Patent Description:
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 <CIT> 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.

<CIT> discloses a hydraulic valve arrangement for a lift comprising a hydraulic operating arrangement including electronically controlled hydraulic valves with solenoid activation arranged to be connected to the hydraulic operating arrangement. A control processor controls the valves via a control output module. The control module is configured to control a current and/ or voltage of a power interface provided to the valves from a power source. The control module monitors the operation of the lift.

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.

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 is defined in claim <NUM>.

The hydraulic valve arrangement has the benefit that the power consumption is reduced in the valve consuming the most power in the system.

In an embodiment the control module is arranged to measure an output voltage and/or an output current supplied to the electronically controlled hydraulic valves 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 <NUM>%. 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 valves 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 valves 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 valves 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 valves 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, configured for the at least two electronically controlled hydraulic valves of the hydraulic valve arrangement (<NUM>) according to claim <NUM> comprised in the dock leveller. The control module has the benefit 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 electronically controlled hydraulic valves 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.

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.

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>, one examples of a docking station <NUM> or docking unit <NUM> is shown. The docking station <NUM> is provided with a door <NUM> opening up to a loading platform <NUM>. In order to allow a truck <NUM> to reverse and conveniently load and/or unload goods <NUM> onto the loading platform <NUM>, a dock leveller <NUM> is comprised in the docking station <NUM>. The dock leveller <NUM> comprises a movable or adjustable platform <NUM> which is controlled by a hydraulic operating arrangement <NUM> arranged to change the position of the movable platform <NUM>. The hydraulic operating arrangements comprise electronically controlled hydraulic actuators connected to the movable platform <NUM>.

The hydraulic operating arrangement may be connected to the movable platform by means of a linkage system or a mounting console. The docking unit <NUM> depicted in <FIG> uses the hydraulic operating arrangement <NUM> to angle the movable platform <NUM> such that the end of the movable platform <NUM> being closest to the truck <NUM> changes its height relative to a ground level G. The end of the movable platform <NUM> 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 <NUM>. The exemplified docking unit <NUM> described with reference to <FIG> should be considered non-limiting examples of one arrangement of a movable platforms <NUM> in docking units <NUM> comprising dock levellers <NUM>. The intention is to provide an understanding of the function and purpose of a dock leveller <NUM> in general and not to specifically detail certain embodiments of dock levellers <NUM>. A typical dock leveller <NUM> uses, as explained above, the hydraulic operating arrangement <NUM> to control the positon of the movable platform <NUM>. The hydraulic operating arrangement <NUM> will move the movable platform <NUM> 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 <NUM> may differ depending on the arrangement of the dock leveller <NUM> but one may envision the default positon being e.g. fully raised or completely lowered. However, said hydraulic operating arrangement <NUM> 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 <NUM> 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>. In <FIG>, a schematic block diagram of an electrically controlled hydraulic valve <NUM> is depicted. The valve <NUM> is a shown with two electrical ports <NUM> connected to an inductive element <NUM> comprised in the valve <NUM>. The function or purpose of the inductive element <NUM> may be e.g. that of a solenoid or of an electromagnet. The valve <NUM> is further provided with at least two hydraulic ports <NUM>, <NUM> where the internal connection <NUM> between the hydraulic ports <NUM>, <NUM> is controlled by activation of the inductive element <NUM>. The internal connection <NUM> between the hydraulic ports <NUM>, <NUM> is shown as a switch and this is simply not to limit the connection <NUM> with particular types of membrane switches etc. The inductive element <NUM> is activated when an electrical current is allowed to flow through the inductive element <NUM>, i.e. when a power source is connected to the electrical ports <NUM>.

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

Looking at the impedance ZL across the inductive element <NUM> at a particular frequency f this is described by Eqn.

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

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

The voltage drop across the inductive element vL(t) is illustrated in <FIG> and the voltage across the resistive element vR(t) is shown in <FIG>. The circuit impedance ZIN, the resistive element <NUM> in series with the inductive element <NUM>, is shown in <FIG> as a function of time. The change over time in circuit impedance ZIN comes from the frequency dependent behavior of the inductive element <NUM> as shown in Eqn. Since the circuit impedance ZIN drops as the voltage increases, the current though the circuit will increase since Eqn. <NUM> 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.

