A constructive arrangement applied to a foot prosthesis manufactured with elastic and shock-absorbing characteristics, and its method for quantifying mechanical energy to be reused.

Abstract

The present invention relates to a foot replacement prosthesis in cases of amputation, composed of a single piece made of material and in a shape designed to increase cushioning areas and provide a larger zone of elasticity, minimizing the impacts of walking. Furthermore, the total height of the prosthesis is close to the geometric limits of the non-amputated foot. The hindfoot has an "hourglass" geometry, in addition to the plantar arch structure. It also features a system for quantifying the potential energy of mechanical energy resulting from direct contact of the prosthetic foot with the ground during walking, which can be transformed into other types of energy. The constructive arrangement applied to a foot prosthesis manufactured with elastic and cushioning characteristics, and its method for quantifying mechanical energy to be reused, is described.The fact that the total height of the prosthesis is close to the geometric limits of the non-amputated foot makes it smaller compared to currently marketed ESR-type models. This difference allows for its use in articulated or active ankle prostheses.

Description

A constructive arrangement applied to a foot prosthesis manufactured with elastic and shock-absorbing characteristics, and its method for quantifying mechanical energy to be reused. FIELD OF THE INVENTION

[001] The rehabilitation of people who have suffered lower limb amputations mostly involves the use of prostheses. In the context of assistive technology, the present invention relates to a prosthesis used to replace an amputated foot. Due to its elastic and cushioning characteristics, it allows the user to perform a greater range of movements and physical efforts. The development process was based on numerical simulations using finite elements. The results presented show that the use of this method enabled a reduction in the number of physical manufacturing cycles. The present invention provides an improvement in the quality of life of the user with transtibial or higher degree of amputation. STATE OF THE ART

[002] Amputation is a serious condition that can drastically affect a person's quality of life, as it results from the surgical or traumatic removal of a body segment, which may be total or partial (SANTOS, ICRV et al. Factors associated with diabetic foot amputations. Jornal Vascular Brasileiro, scielo, v. 14, p. 37-45, 03 2015. ISSN 1677-5449. 1; DELEA, S. et al. Management of diabetic foot disease and amputation in the Irish health system: a qualitative study of patients' attitudes and experiences with health services. BMC Health Services Research, BMC Health Services Research, v. 15, p. 251, 2015. 1; GARLIPPE, L. Epidemiological study of patients with lower limb amputation treated at the regional rehabilitation center of Araraquara, São Paulo state, Brazil. Dissertation (Master's) - Faculty of Medicine, Ribeirão Preto, 2014. 1).

[003] The most common causes of limb amputations are: Petition 870170045511, dated 06 / 29 / 2017, page 7 / 44 2 / 18 • Peripheral vasculopathies, which affect between 70% and 80% of amputees (BRAZIL, Ministry of Health. Guidelines for the care of amputees. 1st ed. Brasília: Ministry of Health, 2013. v. 1. 36 p. ISBN 978-85-334-19810. 1); • Traumatic injuries, which affect a significant number of people due to traffic and workplace accidents; • Malignant bone tumors such as osteosarcoma, which is the most common bone tumor occurring in children and young adults with a prevalence in adolescents (ENE, R. et al. Proximal tibial osteosarcoma in young patients: early diagnosis, modular reconstruction. Romanian Journal of Morphology and Embryology, RJME, v. 56, n. 2, p. 413-417, 2015. 1); • Congenital skeletal defects.

[004] The main levels of lower limb amputations are: Hip disarticulation; Transfemoral; Knee disarticulation; Transtibial; Ankle disarticulation and Partial foot (BRAZIL. Manufacture and maintenance of orthoses, prostheses and assistive devices for locomotion: manufacture and maintenance of lower limb prostheses, ankle-foot orthoses and postural adjustment in wheelchairs. Brasília: Ministry of Health. Secretariat of Labor Management and Health Education, 2013. 224 p. ISBN 978-85-334-2041-0. 8).

