Motion Control & Drives


Robotic snake-arm for tight spaces

February 2013 Motion Control & Drives

Very confined and hazardous spaces are common in many industrial sectors. They are not only difficult for humans to access, but often have to be inspected frequently. Problems occur frequently and, whilst these spaces are difficult for humans to work in, a robot as agile as a snake can explore almost any hidden nook and cranny. OC Robotics in the UK manufactures snake-like robots that are especially suitable for confined spaces and hazardous environments. The snake-arm robots have a slim, flexible design and they can easily fit through small gaps and circumnavigate obstacles with great skill, recording video as they go.

Snake-arm robots have been used in aerospace assembly, in the nuclear energy sector, in medical technology and in security applications; and maxon motors are responsible for the high-precision movements of the multiple degree of freedom robotic snake-arm.

Each snake-arm is customised specifically for the respective application. Furthermore, the head can be equipped with various tools. OC Robotics offers tools for visual inspection with appropriate lighting and cameras, special gripper jaws or lasers for cutting metal and concrete. Depending on the application, the snake-arm robot can be mounted on a stationary or mobile station such as an industrial robot or a gantry.

The snake-arm is capable of performing a whole range of inspection and maintenance tasks without any direct support from its environment. It can be navigated freely across open spaces. The robot is controlled by means of proprietary software which enables the operator to control the snake-arm by means of the ‘nose-following’ principle. A command is transmitted to the tip of the snake-arm by means of a joypad and the rest of the joints follow this specified path. In other words if the operator steers the tip clear of an obstacle, the rest of the snake-arm will follow suit. “With this technology, it becomes a lot easier for people to work in hazardous environments, yet humans are not eliminated completely,” explains Rob Buckingham, managing director of OC Robotics.

In a human arm, the tendons connect the muscles to the bones of the joints. Similarly, in the snake-arm robot, stainless-steel wires are connected to the individual joints of the robot-like tendons. Each individual wire inside the snake-arm is connected to a maxon motor. The snake-like wriggling movements are the result of the motors transmitting the mechanical power to the snake-arm, where the individual joints of the arm are located. Depending on the version, up to 50 maxon motors are installed in each snake-arm. These are not located directly in the arm, but in an actuator pack in the base of the robot. This is advantageous as the electronics are more easily accessible and not exposed to the confined and hazardous environments. Another area of use for the motors is in the tools in the snake-arm’s head, where one or two maxon motors are typically responsible for the movements of the gripper jaws or swage tool.

The biggest challenge for the drives is to provide a high enough power output inside a compact design. The brushless maxon EC-max 30 DC motor (60 W) and the ceramic version of the GP32 planetary gearhead are used for this highly complex application. Thanks to the brushless design, the electronically commutated DC motors are well suited to long operating times. The heart of the maxon motor design is the ironless winding – with inherent benefits being zero cogging torque, high efficiency and excellent control dynamics.

Special modifications were necessary for the motors used in the snake-arm robot. A special cable and fastening holes were required, while the maxon motor planetary gearhead was modified for the application and a special housing was developed for the brake.

For OC Robotics, reliable motors, good customer support, high quality and high power density were the decisive criteria for choosing maxon motor.

For more information contact Hans Burri, DNH Tradeserve, +27 (0)11 468 2722, [email protected], www.dnhtrade.co.za



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