JP6985174B2 - Machine tool accuracy diagnostic equipment - Google Patents

Description

The present invention relates to a method and an apparatus for predicting and diagnosing the influence on the accuracy of a machine tool when the temperature of the environment in which the machine tool is placed changes.

When machining using a machine tool, if the room temperature in the factory changes, thermal displacement occurs in the machine tool, and the machining accuracy of the workpiece deteriorates. As a method of suppressing the thermal displacement of the machine tool, a temperature sensor is attached to each part of the structure of the machine tool (hereinafter, also referred to as the machine body), the displacement amount is calculated based on the measured temperature, and the axial movement amount is correspondingly. Thermal displacement correction that changes the temperature is widely used. However, the accuracy of thermal displacement correction is limited, and an error occurs when the temperature change is large. In particular, when the room temperature changes suddenly when the air conditioner is started up, the error of thermal displacement correction becomes large.

As a countermeasure against such thermal displacement correction problems, by measuring not only the temperature of each part of the structure of the machine tool but also the temperature of the environment such as room temperature and coolant temperature, the temperature change of the part that is not directly measured is estimated. However, a method of performing thermal displacement correction corresponding to a sudden temperature change in the environment has been proposed (Patent Document 1). In addition, a method has been proposed in which the temperature change in the environment in which the machine tool is placed is estimated based on the temperature of the structure of the machine tool, and the installation environment and condition of the machine tool are diagnosed based on the temperature change in the environment. (Patent Document 2). In the diagnostic method of Patent Document 2, the installation environment and state of the machine tool are diagnosed by calculating the time change rate of the temperature of the structure which directly affects the accuracy of the machine tool.

Japanese Unexamined Patent Publication No. 2017-24108 Japanese Patent No. 5912756

Since the method of Patent Document 1 calculates the temperature change and the thermal displacement based on a preset mathematical formula, if there is an error in the parameters set in the mathematical formula, an error also occurs in the thermal displacement correction. In particular, when the temperature change is large and rapid, the tendency becomes remarkable. Further, in the thermal displacement correction as in Patent Document 1, it is difficult to deal with the change in the squareness due to the inclination of the column and the inclination of the cutting edge.

On the other hand, the method of Patent Document 2 may not be able to cope with such a situation because the change in the airframe temperature may continue and become unstable even after the room temperature stabilizes. Further, in the method of Patent Document 2 in which the time change rate of the temperature of the machine is calculated and the diagnosis is performed, the temperature of the machine changes with a delay with respect to the ambient temperature, and the time change rate is calculated by the difference from the past temperature. Since it is calculated, there is a time lag in the diagnosis. In particular, since the temperature change of the airframe caused by the temperature change of the environment is gradual, a high-performance temperature sensor is required to obtain an accurate time change rate in real time, which requires a large cost. It ends up.

An object of the present invention is to solve the problems of the conventional machine tool accuracy diagnosis method as in Patent Documents 1 and 2, to predict the influence of the environmental temperature change on the machine tool accuracy in real time, and to increase the thermal displacement. It is an object of the present invention to provide an accuracy diagnosis device for a machine tool that can appropriately diagnose a situation and can be constructed at low cost.

In order to solve the above problems, the invention according to claim 1 is a machine tool accuracy diagnostic device for diagnosing the influence of thermal displacement of a machine tool on accuracy, and is a temperature change at a predetermined part of the machine tool. Accuracy of calculating the degree of influence of thermal displacement on the machine tool accuracy based on the temperature change rate calculation means that calculates (estimates) the speed of the machine tool and the temperature change rate calculated (estimated) by the temperature change rate calculation means. It is characterized by having a means for calculating the degree of influence.

According to the second aspect of the present invention, in the accuracy diagnosis device for the machine tool according to the first aspect, the temperature change rate calculating means changes the thermal displacement in the + direction of an arbitrary vector due to the temperature change of the machine tool. It is characterized in that the rate of temperature change of a part and the rate of temperature change of a part changing in the-direction are calculated (estimated), respectively.

