JP4358786B2 - Ball screw thermal displacement correction method - Google Patents

Description

  The present invention relates to a method for correcting thermal displacement of a ball screw used in a drive system of an industrial robot, a deburring device, a machine tool, or the like.

  As a machine using a ball screw as a drive system, there is a machine tool of a parallel link mechanism. As a machine tool of a parallel link mechanism, as shown in FIG. 11, a machine tool equipped with a spindle head 12 that freely moves around in a machining space in six axis directions is known. In this machine tool, six universal joints 15 are arranged on the ceiling portion 17. Each universal joint 15 supports an upper end portion of a ball screw 14 that is an expansion / contraction actuator, and is provided with a hollow servomotor 16 that drives the ball screw 14. The ball screw 14 passes through the hollow shaft of the hollow servomotor 16, and the ball screw nut and the hollow shaft are connected.

  A spindle head 12 is supported on the lower ends of the six ball screws 14 via a universal joint 13, and the spindle is rotatably provided on the spindle head 12. Then, by changing the length of the ball screw 14 between the universal joint 13 and the universal joint 15, the spindle head 12 is positioned in an arbitrary posture in the machining space, and a work on the table 11 is mounted with a tool attached to the spindle 18. Is to be processed. A flexible pipe 23 is connected to the spindle head 12 from the outside via the joint 21 and the base 22, and a coolant supply and discharge pipe is passed through the spindle head 12.

In such a machine tool, an accuracy of several μm is required for controlling the position of the spindle head 12. Therefore, it is necessary to accurately control the length of the ball screw 14. However, if the rotation speed of the servo motor 16 is increased, the stator of the motor and the ball screw nut generate heat, and the heat is transmitted to the ball screw shaft. It expands and the position of the spindle head 12 becomes inaccurate.
In the ball screw fixed type drive device, a reference scale is provided, and the moving body is positioned based on the reference scale so that the positioning error of the moving body does not occur even when the ball screw shaft expands. However, it is difficult to provide a reference scale in a structure in which the ball screw itself is movable, such as a parallel link machine tool.

Therefore, as in the ball screw drive devices of Patent Document 1 and Patent Document 2 previously provided by the present applicant, a measure for suppressing the thermal expansion of the ball screw shaft by flowing a coolant through the hollow hole of the ball screw shaft. Can be considered.
Also, as in Patent Document 3, in a parallel link mechanism machine tool in which the ball screw does not rotate, the ball screw shaft is made hollow, and a number of temperature sensors are attached to the hollow portion, thereby measuring the ball screw temperature distribution. It is also known.
Patent Document 4 shows a thermal displacement correction method for a machine tool in which a drive source is considered as a heat source, and a heat generation amount is estimated using the speed and drive torque of the drive source without using a temperature sensor.

JP 2002-266977 A JP 2005-28558 A JP 2002-361541 A Japanese Patent No. 3407972

  In Patent Documents 1 and 2, if the operating rate of the machine tool is increased, the temperature rise of the ball screw shaft may not be suppressed. Furthermore, since a cooling device is added, the structure is complicated, repair and maintenance are difficult, and the manufacturing cost increases. This is the same in Patent Document 3, and a large number of temperature sensors are required, resulting in high costs. Further, the scope of application is limited by being limited to a structure in which the ball screw does not rotate.

On the other hand, the temperature distribution of the ball screw shaft is affected not only by the heat generated by the drive source, but also by the temperature of the environment where the ball screw is installed. It is desirable to measure with a temperature sensor. However, since the correction method of Patent Document 4 does not consider the environmental temperature, the accuracy of temperature distribution estimation may be reduced depending on the environmental temperature, and it cannot be said that accurate thermal displacement correction is possible. In addition, since there is an individual difference in the heat generation of the drive source, the inaccuracy of the estimation of the heat generation amount of the drive source cannot be denied compared with the case of measuring with a temperature sensor.
In the same document, the distribution of the amount of heat of the ball screw is calculated on the assumption that the amount of heat is exchanged between a finite number of section regions. However, if the number of divided sections is increased in order to accurately know the thermal displacement, the calculation time is increased. Will also increase. The only way to prevent a decrease in control performance due to an increase in calculation time is to employ a control device that has an extremely high calculation capacity but is expensive.

