SSI to RS485 communication protocol
SSI is point to point serial communication method usually used to send information from an encoded sensor to a micocontroller or PLC. RS485 is a point to multi-point communication method that has a entirely different protocol, used to link microcontollers or  or PLC's into a network. To convert from one to to another, you would need to design a small circuit with a MCU that had a SSI transceiver and a RS485 Transceiver (either 2 wire or 4 wire), and write code that translated the two protocols. 

HOWEVER, they do sell exactly such a device; here is one already made from HMK:
http://www.hmkdirect.com/shop/IV251/