Title: Biorobotic design criteria for Innovative Limb Prosthesis
Author: prof. Alberto Rovetta N. AC-1

D.A. Winter Biomechanics and motor control of human movement, Wiley-Interscience Publication, 1990

The aim of the research work carried out is to design and develop a prosthesis with the kind of energy store that would enable an amputee to perform almost the same type of (even complex) movements as those performed with a natural limb.

The decision to launch a new system in the high tech devices sector involves the undertaking of a process that is generally not only long and costly in cognitive terms but which also involves various stages: When developing the first K3 knee design, our aim was to simulate as closely as possible the physiology and kinematics of natural joints, by employing joined profiles for the condyle function and connecting rods for that of crossed ligaments. Two ligaments, referred to on account of their position as "crossed ligaments", may be found in the middle of the knee-joint. In the front part of the joint, the antero-external (LCAE) crossed ligament is the most anterior on the tibia and the most external on the tibia. Behind the antero-external crossed ligament there is the postero-internal crossed ligament (LCPI), which is the most posterior on the tibia and the most internal on the femur. There is, however, a difference in inclination between the crossed ligaments. When the knee is extended, the antero-external crossed ligament is the most vertical whilst the postero-internal crossed ligament is the most horizontal.

Since the aim of sensors is to give to the control system an image of the reality in a defined moment, every part of the prosthesis must be sensorized in a functionality way, giving so to each element of the prosthesis a sensor which will gather the condition of the part connected to his function in the prosthesis economy. The knee angle of rotation is identified by the output in a potentiometer connected to the rotation of a rod. The average speed of knee rotation over a fixed time is obtained from rotation sampling. Since the sampling interval is constant, once the rotation value in a certain instance has been stored, an average rotation speed index is provided by the difference between the current rotation value and the previous one. The compression and bending measurement in the artificial tibia is given by two strain-gauge bridge circuits (suitably compensated), placed on the aluminium element comprising it. The presence of a vibration sensor positioned on the stump permits ascertainment of the position and movement of the femur. TLC

Future possible developments
Since the sensorisation level for the prosthesis is high, it is necessary to operate from outside onto the edge electronics in order to make calibration and diagnose operations. A telecontrol system designed ad hoc, very simple but extremely versatile, permits to simplify the software realization for the data transmission between leg and computer control. As a matter of fact the programming step can be done ignoring which will be the data transmission channel, concentrating exclusively on their control; the telecontrol system will then put on their way the data transmitted on the analogical telephone line or, theoretically, ISDN or GSM. Test sessions show the system functionality with these technology; nevertheless it is yet fully operating with analogical line). The device tries to obtain the maximum advantage from the existing technology, and to make up, with a simple stratagem by hardware/software, for the ignored software of the artificial leg. The device is characterized by the maximum portability together with the minimum cost.