JP7370296B2 - Diagnosis method for sliding guide in machine tools - Google Patents

Description

The present invention relates to a method for diagnosing the condition of a sliding guide provided in a machine tool such as a machining center.

Machine tools have a sliding guide made up of a guide surface formed on a structure such as a column or bed, and a slide surface formed on a movable object such as a table that can move on the guide surface. . When the movable body is in operation, lubricating oil is interposed between the guide surface and the slide surface.
In this sliding guide, in order to prevent the slide surface from lifting during high-speed movement or cutting, a jib (also called a "gib") is installed between the slider 1 on the moving body side and the guide 2 on the structure side, as shown in Figure 1. ) 3, the slide surface 1a of the slider 1 is restrained to the guide surface 2a of the guide 2 with a constant surface pressure. However, if the jib 3 is not tightly tightened, the surface pressure will decrease and the machining accuracy will deteriorate due to increased lifting.
Therefore, Patent Document 1 discloses a method for diagnosing the tightening state of a jib by measuring the lost motion of a moving object or the current value of a drive motor using a position detection means such as a scale, and comparing the measured values with a set threshold value. has been done.

JP2013-69192A

In the method of diagnosing the jib tightening state as disclosed in Patent Document 1, a means such as a scale that can detect lost motion with high accuracy is required, which increases the cost of the apparatus.
Furthermore, means for diagnosing using the current value of the drive motor is affected by sliding resistance. This sliding resistance is affected by the viscosity of the lubricating oil, and the viscosity changes depending on the environmental temperature. FIG. 2 shows the relationship between lubricating oil temperature and viscosity, and FIG. 3 shows the value of motor torque (equivalent to motor current) when the lubricating oil viscosity changes. From FIG. 2, it can be seen that the viscosity changes greatly depending on the temperature of the lubricating oil. Also, from FIG. 3, it can be seen that when the viscosity differs, the torque of the motor changes. Therefore, the means for diagnosing using the current value of the drive motor as described in Patent Document 1 cannot accurately diagnose the degree of tightening of the jib. That is, in the conventional technology such as Patent Document 1, in addition to the cost increase due to the installation of scales and the like, there is a problem that accurate diagnosis cannot be performed due to fluctuations in the current value of the drive motor caused by changes in the viscosity of the lubricating oil.

SUMMARY OF THE INVENTION Therefore, the present invention aims to accurately diagnose the degree of tightening of a jib, that is, the state of the sliding guide, at low cost and without using a highly accurate position detection means such as a scale and without being affected by changes in the viscosity of lubricating oil. The purpose of this study is to provide a method for diagnosing sliding guides in machine tools.

In order to achieve the above object, the invention according to claim 1 provides a guide provided with a guide surface, a slider provided with a slide surface that slides on the guide surface, and a space between the guide and the slider. an interposed jib; a lubricating oil flow path provided on either the guide or the slider and capable of supplying lubricating oil between the guide surface and the sliding surface; and a motor for driving the slider. a feed shaft including;
A machine tool comprising: a lubricating oil supply device that supplies lubricating oil to the lubricating oil flow path; and a temperature sensor that detects the temperature of the lubricating oil supplied between the guide surface and the slide surface. A method for diagnosing an abnormality in a sliding guide composed of a guide surface and the sliding surface based on the degree of tightening of the jib, the method comprising:
A first step of performing reciprocating motion of the feed shaft at a plurality of feed speeds and acquiring the motor torque of the motor and temperature information of the temperature sensor at each feed speed;
a second step of calculating a slip characteristic number for each of the feed speeds from each of the feed speeds, each of the temperature information, and the normal surface pressure of the guide surface;
a third step of calculating an approximate function of the relationship between each of the slip characteristic numbers and the motor torque;
a fourth step of comparing the approximation function calculated in the third step with a pre-identified approximation function of the relationship between the slip characteristic number and the motor torque during normal operation;
A fifth step of determining whether there is an abnormality in the degree of tightening of the jib based on the comparison result of the fourth step is executed.
According to a second aspect of the present invention, in the above structure, in the first step, the motor torque at the feed speed in a speed range where the lubrication type is fluid lubrication is measured.
According to a third aspect of the invention, in the above structure, the temperature sensor is provided near the lubricating oil flow path.

