Field of the invention

The present invention relates to a driving device for axially rotating an auger about a longitudinal axis for forming in-situ formed piles. The present invention further relates to a drilling rig for forming in-situ formed piles and to a method of forming in-situ formed piles by means of a drilling rig.

State of the art

At present, drilling rigs are often used to drive or form foundation objects into the ground. An example of thus formed foundation objects is manufactured by rotating an auger in the ground, to form a hole that can be filled with curable substance, like concrete. Strengthening components, such as metallic rebar, can be introduced in the substance, to which an object can be anchored after curing of the curable substance.

Existing drilling rigs typically rely on a crane and a driving device, that is suspended by the crane. The driving device is used to apply a rotary driving force onto the auger, and optionally a downward insertion force, to screw the auger into the ground.

At present, these driving devices are typically driven by hydraulic power packs, powered by diesel engines, that are configured to supply pressurized hydraulic fluid to the driving device. Furthermore, the diesel engine in the hydraulic power pack typically also drives the crane to perform auxiliary tasks, like manoeuvring of the crane.

However, the use of diesel engines inherently results in exhaust gas emissions that harm the environment. Furthermore, diesel power packs typically operate at fixed power output levels, at which the power packs have an optimal efficiency. However, this optimal output level may not necessarily correspond to the desired power demand from the driving device, so that some of the hydraulic power may not be utilized after all.

Object of the invention

It is therefore an object of the invention to provide a driving device that can operate more environmentally friendly and/or more efficiently for different modes of operation.

Detailed description

The present invention provides, according to a first aspect, a driving device for rotating an auger about a longitudinal axis for forming in-situ formed piles, the device comprising: a housing, a connector device, which is rotatably attached to the housing and configured to be connected to the auger, and an actuator, connector to the connector device and configured to rotate the connector device relative to the housing about the longitudinal axis to rotate the auger, characterized in that the actuator comprises multiple electric motors, e.g. multiple synchronous electric motors.

According to the present invention, the driving device relies on electric motors to provide for the rotary movement of the auger. During use, the auger is attached to the connector device, which may for example comprise for an interlocking engagement with the auger. The actuator is attached to the housing and the connector device and is configured to rotate the connector device relative to the housing. This rotation takes place about the longitudinal axis, i.e. parallel to the auger, and may typically be aligned substantially parallel to the vertical direction.

The present driving device is configured to rotate an auger into the ground. Such an auger may comprise a spiral thread along substantially its entire length. Upon rotation of the auger, a downward pulling force may be generated by the auger and any material that has been drilled loose can be transported up to the ground level via the thread. Alternatively, the driving device may be used to drill a pile casing into the ground, which may be embodied as a hollow tube, having a spiral thread at its head end. Such pile casings typically stay in the ground after being used to form the hole in the ground, so that the casings can form a cavity in which the curable substance can be filled. Hereinafter, both the auger and the pile casing are referred to with the term “auger”.

Compared to existing driving devices, the present driving device now comprises electric motors. These motors are powered by electric energy directly, instead of via a hydraulic circuit. The crane, to which the driving device can be attached, may comprise a battery to provide electric energy towards the electric motors in the driving device.

The multiple electric motors are preferably multiple synchronous electric motors, so that all motors can be operated in synchronicity. Alternatively, the electric motors may be asynchronous motors, since all motors may be connected to the connector device via a common gear. However, synchronous motors may be beneficial, due to their generally smaller size. This allows synchronous motors to replace existing hydraulic motors more conveniently, without requiring a significantly different housing and/or connector device. Furthermore, synchronous motors are more reliable and easier to control, thus enabling improved controlling during drilling.

The use of electric motors instead of hydraulic motors offers a range of new functionalities with the present driving device, which could not be achieved in existing driving devices. For example, each of the multiple electric motors can be controlled individually, independent of the other electric motors. The number of activated motors can be selected in dependence on the required power output, e.g. torque on the auger. This is not possible in the existing driving devices, since all hydraulic motors were then subjected to the same flow of hydraulic fluid.

