TECHNICAL FIELD

The present invention relates to docking units and more particularly to the control of hydraulic valves of docking units.

BACKGROUND

A typical docking station for handling of goods can be found in many buildings such as warehouses and logistic centers. The docking station may include a large door at a height over ground level. The outside of the door typically opens up to a loading platform arranged such that a truck or a lorry may load or unload goods directly into the building via the loading platform. In some instances it is possible to service vehicles of different height by bridging the distance between the loading platform and ground level. This is typically achieved by dock levellers. A dock leveller may create a bridge between the loading platform and the vehicle. To achieve the bridging connection, a movable platform is controlled in order to align the loading platform with the vehicle such that smooth loading and unloading of goods is possible.

Common for some of these docking station is that the control of the movable platform is hydraulic since hydraulic control is powerful and accurate. The hydraulic control is such that electrically controlled valves control the hydraulics and when one or more electronic valves are activated, the movable platform will move. One problem with such an arrangement is that if a movable platform is in an activated position during a power failure, the movable platform will automatically return to its resting position i.e. the position which movable platform enters when the hydraulic operating arrangement does not provide any support with a high risk of accidents involving personal injuries and collateral damage. One solution is to introduce a safety valve that will keep the movable platform in position in case of power failure. Such safety valves are also electronic valves but are activated when no power is applied to them, consequently, they are de-activated when power is applied to them.

The electronic valves used to control the hydraulics of the movable platform are typically solenoid valves and one problem with these valves is that they consume significant amounts of power when activated. Since the safety valve is de-activated when power is applied, i.e. in all cases except when there is a power failure, this valve will generate a lot of heat due to its constant current consumption.

In WO 2009/092952 A2 a device for docking a road transport vehicle is presented. The device includes, at the foot of the dock, a horizontal platform for positioning thereon an axle of such a vehicle, and a pneumatic jack system that can be actuated under the plate for raising the same. A solenoid safety valve is mentioned and a pneumatic alternative of the same valve is recommended.

One problem with this solution is that it requires the introduction of pneumatics into the hydraulic system. This will significantly increase cost, size and complexity of the docking system. From the above it is understood that there is room for

improvements.

SUMMARY

An object of the present invention is to provide a new type of hydraulic valve system for dock levellers of docking stations which is improved over prior art and which eliminates or at least mitigates the drawbacks discussed above. More specifically, an object of the invention is to provide a control module that is possible to integrate into existing hydraulic valve systems for docking stations. Another aspect of the invention is that it will reduce the power consumption and enable more environmentally friendly or green docking systems. These objects are achieved by the technique set forth in the appended independent claims with preferred embodiments defined in the dependent claims related thereto.

In a first aspect, a hydraulic valve arrangement for a dock leveller comprising a movable platform and a hydraulic operating arrangement arranged to control the position of the movable platform . The hydraulic valve arrangement comprises at least one hydraulic valve being an electronically controlled hydraulic valve with solenoid activation. The at least one hydraulic valve is arranged to be connected to the hydraulic operating arrangement. The at least one hydraulic valve is operatively connected to a power interface provided by a power source. The hydraulic valve arrangement further comprises at least one control module operatively connected, via the power interface, to the power source and at least one of the electronically controlled hydraulic valves. The control module is configured to control a current and/or voltage of the power interface provided to the hydraulic valve from the power source. This is advantageous since it allows the control module to be retrofitted in existing systems enabling saving in power, cost and environment.

In one embodiment, at least one of said electronically controlled hydraulic valve is a safety valve arranged such that the movable platform is held in a controlled position, e.g. a fixed controlled position, when the safety valve is activated. This has the benefit that the power consumption is reduced in the valve consuming the most power in the system.

In another embodiment the control module is arranged to measure an output voltage and/or an output current supplied to the electronically controlled hydraulic valve via the power interface. Measuring the current and/or voltage will enable a feedback loop in the control performed by the control module and consequently a more accurate and cost effective control can be achieved.

In a further embodiment, the control module pulse width modulates the power interface supplied to the electronically controlled hydraulic valves. Pulse width modulation is a cheap, component efficient and efficient way to achieve current and voltage control.

In yet another embodiment, the pulse width modulation is performed with at least a first duty cycle and a second duty cycle. The first duty cycle is applied for a first period of time starting at the activation of the power interface and the second duty cycle is applied from the lapse of the first period of time. The second duty cycle is lower than the first duty cycle. By starting with a relatively higher duty cycle the magnetization and activation time of the hydraulic valve will be as fast as possible without compromising the saving in power consumption.

