Tuning a line-following hospital delivery trolley with PID

Annapurna's pharmacy sends medicine trays to three wards on the ground floor about 40 times a day. A ward attendant walks each one, a 140 m round trip that takes 6–8 minutes, and attendants are often pulled away from patients to do it. The hospital's biomedical engineering team wants to try a small trolley that follows a black tape line on the corridor floor and stops at each ward.

They built a first version from a hobby kit. It wobbles on straights, cuts the corner at the two 0.6 m-radius bends, and once ran off the line into a wheelchair. Nobody tuned it properly. They copied gains from a video.

The requirements are: - cruise at 0.4 m/s on straights; - stay within 2 cm of the line centre on straights and 4 cm on bends; - stop within 3 cm of a station marker (a short cross-line) and wait for a button press; - stop within 0.5 m of an obstacle in front and wait until it clears.

You will build a model of the trolley and corridor in Webots, a free robot simulator, with a five-sensor infrared array. You will write the controller in Python and tune it step by step: first P, then PD, then PID, logging error data and plotting it at each step.

You do not need a robot kit. If you have one, such as an Arduino car with an IR array, you may test the same controller on it as a bonus.

Done looks like a controller that meets every requirement on the full corridor track in simulation, a set of plots that show how each gain changed the behaviour, and a short report the biomedical team can use to tune the real trolley.