Machine Tool, Machine Tool Control Method, and Machine Tool Control Program

There is provided a technique for more reliably detecting clogging of a filter with chips over conventional techniques. A machine tool that can machine a workpiece includes a storage tank; a discharge unit that discharges coolant stored in the storage tank toward chips resulting from the machining of the workpiece; a filter that removes the chips from the coolant; a collecting pump that brings the coolant back to the storage tank; a first obtaining unit that obtains a first index value indicating an amount of coolant discharged per predetermined time; a second obtaining unit that obtains a second index value indicating an amount of coolant that is brought back to the storage tank per predetermined time; and a notifying unit that notifies of an abnormality in the filter when a result of comparison of the first index value with the second index value satisfies a predetermined abnormality condition.

TECHNICAL FIELD

The present disclosure relates to a technique for detecting an abnormality in a machine tool.

BACKGROUND ART

For a technique for removing chips resulting from machining of a workpiece by coolant. Japanese Patent Laying-Open No. 2018-161688 (PTL 1) discloses a “machine tool including a chip conveyor that more reliably prevents an overflow of coolant”.

The machine tool has a float switch inside the chip conveyor The float switch detects a liquid level of coolant collected by the chip conveyor, and when the liquid level is greater than or equal to a predetermined level, it is determined that an overflow of the coolant has occurred

CITATION LIST

Patent Literate

SUMMARY OF INVENTION

Technical Problem

Coolant circulates inside the machine tool. More specifically, coolant is stored in a storage tank and discharged into the machine tool from the storage tank. By this, chips are removed from within the machine tool. The chips included in the coolant are removed using a filter provided in the machine tool. After removing the chips, the coolant is brought back to the above-described storage tank.

The above-described filter may be clogged with chips. When clogging of the filter occurs, coolant does not circulate in the machine tool.

The machine tool disclosed in the above-described PTL 1 determines whether clogging of the filter has occurred, based on the liquid level of coolant. Hence, when a large amount of coolant has been discharged into the machine tool, the machine tool may erroneously detect clogging of the filter.

The present disclosure is made to solve a problem such as that described above, and an object of a given aspect is to provide a technique for more reliably detecting clogging of a filter with chips over conventional techniques.

Solution to Problem

In an example of the present disclosure, a machine tool that can machine a workpiece includes: a storage tank that stores coolant; a discharge unit that discharges the coolant stored in the storage tank toward chips resulting from the machining of the workpiece; a filter that removes the chips from the coolant having been discharged toward the chips; a collecting pump that brings the coolant having passed through the filter back to the storage tank; a first obtaining unit that obtains a first index value indicating an amount of coolant discharged from the discharge unit per predetermined time; a second obtaining unit that obtains a second index value indicating an amount of coolant that passes through the filter and is brought back to the storage tank per the predetermined time; and a notifying unit that notifies of an abnormality in the filter when a result of comparison of the first index value with the second index value satisfies a predetermined abnormality condition.

In an example of the present disclosure, the machine tool further includes a display unit. The notifying unit displays, on the display unit, an alert indicating occurrence of clogging of the filter with the chips.

In an example of the present disclosure, the predetermined abnormality condition is satisfied when a difference value of the first index value from the second index value exceeds a predetermined value.

In an example of the present disclosure, the machine tool further includes a collecting tank that receives the coolant having passed through the filter.

In an example of the present disclosure, the discharge unit includes: a coolant nozzle; and a discharge pump that sends the coolant to the coolant nozzle from the storage tank. The collecting pump sends the coolant from the collecting tank to the storage tank.

In an example of the present disclosure, the first index value includes a drive frequency of a motor for driving the discharge pump. The second index value includes a drive frequency of a motor for driving the collecting pump.

In another example of the present disclosure, there is provided a control method for a machine tool that can machine a workpiece. The machine tool includes: a storage tank that stores coolant; a discharge unit that discharges the coolant stored in the storage tank toward chips resulting from the machining of the workpiece; a filter that removes the chips from the coolant having been discharged toward the chips; and a collecting pump that brings the coolant having passed through the filter back to the storage tank. The control method includes: obtaining a first index value indicating an amount of coolant discharged from the discharge unit per predetermined time; obtaining a second index value indicating an amount of coolant that passes through the filter and is brought back to the storage tank per the predetermined time; and notifying of an abnormality in the filter when a result of comparison of the first index value with the second index value satisfies a predetermined abnormality condition.

In another example of the present disclosure, there is provided a control program for a machine tool that can machine a workpiece. The machine tool includes a storage tank that stores coolant: a discharge unit that discharges the coolant stored in the storage tank toward chips resulting from the machining of the workpiece; a filter that removes the chips from the coolant having been discharged toward the chips; and a collecting pump that brings the coolant having passed through the filter back to the storage tank. The control program causes the machine tool to perform: obtaining of a first index value indicating an amount of coolant discharged from the discharge unit per predetermined time, obtaining of a second index value indicating an amount of coolant that passes through the filter and is brought back to the storage tank per the predetermined time; and notifying of an abnormality in the filter when a result of comparison of the first index value with the second index value satisfies a predetermined abnormality condition.

