Human Lower Limb

TECHNICAL FIELD

The present disclosure relates to movement assistance apparatuses, more particularly to a cable-driven movement assistance apparatus for human lower limb.

BACKGROUND

The statements herein only provide background information related to the present disclosure, and do not necessarily constitute prior art. In general, a cable-driven lower limb movement assistance apparatus aiming for people with motor deficits, depending on joint(s) at which the apparatus is (are) used, can be roughly divided into two types: 1) apparatus configured to assist a single lower limb joint, such as assist-on ankle apparatuses, assist-on knee apparatuses, both kinds of which are able to provide assistance and support for the knee flexion and extension movements; 2) apparatus configured to assist multi-joints, namely, to assist two or more of hip, knee and ankle joints. Current movement assistance apparatus either operated in a single joint assistance mode or a multi-joints assistance mode. Most of them are unilaterally configured, and have to be fixed very tight to a user’s limb to ensure the stability of force transmission.

SUMMARY

Aspects of the present disclosure are directed to a cable-driven movement assistance apparatus for human lower limb. Additional aspects of the present disclosure will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by the practice of this disclosure.

In accordance with an aspect of the present disclosure, it is provided a movement assistance apparatus for assisting lower limb movement of a user, which includes a backpack containing a control module and a driving source; and a lower limb assembly configured to be worn on a lower limb of the user. The backpack, in use, is attached to the user. The lower limb assembly includes two rotational joint members for assisting at least one joint of the lower limb of the user, and each rotational joint member is arranged to be aligned and rotates in unison with the assisted joint of the user. The two rotational joint members are connected to the driving source through cables. The control module is configured to control the driving source to apply an assistance force, and the assistance force is transmitted to the respective rotational joint member through the cables.

In one embodiment, the housing is a backpack.

In one embodiment, the lower limb assembly further includes two pivot joint members corresponding to the two rotational joint members for assisting at least one joint of the lower limb, the two rotational joint members and the corresponding two pivot joint members being disposed on opposite sides, aligned to rotate in unison with each other and with the assisted at least one joint.

In one embodiment, the rotating in unison with the assisted joint is achieved by aligning an axis of rotation of the rotational joint member and the corresponding pivot joint member with the axis of rotation of the assisted joint.

In one embodiment, the lower limb assembly is a carbon fiber fabricated lower limb exoskeleton configured to be unilaterally worn on the lower limb of the user and deliver assistance.

In one embodiment, the lower limb exoskeleton further includes a waist fixing structure configured for fixing the lower limb exoskeleton to a waist of the user.

In one embodiment, the waist fixing structure includes a belt adjusting unit, through which a length of the waist fixing structure is adjustable.

In one embodiment, the lower limb exoskeleton further includes a knee joint frame configured to be fixed on a femoral and calf region of the lower limb, the rotational joint member disposed on the knee joint frame is configured for assisting rotation of the knee.

In one embodiment, the lower limb exoskeleton further includes an ankle joint frame configured to be fixed on a calf and foot region of the lower limb, the rotational joint member disposed on the ankle joint frame is configured for assisting rotation of the ankle.

In one embodiment, the lower limb exoskeleton further includes a foot support structure configured to be coupled to a foot of the user, and the foot support structure is pivotally connected to the ankle joint frame.

In one embodiment, the movement assistance apparatus also includes one or more sensors for detecting motion information about motion information of the respective assisted joint. The control module in communication with the one or more sensors, is configured to control the driving source in accordance with the motion information.

In one embodiment, at least one of the two rotational joint members includes:an angle sensor for detecting the motion information; and a shaft, bearing, and pulley structure for guiding rotational motion of the rotational joint, where the cables are wound around a pulley of the shaft, bearing, and pulley structure to transit the assistance force to the rotational joint.

In one embodiment, the cables includes cable sheaths and inner cables, and the inner cables slidably housed in the cable sheaths are connected to the pulley and the driving source at opposite ends.

In one embodiment, the inner cables include nylon wires, steel wires or other flexible wires.

In one embodiment, the cable is a combination of steel wire and nylon cable, and hollow screws are provided on cable ends and configured to pre-tighten the cables.

In one embodiment, the knee joint frame is flexibly connected to the waist fixing structure by connecting straps.

In one embodiment, the driving source includes an actuator composed of a brush less DC motor driving the ball screw set, and an absolute encoder is provided to detect a position of the motor.

In accordance with another aspect of the present disclosure, it is provided a movement assistance apparatus for assisting lower limb movement of a user, which includes a backpack containing a control and actuation system and a lower limb exoskeleton configured to be worn on a lower limb of the user. The backpack, in use, being attached the user. The lower limb exoskeleton includes a knee joint frame configured to be fixed on a femoral and calf region of the lower limb, and an ankle joint frame configured to be fixed on a calf and foot region of the lower limb. The knee joint frame including a first rotational joint member is configured to be aligned and rotating in unison with a knee joint of the user. The ankle joint frame including a second rotational joint member is configured to be aligned and rotating in unison with an ankle joint of the user. The control and actuation system is configured to control and apply an assistance force to drive the first and second rotational joint members through cables, respectively, to assist rotation of the knee or ankle joint of the user.

