Modular robots

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Courtesy of Robotics Design Inc.

Although robotics has advanced significantly in the past several decades, efforts have primarily focused on programming and software. Robotic architecture, on the other hand, has largely been limited to six degrees of freedom (DOF): three for positioning and three for orientation. As a result, says Charles Khairallah, M.Eng, robot movement is inefficient, and programming becomes highly complex due to the inherent singularity point, which allows only one possible way for the robot to reach from point A to B. This makes traditional robots infeasible for tasks where obstacles must be avoided and also requires the arm to consume unnecessarily large amounts of power.

'When a traditional robot has to move through a large envelope of work, say 0 to 180 degrees and back after one second, each joint has to make a long trajectory,' he says. 'There is no other choice because there are only three links for positioning. With a modular robot, made of many links, each joint only has to move as little as 3 arc seconds to perform a task and the power consumption is very low.'

For the past 12 years, Khairallah and his company, Montreal-based Robotics Design, have been developing a modular robotics system the company calls Articulated Nimble Adaptable Trunk (ANAT) technology. Composed of H, C and T shaped modules, the chain-type modular robot operates like a multi-jointed arm. Linked together, the modules mimic the movement of a snake, allowing the arm to maneuver in tight spaces and 'slither' around obstacles.

ANAT robots are anchored to the ground by a motorized guide rail that moves the arm up and down. For lateral actuation, each module incorporates a brushless DC servo motor in its central axis. When the modules are connected together, the system's inverse kinematics algorithm, working together with the robot's control algorithm, recognizes the number and type of each module, allowing their movement to be programmed so that they work together to a common purpose much like the cells of an organ.This way, Khairallah says, ANAT robotic arms can reach destinations with a more direct movement path than traditional rigid robots.

'Our robots have more than the six degrees of freedom of traditional robots,' he says. 'This allows industry to do applications that they haven't been able to do before. For example, in the automotive industry, an ANAT arm can maneuver within tight spaces and avoid obstacles to weld or paint within an interior cavity.'

Besides its efficient movement, the benefit of modular robotics, Khairallah says, is its ability to adapt to a target application. Since a chain of connected modules is configurable in multiple ways, the same modular design used in an arc-welder could be repurposed to become a pick-and-place manipulator, by changing the tool attached to its end effector module.

These attributes, Khairallah says, makes a modular ANAT robot highly flexible and well suited to multiple applications within many manufacturing environments.

'Basically, ANAT technology is like LEGO for industry,' he says. 'It provides the ability to design and redesign a robot depending on the application. This way, we can change the methodology so the robot fits the optimum manufacturing process rather than the process being dictated to by the limitations of the robot.'

While other modular robots have been used in industrial manipulation applications, Khairallah says ANAT modular robots are unique due to their uniform components. For example, when connected together, ANAT modules' mechanical linkage evenly distribute load along their length like a Roman arch. This allows ANAT robots to carry heavy payloads and withstand pressure applied to the 'arm' at any point. An added benefit, he says, is that ANAT modular robots reduce maintenance costs since a faulty module can be replaced with an identical one.

Growing out of his post-graduate research work, Khairallah invented Design Robotic's ANAT modular robotics in 1997 and has since secured eight patents on the technology. The company sold its first robot, the AMI-100, to the Montreal ETS University for research purposes. The 'snake-like' arm is composed of a series of identical, motorized modules, which combine redundancy and modularity in a hybrid SCARA articulated configuration.

It has eight DOF and its artificial intelligence allows the robot to perform tasks autonomously. While a central master processor controls the robot's movement, each module has a local control processor as well, allowing them to continue working without constant direction from the central processor.

'With an ANAT modular robot, the control algorithm can coordinate two arms to work simultaneously,' Khairallah says. 'If you use two traditional robots, they can't communicate with each other so the control becomes a matter of timing for coordination.'
Set to be released in late 2009, Robotic Design's ANATERGOARM has the same modular composition as the AMI-100 but lacks motorized modules. Weighing 120 kg, it's designed to manipulate payloads up to 1,000 kg.

The base of the robot supports and balances the arm, which nullifies the effect of gravity and provides it with frictionless movement along the horizontal plane. Motors or a counter-weight allow the load to be moved vertically.

Composed of stainless steel and anodized aluminum, the ANATERGOARM is designed to provide an ergonomic support structure for workers who have to move heavy loads or may be prone to Repetitive Motion Injuries such as carpal tunnel syndrome.

'We've designed the ANATERGOARM so that each module, each part of the arm, doesn't exceed 25kg,' Khairallah says. 'The idea is to make this arm very portable and easy to assemble, while allowing the manipulation of loads up to 1,000kg effortlessly.'

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