CA3196426A1 - Method and system for optimising a drilling parameter during an ongoing drilling process - Google Patents

Abstract

The present invention relates to a method for optimising at least one drilling parameter during an ongoing drilling process, the drilling being carried out by a percussive drilling machine, the drilling machine being set to drill at an operating point, the operating point of the drilling being determined by the setting of a plurality of control parameters.The method comprises determining a first plurality of drilling machine operating points, the operating points being set by said plurality of control parameters. Furthermore, percussive drilling is performed at each of said first plurality of operating points and at least one resulting drilling parameter is evaluated for each of the plurality of operating points. The method also comprises determining a new plurality of drilling machine operating points to be drilled based on said evaluation, and subsequently drilling the new plurality of drilling machine operating points.

Description

METHOD AND SYSTEM FOR OPTIMISING A DRILLING PARAMETER DURING
AN ONGOING DRILLING PROCESS
Field of the invention The present invention relates to percussive rock drilling, and, more specifically, to a method for optimising at least one drilling parameter during an ongoing drilling process. The invention also relates a system that implements the method according to the invention, as well as a rock drilling rig comprising such a system.
Background of the invention Rock drilling rigs may be used in a number of areas of application. For example, rock drilling rigs may be utilised in tunnelling, surface mining, underground mining, rock reinforcement, raise boring, and be used e.g. for drilling blast holes, grout holes, holes for installing rock bolts, water wells and other wells, piling and foundations drilling etc. There is hence a vast use for rock drilling rigs.
The actual breaking of the rock is oftentimes carried out by a drill bit contacting the rock, where the drill bit is connected to a drilling machine, in general by means of a drill string. The drilling can be accomplished in various ways, and e.g. be of a percussive type, where, for example, a percussion element, e.g. in the form of a percussion piston, of a drilling machine repeatedly strikes the drill bit, oftentimes by striking a drill string connecting the drill bit to the drilling machine, to transfer percussive pulses in the form of shock waves, i.e. stress waves, to the drill bit and further into the rock. Percussive drilling may be combined with rotation in order to obtain a drilling where buttons, inserts, of the drill bit strikes fresh rock at each stroke, thereby increasing the efficiency of the drilling.
The drill bit may be pressed against the rock by means of a feed force during drilling to ensure that as much impact energy as possible from the percussion device is transmitted to the rock.
In order to obtain an efficient percussion drilling process, it is important that the various drilling parameters are set such that the percussive drilling is carried out in a way that allows as much as possible of the shock wave energy being induced by the percussion element into the drill string is transferred into the rock for breaking

2 thereof. In this way an efficient breaking of the rock may be obtained. In case a too low shock wave energy is transmitted by the impacts of the percussion element this may have negative impacts on the productivity in the drilling. Also, harmful reflections may also occur in case the shock wave energy is too low in relation to the force by means of which the drill string is pressed against the rock, and/or too low to break the rock. This is also the case when the shock wave contains more energy than is required to break the rock.
In case the drill bit is not firmly pressed against the rock the energy may be reflected to an undesirable extent and return to the drilling machine to potentially cause excessive wear or damage. This is also the case if the joints of the drill string are not sufficiently tightened.
Summary of the invention An object of the invention is to provide a method and system that is capable of optimising at least one drilling parameter during an ongoing drilling process.
According to the present invention, it is provided a method for optimising at least one drilling parameter during an ongoing drilling process. The drilling is carried out by a percussive drilling machine. The drilling machine is set to drill at an operating point, where the operating point of the drilling is determined by the setting of a plurality of control parameters.
The method comprises determining a first plurality of drilling machine operating points to be drilled, the operating points being set by said plurality of control parameters. Furthermore, percussive drilling is performed at each of said first plurality of operating points, and at least one resulting drilling parameter is evaluated for each of the plurality of operating points. The method also comprises determining a new plurality of drilling machine operating points to be drilled based on said evaluation, and subsequently drilling the new plurality of drilling machine operating points.
With regard to the terms "optimisation", "optimising" etc. it is to be understood that optimisation of drilling is the finding of a better operating point than the operating point at which drilling is currently carried out. Optimisation according to the invention

3 is hence a search for a better operating point than a current operating point from a resulting drilling parameter point of view, such as e.g. drill rate.
With regard to rock drilling there exist in general a requirement for efficient drilling, where the efficiency is often measured in productivity, and where the drill rate, i.e. the unit distance per unit time at which the drilling is carried out may form a measure of such productivity. However, while a high productivity is desirable, it must also be ensured that drilling is carried out in a manner that does not unnecessarily subject the drill rig to excessive wear that may cause damages. Drill rigs are oftentimes manually operated, and this imposes a large responsibility on the operator in regard of the result of the drilling. An inexperienced driller may cause ineffective drilling resulting in poor production while simultaneously subjecting the drill rig to excess wear. An experienced driller on the other hand, may control drilling in a manner where a high productivity is obtained while still preserving the drill rig in terms of wear. Drill rigs may also be automatically controlled, where the automatic operation will rely to a large extent on drilling using control parameter settings that initially originates from settings made by an experienced driller or that empirically have been considered to provide efficient drilling.
With regard to productivity and wear, it is in general the case that efficient drilling is obtained when shock waves containing as much energy as possible are transmitted through the drill string to the rock being drilled without large parts of the shock wave energies being reflected back to the drilling machine. Another important factor is that the, normally threaded, joints of the drill string are kept firmly tightened, since otherwise further reflections occur and which deteriorates the drilling. Loose joints also generate heat that both is a loss of energy and that in itself may be harmful to drill string components.
According to the invention, problems caused by less optimal drilling may be mitigated by a system and method where a first plurality of drilling machine operating points are determined, where the drilling machine is set to successively perform drilling at these operating points, and where the drilling machine is set to operate at a particular operating point by setting a plurality of control parameters controlling the drilling.
These control parameters may differ in dependence of the type of drilling technology

