An encoder assembly includes an encoder, a fixing cover for receiving the encoder, and a protecting cover for receiving the fixing cover. The encoder includes a main body, and a trumpet-shaped rubber collar extending from a first end of the main body. The fixing cover includes a first open end and a second open end opposite to the first open end. The second open end engages with an outer side of the rubber collar. The protecting cover includes an open end and a closed end opposite to the open end. A circular protrusion extends from an inner wall of the closed end to engage with an inner side of the rubber collar.