Numerical control device

Abstract

Provided is a numerical control device 30 that achieves both responsiveness and suppression of vibrations due to noise simultaneously. A drive mechanism 20 is provided with a drive shaft 23 that supports a machining head 12. A numerical control device 30 is provided with: a distance acquisition unit 32 that acquires a machining surface distance from a distance detection unit 16; a distance control unit 42 that creates a movement command for the drive shaft 23 to set the machining surface distance to a preset distance; a drive shaft control unit 44 that drives the drive shaft 23; a drive shaft position acquisition unit 38; a distance change amount calculation unit 34 that calculates an amount of change in machining surface distance from the difference between the current machining surface distance and the machining surface distance one control cycle before; a drive shaft position change amount calculation unit 40 that calculates an amount of change in shaft position from the difference between the current shaft position and the shaft position one control cycle before; and a filter unit 36 that calculates the machining surface distance when sensor noise is suppressed by filtering. The strength of the filtering with respect to amounts of change in machining surface distance is stronger than the strength of the filtering with respect to amounts of change in shaft position.

Description

Numerical Control Device

[0001] The present disclosure relates to a numerical control device that controls a machining device.

[0002] There is a processing apparatus that performs laser processing on a processing surface of a workpiece by irradiating the processing surface with a laser from a processing head. An example of controlling the distance from the processing head to the workpiece in the processing apparatus is tracking control. Patent Document 1 discloses a technology for controlling the position of the processing head in the laser processing apparatus.

[0003] Japanese Patent Application Laid-Open No. 2006-122939

[0004] The distance from the machining head to the workpiece is detected by a sensor. The detected distance is input to a numerical control device. The numerical control device is a device that controls the movement of the machining head.

[0005] In tracking control, it is necessary to accurately detect the distance from the machining head to the workpiece. When the distance from the machining head to the workpiece is detected by a sensor, the detected value may fluctuate due to noise. One technique for reducing the value fluctuation due to noise is to process the detected value with a first-order lag filter in a numerical control device.

[0006] When using a first-order lag filter to reduce noise, it is difficult to achieve both responsiveness and suppression of vibrations caused by noise. If the time constant of the first-order lag filter is small, responsiveness is good but suppression of vibrations caused by noise is insufficient. If the time constant of the first-order lag filter is large, suppression of vibrations caused by noise is sufficient but responsiveness is poor.

[0007] Therefore, an object of the present disclosure is to provide a numerical control device that can achieve both responsiveness and suppression of vibrations caused by noise.

[0008] The numerical control device of the present disclosure is a numerical control device that controls a machining device, the machining device comprising: a machining head that machines a workpiece; a drive mechanism that moves the machining head and the workpiece relatively; and a distance detection unit that detects the distance from the machining head to the machining surface of the workpiece with a sensor, the drive mechanism comprising a drive shaft that supports the machining head. The numerical control device comprises: a distance acquisition unit that acquires the machining surface distance from the distance detection unit when the distance from the machining head to the machining surface of the workpiece is defined as the machining surface distance; and a distance control unit that creates a movement command for the drive shaft so that the machining surface distance becomes a preset distance. The system includes a drive axis control unit that drives the drive axis, a drive axis position acquisition unit that acquires the position of the drive axis, a distance change amount calculation unit that calculates a change amount of the machining surface distance from the difference between the current machining surface distance and the machining surface distance one control cycle ago, a drive axis position change amount calculation unit that calculates a change amount of the axis position from the difference between the current axis position and the axis position one control cycle ago when the position of the drive axis is taken as the axis position, and a filter unit that calculates the machining surface distance with noise of the sensor suppressed by filtering, wherein the strength of the filtering process for the change amount of the machining surface distance is stronger than the strength of the filtering process for the change amount of the axis position.

[0009] According to the numerical control device of the present disclosure, it is possible to provide a numerical control device that can achieve both responsiveness and suppression of vibrations caused by noise.

