Automated dent filling

The invention relates to a process for automated filling of a dent in a three- dimensionally shaped damaged substrate. The invention also relates to a system suitable for carrying out the process.

United States patent US 4416068 a process for automated filling of a dent in a three-dimensionally shaped damaged substrate with a hardenable filler composition. The use of computer controlled robotic equipment for analyzing surface imperfections, fairing, applying a sprayable fairing compound, and painting is known from United States patent US 6365221 B. Fairing is a process whereby a less than smooth surface is filled, sanded, and primed in preparation for painting in order to improve the aesthetic quality of the exterior paint finish of marine vessels, in particular yachts.

The known fairing process is only suitable for smoothing minor surface imperfections. However, the precise filling of individual dents caused by damage so as to match the original surface contours of a damaged substrate, such as a dent in an automobile caused by a collision, is not possible with the known fairing process. In the automobile collision repair industry there is an ongoing need for automation of process steps, since labour costs account for an increasing part of the total repair costs.

Therefore, the present invention seeks to provide an automated process suitable for the precise filling of individual dents caused by damage so as to match the original surface contours of a damaged substrate. The process should reduce the labour costs and time of an automobile collision repair.

The invention provides a process for automated filling of a dent in a three- dimensionally shaped damaged substrate with a hardenable filler composition comprising the steps of

a) determination of the actual geometry of the surface of the dent, b) determination of the desired surface geometry after filling of the dent, c) calculation of the difference in geometry between the actual geometry of the surface of the dent and the desired surface geometry and calculation of the volume and geometry to be filled and determination of the position and orientation thereof in space, d) determination whether the volume determined in step c) is below or equal to a predetermined value and i) if the difference is below or equal to the predetermined value, stopping the process, and ii) if the difference is above the predetermined value, continuation with steps e) to g), e) calculation, on the basis of the calculated volume and geometry to be filled, of layers h to I _n corresponding to the volumes and geometries required to fill the dent, wherein n is an integer corresponding to the number of layers required to fill the dent, and h is the layer closest to the damaged substrate, f) application to the damaged substrate of layers h to l _m of a filler composition corresponding to the volume and geometry calculated for the respective layer, layers h to l _m corresponding to the layers which are applied subsequently without intermediate determination of the difference according to step d), and wherein m is an integer which is equal to or smaller than n, g) optionally, determination of the surface geometry after application of layers h to l _m , h) repetition of steps c) to g) until the difference in geometry determined in step c) is below or equal to the predetermined value.

The process is suitable for the precise filling of individual dents caused by damage so as to match the original surface contours of a damaged substrate. The process reduces the labour costs and time of an automobile collision repair. Furthermore, the presently used filler compositions often contain styrene or other toxicologically worrisome substances. In the traditional processes of manually filling dents in automobile bodies the exposure of workers to such substances is of great concern. The automated process according to the invention minimizes or eliminates the exposure of workers to the toxic substances present in filler compositions.

Step a)

The actual geometry of the surface of the dent to be filled can be determined by any suitable technology available. Examples of suitable technologies are point based techniques, line based techniques, and area based techniques. Generally, determination of the geometry of the surface of the dent can be carried out using contact methods or non-contact methods. A typical industrially applied contact method is implemented in a coordinate measuring machine. Further examples of suitable contact methods are the use of a touch probe or a linear position sensor, such as a linear variable differential transformer (LVDT).

Examples of suitable non-contact methods are laser thangulation, time of flight measurements which use time as a surrogate measure for distance, fringe projection, X-ray, photogrammetry, and interferometry. These and other surface geometry determination methods are generally known, for example from the thesis of G. Bradshaw, Non-Contact Surface Geometry Measurement Techniques, Trinity College, Dublin, Ireland, 1998/1999. If required, the geometry of the surface surrounding the damaged area can be determined. The geometry determination of step a) is suitably carried out by a geometry determination unit. The geometry determination unit and the three-dimensionally shaped damaged substrate are moveable with respect to each other. The

geometry determination unit suitably is a computer controlled robotic unit. In one embodiment, the geometry determination unit can be attached to a robotic arm moveable about various control axes. Alternatively, the geometry determination unit can be fixed and the substrate is moveable about various control axes. It is also possible that both the substrate and the geometry determination unit are moveable.

