Pneumatic Drive Cryocooler to Reduce Vibration and Magnetic Fields
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Solution Overview
Problem
Current Gifford-McMahon cryocoolers face limitations such as parasitic magnetic fields, mechanical vibrations, direct acoustic emissions, and limited tunability, which are detrimental for applications like MRI and NMR, due to motor-driven mechanisms and direct mechanical linkages.
Innovation Solution
The implementation of a pneumatically driven cryogenic refrigerator with electronic control valves and a passive force generator, such as springs or magnets, to control the displacer's motion independently of valve actuation, allowing for adjustable displacement profiles and improved thermodynamic cycle efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a motor-driven mechanism with direct mechanical linkage is used to drive the displacer, then the displacer can be driven reciprocally, but mechanical vibrations and direct acoustic emissions are generated
Solution Approach 1:
The patent replaces the motor-driven mechanical linkage system with a pneumatic drive system. The displacer is driven by pressure differential forces applied to a pneumatic drive volume, eliminating direct mechanical linkages between the drive mechanism and displacer. This substitution removes the source of mechanical vibrations and acoustic emissions while maintaining displacer reciprocation capability.
Solution Approach 2:
The patent implements a pneumatic drive mechanism where pressurized gas is used to create force imbalances on the displacer. By controlling gas flow to and from the pneumatic drive volume, the displacer is driven reciprocally without mechanical contact. This pneumatic approach eliminates mechanical vibrations and acoustic emissions associated with motor-driven systems.
2Speed
If a motor-driven mechanism is used to drive the displacer, then the displacer can be driven reciprocally, but parasitic magnetic fields are generated
Solution Approach 1:
The patent replaces the motor-driven system with a pneumatic drive system, eliminating the need for motors and their associated magnetic fields. The displacer is driven by controlled gas pressure forces, completely removing the source of parasitic magnetic fields while maintaining the required reciprocation motion.
3Object-generated harmful factors
If pneumatic forces are used to drive the displacer reciprocally, then mechanical linkages are reduced, but force imbalances cause the displacer to hit the bottom or top of the cylinder
Solution Approach 1:
The patent incorporates feedback control where the actual position of the displacer is monitored and used to adjust the pneumatic drive forces. This closed-loop control prevents the displacer from hitting the cylinder ends by continuously adjusting the gas flow to maintain proper position, eliminating force imbalances while preserving the vibration-free operation.
4Speed
If motor-driven mechanisms are used, then the displacer can be driven, but the device size and weight increase
Solution Approach 1:
The patent replaces heavy motor-driven mechanical systems with a lightweight pneumatic drive system. By using gas pressure forces instead of motors and mechanical linkages, the overall device weight is significantly reduced while maintaining the required displacer reciprocation capability.
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
This solution reduces vibrations, magnetic material usage, and size/weight, enabling more efficient and adaptable cryocooler operation, suitable for applications requiring precise temperature control.
Implementation Method 1
pneumatic forces to cause the displacer to reciprocate within the refrigerator cylinder
Implementation Method 2
Fluid is cooled as it passes through the regenerative matrix
Implementation Method 3
The fluid is then expanded and further cooled at the cold end of the displacer piston
Data Source
AI summary
A Gifford-McMahon cryogenic refrigerator comprises a reciprocating displacer within a refrigeration volume. The displacer is pneumatically driven by a drive piston within a pneumatic drive volume. Pressure in the pneumatic drive volume is controlled by valving that causes the drive piston to follow a programmed displacement profile through stroke of the drive piston. The drive valving may include a proportional valve that provides continuously variable supply and exhaust of drive fluid. In a proportionally controlled feedback system, the valve into the drive volume is controlled to minimize error between a displacement signal and a programmed displacement profile. Valving to the warm end of the refrigeration volume may also be proportional. A passive force generator such as a mechanical spring or magnets may apply force to the piston in opposition to the driving force applied by the drive fluid.