CN112008726B - Composite finite time control method based on exoskeleton robot actuator - Google Patents
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Abstract
The invention discloses a composite finite time control method based on an exoskeleton robot actuator, and belongs to the field of exoskeleton robot systems. Aiming at the problems of complex control scheme, low precision and poor robustness and anti-interference capability in the prior art, the invention provides a composite finite time control method based on an exoskeleton robot actuator, which comprises the following steps: constructing a high-order sliding mode disturbance observer for estimating the state and disturbance of a tracking error system, bringing an estimation result into a tracking error, and then bringing the tracking error into a performance index; constructing a lower triangular nonlinear system finite time controller; constructing a state space model of the actuator; and designing a robust finite time control law by utilizing a composite finite time controller and combining a state space model. According to the method, semi-global control rather than global control is adopted to improve the engineering applicability, the control gain can be realized according to a pole configuration mode, the control speed is improved, and the robustness is enhanced.
Description
Technical Field
The invention relates to the field of robot control systems, in particular to a composite finite time control method based on an exoskeleton robot actuator.
Background
The exoskeleton robot technology is a comprehensive technology which integrates sensing, control, information, fusion and mobile computing and provides a wearable mechanical mechanism for a person as an operator. The present document briefly introduces the development status and trend of exoskeleton world robot technology in the military field. The robot is sleeved outside a human body and is also called a wearable robot. The safety and flexibility of the existing control method need to be improved, and the parameters of the exoskeleton robot are difficult to accurately obtain due to the complexity of mechanical structures, such as nonlinear friction force, clearance and the complexity of a robot actuator. In addition, the dynamic characteristics of subjects vary according to their physiological conditions. The current control methods are not adaptive in the presence of dynamic and motion uncertainties and unknown disturbances of the system.
The Chinese patent application, application No. CN202010132049.8, published as 2020 and 6/16/discloses a self-adaptive compliance control method for an exoskeleton robot for upper limb rehabilitation, wherein the control algorithm consists of two parts: the first part is an admittance control module which is arranged as a control outer ring and can establish a dynamic relation between interaction force between a patient and the exoskeleton and a rehabilitation training track regulating variable, so that the patient can remold a rehabilitation training track according to own active intention; the second part is an adaptive sliding mode control module which is arranged as a control inner ring and used for realizing accurate tracking control of the expected training track and the position adjustment quantity, and the control precision and the system stability are partially dependent on inner ring position control. The method has the disadvantages that the model predictive control of the invention is difficult to process the problems of model uncertainty and interference when the physical control system is processed, and a large amount of calculation is required, which is not beneficial to the realization of the method.
The invention provides a multi-joint combined control system and a method for an exoskeleton robot, which are applied for Chinese patent application, application number CN202010093076.9, and published on 2020, 6, 12.A control system inputs real-time feedback signals of a full sole pressure sensing system and a limb posture sensing system into a multi-signal fusion and decoupling model, completes fusion and decoupling of various signals by the model, outputs various joint motor control variables and controls the operation of a motor; building a multi-signal fusion and decoupling model by using a neural network, and generating a mature application model with multi-signal fusion and decoupling through a large amount of training; the control quantity of various joint motors output by the model is corrected in real time according to a human-computer interaction sensing system in the control system, so that the auxiliary optimization effect is achieved, and the optimal wearing effect of the exoskeleton robot is achieved; in the aspect of joint motor control, the motor is controlled quickly and accurately by real-time current closed-loop control and position (joint angle) closed-loop control of the motor. The method has the disadvantages of more parameters, large calculation amount and complex algorithm realization.
Disclosure of Invention
1. Technical problem to be solved
Aiming at the problems of complex control scheme, low precision and poor robustness and anti-interference capability of the exoskeleton robot in the prior art, the invention provides a finite time control method based on an exoskeleton robot actuator, which adopts semi-global rather than global control to improve the engineering applicability, can realize control gain according to a pole configuration mode, improves the control speed and enhances the robustness.
2. Technical scheme
A composite finite time control method based on exoskeleton robot actuators, comprising the following steps:
and 4, constructing a robust controller with limited time, designing a robust limited time control law by using the composite limited time controller and combining the state space model in the step 3, and thus realizing accurate position control.
Further, in the step 1, a high-order sliding mode disturbance observer of a mechanical arm motion system based on the exoskeleton robot is as follows:
wherein:
in the formula v1(t),v2(t),v3(t),v4(t),v5(t),v6(t) is the adjustable observer gain,is an estimated value generated by a high-order sliding mode disturbance observer,is the disturbance measured by an observer, λ1,λ2,λ3,λ4,λ5,λ6And L is an adjustable parameter.