  Therefore, the present invention has an object to provide a ball screw thermal displacement correction method capable of highly accurate thermal displacement correction with a simple configuration in which the manufacturing cost is relatively reduced while using a temperature sensor. It is.

In order to achieve the above object, a method of correcting a thermal displacement of a ball screw according to the invention of claim 1 is directed to the amount of heat of the first heat source in contact with the ball screw in the drive system of the machine using the ball screw. Estimating from the temperature of the first temperature sensor installed in the vicinity of the first heat source, the distribution of the first ratio of the amount of heat of the first heat source and the amount of heat that the first heat source gives to the entire length of the ball screw is previously determined. storage to with our Ku, the first reading the position of the heat source, and heat of the first said first heat source estimated from the temperature sensors, and distribution of the first ratio of the first heat source The time change of the heat distribution given to the ball screw by the first heat source is estimated from the position, and the time change of the first temperature distribution is estimated from the time change of the estimated heat distribution, while being in contact with the ball screw. Set the temperature of the second heat source not in the vicinity of the second heat source. The second estimated from the temperature sensor, the temperature and the second heat source of the second heat source in conjunction with previously stored to your Ku the distribution of second ratio of temperature applied to the ball screw overall length, the second reads the position of the heat source, the said second temperature of the heat source estimated from the second temperature sensor, and the distribution ratio of the second, the second from the position of the heat source of the second heat source is a ball screw The time variation of the second temperature distribution applied to the first and second temperature distributions is estimated, the temperature distribution of the ball screw is estimated by adding the first and second temperature distributions, and the thermal displacement of the ball screw is estimated using the estimated temperature distribution. This is characterized in that a correction amount is obtained.

  A method for correcting a thermal displacement of a ball screw according to a second aspect of the present invention is the method for correcting a thermal displacement of the first aspect, wherein the amount of heat of the first heat source in contact with the ball screw is determined in the vicinity of the first heat source. When estimating from the temperature of the first temperature sensor installed in the above, a value obtained by multiplying the coefficient of the speed of the ball screw by the temperature of the first temperature sensor is used.

  Note that the first heat source and the second heat source in the present invention do not indicate only a single heat source, but include a plurality of heat sources by distinguishing them according to the presence or absence of contact with the ball screw. For example, the first heat source includes a spline nut or a ball screw nut, and the second heat source includes an ambient temperature or a servo motor. Therefore, the case where a plurality of first and second temperature sensors are provided corresponding to the heat sources is also included.

According to the first aspect of the present invention, in a drive system of a machine using a ball screw, the temperature distribution of the ball screw is estimated using a small number of temperature sensors attached in the vicinity of the heat source, and the ball screw temperature distribution is estimated. The amount of thermal displacement of the ball screw can be estimated using the value. Therefore, it is possible to correct the thermal displacement of the ball screw with high accuracy with a simple configuration in which the manufacturing cost is relatively reduced.
According to the second aspect of the present invention, in addition to the effect of the first aspect, the temperature of the ball screw is accurately estimated regardless of the driving state of the ball screw by considering the speed of the ball screw. It becomes possible.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
According to the correction method of the present invention, the temporal change of the temperature distribution of the ball screw is estimated using the temperature sensor in which the thermal displacement of the ball screw is installed in the heat source and the position information of the heat source. First, the temperature distribution and heat amount distribution given to the ball screw by the heat source are approximated by multiplying a symmetrical curve around the heat source as shown in FIG. 1 with the estimated temperature and the estimated heat amount of the heat source. In the present invention, this curve is expressed as follows. That is, assuming that the heat source Hj is at the position Pj, the temperature ratio distribution curve Ft (Pj) and the heat quantity ratio distribution curve Fq (Pj) at the position Li on the ball screw for which the temperature is to be obtained are expressed by the following equations. . Here, Xi = Li-Pj, Wj is the width of the heat source, Gj is a constant that determines the curve, and each heat source has a value. As shown in FIG. 1, this curve moves from a solid line to a dotted line in accordance with a change in the position Pj of the heat source.

