SOFT EXOSKELETON WEARABLE DEVICE FOR TEMPOROMANDIBULAR DISORDER (TMD) REHABILITATION

Abstract

Disclosed is an exoskeleton wearable device configured to push a condyle out from a glenoid structure of a skull made of two bellows shaped actuators each having an elliptical cross-section; an upper part configured to be fixed on a forehead of a patient and provide a base for the two bellows shaped actuators; and a lower part configured to be fixed on a mandible of the patient and substantially static to the mandible but moveable in a horizontal plane and a vertical plane with respect to the upper part.

Claims

1. An exoskeleton wearable device configured to push a condyle out from a glenoid structure of a skull, comprising: two bellows shaped actuators each having an elliptical cross-section; an upper part configured to be fixed on a forehead of a patient and provide a base for the two bellows shaped actuators; and a lower part configured to be fixed on a mandible of the patient and substantially static to the mandible but moveable in a horizontal plane and a vertical plane with respect to the upper part.

2. The exoskeleton wearable device according to claim 1, wherein the two bellows shaped actuators are pneumatic actuators.

3. The exoskeleton wearable device according to claim 1, with the proviso that the two bellows shaped actuators do not have a circular cross-section.

4. The exoskeleton wearable device according to claim 1, wherein the upper part has a ring shape and configured to be substantially static during mandibular movement.

5. The exoskeleton wearable device according to claim 1, further comprising a pneumatic control system.

6. The exoskeleton wearable device according to claim 5, wherein the pneumatic control system comprises a pressure sensor, a solenoid valve, and a driver board.

7. The exoskeleton wearable device according to claim 1, having a weight of 340 grams or less.

8. A method of treating a temporomandibular disorder, comprising: attaching the exoskeleton wearable device according to claim 1 to the skull of a patient; and using the exoskeleton wearable device according to claim 1 to facilitate at least one of opening or closing a jaw of the patient.

9. The method according to claim 8, wherein using the exoskeleton wearable device comprises actuating at least one of the two bellows shaped actuators.

10. The method according to claim 8, wherein using the exoskeleton wearable device comprises actuating both of the two bellows shaped actuators.

11. An exoskeleton wearable device configured to push a condyle out from a glenoid structure of a skull, comprising: two bellows shaped actuators each having an elliptical cross-section; an upper part configured to be fixed on a forehead of a patient and provide a base for the two bellows shaped actuators; a lower part configured to be fixed on a mandible of the patient and substantially static to the mandible but moveable in a horizontal plane and a vertical plane with respect to the upper part; and a pneumatic controller configured to generate pressure command output according to a desired motion trajectory to facilitate moving the lower part relative to the upper part.

12. The exoskeleton wearable device according to claim 11, wherein the two bellows shaped actuators are pneumatic actuators.

13. The exoskeleton wearable device according to claim 11, with the proviso that the two bellows shaped actuators do not have a circular cross-section.

14. The exoskeleton wearable device according to claim 11, wherein the upper part has a ring shape and configured to be substantially static during mandibular movement.

15. The exoskeleton wearable device according to claim 11, wherein the pneumatic controller comprises a pressure sensor, a solenoid valve, and a driver board.

16. The exoskeleton wearable device according to claim 11, having a weight of 340 grams or less.

Description

BRIEF SUMMARY OF THE DRAWINGS

[0012] FIG. 1 depicts the exoskeleton soft device wearing on a skull model in accordance with one embodiment, a side view (left) and front view (right).

[0013] FIG. 2. depicts an anatomical structure of the human's masticatory system. Upper right shows the closed jaw where the condyle fits in the glenoid structure. Lower right shows the opened jaw where the condyle slides out of the glenoid structure.

[0014] FIG. 3 depicts the TMJ soft robotic joint and the analytical modeling key parameters.

[0015] FIG. 4 depicts an embodiment of a control scheme of the soft robotic joint.

[0016] FIG. 5 depicts an embodiment of a pneumatic control platform.

[0017] FIG. 6 depicts an embodiment of the experimental platform. Left shows the on-table soft robotic joint unit testing platform with two markers for capturing the actual trajectory and the kinematic characteristics of the motion. Right shows the on-skull testing platform with an air cylinder driving the major motion of the jaw opening.

