JP6432424B2 - Machine tool and calculation method - Google Patents

Description

  The present invention relates to a machine tool and a calculation method for calculating the amount of thermal displacement of a screw shaft that is screwed into a nut connected to a main shaft.

  The machine tool includes a main shaft on which a tool is mounted, a nut connected to the main shaft, and a screw shaft screwed onto the nut via a rolling element. A motor is connected to the screw shaft. When the screw shaft and the nut are driven, frictional heat is generated between them, so that the screw shaft extends. The machine tool calculates the displacement amount of the screw shaft based on the frictional heat. A machine tool uses a displacement amount of a screw shaft for driving control of a motor (see, for example, Patent Document 1).

JP 2009-214283 A

  However, when the displacement amount of the screw shaft is calculated based only on the frictional heat, the difference from the actual displacement amount of the screw shaft is large.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a machine tool and a calculation method that accurately calculate the amount of thermal displacement of the screw shaft.

  A machine tool according to the present invention includes a main shaft on which a tool is mounted, a nut for moving the main shaft, a screw shaft that is screwed into the nut via a rolling element, and rotates around the shaft by rotation of a motor. A calculation unit that calculates a thermal displacement amount of the screw shaft based on frictional heat generated by the screw shaft and the nut, wherein the calculation unit includes a grease provided between the nut and the screw shaft. The thermal displacement amount of the screw shaft based on viscous heat generated by the viscosity of is further calculated.

  In the machine tool according to the present invention, the value of the frictional heat is a multiplication value of a first coefficient and the rotation speed of the motor, and the value of the viscous heat generation is a square value of the second coefficient and the rotation speed of the motor. The calculation unit adds the values of the frictional heat and the viscous heat generation, and calculates a thermal displacement amount of the screw shaft based on the added value.

  The machine tool according to the present invention is characterized in that the calculation unit further calculates a thermal displacement amount of the screw shaft based on an inertial force heat generated by an inertial force acting on the nut.

  In the machine tool according to the present invention, the value of the inertial force heat generation is a product of a third coefficient, the rotational acceleration of the motor, the mass of the object connected to the nut and the nut, and the rotational speed of the motor, The calculation unit adds the values of the frictional heat, viscous heat generation, and inertial force heat generation, and calculates a thermal displacement amount of the screw shaft based on the total value.

  The calculation method according to the present invention calculates a thermal displacement amount of the screw shaft based on frictional heat generated by a nut connected to a main shaft on which a tool is mounted and a screw shaft screwed to the nut via a rolling element. In the calculation method, the thermal displacement amount of the screw shaft based on the viscous heat generated by the viscosity of the grease provided between the nut and the screw shaft is further calculated.

  The calculation method according to the present invention is characterized in that a thermal displacement amount of the screw shaft based on inertial force heat generated by inertial force acting on the nut is further calculated.

  In the present invention, the thermal displacement of the screw shaft due to viscous heat generated by the viscosity of the grease is further calculated and added to the thermal displacement due to frictional heat.

  In the present invention, the amount of thermal displacement of the screw shaft due to the inertial force heat generated by the inertial force acting on the nut is further calculated and further added to the amount of thermal displacement due to frictional heat and viscous heat generation.

  In the machine tool and the calculation method according to the present invention, the thermal displacement amount of the screw shaft due to viscous heat generated by the viscosity of the grease is further calculated and added to the thermal displacement amount due to frictional heat. Therefore, the calculation accuracy of the thermal displacement amount is improved.

1 is a perspective view schematically showing a machine tool. It is a schematic diagram which shows an X-axis motor, an X-axis screw shaft, and a nut schematically. It is a block diagram which briefly shows the structure of a control apparatus. It is a conceptual diagram which shows schematically the divided | segmented X-axis screw shaft. It is a conceptual diagram which shows an example of a data area. It is a figure which shows the relationship between the temperature of an X-axis motor, and time. It is a figure which shows the relationship between X-axis motor temperature and elapsed time. It is a functional block diagram which shows the control process of the X-axis motor by a control apparatus. It is a conceptual diagram which shows the temperature and input calorie | heat amount of each division | segmentation area. It is a graph which shows the relationship between the temperature in each position of the ball screw mechanism which concerns on an X-axis motor, and time. It is a flowchart which shows the thermal displacement amount calculation process by a control apparatus.