The invention according to claim 3 is the machine tool accuracy diagnostic apparatus according to claim 1 or 2, wherein the machine body temperature sensor for measuring the temperature of the machine body at each part and the ambient temperature or coolant temperature of the machine tool are used. It is equipped with an environmental temperature sensor that measures at least one of them, and the temperature change rate calculating means has a temperature difference between the machine temperature measured by the machine temperature sensor and the environment temperature measured by the environment temperature sensor, and for each part. It is characterized in that the temperature change rate is obtained by using the time constant of the aircraft temperature change with respect to a predetermined environmental temperature change.

The invention according to claim 4 is the machine tool accuracy diagnostic apparatus according to claim 3, wherein when the temperature change rate calculation means uses a coolant, the coolant temperature is used as the environmental temperature, and the coolant is used. When is not used, the ambient temperature is used as the environmental temperature.

The invention according to claim 5 is the accuracy diagnosis device for the machine tool according to any one of claims 1 to 4, wherein the accuracy influence calculation means is the position accuracy of the machine tool at the cutting edge in each axial direction. It is characterized in that it calculates the degree of influence on any of the inclination at the cutting edge, the expansion / contraction of each straight axis, the change in straightness, and the change in the geometric error between each axis.

The accuracy diagnostic device according to claim 1 appropriately determines the influence on the accuracy due to the thermal displacement of the machine tool by obtaining the degree of influence on the accuracy based on the change speed of the machine temperature instead of the thermal displacement itself of the machine tool. Can be predicted.

The accuracy diagnostic apparatus according to claim 2 obtains the temperature change rate at a portion where the temperature change affects the + direction and a portion where the temperature change affects the − direction, respectively, and obtains a temperature balance (environmental temperature and aircraft temperature). The degree of influence of accuracy is calculated as to how rapidly the equilibrium state) is changing, enabling real-time output. Therefore, according to the accuracy diagnostic apparatus according to claim 2, it can be immediately recognized that the larger the degree of influence on accuracy, the larger the thermal displacement correction error and the higher the possibility that the accuracy deteriorates. It is possible to instantly and accurately determine the measurable timing.

In addition, the general thermal displacement correction method that estimates and corrects the thermal displacement based on the temperature of the aircraft is a deviation between the actual temperature distribution of the aircraft and the detected temperature of the sensor when the temperature balance changes suddenly. However, in the accuracy diagnostic apparatus according to claim 2, even if such a situation does not occur and the temperature balance changes abruptly, the degree of influence of accuracy with a small error tends to increase. Can be calculated.

The accuracy diagnostic device according to claim 3 uses a temperature sensor having a low resolution of about 0.1 ° C. because it obtains the change rate of the body temperature of each part in real time and diagnoses the accuracy from the change rate. Even with an inexpensive configuration, the effect on accuracy can be appropriately diagnosed.

That is, the general method for determining the temperature change rate is to obtain the difference between the current temperature and the temperature before a predetermined time and convert it into the temperature change per fixed time. In addition to the time lag in the temperature change, it is usually difficult to detect the temperature change rate in real time because the change itself is gradual. On the other hand, since the temperature change of the airframe changes depending on the ambient temperature, the change in the airframe temperature can be predicted by measuring the temperature of the ambient environment as well as the airframe temperature. Further, the larger the difference between the airframe temperature and the ambient air temperature, the greater the rate of change in the airframe temperature thereafter. Furthermore, the rate of change in airframe temperature is inversely proportional to the time constant of the airframe's temperature change with respect to changes in the air temperature around the site. Then, in a part where the heat capacity is large and the time constant of the temperature change of the aircraft with respect to the change of the ambient air temperature is large, it is expected that the change rate of the airframe temperature will be slow even if there is a difference between the airframe temperature and the ambient air temperature. On the contrary, in the part where the heat capacity is small and the time constant of the aircraft temperature change with respect to the change of the ambient air temperature is small, it is expected that the change rate of the aircraft temperature will be large even if the temperature difference between the aircraft temperature and the ambient air temperature is small. Therefore, the temperature change time constant of the part where the body temperature is being measured is obtained in advance by experiments, etc., and the change rate of the body temperature of each part is calculated using the measurement results of the machine body temperature and the ambient environment temperature and the time constant. By doing so, the rate of change can be obtained in real time. The accuracy diagnosis device according to claim 3 uses a temperature sensor having a low resolution because the accuracy diagnosis device obtains the change rate of the body temperature of each part in real time based on the above-mentioned idea and diagnoses the accuracy from the change rate. Even with an inexpensive configuration, it is possible to appropriately diagnose the effect on accuracy.

