Method for controlling a powered lower limb exoskeleton during a sit-to-stand motion

Abstract

A method for controlling a powered lower limb exoskeleton during a sit-to-stand motion, the method comprising the steps of: -triggering a sit-to-stand motion of the exoskeleton; and -performing the sit-to-stand motion of the exoskeleton by means of, at least, an actuator of the exoskeleton; The method comprises the steps of, in response to a trunk flexion motion of a patient wearing the exoskeleton, measuring and / or determining a trunk velocity of said trunk flexion motion, wherein if the trunk velocity overcomes a predetermined velocity threshold, a control unit of the exoskeleton triggers the sit-to-stand motion of the exoskeleton.

Description

[0001] The present invention relates to the field of wearable robotics, specifically exoskeleton systems designed to assist individuals with mobility impairments in performing daily activities. The present invention focuses on improving the functionality and usability of exoskeletons, particularly in the context of transitioning from a seated to a standing position.

[0002] Patients with motor neurological impairments, such as spinal cord injuries, strokes, multiple sclerosis, or traumatic brain injuries, often experience limited or no motor function in their lower limbs and trunk, leading to significant mobility and walking disabilities. As part of their physical therapy or rehabilitation program, they may use a robotic exoskeleton for gait training. Exoskeletons allow them to walk in both clinical rehabilitation settings and home environments, resulting in overall health benefits.

[0003] Once the patient has completed the donning process, to begin walking with the exoskeleton, the patient needs to transfer from a sitting position to a standing upright position. This sit-to-stand transition can be challenging for users due to their limited motor function and depending on their injury type they may require different levels of assistance from a clinician to maintain balance with their body while performing the transition. It can be difficult and frustrating for patients if they cannot perform this transition by themselves without requiring a clinician's support. Therefore, it is desirable for an exoskeleton to include means to allow performing the sit-to-stand transition in the most natural and easy way possible, maximizing patient independence.

[0004] The development of exoskeletons has evolved significantly since their inception. Some exoskeletons have enough motor power to perform the sit-to-stand transition with almost no help from the user. However, many existing exoskeleton technologies still require significant manual effort or assistance from another person for users to stand up from a seated position.

[0005] Current exoskeleton devices address the sit-to-stand transition in various ways. Some use a manual trigger and fully assisted sit-to-stand transition, while others exoskeletons will actively assist the user in initially flexing their trunk in response to a sit-to-stand command or trigger, and when the trunk flexion has been completed, the exoskeleton will start the rest of the assisted sit-to-stand motion requiring substantial help from the user. Further examples are those that require the user to flex their trunk forward and lift their body from the chair or bed with their arms using the walking aid or the help of a therapist to trigger the assisted standing-up motion. Once the exoskeleton detects that the user has lifted from the chair or bed, the motors activate and assist the rest of the sit-to-stand motion.

[0006] Patent examples such as EP20383088A and EP22382778A highlight the strides made in this field, showcasing devices that enhance user stability, support and help assist the user during daily activities.

[0007] The present invention addresses the sit-to-stand transition issue by providing an automated and user-controlled procedure that ensures stability and safety throughout the stand-up process while taking advantage of the inertia provided by the user's own motion.

[0008] In particular, the present invention discloses a method for controlling a powered lower limb exoskeleton during a sit-to-stand motion, the method comprising the steps of: triggering a sit-to-stand motion of the knee-powered exoskeleton; and performing the sit-to-stand motion of the knee-powered exoskeleton by means of, at least, an actuator of the exoskeleton; wherein the method comprises the steps of, in response to a trunk flexion motion of a patient wearing the exoskeleton, measuring and / or determining a trunk velocity, preferably a trunk angular velocity, of said trunk flexion motion, wherein if the trunk velocity overcomes a predetermined velocity threshold, a control unit of the exoskeleton triggers the sit-to-stand motion of the exoskeleton.

[0009] Preferably, the method also comprises measuring and / or determining a trunk flexion angle of said trunk flexion motion, wherein if the trunk flexion angle overcomes a predetermined flexion angle threshold and the trunk velocity overcomes the predetermined velocity threshold, the control unit of the exoskeleton triggers the sit-to-stand motion of the exoskeleton.

