| anish k mampetta |
| graduate student, robotics institute |
| carnegie mellon university, pittsburgh, pa |
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| the deepest roots are not withered by the frost |
Here are some of my previous projects (arranged in chronological order)
Design and Fabrication Projects:
Design and Fabrication of a Go-Kart (June-1999): Summer Project. A 98cc Honda Engine with centrifugal clutch powered the cart. Power from the engine was transmitted to the rear wheels through an arrangement of chain and differential. Unlike the existing carts, I had installed shock absorbers for the rear wheels and the rear wheels were fitted with hydraulic disk brake. The chassis of the cart was made from galvanized iron Pipe. The Kart is assembled from an assortment of automobile components. Engine, transmission, differential, suspension, wheels, all comes from different manufactures. The chassis is made to facilitate the assembly of all these components in the most practical way. Steering was achieved through Ackerman’s mechanism. In order to avoid giving toe-in, flexible fire rods were uses as connectors. During cornering, the rods buckle so that the front wheels are aligned at different radius of curvature, as required.
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Design and Fabrication of an Electric Wheel Chair (2000-2001): The chair was driven by two independent .25HP, PMDC motors. The speed of the DC motors was controlled by Intel 8080 microcontroller (pwm). MOSFETs were used for switching (ofcourse, they gave us a lot of trouble and lot of burnouts) The microcontroller made sure that starting and stopping would be jerk free.
Specification:
Independent drives for two front wheels, a single Castor wheel at the rear.
Turning radius: 80cm.
Wheelbase: 72cm.
Flexible Co-Axial Cable drive for robotic manipulators (Nov - 2003): While designing a robotic manipulator, the weight of the DC motor is a major concern. A heavy motor at the joints increases the overall inertia of the arm substantially. I have come up with an indigenous method to fix the motor at the base of the arm and then transfer the motion to the joints via flexible co-axial cable. The salient features of this arrangement are:
- Reduced weight and inertia of the arm:
- Absolute Zero Backlash: since at least one of the two cables is always in tension, we have zero backlash.
- Smooth, jerk free operation.
- Flexibility of arrangement: the driving motor can be placed anywhere, hence a number of different configurations can be achieved.
4 D.O.F robotic manipulator (Dec-2003): A low cost robotic arm was developed using the flexible cable actuation system. All the four DC motors used were mass produced automobile windshield wiper motors, thereby bringing down the cost. The motors were placed at the base of the arm and connected to the joints via coaxial cable drives. The Manipulator is controlled through the parallel port of a PC.
watch video of the arm in action
Proposal for fabrication of 4 D.O.F manipulator; submitted to the Dept of Mechanical Engg., NITC.
Reports: Report 1, Report 2
Gripper for Robotic manipulator (Dec -2003): A parallel jaw gripper was developed for the robotic arm for pick and place operations. To maintain the jaws of the gripper parallel to each other, they were connected through a parallel mechanism of links. A linear actuator actuates the gripper. A CAD model of the gripper mechanism is shown on the right. The mechanism simulation was done in Idea8 mechanism solver.
Low cost incremental optical encoder (Feb - 2003): Since the commercially available encoders were very expensive, we developed low cost incremental optical encoder. The encoder was fitted into a small DC motor case. The encoder was interfaced to the parallel port of a PC and a program was developed in C++ to read the encoder. The second figure shows a test set up used to test the encoder. Note that the encoder is coupled to the joint via belt and pulley arrangement. This is done to get a better resolution; the encoder rotates much faster than the joint speed (12 times faster, in this case). The effective resolution becomes 288 counts per revolution.
Design of a prosthetic arm for below elbow replacement, driven by dc motors(March 2004): The aim is to make a low cost prosthetic arm for people with below elbow amputation. We plan to accomplish this by refurbishing the existing mechanical arm, with suitable DC motors and controls.
Figure 1: Existing prosthetic finger mechanism: The fingers are opened and closed by pulling the nylon string, which will be fastened to the shoulder of the patient. Figure 2: Mechanism design for the prosthetic arm in Ideas 8: The fingers will be controlled by a dc-motor coupled to the disk shown.
Development of a low pressure, rotary hydraulic actuator for Robotic manipulators (March 2004): Hydraulic drives have the advantage of high power density, high torque at all speeds and reliability, hence they are used in large industrial robotic manipulator. At the same time, the problem of leakage and the necessity of a high-pressure fluid source limit their use in mobile robots. I have devised a hydraulic actuator, which I hope will work at low pressure and without leakage.
