Connect, no. 146, January/February 2007, p.3
Saving robot time and money during product changeovers has become a top priority for TWI's manufacturing team recently. It's been focused on offline programming of robots for nearly two years and is now reporting its achievements.
'What we're doing is taking the programming of robots out of the real world and the robot cell, where it is traditionally done, and moving it into a virtual environment...on a computer screen' project leader David Calder toldConnect. 'So expensive programming time, normally conducted online, can take place away from the real manufacturing environment and done offline.'
The main objective of the programme is to help TWI's Industrial Membership, particularly supply chain users of robots, with investment decisions as their robot related businesses evolve.
The traditional method of programming robots uses a teach pendant, which enables the operator to drive the robot manually from point to point in space, and create tag points by teaching it the co-ordinates of each point. This is repeated many times, along the required profile.
'The component we have in the cell at the moment is a 2m long compound curved aerospace part' says Calder. 'If we model the real thing in a virtual cell the programming of the robot doesn't involve expensive robot downtime.'
Often there are dimensional differences between the virtual world and the actual world. They can be very subtle but present important considerations, with respect to the process adopted. The error can be compensated for by calibration, in other words removing the differences between the real and virtual worlds. By using an object that possesses dimensions precisely defined both in the real and virtual worlds, the different versions of the same entity are compared and any residual error between those is the calibration offset.
'The secret in calibration is to do as little as possible to achieve the results you're after' says Calder. 'The crucial aspect of OLP, as it's known, involves creating a virtual representation of the real world by accurately measuring what is there now, and positioning all the parts in that virtual world. The programme, created in the virtual world, is then uploaded, to the robot's computer, and executed in the real world with one quick confirmatory dryrun. It should then be ready to run in production.'
Doing this manually Calder has found that a minimum of 70 tag points was required to maintain positional accuracy along the process path. 'In the real OLP approach we can programme at least twice that many for no more downtime costs' he says. 'We actually have 200 points in the programme now running.'
He believes the UK is behind Germany, Japan and the United States in OLP. 'Uptake of this technology is something which we need to remain competitive so I believe our Membership will soon be asking us for help with this kind of software on a more regular basis.'
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