Non-contact sheet conductivity measurements implementing a rotating magnetic braking system

• US 9,103,653 B2
• Filed: 06/26/2012
• Issued: 08/11/2015
• Est. Priority Date: 06/21/2012
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Gunawan, Oki
• Primary Examiner(s): Vazquez, Arleen M
• Assistant Examiner(s): Andrews, Brent J
• Application Number:
  US13/533,187
• Publication Number:
  US 20130346003A1
• Time in Patent Office: 1,141 Days
• Field of Search: 324/224, 324/207.11, 702/65
• US Class Current: 1/1
• CPC Class Codes: G01B 7/023 for measuring distance between sensor and object G01B7/082 and G01B7/102 take precedence
• CPC Class Codes: G01B 7/087 for measuring of objects while moving G01B7/085 takes precedence
• CPC Class Codes: G01R 27/00 Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom

Abstract

A method for calculating sheet conductivity with an absolute working distance measurement includes selecting a motor frequency f_M for a motor having a first magnet disposed on a shaft, tuning a motor voltage V_M for the motor, measuring a no-load power of the motor, inserting a material adjacent the first magnet, tuning the motor frequency to f_M, measuring the on-load power of the motor, measuring the absolute working distance and calculating the sheet conductivity of the material.

Claims

1. A method for performing a non-contact resistivity measurement of a sheet of material to be measured, the method comprising:

moving, with a motor, a magnet in one of a linear direction and a rotational direction;

determining, with a power measuring device, a first power value used by the motor in moving the magnet when in proximity to the sheet of material, and measuring a second power value used by the motor in moving the magnet when not in proximity to the sheet of material; and

determining, with a computing device, a difference between the first power value and the second power value, wherein the first power value is greater than the second power value due to a magnetic braking effect from an induced eddy current in the sheet by motion of the magnet in proximity to the sheet of material, the computing device using the difference between the first and second power values to compute the resistivity of the sheet of material;

wherein the computing device uses a known distance between the magnet and the sheet of material to compute the resistivity of the sheet of material, and computes the resistivity, σ

_S, of the sheet of material in accordance with the expression;

2. The method of claim 1, wherein:

a disk is coupled to a shaft of the motor; and

the magnet comprises a first magnet embedded in the disk at a distance, R, that is offset from a center of rotation of the disk such that, when the motor is operating, rotation of the disk causes the first magnet to move in the linear direction.

3. The method of claim 2, wherein a second magnet is embedded in the disk opposite the first magnet, at the same distance, R, from the center of rotation of the disk as the first magnet.

4. The method of claim 3, wherein the first and second magnets are spherical magnets.

5. The method of claim 2, wherein the computing device computes the resistivity of the sheet of material without using a known distance between the magnet and the sheet of material by linearization of several P_MB values determined from an initial arbitrary distance between the magnet and the sheet of material, and one or more additional distances of known variation from the initial arbitrary distance, wherein P_MB is a magnetic braking power dissipation value obtained from the difference between the first power value and the second power value.

6. A method for performing a non-contact resistivity measurement of a sheet of material to be measured, the method comprising:

moving, with a motor, a magnet in one of a linear direction and a rotational direction;

determining, with a power measuring device, a first power value used by the motor in moving the magnet when in proximity to the sheet of material, and measuring a second power value used by the motor in moving the magnet when not in proximity to the sheet of material; and

determining, with a computing device, a difference between the first power value and the second power value, wherein the first power value is greater than the second power value due to a magnetic braking effect from an induced eddy current in the sheet by motion of the magnet in proximity to the sheet of material, the computing device using the difference between the first and second power values to compute the resistivity of the sheet of material;

wherein the computing device uses a known distance between the magnet and the sheet of material to compute the resistivity of the sheet of material, and computes the resistivity, σ

_S, of the sheet of material in accordance with the expression;

7. The method of claim 6, wherein:

a disk is coupled to a shaft of the motor; and

the magnet is embedded in the disk at a center of rotation of the disk such that, when the motor is operating, rotation of the disk causes the magnet to move in the rotational direction.

8. The method of claim 7, wherein the magnet is a spherical magnet.

9. The method of claim 7, wherein the computing device computes the resistivity of the sheet of material without using a known distance between the magnet and the sheet of material by linearization of several P_MB values determined from an initial arbitrary distance between the magnet and the sheet of material, and one or more additional distances of known variation from the initial arbitrary distance, wherein P_MB is a magnetic braking power dissipation value obtained from the difference between the first power value and the second power value.