Numerical control

Abstract

Numerical control (1) configured to correct a machine position error based on a torque difference ΔT between a main axis (M) and a secondary axis (S), wherein the numerical control (1) comprises: a motion command unit (101) configured to move the main axis (M) and the secondary axis (S) according to a motion command; a torque difference recovery unit (102) configured to recover the torque difference ΔT after the motion; and a machine position error correction unit (104) configured to correct a machine position error according to a correction amount (ΔT- Tm) based on a value obtained by excluding a torque difference Tm due to mechanical strain from the torque difference ΔT, wherein The motion command unit (101) adds the correction amount (ΔT- Tm) which is reported back by the machine position error correction unit (104) to the subsequent motion command.

Description

BACKGROUND OF THE INVENTION Area of ​​the invention

[0001] The invention relates to a numerical control and in particular a numerical control which is configured to correct a machine position during feed axis synchronization control. State of the art

[0002] Fig. Figure 1 shows a numerical control system with machine position correction in a machine tool using feed axis synchronization of gantries or the like. For example, the published Japanese patent application JP 2003-263 228 A describes a synchronization control system in a drive control device configured for the synchronous drive of multiple drive shafts by means of servomotors to move components that engage in threaded mesh with the drive shafts. In this synchronization control system, vibrations generated by differences in the mechanical stiffness between the drive shafts are suppressed in order to improve the positional accuracy and response of the device.

[0003] A conventional numerical control system takes into account a pitch error between a main axis and a secondary axis, based on the pitch data of a ball screw drive, and corrects the machine position. If the pitches of the main and secondary axes are not adjusted during axis synchronization, the main and secondary axes will deviate from each other, leading to problems such as unstable motor current. Therefore, the machine position is conventionally modified by measuring the actual machine position error using a laser measuring instrument or similar device, in order to correct the pitch error or similar issues. Fig. 2 to be carried out.

[0004] However, the operations for measuring the pitch and the instantaneous machine position error using a laser measuring instrument or similar device to obtain the pitch error correction are very complex. While it is sufficient to correctly set the respective pitches of the main and secondary axes, these pitches cannot be easily adjusted because the secondary axis is dependent on the main axis. Although machine position corrections can be performed to some extent using torque differentials, as described in the published Japanese patent application JP 2003-263 228 A, a precise machine position correction cannot be achieved while taking mechanical strain into account. Mechanical strain, as explained here, corresponds to a deviation in the machine position that occurs during the manufacturing (casting) of the parts.

[0005] Furthermore, DE 10 2016 103 614 A1 discloses further prior art. BRIEF DESCRIPTION OF THE INVENTION

[0006] The invention relates to the solution of the above problems and aims to provide a numerical control system that is set up for correcting a machine position during feed axis synchronization control.

[0007] The problem is solved by a numerical control with the features of claim 1, which is configured to correct a machine position error based on a torque difference ΔT between a main axis and a secondary axis and includes a motion command unit configured to move the main axis and the secondary axis according to a motion command, a torque difference recovery unit configured to recover the torque difference ΔT after the movement, and a machine position error correction unit configured to correct a machine position error by a correction amount based on a value obtained by excluding a torque difference Tm derived from a mechanical strain due to the torque difference ΔT.The motion command unit adds the correction amount, as reported back by the machine position error correction unit, to the subsequent motion command.

[0008] The numerical control can further include a correction amount calculation unit for calculating the torque difference Tm. The motion command unit can move the main axis and the secondary axis to a plurality of monitoring points, the torque difference acquisition unit can measure the torque difference ΔT at each of the multiple monitoring points, and the correction amount calculation unit can define an average of the torque differences ΔT measured individually at the multiple monitoring points as the torque difference Tm.

[0009] The invention provides a numerical control system that is configured to correct a machine position during feed axis synchronization control. BRIEF DESCRIPTION OF THE FIGURES Fig. Figure 1 shows an example of a conventional numerical control system set up for machine position error correction; Fig. Figure 2 shows an example of a conventional machine position error correction method; Fig. Section 3 explains a machine position error correction method using numerical control; Fig. Section 4 explains the machine position error correction method using numerical control; Fig. Section 5 explains the machine position error correction method using numerical control; Fig. Section 6 further explains the machine position error correction method using numerical control; Fig. Figure 7 is a flowchart for the operation of the numerical control; Fig. Figure 8 is a flowchart for the operation of the numerical control; Fig. Section 9 explains a procedure for calculating correction amounts; Fig. Section 10 explains the machine position error correction method using numerical control; Fig. Figure 11 shows the apparatus configuration of the numerical control; and Fig. Figure 12 is a block diagram of the functional configuration of the numerical control: DESCRIPTION OF PREFERRED EXECUTION EXAMPLES IN DETAIL

[0010] The following describes in more detail a configuration of a numerical control 1 according to an embodiment of the invention.

