The power generated in the actuation box is guided to a structure consisting of two aluminum plates which are joined moveable to a linear bearing. These two plates are joined to each other and represent thigh and shank of a human leg.

The Bowden cable is fixed to the thigh. So it has to be guided around the knee in invariable distance to create a torque which moves the leg up and down by varying the knee angle. To hold the distance between the joint and the Bowden cable equal and create this torque, a pulley is non-revolvable fixed to the thigh with two screws (Abb. 1). Its diameter is 68 mm.

<imgcaption image1|Leg with pulley> </imgcaption>

The leg has three rotational joints: One at the knee and two at the ends of the aluminum plates. They represent hip joint and ankle joint of a human leg. These rotational joints are realized by roller bearings of the company SKF. The outer diameter of the bearings is 19 mm.

The bearings on hip and ankle are connected to carriages of a linear bearing with small shafts which are screwed into these carriages.

To prevent the leg from tipping over and to allow it only to move in one axis (perpendicular to the floor), the leg has to be leaded by a linear bearing. This bearing is the same type like the ones in the actuation box.

On the rail of the bearing are two carriages: One for the hip of the leg and one for the ankle.

The linear bearing is fixed to an aluminum profile of the company “Item Industrietechnik GmbH”. The profile size is 40×40 mm (Abb. 2). Its characteristics are the same like the profiles of the actuation box.

<imgcaption image2|Cross-section of aluminum profile 40×40 mm. Source: Item Industrietechnik GmbH> </imgcaption>

The leg consists not only of parts which represent a human leg, but also of a linear bearing to pre- vent the leg from falling down. The bearing is connected to an aluminum profile. The whole structure is fixed to the frame of the actuation box with an angle bracket. To increase the stiffness, the upper end of the leg is fixed to an aluminum profile which is connected to the frame, too. Abb. 3 shows the whole structure of the leg.

<imgcaption image3|Leg. 1: thigh, 2: shank, 3: pulley, 4: ankle, 5: hip, 6: sensors, 7: frame> </imgcaption>
Thigh and shank consist of aluminium plates with 5 mm thickness. In these plates are holes for the roller bearings. The two adapters for the Bowden cable are fixed on them with screws, one on the thigh and one on the shank. The wire of the Bowden cable is fixed to one adapter on the thigh, the shell to the one on the shank.

To prevent the carriages from rolling off the bearing, on both ends of the rail are horse-shoe-shaped bedstops. They are fixed to the aluminum profile with screws and T-slot-nuts (Abb. 4).

Small shafts are screwed into adapters which are fixed to the carriages to carry the roller bearings. They ensure the rotational motion of the joints. The bearings are fixed with circlips.

<imgcaption image4|Ankle joint at end stop> </imgcaption>

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