Such a two-legged body is known from the European patent application EP-A-0 531 731. The known device com- prises two legs which are pivotably fastened at their top end to a horizontally oriented axis and in which each leg at its other end is provided with a foot having an arched surface. The known body is further provided with a pendu- lum also fastened to the axis, which can be made to oscil- late and which in association with a traction force exerted on the known body, is able to provide the body with a movement by reciprocally moving its legs in counter phase, so that the two-legged body makes a walking movement.

A first disadvantage of the known two-legged body is that for the locomotion it is necessary to provide a separate traction force, as the oscillatory motion only suffices to cause the reciprocal movement of the two legs of the body. If such a force is not supplied separately, it can be provided by placing the known body on a sloping surface, so that the known body is provided with a force component in the horizontal plane, thereby allowing the body to move. A second disadvantage of the known two- legged body is that the walking movement is decided once the geometry of the body has been chosen.

The object of the invention is to provide a two- legged body that is able to carry out a walking movement without requiring the provision of a traction force other than the oscillatory motion, in such a manner, that the

energy for locomotion is derived from the autonomous oscillation energy.

To this end the two-legged body according to the invention is characterized in that the oscillation element comprises at least two springs for the generation of anta- gonistic forces, that the springs each are coupled at one side with a leg, and that together with the mass present in the body they are able to form a vibrating mass-spring system, and that the spring stiffness of at least one spring is adjustable. By this measure a two-legged body is provided with legs whose reciprocal movement from which the walking movement is derived, is to a large extent adjustable. The adjustment or alteration of the spring stiffness directly influences the frequency at which the mass-spring system preferentially vibrates. In addition, the alteration of the spring stiffness gives impetus to the mass-spring system, so that such an alteration pro- duces energy from which the locomotive energy of the body can be derived. The amplitude of the vibration of the mass-spring system is also determined by the measure in which the spring stiffness is altered during operation. A large number of aspects of the two-legged body according to the invention can be controlled in this way without the need to provide motors and servo systems which are known as such, for the realization of the desired controllability. Due to the fact that such provisions may be absent, the known two-legged body can be embodied such as to be relatively light, thereby limiting the energy requirements and making the two-legged body very suitable for robotic and rehabilitation purposes. It should be noted that the body according to the invention can also be constructed with only one spring, in such a manner that to provide the antagonistic force for said spring, use is made of the gravitational force. However, compared with the embodiment with two springs, such a construction appears to be less flexible.

A workable embodiment producing a locomotive rhythm that for two-legged bodies appears very natural is charac- terized in that at the side facing away from the coupling

with the leg, each of the springs is coupled with the con- necting element, and that the springs are arranged at both sides of the leg.

This may be realized particularly simply if the connecting element is embodied with a cylindrical rotating spool, via which rotating spool a connecting cable or strip is led which is connected at both its ends with the two springs.

The locomotion of the two-legged body according to the invention may be suitably advanced by an embodiment in which each of the legs is mounted on an individual auxili- ary frame, each auxiliary frame is rotatably mounted on the connecting element, and each leg is adjustable in the longitudinal direction of its auxiliary frame. This pro- vides the two-legged body, again in a natural manner, with a propelling force the moment the reciprocal movement of the respective leg is virtually completed but is still just in contact with the supporting surface from which said leg can push off.

The invention will now be explained in more detail with reference to the drawing which in Fig. 1 and 2 shows a non-limiting exemplary embodiment in front and side view of the two-legged body according to the invention.

Identical parts in the Figures are identified by the same reference numbers.

The two-legged body 1 according to the invention comprises two legs 2,3, an oscillation element 4,5,6, and a connecting element 7 for the mutual coupling of the legs 2,3 and the oscillation element 4,5,6. The legs 2, 3 are pivotable in relation to the connecting element 7, and during operation may undergo a reciprocating angular displacement in relation to the connecting element 7, sub- ject to the oscillation element 4,5,6. The oscillation element 4,5,6 comprises, for example, at least two springs for the generation of antagonistic forces. Each spring 4,5 is coupled at one side with a leg 2,3, form- ing together with the body 7 a vibrating mass-spring sys- tem. Each of the springs 4,5 has an adjustable spring stiffness. So-called McKibben muscles can be conveniently

used for this purpose. Alternatively, the spring stiffness of one of the springs 4,5 may be adjusted to a permanent setting so that only the spring stiffness of the other spring 4,5 is adjustable. The spring that is permanently adjusted may then be replaced by a construction in which the gravitational force is utilized to provide an antagon- istic force in relation to the adjustable spring. At the side facing away from the coupling with the leg 2,3, each of the springs 4,5 is coupled with the connecting element 7, so that the springs are arranged at both sides of the leg 2,3. Preferably the connecting element 7 is embodied with a cylindrical rotating spool 8, and over said rotat- ing spool a connecting cable or strip 6 is led which is connected at the two extreme ends with the two springs 4, 5 and may be connected therebetween, at point 13, with rotating spool 8. Each of the legs 2,3 is mounted on an auxiliary frame 9 which is rotatably mounted on the con- necting element 7. Each leg is adjustable in the longi- tudinal direction of the auxiliary frame 9. This may be realized by means of a spring system 10,11, whereby acti- vation of the spring 10 causes its contraction, thereby moving part 12 in the direction of arrow A, so that the leg 2,3 coupled with part 12 is moved away from the con- necting element 7. When the spring member 10 is released, the force of the spring 11 causes the leg 2,3 to move in the opposite direction.

The two-legged body can be used in a variety of embodiments. The preceding description merely serves as elucidation of the invention as specified in the appended claims. The two-legged body according to the invention is suitable for application in the entertainment industry, in the robotic technology, or in the medical technology for the provision of ortheses or protheses.