FIELD OF THE INVENTION

The present invention is in the field of a device suitable as an exoskeleton for a human body or the like, for supporting the body and motion thereof, in particular for individuals in professions such as assembly lines, construction, agriculture, and nursing work with heavy loads, repetitive motions, and awkward working postures. This often leads to musculoskeletal disorders such as soreness, lower back pain, arm and shoulder pain, and rotator cuff injuries.

BACKGROUND OF THE INVENTION

The present invention is in the field of an exoskeleton, also referred to as exosuit. The exosuit may be used by individuals in professions such as assembly lines, construction, agriculture, and nursing work with heavy loads, repetitive motions, and awkward working postures.

An exoskeleton is the external skeleton that may support and protect a vertebrate’s body. In the present context it relates to a device to be worn by an individual, in particular that is wearable over all or part of a body. It typically provides ergonomic structural support. It may be powered, and is then referred to as an active exoskeleton. Powering can take place by electric motors, pneumatics, levers, hydraulics and the like. The exoskeleton is typically designed to provide better mechanical load tolerance, and its control system aims to sense and synchronize with the user's intended motion and relay the signal to motors which manage the gears. The exoskeleton also protects the user's joints, such as shoulder, waist, back and thigh against overload, and stabilizes movements when lifting and holding heavy items. In an alternative a passive exoskeleton may be referred to. The passive exoskeleton has typically no intrinsic actuator and relies completely on the user's own muscles for movements, adding more stress and making the user more prone to fatigue, although it does provide mechanical benefits and protection to the user. It typically provides for recovery or supports performance of a user. Applications of these exoskeletons can be found in industry, in the military, and for medical and for civilian applications.

Exoskeletons typically have limitations and design issues, such as power supply, weight, costs, flexibility in view of intended use, power control, control in general, power consumption, adaptivity in view of a user and intended use, and so on. In addition when not properly designed exoskeletons may pose danger to a user.

For better understanding, some basic introduction with respect to joints is given. A joint relates to a connection between bones in a body of a vertebrate. The joints and muscles make a skeletal system, having individual elements, to function as a whole. Joints are formed such that the allow for different degrees and types of movement, depending clearly on the function required or permitted. Joints are typically able to withstand compression and maintain loads while still being capable of moving. The present invention is concerned with joints that allow movement, that is having a biomechanical function.

From a biomechanical point of view joints can be subdivided into various groups. A simple joint having two articulation surfaces, a compound joint, having three or more articulation surfaces, such as a radiocarpal joint, and a complex joint, having two or more articulation surfaces and an articular disc or meniscus, such as a knee joint. Examples of joints of the human body are a joint of hand, a shoulder joint, an elbow joint, a wrist joint, an axillary joint, a sternoclavicular joint, a vertebral articulation, a temporomandibular joint, a sacroiliac joint, a hip joint, a knee joint, a jaw joint, and an articulation of a foot.

Joints may be damaged, unfortunately, such as by a trauma to the joint, or trauma to tissues around a joint, such as to muscles, tendons, ligaments, articular cartilage, and bone. Likewise, excessive use, wrong use, etc. may cause damage to a joint.

Many musculoskeletal injuries, like rotator-cuff tears and ligament strains and related surgeries, could be prevented, such as by use of an exoskeleton.

Many individuals in professions such as assembly lines, construction, agriculture, and nursing work with heavy loads, repetitive motions, and awkward working postures. This often leads to musculoskeletal disorders such as soreness, lower back pain, arm and shoulder pain, and rotator cuff injuries. One of the possible solutions to address these disorders is through the use of exoskeletons or exosuits. Exoskeletons typically consist of a rigid frame with links and joints overlapping the biological joints of the wearer. Exosuits on the other hand, are made using soft materials such as fabric, elastomers, and the like, and rely on the wearer’s skeleton for structural support. An exoskeleton is the external skeleton that may support and protect a vertebrate’s body. In the present context it relates to a device to be worn by an individual, in particular that is wearable over all or part of a body. It typically provides ergonomic structural support. It may be powered, and is then referred to as an active exoskeleton. Powering can take place by electric motors, pneumatics, levers, hydraulics and the like. The exoskeleton is typically designed to provide better mechanical load tolerance, and its control system aims to sense and synchronize with the user's intended motion and relay the signal to motors which manage the gears. The exoskeleton also protects the user's joints, such as shoulder, waist, back and thigh against overload, and stabilizes movements when lifting and holding heavy items. In an alternative a passive exoskeleton may be referred to. The passive exoskeleton has typically no intrinsic actuator and relies on elements such as springs, dampers, elastic cords, and flex- ure or torsion producers to assist the user. The motion is generated completely by the user's own muscles and the passive elements simply produce resistive forces and store and release energy to the user, thereby providing mechanical benefits and protection. Exosuits, consist of soft wearable elements connected to the wearer that apply forces and moments across the biological joints so as to share some of the load borne by muscles. As opposed to exoskeletons, exosuits typically do not have any rigid frame, and therefore all the forces and movements generated are supported by the wearer’s skeleton. Existing exosuits can also be classified as active or passive depending on whether energy is consumed while producing forces on the wearer. These function in a similar way to the active and passive exoskeletons described earlier. Applications of these exoskeletons and exosuits can be found in industry, in the military, and for medical and for civilian applications. Among existing exoskeletons and exosuits, there is a trade-off between active and passive devices. Passive devices are lightweight, simple to use, and consume no energy, but they cannot control the amount of assistance, and are usually designed for a small subset of activities. Active devices can assist in a much larger range of activities. But they are bulky, have limited portability, and controlling them to match the wearer’s requirement is still an open challenge. In addition when not properly designed or controlled, these devices may pose danger to a user.