The accuracy diagnostic device according to claim 4 switches the ambient temperature between the coolant temperature and the ambient air temperature according to the presence or absence of the coolant, so that the temperature of a part susceptible to the coolant such as a table such as a machining center changes. Since the speed can be calculated accurately, the influence on the accuracy can be appropriately diagnosed.

The accuracy diagnostic device according to claim 5 determines the degree of accuracy influence due to thermal displacement of the machine tool, such as position error at the cutting edge in each axial direction, tilt error at the cutting edge, expansion / contraction error of each straight axis, and straightness error. Since it is calculated for each thermal displacement component such as geometric error between each axis, it is easy to judge whether there is a risk of poor machining accuracy (risk considering the required accuracy for the work).

It is a conceptual diagram of a machine tool (vertical machining center) equipped with an accuracy diagnosis device. It is a figure which shows the relationship between the error component to be diagnosed, and the part where the temperature change rate is obtained. It is a flowchart which shows the content of the accuracy diagnosis process. It is explanatory drawing which shows the temperature detection result (a), the temperature change rate calculation result (b), and the accuracy diagnosis result (c) in the environment where the room temperature rises sharply. It is explanatory drawing which shows the temperature detection result (a), the temperature change rate calculation result (b), and the accuracy diagnosis result (c) in the environment where the room temperature rises slowly. It is explanatory drawing which shows the accuracy diagnosis result (b) when the temperature change rate is calculated using the temperature detection result (a) and the cutting fluid temperature.

Hereinafter, embodiments of the present invention will be described.

<Configuration of machine tools and accuracy diagnostic equipment>
FIG. 1 is an example of a machine tool (vertical machining center) to which the present invention is applied. In addition, in FIG. 1, in order to show the structure of the machine in an easy-to-understand manner, the description of the cover or the like covering the outer periphery of the machine tool M is omitted.

The machine tool M includes a bed 6 as a base, a spindle 5 on which a cutting tool can be mounted, a saddle 3 for mounting the spindle 5, a vertical plate-shaped column 1 for mounting the saddle 3, and a workpiece. It is composed of a table 8 for mounting, a control device C for controlling operation, and the like. The machine tool M has a shaft configuration in which the spindle 5 moves in the X and Z directions and the table 8 moves in the Y direction.

An X-axis guide 2 is attached to the column 1, so that the saddle 3 can move in the X direction. Further, a Z-axis guide 4 is attached to the saddle 3, so that the spindle 5 can move in the Z-axis direction. On the other hand, a Y-axis guide 7 is attached to the bed 6 so that the table 8 can move in the Y-axis direction. Further, behind the bed 6, a coolant tank 9 for storing the coolant used for cooling the main shaft 5 and the like is installed.

Further, the machine tool M is provided with a column front temperature sensor 11, a column rear temperature sensor 12, a bed temperature sensor 13, and a table temperature sensor 14 as a machine body temperature sensor, and a representative room temperature sensor 20 as an environmental temperature sensor. , The column front ambient temperature sensor 21, the column rear ambient temperature sensor 22, the bed ambient temperature sensor 23, the machining room temperature sensor 24, and the cutting liquid temperature sensor 25 are attached. The airframe temperature sensor and the environmental temperature sensor are connected to the control device C.

On the other hand, the control device C includes a CPU, a storage means, a timer, an input means (keyboard, touch panel, etc.), an output means (monitor, etc.), an interface connecting the input means, the output means, and the CPU. Then, based on the detected temperatures of the machine tool temperature sensor and the environmental temperature sensor described above, the control device C estimates the rate of temperature change at a predetermined portion of the machine tool M according to the program stored in the storage means. Based on the estimated temperature change rate, the degree of influence of thermal displacement on the accuracy of the machine tool is calculated. That is, the machine tool M's accuracy diagnosis device D is configured by the machine tool temperature sensor, the environmental temperature sensor, and the control device C, and the temperature change rate calculation means 31 and the accuracy influence degree calculation means 32 are configured in the control device C. It has become like.

