Media unit leveling assembly for media processing devices

1. A media processing device, comprising:

a platen roller configured to move a media unit along a media processing path to traverse a printhead adjacent to the platen roller;

an upstream drive assembly including (i) an upstream stationary roller disposed along the media processing path on a first side of the platen roller; and (ii) an upstream movable roller adjacent to the upstream stationary roller;

a downstream drive assembly including (i) a downstream stationary roller disposed along the media processing path on a second side of the platen roller; and (ii) a downstream movable roller adjacent to the downstream stationary roller;

a controller configured to:

control a motor to move, according to a predefined sequence, the upstream movable roller and the downstream movable roller between respective engaged and disengaged positions;

responsive to arrival of a leading edge of the media unit at the upstream stationary roller, control the motor to move the upstream movable roller into the engaged position; and

control the motor to maintain the upstream movable roller in the engaged position until the leading edge arrives at the downstream stationary roller.

2. The media processing device of claim 1 , the controller further configured to control the motor to lift the upstream movable roller into the disengaged position prior to a trailing edge of the media unit traversing the upstream stationary roller.

3. The media processing device of claim 1 , the controller further configured to control the motor to lift the downstream movable roller into the disengaged position prior to the leading edge of the media unit traversing the downstream stationary roller.

4. The media processing device of claim 1 , the controller further configured, responsive to the leading edge of the media unit arriving at the downstream stationary roller, to control the motor to:

move the downstream movable roller into the engaged position; and

lift the upstream movable roller into the disengaged position prior to arrival of a trailing edge of the media unit at the upstream movable roller.

5. The media processing device of claim 1 , wherein the upstream drive assembly further comprises a movable upstream roller housing supporting the upstream movable roller; and

wherein the downstream drive assembly further comprises a movable downstream roller housing supporting the downstream movable roller.

6. The media processing device of claim 5 , further comprising:

a registration bar biased toward the media processing path and having a post extending into engagement with the downstream movable roller housing;

the downstream movable roller housing having a cam surface for engaging the post to force the registration bar away from the media processing path when the downstream movable roller housing is lifted into the disengaged position.

7. The media processing device of claim 5 , further comprising:

a motor output connected to a control shaft for driving the control shaft;

a plurality of cam surfaces mounted on the control shaft for engaging the upstream movable roller housing and the downstream movable roller housing.

8. The media processing device of claim 6 , further comprising:

a first cam member mounted on a control shaft and including a first subset of the cam surfaces; and

a second cam member mounted on the control shaft and including a second subset of the cam surfaces.

9. The media processing device of claim 8 , wherein in the upstream moveable roller housing includes a first arm extending into engagement with the first cam member; and

wherein the downstream moveable roller housing includes a second arm extending into engagement with the second cam member.

10. The media processing device of claim 9 , wherein the printhead is adjacent to the platen roller and movable between an idle position and an active position for engaging the media unit.

11. The media processing device of claim 10 , further comprising:

a third cam member mounted on the nip roller control shaft and including a third subset of the cam surfaces.

12. The media processing device of claim 11 , wherein the printhead includes a third arm extending into engagement with the third cam member.

13. The media processing device of claim 12 , the controller further configured to control the motor to move the upstream moveable roller housing, the printhead, and the downstream moveable roller housing according to the predetermined sequence by:

for each of a plurality of stages in the sequence, controlling the motor to advance through a predetermined arc to position the first, second and third cam members.

14. The media processing device of claim 13 , wherein each predetermined arc is defined by a number of steps.

15. The media processing device of claim 1 , wherein in the engaged position, the upstream movable roller is at a first distance from the upstream stationary roller to form a nip for engaging the media unit; and

wherein in the disengaged position, the upstream movable roller is at a second distance, greater than the first distance, from the upstream stationary roller to release the nip.

16. The media processing device of claim 1 , wherein in the engaged position, the downstream movable roller is at a first distance from the downstream stationary roller to form a nip for engaging the media unit; and

wherein in the disengaged position, the downstream movable roller is at a second distance, greater than the first distance, from the downstream stationary roller to release the nip.

17. The media processing device of claim 1 , further comprising:

a ribbon cassette including (i) a supply roller, (ii) a take-up roller driven by a take-up motor, and (iii) a ribbon configured to travel from the supply roller to the take-up roller, traversing the printhead;

a rotational sensor coupled to the take-up roller;

the controller further configured to receive a sensor signal from the rotational sensor indicative of a rotational speed of the take-up roller, and to modulate an operational parameter of the take-up motor based on the sensor signal.

18. The media processing device of claim 17 , wherein the rotational sensor is a quadrature encoder.

19. A media processing device, comprising:

a platen roller configured to move a media unit along a media processing path to traverse a printhead adjacent to the platen roller;

an upstream drive assembly including (i) an upstream stationary roller disposed along the media processing path on a first side of the platen roller; (ii) an upstream movable roller adjacent to the upstream stationary roller; and (iii) a movable upstream roller housing supporting the upstream movable roller;

a downstream drive assembly including (i) a downstream stationary roller disposed along the media processing path on a second side of the platen roller; (ii) a downstream movable roller adjacent to the downstream stationary roller; and (iii) a movable downstream roller housing supporting the downstream movable roller;

a controller configured to control a motor to move, according to a predefined sequence, the upstream movable roller and the downstream movable roller between respective engaged and disengaged positions.

20. A media processing device, comprising:

a platen roller configured to move a media unit along a media processing path to traverse a printhead adjacent to the platen roller;

an upstream drive assembly including (i) an upstream stationary roller disposed along the media processing path on a first side of the platen roller; and (ii) an upstream movable roller adjacent to the upstream stationary roller;

a downstream drive assembly including (i) a downstream stationary roller disposed along the media processing path on a second side of the platen roller; and (ii) a downstream movable roller adjacent to the downstream stationary roller;

a controller configured to control a motor to move, according to a predefined sequence, the upstream movable roller and the downstream movable roller between respective engaged and disengaged positions;

a ribbon cassette including (i) a supply roller, (ii) a take-up roller driven by a take-up motor, and (iii) a ribbon configured to travel from the supply roller to the take-up roller, traversing the printhead;

a rotational sensor coupled to the take-up roller;

the controller further configured to receive a sensor signal from the rotational sensor indicative of a rotational speed of the take-up roller, and to modulate an operational parameter of the take-up motor based on the sensor signal.