An Image Based Method of Finding Better Walking Strategies for Hexapod on Discontinuous Terrains

An Image Based Method of Finding Better An Image Based Method of Finding Better Walking Strategies for Hexapod on Walking Strategies for Hexapod on

Discontinuous TerrainsDiscontinuous Terrains

Kazi Mostafa Kazi Mostafa [email protected]

Professor Innchyn HerProfessor Innchyn [email protected]

Kung-Ting WeiKung-Ting [email protected]

Department of Mechanical & Electro-Mechanical Department of Mechanical & Electro-Mechanical EngineeringEngineering

National Sun Yat-sen University, Taiwan National Sun Yat-sen University, Taiwan

IntroductionIntroduction◦ Previous Research WorkPrevious Research Work◦ ObjectivesObjectives

MethodsMethods◦ Simulate Terrain EnvironmentSimulate Terrain Environment◦ Proposed Hexapod Model Proposed Hexapod Model ◦ Walking Strategy Walking Strategy

ResultsResultsConclusionConclusion

2

Wheeled vs. Wheeled vs. LeggedLegged locomotion. locomotion.

On On discontinuous terrainsdiscontinuous terrains..

Multi legged animals have excellent Multi legged animals have excellent adaptabilityadaptability to traverse over to traverse over rugged terrainrugged terrain. .

Multi-leggedMulti-legged robots that imitate crawling insects. robots that imitate crawling insects.

HexapodHexapod configuration is most configuration is most efficient & efficient & statically stablestatically stable. .

3

Vision system Vision system to recognize to recognize surrounding terrain surrounding terrain

Image based method Image based method of finding of finding walking strategieswalking strategies

To simulate To simulate a complete a complete hexapod hexapod walking modelwalking model

5

Proposed research divided into 3 major Proposed research divided into 3 major steps:steps:A.A.Establishment of Terrain Environment Establishment of Terrain Environment B.B.The Hexapod Gait Model The Hexapod Gait Model

- A simplified forward gait- A simplified forward gait- Rotation- Rotation- Intelligent gait control- Intelligent gait control

C.C.Hexapod’s Walking Strategy Hexapod’s Walking Strategy - - Gait selection methodGait selection method- Walking Strategy - Walking Strategy

6

Proposed research divided into 3 major Proposed research divided into 3 major steps:steps:A.A.Establishment of Terrain Environment Establishment of Terrain Environment

B.B.The Hexapod Gait Model The Hexapod Gait Model - A simplified forward gait- A simplified forward gait- Rotation- Rotation- Intelligent gait control- Intelligent gait control


7

Defined Defined sizesize of the terrain & entered 250 of the terrain & entered 250 circles. circles.

Computer Computer displayeddisplayed a topographic a topographic vector map by using those circles. vector map by using those circles.

Applied Applied Grayscale erosion Grayscale erosion to find the to find the boundary of Circles. boundary of Circles.

8

The white regions are The white regions are standingstanding areas, black regions are areas, black regions are forbiddenforbidden areas & the yellow region is being eroded. areas & the yellow region is being eroded.

The The edgesedges of the terrain changes into a forbidden area. of the terrain changes into a forbidden area.

9

Foothold Zone

Forbidden Zone

Forbidden Zone




10

Semi-circular shaped areas are Hexapod gait Semi-circular shaped areas are Hexapod gait range of motionrange of motion

Maximum range RMaximum range Rmaxmax = 60 (pixels), minimum = 60 (pixels), minimum range Rrange Rminmin = 20 (pixels), length between two = 20 (pixels), length between two successive gaits B = 100 (pixels), width W = 50 successive gaits B = 100 (pixels), width W = 50 (pixels), and the offset value D = 50 (pixels). (pixels), and the offset value D = 50 (pixels).

11

Measured ranges of movement (Measured ranges of movement (KKmm) for various ) for various angle & stored in the matrix. angle & stored in the matrix.

The largest value defined as The largest value defined as 255255 (white), lowest (white), lowest as as 00 (black). (black).

This study choose This study choose 8 forward gait angle 8 forward gait angle matrix matrix databasedatabase[0 °, 15 °, 30 °, 45 °, 60 °, -15 °, -30 °, -45 °][0 °, 15 °, 30 °, 45 °, 60 °, -15 °, -30 °, -45 °]

12

Parameters of forward gait: Parameters of forward gait: forward angle α, stride length S, and Sforward angle α, stride length S, and SXX, S, SYY are the S in X direction and Y direction. are the S in X direction and Y direction.

