EP3334572A1 - Exosuit - Google Patents

Exosuit

Info

Publication number
EP3334572A1
EP3334572A1 EP16835544.4A EP16835544A EP3334572A1 EP 3334572 A1 EP3334572 A1 EP 3334572A1 EP 16835544 A EP16835544 A EP 16835544A EP 3334572 A1 EP3334572 A1 EP 3334572A1
Authority
EP
European Patent Office
Prior art keywords
cable
spool
segment
exosuit
limb
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP16835544.4A
Other languages
German (de)
French (fr)
Other versions
EP3334572A4 (en
Inventor
Leonardo CAPPELLO
Lorenzo Masia
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Universita degli Studi di Genova
Fondazione Istituto Italiano di Tecnologia
Nanyang Technological University
Original Assignee
Universita degli Studi di Genova
Fondazione Istituto Italiano di Tecnologia
Nanyang Technological University
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to SG10201506263R priority Critical
Application filed by Universita degli Studi di Genova, Fondazione Istituto Italiano di Tecnologia, Nanyang Technological University filed Critical Universita degli Studi di Genova
Priority to PCT/SG2016/050383 priority patent/WO2017026943A1/en
Publication of EP3334572A1 publication Critical patent/EP3334572A1/en
Publication of EP3334572A4 publication Critical patent/EP3334572A4/en
Pending legal-status Critical Current

Links

Classifications

    • BPERFORMING OPERATIONS; TRANSPORTING
    • B25HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
    • B25JMANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
    • B25J9/00Programme-controlled manipulators
    • B25J9/10Programme-controlled manipulators characterised by positioning means for manipulator elements
    • B25J9/104Programme-controlled manipulators characterised by positioning means for manipulator elements with cables, chains or ribbons
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B25HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
    • B25JMANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
    • B25J9/00Programme-controlled manipulators
    • B25J9/0006Exoskeletons, i.e. resembling a human figure
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02PCONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P3/00Arrangements for stopping or slowing electric motors, generators, or dynamo-electric converters
    • H02P3/06Arrangements for stopping or slowing electric motors, generators, or dynamo-electric converters for stopping or slowing an individual dynamo-electric motor or dynamo-electric converter
    • H02P3/08Arrangements for stopping or slowing electric motors, generators, or dynamo-electric converters for stopping or slowing an individual dynamo-electric motor or dynamo-electric converter for stopping or slowing a dc motor
    • H02P3/14Arrangements for stopping or slowing electric motors, generators, or dynamo-electric converters for stopping or slowing an individual dynamo-electric motor or dynamo-electric converter for stopping or slowing a dc motor by regenerative braking
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02PCONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P3/00Arrangements for stopping or slowing electric motors, generators, or dynamo-electric converters
    • H02P3/06Arrangements for stopping or slowing electric motors, generators, or dynamo-electric converters for stopping or slowing an individual dynamo-electric motor or dynamo-electric converter
    • H02P3/18Arrangements for stopping or slowing electric motors, generators, or dynamo-electric converters for stopping or slowing an individual dynamo-electric motor or dynamo-electric converter for stopping or slowing an ac motor

Abstract

An exosuit for facilitating movement of a limb comprising an upper segment and a lower segment pivotally connected via a joint, the exosuit comprising: a soft frame configured to be worn by a user over the limb; an actuator attached to the soft frame, the actuator comprising a spool rotatable in a first direction and in a second direction, the spool connected to a shaft of a motor configured to rotate the spool; a first cable having a part of the first cable wound about a first portion of the spool, the first cable extending from the spool along the soft frame, the first cable terminating at a front of the lower segment to cause flexion of the limb when the first cable is wound onto the spool during rotation of the spool in the first direction; a second cable having a part of the second cable wound about a second portion of the spool, the second cable extending from the spool along the soft frame, the second cable terminating at a back of the lower segment to cause extension of the limb when the second cable is wound onto the spool during rotation of the spool in the second direction.

Description

EXOSUIT

FIELD

This invention relates to a wearable device for facilitating movement of a limb. More specifically, this invention is applicable to enable/facilitate movement of the upper limbs and may be adapted for use with the lower limbs using the same transmission technology.

BACKGROUND

Daily living activities require adequate upper limb muscular force and neural control. Persons with neuromotor disabilities arising from various conditions such as muscular atrophies, neural damages, and other disorders and degenerative conditions have difficulty performing such activities. This may give rise to psychological distress in such persons who become reliant on others to carry out basic activities. Where family members are unable to assist, professional help can be costly. Technological solutions include devices that employ actuated frames, i.e., powered exoskeletons, to assist and empower a user. These devices comprise rigid or semi-rigid structures that the user wears. These structures bear the loads and guide the user to perform desired motions. However, such devices are bulky, heavy and uncomfortable, in addition to limiting the biomechanics of the user and producing unnatural postures and movements. Most of the known solutions are unsuitable for out-of-the-laboratory applications due to these problems.

