EP4663895A1

EP4663895A1 - An arrangement for recognizing a change in rock drilling

Info

Publication number: EP4663895A1
Application number: EP24181376.5A
Authority: EP
Inventors: Henna Jussila
Original assignee: Sandvik Mining and Construction Oy
Current assignee: Sandvik Mining and Construction Oy
Priority date: 2024-06-11
Filing date: 2024-06-11
Publication date: 2025-12-17
Also published as: WO2025257057A1

Abstract

An arrangement for recognizing changes in rock drilling is disclosed. Recognized changes can be short-term changes that include cavities, fractures and faults while drilling, or long-term changes, that include wearing of the drill bit. In the arrangement the impact frequency is compared with estimated impact frequency with a give flushing fluid pressure. The difference between the actual impact frequency and the estimated impact frequency can be used in recognizing a change in drilling.

Description

DESCRIPTION OF BACKGROUND

The following disclosure relates to rock drilling and particularly to monitoring changes in rock drilling.
A rock drilling arrangement is a device that uses compressed air, electricity, or hydraulic power to create holes in hard materials such as rocks, concrete, or asphalt. A rock drilling arrangement typically comprises a rock drill, a drill bit and a feed system that controls the drilling depth and direction. A rock drill typically comprises a hammer mechanism that impacts the drill bit and a rotating device that rotates the drill bit. Rock drilling arrangements are used for various applications, such as mining, quarrying, construction, demolition and exploration. Rock drilling arrangements can vary in size, power, and configuration depending on the purpose and environment of use. Some rock drilling arrangements are handheld and portable, while others are mounted on rigs or vehicles and require external power sources.
In the following disclosure so called down-the-hole drilling arrangements are discussed. A down-to-hole rock drill was initially developed for drilling large diameter holes downwards in surface-drilling applications. Commonly a DTH-drill comprises a percussion mechanism that is located typically directly above the drill bit. The drill pipes, that transmit the necessary feed force and rotation, are typically added to a drill string behind the percussion mechanism as the hole gets deeper. Hydraulic fluid, such as air, water or drilling mud, is used to actuate the percussion mechanism and flush the cuttings away. Such down-the-hole drill or drilling arrangement is referred as a rock drilling unit in the following disclosure.
At present, the maintenance of rock drilling arrangements is usually done by a maintenance person following the service program of the rock drill. Additionally, some of the manual inspections can done by a rock drilling arrangement operator who sees the rock drilling arrangement in the daily operation. This involves, for example, inspecting and replacing seals and other parts that wear out and need to be changed from time to time.
One drawback of the service program and manual inspections is that they reveal a potential defect only at an advanced stage. When the defect is found only after it becomes visible or the rock drill's performance has dropped considerably, the rock drilling arrangement may require an additional service break and this can stop the work while the rock drilling arrangement is being serviced. Therefore, there is a need for identifying possible defects automatically and as soon as possible so that unnecessary service breaks are avoided and the service breaks can be scheduled in a way that does not interfere with the work.
Currently, when analyzing the rock quality at the drilling site, the drilled holes are inspected by using a camera. A camera arrangement can be lowered to the drilling hole and images acquired with the camera are used for producing a geological map of the area. These geological maps can be useful in planning mining or blasting process. However, this is an additional step and currently must be performed after drilling. This is time consuming and requires specific tools that need to be brought to the site. Thus, there is a need for improved analysis tools.

