Abstract:
A method for determining slippage of at least one wheel of at least one vehicle having a motor and a processor that communicates velocity commands to the motor for varying a velocity of the vehicle is presented. The method includes determining an actual velocity of the vehicle over regular intervals; comparing, over regular intervals, the actual velocity of the vehicle to the expected velocity from the magnitude of the velocity commands to determine whether there is slip of the wheel of the vehicle; and reducing the magnitude of the velocity commands to equal approximately the actual velocity of the vehicle where there is slip of the wheel. A system and circuit carrying out the method are also presented.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to position control systems. More specifically, the present invention relates to position control systems for vehicles on a fixed path. 
         [0002]    Currently, the monitoring of vehicle motion along a path, such as a railway or a track, is carried out using a central controller or computer. The computer monitors each vehicle&#39;s position on the track and when vehicle spacing is within a predetermined minimum distance, all vehicles on the track are stopped. Such a system, in addition to the computer, includes multiple sensors mounted at various locations along the track and complex wiring for connecting each sensor and the computer. 
         [0003]    For example, U.S. Pat. No. 4,864,306 describes a system in which machine readable trackside markers such as bar code markers are utilized along the track and are read by apparatus on board the train to provide track number identification, milepost identification and train direction. On board the train is equipment to provide train identification and train speed. This information is transmitted through transponders between trains and to a central station and is processed by apparatus on board the respective trains and the central location to provide visual and audible signals indicative of a potential train collision. 
         [0004]    More recently, U.S. Pat. No. 7,182,298 describes a track network incorporating at least one node at which at least two track sections of the track network adjoin one another and also comprising a plurality of vehicles traveling along the track network and each of which comprises a control unit wherein the control of the movements of these vehicles can be effected and wherein the information relating to the successor or the forerunner vehicle is stored in the control unit of the vehicle and is updated when the vehicle passes a node of the track network. 
         [0005]    However, because of the necessary computer, complex wiring, and multiple sensors, the system is difficult to integrate and to costly to maintain. Other disadvantages include the requirement to test and prove system functionality after track installation, the technical challenge of aligning a sensor and target for the vehicle to track interface, the inability to sense a spacing problem until it has become sufficiently severe to violate the minimum spacing, the inability to change spacing criteria without adding additional sensors which makes the system less flexible, and the inability to account for horizontal wheel slip and wheel and tire breakdown. 
         [0006]    Therefore, to date, no suitable method or system for position control for a vehicle on a fixed track exists. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0007]    In one embodiment of the present invention, a method for controlling a plurality of vehicles each having wheels located on a fixed path is presented. The method comprising: mounting a processor on each vehicle; mounting a vehicle sensor device to each vehicle; using each processor and each vehicle sensor device to determine an actual velocity of each vehicle while each vehicle is moving along the path; and using a position control correction module to compare each vehicle&#39;s actual velocity to each vehicle&#39;s velocity commands to determine if wheel slip is occurring and to decrease the magnitude of vehicle velocity commands where wheel slip occurs. 
         [0008]    In another aspect of the invention, a method for determining slippage of at least one wheel of at least one vehicle having a motor and a processor that communicates velocity commands to the motor for varying a velocity of the vehicle is presented. The method comprising determining an actual velocity of the vehicle over regular intervals; comparing, over regular intervals, the actual velocity of the vehicle to the expected velocity from the magnitude of the velocity commands to determine whether there is slip of the wheel of the vehicle; and reducing the magnitude of the velocity commands to equal approximately the actual velocity of the vehicle where there is slip of the wheel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The following detailed description is made with reference to the accompanying drawings, in which: 
           [0010]      FIG. 1  is a diagram showing one vehicle disposed on a portion of a path and wherein the vehicle includes a vehicle control system in accordance with one embodiment of the present invention; 
           [0011]      FIG. 2  is a diagram showing a top view of a portion of the path of  FIG. 1 ; 
           [0012]      FIG. 3  is a block diagram showing details of the vehicle control system of  FIG. 1 ; 
           [0013]      FIG. 4  is a flow diagram showing an embodiment of a position control correction module; 
           [0014]      FIG. 5  is a schematic diagram showing an amusement ride control system; and 
           [0015]      FIG. 6  is a flow chart describing a step-wise method in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0016]    One embodiment of the present invention concerns a control system and method for controlling a plurality of vehicles on a fixed path. One particular embodiment of the system includes a position control and correction module for correcting spacing between vehicles. 
         [0017]    Referring to  FIGS. 1 and 2 , one vehicle  10 , out of a plurality of vehicles of a ride system, is shown with a body  12 , wheels  14  along with a guest  18  seated therein. The vehicle  10  is disposed on a path such as a track  20  which includes rails  22  that are supported by cross beams  24 . A bus bar or energizing rail  26  provides electrical energy from an electrical generator (described below) to the vehicle  10  through means of an electrode  28 . A disc brake  30  is shown mounted to a wheel  14 . 
