JPH06226626A - Machining center control method and control device - Google Patents

Abstract

PURPOSE:To automate grinding work and improve quality and productivity by detecting the quantity of each state such as the surface state of a grinding wheel by a grinding wheel monitoring device, and judging whether the grinding wheel is satisfactorily mounted to a main spindle by an automatic tool changing device and whether truing is necessary. CONSTITUTION:A grinding wheel monitoring device 1 is provided to monitor the quantities of plural states such as the surface state of the grinding face of a grinding wheel serving as a tool, the tool diameter and the tool length. In the control device 2, a judging part 2b judges whether the grinding wheel is mounted satisfactorily. In the case of a negative, a signal for the resetting of the grinding wheel is outputted to an automatic tool changing device 3. In the case of an affirmative, an unstable wear area removing part 2f makes a truing device 4 remove the unstable wear area of the grinding face of the grinding wheel by truing. A truing necessity judging part 2d further compares the detected data with the initial data stored in a storage part 2a. In the case of judging the necessity of truing, a computing part 2e computes the truing quantity on the basis of the detected data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method and a control device for a machining center capable of NC grinding, and more specifically, by performing dimensional control and precision control of a grinding wheel mounted on a spindle, The present invention relates to a machining center control method and control device capable of maintaining machining accuracy and finished surface roughness within a certain range under unmanned operation, and eventually realizing automation of grinding and improvement of quality and productivity.

[0002]

2. Description of the Related Art Conventionally, the problems to be solved by the invention
Regarding the control of the accuracy of the machined work piece, the operator measures the size of the machined work piece with a measuring instrument, not only in the manual general-purpose grinder but also in the NC-controlled general-purpose grinder. By correcting the depth of cut, etc.,
I have managed. Therefore, apart from a dedicated machine for mass-producing the same workpiece, a general-purpose grinder for small-to-medium-scale production cannot operate unattended even when NC control is performed.

On the other hand, the degree of wear of the grinding surface of the grinding wheel becomes a problem in obtaining the processing accuracy. Conventionally, a predetermined molding state can be surely taken into consideration in consideration of the average wear amount of the grinding wheel and the uneven wear of the surface. In order to obtain it, it was formed with a constant truing amount exceeding the required amount. Therefore, the grinding wheel is shortened. Therefore, the present invention provides a control method and a control device for a machining center capable of automating the grinding process and improving quality and productivity by using a grinding wheel measurement and a truing device together on a machining center capable of NC grinding. The purpose is to provide.

[0004]

In order to achieve the above object, a method of controlling a machining center according to a first aspect of the present invention is directed to a grinding wheel as a tool, the surface condition of a grinding surface, a tool diameter, a tool length, a rotational runout, and A method of controlling a machining center, comprising: a grindstone monitoring device for monitoring a plurality of state quantities including a distance from a machining center reference position to a predetermined part of a tool; and a truing device for forming a grinding surface, wherein an unused grindstone is the first spindle It has an initial setting process to be mounted on the, and an actual operating process to actually work, the initial setting process detects the rotational runout of the unused grinding wheel attached to the spindle by the whetstone monitoring device, the detection result However, the process of repeating the setting of the grinding wheel until the value becomes less than or equal to the preset threshold, and the simulated grinding using the set grinding wheel. Or removing the unstable wear region of the grinding surface by performing truing on the grinding wheel with a truing device, and the surface state of the grinding surface of the tool from which the unstable wear region has been removed, the tool diameter and Each initial value of the tool length is detected by a grindstone monitoring device, and the detection result is stored as initial data, and the tool in which each initial data is stored is stored in a tool magazine. The operating process detects the rotational runout of the tool attached to the spindle by the automatic tool changing device by the grindstone monitoring device, and the detection result is a step of repeating the setting of the tool until the value becomes equal to or less than a preset threshold value, The process of machining the workpiece under the machining conditions calculated based on the stored initial data using the set tool, and the periodic In addition, each state quantity of the grinding surface is detected by the grindstone monitoring device, the detection data and the initial data are compared to determine the necessity of truing, and the data of the tool diameter and the tool length are updated based on the detection data. When the process and truing are determined to be necessary, the truing amount to obtain the predetermined molding state is calculated based on the detection data, and the process of truing the tool with the truing device, the detection data and the initial data. And a step of judging the tool life and correcting the machining conditions based on the comparison with the above.