[Equation 1]
When | Xi |> Wj / 2 Fq (Pj), Ft (Pj) = (exp (Gj.Wj / 2) -exp (-Gj.Wj / 2)). Exp (-Gj. | Xi |) / 2

When | Xi | ≦ Wj / 2 Fq (Pj), Ft (Pj) = (1-exp (Gj.Wj / 2). (Exp (Gj.Xi) + exp (-Gj.Xi)) / 2)

The estimation of the ball screw temperature distribution is divided into two methods depending on the type of heat source.
First, when the heat source is in contact with the ball screw (referred to as a type A heat source (first heat source)), the heat amount of the heat source is estimated from the temperature of the temperature sensor installed in the vicinity of the heat source, and the estimated heat amount The amount of heat in the entire length of the ball screw is estimated by multiplying the ratio of the amount of heat given by this heat source to the entire length of the ball screw (Equation 1). Then, the temperature is estimated from the estimated amount of heat. As the type A heat source, a spline nut, a ball screw nut, and the like are conceivable.
On the other hand, when the heat source is not in contact with the ball screw (referred to as a type B heat source (second heat source)), the temperature is estimated from the temperature sensor, and the temperature of this heat source and the temperature that this heat source gives to the total length of the ball screw Is multiplied by the ratio (Equation 1) to estimate the temperature over the entire length of the ball screw. The type B heat source may be the servo motor coil, the ambient temperature around the ball screw, and the like.

  It is generally known that the temperature distribution of a ball screw can be obtained by superimposing the temperature distribution that each heat source gives to the ball screw. Assuming that the temperature that each heat source Hj gives to the ball screw is θj, when m heat sources are assumed, the temperature distribution θ of the ball screw is added to the following formula.

[Equation 2]
θ = θ ₁ + θ ₂ +... + θ _m−1 + θ _m

  Hereinafter, an example in which claims 1 and 2 of the present invention are applied to the ball screw of the machine tool of the parallel link mechanism shown in FIG. 11 will be described in detail. As shown in FIG. 2, the drive system of the machine tool of the parallel link mechanism has a structure in which a spline ball screw is passed through a hollow shaft servomotor. Considering the spline nut 5 and the ball screw nut 6 as type A heat sources, the temperature sensor 2 is attached to estimate the heat quantity of the heat sources. Further, considering the environmental temperature as a type B heat source, a temperature sensor 1 and a temperature sensor 4 are attached to estimate the temperature of the heat source. Similarly, a coil of the servo motor 16 is assumed as a type B heat source, and the temperature sensor 3 is attached to estimate the temperature of the heat source.

  Then, as shown in FIG. 2, the temperature distribution given to the ball screw by each heat source is estimated and added to obtain the temperature distribution of the ball screw. However, in the case of a machine tool with a parallel link mechanism, the thermal expansion amount corresponding to the distance (strut length) between the universal joint rotation centers in FIG. Will be.

Next, the flow of ball screw thermal displacement correction will be described with reference to FIG. In the first step (abbreviated as “S1” in FIG. 3; the same applies to the other steps hereinafter), the division number d for dividing the ball screw to be subjected to thermal displacement correction into d sections, and the length of each element i ΔL _i is determined. Further, the calculation cycle T _S , the linear expansion coefficient α, and the reference temperature H _S are determined. The calculation period TS is an interval for calculating the ball screw thermal displacement. As the calculation period T _S is shortened, the estimation accuracy is improved.
Ball screw thermal displacement amount is calculated by using the relative temperatures of the estimated temperature of the reference temperature H _S and the ball screw. This is due to the following reason.
In the machine tool of the parallel link mechanism, in order to improve machine accuracy, it is necessary to identify the positions of the universal joint 13 and the universal joint 15 and the strut length by calibration. Although details of the calibration are not described here, this is an operation of measuring the relative distance between the table 11 and the spindle 18. Using the temperature at the time of measurement as the reference temperature and calculating the ball screw thermal displacement using the relative temperature between the reference temperature and the estimated temperature of the ball screw, the thermal displacement for the strut length identification value obtained by calibration is obtained. Because.

