[0002] The invention also relates to an apparatus for monitoring the operation of a percussion device, which percussion device comprises a per- cussion piston and a pressure channel for supplying pressure medium to the percussion device for moving the percussion piston, and which apparatus comprises a sensor, arranged in connection with the pressure channel, meas- uring pressure pulsation of the pressure medium acting in the pressure chan- nel and depicting said pressure pulsation as a pressure curve.

[0003] The invention further relates to an arrangement for adjusting the operation of a percussion device, which percussion device comprises a percussion piston and a pressure channel for supplying pressure medium to the percussion device for moving the percussion piston, and which arrange- ment comprises a sensor, arranged in connection with the pressure channel, measuring pressure pulsation of the pressure medium acting in the pressure channel and depicting said pressure as a pressure curve.

[0004] When holes are drilled in a rock with a rock drill machine, the drilling conditions vary in different ways. Layers in the rock mass may vary in hardness, and therefore characteristics affecting the drilling should be adjusted according to drilling resistance. In the drilling, there are simultaneously four different functions in use: rotating the drill in a hole to be drilled, breaking the rock by hitting a drill shank with the percussion piston as well as drill feed and flushing, by which drilling waste is removed from the drilled hole. When rock is broken by striking the drill shank with the percussion piston, impact energy of the percussion piston is transmitted by means of drill rods, which convention- ally serve as extensions of the drill shank, to a drill bit which strikes on the rock making it break. The correct operation of the percussion device thus contrib- utes considerably to the good drilling result. Percussion hammers, in which a tool driven by the percussion device is arranged to break the surface to be broken, do not employ tool rotation nor flushing. It is mainly the operation of

the percussion device that affects the breakage result, if the effect of the tool characteristics is not taken into account. Essential variables for breaking the rock include length of an impact pulse, amplitude of the impact pulse, impact frequency and a suitable bit/rock contact. In practice, of these variables all oth- ers but the length of the impact pulse are adjustable ones.

[0005] However, it is very difficult to control the operation of the per- cussion device such that the best possible drilling or breakage result is achieved, because there has been no reliable solution for monitoring the op- eration of the percussion device. It is difficult to monitor the operation of the percussion device while the drill or the percussion hammer is running. At- tempts have been made to measure the position of the percussion piston with laser-operated or inductive sensoring solutions arranged in the percussion de- vice. US patent 4,699, 223 discloses use of an inductive sensor for measuring the position of a percussion piston. A problem with solutions based on sensors arranged in a percussion device is poor durability of sensors in the demanding conditions, in which the drills and the percussion hammers are used.

[0006] An object of the present invention is to provide a novel solu- tion for monitoring the operation of a percussion device.

[0007] The method of the invention is characterized by determining, from pressure pulsation, parameters depicting the operating state of a percus- sion device and determining the operating state of the percussion device on the basis of said parameters.

[0008] Further, the apparatus of the invention is characterized in that the apparatus further comprises an analyzing device which is arranged to determine parameters depicting the operating state of the percussion device from pressure pulsation and to determine the operating state of the percussion device on the basis of said parameters.

[0009] Further, the arrangement of the invention is characterized in that the arrangement comprises an analyzing device that is arranged to deter- mine parameters depicting the operating state of the percussion device from pressure pulsation and to determine the operating state of the percussion de- vice on the basis of said parameters and that the arrangement comprises a control unit that is arranged to control the operation of the percussion device on the basis of the operating state of the percussion device.

[0010] The basic idea of the invention is that for monitoring the op- eration of the percussion device, which comprises a percussion piston and a

pressure channel for supplying pressure medium to the percussion device for moving the percussion piston, pressure pulsation of the pressure medium act- ing in the pressure channel is measured, which pressure pulsation is depicted as a pressure curve, and parameters depicting the operating state of the per- cussion device are determined from the pressure curve, and the operating state of the percussion device is determined on the basis of said parameters.

In the present document the pressure curve refers to pressure pulsation that is measured at a sampling frequency that is substantially higher than the running frequency of the percussion device, whereby very fast pressure variations can be registered. Pressure pulsation is mainly generated by a reciprocating movement of the percussion piston, an impact of the percussion piston, a re- bound of the percussion piston and hydraulic control provided by a control valve of the percussion device. According to a first embodiment of the inven- tion the operating state of the percussion device is depicted on the basis of at least one of the following parameters: a position of the percussion piston in the percussion device, a piston stroke of the percussion piston, impact velocity of the percussion piston and rebound velocity of the percussion piston. According to a second embodiment of the invention the operating state of the percussion device is controlled on the basis of the parameters depicting the operating state of the percussion device. According to a third embodiment of the inven- tion the percussion device is arranged for use in a rock drill machine and an operating state of the percussion device is determined on the basis of the pa- rameters depicting the operating state of the rock drill machine.