When the accuracy diagnostic device D diagnoses the accuracy of the machine tool M, a total of five thermal displacements of Y-axis direction position, Z-axis direction position, X-axis direction expansion / contraction, Y-axis direction expansion / contraction, and YZ squareness Diagnose the ingredients. In the following description, as shown in FIG. 1, the front direction of the machine tool M is the + direction and the rear direction is the-direction for the Y-axis direction position, and the vertical upward direction is the + direction for the Z-axis direction position. , Vertically downward is the minus direction. For expansion / contraction in the X-axis direction and expansion / contraction expansion / contraction in the Y-axis direction, the direction in which the work size increases is the + direction, and the direction in which the work size decreases is the-direction. When set in this way, the temperature of each part of the machine tool M related to the above-mentioned five thermal displacement components becomes as shown in FIG.

As shown in FIG. 2, when a temperature difference occurs between the front side of the column and the rear side of the column, the column 1 is tilted. Therefore, the temperature difference between the front side of the column and the rear side of the column is the position in the Z-axis direction. Not only that, it also affects the YZ squareness. Further, when the column 1 is tilted, the height of the spindle 5 overhanging from the column 1 also changes, so that the temperature difference between the front side of the column and the rear side of the column affects the position in the Z-axis direction.

The accuracy diagnostic device D changes in the + direction and the-direction when the temperature rises, based on the relationship between the five thermal displacement components shown in FIG. 2 and the temperature of each part of the machine tool M. The accuracy of the machine tool M is diagnosed by calculating the rate of temperature change in each of the parts and calculating the degree of influence on each heat displacement component (degree of accuracy influence) based on the temperature change rate. At that time, each method of calculating the temperature change rate and the degree of accuracy influence performed in the accuracy diagnostic apparatus D is shown below.

<Calculation method of temperature change rate>
The conventional method for obtaining the temperature change rate at each part of the machine tool M is a method of calculating the difference between the current temperature and the temperature before the time Δt and converting it into the temperature change per unit time as in Equation 1. ..

However, as described above, it is difficult to obtain the rate of change in the method of Equation 1 when the temperature change is gradual. On the other hand, the change in the airframe temperature can be expressed by the differential equation of the first-order lag of the following equations 2 and 3 by inputting the ambient air temperature.

As can be seen from Equation 2, the rate of change of the aircraft temperature is proportional to the difference between the aircraft temperature and the ambient air temperature, and is inversely proportional to the time constant of the aircraft temperature change when the ambient air temperature is input. If this time constant is determined in advance by calculation or experiment, the rate of change in the airframe temperature can be calculated from the difference between the airframe temperature and the ambient air temperature.

Further, for a part exposed to coolant during processing such as a table of a machining center, it is possible to calculate by inputting the temperature of the coolant instead of the ambient temperature. In that case, the differential equation showing the change in the airframe temperature is as shown in the following equations 4 and 5. Since the value of the heat transfer coefficient is larger in the liquid than in the air, the time constant in the equations 4 and 5 tends to be a small value.

By the above method, the temperature change rate of the part that affects the + direction and the part that affects the-direction when the temperature rises is calculated, respectively.

<Calculation method of accuracy impact>
Then, from the result of the temperature change rate calculated as described above, the accuracy influence degree E on the corresponding thermal displacement component is calculated by the function f as in Equation 6.

As a typical example of the function f for obtaining the degree of accuracy influence on the thermal displacement component, as shown in the following equation 7, the linear sum of each part affecting the + direction and the part affecting the-direction is obtained, and the difference is obtained. It is a thing.

In the case where there is only one component on the + side and one on the − side, the function f for finding the difference by finding the linear sum is represented by a simple difference between the two, as in Equation 8.