Furthermore, each of the electric motors can be monitored individually, for example by monitoring the electric current fed towards each of the motors or by measuring the rotational velocity of the motors. This allows the driving device to be utilized more effectively and efficiently, for example offering the possibility of adjusting the electric power that is fed towards the motors in dependence of the increased rotational velocity and/or the power required for driving the auger in the ground.

In addition, the present electric motors have the benefit that they are powered by electric energy, of which a voltage and current can be measured and set independent of each other. This may allow for independent controlling of rotational velocity and torque of the motors. This would not be possible with the existing hydraulic motors, in which the hydraulic flow rate, representative for the rotational velocity, is dependent on the fluid pressure, representative for the torque, and vice versa.

More general, the driving device according to the present invention is free of diesel engines, since it contains electric motors only. The driving device thus has no emissions by itself and can operate more environmentally-friendly, compared to the existing devices.

In an embodiment, the electric motors are permanent-magnet synchronous electric motors. It was found by the inventors that the use of such permanent-magnet synchronous electric motors offers improved synchronization between the motors. Furthermore, these permanent-magnet synchronous electric motors can be provided even smaller than non- permanent-magnet synchronous electric motors, thus avoiding the need for an increased size of the driving device.

In an embodiment, the actuator comprises an even number of electric motors, for example two or four synchronous electric motors. The even number of electric motors may offer the benefit of symmetric loading of the connector device by all electric motors, to improve the transfer of the rotational movement onto the auger.

In an embodiment, each of the electric motors comprises a current sensor, each configured to emit a motor current signal representative for the electric current consumed by that motor.

This embodiment offers the possibility to monitor the electric current that is consumed by each electric motor individually. This forms an improvement over the known hydraulic motors, which at most allowed monitoring of the overall flow of hydraulic fluid to all hydraulic motors together.

The monitoring of the electric current may give insight in the resistance of the auger, upon insertion into the ground. In case the load acting on the auger is small, the electric current towards the electric motors will be small as well. Should the auger be loaded heavily, then the electric current towards the electric motors will be large as well.

Furthermore, the monitoring of individual electric currents towards the motors may offer the possibility to detect differences in electric current, thus in energy consumption, between the motors. Should one of the motors draw a larger electric current than the other motors, this difference may be evidence of malfunctioning of that motor. This would not be possible either with the existing hydraulic motors, which only offered the possibility to monitor the flow of hydraulic fluid to all motors in combination.

In an embodiment, the driving device further comprises a rotation sensor, configured to emit a rotation sensor signal representative for the rotational velocity of the connector device, i.e. the auger.

The rotational velocity may be representative for the speed at which the auger is inserted in the ground. Typically, these augers are configured to convert a rotation of the auger about its longitudinal axis into an axial movement. With a large rotational velocity, the auger gets inserted in the ground at a relatively large rate, whereas a small rotational velocity results in a small insertion rate.

In an embodiment, the driving device comprises a control unit, configured to control the electric power supplied to each of the electric motors, preferably in dependence of the motor current signal for that motor and/or of the rotation sensor signal.

The control unit may be configured to adjust the electric power towards the electric motors. For example, in case the resistance of the auger in the ground is relatively large, i.e. when hard layers of soil are penetrated, the required power from the driving device may need to be large as well to ensure that the auger is inserted in the ground any further.

Furthermore, the control unit may set different electric power levels for each of the electric motors individually, should it be desired to deliver different power outputs, e.g. torque levels with the different motors.

The control unit may be configured to control the electric power on the basis of the motor current signal. For example when the motor current signal represents large electric currents consumed by the electric motors, the control unit may control a larger electric power towards the motors to maintain a certain desired insertion rate for the auger. Similarly, if one of the motors has a motor current signal that indicates a larger consumed electric current than the other motors, the control unit may lower or raise the electric power fed towards that electric motor, to balance the loading of all electric motors.

Alternatively or additionally, the control unit may be configured to control the electric power on the basis of the rotation sensor signal. This may offer the possibility to control the motors to maintain a certain desired rotational velocity of the connector device and the auger. Should, for example, the resistance on the auger increase suddenly, then the control unit may be able to increase the electric power fed towards the electric motors to maintain the desired rotational velocity.