[0010] 1 is a configuration diagram of a machining system according to the present disclosure; 2 is a functional block diagram of the machining system; 3 is a diagram showing the positional relationship between a machining head and a workpiece; 4 is a graph showing the machining surface distance detected by a distance detection unit, filter output, etc.; 5 is a graph showing the conventional relationship between responsiveness and noise suppression;

[0011] An embodiment of the present disclosure will be described with reference to the drawings. Fig. 1 is a configuration diagram of a machining system 1 of the present disclosure. The machining system 1 includes a machining device 10 and a numerical control device 30. The machining device 10 is a device that processes a workpiece 18 using a laser or the like. The numerical control device 30 is a device that controls the machining device 10.

[0012] The processing device 10 includes a processing head 12 and a drive mechanism 20. The processing head 12 is a part that irradiates a laser onto a workpiece 18. The processing head 12 processes the workpiece 18 by irradiating the laser. Examples of the processing head 12 are a laser head and a cutting processing head. The cutting processing head is a head equipped with a rotary tool.

[0013] The intensity of the laser emitted by the machining head 12 and the torque of the rotary tool of the machining head 12 are called the output of the machining head 12. The output of the machining head 12 is adjusted by the numerical control device 30.

[0014] A distance detection unit 16 is disposed in the machining head 12. The distance detection unit 16 is a part that detects the distance from the machining head 12 to the workpiece 18. More specifically, the distance detection unit 16 detects the distance from the machining surface 19 of the workpiece 18 to the tip 13 of the machining head 12. The distance from the machining head 12 to the machining surface 19 of the workpiece 18 is called the machining surface distance.

[0015] The distance detection unit 16 detects the machining surface distance using a sensor, examples of which include a capacitance sensor, a laser sensor, and an ultrasonic sensor.

[0016] The machining surface distance can be detected with high accuracy by disposing the distance detection unit 16 in the machining head 11. However, the position where the distance detection unit 16 is disposed is not limited to the machining head 12.

[0017] The distance detection unit 16 detects the machining surface distance at predetermined intervals.

[0018] The drive mechanism 20 is a mechanism for relatively moving the machining head 12 and the workpiece 18. The drive mechanism 20 includes a machining head drive mechanism 22 and a workpiece drive mechanism 24.

[0019] The machining head drive mechanism 22 is a mechanism that moves the machining head 12. The machining head drive mechanism 22 includes a drive shaft 23. The machining head drive mechanism 22 moves the machining head 12 by moving the drive shaft 23. The position of the drive shaft 23 is called the axis position.

[0020] The workpiece driving mechanism 24 is a mechanism that moves the workpiece 18. The workpiece driving mechanism 24 includes a workpiece holding unit 26. The workpiece holding unit 26 is a portion that holds the workpiece 18. The workpiece holding unit 26 includes a table and a chuck. The workpiece 18 is held by the workpiece holding unit 26.

[0021] The workpiece driving mechanism 24 rotates the workpiece 18. The center of rotation in the rotational movement is a workpiece rotation axis 28. When the workpiece 18 rotates, the workpiece holding portion 26 rotates together with the workpiece 18.

[0022] The numerical control device 30 is a device that controls the machining device 10. The numerical control device 30 includes a distance acquisition unit 32, a distance change amount calculation unit 34, a filter unit 36, a drive axis position acquisition unit 38, a drive axis position change amount calculation unit 40, a distance control unit 42, and a drive axis control unit 44.

[0023] The function of the numerical control device 30 will be described with reference to Fig. 2. Fig. 2 is a functional block diagram of the machining system 1.

[0024] The distance acquisition unit 32 is a part that acquires the machining surface distance from the distance detection unit 16 of the machining device 10. The machining surface distance is detected by the distance detection unit 16.

[0025] The drive axis position acquisition unit 38 is a part that acquires the position of the drive axis 23. The drive axis 23 is shown in FIG. 1. The position of the drive axis 23 is determined from at least one of the contents of a movement command to the drive axis 23 and the result of detecting the position of the drive axis 23 using a sensor or the like. An example of the contents of the movement command is a position command in numerical control that is input to the machining head drive mechanism 22. An example of the result of detecting the position of the drive axis 23 is the detection value of an encoder disposed on a motor that changes the position of the drive axis 23. The position of the drive axis 23 is usually detected with higher accuracy than the machining surface distance.

[0026] The drive shaft position acquisition unit 38 acquires the position of the drive shaft 23 at predetermined intervals. The position of the drive shaft 23 is called the shaft position. The cycle at which the drive shaft position acquisition unit 38 acquires the shaft position is equal to the control cycle.

