Rotary series elastic actuator

Abstract

A rotary series elastic actuator (100, 100', 100", 100"', 10Oiv, 100v) comprises an output element (10) rotatable about an X axis; an input element (20) also rotatable about the X axis; a motor unit (30) arranged to drive the input element (20) in rotation with respect to the X axis and having a motor shaft and a motor body (31) with an axis coinciding with the X axis; elastic elements (40) arranged on the side of the motor unit (30) interposed between the input element (20) and the output element (10) in such a way that the relative rotation between the input element (20) and the output element (10) is permitted following deformation of the elastic elements (40); and control means comprising sensor elements (51, 52) and at least one control unit, for controlling the motor unit (30) based on the deformation of the elastic elements (40). The arrangement of the elastic elements (40) on the side of the motor unit and therefore outside the actuator unit consisting of the motor unit (30) itself, the input element (20) and the output element (10) allows multiple advantages, including a slim and compact design and ease of positioning the sensors (51, 52).

Description

[0001] ROTARY SERIES ELASTIC ACTUATOR

[0002] TECHNICAL FIELD

[0003]

[0001] . The object of the present invention is a rotary series elastic actuator.

[0004] STATE OF THE ART

[0005]

[0002] . A series elastic actuator, commonly known in the industry by the acronym SEA, is an actuation unit in which the source of motion is connected to the output by means of an elastic element designed to allow precise force control, impact tolerance and energy storage. An SEA can be linear, when the output is a linear motion, or rotary when the output is a rotational motion relative to the axis of the SEA.

[0006]

[0003] . In the field of robotics, in particular in the design of exoskeletons and rehabilitation devices, SEAs are increasingly used and represent a crucial element of the system. The configuration of the SEAs allows precise control of strength, compliance and adaptability, which are essential characteristics in applications where human-machine interaction is predominant. However, despite the advantages offered by the use of SEAs to create joints, significant technical problems remain that must be solved to improve the performance, reliability and integration thereof in medical and rehabilitation devices.

[0007]

[0004] . Firstly, the need to integrate sensors within SEAs adds a level of complexity to the design of exoskeletons and rehabilitation devices. Conventionally, various types of sensors, such as encoders, force sensors and torque sensors, are used to precisely monitor and control the forces and movements applied by the actuators. The sensors are essential to provide real-time feedback to the control system, allowing accurate force control and ensuring user safety. However, integrating the sensors presents problems, including issues related to the accuracy of the sensors, deviations, noise, and the physical integration of the sensors into the compact and often flexible structure of the device.

[0008]

[0005] . Encoders and (angular) position sensors play a crucial role in the performance and control of a SEA by providing precise measurements of actuator position and movement. The encoders, whichcan be rotary or linear, are used to track the movement of the shaft or actuator mechanism, converting this movement into a readable signal that the control system can use for real-time feedback. These data are essential to ensure that the actuator reaches the desired positions and to maintain the correct output force, especially in dynamic activities in which quick adjustments are required. These sensors must be extremely precise and responsive to capture even the slightest changes in position, which is critical for maintaining the precise control needed in applications such as exoskeletons and rehabilitation devices. However, the integration of these sensors presents several challenges. For example, the accuracy of the encoders can be affected by mechanical clearance, vibrations and electromagnetic interference, causing errors in position estimation. Position sensors can also be subject to difficulties with calibration, alignment and maintaining performance under varying environmental conditions.

[0009]

[0006] . Furthermore, the physical integration of these sensors into the structure of the SEA requires careful consideration to minimize their impact on the mechanical properties of the actuator. Improper positioning can affect the natural elasticity and compliance of the system, potentially compromising the ability of the SEA to accurately replicate human-like movements. Designers also face issues related to sensor noise, which can degrade the quality of feedback and, consequently, control performance. To mitigate these difficulties, advanced filtering techniques, sensor fusion methods, and robust calibration procedures are often employed. Improving the integration and reliability of encoders and position sensors is essential to improving the overall performance, safety, and user experience of SEAs in exoskeletons and rehabilitation devices.

[0010]

[0007] . According to another aspect, achieving precise force control is a fundamental challenge in SEA joints, particularly in exoskeletons and rehabilitation devices that must exert controlled forces on the body. In these joints, the elastic elements can cause delays, overloads or instability in force feedback. The sensors must be sensitive, robust and precisely positioned to provide reliable data without interfering with the mechanics of the joints. Addressing these challenges is essential for creating devices that are safe, effective and easy to use.

