NUMERICAL CONTROL SYSTEM AND ENGINE DRIVE CONTROL

Abstract

Numerical control system that controls machine drive systems (21, 22; 21a, 22a) contained in a machine tool that performs machining using a tool according to a numerical control program, wherein the system comprises: a coordinate transformation unit (12) for detecting a disturbance force or torque applied to each of the machine drive systems (21, 22; 21a, 22a) and for transforming the disturbance force or torque into a tool reference coordinate system for output; and an identification unit (17, 17a) for calculating cutting process parameters that determine characteristics of a cutting process model, and dynamic characteristic parameters that determine characteristics of a dynamic model of the machine tool, using the disturbance force or disturbance torque output from the coordinate transformation unit (12), states of the machine drive systems (21, 22; 21a, 22a), predetermined equation models, and cutting conditions, wherein The equation models define relationships between the cutting process parameters, the dynamic characteristic parameters and the disturbance force or disturbance torque.

Description

Area

[0001] The present invention relates to a numerical control system and a motor drive control for controlling a machine tool. background

[0002] A machine tool is a machine tool used for machining, which removes unwanted sections from a workpiece by applying force or energy to the workpiece using a tool. Specifically, in cutting, which is a type of machining operation, the toothed edge of a tool is brought into contact with a workpiece at a high cutting speed, causing a shear fracture on the workpiece surface and the removal of an unwanted section of the workpiece.

[0003] Cutting is a physical phenomenon in which a cutting process and mechanical dynamics interact. Therefore, it is desirable to manage both simultaneously to control the machining process. Here, a cutting process represents a series of steps in which a tool tooth edge penetrates a workpiece, forming a machined surface while generating chips. Mechanical dynamics represents the behavior of the structures that make up a machine when these structures are set into vibration by a vibration source inside or outside the machine tool. In general, cutting is a phenomenon in which various physical phenomena, including the cutting process and mechanical dynamics as described above, interact in complex ways. Therefore, an integrated analysis of this phenomenon is considered challenging.Therefore, in the production facilities, the items to be assessed are limited to achieving purpose-dependent management of processing.

[0004] For example, a method is used that assesses the positional deviation of a tool relative to an ideal path by measuring the dimensions of the workpiece, and adjusts the cutting depth or width so that the workpiece falls within a desired accuracy. In another example, a method is used that assesses the wear width of a tool tooth edge after machining over a predetermined time or distance to determine a cutting speed that allows the tool to have an extended service life while maintaining machining quality.In yet another example, a method is used that captures detection signals from a force sensor attached to a machine to determine a spindle drive system rotational speed or feed rate at which the cutting load does not become excessive. In yet another example, a method is used that observes the shape or ejection direction of the chips produced during machining to adjust the cutting speed and cutting depth.

[0005] However, due to the assessment procedures of the above methods, which perform an assessment using results measured during non-machining, the assessed items are not in the same state as those during machining. Thus, the measurement results do not represent actual machining. For a cutting process, in which a multitude of physical phenomena influence one another, it is desirable to analyze and assess a machining state during machining, i.e., within the process itself. As a method for managing a machining state within the process, patent literature 1 proposes the following method.

[0006] In the method described in patent literature 1, the machining process performed by a machine tool equipped with a force sensor is simulated. A simulated cutting force is compared with a measured value from the force sensor, and the cutting process information used to calculate the cutting force through simulation is corrected to calculate a final cutting force. This method can calculate a value that reflects the machining state because the cutting process information is updated using a cutting force achieved during the actual machining process. List of citations from patent literature

[0007] Patent literature 1: JP 2013 - 061884 A Brief description of the technical problem

[0008] However, the method described in patent literature 1 only calculates the cutting process information by using pre-stored dynamic characteristic information about a tool. This presents a problem in that if the dynamic rigidity of a structure in the machine changes during machining, the displacement cannot be calculated correctly. It is known that the dynamic rigidity of a spindle drive system generally changes due to heat generation within the spindle drive system, and the dynamic rigidity of a workpiece changes due to a reduction in workpiece mass caused by cutting.The method described in patent literature 1, which does not take mechanical dynamics into account, has a problem in that it cannot exactly identify a cutting process and mechanical dynamics that gradually change during machining.

[0009] The present invention was developed in light of the foregoing. One purpose of the present invention is to provide a numerical control system that can accurately identify a cutting process and its mechanical dynamics. Solution to the problem

[0010] To solve the problems described above and to fulfill the purpose, a numerical control system with the features of claim 1, a motor drive control with the features of claim 16 and a motor drive control with the features of claim 17 are provided. Advantageous effects of the invention

[0011] The numerical control system according to the present invention has the advantage of being able to precisely identify a cutting process and mechanical dynamics. Brief description of the drawings Fig. Figure 1 is a block diagram showing a configuration example of a numerical control system according to a first embodiment. Fig. Figure 2 is a flowchart showing an example of an operational sequence in the numerical control system of the first embodiment. Fig. Figure 3 is a diagram showing relationships between coordinate systems in the first embodiment. Fig. Figure 4 is a schematic diagram showing a state in which a disturbing force is transmitted to a table when a workpiece attached to the table vibrates due to a cutting force, in the first embodiment. Fig. Figure 5 is a diagram showing an example of a rotation angle of a tool with a tool tooth edge touching the workpiece in the first embodiment. Fig. Figure 6 is a diagram showing an example of a rotation angle of the tool with tool tooth edges that do not touch the workpiece in the first embodiment. Fig. Figure 7 is a diagram showing a cutting state at a first tooth edge when a deviation is generated between the tool center and the spindle drive system center in the first embodiment. Fig. Figure 8 is a diagram showing a state of cutting on a second tooth edge when a deviation is generated between the tool center and the spindle drive system center in the first embodiment. Fig. Figure 9 is a diagram showing a configuration example of a processing circuit in the first embodiment. Fig. Figure 10 is a diagram showing a configuration example of a numerical control system according to a second embodiment. Fig. Figure 11 is a block diagram showing a configuration example of a perturbation estimation unit in a third embodiment. Fig. Figure 12 shows an example of a machine drive system model in the third embodiment. Fig. Figure 13 is a diagram showing disturbance force estimation results in a comparative example. Fig. Figure 14 is a diagram showing an example of a disturbance force estimated by the disturbance estimation unit in the third embodiment. Fig. Figure 15 is a block diagram showing a configuration example of a disturbance estimation unit in a fourth embodiment. Fig. Figure 16 is a diagram showing an example of a feed machine drive system modeling in the fourth embodiment. Fig. Figure 17 is a block diagram showing a configuration example of a perturbation estimation unit in a fifth embodiment. Fig. Figure 18 is a block diagram showing a configuration example of a numerical control system according to a sixth embodiment. Fig. Figure 19 is a block diagram showing another configuration example of the numerical control system according to the sixth embodiment. Fig. Figure 20 is a block diagram showing a configuration example of a numerical control system according to a seventh embodiment. Fig. Figure 21 is a block diagram showing another configuration example of the numerical control system according to the seventh embodiment. Description of embodiments

[0012] A numerical control system and a motor drive control system according to embodiments of the present invention are described in detail below with reference to the drawings. These embodiments are not intended to limit the invention. First embodiment.

[0013] Fig. Figure 1 is a block diagram showing a configuration example of a numerical control system according to a first embodiment of the present invention. A numerical control system 1 of the first embodiment controls a machine tool 2.

[0014] The machine tool 2 includes a machine drive system 21 and a machine drive system 22. Machine drive system 21 and machine drive system 22 each include a motor and one or more components connected to the motor. Machine drive system 22 is a spindle drive system that rotates a tool. Machine drive system 21 is a feed drive system that positions the tool. Machine drive systems 22 and 21 are controlled synchronously. Machine drive system 21, as the feed drive system, includes, for example, a servo motor, a coupling, a ball screw, and a table. Machine drive system 22, as the spindle drive system, includes, for example, a spindle motor, a gearbox, a shaft, and a tool system.The machine tool 2 rotates a tool attached to the machine drive system 22 (the spindle drive system) to perform a cutting operation on a workpiece mounted on the table of the machine drive system 21 (the feed drive system). The machine drive systems 21 and 22 are examples of machine drive systems included in the machine tool 2, which performs machining using a tool. The configurations of the machine drive systems 21 and 22 are not limited to the examples described above. Fig. 1 a machine drive system 21 as a feed drive system, the number of feed drive systems can be one or more.

[0015] The servo motor of machine drive system 21 and the spindle motor of machine drive system 22 each include a rotary encoder and output an encoder signal, i.e., a signal detected by the rotary encoder, to the numerical control system 1. Machine drive system 21 detects a motor current applied to the servo motor and outputs a detection result as a motor current signal to the numerical control system 1. Machine drive system 22 detects a motor current applied to the spindle motor and outputs a detection result as a motor current signal to the numerical control system 1.

[0016] The numerical control system 1 controls the machine drive system 21 and the machine drive system 22 according to a numerical control (NC) program that is provided from outside or kept inside.

[0017] The NC program includes a position command for a relative tool position or feed drive system within a predetermined coordinate system, a spindle drive system rotational speed command, and a feed rate command. The coordinate system described above, used in the NC program, is called the NC program coordinate system. The NC program coordinate system is a coordinate system that is, for example, fixed to a workpiece.

[0018] As in Fig. As shown in Figure 1, machine drive system 21 is equipped with an accelerometer 211, and machine drive system 22 is equipped with an accelerometer 221. The accelerometer 211 detects the acceleration in machine drive system 21 in a linear or rotational direction and outputs a detection result as an accelerometer signal to the numerical control system 1. The accelerometer 221 also detects the acceleration in machine drive system 22 in a linear or rotational direction and outputs a detection result as an accelerometer signal to the numerical control system 1. Both the accelerometer 211 and the accelerometer 221 can be integrated into the numerical control system 1. The accelerometer 211 and the accelerometer 221 are examples of sensors that detect the velocity or acceleration of machine drive systems 21 and 22.

[0019] As in Fig. As shown in Figure 1, the numerical control system 1 comprises an instruction value generation unit 11, a coordinate transformation unit 12, machine drive control units 13 and 15, disturbance estimation units 14 and 16, an identification unit 17, and a storage unit 18. The storage unit 18 stores a dynamic model, a cutting process model, and cutting conditions. The dynamic model, the cutting process model, and the cutting conditions are described later. The machine drive control units 13 and 15 and the disturbance estimation units 14 and 16 form a motor drive controller 100.

[0020] Fig. Figure 2 is a flowchart showing an example of an operating sequence in the numerical control system 1 of the first embodiment. The operation of the numerical control system 1 of the first embodiment is described with reference to Fig. 1 and Fig. 2 described.