In a further embodiment, the control unit is configured to selectively activate and deactivate one or more of the electric motors during use. This may offer the benefit that not all electric motors need to be activated when the loading situation of the electric actuator does not require so.

If, for example, the required power for inserting the auger in the ground is relatively low, the control unit may determine that the required power output of the driving device can be achieved with some of the electric motors already. In that case, one or more of the electric motors can be deactivated, whilst the other, i.e. activated electric motors are able to deliver the required power output, e.g. torque level. The deactivating of some of the electric motors may provide the benefit that less electric energy needs to be consumed and that less wear will occur in the electric motors, e.g. the deactivated ones.

Should, after a certain period of time, the auger be subjected to a harder layer of soil, then this may be detected by the control unit as a lowering of the rotational velocity, represented by the rotation sensor signal and/or as an increase of the electric current consumed by the electric motors, represented by the motor current signals. In accordance, the control unit may be configured to activate the deactivated electric motors to increase the power output of the driving device.

By having fewer activated electric motors, the benefit can be obtained that the activated electric motors can operate at an optimal efficiency, whereas this would not be possible when all electric motors were to be activated. Hence, a low number of activated electric motors would be sufficient when the resistance on the auger is low during insertion.

A further benefit of the selective activating and deactivating lies in the fact that less heat, i.e. resistive heat, is produced by the driving device when some of the electric motors are deactivated. As such, the amount of cooling can be less when some of the electric motors are deactivated, so that the amount of power lost for cooling is reduced as well, making the driving device according to the present embodiment even more energy efficient. In an embodiment, the driving device further comprising a cooling device, configured to cool the electric motors. The cooling of the electric motors may be necessary, since the electric motors may be subject to resistive heating, following the electric currents through them. With the cooling device, the temperature of the electric motors may be lowered to diminish any disadvantageous effect of the heating, in order to improve the overall efficiency of the driving device.

The cooling device may comprise a cooling circuit, containing cooling fluid, that passes along the electric motors. As such, residual heat from the electric motors can be absorbed by a circulating flow of cooling fluid in the circuit.

In an embodiment, the connector device comprises an annular gear ring and each of the electric motors comprises a motor gear that is in engagement with the gear ring to transfer rotational movements of the motors towards the auger.

According to this embodiment, all electric motors physically engage with the annular gear ring, each via their own motor gear. This provides the effect that the rotations of all electric motors are synchronized via the annular gear ring and that the connector device is rotated in an equilibrated manner by all motors.

Furthermore, the common annular gear ring for all electric motors may provide that both synchronous electric motors and asynchronous electric motors can be used, since the synchronization of their rotational movements is effected via the annular gear ring.

According to a second aspect, the present invention provides a drilling rig for forming in- situ formed piles, comprising: a crane, a leader, attached to the crane, an auger, extending along the leader along its longitudinal axis, and the driving device as disclosed herein, for example as recited in the claims, wherein the driving device is attached to the leader and axially displaceable along the leader, and wherein the driving device is connectable to the auger and configured to rotate the auger about the longitudinal axis.

The present drilling rig according to the second aspect may comprise one or more of the features and/or benefits disclosed herein in relation to the driving device according to the first aspect of the present invention, in particular as recited in any of the claims.

The present drilling rig comprises a crane for moving the driving device towards a working location, where a pile is to be formed in the ground. The crane has a leader attached to it, along which the auger is aligned during insertion in the ground. The leader may be rotatably connected at a front end of the crane, to establish the tilting of the leader, and thus of the auger, relative to the crane and the ground.

The driving device is attached to the leader, so that the leader forms a counter-support for the driving device when it is used to rotate the auger. During insertion into the ground, the auger is configured to travel parallel to its longitudinal axis. This axial movement of the auger and the driving device is guided by the leader, along which the driving device is displaceable.

