An operator system and related methods (10) for sensing forces on a movable
barrier (12) includes a motor (52), a trolley (30), and a
trolley arm (34) having a first end slidably supported by the trolley (38)
and a second end coupled to the movable barrier. The motor moves the trolley arm
which in turn moves the movable barrier. A force detection mechanism (68)
is coupled to the motor to determine a first component force value applied by the
motor. A controller (54) receives the first component force value and determines
a detected force value by scaling the first component force value with a second
component force value derived from an angular position of the trolley arm's first
end with respect to the trolley. The angular position of the trolley arm may be
fixed or variable. An angle potentiometer (72) is coupled to the trolley
arm to generate an angle signal for use as the second component force value when
the trolley arm's angular position is allowed to vary.
