Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B11/00—Measuring arrangements characterised by the use of optical techniques
  • G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
  • G01B11/06—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material
  • G01B11/0616—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of coating
  • G01B11/0658—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of coating with measurement of emissivity or reradiation

Definitions

• the present invention relates to a device for measuring at least one parameter of a fluid paint film applied by machine on an object, in which at least a target point on the paint film is exposed to a radiation for heating thereof and after ceasing of this radiation the temperature of the radiated point is measured by detecting heat radiation emitted from the paint film point and a dimension of said parameter is calculated from this temperature information, as well as a method according to the preamble of the appended independent method claim.
• Fluid is also to be given a broad sense, and all types of degrees of fluidity are comprised, from thinly fluid to very viscous. However, it is important for the ability of a device of this type to carry out said measurement that the paint film is still fluid so that the radiation from the radiation means may within a short time reach through the entire film. It is not necessary that the detecting member delivers a real temperature value to the calculating member, but "information about the temperature” comprises also indirect such information, i.e. information from which the temperature may be calculated, such as the power of a heat radiation detected.
• a device of this type is particularly well suited for measuring the thickness of a paint film applied by a spray painting robot on a vehicle body, since the most important criterions for such a thickness measurement are fulfilled for that case of use, namely a high contrast is obtained, since it is a question of a system with heat insulator (paint film) on heat conductor (steel sheet), and a penetration depth of the radiation of a said radiation means usually a laser, making it possible to reach the interface between the paint film and the object in a comparatively short time through the existing thickness of such paint films (usually 5-200 ⁇ m). Furthermore, it is important that such a thickness measurement is contactless so as to not damage the paint film.
• the paint film sprayed onto vehicle bodies has such properties that the paint film both gets wear re- sistant and receives a surface appealing to the viewer.
• the material cost for such a paint is not neglectable, so that it is desired to be able to make the paint film very thin while at the same time obtaining a high wear resistance, which requires a thickness of the paint being as homogenous as possible without any thinner regions.
• Varying film thickness in the form of so called "orange-peal-skin" is particularly inconvenient, which results in the case that the surface tension of the paint film is not sufficient high for extracting the individual drips and results in a surface being unacceptable from the appearance point of view of the paint hardened later.
• a device of the type mentioned in the introduction is already known through for example "Sondertik aus “tm-Technisches Messen” 65 (1998), Heft 1 1 , pages 396-399", and such already known devices are used for measuring the thickness of the paint film in connection with spray application of paint on a vehicle body, in which this is done by applying a pulsating laser beam during a short time (some milliseconds) and the temperature development of the radiated surface is recorded by said detecting member after carrying out this radiation and possibly also during the radiation.
• the thickness of the paint film in the point radiated may in this way be determined.
• Information about the paint film in different points is in this way obtained by such a device through utilising a pulsating laser as radiation source.
• This information may then be used to control different parameters of the very spray application of the paint on vehicle bodies not painted yet in the production line, so as to reduce the proportion of vehicle bodies that are not passing a subsequent quality check of the paint film and have to be returned for repainting.
• This proportion may namely well be in the order of 20%, and a remarkable reduction of this proportion would mean a very big saving of costs.
• the object of the present invention is to provide a device and a method of the type defined in the introduction, which manage to deliver information about at least one parameter of a said paint film in a better way than before, so that an obtaining of said saving of costs lies within the frame of the possibilities.
• This object is according to the invention obtained by providing a device of this type, which furthermore comprises an arrangement adapted to cause a movement of the radiation means with respect to the paint film, the radiation means is adapted to continuously radiate the target point moving in this way along the paint film during at least a part of the movement, and said detecting member is adapted to detect the emission of heat radia- tion of the moving target point with a predetermined delay for measuring said parameter of the paint film along a continuos elongated field of the paint film, as well as a method according to the appended independent method claim.
• said parameter such as the thickness
• said parameter such as the thickness
• said parameter such as the thickness
• said parameter such as the thickness
• said parameter may be measured along a continuos elongated field of the paint film, which means that the information about this parameter of the paint film gets considerable more extensive than at the point like measurement through the devices already known.