[0011]

[0008] . The addition to the actuator of an elastic element in series introduces the need for a compromise between force control and response time. Elasticity allows for better shock absorptionand safer interactions, but also reduces actuator bandwidth and slows system response. This is a significant issue in medical devices, where quick and accurate responses to user inputs are necessary for both safety and efficacy. For example, in an exoskeleton that helps lift heavy objects, the system must be able to respond instantly to the user's movements to provide the necessary support. If the actuator response time is too slow, the user may experience delays, which could lead to a lack of synchronization between the user's intent and the exoskeleton's action, potentially causing strain or injury. Furthermore, the slow response time could limit the ability of the device to adapt to rapid changes in motion, reducing the overall usefulness thereof.

[0012]

[0009] . Another key problem in SEAs is the maintenance and quick replacement of elastic components, which are subject to wear due to repeated compression and extension cycles, especially in medical and rehabilitative devices. To ensure safety and functionality, it is essential to design systems that allow for quick and easy replacement of these parts without compromising performance.

[0013]

[0010] . The integration of SEA in exoskeletons and rehabilitation devices also presents challenges related to the human-machine interface. The device must interact fluidly with the human body, adapting to a wide range of user sizes, weights and movement patterns. The compliance provided by SEAs can help to achieve a more natural interaction, but it also complicates the control algorithms needed to manage this interaction. For example, a rehabilitation exoskeleton must be able to adapt to different levels of user capacity, from those with minimal strength to those undergoing recovery and regaining their muscle function. The control systems must be sufficiently sophisticated to handle these variations without requiring extensive calibration or adjustment by the user or physician. Achieving this level of adaptability while maintaining ease of use and ensuring user safety is a significant technical challenge.

[0014]

[0011] . A typical example of rotary SEA that does not effectively solve the problems set forth above is described in the prior art document CN 109262650 A in which a rotary series elastic actuator is presented that shows a motor on whose output shaft a reducer is mounted and on this, coaxial to the motor shaft, an elastic body that comprises an input element in the form of an outer ring and an output element in the form of an inner ring and the elastic elements are arranged in the spacetherebetween. The entire flexible body remains included in the radial dimensions of the motor body but the axial size of the series elastic actuator is high. Furthermore, the elastic elements are boxed between the input element and the output element, whereby they are difficult to access for maintenance and it is difficult to house the sensors.

[0015]

[0012] , Another example of a rotary SEA which does not effectively solve all the problems previously exposed is described in the prior art document WO 2017052223 A1 in which an elastic body for a series elastic actuator is presented. The elastic body comprises a disc-shaped input element with radial protrusions, a disc-shaped output element with corresponding radial protrusions, at least one arcuate elastic element acting between the protrusions of the input element and those of the output element, and an annular casing for enclosing between it and the output element the elastic element and the input element. The motor can be associated with the input element by means of a reducer so that the elastic body is not coaxial with the motor shaft. The elastic element is enclosed within the annular casing which can only be removed after separating the elastic body from the motor or from the relative reducer. Furthermore, the positioning of the sensors is not easy and the dimensions of the actuator are significant.

[0016]

[0013] . Many other types of conventional SEAs are known, however in all of them the elastic elements, usually springs, are positioned between the motor and the output element in a position as close as possible to the axis of the actuator, and boxed inside a casing consisting of or containing the input element and the output element. This configuration allows limiting the radial dimensions of the SEA but does not solve the problems disclosed above.

[0017] SUMMARY OF THE INVENTION

[0018]

[0014] . The object of the present invention is therefore to devise a solution to the shortcomings noted with reference to the prior art.

[0019]

[0015] , In particular, an object of the present invention is to provide a rotary series elastic actuator that allows a constructive configuration in which the elastic compliance function can be defined and adjusted substantially independently with respect to the transmission of the driving torque between the motor unit and the output element, in order to obtain greater design flexibility and a reduction inthe overall axial dimensions of the actuator.

[0020]

[0016] , This and other objects are achieved by means of a rotary series elastic actuator according to claim 1.

[0021]

[0017] , Some advantageous embodiments are the subject-matter of the dependent claims.

