Precision diagnosis device and precision diagnosis method for machine tool

Abstract

The present invention relates to a precision diagnosis device and a precision diagnosis method for a machine tool. The influence of an environmental temperature change on the precision of a machine tool is predicted in real time, a condition in which thermal displacement is large is diagnosed appropriately, and a production plan is easily made. In a machine tool (M), a precision diagnosis device (D) that diagnoses the influence of thermal deformation on precision is provided with: a temperature change speed calculation unit (31) that calculates the speed of a temperature change obtained from a machine body temperature sensor (10) and an environmental temperature sensor (20) as a temperature change speed; a precision influence degree calculation unit (32) that calculates the degree of influence of thermal deformation on the precision of the machine tool (M) as a precision influence degree based on the temperature change speed; and a precision stabilization time calculation unit (33) that calculates the time until the precision of the machine tool (M) is stabilized as a precision stabilization time from the temperature change speed.

Description

Technical Field

[0001] This invention relates to an apparatus and method for predicting and diagnosing the impact of changes in the temperature of the machine tool itself or the temperature of the environment in which the machine tool is placed on the accuracy of the machine tool. Background Technology

[0002] When machining with machine tools, if the room temperature changes, thermal deformation will occur, causing the machine tool structure to expand or bend. As a result, thermal displacement will occur, changing the positional relationship between the tool and the workpiece mounted on the machine tool, thereby deteriorating the machining accuracy of the workpiece.

[0003] As a method to suppress thermal displacement of machine tools, thermal displacement correction is widely used: temperature sensors are installed in various parts of the machine tool structure, and the displacement is calculated based on the measured temperature, with corresponding changes in axis movement. However, the accuracy of thermal displacement correction is limited, and errors will occur under conditions of large temperature changes. In particular, it is believed that the error of thermal displacement correction will increase under conditions of rapid room temperature changes, such as when an air conditioner is turned on.

[0004] As a countermeasure to the above problems, Patent Document 1 discloses a method that calculates the rate of temperature change at a specified part of a machine tool and calculates the influence of thermal displacement on the machine tool's accuracy based on this rate of temperature change. In this method, when a rapid temperature change occurs, a deterioration in the machine tool's accuracy is diagnosed, and the situation is reported. On the other hand, when the temperature change is stable, the machine tool's accuracy is diagnosed as stable, and machining can begin. This prevents poor machining accuracy.

[0005] Patent Document 1: Japanese Patent Application Publication No. 2019-136846

[0006] In the method of Patent Document 1, when a sharp temperature change or other factor is diagnosed as causing a deterioration in the machine tool's accuracy, machining is not performed during that period, thereby preventing poor machining accuracy. However, since machining cannot be performed when accuracy deterioration is diagnosed, it is unknown when the machine tool's accuracy will stabilize again and machining can resume, making it impossible to formulate a production plan. Summary of the Invention

[0007] Therefore, the purpose of this invention is to provide a machine tool accuracy diagnostic device and accuracy diagnostic method, which can predict the impact of temperature changes on the accuracy of the machine tool in real time, properly diagnose the situation of increased thermal displacement, and easily formulate production plans.

[0008] To achieve the above objectives, the first invention of this invention is a precision diagnostic device that diagnoses the influence of thermal deformation on precision in machine tools, characterized by having:

[0009] The temperature change rate calculation unit calculates the rate of temperature change at a specified part of the machine tool and uses it as the temperature change rate.

[0010] The accuracy impact calculation unit calculates the impact of thermal deformation on the machine tool's accuracy based on the rate of temperature change, using this as the accuracy impact value; and

[0011] The accuracy stabilization time calculation unit calculates the time until the machine tool's accuracy stabilizes based on the rate of temperature change, and uses this as the accuracy stabilization time.

[0012] In other aspects of the first invention, in the above structure, the accuracy stabilization time calculation unit compares the current accuracy influence with a pre-defined allowable value for the accuracy influence, and if the current accuracy influence deviates from the allowable value, calculates the time until the accuracy influence returns to within the allowable value as the accuracy stabilization time.

[0013] Another aspect of the first invention is characterized in that, in the above structure, it further includes a precision stabilization time display unit for displaying the precision stabilization time.

