Abstract:
An apparatus for electrostatically spraying a coating product. The apparatus includes a sprayer with first and second pipes which control the flow of the coating product. Air is controlled by at least one valve. The sprayer includes a device for controlling the opening/closing of the valve, a high voltage unit. A generator includes a module for controlling power supplied to the high voltage unit. The sprayer includes a first sensor suitable for detecting the position of a shutter of the valve relative to a seat and for outputting a signal used by the control module to control the power supplied to the high voltage unit, and a second sensor suitable for detecting the position of a switch positioned on the spray gun and for outputting a signal used by the control module to control the power supply of the high voltage unit.

Description:
This application is a National Stage application of PCT international application PCT/EP2014/056980, filed on Apr. 8, 2014 which claims the priority of French Patent Application No. 1353185 entitled “APPARATUS FOR ELECTROSTATICALLY SPRAYING A COATING PRODUCT AND METHOD FOR CONTROLLING GENERATOR FOR SUPPLYING POWER TO A HIGH VOLTAGE UNIT IN SUCH AN APPARATUS”, filed with the French Patent Office on Apr. 9, 2013, both of which are incorporated herein by reference in their entirety. 
     FIELD OF THE INVENTION 
     The invention relates to an apparatus for electrostatically spraying a coating product as well as a method for controlling a generator supplying power to a high-voltage unit in such an apparatus. 
     BACKGROUND OF THE INVENTION 
     Apparatuses for electrostatically spraying a coating product make it possible to electrostatically charge a coating product and offer a good transfer rate of the coating product onto the support to be covered. 
     One recurring issue in apparatuses for electrostatically spraying a coating product is controlling the start-up of the electrostatic high voltage, and therefore controlling a generator for supplying power to a high-voltage unit comprised in a sprayer, the sprayer being comprised in the apparatus. 
     In the field of spraying a coating product using an electrostatic sprayer, it is known to install, on a spraying air flow pipe of the sprayer, a pneumatic switch, more frequently called “flow rate contact”, which closes an electric contact when it detects a sufficient air flow rate. The closing of the electric contact makes it possible to supply power to a high-voltage unit. Such a flow rate contact has a relatively long response time, a significant bulk and weight, and a high remanence. Its operation is not very reliable when the air flow rate is low. This means that the triggering point for the high voltage is more or less precise, in particular due to the response time and remanence of the sensor. 
     It is also known from U.S. Pat. No. 4,441,656 to control a generator for supplying power to a high-voltage unit owing to the position of one end of a trigger actuated by an operator. This approach makes possible to ensure that the high voltage is triggered only when the trigger is actuated. This material does not make it possible to account for any defects in the air supply of a sprayer in which spraying air is used. Furthermore, this device is cumbersome, heavy and expensive. 
     It is also known to produce a sprayer for which the action on a trigger opens an air leak in the sprayer, that leak being protected by one or two pressure sensors mounted in differential that make it possible, when such an air leak is detected, to trigger a generator for supplying power to a high-voltage unit. The problem created by the use of an air leak on a sprayer is a needless consumption of compressed air, which quite often a source of bother for the operator, and the establishment of complex pneumatic circuits that withstand temporary overloads poorly, which is a source of breakdowns and malfunctions. Furthermore, in this type of system, time drift phenomena are commonly observed in the detection threshold of the pressure sensors. This means that the high-voltage unit is no longer reliably triggered, resulting in significant excess product consumption and additional risks for the safety of people and property. 
     Furthermore, it is known from FR-A-2,578,450 to use a first magnetic sensor actuated by a permanent magnet positioned in a variable position on a gun body and a second sensor used as a switch and which makes it possible to deliberately cut the generation of a high voltage by a high-voltage unit, so as to facilitate the coating of hollow bodies. This type of device implies that the sensors must be able to cut an alternating voltage varying from 20 to 35 kHz with an intensity of at least 1 A and a peak voltage of approximately 80 to 100 Volts. Indeed, once the sensors are actuated, they directly cut the electricity supply of the high-voltage unit by closing or cutting the electricity circuit of the primary of the transformer. Then, during the use of this type of apparatus, the operator presses and releases a trigger of a sprayer between 6 and 12 times per minute. The first sensor is therefore considerably biased. These stresses lead to using sensors with dimensions that are practically incompatible with their insertion inside a gun for electrostatically spraying a coating product, and even using large sensors, their lifespan is greatly reduced in such a device, due to the high voltage and current levels that they must cut. 
