Dynamic modeling of a biped has gained lots of attention during past few decades. While stability and energy consumption were among the first issues which were considered by researchers, nowadays achieving maximum speed and improving pattern of motion to reach that speed are the important targets in this field. Walking model of bipeds usually includes two phases, single support phase (SSP), in which only the stance foot is in contact with the ground while the opposite leg is swinging; and double support phase (DSP) in which the swing leg is in contact with the ground in addition to the rear foot. It is common in the simplified model of walking to assume the stance leg foot, flat during the entire SSP; but one may know that for human walking, there is also a sub-phase during SSP in which the heel of stance foot leaves the ground while the whole body is supported by toe link. Actually in this sub phase the stance leg foot rotates around the toe joint. This paper is trying to study the effect of toe-link and heel to toe walking model on dynamic and specially speed of walking compare to flat foot model.

Study of fast motion of bipeds is an interesting subject for researchers. It is well known that for a specified biped, with certain physical parameters and actuation capability, change of kinematic parameters of motion may change the speed of motion. Among such parameters are mean value of hip height, relative horizontal position of hip at the beginning and end of single support phase and top position of ankle and its relative horizontal position. This work presents a parameter study in which a phase-plane analysis for minimum time motion of a biped is used to find maximum speed of biped for different values of each parameter in one step. The frame work of minimum time solution is such that it fulfills zero moment point criterion for stability and friction condition for slippage prevention.

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