The above-described and other objects, features, aspects, and advantages of the present invention will become clear from the following detailed description of the present invention to be understood in conjunction with the accompanying drawings.

DESCRIPTION OF EMBODIMENTS

With reference to the drawings, each embodiment according to the present invention will be described below. In the following description, the same parts and components are given the same reference signs. The names and functions of those parts and components are also the same. Thus, a detailed description of those parts and components is not repeated. Note that embodiments and variants that are described below may be selectively combined together as appropriate.

<A. Outward Appearance of Machine Tool100>

With reference toFIG.1, a machine tool100according to an embodiment will be described.FIG.1is a diagram showing an outward appearance of machine tool100.

A “machine tool” referred to in this specification is a concept including various apparatuses having a function of machining a workpiece In this specification, as an example of machine tool100, a horizontal machining center will be described as an example, but machine tool100is not limited thereto. For example, machine tool100may be a vertical machining center. Alternatively, machine tool100may be a lathe or may be an additional processing machine or may be other machines such as a cutting machine or a grinding machine. Furthermore, machine tool100may be a multitasking machine in which those machines are combined together.

As shown inFIG.1, machine tool100includes a cover130and a control panel140Cover130is also called a splash guard, and forms an outward appearance of machine tool100and sections off and forms a work area AR for a workpiece W (seeFIG.2).

Control panel140is a general-purpose computer and has a display142for displaying various types of information about machining. Display142is, for example, a liquid crystal display, an organic electroluminescence (EL) display, or other display devices. In addition, display142includes a touch panel and receives various operations for machine tool100by touch operations.

<B. Internal Configuration of Machine Tool100>

Next, with reference toFIGS.2and3, an internal configuration of machine tool100will be describedFIG.2is a diagram showing a state of the inside of machine tool100.FIG.3is a diagram showing a state of the inside of machine tool100in a different direction from that ofFIG.2.

As shown inFIGS.2and3, machine tool100includes therein a discharge unit125for coolant, a spindle head131, a tool134, a table136, and a chip conveyor150Spindle head131includes a main spindle132and a housing133.

For convenience of description, in the following description, the axial direction of main spindle132is also referred to as “Z-axis direction”. The direction of gravitational force is also referred to as “Y-axis direction”. A direction orthogonal to both the Y-axis direction and the Z-axis direction is referred to as “X-axis direction”.

Discharge unit125is provided in machine tool100and discharges coolant to drain chips resulting from machining of workpiece W into chip conveyor150. Discharge unit125includes one or more discharge mechanisms. InFIGS.2and3, as an example of discharge unit125, discharge mechanisms125A and125B are shown.

Discharge mechanism125A is provided on spindle head131. Discharge mechanism125A may be of a side-through type in which coolant is discharged from a main spindle end face through housing133of spindle head131, or may be a center-through type in which coolant is discharged from a cutting edge of a tool held in spindle head131through the center of the main spindle of spindle head131. Discharge mechanism125A mainly aims at removing chips attached to main spindle132and tool134or suppressing heat generation at a work point of a workpiece, by discharging coolant to the work point of the workpiece. Discharge mechanism125A is configured to be able to be driven in a rotational direction with the X-axis direction being a rotational axis (i e, an A-axis direction) and is configured to be able to be driven in a rotational direction with the Z-axis direction being a rotational axis (i.e., a C-axis direction) By this, the discharge mechanism125A changes the discharge direction of coolant in the A-axis direction and the C-axis direction.

Discharge mechanism125B is provided at an upper position than discharge mechanism125A. Discharge mechanism125B is mounted, for example, on a ceiling portion of cover130. Discharge mechanism125B mainly aims at draining chips resulting from machining of workpiece W into chip conveyor150from within work area AR by supplying coolant to entire work area AR from cover130.

Main spindle132is provided inside housing133. A tool for machining workpiece W which is a piece of work to be machined is mounted on main spindle132. In an example ofFIGS.2and3, tool134used to mill workpiece W is mounted on main spindle132.

Chip conveyor150for chips is a mechanism for draining chips resulting from machining of workpiece W out of work area AR. Details of chip conveyor150will be described later.

<C. Drive Mechanisms of Machine Tool100>

Next, with reference toFIG.4, various drive mechanisms of machine tool100will be described.FIG.4is a diagram showing an exemplary configuration of drive mechanisms of machine tool100.

“Control unit50” referred to in this specification indicates an apparatus that controls machine tool100. Control unit50may have any apparatus configuration Control unit50may include a single control unit or may include a plurality of control units. In an example ofFIG.4, control unit50includes a CPU unit20serving as a programmable logic controller (PLC); and a computer numerical control (CNC) unit30. CPU unit20and CNC unit30communicate with each other through a communication path B (e.g., a fieldbus or a LAN cable).

CPU unit20controls various units included in machine tool100, according to a PLC program designed in advance. The PLC program is written, for example, in the form of a ladder program.

