KR102175530B1 - Drill condition monitoring system - Google Patents

Abstract

The present invention relates to a drill condition monitoring system. A current sensor measures an electric current introduced into a transfer motor. An infrared sensor module irradiates infrared rays to a drill and measures the intensity of infrared rays reflected from the drill. A system controller determines whether to replace the drill or not by estimating a damage to the drill due to abrasion based on the electric current measured by the current sensor while the drill is drilling an object to be processed, and when no damage to the drill due to abrasion is estimated, determines whether to replace the drill or not by estimating a sudden damage to the drill based on the intensity of infrared rays measured by the infrared sensor module while the drill is rotating by escaping from the object to be processed. According to the present invention, a drill can be replaced at the appropriate time to minimize post-processing, increase of processing time, and economic loss due to drill damage.

Description

Drill condition monitoring system

The present invention relates to a drill condition monitoring system that monitors a drill condition in a drilling process and enables a drill to be replaced at an appropriate time.

Recently, as the 4th industrial revolution has entered the era, the manufacturing industry is actively promoting unmanned processes and automation to secure market competitiveness. To this end, a condition monitoring technology for factors that can self-measure and affect product quality is required. In particular, since tool wear progresses gradually, implementing a system capable of monitoring tool conditions and replacing tools at an appropriate time is one of the biggest challenges of automation.

For example, the drilling process occupies a large portion of the cutting process, accounting for about 25% of the actual machining process. In general, since the drilling process is placed in a lower order in the processing order, abnormal phenomena such as drill breakage cause enormous obstacles to overall productivity improvement.

Meanwhile, a method of measuring the state of a cutting tool such as a drill may be divided into a direct measurement method and an indirect measurement method. The direct measurement method is a method of directly measuring tool wear using an optical microscope, etc., which requires expensive optical equipment and requires separating the tool from the machine tool in order to measure tool wear, resulting in lower productivity and increased cost. There is. The indirect measurement method is a method of measuring the cutting force vibration of the tool using an acceleration sensor as an indirect index related to tool wear. It is vulnerable to signal attenuation and noise according to the sensor installation location, and the installation is low.

An object of the present invention is to provide a drill condition monitoring system that predicts drill breakage in a drilling process and enables immediate and rapid response.

The drill condition monitoring system according to the present invention for achieving the above object is a drill that drills a workpiece on the XY plane as it rotates around the Z axis, a spindle motor that rotates the drill, and a feed that transports the drill in the Z axis direction. A system employed in a drilling machine including a motor to monitor a drill state, and includes a current sensor, an infrared sensor module, and a system controller. The current sensor measures the current drawn into the transfer motor. The infrared sensor module irradiates infrared rays with a drill and measures the intensity of infrared rays reflected from the drill. The system controller predicts the damage of the drill due to wear based on the current measured from the current sensor while the drill is drilling the workpiece, and determines the replacement of the drill. If the damage of the drill due to wear is not predicted, the drill is The replacement of the drill is determined by predicting the sudden damage of the drill based on the infrared intensity measured from the infrared sensor module while rotating away from the workpiece.

Here, if the voltage signal input from the current sensor is greater than or equal to a set threshold value, the system controller may detect the damage prediction signal as a damage prediction signal and predict damage to the drill due to wear.

And, based on the voltage input from the infrared sensor module, the system controller converts the voltage slope over time into a voltage slope vector on the XY axis from the voltage signals at two points forming a section where drill corner wear occurs, and If the ratio of the absolute value of the X-direction component and the Y-direction component of the voltage gradient vector exceeds the set threshold value, the sudden breakage of the drill can be predicted.

The drill condition monitoring system according to the present invention uses a relatively inexpensive current sensor and an infrared sensor module to simultaneously predict damage due to wear and sudden damage in the drilling process, so that the drill is replaced at an appropriate time and Processing, processing time increase and economic loss can be minimized. As a result, it is expected that the drill condition monitoring system can be used as a key technology for advancement of smart factories.

1 is a block diagram of a drill condition monitoring system according to an embodiment of the present invention.
2 is a view showing an example of measuring the corner wear of the drill by the infrared sensor module.
3 is a graph for explaining an example of setting a threshold value for detecting a damage prediction signal of a drill according to an experimental example.
4 is a graph showing an output voltage of an infrared sensor module measuring a drill according to an experimental example.
5 is a graph obtained by converting an output voltage graph of an infrared sensor module into a polar coordinate system according to an experimental example.
6 is a photograph of an actual drill.
7 is a graph showing voltage slopes at two points related to drill corner wear according to an experimental example.
8 is a graph showing a ratio of an absolute value of an X-direction component and a Y-direction component of a voltage gradient vector according to an experimental example.
9 is a flowchart illustrating a method of determining a drill replacement by a drill condition monitoring system according to an embodiment of the present invention.

