JP4772991B2 - Machine tool spindle equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a spindle device of a machine tool, and more particularly to a technique for detecting a tool holding force with which a spindle holds a tool.
[0002]
[Prior art]
In a machine tool, as a method of fixing a tool to a main shaft, a tool bar is attached to a tool holder using a tool holder gripping tool provided at the tip of the draw bar by arranging a draw bar in a through hole opened in the center of the main shaft. A method is known in which the draw bar is pulled into the rear part of the main shaft while grasping the end, and the tool holder is tightly fixed to the main shaft by the pulling force. As a pull-in method at this time, a method of pulling the draw bar into the rear part using the force of the compression spring in order to obtain a tool holding force is widely adopted.
[0003]
An example of a spindle device of a conventional machine tool employing this method is shown in FIG. FIG. 2 is a longitudinal sectional view of the spindle device. Rolling bearings 21 a to 21 e are provided at four lower tip portions and one upper rear portion around the spindle 20, and are rotatably supported in a fixed cylindrical fixed housing 22. The fixed housing 22 is fixed to a spindle head 23, and the spindle head 23 is fixed to a machine body such as a spindle head. The front rolling bearing is, for example, a deep groove ball bearing, an angular ball bearing, or a tapered roller bearing that can receive a radial load and a thrust load in at least one direction, and the rear bearing is a roller bearing or a deep groove that can receive a radial load. Ball bearings or the like are used.
[0004]
A built-in type electric motor 25 is provided as a driving device for rotating the main shaft 20 between the front side rolling bearings 21 a to 21 d and the rear side rolling bearing 21 e, and the electric motor 25 is provided on the outer periphery of the main shaft 20. The rotor 26 and a stator 27 provided on the inner periphery of the spindle head 23 around the rotor 26 are configured.
A tool holder 28 for fixing a processing tool is attached to the main shaft 20, and the tool holder 28 is fixed to the main shaft 20 by a draw bar 31 via a holder gripping tool 29. Further, in order to pull the tool holder 28 into the main shaft 20 and hold it fixedly, a ring 32a fixed to an end face at an arbitrary position inside the main shaft, and a ring 32b fixed to the axial outer diameter portion of the draw bar 31 via a nut, A compression spring 33 is supported between the two and a predetermined compression force is applied to the compression spring 33.
[0005]
In the spindle apparatus as described above, the tool holder 28 for fixing the machining tool is inserted into the tip of the spindle and held by the holder gripping tool 29, and the holder is grasped by the force of the compression spring 33 pushing the draw bar 31 in the longitudinal direction of the spindle. It is fixed in close contact with the main shaft 20 via a tool 29.
[0006]
[Problems to be solved by the invention]
In the case of such a configuration, the contact force of the tool holder 28 is determined by the extension force of the compression spring 33. Therefore, in the actual main shaft, the tool holder 28 is held with a necessary holding force when pulled into the main shaft 20. It is desirable to adjust the compression amount of the compression spring 33 in advance, and if the draw bar 31 is always pulled to the same position when the tool holder 28 is fixed, the generated holding force is always constant, but the tool holder If the longitudinal dimension of the rear part 28 is long or short, the draw bar 31 is naturally retracted and the holding force is also changed. Further, when the compression spring 33 is bent after repeated use, the holding force becomes smaller than the initial value even if the retracted position does not change.
[0007]
Regarding such problems, if the difference in holding force due to dimensional variation of the tool holder is examined, the holding force is proportional to the amount of compression of the compression spring, so the longitudinal position of the draw bar when the tool holder is fixed is accurately determined. It is possible to estimate how much holding force has been detected by detecting the current.
However, since the spring for generating the holding force is generally strong and the holding force changes greatly even with a slight change in the compression amount, it is estimated how much the tool holding force is generated by detecting the longitudinal position of the draw bar. This is because the measuring device for accurately detecting the longitudinal position of the draw bar is expensive and the decrease in holding force due to the spring sag etc. cannot be detected by this method. Not done.
For these reasons, machining is performed without knowing how much holding force is actually generated when the tool holder is fixed.
[0008]
In view of the above problems, an object of the present invention is to enable a holding force to be detected when a tool holder for holding a processing tool is fixed to a spindle in a spindle device of a machine tool.
