CN102602547A - 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 drive controlling method of regulating based on slippage rate

Technical field

The invention belongs to the space technology field; Relating to a kind of is the sliding mode variable structure control method of target to improve the wheeled lunar rover vehicle of rocking arm-bogie truck passability under rugged environment, specially refers to a kind of lunar wheeled vehicle drive controlling method of regulating based on slippage rate.

Background technology

Lunar rover vehicle Drive Control Technique is the realization link of moveable robot movement control; Also be that the lunar rover vehicle is realized one of autonomous gordian technique of walking; Its technical essential is how each wheel drive power to be carried out reasonable distribution, so that the state of kinematic motion between moon wheel that goes on the rugged menology and the wheel is complementary, that avoids that each wheel drive force unreasonable distribution causes skids and sink; Thereby reduce the waste of power and the mechanical wear of the lunar rover vehicle, improve its crossing ability and service life.Although the propulsive effort of the lunar rover vehicle is regulated and control is shown great attention to; But the research of relevant controlling algorithm is less; The limitation of existing control method is: through optimizing the method that the particular constraints condition comes the drive torque to wheel to distribute; Constraint asks the process of optimal solution very complicated, and calculated amount is big; Method to the startup accelerator of the lunar rover vehicle is controlled only is controlled at an expectation value with slippage rate, lunar rover vehicle driving process is not controlled; Adopt PI control algorithm design-calculated PI controller simpler, controlled target is single.

Summary of the invention

To existing control method find the solution complicacy, calculated amount is big; Only slippage rate is controlled at a fixing expectation value; The driving process of the lunar rover vehicle is not controlled, problem such as controlled target is single, the present invention will propose a kind of lunar wheeled vehicle drive controlling method of regulating based on slippage rate; According to lunar rover vehicle acceleration or Reduced Speed Now and the two kinds of operating modes of at the uniform velocity going; Moment to each wheel of the lunar rover vehicle is distributed control, that is: when the lunar rover vehicle is in acceleration or decelerating mode, each wheel slip rate is controlled in the best interval of each wheel drive efficient; When the lunar rover vehicle is at the uniform velocity driving cycle, be controlled target with the average slippage rate of wheel; And find the solution simple, calculated amount is little.

Technical scheme of the present invention is:

A kind of lunar wheeled vehicle drive controlling method of regulating based on slippage rate; 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 the translational velocity and the angular speed of wheel of wheel barycenter through dynam and kinematics analysis, is input to the slippage rate estimation module; The slippage rate estimation module is calculated the slippage rate of each wheel, is input in the Sliding mode variable structure control module, as the controlled target of Sliding mode variable structure control module the moment of wheel is distributed; Should distribute moment to be applied on each wheel at last, accomplish drive controlling wheel; Described drive controlling method specifically may further comprise the steps:

A, operating mode are selected and controlled target is confirmed

A1, when quickening or slow down, need slippage rate be controlled in certain scope because of the lunar rover vehicle; To improve drive efficiency; And at the uniform velocity needing adaptation to the ground to rise and fall in the driving process; Avoid single-wheel trackslip excessive crossing ability that causes and harmony variation, so the driving cycle of the lunar rover vehicle is divided into acceleration or decelerating mode and driving cycle at the uniform velocity;

Controlled target confirms under A2, acceleration or the decelerating mode

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

A3, the confirming of controlled target under the driving cycle at the uniform velocity

At the uniform velocity under the driving cycle, be effectively controlled, thereby reduce the car body waste of power, improve the crossing ability of car body and drive coordination performance in order to make the wheel slip rate; The aviation value of selecting each skidding rate of rotation is a controlled target, if the single-wheel slippage rate is too high, explains that the net tractive force of wheel F that is directed against fixing branch counter-force N is excessive, reduces the consumption that slippage rate has also just reduced unnecessary net tractive force of wheel; If slippage rate is too small; Explain that the tractive force F that is directed against fixing branch counter-force N is too small, be far smaller than the tractive force that ground can give, in order successfully to pass through accidental relieies such as ditch or abrupt slope; Need to increase slippage rate to improve ground traction, improve the lunar rover vehicle in rugged ground-surface through performance;

