Automated liquid dispenser control

• US 4,475,666 A
• Filed: 08/31/1981
• Issued: 10/09/1984
• Est. Priority Date: 08/31/1981
• Status: Expired due to Term

• Current Assignee: Dade Behring, Inc. (Siemens AG)
• Original Assignee: American Hospital Supply Corp. (Baxter International Inc.)
• Inventors: Bilbrey, Robert A., Koball, Bruce R., Loram, John S. H.
• Primary Examiner(s): Rolla, Joseph J.
• Assistant Examiner(s): Miller, Laurence J.
• Application Number:
  US06/297,956
• Time in Patent Office: 1,135 Days
• Field of Search: 222/14-21, 222/23, 222/36, 222/37, 222/41, 222/63-65, 222/71, 222/309, 222/333, 73/864.12, 73/864.16, 73/864.17, 73/864.18, 422/100, 604/4, 604/7, 604/50, 604/65, 604/67, 604/152, 604/155, 250/231 SE
• US Class Current: 222/14
• CPC Class Codes: B01L 3/021 Pipettes, i.e. with only one conduit for withdrawing and redistributing liquids

Abstract

A servo controlled actuator for an automated liquid dispenser for dispensing reagents or diluting samples with reagent automatically in accord with a programmed local microprocessor or remote computer control. The dispenser has at least one reciprocable syringe, valving for it and a syringe actuator driven by a hybrid servo control. The actuator includes a bi-directional variable speed motor and an encoder developing a pulse train which in number is representative of the position of the syringe piston and in repetition rate is representative of piston velocity. A microprocessor controls the piston stroke from the pulse train by comparison to a memory-stored count and controls piston velocity in predetermined relation to the terminal end of piston travel.

Claims

1. In an automated liquid dispenser having at least one metering syringe with a precision bored cylinder and a piston reciprocable within the cylinder, valve means for selectively connecting the syringe cylinder to one or more of a set of intake and delivery valve ports, a syringe actuator having a threaded lead-screw and a lead-screw nut for reciprocating the piston within the syringe cylinder, improved servo controlled drive means for rotating the lead-screw and lead-screw nut relative to one another comprising

a bi-directional variable speed motor rotating one or the other of the lead-screw and nut;

an encoder developing from the motor rotation a train of pulses each representative of an increment of piston travel with their repetition rate representative of piston velocity;

a driver for said motor;

a position counter accumulating the pulses in said encoder pulse train;

a microprocessor for polling the position counter and comparing its accumulated count to a predetermined memory-stored count representative of lengths of piston stroke, and for disabling the motor driver when the accumulated count in the position counter reaches the memory-stored count corresponding to a preselected stroke length;

an error amplifier for supplying a variable velocity control signal to the driver for said motor;

a tachometer converting the pulse train from the encoder to an analog voltage proporational to velocity of piston travel that is supplied to the error amplifier;

a digital-to-analog converter also outputing an analog voltage to the error amplifier; and

a microprocessor supplying a velocity command signal to the digital-to-analog converter in accord with memory-stored values relative to stroke end to cause an increase in converter output voltage during a preselected acceleration portion and a decrease in converter output voltage during a preselected deceleration portion of the piston stroke.

2. The automated liquid dispenser of claim 1 wherein the microprocessor periodically polls the position counter to ascertain the instantaneous position of the piston in its stroke, compares that count with the number of counts remaining in a preselected length of stroke for the piston and then outputs a velocity control command to the digital-to-analog converter corresponding to that position.

3. The automated liquid dispenser of claim 1 wherein a soft home detector senses piston arrival at a home position near one end of the piston stroke and causes the microprocessor to disable the motor driver upon the piston arrival at the home position.

4. In an automated liquid dispenser having at least one metering syringe with a precision bored cylinder and a piston reciprocable within the cylinder, valve means for selectively connecting the syringe cylinder to one or more of a set of intake and delivery valve ports, improved servo controlled drive means for rotating the lead-screw and lead-screw nut relative to one another comprising

a motor rotating one or the other of the lead-screw and nut;

an encoder developing from the motor rotation a train of pulses each representative of an increment of piston travel with their repetition rate representative of piston velocity;

a driver for said motor;

a position counter accumulating the pulses in said encoder pulse train;

a microprocessor for polling the position counter and comparing its accumulated count to a predetermined memory-stored count representative of lengths of piston stroke, and for disabling the motor driver when the accumulated count in the position counter reaches the memory-stored count corresponding to a preselected stroke length; and

a valve position encoder that supplies a position signal to the microprocessor representative of the position of the intake and delivery valve ports

whereby the microprocessor in coordination with reciprocation of the syringe piston switches the valve position in a memory-stored sequence.

5. In an automated liquid dispenser having at least one metering syringe with a precision bored cylinder and a piston reciprocable within the cylinder, valve means for selectively connecting the syringe cylinder to one or more of a set of intake and delivery valve ports, a syringe actuator having a threaded lead-screw and a lead-screw nut for reciprocating the piston within the syringe cylinder, improved servo controlled drive means for rotating the lead-screw and lead-screw nut relative to one another having a velocity mode and a position mode comprising

a bi-directional variable speed motor rotating one or the other of the lead-screw and nut;

an encoder developing from the motor rotation a train of pulses each representative of an increment of piston travel with their repetition rate representative of piston velocity;

a driver for said motor;

a position counter accumulating the pulses in said encoder pulse train;

a microprocessor for polling the position counter and comparing its accumulated count to a predetermined memory-stored count representative of lengths of piston stroke, and for disabling the motor driver when the accumulated count in the position counter reaches the memory-stored count corresponding to a preselected stroke length;

an error amplifier in a velocity mode for supplying a variable velocity control signal to the driver for said motor;

a tachometer converter converting the pulse train from the encoder to an analog output proportional to velocity of piston travel that is supplied to the error amplifier;

a digital-to-analog converter also supplying an analog output to the error amplifier; and

a microprocessor supplying a velocity command signal to the digital-to-analog converter in accord with memory-stored values relative to stroke end to cause an increase in converter output during a preselected acceleration portion and a decrease in converter output during a preselected deceleration portion of the piston stroke,

wherein the microprocessor at the terminal end of each piston displacement switches the error amplifier to position mode to supply a corrective countering output to the motor driver upon receipt of any signal from the tachometer converter.