Plunger operated pipet

• US 4,435,989 A
• Filed: 12/04/1981
• Issued: 03/13/1984
• Est. Priority Date: 07/03/1980
• Status: Expired due to Fees

• Current Assignee: Beckman Instruments, Inc. (Danaher Corporation)
• Original Assignee: Beckman Instruments, Inc. (Danaher Corporation)
• Inventors: Meyer, Richard C., Carroll, Edward L.
• Primary Examiner(s): Swisher, S. Clement
• Application Number:
  US06/327,393
• Time in Patent Office: 830 Days
• Field of Search: 73/864.13, 73/864.14, 73/864.17, 73/864.18
• US Class Current: 73/864.14
• CPC Class Codes: B01L 3/0224 having mechanical means to set stroke length, e.g. movable stops B01L3/0231, B01L3/0234 take precedence

Abstract

Plunger operated pipet operable to execute different lengths of plunger movement during successive fluid pickup and fluid discharge operations or strokes. A stop member is movable between first and second locations in the pipet body to halt plunger movement at two different positions. A drive spring for driving the stop member from one location to the other is energized by a manually operable arming element and is retained in one location against action of the drive spring during a first plunger stroke. A release mechanism responsive to plunger movement during the first stroke disables the retaining means allowing the drive spring to move the stop member to the second location at which position the plunger is halted during the succeeding discharge stroke. The arming element is actuated by and in response to positioning of a replaceable tip on the pipet body. The arming element exerts a force on the tip sufficient to expel the tip from the body unless the tip is properly seated on the body thus ensuring that the pipet is armed if the tip is properly seated. A signalling system is provided which signals the occurrence of the second or fluid dispensing stroke of plunger movement.

Claims

1. Pipetting apparatus comprising:

a generally tubular body having an open forward end for receiving and expelling fluid and adapted to receive a replaceable open tip thereon;

a plunger supported for axial movement in the body to draw fluid into and expel fluid from the open tip on the body with axial movement away from and toward the open end;

stop means movable between first and second locations in the body to halt movement of the plunger in one direction at first and second axial positions thereby establishing different stroke lengths of plunger movement in the body;

spring means for driving the stop means in one direction between the first and second locations;

arming means for energizing the spring means in response to the positioning of the replaceable tip on the body;

means for retaining the stop means in one of the first and second locations against action of the spring means; and

release means responsive to plunger movement away from the forward end during a first plunger stroke following energizing of the spring means for disabling the retaining means and allowing the spring means to drive the stop means to the other of the first and second locations whereby the first plunger stroke and the succeeding plunger stroke are of the different stroke lengths.

2. The apparatus of claim 1 wherein the arming means further includes an arming element movable between unarmed and armed positions and return spring means biasing the arming element toward the unarmed position in which position the arming element obstructs positioning of the tip on the body;

and wherein

the tip, during installation thereof, engages and drives the arming element toward the armed position thereof against the return force of the return spring means engaging the arming element, the return spring force being applied by the arming element to the tip in a direction to expel the tip from the body and being of sufficient strength to so expel the tip unless the tip is properly seated and secured on the body, thereby allowing the arming means to energize the driving spring means only if the tip is properly installed.