Working machinery

Abstract

To provide a machine tool that can reduce power consumption. [Solution] The machine tool comprises a workpiece holder for holding a workpiece to be cut, a tool holder for rotatably holding a rotary tool for cutting the workpiece, a moving mechanism for relatively moving the workpiece held in the workpiece holder and the rotary tool held in the tool holder, a rotating mechanism for rotating the rotary tool held in the tool holder, a drive source for driving the rotating mechanism, and a current limiting unit that can switch between a limiting state that limits the current flowing to the drive source and an unlimiting state that does not limit the current. The current limiting unit switches from the limiting state to the unlimiting state when the distance between the rotary tool held in the tool holder and the workpiece held in the workpiece holder falls below a predetermined value.

Description

Technical Field

[0001] The present invention relates to a machine tool.

Background Art

[0002] In a machine tool that cuts a cutting object with a rotating tool, the rotating tool is driven based on commands of an NC program. At this time, the moving speed and the rotating speed of the rotating tool can be finely controlled. For example, Patent Document 1 discloses a configuration in which the cutting feed speed is changed according to the relative position between the cutting tool and the cutting object (workpiece).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] On the other hand, in the above-described configuration, no disclosure is made regarding the control method when changing the rotating tool to the target rotating speed. When changing the rotating tool to the target rotating speed, such as at the start or stop of rotation of the rotating tool, a large load is applied to the rotating tool and the rotating mechanism that rotates the rotating tool, and a large current flows through the drive source that drives the rotating mechanism. However, from the viewpoint of power saving, it is not preferable that the current flowing through the drive source increases.

[0005] In view of the above problems, an object of the present invention is to provide a machine tool capable of suppressing power consumption.

Means for Solving the Problems

[0006] (Aspect 1) To solve the above problems, a machine tool according to embodiment 1 of the present invention includes: a workpiece holding unit for holding a workpiece to be cut; a tool holding unit for rotatably holding a rotary tool for cutting the workpiece; a moving mechanism for relatively moving the workpiece held in the workpiece holding unit and the rotary tool held in the tool holding unit; a rotating mechanism for rotating the rotary tool held in the tool holding unit; a driving mechanism for driving the rotating mechanism; and a current limiting unit that can switch between a limiting state for limiting the current flowing through the driving mechanism and an unlimiting state for not limiting the current, wherein the current limiting unit switches from the limiting state to the unlimiting state when the distance between the rotary tool held in the tool holding unit and the workpiece held in the workpiece holding unit becomes less than or equal to a predetermined value.

[0007] (Aspect 2) In the above embodiment 1, the current limiting unit may determine whether the distance has become less than or equal to the predetermined value based on the position information of the rotating tool and the position information of the workpiece to be cut.

[0008] (Aspect 3) In the above embodiment 1, the current limiting unit may determine whether the distance has become less than or equal to the predetermined value based on the commands of the NC program that drives the moving mechanism and the rotating mechanism.

[0009] (Aspect 4) In the above embodiment 3, the current limiting unit controls the rotary tool when the command of the NC program is received. When the command switches from a first command, which brings the workpiece closer at a first speed, to a second command, which brings the rotating tool and the workpiece closer at a second speed slower than the first speed, it may be determined that the distance has become less than or equal to the predetermined value.

[0010] (Aspect 5) In the above embodiment 1, a first interference barrier is set around the rotary tool, a second interference barrier is set around the workpiece to be cut, and the current limiting unit further comprises an interference detection unit capable of detecting contact between the first interference barrier and the second interference barrier, wherein the current limiting unit may determine whether the distance has become less than or equal to the predetermined value based on the detection result of the interference detection unit.

[0011] (Aspect 6) In the above embodiment 5, the current limiting unit may determine that the distance has become less than or equal to the predetermined value when the interference detection unit detects that the first interference barrier and the second interference barrier are in contact with each other.

[0012] (Aspect 7) In the above embodiment 1, the tool holding unit is configured to hold a plurality of the rotary tools, and in the restricted state, the upper limit of the current flowing to the drive source may differ for each of the plurality of rotary tools.