As prior art the following documents may be mentioned: US2016/107309 Al, reciting a motion control system including an actuator having an actuation member, the actuation member having a proximal end attached to the actuator on a first side of a joint and a distal end attached to an anchor element attachment point on a second side of the joint, wherein a first sensor is configured to output signals defining a gait cycle and a second sensor is configured to output signals representing a tensile force in the at least one actuation member, and a controller receives the output signals from the sensors and actuates the actuator, during a first portion of the gait cycle, to apply a force greater than a predetermined threshold tensile force to the anchor element attachment point via the actuation member to generate a beneficial moment about the joint and to automatically actuate the actuator; and WO 2917/026943 Al reciting 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.

It is an object of the present invention to overcome one or more disadvantages of the exoskeletons of the prior art and to provide alternatives to current exosuits, without jeopardizing functionality and advantages.

SUMMARY OF THE INVENTION

The present invention describes autonomously adjustable passive exosuits and methods to tune the said exosuits to provide maximum assistance to the wearer. The core aspects of the present invention relate to provision of (1) an autonomous adjustable passive exosuit device: The assistive forces in the adjustable passive exosuit are generated purely through passive components. The properties of the passive elements can be adjusted in a range of values by using the active components without need for wearer’s intervention. The exosuit may have at least one actuator per passive element. Not all passive elements need to be provided with at least one actuator; in particular 1-100% of the passive elements is provided with at least one actuator, more in particular 25-95% of the passive elements, even more in particular 50-90% of the passive elements is provided with at least one actuator. Using passive elements and adjusting these, in particular by using the present at least one actuator, e.g. in terms of starting, stopping, varying, increasing, decreasing, lowering, raising, rotating, and combinations thereof, the exosuit is operated. The present at least one activator is mostly inactive, such as during 25-99.99% of a time of usage, in particular during 50-99.9% of the time of usage, more in particular during 85- 99.8% of the time of usage, such as during 98-99% of the time of usage. (2) Finding bio- mechanically optimal configurations: The present invention provides a method to find the set of values of the passive properties of the said exosuit, which will provide the maximum assistance to the wearer. This optimal set is calculated using musculoskeletal simulations, and in principle can be applied to all exosuit and exoskeleton devices. (3) Generation of a data-driven map of optimally tuned parameters for multiple tasks: Performing musculoskeletal simulations is computationally expensive and difficult to realize for realtime control of exosuits. To address this, the invention describes the generation of a data- driven map via precomputations, that directly outputs the optimal exosuit properties using information about the motion and load on the wearer. (4) Tuning the passive components: Using the outputs of the computationally inexpensive map, the active components tune the passive components to the optimal values. The assistance is then provided completely by the passive elements. (5) Optimizing exosuit geometry: By extending step (2), the inventors describe a method to find the optimal attachment and routing locations of the active and passive elements that can provide the maximum assistance to the wearer. Using this approach, it becomes possible to iterate through different exosuit configurations and optimize or reject baseline designs without expensive and time-consuming trial-and-error methods.

The present invention extends the scope of application of passive and manually adjustable passive exosuits by enabling more tasks and adapting to individual wearers. As the active components are used sparsely to tune the passive components, the present exosuit requires very low energy for operation. Therefore it can last long durations while being compact and lightweight, as compared to conventionally active exosuits. As the assistance is provided only by the passive components, there is no need for predicting the wearer’s intent and continuously adapting the amount of assistance provided, which greatly simplifies the control as compared to active devices. Furthermore, this method has significant flexibility in terms of finding tailored solutions for different tasks, different wearers based on their body proportions, or for addressing specific muscles or joints of the body.

In an exemplary embodiment, the present invention is used to automatically find appropriate attachments and routing locations for a passive exotendon, in a soft exosuit to assist the shoulder.. In this exemplary embodiment, three arm raising-lowering and internal-external rotation motions are used, wherein an attachment point and rest-length of the exotendon are optimised to reduce overall muscle effort. Accurate musculoskeletal modelling and design parameter optimization of soft exosuits is used to achieve that, amongst others. Model predictions are validated by testing with six participants. Inventors adjusted the exotendon parameters for each individual participant by scaling exotendon rest-length to their respective heights. Supporting the predictions from simulations, measured muscle activity shows reductions in the deltoid and trapezius muscles.

In a first aspect the present invention relates to an autonomously adjustable passive soft exosuit comprising a wearable, wherein the wearable comprises at least one fabric, wherein the fabric is configured to substantially cover at least one joint of a wearer, the wearable configured to apply at least one of an adjustable force and of an adjustable moment across the at least one joint of a wearer, wherein the wearable comprises at least one passive element attached to the wearable at a first attachment location and at a second attachment location, wherein the first attachment location and the second attachment location are at a first side of the joint and at a second side of the joint, respectively, at least one actuator, wherein the actuator is configured to adjust at least one status of the at least one passive element, and at least one controller, wherein the controller is configured to identify at least one task of a wearer of the exosuit, to obtain an actual status of the at least one status of the at least one passive element, to establish an optional difference between at least one task status of the at least one passive element and the at least one actual status of the at least one passive element, and to activate or de-activate the at least one actuator to correct the at least one status of the passive element in order to minimize said optional difference. The terms “status” and “state” are considered to overlap. The term “elastic” relates to elasticity, which is considered the ability of a body to resist a distorting influence and to substantially return to its original size and shape, when that influence or force is removed, such as the action of the present actuator on the passive element. The term “fabric” is considered to encompass any comparable, for the invention suitable, type of thin, soft, lightweight, material, or a combination thereof. The present autonomously adjustable passive soft exosuit has properties, or characteristics, that may be tuned, such as according to biomechanics-in-the loop simulations of assistance.