4 PCT/SE2021/051187 being utilised, and may with regard to a hydraulically driven drilling process comprise at least two of: a representation of a percussion pressure, a representation of a feed pressure, a representation of a rotation speed of the drill string, a representation of the flush flow being utilised to flush drilling remnants out of a hole being drilled. A
representation of a hydraulic flow may also be utilised in place of, or as, one or more of the representations of pressures stated above.
In case the drilling process is pneumatically driven, or driven by electrical means, corresponding control parameters are utilised to set the drilling machine to operate at a particular operating point.
According to the invention, drilling is performed at each of the determined plurality of operating points, and at least one resulting drilling parameter is evaluated for each of the plurality of operating points, that is, a parameter being a result of the drilling is evaluated. A new plurality of operating points is then determined based on this evaluation, where the new plurality of operating points may be selected based on the already drilled operating point that was deemed to exhibit the most optimal drilling result of the operating points being drilled, i.e. the most optimal result with regard to the at least one resulting drilling parameter that is evaluated. The new plurality of drilling machine operating points are then drilled and a new evaluation can be made, whereupon a further new set of operating points can be determined based on the operating point that currently is considered to be the most optimal. The resulting drilling parameter on which the evaluation is based may e.g. be the drill rate, where the drilling may be considered more optimal the higher the drill rate is, but may also consist of other, or further, drilling parameters as discussed below.
Operating points may be continuously determined and evaluated during drilling with regard to the at least one resulting drilling parameter for which evaluation is performed, and new sets of operating points may continuously be selected based on the operating point that at present is considered the most optimal. Values of at least one control parameter may be increased and/or decreased when determining the plurality of operating points to be drilled.
The drilling may hence be subjected to a constantly ongoing optimisation, at least until a more optimal operating point than an already evaluated operating point no longer can be identified, in which case drilling can be set to operate at this operating point. According to embodiments of the invention, the optimisation is constantly ongoing during drilling.
In this way, the drill rig can be automatically arranged to control drilling in a manner

5 where an optimal operating point will be identified essentially independent from the start values of the control parameters, since the optimisation according to the invention will strive towards more and more optimal drilling, where the optimisation is performed while drilling is ongoing. This means that when a drill rig is controlled e.g.
by an inexperienced drill rig operator, which may set the drill rig to drill at unfavourable settings, the control according to the invention may mitigate the inexperience of the drill rig operator to a large extent by optimising the settings according to the invention. The invention is also useful in automated drilling where the automated drilling can be optimised, and this is also the case where an experienced drill rig operator controls the drilling, since according to the invention evaluations may continuously be performed to further optimise the drilling.
According to embodiments of the invention, each operating point may be drilled for a predetermined period of time, e.g. in the interval 1-10 s, and/or a predetermined number of impacts, e.g. 50-300 impacts, by the percussion element of the drilling machine prior to switching to the subsequent operating point to be drilled. In this way, drilling may be carried out sufficiently long to allow proper evaluation of the operating point while simultaneously drilling is not carried out for too long in case it would be more favourable to drill at other operating points.
According to embodiments of the invention, the method further comprises, when evaluating the drilled plurality of operating points, evaluating a plurality of resulting drilling parameters for each of the plurality of operating points. As was mentioned, the drill rate is oftentimes an important factor, and which in general is to be maximised.
However, as discussed above, there are situations that may arise and that may be potentially harmful to the drill rig. This includes situations where the impacts of the percussion element gives rise to loose joints, and/or where the impacts occur when the drill string is too firmly pressed against the rock in relation to the energy being transferred to the drill string by the percussion element, and/or where impacts occur

6 when the drill string has poor or non-existent contact with the rock.
Therefore, according to embodiments of the invention, further parameters, in particular parameters being a result of the current settings of the control parameters, may be taken into account when evaluating an operating point being drilled. Such resulting drilling parameters may also impose penalties to the result, and which may thereby render an operating point exhibiting a high drill rate less optimal than an operating point exhibiting a lower drill rate, but also being less penalised. A further example of a parameter that may be taken into account is the energy consumption of the drill rig, where an operating point of the drill rig where the drill rate is e.g. the same but energy consumption is lower is in general more optimal in relation to an operating point having the same drill rate but higher energy consumption.
According to embodiments of the invention, different weights and/or priorities are assigned to the plurality of drilling parameters in the evaluation. In this way the most important drilling parameter, such as drill rate, may be given a higher priority than e.g. energy consumption. Priorities may also be given to drilling parameters that may impose penalties to the result, where e.g. an operating point exhibiting e.g.
a high drill rate may be deemed not to be used in case penalties are high.
According to embodiments of the invention, the method further comprises, when determining the new plurality of drilling machine operating points: selecting the new plurality of operating points starting from a drilling machine operating point of the already drilled plurality of drilling machine operating points that is considered the most optimal operating point of the drilled plurality of operating points. In this way drilling can be continuously improved by finding more and more optimal operating points, the drilling thereby converging towards an optimum.
According to embodiments of the invention, the optimisation is continued at least for as long as a more optimal drilling machine operating point is identified. In case the drilling cannot be further optimised drilling can be arranged to be carried out using the operating point that has been considered the most optimal.
According to embodiments of the invention, when a point that has been considered the most optimal has been found, further operating points may be selected where the control parameters are varied in various degrees. This may be performed to

7 determine whether the optimum that has been located is only a local optimum or a more general optimum given the constraints that the drilling using the drill rig is subjected to in terms of maximum and minimum values etc.
According to embodiments of the invention, in case an evaluation of a drilled plurality of operating points does not identify a more optimal operating point in relation to the operating point from which the drilled plurality of operating points was determined, at least one further plurality of operating points to be drilled may be determined from a previously drilled operating point. According to embodiments of the invention, in such situations, operating points may also be determined from a previously drilled operating point that has not formed basis for determining a new set of operating points. For example, there may exist an operating point that has exhibited essentially the same result as an operating point that has been used to determine further operating points to be drilled, and which may therefore be utilised to generate new operating points to be drilled.
According to embodiments of the invention, a drilling machine operating point may be evaluated while the operating point is being drilled, and it may be determined whether drilling at the operating point being evaluated is to be aborted prior to finishing the predetermined number of percussions and/or period of time of drilling.
For example, it may be determined whether drilling at the operating point gives rise to penalties such as harmful reflections and/or loose joints according to the above, and/or the drill bit becoming jammed, in which case drilling at the operating point may be aborted, and instead switched to drilling a previously drilled operating point, or an operating point that is subsequently to be drilled.
According to embodiments of the invention, at least one resulting drilling parameter, such as reflections or loose joints, may be determined by measuring a reflected stress wave caused by an incident stress wave generated by at least one percussive impact by the impact device of the drilling machine on a drill string of the drill rig.
The result on the at least one drilling parameter may be arranged to be estimated for each stroke by the percussion piston, where the length of the shock wave may be in the order of 200 pS and travel through the drill steel at a velocity of e.g.
5000 m/s.

