Patent Publication Number: US-2022236054-A1

Title: Method of electronically tracking physical deposition of coating material

Description:
TECHNICAL FIELD 
     The invention relates to a sensor kit for a spray gun and processing of data received from the sensor kit. 
     BACKGROUND 
     Spray painting is a technique of using a spray gun to spray a coating through the air onto a surface. The coating may be a paint, ink, varnish, clear coat, or any other type of coating. A spray gun may be hand-held by an operator, and it may require significant skill to apply a thin coating with consistent layer thickness. Whether or not the operator has skill, final thickness of the layer may vary, which may have an impact on durability of the coating and reliability of sensors covered by the coating, like proximity radar systems of cars. 
     SUMMARY 
     In order to track the result of the coating process, it is preferred to have data on the final layer of coating available, in particular with respect to an amount of coating material available on the surface to coat, per unit of area. 
     A first aspect provides a method of electronically tracking of spray coating of a coating fluid on a physical surface by a spray gun arranged to spray the coating fluid in a spray direction. The method comprises, in an electronic computing system receiving, from a distance sensor module comprising at least one distance sensor, the distance sensor module being connected to the spray gun, distance data indicating a physical distance between the spray gun and the surface, obtaining, from an electronic memory, three-dimensional coating model data of a spray cone associated with the spray gun and receiving, from a positional sensing system connected to the spray gun, position data providing an indication of the spray gun relative to a first position on the physical surface. The method further comprises calculating, based on the distance data, the position data and the three-dimensional coating model, coating deposition area data of positional spray coating deposition on an area of the physical surface per unit of time. In addition thereto, the method comprises obtaining curing data related to the coating fluid, calculating, based on the coating deposition area data of positional spray coating deposition on the area of the physical surface per unit of time, thickness of a layer of coating fluid on the physical surface and based on the curing data, determining cured thickness of a cured layer of coating fluid on the physical surface. 
     Spray guns for spraying coating fluids are precision instruments, of which characteristics are well known. One particular characteristic is the shape of the spray cone, the flow rate of coating fluid and the density of fluid in the spray cone. With the flow rate or speed and other characteristics of droplets, a model of the spray cone, a three-dimensional coating model may be construed. Such model may comprise, at various locations in the cone, for example at regular grid points, each grid point representing a particular volume, a mass flow or volume flow within the particular volume. With the distance data, the location of the physical surface on which the coating fluid impinges is known relative to the nozzle of the spray gun may be determined. And with that information, the mass flow or volume flow of coating fluid within the spray cone at the physical surface may be determined as positional spray paint deposition, in this case per unit of time. 
     In particular applications, the thickness of the cured layer is relevant, in particular at certain locations on the physical surface. The thickness of the cured layer is generally less than the thickness of a layer that has just been sprayed. The relation between a just sprayed layer, that may be wet, and a cured layer, that may be dry, may be linear or non-linear. 
     An implementation of the first aspect further comprises calculating, based on the distance data, the position data, the coating deposition area data and time, characteristics of a layer of coating fluid on the physical surface. With a deposition rate of coating fluid known in a plane where the physical surface and the spray cone intersect, building up of a layer by virtue of that deposition may be calculated, including characteristics of that layer. 
     In another implementation, the positional sensing system comprises a first accelerometer for determining a first acceleration substantially perpendicular to the spray direction and a second accelerometer for determining a second acceleration substantially perpendicular to the spray direction, the first direction being substantially perpendicular to the second direction. The method further comprises integrating the first acceleration in time twice over time for obtaining first displacement data in the first direction as a first part of the position data and integrating the second acceleration in time twice over time for obtaining second displacement data in the second direction as a second part of the position data. 
     By integrating acceleration once over time, velocity data may be determined. By integrating the velocity over time—or by integrating the acceleration over time—displacement of the sensor kit may be calculated. And with the sensor kit attached to a spray gun with a pre-determined position and orientation of the nozzle of the spray gun, velocity and displacement of the nozzle may be calculated. And with that, displacement of the spray cone may be determined. With the directions perpendicular to the spray direction of the nozzle and an assumption that an operator will always spray in a direction perpendicular to the physical surface to spray, displacement of the spray cone and the plane of intersection of the spray cone and the surface may be determined. This data may be used to determine deposition of coating fluid on the surface over time, over an area over which the cone is displaced. Additionally, other data, like distance data may be used. 
     Yet another implementation further comprises determining, based the received position data, whether the spray gun is moving in a swinging motion and starting the calculating if it is determined that the spray gun is moving in a swinging motion. Spraying of coating fluids is mostly done by swinging the spray gun. An amount of actuators on the spray kit is preferably kept as low as possible, if possible such actuable inputs are eliminated. By automatic detection of a start of the spraying process, no actuator may be required to start the logging of data. 
     in yet a further implementation, the positional sensing system comprising at least one of a first accelerometer and a second accelerometer and determining whether the spray gun is moving in a swinging motion comprises determining whether the acceleration value of at least one of a first accelerometer and a second accelerometer changes sign at least two times during a pre-determined interval. Swinging may be performed sideways, up and down or a combination thereof. At the extremities of a swing and in the middle of a swing, the value of the acceleration will change sign. 
     In again a further embodiment, determining whether the spray gun is moving in a swinging motion comprises determining whether the acceleration value of at least one of a first accelerometer and a second accelerometer changes sign at least three times during a pre-determined interval and a first time period between a first sign change and a second sign change varies from a second time period between the second sign change and a third sign change by less than a pre-determined amount. In a full swing, from one extremity to another extremity, including the extremities, the acceleration will change sign three times. In an even swing, the time periods between the zero crossing will be substantially the same-give or take 2% to 5% or possibly 5% to 10%. 
     Again another implementation further comprises determining an orientation of the spray gun and the spray direction relative to the physical surface and calculating the coating deposition area data of positional spray coating deposition is also based on the orientation. In case the spray direction of the spray gun is not aimed perpendicularly at the physical surface on which paint or another coating is to be deposited, the coating fluid may not be deposited in the intended circular or elliptical area, but in an area having a different shape. Using data on the orientation of the spray cone relative to the physical surface and using angle data in particular aids in this issue. 
