Current Status of the Insulin Pump Industry

At present, most insulin pumps on the market use DC motors with optical encoders — companies like Medtronic and Dana follow this approach. However, some leading manufacturers have already adopted stepper gear motors combined with photoelectric switches. The advantages and disadvantages of using a stepper gear motor are as follows:

1. Open-loop positioning saves more than just the encoder cost

With a DC motor + encoder, the encoder itself is only part of the cost. The real hidden costs include: decoding the encoder signal (the MCU must allocate timers, external interrupts, or QEI peripherals), plus closed-loop PID algorithms and stall/loss-of-step detection logic.

In contrast, stepper motor drive is mature, simple to implement — the MCU just sends pulses — saving significant development time and cost. Moreover, the cost of a stepper gear motor is far lower than that of a DC gear motor. In terms of material cost, it may be less than 1/10 of a DC gear motor.

2. Low-speed torque characteristics match the insulin pump's operating point perfectly

Many insulin pumps deliver basal rates by injecting once every 3 minutes, which equates to about 20 micro-doses per hour. The motor speed falls in the range of roughly ten to several tens of RPM.

A DC gear motor + encoder at such low speeds requires constant fine-tuning via closed-loop control, resulting in large current ripple and torque pulsation. A stepper gear motor, however, provides steady-state "tooth-meshing" torque output at low speeds.

3. Service life

Brushed DC gear motors typically have a brush life rated around 2,000 hours. Since an insulin pump operates 24/7 for months at a time, carbon brush wear debris and spark-induced EMI are both negative factors for medical safety standards (IEC 60601).

Brushless DC gear motors (higher cost) and stepper gear motors theoretically offer comparable service lives, and neither produces carbon brush debris.

4. Photoelectric switch mounted at the rear of the stepper motor

This prevents loss of steps and enables anomaly detection.

5. Motor efficiency

Stepper motors are less efficient than DC motors. Reference the article "Achieving Low-Power Operation of Stepper Motors: Control Strategies and Hardware Selection Explained"— through proper control, the working efficiency of stepper motors can be greatly improved.