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Pramanik S.,ISRO Inertial Systems Unit | Ghosal A.,Indian Institute of Science
2nd International and 17th National Conference on Machines and Mechanisms, iNaCoMM 2015 | Year: 2015

This paper presents the development of a sun tracking system using a 3-UPU parallel spherical "wrist" manipulator. The 3-UPU manipulator, consisting of a fixed base and an orient-able platform, is actuated by three linear motors at the prismatic (P) joints and has a special geometry which makes the 3-UPU manipulator equivalent to a spherical wrist with three rotational degrees of freedom. A flat mirror is mounted on the top of the platform and by actuating the prismatic joints, the platform can be made to track the sun and focus the incident energy at a distant receiver. The main advantage of the 3-UPU configuration is a result of the parallel nature - it can carry larger mirror (more loads) and has lower tracking error. The azimuth and the elevation angles of the sun change as the sun moves across the sky and are dependent on the date, time and location on the Earth's surface. A set of kinematic equations is derived which can be solved numerically to obtain the translations at the prismatic joints as the azimuth and the elevation angles of the sun change. Though the 3-UPU spherical wrist manipulator has its inherent singularity, the singularity condition is avoided by suitable design of the system and by judicious use of the workspace. The theoretical and numerical simulation results are validated by simulating the sun-tracking system with a CAD model. © 2015, Indian Institute of Technology, IIT. All rights reserved.


Praveen R.P.,Cochin University of Science and Technology | Ravichandran M.H.,ISRO Inertial Systems Unit | Sadasivan Achari V.T.,ISRO Inertial Systems Unit | Jagathy Raj V.P.,Cochin University of Science and Technology | And 2 more authors.
19th International Conference on Electrical Machines, ICEM 2010 | Year: 2010

This paper presents the design and analysis of a novel machine family-Enclosed Rotor Radial flux Halbach array Permanent Magnet Brushless DC motor (PMBLDC) for spacecraft applications. Initial design, selection of major parameters and air gap magnetic flux density are estimated using the analytical model of the machine. The proportion of the halbach array in the machine was optimized using FE to obtain near trapezoidal flux pattern. Enclosed Rotor Halbach array motor configuration is found to deliver high torque density, high efficiency, zero cogging torque, better positional stability, high torque to inertia ratio and zero magnetic stiction suiting space requirements. The machine provides uniform air gap flux density along the radius thus avoiding circulating currents in stator conductors and hence reducing torque ripple. ©2010 IEEE.


Praveen R.P.,Cochin University of Science and Technology | Ravichandran M.H.,ISRO Inertial Systems Unit | Sadasivan Achari V.T.,ISRO Inertial Systems Unit | Jagathy Raj V.P.,Cochin University of Science and Technology | And 2 more authors.
2010 IEEE International Conference on Communication Control and Computing Technologies, ICCCCT 2010 | Year: 2010

This paper presents the design and analysis of a novel machine family of Slotless Permanent Magnet Brushless DC motors (PMBLDC) for precise positioning applications of spacecrafts. Initial design, selection of major parameters and air gap magnetic flux density are estimated using the analytical model of the machine. The proportion of the halbach array in the machine was optimized using FE to obtain near trapezoidal flux pattern. The novel machine topology is found to deliver high torque density, high efficiency, zero cogging torque, better positional stability, high torque to inertia ratio and zero magnetic stiction suiting space requirements. The machine provides uniform air gap flux density along the radius thus avoiding circulating currents in stator conductors and hence reducing torque ripple. ©2010 IEEE.