B, wheel slip rate are estimated

B1, at first the wheel slip rate is defined, all relevant with slippage rate with index because of each item kinematic parameter of the lunar rover vehicle, so slippage rate becomes the emphasis of research, it defines 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 the 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, confirm good controlled target, it is accurately estimated to steps A; At first, the translational velocity of selecting the vision miles counter to come the estimated wheel barycenter; Secondly, utilize vehicle-wheel speed sensor to measure the speed of wheel in real time; Utilize formula (1) to calculate the slippage rate of each wheel at last;

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; Form by car body, suspension fork mechanism and six wheels; Suspension frame structure is made up of the rocking arm and the bogie truck of left and right sides symmetry; The drive motor of model all is installed on each wheel etc., and the near front wheel in left side, left center and three wheel sequence numbers of left rear wheel are respectively 1,3 and 5, and wheel and three wheel sequence numbers of off hind wheel are respectively 2,4,6 in the off front wheel on right side, the right side; The longitudinal movement of Car Body Considering, to six take turns the lunar rover vehicle one-sided model carry out force analysis, it is following to list its kinetics equation:

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

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 _wBe the rotor inertia of single wheel around the wheel axle center, w _iBe 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 full text;

(1) formula is carried out differentiate, and (2) formula substitution is got 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, according to the model that step C sets up, utilize each wheel of Sliding mode variable structure control algorithm computation to distribute moment u _i, concrete steps are following:

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

Controlled target under the operating mode of giving it the gun is expectation slippage rate λ _dAccording to sliding mode control theory, getting the state of the system deviation during acceleration is e _i=λ _i-λ _d, get the state of the system deviation when at the uniform velocity going and do

Choose switching function:

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

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

The aviation value of each wheel slip rate,

Be the first derivative of state of the system deviation, r _1i, r _2iBe the constant weight coefficient;

D12, because of sliding mode control theory under two kinds of operating modes identical; Only the state of the system deviation is different; Driving cycle is an example so this sentences at the uniform velocity; According to sliding mode control theory; If reach desirable sliding mode control, then equivalent control is expressed as

, and associating (4) formula has with

:

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

In order to satisfy the arrival condition of Sliding mode variable structure control, and arrive sliding-mode surface and the system that guarantees has good robustness with the shortest time, weaken the buffeting that produces when arriving simultaneously as far as possible, adopt index convergence rule expression-form:

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

ε＞0 and k＞0 is a controlled variable; In order to guarantee weaken to buffet simultaneously also convergence fast, the numerical value of increase k when reducing ε, wherein symbolic function sgn (s) formula does

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

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

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

Associating (6) and (7) formula, it is following to obtain Sliding mode variable structure control Module Design result:

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

u _iBe the output of Sliding mode variable structure control module;

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

Make lunar rover vehicle speed v as expected with the PID speed control algorithm _dGo; Make that system deviation is e=v _d-v _Cheti, must PID rate control module equation be:

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

V wherein _ChetiBe lunar rover vehicle car body actual travel speed, K _pBe proportionality coefficient, K _iBe integral coefficient, K _dBe differential coefficient, can adjust and revise, T three parameters in the control process _vOutput for the PID rate control module;

D3, distribute the computing formula T of moment according to wheel _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 with lunar rover vehicle driving cycle: a kind ofly be that car body quickens or decelerating mode, the slippage rate of wheel is controlled in the higher scope of drive efficiency, can guarantee the drive efficiency that wheel is higher; A kind of is at the uniform velocity driving cycle of car body, is controlled target with the aviation value of each wheel slip rate, can avoid controlled target single, and the too high or too low energy consumption that causes of single-wheel slippage rate increases problems such as crossing ability variation.Adopt the Sliding mode variable structure control algorithm, find the solution 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.

Description of drawings

The present invention has accompanying drawing 2 width of cloth, wherein:

Fig. 1 is a lunar rover vehicle drive controlling block diagram.

Fig. 2 takes turns the 3D modelling of the wheeled lunar rover vehicle of rocking arm-bogie truck for six of the present invention's research.

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

The specific embodiment

Be described in detail the specific embodiment of the present invention below in conjunction with accompanying drawing.As shown in Figure 1, v _dBe lunar rover vehicle expectation moving velocity; v _ChetiBe lunar rover vehicle car body actual travel speed; u _iOutput for the Sliding mode variable structure control module; T _vOutput for PID speed control piece; T _iDistribution moment for lunar roving vehicle wheel i; λ _iFor the slippage rate of wheel i is estimated; W is an angular speed of wheel, and v is the translational velocity of wheel barycenter.

