JPH0783977B2 - Machine tool thermal displacement compensation method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal displacement correction method for machine tools. More specifically, the temperature of each part of the machine body that composes the machine tool and the ambient temperature around the machine body are detected, and the amount of thermal displacement is calculated using the relational expression of temperature change and deformation obtained in advance. The present invention relates to a thermal displacement correction method for a machine tool that corrects the machine origin position and cancels thermal displacement based on the result.

[0002]

2. Description of the Related Art A numerically controlled machine tool has a machine origin in a machine body. The position of the tool rest, the work table, etc. is controlled according to a program based on this machine origin. However, the machine body of the machine tool is deformed by heat, and the machining accuracy cannot be maintained unless the machine origin position is also corrected accordingly. The thermal displacement reference temperature proposed by the present inventors (the temperature serving as a reference for calculating the temperature change of the machine element) adopts the environmental temperature when the machine power is turned on and each temperature of the constituent elements of the machine tool. (Japanese Patent Laid-Open No. 2-41848).

Further, the machine position (correction origin) at the thermal displacement reference temperature is made to coincide with the machine origin, and the thermal displacement amount is increased / decreased from there to correct. This is to avoid the accumulation of corrections. Many conventional methods simply turn on the machine power.
The machine origin is moved in the direction in which the deformation is found from the relational expression of the amount of temperature change with respect to the machine body temperature and the deformation and the deformation is corrected.

However, in the conventional correction method, when the machine power supply is turned off once during machining and then the machine power supply is turned on again, the reference temperature for thermal deformation up to that point is erased, and the machine temperature at that time is used as the temperature reference. Therefore, the correction amount becomes zero. For this reason, if the power is temporarily cut off during processing, a step is generated on the work.

Therefore, the inventors of the present invention match the machine position (correction origin) at the stored reference temperature with the machine origin so that the correction amount becomes 0 even when the machine is temporarily returned after turning off the machine origin. A thermal displacement correction method that does not return to the origin and a control device therefor have been proposed (JP-A-3-79256).
issue).

That is, the environmental temperature of the machine tool and the temperatures of the constituent elements of the machine tool are sampled at time intervals, and the sampled environmental temperature and the average value of the temperatures of the constituent elements of the machine tool are sampled a plurality of times. Respectively, and the averaged ambient temperature and the temperature of the components constituting the machine tool as the respective reference temperature,
This is a method for correcting thermal displacement of a machine tool that calculates the amount of thermal displacement of each constituent element of the machine tool using the amount of temperature change with respect to the reference temperature.

[0007]

The above-mentioned proposed embodiment corrects the displacement in the Z-axis direction between the tool and the table, including the elongation of the spindle. In the horizontal or vertical machining center, the second deformation occurs in the Z-axis direction in the vertical direction or the front-back direction. However, the content of the proposal does not include correction in the direction orthogonal to the Z-axis direction.

Further, the machine tool measures the thermal deformation in various tests at the time of factory shipment to determine the correction conditions. However, this correction condition needs to be changed depending on the factory where the machine tool is actually used and the cutting conditions. The above-mentioned conventional method has no idea of changing the correction condition. Further, in the above-mentioned proposal, various data required for correction such as sensor data cannot be called up on the screen, and therefore correction work of the correction amount cannot be easily performed. The present invention is
The present invention has been invented in the above background, and achieves the following objects.

An object of the present invention is to provide a thermal displacement correction method for a machine tool which can correct the correction conditions for obtaining the thermal displacement.

Another object of the present invention is to provide a method for correcting thermal displacement of a machine tool for displaying various data for obtaining thermal displacement.

[0011]

Means and Actions for Solving the Problems To solve the above problems, the following means are adopted.