Optionally, the rig may comprise an insertion winch, which is configured to downwardly pull the driving device along the leader. This pulling is configured to induce an insertion force on the auger, so that the entire weight of the rig can contribute in inserting the auger into the ground, instead of only the weight of the driving device and the auger itself. The insertion winch may similarly comprise a synchronous electric motor.

In an embodiment, the drilling rig further comprises a battery, connected to the driving device and configured to supply the driving device with electric energy. The battery may be provided separate from the crane, since the battery may not necessarily be used to provide electric energy towards the crane, but for example only towards the driving device. For example, an auxiliary battery may be provided to supply the crane with electric energy to perform the auxiliary tasks, such as the moving of the crane, moving of the leader and moving of the driving device, for example raising or lowering the driving device and/or the auger along the leader.

The battery may be attached to the crane during use for driving the auger in the ground and removable from the crane during transportation of the crane. This allows the main battery to be moved along with the driving device during use, for example when the crane moves the driving device to another working location. Furthermore, the battery may be used beneficially as a counterweight for stabilizing the rig. With the battery being removable, the rig can be made more compact during transportation of the crane, which may make transportation of the crane more convenient.

In an embodiment, the drilling rig further comprises one or more winches for moving the auger and/or the driving device, i.e. along the leader, and the winches each comprise an electric motor, e.g. a synchronous electric motor for rotating a cable drum thereof.

In existing drilling rigs, the winches were powered by hydraulic motors as well, resulting in the same drawbacks that arose with the hydraulic used for powering the driving device. According to the present embodiment, the winches are powered by electric motors as well, for example by synchronous electric motors. Accordingly, the benefits described above in relation to the electric motors used in the driving device also apply for the electric motors used for the winches according to the present embodiment. According to a third aspect, the present invention provides a method of forming in-situ formed piles by means of the drilling rig as disclosed herein, for example as recited in the claims, comprising the steps of: positioning the auger at a desired position for the pile, rotating the auger by means of the electric motors, lowering the auger in the ground during rotating, filling the auger with a curable substance, and optionally, removing the auger out of the ground.

The present method according to the third aspect may comprise one or more of the features and/or benefits disclosed herein in relation to the driving device according to the first aspect of the present invention and/or to the drilling rig according to the second aspect of the present invention, in particular as recited in any of the claims.

According to the method, the auger is position at a desired posiion, where the pile is to be formed in the ground. The positioning of the auger is typically done with the crane and the leader, attached to the crane.

After the desired position is reached, the auger is rotated by the driving device, by means of the electric motors thereof. The auger may be configured to convert a rotation of the auger about its longitudinal axis into an axial movement, in order to effect the lowering of the auger in the ground.

Meanwhile, the weight of the driving device may rest on the auger, to effect a downward insertion force on the auger. Furthermore, the gravitational force acting on the auger may further contribute to the inserting in the ground.

Optionally, the lowering of the auger in the ground may further comprise downwardly pulling the driving device along the leader with an insertion winch of the rig. This pulling induces an additional insertion force on the auger, so that the entire weight of the rig contributes in inserting the auger into the ground, instead of only the weight of the driving device and the auger itself.

After the auger has reached a desired depth, and optionally after removal of the auger out of the thus formed hole in the ground, the auger or hole is filled with a curable substance. Typically, the curable substance is a concrete material, but other materials can be envisaged as well. Prior to curing, strengthening components, such as metallic rebar, can be introduced in the substance, to which an object can be anchored after curing of the curable substance.

According to the present method, the auger can be removed out of the ground, in order to be re-used for forming another hole in the ground for another pile. Alternatively, where the auger is embodied as a hollow tube for a pile casing, the casing may remain in the ground, in order to be filled with the curable substance. As such, the casing forms a cavity in which the curable substance can be filled.

In an embodiment, the method comprises the steps of: measuring, with the current sensors, an electric current supplied to each of the electric motors, and/or measuring, with the rotation sensor, a rotational velocity of the auger, and controlling, with the control unit, the electric current supplied to each of the electric motors, in dependence of the motor current signal for that motor and/or of the rotation sensor signal.

