In this work, we present the design and the implementation of an innovative knee locking mechanism for a dynamically walking robot. The mechanism consists of a four-bar linkage that realizes a mechanical singularity for locking the knee when the leg is in the extended position. Once extended, the knee remains locked without energy consumption, while unlocking it only costs a small amount of energy. Tests showed that the robot walks robustly and that the energy consumption of the new system is low.

In this article we show that the concept of screws and wrenches gives us tools to geometrically establish the relation between the ground reaction wrench and the Zero-Moment Point. In order to arrive at this, we show how a wrench can be decomposed into separate components. The proposed method gives a general, completely coordinate-free way to find the ZMP and contributes in improving the geometrical insight.

The large number of degrees of freedom in legged robots give rise to complicated dynamics equations. Analyzing these equations or using them for control can therefore be a difficult and non-intuitive task. A simplification of the complex multi-body dynamics can be achieved by instantaneously reducing it to an equivalent single inertial entity called the locked inertia or the composite rigid body inertia.

This paper deals with the analysis of planar bipedal robots, based on passive dynamic walkers, which are actuated only by actuation of the ankle joints. An overview of the major design characteristics of such robots and their influence on the feasibility of a stable limit cycle is presented. It is shown that robots which are fully powered by ankle actuation require a mass ratio of at least 10:1 between the upper and lower limb to obtain sufficient ground clearance during the swing phase at a wide range of walking speeds. The effect and necessity of the offset in the footshapes of many passive dynamic walkers is shown and the influence of the moment of push off on the required energy injection is treated. The results of the analysis are supported by simulations with a dynamic model of such a robot. The simulated model exhibits a very natural looking gait and walks with a wide range of velocities at low mechanical cost of transport. Simulation results are provided which confirm that pushing off before the swing leg collides with the floor is energetically more efficient than pushing off after the impact as also known from previous literature.

A new method is presented for controlling the lateral foot placement of a simple 3D compass biped model. The method is based on the fact that, in the limit cycle, the gait is time-reversal symmetric and that, after a disturbance, the degree of asymmetry is indicated by a single variable. This variable is used for feedback with a proportional controller. Simulation results show that the controller works very well for a large range of gaits, without any adaptation of the parameter values