The present invention will be described in detail with reference to the accompanying drawings as follows. Here, the same reference numerals are used for the same configuration, and repeated descriptions and detailed descriptions of known functions and configurations that may unnecessarily obscure the subject matter of the present invention will be omitted. Embodiments of the present invention are provided in order to more completely describe the present invention to those of ordinary skill in the art. Accordingly, the shapes and sizes of elements in the drawings may be exaggerated for clearer explanation.

1 is a block diagram of a drill condition monitoring system according to an embodiment of the present invention.

Referring to FIG. 1, the drill condition monitoring system 100 according to an embodiment of the present invention is a drill 11 and a drill 11 for drilling a workpiece 1 on an XY plane as it rotates around a Z axis. As a system for monitoring the state of the drill 11, it is adopted in the drilling machine 10 including the main shaft motor 12 to rotate the drill 11 and the feed motor 13 for transporting the drill 11 in the Z-axis direction, 110), an infrared sensor module 120, and a system controller 130.

The drilling machine 10 enters the workpiece 1 by the transfer motor 13 in a state in which the drill 11 is rotated by the main shaft motor 12 to drill the workpiece 1. As the transfer motor 13 transfers the main shaft motor 12 in the Z-axis direction, the drill 11 may be transferred in the Z-axis direction. The workpiece 1 is seated on the worktable 14 and transferred in the X-axis and/or Y-axis directions by the XY transfer mechanism, thereby enabling relative movement with respect to the drill 11.

The current sensor 110 measures the current drawn into the transfer motor 13. The current sensor 110 may include a Hall sensor. The Hall sensor is a sensor using the Hall effect, and when a magnetic field is applied to a conductor through which a current flows, a Hall voltage is generated that is proportional to the intensity of the current. Therefore, by measuring the voltage, the intensity of the current can be measured. Since the Hall sensor is installed on the power supply line of the transfer motor 13 in the control box 15 of the drilling machine 10, it may not interfere with the drilling process.

The voltage signal output from the Hall sensor may be filtered through a moving average filter 111. The moving average filter 111 is a signal generated when the drill 11 moves in the Z-axis direction to a certain height in order to transfer from the machining hole position to the next machining hole position after the drilling process ends, and a static signal and a low frequency signal generated in the drilling process. Is removed from the output voltage signal of the Hall sensor. The signal passing through the moving average filter 111 may be transmitted to the data acquisition device 112, for example, a DAQ board, and stored in the system controller 130.

In general, the breakage of the drill 11 during drilling occurs in the shear direction. The reason is that the cutting thrust and cutting torque applied to the drill 11 immediately before breakage increase rapidly, because the increase rate of the cutting torque is larger than the increase rate of the cutting thrust. Therefore, it is necessary to measure the cutting thrust or cutting torque in order to detect the breakage of the drill 11.

The cutting torque is correlated with the main shaft motor current, and the cutting thrust is correlated with the feed motor current. When the cutting torque is used to detect the breakage of the drill 11, the main shaft motor current has low dynamic sensitivity compared to the feed motor current, and there is a problem of fluctuations in the cutting torque due to repeated pinching and discharge of cutting chips, and the inertia of the spindle system Depending on the inertia of the feed system, there is a time delay that occurs when the drill 11 is damaged, and when the diameter of the drill 11 decreases, it is difficult to distinguish between a cutting section and a non-cutting section.

Therefore, in the embodiment of the present invention, the transfer motor current measured from the current sensor 110 is used to predict the breakage of the drill 11. The relational expression between the cutting thrust and the transfer motor current may be summarized as in Equation 1 below in consideration of the self-weight of the transfer motor 13.

Here, F _trust is the cutting thrust, F _weight is the force due to the self- _weight of the feed motor, K _T is the constant value of the motor for each drilling machine, and I _FM is the feed motor current.

According to Equation 1, it can be seen that the feed motor current follows the cutting thrust applied to the drill 11 and has a proportional relationship with the cutting thrust. Accordingly, since the cutting thrust that rapidly increases immediately before the breakage of the drill 11 can be measured using the transfer motor current, the transfer motor current measured from the current sensor 110 can be used for predicting the breakage of the drill 11.