[0010] Preferably, both the flexion angle and the flexion velocity are measured and / or determined in the sagittal plane, i.e. referring to a movement produced in the sagittal plane or a to a component in the sagittal plane of the movement. The flexion angle and / or velocity can be measured and / or determined on the patient wearing the exoskeleton, on the exoskeleton or by any other method.

[0011] The sit-to-stand motion can have any arbitrary start and end positions within the flexion / extension range of the joints. Thus, for example, the sit-to-stand motion can be any squat movement or any partial squat movement.

[0012] The term "user" refers to either the patient or the clinician / therapist, as both are considered users of the device.

[0013] The trunk flexion angle is preferably a trunk pitch angle but can also be another type of angle, such as the angle measured between a trunk part and a tight part of the exoskeleton (hip flexion angle).

[0014] According to the present invention, the sit-to-stand motion of the exoskeleton is triggered when the patient or the clinician / therapist produces a trunk flexion (i.e. moves forward the trunk around the hip(s), in contrast to an extension movement which is backwards around the hip(s)) and the exoskeleton detects that the trunk velocity surpasses a velocity threshold and, preferably, the trunk flexion surpasses a flexion angle threshold. When these conditions are met, the centre of mass of the user+exoskeleton unit is travelling forward. Under these conditions, the sit-to-stand motion is triggered, i.e., started, when the centre of mass is travelling forward. The forward travelling of the centre of mass helps in the stand-up motion, making it easier due to the related inertia. It also makes it more natural since most people flexes their trunk when standing up, taking advantage of said forward travelling of the centre of mass, which reduces the effort requirements. In short, the method of the invention allows taking advantage of the inertia of the user to perform the sit-to-stand transition, making the standing-up motion feel very natural and requiring less effort from the patient.

[0015] Both the angle and the velocity can be directly measured by corresponding sensors of the exoskeleton or determined from other measurements of the exoskeleton.

[0016] Preferably, the velocity threshold is between 40 and 100 deg / s and more preferably 60 deg / s. Also preferably, the trunk flexion angle threshold is between 10 and 45 deg and more preferably 20 degrees, wherein 0 degrees corresponds with a vertical trunk / fully extended hip joint.

[0017] Preferably, the switch position is situated between 10 and 40 degrees and preferably at10 degrees of knee joint angular motion (toward extension) after the initial point of the sit-to-stand motion.

[0018] The present invention also discloses ways to use inertia during control of the stand-up motion, irrespective of the triggering method used. More specifically, the invention discloses ways to adapt the stand-up motion to the inertia of the motion and the assistance provided by the user.

[0019] In a preferred embodiment, the sit-to-stand motion comprises: performing a first motion part of a knee joint by a knee actuator, until arriving at a switch position angle of the knee joint; and measuring and / or determining a knee joint angular velocity at the switch position angle.

[0020] Also, preferably, the sit-to-stand motion comprises: determining a motion profile of a second knee joint motion part depending on said knee joint angular velocity at the switch position angle start performing by a knee joint actuator of the exoskeleton the second knee joint motion part according to the determined motion profile of the second knee joint motion part.

[0021] Preferably, the first motion part is a force -controlled or torque-controlled motion.

[0022] Also preferably, the second motion part is a position-controlled or velocity-controlled motion.

[0023] If the exoskeleton has two knee joints, preferably, the method is performed for both knee joints.

[0024] Preferably, for example, if no security issue arises during the motion, the second motion part is performed according to the determined motion profile until a target position of the second motion part of the knees, where the second motion ends.

[0025] The first knee join motion part is performed preferably from a sitting position.

[0026] According to the present invention, the motion of the knees can be divided into at least two parts. The first part is an initial part, which can be performed according to a fixed motion profile. Typically, the first motion part is performed at high torque to help lift the user. Then, the velocity is measured or determined, and a motion profile for a second knee joint motion part is determined depending on the said measured or determined velocity. This takes advantage of the existing inertia after an initial lift. Thus, if the patient is contributing to the lift motion at the end of the first motion part, the velocity will be greater. Since the exoskeleton measures or determines the velocity at the end of the first motion part (switch position), it can adjust its the motion profile to the patient's condition.

