Hardware Reference
In-Depth Information
ASSEMBLY: PEG-IN-HOLE INSERTION
Robot assembly has been an active area of research for several years. Assembly tasks
include inserting electronic components on circuit boards, placing armatures, bush-
ings, and end housings on motors, pressing bearings on shafts, and inserting valves in
cylinders.
Theoretical investigations of assembly have focused on the typical problem of insert-
ing a peg into a hole, whose direction is known with some degree of uncertainty. This
task is common to many assembly operations and requires the robot to be actively
compliant during the insertion, as well as to be highly responsive to force changes, in
order to continuously correct its motion and adapt to the hole constraints.
The peg-in-hole insertion task has typically been performed by using a hybrid posi-
tion/force control scheme [Cut85, Whi85, AS88]. According to this method, the robot
is controlled in position along the direction of the hole, whereas it is controlled in force
along the other directions to reduce the reaction forces caused by the contact. Both
position and force servo loops must be executed periodically at a proper frequency
to ensure stability. If the force loop is closed around the position loop, as it usually
happens, then the position loop frequency must be about an order of magnitude higher
to avoid dynamics interference between the two controllers.
SURFACE CLEANING
Cleaning a flat and delicate surface, such as a window glass, implies large arm move-
ments that must be controlled to keep the robot end-effector (such as a brush) within
a plane parallel to the surface to be cleaned. In particular, to efficiently perform this
task, the robot end-effector must be pressed against the glass with a desired constant
force. Because of the high rigidity of the glass, a small misalignment of the robot with
respect to the surface orientation could cause the arm to exert large forces in some
points of the glass surface or lose the contact in some other parts.
Since small misalignments are always possible in real working conditions, the robot
is usually equipped with a force sensing device and is controlled in real time to exert
a constant force on the glass surface. Moreover, the end-effector orientation must be
continuously adjusted to be parallel to the glass plane.
The tasks for controlling the end-effector orientation, exerting a constant force on the
surface, and controlling the position of the arm on the glass must proceed in parallel
and must be coordinated by a global planner, according to the specified goal.
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