Flexible exoskeleton with pneumatic artificial muscle

Abstract

The present invention relates to a flexible exoskeleton having a suit with one or more pneumatic artificial muscles, wherein the pneumatic artificial muscle comprises: a flexible membrane; internal rings spaced apart from one another and wrapped inside the flexible membrane; and external rings that are coupled to the internal rings from the outside of the flexible membrane. The rings and the clips may be manufactured, for example, by means of 3D printing and the membrane may be a thin plastic film or a fabric.

Description

[0001] FLEXIBLE EXOSKELETON WITH PNEUMATIC ARTIFICIAL MUSCLE

[0002] TECHNICAL FIELD

[0003]

[0001] The present invention relates to the technical field of medical engineering, mainly in the area of ​​physiotherapy to help people or patients, for example, infants, specifically in the field of lower limb exoskeletons with at least one vacuum-powered artificial muscle.

[0004] STATE OF THE ART

[0005]

[0002] Currently, exoskeletons and wearable devices exist for lower limb rehabilitation applications in adults. Most of them consist of rigid structures positioned or worn parallel to the user's limbs using straps and rigid drive systems such as gearboxes with DC motors and cable systems. They are generally made of aluminum and feature rotary motors or artificial pneumatic muscles to generate movement at the ankle, hip, and knee.

[0006]

[0003] Exoskeleton-type devices for lower limbs are known in the prior art, such as, for example, patent document CN201870775, a pneumatically driven mechanical exoskeleton structure for a rehabilitation training robot for walking. The structure comprises a support, a lower limb, and a drive device, in which a hip joint of the lower limb and a knee joint are actuated via an air cylinder for bending and straightening, and it also has an ankle joint that is actuated via a pneumatic artificial muscle for bending. The robotic exoskeleton mechanical structure has three degrees of freedom. The air cylinder and the pneumatic artificial muscle are used for walking.

[0007]

[0004] Also known is patent document CN113101134 disclosing an auxiliary system for the rehabilitation of a child's lower limb movement, which is based on an electric exoskeleton comprising a rehabilitation system body with an exercise capacity assessment module, a rehabilitation scheme generation module, an auxiliary training module, and a case management module; the case management module is used to store information about a child patient's case; the exercise capacity assessment module obtains an exercise capacity assessment result according to the information in the child patient's medical record; the rehabilitation scheme generation module is used to generate a corresponding personalized training scheme according to the exercise capacity assessment result;and the auxiliary training module is used to synchronize various data in the pediatric patient training process with the case management module.

[0008]

[0005] For its part, document US2006 / 0260620 discloses a lower limb exoskeleton, configurable to attach to a person, which comprises two leg supports configurable to attach to the lower limbs and configured to rest on the ground during their posture phases. Each leg support comprises a thigh link, a stem link, and two knee joints. Each knee joint is configured to allow flexion and extension between the respective stem link and the respective thigh link. The exoskeleton also comprises an exoskeleton torso configurable to attach to the person's upper body.

[0006] Also known is document MX36797 which describes an adjustable mechanical exoskeleton for a patient with bone and muscle disability, which is made up of a metal structure to house expandable and shortening supports, including a ball joint; conventional electric motors of the linear actuator type, arranged on the horizontal base, a template, a lumbar support, an electrical system made up of a main microprocessor to operate all the components of the system by means of a communication system; magnetic sensors of angular and external position, which are placed on each ball joint with a magnet, a magnetic sensor and a base for a magnetic sensor; force sensors in the templates, an accelerometer in the backrest and an electronic control in real time.

[0009]

[0007] Also known is document LIS2017 / 0001303 which discloses a lower limb exoskeleton, comprising two articulated legs arranged to attach to a user's lower limbs, and a connecting member provided between the upper ends of the legs to which it is articulated and which can be placed in the user's pelvic area, also comprising drive means for moving the articulated legs according to the user's movements.

[0010]

[0008] US2020 / 0375836 discloses a device with leg actuator units that may include an upper arm and a lower arm rotatably coupled via a joint. It also comprises a bellows actuator extending between plates coupled to the respective ends of the upper and lower arms, with the plates coupled to separate rotating portions of the joint. One or more sets of pneumatic lines may be coupled to the bellows actuator to introduce and / or remove fluid from the bellows actuator to cause the bellows actuator to expand and contract.

