08-01-2013, 03:09 PM
DESIGN ANALYSIS AND FABRICATION OF SOLAR PANEL DEPLOYMENT MECHANISM USING TO TORSION SPRING
1DESIGN ANALYSIS.docx (Size: 973.25 KB / Downloads: 137)
INTRODUCTION
In most of satellites, because of the space which is accessible in launcher, solar cells areinstalled on panels that in the beginning of launching are closed then after injectingsatellite in its orbit they will be deployed. Deployment of these solar panels hasconsiderable influence on dynamic and attitude control of satellite and may make
disturbances. To prevent and minimize of these disturbances in attitude control of a
satellite, it is necessary to design a deployment mechanism for the solar panels whichhas appropriate performance and ability to control the disturbances and also can beconstructed. A solar panel in its mission uses some mechanisms such as release,deployment and locking mechanisms.
Satellite solar arrays need to have minimal weight on one hand and a stiff structure with natural frequencies as high as possible at the deployed phase, on the other.
The presented solar array system consists of two wings, each with three panels, stowed around a hexagonal satellite and deployed by torsion and kick springs. As the angle between two panels reaches the deployed state the hinge is locked by a locking mechanism. The deployment process goes on until the whole array is deployed.
Conventional deployment systems are usually kinematic. The displacements, speed and sequence are controlled unlike that concept, this system is dynamic. It is simple, small and low-weighted. However, the deployment principle is based on converting the spring potential energy into panel movement kinetic energy, which, on locking is absorbed by impact and panel oscillations. Designing such system demands the meeting of two contradicting requirements – enough energy to ensure the deployment (including factors of safety) and withstanding the impacts that arise as the movement is locked.
Torsional Description
The system provides an exceptional off-the-shelf solutionto small satellite panel and antenna deploymentrequirements.The SH-9010 hinge system comprises twohinges: a spring-powered drive hinge and a multipledegree-of-freedom floating hinge. This two-hinge approachprovides exceptional stiff ness for 1 G testingand vibration loads, without the need for high-tolerancealignment. Deployment energy is provided by a
double coil torsion spring on the drive hinge. A torsionbar latch engages at the end of travel of the panel. Deployment energy is dissipated as the torsion barwinds and counterwinds around the deployed position.This torsion bar soft-stop also establishes thestiffness of the deployed hinge. The ability to customizethe torsion bar diameter for each applicationallows the deployed panel stiffness to be “tuned,”minimizing latching shock and providing adequatelatched stiffness for spacecraft control.Exceptional off-the-shelf solution to small satellitepanel & antenna deployment
Deployment Mechanism Design
The structural design was kept simple but reliable. Since mass of the satellite should also be kept within a range, therefore the mass of the deployment mechanism was of
main consideration. And to keep the mass within limits (although there is no limit for the deployment mechanism alone but other scientific instruments are of main concern w.r.t mass considerations) minimum number of parts was designed. The main design calculations were for the torsion spring. First there were some initial assumptions such as the force required to deploy the panels and the diameter of the spring.
Parameters of the Torsion Spring
There are a wide variety of coil end configurations to suit different applications and a torsion spring is usually positioned on a shaft. The coils are usually close wound and do not have any initial tension unlike tension springs. The primary stress induced in torsion spring is a bending stress in the wire. During forming residual stresses are built up in the winding process. These residual stresses are in the same direction but of opposite sign to the working stresses resulting when the spring is loaded causing the coils to tighten. Torsion springs are stronger as a result and they are often designed to work at, or above the yield strength.
Design of Latch and Release Mechanism
For latching the panels a simple solution by using a fishing line to hold down was used. The latch and release mechanism is still under development. But for testing purpose a temporary solution was developed to test the deployment mechanism. For this purpose a circuit was designed in which ISOTAN®, a resistive wire, was used in a loop type shape through which the fishing line was passed. Once the circuit was switched on the resistive wire melted the fishing line and the panels are deployed. The circuit diagram can be seen in the figure. The circuit is self-descriptive, as can be seen that a supply voltage is connected to the resistive wire and the resistive wire is connected with the MOSFET. One of the legs of MOSFET is connected to a 180 Ω resistor. The switch is connected to the microcontroller is shorted when a 3.3V is applied. The fishing line is passing through a loop of the resistive wire and when the circuit is switched on the current passing through the resistor heats it up and melts the wire.
CONCLUSION
Design and analysis of a solar panel deployment mechanism was done and designcovered this purpose that angular velocity of solar panels deployment was constant anda spring actuator acted to deploy and a paraphin actuator acted to control the constantrate of deployment. Analytical analysis and software simulation of mechanism showthat analytical results have good agreement with software results and both say thatmechanism deploy the solar panels with 4.5 °/sec angular velocity. Mathematical modeling and software simulation of solar panels deployment of samplesatellite was done. Both kinds of results have good agreementwith each other and say during deployment, displacement of satellite because ofdeployment is about 23mm and also velocity and acceleration of satellite are that muchlow that can be ignored. In point of view of attitude control, roll, pitch and yaw anglesare less than 1° and as attitude control accuracy is 2°, mechanism ,during deployment,doesn’t make angular errors that can’t be controlled