In a further embodiment, the first duty cycle is 100%. This will allow the hydraulic valve to switch as fast as the system allows.

In one embodiment, the control module is arranged to measure an output voltage and/or an output current supplied to the electronically controlled hydraulic valve via the power interface. The control module pulse width modulates the power interface supplied to the electronically controlled hydraulic valves with a duty cycle based on the measured output voltage and/or based on the measured output current. By controlling the duty cycle based on the measured parameters, a control loop with true feedback is achieved enabling stable, efficient and accurate control.

In yet another embodiment, the control module is arranged to measure an output voltage and/or an output current supplied to the electronically controlled hydraulic valve via the power interface. The control module pulse width modulates the power interface supplied to the electronically controlled hydraulic valves. The pulse width modulation is performed with at least a first duty cycle and a second duty cycle, wherein the first duty cycle is applied for a first period of time starting at the activation of the power interface. The first period of time is controlled based on the measured output voltage and/or based on the measured output current. This embodiments enables a very simple and cost effective solution since the higher duty cycle will run for substantially as long as necessary increasing power saving and keeping the switching time of the hydraulic valve short.

In an even further embodiment, the control module is further arranged to pulse width modulate the power interface supplied to the electronically controlled hydraulic valves. The pulse width modulation is performed with at least a first duty cycle and a second duty cycle. The first duty cycle is applied for a first period of time starting at the activation of the power interface. The control module further comprises at least one potentiometer arranged to respectively control at least one of the first duty cycle, the second duty cycle and/or the first period of time. Potentiometers are cheap and simple components that enable simple tuning of the control module where it can be adapted to fit any hydraulic valve.

In an additional embodiment, the control module further comprises a controller arranged to pulse width modulate the power interface supplied to said electronically controlled hydraulic valve with a duty cycle such that the measured output voltage is within a predefined voltage interval and/or the measured output current is within a predefined current interval. By controlling the duty cycle based on the measured parameters, a control loop with true feedback is achieved enabling stable, efficient and accurate control. Having the controller work with predefined limits makes the control of the hydraulic valve configurable and easier to optimize.

In a second aspect, a dock leveller comprising the hydraulic valve arrangement according to the previous aspect and its variants is introduced.

A third aspect introduces a control module, i.e. a control unit, for a hydraulic valve of a hydraulic valve arrangement comprised in a dock leveller. The control module is provided with an input port and an output port. The control module is configured to apply pulse width modulation to a signal received via the input port before the signal is provided to the output port. One benefit of this is that pulse width modulation is a cheap, component efficient and efficient way to achieve current and voltage control.

In one embodiment, the pulse width modulation is performed with at least a first duty cycle and a second duty cycle. The first duty cycle is applied for a first period of time starting at the activation of the signal received via the input port and the second duty cycle is applied from the lapse of the first period of time, wherein the second duty cycle is lower than the first duty cycle. This embodiments enables a very simple and cost effective solution since the higher duty cycle will run for substantially as long as necessary increasing power saving and keeping the switching time of the hydraulic valve short.

In another embodiment, the control module, i.e. the control unit, comprises a circuitry for measuring an output voltage and/or an output current of the signal provided to the output port and for controlling the duty cycle based on the measured output voltage and/or the measured output current. By controlling the duty cycle based on the measured parameters, a control loop with true feedback is achieved enabling stable, efficient and accurate control.

In yet another embodiment, the control module, i.e. the control unit, according comprises a controller arranged to apply pulse width modulation to the signal provided to the output port with a duty cycle such that the measured output voltage is within a predefined voltage interval and/or the measured output current is within a predefined current interval. By controlling the duty cycle based on the measured parameters, a control loop with true feedback is achieved enabling stable, efficient and accurate control. Having the controller work with predefined limits makes the control of the hydraulic valve configurable and easier to optimize.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described in the following; references being made to the appended diagrammatical drawings which illustrate non-limiting examples of how the inventive concept can be reduced into practice.

Fig. l is a side view of a docking station / docking unit comprising a dock leveller.

Fig. 2 is a schematic view of an electrically controlled hydraulic valve.

Fig. 3a is a schematic view of an exemplary circuitry comprising an inductive element and a resistive element connected to a signal source.

