GB1301342A - - Google Patents

Abstract

1301342 Pipettes MICROMEDIC SYSTEMS Inc 23 Feb 1970 [26 Feb 1969] 8600/70 Heading BIX [Also in Divisions F1 and F2] In a pipette for precise metering of very small amounts of liquid, the plunger 14h is moved by rotation of a ring 4 which acts via a ratchet mechanism to rotate a sleeve 15 carrying a nut 15a which engages a screwthread 14e of a member 14 carrying the plunger 14h, the stroke of the plunger in each direction being independently adjustable by graduated rings 3, 5 which control the effective strokes of the ratchet pawls. The angular travel of the ring 4 remains constant. The plunger 14h moves in a straight portion 7a of an inlet/ outlet tube 7. A peg 9c in a tubular handle 9 engages an axial slot 14d of the member 14 to prevent rotation of the latter. A housing 12, rigid with the handle 9 and having an end cover 13, contains the ratchet mechanism. The sleeve 15 carries ratchet wheels 21, 22 having oppositely directed teeth. Diametrically opposite pawls 23, 24 engageable respectively with wheels 21, 22 are carried by a ring 25 pivoted at 26 to an annulus 27 of U-shaped cross-section rotatably supported in the housing 12. Tongues 12A-D (Fig. 5) of the housing act as drag brakes on the annulus. Pins 29a, 29b on the annulus 27 are engageable with a stop 28 to limit rotation of the annulus. A radial pin 25a of the ring 25 extends through a slot 124 to engage the ring 4. Diametrically opposite axial pins 30, 31 of the ring 25 extend through holes 27b, 27c of the annulus 27 and are engageable with cams 37, 36 rotatable in the housing 12 and connected by radial pins 36a, 37a to the rings 3, 5 respectively. Sprung ball detents between the rings 3, 5 respectively. Sprung ball detents between the rings 3, 5 and fixed rings 8A, 8B retain the rings 3, 5 in their selected positions, which determine the angular positions of the cam ring 36, 37. As the ring 4 is rotated over its full travel, carrying with it the ring 25 and annulus 27, the cams 36, 37 control the rocking of ring 25 about pivot 26 relative to the annulus 27 to determine the angle over which a pawl is drivingly engaged with its ratchet wheel. Pawl 23 and cam 36 are involved in the suction stroke during clockwise movement (Fig. 2) of the ring 4, and pawl 24 and cam 37 in the discharge stroke during anticlockwise movement. Either stroke is adjustable in steps from zero to a maximum. To fill the syringe completely, the ratchet drive is bypassed, the syringe being supported on a strand 41, (Fig. 15) so that the sleeve 15 can be rotated by a knob 50 acting via gears 48, (51), 52, (40), the gear (40) being rigid with the sleeve 15 (Fig. 1).