[0027] Another advantage of dividing the sit-to-stand motion in at least to motion part is that it allows that, in the first motion part, position and velocity are not controlled, since it is more important to produce enough force to start the movement. The sit-to-stand (squat) motion begins by a collaboration between the forces produced by the patient and the exoskeleton. Once the movement has begun, when a predetermined switch position has been crossed, a second motion part begins, with controlled position and / or velocities which have into account the velocity at the switch position.

[0028] In a preferred embodiment, the sit-to-stand motion further comprises a step of performing a first motion of a hip joint after the switch position is reached. Preferably, the hip joint performs a first motion profile of the hip joint which depends on the motion profile determined for the second motion part of the knee joint. More preferably, the motion profile of the hip joint depends on the time estimated for the second motion part of the knee joint. Even more preferably, the first motion profile of the hip joint is determined so that the first motion part of the hip ends at the same time as the second motion part of the knee joint. In some embodiments, both knee and hip motion profiles are calculated so that both hip joint and knee joint reach a predefined standing position with null velocity at the same time.

[0029] Preferably, the target position of the second motion part of the knees is set to a knee offset setting, wherein the knee offset setting corresponds to a value predefined for a standing position. Also preferably, a motion target position of the first motion part of the hip is set to a hip offset setting. More preferably, the value for the knee offset setting is selected from the range comprising from 0 degrees, wherein the knee is fully extended and the leg is straight, to 20 degrees, and even more preferably to 10 degrees, wherein the knee is slightly bent, indicating a small degree of flexion. Also more preferably, the hip offset setting is between -10 and 10 degrees, with 0 degrees corresponding to a straight hip joint. Even more preferably, the hip offset setting is between -5 and 5 degrees.

[0030] In a preferred embodiment, the sit-to-stand motion can comprise a third motion part of the knee joint and a second motion part of the hip joint. Preferably, the third motion part of knee joint is performed from the target position of the second part of the knee joint until a knee offset setting. This can be useful to prevent the patient from cramping at the final part of the motion. For example, the skeleton control unit can have a spasticity mitigation function, which if set TRUE changes the target position of the second motion part of the knee joint set to a predetermined value before the knee offset setting, preferably to 20 degrees, with 0 degrees corresponding to a straight knee joint. Such spasticity mitigation function provides further assistance to the user, decreasing the velocity in the last part of the sit-to-stand motion, enhancing the user's safety and comfort, and preventing injures caused by sudden, uncontrolled muscle contractions. The last motion part when the spasticity mitigation function is set to true, i.e., active, is preferably performed at a velocity that is significantly lower than the rest of the motion, in order to prevent spasms. Thus, in a preferred embodiment if the spascity mitigation function is set to true, the last part of the sit-to-stand motion is performed with a velocity equal to or lower than 20 deg / s, more preferably less than 15 deg / s, even more preferably equal to or lower than 8 deg / s. If the spasticity mitigation function is set to TRUE, the target position is preferably set to 20 degrees before the hip offset setting. Preferably, when the spasticity mitigation is on, the last part of the motion of both the knee joint(s) and the hip joint(s) is performed with a low velocity, i.e., equal to or lower than 20 deg / s, more preferably less than 15 deg / s, even more preferably equal to or lower than 8 deg / s. The end of the second first motion of the hip joint(s) in that case, preferably, is set to a predetermined value before the hip offset setting, preferably 20 degrees, with 0 degrees corresponding to a straight knee joint.

[0031] Preferably, the method comprises a previous first step of situating the exoskeleton legs in a fixed legs knee angle, preferably selected from the range comprising from 85 degrees to 100 degrees, more preferably between 90 a 100, even more preferably between 95 and 100 degrees. If possible, the more flexed the better (100 degrees especially preferable).

[0032] The present invention also discloses an exoskeleton control unit which is configured for performing the method according to the invention, and an exoskeleton comprising said exoskeleton control unit. Preferably, the exoskeleton comprises an exoskeleton frame; a lumbar segment, a hip joint and a hip actuator; and two legs segments, each comprising a knee joint and a corresponding knee actuator.