Next, in step S2 in FIG. 3, the initial value θ ₀ of the ball screw temperature distribution is estimated using the ball screw temperature distribution at the time of the previous machine stop and the temperature of the heat source at the time of the current machine start, and in the subsequent S3. The initial value E ₀ of the strut length thermal displacement correction amount is estimated using the initial value θ ₀ of the ball screw temperature distribution.
In S4, updating the temperature compensation of strut length, in S5, performs estimation of the temperature distribution heat source Aj type A has on the ball screw theta _A j (first temperature distribution), in S6, the type B heat source Bj is to estimate the temperature distribution theta _B j which gives the ball screw (second temperature distribution).
In S7, as described with reference to FIG. 2, the temperature distribution given to the ball screw by each heat source is added to estimate the ball screw temperature distribution θ, and in subsequent S8, the thermal displacement correction amount E of the strut length is estimated, In S9, the thermal displacement correction amount for the strut length is updated.
In S10, it is confirmed whether or not the machine power supply is ON. If ON in this determination, the process returns to S5, if OFF, the in S11, and ends the final value theta _END and stop time _{T END} ball screw estimated temperature distribution is recorded in the memory of the numerical controller.

Here, the process of S2 of FIG. 3 will be described in detail with reference to FIG. First, assuming that the temperature of the heat source that exhibits a temperature change similar to the temperature of the ball screw when not in operation is H ₀ , the temperature H ₀ of the heat source is read in S21 in FIG. Next, in S22, the current time _TSTART is read from the numerical controller. At this time, assuming that the time constant of the temperature when the ball screw cools is T ₀ , if 4 · T _{0 has} elapsed from the previous stop time, the ball screw is sufficiently cooled down and becomes equal to the temperature H _{0 of} the heat source. Conceivable. Therefore, in the next S23, the following relationship of Formula 3 is determined.

[Equation 3]
(T _START -T _END )> 4 · T ₀

If the elapsed time exceeds 4 · T ₀ in this determination, the process proceeds to S25, and the initial value θ ₀ of the ball screw temperature distribution is set as the temperature of the heat source H ₀ . If 4 · T ₀ or less, the process proceeds to step S24, the ball screw initial temperature distribution theta using a final value theta _END of the elapsed time T _P and the previous ball screw temperature distribution to the current boot since the last stop ₀ is calculated by the following formula.

[Equation 4]
θ ₀ = H ₀ + (θ _END −H ₀ ) · exp (−T _P / T ₀ )
However, T _P = T _START −T _END

Next, the process of S3 in FIG. This will be described in detail with reference to FIGS. First, in S31 of FIG. 6, the interpoint temperature of the initial value of the temperature distribution of each element i of the ball screw obtained in S2 is linearly interpolated. As a result, the initial value of the temperature distribution of the ball screw is a linear temperature distribution as shown in FIG. Next, in S32, the strut length is fetched from the numerical arithmetic unit. Then, the summing _{S 0} a temperature of up to strut length in S33. For example, when strut length is 1100, shaded range in FIG. 5 is _{S 0.} The ball screw thermal displacement E ₀ is a value obtained by multiplying the linear expansion coefficient α by S ₀ (Equation 5).

[Equation 5]
E ₀ = α · S ₀

Next, the process of S5 in FIG. 3 will be described in detail. First, in S51 in FIG. 7, reads the temperature _{H A} j and the position _{P A} j of the heat source Aj. Next, in S52, and _{H A} j 'multiplied by the temperature _{H A} j suppression coefficient _{C A} j of the heat source Aj (6). This suppression coefficient is varied according to the speed of the ball screw.

