principles of the invention, given by way of example only and with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a schematic diagram of the principle of a coating product application installation according to the invention; [Figure 2] 2 is a fluid and electrical diagram of the installation of FIG. 1; [Figure 3] 3 is a schematic diagram similar to FIG. 2 of an installation according to a second embodiment of the invention; [Figure 4] 3 is a schematic diagram similar to FIG. 2 of an installation according to a third embodiment of the invention; DETAILED DESCRIPTION OF THE INVENTION

[0020] In Figures 2 and 3, thick solid lines are used to represent coating product flow lines, thick dashed lines are used to represent solvent or cleaning product flow lines, thin solid lines are used to represent air flow lines, and thick dashed or dotted lines are used to represent electrical conductors for transmitting electrical signals.

[0021] The installation I shown in Figures 1 and 2 is intended to apply paint to an object O, which in the example of the figures is the body of a car. More precisely, in this figure, the installation I is intended to make it possible to create a band B of contrasting colour, for example black, on the roof of the car body.

[0022] Alternatively, the object to be coated may be a part of an automobile bodywork, such as a bumper, or more generally any object that can be coated, such as, but not limited to, an aircraft cabin or the body of a household appliance.

[0023] Furthermore, the coating product applied by the inventive installation I does not necessarily constitute a strip of contrasting color.

[0024] The coating product may be a paint, primer or varnish or a water-soluble or solvent-based two-component coating. In particular, its kinematic viscosity may be between 50 and 300 mPa·s.

[0025] The installation I comprises a conveyor 2 designed to move an object O along a conveying axis X2 perpendicular to the plane of FIG.

[0026] Furthermore, the installation I comprises a printhead 10 mounted at the end of an arm 22 of a multi-axis robot 20 arranged near the conveyor 2. The printhead 10 is supplied with the coating product to be applied from a supply module 30 which comprises a source of the coating product to be applied, here formed by a pressurized tank 32.

[0027] The module 30 is connected to the printhead 10 by a supply line 40 that runs through the interior of the multi-axis robot 20, and in particular through the interior of its arm 22.

[0028] The module 30 comprises a control solenoid valve 34 connected on its upstream side to a pressurized air source delivering air at a pressure equal to 6 bar. On its downstream side, the solenoid valve 34 is connected to the internal volume V32 of the pressurized tank 32. A pressure gauge 38 makes it possible to know the pressure of the air delivered by the solenoid valve 34.

[0029] An upstream end 42 of the supply line 40 is immersed in the pressurized tank. A first shutoff valve 43 and a first filter 44 are disposed in the supply line 40 within the supply module 30 at the upstream portion of the supply line 40.

[0030] The downstream end of supply line 40 is connected to printhead 10, which is therefore supplied with coating product from a supply of coating product through supply line 40. The pressure of coating product at the inlet of the printhead depends on the pressure of the coating product supplied from the pressurized tank and the pressure drop in the supply line, which is variable depending on the position of arm 22.

[0031] The control module 50 is located near the print head 10, for example in the arm 22 of the multi-axis robot 20. By "near" it is meant that the supply module is located less than 1 meter, preferably less than 50 cm, and more preferably less than 20 cm away from the print head. The supply line 40 passes through the control module 50. In this module 50, the supply line 40 is provided with a second shut-off valve 45 and a second filter 47.

[0032] For example, the first filter 44 may be configured to retain elements having a maximum size greater than 40 μm, while the second filter 47 may be configured to retain elements having a maximum size greater than 20 μm.

[0033] A second supply line 60 for supplying the print head 10 with a solvent or cleaning product is connected to the supply line 40 downstream of the second shut-off valve 45. This supply line 60 is provided with a third shut-off valve 62 and is connected to a solvent source (not shown), which may be a tank or a closed-loop circulation circuit (sometimes called a "circulating" system).

[0034] The printhead 10 is provided with a plurality of nozzles 12, each configured to deliver a jet J12 of coating product to be applied to the object O.

[0035] Each nozzle 12 defines a coating product discharge orifice (not shown) having a diameter of the order of 100-300 μm. Each nozzle 12 is controlled by a valve 14 supplied with coating product through a supply line 40. The valve 14 may be of the type known from EP 2 442 983 or U.S. Pat. No. 9,638,350, the technical teachings of which are incorporated herein by reference.