     In a further implementation, the distance sensor module comprises multiple distance sensors and determining the orientation comprises obtaining multiple distance sensor values from the comprises multiple distance sensors and determining the orientation based on differences between the multiple distance sensor values. With distance sensors provided in a plane perpendicular to the spray direction, distances detected are substantially equal. If the sensor kit and with that, the spray direction is not provided to the physical surface in a perpendicular direction, the distances measures are different and with that, also sensor values. From the sensor values, the angle may be determined. 
     Another implementation further comprises receiving, from the positional sensing system, rotational data indicative of a rotational position of the spray gun transversal to the spray direction and determining, based on the position data and the rotational data, the orientation. This provides another way of determining the orientation. 
     In again another implementation, calculating the coating deposition area data of positional spray coating deposition comprises determining cone intersection plane coating fluid data, based on the distance data and the three-dimensional coating model data and calculating the coating deposition area data of positional spray coating deposition is based on the cone intersection plane coating fluid data. The cone intersection plane coating fluid data may comprise data on a deposition rate in a particular area, for example volume or mass. The intersection of cone and physical surface defines an area and deposition may be determined in that area. And if displacement data over time is used, a layer and thickness thereof on the physical surface may be determined. 
     Again another implementation further comprises receiving an input related to selection of a pre-determined coating fluid; and obtaining the three-dimensional coating model data of the spray cone associated with the spray gun in response to providing data related to the pre-determined coating fluid to the electronic memory. Different types of coating have different characteristics. With this implementation, different characteristics may be taken into account, providing more accurate data. Additionally or alternatively, other data like humidity, temperature, other environmental data on an ambient environment, other data, or a combination thereof may be taken into account. 
     Again a further implementation further comprises obtaining coating fluid flow data providing an indication of a mass flow rate of the coating fluid through the spray gun and adjusting the coating model data based on the coating fluid flow data. Different types of coating may have different spray characteristics, like droplet size, droplet density, viscosity, relative mass, flow rate dependency on air pressure and/or air flow, other, or a combination thereof. This implementation takes that into account, providing more accurate data. Coating fluid data may be indicated by a directly or indirectly measured mass flow or volume flow of coating fluid. A flow of actual coating fluid may be measured and determined. Alternatively of additionally, flow of air, optionally with features including at least one of pressure, mass flow, flow velocity, supply duct bore diameter, other, or a combination thereof and the flow of coating fluid may be determined based on the flow of air and, optionally, other parameters. 
     In yet a further implementation, the coating fluid flow data is provided with a first timestamp the distance data is provided with a second timestamp and the position data is provided with a third timestamp, the method further comprising matching the fluid flow data, the distance data and the position data over time based on the first timestamp, the second timestamp and the third timestamp. Determining flow data may not be possible with the sensor kit, as it may require direct contact with a flow of coating fluid and/or air and the sensor kit is preferably conveniently detachable from the spray gun. Hence, if data from multiple entities is to be used over time, the data may be synchronised using time stamps by matching the time stamps and aligning data based on matching time stamps. 
     Yet a further implementation further comprises obtaining data for providing the first timestamp, the second timestamp and the third timestamp from a network source and providing the coating fluid flow data with the first timestamp, the distance data with the second timestamp and the position data with the third timestamp. Network routers, wired and wireless, may be arranged to provide timing data. With such timing data being synchronised, it may serve providing timestamps suitable for synchronisation. 
     Another implementation further comprises calculating, based on the coating deposition area data of positional spray coating deposition on the area of the physical surface per unit of time, thickness of a layer of coating fluid on the physical surface. With a total mass flow available, distribution of the flow over the cone and the location of the physical surface relative to the cone over time, the total deposition of coating fluid per unit area may be determined over time. At the moment the spray job has ended, thickness of a layer may be determined. 
     A second aspect provides an electronic computing device configured for electronically tracking of spray coating of a coating fluid on a physical surface by a spray gun arranged to spray the coating fluid in a spray direction. The device comprises a communication unit arranged to receive, from a distance sensor module comprising at least one distance sensor, the distance sensor module being connected to the spray gun, distance data indicating a physical distance between the spray gun and the surface, obtain, from an electronic memory, three-dimensional coating model data of a spray cone associated with the spray gun, receive, from a positional sensing system connected to the spray gun, position data providing an indication of the spray gun relative to a first position on the physical surface and obtain curing data related to the coating fluid. The device further comprises a processing unit arranged to calculate, based on the distance data, the position data and the three-dimensional coating model, coating deposition area data of positional spray coating deposition on an area of the physical surface per unit of time, calculate, based on the coating deposition area data of positional spray coating deposition on the area of the physical surface per unit of time, thickness of a layer of coating fluid on the physical surface and based on the curing data, determining cured thickness of a cured layer of coating fluid on the physical surface. The second aspect comprises a device arranged to execute the method according to the first aspect. 
     A third aspect provides a computer program product comprising computer executable instructions causing a computer, when the instructions are executed by a processor comprised by the computer, to execute a method of electronically tracking of spray coating of a coating fluid on a physical surface by a spray gun arranged to spray the coating fluid in a spray direction. The method comprises receiving, from a distance sensor module comprising at least one distance sensor, the distance sensor module being connected to the spray gun, distance data indicating a physical distance between the spray gun and the surface, obtaining, from an electronic memory, three-dimensional coating model data of a spray cone associated with the spray gun, receiving, from a positional sensing system connected to the spray gun, position data providing an indication of the spray gun relative to a first position on the physical surface and calculating, based on the distance data, the position data and the three-dimensional coating model, coating deposition area data of positional spray coating deposition on an area of the physical surface per unit of time, obtaining curing data related to the coating fluid, calculating, based on the coating deposition area data of positional spray coating deposition on the area of the physical surface per unit of time, thickness of a layer of coating fluid on the physical surface and based on the curing data, determining cured thickness of a cured layer of coating fluid on the physical surface. The third aspect relates to a computer program product comprising computer executable instructions causing a computer, when the instructions are executed by a processor comprised by the computer, to execute the method according to the first aspect. 
