EP3781836A1

EP3781836A1 - Magnetic spring

Info

Publication number: EP3781836A1
Application number: EP19718896.4A
Authority: EP
Inventors: Branimir MRAK; Bert Lenaerts; Niels JEURGEN; Walter Driesen
Original assignee: Flanders Make Vzw
Current assignee: Flanders Make Vzw
Priority date: 2018-04-18
Filing date: 2019-04-16
Publication date: 2021-02-24
Also published as: NL2020783B1; WO2019201907A1

Abstract

Disclosed is a magnetic spring assembly (1, 101, 501, 601, 701, 801, 901) comprising a holder (4, 104, 604, 704, 804, 904), a first magnet arrangement (6, 106, 606, 706, 806, 906) configured to be moveable relative to the holder in a first direction, a second magnet arrangement (5, 105, 605, 705, 805, 905) configured to cooperate with the first magnet arrangement to generate a position-dependent force in the first direction, and a clamping mechanism (3, 103, 703, 803, 903) for clamping the second magnet arrangement to the holder. The clamping mechanism has a clamped state wherein a position of the second magnet arrangement is substantially fixed relative to the holder, and a released state, wherein the second magnet arrangement is moveable relative to the holder in the first direction.

Description

Magnetic spring

The invention relates to the technical field of magnetic springs.

Springs, both of the linear and the rotary type, are used in a wide variety of applications to store energy or to assist in accelerating or decelerating motion. Traditional mechanical springs, such as coil springs, have the disadvantage that they are susceptible to wear and fatigue, which makes their lifetime limited. Another disadvantage is that the spring force and the stored energy increase linearly when compressing or stretching the spring.

To solve the above issues, magnetic springs have been proposed. These magnetic springs usually comprise at least two magnet arrangements of magnets facing each other, resulting in magnetic forces which act as the spring force. The first magnet arrangement is arranged to be moveable relative to the second magnet arrangement. Since no contact between the magnet arrangements is required, the lifetime issues are reduced. The resulting magnetic force and thus the spring force are dependent on the location of the first magnet arrangement relative to the second magnet arrangement. In the case of a rotary spring this means that the spring force is dependent on the angular position of the first magnet arrangement, and for a linear spring the spring force is dependent of the axial position of the first magnet arrangement. Usually the amplitude of the spring force is in the form of periodic waveform, e.g. a sine wave, when seen over the motion of the first magnet arrangement. In some apparatuses it may be desired to provide the spring force only during certain applications.

The magnetic spring can be designed to provide the desired spring force dependent on the position of the first magnet arrangement in function of the application wherein the spring is to be used. However, when the required spring force changes over time the design of the magnetic spring might not suffice anymore. The conventional magnetic springs do not allow to adapt the relation between the spring force and the position of the first magnet arrangement.

It is an object of the invention to mitigate these disadvantages or at least provide an alternative magnetic spring.

This object is achieved by magnetic spring assembly comprising:

• a holder,

• a first magnet arrangement configured to be moveable relative to the holder in a first direction, • a second magnet arrangement configured to cooperate with the first magnet arrangement to generate a position-dependent force in the first direction, and

• a clamping mechanism for clamping the second magnet arrangement to the holder,

wherein the clamping mechanism has

• a clamped state wherein a position of the second magnet arrangement is substantially fixed relative to the holder, and

• a released state, wherein the second magnet arrangement is moveable relative to the holder in the first direction.

The magnetic spring assembly according to the invention comprises a first magnet arrangement and a second magnet arrangement. In the context of this invention a magnet arrangement is to be understood as one or more consecutively arranged magnets, e.g. as a linear or (partly) circular row, e.g. adjoining to each other or with an air gap or other material, e.g. ferromagnetic material, in between. The magnets may e.g. be permanent magnets or electromagnets. In an embodiment the magnets may be arranged as a Halbach-array. In an embodiment one of the first and second magnet arrangement is formed by ferromagnetic material and the other comprises permanent magnets. For example, the first or second magnet arrangement may comprise a ferromagnetic member having a variable reluctance, e.g. having a number of protrusions arranged in a row along the first direction. In a further embodiment the number of protrusions is equal to number of poles or pole pairs of the other magnet arrangement.

The magnetic spring assembly according to the invention further comprises a holder. In general the holder may be defined as reference for movements of other components during use of the magnetic spring assembly, e.g. because the holder is stationary during use. The holder may e.g. facilitate the installing of the magnetic spring assembly in the application wherein the magnetic spring assembly is to be used, e.g. an internal combustion engine, pick-and-place robot, etc., but will in most embodiments not be part of e.g. said internal combustion engine. The second magnet arrangement can be clamped to the holder, as will be explained in more detail below. In an embodiment the holder is a housing, e.g. encompassing the second magnet arrangement, e.g. encompassing both the first and the second magnet arrangement, e.g. encompassing all other components of the magnetic spring assembly. In another embodiment the holder may be a shaft or bar, e.g. radially encompassed by the second magnet arrangement, e.g. radially encompassed by both the second and the first magnet arrangement.

The first magnet arrangement is configured to be moveable relative to the holder in a first direction. The first direction may be a translational or a rotational direction. The first magnet arrangement can e.g. be configured to be connected to or be arranged on a shaft, such that rotation of the shaft causes the first magnet arrangement to rotate relative to the holder. The second magnet arrangement can e.g. be configured to cooperate with the first magnet arrangement to generate a position-dependent force in the first direction. The distance between the first and second magnet arrangement is small enough such that at least one or more of the magnets of the first magnet arrangement are located within the magnetic field of at least one or more of the magnets of the second magnet arrangement, and/or vice versa, to create the position-dependent force, which is a magnetic force. The amplitude and/or sense of the position-dependent force depend on the position of the first magnet arrangement relative to the second magnet arrangement in the first direction. In case the first direction is a rotational direction, the position-dependent force generates a torque, e.g. exerted on the first magnet assembly, the torque depending on an angular position of the first magnet arrangement relative to the second magnet arrangement.

The magnetic spring assembly further comprises a clamping mechanism. The clamping mechanism is arranged to clamp the second magnet arrangement to the holder. The clamping mechanism has a clamped state and a released state. In the clamped state a position of the second magnet arrangement is substantially fixed relative to the holder. In this clamped state, when the first magnet arrangement moves in the first direction relative to the holder it therefore also moves relative to the second magnet arrangement. When the first magnet arrangement moves relative to the second magnet arrangement, the position of the magnets of the first magnet arrangement changes relative to the magnets of the second magnet arrangement, and as such the position-dependent force to which the first magnet arrangement is subjected. At some positions of the first magnet arrangement relative to the second magnet arrangement the position-dependent force will counteract the movement of the first magnet arrangement, and as such the movement of e.g. the shaft to which the first magnet arrangement is connected. At other positions the magnetic force will enhance the movement of first magnet arrangement. The position-dependent force functions as a spring force to which the first magnet arrangement is subjected.

In general, if the magnetic fields of the magnets are of equal amplitude and consecutive magnets are arranged to have inversely arranged poles, the position-dependent force may be spatially alternating, e.g. according to a periodic waveform, e.g. in the form of a sine wave or a square wave when seen over movement in the first direction of the first magnet arrangement. However, other arrangements are possible. Furthermore, the shape of the position-dependent force depends on other parameters as well, such as material characteristics and geometry of the applied magnets

In the released state of the clamping mechanism the second magnet arrangement is moveable relative to the holder in the first direction. The clamping mechanism is not clamping the second magnet arrangement. The second magnet arrangement is moveable together with the first magnet arrangement in the first direction. The position-dependent force between the first magnet arrangement and the second magnet arrangement may cause the second magnet arrangement to move when the first magnet arrangement is moving, in the same direction.

This can be understood as follows. The position-dependent force generally has stable and unstable equilibrium points depending on stable and unstable equilibrium points of the position of the first magnet arrangement relative to the second magnet arrangement. When the clamping mechanism is in the released state the position-dependent force causes the second magnet arrangement to move relative to the first magnet arrangement until an equilibrium point has been reached, insofar as not obstructed by friction. If said equilibrium point is unstable, movement of the first magnet arrangement in the first direction will cause the position of the second magnet arrangement relative to the first magnet arrangement to move to a stable equilibrium point. In such stable equilibrium point the position-dependent force will cause the second magnet arrangement to remain in approximately the same position in the first direction relative to the first magnet arrangement. Movement of the first magnet arrangement in the first direction therefore causes the second magnet arrangement to move simultaneously. The position-dependent force may deviate from the equilibrium point by an amplitude required to overcome friction forces, thereby causing the second magnet arrangement to slightly lag behind the first magnet arrangement in the movement in the first direction. In an embodiment the magnetic spring assembly may comprise a bearing, e.g. a ball bearing, to facilitate movement of the second magnet arrangement relative to the holder, e.g. arranged between the second magnet arrangement and the holder.

Since only the friction forces need to be overcome the position-dependent force will remain relatively small in amplitude and as such not have a substantial influence on the first magnet arrangement, and e.g. the shaft on which said first magnet arrangement is arranged. The magnetic spring assembly is essentially decoupled.

When the first and second magnet arrangements are moving together, the changes in the position-dependent force are preferably small, more preferably neglectable, more preferably non-existent. As the position in the first direction of the first magnet arrangement relative to the second magnet arrangement changes little, changes in the position-dependent force may e.g. be caused by changes in friction, e.g. because of changes in the speed of the movement of the first magnet arrangement in the first direction.

In other words, when the clamping mechanism is in the released state, the position- dependent force exerted the first magnet arrangement is preferably configured to be, during movement of the first magnet arrangement in the first direction, substantially zero. Substantially zero is to be understood as to include the forces needed to overcome friction forces during use of the magnetic spring assembly. Preferably the position-dependent force exerted the first magnet arrangement is also configured to be, during movement of the first magnet arrangement in the first direction, substantially constant.

