EP2519387A1

EP2519387A1 - Electromechanical actuator structure

Info

Publication number: EP2519387A1
Application number: EP09835904A
Authority: EP
Inventors: Stefano Roccella
Original assignee: Scuola Superiore di Studi Universitari e di Perfezionamento SantAnna
Current assignee: Scuola Superiore di Studi Universitari e di Perfezionamento SantAnna
Priority date: 2009-12-31
Filing date: 2009-12-31
Publication date: 2012-11-07
Also published as: WO2011080532A1

Abstract

An electromechanical actuator (100) comprising a ferromagnetic unit or a stator (10) which consists of opposite first (11 ) and a second (12) ferromagnetic elements that comprises ferromagnetic portions (16') and magnetic elements (15) that form together a open magnetic circuit. The electromechanical actuator (100) comprises also an electromagnetic unit (20) that is relatively movable with respect to the ferromagnetic unit (10), which comprises a first (21 ) and a second (22) winding integral to each other and arranged, with respect to the ferromagnetic unit (10), such that the respective open magnetic circuit are closed on the first (11 ) and the second (12) ferromagnetic elements. In particular, the first (21 ) and the second windings (22) comprise each a plurality of serially arranged elementary windings (23), which starts from an initial elementary winding (23i) up to a final elementary winding (23f), in particular the elementary windings have an increasing number of loops. The windings (21/22) are oppositely arranged with respect to each other and are respectively run through by opposite currents lag and Ian in such a way that opposite repulsive forces are generated. In particular, the forces are such that an agonist force (Fag), which is generated on one of windings, for example (21), that is run through by current lag, opposes to an antagonist force (Fan), which is generated on the other winding (22), that is run through by current Ian, until a relative position of the electromagnetic unit (10) and of the ferromagnetic unit (20) is achieved in which the above described forces balance each other. The electromechanical actuator (100), comprises furthermore a means for independently controlling the intensity of the opposite currents lag and Ian that circulates within the first (21 ) and the second winding (22) in order to adjust the absolute value of the current intensity difference and therefore adjusting the relative position, where the forces balance each other.

Description

TITLE

ELECTROMECHANICAL ACTUATOR STRUCTURE DESCRIPTION

Field of the invention

The present invention relates to mechatronics and, in particular, it relates to an electromechanical actuator structure which can be used, for instance, in industrial automation, in automotive industry, in electric actuators, in rehabilitation robotics, in robotic manipulators that interact with human beings, or in similar applications.

Description of the prior art

Prior art actuators normally comprise a drive and a mechanical connection or transmission which serves to adapt the action of the drive responsive to the load. This connection is usually stiff, or it can be resilient just enough to compensate any possible misalignment that may occur when assembling the actuator. The machines that comprise such devices are normally position-controlled.

This system is not so efficient if also the forces that are exchanged with the environment have to be controlled, because small position changes give rise to high interaction forces that are actually not easy to keep under control, due to the considerable stiffness of the transmission parts. Furthermore, possible collisions with unexpected obstacles may give rise to high impact forces that are potentially detrimental for the machines and for the obstacle. The problem is particularly felt in the case of machines which interact and cooperate with human beings or which are located in crowded places. For example, in rehabilitation robots or in service robotic manipulators, the interaction with a human being is essential, therefore a safe and efficient operation must be ensured.

Both in industrial and in service robotic applications, and even more in rehabilitation applications, the problems of physical contact between a human being and a robot is a main concern. One of the primary requirements to be taken into account when designing such a system is to ensure a safe operation to the operator and the patient, with whom the robot interacts, reducing the performances of the same as less as possible. According to the prior art, two operation approaches are normally followed.

In the so called "Active Compliance" approach, the stiffness of the robot components is software-adjusted by means of force and position control algorithms that process signals obtained from the respective sensors. The structure of the robot is a traditional one, for example a manipulator that is associated with a motor and with a reduction gear arranged at each joint. In this case, however, problems may arise in case of unexpected and sudden events such as collisions or hits, which last much less than the time the control system takes to react.

Accordingly, a so called "Passive Compliance" approach has been developed, which solves the above-mentioned problem; the robot is conceived with a mechanical structure and with an actuating system that are adapted to spontaneously and passively cope with the external event, by adjusting the stiffness independently from the position. An example of such solution is disclosed in US6040960.

In particular, known structures of this kind consist in most cases of two actuators in agonist/antagonist configuration with additional mechanical elements that are arranged along the load transmission path, in order to establish a not linear relationship between the force that is supplied by the actuator and the displacement of the movable element, for adjusting the stiffness of the motion that is transferred to the system independently from how the position is changed.

In other cases, two actuators are also provided, as well as one resilient member along the load transmission path, where one actuator serves to change the position while the other is used to directly modify the reaction features of the resilient member.

To sum up, the above described systems provide the use of a redundant number of actuators to adjust independently the position and the transmission stiffness, and the use of normally encumbering and heavy additional mechanical components that are arranged along the load transmission path.

Accordingly, the need is felt of an actuator that allows independently adjusting the position and the stiffness with which the motion is transmitted to the system and that has two functions integrated in one actuator, with additional practicality and reliability. Summary of the invention

It is therefore a feature of the present invention to provide an electromechanical actuator that has an intrinsic impedance variation and is therefore well-suited for use in mechatronic systems that interact with human beings.

It is another feature of the present invention to provide an electromechanical actuator that allows adjusting the position and the mechanical impedance independently from each other, and, in particular, it allows adjusting the stiffness with which motion is transmitted to a system to be actuated.

It is still a feature of the present invention to provide an electromechanical actuator for transmitting both an agonist force and an antagonist force to a system to be actuated.

It is also a feature of the present invention to provide an electromechanical actuator that is adapted to be connected with a system to be actuated directly, or at most through an intermediate reduction member to adapt its force and stroke characteristics as required by the load.

It is another feature of the present invention to provide an electromechanical actuator that allows providing actuation groups that are more compact, less bulky, less heavy and more reliable, as a result of the reduction of the number of involved components, as well as a more dynamically efficient electromechanical actuator.

It is also a feature of the present invention to provide an electromechanical actuator that ensures a high reversibility, in order to be used in rehabilitation devices.

It is still another feature of the present invention to provide an electromechanical actuator that ensures wider pass-bands than in the case of well-known actuation systems, further increasing the dynamic performances of the actuated system.