[0011] The invention has an advantage that the operation of the percussion device can be monitored accurately and in real time, which further enables the adjustment of the operation of the percussion device on the basis of information obtained on one or more previous impacts. The pressure curve of the percussion device can be measured in a simple manner and the meas- urement can be carried out in the vicinity of the percussion device, or else- where, on a boom or base carrying the percussion device, whereby it will not be necessary to arrange any fault-prone sensors in the percussion device. Fur- ther, the pressure curve measurement and interpretation make it possible to monitor the trend of the percussion device state and to use it for monitoring the condition of the percussion device.

[0012] In the following the invention will be described in greater de- tail in connection with the attached drawings, wherein

Figure 1 is a schematic side view of a percussion device, partly cut open, to which the solution of the invention is applied; Figure 2 is a schematic view of a pressure curve of pressure me- dium acting in a pressure channel ; Figure 3 is a first pressure curve of a percussion device measured on a rock drill machine; Figure 4 is a second pressure curve of a percussion device meas- ured on a rock drill machine; Figure 5 is a third pressure curve of a percussion device measured on a rock drill machine; Figure 6 shows interdependence of the maximum tensile stress of a stress wave reflecting from the rock to be drilled, feed force and a variable rep- resenting the quality of feed; and Figure 7 shows interdependence of the maximum tensile stress of a stress wave reflecting from the rock to be drilled, feed force and a second vari- able representing the quality of feed.

[0013] Figure 1 is a schematic side view of a percussion device 1, partly cut open. The percussion device 1 comprises a frame 2 and a percus- sion piston 3. The percussion device 1 can be one employed in a drill or a per- cussion hammer. The percussion device 1 is hydraulically operated, and hy- draulic oil, bio-oil or water can be used as hydraulic or pressure fluid. Figure 1 further shows a pump 4 needed for driving the percussion device 1, which pump 4 pumps pressure fluid through a pressure channel 5, in the direction of arrow A, to the percussion device 1 in order to move the percussion piston 3 to the right in Figure 1, i. e. to perform a stroke. During a reverse stroke of the percussion piston 3 the pressure fluid returns to a tank 7 through a return channel 6 in the direction of arrow B. Figure 1 also shows a control valve 19 used for controlling the operation of the percussion device 1. The general structure and operating principle of the percussion device in the rock drill ma- chine or the percussion hammer are known per se to a person skilled in the art, so they need not be described in greater detail herein, and for the sake of clarity the structure of the percussion device 1 is only shown schematically in Figure 1.

[0014] Figure 1 further shows schematically a pressure sensor 8, which measures the pressure of the pressure fluid acting in the pressure chan- nel 5 and which is arranged in connection with the pressure channel 5 of the

percussion device 1. The measurement result obtained is the pressure curve 10 shown schematically in Figure 2 and representing impact pressure pulsa- tion or pressure pulse of the pressure medium acting in the pressure channel 5. The horizontal axis of Figure 2 represents time and the vertical axis repre- sents pressure. A measuring signal, which advantageously is a voltage signal, for instance, of the pressure sensor 8, corresponding to the pressure curve 10, is transmitted through a wire 11 to an analyzing device 9, where variables de- scribing the operating state of the percussion device 1 are determined from the measuring signal corresponding to the pressure curve 10. Parameters depict- ing the operating state of the percussion device 1 or correlating with the oper- ating state of a percussion device include the following parameters, for in- stance: t11 an impact moment, i. e. a moment when the percus- sion piston 3 strikes the drill shank of the rock drill or the tool of the breaking device, t12 back-timing of the control valve 19 of the percussion device 1, when the reverse movement of the percus- sion piston 3 starts decelerating, t13 a back dead centre of the percussion piston 3, when the percussion piston 3 changes its direction of mo- tion, t21 a next impact, Pi the minimum pressure of an impact cycle, i. e. the pressure in the pressure channel 5 at the impact mo- ment, P2 an impact pressure value at time instant tis, p3 the maximum pressure of an impact cycle, i. e. the pressure in the back dead centre.

[0015] For instance, the following auxiliary parameters depicting the operating state of the percussion device 1 can be determined from the above parameters: dt1 = t2-t a variable that is in proportion to the reverse velocity of the percussion piston 3 and to the distance the per-

cussion piston has travelled from the impact point. It is possible to use the variable indirectly for determining the impact point, i. e. the position of the percussion piston 3 at the impact moment and also for identifying the rock type. dt3 = t21-t13 a parameter relating to the impact velocity, ttot = t21-t11 the time of an impact period, i. e. the inverse of run- ning frequency f, x = (P2-P1)/ (P3-P1) a ratio relating to the piston stroke length, which can be used for adjusting the im- pact point, for instance.

[0016] On the basis of the parameters depicting the operating state of the percussion device 1 or the auxiliary parameters determined therefrom it is possible to determine the operating state of the percussion device 1. For instance, the operating state of the percussion device 1 can be depicted by one or more of the following variables: position of the percussion piston 3 in the percussion device 1, piston stroke length of the percussion piston 3, impact velocity, rebound velocity, running frequency of the percussion device 1, or statistical parameters obtainable of the same.