The invention thus provides in a magnetic spring assembly which can be decoupled, i.e. turned on and turned off, by clamping or releasing the second magnet arrangement with the clamping mechanism. This allows to only provide a significant spring force when it is required, thereby increasing the flexibility of the system.

The magnetic spring assembly may e.g. be turned on or off when the first magnet arrangement has been brought to rest, e.g. in between successive operations of the magnetic spring assembly. It is also possible to turn the magnetic spring assembly on or off while the first magnet arrangement is moving. For example, the magnetic spring assembly can be used to assist in reversing motion. The magnetic spring assembly can be arranged to first be turned off while the first magnet arrangement is moving, the clamping mechanism being in the released state and second magnet arrangement moving together with the first magnet arrangement. When the motion is to be reversed the clamping mechanism is brought into the clamped state to clamp the second magnet arrangement while the first magnet arrangement keeps moving. The first magnet arrangement is subjected to the position- dependent force, which will first assist in decelerating the movement of the moveable axis, and then assist in accelerating the moveable axis in the reversed motion. Thereafter the clamping mechanism can be brought back into the released state such that the second magnet arrangement moves together with the first magnet arrangement in the first direction.

In an embodiment the clamping mechanism is configured to clamp the second magnet arrangement to the holder at different positions along the first direction relative to the holder. In this embodiment, the position of the second magnet arrangement relative to the first magnet arrangement can be modified for a given position of the first magnet arrangement in the first direction. This can e.g. be accomplished by arranging the clamping mechanism in the released position and moving the second magnet arrangement together with the first magnet arrangement, and then clamping the second magnet arrangement again with the clamping mechanism when it is in a different position in the first direction relative to the holder. The position of the magnets of the second magnet arrangement relative to the magnets of the first magnet arrangement is changed for a given position of the first magnet arrangement in the first direction, and as such the position-dependent force acting as the spring force. When the first magnet arrangement is arranged on or connecter to a shaft or bar, the position-dependent force to which the shaft or bar is subjected has been changed for the position in the first direction of shaft or bar, e.g. the angular or linear position, respectively. This embodiment is e.g. advantageous when a load changes which is connected to the shaft to which the first magnet arrangement is connected, or when the trajectory of a load changes. An example of this are so-called pick and place robots, which may have to perform a certain motion repetitively for a period of time, followed by another motion repetitively for a period of time.

Often the amplitude of the position-dependent force in function of the position of the first magnet arrangement is a periodic waveform, which can e.g. be described as a sine or a combination of multiple sines. By clamping the second arrangement to the holder at different positions along the first direction a phase of the position-dependent force can be changed or shifted. In the context of this invention the phase of the position-dependent force is considered to be the point on the periodic waveform in function of the position of the first magnet arrangement in the first direction. Shifting of the phase results in the position- dependent force being on a different point of the periodic waveform for a given position of the first magnet arrangement in the first direction. In other words, when the position-dependent force is plotted in function of the position of the first magnet arrangement in the first direction shifting of the phase results in the periodic waveform being shifted.

In an embodiment the second magnet arrangement has a first clamped position and a second clamped position, wherein a position of the second magnet arrangement relative to the holder in the first direction is different in the first clamped position than in the second clamped position. In the first clamped position the position-dependent force exerted on the first magnet arrangement for a given position differs from the second clamped position. Based on the application in which the magnetic spring assembly is used and the load thereof the most advantageous of the first and second clamped position can be chosen. The magnetic spring assembly is more flexible and can be used for different applications and/or loads.

In an embodiment the magnetic spring assembly further comprises a motion conversion mechanism configured to move the second magnet arrangement relative to the holder in a second direction during a movement of the second magnet arrangement in the first direction, wherein the second direction is different from the first direction. The motion conversion mechanism may e.g. be a screw-thread. By moving the second magnet arrangement relative to the holder in the first direction, the motion conversion mechanism causes the relative position between the first and second magnet arrangement in the second direction to vary. The magnetic force between the magnets of the first and second magnet arrangement, and thus the position-dependent force, also varies. In this embodiment the amplitude of the position-dependent force can thus be adjusted. For example, the further the first and second magnet arrangements are spaced from each other, the smaller the amplitude of the position-dependent force is.

Advantageously the motion conversion mechanism is arranged such that a movement of the second magnet arrangement in the first direction guides the second magnet arrangement to move in the second direction. The amplitude of the position-dependent force e.g. can be adjusted by bringing the clamping mechanism in the released state and moving the shaft to which the first magnet arrangement is connected in the first direction. The position-dependent force causes the second magnet arrangement to move together with the first magnet arrangement in the first direction, and the motion conversion mechanism meanwhile causes the second magnet arrangement to also move in the second direction such that the amplitude of the position-dependent force can be adjusted. For example, the first direction may be rotational and the second direction may be translational or the first direction may be translational and the second direction may be rotational. For example, the first direction may be rotational around an axis and the second direction may be translational parallel to said axis. For example, the first direction may be translational and the second direction may be rotational.

In a further embodiment the second magnet arrangement has a third clamped position and a fourth clamped position, wherein a position of the second magnet arrangement relative to the holder in the second direction is different in the third clamped position than in the fourth clamped position. In the third clamped position the clamping mechanism is in the clamping state. The clamping mechanism can be brought to the released state and the second magnet arrangement is moved in the second direction, e.g. by moving the first magnet arrangement in the first direction and using the motion conversion mechanism. The clamping mechanism can then be brought back into the clamping state to clamp the second magnet arrangement in the fourth clamped position. In an embodiment the third clamped position corresponds with the first clamped position.

In an embodiment wherein the magnetic spring assembly comprises the motion conversion mechanism the clamping mechanism may comprise a further released state. In said further released state the second magnet arrangement is arranged to move relative to the holder in the first direction while substantially maintaining its position relative to the holder in the second direction. Thus in the further released state the motion conversion mechanism is not configured to move the second magnet arrangement relative to the holder in the second direction during a movement of the second magnet arrangement in the first direction. In this embodiment, the clamping mechanism thus comprises at least three states in total: in the clamped state the first magnet arrangement can move relative to the second magnet arrangement in the first direction to be subjected to the position-dependent force; in the released state the second magnet arrangement can be moved in the first direction and is meanwhile guided by the motion conversion mechanism in the second direction to change the amplitude of the position-dependent force, and optionally to shift the phase; in the further released state the second magnet arrangement can be moved in the first direction without changing the amplitude of the position-dependent force, e.g. to shift the phase.

For example, in the further released state the motion conversion mechanism can be configured such that movement of the second magnet arrangement in the first direction causes the motion conversion mechanism to move in the first direction as well. For example if the motion conversion mechanism comprises a screw thread, a friction force between the second magnet arrangement and the motion conversion mechanism may be larger than a friction force between the motion conversion mechanism and the holder. In an embodiment the magnetic spring assembly may comprise a bearing, e.g. a ball bearing, to facilitate movement of the motion conversion mechanism relative to the holder, e.g. arranged between the motion conversion mechanism and the holder.

In an embodiment the magnetic spring assembly further comprises a third magnet arrangement configured to cooperate with the first magnet arrangement to generate a second position-dependent force in the first direction. The first magnet arrangement is subjected to a resulting position-dependent force which includes the first and second position-dependent force. By adapting the position, e.g. using the clamping mechanism, of the second magnet arrangement relative to the third magnet arrangement the resulting position-dependent force can be adapted.

For example, third magnet arrangement may comprise magnets which are similar in strength and which are arranged similarly to the magnets on the second magnet arrangement, such that the first and second position dependent-force are equal in amplitude. When the positions in the first direction of the second magnet arrangement and the third magnet arrangement relative to the holder are the same, the first and second position- dependent force are also equal in phase when seen in function of the position of the first magnet arrangement. The resulting position-dependent force then amounts to twice the first or second position-dependent force separately. When the positions in the first direction of the second magnet arrangement and third magnet arrangement relative to the holder are arranged such that their poles are opposite along the first direction, the first and second position dependent force are opposite in phase. Since they are equal in amplitude they will cancel each other, and the resulting position-dependent force is zero. Thus by arranging the position of the second magnet arrangement relative to the third magnet arrangement the resulting position-dependent force can be controlled and as such the amplitude of position- dependent force of the magnetic spring assembly.

In an embodiment a position of the third magnet arrangement is fixed relative to the holder. The position in the first direction of the second magnet arrangement relative to the third magnet arrangement can then be arranged by changing the positon of the second magnet arrangement relative to the holder using the clamping mechanism.

In an embodiment the magnetic spring assembly comprises a second clamping mechanism for clamping the third magnet arrangement to the holder or to a second holder. The second clamping mechanism has a clamped state wherein a position of the third magnet arrangement is substantially fixed relative to the holder, and a released state, wherein the third magnet arrangement is moveable relative to the holder in the first direction. In this embodiment the positions of both the second and the third magnet arrangement can be arranged relative to the holder. The position of the second holder, when present, is substantially fixed relative to the holder. The second clamping mechanism can be embodied and function similarly to the clamping mechanism as described earlier herein; however it is noted that the clamping mechanism and the second clamping mechanism in a single magnetic spring assembly can be embodied different from each other.

In a further embodiment the third magnet arrangement is configured to be moved in the second direction, e.g. with a second motion conversion mechanism which may be embodied and function in any of the ways described with respect to the motion conversion mechanism. This embodiment allows adapting the amplitude of the second position- dependent force. For example, the second and third magnet arrangement can both be moved in the second direction. It may then be advantageous to move them in opposite sense in the second direction to adjust the resulting position-dependent force, to balance the weight and reduce bearing forces.

