Pneumatic circuit and control method of the same

Abstract

To provide a pneumatic circuit which enables reduction of a flow rate of compressed air consumed by an air dryer while maintaining functions of a conventional pneumatic circuit, and to provide a control method of the pneumatic circuit.SOLUTION: A pneumatic circuit 1 includes: an air source 2 configured to generate compressed air; and an air dryer 3 capable of removing moisture from the compressed air. At the primary side of the air dyer 3, a first valve 7 is provided in a first passage 4 formed between the air dryer and the air source 2. At the secondary side of the air dryer 3, the passage is divided in two directions at a branch point B. One passage is referred to as a second passage 5 and the other is referred to as a third passage 6. The third passage 6 joins to the second passage 5 at a joint point J. A second valve 10 is provided at the third passage 6. When a spindle rotates, the first valve 7 and the second valve 10 are opened. When the spindle is stopped and purging of the spindle is needed, the first valve 7 is opened and the second valve 10 is closed. When the spindle is stopped and purging of the spindle is not needed, the first valve 7 and the second valve 10 are closed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a pneumatic circuit for supplying compressed air to a device that rotates at high speed, such as a spindle device of a machine tool, and a method for controlling the pneumatic circuit. [Background technology]

[0002] In machine tools, parts that rotate at high speeds, such as the main spindle, use oil-air mixtures (oil and air) to lubricate the bearings, which consumes compressed air. Taking the spindle as an example, a constant flow of compressed air is required for lubrication while rotating. Even when stopped, the bearings and spindle themselves, heated by high-speed rotation, draw in air from the surrounding atmosphere, i.e., the air near the device, as they cool. For this reason, compressed air is sometimes discharged as purge air for at least a certain period of time to prevent dust, chips, and other debris from entering the bearings. Furthermore, to improve spindle reliability, machine tools sometimes use devices such as air dryers, which discharge dry air from the compressed air supplied to ensure the quality of the air used for spindle lubrication. For example, if the air dryer uses a membrane-type dehumidification method, a large amount of compressed air must be used because a purge air flow rate is required to expel the moisture removed from the compressed air. Meanwhile, from the perspectives of energy conservation and decarbonization, there is a demand for reducing the compressed air flow rate used in machine tools.

[0003] Patent Document 1 discloses a pneumatic circuit in which the flow path on the secondary side of the air dryer is branched into two, the flow rate is adjusted, and a valve is installed in each of the two flow paths, making it possible to switch between the two flow paths with different flow rates.As a result, by switching between the two flow paths depending on whether the main shaft is rotating or not, it is possible to suppress the flow rate of compressed air when the main shaft is not rotating. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-229856 Summary of the Invention [Problem to be solved by the invention]

[0005] On the other hand, as mentioned above, when a membrane air dryer is added to the pneumatic circuit of a machine tool to ensure air quality, the membrane air dryer requires a purge air flow rate to release moisture outside the air dryer for dehumidification, regardless of whether or not secondary air is used. Therefore, simply adding an air dryer increases the amount of compressed air consumed, and therefore the amount of electricity consumed and carbon dioxide emissions, in order to improve air quality. Therefore, it has been desired to reduce the amount of compressed air sent to the air dryer in order to achieve energy savings and decarbonization. However, in the pneumatic circuit of Patent Document 1, the only way to reduce the amount of compressed air sent to the air dryer is to stop the compressed air source, and reuse of the air requires a start-up process for the equipment, making it difficult to achieve further energy savings and decarbonization. Therefore, in order to reduce the amount of compressed air consumed while using an air dryer in a machine tool, reducing the amount of purge air in the air dryer can be an issue.

[0006] Therefore, the present disclosure has been made in consideration of the above problems, and aims to provide a pneumatic circuit and a control method for the pneumatic circuit that can reduce the flow rate of compressed air consumed by the air dryer when the rotating shaft is stopped, while maintaining the functionality of conventional pneumatic circuits with a simple circuit configuration. [Means for solving the problem]