[0021] The command value generation unit 11 analyzes commands described in the NC program and calculates drive commands for the machine drive systems (step S1). Command value generation unit 11 outputs the calculated drive commands to the machine drive control units 13 and 15. Furthermore, command value generation unit 11 outputs setting information for the NC program coordinate system, the relative tool position and the tool rotation angle within the coordinate system, and the drive commands for the machine drive systems to the coordinate transformation unit 12. The setting information for the NC program coordinate system and the relative tool position and the tool rotation angle within the coordinate system is described in the NC program.

[0022] The machine drive control units 13 and 15 control the machine drive systems according to the drive commands calculated by the command value generation unit 11 (step S2). In particular, the machine drive control unit 13 controls the motor current such that the encoder signal output by the rotary encoder of the servo motor of the machine drive system 21 follows the drive command representing a target value. The machine drive control unit 15 controls the motor current such that the encoder signal output by the rotary encoder of the spindle motor of the machine drive system 22 follows the drive command representing a target value. Furthermore, each of the machine drive control units 13 and 15 outputs a machine drive system state to the identification unit 17 described later.Information including a position command, position feedback, speed command, and speed feedback from one of the corresponding machine drive systems. Operations in the machine drive control units 13 and 15 are general operations consistent with the drive commands and are therefore not described in detail.

[0023] The disturbance estimation unit 14 and the disturbance estimation unit 16 estimate disturbances in the machine drive system 21 and the machine drive system 22, respectively (step S3). In particular, the disturbance estimation unit 14 estimates and outputs a disturbance force applied to the machine drive system 21 as a disturbance force acting on a feed drive system, using the encoder signal and the motor current signal output by the machine drive system 21 and the acceleration sensor signal output by the acceleration sensor 211. Specifically, the disturbance force is estimated by considering the feed drive system as a simple inertial drive system, using the following formula (1). Fd1=K1I1−Ma F d1 : disruptive force acting on a machine drive system, K1: Torque constant, I1: Motor current, M: Mass of the machine drive system, a: Acceleration

[0024] A method for estimating the disturbance force acting on a feed drive system is not limited to the example described above. For example, the disturbance estimation unit 14 can calculate the result of formula (1) as the estimated disturbance force, from which a viscous frictional force proportional to the speed of the machine drive system is subtracted.

[0025] The disturbance estimation unit 16 estimates and outputs a disturbance force applied to the spindle drive system, using the encoder signal and the motor current signal output by the machine drive system 22, and the acceleration sensor signal output by the accelerometer 221. The disturbance estimation unit 16 estimates a disturbance force applied to the machine drive system 22 by using a detection result obtained from a sensor that detects the velocity or acceleration of the machine drive system 22. Specifically, the acceleration sensor signal is converted into an angular acceleration, and the disturbance force acting on the spindle drive system is estimated using the following formula (2), where the spindle drive system is considered a single-inertia drive system. Fd2=K2I2−Jω˙r F d2 Disturbing force acting on a spindle drive system K2 torque constant, I2 Motor current, J axial inertia of the main spindle, ω̇ Angular acceleration, r tool radius

[0026] A method for estimating the disturbance force acting on the spindle drive system is not limited to the example described above. For example, the disturbance estimation unit 16 can calculate the result of formula (2) as the estimated disturbance force, from which a viscous frictional force proportional to the angular velocity of the machine drive system is subtracted. The disturbance estimation unit 16 can calculate and output an estimated disturbance torque instead of the estimated disturbance force.

[0027] Returning to the description of Fig. In step S4, the coordinate transformation unit 12 then transforms the disturbance force acting on the feed drive system, calculated by the disturbance estimation unit 14, and the disturbance force acting on the spindle drive system, calculated by the disturbance estimation unit 16, into a tool reference coordinate system for output, based on the setting information for the NC program coordinate system and the relative tool position and tool rotation angle in the NC program coordinate system, which were output by the command value generation unit 11. That is, the coordinate transformation unit 12 detects the disturbance forces or torques applied to the machine drive systems 21 and 22 and transforms the disturbance forces or torques into the tool reference coordinate system for output.In the first embodiment, the coordinate transformation unit 12 detects disturbance forces or disturbance force vectors of the machine drive systems from the disturbance estimation units 14 and 16.

[0028] The tool reference coordinate system is a coordinate system that includes a tool axis direction and two other directions in a plane perpendicular to the tool axis direction. For example, it is a coordinate system relative to the tool in which the tool axis direction is aligned with the Z-axis, one tool movement direction in a plane perpendicular to the tool axis direction is the X-axis, and one direction perpendicular to both the X-axis and the Z-axis is the Y-axis. The tool reference coordinate system is a coordinate system that shifts with the movement of the tool; however, it is a coordinate system that does not account for rotation caused by the tool's rotation.The tool reference coordinate system is not limited to the example described above; it can be any coordinate system that includes a tool axis direction and two other directions in a plane perpendicular to the tool axis direction. The disturbance force acting on the spindle drive system is a quantity whose force direction varies depending on the tool rotation angle, unlike the disturbance force acting on the feed drive system. Thus, the coordinate transformation of the spindle drive system disturbance force is performed at each tool rotation angle.

[0029] The specific processing in the coordinate transformation unit 12 is described with reference to Fig. 3 described. Fig. Figure 3 is a diagram showing the relationships between coordinate systems in the first embodiment. In the Fig. In the example shown, a workpiece 32 is placed on a table 31, which forms the machine drive system 21, and a tool system 34, which forms the machine drive system 22, holds a tool 33. The table 31 is driven by the servo motor (not shown), and the tool system 34 is driven by the spindle motor (not shown). A coordinate system XYZ is the tool reference coordinate system, a coordinate system X'-Y'-Z' is the NC program coordinate system, and a coordinate system X''-Y''-Z'' is a machine coordinate system. A direction 35 indicates a direction of the relative displacement of the front end of the workpiece 32 with respect to the table 31.

[0030] The coordinate transformation unit 12 sets the tool reference coordinate system XYZ using the NC program coordinate system settings and information about the relative tool position. Furthermore, the coordinate transformation unit 12 coordinate-transforms the estimated disturbance force acting on the feed drive system, calculated by the disturbance estimation unit 14, into an estimated disturbance force in the tool reference coordinate system XYZ and outputs it to the identification unit 17. The coordinate transformation unit 12 can also coordinate-transform the estimated disturbance force of the spindle drive system, calculated by the disturbance estimation unit 16, into an estimated disturbance force in the tool reference coordinate system and output it to the identification unit 17.

[0031] Since the estimated disturbance force acting on the feed drive system and the estimated disturbance force acting on the spindle drive system each include components in the X and Y directions in the tool reference coordinate system, the coordinate transformation unit 12 can determine an estimated disturbance force to be output to the identification unit 17 by performing the following processing on the X and Y directions. For example, the coordinate transformation unit 12 takes the mean values ​​of the components in the X and Y directions and adds a Z-axis component of the disturbance force acting on the feed drive system to the mean values ​​to output it as the estimated disturbance force to the identification unit 17.As another example, a machine drive system to be used for an estimated disturbance force can be preset for each machining path, and an estimated disturbance force corresponding to the machine drive system can be coordinate-transformed and output. As yet another example, the mean values ​​of the X-axis and Y-axis components of the disturbance force acting on the feed drive system and the disturbance force acting on the spindle drive system can be calculated, and these mean values ​​can be used as the estimated disturbance force.As yet another example, the coordinate transformation unit 12 can predefine a lower and upper limit for each of the X-axis and Y-axis components for the disturbance force acting on the feed drive system and the disturbance force acting on the spindle drive system, and use as the estimated disturbance force the X-axis component or the Y-axis component of the disturbance force acting on the feed drive system or the disturbance force acting on the spindle drive system that is higher than or equal to the corresponding lower limit and lower than or equal to the corresponding upper limit. If the detected disturbance forces or disturbance moments include components in the same direction on tool reference coordinates, the coordinate transformation unit 12 can select a combination from the detected disturbance forces or disturbance moments in which the directions are independent.As yet another example, the reliability level can be set for each machine drive system, and a machine drive system with a higher reliability level can be used for coordinate transformation. It is known that the estimation accuracy of a multi-inertial drive system is generally lower than that of a single-inertial drive system. Therefore, for example, by setting the reliability level to the reciprocal of the number of inertial bodies that make up a machine drive system, a machine drive system with a simple structure can be used preferentially.As another example of a method for adjusting the reliability level, the reliability level of a machine drive system can be set to high near a workpiece and to low far from the workpiece, preferably using the machine drive system that is sensitive to cutting forces generated on the workpiece. As another example of a method for adjusting the reliability level, the reliability level of a machine drive system can be set to a value higher than zero when the machine drive system is driving and to zero when the machine drive system is at rest, preferably using the driving machine drive system.The above methods for adjusting the reliability level can also be used in combination. Methods for adjusting the reliability level are not limited to those above.

[0032] Returning to the description of Fig. 2. The identification unit 17 calculates parameters such as dynamic characteristic parameters, which determine the characteristics of the dynamic model, and cutting process parameters, which determine the characteristics of the cutting process model (step S5). In particular, the identification unit 17 calculates dynamic characteristic parameters, which determine the characteristics of the dynamic model, and cutting process parameters, which determine the characteristics of the cutting process model, using the estimated disturbance force or estimated disturbance torque output from the coordinate transformation unit 12, the machine drive system states output from the machine drive control units 13 and 15, and the cutting conditions, dynamic model, and cutting process model stored in the storage unit 18.The dynamic characteristic parameters are those that determine the characteristics of the dynamic model to be described later, such as a damping coefficient, a natural frequency, a mass, and a vibration mode vector. The cutting process parameters are those that determine the characteristics of the cutting process model to be described later, such as a specific cutting resistance, an edge force, a tool eccentricity, and a tool wear width.

[0033] Cutting conditions are set using information that includes a feed rate per tooth, a tool diameter, the number of teeth of the tool, a tool twist angle, an axial cutting depth, a radial cutting depth, a workpiece material shape, and a cutting mode that specifies upward or downward cutting.

