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Multi-axis motion system helps create spectacular light show

01 October 2009

Rotalink’s Red Drive motion system has enabled Focus International to implement a 12-axis synchronised motion control system very cost effectively for a spectacular fibre optics based illuminated sign project

Focus International is a leading company that creates bespoke and often spectacular fibre optics based lighting systems for projects ranging from public building to domestic interiors. When a challenging project involving a large illuminated sign for an historic building required complex and high-speed synchronised switching, the company turned to miniature power transmission and controls specialist, Rotalink for a technical solution.

Fibre optic lighting creates spectacular effects and is becoming increasingly popular, thanks to its high efficiency, low energy consumption and intrinsic safety. Projects carried out by Focus International are often unique and usually involve the use of non-standard equipment. Design expertise is required in three main areas to achieve the desired balance of illumination and intensity. These are the light source, containing the lamp with optical modifying components and controls; the fibre optic bundles to transmit the light, and the light fittings that direct light to the illuminated subject and its surrounding space.

For the illuminated sign project, the synchronised high-speed switching pattern was produced using twelve identical light sources, each with a motorised aperture disc, which is rotated to allow or restrict the light path into its corresponding fibre optic bundle. The light source discs are each controlled by a Red Drive and brushed dc servomotor combination, both components being supplied by Rotalink. The motors are each fitted with a high-ratio spur gearbox with position feedback provided by a rear motor mounted, 48 pulse/revolution, dual-channel optical encoder. Synchronisation between each axis is simply achieved by interconnecting the Red Drive’s integral programmable I/O to trigger pre-programmed move sequences.

Focus International had considered using DMX controllers for this application but the stage lighting industry’s standard protocol was deemed by the company to be overly complex in terms of programming and too expensive for a customised multi- axis motion control based lighting system such as this.

Red Drive with its inherent low cost and straightforward drag-and-drop flowchart programming was an attractive alternative that could be quickly integrated into the application. The credit card sized controller was easily installed in the light source housing and its EEPROM memory allowed the complex motion sequences to be conveniently stored in what is essentially a ‘fit-and-forget’ installation. Development costs were further reduced thanks to Rotalink’s ability to both size and supply the complete power train, including motors, gearboxes and ancillary equipment.

As the Windows programmable Red Drive scales the encoder and gearbox resolution into meaningful units at set-up, actual move distances and speeds matched the fixed 90-degree angular aperture rotation. Taking care of the PID servo tuning was simply a matter of entering catalogue values for motor stall torque and no-load speed. The set-up also included assigning each of Red Drives’ complement of nine user-definable digital input and outputs, and linking the homing and reset inputs which were called from subroutines in the flowchart based program.

Red Drives’ graphical drag-and-drop programming methodology allowed Focus International to quickly program acceleration, move and dwell parameters that created the desired lighting effect – and at this point, the subroutine feature allowed a variety of subtly different move profiles to be evaluated with easy retrieval for final use. It was also possible to select alternative move and lighting sequences using Red Drives’ variable and loop commands to provide different lighting effects from input states to highlight various areas of the sign for different purposes.

Since its recent launch, the Red Drive has significantly flattened the entry-level costs for integrated digital servo amplifiers or intelligent drives. For this application, each light source was fitted with a 1A Red Drive and power transmission components for less than £90 - a considerable saving over stand alone digital drives and conventional servo gearheads.

OEMs can use Red Drive to create positioning systems with up to 10Nm torque capacity, both economically and with a significantly improved time-to-market. Other features include a recently introduced analogue input that allows devices such as potentiometers to be connected to provide analogue linear or rotary position feedback.

Following the success of the signage project, Focus International is now using Red Drive for other lighting applications involving fully synchronised colour filter discs for even more spectacular effects.

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