| 摘要 |
The particles are applied to at least one screen (8, 10, 12) set over the surface and the distance between two oblong frame members (14, 16, 18, 20) to which the long side of the screen is fixed varies with oscillation. The screen is curved outwards towards the surface at least with the minimum distance between the two frame members. The distance between the frame members varies between the maximum and minimum value and with maximum distance the screen is stretched over between the frame members
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