Tool changing mechanism of machining center

Abstract

The utility model discloses a tool changing mechanism of a machining center. The tool changing mechanism comprises a linear transfer assembly, a lifting assembly, a reversing assembly and a tool changing assembly which are combined in a matched mode. In the tool changing assembly, an installation shaft is installed on the reversing assembly in a rotating mode and fixedly connected with the center of a positioning plate, U-shaped clamping grooves used for fixing a tool apron are formed in the two sides of the positioning plate, and annular positioning grooves matched with the U-shaped clamping grooves in an embedded mode are formed in the outer wall of the tool apron. And a wedge-shaped clamping groove in the annular positioning groove is matched with an electromagnetic clamping lock of the U-shaped clamping groove, and a wedge-shaped clamping key is assembled on the electromagnetic clamping lock, so that the cutter is stably fixed. Through the optimized design, the tool changing process is simplified, the stability is improved, redundant actions are reduced, the tool changing efficiency is remarkably improved, and the tool changing device has very high practical value and popularization prospects.

Description

Technical Field

[0001] The utility model relates to the technical field of machining, and particularly relates to a tool changing mechanism of a machining center. Background Art

[0002] In modern manufacturing, machining centers are widely used in high-precision and high-efficiency machining. However, due to the structural layout, the assembly directions of the tool magazine and the spindle box are often inconsistent, which brings many challenges to the tool changing operation. Specifically, during the tool changing operation, the existing tool changing mechanisms usually need to perform complex actions, which not only increases the risk of failures during the tool changing process but also may lead to inaccurate tool changing.

[0003] During the tool changing process of traditional tool changing mechanisms, it is necessary to ensure the stable transfer of the tool holder and the tool head between the spindle box and the tool magazine. However, due to design limitations, it is difficult for the existing tool changing mechanisms to ensure the stability of the tool holder and the tool head throughout the process. This instability may cause the tool to shake or even fall off during the transfer process, thereby affecting the machining accuracy and efficiency. In addition, some tool changing mechanisms have redundant action steps in design, which not only prolongs the tool changing time but also increases the complexity and failure rate of the system.

[0004] In order to overcome these drawbacks, there is an urgent need for a new tool changing mechanism that can simplify the actions during the tool changing process, improve the accuracy and stability of tool changing, and reduce redundant actions, thereby enhancing the overall tool changing efficiency and system reliability. Summary of the Utility Model

[0005] Aiming at the above deficiencies existing in the prior art, the purpose of the utility model is to provide a tool changing mechanism of a machining center, which realizes the simplification of the tool changing process, the improvement of stability, the reduction of redundant actions, and the enhancement of the tool changing efficiency, and has significant practical value and popularization prospects.

[0006] The technical solution adopted by the utility model to achieve the above purpose is: a tool changing mechanism of a machining center, including a linearly moving component, a lifting component, a reversing component, and a tool changing component that are assembled in a matching manner. The linearly moving component is arranged between the tool magazine and the spindle box of the machining center. The lifting component is assembled on the moving part of the linearly moving component. The reversing component is assembled on the moving part of the lifting component. The tool changing component is assembled on the moving part of the reversing component.

[0007] The tool changing assembly includes a mounting shaft, a positioning plate, and an electromagnetic lock. The mounting shaft is rotatably mounted on the moving part of the commutation assembly. The mounting shaft is fixedly connected to the center of the positioning plate. U-shaped card slots for fixing the tool holder are provided on both sides of the positioning plate. A tool head is fixedly assembled on the tool holder. An annular positioning groove that nests and fits with the U-shaped card slot is provided on the outer wall of the tool holder. A wedge-shaped card slot is provided in the annular positioning groove. Electromagnetic locks are assembled on both sides of the U-shaped card slot. A wedge-shaped key that nests and fits with the wedge-shaped card slot is assembled on the electromagnetic lock.

[0008] In some of the embodiments, in order to ensure that the linear transfer assembly can be stably assembled in the machining center and ensure that the linear transfer assembly drives the lifting assembly to travel stably in a straight line, the following technical solutions are provided.

