OSU ECE 5463 - Legged-Mobile-Robots (19 pages)

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Legged-Mobile-Robots



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Legged-Mobile-Robots

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Pages:
19
School:
Ohio State University
Course:
Ece 5463 - Introduction to Real Time Robotics Systems
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Mobile Robots Legged Take class notes Legged mobile robots Mobile robots are robots which can move There are two types of mobile robots Legged two four six and eight legs Wheeled one two three and four wheels Legged mobile robot has a longer history than manipulators Professor Robert McGhee developed the first walking machine at USC in the 1960 he later joined OSU At OSU he developed the hexapod walking robot Phony Pony OSU Hexapod Legged robots Legged robots were also developed by industry such as the Walking Truck by Ralph S Mosher of General Electric under a commission from the US Army in 1966 ASV adaptive suspension vehicle developed by OSU in the 80s Humanoid robots booming in recent years Honda ASIMO Japan Toyota Japan Toyota Japan SARCOS USA AIST Japan HUBO Korea Legged robot fundamentals Kinematics inverse kinematics and dynamics of legged robots are similar to robot manipulators but more complicated Consider the body as a mobile base and each leg as a manipulator ZB YB XB YN1 XN1 ZN1 ZF1 ZE YE XE YF1 XF1 You can attached a coordinate frame to each link of a limb using the Denavit Hartenberg convention do you still remember Control the motion You need to specify the motion of the body first The position and orientation of the body in the earth frame ETB t which is function of time Then you can specify the position and orientation of each foot with respect to the body according to the required body motion where m 1 2 3 4 5 or 6 nFmx n B TFm t Fmy nFmz 0 oFmx oFmy aFmx aFmy oFmz 0 aFmz 0 pFmx pFmy pFmz 1 The goal is to achieve ETB t through the motions of individual feet Collaborated motions of the feet form a gait Walking gaits Animals use a few types of gaits Walk trot run gallop difference Gaits are naturally designed to achieve both stability and efficiency In general animals use static or dynamic walking gaits difference Static center of gravity COG always falls in a supporting area Dynamic COG temporarily falls out of the supporting area periodically Running is dynamic Consider a quadruped gait using footprints COG projection Supporting area Right right left left Stability margin shortest distance between the COG and the boundary of the supporting area Foot in the air Right left left right Which one has better stability margin Use trot gait stability margin is small Direction of motion Duty factor Duty factor is the percentage of the a cycle which a foot is on the ground If the duty factor is greater than 50 a gait considered as walk while the one less than 50 is considered run For the two quadruped gaits the duty factor is greater than 75 walk RF right forelimb RH right hindlimb RF RH LH LF 25 50 75 100 Human biped locomotion The first paper on human biped locomotion I read is M Saunders V T Inman and H D Eberhart The major determinants in normal and pathological gait Journal of Bone and Joint Surgery Vol 35 A No 3 July 1953 The paper analyzes the human locomotion as a phenomenon of the most extraordinary complexity using connected rigid bodies for illustration six determinants in locomotion Human locomotion six determinants Compass gait Six determinants of human locomotion 1 Pelvic rotation The pelvis rotates about 4 in either direction during double support As a result the limbs are essentially lengthened in the would be lowest point of the gait cycle to prevent a large drop of the COG Pelvic tilt The pelvis on the side of the swinging leg tilts about 4 5 which lowers COG at mid stance Knee flexion at mid stance The bending of the knee reduces the vertical elevation of the body at midstance by shortening the hip to ankle distance Six determinants of human locomotion 2 Foot and ankle motion Ankle motions smooth the pathway of the COG during stance phase Knee motion When the ankle is depressed the knee extends and when the ankle is elevated the knee flexes Knee motion in this way smooths the pathway of the center of mass and thus conserves energy Lateral pelvic displacement Displacement of pelvic towards the stance foot to make sure that the COG is supported by the foot Human locomotion is much more complicated than we thought The purpose is to make your locomotion most efficient Humanoid robots Humanoid robot was first developed in Japan in 1973 In the U S first one was CURBi developed in 1986 WABOT 1 Wasada Un CURBi Robot now at OSU Zero moment point ZMP Zero moment point ZMP is a classical concept and has been used in the programing and control of humanoid robots for a long time It specifies a point about which the moments of the ground reaction forces the inertia force and the gravity forces are zero If the ZMP is in the supporting area the humanoid robot is stable otherwise it is not A humanoid robot cannot be in the none stable case for too long ZMP Equations Newton Euler equations The ground reaction force is responsible for providing the opposite direction Since ZMP if in and is related to the reference point X the point Z is defined as F 0 n y Ground reaction force ZMP x Legged robot examples Hubo crosses over 2x4 and 4x4 bars Legged robot examples


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