[0036] The valve 14 is controlled electrically or pneumatically in a manner known per se.

[0037] A third exhaust line 70 connects the printhead 10 to a purge 80. An upstream end 72 of the exhaust line 70 is connected to the printhead 10, while a downstream end 76 of the exhaust line 70 leads to the purge 80. A fourth shutoff valve 74 is attached to the exhaust line 70.

[0038] Lines 40 and 70 together form circuit C, which connects source of coating product 32 to purge 80 and passes through printhead 10 .

[0039] A fourth line 90 connects a source 96 of pressurized air to the printhead 10, controlled by a solenoid valve 94 provided with a pressure gauge 98. A pressure sensor 92 is arranged in the line 90 to make it possible to control the supply of the printhead 10 with pressurized air at a predetermined pressure, for example equal to 2 bar. This pressurized air is used to supply the actuators for opening the nozzles.

[0040] The actuator 100 is disposed in the discharge line 70, that is to say downstream of the printhead 10, in the direction of circulation of the coating product between the source of coating product 32 and the purge 80. The accumulator 100 is thus placed in circuit C.

[0041] The accumulator 100 comprises a deformable wall 102 and a rigid shell 104 surrounding the deformable wall.

[0042] The deformable wall 102 in turn defines an internal chamber C102 that is supplied with the coating product that exits the printhead 10. Due to the deformable nature of the wall 102, the internal chamber C102 is of variable volume.

[0043] Respectively, Q10 is the instantaneous flow rate of coating product emitted by printhead 12, Q32 is the flow rate delivered to the printhead by pressurized tank 32, and Q'10 is the flow rate delivered to accumulator 100 by the printhead.

[0044] These have the following relationship: Q32=Q10+Q'10 (formula 1) This can be expressed as follows: Q'10=Q32-Q10 (Formula 2)

[0045] From Equation 2, it is clear that the flow rate Q'10 can be positive or negative. When the flow rate Q10 is strictly less than the flow rate Q32, the flow rate Q'10 is positive, and the variable volume inner chamber C102 is gradually supplied with coating product. When the flow rate Q10 is strictly greater than the flow rate Q32, the flow rate Q'10 is negative, and the variable volume inner chamber C102 is gradually purged of the coating product it contains.

[0046] Meanwhile, a surrounding chamber C104 is defined around the deformable wall 102 and inside the rigid shell 104. Due to the deformable nature of the wall 102, the surrounding chamber C104 is also of variable volume.

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

[0048] Here, the deformable wall 102 is formed in the shape of a sleeve and extends between a first port 106 for the coating product from the print head 10 to enter the inner chamber C102, in other words into the accumulator 100, and a second port 108 for discharging the coating product from the accumulator 100 in the direction of the purge 80.

[0049] The pressure sensor 78 allows for detection of the pressure of the coating product in the portion of the line 70 connecting the printhead 10 and the accumulator 100 .

[0050] Ambient chamber C104 is supplied with pressurized air through a fifth line 110 provided with a control solenoid valve 114, the upstream side of which is connected to a pressurized air source 116, which in turn is connected to a pressure gauge 118. P104 represents the supply pressure of pressurized air to chamber C104 and is determined by elements 110-118. The supply pressure P104 is equal to the nominal operating pressure of printhead 10, i.e., the pressure that the coating product should have at the inlet of the printhead. In particular, the supply pressure P104 of ambient chamber C104 by air is equal to the nominal supply pressure of valve 14 by coating product.

[0051] Advantageously, and in accordance with an unillustrated embodiment of the present invention, the ambient chamber C104 includes an outlet opening that fluidly connects the ambient chamber C104 to an exhaust system or directly to the printhead environment, establishing a continuous flow circulation of air in the chamber C104 between the line 110 and the outlet opening. This ensures that the pressure in the outer chamber C104 remains at a constant value P104, even while the volume of the inner chamber C102 changes. This makes it possible to avoid the constraint of regulating the pressure supply to the outer chamber C104, which would cause a deterioration in the response time and performance of the accumulator 100. This continuous circulation at a regulated pressure ensures that the pressure in the ambient chamber C104 is constant except for the response time, greatly improving pressure regulation performance at the nozzles.