Praveen R.P.,Cochin University of Science and Technology | Praveen R.P.,University of Calicut | Ravichandran M.H.,ISRO Inertial Systems Unit | Sadasivan Achari V.T.,ISRO Inertial Systems Unit | And 4 more authors.
International Review of Electrical Engineering | Year: 2011

This paper presents the optimal design of a surface mounted permanent-magnet (PM) Brushless direct-current (BLDC) motor meant for spacecraft applications. The spacecraft applications requires the choice of a motor with high torque density, minimum cogging torque, better positional stability and high torque to inertia ratio. Performance of two types of machine configurations designed viz Slotted PMBLDC and Slotless PMBLDC with Halbach array and radial magnetization are compared with the help of analytical and finite-element (FE) methods. It is found that unlike a Slotted PMBLDC motor, the Slotless type with Halbach array develops zero cogging torque without reduction in the developed torque, suiting spacecraft applications. Moreover, the machine being coreless provides high torque to inertia ratio and zero magnetic stiction confirming to the requirements of spacecraft applications. © 2011 Praise Worthy Prize S.r.l. -All rights reserved.


Praveen R.P.,Cochin University of Science and Technology | Ravichandran M.H.,ISRO Inertial Systems Unit | Achari V.T.S.,ISRO Inertial Systems Unit | Raj V.P.J.,Cochin University of Science and Technology | And 3 more authors.
2011 International Conference on Emerging Trends in Electrical and Computer Technology, ICETECT 2011 | Year: 2011

This paper presents the optimal design of a surface mounted permanent-magnet (PM) Brushless direct-current (BLDC) motor meant for spacecraft applications. The spacecraft applications requires the choice of a motor with high torque density, minimum cogging torque, better positional stability and high torque to inertia ratio. Performance of two types of machine configurations viz Slotted PMBLDC and Slotless PMBLDC with Halbach array are compared with the help of analytical and finite element (FE) methods. It is found that unlike a Slotted PMBLDC motor, the Slotless type with Halbach array develops zero cogging torque without reduction in the developed torque. Moreover, the machine being coreless provides high torque to inertia ratio and zero magnetic stiction. © 2011 IEEE.


Praveen R.P.,Cochin University of Science and Technology | Ravichandran M.H.,ISRO Inertial Systems Unit | Sadasivan Achari V.T.,ISRO Inertial Systems Unit | Jagathy Raj V.P.,Cochin University of Science and Technology | And 2 more authors.
Transactions on Electrical Engineering, Electronics, and Communications | Year: 2011

This paper presents the optimal design of a surface mounted permanent magnet Brushless DC motor (PMBLDC) meant for spacecraft applications. The spacecraft applications requires the choice of a torques motor with high torque density, minimum cogging torque, better positional stability and high torque to inertia ratio. Performance of two types of machine configurations viz Slotted PMBLDC and Slotless PMBLDC with halbach array are compared with the help of analytical and FE methods. It is found that unlike a Slotted PMBLDC motor, the Slotless type with halbach array develops zero cogging torque without reduction in the developed torque. Moreover, the machine being coreless provides high torque to inertia ratio and zero magnetic stiction.


Praveen R.P.,Cochin University of Science and Technology | Ravichandran M.H.,ISRO Inertial Systems Unit | Sadasivan Achari V.T.,ISRO Inertial Systems Unit | Jagathy Raj V.P.,Cochin University of Science and Technology | And 2 more authors.
International Review of Electrical Engineering | Year: 2010

This paper presents the design, analysis and development of a 400-step hybrid stepper motor for actuating the gimbal of a Control Moment Gyroscope (CMG). The design of the hybrid stepper motor for achieving a specific performance requires the choice of appropriate tooth geometry. In this paper, a detailed account of the results of two-dimensional finite-element (FE) analysis conducted with different tooth width/tooth pitch ratios (t/λ) and also with different tooth/slot shapes such as square and trapezoidal, is presented. The use of equal t/λ ratio on stator and rotor provides nearly 10% more torque than the case with unequal t/λ ratio, but with corresponding increase in detent torque and distorted static torque profile. The hybrid stepper motor for actuating the gimbal of a CMG requires maximum torque density, less-detent torque or cogging torque, better positional accuracy and smooth static torque profile. For the said requirements different pitch slotting with equal tooth width has to be provided. The magnitude of the cogging torque has almost been reduced to 50% from what it was while employing equal t/λ configuration. From the various FE models subjected to analysis, trapezoidal teeth configuration with unequal tooth pitch on the stator and rotor is found to be the best configuration and is selected for fabrication. The designed motor is fabricated and the experimental results are compared with the FE results. © 2010 Praise Worthy Prize S.r.l. - All rights reserved.


