Sensor elements and assemblies, cutting tools comprising same and methods of using same
A sensor element for a cutting tool ( 100 ) has a hard portion ( 110 ) having a sensing surface ( 112 ), first and second electrodes ( 120, 130 ), first and second sets of thermocouple wires ( 122, 132 ) and an electrically insulating portion. The first and second electrodes ( 120, 130 ) are arranged to allow electric current to flow when the sensing surface ( 112 ) contacts external material in response to the cutting tool engaging the external material. A first thermocouple junction ( 124 ) is operable to indicate a temperature of the first electrode and a second thermocouple junction ( 134 ) is operable to measure temperature of the second electrode.
1. A sensor assembly comprising
a sensor element for a cutting tool, the sensor element comprising:
a hard portion having a sensing surface;
a first electrode;
a first set of thermocouple wires;
a second electrode;
a second set of thermocouple wires; and
an electrically insulating portion; wherein:
the hard portion comprises hard and/or super-hard material;
the first electrode and the second electrode each comprising electrically conductive hard and/or super-hard material, and each being attached to the hard portion and exposed at respective areas of the sensing surface;
the hard portion including the electrically insulating portion;
the first electrode, the second electrode and the hard portion being arranged to allow an electric current to flow between with first electrode and the second electrode through external material, when the sensing surface contacts the external material in response to the cutting tool engaging the external material in use; the electrically insulating portion electrically isolating the sensing surface, operable to prevent electric current from flowing through the sensing surface; wherein
the first set of thermocouple wires are electrically connected to the first electrode at a first thermocouple junction operable to indicate a temperature of the first electrode; and
the second set of thermocouple wires are connected to the second electrode at a second thermocouple junction, operable to measure the temperature of the second electrode; wherein the sensor assembly further comprises:
a source of potential difference and electric current;
a current measurement device;
a voltage measurement device connected to the first and second sets of thermocouple wires, operable to indicate the temperatures of the first and second electrodes; and
an impedance spectrometry system, operable to process a measured electric current having one or more frequency components; the source of the electric current being configurable to generate varying electric current, having one or more frequency components;
the first electrode, the second electrode, the source and the current measurement device connected in an electrical circuit, arranged to generate a potential difference between the first electrode and the second electrode, and to allow an electric current to flow between the first electrode and the second electrode, through the external material when the sensing surface contacts the external material in response to the cutting tool engaging the external material in use; and to allow the current measurement device to indicate a magnitude of the electric current.
2. The sensor assembly as claimed in claim 1 , wherein at least the first electrode is electrically connected to the source by the first set of thermocouple wires.
3. A cutting tool comprising
a tool body; and
the sensor assembly as claimed in claim 1 , the sensor assembly being attached to the tool body and being operable so that the sensing surface contacts the external material when the cutting tool engages the external material in use.
4. The cutting tool as claimed in claim 3 , provided as an earth-boring bit, a plurality of cutter elements attached to the bit, operable to cut rock and bore a hole into the earth; the sensor assembly arranged on the earth-boring bit to allow at least an area of the sensing surface to contact the rock.
5. A method of using a cutting tool as claimed in claim 3 , including:
engaging a workpiece body with the cutting tool to remove workpiece material from the workpiece body, and allowing the sensing surface of the sensor assembly to engage the external material containing the workpiece material cut from the workpiece body;
generating the potential difference between the first electrode and the second electrode;
generating the electric current to flow between the first electrode and the second electrode, through the external material contacted by the sensing surface;
measuring the electric current;
measuring temperatures of the first electrode and the second electrode;
determining respective electrical resistance of the first electrode and the second electrode at the respective measured temperatures; and
analysing the measured electric current to determine an electrical characteristic of the external material.
6. The method as claimed in claim 5 , including a computer-implemented method to process the measured electric current, to calculate the electrical characteristic of the external material; and to calculate a quantity indicative of a mechanical characteristic of the workpiece material, based on the electrical characteristic.
7. The sensor assembly as claimed in claim 1 , wherein the first electrode and the second electrode each comprises electrically conductive super-hard material.
8. The sensor assembly as claimed in claim 1 , wherein the hard portion comprises super-hard material comprising any one or more of single crystal diamond, polycrystalline diamond (PCD) material, polycrystalline cubic boron nitride (PCBN) material, and/or chemical vapour deposited diamond.
9. The sensor assembly as claimed in claim 1 , wherein the sensor element is configured as a cutter element; the sensing surface comprising a working surface including a cutting edge and providing a rake face area.
10. The sensor assembly as claimed in claim 1 , wherein the sensor element comprises a cutter element for an earth-boring bit, or a machine tool for machining a workpiece.
11. The sensor assembly as claimed in claim 1 , wherein the electrically insulating portion comprises a volume of the hard portion coterminous with the sensing surface.
12. The sensor assembly as claimed in claim 1 , wherein the hard material portion comprises polycrystalline diamond (PCD) material and includes a surface volume that includes no more than 2 wt. % metallic material.
13. The sensor assembly as claimed in claim 1 , wherein the first electrode comprises boron—and/or phosphorus—doped diamond.