As an example, CPU unit20controls discharge pump109according to the PLC program to control discharge of coolant by discharge unit125. By this, the on and off of discharge of coolant, the amount of coolant discharged, and the like, are controlled.

As another example, CPU unit20controls motor driver111A according to the PLC program. Motor driver111A receives input of a target rotational speed of motor112A from CPU unit20, thereby controlling motor112A By this, the on and off of drive of chip conveyor150, the chip conveying speed of chip conveyor150, and the like, are controlled. Note that motor112A may be an alternating current motor or may be a stepper motor or may be a servomotor or may be other types of motors.

Based on reception of a machining start instruction from CPU unit20, CNC unit30starts execution of a machining program designed in advance. The machining program is written, for example, in the form of a numerical control (NC) program. CNC unit30controls motor drivers111R and111X to111Z according to the machining program, to machine workpiece W fixed on table136.

Motor driver II IR sequentially receives input of a target rotational speed from CNC unit30, thereby controlling motor112R. Motor112R rotationally drives main spindle132about the Z-axis direction Motor112R may be an alternating current motor or may be a stepper motor or may be a servomotor or may be other types of motors.

When motor112R is a servomotor, motor driver111R calculates an actual rotational speed of motor112R from a feedback signal of an encoder (not shown) for detecting an angle of rotation of motor112R. Then, when the calculated actual rotational speed is lower than a target rotational speed, motor driver111R increases the rotational speed of motor112R, and when the calculated actual rotational speed is higher than the target rotational speed, motor driver111R reduces the rotational speed of motor112R. As such, while motor driver111R sequentially receives feedback on the rotational speed of motor112R, motor driver111R approximates the rotational speed of motor112R to the target rotational speed.

Motor driver111X sequentially receives input of a target position from CNC unit30, thereby controlling motor112X. Motor112X feed-drives, through a ball screw (not shown), moving body113having spindle head131mounted thereon, to move main spindle132to any position in the X-direction. A method of controlling motor112X by motor driver111X is the same as that for motor driver111R, and thus, description thereof is not repeated. Note that motor112X may be an alternating current motor or may be a stepper motor or may be a servomotor or may be other types of motors.

Motor driver111Y sequentially receives input of a target position from CNC unit30, thereby controlling motor112Y. Motor112Y feed-drives, through a ball screw (not shown), moving body113having spindle head131mounted thereon, to move main spindle132to any position in the Y-direction. A method of controlling motor112Y by motor driver111Y is the same as that for motor driver111R, and thus, description thereof is not repeated. Note that motor112Y may be an alternating current motor or may be a stepper motor or may be a servomotor or may be other types of motors.

Motor driver111Z sequentially receives input of a target position from CNC unit30, thereby controlling motor112Z. Motor112Z feed-drives, through a ball screw (not shown), moving body113having spindle head131mounted thereon, to move main spindle132to any position in the Z-direction. A method of controlling motor112Z by motor driver111Z is the same as that for motor driver111R and thus, description thereof is not repeated. Note that motor112Z may be an alternating current motor or may be a stepper motor or may be a servomotor or may be other types of motors.

<D Configuration of Chip Conveyor150>

Next, with reference toFIGS.5and6, chip conveyor150included in machine tool100will be described.FIG.5is a diagram showing an outward appearance of chip conveyor150FIG.6is a diagram showing a cross-section of chip conveyor150.

Chip conveyor150is placed attached to cover130that sections off and forms work area AR. Chip conveyor150receives workpiece chips and coolant that are drained from work area AR.

Chip conveyor150has a collecting tank11. Collecting tank11is configured to be able to store coolant. Chip conveyor150conveys chips toward a chip bucket (not shown), and filters coolant, thereby draining clean coolant into collecting tank11.

Chip conveyor150further has a cover body21. Cover body21forms an outward appearance of chip conveyor150. Cover body21has a casing form having space formed inside thereof.

Cover body21has, as its components, a horizontal unit22, a rising unit26, chip receiving units23, and a chip draining unit27.

Cover body21overall has a bending shape between horizontal unit22and rising unit26. Horizontal unit22is placed in collecting tank11. Horizontal unit22has a plate-shaped outward appearance that extends in a horizontal direction. Horizontal unit22has a rectangular-shaped plan view. Rising unit26rises from one end in a longitudinal direction of horizontal unit22and extends in a diagonally upward direction.

Chip receiving units23are provided on horizontal unit22. Chip receiving units23each are formed of a casing provided on a top face of horizontal unit22. Chip receiving units23each are provided with a connection opening24. Connection opening24is formed of a through hole that passes through chip receiving unit23. A chip conveying apparatus12which is equipment in work area AR is connected to chip receiving unit23through connection opening24. Chip conveying apparatus12is configured to include, for example, a gutter body extending in one direction and a spiral conveyor placed in the gutter body.