[0007] In order to achieve the above object, a first configuration of the present disclosure is a pneumatic circuit comprising an air source that generates compressed air and an air dryer that can remove moisture from the compressed air, through which compressed air circulates for bearing lubrication of a rotating shaft, wherein a first valve is provided on the primary side of the air dryer in a first flow path between the air source and the air dryer, and on the secondary side of the air dryer, the flow path branches into two directions at a branch point, one flow path is a second flow path and the other flow path is a third flow path, the third flow path merges with the second flow path at a junction point, a second valve is provided in the third flow path, and the first valve and the second valve are controlled by a control device. Another aspect of the first configuration of the present disclosure is characterized in that, in the above configuration, the first valve is a switching valve capable of selectively switching between two flow paths, the two flow paths being the first flow path and a fourth flow path that circulates compressed air to a mechanical element other than the mechanical element having the rotating shaft, and on the secondary side of the air dryer, a fifth flow path is a flow path branched from the second flow path or the third flow path at a second branch point that branches into two directions, or a flow path other than the second flow path and the third flow path among the flow paths that branch into three directions at the branch point, and the fifth flow path merges with the fourth flow path at a second junction point and is equipped with a check valve that allows flow from the second branch point to the second junction point. Another aspect of the first configuration of the present disclosure is characterized in that, in the above configuration, the second flow path is provided with a second check valve, and the second branch point is provided on the primary side of the second check valve in the second flow path, or between the air dryer and the second valve. Another aspect of the first configuration of the present disclosure is characterized in that, in the above configuration, when the rotating shaft is rotating, the first flow path is opened and the second valve is opened, and when the rotating shaft is stopped and purging of the rotating shaft is required, the first flow path is opened and the second valve is closed, and when the rotating shaft is stopped and purging of the rotating shaft is not required, the first flow path is closed and the second valve is closed. Yet another aspect of the first configuration of the present disclosure is characterized in that, in the above configuration, the first valve is equipped with a timer that can close the first flow path that is in an open state after a predetermined period of time. In order to achieve the above object, a second configuration of the present disclosure is characterized in that, in a pneumatic circuit including an air source that generates compressed air and an air dryer that can remove moisture from the compressed air, and through which compressed air flows for bearing lubrication of a rotating shaft, a first valve is provided on the primary side of the air dryer in a first flow path between the air source, and on the secondary side of the air dryer, the flow path branches into two directions at a branch point, one flow path is a second flow path and the other flow path is a third flow path, and the third flow path merges with the second flow path at a junction point, a second valve is provided in the third flow path, and the first and second valves are controlled by a control device, so that when the rotating shaft is rotating, the first and second valves are opened, and when the rotating shaft is stopped and purging of the rotating shaft is required, the first valve is opened and the second valve is closed, and when the rotating shaft is stopped and purging of the rotating shaft is not required, both the first and second valves are closed. [Effects of the Invention]

[0008] According to the present disclosure, the first valve and the second valve are automatically controlled by the control device according to the condition of the rotating shaft to which the compressed air is supplied, thereby making it possible to reduce the flow rate of compressed air consumed by the air dryer when the spindle is stopped while maintaining the functionality of the conventional pneumatic circuit. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a schematic diagram illustrating a pneumatic circuit according to the embodiment. [Figure 2] 10 is a table summarizing the behavior of the valve according to the operating status of the spindle device. [Figure 3] FIG. 10 is a schematic diagram showing a modified example of a pneumatic circuit. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of a pneumatic circuit according to an embodiment. As shown in FIG. 1, the pneumatic circuit 1 includes an air source 2 such as a compressor, an air dryer 3, a first flow path 4, a second flow path 5, and a third flow path 6. In the present disclosure, the air dryer 3 is a membrane-type air dryer. The second flow path 5 and the third flow path 6 are provided with check valves C1 and C2, respectively. The check valves C1 and C2 are both installed in a direction that allows flow from upstream to downstream and prevents backflow. The check valve C1 installed in the second flow path 5 is an example of a second check valve in the present disclosure. The pneumatic circuit 1 is connected to the spindle of the machine tool, which serves as the rotating shaft of the present disclosure. Compressed air sent from the pneumatic circuit 1 to the spindle is converted into oil-air by a mixing valve (not shown) provided between the pneumatic circuit 1 and the spindle, and is used to lubricate the spindle bearings. Compressed air is also used as purge air to keep the spindle clean during cooling, without being converted into oil-air.

[0011] The first flow path 4 is on the primary side, i.e., upstream, of the air dryer 3 and refers to a flow path between the air source 2. A normally closed solenoid valve serving as a first valve 7 is provided in the first flow path 4. Therefore, the first valve 7 opens the first flow path 4 when in the ON state. The first valve 7 is also provided with a timer 8 that can be turned on and off. When the timer 8 operates while the first valve 7 is in the on state, the timer 8 causes the first valve 7, i.e., the first flow path 4, to transition to a closed state after a predetermined time has elapsed.

