CN102602547B - Wheeled lunar vehicle driving control method based on slip ratio adjustment - Google Patents

Abstract

The invention discloses a wheeled lunar vehicle driving control method based on slip ratio adjustment, which includes the steps: working condition selection and control objective determination; wheel slip ratio estimation; establishment of a lunar vehicle system model; and calculation of wheel distributed moment Ti. Driving conditions of a lunar vehicle include an accelerating or decelerating condition of a vehicle body and a uniform-speed driving condition of the vehicle body, wherein when the vehicle body is under the accelerating or decelerating condition, the slip ratio of each wheel is controlled within a high driving efficiency range, and the high driving efficiency of the wheels can be guaranteed; and when the vehicle body is under the uniform-speed driving condition, the average value of the slip ratio of all the wheels serves as a control objective, so that the problems of singleness of the control objective, energy consumption increase caused by too high or too low single wheel slip ratio, poor trafficability variation and the like can be avoided. By means of a sliding mode variable structure control algorithm, solving is simple, the calculated quantity is small, and the system is guaranteed to have excellent robustness, so that the lunar vehicle can more coordinately move in the rugged environment.

Description

A kind of lunar wheeled vehicle regulating based on slippage rate drives control method

Technical field

The invention belongs to space technology field, relate to a kind of wheeled lunar rover vehicle of raising rocking arm-bogie truck sliding mode variable structure control method that passability is target under rugged environment of take, specially refer to a kind of lunar wheeled vehicle regulating based on slippage rate and drive control method.

Background technology

Lunar rover vehicle Drive Control Technique is the realization link that moveable robot movement is controlled, also be that the lunar rover vehicle is realized one of gordian technique of autonomous, its technical essential is how each wheel propulsive effort to be carried out to reasonable distribution, so that the state of kinematic motion between the moon wheel travelling on rugged menology and wheel matches, that avoids that each wheel drive force unreasonable distribution causes skids and sink, thereby the waste of power and the mechanical wear that reduce the lunar rover vehicle, improve its crossing ability and service life.Although the propulsive effort regulation and control of the lunar rover vehicle is shown great attention to, but the research of relevant controlling algorithm is less, the limitation of existing control method is: the method for the drive torque of wheel being distributed by optimizing particular constraints condition, constraint asks the process of optimal solution very complicated, and calculated amount is large; The method that the Acceleration of starting process of the lunar rover vehicle is controlled, is only controlled at slippage rate an expectation value, lunar rover vehicle driving process is not controlled; Adopt the PI controller of PI control algorithm design simpler, control target single.

Summary of the invention

For existing control method solve complexity, calculated amount is large, only slippage rate is controlled to a fixing expectation value, the driving process of the lunar rover vehicle is not controlled, control the problems such as target is single, the present invention will propose a kind of lunar wheeled vehicle regulating based on slippage rate and drive control method, according to lunar rover vehicle acceleration or deceleration, travel and at the uniform velocity travel two kinds of operating modes, the moment of each wheel of the lunar rover vehicle is distributed to control, that is: when the lunar rover vehicle is during in acceleration or deceleration operating mode, each wheel slip rate is controlled in the interval of each wheel drive efficiency the best; When the lunar rover vehicle is during in driving cycle at the uniform velocity, the average slippage rate of the wheel of take is to control target; And solve simple, calculated amount is little.

Technical scheme of the present invention is:

A kind of lunar wheeled vehicle regulating based on slippage rate drives control method, described driving control system comprises operating mode selection module, slippage rate estimation module, Sliding mode variable structure control module, PID rate control module and lunar rover vehicle system, described lunar rover vehicle system obtains translational velocity and the angular speed of wheel of wheel barycenter by dynam and kinematics analysis, be input to slippage rate estimation module; Slippage rate estimation module is calculated the slippage rate of each wheel, is input in Sliding mode variable structure control module, as the control target of Sliding mode variable structure control module, the moment of wheel is distributed; Finally this distribution moment is applied on each wheel, completes the driving of wheel is controlled; Described driving control method specifically comprises the following steps:

A, operating mode are selected and are controlled target and determine

A1, slippage rate need to be controlled in certain scope when the acceleration or deceleration because of the lunar rover vehicle, to improve drive efficiency, and at the uniform velocity in driving process, needing adaptation to the ground to rise and fall, avoid single-wheel the trackslip excessive crossing ability causing and harmony variation, so the driving cycle of the lunar rover vehicle is divided into acceleration or deceleration operating mode and driving cycle at the uniform velocity;