[0018] FIG. 7 depicts lateral compliance testing. Forces were applied on the illustrated direction to test the displacements. No obvious difference of compliance when being actuated.

[0019] Table 1 reports the structure and material parameters of a soft robotic joint in accordance with one embodiment.

[0020] FIG. 8 depicts testing results of only actuating the upper actuator. The actual trajectory is compared with the calculated trajectory. FIG. 8a shows the actual trajectory agrees well with the calculated one with deviation of less than 1 mm. Grey circle shows the angle variation during the actuating. FIG. 8b shows the kinematic characteristics, including velocity, acceleration, angular velocity and angular acceleration are shown. The sharp slope of the variation shows quick response of the motion once being actuated.

[0021] FIG. 9 depicts testing results of only actuating the lower actuator. FIG. 9a shows trajectory comparison and angle variation. FIG. 9b shows kinematic characteristics.

[0022] FIG. 10 depicts testing results of actuating both two actuators. FIG. 10a shows trajectory comparison and angle variation. The angle barely changed during the actuation. FIG. 10b shows kinematic characteristics. Angular velocity and angular acceleration oscillated within very small range by calculation since the angel changing value is nearly zero.

[0023] FIG. 11. Testing results of trajectory mimicking. FIG. 11a shows the pressures solved inversely by displacement function. The actual pressures follow well with the calculated ones with the pneumatic control platform. FIG. 11b shows trajectory comparison and the angle variation. The actual trajectory's trend agrees well with that of the planned one. FIG. 11c shows kinematic characteristics.

[0024] FIG. 12 depicts testing results on skull. FIG. 12a shows trajectory comparison and the angle variation. Green circle zoomed right side on-skull captured trajectory. Triangles show the captured trajectory of that the device were not actuated, while the dots show the one of being actuated. Grey triangles and dots respectively represent the same trend in the initial period of actuating. Difference is shown by the blue triangles and the red dots that when actuating the device, the end effector could significantly push the condyle out of the glenoid structure. The angle variation curve shows the movement is first rotating then sliding. FIG. 12b shows kinematic characteristics.

DETAILED DESCRIPTION

[0025] The disclosure herein enables the rehabilitation utilizing a soft approach, which is not found in the art. The soft mechanism described herein has at least one of several advantages:

[0026] 1. Considering the real human TMJ mechanism;

[0027] 2. Lightweight, comfort and safety;

[0028] 3. Natural compliance, not causing further injury;

[0029] 4. Trajectory planning and customization.

[0030] Current training devices for TMD are bulky and large not made considering the patients' comfort and safety, which aims to forcibly drive the mandible to move. The disclosure herein provides a lightweight and customizable device adopting soft approach to help the patients train correct jaw moving at home by using soft actuators driven by pneumatic control, which is lightweight and compliant to individual differences. Herein is described a wearable exoskeleton device with trajectory planning by pneumatic control. The preliminary pneumatic control for activating the device to replicate human' jaw motion is achieved. To optimize the performance and the customization, precise control with various payload can be developed.

[0031] Temporomandibular disorder (TMD) cases require correct and sufficient guide to the patients' mandible movement. It is the most ideal application where robotic device is demanded for the movement training apart from the surgical operations done by the doctors. Provided is a two-soft-actuator robotic joint design applied on an exoskeleton soft wearable device with substantial improvements over the existing training device. The soft device helps reduce tremendous weight of the device and reserves the system compliance considering patients' comfort and safety, which brings highly capacity of wearing and self-training. The pneumatic-control-based trajectory planning enables customization of the device for the purpose of satisfying accommodating patients' individual difference. The design, modeling, fabrication, and validation of an exoskeleton soft wearable device for TMD are presented in detail below. Both on-table unit and the on-skull testing are enabled, showing the remarkable ability of guiding the mandible to move according to the real human nature, paving the way for further clinical applications of such disease.

