Patent ID: 6260796
Filing Date: 2001-07-17
Classification: B64C,G05D

Abstract:
A method for forcing the altitude of a flying or hovering craft having three or more thrusters to an arbitrary operator-commanded altitude value, the method comprising:determination of discrete points in time t.sub.k-1, t.sub.k, t.sub.k+1, each point in time being separated by a fixed time interval .DELTA.t;determination, at the time point t.sub.k, of the value of the state variable x.sub.2 representing vertical acceleration of the craft, the vertical acceleration being measured by sensors located on the craft;determination, at the time point t.sub.k, of the value of the state variable X.sub.2 representing vertical velocity of the craft, the vertical velocity being measured, or computed as the vertical velocity at the previous time point t.sub.k-1, plus the vertical acceleration at the previous time point multiplied by the time interval .DELTA.t;determination, at the time point t.sub.k, of the value of the state variable X.sub.1 representing the actual altitude of the craft;determination, at the time point t.sub.k, of the altitude error of the craft, the error being computed as the difference between the actual altitude h.sub.actual and the operator-commanded altitude h.sub.desired as h.sub.error =h.sub.actual -h.sub.desired ;computation, at the time point t.sub.k, of state feedback gains K.sub.1 and K.sub.2 ;computation, at the time point t.sub.k, of the vertical component .nu. of the normal vector to the principal plane of the vehicle, said vertical component being .nu.=cos (.theta.1.sub.actual)*cos (.theta.2.sub.actual), and .theta.1.sub.actual and .theta.2.sub.actual being the actual values of roll angle about axis 1 and axis 2 respectively;computation, at the time point t.sub.k, of the vertical acceleration u.sub.k which will restore the altitude to its operator-commanded value, said acceleration being calculated as the difference u.sub.k =-k.sub.1 *[h.sub.error ].sub.k-1 -k.sub.2.left brkt-bot.X.sub.2.right brkt-bot..sub.k-1 ;computation, at the time point t.sub.k, of the total thrust T.sub.sum which will create the vertical acceleration required to restore the altitude to its operator-commanded value, said total thrust being calculated as ##EQU15##m being the total mass of the craft, and g being the gravitational acceleration;update of the altitude state variables for use in the state calculations at the next time point, specifically [X.sub.1 ].sub.k-1 ]=[X.sub.1 ].sub.k, [X.sub.2 ].sub.k-1 =[X.sub.2 ].sub.k, [{dot over (X)}.sub.2 ].sub.k-1 =[X.sub.2 ].sub.k ;application of the computed total thrust to the control of the thrusters to maintain the desired altitude.