When Oxford MEStar, an Oxford University Institute of Biomedical Engineering spin-out, had an urgent requirement for a semi-automatic parts handling and vision inspection system, it asked motion technology specialist, LG Motion to help with the design and construction.
The system was needed for quality checking and product sorting of specially packaged ‘corneal scaffolds’ - key products that have a niche application in the emerging field of regenerative bioengineering. The cornea and its integral support scaffold, measuring about 35mm diameter, is packaged in a sealed clear plastic blister pack measuring 80 x 100mm.
The near translucent items are suspended in a transparent gel similar to a ‘petri dish’ solution, making it difficult to determine their exact position with relation to the packaging. To resolve this initial challenge, LG Motion worked with imaging specialist Scorpion Vision to develop a suitable camera vision system to evaluate the appearance and location of the corneal scaffold within its special packaging.
The basic machine requirement called for the vison system to be integrated with a two-axis (X,Z) linear positioning system and PC motion control software that included HMI screen prompts and status information. In operation, a technician manually feeds the packages into the machine, which semi-automatically presents the package to the vision system. The scaffold position has to be determined by the vision system within a tolerance of 0.1mm.
The data from the vision system is used to reposition the scaffold to an optimal location within the full view of a customer-supplied laser analysis system, which is used to determine the condition of the cornea from its optical properties. Finally, the package is either accepted or rejected and transferred into pass or fail chutes for further processing.
Oxford MEStar approached LG Motion with an urgent requirement for the complete system, having developed and proven the laser inspection process within the laboratory. They also required a modular automation system that could accommodate upgrades and modifications as the project progressed.
No stranger to special requests and tight build schedules, LG Motion was able to harness its experience of integrating multiple technologies for this project. Rather than agreeing a rigid specification before commencing work - which would have extended the delivery timescale - it called Scorpion Vision in at the early stages for recommendations and a solution to the scaffold location problem to help speed the machine design process.
The motion mechanics – custom stepper driven ballscrew positioning stages with single linear motion guide bearings - are designed specifically for the application to maximise the space on the work platform. With a 500mm travel range for the horizontal axis and 50mm vertical travel, the stages include manual drive wheels to allow the operator to position the axes under power-off conditions.
Using its design, production and quality inspection facilities back in Basingstoke, LG Motion designed and built the machine's essential mechanisms in-house, along with its gripper, brackets and the fixtures for locating the imaging and laser inspection sub-systems. In this way, with bought-in parts kept to an absolute minimum, and the specification concurrently worked on as the project progressed, LG Motion was able to maintain timescales for the mechanical system.
The motion control system was also developed in parallel with the machine building using LG Motion’s modular application development front-end software – a series of ‘building block’ routines’ that allow its applications engineers to create HMI graphical user programs based on multi-axis motion controllers.
The PC software works with stepper drives over Ethernet to build user friendly programs that synchronise motion and machine I/O. Whilst the front-end software is capable of complex machine control, the relatively straightforward repetitive processes which this machine required were easily implemented.
The machine includes a host of safety and machine I/O with emergency stop, over-travel limits, home switches and other sensor interfacing. The HMI touch-screen displays the machine phases - loading the package, automatically locating the cornea and its scaffold, the laser inspection phase and pass or fail for acceptance or rejection – then prompts the technician to load another package.
Move parameters, speeds, time delays and other adjustment features are included along with display of status information such as system state, axis position, I/O condition, axis and drive faults.
The machine is now in operation with Oxford MEStar’s production and research facility in China, where it is helping to develop and improve the quality of the cornea inspection process.