Accelerated Life Testing to Predict Service Life and Reliability for an Appliance Door Hinge

Appliance manufacturers have traditionally performed physical testing using prototypes to assess reliability and service integrity of new product designs. However, for white goods where service lives are measured in years or decades, the use of endurance testing to analyze long time reliability is uneconomical. As accelerated life testing (ALT) is more efficient and less costly than traditional reliability testing, the methodology is finding increased usage by appliance manufacturers. In the present study, a simulation-based ALT approach was used to predict the service life of a polyacetal hinge cam from a consumer refrigerator. A predictive life stress model based on cumulative surface wear under accelerated stress conditions was developed and used to predict time to failure under consumer use. Results show that the life stress model demonstrated good agreement with performance testing data and reasonably predicts hinge life

Control of A High Performance Bipedal Robot using Viscoelastic Liquid Cooled Actuators

This paper describes the control, and evaluation of a new human-scaled biped robot with liquid cooled viscoelastic actuators (VLCA). Based on the lessons learned from previous work from our team on VLCA [1], we present a new system design embodying a Reaction Force Sensing Series Elastic Actuator (RFSEA) and a Force Sensing Series Elastic Actuator (FSEA). These designs are aimed at reducing the size and weight of the robot's actuation system while inheriting the advantages of our designs such as energy efficiency, torque density, impact resistance and position/force controllability. The system design takes into consideration human-inspired kinematics and range-of-motion (ROM), while relying on foot placement to balance. In terms of actuator control, we perform a stability analysis on a Disturbance Observer (DOB) designed for force control. We then evaluate various position control algorithms both in the time and frequency domains for our VLCA actuators. Having the low level baseline established, we first perform a controller evaluation on the legs using Operational Space Control (OSC) [2]. Finally, we move on to evaluating the full bipedal robot by accomplishing unsupported dynamic walking by means of the algorithms to appear in [3].Comment: 8 pages, 8 figure

On the role of -vinylpyrrolidone in the aqueous radical-initiated copolymerization with PEGDA mediated by eosin Y in the presence of O[subscript 2]

The photochemistry of eosin Y has attracted attention for its role in visible-light induced polymerization reactions that proceed in the presence of ambient oxygen to form various macromolecular architectures that are useful for a wide range of applications, including biosensing and drug delivery. N-Vinylpyrrolidone (NVP) has been employed as a comonomer in the eosin-mediated synthesis of hydrogels with polyethylene glycol (PEG) based multifunctional monomers to aid in reducing oxygen inhibition and enhancing the rate of radical polymerization and the final conversion. However, the mechanism by which NVP reduces the oxygen inhibition time (t[subscript inh]) remains unclear. Additionally, no investigations were found on the integration of NVP into the radical-generating photocatalytic mechanism of eosin Y. Towards a better understanding of eosin-mediated synthesis of PEG-based hydrogels, we analyzed the effect of NVP on the steady-state kinetics of the aqueous NVP/PEG-diacrylate copolymerization reaction. In this case, the reduction in t[subscript inh] is lower than that reported for copolymerization with neat (meth)acrylate monomers. We propose the formation of a ground-state complex between eosin and NVP as the main reason for the reduction in oxygen inhibition and contrast it with previous theories. In addition, we discuss the role of this eosin/NVP complex and cross-propagation kinetics to explain the ∼70% increase in the initial rate of polymerization upon addition of NVP. The effect of cross-propagation kinetics is enhanced at the later stages, leading to a 10% increase in final vinyl conversion in this relatively mobile network. By analyzing the change in the scaling of the eosin decay coefficient as a function of light intensity during and after oxygen inhibition, we then link eosin inactivation to radical termination kinetics. Finally, we discuss the role of radical recombination between semireduced eosin and the propagating radicals as an additional eosin inactivation route by which leuco-eosin ends tethered to the network. These insights contribute to a thorough understanding of visible-light activated polymerization in the presence of oxygen and of the role of NVP in eosin-mediated radical production.Consejo Nacional de Ciencia y Tecnología (Mexico) (Award I0010-2015-01-263622/I0010-2016-02-275449)Kwanjeong Educational Foundation (Korea) (Scholarship)National Science Foundation (U.S.). Graduate Research Fellowship ProgramBurroughs Wellcome Fund (Career Award