[0009] From the perspective of scientific literature, the article titled "A Length-adjustable vacuum-powered artificial muscle for wearable physiotherapy assistance in infants" by Samuel Dutra et al., published in Frontiers in Robotics and Artificial Intelligence on May 4, 2023, is known. This article discusses vacuum-powered pneumatic soft artificial muscles (VPAMs) with an adjustable operating length, offering adaptability throughout their use, particularly in environments with variable workspaces. The VPAM features a modular structure consisting of cells that can be trimmed in a collapsed state and released as needed. A case study in pediatric physiotherapy is presented to demonstrate the actuator's capabilities.A dynamic model of the device and a model-based open-loop control system were developed and their accuracy validated in a simulated patient setting, where the results showed that the VPAM maintains its performance as the infant grows.

[0011]

[0010] Also known is the article entitled “A Vacuum-powered Artificial Muscle Designed for Infant Rehabilitation” by Mijai I Jaén Medona et al., published in Micromachines on August 16, 2021, which deals with soft pneumatic actuators. It indicates that most soft pneumatic actuators for rehabilitation exercises have been designed for adult users. Specifically, there is a shortage of soft rehabilitation devices designed for infants with upper and lower limb motor disabilities. We present a low-profile vacuum-powered artificial muscle (LP-VPAM) with dimensions suitable for infants. The actuator produced a maximum force of 26 N at vacuum pressures of 40 kPa.When implemented in an experimental model of a baby's leg in an antagonist-agonist configuration to measure the resulting knee flexion, the actuator generated knee flexion angles of 43° and 61° in prone and sideways positions, respectively.

[0012]

[0011] On the other hand, the article entitled “Design and Performance Analysis of Artificial Muscle Driven by Vacuum with Large Contract Ratio and Large Load.” by Yu He et al., published in Springer Nature Switzerland AG in 2021, is known. This article deals with artificial muscles and establishes that the artificial muscle is one of the most promising research directions in the field of soft robots. It shows a structure built by a closed cavity on one side with a steel ring skeleton inside, where the energy is provided by negative pressure contraction.

[0013]

[0012] In this sense, it is clear that there is still an unmet need to provide a flexible, lightweight, and low-volume exoskeleton comprising one or more pneumatic artificial muscles for infants that allows adaptation to the length of the infant's limbs as the child grows, for example, from 0 months of age to 18 months.

[0014]

[0013] In this respect, the present invention contributes to the state of the art, as it provides a flexible exoskeleton comprising a suit with one or more pneumatic artificial muscles, wherein the pneumatic artificial muscle comprises a flexible membrane; internal rings spaced apart from each other and wrapped inside the flexible membrane; and external rings coupled to the internal rings from outside the flexible membrane, wherein the rings and trim components can be manufactured, for example, by 3D printing and the membrane can be a thin film of plastic or a textile. ABSTRACT

[0015]

[0014] The present invention relates to a flexible exoskeleton comprising a suit with one or more pneumatic artificial muscles, wherein the pneumatic artificial muscle comprises a flexible membrane; internal rings spaced apart from each other and wrapped inside the flexible membrane; and external rings coupled to the internal rings from outside the flexible membrane, wherein the rings and trim components can be manufactured, for example, by 3D printing and the membrane can be a thin film of plastic or a textile.

[0016] DESCRIPTION OF THE FIGURES

[0017]

[0015] Figure 1 shows an isometric view of the pneumatic artificial muscle of the exoskeleton according to the present invention, indicating its main parts.

[0018]

[0016] Figure 2 shows a side view of a schematic of a baby wearing the exoskeleton on its lower limbs.

[0019]

[0017] Figure 3 shows a diagram of the exoskeleton including its electronic and pneumatic components.

[0020]

[0018] Figure 4 shows experimental schemes with A) a comparison of force-contraction profiles, B) a force scheme on a model of an infant's leg, and C) results of the growth validation experiment.

[0019] Figure 5 shows an experimental validation of the Back-Solver model applied to an untrimmed actuator.

[0021]

[0020] Figure 6 shows an experimental validation of the Back-Solver model applied to a trimmed actuator.

[0022]

[0021] Figure 7 shows a photo of the proposed invention placed on both legs of an infant.

