The present invention relates to a method for adjusting drilling of a drilling machine in a drilling machine comprising a frame, a percussion piston arranged to the frame and moving in the longitudinal direction of the frame, an absorber situated in the front end of the travel of the piston portion of the percussion piston, a shank situated in the axial extension of the percussion piston and at least two pistons arranged to the frame moveable in its axial direction, the pistons being situated in axial cylinder spaces formed around the shank and arranged to act on the shank and push it towards the front portion of the drilling machine by means of a pressure medium acting on the rear surface of the pistons, whereby at least during drilling such a pressure of pressure medium is set to act on the rear surface of the pistons that the total force of all the pistons acting on the shank and pushing it forwards exceeds feed force acting on the drilling machine during drilling, wherefore some of the pistons are pushed to the foremost position of their travel by means of the pressure medium, whereby the shank is at its optimal percussion point when being supported by them.

The present invention also relates to a drilling machine which drilling machine comprises a frame, a percussion piston arranged to the frame and moving in the longitudinal direction of the frame, an absorber situated in the front end of the travel of the piston portion of the percussion piston, a shank situated in the axial extension of the percussion piston, and an axial bearing arranged to the frame for receiving axial forces directed to the frame via the

shank, which axial bearing is formed of at least two pistons which are placed in the frame into axial cylinder spaces formed around the shank and arranged to act on the shank and push it towards the front portion of the drilling machine by means of a pressure medium acting on the rear surface of the pistons, whereby at least during drilling such a pressure of pressure medium is set to act on the rear surface of the pistons that the total force of all the pistons acting on the shank and pushing it forwards exceeds the feed force acting on the drilling machine during drilling and whereby the travel of some of the pistons towards the front portion of the drilling machine is restricted in such a manner that when said pistons are in their foremost position, the shank is essentially situated at its optimal percussion point when being supported by them.

When drilling holes with a rock drill, drilling conditions vary in various ways and in some situations it is necessary to be able to adjust fast and effectively the percussion power of the rock drill or other factors having an effect on drilling. In prior art solutions, percussion power is adjusted by adjusting the pressure of the pressure fluid in the percussion machinery, which is, however, quite difficult to realize accurately and in a controlled manner. Further, in prior art solutions, the position of the shank with respect to the percussion piston is always to be kept at a certain so-called optimal percussion point where as great a portion of percussion power as possible moves to the shank and via the shank through the drill rod to the drill bit. Finnish Patent 84,701 discloses a solution where the position of the shank is set by using several pistons, the pressure acting on which together pushes the shank into an

optimal percussion point, but allows it to move backwards by means of a strong return pulse and to receive thus the stress created. In said Finnish Patent some of the pistons can also move farther than the others towards the front end of the drilling machine and thus follow that shank, whereby they receive the return movement and absorb it at an earlier stage during the return pulse.

In prior art solutions, the adjustment of drilling is difficult and the object of this invention is to provide a method and drilling machine where drilling can be easily adjusted as desired. The method according to the invention is characterized in that the pressure acting on at least some of the pistons is adjusted for providing a desired drilling situation.

The drilling machine according to the invention is characterized in that it comprises at least two pistons, pressure channels separate from one another leading to the pressure spaces behind the pistons and means for feeding pressure fluid to the pressure spaces behind the pistons in such a manner that a pressure is acting on them irrespective of one another.

The essential idea of the invention is that drilling is adjusted by adjusting the position of the shank with respect to the optimal percussion point and the force on the shank when it deviates from its optimal percussion point. In that case, in the adjustment of the percussion power, a desired amount of power is transferred via the shank to the drill rod and the remaining portion of the power is absorbed by the absorber in the front end of the travel of the percussion piston. Similarly, when rock contact of a drill bit is to be adjusted, the pressure acting behind the pistons is kept such that a smaller pressure than

feed force is behind the pistons which are capable of moving forwards from their optimal percussion point, the pressure being variable according to the number of drill rods used in long hole drilling in such a manner that at the arrival of a percussion pulse, the drill bit can always be kept as desired in contact with the rock to be drilled without any essential power loss to the absorber. The method can be realized most simply by using several pistons with different travel, the travel of the pistons to the front end of the drilling machine being appropriately restricted. In that case, when feeding a pressure fluid of a suitable pressure behind pistons with different travel, the shank can be moved forwards as desired. An advantage of the invention is that by using pistons moveable to different travel, the shank can be moved mechanically into a desired percussion point that is either the optimal percussion point or one deviating from it. Because the position of the percussion point is precisely determined for all situations, power transfer and thus the percussion power of the machine can be calculated accurately and dimension it according to desired properties during manufacturing. The adjustment of drilling is fast and simple as it can be realized only by adjusting the pressure of pressure fluid acting on the pistons that support the shank.