[0027] The distance control unit 42 is a unit that generates a movement command for the drive axis 23. The distance control unit 42 generates a movement command so that the machining surface distance becomes a preset distance.

[0028] The distance control unit 42 generates a movement command at a predetermined cycle. The cycle at which the distance control unit 42 generates a movement command is called a control cycle. The drive axis position acquisition unit 38 acquires the axis positions at each control cycle.

[0029] The drive axis control unit 44 is a part that drives the drive axis 23. The drive axis 23 is shown in FIG. 1. The drive axis control unit 44 drives the drive axis 23 in accordance with a movement command received from the distance control unit 42. The drive axis 23 is driven via the machining head driving mechanism 22 of the machining device 10. The machining head driving mechanism 22 is shown in FIG. 1.

[0030] The numerical control device 30 of this embodiment further includes a distance change amount calculation unit 34, a drive axis position acquisition unit 38, and a filter unit 36. Before describing each unit, each distance and the like will be described with reference to FIG.

[0031] Fig. 3 is a diagram showing the positional relationship between the machining head 12 and the workpiece 18. In Fig. 3, the machining head 12 one control cycle ago is shown as machining head 121. The current machining head 12 is shown as machining head 122. The tip 13 of the machining head 121 one control cycle ago is shown as tip 131. The tip 13 of the current machining head 122 is shown as tip 132. The distance detection unit 16 of the machining head 121 one control cycle ago is shown as distance detection unit 161. The distance detection unit 16 of the current machining head 122 is shown as distance detection unit 162. An arrow 110 in Fig. 3 indicates the scanning direction in scanning control.

[0032] 3, a distance 101 indicates the machining surface distance one control cycle ago, a distance 102 indicates the current machining surface distance, and a distance 103 indicates the amount of change in the machining surface distance.

[0033] 3, the drive axis 23 one control cycle before is shown as drive axis 231. The current drive axis 23 is shown as drive axis 232. Distance 105 in FIG. 3 indicates the amount of change in axis position.

[0034] 2, the distance change amount calculation unit 34, the drive axis position acquisition unit 38, and the filter unit 36 ​​will be described. The distance change amount calculation unit 34 is a part that calculates the amount of change in the machining surface distance. The distance change amount calculation unit 34 calculates the amount of change in the machining surface distance from the difference between the current machining surface distance and the machining surface distance one control cycle before.

[0035] The current machining surface distance is the machining surface distance most recently detected by the distance detection unit 16. The machining surface distance one control cycle ago is the machining surface distance detected one control cycle ago by the distance detection unit 16. The machining surface distance one control cycle ago may be the filter output calculated by the filter unit 36 ​​one control cycle ago.

[0036] 3, the current machining surface distance is distance 102, and the machining surface distance one control cycle before is distance 101. The amount of change in the machining surface distance is distance 103.

[0037] The drive shaft position change amount calculation unit 40 is a part that calculates the amount of change in the shaft position. The drive shaft position change amount calculation unit 40 calculates the amount of change in the shaft position from the difference between the current shaft position and the shaft position one control cycle before.

[0038] The current axis position is the axis position most recently acquired by the drive axis position acquisition unit 38. The axis position one control cycle ago is the axis position acquired by the drive axis position acquisition unit 38 one control cycle before the most recent acquisition.

[0039] In FIG. 3, the change in axial position is the distance 107 .

[0040] The filter unit 36 ​​is a part that calculates the machining surface distance with noise from the sensor included in the distance detection unit 16 suppressed. The machining surface distance calculated by the filter unit 36 ​​is called the filter output. The filter unit 36 ​​calculates the filter output with noise suppressed by filtering. The filter unit 36 ​​calculates the filter output for each control cycle.

[0041] The filter unit 36 ​​calculates a filter output based on the amount of change in the machined surface distance 103. When calculating the filter output, the filter unit 36 ​​takes into account the amount of change in the axis position 105. An example of taking the amount of change in the axis position 105 into account is to reduce the degree to which the amount of change in the axis position 105 is filtered.