[0032] The Mandible Moving Mechanism

[0033] Human's masticatory system has a well-developed structure being able to perform functions of chewing, stirring and swallowing food. The mandible is mobile achieving various motions by accommodating the attachments of muscles and ligaments, shown in FIG. 2. In theory, due to the rigidity of the mandible, the position can be completely reconstructed using a single point's orientation and position. If the maxilla and hypoid are fixed, the motion of the mandible can be derived knowing the condyle's situation of the TMJ.

[0034] The TMJ is a diarthrodial joint, which can move between bones, consisting of a series of bony and soft tissue components. The bony parts include the condyle of the mandible and the glenoid structure on the skull. Such combination can efficiently act as a pivot for the multi-dimensional movements, as a fulcrum for leverage, and as the guides for mandible movements. While the soft tissues include mainly the articular disc, which is a continuous structure between the bony and articular surfaces of the TMJ.

[0035] This disc is to prevent the bony parts from colliding each other and its moving is also to ensure smooth movement of the condyle. The displacement of the articular disc can also cause the TMD, leading to click sound, synovitis, pain and limitation of motion. With the protection of the disc, the condyle can rotate about a horizontal axis as well as slide along the articular eminence. With the complex structure and the moving mechanism of the TMJ, what is ignored by the current therapy robots is the real motion trajectory of the condyle. To mechanically and forcedly opening patients' mouth causes further damage to the condyle, articular disc or to the whole TMJ.

[0036] The TMJ Soft Robotic Joint Design

[0037] In order to ensure the jaw movement training correct and does not cause further damage, a 2-soft-actuator joint design provides an exoskeleton support actuated as the real TMJ motion trajectory. With the two combined pneumatic actuators, the proposed soft approach is able to replicate the condyle moving trajectory of different unique individuals by pressure control, with much lighter weight and higher compliance for patients' comfort and safety, compared with the existing therapy devices.

[0038] The soft actuators are chosen as well-studied bellows shape ones and are assembled with an angle for having an inherent multiple degree of freedom compared with conventional parallel structure. In addition, since the deformations are within the lateral plane, an ellipse cross-section actuator is chosen for more efficient bending than circle cross-section one. An analytical model is derived for studying the deformation of the proposed joint and the geometrical relationship is denoted in FIG. 3.

[0039] For a bellows shape soft actuator with number of convolutions N, outer diameter/inner diameter ratio α, cross-sectional area S, Young's modulus E, wall thickness t, Poisson's ratio μ, and original length l0, the lengths after being inflated are:

[00001]$\begin{array}{cc}{l}_1=l_0+\frac{P_1.Math.S}{k_y}=l_0+\frac{P_1.Math.S.Math.3N\left(1-{\mu }^2\right)4r^2\left[\ln \alpha -\left(\alpha -1\right)+\frac{{\left(\alpha -1\right)}^2}{2}\right]}{\pi {\mathrm{Et}}^3}& \left(1\right)\end{array}$

where l1 is the elongated length of the actuator 1, ky is the axial stiffness, and P1 is the inner pressures of the actuator 1.

[0040] The torques making the actuators bending are:

M.sub.1=M.sub.1+M.sub.P=M.sub.1+∫.sub.0.sup.l.sup.1∫.sub.0.sup.2.sup.πP.sub.1.Math.r.sup.2 sin.sup.2θdθdx  (2)

where M1 is the torque caused by the end effector, MP is the torque caused by the inner pressure of the actuator, and r is the simplified circle inner radius of the ellipse actuator.

[0041] Then the deflection function w1 of the actuator 1 can be written according to the cantilever beam theory:

[00002]$\begin{array}{cc}\frac{d^2{w}_1}{d^2{x}_1}=\frac{M_I}{{\mathrm{EI}}_x^{\mathrm{ellipse}}}=\frac{M_I}{E\frac{\pi }{4}{a}^{3}t\left(1+\frac{3}{\beta }\right)}=\frac{-f_1\left(l_1-x_1\right)+{\int }_0^{l_1}{\int }_0^{2\pi }{P}_1.Math.r^2{\sin }^2\theta d\theta {\mathrm{dx}}_1}{E\frac{\pi }{4}{a}^{3}t\left(1+\frac{3}{\beta }\right)}& \left(3\right)\end{array}$

where x1 is the position on the actuator in x-axis, lx.sup.ellipse is the momentum of inertia of the ellipse tube in x-plane, and β=b/a is the parameter of the ellipse with half major axis a and half minor axis b.

