Abstract:
A method and apparatus is disclosed for forming lines of weakness in an automotive trim piece so as to enable formation of an airbag deployment opening in the trim piece. A cutting beam, such as a laser is directed at the trim piece surface to be scored and a sensor emits a sensing beam, and a beam combining device receives both the sensor beam and the laser beam and causes downstream beam segments to be collinear with each other as they impinge the trim piece surface. The scoring is thereby able to be carried out in a single pass, and is precise, repeatable and independent of cutting depth, angle of cutting, scoring patterns, material inconsistency, material color, and surface grain variability.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. provisional Serial No. 60/190,719, filed Mar. 17, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention concerns forming lines of weakness in portions of automotive trim pieces overlying airbag safety devices, in order to allow one or more airbag deployment doors to be created when an airbag is inflated. 
     Airbag safety systems are widely used in automotive vehicles and generally comprise an inflatable cushion, referred to as an “airbag”, stored folded in a receptacle and then rapidly inflated when a collision of the vehicle is detected by sensors. 
     The folded airbag is typically mounted behind an automotive interior trim piece such as an instrument panel or a steering wheel cover. One or more airbag deployment doors are forced open when the airbag is inflated to allow deployment of the airbag through the opening created by the deployment door movement. 
     During the last few years, airbag deployment doors that are integrated into the trim piece overlying the airbag receptacle have gained wide acceptance. As described in U.S. Pat. Nos. 5,082,310 and 5,744,776, these integrated doors employ a seamless or invisible construction whereby the deployment door or doors, although part of the trim piece, are not separately delineated and/or visible from the passenger side of the trim piece. 
     For such integrated deployment doors to open during airbag deployment necessitates weakening portions of the trim piece in order to allow trim piece sections to break free and hinge open. Weakening of the trim piece is carried out by creative lines of weakness comprised of scored lines formed by removing material from the trim piece from the back surface along a predetermined deployment door pattern. A critical component of this process is the amount of the trim piece material removed and/or remaining after cutting the score line. Accurate control of this process is critical to reliably producing proper airbag deployments. 
     A widely used method for determining the extent of material removal during scoring involves the use of triangulation type sensors as described in U.S. Pat. No. 5,883,356. These sensors, however, due to their triangulation operating principle, are limited in their ability to reach the bottom of the scoring produced by the cutting device. This is particularly so for narrow, deep penetrations which may be imparted by cutting devices such as lasers and cutting knives. Furthermore, due to their offset mounting, these sensors are not well suited to measure the varying penetration depth that occurs during scoring at a specific location. This is especially true if the scoring penetration is in the form of partial perforations or slots. As such, the process does not lend itself to scoring the trim piece in an adaptive control mode, where both depth sensing and scoring are in registry with each other to impinge the same point on the trim piece, during the progression of scoring of the trim piece. 
     Accordingly it is an object of this invention to provide a process and apparatus for scoring trim components overlying airbag installations in a manner that provides accurate adaptive process control, single-pass processing, improved airbag door deployment, and lower manufacturing costs. 
     SUMMARY OF THE INVENTION 
     According to the invention, the scoring of the trim piece is accomplished by the use of a controllable cutting means, such as a laser beam, which, based on feedback from two sensors, is controlled in intensity together with controlled relative movement between the laser and the trim piece, producing a precise, predetermined penetration into the trim piece along a predetermined pattern. 
     In this process, the laser cutting beam and sensing beam emitted from a first sensor are both directed at a surface on one side of the trim piece. A second sensor may also be positioned on the opposite side of the trim piece in opposition to the cutting laser beam. A beam combining device combines the laser cutting and sensing beams together so as to have collinear segments directed at exactly the same point on the trim piece. The scoring of the trim piece is carried out by the laser beam while the trim piece is moved in a predetermined pattern relative to the laser to form one or more deployment doors defined by the sections of the trim piece within the pattern. The depth of scoring of the trim piece by the laser beam is controlled by real time feedback signals corresponding to the depth of the cut provided by the first sensor. To determine material thickness remaining during scoring of each point along the predetermined pattern, real time feedback from the second sensor can be provided combined with the feedback signals from the first sensor. The sensor feedback can also be utilized to control the movement of the trim piece relative to the laser beam to enhance the weakening process control. 
