Robot uses on-board tracking to catch balls autonomously

A service robot from DLR – German Institute of Robotics and Mechatronics has been given the ability to catch balls completely autonomously using only on-board sensing and tracking.

’Rollin’ Justin’, a humanoid robot, was built around two years ago to carry out everyday household tasks requiring fine manipulation. The intention was to use Justin as a research platform to retrofit new abilities — the latest being the catching of two balls simultaneously.

‘It’s not really easy to catch a ball; it’s a dynamic task that takes dexterity,’ Dr Berthold Bäuml told The Engineer.

‘A child takes quite a long time to have this feeling for a ball, especially when two balls are coming at the same time — we have a handball player in the lab who can do this but for others, like me, that’s very hard.’

The robot’s head is equipped with stereo cameras to precisely track the trajectory of the ball in 3D space. Bäuml said that the addition of an inner ear — or inertial measurement unit (IMU) — allows the robot’s head to follow the ball to the hand.

‘It’s the same thing all humans and animals have in their heads, which allows you to measure the orientation of the head — so when you move your head you still know your relative position to the environment because you track the movement of the head with this inner ear system,’ he said.

The other challenge for the researchers was timing and achieving a sufficiently short latency. This required new algorithms to be developed to analyse the tracking data and feedback co-ordinate instructions to the arms, which have seven degrees of freedom (DOF) each, fingers (2×12 DOF) and head (five DOF).

Currently, the system achieves a spatial and temporal precision of 2cm and 5ms respectively, leading to a catch success rate of around 80 per cent — which Bäuml hopes to improve on.

‘The main point here is that we can do it completely with on-board sensing,’ he said. ’We’re not using some addition external tracking system — we do it all internally.’