[0023] DETAILED DESCRIPTION OF THE INVENTION

[0024]

[0022] With the aim of resolving the deficiencies of the state of the art, the present invention is proposed which refers to a flexible exoskeleton that features a suit with one or more pneumatic artificial muscles, where each pneumatic artificial muscle has a variable operational length for the rehabilitation of infants who suffer from motor disability in the lower limbs.

[0025]

[0023] The pneumatic artificial muscle of the flexible exoskeleton according to the present invention comprises a flexible membrane (4); internal rings (3) spaced apart from each other and wrapped inside the flexible membrane (4); external rings (2) coupled to the internal rings (3) from outside the flexible membrane (4), where each external ring (2) comprises at least one groove (2.1); at least one clip component (1) including a pair of ends (1.1), where each end is removably engaged on an external ring (2); a pair of caps (5) disposed at ends of the flexible membrane (4), where one of the caps (5) has a pneumatic outlet (5).1) suitable for creating a vacuum inside the flexible membrane (4); a pair of non-stretchable straps (6) connected to the caps (5), wherein the straps (6) are connected at two points on the suit, a first point (10) at waist level and a second point (12) at ankle level and wherein the electronic components can be in an external box or casing that protects said components and that can be placed some distance from the infant when wearing the suit.

[0026]

[0024] Now, referring to the figures accompanying this description, as can be seen in Figure 1, in one embodiment of the invention, the outer ring (2) is formed by two L-shaped pieces with a central protrusion (2.1), where said central protrusion (2.1) of the outer ring (2) fits onto a central notch (3.1) of the inner rings (3). Preferably, the inner rings (3) are equally spaced inside the flexible membrane (4) and a trimming component (1) which may be a C-shaped anchoring clip.

[0027]

[0025] With reference to Figure 2, the suit consists of two pieces, namely: a short (9) and an ankle band (12), wherein a first strap (6.1) is connected to the short (9) via an anchor point (10) located on the short (9) and one of the caps (5) of the assembled artificial muscle (7), and the second strap (6.2) is connected to the ankle band (12) and the other cap (5) of the assembled artificial muscle (7), wherein said cap (5) has the pneumatic tubing (8). The ankle band (12) has an IMU (Inertial Measurement Unit) sensor (11), which can be placed on said band, for example, in a pocket.

[0028]

[0026] As shown in Figure 3, a diagram of the flexible exoskeleton according to the present invention is shown, illustrating the connections of its pneumatic and electronic components, where the IMU sensor (11) is connected to an external housing that contains a main controller (16) with a data acquisition card; likewise, said housing includes a touch screen (14), a power switch, and a power cable connection connected to the main controller (16). Additionally, the housing includes a vacuum pump (13) and an electronic vacuum pressure regulator (17) connected to the main controller (16), and the vacuum pump (13) is connected to a second pneumatic tube (8.1) that is connected to the electronic vacuum pressure regulator (17), which in turn is connected to the pneumatic outlet (5.1) (Fig.1) with a first pneumatic tube (8) with the desired vacuum pressure;, where the data acquisition card receives information from the vacuum pressure regulator (17), the pressure sensor and the IMU sensor (11).

[0029]

[0027] Figure 4 shows (A) A comparison of the force-contraction profiles for various trim configurations at constant pressure with a length-based scale. (B) Schematic of the BVA on the infant leg model in prone position indicating the actuator anchoring positions (d1 and d2) as well as the forces involved in knee flexion-extension (foot weight (WF), leg weight (W)). yo(C) Results of the growth validation experiment. For months 0, 3, and 6, the leg configuration and actuator anchoring positions were adjusted to match anthropomorphic data for infants of that age, and the corresponding actuator trim component (1) was used. A stepped input of the same negative pressure was applied for the 0, 3, and 6-month configurations, and the leg angle 9 was measured.

[0030]

[0028] Figure 5 shows the experimental validation of the Back-Solver model applied to an untrimmed actuator, given a variety of sinusoidal target angular trajectories: (A) a baseline trajectory with a period of 6 s, (B) a 4 s period trajectory of the same magnitude, and (C, D) two 6 s period trajectories with different target angle values.

[0031]

[0029] Figure 6 shows the experimental validation of the Back-Solver model applied to a trimmed actuator, comparing the performance between (A) an untrimmed actuator and (B, C) two different target trajectories for an actuator with two trimmed cells.