In a thermal displacement correction method for correcting thermal displacement of components constituting a machine tool, the environmental temperature of the machine tool and the temperature of the components are sampled, and the sampled environmental temperature and the temperature of the components are sampled. First, a reference temperature is determined, and a change amount obtained from the reference temperature, the environmental temperature during processing, and the temperature of the constituent elements is obtained by a previously assumed relational expression of thermal deformation. A correction amount that is the difference between the processing error when processing and measuring is calculated, a correction coefficient that is the ratio of this correction amount and the change amount is calculated, and the thermal displacement amount is corrected by changing the correction coefficient. This is a method for correcting thermal displacement of a machine tool characterized by:

Further, it is convenient for maintenance management to display the correction amount, the correction coefficient, the present temperature of the component and the reference temperature on a screen for maintenance.

Further, it is effective to display the temperature transition of the constituent elements on a screen for each time interval for maintenance.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

Arrangement of Sensors on Machine Tool FIG. 1 is a functional block diagram showing an outline of arrangement of temperature sensors for implementing the method for correcting thermal displacement of a machine tool according to the present invention. The machine tool shown in FIG. 1 is a vertical machining center 1 and shows its components such as a bed 2, a column 3, a moving table 4, a spindle head 5, a spindle 6, a tool 7, and a workpiece table 8. . Tool 7 is spindle 6
It is a tool part such as a cutting tool attached to.

A room temperature sensor Ch1, a column lower sensor Ch2, a column upper temperature sensor Ch3, a carriage temperature sensor Ch4, and a spindle head temperature sensor Ch5 are arranged and attached to the vertical machining center 1, respectively. These sensors can be of any type, but thermistor temperature sensors are preferred. The room temperature sensor Ch1 detects an environmental temperature.

Each sensor Ch1 to Ch5 and each output is A /
It is input to the D converter 10. The input analog signal is converted into a digital signal. This digital signal is
It is input to the thermal displacement correction device 20. Thermal displacement correction device 20
The correction amount calculated in (1) is transmitted to the numerical control device (hereinafter referred to as NC) 30 and the position is corrected.

Thermal Displacement Correcting Device FIG. 2 is a functional block diagram of the thermal displacement correcting device 20. The detection value of each sensor Ch1 to Ch5 is A / D.
It is converted into a digital value by the converter 10 and written into a designated memory address of each sensor in the RAM 12 according to a command from the microprocessor 11. In RAM12,
Data such as temperature data at that time is stored internally so that the average value of the aircraft and environmental temperature at the time of power-on in the past is used as the reference temperature.

Further, the RAM 12 stores temperature data sampled by each sensor at regular intervals. As will be described later, this temperature data is displayed on the display device (not shown) of the NC 30. The ROM 13 stores a program for calculating a relational expression of thermal displacement, a correction coefficient, etc., which will be described later. The clock 14 is a normal clock and is for determining the time for sampling or the like.

Thermal Deformation Correction Principle The work table 8 is provided on the bed 2 and mounts the work W during machining and moves relative to the tool 7. In this embodiment, a thermal displacement error between the tool 7 and the workpiece W on the workpiece table 8 in the Z and X axis directions is corrected. The thermal deformation between them mainly consists of nose thermal deformation, tool thermal deformation, and base thermal deformation. Nose thermal deformation refers to thermal deformation of the spindle 6 portion protruding from the spindle head 5 from the reference temperature in the Z-axis direction.

The tool thermal deformation means the thermal deformation of the portion of the tool 7 protruding from the main shaft 6 from the reference temperature in the Z-axis direction. Base thermal deformation refers to thermal deformation from the reference temperature of the base 1 in the Z-axis direction between the column 3 side and the table 8.
The inventor obtained a relational expression of thermal deformation in the Z-axis direction, as is clear from the description in Japanese Patent Application Laid-Open No. 2-41848, which is the previous application.

For these thermal deformations, the amount of deformation is calculated and corrected by the temperature difference from the reference temperature. Since this reference temperature is each temperature when the vertical machining center 1 is powered on, it automatically increases gradually in summer and gradually decreases in winter. to enable. Since the change in the reference temperature itself is not corrected, the machine shape is not constantly compensated throughout the year. Since these points are disclosed in Japanese Patent Laid-Open No. 3-79256, detailed description will be omitted.