8 The percussions of the percussion piston typically take place at a percussion frequency of 30-120Hz in dependence of the particular drilling machine being used.
A sensor may be utilised which may be in contact with the drill string or a sensor that perform contactless measuring of the stress wave in the drill string using a sensor arranged in the immediate vicinity of the drill string. Such contactless sensors may e.g. operate according to a principle based on measuring changes in the magnetization of the drill string in response to the stress wave travelling in the drill string. A variety of different suitable sensors or sensor combinations of this kind are known to the person skilled in the art of the rock drilling and are therefore not discussed in detail herein.
It is also contemplated that data such as shock waves and control parameter values as well as resulting drilling parameters may be collected during drilling, so that harmful shockwaves may be correlated with particular parameter values. Such data may then be used to identify potentially harmful reflections without actually utilising a shock wave sensor.
According to embodiments of the invention, the method further comprises, when drilling is to be performed at a particular operating point, determining the control parameter settings to be used when drilling at the particular operating point and setting the drilling control parameters to the determined control parameter settings prior to performing drilling at the particular operating point.
According to embodiments of the invention, it may be determined whether a difference in control parameter values between operating points is to be increased or decreased prior to generating a new plurality of operating points. For example, in case operating points of a plurality of operating points that have just been drilled exhibits similar results in the evaluation, the difference in control parameter values for a subsequent plurality of operating points may be increased to allow faster detection of operating points that may be more optimal than a current operating point.
Conversely the difference can be decreased in case there is a large variation in the obtained results, and also in case drilling appears to be close to an optimum point.
According to embodiments of the invention, when drilling is commenced, an initial operating point from which the operating points to be drilled may be determined as

9 an operating point previously being used as an optimal operating point in an earlier drilling session or an empirically determined operating point or an operator initiated operating point. The initial operating point may e.g. also be selected as a previous operating point that have been found to be an optimal point when drilling another hole at a similar depth at a similar position, which e.g. may be determined using any suitable positioning method of the drill rig.
According to embodiments of the invention, the method further comprises optimising drilling by maximising at least one drilling parameter such as drill rate and/or minimising at least one drilling parameter such as power consumption while maintaining a high drill rate. Furthermore, impacts resulting in harmful reflections may also be minimised.
According to embodiments of the invention, the method further comprises respecting maximum and/or minimum limitations of the at least one drilling parameter when determining a subsequent plurality of operating points to be drilled to avoid subjecting the drill rig to harm by exceeding limitations and using operating points at which the drill rig is not designed to operate.
It will be appreciated that the embodiments described in relation to the method aspect of the present invention are all applicable also for the system aspect of the present invention. That is, the system may be configured to perform the method as defined in any of the above described embodiments. Further, the method may be a computer implemented method which e.g. may be implemented in one or more control units of a drill rig.
Further characteristics of the present invention and advantages thereof are indicated in the detailed description of exemplary embodiments set out below and the attached drawings.
Brief description of the drawings Fig. 1 illustrates an exemplary drill rig in which embodiments of the invention may be utilised;
Fig. 2 illustrates a schematical overview of optimisation control according to embodiments of the invention;

Fig. 3 illustrates an exemplary method according to embodiments of the invention;
Fig. 4 illustrates an exemplary result when optimising drilling according to embodiments of the invention.
Fig. 5 illustrates the result of the optimisation process according to fig. 4.
5 Detailed description of exemplary embodiments Embodiments of the present invention will be exemplified in the following in view of a particular kind of drill rig, where drilling is carried out through the use of a percussion device in the form of a top hammer. The drill rig may also be of any other kind where drilling is carried out through the use of a hydraulic percussion device for transmitting

10 stress waves into a drill tool for breaking rock. The invention is also applicable for drill rigs comprising other kinds of percussive drilling machines than hydraulically driven drilling machines, such as drilling machines operated by electrical or pneumatical means.
Fig. 1 illustrates a rock drilling rig 100 according to an exemplary embodiment of the present invention for which an inventive method of optimising at least one drilling parameter during an ongoing drilling process will be described. The drill rig 100 is in the process of drilling a hole, where the drilling currently has reached a depth x.
The rock drilling rig 100 according to the present example constitutes a surface drill rig, although it is to be understood that the drill rig may also be of a type being primarily intended e.g. for underground drilling, or a percussive drill rig for any other use. The rock drilling rig 100 comprises a carrier 101, which carries a boom 102 in a conventional manner. Furthermore, a feed beam 103 is attached to the boom 102.

