A method for coordinated control of excavator position and force based on adaptive impedance control

Abstract

The invention discloses a method for coordinated control of excavator position and force based on adaptive impedance control, which belongs to the field of excavator control technology; the method comprises establishing a load force balance model of an excavator bucket-linked hydraulic system, and establishing an impedance model between the excavator bucket end and the environment; setting the desired trajectory and contact force of the excavator bucket end in an actual construction environment; designing an inner loop position control method to obtain a control quantity expression; designing an outer loop adaptive impedance control method to obtain a desired trajectory offset expression, and bringing the desired trajectory offset expression into the impedance model to obtain a desired trajectory offset; merging the desired trajectory and the desired trajectory offset to obtain a new desired trajectory value, and calculating the control quantity; the control method indirectly adjusts the impedance parameters, so that the excavator bucket end can adapt to environmental position and stiffness changes in real time, mitigate the impact of the hydraulic system, and ensure force tracking accuracy and position tracking accuracy in an uncertain environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of excavator control, and in particular relates to a method for coordinated control of excavator position and force based on adaptive impedance control. Background Art

[0002] Excavators are widely used in various construction tasks, such as digging deep trenches, house demolition and site leveling. Most of the excavator control methods are position control, and research hotspots are also concentrated on position, such as position control, energy-saving optimization and intelligent improvement. However, the use of position control methods alone cannot fully meet the requirements of high efficiency, high precision and safety in construction. The impact phenomenon between the excavator and the construction environment will cause the pressure and oil temperature of the hydraulic system to increase, and excessive impact will even directly damage the hydraulic and mechanical systems. The impact phenomenon actually reflects the unevenness of the contact force, and the contact force between the bucket and the construction environment must be considered. Design a corresponding coordinated control method of the excavator position and force to mitigate the impact and solve the problems of short life, low efficiency, high energy consumption and excessive wear of the working device in complex ground structures such as hard soil, mines, masonry, etc. At the same time, ensure that the excavator is used efficiently within the safe range of the design parameters to avoid accidents.

[0003] At present, the coordinated control methods of position and force include hybrid position / force control method and impedance control. The hybrid position / force control method constantly switches between the position and force control methods, which will produce jitter and affect the tracking accuracy. Impedance control establishes a dynamic relationship between the end effector position and contact force, which is robust to interference and uncertainty and has been widely used in industrial, rehabilitation and service robots. However, the effect of impedance control depends entirely on the accuracy of environmental parameters, that is, impedance parameters. In actual applications of excavators, the construction environment changes in real time, and the environmental parameters cannot be accurately obtained, resulting in large errors in the coordinated control of position and force. Summary of the invention

[0004] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a method for coordinated control of excavator position and force based on adaptive impedance control, which solves the technical problems mentioned in the background technology.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A method for coordinated control of excavator position and force based on adaptive impedance control, comprising the following steps:

[0007] S1. Establish a load force balance model for the excavator bucket hydraulic system, and establish an impedance model between the excavator bucket end and the environment;

[0008] S2, setting the expected trajectory and contact force of the excavator bucket end in the actual construction environment;

[0009] S3. Design the inner loop position control method and obtain the control quantity expression;

[0010] S4, designing an outer loop adaptive impedance control method to obtain an expression for a desired trajectory offset, and substituting the expression for the desired trajectory offset into the impedance model in S1 to obtain the desired trajectory offset;

[0011] S5, combining the desired trajectory of the excavator bucket end obtained in S2 and the desired trajectory offset obtained in S4 to obtain a new desired trajectory value, and inputting it into the position control method in S3 to calculate the control amount.

[0012] Furthermore, the load force balance model of the excavator bucket hydraulic system in S1 is specifically as follows:

[0013]

[0014] Where M is the equivalent moving mass, B is the viscous damping coefficient, K is the stiffness, F is the load, x is the bucket displacement, A1 and A2 are the effective working areas facing the rodless cavity and rod cavity of the bucket hydraulic cylinder, respectively, and p L is the load pressure, p1 and p2 are the working pressures facing the rodless chamber and rod chamber of the bucket hydraulic cylinder respectively.