In one embodiment, the control and actuation system also includes an linear series elastic actuator and a control module. The linear series elastic actuator is connected to the first and second rotational joint members through the cables. The control module is in communication with one or more sensors disposed on the knee and/or ankle joint frames, and configured to control the actuator, in accordance with motion information of the keen and ankle joints of the user detected by the one or more sensors, to apply the assistance force to assist the rotation of the knee or ankle joint of the user. The assistance force is transmitted to the first and/or second rotational joint members through the cables.

In one embodiment, the rotating in unison with the assisted joint is achieved by aligning an axis of rotation of the first or second rotational joint member with the axis of rotation of the respective assisted joint.

In one embodiment, the lower limb exoskeleton further includes a foot support structure configured to be coupled to a foot of the user.

In one embodiment, the ankle joint frame and the knee joint frame are pivotally connected, and the foot support structure the ankle joint frame are pivotally connected.

In one embodiment, each of the first and second rotational joint members includes an angle sensor for detecting the motion information; and a shaft, bearing, and pulley structure for guiding rotational motion of the rotational joint. The cables are wound around a pulley of the shaft, bearing, and pulley structure to transit the assistance force to the rotational joint.

In one embodiment, the cable includes a cable sheath and an inner cable, and the inner cable slidably housed in the cable sheath is connected to the pulley and the driving source at opposite ends.

In one embodiment, the inner cables include nylon wires, steel wires or other flexible wires.

In one embodiment, the cable is a combination of steel wire and nylon cable, and hollow screws are provided on cable ends and configured to pre-tighten the cables.

In one embodiment, the knee joint frame is flexibly connected to the waist fixing structure by connecting straps. In one embodiment, the linear series elastic actuator includes a brush-less DC motor driving the ball screw set, and an absolute encoder is provided to detect a position of the motor.

The movement assistance apparatus disclosed in the present disclosure has bilateral frame structures thus the force transmission can be more stable and smoother. The assistance force is transmitted by cable-driven mechanism without constrains to human hip joint, and enables the actuation system to be separated from the lower limb exoskeleton. The rotational joints of the lower limb exoskeleton are arranged to be aligned and rotate in unison with the respective human joints, the waist fixing structure and the lower limb exoskeleton can be adjusted to fit different body size of users. The lower limb exoskeleton can be reconfigured to assist the ankle joint and knee joint alone, or both joints simultaneously. The actuation and control system are embedded into a compact backpack, which can provide advantages of reducing the burden to the user, and enabling the user to conduct free walking.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, features and advantages of the present disclosure will become more readily appreciated when considered in connection with the following detailed description of various embodiments and accompanying drawings, in the figures of the accompanying drawings like reference numerals refer to similar elements, in which:

FIG. 1 is a perspective view illustrating a movement assistance apparatus in accordance with an exemplary embodiment of the present disclosure;

FIG. 2 is a perspective view illustrating the movement assistance apparatus worn on an impaired limb of a user;

FIG. 3 is a front view illustrating the movement assistance apparatus worn on the impaired limb of a user;

FIG. 4 is a perspective view illustrating a knee joint frame of the movement assistance apparatus in accordance with an exemplary embodiment of the present disclosure;

FIG. 5 schematically shows a flexion or extension motion of the knee joint frame in sagittal plane in accordance with an exemplary embodiment of the present disclosure;

FIG. 6 is a perspective view illustrating an ankle joint frame of the movement assistance apparatus in accordance with an exemplary embodiment of the present disclosure;

FIG. 7 schematically shows a plantarflexion or dorsiflexion motion of the ankle joint frame in the sagittal plane in accordance with an exemplary embodiment of the present disclosure;

FIG. 8 shows a backpack assembly of the movement assistance apparatus, in accordance with an exemplary embodiment of the present disclosure;

FIG. 9 illustrates a hardware implementation of a cable-driven knee-ankle-foot exoskeleton in an example embodiment of the present disclosure;

FIG. 10 illustrates a modeling of the linear series elastic actuator and implemented PD control scheme in the example embodiment of the present disclosure;

FIG. 11 shows force tracking performance with different signals: (A) square signal at 0.5 Hz; (B) 0.5 Hz case of a chirp signal; and (C) 5 Hz case of a chirp signal in accordance with the example embodiment illustrated in FIGS. 9 and 10;

FIG. 12 shows frequency response of a linear series elastic actuator (SEA) in accordance with the example embodiment illustrated in FIGS. 9 and 10;

FIG. 13 shows an experimental process as well as performances, including (A) force tracking performance on the knee joint; and (B) performance of zero-impedance control on both knee and ankle joints in accordance with an example embodiment; and

FIG. 14 shows gait detection results, (A) the detected gait event; (B) the norm value of the ankle angular velocity; and (C) collected angle values of shank and ankle in accordance with the example embodiment shown in FIG 11. The data were collected under treadmill walking of a healthy participant (172 cm, 65 kg) at 3 km/h speed.

DETAILED DESCRIPTION

Before turning to the figures, which illustrate certain exemplary embodiments in detail, it should be understood that the present disclosure is not limited to the details or methodology set forth in the description or illustrated in the figures. It should also be understood that the terminology used herein is for purpose of description only and should not be regarded as limiting.

As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes” and/or “including,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof.

As utilized herein, the terms "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer" and other directions or positional relations are based on the positions or positional relations shown in the drawings, and are only for the convenience of describing the embodiments of the present disclosure and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be configured and operated in a specific orientation, and therefore cannot be understood as a limitation to the embodiments of the present disclosure.

