Patent Application
20240102377
The present invention relates to mining, and, more specifically, to a method and system for detecting a state of a joint of a drill string. The invention also relates to a computer program implementing the method according to 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 impact element is transferred into the rock for breaking thereof. 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, in general threaded joints, are not sufficiently tightened. 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.
When drilling longer holes in, for example, rock, a plurality of drill rods may be joined e.g. by being screwed together in order to lengthen the drill string so that a hole of a desired length may be drilled.
It is an object of the invention to provide a method and system that may identify loosened joints, in particular loosened threaded joints, during percussive drilling.
According to the invention, it is provided a method for determining the state of at least one joint of a drill string of a drill rig, the drill rig comprising a percussion device comprising a percussive element for inducing shock waves into the drill string, and a sensor for sensing stress waves in the drill string caused by impacts of the percussive element, the method comprising, when a stress wave is induced into the drill string by the percussive element. A representation of the incident stress wave caused by the percussive element is determined, as is a representation of a reflected wave representing a reflection of the incident stress when reaching said at least one joint.
A stiffness of the at least one joint is estimated by estimating a force exerted on the at least one joint by said incident wave and a displacement caused by said force, and a signal representing the state of said at least one joint is generated based on said estimated stiffness.
As discussed above, properly tightened joints are a requirement for efficient drilling. The tightening of the normally threaded joints in general also becomes firm as a consequence of the shock waves passing through the joints during drilling. In unfavourable conditions, however, the joints may become loosened which deteriorates the drilling and the threaded joints are subject to excessive wear.
There are also situations when there exists a desire to loosen the joints. Following drilling of a hole the drill string is retracted and the drill rods loosened from each other. During drilling, however, the joints may become so firmly tightened as a consequence of the shock waves passing the joints during drilling that the joints cannot be loosened only with the assistance of a rotation motor of the drilling machine.
In order to solve this, e.g. an operator may end the drilling by letting the impact device exert the drill string to impacts for a short while without pressing the drill string against the rock being drilled in order to loose the joints. Whether or not this is successful may depend on the skills of the operator. This procedure, which may be harmful to components of the drill rig, may be performed for longer than necessary periods of time.
According to the invention such problems may be mitigated by a system and method where the state of the joints in regard of whether they are loose or tight may be accurately estimated, and utilised during drilling as well as when loosening the joints prior to retracting the drill string.
The determination of the state of a joint is performed by estimating a force exerted on the at least one joint by the incident wave generated by the impact of the percussion element and further determine a displacement caused by said force when impacting the joint for which the status is being determined. A signal representing the state of the at least one joint, i.e. whether the joint is tight or loose, may then generated using the estimated stiffness. The signal may be used by a drill rig control system in automated drilling, or by an operator that manually controls the drilling control parameters.
The displacement of the joint may be determined by estimating the velocity vthread of the stress wave when propagating through the drill steel, which may be estimated as: vthread=1/cp(σinc−σref) and integrating the velocity of the stress wave, e.g. according to d=∫vthreaddt.
According to embodiments of the invention, the force acting on a joint because of the incident stress wave may be estimated through a sum of the incident wave and the reflected wave multiplied with a cross sectional area of a component of the drill string, such as the cross sectional area of a drill rod of the drill string.
According to embodiments of the invention at least one of said representation of the incident stress wave and said representation of the reflected stress wave is filtered prior to estimating the stiffness of the joint. In this way, noise in the signals caused e.g. by other reflections in the drill string may be attenuated and/or removed to allow a more accurate estimation of the stiffness of the joint.
According to embodiments of the invention, an offset in said representation of the incident wave and/or reflected wave is removed prior to estimating the stiffness of the joint. The offset may relate to signal levels caused by other reflections in the drill string, and removing the offset may also allow a more accurate estimation of the stiffness of the joint.
According to embodiments of the invention, the stiffness is estimated as a change in force applied by said incident wave on said at least one joint in relation to a change in displacement of the joint caused by said force. This provides a reliable measure of the stiffness of the joint. According to embodiments of the invention it is determined that a joint is properly tightened when a change in force in relation to a change in displacement exceeds a threshold. Conversely, it may determined that a joint is loose when a change in force in relation to a change in displacement is below a threshold.
According to embodiments of the invention, a plurality of thresholds are utilised, so that it may e.g. be determined whether a joint is about to become loose prior to the joint actually have loosened.
According to embodiments of the invention, the estimated stiffness of one or more joints of the drill string are continuously monitored by a drill rig control system, wherein the drill rig control system may adjusting one or more drilling control parameters based on the monitored the estimated stiffness of the at least one joint. Such control parameters may include percussion pressure, feed pressure, feed force, feed velocity, rotation pressure, rotation flow, rotation speed.