[0052] The sensor 102 is connected to the accumulator 100 and is configured to detect deformation of the deformable wall 102. The 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 for detecting the difference between these two flow rates.

[0053] For example, the sensor 120 may be an inductive sensor, comprising an inductive cell 122 that makes it possible to detect the position of a metal element 124 attached to a portion of the deformable wall 102. The inductive sensor 120 emits an oscillating electromagnetic field that makes it possible to induce eddy currents in the metal element in response to the oscillating electromagnetic field, which eddy currents are detected by the sensor. The sensor 120 is therefore a position sensor of the portion of the deformable wall 102 that comprises the element 124. In this case, the metal element 124 is also a means for detecting the difference between the flow rates Q10 and Q32.

[0054] Alternatively, the sensor 120 is an optical sensor, for example a laser sensor, that measures the distance between the deformable wall 102 and the sensor 120, allowing for deduction of the volumetric changes of the inner chamber C102. In this alternative, if the sensor is located outside the outer wall, the rigid shell 104 may be transparent. Alternatively, the sensor 120 is another type of optical sensor, for example a camera that measures the deformation of the wall by image analysis, allowing for deduction of the volumetric changes of the inner chamber C102.

[0055] According to one further alternative, the sensor 120 is a capacitive sensor, which has the advantage that no metal objects are required in the deformable wall 102 .

[0056] According to yet another alternative, the sensor 120 is a probe with a rod that presses against the deformable wall. This type of sensor does not require a metal object in the deformable wall 102. Advantageously, the rod of the probe is coupled to a linear potentiometer.

[0057] The electrical output signal S120 of the sensor 120 is provided directly or indirectly via a first electrical conductor 126 to an electrical control unit 130, which controls the solenoid valve 34 directly or indirectly via the electrical signal S130. Preferably, the electrical control unit 130 is incorporated into a power supply module. A control signal S130 is provided to the solenoid valve 34 via a second electrical conductor 136, the control signal S130 comprising a pressure setpoint value for the pressurized tank 32, i.e., the setpoint value for the pressure of the coated product exiting the pressurized tank.

[0058] The value of the air supply pressure set point for the pressurized tank 32 is therefore adjusted by the electronic control unit 130 in response to the output signal S120 of a sensor 120 which constitutes a device for determining, inter alia, the difference between the instantaneous discharge flow rate Q10 and the supply flow rate Q32.

[0059] The location of the accumulator 100 as close as possible to the printhead 10 makes it possible to issue commands to calibrate the pressure in the pressurized tank 32 that are less dependent on system state parameters, such as temperature, viscosity of the coating product, and pressure drop in the supply lines, than would be possible if the accumulator were located further away from the printhead. Indeed, during pressure changes at the printhead, the volume of the inner chamber C102 changes and reaches an equilibrium state depending on the supply pressure of the surrounding chamber C104. The sensor 120 then measures the deformation of the inner chamber C102.

[0060] In response, the electrical control unit 130 issues a pressure calibration signal by increasing or decreasing the supply pressure in the supply line 40 in response to the volume of the deformable chamber C102, while the pressure at the print head is always the same regardless of the system state parameters. In particular, this limits the need to rely on numerous sensors for the system state and the need for numerous process calculations to adapt the supply pressure setpoint value in response to these various state parameters. This greatly simplifies the system structure, reduces energy consumption, and improves the reliability of the control loop performance.

[0061] By measuring the position of the metal elements 124 , the cells 122 of the sensor 120 detect the deformation of the deformable wall 102 of the accumulator 100 .

[0062] After a calibration that may be performed, the detected position of the metal element 124 makes it possible to know or estimate the volume of the internal chamber C102.

[0063] In particular, the sensor 120 makes it possible to know the direction of displacement of the metal element 124, in other words to detect when the metal element 124 moves away from the cell 122 or when the metal element 124 moves towards the cell 122 along the direction of translation of the metal element 124. This change in position of the metal element along the direction of translation corresponds to a deformation of the deformable inner wall 102.

