Comment on "A nanopositioner for scanning probe microscopy: the KoalaDrive" [Rev. Sci. Instrum. 83, 023703 (2012)]

In a recent paper, Cherepanov et al. [Rev. Sci. Instrum. 83, 023703 (2012)] present two types of piezoelectric nanopositioners: Type I consists of two piezoelectric tubes coaxially mounted in series. At the ends and between the two piezo tubes, three springs are mounted and hold a central tube; Type II nanopositioner (called "a variant of Type I" by the authors) is similar to Type I except that the two tube piezo elements are mounted in parallel with one being coaxially inserted in the other. They both work via concerted axial deformations of the two piezo tubes such that each spring is in turn sliding on the shaft in the same direction while the other two springs hold the shaft by static friction. In this comment, we would like to clarify that both Type I and II nanopositioners are closely related to the one disclosed in our year 2009 paper [Rev. Sci. Instrum. 80, 085104 (2009)] which should therefore be cited.