SUMMARY

In the following disclosure an arrangement for recognizing a change in rock drilling is disclosed. Recognized changes can be short-term changes that include shears, cavities, fractures, joints, faults and other kind of changes in the rock quality and formation, or long-term changes, that include wearing of the drill bit or other slowly evolving changes in a rock frilling unit. In the arrangement the impact frequency is compared with estimated impact frequency with a given flushing fluid pressure. The difference between the actual impact frequency and the estimated impact frequency can be used in recognizing a change in drilling. Flushing fluid is commonly air; however, also other known flushing fluids can be used.
In an example embodiment an apparatus for a rock drilling unit is disclosed. The apparatus comprises at least one processor and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform: retrieve a drilling parameter model; monitor drilling parameters during drilling; estimate drilling parameters using the drilling parameter model; compute a difference between the estimated drilling parameters and the measured drilling parameters; and recognize a change in the drilling process based on the computed difference. The example embodiment is beneficial as it provides a possibility to recognize short-term and long-term changes. The example embodiment removes a need for separate tools to be used when analyzing rock quality at the drilling site. It is possible to use the example embodiment in generating a geological map that may be used in mining, blasting or in other works at the drilling site. Using the drilling parameter model is beneficial as the model can be easily calibrated and re-calibrated if such need occurs. The example embodiment disclosed above is also beneficial as it can be installed to existing rock drilling units and does not require changing the rock drilling machine itself. Importantly, the example embodiment disclosed above facilitates real time analysis if needed.
In an example embodiment the at least one memory and the computer program code are further configured to, with the at least one processor to cause the apparatus to: measure a hole depth; and associate the recognized change with the measured hole depth. It is beneficial to measure the depth of the hole. When the depth is measured during drilling process, the recognized changes can be associated with the depth. This facilitates automatic generation of geological maps and also allows production of informative visualizations.
In an example embodiment the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to: store the values of at least one of the following to the memory: monitored drilling parameters, estimated drilling parameters, associated hole depth and computed differences. It is beneficial to store the measured and computed values for later analysis. This is particularly beneficial when there is a lot of information available and a detailed analysis with all known results is important.
In an example embodiment the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to: monitor at least one of the following as monitored drilling parameters: impact frequency and flushing fluid pressure. It is beneficial to monitor impact frequency and flushing fluid pressure. When the flushing fluid pressure is monitored it is possible to retrieve values from the drilling parameter model using the flushing fluid pressure.
In an example embodiment the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to: estimate the impact frequency from the flushing fluid pressure using the drilling parameter model. When the impact frequency is estimated is possible to compare the estimated values with the monitored value.
In an example embodiment the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to: detect if the recognized change is a short-term change using the stored values; and if the recognized change is a short-term change, the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to: detect a fault or a cavity in the rock. It is beneficial to detect if the change is short-term or long-term. The detection of short-term changes is important as it facilitates analysis of the rock quality.
In an example embodiment the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to: compare the computed difference with a threshold value in order to detect a fault or a cavity in the rock. It is beneficial to have one or more threshold values that can be used in differentiating small fractures, larger cavities and faults from each other.
In an example embodiment the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to: detect if the recognized change is a long-term change using the stored values; and if the recognized change is a long-term change, the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to: detect wear in the drill bit of the rock drilling unit. It is beneficial to detect if the change is short-term or long-term. When the change is long-term, it is typically an indication of a long-term change in the rock drilling unit. The most common long-term change is wear in the drill bit.
In an example embodiment the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to: filter the stored values for removing the high peaks associated with the rock drilling unit configuration. It is beneficial to filter the monitored data. It is common that all measured signals have undesired components and filtering, for example, components that have been caused by known events, such as addition of a drill tube or pipe, the signal becomes more informative and also the need of estimating a peak caused by addition of a tube is removed.
In an example embodiment the drilling parameter model is a regression model of impact frequency and flushing fluid pressure. It is beneficial to use a regression model when it is sufficient as it is simple and reliable way of predicting values of two correlating measure. It is beneficial to use flushing fluid pressure and impact frequency in the regression model as these two values are correlating and are also sufficient for recognizing fractures, cavities and faults in the rock.
In an example embodiment the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to determine if the flushing fluid flow is at normal level; and evaluate the reliability of the drilling parameter model based on the determined flushing fluid flow deviation from the normal level. It is beneficial to detect if the conditions have changed. If the flushing fluid flow deviates from the normal level it may be an indication that the flushing fluid channel is not open. This may be because the rock drilling unit has been broken during drilling or there is dirt or debris in the flushing fluid channel that is preventing normal flow. If the flushing fluid flow is not at the assumed level, it may have an impact to the reliability of the drilling parameter model. Thus, it is beneficial to detect the change in the flow as it can be taken into account when analyzing results with the drilling parameter model. Furthermore, the decreased flow may be an indication of a bigger maintenance need that is beneficial to detect as early as possible.
In an example embodiment a rock drilling unit is disclosed. The rock drilling unit is connected to an apparatus as described in the above. It is beneficial to use an apparatus that has been described in the above. The apparatus may be connected to the rock drilling unit so that it is not part of the rock drilling unit. This is beneficial have a possibility to connect a rock drilling unit to an apparatus as described in the above so that also older rock drilling units can be used.
In an example embodiment the rock drilling unit comprises the apparatus. It is beneficial to have the apparatus as described in the above as an integral part of the rock drilling unit. This facilitates better design of the rock drilling unit with the apparatus as the apparatus can be placed so that it is not prone to the drilling conditions that often have dust and are otherwise demanding.
In an example embodiment the rock drilling unit further comprises at least one of the following: an impact frequency sensor, flushing fluid pressure sensor and hole depth sensor. It is beneficial to have the sensors integrated in the rock drilling unit. Furthermore, this facilitates that the sensors can be placed so that it is not prone to the drilling conditions that often have dust and are otherwise demanding. Also, better integration of sensors may provide easier way of measuring some of the parameters.
In an example embodiment a method for recognizing a change in rock drilling is disclosed. The method comprises: retrieving a drilling parameter model; monitoring drilling parameters during drilling; estimating drilling parameters using the drilling parameter model; computing a difference between the estimated drilling parameters and the measured drilling parameters; and recognizing a change in the drilling process based on the computed difference. The method as described in the above is beneficial as it provides a possibility to recognize short-term and long-term changes. The method removes a need for separate tools to be used when analyzing rock quality at the drilling site. It is possible to use the example embodiment in generating a geological map that may be used in mining, blasting or in other works at the drilling site. Using the drilling parameter model is beneficial as the model can be easily calibrated and re-calibrated if such need occurs. The example embodiment disclosed above is also beneficial as it can be installed to existing rock drilling units and does not require changing the rock drilling machine itself. Importantly, the example embodiment disclosed above facilitates real time analysis if needed.
The example embodiments described in the above remove several drawbacks of the conventional technology. Particularly the embodiments address the automatic detection of rock quality during drilling and help in providing a geological map or other relevant information with regard to the rock quality. Furthermore, in addition to the recognizing the rock quality, the disclosed embodiments provide tools for automatic detection of wear in the rock drilling equipment. This improves maintenance of the rock drilling equipment and thus reduces costs by reducing the down-time of the equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the arrangement for recognizing a change in rock drilling and constitute a part of this specification, illustrate embodiments and together with the description help to explain the principles of the arrangement for recognizing a change in rock drilling. In the drawings:

Fig. 1 is a block diagram of an example of an apparatus,
Fig. 2 is a block diagram of an example embodiment of the present arrangement for recognizing a change in rock drilling,
Fig. 3 is a flow of an example of a method for recognizing a change in drilling,
Fig. 4 is an example of a drilling parameter model,
Fig. 5 is a graph illustrating monitored values,
Fig. 6 is an example of a difference curve; and
Fig. 7 an example of monitored impact frequency.

DETAILED DESCRIPTION

Reference will now be made in detail to the embodiments, examples of which are illustrated in the accompanying drawings.
In figure 1 a block diagram of an example of an apparatus is disclosed. The apparatus may be a small computing unit, controller or similar apparatus that is capable of executing computer program code. In the example of figure 1 the apparatus is a controller that is configured to control a rock drilling unit. The controller 100 comprises at least one processor 102 and at least one memory 104. The at least one memory 104, which may be suitable volatile or non-volatile memory, comprises a computer program code, which when executed, causes the controller to perform a method for recognizing a change in rock drilling as described in below.
The controller is connected to a rock drilling unit. The connection maybe wired or wireless and it is possible to connect several rock drilling units to the controller. The connection to the rock drilling unit and particularly to the sensors of the rock drilling unit may be arranged using common connection so that the interface to the sensors is shared with other controlled features or it may be a specific connection to the sensors. It is possible that the controller 100 and the functionality described in below is integrated with the controller or computer sending instructions to the rock drilling unit with regard drilling. Thus, the controller may be configured to transmit additional information, such as drilling instructions and to receive additional information, such as temperature or similar from the drilling unit. In the present arrangement for recognizing a change in rock drilling the controller receives the values of different parameters from the rock drilling unit.
The change is recognized as explained in detail in below. Using an apparatus, such as the controller as described in the example of figure 1, a rock drilling unit can be configured to detect fractures, cavities, changes in rock and possible wearing of the drill bit while drilling. The feedback from the drill and the controller can be analyzed in real time or stored to a computer, server, cloud or other storage device for later analysis. The later analysis may include processing of the collected data, for example, in form of filtering of undesired components or removal of known events from the collected data. The later analysis may be combined with additional information that has been acquired earlier in similar process or known information, such as a geological map, which may include information also from other sources.
In figure 2 a block diagram of an example embodiment of the present arrangement for recognizing a change in drilling is disclosed. In the figure an example of a rock drilling unit 200 is shown. The rock drilling unit of figure 2 comprises a controlling apparatus 202 similar to the controller of figure 1. The rock drilling unit of the example comprises a rock drilling machine 206. The rock drilling machine 206 is arranged to perform drilling using hammering motion breaking the rock and flushing fluid for removing the broken rock from the drilling hole. In addition to the controller 202 rock drilling machine 206 the rock drilling unit 200 typically comprises sensors 204, however, in another implementation the necessary sensors are not integral part of the rock drilling unit 200. The sensors are used to measure the impact frequency and flushing fluid, such as air, pressure. The sensors 204 may be located in the rock drilling unit 200 or in the vicinity of the rock drilling unit 200. In that case the sensors 200 need to be arranged so that the measurements are possible. For example, the impact frequency can be measured acoustically and the flushing fluid pressure using a measurement device before the pressure is fed to the rock drilling unit 200.
In figure 3 a flow of an example of a method for recognizing a change in drilling is disclosed. In the figure the method is initiated by retrieving a drilling parameter model, step 300. The drilling parameter model may be predetermined or adjusted during drilling. A predetermined model maybe based on calibration, which may be done at the factory or at the drilling site. The predetermined model may be used as it is or, as mentioned, it may be adjusted during drilling. The need for adjustment can be caused, for example, wearing of the drill bit or other changes in drilling conditions.
The predetermined model of the present example comprises values of impact frequency and flushing fluid pressure. These two values have a correlation, and a simple linear regression model can be used to provide a possibility to estimate impact frequency with a given flushing fluid pressure. An example of such a model is shown in figure 4 and will be discussed in more detail in below.