In the embodiments of the present disclosure, unless otherwise clearly specified and defined, the terms “installed/mounted,” “in contact/connection with,” “connected/coupled,” “fixed,” and other terms should be understood in a broad sense. For example, it may be fixedly or detachably connected or may be integrated; it can be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be an internal communication of two components or an interaction relationship between the two components. For those of ordinary skill in the art, the specific meanings of the above- mentioned terms in the embodiments of the present disclosure can be understood according to specific conditions.

A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the figures.

Referring to FIG. 1, it is shown a perspective view of a movement assistance apparatus in accordance with one example embodiment of the present disclosure. Disclosed herein a movement assistance apparatus includes a lower limb assembly which is configured to be worn on a lower limb of a user. The lower limb assembly includes a knee joint frame 1 and an ankle joint frame 2 to provide assistance and support for a knee joint and an ankle joint of a user. In the embodiment, the ankle joint frame 2 may be pivotally connected to the knee joint frame 1 through a rotational joint member 3a. The lower limb assembly may also include a foot support structure configured to support a foot of the user. The foot support structure may be pivotally connected to the ankle joint frame 2 through a rotational joint member 3b. The knee joint frame 1 may be connected to the waist fixing structure 5 using flexible connecting straps 4. The waist fixing structure 5 may be formed of flexible materials so that it can be closely and flexibly attached to a waist of the user. It should be noted that the lower limb assembly can be worn on either a left lower limb or a right lower limb. In some embodiments, the movement assistance apparatus may include two lower limb assemblies respectively worn on the right and left lower limbs to assist both lower limbs movements of the user. In this embodiment, the knee joint frame 1 and the ankle joint frame 2 are respectively provided with rotational joint members 3a, 3b for assisting the lower limb, such that an assistance force can be transmitted by cable-driven mechanism without constrains to the human hip joint, in this way, the actuation system can be separated from the lower limb exoskeleton.

The movement assistance apparatus also includes a housing, which, in use, is attached to the user. In this embodiment, the housing may be a backpack 9. The backpack 9 containing a driving source configured to supply a driving force to the rotational joint member 3a and 3b and a control module for controlling a motion of the movement assistance apparatus. In an embodiment, one or more sensors may be provided on the rotational joint member 3a and 3b, and configured to detect motion information of the lower limb of the user. The control unit is configured to control the motions of rotational joint member 3a and 3b, based on motion information detected by the one or more sensors, thereby driving the ankle joint frame 2 and the foot support structure to conduct accompanying motions. In some embodiments, the backpack 9 may be configured to be attached to a back of the user through braces 6. The backpack 9 is also connected to the waist fixing structure 5 through one or more connecting straps 8. The waist fixing structure is formed of flexible materials, so that it can be adjusted to fit different body size of users. In some example embodiments, the waist fixing structure is provided with a belt adjusting unit, through which a length of the waist fixing structure can be adjusted. It should be understood that the lower limb assembly may also be arranged to be adjustable so as to fit different body size of users.

Referring still to FIG.l, cables 721, 722 are provided having one end being connected to and wound around a pulley in the rotational joint member 3a, and the other end being connected to a driving source. The ankle joint frame 2 may pivot on the rotational joint member 3a based on a contraction and extension of the cables 721, 722. The cables 721, 722 are slidably housed in cable sheathes 701, 702, respectively. By using of the cable sheathes, paths can be routed. The cable sheathes 721, 722 may be fixed on the knee joint frame 1 by means of cable plugs 711, 712, respectively. In an exemplary embodiment, when the cable 722 is contracted by the driving source, it drives the pulley in rotational joint member 3a to rotate, thus drives the ankle joint frame 2 to pivot on the rotational joint member 3a in a knee extension direction. Similarly, when the cable 721 is contracted by the driving source, it also drives the pulley in rotational joint member 3a to rotate, then drives the ankle joint frame 2 to pivot on the rotational joint member 3a in a knee flexion direction.

In an embodiment, cables 723, 724 may also be provided having one end being connected to and wound around the pulley in the rotational joint member 3b, and the other end being connected to the driving source. The foot support structure may pivot on the rotational joint member 3b based on the contraction and extension of the cable 723, 724. The cables 723, 724 are slidably housed in cable sheathes 703, 704, respectively. By using of the cable sheathes, paths can be routed. The cable sheathes 703, 704 my be fixed on the ankle joint frame 2 by means of cable plugs 713, 714, respectively. In an exemplary embodiment, when the cable 723 is contracted by the driving source, it drives the pulley in rotational joint member 3b to rotate, thus drives the foot support structure to pivot on the rotational joint member 3b in an ankle plantarflexion direction. Similarly, when the cable 724 is contracted by the driving source, it also drives the pulley in rotational joint member 3a to rotate, then drives the foot support structure to pivot on the rotational joint member 3b in an ankle dorsiflexion direction. It should be understood that the cables, hereinafter, may be any flexible wires, for example, the nylon wires or steel wires etc. Or the cable may be a combination of steel wire and nylon. In some embodiment, hollow screws may be provided on the cable ends so as to pre-tighten the cables when applied on different subjects.

