Abstract: The simultaneous path-tracking and swing control of cable suspended loads is still an open research field. Admittedly, the active swing control of a suspended load is of industrial interest when considering both overhead cranes and robots. Anti-swing control in overhead cranes could allow reducing maneuver time and residual vibrations in rest-to-rest operations, which may cause a safety hazard for plant personnel. The problem is being thoroughly investigated: both input shaping techniques and feedback control schemes have been proposed so far. Anti-swing control techniques might however find an interesting prospective application in robotics, to reduce liquid sloshing, for example in pouring robots for casting industries. Liquid sloshing may in fact be approximated using the equivalent mechanical model of a simple pendulum.
The objective of this paper is to provide an experimental proof of the effectiveness and ease of implementation of the innovative non-time based active control strategy first introduced in  to suppress undesired load swing in path-tracking control of four-degree-of-freedom overhead cranes. The fundamental difference between the proposed scheme, named DRC, and traditional ones is that it allows reducing load swing while guaranteeing coordinated crane trolley motion and hence the accurate tracking of desired paths through space. Additionally, under certain conditions, it may be implemented by just adding an outer loop to standard position controllers.
The technique is here applied to reduce the oscillation of a load suspended to the moving platform of an Adept QuattroTM parallel robot by means of a cable. A vision system is employed to detect cable swing angles, while the DRC control loop is implemented into a pc running a real-time operative system, and communicating with the robot controller through the internet.