Further, in step 2, the lower triangular nonlinear system finite time controller may take the following form after being compensated:
whereinAre the partial state vector and the full state vector of the system; y is the system output; phi is ai(·),i∈N1:4Is a known smooth non-linear function, and the output reference signal is yrY (t) and its nth derivative.
Further, constructing a finite time controller comprises the steps of:
step 201, firstly defining an auxiliary variable vector InDetermined by the steady state generator given below:
step 202, let z ═ col (z)1,z2,z3,z4) Wherein WhereinIs a bandwidth factor. Without recursive stability analysis, a simple finite time controller could be explicitly pre-configured in the form:
wherein is definedK=[k1,k2,k3,k4]Is the coefficient vector p(s) s of the Helverz polynomial4+k4s3+k3s2+k2s+k1,r=(1,1+τ,1+2τ,1+3τ),
Further, in step 3, the method for constructing the state space model of the exoskeleton robot actuator comprises the following steps:
step 301, a motor is coupled with a ball screw at a joint through a high-rigidity torsion spring, two incremental encoders are used for measuring angular displacement of a motor shaft and the ball screw, and a nominal mathematical model in the following form is established by analogy of a damped dual-mass system and ignoring inevitable unmodeled interference:
wherein m ismIs the moment of inertia of the motor, mlIs the moment of inertia of the connecting rod, bmIs the viscous friction coefficient of the motor, blIs the viscous friction coefficient of the connecting rod, qmIs the angle of rotation of the motor, qlIs the rotation angle of the connecting rod, k is the stiffness coefficient of the cascade elastic driver, FmIs the motor torque.
Step 302, converting the nominal mathematical model established in step 1 into a state space form, and settingIn equation (6), the nominal model is then transformed into the following state space form:
further, in step 4, the method for constructing the robust finite time controller includes the following steps:
by givingThe following is calculated for tracking the reference quantity in a state space form in formula (7):
substituting the above calculated quantities into (5) can construct the following complex finite time control law applicable to exoskeleton robot actuators:
wherein K is [ K ]1,k2,k3,k4]Is a coefficient vector of a helvetz polynomial, whereinIs a bandwidth factor that is a function of,is a disturbance measured by an observer, FmIs the motor torque.
3. Advantageous effects
Compared with the prior art, the invention has the advantages that:
the invention designs a continuous time model prediction control system method based on an exoskeleton robot, and by designing a model prediction control method with a nonlinear disturbance observer, optimal offset-free tracking can be realized under various disturbances. Compared with the traditional model prediction control law, the method has better steady-state performance under the condition of time-varying disturbance; meanwhile, the method provides a new performance index, namely the influence of the control input weight on the stability of the closed loop is definitely analyzed.
Drawings
FIG. 1 is a functional block diagram of the present invention;
FIG. 2 is a schematic view of an exoskeleton robot actuator;
fig. 3 is a schematic diagram of the tracking performance of the actuator based on the present invention when τ is 0;
FIG. 4 is a schematic diagram of the tracking performance of an actuator based on the present invention when τ is-0.05;
FIG. 5 is a schematic diagram of the tracking performance of an actuator based on the present invention when τ is-0.1;
fig. 6 is a schematic diagram showing the tracking performance of the actuator based on the present invention when τ is-0.15.
Detailed Description
The invention is described in detail below with reference to the drawings and specific examples.
Example 1
The appearance of the exoskeleton robot actuator is shown in fig. 2, the exoskeleton robot actuator integrally serves as a connecting rod and comprises two motors, and based on the exoskeleton robot actuator, the invention provides a composite finite time control method based on the exoskeleton robot actuator, which comprises the following steps:
as shown in fig. 1, the estimated value of the higher order sliding mode disturbance observer is expressed as:
in the above formula:
in the formula (2), v1(t),v2(t),v3(t),v4(t),v5(t),v6(t) is the adjustable observer gain,is an estimated value generated by a high-order sliding mode disturbance observer,is the disturbance measured by an observer, λ1,λ2,λ3,λ4,λ5,λ6And L is an adjustable parameter.
as shown in fig. 1, the lower triangular nonlinear system finite time controller may take the following form after compensation:
in the formula (3)Are the partial state vector and the full state vector of the system; y is the system output; phi is ai(·),i∈N1:4Is a known smooth non-linear function, and the output reference signal is yrY (t) and its nth derivative.
