Automatic sampling and metering pipette for laboratory work - in which easily dismantled appts. transfers small quantities completely with accuracy

摘要

A metering appts. with a pipette and a pipette column movable vertically by a rocker arm and rotatable on its vertical axis by a jointing linkage, has an arm on the column carrying the pipette and connected to a suction cylinder. The column consists of a guide bar anchored securely to a baseplate, on which a lifting tube is free to slide and turn under the control of the operating mechanisms. A crank and a rocker arm bring about a motion along a path following a loop, and the suction cylinder is positioned inside the lifting tube above the guide bar. The rotary motion of the lifting tube is brought about by a linkage including a ring from which two journals project, sitting loosely on a ring fixed to the tube. The fixed ring has two flanges to a flat ring resting on the bottom flange of the ring fixed to the lifting tube; a fork from the flat ring engaging with a vertical rod standing parallel to the column on the linkage. between the ring of the rotary motion and the ring for the lifting action there is a compression spring fitted. The driving shaft has a crank formed by a journal offset to the centre of a disk. The journal carries a ball bearing and moves in a long slot in the rocker arm. The lifting tube is in two sections. The lower carries the details for the lifting and turning motion, whilst the suction arrangement is enclosed in the upper section. At its free end the piston rod of the suction cylinder has a centralising device which comes into contact with the end cover of the tube. The suction cylinder is attached to a sliding block and between the top of the cylinder and the lifting tube cover, enclosing the piston rod there is a compression spring. The pipette arm extends through a long slot in the upper section of the lifting tube into the sliding block and there is a channel from the pipette through the arm and the block into the cylinder. Beneath the sliding block, with a spacer ring between them, there is a removable stop ring. The lower end of the slide block is machined down to give a journal with flats forming a nose, whilst in the guide bar there is a corresponding slot, and these engage with each other only in the suction position of the lifting tube. Transfers small quantities of liquids from one vessel to another in very accurate amounts without bubbles. The apparatus is cheap to manufacture, easily dismantled and reassembled.