**Alberto Doria 1, Silvio Cocuzza 1,\*, Nicola Comand 2, Matteo Bottin <sup>2</sup> and Aldo Rossi <sup>1</sup>**


Received: 2 August 2019; Accepted: 9 September 2019; Published: 11 September 2019

**Abstract:** In robotic processes, the compliance of the robot arm plays a very important role. In some conditions, for example, in robotic assembly, robot arm compliance can compensate for small position and orientation errors of the end-effector. In other processes, like machining, robot compliance may generate chatter vibrations with an impairment in the quality of the machined surface. In industrial robots, the compliance of the end-effector is chiefly due to joint compliances. In this paper, joint compliances of a serial six-joint industrial robot are identified with a novel modal method making use of specific modes of vibration dominated by the compliance of only one joint. Then, in order to represent the effect of the identified compliances on robot performance in an intuitive and geometric way, a novel kinematic method based on the concept of "Mozzi axis" of the end-effector is presented and discussed.

**Keywords:** robot; compliance; machining; modal testing; Mozzi axis