  Hereinafter, the present invention will be described based on the drawings showing a machine tool according to an embodiment. In the following description, up and down, left and right, and front and rear indicated by arrows in the figure are used. FIG. 1 is a perspective view schematically showing a machine tool, and FIG. 2 is a schematic view schematically showing an X-axis motor 23, an X-axis screw shaft 22 and a nut 27. In FIG. 1, the illustration of a tool magazine that houses a replacement tool is omitted.

  The machine tool includes a rectangular base 1 extending forward and backward. A work holding unit 3 that holds a work is provided on the front side of the upper portion of the base 1. A support base 2 for supporting a column 4 described later is provided on the rear side of the upper part of the base 1. A Y-axis direction moving mechanism 10 that moves in the front-rear direction is provided on the upper portion of the support base 2. The Y-axis direction moving mechanism 10 includes two rails 11 extending in the front-rear direction, a Y-axis screw shaft 12, a Y-axis motor 13, and a bearing 14.

  The rails 11 are provided on the left and right of the upper part of the support base 2, respectively. The Y-axis screw shaft 12 extends in the front-rear direction and is provided between the two rails 11. A bearing 14 is provided at each of the front end portion and the middle portion of the Y-axis screw shaft 12. In addition, illustration of the bearing provided in the middle part is abbreviate | omitted. The Y-axis motor 13 is connected to the rear end portion of the Y-axis screw shaft 12.

  A nut (not shown) is screwed onto the Y-axis screw shaft 12 via a rolling element (not shown). Grease is applied to the Y-axis screw shaft 12. The rolling element is, for example, a ball. A plurality of sliders 15 are slidably provided on each rail 11. A moving plate 16 is connected to the upper part of the nut and the slider 15. The moving plate 16 extends in the horizontal direction. As the Y-axis motor 13 rotates, the Y-axis screw shaft 12 rotates, the nut moves in the front-rear direction, and the moving plate 16 moves in the front-rear direction. The Y-axis motor 13, the Y-axis screw shaft 12, the nut and the rolling element constitute a ball screw mechanism.

  An X-axis direction moving mechanism 20 that moves in the left-right direction is provided on the upper surface of the moving plate 16. The X-axis direction moving mechanism 20 includes two rails 21 extending left and right, an X-axis screw shaft 22, an X-axis motor 23 (see FIG. 2), and bearings 24 and 25.

  The rails 21 are provided at the front and rear sides of the upper surface of the movable plate 16. The X-axis screw shaft 22 extends left and right and is provided between the two rails 21. As shown in FIG. 2, bearings 24 and 25 are provided at the left end portion and the middle portion of the X-axis screw shaft 22, respectively. The X-axis motor 23 is connected to the rear end portion of the X-axis screw shaft 22.

  As shown in FIG. 2, a nut 27 is screwed to the X-axis screw shaft 22 via a rolling element (not shown). Grease is applied to the X-axis screw shaft 22. A plurality of sliders 26 are slidably provided on each rail 21. The column 4 is connected to the tops of the nut 27 and the slider 26. Column 4 is columnar. As the X-axis motor 23 rotates, the X-axis screw shaft 22 rotates, the nut 27 moves in the left-right direction, and the column 4 moves in the left-right direction. The X-axis motor 23, the X-axis screw shaft 22, the nut 27, and the rolling element constitute a ball screw mechanism.

  A Z-axis direction moving mechanism 30 that moves in the vertical direction is provided on the front surface of the column 4. The Z-axis direction moving mechanism 30 includes two rails 31 extending vertically, a Z-axis screw shaft 32, a Z-axis motor 33, and a bearing 34.

  The rails 31 are provided on the left and right sides of the front surface of the column 4, respectively. The Z-axis screw shaft 32 extends vertically and is provided between the two rails 31. A bearing 34 is provided at each of a lower end portion and a midway portion of the Z-axis screw shaft 32. In addition, illustration of the bearing provided in the middle part is abbreviate | omitted. The Z-axis motor 33 is connected to the upper end portion of the Z-axis screw shaft 32.

  A nut (not shown) is screwed onto the Z-axis screw shaft 32 via a rolling element (not shown). Grease is applied to the Z-axis screw shaft 32. A plurality of sliders 35 are slidably provided on each rail 31. The spindle head 5 is connected to the front part of the nut and the slider 35. The Z-axis screw shaft 32 is rotated by the rotation of the Z-axis motor 33, the nut moves in the vertical direction, and the spindle head 5 moves in the vertical direction. The Z-axis motor 33, the Z-axis screw shaft 32, the nut and the rolling element constitute a ball screw mechanism.