The determined geometry data are generally transmitted from the geometry determination unit to an input unit of a data storage and processing unit capable of reading and processing the geometry data.

Step b)

In the process of the invention, the desired surface geometry after filling of the dent is determined. Generally, the desired surface geometry after filling of the dent is identical to or very similar to the original surface geometry before the damage occurred. In one embodiment, the desired surface geometry after filling of the dent can be determined by a reverse engineering step, such as extrapolation on the basis of the surface surrounding the dent. In particular in the case of relatively simple geometries, this method can be very suitable to determine the original surface geometry at the location of the dent. The surface geometry of some areas of automobiles, such as door panels, hoods, or roofs, can often be described by relatively simple geometrical functions. If the damaged area is sufficiently small, it can sometimes even be approximated as a plane. For such cases extrapolation from the surface surrounding the dent can give a very reliable approximation of the desired surface geometry after filling of the dent.

In the case of symmetrical substrates, it is often possible to find a mirrored surface of the damaged spot on the opposite side of the symmetry plane. Automobiles generally are almost symmetrical about their centre plane. By using geometry information from the corresponding area of the other side of an

automobile it is often possible to reconstruct the geometry of the damaged surface.

In another embodiment, it is possible to use geometrical data provided by the manufacturer of the three-dimensionally shaped substrate. Many articles are developed and manufactured using computer aided design (CAD). If available, CAD data can be used to determine the original surface geometry of the damaged substrate.

Determination of the desired surface geometry after filling of the dent is suitably carried out by a data storage and processing unit under the control of a program.

Step c)

The difference in geometry between the actual geometry of the surface of the dent and the desired surface geometry can be calculated by subtracting the geometry data of the damaged surface from the desired surface geometry data. The result of this step is a volume and geometry that has to be filled with filler composition, and the position and orientation thereof in space. This step is generally carried our by the data storage and processing unit mentioned above.

Step d)

Depending on the required precision of the dent filling process, a value of the difference in geometry is predetermined below which no further filling is required.

Hence, when the difference between the actual and the desired surface geometry is below or equal to the predetermined value, the dent filling process is stopped or not even started. If the difference is above the predetermined value, the process is continued.

Step e)

As mentioned above for step c), the volume and geometry to be filled is determined. This volume and geometry is subdivided into volumes and geometries of filler composition which can be applied in a single step. Typically, the volume and geometry is subdivided into layers I which can be applied in a single step. The total number of layers into which the volume and geometry is subdivided is an integer n, and the layer which is applied first and which therefore is the layer closest to the substrate is labeled h. The subsequent layers are numbered consecutively up to layer I _n . The result of the calculation thus is a number of layers h to I _n which can be applied to fill the dent. The number of layers needed to fill said volume and geometry depends on the filler composition used, the application process, and the characteristics of the optional curing step. The thickness of individual layers need not be the same. In one embodiment, the first layer(s), i.e. the layer(s) closest to the substrate, can be calculated to have a higher layer thickness than the outermost layers. When such a protocol is used, faster filling of a dent can be achieved without compromising the accuracy of the dent filling process.

Step f)

In the following step one or more layers of a filler composition are actually applied to the damaged substrate. Layers h to l _m of a filler composition corresponding to the volume and geometry calculated for the respective layer are applied to the damaged substrate, layers h to l _m corresponding to layers which are applied subsequently without intermediate determination of the difference according to step d), and wherein m is an integer which is equal to or smaller than n. In one embodiment, only a single layer is applied before the subsequent steps are carried out. In that case, m is 1. However, it is also possible to apply a plurality of layers or all required layers n before carrying out the subsequent steps. In that case, m is smaller than n and equal to n, respectively. As mentioned above for step e), the individual layers need not be of the same layer thickness.