Under A2, acceleration or deceleration operating mode, control determining of target

In order to guarantee that lunar rover vehicle wheel when accelerating has enough large drive torque and higher drive efficiency, need to be controlled at the slippage rate of each wheel in the scope of drive efficiency the best;

A3, at the uniform velocity control determining of target under driving cycle

At the uniform velocity, under driving cycle, for wheel slip rate is effectively controlled, thereby reduce the crossing ability of frame energy loss, raising car body and drive coordination performance; The aviation value of selecting each skidding rate of rotation is for controlling target, if single-wheel slippage rate is too high, illustrate for the net tractive force of wheel F of fixing support reaction N excessively, and reduction slippage rate has also just reduced the consumption of unnecessary net tractive force of wheel; If slippage rate is too small, explanation is too small for the tractive force F of fixing support reaction N, is far smaller than the tractive force that ground can give, in order successfully to pass through the accidental relieies such as ditch or abrupt slope, need to increase slippage rate to improve ground traction, improve the lunar rover vehicle in the performance of passing through on rugged ground;

B, wheel slip rate are estimated

B1, first wheel slip rate is defined, all relevant with slippage rate with index because of every kinematic parameter of the lunar rover vehicle, so slippage rate becomes the emphasis of research, it is defined as follows:

$\mathrm{\&lambda;}=\left\{\begin{array}{c}\frac{\mathrm{rw}-v}{\mathrm{rw}}(\mathrm{rw}>v)\\ \frac{\mathrm{rw}-v}{v}(\mathrm{rw}<v)\end{array}\right.---\left(1\right)$

Wherein, λ is wheel slip rate, and r represents radius of wheel, and w represents angular speed of wheel, and v represents the translational velocity of wheel barycenter;

B2, the control target determining for steps A, accurately estimate it; First, select visual odometry to carry out the translational velocity of estimated wheel barycenter; Secondly, utilize vehicle-wheel speed sensor to measure in real time the speed of wheel; Finally utilize formula (1) to calculate the slippage rate of each wheel;

The foundation of C, lunar rover vehicle system model

Research object is six to take turns rocking arm-the turn to posture lunar rover vehicle, by car body, suspension fork mechanism and six wheels, formed, suspension frame structure is comprised of rocking arm and the bogie truck of left and right sides symmetry, the drive motor of model is all installed on each wheel etc., the near front wheel, left center and three wheel sequence numbers of left rear wheel in left side are respectively 1,3 and 5, and the off front wheel on right side, right wheel with three wheel sequence numbers of off hind wheel are respectively 2,4,6; The longitudinal movement of considering car body, carries out force analysis to the six one-sided models of taking turns the lunar rover vehicle, lists its kinetics equation as follows:

$\left\{\begin{array}{c}m\stackrel{\&CenterDot;}{v}=\underset{i=\mathrm{1,3,5}}{\mathrm{\&Sigma;}}(F_{\mathrm{Hi}}-F_{\mathrm{Ri}})\\ I_w{\stackrel{\&CenterDot;}{w}}_i=T_i-T_{\mathrm{ri}}(i=\mathrm{1,3,5})\end{array}\right.---\left(2\right)$

Wherein, m is 1/2 of lunar rover vehicle total quality M, F _hibe the soil propelling force of i wheel, F _ribe the soil resistance force of i wheel, T _rifor ground imposes on the resisting moment of wheel i, I _wfor the rotor inertia of single wheel around wheel axle center, w _ifor the cireular frequency of wheel i, T _ifor imposed on the drive torque of wheel i by actuator, wherein subscript i is the label of one-sided wheel in the text;

(1) formula is carried out to differentiate, and (2) formula substitution is obtained to following formula:

$\stackrel{\&CenterDot;}{\mathrm{\&lambda;}}=f(\mathrm{\&lambda;},v)+B(\mathrm{\&lambda;},v)\&CenterDot;u---\left(3\right)$

