Abstract:
In a dump truck where a monitoring system prevents the raising of the cargo bed when the level of lateral tilt exceeds a safe limit, a keyed switch allows for presetting the maximum safe degree of tilt by simple left or right manipulation of the switch, and to switch the display from current level of left or right tilt to the value of the preset limit.

Description:
FIELD OF THE INVENTION 
   This invention relates to switches and other control interfaces between humans and machines, and more particularly to manipulable control devices used in trucks and other outdoor working environments. 
   BACKGROUND 
   In signal monitoring and limit detection systems used in industrial settings, the presetting of safety limits is often accomplished by a variety of dials or thumbwheel switches that require time and a certain degree of manual dexterity not always available to workers that may be wearing gloves or other protective equipment. The instant invention results from an attempt to allow the operator of a dump truck to monitor the degree of lateral tilt in a vehicle and check it against a predetermined safe limit without having to manipulate complex or delicate switching and adjusting implements. 
   SUMMARY 
   In a signal monitoring and limit detection system in which the current value of an incoming signal, such as the degree of lateral tilt of a dump truck, is constantly monitored and compared to a preset safety limit value before the cargo container is lifted to a dumping position, the setting of the safety limit, as well as the switching of a numerical indicator from the display of the current level of tilt to that of the preset limit, is accomplished by the simple left or right manipulation of a selector switch that only requires a low amount of dexterity. In some embodiments the selector switch is keyed to allow restricted access to actuation of the switch. The adjustment of the safe limit value is accomplished by holding the switch in an increasing or decreasing position until the safety limit is raised by discreet increments to the desired value. 
   The monitoring system can be disabled, and the truck bed allowed to be raised regardless of the amount of lateral tilt of the truck, by raising the tilt limit beyond a maximum level value. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIG. 1  is a block diagram of a dump truck axle tilt monitoring system according to the invention; and 
       FIG. 2  is a flow diagram of the control module operation. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to the drawing, the instant invention will be described in connection with a dump truck having a tilt signal monitoring and exceeded limit detecting system  1 . Mounted on one axle of a truck  2  is a slope or tilt detector  3 . The tilt detector is capable of measuring the lateral tilt of the truck up to 60 degrees left and right. It should be noted that such a high degree of tilt is typically only utilized in a controlled factory setting such as during testing. In the field, much lower degrees of tilt are to be detected. Such detector is commonly used in wheel alignments, navigation systems, joysticks and other game implements as well as on various monitoring instruments. Such a type of tilt sensor is disclosed in Barsky, U.S. Pat. No. 6,249,984, which patent is incorporated in this Specification by this reference. The tilt indicator is commercially available from The Fredericks Company of Huntingdon Valley, Pa. 
   The tilt indicator emits a bi-polar signal  4  which is fed to an electronic control module  5 . 
   Also installed on the truck  2  is a pneumatic valve  6  through which is processed the air line that controls the truck dumping mechanism. A normally open relay  7  associated with the control module  5  controls the supply of power to the pneumatic valve  6 . Those skilled in the art will readily appreciate that the “normal” state of the relay can be selected to be either “open” or “closed”, and that activation of the relay from its “normal” state can be used to trigger various events in the system. In this embodiment the “normal” state has been selected to be “open”. When the relay is open, the pneumatic valve and the dumping mechanism are disabled. A control and display panel  9  preferably mounted on the dashboard of the truck receives and transmits data and control signals  10  from and to the control module  5 . A two-digit numerical display  11  indicates the degree of tilt measured by the tilt detector  3  and interpreted by the control module  5 . A pair of light indicators  12 ,  13  are lit alternately to signal a left or right tilt, respectively. The numerical display  11  can also be used to indicate a maximum safety limit value of tilt as will be explained below. An audio alarm  14  whose volume is controlled by a knob  15  on the panel is energized when the safety limit value has been exceeded. The status of the relay  7  is also shown by a light indicator  16  on the panel, and signals when it is safe to operate the dumping mechanism. A limit-setting switch  17  having a keyed hole  18  and being operated by an insertable and removable key  19  can assume three positions. In the central and neutral position shown on the drawing, the switch is inactive. The switch is biased to resiliently return to this neutral position unless it is forcibly and manually held in one of the right position indicated by a plus sign or the left position indicated by a minus sign. A power interrupter  20  which controls the power supply to the tilt detector  3 , control module  5 , control panel  9 , and audio alarm  14  completes the human interface of the control and display panel. 
   The control module  5  contains a conventional microprocessor and associated circuitry which operate the system according to a program illustrated in the flow diagram of  FIG. 2 . The data coming from the tilt detector  3  is constantly being monitored  21  and displayed  22  on the numerical indicator  11  before being compared to the preset limit value. If that value is not reached  23 , the relay  7  is kept closed  24  allowing operation of the pneumatic valve and dump mechanism. If the limit value has been reached, the relay is open  25 , and the audio alarm is sounded  26 . The opening of the relay immediately disables the dumping mechanism. The control module also monitors the position of the limit switch  27  and detects whether it has been moved off center into the plus or minus position. Since the manipulation of the switch indicates that a new limit value is being set and for safety purpose the relay  7  is open  28  to interrupt any dumping operation. The program next detects  29  in which direction the switch has been turned. If the key has been turned toward the right, the limit value is increased  30 . If the switch has been turned toward the left, the limit value is decreased  31 . 
   Two rates of increase are used, depending whether or not the limit value is within or above 10 degrees. If the limit value is within 10 degrees  32 , it is moved  33  either upward or downward in discrete increments of 1/10 of a degree at periodical intervals of one second each. If the 10 degree limit value has been exceeded, it is stepped up  34  by discrete increments of one degree each every one second or any other convenient interval of time. After a five-second delay has expired  35  following the return of the switch to the central, neutral position, the new limit value is stored  36 . 
   The program then verifies that the limit value has not been set above 20 degrees  37 . If so, this is taken as an indication that the operator wants to disable the monitoring system, and the relay  7  is closed  38 . If the limit value is not above 20 degrees or if the limit switch remains in the center, the monitoring of the data continues and the program cycle is repeated. 
   The implementation of the control module and the programming of the microprocessor according to the sequence illustrated in the flow diagram of  FIG. 2 , as well as the design of the control and display panel are accomplished according to techniques well known in the electronic and data processing arts. 
   While the preferred embodiment of the invention has been described, modifications can be made and other embodiments may be devised without departing from the spirit of the invention and the scope of the appended claims.