Chip draining unit27is provided at an end portion of rising unit26that extends from horizontal unit22in the diagonally upward direction. Chip draining unit27is formed of an opening portion of cover body21that opens in a vertically downward direction. A chip bucket (not shown) for collecting chips is placed below chip draining unit27. Workpiece chips drained from work area AR are received by chip receiving units23into cover body21. The chips are conveyed within cover body21by a chip conveying mechanism which is subsequently described, and are drained through chip draining unit27, by which the chips are collected in the chip bucket.

Chip conveyor150further has a chip conveying unit35, Chip conveying unit35is accommodated in cover body21. Chip conveying unit35is an apparatus for conveying chips within cover body21.

A more specific description will be made Chip conveying unit35has a pair of endless chains34, a drive sprocket37, and a driven sprocket38.

Drive sprocket37is provided at the end portion of rising unit26that extends from horizontal unit22in the diagonally upward direction. Drive sprocket37is disposed above chip draining unit27. Drive sprocket37is supported so as to be rotatable about an axis extending in a direction orthogonal to a plane of paper showingFIG.6(hereinafter, the direction is also referred to as “width direction of chip conveyor150”). An output shaft of aforementioned motor112A (seeFIG.4) is coupled to drive sprocket37. Drive sprocket37rotates by power transmitted thereto from motor112A.

Driven sprocket38is provided at a bending unit between horizontal unit22and rising unit26. Driven sprocket38is supported so as to be rotatable about an axis (central axis AX) extending in the width direction of chip conveyor150.

Pair of endless chains34is disposed in parallel in the width direction of chip conveyor150, with a distance therebetween. Endless chains34are routed in a loop inside cover body21and across horizontal unit22and rising unit26. Endless chains34are routed inside cover body21such that endless chains34move back and forth between a location facing chip receiving units23and a location facing chip draining unit27.

Endless chains34are wrapped around drive sprocket37and driven sprocket38on a path where endless chains34are routed in cover body21, and are guided by a plurality of guide members. When drive sprocket37rotates by receiving power from motor112A, endless chains34rotate in directions indicated by arrows A (hatched arrows) inFIG.6.

Chip conveyor150further has a filtering mechanism40. Filtering mechanism40is configured to filter coolant received from work area AR, thereby draining clean coolant into collecting tank11from within cover body21.

A more specific description will be made. Filtering mechanism40has a filter46in a drum shape Filter46is accommodated in cover body21. Filter46is provided at the bending unit between horizontal unit22and rising unit26. Filter46is configured to be able to catch foreign matter such as chips included in coolant. Filter46has, for example, a cylindrical shape and forms internal space47on an inner side thereof.

Filter46in a drum shape is disposed such that a central axis thereof extends in the width direction of chip conveyor150. Filter46is disposed such that the central axis thereof coincides with central axis AX which is the center of rotation of driven sprocket38. Filter46is connected to driven sprocket38at its both ends in an axial direction of central axis AX.

Note that although the above description is made of filter46in a drum shape, the shape of filter46is not limited to the drum shape. As an example, the shape of filter46may be rectangular or may be circular.

A coolant draining unit28is formed in cover body21. Coolant draining unit28is formed of a through hole that passes through cover body21. Coolant draining unit28is provided such that internal space47of filter46communicates with external space on an outer side of cover body21. Coolant received into cover body21through chip receiving units23is filtered by entering internal space47of filter46. The filtered coolant is drained into collecting tank11through coolant draining unit28.

Next, with reference toFIG.7, a coolant circulation mechanism will be described.FIG.7is a diagram showing an example of a coolant circulation mechanism.

Coolant discharged from discharge unit125circulates in machine tool100. Machine tool100includes, as components of the coolant circulation mechanism, a storage tank10, discharge pump109, a valve110, discharge unit125, chip conveyor150, a liquid level sensor151, a collecting pump152, and passages R1, R2A to R2C, and R3. Discharge unit125includes, for example, discharge mechanisms125A to125C.

Storage tank10stores therein coolant. Storage tank10is connected to one end of passage R1. The other end of passage R1 is connected to passages R2A to R2C.

Passage R2A is connected to discharge mechanism125A. Discharge mechanism125A has, for example, a coolant nozzle (not shown) connected to passage R2A, and discharges coolant pumped through passage R2A toward spindle head131from the coolant nozzle. By this, workpiece chips attached to spindle head131are drained into chip conveyor150.

Passage R2B is connected to discharge mechanism125B Discharge mechanism125B discharges coolant pumped through passage R2B toward entire work area AR. By this, workpiece chips present in work area AR are drained into chip conveyor150.

Passage R2C is connected to discharge mechanism125C. Discharge mechanism125A discharges coolant pumped through passage R2A toward a wall surface of abed BD. By this, chips accumulated on bed BD are drained into chip conveyor150.

Discharge pump109pumps, by being driven, the coolant stored in storage tank10to each of passages R2A to R2C through passage R1. By this, discharge pump109sends the coolant from storage tank10to a coolant nozzle of discharge unit125.

Valve110is provided, for example, at passages R1 and R2A to R2C Valve110is a control valve that controls the flow rate of coolant that is pumped from storage tank10to discharge mechanisms125A to125C. Valve110is controlled by aforementioned control unit50. Note that valve110may be integrally formed with discharge pump109or may be formed separately.