     This process, due to the collinear arrangement of the impinging segments of the sensor and cutting beams, affords several advantages, including single-pass adaptive processing, scoring precision and superior part to part repeatability. The process is also independent of cutting depth, angle of cutting, scoring patterns, material inconsistency, material color, and surface grain variations. 
     Relative motion between the trim piece and the cutting beam to score the trim piece in a predetermined pattern can be provided by different means, including robots and X-Y tables. 
     The trim piece can have a monolayer, multilayer, or composite construction and could be scored on either side. The scoring can be continuous, intermittent or be a combination of both, and extend completely through one or more layers of the trim piece. The trim piece can be a finished part or a component which is subsequently integrated into a finished part. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic view of one form of the apparatus according to the invention including two sensors. 
     FIGS. 2,  2 A and  2 B are fragmentary enlarged views of several alternative designs of the beam combining device incorporated in the apparatus shown in FIG.  1 . 
     FIG. 3 is an automotive instrument panel with an integrated airbag deployment door formed by in a U pattern scoring carried out by the apparatus and process of the present invention. 
     FIGS. 4 through 6 are cross sectional views of sample monolayer and multilayer trim piece constructions on which various types of trim piece weakening scorings have been made. 
     FIG. 7 is a diagrammatic view of one form of the apparatus according to the invention incorporating only a single sensor. 
     FIG. 8 is a diagrammatic view of a second form of the apparatus according to the invention incorporating only a single sensor. 
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, certain specific terminology will be employed for the sake of clarity and particular embodiments described, but it is to be understood that the same is not intended to be limiting and should not be so construed inasmuch as the invention is capable of taking many forms and variations within the scope of the appended claims. 
     This invention describes an improved process and apparatus for forming lines of weakness in an automotive trim piece for an airbag door installation in a way that improves the accuracy of the process, the trim piece quality, the airbag deployment performance, and, also, reduces trim piece production costs. The process will be described with respect to an instrument panel airbag door installation, but it is also applicable to other automotive and non-automotive installations, with or without an airbag. Typical airbag installations include driver side airbags, front passenger airbags, side impact airbags, headliner airbags, knee airbags, and rear passenger airbags. The process will also be described in terms of a laser beam, but is also applicable to other cutting beams as described below. 
     FIG. 1 shows a first embodiment of a trim piece scorning apparatus  10  according to the invention. This includes a cutting beam source  12  which generates a cutting beam such as a laser beam which is used to carry out controlled scoring of a surface  14  on one side of an instrument panel trim piece  16  that would overlie an airbag installation when installed. 
     The trim piece  16  is positioned on a fixture  18 . A first sensor  20  is provided to determine the depth of scoring produced by the laser cutting beam onto the surface  14  of the trim piece  16  to weaken the same. The first sensor  20  and the cutting beam generator  12  are connected to a beam combining device  22 . The beam combining device  22  (shown in detail in FIG. 2) is designed to combine the separately generated sensing beam or beams A emanating from the first sensor  20  and the laser cutting beam B from source  12  so as to be in a collinear relationship and to direct the combined segments of the sensor A and cutting beam B so as to impinge the same precise spot on the trim piece surface  14 . This beam combining device  22  will also redirect any reflected beam or beams required for sensor operation from the trim piece surface  14  back to the first sensor  20  as necessary in carrying out the process. 
     The trim piece  16  is moved relative to the cutting laser beam source  12 , as well as the first sensor  20  and the beam combining device  22  via a motion actuator  24  to cause tracing of a particular scoring pattern and to achieve a precisely controlled rate of scoring. The motion actuator  24  can directly move the trim piece  16  itself or move an optional fixture  18  onto which the trim piece  16  is mounted. Alternatively, the motion actuator  24  could be used to move the laser beam source  12  and the first sensor  20  relative to the trim piece  16 . 
     A second sensor  26  may be located on the side of the trim piece  16  opposite the first sensor  20 , a second sensor beam emanating therefrom, directed at the outer surface  28  of the trim piece  16  and aligned opposite the same trim piece point as is the laser cutting beam and the first sensor beam or beams are directed in order to control the scoring so as to produce a programmed thickness of material remaining after scoring. This is done by combining signals generated by both sensors  20 ,  26  to create a feedback signal corresponding to the thickness of the remaining material. 
     The apparatus  10  is operated via one or more industrial controllers  30  that control the scoring effected by the laser and/or the movement of the motion actuator based on a particular program and feedback signals provided by the sensor  20 ,  26 . 