The resistive element <NUM> is in <FIG> shown as a separate unit simply for the sake of explanation, in implementation the voltage source <NUM> and the inductive element <NUM> may be directly connected. In this case the resistive element <NUM> would be comprised in internal resistance of the voltage source <NUM> and parasitic components of the circuitry in general and the inductive element <NUM> 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 <FIG> a simple solenoid <NUM> will be explained. In <FIG>, the solenoid <NUM> is shown comprising a helical coil <NUM> of wound wire wrapped around a metallic core <NUM>. In <FIG>, an electromagnetic field <NUM> generated by the current <NUM> flowing through the coil <NUM> is shown. The electromagnetic field <NUM> will, although not shown in <FIG>, circle back outside the coil <NUM> such that it describes a closed loop. The metallic core <NUM> will be subjected to the magnetic field <NUM> generated by the coil <NUM> when a current <NUM> is applied to the coil <NUM>. The magnetic field <NUM> will move the metallic core <NUM> by a force relative to the current <NUM> of the coil <NUM> and the metallic core <NUM> will be moved to a positon of equilibrium that will depend on the physical parameters of the metallic core <NUM> and coil <NUM>. The amount of current needed to accelerate the metallic core <NUM> is greater than the current needed to keep the core <NUM> at equilibrium. This is relating to the magnetization, hysteresis and saturation of the metallic core <NUM>. The current required to keep the metallic core <NUM> at equilibrium is sometimes referred to as a holding current. Relating this to the electrical properties of the inductive element <NUM> detailed in earlier sections, the impedance of the coil <NUM> will decrease as the metallic core <NUM> is saturated, i.e. is in a position of equilibrium.

The solenoid <NUM> briefly explained with reference to <FIG> is a simple example to explain the underlying concept of a hydraulic valve. The solenoid <NUM> may be what controls the internal connection <NUM> in the valve <NUM> shown in <FIG>. Typically, the metallic core <NUM> is attached to a membrane that is used to seal or open the internal connection <NUM> of the valve <NUM>.

With reference to <FIG>, a block diagram of a hydraulic valve arrangement <NUM> 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 <NUM>. The hydraulic valve arrangement <NUM> comprises one or more valves <NUM> and at least one the valves <NUM> is an electronically controlled hydraulic valve with solenoid activation <NUM>. The term solenoid activation is meant to mean that the hydraulic valve <NUM> comprises an inductive element <NUM> that is engaged by a current in order to control the internal connection <NUM> of the hydraulic valve <NUM>.

With reference to <FIG>, the hydraulic valve <NUM> is operatively connector to a power source <NUM> via a power interface <NUM>. The power source <NUM> may be any suitable power source <NUM> that is capable of driving the hydraulic valve <NUM>. A common power source is a 24V direct current, DC, power source, that, when activated, outputs 24V as the power interface <NUM>. The power interface <NUM> may be a simple two-wire interface allowing a closed current loop between the inductive element <NUM> of the hydraulic valve <NUM> and the power source <NUM>. It may be that the power interface <NUM> is a single wire power interface <NUM> 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 <NUM> are typically utilizing hydraulics in order to control position of the movable platform <NUM> of the dock leveller <NUM>. 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 <NUM> is not allowed to change its position during a power failure of loss of hydraulic pressure in the primary system.

<FIG> shows a schematic block diagram of a hydraulic valve arrangement <NUM> according to an embodiment. The hydraulic valve arrangement comprises a primary hydraulic system <NUM> and a secondary hydraulic system <NUM>. The hydraulic valve arrangement comprises valves <NUM> which are 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 <NUM>, <NUM> are connected to the hydraulic operating arrangement <NUM> and each comprises at least one electronically controlled hydraulic valve <NUM> and at least one power source <NUM>. Notably there is a difference between the electronically controlled hydraulic valves <NUM> of the primary system <NUM> and the secondary system <NUM>. The secondary system <NUM> acts as a failsafe system and utilizes a electronically controlled hydraulic valve <NUM> operating in a normally closed arrangement which means that when it is activated, the internal connection <NUM> of the electronically controlled hydraulic valve <NUM> will be open, disconnecting the hydraulic ports <NUM>, <NUM> of the electronically controlled hydraulic valve <NUM>, which means that when it is activated, the internal connection <NUM> of the electronically controlled hydraulic valve <NUM> will be open disconnecting the hydraulic ports <NUM>, <NUM> of the electronically controlled hydraulic valve <NUM>. The function of the electronically controlled hydraulic valve <NUM> of the secondary system <NUM> may be described as that of a safety valve of the electronically controlled hydraulic valve arrangement <NUM>. The safety valve is consequently configured to prevent the movable platform <NUM> 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 <NUM> stays in its controlled position even when the power supplied to the hydraulic operating arrangement <NUM> fails. In other words, the safety valve is activated when the primary system <NUM> 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 valve <NUM> of opposite control is be found in the primary hydraulic system <NUM>. This is the electronically controlled hydraulic valve operating in normally open arrangement which means that when it is activated, the internal connection <NUM> of the electronically controlled hydraulic valve <NUM> will be closed, connecting the hydraulic ports <NUM>, <NUM> of the electronically controlled hydraulic valve <NUM>. This means that when the movable platform <NUM> is at its default position, which is the normal state of a movable platform <NUM> of a dock leveller <NUM>, the secondary hydraulic system <NUM> needs to be activated, i.e. the hydraulic valve <NUM> of the secondary hydraulic system <NUM> has to be constantly powered when the movable platform <NUM> is to remain in position, e.g. the default positon. As mentioned earlier, this consumes considerable amounts of current.

