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SCARA robot performance – at half the cost

11 April 2011

Festo has introduced a compact integrated motion control subsystem for automation applications featuring independent programmable rotary and linear movement. The company claims it has SCARA robot capabilities, but at a fraction of the cost

Ideal for parts handling and positioning applications, Festo’s new EHMB integrated motion control module features a novel de-coupled design, enabling rotary and lifting movements to be controlled completely independently from one another. This subsystem is capable of performing similar types of loading and unloading movements as many industrial SCARA robots, with comparable performance, but at less than half the cost.

Users are also able to tailor the EHMB’s price/performance by choosing to use a motor and electrical actuator for the two axes, or a motor and pneumatic cylinder – components that are readily available from Festo's product range.

The rotary axis is always actuated electrically using a stepper or servo motor, whereas the lifting axis can employ a Festo DNCE electric or DNC pneumatic cylinder, depending on the user's performance requirements and technology preferences. A typical low-cost configuration would comprise a stepper-driven rotary axis and a standard DNC pneumatic cylinder to provide simple high accuracy linear movement between two positions.

A more demanding application, requiring freely programmable linear positioning, could use suitable Festo servo motors and controllers for both axes - the linear axis being driven by a DNCE electric cylinder. This all-electric approach enables complex rotary/linear movement to be implemented under software control alone.

There is a choice of two EHMB modules, to simplify application matching. The smaller size 20 model can accommodate payloads of up to 3kg, generate more than 3Nm of torque and handle moments of inertia as high as 30kg/cm/cm. An application example is the integration of Z movement in portal and Cartesian parts handling systems.

The larger size 25 model is suitable for stationary use, such as in loading, unloading and stacking applications. Capable of accommodating payloads of 5kg, it can generate 8.8Nm of torque and handle moments of inertia of up to 100kg/cm/cm. Both modules offer a choice of 100mm and 200mm stroke lengths, and are capable of generating up to 480N of lifting force.

EHMB modules offer exceptionally fast and accurate lifting and rotating capabilities. Depending on the choice of motors and cylinder, both models can handle linear speeds as high as 500mm/s with ±0.1mm repeatability, and rotational speeds of up to 300rpm with a repeatability of ±0.05 degrees. This means that a 1kg load can be rotated through 180 degrees in 250ms.

Mechanically, this unit is similar to the ERMB rotary actuator, but with the platen attached to a guided splined shaft, which is free to move through the actuator's body under control of an adjacently-mounted linear axis. The cylinder's piston rod end is directly attached to the platen support bearing by a ball and socket coupling.

Installation is relatively straightforward. The lifting shaft is hollow - the size 20 module has an internal shaft diameter of 14 mm, while that of the larger module is 21 mm - which provides ample space for routing compressed air tubes and electrical cables up to the platen for controlling attachments such as gripper units. The linear axis can also be mounted on any of three sides of the EHMB module, to suit the layout of the customer's machine.

Overall, the EHMB has a very compact work envelope - the rotating/lifting platen is the only part that extends beyond the confines of the module - and can be installed either way up to suit the application.

Festo can supply several accessories for the EHMB module, including an adjustable end-stop for the lifting shaft (pneumatic version), a support bush for flexible tubes and cables, and a shaft cover kit. An axial motor mounting kit is also available for modules that employ an electrical linear axis.

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