| 摘要 |
<p>A pump unit includes a suction pump and a driving mechanism for driving the suction pump. The suction pump has a pump body provided with a suction port and a discharge port which are axially spaced, and a first piston and a second piston slidably fitted in the pump body to form a suction chamber therebetween. In operation, the driving mechanism moves the first piston away from the second piston to expand the suction chamber so that a negative pressure prevails in the suction chamber and ink is suctioned through the suction port into the suction chamber; moves both the pistons at the same moving speed until the suction chamber is expanded to a predetermined extent, the suction port is closed by the second piston and the first piston opens the discharge port; moves the first piston in the reverse direction until the same comes into contact with the second piston to discharge the ink suctioned into the suction chamber through the discharge port; and moves both the pistons in the reverse direction to return the pistons to their initial position. The pump housing may be of a cylindrical shape or an annular shape. A suction pump in a modification may be provided with a plurality of pairs of pistons forming a plurality of suction chambers each provided with a suction port and a discharge port. <MATH></p> |
