Patent ID: 8442692

Claim:
A method for performing adaptive friction compensation in an actuator while accounting for variation in friction characteristics of a wave gear drive accompanying changes in temperature, the method comprising: using a semi-closed loop system for controlling a position of a load shaft on the basis of a detected position of a motor shaft of a motor to perform drive control of an actuator in which output rotation of the motor is reduced via a wave gear drive and transmitted from the load shaft toward a load; and minimizing a reduction in accuracy with which the load shaft is positioned by the semi-closed loop system, as caused by variation in friction characteristics of the wave gear drive accompanying a change in the ambient temperature; wherein as a friction compensation current i comp applied to a motor drive current for driving the motor, a static friction compensation current i s is used when the motor shaft stops with a deviation, and a Coulomb friction compensation current i c is used in other circumstances, wherein: i comp ⁡ [ k ] = { i s ⁡ [ k ] ⁢ (  e ⁡ [ k ]  > 0 ⁢ ⁢ and ⁢ ⁢ ω m ⁡ [ k ] = 0 ) i c ⁡ [ k ] ⁢ ( otherwise ) ( A ) where k is the present time, e[k] is the motor shaft deviation, and ω m [k] is the motor shaft speed; the static friction compensation current i s is defined wherein: i s ⁡ [ k ] = { sgn ⁡ ( e ⁡ [ k ] ) · ( i ss + i sr ⁡ [ k ] ) (  e ⁡ [ k ]  > 0 ) 0 ( otherwise ) ( B ) wherein a compensation amount i sr of a monotonically increasing ramp function defined by i sr [k]=i sr0 [k]+d sr ·( k−l ) (C) is added to a compensation amount i ss of a step function, where i sr0 is a default value of the ramp-function compensation amount i sr , d sr is the amount of ramp increase, and l is a time at which a friction compensation actuation commences; and the Coulomb friction compensation current i c is a step-function compensation amount i cs or a ramp-function compensation amount i cr , defined by: i c = { sgn ⁡ ( ω m ⁡ [ k ] ) · i cs ( e ⁡ [ k ] ≠ 0 ) i cr ⁡ [ k ] ( e ⁡ [ k ] = 0 ) . ( D )