[005] Amputation is a treatment method for several diseases and is part of a general treatment context, the aim of which is to provide an improvement in the patient's quality of life (BRAZIL. Manufacture and maintenance of orthoses, prostheses and assistive devices for locomotion: manufacture and maintenance of lower limb prostheses, ankle-foot orthoses and postural adjustment in wheelchairs. Brasília: Ministry of Health. Secretariat of Labor Management and Health Education, 2013. 224 p. ISBN 978-85-334-2041-0. 8).

[006] Lower limb amputation generates some difficulties, the most easily observed being altered locomotion in the amputee, but it can also cause some psychological disorders. In this context, the Petition 870170045511, dated 06 / 29 / 2017, page 8 / 44 3 / 18 The rehabilitation process is a crucial step when amputation becomes necessary.

[007] As established by the World Health Organization (WHO), rehabilitation is a set of measures that helps people with disabilities to achieve and maintain optimal functionality in their interaction with the environment (WHO. World report on disability. 1st ed. São Paulo: World Health Organization, 2011. 334 p. ISBN 978 92 4 068521 5. 2).

[008] The rehabilitation of people who have undergone lower limb amputations mostly involves the use of prostheses within the context of assistive technology. In these cases, the prosthesis aims to ensure stability and provide safety during ambulation (DIAZ, CPO CHARACTERIZATION OF HUMAN GAIT USING A BIOMECHANICAL APPROACH: AN EXTENSION FOR THE AMPUTEE CASE. 99 p. Thesis (Doctorate) - Faculty of Technology, Brasília, 2015. 2). A prosthesis is a permanent or temporary device that totally or partially replaces a limb, organ, or tissue (MACHADO, GS TECHNICAL NOTE: Orthoses, prostheses and special materials - Subsidy to the CPI of Orthoses and Prostheses. Brasília, 2015. 2).

[009] Among assistive technologies, lower limb prostheses are usually designed according to the level of amputation. Therefore, in most cases, the use of a foot prosthesis is necessary, from hip prostheses to ankle disarticulation prostheses. The term foot refers to all the structures located distal to the tibia and fibula, being a functional unit of the lower limb and responsible for distributing the body's loads to the ground, both in static and dynamic behavior, being formed by a complex set of highly specialized joints for the execution of its function (LIMA, CS. Articular Movement: Morphological and functional aspects. São Paulo - SP: Manole Ltda, 2010. 11. ISBN 978-85-204-2436-0. 6).

[010] The foot is divided into three major functional segments: hindfoot, midfoot, and forefoot. Each segment consists of a set of bones and one or more Petition 870170045511, dated 06 / 29 / 2017, page 9 / 44 4 / 18 joints. In addition to the functional division, the foot can also be divided into tarsus, metatarsus and phalanges (HAMILL, L; KNUTZEN, K. Biomechanical bases of human movement. SP: Manole, 2012. v. 3. 528 p. ISBN 9788520431559. 6).

[011] The bones of the foot are arranged so that the body weight is supported by the heel and the distal heads of the metatarsal bones. The shape of the bones and their ligamentous and muscular supports condition two arches. The larger and more apparent one, the longitudinal arch, which runs from the calcaneus to the distal heads of the metatarsals, is more pronounced medially than laterally, and therefore the longitudinal arch can be subdivided into lateral and medial. The transverse arch is formed by the bases of the metatarsal bones and the distal tarsal bones (FRANKEL, VH; NORDIN, M. Basic Biomechanics of the Musculoskeletal System. 4th ed. Rio de Janeiro: GUANABARA KOOGAN, 2014. 412 p. ISBN 8527722925. 7).

[012] The main models for describing the medial longitudinal arch of the foot are the beam model and the bragueiro model (SARRAFIAN, SK. Functional characteristics of the foot and plantar aponeurosis under tibiotalar loading. Foot Ankle, v. 8, n. 1, p. 4-18, 1987. 7). The beam model is based on the idea that the longitudinal arch is a curved beam composed of interconnected joints, whose structure depends on the interconnections of the ligament joints for its stability. Tensile forces are produced on the lower surface of the beam and compressive forces are concentrated on the upper surface of the beam. (NORDIN, M.; FRANKEL, V. Basic biomechanics of the musculoskeletal system. 4th ed. Rio de Janeiro: Guanabara Koogan, 2003. ISBN 9788527708234. 7).

