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Etch-a-sketch artwork is up to scratch

04 July, 2013

The I-frame also needed less power than an H-frame with two parallel axes acting horizontally. The linear slides had to be modified by machining material away from their covers and using inverted parallel belt drive adapter plates to make the extruded aluminium profiled beams fit into place.

The slides were specified with stainless-steel cover bands to prevent glass dust from the etching process from entering the ball-guided bearings.

With the main mechanical system design completed, the drives, EMC filters, motion controller, computer, Wi-Fi components and an interfacing panel were placed around the cabinet (above). To achieve the speeds and dynamic performance required, a servomotor-based system was chosen.

Multi-axis motion control is provided by an ABB NextMove e100 multitasking controller which synchronises the motion via its integrated Ethernet Powerlink network. By connecting the distributed MicroFlex e100 drives via Powerlink, the amount of wiring needed was minimised compared to traditional servo systems.

A C++ program running on a PC interprets data from the iPad app (which was commissioned separately) and sends real-time linear position co-ordinate and etching axis on/off information to a Mint program running on the motion controller. This information is stored in the Mint program’s move buffer and can be advanced and started on demand – streaming the positions to create the smooth, co-ordinated and contoured motion needed to recreate the original iPad sketch.

The Mint program synchronises the parallel axes. During start-up, the axes align themselves using a modified datum command, thus ensuring orthogonality with the vertical axis from the beginning.

The third axis of motion – placing the diamond ring against the glass and later removing it – is taken care of by a separate brushless DC motor and drive using the NextMove controller’s torque-limiting function. This enhances the simple on/off input command to soften the impact when placing the diamond against the glass. A combination of hard and soft limits, and torque control, ensures that all axes stay safely inside the cabinet.

Arad is pleased with the end results. “It was a pleasure to work with a company [Heason] that was more of a perfectionist than we ever imaged,” he says. “When things were good enough for us, they weren’t good enough for them and in the end we appreciated and benefited from Heason’s professional attitude in a time-frame that has challenged everyone involved in the project.”

Arad hopes to collaborate with the UK integrator again in the future. “Working on the Last Train project has given us the appetite for other projects that we wish to follow up on,” he says.

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