Patent ID: 7057366

Claim:
A method for estimating load inertia using an inverse model, suitable for an alternating current (AC) servo module, which estimates a load inertia by receiving a speed command and a torque signal, comprising the steps of: setting a first relation as following in an actual system: T ⋓ l = Kt ⁢ ⁢ ⋮ ⁢ ⁢ i + T l = ω J l ⁢ ⋮s ⁢ , wherein, {hacek over (T)} l represents a net torque signal; Kt represents a gain constant; i represents a current signal generated by the actual system; T l represents the torque signal; ω represents a speed signal generated by the actual system; J l represents the load inertia; and the current signal i is generated by the actual system according to the speed command and the feedback speed signal ω; setting a second relation as following in an inverse system: i 0 × Kt = ω 0 J 0 ⁢ ⋮s , wherein, i 0 represents a current signal generated by the inverse system; Kt represents the gain constant; ω 0 represents a speed signal generated by the inverse system; J 0 represents a unit motor inertia; and the current signal i 0 is generated by the inverse system according to the speed signal ω from the actual system and the feedback speed signal ω 0 ; and said speed signal ω substantially equals to said speed signal ω 0 ; deriving a third relation from the first relation and the second relation, as follows: i 0 × Kt = ( Kt : i + T l ) × J l J 0 = 1 η ⁢ T ⋓ l ; when the motor of the AC servo module rotates at a uniform rate, the torque signal T l is derived to be Kt:i according to the third relation; and when the motor of the AC servo module rotates at a variable rate, the net torque signal {hacek over (T)} l is derived to be T l +Kt:i according to the third relation.