[0064] Shut-off valve 74 is assumed to be closed.

[0065] When the metal element 124 moves closer to the cell 122, this means that the volume of the internal chamber C102 increases, and in other words, the coating product tends to accumulate in this internal chamber C102. On the other hand, when the metal element 124 moves away from the cell 122, this means that the volume of the internal chamber C102 decreases, and the coating product tends to flow from the internal chamber C102 towards the valve 14 of the print head 10.

[0066] Normally, the pressure of the coating product exiting the printhead 10, as detected by the pressure sensor 78, does not change. The continuous opening and closing of the valve 14 results in a change in the volume of the inner chamber C102, which accommodates the change in the flow of coating product to the printhead. The deformable wall creates a pressure balance between the inner chamber C102 and the ambient chamber C104, so the coating product pressure in the inner chamber C102 is equal to the air pressure in the ambient chamber C104. In the illustrated example, if the supply pressure to the ambient chamber is 2 bar, the coating product pressure in the inner chamber is also 2 bar. If coating product from the printhead accumulates in the inner chamber C102, this tends to move the metal element 124 closer to the cell 122, which is detected by the sensor 120 and communicated to the electrical control unit 130 as a signal S120. Otherwise, if the coating product flows from the inner chamber C102 to the print head, this causes a displacement of the metal element 124 away from the cell 122, which is detected by the sensor 120 and communicated to the electronic control unit 130 in a signal S120.

[0067] The pressure sensor 78 can be used to detect pressure drift in the variable volume first chamber C102 and communicate a signal of such drift to the control unit 130 via a connection not shown. For example, if a significant amount of coating product reaches the variable volume first chamber C102, as long as the deformable wall 102 presses against the rigid shell 104, the variable volume first chamber C102 will no longer be able to accept more coating product, and the pressure detected by the sensor 78 will tend to increase and move away from the desired nominal value P104. This may be considered a fault. Conversely, a decrease in the pressure detected by the sensor 78 from the desired nominal value P104 is also considered a fault.

[0068] The sensor 120 provides a relatively short response time compared to the response time of the supply module 30, and more particularly compared to the response time of the pressurized tank 32. For example, for an inductive sensor, the response time of the sensor 120 may be on the order of microseconds, e.g., 1-100 μs, while the response time of the supply module 30 and the source of coating product formed by the pressurized tank 32 is on the order of 500 ms.

[0069] The internal volume of the internal chamber C102 changes over a period of the order of 1 millisecond per valve in response to the selective opening and closing of the valve 14. In practice, a printhead may include several valves, e.g., 40-100 valves, and the pressure changes resulting from the opening and closing of each of these valves occur at independent periods, which can cause pressure changes at frequencies of 60 kHz or less. In practice, opening a valve 14 has the effect of circulating the coating product through the nozzle 12 associated with that valve, thereby reducing the coating product pressure upstream of that nozzle.

[0070] Furthermore, a synergistic effect is realized by the simultaneous presence of the nozzle actuator 14 pneumatically supplied by the third supply source 96 and the regulation of the product supply pressure by the accumulator 100 according to the present invention. Indeed, the pressure regulation capability of the accumulator 100 makes it possible to correct for shortcomings in the paint supply response time and avoid excessive pressure imbalances between the coating product pressure in the nozzle and the supply pressure of the nozzle opening / closing actuator. This excessive imbalance can prevent the nozzle from closing, cause leakage, poor cutting of the deposited droplets, and significantly reduce printing performance. It is then necessary to control the air supply pressure regulation of the nozzle actuator, which introduces additional response time and makes printhead operation even more sensitive. The present invention specifically makes it possible to avoid these problems.

[0071] In addition, the movements of the robot tend to change the pressure drop in the supply line 40. These different pressure changes cause displacements of the metal elements towards / away from the cell 122, which are incorporated into a signal S120, processed by the microprocessor 132 of the electrical control unit 130 and incorporated into a signal S130. Taking into account the respective response times of the sensor 120 and the supply module 30, the consideration of the output signal S120 of the sensor 120 by the microcontroller 132 of the control unit 30 does not interfere with the control of the module 30 by the unit 130.

