# US 12,179,310 B2 · Output signal processing apparatus for eddy current sensor > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,179,310 B2 - Document ID: US12179310B2 - Status: Granted - Kind: B2 - Application number: 17/410,099 - Filed: 2021-08-24 - Published: 2022-03-03 - Granted: 2024-12-31 - Earliest claimed: 2020-08-25 - Assignees: Ebara Corporation - Applicants: Ebara Corporation - Inventors: Atsushi Abe; Taro Takahashi; Hiroaki Shibue; Shinpei Tokunaga; Katsuhide Watanabe - Web page: https://patentgrep.com/patent/US12179310B2 ## CPC - B24B 49/105: {using eddy currents} - G01B 5/0014: {due to temperature (on machine tools B23Q11/0003)} - G01B 7/10: {using magnetic means, e.g. by measuring change of reluctance} - G01B 21/045: {Correction of measurements (G01B9/02055 takes precedence)} - B24B 37/013: Devices or means for detecting lapping completion - B24B: MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING (grinding of gear teeth B23F, of screw-threads B23G1/36; by electro-erosion B23H; abrasive or related blasting B24C; tools for grinding, buffing or sharpening B24D; polishing compositions C09G1/00; abrasives C09K3/14; electrolytic etching or polishing C25F3/00; grinding arrangements for use on assembled railway tracks E01B31/17); DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS - G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS ## Abstract An eddy current sensor has an exciting coil and a detection coil. A holding circuit holds reference data indicating a characteristic of an output signal output from the detection coil at a reference state and outputs the reference data at a state other than the reference state. A pseudo signal generating circuit generates and outputs a balance coil pseudo signal corresponding to the output signal output from the detection coil at the reference state from the reference data output from the holding circuit. A bridge circuit, at the state other than the reference state, receives the output signal output from the detection coil and the balance coil pseudo signal and outputs a bridge output signal corresponding to a difference between the output signal and the balance coil pseudo signal as a bridge output signal. ## Claims ### Claim 1 An output signal processing apparatus for an eddy current sensor, the eddy current sensor having an exciting coil configured to form eddy current in a conductor and a detection coil that detects the eddy current formable in the conductor, the eddy current sensor does not include a balance coil, the output signal processing apparatus processing an output signal of the detection coil which is output from the eddy current sensor, the output signal processing apparatus comprising: a holding circuit that holds reference data indicating a characteristic of the output signal output from the detection coil at a reference state and outputs the reference data at a state other than the reference state; a pseudo signal generating circuit that generates, from the reference data output from the holding circuit, a pseudo signal corresponding to the output signal output from the detection coil at the reference state, and outputs the pseudo signal; a bridge circuit that, at the state other than the reference state, receives the output signal output from the detection coil and the pseudo signal and outputs a signal corresponding to a difference between the output signal and the pseudo signal, as a bridge output signal; and a bridge signal processing circuit that processes the bridge output signal output from the bridge circuit. ### Claim 2 (depends on 1) The output signal processing apparatus for the eddy current sensor according to claim 1, wherein at the reference state, when the bridge circuit receives the output signal output from the detection coil and does not receive the pseudo signal, the bridge circuit outputs a reference bridge output signal, the output signal processing apparatus further comprises a reference data generating circuit that generates the reference data from the reference bridge output signal, and the holding circuit holds the reference data output from the reference data generating circuit. ### Claim 3 (depends on 2) The output signal processing apparatus for the eddy current sensor according to claim 2, wherein the bridge signal processing circuit is the reference data generating circuit and, at the reference state, acquires an impedance from the reference bridge output signal in order to process the reference bridge output signal as the impedance, the holding circuit holds the acquired impedance as the reference data, and at the state other than the reference state, the pseudo signal generating circuit receives the impedance from the holding circuit and generates the pseudo signal. ### Claim 4 (depends on 1) The output signal processing apparatus for the eddy current sensor according to claim 1, wherein the reference state is a state that the conductor does not exist in vicinity of the detection coil. ### Claim 5 (depends on 1) The output signal processing apparatus for the eddy current sensor according to claim 1, the output signal processing apparatus further comprising the eddy current sensor, a temperature sensor that measures a temperature of the eddy current sensor, and a correcting circuit that corrects the reference data by using the measured temperature. ### Claim 6 An output signal processing apparatus for an eddy current sensor, the eddy current sensor having an exciting coil configured to form eddy current in