     A fourth aspect provides a non-transitory medium having stored thereon computer program product comprising computer executable instructions causing a computer, when the instructions are executed by a processor comprised by the computer, to execute a method of electronically tracking of spray coating of a coating fluid on a physical surface by a spray gun arranged to spray the coating fluid in a spray direction. The method comprises receiving, from a distance sensor module comprising at least one distance sensor, the distance sensor module being connected to the spray gun, distance data indicating a physical distance between the spray gun and the surface, obtaining, from an electronic memory, three-dimensional coating model data of a spray cone associated with the spray gun, receiving, from a positional sensing system connected to the spray gun, position data providing an indication of the spray gun relative to a first position on the physical surface and calculating, based on the distance data, the position data and the three-dimensional coating model, coating deposition area data of positional spray coating deposition on an area of the physical surface per unit of time obtaining curing data related to the coating fluid, calculating, based on the coating deposition area data of positional spray coating deposition on the area of the physical surface per unit of time, thickness of a layer of coating fluid on the physical surface and based on the curing data, determining cured thickness of a cured layer of coating fluid on the physical surface. The fourth aspect comprises a non-transitory medium having stored thereon computer program product comprising computer executable instructions causing a computer, when the instructions are executed by a processor comprised by the computer, to execute a method according to the first aspect. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The various aspects and embodiments thereof will now be discussed in further details in conjunction with drawings. The drawings show possible implementations of the various aspects and embodiments thereof and are provided as examples and not as any limitation to the subject-matter of the claims. In the Figure, 
         FIG. 1 : shows a schematic overview of an example of a sensor kit, a spray gun and a surface; 
         FIG. 2 : shows a first flowchart of a method for generating a feedback signal in a sensor kit for a spray gun; 
         FIG. 3 : shows a second flowchart of a method for reconstructing coating data; and 
         FIG. 4A to 4F : show various examples of orientations of the nozzle and cross-sections of the surface to 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  depicts a schematic overview of an embodiment of a sensor kit  100  comprising a sensor kit body  102  as a housing. The sensor kit body  102  comprises a spray gun connector  104  as a connection module. A spray gun  140  is connected to the body  102  via the connector  104 . The spray gun  140  comprises a spray gun housing  141 . The spray gun  140  may for example be a High Volume Low Pressure (HVLP) spray gun. 
     Although the sensor kit body  102  is in  FIG. 1  depicted schematically as a rectangle, in different embodiments the body  102  may have a different shape. For example, the body  102  can be shaped around the shape of the spray gun housing  141  to which it is arranged to be connected. The shape of the body  102  and/or centre of gravity of the sensor kit  100  may also be adapted such that, when attached to spray gun  140 , the centre of gravity of the spray gun  140  is kept within a desired range. As such, handling of the spray gun  140  may be minimally affected by connecting the sensor kit  100 . 
     The spray gun  140  may be used for applying a layer of paint  142  as a coating on a car body part  144  as a surface. The spray gun  140  comprises a nozzle  146  from which a mist of aerosol paint  148  can be expelled, and an input for receiving the paint as a coating substance. The spray gun  140  may be a hand-held spray gun  140 , comprising a trigger which a user can operate to control expelling of paint  148  from the spray gun  140  at a certain rate. 
     The trigger may control a throughput area of a conduit leading paint or another coating fluid to the nozzle. Alternatively or additionally, the trigger—or another trigger or a control knob—may control a position of a control needle in a throughput orifice, for example the nozzle  146  or another orifice. In one embodiment, a control needle may be used to accurately control a flow of coating fluid and a trigger may be used to switch between an “on” an “off” state of the nozzle. In addition to the accurate control mechanism, the flow of coating fluid may also be control be varying pressure under which the coating fluid is provided. One or more of the precision control settings, the coating fluid pressure and the trigger state may be considered as optional spray job parameters. 
     The user can move and re-orientate the spray gun  140  as desired, and thus move it further away from the car body part  144  or closer to the car body part  144  with a certain speed and acceleration. The user can further orientate the spray gun  140  as desired, and thus change the orientation of the nozzle  146  relative to the car body part  144  such that paint can be applied from different angles of approach. 
     Provided in the sensor kit body  102  is a distance sensor module  106  comprising one or more time-of-flight sensors as proximity sensors comprised by the distance sensor module  106 . The time-of-flight sensors are arranged for obtaining distance data as spray job parameter values on distances d 1 , d 2  and d 3  between each of the sensors and the car body part  144  and/or the layer of paint  142 . As such, the time-of-flight sensors in the distance sensor module  106  preferably face the same direction as the nozzle  146  when the sensor kit  100  is connected to the spray gun  140 , as the nozzle  146  will also face the car body part  144  and/or the layer of paint  142 . 
     The time-of-flight sensors as the proximity sensor may comprise a laser or LED as an optical transmitter arranged to emit a laser beam as an emitted optical signal. The time-of-flight sensors may further comprise an optical receiver for receiving a reflected optical signal as a reflection of the laser beam. A proximity processor may be used to determine a spray distance between the time-of-flight sensors and the surface  144  based on a relation between the emitted laser beam and the reflected laser beam. 
     The emitted optical signal may have a near infrared wavelength spectrum, for example between 800 and 1140 nm, more in particular between 900 nm and 1000 nm and most preferably 940 nm. Electromagnetic radiation of such wave is not visible; it may travel through substance that may seem opaque to the human eye, but is transparent for electromagnetic radiation between 900 nm and 1000 nm and 940 nm in particular. 
     The sensor kit body  102  may comprise non-translucent materials, and as such light emitted by the time-of-flight sensors may be hindered by the sensor kit body  102 . In the embodiment of  FIG. 1 , the sensor kit body  102  comprises as an option an at least partially translucent viewing window  108  through which light emitted by and reflected back to the time-of-flight sensors can pass. Alternatively, at least part of the sensor kit body  102  through which light should pass may be made of material which is at least partially translucent for wavelengths of light used by the time-of-flight sensors, which may for example be wavelengths in the infra-red spectrum. 
     In one embodiment, the time of flight sensors are spaced apart at such distance that at a normal spraying distance, between 20 centimetres and 50 centimetres, their lights do not interfere. As such, different values for the distances d 1 , d 2  and d 3  may be obtained, particular if the sensor kit  100  is tilted relative to the surface of the car body part  144 . 
     In the embodiment of  FIG. 1 , the sensor kit  100  comprises a microcontroller  110  as a processing unit. The microcontroller  110  comprises a data input  112  as an input module, arranged to receive one or more reference parameter values. The received reference parameter values may be stored on a memory  114 . Distance data may be sent by the time-of-flight sensor  106  to the data input  112  of the microcontroller  110 , and also optionally stored on the memory  114 . 
     The microcontroller  110  is in the embodiment of the sensor kit  100  provided inside the sensor kit body  102 . Embodiments of the sensor kit  100  are also envisioned wherein another microcontroller as part of the processing unit is provided outside the sensor kit body  102 . This other microcontroller may for example be comprised by one or more external computer devices, such as a server, smartphone, tablet, any other computer device, or any combination thereof. 
     When at least part of the processing unit is provided outside the sensor kit body  102 , a wired or wireless connection may be provided between the sensor module and the microcontroller  110  such that exchange of data is made possible. When a wireless connection is used, for example an NFC, Bluetooth, Wi-Fi or any other protocol can be used for exchange of data. 