[0012] On the secondary side, i.e., downstream, of the air dryer 3, the flow path branches into two directions at branch point B. One of the branched flow paths is second flow path 5, and the other is third flow path 6. Second flow path 5 is a flow path for circulating compressed air used as purge air. On the other hand, third flow path 6 is a flow path for circulating compressed air that is converted into oil air to lubricate the bearings of the main shaft. The second flow path 5 is provided with a throttle 9 for adjusting the flow rate of the compressed air passing through it. The third flow path 6 is provided with a normally closed solenoid valve serving as a second valve 10. Therefore, the second valve 10 opens the flow path when in the ON state. The second flow path 5 joins with the third flow path 6 at a joining point J, and the flow path beyond this joins with the spindle device.

[0013] Generally, the air flow rate required for spindle bearing lubrication differs from the air flow rate required for air purging. The air flow rate required for spindle bearing lubrication is greater than the air flow rate required for air purging. Therefore, the flow rates of the compressed air flowing through the second flow path 5 and the third flow path 6 must be adjusted to the desired air flow rates. Therefore, the flow rate of the compressed air flowing through the second flow path 5 is adjusted by a throttle 9 provided in the second flow path 5. Note that the air flow rate adjustment may be achieved by using a piping for the third flow path 6 with a larger diameter than that of the second flow path 5. Furthermore, other known air flow rate adjustment methods may be used as long as they can adjust the compressed air flowing through the second flow path 5 and the third flow path 6 to the desired air flow rates.

[0014] The first valve 7, the second valve 10, the timer 8, and the spindle device are electrically connected to an NC device as a control device. Therefore, the first valve 7, the second valve 10, the timer 8, and the spindle device are automatically controlled based on commands from the NC device. The NC device includes a CPU and a memory connected to the CPU, and realizes its operation by using these.

[0015] The following describes a method for controlling the air pressure circuit 1. Figure 2 is a table summarizing the behavior of the valves according to the operating status of the spindle device. When the spindle unit is rotating, the first valve 7 and the second valve 10 are turned on based on a command from the NC unit. That is, compressed air is allowed to flow through the first flow path 4, the second flow path 5, and the third flow path 6. This makes it possible to send compressed air required for lubricating the spindle bearings to the spindle unit.

[0016] Next, for example, when the spindle unit is hot due to factors such as heat generated by the rotation of the spindle and heat generated by friction between the workpiece and the tool attached to the spindle, such as immediately after a machine tool has completed machining a workpiece, only purge air is required to keep the spindle unit clean. Therefore, based on a command from the NC unit, the first valve 7 is turned on and the second valve 10 is closed. In other words, compressed air is allowed to flow through the first flow path 4 and the second flow path 5. This ensures that only the amount of compressed air required as purge air is sent to the spindle unit. This effectively reduces the compressed air flow rate during non-machining periods.

[0017] Furthermore, when the spindle rotation has completely stopped and the spindle device has cooled sufficiently, there is no need to send compressed air to the spindle device, either for lubricating the spindle bearings or as purge air. Therefore, based on a command from the NC device, the first valve 7 and the second valve 10 are closed. When the first valve 7 is closed, the supply of compressed air to the air dryer 3 is stopped, and no purge air is generated to release moisture outside the air dryer 3. This effectively reduces the flow rate of compressed air used as purge air in the air dryer 3.

[0018] If the timer 8 is programmed in advance to start when the spindle device stops, the first valve 7 will automatically close after a predetermined time has elapsed. Therefore, even if the process of closing the first valve 7 after the spindle device stops is not performed, unnecessary air consumption can be automatically and effectively reduced.

[0019] The pneumatic circuit 1 having the above configuration includes an air source 2 that generates compressed air and an air dryer 3 that can remove moisture from the compressed air. On the primary side of the air dryer 3, a first valve 7 is provided in a first flow path 4 between the air source 2 and the air dryer 3. On the secondary side of the air dryer 3, the flow path branches into two directions at a branch point B, one flow path being a second flow path 5 and the other flow path being a third flow path 6. The third flow path 6 merges with the second flow path 5 at a junction J. A second valve 10 is provided in the third flow path 6. The first valve 7 and the second valve 10 are controlled by an NC device. When the spindle is rotating, the first valve 7 and the second valve 10 are opened. When the spindle is stopped and spindle purging is required, the first valve 7 is opened and the second valve 10 is closed. When the spindle is stopped and spindle purging is not required, the first valve 7 and the second valve 10 are both closed.

[0020] Therefore, by automatically controlling the first valve 7 and the second valve 10 by the NC device in accordance with the condition of the spindle to which compressed air is supplied, it is possible to reduce the flow rate of compressed air consumed by the air dryer 3 when the spindle is stopped while maintaining the functionality of the conventional pneumatic circuit.

