Patent ID: 8061434
Filing Date: 2011-11-22
Classification: B25D,E21B

Abstract:
1. A method for controlling the operation of a pressure fluid operated percussion device comprising: means for feeding pressure fluid into and discharging the fluid from the percussion device; mean for producing a stress wave by means of the pressure fluid pressure to a tool connectable to the percussion device to move in a longitudinal direction in relation to the body thereof, the means for producing the stress wave comprising a working chamber in the body of the percussion device and a transmission piston provided in the working chamber to move a longitudinal direction of the tool in relation to the body of the percussion device, the transmission piston having an energy transfer surface facing the tool to allow it to be brought into contact with an energy receiving surface of the tool or a shank connected to the tool; means for making the pressure fluid pressure prevailing in the working chamber push the transmission piston towards the tool for compressing the tool in the longitudinal direction thereof by means of the pressure fluid pressure acting on the transmission piston so that a stress wave is produced in the tool; and correspondingly means for making the transmission piston return, the method comprising: influencing the shape of the stress wave by setting a clearance (d) between the energy transfer surface of the transmission piston and said energy receiving surface before pressure fluid is allowed to push the transmission piston towards the tool so that when the clearance (d) is at its smallest, the energy transfer surface of the transmission piston is in contact with the energy receiving surface of the tool or of a shank connected to the tool at the moment when the effect of the pressure fluid pressure begins, the stress wave being thus produced substantially by the effect of the pressing force produced by the pressure fluid pressure alone and transmitted to the tool by the transmission piston, the length of the stress wave being substantially equal to the effective time of the pressing force acting on the tool, whereas when the clearance (d) is at its longest, the stress wave is substantially produced by the impact of the transmission piston created as a result of a transmission piston motion caused by the pressure fluid pressure and acting on the energy receiving surface of the tool or a shank connected to the tool, the length of the stress wave being substantially twice the length of the transmission piston, and whereas when the clearance (d) is set to a value between the smallest and largest extent, the stress wave is produced by the combination of initial impact energy of the transmission piston acting on the energy receiving surface of the tool or a shank connected to the tool and transfer energy caused by the pressing force produced by the pressure fluid pressure alone transmitting to the tool by the transmission piston.