A transmission unit mounted on the machine base of an office automation machine and covered with a cover and controlled to turn a first roller and a second roller, including a gear transmission mechanism, a first roller transmission mechanism driven and a second roller transmission mechanism respectively driven by the gear transmission mechanism to turn the rollers, wherein the gear transmission mechanism includes a motor, a rounded seat raised from the machine base, a drive gear mounted on the rounded seat and coupled to the motor, an annular gear holder revolvably mounted around the rounded seat and having an upright gear shaft, an upright axle raised from the machine base adjacent to the rounded seat, a crank having a pivot hole at one end coupled to the upright axle and a gear shaft at an opposite end, a first planet gear revolvably mounted around the gear shaft of the crank and driven by the drive gear to turn the first roller transmission mechanism, a second planet gear revolvably mounted around the gear shaft of the annular gear holder and driven by the drive gear to turn the second roller transmission mechanism; the cover has an arched slot, which receives the gear shaft of the annular gear holder to guide the movement of the second planet gear along the teeth of the drive gear within a fixed angle.

A serial impact printer of the type utilizing a dot matrix print head is specifically adaptable for use as a calculator or adding machine and is characterized by utilizing a common drive source to advance the print head across the paper, advance the paper between printing operations, and selectively advance the print ribbon between the ribbon supply spool and takeup spool. An improved paper-advancing means has been devised which operates in close correlation with the print head drive member to provide a relatively high speed, simplified and inexpensive printer unit; and the ribbon supply spools are so constructed and arranged as to be interchangeable and to permit direct drive through a spool-engaging member on the print head whereby to advance the ribbon in direct response to print head travel.

An apparatus for enabling manual alignment of a flexible sheet in a sheet transport device having automatic detent. An incremental stepping motor providing document detent drives a platen and a tractor feed apparatus via a unique drive train. The drive train includes a first gear rotatably mounted on the platen shaft, a second gear secured to the platen shaft inboard of the first gear and a motion transfer plate slideably and rotatably received on the platen shaft. The motion transfer plate has a pair of arcuately shaped beveled gear surfaces normally engaged with a beveled inner gear surface of the first gear when the transfer plate is in a first position on the platen shaft. The beveled gear surfaces are joined by a pair of wall surfaces which are embraced by a pair of arms integral with the second gear. The motion transfer plate is secured to a control shaft having an adjustment knob, the control shaft being slideably received in a bore in the platen shaft and normally biased by a spring to the first position. The sheet is aligned relative to the detent position by displacing the control shaft inwardly until the motion transfer plate is disengaged from the first gear and by rotating the transfer plate by means of the knob and control shaft to adjust the angular position of the platen, the second gear and the tractor feed apparatus relative to the stepping motor detent position. Upon release, the control shaft and motion transfer plate return under the action of the spring to the first position. A pair of alignment devices are used in conjunction with two independently rotatable platen halves and independently operable drive trains and stepping motors to provide independent alignment of a pair of flexible sheets associated thereto.

A serial printer having a print element capable of printing in both directions across a print form, means for pre-analyzing a succeeding line of print on the form following a preceding line of print to determine the end positions of the succeeding line of print, and means for causing the print element to move from the last position printed on the preceding line of print to the closer end position of the succeeding line of print so that printing of the succeeding line of print may take place beginning from said closer end print position of the succeeding line of print. One embodiment includes hardware for causing the printing element to so move to the closer end print position of the succeeding print line, and another embodiment utilizes a general purpose computer so programmed that this movement of the print element can take place. Means is also provided for causing the print element to move at a faster speed than printing speed if the print element traverses more than five spaces in reaching the closer end print position of the succeeding print line or if a print line includes more than five consecutive blank spaces.

A elongated rail is provided with a carriage which can be connected with a curtain to be pulled and is movable in opposite directions on the rail between at least two positions in which further movement of the carriage is blocked. A burn-out protected reversible electromotor is mounted stationarily relative to the rail and non-slip motion transmitting components, such as a tooth belt with associated gears and rollers, are provided for transmitting motion between the electromotor and the carriage so that the latter is moved when the electromotor is energized. The fact that the electromotor is protected against burn-out permits blocking of the movement of the carriage without requiring the de-energization of the electromotor.