According to the present invention, it is possible to accurately diagnose the tightening degree of a jib, that is, the state of the sliding guide, at low cost without using a highly accurate position detection means such as a scale, and without being affected by changes in the viscosity of lubricating oil. Can be done.

It is an explanatory view showing sliding guidance. It is a graph showing the relationship between temperature and viscosity of lubricating oil. It is a graph showing the relationship between feed speed and motor torque when the viscosity of lubricating oil is different. FIG. 2 is a block configuration diagram of a machine tool. It is a flowchart of the diagnostic method using the coefficient of an approximation function. It is a graph showing the relationship between slip characteristic number and motor torque when jib tightening is normal and when jib tightening is abnormal. It is a graph showing the relationship between slip characteristic number and motor torque when the viscosity of lubricating oil changes. It is a flowchart of the diagnostic method using the difference of an approximation function.

Embodiments of the present invention will be described below based on the drawings.
FIG. 4 is a block diagram showing an example of a machine tool that can execute the diagnostic method of the present invention. In this machine tool, a slider 1 is fixed to a ball screw nut 4, and can move linearly on a guide 2 by driving a motor 6 connected to a ball screw shaft 5, and is used as a feed shaft. As shown in FIG. 1, the slide surface 1a of the slider 1 and the guide surface 2a of the guide 2 constitute a sliding guide. Here, as in FIG. 1, a jib 3 is provided between the slider 1 and the guide 2. The jib 3 is fixed to either the slider 1 or the guide 2. The slider 1, guide 2, and motor 6 are installed on a bed 7.
The NC device 20 of the machine tool is composed of a motion command device 21 and a speed/position command device 22, and the speed/position command device 22 is connected to the motor 6 to control the operation of the feed axis.
A lubricating oil passage 8 is formed inside the slider 1, and lubricating oil is supplied from a lubricating oil supply device 11 through the lubricating oil passage 8 between the slide surface 1a and the guide surface 2a. A temperature sensor 9 is installed near the lubricating oil flow path 8, and the temperature of the lubricating oil can be measured by a temperature measuring device 12.

An ammeter 10 is installed in the motor 6, and a torque calculation device 13 calculates torque from the current value. The value of this torque and the temperature of the lubricating oil are recorded by the recording/arithmetic unit 14, and these values are used to identify an approximate function of the relationship between the slip characteristic number and the motor torque. The diagnostic result determination device 15 calculates the difference between the pre-identified approximation function of the relationship between the number of slip characteristics during normal operation and the motor torque, and the approximation function identified by the recording/calculation device 14, and this difference is set in advance. It is compared with a threshold value to diagnose the degree of tightening of the jib 3, that is, the presence or absence of an abnormality in the sliding guide.

Hereinafter, a diagnosis method using coefficients of an approximation function between the slip characteristic number and the motor torque will be explained based on the flowchart of FIG. 5.
When the machine tool is started, first, at S (abbreviation of "STEP", same hereinafter) 1, the NC device 20 causes the feed shaft to reciprocate at feed speeds of 5000, 10000, 20000, and 40000 mm/min. The selection range of the feed speed is a speed range in which the lubrication form of the sliding guide is fluid lubrication, and the reciprocating operation is performed at two or more types of feed speeds.
Next, in S2, the lubricating oil temperature at each feed rate and the motor torque when the feed rate is in a steady state are recorded in the recording/arithmetic unit 14 (S1, S2: first step).
Next, in S3, the recording/arithmetic device 14 records the lubricating oil temperature θ _LUB. The slip characteristic number α _f at each feed speed V _f is calculated using the following equation 1 (second step). In Equation 1, η is the viscosity of the lubricating oil and the lubricating oil temperature θ _LUB. and P is a function of
This is the normal surface pressure of the guide surface 2a of the guide 2.

Next, in S4, the recording/arithmetic device 14 identifies coefficients A and B of a function that approximates the relationship between the slip characteristic number α _f of each feed speed V _f and the motor torque T _f (third step). . Power approximation is expressed using the following equation 2 using variables x and y and coefficients A and B.