Application of the filler composition is carried out by an application unit, such as a computer controlled robotic unit. The application unit and the damaged substrate are moveable with respect to each other. In one embodiment, the application unit can for example be attached to a robotic arm moveable about various control axes. Alternatively, the application unit can be fixed and the substrate is moveable about various control axes. It is also possible that both the substrate and the application unit are moveable.

The application unit can for example be in the form of a nozzle or a spout which suitably is connected to a reservoir of filler composition. Application by dispensing or dispense jetting is preferred. In the case of dispensing, the filler composition is contained in a barrel and dispensed through a nozzle by applying force or pressure. By this technique individual drops or continuous lines can be dispensed through a nozzle. The nozzle is very close to the surface to which the filler composition is applied in order for the filler composition to make contact with that surface. In the case of dispense jetting, a drop of filler composition is jetted from a nozzle and travels some distance through the air before making contact with the surface. Although dispense jetting is more complex than dispensing, it generally offers higher flexibility and the position of the nozzle is less critical. Suitable filler compositions applied in the process are those materials known to the skilled person and commonly used for filling dents caused by damage, such as liquid or semi-liquid filler compositions or putties. Also so-called hot-melts can be used. Suitable filler compositions harden after application. Hardening can be caused by physical processes, i.e. cooling and/or evaporation of volatile diluents. Alternatively or additionally, hardening can be caused by chemical curing reactions. An optional curing and/or hardening step can be included in the process. Curing and/or hardening can be induced by supply of thermal energy or by actinic radiation, such as UV radiation, depending on the type of filler composition used. Also two-component filler compositions which are mixed immediately prior to application and which cure at ambient temperature can be

used. Curing and/or hardening can be carried out after application of individual layers of filler composition. It is also possible to cure and/or harden a plurality of layers or even all layers together at the end of the filling process.

In one embodiment, the process additionally includes a sanding step. Sanding of the filled dent can improve the smoothness of the surface of the filled dent. Additionally, sanding improves the smoothness of the transition between the filled dent and the surrounding undamaged area. Sanding is usually carried out after all layers of filler composition have been applied and hardened and/or cured. However, it is also possible to sand individual layers. When sanding is carried out, it is possible to use a standard sanding step in order to smooth the surface. Alternatively, sanding can be used to selectively remove hardened filler composition so as to achieve a desired surface geometry. It is also possible to interrupt a sanding step by a geometry determination step in order to determine whether the selective removal of hardened filler composition is sufficient. Sanding is likewise carried out automatically by a sanding unit under control of the data storage and processing unit. The surface geometry data determined in previous steps or determined in step g) as described below can suitably be used as input data for control of a selective sanding step.

Step g)

In one embodiment of the process of the invention, the surface geometry of the damaged area is determined after an application step. Determination of the geometry after application and subsequent repetition of steps c) to g) can improve the accuracy of the process. In particular in cases where the actually applied filler layer or filler layers differ in thickness and/or geometry from the calculated filler layer(s), intermediate geometry determination is beneficial. In that case, deviations from the calculated results can be compensated for in subsequent steps.

Step h)

The above steps c) to g) are repeated until the difference in geometry determined in step c) is below or equal to a predetermined value. This value can be predetermined so as to achieve the required degree of matching of the original surface contours of the damaged substrate. If a high degree of matching is required, a lower predetermined difference in geometry will be selected, possibly leading to a higher number of layers to be applied. On the other hand, if a low degree of matching of the original surface is sufficient in an individual case, a higher predetermined difference will be selected as stop criterion.

Figure 1 is a flowchart which represents an embodiment of the process of the invention. The process starts with the determination of the actual geometry of the surface of a dent, for example a dent in a body panel of a motor vehicle. For this purpose, a computer controlled robotic unit having a laser triangulation unit attached to a robotic arm moveable about four control axes can advantageously be used. Subsequently, the desired surface after filling of the dent is determined. The desired surface geometry data can suitably be extracted from an electronic database containing CAD data of the damaged object. Calculation of the difference between the actual and the desired surface geometry is carried out by a data storage and processing unit. The calculation includes subtraction of the actual surface geometry data from the desired surface geometry data and results in a volume, a geometry, and the position and orientation thereof in space, to be filled. Subsequently, it is determined whether the difference between the actual surface geometry and the desired geometry is below or equal to a predetermined value. If such is the case, the difference is sufficiently low and no further filling is required. The process is then terminated. If the difference in geometry is greater than the predetermined value, the process is continued by subdividing the volume to be filled into layers which can be applied in a single step, for example a total of 5 layers \-\ to I ₅ . The first two layers \-\ and I2 may