In addition to not matching each user's particular needs, most of the known solutions are not energy efficient: exoskeletons are meant to be powered whenever they are worn, resulting in high power consumption and hence limited battery life.

SUMMARY

The exosuit disclosed in the present application provides better ergonomics and prevents unnatural motion. In terms of energy efficiency, a soft exosuit also results in lower energy consumption.

According to a first aspect, there is provided an exosuit for facilitating movement of a limb comprising an upper segment and a lower segment pivotally connected via a joint, the exosuit comprising: a soft frame configured to be worn by a user over the limb; an actuator attached to the soft frame, the actuator comprising a spool rotatable in a first direction and in a second direction, the spool connected to a shaft of a motor configured

l to rotate the spool;a first cable having a part of the first cable wound about a first portion of the spool, the first cable extending from the spool along the soft frame, the first cable terminating at a front of the lower segment to cause flexion of the limb when the first cable is wound onto the spool during rotation of the spool in the first direction; a second cable having a part of the second cable wound about a second portion of the spool, the second cable extending from the spool along the soft frame, the second cable terminating at a back of the lower segment to cause extension of the limb when the second cable is wound onto the spool during rotation of the spool in the second direction. The second portion of the spool may have a larger diameter than the first portion of the spool.

The actuator may further comprise a first pair of rollers and a second pair of rollers, the first cable passing between the first pair of rollers from the spool to the lower segment and the second cable passing between the second pair of rollers from the spool to the lower segment, the first pair of rollers and the second pair of rollers each comprising a monodirectional roller and a conventional roller that is free to rotate in both directions; wherein each monodirectional roller is free to rotate only in a direction to feed the first cable or the second cable from the spool, and wherein each monodirectional roller is locked from rotating when the first cable or the second cable is being wound onto the spool.

The first cable may be connected to the front of the lower segment via a first resilient element at a first end effector attached to the lower segment, and wherein the second cable may be connected to the back of the lower segment via a second resilient element at a second end effector attached to the lower segment.

The first and second resilient elements may each comprise a compression spring. The first and second cables may extend along the soft frame through first and second Bowden sheaths attached to the soft frame respectively, the first Bowden sheath terminating at the front of the first segment and the second Bowden sheath terminating at the back of the first segment. The actuator may further comprise an electromechanical clutch connected to the shaft of the motor, the electromechanical clutch configured to apply a holding torque on the first and second cables when the electromechanical clutch is activated to keep the joint at a stationary angle.

The motor may be connected to a battery via a regenerative braking circuit configured to recharge the battery during movement of the motor caused by rotation of the spool when natural movement of the limb pulls on at least one of the first and second cables to unwind the at least one of the first and second cables from the spool.

Components of the actuator may be housed in a housing attached to the soft frame and configured to be worn on the back of the user.

The exosuit may further comprise sensors configured to detect at least one of: directional movement of the limb, acceleration of the upper segment, acceleration of the lower segment, orientation of the upper segment, orientation of the lower segment, force in the limb, electrical activity of muscles in the limb, and vibration of muscles in the limb for providing feedback to a controller of the actuator to perform at least one of: detect motion intention of the user, control motion trajectory of the limb, and trigger actuation of the exosuit. The exosuit may further comprise tension sensors configured to detect amount of force applied to the first cable and the second cable for providing feedback to a controller of the actuator.

The exosuit may further comprise force sensors configured to detect occurrence of contact of the soft frame with an external environment for providing feedback to a controller of the actuator to modulate force applied by the exosuit.

BRIEF DESCRIPTION OF FIGURES

In order that the invention may be fully understood and readily put into practical effect there shall now be described by way of non-limitative example only exemplary embodiments of the present invention, the description being with reference to the accompanying illustrative drawings.

Fig. 1 is a schematic illustration of a front and back view of an exemplary embodiment of an exosuit of the present invention

Fig. 2 is a perspective cross-sectional view of an exemplary actuator of the exosuit of Fig.

1. Fig. 3 is a functional schematic of an exemplary actuator of the exosuit.

Fig. 4 is a schematic illustration of a feeder assembly comprising a one-way clutch and roller pair engaging a cable that is fed to and from a spool.

Fig. 5 is a perspective view of an exemplary feeder system of the actuator.

Fig. 6 shows side, front and back view illustrations of a soft frame of the exosuit worn on a user's arm.

Fig. 7 is a schematic back view of a preferred embodiment of the exosuit.

Fig. 8 is a schematic front view of the exosuit of Fig. 7.

Fig. 9 is two photographic images of a series elastic element at an end effector of the

cable.

Fig. 10 is a schematic illustration of a flexor tendon with elastic element in series.

Fig. 11 is a graph of theoretical torsional stiffness [Nm/rad] in the range θ = [2α - π],

corresponding to a flexion angle decreasing from 26° to 0°.