The infrared sensor module 120 measures the intensity of infrared rays reflected from the drill 11 by irradiating infrared rays with the drill 11. The infrared sensor module 120 may include a light emitting device 121, an optical fiber 122, and a light receiving device 123.

The light-emitting device 121 emits infrared rays. The optical fiber 122 receives infrared rays emitted from the light emitting device 121 and irradiates them with a drill 11 and receives infrared rays reflected from the drill 11. The light-receiving device 123 measures the intensity of infrared rays transmitted from the optical fiber 122.

The light emitting device 121 may be formed of a light emitting diode or the like. In the optical fiber 122, a light exit part 122a may be formed at one end, and a light emitting device 121 and a light receiving device 123 may be connected to the other end. The light exit portion 122a may be supported by the sensor block 124 in a state disposed toward the drill 11. The light exit part 122a is kept spaced apart from the drill 11 by a set distance, so that infrared rays reflected from the drill 11 can be received after irradiating infrared rays with the drill 11. The light-receiving device 123 may be formed of a phototransistor or the like.

The infrared sensor module 120 receives the light-receiving device 123 when infrared rays irradiated from the light emitting device 121 to the drill 11 through the optical fiber 122 are reflected off the surface of the drill 11 and incident on the optical fiber 122 Light energy is converted into electrical energy by the intensity of one light and converted into voltage.

The analog signal of the voltage output from the light-receiving element 123 may be transmitted to a data acquisition device 126, for example, a DAQ board, through a low pass filter 125, and stored in the system controller 130.

In general, the wear that occurs on the drill 11 in the drilling process is flank wear, crater wear, outer corner wear, margin wear, and chisel edge wear. wear), chipping, etc., among them, flank wear is used as a criterion for determining the life of the drill 11.

However, flank wear that occurs on the clearance surface of the drill 11 is difficult to measure directly because the clearance surface of the drill 11 is inclined by a half angle of the point angle around the drill axis. Since 11) must be measured using an electron microscope or the like after separating it from the drilling machine 10, it may be a factor of increasing processing time and reducing productivity. In addition, the built up edge growing on the main cutting edge of the drill 11 during the drilling process makes it more difficult to accurately measure flank wear.

Accordingly, in the embodiment of the present invention, the corner wear of the drill 11, which is easy to measure compared to the flank wear and is closely related to the life of the drill 11, is used as a criterion for determining the life of the drill 11. Since the corner of the drill 11 is located in a direction perpendicular to the transport direction of the drill 11, if the infrared sensor module 120 is used, it can be easily measured compared to flank wear.

When the drill 11 is rotated at a constant spindle speed while the drill 11 is coupled to the drilling machine 10, the optical fiber 122 and the drill 11 are formed according to the curved shape of the drill 11. As the distance between them changes, a signal waveform that is repeated per revolution appears from the infrared sensor module 120, and this one-turn signal waveform is an outer flute and an inner flute of the drill 11, The shape of the drill 11 is reflected in the voltage signal by the difference in output voltage according to the relative distance of the shape of the drill 11 such as a margin.

The difference in output voltage according to the shape of the drill appears in the voltage signal as the wear of the drill 11 progresses. The reason is that if the drilling process is performed under the same conditions as the workpiece (1), the material of the drill (11), the rotational speed, the feed rate, and the drilling depth, the drill (11) corner is gradually worn and the shape of the drill (11). And the surface roughness changes.

In addition, the reason is that the rotational speed of the drill 11 increases in proportion to the radius as it goes radially from the center, so high heat is generated due to friction caused by the machining wall during processing, so the hardness of the corner edge of the drill 11 This is because it decreases.

As such, when the wear of the corners of the drill 11 gradually progresses, the edge becomes dull and the surface roughness of the drill 11 deteriorates. This causes a small distance difference between the corners of the optical fiber 122 and the drill 11 and diffuse reflection of the surface of the drill 11, and as a result, the amount of light reflected from the corner of the drill 11 and received by the optical fiber 122 is reduced. Therefore, by using the voltage signal of the light-receiving element 123 over time, the wear of the corner of the drill 11 can be measured.

The system controller 130 predicts damage of the drill 11 due to wear based on the current measured from the current sensor 110 while the drill 11 drills the workpiece 1 Judge the replacement. When the voltage signal input from the current sensor 110 is greater than or equal to a set threshold value, the system controller 130 may detect the damage prediction signal as a damage prediction signal and predict damage of the drill 11 due to wear.