[Equation 6]
H _A j ′ = C _A j · H _A j

Next, in S53, the estimated Q _A j ′ of the heat generation equivalent amount of the heat source _A j is calculated by the following equation. Here, I _A j is a constant used when estimating the heat generation amount of the heat source _A j, and n represents the number of calculations.

[Equation 7]
_{Q A j '(n) =} H A j' (n-1) + (H A j '(n) -H A j' (n-1)) / β A j
_{However, β A j = T S /} (T S + I A j)

Next, in S54, the ball screw heat quantity ratio distribution curve Fq (P _A j) of the heat source Aj is read. In S55, the heat generation equivalent quantity distribution Q _A j of the ball screw is calculated by the following equation.

[Equation 8]
Q _A j = Q _A j ′ · _F q (P _A j)

Then, in S56, to calculate the time course of the ball screw temperature distribution by the following formula from the heat equivalent weight distribution Q _{A j.} Here, O _A j is a constant used when estimating the temperature that the heat source _A j gives to the ball screw, and n represents the number of calculations.

[Equation 9]
θ _A j _(n) = θ _A j _(n−1) + (Q _A j _(n−1) −θ _A j _(n−1) ) · γ _A j
γ _A j = T _S / (T _S + O _A j)

Next, the process of S6 in FIG. 3 will be described in detail. In S61 in FIG. 8, it reads the temperature _{H B} j and the position _{P B} j of the heat source Bj, in S62, reads the ballscrew temperature ratio distribution curve Ft heat source Bj _{(P B} j). Next, in S63, the temperature distribution θ _B j ′ of the ball screw is calculated by the following equation.

[Equation 10]
θ _B j ′ = H _B j · Ft (P _B j)

In S64, the change with time of the ball screw temperature distribution is calculated by the following equation. Here, O _B j is a constant used when estimating the temperature that the heat source A j gives to the ball screw, and n represents the number of calculations.

[Equation 11]
θ _B j _(n) = θ _B j _(n−1) + (θ _B j ′ _(n) −θ _B j _(n−1) ) · γ _B j
_{However, γ B j = T S /} (T S + O B j)

  Since S8 in FIG. 3 is the same as S3 described above, a description thereof will be omitted.

  FIG. 9 is a graph of the measured value of the ball screw temperature when the machine is moved at a feed rate of 10 m / min and 20 m / min, and a graph of the temperature distribution of the ball screw estimated using the present invention. FIG. It is a graph of the thermal displacement estimated using the measured value of the thermal displacement between the spindle head 12 and the table 11 when the machine is moved at / min and 20 m / min, and the ball screw thermal displacement amount according to the present invention. By using the present invention, the temperature distribution of the ball screw can be accurately estimated, and the amount of displacement of the ball screw obtained from the estimated temperature distribution of the ball screw can be used to estimate the amount of thermal displacement of the machine. I understand that

As described above, according to the thermal displacement correction method for a ball screw of the above aspect, in a machine tool of a parallel link mechanism using a ball screw, the ball screw full length using a small number of temperature sensors 1 to 4 attached in the vicinity of the heat source. The thermal displacement amount of the ball screw can be estimated using the estimated value of the ball screw temperature distribution. Therefore, it is possible to correct the thermal displacement of the ball screw with high accuracy with a simple configuration in which the manufacturing cost is relatively reduced.
In particular, here, when the amount of heat of a type A heat source in contact with the ball screw is estimated from the temperature of a temperature sensor installed in the vicinity of the heat source, a suppression coefficient that is varied according to the speed of the ball screw is used. by using a value obtained by multiplying the temperature of the temperature sensor (H a _j '), even in any drive state ball screw it becomes possible to estimate the temperature distribution accurately ball screw.