  A main shaft 5 a extending vertically is provided in the main shaft head 5. The main shaft 5a rotates around the axis. A spindle motor 6 is provided at the upper end of the spindle head 5. A tool is attached to the lower end of the main shaft 5a. The spindle 5a is rotated by the rotation of the spindle motor 6, and the tool is rotated. The rotated tool processes the workpiece held in the workpiece holding unit 3.

  The machine tool includes a tool changer (not shown) for changing tools. The tool changer exchanges a tool housed in a tool magazine (not shown) and a tool mounted on the spindle 5a.

  FIG. 3 is a block diagram schematically showing the configuration of the control device 50. The control device 50 (arithmetic unit) includes a CPU 51, a ROM 52, a RAM 53, and an input / output interface 54. When the operator operates the operation unit 7, a signal is input from the operation unit 7 to the input / output interface 54. The operation unit 7 is a keyboard, a button, a touch panel, or the like, for example. The input / output interface 54 outputs a signal to the display unit 8. The display unit 8 displays characters, figures, symbols, and the like. The display unit 8 is, for example, a liquid crystal display panel.

  The control device 50 includes an X-axis control circuit 55 corresponding to the X-axis motor 23, a servo amplifier 55a, and a differentiator 23b. The X-axis motor 23 includes an encoder 23a. The X-axis control circuit 55 outputs a command indicating the amount of current to the servo amplifier 55a based on a command from the CPU 51. The servo amplifier 55a receives the command and outputs a drive current to the X-axis motor 23.

  The encoder 23 a outputs a position feedback signal to the X-axis control circuit 55. The X-axis control circuit 55 performs position feedback control based on the position feedback signal.

  The encoder 23a outputs a position feedback signal to the differentiator 23b, and the differentiator 23b converts the position feedback signal into a speed feedback signal and outputs it to the X-axis control circuit 55. The X-axis control circuit 55 performs speed feedback control based on the speed feedback signal.

  The current detector 55b detects the value of the drive current output from the servo amplifier 55a. The current detector 55 b feeds back the value of the drive current to the X axis control circuit 55. The X axis control circuit 55 executes current control based on the value of the drive current. In general, the drive current flowing through the X-axis motor 23 and the load torque acting on the X-axis motor 23 are substantially the same. Therefore, the current detector 55 b detects the load torque acting on the X-axis motor 23.

  The control device 50 includes a Y-axis control circuit 56 corresponding to the Y-axis motor 13, a servo amplifier 56a, and a differentiator 13b. The Y-axis motor 13 includes an encoder 13a. Based on the command from the CPU 51, the Y-axis control circuit 56 outputs a command indicating the current amount to the servo amplifier 56a. The servo amplifier 56 a receives the command and outputs a drive current to the Y-axis motor 13.

  The encoder 13 a outputs a position feedback signal to the Y-axis control circuit 56. The Y-axis control circuit 56 performs position feedback control based on the position feedback signal.

  The encoder 13a outputs a position feedback signal to the differentiator 13b, and the differentiator 13b converts the position feedback signal into a speed feedback signal and outputs it to the Y-axis control circuit 56. The Y-axis control circuit 56 executes speed feedback control based on the speed feedback signal.

  The current detector 56b detects the value of the drive current output from the servo amplifier 56a. The current detector 56 b feeds back the drive current value to the Y-axis control circuit 56. The Y axis control circuit 56 executes current control based on the value of the drive current. In general, the drive current flowing through the Y-axis motor 13 and the load torque acting on the Y-axis motor 13 are substantially the same. Therefore, the current detector 56b detects the load torque acting on the Y-axis motor 13.

  The control device 50 includes a Z-axis control circuit 57 corresponding to the Z-axis motor 33, a servo amplifier 57a, and a differentiator 33b. The Z-axis motor 33 includes an encoder 33a. Based on the command from the CPU 51, the Z-axis control circuit 57 outputs a command indicating the amount of current to the servo amplifier 57a. The servo amplifier 57a receives the command and outputs a drive current to the Z-axis motor 33.

  The encoder 33 a outputs a position feedback signal to the Z-axis control circuit 57. The Z-axis control circuit 57 performs position feedback control based on the position feedback signal.