[0042] The force caused by the end effector on the actuator 1 and 2 are denoted by f1 and f2 should have the relationship,

P.sub.1.Math.S=f.sub.1.Math.cos γ+f.sub.2  (4)

also due to the connection with the end effector, the two actuators should have the geometrical relationship of:

[00003]$\begin{array}{cc}2\times \left(x_1{.Math.}_{x_1=l_0}-x_2{.Math.}_{x_2=l_0}\right)\times \left(\Delta l_2-\left(w_2{.Math.}_{x_2=l_2}\right).Math.\sin \gamma +\Delta l_2.Math.\cos \gamma \right)+\left(y_1{.Math.}_{x_1=l_0}-y_2{.Math.}_{x_2=l_0}\right)\times \left(w_1{.Math.}_{x_1=l_1}-\left(\left(w_2{.Math.}_{x_2=l_2}\right).Math.\cos \gamma -\Delta l_2.Math.\sin \gamma \right)\right)=-{\left(\Delta l_1-\left(w_2{.Math.}_{x_2=l_2}\right).Math.\sin \gamma +\Delta l_2.Math.\cos \gamma \right)}^2-(w_1{.Math.}_{x_1=l_1}-{\left(\left(w_2{.Math.}_{x_2=l_2}\right).Math.\cos \gamma -\Delta l_2.Math.\sin \gamma \right)}^2& \left(5\right)\end{array}$

where γ is the pre-designed angle of the end effector.

[0043] Applying the boundary conditions at the built-in end as well as the above geometrical relationships:

w.sub.1′|.sub.x.sub.1.sub.=0=0;w.sub.1|.sub.x.sub.1.sub.=0=0  (6)

w.sub.2′|.sub.x.sub.2.sub.=0=0;w.sub.2|.sub.x.sub.2.sub.=0=0  (6)

Δθ=w.sub.1′|.sub.x.sub.1.sub.=l.sub.0=w.sub.2′|.sub.x.sub.2.sub.=l.sub.0  (8)

where μθ is the rotation angle of the end effector, all the constraints of integration can be solved.

[0044] Thus, the relationship of the end effector's displacements and the inner pressure of the actuators could be derived (dx,dy)=f(P1,P2). Solving this equation given the desired displacements of x- and y-axis, the pressure commands can be obtained for trajectory planning.

[0045] The Exoskeleton Wearable Device Design

[0046] Connected by the proposed two-soft-actuator robotic joint, the exoskeleton wearable device comprises two main parts which are both lightweight and wearable, shown in FIG. 1. The upper part is to be fixed on the patients' head and is designed as a thin ring. The ring which is soft and adjustable works as the base for the robotic joint. Thus, the upper part is relatively static with the glenoid structure on the skull and provide fiducial points during the movement. Then, the lower part is fixed on the mandible and relatively static to it. To apply force on the mandible when actuating, a ribbon connecting the left and right parts is tightened on the patients' chin. With the two wearable parts connected by the soft robotic joint, patients have a supportive force and motion when doing the mouth opening training assisted by the pneumatical control. Also, for the purpose of comfort safety and adjustability, the exoskeleton device is fabricated with an elastic material and rubber-like gaskets are attached to the contacting place of the patients' skin.

[0047] The whole device inherently reserves the compliance within all the moving freedoms, including both horizontal and vertical planes. Such compliance ensures the safety by allowing the tolerance to the individual uniqueness, because the real moving trajectory of the humans' mandible is not a simple to-and-fro curve only in one plane. The conventional training device sacrifices such compliance, ignoring the individual difference and the complexity of the motion, which can cause further damage to the patients during training. The herein described device utilizes the soft approach to allow and fit the individual difference, simultaneously provides sufficient support to help push the condyle out from the glenoid structure of the skull.

