The world growth in research and development of High Operating Temperature IR detectors impels the development
process and the optimization of rotary crycoolers at RICOR.
The design aspects of size weight and power and the tradeoffs between them, were taken into consideration during the
development process in order to optimize IDDCA for future hand held thermal sights.
This paper will present optimization tests results performed for rotary crycoolers at the temperature range of 110 - 200K
FPA and also will review the development activities that will be implemented in order to minimize "Idle electronic and
mechanical losses," hence minimizing the regulated power consumption.
As a result of the new approach to Rotary crycoolers for HOT detectors, the improvement in the reliability is analyzed
and will be reported in the paper.
The growing demand for EO applications that work around the clock 24hr/7days a week, such as in border surveillance
systems, emphasizes the need for a highly reliable cryocooler having increased operational availability and decreased
integrated system Life Cycle (ILS) cost. In order to meet this need RICOR has developed a new rotary Stirling
cryocooler, model K508N, intended to double the K508's operating MTTF achieving 20,000 operating MTTF hours.
The K508N employs RICOR's latest mechanical design technologies such as optimized bearings and greases, bearings
preloading, advanced seals, laser welded cold finger and robust design structure with increased natural frequency
compared to the K508 model.
The cooler enhanced MTTF was demonstrated by a Validation and Verification (V&V) plan comprising analytical
means and a comparative accelerated life test between the standard K508 and the K508N models. Particularly, point
estimate and confidence interval for the MTTF improvement factor where calculated periodically during and after the
test. The (V&V) effort revealed that the K508N meets its MTTF design goal. The paper will focus on the technical and
engineering aspects of the new design. In addition it will discuss the market needs and expectations, investigate the
reliability data of the present reference K508 model; and report the accelerate life test data and the statistical analysis
methodology as well as its underlying assumptions and results.
The growth in world demand for infrared missile warning systems (MWS) has impelled the development of new
technologies, in particular, special cryogenic coolers. Since the cryocooler is a core component in MWS RICOR has met
the challenge by developing new models able to withstand high ambient temperatures above 110°C as well as harsh
vibration levels, both derived from airborne fighter applications.
The development focused on a cryocooler regenerator and cold finger optimization in order to achieve high cooling
capacity and a thermodynamic efficiency of about 4.4% at 95°C ambient for one of the cooler models.
In order to withstand harsh environmental vibration, the cold finger and outer Dewar structure have been significantly
ruggedized; efficient heat sinking methods have been applied and also novel vibration isolation methods have been
implemented.
The electronic design concept is based on an analog controller, the PCB of which has been designed with internal heat
sinking paths and special components being able to withstand ambients temperatures up to 125°C.
As a final stage of development, such cryocoolers were successfully qualified by RICOR and system manufacture in
harsh environmental conditions and life demonstration tests were performed.
Over the recent 25 years Ricor has fielded in excess of 50,000 Stirling cryocoolers, among which approximately 30,000
units are of micro integral rotary driven type. The statistical population of the fielded units is counted in thousands/
hundreds per application category. In contrast to MTTF values as gathered and presented based on standard reliability
demonstration tests, where the failure of the weakest component dictates the end of product life, in the case of field
reliability, where design and workmanship failures are counted and considered, the values are usually reported in number
of failures per million hours of operation. These values are important and relevant to the prediction of service capabilities
and plan.
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