A Bertrand curve is a space curve whose principal normal line is the same as the principal normal line of another curve. On the other hand, a Mannheim curve is a space curve whose principal normal line is the same as the binormal line of another curve. By definitions, another curve is a parallel curve with respect to the direction of the principal normal vector. Even if that is the regular case, the existence conditions of the Bertrand and Mannheim curves seem to be wrong in some previous research. Moreover, parallel curves may have singular points. As smooth curves with singular points, we consider framed curves in the Euclidean space. Then we define and investigate Bertrand and Mannheim curves of framed curves. We clarify that the Bertrand and Mannheim curves of framed curves are dependent on the moving frame.
HONDA, SHUN'ICHI and TAKAHASHI, MASATOMO
"Bertrand and Mannheim curves of framed curves in the 3-dimensional Euclidean space,"
Turkish Journal of Mathematics: Vol. 44:
3, Article 18.
Available at: https://journals.tubitak.gov.tr/math/vol44/iss3/18