[0048] Control Scheme

[0049] For the exploration of the impact of the proposed exoskeleton soft wearable device on TMD training, the system is controllable and able to accurately generate pressure command output according to the desired motion trajectory. For the proposed soft actuators, pressures controlled by the solenoid valves whose duty cycle and frequency are particularly able to be adjusted by PWM signal. The overall controller diagram for the wearable device is shown in FIG. 4. The desired motion trajectory is considered by the planner to generate target pressures, which are further evaluated by dedicated frequency and duty cycle controllers of the valves. The generated commands are then passed on to the PWM generator block to generate corresponding PWM signals. Both PWM signals are amplified by the two power amplifiers and sent to valves. Pressure feedback loop is established to monitor the actual pressures for achieving more accurate trajectory.

[0050] To investigate the influences of the proposed exoskeleton soft wearable device on the mandible moving, a prototype of the robot was developed and tested both on a single robotic joint and on a skull model. Results and discussions are presented in detail.

[0051] The Soft Robotic Joint

[0052] The proposed soft robotic joint consisted three parts: a base, an end effector and two bellows-shape ellipse soft actuators, shown in FIG. 6. The base and the end effector are both fabricated by a consumer-grade 3-D printer with PLA material. The soft actuators are fabricated by the means of blow molding and chosen as the parameters shown in Table 1.

[0053] The Pneumatic Control System

[0054] The dedicated experimental platform consists of a pneumatic control system, shown in FIG. 5. The pneumatic pressure source and sink system contain two pumps and two pressure tanks, and the inflation and the deflation of the soft actuators are each controlled by two high-frequency solenoid valves connecting to the source and the sink respectively. The whole system is controlled by a STM board and AD and driver board are used for sensors and valves. Pressure sensors are connected to the source and sink tank for maintaining the high and low level of the pressure. In addition, each soft actuator is monitored by a pressure sensor for feedback control of the pressure. Thus, the pneumatic control system could generate a stable and reliable output of the pressure to the actuation sector of the proposed device.

[0055] The On-Skull Experimental Platform

[0056] In addition to the TMJ structure, the normal jaw opening is actuated by a series of human muscles, including suprahyoid muscles, lateral pterygoid muscles, masseters, digastric muscles, etc. In this testing case, the dysfunction of the muscle group is not considered, which means it is assumed that the patients have the muscle strength to move the jaw, but the joint gets stuck causing pain, or the muscles are not exerted in the correct way. The wearable device helps the patients to gain the correct moving of the jaw. Therefore, the target of the work as an assistance focusing on the TMJ instead of forced opening. Thus, the complex muscle group for moving the jaw is achieved by a simple pneumatic cylinder, shown in FIG. 6. The cylinder with a flexible connection with the chin replicates the slightly curved moving trajectory of the lower dentition. The proposed soft joint and the cylinder simultaneously actuates the mandible to perform normal opening and closing of the mouth mimicking the real biological process.

[0057] Overall, in one embodiment, the fabricated wearable parts of the exoskeleton soft wearable device weighs 340 grams or less connected with the pneumatic control platform by two air tubes.

[0058] Lateral Compliance Tests

[0059] To validate the compliance reserving ability of the soft robotic joint, a group of tests were conducted on the table unit. Forces were applied on the direction shown in FIG. 7 and the vertical displacements were recorded. Being actuated under three group of pressures were tested, including 0 KPa, 20 KPa and 40 KPa. From the results, to achieve same displacements, no difference of load applied were needed, implying that during the actuation period, the compliance in the vertical plane could maintain significantly.

[0060] Soft Robotic Joint Tests

[0061] To validate the trajectory mimicking capability of the proposed soft robotic joint, an on-table testing unit with two ellipse soft actuators was tested actuated by different commands of pneumatic pressure control. Three groups of repeat experiments were conducted, including actuating only the upper actuator, actuating only the lower actuator and actuating both the two actuators, with linear pressure variation. The motion of the two markers was tracked by a camera and computer vision techniques were utilized to fetch the actual trajectory. The testing results are shown in FIG. 8, FIG. 9, and FIG. 10, suggesting excellent fitting with the calculated trajectory with the maximum deviation of no more than 1 mm. The analytical model gives satisfactory simulation of the displacements in the plane. Thus, to inversely solve the displacement function with respect to the pressures then generate the pressure command by the desired trajectory. Applying such command by the pneumatic control platform, the motion are mimicked subject to the desired trajectory.