A, operating mode are selected and controlled target is confirmed

The first step: the desired speed v of definition car body _dActual travel speed v with car body _ChetiThe relative error that exists | (v _d-v _Cheti)/v _d| 100% less than 10% o'clock, belongs at the uniform velocity driving cycle; Quicken or decelerating mode otherwise belong to.

Second step: the confirming of controlled target.

At the uniform velocity under the driving cycle, select each wheel slip rate aviation value

to be controlled target; If accelerating mode, controlled target are 0.1, scope is 0.1～0.3 optional; If decelerating mode, controlled target are-0.1, scope is optional-0.3～-0.1.

B, wheel slip rate are estimated

The computing formula of slippage rate is following:

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

Wherein, radius of wheel r is 120mm; W is an angular speed of wheel, utilizes vehicle-wheel speed sensor can measure the actual speed rw of wheel in real time; V is the translational velocity of wheel barycenter, utilizes the vision miles counter to calculate the translational velocity v of wheel barycenter; Utilize formula (1) to estimate the slippage rate of six wheels at last.

The foundation of C, lunar rover vehicle system model

The longitudinal movement of Car Body Considering, to six take turns the lunar rover vehicle one-sided model carry out force analysis, it is following to list its kinetics equation:

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

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, choose 0.05kgm here around the wheel axle center ², w _iSpin velocity for wheel i is recorded by wheel sensor, T _iFor impose on the drive torque of wheel i by actuator.

Adopt sliding mode variable structure control method that wheel moment is distributed among the present invention, relate to the theory of relevant Sliding mode variable structure control algorithm, Gao Wei Ping has carried out detailed introduction in " becoming structure control theoretical basis " book.Variable T in the relevant lunar rover vehicle car body kinetics equation _Ri, F _Hi, F _RiCalculating, Chen Baichao chapter 4 second portion in Ph D dissertation " lunar rover vehicle novel mobile system design " has carried out finding the solution in detail to it.

(1) formula is carried out differentiate, and (2) formula substitution is got 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 a 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 following:

The first step: because of sliding mode control theory under two kinds of operating modes identical; Only system deviation is different; Driving cycle is an example so this sentences at the uniform velocity; Its controlled target is taken turns average slippage rate

according to sliding mode control theory for each, gets the state of the system deviation and chooses switching function for

:

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

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

Be the first derivative of state of the system deviation, r _1i, r _2iBe the constant weight coefficient, be taken as 0.6,0.4 in the present invention respectively.

Second step: according to sliding mode control theory; If reach desirable sliding mode control, then equivalent control is expressed as

, and associating (4) formula has with

:

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

Adopt the expression-form of index convergence rule:

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

ε＞0 and k＞0 is a controlled variable, is taken as 0.2 and 130 among the present invention respectively.

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

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

Associating (6) and (7) formula, it is following to obtain Sliding mode variable structure control Module Design result:

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

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.Make that system deviation is e=v _d-v _Cheti, can get the output result 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 _ChetiBe lunar rover vehicle body speed of vehicle, can record K in real time through the vision miles counter _pBe proportionality coefficient, K _iBe integral coefficient, K _dBe differential coefficient, value is respectively 24,0,16.T _vOutput for the PID speed control.

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

The above; Be merely the preferable specific embodiment of the present invention; But protection scope of the present invention is not limited thereto; Any technical personnel of being familiar with the present technique field is equal to replacement or change according to technical scheme of the present invention and inventive concept thereof in the technical scope that the present invention discloses, all should be encompassed within protection scope of the present invention.

Claims (1)

1. lunar wheeled vehicle drive controlling method of regulating based on slippage rate; It is characterized in that: 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 the translational velocity and the angular speed of wheel of wheel barycenter through dynam and kinematics analysis, is input to the slippage rate estimation module; The slippage rate estimation module is calculated the slippage rate of each wheel, is input in the Sliding mode variable structure control module, as the controlled target of Sliding mode variable structure control module the moment of wheel is distributed; Should distribute moment to be applied on each wheel at last, accomplish drive controlling wheel; Described drive controlling method specifically may further comprise the steps:

A, operating mode are selected and controlled target is confirmed

A1, when quickening or slow down, need slippage rate be controlled in certain scope because of the lunar rover vehicle; To improve drive efficiency; And at the uniform velocity needing adaptation to the ground to rise and fall in the driving process; Avoid single-wheel trackslip excessive crossing ability that causes and harmony variation, so the driving cycle of the lunar rover vehicle is divided into acceleration or decelerating mode and driving cycle at the uniform velocity;

