Device for interferometric measurements with compensation for tilt and position of measured cylindrical objects

An apparatus for non-contact measurement of objects, including;

• a source of coherent energy and a beam forming means for generating two linearly propagating collimated beams of the coherent energy;
• a beam shaping means for selectively decollimating the beams;
• a beam guide means for receiving the decollimated beams and for orienting the decollimated beams at a predetermined beam angle relative to one another to define a beam plane, said beams interfering with one another over a measuring region at their intersection to form interference fringes that are flared to provide a gradient in a fringe spacing of said fringes throughout the measuring region;
• a support means for positioning the beam plane with respect to an object to cause the object and the measuring region to intersect one another so that the object scatters the coherent energy;
• a coherent energy detector for providing a first phase value based on detecting the scattered coherent energy at a first location spaced apart from the measuring region;
• a means for providing a second phase value;
• and
• a processing means for combining the first and second phase values to generate a phase shift value indicating a transverse dimension of the object;
• wherein the first coherent energy detector intersects the beam plane and is positioned at a predetermined elevation angle relative to a beam axis that bisects the beam angle, and wherein the interference fringes are selectively flared to compensate for changes in the elevation angle due to displacements of the object within the measuring volume.

An apparatus for non-contact measurement of cylindrical objects, including:

• a source of coherent energy and a beam forming means for generating two linearly propagating beams of the coherent energy;
• a beam guide means for orienting the beams at a predetermined beam angle relative to one another to define a beam plane, said beams interfering with one another over a measuring region at their intersection;
• a support means for positioning the beam plane with respect to a cylindrical object to cause the cylindrical object and the measuring region to intersect one another with a longitudinal axis of the cylindrical object substantially perpendicular to the beam plane, so that the object scatters the coherent energy;
• a signal generating means including first and second energy detecting means for generating respective first and second periodic signals based on respective portions of the scattered coherent energy received by the first and second detecting means;
• a phase shift generating means, operatively associated with the signal generating means, for combining the first and second periodic signals to generate a phase shift value indicating a transverse dimension of the cylindrical object;
• wherein each of the first and second energy detecting means has an aperture that intersects the beam plane, is elongate in the direction perpendicular to the beam plane, and extends away from each side of the beam plane by an angle greater than 0.1.degree.;
• wherein each of the energy detecting means has an energy sensitive region greater than twice the image of a width of the measuring volume, where the measuring volume width is defined as the region in which coherent energy intensity is at least 0.135 times a maximum intensity at the center of the measuring volume.

A process for measuring objects, including the steps of:

• generating two linearly propagating beams of coherent energy, angularly separated from one another at a predetermined beam angle, and causing the beams to intersect one another to define a beam plane and to provide a measuring region at the intersection of the beams;
• positioning the beam plane and measuring region with respect to an object to cause the object and the measuring region to intersect one another, so that the object scatters the coherent energy;
• detecting first and second distinct portions of the scattered coherent energy at respective and different first and second locations spaced apart from the measuring region;
• providing first and second phase values based on detecting the scattered coherent energy at said respective and different first and second locations, and further providing a third phase value;
• combining the first and second phase values with the third phase value to generate respective first and second measured phase shift values, wherein each of the first and second measured phase shift values is at most 360 degrees;
• based on the first and second measured phase shift values, determining a number N of 360 degree increments, where N is a positive integer;
• and
• adding N 360 degree increments to the second measured phase shift value and further adding either N or (N-1) 360 degree increments to the first measured phase shift value, as predetermined by the measured phase shift values, to calculate first and second actual phase shift values.