Abstract:
An extension ruler intended for symmetry measurements of vehicles, having a built in measuring device for the extension of the ruler and transfer of data or figures to a display. The measuring device includes a tape extending from one end of the ruler to the other end where the tape is wound on a drum spring biased in the winding direction, which drum is provided with teeth and that the passage of these is detected and counted by a light source and a photo diode and that the drum rotation detected in this way is used to provide a measure of the extending of the ruler.

Description:
BACKGROUND OF THE INVENTION 
     In order to check and measure the damage to crashed cars before, during and after repair, telescopically extendable measuring devices or rulers provided with perpendicularly upwards extending mandrels in both ends are used. A ruler that is provided with a magnetic fastening bracket in one end (SE 9704438-2) is also used in this type of application. These devices are simple, easy to handle and result in surprisingly highly precise work. In reality, however, these devices require writing down or remembering measurements between device measures. Furthermore, the precision of these devices is dependent on the skill or measuring technique of the device operator, since inclining the ruler may change the result. Likewise, operator skill and environmental conditions when reading scales are of essential influence. 
     An additional error source in prior art measuring rulers is that the magnet fastener, which allows fast and simple handling of the device by one person even for long measurements, is prone to mounting that introduces a slight error. Mounting the prior art device in different ways on the left and right side can give different measures even if the measure should be the same. In addition, a little dirt under the magnet gives an inclination the fastener that may cause the device to mis-measure. 
     Thus, the object of this invention is to create a measuring device that overcomes the above problems with the prior art devices without impairing the simplicity and ease of use of the device. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, a telescopically extendable ruler is provided with measurement mandrels or suitable measurement bodies in the ends, the ruler being provided with a digital measuring means. The previous scale is thus replaced with an electronic measuring apparatus and indication of the measure. In this way, it is no longer necessary that the user is in the precisely correct place on the side of the measuring device in order to see the scale. Further, the risk that a user might shadow the scale thereby being unable to read the device is also reduced and, since the device stores measured values, values are ready for comparison, even if several minutes lapse between measurements. If so desired, one can measure absolute values or measure differences between measures taken on an undamaged area of the car, and a measure taken on a damaged area. The later type of technique facilitates, in particular, measurements taken during straightening operations. It is also easier to remember small figures than larger ones. 
     The present invention also joins the ruler to a centering mandrel or cone, while a magnet placed over the cone is moveable. By additionally making the ruler moveable about a universal joint, the ruler can be centered within a hole, from where measurements are to be taken. Thus, the measurements of the current device will not be influenced by the inclination of the magnet, caused by a locally dented surrounding, dirt, underbody coating, etc. 
     Since the force that the centering mandrel or cone is subjected to is exclusively directed towards, a vehicle, the centering tip or cone, which is journaled on a ball, can be provided with some type of snap lock so than one simply snaps the conical tip on the universal joint. In this way one can use different cones of varying length depending on the size of the hole. Thus, it is actually possible to place the universal joint precisely in the center of the hole. One can also contemplate the use of other types of points or tips. 
     In order further to simplify the current device, the device is provided with an adjustable spirit level on the side or on top of the ruler, extending along the length of the ruler. In this way it becomes possible to take a measurement between two known and undamaged points in the longitudinal direction of the car. The measuring mandrel located at the outer end of the ruler is adjusted to the height required to give an orientation to the ruler parallel to the datum plane of the car. The spirit level is now adjusted to an entirely level position. The spirit level together with its fastening bracket is then turned 180° and then the entire ruler is turned or moved so that its ends change position in relation to the vehicle that is to be measured. The spirit level will now, with the ruler placed lengthwise along the car, represent a definition of the datum plane of the vehicle, allowing quick and normalized measuring. A supposition for this is that the vehicle stands comparatively even laterally, but since this normally is the case, it is not a problem. However, it is more common that the vehicle is inclined in its length direction. 
     The electronic digital measuring of the extension of the ruler is preferably done by means of a device located in one of the telescoping tubes. The device comprises a thin metal tape that is fastened in the other end of the ruler. The tape runs over a rotatable drum. A spring device is arranged to pretension the drum so that the tape always is kept stretched. The extended length is then detected by the drum or roller for the tape having a toothed or screen pattern provided wheel that passes between a light source and a photo detector generating pulses as the drum or wheel rotates and the pulses can then simply be counted and transformed to measures shown on a display in the end of the ruler, either in millimeters or in inches. 
    
    
     DESCRIPTION OF THE FIGURES 
     Further advantages and characteristics of the invention are apparent from the following description of a preferred embodiment of the invention with reference to the enclosed drawings. 
     FIG. 1 shows a measuring ruler in accordance with the invention in a perspective view and partly in section; 
     FIG. 2 shows an exploded view of a magnet fastening bracket; 
     FIG. 3 shows the ruler in a perspective view; 
     FIG. 4 shows an adjustable spirit level on top of the ruler; and 
     FIG. 5 shows an adjustable spirit level on the side of the ruler. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A ruler  100  shown in FIGS. 1-4 includes telescoping tubes  1 - 4  with tube  4  positioned inside tube  3 , and so on. A magnetic fastening bracket  5  is provided at one end of ruler  100  in contact with the tube, while at the other end of the ruler, a perpendicular mandrel  6  is arranged with a shaft  15  that can be locked in a bracket  7 . 
