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Human and Humanoid Dynamics

Profile image of Veljko PotkonjakVeljko Potkonjak

2004, Journal of Intelligent and Robotic Systems

https://doi.org/10.1023/B:JINT.0000049169.28413.DF
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Abstract

The questions when and why one needs to use mathematical models, and especially the models of dynamics, represent a still unresolved issue. A general answer would be that dynamic modeling is needed as a tool when designing structure of the system and its control unit. In this case we talk about simulation. The other application is in on-line control of the system – the so-called dynamic control. While for simulation one should generally use the best available model, the control can be based on a reduced dynamics, depending on a particular task. This article considers humans and humanoid robots and addresses a rather important question: what are dynamic effects that one should take care of when modeling and simulating a human or a humanoid? The article suggests the key topics for work and tries to justify them. As a final result a General Human/Humanoid-Dynamics Simulator is seen.

Figures (15)
Figure 1. Active exoskeleton for paraplegics (““M. Pupin” Institute, 1972).
Figure 1. Active exoskeleton for paraplegics (““M. Pupin” Institute, 1972).
Figure 2. WABIAN — humanoid robot built at Waseda University.
Figure 2. WABIAN — humanoid robot built at Waseda University.
Figure 3. HONDA humanoid robot.
Figure 3. HONDA humanoid robot.
ground reactions and friction force are important effects in the system dynamics. The open-chain model is used in single-support phase and the closed-chain model for the double-support phase. As an example, we show the form used for single- support phase,
ground reactions and friction force are important effects in the system dynamics. The open-chain model is used in single-support phase and the closed-chain model for the double-support phase. As an example, we show the form used for single- support phase,
3.1.1. Mechanisms used for modeling must have an anthropomorphic form, that is legs, trunk and arms. It is suggested that the structure should be redundant, meaning that the model can walk and perform manipulation in different manners. This will make the synthesis of motion more complex since, in addition to the stability condition, one will need additional criteria to compensate for the surplus of DOFs. If GHDS is applied to human mechanism, no justification is needed (simply, humans possess redundancy). In the case of humanoid robots, justification for this additional effort comes out from the fact that redundancy gives humans flexibility in executing tasks (avoiding obstacles, avoiding joint limits and singular positions, replacing exhausted actuators by others, improving dynamics capabilities and abil- ities to react in unpredicted situations) and new generation of robots should possess some of these properties. The background for the research in redundancy is rather rich, from pure robotic to pure biological studies.
3.1.1. Mechanisms used for modeling must have an anthropomorphic form, that is legs, trunk and arms. It is suggested that the structure should be redundant, meaning that the model can walk and perform manipulation in different manners. This will make the synthesis of motion more complex since, in addition to the stability condition, one will need additional criteria to compensate for the surplus of DOFs. If GHDS is applied to human mechanism, no justification is needed (simply, humans possess redundancy). In the case of humanoid robots, justification for this additional effort comes out from the fact that redundancy gives humans flexibility in executing tasks (avoiding obstacles, avoiding joint limits and singular positions, replacing exhausted actuators by others, improving dynamics capabilities and abil- ities to react in unpredicted situations) and new generation of robots should possess some of these properties. The background for the research in redundancy is rather rich, from pure robotic to pure biological studies.
Figure 6. Flexible joint — elastic deformation in torque transmission. It is not easy to justify the introduction of such effects. One argument is that de- formation in transmission really takes place (smaller in some kind of transmission and larger with others — like harmonic drive). A counterargument is that flexible transmissions can be avoided by the appropriate design.* Another viewpoint is that joint flexibility may be introduced intentionally to absorb impact stress. If this effect is to be taken into account, one may rely upon experience and results from industrial robotics.
Figure 6. Flexible joint — elastic deformation in torque transmission. It is not easy to justify the introduction of such effects. One argument is that de- formation in transmission really takes place (smaller in some kind of transmission and larger with others — like harmonic drive). A counterargument is that flexible transmissions can be avoided by the appropriate design.* Another viewpoint is that joint flexibility may be introduced intentionally to absorb impact stress. If this effect is to be taken into account, one may rely upon experience and results from industrial robotics.
Figure 7. Deformable sole: deformation has six components; two components are demon- strated.
Figure 7. Deformable sole: deformation has six components; two components are demon- strated.
Figure 8. Deformable support: deformation has six components; two components are demon- strated.
Figure 8. Deformable support: deformation has six components; two components are demon- strated.
Figure 9. Sportsman on a trampoline — two examples.
Figure 9. Sportsman on a trampoline — two examples.
Figure 10. ZMP position: (a) for stable movement (position of the ground reaction); (b) the case of instability — overturning (fictitious point where reaction should act in order to stabilize the motion).
Figure 10. ZMP position: (a) for stable movement (position of the ground reaction); (b) the case of instability — overturning (fictitious point where reaction should act in order to stabilize the motion).
It is clear that the platform can be modeled in different ways; we mention two options. A sequential (linkage) structure may be used to construct the platform. [n this case, well-known algorithms used for linkages can be applied to formulate the dynamic model. The other constructive approach (perhaps primarily expected) refers to the use of special platform structures (e.g., Turin platform [14]), as shown in Figure 12. The mentioned two options may be applied even if the moving support is of some different kind (boat for instance); in this case the suggested platform mechanisms are just models of a true system.
It is clear that the platform can be modeled in different ways; we mention two options. A sequential (linkage) structure may be used to construct the platform. [n this case, well-known algorithms used for linkages can be applied to formulate the dynamic model. The other constructive approach (perhaps primarily expected) refers to the use of special platform structures (e.g., Turin platform [14]), as shown in Figure 12. The mentioned two options may be applied even if the moving support is of some different kind (boat for instance); in this case the suggested platform mechanisms are just models of a true system.
Figure 12. Turin platform system. ee, a What is the form of ‘the dynamic model that covers the introduced dynamic phenomena? The “basic” model formulated above is augmented by introducing new DOFs (due to platform motion and different flexibility effects). Let them form the vector p = (P1, P2, p3,...). The subvector p, describes the position of the platform (six components) and the subvectors p2 and p3 (six components each) regard deformation in the contact zone (on the foot side and the platform side). Additional position coordinates should be introduced in the case of sliding. Some of these additional DOFs are powered and some are not. Following the earlier stated form of single-support-phase model, the set of differential equations is:
Figure 12. Turin platform system. ee, a What is the form of ‘the dynamic model that covers the introduced dynamic phenomena? The “basic” model formulated above is augmented by introducing new DOFs (due to platform motion and different flexibility effects). Let them form the vector p = (P1, P2, p3,...). The subvector p, describes the position of the platform (six components) and the subvectors p2 and p3 (six components each) regard deformation in the contact zone (on the foot side and the platform side). Additional position coordinates should be introduced in the case of sliding. Some of these additional DOFs are powered and some are not. Following the earlier stated form of single-support-phase model, the set of differential equations is:
Figure 14. Example of a balanced motion on one foot — a karate kick.
Figure 14. Example of a balanced motion on one foot — a karate kick.
Figure 15. Skiing — balanced motion with sliding.
Figure 15. Skiing — balanced motion with sliding.

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