The feed beam 103 carries a carriage 104, which is slidably arranged along the feed beam 103 to allow the carriage 104 to run along the feed beam 103. The carriage 104, in turn, carries a percussion device (drilling machine) 105, e.g. also comprising a rotation unit (not shown, but the rotation is indicated by 117), which hence may run along the feed beam 103 by sliding the carriage 104.
The percussion device 105 is, in use, connected to a drill tool, such as a drill bit 106, according to the present example, by means of a drill string 107. For practical reasons (except possibly for very short holes) the drill string 107 in general does not

11 consist of a drill string in one piece, but consists, in general, of a number of drill rods.
When drilling has progressed a distance corresponding to a drill rod length, a new drill rod is threaded together with the one or more drill rods that already has been threaded together to form the drill string, whereby drilling can progress for another drill rod length before a new drill rod is threaded together with existing drill rods. This is illustrated by drill rods 202-204, which are joined together by threaded joints 206, 207. The drill bit 106 is joined with drill rod 204 by means of a threaded joint 208.
Furthermore, the percussion device 105 comprises a drill shank (not shown) on which a percussion element in the form of a percussion piston 115 strikes, and which is connected to drill rod 202 through threaded joint 205. Drill rods of the disclosed kind may be extended essentially to any desired length as drilling progress.
In use, the percussion piston 115 of the percussion device 105 repeatedly strikes the drill shank and thereby the drill rod in order to transfer shock wave energy to the drill string 107 and thereby the drill bit 106 and further into the rock for breaking thereof.
In addition to providing rotation of the drill string, and thereby drill bit 106 during drilling, the percussion device 105, and/or carriage 104, by being subjected to a force acting in the drilling direction, also provides a feed force acting on the drill string 107 to thereby press the drill bit 106 against the rock face being drilled.
According to the illustrated example, the percussion device 105, in particular the percussion piston 115, is powered by pressurised hydraulic fluid being supplied to the percussion device by a hydraulic pump 116 arranged on the carrier 101 and suitable hosing 118. The carrier 101 also comprises a hydraulic fluid tank 119 from which hydraulic fluid is taken and returned to using the hydraulic circuit powering the percussion device. There may be further hydraulic pumps being used to provide pressurised hydraulic fluid in one or more additional hydraulic circuits, such as e.g. a damping circuit.
According to the illustrated example, compressed air is led to the drill bit 106 through a channel (not shown) inside the drill string 107, where the compressed air is supplied to the drill string 107 from a tank 109 through a suitable coupling 110 in a manner known per se, and a hose 113 or other suitable means. The compressed air is generated by a compressor (not shown), which may charge the tank 109 from

12 which the compressed air is supplied to the drill string. The compressed air may be discharged through holes in the drill bit 106 to be used to clean the drill hole from drilling remnants. The compressed air may alternatively e.g. be a mixture of compressed air and water, or of any other suitable kind. With regard to in particular surface drilling, the power consumption of the flushing system may be substantial and constitute a large part of the total power consumption of the drill rig.
The applied flush flow may hence be a control parameter that it is desired to optimise by minimising according to embodiments of the invention.
The hydraulic pump 116 and other power consumers such as the compressor are driven by a power source 111, e.g. in the form of a combustion engine such as a diesel engine or any other suitable power source, such as e.g. an electric motor, or combination of power sources. Fig. 1 also illustrates a sensor 209 being used to measure stress waves being induced into the drill string by the percussion piston 115 and reflections occurring at various locations in the drill string and when the stress wave strikes the rock. As was mentioned above, the sensor 209 may e.g. operate according to a principle based on measuring changes in the magnetization of the drill string in response to the stress wave travelling in the drill string, where various such sensors are known in the art. For example, sensors as exemplified in any of the documents EP 2811110 Al, EP 3266975 BI, WO 2007/082997 Al, US 6,640,205 B2, US 7114576 B2, WO 2017/217905 Al may be utilised when performing estimations according to the invention. A drill rig of the disclosed kind also comprises e.g. various pressure sensors in a manner known per se in order to measure e.g. the pressure in the supply path providing pressurised hydraulic fluid to the percussion piston 115 and the pressure of e.g. a feed mechanism that presses the drill string against the rock during drilling.
The rock drilling rig 100 further comprises a rig control system comprising at least one control unit 120. The control unit 120 is configured to control various of the functions of the drill rig 100, such as controlling the drilling process. In case the drill rig 100 is manually operated, the control unit 120 may receive control signals from the operator, e.g. being present in an operator cabin 114 through operator controllable means such as joysticks and other means requesting various actions to

13 be taken, and where the control signals, such as operator inflicted joystick deflections and/or manoeuvring of other means, may be translated by the control system to suitable control commands. The control unit 120 may, for example, be configured to request motions to be carried out by various actuators such as cylinders/motors/pumps etc., e.g. for manoeuvring boom 102, feeder 103 and controlling the percussion device 105, and various other functions. The described control, as well as other functions, may alternatively be partly or fully autonomously controlled by the control unit 120.
Drill rigs of the disclosed kind may also comprise more than one control unit, e.g. a plurality of control units, where each control unit, respectively, may be arranged to be responsible for monitoring and carrying out various functions of the drill rig 100. For reasons of simplicity, however, it will be assumed in the following that the various functions are controlled by the control unit 120. Such control systems may further utilise any suitable kind of data bus to allow communication between various units of the machine 100. In case the drill rig 100 is manoeuvred by an operator various data may be displayed e.g. on one or more displays in the operator cabin 114.
According to embodiments of the invention, the method for optimising at least one drilling parameter is performed by a control unit of the drill rig, such as control unit 120 of fig. 1, but the optimisation may also be configured to be carried out in any suitable location.
As was discussed above, the present invention relates to a method for optimising a drilling process while drilling is ongoing. A schematic principle according to the invention is shown in fig. 2 where an exemplary representation of parameters that may take part in the optimisation according to embodiments of the invention is illustrated. Embodiments of the invention will be illustrated in the following according to an example where the optimization is controlled in order to obtain as high drill rate as possible while simultaneously avoiding operating points that result in conditions that may be detrimental over time. This is illustrated in fig. 2 as the drill rate being an input drilling parameter which is to be maximised. The illustrated example further uses drilling control parameters in the form of percussion pressure and feed pressure which are varied in order to optimise the drill rate.