[0014] To achieve the above objectives, the second invention of this invention is a precision diagnosis method for diagnosing the impact of thermal deformation on precision in machine tools, characterized by performing the following steps:

[0015] The temperature change rate calculation steps involve calculating the rate of temperature change at a specified part of the machine tool to determine the temperature change rate.

[0016] The steps for calculating the accuracy impact degree include: calculating the impact of thermal deformation on the machine tool's accuracy based on the rate of temperature change, and using this as the accuracy impact degree; and...

[0017] The accuracy stabilization time calculation steps are as follows: the time until the machine tool's accuracy stabilizes is calculated based on the rate of temperature change.

[0018] In another aspect of the second invention, in the above structure, during the accuracy stabilization time calculation step, the current accuracy influence degree is compared with a pre-defined allowable value for the accuracy influence degree. If the current accuracy influence degree deviates from the allowable value, the time until the accuracy influence degree returns to within the allowable value is calculated as the accuracy stabilization time.

[0019] Another aspect of the second invention is characterized in that, in the above structure, a precision stabilization time display step is also performed.

[0020] Invention Effects

[0021] According to the present invention, the influence of thermal displacement of machine tools on accuracy can be appropriately predicted, and when the accuracy is diagnosed as becoming unstable, the time until the accuracy stabilizes can be predicted as the accuracy stabilization time.

[0022] By displaying the predicted results and notifying the operator, it becomes clear when the machine tool's accuracy will stabilize again and production can resume. This makes it easier to plan production while ensuring the required accuracy. For example, if the accuracy stabilization time is short, a plan can be made to wait until accuracy stabilizes before resuming production; if the accuracy stabilization time is long, the plan can be modified to prioritize less precise machining operations. Attached Figure Description

[0023] Figure 1 This is a conceptual diagram of a machine tool (vertical multi-process automatic CNC machine tool) and a precision diagnostic device.

[0024] Figure 2 This is a flowchart of the accuracy diagnosis method.

[0025] Figure 3 This is an example of displaying the accuracy diagnostic results and accuracy stabilization time.

[0026] Label Explanation

[0027] M: Machine tool (multi-process automatic CNC machine tool); C: Control device; D: Precision diagnostic device; 10: Machine body temperature sensor; 20: Ambient temperature sensor; 31: Temperature change rate calculation unit; 32: Precision influence calculation unit; 33: Precision stabilization time calculation unit; 34: Precision stabilization time display unit. Detailed Implementation

[0028] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0029] Figure 1 This is an example of a machine tool (vertical multi-process automatic CNC machine tool) that utilizes the present invention. Additionally, in Figure 1 In order to illustrate the mechanical structure in a way that is easy to understand, descriptions of covers such as those covering the outer periphery of the machine tool M have been omitted. Furthermore, the machine tool used can be a multi-process automatic CNC machine tool other than a vertical multi-process automatic CNC machine tool; it can be a lathe, grinding machine, or other types of machine tools.

[0030] A body temperature sensor 10 and an ambient temperature sensor 20, which measure the ambient room temperature and the temperature of the cutting fluid, are installed on the machine tool M and connected to the control device C. The body temperature sensor 10 and the ambient temperature sensor 20 are... Figure 1 There is one location for each of the two sensors, but multiple locations can be set as needed. The ambient temperature sensor 20 can also be omitted.

[0031] On the other hand, the control device C includes a CPU, a storage unit, a timer, an input unit (keyboard, touch panel, etc.), an output unit (display, etc.), and an interface connecting these input units, output units, and the CPU.

[0032] Furthermore, the control device C includes a temperature change rate calculation unit 31, which estimates the rate of temperature change at a specified part of the machine tool M based on the detected temperatures of the machine body temperature sensor 10 and the ambient temperature sensor 20, according to the accuracy diagnostic program stored in the storage unit.

[0033] In addition, the control device C includes a precision influence calculation unit 32, which calculates the influence of thermal displacement on the precision of the machine tool M based on the temperature change rate estimated by the temperature change rate calculation unit 31, according to the precision diagnostic program.

[0034] Furthermore, the control device C includes a precision stabilization time calculation unit 33. When it is diagnosed that the machine tool M has a large impact on its precision and its precision has deteriorated, the precision stabilization time calculation unit 33 calculates the time required until the precision stabilizes again based on the temperature change rate estimated by the temperature change rate calculation unit 31, according to the precision diagnosis procedure.