[0022]

[0018] . According to an aspect of the invention, a rotary series elastic actuator comprises:

[0023] - an output element rotatable about an X axis;

[0024] - an input element rotatable about the X axis;

[0025] - a motor unit arranged to drive the input element in rotation with respect to the X axis and having a motor shaft and a motor body with an axis coinciding with the X axis;

[0026] - elastic elements interposed between the input element and the output element in such a way that relative rotation between the input element and the output element is permitted following deformation of the elastic elements;

[0027] - control means comprising sensor elements and at least one control unit, wherein the control means are suitable for controlling the motor unit based on the deformation of the elastic elements.

[0028] According to a characteristic aspect of the invention, the elastic elements are arranged on the side of the motor unit at a distance from the X axis greater than the radial dimension of the motor body.

[0029]

[0019] . The arrangement of the elastic elements allows to significantly reduce the axial dimensions of the actuator.

[0030]

[0020] . The elastic elements are not boxed in a closed body comprising the actuator, the input element and the output element, whereby they are easily accessible for maintenance or replacement operations which are therefore very simplified.

[0031]

[0021] . According to an embodiment, the sensor elements of the control means comprise position sensors associated with the motor shaft of the motor unit.

[0032]

[0022] . Advantageously, further sensors, which can be force sensors and / or position sensors, are associated with the elastic elements.

[0033]

[0023] . The position sensors can be comfortably and effectively associated with the motor shaft inthe space that in conventional SEAs is dedicated to housing the elastic elements. In addition to these, or as an alternative, the sensors can be housed at the elastic elements, therefore also on the side of the motor unit, so that both installation and maintenance are simplified.

[0034]

[0024] . According to an embodiment, the output element is an elongated element extending in the radial direction and comprises:

[0035] - means for applying an external load arranged at a distance from the X axis greater than the radial dimension of the motor body;

[0036] - at least one restrain member for said elastic elements placed at a distance from the X axis greater than the radial dimension of the motor body.

[0037]

[0025] , In applications such as an exoskeleton, in which the SEA apparatus is arranged at a shoulder or hip joint, the load is applied at a certain distance from the axis of rotation, for example by means of an anchoring band to an arm or leg. In these applications, the output element is elongated in the radial direction at least up to the distance of application of the load and a restrain member for the elastic elements can advantageously be provided on the output element between the load application means and the motor body.

[0038]

[0026] . Further features and embodiments are specified in the dependent claims.

[0039] BRIEF DESCRIPTION OF THE DRAWINGS

[0040]

[0027] , Further features and advantages of the invention will appear from the following description of preferred embodiments with reference to the accompanying figures, given by way of non-limiting example, wherein:

[0041] - Figure 1 shows in perspective view a series elastic actuator according to a first embodiment of the invention;

[0042] - Figure 2 shows the actuator of Fig. 1 in a further perspective view;

[0043] - Figure 3 shows the actuator of Fig. 1 in frontal view;

[0044] - Figure 4 shows the actuator of Fig. 1 in side view;

[0045] - Figure 5 shows an exploded perspective view of the actuator of Fig. 1;

[0046] - Figure 6 shows the actuator of Fig. 1 associated with an exoskeleton applied to a person, arranged to form a shoulder joint;- Figure 7 shows in perspective view a series elastic actuator according to a second embodiment of the invention;

[0047] - Figure 8 shows the actuator of Fig. 7 in a further perspective view;

[0048] - Figure 9 shows in perspective view a series elastic actuator according to a third embodiment of the invention;

[0049] - Figure 10 shows in perspective view a series elastic actuator according to a fourth embodiment of the invention;

[0050] - Figure 11 shows the actuator of Fig. 10 in a further frontal view;

[0051] - Figure 12 shows in perspective view a series elastic actuator according to a fifth embodiment of the invention;

[0052] - Figure 13 shows the actuator of Fig. 12 in a front view;

[0053] - Figure 14 shows in side view a series elastic actuator according to a sixth embodiment of the invention;

[0054] - Figure 15 shows the actuator of Fig. 14 in a perspective view.

[0055]

[0028] . Of course, in this disclosure reference to "one" embodiment is not necessarily intended to indicate the same embodiment and is to be understood as at least one. Furthermore, for reasons of remaining concise and reducing the total number of figures, a certain figure can be used to illustrate the features of more than one embodiment, not all the elements of the figure can be necessary for a certain embodiment, some features represented in a figure could also be applicable to embodiments represented in other figures or in yet other embodiments.