Further, the grinding wheel is of a type that does not require truing, and the truing for removing the unstable wear region during the initial setting process and the truing during the actual operation process are omitted. It may be a feature. Further, it may be characterized in that whether or not to include truing in the process is changed based on whether or not the grinding wheel is of a type that requires truing.

According to a fourth aspect of the present invention, there is provided a control device for a machining center, which includes a plurality of grinding wheels as tools, including a surface state of a grinding surface, a tool diameter, a tool length, a rotational runout, and a distance from a machining center reference position to a predetermined tool portion. A control device for a machining center including a grindstone monitoring device for monitoring the state quantity, and a truing device for molding a grinding surface, wherein the rotational runout of the grinding wheel detected by the grindstone monitoring device and a preset threshold value Based on the comparison with, determine whether the grinding wheel was installed properly,
When the detected value exceeds the threshold value, a grindstone mountability determination unit that outputs a signal for resetting the grinding wheel, a simulated grinding or truing device depending on the completion of setting of the unused grinding wheel The unstable wear area removal control unit that removes the unstable wear area of the grinding wheel by the truing by the tool, the initial data storage unit that stores the initial data of the tool previously detected by the grinding wheel monitoring device, the initial data stored in the initial data storage unit Based on the comparison between the data and the detection data detected by the whetstone monitoring device at a predetermined time, the truing necessity determination unit that determines the truing necessity of the grinding wheel, the truing necessity determination unit determines that truing is necessary. The minimum amount of truing to obtain the desired molding condition, based on the above detection data. Truing amount calculating section for stomach operation, based on a comparison between the initial data and the detected data,
It is characterized by including at least a grindstone life judging section for judging the grindstone life, and a machining condition correcting section for correcting the machining condition based on the comparison between the initial data and the detected data.

Further, it is preferable that the truing device has a truing grindstone capable of truing in at least two directions. Further, it is preferable that the truing device employs a traction drive in the diamond wheel rotating portion of the truer and is provided with a speed increasing mechanism for speeding up the rotation of the truer.

Further, the grindstone monitoring device includes a ceramic stylus contacting the grinding surface of the grinding wheel, a leaf spring for pressing the stylus toward the grinding surface, and a displacement gauge for measuring the displacement of the stylus. It is preferable that a plurality of measuring devices are built in.

[0009]

According to the control method of the present invention, the grindstone monitoring device can detect each state quantity of the grindstone and judge whether or not the mountability of the grindstone by the automatic tool changer is good or bad. Then, when the mountability is poor, the grinding wheel is set again so that a good mount state can be reliably and automatically obtained. As a result, the processing accuracy of the work can be ensured and the quality can be improved. Moreover, based on the comparison between the initial data of each state quantity of the grinding wheel and the detection data at a predetermined time, the necessity of truing, the judgment of whether or not the tool life has been reached, and the modification of the machining conditions are performed. . Then, when truing is necessary, the truing amount for obtaining a predetermined molding state is calculated, and truing is performed based on this. In this way, the wear condition of the grinding wheel, which affects the processing accuracy, is regularly monitored and necessary measures such as truing, tool replacement and modification of the processing conditions are performed. Productivity improvement can be achieved.

In the case of a grinding wheel of a type that does not require truing, such as an electrodeposition grinding wheel, a control method adapted to the type of the grinding wheel can be achieved by omitting the truing step. In this case, different types of grinding wheels can be dealt with by changing whether or not the control method includes truing based on whether or not the grinding wheel is of a type that requires truing.

Further, according to the control device of the above invention, the grindstone mountability determining unit determines whether or not the grindstone is properly mounted, and when the grindstone is defective, the grindstone is reset. A good wearing state can be obtained reliably and automatically. Then, the unstable wear area removal control unit automatically removes the unstable wear area of the grinding wheel by simulated grinding or by truing by a truing device in accordance with the completion of setting of the unused grinding wheel. Further, based on a comparison between the initial data stored in the initial data storage unit and the detection data detected by the grindstone monitoring device at a predetermined time, the truing necessity determination unit determines whether truing is required for the grinding wheel.
When truing is necessary, the truing calculator calculates the truing amount for obtaining a predetermined molding state. In this case, since the truing amount can be set to the necessary minimum, the life of the grindstone can be extended. on the other hand,
Based on the comparison of the initial data and the detected data, the life of the grindstone is determined by the grindstone life determining unit,
The processing conditions are corrected by the processing condition correction unit. The wear condition of the grinding wheel, which affects the processing accuracy, is regularly monitored and necessary measures such as truing, tool replacement and modification of the processing conditions are performed, so automation of grinding and improvement of quality and productivity Can be achieved.