Fig. 3b is a time plot of the voltage across the inductive element of Fig. 3a.

Fig. 3c is a time plot of the voltage across the resistive element of Fig. 3a.

Fig. 3d is a time plot of the impedance experienced by the signal source of Fig. 3a.

Fig. 4a is a simplified side view of a solenoid.

Fig. 4b is a view of the magnetic field and currents in the solenoid of Fig. 4a. Fig. 5 is a schematic view of a hydraulic valve arrangement for a docking unit. Fig. 6 is a schematic view of dual hydraulic valve arrangements controlling one door.

Fig. 7 is a schematic view of a novel hydraulic valve arrangement for a docking unit.

Fig. 8 is a perspective view of a control module according to one embodiment. Fig. 9a is a plot of the input voltage provided to the control module according to one embodiment.

Fig. 9b is a plot of the unloaded output voltage delivered by the control module according to one embodiment.

Fig. 9c is a plot of the loaded output voltage delivered by the control module according to one embodiment. Fig. 9d is a plot of the loaded output current delivered by the control module according to one embodiment.

Fig. 10 is a plot of the unloaded output voltage delivered by the control module according to one embodiment.

Fig. 11 is a schematic view of a flowchart for controlling a hydraulic valve.

Fig. 12 is a schematic view of a control module according to one embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, certain embodiments will be described more fully with reference to the accompanying drawings. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention, such as it is defined in the appended claims, to those skilled in the art.

With reference to Fig 1, one examples of a docking station 10 or docking unit 10 is shown. The docking station 10 is provided with a door 140 opening up to a loading platform 130. In order to allow a truck 110 to reverse and conveniently load and/or unload goods 150 onto the loading platform 130, a dock leveller 20 is comprised in the docking station 10. The dock leveller 20 comprises a movable or adjustable platform 120 which is controlled by a hydraulic operating arrangement 160 arranged to change the position of the movable platform 120. The hydraulic operating arrangements may comprise at least one hydraulic actuator connected to the movable platform 120. The hydraulic operating arrangement may be connected to the movable platform by means of a linkage system or a mounting console. The docking unit 10 depicted in Fig.

1 uses the hydraulic operating arrangement 160 to angle the movable platform 120 such that the end of the movable platform 120 being closest to the truck 110 changes its height relative to a ground level G. The end of the movable platform 120 being closest to the loading platform will typically have its height essentially fixed at a level above ground level G being essentially the same as the height of the loading platform 130. The exemplified docking unit 10 described with reference to Fig. 1 should be considered non-limiting examples of one arrangement of a movable platforms 120 in docking units 10 comprising dock levellers 20. The intention is to provide an understanding of the function and purpose of a dock leveller 20 in general and not to specifically detail certain embodiments of dock levellers 20. A typical dock leveller 20 uses, as explained above, the hydraulic operating arrangement 160 to control the positon of the movable platform 120. The hydraulic operating arrangement 160 will move the movable platform 120 from a default position to a controlled position, i.e. a position where the hydraulic operating arrangement is activated and has urged a movement of the platform. The controlled position may be considered an active position of the movable platform. The default position of the movable platform 120 may differ depending on the arrangement of the dock leveller 20 but one may envision the default positon being e.g. fully raised or completely lowered. However, said hydraulic operating arrangement 160 is controlled by hydraulic valves and these valves, the arrangement comprising the valves and the control of these valves is what will be discussed in the coming sections.

It should be mentioned that the term operatively connected when referring to hydraulics in general and the hydraulic operating arrangement 160 in particular is meant to comprise any all or some of a mechanical connection, an electrical connection, a fluid connection or an electromagnetic connection.

The basic function of one of these valves will be explained with reference to Fig. 2. In Fig. 2, a schematic block diagram of an electrically controlled hydraulic valve 200 is depicted. The valve 200 is a shown with two electrical ports 210 connected to an inductive element 240 comprised in the valve 200. The function or purpose of the inductive element 240 may be e.g. that of a solenoid or of an electromagnet. The valve 200 is further provided with at least two hydraulic ports 220, 230 where the internal connection 250 between the hydraulic ports 220, 230 is controlled by activation of the inductive element 240. The internal connection 250 between the hydraulic ports 220, 230 is shown as a switch and this is simply not to limit the connection 250 with particular types of membrane switches etc. The inductive element 240 is activated when an electrical current is allowed to flow through the inductive element 240, i.e. when a power source is connected to the electrical ports 210.