The accuracy diagnostic device D uses the differential equations shown in Eqs. 2, 3 or 4, 5 in the control device C according to a predetermined program, and a part that changes in the + direction when the temperature rises and a portion. -Calculate the temperature change rate at each of the parts that change in the direction, and calculate the degree of accuracy influence on the thermal displacement component from those temperature change rates using the function f shown in Equation 7 or Equation 8. By doing so, the accuracy of the machine tool M is diagnosed. Hereinafter, two examples of diagnosing the change in the accuracy of the machine tool due to the change in the environmental temperature by using the accuracy diagnosis device D will be shown.

<Example of machine tool accuracy diagnosis 1>
In the accuracy diagnosis example 1, a method of diagnosing a change in the YZ squareness based on the temperature change rate on the front side of the column and the rear side of the column will be described with reference to the drawings. This accuracy diagnosis example 1 is a diagnosis example when the air conditioning in the factory is turned on and the room temperature in the factory rises sharply from 10 ° C to 20 ° C.

The diagnosis of the change in the YZ squareness is executed according to the program stored in the storage means of the control device C. FIG. 3 is a flowchart showing the processing content. When diagnosing a change in the YZ squareness, the operator inputs a diagnosis start signal in S (step) 1, and the subsequent S2 is the ambient temperature on the front side of the column. The sensor 21 and the column front temperature sensor 11 are used to detect the ambient air temperature before and after the column 1 and the body temperature before and after the column 1.

FIG. 4A is a plot of the ambient air temperature before and after the column 1 and the airframe temperature before and after the column 1 with respect to the passage of time from the start-up of the air conditioner in the factory. As shown in FIG. 4A, when the air temperature around the machine tool M rises sharply due to the start-up of the air conditioner, the airframe temperature before and after the column 1 also changes behind the ambient air temperature. At this time, the rear side of the column changes rapidly because the time constant is small. On the other hand, the front side of the column changes slowly due to the large time constant. The machine machine M has a structure in which the YZ squareness changes to the + side when the temperature on the rear side of the column rises, and the YZ squareness changes to the-side when the temperature on the front side of the column rises. When the temperature difference before and after the column changes due to the difference, the YZ squareness changes.

As described above, after detecting the ambient temperature before and after the column 1 and the airframe temperature before and after the column 1 in S2, in the following S3, based on the equation 2, for each of the front side and the rear side of the column. Obtain the difference between the ambient air temperature and the airframe temperature, and calculate the rate of change in the airframe temperature. That is, for the front side of the column 1, the difference between the ambient temperature on the front side of the column and the temperature of the aircraft on the front side of the column is obtained based on the detection results of the ambient temperature sensor 21 on the front side of the column and the temperature sensor 11 on the front side of the column. , 3 is used to calculate the rate of change in the air temperature of the aircraft by dividing the temperature difference by a time constant (for example, 150 minutes) obtained in advance by an experiment.

Similarly, for the rear side of the column, the difference between the ambient temperature on the rear side of the column and the temperature of the aircraft on the rear side of the column is obtained based on the detection results of the ambient temperature sensor 22 on the rear side of the column and the temperature sensor 12 on the rear side of the column. By using the above equations 2 and 3 and dividing the temperature difference by a time constant (for example, 75 minutes) obtained in advance by an experiment, the rate of change in the air temperature of the aircraft is calculated. FIG. 4B is a plot of the rate of change in the airframe temperature before and after column 1 with respect to the passage of time from the start-up of the air conditioner in the factory.

As described above, after calculating the change rate of the airframe temperature in S3, the change rate of the airframe temperature on the front side of the column 1 and the change rate on the rear side of the column 1 calculated by using the above equation 8 in the following S4. The degree of influence on accuracy is calculated by obtaining the difference from the rate of change in the airframe temperature. FIG. 4C is a plot of the difference in the rate of change in the airframe temperature before and after column 1 (= accuracy influence) with respect to the passage of time from the start-up of the air conditioner in the factory. Looking at the difference in the rate of temperature change (= accuracy impact) shown in FIG. 4 (c), the accuracy impact increased significantly immediately after the air conditioner was started, peaked about 10 minutes later, and then reached a peak. It can be seen that it gradually decreases. That is, when the temperature immediately after the start-up of the air conditioner (particularly, the ambient air temperature before and after the column 1) changes suddenly, the accuracy of the machine tool M is unstable, but it becomes stable again after a lapse of time. You can see that it will return.

