Precision motion slideways
AssigneeThe Secretary of State for Trade and Industry in Her Britannic Majesty's Government of the United Kingdom of Great Britain and Northern Ireland
InventorsKevin Lindsey, Stuart T. Smith
Life of this patent
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Abstract
A plain bearing slide system has a carriage mounted on a slide by use of bearing pads. Each bearing pad is coated with a layer of polymeric material having a convex surface, and is arranged to ride on a counterface. The combined thickness of the layer and a layer providing the counterface is such that the difference between the static and dynamic coefficients of friction is substantially less than the difference associated with the material when used in bulk bearings. A slide system using PTFE, and with a combined thickness of the layers of 2 to 3 micrometers, operated as a measuring instrument under ambient conditions such that the PTFE is substantially non-eroding, has proved capable of providing measurements to an accuracy of 0.05 nanometers.
Claims32
A plain bearing slide system including a carriage (10) mounted on a slide (11), the carriage (10) being kenematically constrainable to move along an accurately defined paath by means of bearing pads (14) between the carriage (10) and slide (11), characterised in that the surface of each bearing pad (14) is of convex shape, is coated with a thin layer (22, 41) of sybstantially non-eroding polymeric material having a convex surface (24), and is arranged to ride along a counterface in the form of a surface (25) of a thin layer (23, 42) of substantially non-eroding polymeric material, the combined thickness of the two layers (22, 23, 41, 42) of the substantially non-eroding polymeric material being such that the difference between the static and dynamic coefficients of friction is considerably less than the difference between the static and dynamic bulk coefficients of friction and that the fluctuation in dynamic coefficient of friction is correspondingly reduced.
A process of constructing a plain bearing slide system having a carriage (10) mounted on a slide (11), the carriage being kinematically constrainable to move along an accurately defined path by means including bearing pads (14) between the darriage (10) and the slide (11), the system being characterised in having the surface of each pad (14) of convex shape, coated with a thin layer (22,41) of sybstantially non-eroding polymeric material, and arranged to ride along a counterface (25) on a thin layer (23,42) of substantially non-eroding material, the process being characterised in including the steps of;
- selecting a polymeric substance which, at the planned operating conditions of the slide system, has a thin layer difference of static and dynamic coefficients of friction substantislly less than the bulk difference and a correspondingly reduced fluctuation in dynamic coefficient of friction, and which is capable of providing a counterface (25) having a roughness no greater than 5 nanometers Ra;
- determining a combined thickness of the thin layers (22, 23;
- 41,42) which gives a reduced difference in coefficient of friction and a reduced fluctuation in dynamic coefficient of friction appropriate to the required accuracy of the instrument;
- establishing limits of radius of curvature of a surface (24,44) of the thin layer (22,41) of each bearing pad (14) within which, in use, any variation of interface contact position or area and any inadequacy in averaging out geometrical imperfections are not too great to prevent the required accuracy from being attained, and within which interface stress remains within acceptable limits;
- and
- constructing the bearing pads (14), assembling the carriage (10), slide (11) and bearing pads (14) and adding the layer (23,42) of material to provide the counterface (25) for each bearing pad (14) such that the combined thickness of the thin layers (22, 23;
- 41, 42) is no greater than that which has been determined to give coefficient of friction characteristics appropriate to the desired accuracy.
Dependencies are inferred from the claim text.