When the drill 11 is damaged, the feed motor current increases rapidly, and the rapid increase in current appears as a rapid increase in the RMS voltage signal of the Hall sensor. This is the same result as the drill 11 breakage mechanism in which the rate of increase of the cutting thrust immediately before the breakage of the drill 11 increases rapidly.

In addition, a damage prediction signal appears in which the analog voltage signal of the Hall sensor rapidly increases during drilling just before the damage. The damage prediction signal moves to the next hole position while the hardness of the drill 11 sharply decreases due to deterioration due to an increase in the cutting load applied to the drill 11 as the wear of the drill 11 progresses during continuous drilling. It is a signal measured at the moment when the drill 11 is pulled out in the reverse direction of the machining direction.

Therefore, if the damage prediction signal is measured, the damage of the drill 11 can be predicted, and when the RMS signal value exceeding the set threshold is measured, it can be determined that there is a risk of damage of the drill 11. As shown in FIG. 3, the set threshold is 7% compared to the average value of the Hall sensor voltage measured during drilling in a normal state, in which the voltage of the Hall sensor measured at the position of the hole immediately before damage is based on the data through the experiment. It can be set to an elevated value. When the voltage signal input from the current sensor 110 is 7% or more, the system controller 130 may detect the damage prediction signal as a damage prediction signal and predict damage to the drill 11 due to wear.

When the damage of the drill 11 due to wear is not predicted, the system controller 130 drills based on the infrared intensity measured from the infrared sensor module 120 while the drill 11 moves away from the workpiece 1 and rotates. By predicting the sudden damage of (11), the replacement of the drill (11) is determined.

Based on the voltage input from the infrared sensor module 120, the system controller 130 calculates the voltage slope over time from the voltage signals at the two points forming the section where the corner wear of the drill 11 occurs. When the ratio of the absolute value of the X-direction component and the Y-direction component of the converted voltage gradient vector exceeds a set threshold value, sudden breakage of the drill 11 can be predicted.

The two points constituting the section where the corner wear of the drill 11 occurs may be selected in advance through an experiment. This will be described with reference to FIGS. 4 to 8 as follows. First, as shown in Fig. 4, the voltage signal measured from the light receiving element 123 of the infrared sensor module 120 is 5 inflection points (A, B, C, D, E) per 1/2 rotation of the drill 11 ) Occurs.

As shown in Fig. 5, the voltage graph over time is converted into a polar coordinate system of radians and voltages to select an inflection point related to corner wear of the actual drill 11 among five inflection points (A, B, C, D, E). I did. Since the position of the optical fiber 122 of the infrared sensor module 120, that is, the position of the sensor is fixed, using the coordinates of each of the inflection points (A, B, C, D, E) of the polar coordinate system, the angle from the sensor position is changed to each inflection point ( A, B, C, D, E) can be calculated. As shown in FIG. 6, the position of each inflection point (A, B, C, D, E) of the polar coordinate system is compared with a picture of an actual drill 11 taken with a field emission transmission electron microscope. Thus, two inflection points (A, B) related to the actual drill 11 corner wear were selected.

As shown in FIG. 7, the voltage slope over time in the voltage signals of the two selected points (A, B) gradually changed from the normal state of the drill 11 and rapidly changed after drilling just before the breakage. . This is the same result as the drill 11 breakage mechanism leading to a sudden breakage after the wear of the drill 11 gradually occurs.

(n번째 구멍의 전압 기울기 벡터)로 변환하였고, 변환된 전압 기울기 벡터의 X방향 성분과 Y방향 성분을 살펴본 결과, 모든 실험 조건에서 드릴(11)의 파손 직전 가공홀 위치에서 X방향 성분과 Y방향 성분의 절대값의 비가 모두 1 ΔV/Δt 를 초과하였다. 이는 드릴(11)의 파손직전 가공홀 위치에서 두 방향 성분이 이루는 각도가 45도를 벗어난 경우로 모든 실험조건에서 동일하게 나타났다.Based on this tendency, as shown in FIG. 8, the voltage slope of the two points A and B is a voltage slope vector on the XY axis,

(Voltage gradient vector of the n-th hole), and as a result of examining the X-direction and Y-direction components of the converted voltage gradient vector, under all experimental conditions, the X-direction component and Y The ratios of the absolute values of the fragrance components all exceeded 1 ΔV/Δt. This is a case where the angle formed by the two direction components at the position of the drilling hole just before the breakage of the drill 11 is out of 45 degrees, and it was the same in all experimental conditions.