Therefore, the accuracy diagnosis device D diagnoses that the larger the absolute value of the calculated accuracy influence degree is, the more rapidly the state of the machine tool M is changed and the more unstable the state is. Then, when the degree of influence on accuracy exceeds a preset threshold value, the output means of the control device C is used in S5 to notify that fact. For example, in FIG. 4C, when the threshold value is set to 2 ° C./hour, the change falls below the threshold value about 40 minutes after the start of air conditioning, so that the accuracy diagnosis device D can start machining. Diagnose that there is, and notify that fact.

Note that FIG. 4 shows an example of diagnosis when the room temperature in the factory is rapidly increased from 10 ° C to 20 ° C, but the case where the room temperature is gradually increased will be examined. FIG. 5 shows an example of diagnosis in the case where the temperature is gradually increased by 2 ° C every 20 minutes from 10 ° C to 20 ° C. When the room temperature is gradually increased in such a step, the difference in the temperature change rate (= accuracy influence) becomes smaller than when the room temperature is rapidly increased. It can be seen that the time is also within the threshold value of 2 ° C./hour or less. From this diagnostic example, it can be seen that even if the temperature change width is the same at room temperature, if the change is gradual, the degree of accuracy influence becomes small and the accuracy change (error of thermal displacement correction) of the machine tool M becomes small. ..

As described above, the accuracy diagnostic device D diagnoses the influence of the sudden temperature change at room temperature on the accuracy by obtaining the difference between the change rate of the machine temperature on the front side of the column and the change rate of the body temperature on the rear side of the column. can do.

<Example 2 of machine tool accuracy diagnosis>
In the accuracy diagnosis example 2, a method of diagnosing the expansion / contraction state in the X-axis direction based on the rate of change in temperature between the front side of the column 1 and the table 8 will be described with reference to the drawings. In this accuracy diagnosis example 2, at the time of starting machining, the room temperature and the temperature on the front side of the column are both 20 ° C, the temperature in the machining chamber is 21 ° C, and the temperature of the coolant is significantly lower than the machine tool temperature and room temperature. This is an example of diagnosis when the temperature is 15 ° C., and 60 minutes after the power is turned on to the machine tool M, the coolant is started to be discharged and the processing is started.

When diagnosing the expansion / contraction status in the X-axis direction, in S1, when the operator inputs the diagnosis start signal, in the following S2, the column front ambient temperature sensor 21, the column front temperature sensor 11, the table temperature sensor 14, And using the processing room air temperature sensor 24, the ambient air temperature on the front side of the column 1 (= ambient air temperature on the table 8), the air temperature on the front side of the column 1, the air temperature on the table 8, and the air temperature in the processing room (that is, illustrated). Does not detect the temperature of the processing space covered by the cover). FIG. 6A plots the ambient air temperature before and after column 1, the machine temperature before and after column 1, the coolant temperature, and the machine temperature of table 8 with respect to the passage of time from turning on the power to the machine tool M. It was done. As shown in FIG. 6A, when the table 8 is exposed to coolant 60 minutes after the power is turned on to the machine tool M, the temperature of the table 8 drops sharply. Then, about 30 minutes after the table 8 begins to be exposed to the coolant, the temperature of the table 8 becomes substantially the same as the temperature of the coolant, and then gradually approaches the room temperature.

As described above, after detecting the ambient temperature on the front side of the column 1, the air temperature on the front side of the column 1, the air temperature on the table 8, and the air temperature in the processing room in S2, in the following S3, based on the formula 2, For each of the front side of the column and the table 8, the difference between the ambient air temperature and the airframe temperature is obtained, and the change rate of the airframe temperature is calculated. That is, for the front side of the column 1, the column front ambient temperature sensor 21 and the column front temperature sensor 11 are used to obtain the difference between the column front ambient temperature and the column front aircraft temperature, and the above equations 2 and 3 are used. , The change rate of the air temperature of the machine is calculated by dividing the temperature difference by a time constant (for example, 150 minutes) obtained in advance by an experiment.