[0011] Fig. Figure 11 schematically shows the apparatus structure of the main components of the numerical control 1 according to the embodiment of the invention.

[0012] A CPU 11 of the numerical control 1 is a processor for the overall control of the numerical control 1 and the CPU reads a program stored in a non-volatile memory 14 via a bus 20 and controls the entire numerical control 1 according to the program.

[0013] The non-volatile memory 14 is, for example, battery-backed (not shown) so that its memory state is retained even if the numerical control 1 is switched off. Programs and data stored in the non-volatile memory 14 can be transferred to a volatile memory 13 during operation. The volatile memory 13 is loaded with temporarily active computational and display data, data entered via an input device, and the like, as well as with programs and data from the non-volatile memory 14.

[0014] A display / MDI unit 70 is a data input / output device equipped with a display, a keyboard, and the like. Commands and data entered via the keyboard of the display / MDI unit 70 are transmitted to the CPU 11 via an interface 15. Display data output by the CPU 11 is made available for display on the display / MDI unit 70 via interface 15.

[0015] A servo controller 80 controls a servo motor that drives the main and auxiliary axes. A servo motor drive command, issued by the CPU 11, is transmitted to the servo controller 80 via an interface 16. The servo controller 80 transmits information, such as the load on the servo motor, to the CPU 11 via interface 16.

[0016] Fig. Figure 12 shows, as a block diagram, the functional configuration of the numerical control 1 according to this embodiment of the invention.

[0017] The numerical control unit 1 has a motion command unit 101, a torque difference acquisition unit 102, a correction amount calculation unit 103, and a machine position error correction unit 104. The motion command unit 101 moves the main and auxiliary axes. The torque difference acquisition unit 102 acquires a torque difference between the main and auxiliary axes. The correction amount calculation unit 103 determines torque differences derived from mechanical strain based on torque differences acquired at multiple monitoring points and calculates a corresponding correction amount. The machine position error correction unit 104 corrects a machine position error based on the correction amount.

[0018] The basic structure of the machine position error correction by the numerical control 1 according to this embodiment will now be described in more detail with reference to the Fig. 3 to 5 and 10. The numerical control 1 has two operating modes for this purpose: a data acquisition mode and a correction mode.

[0019] In data acquisition mode, the numerical control measures 1 torque difference ΔT = T M - (-T s ) between the main axis and the secondary axis, as in Fig. 3 explains that at several monitoring points 1, 2, ..., n, as Fig. 10 shows. This includes T M and T sThe torque values ​​of the main axis and secondary axis (M: master, S: slave). The torque difference ΔT at each monitoring point includes components derived from a pitch error, torsion due to the workpiece load, and machine position deviation due to thermal displacement, as well as a component resulting from mechanical strain, which is specific to each machine.

[0020] In correction mode, the numerical control 1 makes a correction with respect to an optimal machine position by providing feedback of a correction value based on the torque difference ΔT to the motion command. In particular, the numerical control 1 performs a machine position correction based on the torque differences ΔT with each actuation of the main and auxiliary axes. How Fig. Figure 4 shows that a torque difference ΔT is generated between the main shaft and the auxiliary shaft due to a positional deviation between the main and auxiliary shafts, or similar, at an actuation point (here assumed to be a monitoring point A). The synchronization control can be executed using this torque difference ΔT as a correction value (i.e., by performing the correction in such a way that the motor is not loaded (load on motor = 0)).

[0021] Initially, the numerical control 1 can perform machine position correction based on the torque difference ΔT at the individual monitoring points, which are acquired in data acquisition mode. Subsequently, however, the numerical control 1 can perform more precise machine position corrections in real time, taking into account the influence of thermal displacements and similar factors, which change at any time. This is achieved by acquiring the torque differences ΔT and calculating and providing feedback of the correction value for each operation.

[0022] Optimal synchronization control cannot be achieved solely by performing a correction for a position where the torque difference ΔT is not generated in this way. This is because the torque differences ΔT also represent a torque load T. mThis includes deviations caused by mechanical strain. In particular, if the machine position correction is simply performed using the torque difference ΔT as the correction value, this results in an excess correction by an amount corresponding to the torque load T. m , How Fig. Figure 5 shows that the machining point inevitably deviates from an ideal correction position. If a laser measuring instrument or similar device is used for machine position correction, the positioning is carried out in such a way that the influence of mechanical strain is prevented, so that this problem does not occur. To overcome this problem, which concerns machine position correction using the torque difference, the procedure should be carried out such that the correction value T m not included.