     The microcontroller  112  as a processing unit further comprises a comparison module  116  arranged to compare at least part of the obtained spray job parameter values to corresponding one or more reference parameter values. The comparison module  116  may thus be arranged to receive at least part of the spray job parameter values and at least part of the reference parameter values, for example from the data input  112 , and/or retrieve at least part of the spray job parameter values and at least part of the reference parameter values from the memory  114 . 
     The comparison module  116  is further arranged to generate a comparison data signal based on the outcome of the comparison. The comparison data signal may be received by an output module  118 , which may be arranged to and used to send the comparison data signal to other components of the sensor kit  100 . In embodiments, the output module  118  may be comprised by the processing unit, the comparison module, the sensor module, or by the sensor kit  100  in general. 
     The data input  112  may be arranged for receiving user identification data, which may be indicative of a specific user or group of users. For example, user identification data may comprise employer data, a name, and/or any other data from which a specific user of group of user may be identified. The user identification data may be stored on the memory  114 . When user identification data is stored on the memory  114 , the particular sensor kit  110  may be linked to a specific user. 
     For providing feedback to a user using the spray gun  140  with the sensor kit  100 , a feedback controller  120  as a user feedback module is comprised by the sensor kit  100 . The feedback controller  120  is arranged to generate a user feedback signal based on at least part of the comparison data signal. The feedback controller  120  may further be arranged to receive at least part of the comparison data signal from the data output  118  and/or retrieve at least part of the comparison data signal from the memory  144 . 
     In the embodiment of  FIG. 1 , the feedback controller  120  is provided inside the sensor kit body  102 . Embodiments are also envisioned wherein at least part of the feedback controller  120  is provided outside the sensor kit body  102 . In such embodiments, at least part of the generated feedback signal may be sent via a wired or wireless connection to an external feedback device, such as a speaker, display, or light. 
     The feedback controller  120  comprises in the embodiment of  FIG. 1  a display  122 , arranged for providing a visual signal based on the feedback signal. The display  122  is depicted as being placed in the sensor kit body  102 . In embodiments, the display  122  may also be placed at a different location, and the display  122  may for example be a display of a smartphone, tablet, head-up display (HUD), smartwatch, smart glasses, or any other display. 
     For obtaining orientation data indicative of an orientation of the spray gun  140 , embodiments of the sensor kit  100  may comprise an orientation sensor  130  which may be an absolute or a relative orientation sensor  130 . The orientation sensor  130  may comprise a magnetometer, accelerometer, compass, gyroscope, any other sensor or any combination thereof. The orientation sensor  130  is arranged to measure angles of the sensor kit and preferably an angle relative to a horizontal plane. Preferably, the orientation sensor is arranged to provide three signals indicative of a first rotation φ over a first axis perpendicular to the spray direction of the nozzle  146 , a second rotation 0 over a second axis perpendicular to the spray direction and perpendicular to the first axis and a third rotation ψ over a third axis parallel to the spray direction. 
     As such, the orientation data may comprise data indicative of a roll, yaw and pitch of the spray gun  140 . Because the housing body  102  is preferably rigidly connected to the spray gun  140 , the roll, yaw, and pitch of the orientation sensor  130  may substantially correspond to the roll, yaw, and pitch of the spray gun  140  or may at least be transformed to the roll, yaw, and pitch of the spray gun  140 . Any output parameter or parameters of the orientation sensor  130  may be considered as optional spray job parameters. 
     Additionally or alternatively, the orientation sensor  130  is arranged to determine at least one angle of the orientation sensor relative to a reference plane. The reference plane may for example be a horizontal plane, a vertical plane, or a plane representing the surface  144  on which the coating  142  is to be applied. 
     For obtaining movement data indicative of a movement of the spray gun  140 , embodiments of the sensor kit  100  may comprise an accelerometer  132  as an example of a movement sensor. The accelerometer  132  is preferably arranged to provide three signals indicative of accelerations in three directions. In a preferred implementation, a first acceleration is measured in a first direction x, a second direction y and a third direction z. In a more preferred embodiment, each direction is parallel to an axis of rotation as discussed above. For example, the first direction is parallel to the first axis, the second direction is parallel to the second axis and the third direction is parallel to the third axis, though other options may be envisaged as well. 
     The movement data may comprise data indicative of a speed and/or acceleration and/or displacement of the spray gun  140  in one or more directions. Because the housing body  102  is preferably rigidly connected to the spray gun  140 , the speed and/or acceleration of the movement sensor  132  may substantially correspond to the speed and/or acceleration of the spray gun  140  or may at least be transformed to the speed and/or acceleration of the spray gun  140 . One or more of the speed, acceleration and displacement—either as scalar or vector—may be considered as optional spray job parameters. 
     As an option, the embodiment of the sensor kit  100  as shown in  FIG. 1  comprises a speaker  126  as a speaker for providing an audio signal based on the feedback signal. Depending on the feedback signal, the audio signal may for example have a different volume and/or frequency to indicate a specific type of feedback to the user. 
     As a further option, the embodiment of the sensor kit  100  as shown in  FIG. 1  comprises a vibration unit  128  as a haptic module for providing a vibration as a haptic signal based on the feedback signal. The vibration may be transferred via the connection  104  to the spray gun body  141  which may be held by the user of the spray gun  140 . Hence, the user may feel the vibration when holding the spray gun  140 . 
     As an even further option, embodiments of the sensor kit  100  are envisioned wherein the sensor module comprises a temperature sensor for obtaining temperature data indicative of a temperature of the surface  144  that is to be spray painted. In such embodiments, the reference parameter values may comprise a minimum temperature the surface  144  should have. If the comparison module provides a comparison data signal indicative that the temperature of the surface  144  is lower than the minimum temperature, the user feedback module may indicate to the user that the temperature of the surface  144  is too low. 
     For powering components of the sensor kit  100  requiring electrical energy, the sensor kit  100  may comprise a battery  134  on which electrical energy may be stored. In particular embodiments, the sensor kit housing  102  is substantially sealed, for example to prevent fluids from entering the housing and/or to prevent electrical components to be exposed to paint fumes. Being substantially sealed, it may not be possible to use a wired connection for charging the battery  134  and/or to easily replace a depleted battery. 
     A coil  136  as a wireless charging module for charging the battery  134  may be comprised by the sensor kit  100 , and may be placed inside the sensor kit housing  102  together with the battery  134 . By using for example inductive charging, electrical energy may be supplied to the battery  134  via the coil  136 . Because this transfer of electrical energy is wireless, no connector has to be placed in the housing  102  and no electrical components have to be exposed to ambient air which may contain flammable coating substances in aerosols. 
     An embodiment of a method for generating a feedback signal in a sensor kit for a spray gun is schematically depicted in  FIG. 2 , and will be elaborated on in conjunction with the sensor kit  100  as shown in  FIG. 1 . It will be understood that the method may also be applied in conjunction with other embodiments of the sensor kit  100 , and that the sensor kit  100  of  FIG. 1  may be used in conjunction with other embodiments of the method depicted by the first flowchart  200 . The various parts of the flowchart  200  are briefly summarised below: 
     