Fig. 12 is an illustration of agonist/antagonist actuation of a joint taken from A

Mathematical Introduction to Robotic Manipulation by R. M. Murray.

Fig. 13 is a graph of cable elongation and difference against joint angle for a same spool diameter for both extensor and flexor cables.

Fig.14 is a graph of cable elongation and difference against joint angle where spool

diameter for the extensor cable is corrected by a factor equal to pendency of a first-order fitting curve of elongation of the flexor cable in a joint range of 0° to 90°. Fig. 15 is a photograph of a simulation of the actuator on a test bench.

Fig. 16 is a graph of a sine-chirp trajectory following test.

Fig. 17 is an exemplary regenerative circuit illustrating current flow during forward

motoring.

Fig. 18 is the regenerative circuit of Fig. 17 illustrating current flow during forward braking.

DETAILED DESCRIPTION

Exemplary embodiments of the exosuit 99 will be described below with reference to Figs. 1 to 18. The same reference numerals are used throughout the figures to denote the same or similar parts among the various embodiments.

As shown in Fig. 1 , the exosuit 99 comprises an actuation means or actuator 100 and a soft frame 200. The exosuit 99 is described below with reference to being implemented on an upper limb of a user's body (arm), the limb comprising an upper segment 1 1 (upper arm) and a lower segment 12 (forearm) pivotally connected via a joint 10 (elbow). The exosuit 99 may also be adapted to be implemented on a lower limb or leg for use to facilitate movement of the lower limbs, or any two body parts connected pivotally via a joint 10.

Actuation

In general, the actuator 100 as shown in cross-section in Fig. 2 and schematically illustrated in Fig. 3 comprises a housing 80 in which are provided conventional actuator means such as an electromechanical DC motor 20 which may be coupled with a reduction means 30 such as gear reduction, belt reduction, etc. The motor 20 is configured to rotate in a first direction and a second direction, and is preferably powered by a battery 22. The reduction means 30 are connected to a spool 40 around which a set of at least two first and second cables 51 , 52 are coiled (referred to as the motor assembly). The spool 40 is rotatable in the first direction and in the second direction by the motor 20. At least one first cable 51 is coiled clockwise about a first portion of the spool 40 and at least one second cable 52 is coiled counter-clockwise about a second portion of the spool 40 with respect to the spool 40, so that the first and second cables 51 , 52 act in agonist-antagonist fashion respectively whenever the spool 40 rotates in either the first direction or the second direction, in a fashion similar to the tendons in a human arm. The actuator 100 further comprises a feeder system 60 in the housing 80 for the first and second cables 51 , 52 to prevent slack in the first and second cables 51 , 52 and to prevent the first and second cables 51 , 52 from uncoiling from the spool 40. At least two Bowden sheaths 81 , 82 that are connected with the soft frame 200 are provided, inside which the first and second cables 51 , 52 are routed, and at least two elastic elements 91 , 92 such as metallic springs, gas springs, composite springs etc. are placed in proximity of the joint 90 in series with the Bowden transmission comprising the Bowden sheaths 81 , 82 and the first and second cables 51 , 52 respectively. A locking system such as an electromechanical clutch, a brake, etc. 25 is provided in parallel with the motor axis (referred as the clutch assembly) in the housing 80, before the gear reduction 30. A possible embodiment of the motor assembly comprises a brushless DC motor 20 without gearhead reduction coupled with an epicyclical gear (reduction ratio 5: 1) 30 as the reduction means 30. The spool 40 is placed after the reduction gear 30, relative to the motor 20. The planets of the gear 30 drive the spool 40 around which the tendon first and second cables 51 , 52 are coiled. In the feeder system or assembly 60, a monodirectional roller (e.g. a one-way clutch) 61 , 62 and a conventional roller 71 , 72 that is free to rotate in both directions are provided as a pair of rollers P1 (comprising monodirectional roller 61 and conventional roller 71) or P2 (comprising monodirectional roller 62 and conventional roller 72), for each cable 51 or 52 respectively, as shown in Fig. 4. In an exemplary embodiment, each cable 51 , 52 passes from the spool 40 between the pair of rollers P1 , P2 and is routed into a Bowden sheath 81 , 82 to be connected to the lower segment 12 through a serial spring 91 , 92 respectively, as illustrated in Fig. 3. As can be seen in Figs. 3 and 5, the first cable 51 is fed from one side of the spool 40 between the first pair of rollers P1 while the second cable 52 is fed from a diametrically opposite side of the spool 40 between the second pair of rollers P2.