[0042] With the above configuration, the numerical control device 30 of this embodiment can maintain responsiveness to axis movement even when the time constant of the filter included in the filter unit 36 ​​is large, for example.

[0043] The filter processing will be described in more detail. The filter unit 36 ​​includes a first-order lag filter. The filter unit 36 ​​filters the input machining surface distance using the first-order lag filter. The value after filtering is the filter output. The filter unit 36 ​​calculates the filter output and outputs it to the distance control unit 42.

[0044] The filter included in the filter unit 36 ​​is not limited to a first-order lag filter, but may be, for example, a filter that performs moving average processing.

[0045] An example of reducing the contribution of the change amount 105 of the axis position in the filtering process is to make the strength of the filtering process for the change amount 103 of the machining surface distance stronger than the strength of the filtering process for the change amount 105 of the axis position.

[0046] The main factors that cause changes in the machining surface distance are the following factors 1 to 3. Factor 1 is a change in the position of distance detection unit 16. Distance 107 in FIG. 3 indicates the difference in position between distance detection unit 161 and distance detection unit 162. Distance 107 indicates the amount of change in the position of distance detection unit 16.

[0047] The distance detection unit 16 is provided on the machining head 12. The machining head 12 moves together with the drive shaft 23. Therefore, the amount of change 107 in the position of the distance detection unit 16 is equal to the amount of change in the shaft position 105.

[0048] The factor 2 is a change in the position of the workpiece 18. An example of a cause of the change in the position of the workpiece 18 is unevenness of the workpiece 18.

[0049] The third factor is noise from peripheral devices of the machining system 1.

[0050] The change in factor 1 occurs at high speed. The amount of change in factor 1 is greater than the amount of change in factor 2 and the amount of change in factor 3. The noise in factor 3 is high frequency.

[0051] In the numerical control device 30 of this embodiment, the strength of the filtering process for factor 1 is set lower than the strength of the filtering process for factors 2 and 3. Preferably, factor 1 is not subject to filtering, and factors 2 and 3 are subject to filtering. For factor 1, filtering is not performed, and the value is used as is to determine the content of control of the machining device 10.

[0052] This makes it possible to remove noise components while maintaining responsiveness.

[0053] As described above, a preferable example of taking the amount of change in shaft position into consideration is to exclude the amount of change in shaft position from the target of filtering. The filter unit 36 ​​calculates the filter output by excluding the amount of change in shaft position. The details of the filtering process will be described below using an example in which the amount of change in shaft position is excluded from the target of filtering.

[0054] Regarding the filter processing, the filter unit 36 ​​is configured as a first-order lag filter. An example of a first-order lag filter is a low-pass filter. Processing of the machining surface distance by the first-order lag filter can generally be expressed by the following formula 1. Formula 1: Filter output = (1 - coefficient) x filter output one control cycle ago + coefficient x machining surface distance

[0055] The machining surface distance is detected by the distance detection unit 16. The coefficient can be expressed by the following equation 2: Coefficient = Control Period / (Control Period + Time Constant) Here, the control period is also called the sampling period. The time constant is the time constant of a first-order lag filter.

[0056] Formula 1 can be expressed by the following formula 3 by rearranging it using the coefficients. Formula 3: Filter output = Filter output one control cycle ago + coefficient × (machined surface distance - filter output one control cycle ago)

[0057] In the numerical control device 30 of this embodiment, the target of filtering does not include the amount of change in axis position. The first-order lag filter can be expressed by the following equation 4.

[0058] Formula 4: Filter output = filter output one control cycle ago + change in axis position + coefficient × (machined surface distance - filter output one control cycle ago - change in axis position)

[0059] In Equation 4, the items multiplied by the coefficients are the items to be filtered. In Equation 4, the amount of change in axis position is excluded from the items to be filtered.

[0060] Furthermore, in Equation 4, the amount of change in axis position is added to the item that is not multiplied by a coefficient. This addition allows the amount of change in axis position to be used as a value that is not subjected to filtering. In other words, when determining the content of control for the machining device 10, the amount of change in axis position is used as a value that is not subjected to filtering.

[0061] Fig. 4 is a diagram showing the machined surface distance detected by the distance detection unit 16, the filter output, etc. The X axis of the graph in Fig. 4 represents time, and the Y axis of the graph in Fig. 4 represents the sensor value.