[0034] The dynamic model is a mathematical model that describes the dynamic characteristics of mechanical structures within machine tool 2. An example of the dynamic model is described below. Fig. Figure 4 is a schematic diagram illustrating a state in which a disturbance force is transmitted to the table 31 when the workpiece 32, attached to the table 31, vibrates due to a cutting force, in the first embodiment. As shown in Figure 4, the following applies: Fig. The 3 illustrated example is based on Fig. 4 on a configuration example where the workpiece 32 is placed on the table 31 of the machine drive system 21 and the tool system 34 of the machine drive system 22 holds the tool 33. In Fig. Equation 4 specifies a relative displacement 36, a relative displacement of the front end of the workpiece 32 in a vibration mode vector direction with respect to the table 31; a cutting force 37 specifies the cutting force in the workpiece 32; and a disturbance force 38 specifies the disturbance force transmitted to the table 31. The relationships between the cutting force 37, the disturbance force 38, and the relative displacement 36 at this time can be expressed by the following formula (3). The dynamic model presented in formula (3) is a mathematical model for calculating a disturbance force transmitted to a machine drive system by a mechanical structure containing a tool or workpiece when a cutting force is generated, and for calculating a positional deviation generated by the mechanical structure in any machine drive system when the cutting force is generated. fc=mtx¨+ctx˙+ktx fd=ctx˙+ktx f c Cutting power, F d Disruptive force m t equivalent mass, c t equivalent damping coefficient, k t equivalent spring constant, x relative displacement of the cutting part of the workpiece in the vibration mode vector direction with respect to the table

[0035] The dynamic model described in equation (3) is a model in which the workpiece 32 on the table 31 is described as a vibration system with one degree of freedom. However, the dynamic model is not limited to the example above. For example, the dynamic model can be described as a vibration system with multiple degrees of freedom, which includes a mounting section for securing the workpiece 32 and the table 31. Furthermore, a dynamic model can be created for the tool-side structure, including the tool 33, the tool system 34, and the spindle motor. Finally, a dynamic model can be created as a vibration system in which the structure on the workpiece 32 side and the structure on the tool 33 side are combined.

[0036] The cutting process model is a mathematical model that describes a cutting process between the tool 33 and the workpiece 32. An example of the cutting process model is shown in the following formula (4). fc=Kcah(φ(t))⋅g(φ(t)) f c Cutting power, K c specific cutting resistance, a axial cutting depth, h uncut chip thickness, φ Tool rotation angle, t time g(φ(t))={1(φs≤φ(t)≤φf)0(φ(t)<φs,φf<φ(t)) φ s Tool engagement angle, φ f Tool release angle

[0037] The above formula (4) is a numerical formula for calculating a cutting force to be exerted by the tool on the workpiece, starting from an uncut chip thickness corresponding to a tool rotation angle at any given time. Here, the uncut chip thickness refers to the thickness with which a tool tooth edge, i.e., a tooth edge of the tool 33, cuts the workpiece 32 as it penetrates the workpiece 32. As in Fig. 5 and Fig. As shown in Figure 6, if a tool tooth edge has an angle at which it touches the workpiece 32, the cutting force is calculated to a value higher than or equal to zero, and if the tool tooth edge has an angle at which it does not touch the workpiece 32, the cutting force is calculated to zero. Fig. Figure 5 is a diagram showing an example of the rotation angle of the tool 33 in which a tool tooth edge touches the workpiece 32. Fig. Figure 6 is a diagram showing an example of the rotation angle of tool 33 in which no tool tooth edges touch the workpiece 32. That is, based on a positional deviation at each rotation angle of tool 33, or at any given time, it is determined whether a tooth edge touches the workpiece 32. If a tool tooth edge touches the workpiece 32, the uncut chip thickness is calculated. If no tool tooth edges touch the workpiece 32, the uncut chip thickness is calculated as zero.

[0038] By performing the calculation shown in formula (4) with three directions—a tangential direction, a radial direction, and an axial direction of the tool—a cutting force in these three directions can be calculated. In the cutting process model, the cutting force is calculated in the tool reference coordinate system by multiplying a cutting force, which has components in the three directions, by a rotation matrix corresponding to a tool rotation angle for coordinate transformation. An example of the coordinate transformation is shown in formula (5). [FxcFycFzc]=[cos φ(t)sin φ(t) 0−sin φ(t)cos φ(t)0001][FtcFrcFac] Cutting force in the X-axis direction in the tool reference coordinate system, Cutting force in the Y-axis direction in the tool reference coordinate system, Cutting force in the Z-axis direction in the tool reference coordinate system, Cutting force in the tangential direction of the tool, Cutting force in the radial direction of the tool, Cutting force in the axial direction of the tool

[0039] By performing the calculations shown in formulas (4) and (5) above for each tool tooth edge, a final cutting force is calculated. The cutting process model shown in formula (4) is a mathematical model for calculating an uncut chip thickness based on a tool rotation angle and a relative position between a tool tooth edge and a workpiece being machined by the tool, and for calculating a cutting force generated between the tool and the workpiece based on the uncut chip thickness. An uncut chip thickness in formula (4) can be calculated using formula (6) by applying a feed rate per tooth and a tool rotation angle. h(φ(t))=c sin φ(t) c Feed rate per tooth

[0040] As another example, an uncut chip thickness can also be calculated using formula (7). h(φ(t))=c sin φ(t)+{ν(φ,t)−w(φ,t)}+Δr(φ,t,Ntooth) v Amount of displacement of the tool center in the radial direction of the tool, w Amount of displacement of the previously machined surface in the radial direction of the tool, T cutting cycle, Δr correction amount, which corresponds to the tooth edge of a tool and the tool rotation angle, N Zahn Number of teeth

[0041] Formula (7) is a formula for calculating an uncut chip thickness, obtained by adding to formula (6) a change calculated from the difference between a current tool displacement and a previously machined surface, and by further adding a correction amount corresponding to each tool tooth edge. In the calculation shown in formula (7), an uncut chip thickness is corrected by the difference between the amount of displacement that has influenced the shape of the machined surface, among the amounts of displacement produced at tool tooth edges one or more teeth prior, and the amount of displacement produced at the current tool tooth edge.The uncut chip thickness is calculated based on the difference between the path path generated by the current cutting tool edge and the path path of a cutting tool edge that influenced the machined surface shape, located one or more teeth upstream of the current cutting tool edge. Here, the cutting tool edge one or more teeth upstream is a cutting tool edge that was involved in cutting at a time prior to the current cutting tool edge.For example, in a two-tooth tool, if the currently cutting tool tooth edge is the second tooth, a tool tooth edge one tooth before it is the first tooth before a rotation greater than 180 degrees, a tool tooth edge two teeth before it is the second tooth before a rotation greater than 360 degrees, and a tool tooth edge three teeth before it is the first tooth before a rotation greater than 540 degrees. If the tool is displaced during cutting and the tooth edges temporarily move away from the workpiece, the current tool tooth edge cuts not only a previously machined surface created by a tool tooth edge one tooth before it, but also a previously machined surface created by a tool tooth edge two or more teeth before it.

[0042] Furthermore, in the calculation shown in formula (7), an uncut chip thickness is corrected by a correction amount corresponding to a tool tooth edge number (i.e., a number that specifies a tool tooth edge) and a tool rotation angle. This correction amount is introduced to account for changes in the uncut chip thickness due to cutting by tool tooth edges with different radii of rotation. The following are examples where the correction amount must be introduced. For instance, if a particular tool tooth edge experiences wear or material removal, the rotation radius of that tool tooth edge becomes shorter than that of the other tool tooth edge(s). Therefore, a correction amount is added that corresponds to the wear width or material removal width of the tool.As another example, if an error occurs in the attachment of the tool tooth edge on an interchangeable tooth edge tool, a correction amount equal to the attachment error is added. As another example, if the spindle drive system center point does not coincide with the tool center point, i.e., if there is tool eccentricity, a correction amount equal to the tool eccentricity is added. The tool center point is the center of the circumcircle of the tool 33. The tool eccentricity is the correction amount of an uncut chip thickness for each tool tooth edge by the amount of an increase or decrease in the rotation radius of the tool tooth edge when a misalignment amount is generated between the tool center point and the spindle drive system center point, as described in . Fig. 7 and Fig. 8 is shown. Fig. Figure 7 is a diagram showing a cutting condition at the first tooth edge when a misalignment amount is generated between the tool center and the spindle drive system center. Fig. Figure 8 is a diagram showing a cutting condition at the second tooth edge when a misalignment amount is generated between the tool center and the spindle drive system center. A first tooth edge 43 and a second tooth edge 44 are the tooth edges of the tool 33. In the Fig. 7 and Fig. In the example shown in Figure 8, there is a misalignment between the tool center and the spindle drive system center 42. In this case, it is necessary to correct the uncut chip thickness relative to the uncut chip thickness when no misalignment is present. The tool eccentricity specifies the correction amount at this time. That is, the tool eccentricity, which corresponds to the rotation angle of the tool, is added to or subtracted from the uncut chip thickness. Examples of correcting an uncut chip thickness with a correction amount are not limited to the examples above. The correction amount can be changed according to a process occurring at a tooth edge.

[0043] The cutting process model is not limited to formula (4). For example, using formula (4), the value of the specific cutting resistance can be modified when the cutting speed is high, higher than or equal to a threshold, and vice versa when the cutting speed is low, lower than the threshold. Furthermore, a model can be used in which an edge force component is added as a constant term to the right-hand side of formula (4). Another model can be used in which a process damping force is added to the right-hand side of formula (4). Here, the process damping force is a force generated by a flank area of ​​a tool tooth edge contacting a workpiece. As another example, a cutting process model can be used for a tool with a twist angle.In particular, a model can be used that divides a tool into thin tool segments in an axial direction, calculates a cutting force at each thin tool segment, and adds the cutting forces in the tool axis direction to calculate a final cutting force. As yet another example, a model can be used that calculates the uncut chip thickness and cutting force using finite element analysis.

