Patent Publication Number: US-5896935-A

Title: Arrangement in boom for rock drilling unit

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     This invention relates to an arrangement in a boom for a rock drilling unit, comprising a boom pivotally connected to a frame, relative thereto, about a first shaft, and at the other end of the boom, relative thereto, a feed beam pivotally connected about a second shaft, parallel to the first shaft, a lift cylinder between the boom and the frame for turning the boom relative to the frame, a swing cylinder between the feed beam and the boom for turning the feed beam relative to the boom, wherein the lift cylinder comprises a first and a second cylinder space where hydraulic fluid is fed for turning the boom in different directions relative to the frame, and the swing cylinder comprises respective cylinder spaces where hydraulic fluid is fed for turning the feed beam into different directions relative to the boom. 
     A problem with rock drilling units is to maintain the alignment of the feed beam of the rock drill when the boom between the frame or the feed beam is horizontally or vertically turned for placing the drill rod at a new hole to be drilled. For this purpose so-called parallel automatism is normally used, wherein the pivotal movement of the boom relative to the frame is compensated for in joints between the feed beam and the boom by using separate servo cylinders, whereat the turning of the boom causes the length of one servo cylinder to change, which again causes the hydraulic fluid in a servo cylinder between the boom and the feed beam to shift so that the length of that cylinder is correspondingly changed and consequently the feed beam turns into a reverse direction relative to the end of the boom as compared with the boom relative to the frame. Such solutions are disclosed e.g. in SE patent 227821. 
     In known solutions, separate hydraulic cylinders, interconnected to form a closed circuit, are needed to maintain parallelism. Such a structure is, however, expensive and requires extra space around joints simultaneously increasing the number of wear components. A further problem is that, because the functioning of these cylinders has to be secured by using separate pressure-controlled non-return valves which close the pressure ducts of the cylinders so that a possible breakage of a hose does not allow the feed beam to turn freely, the amount of pressure needed to open these valves is harmful to the turning function of the boom as it resists the turning until an adequate pressure level is reached. As a result, boom control may be unsteady in the extreme angular positions, and in some cases the feed beam may even have to be moved to a more suitable position of equilibrium for proper control. This again complicates the drilling work and impairs the usability of the unit. 
     The object of the present invention is to provide an arrangement which eliminates problems of known solutions and provides a simple, easily and reliably functioning parallel control for a feed beam. The arrangement of the invention is characterized in that the piston rod of a lift cylinder is hollow, that the lift cylinder comprises a separate fixed piston extending into the piston rod, whereat a third cylinder space inside the piston rod is completely separate from the cylinder space, that the third cylinder space of the lift cylinder is connected with a first cylinder space of a swing cylinder, and that a second cylinder space of the swing cylinder is connectable with either a hydraulic fluid supply or correspondingly a hydraulic fluid tank simultaneously with a first cylinder space of the lift cylinder, whereat, when the lift cylinder retracts, the swing cylinder retracts correspondingly, and when the lift cylinder extends, the swing cylinder extends so as to essentially maintain the alignment of the feed beam irrespective of the swing angle of the boom. 
     It is an essential idea of the invention that a hydraulic cylinder between a boom and a frame is used for controlling the swing angle between a feed beam and the boom, said cylinder comprising a hollow piston rod and a separate fixed servo piston inside the piston rod so that with the piston moving relative to the cylinder, the volume of the space inside the piston rod changes correspondingly, proportionally to the travel length, whereat, with the piston rod extending inside the cylinder, the hydraulic fluid in said space flows out and may be used for controlling the cylinder between the feed beam and the boom. It is a further essential idea of the invention that hydraulic fluid is fed into a second space of the swing cylinder between the feed beam and the boom simultaneously as hydraulic fluid is fed into a cylinder between the boom and the frame, so that the fluid causes the boom to rise by feeding the swing cylinder between the feed beam and the boom into a direction where the hydraulic fluid discharged from it transmits feed pressure into the space inside the piston rod so that with the cylinder extending, i.e. the boom being lifted, both the area of the fixed piston inside the piston rod and the area of the moving piston have a parallel effect. 
     It is an advantage of the solution of the invention that when a boom is lifted upward, a large area may be used for the lifting, as the hydraulic fluid pressure being fed has a parallel effect in both cylinder spaces. Similarly, when a cylinder is lowered, the pressure retracting the cylinder works parallel with the weight effect of the boom, but in the cylinder space inside the piston rod, the pressure has a reverse effect thus compensating for the weight effect of the boom. Thus a better control in the lifting and lowering of the boom is achieved and simultaneously the desired parallelism in a feed beam is also maintained. 
