Construction equipment with a bucket shake function and a method for emptying a bucket of construction equipmen

Abstract

Construction equipment (100) comprising a tool carrier arm (150) and a control unit (110) arranged to control hydraulic cylinders (C3, C4) on the tool carrier arm (150), where the tool carrier arm (150) comprises a tool interface (140) arranged at its distal end to hold a bucket (1000), andwhere the control unit (110) is arranged to execute an automated bucket shake function comprising joint actuation by the control unit (110) of at least two hydraulic cylinders (C3, C4) on the tool carrier arm (150).

Description

The present disclosure relates to hydraulically powered construction equipment, such as tracked demolition robots. There are disclosed hydraulic systems, methods, and control units for operating a bucket arranged on a tool carrier arm.BACKGROUNDDemolition robots are relatively light-weight and agile construction machines which can be used for various tasks, such as smaller excavation jobs, transportation, and of course demolition tasks.A demolition robot comprises a tool carrier arm that can be used to support a bucket tool at its distal end.It may be difficult to use the bucket in some scenarios, such as when the material in the bucket tends to stick to the bucket.SUMMARYIt is an object of the present disclosure to provide improved techniques for operating a bucket arranged on the tool carrier arm of construction equipment, such as a tracked demolition robot. This object is at least in part obtained by construction equipment comprising an automated bucket shake function. The construction equipment comprises a control unit and a tool carrier arm with a tool interface arranged distally on the arm to hold a bucket. The arm comprises at least a second arm segment and a third arm segment. The third arm segment is rotatably connected at its proximal end to a distal end of the second arm segment and a third hydraulic cylinder is arranged to rotate the third arm segment relative to the second arm segment about a third axis. The tool interface is rotatably connected to a distal end of the third arm segment and a fourth hydraulic cylinder is arranged to rotate the tool interface relative to the third arm segment about a fourth axis. The control unit is configured to execute the automated bucket shake function by jointly controlling the third hydraulic cylinder and the fourth hydraulic cylinder to repeatedly extend and retract over predetermined respective cylinder extension ranges in response to a bucket shake command. This way a bucket holding material that has become stuck in the bucket can be efficiently emptied at a desired location. The joint control of the third and the fourth hydraulic cylinders provides a more pronounced shaking motion compared to if only a single cylinder had been used to cause the shaking motion by the bucket during the automated bucket shaking operation.To achieve even better performance, the control unit can be arranged to control the third hydraulic cylinder and the fourth hydraulic cylinder in a time synchronized manner to repeatedly extend and retract in non-identical phase. This increases the pivoting speed of the bucket, which improves the bucket emptying operation. The control unit can for instance be arranged to control the third hydraulic cylinder and the fourth hydraulic cylinder in opposite directions in response to the bucket shake operator command. I.e., when the third cylinder is extended the fourth cylinder is retracted, and vice versa.According to some aspects, the control unit is arranged to initiate execution of the bucket shake function by controlling the third cylinder to move the bucket upwards away from the ground and the fourth cylinder to move the bucket upwards away from the ground. This way the automated bucket shake operation is less likely to slam the bucket into the ground or into some nearby object, since the first move of the bucket shake operation is to lift the bucket upwards away from the ground or away from a container. The lower extreme point of the bucket during the bucket shake operation will be the position of the bucket when the bucket shake operation was started.The predetermined respective cylinder extension ranges, and optionally also the cylinder speeds during the bucket shake operation, may be configurable by an operator of the construction equipment. This way an operator can configure a desired magnitude or intensity of the bucket shaking, from a low intensity smaller bucket shake to a very strong bucket shake operation capable of dislodging most stuck materials.The construction equipment preferably comprises an input device such as a button on a remote control device that is arranged to generate the bucket shake command in response to manipulation by an operator. An operator can then simply press a button, e.g., on a joystick of the remote control, in order to trigger the automated bucket shake operation. The bucket shake operation may persist for a predetermined or configurable time period after started or persist for as long as the operator manipulates the input device.The construction equipment may also comprise a dust control system such as a liquid spray or misting system. The control unit can in this case be arranged to trigger activation of the dust control system in coordination with the automated bucket shake function.There are also disclosed herein methods and various forms of construction equipment associated with the same advantages as discussed above in connection to the control units.Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a / an / the element, apparatus, component, means, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realizes that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention.BRIEF DESCRIPTION OF THE DRAWINGSThe present disclosure will now be described in more detail with reference to the appended drawings, where:Figure 1 illustrates an example demolition robot;Figures 2A-D show example hydraulically powered tools;Figure 3 is a graph illustrating hydraulic power as function of pressure and flow;Figure 4 schematically illustrates a hydraulic system;Figure 5 is a graph that illustrates tripping characteristics of an example fuse;Figure 6 shows an example remote control device for controlling a demolition robot;Figure 7 is a flow chart illustrating methods;Figure 8 schematically illustrates a control unit;Figure 9 schematically illustrates a computer program product;Figure 10 illustrates a bucket for a demolition robot;Figure 11 schematically illustrates a bucket shaking operation;Figure 12 illustrates a tool carrier arm with hydraulic actuator cylinders;Figure 13 is a graph illustrating hydraulic cylinder extension and retraction; andFigure 14 is a flow chart illustrating methods.DETAILED DESCRIPTIONAspects of the present disclosure will now be described more fully with reference to the accompanying drawings. The different devices and methods disclosed herein can, however, be realized in many different forms and should not be construed as being limited to the aspects set forth herein. Like numbers in the drawings refer to like elements throughout.The terminology used herein is for describing aspects of the disclosure only and is not intended to limit the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.Figure 1 illustrates example construction equipment 100, in this case a demolition robot. A demolition robot is a light-weight construction machine which can be used for various work tasks, such as smaller demolition tasks. A demolition robot is often tracked, i.e., comprises tracks 130 for support on the ground surface and for propulsion. The construction equipment 100 comprises a control unit 110 which controls the general operation of the machine, and a hydraulic system 120 that powers the different actuators on the robot, such as its tracks 130 and the tool interface 140 comprised on the tool carrier arm 150. The control unit 110 is configured to generate control signals which control the operation of various hydraulic cylinders and other hydraulic actuators on the machine.The example robot 100 is powered via a cable 160 arranged to connect the robot to electrical mains. Battery electric versions of demolition robots are also known, as well as hybrid electric designs powered partly from a battery bank and partly from electrical mains.The present disclosure is also applicable to other forms of construction equipment, although most of the functions herein are most advantageously used in remote controlled demolition