According to this embodiment, the electric motors may each comprise a current sensor, which emits a motor current signal representative for the electric current consumed by that motor. During use, this offers the possibility to monitor the electric current that is consumed by each electric motor individually. The monitoring of the electric current may give insight in the resistance of the auger, upon insertion into the ground. In case the load acting on the auger is small, the electric current towards the electric motors will be small as well. Should the auger be loaded heavily, then the electric current towards the electric motors will be large as well. Furthermore, the monitoring of individual electric currents towards the motors may offer the possibility to detect differences in electric current, thus in energy consumption, between the motors. Should one of the motors draw a larger electric current than the other motors, this difference may be evidence of malfunctioning of that motor.

Alternatively or additionally, the driving device further comprises a rotation sensor, which emits a rotation sensor signal representative for the rotational velocity of the connector device, i.e. the auger. The rotational velocity may be representative for the speed at which the auger is inserted in the ground.

According to this embodiment of the method, the control unit controls the electric power supplied to each of the electric motors, in dependence of the motor current signal for that motor and/or of the rotation sensor signal. This controlling may for example involve adjusting the electric power towards the electric motors. For example, in case the resistance of the auger in the ground is relatively large, i.e. when hard layers of soil are penetrated, the required power, e.g. torque from the driving device may need to be large as well to ensure that the auger is inserted in the ground any further. Furthermore, the control unit may set different electric power levels for each of the electric motors individually, should it be desired to deliver different power outputs, e.g. torque levels with the different motors.

The control unit may control the electric power on the basis of the motor current signal. For example when the motor current signal represents large electric currents consumed by the electric motors, the control unit may control a larger electric power towards the motors to maintain a certain desired insertion rate for the auger. Similarly, if one of the motors has a motor current signal that indicates a larger consumed electric current than the other motors, the control unit may lower or raise the electric power fed towards that electric motor, to balance the loading of all electric motors.

Alternatively or additionally, the control unit may control the electric power on the basis of the rotation sensor signal. This may offer the possibility to control the motors to maintain a certain desired rotational velocity of the connector device and the auger. Should, for example, the resistance on the auger increase suddenly, then the control unit may be able to increase the electric power fed towards the electric motors to maintain the desired rotational velocity.

In a further embodiment, the step of controlling comprises selectively activating and/or deactivating one or more of the electric motors. This may offer the benefit that not all electric motors need to be activated when the loading situation of the electric actuator does not require so.

If, for example, the required power for inserting the auger in the ground is relatively low, the control unit may determine that the required power output of the driving device can be achieved with some of the electric motors already. In that case, one or more of the electric motors can be deactivated, whilst the other, i.e. activated electric motors are able to deliver the required power output, e.g. torque level. The deactivating of some of the electric motors may provide the benefit that less electric energy needs to be consumed and that less wear will occur in the electric motors, e.g. the deactivated ones.

Should, after a certain period of time, the auger be subjected to a harder layer of soil, then this may be detected by the control unit as a lowering of the rotational velocity, represented by the rotation sensor signal and/or as an increase of the electric current consumed by the electric motors, represented by the motor current signals. In accordance, the control unit may be configured to activate the deactivated electric motors to increase the power output of the driving device.

By having fewer activated electric motors, the benefit can be obtained that the activated electric motors can operate at an optimal efficiency, whereas this would not be possible when all electric motors were to be activated. Hence, a low number of activated electric motors would be sufficient when the resistance on the auger is low during insertion.

Brief description of drawings

Further characteristics of the invention will be explained below, with reference to embodiments, which are displayed in the appended drawings, in which: Figure 1 schematically depicts an embodiment of a drilling rig according to the present invention, and

Figure 2 schematically depicts a functional layout of the rig in figure 1.

Throughout the figures, the same reference numerals are used to refer to corresponding components or to components that have a corresponding function.

Detailed description of embodiments

Figure 1 schematically depicts an embodiment of the drilling rig according to the present invention, to which is referred with reference numeral 1. The rig 1 is configured to drive an auger 5 in the ground, after which a foundation pile can be formed in the hole created by the auger 5.