It is noted that the third magnet arrangement is not the same magnet arrangement as the first or second magnet arrangement.

In an embodiment the magnetic spring assembly further comprises a fourth magnet arrangement and a fifth magnet arrangement. The fourth magnet arrangement is configured to be moveable relative to the holder in the first direction, optionally together with the first magnet arrangement. The fifth magnet arrangement is configured to cooperate with the fourth magnet arrangement to generate a third position-dependent force in the first direction.

It is noted that the fourth and fight magnet arrangement are both not the same magnet arrangement as one of the first, second or third magnet arrangement.

The fourth magnet arrangement can be moved in the same ways as the first magnet arrangement. Preferably, the first and fourth magnet arrangement are moved together, e.g. by being arranged on or connected to the same shaft. The fourth magnet arrangement may be embodied in any of the ways as described with respect to the first magnet arrangement. Optionally the magnets of the first and fourth magnet arrangement are similar and arranged similarly. The fifth magnet arrangement may be embodied in any of the ways as described with respect to the second magnet arrangement. Optionally the magnets of the second and fifth magnet arrangement are similar and arranged similarly.

The fourth and fifth magnet arrangement cooperate in a way similar to how the first and second magnet arrangement cooperate, resulting in the third position-dependent force. When the first and fourth magnet arrangement are arranged to be moved together in the first direction, they are subjected to a resulting position-dependent force in the first direction, which includes the first and the third position-dependent force. The resulting position- dependent force can be adapted by adapting the position in the first direction of second magnet arrangement relative to the first magnet arrangement, or of the fourth magnet arrangement relative to the fifth magnet arrangement. As such the amplitude of the resulting position-dependent force can be adapted similarly to the embodiment with the third magnet arrangement. The present embodiment however has an additional advantage that in an embodiment the fourth and fifth magnet arrangement may be different from the first and second magnet arrangement, respectively, e.g. by comprises a different number of poles, magnets of different strength, or differently arranged magnets. The third position-dependent force in function of the position in the first direction of the fourth magnet arrangement is then different from the first position-dependent force in function of the position in the first direction of the first magnet arrangement. As such there are more possibilities for combinations of the first and third position-dependent force contributing to a different resulting position-dependent force.

In an embodiment a position of the fifth magnet arrangement is fixed relative to the holder.

In an embodiment the magnetic spring assembly further comprises a third clamping mechanism for clamping the fifth magnet arrangement to the holder or to a third holder. The third clamping mechanism has a clamped state wherein a position of the fifth magnet arrangement is substantially fixed relative to the holder, and a released state, wherein the fifth magnet arrangement is moveable relative to the holder in the first direction. The third clamping mechanism may be embodied similar as the first clamping mechanism, however in a single magnetic spring assembly the first and third, and second when present, clamping mechanism may be embodied different from each other.

It is noted that in an embodiment the magnetic spring assembly may comprise the fourth and fifth magnet arrangement but not the third magnet arrangement, and in an embodiment the magnetic spring assembly may comprise the third clamping mechanism but not the second clamping mechanism.

In an embodiment the magnetic spring assembly may comprise more than 5 magnet arrangements. For example, the magnetic spring assembly may comprise multiple sets of magnet arrangements cooperating with each other to compensate for multiple harmonic components, e.g. of a motor, e.g. an internal combustion engine.

In an embodiment wherein the third magnet arrangement and/or the combination of the fourth and fifth magnet arrangement is present, the first direction is a translational direction. The magnetic spring assembly is a linear spring. For example, the first magnet arrangement may be arranged on a bar. Several advantageous embodiments using a third magnet arrangement and/or the combination of the fourth and fifth magnet arrangement. For example, the second magnet arrangement may comprises permanent magnets with a different magnitude of magnetic field, a different magnetic polarization, and/or a different distance between them in the first direction, when seen relative to the third or fifth magnet arrangement, relatively. Such relative different arrangements are also possible for the first magnet arrangement relative to the fourth magnet arrangement. This allows to create a variety of different relations between the position-dependent force and the position of the first magnet arrangement and/or the fourth magnet arrangement.

In an embodiment the magnetic spring assembly further comprises at least one electromagnetic coil configured to cooperate with the first magnet arrangement. By creating a magnetic field with the electromagnetic coil a magnetic force is exerted on the first magnet arrangement. A resulting position-dependent including said magnetic force and the position- dependent force can be controlled by controlling current through the electromagnetic coil. For example, the electromagnetic coil may be arranged adjacent to the second magnet arrangement in the second direction, for example on the holder. In an embodiment there may be an electromagnetic coil on each side of the second magnet arrangement in the second direction.

In an embodiment the clamping mechanism comprises a force-closed clamp, e.g. a clutch, e.g. a mechanical (friction) clutch or brake, e.g. an axial plate friction clutch, e.g. a drum brake.

In an embodiment the clamping mechanism comprises a form-closed clamp. For example, the form-closed clamp may comprise a hydraulic or pneumatic clamp or actuator which clamps the second magnet arrangement to the holder, and which may in a further embodiment be electronically controlled. For example, the form-closed clamp may comprise one or more pins which can be introduced in a slot comprised by the second magnet arrangement and a slot comprised by the holder to clamp the second magnet arrangement to the holder. In an embodiment the first and second magnet arrangement are an n-pole permanent magnet arrangement, n being equal to 1 , 2, 4, 6 or 20. It is noted that it is possible that the first and second magnet arrangement may have a different number of poles, e.g. when one of the first and second magnet arrangement is formed by ferromagnetic material or in applications with field modulation such as in magnetic gears, or in an embodiment wherein the first direction is translational.

In an embodiment the arrangement of the magnets of first and/or second magnet arrangement is determined based on the application. For example, if a certain profile of the position-dependent force in function of the position of the first magnet arrangement is required, a phase profile of the position-dependent force can be determined using a Fourier transformation. Based on this the first and/or second magnet arrangement, and/or the third magnet arrangement, and/or the fourth and/or the fifth magnet arrangement, can be designed.

In an embodiment the first direction is a translational direction. The magnetic spring assembly is a linear spring. The second direction may e.g. be a rotational direction or a translational direction perpendicular to the first direction.

In an embodiment wherein the first direction is a translational direction, the second magnet arrangement may comprise a plurality of magnets, e.g. permanent magnets, which can be clamped in multiple groups or even individually, by the clamping mechanism. By releasing one or more of said groups or individual magnets, the distance between magnets or groups of magnets of the second magnet arrangement can be adapted, thereby allowing to adapt the position-dependent force.

In an embodiment wherein the first direction is a translational direction, the clamping mechanism may comprise a further released state in which the second magnet arrangement is moveable relative to the holder in a second direction, which is a translational direction. This may e.g. be achieved by rotating the first magnet arrangement or with a motion conversion mechanism by moving the first magnet arrangement in the first direction. Advantageously the amplitude of the position-dependent force can be adjusted, e.g. when the second magnet arrangement comprises diametrically polarized magnets.

In an embodiment the first direction is a rotational direction. The magnetic spring assembly is a linear spring is a rotational spring. The second direction may e.g. a translational direction, e.g. parallel to an axis around which the first magnet arrangement is arranged to rotate. For example, the first magnet arrangement is arranged on a rotor. The second magnet arrangement is arranged to be a stator when the clamping mechanism is in the clamped state and a second rotor when the clamping mechanism is in the released state.

The invention further relates to a motor comprising the magnetic spring assembly according to the invention, wherein the first magnet arrangement is arranged to be rotated by rotation of an output shaft of the motor. The output shaft may e.g. be connected to a load, e.g. an inertial load. The motor may e.g. provide an output torque with is dependent on the angular position of the output shaft.

The position in the first direction of the second magnet arrangement relative to the first magnet arrangement can be arranged such that the position-dependent force delivers part of a load torque, and as such relieves the motor from it. For example, the torque to which the load subjects the output shaft of the motor may comprise a ripple which is dependent on the angular position of the output shaft. The magnetic spring assembly can then reduce said ripple such that the torque that the motor must provide is less varying, i.e. more constant. Furthermore, said ripple of the torque may be different in magnitude at different speeds. The magnetic spring assembly being adjustable allows to better match this torque for any speed. At very low speeds, when there is little torque to compensate, the magnetic spring assembly may be decoupled, i.e. the clamping mechanism may be arranged in the released state.

The position in the first direction of the second magnet arrangement relative to the second magnet arrangement can also be arranged such that the position-dependent force is out of phase with the output torque, e.g. in opposite phase. The magnetic spring assembly thereby reduces the ripple on the output torque generated by the motor or a gearbox between the motor and the magnetic spring assembly. The load is as such subjected to a torque that is less varying, i.e. more constant. Optionally the motor may comprise multiple magnetic spring assemblies according to the invention or a magnetic spring assembly with more than two magnet arrangements, arranged to compensate one or more harmonic components of the motor.

For example, the motor may be an internal combustion engine arranged to drive the output shaft on which the first magnet arrangement is arranged or connected to. The output shaft may e.g. be connected to the wheels of a vehicle.

For example, the motor may be an electromotor arranged to drive the output shaft on which the first magnet arrangement is arranged or connected to. In a further embodiment the magnetic spring assembly may be incorporated in the electromotor in the same housing. The invention further relates to other applications in which the magnetic spring assembly can be applied. For example, the magnetic spring assembly can be applied in an agricultural vehicle, e.g. in a combine harvester, e.g. in a cleaning system of a combine harvester to reciprocate motion. For example, the magnetic spring assembly can be applied in a compressor, pump or fan. For example, the magnetic spring assembly can be applied in a gear system, e.g. a wind turbine gear system, to reduce noise and vibration. For example, the magnetic spring assembly may be a linear spring arranged on a large printer to reverse translational motion. For example, the magnetic spring assembly may be a linear spring arranged on a scanner to reverse translational motion, e.g. a scanner used in a lithographic process or in a lithographic apparatus. For example, the magnetic spring assembly can be applied in a punching machine or a bending machine.