Since the valve 200 comprises an inductive element 240, the inductive element will have an inductance L. Consequently, a time variant current i(t) applied to the electrical ports 210 will give rise to a time variant voltage v(t) according to Eqn. 1 below.

Looking at the impedance ZL across the inductive element 240 at a particular frequency /this is described by Eqn. 2.

Z _L = j < - L = 2 - n - f - L Eqn. 2

The commonly known Ohm’s law giving a clear relationship between a current/, a voltage V and an impedance Z is presented in Eqn. 3.

V = Z I Eqn. 3

All the equations above describe the same basic concept relating to the inductive element 240, either as a steady state function (Eqn. 3), a time variant differential function (Eqn. 1) or in the frequency domain (Eqn. 2 through e.g. Laplace transform of Eqn. 1). The conceptual understanding of the relationship between the inductive element 240 and applied current i(t) and voltage v(t) will now be applied to the exemplary circuit shown in Fig. 3a where the inductive element 240 is placed in series with a resistive element 320 and voltage step with an amplitude of vo applied via a voltage source 310.

The voltage drop across the inductive element VL(F) is illustrated in Fig. 3b and the voltage across the resistive element VR(F) is shown in Fig. 3c. The circuit impedance ZIN, the resistive element 320 in series with the inductive element 240, is shown in Fig. 3d as a function of time. The change over time in circuit impedance ZIN comes from the frequency dependent behavior of the inductive element 240 as shown in Eqn. 2. Since the circuit impedance ZIN drops as the voltage increases, the current though the circuit will increase since Eqn. 3 must be fulfilled. As both the current and voltage increases, the power dissipation of the inductive element will increase accordingly as electrical power P is described according to Eqn. 4.

The resistive element 320 is in Fig. 3a shown as a separate unit simply for the sake of explanation, in implementation the voltage source 310 and the inductive element 240 may be directly connected. In this case the resistive element 320 would be comprised in internal resistance of the voltage source 310 and parasitic components of the circuitry in general and the inductive element 240 in particular.

The reason for the electrical behavior of the inductive element is related to the electromagnetic field that is created when a coil is subjected to a time variant current. This electromagnetic field is what enables electromagnets and electromagnets are used in solenoids.

With reference to Figs. 4a and 4b a simple solenoid 400 will be explained. In Fig 4a, the solenoid 400 is shown comprising a helical coil 420 of wound wire wrapped around a metallic core 410. In Fig. 4b, an electromagnetic field 430 generated by the current 440 flowing through the coil 420 is shown. The electromagnetic field 430 will, although not shown in Fig. 4b, circle back outside the coil 420 such that it describes a closed loop. The metallic core 410 will be subjected to the magnetic field 430 generated by the coil 420 when a current 440 is applied to the coil 420. The magnetic field 430 will move the metallic core 410 by a force relative to the current 440 of the coil 420 and the metallic core 410 will be moved to a positon of equilibrium that will depend on the physical parameters of the metallic core 410 and coil 420. The amount of current needed to accelerate the metallic core 410 is greater than the current needed to keep the core 410 at equilibrium. This is relating to the magnetization, hysteresis and saturation of the metallic core 410. The current required to keep the metallic core 410 at equilibrium is sometimes referred to as a holding current. Relating this to the electrical properties of the inductive element 240 detailed in earlier sections, the impedance of the coil 420 will decrease as the metallic core 410 is saturated, i.e. is in a position of equilibrium. The solenoid 400 briefly explained with reference to Figs. 4a and 4b is a simple example to explain the underlying concept of a hydraulic valve. The solenoid 400 may be what controls the internal connection 250 in the valve 200 shown in Fig. 2. Typically, the metallic core 410 is attached to a membrane that is used to seal or open the internal connection 250 of the valve 200.

With reference to Fig. 5, a block diagram of a hydraulic valve arrangement 500 for a dock leveller according to prior art is shown. The dock leveller may have a suitable dock leveller control system comprising hydraulic valve arrangements 500. The hydraulic valve arrangement 500 comprises one or more valves 200 and at least one the valves 200 is an electronically controlled hydraulic valve with solenoid activation 200. The term solenoid activation is meant to mean that the hydraulic valve 200 comprises an inductive element 240 that is engaged by a current in order to control the internal connection 250 of the hydraulic valve 200.

