Numerical control device

Abstract

The present invention provides a numerical control device. In a turning machine having a plurality of tool holders on which tools are respectively mounted, the numerical control device simultaneously controls so that a workpiece is cut in sequence in the direction of a rotating axis by the plurality of tools, generates movement instruction data for positioning so that the plurality of tools cut into the workpiece with the same cutting amount, controls the relative speed and relative position between the plurality of tools so that the cutting points of the plurality of tools move forward and backward in sequence, generates interpolation data based on the movement instruction data, and controls a motor driving the machine based on the interpolation data.

Description

Technical Field

[0001] The present invention relates to a numerical control device, and more particularly, to a numerical control device for controlling a lathe for machining a workpiece in a coordinated manner using a plurality of tools. Background Art

[0002] Typically, turning involves continuous cutting, resulting in long, continuous chips. These chips can become entangled with the tool or workpiece, potentially damaging the tool or the workpiece. Therefore, the following functions are provided: a chip cutting function that cuts off the chips by temporarily feeding the tool in the opposite direction during continuous cutting; and an oscillating cutting function that cuts off the chips while the tool is oscillating during machining. Devices with such functions are disclosed, for example, in Japanese Patent Application Publication No. 2011-248473, Japanese Patent Application Publication No. 2017-056515, and International Publication No. 2017 / 051745.

[0003] In the case of the chip cutting function, which cuts off the chips by temporarily feeding the tool in the opposite direction, non-cutting time occurs, thereby increasing the processing time compared to conventional cutting. In addition, in the case of oscillating cutting, if the oscillation amplitude and oscillation frequency increase, the vibration becomes greater than when not oscillating, and the load on the machine increases. Therefore, it may have a negative impact on the life of the machine (ball screw, bearings, etc.) or the tool life. In order to suppress the oscillation amplitude and oscillation frequency, it is necessary to reduce the feed speed, resulting in an increase in processing time compared to conventional cutting. Summary of the Invention

[0004] Therefore, a technology for cutting off cut chips without increasing machining time or causing the machine life or tool life to expire is desired.

[0005] A numerical controller according to one embodiment of the present invention solves the above-mentioned problem by controlling the relative speeds and positions between the plurality of tools so as to cut off chips in a machining method in which cutting is performed using a machine configured to simultaneously control a plurality of tools.

[0006] More specifically, while the first tool is continuously cutting, the speed and position of the second tool are controlled so that it advances ahead of the first cutting point. Thus, while the second tool is ahead of the first tool, the first tool is in a non-cutting state, where it is not cutting. When the first tool transitions from the cutting state to the non-cutting state, the chips generated by the first tool's cutting are sheared off.

[0007] Next, once the first tool has cut the chips, the speed and position of the second tool are reversed, this time moving it further back than the first. While the first tool is ahead of the second tool, the second tool is in a non-cutting state, performing no cutting. When the second tool transitions from the cutting state to the non-cutting state, the chips generated by the second tool's cutting are cut. In this way, the relative speeds and positions of the first and second tools are controlled so that the cutting points alternately move forward and backward, thereby cutting the chips.

[0008] Furthermore, one embodiment of the present invention is a numerical control device that, in a turning machine having multiple tool holders on which tools are respectively mounted, simultaneously controls the multiple tools so that a workpiece is cut sequentially in the direction of a rotation axis. The numerical control device comprises: an analysis unit that generates movement instruction data, the movement instruction data being used for positioning so that the multiple tools cut into the workpiece with the same cutting amount, and for controlling the relative speed and relative position between the multiple tools so that the cutting points of the multiple tools move back and forth sequentially; an interpolation unit that generates interpolation data based on the movement instruction data; and a servo control unit that controls the motor that drives the machine based on the interpolation data.

[0009] According to the present invention, the cut chips can be cut off without increasing the machining time or causing the machine life or tool life to expire. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The above and other objects and features of the present invention will become more apparent from the following description of embodiments with reference to the accompanying drawings.

[0011] Figure 1 This is a schematic hardware configuration diagram of one embodiment of the numerical control device of the present invention.

[0012] Figure 2 This is a schematic functional block diagram of one embodiment of the numerical control device of the present invention.

