US Patent 10149947 Automatic drug injection device with sophisticated drive mechanism

A drug delivery device for setting and dispensing of a dose of a medicament includes a housing extending in an axial direction and a piston rod to operably engage with a piston of a cartridge to displace the piston in a distal axial direction. The drug delivery device further includes a drive spindle operably engageable with the piston rod during dose dispensing and a drive member axially displaceable relative to the drive spindle against the action of a spring element during dose setting and being threadedly engaged with the drive spindle to form a spindle gear.