In the above embodiment, the amount of heat of the heat source is estimated using a suppression coefficient that is varied according to the speed of the ball screw.However, if the influence of the speed of the ball screw is small, the amount of heat can be determined without using the suppression coefficient. You can make an estimate.
The temperature sensor attached to the motor may be replaced with an encoder temperature sensor built in the servo motor. In this way, the components can be shared and the configuration becomes more rational.
On the other hand, in a parallel link mechanism machine tool, the thermal displacement amount is estimated more accurately than the result of FIG. 10 by considering not only the thermal expansion of the ball screw (strut) but also the thermal expansion of the joint rotation center. It is possible.
In addition, the ambient temperature and the servo motor coil are cited as the heat source that does not come into contact with the ball screw. In addition, the servo motor bearings and the like can be estimated in the same manner.

It is explanatory drawing of a ball screw temperature distribution ratio and a ball screw heat quantity distribution ratio. The cross-sectional view of the drive system of the machine tool of the parallel link mechanism to which the present invention is applied, the heat amount distribution that each heat source gives to the ball screw, the temperature distribution that each heat source gives to the ball screw, and the positional relationship of the temperature distribution of the ball screw It is explanatory drawing. It is a flowchart of the correction method of the ball screw thermal displacement of this invention. It is a flowchart of calculation of initial value (theta) ₀ of the ball screw temperature distribution of this invention. It is a figure explaining the temperature distribution of the ball screw interpolated between each element, and the calculation method of the temperature of strut length. It is a flowchart of estimation of the thermal displacement correction amount initial value of strut length. Heat Aj type A is a flowchart of estimating the temperature distribution theta _{A j} applied to the ball screw. Heat source Bj of type B is a flowchart of estimating the temperature distribution theta _{B j} given to the ball screw. It is a graph of the estimated value of the ball screw temperature according to the present invention and the measured value of the ball screw temperature when driven at different feed speeds. It is the graph of the estimated value of the thermal displacement amount of the Z-axis direction of the machine estimated using the ball screw thermal displacement amount according to the present invention when the feed speed is changed, and the measured value. It is a perspective view of a machine tool using a parallel link mechanism.

Explanation of symbols

1 to 4 ··· Temperature sensor 5 · · Spline nut 6 · · Ball screw nut 11 · · Table 12 · · Spindle head · 13 · Universal joint 14 · · Ball screw 15 · · Universal joint 16 .. Servo motor, 17 .. Ceiling, 18 .. Main shaft, 21 .. Joint, 22 .. Base, 23 .. Flexible tube.

Claims (2)

In the drive system of a machine using a ball screw,
The amount of heat of the first heat source in contact with the ball screw is estimated from the temperature of the first temperature sensor installed in the vicinity of the first heat source, and the amount of heat of the first heat source and the first heat source are the first distribution together with our Ku previously stored to the ratio of the amount of heat applied to the ball screw overall length, and the amount of heat of the first reading the position of the heat source, the first the first heat source estimated from the temperature sensor, the distribution of the first ratio, the first of the first heat source and a position of the heat source estimates the time variation of heat distribution giving the ball screw, a first temperature from the time variation of the estimated amount of heat distribution While estimating the time variation of the distribution,
The temperature of the second heat source not in contact with the ball screw is estimated from a second temperature sensor installed in the vicinity of the second heat source, and the temperature of the second heat source and the second heat source are the distribution of the second ratio previously stored in conjunction with our Ku temperature giving the length, and the second loading position of the heat source, the temperature of the second second heat source estimated from the temperature sensor, said and distribution of the two ratios, the second heat source from the position of the second heat source to estimate the time change of the second temperature distribution applied to the ball screw,
The temperature distribution of the ball screw is estimated by adding the first and second temperature distributions to estimate the temperature distribution of the ball screw, and using the estimated temperature distribution to determine a thermal displacement correction amount of the ball screw. Correction method. When estimating the amount of heat of the first heat source in contact with the ball screw from the temperature of the first temperature sensor installed in the vicinity of the first heat source, a coefficient corresponding to the speed of the ball screw is calculated. 2. The method of correcting a ball screw thermal displacement according to claim 1, wherein a value obtained by multiplying the temperature of said temperature sensor is used.

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