| 摘要 |
<p>Positioning apparatus enabling an article such as, for example, a wafer (15) to be subjected to a photo-lithographic exposure, to be positioned accurately, for example in relation to an exposure mask (12). The article rests in frictional engagement on a support (22) coupled to piezoelectric transducers (17). The article may be moved through very small distances by applying suitable DC voltages to the piezoelectric transducers. For greater movements an asymmetric waveform may be applied to the transducers, causing the article to move with a jogging motion through much greater distances. The asymmetric waveform may be obtained, for example, by charging and discharging the capacity of the transducers through resistors of suitable value, or by applying a full wave rectified AC voltage to them. Four transducers may be used to enable the article to be moved in either of two mutually perpendicular directions or rotated about an axis. The supports (22) may be tubular and means (26, 27) may be provided for applying vacuum through them to increase the pressure of frictional engagement. </p> |