Wherein, λ=[λ ₁, λ ₃, λ ₅] ^t, u=[T ₁, T ₃, T ₅] ^t, f (λ, v)=[f ₁(λ, v), f ₃(λ, v), f ₅(λ, v)] ^t, $f_i(\mathrm{\&lambda;},v)=-(1-{\mathrm{\&lambda;}}_i)[\underset{i=\mathrm{1,3,5}}{\mathrm{\&Sigma;}}{F}_{\mathrm{Hi}}-\underset{i=\mathrm{1,3,5}}{\mathrm{\&Sigma;}}{F}_{\mathrm{Ri}}]/\mathrm{Mv}-r{(1-{\mathrm{\&lambda;}}_i)}^2{T}_{\mathrm{ri}}/I_{w}v,$ B _i(λ，v)＝r(1-λ _i) ²/I _wv，i＝1、3、5；

D, wheel distribute moment T _icalculating

D1, the model of setting up according to step C, utilize Sliding mode variable structure control algorithm to calculate each wheel and distribute moment u _i, concrete steps are as follows:

D11, at the uniform velocity the control target under driving cycle is taken turns average slippage rate for each control target under the operating mode of giving it the gun is expectation slippage rate λ _d; According to sliding mode control theory, during acceleration, getting state of the system deviation is e _i=λ _i-λ _d, while at the uniform velocity travelling, get state of the system deviation and be

choose switching function:

$s_i=r_{1i}{e}_i+r_{2i}{\stackrel{\&CenterDot;}{e}}_i---\left(4\right)$

λ wherein _ifor wheel i, the slippage rate of i=1～6,

the aviation value of each wheel slip rate,

for the first derivative of state of the system deviation, r _1i, r _2ifor constant weight coefficient;

D12, because sliding mode control theory under two kinds of operating modes is identical, only state of the system deviation is different, so this sentences at the uniform velocity driving cycle, is example, according to sliding mode control theory, if reach desirable sliding mode, controls, equivalent control is expressed as

associating (4) formula with

have:

${\stackrel{\&CenterDot;}{s}}_i=r_{1i}{\stackrel{\&CenterDot;}{\mathrm{\&lambda;}}}_i-r_{1i}\stackrel{\&CenterDot;}{\stackrel{\&OverBar;}{\mathrm{\&lambda;}}}+r_{2i}{\stackrel{\&CenterDot;\&CenterDot;}{\mathrm{\&lambda;}}}_i-r_{2i}\stackrel{\&CenterDot;\&CenterDot;}{\stackrel{\&OverBar;}{\mathrm{\&lambda;}}}=0---\left(5\right)$

In order to meet the arrival condition of Sliding mode variable structure control, and there is good robustness with shortest time arrival sliding-mode surface the system that guarantees, weaken the buffeting producing while arriving simultaneously as far as possible, employing exponential approach rule expression-form:

${\stackrel{\&CenterDot;}{s}}_i=-\mathrm{\&epsiv;sgn}{s}_i-k{s}_i---\left(6\right)$

ε > 0 and k > 0 are for controlling parameter; In order to guarantee weaken to buffet simultaneously also convergence fast, in minimizing ε, increase the numerical value of k, wherein symbolic function sgn (s) formula is

$\mathrm{sgn}\left(s\right)=\left\{\begin{array}{c}1,s>0\\ 0,s=0\\ -1,s<0\end{array}\right..$

(3) formula is brought in (5) formula and is obtained:

${\stackrel{\&CenterDot;}{s}}_i=r_{1i}(f_i(\mathrm{\&lambda;},v)+B_i(\mathrm{\&lambda;},v){\&CenterDot;u}_i)-r_{1i}\stackrel{\&CenterDot;}{\stackrel{\&OverBar;}{\mathrm{\&lambda;}}}+r_{2i}{\stackrel{\&CenterDot;\&CenterDot;}{\mathrm{\&lambda;}}}_i-r_{2i}\stackrel{\&CenterDot;\&CenterDot;}{\stackrel{\&OverBar;}{\mathrm{\&lambda;}}}---\left(7\right)$

Associating (6) and (7) formula, the design result that obtains Sliding mode variable structure control module is as follows:

$u_i=\frac{\mathrm{\&epsiv;}\left|s_i\right|\mathrm{sgn}\left(s_i\right)+{\mathrm{ks}}_i-r_{1i}\stackrel{\&OverBar;}{\mathrm{\&lambda;}}+r_{2i}{\stackrel{\&CenterDot;\&CenterDot;}{\mathrm{\&lambda;}}}_l-r_{2i}\stackrel{\&CenterDot;\&CenterDot;}{\stackrel{\&OverBar;}{\mathrm{\&lambda;}}}+r_{1i}\&CenterDot;f_i(\mathrm{\&lambda;},v)}{r_{1i}\&CenterDot;B_i(\mathrm{\&lambda;},v)}---\left(8\right)$