[0056] DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

[0057]

[0029] . With reference to Figures 1 to 6, a rotary series elastic actuator according to the present invention is indicated overall with 100. The series elastic actuator 100 comprises, mounted in succession in the direction of an X axis, a motor unit 30, an annular flange 70 for supporting the motor unit 30, an input element 20 and an output element 10 comprising means for applying an external load 60. The motor unit 30 comprises a motor body 31 adapted to be made integral with the annular flange 70. A motor shaft keyed to the input element 20 projects through the annularflange 70 from the motor body 31 to drive the input element 20 in rotation with respect to the X axis. The output element 10 is rotatably mounted with respect to the input element 20 between the input element 20 and the output element 10; elastic elements 40 are interposed so that the relative rotation between the input element 20 and the output element 10 is permitted following deformation of said elastic elements 40. As seen in particular in FIGS. 1-5, the compliance elastic modulus comprising the elastic elements (40) is mounted between a portion (21) of the input element (20) and a restrain member (11) of the output element (10) that extend radially with respect to the axis (X). In such a configuration, the compliance elastic modulus is arranged externally with respect to a drive torque transmission chain between the motor unit (30) and the output element (10), so that deformation of the elastic elements (40) occurs outside a drive torque transmission path between the motor unit (30) and the output element (10). In other words, the compliance elastic modulus is not integrated in the kinematic transmission between the motor unit (30) and the output element (10), but is structurally separate therefrom.

[0058]

[0030] . Such an arrangement allows to functionally decouple the transmission of the drive torque from the elastic compliance function, allowing to design and size the elastic modulus independently of the kinematic transmission of the motor unit (30). This also allows to reduce the axial dimensions of the actuator, improve the accessibility to the elastic elements (40) for maintenance purposes and allow an adjustment of the characteristics of elastic compliance without modifying the transmission of the drive torque.

[0059]

[0031] . Along the X axis, a spacer, 16, is interposed between the input element 20 and the output element 10 and a bearing, 17, is arranged between the output element 10 and a mounting plate, 18, adapted to be made integral with the output element 10 so that the motor unit 30, the annular flange 70, the input element 20 and the output element 10 are axially constrained. The series elastic actuator 100 is lastly provided with control means comprising sensor elements, 51, 52 and at least one control unit. The control means are suitable for controlling the motor unit 30 based on the deformation of the elastic elements 40 measured by the sensor elements 51, 52. Advantageously, a position sensor 51 is integrated in a connecting flange between the shaft of the motor unit 30 and the input element 20 which is arranged inside the annular flange 70. Alternatively, or additionally,position and / or force sensors 52 are provided, associated with the elastic elements 40 and therefore arranged externally with respect to the radial dimensions of the motor unit 30. The control unit of the control means can be physically associated with the series elastic actuator 100 but could also be external thereto and associated through wired or wireless power and communication lines.

[0060]

[0032] . The output element 10 is an elongated element extending in the radial direction (perpendicular to the X axis) and comprises the means for applying an external load 60 arranged at a distance from the X axis greater than the radial dimension of the motor unit 30 and at least one restrain member, 11, for the elastic elements 40 also placed at a distance from the X axis greater than the radial dimension of the motor unit 30. The output element 10 is provided with a track, 15, on which a slide, 14, can slide, to which the means for applying an external load 60 are associated so that the distance of these from the X axis can be adjusted. As shown in Figure 6, the series elastic actuator 100 can be used at the shoulder joint in an exoskeleton, E, and the means for applying an external load 60 are band elements for stably associating the output element 10 to the arm of a user.

[0061] Advantageously, the input element 20 comprises a fork portion, 21, which extends radially at a distance from the X axis greater than the radial dimension of the motor unit 30. The prongs, 22, 23 of the fork portion 21 face the restrain member 11 of the output element 10 and the elastic elements 40 consist of a pair of elastic elements, advantageously compression coil springs, 40a, arranged specularly with each other between the restrain member 11 and each of the prongs 22, 23 of the fork portion 21. Advantageously, force sensors 52 are arranged between the prongs 22, 23 and the elastic elements 40. The relative rotation between the input element 20 and the output element 10 causes the deformation of the elastic elements 40 which is measured by the force sensors 52. Advantageously, the sensors 52 are integrated in means for adjusting the preload of the elastic elements 40a.