Chip conveyor150has collecting tank11and filter46. Filter46is configured to be able to catch foreign matter such as chips included in coolant. Coolant from which chips are removed by filter46is drained into collecting tank11from within cover body21of chip conveyor150. As such, collecting tank11is configured to receive coolant having passed through filter46.

Liquid level sensor151detects the height of the liquid level of coolant accumulated in collecting tank11. The detected height is outputted to aforementioned control unit50. Control unit50adjusts the amount of coolant pumped up by collecting pump152such that the height is constant.

Collecting pump152is connected to passage R3 Collecting pump152pumps up coolant having passed through filter46and having been accumulated in collecting tank11, and brings the coolant back to storage tank10through passage R3 By this, storage tank10sends the coolant from collecting tank11to storage tank10.

Subsequently, with reference toFIG.7, an overview of a method of detecting clogging of filter46will be described.

As described above, coolant discharged into work area AR passes through filter46and is drained into collecting tank11from within cover body21of chip conveyor150. In this process, filter46removes chips from the coolant. Upon the removal, if clogging of filter46has occurred, then the coolant does not circulate in machine tool100. Hence, machine tool100detects clogging of filter46, and when the clogging has occurred, machine tool100notifies of an abnormality in filter46.

More specifically, when clogging of filter46has occurred, coolant cannot pass through filter46, and thus, the amount of coolant collected is small relative to the amount of coolant discharged. With this in view, machine tool100obtains a first index value indicating the amount of coolant discharged from discharge unit125per predetermined time and a second index value indicating the amount of coolant that passes through filter46and is brought back to storage tank10per predetermined time. A specific example of the first index value and the second index value will be described later.

Thereafter, when a result of comparison of the first index value with the second index value satisfies a predetermined abnormality condition, machine tool100notifies of an abnormality in filter46. Machine tool100determines whether the amount of coolant collected relative to the amount of coolant discharged is smaller than a predetermined amount, by determining whether the abnormality condition is satisfied. A specific example of the abnormality condition will be described later.

As such, by taking notice of the amount of coolant collected relative to the amount of coolant discharged, machine tool100detects clogging of filter46. By this, machine tool100can detect clogging of filter46regardless of whether the amount of coolant discharged is small or large.

Next, with reference toFIG.8, functional components of machine tool100will be described.FIG.8is a diagram showing an example of functional components of machine tool100.

Control unit50of machine tool100includes, as an example of functional components, a first obtaining unit S1, a second obtaining unit52, a determining unit54, and a notifying unit56. The following describes these functional components in turn.

Note that first obtaining unit51may be mounted on CPU unit20(seeFIG.4) or may be mounted on CNC unit30(seeFIG.4). Likewise, second obtaining unit52may be mounted on CPU unit20or may be mounted on CNC unit30. Likewise, determining unit54may be mounted on CPU unit20or may be mounted on CNC unit30. Likewise, notifying unit56may be mounted on CPU unit20or may be mounted on CNC unit30.

First, with reference to the aforementionedFIG.7, a function of first obtaining unit51shown inFIG.8will be described.

First obtaining unit SI obtains an index value D(t) (first index value) indicating the amount of coolant discharged from discharge unit125per predetermined time. The length of the predetermined time may be determined in advance upon designing a program, etc., or may be arbitrarily set by a user. As an example, the length of the predetermined time is about 1 to 10 minutes.

The index value D(t) is data obtained by averaging or adding up, on a per certain section (unit time) basis, time-series data on the amount of coolant discharged from discharge unit125. The index value D(t) can include various physical quantities correlated with the amount of coolant discharged. Typically, the index value D(t) is detected using various sensors provided on a more upstream side than filter46. The following describes specific examples of the index value D(t).

(a) Specific Example 1 of the Index Value D(T)

As an example, the index value D(t) includes output to discharge pump109. More specifically, discharge pump109has a motor (not shown). The amount of coolant discharged from discharge unit125is adjusted based on the frequency of alternating current outputted to the motor (hereinafter, also referred to as “drive frequency”.). Typically, the higher the drive frequency, the larger the amount of coolant discharged, and the lower the frequency of the drive frequency, the smaller the amount of coolant discharged. As such, the amount of coolant discharged is correlated with the drive frequency outputted to discharge pump109. Hence, the drive frequency of discharge pump109can be the index value D(t).

(b) Specific Example 2 of the Index Value D(t)

As another example, the index value D(t) includes an output value of a liquid level sensor (not shown) provided on a more upstream side than filter46. The liquid level sensor is provided, for example, inside cover body21of chip conveyor150and detects the height of the liquid level of coolant accumulated in cover body21. The height may be represented by a distance from the bottom of cover body21to the liquid level of coolant or may be represented by a distance from the liquid level of coolant to the liquid level sensor. The height of the liquid level is correlated with the amount of coolant discharged from discharge unit125. More specifically, the larger the amount of coolant discharged, the higher the liquid level, and the smaller the amount of coolant discharged, the lower the liquid level. Hence, the height of the liquid level of coolant in cover body21can be the index value D(t).