[0072] Advantageously, however, the accumulator 100 is configured such that the maximum deformation of the deformable wall 102 accommodates a change in the volume of the internal chamber C102 equal to the sum of the maximum flow rate of the nozzles 12 of the printhead 10 multiplied by the response time of the pressurized tank 32. Thus, the internal chamber C102 of the accumulator 100 is capable of accommodating changes in the flow rate of the coating product applied by the printhead 10 in response to selectively opening the valve 14 without a significant change in the pressure P102 in the internal chamber C102, which remains equal to the pressure P104 in the ambient chamber C104, which is set to a predetermined value by elements 110-118, as described above. In other words, assuming a slight hysteresis, the pressures P102 and P104 are constant and equal.

[0073] Under these conditions, the accumulator 100 can temporarily contain coating product when the variable-volume first chamber C102 is supplied with coating product during the application of the set pressure of the pressurized tank 32, or can expel a specific amount of coating product when the variable-volume first chamber C102 is purged of coating product, while this inner chamber C102 remains at a constant pressure P102, which allows the supply pressure of the nozzle 14 to be maintained at this value. In fact, by ignoring pressure losses in the portion of the line 70 located between elements 10 and 100, the pressure at the outlet of the printhead 10 at the upstream end 72 of the line 70 is maintained equal to pressure P102. This pressure at the printhead outlet is equal to the pressure in the supply line for the valve 14 provided in the printhead 10. In this way, the valve 14 is supplied with a pressure that is constant and can be considered equal to pressure P102 or P104.

[0074] In a not shown alternative to the first embodiment, the electric control unit 130 is integrated into the automaton that controls the solenoid valve 34. The electric control unit does not increase the cost of the installation I.

[0075] In the second and third embodiments of the present invention shown in Figures 3 and 4, elements similar to those of the first embodiment are labeled with the same reference numerals. When an element is shown in these figures without being specifically mentioned herein, it is the element having the same reference numeral as in the first embodiment. When an element is referred to herein by reference numeral without being identified by a number in these figures, it corresponds to the element having the same reference numeral as in the first embodiment.

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

[0077] In a second embodiment, the source of coating product is a tank 32 comprising a piston 33 whose displacement is controlled by an electric motor 34 driven by an electronic control unit 130 with a control signal S130. More precisely, the motor 34 comprises a control card 35, best referred to as a "variator", which receives set points or operating instructions from the electronic control unit 130, these set points incorporating in particular values ​​for the speed of displacement of the piston 33 or the speed of rotation of the motor 34, which values ​​are expressly related to the flow rate Q32 of coating product conveyed by the tank 32 to the supply line 40, which flow rate Q32 being the rate at which the print head 10 is supplied with coating product.

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

[0079] The solvent or cleaning agent is supplied to the printhead 10 by a second line 60 controlled by a third shutoff valve 62 .

[0080] A third line 70 connects the printhead 10 to a purge 80 and is provided with a fourth shutoff valve 74 .

[0081] The accumulator 100 is attached to the supply line 40 upstream of its second end 46 and, similar to the first embodiment, comprises a deformable wall 102 and a rigid shell 104. The accumulator is thus attached upstream of the printhead in a circuit C connecting the coating product source tank 32 to the purge 80. An inner chamber C102 and a surrounding chamber C104, both of variable volume, are defined in the accumulator 100, similar to the first embodiment. A sensor 120 is capable of detecting deformation of the deformable wall 102 and transmitting a signal S120 to an electronic control unit 130, which signal S120 is representative of the detected deformation, the difference in potential between the flow rates Q10 and Q32.

[0082] The pressure sensor 78 makes it possible to know the pressure in the supply line 40 upstream of the accumulator 100. Alternatively, the pressure sensor 78 is installed in the line connecting the accumulator 100 to the printhead 10, making it possible to know the pressure in the supply line 40 downstream of the accumulator 100.

[0083] A fourth line 90 supplies the valve 14 with pressurized air from a source 96 controlled by a solenoid valve 94 connected to a pressure gauge 98. A pressure sensor 92 makes it possible to know the pressure in the line 90. For example, here the pressure supplied to the valve 14 by the line 90 is considered to be constant and equal to 2 bar.