Various parameters of forward gait

13

α -15° -30° -45° 0° 15° 30° 45° 60°S 111.6 101.2 83.4 112 111.6 101.2 83.4 67.2

SX -28 -50 -59 0 28 50 59 58

SY 108 88 59 112 108 88 59 34

Measurement of gait rotation can be divided into Measurement of gait rotation can be divided into two steps; two steps; FirstFirst, we calculated the distance , we calculated the distance between each point of motion range and C.G. between each point of motion range and C.G.

SecondSecond, used same size of matrix to store the , used same size of matrix to store the range of movement .range of movement .

14

Rotation Angleθ2

θ3

θ6

When the hexapod robot rotates clockwise, the When the hexapod robot rotates clockwise, the center of rotationcenter of rotation move to right direction. move to right direction.

The value of θThe value of θ33 decreases & θ decreases & θ22,θ,θ6 6 increases increases gradually. gradually.

When θWhen θ22, θ, θ33, θ, θ66 turned turned equalequal, hexapod could get , hexapod could get maximum rotation anglemaximum rotation angle. .

The location of OThe location of OTT is is 6262 units right from CG units right from CG

15

62 Units

The rotation around CG has The rotation around CG has nono forward movement. forward movement.

But, for the maximum rotation angle of 37.7° gait, But, for the maximum rotation angle of 37.7° gait, the robot can move forward of the robot can move forward of 40.2 units40.2 units, which , which includes 13 units in X direction, 38 units Y direction. includes 13 units in X direction, 38 units Y direction.

16

θ S SX SY R

Rotation around C.G. 30.03° 0 0 0 0

Max. angle of rotation 37.67° 40.1640.16 1313 3838 6262

This method assumes that the target point is in This method assumes that the target point is in front of the robot & center of rotation is in the front of the robot & center of rotation is in the right rear. right rear.

In each step robot can rotate θ degree depends In each step robot can rotate θ degree depends on the condition and distance of movement. on the condition and distance of movement.

After finished movement, hexapod’s center of After finished movement, hexapod’s center of rotation can be measured. rotation can be measured.

Then, by using previously mentioned method, Then, by using previously mentioned method, measured the radius of rotation and measured the radius of rotation and parameters for 5° and 10° of rotation. parameters for 5° and 10° of rotation.

17

Stride length S for 5° is 101.9 unit and for 10° is 93 Stride length S for 5° is 101.9 unit and for 10° is 93 unit. unit.

For10°, the hexapod moved less distance in the Y For10°, the hexapod moved less distance in the Y direction, but it added value in rotation. direction, but it added value in rotation.

If Hexapod needs to move & want to rotate If Hexapod needs to move & want to rotate simultaneously, it should choose 5° of rotational gait. simultaneously, it should choose 5° of rotational gait.

If the greater rotation is needed, hexapod might be If the greater rotation is needed, hexapod might be choosing 10°. choosing 10°.

18

θ S SX SY R

5° 101.92 28 98 1162.3

10° 93.01 27 89 527.68

First, take snapshot & pre-calculated the next First, take snapshot & pre-calculated the next foothold point.foothold point.

Based on the terrain's ranges overlap with the Based on the terrain's ranges overlap with the gait ranges of motion, the gait ranges of motion, the 33rdrd gait gait is beyond the is beyond the region. region.

So the robot chooses 1-4-5 gait sequence for So the robot chooses 1-4-5 gait sequence for foothold. And select the maximum number of foothold. And select the maximum number of points (gray region). points (gray region).

19

Terrain’s Foothold Zone

Gait Ranges of Motion

Overlapped No Foothold

1

4

5

Started with tripod gait. Difficulties in transformation Started with tripod gait. Difficulties in transformation between 1-4-5 and 2-3-6 gait. Gait number 2 had no between 1-4-5 and 2-3-6 gait. Gait number 2 had no foothold. foothold.

Hexapod using symmetrical gait (1-3-4-6) for foothold and Hexapod using symmetrical gait (1-3-4-6) for foothold and move.move.

Hexapod again converted back in to tripod gait (2-3-6). Hexapod again converted back in to tripod gait (2-3-6). Thus, if hexapod stuck again it will transformed 1-4-5 gait Thus, if hexapod stuck again it will transformed 1-4-5 gait sequence to continue walk. sequence to continue walk.

20

Current Km

Residual Km

1

3 4

6

No Foothold

211-4-5 Gait Sequence

2-3-6 Gait Sequence

Symmetrical Gait

Target




22

Proposed hexapod has 8 different angles of forward gait. Proposed hexapod has 8 different angles of forward gait. In total 64 combinations of gaits. But, 0° forward gait is a In total 64 combinations of gaits. But, 0° forward gait is a first choice. first choice.

Categorized these 64 combination of gait into 3 groups. Categorized these 64 combination of gait into 3 groups. The combination of smaller angle gait is the most The combination of smaller angle gait is the most

preferred one. preferred one. In every step, hexapod compared stride length with Table In every step, hexapod compared stride length with Table

11. If stride length is at least 80% of table . If stride length is at least 80% of table 11, hexapod walk , hexapod walk by 0° forward gait. by 0° forward gait.