have a higher layer thickness than subsequent layers I ₃ to I ₅ . The calculation is typically carried out by the data storage and processing unit under the control of a program. In the next step, the first layer \- _\ of filler composition is automatically applied to the dent. Application is typically carried out by a computer controlled robotic unit having a nozzle attached to a robotic arm moveable about four control axes. The nozzle is connected to a reservoir of liquid filler composition which is dispensed through the nozzle by application of pressure. In a typical embodiment, the filler composition is a two-component material which cures at ambient temperature. After application of the first layer, the actual geometry of the damaged surface is determined again, as described above. The calculation of the difference between the actual and the desired surface geometry and all subsequent steps are repeated until the condition for termination of the process is achieved, i.e. the difference in surface geometry is below or equal to the predetermined value.

The invention also relates to a system suitable for carrying out the process for automated dent filling. The system comprises a) a geometry determination unit capable of determining the geometry data of a damaged surface and transmitting said geometry data, wherein the geometry determination unit and the damaged substrate are moveable with respect to each other, b) a data storage and processing unit under the control of a program, configured to receive and process geometry data and capable of controlling an application unit, and c) an application unit for applying a filler composition which is under the control of the data storage and processing unit b), wherein the application unit and the damaged substrate are moveable with respect to each other.

The system may be positioned on glide tracks or a gantry for movement along the substrate having a dent to be filled, such as an automobile.

The system generally is implemented as a computer controlled robotic unit, having arms provided with various attachments, moveable about various control axes. It is also possible to use a computer controlled robotic unit having only a single arm moveable about various control axes and having exchangeable attachments, such that specific tools as required can be affixed to the arm. Movement of the arms can be caused hydraulically or electrically, or by other suitable means known in the art.

In a typical embodiment, the geometry determination unit is attached to such a robotic arm moveable about various control axes. The geometry determination unit may be implemented as a coordinate measuring machine. Further examples of suitable geometry determinations units are a touch probe or a linear position sensor, such as a linear variable differential transformer (LVDT). Examples of further suitable tools for geometry determination are those making use of laser triangulation, time of flight measurements, fringe projection, X-ray, photogrammetry, and interferometry.

The data storage and processing unit is under the control of the program. The data storage and processing unit is implemented to receive and read geometry data from the geometry determination unit and optionally from other sources, such as a computer readable geometry data file. The data storage and processing unit is programmed to carry out steps b) to e) of the process according to the invention.

The data storage and processing unit also serves as controller for directing the movement of the moveable units of the system.

Like the geometry determination unit described above, the moveable application unit suitably is attached to a robotic arm moveable about various control axes. The application unit may be implemented as a nozzle or spout connected to a reservoir of filler composition. Suitable means for controlled release of the filler composition from the nozzle or spout, such as valves and pressurizing equipment, are present as well. If filler composition of relatively low viscosity is

used, the application unit may alternatively be implemented in the form of a spray gun, for example an air spray gun. Also air brush equipment may be suitable as an application unit.

Optionally, the system also comprises a curing unit for curing the applied filler composition. The curing unit and the substrate are likewise moveable with respect to each other. In one embodiment, the curing unit is attached to a robotic arm moveable about various control axes. Depending on the curing mechanism of the filler composition employed, a suitable curing unit can be selected. If, for example, UV-curable filler composition is employed, the curing unit would be implemented as a source of UV radiation. For thermally curable filler compositions the curing unit may be implemented as a hot air blower or as a source of (near)infrared radiation.

Optionally, the system may further comprise a sanding unit. The sanding unit is likewise suitably attached to a robotic arm moveable about various control axes. The sanding unit may be implemented as an electrically driven rotating sanding head.