robots, i.e. , hydraulically powered smaller tracked vehicles with a single tool carrier arm 150 that are controlled by remote control from a location in vicinity of the machine, such as within 30 meters of the machine or so. An example remote control will be discussed in more detail below in connection to Figure 6.A problem, as noted above, is that the fusing of an electrical mains connection at a work site may be smaller than the maximum current consumption of the demolition robot 100, i.e., the fuses may have a rated current IN below a maximum current consumption of the machine 100. In order to not trip a fuse on the incoming power to the machine 100, a setting can be made available, e.g., in the remote control device 600 to limit the maximum current or power drawn by the machine 100 via the electrical mains connection 160.The same problem may occur on a battery electric demolition robot or a hybrid electric demolition robot in case the batteries are not able to provide a high enough output current. This may, e.g., be the case if the batteries are cold or under-dimensioned for some work task.The hydraulic power generated in the hydraulic system 120 is proportional to both hydraulic flow and hydraulic pressure in the system. This means that when flow and pressure increases at the same time the power consumption of the hydraulic system 120 also increases. In order not to trip fuses and potentially stall the hydraulic pump drive motor of the machine when there is a high flow and a high pressure at the same time there is a need for power limitation.Figures 2A-D illustrate some example hydraulic tools 200 that can be used with the construction equipment 100. The example hydraulic tools 200 in Figures 2A and 2B are crushers that comprise two opposing and cooperating jaw members 210 arranged to be powered by the hydraulic system 120. Figure 2C shows shears that can be used to cut hard materials such as steel rebar structures and the like. The shears comprise two opposing and cooperating jaw members 210 arranged to be powered by the hydraulic system 120. Figure 2D illustrates a type of grapple which also comprises two opposing and cooperating jaw members 210 arranged to be powered by the hydraulic system 120. The example tools in Figures 2A-D can be attached to the tool interface 140 on the tool carrier arm 150 of the construction equipment 100 via respective tool interfaces 220. The movement of the jaw members 210 is controlled by the control unit 110.When using, for example a concrete crusher, shears, or grapple device on a demolition robot there is an initial need for a high flow in order to close the cooperating jaw members 210 quickly. There is also a need for high pressure in order to achieve a high crushing force from the actuator hydraulic cylinder. After crushing there is once more a need for high flow such that the opposing jaw members can be opened up again. However, with a crusher, shears or grapple tool, there is little or no need for both high flow and high pressure at the same time since the high pressure need arises when the opposing jaws are more or less stationary.It has been realized that power consumption in construction equipment comprising the type of hydraulic tool 200 that has two opposing and cooperating jaw members 210 arranged to be powered by the hydraulic system 120 can be efficiently limited with very small impact on user experience if hydraulic flow is limited as function of hydraulic pressure to the tool, or alternatively as function of pump motor consumed current and / or axle torque during use of the tool. This way a concrete crusher or the like will close its jaws quickly due to the high flow (and low pressure), but when the jaws make contact with an object the pressure will increase due to the increase in mechanical resistance, and flow will automatically be lowered to maintain hydraulic power outtake within an acceptable range.This method is not suitable for all types of hydraulic tools. Hence, the construction equipment 100 is advantageously configurable in a “jaw-tool” or “flow-limiting” mode of operation which can be manually or automatically activated when a hydraulic tool with two opposing and cooperating jaw members powered by the hydraulic system 120 are attached to the construction equipment 100. The selection of operating mode, i.e. , the activation of the flow limitation function described herein, can be performed by operator input via a remote control device, or automatically by detecting that a certain type of tool has been attached to the arm 150. Detection of tool type can be done by using a radio frequency identification device (RFID) on the tool and a corresponding RFID reader on the tool interface 140.Figure 3 shows an example graph 300 that illustrates a relationship or mapping between hydraulic pressure, hydraulic flow, and hydraulic power outtake in the system. The hydraulic pressure can, e.g., be defined as a hydraulic pressure to the hydraulic tool, while hydraulic flow can be defined as hydraulic flow to the tool, or as a total hydraulic flow from the hydraulic pump in the hydraulic system. The hydraulic pressure can also be a hydraulic pressure at the pump outlet. The hydraulic power is related to the total power consumption of the construction equipment 100 in a known manner, and it is approximately proportional to both the pressure and the flow. As a simple approximation, hydraulic power equals the product of hydraulic flow and hydraulic pressure in the hydraulic system. In simplified terms, the formula for hydraulic power output (in Watts) is Power = Q x P, where Q is the flow rate in liters per minute, and P is the pressure in bars.The graph 300 illustrates a sequence of 25 example hydraulic pressures (labelled 1-25) with corresponding hydraulic flow levels. Note that the hydraulic power increases as pressure builds. The hydraulic power then reaches a maximum allowable value 310 where it saturates. This is because the system has started to limit the flow in the system, which can be seen from the gradually reduced flow levels. The graph does not show absolute levels since these are system dependent.To summarize, the present disclosure relates to construction equipment 100 comprising a control unit 110, a hydraulic system 120, and a hydraulic tool 200 with two opposing and cooperating jaw members 210 arranged to be powered by the hydraulic system 120 of the construction equipment. The hydraulic tool 200 may for instance be a crusher, shears, or a grapple. These types of plier-like or scissor-like tools are preferably closed and opened quickly in response to operator control input, which requires high levels of hydraulic flow to move the jaw members 210. The tools also require high pressure to generate a large force when engaging an object. However, the jaws will not move much while engaging an object, and hence high flow and large pressure will not be required at the same time. Hence a flow limitation in the system as function of pressure, where the hydraulic flow is limited to maintain a hydraulic power outtake (the product of the pressure and the flow) which satisfies an acceptance criterion (such as being below a threshold) will not impact user experience to any significant degree.The construction equipment 100 is preferably a tracked demolition robot. A tracked demolition robot is a relatively small machine (smaller than a full size excavator or the like) without a cab or seat for an operator, that normally comprises a single tool carrier arm. A demolition robot is remote controlled, which means that the machine is controlled from a distance by a wireless or wired remote control device, such as the portable remote control device 600 illustrated in Figure 6.The control unit 110 is configured to obtain data related to a hydraulic pressure of the hydraulic tool 200. As explained above, this hydraulic pressure will remain relatively low as the jaws 210 are moved back and forth between their open and closed positions. However, once the hydraulic tool engages an object between the two opposing and cooperating jaw members 210, the hydraulic pressure will rise. This rise in pressure will be apparent from the obtained data.The data related to the hydraulic pressure of the hydraulic tool 200 can be obtained in several different ways. The most straight forward way is perhaps to arrange a hydraulic pressure sensor in connection to the tool 200 to continuously measure the pressure to the tool 200. The signal from this pressure sensor will indicate if the tool is engaging an object between its jaws or not, where a high pressure