In the following, the invention will be explained in more detail in the appended drawings, in which Figure 1 shows a schematic view of one construction in a drilling machine suitable for realizing the method according to the invention,

Figure 2 shows a schematic view of the adjustment of the drilling machine according to Figure 1 in different power adjustment situations,

Figure 3 shows a schematic view of a second construction in a drilling machine suitable for realizing the method according to the invention,

Figure 4 shows a schematic view of forces caused by pressures present in connection with one realization of the method according to the invention, and

Figure 5 shows a schematic view of a third construction in a drilling machine suitable for realizing the method according to the invention.

Figure 1 shows a schematic view of a drilling machine comprising a percussion piston 1 and a shank 2 situated coaxially with the percussion piston. The shank 2 is rotated in a manner known per se by means of a rotation motor (not shown) by rotating a bushing 3 around the shank 2 which can move in the axial direction with respect to the bushing. The bushing 3 supports the shank 2 on a slanted supporting surface 3a that is in contact with a corresponding slanted supporting surface 2a of the shank. There are several pistons 4a and 4b behind the bushing 3 connected to or indirectly act mechanically on the rear surface of the bushing 3. A restricting ring 5 is around the bushing 3 restricting the movement of the pistons 4a and 4b towards the front end of the drilling machine. The pistons 4a and 4b are situated in cylinder spaces which have been drilled to the frame 6 and which are parallel to the axle of the percussion piston 1 and pressure fluid channels 7a and 7b lead to the cylinder spaces . There are several pistons 4a and 4b in the frame 6 of the drilling machine and they are divided into groups in such a manner that there are at least two separate groups whose travel towards the front end of the drilling machine is different. This construction is described in more detail in Finnish Patent 84,701, the

contents of which are considered to be included in the specification of the present application. Further, the drilling machine comprises an absorber 8 in the front end of the cylinder space of the percussion piston 1, that is, in the travel of the piston portion la of the percussion piston 1 in the front end of the drilling machine and the front end of the piston portion lb strikes the absorber when the percussion piston for some reason should strike past its normal optimal percussion point. This construction is generally known per se and used to stop the drilling machine from getting broken and therefore it is not explained in more detail herein.

By means of the method according to the invention, the position of the shank of the drilling machine and thus e.g. percussion power or rock contact of the drill bit can be adjusted by using this construction. This takes place so that during normal drilling the pressure fed behind the pistons is kept such that the pistons push the shank into its optimal percussion point, but cannot push it any farther as the power caused by pistons 4b with longer travel via the bushing 3 to the shank 2 is smaller than the feed force of the drilling machine. During the stroke, when the body of the drilling machine does not have time to move with the drill rod, the pistons follow the shank and thus support the drill bit against the rock by the pressure of the force set to act on them, until the drilling machine has had time to move. When the percussion power is to be diminished, at least such a pressure of the pressure fluid is fed behind the pistons 4b that the pistons 4b with longer travel are able to push the shank their allowed travel forwards, whereby the percussion piston 1 strikes the shank 2 later than usual and thus some of its percussion energy

is absorbed in the absorber 8 of the percussion piston. When three different percussion powers, for example, are to be used, three piston groups with a different percussion length are also used, whereby by appropriately feeding pressure behind the pistons, the shank can be moved to a desired power transmission position.