[0033] The present invention discloses methods for assisting users of exoskeletons in standing up from a seated position. It can feature a support mechanism, sensors, motor powered-knee means and preferably includes motor powered hip joints. Specifically, the method allows taking advantage of the inertia of the user to perform the sit-to-stand transition, making the standing-up motion feel very natural and require less effort from the patient. The combination of these features provides a reliable and secure method for users to achieve a standing posture.

[0034] The term "exoskeleton" as disclosed herein refers to a wearable robotic device that supports and / or enhances the patient's physical capabilities, particularly by augmenting the movement and / or strength of their limbs and trunk. It is designed to assist individuals with mobility impairments or to enhance the physical performance of able-bodied users.

[0035] The term "hip joint" as disclosed herein refers to the segment of the exoskeleton that interfaces with the user's torso. This joint can typically facilitate motions such as flexion, extension, lateral bending, and / or rotation, aiding in activities that require bending or twisting of the upper body.

[0036] The term "trunk flexion motion" as disclosed herein refers to the forward bending movement of a torso or trunk.

[0037] The term "trunk angular velocity" as disclosed herein refers to the rate of change of the trunk's angular position over time during motion. It measures how quickly the trunk is bending in a given direction and is usually expressed in degrees per second (° / s).

[0038] The term "trunk pitch angle" as disclosed herein refers to the angle at which the trunk is inclined forward or backward relative to an upright vertical position. This angle is used for assessing posture and balance.

[0039] The term "knee joint" as disclosed herein refers to the mechanical joint in the exoskeleton that aligns with the user's natural knee joint. It facilitates movements such as bending (flexion) and straightening (extension) of the exoskeleton's leg components, mimicking the motion of the human knee. This joint is designed to support and enhance the user's mobility by providing powered assistance or resistance during activities involving knee movement, such as standing up.

[0040] The term "control unit" as disclosed herein refers to the electronic or computerized component of the exoskeleton that processes input from sensors, executes control algorithms, and sends commands to actuators. The control unit coordinates the movement of the exoskeleton based on real-time data to ensure smooth and responsive assistance to the user's movements.

[0041] The term "actuator" as disclosed herein refers to a mechanical device within the exoskeleton that converts energy (usually electrical) into motion. Actuators are responsible for driving the movements of the exoskeleton's joints, such as the knee joint and hip joint, by following the commands from a control unit. They play a role in delivering the necessary force / torque and precision to assist or enhance the user's natural movements.

[0042] For a better understanding, there are attached, by way of explanation and not limitation, some figures related to a possible realization of a method and a device that carries it out in accordance with the present invention. Fig. 1 shows an example of an exoskeleton which performs methods according to the present invention. Fig. 2 shows schematically a process of triggering a stand-up motion. Fig. 3 is a diagram which shows the evolution of different parameters during the stand-up motion. Fig 4 is a flow diagram of a stand-up motion.

[0043] Fig. 1 shows an exoskeleton 1. The exoskeleton 1 shown is a wearable powered lower-limb exoskeleton that can actively assist individuals with impairments to stand up, walk and sit down. It is a bilateral robotic exoskeleton with four battery-powered motors that drive the knee and hip joints assisting in flexion-extension movements. The exoskeleton attaches to the user's torso, legs and feet via straps and supports.

[0044] The exoskeleton is composed of a lumbar segment 13 and two leg segments. The lumbar segment 13 sits against the user's back and houses two rechargeable and swappable battery packs 11, a control unit including an inertial measurement unit (IMU) as well as communication modules, like, for example, Wi-Fi and Bluetooth modules. Each leg segment houses electrical actuators 31, 21 in the knee joints 3 and hip joints 2, respectively, servo drivers to control them, an electromagnetic safety brake at the knee, and an IMU sensor. The lumbar segment 13 rotates around the hip joints, while the leg segments can rotate around the hip joints 2 and / or knee joints 3. The shank segment can rotate around the knee joint 3. In this exoskeleton, all allowed movements are within the sagittal plane.

[0045] Other degrees of freedom of the hip and knee joints are restricted. The ankle joint 4 of the exoskeleton is passively articulated with a spring (not shown in the picture) within a limited range of motion.