indicates engagement and a low pressure indicates that the jaws are not in engagement with an object. A hydraulic pressure sensor is sometimes referred to as a hydraulic pressure transducer. Hydraulic pressure sensors are generally known and will therefore not be discussed in more detail herein.Alternatively, or as a complement to the signal from the pressure sensor, the control unit 110 can be configured to obtain the data related to the hydraulic pressure of the hydraulic tool 200 at least in part as an applied motor torque and / or current of a hydraulic system pump 410 drive motor comprised in the construction equipment 100. The drive torque applied by the drive motor will rise as pressure builds in the system, thus drive torque can be used as an indication of the hydraulic pressure in the system. Likewise, the current consumption of the drive motor will increase as pressure builds in the system. Motor data of this kind can be processed jointly with the signal from the pressure sensor in order to obtain a more reliable indication of hydraulic pressure, such that the hydraulic flow control can be performed in a more reliable manner.The control unit 110 is also configured to determine an acceptable level of hydraulic flow in the hydraulic system 120 based on the hydraulic pressure in the tool, such that a hydraulic power as function of pressure and flow in the hydraulic system 120 satisfies an acceptance criterion. Having regard to this acceptable level of hydraulic flow, the control unit 110 controls the hydraulic flow to the hydraulic tool 200 so as to be at or below the acceptable level of hydraulic flow. Thus, the control unit modulates the flow level in the system based on the pressure to the tool, so as to keep the hydraulic power outtake within acceptable limits. The acceptable limits of the hydraulic power outtake may be manually configured by an operator based on a fuse rating at the work site, or as a maximum current level of the machine that is not to be exceeded.According to some examples, the control unit 110 is configured to determine the acceptable level of hydraulic flow based on a predetermined mapping between the data related to the hydraulic pressure of the hydraulic tool 200 and acceptable level of hydraulic flow. For instance, suppose that there is a pressure sensor arranged in connection to the tool, and that this pressure sensor continuously measures the pressure delivered to the tool as the jaws are moved together to crush, shear, or grip an object. The mapping may then resemble that illustrated in Figure 3. I.e., for each pressure level there is a corresponding maximum allowable flow. The mapping between pressure and allowable flow may also be in the form of a predetermined function. It is appreciated that the acceptable level of hydraulic flow may be indicated by a valve setting of the tool, or by an actual flow level.According to some aspects, the acceptable level of hydraulic flow in the system is determined as a function of pressure and also an allowable power consumption by the system. Thus, if the machine is connected to a high power source, such as a 32A fuse or 64A fuse electrical mains, then a higher flow is permitted for a given pressure compared to if the machine is connected to a 16A fuse electrical mains. The type of electrical mains can, e.g., be configured by an operator. The operator can also configure a power limitation level by the control unit 110, and the control unit will then determine the acceptable level of hydraulic flow for different system pressures accordingly.The techniques disclosed herein may be generalized to construction equipment 100 that comprises a control unit 110, a hydraulic system 120, and a hydraulic tool connected to the hydraulic system 120, such as one of the tools illustrated in Figures 2A-D or some other type of hydraulic tool suitable for use with construction equipment of the kind discussed herein, not necessarily comprising cooperating jaw members.The hydraulic tool 200 is operable in at least a first operation stage and a second operation stage, where the second operation stage is associated with a higher hydraulic pressure compared to the first operation stage. The tool may for instance have a mode of operation where it moves in position relative to a work object, in which mode the tool mainly moves and does not interact with the work object, and another mode where the tool engages with the work object. The control unit 110 can be arranged to obtain data related to a current operation stage of the hydraulic tool 200, e.g., by sensing a hydraulic pressure of the tool, by detecting a pose of the tool, or by detecting a position of the tool relative to the work object using a position sensor or a camera. The control unit 110 is also configured to control the hydraulic system 120 to deliver a reduced hydraulic flow to the tool 200 when in the second operation stage compared to when in the first operation stage. The delivered hydraulic flow for the different modes may be configured as a flow limit, or as a function of the hydraulic pressure as discussed above.Thus, at least some of the construction equipment discussed herein are arranged to carry and operate hydraulic tools associated with two or more modes of operation, such as a closing stage of operation and an engagement state of operation. A first mode of operation is then associated with a first flow limit and the second mode of operation is associated with a second flow limit that is smaller than the first flow limit.Figure 4 schematically illustrates an example 400 of the hydraulic system 120. The system comprises a pump 410 that powers a hydraulic tool 420. The hydraulic tool 420 comprises a valve 430 that is controlled by the control unit 110 to operate the actuator 440 of the tool 420. It is appreciated that the valve 430 is normally arranged on the machine, while the hydraulic cylinder of the actuator is arranged on the tool. The actuator may, e.g., be the opposing jaws 210 of a crusher, shears, or grapple tool. An optional pressure sensor 450 monitors the hydraulic pressure delivered to the actuator.According to some aspects, the hydraulic tool 200 comprises a proportional hydraulic valve 430, and the control unit 110 is configured to control the hydraulic flow by adjusting the state of the proportional hydraulic valve 430. A proportional hydraulic valve is a valve which is arranged to control hydraulic flow to the tool 200 in proportion to an input signal from the control unit 110. The wider the proportional valve is opened, the higher the flow and the faster the opposing jaws move. As the jaws encounter resistance, the pressure in the system builds up. When this happens the control unit will at some point limit the flow in the system by adjusting the state of the proportional valve. The proportional valve is preferably a pressure compensated proportional valve. The advantage in using a pressure compensated proportional valve is that the compensator function makes sure that the flow to the tool is not effected by other valve functions that may run in parallel, such as hydraulic cylinders used to control the position of the arm 150 and / or hydraulic motors used to operate the tracks 130.The hydraulic system 120 optionally comprises a variable displacement hydraulic pump, and the control unit 110 is configured to control the hydraulic flow by adjusting the state of the variable displacement hydraulic pump. In case of a variable displacement pump there is no need for a proportional valve since the flow can be controlled directly at the pump. A combination of proportional valve control and control of variable displacement of the pump can also be used. A suitable combination of the two can, e.g., be determined such as to improve the operating efficiency of the drive motor used to power the pump 410.According to one example the control unit imposes a strict limitation on instantaneous current or power drawn by the construction equipment 100, by limiting hydraulic flow as function of pressure in the hydraulic system.However, as will be explained in the following, it may be advantageous to not impose a strict limitation, but instead allow current or power to breach a nominal limit as long as the breach is temporary. It is proposed herein to calculate average current or power consumptions over different time windows, and associate separate acceptance criteria with each such time window, e.g., in dependence of the current fuse configuration at a given work site and / or specification of a battery pack of the construction equipment. This allows the