The invention further relates to a system for converting unidirectional motion to reciprocating motion and/or vice versa. The system comprises a shaft arranged to be rotated around its longitudinal axis and a motion conversion system, e.g. a bar linkage or cam- follower mechanism.. The motion conversion system is connected to the shaft in a manner that rotation, e.g. unidirectional rotation, e.g. continuous unidirectional rotation, of the shaft causes an end-connector of the motion conversion mechanism to move back and forth and/or vice versa. The end-connecter is configured to provide a reciprocating motion, and e.g. configured to be connected to an inertial load or an end-effector. The system further comprises a magnetic spring assembly according to the invention, the second magnet arrangement being arranged relative to the holder such that magnetic spring assembly at least partially compensates a position-dependent load torque exerted on the shaft. Preferably the first magnet arrangement is arranged to be rotated by the shaft.

The shaft and motion conversion system in this system are connected to each other such that movement of one of both causes the other to move as well. The shaft is arranged to be rotated around its longitudinal axis and an end-connector of the motion conversion system is arranged to be moved back and forth. The end- connector may be configured to be connected to an inertial load and drive said inertial load, e.g. if the shaft is driven by a driving mechanism, e.g. by an actuator or a motor. The shaft is subjected to a position-dependent load torque, being dependent on the angular position of the shaft. The magnetic spring assembly according to the invention is therefore provided, the position of the second magnet arrangement relative to the holder being such that the position-dependent force is translated into a position-dependent torque which at least partially compensates the position dependent load torque. The magnetic spring assembly hence relieves an actuator or motor driving the shaft from the position-dependent load torque, which may be alternating, required for subsequent acceleration and deceleration of the inertial load or end-connector. Advantageously with the magnetic spring assembly according to the invention when the position-dependent load torque is changed, e.g. when the system is used at another speed, for another application or with another inertial load, the magnetic spring assembly can be decoupled or the position of the second magnet arrangement relative to the holder can be adapted. In a possible embodiment the end-connector is configured to be connected to the inertial load radially outwards of the shaft. In other words, location of the motion conversion system that is connected to the inertial load is spaced from the longitudinal axis of the shaft in the radial direction of the shaft by a distance that is larger than the radius of the shaft.

It is noted that it is also possible to use a magnetic spring assembly according to the invention with the first direction being a translational direction, e.g. the first magnet arrangement being arranged on a member of the motion conversion system which is arranged to move in a translational direction.

It is noted that alternatively in such system the spring assembly may be a spring having a linear relation between the spring force and displacement, e.g. a conventional mechanical spring, arranged at the inertial load or end-effector or at least being configured to be moved by inertial load, or the end-connector. However usually in such systems the available space on such components as the inertial load and the end-connector is limited. The magnetic spring assembly according to the invention can be arranged such that the position-dependent force has an amplitude according to a periodic waveform, e.g. in the form of a sine wave or a square wave when seen over movement in the first direction of the first magnet arrangement. This allows to arrange the magnetic spring assembly at the components which have a continuous or unidirectional motion rather than a reciprocating motion, where there is more space available, e.g. on the shaft arranged to be rotated around its longitudinal axis in a unidirectional motion.

General examples of a system according to the invention include four-bar-linkage systems, slider-crank-mechanisms and cam mechanisms which are used in a wide variety of applications.

Another example of a system according to the invention is a parallel robot, also referred to as a parallel manipulator. A parallel robot usually comprises two, three, four, five, six, seven or more actuators which are each via an arm connected to an end-effector. For example when the actuator are rotary actuators, the magnetic spring assembly can advantageously be a rotary spring which can arranged on the output shaft of the actuator, such that each actuator can individually be provided with a magnetic spring assembly, each magnetic spring assembly being arranged to compensate the position-dependent torque the respective actuator is subjected to.

Another example of a system according to the invention is a pick-and-place robot. These systems are usually used in manufacturing processes to pick up a product and place it somewhere else in the manufacturing process. They are therefore often arranged to perform the same reciprocating movement repetitively for a period of time. However after a certain period the movement they have to make might change or the load they have to pick up might change. The position of the second magnet arrangement relative to the holder may than advantageously be adapted to compensate the changed position-dependent torque.

Another example of a system according to the invention is an exoskeletons or humanoid robot, wherein the magnetic spring assembly can e.g. be arranged on a shaft arranged to rotate, e.g. to provide the function of a joint, e.g. a knee, elbow, ankle or wrist.

The invention further relates to several methods. The methods according to the invention can be applied to and performed with the magnetic spring assembly according to the invention; however, the methods according to the invention are not limited thereto. Nevertheless, components and definitions will have the same meaning with respect to the methods according to the invention as they do with respect to the magnetic spring assembly according to the invention, unless specifically stated otherwise. Furthermore, features described with respect to the magnetic spring assembly according to the invention can be added to the magnetic spring assembly used in the method according to the invention, as can the associated uses and effects be added to the method itself.

The first method according to the invention is a method for operating a magnetic spring assembly comprising a holder, a first magnet arrangement configured to be moveable relative to the holder in a first direction, a second magnet arrangement configured to cooperate with the first magnet arrangement to generate a position-dependent force in the first direction, and a clamping mechanism for clamping the second magnet arrangement to the holder,

the method comprising the following steps:

• arranging the clamping mechanism in a clamped state wherein a position of the second magnet arrangement is substantially fixed relative to the holder, and

• arranging the clamping mechanism in a released state, wherein the second magnet arrangement is moveable relative to the holder in the first direction.

The invention thus provides in a method to couple and decouple the magnetic spring assembly, i.e. turning it on and turning it off, by clamping the second magnet arrangement with the clamping mechanism. This allows to only provide the spring force when it is required, thereby increasing the flexibility of the system. In an embodiment, the method further comprises a step of using the magnetic spring assembly while the clamping mechanism is in the released state, i.e. being decoupled, wherein the first and second magnet arrangement are moving together. Preferable the position-dependent force between the first magnet arrangement and the second magnet arrangement causes the second magnet arrangement to move when the first magnet arrangement is moving, in the same direction. Preferably the position-dependent force causes the second magnet arrangement to remain in approximately the same position in the first direction relative to the first magnet arrangement.

In an embodiment the method comprises a step of arranging the second magnet arrangement in a first clamped position, and a step of arranging the second magnet arrangement in a second clamped position, wherein the position of the second magnet arrangement relative to the holder in the first direction is different in the first clamped position than in the second clamped position.

The invention provides in a method to adapt the position-dependent force in function of the position of the first magnet arrangement. Based on the application in which the magnetic spring assembly is used and the load thereof the most advantageous of the first and second clamped position can be chosen. The magnetic spring assembly is more flexible and can be used for different applications and/or loads.

In an embodiment the step of arranging the second magnet arrangement in a second clamped position, includes the following steps: arranging the clamping mechanism in the released state; moving the second magnet arrangement together with the first magnet arrangement, wherein the position-dependent force between the first magnet arrangement and the second magnet arrangement causes the second magnet arrangement to move when the first magnet arrangement is moving, in the same direction; and then clamping the second magnet arrangement again with the clamping mechanism in the second clamped position.

In an embodiment the magnetic spring assembly is arranged on a bar which is arranged to be moved in a translational direction, the first direction a translational direction parallel to the direction in which the bar is arranged to move, wherein the step of arranging the second magnet arrangement in the second clamped position includes the moving the first magnet arrangement partially or completely passed the second magnet arrangement in the first direction while the clamping mechanism is in the clamped state; arranging the clamping mechanism in the released state; moving the second magnet arrangement together with the first magnet arrangement, wherein the position-dependent force between the first magnet arrangement and the second magnet arrangement causes the second magnet arrangement to move when the first magnet arrangement is moving, in the same direction; and then clamping the second magnet arrangement again with the clamping mechanism in the second clamped position.

In an embodiment the magnetic spring assembly further comprises a motion conversion mechanism, e.g. a screw thread, and the method further comprises the following steps:

• arranging the second magnet arrangement in a third clamped position,

• arranging the second magnet arrangement in the released position,

• moving the second magnet arrangement together with the first magnet arrangement in the first direction relative to the holder,

• while moving the second magnet arrangement together with the first magnet arrangement in the first direction, moving the second magnet arrangement relative to the holder in a second direction, said moving being guided by the motion conversion mechanism, wherein the second direction is different from the first direction,

• arranging the second magnet arrangement in fourth clamped position, wherein a position of the second magnet arrangement relative to the holder in the second direction is different in the third clamped position than in the fourth clamped position.

The invention further relates to a method for reversing motion with a magnetic spring assembly comprising a holder, a first magnet arrangement configured to be moveable relative to the holder in a first direction, a second magnet arrangement configured to cooperate with the first magnet arrangement to generate a position-dependent force in the first direction, and a clamping mechanism for clamping the second magnet arrangement to the holder,

the method comprising the following steps:

• arranging the clamping mechanism in a released state, wherein the second magnet arrangement is moveable relative to the holder in the first direction,

• moving the second magnet arrangement together with the first magnet arrangement,

• while the first and second magnet arrangement are moving together, arranging the clamping mechanism in a clamped state wherein a position of the second magnet arrangement is substantially fixed relative to the holder, thereby counteracting the movement of the first magnet arrangement in the first direction.

In this method the first magnet arrangement is only subjected to the position- dependent while it is already moving in the first direction. Once the clamping mechanism is arranged in the clamped state the second magnet arrangement stops moving relative to holder. The position-dependent force will attract the first magnet arrangement to the second magnet arrangement, thereby counteracting the movement of the first magnet arrangement in the first direction at first, i.e. slowing down the first magnet arrangement. Once the movement of the first magnet arrangement is stopped, the second magnet arrangement still attracts the first magnet arrangement, causing the first magnet arrangement to move towards the second magnet arrangement in the first direction and starting the reversed motion.