[013] Lower limb prostheses can be defined according to the principle of construction (BRAZIL. Manufacture and maintenance of orthoses, prostheses and assistive devices for locomotion: manufacture and maintenance of lower limb prostheses, ankle-foot orthoses and postural adjustment in wheelchairs. Brasília: Ministry of Health. Secretariat of Labor Management and Health Education, 2013. 224 p. ISBN 978-85-334-2041-0. 8): • Conventional or exoskeletal devices have a rigid external structure; Petition 870170045511, dated 06 / 29 / 2017, page 10 / 44 5 / 18 • Modular or endoskeletal structures have an internal support structure formed by modular components.

[014] There are a variety of prosthetic feet currently available that aim to restore, or improve, the gait of amputees. The most common types are SACH and ESR type feet. The SACH (Solid Ankle Cushion Heel) foot is the most basic prosthetic foot and is usually made of wood and rubber. The ESR (Energy Storing and Returning) foot is essentially a prosthesis with elastic and cushioning characteristics (BRACKX, B. et al. Passive AnkleFoot Prosthesis Prototype with Extended Push-Off International Journal of Advanced Robotic Systems, v. 10, 2013. 8).

[015] Rehabilitation Centers in Brazil typically import the feet they use in their prostheses, as there are no specialized companies in the national market that produce prosthetic feet on a large scale and at an affordable price, possibly due to the absence of applicable national standards in force.

[016] Brazilian patent application PI1103840-3; US patents US7354456, US7572299; and US patent applications US2016106555A1, US20040153168, US20060069450, US20090287315, US20110029097, US20120116540, US20130173023, US20140012397, disclose technologies relating to foot prostheses, all of which are designed to provide comfort and cushioning to the user. The present invention differs from these models by having three distinct and unique cushioning regions. In addition to having a system that quantifies the potential mechanical energy resulting from the direct contact of the prosthetic foot with the ground during walking, which can be transformed into other types of energy.

[017] The process of designing a product involves creating a plan to investigate all engineering, safety, and quality issues. The use of computational environments can assist in the development and manufacturing stage of a given product; however, it is necessary to define a stable method so that the simulated results can reproduce or approximate experimental data, when applicable. Petition 870170045511, dated 06 / 29 / 2017, page 11 / 44 6 / 18

[018] Finite element analysis (FEA) is a widely used and well-established technique in project analysis and product development across a wide range of fields. The method was developed for the analysis of continuous media, enabling the analysis of a large portion of existing physical systems. Continuous media are usually too complex to be analyzed exactly, so simplifying assumptions are adopted to create an approximate mathematical model of the original physical system.

[019] In FEA, the elements and their interrelationships are converted into a system of equations that are solved numerically. The overall process is divided into small steps, including: preprocessing, processing, mesh refinement, and report generation. Some characteristics must be observed to ensure that the numerical solution is representative, including: consistency, stability, and convergence.

[020] To describe the behavior of a physical system, one must first conceive a conceptual (or idealized) model of that system; a mathematical model can be understood as formulations that express the essential characteristics of a system in mathematical terms. Therefore, the challenge in mathematical modeling is to produce the simplest possible model that incorporates the main characteristics of the phenomenon of interest (BRASIL, RMLR d. F.; BALTHAZAR, JM; GÓIS, W. Numerical and Computational Methods in Engineering and Science Practice. São Paulo: Blücher, 2015. ISBN 978-85-212-0934-8. 14).

[021] Among modeling techniques, in general, it is necessary to find mechanisms that allow the construction of models that utilize concepts from both theoretical and empirical modeling (AGUIRRE, L. Introduction to System Identification - Linear and Non-Linear Techniques Applied to Real Systems. Brazil: Editora UFMG, 2007. v. 3. ISBN 9788570415844. 14).

[022] Bond graph (BG) modeling is a unified representation of dynamic systems, in which elements interact with each other through gates located within the system, where the exchange of Petition 870170045511, dated 06 / 29 / 2017, page 12 / 44 7 / 18 Energy. The BG technique for modeling dynamic systems is based on the concept of energy and can be applied to different systems with different physical domains.

