Linear positioning

3 min read

Festo has launched a linear positioning system that comprises just two elements.


has launched a linear positioning system that comprises just two elements - the linear handling axis itself and a programmable positioning controller incorporating all the power electronics.

Featuring a precision guide assembly with a linear servomotor and displacement encoder, the HME axis provides a solution for a range of precision positioning tasks. It is suited to highly dynamic applications, such as high speed pick and place machines, linear and 3D gantries, and workpiece assembly systems.

Unlike competitive linear motor based actuators, the HME has a built-in precision heavy duty guide system to ensure consistent performance throughout its stroke, without need of any additional mechanical components.

The guide combines precision ground and hardened bearing tracks with recirculating ball bearings to provide backlash-free operation, and provides high torsional stability. The largest model, for example, can accommodate up to 50 Nm of torque and up to 500N of cantilever force on its yoke plate, without affecting performance. Festo claims that these figures are completely outside the domain of conventional linear motor axes, which require complicated integration with sophisticated guidance systems to approach this level of load tolerance.

Festo HME handling axes offer a choice of two thrust forces and various stroke lengths to facilitate application matching. The HME-16 has a thrust rating of 40N nominal, 160N peak, and is available with stroke lengths of 100, 200 or 300 mm.

A higher power HME-25 is rated at 85 N nominal, 220 N peak, and offers stroke lengths of 100, 200, 320 or 400 mm. All HME handling axes can be used in thrust, speed, or position control modes; they accommodate up to 3 m/s travel velocity, and provide a very high repeatable positioning accuracy of ±0.03 mm.

The HME's linear servo motor is a patented high performance three-phase unit, featuring an all-tubular construction. Designed, developed and manufactured by Festo, it uses high flux density radial magnets and special coil wiring technology to shrink cross-sectional area.

The design has a number of key advantages over conventional linear motors, according to Festo. It is more compact, and maintains uniform performance throughout its travel - whereas most linear motors change characteristics as the magnets move, making them difficult to tune. Furthermore, the motor has no external magnets, enabling the HME to be used in environments where metallic swarf is present, such as machine shops.

The handling axis is a completely self-contained unit. It features an integrated proximity displacement encoder - the measurement band is directly attached to the moving guide rod - and is sealed to IP40 rating against the ingress of contaminants. The yoke plate is mechanically compatible with a wide range of Festo electrical and pneumatic products, including linear and rotary drives, grippers and adaptors, enabling OEMs and machine builders to integrate the unit very quickly and easily.

All motor drive electronics are housed in the Festo SFC-LAC positioning controller that is supplied as part of the package. The controller is sealed to IP54 and can either be sited adjacent to the handling axis, or mounted in a control cabinet. It uses a single interconnecting cable for all motor drive and encoder feedback signals, and only requires the addition of a 48 Vdc power supply to complete the installation. The controller can store up to 31 travel profiles in non-volatile memory, and can operate in response to external signals fed via its I/O interface or via fieldbus signals.

Configuration and set-up is simple, thanks to the supplied Festo Configuration Tool (FCT) software. This PC-based software provides an menu-driven environment which enables all motion control parameters and profiles to be defined, verified and downloaded to the controller via its built-in RS232 interface with minimal time overhead.

Virtually no system tuning is involved, because the software is aware of all key mechanical and electrical characteristics of the HME - the fully integrated nature of the axis means that there are no other factors, such as external bearing friction, to take into account.

Festo FCT software also provides a number of features to help speed system commissioning, including reference travel and diagnostic functions, and an interactive 'teach-in' mode of operation which enables the handling axis to be directly controlled from the PC.

The SMC-LAC controller is optionally available with front panel pushbuttons and display for localised system set-up, and offers the same commissioning facilities - including 'teach-in' - as the PC-controlled version.

Festo HME positioning axes can be installed in any position, are suitable for use in ambient temperatures from 0 to +60 degrees Celsius, and have a service life in excess of 5,000 km of travel.