Drug delivery system with multipolar magnet and sensor system

An add-on device adapted to be releasably mounted on a drug delivery device, the drug delivery device comprising:

• a housing forming a reference component,
• a drug reservoir or structure for receiving a drug reservoir,
• drug expelling structure comprising:
• a rotatable dose setting member allowing a user to set a dose amount of drug to be expelled, and
• allows a user to set a dose amount of drug to be expelled with a resolution of at least 18 degrees corresponding to 20 increments for a full rotation of the rotatable dose setting member;
• a release member actuatable between a proximal position and a distal position, the proximal position allowing a dose amount to be set, the distal position allowing the drug expelling structure to expel a set dose,
• a drive spring arranged to be strained during dose setting and released by the release member to thereby drive expelling of an amount of drug from the drug reservoir, the drive spring being formed from a magnetisable material, and
• an indicator element comprising 2, 3 or 4 dipole magnets and being adapted to rotate relative to the reference component and corresponding to a reference axis during setting and/or expelling of a dose amount, the amount of rotation being indicative of the size of the set and/or expelled dose amount,
• the add-on device comprising:
• a plurality of magnetometers arranged non-rotational relative to the reference component and adapted to determine continuous magnetic field values from the plurality of dipole magnets, and
• processor structure configured to determine on the basis of measured values from the plurality of magnetometers a rotational position and/or a rotational movement of the indicator element with a resolution of at least 18 degrees,
• wherein the determined rotational position and/or a rotational movement of the indicator element correspond to a set and/or expelled dose amount.

A drug delivery device adapted to be used in combination with an add-on device adapted to be releasably mounted thereon, the drug delivery device comprising:

• a housing forming a reference component,
• a drug reservoir or structure for receiving a drug reservoir,
• a drug expelling structure comprising a rotatable dose setting member allowing a user to set a dose amount of drug to be expelled
• a release member actuatable between a proximal position and a distal position, the proximal position allowing a dose amount to be set, the distal position allowing the drug expelling structure to expel a set dose,
• a drive spring arranged to be strained during dose setting and released by the release member to thereby drive expelling of an amount of drug from the drug reservoir, the drive spring being formed from a magnetisable material, and
• an indicator element comprising 2, 3, or 4 dipole magnets and being adapted to rotate relative to the reference component and corresponding to a reference axis during setting and/or expelling of a dose amount, the amount of rotation being indicative of the size of the set and/or expelled dose amount, and
• the drug expelling structure allows a user to set a dose amount of drug to be expelled with a resolution of at least 18 degrees corresponding to 20 increments for a full rotation of the rotatable dose setting member.