[023] The Bond Graph technique for modeling dynamic systems is based on the concept of energy and can be applied to different systems with different physical domains, such as mechanical, electrical, thermal, hydraulic, acoustic, among others (PETERS, DL. Modeling of Dynamic Systems: Notes on Bond Graph. USA: Spring, 2015. v. 1. 14, 27, 28, 30). Therefore, the Bond Graph modeling technique aims to represent the energy exchange between components of a physical system, where the energy variable is characterized by the integrated variables of accumulated effort pe and accumulated flow q (KARNOPP, D. C., MARGOLIS, D.; ROSENBERG, R. System Dynamics: Modeling and Simulation of Mechatronic Systems. New York: Wiley, 2000. (A Wiley-Interscience publication). ISBN 9780471333012. 14).

[024] During the stance phase of gait, there is a contact force between the foot or shoe and the ground and the corresponding reaction force, as established in Newton's third law. By analyzing this physical interaction, it is possible to estimate the potential energy that is not used during gait and its subsequent utilization. Small amounts of energy are wasted, which could be useful if used; recovering a fraction of this energy has a significant economic and environmental impact.

[025] The process that utilizes small amounts of energy that would otherwise be lost, such as heat, light, sound, vibration, or movement, is defined as Energy Harvesting (SYTA, A. et al. Experimental analysis of the dynamical response of energy harvesting devices based on bistable laminated plates. Meccanica, Springer Netherlands, v. 50, n. 8, p. 1961-1970, Mar 2015. ISSN 0025-6455 1572-9648. 3, 18). This concept is being implemented in the capture and utilization of electrical potentials that the human body converts during its functioning. Petition 870170045511, dated 06 / 29 / 2017, page 13 / 44 8 / 18

[026] A project developed utilizes the concept of Energy Harvesting in upper limb movements, applying it to miniaturized generators powered by human strength. The prototype developed showed an average energy conversion efficiency of 30.98 and an average power output of 0.32 W with a maximum of 1.89 W (YEO, 1.; RYU, M.-h.; YANG, Y. Energy Harvesting from Upper-Limb Pulling Motions for Miniaturized Human-Powered Generators. Sensors, v. 15, n. 7, p. 15853, 2015. ISSN 1424- 8220. 19).

[027] A comparison of the biomechanical application of energy harvesting systems versus the use of batteries is proposed by authors who compare the use of biomechanical metabolic power from walking with the use of batteries that provide the same amount of energy. A mathematical model was presented that considers the following parameters: the mass of the device, its location on the human body, the production of electrical energy, energy harvesting costs, walking time, and the specific energy of the battery. The case studies in the aforementioned work reveal that energy harvesting devices located on the ankle, knee, or back should be preferred over batteries, requiring a walking time of 227 hours, 98 hours, or 260 hours, respectively. Replacing batteries weighing 6.81 kg (ankle), 5.88 kg (knee), or 2.6 kg (back).

[028] The authors conclude that for energy harvesting devices to be preferred over batteries, the device design parameters should indicate a lower metabolic power for energy generation using the SCE than when using batteries (SCHERTZER, E.; RIEMER, R. Harvesting biomechanical energy or carrying batteries? An evaluation method based on a comparison of metabolic power. Journal of NeuroEngineering and Rehabilitation, BioMed Central, v. 12, p.

[029] A lower limb-oriented energy harvesting system capable of generating approximately 9 Watts of electricity has been developed. The authors introduce a novel performance measure to quantify the device's performance, the total cost of capture (TCOH), which assesses the overall efficiency of a Petition 870170045511, dated 06 / 29 / 2017, p. 14 / 44 9 / 18 SCE including the transport cost device. The new SCE captures the movement of both lower limbs. From a test with ten individuals under different walking conditions, the SCE achieved an average TCOH of 6.1, which is comparable to the estimated TCOH for a conventional energy generation method of 6.2. The study results indicate that the energy produced was generated primarily from the knee, and was associated with a small additional effort on the part of the user. (SHEPERTYCKY, M.; LI, Q. Generating Electricity during Walking with a Lower Limb-Driven Energy Harvester: Targeting a Minimum User Effort. PLOS ONE, v. 10, n. 6, 2015. 19)

[030] The results presented in a study show measurements of electrical quantities and energy generated from locomotion activities, using commercial portable piezoelectric sensors to measure the energy capture from human body movement. The tests were performed by applying the transducers to the neck, shoulder, elbow, wrist, hip, knee, and ankle regions. Four activities (climbing stairs, descending stairs, walking, and running) were chosen for the tests. The power output values, measured during the five activities, ranged from 6 pW to 74 pW.