(c) Specific Example 3 of the Index Value D(t)

As another example, the index value D(t) includes an output value of a flowmeter (not shown) included in machine tool100. The flowmeter detects a (low rate of coolant before passing through filter46. The flowmeter is provided, for example, in a passage present on a more upstream side than filter46. Namely, coolant discharged from discharge unit125passes through the passage and then passes through filter46. Hence, the larger the amount of coolant discharged, the larger the output value of the flowmeter, and the smaller the amount of coolant discharged, the smaller the output value of the flowmeter. As such, the output value of the flowmeter is correlated with the amount of coolant discharged and thus can be the index value D(t).

(d) Specific Example 4 of the Index Value D(t)

As another example, the index value D(t) includes a value indicating a machining mode of machine tool100. The frequency of alternating current outputted to the motor of discharge pump109is changed depending on the machining mode of machine tool100. More specifically, the output frequency is determined in advance for each machining mode, and machine tool100changes the machining mode according to a machining program. As such, the machining mode of machine tool100is correlated with the amount of coolant discharged and thus can be the index value D(t).

(e) Specific Example 5 of the Index Value D(t)

As another example, the index value D(t) includes an output value of a mist sensor (not shown) included in machine tool100. The mist sensor is provided, for example, in work area AR in machine tool100and detects the amount of mist in air. The mist sensor is, for example, a photosensor The amount of mist in work area AR increases as the amount of coolant discharged from discharge unit125increases. Hence, the larger the amount of coolant discharged, the larger the output value of the mist sensor, and the smaller the amount of coolant discharged, the smaller the output value of the mist sensor As such, the output value of the mist sensor is correlated with the amount of coolant discharged and thus can be the index value D(t).

(f) Specific Example 6 of the Index Value D(t)

As another example, the index value D(t) may be estimated based on an image obtained from a camera included in machine tool100. The camera is provided so as to photograph work area AR in machine tool100. An edge portion that appears in an image obtained from the camera increases as the amount of coolant discharged from discharge unit125increases. Namely, the amount of edge occupied in the image is correlated with the amount of coolant discharged. First obtaining unit51obtains the amount of edge occupied in the image, as the index value D(t).

Next, with reference to the aforementionedFIG.7, a function of second obtaining unit52shown inFIG.8will be described.

Second obtaining unit52obtains an index value R(t) (second index value) indicating the amount of collected coolant that passes through filter46and is brought back to storage tank10per predetermined time. The length of the predetermined time may be determined in advance upon designing a program, etc., or may be arbitrarily set by the user. As an example, the length of the predetermined time is about 1 to 10 minutes.

The index value R(t) is data obtained by averaging or adding up, on a per certain section (unit time) basis, time-series data on the amount of coolant passing through filter46. The index value R(t) can include various physical quantities correlated with the amount of coolant passing through filter46. Typically, the index value R(t) is detected using various sensors provided on a more downstream side than filter46. The following describes specific examples of the index value R(t).

(a) Specific Example 1 of the Index Value R(t)

As an example, the index value R(t) includes an output value of liquid level sensor151provided in collecting tank11. Liquid level sensor151is provided inside collecting tank11and detects the height of the liquid level of coolant accumulated in collecting tank11. The height may be represented by a distance from the bottom of collecting tank11to the liquid level of coolant or may be represented by a distance from the liquid level of coolant to liquid level sensor151. The height of the liquid level is correlated with the amount of coolant having passed through filter46. More specifically, the larger the amount of coolant passing through filter46, the higher the liquid level, and the smaller the amount of coolant passing through filter46, the lower the liquid level. As such, the amount of coolant passing through filter46is correlated with the output value of liquid level sensor151and thus can be the index value R(t).

(b) Specific Example 2 of the Index Value R(t)

As another example, the index value R(t) includes output to collecting pump152. As described above, control unit50of machine tool100controls collecting pump152such that the output value of liquid level sensor151is constant. As a result, control unit50increases the amount of coolant pumped up by collecting pump152as the amount of coolant having passed through filter46increases In this case, the amount of coolant having passed through filter46is correlated with the output value to collecting pump152.

Move specifically, collecting pump152has a motor (not shown). The amount of coolant collected by collecting pump152is adjusted based on the frequency of alternating current outputted to the motor (hereinafter, also referred to as “drive frequency”.). Typically, control unit50increases the drive frequency as the amount of coolant passing through filter46increases, and reduces the drive frequency as the amount of coolant passing through filter46decreases. As such, the amount of coolant passing through filter46is correlated with the drive frequency of collecting pump152. Hence, the drive frequency of collecting pump152can be the index value R(t).