Harikumar G.,ISRO Inertial Systems Unit | Karthikeyan K.,ISRO Inertial Systems Unit | Syamala S.,ISRO Inertial Systems Unit | Radhakrishna Pillai C.,ISRO Inertial Systems Unit | And 3 more authors.
Indian Journal of Radio and Space Physics | Year: 2013

Conventional Global Positioning System (GPS) receivers track GPS satellites above 5 degree horizon to avoid multipath effects. In order to improve vertical dilution of precision (VDOP), it is an attractive prospect to utilize GPS satellites below the horizon in addition to those above, for navigation computations in GPS receivers used by vehicles operating at high altitude trajectories. This paper, however, exposes a possible risk of navigation output degradation in adopting this scheme due to unintentional occultation of GPS signals from satellites below the earth tangent horizon. The error on GPS range and range rate measurements induced by troposphere are simulated using a model based approach. Results indicate position errors up to 150 m and velocity errors up to 14 ms-1 over a period of 15 s under practical conditions. Such slowly varying errors being uncharacteristic of GPS receivers are not rejected by the usual protection features in GPS-Inertial Navigation System (INS) integration schemes. Thereby, the integrated system performance is degraded. In the uncoupled GPS-INS scheme studied, GPS error of the above order resulted in integrated system output error of 100 m in position and 5 ms-1 in velocity, respectively. An altitude based elevation cut off scheme that can be incorporated in the GPS receiver for retaining the advantages of using negative elevation satellites, while avoiding occulted measurements, is presented in this paper. A method for strengthening integrated scheme protection, using innovation residuals, for rejecting such slow GPS errors is also presented.


Srinath J.,Vikram Sarabhai Space Center | Sudarshan Rao G.,Vikram Sarabhai Space Center | Nagamalleswara Rao G.,ISRO Inertial Systems Unit | Chaman J.J.,ISRO Inertial Systems Unit | And 3 more authors.
Materials Science Forum | Year: 2015

Gyroscope is an orientation determining sensor whose performance is mainly dependant on one of the critical element called the gimbal flexure. Thinner the flexure, better is the performance. To have sufficient strength, M300 maraging steel is used to fabricate the thin flexures machined by Electrical Discharge Machining (EDM) process down to the required thickness of 0.05 mm in various stages. After the EDM processing, the recast layer formed can cause degradation in the microstructure and mechanical properties. Micro-abrasive machining was carried out to remove the recast layer. An attempt was made to understand the changes that occurred after EDM and after micro-abrasive machining with respect to the microstructure using optical and Scanning Electron Microscopy (SEM) and with respect to mechanical properties using nanoindentation. Nanoindentation technique was adopted as the recast layer was just few microns thick. Indentations were carried out on the base material, as EDM cut flexure, and the micro-abrasive machined EDM cut flexure to obtain elastic modulus and hardness values for each condition and the results were analyzed. © (2015) Trans Tech Publications, Switzerland.


Chacko R.,ISRO Inertial Systems Unit | Ravichandran M.H.,ISRO Inertial Systems Unit | Sanoop M.K.,ISRO Inertial Systems Unit | Sabu T.,ISRO Inertial Systems Unit | And 2 more authors.
2014 Annual International Conference on Emerging Research Areas: Magnetics, Machines and Drives, AICERA/iCMMD 2014 - Proceedings | Year: 2014

This paper describes a novel non-contact signal transfer mechanism for transferring multiple signals over the rotating interface through electromagnetic means. This signal transfer mechanism is configured for the transfer of temperature signals of a Spacecraft Mechanism. FE Analysis of rotary transformer was carried out for optimization of size and operating parameters. In the Signal Electronics portion, operating range of JFET is optimized to achieve uniform gain during amplitude modulation. The system was realized and linearity of 2 % and resolution of 1% of Full Scale Division (FSD) was achieved. © 2014 IEEE.

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