It is always another feature of the present invention to provide an electromechanical actuator that is adapted to transmit an action of one of its movable elements, such that no further components are required for transmitting this action.

It is still a feature of the present invention to provide an electromechanical actuator that can be used as an automotive active suspension.

These and other objects are achieved by an electromechanical actuator comprising:

- a ferromagnetic unit consisting of a first and of a second ferromagnetic element, said ferromagnetic elements arranged oppositely to each other, each ferromagnetic element comprising ferromagnetic portions and at least one magnetic element, said ferromagnetic portions and said magnetic element forming together a respective open magnetic circuit;

- an electromagnetic unit that comprises a first and a second winding integral to each other, said first and said second windings arranged with respect to said ferromagnetic unit in such a way that they close the respective open magnetic circuit of said first and of said second ferromagnetic elements;

wherein each of said first and said second windings comprises a plurality of elementary windings that are sequentially arranged with respect to each other starting from an initial elementary winding to a final elementary winding, and wherein said first and said second windings are oppositely arranged with respect to each other, and

wherein at least two respective elementary windings of said first and of said second windings are run through by driving currents lag and Ian in such a way that:

- said elementary windings that are run through by said driving currents generate repulsive forces on said magnetic elements of the respective ferromagnetic element;

- an agonist force (Fag), which is generated on said or on each elementary winding of the first winding, said elementary winding of the first winding run through by current lag, opposes to an antagonist force (Fan),which is generated on said or each elementary winding of the second winding, said elementary winding of the second winding run through by current Ian, until a relative position of said electromagnetic unit with respect to said ferromagnetic unit is attained at which said forces balance each other,

- a control means for independently controlling the intensity of said opposite currents lag and Ian that run through the respective elementary windings of said first and of said second windings, in order to adjust the absolute value of the intensity difference of said currents and therefore to adjust said relative position, at which said forces balance each other.

This way, by changing the intensity of the current that runs through said windings, it is possible to adjust both the relative position of said electromagnetic unit with respect to said ferromagnetic unit, and the stiffness that is opposed to an external force that attempts to relatively move the electromagnetic unit with respect to the ferromagnetic unit.

In particular, by changing the intensity of the current in said windings, but maintaining the intensity difference between said currents at a prefixed value, said program means is adapted to adjust the stiffness of the actuator under a same relative position of the electromagnetic unit with respect to the ferromagnetic unit. Instead, by changing the intensity difference between said currents it is possible to adjust the relative position of the electromagnetic unit with respect to the ferromagnetic unit, maintaining the stiffness at a prefixed value.

This way, in order to increase the stiffness of the actuator and to maintain the electromagnetic unit substantially in equilibrium with respect to the ferromagnetic unit, the agonist force must have the same absolute value of the antagonist force (Fag=Fan) i.e., in other words, the slope of respective force-movement curves must change according to a same trend. On the contrary, by suitably unbalancing the currents, for instance, such that lag > Ian, a non-zero resultant force AF=Fag-Fan arises that acts on the electromagnetic unit, which gives rise to an acceleration that tends to move it until a different equilibrium configuration is reached, where it is again F'ag=F'an.

In a particular exemplary embodiment, each of said first and said second windings comprises a plurality of elementary windings that are sequentially arranged with respect to each other and have a number of loops that increases starting from an initial elementary winding up to a final elementary winding.

In this case, the achievement of the new equilibrium position is ensured by the fact that two consecutive elementary windings have a different number of loops (Ni), which generates an agonist force and an antagonist force that change during the movement. In fact, even if the currents in the two windings are maintained at respective values that are different from each other, during the relative translation of the electromagnetic unit with respect to the ferromagnetic unit, the forces on each winding change in an opposite way, such that it is always possible to achieve an equilibrium position.

Preferably, a program means is provided which is associated with said control means, for controlling said opposite currents lag and Ian, said program means allowing to adjust a force-movement characteristic curve. Moreover, the program means allows adjusting the stiffness independently from the position. Due to the variation of the number of loops that are provided along the axis of the windings, the trend of the force-movement characteristic depends upon how the number of loops changes, and its slope is proportional to the current which is imposed to it. For example, the electromagnetic unit can be maintained at a prefixed position by increasing or decreasing the currents in the two windings by the same amount. This way, the slope of the characteristic curves of the windings at the equilibrium position increases or decreases, and the stiffness, i.e. the ratio between the resultant force perturbation (AF'pert and AFpert) that corresponds to a position perturbation (Azpert), and the position perturbation itself, increases or decreases accordingly. Therefore, the stiffness change is not obtained by changing the rest length of the non-linear element, as in the case of the available systems, but by changing the slope of the force-movement characteristic curve of each winding via a change of the respective driving current.

Advantageously, each of said first and said second windings comprises serially arranged winding sections, which constitute said elementary windings, said winding sections separated from each other by means of shielding walls. In this case, each elementary winding is serially connected to the others, such that there is a single winding in which the respective current circulates that circulates through the whole winding.

In a particular exemplary embodiment, said elementary windings are electrically independent from each other and are selectively run through by said driving currents. This way, if the control system is aware of the position of the electromagnetic unit, for example by means of a position sensor, it can send the driving currents lag and Ian only to the windings that are concerned by the magnetic flow of the permanent magnet of the ferromagnetic unit. The usefulness of this solution consists in that it lowers energy consumption and heat dissipation, since the copper wire that is run through by the current of the two elementary windings that are concerned is less than in the case in which all the elementary windings are serially connected to one another, the serial connection excluding all the windings that are not concerned by the control.

In alternative, said electrically independent elementary windings have a prefixed number of loops, and the electromagnetic unit has a cylindrical shape instead of a conical shape. Furthermore, said program means is adapted to adjust the driving currents which flow in each respective agonist and antagonist elementary windings independently from each other such that the predetermined force-movement curve is obtained while that elementary winding moves through the magnetic flux. This allows using windings which have the same number of loops and which do not have therefore a conical profile, but a stepped profile whose external diameters change from one step to another, which reduces therefore the overall dimensions, brings the magnetic elements close to the spacer elements and increases this way the magnetic field in the zone where the loops are present, thus increasing the forces that are supplied by the actuator.

