EP-4740073-A1 - TOOL HOLDER APPARATUS, A TOOL, AND A METHOD OF WORKING AN OBJECT WITH A TOOL

Abstract

This invention relates to a tool holder apparatus, a method of working an object and a tool, particularly for single point diamond turning (SPOT). The tool holder apparatus typically comprises: a tool holder which comprises: a base; a tool support extending from the base; a seat for a tool provided on the tool support, wherein the tool is locatable in the seat, in use; a sensor arrangement configured to generate electrical measurement signals indicative of, or associated with, at least an applied force to the tool, in use; and a piezoelectric actuator arrangement comprising at least one piezoelectric actuator operatively connected to the tool support, wherein the at least one piezoelectric actuator is configured to displace the tool support, or at least a part thereof, in use, in response to receiving suitable electrical control signal/s thereby to maintain a desired applied force to the tool, in use.

Inventors

• HATEFI, SHAHROKH
• SMITH, FAROUK

Assignees

• Nelson Mandela University

Dates

Publication Date

20260513

Application Date

20240614

Claims (20)

1. 1 . A tool holder apparatus, wherein the tool holder apparatus comprises: a tool holder, wherein the tool holder comprises: a base; a tool support extending from the base; a seat for a tool provided on the tool support, wherein the tool is locatable in the seat, in use; a sensor arrangement comprising a strain gauge array operatively connected to the tool support, wherein the strain gauge array is configured to generate electrical measurement signal/s indicative of, or associated with, surface strain experienced by the tool support, which is indicative of at least an applied force to the tool and/or position errors of the tool support from an initial position, in use ; and a piezoelectric actuator arrangement comprising at least one piezoelectric actuator operatively connected to the tool support, wherein the at least one piezoelectric actuator is configured to displace the tool support, or at least a part thereof, in use, in response to receiving suitable electrical control signal/s thereby to maintain a desired applied force to the tool, in use.
2. 2. A tool holder apparatus as claimed in claim 1 , wherein the suitable electrical control signal/s received by the at least one piezoelectric actuator is/are associated with the electrical measurement signal/s generated by the sensor arrangement.
3. 3. A tool holder as claimed in either claim 1 or 2, wherein the suitable control signal/s received by the at least one piezoelectric actuator is/are proportionally and/or integrally related to the electrical measurement signal/s generated by the sensor arrangement.
4. 4. A tool holder apparatus as claimed in any one of the preceding claims, wherein the tool holder apparatus comprises a processor, wherein the processor is configured to: receive electrical measurement signal/s generated by the sensor arrangement; compare the received electrical measurement signal/s with a precalibrated threshold, or range; generate suitable electrical control signal/s to control the piezoelectric actuator arrangement in a manner which is at least proportional to a deviation of received electrical measurement signal/s from the pre-calibrated threshold, or range; and transmit the suitable electrical control signal/s to the piezoelectric actuator arrangement.
5. 5. A tool holder apparatus as claimed in claim 4, wherein the processor is configured to generate suitable electrical control signals to control the piezoelectric actuator arrangement to displace the tool support, or at least a part thereof, in a manner to maintain the electrical measurement signal/s, and thus the applied force to the tool, within the pre-calibrated threshold, or range.
6. 6. A tool holder apparatus as claimed in any one of the preceding claims, wherein the tool holder apparatus comprises a suitable transmitter or transceiver device to transmit the electrical measurement signal/s from the tool holder apparatus to a remote receiver or transceiver.
7. 7. A tool holder apparatus as claimed in any one of the preceding claims, wherein the sensor arrangement comprises the piezoelectric actuator arrangement, wherein the piezoelectric actuator arrangement is configured to generate electrical measurement signal/s indicative of, or associated with, at least an applied force to the tool, in use.
8. 8. A tool holder apparatus as claimed in claim 7, wherein the electrical measurement signal/s generated by the piezoelectric actuator arrangement is indicative of, or associated with, an applied force which is lower than an applied force measured, or measurable, by the strain gauge array.
