An infrared sensor based in situ monitoring method and system for workpiece and tool condition monitoring in machining

Abstract

The present invention relates to a system and a method for in-situ monitoring of a machining process, especially milling process with at least one non-contact optic sensor unit (1) in order to determine the deflection of a workpiece (2) and / or a tool (3) which working on the workpiece (2).

Description

[0001] AN INFRARED SENSOR BASED IN SITU MONITORING METHOD AND SYSTEM FOR WORKPIECE AND TOOL CONDITION MONITORING IN MACHINING

[0002] The present invention is about a method and a system which can be used for in situ on machine monitoring especially for milling process of the machined parts (workpiece) and cutting tools with a low -cost optical sensor unit. The developed system and method perform as good as the commercially available state of the art sensors e.g., laser sensor or accelerometer which may cost up to 5000$ or even higher.

[0003] The present invention is used in the field of machining, especially milling. Precision machined parts are critical components of modem machines and aerospace structures, thanks to the accuracy of the CNC machines and availability of the precision cutting tools. However, the limitations imposed by the conditions of the cutting process and the material seriously affect the quality of these parts and a lot of machined components are rejected at the finishing stage. Two major reasons for rejection of machined parts are the deviation from the desired profile, shape and, not meeting required surface finish due to chatter. Especially, thin-walled parts which are a major portion of aerospace structures are greatly affected by the part deflection, deformation and chatter during the machining process. The machining process is generally carried out step by step in multiple machining passes and, each machining pass exerts its own cutting loads and introduce corresponding errors on the workpiece. These errors and deviations tend to accumulate as the machining progresses towards the finishing of the part. Generally, the deviations of finished parts are inspected after removal from the machine and those having deviation values larger than the allowable tolerances are rejected. This results in huge loss of resources and time. Knowing the state of the part during the machining process gives an opportunity to control the machining process and adjust the various machining passes to get the desired final quality of the part. Another reason for not meeting the desired tolerances of machining parts is the tool wear. If the tool wear goes unnoticed during the process, the change in sizes of the tool may lead to deviation in sizes from the design values.

[0004] The developed system and method are used for in-situ measurement of thin-walled workpiece deformations, chatter, as well as deflection and wear of tool during the machining process. It allows to assess the condition of the machined part (workpiece) and the cutting tool during the machining process thus allowing to make any necessary changes at the intermediate stages to get the qualified final product.

[0005] Normally, in-process measurement of workpiece deformation or surface quality requires its removal from the machine. Similarly, tool wear is diagnosed by inspection of the cutting tool at intervals by halting the process or is diagnosed after the machining process. This result in wastage of a lot of time. With the developed method and system comprising the optical sensor unit, various aspects of the machining process such as the workpiece deformation, chatter, tool wear and tool deflection can be identified during the machining process.

[0006] There are already some industrial measurement solutions available for the measurement and condition monitoring of the workpiece and tool during the machining process. These include measurement touch probes, eddy current displacement sensor, optical sensors such as lasers, accelerometers, microphones and dynamometers etc. Each of these solutions have pros and cons. The present invention has an advantage to use a low-cost infrared based optical sensor easy to implement alternative to these industrial solutions.

[0007] In the state of the art, the acoustic sensors may be used for the chatter detection. However, the acoustic sensors are prone to the background factory noise requiring rigorous signal processing. The present invention is not affected by the acoustic noise common in the machine shops.

[0008] In the state of the art, W02022004929A1 international patent application discloses a strain sensor-based monitoring of the workpiece during machining. In this invention, the workpiece displacement and vibration data are collected using the strain sensor applied directly on the workpiece. It is thus a measuring technique using direct contact between the sensor and the workpiece. Moreover, the strain-based sensors are prone to temperature variations and results in erroneous output. The strain sensor-based chatter detection technique as presented in this patent is a contact-based technique requiring very sophisticated installation of the strain gauges on the workpiece surface. Moreover, machining of the workpiece at the location of strain gauge installation would require a priori removal of the strain gauges during the process. The developed invention method being a non-contact based is oblivious to such disadvantages. In the state of the art, CN105904012A Chinese patent application discloses a real-time deformation compensation function for thin-walled parts hence it is more focused on the control side. The deformation sensor used in the patent is a laser senor which is different than a low- cost infrared based sensor.