  The encoder 33a outputs a position feedback signal to the differentiator 33b, and the differentiator 33b converts the position feedback signal into a speed feedback signal and outputs it to the Z-axis control circuit 57. The Z-axis control circuit 57 performs speed feedback control based on the speed feedback signal.

  The current detector 57b detects the value of the drive current output from the servo amplifier 57a. The current detector 57 b feeds back the value of the drive current to the Z-axis control circuit 57. The Z-axis control circuit 57 executes current control based on the drive current value. In general, the drive current flowing through the Z-axis motor 33 and the load torque acting on the Z-axis motor 33 are substantially the same. Therefore, the current detector 57b detects the load torque acting on the Z-axis motor 33.

  The tool magazine includes a magazine motor 60. The tool magazine is driven by the rotation of the magazine motor 60. The control device 50 includes a magazine control circuit 58. The magazine control circuit 58 controls the rotation of the magazine motor 60 based on a command from the CPU 51. The control device 50 also performs feedback control similar to that of the X to Z axis motors 11, 12, and 13 with respect to the spindle motor 6.

  Next, a method for calculating the amount of thermal displacement in the X-axis direction moving mechanism 20 will be described. Note that the method for calculating the thermal displacement amount in the Y-axis direction moving mechanism 10 and the Z-axis direction moving mechanism 30 is the same as the method for calculating the thermal displacement amount in the X-axis direction moving mechanism 20, and a description thereof will be omitted.

  As a method of calculating the thermal displacement amount, the amount of heat generated in three regions of the bearing 25 on the X-axis motor 23 side (right side), the moving section of the nut 27 and the bearing 24 on the opposite side (left side) of the X-axis motor 23 is obtained. The moving section corresponds to between the two bearings 24 and 25. Further, the moving section is divided into a plurality of sections (divided sections), and the heat generation amount for each section is obtained.

(Calculation of total calorific value)
FIG. 4 is a conceptual diagram schematically showing the divided X-axis screw shaft 22. As shown in FIG. 4, the control device 50 divides the movement section (length is indicated by L) in which the nut 27 of the X-axis screw shaft 22 moves into n parts. The divided section where the nut 27 is located is determined every certain time (for example, 50 ms). The control device 50 obtains the heat generation amount of the divided section located from the actual rotation speed of the motor and stores it in the data area of the temperature distribution calculation circuit 51c described later. The calorific value is obtained by the following formula. The section where the nut 27 is located can be determined based on the signal output from the encoder 23a.

Q = d ₁ · ω + d ₂ · ω ² + d ₃ · a · m · ω (1)
Here, Q is the amount of heat generation, d _{1 to} d ₃ are coefficients (first coefficient, second coefficient and third coefficient), ω is the rotational speed of the X-axis motor 23, a is the rotational acceleration of the X-axis motor 23, and m is This is the mass of the object that is moved by the X-axis screw shaft 22.

In Equation (1), d ₁ · ω represents the heat generation amount (value) of the frictional heat generated by the X-axis screw shaft 22 and the nut 27, and d ₂ · ω ² is between the nut 27 and the X-axis screw shaft 22. A heating value (value) of viscous heat generated by the viscosity of the provided grease is shown, and d ₃ · a · m · ω indicates a heating value (value) of inertial force generated by the inertial force acting on the nut 27. If the heat generation amount of inertial force heat generation is sufficiently small with respect to the heat generation amount due to viscous heat generation or frictional heat, the heat generation amount of inertial force heat generation may be omitted in Equation (1). The inertial force heat generation is due to the fact that the load on the nut 27 increases due to the inertial force, and the frictional force increases as the load on the nut 27 increases.

FIG. 5 is a conceptual diagram showing an example of a data area. As shown in FIG. 5, the control device 50 calculates the amount of heat generated by the movement of the nut 27 in the divided section where the nut 27 is located every 50 ms using the equation (1). This process is repeated for a certain time. The certain time is 6400 ms, for example. In this case, the control device 50 calculates 128 times. The control device 50 totals the heat generation amount for each divided section, obtains the total heat generation amount Q _Ni , and stores it in the data area corresponding to each of the sections 1 to n.

  Next, the calorific value of the left bearing 24 is obtained by the following equation.

Q _L = D · ω
Here, Q _L is the amount of heat generated by the left bearing 24, D is a coefficient (fourth coefficient), and ω is the rotational speed of the X-axis motor 23.

