Chemical apparatus and process disinfecting – deodorizing – preser – Control element responsive to a sensed operating condition
Patent
1997-02-11
1998-06-23
Ludlow, Jan
Chemical apparatus and process disinfecting, deodorizing, preser
Control element responsive to a sensed operating condition
7386402, 7386413, 7386416, 7386487, 222287, 222309, 222631, B01L 302
Patent
active
057701598
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a pipette for dispensing successive volumes of liquid by repeated action on a pusher.
BACKGROUND OF THE INVENTION
French patent application No. 2 432 161 describes a pipette comprising a housing of oblong shape incorporating a mechanism for adjusting the volume to be dispensed, and a syringe for fixing removably to the bottom end of said housing. A piston suitable for moving in sealed manner inside the syringe body is mounted at the bottom end of a pushrod capable of sliding longitudinally through the housing. In order to dispense a predetermined volume of liquid, the pushrod is driven downwards by action on a pusher via a drive lever that is capable of moving over a predetermined stroke between a fixed bottom abutment and an adjustable top abutment. The lever comprises a first portion pierced by a hole enabling the pushrod to pass therethrough with small clearance, and a second portion extending transversely to the axis of said hole. The pusher is disposed to exert a pressure force in the vicinity of the free end of the second portion of the lever, and by a wedging effect to drive the thrust rod. The lever is also subjected to upwards resilient biasing so as to ensure that it returns automatically to its rest position against the top abutment when the pusher is released. That type of pipette has given satisfaction. However, in the long run, wear on the various component parts of the pipette gives rise to reduced accuracy.
SUMMARY OF THE INVENTION
An object of the present invention is to propose a novel pipette presenting greater accuracy than known pipettes, even after prolonged use.
The pipette of the invention is of the type comprising: volume of liquid to be dispensed; syringe body provided with a fluid-passing orifice and a piston rod mounted to move inside said syringe body; removably connected at one end to said piston rod; said liquid-passing orifice, the lever extending transversely to the longitudinal axis of the thrust rod and being provided with a hole through which the thrust rod passes with a small amount of clearance, the lever also being mounted with the ability to move inside the housing over a stroke that is adjustable in the longitudinal direction of the thrust rod between a rest position defined by an adjustable abutment of the adjustment mechanism and an end-of-stroke position defined by a fixed abutment, and being returned towards said rest position by resilient return means; and being provided at one end extending outside the housing with a pushbutton and being capable of acting via its other end on the lever to tilt it obliquely relative to the thrust rod and then to drive the thrust rod by wedging towards the fluid-passing orifice together with the piston rod so as to expel a predetermined volume of liquid as defined by the stroke of the lever between said rest position and said end of stroke position, return movement of the lever towards its rest position after each action on the pushbutton taking place under drive from said resilient return means while the piston rod retains its position within the body of the syringe.
In characteristic manner, the lever is mounted to rotate about an axis that intersects the axis of said hole perpendicularly and substantially halfway along the hole.
Thus, however much the clearance for the rod in the hole through the lever may increase due to wear, the lever continues to tilt about the same geometrical axis of rotation until the thrust rod is wedged in the hole; if there is considerable wear, then the lever tilts further, but unlike known pipettes, that has no effect on the stroke of the thrust rod. In known pipettes, the lever is not guided during its tilting movement and said movement can be accompanied by a small amount of sliding over the thrust rod, with the result that the thrust rod is not driven over the full distance defined by the difference between the fixed and adjustable abutments, with the result that the accuracy of the pipette is reduced.
Advantageously, the lever is d
REFERENCES:
patent: 2534857 (1950-12-01), Crewe
patent: 4033484 (1977-07-01), Ornsteen
patent: 4249419 (1981-02-01), Thomas
patent: 4339058 (1982-07-01), Wendt
patent: 4467942 (1984-08-01), Oshikubo
patent: 4589870 (1986-05-01), Citrin et al.
patent: 4967604 (1990-11-01), Arpagaus et al.
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