system to place different limits on different time scales, such that a higher power limit can be used for transient behavior and a lower limit can be used for more long-term power consumption by the construction equipment. The current or power consumption is determined in proportion to the pressure and to the flow as discussed above, e.g., as a function of the product of pressure and flow, possibly after adding weights to the current pressure value and to the current flow value.Miniature circuit breakers (MCB) are made according to different tripping characteristics, referred to as an MCB class. MCB classes B, C, D, K and Z are known. The techniques disclosed herein are, however, not limited to any particular MCB class of fuses.According to an example of the herein proposed techniques, average current, or power consumptions ITw by the machine 100 are calculated over one or more time windows of different lengths. In other words, a metric such aswhere i(t) is instantaneous power or current as function of time t, can be determined for some different time window durations Tw, such as 1, 5, 10, 20 and 60 minutes. It is noted that many different types of averages can be calculated, such as weighted averages. The present disclosure is not limited to any particular form of averaging operation. Each average value metric will have a different acceptance criterion, such as a threshold value. For example:where IN is, e.g., the rated current of the fuses at the construction work site. The different average values can then be updated for example every minute or computed as moving averages. If the average current is above the threshold value for some of the time windows, the maximum allowable power consumption by the machine 100 can, for instance, be lowered by 5% or by some other pre-determined value. The test can then be repeated regularly, and the power consumption will therefore go down gracefully without tripping the fuses on the work site. If all averages are below their respective thresholds, then the allowable current consumption by the machine 100 can be increased again, preferably according to a graceful function, such as by gradual relative increases. The averaging filters may also comprise elements of prediction, i.e., the output of the filters may be designed so as to represent an estimated future value of an averaging filter output. This can be achieved by implementing, e.g., Kalman filter based on a constant current consumption model, or a constant change current consumption model. Kalman filters are generally known, as are Kalman filter predictors, and will therefore not be discussed in more detail herein.The acceptance criteria and the different averaging filters are preferably matched to the tripping characteristics of the MCB in use at the work site and / or to the specification of a battery pack or other energy source of the construction equipment 100. For a class C MCB, with tripping characteristics 500 illustrated in Figure 5, the time periods for averaging and the associated thresholds can be configured as illustrated by the triangles 510, 520, 530, 540 in Figure 5, i.e., spread out along the lower border of the tripping characteristic curve. It is noted that the number of averaging filters used may vary, as well as their location on the x-axis and the y-axis of the tripping characteristic.The fuse tripping characteristics exemplified in Figure 5 are generally known as a trip curve. The characteristics shown in Figure 5 is a class C trip curve and is included herein for illustrative purposes only. The x-axis shows multiple of rated current IN and the y-axis shows time in seconds. MCBs are generally available with class B, C, D, K and Z trip curve characteristics. An MCB with class B trip characteristics trips when the current flowing through it reaches between 3 to 5 times rated current. These MCBs are suitable for cable protection. MCBs with class C trip characteristics trips more or less instantaneously when the current flowing through it reaches between 5 to 10 times the rated current. MCBs with class C characteristics are commonly found in domestic and residential sites where they are used for electromagnetic starting loads with medium starting currents. An MCB with class D trip characteristics trips when the current flowing through it reaches above 10 to 20 times the rated current. Class D MCBs are suitable for inductive and motor loads with high starting currents. Class K MCBs trip when the current flowing through it reaches between 8 to 12 times the rated current. They are suitable for inductive loads and motor loads with high inrush currents. Class Z MCBs are used with highly sensitive devices such as semiconductor devices, and almost never found at construction sites. Hence, it is appreciated that acceptance criteria for current consumption over different time periods is advantageously configured differently. A short burst of high current (e.g., at five times the rated current IN) drawn by the machine will most likely not trip a class C MCB as long as the burst is limited to a time duration below one second or so. The same fuse will be tripped if a current at two times the rated current IN is drawn for two minutes or so.With reference also to Figure 6 and Figure 8, there is disclosed herein a control unit 110, 600, 800 for controlling power consumption by construction equipment 100 powered at least partly via an electrical mains cable connection 160 and / or by a battery pack. The control unit is arranged to obtain data indicative of a current or power drawn by the construction equipment 100 as function of time, either continuously, periodically, or in response to some event or trigger signal. An example of the data indicative of a current or power drawn by the construction equipment 100 is of course the hydraulic pressure and the hydraulic flow in the hydraulic system, which together are indicative of hydraulic power outtake by the construction equipment 100 as discussed above.The control unit 110 may in some case be connectable to a current sensor arranged to measure a current drawn via the electrical mains cable connection 160, in which case the data indicative of the current drawn by the construction equipment 100 is obtained at least in part from the current sensor. In this way the actual current consumption can be closely monitored, which is an advantage since more accurate current data is obtained. However, the control unit can also be arranged to estimate and / or predict the current drawn by the construction equipment 100 based on a generated hydraulic pressure and flow in a hydraulic system 120 of the construction equipment 100, perhaps measured by a pressure sensor in the hydraulic system 120 or indirectly determined based on hydraulic valve state. It is also possible to estimate and / or predict current consumption based on control commands given to an electric machine or electric actuator of the construction equipment 100. The data indicative of the current drawn by the construction equipment 100 then comprises the estimated and / or predicted current consumption. It is noted that pressure in a hydraulic system is measurable in a cost-efficient manner, while flow is more difficult / costly to measure. Hence, realizations of the techniques discussed herein for hydraulic system which comprises data obtained from pressure sensors will most likely be more common than realizations comprising actual measurement of hydraulic flow.The control unit 110, 600, 800 can be arranged to filter the obtained data using at least a first and a second averaging filter, where the first averaging filter is associated with a shorter averaging time window Tw1 compared to the second filter Tw2. The term “averaging filter” is to be construed broadly herein, to encompass any two operations of different time constants or filtering bandwidths, as discussed in more detail below. A shorter averaging time window filter can also be said to have a larger filtering bandwidth, or to let faster changes in a filter signal through with less attenuation compared to a smaller filtering bandwidth filter.The outputs of the at least two filters are associated with respective filter acceptance criteria, i.e., some form of test which determines if the output of the filter is acceptable, or if some action to reduce current consumption is required. A threshold value can be used as acceptance criteria, as discussed above, in which case the output of each filter is continuously or at least periodically checked against the respective threshold, in order to determine if the output satisfies