[0015] Furthermore, the impedance model between the excavator bucket end and the environment in S1 is:

[0016]

[0017] Where m, b, and k are the equivalent mass, damping, and stiffness of the excavator bucket end, respectively. r is the desired position, x e is the construction environment location, k e is the environmental stiffness, f r is the expected contact force between the excavator and the environment, f is the actual contact force between the excavator and the environment, and e is the error between the expected contact force and the actual contact force.

[0018] Furthermore, the contact force f in S2 r Directly given, the expected trajectory x of the excavator bucket end in the actual construction environment r0 for:

[0019] x r0 =a0+a1t+...+a n-2 t n-2 +a n-1 t n-1 (n=6) (3)

[0020] In the formula, a0 to a n-1 is the coefficient and t is the time.

[0021] Furthermore, in S2, x r0 Also set the movement time t with the starting point x0, the end point x1, and the trajectory b The constraints are as follows:

[0022]

[0023] Furthermore, the inner loop position control method in S3 is PID control, and the calculation formula of the control quantity u is:

[0024]

[0025] Among them, K P , K I , K D They are the proportional coefficient, integral coefficient and differential coefficient respectively.

[0026] Furthermore, the expected trajectory offset △x in S4 r The calculation expression is:

[0027]

[0028] Among them, p(t) and d(t) are the proportional factor and differential factor respectively, and g(t) is a supplementary term used to compensate for static errors.

[0029] Furthermore, in S4, the expected trajectory offset expression is substituted into the impedance model in S1, specifically:

[0030]

[0031] Furthermore, it is characterized in that the derivation formulas of p(t), d(t), and g(t) are:

[0032]

[0033] Among them, λ1 and λ0 are positive weighting factors, is the positive integral gain, d0, p0, g0 are the initial values ​​of the adaptive law.

[0034] Furthermore, the step of obtaining the control amount in S5 is:

[0035] 1) The new expected trajectory value obtained by merging is:

[0036] x r =x r0 +Δx r (9)

[0037] 2) Input the new desired trajectory value into the position control method of S3 and calculate the control amount in real time.

[0038] Beneficial effects of the present invention:

[0039] 1. The present invention proposes a method for coordinated control of excavator position and force based on adaptive impedance control, which indirectly adjusts the impedance parameters and can ensure both force tracking accuracy and position tracking accuracy;

[0040] 2. The present invention has made a unique contribution to the intelligent control method of excavator construction, and has a certain reference significance for operators, especially operators in complex ground construction sites such as large-scale ground, mines, earthquakes, etc.;

[0041] 3. This method also provides construction managers and other practitioners with an option for impedance control methods during construction, which can save labor costs, improve production efficiency, and accelerate the transformation of the digital and intelligent construction industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0043] Figure 1 It is the block diagram of the excavator system;

[0044] Figure 2 It is a block diagram of the method for coordinated control of excavator position and force;

[0045] Figure 3 It is a schematic diagram of the impedance control model when the excavator bucket contacts the environment;

[0046] Figure 4 Comparison results for the ramp trajectory condition with constant force tracking: (a) position tracking and (b) force tracking results;

[0047] Figure 5 To change the environmental stiffness k e Comparison results of force tracking conditions: (a) position tracking and (b) force tracking results;

[0048] Figure 6 Comparison results for the dynamic force tracking condition: (a) position tracking and (b) force tracking results. DETAILED DESCRIPTION

[0049] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] Example:

[0051] The position and force coordinated control method of the present invention is implemented on a typical 23-ton excavator. The system block diagram of the excavator is as follows: Figure 1 As shown in the figure, the excavator control system mainly includes a control handle, a host computer, a pilot valve, a main valve, a working device, a controller, and sensors such as pressure and displacement. The pilot valve adjusts the size and direction of the pilot pressure according to the control signal in the controller, and the pilot pressure then acts on the main valve, and then the valve core will move; the movement of the main valve is directly connected to the hydraulic cylinder, and the piston rod will retract or extend; pressure sensors are installed in the rod chamber and rodless chamber of the hydraulic cylinder to measure the working pressure; the displacement sensor is installed outside the hydraulic cylinder to measure the displacement.