[0062] In addition, the kinetic characteristics were calculated with the computer vision. The velocity, acceleration, angular velocity and angular acceleration were presented. The response of the actuation is quick, and the motion performance could be monitored and cooperated with the control system, the device has the potential to let patients individually adjust the training process.

[0063] Applying the validated soft robotic joint, the desired trajectory mimicking was tested. A moving trajectory of the end effector was planned according to the real humans' condyle motion. With the planned trajectory, pressure commands were inversely solved by the relation function. Then the actual trajectory was captured and compared with the planned one, shown in FIG. 11. The actual pressures monitored follows well with the pressure command under the control of the pneumatic platform, and the trend of the motion well agreed with the planned trajectory, however, due to the control accuracy of the adopted valve, the motion of the end effector was a little oscillated.

[0064] With the validation of the soft robotic joint, the motion performed by the proposed wearable device can be adopted on a real situation.

[0065] On-Skull Tests

[0066] To further investigate the influences of the proposed wearable device on the mouth opening, the on-skull testing was conducted. The head ring was fixed on the skull and the end effector of the device was fixed on the mandible of the model both by soft ribbons. The skull is assumed to be static and fixed on a shelf. The lower jaw was connected to an air cylinder and the major motion of opening is actuated by the cylinder. Both opening trajectories were captured and analyzed of: 1) not actuating the device; 2) actuating the device. The trajectories were compared and shown in FIG. 12. A sliding motion can be obviously observed applying the proposed device for pushing the model condyle out of the glenoid structure, which conforms to the humans' nature, shown by the blue triangles and red dots in the figure. Such sliding exoskeleton support could train the patients to correctly open their mouth without further damage to the TMJ.

[0067] The experimental results and observations are of remarkable importance to TMD rehabilitation device development. The proposed exoskeleton soft device design brought three main contributions compared to the current therapy methods: 1) substantially mimicking the real human's jaw motion trajectory, reducing the total weight of the wearable parts considering the patients' comfort and safety; 2) reserving the system other-direction compliance while being actuated in jaw-sliding plane, reducing further damage during training due to individual difference; 3) fitting with TMJ features, enabling a customizable trajectory planning by pneumatic control, paving the way for further TMD treatment. Moreover, it is demonstrated on a skull model that the condyle of the mandible can be effectively pushed out of the glenoid structure with the support of the proposed wearable device.

[0068] This disclosure tackled the challenges in exoskeleton wearable device for TMD treatments by offering a soft approach to TMJ motion generation. The two-actuator soft robotic joint are investigated, showing their superior performance in trajectory mimicking with the pneumatic control. An exoskeleton soft wearable device is developed using blow molding and 3D printing techniques to provide a mandible movement guide. Experiments and computer vision capturing are conducted on both proposed soft robotic joint and a skull model, revealing underlying mechanisms and distinctive characteristics of the TMJ motion. Compared with the current training methods, the proposed exoskeleton soft wearable device is hyper light weight, comfortable and safe to the patients, and performs accustomed to the human nature.

[0069] The disclosure also offers insights to rehabilitation device design, offering a variable solution to patients training with system compliance with soft approach. Moreover, convenient trajectory planning to accommodate individual difference by pneumatic control enables capability of customization for different patients' physiological structure. Such prodigious customized ability brings usability and safety to the application of rehabilitation device on complicated disease.

[0070] Unless otherwise indicated in the examples and elsewhere in the specification and claims, all parts and percentages are by weight, all temperatures are in degrees Centigrade, and pressure is at or near atmospheric pressure.

[0071] With respect to any figure or numerical range for a given characteristic, a figure or a parameter from one range may be combined with another figure or a parameter from a different range for the same characteristic to generate a numerical range.

[0072] Other than in the operating examples, or where otherwise indicated, all numbers, values and/or expressions referring to quantities of ingredients, reaction conditions, etc., used in the specification and claims are to be understood as modified in all instances by the term “about.”

[0073] While the invention is explained in relation to certain embodiments, it is to be understood that various modifications thereof will become apparent to those skilled in the art upon reading the specification. Therefore, it is to be understood that the invention disclosed herein is intended to cover such modifications as fall within the scope of the appended claims.