[0013] (Pattern 8) In the above embodiment 7, the predetermined value may be different for each of the multiple rotary tools. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a machine tool that can suppress power consumption. [Brief explanation of the drawing]

[0015] [Figure 1] This is a schematic diagram of the machine tool according to the first embodiment. [Figure 2] This is a control block diagram of a machine tool according to the first embodiment. [Figure 3] This is an explanatory diagram of the method for switching the current limiting state according to the first embodiment. [Figure 4] This is a comparison diagram showing the difference between a state with and without current limiting. [Figure 5] This diagram shows the switching flow of the current limiting state according to the first embodiment. [Figure 6]It is an explanatory diagram of a method for switching the current limit state according to the second embodiment. [Figure 7] It is a diagram showing a switching flow of the current limit state according to the second embodiment. [Figure 8] It is an explanatory diagram of a method for switching the current limit state according to the third embodiment. [Figure 9] It is a control block diagram of a machine tool according to the third embodiment. [Figure 10] It is a diagram showing a switching flow of the current limit state according to the third embodiment.

Embodiments for Carrying Out the Invention

[0016] Hereinafter, embodiments for carrying out this invention will be exemplarily and detailedly described based on the embodiments with reference to the drawings. Note that the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the device to which the invention is applied and various conditions. That is, the scope of this invention is not intended to be limited to the following embodiments.

[0017] <First Embodiment> As an example of a machine tool according to the present invention, a lathe device capable of attaching a rotary tool will be described. However, the application of the present invention is not limited to the lathe device as described below, and is applicable to known machine tools that perform cutting with a rotary tool.

[0018] (Machine Tool) The configuration of a machine tool 100 according to the first embodiment of the present invention will be described. The machine tool 100 is a so-called lathe device. The machine tool 100 is a device that rotates a cutting object (workpiece), which is, for example, a long bar, and applies a cutting tool (processing tool) thereto to perform cutting. Also, the machine tool 100 can perform cutting by applying a rotating rotary tool to a fixed cutting object without rotating it.

[0019] The configuration of the machine tool 100 will be described with reference to Figure 1. Figure 1 is a schematic diagram of the machine tool 100 according to the first embodiment, and is a diagram that simply shows the configuration of each part. The machine tool 100 includes a workpiece holder 10 to which the workpiece W, which is the object to be cut, is attached, and a first tool holder 20 and a second tool holder 30 as tool holders to which a plurality of cutting tools are attached.

[0020] The machine tool 100 includes a feed mechanism 51 for feeding the workpiece W in the feed direction, and a first moving mechanism 52 and a second moving mechanism 53 for moving each tool holder. Various known technologies can be used for the feed mechanism and the moving mechanism, such as a motor as a drive source, a ball screw mechanism, or a rack and pinion mechanism. The machine tool 100 also includes a first rotating mechanism 54, a second rotating mechanism 55, and a third rotating mechanism 56 for rotating the workpiece W and cutting tools. Known technologies can be used for the rotating mechanisms, such as a motor as a drive source or a mechanism with multiple gear members.

[0021] The workpiece holder 10 includes a spindle 11 that holds the workpiece W and rotates integrally with the workpiece W. A chuck for holding the workpiece W is provided at the tip of the spindle 11. In the workpiece holder 10, the workpiece W is fed in the feed direction by a feed mechanism 51 and rotated by a first rotation mechanism 54 around a rotation axis parallel to the feed direction. While the workpiece W is held in the workpiece holder 10, it is cut (machined) by a cutting tool while rotating or stopped rotating.

[0022] In the following description, the feeding direction of the workpiece W in the workpiece holding unit 10 is defined as the Z direction. The direction intersecting the Z direction (orthogonal in this example) is defined as the Y direction, and the direction intersecting both the Y and Z directions (orthogonal in this example) is defined as the X direction. In this example, the X direction is parallel to the direction of gravity (vertical direction), and the Y and Z directions are parallel to the horizontal direction.

[0023] The first tool holder 20 is configured to accommodate multiple rotary tools. Figure 1 shows three rotary tools 21 mounted on the first tool holder 20. In the first tool holder 20, the rotary tools 21 are mounted so that their axis of rotation is parallel to the Y direction.

[0024] The first tool holder 20 is configured to be movable in both the X and Y directions by the first moving mechanism 52. In other words, the first moving mechanism 52 moves the rotary tool 21 held in the first tool holder 20 relative to the workpiece W held in the workpiece holder 10. The rotary tool 21 held in the first tool holder 20 is rotated by the second rotating mechanism 55.

[0025] The first tool holder 20 may be configured to be movable in the Z direction. Furthermore, the first tool holder 20 may be configured to be rotatable about a rotation axis parallel to the X direction. With this configuration, the end face (tip face) of the workpiece W held by the workpiece holder 10 can be machined by a rotary tool 21 such as a drill held by the first tool holder 20.