14 There are also penalty drilling parameters input into the control. As was explained, even though the drill rate may be high a particular operating point may still be undesirable. This relates, for example, to loose joints where e.g. an indication of one or more loose joints may be used to determine that an operating point giving rise to a high drill rate may still be undesirable. This also relates to impacts with poor or non-existent rock contact, in which case a high portion of the initial impact energy will be reflected and returned to the drilling machine. Similarly, when the drill string is too firmly pressed against the rock, the impact energy many not be sufficient to break the rock and will therefore also be reflected back towards the drilling machine.
These parameters are therefore illustrated in fig. 2 as penalty parameters, where e.g. a number of occurrences during a predetermined time or number of impacts by the percussion element may be used as an indication that the particular operating point should not be utilised. The control according to the invention will be explained further with reference to fig. 3, in which a basic search method is utilised to optimise the drilling. This, however, only constitutes an exemplary method, and any other suitable method, such as e.g. simplex algorithm optimisation or any other optimisation algorithm may be utilised.
Furthermore, according to the below example, two control parameters, i.e.
percussion pressure and feed pressure are utilised to control the drilling. As is indicated in fig. 2, further control parameters may be utilised, such as e.g.
rotation speed and flush flow, which also constitutes a parameter that it is desirable to minimise. As was mentioned above, in particular with regard to surface drilling the flush flow may constitute a substantial part of the overall power consumption of the drill rig. Furthermore, if the power consumption can be reduced while maintaining a high drill rate a lower power consumption will naturally be considered as more optimal than a higher power consumption for the same drill rate. With regard to the example of fig. 2 the optimisation hence strives to reach as high drill rate as possible, where this is performed by controlling percussion pressure and feed pressure (and optionally flush flow and/or rotation pressure). These parameters are in general also subject to maximum and minimum limits that must be respected as described below.

The drilling machine is set to drill at an operating point, where the operating point of the drilling is determined by the setting of a plurality of control parameters. The control parameters may e.g. be rotation pressure, percussion pressure, and feed pressure.
5 An exemplary method 300 according to embodiments of the invention will be discussed in the following with reference to fig. 3. The method 300 is performed to optimise at least one drilling parameter during an ongoing drilling process carried out by a percussive drilling machine, such as e.g. the rock drilling rig shown in fig. 1.
With regard to the exemplary method of fig. 3, the method starts in step 301 where it 10 is determined whether drilling is to be carried out according to the automatic drilling optimization according to embodiments of the invention. According to embodiments of the invention, this may be arranged to be carried out as soon as drilling is commenced, i.e irrespective of whether drilling of a new hole is commenced or whether an ongoing hole is continued, e.g. following the adding of a drill rod. The use

15 of the optimisation may also be arranged to be selectable e.g. by an operator of the drill rig in case it sometimes would be desirable to perform the drilling in a manual manner. It is contemplated, however, that automatic optimisation will be used essentially all the time when drilling is in progress.
When drilling optimisation according to the invention is to be carried out the method continues to step 302, where initial settings for the optimisation are determined. The initial settings may include, for example, to set the control parameters (percussion pressure and feed pressure according to the present example) to initial values which hence represents an initial operating point of the drilling.
The initial operating point may e.g. be an operating point that has been found to be most optimal for of a previously drilled hole or e.g. control parameters that has previously been determined as providing efficient drilling. In case a hole has been recently drilled parameters that was found optimal when drilling this hole may advantageously be utilized. Alternatively, for example, stored parameters of a previous drilling may be utilized where e.g. the type of rock may be input by an operator to select parameters that has previously been considered to provide desirable results. The initial operating points may also be predetermined, e.g

16 empirically determined, and stored during manufacturing of the drill rig.
According to embodiments of the invention the initial settings may also be obtained as set by an operator.
The method then continues to step 303 where a "box" is generated, which defines a set of operating points that are to be drilled and evaluated in relation to the initial operating point. The initial operating point will be replaced by the currently most optimal operating point which will change as optimisation progress according to the below.
When determining the operating points to be drilled in step 303, these are determined taking into account a difference in parameter values in relation to the initial operating point of the particular parameters being controlled, i.e.
percussion pressure and feed pressure according to the present example. That is, when determining the set of operating points to be drilled for subsequent evaluation, the operating points will have differing values in at least one of the control parameters by means of which the drilling is controlled. The operating points to be drilled may be arranged to differ in one or more of such drilling control parameters.
According to the present example, there are two control parameters, and four operating points are defined, where each control parameter is allowed to be increased and decreased in relation to the initial operating point, thereby generating four operating points.
According to embodiments of the invention, further operating points may be defined, and parameter values need not both be increased and decreased in relation to the initial value. In case three control parameters are utilised, this may give rise to eight operating points if all possible combinations of increased and decreased values are utilised. Similarly, four control parameters give rise to 16 operating points using this particular method. However, it is to be noted that any number of operating points may be determined, i.e. both a higher and a lower number may be utilised. The allowable difference in value of a specific control parameter, where the allowable difference may be arranged to vary during optimisation, define the "box" within which the set of operating points will be selected.
According to the present example, since the operating points are determined by varying two control parameters, i.e. percussion pressure and feed pressure, different

17 percussion pressures and/or different feed pressures are utilized in the set of operating points that are to be drilled, and the box represents a two-dimensional area according to the illustrated example.
The possible further control parameters may, for example, be a rotation pressure or flush flow as mentioned above.
It is further to be noted that the invention is exemplified herein with regard to a hydraulic drilling system where in particular pressures are controlled. As was discussed above, e.g. flows may be controlled instead, and in case drilling is carried out using any other drilling technology, such as electrical drilling or pneumatic drilling, any other suitable control parameter may be controlled and altered in the same manner as is discussed for feed pressure and rotation pressure herein. It is also to be noted that hydraulic flows may be utilised in place of one or more of percussion pressure, feed pressure, rotation pressure.
Hence in step 303 the operating points to be drilled are determined with a separation between the drilling control parameters for the settings to be drilled. This separation, or difference, may, as will be explained below, be arranged to be increased or decreased as drilling progress. According to embodiments of the invention, drilling may begin utilising a large difference between parameter values and then select the most promising of the relatively largely spaced operating points. The spacing between individual operating points may then be, e.g. gradually, decreased to allow optimisation about the most promising operating point. Conversely, the spacing between control parameters may also be arranged to be increased in case, for example, essentially the same results are obtained for a drilled set of operating points. It is also possible to determine gradients. If, for example the optimisation tend to go in a particular direction the box may be selected e.g. with points only in that direction.
Furthermore, when generating the box in step 303 maximum and minimum limits for drilling control parameters may be used to ensure that the machine is not set to be drilled utilizing parameters that deviate e.g. from the maximum and minimum allowed values from a constructional point of view. Such limits may include maximum and minimum percussion pressures, maximum and minimum feed pressure, maximum