In particular, if the current of the agonist winding is increased with respect to the current of the antagonist winding (Iag>Ian), the agonist force is greater than the antagonist force (Fag>Fan) and the translating element moves towards the agonist winding (Δζ>0). Since the number of loops that are influenced by the magnetic field of the agonist winding decreases during the movement, while the number of loops of the antagonist winding increases, if the two currents are maintained at respective constant and different values, the agonist force decreases and the antagonist force increases, until the new equilibrium condition is obtained accordingly. If the current of the agonist winding is lowered with respect to the current of the antagonist winding (Iag<Ian), a condition that is opposite to the above occurs, and an equilibrium condition is in any case achieved.

In a first particular aspect of the invention, said electromechanical actuator is a linear actuator that comprises a transmission shaft integrally arranged with said electromagnetic unit, said transmission shaft having a longitudinal axis, said transmission shaft relatively movable along said longitudinal axis within said ferromagnetic unit, said ferromagnetic unit comprising said magnetic element oriented towards the inside of said ferromagnetic unit such that said first and said second windings move within said magnetic element at such a short distance that the magnetic circuit is closed,

wherein said first and said second windings are aligned along said shaft and coaxially arranged to the longitudinal axis such that the respective initial elementary windings of said first and of said second windings face each other, and the final elementary windings of said first and of said second windings are located at opposite ends of said electromagnetic unit.

In particular, said ferromagnetic unit of said linear electromechanical actuator comprises a stator body made of a ferromagnetic material, said stator body having a substantially ring shape, said electromagnetic unit sliding within said stator body, said body comprising:

- a first and a second couple of stator ring portions that are made of a ferromagnetic material, each couple defining said respective first and second ferromagnetic elements, said first and second couples of stator ring portions spaced apart from each other by means of connection rods, in particular four connection rods are provided arranged at 90° with respect to each other;

- wherein the ring portions of each couple are connected to each other by means of peripheral connection members and by means of a central connection member, such that each ferromagnetic element forms said open magnetic circuit that comprises in turn said magnetic element, a first ring portion, an upper peripheral connection member, a second ring portion and said central connection member, such that said magnetic circuit is closed between said magnetic element and said central connection member on the respective winding.

Advantageously, at least said magnetic element is mounted on said ring portions, said magnetic element preferably comprising a plurality of permanent magnets that face the inside of said electromagnetic unit. Alternatively, said magnetic element comprises windings that are run through by currents and therefore comprises electromagnets that are adapted to provide a constant magnetic field, instead of permanent magnets.

In particular said electromagnetic unit that comprises said first and said second windings has a substantially tubular shape and defines a central hole, said central hole having an axis that is co-axial with respect to the longitudinal axis, the central connection member of said stator body slidingly engaging with said central hole. In particular, each central connection member has an enlargement ring at said magnetic element, said enlargement ring engaging with the tubular hole of said electromagnetic unit. Preferably, each central connection member is a tubular element that has an inner hole in which said shaft slides.

In particular, said first and said second windings of said electromagnetic unit are keyed to the shaft by means of a connection disc, whereby the stroke of said electromagnetic unit is defined by the stroke that said connection disc can perform between said two central connection members. In particular, said connection disc comprises two disc elements, each disc element integral to the respective first or second winding, said disc elements spaced apart from each other by a spacer made of paramagnetic material.

In particular, a housing for a bearing is provided on each of said second ring portions of each of said enlargements ring, in particular an axial sleeve ball bearing.

Alternatively, said electromechanical actuator is a linear actuator that comprises a shaft integrally arranged with said electromagnetic unit and has a longitudinal axis, said shaft being relatively movable with respect to the longitudinal axis within said ferromagnetic unit, said ferromagnetic unit comprising said magnetic element which is oriented towards the inside of said ferromagnetic unit such that said first and said second windings move within said magnetic element at such a short distance that the circuit is closed, wherein said first and said second windings are arranged on said shaft coaxially to the longitudinal axis such that the respective final elementary windings of said first and of said second windings face each other, and the initial elementary windings of said first and of said second windings are located at opposite ends of said electromagnetic unit. In this case, the direction of the forces is inverted with respect to the case of convergent conical shapes. This is necessary since the force supplied by each winding must be opposite to the movement direction, and must increase if the movement to be obtained increases (each winding must work as a pull spring). To this end, the direction of the magnetic field must be reversed, as well as the direction of the magnets, while the direction of the currents is maintained the same as in the case of not opposed conical shapes. However, in this case the field which is established in the part of stator that crosses the windings has a direction opposite to the direction of the field which is generated by the windings within the relatively movable element, and therefore the resulting field established in the part of stator that crosses the windings is weakened. This reduces the force that can be supplied by the actuator. It is possible to show that this occurs for any possible combination of current direction in the windings and magnets orientation.

In a third particular aspect of the invention, said electromechanical actuator is a linear actuator that comprises said electromagnetic unit that is arranged externally to said ferromagnetic unit, and a ferromagnetic external casing is provided which forms the open magnetic circuit together with the ferromagnetic unit.

In a particular exemplary embodiment, said electromagnetic unit is integral to said ferromagnetic casing, and said ferromagnetic unit is movable with respect to said casing and with respect to said electromagnetic unit. In this case, a movable shaft integral to said ferromagnetic unit can be provided, said movable shaft having a longitudinal axis, said shaft movable along said longitudinal axis within said electromagnetic unit, said electromagnetic unit arranged within said ferromagnetic casing such that said first and said second windings are located outside said ferromagnetic unit,

and wherein said magnetic element is arranged on said shaft in such a way that said first and said second windings face each other within said ferromagnetic unit.

In particular, said ferromagnetic casing has a substantially tubular shape within which said first and said second windings are mounted to define a substantially tubular inner space in which said ferromagnetic unit slides,

wherein said first and said second ferromagnetic elements, which are coaxially arranged on said shaft, comprise respectively:

- a first and a second enlargement rings opposite to each another and facing each another,

- a respective magnetic element;

- a first and a second substantially cylindrical side walls, which slidingly engage with said tubular support structure,

wherein a respective side wall is arranged at an end opposite with respect to said enlargement ring and said magnetic element is set between said enlargement ring and said side wall,

such that said open magnetic circuit is in turn formed by said enlargement ring, said magnetic element, said side wall, a portion of said tubular casing, and is closed at said enlargement ring on one of said elementary windings.

In particular, a plurality of ring magnetic elements are provided mounted consecutively to each other on said shaft.

Advantageously, the respective initial elementary windings of said first and of said second windings face each other, and the final elementary windings of said first and of said second windings are located at opposite ends of said electromagnetic unit.