The rig 1 comprises a crane, a driving device 10 that is configured to apply a driving force onto the auger 5, and a power source to provide power to the driving device 10 and to the crane. The driving device 10 is configured to rotate the auger 5 into the ground, which rotation takes place about a longitudinal axis L. In the present embodiment, the auger 5 comprises a spiral thread along substantially its entire length. Upon rotation of the auger 5, a downward pulling force is generated by the auger 5 and any material that has been drilled loose can be transported up to the ground level via the thread.

The crane comprises an undercarriage 2, for supporting and moving the rig 1. A superstructure 3 of the crane is rotatably arranged on the undercarriage 2 and is configured to support the driving device 10 of the rig 1. The driving device 10 is suspended from a leader 4 of the crane, which is attached to the superstructure 3 and which can be brought in an erected position, as shown in figure 1 , during use of the rig 1 for inserting the auger 5 in the ground. The leader 4 can also be brought into a substantially horizontal transport position, in which the leader 4 is accommodated in a horizontal through slot in the superstructure 3.

The driving device 10 is attached to the leader, so that the leader 4 forms a countersupport for the driving device 10 when it is used to rotate the auger 5. During insertion into the ground, the auger 5 is configured to travel parallel to its longitudinal axis L. This axial movement of the auger 5 and the driving device 10 is guided by the leader 4, along which the driving device 10 is displaceable.

In the embodiment of the rig 1 shown in figure 1 , the driving device 10 comprises a main electric actuator 11, to directly apply a driving force to the auger 5. The driving device 10 can thereby be free of hydraulic components to offer a more simple driving device 10, compared to the existing hydraulic drives.

The rig 1 further comprises a main battery 12, configured to supply the main electric actuator 11 with electric energy. The main battery 12 is arranged at a rear end of the superstructure 3, i.e. opposite to the driving device 10 and the leader 4, to act as a counterweight for the driving device 10, the leader 4 and the auger 5. Furthermore, the main battery 12 is removable from the superstructure 3 during transportation of the crane. With the main battery 12 being removable, the rig 1 can be made more compact and lighter during transportation of the crane, which may make transportation of the crane more convenient.

It is shown schematically in figure 2 that the present driving device 10 relies on electric motors to provide for the rotary movement of the auger 5. The main electric actuator 11 in particular comprises four permanent-magnet synchronous electric motors 111 , 112, 113, 114.

During use, the auger 5 is attached to a connector device of the driving device 10. The connector device comprises an annular gear ring 116 and each of the electric motors 111, 112, 113, 114 comprises a motor gear 117 that is in engagement with the gear ring 116 to transfer rotational movements of the electric motors 111, 112, 113, 114 towards the auger 5. As such, all electric motors 111, 112, 113, 114 physically engage with the annular gear ring 116, each via their own motor gear 117. This provides the effect that the rotations of all electric motors 111, 112, 113, 114 are synchronized via the annular gear ring 116 and that the connector device is rotated in an equilibrated manner by all motors.

Each of the electric motors 111, 112, 113, 114 comprises a current sensor 111’, 112’, 113’, 114’, not visible in the figures, each configured to emit a motor current signal representative for the electric current consumed by that motor. The current sensors 111’, 112’, 113’, 114 offer the possibility to monitor the electric current that is consumed by each electric motor 111, 112, 113, 114 individually. This may give insight in the resistance of the auger 5, upon insertion into the ground. Hence, in case the load acting on the auger 5 is small, the electric current towards the electric motors 111, 112, 113, 114 will be small as well. Should the auger 5 be loaded heavily, then the electric current towards the electric motors 111 , 112, 113, 114 will be large as well. Furthermore, the monitoring of individual electric currents towards the motors 111, 112, 113, 114 may offer the possibility to detect differences in electric current, thus in energy consumption, between the motors 111, 112, 113, 114. Should one of the motors draw a larger electric current than the other motors, this difference may be evidence of malfunctioning of that motor.