     The invention will be described in greater detail with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 schematically shows the arrangement of the invention for controlling vertical movements of a boom and a feed beam, 
     FIG. 2 schematically shows a hydraulic coupling of the arrangement of the invention. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     FIG. 1 schematically shows a boom 1, pivotally connected to a frame 2 about a horizontal first shaft 3. A lift cylinder 4, between the boom 1 and the frame 2, is connected at its ends by means of joints 5 and 6 to the frame and the boom, respectively. The other end of the boom 1 comprises a feed beam 8, pivotally connected about a horizontal second shaft 7, with a rock drill 9 moving along said feed beam 8. A swing cylinder 10, between the feed beam 8 and the boom 1, is coupled by means of joints 11 and 12 to the feed beam 8 and the boom 1, respectively. 
     FIG. 2 schematically shows a hydraulic coupling of the apparatus of FIG. 1 relative to the lift cylinder 4 and the swing cylinder 10. As is evident from the Figure, the lift cylinder 4 comprises three cylinder spaces, with a piston 4a moving inside the lift cylinder 4. On both sides of the piston 4a, are cylinder spaces 13a and 13b, wherein hydraulic fluid is fed according to whether the piston 4a is required to move into the lift cylinder 4 or outward from it. A piston rod 4b is hollow, and the lift cylinder 4 has inside it, in the middle, a fixed servo piston 4c, extending into the piston rod 4b, whereat a third cylinder space 13c inside the piston rod 4b increases or decreases depending on the movement of the piston 4a relative to the cylinder 4. A first and a second hydraulic fluid line, 14a and 14b, lead to the cylinder spaces 13a and 13b, respectively. 
     A third and a fourth hydraulic fluid line 15a and 15b is connected to the lift cylinder 10 for separate turning of the feed beam 8, said lines being connected via pressure-controlled non-return valves 16a and 16b to pressure-controlled over-center valves 17a and 17b of the swing cylinder, and further to a first and a second hydraulic fluid space 18a and 18b, respectively, of the swing cylinder 10. Feeding hydraulic fluid into one of the lines 15a and 15b makes the swing cylinder 10 extend or retract, thereby turning the feed beam 8 relative to the boom 1. The third cylinder space 13c inside the piston rod 4b is connected via a connecting line 19 between the non-return valve 16a and the over-center valve 17a of the third hydraulic fluid line 15a. Respectively, the hydraulic fluid lines 14a and 14b of the lift cylinder 4 comprise over-center valves 20a and 20b. The first hydraulic fluid line 14a of the lift cylinder is connected via a pressure-controlled shuttle valve 21 between the pressure-controlled non-return valve 16b and the over-center valve 17b of the fourth hydraulic fluid line 15b, and the control pressure line of the shuttle valve 21 is connected to the second hydraulic fluid line 14b. The purpose of the over-center valves 17a, 17b and 20a, 20b is to keep the cylinders 10 and 4 immovable, i.e. hydraulically closed, when hydraulic fluid is not fed to either of them in any manner. Additionally, in case of overload, they allow the flow of hydraulic fluid for preventing the devices from breakage. Their function and use is obvious and generally completely known p and is thus not described here in any greater detail. 
     When hydraulic fluid is fed into the first cylinder space 13a of the lift cylinder 4, the fluid drives the piston 4a outward from inside the lift cylinder 4 simultaneously as hydraulic fluid flows from the second cylinder space 13b via the over-center valve 20b, opened by the incoming pressure of the first hydraulic fluid line 14a, into the second hydraulic fluid line 14b and further into a hydraulic fluid tank. Simultaneously the third cylinder space 13c, inside the piston rod 4b, increases in size. The hydraulic fluid fed into the line 14a affects, via the shuttle valve 21, the fourth hydraulic fluid line 15b, i.e. that of the swing cylinder 10, and further, via a non-return valve in its over-center valve 17b, the swing cylinder 10 in its cylinder space 18b. The hydraulic fluid pressure is transmitted via a piston 10a of the swing cylinder 10 to the cylinder space 18a and further via the over-center valve 17a, opened by the pressure in the line 15b, along the connecting line 19 to the cylinder space 13c of the piston rod 4a of the lift cylinder 4, whereat the pressure effect of the hydraulic fluid in the cylinder spaces 13a and 13c is parallel and thus facilitates the upward turning of the boom 1 in spite of its weight. Simultaneously, as the hydraulic fluid flows, it drives the piston 10a of the swing cylinder 10 outward from the swing cylinder 10 and consequently turns the feed beam 8 relative to the boom 1 as much as the lift cylinder 4 turns the boom 1 relative to the frame 2. 