[0009] The linear transfer assembly includes an assembly base, a guide groove, a driving motor A, an adjusting lead screw, and a sliding assembly seat. The guide groove and the driving motor A are both fixedly installed on the assembly base. The adjusting lead screw is rotatably installed in the guide groove and fixedly connected to the output shaft of the driving motor A. The sliding assembly seat is slidably installed in the guide groove and is threadedly connected to the adjusting lead screw.

[0010] In some of the embodiments, in order to ensure that the lifting assembly can be stably assembled and operated on the linear transfer assembly and ensure that the lifting assembly can drive the commutation assembly to lift stably, the following technical solutions are provided.

[0011] A horizontally arranged assembly backing plate is fixedly connected to the sliding assembly seat. The assembly backing plate is perpendicular to the guide groove. The lifting assembly includes a first L-shaped bracket, a telescopic cylinder, and a guide shaft. A vertically arranged guide shaft is fixedly connected to the first L-shaped bracket. The guide shaft is slidably inserted into the assembly backing plate. The telescopic cylinder is fixedly installed on the assembly backing plate, and the movable end of the telescopic cylinder is fixedly connected to the transverse section of the first L-shaped bracket.

[0012] In some of the embodiments, in order to ensure that the commutation assembly can be stably assembled and operated on the lifting assembly and ensure that there is no spatial movement interference between the commutation assembly and the lifting assembly during operation, the following technical solutions are provided.

[0013] The commutation assembly includes a second L-shaped bracket, a driving motor B, and a matching combination of a worm gear A and a worm A. A rotating seat is fixedly connected to one end of the second L-shaped bracket. The rotating seat is rotatably installed on the longitudinal section of the first L-shaped bracket. The mounting shaft is rotatably installed at the other end of the second L-shaped bracket. The driving motor B is fixedly installed on the longitudinal section of the first L-shaped bracket, and a worm A is fixedly connected to the output shaft of the driving motor B. The worm gear A is fixedly installed on the rotating seat.

[0014] In some of the implementations, in order to achieve the control of the installation shaft, the positioning plate and the assembled tool holder and the tool head in the tool changing assembly to change positions, the following technical solutions are provided.

[0015] The tool changing assembly also includes a driving motor C and a matching combination of a worm wheel B and a worm B. The driving motor C is fixedly mounted on the second L-shaped bracket, and a worm B is fixedly connected to the output shaft of the driving motor C. The worm wheel B is coaxially fixedly connected to the mounting shaft.

[0016] In some of the implementations, in order to ensure that the wedge-shaped key can be driven by the electromagnetic lock to achieve precise cooperation with the wedge-shaped slot, and thus effectively fix the tool holder to the U-shaped slot, the following technical solutions are provided.

[0017] A guide through hole is opened on the side wall of the U-shaped slot, the wedge-shaped key is slidably assembled in the guide through hole, the electromagnetic lock is fixedly installed on the outer side of the positioning plate, and the movable end of the electromagnetic lock is fixedly connected to the outer end of the wedge-shaped key.

[0018] Beneficial effects of the utility model:

[0019] 1. Simplify the tool changing process:

[0020] The combined design of the linear transfer component, the lifting component, the reversing component, and the tool changing component makes the action during the tool changing process more concise. This design reduces the complex operation steps between the tool magazine and the spindle box, thereby reducing the risk of failure and improving the accuracy of tool changing.

[0021] 2. Improve tool change stability:

[0022] The use of guide grooves, adjusting screws, telescopic cylinders, guide shafts and other structures ensures the stability of the tool holder and tool head during the transfer process between the spindle box and the tool magazine. The synergy of these components effectively prevents the tool from shaking or falling off during the transfer process, ensuring the smooth progress of the tool change process.

[0023] 3. Reduce unnecessary movements:

[0024] Through reasonable structural design, redundant action steps in the traditional tool changing mechanism are avoided. The optimized tool changing mechanism reduces the complexity of the system, not only improves the tool changing efficiency, but also reduces the failure rate caused by redundant actions.

[0025] 4. Improve tool changing efficiency:

[0026] The design of the tool change assembly makes the tool change process more efficient and shortens the tool change time. Through the optimized combination of the two key actions of linear transfer and lifting, the entire tool change process becomes smoother and faster, thereby improving the overall production efficiency of the equipment.