[0044] The following describes the processing to identify an equivalent damping coefficient and an equivalent natural frequency as dynamic characteristic parameters and to identify a specific cutting resistance as a cutting process parameter, given that the dynamic model is formula (3) and the cutting process model consists of formulas (4) and (6). The dynamic model can be expressed in a form shown in formula (8) below by deformation and time differentiation of formula (3). f¨d=2ςωn(f˙c−f˙d)+ωn2(fc−fd) ζ equivalent damping coefficient, ω n equivalent natural frequency

[0045] Substituting formula (4), i.e., the cutting process model, into formula (8) above yields formula (9) below. f¨d=2ςωn(Kca(h˙(φ(t))g(φ(t))+h(φ(t))g¯(φ(t)))−f˙d)+ωn2(Kcah(φ(t))g(φ(t))−fd) g¯(φ(t))={1(φ=φs,φf)0(otherwise)

[0046] Furthermore, if the right side of formula (9) is expressed by separating it into known numbers and unknown numbers, formula (10) is obtained. f¨d=[a(h˙(φ(t))g(φ(t))+h(φ(t))g¯(φ(t)))−f˙d ah(φ(t))g(φ(t))−fd][2ςωnKc2ςωnωn2Kcωn2]

[0047] Formula (10) is an equation model for calculating the second derivative of a disturbance force when the dynamic characteristic parameters and the cutting process parameters are provided. The identification unit 17 inserts the estimated disturbance force, transformed into the tool reference coordinate system by the coordinate transformation unit 12, into formula (10) to calculate the dynamic characteristic parameters and the cutting process parameters that satisfy formula (10). For example, by arranging as many formulas (10) as n (n being an integer of one or more) time points, they can be expressed in a matrix form of formula (11). The identification unit 17 can calculate the dynamic characteristic parameters and the cutting process parameters by applying the method of least squares to formula (11). [f¨d,1⋮f¨d,n]=[a(h˙1g1+h1g¯1)−f˙d,1ah1g1−fd,1⋮⋮⋮⋮a(h˙ngn+hng¯n)−f˙d,nahngn−fd,n][2ςωnKc2ςωnωn2Kcωn2]

[0048] Above, a procedure for deriving formulas (10) and (11) from formula (9) and for calculating the dynamic characteristic parameters and the cutting process parameters based on either formula (10) or formula (11) was described. Formula (12) can be used instead of formula (9) to perform the same calculation. In formula (12), a cutting determination function g(φ(t)) in formula (9) is replaced by a differentiable function δ(φ(t)). δ(φ(t)) can be any differentiable function that can approximate the cutting determination function g(φ(t)) and is not restricted to the form shown below. f¨d=2ςωn(Kca(h˙(φ(t))δ(φ(t))+h(φ(t))δ˙(φ(t)))−f˙d)+ωn2(Kcah(φ(t))δ(φ(t))−fd) δ(φ(t))=ς(φ(t),φs)−ς(φ(t),φf) ς(x,y)=11+e−b(x−y)

[0049] As another example, by multiplying the two sides of formula (10) or formula (11) with a smoothing window function, the dynamic characteristic parameters and the cutting process parameters can be calculated without being affected by difference errors.

[0050] As yet another example, the identification unit 17 can perform a repetitive operation by using a search algorithm to look for the dynamic characteristic parameters and the cutting process parameters of formula (10) or formula (11). The calculation of the dynamic characteristic parameters and the cutting process parameters in the identification unit 17 is not limited to the operation using formula (10) and formula (11). By first creating an equation model of the dynamic characteristic parameters, the cutting process parameters, and the disturbance force or torque according to the forms of the dynamic model and the cutting process model, the dynamic characteristic parameters and the cutting process parameters can be calculated from the equation model and the estimated disturbance force or torque.

[0051] Furthermore, identifiable parameters are not limited to the equivalent damping coefficient, the equivalent natural frequency, and the specific cutting resistance. For example, by configuring a dynamic model that includes a vibration mode vector in the dynamic characteristic parameters and by creating an equation model of the dynamic characteristic parameters, the cutting process parameters, and the disturbance force, the identification unit 17 can identify the dynamic characteristic parameters that include the vibration mode vector. As another example, by configuring a cutting process model using formula (7) that includes tool eccentricity in the cutting process parameters and by creating an equation model of the dynamic characteristic parameters, the cutting process parameters, and the disturbance force, the identification unit 17 can identify the cutting process parameters.

[0052] As described above, the identification unit 17 calculates the cutting process parameters, which determine the characteristics of the cutting process model, and the dynamic characteristic parameters, which determine the characteristics of the dynamic model of the machine tool 2, using the disturbance force output by the coordinate transformation unit 12, the predetermined equation models, and the cutting conditions. The equation models above define the relationships between the cutting process parameters, the dynamic characteristic parameters, and the disturbance force.

[0053] A hardware configuration of the numerical control system 1 is then described. The instruction value generation unit 11, the coordinate transformation unit 12, at least part of the machine drive control units 13 and 15, the disturbance estimation units 14 and 16, and the identification unit 17, which are located in Fig. The components shown in Figure 1 are implemented by a processing circuit. The machine drive control units 13 and 15 can include a circuit such as an inverter that generates motor current. The storage unit 18 is implemented by a memory. The processing circuit can be a circuit that includes a processor, or it can be separate hardware.

[0054] If the processing circuit is a circuit that includes a processor, then the processing circuit is, for example, a processing circuit with a configuration that is in Fig. 9 is shown. Fig. Figure 9 is a diagram showing a configuration example of the processing circuit. A processing circuit 200 includes a processor 201 and a memory 202. If the instruction value generation unit 11, the coordinate transformation unit 12, at least part of the machine drive control units 13 and 15, the disturbance estimation units 14 and 16, and the identification unit 17 are replaced by the in Fig. The processing circuit 200 shown in Figure 9 is implemented by the processor 201, which reads and executes programs stored in the memory 202. That is, if the instruction value generation unit 11, the coordinate transformation unit 12, at least part of the machine drive control units 13 and 15, the disturbance estimation units 14 and 16, and the identification unit 17 are implemented by the processing circuit 200 shown in Figure 9, then the processing circuit 200 is implemented by the processor 201, which reads and executes programs stored in the memory 202. Fig. The processing circuit 200 shown in Figure 9 is implemented, and its functions are implemented using programs, i.e., software. Memory 202 is also used as the working area of ​​the processor 201. The processor 201 is a central processing unit (CPU) or the like. Memory 202 corresponds to non-volatile or volatile semiconductor memory, such as random-access memory (RAM), read-only memory (ROM), flash memory, a magnetic disk, or the like. The memory implementing memory unit 18 can be the same as memory 202 or different from it.

[0055] If the processing circuit implementing the instruction value generation unit 11, the coordinate transformation unit 12, at least part of the machine drive control units 13 and 15, the disturbance estimation units 14 and 16, and the identification unit 17 is dedicated hardware, the processing circuit is, for example, a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC). The instruction value generation unit 11, the coordinate transformation unit 12, at least part of the machine drive control units 13 and 15, the disturbance estimation units 14 and 16, and the identification unit 17 can be implemented by a combination of a processing circuit containing a processor and dedicated hardware.The instruction value generation unit 11, the coordinate transformation unit 12, at least a part of the machine drive control units 13 and 15, the disturbance estimation units 14 and 16 and the identification unit 17 can be implemented by a variety of processing circuits.

[0056] As described above, in the numerical control system 1 of the first embodiment, the coordinate transformation unit 12 coordinate-transforms estimated disturbance forces, calculated by the disturbance estimation units 14 and 16, into the tool reference coordinate system, and the identification unit 17 identifies the dynamic characteristic parameters and the cutting process parameters from the equation models of the dynamic characteristic parameters, the cutting process parameters, and the disturbance force, which are constructed based on the dynamic model, the cutting process model, and the cutting conditions. Thus, the numerical control system 1 has the advantage of being able to simultaneously calculate the dynamic characteristic parameters and the cutting process parameters, which are the dominant cutting parameters.

[0057] As a comparative example, an identification of cutting process parameters based on detection results from force sensors integrated into machine drive systems and a cutting process model is considered. The force sensor detection results are the detection of forces caused by a cutting force transmitted through mechanical structures, i.e., disturbance forces. Thus, the comparative example does not account for the fact that a cutting force is transmitted as disturbance forces through mechanical dynamics. Therefore, the comparative example cannot identify exact cutting process parameters.In contrast, in the first embodiment, the disturbance estimation units 14 and 16 estimate disturbance forces, and the identification unit 17 identifies the dynamic characteristic parameters and the cutting process parameters from the equation models of the dynamic characteristic parameters, the cutting process parameters, and the disturbance force, which are constructed based on the dynamic model, the cutting process model, and the cutting conditions. Therefore, the first embodiment can define the cutting process parameters more precisely than the comparison example.

[0058] In the first embodiment, acceleration sensors are provided on all machine drive systems, which include a spindle drive system and a feed drive system. However, the number of machine drive systems in which acceleration sensors are installed is not limited to the total number of machine drive systems. For example, acceleration sensors can be provided on three linear feed drive systems without providing an acceleration sensor on a spindle drive system, whereby a disturbance force vector can be calculated from the results of the detection by the acceleration sensors of the three linear feed drive systems.Alternatively, acceleration sensors can be provided on two linear feed drive systems without providing an acceleration sensor on a spindle drive system, whereby a two-dimensional disturbance force vector in a plane formed by the feed drive systems can be calculated from the results of the detection by the acceleration sensors in order to calculate dynamic characteristic parameters and cutting process parameters in the plane.Alternatively, a two-dimensional disturbance force vector in a plane perpendicular to a spindle drive system can be calculated from a detection result by an accelerometer provided on the spindle drive system, and a disturbance force in the direction of a feed drive system parallel to the spindle drive system from a detection result of an accelerometer provided on the feed drive system can be added to this to calculate a three-dimensional disturbance force vector.

[0059] Furthermore, the first embodiment described a configuration for a machine tool comprising three linear feed drive systems and one spindle drive system; however, the present invention is not limited to machine tools with this shaft configuration. For example, if a machine tool includes one or more rotary feed drive systems in addition to three linear feed drive systems and one spindle drive system, the following configuration can achieve effects equivalent to those of the first embodiment.In particular, the command value generation unit 11 outputs a relative position of the tool in the NC program coordinate system to the coordinate transformation unit 12, and the coordinate transformation unit 12 coordinate-transforms a disturbance force acting on the feed drive system and a disturbance force acting on the spindle drive system into the tool reference coordinate system, taking into account the relative position of the tool, so that, as in the first embodiment, an estimated disturbance force vector can be calculated.

[0060] Furthermore, in the first embodiment, acceleration sensors are used as a means of detecting the acceleration of machine drive systems; however, the physical quantities to be detected are not limited to acceleration. Sensors that directly detect velocity can be used, such as velocity sensors, gyroscopes, or laser Doppler measuring devices. That is, the use of sensors that can detect a physical quantity obtained by a first- or higher-order time derivative of the magnitude of the displacement does not deviate from the essence of the present invention.

[0061] Furthermore, the numerical control system 1 described in the first embodiment can be formed from a plurality of devices. For example, the motor drive control 100, which includes the machine drive control units 13 and 15 and the disturbance estimation units 14 and 16, and the other components of the numerical control system 1 can be designed as separate devices. The numerical control system 1 can consist of a numerical control device, which includes the instruction value generation unit 11, the machine drive control units 13 and 15, the disturbance estimation units 14 and 16, and the coordinate transformation unit 12, as well as an industrial computer, which includes the identification unit 17 and the storage unit 18. The industrial computer can be installed near the machine tool 2, or it can be installed at a location remote from the machine tool 2.The industrial computer can be connected to a variety of machine tools 2. The industrial computer can be connected to the outside world via a public line, such as a wired or wireless internet connection. If the numerical control system 1 consists of a variety of devices, the instruction value generation unit 11, the coordinate transformation unit 12, at least part of the machine drive control units 13 and 15, the disturbance estimation units 14 and 16, and the identification unit 17 are implemented by processing circuits mounted on the devices to which they are mounted. These processing circuits can each be a processing circuit including a processor, standalone hardware, or a combination of a processing circuit including a processor and standalone hardware, such as the processing circuit described above.

