Pan Controls Case Studies

    High Speed cutting for Powergrind

Powergrind, of High Wycombe, are one of the leading European suppliers of glass handling and cutting machinery. In pursuit of technical superiority over their competitors they have commissioned Pan Controls to design a high performance control system for their UNICUT glass scoring tables. The scored glass is subsequently fed into a separate machine which cracks the glass along the scores.

On the UNICUT machine a moving gantry traverses a sheet of blank glass up to 6m x 3m. A scoring wheel is carried on the gantry and is rotated to stay in line with the direction of travel. The control problem is therefore a three dimensional problem. What makes this problem unique is the need for very high speeds - up to 2m/s and accelerations of 4m/s/s - and that all of this is achieved on curves as well as on straight lines.

                   |    PTS main processor     |      ----------
 ------------      |---------------------------|     |  Rugged  |
|  Office PC |     |  Operator menu software   |-----| terminal |
|------------|     |...........................|      ----------
|  Pattern   |     |                           |
| generation |-----|   G-Code interpolation    |
|  software  |     |        software           |
 ------------      |...........................|
                   | Position broadcasting and |
                   |  I/O monitoring software  |
                       .         |         .
                    .            |            .
                 .               |               .
         -------------     -------------     -------------
        |   "X" axis  |   |   "Y" axis  |   |   "C" axis  |
        |  controller |   |  controller |   |  controller |
        |-------------|   |-------------|   |-------------|
        | PID control |   | PID control |   | PID control |
         -------------     -------------     -------------

The score patterns are produced as a series of "G-Codes" by a software package running on an office computer. The patterns are transferred to the shop floor on a floppy disc. The control system reads the floppy discs and converts the "G-Codes" into machine coordinates which are then broadcast to the axis control cards. Three standard motor control cards are used to control the individual motors. Suitable PID and velocity feed-forward terms are used to achieve tight closed-loop control and accurate following of the desired patterns even at high speeds. The distribution of the PID control to individual axis controllers leaves the main processor free to do the processor intensive circular interpolation. The system is also linked to various limit switches and a pneumatically operated up/down drive on the cutting wheel. The system is operated via a terminal and keyboard suitable for use in an industrial environment. The user interface consists of simple menus for the operator to select and adjust parameters.

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