Next, the control unit 50 calculates the calorific value (right bearing calorific value) Q _R of the right bearing 25. The right-side bearing heat generation amount is due to heat input due to the rising temperature of the X-axis motor 23. The control device 50 calculates the temperature of the X-axis motor 23, and based on the difference between the calculated temperature and the temperature of the end of the X-axis screw shaft 22, the amount of heat input at the end of the X-axis screw shaft 22, that is, the right-side bearing heat generation amount Q. _{Find R.}

FIG. 6 is a diagram showing the relationship between the temperature of the X-axis motor 23 and time. As shown in FIG. 6, when the maximum saturation temperature is L _1a , the X-axis motor temperature Θ _M during driving of the machine tool draws an asymptotic line 150 with respect to the straight line P = L _1a . When the machine tool is stopped after the X-axis motor temperature Θ _M reaches the maximum saturation temperature L _1a (at time t = 8 hours in FIG. 6), the X-axis motor body temperature Θ _M is an asymptotic line 151 with respect to the straight line Q = 0. Draw.

Asymptote 150 is
L _1a = K ₂ · ω + K ₃ · i ₂ (2)
Θ _M = L _1a · (1−exp (−γ · t)) (3)
Can be expressed as

Asymptote 151 is
Θ _M = L _1a · exp (−γ · t) (4)
It is represented by Here, i is the current flowing through the X-axis motor 23, ω is the motor rotation speed, L _1a is the saturation temperature, and γ, K ₂ , and K ₃ are constants specific to the X-axis motor 23.
The motor body temperature Θ _M1a after a minute from the start of driving of the machine tool is
Θ _M1a = L _1a · {1-exp (−γ · a / 60)}
It becomes.
The motor body temperature Θ _M-1a after a minute after the machine tool stops is
Θ _M-1a = L _1a · exp (−γ · a / 60)
It becomes. The X-axis motor temperature Θ _M during the elapsed time is calculated mainly using equation (3). In the following description, it is assumed that time t1, t2,... (Minutes) have elapsed since the machine tool was driven. That is, the interval between times t1, t2,... Is the elapsed time in each process.

  FIG. 7 is a diagram showing the relationship between the X-axis motor temperature and the elapsed time. FIG. 7A is a relationship diagram between the X-axis motor temperature and the elapsed time from 0 to t1 after the start of driving, FIG. 7B is a relationship diagram between the X-axis motor temperature and the elapsed time from the start of driving to t1 to t2, and FIG. FIG. 7D is a relationship diagram between the X-axis motor temperature and the elapsed time from 0 to t3 after the start of driving. In FIG. 7, the vertical axis indicates Celsius (° C.), and the horizontal axis indicates minutes as described above.

In the present embodiment, when the X-axis motor temperature Θ _M is calculated based on the elapsed time, the X-axis motor temperature Θ _M subsequently decreases according to the equation (4). That is, as indicated by a curve 301 in FIG. 7A, the value Θ _{Mt1-1 at} time t1 of the X-axis motor temperature Θ _Mt1 calculated based on the elapsed time from time 0 to time t1 is Θ _{Mt1− 1} = L _t1 · {1−exp (−γ · t 1/60)}
It becomes. However, L _t1 is the maximum saturation temperature calculated based on the elapsed time from time 0 to time t1. Then, the value Θ _Mt1-2 of the X-axis motor temperature Θ _Mt2 at time t2 is _expressed by the following equation (4).
Θ _Mt1-2 = Θ _Mt1-1 · exp {−γ · (t2-t1) / 60}
Similarly, the values Θ _Mt1-3 and Θ _Mt1-4 of the X-axis motor temperature Θ _Mt1 at times t3 and t4 are
Θ _Mt1-3 = Θ _Mt1-1 · exp {−γ · (t3−t1) / 60}
Θ _Mt1-4 = Θ _Mt1-1 · exp {−γ · (t4-t1) / 60}
It becomes. Similarly, when the maximum saturation temperature L _t2 is calculated based on the elapsed time from time t1 to time t2, the corresponding X-axis motor temperature Θ _Mt2 changes as illustrated by the curve 302 in FIG. Θ _Mt2-1 , Θ _Mt2-2 , and Θ _{Mt2-3 at} times t2, t3, and t4 are _respectively
Θ _Mt2-1 = L _t2 · [1-exp {−γ · (t2−t1) / 60}]
Θ _Mt2-2 = Θ _Mt2-1 exp {−γ · (t3−t2) / 60}
Θ _Mt2-3 = Θ _Mt2-1 · exp {−γ · (t4-t2) / 60}
It becomes. FIG. 7C shows the temperature change of the X-axis motor temperature Θ _Mt3 , and Θ _Mt3-1 , Θ _Mt3-2 , and Θ _Mt3-3 can be obtained in the same manner as described above.