     Lasers are particularly desirable for carrying out this type of scoring processes and they can be of the carbon dioxide, excimer, solid state, argon gas, or diode type. However, based on the primary trim piece materials utilized (polymers, fabrics, wood, leather), the carbon dioxide laser is likely to be the most preferable in terms of operability, efficiency and cost. The laser can be operated either continuously or in a pulsed mode. 
     Different type of sensors can be utilized to measure the extent of material removed or remaining during scoring of the trim piece. For the first sensor  20 , connected to the beam combining device  22 , a preferred type is a closed loop device that sends and receives a specific beam of electromagnetic radiation in order to determine the depth of scoring effected by the laser. The Conoprobe sensors offered by Optimet and based on the technique of conoscopic holography, is one such sensor commercially available. In this type of sensor, an emitted laser beam and reflected return beams of visible light have segments also traveling in a collinear relationship with each other and the laser beam. Another type of sensor that could be utilized is one that detects reflected light beams such as a high speed CCD camera. In this application, the reflected beam will be reflected from the trim piece surface being scored by the cutting beam. 
     For the second sensor  26  aimed at the outside surface of the trim piece, which is generally smooth and accessible, there are more numerous options including, infrared, laser, ultrasonic, conoscopic, CCD camera, proximity and contact type sensors. 
     The signal spot size of the sensor beam selected can vary significantly. Generally the smaller the spot size the better. For the first sensor, the preferred size would not exceed the size of the scoring produced on the trim piece by the cutting laser beam. For the second sensor, if surface finish variations, so called grain, are significant, its spot size should preferably not exceed 300 microns. 
     There are numerous ways for combining the separately originated cutting laser beam B and sensor beam A to create collinear segments thereof. FIG. 2 shows the inner details of the beam combining device  22  which combines the separate laser beam A and the first sensor beam B to create collinear segments which impinge the trim piece surface  14 . The beam combining device  22  includes a reflector  32  having coatings causing reflection of light of the wavelength of the sensor beam A from its inclined surface while allowing the cutting laser beam B to be transmitted. 
     Such coated selective reflectors are commercially available. This of course requires that the laser and sensor beams be of different wavelengths. 
     A side entrance tube  29  directed at the reflector  32  is connected to the first sensor  20 . The main tube  31  mounts the reflector  32 , main tube  31  having an end opening  33  directed at the trim piece  16 . 
     The segment of the sensor beam A reflected from the reflector  32  is caused to be collinear, i.e., aligned and coextensive with the segment of the laser beam B past the reflector  32 , with both collinear segments then impinging the surface  14  at the same precise point. 
     FIG. 2A shows a second form of a beam combining device  22 A having an inclined reflector  32 A having coatings causing reflection of a beam having the wavelength of the cutting laser beam B, while allowing transmission of the beam having wavelengths of the sensor beam A to be transmitted therethrough to reverse the relationship shown in FIG.  2 . 
     FIG. 2B is a simplified diagrammatic view of another form of the beam combining device  22 B combining the cutting laser beam B and the first sensor beam A to produce collinear downstream segments thereof. This embodiment includes a simple mirror reflector  36  having a through hole  34 . The hole  34  is small in diameter relative to the diameter of the cutting laser beam B in order to minimize or eliminate the effect that the presence of the hole  34  may have on reflecting the cutting laser beam B from the mirror reflector  36  to redirect the cutting laser beam B. Such a mirror does not require coatings that are wavelength-selective such as those shown in FIGS. 2 and 2A in order to combine segments of the beams into a collinear relationship. In this particular arrangement, the first sensor  20  could be a CCD camera receiving beams reflected from the trim piece surface being scored by the laser beam. 
     The trim piece can be any of many automotive parts including instrument panels and/or their components (skins, substrates, foams, scrims, etc.), driver side airbag covers, door panels, seat covers, headliners, bumpers and seat belts. The scoring can be applied on either side of the trim piece but is preferably applied from the inside so that is substantially invisible from the outside surface facing the passenger. As shown in FIG. 3, the scoring does not penetrate the outer surface  28  of the trim piece  16  shown as an instrument panel and would be essentially invisible to the passenger. Different materials could be utilized in a trim piece including metals, polymers (TPUs, TPOs, PVC, TPEs, etc.), leather, fabrics, wood and wood composites. As shown in FIGS. 4 through 6, the trim piece  16 ,  16 A,  16 B may consist of one or more layers of similar or dissimilar materials. In multilayer constructions, the scorings  40 ,  40 A,  40 B could be applied to any one layer or any combination thereof as shown. 
