Pipettor stroke control mechanism

Claim 2

A pipette assembly, comprising; barrel means, reciprocal piston means slidable in said barrel means to draw fluid into and expel fluid from a reservoir communicating with said barrel means, pushbutton means for actuating said piston means, means providing alternate changes in stroke length including an indexing member rotatably carried by said piston means, said indexing member having high and low stops thereon, abutment means for selectively engaging said high and low stops on the indexing member, means selectively rotating the stops into alignment with the abutment means including a plurality of axially opposed fingers on said indexing member, cam means engageable with said fingers to rotate the indexing member, said cam means including a first cam surface engageable with one set of opposed fingers and a second cam surface engageable with another set of fingers, said fingers being circumferentially spaced so that when one of the fingers of one set completes engagement with said one cam surface, one of the fingers of the other set is in axial alignment with a portion of the other cam surface so that the indexing member continues rotation in the same direction upon reverse movement of the piston means.

Claim 3

A pipette assembly as defined in claim 1, wherein at least one set of said fingers is flexible, the fingers of one set being out of phase rotationally with respect to the fingers on the other set, the fingers being sufficiently long so that the distance between opposed fingers is less than the distance between the cam surfaces thereby requiring bending of the flexible fingers and providing positive rotation of the indexing member.

Claim 4

A pipette assembly as defined in claim 2, including four fingers in each set cantilevered on said indexing member, said fingers each being chamferred to provide camming surfaces parallel to the cam surfaces of said cam means, said cam having four camming surfaces, each of said surfaces being parallel to another of said surfaces thereby defining a parallelogram.

Claim 5

A pipette assembly as defined in claim 2, wherein said indexing member is a sleeve surrounding said piston means and rotatable relative thereto, each set of fingers consisting of four fingers cantilevered at each end of the sleeve and projecting toward the other set, one set of fingers being 45* out of phase with the other set of fingers.

Claim 6

A pipette assembly as defined in claim 2, said stops on the indexing member including an annular flange on one end of the indexing member, and recessed portions on said flange defining alternate high and low stops.

Claim 7

A pipette assembly as defined in claim 5, wherein said abutment means is stationary with respect to the barrel means.

Claim 8

A pipette assembly comprising barrel means for communication with a fluid reservoir, piston means axially movable in saId barrel means to draw fluid into and expel fluid from the reservoir respectively on intake and discharge strokes of said piston means, means including pushbutton means for actuating said piston means to move said piston means in one and the opposite direction, and means controlling changes in the stroke length of the piston means and operatively connected with said piston means and said pushbutton means, said means controlling changes in the stroke length comprising an indexing member having connected thereto opposed first and second sets of circumferentially spaced fingers, and a cam member having at least one cam means thereon engageable with said fingers, one of said members being axially movable relative to the other of said members in response to ax1al movement of said piston means in one direction to effect camming engagement between said cam means and at least one of said fingers of said first set, said cam means and said one finger of said first set effecting relative indexing rotation of one of said members in a predetermined direction of rotation by said camming engagement, said axially movable member moving axially in response to axial movement of said piston means in the opposite direction to effect camming engagement between said cam means and one of said fingers of said second set, said cam means and said one finger of said second set effecting relative indexing rotation of said rotated one of said members in said predetermined direction of rotation by said last named camming engagement, first engagement means on said axially movable one of said members, and second engagement means within the assembly and engageable with said first engagement means, one of said first and second engagement means including high and low stop means alternately engageable with the other of said engagement means for stopping the axial movement of said axial movable one of said members to effect strokes of different lengths on alternate strokes of said piston means.

Claim 9

A pipette assembly comprising barrel means for communication with a fluid reservoir, piston means axially movable in saId barrel means to draw fluid into and expel fluid from the reservoir respectively on intake and discharge strokes of said piston means, means including pushbutton means for actuating said piston means to move said piston means in one and the opposite direction, and means controlling changes in the stroke length of the piston means and operatively connected with said piston means and said pushbutton means, said means controlling changes in the stroke length comprising an indexing member having connected thereto opposed first and second sets of circumferentially spaced fingers, and a cam member having at least one cam means thereon engageable with said fingers, one of said members being axially movable relative to the other of said members in response to ax1al movement of said piston means in one direction to effect camming engagement between said cam means and at least one of said fingers of said first set, said cam means and said one finger of said first set effecting relative indexing rotation of one of said members in a predetermined direction of rotation by said camming engagement, said axially movable member moving axially in response to axial movement of said piston means in the opposite direction to effect camming engagement between said cam means and one of said fingers of said second set, said cam means and said one finger of said second set effecting relative indexing rotation of said rotated one of said members in said predetermined direction of rotation by said last named camming engagement, first engagement means on said axially movable one of said members, and second engagement means within the assembly and engageable with said first engagement means, one of said first and second engagement means including high and low stop means alternately engageable with the other of said engagement means for stopping the axial movement of said axial movable one of said members to effect strokes of different lengths on alternate strokes of said piston means.

Claim 10

The pipette assembly according to claim 7 wherein each of said sets of fingers comprises a plurality of equally circumferentially spaced fingers, the fingers of one of said sets being angularly offset from the fingers of the other of said sets.

Claim 11

The pipette assembly according to claim 7 wherein each of said fingers is resiliently flexible in a circumferential direction, and said cam means is sized relative to the spacing of said fingers to effect spreading apart movement of adjacent fingers respectively from said first and second sets of fingers during each piston means stroke, and return movement of said adjacent fingers upon each piston means stroke to hold said rotated member in an indexed position.

Claim 12

The pipette assembly according to claim 7 wherein said indexing member is said axially movable member.

Claim 13

The pipette according to claim 10 wherein said one engagement means is disposed on said indexing member.

Claim 14

The pipette according to claim 10 further including fixed shoulder means connected with said barrel means, and wherein said cam member is engaged by and axially movable with said indexing member into engagement with said shoulder means in response to a predetermined amount of axial movement of said indexing member in a given direction, said indexing member and said cam member being relatively rotatable upon further movement of said indexing member in said given direction to effect indexing movement between said members.

Claim 15

The pipette assembly according to claim 7 wherein said rotated one of said members is said indexing member.

Claim 16

The pipette according to claim 13 wherein said indexing member is also said axially movable member.

Claim 17

The pipette according to claim 7 wherein said first and second engagement means comprise engaging surfaces spaced from said fingers and lying in planes normal to the axis of rotation of said rotated one of said members.

Claim 18

The pipette assembly according to claim 7 wherein the fingers of said first set are in fixed axially spaced relation with the finGers of said second set.

Claim 19

The pipette assembly according to claim 16 wherein at least one of said sets of fingers are resiliently flexible and predeterminately spaced from the fingers of the other of said sets of fingers so that said flexible fingers are flexed during strokes of said piston means providing positive rotation of said rotated one of said members.