A stand-alone electronic controller drives a stepper motor which moves a sliding block by means of a threaded rod, and actuating the syringe pusher.
The man-machine interface is made up of a keyboard (4 push buttons), an alphanumeric display (4 x 20 characters), 2 leds and a buzzer. Parameter setting and supervision are performed through this interface.
Several control mechanisms are provided to continuously check the correct operation of the unit and alert in case of problems (pressure sensor on the syringe plunger, carriage position sensor and electronic watchdog).
The unit is powered by an external 12V power supply.
Optionally, a battery (similar to a cordless tool battery) can be installed in order to give autonomy to the device in case of power failure or patient displacement.
Three types of syringes can be installed in the device: 10 ml, 20 ml and 50 ml.
The selection of the syringe type is made by the user via the keypad. A confirmation is requested to minimize the risk of wrong selection (human error).
The selected syringe type is permanently displayed on the screen.
In some situations several simultaneous injections are necessary for the same patient (up to 6).
The mechanical design of the supports allows stacking the devices.
The electronic assembly has dedicated connectors allowing the chaining of the power supply in order to use only one PSU for the whole unit. The power supply unit is dimensioned accordingly.
Power supply section
In the usual operating configuration, the device is powered by an external 12V DC power supply unit.
It is possible to run the device with an external battery (Ryobi 18V type, reference RB18Lxx) to temporarily take over the power supply in case of power failure or patient displacement.
On power-up, the device starts spontaneously and displays an alarm status. This alerts the practitioner that a restart has occurred, either following a power failure or following a restart due to a technical problem.
The device is able to save its settings and its instantaneous operating information, thus making it possible – in the event of a loss of power – to resume injection where it was interrupted, i.e. at the precise moment when the lack of electrical power was detected.
If there is a dual power supply (mains + battery), the presence of the mains disconnects the battery. The device does not recharge the battery. The battery is removable and must be recharged in its original charger.
This design allows, when several OpenSyringePumps are used, a high degree of flexibility regarding the power source:
- use of only one battery for the entire syringe pump battery,
- hot swapping of batteries using the battery holder of another OpenSyringePump battery on the stack
- In extreme situations, full battery operation is possible. One battery allows an OpenSyringePump to run autonomously for 10 hours on a 15 minute charge. In this case, the battery is replaced when the syringe is changed.
The device is equipped with a force sensor placed on the movable pusher and measures the pressure applied to the syringe plunger.
This system ensures a supervision of the operation and allows to alert in case of possible anomalies:
- Abnormal overpressure (blocked plunger, misplaced syringe, occlusion…)
- Insufficient contact pressure (missing syringe, poor physical contact of the mobile carriage with the syringe plunger)
The device is equipped with a position sensor (encoder) to know the position of the mobile pusher.
This system ensures a supervision of the operation and triggers an alert in case of movement inconsistent with the commands.
- Incoherent pusher displacement
An automatic calibration allows the device to reset the mechanical origin of the pusher thanks to a limit switch at the beginning of each cycle.
An automatic calibration mode allows the precision of the electromechanical assembly to be calibrated.
The sliding pusher is driven by a stepper motor. The speed of movement for injection is determined according to the user-defined parameters.
The plunger is equipped with force and position sensors.