[031] The authors show that, among the regions analyzed, the knee joint provides the greatest energy uptake in all activities, with the highest modulus occurring during running. (PROTO, A. et al. Measurements of Generated Energy / Electrical Quantities from Locomotion Activities Using Piezoelectric Wearable Sensors for Body Motion Energy Harvesting. Sensors, v. 16, n. 4, p. 524, 2016. ISSN 1424-8220. Available at: http: / / www.mdpi.comlI424-8220 / 16 / 4 / 524. 20)

[032] The present invention relates to a foot prosthesis with the following characteristics: lighter than a structure made of steel; manufactured with easily manufactured material; conditions for large-scale production. Another difference of the prosthesis is the fact that the total height is close to the geometric limits of the non-amputated foot. Being smaller in comparison with ESR type prostheses. Petition 870170045511, dated 06 / 29 / 2017, page 15 / 44 10 / 18 marketed. This difference was designed so that it can be used in articulated or active ankle prostheses. And for the design and manufacture, it was decided to use the current international standards in accordance with the criteria defined in the good manufacturing practices of the National Health Surveillance Agency (ANVISA. Guide to Assist in the Implementation of Good Practices in Health Products. [S.l.], 2013. 9,10).

[033] During the stance phase of gait, there is a contact force between the foot or shoe and the ground and the corresponding reaction force, as established in Newton's third law. By analyzing this physical interaction, an opportunity was observed to estimate the potential energy that is not used during gait and its subsequent utilization, thus being the second main contribution of this invention. DESCRIPTION OF THE FIGURES

[034] Figure 1 shows an isometric perspective representation of the prosthesis and its heel support region (1), forefoot support region (2), lower limit of the plantar arch (3), upper limit of the plantar arch (4), first cushioning region of the plantar arch (5), second cushioning region of the plantar arch (6), proximal lateral limit of the main stabilization and cushioning structure (7), distal lateral limit of the main stabilization and cushioning structure (8), main stabilization and cushioning structure (9) and prosthesis fixation region to the user (10).

[035] Figure 2 shows a side view, in section, of the present invention with its following elements: heel support region (1), forefoot support region (2), lower limit of the plantar arch (3), upper limit of the plantar arch (4), first cushioning region of the plantar arch (5), second cushioning region of the plantar arch (6), proximal lateral limit of the main stabilization and cushioning structure (7), distal lateral limit of the main stabilization and cushioning structure (8), main stabilization and cushioning structure (9) and prosthesis attachment region to the user (10). Petition 870170045511, dated 06 / 29 / 2017, page 16 / 44 11 / 18

[036] Figure 3 shows the graph of instantaneous power (W) versus deflection (mm), generated by the prosthesis in contact with the ground, calculated using the Bond Graph method. DETAILED DESCRIPTION OF THE INVENTION

[037] The present invention relates to a prosthesis for foot replacement in the case of amputation, consisting of only one piece manufactured from material and in a shape that aims to increase the cushioning areas and provide a greater zone of elasticity, minimizing the impacts from walking. In addition, the total height of the prosthesis is close to the geometric limits of the non-amputated foot. The hindfoot has an "hourglass" type geometry, in addition to the plantar arch structure.

[038] It also presents a system for quantifying the potential energy of mechanical energy, resulting from the direct contact of the prosthetic foot with the ground during gait, which can be transformed into other types of energy.

[039] The manufacturing material and design of the prosthesis were conceived to make it lighter than commercially available models, which are typically made of steel. The prosthesis has an easy manufacturing process, enabling large-scale production.

