CN108189037B - Manipulator primary and secondary coordination control method based on disturbance observer - Google Patents

Manipulator primary and secondary coordination control method based on disturbance observer Download PDF

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CN108189037B
CN108189037B CN201810049340.1A CN201810049340A CN108189037B CN 108189037 B CN108189037 B CN 108189037B CN 201810049340 A CN201810049340 A CN 201810049340A CN 108189037 B CN108189037 B CN 108189037B
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邓华
张翼
钟国梁
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Central South University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
    • B25J—MANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
    • B25J9/00—Programme-controlled manipulators
    • B25J9/16—Programme controls
    • B25J9/1602—Programme controls characterised by the control system, structure, architecture
    • B25J9/1605—Simulation of manipulator lay-out, design, modelling of manipulator
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
    • B25J—MANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
    • B25J9/00—Programme-controlled manipulators
    • B25J9/16—Programme controls
    • B25J9/1694—Programme controls characterised by use of sensors other than normal servo-feedback from position, speed or acceleration sensors, perception control, multi-sensor controlled systems, sensor fusion

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Abstract

The invention provides a disturbance observer and primary and secondary coordination control method for a manipulator, which aims at the problems that when the manipulator grabs an object, the operation environment is complex, the information of the grabbed object is unknown, the sensor is lack, the disturbance exists in the environment, and the existing force sensor is limited by uncertain contact points, incomplete detection information and the like. The method replaces the traditional method that disturbance information can only be obtained through a high-cost sensor, is simple and effective, improves the efficiency of the manipulator in the problem of stable and reliable grabbing, analyzes the error of the disturbance observer, and lays a foundation for accurately analyzing the disturbance in the manipulator grabbing process.