In a further embodiment the method comprises a step of arranging the clamping mechanism in the released position when the first magnet arrangement is returned to approximately the same position relative to the second magnet arrangement as when the clamping mechanism was arranged in the clamped position.

Examples of the invention will now be described with references to the accompanying figures, wherein like reference numerals indicate like features. It is noted that these figures are only examples illustrative for the understanding of the invention, and are in no way meant to be limiting to the scope of the invention.

In the figures:

Fig. 1a shows a side view first embodiment of the magnetic spring assembly according to the invention.

Fig. 1 b shows a cross-section of the magnetic spring assembly on intersection line GG shown in fig. 1a with the second magnet arrangement in a first clamped position.

Fig. 1 c shows a cross-section of the magnetic spring assembly on intersection line GG shown in fig. 1a with the second magnet arrangement in a second clamped position.

Fig. 1 d illustrates the position-dependent force in function of the position of the first magnet arrangement when the second magnet arrangement is in the first and second clamped position respectively.

Fig. 2a shows a front view of a second embodiment of the magnetic spring assembly according to the invention.

Fig. 2b shows a cross-section of the magnetic spring assembly shown in fig. 2a.

Fig. 2c shows a cross-section of the magnetic spring assembly on intersection line DD shown in fig. 2a.

Fig. 2d shows a close up of the clamping mechanism being in the clamped state.

Fig. 2e shows a close up of the clamping mechanism being in the released state.

Fig. 2f shows a close up of the clamping mechanism being in the further released state. Fig. 3a-3b show the second embodiment of the magnetic spring assembly with the second magnet arrangement in the third clamped position.

Fig. 3c-3d show the second embodiment of the magnetic spring assembly with the second magnet arrangement in the fourth clamped position.

Fig. 3e illustrates the position-dependent force in function of the position of the first magnet arrangement when the second magnet arrangement is in the third and fourth clamped position respectively.

Fig. 4a shows a front view of a third embodiment of the magnetic spring assembly according to the invention.

Fig. 4b shows a side view of the third embodiment of the magnetic spring assembly according to the invention.

Fig. 4c shows a cross-section of the magnetic spring assembly according to intersection line AA shown in fig. 4a

Fig. 4d shows a cross-section of the magnetic spring assembly according to intersection line BB shown in fig. 4b

Fig. 4e shows a cross-section of the magnetic spring assembly shown in fig. 4a-4d

Fig. 5a shows a system according to the invention comprising a magnetic spring assembly according to the invention.

Fig. 5b illustrates how the magnetic spring assembly compensates position- dependent torque in the system shown in fig. 5a.

Fig. 6a shows cross-section of a fourth embodiment of a magnetic spring assembly according to the invention.

Fig. 6b illustrates the position-dependent force in function of the position of the first magnet arrangement for the embodiment shown in fig. 6a

Fig. 7 shows a cross-section of a fifth embodiment of a magnetic spring assembly according to the invention.

Fig. 8a shows a cross-section of a sixth embodiment of a magnetic spring assembly according to the invention.

Fig. 8b shows a side view of the embodiment shown in fig. 8a.

Fig. 8c illustrates the position-dependent force in function of the position of the first magnet arrangement for the embodiment shown in fig. 8a-8b.

Fig. 1a shows a side view first embodiment of a magnetic spring assembly 1 according to the invention and fig. 1 b shows a cross-section G-G of the magnetic spring assembly 1 shown in fig. 1a. The magnetic spring assembly 1 is arranged on a shaft 2 which is arranged to be rotated around its longitudinal axis. Although a holder 4 encompasses most components of the magnetic spring assembly 1 , a clamping mechanism 3 is visible in fig. 1 a. In the cross-section in fig. 1 b a first magnet arrangement 6 is shown. In the shown embodiment the first magnet arrangement 6 comprises two pole pairs comprising four permanent magnets which are arranged alternating when seen in a first direction, which is a rotational direction, in particular rotation around the longitudinal axis of the shaft 2. It is noted however that any number of magnets could be used. The first magnet arrangement 6 is arranged on the shaft 2 such that rotation of the shaft 2 causes the first magnet arrangement to rotate as well relative to the holder 4.

The magnetic spring assembly 1 further comprises a second magnet arrangement 5 which is configured to cooperate with the first magnet arrangement 6 to generate a position- dependent force in the first direction. The position-dependent force is dependent of the position of the first magnet arrangement 6 relative to the second magnet arrangement 5 in the first direction. The second magnet arrangement 5 is spaced from the first magnet arrangement by a small air gap 99. In the shown embodiment the second magnet arrangement 5 comprises two pole pairs comprising four permanent magnets which are arranged alternating when seen in the first direction. The second magnet arrangement 5 further comprises a ferromagnetic part 5.1 on which the permanent magnets are arranged for providing a magnetic path and a holding part 5.2 to which the ferromagnetic part 5.1 is fixed.

The magnetic spring assembly 1 further comprises the clamping mechanism 3 which comprises three pins 1 1 . Six slots 13 extend through the holder 4 and the holding part 5.2 of the second magnet arrangement 5 in which the pins 1 1 can be introduced. When the pins 1 1 are introduced in the slots 13 the clamping mechanism 3 is in a clamped state and the second magnet arrangement 5 cannot move in the first direction relative to the holder 4. Therefore rotation of the first magnet arrangement 6 by rotating the shaft 2 changes the position of the first magnet arrangement 6 relative to the second magnet arrangement 5 in the first direction. The first magnet arrangement 5 and as such the shaft 2 are subjected to the position-dependent force which functions as a spring force on the shaft 2.

The clamping mechanism 3 further comprises three solenoids 12 with which the pins 1 1 can be actuated. By moving the pins 1 1 radially outward they can be pulled out of the part of the slots 13 extending in the second magnet arrangement 5 to arrange the clamping mechanism in a released state. In the released state the second magnet arrangement 5 is movable relative to the holder 4. The second magnet arrangement 5 will move towards an equilibrium point relative to the first magnet arrangement 6. Rotation of the first magnet arrangement 6 by rotating the shaft 2 subjects the second magnet arrangement 5 to the position-dependent force in the first direction, which causes the second magnet arrangement 5 to rotate as well. During said rotation the position of the second magnet arrangement 5 relative to the first magnet arrangement 6 remains substantially the same, being such that the position-dependent force is sufficient to overcome friction forces. However the position- dependent force remains small. The first magnet arrangement 6 and as such the shaft 2 are subjected to said small position-dependent force, which has only little to substantially no effect on the shaft 2. The magnetic spring assembly 1 is thus functionally decoupled from the shaft 2. In the clamped state the second magnet arrangement 5 functions as a stator while in the released state in functions as a rotor.

In fig. 1 b the second magnet arrangement 5 is shown in a first clamped position, while in fig. 1 c the second magnet arrangement 5 is shown in a second clamped position. A position of the second magnet arrangement 5 relative to the holder 4 in the first direction is different in the first clamped position than in the second clamped position. In the shown embodiment the second clamped position differs from the first clamped positon in that the slots 13 in which the pins 1 1 are introduced in the second clamped position are free in the first clamped position and vice versa. The second magnet arrangement 5 can be arranged from the first to second clamped position by arranging the clamping mechanism 3 into the released state and rotating the second magnet arrangement 5 by rotation of the shaft 2 and the first magnet arrangement 6 until the correct slots 13 are aligned with the pins 1 1 , which can then be introduced further in the slots 13 to clamp the second magnet arrangement 5 to the holder 4 in the second clamped position.

In the shown embodiment the position of first magnet arrangement 6 for a given position of the shaft 2 is rotated by -60 degrees in the second clamped position relative to the first clamped position. Fig. 1 d shows a graph 21 of the position-dependent force F in function of the position P of the first magnet arrangement 6 when the second magnet arrangement 5 is in the first clamped position and a graph 22 of the position-dependent force F in function of the position P of the first magnet arrangement 6 when the second magnet arrangement 5 is in the second clamped position. It is noted that with the first direction being a rotational direction due to the position-dependent force F a position-dependent torque is exerted on the first magnet arrangement, which is proportional to the position-dependent force F. Since the first magnet arrangement 6 comprises two pole pairs the graphs 21 , 22 show two sines over 360 degrees rotation of the first magnet arrangement 6. Flowever, graph 22 lags -60 degrees behind graph 21 when seen in function of the position of the first magnet arrangement. The phase of the position-dependent force is shifted in the second clamped position relative to the first clamped position. The invention thus provides in a magnetic spring assembly of which the position-dependent force can be adjusted in function of the application, e.g. in function of a load driven by the shaft 2.

Fig. 2a shows a front view of a second embodiment of a magnetic spring assembly 101 according to the invention, and fig. 2b and 2c show cross-sections of the magnetic spring assembly shown in fig. 2a according to intersection line DD. The magnetic spring assembly 101 again comprises a first magnet arrangement 106 which is arranged on a shaft 2 which can be rotated in a first direction, and a second magnet arrangement 105 which cooperates with the first magnet arrangement 106 to generate a position-dependent force in the first direction. Both the first 106 and the second magnet arrangement 105 comprises one pole pair. The second magnet arrangement 105 comprises a ferromagnetic part 105.1 and a holding part 105.2. A clamping mechanism 103 comprises thee pins 1 11 which can be actuated by solenoids 1 12 for arranging them in slots 113. The shown magnetic spring assembly 101 further comprises a front cover 151 and a similar back cover (not shown).