(c) Specific Example 3 of the Index Value R(t)

As another example, the index value R(t) includes an output value of a flowmeter (not shown) included in machine tool100. The flowmeter detects a flow rate of coolant having passed through filter46. The flowmeter is provided, for example, in a passage present on a more downstream side than filter46. Namely, coolant discharged from discharge unit125passes through filter46and then passes through the passage. As a result, the larger the amount of coolant passing through filter46, the larger the output value of the flowmeter, and the smaller the amount of coolant passing through filter46, the smaller the output value of the flowmeter. As such, the output value of the flowmeter is correlated with the amount of coolant passing through filter46and thus can be the index value R(t).

Next, with reference toFIG.9, a function of determining unit54shown inFIG.8will be described.FIG.9is a diagram showing a transition of the index value D(t) obtained by first obtaining unit51and a transition of the index value R(t) obtained by second obtaining unit52.

Determining unit54determines whether a result of comparison of the index value D(t) indicating the amount of coolant discharged with the index value R(t) after passing through filter46satisfies a predetermined abnormality condition. The abnormality condition is satisfied when the amount of coolant passing through filter46is small relative to the amount of coolant discharged. The abnormality condition is satisfied, for example, when a difference value of the index value D(t) from the index value R(t) exceeds a predetermined value th.

As an example, at time T1, determining unit54obtains a difference of an index value D(T1) from an index value D(T1), thereby calculating a difference value ΔC1 therebetween. The difference value ΔC1 is smaller than the predetermined value th, and thus, determining unit54determines that the predetermined abnormality condition is not satisfied.

As another example, at time T2, determining unit54obtains a difference of an index value D(T2) from an index value D(T2), thereby calculating a difference value ΔC2 therebetween. The difference value ΔC2 is larger than the predetermined value th, and thus, determining unit54determines that the predetermined abnormality condition is satisfied.

Note that although the above description is made of an example in which a determination as to whether the abnormality condition is satisfied is made by comparing index values D(t) and R(t) obtained at the same time, determining unit54may compare index values D(t) and R(t) obtained at different times. As an example, it takes some time before coolant passes through filter46after the coolant is discharged. Taking into account the time, determining unit54may compare an index value D(t) with an index value R(t+ΔT). The length of predetermined time ΔT may be determined in advance upon designing a program, etc., or may be arbitrarily set by the user.

In this case, determining unit54obtains a difference of the index value D(t-AT) from the index value D(t), and when the difference value is larger than the predetermined value th, determining unit54determines that the abnormality condition is satisfied. On the other hand, when the difference value is smaller than the predetermined value th, determining unit54determines that the abnormality condition is not satisfied.

Next, with reference toFIG.10, a function of notifying unit56shown inFIG.8will be described.FIG.1) is a diagram showing an example of a mode of notification provided by notifying unit56.

When aforementioned determining unit54determines that the abnormality condition is satisfied, notifying unit56notifies of occurrence of an abnormality in filter46. As an example, notifying unit56displays an alert144on display142of control panel140. Alert144includes a message saying that clogging has occurred in filter46of chip conveyor ISO. By this, an operator can grasp that clogging has occurred in filter46of chip conveyor150.

As another example, notifying unit56notifies of an alert indicating occurrence of clogging in filter46, by sound such as a buzzer or voice. By this, an operator can notice an abnormality in filter46without looking at display142.

As another example, notifying unit56transmits an alert indicating occurrence of clogging in filter46to another communication terminal by email, etc. By this, an operator or a manager present at a location away from machine tool100can notice an abnormality in filter46.

<H. Hardware Configuration of Control Unit50>

Next, with reference toFIG.11, a hardware configuration of control unit50shown inFIG.4will be describedFIG.11is a diagram showing an example of a hardware configuration of control unit50.

As shown inFIG.11, control unit50includes CPU unit20and CNC unit30. CPU unit20and CNC unit30are connected to each other, for example, through communication path B.

The following describes a hardware configuration of CPU unit20and a hardware configuration of CNC unit30in turn.

(H1. Hardware configuration of CPU unit20)

CPU unit20includes a control circuit201, a read only memory (ROM)202, a random access memory (RAM)203, communication interfaces204and205, and an auxiliary storage apparatus220. These components are connected to an internal bus209.

Control circuit201includes, for example, at least one integrated circuit. The integrated circuit can include, for example, at least one CPU, at least one graphics processing unit (GPU), at least one application specific integrated circuit (ASIC), at least one field programmable gate array (FPGA), or a combination thereof.

Control circuit201controls the operation of CPU unit20by executing various programs such as a control program222. The control program222defines instructions for controlling various apparatuses in machine tool100. Based on reception of an instruction to execute control program222, control circuit201reads control program222into RAM203from auxiliary storage apparatus220or ROM202. RAM203functions as a working memory and temporarily stores various types of data required to execute control program222.

Communication interface204is an interface for implementing communication that uses a local area network (LAN) cable, a wireless LAN (WLAN), Bluetooth (registered trademark), or the like. As an example, CPU unit20implements communication with external devices such as discharge pump109, valve110, and collecting pump152through communication interface305.

Communication interface205is an interface for implementing communication with various units connected to a fieldbus. Examples of the units connected to the fieldbus include CNC unit30and an I/O unit (not shown).