When the truing device has a dresser capable of truing in at least two directions, it can handle a plurality of grinding surfaces. Further, when the above-mentioned truing device adopts a traction drive and is provided with a speed increasing mechanism for speeding up the rotation of the truer, the rotational inertia force of the main shaft is increased to suppress the rotational unevenness and vibration of the main shaft. can do.

When the grindstone monitoring device is equipped with a plurality of measuring devices including a ceramic measuring element, a leaf spring, and a displacement gauge for measuring the displacement of the measuring element, it is possible to monitor a plurality of grinding surfaces. It is suitable.

[0014]

Embodiments will be described in detail below with reference to the accompanying drawings showing embodiments. 1 and 2 are flowcharts showing a flow of a method of controlling a machining center according to an embodiment of the present invention, FIG. 3 is a block diagram of a control device, and FIG. 4 is a schematic configuration diagram of a grindstone monitoring device and a truing device. Is.

Referring to FIGS. 3 and 4, this control device 2
Is a plurality of state quantities including the surface condition of the grinding surfaces K1 and K2 of the grinding wheel K as a tool, the tool diameter, the tool length, the rotational runout, and the distance from the machining center reference position to the predetermined part of the tool (for example, the grinding surface K1). It is mounted on a machining center equipped with a grindstone monitoring device 1 for monitoring the grinding surface and a truing device 4 for molding the grinding surfaces K1, K2.

The control device 2 includes an initial data storage unit 2a, a grindstone mountability determination unit 2b, a grindstone life determination unit 2c, a truing necessity determination unit 2d, a truing amount calculation unit 2e, an unstable wear area removal control unit 2f and machining. The condition correction unit 2g is included. The grindstone mountability determination unit 2b, based on a comparison between the rotational shake of the grinding wheel K detected by the grindstone monitoring device 1 and a preset threshold value F, the grinding wheel K is determined.
If the detected value exceeds the threshold value F, a signal for resetting the grinding wheel is output to the automatic tool changer 3.

The unstable wear area removing section 2f simulates the grindstone mountability judging section 2b in accordance with the judgment that the grindstone K has been mounted satisfactorily (in accordance with the completion of setting of the unused grindstone). By grinding or truing by the truing device 4, the unstable wear regions of the grinding surfaces K1 and K2 of the grinding wheel K are removed. The initial data storage unit 2a stores initial data of the tool for each state quantity in the grinding wheel K from which the unstable wear region has been removed.

The truing necessity determining section 2d compares the initial data stored in the initial data storage section 2a with the detection data detected by the grindstone monitoring device 1 at a predetermined time and determines whether truing is necessary for the grinding wheel K. Judge whether or not. The truing amount calculation unit 2e calculates the truing amount for obtaining a predetermined molding state based on the detection data when the truing necessity determination unit 2d determines that truing is necessary.

The grindstone life determining unit 2c judges the life of the grindstone based on the comparison between the initial data and the detected data. The processing condition correction unit 2g corrects the processing condition based on the comparison between the initial data and the detected data. With reference to FIG. 4, the grinding wheel K is feed-controlled in the directions of the two axes P and Q and an axis (not shown) orthogonal to these axes. The truing device 4 includes a main shaft 30 rotatably supported by a main body of the truing device 4, a truer 40 attached to the tip of the main shaft 30 and integrally rotated, and a flexible rotating shaft of a motor as a driving side. A known planetary roller type speed increasing mechanism 6 as a traction drive, which is connected via a shaft 5 and is also connected to the main shaft 30;
The grinding wheel monitoring device 1 includes a plurality of measuring devices 7 and 8 for detecting changes in the shapes of the grinding surfaces K1 and K2 of the grinding wheel K (shape collapse, wear amount, etc.).