[0062]

[0033] . With reference to Figures 7 and 8, in one embodiment a series elastic actuator 100’ as described above provides an output element 10 that extends from said X axis in two radially opposite directions so as to identify a first branch, 12 and a second branch, 13. The means for applying an external load 60 are arranged along the first branch 12, while the restrain member 11is arranged along the second branch 13. The input element 20 is rotated by 180° with respect to the configuration of Figures 1 to 6 with the fork portion 21 extending in the same direction as the second branch 13 so that the restrain member 11 is arranged between the prongs 22, 23 with the compression coil springs 40a arranged specularly between the prongs 22, 23 and the restrain member 11.

[0063]

[0034] , With reference to Figure 9, in one embodiment a series elastic actuator 100” as described with reference to Figures 1 to 6 provides elastic elements 40 consisting of bodies in elastic or viscoelastic material.

[0064]

[0035] . With reference to Figures 10 and 11, in one embodiment a series elastic actuator 100”’ as described with reference to Figures 1 to 6 provides elastic elements 40 consisting of torsion springs 40b. The output element 10 comprises a pair of pins, 11b, which provide anchoring supports for the wire-type torsion springs 40b whose operating ends lie on one side on the restrain member 11 and on the other on the force sensor 52 associated with a respective prong 22, 23 of the fork portion 21.

[0065]

[0036] . With reference to Figures 12 and 13, in one embodiment a series elastic actuator 1001V as described with reference to Figures 1 to 6, provides elastic elements 40 consisting of helical traction springs, 40d. The output element 10 comprises specularly arranged protrusions arranged at a radial distance from the X axis which is greater than the radial dimension of the motor unit 30, extending transversely with respect to the elongation direction of the output element 10 itself and form restrain members 11 for the helical traction springs 40d. The input element 20 has an annular shape and on the outer side surface there are, in diametrically opposite positions, two constraining elements, 25, of the helical traction springs 40d which are therefore anchored between the aforesaid constraining means 25 of the input element 20 and the relative restrain member 11 of the output element 10.

[0066]

[0037] , With reference to Figures 14 and 15, in one embodiment a series elastic actuator 100V as described with reference to Figures 1 to 6, provides elastic elements 40 consisting of helical traction springs, 40d. The output element 10 comprises a protrusion extending in the direction of the X axis arranged at a radial distance from the X axis which is greater than the radial dimension of the motorunit 30 and forming a restrain member 11 for the helical traction springs 40d. The input element 20 has an annular shape and on the outer side surface there are, in angularly offset positions, two constraining elements, 25, of the helical traction springs 40d which are therefore anchored between the aforesaid constraining means 25 of the input element 20 and the relative restrain member 11 of the output element 10.

[0067]

[0038] . In all the embodiments illustrated in FIGS. 7-15, regardless of the type of elastic element employed, the compliance elastic modulus is mounted between radially protruding portions of the input element (20) and the output element (10), remaining external to the drive torque transmission chain between the motor unit (30) and the output element (10).

[0068]

[0039] . Of course, the features described with respect to one embodiment can be implemented and combined in a different embodiment.

[0069]

[0040] . In all the embodiments described above, the elastic elements 40, which can be a single elastic element or a plurality of elastic elements, are all peculiarly arranged on the side of the motor unit 30, i.e. at a distance from the X axis which is greater than the radial dimension of the motor unit 30.

[0070]

[0041] . The lateral positioning of the elastic elements 40 radically transforms the configuration of the rotary series elastic actuator 100 with respect to those of the prior art, leading to a significantly thinner and more compact profile of the actuator unit. The lateral positioning of the elastic elements minimizes the length of the actuator 100 in the direction of the X axis, making it more suitable for applications requiring a thin design, such as wearable exoskeletons and rehabilitation devices. This compactness does not compromise performance, but rather increases the versatility of the actuator 100 and its potential for integration in various robotic systems.

[0071]

[0042] , One of the most obvious advantages of an actuator 100 according to the invention is the creation of additional space within the actuator unit, which facilitates the integration of the sensors. The position sensors 51 can be incorporated without problems of space in the area of the motor shaft where the elastic elements are conventionally housed, ensuring an accurate and real-time tracking of the movements of the actuator without interfering with the mechanical structure or operation. This positioning directly improves the responsiveness and accuracy of the controlsystem, essential factors in applications that require precise movement control.

[0072]

[0043] , Furthermore, the design of the actuator 100 according to the present invention allows to easily position the sensors also close to the elastic elements 40. The sensors 52 positioned at the elastic elements 40 can be alternative to the sensors 51 positioned along the X axis, or they can be additional position or force sensors. This separate and accessible positioning of the sensors 52 simplifies calibration and maintenance processes and reduces the danger of sensor interference. The clear separation of the components not only increases the reliability and accuracy of the force measurement, but also improves the overall robustness of the actuator.

