Pneumatics nip at electricity’s heels

Festo has deployed advanced pneumatics and closed-loop control in the core of its new robotic handling system, the Kinematic Robot.

Traditionally, pneumatic drives have been used for a variety of motion functions but electrical drives have dominated precision closed loop axis controls in most industrial robots on the market.

A typical feature of pneumatic drive applications is fixed repetitive motion sequences but applications demanding a high-speed approach to variable intermediate positioning or flexible motion profiles require freely programmable drives.

The Kinematic robot is a mechatronics handling system employing parallel kinematics to achieve higher accuracy and motion speeds than conventional Cartesian servoelectric configurations. Additionally, the three-axis device is said to offer low moving masses with high rigidity.

The drives deployed are three identical rodless pneumatic cylinders featuring integrated displacement encoders and pressure sensors.

Fundamental to the project was a concurrent process of simulating the desired handling model in software.

‘This permitted various concepts to be analysed and feasibility studies undertaken as rapidly as possible to ensure that the required specification could be achieved,’ says Festo product manager Steve Sands. During the project design phase, the simulation was used to test and optimise closed- and open-loop control strategies. Automatic code generation then allowed the real controllers to be tested as soon as a prototype was ready.

To operate the Kinematic Robot, the development team programs a motion sequence for the end effector in a global Cartesian co-ordinate system.

A multi-axis continuous path controller processes the co-ordinates on-the-fly to generate spatial points linked by straight lines or curved arcs and derives setpoints for the individual axes.

Independent acceleration and velocity profiles are defined for each path to facilitate the high-speed movement and accurate positioning of the end effector. The path setpoints also assist the controller to compensate for other forces in its acceleration force calculations.

A typical test to confirm performance and accuracy of the Kinematic Robot comprised the end effector describing a circular motion track initially of 0.45 metres diameter at a path velocity of 1.0 m/s, then at 0.675 metres diameter with path velocity up to 3.5 m/s and acceleration onto the path of 50 m/s2. During this motion operation, contouring errors are less than 2mm with repeatability of just 0.1mm.

‘These levels of performance and accuracy are in the same domain as precision electrical drives,’ concludes Sands.

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