In alternative, the respective final elementary windings of said first and of said second windings face each other, and the initial elementary windings of said first and of said second windings are located at opposite ends of said electromagnetic unit.

In alternative, said electromechanical actuator is a rotational actuator comprising:

an electromagnetic armature, said armature having an axis of rotation, said electromagnetic armature relatively movable with respect to the rotation axis within a ferromagnetic stator, said ferromagnetic stator comprising said magnetic element oriented towards the inside of said ferromagnetic stator, such that said first and said second windings move at such a short distance from said magnetic element that said magnetic circuit is closed,

wherein said first and said second windings are arranged on said electromagnetic armature at respective positions that are diametrically opposed with respect to the rotation axis, such that the respective initial elementary windings of said first and of said second windings are circumferentially consecutive with respect to each other, and the final elementary windings of said first and of said second windings are circumferentially consecutive with respect to each other.

In particular, said ferromagnetic stator comprises said first and said second ferromagnetic elements which are diametrically opposed.

In a first exemplary embodiment, said first and said second ferromagnetic elements are shaped as two opposite "C" elements between which said armature rotates. In particular, the "C" element consists of two branches and a central portion that are connected to each other, and said magnetic element is arranged between said "C" elements, the branches of each "C" element furthermore connected to each other, by a respective ferromagnetic connection element, and two ferromagnetic material arch portions are provided that extend from respective ferromagnetic connection elements and cross said windings. This way, two respective magnetic circuits are formed which respectively consist of said branches, of said ferromagnetic connection element and of said arch portion.

In particular, said first and said second ferromagnetic elements together form a case consisting of said two coplanar and opposite "C" elements, said connection member orthogonal to said two "C" elements, and of said arch portions, which extend from said connection element to opposite sides of a central position between the branches of the respective opposite "C" elements.

In particular, said actuator can be used as an active suspension, in particular for a vehicle.

Brief description of the drawings

The invention will be made clearer with the following description of some exemplary embodiments, exemplifying but not limitative, with reference to the attached drawings wherein:

- figure 1 shows a perspective view of a first exemplary embodiment of the electromagnetic actuator, in particular a linear actuator in which a ferromagnetic unit is provided and an electromagnetic unit is provided that comprises two opposite windings with a number of loops that increases starting from the middle line towards the end of the winding;

- figures 2 and 3 show a diagrammatical view of the linear actuator of Fig. 1 and the magnetic circuit that is provided between the ferromagnetic unit and the electromagnetic unit of said actuator;

- figures 4 and 5 show a diagrammatical view of the electromagnetic actuator of Fig. 1 in which a force-movement curve is shown highlighting the stiffness and position change as they are obtained by changing the current that runs through said windings;

- figure 6 shows a diagrammatical view of an exemplary embodiment of the electromagnetic actuator where the conical profile of the windings is reversed with respect to the exemplary embodiment of Fig. 2;

- figure 7 shows a diagrammatical view of a third exemplary embodiment of the electromagnetic actuator in which the ferromagnetic unit is relatively movable with respect to the electromagnetic unit, such that the magnetic elements are arranged within the first and the second windings, which are mounted integral to an external ferromagnetic casing;

- figure 8 shows a perspective view of a rotational exemplary embodiment of the electromechanical actuator;

- figure 9 shows a top plan view of the rotational electromechanical actuator of Fig. 8, which shows the directions of the agonist and antagonist forces that are produced by the first and the second windings;

- figure 10 shows a cross sectional view of the rotational electromechanical actuator of Fig. 8, which depicts the structure of the external ferromagnetic casings and shows the forces of the magnetic field as well as the direction of the currents that run through the two windings,

- figures 11 and 11A show an exemplary embodiment of the electromagnetic unit in which each winding consists of elementary windings that are electrically independent from each other, that have a variable number of loops and in which constant driving currents circulate;

- Figs. 12 and 12A show an exemplary embodiment of the electromagnetic unit in which each elementary winding is electrically independent but has the same number of loops and is run through by a variable driving current. Detailed description of some exemplary embodiments

In the following description, with reference to Fig. 1 , an electromechanical actuator 100, according to the invention, comprises a ferromagnetic unit or a stator 10 that consists of a first ferromagnetic element 11 and of an opposite second ferromagnetic element 12; first 11 and second

12 ferromagnetic elements are located at a predetermined distance D from each other. In particular, each ferromagnetic element 11/12 comprises ferromagnetic portions 6' and magnetic elements 15 that form together an open magnetic circuit A, as shown in Fig. 2. Electromechanical actuator 100 comprises furthermore, an electromagnetic unit 20 that is relatively movable with respect to ferromagnetic unit 10, which comprises a first 21 and a second 22 winding integral to each other and arranged with respect to ferromagnetic unit 10 in such a way that they close respective open magnetic circuits A of first 11 and of second 12 ferromagnetic elements.

In particular, first 21 and second 22 winding comprise each a plurality of serially arranged elementary windings 23, with a number of loops that increases starting from an initial elementary winding 23i up to a final elementary winding 23f.

Windings 21/22 are oppositely arranged with respect to each other and are respectively run through by opposite currents lag and Ian, as shown in Fig. 2 and 3, in such a way that they are adapted to generate opposite repulsive forces. In particular, windings 21/22 are oppositely arranged in such a way that an agonist force (Fag), which is generated on a winding, for example on winding 21 , which is run through by current lag, opposes to an antagonist force (Fan), which is generated on other winding 22, which is run through by current Ian, until a relative position is attained of electromagnetic unit 10 with respect to ferromagnetic unit 20, in which the above described forces equilibrates (Fig. 2). In particular, current lag or Ian that circulates within the loops of windings 21/22, and interacts with the magnetic field of permanent magnets 15 orthogonal to its direction, generates a force (Lorentz Force) that has the same direction of the axis, as detailed herein.

Electromechanical actuator 100, furthermore comprises a control means for independently controlling the intensity of the opposite currents lag and Ian that circulates within first 21 and second winding 22, in order to adjust the absolute value of the current intensity difference and therefore the relative position, at which the forces equilibrates, as shown in Fig. 3.

More in detail, by changing the current intensities lag and Ian that circulates within windings 21/22, it is possible adjust both the relative position of electromagnetic unit 20 and ferromagnetic unit 10, and the stiffness of electromagnetic unit 20 with respect to an external force that attempts to move it.