18 and minimum rotation pressure etc. Such maximum and minimum values may be predetermined e.g. in order to ensure that components are not subjected to higher stress and strain than they are designed for. In addition to, or as an alternative to having maximum and minimum limits on pressures the limitations may also relate to other corresponding parameters such as e.g. hydraulic flows. Also, in case the drilling is not performed using a hydraulic drilling machine, similar limitations may in general be utilized for the particular drilling technology being used.
When the operating points to be drilled have been determined, the method continues to step 304 where it is determined which operating point that is to be drilled. This selection may be performed, for example by selecting lower values of drilling control parameters first, higher values of drilling control parameters first. The order of drilling may also be randomized. When an operating point to be drilled has been determined, the operating point is drilled in step 305.
In step 305 the particular parameters according to which drilling is to be carried out are first provided to the rig control system (RCS) or the part of the rig control system performing the actual drilling in case the determinations According to embodiments of the invention are also performed in the rig control system as the case may be.
When the drilling control parameters to be utilized has been provided to the rig control system, a predetermined period of time may be allowed to lapse in order to ensure that the desired parameter values are set such that drilling is actually carried out using the intended parameter values. The drilling may also be arranged to be carried out for a predetermined number of impacts and/or a predetermined period of time to stabilize the drilling using the new control parameter values prior to collecting data to be used in the evaluation of the drilling to thereby obtain representative measurement results.
The resulting drilling result caused by the impacts of the percussion piston using the set drilling control parameters according to the present example are then monitored, and results for the drilling of the particular setting is stored for later evaluation. This includes e.g. a representation of the drill rate and possible other parameters that take part in the evaluation. The drilling using a particular operating point may be arranged to be carried out for a predetermined number of impacts (e.g. any suitable number of

19 impacts in the interval 50-500) and/or a predetermined period of time. Data relating to the drilling is collected during this time for later evaluation, and examples of particular data being collected for the evaluation is exemplified below When drilling at a particular operating point has been completed the method returns to step 304 where it is determined whether the set of different operating points have been completed, or whether there are other operating points to first be drilled.
For as long as there are other operating points to be drilled the method returns to step 305 for drilling according to the next settings. When the full set of predetermined operating points have been drilled, and data been collected for these different settings, the method continues to step 306 for evaluation in accordance with the below.
However, with further regard to step 305, it may not always be the case that drilling is performed for the full number of impacts/full period of time for a particular operating point. This is because the particular operating point being drilled may exhibit poor and possibly detrimental results in some regards even though e.g. the drill rate may be high. As was discussed, various penalty generating parameters may be monitored during the actual drilling at a particular operating point to determine whether drilling is to be prematurely aborted to avoid excess wear at a particular setting. The penalty parameters may be any parameter or occurrence that is considered to give rise to harmful drilling. With reference to fig. 2 this may be the case, for example, in case it is detected that the joints become, or may become, loose, or the drilling gives rise to impacts were the drill string is to firmly pressed against the rock in relation to the impact pressure/energy. This causes the stress wave energy to be reflected back towards the drilling machine. Similarly it may be determined whether the drill string has little or no contact with the rock when the percussion piston strikes the drill string with undesirable reflections as result. It may e.g. also be determined whether the drilling causes the drill bit to become jammed, i.e. get stuck, and also whether the operating point gives rise to clogging, i.e. the flushing of drilled remnants is not working properly. This may particularly be evaluated in case flush flow is utilised as one of the drilling control parameters.

The drilling may therefore be continuously evaluated while drilling according to a particular setting is ongoing, and if it is determined that the presence of penalty generating occurrences are considered too high, e.g. exceeding a threshold, drilling at the current operating points may be aborted prior to all intended impacts for the 5 particular setting have been carried out. This may be the case, for example, if the number of impacts that gives rise to penalty generating occurrences exceeds a predetermined threshold, in which case drilling at the current settings is aborted prior to completing drilling at the particular settings.
With regard to determining whether harmful reflections arise, this may be performed 10 in any suitable manner, and is carried out according to the present example by analysing the reflections caused by the stress waves that are induced by the percussion element. This is performed by measuring the reflected waves in the drill string using the contactless sensor 209, where any suitable method may be utilised for estimating whether one or more joints are loose, and whether the reflections 15 reach a harmful level. Such determination is well described in the art, and the parallel application SE 2051xxx-x having the same assignee and filing date as the present application illustrates a method where e.g. loose joints can be identified by estimating the stiffness of the joints of the drill string, and where this may be performed for each stroke of the percussion element. However, as was mentioned, any other suitable

20 method may be utilised to perform the determinations according the invention.
As was mentioned, when all operating points have been drilled, the method continues to step 306 where the results of the various settings are evaluated to determine which of the currently drilled settings/operating points that provided the most optimal results in regard of at least one resulting drilling parameter.
As is realised the term "optimal" is relative herein, and drilling is optimised when a new operating point is found that provides more optimal drilling than a previous operating point.
As discussed, the resulting drill rate is utilised according to the present example to determine the most optimal operating point. However, in order to obtain efficient drilling over time it is also important to ensure that drilling is not performed using control parameter is that causes the drilling that may give rise to excessive wear of