[0046] The exoskeleton can be controlled using either a therapist interface (up and down buttons located on the lumbar segment) or a patient interface (up and down buttons located on a remote control device (not shown in the picture), a wireless device that can, for example, be mounted on the walker or crutches). These interfaces allow the user to transfer between the different states of the exoskeleton, like, for example: (1) from the sitting position to a transfer state, where the patient can put on the exoskeleton; (2) performing a sit-to-stand transition, where the exoskeleton 1 actively assists the knee and hip joints; (3) to standing, where the actuators apply the necessary torque to hold the user's legs straight and their trunk upright; (4) to walking, where the exoskeleton 1 moves the knee and hip joints following a natural gait pattern; (5) performing the stand-to-sit transition, where the exoskeleton actively assists the knee and hip joints to sit down on a chair or medical bed.

[0047] The lumbar segment 13 accommodates the control unit, the batteries 11 and has a port for receiving a phone device 12 which acts as a display screen by means of an app. The lumbar segment also comprises a modular structural back part 14 which, if needed, attaches to the lumbar segment 13 providing additional back postural support. The back part 14 can be fixed to the patient via shoulder straps for those users with higher injuries or limited trunk control. The lumbar segment also comprises handles 15 for use by a therapist. The said up and down buttons for the therapist (not shown in the pictures) can be located on top of the handles 15.

[0048] The lumbar segment 13 connects, via respective hip joints 2 to a tight part. The tight part extends from the hip joint 2 to the knee joint 3. Each hip joint 2 has a hip actuator 21, and each knee joint 3 has a knee actuator 31. The actuators 21, 31 apply force to move the legs of the exoskeleton to assist the patient in the motion of walking. The actuators 21, 31 are also used to facilitate the transfer of the patient to the exoskeleton, by positioning the exoskeleton 1 in a certain position and locking the hip and knee joints. Each of the tight parts and the lumbar part 13 have, respectively a 9-degree-of-freedom movement sensor (each sensor has a 3-axis gyroscope, a 3-axis accelerometer, and a 3-axis magnetometer).

[0049] The shank part has no actuators. It comprises respective footplates 42 which are rotatably connected to an ankle part 41. The ankle part 41 houses a spring (not shown in the pictures), allowing the ankle joint 4 to move in plantarflexion and dorsiflexion. This rotation is loaded with the spring, which returns the user to a "neutral" position.

[0050] Each leg (tight) part also has a rigid support 22 and each shank part has a respective rigid support 32, which helps transfer the load and movement from the user to the exoskeleton frame, and vice-versa.

[0051] Straps for connection to the patient as well as padding parts, are not shown in the picture. Size adjustments to the exoskeleton can be made through telescopic parts and pin locking mechanisms.

[0052] To use the dynamic trigger of a stand-up, the following steps are performed with the device. In these steps, the word "user" denotes either the patient or the clinician / therapist, as both are considered users of the device. Some steps can be performed by either user.

[0053] Referring to Fig. 2, in an initial step, the user can be in a sitting state 1000 with both hip and knee actuators disabled. In that case, the user manually triggers via any interface a state transition to a fixed legs state 1001. Knee actuators 31 are enabled and move to reach a predetermined fixed legs knee angle. This motion can be performed with saturation on both velocity and torque to prevent fast motions. Once the knee joints reach the target fixed legs knee angle, the exoskeleton transitions to a ready to stand-up state 1002. In this state, the exoskeleton is waiting for a user command to start a sit-to-stand motion.

[0054] Then, in a dynamic stand-up mode, the user performs a 1003 trunk flexion motion. In other words, the patient flexes his trunk, or the clinician flexes the lumbar part of the exoskeleton around the hip joint. If the trunk angular velocity and the trunk pitch angle, measured and / or determined by the exoskeleton, exceed respective predetermined thresholds, the control unit of the exoskeleton interprets this as a stand-up command and triggers the sit-to-stand motion 1004, transitioning the exoskeleton to a standing-up state. Since the stand-up movement is triggered, preferably, while the trunk is being flexed, both the exoskeleton and the patient can take advantage of the inertia of the trunk flexing movement.

[0055] Alternatively, the stand-up motion can be triggered by the exoskeleton following a manual order via any user interface, or any known method.

