Stepper Motor PWM Control for Infusion Pump Occlusion Detection
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Solution Overview
Problem
Infusion pump devices face challenges in reducing power consumption of stepper motors, leading to shortened battery life in portable medical devices, and lack effective feedback mechanisms for precise control and occlusion detection.
Innovation Solution
A motor control system that uses a modulation module to generate a modulated voltage with adjustable duty cycle, allowing for precise control of stepper motor rotation and detection of occlusions in the fluid path by monitoring the duty cycle changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a direct current voltage is supplied to the stepper motor to control and maintain position, then the stepper motor achieves precise position control, but the motor continuously consumes power during use
Solution Approach 1:
The patent applies periodic action by using pulse-width modulation (PWM) to supply intermittent voltage pulses to the stepper motor windings instead of continuous DC voltage. The motor is energized only during the time needed to achieve and maintain each step position, with the voltage periodically switched on and off. This reduces continuous power consumption while maintaining precise position control through timed electromagnetic actuation.
Solution Approach 2:
The patent implements dynamics by transitioning from static continuous voltage application to dynamic pulsed voltage control. The PWM controller dynamically adjusts the timing and duration of voltage application to each motor phase based on the required motion profile and position feedback, optimizing power delivery to match actual motor needs rather than providing constant power.
2Reliability
If a large voltage is applied to the stepper motor to ensure sufficient torque meets maximum requirements, then the motor achieves commanded steps reliably, but power consumption increases
Solution Approach 1:
The patent applies dynamics by using PWM to dynamically adjust voltage application timing rather than maintaining constant high voltage. The controller energizes motor phases only during the brief intervals needed to generate required torque for each step, reducing overall power consumption while maintaining reliable torque delivery when needed. The dynamic switching allows high peak voltages for torque generation without continuous power dissipation.
Solution Approach 2:
The patent implements preliminary action by pre-calculating and planning the voltage application sequence through PWM control before motor movement begins. The controller determines the exact timing and duration of voltage pulses needed to achieve the desired motion profile, applying voltage only when and where needed to generate sufficient torque, rather than continuously applying maximum voltage.
3Device complexity
If an open-loop control scheme is used with large voltage to ensure stepper motor torque meets requirements, then feedback mechanisms are obviated, but power consumption increases and occlusion detection capability is lost
Solution Approach 1:
The patent applies feedback by incorporating sensors (such as encoders or Hall effect sensors) that monitor actual motor position and feedback signals to the PWM controller. This closed-loop feedback enables the controller to adjust voltage pulse timing and duration in real-time, optimizing power consumption while maintaining reliable torque delivery and enabling occlusion detection through monitoring of current draw and position feedback discrepancies.
Solution Approach 2:
The patent implements universality by designing the PWM control system to perform multiple functions: precise position control, power optimization, and occlusion detection. The same PWM controller and feedback infrastructure used for motion control also monitor motor current and position accuracy to detect occlusions, eliminating the need for separate dedicated detection hardware and reducing overall system complexity.
4Ease of operation
If continuous DC voltage is applied to the stepper motor, then simple control is achieved, but battery life is shortened
Solution Approach 1:
The patent applies periodic action by replacing continuous DC voltage with PWM-generated pulsed voltage sequences. The motor receives voltage in periodic bursts synchronized with the desired step sequence, maintaining simple control logic through programmable pulse timing while dramatically reducing average power consumption and extending battery life in portable infusion pump devices.
Data Source
AI summary
Apparatus are provided for motor control systems and related medical devices. In one embodiment, a control system includes a motor having a rotor, a modulation module coupled to the motor, and a control module coupled to the modulation module. The modulation module generates a modulated voltage that is applied to the motor and rotates the rotor to deliver fluid via a fluid path. The control module adjusts a duty cycle of the modulated voltage to achieve a commanded rotation of the rotor and detects an occlusion condition in the fluid path based on the duty cycle.