Discrete dose control and overdose prevention mechanism

A fluid delivery device comprising a drive mechanism with a rotary input to control fluid delivery components, an actuator to operate the drive mechanism, and an overrun prevention mechanism, the overrun prevention mechanism comprising:

• first and second spur gears comprising gear teeth and disposed adjacent to each other, a selected number of the gear teeth of the first spur gear configured to engage a selected number of the gear teeth of the second spur gear which correspond to the selected number of the gear teeth of the first spur gear, the first spur gear rotatable clockwise and the second spur gear rotatable counterclockwise;
• and
• a plate with a pin configured to be actuated by the actuator in the fluid delivery device to rotate a controlled amount during a cycle among alternating cycles to move the pin in an arc path relative to the first and second spur gears, the plate configured to be actuated to rotate in clockwise and counterclockwise directions in the alternating cycles;
• wherein the first and second spur gears each have a face directed toward the plate with the pin, each face being configured with at least one surface feature along which the pin can follow as the plate is rotating, the at least one surface feature of each of the first and second spur gears configured to be contacted by the pin when traveling toward respective ends of the arc path to rotate the corresponding one of the first and second spur gears by a selected amount and teeth of the corresponding one of the first and second spur gears engaging teeth of the other one of the first and second spur gears to impart rotation, the at least one surface feature of each of the first and second spur gears is also configured to disengage with the pin at each of the respective ends of the arc path before the actuator reverses a direction of rotation of the plate to commence another cycle among the alternating cycles.