U _ibe the output of Sliding mode variable structure control module;

The output T of D2, calculating PID rate control module _v

With PID speed control algorithm, make the lunar rover vehicle by expectation speed v _dtravel; Making system deviation is e=v _d-v _cheti, obtain PID rate control module equation and be:

$T_v=K_p\&CenterDot;e+K_d\&CenterDot;\stackrel{\&CenterDot;}{e}+K_i\&CenterDot;\&Integral;\mathrm{edt}---\left(9\right)$

V wherein _chetifor lunar rover vehicle car body actual travel speed, K _pfor proportionality coefficient, K _ifor integral coefficient, K _dfor differential coefficient, in control process, can three parameters be adjusted and be revised, T _voutput for PID rate control module;

D3, according to wheel, distribute the computing formula T of moment _i=u _i+ T _v, can obtain the distribution moment T of each wheel of the lunar rover vehicle _i.

Compared with prior art, effect of the present invention and benefit are:

The present invention is divided into two kinds by lunar rover vehicle driving cycle: a kind of is car body acceleration or deceleration operating mode, and the slippage rate of wheel is controlled in the scope that drive efficiency is higher, can guarantee the drive efficiency that wheel is higher; Be an at the uniform velocity driving cycle of car body, take the aviation value of each wheel slip rate as controlling target, can avoid controlling target single, the too high or too low energy consumption causing of single-wheel slippage rate increases, the problems such as crossing ability variation.Adopt Sliding mode variable structure control algorithm, solve simply, calculated amount is little, and the system that guaranteed has good robustness, and the motion of the lunar rover vehicle under rugged environment coordinated more.

Accompanying drawing explanation

The present invention has accompanying drawing 2 width, wherein:

Fig. 1 is that the lunar rover vehicle drives control block diagram.

Fig. 2 is six 3D modellings of taking turns the wheeled lunar rover vehicle of rocking arm-bogie truck that the present invention studies.

In figure, 1, the near front wheel, 2, off front wheel, 3, left center, 4, right wheel, 5, left rear wheel, 6, off hind wheel, 7, rocking arm, 8, bogie truck, 9, car body.

The specific embodiment

Below in conjunction with accompanying drawing, describe the specific embodiment of the present invention in detail.As shown in Figure 1, v _dfor lunar rover vehicle expectation moving velocity; v _chetifor lunar rover vehicle car body actual travel speed; u _ioutput for Sliding mode variable structure control module; T _voutput for PID speed controll block; T _idistribution moment for lunar roving vehicle wheel i; λ _ifor the slippage rate of wheel i is estimated; W is angular speed of wheel, and v is the translational velocity of wheel barycenter.

A, operating mode are selected and are controlled target and determine

The first step: the desired speed v of definition car body _dactual travel speed v with car body _chetithe relative error existing | (v _d-v _cheti)/v _d| 100% while being less than 10%, belongs at the uniform velocity driving cycle; Otherwise belong to acceleration or deceleration operating mode.

Second step: control determining of target.

At the uniform velocity, under driving cycle, select each wheel slip rate aviation value for controlling target; If accelerating mode, controlling target is 0.1, and scope is 0.1～0.3 optional; If decelerating mode, controlling target is-0.1, and scope is optional-0.3～-0.1.

B, wheel slip rate are estimated

The computing formula of slippage rate is as follows:

$\mathrm{\&lambda;}=\left\{\begin{array}{c}\frac{\mathrm{rw}-v}{\mathrm{rw}}(\mathrm{rw}>v)\\ \frac{\mathrm{rw}-v}{v}(\mathrm{rw}<v)\end{array}\right.---\left(1\right)$

Wherein, radius of wheel r is 120mm; W is angular speed of wheel, utilizes vehicle-wheel speed sensor can measure in real time the actual speed rw of wheel; V is the translational velocity of wheel barycenter, utilizes visual odometry to calculate the translational velocity v of wheel barycenter; Finally utilize formula (1) to estimate the slippage rate of six wheels.