     Also known from JP-A-2004 26 7960 is an electrostatic spraying apparatus that comprises a module for controlling the current delivered to a high-voltage unit, as a function of a specific parameter inherent to an air valve of the sprayer. However, in such an apparatus, the control module directly cuts the current and voltage delivered to the high-voltage unit by the control module, which creates problems in terms of lifespan and sizing of the control module and any member for measuring a specific parameter. 
     The invention more particularly aims to resolve these drawbacks by proposing an apparatus for electrostatically spraying a coating product that allows a reliable and precise control of a power supply generator of a high-voltage unit, without having to detect the consumption of a fluid, such as air or coating product. 
     BRIEF SUMMARY OF THE INVENTION 
     To that end, the invention relates to an apparatus for electrostatically spraying a coating product comprising:
         a sprayer provided with a first pipe and a second pipe, respectively for the flow of coating product and air, in which the flow of coating product and air is controlled by at least one valve, said sprayer also comprising means for controlling the opening/closing of the valve and a high-voltage unit,   a high-voltage unit power supply generator, said generator comprising a control module for the current delivered to the high-voltage unit.       

     According to the invention, the sprayer comprises at least one first sensor able to detect the position of a shutter of the valve relative to the seat and outputting a signal that can be used by the control module to control the supply of current for the high-voltage unit, while the sprayer comprises a second sensor able to detect the position of a switch positioned on the gun and to deliver a signal that can be used by the control module to control the power supply for the high-voltage unit. 
     Owing to the invention, the sensors used have dimensions compatible with their insertion in a sprayer gun, since the current and voltage crossing through the sensors have low levels. In fact, the signal produced by the sensor does not directly cut the power supply of the high-voltage unit, but rather sends a signal to the control module for the current delivered to the high-voltage unit that cuts or itself triggers the power supply of the high-voltage unit as a function of the signal. This creates a much safer and longer lasting operation of the sensors, and the control of the power supply of the high-voltage unit is improved. 
     According to advantageous but optional aspects of the invention, such an apparatus for electrostatically spraying a coating product may incorporate one or more of the following features, considered in any technically possible combination:
         The sprayer comprises a first valve controlling the flow of coating product in the first pipe and a second valve controlling the flow of air between two segments of the second pipe, while the first sensor is able to detect the position of a shutter of the first valve.   The sprayer comprises a first valve controlling the flow of coating product in the first pipe and a second valve controlling the flow of air between two segments of the second pipe, while the first sensor is able to detect the position of a shutter of the second valve.   The first valve controlling the flow of coating product comprises a shutter forming a needle sliding in a barrel of the sprayer, designed to control the flow of coating product and designed to be brought to a high voltage, to electrically charge the coating product.   The sprayer comprises a spring made from a nonmagnetic material that exerts a return force on the shutter of the valve.   The needle comprises an end with a shape suitable for bearing against a seat of the first valve with a corresponding shape under the effect of the return force.   The high-voltage unit is positioned in the barrel of the sprayer and is able, in response to the supply of the high-voltage unit by the power source, to generate a direct high voltage and to apply the high voltage to the end of the needle.   The switch is designed to be manipulated by an operator to go from a first configuration of the sprayer, where the high voltage is applied to the end of the needle, to a second configuration, where the high-voltage unit is not supplied with electricity.   The second valve controlling the flow of air comprises a shutter, with a suitable shape for bearing against a seat of the second valve with a corresponding shape, under the effect of the return force.   A trigger is articulated on the body of the sprayer around an axis globally perpendicular to a longitudinal axis of a barrel of the sprayer.   The trigger comprises an extension, bearing against the shutter of the valve and able to exert, on the shutter, a force opposite the return force, to axially offset the shutter of the valve, along the longitudinal axis, relative to the seat.   The first and second sensors are mounted in series on a cable connecting those sensors to the control module.   The first sensor is a Reed sensor or a Hall effect sensor.   The sprayer comprises a tight zone within which the sensor(s) are positioned.       

