Pneumatic Stepper Motor Architecture for MRI-Compatible Actuation
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Solution Overview
Problem
Existing stepper motors, particularly those used in MRI-compatible systems and high-voltage switchgear, face challenges due to their electromagnetic nature, which interferes with magnetic fields and are complex to manufacture, and lack customizability and lightweight alternatives.
Innovation Solution
A pneumatic stepper motor design comprising a housing with a rack or geared axle and two pistons, each with engagement surfaces, allowing for a compact, customizable, and metal-free actuation system that can be rapidly prototyped using 3D printing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electromagnetic stepper motors are used, then actuation force and precision are achieved, but the motor distorts magnetic fields and is not MRI-compatible
Solution Approach 1:
The patent replaces electromagnetic actuation with pneumatic actuation. The pneumatic stepper motor uses compressed air to drive pistons that move along a rack with engagement surfaces, eliminating all electromagnetic components including coils, magnets, and sensors. This mechanical-pneumatic system produces no magnetic field distortion, making it fully MRI-compatible while maintaining precise step-wise motion control through pneumatic valve sequencing.
Solution Approach 2:
The invention implements a complete pneumatic actuation system where compressed air is supplied to multiple chambers through valves that control pressure distribution. The pneumatic pressure drives pistons to engage with teeth on a rack, producing controlled linear or rotational motion. This pneumatic approach replaces the electromagnetic force generation mechanism entirely, achieving MRI-compatibility by using gas pressure instead of electromagnetic fields.
2Reliability
If traditional electromagnetic motors are used, then reliable actuation is achieved, but manufacturing complexity and cost increase
Solution Approach 1:
The pneumatic stepper motor is designed as a segmented system with distinct functional modules: a housing containing multiple pneumatic chambers, a rack with engagement surfaces, separate pistons for each chamber, and valve ports. This segmentation allows each component to be manufactured independently using additive manufacturing, simplifying production compared to the integrated electromagnetic assemblies required in traditional motors. The modular structure also facilitates assembly and maintenance.
Solution Approach 2:
The invention utilizes parameter changes in pneumatic pressure to achieve actuation. By varying the pressure applied to different chambers through controlled valve operation, the system produces step-wise motion without requiring complex electromagnetic control circuits. The pressure parameters can be easily adjusted and controlled, simplifying both manufacturing and operation compared to electromagnetic motor control systems.
3Reliability
If metal-free construction is implemented for MRI-compatibility, then MRI-compatibility is achieved, but device complexity increases
Solution Approach 1:
The rack component serves multiple functions simultaneously: it provides the engagement surfaces for piston teeth, acts as a guide for linear motion, and serves as a structural support element for the housing. The pistons both seal the pneumatic chambers and provide the engagement teeth for motion transfer. This multi-functionality reduces the total number of components needed, simplifying the overall structure despite the metal-free requirement.
Solution Approach 2:
The patent employs composite material construction, primarily using plastic materials for all motor components including the housing, rack, and pistons. These plastic components can be manufactured as single pieces using additive manufacturing, reducing assembly complexity. The composite plastic structure provides sufficient mechanical strength and wear resistance without requiring metal parts, maintaining MRI-compatibility while simplifying the overall device architecture.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design provides a lightweight, MRI-compatible, and easily manufacturable stepper motor with high output power and torque, suitable for applications requiring precise actuation in challenging environments.
Implementation Method 1
air is supplied via a pneumatic tube to one longitudinal end at a time in order to drive a respective piston in the direction of the other longitudinal end of that chamber
Data Source
AI summary
A pneumatic stepper motor includes a housing, said housing accommodating at least part of: a rack or geared axle comprising a plurality of gear elements; and two pistons, each comprising at least two teeth, said pistons being arranged to cooperate with said rack or geared axle. The racks may either be straight or curved. The pistons are preferably double-acting pistons. A device includes at least one, and preferably a plurality of, such pneumatic stepper motor(s). The device may in particular be an MRI-compatible robotic system, more in particular for example an MRI-guided breast biopsy device.