[0084] A fifth line 110 connects a source of pressurized air 116 to the ambient chamber C104 through a solenoid valve 114 connected to a pressure gauge 118. The supply pressure of the valve 14, for example through line 90, is also considered to be constant and equal to 2 bar. Advantageously, the supply pressure of the ambient chamber C104 by pressurized air is equal to the nominal supply pressure of the print head 10 by the coating product.

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

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

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

[0088] In either the first or second embodiment, the method for controlling System I comprises the following steps: a) deduction of information about the direction of development of the size of the inner container of the variable volume chamber C102 from the deformation or displacement of the wall 102; b) adjusting downward the operating set point of the coating product source 32, which is part of the electrical control signal S130, if the information estimated in step a) corresponds to an increase in the internal volume; and c) adjusting the operating set point of the coating product 32 upward if the information estimated in step a) corresponds to a decrease in the inner container. may include:

[0089] In either embodiment, the sensor may be an inductive sensor, as described with reference to the first embodiment. Alternatively, the sensor may be a capacitive sensor, an optical sensor, or a contact probe, or other types of sensors may be used.

[0090] In either embodiment, the functions of the inner chamber C102 and the surrounding chamber C104 may be reversed relative to the illustrated example: in other words, the surrounding chamber C104 may be connected to the print head and supplied with the coating product, while the inner chamber may be supplied with pressurized air.

[0091] The present invention is not limited to the case where the deformable wall 102 forms a sleeve that completely surrounds the internal chamber C102. In particular, the deformable wall 102 may only partially define the internal chamber C102, with the internal chamber C102 otherwise being defined by a solid wall, as in the case of the example peripheral chamber C104.

[0092] 4, which is compatible with all embodiments of the present invention, the accumulator 100 may provide a generally spherical or cylindrical outer wall 104 defining an interior volume, with the deformable wall 102 arranged to divide the volume defined by the outer wall 104 into a first chamber C102 and a second chamber C104, one of which is in fluid communication with the printhead and the other of which is supplied with controlled air by a pressurized air source 116. After pressure equilibration, the deformable wall 102 deforms and a sensor 120 measures this deformation.

[0093] According to another alternative of the first and second embodiments, not shown, the deformable wall 102 may be replaced by a piston, which is a rigid part. In other words, the wall separating the variable-volume chambers C102 and C104 is a piston, which makes it possible to improve the accuracy of the measurements made by the sensor 120, since the volume change and the displacement of the piston are linear. Such an approach requires the provision of a seal between the two variable-volume chambers C102 and C104, which is not necessary with a deformable wall. In this case, the translational movement of the piston allows the pressures P102 and P104 in the two chambers C102 and C104, respectively, to equilibrate.

[0094] When the wall 102 is deformable, it may be made of an elastomer, such as FKM (fluorocarbon) or FFKM (perfluoroelastomer) or any other elastically deformable product, such as rubber, possibly with a tetrafluoroethylene coating that ensures the chemical resistance of the rubber to the coating product.

[0095] 4, variable volume chambers C102 and C104 are separated by a deforming wall 102, which, in the event of a temporary pressure difference between these chambers, forces the pressure P102 in chamber C102 and the pressure P104 in chamber C104 to equalize as soon as an imbalance occurs. Unlike the first and second embodiments and the alternatives described above with pistons, the position of 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 from the print head is determined. This can be done by measurement or, after calibration, by extrapolating that the size and / or mass of the droplets of coating product exiting the nozzle 12 is known. As a non-limiting example, a control unit 121 incorporated into the print head 10 can be used to determine the number of openings and closings of the valve 14 over a given period of time. Assuming each opening and closing ejects a droplet, the number of droplets ejected over that period, and therefore the flow Q10, is known. The number of openings and closings is known from the control signal received by the control unit 121, so the control unit does not need to count the number of openings and closings. This number is communicated to the electrical control unit 130 in the output signal S121 of the control unit 121, which travels over the electrical conductor 126. The microprocessor 132 can then calculate the instantaneous flow rate Q10.