Note that <FIG> 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> is intentionally illustrating the connection between valves <NUM> and the door <NUM> as electrical signals, although only the connection between power sources <NUM> and the valves would be electrical. The connection between the movable platform <NUM> and the valves would be hydraulic.

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

<FIG> shows a valve arrangement <NUM> where the current is controlled. In <FIG>, the hydraulic valve arrangement <NUM> has been modified by the addition of a control module <NUM> that is operatively connected between the power source <NUM> and the electronically controlled hydraulic valve <NUM>. The control module <NUM> may be connected in line with the power interface <NUM> such that the control module <NUM> is connected in series with the power interface <NUM>. The control module <NUM> can also be referred to as a power saving module or a current control module <NUM>.

The control module <NUM> may be a physical enclosure as illustrated in <FIG>, with two ports <NUM>, <NUM> where each port <NUM>, <NUM> may comprise more than one signal. Typically one of the ports <NUM>, <NUM> is an input port <NUM> and another of the ports <NUM>, <NUM> is an output port <NUM>. The input port <NUM> is connected towards the power source <NUM> and the output port is connected towards the electronically controlled hydraulic valve <NUM>. Typically the ports <NUM>, <NUM> would be of the same shape, form and size as the corresponding ports of the power source <NUM> and the electronically controlled hydraulic valve <NUM> enabling simple connection and disconnection of the power control module <NUM> from the hydraulic valve arrangement.

The control module <NUM> shown in <FIG> is shown with two ports <NUM>, <NUM> but it should be understood that this is a non-limiting example and any number of ports necessary for the control module <NUM> to be successfully connected in series with the power interface <NUM>, i.e. the closed current loop between the inductive element <NUM> and the power source as described earlier. Each port <NUM>, <NUM> 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 <NUM> shown as a standalone device in <FIG> may very well be integrated into other parts of a hydraulic arrangement <NUM> e.g. the power source <NUM> or even the electronically controlled hydraulic valve <NUM>. It may even be that the control module is distributed in the sense that the components comprising the control module <NUM> may be comprised in any or all of e.g. the power source <NUM>, the electronically controlled hydraulic valve <NUM> or in a remote location accessed by a communications interface.

In one embodiment, the control module <NUM> receives, via e.g. the input port <NUM>, an input voltage VIN with an amplitude V<NUM> provided by the power source <NUM>. A diagram of VIN as a function of time t is presented in <FIG>. The power source <NUM> is activated at a start time t<NUM>. The control module <NUM> will periodically manipulate the input voltage VIN such that an output voltage VOUT feed by the control module <NUM> to its output port <NUM> is substantially a zero potential, see <FIG>. The output voltage VOUT will be manipulated at manipulation times t<NUM>, t<NUM>, t<NUM>, t<NUM>. However, due to the inductive element <NUM> of the electronically controlled hydraulic valve <NUM>, being operatively connected to the output port <NUM> of the control module <NUM>, the output voltage VOUT will not directly follow the curve of <FIG>. The output voltage VOUT will have the low pass filtered behavior of <FIG>. In <FIG>, the solid line is output voltage VOUT when electronically controlled hydraulic valve <NUM> is in connection with the output port <NUM> of the control module <NUM> and the dashed line is the control voltage as introduced with reference to <FIG>. Analogously to the technical explanation given in relation to <FIG>, an output current IOUT feed by the control module <NUM> to its output port <NUM> will have a similarly low pass filtered shaped, see <FIG>. In <FIG>, 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 <NUM> 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 t<NUM>, t<NUM>, t<NUM>, t<NUM> hard coded as e.g. times relative to the start time t<NUM>.

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>, there are at least two duty cycles visible, a first duty cycle as t<NUM>-t<NUM> divided by t<NUM>-t<NUM> and a second duty cycle of t<NUM>-t<NUM> divided by t<NUM>-t<NUM>. In <FIG>, 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 t<NUM>, t<NUM>, t<NUM>, t<NUM> the average current of <FIG> will change. If e.g. the first manipulation time t<NUM> is occurring more shortly after the start time t<NUM>, the current in <FIG> at the first manipulation time t<NUM> would decrease. So, by manipulating the duty cycle of the pulse width modulation, the output current IOUT of the control module <NUM> may be controlled.