The hydraulic valve 200 is operatively connector to a power source 510 via a power interface 530. The power source 510 may be any suitable power source 510 that is capable of driving the hydraulic valve 200. A common power source is a 24V direct current, DC, power source, that, when activated, outputs 24V as the power interface 530. The power interface 530 may be a simple two-wire interface allowing a closed current loop between the inductive element 240 of the hydraulic valve 200 and the power source 510. It may be that the power interface 530 is a single wire power interface 530 and that a closed current loop is achieved by e.g. a common system potential e.g. a common ground reference, or a chassi ground.

As mentioned in the background section, docking stations 10 are typically utilizing hydraulics in order to control position of the movable platform 120 of the dock leveller 20. The control of the hydraulic operating arrangement is accomplished by hydraulic valves that are electrically controlled. Typically, the hydraulic operating arrangement operates with redundant hydraulic systems where one system acts as a backup system to a primary system. There are regulatory requirements for the backup systems, where for instance, the movable platform 120 is not allowed to change its position during a power failure of loss of hydraulic pressure in the primary system. Fig. 6 shows a schematic block diagram of a hydraulic valve arrangement 500 according to an embodiment. The hydraulic valve arrangement comprises a primary hydraulic system 610 and a secondary hydraulic system 620. The hydraulic valve arrangement may comprise the at least one valve 200 which may be arranged to be connected to the hydraulic operating arrangement, e.g. via a fluid connection. In one embodiment, the hydraulic valve arrangement is arranged to control the hydraulic operating arrangement. Both systems 610, 620 are connected to the hydraulic operating arrangement 160 and each comprises at least one hydraulic valve 200 and at least one power source 510. Notably there is a difference between the hydraulic valves 200 of the primary system 610 and the secondary system 620. The secondary system 620 acts as a failsafe system and utilizes a hydraulic valve 200 operating in a normally closed arrangement which means that when it is activated, the internal connection 250 of the hydraulic valve 200 will be open, disconnecting the hydraulic ports 220, 230 of the hydraulic valve 200, which means that when it is activated, the internal connection 250 of the hydraulic valve 200 will be open disconnecting the hydraulic ports 220, 230 of the hydraulic valve 200. The function of the hydraulic valve 200 of the secondary system 620 may be described as that of a safety valve of the hydraulic valve

arrangement 500. The safety valve is consequently configured to prevent the movable platform 120 to revert back to a resting position when no power is supplied to the hydraulic operating arrangement. The resting position is herein defined as the position which the movable platform would take if the hydraulic operating arrangement provides no support. Depending on the design of the dock leveller, the resting position may coincide with the default position of the movable platform. The safety valve is arranged such that the movable platform 120 stays in its controlled position even when the power supplied to the hydraulic operating arrangement 160 fails. In other words, the safety valve is activated when the primary system 610 fails which may be e.g. due to a power failure. The safety valve is hence arranged to urge the hydraulic operating arrangement to hold the movable platform in position, e.g. in the controlled position, when activated. A hydraulic valve 200 of opposite control can be found in the primary hydraulic system 610. This is a hydraulic valve operating in normally open arrangement which means that when it is activated, the internal connection 250 of the hydraulic valve 200 will be closed, connecting the hydraulic ports 220, 230 of the hydraulic valve 200. This means that when the movable platform 120 is at its default position, which is the normal state of a movable platform 120 of a dock leveller 20, the secondary hydraulic system 620 needs to be activated, i.e. the hydraulic valve 200 of the secondary hydraulic system 620 has to be constantly powered when the movable platform 120 is to remain in position, e.g. the default positon. As mentioned earlier, this consumes considerable amounts of current.

Note that Fig. 6 and the description given above is supposed to give added understanding of the inventiveness of the present disclosure and is in no way intended to be complete or give a working presentation of a hydraulic system. General hydraulic systems are known from the art. Rather, Fig. 6 is intentionally illustrating the connection between hydraulic valves 200 and the door 140 as electrical signals, although only the connection between power sources 510 and the hydraulic valves would be electrical. The connection between the movable platform 120 and the hydraulic valves would be hydraulic.

The inventors behind this disclosure, have, after considerable inventive thinking concluded that the current consumption of a hydraulic valve 200 in general and a safety valve of a hydraulic valve arrangement 500 in particular, can be significantly reduced by controlling the current supplied to a hydraulic valve 200.