Therefore, based on the experimental result, the set threshold may be set to 1 ΔV/Δt, and the system controller 130 has a ratio of the absolute value of the X-direction component and the Y-direction component of the voltage gradient vector to 1 ΔV/Δt If exceeded, it is possible to predict the sudden breakage of the drill (11).

For an example of a process of determining the replacement of the drill 11 by predicting damage of the drill 11 due to wear and sudden damage of the drill 11 by the above-described drill condition monitoring system 100, referring to FIG. It is as follows.

First, the current is measured by the current sensor 110 while the drill 11 is drilling the workpiece 1. After the RMS value of the voltage signal output from the current sensor 110 is calculated, the calculated RMS value is filtered by the moving average filter 111. Thereafter, when the damage prediction signal is detected in the voltage signal, it is determined as replacement of the drill 11.

If the damage prediction signal is not detected, the drill 11 corner wear is measured by the infrared sensor module 120 while the drill 11 is rotated, and the voltage signal output from the infrared sensor module 120 is passed through a low band. Filtered by filter 125. Thereafter, the voltage gradient over time is converted into a voltage gradient vector on the XY axis from the voltage signals of the two points (A, B) forming the section where the corner wear of the drill 11 occurs, and the X direction of the converted voltage gradient vector If the ratio of the absolute value of the component and the component in the Y direction exceeds the set threshold, it is determined that the drill 11 is replaced. If the ratio of the absolute value of the component in the X direction and the component in the Y direction does not exceed the set threshold value, drilling is continued and the current is measured from the current sensor 110.

As described above, according to the drill condition monitoring system 100, damage of the drill 11 due to wear in the drilling process and sudden damage of the drill 11 by using the relatively inexpensive current sensor 110 and the infrared sensor module 120 Since the damage can be predicted at the same time, it is possible to minimize the post-treatment, processing time increase, and economic loss due to the damage of the drill 11 by replacing the drill 11 at an appropriate time. As a result, it is expected that the drill condition monitoring system 100 can be utilized as a core technology for advancement of a smart factory.

The present invention has been described with reference to one embodiment shown in the accompanying drawings, but this is only illustrative, and those of ordinary skill in the art will understand that various modifications and other equivalent embodiments are possible therefrom. I will be able to. Therefore, the true scope of protection of the present invention should be determined only by the appended claims.

11.. Drill
12..spindle motor
13..Transfer motor
110..current sensor
120..Infrared ray sensor module
130..System controller

Claims (5)

It is adopted in a drilling machine that includes a drill that drills a workpiece on the XY plane as it rotates around the Z-axis, a spindle motor that rotates the drill, and a feed motor that transfers the drill in the Z-axis direction to monitor the state of the drill. As a system to do,
A current sensor that measures a current drawn into the transfer motor;
An infrared sensor module measuring infrared intensity reflected from the drill by irradiating infrared rays with the drill; And
While the drill is drilling the workpiece, it predicts the damage of the drill due to wear based on the current measured from the current sensor to determine the replacement of the drill.If the damage of the drill due to wear is not predicted, the drill is Including; a system controller for determining the replacement of the drill by predicting the sudden damage of the drill based on the infrared intensity measured from the infrared sensor module while rotating away from the workpiece,
The system controller converts the voltage slope over time into a voltage slope vector on the XY axis from the voltage signals at two points forming a section where drill corner wear occurs, based on the voltage input from the infrared sensor module, and the converted A drill condition monitoring system, characterized in that, when a ratio of an absolute value of an X-direction component and a Y-direction component of a voltage gradient vector exceeds a set threshold value, the drill condition monitoring system predicts accidental breakage of the drill.
The method of claim 1,
The system controller detects as a damage prediction signal when the voltage signal input from the current sensor is greater than or equal to a set threshold value and predicts the damage of the drill due to wear.
The method of claim 1,
The current sensor is a drill condition monitoring system, characterized in that it comprises a Hall sensor.
delete The method of claim 1,
The infrared sensor module,
A light emitting element that emits infrared rays,
An optical fiber that receives infrared rays emitted from the light emitting device, irradiates with the drill, and receives infrared rays reflected from the drill, and
Drill condition monitoring system comprising a light receiving device for measuring the intensity of infrared transmitted from the optical fiber.

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