| 摘要 |
To render the grey scale of recording on an electrosensitive recording medium (16) independent of voltage applied by an electrode (22) while maintaining a predetermined relationship between a command voltage (Uc) and the resulting grey scale of the recording, the command voltage (Uc) is compared in a comparator (44) with energy being supplied from an external source through a coil (32) having a primary winding (34) to which a capacitor (36) is connected in parallel to form an oscillatory circuit by a transistor (40). Upon controlling the transistor to conduction, for example in pulses supplied by a pulse source (48), energy will be stored in the L/C circuit 34/36 until the transistor is controlled to cut off when the command signal (Uc) and a signal across a dropping resistor (42) indicates a predetermined relationship, for example equality, and representative of the energy required to burn out an area of the metalized coating corresponding to the selected grey scale. Transition of the transistor (40) to cut off or blocking state results in a pulse being transmitted to a secondary winding (50) coupled with the primary (34) of the coil, the secondary being coupled to the writing electrode. Thus, the voltage across the writing electrode (22) and the metalized coating (20) of the recording carrier (16) will be independent of the applied signal, but the energy content thereof varying in accordance with the applied signal. The result will be a burn-out trace, the width of which underneath the recording stylus varies (see FIG. 3) in accordance with applied energy, leaving variable amounts of non-removed metalized coating on the carrier, thus resulting in a grey tone, similar to half-tone printing, of the applied command signal.
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