[0027] In summary, through the innovative design of the tool changing mechanism, the solution of this application overcomes many deficiencies in the prior art, simplifies the tool changing process, improves stability, reduces redundant actions, and enhances the tool changing efficiency, with significant practical value and popularization prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a schematic structural diagram of the present utility model;

[0029] Figure 2 is a schematic structural diagram of the linear transfer component;

[0030] Figure 3 is a schematic structural diagram of the combined supporting structure of the lifting component, the commutation component, and the tool changing component;

[0031] Figure 4 is a schematic structural diagram of the combined supporting structure of the tool changing component and the commutation component;

[0032] Figure 5 is a schematic structural diagram of the tool changing component;

[0033] Figure 6 is a schematic structural diagram of the combined supporting structure of the tool holder and the electromagnetic lock.

[0034] In the figure: 1 linear transfer component, 11 assembly base, 12 guide groove, 13 drive motor A, 14 adjustment lead screw, 15 sliding assembly seat, 16 assembly backing plate, 2 lifting component, 21 first L-shaped bracket, 22 telescopic cylinder, 23 guide shaft, 3 commutation component, 31 second L-shaped bracket, 311 rotating seat, 32 drive motor B, 33 worm gear A, 34 worm A, 4 tool changing component, 41 mounting shaft, 42 positioning plate, 421 U-shaped card slot, 43 electromagnetic lock, 431 wedge-shaped key, 44 drive motor C, 45 worm gear B, 46 worm B, 51 tool holder, 511 annular positioning groove, 512 wedge-shaped card slot, 52 tool bit. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] The technical solutions in the embodiments of the present utility model will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present utility model.

[0036] Please refer to Figure 1-6 , a tool changing mechanism of a machining center, including a combined supporting linear transfer component 1, a lifting component 2, a commutation component 3, and a tool changing component 4. The linear transfer component 1 is arranged between the tool magazine and the spindle box of the machining center. The lifting component 2 is assembled on the moving part of the linear transfer component 1. The commutation component 3 is assembled on the moving part of the lifting component 2. The tool changing component 4 is assembled on the moving part of the commutation component 3.

[0037] The tool changing assembly 4 includes a mounting shaft 41, a positioning plate 42, and an electromagnetic lock 43. The mounting shaft 41 is rotatably mounted on the movable part of the commutation assembly 3. The mounting shaft 41 is fixedly connected to the center of the positioning plate 42. U-shaped card slots 421 for fixing the tool holder 51 are provided on both sides of the positioning plate 42. A tool head 52 is fixedly assembled on the tool holder 51. An annular positioning groove 511 nested and fitted with the U-shaped card slot 421 is provided on the outer wall of the tool holder 51. A wedge-shaped card slot 512 is provided in the annular positioning groove 511. Electromagnetic locks 43 are assembled on both sides of the U-shaped card slot 421. A wedge-shaped key 431 nested and fitted with the wedge-shaped card slot 512 is assembled on the electromagnetic lock 43.

[0038] The linear transfer assembly 1 can drive the lifting assembly 2, the commutation assembly 3, and the tool changing assembly 4 to transfer between the tool magazine and the spindle box of the machining center. The lifting assembly 2, the commutation assembly 3, and the tool changing assembly 4 cooperate to operate, and can assemble the tool holder 51 equipped with a specific tool head 52 in the tool magazine into the vacant U-shaped card slot 421, and fix it through the electromagnetic lock 43 and the wedge-shaped key 431, and assemble the tool holder 51 removed from the spindle box and assembled in the U-shaped card slot 421 to a specific position in the tool magazine. It can also remove the tool holder 51 assembled on the spindle box and assemble it into the vacant U-shaped card slot 421, and assemble the tool holder 51 taken out from the tool magazine and assembled in the U-shaped card slot 421 onto the spindle box.

[0039] When the mounting shaft 41 in the tool changing assembly 4 operates, it can drive the positioning plate 42 to rotate around the mounting shaft 41, and then replace the positions of the two groups of U-shaped card slots 421 on the positioning plate 42 and the tool holders 51 assembled therein, so as to replace or pick up and place the tool holder 51 in the tool magazine or the spindle box.