The magnetic spring assembly 101 in the shown embodiment further comprises a motion conversion mechanism 152.1 which in the shown example comprises a screw thread 152. The screw thread 152 is configured to cause the second magnet arrangement 106 to move in a second direction while rotating in the first direction. In the shown embodiment the second direction is a translational direction parallel to the longitudinal axis of the shaft 102. The holding part 105.2 of the second magnet arrangement 105 is provided with a screw thread on its outer surface to interact with the screw thread 152 of the motion conversion mechanism 152.1.

The clamping mechanism 103 in the shown embodiment has three states, which are shown in fig. 2d-2f. Fig. 2d shows the clamping mechanism is a clamped state, wherein the pins 1 1 1 are inserted in slots 113 which extend in both the motion conversion mechanism 152.1 and the holding part 105.2 of the second magnet arrangement 105, which are therefore both clamped to the holder 104, their positions in the first direction being fixed relative to the holder 104. Similarly to the clamped state as described with respect to the first embodiment, in the clamped state shown in fig. 2d rotation of the shaft 102 will cause the first magnet arrangement 106 to rotate relative to the second magnet arrangement 105 and the holder 104, resulting in the shaft 102 being subjected to the position-dependent force which varies during rotation of the shaft 102.

Fig. 2e shows a released state of the clamping mechanism 103. In this state the pin 1 1 1 is arranged in the part of slot 1 13 extending in the motion conversion mechanism 152.1 but not in the part of slot 1 13 extending in the holding part 105.2 of the second magnet arrangement 105. The position of the motion conversion mechanism 152.1 is as such fixed relative to the holder 104, but the second magnet arrangement 105 can move relative to the both the motion conversion mechanism 152.1 and the holder 104. Rotation of the first magnet arrangement 106 by rotating the shaft 102 therefore causes the second magnet arrangement 105 to rotate relative to the motion conversion mechanism 152.1 due to the position-dependent force. The screw thread 152 simultaneously causes the second magnet arrangement 105 to move in the second direction, which in fig. 2e is to the left or to the right, depending on how the shaft 102 is rotated. Fig. 2f shows the clamping mechanism 103 in a further released state, wherein the pin 1 11 is arranged outside of the slots 1 13 of the motion conversion mechanism 152.1 and the holding part 105.2 of the second magnet arrangement 105, which are as such both moveable in the first direction relative to the holder 104. A friction force between the second magnet arrangement 105, in particular the holding part 105.2, and the motion conversion mechanism 152.1 is larger than a friction force between the motion conversion mechanism 152.1 and the holder 104. Therefore rotation of the first magnet arrangement 106 will not only cause the second magnet arrangement 105 to rotate relative to the holder 104 but also the motion conversion mechanism 152.1. The second magnet arrangement 105 will in this state not move in the second direction when it is moved in the first direction. It noted however that in another embodiment the magnetic spring assembly comprising a motion conversion mechanism may comprise a clamping mechanism having only the clamped and the released state.

Fig. 3a-3b show the magnetic spring assembly of fig. 2a-2f with the second magnet arrangement 105 in a third clamped position while in fig. 3c-3d the second magnet arrangement 105 is in a fourth clamped position. A position of the second magnet arrangement 105 relative to the holder 104 in the second direction is different in the third clamped position than in the fourth clamped position. The second magnet arrangement 105 can be arranged from the third to fourth clamped position by arranging the clamping mechanism 103 into the released state and rotating the second magnet arrangement 105 by rotation of the shaft 102. The screw thread 152 causes the second magnet arrangement 105 to move in the second direction. When the correct slots 1 13 are aligned with the pins 1 11 , said pins 1 1 can then be introduced in the slots 1 13 to clamp the second magnet arrangement 105 to the holder 104 in the second clamped position. In this embodiment the magnetic spring assembly comprises multiple sets of slots along the second direction, each set comprising six angularly spaced slots.

Fig. 3e shows a graph 121 of the position-dependent force F in function of the angular position P of the first magnet arrangement 106 when the second magnet arrangement 105 is in the third clamped position and a graph 122 of the position-dependent force F in function of the position P of the first magnet arrangement 106 when the second magnet arrangement 105 is in the fourth clamped position. It is noted that with the first direction being a rotational direction due to the position-dependent force F a position-dependent torque is exerted on the first magnet arrangement, which is proportional to the position-dependent force F. Since the first magnet arrangement 106 comprises one pole pair the graphs 21 , 22 show only one sine over 360 degrees rotation of the first magnet arrangement 106. Since there is less radial overlap between the first 106 and second magnet arrangement 105 in the fourth clamped position compared to the third clamped position, the position-dependent force is smaller in amplitude in the fourth clamped position, as is shown by graph 122. The force to which the shaft is subjected is therefore also smaller. Using the motion conversion mechanism 152.1 the amplitude of the position-dependent force can be adjusted.

It is noted that although graphs 121 and 122 are in phase with each other, this is not required. By changing the position in the first direction of the second magnet arrangement 106 relative to the holder 104 in the third clamped position relative to the fourth clamped position the phase of the position-dependent force may be adjusted together with the amplitude.

Fig. 4a shows a front view of a third embodiment of the magnetic spring assembly 701 according to the invention, while fig. 4b shows a side view of the same magnetic spring assembly 701. The magnetic spring assembly is again arranged on a shaft 702, and in fig. 4c, which shows a cross-section of the magnetic spring assembly 701 according to intersection line AA shown in fig. 4a, it can be seen that a holder 704 comprises a first magnet arrangement 706 and a second magnet arrangement 705. Similarly to the embodiments in previous figures, the first 706 and second magnet arrangement 705 cooperate with each other to generate a position-dependent force in a first direction, which is the rotational direction in which the shaft 702 rotates around its longitudinal axis.

The magnetic springs assembly 701 further comprises a clamping mechanism 703 arranged to clamp the second magnet arrangement 705 to the holder 704. However, whereas the clamping mechanisms 3, 103 shown in fig. 1 a-1 c and fig. 2a-3d, respectively, were form-closed clamping mechanisms, the clamping mechanism 703 in the third embodiment shown in fig. 4a-4e is a force-closed clamping mechanism, in particular a drum brake, in particular an external contracting clutch.

Fig. 4d shows a cross-section of the magnetic spring assembly according to intersection line BB shown in fig. 4b and fig. 4e shows a cross-section of the magnetic spring assembly shown in fig. 4a-4d. The clamping mechanism 703 comprises two external shoes 733,734 which are preloaded with a spring (not shown). A clamping member 735 is subjected to a radial force by the external shoes 733, 734 to clamp the second magnet arrangement 705 such that the position of the second magnet arrangement 705 relative to the holder 704 is fixed. A cam 732 can be rotated by applying a torque with a rotational actuator 731 , which e.g. can be a stepper motor. By rotating the cam 732 the external shoes 733, 734 can be opened such that the clamping member 735 does not clamp the second magnet arrangement 705, thereby allowing movement of the second magnet arrangement 705 relative to the holder 704 in the first direction. Fig. 5a shows a system 500 according to the invention, which in the shown embodiment is a four bar linkage system. The system 500 comprises a shaft 502 which is arranged to be rotated around its longitudinal axis. In fig. 5a said longitudinal axis extends perpendicular to the paper, as the shaft 502 is shown in a front view. The system further motion conversion system which comprises a first member 503 which is connected to the shaft 502 such that rotation of the shaft 502 causes the first member 502 to move. A second member 504, a third member 505 and a fourth member 506 are further provided to form a closed motion conversion system. The system further comprises a shaft 508 which is rotated by movement of the third member 505. The system 500 comprises an end-connector (not shown) which can be connected to an inertial load (not shown), e.g. at shaft 508, or somewhere on the third member 505, or at connection point 509.

By rotating the shaft 502 around its longitudinal axis the first member 503 is rotated such that a connection point 503.1 follows a trajectory 51 1. The arrangement of the system 500 is such that the connection point 509 follows a trajectory 512 as a reciprocating motion, which defines a trajectory of the movement of the end-connector and as such the inertial load. The system 500 thus converts a unidirectional motion into a reciprocating motion.

During said motion the inertial load exerts a force on the system 500 which translated to a position-dependent torque on the shaft 502. Fig. 5b shows a graph 552 of said position- dependent torque in function of the angular position P of the shaft for a constant rotational speed of the shaft. As can be seen said position-dependent torque approximately has a sine shaped amplitude in function of the angular position P of the shaft.

The system 500 in fig. 5a is provided with a magnetic spring assembly 501 according to the invention, which is arranged on the shaft 502 such that the first magnet arrangement is rotated by the shaft 502. In fig. 5a the magnetic spring assembly 501 is schematically indicated by a dashed line. Said magnetic spring assembly 501 may for example be embodied similar to the embodiment shown in fig. 1 a-1c, the shaft 2 in therein corresponding with the shaft 502 in fig. 5a, or the embodiment shown in fig. 2a-3d, the shaft 102 in therein corresponding with the shaft 502 in fig. 5a, or the embodiment shown in fig. 4a-4e, the shaft 702 therein corresponding with the shaft 502 in fig. 5a. The first and second magnet arrangements of magnetic spring assembly 501 in the system 500 each comprise two pole pairs. The second magnet arrangement is arranged relative to the holder such that the position-dependent force of the magnetic spring assembly 501 is translated into a torque on the shaft 502 which corresponds to graph 551 in fig. 5b. As can be seen graph 551 and graph 552 approximate each other. The magnetic spring assembly 501 as such at least partially compensates the position-dependent torque exerted on the shaft 502.

Advantageously the magnetic spring assembly 501 according to the invention can be arranged on the rotating shaft 502 instead of on shaft 508 or at the inertial load where usually available space is limited. In addition, the phase or amplitude can be adjusted based on the inertial load and the rotation speed, as has been explained with reference to figs. 1 a-4e.

