Variable Pitch Thread Autoinjector for Viscous Medicines

The patent applies a variable pitch thread instead of a constant pitch thread. The pitch of the thread varies along its length, with a larger pitch at the beginning and a smaller pitch toward the end. This dynamic geometric variation allows the mechanism to compensate for the decreasing spring torque during dispensing, maintaining sufficient dispensing force throughout the entire process while managing the complexity through a straightforward geometric modification.

The patent modifies the geometric parameters of the thread by varying the pitch along its length. This parameter change allows the thread to convert a greater portion of the spring's rotational movement into axial displacement early in the dispensing process, and less later on, thereby compensating for the decreasing spring torque and maintaining consistent dispensing efficiency throughout the process.

The variable pitch thread creates a dynamic relationship between rotational and axial movement. The varying pitch ensures that as the spring torque decreases during dispensing, the thread geometry compensates by requiring more rotational input for the same axial displacement, thereby maintaining sufficient force even at the end of the dispensing process.