The present invention relates to an electromagnetic actuator with variable compliance of the type specified in the preamble of the first claim. It can be used in a robot (industrial, prosthetic or other), or any other device to move two components together by varying the mutual compliance. For example, the variable compliance actuator is suitable for use in applications in which a person may be present inside or near the operating area of the robot/device

(hereinafter identified with the term robot for simplicity). In addition, it can be used in other applications such as servo-actuators, preferably with controlled force feedback.

As is known, one of the most important elements of a robot is the actuator, which, based on the ease of relative movement between the internal components, determined the compliance of the robot itself. In other words, the compliance of an actuator affects the force that the robot exchanges with the external environment during planned and/or accidental interactions.

For example, in order to ensure the correct positioning of the piece, the robot must have a rigid structure, or rather with low compliance, so as to ensure high stability and low vibrations. Furthermore, it is increasingly common for an operator to work near a robot and it is therefore necessary to ensure a high degree of safety. In fact, during the motion, the robot can accidentally hit the operator and therefore it is necessary that the structure of the robot is characterized by a high compliance, or rather that its elasticity is maximum so that the robot can absorb all the energy of impact avoiding injury to the operator and damage to components inside the robotic system.

Currently, two types of actuators can be basically distinguished: the rigid ones and those with variable compliance.

In the early the compliance is not variable during processing. Examples of such first actuators are described in US2009230787 and US4739241. Variable compliance actuators in processing are described in US2012096973 and

ITPI20110057. In these solutions, actuators are presented which use elastic means and/or cables whose tensioning is modified in real-time according to the desired compliance. The known technique described comprises some important drawbacks.

In fact, known actuators with fixed compliance are unsuitable for responding to changing work requirements.

A drawback of those with variable compliance is the construction and/or mechanical complexity which makes the realization expensive and the frequency of failures relevant. In this situation, the technical task underlying the present invention is to devise a variable compliance electromagnetic actuator capable of substantially obviating at least part of the aforementioned drawbacks.

Within the scope of said technical task, an important object of the invention is to obtain an electromagnetic actuator with variable compliance which is simple and easy to construct and therefore resulting economical and reliable.

The technical task and the specified aims are achieved by an electromagnetic actuator with variable compliance as claimed in the attached claim 1.

Preferred technical solutions are highlighted in the dependent claims.

The features and advantages of the invention are clarified below by the detailed description of preferred embodiments of the invention, with reference to the accompanying drawings, wherein: the Fig. 1 shows a sectional perspective view of an electromagnetic actuator with variable compliance, of the triaxial type spherical shape, according to the invention; the Fig. 2 illustrates a transversal view of the actuator of Fig.1; the Fig. 3 is a transversal view of an electromagnetic actuator with variable compliance, of uniaxial type and cylindrical shape, according to the invention in a first embodiment; and the Fig. 4 represents a transversal view of an electromagnetic actuator with variable compliance, of uniaxial mouse and cylindrical shape, according to the invention in a second embodiment.

In the present document, the measurements, values, shapes and geometric references (such as perpendicularity and parallelism), when associated with words like “about” or other similar terms such as “approximately" or “substantially”, are to be considered as except for measurement errors or inaccuracies due to production and/or manufacturing errors, and, above all, except for a slight divergence from the value, measurements, shape, or geometric reference with which it is associated. For instance, these terms, if associated with a value, preferably indicate a divergence of not more than 10% of the value. Moreover, when used, terms such as “first”, “second”, “higher”, “lower”, “main” and

“secondary” do not necessarily identify an order, a priority of relationship or a relative position, but can simply be used to clearly distinguish between their different components.

Unless otherwise specified, as results in the following discussions, terms such as

“treatment”, “computing”, “determination”, “calculation”, or similar, refer to the action and/or processes of a computer or similar electronic calculation device that manipulates and/or transforms data represented as physical, such as electronic quantities of registers of a computer system and/or memories in, other data similarly represented as physical quantities within computer systems, registers or other storage, transmission or information displaying devices.

The measurements and data reported in this text are to be considered, unless otherwise indicated, as performed in the International Standard Atmosphere ICAO

(ISO 2533:1975).

With reference to the drawings, electromagnetic actuator with variable compliance according to the invention is globally indicated with the number 1.

