Rockwell Automation Publication 750-AT006D-EN-P - January 2022
101
Chapter 7 Applications
Viscous friction compensation is applied only when the motor is being commanded to move. A rated friction compensation torque parameter
sets the amount of friction compensation torque that is applied when the velocity reference signal is at nameplate velocity. This torque also
includes the constant level of sliding friction torque set by the slip parameter. The viscous friction compensation component decreases
linearly with the velocity reference signal until just the stick component exists just outside the velocity reference window.
Configuration
The parameters in
are used to configure friction compensation.
shows the friction compensation configuration and how it comes before the torque filters.
Figure 82 - Friction Compensation Configuration
The load observer is often used to compensate for friction instead because the user is not required to know or measure various friction
parameters.
shows how the friction compensation parameters relate to the torque and speed.
Table 36 - Friction Compensation Parameters
Parameter No.
Parameter Name
Description
10:2050
[FrctnComp Mode]
• Determines which velocity reference signal is used by the friction compensation function to counteract load friction.
10:2051
[FrctnComp Trig]
• Sets the starting speed or trigger speed that the friction compensation is applied when leaving the region near zero speed.
10:2052
[FrctnComp Hyst]
• Establishes a velocity band around zero speed where the friction compensation function is inactive.
• The friction compensation function is inactive with zero output when the velocity signal is inside this band and active when
outside.
10:2053
[FrctnComp Time]
• Sets the time interval that the static friction torque is applied. When initially leaving the zero speed region, 10:2054
[FrctnComp Stick] is used for the non-viscous friction term.
• After the time period set by this parameter, the non-viscous friction ramps down to the value set in 10:2055 [FrctnComp Slip].
• The remainder of the time that 10:2057 [FrctnComp Out] remains nonzero, the non-viscous friction remains constant at the
value of 10:2055 [FrctnComp Slip].
10:2054
[FrctnComp Stick]
• Sets the level for the static friction torque. It is the torque level that is required to break away from zero speed.
• When initially leaving the zero speed region, this level is used for the non-viscous friction term.
• After the time period set by 10:2053 [FrctnComp Time], the non-viscous friction ramps down to the value set in 10:2055
[FrctnComp Slip].
10:2055
[FrctnComp Slip]
• Sets the torque level that is maintained at low speed after breakaway has been achieved.
• It is always set to less than the level in 10:2054 [FrctnComp Stick].
• After the time period set by 10:2053 [FrctnComp Time], the non-viscous friction ramps down to this value.
10:2056
[FrctnComp Rated]
• Sets the torque level that is output at rated motor speed.
• The friction compensation function assumes a linear viscous component that varies in direct proportion to velocity. 10:2057
[FrctnComp Out] increases with velocity and equals the level set by this parameter at rated motor speed.
• At the outside edge of the zero speed window, the torque level has decreased to the torque level set by the slip parameter.
10:2057
[FrctnComp Out]
• Displays the torque reference output of the friction compensation function.
• It is summed to the Selected Torque Reference signal.
Trq Filt
2077
Torque
Step
2076
Trq Ref Selected
VReg Vect
+
FrctnComp Trig
2051
2057
FrctnComp Out
Friction
Comp
FrctnComp Mode
2050
1978
0
Disabled
0
1
2
Ext Ramped Ref
FrctnComp Hyst
2052
FrctnComp Time
2053
FrctnComp Stick
2054
FrctnComp Slip
2055
FrctnComp Rated
2056
1042
3
Vel Fb Active
+
+
+
+
+
1925
2150
Trq Ref Filt In
VRef Vect
Trq Filt
2077
Torque
Step
2076
Trq Ref Selected
VReg Vect
+
FrctnComp Trig
2051
2057
FrctnComp Out
Friction
Comp
FrctnComp Mode
2050
1978
0
Disabled
0
1
2
Ext Ramped Ref
FrctnComp Hyst
2052
FrctnComp Time
2053
FrctnComp Stick
2054
FrctnComp Slip
2055
FrctnComp Rated
2056
1042
3
Vel Fb Active
+
+
+
1925
2150
Trq Ref Filt In
VRef Vect