[0062] The first embodiment described a machine tool that performs milling by rotating a tool. The present invention is also applicable to a machine tool that performs turning by rotating a workpiece. Second embodiment.

[0063] Fig. Figure 10 is a diagram showing a configuration example of a numerical control system 1a according to a second embodiment of the present invention. The numerical control system 1a of the second embodiment controls a machine tool 2a.

[0064] The machine tool 2a includes a machine drive system 21a as a feed drive system and a machine drive system 22a as a spindle drive system. The machine drive systems 21a and 22a are identical to the machine drive systems 21 and 22, respectively, of the first embodiment, except that they are not equipped with an acceleration sensor. A force sensor 23 is provided on the machine tool 2a. The force sensor 23 is, for example, installed on or inside the table 31, which is located in Fig. Figure 4 illustrates this. The installation location of the force sensor 23 is not limited to this example. The force sensor 23 can be installed anywhere it can detect forces applied to the machine drive systems. The force sensor 23 is an example of a sensor that detects forces or torques applied to the machine drive systems 21a and 22a.

[0065] In the first embodiment, disturbance forces are estimated using results detected by acceleration sensors, encoder signals, and motor current signals. In the second embodiment, the use of the force sensor 23 eliminates the need to include the disturbance estimation units 14 and 16 in the numerical control system 1a. The numerical control system 1a of the second embodiment is configured by removing the disturbance estimation units 14 and 16 from the numerical control system 1a of the first embodiment, and the results of the detection by the force sensor 23 are input into the coordinate transformation unit 12. The same reference numerals as those of the first embodiment are assigned, without further explanation, to components that have the same functions as those of the first embodiment. Differences from the first embodiment are described below.

[0066] The coordinate transformation unit 12 performs a coordinate transformation as in the first embodiment by using results from the detection by the force sensor 23 instead of a disturbance force acting on the feed drive system or a disturbance force acting on the spindle drive system, which are input by the disturbance estimation units 14 and 16, and outputs a coordinate-transformed disturbance force to the identification unit 17, as in the first embodiment. That is, in the second embodiment, the coordinate transformation unit 12 detects disturbance forces from detection results obtained by a sensor that detects forces or torques applied to the machine drive systems 21a and 22a.If this sensor is a torque-detecting sensor, the coordinate transformation unit 12 performs a coordinate transformation after converting the torques into forces. The identification unit 17 calculates the dynamic characteristic parameters and the cutting process parameters as in the first embodiment. The operation of the numerical control system 1a, except as described above, is the same as the operation of the numerical control system 1 of the first embodiment. The coordinate transformation unit 12 can coordinate transform a detected torque and output it to the identification unit 17, and the identification unit 17 can calculate the dynamic characteristic parameters and the cutting process parameters using the coordinate-transformed torque.

[0067] As described above, in the second embodiment, by using the force sensor 23 without the acceleration sensors and the disturbance estimation units 14 and 16, the dynamic characteristic parameters and the cutting process parameters can be calculated as in the first embodiment. Thus, the second embodiment has the same effects as the first embodiment. Third embodiment.

[0068] Fig. Figure 11 is a block diagram showing a configuration example of a disturbance estimation unit according to a third embodiment of the present invention. A numerical control system of the third embodiment is the same as the numerical control system 1 of the first embodiment, except that it includes a disturbance estimation unit 14a instead of the disturbance estimation unit 14 of the first embodiment. Differences from the first embodiment are described below.

[0069] The disturbance estimation unit 14 of the first embodiment acquires a machine drive system signal and an acceleration sensor signal from the machine drive system 21, which is modeled as a single-inertia system, in order to calculate a disturbance force in a high-frequency band using the acceleration sensor, which cannot be estimated solely from the signal in the machine drive system. A machine drive system of a machine tool is generally designed as a structure that has a variety of inertial elements, such as a motor, a ball screw, and a table.

[0070] Fig. Figure 12 is a diagram showing an example of a model of the machine drive system 21. Fig. Figure 12 shows an example of a model of the machine drive system 21, which is modeled as a system with three inertias corresponding to a motor (servo motor), a ball screw, and a table, when the machine drive system 21 includes the servo motor, the ball screw, and the table. m denotes a motor torque, θ m denotes an engine angle, J m and J b denotes inertia, M t denotes a mass, D m , D b Ct denotes damping coefficients, K g and K t denote spring constants, R denotes a ball screw pitch, and x t denotes a position. Here, m, b and t are subscripts indicating the motor, the ball screw and the table respectively.

[0071] Since the machine drive system 21 generally has a structure exhibiting a multitude of inertias, as described above, it is desirable to divide the structure into a multitude of segments for modeling purposes in order to accurately model the structure's behavior. Therefore, the disturbance estimation unit 14a of the third embodiment divides the structure into a multitude of segments for modeling, divides an accelerometer signal output by the accelerometer 211 according to frequency bands, and estimates a disturbance force using inverse models according to the bands.

[0072] This is how it is described in Fig. Figure 11 shows that the machine drive system 21 is divided into a first structure 213 and a second structure 212 for modeling purposes. That is, the machine drive system 21 comprises the first structure 213 and the second structure 212, which contains the motor. The disturbance estimation unit 14a calculates an actual power of the machine drive system, i.e., the resultant of forces applied to the first structure 213, based on a variety of first structural models of the first structure 213 and the acceleration sensor signal. The disturbance estimation unit 14a also calculates a power command of the machine drive system, i.e., a force applied to the machine drive system by the motor, based on a second structural model of the second structure 212, a detection result of a motor current flowing through the motor, and a detection result of the motor's position.Subsequently, the disturbance estimation unit 14a estimates a disturbance force using the actual power of the machine drive system and the command power of the machine drive system. The numerous initial structural models have different frequency characteristics, which are determined according to the subdivided frequency bands.

[0073] In the machine drive system 21 of Fig. Figure 11 shows equivalent models of the first structure 213 and the second structure 212. ref denotes a motor current, K denotes a torque constant, v t denotes a table speed, and F d denotes a disturbing force. a t expis an acceleration sensor signal output by the acceleration sensor 211. The subscript ref indicates that it is a reference value calculated by the machine drive control unit 13, and the superscript exp indicates that it is a signal detected directly by the acceleration sensor. The other characters have the same definitions as those in Fig. 12. The first structure is equipped with the acceleration sensor 211. Here, the first structure is, for example, the table, and the second structure 212 is, for example, a mechanical structure in which the servo motor and the ball screw are combined. A disturbance force is applied externally to the first structure 213 by the machine drive system 21. Furthermore, a command signal from the machine drive system, resulting from a torque output of the servo motor, is applied to the first structure 213, so that the position of the first structure 213 is indirectly controlled by the machine drive control unit 13.

[0074] The in Fig. The disturbance estimation unit 14a shown in Figure 11 estimates a disturbance force applied to the machine drive system 21 as an estimated disturbance force acting on the feed drive system, based on an encoder signal and a motor current signal output by the machine drive system 21 and an acceleration sensor signal output by the acceleration sensor 211.

[0075] In particular, the perturbation estimation unit 14a includes first structural model units 143 and 144, corresponding to the first structure 213, a second structural model unit 141, corresponding to the second structure, and a synthesis unit 142. In the perturbation estimation unit 14a of Fig. Figure 11 shows inverse models of the corresponding structures of the units. LPF denotes a low-pass filter, and HPF denotes a high-pass filter. Symbols with a roof over them indicate estimated values.

[0076] The first structural model unit 143 and the first structural model unit 144 each calculate the actual power output of the machine drive system, i.e., a force applied to the first structure 213, based on the accelerometer signal. The first structural model unit 143 includes the low-pass filter, and the first structural model unit 144 includes the high-pass filter. These filters serve to separate the accelerometer signal into a first frequency band and a second frequency band with a predetermined cutoff frequency. The cutoff frequency of the low-pass filter and the high-pass filter is an upper frequency limit that the machine drive control unit 13 can use, for example, to control the machine drive system 21.The acceleration sensor signal, separated into the two bands, passes through the first structural model unit 143 and the first structural model unit 144, so that the first structural model unit 143 outputs a first actual power of the machine drive system, i.e., an actual power of the machine drive system on the low-frequency side, and the first structural model unit 144 outputs a second actual power of the machine drive system, i.e., an actual power of the machine drive system on the high-frequency side.

[0077] The second structural model unit 141 calculates a command power of the machine drive system, i.e., a driving force for the motor to operate the machine drive system 21, using the motor current signal and the encoder signal. The synthesis unit 142 calculates the sum of the first actual power of the machine drive system and the second actual power of the machine drive system and subtracts the command power of the machine drive system from the calculated sum, thereby enabling it to calculate a disturbance force F. d to estimate, which is applied to the machine drive system 21.

[0078] In the Fig. In the example shown in Figure 11, the machine drive system 21 is expressed as a model consisting of three inertias, spring elements coupling the inertias, and damper elements representing viscous friction. The model of the machine drive system 21 is not limited to this. The machine drive system 21 can be expressed as a model that takes into account the dead time due to communication from the encoder or accelerometer and Coulomb friction. In this case, two first structural model units and a single second structural model unit corresponding to them can be contained in the disturbance estimation unit 14a.

[0079] Parameters included in the inverse models used by the disturbance estimation unit 14a can be calculated using a procedure described below. For example, the machine drive control unit 13 provides a pulse excitation command, a random excitation command, or a sweeping sine excitation command to the motor of the machine drive system 21. The parameters can be adjusted based on a frequency response obtained at that time from an encoder signal and an accelerometer signal. As another example, instead of using the servo motor as the excitation source, the feed drive system can be externally excited using a pulse hammer to adjust the parameters.As yet another example, a test operation can be performed that generates a pre-known disturbance force, and the parameters can be adjusted using a motor current signal, an encoder signal, and an accelerometer signal output at that time. Alternatively, the parameters can be calculated using finite element analysis. Furthermore, the parameters can be determined by a combination of the methods described above.