FIG. 7D shows values obtained by adding the values at the respective times of the calculated X-axis motor temperatures Θ _Mt1 , Θ _Mt2 . For example, when the X-axis motor temperature Θ _M illustrated by the curves 301, 302, 303... In FIG. 7D is calculated based on the elapsed time between times t1, t2, t3,. The motor temperature Θ _M changes as illustrated by curve 304 in FIG. 7D.

Using the X-axis motor temperature theta _M, in order to calculate the right bearing calorific value Q _R, the following equation,
Q _R = K ₄ (Θ _M −Θ _S ) (5)
It becomes. Here, K ₄ : coefficient, Θ _S : X-axis screw shaft end temperature. Note that the X-axis screw end temperature is the temperature of the portion of the X-axis screw shaft 22 supported by the right bearing 25.

(Calculation of temperature distribution)
As described above, when the heat generation amount of the moving section and each of the bearings 24 and 25 is obtained, the temperature distribution is calculated from these heat generation amounts. The temperature distribution is the following unsteady heat conduction equation:
[C] d {θ} / dt + [H] {θ} + {Q} = 0 (6)
Is solved under the initial conditions {θ} t = 0 and d {θ} / dt _{t = 0} .
Here, [C]: heat capacity matrix, [H]: heat conduction matrix, {θ}: temperature distribution, {Q}: calorific value, t: time.

(Calculation of thermal displacement)
When the temperature distribution of each part of the X-axis screw shaft 22 is obtained, the amount of thermal displacement is calculated therefrom. The amount of thermal displacement is
_{^{ΔL = ∫ L 0 β × θ}} (L) dL ··· (7)
Ask for. Here, ΔL: thermal displacement amount, β: linear expansion coefficient of the material of the X-axis screw shaft 22.

  FIG. 8 is a functional block diagram showing control processing of the X-axis motor 23 by the control device 50. The same processing is performed for the Y-axis motor 13 and the Z-axis motor 33.

  The interpolation control circuit 51 a is a circuit that calculates the feed amount of the ball screw mechanism based on the machining data read into the RAM 53. The RAM 53 includes a position register 53b. The signal distributor 51b distributes the feed amount signal corresponding to the feed amount of the ball screw mechanism to each axis, and gives the feed amount signal to the X-axis control circuit 55. The signal distributor 51b gives the feed amount signal to the position register 53b, and stores the position data of the nut 27 in the position register 53b. The encoder 23a constantly detects the rotational speed of the X-axis motor 23 and inputs a detection signal to the X-axis control circuit 55 and the temperature distribution calculation circuit 51c. A broken line indicates the control device 50.

The RAM 53 includes a parameter memory 53a. The parameter memory 53a includes parameters relating to the mechanical structure such as the length and diameter of the X-axis screw shaft 22, density, specific heat, parameters relating to physical properties such as γ used in the equations (3) and (4), and the heat distribution coefficient ( Ratio) ηN, ηB, etc. are stored. The temperature distribution calculation circuit 51c calculates the heat generation amount of the moving section of the X-axis screw shaft 22 every 50 ms from the rotation speed detection signal of the X-axis motor 23 based on the equation (1), and after 6400 ms, the total heat generation amount Q of each divided section is calculated. Calculate _Ni .

Regarding the right bearing heat generation amount, the temperature distribution calculation circuit 51c applies the current from the current detector 55b and the rotation speed of the X-axis motor 23 to the equation (2) to calculate the saturation temperature of the X-axis motor 23, Applying to Equations (3) and (4), the X-axis motor temperature Θ _M is calculated. Further, the X-axis screw shaft end temperature Θ _s is obtained by the equation (6). The calculation of the right bearing calorific value Q _R based from the X-axis motor temperature theta _M and X-axis threaded shaft end temperature theta _s in equation (5). The left bearing heat generation amount Q _L is calculated based on the rotational speed of the X-axis motor 23.

