Since 1904 Codivilla report lengthening, limb lengthening has developed more than 100 years, bone regeneration theory slowly stretch has been formed and constantly improve, at the same time limb lengthening instruments is constantly developing.
The present limb lengthening surgical technique and equipment has undergone three phases [1]: (1) external fixation technology; (2) nail combined with external fixation; (3) fully implantable limb lengthening. External fixation technology with the artificial external control bone orthosis stretch, stretch control accuracy is low, the operation is difficult, the clinical application of easily-track infection, is not conducive to extend the zone of bone healing, while at the same time bring external fixation in the patient's physiological and psychological effects. Intramedullary nail combined with external fixation technology in extended precision, stability, has made great progress, but still cannot avoid external fixation for adverse consequences. Fully implantable bone Extenders, because of its built-in power generation device can accurately control extension rate while avoiding needle tract infection problems, become a bone Extenders. Now this technology is the most mature and most representative is the ORTHOFIX company developed bone marrow built-in power Extenders (ISKD), it consists of an external monitor and surgical implantation of similar scale telescope barrel of nails, its basic principle is to rely on patients ' joint activities rotary internal distractor stretch. But the drawback is the only stretch, not recoil pressure fixed, once the activity level, more than a single stretch length, no recoil, could lead to broken facial types cannot grow, there is a great risk of clinical application.At present, China's limb lengthening surgical technique and equipment also remain in a second phase [2], lagging far behind the developed countries.
Our national medium-and long-term science and technology development program, have a new medical device research and development to encourage investment and innovation in new areas. Therefore, this article has designed a MSP430F169 microcontroller core, high precision, self-control bone orthosis. The bone orthosis not only overcome the disadvantages of external fixators, and overcome ISKD cannot recoil pressure fixed shortcomings. Motor control, simple operation, the user can control bone orthosis for expansion, extension of high precision, has broad application prospects.1 system design
System by implantation of long bone bone bone marrow cavity of internal and external orthoses made up of two parts of the controller.
External controller through bio-silicone tube inlet and internal bone orthosis, mainly by MSP430F169 microcontroller, motor driver circuit, power modules, signal processing module, keyboard and LCD display system and other related modules. In vivo bone orthosis by precision motor runs its own expansion, SCM through magnetic sensor feedback module consisting of parameters and signal processing module implementation on bone orthosis for precise control. System architecture diagram shown in Figure 1.To meet the requirements of users of portability, orthosis systems using battery power.
Therefore low power is one of the main indicators of the system, the system selects with ultra-low power consumption characteristics of the MSP430 series monolithic integrated circuits. In MSP430F169 microcontroller based on build system platform to support a software interrupt handling, very good system of low-power indicators. High precision control system with another key indicator of bone Orthotics must maintain high precision control stretch, recoil, no error will be negative impact to the user. The system uses the ZP series sensor back to micro-motor run signal, the signal is amplified and sent back to the SCM process, for precise control. According to software design, system implementation running accuracy 0.1 mm, its accuracy is much higher than the existing orthosis.2 system hardware design
2.1 MSP430F169 microcontroller
Microcontroller MSP430F169 [3] is a United States Texas Instruments ' production with ultra-low power consumption, powerful 16-bit MCU.
It uses the "Feng · Neumann" structure, RAM, ROM and all peripheral modules are located in the same address space, maximum addressing address is 62 KB; powerful interrupt function, 48 I/O pin I/O port, each with a corresponding input, output, feature selection, interrupt, etc more registers, on the same I/O port operation, select the features you want to implement to achieve function and reuse of common i/o port, greatly enhances the power and flexibility of the port; MSP430F series Super microcontroller with Flash memory, running at 1 MHz clock conditions, operating current visual work mode only 0.1 ~ 280 μ A; at the same time it has a good simulation development technology, setting a JTAG emulation interface and high-level language compiler.2.2 bone orthosis systems
2.2.1 orthosis machinery
Orthoses mechanical structure as shown in Figure 2.
Figure in the left side of the head (1) and the right end (11) respectively and the external parts count on screw fixing. The left side of the head (1) and (3) motor, motor bracket (4) and the outer sleeve (7) rely on interference-solid with together, the left part. While the right side of the head (11) and internal sleeve (8) rely on thread-solid with together, the right part. The sleeve and the outer sleeve, so that there's one-key (6), it can limit the internal sleeve and the outer sleeve between peripheral rotational movement and achieving in length direction, travel range (100 mm) of the freedom movement. The left part and the right-side parts of the sliding along the length direction is achieved by motor. Motor output after reducer, Motor reducer motor output shaft through thin keys will center screw (9) driven rotation, and then push through Central screw threads are oriented key week to fixed internal sleeve forward for the entire system. Precise control of motors is the core of the orthosis systems. e="TEXT-ALIGN: center" align=center>2.2.2 motor drive
Bone orthosis internal precision motor maximum withstand voltage of 6 V, its driving voltage is 4 V, V voltage drop 1 each, motor speed drops 2 800 r/m, motor driver requires not only a great drive capability, and its output also requires a high level of stability.
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