The foundation of C, lunar rover vehicle system model

The longitudinal movement of considering car body, carries out force analysis to the six one-sided models of taking turns the lunar rover vehicle, lists its kinetics equation as follows:

$\left\{\begin{array}{c}m\stackrel{\&CenterDot;}{v}=\underset{i=\mathrm{1,3,5}}{\mathrm{\&Sigma;}}(F_{\mathrm{Hi}}-F_{\mathrm{Ri}})\\ I_w{\stackrel{\&CenterDot;}{w}}_i=T_i-T_{\mathrm{ri}}(i=\mathrm{1,3,5})\end{array}\right.---\left(2\right)$

Wherein m is 1/2 of lunar rover vehicle total quality M, and m is taken as 60kg, F _hibe the soil propelling force of i wheel, F _ribe the soil resistance force of i wheel, T _rifor ground imposes on the resistance distance of wheel i, I _wfor the rotor inertia of single wheel around wheel axle center, choose 0.05kgm herein ², w _ispin velocity for wheel i, is recorded by wheel sensor, T _ifor imposed on the drive torque of wheel i by actuator.

In the present invention, adopt sliding mode variable structure control method to distribute wheel moment, relate to the theory of relevant Sliding mode variable structure control algorithm, Gao Wei Ping becomes in structure control theoretical basis > > mono-book and is described in detail at < <.Relevant lunar rover vehicle body powered is learned variable T in equation _ri, F _hi, F _ricalculating, Chen Baichao chapter 4 second portion in Ph D dissertation < < lunar rover vehicle Novel moving system design > > has carried out solving in detail to it.

(1) formula is carried out to differentiate, and (2) formula substitution is obtained to following formula:

$\stackrel{\&CenterDot;}{\mathrm{\&lambda;}}=f(\mathrm{\&lambda;},v)+B(\mathrm{\&lambda;},v)\&CenterDot;u---\left(3\right)$

λ=[λ wherein ₁, λ ₃, λ ₅] ^t, u=[T ₁, T ₃, T ₅] ^t, f (λ, v)=[f ₁(λ, v), f ₃(λ, v), f ₅(λ, v)] ^t, $f_i(\mathrm{\&lambda;},v)=-(1-{\mathrm{\&lambda;}}_i)[\underset{i=\mathrm{1,3,5}}{\mathrm{\&Sigma;}}{F}_{\mathrm{Hi}}-\underset{i=\mathrm{1,3,5}}{\mathrm{\&Sigma;}}{F}_{\mathrm{Ri}}]/\mathrm{Mv}-r{(1-{\mathrm{\&lambda;}}_i)}^2{T}_{\mathrm{ri}}/I_{w}v,$ B _i(λ, v)=r (1-λ _i) ²/ I _wv, (i=1,3,5), M is lunar rover vehicle total quality, gets 120kg.

D, wheel distribute moment T _icalculating

D1, Sliding mode variable structure control module output u _ithe concrete steps of calculating are as follows:

The first step: because sliding mode control theory under two kinds of operating modes is identical, only system deviation is different, is example so this sentences at the uniform velocity driving cycle, and it controls target and takes turns average slippage rate for each according to sliding mode control theory, get state of the system deviation and be

choose switching function:

$s_i=r_{1i}{e}_i+r_{2i}{\stackrel{\&CenterDot;}{e}}_i---\left(4\right)$

λ wherein _ifor the slippage rate of wheel i (i=1～6),

for the first derivative of state of the system deviation, r _1i, r _2ifor constant weight coefficient, be taken as respectively in the present invention 0.6,0.4.

Second step: according to sliding mode control theory, control if reach desirable sliding mode, equivalent control is expressed as associating (4) formula with

have:

${\stackrel{\&CenterDot;}{s}}_i=r_{1i}{\stackrel{\&CenterDot;}{\mathrm{\&lambda;}}}_i-r_{1i}\stackrel{\&CenterDot;}{\stackrel{\&OverBar;}{\mathrm{\&lambda;}}}+r_{2i}{\stackrel{\&CenterDot;\&CenterDot;}{\mathrm{\&lambda;}}}_i-r_{2i}\stackrel{\&CenterDot;\&CenterDot;}{\stackrel{\&OverBar;}{\mathrm{\&lambda;}}}=0---\left(5\right)$

Adopt the expression-form of exponential approach rule:

${\stackrel{\&CenterDot;}{s}}_i=-\mathrm{\&epsiv;sgn}{s}_i-k{s}_i---\left(6\right)$

ε > 0 and k > 0, for controlling parameter, are taken as respectively 0.2 and 130 in the present invention.