[0009] The aim of the present invention is to provide a workpiece monitoring method and system for a machining process especially for milling with a non-contact optical sensor unit.

[0010] The deformation measurement feature of the developed invention can be very useful for in-situ monitoring and control of the distortion of machined components especially, in the case of large thin-walled aerospace parts. Normally, such measurements are made by using expensive systems such as laser sensor systems or by measurement probes. With the developed invention, multiple sensors can be installed at various locations along the large workpiece surface due to the flexibility in its installation. The data acquired from the sensors provide real-time elastic as well as plastic deformation value during the milling operation. These deformation values can be used for optimization of the machining process during multiple cutting passes.

[0011] The first advantage of this invention over the commercially available measurement probes, lasers and acceleration sensors is its very low cost without any accuracy and reliability compromise. Multiple optical sensor units can be installed at various location of the large parts to get the accurate assessment of the local cutting conditions. The chatter detection feature of the invention gives a low-cost solution for the detection of chatter during the machining of the workpiece.

[0012] The tool wear detection feature of the invention allows the qualitative detection of tool wear during the machining process from the displacement data collected from the workpiece or tool without any need for any extra tool inspection.

[0013] Another very important aspect of the developed method is the versatility of its application. As the single optical sensor unit might be used for several different applications e.g., part deformation measurement, chatter detection, tool deflection, tool wear detection etc. By the help of the present invention a non-contact measurement of workpiece and the tool is provided, and the method of the present invention does not require any direct installation on the workpiece.

[0014] The monitoring system and the method which is realized in order to achieve the aim of the present invention is shown in the attached figure;

[0015] Figure 1- is a schematic view of a workpiece, tool and an optical sensor unit which is placed in in-situ monitoring in an embodiment of the present invention.

[0016] The elements illustrated in the figures are numbered as follows:

[0017] 1. Optical sensor unit

[0018] 2. Workpiece

[0019] 3. Tool

[0020] The monitoring system for a milling process comprising: a workpiece (2) where the milling process is performed and a tool (3) working on the workpiece (2), an optical sensor unit (1) comprising a transmitter and a receiver,

[0021] - the optical sensor unit (1) is provided outside the workpiece (2) in such a way that the optical sensor unit (1) senses the deflection and / or chattering of the workpiece (2) and / or the tool (3) in a non-contact manner and a control unit is configured to determine the deflection level and / or chattering of the workpiece (2) and / or the tool (3) according to a voltage output obtained from the optical sensor unit (1).

[0022] The monitoring system comprising at least one optical sensor unit (1) which comprising a transmitter and a receiver. The optical sensor unit (1) is placed in front of the workpiece during the milling operation. The optical sensor unit (1) receives the transmitted rays on the deflection of the workpiece during the milling operation and according to the voltage output obtained from the optical sensor unit (1), the control unit determines the deflection level and / or chattering level of the workpiece (2) and / or the tool (3). The data is continuously acquired and processed during the machining process. The workpiece (2) deformation is directly measured from the already calibrated voltage signals from the optical sensor unit (1). The control unit has all the data about calibrated voltage signals and the deflection distances corresponding to these voltage signals. Chatter is identified by analyzing the acquired signals in the frequency domain and identifying the signal frequencies which are different from the known frequencies of the system. To determine tool (3) wear, the acquired signals corresponding to tooth passing period of the tool are analyzed for any difference in the peak values of the signal.

[0023] In an embodiment of the present invention, the optical sensor unit (1) was calibrated with the help of a laser sensor for the deformation / deflection measurement. In this embodiment, both the laser sensor and the optical sensor unit (1) were installed in front of the workpiece (2), then the workpiece (2) was deformed with the help of the tool (3). The workpiece (2) was moved at an increment of 1 micron, the output voltage form the optical sensor unit (1) was recorded and compared with the distance value of the laser sensor.

[0024] In an embodiment of the invention the system comprising the optical sensor unit (1) comprising an infrared emitter and a phototransistor, operating in short infrared range. Short infrared range covering the wavelengths ranging from 760 to 1500 nanometers. In this way, a system that makes the cost much cheaper is obtained.

[0025] In an embodiment of the present invention, the monitoring system comprising a plurality of the optical sensor units (1) which is provided in the vicinity of the workpiece (2). By the help of this, more precise measurement can be achieved.