[0013] Figure 3A as well as Figure 3B The following describes, as an example, the transition of the movement speeds of the first tool post and the second tool post in the Z-axis direction based on the movement command data generated by the analysis unit.

[0014] Figure 4 This indicates the positional relationship between the workpiece and the respective tools when the first tool mounted on the first tool holder is positioned ahead of the second tool mounted on the second tool holder.

[0015] Figure 5 It shows the positional relationship between the workpiece and each tool when the second tool mounted on the second tool holder is located ahead of the first tool mounted on the first tool holder.

[0016] Figure 6 This indicates the positional relationship between the workpiece and the respective tools when the first tool mounted on the first tool holder is positioned ahead of the second tool mounted on the second tool holder.

[0017] Figure 7A as well as Figure 7B Another example of the transition of the moving speed of the first tool rest and the second tool rest in the Z-axis direction is shown.

[0018] Figure 8A as well as Figure 8B Another example of the transition of the moving speed of the first tool rest and the second tool rest in the Z-axis direction is shown.

[0019] Figure 9 This is a schematic functional block diagram of a numerical controller according to another embodiment. DETAILED DESCRIPTION

[0020] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0021] Figure 1 This is a schematic hardware configuration diagram showing the main components of an embodiment of a numerical controller according to the present invention. The numerical controller 1 of this embodiment can be installed on a lathe as a numerical controller that controls the lathe according to a program, for example.

[0022] The numerical controller 1 includes a CPU (Central Processing Unit) 11, a ROM (Read Only Memory) 12, a RAM (Random Access Memory) 13, and a nonvolatile memory 14. The numerical controller 1 also includes an interface 15, a PMC (Programmable Machine Controller) 16, an I / O unit (Input / Output) 17, and other interfaces 18 and 19. The numerical controller 1 is also connected to a servo motor 50, a spindle motor 62, a display / MDI (Manual Data Input) unit 70, and an operation panel 71.

[0023] The CPU 11 included in the numerical controller 1 of this embodiment is a processor that controls the entire numerical controller 1. The CPU 11 reads a system program stored in the ROM 12 via the bus 20 and controls the entire numerical controller 1 according to the system program. The RAM 13 temporarily stores temporary calculation data, display data, and various data input from the outside.

[0024] The nonvolatile memory 14 is composed of, for example, a battery-backed memory (not shown) and an SSD (Solid State Drive). It maintains stored data even when the power to the numerical controller 1 is turned off. The nonvolatile memory 14 stores programs read from an external device 72 via the interface 15 and programs input via the display / MDI unit 70. Programs and various data stored in the nonvolatile memory 14 can be expanded into the RAM 13 during execution or use. Furthermore, various system programs, such as well-known analysis programs, are pre-written in the ROM 12.

[0025] The interface 15 is an interface for connecting the CPU 11 of the numerical controller 1 to an external device 72 such as a USB device. Programs and various parameters used to control the lathe are read from the external device 72. Furthermore, programs and various parameters edited within the numerical controller 1 can be stored in an external storage unit via the external device 72. The PMC (Programmable Machine Controller) 16 outputs signals to the lathe and its peripheral devices via the I / O unit 17 using a timing program built into the numerical controller 1, thereby controlling the lathe. Examples of peripheral devices that output such signals include tool changers, actuators such as robots, and sensors mounted on the lathe. Furthermore, signals from various switches and peripheral devices on the operating panel of the lathe body are received and, after necessary signal processing, are transmitted to the CPU 11.

[0026] The display / MDI unit 70 is a manual data input device equipped with a display and keyboard. Interface 18 receives commands and data from the keyboard of the display / MDI unit 70 and transmits them to CPU 11. Interface 19 is connected to the operation panel 17, which is equipped with a manual pulse generator used for manually driving each axis.

[0027] The axis control circuit 30 for controlling the axis of the lathe receives the axis movement instruction from the CPU 11 and outputs the axis instruction to the servo amplifier 40. The servo amplifier 40 receives the instruction and drives the servo motor 50 that moves the axis of the lathe. The servo motor 50 of the axis has a built-in position / speed detector. The position / speed feedback signal from the position / speed detector is fed back to the axis control circuit 30, and the axis control circuit 30 performs position / speed feedback control. In addition, Figure 1The hardware configuration diagram shows only one axis control circuit 30, servo amplifier 40, and servo motor 50 each. However, in practice, the lathe to be controlled has a number of axes. For example, when controlling a lathe equipped with two tool posts, as in the present invention, two sets of axis control circuits 30, servo amplifiers 40, and servo motors 50 are provided to drive the first tool post, which is mounted with a first tool, in the X- and Z-axis directions, respectively; and two sets of axis control circuits 30, servo amplifiers 40, and servo motors 50 are provided to drive the second tool post, which is mounted with a second tool, in the X- and Z-axis directions, respectively.