The temperature distribution calculation circuit 51c solves the equation (6) from the total calorific value Q _ni , the right bearing calorific value Q _R , the left bearing calorific value Q _L and the various data stored in the parameter memory 53a in each divided section, The temperature distribution of the two bearings 24 and 25 is calculated. Specifically, after the machine tool is driven (t = 0), the calculation of the temperature distribution when the time elapses as t1, t2,... (Minutes) is performed as follows.
FIG. 9 is a conceptual diagram showing the temperature and input heat amount of each divided section. In FIG. 9, the unit of the temperature Θ _s is Celsius. Using FIG. 9, equation (6) can be expressed as

と表現できる。

Can be expressed as

FIG. 10 is a graph showing the relationship between temperature and time at each position of the ball screw mechanism according to the X-axis motor 23. In FIG. 10, the vertical axis indicates Celsius (° C.), and the horizontal axis indicates minutes.
Time t = 0 the temperature {theta} of the mobile section and the two bearings 24, 25 at the time of, and the motor body temperature theta _M can be obtained from Q _R for known formula (5). Further, Q _{N1 to} Q _Nn from the expression (1) and Q _L are also known from the rotational speed of the X-axis motor 23. By substituting these values into the right side of equation (8), the speed at which the temperature rises at each position (d {θ} _{t = 0} / dt), that is, the slope, can be obtained as shown in FIG. From this inclination, the temperature {θ} of each part at t = 1 can be obtained by the following equation.
{Θ} _{t = t1} = {θ} _{t = to} + (d {θ} _{t = 0} / dt) · t1

{Θ} _{t = t0} X-axis threaded shaft end temperature theta _S and expressions (3), (4) from the motor body temperature theta _M which is obtained by, Q _R at t = 1 is obtained from the equation (5). Substituting these values into equation (8),
When d {θ} _{t = 1} / dt is obtained, the temperature of each part at t = 2 is {θ} _{t = t2} = {θ} _{t = t1} + (d {θ} _{t = 1} / dt) × (t2−t1) )
It is obtained by In this way, the temperature at t = t3,... Can be obtained in the same manner.

  The correction data calculation circuit 51d calculates a correction amount based on the equation (7) from the temperature distribution calculated by the temperature distribution calculation circuit 51c. The correction signal generation unit 51e gives the X-axis control circuit 55 a correction signal corresponding to the correction amount calculated by the correction data calculation circuit 51d. Each of the circuits, the signal distribution unit 51b, and the correction signal generation unit 51e constitute a CPU 51.

FIG. 11 is a flowchart showing thermal displacement amount calculation processing by the control device 50. The CPU 51 of the control device 50 divides the moving section of the X-axis screw shaft 22 into a finite number of divided sections (step S1, see FIG. 4). The CPU 51 forms a region of the heat distribution model by dividing the moving section. Corresponding to each divided section i, the RAM 53 has a memory area for storing the current outside air temperature θ _air , the initial position, the current position, the displacement, the linear expansion coefficient, the heat capacity, the heat transfer coefficient, and the like.

Next, the CPU 51 sets an initial temperature {θ} _{t = o} in each divided section i (step S2). The initial temperature {θ} _{t = o} can be individually set for each divided section. When handling that the temperature of the machine tool coincides with the outside air temperature θ _air , the initial temperature {θ} _{t = o} is set to the outside air temperature θ _air for all the divided sections. When a temperature difference is generated between the divided sections by driving the machine tool, an initial temperature is set for each divided section. The initial temperature {θ} _{t = 0} is stored in the memory. The CPU 51 also measures and stores a reference value such as an initial position.

  Data on the current position and feed rate of the nut 27 is input to the temperature distribution calculation circuit 51c every 50 ms. The temperature distribution calculation circuit 51c, that is, the CPU 51 calculates the heat generation amount for each divided section of the nut 27 based on the equation (1) (step S3). The left bearing heat generation amount is calculated from the rotational speed of the X-axis motor 23 (step S4).

  The CPU 51 obtains the saturation temperature based on the equation (2) using the current flowing through the X-axis motor 23 and the motor rotation speed, and the temperature of the X-axis motor 23 is calculated based on the saturation temperature and the equations (3) and (4). A change is obtained (step S5). From the temperature change of the X-axis motor 23 and the X-axis screw shaft end temperature, the heat input to the divided section adjacent to the X-axis motor 23, that is, the so-called right-side bearing heat generation amount is calculated based on the equation (5) (step S6). .