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

[0098] Alternatively, the control unit 121 may 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 from the outlet of the tank 32, which is the theoretical flow rate for supplying the coating product to the printhead 10, is calculated by the control card 35 depending on the speed of displacement of the piston 33, which is obviously related to the speed of rotation of the motor 34.

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

[0101] The electronic unit 35, 121 or equivalent makes it possible to detect when the flows Q10 and Q32 differ and constitutes a means for detecting the difference between the instantaneous discharge flow Q10 and the supply flow Q32.

[0102] The microprocessor 132 can then compare the flow rates Q10 and Q32 and adjust the flow rate Q32 to match the flow rate Q10. In other words, the microprocessor 132 can calculate the 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 point for 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 point for the flow rate Q32.

[0103] In this way, particularly in the case of a supply module 30 having a motor / piston or gear pump, in other words when introducing volume, it is possible to adjust the supply flow rate Q32 depending on the instantaneous flow rate Q10 of the printhead operating at constant pressure.

[0104] In this third embodiment, the accumulator 100 is used only to absorb, in other words compensate for, momentary changes in flow rate and pressure, while adjustments are made by the control unit 130 based on the cumulative volume deviations of the discharge Q10 and supply Q32.

[0105] This third embodiment requires knowing the size and / or mass of the droplets to determine the instantaneous volume Q10, so that the difference between the flow rates Q10 and Q32 is compensated for by the accumulator 100. Knowing the droplet size is more complicated than measuring displacement as in the first and second embodiments, but is feasible because this size or mass can be determined optically by a device capable of measuring the droplets prior to application, or by measuring the total volume with each coating product.

[0106] In this third embodiment, pressure sensor 78 functions similarly to the first embodiment, but is more important since the deformation of the deformable wall is not detected due to the absence of sensor 120.

[0107] In this alternative third embodiment, the flow rate Q32 is calculated in the control unit 130.

[0108] In an alternative to the first and second embodiments, and / or in a third embodiment, in which the wall 102 is replaced by a piston, advantageously the maximum stroke of the piston corresponds to a change in the volume of the variable volume first chamber C102 equal to the sum of the maximum flow rate of the nozzles 12 of the print head 10 multiplied by the response time of the coating product source 32.

[0109] Alternatively, in the second and third embodiments, the electrical control unit 130 and the control card 35 are integrated into a single electrical device, advantageously incorporated into the motor 34. In this case, the signal S120 or S121 is fed directly to the motor, and the set points for motor operation are generated in this electrical device.

[0110] Alternatively, and regardless of embodiment, the source of coating product may be different from the example shown in the figures and labeled 32. For example, the source of coating product may be a pressure regulator, a gear pump, supplied at a pressure higher than the printhead supply pressure, to adjust the supply pressure in supply line 40.

[0111] The value of the control pressure P104 may be, for example, about 2 bar and can be adjusted depending on the viscoelastic properties of the coating product, the temperature, and the state parameters of the system.

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

[0113] Instead, at least one of signals S120, S121, and S130 is conveyed over a wireless path.

[0114] According to one other alternative of the invention not shown, the circuit C is a closed loop for circulating the coating product, with the coating product from the outlet 108 of the first variable volume chamber C102 returning to the tank 32.

[0115] According to one other alternative of the invention, not shown, the coating product tank 32 is included in the print head 10 or is located in the immediate vicinity of this head, downstream of the second filter 47. In this case, the effect of pressure loss in the arm 22 of the robot 20 is minimized.

[0116] According to one other, not shown, alternative of the invention, the coating product source is a volumetric pump, in which case the operating setpoint value delivered by the electronic control unit is the value of the speed of rotation of this pump.

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

[0118] The above-considered embodiments and alternatives may be combined with one another in the construction of the appended claims.

