What dynamics should impedance-controlled robots render?

While impedance control is the standard framework for physically interactive robots, the design choice of what dynamics should be rendered requires additional information (assumptions on environment, in-situ data). The range of dynamics which can be rendered by a robot is informed by its mechatronic design (actuators, physical compliance, innerloop control), and these mechanical design decisions must be made in advance. How can a mechatronic design be evaluated when the system objectives and environment dynamics are not quantified? This paper presents performance metrics proposed for pHRI in literature, and seeks to move towards a unified methodology for mechatronic design on interactive robots: supporting potential performance and safety over a set of environments.