In a second aspect the present invention relates to A data-processing apparatus comprising a processor configured for controlling the present exosuit.

In a third aspect the present invention relates to a computer program product comprising instructions which, when the program is executed by a computer, cause the computer to control the present exosuit.

In a fourth aspect the present invention relates to a method of designing the present exosuit, or for that matter, any exosuit in general, comprising (1) providing an exosuit design, the design comprising a wearable, wherein the wearable comprises at least one fabric, wherein the fabric is configured to substantially cover at least one joint of a wearer, the wearable configured to apply at least one of an adjustable force and of an adjustable moment across the at least one joint of a wearer, wherein the wearable comprises at least one passive element attached to the wearable at a first attachment location and at a second attachment location, wherein the first attachment location and the second attachment location are at a first side of the joint and at a second side of the joint, respectively, and at least one actuator, wherein the actuator is configured to adjust at least one status of the at least one passive element, (2) applying at least one of an adjustable force and of an adjustable moment across the at least one joint of the design, (3) iterating through different design configurations, and (4) optimizing or rejecting baseline exosuit designs by repeating steps (2) and (3), in particular at least one of steps ( 1 )-(4) is performed on a computer, in particular wherein the computer further comprises an exoskeleton model, in particular by optimizing at least one rest-length of a passive element.

The present control is amongst others provided by a detailed biomechanical model of the joints and muscles involved in the tasks to be performed, providing a safer and more effective operation of the exosuit. For instance, using the exosuit and external sensors, the position, velocity and forces applied to the user are measured, which provide an actual status of the subject, and can be applied to the biomechanical model during movement. From this actual state of the model, the forces in tissues can be estimated and the risk of injury assessed during the movement. The shoulder is used as an exemplary embodiment to demonstrate the feasibility of exosuit. With the present exosuit inventors make use of the concept of "tissue function maps " that identify e.g. how much muscle strain is induced in any given state of the user and how much effort a change of status involves. As a result, the precomputed strain maps plus the current state of the user can inform the exosuit about how much strain is being put on the healing muscles in any given configuration of the shoulder including interaction forces applied by the exosuit. The present invention relates amongst others to creation, storage, navigation or use of physiological (tissue function) maps of neuromusculoskeletal information space: e.g.: tissue force, strains, stresses, EMG level, and collagen growth/alignment. Furthermore, the map is directly related to the subject's joint position, velocity and/or applied muscle, implanted and external forces, where there is a transfer function (or algorithm) between the physiological map and the physical (motion) space of the user. The present tissue function map differentiates from maps of the physical space which may be common place. The present Exosuit can operate at any time, with a large variety of applications (greater range-of-motion, different speeds and loads), targeting to individual tissues, such as muscles/tendons, a realtime feedback about the safety /injury -risk of specific muscles according to the position, movement and loading of the user's shoulder, and a quantitative monitoring to track progress and responsiveness to therapy over time. The present invention therefore relates to obtaining and implementing tissue function maps, such as muscle strain maps, such as in an exosuit, which can induce lower strains and safer movements, use of the tissue function maps , optionally with an impedance controller, trajectory planning within the safer regions of the strain map, and a physical prototype of the Exosuit demonstrating safety and execution of the modelling and control algorithms. The strain maps provide multi-dimensional movement with a larger range of motion while minimizing the risk of reinjury. Furthermore, the strain maps allow to quantify the strain or load for the user.

The loads and strains on the muscles, tendons, bones and ligaments can typically not be measured with a simple sensor or from external observation. The loads and strains on the muscles, tendons, bones and ligaments may be measured with the help of a sensor, such as an ultrasound sensor at least for the muscle strain. A sensor for measuring loads may provide real-time feedback for updating the strain maps for thereafter adapting the exercise path.

A collaborative exosuit may incorporate a user-specific biomechanical model to inform exosuit trajectory planning, user state estimation and impedance control. This integration of musculoskeletal modelling within the system allows it to plan trajectories to reduce the strain of muscles and tendons. For the tests on the rotator cuff detailed below, only the glenohumeral joint is modelled and only the movement or state of the humerus (upper arm) relative to scapula (shoulder blade) is taken into account. This model allows safe predictions regarding load or strain for the different bones, tendons, ligaments and tendons. To limit the amount of data of the strain maps, the strain maps were calculated with 4 degree increments for each position of the rotator cuff. These strain maps were precomputed for each muscle, tendon, ligament and bone, therewith reducing computational complexity. Interpolation may be used to provide trajectory planning with a higher degree of accuracy.

The tissue function map may be a biomechanical impact map, or a load impact map. Where the term “load” is used, depending on the tissue, and in so far as applicable, also the terms “strain”, “stress”, “force”, and “torque”, are included, or the term can be replaced by said further terms. The tissue function map may be a load map or a strain map. The Typically for each tissue a map is composed. Multiple maps are typically combined to form one overall or combined strain map. The tissue function map typically maps the exerted load, such as exerted stress, strain and/or torque. The exerted load is typically a resultant of the combination of the state of the joint, load exerted on the joint and activation of a muscle that span the joint. The load exerted on the joint may also include the weight (due to gravity) of the limb attached to the joint. The state of the joint is at least the position of the joint. The state of the joint may also comprise the speed of the joint at that specific position. The state of the joint may also comprise the acceleration of the joint at that specific position. The state of the joint may also comprise the jerk of that joint at that specific position. The state may comprise combinations of at least the position with one or more of speed, acceleration and jerk.