[0026] The second tool holder 30 is configured to accommodate multiple rotary tools and turning tools. Figure 1 shows three rotary tools 31 and six turning tools 33 mounted on the second tool holder 30. In the second tool holder 30, the rotary tools 31 are mounted so that their axis of rotation is parallel to the X direction.

[0027] The second tool holder 30 is configured to be movable in both the X and Y directions by the second moving mechanism 53. In other words, the second moving mechanism 53 moves the rotary tool 31 and turning tool 33 held in the second tool holder 30 relative to the workpiece W held in the workpiece holder 10. The rotary tool 31 held in the second tool holder 30 is rotated by the third rotating mechanism 56. However, the configuration of these tool holders is merely an example, and the types and number of tools that can be attached can be changed. Also, the tool holder may be comb-shaped or turret-shaped.

[0028] Figure 2 is a control block diagram of the machine tool 100. The machine tool 100 includes a control unit 60 for controlling the operation of each part. The control unit 60 can be configured with a computer having a processor, memory (storage device), storage, I / O, etc. The main components of the control unit 60 will be described below.

[0029] The control unit 60 includes a drive unit 61 and a current limiting unit 63. The drive unit 61 drives the feed mechanism 51, the first moving mechanism 52, the second moving mechanism 53, the first rotating mechanism 54, the second rotating mechanism 55, and the third rotating mechanism 56 according to the commands of the NC program (machining instruction data).

[0030] The current limiting unit 63 limits the current to the drive sources of the second rotation mechanism 55 and the third rotation mechanism 56 for rotating the rotary tool. Limiting the current means limiting the current value flowing to the drive source so that it does not exceed a predetermined threshold, that is, so that the current value stays within a predetermined range. In this embodiment, a servo motor 55a is provided as the drive source for the second rotation mechanism 55, and a servo motor 56a is provided as the drive source for the third rotation mechanism 56. The current limiting unit 63 is configured to limit the current values ​​of the servo motors 55a and 56a, respectively.

[0031] Furthermore, the current limiting unit 63 is configured to be switchable between a limiting state, which limits the current flowing to the servo motors 55a and 56a, and an unlimiting state, which does not limit the current. The switching between the limiting state and the unlimiting state of the current limiting unit 63 will be described in detail later.

[0032] The current limiting unit 63 includes a coordinate storage unit 65, a calculation unit 67, and a monitoring unit 69. The coordinate storage unit 65 stores the position coordinates of the cutting tools attached to each tool holder. The calculation unit 67 performs various calculations. For example, the calculation unit 67 calculates the distance between the cutting tool attached to the tool holder and the workpiece W held in the workpiece holder 10. The monitoring unit 69 monitors whether the cutting tool and the workpiece W are in close proximity based on the distance between the cutting tool and the workpiece W calculated by the calculation unit 67.

[0033] (Method for switching between current-limited state and unlimited state) The method for switching between the current-limiting state and the unlimited state of the current-limiting unit 63 will now be described. In the first embodiment, the current of the drive source is limited when the distance between the rotating tool and the workpiece W falls below a predetermined value. The switching method will be described in more detail below, using a rotating tool 21 held in the first tool holder 20 as an example. The switching method is the same for other rotating tools 21 held in the first tool holder 20 and for the rotating tool 31 held in the second tool holder 30.

[0034] Figure 3 is an explanatory diagram of the switching method according to the first embodiment. The rotary tool 21 is in the standby position ( When the rotating tool 21 is in its initial position and stopped, the current limiting unit 63 is in a limiting state. When the rotating tool 21 approaches the workpiece W, the current limiting unit 63 switches from the limiting state to the released state.

[0035] In the first embodiment, the distance between the rotary tool 21 and the workpiece W is obtained based on the position of the tip of the rotary tool 21 on the rotation axis and the position of the workpiece W on the rotation axis, and it is determined (monitored) whether the rotary tool 21 has approached the workpiece W. When the distance in the X direction between the rotary tool 21 and the workpiece W becomes less than or equal to a threshold Dx and the distance in the Y direction becomes less than or equal to a threshold Dy, the current limiting unit 63 determines that the rotary tool 21 has approached the workpiece W and switches from the limiting state to the release state.

[0036] In other words, the current limiting unit 63 is in a limiting state when the rotating tool 21 and the workpiece W are far apart, and the current limiting unit 63 is in an unlocked state when the rotating tool 21 and the workpiece W are close together. With this configuration, for example, the current flowing to the servo motor 55a can be limited when the rotating tool 21, which carries a large current, starts rotating or stops rotating.