the acceptance criteria of the filter or not. The thresholds can advantageously be determined in dependence of construction site fuse setting, i.e., as a factor multiplied with the fuse rated current, as exemplified above. The control unit 110, 600, 800 is also arranged to limit the current or power drawn by the demolition robot 100 in case any of the filter outputs does not meet the respective filter acceptance criterion by reducing the hydraulic flow in the system as discussed above. In addition to limiting current by reducing hydraulic flow, the control unit may also trigger a notification to a user in case in case any of the filter outputs does not meet the respective filter acceptance criterion.An averaging filter is to be interpreted broadly herein to comprise any filter predominantly having a low-pass filter characteristic which suppresses fast variation (where fast is defined relative to the averaging time window). An averaging operation determined for a given time window is the output of an averaging filter, and so is the output of a moving average filter. A filter having a forgetting factor w « 1, i.e., a filter which outputs a result Ik+1 according toIk+1 = (1 - w)Ik + w(ik - Ik)where k is a time index, and ik is a current drawn by the machine at time index k, is also a form of averaging filter, with an averaging time window determined by the magnitude of w.At least one of the first and the second averaging filter can also be realized by a machine learning (ML) algorithm, or an algorithm based on artificial intelligence, such as a random forest method or a neural network, configured to determine if a respective acceptance criteria is fulfilled based on training data comprising power consumption patterns and power outages for different construction site fuse settings. In this case a data set of current consumption for machines which tripped a given fuse and a data set of current consumption which did not trip the given fuse is used to train the ML structure into outputting a result which indicates if the current operation of the machine meets the acceptance criteria of the first and second filters, or if one or more acceptance criterions have been breached. The ML structure is advantageously trained for different MCB classes, such that the ML structure can be configured in dependence of a work site MCB class. To train an ML structure in this manner, real world data on time-stamped current consumption can be collected for different demolition robots 100, along with time instants where a fuse was tripped. The data can be collected for different MCB classes, and the ML structure can then be configured to output information related to whether the acceptance criteria are fulfilled or not. The control unit 110 can then use the output of the ML structure to adjust the power consumption of the construction equipment 100 to suit a given fuse installation or battery pack specification.The flow in the hydraulic system 120 can as discussed above be limited by adjusting the state of a proportional valve of the tool 200. The total flow limitation can, for instance be set at 70 liters / minute (LPM), in a system where two or more cylinders draw 40 LPM each at full speed. In this case a single cylinder can run at full speed, while two cylinders running actuated concurrently will not be able to reach full speed. Yet another way to perform a limitation on the current drawn by the machine 100 is to adjust the maximum value of the flow according to the pressure that prevails in the machine. If the machine is operating at low pressure, it may be possible to run two or more cylinders at full speed (40 LPM), but if the pressure rises, the control unit can lower the maximum currents to the control valves, i.e., lower the maximum flow through the valves, so that the output / current does not exceed a given limit.The control unit 110, 600, 800 is preferably arranged to gradually limit the current drawn according to a pre-determined function in case any of the filter outputs does not meet the respective filter acceptance criterion, as well as to gradually remove an imposed limitation on the current drawn according to a pre-determined function in case all of the filter outputs meet the respective filter acceptance criterion.If a power outage should be experienced despite the hydraulic flow limiting operations performed by the control unit, i.e., if a fuse on the work site is tripped despite the actions of the control unit 110 discussed herein, it may be advantageous to reconfigure the acceptance criteria in order to be better suited for a given work site and / or work task. Towards this end, the control unit can be arranged to store a recently drawn current in the event of an electrical mains power outage in a storage medium 830 of the control unit. A user can then access the memory and discover at which current level the fuse was tripped. This information may allow the user or some form of automatic control system to reconfigure the acceptance criteria to be more suited to a given work site.The control unit 110, 600, 800 may also be arranged to store recent filter outputs in the event of an electrical mains power outage in a storage medium 830 of the control unit, and optionally also to re-configure one or more of the acceptance criteria based on the stored recent filter outputs in response to an electrical mains power outage. This information may advantageously be displayed in the remote control, e.g., by the display 610.Indeed, the current fusing at a work site may not be known a-priori, and this feature allows fuse information of a work site to be discerned in an efficient manner. A power outage event may also be communicated to a remote server, along with the averaging filter data and / or a time record of instantaneous current drawn by the machine 100. This data can then be used for analysis at the remote server, and also for fine-tuning the ML structure discussed above.To summarize, according to some aspects the control unit 110 is arranged to obtain data indicative of a power drawn by the construction equipment 100 as function of time, such as the hydraulic pressure and the hydraulic flow in the system 120. The control unit 110 is also arranged to filter the obtained data using at least a first and a second averaging filter, where the first averaging filter is associated with a shorter averaging time window Tw1 compared to the second filter Tw2, and where the outputs of the at least two filters are associated with respective filter acceptance criteria. The control unit 110 is configured to control the hydraulic flow to the hydraulic tool 200 so as to be at or below the acceptable level of hydraulic flow in case any of the filter outputs does not meet the respective filter acceptance criterion. This means that a relatively high flow will be permitted, even if the pressure is high, as long as this high flow is of a limited time duration, e.g., a time duration that lies within the limits of the fuse tripping characteristics of the work site. The flow in the system is only limited if the high power outtake persists for too long. The control unit 110 is preferably also configured to gradually limit the hydraulic flow to the hydraulic tool 200 according to a pre-determined function in case any of the filter outputs does not meet the respective filter acceptance criterion, i.e., not limit the flow abruptly, since this may have a negative effect on user experience.Figure 6 illustrates an example remote control device 600 which can be used to control the construction equipment 100. The remote control device is a portable device, i.e., a device which can be carried by an operator walking next to the machine 100. The range of the remote control device may be on the order of 20-50 meters or so.The remote control device 600 comprises a display 610 and a speaker or buzzer device 620. The display can be used to show messages to the operator, such as notifications and warning messages. The speaker or buzzer 620 can be used to notify the operator of some event.The remote control device 600 comprises two joysticks, although a single joystick is also possible. This joystick may be arranged to generate haptic feedback, i.e., vibration may be generated in one or more of the joysticks to notify the operator of some event, such as excessive power consumption by the construction equipment 100.Figure 7 is a flow chart that illustrates a computer-implemented method performed by a construction equipment control unit 110, for controlling power consumption by the construction equipment 100, the construction