The stiffness may be estimated for a plurality, or all, of the joints of the drill string. The generated signal may indicate whether a particular joint is loose, or alternatively whether any or all joints are loose.
According to embodiments of the invention, in a situation when all joints are to be loosened, such as when the drill string is to be retracted from a drilled hole, it may be determined for each joint whether the joint is loose and when all joints are loose a signal indicating that all joints are loosened may be generated. In this way e.g. applying percussions by operator or rig control system may be aborted as soon as the joints are loose so that excessive impacts may be avoided. For example, the rig control system can stop applying impacts to the drill string as soon as it is determined that all joints are loosened.
A state of a particular joint can be determined by estimating when in time the reflection stemming from the particular joint is detectable by the sensor.
According to embodiments of the invention, when the first joint is at a distance from the sensor such that the incident wave is mixed with the reflected wave, the representation of the incident wave may be compensated for the reflection such that the representation of the incident wave is valid also when used for estimation of the stiffness of joints further away from the sensor.
According to embodiments of the invention a first sensor element, such as part of a sensor, or a separate sensor, is used for determining a representation of the incident wave and a second sensor element is used for determining a representation of the reflected wave. A combination of the sensors may also be utilised to determine the incident wave and reflected wave. In this way e.g. the incident wave need not be compensated for a reflected wave even if these coincide in time at the location of the sensor elements.
With further regard to the sensor, 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.
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.
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 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.
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 105 such as a drilling machine, 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. The drill string may consist of a single drill rod being threaded together with the drilling machine, and to which the drill bit is threaded. This is common e.g. in tunnelling. The drill string 107, however, oftentimes does not consist of a drill string in one piece, but, instead, 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 (see
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 (see below).
As is also in general the case, flushing fluid such as e.g. compressed air or a mixture of compressed air and water, or of any other suitable kind, may be led to the drill bit 106 through a channel (not shown) inside the drill string 107, where the compressed air may be supplied to the drill string 107 from a tank in a manner known per se and which is not illustrated herein.
The hydraulic pump 116 and other power consumers such as e.g. compressors and further hydraulic pumps 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.
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 be taken, and where the control signals, such as operator inflicted joystick deflections and/or maneuvering 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 maneuvering 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 maneuvered 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 determination of the status of one or more joints of the drill rig is performed by a control unit of the drill rig, such as control unit 120 of
As was discussed above, it is crucial that the threads are suitably tightened during drilling to avoid excess wear of the drill string components. A loose joint will also give rise to potentially harmful reflections i.e., a larger part of the induced shockwaves would be reflected at the joint instead of being transmitted to the drill bit and ultimately the rock to be broken. These reflections may be harmful not only to the drill string but also the percussion device and other components of the drill rig. The ability to detect a loose joint during ordinary drilling may reduce such unfavourable situations from being undetected for periods of time. However, as was also discussed above, it is not only during ordinary/regular drilling that the ability of detecting a loose joint may be desirable. When the drilling of a hole is finished, the drill rod is retracted from the drilled hole where, during the retraction, the components forming the drill string are loosened from each other as the drill string is being pulled out. During drilling, however, the joints may become tightened to a degree where rotation/torque that may be applied by the rotation motor will not alone be sufficient to loosen the joints. Therefore, a method is commonly used where the percussion piston repeatedly strikes the drill string in a state where the drill bit does not contact the rock. This is because such procedure may loosen the joints.
An experienced driller may be capable of determining when the repeated strikes on the drill string will have caused all joints of the drill string to be sufficiently loosened such that the drill string may be retracted in a straightforward manner. An inexperienced driller, however, may utilize percussive action for a longer than necessary time with the result that excessive wear may arise and, potentially, the threads may actually be welded together instead of being loosened by the heat that is caused by stress waves acting on already loosened threads. Alternatively, the applied percussive action may not be sufficient with the result that all joints may not be loosened. This may cause problems when retracting the drill string and necessitate that the drilling machine is again connected to the drill string to further loosen the joints.
According to embodiments of the invention, such problems may be mitigated by a system which is capable of determining whether or not the joints of the drill string are either sufficiently tightened for proper drilling or, as the case may be, sufficiently loose to allow proper retraction of the drill string.
