*Article* **A New Stiffness Performance Index: Volumetric Isotropy Index**

#### **˙ Ibrahimcan Görgülü \* and Mehmet ˙ Ismet Can Dede**

Department of Mechanical Engineering, Izmir Institute of Technology, Urla, ˙ Izmir 35430, Turkey; candede@iyte.edu.tr

**\*** Correspondence: ibrahimcangorgulu@iyte.edu.tr

Received: 8 April 2019; Accepted: 17 June 2019; Published: 18 June 2019

**Abstract:** A new index for a precise calculation of a manipulator's stiffness isotropy is introduced. The proposed index is compared with the conventionally used stiffness isotropy index by making use of the investigation on R-CUBE manipulator. The proposed index is shown to produce relatively more precise results from which a higher number of isotropic poses are detected.

**Keywords:** stiffness modelling; performance indices; condition number; volumetric isotropy index; parallel manipulator
