Control system for surgical robot system with safety device

A method of selectively filtering communications to and/or from of a main controller of a surgical robot system, the surgical robot system comprising a surgical robot, the surgical robot comprising a base, and an arm extending from the base to an attachment for an instrument, the arm comprising a plurality of joints whereby the configuration of the arm can be altered, the main controller configured to receive communications identifying inputs from an operator of the surgical robot, generate control signals for controlling the movement of the surgical robot arm based on the inputs, and send communications to the surgical robot identifying the control signals, the method comprising:

• receiving at a safety device a communication to or from the main controller;
• determining whether at least one filter criteria has been specified;
• in response to determining that at least one filter criteria has been specified, comparing the received communication to the at least one specified filter criteria;
• in response to determining that the received communication matches at least one of the at least one filter criteria, rejecting the received communication;
• and
• in response to determining that the received communication does not match any of the at least one filter criteria, outputting the received communication to the relevant device.