The monodirectional rollers 61 , 62 are oriented such that their free-to- rotate direction is in the feeding of their respective first and second cables 51 , 52 from the spool 40 (as indicated by the curved arrows in Figs. 3 to 5), while they are locked from rotating when their respective first and second cables 51 , 52 are being coiled back or wound onto the spool 40. This prevents any slack in the first and second cables 51 , 52 after the feeder propagates inside the mechanism: the first and second cables 51 , 52 are hence always properly coiled around the spool 40 even if the first and second cables 51 , 52 are slack. The function of each pair of rollers P1 , P2 thus presents a near-zero friction when the cable 51 or 52 is uncoiled by the spool 40 since the monodirectional roller 61 , 62 is free to rotate in the feed direction. At the same time, the pairs of rollers P1 , P2 provide a certain amount of friction when the cable 51 or 52 is coiled back onto the spool 40 since the monodirectional roller 61 or 62 is locked and the cable 51 or 52 slides with respect to the monodirectional roller 61 or 62 respectively. This friction is enough to prevent the slack cable 51 or 52 to pass the feeder 60, thereby ensuring that the cable 51 , 52 is neatly wound onto the spool 40 when it is coiled back, as the axial force exerted by the slack cable 51 or 52 is not sufficient to overcome the static friction with the monodirectional roller 61 or 62 respectively. Such friction however is little enough to be easily overcome by the action of the motor 20 when it is rotating the spool 40 and coiling the cable 51 or 52 onto the spool 40. In order to increase such static friction, a layer of synthetic coating can be added on the metallic surface of the monodirectional rollers 61 , 62 if desired or necessary.

An exemplary embodiment of the feeder assembly 60 comprising the pairs of rollers P1 , P2 is shown in Fig. 5. As can be seen, the exemplary feeder assembly 60 comprises three kingpins 63, 64, 65: a central kingpin 63 holding the two monodirectional rollers 61 , 62 along a same first rotational axis L1 , and two side kingpins 64, 65, on the sides holding one conventional roller 71 , 72 each on a second rotational axis L2 and a third rotational axis L3 respectively, the central kingpin 63 being positioned between the two side kingpins 64, 65. The second and third rotational axes L2, L3 are thus spaced apart from the first rotational axis L1 , and are preferably on a same plane as the first rotational axis L1. The spool 40 is on a same rotational axis Lx as the motor shaft 21. The motor shaft axis Lx is spaced apart from the first rotational axis L1 of the central kingpin 63 and is on a different plane from the second and third rotational axes L2, L3. The shaft 21 of the motor 20 passes through the spool 40 and is coupled with the electromechanical (EM) clutch 70, as can be seen in Fig. 2. The clutch assembly comprises the EM clutch 70, a frame or the housing 80 of the actuator 100 which holds the EM clutch 70 and a kingpin 72 anchored to the housing 80 by which the EM clutch 70 engages the frame 80. When the clutch 70 is active, the torque applied by the motor shaft 21 is transferred to the housing 80 via the clutch 70 (instead of transferred to the spool 40), as well as to any external force acting on the first and second cables 51 , 52.

During normal operation, the clutch 70 is disconnected, hence the motor 20 torque is transferred after the reduction stage 30 to the spool 40. The spool 40 pulls one cable 51 (agonist tendon) to coil around the spool 40, and releases the other cable 52 (antagonist tendon) from the spool 40. Such torque is transferred to the limb through the first and second cables 51 , 52 routed by the Bowden sheaths 81 , 82 respectively.

When the joint position needs to be stationary, instead of exploiting the DC motor 20 to apply a holding torque on the first and second cables 51 , 52, the electromechanical clutch/brake 70 can be deployed. It 70 is preferably placed before the reduction stage 30 so that the necessary torque that is required is minimized. The electromechanical clutch 70 is preferred to a motor for its low power consumption. Soft Frame

To transfer the torque generated by the actuation 100 to the limb 11 , 12, a soft frame 200 is used. It 200 is made of different fabrics (stretchable and non-stretchable with different strength/flexibility) in order to maximize the durability, the flexibility and the ergonomics whilst retaining the ability to bear the loads and to transmit power to the limbs 1 1 , 12. Variations of the design and fabric types are possible to customize the design for different environmental and working conditions. For example, dry fit material may be used in hot and humid climates. An example of a possible implementation of the soft frame 200 is shown in Fig. 6, in which a strong unstretchable fabric 210 is shown striped in black, a strong stretchable fabric 220 is shown in dark grey, a soft stretchable fabric 230 is shown in light grey, and a rigid elbow protection 240 is shown in black. A window 250 may be provided in the garment 99 to allow access to the skin to place EMG electrodes or other sensors if desired.

The strong and unstretchable fabric 210 is used where the application points of the tendons (mounting/securing point of the first and second cables 51 , 52) are located (i.e. in direct proximity of joints). It is meant to distribute the action of the tendons 51 , 52 to the limb 1 1 , 12. Being unstretchable and strapped snugly to the body part, it also prevents any undesired and unpredictable deformation caused by the forces applied by the tendons 51 , 52. Its use is also intended to hold the tendons 51 , 52 in position with respect to the user's limb 11 , 12 and hence to avoid undesired misplacements which may lead to system failure.