       
         
           
               
               
             
               
                   
               
             
            
               
                 202 
                 start 
               
               
                 204 
                 receive reference parameter values 
               
               
                 206 
                 obtain spray job parameter values 
               
               
                 208 
                 compare spray job parameter values to reference values 
               
               
                 210 
                 output comparison data signal 
               
               
                 212 
                 receive comparison data signal 
               
               
                 214 
                 end 
               
               
                   
               
            
           
         
       
     
     The method starts in a terminator  202 . A second step  204  in the method comprises receiving reference parameter values, for example by the data input  112 . At least part of the reference parameter values may be received from an external source, for example a server  150 . The connection between the sensor kit  100  and the data output  118  in particular on one hand and the server  150  on the other hand may be executed using Wi-Fi (IEEE 802.11), Bluetooth, any cellular telecommunication standard, including, but not limited to 4G (LTE) and 5G. 
     The server  150  may comprise a processing unit  152  and at least have access to a mass memory  154  with stored thereon a database comprising reference parameter values. In further embodiments, at least part of the reference parameter values may already be present on the memory  114  of the sensor kit  100 . 
     The memory  154  may be comprised by the server  150 , which may be located at the premises where the spray gun  140  is used or any other place; the mass memory  154  may also be located at another position. The mass memory  154  may also have stored thereon computer executable code for programming the processing unit  152  to execute the method discussed below in conjunction with  FIG. 3 . As such, the mass memory  154  preferably comprises a non-volatile memory. 
     The server  150  comprises a communication module  156  for communicating with the sensor kit  100  and in particular with the data output  118  and the data input  112 . 
     The server  150  further comprises a server processing unit  152 , comprising various sub-unit for dedicated tasks. The sub-units may be hardwired or programmed in the processing unit by means of non-volatile (re-) programmable memories or volatile memories. The server processing unit  152  may comprises an integration unit  160 , a spatial calculation unit  162 , a convolution unit  164 , a synchronisation unit  166  and a process calculation unit  168  for performing various functions as discussed in conjunction with a first flowchart  200  ( FIG. 2 ) and a second flowchart  200  ( FIG. 3 ) as discussed below. 
     The reference parameter values may comprise a set of coating types and corresponding preferred spraying parameters. Spraying parameters may be specific for a type of coatings. For example, for a particular first coating type, a preferred spraying distance between the nozzle  146  and the surface  144  lies within a first distance interval. Preferred spraying parameters may be provided to the sensor kit upon an operator selecting particular coating by means of the server  150 . 
     The reference parameter values may in examples comprise data relating to a minimum and/or maximum speed, orientation, and/or acceleration of the spray gun  140 , a minimum or maximum operating temperature and/or pressure, a minimum or maximum flow of coating fluid and/or any other data which may be relevant to a spray job or any combination thereof. 
     In step  206 , spray job parameter values are obtained using at least some sensors comprised by the distance sensor module  106 , for example one or more time-of-flight sensors. The third step  206  may commence after the sensor kit  100  is initialised, or when the actual spray job has started. The spray job parameter values may be obtained at a certain amount of data points per second, for a pre-determined amount of time or until it is determined that the spray job has been finished or temporarily paused. 
     In step  208 , which may take place simultaneously with the third step  206 , at least part of the spray job parameter values are compared to at least part of the received reference parameter values, for example using comparison module  116 . 
     In step  210 , which may take place simultaneously with any of the third step  206  and the fourth step  208 , the comparison data signal is outputted to the feedback controller  120  as the user feedback module, for example by the data output  118 . This allows the feedback controller  120  to act based on the comparison data signal, or at least a part thereof. 
     In step  212 , which may take place simultaneously with any of the third step  206 , the fourth step  208 , and step  210 , the comparison data signal is received by the feedback controller  120  and a feedback signal is generated based on at least part of the comparison data signal. 
     The method  200  ends in a terminator  214 , for example when the spray job is finished. While the spray gun  140  is being used, any of the second, third, fourth, fifth and sixth steps may be repeated, optionally simultaneously, parallel and/or on a step-by-step basis, preferably real-time or at least substantially real-time such that the operator of the spray gun  140  can react to the feedback. 
     As an example, the method  200  will be discussed wherein the sensor kit  100  is used for providing feedback to a user using the spray gun  140  on the distance d between the sensor kit  100  and the surface  144 . 
     The method  200  is initialised by the user connecting the sensor kit  100  to the spray gun  140 . For example may the spray gun  140  be provided with a magnet, arranged to manipulate a magnetic switch like a reed contact comprised by the sensor kit  100  for switching on the sensor kit  100 . 
     Next, the user selects the type of coating to be sprayed by the spray gun  140 , for example by selecting this type via a graphical user interface arranged to allow user interaction with the server  150 . Alternatively, the server  150  may be embodied as an application on a smartphone, tablet, personal computer device, or any other device which allows to user to select a type of coating. In embodiments a barcode scanner may be provided for scanning a barcode on a container of coating substance for obtaining data indicative of the type of coating. Parts of the scanner may be incorporated in the sensor kit  100 . 
     Upon the user selecting the type of coating, the server  150  looks up reference parameter values corresponding to the type of coating, for example in an internal or external memory, directly or via a connection such as a LAN, WAN, internet, Wi-Fi, Bluetooth, or any other wired or wireless connection. A part of the reference parameter values may be provided locally, whereas another part of the reference parameter values may be provided at a remote location. 
     The server  150  sends the reference parameter values to the sensor kit  100 , of which the data input  112  receives the reference parameter values and stores it on the memory  114 . The reference parameter values in this example comprise a desired distance range, particular to the selected type of coating. The sensor kit  100  may aid the user in keeping the spray gun  140  within this desired distance range, by providing feedback. The desired distance range as an example of reference parameter values may have been supplied by the manufacturer of the coating. 
     The desired distance range may correspond to the distance between the nozzle  146  of the spray gun and the surface  144 , or between any other component of the spray gun and the surface  144 , or to the distance d between the time-of-flight sensor  106  and the surface  144 . In any case, because the connection between the sensor kit body  102  and the spray gun  140  is preferably substantially rigid and the dimension of components of the sensor kit  100  will be known, any of these distances may be indicative for the distance between the nozzle  146  and the surface  144 . 
     Alternatively, when the housing of the sensor kit is not substantially rigidly connected to the spray gun, a dynamic model of the substantially not rigid connection may be used for mapping data obtained by the sensor kit to data relevant to the spray gun. 
     During the use of the spray gun  140 , which period of time may be referred to as the spray job, the time-of-flight sensor  106  obtains distance data indicative of the distance d between the time-of-flight sensor  106  and the surface  144  facing the time-of-flight sensor  106 . This distance data is then used by the comparison module  116  which compares the obtained data to the desired distance range. 
     A result of this comparison may comprise a value indicating whether a particular data point in the distance data lies within the range, or falls outside the range. A result of this comparison may alternatively or additionally comprise a value indicating, when a particular data point falls outside the range, if the particular data point is too large, to small, and/or by what amount the data point falls outside the range. 
     The output module outputs the comparison data signal to the feedback controller  120 , which may be arranged to provide feedback of the comparison data signal to the user using the spray gun  140 . The feedback is preferably provided substantially in real-time such that the user can alter his usage of the spray gun  140  adequately in accordance with the provided feedback. 
     After having received the comparison data signal, the feedback controller  140  generates a feedback signal based on at least part of the comparison data signal. 
     In a particular embodiment, the feedback controller  140  comprises an LED-module  126  comprised by an optical module for providing a visual signal to the user based on the generated feedback signal. The LED-module  126  may comprise one or more LEDs, which may be arranged to provide light of a single colour or may be controllable to provide light of different colours, for example red, green, blue, or a combination thereof. 
     When an obtained distance lies within the desired distance range, the feedback controller  140  may control the LED-module  126  to show a green light as an example of coloured light. When an obtained distance falls out of the desired distance range, the feedback controller  140  may control the LED-module  126  to show a red light as an example of a differently coloured light. 
     In embodiments, the feedback controller  140  comprises a display  122  as part of the optical module, arranged for providing a visual signal based on the feedback signal. The display  122  may be arranged to show a value corresponding to the actual distance data obtained by the time-of-flight sensor  106 , and may thus be arranged to show numerical values corresponding for example to the measured distance in millimetres or inches. The obtained distance data may either be supplied to the display  122  directly, or via the feedback controller  140 . 
     If the feedback controller  140  receives comparison data signals corresponding to distance data falling outside the desired range for a pre-determined amount of time, the feedback controller  140  may be arranged to generate a feedback signal to control the vibration unit  128  to provide the user with haptic feedback indicating that the desired distance has not been met for the pre-determined amount of time. 
       FIG. 3  depicts a second flowchart  300  of reconstructing coating data, which may be performed in the server system  150  for communicating with a sensor kit  100  for the spray gun  140 , or on a different computer device such as a smartphone or tablet computer. The various parts of the second flowchart  300  are briefly summarised below: 
     
       
         
           
               
               
             
               
                   
