Simplify the following text for a Grade 10 native English-speaking person.
Original: Later , he set about designing and then patenting different types of tray : a metal tray with rubber separators , a metal tray with individual rubber cups , and a tray made completely of rubber .
Simplified: Later , he made and patented several kinds of tray : a metal tray with rubber separators , a metal tray with individual rubber cups , and a tray made of only rubber .