A linear extended observer, an inverse controller and an exoskeleton device

Abstract

The present invention discloses a linear extended observer, an inverse controller and an exoskeleton device, which are applied to the field of exoskeleton robots. Aiming at the problem of low tracking accuracy in the prior art due to unmeasured joint velocities and lumped uncertainties, the present invention designs a linear extended state observer to estimate the joint velocities and lumped uncertainties; and then designs an inverse controller based on the observer to obtain the torque for driving the lower limb exoskeleton, thereby realizing the stable control of the lower limb exoskeleton system.

Description

Technical Field

[0001] The present invention belongs to the field of exoskeleton robots, and particularly relates to an inverse control technology for lower limb exoskeletons. Background Art

[0002] As a type of wearable robot, an exoskeleton forms a human-machine coupling system when worn by an operator, and can effectively coordinate the wisdom of the human body and the strength of the robot to complete high-intensity tasks that are difficult for the human body to complete. The main function of a lower limb exoskeleton is to assist the human body in completing lower limb movements such as walking, going up and down stairs, squatting and standing up. Its leg part of the exoskeleton is connected and strapped to the human leg, and according to the real-time movement intention of the human body and in a way driven by an exoskeleton motor, it helps an operator with walking disabilities or loss of walking ability to achieve independent walking. In addition, according to the different body shapes, gait characteristics and walking speeds of the operator, the exoskeleton can ensure the adaptability of human coupling and the comfort of the human body by adjusting the control mode and mechanical configuration. In the current model-based control technology for lower limb exoskeletons, the unmeasurability of joint angular velocity, system model uncertainty and external dynamic interference on the control performance of the exoskeleton are generally less considered, thus affecting the coordination, compliance and safety of human-machine coupling.

[0003] An exoskeleton mainly consists of the following parts: (1) Mechanical configuration part. Load-bearing enhanced exoskeletons have high requirements for the load mass, so a three-joint structure (hip joint, knee joint and ankle joint) is mostly used. For rehabilitation exoskeletons, since they are mostly used for patients, the activities of joints and the burden on patients need to be reduced, so lightweight materials and a two-joint structure (hip joint and knee joint) are mostly used. The mechanical structure mostly uses high-strength and anti-fatigue materials such as carbon fiber, titanium alloy, high-strength nano materials, etc.; (2) Actuation system. The function of the actuation system of the exoskeleton is to provide power for the movement of the human body and the exoskeleton. The power system mostly uses high energy density actuators such as servo motor systems, electro-hydraulic servo systems, pneumatic servo systems, etc.; (3) Sensor system. The sensor system of the exoskeleton is mainly used to monitor human physiological signals, exoskeleton motion state signals, human-machine coupling signals, etc. in real time, to judge the motion states of the human body and the exoskeleton, such as human-machine coupling force sensors, absolute encoders, electromyography sensors, etc.; (4) Control system. Usually, the proposed core control strategies and algorithms are implemented using Matlab software, and the control program of the exoskeleton system is implemented using Labview software, and finally the program is loaded into the hardware controller. Summary of the Invention

[0004] To solve the above technical problems, the present invention proposes a linear extended observer, an inverse controller and an exoskeleton device, and realizes the stable control of the lower limb exoskeleton system by using an inverse controller based on a linear extended state observer.

[0005] One of the technical solutions adopted by the present invention is: a linear extended observer, and the extended state observer obtains the estimated position according to the input external exoskeleton double-joint torque τ and the joint position q. Estimated velocity Estimated lumped uncertainty term

[0006] The linear extended observer is designed as:

[0007]

[0008] Wherein, is the estimated value of the state x, is the estimated value of the state x1, H is the observer gain, and ω0 is the adjustable observer bandwidth.

[0009] Another technical solution adopted by the present invention is: a backstepping controller based on a linear extended state observer. The backstepping controller calculates the driving torque τ of the external exoskeleton double-joint according to the ideal input position information q d , the ideal velocity information obtained by differentiation , and the estimated position estimated velocity estimated lumped uncertainty term output by the linear extended state observer.