[0032]

[0030] Figure 7 shows a photograph of a prototype of the flexible exoskeleton according to the present invention with two pneumatic artificial muscles, one on each leg. In a preferred embodiment, the exoskeleton could include up to four pneumatic artificial muscles, two on each leg. This figure shows in greater detail the separation of the rings and their connection to the flexible membrane (4).

[0033]

[0031] Preferably, the flexible membrane (4) may be made of a polyethylene sheet or a textile that encapsulates the inner rings (3). This membrane (4) may have a thickness from 0.05 to 0.25 mm. The trimming component is preferably a C-shaped anchor clip, i.e., it consists of a bar with two protrusions or ends, which engage in the grooves of a pair of outer rings (2), securing and bringing them together. This allows for changes in the length of the pneumatic artificial muscle. For the purposes of the present invention, inextensible straps shall be understood to mean straps made of an inelastic material.

[0034]

[0032] Taking into account the growth of infants, the pneumatic actuator of the present invention has the ability to vary or change its initial length by means of a trimming component (1). The pneumatic actuator or flexible artificial muscle of the exoskeleton of the present invention consists of 5 main components: inner rings (3), outer rings (2), a flexible membrane (4), and trimming components (1). The inner rings (3) slide on a band-shaped membrane (4), and the outer rings (2) are placed in the central notches (3.1) of the inner rings (3), forming a chain of air chambers, without a solid skeleton in between. By inserting the trimming components (1), the muscle can activate or deactivate its air chambers, adapting to the infant's growth.In terms of manufacturing, the rings (2 and 3) and the trim components (1) are preferably manufactured using 3D printing, and the membrane (4) can be a thin plastic film or a textile. Similarly, the muscle has an outlet at its ends for a pneumatic tube (5.1) between 3 and 6 mm in diameter, preferably 4 mm in diameter, and buckle-like structures on the caps (5) for attaching straps from the suit.

[0035]

[0033] The suit can be made of common textiles and may consist of a single garment, such as pants, or two garments, such as shorts and ankle bands. The shorts are worn by the infant, covering their abdomen and part of their thighs. One of the main advantages of the shorts is that the fabric is flexible, making them comfortable for the infant and preventing discomfort while wearing the diaper. The ankle band, on the other hand, is worn around the infant's ankles and has a pocket for carrying an Industrial Measurement Unit (IMU) sensor. To prevent the garments from slipping on the infant, they may have Velcro straps for adjustment. While both garments are being worn, they act as a flexible mechanical structure with non-stretchable straps. These straps are crucial for securing the artificial muscle; that is, they act as attachment points.

[0036]

[0034] The exoskeleton of the proposed invention may include an external casing that protects the electronic components necessary for the operation of the exoskeleton, but does not require the infant to wear it. This external casing is made of plastic and consists of a single rectangular section. A touchscreen displaying the equipment's operating parameters is located primarily on the front of the external casing.

[0037]

[0035] On the same front of the outer casing as the touchscreen are the power switch and the power cable connection, while to the right of the screen are the pneumatic connections for the air exhaust of the pneumatic system and the vacuum pressure supply for the exoskeleton's artificial muscles. Small feet are located at the base of the outer casing so that it can rest on a flat surface.

[0038]

[0036] The outer casing includes two plastic parts that are preferably bolted together. Inside the outer casing, we find the vacuum pump (preferably with a capacity of 5 LPM) and its electronic pressure regulator (operating range between -1 and -100 kPa), located near the pneumatic connections. The pump and pressure regulator are attached to and secured to the bottom cover of the drawer with four bolts each. One pneumatic tube from the pump is directed to the pressure regulator as an air suction inlet, while the regulator has another pneumatic outlet tube with the desired vacuum pressure, which is directed to a T-type pneumatic connection. Two pneumatic tubes are connected to this pneumatic connection, one directed to a pressure sensor and the other to the vacuum pressure supply for the artificial muscles.Regarding pneumatic systems, tubing with a diameter between 3 mm and 6 mm is primarily used.