The driving device 10 further comprises a rotation sensor 118, configured to emit a rotation sensor signal representative for the rotational velocity of the connector device, i.e. the auger 5. The rotational velocity may be representative for the speed at which the auger 5 is inserted in the ground. With a large rotational velocity, the auger 5 gets inserted in the ground at a relatively large rate, whereas a small rotational velocity results in a small insertion rate.

The driving device comprises a control unit 115, connected to the current sensors 111’, 112’, 113’, 114’ and the rotation sensor 118 - shown in figures 2 by means of dashed lines - and configured to control the electric power supplied to each of the electric motors 111, 112, 113, 114, in dependence of the motor current signal for that motor and/or of the rotation sensor signal. For example, in case the resistance of the auger 5 in the ground is relatively large, i.e. when hard layers of soil are penetrated, the required power from the driving device 10 may need to be large as well to ensure that the auger 5 is inserted in the ground any further. Furthermore, the control unit 115 may set different electric power levels for each of the electric motors 111 , 112, 113, 114 individually, should it be desired to deliver different power outputs, e.g. torque levels with the different motors 111, 112, 113, 114.

The control unit 115 is configured to control the electric power on the basis of the motor current signal. For example when the motor current signal represents large electric currents consumed by the electric motors 111, 112, 113, 114, the control unit 115 may control a larger electric power towards the motors 111 , 112, 113, 114 to maintain a certain desired insertion rate for the auger 5.

Similarly, if one of the motors 111 has a motor current signal that indicates a larger consumed electric current than the other motors 112, 113, 114, the control unit 115 may lower or raise the electric power fed towards that electric motor 111 , to balance the loading of all electric motors 111, 112, 113, 114.

The control unit 115 is further configured to control the electric power on the basis of the rotation sensor signal. This may offer the possibility to control the motors 111 , 112, 113, 114 to maintain a certain desired rotational velocity of the connector device and the auger 5. Should, for example, the resistance on the auger 5 increase suddenly, then the control unit 115 is able to increase the electric power fed towards the electric motors 111, 112, 113, 114 to maintain the desired rotational velocity.

The control unit 115 is further configured to selectively activate and deactivate one or more of the electric motors 111, 112, 113, 114 during use. This may offer the benefit that not all electric motors 111, 112, 113, 114 need to be activated when the loading situation of the electric actuator 11 does not require so.

If, for example, the required power for inserting the auger 5 in the ground is relatively low, the control unit 115 may determine that the required power output, e.g. torque level of the driving device 10 can be achieved with some of the electric motors 112, 114 already. In that case, the other two electric motors 111, 113 can be deactivated, whilst the other, i.e. activated electric motors 112, 114 are able to deliver the required power output, e.g. torque level. Should, after a certain period of time, the auger 5 be subjected to a harder layer of soil, then this may be detected by the control unit 115 as a lowering of the rotational velocity, represented by the rotation sensor signal and/or as an increase of the electric current consumed by the electric motors 112, 114, represented by the motor current signals. In accordance, the control unit 115 may be configured to activate the deactivated electric motors 111 , 113 to increase the power output of the driving device 10. The driving device 10 further comprising a cooling device, not shown in the figures, configured to cool the electric motors 111 , 112, 113, 114. The cooling of the electric motors 111 , 112, 113, 114 may be necessary, since the electric motors 111 , 112, 113, 114 may be subject to resistive heating, following the electric currents through them. With the cooling device, the temperature of the electric motors 111 , 112, 113, 114 may be lowered to diminish any disadvantageous effect of the heating, in order to improve the overall efficiency of the driving device 10.

It is best shown in figure 1 that the drilling rig 1 further comprises a lifting winch 41 for lifting the driving device 10 and the auger 5 that is attached to it. The lifting winch 41 comprises a synchronous electric motor for rotating a cable drum of the winch 41.

The rig 1 further comprises an insertion winch 42, which is configured to downwardly pull the driving device 10 along the leader 4. This pulling is configured to induce an insertion force F on the auger 5, so that the entire weight of the rig 1 can contribute in inserting the auger 5 into the ground, instead of only the weight of the driving device 10 and the auger 5 itself. The insertion winch 42 similarly comprises a synchronous electric motor.