It is, like any motor, capable of handling external objects. For example, the actuator 1 can create a joint, for example spherical, applicable inside robots (for example robotic prostheses) in such a way as to define a controllable coordination.

In addition, or alternative, the actuator 1 can be used in non-robotic applications such as servo-actuators preferably with controlled force feedback.

In this regard, the actuator 1 comprises a motor shaft 2 defining the motion output from the actuator 1 and in particular an output axis 2a of the motion. Substantially, therefore, the motor shaft 2 connects to external objects along the output axis 2a in such a way that the external object, for example a phalanx of a robotic hand (alternatively an elbow, a knee or other joint), is integral with the motor shaft 2 with respect to the output axis 2a.

In detail, the motor shaft 2 defines the output of a rotary motion of the axis of the output axis 2a.

The motor shaft 2 is, for example, an elongated element extending along the output axis 2a. The actuator 1 also comprises a rotor 3.

The rotor 3 is preferably constrained, suitably solidly, to the motor shaft 2. In particular, the rotor 3 directly moves the motor shaft 2. Therefore, the motor shaft 2 can be separated and constrained, whether in a resolvable way or not, to the rotor 3, or it can be in one piece with it.

The rotor 3 can be moved in response to the application of a first magnetic field.

Therefore, it preferably comprises, at least partially, a ferromagnetic layer 300.

Said ferromagnetic layer is made of ferromagnetic material suitably having magnetic permeability at least equal to 500 and in detail to 1000 (such as the iron). The rotor 3 is naturally adapted to cooperate with at least one stator.

In detail, the actuator 1 preferably comprises a first stator 4 and a second stator 5.

The stators 4 an-d 5 can be distinct and separate, or they can be portions of the same stator.

Preferably, moreover, the first stator 4 and the second stator 5 make a chamber 45 inside which the rotor 3 is at least partially housed.

In particular, the first stator 4 can define a housing compartment for the second stator 5 and the rotor 3 and the chamber 45 can be a portion of said housing compartment. The first stator 4 can define a closed or preferably partially closed casing with a suitably open sector and closed in detail by the rotor 3. The first stator 4 can define the external profile of the actuator 1.

Alternatively, the second stator 5 can define a housing compartment for the first stator 4 and the rotor 3 and the chamber 45 can be a portion of said housing compartment. In this case, the second stator 5 can define a closed or preferably partially closed casing with a suitably open sector and closed in detail by the rotor 3. The second stator 5 can define the external profile of the actuator 1. Preferably, the first stator 4 comprises a first wall 40, while the second stator 5 comprises a second wall 50.

The first wall 40 and the second wall 50 delimit, at least partially, at least one chamber 45 and preferably a single chamber 45. The chamber 45 is preferably a closed or partially closed casing, for example with an open sector and closed with the rotor 3, preferably including at least part of the rotor 3.

The rotor 3 comprises a partition wall 30.

The partition wall 30 is preferably dividing the chamber 45 into a first portion 45a and a second portion 45b. The partition wall 30 comprises the ferromagnetic layer 300. It should be noted that the rest of the stator can be made of any other material.

The first portion 45a and the second portion 45b can be parts of the chamber 45, that is, actual sub-chambers, or they can also define, one or both, a slot of considerably reduced thickness. The first portion 45a is defined between the first wall 40 and the partition wall 30, while the second portion 45b is defined between the second wall 50 and the partition wall 30.

Preferably, the partition wall 30 is arranged almost in contact with the first wall 40.

Therefore, preferably, in a preferred embodiment, the first portion 45a is substantially a slot arranged between part of the rotor 3 and the first stator 4 defining a thickness minimum mainly suitable for allowing the clearance between rotor 3 and the first stator 4.

Preferably the second portion 45b occupies most of the chamber 45 and is a real sub-chamber of dimensions almost similar to the chamber 45, as shown for example on the Figs. 1-2. The walls 30, 40, 50 can also define a plurality of shapes and sizes. In particular, the shape of the walls can determine the operation of the actuator 1 which can be, for example, uniaxial, biaxial or even triaxial.

In a preferred embodiment, shown in the Figs. 1 -2, the walls 30, 40, 50 define spherical bodies coaxial and mutually concentric with respect to a reference center

(better described below).

