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This paper describes the algorithm development and experimental results of a vision-guided multiprobe microassembly system. The key focus is to develop the capabilities required for the construction of 3-D structures using only planar microfabricated parts. Instead of using grippers, multiple sharp-tipped probes are coordinated to manipulate parts by using vision feedback. This novel probe-based approach offers both stable part grasping and dexterous part manipulation. The light weight of the part and relatively slow motion means that only kinematics-based control is required. However, probe motions need to be carefully coordinated to ensure reliable and repeatable part grasping and manipulation. Machine vision with multiple cameras is used to guide the motion. No contact force sensor is used; instead, vision sensing of the probe bending is used for the grasp force control. By combining preplanned manipulation sequences and vision-based manipulation, repeatable spatial (in contrast with planar) manipulation and insertion of a submillimeter part have been demonstrated with an experimental testbed consisting of two actuated probes, a passive probe, an actuated die stage, and two cameras for vision feedback. [ABSTRACT FROM AUTHOR]

Abstract: Parallel channel heat transfer system is an attractive means to enhance heat transfer by increasing the total surface area in the heat exchanger. Uniform distribution of flow in the channels is an important operation attribute in order to avoid channel dryout and the subsequent hot spots and possible device failure. For the system operating in the single-phase regime, uniform flow distribution is a stable equilibrium. However, in the two-phase boiling regime, stable equilibrium bifurcates – the uniform distribution becomes unstable, and new stable or unstable non-uniform distributions, or maldistributions, equilibria emerge. As a result, parallel channel heat exchangers typically operate in the single phase regime to avoid such “maldistribution instability”. This paper presents a stability analysis and active flow and temperature control of a parallel channel evaporator in a pumped two-phase boiling heat transfer loop. We show that for identical channels, the system is uncontrollable with the pump alone and unobservable from the overall flow rate measurement. A conventional solution involves introducing additional valve-induced pressure drop, but the drawback is a resulting higher pumping power. We present a new, somewhat surprising, result that if the channel characteristics are all distinct, the system actually becomes controllable from the pump and observable from the total loop flow rate. For non-identical parallel systems, we show a controller design approach and demonstrate its efficacy through a simulation example. [Copyright &y& Elsevier]

Abstract: Two-loop refrigeration systems are being explored for two-phase cooling of ultra high power electronic components. For effective and efficient thermal management of electronic systems, active control methods are desired to suppress inherent flow instabilities especially in transient applications. This paper presents a framework for the transient analysis and active control of pressure-drop flow instabilities under varying imposed heat loads. The external effects on boiling flow characteristics and the boiling oscillatory flow responses to transient heat load changes are studied. Flow instability margins can be quantitatively predicted from an analytical two-phase flow model. In addition, the effects of wall thermal inertia on flow oscillations is systematically investigated. Based on the theoretical analysis of oscillatory flow boiling of refrigerants, a set of active control schemes are developed and studied to suppress flow oscillations and to increase the critical heat flux. With the available control devices – inlet valve and supply pump – different active control schemes are studied to improve the transient two-phase cooling performance. [Copyright &y& Elsevier]