Dispenser having a sub-assembly for selectively engaging and disengaging a plunger rod

1. A dispenser comprising:

a body having a longitudinal axis;

a plunger rod extending into the body along the longitudinal axis and coupled thereto to permit advancement along and rotation about the longitudinal axis;

a handle operable to advance the plunger rod into the body;

a sub-assembly including a ratchet and a cam member;

wherein the sub-assembly is in operative relation between the handle and the plunger rod and the sub-assembly is configured to shift between an engagement and a disengagement of the handle with the plunger rod;

wherein the ratchet is biased into engagement with the plunger rod, when the sub-assembly is engaged, to effect forward advancement of the plunger rod along the longitudinal axis upon actuation of the handle; and

wherein the cam member is coupled with the ratchet and the plunger rod and the cam member is positioned, upon rotation of the plunger rod about the longitudinal axis, to counter bias the ratchet away from the plunger rod to disengage the ratchet from the plunger rod and to permit rearward advancement of the plunger rod along the longitudinal axis.

2. The dispenser of claim 1 , further comprising a retainer housing of the sub-assembly and coupled to both the handle and to the cam member, the retainer housing supporting the ratchet.

3. The dispenser of claim 2 , wherein the retainer housing defines a yoke to rotatably receive at least a portion of the cam member therein.

4. The dispenser of claim 1 , wherein the cam member is mounted to the plunger rod through a keyed relationship.

5. The dispenser of claim 4 , wherein the keyed relationship includes a D-shaped outer surface profile of the plunger rod and a corresponding D-shaped profile on a throughbore of the cam member.

6. The dispenser of claim 1 , wherein the cam member includes a cylindrical body defining a bore therethrough, the plunger rod extending through the bore.

7. The dispenser of claim 1 , wherein the cam member includes a cylindrical body and further includes a camming lobe extending radially outward and circumferentially about the cam member body.

8. The dispenser of claim 7 , wherein the camming lobe defines a first camming surface extending a radial distance from the cam member body and a second camming surface extending a second radially farther distance from the cam member body.

9. The dispenser of claim 8 , wherein the second camming surface is circumferentially spaced about 30 to about 60° from the first camming surface.

10. The dispenser of claim 8 , wherein the second camming surface of the camming lobe is configured to counter bias the ratchet away from the plunger rod upon rotation of the plunger rod and the cam member about the longitudinal axis.

11. The dispenser of claim 7 , wherein the cam member defines a pair of stop surfaces proximate to the first and second camming surfaces.

12. The dispenser of claim 1 , further including a needle mounted to the body.

13. A dispenser comprising:

a dispenser body defining a first and second end thereof and having a longitudinal axis extending between the first and second ends;

a barrel mounted to the first end of the dispenser body;

a plunger rod extending into the dispenser body from the second end and mounted for advancement along and for rotation about the longitudinal axis;

a handle coupled to the plunger rod;

a ratchet biased into engagement with the plunger rod;

a ratchet retainer housing the ratchet and coupled to the handle; and

a rotatable cam member mounted to the plunger rod and defining a cam surface positioned to counter bias the ratchet away from the plunger rod to disengage the handle from the plunger rod upon rotation thereof.

14. The dispenser of claim 13 , wherein the ratchet retainer defines a yoke to rotatably receive a portion of the rotatable cam member therein.

15. The dispenser of claim 13 , wherein the rotatable cam member is mounted to the plunger rod through a keyed relationship.

16. The dispenser of claim 15 , wherein the keyed relationship includes a D-shaped outer surface profile of the plunger rod and a corresponding D-shaped throughbore of the rotatable cam member.

17. The dispenser of claim 13 , wherein the rotatable cam member includes a cylindrical body defining a bore therethrough, the plunger rod extending through the bore.

18. The dispenser of claim 17 , wherein the rotatable cam member includes a cylindrical body and wherein the rotatable cam member further includes a camming lobe extending radially outward and circumferentially about the rotatable cam member body.

19. The dispenser of claim 18 , wherein the camming lobe defines a first camming surface extending a radial distance from the cam member body at one end thereof and a second camming surface extending a second radially farther distance from the rotatable cam member body, the second camming surface circumferentially spaced from the first camming surface.

20. The dispenser of claim 19 , wherein the second camming surface of the camming lobe is configured to counter bias the ratchet away from the plunger rod upon rotation of the plunger rod and the rotatable cam member about the longitudinal axis.

21. The dispenser of claim 18 , wherein the cam member defines a pair of stop surfaces proximate to the first and second camming surfaces.

22. The dispenser of claim 13 , further including a needle mounted to an end of the barrel.