[0037] Figures 4(a) and 4(b) are comparison diagrams of the unrestricted state (no current limit) and the restricted state (current limit). Figure 4(a) shows a graph illustrating the changes in current and rotational speed from the start to the stop of rotation of the rotary tool 21 in the unrestricted state (no current limit). Figure 4(b) shows a graph illustrating the changes in current and rotational speed from the start to the stop of rotation of the rotary tool 21 in the restricted state (current limit). Figures 4(a) and 4(b) show a graph with the current flowing to the servo motor 55a of the second rotation mechanism 55 on the vertical axis and time on the horizontal axis, and a graph with the rotational speed of the rotary tool 21 on the vertical axis and time on the horizontal axis.

[0038] As shown in Figure 4(a), in the released state, when the rotary tool 21 starts rotating by the second rotation mechanism 55 and the rotational speed increases, the current flowing to the servo motor 55a rises sharply to value IAa. Then, when the rotational speed rises to the desired rotational speed RS and is controlled to a constant level, the current decreases and stabilizes at a value smaller than IAa.

[0039] Subsequently, as the rotational speed of the rotary tool 21 begins to decrease in order to stop its rotation, the current flowing through the servo motor 55a drops sharply to a negative value, IAb. Then, when the rotational speed becomes zero and the rotary tool 21 stops rotating, the current also becomes zero.

[0040] Thus, when the rotating tool 21 starts rotating or stops rotating, a current with a larger absolute value flows to the servo motor 55a compared to when the rotation speed is constant. The flow of a current with a larger absolute value results in higher power consumption. In addition, rapidly changing the rotation speed increases the load on the rotating tool 21, the servo motor 55a and gear members of the second rotating mechanism 55, and the first tool holding part 20.

[0041] On the other hand, as shown in Figure 4(b), in the restricted state, when the rotary tool 21 starts rotating due to the second rotation mechanism 55 and the rotational speed increases, the current flowing through the servo motor 55a is limited to an upper limit value IBa, which is smaller than the value IAa. Similarly, when the rotational speed decreases due to the rotation of the rotary tool 21 stopping, the current flowing through the servo motor 55a is limited to a lower limit value IBb, which is smaller in absolute value than the value IAb.

[0042] When current is limited, the time it takes to increase the rotational speed from zero to the desired rotational speed RS, and the time it takes to decrease it from the desired rotational speed RS back to zero, are longer compared to when there is no current limit. In other words, by implementing a current limit, the rotational speed of the rotary tool can be changed more gradually.

[0043] The timing of the switch from the restricted state to the released state shown in Figure 4(b) is when the rotating tool 21 The first tool holder 20 moves in a direction toward the workpiece W, and the distance between the rotating tool 21 and the workpiece W in the X direction becomes less than or equal to threshold Dx, and the distance in the Y direction becomes less than or equal to threshold Dy. The timing of switching from the released state to the restricted state is when the first tool holder 20 moves in a direction toward the rotating tool 21 toward the workpiece W, and the distance between the rotating tool 21 and the workpiece W in the X direction exceeds threshold Dx, or the distance in the Y direction exceeds threshold Dy. In other words, in the first embodiment, thresholds Dx and Dy are determined such that the current limiting unit 63 is released during the period after the rotational speed has been gradually increased to the desired rotational speed RS, and before the rotational speed is gradually decreased from the desired rotational speed RS.

[0044] In this way, by setting an upper limit IBa and a lower limit IBb as current limiting thresholds and limiting the current flowing to the servo motor 55a, power consumption can be reduced and the load on the second rotating mechanism 55 and other components can be suppressed. In other words, in the first embodiment, a predetermined value (distance between the rotating tool and the workpiece W) that serves as the switching criterion for the current limiting state is determined by thresholds Dx and Dy.

[0045] The upper limit IBa and lower limit IBa can be set according to the type of drive source; for example, 50% of the rated current can be used as the threshold. Furthermore, the upper limit IBa and lower limit IBa may be set differently for each of the multiple rotary tools, and it is preferable to set values ​​corresponding to the type and size of the rotary tool. Similarly, the thresholds Dx and Dy may also differ for each of the multiple rotary tools. In other words, the predetermined value that serves as the switching criterion for the current limiting state with respect to the distance between the rotary tool and the workpiece W may differ for each of the multiple rotary tools.

[0046] Figure 5 is a diagram showing the switching flow between the current-limiting state and the unlimiting state according to the first embodiment. The method for switching between the current-limiting state and the unlimiting state will be explained exemplified according to the flowchart shown in Figure 5. In the following, an example will be described in which the current-limiting unit 63 switches from the limiting state to the unlimiting state as the rotating tool 21 of the first tool holding unit 20 moves.

