NI sheds light on machine control challenge

15 July 2008

Sylvania Lighting, artificial light source manufacturer, has installed a new production machine to manufacture a smaller type of lamp.

The operator screen displays the position of electrodes, as well as important process variables
The operator screen displays the position of electrodes, as well as important process variables

Metal halide lamps are manufactured at the Sylvania plant in Tienen, Belgium, and the smaller design required a production machine that would allow all process parameters to be adapted easily.

Danny Hendrikx, of Sylvania Lighting International, explained: ‘The standard ‘pinch process,’ in which two metal blocks press melted glass around electrode-foil wires to created an impermeable bond, is not capable of producing these new lamps.

‘Therefore, we developed a new process to melt the glass directly around the foil, requiring a totally new machine and a new, optimised production process.’

Hendrikx stressed that the new system must allow the developers to change the process steps and their parameters as well as the order of the steps. Furthermore, the developers wanted to build their own sequential programs from the different process steps.

‘An operator needs to run the completed automated program to call in the process steps in the required order and give handling instructions to the operator,’ he added.

‘The machine must also be flexible in order to produce a wide range of lighting products, and should allow easy and quick set-up to facilitate changing from one type of light bulb production to another.’

Sylvania decided existing PLC systems did not offer the flexibility needed and decided to develop its own system based on a Windows PC architecture and National Instruments hardware and software.

‘National Instruments helped us consider our options given our requirements, including interfacing to both servo and stepper motors and controlling a CO2 laser using a pulse-width modulation (PWM) signal, along with the need for an overlooking security mechanism,’ said Hendrikx.

‘We decided to use a PC architecture with three National Instruments boards – an NI PCI-7831R reconfigurable I/O device, an NI PCI-7356 high-performance motion controller and an NI PCI-8252 IEEE 1394 interface device to interface with a digital camera. To develop the software, we used National Instruments LabVIEW, NI Vision Assistant and NI LabVIEW FPGA.’

The new system uses a Basler digital IEEE 1394 camera connected to the PCI-8252 board to take images of the glass bulb. Using algorithms developed previously in NI Vision Assistant and migrated to LabVIEW, Hendrikx claims the company can measure the centre of the bulb and the exact location where the electrodes need to be placed. The bulb is then aligned using a linear servo motor capable of travelling 30cm with 1.2mm accuracy. The PCI-7356 board controls the servo motors and the two stepper motors that place the electrodes in the bulb and manipulate the foil. The PCI-7831R controls the CO2 laser with a 5 kHz PWM signal and controls and monitors all safety requirements and emergency stops.

LabVIEW graphical programming is at the heart of the system. Each function, including PID control and burner time, is implemented separately, and can be called manually or automatically. A recipe can be created in tabular format that calls these different functions sequentially.

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