[0028] The spindle control circuit 60 receives a spindle rotation command and outputs a spindle speed signal to the spindle amplifier 61. The spindle amplifier 61 receives this spindle speed signal and rotates the lathe's spindle motor 62 at the commanded speed, driving the tool. A position encoder 63 is coupled to the spindle motor 62 and outputs feedback pulses to the spindle control circuit 60 in sync with the spindle's rotation. The feedback pulses output to the circuit 60 are read by the CPU 11.

[0029] Figure 2 This is a schematic functional block diagram of a numerical controller 1 according to one embodiment of the present invention.

[0030] Figure 1 The CPU 11 of the numerical control device 1 shown in the figure executes the system program to control the operation of each part of the numerical control device 1, thereby realizing Figure 2 The numerical controller 1 of the present embodiment controls a lathe that processes a workpiece mounted on a spindle by driving a first tool rest mounted thereon and a second tool rest mounted thereon, respectively.

[0031] The numerical controller 1 of this embodiment includes an analysis unit 100, a first interpolation unit 122, a second interpolation unit 124, servo control units 130x1, 130z1, 130x2, and 130z, and a spindle control unit 140. Furthermore, the nonvolatile memory 14 of the numerical controller 1 pre-stores a program 200 for controlling the driving of tools mounted on two tool holders to machine a workpiece.

[0032] Figure 1 The CPU 11 included in the numerical controller 1 shown executes a system program read from the ROM 12. The CPU 11 primarily performs computational processing using the RAM 13 and nonvolatile memory 14, thereby implementing an analysis unit 100. The analysis unit 100 is a functional unit that reads and analyzes program blocks of the program 200 to generate movement command data for the servo motors that drive the first and second tool posts and spindle command data that indicates the spindle's rotational speed.

[0033] The analysis unit 100 generates movement command data for the servo motors 50x1 and 50z1 that drive the first tool post, and movement command data for the servo motors 50x2 and 50z2 that drive the second tool post, based on the feed command indicated by the program block of program 200. Furthermore, the analysis unit 100 generates spindle command data based on the spindle rotation command indicated by the program block of program 200.

[0034] The analysis unit 100 of this embodiment generates movement command data at the start of workpiece machining. More specifically, the analysis unit 100 generates movement command data to position the Z-axis coordinates of the first and second tool rests so that the penetration depth of the first tool mounted on the first tool rest and the penetration depth of the second tool mounted on the second tool rest into the workpiece correspond to the penetration depths indicated by the program 200 or pre-set. Furthermore, the analysis unit 100 generates Z-axis movement command data that adjusts the relative speed between the Z-axis feed rate of the first tool rest and the Z-axis feed rate of the second tool rest, so that the first and second tools are positioned to alternately machine the workpiece.

[0035] Figure 1 The CPU 11 included in the numerical controller 1 shown executes a system program read from the ROM 12 . The CPU 11 mainly performs arithmetic processing using the RAM 13 and the nonvolatile memory 14 , thereby realizing the first interpolation unit 122 and the second interpolation unit 124 .

[0036] Based on the movement command data generated by the analysis unit 100, the first interpolation unit 122 generates interpolated data by performing interpolation calculations at an interpolation cycle (control cycle) for points on the command path of the first tool mounted on the first tool holder, as indicated by the movement command data. Furthermore, based on the movement command data generated by the analysis unit 100, the second interpolation unit 124 generates interpolated data by performing interpolation calculations at an interpolation cycle for points on the command path of the second tool mounted on the second tool holder, as indicated by the movement command data. The interpolation processing performed by the first interpolation unit 122 and the second interpolation unit 124 is performed at each interpolation cycle.