               
             
            
               
                 302 
                 Start 
               
               
                 304 
                 Obtain coating data 
               
               
                 306 
                 Obtain paint model data 
               
               
                 308 
                 Monitor acceleration data 
               
               
                 310 
                 Zero crossing 
               
               
                 312 
                 Monitor flow data 
               
               
                 314 
                 Flow 
               
               
                 316 
                 Monitor distance data 
               
               
                 318 
                 Monitor rotational data 
               
               
                 320 
                 Monitor acceleration data 
               
               
                 322 
                 Monitor flow data 
               
               
                 324 
                 Calculate movement data 
               
               
                 326 
                 Determine surface orientation 
               
               
                 328 
                 Determine angle to surface 
               
               
                 330 
                 Calculate intersection surface to spray cone 
               
               
                 332 
                 Determine coat parameters in intersection plane 
               
               
                 334 
                 Synchronise flow data and sensor kit data 
               
               
                 336 
                 Calculate coating deposition rate in intersection plane 
               
               
                 338 
                 Calculate coating layer thickness on surface 
               
               
                 340 
                 Calculate cured layer thickness on surface 
               
               
                 342 
                 Monitor flow data 
               
               
                 344 
                 Flow 
               
               
                 346 
                 End 
               
               
                   
               
            
           
         
       
     
