Cryocooler Motor Trim Winding for Precise Vibration Cancellation
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Solution Overview
Problem
Conventional cryocoolers experience unacceptable levels of vibration due to motor-driven piston or displacer motion, which degrades the performance of cooled items like optical detectors, and existing vibration reduction methods using dual-opposed motors and active feedback systems are limited by low resolution and high distortion, making precise vibration control challenging.
Innovation Solution
A Stirling class cryocooler design featuring a motor with both a main drive winding and a separate trim winding, where a main drive signal is used for cooling and a vibration reduction signal is applied to the trim winding to minimize vibration, allowing for precise control and overcoming limitations of existing systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If dual opposed motors with active vibration feedback and cancellation system are used, then vibration is reduced, but the system complexity increases and the minimum motor current resolution is limited by the least significant bit
Solution Approach 1:
The motor control is segmented into two independent control paths: a main drive control for temperature regulation and a separate trim control for vibration cancellation. This allows each control path to be optimized independently, with the trim path using high-resolution DACs specifically for vibration signals without being constrained by the main drive's resolution requirements.
Solution Approach 2:
A separate trim signal path with its own DAC and amplifier serves as an intermediary between the vibration feedback sensor and the motor trim winding. This intermediary path provides high-resolution control specifically for vibration cancellation, bypassing the resolution limitations of the main drive amplifier.
2Use of energy by moving object
If PWM amplifier is used for efficiency, then energy consumption is reduced, but total harmonic distortion increases which interferes with fine trim signals
Solution Approach 1:
The amplifier system is segmented into two separate amplifiers: a PWM amplifier for the main drive signal that prioritizes efficiency, and a linear amplifier for the trim signal that prioritizes low distortion. This segmentation allows each amplifier to be optimized for its specific function without compromise.
Solution Approach 2:
Different quality requirements are applied to different signal paths: the main drive path uses PWM for high efficiency, while the trim path uses linear amplification for high fidelity. Each path has the appropriate amplifier type localized to its specific function, allowing optimal performance for both efficiency and low distortion where needed.
3Measurement precision
If the number of time steps in PWM amplifier is increased to improve resolution, then vibration control resolution improves, but the turn-on time of power MOSFETs becomes significant relative to duty cycle time step size
Solution Approach 1:
The control system is segmented into two resolution paths: the main drive uses PWM with coarser resolution acceptable for temperature control, while the trim path uses a separate DAC with high resolution specifically for vibration control. This eliminates the need to increase PWM time steps, avoiding MOSFET turn-on time issues.
Solution Approach 2:
A high-resolution DAC serves as an intermediary for the trim signal, providing fine resolution control without relying on PWM time stepping. This intermediary device bypasses the MOSFET turn-on time limitation by using a different control mechanism that doesn't suffer from switching delays.
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 approach enables a two to three order of magnitude reduction in vibration, improving the performance of cooled devices by allowing for finer control over motor operation with low power consumption and reducing distortion, enhancing the accuracy of infrared sensors and other sensitive optical instruments.
Implementation Method 1
a motor with both a main drive winding and a separate trim winding
Data Source
AI summary
Disclosed are a low vibration cryocooler and a method of reducing vibration in a cryocooler. The cryocooler can be a Stirling class cryocooler includes at least one motor that drives a mass, the motor having a main drive winding and a separate trim winding. A motor controller outputs a main drive signal that is coupled to the main drive winding and a separate vibration reducing signal that is coupled to the trim winding.