Specifically, constructing a simple finite time controller includes the following steps:
step 201, firstly defining an auxiliary variable vector WhereinDetermined by the steady state generator given below:
As shown in fig. 1, without recursive stability analysis, a simple finite time controller can be explicitly pre-configured in the form:
wherein is definedK=[k1,k2,k3,k4]Is the coefficient vector p(s) s of the Helverz polynomial4+k4s3+k3s2+k2s+k1,r=(1,1+τ,1+2τ,1+3τ),
step 301, as shown in fig. 2, a motor is coupled with a ball screw at a joint through a high-stiffness torsion spring, angular displacements of a motor shaft and the ball screw are measured through two incremental encoders, inevitable unmodeled interference is ignored through analogy of a damped dual-mass system, and a nominal mathematical model in the following form is established:
m in formula (6)mIs the moment of inertia of the motor, mlIs the moment of inertia of the connecting rod, bmIs the viscous friction coefficient of the motor, blIs the viscous friction coefficient of the connecting rod, qmIs the angle of rotation of the motor, qlIs the rotation angle of the connecting rod, k is the stiffness coefficient of the cascade elastic driver, FmIs the motor torque.
Step 302, converting the nominal mathematical model established in step 301 into a state space form: is provided withIn the formula (6), the nominal model can be transformed into the following state space form
first pass through givenSubstituting the tracking reference quantity into the state space form in (7) to calculate:
substituting the above calculated quantities into (5) can construct the following complex finite time control law applicable to the exoskeleton robot actuator:
fig. 3 to 6 show that simulation software is used to simulate the exoskeleton robot trajectory tracking graph based on the control method of the present invention, and K ═ 0.5,0.01,0.1,0.01 are respectively simulated],Time of day, trajectory tracking performance under finite time controllers of different uniformity τ. The right side picture shows the progressive tracking performance of the state feedback controller, and compared with the original track represented by the black dotted line in the left side picture, it can be seen that when τ is a negative value, the control performance is obviously improved, and by comprehensively comparing fig. 3 to fig. 6, it can be seen that the smaller τ is, the faster the convergence speed is, and the smaller the steady-state error is.
The invention and its embodiments have been described above schematically, without limitation, and the invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The representation in the drawings is only one of the embodiments of the invention, the actual construction is not limited thereto, and any reference signs in the claims shall not limit the claims concerned. Therefore, if a person skilled in the art receives the teachings of the present invention, without inventive design, a similar structure and an embodiment to the above technical solution should be covered by the protection scope of the present patent. Furthermore, the word "comprising" does not exclude other elements or steps, and the word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. Several of the elements recited in the product claims may also be implemented by one element in software or hardware. The terms first, second, etc. are used to denote names, but not any particular order.
Claims (5)
1. A composite finite time control method based on exoskeleton robot actuators, comprising the steps of:
step 1, constructing a high-order sliding mode disturbance observer for estimating the state and disturbance of a tracking error system, bringing the obtained estimation into a future tracking error, and then bringing the tracking error into a performance index;
step 2, constructing a lower triangular nonlinear system finite time controller based on the observer in the step 1;
step 3, constructing a state space model of the exoskeleton robot actuator, establishing a nominal mathematical model after neglecting interference through analogy of a damped dual-mass system, and converting the mathematical model into a state space form;
step 4, constructing a finite time robust controller, and designing a robust finite time control law by using the composite finite time controller in the step 2 and combining the state space model in the step 3; in the step 1, the constructed high-order sliding mode disturbance observer is as follows:
wherein:
2. A method for compound finite time control based on exoskeleton robot actuators as claimed in claim 1 wherein in step 2, the lower triangular nonlinear system finite time controller takes the form of:
3. A method for compound finite time control based on exoskeleton robot actuators as claimed in claim 2 wherein the method of constructing the finite time controller includes the steps of:
step 201, firstly defining an auxiliary variable vector InDetermined by the steady state generator given below:
without recursive stability analysis, the finite time controller, after compensation, can be explicitly pre-configured in the form:
4. A method for compound finite time control based on exoskeleton robot actuators as claimed in claim 3 wherein in step 3 the method of establishing a state space model of the exoskeleton robot actuators comprises:
step 301, a motor is coupled with a ball screw at a joint through a high-rigidity torsion spring, two incremental encoders are used for measuring angular displacement of a motor shaft and the ball screw, and a nominal mathematical model in the following form is established by analogy of a damped dual-mass system and ignoring inevitable unmodeled interference:
wherein m ismIs the moment of inertia of the motor, mlIs the moment of inertia of the connecting rod, bmIs the viscous friction coefficient of the motor, blIs the viscous friction coefficient of the connecting rod, qmIs the angle of rotation of the motor, qlIs the rotation angle of the connecting rod, k is the stiffness coefficient of the cascade elastic driver, FmIs the motor torque;
step 302, converting the nominal mathematical model established in step 1 into a state space form, and settingIn equation (6), the nominal model is then transformed into the following state space form:
5. a method for composite finite time control based on exoskeleton robot actuators as claimed in claim 4 wherein in step 4, the method for constructing a robust finite time controller is as follows:
given aFor tracking the reference quantity and substituting it into the state space form in equation (7):
substituting equation (8) into equation (5) may construct the following complex finite time control law applicable to exoskeleton robot actuators:
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