For example, considering the exemplary embodiment of Fig. 1 , in which electromagnetic unit 20 is internally movable with respect to ferromagnetic unit 0, by changing the current intensity in windings 21/22, and maintaining the intensity difference of currents lag and Ian at a prefixed value, the program means 200, as diagrammatically shown, is adapted to adjust the stiffness of actuator 100 and at the same time to maintain the relative position of electromagnetic unit 20 and ferromagnetic unit 10. Instead, by changing the intensity difference of currents lag and Ian, it is possible to adjust the relative position of electromagnetic unit 20 and ferromagnetic unit 10 and at the same time to maintain the stiffness.

This way, as shown in Fig. 4, in order to increase the stiffness of actuator 100 and at the same time to maintain electromagnetic unit 20 substantially in equilibrium, the agonist force must have the same modulus as the antagonist force (Fag=Fan) i.e., in other words, the slope of relative force- movement curve must change in the same way to maintain equilibrium points E1 and E1' at respective prefixed positions. Vice-versa, if the currents are unbalanced in such a way that, for instance, lag > Ian, a non zero resultant force AF=Fag-Fan arises that acts on electromagnetic unit 20, which creates an acceleration that tends to move it until another equilibrium configuration E2 is attained, which is different from the starting configuration, and in which, again, F'ag=F'an.

The new equilibrium position E2 can be attained since the number of loops (Ni) of each winding 21/22 is different at different respective elementary windings, which generates an agonist force and an antagonist force that act on electromagnetic unit 20, and that changes during the movement. In fact, even if constant and unbalanced currents lag and Ian are maintained within two windings 21/22, during the translation forces Fag and Fan, which acts on the windings, change oppositely, therefore a new equilibrium position can always be achieved.

On the other hand, as shown in Fig. 5, if the current of the agonist winding is increased with respect to the current of the antagonist winding (Iag>Ian), the agonist force is greater than the antagonist force (Fag>Fan) and electromagnetic unit 20 moves towards the agonist winding (Δζ>0). Since the number of loops that are influenced by the magnetic field of the agonist winding decreases while the number of loops of the antagonist winding increases during the movement, if two currents lag and Ian are unbalanced and maintained at a prefixed value, the agonist force decreases, while the antagonist force increases, which leads therefore to a new equilibrium condition E3. If the current of the agonist winding is lowered with respect to the current of the antagonist winding (Iag<Ian), the opposite of the above occurs, and a new equilibrium condition is always achieved.

In other words, the same actuating mechanism allows adjusting the stiffness independently from the position. Due to the variation of the number of loops Ni that are arranged along the axis of the windings 21/22, the trend of the force-movement characteristic depends upon how the number of loops changes, and its slope is proportional to the current which is imposed to it. A prefixed position of electromagnetic unit 20 can therefore be maintained by increasing or decreasing the currents in two windings 21/22 by the same amount. This way, however, the slope of the characteristic curves of the windings at the equilibrium position increases or decreases, and the stiffness, i.e. the ratio between the resultant force perturbation (AF'pert and AFpert) that . corresponds to a position perturbation (Azpert), and the position perturbation itself, increases or decreases accordingly. Therefore, the stiffness change is not obtained by changing the rest length of the non-linear element, as in the case of the available systems, but by changing the slope of the force- movement characteristic curve of each winding via a change of the respective driving current (Fig. 5).

Similarly, by properly changing driving currents lag and Ian of two windings 21/22, the position of electromagnetic unit 20 can be modified maintaining without changing the stiffness. Due to its principle, and since no mechanical parts are provided for transmitting the thrust, which is supplied via a remote action of the permanent magnets on the loops of windings 21/22, where a current circulates, actuator 100 is highly reversible (the movement direction can be remotely reversed without generating any sensible passive resistance).

In particular, from a structural viewpoint, first 21 and second 22 winding comprise each winding sections 24 that ate serially arranged with respect to each other, such winding sections 24 are separated from each other by means of shielding walls 22c. This way, elementary windings can be arranged adjacent to one another to create an increasing trend of the loops number. The same result can be achieved by conically arranging the loops on one elementary winding.

According to a first particular aspect of the invention, the above defined electromechanical actuator, as shown in Fig. 1 , is a linear actuator 100 that comprises a shaft 30 integral to electromagnetic unit 20 about a longitudinal axis 31. In particular, shaft 30 is relatively movable within ferromagnetic unit 10, with respect to longitudinal axis 31 ; as previously described, ferromagnetic unit 10 comprises several magnetic elements 15 oriented towards the inside of ferromagnetic unit 20, such that first 21 and second 22 winding move within magnetic elements 15. In this case, first 21 and second 22 winding are coaxially arranged with respect to longitudinal axis 31 about shaft 30, such that respective initial elementary windings 23i of first 21 and of second 22 winding face each other, and final elementary windings 23f are located at the opposite ends of electromagnetic unit 20. This way, the thrust is generated by the interaction between permanent magnets or magnetic elements 15 and the loops, in which the current of each winding 21/22 circulates (Lorentz Force). In particular, opposite stator elements 11/12 serve to support magnets 15 and to close the magnetic circuit on the windings integral to electromagnetic unit 20, which consists of opposite windings 21/22, whose loops number decreases from each end to the middle. In detail, magnets 15 are arranged on stators 11/12 with the same direction and with a radial polarization direction, whereas two windings 21/22 are run through by independently controllable and opposite currents (lag and Ian). This way, the Lorentz Forces that acts on each winding 21/22 due to the surrounding magnetic field, are opposite with respect to each other, and tend to expel electromagnetic unit 20, whereby electromagnetic unit 20 receives agonist force (Fag) and antagonist force (Fan).

From a structural viewpoint, the ferromagnetic unit of actuator 100 comprises a substantially ring-shaped ferromagnetic body 10, inside which electromagnetic unit 20 slides.

In detail, body 10 comprises a first 11 a/11b and a second 12a/12b couple of ring-shaped ferromagnetic stator portions that are spaced apart by means of spacer rods 27; each couple 11 a/11b and 12a/12b defines respective first 11 and second 12 ferromagnetic element. In particular, four spacer rods 27 are arranged at 90° with respect to each other.

In particular, ring portions 11 a/11b and 12a/12b of each couple are connected to each other by means of peripheral connection members 17 and by means of a central connection member 18, such that each ferromagnetic element 11/12 forms open magnetic circuit A, as shown in Fig. 2, which comprises in turn magnetic element 15, a first ring portion 11 a/12a, a peripheral connection member 17, a second ring portion 11 b/12b and central connection member 18, such that the magnetic circuit is closed between magnetic element 15 and peripheral connection member central 18 on respective windings 21/22.