• information about said parameter over a continuous surface which may extend over a considerable length, is here obtained instead, which means that eminent information about the development of the parameter along the surface is obtained.
• thickness measurement this means that the existence of varying thickness, also very small such variations, may be reliably detected.
• the probability for detecting an existing so called "orange-peal-skin" increases.
• the use of a device according to the invention means in the practice that a better supervision of the quality than before may be obtained in a paint film obtained through spray app- lication, so that the parameters controlling the spray application may be adjusted in the most suitable way, would a need thereof exist, and the proportion of paint films refused may by that be reduced.
• the detecting member may be moved with respect to the paint film in a path of movement defined by the movement of the radiation means. It is advantageous to move the detecting member with respect to the paint film in this way for accomplishing a reliable detection of the surface portions of the paint film radiated with said predetermined delay and while obtaining comparable values in each point along the path of movement of the radiation means.
• the radiation means and the detecting member are arranged at a fixed mutual orientation on the carrier in common, and the arrangement is adapted to cause a movement of the carrier with respect to the object and by that the paint film while maintaining a substantially constant instantaneous time distance between the target point for the radiation and the point for the heat radiation detection.
• the calculating member is adapted to send information about said calculated parameter to a unit for setting parameters for control of the paint application on said objects not painted yet, which makes it possible to take advantage of the measuring result of the device for improving the painting result of objects not painted yet. It is then particularly advantageous if the calculating member is adapted to send out information about said cal- culated parameter to a unit for control of parameters with respect to the environment, such as degree of moisture and/or air flow velocity and/or temperature, in the place for painting the next object. This place may be a cabin for a spray application of paint on a vehicle body.
• the measuring results may also be used for making the painting process an optimum, i.e. controlling the paint flow, the paint atomizing and the paint velocity and the distance between applicator and spraying object.
• the device comprises at least two said detecting members adapted to detect heat radiation emitted by radiated target points on the paint film having mutually different lengths of said delay.
• This may be obtained by arranging a plurality of consecutive detecting members on a line along a path for a relative movement of them and the paint film, so that they will successively reach a point radiated earlier. This means that still more information about each point may be obtained, since in this way a development of the temperature over the time of the point in question may be achieved at the same time as a continuos measurement over an elongated field is obtained.
• the invention also relates to a use of a device of the type according to the invention for measuring at least one parameter of the paint film applied by machine on an object, and more particular a use in connection with spray application of paint on vehicle bodies.
• Fig. 1 is a very schematic view of a robot for spray application of paint on a vehicle body
• Fig. 2 is a side elevation of a device according to the invention in operation for measuring thickness and waviness of the paint film
• Fig. 3 is a graph illustrating on one hand how the radiation of a point on the paint film by the device according to the invention according to Fig . 2 develops over time, and on the other how a temperature of this point develops over time,
• Fig. 4 is a graph of the development of the temperature over time of fluid paint films having different thicknesses and being radiated
• Fig. 5 is a view illustrating how a device according to the invention measures parameters of a paint film according to another possible embodiment of the invention.
• a spray painting robot having different robot arms interconnected through hinges is very schematically illustrated in Fig. 1 .
• a spray nozzle 1 adapted for spray application of atomized paint on an object 2, here a vehicle body, is arranged outermost on these robot arms.
• the spray nozzle is connected to members 3 schematically indicated for atomizing the paint delivered to the paint nozzle 1 controlled by a paint process unit 4.
• Such a spray application robot is usually arranged in a so called painting cabin, in which the environment is controlled in a very careful way through setting temperature, degree of moisture, air flows through the cabin and the like for obtaining an optimum result at the painting.
• the device according to the invention for measuring at least one parameter, such as the thickness or the waviness, of the fluid paint film 6 applied on an object 5, here a steel sheet of a vehicle body, is schematically illustrated in Fig. 2.
• a paint film may have a thickness of 5-200 ⁇ m and has usually a thickness of 10-30 ⁇ m.
• the device comprises a member 7, here in the form of a laser, adapted to continuously emit a beam 8 having a well defined wave length towards the paint film 6. The beam 8 will were it strikes the paint film heat it all the way down to the sheet 5.
