Abstract: A drive roll 14 carries a gear (60) that engages a reversing gear (58) driven by a planetary gear (56) on a pivot arm (50). The planetary gear (56) is driven by a sun gear (48) that rotates about the pivot axis of the pivot arm (50) and in turn is driven ultimately by a motor (30). A unidirectioal roller clutch (52) is connected between the pivot arm (50) and the sun gear (48) so as to permit relative rotation between the sun gear and the pivot arm in one direction but prevent it in the other direction. As a result, when the sun gear (48) is driven in one direction, it permits the pivot arm to remain in the position in which the planetary gear (56) engages the reversing gear (58). When the sun gear (48) is driven in the other direction, on the other hand, the pivot arm (50) is caused to pivot with rotation at the sun gear (48) to bring the planetary gear (56) out of engagement with the reversing gear (58).

Abstract: The housing (12) of a printer-plotter (10) includes a top cover (14) and a front cover (30) on adjoining housing walls. The top cover (14) is biased toward its open position by a gas spring (20) that is held closed by cooperating latch mechanisms on the top cover (14) and the front cover (30) in such a manner that the top cover (14) opens automatically when the front cover (30) is opened. When the top cover (14) is initially closed, a pivotable latch (22) on the top cover (14) engages a catch (24) on the housing (12) to hold the top cover (14) closed. When the front cover (30) is subsequently closed, a disengaging plate (48) causes the latch (22) to pivot out of engagement with the catch (24) and thus permit the top cover (14) to pivot slightly. However, a stop member (54) on the disengaging plate (48) prevents the top cover (14) from opening. Since the latch (22) no longer engages the catch (24), the top cover (14) automatically opens under the force of the gas spring (20) when the front cover (30) opens.