[0056] Dynamic stand-up (i.e. triggering the stand-up motion when both the pitch trunk angle and the pitch trunk velocity reach a threshold), allows the user to take advantage of the inertia of the trunk motion, making the sit-to-stand transition more natural, efficient, smooth and easier for the patient compared to methods that initiate the sit-to-stand transition from a static pose. The trunk flexion motion required to trigger the sit-to-stand motion can be performed either by the patient pulling from the walking aid or using trunk muscles, or by the therapist pushing from the back (holding the exoskeleton trunk) or pulling from the front of the patient (holding the arms of the patient).Sit-to-stand motion

[0057] Irrespective of the triggering mode, the sit-to-stand motion, according to the present invention, can be divided into at least two parts.

[0058] In a first motion part, the knee actuators perform a motion to lift the user from the sitting position. In this part, the knees can perform a motion with high torque (for example, around 60 Nm).

[0059] Once the knees reach a switch position which is, for example, set at 10 deg (towards extension) from the fixed legs knee angle (which is for example, set at 95 deg), the first motion part is considered as finished and the second motion part begins. The motion profile of the knees in this second part is different.

[0060] In this second part, the control unit of the exoskeleton makes the knee joints execute a motion profile configured based on the velocity that the knee joints have at the moment that they reach the switch position.

[0061] The target or end position of the second motion part of the knees is set to the knee offset setting (i.e., a value predefined for a standing position). However, if the spasticity mitigation setting is set to TRUE, in which case the target or end position of the second motion part of the knee joints is set to a predetermined value before the knee offset setting (for example, 20 degrees).

[0062] When using a spasticity mitigation function, the last part of the sit-to-stand motion is performed at a very slow velocity (i.e., below 20 deg / s and preferably 8 deg / s or less) to reduce the muscular spasms that patients often have when stretching their body into the standing upright position.

[0063] Movement of the hip joints can start after the switch position is reached. Hips can perform a motion profile that is configured considering the motion time estimated for the second motion part of the knees, preferably so that both hip joints and knee joints reach a predefined standing position (with null velocity) at the same time. Like in the knees, the target position of the first motion part of the hips is set to a hip offset setting (i.e. to a predefined standing position), unless a spasticity mitigation setting for the end of the movement is set to TRUE in which case the target position of the second motion part of the hips is set to a predetermined value before the hip offset setting (for example, 20 degrees).

[0064] In the event that the spasticity mitigation setting is set to true, both the knee joints and hip joints need to perform an additional motion to move from the target position of the previous motion. This final motion is performed at a very slow velocity to prevent spams in the patient.

[0065] An example of a determination of the velocity profile for the second motion part of the knee joints is the following: The control unit has predefined values regarding the target position to reach the standing upright position, a target position when a spasticity mitigation function is activated, predefined desired acceleration and deceleration values and a desired predefined velocity parameter.

[0066] Ideally, the desired velocity parameter includes an acceleration phase from the initial velocity at the switch point, a time at the desired velocity and a deceleration time at the desired deceleration value used for the calculation. However, in some circumstances, this is not possible. For example, if the initial velocity is greater than the desired velocity, then the first phase can be a deceleration from the initial velocity to the desired velocity, or, if the initial velocity is great enough, the velocity profile of the second motion of the hips can consist of only one deceleration phase. Finally, in some cases, there can be no time / displacement enough to reach the desired velocity, in which case the velocity profile will contain just a first acceleration phase and a second deceleration phase without any constant velocity phase. There are several ways to implement this. One way of doing it is the following: First, the control unit determines the target position of the second part of the movement. As explained before, this depends on whether the spasticity mitigation function is activated or not. Also, the value of the angular velocity of the knee joint is used.

[0067] Since the velocity at the switch point is known, as well as the displacement between the switch point and the end of the second part of the movement, a minimal deceleration to avoid overshoot can be calculated (assuming constant deceleration). A safety parameter factor can be used in this calculation. The desired deceleration parameter used by the control unit in calculating the velocity profile can be the higher value between the predefined desired deceleration value and the calculated minimal deceleration to avoid overshoot.

[0068] A time for reaching the desired velocity can be determined using the initial velocity, the desired velocity, and the desired acceleration.

[0069] A deceleration time can be determined using the desired velocity and the desired deceleration used for the calculation.