In determining the strain of each of the muscle tendons, the strains of those parts were compared for each muscle at each position and the highest strain value was taken to be representative of the strain of the entire muscle tendon. This way, the strain space includes the highest possible strain the tendon will undergo at any given position. In an alternative calculation method, the contribution of all the tissue under load or strain is taken into account, such as adding all the values per position or weighted adding all the values per position.

Typically, the tissue function map of the tissue is supplemented with information at particular states of the joint representing the injury at a specific state of the joint.

A cost function may be a summation of all the values associated with a particular strain or load of the tissue at a particular state of the joint. The cost function may alternatively be a weighted summation of all the values associated with a particular strain or load of the tissue at a particular state of the joint. The cost function may alternatively be the maximum strain or load of the tissue during traversing the exercise path.

The biomechanical model of a Musculoskeletal structure of the mammal comprises at least one joint. The joint may comprise a first bone and a second bone both shaped to limit the relative motion between the bones. Forces, loads or strains on the bones associated with a joint may be of interest for Osteoarthritis and osteoporosis. A load may be a force or a torque acting upon a joint of the first or second bone of the joint. A muscle may be modelled as a spring-damper. Inventors can compute forces between two rigid bodies (bones), as long as they are connected, and even for those that can be welded together with 0 degrees of freedom. This can be interesting to look at loads through joints that have fused.

In a method for compiling a tissue function map of at least part of a musculoskeletal system for a mammal, such as a strain map, may comprise the steps of providing at least part of a biomechanical model of a musculoskeletal structure of the mammal comprising at least one joint; defining at least two tissues in the biomechanical model, typically at least three tissues, wherein the at least one tissue is selected from a muscle effecting the at least one joint, a ligament providing stability to the at least one joint, a tendon connecting a muscle effecting the at least one joint and a bone providing one side of the joint; for a plurality of states of the joint and the Musculoskeletal structure and based on said biomechanical model, deriving for each state the exerted load on the at least one tissue; wherein the plurality typically relates to at least 50% of states possible within boundary conditions of joint, wherein separate states are spaced apart sufficiently to allow resolution of individual states and yet also providing spatially dense enough distributed states, for instance where states are taken 0.01mm-5 mm spaced apart, or wherein states are taken 0.01-5 degrees spaced apart, or both, and aggregating the derived exerted load on the at least one tissue in a tissue function map.

Further the invention relates to a method according to the invention and/or the exosuit according to the invention and/or the data processing apparatus according to the invention and/or the computer program product according to the invention, further comprising one or more elements according to the description, in particular according to the examples, using incremental steps in time and/or space, using stiffness and/or damping, using a reference velocity, providing a exosuit feedback force, using a exosuit commanded pose, using a exosuit actual pose, using a movement drag force, projecting movement of an individual on at least one tissue strain map, visualizing data, using a control loop at a higher frequency than that of visualized data, providing interaction between an individual and the exosuit, and tuning positional and/or rotational stiffness of the exosuit.

DETAILED DESCRIPTION OF THE INVENTION

In an exemplary embodiment of the present autonomously adjustable passive soft exosuit the controller is further configured to autonomously activate or to de-activate the at least one actuator during use of the soft exosuit, in particular wherein the controller is configured to activate or de-activate at an operational frequency of >10Hz, more in particular > 100 Hz [real-time], more in particular wherein activating or to de-activating the at least one actuator adjusts a status of the at least one passive element, wherein adjusting is selected from starting, stopping, varying, increasing, decreasing, lowering, raising, rotating, velocity, acceleration, deceleration, and combinations thereof. In an exemplary embodiment of the present autonomously adjustable passive soft exosuit the task is selected from biomechanical actions, in particular selected from load movements, from flexion-extension, from abduction-adduction, from internal external rotation, wherein the load is selected from a load imposed by the wearer, from an external load, and a combination thereof. Examples thereof are work in assembly lines, in construction, in agriculture, and in nursing work with heavy loads, repetitive motions in general, and awkward working postures.

In an exemplary embodiment of the present autonomously adjustable passive soft exosuit the wearable comprises at least one passive element selected from a spring, a damper, a chord, a band, a rod, an element providing flexure, an element providing torque, and/or wherein the actuator is selected from a motor, a piston, a deformable element, an inflator, a deflator, a pneumatic, a lever, a hydraulics, and a clutch.

In an exemplary embodiment of the present autonomously adjustable passive soft exosuit at least one dimension of the exosuit is configured to be adaptable in view of characteristics of a wearer, such as size. As such the exosuit may be further optimized, e.g. in terms of a cost function.

In an exemplary embodiment the present autonomously adjustable passive soft exosuit comprises at least one exosuit-body fixator, in particular wherein the fixator is adjustable, more in particular wherein the fixator is configured to be length-adjustable in view of a wearer.

In an exemplary embodiment the present autonomously adjustable passive soft exosuit comprises at least one sensor configured to measure at least one of a wearers motion, and a wearer’s effort. Therewith the present exosuit is adjustable and adaptable. The sensor is typically configure to provide input to the at least one controller, and thereafter the controller can provide input to at least one actuator, or not.