[0052] like Figure 2 As shown, a method for coordinated control of excavator position and force based on adaptive impedance control comprises the following steps:

[0053] S1. Establish a load force balance model for the excavator bucket hydraulic system (through this model, obtain the actual contact force F between the excavator and the environment), and establish an impedance model between the excavator bucket end and the environment, such as Figure 3 As shown;

[0054] The load force balance model of the excavator bucket hydraulic system is as follows:

[0055]

[0056] Where M is the equivalent moving mass, B is the viscous damping coefficient, K is the stiffness, F is the load, x is the bucket displacement, A1 and A2 are the effective working areas facing the rodless cavity and the rod cavity of the bucket hydraulic cylinder, respectively, and p L is the load pressure, p1 and p2 are the working pressures facing the rodless chamber and rod chamber of the bucket hydraulic cylinder respectively;

[0057] The impedance model between the excavator bucket end and the environment is a linear second-order system, as follows:

[0058]

[0059] Where m, b, and k are the equivalent mass, damping, and stiffness of the excavator bucket end, respectively. r is the desired position, xe is the construction environment location, k e is the environmental stiffness, f r is the expected contact force between the excavator and the environment, f is the actual contact force between the excavator and the environment, and e is the error between the expected contact force and the actual contact force.

[0060] S2, setting the expected trajectory and contact force of the excavator bucket end in the actual construction environment;

[0061] Where, the contact force f r Given directly, the fifth-order polynomial trajectory planning method is used to calculate the expected trajectory x of the excavator bucket end r0 , specifically:

[0062] x r0 =a0+a1t+...+a n-2 t n-2 +a n-1 t n-1 (n=6) (3)

[0063] In the formula, a0 to a n-1 is the coefficient, t is the time, and x r0 Also set the movement time t with the starting point x0, the end point x1, and the trajectory b The constraints are as follows:

[0064]

[0065] S3. Design an inner loop position control method to reduce the error between the actual position and the expected position;

[0066] The inner loop position control method is PID control, which performs proportional, integral and differential operations based on the set expected value and actual value error to obtain the control quantity u, which is specifically:

[0067]

[0068] In the formula, K P , K I , K D They are the proportional coefficient, integral coefficient and differential coefficient respectively.

[0069] S4, design an outer loop adaptive impedance control method to reduce the error between the actual contact force and the expected contact force, and calculate the expected trajectory offset;

[0070] The expected trajectory deviation is △x r , specifically:

[0071]

[0072] Where p(t) and d(t) are the proportional factor and differential factor, respectively, g(t) is a supplementary term used to compensate for static error, and x r Constantly corrected, superimposed △x r It can ensure that the actual contact force can track the expected contact force;

[0073] The outer loop adaptive impedance control method is to offset the desired trajectory by △x r Substitute the impedance model in S1, which is:

[0074]

[0075] The three adaptive laws mentioned above, p(t), d(t), and g(t), are related to the expected trajectory offset. The specific derivation process is based on the model reference adaptive control theory and is obtained through the Lyapunov stability method. The derived adaptive law is:

[0076]

[0077] Among them, λ1 and λ0 are positive weighting factors, is the positive integral gain, d0, p0, g0 are the initial values ​​of the adaptive law.

[0078] S5, combining the new expected trajectory value of the force into consideration, inputting it into the position control method of S3, and calculating the control amount;

[0079] The new expected trajectory value of the combined composition consideration force is specifically:

[0080] x r =x r0 +Δx r (9)

[0081] The new expected trajectory value is input into the position control method of S3, and the control amount is calculated in real time, so as to indirectly adjust the impedance parameters to adapt to the environmental position and stiffness in real time, so as to achieve the goal of accurate force and position tracking in uncertain environments.

[0082] Comparative Example:

[0083] In the ramp trajectory with constant force tracking, changing the environmental stiffness k e Simulations were carried out under three working conditions: time-dependent force tracking and dynamic force tracking, and the traditional impedance control method (IC) was compared with the control method (AIC) proposed in the present invention.

[0084] Slope trajectory condition with constant force tracking, setting the desired contact force f r =20kN,ke=100000N / m.

