| 摘要 |
<p>Conventionally, high positionally accuracy is available at modest expense -- but with rather poor resolution -- by using close coupling between a most-direct print-medium drive element and an inexpensive encoder (for instance by operating an encoder (41) from a print-medium (1) advancing platen (11) or final drive roller). Conversely, high resolution is conventionally available at modest expense -- with rather poor accuracy -- by using a remote coupling (22, 23), through a large mechanical advantage (21), between an encoder (51) and that most-direct drive element (11). Where both high accuracy and resolution are required, the state of the art calls for an expensive encoder system or gear train (or other mechanical-advantage module) -- or both. The invention uses two very inexpensive rotary encoders (41, 51) in combination -- a close-coupled one (41, 243 b) (or more) for high accuracy, and a remote-coupled one (51) for high resolution. High-accuracy information (44) is then combined with high resolution information (54) in a digital processing system (61) to yield composite information that is high in both accuracy and resolution. This information can be used (62) to establish image positioning (13) on a print medium (1). The overall system cost is lower than with an equivalent single encoder. Insidious cyclical errors in the coupling system (gear train or the like) (21) are removable without expensive high tolerances and assembly or text fixtures. Residual cyclical error due to eccentric mounting or other error in the direct-coupled encoder scale (42, 242) also can be substantially removed, if desired, by adding another one (243 b) or more encoders reading that scale (242), and suitably combining the information about that scale (242) from the different sensors (243). The information is combined in such a way that the systematic cyclical errors cancel -- or are quantified for use in explicit correction. <IMAGE></p> |