equipment 100 comprising a hydraulic system 120, and a hydraulic tool 200 with two opposing and cooperating jaw members 210 arranged to be powered by the hydraulic system 120. The method comprises obtaining SA1, by the control unit 110, data related to a hydraulic pressure of the hydraulic tool 200, determining SA2, by the control unit 110, an acceptable level of hydraulic flow in the hydraulic system 120 based on the hydraulic pressure in the tool, such that a hydraulic power as function of pressure and flow in the hydraulic system 120 satisfies an acceptance criterion, and limiting SA3 the hydraulic flow to the hydraulic tool 200, by the control unit 110, so as to be at or below the acceptable level of hydraulic flow.Figure 8 schematically illustrates, in terms of a number of functional units, the general components of the control unit 800, such as the control units 110, 210 discussed above. Processing circuitry 810 is provided using any combination of one or more of a suitable central processing unit CPU, multiprocessor, microcontroller, digital signal processor DSP, etc., capable of executing software instructions stored in a computer program product, e.g., in the form of a storage medium 830. The processing circuitry 810 may further be provided as at least one application specific integrated circuit ASIC, or field programmable gate array FPGA.Particularly, the processing circuitry 810 is configured to cause the demolition robot 100 to perform a set of operations, or steps, such as the methods discussed in connection to Figure 5 and the discussions above. For example, the storage medium 830 may store the set of operations, and the processing circuitry 810 may be configured to retrieve the set of operations from the storage medium 830 to cause the device to perform the set of operations. The set of operations may be provided as a set of executable instructions. Thus, the processing circuitry 810 is thereby arranged to execute methods as herein disclosed.The storage medium 830 may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory.The control unit 800 may further comprise an interface 820 for communications with at least one external device. As such the interface 820 may comprise one or more transmitters and receivers, comprising analogue and digital components and a suitable number of ports for wireline or wireless communication.The processing circuitry 810 controls the general operation of the control unit 800, e.g., by sending data and control signals to the interface 820 and the storage medium 830, by receiving data and reports from the interface 820, and by retrieving data and instructions from the storage medium 830.Figure 9 illustrates a computer readable medium 910 carrying a computer program comprising program code means 920 for performing the methods illustrated in Figure 7, when said program product is run on a computer. The computer readable medium and the code means may together form a computer program product 900.Figure 10 illustrates an example bucket 1000. Bucket tools can be attached to the tool interface 140 of the tool carrier arm 150 of a demolition robot or other type of construction equipment 100, where it can be used to move material from one place to another in a known manner and also to excavate material. The bucket is pivoted 1010 in use to position the front edge 1020 of the bucket 1000 to scoop up material which can then be deposited at some other location. In the example arm 150 shown in Figure 12, the bucket pivots about axis A4 in response to actuation by hydraulic cylinder C4. Buckets such as the example bucket 1000 are well known in the art and will therefore not be discussed in more detail herein.Sometimes material held in the bucket sticks to the bucket and does not fall out easily despite pivoting of the bucket. To facilitate bucket emptying, an automated bucket shaking function can be implemented. When an operator activates the bucket shaking function, the construction equipment 100 rapidly pivots the bucket back and forth so as to dislodge any material remaining in the bucket. The pivoting by the bucket is controlled by the control unit in an automated manner to achieve an efficient emptying operation, beyond what is possible to manually moving the joysticks 630 of a remote control device 600.In other words, at least some of the construction equipment 100 described herein comprises an automated bucket shake function which can be used to facilitate emptying of the bucket at a desired location. The construction equipment comprises a control unit 110 as discussed above, e.g., in connection to Figure 8, and a tool carrier arm 150 with a tool interface 140 arranged distally on the arm 150 to hold a bucket 1000.The arm 150 comprises at least a second arm segment 1220 and a third arm segment 1230, and may also comprise a first arm segment 1210, as illustrated in Figure 12. The second arm segment 1220 can be attached to the chassis of the construction equipment 100. However, a more versatile arm is obtained if the arm also comprises a first segment 1210 as illustrated in Figure 12. The first arm segment 1210 is pivotably attached to the chassis or body of the construction equipment 100, as exemplified in Figure 1, which means that the entire arm 150 can pivot about axis A1. The pivoting of the arm 150 about axis A1 is controlled by a first hydraulic cylinder C1 as shown in Figure 12. The first arm segment 1210 is pivotably connected to a second arm segment 1220 at a first arm joint J1. The second arm segment 1220 can pivot about axis A2 relative to the distal end of the first arm segment 1210, which pivoting is controlled by a second hydraulic cylinder C2. A second arm joint J2 is located between the second arm segment 1220 and the third arm segment 1230. The third arm segment 1230 is arranged to pivot about axis A3 relative to the distal end of the second arm segment 1220. This pivoting by the third arm segment 1230 is controlled by the third hydraulic cylinder C3.Figure 12 is an example of a tool carrier arm 150 that comprises a first segment 1210, a second segment 1220, and a third segment 1230 that are pivotably interconnected in sequence. The third arm segment 1230 is closest to the tool interface 140, the first arm segment 1210 is closest to the machine chassis, and the second arm segment 1220 is located inbetween the first and third arm segment. The example tool carrier arm 150 in Figure 12 comprises four hydraulic cylinders C1, C2, C3, C4 arranged to control relative motion of the arm segments as described above. It has been found that the bucket shaking function discussed herein works well if the third and fourth hydraulic cylinders, i.e., C3 and C4, are jointly actuated during execution of the automated bucket shaking function, while the first and second hydraulic cylinders (C1 and C2) are kept stationary.Actuating two hydraulic cylinders jointly in this manner allows for a larger magnitude bucket motion compared to only using one cylinder, i.e., the bucket can be made to move according to a longer repetitive path compared to if only one cylinder is actuated. The change in motion by the bucket also becomes more abrupt since the direction of two hydraulic cylinders can be changed jointly, and preferably synchronously as will be discussed below.The tool interface 140 is pivotably arranged at the distal end of the third arm segment 1230 to pivot about axis A4 as illustrated in Figure 12. The pivoting by the tool interface 140 is controlled by a fourth hydraulic cylinder C4.The control unit 110 controls all four hydraulic cylinders C1, C2, C3, C4 of the arm 150, e.g., in response to operator input via the remote control device 600.It is appreciated that the hydraulic cylinders C1, C2, C3, C4 can be located above, below, or to the side of an arm segment. The position of the hydraulic cylinder in relation to the corresponding pivot axis determines what pivoting motion that is obtained when extending or retracting a hydraulic cylinder. Herein, extending and retracting a hydraulic cylinder, respectively refers to the piston moving out of the cylinder and back into the cylinder.According to at least some of the teachings herein, the third arm segment 1230 is rotatably connected at its proximal end to a distal end of the second arm segment 1220, and the third hydraulic cylinder C3 is arranged to rotate the third arm segment 1230 relative to the second arm segment 1220 about the third axis A3. The tool interface 140 is rotatably connected to a distal end of the third arm segment 1230, and the fourth hydraulic cylinder C4 is arranged to