This determination may, according to embodiments be performed individually for each joint, and
The detected signal is then signal processed according to the below. However, in order to facilitate signal processing, and reduce computations, it is not necessary to process the complete detected signal by the sensor 209 but instead it may be sufficient to process suitable portions of the detected signal. This is illustrated in
As is illustrated in the figure, the respective reflections occur at different points in time because of the time it takes for the stress wave to propagate from the impact surface A through the drill string through the drill string and be reflected at the various points of reflection along the drill string and travel back to the position of the sensor 209.
The determination of when in time a particular joint is to be evaluated may be determined in various ways. For example, this can be determined in a straightforward manner through the use firstly of the distance from the sensor 209 to the one or more threads that are to be evaluated. There are a number of parameters that may influence this determination. For example, information such as drill steel length, and the distance to the tip of the thread. Furthermore, the correct steel length, i.e. the distance that the stress wave travels in steel from impact by the percussion piston needs to be known.
Such information, however, is in general stored in the drill rig control system. For example, the length of the shank adapter may be stored. The type of drill rods being used is in general already input into the control system for use in other parts of the drill rig control, where such data may include e.g. the length of the drill rods, cross sectional area and type of steel being used in the manufacturing. The propagation velocity of the stress wave in the steel may be accurately determined through the length of steel, Young's modulus of drill steel and the density of the drill steel. The velocity may also be calibrated using knowledge of the length of the drill steels, which in general is stored in the rig control system, and by analysing the time of arrival of the incident wave and the reflected wave and/or a plurality of reflected waves and secondary incident waves (reflected waves that reaches the drill shank and are reflected again back towards the rock, and so on) from different part of the drill string to determine a time of travel from which the velocity can be determined.
The propagation velocity of the stress wave in the drill string can hence be straightforwardly determined through methods known per se, which also allows a correct determination of time-accurate “cutouts” of the sensor signals of the sensor 209 that are to be used in the determination of the status of the joints according to embodiments of the invention. The lengths of the joints are preferably also taken into consideration when determining the cutouts. The reflection will commence at the tip of the thread and reflection will occur throughout the length of the thread. According to embodiments of the invention, however, cutouts are not utilised but instead the complete signals of the sensor 209 are utilised, where still expected time of arrivals of the various reflections may be determined in the same manner.
The actual processing of the detected/receive sensor signals from sensor 209 in order to determine whether or not a joint is loose will be explained in the following with reference to
With regard to the first joint, i.e. the joint 205 where the drill shank is connected to drill rod 202, the reflection from this joint will, according to the present example, reach the sensor 209 prior to the complete stress wave has been induced into the drill string and completely propagated away towards the drill bit 106. This is because the time it takes for the full length of the stress wave to pass e.g. the sensor 209 will depend on the length of the percussion piston, and this time may be longer than e.g. the time it takes for the incident flank of the stress wave to reach the first joint 205 and be reflected back to the sensor 209. Even if this is not the case, this situation may still arise e.g. in dependence of the particular location of the sensor 209. This may in particular be the case when the sensor is located in the vicinity of the joint between drill shank and the first drill rod of the drill string. In case the piston length is stored in the control system, this may be utilised to determine the pulse length of the incident stress wave.
If the first thread is close to the sensor as in the present example, and also loose, the incident wave will be mixed with the reflected wave of the loose joint. This may be compensated for, in particular to obtain accurate results from the joints further down the drill string.
Such compensation can be carried out by adjust the signals to remove the reflection of the first joint, or use a stored reference signal from a same combination of shank and piston when the joint is tightened so that the reflection can be estimated as the difference in relation to this reference. Such reference signals can be determined beforehand and stored in the control system. Alternatively, the reference signal may be stored from a previous impact where the joint has been considered to be tightened. It is also possible to use a sensor, or a sensor combination that is capable of separating the incident wave and reflected wave from each other. This may be performed, for example, by the individual sensors or individual sensor elements of a single sensor measuring the stress waves with an offset so that the incident wave and reflected wave can be solved from the two measurements.
In steps 505, the reflected wave is subjected to filtering and an offset adjustment. With regard to filtering, this may be performed in any suitable manner, e.g. to remove ripples caused by reflections from other lose joints and/or irregularities in the drill string etc. This may, for example, be performed by utilising a moving average filtering, but it may also be performed by filtering in any other suitable way, such as finite impulse response (FIR) filtering and/or infinite impulse response (IIR) filtering. In addition to filtering the reflected wave in step 505, the reflected wave may be subjected to an offset adjustment to remove any offset in the signal that is not caused by the particular reflection being evaluated. This may be performed by subtracting a reference offset or by utilizing a measurement value from the beginning of the cutout time window as reference.