     The magnetic fastening bracket  5  includes a conical mandrel  8  that is internally snapped over a ball, that in turn, using a short essentially cylindrical shaft  10 , is detachably fastened to an end piece  11  positioned at the outer end of the ruler. On the conical mandrel  8 , a circular magnet  12  is displaceable axially, and fastened in a casing  14  that holds a pressure spring  13 . Using the spring  13 , the casing  14  is pushed away from the cone  8  and the ball  9  towards the ruler itself. The spring  13  is, however, sufficiently weak in relation to the force exerted by the magnet so that when the cone is positioned in the intended measuring hole, the magnet is moved, against the force of the spring, into contact with the metal around the hole. The resulting force of the magnet pushes against the hole using the ball and spring. By choosing cone  8  according to hole diameter, and simply snapping off and on different cones  8 , the universal joint can be located with its center of movement level with the hole. Thus, the ruler will measure distances precisely to the center of the hole. 
     At the other end of the ruler, a digital display is arranged so that it is integrated with the bracket  7  for the mandrel  6 . The digital display includes a number of control buttons. The display can either indicate the measured distance between the center of the universal joint and the tip of the mandrel  6 , or, alternatively may be adjusted so that it shows  0  for a first measure and then only displays differences relative to this value so that users get a displacement measurement so that the vehicle can be repaired. 
     The length of measurements obtained by the ruler are sent to the digital display using a thin metal tape  16 , a drum  102 , teeth  104 , a light source  200  and photo sensitive element  201 . The thin metal tape  16  extends from the end of the ruler that includes magnetic fastening bracket  5  to the inner end of an innermost tube  4 . A measuring unit  17  is fastened to the innermost tube  4 . The tape  16  is wound on a small drum  102  inside measuring unit  1 . On the same drum  102  a band  18  is arranged with a winding direction opposite that of tape  16 , and extends in the opposite direction to tape  16 , i.e., towards the bracket  7 . The band  18  is connected via a pulling spring  19  to the bracket  7 . Since the area of the drum  102  where the band  18  is wound has a smaller diameter than the area of the drum  102  where the measuring tape  16  is wound, the spring length required to keep the metal tape  16  stretched is reduced. 
     The drum  102  is further provided with a radially extending rim of small pins or teeth  104 . When the drum  102  rotates, the pins  104  pass between a light source and a photosensitive element so that each pin emits a pulse. These pulses can then be counted by the digital display device [not shown] and used as data for the measuring function of ruler  100 . Furthermore, measuring unit changes, i.e., from inches to millimeters, and changes in the diameter of coil diameter of tape  16  are accounted for by the digital display device, and the data is adjusted accordingly. 
     In addition, the above described digital display device is very light and robust so that it will not be damaged if the ruler is handled carelessly. 
     As previously mentioned, the ruler  102  consists of guides for telescoping tubes  1 - 4 . The innermost tube  4  has a guide [not shown] positioned in the next smallest tube  3 . Also, the two middle tubes  2  and  3  have guides  24  and  25 , respectively, positioned inside said tubes. The guides  24  and  25  are also provided with spring biased contact heels  26  to eliminate any play. These contact heels also serve to prevent the tubes from being drawn out of each other. The tubes  1 - 3  also have outer guides  27 - 29  that serve as seals. 
     Tube  4  is preferably at the same end provided with a spirit level  20 . The inclination of the spirit level  20  is adjustable in relation to the longitudinal direction of the ruler. This inclination adjustment is carried out by the spirit level being positioned in a bracket  21  in spirit level end  22 , and using an adjustment screw  23  located at the opposite end  107 . The bracket is furthermore able to swivel in the bracket  7  around an axle arranged vertically and perpendicular relative to the length direction of the ruler. In this way it becomes possible to adjust the spirit level so that it is horizontal by first applying the ruler to undamaged parts of the car and with a mandrel length that locates the ruler in the datum plane of the car or parallel therewith. As soon as the spirit level is horizontal the ruler is parallel to the datum plane. In this way, precise height measurements become possible. If the adjustment of the spirit level is necessary or practical for the ruler to extend in the opposite direction of the vehicle, the spirit level bracket  21  is pivoted one half turn around the vertical pivot axle so that despite the turn about of the ruler, the spirit level can indicate the datum plane. In this way, the number of errors is considerably reduced and the precision of executed measurements increases. The spirit level may either, as shown in FIG. 4, be located on top of the ruler facing the vehicle that is to be measured, or alternatively the spirit level may be arranged on the side of the ruler but so that it still can be swiveled 180° to enable the above operation, as shown in FIG.  5 . 
     The device described above is extremely easy to handle, precise and dramatically facilitates repair work. The above disclosure is in no way limiting, and one skilled in the art would recognize that the ruler may be provided with different types of adaptation pieces that may be added at both ends of the ruler for adapting to specific types of measurements and/or objects on which the ruler is used. Furthermore, one might consider that instead of measuring sizes, height, depth, etc., an expected or prescribed value for a measurement can first be entered and the ruler applied to an object to obtain a value difference. 
     The spirit level may also be illuminated with a light emitting diode or the like.