Having a problem using Epson WF-4640 on home network with iMac

Have a new Epson WF-4640 which can be seen on the home network from PCs. Will work with MacBook Air if plugged into USB port on the MacBook Air. Cannot get it to connect via wireless or ethernet (through home router) from my iMac running 10.10.5. Have downloaded the latest Epson printer driver from Apple. Have made the MF WF-4640 with a dedicated port on the router but still no joy. Any ideas out there? Thanks.