[0062] 4, L1 indicates a change in the machining surface distance due to a change in the axis position, and L2 indicates the machining surface distance detected by the distance detection unit 16. The sampling period of L2 is 2 ms.

[0063] 4, L3 indicates the filter output in this embodiment, and L13 indicates the output of a conventional filter. In both L3 and L13, the filter time constant is 300 ms.

[0064] Box R2 in FIG. 4 is an enlarged view of box R1.

[0065] As indicated by L2 in FIG. 4, the machined surface distance detected by the distance detection unit 16 contains a lot of vibration due to noise.

[0066] In contrast, in the filter output of this embodiment shown by L3, the vibration caused by noise shown by L2 is suppressed.

[0067] Furthermore, the filter output of this embodiment shown by L3 almost overlaps with the change in the machined surface distance due to the change in the axis position shown by L1.

[0068] In this way, the filter output of this embodiment can maintain high responsiveness and suppress vibrations caused by noise, even when the time constant is set to a large value such as 300 ms.

[0069] 4, the vibration caused by the noise shown in L2 is suppressed, but the time constant is as large as 300 ms, resulting in poor response.

[0070] Figure 5 is a graph showing the relationship between responsiveness and noise suppression in a conventional filter. The X-axis of the graph in Figure 5 represents time, as in Figure 4. The Y-axis of the graph in Figure 5 represents the sensor value, as in Figure 4. Box R4 in Figure 5 is an enlarged view of box R3. The double-headed arrow 112 in Figure 5 indicates the direction of the small (-) or large (+) time constant.

[0071] L1, L2, and L13 in Fig. 5 represent the same as L1, L2, and L13 in Fig. 4. L11 and L12 represent conventional filter outputs. The filter time constant for L11 is 10 ms. The filter time constant for L12 is 100 ms.

[0072] For L11 to L13, the time constants become larger such that L11<L12<L13. As shown in FIG. 5, when the time constant is small, responsiveness is ensured. However, when the time constant is small, vibrations caused by noise cannot be suppressed. On the other hand, when the time constant is large, vibrations caused by noise are suppressed. However, responsiveness deteriorates. As such, with conventional first-order lag filters, it is difficult to achieve both responsiveness and suppression of vibrations caused by noise.

[0073] In contrast, in the numerical control device 30 of this embodiment, even if the time constant of the filter is increased, as shown by L3 in FIG. 4, it is possible to suppress vibrations caused by noise while maintaining high responsiveness.

[0074] The numerical control device 30 may be realized by one or more computers having a memory, a processor CPU, an input / output interface, etc., and executing an appropriate control program. The components of the numerical control device 30 described above are classifications of the functions of the numerical control device 30, and do not necessarily have to be clearly distinguishable in terms of physical configuration and program configuration. Furthermore, each function of the numerical control device 30 may be realized by a combination of hardware and software. Alternatively, each function may be realized only by hardware. Here, hardware refers to, for example, an electronic circuit.

[0075] The present disclosure is not limited to the above-described embodiments and modifications, and includes modifications and improvements within the scope of achieving the object of the present disclosure.

[0076] The following additional notes are provided regarding the above-described embodiment and modifications.

[0077] (Supplementary Note 1) A numerical control device (30) for controlling a machining device (10), wherein the machining device (10) comprises: a machining head (12) for machining a workpiece (18); a drive mechanism (20) for relatively moving the machining head (12) and the workpiece (18); and a distance detection unit (16) for detecting a distance from the machining head (12) to a machining surface (19) of the workpiece (18) using a sensor, wherein the drive mechanism (20) comprises a drive shaft (23) for supporting the machining head (12). The numerical control device (30) comprises: a distance acquisition unit (32) for acquiring a machining surface distance from the distance detection unit (16) when the distance from the machining head (12) to the machining surface (19) of the workpiece (18) is defined as a machining surface distance; and a distance control unit (42) for creating a movement command for the drive shaft (23) so that the machining surface distance becomes a preset distance. a drive axis control unit (44) that drives the drive axis (23); a drive axis position acquisition unit (38) that acquires the position of the drive axis (23); a distance change amount calculation unit (34) that calculates an amount of change in the machining surface distance from the difference between the current machining surface distance and the machining surface distance one control cycle ago; a drive axis position change amount calculation unit (40) that calculates an amount of change in the axis position from the difference between the current axis position and the axis position one control cycle ago when the position of the drive axis (23) is taken as the axis position; and a filter unit (36) that calculates the machining surface distance with noise of the sensor suppressed by filtering, wherein the strength of the filtering process for the amount of change in the machining surface distance is stronger than the strength of the filtering process for the amount of change in the axis position.