In an embodiment, a first fixing member 10 may be provided in connection with the knee joint frame 1. The first fixing member 10 is configured to mount the knee joint frame 1 on a femoral region of the user. In an embodiment, a second fixing member 11 may be provided in connection with the ankle joint frame 2. The second fixing member 11 is configured to mount the ankle joint frame 2 on a calf region of the user. As a user wears the movement assistance apparatus, the ankle joint frame 2 may be extended in a length direction of a leg of the user. The ankle joint frame 2 may include a plurality of links. The assistance force is transmitted by cable-driven mechanism without constrains to the human hip joint, the joints of the exoskeleton are able to rotate aligned to the human joints, the waist fixing structure and exoskeleton can be adjusted to fit different body size of users, and the modular exoskeleton can be reconfigured to assist the ankle joint and knee joint alone, or both joints simultaneously.

Referring to FIG. 2 and FIG. 3, a perspective view as well as a front view illustrating the movement assistance apparatus worn on an impaired lower limb of a user in accordance with one example embodiment of the present disclosure are shown. In this embodiment, the movement assistance apparatus may be worn on any side of the lower limb of the user.

Hereinafter, the knee joint frame 1 and ankle joint frame 2 in accordance with one example embodiment of the present disclosure will be further described in detail by referring to the accompanying drawings.

FIG. 4 is a perspective view illustrating the knee joint frame of the movement assistance apparatus in accordance with one example embodiment of the present disclosure. FIG. 5 schematically shows a flexion or extension motion of the knee joint frame in sagittal plane in accordance with one example embodiment of the present disclosure. In an exemplary embodiment, the knee joint frame 1 may actively pivot on the rotational joint member 3a to provide assistance at the knee joint for the user wearing the knee joint frame 1 to move in the flexion or extension direction. In this embodiment, the knee joint frame 1 may include a first knee plate 101, a second knee plate 106, a third knee plate 104 and a fourth knee plate 108. The first and second knee plates 101, 106 are coupled to the waist fixing structure 5 through connecting straps 4. The third and fourth knee plates 104, 108 are connected to the ankle joint frame 2, respectively. Upper ends of the first and second knee plates 101, 106 are connected through a rigid curved member 105 in a direction transverse to the leg of the user. The rigid curved member 105, combing with strap fixing elements 110a, 110b and a first fixing member 10, enables the knee joint frame 1 to be mounted on a femoral region of the user. Upper ends of the third and the fourth knee plates 104, 108 are connected through a rigid curved member 109 in the direction transverse to the leg of the user. The rigid curved member 109, combing with strap fixing elements 110c, llOd and a second fixing member 11, enables the knee joint frame 1 to be mounted on a calf region of the user. The rotational joint member 3a may include an angle sensor 301, a joint plate 302, a shaft 303, a bearing 304, two idle pulleys 305a, 305b, a pulley 306, and a gasket structure 307. The cables 721, 722 may be wound around the pulley 306. By connecting the first knee plate 101 and the joint plate 302 having a gasket structure 307, the rotational joint member 3a is fixed on the first knee plate 101. The third knee plate 104 is connected to the pulley 306. The angle sensor 301 mounted on the joint plate 302 is configured to detect motion information of the knee joint of the user, and the detected motion information from angle sensor 301 may be transmitted to the control module. The control module is configured to control a motion of the driving source such as to constrict or release the cables 721, 722, based on the detected motion information, and then control motions of rotational joint member 3a, thereby assisting the ankle joint frame 2 to conduct accompanying motions.

In an embodiment, a lower end of the first knee plate 101 is connected to an upper end of the third knee plate 104 through a rotational joint member 3 a, and a lower end of the second knee plate 106 s connected to an upper end of the fourth knee plate 108 through a pivot joint member 107. Hence, the third knee plate 104 and fourth knee plate 108 can pivot on the rotational joint member 3a and the pivot joint member 107, respectively, such that the ankle joint frame 2 can rotate in the same direction accordingly, and the rotational joint member 3a and the pivot joint member 107 are aligned.

In an embodiment, the first knee plate 101 is provided with a cable end base 102 on which the cable sheaths 701, 702 are respectively fixed by means of cable plugs 711, 712. In an embodiment, the first knee plate 101 is further provided with a reinforcing knee plate 103 to reinforce the knee joint frame 1.

FIG. 6 is a perspective view illustrating the ankle joint frame of the movement assistance apparatus in accordance with one example embodiment of the present disclosure. FIG. 7 schematically shows a plantarflexion or dorsiflexion motion of the ankle joint frame in sagittal plane in accordance with an exemplary embodiment of the present disclosure. In an exemplary embodiment, the ankle joint frame 2 may actively pivot on the rotational joint member 3b to provide assistance for the calf and ankle of the user wearing the ankle joint frame 2 to conduct the plantarflexion or dorsiflexion motions. In this embodiment, the ankle joint frame 2 may include first ankle plates 201a, 201b, a second ankle plate 206 a third ankle plate 203 and a fourth ankle plate 208. The first and second ankle plates 201a, 201b, 206 are connected to the knee joint frame 1, respectively. The third and fourth ankle plates 203, 208 are connected to the rotational joint member 3b and foot support structure 210, respectively. Upper ends of the first ankle plate 201b and the second ankle plate 206 are connected through a rigid curved member 109 in a direction transverse to a calf of the user. Upper ends of the third ankle plate 203 and the fourth ankle plate 208 are connected through a rigid curved member 205 in the direction transverse to the calf of the user. The rigid curved members 109, 205, combing with the strap fixing elements 110c, llOd, 212a, 212b and two second fixing members 11, enables the ankle joint frame 2 to be mounted on a calf region of the user. The rotational joint member 3b is the same as rotational joint member 3 a, thus the detail configuration of rotational joint member 3b will not be repeated here. The cables 723, 724 may be wound around the pulley 306. By connecting the third ankle plate 203 and the joint plate 302 having a gasket structure 307, the rotational joint member 3b is fixed on the third ankle plate 203. The foot support structure 210 is connected to the pulley 306. In some example embodiments, the foot support structure in the ankle joint may be a shoe.

