Fork level indicator for lift trucks

Abstract

A fork lift truck includes a fork level sensor located in the forks, away from the vertical mast of a lift truck for detecting the true level of the forks, and a vision system including a camera which may take several forms. In one form, a single camera is mounted in a housing which may be moved to a protected location vertically either by sliding in the carriage assembly, or by use of a parallelogram device. In another form, multiple cameras are employed where a second camera may be either mounted above the first camera in the same housing or mounted between the forks. Alternatively, the first camera may perform multiple roles by being moved vertically from a first predetermined location below the bottom of the forks to a higher elevation a second predetermined location relative to the forks. A video display terminal, which shows the view observed by the camera, may also include a fork level indicator, a reticle for assisting in adjusting the vertical position of the forks, and an indicator showing the specific truck function selected by the operator.

What is claimed is:  
     
       1. A fork lift truck including 
       a pair of forks for supporting a load,  
       means for raising and lowering said forks,  
       means for tilting said forks relative to a body of said truck,  
       a level sensor mounted on at least one of said forks for providing an indication of the level position of said forks with respect to a horizontal plane,  
       a display terminal including a screen mounted for viewing by an operator during normal operation of said truck, and  
       means responsive to said level sensor for displaying an indication of the level position of said forks with respect to the horizontal plane on said screen of said display terminal, including a reference bar on said screen representing the horizontal plane, and an indicator on said screen for showing the actual position of said forks with respect to the horizontal plane, thereby to assist the operator in adjusting the level of said forks prior to loading, moving or unloading a load from said forks.  
     
     
       2. The fork lift truck of claim  1  wherein said level sensor is mounted approximately midway the length of at least one of said forks. 
     
     
       3. The fork lift truck of claim  1  wherein said level sensor is an electrolytic tilt sensor. 
     
     
       4. In a fork lift truck including 
       a pair of forks for supporting a load,  
       means for raising and lowering said forks and for tilting said forks relative to a body of the truck,  
       a camera mounted near a plane of said forks, said camera having a lens for viewing the scene immediately in front of the forks,  
       a display terminal including a screen for presenting to an operator an image of the scene viewed by the lens,  
       the improvement including  
       said display terminal being mounted to said truck during normal operation thereof, 
       a level sensor mounted on at least one of said forks for providing an indication of the level position of said forks with respect to a horizontal plane, and 
       means for displaying an indication of the level position of said forks on said display terminal, including a reference bar on said screen representing the horizontal plane, and an indicator on said screen for showing the actual position of said forks with respect to the horizontal plane, whereby the operator is provided with both an image of the scene in front of the forks and an indication of the level of the forks thereby to assist the operator in adjusting the vertical position and level of said forks prior to loading, moving or unloading a load from said forks.  
     
     
       5. The fork lift truck of claim  4  wherein said display terminal includes a television screen. 
     
     
       6. The fork lift truck of claim  4  wherein said camera is aligned to define the horizontal plane through its center of view, and 
       means for generating a reticle, including a visual representation of said horizontal plane, on said display terminal to assist an operator in vertically positioning said carriage assembly.