Infusion devices and methods are provided for a drug delivery system and can include an infusion needle (1) having a tip end (2) and a drive unit (D) coupled to the infusion needle and arranged for advancing the tip end of the infusion needle to penetrate any fibrosis when the infusion device is implanted in a patient's body. The infusion needle and drive unit are designed for implantation in a patient's body. Other components of the drug delivery system may be part of the implantable infusion device or, alternatively, be for extracorporal use cooperating with the implanted infusion device. Preferably, the infusion needle can be advanced and retracted with each infusion cycle. Furthermore, upon each advancement and/or retraction, the needle may be moved laterally so as to vary the injection site. Needle (1) and drive unit (D) are preferably disposed within a body (15), with the infusion needle being arranged for penetrating a self-sealing penetration membrane (18).

A method of detecting a fault condition in an infusion process, the method includes receiving a programmed flow rate pertaining to a fluid infusion provided by an infusion device; determining, a first weight of an infusion container associated with the fluid infusion provided by the infusion device at a first time; determining a second weight of the infusion container at a second time; determining based on the first weight and the second weight, a determined flow rate of the fluid infusion provided by the infusion device between the first time and the second time. The method includes determining a difference between the determined flow rate and the programmed flow rate. When a magnitude of the difference between the determined flow rate and the programmed flow rate satisfies a predetermined threshold, by the processor: causing an output of the infusion device or the weight sensor to indicate the fault condition.