[0026] In an embodiment of the present invention, the optical sensor units (1) are positioned aligned with a surface of the workpiece (2) where the milling process is performed. By means of this, a more precise deflection measurement can be made.

[0027] In an embodiment of the present invention the monitoring system comprising the optical sensor unit (1) which is provided at a distance of 2 to 15 mm from the workpiece (2). These distances are the ideal distance where the sensor should be positioned for measurement and facilitate accurate measurement. In an embodiment of the present invention the monitoring system comprising the optical sensor unit (1) is provided at an angle of 85 to 95 degree with respect to the workpiece (2).

[0028] In an embodiment of the present invention the monitoring system comprising a memory for recording the deflection levels corresponding to the voltage outputs.

[0029] In an embodiment of the present invention the monitoring system comprising a wireless communication unit for transferring the deflection level data to an external computer or a mobile device. The wireless communication unit may be a Bluetooth or NFC.

[0030] The method of monitoring a workpiece (2) milling process which a tool (3) working on the workpiece (2), based on an optical sensor unit (1) comprising a transmitter and a receiver comprising the steps of;

[0031] - providing the optical sensor unit (1) outside the workpiece (2) in such a way that the optical sensor unit (1) senses the deflection and / or chattering of the workpiece (2) and / or the tool (3) in a non-contact manner,

[0032] - generating a voltage output corresponding the deflection of the workpiece (2) and / or the tool (3), by the optical sensor unit (1), determining the dimension of the deflection by using the voltage output, by the control unit.

[0033] The method further comprises the step of, recording the deflection levels corresponding to the voltage outputs in a memory.

[0034] The method further comprising the step of calibrating the optical sensor unit (1) with the help of a laser sensor for the deformation / deflection measurement.

Claims

CLAIMS1. A monitoring system for a milling process comprising: a workpiece (2) where the milling process is performed and a tool (3) working on the workpiece (2), an optical sensor unit (1) comprising a transmitter and a receiver, characterized in that;- the optical sensor unit (1) is provided outside the workpiece (2) in such a way that the optical sensor unit (1) senses the deflection and / or chattering of the workpiece (2) and / or the tool (3) in a non-contact manner and a control unit is configured to determine the deflection level and / or chattering of the workpiece (2) and / or the tool (3) according to a voltage output obtained from the optical sensor unit (1).

2. A monitoring system according to claim 1, wherein the optical sensor unit (1) comprising an infrared emitter as the transmitter and a phototransistor as the receiver operating in short infrared range.

3. A monitoring system according to claim 1 or 2, wherein the system further comprising a laser sensor for calibrating the optical sensor unit (1) to measure the deflection.

4. A monitoring system according to any one of the claims 1 or 3, wherein a plurality of the optical sensor units (1) is provided in the vicinity of the workpiece (2).

5. A monitoring system according to claim 4, wherein the optical sensor units (1) are positioned aligned with a surface of the workpiece (2) where the milling process is performed.

6. A monitoring system according to any one of the preceding claims, wherein the optical sensor unit (1) is provided at a distance of 2 to 15 mm from the workpiece (2).

7. A monitoring system according to any one of the preceding claims, wherein the optical sensor unit (1) is provided at an angle of 85 to 95 degree with respect to the workpiece (2).

8. A monitoring system according to any one of the preceding claims, wherein the system comprising a memory for recording the deflection levels corresponding to the voltage outputs.

9. A monitoring system according to any one of the preceding claims, wherein the system comprising a wireless communication unit for transferring the deflection level data to an external computer or a mobile device.

10. A method of monitoring a workpiece (2) milling process which a tool (3) working on the workpiece (2), based on an optical sensor unit (1) comprising a transmitter and a receiver comprising the steps of;- providing the optical sensor unit (1) outside the workpiece (2) in such a way that the optical sensor unit (1) senses the deflection and / or chattering of the workpiece (2) and / or the tool (3) in a non-contact manner,- generating a voltage output corresponding the deflection of the workpiece (2) and / or the tool (3), by the optical sensor unit (1), determining the dimension of the deflection by using the voltage output, by the control unit.

11. The method according to claim 8, further comprising the step of: calibrating the optical sensor unit (1) with the help of a laser sensor for the deformation / deflection measurement.

12. The method according to claim 8 or 9, further comprises the step of: recording the deflection levels corresponding to the voltage outputs in a memory.

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