[0021] The configurations of the pneumatic circuit and the control method thereof of the present disclosure are not limited to the aspects described in the above embodiments, and can be modified as needed without departing from the spirit of the invention. For example, the first valve and the second valve are not limited to solenoid valves as long as they can close the first flow path and the third flow path. Furthermore, the control device's commands to the first valve and the second valve may be based on information related to the rotation of the spindle obtained by the control device, or may be based on commands sent from the control device to the spindle device. Furthermore, the timer may be a physical device or a program stored in a control device.

[0022] Modifications of the present disclosure will be described below. 3 is a schematic diagram showing the configuration of a pneumatic circuit according to a modified example, and a description of the same configuration as in the above-mentioned FIG.

[0023] In the pneumatic circuit 1a of the modified example, as shown in FIG. 3, a three-way switching valve is provided in the first flow path 4 as the first valve 7a. The first valve 7a is connected to a flow path connected to the air source 2, the first flow path 4, and a fourth flow path 11. The fourth flow path 11 is a flow path for circulating compressed air to a position detection device, which is a predetermined mechanical element that uses compressed air. When the first valve 7a is in the ON state, it opens the first flow path 4 and closes the fourth flow path 11. When the first valve 7a is in the OFF state, it closes the first flow path 4 and opens the fourth flow path 11. That is, when the first valve 7a is in the OFF state, compressed air sent from the air source 2 flows only through the fourth flow path 11. The switching valve is not limited to a three-way valve as long as it can switch the flow path. Furthermore, the predetermined mechanical element that uses compressed air is not limited to a position detection device.

[0024] The first flow path 4 branches into two directions at a second branch point B' provided upstream of the branch point B, and the flow path branching from the first flow path 4 is a fifth flow path 12. The fifth flow path 12 is a flow path that circulates a portion of the clean compressed air filtered by the air dryer 3 for purposes other than lubricating the bearings of the main shaft, i.e., for purging the position detection device. Fifth flow path 12 merges with fourth flow path 11 at a second junction J', and the fourth flow path 11, which merges with fifth flow path 12, is ultimately connected to a position detection device that uses clean compressed air. Fifth flow path 12 also includes a check valve C3. Check valve C3 is installed in a direction that allows flow from upstream to downstream and prevents backflow.

[0025] Note that downstream of the second junction J', the fourth flow path 11 may branch into a plurality of paths and be connected to a plurality of machine elements that use compressed air. Furthermore, the second branch point B' may be provided downstream of the branch point B, i.e., in the second flow path 5 and the third flow path 6. Alternatively, the branch point B may also serve as the second branch point B', and the flow path may branch at the branch point B into three directions: the second flow path 5, the third flow path 6, and the fifth flow path 12. However, the second branch point B' is preferably provided on the primary side of the second check valve C1 in the second flow path 5, or between the air dryer 3 and the second valve 10. By locating the second branch point B' upstream of the second check valve C1 and the second valve 10, the second check valve C1 and / or the second valve 10 can prevent foreign matter from flowing back from the spindle device side, thereby reducing the occurrence of malfunctions caused by the intrusion of foreign matter in certain mechanical elements that use compressed air.

[0026] A method for controlling the air pressure circuit 1a will be described below. When the spindle unit is rotating, the first valve 7a and the second valve 10 are turned on based on a command from the NC unit. That is, compressed air is allowed to flow through the first flow path 4, the second flow path 5, the third flow path 6, and the fifth flow path 12. This allows compressed air purified by the air dryer 3 to be sent to the spindle unit, and also to the position detection device.

[0027] Next, when machining is not in progress but only purge air is needed to keep the spindle unit clean, the first valve 7a is turned on and the second valve 10 is closed based on a command from the NC device. That is, compressed air is allowed to flow through the first flow path 4, the second flow path 5, and the fifth flow path 12. This allows clean compressed air to be used by the position detection device while ensuring that only compressed air with the required flow rate as purge air is sent to the spindle unit.

[0028] Furthermore, when the spindle rotation is completely stopped and the spindle device is sufficiently cooled, there is no need to send compressed air to the spindle device for spindle bearing lubrication or purge air. However, if compressed air is to be used in the position detection device, the first valve 7a is turned OFF and the second valve 10 is closed based on a command from the NC device. In other words, compressed air flows only through the fourth flow path 11. Therefore, compressed air can be used in the position detection device. Furthermore, the check valve C3 in the fifth flow path 12 prevents compressed air from flowing back through the fifth flow path 12 from the junction J' toward the branch point B'. Therefore, compressed air that has not passed through the air dryer 3, i.e., unpurified, does not flow into the secondary flow path of the air dryer 3. On the other hand, turning the first valve 7a OFF stops the supply of compressed air to the air dryer 3, and therefore purge air is not generated to release moisture outside the air dryer 3. Therefore, the flow rate of the compressed air used as purge air in the air dryer 3 can be effectively reduced.