[0023] After the torque differences ΔT have been measured at a plurality of monitoring points during data acquisition operation, the numerical control 1 calculates a torque difference that acts regularly at these observation points and takes this as the torque difference T. m , which results from the mechanical strain. In detail: the numerical control 1 obtains torque differences ΔT1, ΔT2, ..., ΔTn between the main axis and the secondary axis at the monitoring points 1, 2, ..., n according to Fig. 6. The numerical control 1 then obtains the mean value of these torque differences, that is, it obtains the value according to the following equation (1): Tm=(ΔT1+ΔT2+…+ΔTn) / n

[0024] The numerical control 1 then performs the machine position correction using the correction value obtained by excluding the torque difference Tm from the torque differences ΔT, i.e., without correcting the value Tm resulting from mechanical strain. In this way, the machining point can be optimally positioned by taking into account the necessary torque difference Tm corresponding to the correction for mechanical strain and by correcting only the pitch error, the torsion due to the workpiece load, and the machining position deviation due to thermal displacement.

[0025] The operation of the numerical control system 1 is now described in its temporal sequence with reference to the Fig. 7 and Fig. 8 described in more detail.

[0026] Fig. Figure 7 is a flowchart illustrating the operation of the numerical control 1 in data acquisition mode. Typically, the numerical control 1 operates in data acquisition mode before machining begins and acquires torque differences that are statically generated at multiple monitoring points. These torque differences are primarily due to pitch errors, mechanical strain, and the like, without the influence of workpiece load or thermal displacement. The numerical control 1 calculates the torque difference Tm that is regularly generated at each monitoring point and identifies the torque difference component resulting from mechanical strain.

[0027] Step S101: The motion command unit 101 sends the motion command to the servo motor for the main axis and the secondary axis to a predetermined monitoring point.

[0028] Step S102: In accordance with the movement command according to step S101, the servo motor for the main axis and the secondary axis is driven to move the machine to the monitoring point.

[0029] Step S103: The torque difference recovery unit 102 recovers the torque differences ΔT between the main and secondary axes.

[0030] Step S104: If the processing according to steps S101 to S103 has been completed for all monitoring points (n in number), the program proceeds to step S105. Otherwise, the program returns to step S101, after which the process is repeated for the next monitoring point.

[0031] Step S105: The storage unit 105 calculates the average of the torque differences ΔT, which were individually obtained for the n monitoring points by inserting movements towards and away from the workpiece during the rotation of the lathe. The average value is a torque difference that is regularly generated at each monitoring point, and this value can be assumed to be a torque difference attributable to mechanical strain.

[0032] Step S106: The correction amount calculation unit 103 calculates a correction amount for each monitoring point and reads it into a predefined memory area in the volatile memory 13 or the like. The correction amount can be calculated based on a torque difference obtained by excluding the torque difference Tm due to mechanical strain from the torque differences that are statically generated at the individual monitoring points. If the torque differences at monitoring points 1, 2, ..., n are ΔT1, ΔT2, ..., ΔTn, correction amounts at monitoring points 1, 2, ..., n are determined based on the differences ΔT1 - Tm, ΔT2 - Tm, ..., ΔTn - Tm.

[0033] A method for calculating the correction amounts based on the torque differences is now being developed with regard to Fig. 9 described in more detail.

[0034] The correction amount calculation unit 103 first determines a load F[N] based on the machine position deviation according to a torque T[Nm]. It then calculates a mechanical strain ΔL[m] due to the load F[N]. This mechanical strain ΔL(m) is the correction amount.

[0035] The relationship between the torque T[Nm] and the load F[N] can be obtained according to the following equation (2).

[0036] The relationship between the load F[N] and the stress can be obtained according to the following equation (3). The relationship between the stress and the mechanical strain ΔL[m] is given by the stress-strain diagram. T=[(F×pb / 2η)×η)+(μ0×F0×Pb / 2η)] / Sf / i, F=voltage×mg(sinθ+μcosθ).

[0037] Here, m is the weight of the table and workpiece; Pb: pitch of the ball screw drive; i: reduction ratio; F0: preload on the ball screw drive; µ: coefficient of friction of a sliding surface; µ0: internal coefficient of friction of a loaded nut; Sf: safety factor; and θ: inclination angle of the ball screw drive.