Description

Manipulator primary and secondary coordination control method based on disturbance observer
Technical Field
The invention relates to a manipulator primary and secondary coordination control method based on a disturbance observer, which is particularly suitable for operations of a manipulator for grabbing objects under an uncertain environment and the like.
Background
The manipulator imitates a human hand, the operation environment is very complex, the objects are different in gripping, different gripping forces are required for objects with different qualities, and various disturbances exist in the environment. When a person grasps an object in a disturbance environment, the touch sense of the hand of the person feels a sliding signal of the object, the brain of the person can estimate a proper grasping force according to the characteristics of the object, and stable grasping of the object is achieved through a nervous system. For the manipulator, only a few sensors are provided, and the manipulator is not as flexible as a human hand, cannot know the gripping state of a gripped object, and cannot adjust the gripping force of the manipulator according to the change of the gripping state of the gripped object. The force adjustment is thus not real-time. Moreover, if the gripping force of the manipulator is too small, the gripping force is not timely increased, the object may slip, conversely, if the gripping force is too large, and the gripping force is not timely decreased, the object may be deformed or even destroyed, and meanwhile, the weight, the material and the rigidity of daily articles are not known, and external disturbance is uncertain, so that the control of the gripping force is very difficult. How to determine the proper gripping force of the manipulator, and when the gripping force is too small or is disturbed by the environment, how to adjust the size of the gripping force becomes a difficult problem which needs to be solved urgently in the application of the manipulator. In order to improve the disturbance resistance of the manipulator, a plurality of scholars at home and abroad carry out extensive research, mainly comprising open-loop control and closed-loop control.
The open-loop control of the manipulator is mainly researched by adopting a biological decoding technology to directly control the manipulator. The main biological signals studied are electromyographic signals (EMG), electroencephalographic signals (EEG) and Peripheral Nerve Signals (PNS). The human sport will is obtained by directly decoding the biological signal, and then the manipulator is directly controlled by amplifying the scale. When the manipulator is not stably gripped, the output biological signal is adjusted through visual feedback, and the gripping force state is adjusted according to the change of the biological signal. However, the bio-decoding signal is very weak and changes continuously with the lapse of time. The signals from the brain are coupled spatiotemporally from the central nerve, the spinal nerve, the human nerve to the muscle. In addition, the collection of physiological signals has great relation with the application position of the sensor, the degree of dense distribution and the quality of decoding effect. The fatigue state of the human body also brings the change of the electromyographic signals, thereby causing the mismatch of the classification decoder and the signals. And the decoding control algorithm is complex, the operation time is long, and the stability is poor. The closed-loop control of the manipulator is studied on the basis of sensors for force, position and slip. A commonly used control strategy is impedance control, which indirectly controls the magnitude of the gripping force by controlling the reference position of the manipulator through position feedback of the manipulator, and this control method enables the manipulator to smoothly transit between the free motion space and the constrained motion space. Closed loop force control has better stability than open loop control, and has certain regulating force capability to force overshoot. To cope with the problem of environmental disturbance, reflection control is proposed. The main problem solved is how to detect external disturbance, how much force needs to be increased, and the reflection control is faster than the reflection control response of the myoelectricity open loop, and the real-time performance is better.
For a manipulator, the design requires that the weight and the size of the manipulator are limited, a plurality of sensors cannot be configured, and a plurality of sensors can be arranged at limited positions. Torque sensors are typically large in size and expensive, and are difficult to incorporate into compact manipulators, such as manipulators. Generally, a mechanical arm has a plurality of force sensors, however, when the mechanical arm contacts with an object, the contact point is uncertain, that is, the sensor may not detect whether the mechanical arm grabs the object or not, or may not detect the information completely. Lack of sufficient sensor feedback tends to cause the gripping force to exceed the desired gripping force and not be adjusted in time, possibly damaging the gripped object, and more likely causing damage to the manipulator. Therefore, there is a need to obtain disturbance information in the environment by an effective method, predict and control a proper gripping force during the gripping process, and achieve the purpose of stably gripping an object.
Disclosure of Invention
The invention aims to provide a disturbance controller for estimating disturbance information in an environment, and simultaneously provides a primary and secondary coordination control strategy for predicting and controlling gripping force according to the estimated disturbance information, so as to replace the functions of a force sensor and torque sensing or add protection to the force overload of a manipulator. The method comprises the steps of firstly establishing a dynamic model of the manipulator, capturing force information due to the manipulator force sensor, establishing a nonlinear disturbance observer based on the force information, and analyzing errors of the disturbance observer. And finally, establishing a primary and secondary coordination control strategy by combining a primary mode control method, and controlling the manipulator to stably grab the object under the action of disturbance.
The technical scheme adopted by the invention for solving the technical problems is as follows:
a disturbance observer and primary and secondary coordination control method of a manipulator comprises the following steps:
step 1: establishing a dynamic model of the manipulator according to the stress condition when the manipulator grips an object;
step 2: establishing a nonlinear disturbance observer by taking the gripping force of a tracking manipulator, the speed term and the disturbance quantity of the gripping force as state variables, and analyzing the error of the disturbance observer by adopting a Lyapunov function;