[040] The fact that the total height of the prosthesis is close to the geometric limits of the non-amputated foot makes it smaller compared to currently marketed ESR-type models. This difference allows its use in articulated or active ankle prostheses.

[041] The prosthesis is symmetrical in the sagittal plane and does not have restrictive dimensional measurements, its design being focused on the proportions between specific points of the foot. In this way, the present invention can be manufactured to resemble any foot size, according to the user's needs.

[042] The manufacturing material is of the polymeric type due to its low specific mass modulus compared to steel. It behaves with thermoplastic characteristics, allowing for future recycling. It allows for the molding process. Petition 870170045511, dated 06 / 29 / 2017, page 17 / 44 12 / 18 injection molding, which reduces manufacturing costs and waste when production is high.

[043] The preferred raw material selected is polyoxide methylene (POM), which is a thermoplastic and homogeneous material, facilitating the machining process and is also an isotropic material that facilitates the numerical simulation process.

[044] The prosthesis is manufactured by milling, mainly due to the complexity of its geometry, preferably by the CNC (Computer Numerical Control) method in a vertical machining center.

[045] It should be noted that the procedures described above can be performed using only the machining center, without the aid of an external computer, as this type of equipment has a keyboard panel that allows the creation and editing of programs. However, this procedure is quite time-consuming and complex if applied to unconventional geometries.

[046] In the milling process, two high-speed steel milling cutters are used, one with a diameter of 20 mm and the other with a diameter of 4 mm, both with a working length of approximately 55 mm. For the machining process of the prosthesis profile, a computer program is used, which generates the mechanical drawing, the finite element method analysis, and a source code, sending the programming lines so that the milling tools perform the manufacturing.

[047] The prosthesis is designed to stably withstand a static load of 1600 N. It thus fits into the prosthesis model that meets the P3 test standard defined in ISO 22675 / 2006.

[048] The present invention is designed to cushion impacts from walking, acting on the elastic zone of the prosthesis. The prosthesis provides a movement with good energy return, that is, the energy stored in the compression phase is used to gently propel the individual forward. Petition 870170045511, dated 06 / 29 / 2017, page 18 / 44 13 / 18 Its behavior is elastic, meaning that once the forces acting on the prosthesis are removed, it returns to its resting configuration.

[049] The response to damping and energy return may vary according to the user's physical conditions, for example, weight, height, age, walking speed, among others.

[050] The numerical simulation process for planning the manufacture of the prosthesis reduced the manufacturing time by at least six times and considerably reduced the final project costs.

[051] The indications regarding the use, type and level of amputation that the prosthesis can accommodate are the responsibility of the multidisciplinary team responsible for the amputee's rehabilitation.

[052] The system that quantifies the potential energy of mechanical energy from direct contact of the prosthesis with the ground during gait makes use of the Bond Graph technique. The accumulated energy can be transformed into other types of energy, demonstrating that the method is effective in modeling biological systems. EXAMPLES

[053] In vitro tests and computer simulations will adopt the requirements established in the standards of the International Organization for Standardization (ISO): • ISO 22675:2006 - Prosthetics - Testing of ankle-foot deviations and foot units - Requirements and test methods; • ISO 22676:2006 - Prosthetics - Testing of ankle-foot devices and foot units - Guidance on the application of the test loading conditions of ISO 22675 and on the design of appropriate test equipment; • ISO 10328:2006 - Prostheties - Structural testing of lower-limb prostheses Requirements and test methods.

[054] EXPERIMENTAL PROCEDURE FOR IN VITRO TESTS Petition 870170045511, dated 06 / 29 / 2017, page 19 / 44 14 / 18

[055] Each test setup was defined in a two-dimensional rectangular coordinate system. The minimum number of tests required for each type of test prescribed in the static proof test and the static maximum strength test was ten units. Data were collected every 0.1 seconds of testing.

[056] The accessories are non-prosthetic extensions used for the proper application of the loads specified in the implemented tests. Measuring the maximum deflection and maximum permanent deformation is the objective of the tests on the accessories, for user and test safety reasons.

[057] The developed accessories were machined from SAE 1020 carbon steel with a modulus of elasticity of 205 GPa.

