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A mobile robot that does not slip

  • A mobile robot that does not slip

Robotic engineers at IISc have designed a wheeled mobile robot that can move in a stable manner on an uneven terrain with minimal slipping. Prof. Ashitava Ghosal from the Department of Mechanical Engineering, Indian Institute of Science, Bangalore and Dr. Tharakeshwar Appala from SSJ Engineering College, Hyderabad have successfully demonstrated a prototype of an “autonomous mobile robot” that can travel in a straight line, make turns and also switch lanes on bumpy terrain, without the risk of falling off and with minimal slip.

Autonomous mobile robots are capable of navigating in unknown and unstructured environments and have the capability of negotiating rough terrains with minimal intervention from human operators. This makes them suitable for activities such as household cleaning, delivering goods and services and planetary exploration. NASA’s ‘Curiosity’ Mars rover, an excellent example of an autonomous mobile robot, is currently exploring the surface of Mars and has detected minerals which indicate existence of water on the Martian surface in the past.

A common problem with these robots is slip at the wheel-ground contact. “A key not completely solved problem in wheeled mobile robots is Simultaneous Localization and Mapping (SLAM). A mobile robot must know its location and be able to make a map of its environment to operate autonomously. An odometer – an instrument to measure the rotation of the wheel—is used to obtain the location of the robot. When a wheel slips, during the rotation of the wheel, the robot’s location is unchanged and this leads to localization errors”, explains Prof. Ghosal. He also notes that wheel slip leads to power wastage – a premium resource in planetary exploration. Wheel slip can also lead to unstable motion and the robot can tip over or fall on the uneven terrain. Motivated by this challenge, the team at IISc focused on designing robots that do not slip and are stable in such terrains.

In the proposed design, the robot consists of one front wheel and two torus-shaped rear wheels connected to a platform. The wheels are designed to always keep contact with the ground and they are driven by motors. The rear wheels are connected to the platform through a suspension mechanism having four links. Two of the links are fixed and the other two are free to move at an angle. This enables lateral tilting of the wheel, thus preventing a slip. The wheels are coated with rubber to enhance friction. The team also tested the designed prototype to assess its functionality. They simulated the functioning of the robot with ADAMS – a software that enables users to provide arbitrary inputs to simulate the motions of a robot. The performance of the robot was assessed for three types of desired paths: straight line, a circular motion of 30° and a lane change.With the new design, the team observed 50% reduced slippage in comparison with previous models.

The applications of such autonomous wheeled robots are enormous.“A rover called ‘Opportunity’ sent by NASA has been operating successfully in exploring Planet Mars for more than 7 years now. In my opinion, apart from planetary missions, the wheeled robots will find increasing use in industry and security related applications in India”, points out Prof. Ghosal. With India’s Mangalyaan and Chandrayaan making strides and plans to send a rover to the moon for exploration, this research work may complement the country’s journey into space.

Contact Information:

Prof. Ashitava Ghosal

Department of Mechanical Engineering

Indian Institute of Science, Bangalore

Phone: +91 80 2293 2956

Email: asitava@mecheng.iisc.ernet.in

Author(s) Information:

Dr. Ghosal is a Professor at the Department of Mechanical Engineering, Indian Institute of Science, Bangalore. He has published a book on robotics and many journal articles on areas related to robotics. He has patented 3 designs in the Indian Patent base along with other researchers. Dr. Tharakeshwar heads the Department of Mechanical Engineering at SSJ Engineering College and is also a member of Robotic Society of India and the Association for Mechanisms and Machines. This research work was published in the “Mechanism and Machine Theory” Journal, Vol 93, 2015 under the title “A mobile robot with a two-degree-of-freedom suspension for traversing uneven terrain with minimal slip: Modeling, simulation and experiments”.