and step 3: determining expected gripping force of the manipulator under the disturbance condition according to the disturbance amounts estimated in the step 1 and the step 2, and simultaneously, controlling gripping by combining a main mode, and obtaining total expected gripping force of each finger according to the expected gripping force of each finger determined by a multi-finger coordination control strategy;
and 4, step 4: and determining primary and secondary control quantities based on fuzzy control according to a primary and secondary coordination control principle, and determining the primary and secondary coordination control quantities by combining the control quantities determined by the disturbance observer to control the gripping of the manipulator.
Drawings
FIG. 1 is a schematic diagram of the process of the present invention.
Fig. 2 is a schematic diagram of a disturbance observer of a robot according to the present invention.
Fig. 3 is a schematic diagram of primary and secondary cooperative control of the robot of the present invention.
Detailed Description
The invention is further described with reference to the following figures and detailed description.
As shown in fig. 1, the specific steps of establishing the disturbance observer and the primary and secondary coordination control method of the manipulator are as follows:
step 1: establishment of manipulator dynamic model
The dynamic model of the manipulator is
Figure GDA0002928469260000021
Where q is the angular displacement of the joint, H (q) is an inertia matrix,
Figure GDA0002928469260000022
the torque is joint torque caused by gravity, friction and the like, tau is driving torque, r is a coupling coefficient of the driving torque to a certain joint of the manipulator (for the manipulator with single degree of freedom, r is 1), and J is a Jacobian matrix; f represents the reaction force of the gripped object to the manipulator, and can be represented by the following model:
Figure GDA0002928469260000024
wherein: x represents the position of the contact point of the manipulator and the grasped object, K represents the rigidity matrix of the grasped object, and L represents the distance matrix from the contact point to the joint point.
The formula (2) is substituted for the formula (1) to obtain
Figure GDA0002928469260000023
In the formula
Figure GDA0002928469260000031
Step 2: establishment of disturbance observer
Refer to FIG. 2
Figure GDA0002928469260000032
In the formula, p (f)1,f2) Is a non-linear function expressed as
Figure GDA0002928469260000033
Where w represents the amount of disturbance.
Based on (4), a nonlinear disturbance observer is established
Figure GDA0002928469260000034
In the formula z1,z2,z3Is a state variable, f is a manipulator grasping force, beta1,β2,β3B is a coefficient, sat (-) represents a saturation function.
Error analysis using the Lyapunov function of the form
Figure GDA0002928469260000035
In the formula e2＝z2-f2And A, B and C represent normal numbers.
Figure GDA0002928469260000036
Is derived to obtain
Figure GDA0002928469260000037
Wherein X is (1.5A beta)1-Bβ2)，Y＝(1.5A-2Cβ2+Bβ2|e1|0.5)|e1|-0.25And Z is B, and p is a nonlinear function given by the formula (5).
The condition for the quadratic part of the quadratic function to be negative is
X＞0,Y＞0,Z＞0,Y2-4XZ＜0 (9)
Based on this condition, the following parameter design principle can be derived
Figure GDA0002928469260000041
When the quadratic function (8) does not satisfy the negative definite condition, that is, the region taking the positive value is the variable
Figure GDA0002928469260000042
And e2Paraboloid of
Figure GDA0002928469260000043
And variable e1And e2Plane g (f) of1,f2,w)
Figure GDA0002928469260000044
The upper part of the intersection, and the variable e at this intersection1Is the order of
Figure GDA0002928469260000045
Root of (E)1＝(Bg/X)2And (4) the same level. The expression of X indicates that X and B beta2Same level, therefore root e1And (Bg/beta)2)2And (4) the same level. Therefore, only take β2＞＞g(f1,f2W) of
Figure GDA0002928469260000046
The right side in the equation is the error of the linear observer. This result demonstrates that the state tracking efficiency of the non-linear disturbance observer is much higher than that of the linear state observer. From the above disturbance observer and error analysis, wherein z1Is to track the gripping force of the manipulator, z2Is the velocity term of the grip force, and z3Is the amount of disturbance. The disturbance observer is applied to disturbance observation of the gripping force of the manipulator. Once the disturbance amount is estimated, the estimated mass, stiffness and friction coefficient of the surface of the grasped object are combined, so that the reflecting grasping force in the reflecting control can be reasonably estimated.
And step 3: establishment of primary and secondary coordination control strategies
When the object to be grabbed is detected to slide, the grabbing force of the mechanical arm needs to be adjusted, and the adjustment of the grabbing force is carried out in the following self-adaptive mode
(a) The grip force of the main mode is small, and mg-2f exists in the casedMu is more than 0, the object to be grabbed slides under the action of gravity, and the expected grabbing force of reflection is taken as
Figure GDA0002928469260000047
In the formula z3For the output of the disturbance observer, z0Z before obtaining slip information3Amount of (eta) (. eta.)1And η2For the weighting coefficient, δ is the following expression
Figure GDA0002928469260000048
(b) The main mode gripping force can stably gripWhen the object is held but the outside disturbance causes the gripped object to slide, the mg-2f exists at the momentdMu is less than 0, the grabbed object generates slippage under the action of disturbance, and the disturbance self-adaptive adjustment mode is designed as
Figure GDA0002928469260000051
Under the control of the main mode, according to the multi-finger coordination control strategy, the expected value of the gripping force of each finger of the manipulator is
Figure GDA0002928469260000052
R represents the number of fingers participating in the grip. In the same way, according to the expected gripping force of the manipulator
Figure GDA0002928469260000053
Obtaining the expected gripping force of each finger as
Figure GDA0002928469260000054
According to the principle of primary and secondary coordinated control, the final primary and secondary control increments are as follows
Figure GDA0002928469260000055
Where g (-) denotes a fuzzy controller, i.e. the input is
Figure GDA0002928469260000056
Mapping of delta, f to control output um。
Based on the disturbance observer mentioned above, obtain
Figure GDA0002928469260000057
In the formula
Figure GDA0002928469260000058
Finally, the primary and secondary coordination control quantity is obtained
u＝um+ur (20)。