On the other hand, for the table 8, the temperature change rate is calculated by changing the calculation method depending on whether or not the coolant is used. That is, when the coolant is not used (until 60 minutes have passed from the time when the power is turned on), the temperature in the processing room and the body temperature of the table 8 are used by using the temperature detected by the processing room temperature sensor 24 and the table temperature sensor 14. The temperature difference is calculated by dividing the temperature difference by the time constant (for example, 75 minutes) obtained in advance by the experiment using the above equations 2 and 3, and the change rate of the air temperature of the aircraft is calculated.

When the coolant is used (60 minutes after the power is turned on), the temperature detected by the cutting fluid temperature sensor 25 and the table temperature sensor 14 is used to determine the temperature of the coolant and the body temperature of the table 8. The change rate of the aircraft temperature is calculated by obtaining the difference and dividing the temperature difference by the time constant (for example, 15 minutes) obtained in advance by the experiment using the above equations 4 and 5. Under the conditions assumed as described above, regarding the front side of the column 1, the ambient temperature on the front side of the column 1 detected by the column front ambient temperature sensor 21 and the column 1 detected by the column front temperature sensor 11 Since the airframe temperatures on the front side are both 20 ° C., no temperature change occurs, so the rate of change is 0.

As described above, after calculating the change rate of the machine temperature in S3, in the following S4, using the above equation 8, the change rate of the machine temperature on the front side of the column 1 and the body temperature of the table 8 are calculated. The degree of influence on accuracy is calculated by finding the difference from the rate of change. FIG. 6B is a plot of the difference in the rate of change in the body temperature between the front side of the column 1 and the table 8 (= degree of influence on accuracy) with respect to the passage of time from turning on the power to the machine tool M. .. From FIG. 6B, the difference (= accuracy influence) between the temperature change rate on the front side of the column 1 and the temperature change rate on the table 8 becomes the largest negative value at the moment when the coolant discharge is started. After that, it can be seen that it gradually approaches 0.

Therefore, the accuracy diagnosis device D diagnoses that the larger the absolute value of the calculated accuracy influence degree is, the more rapidly the state of the machine tool M is changed and the more unstable the state is. Then, when the degree of influence on accuracy is lower than the preset threshold value, the output means of the control device C is used in S5 to notify the fact. For example, in FIG. 6B, when the threshold value is set to ± 2 ° C./hour, the temperature rises about 75 minutes after the power is turned on to the machine tool M (15 minutes after the start of coolant discharge). Since the difference in the rate of change (degree of influence on accuracy) is within the threshold value, the accuracy diagnosis device D diagnoses that the machining can be started and notifies that fact.

As described above, the accuracy diagnosis device D can diagnose the influence of the sudden temperature change due to the coolant on the accuracy by obtaining the temperature change rate based on the difference between the coolant temperature and the airframe temperature.

<Effect of accuracy diagnostic device>
As described above, the accuracy diagnostic apparatus D is based on the temperature change rate calculating means 31 for estimating the temperature change rate at a predetermined portion of the machine tool M and the temperature change rate estimated by the temperature change rate calculating means 31. Since it is provided with the accuracy influence degree calculating means 32 for calculating the influence degree on the accuracy of the machine tool M due to the thermal displacement, the influence on the accuracy due to the thermal displacement of the machine tool M can be appropriately predicted.

<Example of change of accuracy diagnostic device>
The configuration of the accuracy diagnostic apparatus according to the present invention is not limited to the embodiment of the above embodiment, and is configured such as a temperature change rate calculating means, an accuracy influence degree calculating means, a machine temperature sensor, an environmental temperature sensor, and the like. Can be appropriately changed as necessary without departing from the spirit of the present invention.

For example, in the above-mentioned accuracy diagnosis example 1, a temperature sensor (column front ambient temperature sensor 21, column rear ambient temperature sensor 22) is attached around each of the front side and the rear side of the column, and the difference between the ambient temperature and the aircraft temperature is attached. However, it is also possible to adopt a method of finding the difference between the ambient air temperature and the aircraft temperature by using the result of the representative room temperature sensor (for example, the representative room temperature sensor 20 in FIG. 1) instead of those temperature sensors. Is. In the method of providing the ambient air temperature sensor for each part as in the above-mentioned accuracy diagnosis example 1, accurate diagnosis is possible because the distribution of the ambient air temperature can be grasped more accurately, but the number of sensors increases. There is also the drawback that it will end up. On the other hand, as described above, the method using the detected temperature of the representative room temperature sensor has a drawback that the accuracy of diagnosis is lowered when the temperature distribution of the ambient air temperature is large, but the value of the small room temperature sensor is regarded as the ambient temperature of each part. It is possible to reduce the number of sensors by performing the calculation.