In an exemplary embodiment the present autonomously adjustable passive soft exosuit is configured for mammal motion support, in particular for work support, wherein the mammal is selected from human beings, and from other vertebrates, in particular from horses, dogs, and cats.

In an exemplary embodiment of the present autonomously adjustable passive soft exosuit the motion support is selected from repetitive motion support, from load motion support, wherein the load in particular is > 1 kg, and from posture motion support.

In an exemplary embodiment of the present autonomously adjustable passive soft exosuit the fabric comprises at least one lightweight material, wherein the lightweight material is selected from elastomeric materials, from polymeric materials, such as polyesters, polyamides, such as nylon, poly urethanes, such as Lycra, poly ethers, poly urea’s, copolymers thereof, such as Spandex, and from cotton, and combinations thereof. In an exemplary embodiment of the present autonomously adjustable passive soft exosuit the fabric is configured to substantially cover at least one joint of a wearer and substantially a surface are adjacent to the joint, in particular 1-50% of a surface area of the wearers body.

In an exemplary embodiment of the present autonomously adjustable passive soft exosuit the fabric comprises a covering at an internal side thereof, in particular a 2-10 mm thick covering, such as a foam.

In an exemplary embodiment of the present autonomously adjustable passive soft exosuit the at least one status is selected from tension, pre-tension, moment, rest-length, damping coefficient, and stiffness.

In an exemplary embodiment of the present autonomously adjustable passive soft exosuit the controller is configured to activate or de-activate the at least one actuator based on a look-up table, based on output of a neural network, based on artificial intelligence, and a combination thereof, in particular wherein the controller is configured as a wireless transceiver.

In an exemplary embodiment of the present autonomously adjustable passive soft exosuit the at least one controller is configured to correct the status of the at least one passive element of the exosuit therewith providing on the musculoskeletal system of the wearer at least one of a minimal effort, a minimal strain thereon, a minimal energy consumption, a minimal joint loading.

In an exemplary embodiment of the present autonomously adjustable passive soft exosuit the at least one controller is configured to minimize energy consumption across the at least one joint of a wearer, in particular wherein minimization of energy consumption is based on the output provided by a musculoskeletal model of the wearer.

In an exemplary embodiment of the present autonomously adjustable passive soft exosuit the controller is configured to use pre-computed information for correcting the at least one status of the passive element.

In an exemplary embodiment of the present autonomously adjustable passive soft exosuit the exosuit comprises embedded software and data loaded on a data carrier, in particular a small data carrier, such as a memory.

In an exemplary embodiment of the present autonomously adjustable passive soft exosuit the at least one task status is obtained by a method for compiling at least two tissue function maps of at least part of a musculoskeletal system for a mammal, comprising the steps of:

- providing at least part of a biomechanical model of a Musculoskeletal structure of the mammal comprising at least one joint;

- defining at least one tissue in the biomechanical model, wherein the at least one tissue is selected from a muscle effecting the at least one joint, a ligament providing stability to the at least one joint, a tendon connecting a muscle effecting the at least one joint, a bone providing one side of the joint, and a combination thereof;

- for a plurality of states of the joint and the Musculoskeletal structure and based on said biomechanical model, deriving for each state the exerted load on the at least one tissue; and

- aggregating the derived exerted load on the at least one tissue in a tissue function map.

In an exemplary embodiment of the present autonomously adjustable passive soft exosuit said biomechanical model further comprises a cost function, in said cost function:

- calculating for each state the exerted load on at least one first tissue and on at least one second tissue; and

- combining the first tissue function map and the second tissue function map to obtain a combined tissue function map, such as using a cost function, in particular said cost function comprising (i) a sum of loads of the at least one tissue of a specific state of said tissues, such as a weighted sum, (ii) a product of the mean of said loads with an Euclidian distance, (iii) the maximum or minimum load across at least one tissue, or (iv) a combination thereof, and/or wherein the method further comprises providing a or the cost function, in said cost function calculating at a particular state the derived exerted load based on adding, such as weighted adding, the strain on said at least one tissue derived from said tissue function map, and/or wherein the step of combining comprises the step of selecting at a particular state for at least one tissue a load, and comparing said load with a threshold load, and/or wherein the step of deriving comprises the step of calculating the exerted load based on at least one of a characteristic or constitutive curve that relate force to displacement (strain), force to area (stress, pressure), and velocity (damping, viscosity), such as wherein the step of deriving comprises the step of calculating the exerted load based on at least one of an active force-length curve, a passive force-length curve, tendon force-length curve, and a normalized tendon force-length curve, and/or wherein the at least one tissue is a muscle; and wherein the step of deriving is based on muscle activation, and/or wherein the at least one joint comprises a first part and a second part arranged for forming the at least one joint; wherein the state of the at least one joint comprises the position of the first part relative to the second part, preferably also comprising the velocity of the first part relative to the second part, more preferably also comprising the acceleration of the first part relative to the second part, most preferably also comprising the jerk of the first part relative to the second part; and wherein the step of deriving is based on the state of the at least one joint, and/or wherein the at least one tissue is a tendon; and wherein the step of deriving comprises the step of calculating the exerted load based on a normalized tendon force-length curve, and/or comprising the step of introducing in the biomechanical model an injury in the at least one tissue for making the biomechanical model mammal individual-specific and/or comprising the step of calculating an exercise path for the at least one joint to traverse, wherein the exercise path limiting a load to said at least one of the at least one tissue, and/or wherein the step of calculating comprises the step of setting a load threshold, wherein the exercise path remains below the load threshold, in particular wherein said at least one load threshold defines an injury in at least one tissue in said biomechanical model, and/or wherein the at least one joint has a range of motion; and wherein the step of calculating comprises the steps of:

- selecting waypoints such that use of the range of motion is optimized; and

- calculating a path between waypoints such that the cost function does not exceed a threshold level or load threshold, and/or wherein the step of selecting waypoints also comprises selecting a velocity and direction of the velocity at the waypoint, preferably also selecting an acceleration and direction of the acceleration at the waypoint, more preferably also selecting a jerk and direction of the jerk at the waypoint, more in particular a combination thereof, and/or wherein the tissue function map is a precomputed tissue function map, and/or wherein the at least one joint is a monoarticular joint, an oligoarticular joint, or a poly-articular joint, a simple joint, a shoulder joint, a hip joint, a compound joint, a radiocarpal joint, a complex joint, or a knee joint, and/or wherein the biomechanical model models a hand, an elbow joint, a wrist joint, an axillary joint, a sternoclavicular joint, a vertebral articulation, a temporomandibular joint, a sacroiliac joint, a hip joint, a knee joint, a jaw joint, glenohumeral joint, or an articulation of a foot.

The present invention is also topic of a to be published scientific article entitled “Minimalistic soft exosuit for assisting the shoulder via biomechanics-aware optimization”, by S. Joshi et al., which article and its contents are incorporated by reference. For better understanding of the tissue function map and other details, PCT/NL2022/050392 may be referred to, which document, and its content, is incorporated by reference.

FIGURES

Figs. 1-7 show examples and results of the present exosuit. DETAILED DESCITPTION OF THE FIGURES

In the figures:

1 soft fabric

2 passive element

3 actuator

4 sensor

Fig. 1. Prototype of the minimalistic passive soft exosuit for the shoulder that we propose and optimize in this work using a biomechanics-aware strategy. The exosuit interfaces to the wearer at the waist and the arm, connected with an elastic element overlapping the shoulder. (A) Back view, arm flexed. (B) back view, arm extended, (C) front view, arm flexed.

Fig. 2. Exemplary biomechanical model including the musculoskeletal model (with 33 muscles in red and 11 joints) and the exotendon attached at the forearm and waist. Both back and front view are shown. The effect of varying the waist attachment location can be shown thereby.

Fig. 3. Prototypes of the minimalistic passive soft exosuit for the shoulder. It interfaces to the wearer at the waist and the arm, and overlaps the shoulder over free rotating rods on a support bracket. Additional attachments at the fore-arm and thigh help to safely transmit forces to the user by applying predominantly normal forces on the skin. (A) The fabricated prototype. (B) Schematic of the exosuit showing the front side. (C) Schematic of the exosuit showing the back side. (D) The exosuit consists of an exotendon attached to the user's arm and waist, and overlapping over the shoulder. One of the ends of the exotendon is attached to a cable-driven actuator that can change the rest-length of the exotendon (passive element). Additionally, sensors are placed on the body that can measure the user's motion and/or effort. When the user starts performing a repetitive task, the sensors detect the motion and/or effort, and the control system searches the precomputed mapping (figs. 4e-h) to find the optimal rest-length (star) of the elastic element that would minimize the user effort. By controlling the cable driven actuator, the exosuit changes the restlength of the elastic element to the optimal value (fig. 4i).

Fig. 4. Selected motions (4a-d) for the study shown via the musculoskeletal model, and evolution of (1) when varying the two design parameters. Evaluating the cost entails solving the muscle redundancy problem (2) at each time step and summing for the entire motion. Staring point may be considered to be fig. 3d. Inventors report the results for four different motions: (A) Selected motion 1 : Flexion-extension of the shoulder from - 450 to + 900 and back. (B) Selected motion 2: Abduction-adduction of the shoulder from - 450 to + 900 and back. (C) Selected motion 3 : Internal -external rotation of the shoulder from - 450 to + 450 and back, and motion 4. Precomputation is done to determine a user effort via musculoskeletal simulations. Normalized cost functions are then obtained. (E) Normalized cost surface for motion 1, (F) Normalized cost surface for motion 2, (G) Normalized cost surface for motion 3, and (H) for motion 4. Figs. 4e-h show cost function maps, identifying optimal values indicated with a star for motions 1-4. Fig. 4i, dotted lines, show use power consumption without the present exosuit, and solid lines, with the present exosuit, for motions 1-4. The bars in the lower graph show activation of the at least one actuator, and power consumption thereof. Note that the at least one actuator, per passive element, is mostly inactive, and only at some instances active.

Fig. 5. Experimental testing with the exosuit: (A) Placement of the surface EMG sensors, (B) Bar plots showing root-mean-squared values and standard deviations of activation values of four muscles of the six participants while performing Motion 1. In all figures, blue and red bars represent no exosuit and exosuit condition respectively.

Fig. 6. Simulated vs. measured muscle activation of participant 4 while performing motion 1. The continuous and dotted curves correspond to simulated and measured values respectively. Similarly, the blue and red curves represent no exosuit condition and exosuit condition respectively. The shaded regions show the standard deviation for each corresponding condition.