[0070] A travel displacement while accelerating and decelerating can then be determined using the previously determined times.

[0071] Then a travel displacement at constant velocity can be determined by subtracting the previously determined travel displacements from the total displacement. If this value is positive, then, there is a period of constant velocity, and a time of the period at constant velocity and a total time of the second motion part can be determined.

[0072] However, if the determined value of the travel displacement at constant velocity is negative, then there is no period of constant velocity. In this case, the exoskeleton has no time to reach the given parameters. Then, the knee actuator will start with a first acceleration / deceleration period towards the desired velocity, but before reaching the desired velocity, it will need to start decelerating. Velocity can be calculated by matching the total travel with the travel accelerating plus the travel decelerating. Initial acceleration is negative if the initial velocity is greater than the desired velocity. Once the initial acceleration is determined, and knowing the desired deceleration for the calculation, the initial velocity and the total displacement of the second motion part, the velocity period will reach before starting decelerating can be determined. Then the total travel time of the second motion part of the knees can be determined as the sum of the determined acceleration and deceleration periods.

[0073] Once the velocity profile for the second motion part of the knees has been determined, the control unit sends the profile parameters to the motor drivers of the knee actuators.

[0074] Once the velocity profile parameters for the knee actuators have been determined, then the velocity profile for the hip actuators can be determined, for example, as follows: It is possible to estimate profile position parameters for the hip stand up profile (velocity, acceleration, and deceleration) based on the stand-up time calculated for the knees and considering the initial velocity. For doing this, for example, predefined acceleration and deceleration time fractions can be used. Once the acceleration, constant velocity and deceleration times are determined, then the target velocity, acceleration, and deceleration for the hips can be determined. After the velocity profile has been determined, the control unit sends the appropriate position profile parameters to the actuator drivers of the hips.

[0075] Fig. 3 shows a plot showing an example of a sequence of a sit-to-stand motion as previously described. The upper plot shows the angle of both the hip joint 2 and the knee joint 3 at different times. The middle plot shows the trunk pitch angle 5 at different times. The lower plot shows the trunk pitch velocity at different times. The following times have been indicated: stand-up motion triggering 2001, switch position arrival 2002 and spasticity mitigation beginning 2003. Also, the trunk pitch angle threshold 2005, the trunk pitch angle velocity threshold 2006 and the spasticity mitigation beginning position 2007 have been represented with horizontal lines.

[0076] After the sit-to-stand motion is triggered by the user flexing the trunk forward (trunk pitch increases) and reaching a trunk pitch angle threshold 2005 and a trunk angular velocity threshold 2006, the first knee motion part 3001 is executed. Once the switch position 2004 of the knee joint is reached, the second motion part 3002 of the knee joints and the first motion part 3003 of the hip joints are executed. When both the knee and hip joints reach their target positions (i.e. spasticity mitigation beginning position 2007), the knee joints execute a third motion part, and the hip joints execute their second motion profile to reach the standing upright position (i.e. both joints reach their offset position).

[0077] Fig. 4 shows a flow diagram of a sit to stand motion. After the sit-to-stand triggering 2001 (for example, because the trunk pitch angle 5 and angular velocity trespass their respective thresholds, or by a manual triggering) and, if needed, any motion preparation, the exoskeleton performs the first knee motion part 3001 until a switch position 2004 is reached. On switch position arrival 2002 and using parameters at switch position (angular velocity 4002 and position at the knee joints), the control unit proceeds to determine the position and / or travel parameters for the second motion part of the knees. The determination can depend on whether the second motion part ends in the stand-up position or whether there is a third motion part 4003 (like a spasticity mitigation final part at very low velocity). If there is no third motion part, then the control unit calculates 5001 the parameters for the second motion part based on the angular velocity of the knee joint at the switch position, then calculates 5002 the first motion part for the hips based on the previous calculation and the angular velocity of the hip joint at the switch position, and sends to the drivers the determined parameters in order to execute the determined movements 3002, 3003 for both the knee joint and the hip joint.