[058] The prosthesis was developed to meet the requirements of the P3 level tests, therefore the accessories were tested at the same P3 level.

[059] IN VITRO TESTS

[060] As a result of experimental tests on the accessories, the maximum deflection (D1) and maximum permanent deflection (D2) values ​​have the following magnitudes: • In the heel region, DI = 0.356 mm and D2 = 0.115 mm; • In the forefoot region, DI = 1.654 mm and D2 = 0.631 mm.

[061] The greater deflection observed in the forefoot region, compared to what occurred in the heel region, was expected, since the distance of the force application in relation to the structure's locking point (moment) is greater in the forefoot region than the moment in the heel.

[062] STATIC TEST

[063] The static test was performed by applying the test force, initially, to the heel position and, subsequently, to the forefoot position on the same sample. The angles used were 15° at the heel and 20° at the forefoot. Petition 870170045511, dated 06 / 29 / 2017, page 20 / 44 15 / 18

[064] In order to pass the static test, a test sample must withstand the static load on the heel and subsequently the load applied to the forefoot by the test forces at the prescribed values ​​and inclinations for approximately 30 seconds.

[065] The test force applied to the forefoot of the sample to be tested was smoothly increased at a rate of 100 N / s up to the specified value of 1600 N. The applied force was maintained at the prescribed value for approximately 30 seconds and then the force was reduced to zero. The prosthesis behaved elastically in the static test, i.e., with the acting forces on the prosthesis removed. Subsequently, it returned to its resting configuration. This situation indicates that the prosthesis can be used without restrictions up to a maximum force value of 1600 N. This force value was considered as a design parameter to characterize the upper limits of use of the prosthetic foot, as well as its respective safety coefficient.

[066] MAXIMUM STRENGTH STATIC TEST

[067] Static maximum force tests were performed on different test samples, first performed on the heel and then on the forefoot.

[068] A test force of 50N was applied to the heel region and increased at a rate of 100 N / s up to the specified value of 2400N; the procedure was repeated for the forefoot region.

[069] The prosthesis passed all Static Ultimate Strength Tests performed, as it remained intact, i.e., there was no rupture or visible damage.

[070] MACHINES AND EQUIPMENT USED IN THE TESTS

[071] The in vitro experimental tests were performed on the INSTRON 8801 testing machine. The load cell of this equipment has a mass of 10 kg and a dynamic rating of 100 kN for both compression and tension, meaning that the equipment can be used in tests that do not exceed forces on the order of 100 kN. Petition 870170045511, dated 06 / 29 / 2017, p. 21 / 44 16 / 18

[072] BOND GRAPH METHOD

[073] The methodology for obtaining the model via the BG tool was defined in three steps: specifying the analog system based on the real physical model, determining the energy domains, and defining the simplification of hypotheses and the input and output variables of the system. An analog system (mass-spring-damper), where mass is the parameter that characterizes the mass of the prosthetic foot that will be acted upon by an external force, and the spring-damper component follows the Kelvin-Voight model, containing a spring with elasticity k arranged in parallel with a damper of viscosity b.

[074] Using the adopted BG methodology, it is possible to estimate the prototype's response when an excitation force is applied and compare it with the experimental result.

[075] Figure 3 shows the instantaneous power result for the simulated prosthetic foot via BG modeling, highlighting two distinct regions:

[076] The first region is between deflections of 0 mm to 17.92 mm, in which the instantaneous power has a negatively skewed distribution and a maximum value of approximately 76 W. This region is important because it quantifies the maximum dynamic potential of mechanical energy that can be used under the expected operating conditions of the developed prototype, i.e., with a GRF of approximately 800 N;

[077] The second region, corresponding to deflections greater than 18 mm, shows a tendency for symmetrical behavior. This region has the greatest potential for energy harvesting. However, it is not recommended to operate in a force range greater than 900 N, as these force moduli result in a von Mises stress greater than 30 MPa and, consequently, in a reduction in service life.