The, during drilling, the parameters of the drilling parameter model are monitored, step 302. In the simple implementation only the impact frequency and flushing fluid pressure are monitored. Monitoring means here that the selected parameters are at least measured for a special purpose continuously or at certain intervals. It is possible to include also other parameters for the process of recognizing changes in drilling. The measurements can be done with sensors that have been included in the rock drilling unit, or with separate sensors. In addition to the parameters that are associated with the drilling parameter model, also other parameters, such as drilling depth, may be measured using different sensors suitable for the measurement.
The retrieved drilling parameter model is then used to estimate impact frequency with a given flushing fluid pressure, step 304. As explained in the above, the drilling parameter model may be used for predicting the impact frequency of a rock drilling unit when the drilling is in progress. When the flushing fluid pressure is measured, the measured flushing fluid pressure can be used in estimating the impact frequency. The measured flushing fluid pressure, which is related to the flushing fluid flow through the hammer of the rock drilling unit, can be additionally used in the drilling parameter model. Particularly the flushing fluid flow can be used in evaluating the validity and uncertainty of the analysis.
The steps of monitoring and estimating are presented as sequential in the figure; however, they may be continuous processes, wherein the parameters are monitored continuously, and the estimation based that is based on measured parameters is also done continuously. In the estimating step 304, flushing fluid pressure is received as an input parameter for the estimation and the parameter model is used to estimate the impact frequency. The estimation gives the an estimate of the impact frequency, wherein the value of the impact frequency is how the impact frequency should be without any fractures, cavities, faults or other changes in the rock quality.
After the impact frequency has been measured and estimated, a difference between these two is computed. The monitored, estimated and computed values may be stored for a later use and associated with other measurements that are made at the same time. The computed difference is also called a residual and indicates that the drilling process included a change as the estimated and the monitored value are not the same.
Lastly, changes are recognized from the measured, estimated and computed parameters. The changes can be detected from graphs or curves visualized in figures 5, 6 and 7. The recognizing process is explained in more detail with discussion of the visualizations.
Additionally, it is also possible to monitor the stability of the flushing fluid flow. When the rock drilling unit is working in normal conditions, the flushing fluid flow should be substantially stable. If the flushing fluid flow is reduced, it is possible that the flushing fluid channel is not open or has been damaged during drilling. For example, if there are obstacles, deformations, or leaks, it is possible that the flushing fluid flow in the rock drilling machine part of the rock drilling unit is reduced. The reduced flushing fluid flow will reduce the functionality and reliability of the drilling parameter model. When the flushing fluid flow is monitored the possible decrease in the flow can be taken into account when using the drilling parameter model. Additionally this may be used in determining a need for maintenance.
In figure 4 an example of a drilling parameter model is shown. In the model impact frequency is shown on the y-axis in impacts per second? and flushing fluid pressure is shown on the x-axis bars. The values points shown are indicating an impact frequency for certain values of flushing fluid pressure. The image shows a correlation between the flushing fluid pressure and the impact frequency so that a linear regression model with R=0,84 has been developed. Linear regression of two parameters is a simple version of a drilling parameter model that fits the purpose. More sophisticated models including more parameters or machine learning approach instead of a simple linear regression model can be used. The values for the model can be derived from factor or onsite calibration. Instead of a rock drilling unit specific calibration it is possible to use data from a similar rock drilling unit and adjust the data during drilling so that the drilling parameter model is adjusted to a particular rock drilling unit in the current state of the rock drilling unit. Accordingly, the drilling parameter model may be adjusted when the rock drilling unit has been used for some time and is worn or otherwise changed.
The regression model, which is shown in figure 4 and can be used as a drilling parameter model, is generated using a sweep test. In the sweep test the flushing fluid pressure is changed from low to high at rock drilling machines operating pressure level. This is typically done when the drill bit is changed. The sweep test needs to be done only with one drill tube or pipe. Even if during drilling several tubes are used, there is no need to calibrate the rock drilling unit using sweep test with all drill tubes.