[0040] The commutation assembly 3 can adjust the posture of the tool changing assembly 4 to turn the positioning plate 42 to a horizontal state or a vertical state, so that the U-shaped card slot 421 on the positioning plate 42 can effectively cooperate with the spindle box or the tool magazine to realize the picking up, placing, and replacing operations of the tool holder 51.

[0041] Provide an embodiment. The tool holders 51 and tool heads 52 loaded in the tool magazine are arranged in the horizontal direction, the axis of the spindle box is arranged in the vertical direction, and the commutation assembly 3 can drive the tool changing assembly 4 and the tool holders 51 and tool heads 52 assembled thereon to turn to a horizontal state or a vertical state, so that the tool holder 51 is docked with the tool magazine or the spindle box.

[0042] The lifting assembly 2 can drive the commutation assembly 3, the tool changing assembly 4, and the tool holders 51 and tool heads 52 assembled thereon to perform lifting operations as a whole, thereby realizing the nested insertion of the U-shaped card slot 421 on the positioning plate 42 in the tool changing assembly 4 and the annular positioning groove 511 in the tool holder 51, or realizing the fixed assembly of the tool holder 51 on the spindle box.

[0043] To ensure the stable assembly of the linear transfer component 1 in the machining center and ensure that the linear transfer component 1 drives the lifting component 2 to move stably in a straight line, the following technical solutions are provided.

[0044] The linear transfer component 1 includes an assembly base 11, a guide groove 12, a drive motor A 13, an adjustment lead screw 14, and a sliding assembly seat 15. The guide groove 12 and the drive motor A 13 are both fixedly installed on the assembly base 11. The adjustment lead screw 14 is rotatably installed in the guide groove 12 and fixedly connected to the output shaft of the drive motor A 13. The sliding assembly seat 15 is slidably installed in the guide groove 12 and is threadedly connected to the adjustment lead screw 14.

[0045] The assembly base 11 is fixedly installed in the machining center. The guide groove 12 is arranged between the tool magazine and the spindle box. The setting of the guide groove 12 can ensure the stable operation of the sliding assembly seat 15 along the straight line where the guide groove 12 is located. During the operation of the drive motor A 13 and the drive of the adjustment lead screw 14, the sliding assembly seat 15 can be driven to operate stably between the tool magazine and the spindle box, thereby realizing the transfer of the tool holder 51 and the tool between the tool magazine and the spindle box.

[0046] To ensure the stable assembly and operation of the lifting component 2 on the linear transfer component 1 and ensure that the lifting component 2 can drive the commutation component 3 to lift stably, the following technical solutions are provided.

[0047] A horizontally arranged assembly backing plate 16 is fixedly connected to the sliding assembly seat 15, and the assembly backing plate 16 is perpendicular to the guide groove 12; the lifting component 2 includes a first L-shaped bracket 21, a telescopic cylinder 22, and a guide shaft 23. A vertically arranged guide shaft 23 is fixedly connected to the first L-shaped bracket 21. The guide shaft 23 is slidably inserted into the assembly backing plate 16. The telescopic cylinder 22 is fixedly installed on the assembly backing plate 16, and the movable end of the telescopic cylinder 22 is fixedly connected to the horizontal section of the first L-shaped bracket 21.

[0048] The sliding insertion of the guide shaft 23 into the assembly backing plate 16 on the sliding assembly seat 15 can ensure the stable lifting of the first L-shaped bracket 21 in the vertical direction. During the telescopic movement of the telescopic cylinder 22, the first L-shaped bracket 21 can be driven to move up and down in the vertical direction. The setting of the first L-shaped bracket 21 can ensure the stable assembly of the commutation component 3 and the tool changing component 4 and ensure that there is no spatial movement interference between the commutation component 3 and the tool changing component 4 and the lifting component 2 during operation.

[0049] To ensure the stable assembly and operation of the commutation component 3 on the lifting component 2 and ensure that there is no spatial movement interference between the commutation component 3 and the lifting component 2 during operation, the following technical solutions are provided.

