Steerability Analysis on Slopes of a Mobile Robot with a Ground Contact Arm

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Departamento de Ingeniería de Sistemas y AutomáticaDepartamento de Ingeniería de Sistemas y Automática

Steerability Analysis on Slopes of a Mobile Robot with a Ground Contact Arm

Jesús M. García

Universidad Nacional Experimental del Táchira, San Cristóbal, Venezuela

Jorge L. Martínez, Anthony Mandow and Alfonso García-Cerezo

Dpto. Ingeniería de Sistemas y Automática, Universidad de Málaga, Spain

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OUTLINE

1.  THE LAZARO MOBILE ROBOT 2.  NAVIGABILITY INDICES

3.  TIP-OVER AVOIDANCE

4.  EXPERIMENTAL RESULTS 5.  CONCLUSIONS

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1. THE LAZARO MOBILE ROBOT

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THE LAZARO MOBILE ROBOT

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n  Specially designed to have an additional contact point with the ground

θ

₁

d

₂

Four-wheeled skid-steered vehicle Two degrees of freedom arm,

whose end-effector is a caster wheel

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THE LAZARO MOBILE ROBOT

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n  Supporting forces of the wheels: F

_1z

, F

_2z

, F

_3z

, F

_4z

can be estimated knowing the pitch and roll angles on the plane, angle θ

₁

, length d

₂

and the force exerted by the caster wheel F

_5z

Supporting forces of the wheels

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2. NAVIGABILITY INDICES

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NAVIGABILITY INDICES

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n  Tip-over stability index: based on the minimum supporting force F

_min

that depends on the number of contact points with the ground

Denominator normalize index between 0 and 1

n  Four contact points: F

_min

is calculated as the minimum supporting forces of the axes between adjacent traction wheels

Supporting forces of the axis

between adjacent wheels i and j:

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NAVIGABILITY INDICES

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n  Three contact points: F

_min

is calculated as the minimum supporting forces of the three wheels in contact with the ground

n  Five contact points: It is an intermediate case between four and

three contact points

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NAVIGABILITY INDICES

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n  Steerability index: calculated as the minimum supporting forces of the longitudinal axes of the vehicle

The caster wheel does not provide traction

Axis 1-4 Axis 2-3

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3. TIP-OVER AVOIDANCE

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TIP-OVER AVOIDANCE

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n  COG control strategy: COG is modified by actuating on arm rotation θ

₁

without additional contact with the ground (F

_5z

=0)

Optimal θ

₁

for every combination of pitch and roll angles

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TIP-OVER AVOIDANCE

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n  Additional contact strategy: by exerting a certain force F

_5z

against the ground with the caster wheel

Optimal θ

₁

angles

Optimal F

_5z

forces

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TIP-OVER AVOIDANCE

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n  Static comparison: Additional contact strategy obtains the best values for tip-over prevention. COG control achieves the best results for

steerability

Mean and standard deviation of the navigation indices

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4. EXPERIMENTAL RESULTS

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EXPERIMENTAL RESULTS

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n  ADAMS simulations: straight line motion along an undulating ramp

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EXPERIMENTAL RESULTS

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n  Downward motion

Navigation with an additional ground contact point

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EXPERIMENTAL RESULTS

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n  Downward motion

The θ

₁

angle and the F

_5z

force The tip-over and steering indices

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EXPERIMENTAL RESULTS

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n  Upward motion

Navigation with an additional ground contact point

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EXPERIMENTAL RESULTS

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n  Upward motion

The θ

₁

angle and the F

_5z

force The tip-over and steering indices

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5. CONCLUSIONS

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Steerability Analysis on Slopes of a Mobile Robot with a Ground Contact Arm

Steerability Analysis on Slopes of a Mobile Robot with a Ground Contact Arm

Jesús M. García

Universidad Nacional Experimental del Táchira, San Cristóbal, Venezuela

Jorge L. Martínez, Anthony Mandow and Alfonso García-Cerezo

Dpto. Ingeniería de Sistemas y Automática, Universidad de Málaga, Spain

OUTLINE

1. THE LAZARO MOBILE ROBOT 2. NAVIGABILITY INDICES

3. TIP-OVER AVOIDANCE

4. EXPERIMENTAL RESULTS 5. CONCLUSIONS

1.