In an embodiment, an upper end of the third ankle plate 203 is connected between lower ends of the first ankle plates 201a and 201b, and an upper end of the fourth ankle plate 208 is connected to a lower end of the second ankle plate 206 through a sliding connector 207, allowing the third ankle plate 203 and fourth ankle plate 208 to be extended in a length direction of the leg of the user. In an embodiment, a lower end of the third ankle plate 203 is connected to the foot support structure 210 through a rotational joint member 3b, and a lower end of the fourth ankle plate 208 is connected to the foot support structure 210 through a pivot joint member 209. Hence, the foot support structure 210 can pivot on the rotational joint member 3b and pivot joint member 209 such that provide ankle assistance in the same direction accordingly, and the rotational joint member 3 a and the pivot joint member 209 are aligned. In an embodiment, the first ankle plate 201 is provided with a cable end base 211 on which the cable sheaths 703, 704 are respectively fixed by means of cable plugs 713, 714. In an embodiment, the first ankle plate 201 is also provided with a reinforcing ankle plate 204 to reinforce the ankle joint frame 2. In varies embodiments of the present disclosure, the bilateral frame structure enables a more stable and smoother force transmission.

In some example embodiments, the movement assistance apparatus may also include a hip joint assistance mechanism.

In some example embodiments, the connecting straps can be configured to be a bracket having a universal joint aligned to the wear’s hip joint when the apparatus is in a mounted state, connecting the lower limb exoskeleton and the waist fixing structure.

Referring to FIG. 8, it is shown a backpack of the movement assistance apparatus in accordance with one example embodiment of the present disclosure. As aforementioned, the backpack 9 may be attached to a back of the user through flexible braces 6, the backpack 9 is also connected to the waist fixing structure 5 closely and flexibly through connecting straps 8. In an example embodiment, the backpack 9 may include a base plate 901 and a protection shell 906. On the base plate 1, a control module including a driver unit 903, a control unit 904 and a battery 905 is disposed. The base plate 1 is also disposed with a driving source 902. The driving source 902 may include an actuator embedded inside, for example, a linear actuator, DC motor or hydraulic actuator or any other force controllable actuators, which will not be limited here. The control module in communication with one or more sensors disposed on the knee and/or ankle joint frames, such as angle sensors mounted on one or two of the rotational joint members 3a, 3b, as above mentioned. The one or more sensors are configured to detect motion information of the lower limb of user. The control unit 904 is configured to generate and provide a control signal to the driver unit 903 based on the detected motion information, so as to control a motion of the driving source 902 to apply a driving force so as to assist the user’s knee joint movement, ankle joint movement and/or bi-joints movements. The battery 905 is configured to supply power to the control and actuation system. It should be noted that the movement assistance apparatus may assist the user to complete three movements, which are knee joint movement, ankle joint movement, and bi-joints movements, successively. Moreover, it can be anticipated that the movement assistance apparatus may also be operated in single joint assistance mode, which provides assistance to knee joint or ankle joint alone.

Referring still to FIG. 8, The cable sheaths 701, 702, 703, and 704 are connected to the driving source 902 using cable plugs 731, 732, 733, and 744, respectively. The cable 721, 722, 723, and 724 are directly connected to the actuator embedded in the driving source 902. The protection shell 906 is provided to protect the control and actuation system. In some example embodiments, inner cables of the cable-driven based force transmission mechanism may be any flexible wires, for example, the nylon wires or steel wires etc.

In various embodiments, the wearable movement assistance apparatus provided in the present disclosure has a compact series elastic actuators and Boden-cable transmission mechanism, which contributes to a portable and lightweight system. The movement assistance apparatus capable of assisting impaired lower limb of a user provided in the present disclosure can be operated in the single joint assistance mode or the multi joints assistance mode. The movement assistance apparatus has bilateral frame structures thus the force transmission can be more stable and smoother. The assistance force is transmitted by cable-driven mechanism without constrains to the human hip joint, and enables the actuation system to be separated from the lower limb exoskeleton. The joints of the lower limb exoskeleton are able to rotate aligned to the human joints, the waist fixing structure and the lower limb exoskeleton can be adjusted to fit different body size of users. The lower limb exoskeleton can be reconfigured to assist the ankle joint and knee joint alone, or both joints simultaneously. The actuation and control system are embedded into a compact backpack, which can provide advantages of reducing the burden to the user, and enabling the user to conduct free walking.

Examples of the present disclosure are directed to a cable-driven knee-ankle-foot exoskeleton. In the following descriptions, methods including the mechanical design of the linear series elastic actuators, gait detection based on inertial measurement units, design of the lower limb exoskeleton, and modeling and controller design of actuator are presented. In addition, the performance evaluation of the linear series elastic actuator and a validation experiment on a human wearer were carried out.

Linear SEA design

SEA has been widely adopted in rehabilitation robotics to maintain a safe and efficient human-robot interaction. The following aspects feature the performance of the linear series elastic actuators in the human-friendly robotics domain: intrinsic compliance with low impedance and better back-drivability compared to stiff actuators, excellent capability to absorb unexpected interaction impacts, and high force controllability and smooth force transmission.