The strong yet stretchable fabric 220 is used for the other parts and serves the following purposes: it bears the tendons sheaths 81 , 82 and prevents any relative movement between the limb 1 1 , 12 and the unstretchable fabric 210, keeping the unstretchable fabric 210 snugly in place. Its shape follows the biological structures (bones, muscles and ligaments) of the limb 11 , 12 for increased ergonomics and hence optimal load distribution. The soft fabric 230 is used to connect the previously described structures 210, 220 in a continuous garment. This enables the user to conveniently wear the suit 99 like a piece of clothing instead of having to assemble or strap the different parts of the exosuit 99 separately onto the body. One or more special windows 250 allow access to the muscles to place electrodes on the skin where EEG control is required.

The special elbow protection 240 may be used to avoid peaks of tension due to the action of the extensor tendon 52. It is a rigid shell placed over the joint 10 and provided with a special groove that routes the tendon 52. It is merged with the fabric 220 through proper gluing and sewing.

Finally, a harness 260 as shown in Figs. 7 and 8 may preferably be used to connect the garment 99 to the torso of the user and to bear and distribute the weight of the actuators 100 on the back of the user. A semi-rigid structure 262 may be embedded in the back side of the harness 260 in order to avoid peaks of tension on the torso.

The Bowden sheaths 81 , 82 are routed in the suit 99: they emerge from the fabric in proximity of the actuator 100, i.e. in the back, and in proximity of the joint 10. The Bowden sheaths 81 , 82 extend from the housing 80 of the actuator 100 along the soft frame 200 to terminate at the upper segment 11 of the limb. The first and second cables 51 , 52 are routed through the Bowden sheaths 81 , 82 and terminate at first and second end effectors 53, 54 at the lower segment 12 of the limb respectively. The first and second cables 51 , 52 thus extend beyond the termination of the Bowden sheaths 81 , 82 on the upper segment 11 , going past the pivoting joint 10. In the exemplary embodiment, the first cable 51 is provided in front of the elbow 10, terminating at a front of the lower segment 12 to cause flexion when the cable 51 is wound around the spool 40, and the second cable 52 is provided behind the elbow 10, terminating at a back of the lower segment 12 to cause extension when the cable 52 is wound around the spool 40.

Resilience At End Effectors

As shown in Fig. 9 (and schematically illustrated in Fig. 3), springs or resilient means or elastic elements 91 , 92 that are placed in series with the first and second cables 51 , 52 generate compliance at the end effectors 53, 54 respectively. In this way, the first and second cables 51 , 52 act on first and second end effector elements 53, 54 connected with the soft suit or frame 200 by means of the serial springs 91 , 92 respectively. The first and second cables 51 , 52 are preferably connected to the springs 91 , 92 by threading the ends 56, 57 of the first and second cables 51 , 52 through the springs 91 , 92 and engaging the cable ends 56, 57 with the distal ends 96, 97 of the springs 91 , 92 respectively (for example by enlarging the cable ends 56, 57 to be greater than the internal diameter of the springs 91 , 92). In this way, when the cable 51 , 52 is pulled, it compresses the spring 91 , 92 and the load is then transferred to the end effector 53, 54 and hence to the joint 10 via the spring 91 , 92 respectively.

Such springs 91 , 92 advantageously add further compliance to the natural compliance generated by the muscles and soft tissues of the user where the suit 99 is linked to the body: natural compliance is however hard to predict given that it varies from user to user and it is also a function of muscular tone. Putting the springs 91 , 92 in series, the motion applied by the motor 20 is not rigid: if any obstacle obstructs the trajectory, the springs 91 , 92 advantageously absorb the deformation, and the risk of harming the user or damaging the system is reduced. Moreover, if any impact occurs, it is absorbed or partially absorbed by the resilient means 91 , 92 and reduces direct impact to the motor 20 to avoid damaging or straining the motor.

For the application of the exosuit 99 to the upper segment 11 and lower segment 12 about the elbow joint 10, as schematically represented in Fig. 10 which exemplifies a joint 10 flexed by a tendon 51 (agonist) with a serial spring 91 , it is possible to calculate the resulting torque stiffness corresponding to the linear stiffness of the employed spring 91 , as discussed below.

Considering Hooke's law and the fact that the only the component Ft of the cable tension directed perpendicularly to the segment r generates torque M:

M = Ft * r (1)

= F cos a (2)

F = kA£ (3) and considering the length I of the cable 51 as the chord of the circumference intercepting the two anchor points (the first anchor point being at the termination of the Bowden sheath 81 on the upper segment 1 1 and the second anchor point being at the end effector 53 on the lower segment) and centered on the joint 10:

{ = r * crd(6— 2a) =

it is possible to express the elastic torque as:

z = FT * (r = 2 * k * a2 + b2) * sin — a * cos — a = (5)

= k(a2 + b2) * sin(0 - 2a) (6)

In order to compute the resulting torsional stiffness, assuming the general formulation of (7), it is possible to express it as (8): τ

(7) k(a2 + b2)) sin(0 — 2 )

(8)

Θ

Using a spring 91 with elastic constant of k = 4.9 N/mm and the following parameters, based on anthropometric data of elbow joint, a = 50 mm, b = 00 mm, the resulting stiffness of the system is depicted in Fig. 1 1.