21 components. The evaluation in step 306 may therefore consist of a determination of the particular operating point of the set of operating points that has been drilled that provided the highest drill rate while simultaneously not violating penalty restrictions regarding loose joints etc. Various parameters may hence participate in the evaluation in step 306 so that a high drill rate may be obtained but which simultaneously takes into account negative contributions from parameters that may exhibit the drill rig to excessive wear.
Following the evaluation in step 306, the most optimum drill settings of the round of settings that has just been drilled is selected in step 307 and may also be communicated to the rig control system as settings to be used when in case no other settings are received. The method then continues to step 308 where new prerequisites are determined and which are to be used when determining the next round of operating points to be drilled in step 303. This will include the selection of the operating point that resulted in the most optimal drilling, and may also include a determination of whether the difference in parameter values between operating points are to be increased or decreased. In case the different operating points that have just been drilled exhibit similar results the differences may be increased so that the next set of operating points to be drilled are further spaced apart whereas in case highly different results are obtained the next set of parameters to be drilled may instead be arranged to be closer to each other. In step 309 it is determined whether the method is to be ended in step 310 e.g. because drilling is ended, otherwise the prerequisites of step 308 are utilised in step 303 to determine a new set of operating points to be drilled in accordance with the above. The operating points are then selected in relation to the operating point that was considered the most optimal in the evaluation in step 307, and which may also be stored as a new initial operating point to be used in the determination of operating points to be drilled the next time the optimisation process according to the invention is started. As is realised, this initial operating point may be altered for a large number of times during a drilling session.
Furthermore, when determining the operating points in step 303 it may, according to embodiments of the invention, be ensured that there is no overlap with previously drilled operating points. It may also be the case that none of the just drilled operating

22 points exhibits a more optimal drilling than the setting from which the operating points originated. A new set may then be selected based on the "old" operating point that was lastly used and hence still is considered the most optimal. The "box" may then e.g. be increased and/or e.g. be arranged such that values only increase (or decrease). It is also contemplated that operating points in such situations may be determined from a previously drilled operating point that although it may not have formed basis for determining a new set of operating points may still exhibit an efficiency (optimisation) that may be essentially the same as an operating point for which further optimisation has been attempted.
In this way drilling may continuously be optimized during ongoing drilling where this optimization is performed automatically by the rig control system. This allows, for example, efficient drilling not only when drilling is fully automated but also e.g. when the drilling is partly manually controlled so that e.g. settings set by an inexperienced driller may be altered and optimized by the rig control system during drilling with the result that the drilling will be efficient also when the drilling rig is under the hands of an inexperienced operator. This also allows that the drilling continuously takes into account e.g. changes in rock property as drilling progress.
Fig. 4A illustrates an example of the manner in which the control parameter settings, i.e. operating points, may change during drilling when drilling is carried out according to embodiments of the invention. As discussed, the number of dimensions being controlled will depend on the number of control parameters participating in the optimisation. According to the present example, the drilling process is optimised with respect to percussion pressure and feed pressure, hence resulting in a two-dimensional search space for settings that optimise drilling, where dot 401 represents the initial operating point from which the optimisation commences, e.g.
according to the method of fig. 3. The first set of operating points to be drilled are then determined according to the above as dots 401a-d. Operating point 401c is determined to be the most optimal of the evaluated operating points 401a-d (and operating point 401) and is hence used as the operating point from which new operating points are selected, one of which coinciding with point 401 according to the present example and hence need not be drilled. Operating points 402b-d are, however, drilled, and operating

23 point 402d is considered to be more optimal than operating point 401c and is therefore used as new "basis" for the next determination of operating points to be drilled.
The next set of operating points to be drilled comprises points 403c and 403d, and also points that essentially coincide with points 401c and d, respectively.
Operating point 403d is found to be the most optimal, and is hence selected. Similarly operating point 404b is selected in a subsequent step. In this case the box has also been reduced, which e.g. can be arranged to be performed based on various criteria, such as e.g. the relative improvement from one operating point to another. The method then continues in this manner, selecting points 405, 406, 407, 408 and so on, converging towards an operating point representing the most optimal operating point in regard of drill rate given the particular prerequisites of the rock being drilled.
Fig 4 illustrates a solution where the optimisation goes in various directions in the search space represented by the figure, and also goes in the reverse direction, see e.g. 402d->403d and the return to 404b. In case gradients are utilised instead, it could, for example, be determined in point 402d that given the start in point 401 it might be advantageous to attempt drilling further along the line intersecting points 401 and 402d.
Fig. 5 illustrates the optimisation process of fig. 4 in terms of the evolvement of the drill rate (y axis) as a function of iterations according to fig. 3 (x axis).
As can be seen from the figure an optimal operating point (in relation to other operating points) is found after about 15 iterations. The particular values of the drill rate are only given as a parameter value being any suitable representation of the drill rate.
The present invention may be utilised for essentially any kind of drill rig where hydraulic percussive drilling is utilised. Similarly, the invention is applicable for any other kind of percussion drilling technology. The invention is also applicable for underground drill rigs as well drill rigs operating above ground.

Claims (19)

Claims

1. A method for optimising at least one drilling parameter during an ongoing drilling process, the drilling being carried out by a percussive drilling machine (105), the drilling machine (105) being set to drill at an operating point, the operating point of the drilling being determined by the setting of a plurality of control parameters, characterized in the method comprising:
determining a first plurality of drilling machine operating points (401a-d;402b-d;403c-d;404a-d), the operating points (401a-d; 402b-d; 403c-d; 404a-d) being set by said plurality of control parameters, performing percussive drilling at each of said first plurality of operating points (401a-d; 402b-d; 403c-d; 404a-d), evaluating at least one resulting drilling parameter for each of the plurality of operating points (401a-d; 402b-d; 403c-d; 404a-d), determining a new plurality of drilling machine operating points (401a-d;
402b-d; 403c-d; 404a-d) to be drilled based on said evaluation, and drilling the new plurality of drilling machine operating points (401a-d;
402b-d; 403c-d; 404a-d).

2. Method according to claim 1, further comprising:
continuously determining operating points (401a-d; 402b-d; 403c-d;
404a-d) during ongoing drilling based on evaluation of drilled operating points (401a-d; 402b-d; 403c-d; 404a-d), and continuously drilling and evaluating the determined operating points (401a-d; 402b-d; 403c-d; 404a-d).

3. Method according to claim 1 or 2, further comprising:
when evaluating at least one drilling parameter for each of the drilled plurality of operating points (401a-d; 402b-d; 403c-d; 404a-d), evaluating a plurality of drilling parameters for each of the plurality of operating points (401a-d; 402b-d; 403c-d; 404a-d).