The temperature at the start of work start on that day does not match the above-mentioned reference temperature. The factory environment in which the parts to be processed, the measuring tool and the machining center are located on that day is used as the standard for thermal deformation on that day (see FIG. 3). For example, when the vertical machining center 1 is turned on in the morning, the temperature of the airframe normally rises gradually. Due to this temperature rise, the airframe is deformed.

In order to allow for the deformation delay when the environmental temperature changes greatly during the day, the change in the environmental temperature is approximated by a straight line within 5 lines, and the environmental temperature changes linearly at each time. It is assumed to change. When the environmental temperature changes linearly, the deformation delay of the machine can be easily estimated by the "ramp response formula (general formula) of the primary delay element". In this way, the thermal deformation of the part where the temperature is not directly detected is estimated from the change in the ambient temperature (see FIG. 4). The details of the method of correcting the thermal deformation have been disclosed in Japanese Patent Laid-Open No. 2-41848, and thus detailed description will be omitted.

Therefore, the tool correction value is usually determined at the time when the dimension of the work piece is at the center of the drawing tolerance in consideration of the thermal deformation of the machine. With the correction function, the tool correction value can be set at an arbitrary time, and the reliability in tracking the change in the tool dimension due to wear using a touch sensor or the like increases.

Correction Factor The mechanical precision required for practical use is required to satisfy the dimensions and finishing precision of machined parts cut with tools of various shapes. There are cutting conditions that are different from the thermal deformation test using the test bar at the time of factory shipment, and it can be said that these conditions are various depending on the content of the processed product, the processing conditions, and the like. Therefore, it is possible to easily correct the correction amount [μm] (correction coefficient 1.0, see FIG. 3) set based on the test bar at the time of factory shipment using the following calculation formula. It has become.

Correction coefficient = (change amount of correction amount per day-machining error) / change amount of correction amount per day However, the meaning of "change amount of correction amount per day" is that the thermal deformation correction amount is operating. Sometimes that number increases (or decreases). From power-on to its operation, the amount of change (± signed μ
m). Therefore, one day here is the amount of change from when the power is turned on to the present, and does not mean a normal day.

The "machining error" is a value (.mu.m with. +-. Sign) calculated by subtracting the design target dimension from the actually measured finished dimension. In other words, if the processing error is 0, the correction coefficient will be 1.0, but when the finished size is small (processing error <0), the correction will be insufficient, so the correction coefficient will be a value larger than 1.0, and the machine Save further to the + side.

When the correction coefficient is to be corrected, the initial screen (FIG. 5) is first called. The thermal displacement in the Z-axis direction between the tool and the table, including the elongation of the spindle, is usually larger than that in the X and Y axes, and is suppressed only by the spindle cooling device (jacket bearing jacket cooling) during high speed rotation. Is difficult. Also in the thermal displacement correction method of this embodiment, the thermal displacement correction in the Z-axis direction is preferentially adopted, and yet another axis can be selectively corrected.

Conventionally, a horizontal or vertical machining center has been designed symmetrically as a basic measure against heat when viewed from the front of the machine tool, but in the vertical direction or in the front-back direction, the second deformation occurs in the Z-axis direction. . In particular, as the size of the machine increases, the amount of deformation increases. RA
By properly setting the parameter of M12, the additional correction axis according to the model is selected. On the upper left of the initial screen (main screen) of the thermal displacement correction device, the selected correction axis name is displayed together with the correction coefficient and the correction amount [μm].

When the correction coefficient is to be changed, the screen of FIG. 5 is called up, and when the function key for changing the correction coefficient is pressed, the corresponding correction coefficient column is highlighted. After this,
Enter the correction factor from the keyboard. In this example,
The correction coefficient is calculated manually. An area for displaying error contents is provided on the right side of the cross section of FIG. 5, and shows disconnection of each sensor, correction calculation error, excessive change amount, and the like.