         [0018]    A distance/speed sensor  116  may comprise a magnet  120  and a magnetic field or optical sensor  122 , which together function in a known manner to provide electrical pulses to a processor (not shown), which correspond to a distance traveled by wheel  14 . A processor, memory, timer, distance and a driving and stopping system (each to be discussed further with reference to  FIG. 3 ) may be located within compartment  119 . 
         [0019]    Referring now to  FIG. 3 , one embodiment of a vehicle control system for controlling a plurality of vehicles on a fixed path in accordance with the present invention is illustrated generally at  300 . In this embodiment, the control system  300  comprises a processor  310 , a memory  312 , a timer  314 , a distance/speed sensor  316  and a vehicle driving and stopping system  318 . 
         [0020]    The processor  310  may be any suitable processor such as a programmable logic controller. The memory  312  may be any suitable type including but not limited to RAM, ROM, EPROM, and flash. The memory  312  may store a program for the processor  310  and store a look up table for a predicted range of locations given a duration that a vehicle is traveling along the track. The memory may also be configured to store wheel diameter measurement, horizontal wheel slip measurements and vehicle spacing measurement, e.g., how far each vehicle is from a corresponding vehicle at any particular time. 
         [0021]    The timer  314  provides a timing function that may be used by the processor  310  to time an actual duration that the vehicle is traveling along the track. 
         [0022]    The distance/speed sensor  316  may comprise a magnet and a magnetic field or optical sensor which together function in a known manner to provide electrical pulses to the processor  310  which correspond to a distance traveled by the wheel. Optionally, other sensors such as a multi-turn encoder may be employed. To determine the distance, the pulses may be counted or directly measured by the processor  310  to determine a distance and, therefrom, a location of the vehicle along the track. 
         [0023]    The vehicle driving and stopping system  318  may be interconnected with a drive motor  334  including a motor controller (not shown) and a brake  332  such as the disc brake  30  ( FIG. 1 ). The drive motor  334  may be connected to drive one or more of the wheels  14  ( FIG. 1 ) via velocity commands generated by the processor  310  and sent to the motor controller in a known manner. It will be understood for purposes herein that the greater the magnitude of the velocity command the greater the velocity of the vehicle. 
         [0024]    The processor  310  is configured, via any suitable means such as software or firmware, to receive an initial signal from a start indicator  324  that the vehicle has started traveling along the track and thereafter, to continuously, or at regular intervals, calculate an actual location for the vehicle along the track. Optionally, transponders (not shown) may be located along the track and a sensor may be provided for ascertaining an actual location for the vehicle. 
         [0025]    The calculated actual location may be used by the processor  310  to control, via the vehicle driving and stopping system  318 , the distance between a plurality of vehicles so that vehicles maintain a predetermined spacing from one another. However, position errors may accumulate during operation because of, e.g., vehicle wheel wear or wheel slippage. For example, as the vehicle increases in age, tires may begin to wear and become smaller, velocity and position errors may accumulate. Also, when vehicles start out or round corners wheel slippage may occur causing further velocity and position errors. To reduce these errors, a position control correction module  330  is provided which may be configured to receive velocity commands from the processor  310 , and return a signal to the processor correcting the velocity commands based on velocity and position errors. Accordingly, the position control correction module  330  advantageously reduces variation in predetermined distance between vehicles to reduce undesirable vehicle contact. 
         [0026]    To compensate for wheel wear, the position control correction module  330  working with the processor  310 , may be configured to calculate a distance between fixed points, e.g., illuminated by transponders, that are located along a path and identified by additional vehicle position sensors and then compare that value with a known number of wheel revolutions sensed, e.g., by the sensor  116 . Current wheel diameter may be calculated and then applied to correct the measured velocity and acceleration. 
         [0027]    Generally, to compensate for wheel slip, e.g., during acceleration, the position control correction module  330  may compare a velocity command (V N ), described above, to an actual velocity that the vehicle is traveling along the fixed path. If there is a difference between the velocity of the vehicle expected from the velocity command and the actual velocity of the vehicle, the velocity command may be reduced in magnitude such as to the actual velocity to eliminate the slippage and regain frictional engagement with the fixed path. Thereafter, the velocity commands may be slowly ramped up in magnitude, described below, to thereby retain frictional engagement with the fixed path. 
         [0028]    Referring now to the flow diagram of  FIG. 4 , further details of a position control correction module  330  for calculating corrected velocity commands, is shown. The position control correction module  330  comprises a primary loop  402  including calculator  404  for calculating a smoothed transition speed (see below), a timer  406 , a speed control function  408 , a summation  410  and a summation  412 . Secondary loops  414  and  416  are provided for calculating error in velocity and error in position, respectively. More specifically, the secondary loop  414  comprises a calculator for calculating error in velocity (E v ) via F(K v )/T and the secondary loop  416  comprises a calculator for calculating error in position (E p ) via F(K p ). Reference may be had below for an understanding of the terms F(K v ) and F(K p ). The secondary loops  414  and  416  contain gain functions  418  and  420  to calculate and weigh the position and velocity errors for the summation  422 . 