Cable Spooling

In the proposed actuator 100, the spool 40 pulls the first and second cables 51 , 52 along two directions: flexing and extending the joint 10 in an agonist-antagonist fashion. Flexing occurs when the cable 51 is wound around the spool 40 and the cable 52 is fed from the spool 40, while extending occurs when the cable 52 is wound around the spool 40 and the cable 51 is fed from the spool 40. The cable routing leads to a nonlinear cable elongation of the flexor tendon or cable 51 , depending on the joint angle as described by (1), while the elongation of the extensor tendon or cable 52 is linear with the joint angle as described by (2). The predictable linear component of such difference can be compensated by a different diameter of the spool 40 dedicated to flexion (for cable 51) with respect to the one dedicated to extension (for cable 52). The nonlinear component of such difference (and the unpredictable ones due to several causes like misalignments, relative movements of the fabric with respect to the body, etc.) are absorbed by the serial springs which actively take part to the correct functioning and by the soft fabric of the soft frame 200.

The equations (8) and (9) below describe the different elongations of the first and second cables 51 , 52, as shown in Fig. 12 which is adapted from A Mathematical Introduction to Robotic Manipulation by R. M. Murray.

h2 (e) = l2 + Re Θ > 0, 0) As can be seen in Fig. 12, during flexion, the flexor tendon (hi) 51 gets shortened more than the extensor 52 gets elongated. Conversely, during extension, more of the flexor cable 51 needs to be fed from the spool 40 than the amount of extensor cable 52 is wound onto the spool 40. This difference in the change in length of the first and second cables 51 , 52 during actuation results in a tension of the series spring 91 connected to the flexor cable 51 (especially during extension), which is then transferred to the articular joint 10. Such internal tension may result in discomfort and pain when it is too high, as well as in mechanism failure. With reference to Fig. 12, using the following parameters (based on anthropometric data of the elbow joint 10) where a = 50 mm, b = 100 mm, R = 50 mm and θ = [0°-90°], the resulting extension of the first and second cables 51 , 52 is depicted in Fig. 13, where a maximum difference in elongation of the first and second cables 51 , 52 of more than 50 mm is generated. With a series spring 91 stiffness of 5 N/mm, this would result in an undesired tension of 250 N in the flexor cable 51.

By fitting a nonlinear shortening of the flexor cable 51 and imposing no pretension at the beginning of the motion (which means that when the joint is fully extended the first and second cables 51 , 52 are relaxed) it is possible to obtain a correction factor of approximately 1.51 for the diameter of the extensor pulley or spool 40 about which the extensor cable 52 is wound, such that the internal tension is minimized. Fig. 14 shows elongation of the first and second cables 51 , 52 and their difference when the spool diameter is corrected by a factor equal to the pendency of the first-order fitting curve of the flexor 51 elongation in the joint angle range of 0° to 90°. The resulting nonlinear elongation difference (which maximum value is about 10 mm) is absorbed by the soft fabric and the series springs without resulting in any pain or discomfort. The initial positive difference as can be seen in Fig. 14 in which the extensor cable 52 elongates more than the flexor cable 51 results instead in a slack of the extension cable 52 during flexion, but the presence of the feeder system 60 allows such slack without allowing the cable 52 to uncoil from the spool 40. Uncoiling should be avoided because if this could happen, the mechanism would fail.

By using the two first and second cables 51 , 52 in agonist-antagonist fashion, it is thus possible to apply a motion also when the joint 10 is not oriented in a particular way (e.g. the limb can be upside down or the user supine and still the joint can be properly actuated). This technical feature is particularly important for manipulation. It also leads to a more efficient actuation since it requires only one motor 20 to actuate two directions.

Trajectory following test

A sine-chirp trajectory-following test was performed with the actuator 100 connected to a test bench as shown in Fig. 15, where the simulated joint angle was measured by a rotary encoder 400. In this test, the different elongation of the extensor cable 52 and flexor cable 51 were not considered.

Results of the sine-chirp trajectory following test shown in Fig. 16 highlight a good trajectory tracking performance of the present exosuit 99 in bidirectional motions (i.e. directed against and towards the gravity). This kind of motion is impossible to achieve with a monodirectional actuation (i.e. a single actuated direction).