Fig. 7 shows a novel and inventive hydraulic valve arrangement 500 where the current is controlled. In Fig. 7, the hydraulic valve arrangement 500 has been modified by the addition of a control module 700 that is operatively connected between the power source 510 and the hydraulic valve 200. The control module 700 may be connected in line with the power interface 530 such that the control module 700 is connected in series with the power interface 530. The control module 700 can also be referred to as a power saving module or a current control module 700.

The control module 700 may be a physical enclosure as illustrated in Fig. 8, with two ports 810, 820 where each port 810, 820 may comprise more than one signal. Typically one of the ports 810, 820 is an input port 810 and another of the ports 810,

820 is an output port 820. The input port 810 is connected towards the power source 510 and the output port is connected towards the hydraulic valve 200. Typically the ports 810, 820 would be of the same shape, form and size as the corresponding ports of the power source 510 and the hydraulic valve 200 enabling simple connection and disconnection of the power control module 700 from the hydraulic valve arrangement.

The control module 700 shown in Fig. 8 is shown with two ports 810, 820 but it should be understood that this is a non-limiting example and any number of ports necessary for the control module 700 to be successfully connected in series with the power interface 530, i.e. the closed current loop between the inductive element 240 and the power source as described earlier. Each port 810, 820 may be provided with more than one signal, e.g. both positive and negative DC signals, all depending on suitability for each particular hydraulic valve arrangement. It should also be emphasized that the control module 700 shown as a standalone device in Fig. 7 may very well be integrated into other parts of a hydraulic arrangement 500 e.g. the power source 510 or even the hydraulic valve 200. It may even be that the control module is distributed in the sense that the components comprising the control module 700 may be comprised in any or all of e.g. the power source 510, the hydraulic valve 200 or in a remote location accessed by a communications interface.

In one embodiment, the control module 700 receives, via e.g. the input port 810, an input voltage VIN with an amplitude Vo provided by the power source 510. A diagram of VIN as a function of time t is presented in Fig. 9a. The power source 510 is activated at a start time to. The control module 700 will periodically manipulate the input voltage VIN such that an output voltage VOUT feed by the control module 700 to its output port 820 is substantially a zero potential, see Fig. 9b. The output voltage VOUT will be manipulated at manipulation times ti, t2, t3, U. However, due to the inductive element 240 of the hydraulic valve 200, being operatively connected to the output port 820 of the control module 700, the output voltage VOUT will not directly follow the curve of Fig. 9b. The output voltage VOUT will have the low pass filtered behavior of Fig. 9c. In Fig. 9c, the solid line is output voltage VOUT when hydraulic valve 200 is in connection with the output port 820 of the control module 700 and the dashed line is the control voltage as introduced with reference to Fig. 9b. Analogously to the technical explanation given in relation to Figs. 3a-d, an output current IOUT feed by the control module 700 to its output port 820 will have a similarly low pass filtered shaped, see Fig. 9d. In Fig 9d, the solid line is the output current IOUT and the dashed line is for reference only to show the times when the output is switched. The manipulation performed by the control module 700 in the examples presented above is called pulse width modulation. The pulse width modulation may be performed in any number of ways, one

straightforward approach is to have the manipulation times ti, t2, t3, U hard coded as e.g. times relative to the start time to.

In relation to pulse width modulation, a duty cycle is typically specified. The duty cycle is defined as the active time or on-time divided by the period time or the sum of the on-time and the off-time. Looking again at Fig. 9b, there are at least two duty cycles visible, a first duty cycle as ti-to divided by t2-to and a second duty cycle of t3-t2 divided by t4-t2. In Fig. 9b, the period times for the first and second duty cycle appear to be different, this may be the case in some implementations but in other implementations the period time may be kept constant. By changing the manipulation times ti, t2, t3, t4 the average current of Fig. 9d will change. If e.g. the first manipulation time ti is occurring more shortly after the start time to, the current in Fig. 9d at the first manipulation time ti would decrease. So, by manipulating the duty cycle of the pulse width modulation, the output current IOUT of the control module 700 may be controlled.

By controlling the output current IOUT of the control module 700 by pulse width modulation, the average current provided to the hydraulic valve 200 can be controlled at a level that approximately equals the holding current of the solenoid 400.