[0029] For example, adding a solenoid valve to the pneumatic circuit 1 described above to create flow paths corresponding to the fourth and fifth flow paths 11 and 12 in the pneumatic circuit 1a would achieve the same effect as the pneumatic circuit 1a. However, adding a solenoid valve increases costs. In contrast, as described above, the pneumatic circuit 1a uses a three-way valve for the first valve 7a. This reduces the compressed air flow rate by eliminating the need for purge air to expel moisture from the air dryer 3, while avoiding cost increases. Furthermore, it allows for the use of clean compressed air filtered by the air dryer 3 in certain mechanical components that use compressed air, such as position detection devices. In the case of a position detection device, purging compressed air to increase internal pressure prevents the intrusion of foreign matter, such as cutting chips and oil, from the outside. In a position detection device, the compressed air used to increase internal pressure does not necessarily need to pass through the air dryer 3. However, considering the impact of the cleanliness of the position detection device's interior on detection accuracy, using clean compressed air can improve the reliability of the scale. In this way, by using clean compressed air in certain machine elements that use compressed air, such as position detection devices, the reliability of the entire machine can be improved. [Explanation of symbols]

[0030] 1,1a··Air pressure circuit, 2··Air source, 3··Air dryer, 4··First flow path, 5··Second flow path, 6··Third flow path, 7,7a··First valve, 8··Timer, 10··Second valve, 11··Fourth flow path, 12··Fifth flow path, B,B'··Branch point, C1,C3··Check valve, C2··Second check valve, J,J'··Confluence point.

Claims

1. A pneumatic circuit including an air source that generates compressed air and an air dryer that can remove moisture from the compressed air, and through which compressed air flows for lubricating bearings of a rotating shaft, a first valve is provided in a first flow path between the primary side of the air dryer and the air source; On the secondary side of the air dryer, the flow path branches into two directions at a branch point, one of the flow paths is a second flow path and the other flow path is a third flow path, and the third flow path merges with the second flow path at a junction point, a second valve is provided in the third flow path; The pneumatic circuit is characterized in that the first valve and the second valve are controlled by a control device.

2. the first valve is a switching valve that can selectively switch between two flow paths, the two flow paths are the first flow path and a fourth flow path that distributes the compressed air to a mechanical element other than a mechanical element including the rotating shaft, On the secondary side of the air dryer, a flow path branched from the second flow path or the third flow path at a second branch point branching in two directions, or a flow path other than the second flow path and the third flow path among the flow paths branched in three directions at the branch point, is defined as a fifth flow path, 2. The pneumatic circuit according to claim 1, wherein the fifth flow path merges with the fourth flow path at a second junction point, and includes a check valve that allows flow from the second junction point to the second junction point.

3. the second flow path includes a second check valve; The pneumatic device according to claim 2, wherein the second branch point is provided on the primary side of the second check valve in the second flow path or between the air dryer and the second valve.

4. When the rotary shaft rotates, the first flow path is opened and the second valve is opened, When the rotating shaft is stopped and purging of the rotating shaft is required, the first flow path is opened and the second valve is closed; 4. The pneumatic circuit according to claim 1, wherein when the rotating shaft is stopped and purging of the rotating shaft is not required, the first flow path is closed and the second valve is closed.

5. 4. The pneumatic circuit according to claim 1, wherein the first valve includes a timer that can close the first flow path that is in an open state after a predetermined time.

6. 5. The pneumatic circuit according to claim 4, wherein the first valve includes a timer that can close the first flow path that is in an open state after a predetermined time.

7. 1. A pneumatic circuit comprising an air source that generates compressed air and an air dryer that can remove moisture from the compressed air, and through which compressed air flows for lubricating bearings of a rotating shaft, a first valve is provided in a first flow path between the primary side of the air dryer and the air source; On the secondary side of the air dryer, the flow path branches into two directions at a branch point, one of the flow paths is a second flow path and the other flow path is a third flow path, and the third flow path merges with the second flow path at a junction point, a second valve is provided in the third flow path; The first valve and the second valve are controlled by a control device; When the rotary shaft rotates, the first valve and the second valve are opened; When the rotating shaft is stopped and purging of the rotating shaft is required, the first valve is opened and the second valve is closed; a pneumatic circuit control method comprising: closing both the first valve and the second valve when the rotating shaft is stopped and purging of the rotating shaft is not required;

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