[0035] Furthermore, the control device C includes a precision stabilization time display unit 34, which displays the calculated precision stabilization time on a screen according to the precision diagnostic program. In other words, the machine body temperature sensor 10, the ambient temperature sensor 20, and the control device C constitute the precision diagnostic device D for the machine tool M.

[0036] Next, based on Figure 2 The flowchart illustrates the process of each procedure performed by the accuracy diagnostic device D, as well as the methods for calculating the rate of temperature change, the impact on accuracy, and the accuracy stabilization time.

[0037] In the event of a change in the accuracy of machine tool M, in step S1, the accuracy diagnostic process begins when the operator inputs a diagnostic start signal. In the following step S2, temperature is detected using temperature sensors 10 and 20 located at various points on machine tool M. However, step S1 can be omitted, and the diagnostic start signal can be omitted; instead, the accuracy diagnostic processes S2 through S7 can be executed automatically at predetermined time intervals.

[0038] In S3, the rate of temperature change of each part of the computer bed M is calculated (temperature change rate calculation steps). The rate of temperature change is calculated, for example, as shown in Equation 1 below, by calculating the difference between the current temperature and the temperature before time Δt and converting it into the temperature change per unit time.

[0039]

[0040] Δt: Time interval (s)

[0041] θ m (t): Body temperature (°C)

[0042]

[0043] Equation 1 is one example of the calculation method. The rate of temperature change can also be calculated using other methods, such as numerical differentiation with a filter, or by solving the problem based on the difference between the body temperature and the ambient temperature as described in Patent Document 1.

[0044] In S4, based on the temperature change rate calculated in S3, the accuracy influence E is calculated using the function f (accuracy influence calculation step), as shown in Equation 2 below. Then, in S5, the calculated accuracy influence E is output. The method for outputting this information will be explained in detail later.

[0045]

[0046] E: Accuracy Influence

[0047]

[0048] In S6, based on the temperature change rate calculated in S3, the time until accuracy stabilizes, i.e., the accuracy stabilization time Ts, is then calculated (accuracy stabilization time calculation step). Next, in S7, the calculated accuracy stabilization time Ts is output (accuracy stabilization time display step). The output method will be explained in detail later. The accuracy stabilization time Ts can also be expressed as a function of the temperature change rate, similar to the accuracy influence E, as shown in Equation 3 below.

[0049]

[0050] Ts: Accuracy stabilization time

[0051]

[0052] Examples of specific calculations for the accuracy stabilization time Ts are shown in Equations 4a to 4c below. In these examples, the accuracy influence E is defined as having a larger value when accuracy is unstable and a smaller value when accuracy is stable. The rate of change of the accuracy influence E is then calculated. The current accuracy influence E exceeds the threshold (allowable value) E that is considered to be accuracy stable. limitFurthermore, the rate of change of the accuracy influence degree E is positive, meaning that the accuracy will become more unstable and the value of the accuracy influence degree E is increasing, making it impossible to calculate the accuracy stabilization time, which becomes infinite (Equation 4a). On the other hand, when the current accuracy influence degree E exceeds the threshold E... limit However, the rate of change of the accuracy influence E is also negative, meaning that the accuracy tends to stabilize, and the value of the accuracy influence E is decreasing. We can assume that the accuracy influence E changes at the current rate and calculate until it reaches the threshold E again. limit The following is the time up to (Equation 4b). If the current accuracy impact value E is the threshold E limit The accuracy stabilization time is then 0 (Equation 4c).

[0053]

[0054]

[0055] Ts(t)=0 E(t)≤E limit (Equation 4c)

[0056] E limit The threshold of accuracy influence E

[0057] The accuracy influence E in equations 4a to 4c is a function of the temperature change rate, as shown in equation 2. Therefore, the accuracy stabilization time Ts can be calculated based on the temperature change rate. Alternatively, a threshold can be set instead of E. limit The calculation is performed with a value of 0. Furthermore, when the accuracy influence E is defined as a smaller value when accuracy is unstable and a larger value when accuracy is stable, the calculation can be performed by reversing the relationships in equations 4a to 4c.