rotate the tool interface 140 relative to the third arm segment 1230 about a fourth axis A4. Thus, actuation by the third and the fourth hydraulic cylinder causes a bucket attached to the tool interface 140 to move.More generally, the disclosed construction equipment 100 comprises a tool carrier arm 150 with a tool interface 140 at its distal end. A control unit 110 of the equipment 100 is arranged to execute an automated bucket shake function, where the bucket shake function comprises joint actuation by the control unit 110 of at least two hydraulic cylinders C3, C4 arranged on the tool carrier arm 150.The control unit 110 can be configured to execute a bucket shake function by controlling the at least two hydraulic cylinders, e.g., the third hydraulic cylinder C3 and the fourth hydraulic cylinder C4, in combination to repeatedly extend and retract over predetermined respective cylinder extension ranges in response to a bucket shake command. This provides a bucket shaking action which can dislodge material that has stuck in the bucket. During the shaking operation, the third and fourth cylinders are actuated in combination to extend and retract over a limited range, such as below 5% of the total cylinder strokes. The extension and retraction is preferably centered about a mean piston location, which means that the average location of the bucket remains the same during the bucket shaking operation. Figure 11 schematically illustrates the bucket shaking operation.The construction equipment 100 may as discussed above comprise an input device such the example remote control device 600 in Figure 6 with buttons 631, 632, 640 arranged to generate the bucket shake command in response to manipulation by an operator. The bucket shaking may persist for as long as the operator presses the button, or for a predetermined time duration that may of course be configurable. In other words, the construction equipment 100 may be controlled by a remote control device 600, as exemplified in Figure 6. The control unit 110 can be arranged to execute the automated bucket shake function in response to a control signal from the remote control device 600.According to some aspects, the predetermined respective cylinder extension ranges are configurable by an operator of the construction equipment 100. This means that an operator can configure the magnitude of the bucket shaking operation, e.g., by inputting a configuration via the remote control device 600. It may, for instance, be possible for the operator to select between a strong shaking, a medium shaking, or a weak shaking operation. It may also be possible for an operator to indicate the magnitude of the shaking operation by choosing a value on a scale from, say, 1-10. A strong selected shaking operation will then result in a larger magnitude shaking compared to a less strong selected shaking operation.The respective speeds of the actuation of the at least two hydraulic cylinders, such as the third cylinder C3 and of the fourth hydraulic cylinder C4, during extension and retraction over the predetermined respective cylinder extension ranges may also be configurable by an operator of the construction equipment 100. The faster the pistons move the faster the bucket will shake. An operator may be allowed to configure the speed of the cylinders during the shaking operation manually. The speed of the cylinder actuation during the shaking operation may also be jointly configured with the cylinder extension ranges.The control unit 110 is preferably arranged to control the at least two hydraulic cylinders in a time synchronized manner to repeatedly extend and retract in nonidentical phase. This joint control of the third and the fourth hydraulic cylinders to shake the bucket improves the efficiency of the bucket shaking. To further improve the efficiency of the bucket shaking operation, the speed of the bucket front edge 1020 can be optimized. This can be done by controlling the third hydraulic cylinder C3 and the fourth hydraulic cylinder C4 in opposite directions in response to the bucket shake operator command. This opposite phase actuation of the third and fourth cylinders improves the speed at which the front edge of the bucket moves through the air, which tends to improve the bucket shaking operation.Figure 13 illustrates an example bucket shaking operation. The y-axis indicates the hydraulic cylinder control commands (in for retraction of the cylinder and out for extension of the hydraulic cylinder). Note that the third cylinder C3 is retracted at the same time as the fourth cylinder C4 is extended, and vice versa. In this example the bucket shaking operation comprises four cylinder periods for both cylinders. I.e. , each cylinder is extended and retracted four times.The control unit 110 can be arranged to initiate execution of the bucket shake function by controlling the third cylinder C3 to move the bucket upwards away from the ground and the fourth cylinder C4 to move the bucket upwards away from the ground, i.e., by controlling both of the at least two hydraulic cylinders to move the tool interface 140 upwards U, as indicated in Figure 11 . This way the bucket shake operation is less likely to cause the bucket to slam into some object such as the ground surface, a container, or the bed of a dump truck or other vehicle.The tool carrier arm 150 and / or some of the tools 200 may comprise on-board dust control systems 170. A dust control system is a system which reduces the amount of dust in the air at the work site, e.g., by dispensing a liquid such as a water mist or the like to trap the dust. Liquid spray systems are also known, where, e.g., water is sprayed onto an area in order to reduce the amount of airborne dust. A water misting system, or a water spray system, can be arranged on the tool carrier arm 150, in connection to the tool carrier interface 140, or integrated with the tool 200. This water misting system or water spray system can be controlled directly by the control unit 110 or by some other dedicated controller. The control unit 110 can then initiate activation of the dust control system, e.g., by sending a message to the controller of the water misting or spray system.One or more external dust control systems may also be arranged at the work site where the demolition robot is operating. These external dust control systems may comprise misting systems and / or spray systems that emit liquid such as water in the form of small droplets to trap dust particles, and also air cleaners which actively filter the air at the work site to trap and hold dust particles.It is undesired to use liquid dispensers such as water misting systems and water spray systems more than necessary, since the liquid may run out if taken from a tank, and also because the liquid may cause problems at the work site, such as dirtying the work site and damaging water-sensitive materials.To reduce the usage time of the dust control system, the control unit 110 can be arranged to trigger activation of the dust control system in coordination with the automated bucket shake function. The dust control system is then operated concurrently with the bucket shaking, to suppress dust generated while emptying the bucket.Figure 14 is a flow chart that illustrates a method for emptying a bucket 1000 attached to a tool interface 140 on an arm 150 of construction equipment 100. The arm 150 comprises at least a second arm segment 1220 and a third arm segment 1230. The third arm segment 1230 is rotatably connected at its proximal end to a distal end of the second arm segment 1220, where a third hydraulic cylinder C3 is arranged to rotate the third arm segment 1230 relative to the second arm segment 1220 about a third axis A3. The tool interface 140 is rotatably connected to a distal end of the third arm segment 1230, and a fourth hydraulic cylinder C4 is arranged to rotate the tool interface 140 relative to the third arm segment 1230 about a fourth axis A4. The method comprisescontrolling Sb1 the third hydraulic cylinder C3 to repeatedly extend and retract over a cylinder extension range of the third cylinder, andcontrolling Sb2 the fourth hydraulic cylinder C4 to repeatedly extend and retract over a cylinder extension range of the fourth cylinder.The actuation of the cylinders is, as discussed above, preferably coordinated so as to maximize the pivoting speed of the bucket during the shaking operation. In the example of Figure 1 and Figure 12, this means that the third cylinder is extended while the fourth cylinder is retracted, and vice versa, as exemplified in Figure 13.