[0037] Figure 1The CPU 11 included in the numerical controller 1 shown executes a system program read from the ROM 12. This performs computational processing primarily performed by the CPU 11 using the RAM 13 and nonvolatile memory 14, and control processing of the servo motor 50 by the axis control circuit 30 and servo amplifier 40. This implements servo control units 130x1 and 130z1. The servo control units 130x1 and 130z1 control the servo motors 50x1 and 50z1, respectively, which drive the first tool post in the X-axis direction and the first tool post in the Z-axis direction, based on interpolation data generated by the first interpolation unit 122. In this manner, the servo control units 130x1 and 130z1 drive the first tool post of the controlled machine.

[0038] Similarly, the CPU 11 executes the system program read from the ROM 12, primarily performing computational processing by the CPU 11 using the RAM 13 and nonvolatile memory 14, and controlling the servo motor 50 using the axis control circuit 30 and servo amplifier 40. This implements the servo control units 130x2 and 130z2. The servo control units 130x2 and 130z2 control the servo motors 50x2 and 50z2, respectively, that drive the first tool post in the X-axis direction and the servo motor 50z2 that drives the first tool post in the Z-axis direction, based on the interpolation data generated by the second interpolation unit 124. Thus, the servo control units 130x2 and 130z2 drive the second tool post of the controlled machine.

[0039] Figure 1 The CPU 11 included in the numerical controller 1 shown executes a system program read from the ROM 12. The CPU 11 primarily performs arithmetic processing using the RAM 13 and nonvolatile memory 14, and controls the spindle motor 62 using the spindle control circuit 60 and the spindle amplifier 61, thereby realizing a spindle control unit 140. The spindle control unit 140 controls the spindle motor 62, which rotates the spindle of the controlled machine, based on spindle command data generated by the analysis unit 100.

[0040] Figure 3A as well as Figure 3B An example of the transition of the moving speed of the first tool rest and the second tool rest in the Z-axis direction based on the moving command data generated by the analysis unit 100 is shown. Figure 3A As shown in FIG, the feed speed of the first tool rest 3 in the Z-axis direction is always F1 except for the acceleration and deceleration at the start and end of movement. Figure 3B As shown, the feed speed of the second tool holder in the Z-axis direction is F2 (<F1)~F2’(> F1) to adjust the relative speed between the feed speed in the Z-axis direction of the first tool holder and the feed speed in the Z-axis direction of the second tool holder.

[0041] When adjusting the speed as in Figure 3A and Figure 3B the first tool initially installed on the first tool rest moving at a speed F1 (> F2) cuts the workpiece before the second tool installed on the second tool rest. And if the speed of the second tool rest rises from F2 to F2' (> F1) midway, the second tool installed on the second tool rest catches up with the first tool installed on the first tool rest at the time point of t1. After that, the second tool installed on the second tool rest cuts the workpiece before the first tool installed on the first tool rest. Then, if the speed of the second tool rest drops from F2' to F2 (< F1), the second tool installed on the second tool rest is caught up with by the first tool installed on the first tool rest at the time point of t2. After that, the first tool installed on the first tool rest cuts the workpiece before the second tool installed on the second tool rest.

[0042] By repeating such speed adjustments, the relative positions are adjusted such that the first tool installed on the first tool rest and the second tool installed on the second tool rest become positions for alternately machining the workpiece. The analysis unit 100 of the present embodiment generates movement command data for adjusting the feed speed of the first tool rest and the feed speed of the second tool rest in such a way as to become Figure 3A [[ID=IO]]and [[ID=II]] Figure 3B the speed transition exemplified.

[0043] Using Figures 4 to 6 explain the machining of the workpiece 7 by the first tool 5 installed on the first tool rest 3 and the second tool 6 installed on the second tool rest 4 when moving each tool rest at the speed transition exemplified by Figure 3A , Figure 3B In the machining examples shown in these drawings, the workpiece 7 is installed on the machine tool 2, more specifically, on the spindle table of the machine tool 2.