(3) formula is brought in (5) formula and is obtained:

${\stackrel{\&CenterDot;}{s}}_i=r_{1i}(f_i(\mathrm{\&lambda;},v)+B_i(\mathrm{\&lambda;},v){\&CenterDot;u}_i)-r_{1i}\stackrel{\&CenterDot;}{\stackrel{\&OverBar;}{\mathrm{\&lambda;}}}+r_{2i}{\stackrel{\&CenterDot;\&CenterDot;}{\mathrm{\&lambda;}}}_i-r_{2i}\stackrel{\&CenterDot;\&CenterDot;}{\stackrel{\&OverBar;}{\mathrm{\&lambda;}}}---\left(7\right)$

Associating (6) and (7) formula, the design result that obtains Sliding mode variable structure control module is as follows:

$u_i=-\frac{\mathrm{\&epsiv;}\left|s_i\right|\mathrm{sgn}\left(s_i\right)+{\mathrm{ks}}_i-r_{1i}\stackrel{\&OverBar;}{\mathrm{\&lambda;}}+r_{2i}{\stackrel{\&CenterDot;\&CenterDot;}{\mathrm{\&lambda;}}}_l-r_{2i}\stackrel{\&CenterDot;\&CenterDot;}{\stackrel{\&OverBar;}{\mathrm{\&lambda;}}}+r_{1i}\&CenterDot;f_i(\mathrm{\&lambda;},v)}{r_{1i}\&CenterDot;B_i(\mathrm{\&lambda;},v)}---\left(8\right)$

U _ibe the output of Sliding mode variable structure control module.

The output T of D2, PID rate control module _vcalculating.

Generally speaking, the expectation moving velocity v of lunar rover vehicle roaming _dbe 0～200m/h, get 200m/h here.Making system deviation is e=v _d-v _cheti, can obtain the Output rusults of PID rate control module:

$T_v=K_p\&CenterDot;e+K_d\&CenterDot;\stackrel{\&CenterDot;}{e}+K_i\&CenterDot;\&Integral;\mathrm{edt}---\left(9\right)$

V wherein _chetifor lunar rover vehicle body speed of vehicle, can record in real time by visual odometry K _pfor proportionality coefficient, K _ifor integral coefficient, K _dfor differential coefficient, value is respectively 24,0,16.T _voutput for the control of PID speed.

D3, according to wheel, distribute the computing formula T of moment _i=u _i+ T _v, can obtain the distribution moment T of each wheel of the lunar rover vehicle _i.

The above; it is only the preferably specific embodiment of the present invention; but protection scope of the present invention is not limited to this; anyly be familiar with those skilled in the art in the technical scope that the present invention discloses; according to technical scheme of the present invention and inventive concept thereof, be equal to replacement or changed, within all should being encompassed in protection scope of the present invention.

Claims (1)

1. the lunar wheeled vehicle regulating based on slippage rate drives control method, it is characterized in that: described driving is controlled and selected module, slippage rate estimation module, Sliding mode variable structure control module, PID rate control module and lunar rover vehicle system to control by operating mode, described lunar rover vehicle system obtains translational velocity and the angular speed of wheel of wheel barycenter by dynam and kinematics analysis, be input to slippage rate estimation module; Slippage rate estimation module is calculated the slippage rate of each wheel, is input in Sliding mode variable structure control module, as the control target of Sliding mode variable structure control module, the moment of wheel is distributed; Finally this distribution moment is applied on each wheel, completes the driving of wheel is controlled; Described driving control method specifically comprises the following steps:

A, operating mode are selected and are controlled target and determine

A1, slippage rate need to be controlled in certain scope when the acceleration or deceleration because of the lunar rover vehicle, to improve drive efficiency, and at the uniform velocity in driving process, needing adaptation to the ground to rise and fall, avoid single-wheel the trackslip excessive crossing ability causing and harmony variation, so the driving cycle of the lunar rover vehicle is divided into acceleration or deceleration operating mode and driving cycle at the uniform velocity;

Under A2, acceleration or deceleration operating mode, control determining of target

In order to guarantee that lunar rover vehicle wheel when accelerating has enough large drive torque and higher drive efficiency, need to be controlled at the slippage rate of each wheel in the scope of drive efficiency the best;

A3, at the uniform velocity control determining of target under driving cycle

At the uniform velocity, under driving cycle, for wheel slip rate is effectively controlled, thereby reduce the crossing ability of frame energy loss, raising car body and drive coordination performance; Select the aviation value of each skidding rate of rotation for controlling target;