In figure 5 monitored values are illustrated as a graph. Solid curve 500 represents estimated impact frequency and dashed curve 502 represents measured impact frequency. On the y-axis is again the impact frequency in Hz. On the x-axis is the depth of the hole as a function of time. The reference numbers 500 and 502 are pointing to substantially same point of distance and time so that it can be seen that curves do not exactly follow each other. In the point indicated by reference numbers the monitored actual impact frequency is measured to be less than the impact frequency estimated by the drilling parameter model. The difference, also known as residual, represents a change in drilling process. There may be faults, fractures or cavities in rock. The recognition of a change in drilling maybe based on a threshold with the difference. When the difference is small, it is possible that there is change in drilling but the difference is caused, for example, by measuring inaccuracies.
Figure 6 shows an example of a difference curve, wherein the difference between the estimated and monitored impact frequency is shown. It can be seen that the differences are not constant but vary as also the rock being drilled does. The computation of the curve of figure 6 is not necessary. The curve is shown here only for illustrative reasons. However, even if the curve is not necessary, it may be useful for operator to see a difference curve instead of the two curves of figure 5. As the difference curve shows only the difference, all necessary information is available also from the curves of figure 5.
Figure 7 shows another illustration of impact frequency. In figure 7 it can be seen that the impact frequency, which is again on the y-axis in Hz is rising over the time, which is on the x-axis. This typically means that the drill bit is worn. The continuous rising of the impact frequency is an indicator of wearing and can be detected as a trend from the figure. The curve has very steep peaks, however, these typically relate to an addition of drill tube or pipe. Even if the peaks do not have significant effect to the trend, they may be filtered out in order to get a better picture of the situation. In addition to the event of addition of drill tubes or pipes also other artifacts or events that are not desired may be filtered out from the material. This, however, is optional and not necessary for the implementation of the current arrangements for recognizing changes in the drilling process.
In an embodiment the long-term changes are detected by storing the monitored values without estimating values from the drilling parameter model. Thus, it is sufficient only to detect the rise in the impact frequency. In that embodiment it is not possible to detect short-term changes in the drilling process. However, sometimes this may be sufficient. In another embodiment the long-term changes are detected from a rise in the difference curve. This happens if the drilling parameter model is not recalibrated often enough or if the threshold values are not adjusted when the difference rises slowly because of the wear.
In the above examples of detecting changes have been discussed. The changes can be associated with drilling depth so that it facilitates generating a geological map of the mine. The measurements may also be associated with time so that additional information with regard wearing of the drill bit can be generated. As there are several parameters that are estimated and measured, the parameters may be stored to a computing device for later use. When recognizing a change in the drilling process a threshold value for the computed difference may be used in order to decide if there is a change in the drilling process or if the difference is ordinary fluctuation. When recognizing the change, it is possible to detect long-term changes in addition to the short-term changes. Long-term changes typically indicate wear in the drill bit. These adjustments can be done automatically, however, experienced operator is able to see the wear from the generated curves without undue burden.
The above-mentioned method may be implemented as computer software which is executed in a computing device able to communicate a rock drilling unit. When the software is executed in a computing device it is configured to cause performing the method described above. The software is embodied on a computer readable medium so that it can be provided to the computing device, such as the controller 100 of figure 1.
As stated above, the components of the exemplary implementations can include computer readable medium or memories for holding instructions programmed according to the teachings of the present inventions and for holding data structures, tables, records, and/or other data described herein. Computer readable medium can include any suitable medium that participates in providing instructions to a processor for execution. Common forms of computer-readable media can include, for example, a floppy disk, hard disk, magnetic tape, any other suitable magnetic medium, a suitable optical medium, a RAM, a PROM, an EPROM, a FLASH-EPROM, any other suitable memory chip or cartridge, a carrier wave or any other suitable medium from which a computer can read.
It is obvious to a person skilled in the art that with the advancement of technology, the basic idea of the arrangement for recognizing a change in rock drilling may be implemented in various ways. The arrangement for recognizing a change in rock drilling and its implementations are thus not limited to the examples described above; instead they may vary within the scope of the claims.