[078] The results relating to the Energy Harvesting System, modeled using the Bond Graph technique, proved to be stable in all numerical simulations performed. With the evidence of the stability of the mathematical model, Petition 870170045511, dated 06 / 29 / 2017, page 22 / 44 17 / 18 The proposed analysis of the analogous model (mass-spring-damper) for the prosthetic foot can be substantiated, making it possible to study the dynamics of the foot's behavior as a function of displacement via BG modeling. It is observed that the simulated values ​​converge to the experimental result when the focus is on average values, since the periodic behavior is centered on in vitro data. With these considerations, the main results of this section can be summarized, among which the following stand out:

[079] The average values ​​of the simulated results converge to the experimental results, demonstrating the consistency, stability and convergence of the model;

[080] The prosthetic foot passed the static test and the maximum static force test, performed experimentally in vitro, according to criteria defined in the adopted standards, indicating viability for use in humans;

[081] The use of the Bond Graph technique made it possible to quantify the maximum instantaneous power at 75 W per step on each foot, thus being the potential mechanical energy, resulting from the direct contact of the prosthetic foot with the ground during gait, which can be transformed into other types of energy under the defined design conditions.

[082] STAGES OF THE MACHINING MANUFACTURING PROCESS

[083] The steps are defined as:

[084] Mechanical design - Definition of the origin position of the virtual Cartesian axes and the dimensions of the block that will be machined to the geometry of interest;

[085] Tool selection - Inform the software of the types, geometry and positioning of the tools available on the machine for manufacturing;

[086] Blank (raw workpiece) clamping - Define the clamping method, from the blank to the machine table, that is most suitable for the procedure. This step is important to avoid collisions; the software plans a cutting strategy that machines only the desired material; Petition 870170045511, dated 06 / 29 / 2017, page 23 / 44 18 / 18

[087] Machining plan - Definition of the machining method, such as the directions of rotation and displacement strategy. In addition to stipulating which geometries should be worked on in the machining process, such as cavities and external contours;

[088] Cutting parameters - Definitions of parameters such as cutting speed, feed, depth of cut and cooling requirements. This step is critical, as errors in these parameters can cause tool breakage, workpiece detachment from the clamping system and serious machine collisions, as well as affecting the surface finish of the final product.

[089] Physical References - In this step, the machine where the workpiece zero indicated to the software in the Mechanical Design step is physically specified. It is necessary to make, or check, the preset of the physical height of each tool;

[090] G-code - All the above information is converted into machine language;

[091] Transmission - Communication between computer and machining center, typically via RS232 serial communication or PCMCIA memory card;

[092] Tests - Testing the code generated by the software on the equipment's own control panel, graphical movement test for tool path analysis, empty tests to verify that there will be no displacement that exceeds the table's movement limits or those planned via software;

[093] Machining - Monitoring of the manufacturing process by chip removal.

Claims

1. CONSTRUCTIONAL ARRANGEMENT APPLIED TO A FOOT PROSTHESIS comprising a single piece made of polymeric material featuring a heel support region (1), forefoot support region (2), lower limit of the plantar arch (3), upper limit of the plantar arch (4) and a region for attaching the prosthesis to the user (10), characterized by the hindfoot having an hourglass-type geometry defined by the proximal (7) and distal (8) lateral limits of a main stabilization and cushioning structure (9), which comprises a first cushioning region (5) and a second cushioning region (6) arranged internally to the body of said structure (9) to provide zones of elasticity and cushioning.

2. CONSTRUCTIONAL ARRANGEMENT, according to claim 1, characterized by being symmetrical in the sagittal plane and having a total height of the main structure (9) dimensioned for integration into articulated or active ankle systems.

3. CONSTRUCTIONAL ARRANGEMENT, according to any of the preceding claims, characterized in that the polymeric material is polymethylene oxide (POM).

4. CONSTRUCTIONAL ARRANGEMENT, according to any of the preceding claims, characterized by withstanding a static load level of 1600 N, meeting the P3 test standard of ISO 22675 / 2006.

5. METHOD FOR QUANTIFYING REUSABLE MECHANICAL ENERGY from the constructive arrangement defined in claim 1, characterized by determining the potential mechanical energy from the support regions (1, 2) with the ground by means of the Bond Graph modeling technique.

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