Claims

1. Construction equipment (100) comprising a tool carrier arm (150) and a control unit (110) arranged to control hydraulic cylinders (C3, C4) on the tool carrier arm (150),where the tool carrier arm (150) comprises a tool interface (140) arranged at its distal end to hold a bucket (1000), andwhere the control unit (110) is arranged to execute an automated bucket shake function comprising joint actuation by the control unit (110) of at least two hydraulic cylinders (C3, C4) on the tool carrier arm (150).

2. The construction equipment (100) according to claim 1, where the tool carrier arm (150) comprises a first segment (1210), a second segment (1220), and a third segment (1230) pivotably interconnected in sequence, and four hydraulic cylinders (C1, C2, C3, C4) arranged to control relative motion of the arm segments.

3. The construction equipment (100) according to claim 2, where two out of the four tool arm cylinders (C3, C4) are jointly actuated to execute the automated bucket shake function, while the other two cylinders (C1, C2) are kept stationary during execution of the automated bucket shake function.

4. The construction equipment (100) according to any previous claim, where the joint actuation by the control unit (110) of the at least two hydraulic cylinders (C3, C4) comprises repeatedly extending and retracting the cylinders over predetermined respective cylinder extension ranges.

5. The construction equipment (100) according to claim 4, where the predetermined respective cylinder extension ranges are configurable by an operator of the construction equipment (100).

6. The construction equipment (100) according to any previous claim, where respective speeds of the at least two cylinders during execution of the automated bucket shake function are configurable by an operator of the construction equipment (100).

7. The construction equipment (100) according to any previous claim, where the control unit (110) is arranged to control the at least two hydraulic cylinders (C3, C4) in a time synchronized manner to repeatedly extend and retract in non-identical phase.

8. The construction equipment (100) according to any previous claim, where the control unit (110) is arranged to control the at least two hydraulic cylinders (C3, C4) in opposite directions during execution of the automated bucket shake function.

9. The construction equipment (100) according to any previous claim, where the control unit (110) is arranged to initiate execution of the bucket shake function by controlling the at least two hydraulic cylinders (C3, C4) to move the bucket upwards (U) away from the ground.

10. The construction equipment (100) according to any previous claim, comprising an input device (631, 632, 640) arranged to trigger execution of the automated bucket shake function in response to manipulation by an operator.

11. The construction equipment (100) according to any previous claim, where the tool carrier arm (150) comprises at least a second arm segment (1220) and a third arm segment (1230),where the third arm segment (1230) is rotatably connected at its proximal end to a distal end of the second arm segment (1220), where a third hydraulic cylinder (C3) is arranged to rotate the third arm segment (1230) relative to the second arm segment (1220) about a third axis (A3),where the tool interface (140) is rotatably connected to a distal end of the third arm segment (1230), where a fourth hydraulic cylinder (C4) is arranged to rotate the tool interface (140) relative to the third arm segment (1230) about a fourth axis (A4),where the control unit (110) is configured to execute the automated bucket shake function by jointly controlling the third hydraulic cylinder (C3) and the fourth hydraulic cylinder (C4) to repeatedly extend and retract over the predetermined respective cylinder extension ranges in response to a bucket shake command.

12. The construction equipment (100) according to any previous claim, arranged to be controlled by a remote control device (600), where the control unit (110) is arranged to execute the automated bucket shake function in response to a control signal from the remote control device (600).

13. The construction equipment (100) according to any previous claim, comprising a dust control system (170), where the control unit (110) is arranged to trigger activation of the dust control system in coordination with the automated bucket shake function.

14. A method for emptying a bucket (1000) attached to a tool interface (140) on an arm (150) of construction equipment (100), the arm (150) comprising at least a second arm segment (1220) and a third arm segment (1230),where the third arm segment (1230) is rotatably connected at its proximal end to a distal end of the second arm segment (1220), where a third hydraulic cylinder (C3) is arranged to rotate the third arm segment (1230) relative to the second arm segment (1220) about a third axis (A3),where the tool interface (140) is rotatably connected to a distal end of the third arm segment (1230), where a fourth hydraulic cylinder (C4) is arranged to rotate the tool interface (140) relative to the third arm segment (1230) about a fourth axis (A4),the method comprisingcontrolling (Sb1) the third hydraulic cylinder (C3) to repeatedly extend and retract over a cylinder extension range of the third cylinder, andcontrolling (Sb2) the fourth hydraulic cylinder (C4) to repeatedly extend and retract over a cylinder extension range of the fourth cylinder.