     When the boom 1 is turned downward, hydraulic fluid is fed into the second cylinder space 13b of the lift cylinder 4, whereat the piston 4a is driven into the lift cylinder 4 and hydraulic fluid flows from the cylinder space 13a via the over-center valve 20a into a hydraulic fluid tank. Simultaneously, as the cylinder retracts, decreasing space causes pressure to the third cylinder space of the lift cylinder, and this pressure causes the hydraulic fluid to flow via the line 19 into the cylinder space 18a of the swing cylinder 10 thus shortening the swing cylinder 10. Correspondingly, hydraulic fluid flows from the second hydraulic fluid space 18b of the swing cylinder 10 via the pressure-controlled shuttle valve 21 opened by the pressure, in the hydraulic fluid line 14b, into a hydraulic fluid tank. In this way the force turning the boom 1 downward is weakened and the movement of the boom 1 becomes slower and controlled. With the piston 4a of the lift cylinder 4 receding into the cylinder, and thus the cylinder becoming shorter, the piston 10a of the swing cylinder 10 recedes therein, whereat the shortening of the whole swing cylinder corresponds to the change in the length of the lift cylinder 4, and thus the feed beam 8 turns as much as the boom 1 turns relative to the frame 2, and the feed beam is kept aligned. Simultaneously, hydraulic fluid flows from the second cylinder space 18b of the swing cylinder 10 via the over-center valve 17b, opened by the pressure from the line 19, and further via the pressure-controlled shuttle valve 21, opened by the pressure acting in the line 14b of the lift cylinder 4, into the line 14a and further into a hydraulic fluid tank. 
     If desired, the swing cylinder 10 may by turned for swinging the feed beam in another direction without turning the lift cylinder 4, by feeding hydraulic fluid into the third or fourth hydraulic fluid line 15a and 15b. In this case, when hydraulic fluid is fed into the line 15a, it flows through the non-return valve 16a and further through the over-center valve 17a into the cylinder space 18a, whereat the piston 10a penetrates into the cylinder 10. Similarly, hydraulic fluid flows from the cylinder space 18a through the over-center valve 17b, opened by the pressure of the hydraulic fluid incoming via the line 15a, and through the non-return valve 16b out via the line 15b and further into a hydraulic fluid tank. Similarly, when hydraulic fluid is fed into the line 15b, the reverse happens, whereat the piston 10a is expelled from the swing cylinder 10 and the discharging hydraulic fluid flows via the line 15a into a hydraulic fluid tank. The valves used for controlling both the lift cylinder 4 and the swing cylinder 10 are either on-off valves or proportional valves, generally known per se, by means of which the hydraulic fluid originating from a hydraulic fluid supply, such as a hydraulic fluid pump, may be directed into one of the lines simultaneously as the other line is in some manner connected to a non-pressure hydraulic fluid tank or to lower pressure. Such control valves and their function and use are also completely known per se and are therefore not described in any greater detail in this connection. 
     In the above description and in the drawings the invention has been described only by way of example, and it is by no means to be so restricted. Although only the vertical parallel action of the boom 1 and the arrangement needed for its realization is described in the description and the drawings, it is obvious that the same structure may suitably be applied also to controlling the horizontal movements and turning of the boom 1. It is further obvious that although no common security etc. valves are shown in the figures, they may be used in a manner known per se and be combined with the arrangement of the invention without changing the nature or idea of the invention. Input and pump solutions for hydraulic fluid may also be any kind of known solutions. 
     The cross-sectional area of the servo cylinder 4c in the lift cylinder 4 and the area of the piston connected to said cylinder space of the swing cylinder 10 do not need to be equal, as their travel lengths and cross-sectional areas may be dimensioned in different ways, provided the quantity of hydraulic fluid shifting and the dimensions of the triangles formed by the cylinder joints and swinging joints, i.e. triangles 4, 5, 6 and 7, 11, 12, respectively, are suitably similar so that a certain angle change between the boom 1 and the frame 2 results in an angle change of a corresponding width between the feed beam and the boom 1 to a reverse direction.