[0080] The effects of the third embodiment are described here. Fig. Figure 13 is a diagram showing disturbance force estimation results in a comparative example. In the comparative example, whose estimation results are shown in Fig. As shown in Figure 13, the state variables of the motor and the ball screw are estimated, as in the technique according to the third embodiment. That is, the first structure is estimated using the motor current signal and the encoder signal, the state variable of the table is estimated using the accelerometer signal, and the disturbance is estimated using these estimation results. The difference between the third embodiment and the comparative example is that the comparative example is not, as in Figure 13, estimated using the motor current signal and the encoder signal signal, the state variable of the table is estimated using the accelerometer signal. Fig. 11 does not contain a multitude of first structural model units, but rather a single first structural model unit. That is, in the technique of the comparative example, the mass of the table equipped with the accelerometer is not decomposed into frequency bands. In a top row of Fig. Figure 13 shows an actual disturbance force, i.e., a disturbance force that was actually measured using a force sensor, and in a lower row of Fig. Figure 13 shows results estimated using the comparative example. As shown from Fig. As can be seen in Figure 13, the estimated values ​​in the comparison example do not coincide with the values ​​actually measured by the force sensor in a high-frequency band. This means that the technique used in the comparison example, which does not decompose the mass of the table equipped with the accelerometer according to frequency bands for a multi-inertia drive system embodied by a ball screw drive, cannot accurately estimate the disturbance force.

[0081] In contrast, in the third embodiment, an accelerometer signal is divided into frequency bands, and different inverse models are provided to the different bands to estimate a disturbance force. Fig. Figure 14 is a diagram showing an example of a disturbance force estimated by the disturbance estimation unit 14a of the third embodiment. In a top row of Fig. Figure 14 shows an actual disturbance force, i.e., a disturbance force that was actually measured using a force sensor, and in a lower row of Fig. Figure 14 shows the results estimated by the disturbance estimation unit 14a of the third embodiment. As shown from Fig. As can be seen from Figure 14, by using the disturbance estimation unit 14a of the third embodiment, estimation results can be obtained that are equivalent to the results of the measurement by the force sensor. That is, the disturbance estimation unit 14a of the third embodiment has the advantage of being able to accurately estimate a disturbance force applied to a machine drive system in a machine tool that includes a multi-inertia drive system embodied by a ball screw drive.

[0082] In the above description, the accelerometer is used as a means for detecting the acceleration of the machine drive system 21; however, the physical quantity to be detected is not limited to acceleration. Sensors that directly detect velocity can be used, such as velocity sensors, gyroscopes, or laser Doppler measuring devices. That is, the use of sensors that can detect a physical quantity obtained by a first- or higher-order time differentiation of the magnitude of the displacement does not deviate from the essence of the present invention.

[0083] Although the third embodiment describes a ball screw machine tool, the disturbance force estimation technique described in the third embodiment is not limited to ball screw machine tools. The technique is also applicable to a feed drive system and a spindle drive system driven by means other than a ball screw, as long as they are machine drive systems that can be modeled as a multiple inertial system, i.e., machine drive systems composed of a plurality of inertial bodies.

[0084] In the third embodiment, the two first structural models are provided in the perturbation estimation unit 14a to divide the frequency band into two bands; however, the number of first structural models and the number of filters are not limited to two. For example, three or more first structural models may be provided, and their filters may be designed to divide the frequency band into the same number of bands as the number of first structural models.

[0085] The above description described the example of using the disturbance estimation unit 14a instead of the disturbance estimation unit 14 of the numerical control system 1 of the first embodiment. If the in Fig. However, if the motor drive control 100 shown is provided separately, the fault estimation unit 14a can be used instead of the fault estimation unit 14. Fourth embodiment.

[0086] Fig. Figure 15 is a block diagram showing a configuration example of a disturbance estimation unit according to a fourth embodiment of the present invention. A numerical control system of the fourth embodiment is the same as the numerical control system 1 of the first embodiment, except that it includes a disturbance estimation unit 14b instead of the disturbance estimation unit 14 of the first embodiment. Differences from the first embodiment are described below.

[0087] The disturbance estimation unit 14a of the third embodiment divides an accelerometer signal into frequency bands and provides different inverse models for the different bands to estimate a disturbance force. The disturbance estimation unit 14b of the fourth embodiment uses a model in which a table equipped with an accelerometer is divided into a first table inertia, estimated using an encoder signal and a motor current signal, and a second table inertia, estimated using an accelerometer signal, to estimate a disturbance force. Fig. Figure 16 is a diagram showing an example of the modeling of the machine drive system 21 in the fourth embodiment. The symbols in Fig. The 16 are the same as those in the third embodiment. It should be noted that those with a subscript containing 1 correspond to a first table inertia model, and those with a subscript containing 2 correspond to a second table inertia model.

[0088] In particular, the disturbance estimation unit 14b calculates an actual power of the machine drive system, corresponding to a first structural model of the machine drive system 21, based on the first structural model and the acceleration sensor signal. The disturbance estimation unit 14b also calculates a command power of the machine drive system, i.e., a force applied to the machine drive system 21 by the motor, based on a second structural model of the machine drive system 21, which includes the motor of the machine drive system 21, a detection result of a motor current flowing through the motor, and a detection result of the motor's position. The disturbance estimation unit 14b estimates a disturbance force using the actual power of the machine drive system and the command power of the machine drive system.One of the many structures that make up the machine drive system is divided into a first inertial body model and a second inertial body model for modeling purposes. The second structural model incorporates the first inertial body model, and the second structural model incorporates the second inertial body model. An example of the first and second inertial body models is the first table inertial model and second table inertial model described above.

[0089] The definitions of the symbols in Fig. 15 are the same as those in the third embodiment. The machine drive system 21 includes, as in the third embodiment, a table, a servo motor, and a ball screw. In the fourth embodiment, the table model is divided into two models, a first table inertia and a second table inertia, and the modeling is carried out with a first structure 213a, which is considered the table, and a second structure 212a, which is considered the mechanical structure in which the table, the motor, and the ball screw are combined.

[0090] The disturbance estimation unit 14b estimates a disturbance force applied to the machine drive system 21 as a disturbance force acting on the feed drive system on the basis of an encoder signal and a motor current signal output by the machine drive system 21, and an acceleration sensor signal output by the acceleration sensor 211.

[0091] A disturbance force is applied externally to the first structure 213a via the machine drive system 21. Furthermore, a command signal from the machine drive system, resulting from a torque output of the servo motor, is applied to the first structure 213a, so that the position of the first structure 213a is indirectly controlled by the machine drive control unit 13.

[0092] The disturbance estimation unit 14b comprises a first structural model unit 143a, corresponding to the first structure 213a, a second structural model unit 141a, corresponding to the second structure 212a, and a synthesis unit 142a. The first structural model unit 143a calculates the actual power of the machine drive system, i.e., the resultant of forces applied to the first structure 213a, based on the accelerometer signal. The first structural model unit 143a includes a low-pass filter (LPF) for noise reduction.

[0093] The second structural model unit 141a calculates a command power of the machine drive system, i.e., a driving force for the motor to operate the machine drive system 21, using the motor current signal and the encoder signal. In contrast to the second structure 212 in the third embodiment, the model of the second structure 212a is a model that includes the second table inertia, i.e., a subdivision of the table's inertia. The synthesis unit 142a can calculate a disturbance force F. d estimate the power applied to the machine drive system by adding the actual power of the machine drive system and the command power of the machine drive system.

[0094] A method for calculating parameters contained in the inverse models used in the perturbation estimation unit 14b is the same as the method for calculating the parameters contained in the inverse models used in the perturbation estimation unit 14a of the third embodiment.

[0095] As described above, the disturbance estimation unit 14b of the fourth embodiment estimates a disturbance force using the models obtained by dividing the table into the first table inertia, estimated using the machine drive system signal, and the second table inertia, estimated using the accelerometer signal. By dividing a structure equipped with an accelerometer of the structures forming the machine drive system 21 into two segments for modeling purposes in this way, the same effects as those of the first embodiment can be achieved, and a disturbance force can be estimated accurately.

[0096] The above description described the example of using the perturbation estimation unit 14b instead of the perturbation estimation unit 14 of the numerical control system 1 of the first embodiment. If the in Fig. If the motor drive control 100 shown is provided individually, the fault estimation unit 14b can be used instead of the fault estimation unit 14. Fifth embodiment.

[0097] Fig. Figure 17 is a block diagram showing a configuration example of a disturbance estimation unit according to a fifth embodiment of the present invention. A numerical control system of the fifth embodiment is the same as the numerical control system 1 of the first embodiment, except that it includes a disturbance estimation unit 14c instead of the disturbance estimation unit 14 of the first embodiment. Differences from the first embodiment are described below.

[0098] The first, third, and fourth embodiments are designed to estimate a disturbance force by the combined use of the encoder signal, the motor current signal, and the acceleration sensor signal. The motor current signal, the encoder signal, and the acceleration sensor signal are signals generated by different signal sources. Thus, the times at which the disturbance estimation unit acquires the signals are not necessarily synchronized, and synchronization errors generally occur. Therefore, as described in Fig. Figure 17 shows the disturbance estimation unit 14c of the fifth embodiment in a configuration in which a signal synchronization unit 145 is added to the disturbance estimation unit 14b described in the fourth embodiment.

[0099] The signal synchronization unit 145 has a preset first correction time for the encoder signal and a preset second correction time for the acceleration sensor signal. The first correction time is a time delay of the encoder signal relative to the motor current signal. The second correction time is a time delay of the acceleration sensor signal relative to the motor current signal. Furthermore, the signal synchronization unit 145 can record the encoder signal corresponding to the first correction time and the acceleration sensor signal corresponding to the second correction time.When the motor current signal is input at a specific time, the signal synchronization unit 145 outputs the encoder signal at a time differing from the specified time by the first correction time, and the accelerometer signal at a time differing from the specified time by the second correction time, along with the motor current signal. If the sampling rates of the motor current signal, the encoder signal, and the accelerometer signal differ from each other, the encoder signal and the accelerometer signal can be calculated at times differing from the specified time by the first and second correction times, respectively, by time interpolation or extrapolation.As described above, the disturbance estimation unit 14c corrects the time delays that arise between the motor current signal, the encoder signal, and the accelerometer signal, and estimates the disturbance force using the signals corrected for these time delays. Here, a method for synchronizing the timing of the encoder signal and the accelerometer signal with the motor current signal has been described. Alternatively, the signals can be synchronized with respect to a reference signal from the encoder signal and the accelerometer signal. Alternatively, a reference trigger signal for synchronization can be generated in the signal synchronization unit 145, and the signals can be synchronized based on this reference trigger signal.

[0100] As described above, the disturbance estimation unit 14c of the fifth embodiment is provided with the signal synchronization unit 145 to correct time synchronization errors between the signals, thereby reducing time synchronization errors and accurately estimating the disturbance force.

[0101] In the example described above, the signal synchronization unit 145 is added to the disturbance estimation unit 14b of the fourth embodiment. Similarly, time synchronization errors can be corrected in a similar manner by adding the signal synchronization unit 145 to the disturbance estimation unit 14 of the first embodiment and the disturbance estimation unit 14a of the third embodiment. Sixth embodiment.