EXAMPLE

BASELINE DESIGN OF THE EXOSUIT

Inventors find that a completely passive device has the potential to offset loads taken by the biological joints of a wearers body. Furthermore, as the functionality may be pre-programmed mechanically into the device, it does not require additional control methods. Inventors focused on assisting the shoulder joint, as muscles acting at this joint are considered to be affected the most during elevated and overhead tasks. For this first study, a minimalistic approach was adopted and a baseline design for the present shoulder exosuit as shown in Fig. 1 was used, consisting of a single passive exotendon attached at the arm and waist, and overlapping the shoulder. As the arm moves, the passive exotendon will store and release energy at the shoulder joint, thereby assisting the wearer. For improved wearability and performance, use of low-friction elements on the shoulder to support the exotendon, and extending the attachments on the arm and waist to larger regions on the body to distribute the exotendon forces, reduces shear on skin, and increases stiffness of the exosuit-human interface.

Even with such a minimalistic approach, the forces applied by the exosuit on the wearer are governed by several design parameters, both functional (stiffness and rest-length), and geometric (attachment locations, routing locations, moment arm over shoulder). Here, rest-length and attachment point at the waist were used. Other parameters, namely - stiffness, arm attachment location, and wrapping over the shoulder, were fixed (static). HUMAN AND EXOSUIT MODEL

A human-exosuit musculoskeletal model as depicted in Fig. 2 is used. The human model is based on a thoraco-scapular musculoskeletal model. This model is characterized by (i) eleven degrees of freedom of the right arm - three rotations for the glenohumeral joint, two rotations for the clavicle with respect to the thorax, four rotations for the scapula gliding over the thorax, and one each for elbow extension-flexion, and elbow pronation-supination, (ii) a point constraint on the scapula and clavicle, representing the acromion joint, and (iii) thirty -three Millard-type musculotendon actuators representing the muscles of the upper torso and arm. The forces applied by the muscles are a function of the activation values and are governed by a maximum isometric force value, and characteristic curves defining the force-stretch, force-velocity, and passive force-stretch properties. The muscle forces create moments across joints, which drive the motion. During a dynamic task, the muscle activation values evolve over time in order to support the inertial and external moments on the joints at each instant. To model the exosuit, exotendon interaction forces are considered. An exotendon applies tension forces at its points of attachment and reaction forces at regions where it overlaps the wearer’s body. In the present exemplary exosuit, the exotendon is attached at the arm and waist, and overlaps the shoulder. Low-friction elements were used in the exosuit. Equal tension at the two attachment points of the passive elements is assumed. Inventors use a path spring object to model, which is defined by its path constraints and mechanical properties. It applies only tension force linearly proportional to its stiffness (K) and extension as follows: F _s = K * (extended Length - rest Length). The path spring is constrained to pass through points defined, and to wrap around surfaces. When stretched, the path spring applies tension forces at its end points, and reaction forces at the intermediate points and surfaces respectively. These reaction forces are calculated based on change in direction of the path spring at the corresponding intermediate points and surfaces. In an example the path spring is anchored on the humerus at the elbow joint centre (between medial and lateral epicondyles), and at the waist at an adjustable point on the line connecting the left and right PSIS (posterior edges of the iliac crest). Additionally, the path spring is constrained to (i) overlap the upper back, modelled using a wrapping ellipsoid on the torso and (ii) pass over a shoulder support bracket, modelled using one path point and two wrapping cylinders, placed on the right clavicle. The final routing path of the path spring is: waist path point - upper torso wrapping ellipsoid - shoulder wrapping cylinder 1 - shoulder path point - shoulder wrapping cylinder 2 - humerus path point. The resulting model is shown Fig. 2. The stiffness is set to 500 N/m, equal to the elastic resistance band (Kaytan Latex resistance band - light) that is used in the prototype. The rest length and location of the waist attachment point represent the functional and geometric parameters respectively for our exotendon design optimization. EXOTENDON OPTIMIZATION

This section introduces the biomechanics-aware optimization, which relies on the present model.

Defining the objective function

In order to optimize the exotendon design parameters, a reliable method to quantify its effect on the wearer was used. A metric to represent the cumulative muscle effort required to perform a given task was used.

The muscle activations are determined by the present neuromuscular model so as to produce the desired motion at the joints. Thus, for finding the optimal exosuit configuration, the muscle activations were predicted.

Solving muscle redundancy

The present neuromuscular system uses the muscles efficiently so as to minimize overall effort or energy while producing the desired motion. Static optimization, desired velocities and accelerations by filtering and differentiating the joint kinematics data of the motion, joint accelerations generated by the muscles as a function of their activation values, and a cost function as the norm of muscle activations, were used in calculations and predictions.

The quantities are defined for a single time step, and the muscle activations for dynamic motions are calculated by conducting the above static optimization for each time step.

Considered motions

Four motions of the shoulder task were considered: flexion-extension from - 450 to the horizontal, to 900 and back to - 450, as shown in Fig. 4A abduction-adduction from - 450 to the horizontal, to 900 and back to - 450, as shown in Fig. 4B , internal-external rotation from - 450 to the forward axis to 450, and back as shown in Fig. 4C.

Simulation study

Different configurations for the exotendon in its parameter space were simulated and the cumulative muscle effort required to perform the three motions were calculated. A grid of 21x21 values for the rest-length - between 0.4 and 1 m; and waist attachment point - between -0.1 m (left side) +0.1 m (right side), were used. While changing the attachment location also changes the exotendon pretension, this effect is negligible as compared to the range of considered exotendon rest-lengths. Each condition for the three considered motions was simulated. Fig. 3D-F show the cost surfaces for different exotendon configurations while performing the three considered motions. The cost surfaces have been normalized with the no exosuit condition such that a value of 1 corresponds to a cumulative muscle effort without an exosuit. The flat regions on all three cost surfaces with value of 1 correspond to the conditions when the exotendon has a large rest-length making it slack for the entire motion, and therefore applying no force on the human.

