Medical injection device with electric motor drive control
An injection device for delivering a medicament to the human or animal body. The injection device comprising a housing, a piston rod for driving a bung of a medicament container, a drive mechanism including a motor for providing an output drive to the piston rod for delivering the medicament; and controller for controlling operation of the device.
1. An injection device for delivering a medicament to a patient, wherein the injection device comprises:
a housing;
a piston rod for driving a bung of a replaceable medicament container, the piston rod retractable to a backstop position;
a drive mechanism including a motor for providing an output drive to the piston rod for delivering a user settable dose of the medicament and retracting the piston rod to the backstop position; and
a controller that controls operation of the device; wherein:
the controller comprises:
a drive signal generator that generates an input drive signal for the motor;
an encoder that generates an encoder output signal indicative of the output drive of the motor;
wherein the controller varies the operational control of the device in dependence on a comparison between the input drive signal and the encoder output,
wherein the encoder output signal is a pulsed signal having a timing characteristic that corresponds to the output drive of the motor,
wherein a comparison between counts of the encoder output with counts of stepper pulses is indicative of motor stall or motor slip,
wherein the motor is deliberately stalled against a predetermined reference point when the quantum of slip exceeds a predetermined threshold value, and
wherein the controller calculates the deficit in the medicament administered and performs administration of this dose.
2. An injection device according to claim 1 , wherein the input drive signal comprises stepper pulses for driving the motor.
3. An injection device according to claim 1 , wherein a plurality of reference points are included in the device, each reference point being indicative of a different operational aspect of the device.
4. An injection device according to claim 3 , wherein the reference points include any one or more of: backstop position; dose delivered; door position; drive position; and reset threshold.
5. An injection device according to claim 3 , wherein the reference points relate to the input drive signal such that respective reference points correspond to respective counts of stepper pulses with reference to a device datum.
6. An injection device according to claim 3 , wherein in an event that motor slip or stall is detected the controller is operative for determining a quantum of slip relative to one of the reference points whereupon said controller adjusts the operational control of the device according to a predetermined criteria.