9. 9. A tool holder apparatus as claimed in any one of the preceding claims, wherein the tool support comprises a plurality of arms extending along respective axes, wherein the sensor arrangement comprises a strain gauge array operatively connected to each arm, and wherein the piezoelectric actuator arrangement comprises a plurality of piezoelectric actuators operatively connected to each arm, wherein the piezoelectric actuators are configured to displace each respective arm, or a part thereof, along their respective axes, in use, in response to receiving suitable electrical control signal/s
10. 10. A tool holder apparatus as claimed in any one of the preceding claims, wherein the tool support comprises: a first arm extending from the base along a first axis; a second arm extending from the base along a second axis, transverse to the first axis; and a third arm extending from the base along a third axis, transverse to the first and second axes, wherein the seat is provided at an intersection of the first, second and third arms.
11. 11. A tool holder apparatus as claimed in claim 10, wherein the first, second, and third arms extend cantilever fashion from the base.
12. 12. A tool holder apparatus as claimed in either claim 10 or 11 , wherein the sensor arrangement comprises: a first strain gauge array operatively connected to the first arm, wherein the first strain gauge array is configured to generate electrical measurement signal/s indicative of surface strain experienced by the first arm, in use, which is indicative of the applied force to the tool along the first axis; a second strain gauge array operatively connected to the second arm, wherein the second strain gauge array is configured to generate electrical measurement signal/s indicative of surface strain experienced by the second arm, in use, which is indicative of the applied force to the tool along the second axis; and a third strain gauge array operatively connected to the third arm, wherein the third strain gauge array is configured to generate electrical measurement signal/s indicative of surface strain experienced by the third arm, in use, which is indicative of the applied force to the tool along the third axis.
13. 13. A tool holder apparatus as claimed in any one of claims 10 to 12, wherein the piezoelectric actuator arrangement comprises: a first piezoelectric actuator operatively connected to the first arm, wherein the first piezoelectric actuator is configured to displace the first arm, or a part thereof, along the first axis, in use, in response to receiving suitable electrical control signal/s; a second piezoelectric actuator operatively connected to the second arm, wherein the second piezoelectric actuator is configured to displace the second arm, or a part thereof, along the second axis, in use, in response to receiving suitable electrical control signal/s; and a third piezoelectric actuator operatively connected to the third arm, wherein the third piezoelectric actuator is configured to displace the third arm, or a part thereof, along the third axis, in use, in response to receiving suitable electrical control signal/s.
14. 14. A tool holder apparatus as claimed in any one of the preceding claims, wherein the tool is a cutting tool.
15. 15. A tool holder apparatus as claimed in any one of the preceding claims, wherein the tool is a diamond cutting tool.
16. 16. A method of working an object with a tool, wherein the method comprises: measuring applied forces to the tool, during use of the tool working on the object, with a sensor arrangement comprising one or more strain gauge arrays; comparing the measured applied forces with a pre-calibrated threshold or range; and displacing with tool with a piezoelectric actuator arrangement to maintain the pre-calibrated applied force threshold or range, in response to said comparing.
17. 17. A method of working an object with a tool as claimed in claim 16, wherein the method comprises: measuring applied forces to the tool along three transverse axes relative to the tool; comparing the measured applied forces with a pre-calibrated threshold or range for each of the axes; displacing the tool with the piezoelectric actuator arrangement comprising one or more piezoelectric actuators along each of the axes to maintain the pre-calibrated threshold or range for each of the axes, in response to said comparing.
18. 18. A method of working an object with a tool as claimed in either claim 16 or claim 17, wherein the method comprises measuring the applied forces to the tool with the piezoelectric actuator arrangement.
19. 19. A method of working an object with a tool as claimed in claim 18, wherein the applied forces measured by the piezoelectric actuator arrangement is smaller than the applied forces measurable by the one or more strain gauge arrays.
20. 20. A method of working an object with a tool as claimed in any one of claims 16 to 18, wherein the method comprises transmitting electrical measurement signals indicative of, or associated with, the measured applied forces to a remote endpoint device.