For motions 1 and 2, the exosuit reduces muscle effort in some configurations. The rest-length is preferably not too short in view of muscle effort. This is because for these shorter rest-lengths, the body has to act against the spring, requiring more effort. For motions 1 and 2, the optimal location of the waist attachment is -0. Im, which corresponds to the side of the body opposite of the supported arm. Lastly, for an optimal exosuit configuration, the muscle effort is significantly reduced for motion 1, close to 50% of no-exosuit condition. For motion 2, the best exosuit configuration reduces effort by only 10% than the no exosuit case. This suggests that the exosuit baseline design is well-suited for motion 1, but could be improved for motion 2. This can be done by changing some of the fixed parameters such as stiffness, and allowable attachment locations. For motion 3, there is an increase in the muscle effort while using the exosuit in all simulation conditions. This suggests that the baseline exosuit design presented is not suitable to support this motion, and therefore needs to be modified, either by changing the attachment regions completely, or the stiffness of the exotendon. These simulation results help to identify the optimal exotendon attachment points and thus aid in customizing exosuit design to the desired motion. This methodology also helps to filter out baseline designs for the given motion without requiring expensive fabrication and testing cycles. Lastly, small spikes on the cost surface for all three motion are seen. This can be attributed to the presence of the acromion joint constraint between the clavicle and scapula motions, which may be considered when finding the joint velocities and accelerations during static optimization.

EXOSUIT DESIGN AND FABRICATION

For the exosuit design, focus was on assisting motion 1 and selecting the optimized parameters of attachment location and rest-length using the simulation results from Fig. 3D. The main considerations for the exosuit design were: (i) device should be lightweight, (ii) anchor locations should be at load-bearing locations with suitable padding wherever necessary, (iii) interaction forces should act normally on the skin, (iv) exosuit size should be easy to adjust for different participants, (v) friction should low on the shoulder to allow free motion of the exotendon. Based on these, the exosuit as shown in Fig. 4 was made. The exosuit is primarily made using nylon webbing and the various sections are fastened on the wearer via length-adjustable buckles and Velcro® fasteners. The exotendon [passive element] itself is made using an elastic resistance band (Kaytan Latex resistance band, stiffness = 500N/m). It is affixed at the arm webbing with an inextensible Dyneeema® rope (2mm diameter) and at the waist with a webbing strap. The exotendon rest-length was defined as the length between the arm and waist attachments when the elastic band just begins to stretch. A length-adjustment buckle at the waist allows to easily change the exotendon rest-length. To minimize shear forces on the arm, the webbing straps over the forearm were extended and the exotendon forces were transferred to the hand using a glove. Similarly, at the waist, the exosuit consists of a waist belt reinforced with additional webbing straps that transfer XXXX six freely rotating steel rods to support and redirect the exotendon with minimal friction. By having two horizontal and two vertical rods at the front-side, this attachment can support the exotendon when the arm is flexing to the front or the side. Lastly, to safely distribute the loads from the exosuit to the user, the inner side of the entire exosuit is padded with 4mm thick ethylene copolymer foam. The fabricated exosuit weighs 600 grams.

EXPERIMENTAL VALIDATION

Testing conditions

The exosuit was tested with six male participants (H: 1.78±0.06m; W: 72 ± 6.8kg) and their muscle activity was measured while performing motion #1. The optimal exotendon rest-length for each participant scaled according to their height was calculated, and this value was set using the length adjustment buckle at the waist. The participants then flexed and extended the arm ten times, performing motion #1. During the test, the surface electromyography (EMG) activity of four muscles - deltoid anterior, mid, and posterior, and trapezius scapula - using Delsys® surface EMG sensors (inter-electrode distance of 20mm) was measured. The sensors were placed as shown in Fig. 5A. The test was repeated under two conditions: with and without exosuit. After data collection, the raw EMG was processed by first high pass filtering at 100 Hz, followed by full-wave rectification, and then low-pass filtering at 4 Hz. The processed EMG data was normalized by maximum voluntary contractions measured at the end of the experiment.

Results

Fig. 5B shows the root-mean-squared (RMS) and standard deviations of the measured EMG activity of the six participants under the two conditions above. The use of the exosuit reduces muscle activity of almost all the measured muscles for all participants. This reaffirms the fact that the exotendon is able to share the load taken by the muscles while performing the task. At the same time, an increase in activity of the deltoid posterior for participants 5 and 6 is seen. As this muscle is the primary shoulder extensor, an increase in its activity while using the exosuit suggests that for participants 5 and 6, the rest-length was too small and the participants had to counteract the exotendon forces in order to extend the arm back, showing that a proper design is important. Furthermore, participant 6 also shows an increase in trapezius muscle activity. As the exosuit forces try to depress the clavicle and scapula, the trapezius has to act to lift and support the shoulder. By scaling the model appropriately for each individual participant according to the invention the participant-specific optimal exotendon configuration is found.

Fig. 6 shows the evolution of muscle activity of Subject 4 while performing the flexion-extension task. The continuous curves correspond to simulated values and the dotted curves correspond to the RMS measured values, averaged over the ten cycles. The shaded regions show the corresponding standard deviation at each time step. The simulations and measured values of the deltoid anterior muscle correlate sufficiently. Differ- ences clearly relate to parameters not taken int account in the simulations, yet.