[0047] The switching flow between the current-limited state and the unlimited state can be initiated, for example, by receiving a movement command or rotation command for the first tool holder 20, or by the start of a cutting command.

[0048] When switching between the current-limited state and the unlimited state, first, in step (hereinafter referred to as S) 501, thresholds Dx and Dy are set. Then, in S502, the rotary tool to start rotating is selected. In this example, it is explained that the rotary tool 21 of the first tool holder 20 is selected. Each threshold may be set, for example, by the user entering an arbitrary value, or by reading a value stored in the machine tool 100. Alternatively, the rotary tool may be selected in S502 first, and then S501 may be executed, and each threshold may be set according to the selected rotary tool.

[0049] Next, in S503, the calculation unit 67 calculates the difference between the distance between the rotary tool 21 and the workpiece W and the threshold value. In this example, the X coordinate of the rotary tool 21 is Ex and the Y coordinate is Ey, assuming the X coordinate and Y coordinate of the workpiece W are both 0 (Ex>0, Ey>0). Thus, in the first embodiment, coordinates are used as positional information for the rotary tool 21 and the workpiece W. At this time, the calculation unit 67 calculates the difference Ex-Dx, which is the difference between the X coordinate Ex of the rotary tool 21 and the threshold value Dx. Furthermore, the calculation unit 67 calculates the difference Ey-Dy, which is the difference between the Y coordinate Ey of the rotary tool 21 and the threshold value Dy.

[0050] Next, in S504, the monitoring unit 69 starts monitoring the difference Ex-Dx and difference Ey-Dy. Specifically, the monitoring unit 69 monitors (determines) whether the difference Ex-Dx and difference Ey-Dy, which are successively acquired by the calculation unit 67 based on the X coordinate Ex and Y coordinate Ey that change as the rotary tool 21 (first tool holding unit 20) moves, have become zero or less.

[0051] Next, in S505, the rotation and movement of the rotary tool 21 are started by the second rotation mechanism 55 and the first movement mechanism 52. At this time, the current limiting unit 63 is in a limiting state. As a result, the rotary tool 21 starts rotating with the upper limit value IBa and lower limit value IBb of the current defined. The rotary tool 21 then gradually approaches the workpiece W, and the difference Ex-Dx and difference Ey-Dy gradually decrease. Note that S504 and S505 may be executed at the same time.

[0052] In S506, the monitoring unit 69 determines whether Ex-Dx≦0 and Ey-Dy≦0. If the answer in S506 is NO, i.e., Ex-Dx>0 or Ey-Dy>0, the process proceeds to S507, where the current limiting unit 63 remains in the limiting state, and monitoring of the differential Ex-Dx and differential Ey-Dy continues.

[0053] On the other hand, if the answer to S506 is YES, that is, if Ex-Dx≦0 and Ey-Dy≦0, the process proceeds to S508, and the current limiting unit 63 switches from the limiting state to the release state. The switching flow between the current limiting state and the release state then ends.

[0054] This switching method allows the current limiting unit 63 to be switched from a limiting state to an unlocked state when the distance between the rotating tool 21 and the workpiece W falls below a predetermined value.

[0055] Furthermore, the switch from the restricted state to the released state is performed by calculating and monitoring the differential Ex-Dx and differential Ey-Dy, similar to S503 and S504, and occurs when Ex-Dx > 0 or Ey-Dy > 0. This switching method allows the current limiting unit 63 to be switched from the released state to the restricted state when the distance between the rotary tool 21 and the workpiece W exceeds a predetermined value.

[0056] The above method for switching between current-limited and unlimited states allows for limiting the current when a large current flows through the drive source of the rotating mechanism. By switching between the limited and unlimited states according to the proximity and separation between the cutting tool and the workpiece W, power consumption can be reduced, and the load on the rotating tool, rotating mechanism, and tool holder can be decreased.

[0057] In the first embodiment, the switching was performed based on the X-direction distance and Y-direction distance between the rotary tool 21 and the workpiece W, but the configuration is not limited to this. For example, the Z-direction distance between the rotary tool 21 and the workpiece W may be incorporated as a criterion. Alternatively, the shortest distance from the rotary tool 21 to the workpiece W may be used as a criterion. Furthermore, instead of the rotation center of the workpiece W, the distance between the outer surface and the rotary tool 21 may be used.

