Abstract: There is shown an arrangement for detecting elastic deformation of a tool shaft carried by a machine tool and, in turn, carrying a cutting bit. An optical fibre section is mounted in or on the shaft at a distance from its neutral bending line in the longitudinal direction of said shaft. The optical fibre section, which follows the elastic deformation of the shaft, extends parallel with and at a constant distance fro the neutral bending axis of said shaft, so that elongation of the fibre section forms a measurement of bending of the shaft in an axial plane that includes the optical fibre section. The optical fibre section has at least two longitudinally spaced partial reflection means and means are connected to the optical fibre section to determine interferometrically a change in distance between the partial reflection means in the optical fibre section, wherein the change in distance forms a measurement of shaft curvature between the two partial reflection means.

Abstract: Apparatus for determining the curvature of an elongated channel, such as a drill hole in rock for instance, wherein the apparatus includes a probe (1) which may be constructed for movement through the channel and to assume the curvature of the channel at the different positions into which the probe is moved along the channel, wherein the probe (1) includes means (3, 31, 10) for sensing the curvature of the probe, and thus also the curvature of the channel, between at least two longitudinally spaced positions (A, B) on the probe (1), and wherein the apparatus can be connected to means (10) for determining the extension of the channel by registering curvature of the probe, for instance in different positions of the probe along the channel.