Abstract: The alignment of the drill stem and bit of a rock drill rig is corrected when the force of drilling and the feeding power on the drilling machine of the rig has resulted in a change in the direction of the drill stem because of deformation of the articulated and extensible drill boom of the rig and of its pivotally supported drill support on the drill boom. The drill rig is of the type that includes elements for measuring boom lengths and articulation angles, servos for controlling such lengths and angles and a control unit which is connected to the measuring elements and servos for adjusting the drill stem and bit. The various articulation angles which are required to compensate for deformations of the drill boom and drill support are determined as if the drill boom and support were in an unloaded condition, on the basis of measured values of the boom lengths and articulation angles which have been registered in the control unit in an unloaded condition.

Abstract: The feed support of a rock drilling unit is adjusted to be a given distance from a rock surface wherein holes are to be drilled. A drill bit is moved into abutment with the rock surface. The feed support is moved relative to the bit toward the rock surface. Such movement is stopped when a depth measuring instrument determines that the feed support is at a position spaced the given distance from the rock surface.

Abstract: A method of drilling long and straight holes in rocks is based on the use of a drill rig which may be aligned by means of a laser beam and which comprises a hollow drill stem with a pressure device for guiding the drill stem in a correct direction on applying pressure against the wall of the drilled hole. The laser beam is sent into the hollow drill stem towards an optical detecting unit placed inside a hollow control arrangement joined into the drill stem behind its drill bit, the control arrangement being operated by means of signals from the detecting unit. The arrangement constituted a connecting piece of the drill stem and comprises a pressure device which is in contact with the wall of the hole. The optical detecting unit is arranged with free sight to the source of the laser beam as long as the drill stem is sufficiently straight.

Abstract: A directional coupler for duplex transmission for use with a transmitter/receiver unit is described. It includes a memory unit for providing a correction signal and a compensation circuit to which the correction signal is applied to supress that portion of the received signal which is derived from the transmitter. The memory unit is capable of storing values of the correction signal, the values being assigned to the different possible varients within a selected period of time, of time functions coming from the transmitter, and a decoder connected between the transmitter and the memory unit for detection of actual, transmitted signal variants. The decoder includes means for selection in the memory unit of the values of the correction signal assigned to the actual signal variants.