Description

TOOL HOLDER APPARATUS, A TOOL, AND A METHOD OF WORKING AN OBJECT WITH A TOOL FIELD OF INVENTION THIS INVENTION relates in general to metrology, a tool holder apparatus, a tool, and a method of working an object with a tool. In particular, though not necessarily exclusively, the invention relates to a cutting tool holder apparatus, a cutting tool, and a method of cutting or working on an object with a cutting tool in ultra-precision single-point diamond turning (SPDT). BACKGROUND OF THE INVENTION Ultra-precision single-point diamond turning (SPDT) technology is typically used to manufacture optical surfaces with optical surface finish with an average surface roughness down to one nanometre. The SPDT products have a wide range of applications in different fields of industry, aerospace, military, biomedical, electronics, and entertainment. There are different factors that influence the outcome of the SPDT process in terms of the quality of surface finish. Different factors can negatively affect the surface generation mechanisms and increase the surface roughness. It is well stablished that cutting force is a critical factor for the cutting mechanisms and machining conditions. Increasing the cutting force can induce tool wear and friction, decrease the diamond tool life, and negatively affect the cutting stability and machining conditions. The cutting force can also induce cutting temperature and the positioning errors of the machine tool and decrease the surface accuracy of the machined product. Cutting force can be monitored as a signal for monitoring tool wear and surface defects. The mentioned effects are induced in machining hard-to-cut materials, including titanium alloys and stainless steel, which have poor machinability with SPDT technology. It is important to measure the cutting force during the cutting process and determine the optimum cutting parameters and machining conditions. In ultra-precision SPDT applications, measuring the cutting force is important in determining the stable built-up-edge and minimum chip thickness during the SPDT process. In the diamond cutting process, tool edge radius can be increased to compensate for the uncut chip thickness and the effect of material elastic recovery. Increasing the tool edge radius can increase the minimum chip thickness. Measurement of the minimum chip thickness is complicated. Cutting force is used as a factor that has a correlation with the tool edge radius for modelling and estimating the minimum chip thickness. Cutting force can be used as a factor to monitor tool wear, tool life, and tool breakage. To achieve the best possible machining conditions and maximum quality of surface finish with minimum surface roughness, it is important to precisely measure the cutting force in diamond cutting of different engineering materials. In this regard, it is desirable to have smart cutting tools for in-process measurement of cutting force in SPDT process that provides real-time measurement of cutting force with high sampling rate and quick response of the measurement system. These tools should have high precision, reliability, resolution, and repeatability. Different techniques have been used in development of metrology systems for in-process measurement of cutting forces in high-precision machining applications, including piezoelectric, capacitive, optoelectronic, and strain gauge. There are many developments on the application of force sensors in different machining applications including milling and lathe machining processes. However, a limited number of attention has been given to specific high-precision force measurement systems with high performance for ultra-precision SPDT applications. In ultra-high-precision SPDT process, the application of so-called “smart” cutting tools has been emerging for improving the machining conditions and enabling in-process metrology of machining factors including cutting force and cutting temperature. Two types of force measurement techniques can be used for in-process metrology of cutting force in SPDT process. Acoustic waves could be used for measuring the change in the surface strain using contactless passive acoustic waves. Piezoelectric ceramic films are a category of solutions that have been widely used for different force measurement applications, including cutting force measurement in ultra-precision machining applications. Some smart cutting tools make use of piezoelectric films for measuring the applied force in SPDT process as variation of the applied force changes the resistivity of the piezoelectric films, and the applied force can be measured by sensing the change in the resistance of the piezoelectric element. This technique enables measuring cutting force during the ultra-precision cutting process with high precision. Other smart cutting tools use piezoceramic material, for real-time measurement of cutting forces along X, Y, and Z axes. In these tools, piezoelectric sensor arrays were implemented in the