The determining factor of a SEA's performance is the elastic element. Spring is the most commonly used elastic element. Low spring stiffness contributes to the high fidelity of force control, low output impedance, and low stiction. In contrast, high spring stiffness contributes to higher force range and bandwidth. Hence, trade-off always happens when developing appropriate SEAs. Before designing, it is essential to analyze human biomechanics to select a proper spring constant. Previous biomechanical studies showed that the needed assistive torque on the lower limb joints during gait rehabilitation is much lower than the joint peak torque, needed assistance torque is about 30% of the peak torque, which is around 6 Nm for the knee joint and 10.5 Nm for ankle joint at a walking speed of 1.1 m/s. Hence, the actuator would be operated in a low force range most of the time, which means that a strong spring would not be necessary to develop SEA for assisting the target patients.

The SEA works as the pure torque source of this system. As mentioned, the spring determines the performance of the actuator. A previous linear SEA adopted springs with 24 N/mm stiffness for the low force range control based on the biomechanical analysis. However, the cable sheaths in this system would induce extra transmission friction, which would lead to 33% ~ 44% force transmission reduction (tested cable sheath length: 2.2 m, inner cable diameter: 1.2 mm). Hence, the spring selected here has larger stiffness at 40 N/mm to ensure a maximum 400 N spring-based output force equivalent to a maximum 14 Nm output torque in this system, which can meet the mentioned joint assistance requirements.

In the above-mentioned embodiments, the portable system incorporates the backpack mounted on wearer’s back containing actuation system and battery, Bowden- cable based transmissions, and a modular knee-ankle-foot exoskeleton. In this embodiment, the actuator is composed of a brush-less DC motor driving the ball screw set. An absolute encoder is provided to detect the position of the motor, and the pitch of the ball screw is 2 mm/rev with an output ability of more than 1000 N and excellent transmission efficiency (typically above 90%). The stroke of this actuator is 65 mm, and the maximum output speed is 0.226 m/s (equivalent to a joint rotational speed at 7.6 rad/s). A sliding carriage was designed to contain two linear springs to transmit the compression force into the output. A high precision linear encoder was used to measure the deflection of the springs, and then the information is utilized to control the interaction force according to Hooke's Law. Converting force control into position control is another outstanding advantage of the SEA, which significantly ameliorates the stability and precision of force control. In this embodiment, the cable is a combination of steel wire and nylon cable. The hollow screws are provided on the cable ends which can be used to pre-tighten the cables when applied on different subjects; it may be essential to maintain the cable tensioned for efficient force transmission. All the specifications of the SEA are presented in Table 1. The weight of the proposed SEA is lighter than the existing linear SEAs with comparable force delivery ability. Table 1. Specifications of the actuator

Parameters for Parameters for

Description rotational motion translational motion

Maximum 8000

Motor speed Speedmax= 0.266 m/s rpm

Motor torque Maximum 0.3 Nm Forcemax> 840 N Rotary encoder Resolution: 12 bits Resolution: 0.488 pm Linear spring k = 40 kN/m Force range: 0- 400 N Ball screw Ph= 2 mm/rev / Stroke 32.5 rev 65 mm

Linear resolution: 1 pm

Linear encoder / Force resolution: 0.04 N Total weight 720 g

Mechanical Design of the Cable-driven Knee- Ankle-Foot Exoskeleton

Possible lower limb deficits of chronic post-stroke patients include decreased ankle plantarflexion and knee hyperextension in the stance phase; decreased knee flexion and ankle dorsiflexion caused by foot-drop during the swing phase, which leads to a slow and metabolic expensive pathological gait. Besides, several design principles should also be identified to meet the inherent requirements and challenges of the gait assistance: Firstly, the wearable system must be lightweight and induce less inertia to the human limbs to improve its portability and mitigate metabolic detriment. Secondly, the exoskeleton structure should be ergonomically adaptive to a range of lower limb lengths. Thirdly, the system should not induce additional constraints to hinder human natural walking movements.

In this embodiment, the whole system is composed of a compact backpack configured to contain the controller, actuation system, and a power source; a waist belt and braces configured to distribute through the backpack over the wearer’s waist and back; a carbon fiber fabricated lower limb exoskeletons configured to be unilaterally worn on the impaired lower limb and deliver assistance, and a suite of two IMUs adopted to detect the real-time gait phase. The total weight of this device is 5.1 kg, which is lighter than many commercial portable devices. Thanks to the cable-driven mechanism, the actuation system and power source are allowed to be placed away from the limbs of the wearer. More than 74 % (3.8 kg) of the total mass is located above the waist and only 1.3 kg add-on mass on the impaired limb.

In the above embodiment, generated forces are transmitted by Bowden-cable based mechanism. On robotic joints, the inner cables wound around a rotational pulley at a 35 mm diameter antagonistically to assist the human joints with flexion or extension deficits. It is worth noting that in the present disclosure a combination of cables to the transmission mechanism is applied. At an output side of the SEA and the terminal side where a small radius of rotation exists, it is used high strength nylon cables with a load capacity of 800 N and 2 mm in diameter. At the same time, steel cables with a 1.5 mm diameter were used as inner cables to reduce the friction induced by the sheaths. The bilateral structure of the exoskeleton enables the generated assistance torque to be transmitted more steadily and eliminates undesired shear forces. Besides, such bilateral design can provide better accommodation for heterogeneous joint deficits, such as ankle inversion and eversion. It is also shown a capability of assisting the knee and ankle joints simultaneously or be reconfigured to be a single joint exoskeleton, which extends its application scenarios. Moreover, a series of location holes have been designed on the connecting sides of two modules, so the length of the shank structure can be adjusted from 37 cm to 41 cm, suitable for subjects with a height from 162 cm to 182 cm. And the lengths of the cable sheaths, which are 60 cm (on knee joint) and 100 cm (on ankle joint), were selected according to the maximum height of a wearer (182 cm).