Controlled target confirms under A2, acceleration or the decelerating mode

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

A3, the confirming of controlled target under the driving cycle at the uniform velocity

At the uniform velocity under the driving cycle, be effectively controlled, thereby reduce the car body waste of power, improve the crossing ability of car body and drive coordination performance in order to make the wheel slip rate; The aviation value of selecting each skidding rate of rotation is a controlled target, if the single-wheel slippage rate is too high, explains that the net tractive force of wheel F that is directed against fixing branch counter-force N is excessive, reduces the consumption that slippage rate has also just reduced unnecessary net tractive force of wheel; If slippage rate is too small; Explain that the tractive force F that is directed against fixing branch counter-force N is too small, be far smaller than the tractive force that ground can give, in order successfully to pass through accidental relieies such as ditch or abrupt slope; Need to increase slippage rate to improve ground traction, improve the lunar rover vehicle in rugged ground-surface through performance;

B, wheel slip rate are estimated

B1, at first the wheel slip rate is defined, all relevant with slippage rate with index because of each item kinematic parameter of the lunar rover vehicle, so slippage rate becomes the emphasis of research, it defines 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 the 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, confirm good controlled target, it is accurately estimated to steps A; At first, the translational velocity of selecting the vision miles counter to come the estimated wheel barycenter; Secondly, utilize vehicle-wheel speed sensor to measure the speed of wheel in real time; Utilize formula (1) to calculate the slippage rate of each wheel at last;

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; Form by car body (9), suspension fork mechanism and six wheels; Suspension frame structure is made up of the rocking arm (7) and the bogie truck (8) of left and right sides symmetry; The drive motor of model all is installed on each wheel etc., and the near front wheel in left side (1), left center (3) and (5) three wheel sequence numbers of left rear wheel are respectively 1,3 and 5, and wheel (4) and (6) three wheel sequence numbers of off hind wheel are respectively 2,4,6 in the off front wheel on right side (2), the right side; The longitudinal movement of Car Body Considering, to six take turns the lunar rover vehicle one-sided model carry out force analysis, it is following to list its kinetics equation:

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

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 _wBe the rotor inertia of single wheel around the wheel axle center, w _iBe 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 full text;

(1) formula is carried out differentiate, and (2) formula substitution is got 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, according to the model that step C sets up, utilize each wheel of Sliding mode variable structure control algorithm computation to distribute moment u _i, concrete steps are following:

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

Controlled target under the operating mode of giving it the gun is expectation slippage rate λ _dAccording to sliding mode control theory, getting the state of the system deviation during acceleration is e _i=λ _i-λ _d, get the state of the system deviation when at the uniform velocity going and do

Choose switching function:

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

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

The aviation value of each wheel slip rate,

Be the first derivative of state of the system deviation, r _1i, r _2iBe the constant weight coefficient;

D12, because of sliding mode control theory under two kinds of operating modes identical; Only the state of the system deviation is different; Driving cycle is an example so this sentences at the uniform velocity; According to sliding mode control theory; If reach desirable sliding mode control, then equivalent control is expressed as

, and associating (4) formula has with

:

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

In order to satisfy the arrival condition of Sliding mode variable structure control, and arrive sliding-mode surface and the system that guarantees has good robustness with the shortest time, weaken the buffeting that produces when arriving simultaneously as far as possible, adopt index convergence rule expression-form:

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

ε＞0 and k＞0 is a controlled variable; In order to guarantee weaken to buffet simultaneously also convergence fast, the numerical value of increase k when reducing ε, wherein symbolic function sgn (s) formula does

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

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

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

Associating (6) and (7) formula, it is following to obtain Sliding mode variable structure control Module Design result:

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

u _iBe the output of Sliding mode variable structure control module;

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

Make lunar rover vehicle speed v as expected with the PID speed control algorithm _dGo; Make that system deviation is e=v _d-v _Cheti, must PID rate control module equation be:

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

V wherein _ChetiBe lunar rover vehicle car body actual travel speed, K _pBe proportionality coefficient, K _iBe integral coefficient, K _dBe differential coefficient, can adjust and revise, T three parameters in the control process _vOutput for the PID rate control module;

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

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