DK200500116U1 - Motor-powered injection apparatus - Google Patents

Description

DK 2005 00116 W

Motor driven injection apparatus

This invention relates to a motor-powered injection apparatus. from WO 02/058766. Here is described an injection apparatus where the dose size is set electronically and where a motor is used to propel the plunger in accordance with the set dose size.

Injectors of this type are usually provided with a replaceable cartridge containing liquid medicine. A cartridge is usually made of glass and open at both ends. At the distal end, the cartridge is provided with a rubber barrier through which an injection needle can penetrate, and at its proximal end, it is provided with a rubber plunger which can be displaced forwardly in the cartridge to eject the liquid drug through the injection needle. When such a cartridge is empty, it is replaced with a new, filled cartridge. When replacing the cartridge, the piston rod must be returned to its starting point after which the now empty cartridge can be removed. After inserting the new cartridge, the piston rod must be driven forward until it meets the rubber piston in the cartridge.

With this invention, it is desired to provide an injection apparatus with a mechanism which can detect when the plunger rod contacts the rubber plunger and is capable of indicating this to the user of the injection apparatus.

Requirement 2:

This mechanism may, for example, have a contact sensor or a proximity sensor located at the distal end of the piston rod, which can detect when physical contact is established between the piston rod and the rubber piston. This can be realized in various ways by, for example, using an electrical contact with low actuation force, electrical resistance measurement or capacity measurement between the piston rod and the rubber piston, optical or magnetic measuring principles of the distance between the piston rod and the rubber piston, a simple force sensor measuring the contact force between the piston rod and the rubber piston. In addition, there are other ways of measuring distance between two subjects or other ways of measuring whether there is contact between two subjects.

Requirement 3: In another example, the mechanism may be an engine current monitor.

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DK 2005 00116 W

During the detection of the rubber piston, the motor current (1 motor) is measured. When the motor current exceeds a threshold, it indicates that the piston rod has made contact with the rubber piston and the driving force is increasing.

It can be expected that lmatQr will change with wear and tear and external influences. Also, it depends on where the rubber piston is in relation to the piston rod when detection starts.

Furthermore, it is to be expected that there will always be a known minimum distance to the rubber piston and the piston rod. This can be utilized to compensate for the external influences e.g. by measuring and midi the unloaded motor current (U toa <i) until the piston rod reaches the rubber piston. During detection, Ι ^ γ is compared to Ideiew (= lnoioad4 * a detection threshold). Exceeded detector is rubber stamp detect!

To remove noise in the measurement and make a time delay of lnotoad. Submarine is calculated via an auto-regressive mean, where the latest measurement is weighted in relation to previously measured values. By weighting new measurements low (1-5%), a mean is obtained which is slowly updated during detection. However, not so quickly that the Ui03d changes at the same rate as the engine when the piston rod meets the rubber piston.

To measure the motor current, a current sense amplifier is used which measures the voltage across a resistor passing through the motor current, and subsequent filtering gives a proportional representation of the motor current.

Requirement 4:

To ensure good dosing accuracy, it is necessary that the cartridge holder and housing of the injector are tightly connected. This avoids deflection of the cartridge holders relative to the housing. In addition to a more precise dosing, this also results in a more accurate detection of the rubber stamp of the cartridge.

Figure 1 shows an injection apparatus according to the invention.

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DK 2005 00116 W

Figure 1 shows an injection apparatus consisting of a housing 1 containing a drive mechanism 2 and an electric motor 3. A cartridge holder 4 is coupled to the housing 1 and contains a liquid medicine cartridge 5. To the distal end of the cartridge 5 is coupled an injection needle 6 and the proximal end is closed with a displaceable rubber piston 7.

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The rubber piston 7 is driven forward by a piston rod 8 driven by the drive mechanism 2 and the electric motor 3. Between the rubber piston 7 and the piston rod 8, for example, a piston rod foot 9 may be arranged.

The piston rod 8 or alternatively the piston rod foot 9 may, on the side facing the rubber piston 7, be provided with a contact element 10 which can emit an electrical signal when the piston rod 8 (or the piston rod foot 9) comes into contact with the rubber piston 7 4.

DK 2005 00116 W

UTILITY MODEL REQUIREMENTS

An injection apparatus comprising: - a liquid medicine cartridge (5), said cartridge (5) containing a displaceable rubber piston (7) that can be displaced forward to dose the liquid medicine, - a piston rod (8) for displacing the rubber piston (7) further, - an electric motor for driving the piston rod (8), - which injection apparatus is new, - further comprising a mechanism indicating when the piston rod (8) is in contact with the rubber piston (7).

An injection apparatus according to claim 1, which is new in that the mechanism is a sensor built into the piston rod (8).

The injection apparatus according to claim 1, which is new in that the mechanism is a monitoring of the motor current.

The injection apparatus according to claims 1-3, which is new in that the cartridge (5) is held in a cartridge holder (4) which can be secured to the housing of the injection device (1) through a rigid connection.

DK 2005 00116 W