[0010] The backstepping controller based on a linear extended state observer is designed as:

[0011]

[0012] Wherein, is the estimated value of z2, and z2 is the system error, is the estimated value of the state x2, and β is the virtual control quantity, is the dynamic term obtained from the parameter identification result, is the deviation term caused by the parameter identification error, K1 is a positive definite matrix.

[0013] Another technical solution adopted by the present invention is: an exoskeleton device, which uses the backstepping controller based on a linear extended state observer described above for motor drive.

[0014] The beneficial effects of the present invention: The present invention designs a linear extended state observer, which can obtain the estimated position estimated velocity estimated lumped uncertainty term The present invention uses a linear extended state observer to observe unknown lumped uncertainties and estimate unmeasurable states, reducing the impact brought by them; thus, it is used for the inverse control of the lower limb exoskeleton. The present invention also provides an inverse controller, which can calculate the driving torque τ of the exoskeleton's double joints according to the position information q of the ideal input d , the ideal velocity information obtained by differentiation , the estimated position output by the linear extended state observer , the estimated velocity , and the estimated lumped uncertainty term . The driving torque τ is used to drive the lower limb exoskeleton system to act. The present invention uses an inverse controller based on a linear extended state observer to achieve the stable control of the lower limb exoskeleton system. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 FIG. is a system block diagram provided by an embodiment of the present invention.

[0016] Figure 2 FIG. is a control flow chart of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] To facilitate those skilled in the art to understand the technical content of the present invention, the following further elaborates on the content of the present invention in conjunction with the attached Figure 1 drawings.

[0018] The present invention specifically includes the following content:

[0019] 1. In this embodiment, the following example of the system block diagram of the lower limb exoskeleton shown in Figure 1 is used for illustration:

[0020] The system block diagram mainly includes an inverse controller, a lower limb exoskeleton system module, and an extended state observer. As shown in Figure 1 ; among them, the inverse controller can calculate the driving torque τ of the exoskeleton's double joints according to the position information q of the ideal input d , the ideal velocity information obtained by differentiation , the estimated position output by the extended state observer , the estimated velocity , and the estimated lumped uncertainty term . The lower limb exoskeleton system can obtain the real-time joint position q and joint velocity according to the input exoskeleton double joint torque; the lower limb exoskeleton mainly obtains the real-time joint position q and joint velocity by sensors based on the exoskeleton double joint torque . Among them, the extended state observer can obtain the estimated position according to the input exoskeleton double joint torque τ and the joint position q , the estimated velocity , and the estimated lumped uncertainty term In the present invention, respectively represent the time derivative, second time derivative, estimated value, and estimation deviation of ·, where the symbol "·" represents a general reference.

[0021] 2. Design of an Inverse Controller for a Lower Limb Exoskeleton Based on a Linear Extended State Observer

[0022] 21. Modeling of the Dynamics Model of a Lower Limb Exoskeleton

[0023] The dynamics model of a two-degree-of-freedom lower limb exoskeleton is described as follows

[0024]

[0025] where q represents the set vector of the joint positions of the exoskeleton hip joint and knee joint, represents the time derivative of q, represents the second time derivative of q, and are the system inertia matrix, Coriolis matrix, gravity term, friction term, and lumped uncertainty term respectively. is the motor driving torque of the exoskeleton hip joint and knee joint, is the human-machine coupling torque, represents the real number symbol, represents two-dimensional real numbers.

[0026] where M(q), G(q), and can be expressed as

[0027]

[0028] where M0(q), G0(q), are the dynamic terms obtained from the parameter identification results, and M △ (q), G △ (q), are the bias terms caused by the parameter identification errors.

[0029] Therefore, (1) can be rewritten in the following form

[0030]

[0031] where the lumped uncertainty term can be expressed as

[0032]

[0033] 22. Design of a Linear Extended State Observer

[0034] To solve the problem of unmeasured joint velocities and the lumped uncertainty d(t), an inverse controller based on a linear extended state observer is designed to improve the corresponding effect and tracking accuracy.

