A team of final-year engineering students from Temasek Polytechnic has come up with a way to get people to clear and return their trays - do it, or forfeit a dollar.

Mr Chen I Chieh, 25, Mr Sanasi Sadish Rao Hari, 24 and Mr Effendy Parman, 24, designed special aluminium frames that when fitted with modified food trays transform into tables. Without the trays, diners have no table to eat on.

Using the same concept as supermarket trolleys, these trays can only be removed from a rack when a $1 coin is inserted into a coin slot at the bottom of each tray. The money can be retrieved when the tray is cleared and slotted back vertically into the rack.

Their final-year project, nominated for the 2013 Tan Kah Kee Young Inventors' Award, was one of 66 showcased at the polytechnic's Engineering Project Show, held at its Temasek Convention Centre. The exhibition ends Tuesday.