[0058] <Second Embodiment> Next, a second embodiment of the present invention will be described. The second embodiment differs from the first embodiment in the criteria used for switching between the current-limited state and the unlimited state. Hereinafter, only the differences between the configuration of the second embodiment and the configuration of the first embodiment will be described. Components in the second embodiment that are the same as those in the first embodiment are denoted by the same reference numerals and their descriptions are omitted.

[0059] (Method for switching between current-limited state and unlimited state) The method for switching between the current-limiting state and the unlimiting state of the current-limiting unit 63 according to the second embodiment will now be described. The second embodiment is similar to the first embodiment in that the current of the drive source is limited when the distance between the rotating tool and the workpiece W falls below a predetermined value, but the method for determining whether or not the distance between the rotating tool and the workpiece W has fallen below a predetermined value differs from the first embodiment. The switching method will be described in more detail below using a rotating tool 21 held in the first tool holding unit 20 as an example.

[0060] Figure 6 is an explanatory diagram of the switching method according to the second embodiment. In the second embodiment, the current limiting unit 63 determines whether the distance between the rotating tool and the workpiece W has fallen below a predetermined value based on the commands of the NC program that drives each moving mechanism and rotating mechanism, and switches between a current limiting state and an unlimited state.

[0061] In machining, control is sometimes employed to move the cutting tool at high speed when the distance between the cutting tool and the workpiece W is large, and at low speed when the distance is small. In other words, when interference between the cutting tool and the workpiece W is unlikely and no cutting is being performed, the machining time is shortened by moving the cutting tool at high speed using a rapid traverse command (first command). Then, when the workpiece W is being cut by the cutting tool, the cutting process is performed using a cutting feed command (second command) that moves the cutting tool at a slower speed than the rapid traverse command. In short, the rapid traverse command and the cutting feed command have different speeds at which the cutting tool approaches and moves away from the workpiece W.

[0062] In the machine tool 100 according to the second embodiment, the current limiting unit 63 is configured to switch from a limited state to an unlocked state when switching from a rapid traverse command (first command) to a cutting feed command (second command). If the cutting tool's movement speed in the rapid traverse command is the first speed, then the cutting tool's movement speed in the cutting feed command is the second speed, which is slower than the first speed.

[0063] Figure 6 shows that the region in which the rotary tool 21 moves according to the rapid traverse command is FA1, and the region in which it moves according to the cutting feed command is FA2. In the second embodiment, the current limiting unit 63 is in a limiting state when the rotary tool 21 is in region FA1, and the current limiting unit 63 is in a release state when the rotary tool 21 is in region FA2.

[0064] On the other hand, when the rotary tool 21 moves away from the workpiece W, the current limiting unit 63 switches from the unlocked state to the restricted state when the cutting feed command switches to the rapid traverse command. With this configuration, the current limiting unit 63 remains in the restricted state even when the rotary tool 21 stops rotating.

[0065] In the second embodiment, the switching position between the current-limited state and the unrestricted state can be adjusted by changing the position of the boundary between the rapid traverse command region FA1 and the cutting feed command region FA2. In other words, in the second embodiment, the predetermined value that serves as the switching criterion (the distance between the rotary tool and the workpiece W) is determined by the position of the boundary between the rapid traverse command region FA1 and the cutting feed command region FA2.

[0066] With this configuration, the current is not limited when the rotating tool 21 and the workpiece W are close together, and the current can be limited when the rotating tool 21 and the workpiece W are far apart. In other words, the current can be limited by the current limiting unit 63 when the rotating tool 21 starts rotating or stops rotating, when a large current flows through the servo motor 55a of the second rotating mechanism 55.

[0067] Figure 7 is a diagram showing the switching flow according to the second embodiment. The switching method will be explained illustratively according to the flowchart shown in Figure 7. In the following, an example will be described in which the current limiting unit 63 switches from a limited state to an unlocked state as the rotating tool 21 of the first tool holding unit 20 moves, and then switches back to a limited state. In this example, the switching flow starts from the start of rotation of the rotating tool 21.

[0068] First, in S701, a rotation command for the rotary tool 21 is executed. At this time, the current limiting unit 63 is in a limiting state. Therefore, the rotary tool 21 starts rotating with the current limited.

[0069] Next, in S702, a rapid traverse command is executed to bring the rotary tool 21 closer to the workpiece W. The rapid traverse command causes the rotary tool 21 to approach the workpiece W at a first speed. Once the rapid traverse command is complete and the rotary tool 21 has moved to a predetermined position, a cutting feed command is executed in S703. In the cutting feed command, the rotary tool 21 approaches and contacts the workpiece W at a second speed, which is slower than the first speed. Simultaneously with the start of the cutting feed command, in S704, the current limiting unit 63 is switched from a limited state to an unlocked state.