If it is less, hexapod will choose other optimum gait angle. If it is less, hexapod will choose other optimum gait angle.

23

α -15° -30° -45° 0° 15° 30° 45° 60°S 111.6 101.2 83.4 112 111.6 101.2 83.4 67.2

SX -28 -50 -59 0 28 50 59 58

SY 108 88 59 112 108 88 59 34

Table 1

Group 01Group 010°0° 0°, 15°, -15° 0°, 15°, -15°

15°15° 30°, 0° 30°, 0°-15°-15° 30°, 0° 30°, 0°

Measure Stride Measure Stride LengthLength

Stride Stride length is length is 80% of 80% of

max max stridestride

Keep Keep MovingMoving

Group 02Group 020°0° 30°, -30° 30°, -30°15°15° 45°, -15° 45°, -15°-15°-15° -45°, 15° -45°, 15°

30°30° 0°, 15°, 45° 0°, 15°, 45°-30°-30° 0°,-15°,-45° 0°,-15°,-45°

Measure Stride Measure Stride LengthLength

Stride Stride length is length is 80% of 80% of

max max stridestride

Keep Keep MovingMoving

YesYes

NoNo

…NoNoYesYes

The walking strategy database contains 8 kinds The walking strategy database contains 8 kinds of linear motion, 4 rotational movements, and of linear motion, 4 rotational movements, and the tripod gait and the symmetrical gait. the tripod gait and the symmetrical gait.

The hexapod’s first choice is 0 ° forward gait for The hexapod’s first choice is 0 ° forward gait for largest stride length and ± 10 ° is second. largest stride length and ± 10 ° is second.

If the angle between the robot and the target is If the angle between the robot and the target is greater than 45°, then hexapod choose the greater than 45°, then hexapod choose the rotation gait. rotation gait.

If the angle between the robot and the target is If the angle between the robot and the target is less than 45 °, then 5 ° or 10 ° of rotation gait less than 45 °, then 5 ° or 10 ° of rotation gait can be used. can be used. 25

26

Angle (α) of Target

Less than 5°

0° Straight Forward

GaitNext step

footholdYes

Hexapod moving to

targetReaches Target PointYes

Complete

No

Greater

than 5°

Angle (α) of Target

Greater than 45°

Max angle of rotation

Less than 45°Rotation

around any pointAngle (α) of Target

Greater

than 5°Less than

5°

Transform to symmetrical

gaitNo

Next step

foothold

Yes


MethodsMethods◦ Simulate Terrain EnvironmentSimulate Terrain Environment◦ Hexapod Model Hexapod Model ◦ Walking Strategy Walking Strategy


27

In proposed simulated terrain, there are 250 In proposed simulated terrain, there are 250 circles with radius 15, 30, 45, 60, 75 where circles with radius 15, 30, 45, 60, 75 where hexapod can stand. The average radius of hexapod can stand. The average radius of these circles is 29.7. these circles is 29.7.

The significant advantage of proposed The significant advantage of proposed hexapod is use of databases with image hexapod is use of databases with image processing technique. processing technique.

Hexapod can use database to reduce Hexapod can use database to reduce computation time. computation time.

Proposed design is based on KProposed design is based on Kmm to select gait to select gait and foothold. and foothold.

28


MethodsMethods◦ Simulate Terrain EnvironmentSimulate Terrain Environment◦ Hexapod Model Hexapod Model ◦ Walking Strategy Walking Strategy


30

This study showed the use of image processing This study showed the use of image processing based technique to design an adaptive gait.based technique to design an adaptive gait.

Matrix database combined with image Matrix database combined with image processing method made the hexapod’s processing method made the hexapod’s walking strategy easy to determine. walking strategy easy to determine.

Thus, the robot can simulate routes in Thus, the robot can simulate routes in advance, and achieve the artificial intelligence advance, and achieve the artificial intelligence capabilities. capabilities.

Finally, we hope that the proposed research Finally, we hope that the proposed research method and strategy can provide a reference method and strategy can provide a reference for future research to scholars.for future research to scholars.

31

As part of our continuing research, we As part of our continuing research, we are developing a physical model by are developing a physical model by using proposed computer simulation using proposed computer simulation results and improving efficiency for results and improving efficiency for real-time control application to proof real-time control application to proof the optimality of the design. the optimality of the design.

32

An Image Based Method of Finding Better Walking Strategies for Hexapod on Discontinuous Terrains

Engineering

Transcript of An Image Based Method of Finding Better Walking Strategies for Hexapod on Discontinuous Terrains