a conductor and a detection coil that detects the eddy current formable in the conductor, the eddy current sensor does not include a balance coil, the output signal processing apparatus processing an output signal of the detection coil which is output from the eddy current sensor, the processing apparatus comprising: a holding circuit that holds reference data indicating a characteristic of the output signal output from the detection coil at a reference state and outputs the reference data at a state other than the reference state; and a difference circuit that receives characteristic data indicating a characteristic of the output signal output from the detection coil at the state other than the reference state and the reference data output from the holding circuit and acquires a difference between the characteristic data and the reference data. ### Claim 7 (depends on 6) The output signal processing apparatus for the eddy current sensor according to claim 6, the processing apparatus further comprising: an impedance output circuit that acquires an impedance from the output signal output from the detection coil in order to process the output signal as the impedance, wherein the holding circuit holds the impedance output from the impedance output circuit at the reference state as the reference data, and the difference circuit, at the state other than the reference state, acquires a difference between the impedance output from the impedance output circuit and the reference data output from the holding circuit. ### Claim 8 A polishing apparatus comprising: a polishing table configured to hold a polishing pad that polishes a workpiece; a holder that holds the workpiece and can press the workpiece against the polishing pad; an eddy current sensor that has an exciting coil configured to form eddy current in the workpiece and a detection coil that detects the eddy current formable in the workpiece, the eddy current sensor does not include a balance coil; and an output signal processing apparatus for an eddy current sensor, the output signal processing apparatus processing an output signal of the detection coil which is output from the eddy current sensor, wherein the output signal processing apparatus has a holding circuit that holds reference data indicating a characteristic of the output signal output from the detection coil at a reference state and outputs the reference data at a state other than the reference state; a pseudo signal generating circuit that generates, from the reference data output from the holding circuit, a pseudo signal corresponding to the output signal output from the detection coil at the reference state, and outputs the pseudo signal; a bridge circuit that, at the state other than the reference state, receives an output signal output from the detection coil and the pseudo signal and outputs a signal corresponding to a difference between the output signal and the pseudo signal, as a bridge output signal; and a bridge signal processing circuit that processes the bridge output signal output from the bridge circuit. ### Claim 9 (depends on 8) The polishing apparatus according to claim 8, wherein at the reference state, when the bridge circuit receives the output signal output from the detection coil and does not receive the pseudo signal, the bridge circuit outputs a reference bridge output signal, the output signal processing apparatus further comprises a reference data generating circuit that generates the reference data from the reference bridge output signal, and the holding circuit holds the reference data output from the reference data generating circuit. ### Claim 10 (depends on 8) The polishing apparatus according to claim 8, wherein the bridge signal processing circuit is the reference data generating circuit and, at the reference state, acquires an impedance from the reference bridge output signal in order to process the reference bridge output signal as the impedance, the holding circuit holds the acquired impedance as the reference data, and at the state other than the reference state, the pseudo signal generating circuit receives the impedance from the holding circuit and generates the pseudo signal. ### Claim 11 (depends on 8) The polishing apparatus according to claim 8, wherein the reference state is a state that the conductor does not exist in vicinity of the detection coil. ### Claim 12 (depends on 8) The polishing apparatus according to claim 8, the output signal processing apparatus further having a temperature sensor that measures a temperature of the eddy current sensor, and a correcting circuit that corrects the reference data by using the measured temperature. ### Claim 13 A polishing apparatus comprising: a polishing table configured to hold a polishing pad that polishes a workpiece; a holder that holds the workpiece and can press the workpiece against the polishing pad; an eddy current sensor that has an exciting coil configured to form eddy current in the workpiece and a detection coil that detects the eddy current formable in the workpiece, the eddy current sensor does not include a balance coil; and an output signal processing apparatus for an eddy current sensor, the output signal processing apparatus processing an output signal of the detection coil which is output from the eddy current sensor, wherein the output signal processing apparatus has a holding circuit that holds reference data indicating a characteristic of the output signal output from the detection coil at a reference