[0078] (Note 2) When the processed surface distance calculated by the filter unit (36) is used as a filter output, the filter unit (36) calculates the filter output by excluding the amount of change in the axis position from the target of filtering.

[0079] (Note 3) When the period during which the distance control unit (42) creates the movement command is set as the control period, the filter unit (36) calculates the filter output using the following formula: Filter output = filter output from one control period before + amount of change in axis position + coefficient × (machined surface distance - filter output from one control period before - amount of change in axis position).

[0080] (Supplementary Note 4) The filter unit (36) calculates the filter output using a first-order lag filter, and the coefficient is a control period / (control period+time constant of the first-order lag filter).

[0081] (Note 5) The amount of change in the axis position is calculated based on at least one of the contents of a movement command for the drive axis (23) and the result of detecting the position of the drive axis (23).

[0082] REFERENCE SIGNS LIST 1 Machining system 10 Machining device 12 Machining head 13 Tip of machining head 16 Distance detection unit 18 Workpiece 19 Machining surface of workpiece 20 Drive mechanism 22 Machining head drive mechanism 23 Drive axis 24 Workpiece drive mechanism 26 Workpiece holding unit 28 Workpiece rotation axis 30 Numerical control device, 32 Distance acquisition unit 34 Distance change amount calculation unit 36 ​​Filter unit 38 Drive axis position acquisition unit 40 Drive axis position change amount calculation unit 42 Distance control unit 44 Drive axis control unit 103 Amount of change in machining surface distance 105 Amount of change in axis position 107 Amount of change in position of distance detection unit 110 Scanning direction 112 Time constant

Claims

1. A numerical control device for controlling a machining device, the machining device comprising: a machining head for machining a workpiece; a drive mechanism for relatively moving the machining head and the workpiece; and a distance detection unit for detecting the distance from the machining head to the machined surface of the workpiece with a sensor, the drive mechanism comprising a drive shaft for supporting the machining head; the numerical control device comprising: a distance acquisition unit for acquiring the machined surface distance from the distance detection unit when the distance from the machining head to the machined surface of the workpiece is defined as the machined surface distance; a distance control unit for creating a movement command for the drive shaft so that the machined surface distance becomes a preset distance; a drive shaft control unit for driving the drive shaft; a drive shaft position acquisition unit for acquiring the position of the drive shaft; a distance change amount calculation unit for calculating a change amount of the machined surface distance from the difference between the current machined surface distance and the machined surface distance of one control cycle before; and a drive shaft position change amount calculation unit for calculating a change amount of the axis position from the difference between the current axis position and the axis position of one control cycle before when the position of the drive shaft is defined as an axis position. a filter unit that calculates the machined surface distance in which noise from the sensor is suppressed by filtering, wherein a strength of the filtering process applied to an amount of change in the machined surface distance is stronger than a strength of the filtering process applied to an amount of change in the axis position.

2. The numerical control device according to claim 1, wherein when the machined surface distance calculated by the filter unit is used as a filter output, the filter unit calculates the filter output by excluding the amount of change in the axis position from the target of filtering.

3. The numerical control device according to claim 2, wherein, when the period during which the distance control unit creates the movement command is defined as a control period, the filter unit calculates the filter output according to the formula: Filter output = filter output one control period ago + amount of change in axis position + coefficient x (machining surface distance - filter output one control period ago - amount of change in axis position).

4. The numerical control device according to claim 3, wherein the filter section calculates the filter output using a first-order lag filter, and the coefficient is control period / (control period+time constant of a first-order lag filter).

5. A numerical control device according to claim 1 or 2, wherein the amount of change in the axis position is calculated based on at least one of the contents of a movement command for the drive axis and a result of detecting the position of the drive axis.

Images