• a C0 2 -laser or YAG-laser may be particularly well suited, since the radiation thereof is absorbed nearly just as much by different colours. In some cases it may as a consequence of the physical size of the laser 7 be necessary to locate it in another place. The member 7 will then produce the beam 8 towards the surface through a flexible optical conductor.
• the device has also a member 9 adapted to detect the heat radiation emitted from the point of the paint it is directed towards.
• This detecting member 9 may be different types of IR-detectors, such as semiconductor based sensors.
• the radiation means 7 and the detecting member 9 are arranged on a carrier 10 in common in a fixed mutual orientation, but the essential thing is that the beam 8 and the detecting member 9 has a fixed mutual orientation (the radiation means could be arranged anywhere else and the end of an optical conductor connected thereto could be fixed on the carrier) and this carrier is adapted to be controlled to move along the paint film 6 with a substantially constant velocity by a moving arrangement 1 1 schematically in- dicated.
• the carrier is adapted to keep the beam 8 and the de- tecting member 9 at a substantially constant distance from the paint film during this movement.
• the radiation means 7 will through the beam 8 thereof through the movement along the paint film 6 radially heat the paint film along an elongated continous field having a width determined by the diameter of the beam 8.
• the detecting member 9 will with a certain time delay arrive to the respective point of the paint film which has been radiated and then indirectly measure the temperature of this point by detecting the amount of heat energy emitted thereby, so that the detecting member 9 in this way carries out a measurement along the entire said elon- gated field.
• the member 9 then digitalises the measuring information with a high detecting frequency.
• the detecting member 9 is advantageously arranged to be directed towards a paint film region being separated from the region towards which the radiation means 7 is arranged to simultaneously be directed to.
• the radiation through the radiation means of a point on the paint film is illustrated through the rectangular pulse 12, while the temperature of this point over the time is illustrated through the curve 1 3. It is intended that the detection through the detecting member 9 takes place at the time 14. How rapidly the temperature of the paint film sinks with the time depends upon the thickness of the paint film, which is illustrated in Fig. 4, where the uppermost curve shows how much the temperature has fallen at a given time for a paint film having a thickness of 19 ⁇ m, while the lower of the two curves shows how much the temperature has fallen for a paint film having a thickness of 15 ⁇ m.
• Information about heat radiation reflected by the paint film is sent from the detecting member 9 to a member 15 schematically indicated for calculation of the thickness of the paint film on the basis of this indirect temperature information. These data may then be utilised for setting parameters of the very spray application, such as the environment in which the spray application robot is located.
• a said elongated field which extends over the entire object in question, but it is also within the scope of the invention to proceed in the way schematically illustrated in Fig . 5, i.e. carry out a measurement along an elongated field 18 and then make a certain interruption of the measurement before the measurement along an additional such field 19 is carried out.
• the measuring device may also be carried by an industrial robot having 6 degrees of freedom, which enables totally optional measuring paths and positions of the object.
• the arrangement is adapted to cause a movement of the radiation means with a substantially constant velocity with respect to the paint film
• also is intended to com- prise the case of a construction allowing a movement of the radiation means by hand with respect to the paint film while ensuring a substantially constant movement velocity.
• the arrangement could also be made of something causing a movement of the object in question past the stationary radiation means, in which such an arrangement in the case of painting vehicle bodies could be a belt conveyor or the like through which the vehicle body moves through a station for measuring through the device.
• the different members being a part of the device do not have to be formed by parts physically separated and connected through a communication connection, but for example the detecting member and the calculating member could be integrated into one and the same component.
• the calculating member could also be physically separated from the rest of the device and for example be made of a computer. It is then possible that the detecting member collects data during the movement thereof with respect to the object on a carrier, such as a floppy disc, and this then after terminating the measurement on an object by an operator is loaded into a computer and then different values for the parameter, such as the thickness, is calculated afterwards for the entire measuring procedure.
• a carrier such as a floppy disc

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Spray Control Apparatus (AREA)
• Length Measuring Devices By Optical Means (AREA)
• Investigating Or Analyzing Materials Using Thermal Means (AREA)
• Length Measuring Devices With Unspecified Measuring Means (AREA)
• Application Of Or Painting With Fluid Materials (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

Country Status (3)

Cited By (4)

Citations (5)

• 1999
  • 1999-10-19 SE SE9903749A patent/SE518278C2/sv not_active IP Right Cessation
• 2000
  • 2000-10-19 AU AU10453/01A patent/AU1045301A/en not_active Abandoned
  • 2000-10-19 WO PCT/IB2000/001506 patent/WO2001031293A1/en active Application Filing

Patent Citations (5)

Non-Patent Citations (2)

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