Notably, the human hip joint is not assisted. Since the deficit on the hip joint, known as hip hiking, usually happens to increase the toe clearance of the impaired leg, and it can be significantly relieved after providing proper assistance and correction on knee and ankle joints. Then only a soft brace is used to connect the lower limb exoskeletons and waist belt to avoid slippage of the lower limb exoskeletons during walking. Such structural design minimizes the movement constraints of unassisted joints.

Hardware Implementation of Cable-driven Knee- Ankle-Foot Exoskeleton

As mentioned, a compact backpack was designed to contain the actuation system, controller, and power source and placed close to the body's center of mass, which reduced the energy cost during walking. In this embodiment, the actuation system consists of two SEA modules. Each SEA module uses one brushless DC motor (24 V, 330 W) integrated with a motor driver, which is controlled by a microcontroller using the analog command. The chosen power source is a 24V, 3800 m Ah capacity lithium battery. As shown in FIG. 9, a suite of two IMU sensors RS485 protocol were attached on the shank and foot to determine the gait information. The detection method and results will be presented later below. Then the force profiles and assistive timings would be adjusted accordingly. The joint angle information would also provide a quantitative measure of the recovery progress based on the range of motion. It can also be utilized as feedback to tune the assistive torques for the impaired leg.

Modeling and controller design of the SEA

FIG. 10 shows the model and controller of the SEA system. The SEA is modeled as a system that converts the rotary movements to equivalent translational movements with translational elements (springs and damping).

In this model, F _m is the generalized motor force between the ground base and a lumped sprung mass (mi + m2), where mi is the equivalent mass of the rotor and a coupler, and m2 is the equivalent mass of the ball screw. A viscous back-driving damping bm is generated from transmission friction and motor friction. Springs with stiffness (k) transfer the output force (F _k ) to the load mass (m ₃ ), and viscous friction (b _k ) is generated between the ball screw and springs support mechanism. The xi and X2 are the positions of the motor and load mass, respectively. The sprung mass contains a summation of forces from the motor (F _m = c u, where c denotes the motor torque constant and u denotes the input current to the motor), the spring (F _k =k Ax), and the viscous friction (F _b ). Hence, the equation of motion can be expressed as below according to Newton's second law:

In the case of non-fixed load, the linear encoder can measure the spring deflection (Dc =xi - X2). To simplify the force controller design, it is assumed that the load side is fixed, which refers to a high-output impedance configuration in actual application. Then, X2 = 0, F _k =kx ₁ , and F _k =kx _1. So, (1) can be rewritten as:

Finally, the transfer function between Fk and u after Laplace Transformation can be given by:

The force dynamics can be formulated as a second-order linear model. For the force control of the SEA, a PD controller is designed according to the linear dynamic model, and the control scheme can be illustrated as FIG. 10.

The PD controller is denoted as: u = k _p + k _d s with gains k _p and k _{d .}

Therefore, the closed-loop dynamics can be deduced as:

F _k (s) ckk _d s+ckk _p

F _d (s) (m ₁ +m ₂ )s ² +(b _m -l-b _k -l-ckk _d )s-l-ckk _p -l-k (4.)

Then the control performance can be easily tuned with the zero-pole assignment method.

In accordance with the above example embodiment, the testing results of the SEA with a fixed load end and a validation experiment with the exoskeleton worn on a human user are further presented below.

Characterization of the SEA System Identification: It is imperative to identify the force dynamics before the force control application. By sending the current command referred to a chirp signal with frequencies from 0.5 to 20 Hz, the main characteristics of the SEA could be excited. By utilizing the System Identification Toolbox of MATLAB, the identified linear model can be obtained as below:

F _k ( ^s ) _ 3.0081X10 ⁵ ^

U(s) ^_ s ² + 11.9893s+494.6976 ^ ^

Then the PD control parameters were tuned accordingly, where k _p = 0.2, k _d = 0.1.

Force control performance: Accurate force delivery is a crucial factor in exoskeleton design and assistance control for target patients. To evaluate the effectiveness of the proposed PD controller, the force control performance is evaluated by force tracking of a square signal at 0.5 Hz and a chirp signal with frequencies ranging from 0.5 to 5 Hz. The amplitude of force trajectory is 90 N and 50 N for the chirp and square signal, respectively.

FIG. 11 A shows that the SEA can quickly track the square-desired force, which is characterized by a short rising time, small steady-state error, and a fast convergence speed. FIG. 11 B and FIG. 11C show the force tracking results of a chirp specifically at the 0.5 Hz and 5 Hz cases. When the frequency is 0.5 Hz, the maximum tracking error is 3 %, and the root means square error (RMSE) of the actual force calculated by Hooke’s law, and the desired force is 0.855 N. When the frequency increased to 5 Hz, it can be obtained that the tracking error grows with a maximum value of 8 % (RSME: 3.11 N), but the tracking error is still acceptable without phase lag. These results indicate a comparable force fidelity when compared to other linear SEA designs. Moreover, according to the Clinical Gait Analysis database, the rotary frequency of human joints during normal walking is no more than 2 Hz, which means our SEA can deliver force for the walking assistance precisely.