Claims (1)

1. A disturbance observer and primary and secondary coordination control method of a manipulator is suitable for the manipulator to grab the operation of an object under an uncertain environment, and is characterized in that: firstly, establishing a dynamic model of a manipulator, acquiring a grabbing force according to a force sensor arranged on the manipulator, establishing a nonlinear disturbance observer, and analyzing the error of the disturbance observer; estimating the reflection gripping force in reflection control by using the estimated disturbance quantity and combining the estimated mass and rigidity of the gripped object and the friction coefficient of the surface of the gripped object; finally, a primary and secondary coordination control strategy is established by combining a primary mode control method, and the manipulator is controlled to stably grab the object under the disturbance action; the specific steps of establishing the nonlinear disturbance observer and the primary and secondary coordination control strategies are as follows:
firstly, establishing a mechanical arm dynamic model:
Figure FDA0002928469250000018
where q is the angular displacement of the joint, H (q) is an inertia matrix,
Figure FDA0002928469250000011
for a single-degree-of-freedom manipulator, r is 1, J is a jacobian matrix, f represents the reaction force of a grabbed object on the manipulator, and can be represented by the following model:
Figure FDA0002928469250000012
wherein: x represents the position of the contact point of the manipulator and the grasped object, K represents the rigidity matrix of the grasped object, L represents the distance matrix from the contact point to the joint point,
the formula (2) is substituted for the formula (1) to obtain
Figure FDA0002928469250000013
In the formula
Figure FDA0002928469250000014
The second step is that: establishing a nonlinear disturbance observer:
is provided with
Figure FDA0002928469250000015
In the formula, p (f)1,f2) Is a nonlinear function, and the expression is:
Figure FDA0002928469250000016
wherein w represents the disturbance quantity, and according to the formula (4), a nonlinear disturbance observer is established:
Figure FDA0002928469250000017
in the formula z1,z2,z3Is a state variable, beta1,β2,β3B is a coefficient, sat (-) represents a saturation function,
error analysis was performed using the lyapunov function of the form:
Figure FDA0002928469250000021
in the formula e2＝z2-f2A, B and C represent normal numbers,
the derivation yields:
Figure FDA0002928469250000022
wherein X is (1.5A beta)1-Bβ2)，Y＝(1.5A-2Cβ2+Bβ2|e1|0.5)|e1|-0.25Z ═ B, p is a nonlinear function given by formula (5);
thirdly, establishing a primary and secondary coordination control strategy:
when the object to be grabbed is detected to slide, the grabbing force of the manipulator needs to be adjusted, and the adjustment of the grabbing force is carried out in the following self-adaptive mode:
if the grip of the master mode is small, mg-2f is presentdμ＞0，fdIn order to expect the gripping force, the gripped object slides under the action of gravity, and the expected gripping force of the reflection control is:
Figure FDA0002928469250000023
in the formula z3For the output of the disturbance observer, z0Z before obtaining slip information3Amount of (eta) (. eta.)1And η2For the weighting coefficients, δ is the following expression:
Figure FDA0002928469250000024
secondly, if the gripping force of the main mode can stably grip the gripped object, but when the gripped object slides due to external disturbance, mg-2f exists at the momentdMu is less than 0, the grabbed object generates slippage under the action of disturbance, and the designed disturbance self-adaptive adjustment mode is as follows:
Figure FDA0002928469250000025
under the control of the main mode, according to the multi-finger coordination control strategy, the expected value of the gripping force of each finger of the manipulator is
Figure FDA0002928469250000026
R1, …, R, R representing the number of fingers involved in the grip, depending on the desired grip of the manipulator
Figure FDA0002928469250000027
Obtaining the expected gripping force of each finger as
Figure FDA0002928469250000028
According to the principle of primary and secondary coordinated control, the final primary and secondary control increments are as follows:
Figure FDA0002928469250000029
where g (-) denotes a fuzzy controller, i.e. the input is
Figure FDA00029284692500000210
Mapping of delta, f to control output um，
Based on the aforementioned disturbance observer, we obtain:
Figure FDA00029284692500000211
in the formula
Figure FDA0002928469250000031
And finally obtaining:
u＝um+ur (14)
the control quantity is coordinated for the primary and the secondary.
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