Automatic feeders should be cleaned regularly. Some have dishwasher-safe parts, others should be cleaned by hand.
Vending machines for dogs and cats often have removable bowl parts, which can be dishwasher safe depending on the model.
For the rest of the machine, cleaning by hand with a damp cloth is best. Especially for models with a sensor, it is important to keep it clean so that it recognises your pet. Wire brushes can also be a good tool to get into all the corners.