Non-contact sensor and method using inductance and laser distance measurements for measuring the thickness of a layer of material overlaying a substrate

• US 5,355,083 A
• Filed: 08/29/1989
• Issued: 10/11/1994
• Est. Priority Date: 11/16/1988
• Status: Expired due to Term

• Current Assignee: Measurex Corporation (Honeywell International Inc.)
• Original Assignee: Measurex Corporation (Honeywell International Inc.)
• Inventors: George, Alan R., Dahlquist, John A.
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US07/399,845
• Time in Patent Office: 1,869 Days
• Field of Search: 324/207, 324/208, 324/226, 324/227, 324/229-231, 73/159, 356/375, 356/376, 356/381, 250/559, 250/560, 250/561, 264/40.2, 118/665, 118/712, 425/141
• US Class Current: 324/229
• CPC Class Codes: G01B 11/06 for measuring thickness ; e.g. of sheet material thickness measurement by thermal means G01B21/085
• CPC Class Codes: G01B 21/08 for measuring thickness
• CPC Class Codes: G01B 7/023 for measuring distance between sensor and object G01B7/082 and G01B7/102 take precedence
• CPC Class Codes: G01B 7/10 using magnetic means, e.g. by measuring change of reluctance

Abstract

A non-contact thickness measuring sensor is disclosed which determines the thickness of an overlying material on a substrate. The sensor includes two non-contact separation distance measuring devices which may be utilized to measure the distance from the first device to a portion of the interface between the substrate and the overlying material, while the second device determines the distance from the second device to a portion of the surface of the overlying layer. The difference in the measured distances is related to the thickness of the overlying material. In one embodiment, two lasers are used to measure the separation distances. In another embodiment, the two measured distances are coincident. Because of the coincident geometry of these two measurements, the thickness measuring sensor of this embodiment is substantially insensitive to misalignment of the sensor from the normal to the surface of the overlying layer being measured.

Claims

1. A thickness measuring sensor for measuring the thickness of a solid material overlying an electrically conductive material without contacting the solid material, comprising:

an inductive separation distance measuring device, including a coil, for measuring a first distance between a portion of the conductive material/overlying material interface and a first reference location spaced from the overlying material; and

a laser separation distance measuring device, including a laser disposed to direct a laser beam through the coil, for measuring a second distance between a portion of the exposed surface of the overlying material and a second reference location spaced from the overlying material.

2. The sensor of claim 1, wherein the inductive separation distance measuring device includes a first electric circuit operatively coupled to the coil for producing a first signal indicative of the first distance between the coil and the conductive material, and wherein the laser separation distance measuring device includes a second electric circuit for producing a second signal indicative of the second distance between the exposed surface of the material overlying the conductive material and the laser device, the sensor further comprising a computer operatively coupled to the first and second circuits for determining the thickness of the overlying material based upon the first and second signals.

3. The thickness measuring sensor of claim 1, wherein the laser projects an image within a magnetic field pattern generated by the inductive separation distance measuring device.

4. The thickness measuring sensor of claim 1, wherein the laser image and the magnetic pattern are projected along a common axis substantially normal to the sheet so that any error in the thickness measurement caused by tilting the common axis from normal to the surface is minimized.

5. The thickness measuring sensor of claim 3, wherein the laser image and the magnetic pattern are concentric with respect to each other.

6. A system for controlling the thickness of a sheet of material adjacent to a substrate, comprising:

means for producing a sheet of variable thickness;

an inductance separation distance measuring device including a coil for sensing a first separation distance between a portion of the substrate/sheet interface and a first reference location and for generating a first signal indicative of the sensed first distance;

a laser separation distance measuring device, spaced from the sheet, disposed to direct a laser beam through the coil, for sensing the second separation distance between a portion of the sheet surface opposite the substrate and a second reference location and being operable to generate a second signal indicative of the sensed second distance, wherein the laser separation distance measuring device emits a beam along an optical axis which is substantially normal to the portion of the sheet surface, the inductance separation distance measuring device and the laser separation distance measuring device being disposed such that the portion of the sheet surface opposite the substrate overlies the portion of the substrate/sheet interface and the inductance separation distance measuring device and the laser separation distance measuring device being spaced from the sheet and the substrate; and

a controller, operatively, coupled to the inductance separation distance measuring device and the laser separation distance measuring device, wherein the controller is operable to control the sheet producing means based upon the first and second signals such that the sheet producing means produces a sheet having a desired thickness.

7. A method for measuring the thickness of a material overlying a substrate, comprising the steps of:

measuring a first distance between a portion of the substrate/overlying material interface and a first reference location with a non-contact distance measuring device, including an inductive coil;

measuring a second distance between a portion of the surface of the overlying material opposite the substrate and a second reference location with a laser triangulation device including a laser disposed to direct a laser beam through the coil, wherein the first and second distance measurements are coincident even when sensor tilting or misalignment occurs; and

calculating the difference between the measured distances and determining the thickness of the overlying material based upon the calculated difference.

8. A non-contact sensor for measuring the thickness of a material overlying a substrate, comprising:

an inductive separation distance measuring device for measuring a separation distance between a portion of the substrate/overlying material interface and a first reference location; and

a laser separation distance measuring device, spaced from the material, for measuring a separation distance between a portion of the surface of the overlying sheet of material and a second reference location, the inductive separation distance measuring device and the laser separation distance measuring device transmitting along a common axis and being disposed such that the portion of the surface the overlying material overlies the portion of the substrate/overlying material interface.