When x in equation 2 is applied to the slip characteristic number α _f and y is applied to the motor torque T _f , the coefficients A and B are expressed by the following equations 3 and 4. In Equation 3, V _f,min is the minimum value of the commanded feed rate, and V _f,max is the maximum value of the commanded feed rate.
In addition, in Equations 3 and 4, α _f with ￣ (overline) is the average value of the slip characteristic number α _f for each feed rate V _f , and T _f with ￣ (overline) is the motor torque T _f . It is an average value.

Next, in S5, the diagnostic result determination device 15 identifies coefficients A _S and B _S , which are coefficients of a function obtained by approximating the slip characteristic number α _f during normal operation obtained in advance and the motor torque T _f , to a power. Using the calculated coefficients A and B, calculate the absolute value of each difference between A and A _S and B and B _S and compare them with preset thresholds Th1 and Th2, respectively, to diagnose the surface pressure state of the jib 3. (4th step).
In this determination, if the absolute value of at least one difference exceeds the threshold, the surface pressure (tightening degree, the same applies hereinafter) of jib 3 is diagnosed as abnormal in S6, and if the absolute value of neither difference exceeds the threshold In S7, it is determined that the surface pressure of the jib 3 is normal (fifth step). Then, in S8, it is determined whether or not to continue the diagnosis. If the diagnosis is to be continued, the process returns to S1, and if it is not to be continued, the process ends.

FIG. 6 shows an example in which the relationship between the slip characteristic number and the motor torque is approximated to a power when the jib surface pressure is normal and when the jib surface pressure is abnormal and decreased in the present invention. The coefficient A in the normal case is 164.2, while in the abnormal case where the surface pressure has decreased, it is 82.1, and there is a difference between the two. Therefore, it can be said that this method allows accurate diagnosis of surface pressure abnormalities.
FIG. 7 shows the relationship between the slip characteristic number and the motor torque when the viscosity of the lubricating oil changes in the present invention. From this graph, it can be seen that even if the viscosity of the lubricating oil changes, since the surface pressure of the jib remains constant, power approximation can be performed using the same coefficient. In other words, even if the viscosity of the lubricating oil changes due to temperature changes, it is possible to stably diagnose the surface pressure of the jib.

As described above, according to the sliding guide diagnosis method of the above embodiment, the reciprocating motion of the feed shaft is performed at a plurality of feed speeds, and the motor torque of the motor 6 and the temperature information of the temperature sensor 9 at each feed speed are acquired. The first step (S1, S2), the second step (S3) of calculating the slip characteristic number for each feed speed from each feed speed, each temperature information, and the normal surface pressure of the guide surface 2a, and each slip characteristic a third step (S4) of calculating an approximation function of the relationship between the number and the motor torque; an approximation function calculated in the third step; and an approximation function of the relationship between the slip characteristic number and the motor torque during normal conditions identified in advance. By performing the fourth step (S5) in which the motor torque Using information that can be detected at relatively low cost, such as information, temperature information, and feed rate information, it is possible to accurately diagnose the degree of tightening of the jib 3, that is, the state of the sliding guide, without being affected by changes in the viscosity of the lubricating oil. can.

In addition, in the above embodiment, the presence or absence of an abnormality in the sliding guide is diagnosed using the coefficient of the approximation function of the relationship between the slip characteristic number and the motor torque, but it is also possible to diagnose using the difference between the approximation functions. .
Hereinafter, a flowchart of the diagnosis method using the difference between approximate functions will be explained based on FIG. 8.
The processing from S1 to S4 is similar to the diagnostic flow shown in FIG. 5 (first to third steps).
Next, in S5, using the power approximation function identified in S4, _{the motor torque value Tf αf (} f = minimum feed speed V _f.min ~ maximum feed speed V _f.max ) is calculated (third step).
Next, in S6, the motor torque value Tf no. calculated for each slip characteristic number α _f obtained in S3 is calculated using a function obtained by approximating the slip characteristic number _{α f} during normal operation obtained in advance and the motor torque T f to a power _. The absolute value of the difference between and the motor torque value Tf _αf determined in S5 is calculated for each slip characteristic number α _f , and the maximum value of the determined absolute values of the differences is compared with the threshold Th3 (fourth step).
If the threshold value is exceeded, the surface pressure of the jib 3 is diagnosed as abnormal in S7, and if the threshold value is not exceeded, the surface pressure of the jib 3 is determined to be normal in S8 (fifth step). In S9, it is determined whether or not to continue the diagnosis. If the diagnosis is to be continued, the process returns to S1, and if it is not to be continued, the process ends.
This diagnostic method also uses information that can be detected at relatively low cost, such as motor torque information, temperature information, and feed rate information, to determine the degree of tightening of the jib 3, that is, the sliding guide, without being affected by changes in the viscosity of the lubricating oil. The condition can be diagnosed accurately.