state and outputs the reference data at a state other than the reference state; and a difference circuit that receives characteristic data indicating a characteristic of the output signal output from the detection coil at the state other than the reference state and the reference data output from the holding circuit and acquires a difference between the characteristic data and the reference data. ### Claim 14 (depends on 13) The polishing apparatus according to claim 13, the output signal processing apparatus further having an impedance output circuit that acquires an impedance from the output signal in order to process the output signal output from the detection coil as the impedance, wherein the holding circuit holds the impedance output from the impedance output circuit at the reference state as the reference data, and the difference circuit, at the state other than the reference state, acquires a difference between the impedance output from the impedance output circuit and the reference data output from the holding circuit. ### Claim 15 A polishing method that performs polishing by using a polishing apparatus having a polishing table configured to hold a polishing pad that polishes a workpiece; a holder that holds the workpiece and can press the workpiece against the polishing pad; and an eddy current sensor that includes an exciting coil configured to form eddy current in the workpiece and a detection coil that detects the eddy current formable in the workpiece, the eddy current sensor does not include a balance coil, the method comprising: by a holding circuit, holding reference data indicating a characteristic of the output signal output from the detection coil at a reference state and outputting the reference data at a state other than the reference state; by a pseudo signal generating circuit, generating, from the held reference data, a pseudo signal corresponding to the output signal output from the detection coil at the reference state and outputting the pseudo signal; by a bridge circuit, at the state other than the reference state, receiving the output signal output from the detection coil and the pseudo signal and outputting a signal corresponding to a difference between the output signal and the pseudo signal, as a bridge output signal; and by a bridge signal processing circuit, processing the bridge output signal. ### Claim 16 (depends on 15) The polishing method according to claim 15, wherein at the reference state, when the bridge circuit receives the output signal output from the detection coil and does not receive the pseudo signal, the bridge circuit outputs a reference bridge output signal, a reference data generating circuit generates the reference data from the reference bridge output signal, and the holding circuit holds the reference data output from the reference data generating circuit. ### Claim 17 (depends on 15) The polishing method according to claim 15, wherein the bridge signal processing circuit is the reference data generating circuit and, at the reference state, acquires an impedance from the reference bridge output signal in order to process the reference bridge output signal as the impedance, the holding circuit holds the acquired impedance as the reference data, and at the state other than the reference state, the pseudo signal generating circuit receives the impedance from the holding circuit and generates the pseudo signal. ### Claim 18 (depends on 15) The polishing method according to claim 15, wherein the reference state is a state that the workpiece does not exist in vicinity of the detection coil. ### Claim 19 (depends on 15) The polishing method according to claim 15, wherein a temperature sensor measures a temperature of the eddy current sensor, and a correcting circuit corrects the reference data by using the measured temperature. ### Claim 20 A polishing method that performs polishing by using a polishing apparatus having a polishing table configured to hold a polishing pad that polishes a workpiece; a holder that holds the workpiece and can press the workpiece against the polishing pad; and an eddy current sensor that includes an exciting coil configured to form eddy current in the workpiece and a detection coil that detects the eddy current formable in the workpiece, the eddy current sensor does not include a balance coil, the method comprising: by a holding circuit, holding reference data indicating a characteristic of the output signal output from the detection coil at a reference state and outputting the reference data at a state other than the reference state; and by a difference circuit, receiving characteristic data indicating a characteristic of the output signal output from the detection coil at the state other than the reference state and the reference data output from the holding circuit and acquiring a difference between the characteristic data and the reference data. ### Claim 21 (depends on 20) The polishing method according to claim 20, further comprising: by an impedance output circuit, acquiring an impedance from the output signal output from the detection coil in order to process the output signal as the impedance, by the holding circuit, holding the impedance output from the impedance output circuit at the reference state as the reference data, and by the difference circuit, at the state other than the reference state, acquiring a difference between the impedance output from the impedance output circuit and the reference data output from the holding circuit.