  CPU51 calculates | requires the temperature distribution of each division | segmentation area using the emitted-heat amount calculated | required by step S3-S6, and unsteady heat conduction equation (6) (step S7). The CPU 51 calculates the thermal displacement amount of each divided section based on the temperature distribution obtained in step S7 using equation (7) (step S8), and calculates the thermal displacement amount from the reference position stored in step S2 ( Step S9). The thermal displacement amount corresponds to a correction amount used for machining control. The CPU 51 (correction signal generator 51e) outputs a feed amount signal corresponding to the thermal displacement amount (correction amount) obtained in step S9 to the axis control circuit 61a (step S10). The CPU 51 returns the process to step S1.

  The machine tool according to the embodiment further calculates the thermal displacement amount of the X-axis screw shaft to the Z-axis screw shafts 22, 12, and 32 due to viscous heat generated by the viscosity of the grease, and adds it to the thermal displacement amount due to frictional heat. . Therefore, the calculation accuracy of the thermal displacement amount is improved.

  As shown in equation (1), viscous heat generation is proportional to the square of speed. Therefore, when the thermal displacement amount of the X-axis screw shaft 22 is calculated without considering viscous heat generation, the difference between the calculated value and the measured value increases as the speed increases. By considering viscous heat generation, the calculation accuracy of the thermal displacement amount of the X-axis screw shaft 22 is improved. The same applies to the calculation of the amount of thermal displacement of the Y-axis screw shaft 12 and the Z-axis screw shaft 32.

  Further, the heat displacement amount of the X-axis screw shaft to the Z-axis screw shafts 22, 12, and 32 due to the inertial force heat generated by the inertial force acting on the nut is further calculated, and is further added to the heat displacement amount due to frictional heat and viscous heat generation. . Therefore, the calculation accuracy of the thermal displacement amount is further improved.

  Inertia force when the acceleration / deceleration frequency is high or the mass of the object connected to the nut 27 and the nut 27 is large (the mass of the column 4 and the spindle head 5 connected to the nut 27 may exceed 100 kg). When the amount of thermal displacement of the X-axis screw shaft 22 is calculated without considering heat generation, the difference between the calculated value and the measured value increases. By considering the inertial force heat generation, the calculation accuracy of the thermal displacement amount of the X-axis screw shaft 22 is improved. The same applies to the calculation of the amount of thermal displacement of the Y-axis screw shaft 12 and the Z-axis screw shaft 32.

5a Main shaft 10 Y-axis direction moving mechanism 12 Y-axis screw shaft (screw shaft)
20 X-axis direction moving mechanism 22 X-axis screw shaft (screw shaft)
27 Nut 30 Z-axis direction moving mechanism 32 Z-axis screw shaft (screw shaft)
50 Control device (calculation unit)
51 CPU
52 ROM
53 RAM

Claims (4)

A main shaft on which a tool is mounted, a nut for moving the main shaft, a screw shaft that is screwed to the nut via a rolling element, and rotates about the shaft by rotation of the motor, and the screw shaft and nut are generated. In a machine tool comprising a calculation unit that calculates a thermal displacement amount of the screw shaft based on frictional heat to be
The computing unit is
Further calculating the amount of thermal displacement of the screw shaft based on viscous heat generated by the viscosity of the grease provided between the nut and the screw shaft ;
A machine tool characterized by further calculating a thermal displacement amount of the screw shaft based on an inertial force heat generated by an inertial force acting on the nut . The value of the frictional heat is a multiplication value of the first coefficient and the rotation speed of the motor,
The value of the viscous heat generation is a product of the second coefficient and the square value of the rotational speed of the motor.
2. The machine tool according to claim 1, wherein the calculation unit adds the values of the frictional heat and the viscous heat, and calculates a thermal displacement amount of the screw shaft based on the added value. The value of the inertial force heat generation is a product of the third coefficient, the rotational acceleration of the motor, the mass of the object connected to the nut and the nut, and the rotational speed of the motor,
The arithmetic unit, the frictional heat, summing the values of viscous heating and inertia heating, based on the summed value, according to claim 1 or 2, characterized in that for calculating the thermal displacement amount of the threaded shaft Machine tools. In a calculation method for calculating a thermal displacement amount of the screw shaft based on friction heat generated by a nut connected to a main shaft on which a tool is mounted and a screw shaft screwed to the nut via a rolling element,
Further calculating the amount of thermal displacement of the screw shaft based on viscous heat generated by the viscosity of the grease provided between the nut and the screw shaft ;
A calculation method further comprising: calculating a thermal displacement amount of the screw shaft based on an inertial force heat generated by an inertial force acting on the nut .

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