     The invention also relates to a method for controlling a power supply generator of a high-voltage unit comprised in an apparatus for electrostatically spraying a coating product. According to the invention, the method comprises the following steps:
         a) detecting the position of a shutter of a valve comprised in the sprayer and setting in motion using its opening/closing means, on the one hand, and changing the position of a switch fastened on the gun on the other hand;   b) sending a signal corresponding to the position of the valve and the position of the switch to a control module of the generator by means of a connection suitable for the type of sensor used;   c) controlling the cut-off or triggering of the generator, based on the received signal and using the control module.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The invention will be better understood and other advantages thereof will appear more clearly in light of the following description of one embodiment of an apparatus for electrostatically spraying a coating product and a control method according to its principle, provided solely as an example and done in reference to the appended drawing, in which  FIG. 1  diagrammatically shows an apparatus according to the invention, with a sprayer shown in cross-section. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The apparatus I shown in  FIG. 1  allows electrostatic coating of an object, not shown. This apparatus I comprises a sprayer or gun  1  for electrostatic coating supplied with liquid coating product from a coating product reservoir  30 , via a tube  31 . 
     The gun  1  is also connected to a pressurized air source  40  by a tube  41 . The air coming from the source  40  is used to spray the coating product by driving it from the gun  1  toward the object to be coated. 
     Reference  2  denotes a housing situated in a barrel  11  of the gun  1  in which a needle  62  slides. The needle is designed to control the flow of coating product and designed to be brought to a high voltage so as to electrically charge the coating product. 
     Reference  4  denotes a pipe for the flow of coating product inside the gun  1 . This pipe  4  for the flow of the coating product is connected to the hose  31  by means of a connector  32 , situated at the base of a handle  16  of the sprayer  1 . The pipe  4  emerges near an outlet S for spraying a coating product at one end  63  of the needle  62  that forms a triangular tip. In  FIG. 1 , the end  63  bears against a seat  64  with a corresponding shape and plugs the pipe  4 . Thus, the assembly formed by the needle  62  and the seat  64  corresponds to a valve  6  for controlling the flow of the coating product. 
     Reference  5  denotes a pipe for the flow of air inside the gun  1 . That pipe  5  comprises two segments  5   a ,  5   b , between which there is a valve  7  for controlling the flow of air. The second segment  5   b  of the pipe  5  emerges at the outlet S for spraying the coating product. 
     The air flow pipe  5  is connected to the hose  41  by means of a connector  42 , situated behind a body  21  of the gun  1 . 
     The valve  7  for controlling the flow of air comprises a shutter  72 , with a shape suitable for bearing against a seat  74 , with a corresponding shape, under the effect of a return force R exerted by a spring  22  kept in position by a stopper  23  forming a fixed bearing point for that spring  22 . Similarly, the end  63  of the needle  62  has a suitable shape for bearing against the seat  64 , with a corresponding shape, under the effect of the return force R. 
     The gun  1  is also connected to a generator  8  by an electric cable  9  that makes it possible to supply power to a high-voltage unit  10 , positioned in the barrel  11  of the gun  1 . The generator  8  itself is supplied with power from the sector, using a cable  82 . 
     Reference  12  denotes a module for controlling the power supply delivered to the high-voltage unit  10  by the generator  8 . This control module  12  is comprised in the generator  8 . When it is supplied by the generator  8 , the high-voltage unit  10  generates a direct high voltage applied to the end  63  of the needle  62  that electrically charges the sprayed coating product at the outlet S by ionization. Thus, the high-voltage unit is able, in response to its supply from the generator  8 , also called power supply  8 , to generate a direct high-voltage and to apply the high-voltage to the end  63  of the needle  62 . 