In one embodiment of the control module 700, the controlling of the output current IOUT by pulse width modulation is performed based on at least two pre-defmed duty cycles. The resulting output voltage VOUT is depicted in Fig. 10. A first duty cycle DCi is initiated at the start time to and a second duty cycle DC2 is initiated after a first time period TDCI. The conceptual idea is to apply the first duty cycle DCi until the holding current of the solenoid 400 is achieved, typically the first first duty cycle DCi is 100 % and not, as shown in Fig. 10, less than 100 %. One reason for keeping the first duty cycle below 100% may be to reduce the peak current required by the power supply 510. Once the holding current is achieved with an optional margin, or when the first time period TDCI has lapsed, the second duty cycle DC2 is applied. The second duty cycle DC2 is lower than the first duty cycle DCi since the hysteresis of the inductive element 200 and the metallic core 410 will cause the output current to fall with a limited slew rate as explained in relation to e.g. Fig. 9d.

The duration of the first duty cycle TDCI may, in some variants be configurable e.g. by manipulation of variable resistor such as a potentiometer, through interaction with a user interface or by changing positions of jumpers. The same or similar level of configurability may, in some variants be available to the different duty cycles DCi, DC2 utilized.

Note that the examples given where two duty cycles DCi, DC2 are presented that way simply for simplicity and ease of explanation. There may be any number duty cycles implemented and they may be of different duty cycle and the skilled person will, after digesting this disclosure understand how to configure and implement a system with any number of duty cycles. This also implies that first time period TDCI associated with the first duty cycle DCi may very well be followed by consecutive time period(s) associated with corresponding consecutive duty cycles.

So far examples of control modules 700 with fixed or configurable duty cycles DCi, DC2 and associated time periods TDCI have been shown. The duty cycle, and/or the time period may be automatically controlled by measuring the output voltage VOUT, the output current IOUT and/or an input current IIN. The input current IIN is the current received at the input port 810 of the control module 700. By monitoring the mentioned measured parameters VOUT, IOUT, IIN, the signal provided to the output port 820 may be controlled by e.g. turning off the signal provided to the output port 820 when one of the measured parameters VOUT, IOUT, IIN, reaches a first threshold. The signal may be kept turned off until the measured parameter VOUT, IOUT, IIN reaches a second threshold at which point it is turned on again until the VOUT, IOUT, IIN reaches the first threshold again. The difference between the first and the second threshold defines a voltage interval or current interval depending on the associated measured parameter VOUT, IOUT, IIN.

Controlling the signal provided to the output port 820 based on the measured parameter may be done in many ways. In some variants, a controller comprising a simple comparator with fixed or tunable regions for the first and second threshold may be implemented. In other or further embodiments, the controller may comprise devices such as e.g. an MCU, a processor, DSP or FPGA. The controller may be included in the control module 700 and this controller may be configured with the thresholds as described above. The configuration of the controller may be done e.g. using

predetermined parameters or during operation via a suitable interface. The controller may alternatively or additionally be configured to perform control of duty cycles and associated time periods as presented earlier.

The safety valve of the secondary system 620, presented earlier with reference to Fig. 6, will during normal operation benefit especially from the introduction of the control module 700. Since the safety valve is activated when the movable platform 120 of the docking leveller 20 is at its default position, the control module 700 will reduce the power consumption of the secondary system 620. The power consumption of the primary system 610 will also be decreased by the introduction of the control module 700. But, since the primary system 610 typically is activated only when the movable platform is in a particular position, i.e. not in the default position of the movable platform 120, the total decrease of power consumption will not be as significant as for the secondary system 620.

With reference to Fig. 11, a simplified flow chart detailing a method 1100 performed by the control module 700 will be explained. The method 1100 is initiated by receiving 1110, via the input port 810, an input voltage from the power source 510. The received voltage is typically used as the trigger for the start of the method 1100 but other signals may be used in order to initialize the method 1100.

Once started, the method 1100 will start output control 1120 which comprises control of the output port 820 of the control module 700 between an on state and an off state. The on state may in some embodiments be a voltage of substantially the same level as the input voltage. In embodiments wherein the control module 700 comprises voltage transformation means, e.g. transformers, flyback converters, buck converters, boost converters, LDOs etc., the on state may comprise controlling the output port 820 to a level above or below the input voltage. The off state may in some embodiments comprise controlling the off state to a level substantially equal to a ground or zero voltage potential. The on and off states are described in relation to voltages but the control module 700 may very well be designed to comprise a current controller and the skilled person knows how to adapt the reasoning above to currents rather than voltages. The method 1100 would typically start with changing the status of the output port 820 to the on state but this may be performed after a predefined or configurable time delay in order to avoid transients due to e.g. inrush currents. The on state may also in embodiments be transitioned into by a configurable of predefined slew rate.