         [0029]    In operation and during regular intervals, a summation  422  combines calculated velocity and position errors (E v ), (E p ) which are, in turn, fed to the summation  410  that subtracts the error values from the velocity at a particular sensed position (V sp ) to achieve a corrected velocity G(v). The corrected velocity G(v) and the actual velocity (not shown) may be provided at  408  and communicated to the processor  310  ( FIG. 3 ) for use in determining whether slippage of the wheel(s)  30  is occurring. If wheel slippage is determined to be occurring by the processor  310 , the processor may reduce the magnitude of the velocity commands to the motor to stop the slippage and then to begin to slowly ramp up the magnitude of the velocity commands to the drive motor as described above. 
         [0030]    The corrected velocity G(v) is thereafter output to the secondary loop  414  to calculate a new error in velocity (E v ) and combined with the output from the timer  406  for use in the secondary loop  416  to calculate a new error in position (E p ). It is also communicated to the processor  310  to determine whether velocity needs to be increased to correct an error in position and thus spacing between vehicles. 
         [0031]    Optionally, to smooth and slowly ramp up vehicle transition speeds F(V sp ) and prevent the error from accumulating in the system, the vehicle velocity commands (V N ) may be applied to an algorithm such as that provided below. 
         [0000]        F ( V   sp )=Σ[ θ−2π,λ   π (cos(θ)+1)·[½·( V   Nnew   −V   Nold )]] where: 
         [0000]      θ=θ+λ, where λ= F ( a )/π 
         [0000]      if V Nold ≠V Nnew , θ=π 
         [0000]      V N =velocity command 
         [0032]    The acceleration function F(a) of a vehicle may be calculated from the following equation where acceleration is limited by a percentage of the change in velocity to further reduce possible slip during acceleration. 
         [0000]        F ( a )= a   N ·[( V   N   −V   actual )/ V   N ]% 
         [0000]      where: 
         [0000]        V   actual   =F ( V   sp )( V   N ) 
         [0000]      a N =acceleration command 
         [0033]    A function of a gain term (K) for (used in calculating an error in velocity (E v ) and an error in position (E p ) see above) velocity K v  and position K p  weigh the respective terms so that speed correction is smooth. These may be calculated as follows: 
         [0000]        F ( K   v,p )= K   v,p   ·K   v,p   ·K   wheel ø , 
         [0000]        K   wheel ø =1−[(actual−measured)/actual)]% 
         [0000]      If  E   v &gt;&gt;ø, θ=π,  F ( a )= F ( a )· K   correction    
         [0034]    Referring now to  FIG. 5 , a schematic diagram showing a ride control system, usable with one embodiment of the present invention, is shown generally at  50 . As shown, the ride control system  50  comprises a path or track processor  52  which is in circuit with the energizing rail  26  comprising a number of circuit connections (not numbered) and a plurality of vehicle  310  ( FIG. 3 ) each being located with a vehicle  10  ( FIG. 1 ). It will be appreciated that in an optional embodiment (not shown), the track processor  52  may communicate via wireless communications with each vehicle processor  310  rather than, e.g., via the energizing rail  26 . The track processor  52  may comprise a programmable logic controller and monitors track functions such as mode of the track machine, stopping and starting functions, and control of all track-switching elements via fail-safe signals. The track processor  52  and each vehicle processor  310  may communicate to ensure the mode of the track machine is safely controlled for the all vehicles mounted to the track. If there is disagreement of the mode of the track or if the vehicle senses itself out of range for position, velocity, or acceleration parameters or other fault conditions, the vehicle will communicate to the track processor and/or other vehicle processors to cause a stop or other reaction for each vehicle  10 . 
         [0035]    The track processor  52  may also be configured to determine and broadcast an ideal location of each vehicle to each vehicle on the path according to some predetermined plan such as every vehicle is spaced equally along the path. Each vehicle, via each processor  310 , may then synchronize or vary its position along the path by increasing velocity or braking, as described above, to correct its spacing from other vehicles. 
         [0036]    A method of monitoring and controlling location of a plurality of vehicles movable along a path in accordance with another embodiment of the present invention is illustrated generally at  600  in  FIG. 6 . The method for controlling a plurality of vehicles on a fixed path comprises mounting a processor to each vehicle as shown at  602  and mounting a vehicle sensor device to each vehicle as shown at  604 . The method further comprises using each processor and each vehicle sensor device to determine an actual location of each vehicle while each vehicle is moving along the path step  606  and, at step  608 , using a position control correction module to compare each vehicle&#39;s actual velocity to each vehicle&#39;s velocity commands to determine if wheel slip is occurring and to decrease the magnitude of vehicle velocity commands where wheel slip occurs. 
         [0037]    Technical effects of the herein described systems and methods include correcting a velocity of a vehicle to account for wheel slip. Other technical effects include correcting a vehicle spacing on a track. 
         [0038]    While the present invention has been described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the present invention is not limited to these herein disclosed embodiments. Rather, the present invention is intended to cover all of the various modifications and equivalent arrangements included within the spirit and scope of the appended claims.