[0035] The exoskeleton state variables can be defined as x1 = [q1, q2] T , and the extended state variable Therefore, the state - space equation of (3) can be expressed as

[0036]

[0037] where δ(t) is the time derivative of x3.

[0038] If the total state vector can be defined as [x1, x2, x3] T , then (5) can be expressed as

[0039]

[0040] where represent the time derivatives of the state variables x1, x2, x3 respectively, I 2×2 represents the 2 - by - 2 identity matrix, and

[0041] u = τ,

[0042]

[0043]

[0044]

[0045] The exoskeleton joint position q and the human - machine coupling torque τ ext can be measured by an absolute encoder and a three - dimensional force sensor, but the joint velocity cannot be directly obtained by the absolute encoder. Therefore, the design of the linear extended state observer not only needs to estimate the unmeasured system state x2, but also needs to estimate the total uncertainty x3.

[0046] According to (7), the linear extended state observer can be designed in the following form

[0047]

[0048] where is the estimated value of state x, is the estimated value of state x1, Denote the estimation deviation with respect to the state variable x2 is the observer gain, and ω0 is the adjustable observer bandwidth.

[0049] 23. Design of the backstepping controller

[0050] According to the exoskeleton dynamics model (6), let x1 = [q1, q2] T , The state - space expression is

[0051]

[0052] Define the system error

[0053]

[0054] where, x d is the desired trajectory, is the virtual control input, denotes the time derivative of the desired trajectory x d , is a positive - definite matrix.

[0055] The backstepping controller based on the linear extended - state observer can be designed as

[0056]

[0057] where, respectively denote x d 's time derivative and second - order time derivative.

[0058] As Figure 2 shown, the present invention obtains the torque for driving the lower - limb exoskeleton by designing a backstepping controller based on the linear extended - state observer, thereby realizing the stable control of the lower - limb exoskeleton system.

[0059] Those skilled in the art should note that the technical solution of the present invention is not limited to the 2 - degree - of - freedom lower - limb exoskeleton, and is also applicable to exoskeletons with other degrees of freedom (exoskeletons include upper - limb exoskeletons and lower - limb exoskeletons).

[0060] Ordinary skilled artisans in the art will realize that the embodiments described herein are to assist the reader in understanding the principles of the present invention, and it should be understood that the scope of protection of the present invention is not limited to such specific statements and embodiments. Various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc., made within the spirit and principle of the present invention shall be included within the scope of the claims of the present invention.

Claims

1. A linear extended observer, characterized in that, The linear extended state observer obtains the estimated position according to the input exoskeleton double-joint torque τ and the joint position q estimated velocity estimated lumped uncertainty term The linear extended observer is designed as follows: Among them, is the estimated value of state x, is the estimated value of state x1, H is the observer gain, M0(q) and G0(q) are the dynamic terms obtained from the parameter identification results, I 2×2 represents the 2-by-2 identity matrix, τ ext is the human-machine coupling torque, represents the estimation deviation with respect to the state variable x2.

2. An inversion controller, characterized in that, The inversion controller calculates the driving torque τ of the exoskeleton's double joint based on the position information q of the ideal input d , the ideal velocity information obtained by differentiation , the estimated position , estimated velocity , and the estimated lumped uncertainty term output by the linear extended state observer described in claim 1; The backstepping controller based on the linear extended state observer is designed as follows: Among them, is the estimated value of z2, where z2 is the system error, is the estimated value of state x2, and x3 is the extended state variable, is the estimated value of x3, and β is the virtual control variable, is the dynamic term obtained from the parameter identification result, is the deviation term caused by the parameter identification error, K1 is a positive definite matrix, τ ext is the human-machine coupling torque, and z1 is the system error, represents the desired trajectory x d 's time derivative, represents x d 's second-order time derivative, represents 's time derivative.

3. An exoskeleton device, characterized in that, The backstepping controller described in claim 2 is used for motor drive.

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