[0044] Figure 4 represents the positional relationship between the workpiece 7 and each tool when the first tool 5 installed on the first tool rest 3 is in a position more advanced than the second tool 6 installed on the second tool rest 4 ( Figure 3A , Figure 3B at the time from time O to time t1). In the state shown in Figure 4 the feed speed of the second tool rest in the Z-axis direction is F2 (< F1). In this state, the workpiece 7 is cut by the first tool 5, and chips 8 are generated from this machining position. After that, the feed speed of the second tool rest 4 in the Z-axis direction is accelerated to F2' (> F1). And if the second tool 6 installed on the second tool rest 4 is ahead of the first tool 5 installed on the first tool rest 3 and starts cutting the workpiece 7 by the second tool 6, the first tool becomes a non-cutting state, and the chips 8 generated by the cutting of the first tool 5 are cut off.

[0045] Figure 5 It represents the positional relationship between the workpiece 7 and each tool at the time t1 to time t2 when the second tool 6 installed on the second tool rest 4 is in a position more advanced than the first tool 5 installed on the first tool rest 3. Figure 3A and Figure 3B At the time (from time t1 to time t2). In the Figure 5 In the state shown, the feed speed of the second tool rest 4 in the Z-axis direction is F2’ (>F1). In this state, the workpiece 7 is machined by the second tool 6, and chips 8 are generated from the machining position. After that, the feed speed of the second tool rest 4 in the Z-axis direction is decelerated to F2 (<F1). And if the first tool 5 installed on the first tool rest 3 is ahead of the second tool 6 installed on the second tool rest 4 and starts machining the workpiece 7 by the first tool 5, the second tool becomes a non-cutting state, and the chips 8 generated by the machining of the second tool 6 are cut off.

[0046] Figure 6 It represents the positional relationship between the workpiece 7 and each tool at the time t2 to time t3 when the first tool 5 installed on the first tool rest 3 is in a position more advanced than the second tool 6 installed on the second tool rest 4. Figure 3A and Figure 3B At the time (from time t2 to time t3). In the Figure 6 In the state shown, the feed speed of the second tool rest in the Z-axis direction is F2 (<F1). In this state, the workpiece 7 is machined by the first tool 5, and chips 8 are generated from the machining position.

[0047] In this way, by repeatedly adjusting the relative speed between the first tool rest 3 on which the first tool 5 is installed and the second tool rest 4 on which the second tool 6 is installed, in the lathe controlled by the numerical control device 1 of the present embodiment, a state in which one of the first tool 5 and the second tool 6 is always performing cutting machining is maintained. In addition, a state in which the first tool 5 and the second tool 6 perform cutting machining alternately can be formed. As a result, the cutting machining states of the first tool 5 and the second tool 6 can be switched and alternately become non-cutting states, whereby the chips can be cut off. On the other hand, the workpiece 7 can be maintained in a state of being always machined by cutting. Therefore, no non-cutting time is generated, and the machining time is no different from the case of normal continuous cutting.

[0048] In addition, in the lathe controlled by the numerical control device 1 of the present embodiment, the forward direction of each tool is always a fixed direction, and there is no need to reverse in the opposite direction like in oscillatory cutting. In addition, there is no need to always swing the tool like in oscillatory cutting, and only when it is necessary to cut off the chips 8, the tool performing the cutting machining needs to be switched. Therefore, compared with oscillatory cutting, vibration can be suppressed, and the influence on the mechanical life (ball screw, bearing, etc.) or tool life is small.

[0049] In a lathe controlled by the numerical controller 1 of this embodiment, each tool is alternately placed in a non-cutting state, so the tool can be sufficiently cooled by the coolant. This can extend the tool life and improve the quality of the workpiece machined surface.

[0050] In a lathe controlled by the numerical controller 1 of this embodiment, the first tool 5 and the second tool 6 perform cutting processing on the workpiece 7 under identical conditions. Therefore, even if the material of the workpiece 7 changes, for example, cutting depth, spindle speed, feed rate, and other cutting conditions change, each tool post can simply move back and forth relative to the other tool post. This eliminates the need for individual tool adjustments, which can be time-consuming.

[0051] Although one embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment and can be implemented in various forms by adding appropriate changes.