[0102] Fig. Figure 18 is a block diagram showing a configuration example of a numerical control system according to a sixth embodiment of the present invention. In a numerical control system 1b of the sixth embodiment, a simulation unit 19 is added to the numerical control system 1 of the first embodiment, and an instruction value generation unit 11a and an identification unit 17a are provided instead of the instruction value generation unit 11 and the identification unit 17. Apart from this, the numerical control system 1b of the sixth embodiment is the same as the numerical control system 1 of the first embodiment. The same reference numerals as in the first embodiment are assigned, without further explanation, to components that have the same functions as those in the first embodiment. The following section mainly describes the differences from the first embodiment.

[0103] In the sixth embodiment, in addition to the command for the relative tool position or the command for the position of the feed drive system in the NC program coordinate system, the command for the rotation of the spindle drive system, and the feed rate command, an identification command is described in the NC program. Here, the identification command is a command that causes the identification unit 17a to start the identification processing with the dynamic characteristic parameters and the cutting process parameters.

[0104] The instruction value generation unit 11a analyzes instructions described in the NC program, generates machine drive system instructions for the machine drive systems 21 and 22 as in the first embodiment, and outputs them to the corresponding machine drive control units 13 and 15. If the analyzed instructions include the identification instruction, the instruction value generation unit 11a outputs the identification instruction to the identification unit 17a. That is, if the NC program contains an instruction that commands the identification unit 17a to perform an identification, the instruction value generation unit 11a instructs the identification unit 17a to calculate the cutting process parameters and the dynamic characteristic parameters.Furthermore, the command value generation unit 11a corrects the machine drive system commands according to the simulation results of the mechanical dynamics and the cutting process described below, which are output by the simulation unit 19.

[0105] When the identification command issued by the command value generation unit 11a is entered, the identification unit 17a calculates the dynamic characteristic parameters and the cutting process parameters using the same procedure as described in the first embodiment and outputs the calculated results to the simulation unit 19. Furthermore, the identification unit 17a compares an estimated disturbance force output by the coordinate transformation unit 12 with a simulated disturbance force output by the simulation unit 19. Here, the estimated disturbance force is a cutting force calculated by the disturbance estimation units and coordinate-transformed by the coordinate transformation unit, and the simulated disturbance force is a cutting force calculated by the simulation unit 19.If the difference between the estimated disturbance force and the simulated disturbance force exceeds a threshold, the identification unit 17a determines that the processing state has changed and re-executes the identification processing. That is, the identification unit 17a calculates the difference between a disturbance force output by the coordinate transformation unit 12 and a disturbance force simulated by the simulation unit 19. If the difference exceeds the threshold, the identification unit 17a calculates the cutting process parameters and the dynamic characteristic parameters. If the estimated disturbance force and the simulated disturbance force are calculated as vectors, the identification unit 17a can calculate the difference between the estimated and simulated disturbance forces by calculating norms for their respective cutting forces and comparing these norms.As another example, the identification unit 17a can calculate the difference between the estimated disturbance force and the simulated disturbance force in a specific direction, such as a tool movement direction, and compare the difference with the threshold value.

[0106] The simulation unit 19 calculates machine drive system positions based on encoder signals output from the machine drive systems 21 and 22, and simulates vibrations of the structures around the tool and the workpiece and the cutting process between the tool and the workpiece using the dynamic model, the cutting process model and the cutting conditions.

[0107] The vibrations of the structures around the tool and the workpiece are simulated as follows. Using the dynamic model, simulation unit 19 calculates relative displacements in the structures generated by one or both the workpiece-side and tool-side structures when a cutting force is applied. Simulation unit 19 calculates a positional deviation of the tool from the calculated relative displacements in the structures and the positions of the machine drive systems 21 and 22, and calculates disturbance forces applied to the machine drive systems 21 and 22. Here, the positional deviation of the tool is the difference between a tool position when no cutting force is applied to the tool and a tool position when a cutting force is applied to the tool.

[0108] The cutting process is simulated as follows. Simulation unit 19 calculates the path of a tool tooth edge based on the tool's positional deviation relative to the workpiece and the tool rotation angle, using the cutting conditions and the cutting process model. Simulation unit 19 calculates the uncut chip thickness based on the path of the tool tooth edge and calculates a cutting force corresponding to this uncut chip thickness. The calculated cutting force is then output to identification unit 17a.

[0109] As described above, a cutting force used in the dynamics model is calculated using the cutting process model, and a positional deviation of the tool used in the cutting process is calculated using the dynamics model. Thus, by alternately repeating the calculation using the dynamics model and the calculation using the cutting process model, simulation unit 19 can simultaneously simulate the mechanical dynamics and the cutting process from moment to moment.In other words, the simulation unit 19 can simulate the cutting force generated between the tool and the workpiece based on the motor current signal, the encoder signal, the cutting conditions and the cutting process model, and simulate the disturbance forces generated on the machine drive systems and the relative positional deviations of the tool and the workpiece when the cutting force is generated, based on the dynamic model.

[0110] This section describes the correction processing performed by the command value generation unit 11a based on the results of the mechanical dynamics simulation and the cutting process performed by the simulation unit 19. Using the tool positional deviation simulated by the simulation unit 19, the command value generation unit 11a adds a motion amount corresponding to the deviation to the machine drive system commands for the feed drive systems. This correction reduces dimensional errors caused by the tool positional deviation.

[0111] As another correction method, the command value generation unit 11a can compare the thicknesses cut by the tool tooth edges, simulated by the simulation unit 19, and correct the feed rate per tooth or the feed drive system positions so that the maximum uncut chip thicknesses produced by the tooth edges are equal. This correction can reduce vibrations of the tool tooth edges caused by changes in the uncut chip thickness. Alternatively, the command value generation unit 11a can calculate the maximum or average value within a specified time using cutting forces simulated by the simulation unit 19 and reduce the feed rate per tooth if the calculated result exceeds a predetermined cutting force limit.This correction allows the cutting force to be limited to or below the upper limit. Tool breakage due to excessive cutting force can be avoided.

[0112] As yet another correction method, the command value generation unit 11a can compare the cutting forces generated by the tooth edges during a rotation of the tool by using cutting forces simulated by the simulation unit 19 and correcting the feed rate per tooth or the spindle drive system rotational speed so that the maximum values ​​of the cutting forces generated by the tooth edges are equal. This correction reduces the cutting force applied to a particular tooth edge, thus ensuring that cutting forces are generated uniformly across the tooth edges.

[0113] As yet another correction method, the command value generation unit 11a can calculate the roughness of the machined surface based on the path of a tool tooth edge, simulated by the simulation unit 19, and reduce the feed rate per tooth if the roughness of the machined surface exceeds a predetermined upper limit. This correction results in a finished surface with a roughness that is less than or equal to the upper limit. A variety of the correction processes described above can be combined.

[0114] As described above, the numerical control system 1b of the sixth embodiment identifies the dynamic characteristic parameters and the cutting process parameters at a time specified in the NC program, or at a time when it is determined that the machining state has changed, and furthermore simulates the mechanical dynamics and the cutting process, and corrects the machine drive system commands based on the simulation results via the command value generation unit. In this way, the following effects are achieved.

[0115] Since the identification unit 17a performs processing upon receiving the identification command, the numerical control system 1b can identify the dynamic characteristic parameters and the cutting process parameters at a time specified by the NC program. Therefore, even if the machining state changes during the same NC program, the dynamic characteristic parameters and the cutting process parameters can be identified at a time described in the NC program.

[0116] Furthermore, the identification unit 17a compares an estimated disturbance force with a simulated disturbance force, allowing verification of the dynamic characteristic parameters and the cutting process parameters that determine the characteristics of the dynamic model and the cutting process model. Therefore, if the mechanical dynamics or the cutting process has changed, the identification processing can be performed in such a way that the simulation unit can correctly simulate the disturbance force compared to the estimated disturbance force. Additionally, the simulation unit 19 simulates the mechanical dynamics and the cutting process, enabling real-time modification of the cutting process.

[0117] Thus, the numerical control system 1b described in the sixth embodiment can execute the identification processing at a time not specified in the NC program, in addition to the time specified in the NC program, if the mechanical dynamics or the cutting process has changed. By performing a simulation using the dynamic model and the cutting process model, whose characteristics are determined by the dynamic characteristic parameters and the cutting process parameters obtained from the identification processing, the instruction value generation unit can make corrections to the machine drive systems based on the simulation results.

[0118] Fig. Figure 19 is a block diagram showing another configuration example of the numerical control system of the sixth embodiment. In the Fig. In the example shown in Figure 18, feedback positions, specified by encoder signals that can be detected by the machine drive systems 21 and 22, are entered into the simulation unit 19. In the example shown in Figure 18, the following applies: Fig. In the configuration example shown in Figure 19, command positions generated in the machine drive control units 13 and 15 are entered into the simulation unit 19 instead of the reset positions. The simulation unit 19 performs a simulation as described in Figure 19. Fig. The configuration example shown in 18 is implemented by using the command positions generated in the machine drive control units 13 and 15 instead of the reset positions. Operation in the configuration shown in Fig. The configuration example shown in section 19 is the same as the operation in which it is described. Fig. The configuration example shown in section 18, with the exception of the point described above. Fig. 19. The same reference numerals are assigned to components which are in Fig. The 18 functions shown are... Fig. The configuration shown in Figure 19 can achieve effects equivalent to those of the configuration shown in Figure 19. Fig. 18 shown numerical control system 1b are. Seventh embodiment.

[0119] Fig. Figure 20 is a block diagram showing a configuration example of a numerical control system according to a seventh embodiment of the present invention. A numerical control system 1c of the seventh embodiment is configured by adding a simulation unit 19 to the numerical control system 1a of the second embodiment. Apart from this, the numerical control system 1c of the seventh embodiment is identical to the numerical control system 1a of the second embodiment. The same reference numerals as in the second embodiment are assigned, without further explanation, to components that have the same functions as those of the second and sixth embodiments.

[0120] Thus, in the seventh embodiment, the dynamic characteristic parameters and the cutting process parameters are calculated as in the first embodiment, using the force sensor 23 without the acceleration sensors and the disturbance estimation units 14 and 16. Furthermore, the dynamic characteristic parameters and the cutting process parameters are identified at a time specified in the NC program or at a time when it is determined that the machining state has changed. Additionally, the mechanical dynamics and the cutting process are simulated, and the instruction value generation unit corrects machine drive system commands based on the simulation results. Therefore, the seventh embodiment has the same effects as the sixth embodiment.