In general, the reference offset may be determined in various different ways. For example, there may be stored in the control system sensor signals representing a stroke on a drill string having the same drill shank and drill bit and possibly drill rods. An offset may be determined and used as reference, where this reference may then be subtracted from the measured signals. Alternatively, or in addition, a sample may be taken in the beginning, such as in the beginning of the stress wave when measurements are made on the incoming wave or at the beginning of the time period for which the analysis is performed. It is also possible to use a reference offset of a previous stroke, i.e. that has been stored when measured for a previous stroke. The signal may be compensated for the offset both before being filtered as well as after the filtering in order to remove any remnant offset following filtering. Furthermore, it may be necessary to take into account whether the first joint, i.e. between drill shank and the first drill rod is loose such that this is compensated for when analysing reflexes of the joint between the first and second drill rod.
In step 506, the incident wave signal is subjected to a similar kind of filtering e.g. also using a moving average filtering or any other suitable kind of filtering. Furthermore, any offset is also removed where this may be determined in a similar manner. The incident wave may also be subjected to a scaling in order to scale the incident wave to a level corresponding to the level of the reflected wave. This scaling may be performed e.g. because the cross-sectional area of the joint may be higher than the cross-sectional area of the drill rod, which thereby has an impact on the level of the reflected wave. This is schematically illustrated in
In step 507 the force that the joint withstands when subjected to the incident wave is estimated, e.g. according to the following equation:
F=A
rod(σinc+σref) (eq. 1)
The representations preferably have a corresponding length in time.
In step 508, the velocity vthread of the stress wave when propagating through the drill steel is estimated, where this estimation of the propagation velocity may be estimated as:
These parameters may be stored in the control system of the drill rig for various drill rods in case parameters vary.
The estimated velocity is integrated in step 509 to obtain a displacement, where the displacement is a measure of the compression (or extension) of the joint when subjected to the incident wave.
d=∫v
thread
dt (eq. 3)
The stiffer the joint is, the smaller will the displacement d be in relation to applied force. The extent to which the joint is compressed, and the force required to accomplish the compression (or extension as the case may be), i.e. longitudinal displacement of the joint, is therefore used to determine a representation of the stiffness of the joint according to embodiments of the invention.
This is illustrated in
The stiffness can hence be determined as the change in increase in force in relation to the concurrent displacement, i.e. ΔF/Δd. For as long as the estimated stiffness exceeds e.g. a threshold ΔFthres/Δdthres, the joint is determined to be sufficiently tightened.
This is illustrated in
With regard to the example of
When the stiffness of a particular joint, or any joint as the case may be as been determined in box 510 in
This may then be used either by the control system in automated drilling or by an operator so that control parameters for controlling the drilling can be automatically or manually adjusted in case deemed necessary. During normal drilling it may be sufficient to indicate if any of the joints of the drill string is considered at least partly lose or such that the operator may take necessary action if necessary. For example, this may include adjusting the drilling control parameters e.g. by increasing and/or decreasing any of the control parameters percussion pressure, feed pressure and rotation pressure.
In case the drill string is to be retracted, there may, instead and/or in addition, be an indicator indicating whether or not all joints are determined to be loosened. The estimation of the stiffness of the joints may also be used in automated drilling where the drill rig control system may adjust drilling control parameters in response to estimations of the statuses of the joints. Similarly, when the drill string is to be retracted the control system may apply percussions to an extent such that the joints precisely are loosened but while simultaneously excessive percussions are avoided.
According to the invention, it is hence provided a method that accurately may estimate the stiffness of a joint using reflected waves that may be very difficult to analyse in themselves, as is apparent when looking at the curves of
According to the above example, the determination has been performed as an estimation whether the joint is either tightened or loose. According to embodiments of the invention, the presentation to user or control system control may also be e.g. a number of loose threads per a particular number of impacts, e.g. expressed as a percentage. The determination according to the invention may be arranged to be commenced as soon as drilling commences. Results form the estimation of the status of the joints may also be stored e.g. in a storage 512 e.g. to allow use of historical data.
The invention also allows that different thresholds of the change in increase in force in relation to the displacement. This may be used to detect whether one or more joints are about to become loose, such that proper actions may be taken prior to the joint actually has become loose. Furthermore, the thresholds may be different for different joints of the drill string.
The present invention may be utilised for essentially any kind of drill rig where hydraulic percussive drilling is utilised in combination with joints that may be loosened during drilling. Similarly, the invention is applicable for any other kind of percussion drilling technology. The invention is applicable for underground drill rigs as well drill rigs operating above ground.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2051525-0 | Dec 2020 | SE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/SE2021/051188 | 11/30/2021 | WO |
