This paper aims to present the integrated design, development, and testing procedures for a state-of-the-art torsion-based series elastic actuator that could be reliably employed for long-term use in force-controlled robot applications. The main objective in designing the actuator was to meet weight and dimensional requirements whilst improving the long-term durability, ensuring high torque output, and containing its total weight. A four-fold design approach was implemented: (i) following recursive design-and-test procedures, an optimal torsional spring topology was unveiled with the help of SIMP (Solid Isotropic Material with Penalization) topology optimization method, (ii) the proposed spring was manufactured and multiple specimens were experimentally tested via a torsional test machine to validate linearity, loading rate response, and mechanical limits, (iii) the actuator’s thermal response was experimentally scrutinized to ensure that the generated heat was dissipated for long-term use, and (iv) the fatigue life of the spring was computed with the help of real-life experiment data. Having concluded the development and verification procedures, two different versions of the actuator were built, and preliminary torque control experiments were conducted. In conclusion, favorable torque tracking with a bandwidth of 19 Hz was achieved while peak-to-peak torque input was 20 Nm.
Cold plates are at the heart of pumped liquid cooling systems. In this paper, we report on combined experimental, analytical, and computational efforts to characterize and model the thermal performance of advanced cold plates in order to establish their performance limits. A novel effectiveness-NTU formulation is introduced that models the fin array as a secondary “pseudo-fluid” such that accurate crossflow effectiveness models can be utilized to model the cold plates using well-known formulations. Experimental measurements and conjugate CFD simulations were made on cold plates with fin and channel features of order 100 um with water-propylene glycol (PG) mixtures as coolants. We show that for a fixed fin geometry, the best thermal performance, regardless of the pressure drop, is achieved when the flow rate is high enough to approach the low NTU convective limit which occurs for NTU approaching zero. For the model cold plate evaluated in this study, the lowest thermal resistance achieved at a flow rate of 4 LPM was 0.01 C/W, and the convective limit was 0.005 C/W. However, for a fixed pressure drop, the optimal cold plate should be designed to meet its TDP at the highest possible effectiveness in which the lower limit of thermal resistance is the advective limit achieved for NTU > 7. For the tested cold plate the advective limit for the thermal resistance is 0.003 C/W, but this limit can only be achieved if it is practically feasible to increase the surface area and heat transfer coefficient to maximize NTU for a targeted TDP.
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