B, wheel slip rate are estimated

B1, first wheel slip rate is defined, it is defined as follows:

$\mathrm{\&lambda;}=\left\{\begin{array}{c}\frac{\mathrm{rw}-v}{\mathrm{rw}}(\mathrm{rw}>v)\\ \frac{\mathrm{rw}-v}{v}(\mathrm{rw}<v)\end{array}\right.---\left(1\right)$

Wherein, λ is wheel slip rate, and r represents radius of wheel, and w represents angular speed of wheel, and v represents the translational velocity of wheel barycenter;

B2, the control target determining for steps A, accurately estimate it; First, select visual odometry to carry out the translational velocity of estimated wheel barycenter; Secondly, utilize vehicle-wheel speed sensor to measure in real time the speed of wheel; Finally utilize formula (1) to calculate the slippage rate of each wheel;

The foundation of C, lunar rover vehicle system model

Research object is six to take turns rocking arm-the turn to posture lunar rover vehicle, by car body (9), suspension fork mechanism and six wheels, formed, suspension frame structure is comprised of rocking arm (7) and the bogie truck (8) of left and right sides symmetry, the drive motor of model is all installed on each wheel etc., the near front wheel (1), left center (3) and (5) three wheel sequence numbers of left rear wheel in left side are respectively 1,3 and 5, and the off front wheel on right side (2), right wheel (4) and (6) three wheel sequence numbers of off hind wheel are respectively 2,4,6; The longitudinal movement of considering car body, carries out force analysis to the six one-sided models of taking turns the lunar rover vehicle, lists its kinetics equation as follows:

$\left\{\begin{array}{c}m\stackrel{\&CenterDot;}{v}=\underset{i=\mathrm{1,3,5}}{\mathrm{\&Sigma;}}(F_{\mathrm{Hi}}-F_{\mathrm{Ri}})\\ I_w{\stackrel{\&CenterDot;}{w}}_i=T_i-T_{\mathrm{ri}}(i=\mathrm{1,3,5})\end{array}\right.---\left(2\right)$

Wherein, m is 1/2 of lunar rover vehicle total quality M, F _hibe the soil propelling force of i wheel, F _ribe the soil resistance force of i wheel, T _rifor ground imposes on the resisting moment of wheel i, I _wfor the rotor inertia of single wheel around wheel axle center, w _ifor the cireular frequency of wheel i, T _ifor imposed on the drive torque of wheel i by actuator, wherein subscript i is the label of one-sided wheel in the text;

(1) formula is carried out to differentiate, and (2) formula substitution is obtained to following formula:

$\stackrel{\&CenterDot;}{\mathrm{\&lambda;}}=f(\mathrm{\&lambda;},v)+B(\mathrm{\&lambda;},v)\&CenterDot;u---\left(3\right)$

Wherein, λ=[λ ₁, λ ₃, λ ₅] ^t, u=[T ₁, T ₃, T ₅] ^t, f (λ, v)=[f ₁(λ, v), f ₃(λ, v), f ₅(λ, v)] ^t,

$f_i(\mathrm{\&lambda;},v)=-\left({1-\mathrm{\&lambda;}}_i\right)[\underset{i=,\mathrm{1,3,5}}{\mathrm{\&Sigma;}}{F}_{\mathrm{Hi}}-\underset{i=\mathrm{1,3,5}}{\mathrm{\&Sigma;}}{F}_{\mathrm{Ri}}]/\mathrm{Mv}-r{\left({1-\mathrm{\&lambda;}}_i\right)}^2{T}_{\mathrm{ri}}/I_{w}v,B_i(\mathrm{\&lambda;},v)=r{\left({1-\mathrm{\&lambda;}}_i\right)}^2/I_{w}v,$

i=1、3、5；

D, wheel distribute moment T _icalculating

D1, the model of setting up according to step C, utilize Sliding mode variable structure control algorithm to calculate each wheel and distribute moment u _i, concrete steps are as follows:

D11, at the uniform velocity the control target under driving cycle is taken turns average slippage rate for each

control target under the operating mode of giving it the gun is expectation slippage rate λ _d; According to sliding mode control theory, while giving it the gun, getting state of the system deviation is e _i=λ _i-λ _d, while at the uniform velocity travelling, get state of the system deviation and be

choose switching function:

$S_i=r_{1i}{e}_i+r_{2i}{\stackrel{\&CenterDot;}{e}}_i---\left(4\right)$

λ wherein _ifor wheel i, the slippage rate of i=1～6,

for the first derivative of state of the system deviation, r _1i, r _2ifor constant weight coefficient;

D12, at the uniform velocity driving cycle is identical with sliding mode control theory under these the two kinds of operating modes of operating mode of giving it the gun, and state of the system deviation is different, under driving cycle at the uniform velocity, according to sliding mode control theory, if reach desirable sliding mode, controls, and equivalent control is expressed as associating (4) formula with

have:

${\stackrel{\&CenterDot;}{s}}_i=r_{1i}{\stackrel{\&CenterDot;}{\mathrm{\&lambda;}}}_i-r_{1i}\stackrel{\&CenterDot;}{\stackrel{\&OverBar;}{\mathrm{\&lambda;}}}+r_{2i}{\stackrel{\&CenterDot;\&CenterDot;}{\mathrm{\&lambda;}}}_i-r_{2i}\stackrel{\&CenterDot;\&CenterDot;}{\stackrel{\&OverBar;}{\mathrm{\&lambda;}}}=0---\left(5\right)$

In order to meet the arrival condition of Sliding mode variable structure control, and there is good robustness with shortest time arrival sliding-mode surface the system that guarantees, weaken the buffeting producing while arriving simultaneously as far as possible, employing exponential approach rule expression-form:

s _i＝-εsgn(s _i)-ks _i （6）

ε >0 and k>0 are for controlling parameter; In order to guarantee weaken to buffet simultaneously also convergence fast, in minimizing ε, increase the numerical value of k, wherein symbolic function sgn(s _i) formula is

$\mathrm{sgn}\left(s_i\right)=\left\{\begin{array}{c}1,s_i>0\\ 0,s_i=0\\ -1,s_i<0\end{array}\right.$

(3) formula is brought in (5) formula and is obtained:

${\stackrel{\&CenterDot;}{s}}_i=r_{1i}(f_i(\mathrm{\&lambda;},v)+B_i(\mathrm{\&lambda;},v)\&CenterDot;u_i)-r_{1i}\stackrel{\&CenterDot;}{\stackrel{\&OverBar;}{\mathrm{\&lambda;}}}+r_{2i}{\stackrel{\&CenterDot;\&CenterDot;}{\mathrm{\&lambda;}}}_i-r_{2i}\stackrel{\&CenterDot;\&CenterDot;}{\stackrel{\&OverBar;}{\mathrm{\&lambda;}}}---\left(7\right)$

Associating (6) and (7) formula, the design result that obtains Sliding mode variable structure control module is as follows:

$u_i=-\frac{\mathrm{\&epsiv;}\left|s_i\right|\mathrm{sgn}\left(s_i\right)+{\mathrm{ks}}_i-r_{1i}\stackrel{\&OverBar;}{\mathrm{\&lambda;}}+r_{2i}{\stackrel{\&CenterDot;\&CenterDot;}{\mathrm{\&lambda;}}}_i\stackrel{\&CenterDot;\&CenterDot;}{\stackrel{\&OverBar;}{\mathrm{\&lambda;}}}{+r}_{1i}\&CenterDot;f_i(\mathrm{\&lambda;},v)}{r_{1i}\&CenterDot;B_i(\mathrm{\&lambda;},v)}---\left(8\right)$

U _ieach wheel that is the output of Sliding mode variable structure control module distributes moment;

The output T of D2, calculating PID rate control module _v

With PID speed control algorithm, make the lunar rover vehicle by expectation speed v _dtravel; Making system deviation is e=v _d– v _cheti, obtain PID rate control module equation and be:

$T_v=K_p\&CenterDot;e+K_d\&CenterDot;\stackrel{\&CenterDot;}{e}+K_i\&CenterDot;\&Integral;\mathrm{edt}---\left(9\right)$ V wherein _chetifor lunar rover vehicle car body actual travel speed, K _pfor proportionality coefficient, K _ifor integral coefficient, K _dfor differential coefficient, in control process, can three parameters be adjusted and be revised, T _voutput for PID rate control module;

D3, according to wheel, distribute the computing formula T of moment _i=u _i+ T _v, can obtain the distribution moment T of each wheel of the lunar rover vehicle _i.

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