Further, in the above-mentioned accuracy diagnosis example 1, a simple difference is calculated as the degree of influence of accuracy between the temperature change rate of the portion changing to the + side and the temperature change rate of the portion changing to the-side when the temperature rises. The calculation method of the accuracy influence is not limited to such a method, and a method of evaluating the sum of the absolute value of the + side component and the absolute value of the-side component as the accuracy influence degree and the calculated temperature change rate. It is also possible to adopt a method of evaluating a numerical value using an arbitrary function as the degree of influence on accuracy.

Further, the accuracy diagnosis device has a total of five heats of Y-axis direction position, Z-axis direction position, X-axis direction expansion / contraction, Y-axis direction expansion / contraction, and YZ squareness, as in the above-mentioned accuracy diagnosis examples 1 and 2. The displacement component is not limited to the one for diagnosing, and a part of those thermal displacement components may be diagnosed, or another thermal displacement component may be diagnosed.

M ... Machine tool (vertical machining center)
D ... Accuracy diagnostic device 11 ... Column front temperature sensor (airframe temperature sensor)
12 ... Column rear temperature sensor (airframe temperature sensor)
13 ... Bed temperature sensor (airframe temperature sensor)
14 ... Table temperature sensor (airframe temperature sensor)
20 ... Representative room temperature sensor (environmental temperature sensor)
21 ... Column Front ambient temperature sensor (environmental temperature sensor)
22 ... Column Rear ambient air temperature sensor (environmental temperature sensor)
23 ... Bed ambient temperature sensor (environmental temperature sensor)
24 ... Processing indoor air temperature sensor (environmental temperature sensor)
25 ... Cutting fluid temperature sensor (environmental temperature sensor)
31 ... Temperature change rate calculation means 32 ... Accuracy impact calculation means

Claims (5)

It is a machine tool accuracy diagnostic device that diagnoses the effect of thermal displacement of a machine tool on accuracy.
A temperature change rate calculating means for calculating the temperature change rate at a predetermined part of a machine tool,
Accuracy diagnosis of a machine tool characterized by being provided with an accuracy influence calculation means for calculating the influence of thermal displacement on the accuracy of the machine tool based on the temperature change speed calculated by the temperature change speed calculation means. Device. The temperature change rate calculating means calculates the rate of temperature change at the portion where the thermal displacement changes in the + direction of an arbitrary vector due to the temperature change of the machine tool, and the rate of temperature change at the portion where the thermal displacement changes in the − direction, respectively. The accuracy diagnosis device for a machine tool according to claim 1, wherein the device is to be used. An airframe temperature sensor that measures the airframe temperature of each part,
Equipped with an environmental temperature sensor that measures at least one of the machine tool's ambient or coolant temperatures.
The temperature change rate calculation means is
The temperature change rate is determined by using the temperature difference between the machine temperature measured by the machine temperature sensor and the environment temperature measured by the environment temperature sensor, and the time constant of the machine temperature change with respect to the environment temperature change determined for each part. The accuracy diagnostic device for a machine tool according to claim 1 or 2, wherein the temperature is what is required. The temperature change rate calculation means is
When using coolant, use the coolant temperature as the environmental temperature.
The accuracy diagnostic device for a machine tool according to claim 3, wherein when no coolant is used, the ambient air temperature is used as the environmental temperature. The accuracy influence calculation means is the position accuracy at the cutting edge of the machine tool in each axial direction, the inclination at the cutting edge, the expansion / contraction of each straight axis, the change in straightness, and the change in the geometric error between the axes due to thermal displacement. The accuracy diagnosis device for a machine tool according to any one of claims 1 to 4, wherein the degree of influence on any of the above is calculated.

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