Furthermore, preferably, one of the first stator 4 and the second stator 5 contains at least part of the rotor 3. In turn, preferably, the rotor 3 contains at least part of the other between the second stator 5 and the first stator 4. In particular, in the Figs. 1-2, a configuration is shown in which the second stator 5 encloses the rotor 3 and the rotor 3 partially encloses the first stator 4.

Alternatively, the walls 30, 40, 50 could define cylindrical bodies coaxial and centered with respect to the main rotation axis 2a. Also in this case, one between the first stator 4 and the second stator 5 can contain at least part of the rotor 3 and the latter could contain, in turn, at least part of the other between the second stator

5 and the first stator 4.

In the first embodiment of Fig. 3, the first stator 4 includes part of the rotor 3 and the rotor 3 includes the second stator 5. In contrast, in the alternative embodiment of Fig. 4, the second stator 5 includes part of the rotor 3 and the rotor 3 includes the first stator 4.

Preferably, in any case, the first stator 4 is configured to generate the first magnetic field, suitable for moving the rotor 3. Said first magnetic field can be proportional to a first electrical signal.

In particular, the first stator 4 can be connected to a first electric generator suitably with non-direct current preferably with a modulable and more preferably alternating wave form. Of course, the first stator 4 can also include the first electrical generator.

In any configuration, preferably, the first electric generator is suitable for determining the first electric signal, or to generate the first magnetic field. It is nondirect current preferably with a modulable and more preferably alternating wave form.

In order to convert the electric signal into a magnetic signal, preferably, the first stator 4 includes at least a first coil 41 housed within the first wall 40. The first coil

41 is, therefore, preferably connected to the first generator and suitable for forming the first magnetic field.

Preferably (see Figs. 1 -2) the first stator 4 includes a plurality of first coils 41.

These first coils 41 housed in distinct and separate positions of the wall 40 and can be independently controlled/powered in such a way that the first magnetic field can move (in detail to rotate) the rotor 3 and therefore the motor shaft 2 with respect to the stators 4 and 5 around a plurality of rotation axes also distinct from the output axis 2a.

In this way, in fact, the motor shaft 2 and therefore the output axis 2a rotate with respect to the stators 4 and 5 and therefore to an absolute reference system. In conclusion, it is thus possible to rotate the same output axis 2a around the axes of rotation.

Even more in detail, the first coil 41 are preferably concentric with respect to at least one reference axis (for example one in the case of a single-axis actuator) and capable of being only partially activated so as to control the rotation of the rotor 3 and therefore the motor shaft 2 with respect to at least one rotation axis suitably coincident with said reference axis. Alternatively, the first coils 41 are preferably concentric with respect to a reference center and suitable for being partially activated so as to control the rotation of the rotor 3 and therefore the motor shaft 2 with respect to at least one rotation axis substantially passing through said center of reference. Furthermore, optionally, the first coils 41 can be activated along a spherical zone, or circumference, concentric (and suitably barycentric) with respect to said axis/center of reference so as to rotate the rotor 3 and therefore the motor shaft 2 with respect to the axis of rotation by arranging the output axis 2a perpendicular to the spherical zone, or circumference. The second stator 5 is also preferably configured to generate a second magnetic field in proportion to a second electrical signal.

The second electrical signal, however, is preferably determined by a second electric generator suitably direct current conveniently of modulable amplitude. The second generator can also be external to the second stator 5 or included in it. Furthermore, the second stator 5 also comprises at least a second coil 51.

The second coil 51 is preferably housed in the second wall 50. Furthermore, it is preferably connected to said second generator and suitable for forming the second magnetic field.

Preferably (see Figs. 1-2) the second stator 5 comprises several second coils 51. These second coils 51 are housed in distinct and separate positions of the second wall 50 and can be independently control lable/feedable.

Even more in detail, the second coils 51 are preferably concentric with respect to at least one reference axis (for example one in the case of a uniaxial actuator) and capable of being only partially activated. Alternatively, the second coils 51 are preferably concentric with respect to a reference center and suitable for being only partially.

Optionally, the second coils 51 can be activated along a spherical zone, or circumference, concentric (and suitably barycentric) with respect to said axis/center of reference.

Unlike the first stator 4, which is suitable for interacting with the rotor 3, the second stator 5 is preferably suitable for interacting with a magnetorheological fluid 6.

