This invention relates generally to a printer, and particularly to a miniaturized serial printer wherein a print head is adapted to be displaced reversibly across a recording medium. In conventional serial printers, a print head is reversibly displaced across the recording medium by rotating a cylindrical cam. The cylindrical cam may include a closed loop spiral groove and the print head support includes a projection for following the closed loop sprial groove, in camming like fashion. The cam is rotated in one direction and displacement of the print head occurs as the print head follows the closed loop.
Alternatively, a conventional serial printer may include a cylindrical cam having an open loop spiral groove wherein the direction is reversed by reversing the rotating direction of the cylindrical cam. The print head support in this construction also includes a projection for following the groove in camming like fashion. Displacement of the print head is reversed by reversing the rotating direction of the cylindrical cam. This reversal is usually accomplished by a two directional motor.
In both types of conventional serial printers, the recording medium is advanced by a mechanical or electrical trigger driven by the printer motor. Both types of cylindrical cams always rotate while the motor rotates thereby displacing the print head. Thus, recording medium advancing also occurs while the print head is being displaced. For this reason, loads due to print medium advancing and displacing the print head are placed on the motor simultaneously. Accordingly, it is difficult to reduce the power consumption of the motor. Such operation also is a principal cause of mechanical problems as the print medium advancing mechanism tends to jam or the print medium tends to feed improperly. Additionally, the distance which the print head must be reversibly displaced includes the print range and an additional distance for the print medium advancing operation. Thus, the print heads are required to be displaced at a greater distance than merely the print range or margin. This latter point has been an obstacle to further miniaturization of serial printers.
An example of a serial printer including a rotating cylindrical cam having a closed helical groove in the form of a continuous loop is shown in U.S. Pat. No. 4,046,246. An alternative type of rotating cam is a rotating disc as shown in U.S. Pat. No. 4,175,876 issued to Seiji Hanaoka on Nov. 27, 1979 and assigned to the same assignees as the subject application. In the Hanaoka printer, the rotating disc drives the various mechanisms of the printer, including the print head and print tape advancing assembly.
A cylindrical cam having a closed loop spiral groove is generally expensive to prepare. Alternatively, utilizing an open loop requires a more complex driving circuit in combination with a reversible motor in view of the need to reverse the direction of the rotation of the cam. This raises additional obstacles to reduction in manufacturing costs for a serial printer. Additionally, a reversible motor necessarily involves increased power consumption. Furthermore, when using a DC motor, the large power consumption generally leads to a decrease in the lifetime of the motor brushes. Accordingly, it would be desirable to provide a construction for a serial printer including a unidirectional motor and cylindrical cam having an open loop groove for displacing the print head.