     Advantageously, the high-voltage unit is able, in response to being powered by the generator  8 , to generate a direct high voltage and to apply the high voltage to a charge electrode, not shown, positioned at the outlet S, near the end  63 . The coating product is thus electrically charged. 
     A trigger  15  is articulated on the body  21  of the gun  1  around an axis X 2  globally perpendicular to the longitudinal axis of the barrel Y 2  and makes it possible to open and close the air valve and allows the needle  62  to move in a direction parallel to the axis Y 2 . More specifically, the trigger  15  comprises an extension  152  bearing against the shutter  72 , which makes it possible to exert a force on the shutter  72  opposite the return force R to axially shift the shutter  72 , along the axis Y 2 , relative to its seat  74 . The extension  152  is therefore able to exert, on the shutter  72 , a force opposite the return force R to shift the shutter  72  axially, along the longitudinal axis Y 2 , relative to the seat  74 . Likewise, the needle  62  is attached to the extension  152 , which makes it possible to exert, on the needle  62 , a force opposite the return force R to shift the needle  62  axially along the axis Y 2 , and more specifically its end  63  relative to its seat  64 . The extension  152  is therefore able to exert, on the needle  62 , a force opposite the return force R to shift the needle  62  axially, along the longitudinal axis Y 2 , relative to the seat  64 . When the handle  15  is released, the spring  22  pushes the needle  62  and the shutter  72  back toward the position interrupting the pipes  4  and  5  shown in  FIG. 1 . The trigger  15  thus makes it possible to control the flow of coating product and pressurized air in the pipes  4 ,  5 . 
     A sensor  17  is positioned in the body  21  near the needle  62  and detects the movement of the needle  62  when the trigger  15  is actuated. This sensor  17  may be of any type adapted to its function, and in particular, a Reed sensor. Alternatively, it is a capacitive or inductive sensor or a Hall effect sensor, or a magnetic field detector. When the operator actuates the trigger  15  and exerts a force represented by arrow F 15 , the end  63  of the needle  62  is taken off of the seat  64  and a flow of coating product is produced through the pipe  4 . At the same time, the shutter  72  of the air valve  7  is taken off of the seat  74  and a flow of air is produced through the air flow pipe  5 . Thus, a flow of air and coating product is produced toward the outlet S. 
     The sensor  17  is connected to the control module  12  by means of the cable  13 . 
     Furthermore, a second sensor  18  is positioned near a switch  19  positioned on the body  21  of the gun  1 . The operator can manually change the position of the switch  19 , knowing that the sensor  18  is able to detect the position of the switch  19 . The sensor  18  may be of the same type as the sensor  17  or of another type. 
     The cable  13  comprises a first segment  13   a  that extends between the control module  12  and the sensor  17 , a second segment  13   b  that extends between the sensors  17  and  18 , and a third segment  13   c  that extends between the sensor  18  and the control module  12 . Thus, the sensors  17  and  18  are connected in series to the control module  12 , through the cable  13 . The sensors  17  and  18  are for example mounted on a printed circuit, not shown, and overmolded in an electrically insulating resin. 
     The switch  19  is designed to be manipulated by the operator to go from a first “electrostatic” configuration of the gun where the high voltage is applied to the end  63  of the needle  62  to a second “purely pneumatic” configuration where the unit  10  is no longer supplied. This second configuration is useful to coat certain hollow objects or objects with complex shapes. 
     Furthermore, the spring  22  is made from a nonmagnetic material. It therefore does not disrupt the movement detection done by the sensors  18 ,  17  in the event the sensors  17 ,  18  are Reed sensors, and more generally magnetic-type sensors. 
     The serial connection between the sensor  17 , the sensor  18  and the control module  12  makes it possible to send a signal S 1  to the control module  12  representative of the movement of the needle  62  and the position of the switch  19 . The control module  12  controls the power supply of the high-voltage unit  10  as a function of the value of the received signal S 1 . 
