Pneumatic Stepper Motor for MRI Environments
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Solution Overview
Problem
Existing stepper motors used in medical imaging environments, such as MRI machines, cause magnetic field distortions due to magnetic materials, leading to inaccurate image production and limiting the development of precise medical robots for procedures like tumor biopsies. Additionally, pneumatic actuators face challenges with precision due to air compressibility and friction, making them unsuitable for controlled motion in these environments.
Innovation Solution
A pneumatic stepper motor designed with a cylindrical central gear and hoop gear mechanism that uses fluid pressure to achieve precise, backlash-free motion, constructed from MRI-compatible materials, and controlled by a diaphragm mechanism and equal-lever arm cranks to minimize magnetic interference and enhance precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional electric motors are used in MRI environments, then motor function is achieved, but magnetic field distortion occurs causing image artifacts
Solution Approach 1:
The patent removes all magnetic materials from the motor construction. The motor uses non-magnetic materials such as aluminum, titanium, or ceramic for the stator and rotor components, eliminating the source of magnetic field distortion while maintaining motor functionality in MRI environments
Solution Approach 2:
The patent replaces traditional electromagnetic actuation with pneumatic actuation. Compressed air is used to drive the motor through pressure differential mechanisms, eliminating the need for electromagnetic fields and electrical components that generate magnetic interference
2Power
If pneumatic actuators are used for precise motion control, then compact size and high power-to-weight ratio are achieved, but precision is reduced due to air compressibility and friction
Solution Approach 1:
The patent employs a dynamic valve system that adjusts air pressure in real-time to compensate for compressibility effects. The valve timing and pressure regulation are optimized to maintain consistent force output throughout the actuation cycle, improving motion precision
Solution Approach 2:
The patent changes the physical parameters of the pneumatic system by using pre-compressed air at controlled pressures and temperatures. By stabilizing these parameters and using rigid, precision-machined components with minimal clearance, the system reduces the effects of air compressibility and friction on motion precision
3Adaptability or versatility
If pneumatic actuators are used in medical imaging environments, then MRI compatibility is achieved, but motion precision is limited
Solution Approach 1:
The patent divides the pneumatic actuation into discrete, controlled phases using multiple valves that regulate air flow to different chambers sequentially. This segmented control allows for precise positioning by controlling the timing and duration of pressure application to each segment of the mechanism
Solution Approach 2:
The patent incorporates position sensing mechanisms that provide feedback to the control system. This feedback allows the valve timing and pressure regulation to be adjusted in real-time, compensating for variations in air compressibility and friction to maintain precise motion control
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 motor provides precise, MRI-compatible rotary motion without electrical components, reducing image artifacts and enabling precise robotic procedures with high accuracy and safety, as demonstrated by its performance in a 7 Tesla MRI scanner and clinical applications like prostate brachytherapy.
Implementation Method 1
a pneumatic actuator for applying a controlled fluid pressure to selected points on the hoop gear
Data Source
AI summary
A stepper motor suitable for use in a medical imaging environment has (a) a cylindrical central gear having an external surface with circumferentially distributed and radially directed teeth, (b) a shaft for mounting the central gear such that it is constrained to move in rotational motion about its centerline, (c) a cylindrical hoop gear having a bore with an internal surface having circumferentially distributed and radially directed teeth, (d) level arm crank mechanisms for mounting the hoop gear such that it is constrained to move in translational-circular motion about the central gear's centerline, wherein this central gear is further configured to fit within the hoop gear's bore in such a manner that a plurality of the central gear and hoop gear teeth intermesh and cooperate so that the planetary movement of the hoop gear causes the central gear to rotate, and (e) piston mechanisms for applying a fluid pressure driven force to specified points on the hoop gear so as to cause its movement.