[0085] Changing the environmental stiffness k eWhen the force tracking condition is set, f r =20kN, x e =1m, that is, the contact environment is a horizontal line, changing the environment stiffness k e for:

[0086]

[0087] Dynamic force tracking condition, assuming x e =1m,k e =100000N / m, and the expected contact force is set to a sine wave with a frequency of 0.25Hz and an amplitude of 2kN.

[0088] The comparison results of tracking trajectory and force are as follows Figure 4-6 The conventional impedance control method cannot stably track the desired force and has hysteresis. Compared with the impedance control, the control method of the present invention shows its superiority in various performance indicators, can adapt to the changes in environmental position, and can achieve good force tracking and trajectory tracking performance in an uncertain environment.

[0089] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0090] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A method for coordinated control of excavator position and force based on adaptive impedance control, characterized in that: The following steps are involved: S1. Establish a load force balance model for the excavator bucket hydraulic system, and establish an impedance model between the excavator bucket end and the environment; S2, setting the expected trajectory and contact force of the excavator bucket end in the actual construction environment; S3. Design the inner loop position control method and obtain the control quantity expression; S4, designing an outer loop adaptive impedance control method to obtain an expression for a desired trajectory offset, and substituting the expression for the desired trajectory offset into the impedance model in S1 to obtain the desired trajectory offset; S5, combining the desired trajectory of the excavator bucket end obtained in S2 and the desired trajectory offset obtained in S4 to obtain a new desired trajectory value, and inputting it into the position control method in S3 to calculate the control amount; The load force balance model of the excavator bucket hydraulic system in S1 is as follows: Where M is the equivalent moving mass, B is the viscous damping coefficient, K is the stiffness, F is the load, x is the bucket displacement, A1 and A2 are the effective working areas facing the rodless cavity and rod cavity of the bucket hydraulic cylinder, respectively, and p L is the load pressure, p1 and p2 are the working pressures facing the rodless chamber and rod chamber of the bucket hydraulic cylinder respectively; The impedance model between the excavator bucket end and the environment in S1 is: Where m, b, and k are the equivalent mass, damping, and stiffness of the excavator bucket end, respectively. r is the desired position, x e is the construction environment location, k e is the environmental stiffness, f r is the expected contact force between the excavator and the environment, f is the actual contact force between the excavator and the environment, and e is the error between the expected contact force and the actual contact force; The expected trajectory offset △x in S4 r The calculation expression is: Among them, p(t) and d(t) are the proportional factor and differential factor respectively, and g(t) is a supplementary term used to compensate for static errors; In S4, the expression of the expected trajectory offset is substituted into the impedance model in S1, specifically: Among them, x r0 It is the expected trajectory of the excavator bucket end in the actual construction environment.

2. The method for coordinated control of excavator position and force based on adaptive impedance control according to claim 1, characterized in that: The contact force f in S2 r Directly given, the expected trajectory x of the excavator bucket end in the actual construction environment r0 for: x r0 =a0+a1t+...+a n-2 t n-2 +a n-1 t n-1 ,n=6 (3) In the formula, a0 to a n-1 is the coefficient and t is the time.

3. The method according to claim 2, characterized in that In S2, x r0 Also set the movement time t with the starting point x0, the end point x1, and the trajectory b The constraints are as follows:

4. The method for coordinated control of excavator position and force based on adaptive impedance control according to claim 3, characterized in that: The inner loop position control method in S3 is PID control, and the calculation formula of the control quantity u is: Among them, K P , K I , K D They are the proportional coefficient, integral coefficient and differential coefficient respectively.

5. The method for coordinated control of excavator position and force based on adaptive impedance control according to claim 1, characterized in that: The derivation formulas of p(t), d(t), and g(t) are: Among them, λ1 and λ0 are positive weighting factors, is the positive integral gain, d0, p0, g0 are the initial values ​​of the adaptive law.

6. The method for coordinated control of excavator position and force based on adaptive impedance control according to claim 5, characterized in that: The steps to obtain the control quantity in S5 are: 1) The new expected trajectory value obtained by merging is: x r =x r0 +Δx r (9) 2) Input the new desired trajectory value into the position control method of S3 and calculate the control amount in real time.

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