Patent Number: 050858246
Section: claims

1. A drive system comprising: a gantry including a bridge having longitudinal and transverse axes and supported by spaced first and second end frames joined to first and second drive trucks for moving said bridge along said transverse axis;  first means for driving said first drive truck;  second means for driving said second drive truck being independent from said first driving means; and  means for controlling said first and second driving means for reducing differential transverse travel between said first and second drive trucks, due to a skewing torque acting on said bridge, to less than a predetermined maximum, said controlling means being in the form of an electrical central processing unit and including:  said first and second driving means include first and second motors driving first and second transmissions, respectively, said first and second transmissions driving first and second driven wheels of said first and second drive trucks, respectively;  said gantry further includes a trolley selectively movable along said bridge longitudinal axis, and a main hoist joined to said trolley;  said differential transverse travel being effected by at least one of backlash in said first and second transmissions and transverse flexibility of said bridge; and  said travel control means including a predetermined correction model indicative of said at least one of said backlash and said transverse flexibility. 2. A drive system according to claim 1 wherein said controlling means is effective for subtracting said travel error signal from said at least one command signal for decreasing velocity of said respective one of said first and second drive trucks which travels more than the other thereof. 3. A drive system according to claim 1 wherein said controlling means is effective for adding said travel error signal to said at least one command signal for increasing velocity of said respective one of said first and second drive trucks which tends to travel less than the other thereof. 4. A drive system according to claim 1 wherein said controlling means is effective for adding said travel error signal to said first command signal for increasing velocity of said first drive truck which tends to travel less than said second drive truck; and subtracting said travel error signal from said second command signal for decreasing velocity of said second drive truck. 5. A drive system according to claim 1 wherein: 6. A drive system according to claim 5 wherein said travel control means further includes first and second travel sensors for providing first and second travel signals indicative of transverse positions of said first and second drive trucks, respectively, and said travel error signal is proportional to the difference of said first and second travel signals. 7. A drive system according to claim 6 wherein said first and second travel sensors measure rotational position of first and second undriven wheels of said first and second drive trucks, respectively. 8. A drive system according to claim 6 wherein said first and second transmissions each include reduction chain drives for reducing rotational speed from said first and second motors to said first and second driven wheels, respectively. 9. A drive system according to claim 6 wherein said first and second transmissions each include reduction gear drives for reducing rotational speed from said first and second motors to said first and second driven wheels, respectively. 10. A drive system according to claim 6 wherein said first and second velocity control means each includes first and second motor sensors for providing first and second feedback signals indicative of rotational velocity of said first and second motors, respectively, and means for subtracting said first and second feedback signals from said first and second command signals, respectively, for providing first and second velocity error signals for controlling said first and second motors, respectively. 11. A drive system according to claim 10 wherein said gantry is a nuclear refueling platform and said main hoist is effective for raising and lowering a nuclear fuel bundle. 12. A drive system according to claim 11 wherein said controlling means is effective for subtracting said travel error signal from said at least one command signal for decreasing velocity of said respective one of said first and second drive trucks which travels more than the other thereof. 13. A drive system according to claim 6 wherein said travel control means correction model is indicative of both said backlash and said transverse flexibility. 14. A drive system according to claim 13 further including guide rails upon which said first and second driven wheels are movable, and wherein said travel control means correction model is indicative also of slippage between said first and second driven wheels and said guide rails.