1. Yoshihiro NAKATA Intelligent Robotics Laboratory Dep. of Systems Innovation Graduate School of Engineering Science Osaka University T OWARD R EALIZING H OPPING OF M ONOPEDAL R OBOT BY C OMPLIANCE C ONTROL --- Development and application of an electromagnetic linear actuator --- The 28th Brush-up School of GCOE: Cognitive Neuroscience Robotics Feb. 17th, 2011

2. Introduction Electromagnetic Linear Actuator for Artificial Muscle Planer Biped Robot How can robot realize dynamical motion in complicated environment? Athlete Robot Actuator is the key device: Robust for disturbance Impact absorption Low processing cost

3. Important factors of actuators for robots Electromagnetic Linear Actuator for Artificial Muscle Large output force Small size ・ Actuator + Controller + Power source Change spring and damper characteristics Quick response It is difficult to realize variable viscoelastic characteristics in small system x spring dumper actuator

4. Variable compliance actuator Electromagnetic Linear Actuator for Artificial Muscle This actuator can change spring and damper characteristics Quick response Small system ・ Electric power Interaction with human 180mm φ20 Weight: 170g Force: 5.7N/A (Effective current 1A)

5. The electromagnetic linear actuator Electromagnetic Linear Actuator for Artificial Muscle Basic structure ・ The effective radial component of flux with an inward and outward direction from the magnetic core ・ The structure of the mover can generate high magnetic flux High power ・ The mover is robust structure Stator Mover This actuator can control output force by controlling exciting current depending on the position of the mover.

6. Hopping of Monopedal Robot Electromagnetic Linear Actuator for Artificial Muscle

7. Concept of the monopedal robot Electromagnetic Linear Actuator for Artificial Muscle Variable compliance actuator Electromagnetic linear actuator In this research, we focus on controlling stiffness in hopping x spring dumper actuator Implement the actuator as bi-articular muscle to the monopedal robot Control the stiffness ellipse at foot of the robot Simple control method is proposed

8. Structure of the human leg Electromagnetic Linear Actuator for Artificial Muscle Pelvis Femur Tibia Fibula Calcaneus Hip Knee Hip Knee Patella

9. Stiffness ellipse Electromagnetic Linear Actuator for Artificial Muscle Hip Knee Control the direction by adjusting axes The stiffness of the leg is expressed as ellipse and its gradient of long axis Stiffness ellipse Hard Soft The major axis of the stiffness ellipse is oriented along the direction of maximum stiffness The minor axis of the stiffness ellipse is oriented along the direction of minimum stiffness

10. Relationship between stiffness ellipse and stiffness of muscles Electromagnetic Linear Actuator for Artificial Muscle The stiffness of f 1 e 1 become large The stiffness ellipse rotates in the clockwise direction The foot move backupward and the robot leans forward Hard Stiffness ellipse at foot Mono-articular muscle

11. Relationship between stiffness ellipse and stiffness of muscles Electromagnetic Linear Actuator for Artificial Muscle Hard The stiffness of f 2 e 2 become large The stiffness ellipse dose not rotate Stiffness ellipse at foot Mono-articular muscle

12. Relationship between stiffness ellipse and stiffness of muscles Electromagnetic Linear Actuator for Artificial Muscle Hard The stiffness of f 3 e 3 become large The stiffness ellipse rotates in the counter clockwise direction The foot move foreupward and the robot leans backward Stiffness ellipse at foot Bi-articular muscle

13. Control of the bouncing direction (Simulation) Electromagnetic Linear Actuator for Artificial Muscle Hopping direction [°] Stiffness (f 3, e 3 ) [N/m]Stiffness (f 1, e 1 ) [N/m] Evaluate the relationship between bouncing direction and stiffness Stiffness f 3, e 3 > f 1, e 1 Stiffness f 1, e 1 > f 3, e 3

14. Monopedal robot with electromagnetic linear actuators Electromagnetic Linear Actuator for Artificial Muscle We will do experiment using this robot. Beam Counter weight > In the simulator, weight and inertia of monopedal robot are considered A 1 (M 1 ) A 3 (M 3 ) A 2,1 (M 2 ) Hip Knee A 2,2 (M 2 ) 210mm Weight:1.2kg

15. Hopping of the robot (Simulation) Electromagnetic Linear Actuator for Artificial Muscle Ground kckc Touch down 130ms Stiffness [N/m] kmkm Time[s] Take off f 1, e 1 f 3, e 3 f 2, e 2 Control the bouncing direction: Distribute jumping energy: Actuator ( f 1, e 1 ) = 500 [N/m] Actuator ( f 3, e 3 ) = 340 [N/m] k c =310 [N/m] k m =370 [N/m]

16. Hopping of the robot (Simulation) Electromagnetic Linear Actuator for Artificial Muscle 0 x y x y Return map Hip position

17. Conclusions Electromagnetic Linear Actuator for Artificial Muscle Development of the electromagnetic linear actuator as a variable compliance actuator Stiffness ellipse is controllable Variable stiffness reduces complexity of control rule Experiment using the prototype Control bouncing direction in hopping Evaluate the effect of viscosity properties for stable hopping Future works