     Manufacturing of the trim piece can be done in several ways using different materials. Many of these materials can be formed in a solid state or in a cellular state. Polymeric trim pieces can be formed by processes such as extrusion, injection molding, low pressure insert molding, blow molding, casting, thermoforming, lamination and foaming. 
     The scoring applied can be in any shape, including a U, H, I, T, X, W, S and Y pattern, required to form an opening for the airbag to deploy. The opening could include one or more door panels. The scoring can be either continuous or discontinuous including grooves, blind holes and dashes. Furthermore, the cut orientation can be straight or offset. For successful and consistent airbag deployments, the degree of precision of cutting is particularly important to ensure that the amount of material remaining along the predetermined pattern is as intended. 
     The penetration or depth of scoring, for an invisible airbag door application, can be up to about 95% of the trim piece thickness. 
     In order to apply the complete scoring pattern, the trim piece is preferably moved relative to the laser beam and/or the sensors. The relative motion can be applied by a number of motion actuators including robots and X-Y tables. During cutting, the sensor thickness data can also be used to control the movement of the motion device in order to apply the scoring along the predetermined pattern. The trim piece may be held directly by the motion device or be attached to a holding fixture held by the motion device. The holding fixture may be shaped to match the shape of the trim piece and/or be designed to register specific surface features of the trim piece. Vacuum or clamps could also be applied to the holding fixture to hold the trim piece surface in better contact with the fixture  18 . The fixture  18  can be designed to allow the second sensor  26  to have physical and/or optical access to the surface  28  of the trim piece (i.e., transparent fixture wall, opening in fixture wall, etc.). 
     The process controller  30  is designed to control the operation of the laser and/or motion actuator based on the feedback signals provided by the two sensors  20 ,  26  which, from opposites sides or surfaces of the trim piece  16 , monitor the location being scored. The two sensors  20 ,  26  working in tandem determine the remaining thickness of the trim piece  16  at any point they are directed to. During laser scoring at a given point, the two sensors  20 ,  26  provide signals from which a measurement of the material thickness remaining after the scoring can be derived by the control device  30 . Based on this real-time thickness determination, the control device  30  controls the operation of the cutting beam source  12  to effect only the desired extent of material removal intended for any given point on the trim piece  16 . The remaining thickness data can also be used to control the motion actuator  24  to move the trim piece to the next desired location along the predetermined scoring pattern. 
     Due to the collinearity of the impinging segments of the first sensor beam and the cutting beam, several advantages are realized that could not be attained by any of the existing processes. Since the first sensor beam and the laser beam are always impinging on the same point on the trim piece, the process becomes insensitive to a large number of key variables, including the angle of cutting, the depth of the penetration, the trim piece thickness, the configuration of the weakening pattern and, to a large extent, the speed of cutting. Also, the combination of the two sensors provides for a direct remaining thickness measurement, superior scoring precision and excellent part to part repeatability. In addition, the process enables the user to overcome variations in trim piece thickness, material properties such as density, color, voids and surface grain. These and other benefits are obtained while operating with rapid adaptive control in a single-pass mode. 
     A second embodiment of the apparatus  44  according to the invention is shown in FIG. 7 where the outer surface  42  of the trim piece  16  is in intimate contact with the inner fixture wall  46 . In this arrangement, the distance between the first sensor  48  and the fixture inner wall  46 , along the predetermined scoring pattern, can be measured prior to starting the scoring operation. If this distance can be maintained constant from pass to pass, then the second outside sensor would not be necessary while still running the process in a single-pass, adaptive control mode. 
     FIG. 8 shows another embodiment of the apparatus  50  where the first sensor  52  is mounted immediately alongside the cutting beam source  12  so that both beams A, B are substantially collinear with each other to approximate the effect of using the beam combining device  22  described. 
     The laser cutting beam may also function as the sensor. This arrangement also maintains the collinear configuration as the sensing signals and the laser beam are generated by the same laser. Under this approach, the laser beam characteristics and control would be manipulated to conduct sensing measurements during or between cutting intervals (i.e., sensing after a preset number of cutting pulses).