Regenerative Braking

The system 99 may be integrated with a module for regenerative braking. In such implementation, it is possible to store energy which is lost during active braking to extend the battery life. The DC motor 20 of each actuator 100 in the exosuit 99 can be configured to generate current by induction when motion is applied to their shaft 21. Such current is normally dissipated but can be stored instead. As the system is backdrivable, several scenarios can be exploited for energy harvesting. During walking, e.g., natural arm movement can be translated into electric power to recharge the batteries. Alternatively in another scenario, when the user wants to lower a load (i.e. to move in direction of gravity pull), instead of actively driving the end effector 53, 54, it is possible to engage regenerative braking to convert the potential energy into electrical energy.

An example of the regenerative braking circuit 25 is shown in Figs. 17 and 18 in which four pairs of power transistor and power diodes (T1 and D1 , T2 and D2, T3 and D3, T4 and D4) are provided in the connection of the motor 20 with the battery 22. The regenerative breaking circuit 25 has a form of a bridge circuit in which the motor 20 bridges between two pairs of the power transistor and power diodes that are provided in parallel with the battery 22, as shown in Figs. 17 and 18. During forward motoring function as shown in Fig. 17, the current flows from the battery pack 22 to the motor 20 driving it forward (i.e. clockwise) via the two power transistors T1 and T4 that are bridged by the motor 20. During forward braking function, as shown in Fig. 18, the current flows from the motor 20 moving forward (i.e. clockwise) to the battery 22 thanks to the power diodes D1 and D4 that are bridged by the motor 20. Sensors (not shown) may be incorporated in the suit 99 to detect the movement of the body (directional motion or force detection) and to extract bio-signals (electrical activity of the muscles or their vibration) so that a corresponding activation of the actuator enables the augmentation of the movement using the proposed system. Such sensors may be used as feedback to increase the robustness of the control architecture and to detect the user's motion intention. In a particular embodiment, inertial measurement units (IMUs) detect the segments accelerations and orientations in space to extract the body kinematics in order to finely control the motion trajectories. Tension sensors in the first and second cables 51 , 52 detect the amount of force applied by the system to feedback it to a controller (not shown) of the actuator 100. In another embodiment, electromyography sensors (EMG) may be used to detect muscular activation and translate them into triggers for the system. Mechanomyography sensors (MMG) may be used in other embodiments to extract motion intention exploiting the high frequency vibrations corresponding to muscular activation. Force sensors embedded in the fabric 200 detect contact occurrences with the external environment and modulate the force applied by the system 99 in order to prevent injuries to the user and damage to the system 99.

The exosuit 99 also comprises other remaining hardware such as the batteries, the motor drivers and the controller (which may be a microcontroller) which are placed preferably in the proximity of the actuator 100 to minimize connecting wires. The microcontroller is devoted to control the motor drivers connected to deliver power to the actuator 100 when the user needs assistance to motion. The microcontroller can be connected to the sensors to detect user intention: these sensors can detect electromyography signals from muscle activity, pressure and strain which indicate the user's attempts to move. These signals detected by the sensors communicate with the microcontroller, and have the role to trigger the microcontroller and consequently drive the actuator 100 via the motor drivers.

Distinctive Features Of the invention

• The exosuit 99 assists upper limb joints 10 by applying torque to them without constraining the kinematics. The exosuit 99 may be adapted for lower limb joints. The exosuit 99 is soft, lightweight, ergonomic and biomimetic.

When the muscular force is not enough to perform an action, the device 99 can be activated to generate assistive force.

The user is free to move the targeted joint 10 when no extra force is required since the actuator 100 is backdrivable.

To relieve the user from isometric efforts, the first and second cables 51 , 52 can be locked with low power consumption using the clutch 70.

The natural oscillations/movement of the arm or limb can be exploited to regenerate the batteries 22.

Technical Advantages

• An impaired person with little to none ability to voluntarily move a joint may be assisted and empowered with the exosuit 99. The user activates the exosuit 99 which will move the targeted joint.

• A healthy user performing fatiguing operations (e.g. rescuers or laborers) can benefit from the exosuit 99: when a particular effort is fatiguing, the user activates the exosuit 99 which will bear partially or fully the load. When no extra force is needed, the exosuit 99 is deactivated without any constraint for the user.

• The exosuit 99 can be worn under normal clothing. Impaired users benefit from this feature in terms of comfort and aesthetics. Healthy users benefit also in terms of adaptability to the particular environment. For example, rescuers and laborers can wear normal personal protective equipment (PPE) like hazmat suits without needing to adapt them to the exosuit 99.

• When an isometric contraction is required (e.g. to carry a load), a user can lock the actuation with the bi-directional electro-mechanic clutch 70 so that the user's muscles are hence unloaded. The clutch 70 operates with low power consumption, thereby extending battery life of the exosuit 99.

• When undesired movements occur, when braking force is needed or simply when extra battery charge is required, the exosuit 99 can reverse the energy flow and use the mechanical energy coming from the joint to regenerate the battery 20. This results in increased battery life.