     The process starts in a terminator  302  and continues with step  304  in which coating data is obtained. Such coating data may be obtained on received data from a user of the spray gun  140 . The input may be provided manually, by receiving data from a keyboard, by means of a barcode scanner, by receiving input through selection of an icon, other, or a combination thereof. The coating data comprises characteristics specifically related to at least one of the coating liquid, like viscosity, brand name, solution liquid content, data on layer thickness reduction over curing, desired distance to the surface to coat, other, or a combination thereof. 
     In step  306 , paint model data is obtained. The paint model data comprises data mainly related to the spray gun  140 . The paint model data comprises data on the structure of the spray gun  140  and the structure of a spray cone provided by the nozzle  146 . The data may be two-dimensional, only perpendicular to the direction of spraying, or three-dimensional. The paint model data may comprise average flow density, median flow density, maximum flow density, minimum flow density, flow density as a function of location within the cone, cone apex, cone shape (circular or non-circular elliptical) and one or more of these parameters having a value depending on distance from the spray gun  140  or the nozzle  141  to the surface of the car body part, coating material characteristics, air pressure, air flow, air flow velocity, other, or a combination thereof. 
     The actual data of the spray cone may be dependent on characteristics of the coating material, air pressure, an amount of movement of a trigger of the spray gun  140 , distance to the car body part  144 , other, or a combination thereof. The paint model data may be obtained in the same fashion as the coating data. The data thus described as being obtained may be obtained from the mass memory  214  by the processing unit  152 . 
     In step  308 , acceleration data as received from the accelerometer  132  as comprised by the sensor kit  100  is monitored. If the acceleration in a particular direction, in particular in a direction perpendicular to the spray direction and in a left-right direction when the spray gun  140  is held by an operator, crosses zero at least one time and preferably two or more times, it is detected, in step  310 , that the spray gun  140  is in use for spraying. 
     To reduce a risk of erroneous detection, the detection of zero crossings of the acceleration value may be combined with determining that the time period between two or more subsequent crossings is substantially the same. In this way, a swinging movement of the spray gun  140  may be detected as an indication of the operator executing a paint job. 
     Alternatively or additionally, flow data may be monitored. Flow data may be monitored by monitoring whether a trigger of the spray gun  140  is pulled, for example by receiving a signal from a trigger sensor (not shown), which may be a binary, otherwise digital or analogue continues signal. The flow rate may be provided with a timestamp, providing indications of the flow rate at multiple moments in time. 
     From the flow data, a mass flow rate or a volume flow rate through the nozzle may be determined. By determining whether the trigger is opened or not and combining the determined state of the trigger with a nominal flow rate of the nozzle, a total mass flow rate or a total volume flow rate may be determined at a particular moment the trigger is operated. By determining how far or how much the trigger is operated, combined with a relation between trigger operation and mass flow rate or volume flow rate, an actual flow rate at a particular moment may be determined. 
     Alternatively or additionally, at least one of a flow of air and a flow of coating material may be monitored by means of a flow sensor (not shown) and the signal provided by such sensor may be monitored by means of the processing unit  152 . The total flow data—mass flow (rate) or volume flow (rate)—may thus be obtained directly by means of a flow sensor. 
     If at least one of a flow of the air, pressing of the trigger and flow of the coating material, is detected, it is determined in step  314  that the spray job has started. In on embodiment, the determination is only made if the signal is detected for a time period longer than a pre-determined time interval. 
     If, based on evaluation of sensor data, it has been determined that the paint job has started, distance data provided by the distance sensor module  106  is monitored in step  316 , rotational data provided by the orientation sensor  130  is monitored in step  318 , acceleration data as provided by the accelerometer  130  is monitored in step  320  and flow data provided by sensors as discussed above is monitored in step  322 . The monitoring steps may be executed in parallel or, intermittently and repeatedly (interweaved), in series. 
     Based on the accelerometer data, the speed by which the operator moves the spray gun  140  and the distance by which the operation moves the spray gun  140  may be calculated by integrating the data received from the accelerometer one or two times over time; this action may be performed by the integration unit  160 . Prior to integration, data provided by the accelerometers may be processed using statistical parameters, for example by removing outliers, smoothing a signal over time, for example by determining a moving average or average median, determining what an outlier is, for example based on a standard deviation, for example over time. Alternatively or additionally, the acceleration data signals may be filtered, for example using a Kalman filter. Alternatively or additionally, displacement data is obtained differently, for example using beacons in a spray room. 
     If the spray gun is properly aimed at the car body part  144 , data of acceleration in directions parallel to the car body part  144  is sufficient as the spray direction is always to be perpendicular to the surface of the car body part. However, this may not always be the case, for which reason it is preferred to process acceleration in all directions. 
     In step  326  may, optionally, orientation of surface of the car body part  144  be determined. In one implementation, the surface is assumed to be horizontal or vertical. 
     In another implementation, the spray gun is assumed to be mainly held in a fashion perpendicular to the surface. Based on the orientation data provided by the orientation sensor  130 , the orientation of the surface may be determined, under an assumption that the spray gun  140 , at least on average, follows the surface. 
     In step  328  orientation of the spray gun  140  relative to the surface of the car body part  144  may be determined. In one implementation, data on the distance to the surface may be taken into account. If the distance sensor module  106  comprises multiple time of flight sensor or other sensors having equivalent functionality and all measured distances are the same, the spray gun  140  is aimed perpendicularly at the surface. If the distances are different, an orientation of the spray gun  140  or the orientation of the spray cone provided by the nozzle  146  may be determined, other than perpendicular. 
