| 摘要 |
The apparatus includes a guide surface and a thin, resiliently flexible endless band. The guide surface provides a continuous cyclic path for the band. The length of each cycle of the guide surface is substantially less than the cyclic length of the band and the band is arched away from the guide surface in a lobe. Portions of the band on opposite sides of the lobe frictionally engage the surface to prevent the lobe from collapsing. The lobe is capable of progressing along the band to displace the lobe relative to the guide surface. Each cycle of the band relative to the guide surface advances the band a predetermined distance along the guide surface.
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