Electrical Projects
Design of switching unit for robotic arm, using double contact solenoid relays (Dec- 2003): While controlling high power DC motors, high inductance of the motor windings causes sparks at the control switch and can damage the switch. Controlling the motors through solenoid relays solved this problem. Two double contact relays wired together to form a H-Bridge arrangement was used to switch and control the direction of each motor.In the figure, the relays are on the right side of the box. The box also contains the computer interface circuit and the power supply transformers. Separate power supply is used to switch the relays and drive the motors. The relays can be switched using the test pendant (for testing) as well as by the computer through the computer interface (for sequence operation).
Parallel port interface for DC motor using MOSFET’s (Feb 2004): The output from the parallel port of the computer is 5V and the computer can source only a very small amount of current. A high current (load) motor can be controlled from the parallel port by either -
Amplify the current from the port to the required level. Or,
Switch the motor by using the signals from the parallel port.
A circuit to switch the dc motor by using the signals from the parallel port was developed. MOSFET’s (IRF 530 and IRF 9530) arranged in H-Bridge configuration was used to run the motors. The signals from the parallel port is amplified to 12V and used to switch the MOSFET’s. The MOSFET then drives high current DC motors. Using this arrangement, motors were tested up to loads of 20 Ampere.
Figure 1: Parallel Port Interface: This interface reads 5V signals from the parallel port of a PC and then switches this signal to 12V. The 12V signals are used to switch the MOSFETs or the Relays to run the Motors. This interface can read up to 8 bit at a time.
Figure 2: MOSFET H-Bridge: Used to control the speed of the Motors by PWM. Each arm of the bridge is composed of 3 MOSFETs connected in parallel. Two bit (signals from computer) is needed to operate this arrangement. One bit for direction, second bit controlling speed.
Software Projects:
A macro in Visual Basic for automatic report generation in Microsoft Excel (Sep-2002): This was my Six-Sigma project at TATA Consultancy Services, Chennai. The results of an FEA analysis in CAESAR (FEA package for pipe stress analysis) were only available in a text format. It is difficult to interpret the results in a text format, hence we developed a macro to read the results from the text file and then transfer the results into a excel spreadsheet, in a predefined format. This project gave a six-sigma savings of around 200%, reduction in time.
Class Manger (Aug 2003): Class Manager is a Microsoft Excel based student data management system. It manages the attendance details, assignment and test marks of students. Class Manager can also prepared students performance report from the given data.
Parallel Port programming in C++ for control of robotic arm (Feb-2004): Developed a program in Turbo C++ to control the 4 dof robotic manipulator through the parallel port of a personal computer. The robot can be controlled in two modes.
Through the Key Board: the keyboard of the pc can be used as a teach pendant to control and test the root.
In the second mode, a sequence of motion can be stored and then executed automatically.
Acknowledgement:
1. Dr. K Prabhakaran Nair, H.O.D, Mechanical Engg. Dept., NIT Calicut, for approving and sanctioning the funds for the fabrication of 4 D.O.F robotic manipulator.
2. Mr. Sibi Chacko, Senior Lecturer, M.E.D, NIT Calicut, for his guidance and support in executing projects like Robotic manipulator, coaxial cable actuator, automated prosthetic arm, and design of hydraulic actuator.
3. Dr. Mohammed Ameen, Director, Bio-Mechanics Lab, NIT Calicut, for providing the opportunity to work on DC-motor actuated prosthetic arm.
4. Kishore K, Lecturer, MED, NIT Calciut, for his help in CAD modeling of Prosthetic arm mechanism.
5. AYEM Industries, Kunnamangalam, Calicut, India., for lending facility and expertise for the fabrication of Robotic Manipulator.
6. I.K. Electronics, East Hill, Calicut, India., for their valuable advice and consultation on the electronic systems for computer interface and dc motor controller for automatic wheel chair.
7. Vijay Govindrajan, Project Leader, GE-Piping, TATA Consultancy Services, Chennai, India., for his help in implementing the automatic report generation tool for CAESARII.
8. Dr. George Varghese, Professor, MED, NIT Calicut, for his guidance in the design and fabrication of Automatic Wheel Chair.
9. Sree Devi Industrials, Nadakavu, Calicut, India., for lending space and facility in their machine shop for the fabrication of Go-Kart.