[0058] Next, according to Figure 3 Examples of "S5: Accuracy Impact Output" and "S7: Accuracy Stabilization Time Output" will be provided.

[0059] Figure 3 (A) Figure 3 (B) Figure 3 (C) is an example of the display screen of the accuracy diagnostic device D. This display screen is shown on the monitor of the control device C of the machine tool M. However, it can also be displayed on the screen of a PC or the like connected to the machine tool M. The display screen of the accuracy diagnostic device D includes a diagnostic result display bar M1 that displays the diagnostic results as "good" or "bad", a precision stabilization time display bar M2, a precision influence display bar M3, and a threshold setting bar M4. Furthermore, to facilitate understanding of the results, a graph display bar M5 and a message display bar M6 are provided as needed.

[0060] The accuracy impact value E calculated using Equation 2 is displayed in the accuracy impact value display panel M3. The threshold value E, which is considered stable for accuracy, is set in the threshold setting panel M4. limit The settings and display. In the diagnostic results display column M1, when the accuracy impact E is greater than the threshold E... limit In cases where the value is less than the threshold E, it will be displayed as "bad". limit In this case, the message is displayed as "Good" (the accuracy impact factor E is defined as a value that is large when accuracy is unstable and small when accuracy is stable). In this example, the message is displayed on the screen as "Good" or "Bad," but it could also be displayed using other methods such as changing the color. Furthermore, it's also possible to consider generating an alarm in the "Bad" case, notifying the user via an alarm sound or email notification, or stopping the machine tool. Additionally, the threshold E... limit Alternatively, it can be set to a fixed value, thus omitting the threshold setting column M4.

[0061] The accuracy stabilization time Ts is displayed in the accuracy stabilization time display bar M2. At this time, the results of equations 4a to 4c can also be displayed directly, or Ts'(t) after transformation of Ts(t) can be displayed as shown in equations 5a to 5b below.

[0062] Ts′(t)=Ts limit (Ts(t)≥Ts limit (Equation 5a)

[0063] Ts′(t)=Ts(t) (Ts(t<Ts) limit (Equation 5b)

[0064] Ts(t): The calculated value of time when the accuracy is stable.

[0065] Ts′(t): Display value of accuracy settling time

[0066] T slimit Upper limit of accuracy stabilization time Ts

[0067] The value of Ts'(t) calculated using equations 4a to 4c is greater than the preset upper limit value Ts. limit In this case, set it to Ts limit That is, when the value of the accuracy impact factor E is deteriorating, or when it is recovering but recovering very slowly, and it is predicted that it will take a very long time before it recovers, it is difficult to calculate the accuracy stabilization time with high accuracy, and therefore it is displayed as a fixed value or higher.

[0068] Figure 3 (A) shows an example of the display screen in the case of Equation 5b. Figure 3 (B) shows an example of the display screen in the case of Equation 5a. In this example, Tslimit =120, in Figure 3 In section (B), the accuracy stabilization time is displayed as "more than 120 minutes". Additionally, if the accuracy impact factor E is less than the threshold, i.e., if "good" is displayed in the diagnostic result display column M1, the accuracy stabilization time does not need to be displayed. Figure 3 Example of this case is shown in (C).

[0069] like Figure 3 (A) Figure 3 As shown in (C), by displaying the accuracy diagnostic results as "good" or "bad" and showing the expected time (accuracy stabilization time) until the diagnostic result becomes "good," operators can easily formulate production plans while maintaining accuracy. For example, even if the diagnostic result is "bad," if the accuracy stabilization time is short, a plan can be made to wait until the accuracy stabilizes before resuming processing. If the accuracy stabilization time is long, the plan can be changed to perform processing with lower accuracy requirements first, or countermeasures such as checking the factory environment (air conditioning, etc.) can be implemented to stabilize the machine tool's accuracy.

[0070] According to the accuracy diagnostic device D and accuracy diagnostic method described above, the rate of temperature change at a specified part of the machine tool M is calculated as the temperature change rate. Based on the temperature change rate, the influence of thermal deformation on the accuracy of the machine tool M is calculated as the accuracy influence rate E. Based on the temperature change rate, the time until the accuracy of the machine tool M stabilizes is calculated as the accuracy stabilization time Ts.

