Dynamic PWM Motor Control for Infusion Pumps

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Solution Overview

Problem

Infusion pump devices face challenges in reducing power consumption of stepper motors, which are typically used in fluid infusion systems, leading to shortened battery life in portable medical devices due to continuous power consumption and reliance on open-loop control schemes without feedback mechanisms.

Innovation Solution

A motor control system that adjusts the duty cycle of a modulated voltage applied to the motor based on the difference between expected and measured displacement, allowing for dynamic control of motor rotation and reducing power consumption by only applying voltage when necessary.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a stepper motor is supplied with a direct current voltage to control and maintain position, then the motor can reliably achieve commanded steps, but the motor continuously consumes power during use

Engineering Contradiction:

Improvemotor position control reliabilityVSAvoidmotor power consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent applies pulse-width modulation (PWM) to convert continuous DC voltage into periodic pulsed voltage applied to the stepper motor. The motor receives voltage in controlled pulses rather than continuously, enabling position control through sequences of pulsed steps while consuming power only during active pulsing periods, thus resolving the contradiction between reliable position control and continuous power consumption

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent implements dynamic adjustment of the PWM duty cycle based on feedback from position sensors. The control system continuously monitors actual motor position and adjusts the voltage pulse width dynamically to match the difference between commanded and actual positions, optimizing power consumption while maintaining control reliability under varying operational conditions

Inventive Principle:

Principle #15Dynamics

2Force

If the voltage applied to the stepper motor is chosen to be large enough to ensure the motor provides torque that meets maximum requirements, then the motor can meet all torque demands, but power consumption increases

Engineering Contradiction:

Improvemotor torqueVSAvoidmotor power consumption

Core Design Contradiction:

ForceVSUse of energy by moving object

Solution Approach 1:

The control system dynamically adjusts the PWM duty cycle based on real-time feedback from position sensors and comparison with commanded positions. This dynamic control enables the motor to receive high voltage pulses only when high torque is actually needed to correct position errors or overcome load variations, while using lower voltage during normal operation, thus meeting torque demands without continuous high power consumption

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent incorporates feedback mechanisms using position sensors to monitor actual motor position and feed this information back to the control system. The control system uses this feedback to calculate the difference between commanded and actual positions and adjusts the PWM voltage accordingly, ensuring sufficient torque is applied only when position correction is needed rather than continuously applying maximum voltage

Inventive Principle:

Principle #23Feedback

3Device complexity

If open-loop control is used without feedback mechanisms, then the control system is simpler, but there is no way to verify actual motor position or compensate for errors

Engineering Contradiction:

Improvecontrol system complexityVSAvoidmotor position accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent incorporates position sensors (such as encoders or Hall effect sensors) to measure actual motor position and feeds this information back to the control system. The control system compares commanded position with actual position and adjusts PWM voltage pulses to correct any position errors, thereby achieving precise position control while maintaining relatively simple control logic

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent replaces complex mechanical position feedback mechanisms with electronic sensing methods using sensors that detect rotor position electrically. This substitution reduces mechanical complexity while enabling precise position measurement and feedback control through electronic signal processing

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS10228663B2Dynamic pulse-width modulation motor control and medical device incorporating same

Publication Date: 2019.03.12 MEDTRONIC MINIMED INC

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 sensor to obtain a measured displacement that is influenced by rotation of the rotor, and a control module coupled to the sensor. The control module adjusts a duty cycle for a modulated voltage applied to the motor in response to a difference between an expected displacement and the measured displacement. The expected displacement is influenced by or otherwise corresponds to a commanded rotation of the rotor.