[0078] If there is a third motion part for the knees and hips, then the exoskeleton determines the parameters for the second motion part of the knees 5001' and the first motion part of the hip 5002' as explained before and executes the determined movements 3002, 3003 for both the knee joint and the hip joint. When the spasticity mitigation part begins 2003, the exoskeleton calculates 5003, if needed, the parameters for the third motion part of the knees and the second motion part of the hips and then executes 3004 the determined movement 3004.

[0079] After the first motion part, according to the invention, the hip and knee motions coordinate their motion and adapt to the velocity of the initial lift (first motion profile of the knee joints) resulting in a smooth sit-to-stand motion.

[0080] The predefined parameters can be changed by the user. For example, the user can choose a fast or slow velocity setting that will adjust the velocity of the second motion part of the knee joints and the first motion part of the hip joints.

[0081] Although the invention has been presented and described with reference to embodiments thereof, it will be appreciated that these are non-limiting embodiments of the invention, and therefore several different structural or other details could become obvious to a person skilled in the art after interpreting the subject matter disclosed in the present description, claims and drawings. Consequently, the present invention encompasses all variants and equivalents if they can be considered to fall within the broadest scope of the claims which follow.

Claims

1. A method for controlling a powered lower limb exoskeleton during a sit-to-stand motion, the method comprising the steps of: - triggering a sit-to-stand motion of the exoskeleton; and - performing the sit-to-stand motion of the exoskeleton by means of, at least, an actuator of the exoskeleton; characterized in that it comprises the steps of, in response to a trunk flexion motion of a patient wearing the exoskeleton, measuring and / or determining a trunk velocity of said trunk flexion motion, wherein if the trunk velocity overcomes a predetermined velocity threshold, a control unit of the exoskeleton triggers the sit-to-stand motion of the exoskeleton.

2. The method according to claim 1, characterized in that the method also comprises measuring and / or determining a trunk flexion angle of said trunk flexion motion, wherein if the trunk flexion angle overcomes a predetermined flexion angle threshold and the trunk velocity overcomes the predetermined velocity threshold, the control unit of the exoskeleton triggers the sit-to-stand motion of the exoskeleton.

3. The method according to claim 1 or 2, characterized in that the sit-to-stand motion comprises: - performing a first motion part of a knee joint of the exoskeleton by a knee actuator of the exoskeleton until arriving at a switch position angle of the knee joint; and - measuring and / or determining a knee joint angular velocity at the switch position angle.

4. The method according to claim 3, characterized in that the first motion part is a force-controlled or torque-controlled motion.

5. The method according to claim 3 or 4, characterized in that the sit-to-stand motion comprises: - determining a motion profile of a second motion part of the knee joint depending on said knee joint angular velocity at the switch position angle - start performing the second knee joint motion part according to the determined motion profile of the second motion part of the knee joint.

6. The method according to claim 5, characterized in that the second motion part is a position-controlled or velocity-controlled motion.

7. The method according to anyone of claims 3 to 6, wherein the second motion part of the knee joint is performed until a target position of the second motion part of the knees is reached wherein the target position of the second motion part of the knee joint is set to a knee offset setting, wherein the offset setting corresponds to a value predefined for a standing position.

8. The method according to anyone of claims 1 to 7, wherein the target position of the second motion part of the knee joint is set to a predetermined value before a knee offset setting.

9. The method of claim 8, wherein a third motion part of the knee joint is performed from said target position of the second motion part of the knee joint until the knee offset setting with a velocity lower than a desired velocity for the second motion part of the knee joint for preventing spams of the patient wearing the exoskeleton.

10. The method according to any one of claims 3 to 9, wherein it further comprises a step of performing a first motion profile of a hip joint after the switch position is reached.

11. The method according to claim 10, wherein the hip joint performs a first motion profile of the hip joint which depends on the motion profile determined for the second motion part of the knee joint.

12. The method according to claim 11, wherein the first motion profile of the hip joint is determined so that the first motion part of the hip ends at the same time as the second motion part of the knee joint.

13. The method according to claims 9 and 12, wherein a second motion of the hip joint is performed with said velocity lower than a desired velocity for the second motion part of the knee joint for preventing spams of the patient wearing the exoskeleton.

14. Exoskeleton control unit which is configured for performing a method according to anyone of the preceding claims.

15. Exoskeleton comprising a control unit according to the preceding claim.

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