Multi-disciplinary Design Optimization for Human Well-Being

Gino Duffett, Hiram Badillo (APERIO), Sylvain Carbes, Arne Kiis (AnyBody Technology)

Human well-being and system performance is a multi-faceted field that often requires optimisation within the field of ergonomics. The simulation software AnyBody Modelling System provides a useful tool for analysing the muscular-skeletal system of humans (and animals) that for given movements allows computing muscle forces, joint reactions, metabolism, mechanical work and efficiency. The use of this analysis tool permits us to quantitatively analyse movement patterns, working positions and anthropometric data, which in turn enables automatic optimization to be carried out.







This paper briefly describes the use of the modeFRONTIER optimization software integrating the AnyBody muscular-skeletal software to carry out optimizations relating to the human body for the design of components for the automobile and medical/rehabilitation sectors.

Even simple model problems like these are too complicated to be thoroughly investigated by experimental methods and therefore automatic optimization methodologies are the solution.

Accelerator pedal design (automotive)
According to the automotive industry a good pedal design should provide an effortless and yet precise operation. Consider a pedal hinged at one end and equipped with a torsion spring that stretches when the pedal is depressed. The dilemma is that if the spring is too weak, then the pedal will not provide much support for the leg, and the operator consequently has to extend the leg and hold it up against gravity, this will become very tiring. On the other hand, if the spring is too rigid, then the muscular effort of depressing it will become too large and repetitive operation of the pedal or static maintenance of a particular pedal position will cause fatigue. Similarly, different seat positions influence the muscular effort.

Coupling the AnyBody muscular-skeletal modelling software inside the modeFRONTIER optimization software it is possible to perform a systematic optimization to find the best solution of the spring stiffness and the seat position to reduce the muscular effort. It was found that the vital parameter is the pedal spring stiffness, almost irrespective of the distance of the seat from the pedal, since the correlation factor between muscle activity and the spring stiffness is 0.66, meanwhile for the case of the pedal distance is only 0.1.

Wheel chair optimization (medical/rehabilitation)
A very large proportion of wheelchair users experience load-induced shoulder pain. This happens after several years of use, and it can be a very serious condition for an individual relying entirely on the arms for ambulation. The wheelchair parameters such as wheel diameter, push-rim position, axle position, and camber influence the shoulder forces during use. But precisely how? The model investigates the gleno-humeral joint forces as a function of the axle position through a forward push on the push-rim. This is done via the model parameters: seat height relative to the axel, and seat position as the forward distance between the pelvis and axes.

The problem was integrated into modeFRONTIER to find the optimum design producing the least shoulder force. The optimised results indicate that even a slight movement of the seat can be important to the forces required to move the wheelchair. Comparing with the original design we obtained a reduction of 22.4 % in the shoulder force by lowering the seat height by 64mm and moving the seat position backwards by 92.4mm.