In detail, magnetic elements 15 are mounted on ring portions 1 a/12a, and are substantially a plurality of serially arranged permanent magnets that faces inside towards electromagnetic unit 20. The above is an easy and cheap construction which offers the same efficiency as a single permanent magnet.

Still in particular, electromagnetic unit 20, which comprises first 21 and second 22 windings, has a substantially tubular shape and defines a central hole 26, (Fig.1 ) about longitudinal axis 31 , which is slidingly engaged by central connection member 18 of the stator body. In particular, each central connection member 18 has an enlargement ring 18a/18b at magnetic element 15; enlargement ring 18a/18b engages tubular hole 26 of electromagnetic unit 20. Preferably, each central connection member 18 has an inner hole 18f in which shaft 30 slides, wherein first 21 and second 22 windings of electromagnetic unit 20 are keyed to shaft 30 by a connection disc 19, whereby the stroke of electromagnetic unit 20 is defined by the stroke that connection disc 19 performs between two enlargement 18a/18b of central connection members 18. In particular, connection disc 19 comprises two disc elements 19a/19b, each disc element integral to the respective first or second winding 21/22, said disc elements spaced apart from each other by a paramagnetic spacer 19c in order to minimize the mutual interferences and inductions of the magnetic field.

Still as shown in Fig. 1 , a bearing 33 is provided on each second ring portions 11 b/12b, at each enlargement ring 18a/18b, in particular in particular an axial sleeve ball bearing.

In alternative, as shown in Fig. 6, electromechanical actuator 100A is a linear actuator that comprises shaft 30 integral to electromagnetic unit 20, wherein first 21 and second 22 windings are coaxially arranged with respect to longitudinal axis 31 about shaft 30 such that respective final elementary windings 23f of first 21 and of second 22 winding face each other, and initial elementary windings 23i are located at the opposite ends of electromagnetic unit 20. In this case, the direction of the forces is reversed with respect to the case of convergent conical shapes of Fig. 2. This is necessary since the force supplied by each winding 21722' must be opposite to the movement direction and must increase as the imposed displacement increases (each winding must work as a traction spring). To this end, the direction of the magnetic field and therefore the direction of the magnets 15 must be reversed, while the direction of the currents lag and Ian must remain unchanged with respect to the case of non-reversed conical shapes of Fig. 2. In the present case case, however, the field in the part of stator 11 that crosses the windings has direction opposite to the field that is generated by windings 21/22 within electromagnetic unit 20, therefore the resulting field within the part of stator 11 that crosses the windings is weakened. This causes a reduction of the force that can be supplied by the actuator. It is possible to show that this occur for any possible combination of windings current direction and magnets direction.

In a further exemplary embodiment structure, as shown in Fig. 7, the electromechanical actuator is a linear actuator that comprises electromagnetic unit 20 that is externally arranged about ferromagnetic unit 10. In this case, a ferromagnetic external case 10' is provided which forms the open magnetic circuit together with ferromagnetic unit 10.

In particular electromagnetic unit 20 is integral to ferromagnetic casing 10', and ferromagnetic unit 10 is movable with respect to case 10' and to electromagnetic unit 20.

In particular, ferromagnetic casing 10' has a substantially tubular shape within which first 21 and second 22 windings are mounted to define in turn a substantially tubular inner space 20a in which ferromagnetic unit 10 slides. In this case, a movable shaft 30 can be provided integral to ferromagnetic unit 10 about a longitudinal axis 31. Shaft 30 is movable along longitudinal axis 31 within electromagnetic unit 20 that is arranged within ferromagnetic casing 10', such that first 21 and second 22 windings are located outside ferromagnetic unit 10. In particular, first 21 and second 22 windings are arranged aligned on shaft 30 coaxially to longitudinal axis 31 such that the respective initial elementary windings 23i face each other, and final elementary windings 23f is located at the opposite ends of electromagnetic unit 20. In alternative, in an exemplary embodiment, not shown, respective final elementary windings 23f of first 21 and of second 22 windings face each other, and initial elementary windings 23i are located at the opposite ends of electromagnetic unit 20.

More in detail, first 11 and second 12 ferromagnetic elements are coaxially arranged on shaft 30 and comprise respectively:

- a first 18a and a second 18b enlargement rings opposite to each another and facing each another,

- a respective magnetic element 15,

- a first 11d and a second 11e substantially cylindrical side walls, which slidingly engage with tubular casing 10'. In detail, a respective side wall 11d/11e is arranged at the opposite end with respect to enlargement rings 18a/18b and each magnetic element 15 is located between respective enlargement ring 18a/18b and side wall 11d/11e.

This way, the open magnetic circuit is respectively formed by enlargement ring 18a/18b, by magnetic element 15, by side wall 11d/11e, and by a portion of tubular casing 10', and is closed at enlargement ring 18a/18b on one of the elementary windings, as highlighted by the arrows in Fig. 7.

In particular, a plurality of magnetic elements 15 are provided serially arranged to each other on shaft 30.

In Figs. 8, 9 and 10 a rotational actuator 100C is shown which comprises a electromagnetic unit, i.e. armature 20, which is pivotally arranged within ferromagnetic unit i.e. stator 10, about a rotating shaft 30' and its rotation axis 31'. In particular, ferromagnetic stator 10 comprises magnetic element 15 that is oriented towards the inside, such that first 21 and second 22 windings move within magnetic element 15 at such a short distance that the magnetic circuit is closed. Even in this case, first 21 and second 22 windings are arranged diametrically opposed to rotation axis 31' on electromagnetic armature 20, such that respective initial elementary windings 23i of first 21 and second 22 winding are circumferentially consecutive with respect to each other, and final elementary windings 23f of the first and second winding are arranged circumferentially consecutive with respect to each other. In particular, ferromagnetic stator 10 comprises first 11 ' and second 12' diametrically opposed ferromagnetic elements.

As better shown in Fig. 10, first 11' and second 12' ferromagnetic elements have the shape of two opposite "C" elements between which armature 20 rotates. In particular, the "C" elements consist of two branches 17a and a central portion 17b connected to one another, and magnetic element 15 is arranged between the "C" elements. In this case, magnetic element 15 comprises prismatic portions that are respectively connected with the inner face of upper and lower branch 17a, and with central portion 17b.