[0050] The commutation assembly 3 includes a second L-shaped bracket 31, a driving motor B32, and a matching combination of a worm gear A33 and a worm A34. One end of the second L-shaped bracket 31 is fixedly connected with a rotating seat 311, and the rotating seat 311 is rotatably installed on the longitudinal section of the first L-shaped bracket 21. The other end of the second L-shaped bracket 31 is rotatably installed with a mounting shaft 41. The driving motor B32 is fixedly installed on the longitudinal section of the first L-shaped bracket 21, and the worm A34 is fixedly connected to the output shaft of the driving motor B32. The worm gear A33 is fixedly installed on the rotating seat 311.

[0051] The size of the second L-shaped bracket 31 is smaller than that of the first L-shaped bracket 21, so that the second L-shaped bracket 31 can operate stably inside the first L-shaped bracket 21. When the driving motor B32 drives the worm A34 to operate, it can drive the worm gear A33 to operate stably, and then drive the rotating seat 311 and the second L-shaped bracket 31 to rotate stably around the axis where the rotating seat 311 is located, so as to realize the stable flipping of the tool changing assembly 4 assembled on the second L-shaped bracket 31, and further realize the attitude adjustment of the tool holder 51 and the tool head 52 assembled on the tool changing assembly 4.

[0052] In order to realize the position swapping of the mounting shaft 41, the positioning plate 42, and the assembled tool holder 51 and tool head 52 in the tool changing assembly 4, the following technical solutions are provided.

[0053] The tool changing assembly 4 further includes a driving motor C44 and a matching combination of a worm gear B45 and a worm B46. The driving motor C44 is fixedly installed on the second L-shaped bracket 31, and the worm B46 is fixedly connected to the output shaft of the driving motor C44. The worm gear B45 is fixedly connected coaxially with the mounting shaft 41.

[0054] Due to the settings of the first L-shaped bracket 21 and the second L-shaped bracket 31, during the operation of the two and the operation of the tool changing assembly 4, the spatial movement interference of the mounting shaft 41, the positioning plate 42, the first L-shaped bracket 21, and the second L-shaped bracket 31 can always be avoided, ensuring the stable operation of each component to achieve its designed function.

[0055] When the driving motor C44 drives the worm B46 to operate, it can drive the worm gear B45 to operate, and then drive the mounting shaft 41 and the positioning plate 42 to rotate stably, so as to realize the position swapping operation of the two U-shaped card slots 421 on the positioning plate 42 and the tool holder 51 assembled therein.

[0056] Due to the structural characteristics of the worm and the worm gear, which have the effects of speed reduction and torque increase and self-locking, when the worm transmits power to the worm gear, it can reduce the operating speed at the worm gear end and increase the torque to drive the reversing assembly 3 or the tool changing assembly 4 to operate stably to achieve attitude adjustment. Moreover, the power of the worm can only be transmitted unidirectionally to the worm gear. When the power transmission stops at the worm end, the worm gear is in a locked state, which can ensure the stability of the states of the reversing assembly 3 and the tool changing assembly 4 themselves.

[0057] To ensure that the wedge-shaped key 431 can be driven by the electromagnetic lock 43 to achieve precise cooperation with the wedge-shaped slot 512, and further to effectively fix the tool holder 51 into the U-shaped slot 421, the following technical solutions are provided.

[0058] A guiding through hole is provided in the side wall position of the U-shaped slot 421. The wedge-shaped key 431 is slidably assembled in the guiding through hole. The electromagnetic lock 43 is fixedly installed on the outer side of the positioning plate 42, and the movable end of the electromagnetic lock 43 is fixedly connected to the outer side end of the wedge-shaped key 431.

[0059] The setting of the guiding through hole can ensure that the wedge-shaped key 431 can slide stably along a straight line. When the wedge-shaped key 431 is driven by the electromagnetic lock 43 to retract and extend in the U-shaped slot 421, the wedge-shaped key 431 and the wedge-shaped slot 512 can be effectively combined within a certain range of assembly errors to effectively fix the tool holder 51.

[0060] For those skilled in the art, it is obvious that the present utility model is not limited to the details of the above-described exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic characteristics of the present utility model. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present utility model is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present utility model. Any reference signs in the claims should not be regarded as limiting the claimed rights.

