Precision linear measuring suspension system having sliding contact between the scale and the pick-off
First Claim
1. A linear measuring apparatus comprising:
- a housing;
a scale slidably mounted within said housing so that said scale can move in an axial direction;
a pick-off body coupled to said housing, said pick-off body having a front surface retained in sliding contact with said scale, said pick-off body including a sensor for measuring movement of said scale with respect to said pick-off body; and
a spring assembly coupled to said pick-off body and to said housing and resiliently biasing said pick-off body into abutting contact with said scale as said scale slides on a surface of said pick-off body, said spring assembly restraining movement of said pick-off body in said axial direction while permitting movement normal to said axial direction so that axial movement of said scale is accurately sensed.
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Accused Products
Abstract
In a capacitive-type linear displacement measuring device, a pick-off body is resiliently biased into sliding contact with a scale. The pick-off body is supported by a flat spring and resiliently biased towards the scale by a leaf spring. The front surface of the scale slides in abutting contact with the front surface of the pick-off body. The flat spring restrains non-axial movement of the pick-off body but permits movement normal to the axial movement so that the pick-off body accurately tracks and remains in abutting contact with the scale as it slides in an axial direction. Changes in capacitance caused by axial displacement of the scale are accurately sensed and changes in capacitance caused by non-axial motion are avoided. According to an alternative embodiment, the pick-off body and scale are positioned with their sliding surfaces aligned with the axis of the support member to reduce the moment arm for any friction forces to zero, further reducing the likelihood of inaccurately sensing the axial movement of the scale.
38 Citations
30 Claims
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1. A linear measuring apparatus comprising:
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a housing; a scale slidably mounted within said housing so that said scale can move in an axial direction; a pick-off body coupled to said housing, said pick-off body having a front surface retained in sliding contact with said scale, said pick-off body including a sensor for measuring movement of said scale with respect to said pick-off body; and a spring assembly coupled to said pick-off body and to said housing and resiliently biasing said pick-off body into abutting contact with said scale as said scale slides on a surface of said pick-off body, said spring assembly restraining movement of said pick-off body in said axial direction while permitting movement normal to said axial direction so that axial movement of said scale is accurately sensed. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A linear measuring apparatus comprising:
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a scale means slidably coupled within a housing for moving axially in response to motion of an object whose displacement is to be measured, said scale means including a periodic pattern means for providing sensing of axial motion of said scale means; a sensor means within said housing for sensing axial movement of said scale means, said sensor means including a pick-off body having a front surface in abutting contact with said scale means; and a spring assembly means coupled to said pick-off body for biasing said pick-off body into abutting contact with said scale means as said scale means moves axially within said housing means and for permitting said pick-off body to move normal to said axial motion and for restraining said pick-off body from moving axially to minimize errors caused by non-axial motion of said pick-off body relative to said scale and to accurately sense axial motion of said scale. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23)
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24. A linear measuring apparatus comprising:
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a scale slidably coupled within a housing and adapted to be coupled to an object whose movement is to be measured, said scale moving axially in response to movement by said object, said scale having a front surface; a capacitive grating mounted in said front surface of said scale; a thin dielectric layer on said front surface of said scale and overlaying said capacitive grating, said dielectric layer being generally planar and smooth to provide a large area, low friction surface area for sliding contact; a pick-off member mounted within said housing in abutting contact with said scale, said pick-off member being mounted to maintain a fixed axial location while said scale undergoes axial motion for detecting axial motion of said scale, said pick-off member having a front surface; a capacitive grating mounted in said front surface of said pick-off member; a thin dielectric layer on said front surface of said pick-off member and overlaying said capacitive grating, said dielectric layer being in abutting contact with said dielectric layer of said scale and being generally planar and smooth to provide a large contact area, low friction surface for sliding contact with said scale; an electrical circuit within said housing and coupled to said respective capacitive gratings to form a capacitor, said two capacitive grating forming the plates of said capacitor and said thin dielectric layers being the dielectric material between said plates, the axial movement of said scale being sensed based on changes in the capacitance of said capacitor between said scale and said pick-off body. - View Dependent Claims (25, 26, 27, 28, 29, 30)
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Specification