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

In one embodiment of the control module <NUM>, the controlling of the output current IOUT by pulse width modulation is performed based on at least two pre-defined duty cycles. The resulting output voltage VOUT is depicted in <FIG>. A first duty cycle DC<NUM> is initiated at the start time t<NUM> and a second duty cycle DC<NUM> is initiated after a first time period TDC1. The conceptual idea is to apply the first duty cycle DC<NUM> until the holding current of the solenoid <NUM> is achieved, typically the first first duty cycle DC<NUM> is <NUM> % and not, as shown in <FIG>, less than <NUM> %. One reason for keeping the first duty cycle below <NUM>% may be to reduce the peak current required by the power supply <NUM>. Once the holding current is achieved with an optional margin, or when the first time period TDC1 has lapsed, the second duty cycle DC<NUM> is applied. The second duty cycle DC<NUM> is lower than the first duty cycle DC<NUM> since the hysteresis of the inductive element <NUM> and the metallic core <NUM> will cause the output current to fall with a limited slew rate as explained in relation to e.g. <FIG>.

The duration of the first duty cycle TDC1 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 DC<NUM>, DC<NUM> utilized.

Note that the examples given where two duty cycles DC<NUM>, DC<NUM> 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 TDC1 associated with the first duty cycle DC<NUM> may very well be followed by consecutive time period(s) associated with corresponding consecutive duty cycles.

So far examples of control modules <NUM> with fixed or configurable duty cycles DC<NUM>, DC<NUM> and associated time periods TDC1 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 <NUM> of the control module <NUM>. By monitoring the mentioned measured parameters VOUT, IOUT, IIN, the signal provided to the output port <NUM> may be controlled by e.g. turning off the signal provided to the output port <NUM> 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 <NUM> 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 <NUM> 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 <NUM>, presented earlier with reference to <FIG>, will during normal operation benefit especially from the introduction of the control module <NUM>. Since the safety valve is activated when the movable platform <NUM> of the docking leveller <NUM> is at its default position, the control module <NUM> will reduce the power consumption of the secondary system <NUM>. The power consumption of the primary system <NUM> will also be decreased by the introduction of the control module <NUM>. But, since the primary system <NUM> typically is activated only when the movable platform is in a particular position, i.e. not in the default position of the movable platform <NUM>, the total decrease of power consumption will not be as significant as for the secondary system <NUM>.

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

Once started, the method <NUM> will start output control <NUM> which comprises control of the output port <NUM> of the control module <NUM> 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 <NUM> comprises voltage transformation means, e.g. transformers, flyback converters, buck converters, boost converters, LDOs etc., the on state may comprise controlling the output port <NUM> 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 <NUM> 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 <NUM> would typically start with changing the status of the output port <NUM> 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 <NUM> an output voltage VOUT and/or an output current IOUT at the output port <NUM> of the control module <NUM>. Depending on the internal makings of the control module <NUM>, the measured parameters may be collected at the input port <NUM> of the control module <NUM>. The controlling <NUM> may utilize the measured parameter in order to control the output port <NUM> of the control module <NUM> 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 <NUM> may, in some embodiments, additionally or alternatively comprise the optional step of pulse width modulating <NUM> the power interface <NUM> supplied to the output port <NUM> of the control module <NUM>. The step of pulse width modulation <NUM> may comprise utilizing a number of duty cycles and associated duty cycle times as detailed earlier with reference to <FIG>. It may be that the first duty cycle DC1 is <NUM>% in some embodiments.

Some embodiments of the controlling <NUM> step may comprise both the step of measuring <NUM> and the step of pulse width modulating <NUM>. In such embodiments, the output port <NUM> may be controlled <NUM> 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.

Claim 1:
A hydraulic valve arrangement for a dock leveller (<NUM>) comprising a movable platform (<NUM>) and a hydraulic operating arrangement (<NUM>) arranged to control the position of the movable platform (<NUM>), the hydraulic valve arrangement (<NUM>) comprises:
at least two electronically controlled hydraulic valves (<NUM>) with solenoid activation arranged to be connected to the hydraulic operating arrangement (<NUM>), wherein the electronically controlled hydraulic valves (<NUM>) are operatively connected to a power interface (<NUM>) provided by a power source (<NUM>), and
at least one control module (<NUM>) operatively connected, via the power interface (<NUM>), to the power source (<NUM>) and the electronically controlled hydraulic valves (<NUM>),
wherein the control module (<NUM>) is configured to control a current and/or voltage of the power interface (<NUM>) provided to the electronically controlled hydraulic valves (<NUM>) from the power source (<NUM>), wherein at least one of said electronically controlled hydraulic valves (<NUM>) is a safety valve arranged such that the movable platform (<NUM>) is held in a fixed controlled position when the safety valve is activated, when no power is supplied to the at least other one of the electronically controlled hydraulic valves (<NUM>).