[0061] In addition, it should be understood that although this specification is described in terms of embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A tool changing mechanism for a machining center, characterized in that: It includes a matching and combined linear transfer component (1), a lifting component (2), a commutation component (3), and a tool changing component (4). The linear transfer component (1) is arranged between the tool magazine and the spindle box of the machining center. The lifting component (2) is assembled on the moving part of the linear transfer component (1). The commutation component (3) is assembled on the moving part of the lifting component (2). The tool changing component (4) is assembled on the moving part of the commutation component (3). The tool changing component (4) includes a mounting shaft (41), a positioning plate (42), and an electromagnetic chuck (43). The mounting shaft (41) is rotatably installed on the moving part of the commutation component (3). The mounting shaft (41) is fixedly connected to the center of the positioning plate (42). U-shaped card slots (421) for fixing the tool holder (51) are formed on both sides of the positioning plate (42). A tool head (52) is fixedly assembled on the tool holder (51). An annular positioning groove (511) nested and fitted with the U-shaped card slot (421) is formed on the outer wall of the tool holder (51). A wedge-shaped card slot (512) is formed in the annular positioning groove (511). Electromagnetic chucks (43) are assembled on both sides of the U-shaped card slot (421). A wedge-shaped key (431) nested and fitted with the wedge-shaped card slot (512) is assembled on the electromagnetic chuck (43).

2. The tool changing mechanism of a machining center according to claim 1, wherein: The linear transfer component (1) includes an assembly base (11), a guide groove (12), a driving motor A (13), an adjusting lead screw (14), and a sliding assembly seat (15). The guide groove (12) and the driving motor A (13) are both fixedly installed on the assembly base (11). The adjusting lead screw (14) is rotatably installed in the guide groove (12) and fixedly connected to the output shaft of the driving motor A (13). The sliding assembly seat (15) is slidably installed in the guide groove (12) and is threadedly connected to the adjusting lead screw (14).

3. The tool changing mechanism of a machining center according to claim 2, characterized in that: An assembly backing plate (16) arranged horizontally is fixedly connected to the sliding assembly seat (15). The assembly backing plate (16) is perpendicular to the guide groove (12). The lifting component (2) includes a first L-shaped bracket (21), a telescopic cylinder (22), and a guide shaft (23). A vertically arranged guide shaft (23) is fixedly connected to the first L-shaped bracket (21). The guide shaft (23) is slidably inserted into the assembly backing plate (16). The telescopic cylinder (22) is fixedly installed on the assembly backing plate (16), and the moving end of the telescopic cylinder (22) is fixedly connected to the horizontal section of the first L-shaped bracket (21).

4. The tool changing mechanism of a machining center according to claim 3, characterized in that: The commutation assembly (3) includes a second L-shaped bracket (31), a drive motor B (32), and a matched combination of a worm gear A (33) and a worm A (34). One end of the second L-shaped bracket (31) is fixedly connected with a rotating seat (311), and the rotating seat (311) is rotatably installed on the longitudinal section of the first L-shaped bracket (21). The other end of the second L-shaped bracket (31) is rotatably installed with the installation shaft (41). The drive motor B (32) is fixedly installed on the longitudinal section of the first L-shaped bracket (21), and a worm A (34) is fixedly connected to the output shaft of the drive motor B (32). The worm gear A (33) is fixedly installed on the rotating seat (311).

5. The tool changing mechanism of a machining center according to claim 4, characterized in that: The tool changing assembly (4) further includes a drive motor C (44) and a matched combination of a worm gear B (45) and a worm B (46). The drive motor C (44) is fixedly installed on the second L-shaped bracket (31), and a worm B (46) is fixedly connected to the output shaft of the drive motor C (44). The worm gear B (45) is fixedly connected coaxially with the installation shaft (41).

6. The tool changing mechanism of a machining center according to claim 1, characterized in that: A guiding through hole is formed in the side wall position of the U-shaped card slot (421). The wedge-shaped key (431) is slidably assembled in the guiding through hole. The electromagnetic lock (43) is fixedly installed on the outer side of the positioning plate (42), and the movable end of the electromagnetic lock (43) is fixedly connected to the outer side end of the wedge-shaped key (431).

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