Whilst there has been described in the foregoing description exemplary embodiments of the present invention, it will be understood by those skilled in the technology concerned that many variations and combinations in details of design, construction and/or operation may be made without departing from the present invention.

Claims

An exosuit for facilitating movement of a limb comprising an upper segment and a lower segment pivotally connected via a joint, the exosuit comprising:
a soft frame configured to be worn by a user over the limb;
an actuator attached to the soft frame, the actuator comprising
a spool rotatable in a first direction and in a second direction, the spool connected to a shaft of a motor configured to rotate the spool;
a first cable having a part of the first cable wound about a first portion of the spool, the first cable extending from the spool along the soft frame, the first cable terminating at a front of the lower segment to cause flexion of the limb when the first cable is wound onto the spool during rotation of the spool in the first direction; a second cable having a part of the second cable wound about a second portion of the spool, the second cable extending from the spool along the soft frame, the second cable terminating at a back of the lower segment to cause extension of the limb when the second cable is wound onto the spool during rotation of the spool in the second direction.
The exosuit of claim 1 , wherein the second portion of the spool has a larger diameter than the first portion of the spool.
The exosuit of claim 1 or claim 2, wherein the actuator further comprises a first pair of rollers and a second pair of rollers, the first cable passing between the first pair of rollers from the spool to the lower segment and the second cable passing between the second pair of rollers from the spool to the lower segment, the first pair of rollers and the second pair of rollers each comprising a monodirectional roller and a conventional roller that is free to rotate in both directions; wherein each monodirectional roller is free to rotate only in a direction to feed the first cable or the second cable from the spool, and wherein each monodirectional roller is locked from rotating when the first cable or the second cable is being wound onto the spool.
The exosuit of any preceding claim, wherein the first cable is connected to the front of the lower segment via a first resilient element at a first end effector attached to the lower segment, and wherein the second cable is connected to the back of the lower segment via a second resilient element at a second end effector attached to the lower segment.
5. The exosuit of claim 4, wherein the first and second resilient elements each comprise a compression spring.
6. The exosuit of any preceding claim, wherein the first and second cables extend along the soft frame through first and second Bowden sheaths attached to the soft frame respectively, the first Bowden sheath terminating at the front of the first segment and the second Bowden sheath terminating at the back of the first segment.
7. The exosuit of any preceding claim, wherein the actuator further comprises an electromechanical clutch connected to the shaft of the motor, the electromechanical clutch configured to apply a holding torque on the first and second cables when the electromechanical clutch is activated to keep the joint at a stationary angle.
8. The exosuit of any preceding claim, wherein the motor is connected to a battery via a regenerative braking circuit configured to recharge the battery during movement of the motor caused by rotation of the spool when natural movement of the limb pulls on at least one of the first and second cables to unwind the at least one of the first and second cables from the spool.
9. The exosuit of any preceding claim, wherein components of the actuator are housed in a housing attached to the soft frame and configured to be worn on the back of the user.
10. The exosuit of any preceding claim, further comprising sensors configured to detect at least one of: directional movement of the limb, acceleration of the upper segment, acceleration of the lower segment, orientation of the upper segment, orientation of the lower segment, force in the limb, electrical activity of muscles in the limb, and vibration of muscles in the limb for providing feedback to a controller of the actuator to perform at least one of: detect motion intention of the user, control motion trajectory of the limb, and trigger actuation of the exosuit.
1 1. The exosuit of any preceding claim, further comprising tension sensors configured to detect amount of force applied to the first cable and the second cable for providing feedback to a controller of the actuator.
12. The exosuit of any preceding claim, further comprising force sensors configured to detect occurrence of contact of the soft frame with an external environment for providing feedback to a controller of the actuator to modulate force applied by the exosuit.
EP16835544.4A 2015-08-11 2016-08-11 Exosuit Pending EP3334572A4 (en)

Priority Applications (2)

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PCT/SG2016/050383 WO2017026943A1 (en) 2015-08-11 2016-08-11 Exosuit

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FR3074078B1 (en) * 2017-11-28 2019-11-08 Commissariat A L`Energie Atomique Et Aux Energies Alternatives LOWER MEMBER OF EXOSQUELETTE
US20190160651A1 (en) * 2017-11-28 2019-05-30 Seismic Holdings, Inc. Exosuit systems and methods
CN109124982A (en) * 2018-06-29 2019-01-04 燕山大学 A kind of wearable rehabilitation power-assisted flexible pneumatic joint
WO2020049164A1 (en) * 2018-09-06 2020-03-12 Myoswiss Ag Wearable active assisting device
FR3085838A1 (en) 2018-09-19 2020-03-20 Lilas Deville DEVICE AND METHOD FOR ASSISTING THE MOBILIZATION OF A JOINT

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EP3334572A4 (en) 2019-04-10
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CN107921628A (en) 2018-04-17

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