4. Method according to claim 3, further comprising:
assigning different weights and/or priorities to the plurality of drilling parameters in the evaluation.

5. Method according to any one of the claims 1-4, further comprising, when determining the new plurality of drilling machine operating points (401a-d;
402b-d; 403c-d; 404a-d):
selecting the new plurality of operating points (401a-d; 402b-d; 403c-d;
404a-d) starting from a drilling machine operating point (401; 401c; 402d;
403d; 404b;405-408) of the drilled plurality of drilling machine operating points (401a-d; 402b-d; 403c-d; 404a-d) being considered the most optimal operating point (401; 401c; 402d; 403d; 404b;405-408) of the drilled plurality of operating points (401a-d; 402b-d; 403c-d; 404a-d).

6. Method according to any one of the claims 1-5, further comprising:
continuing optimisation of the drilling machine operating point (401;
401c; 402d; 403d; 404b;405-408) by determining a new plurality of operating points (401a-d; 402b-d; 403c-d; 404a-d) to be drilled at least for as long as a more optimal drilling machine operating point (401; 401c; 402d; 403d;
404b;405-408) is identified among the new plurality of operating points (401a-d; 402b-d; 403c-d; 404a-d).

7. Method according to claim 6, further comprising:
when evaluation of a drilled plurality of operating points (401a-d; 402b-d; 403c-d; 404a-d) does not identify a more optimal operating point (401;
401c;
402d; 403d; 404b;405-408) in relation to the operating point (401; 401c; 402d;

403d; 404b;405-408) from which the drilled plurality of operating points (401a-d; 402b-d; 403c-d; 404a-d) was determined, determining at least one further plurality of operating points (401a-d; 402b-d; 403c-d; 404a-d) to be drilled from a previously drilled operating point (401; 401c; 402d; 403d; 404b;405-408) that has not formed basis for determining a new set of operating points (401a-d;
402b-d; 403c-d; 4042-d).

8. Method according to any one of the claims 1-7, further comprising, prior to evaluating a drilling machine operating point:
performing percussive drilling for at least a predetermined number of percussions and/or a predetermined period of time at the operating point to be evaluated.

9. Method according to claim 8, further comprising:
evaluating a drilling machine operating point while the operating point is being drilled, determining whether drilling at the operating point being evaluated is to be aborted, and switching drilling to a previously drilled, or subsequent operating point to be drilled, prior to finishing the predetermined number of percussions and/or period of time of drilling when the evaluation deems that drilling at the current operating point is to be aborted.

10. Method according to any one of the claims 1-9, further comprising:
determining at least one drilling parameter by measuring a reflected stress wave caused by an incident stress wave generated by at least one percussive impact by the impact device of the drilling machine (105) on a drill string of the drill rig.

11. Method according to any one of the claims 1-10, further comprising, when drilling is to be performed at a particular operating point:
determining the control parameter settings to be used when drilling at the particular operating point;
setting the drilling control parameters to the determined control parameter settings; and performing drilling at the particular operating point following setting of the control parameters.

12.A method according to any one of the claims 1-11, further comprising:
prior to determining a plurality of operating points (4012-d; 402b-d;
403c-d; 404a-d) to be drilled based on a previously drilled operating point (401; 401c; 402d; 403d; 404b;405-408), determining whether a difference in control parameter values between operating points (4012-d; 402b-d; 403c-d;
404a-d) is to be increased or decreased prior to generating a new plurality of operating points (401a-d; 402b-d; 403c-d; 404a-d).

13.A method according to any one of the claims 1-12, further comprising, when drilling is commenced:

selecting an initial operating point (401) as an operating point previously being used as an optimal operating point in an earlier drilling session, an operating point set by an operator of the drill rig or an empirically determined operating points (401a-d; 402b-d; 403c-d; 404a-d).

14.A method according to any one of the claims 1-13, further comprising:
optimising drilling by maximising at least one drilling parameter and/or minimising at least one drilling parameter.

15.A method according to any one of the claims 1-14, wherein the plurality of control parameters comprises two or more from the group: rotation pressure, percussion pressure, feed pressure, flush flow.

16. Method according to any one of the claims 1-15, further comprising, when determining a plurality of operating points (401a-d; 402b-d; 403c-d; 404a-d) to be drilled starting from a drilling machine operating point (401; 401c; 402d;
403d; 404b;405-408) being considered the most optimal operating point (401;
401c; 402d; 403d; 404b;405-408) of a drilled plurality of operating points (401a-d; 402b-d; 403c-d; 404a-d):
selecting higher and/or lower values of control parameters in relation to the drilling machine operating point (401; 401c; 402d; 403d; 404b;405-408) being considered the most optimal operating point.

17. Method according to claim 15 or 16, further comprising:
respecting maximum and/or minimum limitations of the at least one drilling parameter when determining a subsequent plurality of operating points (401a-d; 402b-d; 403c-d; 404a-d) to be drilled.

18.A system for optimising at least one drilling parameter during an ongoing drilling process, the drilling being carried out by a percussive drilling machine (105), wherein, during drilling, the drilling machine (105) is set to drill at an operating point, the operating point of the drilling being determined by the setting of a plurality of control parameters, characterized in the system comprising:
means for determining a plurality of drilling machine operating points (401a-d; 402b-d; 403c-d; 404a-d), the operating points (401a-d; 402b-d; 403c-d; 404a-d) being set by said plurality of control parameters, means for performing percussive drilling at each of said determined plurality of operating points (401a-d; 402b-d; 403c-d; 404a-d), means for evaluating at least one resulting drilling parameter for each of the plurality of drilling machine operating points (401a-d; 402b-d; 403c-d;
404a-d), means for determining a new plurality of drilling machine operating points (401a-d; 402b-d; 403c-d; 404a-d) to be drilled based on said evaluation, and means for drilling the new plurality of drilling machine operating points (401a-d; 402b-d; 403c-d; 404a-d).

19.A rock drilling rig characterised in comprising a system according to claim 18.