[0071] Based on this structure, the impact of thermal displacement of machine tool M on accuracy can be accurately predicted, and in cases where accuracy becomes unstable, the time until accuracy stabilizes is predicted as the accuracy stabilization time Ts. Therefore, by displaying the predicted results and notifying the operator, it is possible to know when the accuracy of machine tool M can stabilize again and begin machining. This makes it easy to formulate production plans while ensuring the required accuracy.

[0072] In addition, although the above method uses a function of the rate of temperature change to calculate the accuracy impact and accuracy stabilization time, it is also possible to pre-generate a database that sets the relationship between the value or specified range of the rate of temperature change and the corresponding accuracy impact and accuracy stabilization time, and to calculate the accuracy impact and accuracy stabilization time based on the rate of temperature change by referring to the database.

[0073] Furthermore, the accuracy diagnostic device is not limited to being constructed using the machine tool's control unit. For example, it can also be configured in an external server computer with a temperature change rate calculation unit, an accuracy impact calculation unit, an accuracy stabilization time calculation unit, and an accuracy stabilization time display unit, and send the temperature detected by the temperature sensor to the server computer for accuracy diagnostics. In this case, multiple machine tools can be diagnosed at one location. Alternatively, a portion of the accuracy diagnostics, such as the calculation of accuracy stabilization time, can be performed externally, and the accuracy stabilization time can be displayed on each machine tool.

Claims

1. A precision diagnostic device for a machine tool, characterized in that, it diagnoses the influence of thermal deformation on the precision of the machine tool. The machine tool's accuracy diagnostic device has the following features: The temperature change rate calculation unit calculates the rate of temperature change at a specified part of the machine tool as the temperature change rate. The accuracy impact calculation unit calculates the impact of thermal deformation on the accuracy of the machine tool based on the rate of temperature change, and uses this as the accuracy impact. as well as The accuracy stabilization time calculation unit calculates the time until the machine tool's accuracy stabilizes based on the rate of temperature change, and uses this time as the accuracy stabilization time. The accuracy stabilization time calculation unit performs the following processing: Based on whether the rate of change of the accuracy influence is positive or negative, it is determined whether the accuracy is trending towards stability, and the current accuracy influence is compared with a pre-defined allowable value for the accuracy influence. If the current accuracy impact exceeds the allowable value, and the rate of change of the accuracy impact is positive, thus making the accuracy more unstable, then the accuracy stabilization time is calculated to be infinite. When the current accuracy impact exceeds the allowable value, and the rate of change of the accuracy impact is negative, thus the accuracy is stabilizing, the time until the accuracy impact falls back below the allowable value is calculated using the rate of change of the accuracy impact as the accuracy stabilization time.

2. The machine tool precision diagnostic device according to claim 1, characterized in that, The machine tool's precision diagnostic device also includes a precision stabilization time display unit that displays the precision stabilization time.

3. A method for diagnosing the accuracy of a machine tool, characterized in that, Perform the following steps: The temperature change rate calculation step calculates the rate of temperature change at a specified part of the machine tool as the temperature change rate. The accuracy impact calculation step involves calculating the impact of thermal deformation on the machine tool's accuracy based on the temperature change rate, using this as the accuracy impact value; and... The accuracy stabilization time calculation step involves calculating the time until the machine tool's accuracy stabilizes based on the rate of temperature change, and using this time as the accuracy stabilization time. The following processing is performed in the accuracy stabilization time calculation step: Based on whether the rate of change of the accuracy influence is positive or negative, it is determined whether the accuracy is trending towards stability, and the current accuracy influence is compared with a pre-defined allowable value for the accuracy influence. If the current accuracy impact exceeds the allowable value, and the rate of change of the accuracy impact is positive, thus making the accuracy more unstable, then the accuracy stabilization time is calculated to be infinite. When the current accuracy impact exceeds the allowable value, and the rate of change of the accuracy impact is negative, thus the accuracy is stabilizing, the time until the accuracy impact falls back below the allowable value is calculated using the rate of change of the accuracy impact as the accuracy stabilization time.

4. The machine tool accuracy diagnosis method according to claim 3, characterized in that, The precision stabilization time display step is also performed.

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