Roaming beds for Carsten Höller
From 10th of June to 6th of September 2015 two robot beds are roaming around at Hayward Gallery in London. They carry sleeping visitors who have brushed their teeth with dream-enhancing tooth paste. With help of lasers and ultra wideband radio the beds perform choreographed dance at the astonishing speed of 0.5-1 meters per minute.

The robot beds are of a classic "unicycle cart" model, i.e. two drive wheels along an axis with an offset caster wheel for balance. Just as a car such a configuration can not be moved sideways, but the unicycle cart can turn on a penny. That nice feature greatly simplifies the robot control algorithms.
One of the main problems has been achieving both silent motion and low speed. A lot of time was spent sneaking up on senior citizens to listen to their wheelchairs and permobiles. Some very silent models were found to build beds around, but it turned out their motors and gear boxes were not suitable for our needs. As it turns out not many robots are intentionally built to roam around at only 0.5-1 meters per minute, so there were no standard parts available to be used in the beds. In the end we had to do everything from scratch combining a brushless servo motor with two worm gears to get enough gear reduction.
A bed can, with help of a linear actuator, keep the sleeping passenger horizontal even when going up a ramp with a maximum inclination of 8°. Activation of the bed levelling algorithm is location and accelerometer based. That way a little bump on a flat floor will not accidentally trigger the bed levelling and surprise the passenger.
Navigation is done with a combination of a LIDAR and a home made "indoor GPS" (LPS) with 10 cm accuracy:
To get redundancy the beds also perform odometry, got bumpers in each bed corner and measures the motor current to see if the bed is stuck. LPS relies on accurate maps and can not handle unknown objects. The LIDAR can detect both fixed objects (walls) and moving obstacles (people), but will lose reference to the room if too many visitor surrounds it. Combining them booth gives the best of two worlds.

On top of all the measuring and calculations to find the beds position, there is a program that does trajectory planning / formation control for both beds. It decides "lets go to the other end of the gallery, but hey, lets go there in alternating semi circles, just for the fun of it!" and then carries out all steps needed to follow up its plan. This sort of abstract thinking can also be used to let cars on a motorway automatically form a "train" so that the drivers can go to sleep. Luckily the fun alternating semi circles are not part of the behaviour on the motorway.
Early prototyping was made with a robotic vacuum cleaner with the addition of LPS boards to simulate a full size robot bed. A robot simulator was written in matlab to show examples of possible robot trajectories. In the beginning just with single beds, but later on with both beds performing choreograped dance:

Loligo is a too small company to develop all of this by itself. We did project management and electronics design. Lasse Hässler (Prototal) and Isak Nordell (Artmek) helped out with the mechanics. Niklas Casaril (Nipe) did most of the programming. Stefan Petersen (Ciellt) made low level drivers for motor control and LIDAR. Tove Gustavi, who normally works for FOI, helped out with algorithms for trajectory planning and formation control. It was fun working with you all!

More pictures from the robot bed development can be found here (you might need to scroll a bit, new pictures are added at irregular intervals):
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