[0017] The parameters depicting the operating state of the percus- sion device 1 or auxiliary parameters determined therefrom and thus the oper- ating state of the percussion device 1 can be used for determining the drilling conditions. The drilling conditions refer to a drilling state, which is affected by the rock to be drilled, drilling equipment used and drilling parameters, such as impact power, feed force, rotating torque and flushing pressure, the measur- able variables directly proportional to them being impact pressure, feed pres- sure, rotating pressure and flushing pressure.

[0018] Thanks to the solution the operation of the percussion device 1 can be monitored accurately and in real time. This also enables the control of the operation of the percussion device 1 in real time on the basis of the pa- rameters depicting the operating state of the percussion device 1 and obtained from one or more previous impacts, and thus on the basis of the operating

state of the percussion device 1. The pressure curve 10 of the percussion de- vice 1 can be measured in a simple manner. It is not necessary to arrange any fault-prone sensors in the percussion device 1, but the measurement can be carried out in the vicinity of the percussion device, or elsewhere, on a boom or base carrying the percussion device. The pressure curve 10 measurement and interpretation make it possible to monitor the trend of the percussion device state and use it for monitoring the condition of the percussion device 1 and the whole rock drill or percussion hammer, for instance, in situations where the pressure curve 10 changes as pre-charge of the rock drill or the percussion hammer accumulator changes or as the accumulator diaphragm breaks or in situations where the pressure curve 10 changes as the rock drill shank wears.

[0019] Figure 3 shows a percussion device pressure curve 12 measured from a rock drill. The pressure curve 12 is measured in a situation where the drilling conditions have remained substantially constant. Figure 3 also shows a point that corresponds to the minimum pressure of the impact cycle, i. e. pressure pi in the pressure channel 5 at an impact moment, a point corresponding to an impact pressure value P2 at a time instant t12 and a point corresponding to the maximum pressure p3 of the impact cycle, i. e. the pres- sure at the back dead centre. Figure 4, in turn, shows a percussion device pressure curve 13 measured from a rock drill, when it hits a void. In the situa- tion of Figure 4 the parameter dt1 corresponding to linear momentum of the percussion piston and the parameter x corresponding to the piston stroke length have increased, because feed resistance has decreased. When the pa- rameters dt1 and x rise to a sufficiently high level, it indicates that the rock drill has hit a void, as has happened in the case of Figure 4. Figure 5 shows yet another percussion device pressure curve 14 measured from a rock drill in a situation, where transfer from underfeed to sufficient feed has taken place by increasing the feed. The underfeed was detected on the basis of the parame- ter x.

[0020] Figure 6 shows the maximum tensile stress 15 of a stress wave reflected from the rock to be drilled, feed force 16 and a parameter x in- dicated by curve 17 as measured from a rock drill. On the basis of the parame- ter x it is possible to determine whether the impact energy is excessive in rela- tion to the feed pressure. When the feed is sufficient, the tensile stresses do not decrease substantially and the value of the parameter x stabilizes. The level of the tensile stress indicates the actual quality of drilling. Because it is

very difficult to measure the tensile stress during the drilling, the same objec- tive will be achieved by means the parameter x.

[0021] Figure 7 shows the maximum tensile stress 15 of a stress wave reflected from the rock to be drilled, feed force 16 and moving standard deviation 18 of the impact frequency determined from the pressure curve of the percussion device pressure fluid as measured from a rock drill. It appears from Figure 7 that, when the feed force is increased and when it has reached a given value, a drilling situation is achieved which corresponds to sufficient feed and in which the tensile stresses will not substantially decrease. This can also be detected by the fact that the moving standard deviation 18 value of the fre- quency stabilizes.

[0022] Figure 1 also shows a control unit 20, which is arranged to control the operating state of the percussion device 1 on the basis of the per- cussion device operating state determined in the analyzing device 9. The op- erating state of the percussion device 1 is conveyed from the analyzing device 9 to the control unit 20. Instead of being two separate units, the analyzing de- vice 9 and the control unit 20 can be integrated into one device or unit. In Fig- ure 1, the control unit 20 is arranged to control the operation of the pump 4, for instance, by changing the rotating speed or cycle volume of the pump 4. In- stead of or in addition to the pump 4 control, it is also possible to control the operation of the percussion device 1 in a variety of ways, for instance, by con- trolling the operation of the control valve 19. It is also possible to control the operating state of the percussion device 1, for instance, by controlling the feed force as described in connection with Figures 6 and 7.

[0023] The drawings and the relating description are only intended to illustrate the inventive idea. The details of the invention may vary within the scope of the claims. Hence, the percussion device 1 can also be operated by compressed air, whereby air, and not pressure liquid, is used as pressure me- dium, and the pump 4 can be replaced by a compressor and return air can be discharged directly into ambient air. Further, it should be noted that the pres- sure curve pulsation may vary, for instance, due to various pressure losses as hydraulic tubing is changed.