The grinding wheel K has a cylindrical shape whose rotation axis Ka is parallel to the axis P. The grinding surface K1 is composed of the peripheral surface of the cylinder and extends along the direction of the axis P. The grinding surface K2 is formed by the flat end surface of the cylinder and is parallel to the axis Q. The grinding wheel K is attached to the main shaft of the machining center, is controlled to be fed in the directions of the axes P and Q, and comes into contact with the measuring elements 71 and 81 of the measuring devices 7 and 8 and the truer 40 which will be described later. There is.

The main shaft 30 has four axes in the directions of the two axes P and Q.
The truer 40 is arranged at an angle of 5 degrees, and the truer 40 has a truer surface 40a that is a conical surface. The generatrix of the conical surface is inclined so as to form an angle of 45 degrees with the extension line of the main shaft 30. As a result, the truing surface 40a is parallel to the above-mentioned two axes P and Q, and the grinding surfaces K1 and K of the grinding wheel K at the time of molding.
The measuring device 7 that has the first and second lines of action 41 and 42 as a dress portion that is slidably contacted with 2 is a flat contact surface that is made of ceramics such as silicon nitride and that contacts the grinding surface K1. Probe 71 having 71a and probe 7
1 and a leaf spring 72 that supports the back surface 71b of the leaf spring 1.
The second displacement sensor 73 is provided close to the second rear surface 72a and includes an eddy current gap sensor that changes an output signal according to the size of the gap G between the rear surface 72a and the rear surface 72a. When the grinding wheel K is moved in the direction along the axis P while the grinding surface K1 of the rotating grinding wheel K is in contact with the contact surface 71a, the radius reduction amount (wear amount) over the entire circumference becomes the entire length in the axial direction. Detected over. In the free state of the leaf spring 72, the contact surface 71a of the contact body 71 is located on the same plane as the first action line 41 of the truing surface 40a of the truer 40.

In the same manner, the measuring device 8 includes a tracing stylus 81,
A leaf spring 82 and a displacement meter 83 are provided. When the grinding wheel K is moved in the direction along the axis Q with the grinding surface K2 of the rotating grinding wheel K in contact with the contact surface 81a of the contact body 81, the amount of wear over the entire grinding surface K2 is detected. . The contact surface 81a of the contact body 81 in the free state of the leaf spring 82
Are located on the same plane as the second line of action 42 of the truing surface 40a of the truer 40.

Next, the operation of the control device will be described with reference to the flow charts of FIGS. Step S
1 to step S14 show the flow of the initial setting process. The grinding wheel K starts from an unused state (step S
1) After attaching the grinding wheel K to the tool holder (step S2), attach it to the spindle (step S)
3). Here, the rotational runout of the grinding stone K is measured by the grindstone monitoring device 1 (step S4), and this detected value is compared with a predetermined threshold value F (step S5).
When the shake detection value is larger than the threshold value F, the tool is removed (step S6), the process returns to step S3, and the tool is reattached to the spindle. Then, this is repeated until the detected value becomes equal to or less than the threshold value F, and when the detected value becomes equal to or less than the threshold value F, the process proceeds to the next step S7.

In step S7, the unstable wear area removing portion 2f performs truing with a predetermined constant truing amount or simulated grinding (which is to be performed is preset) (step S7). , Remove the unstable wear area of the grinding surface. Then, the rotational shake is measured by the grindstone monitoring device 1 (step S9),
If the shake exceeds the threshold value F, the process returns to step S7 and steps S7 to S10 are repeated. Then, when the detected value of the shake becomes equal to or less than the threshold value F, the process proceeds to step S11.

In step S11, the surface condition of the grinding wheel K is measured by the wheel monitoring device 1. On the other hand, the surface position of the work is measured (step S12),
These data are stored as initial data and the initial value of the tool radius is calculated (step S13). As a result, the initial setting process is completed and the tool is stored in the tool magazine (step S14).

Steps S15 to S26 show the flow of the actual operation process. When the tool is changed by the automatic tool changer 3 which has received the tool change command (step S
15) The rotational deviation of the grinding surface is measured by the grindstone monitoring device 1 (step S16), and it is determined whether the detected value exceeds the threshold value F (step S1).
7). If the detected value exceeds the threshold value F in step S17, the process returns to step S15 and the reattachment is performed. On the other hand, when the shake is equal to or less than the threshold value F, the process proceeds to the next step S18, and the work is processed.

Next, in step S19, the surface condition of the grinding wheel is periodically measured by the wheel monitoring device 1 and the reduction amount (wear amount) of the tool radius is calculated (step S20). As a result, in step S21, processing conditions such as tool radius correction are corrected. next,
In step S22, the wear amount (or surface condition)
, It is determined whether or not a preset threshold M1 for determining the necessity of truing is exceeded, and if not, grinding is performed (step S2).
3). In step S22, the amount of wear is the threshold value M1.
If it exceeds, the process proceeds to step S24, and it is determined whether or not the wear amount exceeds a preset threshold M2 for determining the life of the grindstone. If the amount of wear does not exceed the threshold value M2, truing is performed (step S25), and if it exceeds the threshold value M2, it is determined that the grindstone has reached the end of its life (step S26). .

According to this embodiment, each state quantity such as the surface state of the grinding wheel K is detected by the grindstone monitoring apparatus 1, and thereby the mountability of the grinding wheel K on the spindle by the automatic tool changer 3 is detected. Whether or not truing is necessary is determined, and based on the result, reattachment of the grinding wheel K or truing is performed. As described above, by using the grinding wheel measurement and the truing device together on the NC-grindable machining center, automation of the grinding process and improvement in quality and productivity can be achieved.

Moreover, since the truing amount is determined according to the actual measurement data of the grinding wheel K, the grinding wheel K is not unnecessarily scraped and the grinding wheel K is not cut.
The life of can be extended. Further, since the main shaft 30 can be rotated at high speed by the planetary roller type speed increasing mechanism 6, it is possible to increase the rotational inertial force of the main shaft 30 and suppress uneven rotation and vibration of the rotary main shaft 30.

The truer surface 40a of the truer 40 is
Since the lines of action 41 and 42 are provided as dressing portions parallel to the two axes P and Q, respectively, two surfaces of the grinding wheel can be dressed by a single truing wheel. In the above embodiment, a control method for a grinding wheel of a type that requires truing such as a vitrified bond grindstone is shown, but for a type of grinding wheel that does not require truing such as an electrodeposition grindstone, a step is performed. A control method which omits the truing of S7 and step S22 is adopted. In this case, if a program that automatically changes the control method according to the type of grindstone (whether it is an electroplated grindstone or a vitrified bond grindstone can be judged based on the presence or absence of a binder) is used for automation. Is preferred.

When judging the life of the grindstone, the number of repetitions of steps S15 to S17 in the flowchart of FIG. 2, that is, the number of times of tool reattachment by ATC is counted. It is also possible to re-attach to the holder, measure the shake, and if the shake exceeds the threshold value F, determine that it is the life of the grindstone.

Further, the present invention is not limited to the above embodiment, and for example, the displacement gauges 73, 73
As the gap sensor forming 83, another known one such as an optical type can be used. In addition, various design changes can be made without changing the gist of the present invention.

[0033]

As described above, according to the method and apparatus of the present invention, each state quantity such as the surface state of the grinding wheel is detected by the grindstone monitoring apparatus, and the automatic tool changer allows the grinding wheel to be attached to the spindle. The wearability of the tool, the necessity of truing, etc. are determined, and based on this result, the reattachment of the grinding wheel, truing, etc. are performed. Thus N
By using a grinding wheel and a truing device together on a machining center that can grind C, it is possible to automate the grinding process and improve quality and productivity.

[Brief description of drawings]

FIG. 1 is a diagram showing a flowchart of an initial setting process of a control method for a machining center according to an embodiment of the present invention.

FIG. 2 is a diagram showing a flowchart of the actual operation process.

FIG. 3 is a block diagram showing a schematic configuration of a control device.

FIG. 4 is a schematic configuration diagram of a truing device.

[Explanation of symbols]

 1 grindstone monitoring device 2 control device 2a initial data storage unit 2b grindstone mountability determination unit 2c grindstone life determination unit 2d truing necessity determination unit 2e truing amount calculation unit 2f unstable wear area removal control unit 2g machining condition correction unit 3 automatic tool Exchange device 4 Truing device 40 Truer 6 Planetary roller type speed increasing mechanism (speed increasing mechanism) 7,8 Measuring device 71,81 Measuring element 72,82 Leaf spring 73,83 Displacement meter K Grinding wheel K1, K2 Grinding surface P, Q axis

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Akira Chikamori 3-5-8 Minamisenba, Chuo-ku, Osaka Koyo Seiko Co., Ltd. (72) Inventor Eiichi Katayama 2-144, Amamihigashi, Matsubara-shi, Osaka

Claims (7)

[Claims] 1. A grindstone monitoring device for monitoring a plurality of state quantities of a grinding wheel as a tool, including the surface condition of a grinding surface, a tool diameter, a tool length, a rotational runout, and a distance from a machining center reference position to a predetermined part of a tool. , A method of controlling a machining center having a truing device for forming a grinding surface, which has an initial setting step in which an unused grinding wheel is first mounted on a spindle, and an actual operation step for actually performing a work. The setting step detects the rotational runout of the unused grinding wheel attached to the main spindle by the grinding wheel monitoring device, and the detection result is a step of repeating the setting of the grinding wheel until the preset threshold value or less, Perform simulated grinding using a grinding wheel that has been set,
Alternatively, the step of removing the unstable wear region of the grinding surface by performing truing on the grinding wheel with a truing device, and the surface condition of the grinding surface, tool diameter and tool length of the tool from which the unstable wear region has been removed Each initial value is detected by the whetstone monitoring device, and the detection result is stored as initial data, and the tool storing each initial data is stored in the tool magazine. The process of detecting the rotational runout of the tool mounted on the spindle by the automatic tool changer by the grindstone monitoring device and repeating the tool setting until the detection result becomes less than the preset threshold, and the setting is completed. Machining the workpiece under the machining conditions calculated based on the stored initial data using the tool Detecting each state quantity of the grinding surface by the stone monitoring device, comparing the detection data with the initial data to determine the necessity of truing, and updating the tool diameter and tool length data based on the detected data. When it is determined that truing is necessary, the truing amount for obtaining a predetermined molding state is calculated based on the detected data, and the truing device performs the truing on the tool. A method of controlling a machining center, comprising the steps of determining the tool life and correcting the processing conditions based on the comparison. 2. The grinding wheel is of a type that does not require truing, and the truing for removing the unstable wear region during the initial setting process and the truing during the actual operation process are omitted. The method of controlling a machining center according to claim 1, wherein 3. The method of controlling a machining center according to claim 1, wherein whether or not to include truing in the process is changed based on whether or not the grinding wheel is of a type that requires truing. 4. A grindstone monitoring device for monitoring a plurality of state quantities of a grinding grindstone as a tool, including a surface condition of a grinding surface, a tool diameter, a tool length, a rotational runout, and a distance from a machining center reference position to a predetermined part of a tool. , A control device of a machining center having a truing device for shaping a grinding surface, which is based on a comparison between a rotational deviation of the grinding wheel detected by a grinding wheel monitoring device and a preset threshold value. If the detected value exceeds the threshold value, the grindstone mountability determination unit that outputs a signal to reset the grindstone, Depending on the completion of setting, the unstable wear area removal control unit that removes the unstable wear area of the grinding wheel by simulated grinding or truing with a truing device Based on a comparison between the initial data storage unit that stores the initial data of the tool previously detected by the monitoring device, the initial data stored in the initial data storage unit, and the detection data detected by the grindstone monitoring device at a predetermined time, When the truing necessity determination unit determines whether truing is necessary for the grindstone, and the truing necessity determination unit determines that truing is necessary, the truing amount for obtaining a predetermined molding state is calculated based on the above detection data. A truing amount calculation unit, a grindstone life determining unit that determines the life of the grindstone based on the comparison between the initial data and the detected data, and a machining that corrects the processing conditions based on the comparison between the initial data and the detected data. Control of a machining center characterized by including at least a condition correction section Location. 5. The machining center control device according to claim 4, wherein the truing device has a truing grindstone capable of truing in at least two directions. 6. The truing device employs a traction drive for a diamond wheel rotating portion of the truer and is provided with a speed increasing mechanism for speeding up the rotation of the truer. The control device of the described machining center. 7. The grindstone monitoring device includes a ceramic measuring element that contacts the grinding surface of the grinding wheel, a leaf spring that presses the measuring element toward the grinding surface, and a displacement gauge that measures the displacement of the measuring element. The control device for a machining center according to claim 4, wherein a plurality of measuring devices are incorporated.