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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
First Claim
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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 comprisinga 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.

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