[0073]

[0044] . In addition to providing a compact and efficient layout, the actuator 100 offers significant advantages in terms of simplicity of construction and assembly. The simplified design reduces the number of components and connections, which can reduce manufacturing costs and improve actuator reliability, reducing potential failure points. The simplicity of the mechanical layout makes the actuator 100 easier to repair and maintain, an important aspect for long-term use in rehabilitation and support devices.

[0074]

[0045] . Overall, the actuator 100 represents an intelligent and space-efficient solution, which enhances conventional rotary series elastic actuators by optimizing the mechanical design and integration of the sensors. Its unique configuration makes it particularly advantageous for applications that require a combination of compactness, compliance, and precise control, positioning the actuator 100 as a superior choice in the development of advanced exoskeletons, prosthetics, and other robotic devices.

[0075]

[0046] . The described embodiments of a series elastic actuator according to the invention are to be understood as exemplary and non-limiting, therefore, possible variants of detail that may be necessary for technical and / or functional reasons, are considered from now falling within the same protective scope defined by the claims indicated below.

Claims

CLAIMS1. Rotary series elastic actuator (100, 100’, 100”, 100”’, 100iv, 100v) comprising:- an output element (10) rotatable about an X axis;- an input element (20) rotatable about the X axis;- a motor unit (30) arranged to drive the input element (20) in rotation with respect to the X axis, said motor unit (30) having a motor shaft and a motor body (31) with an axis coinciding with said X axis; - elastic elements (40) interposed between the input element (20) and the output element (10) in such a way that relative rotation between the input element (20) and the output element (10) is permitted following deformation of said elastic elements (40);- control means comprising sensor elements (51 , 52) and at least one control unit, said control means being suitable for controlling the motor unit (30) based on the deformation of said elastic elements (40);said series elastic actuator being characterized in that the elastic elements (40) are arranged on the side of said motor unit (30) at a distance from the X axis greater than the radial dimension of the motor unit (30).

2. Series elastic actuator (100, 100’, 100”, 100’”, 10Oiv, 100v) according to claim 1, characterized in that said sensor elements (51, 52) comprise position sensors (51) associated with the motor shaft of said motor unit (30).

3. Series elastic actuator (100, 100’, 100”, 100’”, 100iv, 100v) according to claim 1 or 2, characterized in that said sensor elements (51, 52) comprise position and / or force sensors (52) associated with said elastic elements (40).

4. Series elastic actuator according to one of the preceding claims, characterized in that the output element (10) is an elongated element extending in the radial direction and comprises:- means for applying an external load (60) arranged at a distance from the X axis greater than the radial dimension of the motor unit (30);- at least one restrain member (11) for said elastic elements (40) placed at a distance from the X axis greater than the radial dimension of the motor unit (30).

5. Series elastic actuator (100') according to claim 4, characterized in that said output element (10)extends from said X axis in two radially opposite directions so as to identify a first branch (12) and a second branch (13), said means for applying an external load (60) being arranged along said first branch (12), said restrain member (11) being arranged along said second branch (13).

6. Series elastic actuator (100, 100’, 100”, 100”’) according to claim 4 or 5, characterized in that:- the input element (20) comprises a fork portion (21) extending radially at a distance from the X axis greater than the radial dimensions of the motor unit (30);- said elastic elements (40) are a pair of elastic elements arranged symmetrically with respect to each other between said restrain member (11) and each of the prongs (22, 23) of said fork portion (21).

7. Series elastic actuator (100, 100’, 100”, 100’”) according to the previous claim, characterized in that said elastic elements (40) consist of one of the following: compression coil springs (40a), torsion springs (40b), parts made of elastic (linear) or viscoelastic material (40c).

8. Series elastic actuator (1001V, 100V) according to claim 4 or 5, characterized in that said elastic elements (40) comprise helical traction springs (40d) arranged between said restrain member (11) and said input element (20).

9. Series elastic actuator (100, 100', 100", 100”, 100iv, 100v) according to one of the previous claims, characterized in that it comprises, mounted in succession in the direction of the X axis, said motor unit (30), an annular flange (70) supporting the motor unit (30), said input element (20) and said output element (10); a position sensor (51) being associated with the motor shaft of said motor unit (30) and disposed within said annular flange (70) between said motor unit (30) and said input element

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