Auxiliary storage apparatus220is, for example, a storage medium such as a hard disk or a flash memory. Auxiliary storage apparatus220stores control program222, etc. A storage location of control program222is not limited to auxiliary storage apparatus220, and control program222may be stored in a storage area (e.g., a cache memory) of control circuit201, ROM202, RAM203, an external device (e.g, a server), etc.

Note that control program222may be provided included in a part of any program, instead of being a single program. In this case, various processes according to the present embodiment are implemented in cooperation with any program Even if the program is such a program that does not include some modules, it does not depart from the spirit of control program222according to the present embodiment. Furthermore, some or all of functions provided by control program222may be implemented by dedicated hardware. Furthermore, CPU unit20may be formed in a mode such as a so-called cloud service in which at least one server performs some of processes performed by control program222.

(H2. Hardware Configuration of CPU Unit20)

Subsequently, with reference toFIG.11, a hardware configuration of CNC unit30will be described.

CNC unit30includes a control circuit301, a ROM302, a RAM303, a communication interface305, a communication interface305, and an auxiliary storage apparatus320. These components are connected to an internal bus300.

Control circuit301includes, for example, at least one integrated circuit. The integrated circuit can include, for example, at least one CPU, at least one ASIC, at least one FPGA, or a combination thereof.

Control circuit301controls the operation of CNC unit30by executing various programs such as a machining program322. The machining program322is a program for implementing machining of a workpiece. Based on reception of an instruction to execute machining program322, control circuit301reads machining program322into RAM303from ROM302. RAM303functions as a working memory and temporarily stores various types of data required to execute machining program322.

Communication interface305is an interface for implementing communication that uses a LAN, a WLAN, Bluetooth, or the like. As an example, CNC unit30implements communication with CPU unit20through communication interface305. In addition, CNC unit30implements communication with various drive units for machining of a workpiece (e.g., motor drivers111R and111X to111Z) through communication interface305or other communication interfaces.

Auxiliary storage apparatus320is, for example, a storage medium such as a hard disk or a flash memory. Auxiliary storage apparatus320stores machining program322, etc. A storage location of machining program322is not limited to auxiliary storage apparatus320, and machining program322may be stored in a storage area (e.g., a cache memory) of control circuit301, ROM302, RAM303, an external device (e.g., a server), etc.

Next, with reference toFIG.12, a control structure of machine tool100will be described.FIG.12is a flowchart showing some of processes performed by machine tool100.

The processes shown inFIG.12are implemented by control unit50of machine tool100executing aforementioned control program222. In another aspect, some or all of the processes may be performed by a circuit element or other hardware.

In step S110. control unit50determines whether timing for performing an abnormality check process related to clogging of filter46has come.

As an example, the timing for performing an abnormality check process is one timing at which discharge of coolant from discharge unit125is performed. A determination as to whether discharge of coolant is performed is made, for example, based on control program222(seeFIG.11). Control program222includes, for example, various instruction codes related to drive of discharge unit125. The instruction codes include an instruction code for specifying the on or off of discharge of coolant from discharge unit125, etc. Based on the fact that a specific instruction code indicating that discharge unit125is being driven is executed, control unit50determines that coolant is being discharged, and determines that timing for performing an abnormality check process has come.

If control unit50determines that timing for performing an abnormality check process related to clogging of filter46has come (YES in step S110), then control unit50switches the control to step S112. If not (NO in step S110), then control unit50performs the process in step S110again.

In step S112, control unit50functions as first obtaining unit51(seeFIG.8) and obtains the aforementioned index value D(t). The index value D(t) indicates the amount of coolant discharged from discharge unit125per predetermined time. The index value D(t) is as described above and thus description thereof is not repeated.

In step S114, control unit50functions as second obtaining unit52(seeFIG.8) and obtains the aforementioned index value R(t). The index value R(t) indicates the amount of collected coolant that passes through filter46and is brought back to storage tank10per predetermined time. The index value R(t) is as described above and thus description thereof is not repeated.

In step S120, control unit50functions as aforementioned determining unit54(seeFIG.8) and determines whether a predetermined abnormality condition is satisfied, by comparing the index value D(t) obtained in step S112with the index value R(t) obtained in step S114. As an example, control unit50obtains a difference of the index value R(t) from the index value D(t), and when the difference value exceeds a predetermined value, control unit50determines that the predetermined abnormality condition is satisfied. If control unit50determines that the predetermined abnormality condition is satisfied (YES in step S120), then control unit50switches the control to step S122If not (NO in step S120), then control unit50switches the control to step S124.

In step S122, control unit50functions as aforementioned notifying unit56(seeFIG.8) and notifies of occurrence of clogging of filter46.

In step S124, control unit50functions as aforementioned notifying unit56(seeFIG.8) and notifies of the fact that filter46is functioning normally. Note that the process in step S124may not be performed.

After performing step S122and S124, control unit50brings the control back to step S112. The processes shown inFIG.12are stopped, for example, when a user's stop operation is received or based on the fact that machining is finished.

REFERENCE SIGNS LIST