FLUID POWER HANDBOOK
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MINIATURE
FLUID POWER CONTROLS MICROHYDRAULICS Fluid power systems are noted for their high power density — permitting high force and torque output from relatively small components when compared to electromechanical systems. Microhydraulics makes it feasible to obtain a significant amount of force from a minimal power source within a very restricted space I M AG
envelope. Thus, it can provide a straightforward solution
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to problems that are often beyond the limits of traditional mechanical options. In many cases, these systems are ideally suited for wideranging applications like medical orthotic and prosthetic equipment, human-assist lifts, exoskeletons, hand tools, rescue robots, aircraft and missiles, race cars and oceanographic instrumentation. Engineers might be tempted to simply downsize typical commercial components when the need arises to control motion and force in very small powered systems. However, the reality is a bit more complex because scaling laws are not intuitive, according to researchers Jicheng Xia and William Durfee of the University of Minnesota. For example, they note that in a cylinder, force is proportional to area (L2) while weight is proportional to volume (L3). On the other hand, the thickness and weight of a cylinder wall required to contain a fixed pressure goes down with bore size. Thus, the final weight of a hydraulic system at small scale cannot be determined by proportionally scaling a large system.
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Miniature Fluid Power Controls 7-19_FPW Vs3.indd 102
7 • 2019
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7/15/19 10:26 AM
