THE 'SLOTH' ROBOT
|Device designer||Alessandro Tasora|
|RT control software||Steven Chatterton|
|Lab||Prof.Paolo Righettini, Politecnico di Milano|
The SLOTH robot is a 3-degrees-of-freedom manipulator based on the parallel kinematic machine design (PKM).
As in most parallel robots, the operating speed is very high: for example we could achieve more than six pick&place trajectories per second, yet with high precision.
The motion of the end effector is obtained by moving three linear guides connected by six stiff spatial linkages. The rollers are driven by three high-precision ball-screws, with zero clearance. Thank to the removal of backlashes, the robot provides an excellent repeatability and can draw trajectories with trajectory-following errors as low as 0.1mm.
Using my simulation software CHRONO I optimized motors and transmission ratios, hence designing a very fast device that can reach 90m/s2 accelerations.
The robot is controlled with an industrial PC endorsing a Linux Real Time OS. A first version of the control system performed a digital feedback of motors on the PC, by acquiring resolver rotations in real-time and feeding three analog speed setpoints to motor drives. A later version uses a realtime setpoint control via CAN-open buses.
The working volume of the SLOTH robot, as for most parallel robots, is small. The picture above shows that the working volume has been deliberately 'cut' at its sides.
The kinematical properties of the SLOTH robot aren't the same everywhere: this picture, obtained with a custom tool based on my software CHRONO, shows how the conditioning of the inverse kinematics decreases near the borders of the working volume.
The SLOTH robot proved to be an useful test bed for further developements in the field of parallel robots: the picture above shows a study for a 'next generation' version. Parts of these results led to the CHEOPE robot, from the G.Legnani group at the University of Brescia.
Download the AVI simulation (requires DivX codec)
The animation above has been computed with my CHRONO software.
Download the film of the SLOTH robot (requires DivX codec)
Footage from the real robot.
Download the article, presented at the RAAD2002 conference