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Hydraulic cylinder with position encoder

  • US 7,367,257 B2
  • Filed: 08/17/2005
  • Issued: 05/06/2008
  • Est. Priority Date: 11/06/1996
  • Status: Expired due to Fees
First Claim
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1. An actuator having a cylinder and a piston assembly moveable within said cylinder, said piston assembly including a piston rod projecting from said cylinder and having a surface that presents to a predetermined location on said cylinder a varying discernible characteristic as said surface moves relative to said cylinder, and a sensor assembly to monitor said varying discernible characteristic and to measure changes therein to provide an indication of movement of said piston assembly relative to said cylinder, said varying discernible characteristic being provided by an interface on said piston assembly exhibiting a change in said discernible characteristic and defined by a helical groove having oppositely directed convergent flanks inclined to the direction of travel of the rod and defining a series of peaks, said sensor assembly including three transducers circumferentially spaced about said piston rod and positioned relative to one another such that when one of said transducers is aligned with one of said series of peaks, a pair of said transducers are aligned with respective ones of said convergent flanks, the distance between said interface and each of said transducers varying progressively and continuously as said piston assembly moves relative to said cylinder, said pair of transducers providing a pair of phase shifted signals as said piston moves past said sensor assembly, a function of said pair of phase shifted signals providing said indication of movement.

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