Fig. 6a shows cross-section of a fourth embodiment of a magnetic spring assembly 801 according to the invention. The magnetic spring assembly 801 is arranged on a bar 802 which is arranged to be moved in a translational direction, which in fig. 6a is to the left and right. A holder 804 comprises a first magnet arrangement 806 and a second magnet arrangement 805, which are configured to cooperate with each other to generate a position- dependent force in a first direction, which is a translational direction parallel to the direction in which the bar 802 is arranged to move, thus in fig. 6a is to the left and right. The second magnet arrangement 805 comprises an upper magnet arrangement 805.1 and a lower magnet arrangement 805.2, which in the shown embodiment both have a shape of a rectangular cuboid.

The magnetic spring assembly 801 further comprises a clamping mechanism (not shown) for clamping the second magnet arrangement 805 to the holder 804. The clamping mechanism has a clamped state wherein a position of the second magnet arrangement 805 is substantially fixed relative to the holder 804, and a released state wherein the second magnet arrangement 805 is moveable relative to the holder 804 in the first direction. The clamping mechanism may e.g. be embodied similar to the clamping mechanisms in the first to third embodiments of the magnetic spring assembly according to the invention. The clamping mechanism may comprise an upper clamping mechanism for clamping the upper magnet arrangement 805.1 and a lower clamping mechanism for clamping the lower magnet arrangement 805.2. It is also possible that the clamping mechanism clamps only one of the upper 805.1 and lower magnet arrangement 805.2, and that said upper 805.1 and lower magnet arrangement 805.2 are fixed to each other.

The first magnet arrangement 806 is arranged on the bar 802 such that translational movement of the bar 802 causes the first magnet arrangement 806 to move simultaneously with the bar 802. When the first magnet arrangement 806 approaches the second magnet arrangement 805 and the clamping mechanism is in the clamped state, the position- dependent force increases which will act as a spring force on the first magnet arrangement 805, counteracting the movement of the first magnet arrangement 805.

When the clamping mechanism is in the released state, the position-dependent force can cause the second magnet arrangement 805 to move together with the first magnet arrangement 806 in the first direction. It is noted that to move the second magnet arrangement 805 to what in fig. 6a is the right side, it may be necessary to first move the first magnet arrangement 806 at least partially passed the second magnet arrangement 805 before releasing the second magnet arrangement 805. The second magnet arrangement 805 can be moved in the first direction and clamped with the clamping mechanism in another position along the first direction. The magnetic spring assembly 801 can as such be adapted to another application in which the length of the translational movement is different. It may also be possible that a biasing means, e.g. a spring, is provided for moving the second magnet arrangement 805 when the clamping mechanism is in the released state. For example, in the embodiment shown in fig. 6a the biasing means can be used to move the second magnet arrangement 805 to the right side, and the first magnet arrangement 806 can be used to move the second magnet arrangement to the left side.

The magnetic spring assembly 801 further comprises an optional third magnet arrangement 815 and a second clamping mechanism (not shown) for clamping the third magnet arrangement 815 to the holder 804. The third magnet arrangement 815 comprises an upper magnet arrangement 815.1 and a lower magnet arrangement 815.2 which in the shown embodiment both have a shape of a rectangular cuboid.

As such the magnetic spring assembly 801 functions as a spring on both ends of the translational movement of the bar 802.

By adapting the positions of the second 805 and/or third magnet arrangement 815 the magnetic spring assembly 801 can be adapted to the length of said translational movement of the bar 802. In addition the magnetic spring assembly 801 assist in decelerating and accelerating the motion of the bar 802, meaning that less space is required for this.

This is for example illustrated with the graph shown in fig. 6b, which indicates the position-dependent force F in function of the position P of the first magnet arrangement 806. For this example dimensionless numbers are chosen to merely illustrate the principle, since actual values depend on the application of the magnetic spring assembly 801. A first graph 851 corresponds with the situation shown in fig. 6a, wherein the second magnet arrangement 805 is arranged on position -1 and the third magnet arrangement is arranged on position 1. As can be seen in fig. 6b, the amplitude of the position-dependent force increases as the first magnet arrangement approaches the second 805 or third magnet arrangement 815. A second graph 851 illustrates a situation wherein the second 805 and third magnet arrangement 815 have been arranged closer to each other. As can be seen, a high amplitude of position-dependent force is present within a smaller movement of the first magnet arrangement 806. The situation illustrated by the second graph 852 may be suitable when a smaller stroke of movement of the first magnet arrangement 806 is required. Furthermore, at any position of the first magnet arrangement 806 in between the second 805 and third magnet arrangement 806, the amplitude of the position-dependent force has increased as well. Fig. 7 shows cross-section of a fifth embodiment of a magnetic spring assembly 901 according to the invention. Like the fourth embodiment shown in fig. 6a, this fifth embodiment is a linear magnetic spring assembly, i.e. the first direction being a translational direction; however, unlike the fourth embodiment shown in fig. 6a, this fifth embodiment is circular symmetrical around the center axis of a bar 902.

The magnetic spring assembly 901 is arranged on a bar 902 which is arranged to be moved in a translational direction, which in fig. 7 is to the left and right. A holder 904 comprises a first magnet arrangement 906 and a second magnet arrangement 905, which are configured to cooperate with each other to generate a position-dependent force in a first direction, which is a translational direction parallel to the direction in which the bar 902 is arranged to move, thus in fig. 7 is to the left and right. In the shown embodiment, the first magnet arrangement 906 and the second magnet arrangement are radially polarized.

The magnetic spring assembly 901 further comprises a clamping mechanism (not shown) for clamping the second magnet arrangement 905 to the holder 904. The clamping mechanism has a clamped state wherein a position of the second magnet arrangement 905 is substantially fixed relative to the holder 904, and a released state wherein the second magnet arrangement 905 is moveable relative to the holder 904 in the first direction. The clamping mechanism may e.g. be embodied similar to the clamping mechanisms in the first to third embodiments of the magnetic spring assembly according to the invention.

In the shown embodiment the second magnet arrangement 905 comprises more permanent magnets than the first magnet arrangement 906. The magnets of the second magnet arrangement 906 are optionally arranged as a Halbach-array. The position- dependent force alternates depending on the position of the first magnet arrangement 906 relative to the first magnet arrangement 905 and has a shape according to a periodic waveform when plotted in function of the position of the bar 902. According to the invention the position of the second magnet arrangement 905 relative to the holder 904 can be adjusted by arranging the clamping mechanism in the released state and moving the second magnet arrangement 905 together with the first magnet arrangement 906. As such the phase of the position-dependent force in function of the position of the bar 902 can be shifted. Optionally the length of the movement of the bar 902 in the first direction is shorter than the length of the second magnet arrangement 905 in the first direction, such that the bar 902 is subjected to the position-dependent force along the entire movement. Optionally the first magnet arrangement 906 may be arranged partially or completely outside of the second magnet arrangement 905 as seen in the first direction to reduce the position-dependent force or even decouple the magnetic spring assembly. Fig. 8a shows a cross-section of a sixth embodiment of a magnetic spring assembly according to the invention, and fig. 8b shows a side view of this embodiment. Like the fourth embodiment shown in fig. 6a and the fifth embodiment shown in fig. 7, this sixth embodiment is a linear magnetic spring assembly, i.e. the first direction being a translational direction. The fifth embodiment is circular symmetrical around the center axis of a bar 602.

The magnetic spring assembly 601 is arranged on a bar 602 which is arranged to be moved in a translational direction, which in fig. 8a is to the left and right. A holder 604 comprises a first magnet arrangement 606 and a second magnet arrangement 605, which are configured to cooperate with each other to generate a position-dependent force in a first direction, which is a translational direction parallel to the direction in which the bar 602 is arranged to move, thus in fig. 8a is to the left and right. In the shown embodiment the first magnet arrangement 606 comprises diametrically polarized ring magnets, and the second magnet arrangement 605 is comprises diametrically polarized cylindrical magnets.

The magnetic spring assembly 601 further comprises a clamping mechanism (not shown) for clamping the second magnet arrangement 605 to the holder 604. The clamping mechanism has a clamped state wherein a position of the second magnet arrangement 605 is substantially fixed relative to the holder 604, and a released state wherein the second magnet arrangement 605 is moveable relative to the holder 604 in the first direction. The clamping mechanism may e.g. be embodied similar to the clamping mechanisms in the first to third embodiments of the magnetic spring assembly according to the invention.

In the show embodiment, both the first 606 and the second magnet arrangement 604 comprise multiple permanent magnets arranged with spatially alternating magnetic polarization. This results in a position-dependent force in function of a position of the first magnet arrangement 606 which is illustrated by a first graph 651 in fig. 8c. As can be seen, multiple peak values of amplitude of the position-dependent force can be achieved during a stroke of the bar 602. In the shown example, the position-dependent force is in the form of a periodic waveform, in this case a sine, and multiple periods are present in a single stroke of the bar 602. Similarly as in the other embodiments, by arranging the clamping mechanism in the releases state, the magnetic spring assembly 601 can be decoupled. The second magnet arrangement 605 can be moved due to the position-dependent force when the first magnet arrangement 606 is moving. By arranging the clamping mechanism back in the clamped state when the second magnet arrangement 605 is in another position, another relation between the position-dependent force and the position of the first magnet arrangement 606 can be accomplished. This is for example illustrated by a second graph 852 shown in fig. 8c. As can be seen, in this case the position-dependent force is shifted in phase. In particular, the phase of the second graph 852 is opposite of the phase of the first graph 851. In the shown embodiment, the second magnet arrangement 605 can also be moved in a second direction, being a rotational direction. The clamping mechanism may e.g. have at least three states, being the clamped state, the released state wherein the second magnet arrangement 605 can move relative to the holder 604 in the translational direction, and a further released state wherein the second magnet arrangement 605 can move relative to the holder 604 in both the translational direction and the rotational direction. Movement in the rotational direction can e.g. be achieved with the position-dependent force by rotating the first magnet arrangement 606, e.g. by rotating the bar 602,. It may also be possible to achieve movement in the rotational direction with a motion conversion mechanism (not shown), which causes the second magnet arrangement 605 to rotate while moving in the translational direction when the clamping mechanism is in the further released state.