[0037] Additionally, the outer casing protects the pressure sensor's electronic board, the main controller, and the touchscreen. The touchscreen is secured to the front of the outer casing with screws, and operating parameters such as the desired range of motion and graphs of the infant's knee movement angles during operation can be entered from it, as well as system alarms. When the front of the outer casing is removed, the electronic boards are located in the center, the power supply on the left, and the mechanical components on the right. The power supply is prismatic in shape and is bolted to the lower base of the outer casing.It also connects to the power cord and the power switch, as well as to the voltage supply board. Finally, the data acquisition board receives information from the pressure regulator, the pressure sensor, and the IMU sensor. This board is also powered by the voltage supply board, which provides suitable and consistent voltages for its operation.

[0039]

[0038] The present invention also relates to a pneumatic artificial muscle characterized in that it comprises internal rings (3) spaced apart from each other and encased within a flexible membrane (4); external rings (2) coupled to the internal rings (3) from outside the flexible membrane (4), where each external ring (2) comprises at least one groove (2.1); at least one clip component (1) including a pair of ends, where each end is removably engaged over the groove of an external ring (2); and a pair of caps (5) disposed at one end of the flexible membrane, where one of the caps has a pneumatic outlet. Tests performed: a) Quasi-static test using various clip configurations

[0040]

[0039] A quasi-static test was performed to compare the force-contraction profile of the vacuum actuator (VVA) using the clipping component. Figure 4A shows a comparison of the BVA's output force-contraction profile for different clipped states, three trials each with an inlet pressure of -20 kPa. Contraction was calculated as the contracted distance over the total contractile length of the actuator. As would be expected from a vacuum-actuated pneumatic artificial muscle (VRAM), we observed a non-linear trend, with the highest output force at the beginning of contraction. The maximum output force of the unclipped BVA was 25.6 ± 1.2 N. There was no significant difference in the maximum output force of the unclipped VRAM and each of the clipped configurations.The discrepancies between a VRAM without a clipping component and a VRAM with a clipping component are likely due to slight differences in the ring arrangement during manufacturing and the wrinkled and compressed skin on the cell with the clipping component (clip). More importantly, various clipping configurations did not affect the output FCP of the BVA. b) Simulated leg growth experiment.

[0041]

[0040] Figure 4C shows the results of the simulated leg growth experiment, where the geometry and masses of the leg representatives were adjusted to simulate infant growth. The model represents an infant's leg, viewed from below the hip, in the prone position used by clinicians for passive knee ROM exercises (Passo, 1974).

[0041] A reference value of 54° was defined for our BVA when activated on the infant leg model, based on the knee ROM for a kicking motion of healthy infants at 3 months of age (Sargent et al., 2015). The BVA produced a knee angle of 60.66° ± 0.6° at 0 months of age, 65.40° ± 0.6° at 3 months of age, and 62.54° ± 0.6° at 6 months of age. Experimental measurements on the infant leg model exceeded our target range of motion by ~13%.The differences between the experimental results for each month are likely due to slight discrepancies in BVA assembly (e.g., ring misalignment) and sealing process issues. The flexible membrane may affect the contractile outlet length, as it can fold between two rings in a pattern that allows for easier contraction. The outlet angle in the experimental results is proportional to the BVA contraction. Therefore, as expected, when a cell was cut, the maximum knee angle decreased due to the reduction in the total contractile length of the BVA. Our experimental ROM values ​​for therapy exercises are within the range of reported values ​​(Mendoza et al., 2021).

[0042]

[0042] In addition to the angular range of flexion, the speed of the ROM exercise is relevant. The maximum angular speed obtained from our experiments was greater than 55°. s" 1for knee flexion. These results indicate that the BVA can produce knee flexion-extension exercises in less than the required time of 3 s (according to clinical collaborators), and the operating window should be adjusted to ensure patient safety. c) Experimental validation of Back-Solver

[0043]

[0043] To evaluate the performance of the proposed invention as an approach for open-loop leg control, pressure input curves were derived for different sinusoidal target trajectories and how closely the experimental trajectory matched the target was compared, as seen in Figure 5.

[0044]

[0044] This open-loop input can closely track the shape and angular magnitudes of different sinusoidal targets, ensuring smooth flexion and extension movement, a key safety design parameter for our physiotherapy platform. The experiment tends to overestimate the minimum trajectory angle, a result that can be well explained by the actuator hysteresis mentioned earlier. Since the proposed model does not capture the increase in actuator force output after contraction, it overestimates the pressure required during leg descent. It is observed that the result of this overestimation is that the experimental minimum angle is above the target minimum.

