Method and device for robust rejection of periodic disturbances in an axis-position control loop

Method for robust rejection of the periodic disturbances in a motor-position control structure, the periodic disturbances being liken to at least one sinusoidal oscillation at a determinable frequency proportional to the angular speed, the control structure receiving a position reference input signal c(t) implementing a loop for controlling the position said motor axis, said control structure being of the RST controller type and being sampled so that numerical computations can be made in a programmable calculator to produce results intended to control the motor, the RST controller implementing computing means corresponding, on the one hand, to a function 1/So(z−1) upstream from the motor and producing a control signal u(t) and, on the other hand, a function Ro(z−1) in the loop thereof which receives as an input a position signal θ(t) from a position sensor on said motor axis, wherein the assembly including the motor, the position sensor, the means for computing the functions 1/So(z−1) and Ro(z−1), in a loop, is called central controller,

• characterized in that:
• to the central controller are added two additional computing means, the first one being an estimator block E(z−1) and the second one a modifier block Q(z−1), as well as an additional loop,
• the motor is modeled as a modeled system subjected to a load disturbance v(t), said modeled system receiving the control signal u(t) as an input and producing the position signal θ(t) as an output, the system model applying a function z−1B(z−1) to the control signal u(t) to produce a signal added to the load disturbance v(t), the resultant being subjected to a function 1/A(z−1) to produce the position signal θ(t),
• a load disturbance estimation signal {circumflex over (v)}(t) is computed in the estimator block E(z−1) that receives the control signal u(t) as a first input and the position signal θ(t) as a second input, and in which the control signal u(t) is subjected to the function z−1B(z−1) to produce a signal, which is then subtracted from the result of the application of the function A(z−1) to the position signal θ(t), this subtraction giving the load disturbance estimation signal {circumflex over (v)}(t),
• the load disturbance estimation signal {circumflex over (v)}(t) is applied to the modifier block Q(z−1) to produce a modified signal, which is applied to a negative input of an additional adder arranged upstream from the means for computing the function 1/So(z−1) and then forming the additional loop, the modifier block having a transfer function that varies as a function of the at least one determinable frequency and which is computed in real or quasi-real time under the constraint that the position sensitivity function Sθp of the control structure comprises a notch for the at least one determinable frequency.