[0070] After the cutting operation is performed with the current limiting unit 63 in the released state, the rotary tool 21 is moved away from the workpiece W at a second speed by the cutting feed command. When the cutting feed command is completed and the rotary tool 21 has moved to a predetermined position, a rapid traverse command is executed in S705 to separate the rotary tool 21 from the workpiece W. At this time, the rotary tool 21 moves away from the workpiece W at a first speed. Simultaneously with the start of the rapid traverse command, the system switches from the released state to the limited state in S706.

[0071] Finally, once the rapid traverse command is completed and the rotary tool 21 has moved to the predetermined position, a rotation stop command is executed in S707. Then, with the current limited, the rotary tool 21 stops rotating.

[0072] By switching between the current-limited and unlimited states as described above, the current can be limited when a large current flows to the drive source of the rotating mechanism, similar to the first embodiment. In this way, by switching between the current-limited state and the unlimited state according to the proximity and separation between the cutting tool and the workpiece W, power consumption can be reduced and the load on the rotating tool, rotating mechanism, and tool holder can be reduced.

[0073] <Third Embodiment> Next, a third embodiment of the present invention will be described. The third embodiment differs from the first embodiment in the criteria used for switching between the current-limited state and the unlimited state. Hereinafter, only the differences between the configuration of the third embodiment and the configuration of the first embodiment will be described. Components in the third embodiment that are the same as those in the first embodiment are denoted by the same reference numerals and their descriptions are omitted.

[0074] (Method for switching between current-limited state and unlimited state) The method for switching between the current-limiting state and the unlimited state of the current-limiting unit 63 according to the third embodiment will now be described. The third embodiment is similar to the first embodiment in that the current of the drive source is limited when the distance between the rotating tool and the workpiece W falls below a predetermined value, but the method for determining whether or not the distance between the rotating tool and the workpiece W has fallen below a predetermined value differs from that of the first embodiment. The switching method will be described in more detail below using a rotating tool 21 held in the first tool holding unit 20 as an example.

[0075] Figure 8 is an explanatory diagram of the switching method according to the third embodiment. In the third embodiment, the current limiting unit 63 determines whether the distance between the rotary tool 21 and the workpiece W has become less than or equal to a predetermined value based on whether or not there is interference between the interference barrier set on the rotary tool 21 and the interference barrier set on the workpiece W, and switches between a current limiting state and an unlimited state.

[0076] In machine tools, interference barriers are sometimes set as virtual extension areas around cutting tools and workpieces to prevent unintended interference. For example, an interference barrier can be set by extending the outermost surface of the cutting tool or workpiece by 1 mm outward. When an interference barrier is set, interference between the cutting tool and workpiece can be prevented by stopping the operation of the respective moving and rotating mechanisms if the interference barrier unintentionally interferes with something else during the movement of the cutting tool or during cutting.

[0077] Figure 8 shows the first interference barrier BA1 of the rotary tool 21 and the second interference barrier BA2 of the workpiece W as dashed lines. In the machine tool 100 according to the third embodiment, the current limiting unit 63 switches from the unlocked state to the limited state when the first interference barrier BA1 and the second interference barrier BA2 interfere, and switches from the limited state to the unlocked state when the interference between the first interference barrier BA1 and the second interference barrier BA2 is released. In other words, in the third embodiment, a predetermined value (distance between the rotary tool and the workpiece W) that serves as the criterion for switching between the current limiting state and the unlocked state is determined by the size of the first interference barrier BA1 and the second interference barrier BA2.

[0078] With this configuration, the current is not limited when the rotating tool 21 and the workpiece W are close together, and the current can be limited when the rotating tool 21 and the workpiece W are far apart. In other words, the current can be limited by the current limiting unit 63 when the rotating tool 21 starts rotating or stops rotating, when a large current flows through the servo motor 55a of the second rotating mechanism 55.

[0079] Figure 9 is a control block diagram of a machine tool 100 according to the third embodiment. The current limiting unit 63 of the machine tool 100 has a barrier interference detection unit 71 that can detect interference from each interference barrier. The current limiting unit 63 switches between a limited state and an unlimited state based on the detection result of the barrier interference detection unit 71.

[0080] Figure 10 is a diagram showing the current limiting state switching flow according to the third embodiment. The method for switching the current limiting state will be explained exemplified according to the flowchart shown in Figure 10. In the following, an example will be described in which the current limiting unit 63 switches from a current limiting state to an unlimited state, and then switches back to a current limiting state, as the rotating tool 21 of the first tool holding unit 20 moves. In this example, the switching flow starts from the start of movement of the rotating tool 21.

