Thermal recording apparatus having a movable platen roller

A thermal recording apparatus comprising:

• a thermal printhead provided with a plurality of heat-producing elements;
• a platen roller which is driven to rotate to cause a sheet of recording paper sandwiched between said thermal printhead and said platen roller to be transported;
• supporting means for rotatably supporting said platen roller, said supporting means comprising a support member which is movable between first and second positions to locate said platen roller between a stand-by position where said platen roller is located separated away form said heat-producing elements and a recording position where said platen roller is located adjacent to said heat-producing elements;
• and
• position control means for controlling the position of said supporting means, said position control means positioning said supporting means at said first position during a non-recording mode and at said second position during a recording mode;
• wherein said position control means comprises spring means for selectively biasing said support member toward one of said first and second positions and gear means for selectively urging said support member against said spring biasing toward the other of said first and second positions, and wherein said position control means includes a lock lever formed with a cut-away portion and a pin fixedly attached to said support member and in engagement with said cut-away portion of said lever, said lock lever being pivotally supported and said cut-away portion having a first engagement portion which is engaged by said pin when said supporting means takes said first position and a second engagement portion which is engaged by said pin when said supporting means takes said second position;
• wherein said gear means comprises a platen gear attached to one end of said platen roller, said platen gear being in mesh with a coupling gear which cooperates with a drive gear, such that when the stand-by position is located rearwardly of the recording position with respect to the thermal printhead, the coupling gear in mesh with the platen gear is meshed at a side which is opposite to a side where the platen is in contact with the thermal printhead to rotate the platen clockwise and the support member is urged toward the stand-by position by the spring means, and when the stand-by position is located forward of the recording position with respect to the thermal printhead, the coupling gear in mesh with the platen gear is meshed at a side which is the same as the side where the platen is in contact with the thermal printhead to rotate the platen clockwise and the support member is urged toward the standby position by the spring means.