Method and device for checking symmetry

Abstract: A method for the measuring of symmetry when in particular repairing cars including the use of a measurement bar comprising in each end a laser head that can be swiveled around the length axis of the bar. The laser heads can emit light beams perpendicular to the length axis of the bar. The bar is on a straightening bench (on which the car is mounted) mounted perpendicular to the length axis of the car. When the laser heads are swiveled their beams construct parallel planes on each side of the car from which measures can be taken to the sides of the car in order to establish i symmetry exist or how great the necessary correction has to be.

Description: When repairing panel damages on cars, and then in particular damages resulting from collisions, it is for the correct mounting of new parts as well as for the straightening of deformed parts important that this can be done so that correct final measurements are achieved. If this is not done the new panel parts will not fit well and the car may become skew or unsymmetrical after the repair. In order to solve this problems it is known to mount a frame in the shape of an inverted U over the part of the vehicle that is to be repaired. Measuring can than be done on opposite sides of the car to the vertical legs of the frame, so that if one side is damaged the opposite side can be straightened and new parts mounted symmetrically by measuring in relative the frame on both sides. Such a frame is for instance shown in US-A-4 630 379. In US-A-4 630 379 is also shown how laser beams with horizontally and vertically extending portions define a horizontal datum plane from which measurements can be taken to the vehicle to determine the correct positions of datum points on the vehicle. The use of such a frame is a particularly time consuming work. Not only does the man carrying out the repairs have to walk from side to side to take the measurement but usually the measuring frame will also be in the way of the work itself. This is in particular the case if the work includes the straightening of the supporting parts of the car body when powerful pulling means must be arranged pulling out from the body of the car in order to pull out parts that have been pushed in in the collision. Since the measuring can not take place simultaneously with the straightening the apparatus used for straightening must be demounted or removed in some way before the frame is mounted and measuring can take place, likewise the measuring frame has to be removed between straightening steps. Also the frame repeatedly has to be moved along the car body for measurements at different locations. In most cases this time consuming multi step method must be repeated a great number of times until correct positions are obtained. Furthermore the measuring frame require in order to function properly an exactly centered mounting and a mounting so that its vertical legs really are vertical. Furthermore of course the frame must be placed so that its plane is perpendicular to the length axis of the vehicle. This is normally achieved by mounting the frame on a measuring flame that in turn is mounted to a so called straightening frame or bench on which the car in the normal case is fixed during the repair work. The repeated mounting and demounting of the frame will wear on the fastening brackets increasing the risk of faulty mounting positions. The frame, that has to be light and slender to be possible to handle, may also easily be bent or otherwise damaged in the handling. Also there is the risk that the frame when handled damage the car body. In view of the above problems there exists a need for a simple, easily handled method and apparatus for the securing of symmetry when repairing structural or panel damages on cars. Such a measuring possibility is in accordance with the invention achieved in a surprisingly simple way. In accordance with the invention a measuring bar is used, extending horizontally and perpendicularly to the length direction of the car. The bar is provided with fastening means, preferably at least two for the fastening of the bar on the straightening frame or bench. In the outer ends of the bar swivelable or rotatable light beam emitting means are arranged, preferably lasers, which light emitting means emit light beams or rays in parallel planes that are vertical and parallel with the length direction of the car when the bar is mounted perpendicular to the length direction of the car. With the bar mounted fixedly in relation to the car on the same straightening bench on which the car is fastened the light beam or in particular the laser beam on the undamaged side of the car can be directed so that it falls on a scale that is held against a measuring point. The reading on the scale is taken and used when adjusting or mounting corresponding parts on the other side of the vehicle by turning the laser beam also on that side so that it impinges on the scale that can be the same scale as on the other side held against a point corresponding to the measurement point on the undamaged side. As is realized from the above the invented method will give a great decrease in the work required for mounting and controlling the symmetry. The device will also be more simple to use when work is carried out, in particular since the laser beams with a simple turning of the rotatable or turnable laser heads can be directed against any scale or rule held against a car body. With known technique it would be necessary to remove the frame repeatedly to secure that the measuring frame is located precisely outside of the desired measuring points. The measuring method according to the invention makes use of the fact that in order to secure symmetry it is sufficient with an instrument or method only indicating the widths positions or distances from the center plane of the vehicle. Normally it is not necessary to make any measurements lengthwise or heightwise of the car. The reason for this is that the height and the length positions or coordinates in general will be quite sufficiently defined by the panel parts that are mounted on car or are to be mounted on it. In other words measuring normally take place against specific points along the contour of the panel part. To check length and height measurements for instance for a door opening or the like as simple means as rules or scales in one form or another will be quite sufficient. In a further development of the invented method the light beam sources or lasers are axially displacable in the ends of the bar for the adaption to different vehicles widths. Alternatively the widths of the bar or the distance between the light beam sources can be adjusted so that the measurements achieved when measuring from the light beams against the vehicle coincide with measures given in data sheets for the car provided by the manufacturer. Preferably the extendable means for the laser heads includes a scale. By using lasers it is possible to use the device also at full lighting. In order to enable the adaption of the extendable scales for different cars additional scale indicators can be used. This may in particular be the case if one can not guarantee an exactly centered mounting of the bar. It should also be mentioned that a correct centering of the bar can be checked by measuring or directing the laser beams so that readings can be taken against undamaged parts on both sides of the car. It is possible to use the laser beams also to check that the bar really is perpendicular to the car length axis by measuring relative known points lengthwise of the vehicle. By providing lines in the ceiling above the car perpendicular to the cars length direction it is possible further to facilitate coordination of the laser beams on the two sides of the vehicle. By providing also a few lines lengthwise of the vehicle it is also easy to check or adjust the car's position. The invention is in particular intended for the use together with straightening benches existing on the market. No mounting or demounting of any measuring device is necessary between measuring and straightening and in fact the measuring can be continued concurrent with the straightening so that the straightening can be carried out directly to the final measure. In order to facilitate this for instance a rule provided with a magnet can be mounted on the part that is to be straightened, alternatively the mechanic may with a first hand direct the laser beams against the rule that he holds with the other hand and then he can control the straightening work with the first hand until the intended measure has been reached. This procedure will be simple, comfortable and exact also when a certain return springing exist after the removal of the straightening forces. The device used for the symmetrical measurements according to the invention may for instance further comprise locking means for the locking of the laser heads, a coupling together of the swiveling movements of the laser heads or a coupling together of the extension of the laser heads so that they always extend the same distance from the bar itself. Additional features and characteristics of the invention as well as possible developments of this are apparent from the following description of a preferred embodiment of the invention shown in the drawing and from the patent claims. In the drawing is shown how an instrument according to the invention is used on a car that is to be measured in accordance to invention. In the drawing the symmetrical measurement device according to the invention includes a bar 1 that with two brackets 2 and 3 is held to a measuring frame, that in turn is fastened to a straightening bench 5. In the outer ends of the bar laser heads 6 arranged. These comprise a laser diode, a battery, a switch and a bearing. The lasers are very carefully adjusted so that they emit beams exactly perpendicular to the symmetry axis of the bar. The laser heads are in the bearings 7 turnable or swivable arranged in the bar extensions 8. Each bar extension 8 is arranged adjustable in the bar 1 and lockable relative this by means of a screw 9. On the upper side of the bar extension furthermore a measuring scale is arranged. The symmetry axis of the turning of the laser head is in parallel with the length axis of the bar and the direction of the laser beam is perpendicular to this direction. The extensions 8 are on their lower sides V-shaped and slidable in a likewise V-shaped profile on the inside of the bar 1. Furthermore in the inner ends of the extensions a plastic knob or slide shoe is arranged on the top of the extensions pressing the extensions down against the V-shaped guide in the bar 1. At the very bottom of each extension in the apex of the V-shape of the extension an undercut slit or recess is arranged so that an essentially rectangular channel is obtained. In this channel a block is arranged, provided with a threaded hole in which the locking screw is threaded. This means that when the screw is tightened the extension is pressed down in its outer end against the V-shaped guide in the bar. The sliding shoe in the inner end and the locking screw together will secure that the extension will be parallel with the bar even if their profiles are extruded in aluminum and therefore in themselves may be slightly distorted. On the straightening bench a car 10 is mounted. When measuring the laser beam is activated or switched on and the laser head is turned so that the laser beam is directed towards the rule, scale or pocket rule held against an intended measuring point. The user holds the rule with one hand and directs the laser beam with the other one. In order to find the position of the rule that is parallel with the measuring bar the rule can for instance be tilted slightly here and there until the lowest reading is obtained corresponding to parallel conditions. The mechanic then goes to the other side of the car and measures there and will either receive an indication that a correct position has been obtained or can easily see how much correction that is needed. If it is practical one can of course on the undamaged side note the measurements at a number of points to save walking time between the right and the left side. The precision obtained in this remarkably simple way is far greater than that existing between left and right sides of the cars when fabricated and is therefor more than enough for repair purposes. The possibility to mount the symmetrical measuring device comparatively close to the measuring location contributes to the good precision achievable by the method and device according to the present invention, so that possible misalignments will be of little importance.