By moving the second magnet arrangement 605 in the rotational direction, the amplitude of the position-dependent force can be adjusted, since the cooperation between the first 606 and second magnet arrangement 605 is adjusted. For example, by rotating the second magnet arrangement 605 by 180 degrees, the amplitude changes sign, similar to the 180 degrees phase-shifted graph 852 in fig. 8c. For example, by rotating the second magnet arrangement 605 by 90 degrees, the position dependent force becomes substantially zero for all positions of the first magnet arrangement 606 in the first direction.

It is noted that although in the shown embodiments the holder is a housing to which the second magnet arrangement can be clamped, it is also envisaged that the holder may be a shaft to which the second magnet arrangement can be clamped. In that embodiment the second magnet arrangement could be arranged radially inwards from the first magnet arrangement.

Claims

1. Magnetic spring assembly comprising:

• a holder,

• a first magnet arrangement configured to be moveable relative to the holder in a first direction,

• a second magnet arrangement configured to cooperate with the first magnet arrangement to generate a position-dependent force in the first direction, and

wherein the clamping mechanism has

2. Magnetic spring assembly according to claim 1 , wherein the magnetic spring assembly is configured to be decoupled by arranging the clamping mechanism in the released state.

3. Magnetic spring assembly according to claim 1 or claim 2, wherein, when the clamping mechanism is in the released state, the position-dependent force between the first magnet arrangement and the second magnet arrangement is configured to cause the second magnet arrangement to move when the first magnet arrangement is moving, in the same direction.

4. Magnetic spring assembly to any of the preceding claims, wherein, when the clamping mechanism is in the released state, the position-dependent force exerted the first magnet arrangement is configured to be, during movement of the first magnet arrangement in the first direction, substantially zero.

5. Magnetic spring assembly according to one or more of the preceding claims, wherein the clamping mechanism is configured to clamp the second magnet arrangement to the holder at different positions along the first direction relative to the holder.

6. Magnetic spring assembly according to one or more of the preceding claims, wherein the second magnet arrangement has a first clamped position and a second clamped position, wherein a position of the second magnet arrangement relative to the holder in the first direction is different in the first clamped position than in the second clamped position.

7. Magnetic spring assembly according one or more of the preceding claims, further comprising a motion conversion mechanism, e.g. a screw thread, configured to move the second magnet arrangement relative to the holder in a second direction during a movement of the second magnet arrangement in the first direction, wherein the second direction is different from the first direction.

8. Magnetic spring assembly according to claim 7, wherein the second magnet arrangement has a third clamped position and a fourth clamped position, wherein a position of the second magnet arrangement relative to the holder in the second direction is different in the third clamped position than in the fourth clamped position.

9. Magnetic spring assembly according to claim 7 or claim 8, wherein the clamping mechanism comprises a further released state wherein the second magnet arrangement is moveable relative to the holder in the first direction while substantially maintaining its position relative to the holder in the second direction.

10. Magnetic spring assembly according to one or more of the preceding claims, further comprising a third magnet arrangement configured to cooperate with the first magnet arrangement to generate a second position-dependent force in the first direction.

1 1. Magnetic spring assembly according to claim 10, wherein a position of the third magnet arrangement is fixed relative to the holder.

12. Magnetic spring assembly according to claim 10, further comprising a second clamping mechanism for clamping the third magnet arrangement to the holder or to a second holder,

wherein the second clamping mechanism has

• a clamped state wherein a position of the third magnet arrangement is substantially fixed relative to the holder, and

• a released state, wherein the third magnet arrangement is moveable relative to the holder in the first direction.

13. Magnetic spring assembly according to one or more of the preceding claims, further comprising: • a fourth magnet arrangement configured to be moveable relative to the holder in the first direction, optionally together with the first magnet arrangement,

• a fifth magnet arrangement configured to cooperate with the fourth magnet arrangement to generate a third position-dependent force in the first direction.

14. Magnetic spring assembly according to claim 13, wherein a position of the fifth magnet arrangement is fixed relative to the holder.

15. Magnetic spring assembly according to claim 13, further comprising a third clamping mechanism for clamping the fifth magnet arrangement to the holder or to a third holder,

wherein the third clamping mechanism has

• a clamped state wherein a position of the fifth magnet arrangement is substantially fixed relative to the holder, and

• a released state, wherein the fifth magnet arrangement is moveable relative to the holder in the first direction.

16. Magnetic spring assembly according to one or more of the preceding claims, further comprising at least one electromagnetic coil configured to cooperate with the first magnet arrangement.

17. Magnetic spring assembly according to one or more of the preceding claims, wherein the clamping mechanism comprises a force-closed clamp, e.g. a clutch.

18. Magnetic spring assembly according to one or more of the preceding claims, wherein the clamping mechanism comprises a form-closed clamp.

19. Magnetic spring assembly according to one or more of the preceding claims, wherein the first and second magnet arrangement are an n-pole permanent magnet arrangement, e.g. n being equal to 2, 4, 6 or 20.

20. Magnetic spring assembly according to one or more of the preceding claims, wherein the first direction is a translational direction.

21. Magnetic spring assembly according to one or more of the claims 1-19, wherein the first direction is a rotational direction

22. Motor comprising the magnetic spring assembly according to claim 21 , wherein the first magnet arrangement is arranged to be rotated by rotation of an output shaft of the motor.

23. System for converting unidirectional motion to reciprocating motion and/or vice versa, comprising

• a shaft arranged to be rotated around its longitudinal axis,

• a motion conversion system comprising an end-connector configured to provide a reciprocating motion, and e.g. configured to be connected to an inertial load or an end-effector, wherein the motion conversion system is connected to the shaft in a manner that rotation of the shaft causes the end- connector to move back and forth and/or vice versa,

• the magnetic spring assembly according to claim 21 , the first magnet arrangement being arranged to be rotated by the shaft, and the second magnet arrangement being arranged relative to the holder such that magnetic spring assembly at least partially compensates a position-dependent load torque exerted on the shaft.

24. System comprising at least one magnetic spring according to one or more of the claims 1-21 , wherein the system is one of: a motor, an internal combustion engine, an agricultural vehicle, combine harvester, a cleaning system for a combine harvester, a compressor, a fan, a pump, a gear system, a wind turbine, a printer, a scanner, a lithographic apparatus, a four-bar-linkage system, a slider-crank-mechanism, a cam mechanism, a parallel robot, a parallel manipulator, a pick-and-place robot, a punching machine, a bending machine, an exoskeletons, a humanoid robot.

25. Method for operating a magnetic spring assembly comprising a holder, a first magnet arrangement configured to be moveable relative to the holder in a first direction, a second magnet arrangement configured to cooperate with the first magnet arrangement to generate a position-dependent force in the first direction, and a clamping mechanism for clamping the second magnet arrangement to the holder, the method comprising the following steps:

26. Method according to claim 25, further comprising of a step of using the magnetic spring assembly while the clamping mechanism is in the released state, wherein the first and second magnet arrangement are moving together, wherein the position- dependent force between the first magnet arrangement and the second magnet arrangement causes the second magnet arrangement to move when the first magnet arrangement is moving, in the same direction.

27. Method according to claim 25 or claim 26, further comprising the steps of

• arranging the second magnet arrangement in a first clamped position, and

• arranging the second magnet arrangement in a second clamped position, wherein the position of the second magnet arrangement relative to the holder in the first direction is different in the first clamped position than in the second clamped position.

28. Method according to one or more of the claims 25-27, wherein the step of arranging the second magnet arrangement in a second clamped position, includes the following steps:

• arranging the clamping mechanism in the released state;

• moving the second magnet arrangement together with the first magnet arrangement, wherein the position-dependent force between the first magnet arrangement and the second magnet arrangement causes the second magnet arrangement to move when the first magnet arrangement is moving, in the same direction; and

• then clamping the second magnet arrangement again with the clamping mechanism in the second clamped position.

29. Method according to one or more of the claims 25-28, wherein the magnetic spring assembly is arranged on a bar which is arranged to be moved in a translational direction, the first direction a translational direction parallel to the direction in which the bar is arranged to move, wherein the step of arranging the second magnet arrangement in the second clamped position includes:

• moving the first magnet arrangement partially or completely passed the second magnet arrangement in the first direction while the clamping mechanism is in the clamped state;

• arranging the clamping mechanism in the released state;

30. Method according to one or more of the claims 25-29, wherein the magnetic spring assembly further comprises a motion conversion mechanism, e.g. a screw thread, wherein the method further comprises the following steps:

• arranging the second magnet arrangement in a third clamped position,

• arranging the clamping mechanism in the released state,

• while moving the second magnet arrangement together with the first magnet arrangement in the first direction, moving the second magnet arrangement relative to the holder in a second direction, said moving in the second direction being guided by the motion conversion mechanism, wherein the second direction is different from the first direction,

• arranging the second magnet arrangement in a fourth clamped position, wherein a position of the second magnet arrangement relative to the holder in the second direction is different in the third clamped position than in the fourth clamped position.

31. Method for reversing motion with a magnetic spring assembly comprising a holder, a first magnet arrangement configured to be moveable relative to the holder in a first direction, a second magnet arrangement configured to cooperate with the first magnet arrangement to generate a position-dependent force in the first direction, and a clamping mechanism for clamping the second magnet arrangement to the holder, the method comprising the following steps: