KR20140092078A - Thermal deformation correction method for ball screw of machining centers - Google Patents

Abstract

The present invention, for a thermal deformation correction method of a ball screw which occurs during the operation of a machining center, relates to a thermal deformation correction method of a ball screw which is not affected by operation environment of the machining center and an irregular operation time. The present invention can correct thermal deformation amount of the ball screw to suit some operating environments of some because an operator actually measures the thermal deformation amount of an X, Y, and Z axes in the operating environment of the machining center by combining a correction machine formed to be inclined by 45 degrees simply to a tool length correction device only capable of correcting the Z axis of the machining center.

Description

Technical Field [0001] The present invention relates to a method of correcting thermal deformation of a ball screw,

The present invention relates to a method of correcting thermal displacement of a ball screw generated during operation of a machining center, and a method of correcting thermal displacement of a machining center ball screw that is not affected by an operating environment of the machining center and irregular operation time.

The machining center is composed of a main shaft that operates in the Z axis and a table that operates in the X and Y axes, and the table is transported by the ball screw.

The ball screw rises in temperature due to the frictional resistance and the heat of the servo motor, thereby generating a sliding surface.

As described above, when an error occurs on the heat side of the ball screw, it is inevitable that it requires precision in terms of the characteristics of the workpiece of the machining center.

Generally, it is general that the machining center enters the main machining after anticipating it to reach the maximum value of the thermal displacement of the ball screw by performing the ball operation for about 1 hour without the workpiece before machining the workpiece.

Thus, conventionally, a method of calibrating a thermal displacement is proposed by measuring the number of revolutions and heat of a servo motor, the end temperature of a ball screw, etc., and programming certain data in a machining center.

However, the above-mentioned thermal displacement correction method is a fixed fixed value, and it does not consider the operation environment condition of the machining center and the operation propensity of the machining center (cutting flow rate, operation speed, bearing expansion, etc.) There is a problem that there is no corresponding countermeasure against various factors as described above because the thermal compensation is performed only by the expected data value.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a method of correcting thermal displacement of a machining center ball screw by measuring an amount of thermal displacement of a ball screw in an environment in which an operator operates an actual machining center, The purpose is to provide.

According to the present invention, there is provided a method for correcting thermal displacement of a machining center ball screw, which comprises a main shaft for machining a workpiece with a tool mounted on the chuck and rotating and raising / lowering the workpiece, And a tool length correcting device coupled to one side of the table, characterized in that the upper tool has an upper edge on the tool touch portion of the tool length correcting device in contact with a tool provided on the main axis Assembling a cap type correction mechanism formed at an angle of 45 degrees; Wherein the tool length correction device to which the correction mechanism is coupled while the machining center processes the workpiece measures the thermal expansion amount of the ball screw due to thermal friction every time the tool of the chuck contacts the corner portion inclined by 45 deg. Measuring a thermal expansion amount; A thermal expansion amount time constant measurement step of measuring a time (thermal expansion amount time constant) at which the thermal expansion amount measured in the thermal expansion amount measurement step reaches a point at which the thermal expansion amount is 63.2% of the maximum thermal expansion amount (saturation value); Calculating a thermal expansion amount of the ball screw at a point at which the table is located on the x and y axes at an arbitrary time by substituting the thermal expansion amount time constant measured in the thermal expansion amount time constant measuring step into a continuous curve graphing step; Wherein the machining center stops the operation of the table, and the tool of the chuck is brought into contact with the corner portion of the correction mechanism at an angle of 45 deg. At a designated time to measure the amount of heat shrinkage of the ball screw due to natural cooling Measuring step; Measuring a time of shrinkage quantity time constant measuring a time (heat shrinkage quantity time constant) in which a heat shrinkage amount measured in the heat shrinkage amount measuring step reaches 36.8% of a maximum heat shrinkage amount (saturation value); Calculating a heat shrinkage amount of the ball screw at a position where the table is located on the x and y axes at an arbitrary time by substituting the time constants of the heat shrinkage time constant measured in the step of measuring the heat shrinkage time constant into a continuous curve graphing step; Storing a ball screw thermal expansion amount and a heat shrinkage amount at a point where the table is located on the x, y axes at a predetermined time calculated in the above-described manner in a control system of a machining center; Correcting the x and y axis transfer distances of the table using the thermal expansion amount value and the heat shrinkage amount value stored in the control system; .

The present invention having the above-described structure can be applied to a tool length correcting device capable of only correcting the Z-axis of a machining center by simply combining a correcting mechanism formed with an angle of 45 degrees inclined so that an operator can adjust the X, Y, It is possible to correct the amount of thermal displacement of the ball screw in accordance with various operating environments.

In addition, it is possible to calculate the amount of thermal displacement during irregular operation time of the machining center by applying not only the thermal expansion amount during operation of the ball screw but also the heat shrinkage amount due to natural cooling during operation stoppage.

1 is a cross-sectional view showing a state in which a correction mechanism is combined with a conventional tool length compensation device in the present invention
2 is a side view of a machining center incorporating the correction mechanism of the present invention;
3 is a flow chart of a method of correcting thermal displacement of a machining center ball screw of the present invention.

Hereinafter, a method of correcting thermal displacement of a machining center ball screw according to the present invention will be described in detail.

First, the machining center 10 includes a main shaft 11 on which a tool 11a is mounted and which rotates and wins / descends to process the workpiece. A workpiece is mounted on the top surface of the main shaft 11, A commonly used spindle-fixed machining center 10 having a table 13 that is moved forward and backward and rightward and leftward and a tool length correcting device 14 at one side of the table 13.

The step of assembling the correction mechanism 20 may include a step of forming a cap shape in which the upper edge is inclined at an angle of 45 degrees with respect to the tool touch portion of the tool length correcting device 14 in contact with the tool 11a provided on the main shaft 11 And the correction mechanism 20 is assembled.

The tool length compensating device 14 is preferably coupled to one side of the table 13 as shown in FIG. 2, and is coupled to the maximum stroke end.

The reason for coupling the correcting mechanism 20 to the tool length correcting device 14 is that the conventional tool length correcting device 14 is made of a rigid material at the top of the tool length correcting device 14 When the tool is in contact with the upper surface of the correcting mechanism 20 as shown in FIG. 1, the Z-axis and the tool (not shown) When the X-axis and the tool contact the 45th view in the Y-axis direction of the correcting mechanism 20, the displacement amount in the Y-axis can be measured, ), The X-axis and Y-axis displacements are equal to the Z-axis displacements of the tool.

Therefore, the correction mechanism 20 is a construction for joining only the correction mechanism 20 without replacing the conventional tool length correction device 14, and forms a 45-degree corner on the tool length correction device 14 itself, It may be made of a hard material so as not to be abraded even if it is brought into contact with it.

In the next step of measuring the thermal expansion amount, the tool length correcting device 14, to which the correcting mechanism 20 is coupled, while the machining center is processing the workpiece, And the amount of thermal expansion of the ball screw 12 due to thermal friction is measured every time it contacts the tilted corner portion.

The thermal expansion measuring step is different from the conventional tool length correcting device 14 in that it is in contact in the same manner but in addition to the Z-axis as well as the tilted corner of the X, Y axis 45 ° of the correcting mechanism 20.

Therefore, the thermal expansion amount measuring step is performed by measuring the abraded length of the tool 11a with the conventional tool length correcting device 14 in contact with the upper surface of the correcting mechanism 20, The amount of thermal expansion is determined by the distance that the correcting mechanism 20 is displaced in the x and y axes due to the thermal deformation of the ball screw 12 due to the contact of the tool 11a with the 45 ° inclined corner of the correction mechanism 20. [ Since the tool 11a is displaced in the z-axis, the amount of thermal expansion of the ball screw 12 can be measured.

The next step of measuring the thermal expansion amount time constant is a step of measuring the time (thermal expansion amount time constant) at which the thermal expansion amount of the thermal expansion amount measured in the thermal expansion amount measurement step reaches 63.2% of the maximum thermal expansion amount (saturation value).

In the step of measuring the thermal expansion amount time constant, the time (time constant) at which the ball screw 12 reaches 63.2% of the maximum thermal expansion amount (saturation value) due to natural cooling even when the thermal expansion progresses due to thermal friction And measuring the thermal expansion amount through the thermal expansion measurement step.

In the next step of calculating the thermal expansion amount of the ball screw, the thermal expansion amount time constant measured in the thermal expansion amount time constant measuring step is substituted into a continuous curve graphing step, and the temperature of the point at which the table is located on the x, The ball screw thermal expansion amount calculating step.

In the calculation of the thermal expansion amount of the ball screw, a continuous curved line graph is obtained. When the tool 11a of the machining center repeatedly touches the correction mechanism 20 and graphs the calculated value, a point curve is formed Since the time point value between the point and the point can not be measured, the continuous thermal expansion amount measured in the thermal expansion amount measurement step is calculated by a continuous curve graph.

Then, the amount of thermal expansion of the ball screw at the position where the table is located on the x and y axes is calculated at an arbitrary time by substituting the above-mentioned curved graphical thermal expansion amount into the equation.

The equation to be substituted in the ball screw thermal expansion amount calculating step is as follows.

Here, x (∞) = the maximum thermal expansion amount at the x-axis end, t = time, τxr = time required to reach 63.2% of the maximum thermal expansion amount of the x axis (time constant), and Exp (natural constant e) = 2.718.

The thermal expansion amount of the ball screw 12 measured through the correction mechanism 20 in the thermal expansion amount measuring step by substituting the above equation is curved as follows.

<Graph of thermal expansion curve over time>

The following equation is used to calculate the ball screw thermal expansion amount at the position where the table is located on the x and y axes at the next arbitrary time.

Where L = table arbitrary position, and 500 = x-axis ball screw length.

The amount of thermal expansion of the ball screw at the position where the table is located on the x and y axes can be calculated at any time by substituting the curved graphical thermal expansion amount by time into the above equation.

In the above equation, although written in the x-axis, the same applies to the y-axis.

The next heat shrinkage amount measuring step is a step of measuring the amount of heat shrinkage by contacting the tool 11a of the chuck with a corner portion inclined by 45 degrees of the correction mechanism 20 at a designated time in a state where the machining center stops the operation of the table 13, (14) measures the amount of heat shrinkage of the ball screw (12) by natural cooling.

Measuring the amount of heat shrinkage of the ball screw 12 as the temperature of the ball screw is lowered by natural cooling when the machining center stops operating, to be.

The next step of measuring the heat shrinkage time constant is a step of measuring a time (heat shrinkage time constant) during which the heat shrinkage amount measured in the heat shrinkage amount measurement step reaches 36.8% of the maximum heat shrinkage amount (saturation value).

Next, the ballscrew heat shrinkage amount calculating step may be performed by substituting the time constant of heat shrinkage time measured in the step of measuring the heat shrinkage time constant into a continuous curve graph, This is the step of calculating the heat shrinkage amount of the ball screw.

In the step of calculating the heat shrinkage amount of the ball screw, the continuous curve drawing of the heat shrinkage amount is performed by making a point curve when the tool 11a of the machining center repeatedly touches the correction mechanism 20 and graphs the calculated value Since the time-point value between the points can not be measured, the time-dependent heat shrinkage amount measured in the heat shrinkage amount measuring step is calculated by a continuous curve graph.

The amount of heat shrinkage of the ball screw at the position where the table is located on the x and y axes is calculated at a given time by substituting the curved graph of the heat shrinkage amount by time into the equation.

The equation to be substituted in the ball screw heat shrinkage amount calculating step is as follows.

Exp (natural constant e) = the time taken to shrink to 36.8% of the maximum maximum heat shrinkage (saturation value) of the x axis = x (∞) = maximum thermal expansion of the x- 2.718.

The heat shrinkage amount of the ball screw 12 measured through the correction mechanism 20 in the heat shrinkage amount measuring step by substituting the above equation is plotted as a curve as shown below.

<Graph of Heat Shrinkage Curve Over Time>

The following equation is used to calculate the ballscrew heat shrinkage amount at the position where the table is located on the x and y axes at the next arbitrary time.

Where L = table arbitrary position, and 500 = x-axis ball screw length.

The amount of heat shrinkage of the ball screw at the position where the table is located on the x and y axes can be calculated at any time by substituting the curved graph of the heat shrinkage amount by time into the above equation.

In the above equation, although written in the x-axis, the same applies to the y-axis.

The Exp of the above equation has a definition of a natural constant e used in the mathematical expression.

The step of storing in the control system of the next machining center is a step of storing in the control system of the machining center the thermal expansion amount and the thermal shrinkage amount of the ball screw at the position where the table is located on the x and y axes at the arbitrary time calculated above.

Next, the x and y axis transfer distances of the table 13 are corrected using the thermal expansion amount value and the heat shrinkage amount value stored in the control system.

It is preferable that the above-described thermal displacement correction method is applied to a program so that the user can check and input the calculated value in the parameter window.

Since the thermal displacement amount of the ball screw is measured in accordance with the operating environment of the actual machining center of the operator through the thermal displacement correction method of the machining center table as described above, more accurate measurement is possible than in the prior art, It is possible to correct the thermal displacement of the ball screw in response to the irregular operation and the operation stop of the machining center since the thermal expansion amount of the screw is measured as well as the time heat shrinkage amount according to the operation stop.

11: Spindle 11a: Tool
12: Ball Screw 13: Table
14: Tool length compensation device 20: Correction mechanism

Claims (3)

A spindle 11 for machining a workpiece while the tool 11a is mounted on the chuck and rotating and raising / lowering the workpiece; a table 13 for transferring workpieces to the upper surface by the ball screw 12 to move it back and forth; And a tool length correcting device (14) coupled to one side of the tool holder
(20) having a top edge inclined at 45 degrees to a tool touch area of the tool length correcting device (14) to which a tool (11a) provided on a main shaft is contacted;
The tool length correcting device 14 to which the correcting mechanism 20 is coupled while the machining center is processing the workpiece is configured such that the tool 11a of the chuck is contacted to a corner portion inclined by 45 degrees of the correcting mechanism 20 A thermal expansion amount measurement step of measuring a thermal expansion amount of the ball screw 12 due to thermal friction every time it is performed;
A thermal expansion amount time constant measurement step of measuring a time (thermal expansion amount time constant) at which the thermal expansion amount measured in the thermal expansion amount measurement step reaches a point at which the thermal expansion amount is 63.2% of the maximum thermal expansion amount (saturation value);
Calculating a thermal expansion amount of the ball screw at a point at which the table is located on the x and y axes at an arbitrary time by substituting the thermal expansion amount time constant measured in the thermal expansion amount time constant measuring step into a continuous curve graphing step;

The tool 11a of the chuck is brought into contact with the corner portion of the correction mechanism 20 inclined by 45 degrees at the designated time in a state where the machining center stops the operation of the table 13, A heat shrinkage amount measurement step of measuring a heat shrinkage amount of the ball screw (12)
Measuring a time of shrinkage quantity time constant measuring a time (heat shrinkage quantity time constant) in which a heat shrinkage amount measured in the heat shrinkage amount measuring step reaches 36.8% of a maximum heat shrinkage amount (saturation value);
Calculating a heat shrinkage amount of the ball screw at a position where the table is located on the x and y axes at an arbitrary time by substituting the time constants of the heat shrinkage time constant measured in the step of measuring the heat shrinkage time constant into a continuous curve graphing step;
Storing a ball screw thermal expansion amount and a heat shrinkage amount at a point where the table is located on the x, y axes at a predetermined time calculated in the above-described manner in a control system of a machining center;
Correcting the x- and y-axis transfer distances of the table (13) using the thermal expansion amount value and the heat shrinkage amount value stored in the control system;
Wherein the machining center ball screw comprises a plurality of balls.
The method according to claim 1,
The equation of the thermal expansion amount calculating step is as follows: x (∞) = maximum thermal expansion amount at the x-axis end, t = time, τxr = time required to reach 63.2% of the maximum thermal expansion amount in the x axis, Exp = natural constant, L = Axis position, 500 = x axis Ball screw length
the thermal expansion amount of the ball screw 12 measured through the correction mechanism 20 in the thermal expansion amount measurement step is substituted into a function of f (x) = x (?) * 1-Exp (-t /? xr) (T) = (L / 500) * f (x), when the curvilinear time-scale thermal expansion amount by time is substituted into a function of x (t) = And the amount of thermal expansion of the ball screw of the machining center ball screw is calculated.
The method according to claim 1,
The equation of the heat shrinkage amount calculation step is as follows: x (∞) = maximum thermal expansion amount at the x-axis end, t = time, τxr = time taken to reach 36.8% of the maximum heat shrinkage amount in the x axis, Exp = natural constant, L = Axis position, 500 = x axis Ball screw length
The heat shrinkage amount of the ball screw 12 measured through the correction mechanism 20 in the heat shrinkage amount measurement step is substituted into a function of f (x) = x (?) * (1-Exp (T) = (L / 500) * f (x), and the point at which the table is located on the x and y axes at any time is obtained by substituting the curvilinear time- And the heat-shrinkage amount of the ball screw of the machining center ball screw is calculated.

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