Printing apparatus and printing method

1. A printing apparatus comprising:

(A) a transport mechanism transporting a medium in a forward direction and a backward direction;

(B) a head printing dots on the medium;

(C) a sensor sensing existence of the medium in a non-contact manner;

(D) a reversion mechanism reversing the medium; and

(E) a controller controlling the sensor to sense an end of the medium when the transport mechanism transports the medium in the forward direction so as to allow the head to print the dots on a surface of the medium and controlling the sensor to sense the end of the medium when the transport mechanism transports the medium in the backward direction so as to allow the reversion mechanism to reverse the medium after the dots are printed on the surface thereof wherein the sensor includes a light-emitting portion and a light-receiving portion, and wherein the printing apparatus further comprises a lower guide and an upper guide for guiding the medium between the light-emitting portion and the light-receiving portion; and wherein the sensor includes an upper protrusion portion and a lower protrusion portion, wherein the upper protrusion portion includes one of the light-emitting portion and the light-receiving portion and the lower protrusion portion includes the other thereof, wherein the lower guide includes a base surface, ribs protruding upward from the base surface so as to come in contact with the medium, and an insertion portion in which the lower protrusion portion is inserted, and wherein an opening is provided at a position of an optical axis of the sensor in the lower guide and the opening is formed in the base surface between the ribs.

2. The printing apparatus according to claim 1 , wherein the top surface of the lower protrusion portion is positioned above the base surface of the lower guide.

3. The printing apparatus according to claim 1 ,

wherein the lower guide further includes a lift portion covering the lower protrusion portion, and

wherein an inclined plane is formed between the base surface on an upstream side and a downstream side of the uplift portion in the forward direction.

4. The printing apparatus according to claim 1 , further comprising a flexible seal member,

wherein the sensor is fixed to the lower guide,

wherein the upper guide is pivotable on the lower guide, and

wherein the seal member seals a boundary between the sensor and the upper guide.

5. The printing apparatus according to claim 1 , further comprising:

a first bulge supporting the medium;

a second bulge supporting the medium and being provided more downstream in the forward direction than the first bulge; and

a groove formed between the first bulge and the second bulge,

wherein the controller controls the transport mechanism to transport the medium so as not to position the rear of the medium more downstream than the first bulge, and simultaneously controls the head to print the dots on one surface of the medium, and

wherein the controller controls the transport mechanism to transport the medium so as to position the rear of the medium in the groove, and simultaneously controls the head to print the dots on the rear end of the medium when printing the dots on the other-side of the medium.