     In an implementation wherein the surface is assumed to be horizontal or vertical, using data from the orientation sensor  130 , over one or more axes, may be used to determine an orientation of the spray gun relative to the surface. 
     In another implementation, where the orientation of the surface is determined using the data from the orientation sensor module  130 , the orientation of the spray gun  140  relative to the surface may be determined by detecting deviations in the signal from the orientation sensors from an average obtained over time, for example over two, five or ten seconds. 
     Based on the data calculated in step  328 , data from the distance sensor module  106 , the paint model data, coating data, other, or a combination thereof, an intersection or intersection plane of the spray cone and the surface of the car body part  144  is determined in step  330 ; this action may be performed by the spatial calculation unit  162 . With the information of the intersection plane, coating parameters in the intersection plane may be determined, taking into account the paint model data and, optionally, the coating data. 
     With the paint model comprising flow density data as a function of a location in the cone, in a numerical representation, analytical representation, other, or a combination thereof, coat parameters and in particular data related to flow density may be determined in step  332 . For particular locations in the intersection plane, mass or coat volume per volume per reference point per second or other time unit may be determined. In this way, deposition of coating, in mass, volume, or both, per unit area per unit time may be determined in step  334 . 
     Optionally, flow data may be taken into account in the deposition model, if such data is available and varies over time. Preferably, the flow data and the data from the sensor kit  100  is synchronised over time in step  332 , prior to determining the deposition rate per unit area per time; this may be handled by the synchronisation unit  166 . The data from the sensor kit  100  and the data from a sensor providing a signal indicative of flow of coating material may be time stamped using network data, from a network over which both sensor packages provided data to the server  150 . Other sources of time and preferably a single time source or multiple synchronised time sources may be considered as well. 
       FIG. 4A  through  FIG. 4F  depict the result of step  332 . 
       FIG. 4A  shows the nozzle  146  providing a spray cone  148  at a first distance towards the surface of the car body part  144 , depositing a layer  142  of coating material.  FIG. 4B  shows an indication of flow density in the plane where the spray cone  148  intersects the surface. The darker the colour, the higher the flow rate density. In  FIG. 4B , the spray cone is assumed to have an elliptical, non-circular cross-section, which corresponds to a significant amount of spray-guns commercially available. Alternatively, the spray cone as defined by the paint model data may have a circular cross-section. 
       FIG. 4C  shows the nozzle  146  at a second distance from the surface, the second distance being smaller than the first distance shown in  FIG. 4A . the smaller distance results in a smaller cross-sectional area in the cross-section between the spray cone  148  and the surface of the car body part  144 . Hence, the elliptical spray density as depicted by  FIG. 4D  is smaller. 
     The density distribution within the cross-sectional area is equivalent. It is noted that the total density, over the whole cross-sectional area, i.e. the integration of the flow density per unit area over the area over the cross-sectional area, is preferably the same for  FIG. 4B  and  FIG. 4D . In another implementation, loss of coating material per distance away from the nozzle  146  may be taken into account. 
       FIG. 4E  shows the nozzle  146  being placed under and angle relative to the surface of the car body part  144 . With an elliptical cross-section of the spray cone  148 , this may result in a cross-sectional area  142  as depicted by  FIG. 4F . In further implementations, occlusions due obstructions protruding from the surface or indentations in the surface may also be taken into account when determining deposition of coating on the surface per unit area and per unit time. 
     Next, taking into account the data as depicted by  FIG. 4B ,  FIG. 4D  and  FIG. 4F —whichever may be applicable-, the movement data or displacement data obtained by dual integration of the acceleration data—or other data indicative of movement—and time, the total amount of deposited coating material may be determined in step  338 . One option to do so is by convolution of the movement of the spray gun over time and the deposition rate over time, which may be handled by the convolution unit  164 . Also other data may be taken into account, including, but not limited to ambient pressure, ambient temperature, humidity 
     In step  340 , coating data on curing of the coating material may be used to determine, based on the result of step  338 , a thickness of the coating layer after curing, by the process calculation unit  168 . 
     The process as discussed above may be executed continuously, while spraying continues. In particular determining final coating thickness, before or after curing, may be determined after the coating process is finished. Alternatively, some steps are executed when the spray job is finished. 
     An end of the spray job may be determined as a point when monitored flow data indicates that no flow is present, momentarily or during a particular time interval. Alternatively or additionally, absence of detection of a swinging motion, as discussed above, may also be considered for determining that the spray process has ended. Once the process is finalised, the procedure ends in a terminator  346 . 
     In summary, the various aspects and implementations thereof relate to reconstruction of a layer of coating; by measuring a position of a spray gun relative to a physical surface to coat, using data on technical characteristics of the spray gun, like a spray cone the spray gun may produce and data on a coating fluid used, characteristics of a coating layer thus physically deposited may be reconstructed. With data being recording during the spray job, this is faster and more accurate than measuring layer thickness at various locations, either pre-determined or randomly. By determining flow characteristics in a spray cone and position of the spray cone relative to the surface over time and using a model of the spray cone, deposition of the layer of coating may be determined and the final layer, cured or uncured, may be reconstructed, including thickness.