Multi-channel pipetting head

A multi-channel head of a liquid handling apparatus for aspirating and dispensing a metered amount of liquid via an array of disposable tips each having a tip collar, the multi-channel head comprising:

• an array of connectors for picking up the array of disposable tips, wherein a peripheral end of each connector includes a seat and an elastomeric seal which is arranged on the seat that surrounds an outer circumference of the connector;
• an alignment plate that is moveable in a z-direction, parallel to a centre axis of the disposable tips, the alignment plate having a plurality of openings through which the connectors extend, and an underside that defines an alignment plane which is adapted to contact upper surfaces of the tip collars of each disposable tip during an alignment action to thereby align the upper surfaces of the tip collars along the alignment plane of the moveable alignment plate;
• a motor and a linear displacement mechanism, driven by the motor, for moving the alignment plate in a z-direction relative to the connectors, and
• a controller for controlling the motor;
• wherein
• the multi-channel head is configured to attach the array of disposable tips to the array of connectors in a pick-up action, when the alignment plate is in a stop position, in which the multi-channel head is lowered relative to the disposable tips so as to insert each connector into an internal passageway of a corresponding disposable tip by an amount sufficient to bring the upper surface of a collar of the disposable tips into contact with the underside of the alignment plate, wherein the insertion of each connector deforms the elastomeric seal against the disposable tip internal passageway so as to form a sealing contact therewith that provides the sole attachment force between each disposable tip and the respective connector;
• and wherein
• the controller is programmed to cause an alignment action to be performed, once the pick-up action is complete, in which the linear displacement mechanism moves the alignment plate from the stop position by a first amount, which is sufficient to close any gap between the underside of the alignment plate and the upper surface of the tip collars, which exists due to relaxation of the deformed elastomeric seals and/or due to small positional variations in z-direction when the disposable tips are picked up from a holder and thereby align the upper surfaces of the tip collars along the alignment plane of the moveable alignment plate.