[0045]

[0045] Finally, we demonstrate the ability of the same model to predict pressure inputs when the actuator is trimmed. We use the same force-contraction profile (FCP) derived from the quasi-static experiment without trimming, while normalizing the x-axis by the new actuator length, since the scaled FCP for a bellows actuator is unaffected by the number of cells (as seen in the results in Figure 4A). With this scaled FCP, the same process is used as for modeling without the trimming component (without trimming).

[0046]

[0046] Figure 6 shows the performance of the pressure curve generated by the model, calculated for an untrimmed actuator and an actuator with two trimmed cells out of eight. As with the untrimmed case, the open-loop curve closely approximates the target shape and maximum angles, although the lower angle is overestimated. This effect is exacerbated when the minimum angle value is increased, and we assume this is due to the greater discrepancy in the hysteretic profile in the mid-range of actuator contraction (as opposed to the extremes of full contraction and extension), as is achieved when using a larger lower angle.

[0047] The above demonstrates that the Back-Solver model is capable of generating an open-loop curve for the system with angular magnitudes and shapes similar to the trajectory of the desired target, showing good agreement in terms of shape and target angles. Furthermore, it is shown that the proposed BVA can function successfully in terms of range of motion and cycle time for therapy exercises across different ages in infants.

[0047]

[0048] A person versed in the subject will understand that there are modifications in the configuration and materials of the flexible exoskeleton with pneumatic muscle that do not depart from the spirit of the present invention.

Claims

CLAIMS 1. A flexible exoskeleton with pneumatic artificial muscle, characterized in that it comprises a suit and one or more pneumatic artificial muscles, wherein each pneumatic artificial muscle comprises a flexible membrane (4); internal rings (3) spaced apart from each other and wrapped inside the flexible membrane (4); external rings (2) coupled to the internal rings (3) from outside the flexible membrane (4), wherein each external ring (2) comprises at least one slot; at least one clip component (1) including a pair of ends, each end being removably hooked onto an external ring (2); a pair of caps (5) disposed at ends of the flexible membrane (4), one of the caps (5) having a pneumatic outlet (5.1); a pair of inextensible straps (6) connected to the caps (5), wherein the straps (6) are connected at two points on the suit.

2. The flexible exoskeleton with pneumatic artificial muscle according to claim 1, characterized in that the clipping component (1) is a “C” shaped anchoring clip 3. The flexible exoskeleton with pneumatic artificial muscle according to claim 1, characterized in that the suit is formed by a short (9) and an ankle band (12), wherein a first strap (6) is connected to the short (9) and the second strap (6) is connected to the ankle band (12).

4. The flexible exoskeleton with pneumatic artificial muscle according to claim 3, characterized in that the ankle band (12) has a pocket carrying an industrial measuring unit (IMU) sensor (11).

5. The flexible exoskeleton with pneumatic artificial muscle according to claim 3, characterized in that the IMU sensor (11) is connected to an external housing which contains a main controller with a data acquisition card (16); and wherein said housing includes a touch screen (14), a power switch and a connection for a power cable connected to the main controller, an artificial muscle pressure sensor (15), power batteries (18) and a voltage power supply card (19).

6. The flexible exoskeleton with pneumatic artificial muscle according to claim 5, characterized in that the housing further includes a vacuum pump (13) and an electronic vacuum pressure regulator (17) connected to the main controller (16), and the vacuum pump (13) is connected to a first pneumatic tube which is in turn connected to the pneumatic outlet (5.1); while the electronic pressure regulator (17) is connected to a second pneumatic tube with the desired vacuum pressure, wherein the data acquisition card receives information from the electronic pressure regulator (17), the pressure sensor (15), and the IMU sensor (11).

7. A pneumatic artificial muscle characterized in that it comprises internal rings (3) spaced apart from each other and enclosed within a flexible membrane (4); external rings (2) coupled to the internal rings (3) from outside the flexible membrane (4), wherein each external ring (2) comprises at least one groove (2.1); at least one clip component (1) including a pair of ends, each end removably engages over the groove of an external ring (2); and a pair of caps (5) disposed at ends of the flexible membrane, one of the caps having a pneumatic outlet.

Images