Claims

An apparatus for a rock drilling unit comprising:
at least one processor (102) and at least one memory (104) including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform:
retrieve a drilling parameter model;

monitor drilling parameters during drilling;

estimate drilling parameters using the drilling parameter model;

compute a difference between the estimated drilling parameters and the measured drilling parameters; and

recognize a change in the drilling process based on the computed difference.
An apparatus according to claim 1, wherein the at least one memory (104) and the computer program code are configured to, with the at least one processor (102), cause the apparatus to:
measure a hole depth; and

associate the recognized change with the measured hole depth.
An apparatus according to claim 1 or 2, wherein the at least one memory (104) and the computer program code are configured to, with the at least one processor (102), cause the apparatus to:
store the values of at least one of the following to the memory: monitored drilling parameters,

estimated drilling parameters, associated hole depth and computed differences.
An apparatus according to any of preceding claim 1 - 3, wherein the at least one memory (104) and the computer program code are configured to, with the at least one processor (102), cause the apparatus to:
monitor at least one of the following as monitored drilling parameters: impact frequency and flushing fluid pressure.
An apparatus according to any of preceding claim 1 - 4, wherein the at least one memory (104) and the computer program code are configured to, with the at least one processor (102), cause the apparatus to:
estimate the impact frequency from the flushing fluid pressure using the drilling parameter model.
An apparatus according to any of preceding claim 3 - 5, wherein the at least one memory (104) and the computer program code are configured to, with the at least one processor (102), cause the apparatus to:
detect if the recognized change is a short-term change using the stored values; and

if the recognized change is a short-term change, the at least one memory (104) and the computer program code are configured to, with the at least one processor (102), cause the apparatus to:
detect a fault or a cavity in the rock.
An apparatus according to claim 6, wherein the at least one memory (104) and the computer program code are configured to, with the at least one processor (102), cause the apparatus to:
compare the computed difference with a threshold value in order to detect a fault or a cavity in the rock.
An apparatus according to any of preceding claim 3 - 7, wherein the at least one memory (104) and the computer program code are configured to, with the at least one processor (102), cause the apparatus to:
detect if the recognized change is a long-term change using the stored values; and

if the recognized change is a long-term change, the at least one memory (104) and the computer program code are configured to, with the at least one processor (102), cause the apparatus to:
detect wear in the drill bit of the rock drilling unit.
An apparatus according to any of claims 6 - 8, wherein the at least one memory (104) and the computer program code are configured to, with the at least one processor (102), cause the apparatus to:
filter the stored values for removing the high peaks associated with the rock drilling unit configuration.
An apparatus according to any of claims 1 - 9, wherein the drilling parameter model is a regression model of impact frequency and flushing fluid pressure.
An apparatus according to any of claims 1 - 10, wherein the at least one memory (104) and the computer program code are configured to, with the at least one processor (102), cause the apparatus to:
determine if the flushing fluid flow is at normal level; and
evaluate the reliability of the drilling parameter model based on the determined flushing fluid flow deviation from the normal level.
A rock drilling unit, wherein the rock drilling unit is connected to an apparatus according to any of preceding claims 1 - 11.
A rock drilling unit according to claim 12, wherein the rock drilling unit comprises the apparatus.
A rock drilling unit according to claim 12 or 13, wherein the rock drilling unit further comprises at least one of the following: an impact frequency sensor, flushing fluid pressure sensor and hole depth sensor.
A method for recognizing a change in rock drilling, the method comprising:
retrieving a drilling parameter model;

monitoring drilling parameters during drilling;

estimating drilling parameters using the drilling parameter model;

computing a difference between the estimated drilling parameters and the measured drilling parameters; and

recognizing a change in the drilling process based on the computed difference.