The step of controlling may, in some embodiments, comprise the optional step of measuring 1 121 an output voltage VOUT and/or an output current IOUT at the output port 820 of the control module 700. Depending on the internal makings of the control module 700, the measured parameters may be collected at the input port 810 of the control module 700. The controlling 1120 may utilize the measured parameter in order to control the output port 820 of the control module 700 such that a wanted level of current and/or current is substantially maintained. In embodiments with voltage and/or current transformation means this may imply increasing or decreasing the current and or voltage such that the wanted level is maintained.

The step of controlling 1120 may, in some embodiments, additionally or alternatively comprise the optional step of pulse width modulating 1122 the power interface 530 supplied to the output port 820 of the control module 700. The step of pulse width modulation 1122 may comprise utilizing a number of duty cycles and associated duty cycle times as detailed earlier with reference to Fig. 10. It may be that the first duty cycle DC1 is 100% in some embodiments.

Some embodiments of the controlling 1110 step may comprise both the step of measuring 1121 and the step of pulse width modulating 1122. In such embodiments, the output port 820 may be controlled 1120 based on the measured parameter and e.g. transitioned into an on-state when the measured parameter is too low and analogously transitioned into an off-state when the measured parameter is in an off state. This example is given with control of the positive signal circuit, if the signal is measured and/or controlled on the negative signal circuit the control needs to be adjusted accordingly.

For completeness, Fig. 12 will be used to present a non-limiting example of the functional blocks comprised in the control module 700. As detailed with reference to Fig. 8, the control module 700 comprises an input port 810 and an output port 820. These ports 810, 820 are internally connected via a connection means 1210. The connection means 1210 may be any suitable connection means e.g. a transistor, a relay etc. It may be that the connection means 1210 is controllable in such a say that it may limit or reduce the signal provided from the input port 810 before it is delivered to the output port 820. As mentioned earlier, but not visible in Fig. 12, the connection means 1210 may be a device that enables the absolute level at the output port 820 to be higher than that at the input port 810. The connection means 1210 is operatively connected to a controller 1220 arranged to control the state of the connection means.

The controller may be any suitable controller as detailed and exemplified earlier. In some embodiments, the control module 700 further comprises a measuring device 1230 arranged to provide a measured parameter to the controller 1220. The measuring device 1230 may be arranged to measure a parameter received at the input port 810 or to measure a parameter supplied to the output port 820. In some embodiments, more than one measuring device 1230 may be available and arranged to measure one or more parameters at the input port 810 and/or the output port 820 respectively. The measuring device 1230 may be realized in numerous ways and cost effective measure of the voltage provided to the output port 820 may be measured via a simple connection between the output port 820 and the controller 1220. A measuring device 1230 arranged to measure the current provided to the output port 820 may be a simple series resistor of a known resistance. Depending on the controller 1220, evaluation of the measured parameter may be performed simply by voltage division and a comparator or more advanced measured with analogue to digital converters comprised in a MCU or similar. The invention presented in the previous sections solves a great number of technical problems and has numerous benefits over solutions found in the art. The control module 700, or power saving arrangement, introduced is possible to retrofit in hydraulic arrangements 800 utilized in docking systems. This makes the solution cost effective at least due to the fact that many components may be reused when a system is upgraded. This is also an environmental benefit since waste is minimized. An even greater environmental benefit is the reduction of power consumption when the current is controlled around the holding current rather than allowed to freely feed the hydraulic valve 200 well into saturation. The reduced current will also reduce cost of electricity and the heat dissipated in the component and consequently their lifetime. It may be possible to reduce the size and consequently the cost of power sources 510 since lower currents are required, also current of cabling may be possible to reduce, further decreasing the cost of the system. Many of the embodiments presented describe solutions for configurability, controllability and flexibility of parameters relating to the control of a hydraulic valve, this enables the same control module 700 to be used with different types of hydraulic valves 200 having diverse e.g. holding currents and saturation levels.