[0052] In the above embodiment, the speed of the first tool 5 is fixed and the speed of the second tool 6 is changed, thereby changing the relative speed between the moving speed of the first tool 5 and the moving speed of the second tool 6. Figure 7A as well as Figure 7B As shown in the example, the speeds of the first tool 5 and the second tool 6 can be changed so that the relative positions of the first tool 5 and the second tool 6 are alternately moved back and forth. Figure 8A as well as Figure 8B As shown in the example, a curve such as a sine curve is used as a basis. When performing this control, for example, the speed can be varied so that the sum of the speeds of the first tool rest 3 and the second tool rest 4 is always the same. By varying the speed in this way, the amount of cutting per unit time of the first tool 5 and the amount of cutting per unit time of the second tool 6 can be easily maintained constant. Furthermore, by reducing and stabilizing the load applied to the tool and workpiece, vibrations generated during machining can be reduced, and the quality of the machined workpiece surface can be easily improved.

[0053] Furthermore, the relative positions of the first tool 5 and the second tool 6 can be controlled so that they alternately move back and forth based on the tool's cutting distance, cutting time, and spindle speed (number of cutting cycles). The X-coordinate position of the tool at a predetermined time t after the start of cutting can be calculated as the integral of the time-feed speed curve shown in the accompanying figure. The cutting distance and spindle speed can then be calculated based on this calculated integral, and the speed can be adjusted based on the calculated cutting distance so that the first tool 5 and the second tool 6 perform cutting alternately.

[0054] Further, if Figure 9 As shown, vibration sensors 82 and 84 are pre-installed on servo motors 50x1 and 50x2, respectively. The analysis unit 100 is configured to accumulate the amplitude of vibration detected by the vibration sensors attached to the servo motor 50, which moves the tool in a cutting state, at predetermined intervals. Based on this configuration, the analysis unit 100 can generate movement command data to adjust the relative speed and relative position of the first tool 5 and the second tool 6, such that when the accumulated value exceeds a predetermined threshold, the tool in a cutting state enters a non-cutting state. Instead of the values ​​detected by the vibration sensors 82 and 84, the analysis unit 100 can accumulate the load value of the servo motor 50, estimated from the current value of the servo motor 50, which moves the tool in a cutting state. Based on this configuration, the analysis unit 100 can generate movement command data to adjust the relative speed and relative position of the first tool 5 and the second tool 6, such that when the accumulated value exceeds a predetermined threshold, the tool in a cutting state enters a non-cutting state.

[0055] The above embodiment illustrates an example of a lathe in which the tool rests are positioned relative to each other. However, any lathe configuration is acceptable as long as the workpiece can be cut and the first and second tools are positioned so as to be able to move relative to each other. The number of tools need not be limited to two; as long as the relative speed and position of each tool can be adjusted, the present invention can also be applied to the control of a lathe using three or more tools.

[0056] In the above embodiment, an example is shown in which tool rests with attached tools are moved individually to machine a workpiece. However, the technology of the present invention can also be applied to a structure in which, for example, a fixed tool, a movable tool, and a workpiece (spindle) are moved.

Claims

1. A numerical control device for simultaneously controlling a turning machine having a plurality of tool holders on which tools are respectively mounted so that a workpiece is cut sequentially in a rotation axis direction by the plurality of tools, characterized in that: The numerical control device has: an analyzing unit, which generates movement instruction data, the movement instruction data being used to always keep the advancing direction of the plurality of tools in a fixed direction when the plurality of tools are moved on a path along the rotation axis of the workpiece in a manner that the plurality of tools cut into the workpiece with the same cutting amount at the positioned position after positioning them in a direction intersecting the rotation axis of the workpiece, and to control the speed and position of each tool so that, in a state where cutting is continuously performed by a certain tool, other tools are advanced to a position further forward than their cutting points, thereby controlling the relative speed and relative position of the plurality of tools so that the respective cutting points of the plurality of tools move forward and backward in sequence; an interpolation unit that generates interpolation data based on the movement instruction data; and A servo control unit controls a motor that drives the mechanism based on the interpolation data.

2. The numerical control device according to claim 1, characterized in that: When a preset condition is met, the analysis unit generates movement instruction data, which controls the relative speed and relative position between the plurality of tools so that the cutting points of the plurality of tools move forward and backward in sequence. The above conditions are cutting distance, time or spindle speed.

3. The numerical control device according to claim 1, characterized in that: When the preset conditions are met, the analysis unit generates movement instruction data, which controls the relative speed and relative position between the plurality of tools so that the cutting points of the plurality of tools move forward and backward in sequence. The above-mentioned condition is when the amplitude value of the vibration detected by the vibration sensor or the load value of the servo motor exceeds a preset threshold value.

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