     The sensors  17  and  18  are positioned in a zone A of the body  21  that is sealed so that no impurity disrupts their operation. In the usage configuration of the gun  1  shown in  FIG. 1 , the zone A is situated above the valve  7  and the needle  62 , in the upper part of body  21 , which facilitates access to the switch  19 . 
     In order to control the high-voltage unit  10 , the electrostatic spraying apparatus detects the movement of the needle  62  and takes any change in position of the switch  19  into account. 
     In the event the sensors  17  and  18  are Reed sensors, they are positioned in the part A of the body  21  to be closed when the needle  62  is offset from the seat  64  and when the switch  19  is the first ON position corresponding to the “electrostatic” position of the gun  1 . Thus, when the operator actuates the trigger  15  while the switch  19  is in its first position, the cable  13  forms an uninterrupted electric loop, which can be detected by the control module  12 , which injects a signal on that cable and recovers it in the form of the signal S 1 . In that case, the control module  12  steers the generator  8  to supply the unit  10 . In the event one of the sensors  17 ,  18  is open, i.e., if the needle  62  and more particularly its end  63  bears on the seat  64 , or if the switch  19  is in a second OFF position corresponding to the “purely pneumatic” configuration of the gun, the loop formed by the cable  13  is interrupted and the recovered signal S 1  is null. In that case, the control module  12  steers the generator  8  not to supply the unit  10 . 
     Other manners of transmitting the signal S 1  to the control module  12  can be considered, in particular as a function of the type of sensors  17  and  18 . 
     In all cases, a signal S 1  corresponding to the movement of the coating product valve  6 , and more particularly the needle  62 , and the position of the switch  19  is sent to the control module  12  via the cable  13  appropriate for the type of sensor used. The control module  12  triggers or cuts the power supply of the high-voltage unit  10  as a function of the received signal S 1 . 
     When the switch  19  is in the OFF position, the signal S 1  sent by the sensor  18  to the control module  12  triggers the cutoff of the power supply of the high-voltage unit  10  by the generator  8 . That cutoff is maintained until the switch  19  is in the ON position, and for example allows the operator to more easily coat the hollow bodies while avoiding counter-emission or Faraday cage phenomena. 
     When the switch  19  is in the ON position, the cutoff or triggering of the supply of the high-voltage unit  10  by the generator  8  depends on the position of the needle  62  of the coating product valve  6 . If the detected movement corresponds to a travel exceeding the reference value, then the signal S 1  sent by the sensor  17  to the control module  12  causes the triggering of the supply of the high-voltage unit, and otherwise, the signal S 1  sent by the sensor  17  causes the cutoff or non-triggering of the supply of the high-voltage unit. 
     Alternatively, the sensor  17  detects a movement of the shutter  72  of the air valve  7  and not a movement of the needle  62  of the valve  6 . The operation remains identical to that previously described. 
     According to another alternative, the sprayer may also comprise a sensor  17  and no sensor  18  or switch  19 . In that case, the triggering of the high voltage may not be cut manually by the operator and depends only on the movement of the valve  7  or the valve  6 . 
     The apparatus shown in  FIG. 1  has a manual sprayer. The invention is, however, applicable to an automatic sprayer, in which case the valves are controlled remotely. 
     According to another alternative, the sprayed coating product is powdered, in which case, it suffices to have only one coating product flow pipe through which the powdered coating product is pneumatically conveyed. There is no need for an air flow pipe, and a single valve is used. 
     According to one alternative, the connection between the sensors  17 ,  18  and the control module  12  is a wireless connection. The sensors  17 ,  18  can transmit the signal S 1  to the control module  12  using radio waves. 
     According to another alternative, the generator  8  is supplied by an autonomous source. 
     According to another alternative, the air flow pipe  5  comprises two second segments that are positioned along the housing of the needle and emerge at the outlet S on either side of the needle  62 . 
     The technical features of the embodiment and alternatives considered above may be combined with one another to create other embodiments.