Frequency response: To evaluate the force control bandwidth of the SEA, it was controlled to track a chirp force with frequencies ranging from 0.5 to 20 Hz and force amplitude of 90 N. Collected results were analyzed via a fast Fourier transformation to determine the magnitude and phase shift between the desired and the actual forces. FIG. 12 shows that the force control bandwidth is approximately 8.5 Hz.

Preliminary Human User Experiments

The experiments with a human wearer (172 cm, 65 kg) were also necessary to evaluate the capability of cable-driven knee-ankle-foot exoskeleton of providing desired force trajectories on the assisted joints when the human factor is involved. The experimental process is shown at the top of FIG. 13. Force control performance with human-in-loop: In the experiment, it is adopted a sinusoidal signal as the desired force reference trajectory the tracking performance is tested only on the knee joint at an amplitude of 50 N and a frequency of 1 Hz. The wearer is required to follow the force generated by the exoskeleton to conduct swing motions. FIG. 13 A shows the force tracking performance. The maximum tracking error is 7.8 % (RSME: 0.9385 N), which is proportionally larger when compared to the force tracking result without the human factor involved in the control loop. There are two main reasons for this: first, extra uncertainties and disturbance induced by human movements; second, the friction of inner cable and sheaths. However, the current control performance is acceptable, and it can be optimized via a more advanced control scheme. Nevertheless, the proposed closed-loop control method remained stable and shows the capability of providing walking assistance.

Zero-impedance control: During the time domain shown in FIG. 13B, the wearer completed three movements, which are knee joint movement, ankle joint movement, and bi-joints movements, successively. The maximum interaction force on the knee joint and ankle joint is 3.28 N (RSME: 0. 945 N) and 6.50 N (RSME: 1.145 N), respectively. The results demonstrate that the wear felt almost no restrictions during the movements.

Gait Detection

Accurate gait event recognition is significant for the proper generation of the assistance force. Since the device is unilaterally worn on the paretic leg. Thus, all the critical gait events are defined in terms of the paretic leg in this study. The controller was designed to distinguish four typical gait events, including the foot-rest (FT, gait event value = 1), heel-off (HO, gait event value = 2), toe-off (TO, gait event value = 3), and initial contact (IC, gait event value = 4). It is adopted a threshold-based method that uses foot accelerations and angular rates and adapts itself to the subjects’ gait velocity. In this method, the measurements of the angular velocity oi(t) R3, real-time angle value Angleit) are used. The HO event is significant during a full gait cycle since the desired assistance would be delivered when the HO event was detected. The norm vector value of the angular velocity 11 w (t) 11 ₂ e R>0 is extremely sensitive to the change of co, especially on the ankle joint during walking. Hence, a threshold value ( Threshold = 2 in this study as shown in FIG.14B) is set, to distinguish the FT and HO phases. When the signal value is continuously lower than the Threshold for at least nff DN>0 (which was set as 3) samples, it is classified as FT phase. In contrast, it is the HO phase. It can be obtained from the angle curves in FIG. 14C. The peaks and troughs of the joint angles correspond to the IC phase and TO phase, respectively. Then the duration between these phases would be adopted to tune the force profile functions, such as Sigmoid or Gaussian Function , in a quasi-real-time approach. All the defined gait events can be correctly detected as shown in FIG. 14 A.

In the above experiment, tests were carried out to evaluate the force tracking performance, and the results showed the high force fidelity of the SEA and the force control bandwidth is 8.5 Hz. As a feasibility test, walking experiments with human wear have also been conducted, and the obtained results supported the potential of cable- driven knee-ankle-foot exoskeleton in useful walking assistance and incorporation with a more advanced control strategy. The improved mechanical configuration of the exoskeleton ergonomically avoids slippage and the usage of tight straps and guarantees stable torque transmission. A compact linear SEA is designed for good force control performance and mechanical compliance with high repeatability. A portable and re- configurable device of cable-driven knee-ankle-foot exoskeleton has been developed with great potential of clinical walking assistance for post-stroke patients with residual ambulatory ability.

It should be noted that the term “exemplary” and variations thereof, as used herein to describe various embodiments, are intended to indicate that such embodiments are possible examples, representations, or illustrations of possible embodiments (and such terms are not intended to connote that such embodiments are necessarily extraordinary or superlative examples). It should also be noted that the terms “approximately” and “substantially,” as used herein are intended to have a broad meaning in harmony with the common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains.

The term “or,” as used herein, is used in its inclusive sense (and not in its exclusive sense) so that when used to connect a list of elements, the term “or” means one, some, or all of the elements in the list. Conjunctive language such as the phrase “at least one of X, Y, and Z,” unless specifically stated otherwise, is understood to convey that an element may be either X, Y, Z; X and Y; X and Z; Y and Z; or X, Y, and Z (i.e., any combination of X, Y, and Z). Thus, such conjunctive language is not generally intended to imply that certain embodiments require at least one of X, at least one of Y, and at least one of Z to each be present, unless otherwise indicated.

While the present disclosure has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this present disclosure, but that the present disclosure will include all embodiments falling within the scope of the claims.