[0121] Fig. Figure 21 is a block diagram showing another configuration example of the numerical control system of the seventh embodiment. In the Fig. In the example shown in Figure 20, reset positions, specified by encoder signals that can be detected by the machine drive systems 21a and 22a, are entered into the simulation unit 19. In the example shown in Figure 20, the following applies: Fig. In the configuration example shown in Figure 21, command positions generated in the machine drive control units 13 and 15 are entered into the simulation unit 19 instead of the reset positions. The simulation unit 19 performs a simulation as described in Figure 21. Fig. The configuration example shown in Figure 20 is implemented by using the command positions generated in the machine drive control units 13 and 15 instead of the reset positions. Operation in the configuration shown in Figure 20 is carried out by using the command positions generated in the machine drive control units 13 and 15 instead of the reset positions. Fig. The configuration example shown in section 21 is the same as the operation in which it is described. Fig. The configuration example shown in 20, with the exception of the point described above. Fig. 21. The same reference numerals are assigned to components that are in Fig. The 20 functions shown are included. Fig. The configuration shown in Figure 21 can achieve effects equivalent to those of the configuration shown in Figure 21. Fig. The numerical control system 1c shown in the 20 images is shown.

[0122] The configurations described in the above embodiments show an example of the subject matter of the present invention and can be combined with another known technique and can be partially omitted or modified without deviating from the scope of protection of the present invention. Reference symbol list

[0123] 1, 1a, 1b, 1c Numerical control system; 2, 2a Machine tool; 11, 11a Command value generation unit; 12 Coordinate transformation unit; 13, 15 Machine drive control unit; 14, 14a, 14b, 14c, 16 Fault estimation unit; 17, 17a Identification unit; 18 Storage unit; 21, 21a, 22, 22a Machine drive system; 23 Force sensor; 31 Table; 32 Workpiece; 33 Tool; 100 Motor drive control; 211, 221 Accelerometer.

Claims

[1] A numerical control system that controls machine drive systems (21, 22; 21a, 22a) included in a machine tool that performs machining using a tool according to a numerical control program, the system comprising: a coordinate transformation unit (12) for detecting a disturbance force or a disturbance torque applied to each of the machine drive systems (21, 22; 21a, 22a) and for coordinate transformation of the disturbance force or the disturbance torque into a tool reference coordinate system for output; and an identification unit (17, 17a) for calculating cutting process parameters that determine characteristics of a cutting process model and dynamic characteristic parameters that determine characteristics of a dynamic model of the machine tool, using the disturbance force or the disturbance torque output from the coordinate transformation unit (12), states of the machine drive systems (21, 22; 21a, 22a), predetermined equation models and cutting conditions, wherein the equation models define relationships between the cutting process parameters, the dynamic characteristic parameters and the disturbance force or the disturbance torque. [2] The numerical control system (1a) according to claim 1, wherein the coordinate transformation unit (12) detects the disturbance force or the disturbance torque from a detection result detected by a sensor (23) for detecting a disturbance force or a disturbance torque applied to each of the machine drive systems (21a, 22a). [3] Numerical control system (1) according to claim 1, further comprising: a disturbance estimation unit (14, 16) for estimating the disturbance force or the disturbance torque applied to each of the machine drive systems (21, 22) using a detection result detected by one or more sensors (211, 221) each detecting the speed or acceleration of a corresponding one of the machine drive systems (21, 22), wherein the coordinate transformation unit (12) detects the disturbance force or the disturbance torque from the disturbance estimation unit (14, 16). [4] Numerical control system (1) according to one of claims 1 to 3, wherein, when the detected disturbance forces or disturbance moments include components in the same direction on tool reference coordinates, the coordinate transformation unit (12) selects a combination in which directions are independent of each other from the detected disturbance forces or disturbance moments. [5] Numerical control system (1) according to claim 3, wherein one of the machine drive systems (21) includes a first structure (213) and a second structure (212) including a motor, the disturbance estimation unit (14a) calculates an actual power of the machine drive system, i.e., a resultant of forces applied to the first structure (213), based on a plurality of first structural models (143, 144) of the first structure (213) and the detection result, calculates a command power of the machine drive system, i.e., a force applied by the motor to one of the machine drive systems, based on a second structural model (141) of the second structure (212), a detection result of a motor current flowing through the motor, and a detection result of a position of the motor, and estimates the disturbance force or the disturbance torque using the actual power of the machine drive system and the power command of the machine drive system, and the plurality of first structural models (142, 144) have different frequency characteristics determined according to a plurality of divided frequency bands. [6] Numerical control system (1) according to claim 3, wherein one of the machine drive systems (21) includes a first structure (213a) and a second structure (212a) including a motor, the disturbance estimation unit (14b) calculates an actual power of the machine drive system, i.e., a resultant of forces applied to the first structure (213a), based on a first structural model (143a) of the first structure (213a) and the detection result, calculates a power command of the machine drive system, i.e., a force applied by the motor to one of the machine drive systems, based on a second structural model (141a) of the machine drive system, which includes the motor of the machine drive system, a detection result of a motor current flowing through the motor, and a detection result of a position of the motor, and estimates the disturbance force or the disturbance torque using the actual power of the machine drive system and the power command of the machine drive system, and one of the structures constituting said one of the machine drive systems (21) is divided into a first inertial body model and a second inertial body model for modeling, wherein the first structural model (143a) includes the first inertial body model and the second structural model (141a) includes the second inertial body model. [7] The numerical control system (1) according to claim 5 or 6, wherein the disturbance estimation unit (14c) corrects time delays generated between a signal indicating the detection result of the motor current, a signal indicating the detection result of the position of the motor, and a signal indicating the detection result of the sensor (23), and estimates the disturbance force or the disturbance torque using the signals corrected in the time delays. [8] Numerical control system (1b; 1c) according to one of claims 1 to 7, wherein one of the machine drive systems (21; 21a) includes a first structure (213) and a second structure (212) including a motor, the numerical control system further comprises a simulation unit (19) for simulating a cutting force generated between the tool and a workpiece machined by the tool based on a detection result of a motor current flowing through the motor, a detection result of a position of the motor, the cutting conditions, and the cutting process model, and for simulating a disturbance force or a disturbance torque generated in each of the machine drive systems (21, 22; 21a, 22a) and a relative positional deviation between the tool and the workpiece when a cutting force is generated based on the dynamic model. [9] The numerical control system (1b) according to claim 8, wherein the identification unit (17a) calculates a difference between the disturbance force output from the coordinate transformation unit (12) and the disturbance force simulated by the simulation unit (19) or a difference between the disturbance torque output from the coordinate transformation unit (12) and the disturbance torque simulated by the simulation unit (19), and calculates the cutting process parameters and the dynamic characteristic parameters when the calculated difference is greater than a threshold value. [10] The numerical control system (1b) according to claim 8 or 9, further comprising a command value generation unit (11a) for commanding the identification unit to execute a calculation of the cutting process parameters and the dynamic characteristic parameters when the numerical control program includes a command commanding execution of an identification by the identification unit. [11] A numerical control system (1b) according to claim 10, wherein the command value generation unit (11a) corrects commands for the machine drive systems according to results simulated by the simulation unit (19). [12] Numerical control system (1; 1a; 1b; 1c) according to one of claims 1 to 11, wherein the cutting process model is a mathematical model for calculating an uncut chip thickness based on a tool rotation angle and a relative displacement between a tooth edge of the tool and a workpiece machined by the tool, and for calculating a generated cutting force based on the uncut chip thickness between the tool and the workpiece, and the dynamic model is a mathematical model for calculating disturbance forces or disturbance torques transmitted to the machine drive systems by mechanical structures containing the tool or workpiece when the cutting force is generated, and for calculating positional deviations generated on the machine drive systems by the mechanical structures when the cutting force is generated. [13] Numerical control system (1; 1a; 1b; 1c) according to claim 12, wherein the cutting process model is a model in which the uncut chip thickness is calculated based on a difference between a path formed by a tooth edge of the tool involved in cutting and a previous machined surface formed by a tooth edge one or more teeth before the tooth edge involved in cutting. [14] The numerical control system (1; 1a; 1b; 1c) according to claim 12, wherein the cutting process model is a model in which a correction amount corresponding to a number indicating the tooth edge of the tool and a rotation angle of the tool is added to or subtracted from the uncut chip thickness. [15] Numerical control system (1; 1a; 1b; 1c) according to claim 12, wherein the cutting process model is a model in which it is determined whether the tooth edge contacts the workpiece based on the positional deviation at each rotation angle of the tool or at any time, and when the tooth edge contacts the workpiece, the uncut chip thickness is calculated, and when the tooth edge does not contact the workpiece, the uncut chip thickness is calculated to be zero. [16] Motor drive control (100), comprising: a machine drive control unit (13, 15) for controlling a machine drive system (21) including an engine; and a disturbance estimation unit (14a) for estimating a disturbance force or a disturbance torque applied to the machine drive system (21) using a detection result detected by a sensor for detecting the speed or acceleration of the machine drive system (21), wherein the disturbance estimation unit (14a) calculates the actual power of the machine drive system, which corresponds one-to-one to a plurality of first structural models (143, 144) of the machine drive system (21), from the detection result based on the first structural models (143, 144), calculates a command power of the machine drive system, i.e., a force applied by the motor to the machine drive system (21), based on a second structural model (141) of the machine drive system (21) including the motor of the machine drive system (21), a detection result of a motor current flowing through the motor, and a detection result of a position of the motor, and estimates the disturbance force or the disturbance torque using the actual power of the machine drive system and the command power of the machine drive system, and the plurality of first structural models (143, 144) have different frequency characteristics determined according to a plurality of divided frequency bands. [17] Motor drive control (100), comprising: a machine drive control unit (13) for controlling a machine drive system (21) including an engine; and a disturbance estimation unit (14b) for estimating a disturbance force or a disturbance torque applied to the machine drive system (21) using a detection result detected by a sensor (211) for detecting the speed or acceleration of the machine drive system (21), wherein the disturbance estimation unit (14b) calculates an actual power of the machine drive system corresponding to a first structural model (143a) of the machine drive system (21) from the detection result based on the first structural model (143a), calculates a power command of the machine drive system, i.e., a force applied by the motor to the machine drive system (21), based on a second structural model (141a) of the machine drive system (21) including the motor of the machine drive system (21), a detection result of a motor current flowing through the motor, and a detection result of a position of the motor, and estimates the disturbance force or the disturbance torque using the actual power of the machine drive system and the power command of the machine drive system, and one of a plurality of structures constituting the machine drive system (21) is divided into a first inertial body model and a second inertial body model for modeling, wherein the first structural model (143a) includes the first inertial body model and the second structural model (141a) includes the second inertial body model. [18] The motor drive controller (100) according to claim 16 or 17, wherein the disturbance estimation unit (14c) corrects time delays generated between a signal indicating the detection result of the motor current, a signal indicating the detection result of the position of the motor, and a signal indicating the detection result of the sensor, and estimates the disturbance force or the disturbance torque using the signals corrected in the time delays.

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