Claims: Method for the measuring and checking of symmetry at car bodies, characterized in that on a straightening bench (5) on which the car (10) is fastened a bar is provided with turnable light beam emitting means (6) at its ends, which light beam emitting means (6) can emit light beams in parallel planes that are perpendicular to the length axis of the bar and parallel with the length axis of the car, the light beam emitting means giving measurement planes on each side of the car from which planes the distance to any point on the car's body can be measured by means of a simple rule or scale, held with one hand while the other hand turns the light beam emitting means so that its beam falls on the scale. Method according to claim 1 characterized in that the lateral positions of the light beams are so adjusted laterally and the scales so marked that the readings obtained on the scales corresponds to data figures given for the vehicle by the maker. Method according to claim 1 characterized in that lines parallel to the bar are arranged in the ceiling above the car to assist in directing the light beams on the different sides so that they will be parallel. Device for the checking of symmetry on cars, characterized in that it comprises a bar (1) at the ends of which laser heads (6) are arranged swivable around an axis that is parallel to the length direction of the bar, and that lasers in the laser heads (6) are directed so that they can emit beams of light perpendicular to the axis of the bar, and that the bar is provided with fastening means (2, 3) for fastening it on a straightening bench (5). Device according to claim 4 characterized in that the laser heads are arranged on extensions (8) that are slidable and lockable in the bar (1). Device according to claim 5 characterized in that the extensions (8) are provided with scales indicating the degree of extension. Device according to claim 5 characterized in that the extensions are slidable in the bar in a V-shaped guide, the extension also having a V-shaped cross section. Device according to claim 7 characterized in that the extensions in the bar are pressed against the V-shaped guide in the bar by a sliding shoe on top of the inner end of the extension and a locking screw is threaded in a block sliding in a downwards partly open channel in the extension.

Inventors: JOHANSSON HAKAN, NILSSON LARS, JOHANSSON, HAKAN, NILSSON, LARS
Applicants: JNE AB
Application year: 1995
Main classification: G01B11
IPC codes: G01B11, G01B5