07-07-2014, 01:43 PM
VISNAV
[attachment=65680]
INTRODUCTION
Now days there are several navigation systems for positioning the objects. Several research efforts have been carried out in the field of Six Degrees Of Freedom estimation for rendezvous and proximity operations.
One such navigation system used in the field of Six Degrees of Freedom position and attitude estimation is the VISion based NAVigation system. It is aimed at achieving better accuracies in Six Degrees Of Freedom estimation using a more simpler and robust approach.
SIX DEGREES OF FREEDOM
Six degrees of freedom (6DoF) refers to motion of a rigid body in three-dimensional space, namely the ability to move forward/backward, up/down, left/right(translation in three perpendicular axes)combined with rotation about three perpendicular axes (pitch, yaw, roll). As the movement along each of the three axes is independent of each other and independent of the rotation about any of these axes, the motion indeed has six degrees of freedom.
POSITION SENSITIVE DIODE SENSOR
The Position Sensitive Diode (PSD) is a single substrate photodiode capable of finding or locating a light beam within defined sensing area.
When photons meet the PSD sensor active area electrical currents are generated that flow through its four terminals. The closer the incident light centroid is to a particular terminal, the larger the position of current that flows through that load comparison of these four currents determines the centroid location of the incident light.
DSP IMPLEMENTATION
The beacons are multiplexed in FDM mode. A low power fixed point DSP, TMS320C55x is utilized for the algorithm of beacon separation and demodulation. Asynchronous analog to digital converter samples the sensor’s four currents to feed estimates to the TMS320C55x.
TMS320C55x communicates the demodulated beacon currents to the TMS320VC33 for subsequent navigation solution. The TMS320VC33 estimates the Six Degree Of Freedom position and attitude according to the beacon currents.
The algorithm for the Six Degree Of Freedom estimation is implemented on this processor. It also provides feedback control signals to the beacon controller.
VisNaV APPLICATION AERIAL REFUELING
The aim of this application is to extend the operational envelop by designing an autonomous in flight refueling system. One of the most difficult technical problems in autonomous flight refueling is the accuracy. That is it needs high accurate sensor to measure the location of the tanker and the aircraft. Currently Global Positioning System (GPS) is limited by an accuracy of one foot approximately.
The VISNAV system is capable of providing the needed Six Degree Of Freedom information for real time navigation and can enable accurate autonomous aerial refueling without extensive alterations in the current refueling system.
In order to implement VISNAV system the only thing that is to attach the beacons on the refueling target frame ‘A’ and an optical sensor called Position Sensitive Diode (PSD) on the aircraft frame ‘B’. The aerial refueling using VISNAV can be used in the 100% of cloud cover, total darkness and adverse weather conditions.
CONCLUSION
It is shown that target differentiation based on FDM yields higher signal to noise ratios for the sensor measurements and the demodulation in the digital domain using multirate signal processing techniques brings reliability and flexibility to the sensor system.
The algorithm that is implemented on DSP is robust when there are four or more of line of sight measurements except near certain geometric conditions that are rarely encountered. It is shown that this algorithm is computationally efficient and achieves better results.
[attachment=65680]
INTRODUCTION
Now days there are several navigation systems for positioning the objects. Several research efforts have been carried out in the field of Six Degrees Of Freedom estimation for rendezvous and proximity operations.
One such navigation system used in the field of Six Degrees of Freedom position and attitude estimation is the VISion based NAVigation system. It is aimed at achieving better accuracies in Six Degrees Of Freedom estimation using a more simpler and robust approach.
SIX DEGREES OF FREEDOM
Six degrees of freedom (6DoF) refers to motion of a rigid body in three-dimensional space, namely the ability to move forward/backward, up/down, left/right(translation in three perpendicular axes)combined with rotation about three perpendicular axes (pitch, yaw, roll). As the movement along each of the three axes is independent of each other and independent of the rotation about any of these axes, the motion indeed has six degrees of freedom.
POSITION SENSITIVE DIODE SENSOR
The Position Sensitive Diode (PSD) is a single substrate photodiode capable of finding or locating a light beam within defined sensing area.
When photons meet the PSD sensor active area electrical currents are generated that flow through its four terminals. The closer the incident light centroid is to a particular terminal, the larger the position of current that flows through that load comparison of these four currents determines the centroid location of the incident light.
DSP IMPLEMENTATION
The beacons are multiplexed in FDM mode. A low power fixed point DSP, TMS320C55x is utilized for the algorithm of beacon separation and demodulation. Asynchronous analog to digital converter samples the sensor’s four currents to feed estimates to the TMS320C55x.
TMS320C55x communicates the demodulated beacon currents to the TMS320VC33 for subsequent navigation solution. The TMS320VC33 estimates the Six Degree Of Freedom position and attitude according to the beacon currents.
The algorithm for the Six Degree Of Freedom estimation is implemented on this processor. It also provides feedback control signals to the beacon controller.
VisNaV APPLICATION AERIAL REFUELING
The aim of this application is to extend the operational envelop by designing an autonomous in flight refueling system. One of the most difficult technical problems in autonomous flight refueling is the accuracy. That is it needs high accurate sensor to measure the location of the tanker and the aircraft. Currently Global Positioning System (GPS) is limited by an accuracy of one foot approximately.
The VISNAV system is capable of providing the needed Six Degree Of Freedom information for real time navigation and can enable accurate autonomous aerial refueling without extensive alterations in the current refueling system.
In order to implement VISNAV system the only thing that is to attach the beacons on the refueling target frame ‘A’ and an optical sensor called Position Sensitive Diode (PSD) on the aircraft frame ‘B’. The aerial refueling using VISNAV can be used in the 100% of cloud cover, total darkness and adverse weather conditions.
CONCLUSION
It is shown that target differentiation based on FDM yields higher signal to noise ratios for the sensor measurements and the demodulation in the digital domain using multirate signal processing techniques brings reliability and flexibility to the sensor system.
The algorithm that is implemented on DSP is robust when there are four or more of line of sight measurements except near certain geometric conditions that are rarely encountered. It is shown that this algorithm is computationally efficient and achieves better results.