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