In fact, preferably, the actuator comprises at least one magnetorheological fluid 6 housed in at least part of the at least one chamber 45 and configured to oppose the motion of the rotor 3 appropriately proportionally (preferably in the opposite way) to its compliance.

In particular, preferably, the magnetorheological fluid 6 is housed in the second portion 45b.

Therefore, while the first stator 4 substantially defines the driving force of the actuator 1 , the magnetorheological fluid 6 and, in particular its viscosity, define the compliance of the actuator 1.

The magnetorheological fluid 6, however, not only passively reacts to the movement of the rotor 3, but can preferably be activated on command.

In fact, the second stator 5 generates the second magnetic field in such a way as to vary, on command, the viscosity of the magnetorheological fluid 6.

The second magnetic field is proportional, preferably inversely, to the compliance of the actuator 1.

The first magnetic field is proportional, preferably directly, to the torque generated by the actuator 1. Preferably, therefore, since the first stator 4 and the second stator 5 are adapted to interact with different parts of the actuator 1 and with different functions, the wall

30, preferably, magnetic isolates the first portion 45a and the second portion 45b.

Naturally, with that it is not intended that the partition wall 30 is configured to completely isolate the first stator 4 and the second stator 5, but that the partition wall 30 isolates the first stator 4 and the second stator 5 at least where interposed between them. For example, in the case of several first coils 41 placed concentric with respect to said reference center and partially activated, the partition wall 30 magnetically isolates the first stator 4 from the second stator 5 at least in correspondence with said first activated coils 41.

For this purpose, the partition wall 30 comprises a conductive layer 301. In detail it comprises and preferably consists of the ferromagnetic layer 300 and the conductive layer 301.

The conducting layer 301 faces to the first stator 4. In particular, the conducting layer 301 is preferably suitable for allowing the first magnetic field to generate induced currents capable of allowing the motion of the rotor 3 to be controlled.

The conductive layer 301 can be made of aluminum, cooper or other electrically similar material.

Preferably the conducting layer 301 faces the first wall 40 and the ferromagnetic layer 300 faces the second wall 50.

In order to avoid interference between the first and second magnetic fields, the ferromagnetic layer 300 is such as to allow the field lines of said magnetic fields to close on said ferromagnetic layer 300 without interfering with each other. It can therefore have a thickness substantially comprised between 0.1 cm and 2 cm and in detail between 0.5 ad 1 cm. In some case, the actuator 1 may comprise sealing means 7 suitable for avoiding a passage of magnetorheological fluid 6 between the portions 45a and 45b.

The sealing means 7 are arranged at least between the partition wall 30 and the second wall 50 in such a way that the second portion 45b is watertight. Sealing means 7 of this type may include, for example, elastomeric elements such as O-ring, gaskets and other similar elements.

Finally, it should be noted that the actuator 1 can provide an access pipe to the housing compartment for supply wires of at least one of the at least one first coil

41 and the at least one second coil 51. The operation of the actuator 1 previously described in structural terms is as follows.

Depending on the application of the first magnetic field and the second magnetic field, on the basis of the main and secondary electrical signals, it is possible to determine both the driving force, in particular the torque, and the compliance of the rotor motor shaft 2.

The actuator 1 according to the invention achieves, therefore, important advantages.

In fact, the actuator 1 allows you to completely control the braking means which are, for the actuator, active means and controllable by the user. Furthermore, the use of magnetorheological fluid 6 allows you to integrate both functions in a small actuator. This advantage has considerable prominence especially when the actuator is applied above robotic structures such as protheses.

In conclusion, all the functions are implemented without overly complicating the structure of the actuator 1 with obvious economic and reliability advantages. Another fundamental advantage lies in the fact that, thanks to the particular arrangement and/or possibility of independent feeding of the first coils 41 and/or of the second coils 51 , the actuator 1 , for example in the case of spherical actuator 1 , allows to select the compliance and/or the torque output on one or more axes. The invention is susceptible of variants falling within the scope of the inventive concept defined by the claims.

For example, as already mentioned, the actuator can be mono, bi or triaxial depending on the configurations adopted by the walls 30, 40, 50 while falling within the same inventive concept. In this context, all the details can be replaced by equivalent elements and the materials, shapes and dimensions can be any.