[0038] Fig. Figure 8 is a flowchart illustrating the operation of the numerical control in correction mode. During machining, the numerical control 1 performs a correction operation and corrects in real time, taking into account torque differences due to dynamically generated torque differences, i.e., the workpiece load and thermal displacement. Therefore, the numerical control 1 does not correct the torque difference Tm due to mechanical strain.

[0039] Step S201: The motion command unit 101 sends the motion commands to the servomotors for the main axis and secondary axis to a predefined monitoring point.

[0040] Step S202: The machine position error correction unit 104 checks whether correction information is present in a predefined memory area. Correction information is a correction amount (hereinafter referred to as the "initial correction amount") at each monitoring point, which is entered in step S106 according to the flowchart. Fig. The program checks whether the information is stored in step 7 or whether it is a correction based on a returned value, as described in more detail below. If correction information is present, the program proceeds to step S203 and then executes step S204. If no correction information is present, the program proceeds to step S202.

[0041] Step S203: If a correction information feedback value is available, the machine position error correction unit 104 adds it to the motion command. If no correction information feedback value is available, the initial correction value according to the monitoring point is added to the motion command.

[0042] Step S204: According to the movement command in step S201 or the movement command corrected in step S203, the servomotors for the main and secondary axes are driven to move the machine to the monitoring point.

[0043] Step S205: The torque difference recovery unit 102 recovers the torque differences ΔT between the main and secondary axes.

[0044] Step S206: The machine position error correction unit 104 checks whether the torque differences ΔT according to step S205 exceed a predefined correction threshold. If the correction threshold is exceeded, the program proceeds to S207. If not, processing is terminated.

[0045] Step S207: The machine position error correction unit 104 corrects the machine position according to the correction amount (ΔT - Tm) obtained excluding the torque difference Tm due to mechanical strain from the torque difference ΔT.

[0046] Step S208: The machine position error correction unit 104 stores the correction amount used in step S207 as the correction information feedback value in a predefined memory area.

[0047] The correction information feedback value thus secured is used in the processing according to step S203 during the subsequent execution of the motion command. The numerical control 1 then executes the motion command taking the preceding correction amount into account, thereby reducing the generated machine position error. Through repeated execution of the motion command, the correction is continuously applied, taking into account dynamically generated machine position errors such as thermal displacement.

[0048] In this embodiment, the numerical control 1, operating in data acquisition mode, calculates the torque differences Tm that are regularly generated at a plurality of monitoring points. In this way, the torque difference resulting from mechanical strain can be determined. When the motion command is executed, the machine position error is corrected according to a correction amount (ΔT - Tm) obtained by subtracting the torque difference Tm resulting from mechanical strain from the actually measured torque difference ΔT, thus providing an appropriate correction that is unaffected by the mechanical strain.According to the present embodiment, the numerical control 1 reports the previous correction amount as a correction information feedback value and executes the movement command taking into account the previous and prior correction amounts, so that a technically sophisticated and effective correction is carried out in accordance with the dynamically generated machine position error, such as thermal displacement.

[0049] The invention is not limited to the above embodiment and can be implemented in various forms and modifications. For example, in the present embodiment, the value Tm is obtained in data acquisition mode based on the torque differences ΔT at several monitoring points, and the average value is calculated. However, the invention is not limited to this, and the torque difference Tm due to mechanical strain can also be obtained using other methods. For example, the torque difference ΔT can be obtained with a modified machining position using a conventional laser measuring instrument, so that this value can then be used for Tm.

Claims

[1] Numerical control (1) configured to correct a machine position error based on a torque difference ΔT between a main axis (M) and a secondary axis (S), wherein the numerical control (1) comprises: a motion command unit (101) configured to move the main axis (M) and the secondary axis (S) according to a motion command; a torque difference recovery unit (102) configured to recover the torque difference ΔT after the motion; and a machine position error correction unit (104) configured to correct a machine position error according to a correction amount (ΔT- Tm) based on a value obtained by excluding a torque difference Tm due to mechanical strain from the torque difference ΔT, wherein The motion command unit (101) adds the correction amount (ΔT- Tm) which is reported back by the machine position error correction unit (104) to the subsequent motion command. [2] Numerical control (1) according to claim 1, further comprising a correction amount calculation unit (103) for calculating the torque difference Tm, wherein the motion command unit (101) moves the main axis (M) and the secondary axis (S) to a plurality of monitoring points, the torque difference acquisition unit (102) measures the torque difference ΔT at each of the multiple monitoring points, and The correction amount calculation unit (103) defines a mean value of the torque differences ΔT measured at the individual monitoring points as the torque difference Tm.

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