[0081] First, in S1001, a command to move the rotary tool 21 (first tool holder 20) is executed. At this time, the current limiting unit 63 is in a limiting state. Next, in S1002, a command to rotate the rotary tool 21 is executed. Therefore, the rotary tool 21 starts rotating while the current is limited.

[0082] As the rotating tool 21 continues to move while rotating, the rotating tool 21 and the workpiece W approach each other, and in S1003, the first interference barrier BA1 and the second interference barrier BA2 interfere with each other. When the barrier interference detection unit 71 detects the interference between the first interference barrier BA1 and the second interference barrier BA2, in S1004, the current limiting unit 63 is switched from the limiting state to the release state.

[0083] Then, after the cutting operation is performed with the current limiting unit 63 in the released state, the rotary tool 21 is separated from the workpiece W. During the process of separating the rotary tool 21 from the workpiece W, the interference between the first interference barrier BA1 and the second interference barrier BA2 is released in S1005. When the barrier interference detection unit 71 detects that the interference between the first interference barrier BA1 and the second interference barrier BA2 has been released, the system switches from the released state to the limited state in S1006.

[0084] Finally, once the movement command is completed and the rotary tool 21 has moved to the predetermined position, a rotation stop command is executed in S1007. Then, with the current limited, the rotary tool 21 stops rotating.

[0085] By switching between the current-limited state and the unlimited state as described above, the current can be limited when a large current flows to the drive source of the rotating mechanism, similar to the first embodiment, in the third embodiment as well. In this way, by switching between the current-limited state and the unlimited state according to the proximity and separation between the cutting tool and the workpiece W, power consumption can be reduced, and the rotating tool, rotating mechanism, and tool holder can be improved. This can reduce the load on the unit. [Explanation of Symbols]

[0086] 10...Workpiece holding section, 20...First tool holding section (tool holding section), 52...First moving mechanism (moving mechanism), 55...Second rotation mechanism (rotating mechanism), 55a...Servo motor (drive source), 63...Current limiting section, 100...Machine tool, W...Workpiece (object to be cut)

Claims

1. A workpiece holding section that holds the object to be cut, A tool holder that rotatably holds a rotary tool for cutting the object to be cut, A moving mechanism for relatively moving the workpiece to be cut, which is held in the workpiece holding section, and the rotating tool, which is held in the tool holding section, A rotating mechanism for rotating the rotating tool held in the tool holding part, A drive source that drives the aforementioned rotation mechanism, A current limiting unit that can switch between a limiting state in which the current flowing to the drive source is limited and an unlimiting state in which the current is not limited, Equipped with, The machine tool is characterized in that the current limiting unit switches from the limiting state to the release state when the distance between the rotating tool held in the tool holding unit and the workpiece held in the workpiece holding unit falls below a predetermined value.

2. The machine tool according to claim 1, characterized in that the current limiting unit determines whether the distance has become less than or equal to the predetermined value based on the position information of the rotating tool and the position information of the workpiece to be cut.

3. The machine tool according to claim 1, characterized in that the current limiting unit determines whether the distance has become less than or equal to the predetermined value based on the commands of the NC program that drives the moving mechanism and the rotating mechanism.

4. The machine tool according to claim 3, characterized in that the current limiting unit determines that the distance has become less than or equal to the predetermined value when the command of the NC program switches from a first command to bring the rotating tool and the workpiece closer together at a first speed to a second command to bring the rotating tool and the workpiece closer together at a second speed slower than the first speed.

5. A first interference barrier is set around the rotating tool, a second interference barrier is set around the workpiece to be cut, and the system further includes an interference detection unit capable of detecting contact between the first and second interference barriers. The machine tool according to claim 1, characterized in that the current limiting unit determines whether the distance has become less than or equal to the predetermined value based on the detection result of the interference detection unit.

6. The machine tool according to claim 5, characterized in that the current limiting unit determines that the distance has become less than or equal to the predetermined value when the interference detection unit detects that the first interference barrier and the second interference barrier are in contact with each other.

7. The tool holding section is configured to hold a plurality of the rotary tools, The machine tool according to claim 1, characterized in that, in the aforementioned restricted state, the upper limit of the current flowing to the drive source is different for each of the multiple rotary tools.

8. The machine tool according to claim 7, characterized in that the predetermined value differs for each of the multiple rotary tools.

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