Claims

1. Equipment (I) for applying a coating product, wherein equipment (I) comprises a print head (10) having a plurality of nozzles (12) and supplied by a coating product supply source (32), and each nozzle is controlled by a valve (14) supplied by the coating product supply source. The equipment includes a coating product accumulator (100) installed in a circuit (C) for the circulation of the coating product that passes through the print head (10); The accumulator comprises a deformable or movable wall (102) that at least partially defines a first variable-volume chamber (C102) supplied by a coating product and a second variable-volume chamber (C104) supplied by gas under a predetermined pressure (P104); The predetermined value (P104) for supplying the variable-volume second chamber (C104) is equal to the nominal operating pressure of the print head (10); A variable-volume first chamber (C102) is either supplied with or purged of coating product by the difference between the instantaneous flow rate of coating product released from the print head (10) (Q10) and the supply flow rate (Q32) from the coating product supply source (32) to the print head (10); The equipment is equipped with means (120, 124; 121, 35) for detecting the difference between the instantaneous discharge flow rate (Q10) and the supply flow rate (Q32); and The equipment includes a control unit (130) configured to adjust the value (S130) of the operating setpoint of the coating product supply source (32) in a direction that reduces the difference between the instantaneous discharge flow rate (Q10) and the supply flow rate (Q32). A facility characterized by the following:

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

3. The apparatus according to claim 2, characterized in that the sensor (120) is an inductive sensor, a capacitive sensor, an optical sensor, or a probe sensor.

4. The apparatus according to claim 1, characterized in that the means for detecting the difference between an instantaneous discharge flow rate (Q10) and a supply flow rate (Q32) comprises a first unit (121) for determining the instantaneous discharge flow rate (Q10) and a second unit (35) for determining the supply flow rate (Q32), and the control unit (130) is configured to adjust the value of an operation setpoint according to the difference between the instantaneous discharge flow rate (Q10) determined by the first unit and the supply flow rate (Q32) determined by the second unit.

5. The apparatus according to any one of claims 1 to 4, characterized in that the wall (102) is elastically deformable under the nominal operating conditions of the apparatus (I).

6. The apparatus according to claim 5, characterized in that the wall has an element (124) and the position of the element (124) can be detected by a sensor (120).

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

8. The apparatus according to claim 5, characterized in that the deformable wall (102) is sleeve-shaped and extends between a first port (104) for the coating product to enter the accumulator (100) and a second port (108) for the coating product to be discharged from the accumulator.

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

10. The apparatus according to claim 5, characterized in that the maximum deformation of the deformable wall (102) or the displacement stroke of the movable piston corresponds to a change in the volume of a variable-volume first chamber (C102), wherein the maximum flow rate of the nozzle (12) of the print head (10) multiplied by the response time of the coating product supply source (32).

11. The apparatus according to any one of claims 1 to 4, characterized in that a second variable-volume chamber (C104) is provided with an outlet opening, and the second variable-volume chamber is supplied by a continuous gas flow between a supply line (110) and its outlet opening.

12. The apparatus according to any one of claims 1 to 4, characterized in that the accumulator (100) is installed downstream of the print head (10) in the circuit (C).

13. The apparatus according to any one of claims 1 to 4, characterized in that the accumulator (100) is installed upstream of the print head (10) in the circuit (C).

14. A method for controlling equipment (I) for applying the coating product described in claim 2, a) A step of estimating information about the direction of change in the size of the internal volume of the first chamber (C102) of the variable volume of the accumulator (100) from the deformation or displacement of the wall (102); b) If the information estimated in step a) corresponds to an increase in the internal volume, the step of adjusting the value of the operating setpoint (S130) of the coating product supply source (32) downwards; and c) If the information estimated in step a) corresponds to a decrease in the internal volume, the step of adjusting the value of the operating setpoint (S130) upward. A method characterized by comprising at least the following.

15. The method according to claim 14, characterized in that the operating setting point is the control pressure of the pressurized tank (32), the displacement speed of the piston (33) of the tank equipped with the piston, or the rotational speed of the positive displacement pump.

16. A method for controlling equipment (I) for applying the coating product described in claim 4, a') A step of calculating the difference between the instantaneous flow rate (Q10) of the coating product passing through the print head (10) and the flow rate (Q32) of the coating product supplied to the print head; b') If the difference calculated in step a') is positive, the step of adjusting the print head coating product flow rate (Q32) setting point upward; and c') If the difference calculated in step a') is negative, adjust the printhead coating product flow rate (Q32) setting point downward. A method characterized by comprising at least the following.

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