US4912409A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Actuator displacement transducer having external flux excluding tube
Assignee: Sunpower Inc
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Filing: 1989-04-10
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Granted: 1990-03-27
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Expires: 2009-04-10
Abstract
Abstract A linear displacement transducer has an elongated current conducting, tubular coil which is mounted to an end cap in a hydraulic or pneumatic cylinder and extends into a hole bored in the piston/piston rod unit within the cylinder. An electrically conducting, nonferromagnetic tube lines the wall of the bore and reciprocates axially with the piston/piston rod unit varying its overlap of the coil and thereby varying the inductance of the coil at an applied frequency. An AC electrical energy source is connected to apply an AC signal to the coil, the frequency of this signal being at least high enough that the skin depth in the tubular wall is less than the physical depth of the tubular wall. A detector circuit means is connected to the coil for detecting a signal which is proportional to the coil inductance and therefore is proportional to the displacement of the piston/piston rod unit within the cylinder.
Inventors
- 👤 Robert W. Redlich
- 👤 Christopher G. Scheck
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-29 21:18
CPC Classifications
G; G01; G01D; G01D3/00; G01D3/028; G01D5/00; G01D5/12; G01D5/14; G01D5/20; G01D5/2006; G01D5/202
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
198 words
An improved apparatus for measuring the relative displacement of a piston/piston rod unit sealingly slidable within the ferromagnetic cylinder of a pressurized cylinder actuator, the improvement comprising: (a) an elongated, current conducting coil mounted at an end of the reciprocation path of the piston/piston rod unit; (b) an electrically conducting, non-ferromagnetic wall around at least a portion of the coil, said wall being mounted to and having an axis parallel to the axis of the piston/piston rod unit for telescoping axial reciprocation relative to the coil for varying the overlap of the coil by the wall to thereby vary the inductance of the coil in proportion to that overlap at an applied frequency; (c) said ferromagnetic cylinder providing a substantially constant flux path surrounding the nonoverlapped portion of the coil and a shield against external fields; (d) an AC electrical energy source connected to apply an AC signal to said coil, the frequency of the signal being at least high enough that the skin depth in said wall is less than the physical depth of said wall; and (e) a detector circuit means connected to the coil for detecting a signal which is proportional to the coil inductance.
Claim 2
Dependent Claim
198 words
An improved apparatus for measuring the relative displacement of a piston/piston rod unit sealingly slidable within the ferromagnetic cylinder of a pressurized cylinder actuator, the improvement comprising: (a) an elongated, current conducting coil mounted at an end of the reciprocation path of the piston/piston rod unit; (b) an electrically conducting, non-ferromagnetic wall around at least a portion of the coil, said wall being mounted to and having an axis parallel to the axis of the piston/piston rod unit for telescoping axial reciprocation relative to the coil for varying the overlap of the coil by the wall to thereby vary the inductance of the coil in proportion to that overlap at an applied frequency; (c) said ferromagnetic cylinder providing a substantially constant flux path surrounding the nonoverlapped portion of the coil and a shield against external fields; (d) an AC electrical energy source connected to apply an AC signal to said coil, the frequency of the signal being at least high enough that the skin depth in said wall is less than the physical depth of said wall; and (e) a detector circuit means connected to the coil for detecting a signal which is proportional to the coil inductance.
Claim 3
Dependent Claim
35 words
An apparatus in accordance with claim 1 wherein the coil is helical with a linear axis and the wall is a tube lining a hole formed in the piston/piston rod unit and surrounding the coil.
Claim 4
Dependent Claim
37 words
An apparatus in accordance with claim 2 or 1 wherein a fluid impervious, non-ferromagnetic jacket surrounds the coil and is interposed between the coil and said wall for protecting the coil from the environment of the wall.
Claim 5
Dependent Claim
73 words
An apparatus in accordance with claim 2 in combination with a pressurized cylinder actuator of the type including end caps for sealing the ends of the cylinder and a piston/piston rod unit sealingly slidable in the cylinder, wherein said coil is mounted to an end cap and extends into a hole in and parallel to the axis of the piston/piston rod unit; and wherein the tubular wall is a sleeve lining said hole.
Claim 6
Dependent Claim
33 words
An apparatus in accordance with claim 4 wherein the hydraulic cylinder is a ferromagnetic material to form a shield around the coil and to provide a low reluctance flux path for the coil.
Claim 7
Dependent Claim
58 words
An apparatus in accordance with claim 5 wherein a fluid impervious, non-ferromagnetic jacket surrounds the coil within the cylinder, is interposed between the coil and said tubular wall and extends through said end cap to open to the exterior of the cylinder and wherein the electrical connections to the coil are made through the opening of the jacket.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1993-03-26 | 1993-09-25 | 1994-03-27 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1997-03-26 | 1997-09-25 | 1998-03-27 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2001-03-26 | 2001-09-25 | 2002-03-27 | $7700.00 | Window Closed / Lapsed |