The maintenance screen daily maintenance screen 1 as readable numerical data and correction career temperature change (FIG. 6) maintenance screen 2 (FIG. 7) are prepared. In the maintenance screen 1 shown in FIG. 6, the change in each of the machine parts and the environmental temperature sensors Ch1 to Ch5 is 15
It is stored and recorded for 9 hours as numerical data for each minute.
After that, the previous data is sequentially deleted. Since the temperature change of each part of the machine can be constantly monitored, the temperature abnormality can be promptly judged. The sensor is always assigned to detect the ambient temperature regardless of the model.

Although the correction value is rewritten by the correction calculation performed every 15 minutes, the correction value is actually reflected on the servo axis of the machine when the power is turned on and when the tool is changed (M6).
Command is issued (simultaneously for 2 axes). Since the correction amount is given as an external offset of NC, it does not directly affect the work coordinates. An operator can create a machining program without paying particular attention to the thermal displacement correction function.

However, in continuous machining in which the tool change interval is extremely long, even if the correction calculation is performed, the correction operation itself does not work (M6 does not occur). Alternatively, when the disturbance to the temperature sensor is large, or when the sensor is disconnected, the correction function may be temporarily stopped. The following auxiliary functions (M code) to deal with such cases
Is prepared.

M110: One-shot correction is performed. This can be set at any position such as the cutting direction switching position.

M111: Stop the correction function. M110
The correction function can be restored again with.

Graffic Function On the maintenance screen 2 shown in FIG. 7, the numerical data of the temperature change recorded on the maintenance screen 1 and the output history of the correction are graphically displayed. In addition, the amount of deformation due to the temperature change of each part of the machine is displayed for each axis (upper: Z axis, lower: additional axis). The amount of deformation delay due to a sudden change in the environmental temperature is also displayed as a numerical value together with the fitting of the linear approximation to the Ch1 sensor data. The maintenance screen 2 is mainly used to read the amount of change in the correction amount used when changing the correction coefficient described above.

[0039]

As described above in detail, the present invention introduces the concept of the correction coefficient for correcting the calculated thermal deformation amount in more detail by using the environmental temperature of the machine tool and the temperature of the constituent elements. The thermal deformation can be corrected. Further, since various data regarding thermal deformation can be displayed on the screen, the correction coefficient can be easily extracted.

[Brief description of drawings]

FIG. 1 is a layout view of a sensor on a machining center.

FIG. 2 is a functional block diagram showing an outline of a thermal displacement correction device.

FIG. 3 is a diagram showing a relationship between time and temperature change.

FIG. 4 is a diagram showing a relationship between time and estimation of deformation (temperature) delay.

FIG. 5 shows an initial screen and a correction coefficient change screen for maintenance of the thermal displacement correction device.

FIG. 6 is a screen showing temperature data of each temperature sensor.

FIG. 7 is a graph showing a relationship between temperature and correction.

[Explanation of symbols]

1 ... Vertical machining center, 2 ... Bed, 3 columns, 4
... moving table, 5 ... spindle head, 6 ... spindle, 7 ... tool, 8 ... workpiece table, 20 ... thermal displacement compensator, 30 ... numerical controller

Claims (3)

[Claims] 1. A thermal displacement correction method for correcting thermal displacement of a constituent element of a machine tool, wherein an environmental temperature of the machine tool and a temperature of the constituent element are sampled, and the sampled environmental temperature and the constituent element The reference temperature is first determined from the temperature, and the change obtained from the reference temperature, the environmental temperature during processing, and the temperature of the constituent elements is calculated by a previously assumed relational expression of thermal deformation. The correction amount, which is the difference between the machining error when the workpiece is machined and measured, is calculated, the correction coefficient that is the ratio of this correction amount and the change is calculated, and the thermal displacement amount is changed by changing the correction coefficient. A method for correcting thermal displacement of a machine tool, which comprises: 2. The method for correcting thermal displacement of a machine tool according to claim 1, wherein the correction amount, the correction coefficient, the current temperature of the component and the reference temperature are displayed on a screen for maintenance. 3. The method for correcting thermal displacement of a machine tool according to claim 1, wherein the temperature transition of the component is displayed on a screen for each time interval for maintenance.