Figure 2 shows a schematic view of the adjustment of percussion power in another way. In this case, pistons with different travel, which are indicated by numerals 4a to 4d, are each connected to a specific group and to a specific feed channel 7a to 7d of pressure fluid separate from other piston groups. In the figure, one piston 4a, 4b, 4c and 4b, respectively, refers schematically to all pistons of one group. The figure also shows schematically by numerals 5a to 5d the portions of the restricting ring 5 that restrict the travel of different pistons 4a to 4d in different ways. Similarly, the figure also shows with broken lines La to Ld the travel which each piston or piston group can move with, respect to one another and broken line La describes the position corresponding to the optimal percussion length of the shank and lines Lb to Ld positions corresponding to the transfer of pistons 4b and 4c that have moved forwards with respect to the optimal percussion point where the piston portion la of the percussion piston 1 strikes a shorter or a longer distance, respectively, to the absorber 8 or the percussion piston has otherwise moved away from its optimal percussion point. When the cross section of the pistons with respect to the hydraulic pressure to be used is dimensioned appropriately, a pressure fluid Pa to Pd with a different pressure can be fed behind each piston group independently of the others and then it can be easily selected with which travel of the

pistons 4a to 4d the percussion point of the shank is to be set. Correspondingly, this can be attended to by maintaining the same pressure behind all pistons, whereby by selecting appropriately the area and the number of pistons and by adjusting the active pressure, the desired forces are obtained for the desired piston groups.

The adjustment of percussion power is carried out automatically by adjusting the values of the pressure of the pressure fluid acting behind the pistons 4a to 4d suitable ones with respect to the feed force of the drilling machine. In that case, if the penetration of the drilling tool is for some reason, e.g. because of poor rock material or the like, greater than the feed speed, the shank moves because of the pressure acting behind the pistons 4a to 4d forwards to a position where the percussion point is no longer optimal. Depending on behind which pistons pressure of pressure fluid is fed or how great a pressure is set behind the pistons, the shank either moves somewhat forwards from its optimal percussion point, but only such a distance so that the percussion piston does not strike the absorber or, if it moves the distance specified by the pistons 4c and 4d, it partly strikes the absorber 8. The farther the shank can penetrate, the smaller the transfer of percussion power will be between the percussion piston 1 and the shank 2. When starting drilling or with certain types of rock or when the conditions thus require, transfer capacity can be selected by using sufficient pressure behind a desired piston group 4a to 4d or behind all groups, whereby a sufficiently small percussion power is provided for each differing drilling situation.

Figure 3 shows a schematic view of a second construction in a drilling machine suitable for

realizing the invention, whereby corresponding parts in Figure 3 are referred to by the same numerals as in Figure 1. In the embodiment shown in Figure 3, bushing¬ like pistons are used instead of several separate pistons and the bushing-like pistons are placed around the percussion piston coaxially with it. In this case, pistons 14a and 14b are placed in such a manner that the piston 14a is outmost and a pressure channel 17a leads to it by means of which channel the piston 14a can be pushed forwards. The piston 14a stops at an abutment surface 15a in the frame, whereby when the piston is in that position and when the shank 2 is supported to the piston 14a, it is at its optimal percussion point. The piston 14b is coaxially inside the piston 14a and behind it pressure fluid enters along a channel 17b. The piston 14b also has a projection 14b' extending to the supporting surface 14a' in the front of the piston 14a in such a manner that the piston 14a can push the piston 14b towards the front end of the shank. The piston 14b pushes the shank with the help of the bushing 3. Correspondingly, when the shank 2 pushes the piston 14b backwards, it is pushing the piston 14a by means of its projections. Furthermore, the travel of the piston 14b towards the front portion of the drilling machine is restricted by an abutment surface 15b, whereby when the piston 14b is against the abutment surface 15b, the shank 2 is at a new percussion point differing from the optimal percussion point. In a normal situation, the pistons 14a and 14b are as shown in the figure when the shank is at the optimal percussion point. If the pressure behind the piston 14b is added through the channel 17b, the pressure will, when it rises high enough, cause a force exceeding the feed force of the drilling machine and

move the shank and the drilling machine with respect to one another in such a manner that the shank 2 is in the front of its normal percussion point .

This embodiment can be realized in different ways, whereby there may be a separate transmission ring or separate pins that transmit power from the piston 14b to the bushing 3. Similarly, the pistons 14a and 14b can be in the way shown in the figure or in the opposite way in such a manner that the piston 14b is outermost and the piston 14a is innermost. Further, the pistons may also be one after the other in the axial direction of the shank. Similarly, several pistons may be annularly concentric as shown in the figure and cylindrical pistons of Figure 1 can also be used at the same time as and in addition to annular pistons.