THE LAZARO MOBILE ROBOT

THE LAZARO MOBILE ROBOT

n Specially designed to have an additional contact point with the ground

θ

d

Four-wheeled skid-steered vehicle Two degrees of freedom arm,

whose end-effector is a caster wheel

THE LAZARO MOBILE ROBOT

n Supporting forces of the wheels: F

, F

, F

, F

can be estimated knowing the pitch and roll angles on the plane, angle θ

, length d

and the force exerted by the caster wheel F

Supporting forces of the wheels

2.

NAVIGABILITY INDICES

NAVIGABILITY INDICES

n Tip-over stability index: based on the minimum supporting force F

that depends on the number of contact points with the ground

Denominator normalize index between 0 and 1

n Four contact points: F

is calculated as the minimum supporting forces of the axes between adjacent traction wheels

Supporting forces of the axis

between adjacent wheels i and j:

NAVIGABILITY INDICES

n Three contact points: F

is calculated as the minimum supporting forces of the three wheels in contact with the ground

n Five contact points: It is an intermediate case between four and

three contact points

NAVIGABILITY INDICES

n Steerability index: calculated as the minimum supporting forces of the longitudinal axes of the vehicle

The caster wheel does not provide traction

3.

TIP-OVER AVOIDANCE

TIP-OVER AVOIDANCE

n COG control strategy: COG is modified by actuating on arm rotation θ

without additional contact with the ground (F

=0)

Optimal θ

for every combination of pitch and roll angles

TIP-OVER AVOIDANCE

n Additional contact strategy: by exerting a certain force F

against the ground with the caster wheel

Optimal θ

angles

Optimal F

forces

TIP-OVER AVOIDANCE

n Static comparison: Additional contact strategy obtains the best values for tip-over prevention. COG control achieves the best results for

steerability

Mean and standard deviation of the navigation indices

4.

EXPERIMENTAL RESULTS

EXPERIMENTAL RESULTS

n ADAMS simulations: straight line motion along an undulating ramp

EXPERIMENTAL RESULTS

n Downward motion

Navigation with an additional ground contact point

EXPERIMENTAL RESULTS

n Downward motion

The θ

angle and the F

force The tip-over and steering indices

EXPERIMENTAL RESULTS

n Upward motion

Navigation with an additional ground contact point

EXPERIMENTAL RESULTS

1.  THE LAZARO MOBILE ROBOT 2.  NAVIGABILITY INDICES

3.  TIP-OVER AVOIDANCE

4.  EXPERIMENTAL RESULTS 5.  CONCLUSIONS

n  Specially designed to have an additional contact point with the ground

n  Supporting forces of the wheels: F

n  Tip-over stability index: based on the minimum supporting force F

n  Four contact points: F

n  Three contact points: F

n  Five contact points: It is an intermediate case between four and

n  Steerability index: calculated as the minimum supporting forces of the longitudinal axes of the vehicle

n  COG control strategy: COG is modified by actuating on arm rotation θ

n  Additional contact strategy: by exerting a certain force F

n  Static comparison: Additional contact strategy obtains the best values for tip-over prevention. COG control achieves the best results for

n  ADAMS simulations: straight line motion along an undulating ramp

n  Downward motion

n  Downward motion

n  Upward motion

n  Upward motion

n  The effect on vehicle steerability of an arm ground contact have been analyzed

n  The case study of the mobile robot Lazaro whose end- effector is a caster wheel have been presented

►  Simulation results with ADAMS show that tip-over can be improved with an additional ground contact but it can also provoke a loss in steerability

►  COG control of the on-board arm obtains goods results both in tip- over and steering indices

n  Future work

►  To complete navigability analysis with an sliding index

►  To obtain real data from experiments with Lazaro