In addition, as shown in Fig. 9, branches 17a of each "C" are connected to each other through a respective ferromagnetic connection element of 16, which in turn comprises higher and lower branches 16b and a central connection portion 16a that connects branches 16b.

Still in addition, two ferromagnetic portions of arch 17c are provided that extend from respective ferromagnetic connection elements 16, in particular from the midline of central portion 16a, and cross windings 21/22. This way, two respective magnetic circuits are formed that respectively consist of branches 17a/17b of the first and of the second C ferromagnetic element 11712', and of the ferromagnetic connection element 16 and of portions of arch 17c. More in detail, first 11' and second 12' ferromagnetic elements together form a stator case 10 consisting of the two coplanar and opposite "C" elements 11712', of connection member 16 orthogonal to two "C" elements 11712' and by portions of arch 17c, which extend from connection member 16 to opposite sides of a central position between branches 17a/17b of the respective opposite "C" elements.

Figures 11 to 12A show different configurations of windings 21/22 of electromagnetic unit 20.

In particular, Figs. 11 and 11A show a solution structure of the windings in which electrically independent elementary windings 23 are obtained from winding sections 24 (shown in Fig. 1); elementary windings 23 are selectively run through by currents different. This way, if the control system 200, as diagrammatically shown in Fig. 1 , is aware of the position of the electromagnetic unit 20, for example by means of a position sensor, it can actuate only windings 23 that are concerned by the magnetic flow of the permanent magnet 15 of the ferromagnetic unit 10. The usefulness of this solution consists in that it lowers energy consumption and heat dissipation, since the copper wire that is run through by the current of the two elementary windings that are concerned is less than in the case in which all the elementary windings are serially connected to one another, the serial connection excluding all the windings that are not concerned by the control.

In a further alternative, as shown in Figs. 12 and 12A, elementary windings 23 are electrically independent from each other and have a prefixed number of loops. In this case, electromagnetic unit 20 has a cylindrical shape and does not have a conical shape. Furthermore, control system 200 is adapted to adjust the driving currents independently from each other, said driving currents flowing in each respective elementary agonist winding 23 and elementary antagonist winding 23', such that the predetermined force- movement curve is obtained, while that elementary winding moves through the magnetic flux. More precisely, for each agonist elementary winding 23 where a current Tag circulates, there will be an antagonist elementary winding 23' where a current I'an circulates, but in agonist elementary windings 23 and antagonist elementary windings 23', the driving currents will become I"ag and Fan, and so on.

This allows using windings which have the same number of loops and which do not have therefore a conical profile, but a stepped profile whose external diameters change from a step to another, which reduces therefore the overall dimensions, brings magnetic elements 15 close to spacer elements 8 and increases this way the magnetic field in the zone where the loops are present, thus increasing the forces that are supplied by the actuator.

The actuator, according to the invention, in its different exemplary embodiments is different from prior art solutions since its operation principle allows intrinsically adjusting the stiffness and the position independently form each other, via a suitable regulation of the currents that circulate in the two antagonist windings. The so-called VIAM actuator can be directly connected to the system to be actuated, or at most to an intermediate reduction member to adapt its force and stroke characteristics according to the load but, unlike the well-known solutions, it does not require a second actuator to adjust the features of the resilient element located in the transmission or for completing the agonist/antagonist configuration. In fact, the stiffness regulation is intrinsically provided by the actuator itself, as a result of the shape and of the arrangement of the windings which comprise the loops where a current circulates, and which interact with the permanent magnets. This way, actuator groups can be provided that are more compact, less bulky, less heavy and more reliable, as a result of the reduction of the number of involved components. This feature is the origin of all the advantages (reduced masses, reduced inertia and better dynamic performances) which improve the performances and the safety of the mechatronic systems of interest. The absence of intermediate mechanical parts for transmitting the thrust ensures high actuator reversibility, and makes the actuator well suited as a basic component in the development of a new generation of rehabilitation devices, for which this requirement is essential. The electromagnetic generation of the thrust ensures wider pass-bands than in the case of presently known actuation systems, which further increases the dynamic performances of the actuated system.

The actuator is also suitable for automotive applications, as an active suspension that can be electronically controlled, such that, for example, in a car a selection among several configurations can be made to cope with a particular ground and/or to fit a user's driving habits or style.

The foregoing description of specific embodiments will so fully reveal the invention according to the conceptual point of view, such that others, by applying current knowledge, will be able to modify and/or adapt for various applications such embodiments without further research and without parting from the invention, and it is therefore to be understood that such adaptations and modifications will have to be considered as equivalent to the specific embodiments. The means and the materials to realise the different functions described herein could have a different nature without, for this reason, departing from the field of the invention. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

Claims

1. An electromechanical actuator comprising:

- a ferromagnetic unit consisting of a first and of a second ferromagnetic element, said ferromagnetic elements arranged opposite to each other, each ferromagnetic element comprising ferromagnetic portions and at least one magnetic element, said ferromagnetic portions and said magnetic element forming together a respective open magnetic circuit;

- an agonist force (Fag), which is generated on said or on each elementary winding of the first winding, said elementary winding of the first winding run through by a current lag, opposes to an antagonist force (Fan), which is generated on said or each elementary winding of the second winding, said elementary winding of the second winding run through by a current Ian, until a relative position of said electromagnetic unit with respect to said ferromagnetic unit is attained at which said forces balance each other,

- a control means for independently controlling the intensity of said opposite currents lag and Ian that run through the respective elementary windings of said first and of said second windings, in order to adjust the absolute value of the intensity difference of said currents and therefore to adjust said relative position, in which said forces balance each other.

2. An actuator, according to claim 1 , wherein each of said first and said second windings comprises a plurality of elementary windings that are sequentially arranged with respect to each other and have a number of loops that increases starting from the initial elementary winding up to the final elementary winding.

3. An actuator, according to claim 1 , wherein a program means is provided which is associated with said control means, for controlling said opposite currents lag and Ian, said program means allowing an adjustment of a force- movement characteristic curve, in particular said program means allows adjusting the stiffness independently from the position.

4. An actuator, according to claim 1 , wherein each of said first and said second windings comprises serially arranged winding sections, which constitute said elementary windings, said winding sections separated from each other by means of shielding walls.