Note that the method for diagnosing sliding guide in a machine tool according to the present invention is not limited to the aspects of the above-described embodiment, but can be performed using the mounting position of the lubricating oil temperature sensor, the approximate function of the number of slip characteristics, the motor torque, and the guide. The type of machine tool having a surface, etc. can be changed as necessary without departing from the spirit of the present invention.
For example, a temperature sensor is installed near the lubricant flow path inside the slider, but there is no problem in measuring near the guide or lubricant piping as long as the temperature of the lubricant can be detected. . Further, a lubricating oil flow path may be provided inside the guide.

In addition, in the above embodiment, the approximation function between the slip characteristic number and the motor torque is a power approximation, but there is no problem in using other functions such as polynomial approximation. Furthermore, in FIG. 5, the absolute value of the difference between the coefficients of the approximated function is compared with the threshold value, and in FIG. 8, the maximum value of the absolute value of the difference in the motor torque value of the function is compared with the threshold value. The maximum value of the differences or the average value of the differences may be compared with the threshold value instead of the value. If it is possible to compare approximate functions, the difference may be calculated using values other than coefficients and motor torque values.
Further, in the above embodiment, a drive device using a ball screw and a motor is taken as an example, but the present invention can be applied to a drive device using a linear motor without any problem.

1...Slider, 1a...Slide surface, 2...Guide, 2a...Guide surface, 3...Jib, 4...Ball screw nut, 5...Ball screw shaft, 6...Motor, 7...Bed , 8...Lubricating oil flow path, 9...Temperature sensor, 10...Ammeter, 11...Lubricating oil supply device, 12...Temperature measuring device, 13...Torque calculation device, 14...Recording/arithmetic device , 15...Diagnosis result determination device, 20...NC device.

Claims (3)

a guide provided with a guide surface, a slider provided with a slide surface that slides on the guide surface, a jib interposed between the guide and the slider, and one of the guide and the slider. a feed shaft that is provided and includes a lubricating oil flow path that can supply lubricating oil between the guide surface and the sliding surface, and a motor that drives the slider;
A machine tool comprising: a lubricating oil supply device that supplies lubricating oil to the lubricating oil flow path; and a temperature sensor that detects the temperature of the lubricating oil supplied between the guide surface and the slide surface. A method for diagnosing an abnormality in a sliding guide composed of a guide surface and the sliding surface based on the degree of tightening of the jib, the method comprising:
A first step of performing reciprocating motion of the feed shaft at a plurality of feed speeds and acquiring the motor torque of the motor and temperature information of the temperature sensor at each feed speed;
a second step of calculating a slip characteristic number for each of the feed speeds from each of the feed speeds, each of the temperature information, and the normal surface pressure of the guide surface;
a third step of calculating an approximate function of the relationship between each of the slip characteristic numbers and the motor torque;
a fourth step of comparing the approximation function calculated in the third step with a pre-identified approximation function of the relationship between the slip characteristic number and the motor torque during normal operation;
a fifth step of determining whether there is an abnormality in the degree of tightening of the jib based on the comparison result of the fourth step;
A method for diagnosing sliding guide in a machine tool, characterized by performing the following. 2. The method for diagnosing sliding guide in a machine tool according to claim 1, wherein in the first step, the motor torque at the feed speed in a speed range where the lubrication type is fluid lubrication. 3. The method for diagnosing sliding guide in a machine tool according to claim 1, wherein the temperature sensor is provided near the lubricating oil flow path.

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