Some models of virtual prototypes device for leg orthoses.

Barbu, Ion ; Barbu, Daniela Mariana ; Lache, Simona 等

1. INTRODUCTION

An orthosis is a device used to support a weakened, unstable, injured or overloaded part of the body. There are orthoses for the back, the arm and shoulder, the lower limb, the neck and so on. Many types are produced just for the foot. Even a small custom made shoe insert which appears simple to the eye is the end result of a process of carefully matching a product to the specific needs of the recipient. We fabricate custom orthoses which are anatomically matched to each patient. Each custom made or custom fitted orthosis is prepared following a prescription by a physician.

Orthotics is an allied health care medical profession or field that is concerned with the design, development, fitting and manufacturing of orthoses, which are devices that support or correct musculoskeletal deformities and/or abnormalities of the human body. The term is derived from the "ortho", meaning to straighten. Sciences such as materials engineering, gait analysis, anatomy and physiology, and psychology contribute to the work done by orthotists, professionals engaged in the field of orthotics. Individuals who benefit from a complex orthosis may have an orthopedic condition such as scoliosis or a fracture or have sustained a physical impairment from a stroke or spinal cord injury, or a congenital abnormality such as spina bifida or cerebral palsy.

The professionals listed above: doctors and therapists, along with ancillary clinical support personnel, also can be found fitting orthotic devices. The orthotist generally works by prescription. Some prefabricated orthoses can be found in a pharmacy. Some prefabricated orthoses, or supports, are soft and can be purchased as a retail item. Care in proper fit of any device that applies force to the body must be taken to ensure good results and to prevent unwanted problems from an orthosis that is too tight or otherwise uncomfortable.

2. ORTHOSES FUNCTION

Foot orthotics takes various forms and they are constructed of various materials. All have the goal of improving foot function and minimizing stress forces that could ultimately cause foot deformity and pain. There are three broad categories of orthotics: those that primarily attempt to change foot function, those that are mainly protective or accommodative in nature, and those that combine functional control and accommodation. While orthotics can be made by several different processes, most orthotist's make a plaster mold of the patient's foot and send it to a laboratory with a prescription. At the lab, technicians pour plaster into the mold, and when it hardens; it exactly reproduces the bottom of the individual's foot, although it is common for labs to "cast correct" by partially filling in the arch. This decreases the arch height of the orthotic and is done for comfort reasons.

Rigid orthotic devices are designed to control foot function, and may be made from a firm material such as plastic or carbon fiber. These types of orthotics are mainly designed to control motion in two major foot joints, which lie directly below the ankle joint. This type of orthotic is often used to improve or eliminate pain in the legs, thighs and lower back due to abnormal function of the foot.

Soft orthotic devices help to attenuate shock, improve balance and take pressure off uncomfortable or sore spots. They are usually made of soft, compressible materials. This type of orthotic is effective for arthritis or deformities where there is a loss of protective fatty tissue on the side of the foot. They are also helpful for diabetic people.

Semi-rigid orthotic devices are often used to treat athletes. It allows for dynamic balance of the foot while running or participating in sports. By guiding the foot through proper functions, it allows the muscles and tendons to perform more efficiently. It is constructed of layers of soft materials, reinforced with more rigid materials.

Calibrated orthotic devices are those based on the correction model and manufacturing technique advocated by Glaser (MASS position). It factors in the individual's body weight, foot flexibility and activity level to deliver a custom calibrated level of support that delivers firm but comfortable functional control while maintaining the properties of an accommodative device. (http://en.wikipedia.org/)

3. THE VIRTUAL PROTOTYPES OF ORTHOSES

One of the most important for virtual prototyping concept is to test as it simulates. Physical testing of prototypes in classical (traditional) laboratory tests and field in various configurations, resulting in high costs and time. The virtual prototyping concept it's used to reproduce the test procedures and operating conditions of the product at much lower cost and time. Virtual Prototyping allows building models that simulate the actual operation of the product, for example facilities (stands) for testing any type of dynamic system. Testing is an important component of virtual prototyping during the design cycle. Virtual testing is performed continuously while the physical testing is introduced only in certain stages to model virtual revalidated after a finishing significant.

To simulate the dynamics of orthoses's mechanical system was used a specialized software MBS (multi-body systems) and this software involves going through three stages:

* preprocessor (modeling system);

* processing (model run);

* postprocessor (processing results).

In mechanical systems using dynamic simulation are frequently addressed three working models:

* kinematic model, which, in addition to the structural and geometric parameters includes defining the system and to establish laws of motion (position, speed and acceleration) of elements in the movement of time (known / required) element leader;

* dynamic model, which, in addition to the kinematic model, and contains the mass of elements (mass, moments and products of inertia) and the forces (external and internal) acting on the system, this model determines the movement elements under the action of forces.

In this case was creating two model orthoses device with particular design and functionality. For choose the optimizing model to be made for laboratory testing we make two virtual prototypes using CAD models and MBS software, figure 1 and 2. (http://www.lmsintl.com/)

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

The steps followed are:

* design CAD models to the orthoses's mechanical system components;

* have been calculated, using MBS software, the inertial mass characteristics, all body's mass and center of mass position;

* was the connection between bodies (geometric restrictions in body movement) - the geometric restrictions in the movement of bodies used cylindrical kinematics joint;

* introduced a law of movements to mobile body using a hyperbolic function which be calculate the torque which needed and the tasks that occur in the joint. (http://www. mscsoftware.com/)

For simulate we use the law of motion type hyperbolic for enforce the dynamic movement for the virtual prototypes and makes the graphics for forces and torques from the principal joints. The graphics can be seen in fig.3. There appear the maximal and minimal values for virtual prototype devices from fig. 2(we concentrate more for device from fig. 2 because it's more easy and cheaper to manufacture it), which is necessary for us to evaluate the power of the electrical motor which can doing the movements of this device when we manufacture the real prototype.

[FIGURE 3 OMITTED]

4. CONCLUSION

After the virtual prototypes simulations reached the following conclusions: each of the models are functional and they will be manufacturing for laboratory testing in real mode, and most important is the values of forces and moments calculated from mechanic system which are necessary for choose the electrical motors for orthoses motion. Use the result of simulations the mechanical system of those devices can be operable with an electrical motor with follows characteristics:

--12 [V] Voltage Power, 17 [W] Power, 1.2 [Nm] Max Torque and 20 [rot/min] Speed.

5. ACKNOWLEDGMENT

This research is the main object of the IDEI Program Project ID_147 (2007-2010), hence the paper is financed from this project's budget.

6. REFERENCES

Barbu, I.; Barbu, D.M. (2009). Design a prototype for rehabilitation orthotic device, Proceedings of Annals of the ORADEA University, pp.96-99, ISSN 1583-0691, Oradea-28-May-2009.

Barbu, D.M. & Barbu, I. (2009). Dynamical Model for an Original Mechatronical Rehabilitation System, The 8th WSEAS InternationalbConference on System Science and Simulation in Engineering, Genova, Italy, October 17-19, 2009, pp 626-273

*** http://en.wikipedia.org/, Accessed on: 2009-09-09

*** http://www.lmsintl.com/, Accessed on: 2009-09-09

*** http://www.mscsoftware.com/, Accessed on: 2009-09-09