5. An actuator, according to claim 1 , wherein said elementary windings are electrically independent from each other and are selectively run through by said driving currents.

6. An actuator, according to claim 1 , wherein all of said electrically independent elementary windings have a prefixed number of loops, and the electromagnetic unit has a cylindrical shape and said program means is adapted to adjust the driving currents which flow in each respective agonist and antagonist elementary windings independently from each other, such that a predetermined force-movement curve is obtained while that elementary winding moves through the magnetic flux.

7. An actuator, according to claim 1 , wherein said electromechanical actuator is a linear actuator that comprises a transmission shaft integrally arranged with said electromagnetic unit, said transmission shaft having a longitudinal axis, said transmission shaft relatively movable along said longitudinal axis within said ferromagnetic unit, said ferromagnetic unit comprising said magnetic element oriented towards the inside of said ferromagnetic unit such that said first and said second windings move within said magnetic element at such a short distance that the magnetic circuit is closed,

8. An actuator, according to claim 7, wherein said ferromagnetic unit of said linear electromechanical actuator comprises a stator body made of a ferromagnetic material, said stator body having a substantially ring shape, said electromagnetic unit sliding within said stator body, said body comprising:

9. An actuator, according to claim 8, wherein at least said magnetic element is mounted on said ring portions, said magnetic element preferably comprising a plurality of permanent magnets that faces the inside of said electromagnetic unit.

10. An actuator, according to claim 1 , wherein said magnetic element comprises windings that are run through by currents and therefore comprises electromagnets that are adapted to provide a constant magnetic field.

11. An actuator, according to claim 7, wherein said electromagnetic unit that comprises said first and said second windings has a substantially tubular shape and defines a central hole, said central hole having an axis that is coaxial with respect to the longitudinal axis, the central connection member of said stator body slidingly engaging with said central hole, in particular each central connection member has an enlargement ring at said magnetic element, said enlargement ring engaging with the tubular hole of said electromagnetic unit, preferably, each central connection member is a tubular element that has an inner hole in which said shaft slides.

12. An actuator, according to claim 7, wherein said first and said second windings of said electromagnetic unit are keyed to the shaft by means of a connection disc, whereby the stroke of said electromagnetic unit is defined by the stroke that said connection disc can perform between said two central connection members, in particular said connection disc comprises two disc elements, each disc element integral to the respective first or second winding, said disc elements spaced apart from each other by a spacer made of paramagnetic material.

13. An actuator, according to claim 1 , wherein said electromechanical actuator is a linear actuator that comprises a shaft integrally arranged with said electromagnetic unit and has a longitudinal axis, said shaft being relatively movable with respect to the longitudinal axis within said ferromagnetic unit, said ferromagnetic unit comprising said magnetic element which is oriented towards the inside of said ferromagnetic unit such that said first and said second windings move within said magnetic element at such a short distance that the circuit is closed,

wherein said first and said second windings are arranged on said shaft coaxially to the longitudinal axis such that the respective final elementary windings of said first and of said second windings face each other, and the initial elementary windings of said first and of said second windings are located at opposite ends of said electromagnetic unit.

14. An actuator, according to claim 1 , wherein said electromechanical actuator is a linear actuator that comprises said electromagnetic unit that is arranged externally to said ferromagnetic unit, and a ferromagnetic external casing is provided which forms the open magnetic circuit together with the ferromagnetic unit, in particular said electromagnetic unit is integral to said ferromagnetic casing, and said ferromagnetic unit is movable with respect to 5 said casing and with respect to said electromagnetic unit.

15. An actuator, according to claim 14, wherein a movable shaft is provided integral to said ferromagnetic unit, said shaft having a longitudinal axis, said shaft movable along said longitudinal axis within said electromagnetic unit, said electromagnetic unit arranged within said ferromagnetic casing such that

10 said first and said second windings are located outside said ferromagnetic unit.

16. An actuator, according to claim 14, wherein said magnetic element is arranged on said shaft in such a way that said first and said second windings face the inside of said ferromagnetic unit.

15 17. An actuator, according to claim 14, wherein said ferromagnetic casing has a substantially tubular shape within which said first and said second windings are mounted to define a substantially tubular inner space in which said ferromagnetic unit slides,

wherein said first and said second ferromagnetic elements, which are 20 coaxially arranged on said shaft, comprise respectively:

- a respective magnetic element;

- a first and a second substantially cylindrical side walls, which slidingly 25 engage with said tubular support structure,

such that said open magnetic circuit is in turn formed by said enlargement 30 ring, said magnetic element, said side wall, a portion of said tubular casing, and is closed at said enlargement ring on one of said elementary windings.

18. An actuator, according to claim 14, wherein the respective initial elementary windings of said first and of said second windings face each other, and the final elementary windings of said first and of said second windings are located at opposite ends of said electromagnetic unit.

19. An actuator, according to claim 14, wherein the respective final elementary windings of said first and of said second windings face each other, and the initial elementary windings of said first and of said second windings are located at opposite ends of said electromagnetic unit.

20. An actuator, according to claim , wherein said electromechanical actuator is a rotational actuator comprising:

wherein said first and said second windings are arranged on said electromagnetic armature at respective positions that are diametrically opposed with respect to the rotation axis, such that the respective initial elementary windings of said first and of said second windings are circumferentially consecutive with respect to each other, and the final elementary windings of said first and of said second windings are circumferentially consecutive with respect to each other, in particular said ferromagnetic stator comprises said first and said second ferromagnetic elements which are diametrically opposed.

21. An actuator, according to claim 20, wherein said first and said second ferromagnetic elements are shaped as two opposite "C" elements between which said armature rotates, in particular, said "C" consist of two branches and a central portion that are connected to each other, and said magnetic element is arranged between said "C" elements, the branches of each "C" element furthermore connected to each other, by a respective ferromagnetic connection element, and two ferromagnetic material arch portions are provided that extend from respective ferromagnetic connection elements and cross said windings, this way, two respective magnetic circuits are formed which respectively consist of said branches, of said ferromagnetic connection element and of said arch portion.

22. An actuator, according to claim 21 , wherein said first and said second ferromagnetic elements together form a case consisting of said two coplanar and opposite "C" elements, said connection member orthogonal to said two "C" elements, and of said arch portions, which extend from said connection element to opposite sides of a central position between the branches of the respective opposite "C" elements.

23. The use of an actuator according to the previous claims, as an active suspension, in particular as a vehicle active suspension.