Gregor Harih

Finite element evaluation of the effect of fingertip geometry on contact pressure during flat contact

Several studies investigated the mechanical loads developing in the hands during the use of various products in order to enhance users performance, increase satisfaction and lower the risk of acute and cumulative trauma disorders. Values of pressure discomfort (PDT) and pressure-pain threshold (PPT) were, hence, provided. PDT and PPT may differ significantly for each subject and area of the hand because of psychological and physiological factors. A finite element study of the effect of fingertip anthropometry and anatomy geometry on mechanical loads developed during grasping is carried out in this research in order to assess physiological aspects behind variations of PDT and PPT existing between different subjects. It is found that the underlying anatomical structure and geometry (especially of the bone) significantly affect contact pressure distributions and pressure peak values. The largest difference in peak contact pressure between two different fingertips was in fact 27% for the same applied force. Furthermore, contact pressure distributions varied significantly between different subjects. The findings of this research provide novel insight into the phenomena of human grasping and the variation of contact pressure from subject to subject.

Justification for a 2D versus 3D fingertip finite element model during static contact simulations

Abstract The biomechanical response of a human hand during contact with various products has not been investigated in details yet. It has been shown that excessive contact pressure on the soft tissue can result in discomfort, pain and also cumulative traumatic disorders. This manuscript explores the benefits and limitations of a simplified two-dimensional vs. an anatomically correct three-dimensional finite element model of a human fingertip. Most authors still use 2D FE fingertip models due to their simplicity and reduced computational costs. However we show that an anatomically correct 3D FE fingertip model can provide additional insight into the biomechanical behaviour. The use of 2D fingertip FE models is justified when observing peak contact pressure values as well as displacement during the contact for the given studied cross-section. On the other hand, an anatomically correct 3D FE fingertip model provides a contact pressure distribution, which reflects the fingertip’s anatomy.

Development of a Finite Element Digital Human Hand Model

The aim of this research was to develop an anatomically accurate and numerically feasible and stable finite element digital human hand model, which would allow accurate bio-mechanical behavior during movement and grasping. Therefore, correct anatomical geometry of the hand has been defined based on CT images, which has been then used for the definition of the finite element model. Using the finite element software, material properties and boundary conditions have been defined to obtain accurate movement of the bones and deformation of the skin. The result of the conducted research is a developed angle-driven finite element digital human hand model, which is numerically stable. Using the accurate geometry and correct definition of the material properties and boundary conditions, the finite element digital human hand model shows reasonable bio-mechanical behavior under movement.

Finite Element Digital Human Hand Model-Case Study of Grasping a Cylindrical Handle

Products are becoming increasingly complex, therefore designers are faced with a challenging task to incorporate new or improved functionality, higher performance and optimal shape design. Traditional user-centered design techniques such as designing with anthropometric data do not incorporate enough user data to design better products for the target population. Measurements of contact pressure and contact area using traditional methods are time consuming and require actual product prototype and expensive measurement systems. In order to overcome these limitations, several researchers already proposed the use of computer simulations using finite element (FE) method. Therefore the aim of this research was to develop an anatomically accurate and numerically feasible and stable finite element digital human hand model with bio-mechanically accurate hand movement and grasping, which would allow virtual analyses of stresses on the soft tissue. The usability of the developed model is presented on a case study grasping a cylindrical handle.

Development of a Tendon Driven Finger Joint Model Using Finite Element Method

Due to certain demanding manual tasks the loads on the human hand can be high, which can cause several disorders, among which are also tendon disorders. Many researchers tried to quantify the loads and provide mathematical models for the tendons of the hand. Since experiments and measurements in vivo are complex and usually not viable, we developed a finite element model of a finger joint, which utilizes tendon/muscle force for the joint movement. Initial simulations of the fingertip finite element model with the developed tendon joint model have shown accurate biomechanical behavior of finger movement and soft tissue deformation. We also compared the results in terms of relationship between tendon force and resulting fingertip (reaction) force from the simulation to an in vivo experiment and have confirmed that the results of the developed finite element model correspond well to the experimental results.

Grasping Simulations Using Finite Element Digital Human Hand Model

When developing new handheld products, engineers must consider ergonomics to increase the human-product performance, comfort, and lower the risk of cumulative trauma disorders. Extensive knowledge and lack of computer aided design software in terms of hand ergonomics prevents the improvement of handheld product ergonomics. The main research topic is therefore prehensile hand grasp with a handheld object. The nature of the human hand has prevented direct measurements of stresses, strains, forces, and contact pressure on the hand during movement and grasping. Therefore, several researchers tried to develop a feasible digital human hand model for hand biomechanics and product ergonomics. In this paper we present a viable method to determine realistic human hand movement and use this data to drive the developed finite element hand model for usage in hand biomechanics and product ergonomics. The model geometry has been acquired using medical imaging and appropriate numerical model definition inside finite element software has been defined. Grasping techniques and hand movement were then recorded using motion capture system and were input into the model. Based on numerical tests, the model has proven to be numerically feasible and stable. It shows reasonable biomechanical behaviour of movement and soft tissue deformation and corresponds well with experiments of contact area and pressure measurement and tendon/muscle force.

Optimisation of Product’s Hand-Handle Interface Material Parameters for Improved Ergonomics

Most authors have focused on the sizes and the shapes of the product handles, but neglected those interface materials of the handles, which could further improve the ergonomics of the product. Therefore we utilized optimisation method to determine optimal interface material properties of a product for optimal mechanical response of the system using numerical simulations of a fingertip model grasping a product’s handle. Objective function was set to find material parameters in such way that the interface material of the product stays firm during low grasping forces to provide stability of the product in hands and deforms when a critical contact pressure is reached to provide higher contact area. This increases comfort and lowers the contact pressure on the hand and thereby the risk of injury development.

Intelligent support used for providing a pleasant user experience

This paper presents a prototype of intelligent advisory system based on the aesthetic factors regarding product design, with the emphasis on appurtenant design recommendations. Aesthetics certainly belong to the more complex design factors. Although some literature can be found about the aesthetic design of consumer goods, the designer still has to amass quite a lot of experience and knowledge in the field of aesthetics, in order to choose and carry out appropriate design actions for improving the aesthetic value of the product. The aim of the paper is not to discuss aesthetics from philosophical point of view, but to present problematic of aesthetics trough eyes of the mechanical design engineer, who is responsible for outer shape of the product already in conceptual design phase, where various influential factors determine the design.