Figure 4 shows a schematic view of forces caused in connection with one embodiment of the invention by pressure changes when drilling upwards with long hole drilling. The force shown with a horizontal line FS in the figure is caused by the pressure behind the pistons 4a, 14a which support the shank at its optimal percussion point. Stepped line FC describes the sum of the forces caused by means of the pressure set behind the pistons 4b to 4d, 14b which are capable of moving towards the front end of the drilling machine during drilling. Whenever one drill rod is added to the drill rod set, the pressure behind the pistons 4b to 4d, 14b is raised in such a manner that the addition of mass is compensated by the addition of pressure and thus the drill bit is supported in the front of the percussion point essentially with a constant power. The sum of the force caused by the pressures behind the pistons 4a; 14a and 4b to 4d; 14b, respectively, is greater than feed force and thus it is able to retain the shank at the optimal percussion

point, but the sum of the forces caused by the pistons 4b to 4d; 14b remains to be at a smaller value than the feed force of the drilling machine. Feed force is described by broken line FF, whereby feed force is kept at the beginning of drilling so small that the sum of the forces caused by the pistons 4b to 4d moves the shank forwards and the percussion piston strikes the absorber. In this situation, as shown in the figure, the force caused by the piston 4d stays on to support the drill bit in the front of the percussion point and enables the drilling to be controlled. Percussion power can thus be adjusted until drilling has started and normal drilling has begun. On the other hand, it happens sometimes in connection with normal drilling that rock is soft or broken, which can be seen in the figure when broken line FF falls abruptly and rises up after that at point A. In this situation, the active force of the pistons 4b to 4d; 14b exceeds the feed force, whereby the shank penetrates into a new percussion point and the percussion piston strikes the absorber and the percussion power will diminish until ordinary rock is reached. When adding drill rods, feed force is also added to compensate for the mass, whereby a stepped line is formed as shown in the figure. Point B is in a situation where the drill rod has started to resonate or it is known to resonate. In this situation, the force pushing the pistons 4b to 4d forwards is adjusted to be greater than the feed force by adjusting the pressure. Here the travel of the pistons 4b is restricted in such a manner that the movement of the shank forwards does not move the percussion piston to the absorber at the end of the stroke so that the percussion power will not change essentially. As a result of the moving of the shank, the percussion length of the percussion piston and thus

the frequency of percussion change and resonance is thus avoided. On the other hand, the pressure level of the pistons 4c and possibly of the piston 4d and the force caused by it is raised at the same time so that bit contact, that is, supporting force in the front of the percussion point remains essentially unchanged. After adding one or more drill rods, a normal pressure level and thus the optimal percussion point of the shank for the stroke can be regained. Also, the pressure acting behind the pistons and retaining the shank at its normal percussion point can be adjusted by the number of the drill rods to be used, whereby straight line FS will be stepped in such a manner that the recoil receiving difference force of the piston force and the feed force is constant, for example.

Figure 5 shows a schematic view of the embodiment of the invention corresponding to Figure 3 in other respects but that a uniform pressure acts there behind the pistons 14a, 14b at the same time. In that case, the adjustment of the percussion point of the shank 2 and percussion adjustment is carried out only by adjusting the pressure of the pressure fluid acting through the channel 17a, an increase of which pressure will make the piston 14b to push the shank 2 forwards. In addition, this embodiment comprises separate transmission parts 18 between the piston 14b and the bushing acting on the shank 2 for transmitting power forwards from the piston 14b to the bushing 3 and further via the bushing to the shank 2. The invention has been described and shown in the description above and the drawings only by way of example, and it is in no way restricted to this example. Different automatic pressure adjustment methods and apparatuses can be combined, when desired, to the method according to the invention for attaining

automatic power adjustment. Similarly, the same pressure can be fed behind all the pistons, whereby the required transfer of the shank forwards requires a sufficient pressure with respect to the number of the pistons which are capable of moving forwards . The pistons can be, as shown in drawings, of a singleit comprises at least two pistons, pressure channels separate from one another leading to the pressure spaces behind the pistons and means for feeding pressure fluid to the pressure spaces behind the pistons in such a manner that a pressure is acting on them irrespective of one another construction but also different piston constructions which have between the piston portions and the shank separate piston portions and different transmission bushings and bearing portions through which the pistons act on the shank mechanically and push it forwards.