[0009]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the invention of claim 1 is directed to a spindle device of a machine tool having a draw bar for attaching and operating a tool holder to a spindle in a spindle hollow cylindrical portion. Attach and make it possible to measure the amount of elastic deformation of the draw bar by changing the resistance of the gauge sensitive part, and connect the wire that detects the resistance change of the gauge sensitive part to the contact point provided at the rear of the draw bar, while A contact that can contact the drawbar side contact is provided at the drawbar contact portion of the piston to be moved, and when the piston presses the drawbar, both contacts come into contact with each other, and the resistance change amount of the gauge sensing portion is measured via the piston. possible and the fact characterized by, this configuration can measure the tool holding force regardless of the longitudinal position of the draw bar, the tool with less holding force occurs bug Can be reliably detected even when it is constant, it is still the tool weak holding force can be eliminated from rotating.
[0010]
In addition, since the tool holding force can be measured via a piston that does not rotate, there is no need to energize the gauge sensor via a rotating contact such as a slip ring via the rotating part. The change in resistance can be detected with high accuracy without being affected by the change in contact resistance. As a result, the measurement can be performed with a simple configuration, and the strain amount measuring device and the tool holding force determination device of the gauge sensor used at this time can be configured at a relatively low cost, so that the entire measurement system can be configured at a low cost.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of the invention will be described in detail with reference to the drawings. FIG. 1 shows a longitudinal sectional view of a main shaft, which is a main part of the main shaft device according to the present invention. In FIG. 1, a main shaft 1 has a through hole 2 (hollow cylindrical portion) formed in a central shaft portion, and a draw bar 3 is inserted and arranged. A holder grip 4 is provided at the tip of the draw bar 3. A piston unit 6 includes a piston 7 that moves the draw bar 3 back and forth. The piston 7 is connected to a hydraulic device (not shown), and is moved up and down by hydraulic operation from the hydraulic device. The clamping operation of the tool holder 5 by the holder gripper 4 is operated by pressing.
An electric motor for rotating the main shaft 1 as shown in FIG. 2 is arranged around the main shaft 1, and the main shaft 1 has rolling bearings at several positions on the lower front end and one upper rear as in FIG. 2. It is provided and rotatably supported in a fixed housing, the housing is fixed to the spindle head, and the spindle head is fixed to a machine body such as a spindle head.
[0012]
A gauge sensitive portion 9 that is a strain detecting element is attached to the narrow diameter portion near the tip of the draw bar 3. The gauge sensing part 9 is selected and stuck so that the resistance value changes according to the elastic deformation amount of the sticking part. The gauge sensor 9 can detect the amount of elastic deformation when a tensile stress is applied in the drawbar longitudinal direction.
[0013]
An electric wire for energizing the gauge sensing unit 9 passes through the inside of the draw bar 3 and is connected to a contact 10 provided at an arbitrary position on the rear end face of the draw bar 3. A corresponding contact 11 is provided on the front end surface of the piston 7 of the piston unit 6 provided above the main shaft at the rear of the draw bar 3 so that the contacts 10 and 11 come into contact with each other when the piston 7 pushes the draw bar 3. It has become. The contact point 11 on the piston 7 side is connected to a separately installed strain amount measuring device 13, and the strain amount measuring device further receives a change in the characteristics of the gauge sensor 9 to determine the tool holding state determining means. 14.
In addition, since the internal electrical resistance value changes due to the expansion and contraction of the gauge sensitive part, if the relationship between the electrical resistance change and the tool lifting force is examined in advance, electricity is passed through the element, the current at that time, The lifting force of the tool can be indirectly known from the correlation between voltage and resistance.
[0014]
The operation when exchanging the tool in the above configuration will be described. First, after stopping the rotation of the main shaft 1, oil is injected from a hydraulic device or the like to advance the piston 7, and the draw bar 3 is pushed down to unclamp the tool holder 5. State. At this time, when the piston 7 comes into contact with the draw bar 3, the contact points 10 and 11 come into contact with each other, and the tensile stress applied to the draw bar 3 can be measured by energizing the gauge sensing unit from the strain amount measuring device 13.
[0015]
Then, after the tool holder 5 is grasped, when the piston 7 starts to rise to hold it, a tensile stress is gradually applied to the draw bar 3. Since the draw bar 3 grips the tool holder and retracts to the position where it stops, the position where the draw bar 3 stops becomes the position where the maximum tensile stress is applied to the draw bar 3, and the tool holder holding force, that is, the tool holding force is also determined by the stress. Therefore, the draw bar 3 stops moving backward, and the tensile stress just before leaving the piston 7 is measured. Based on the measured value, the tool holding state determining means 14 determines whether a predetermined tool holding force is secured.
[0016]
In this way, the tool holding force can be measured regardless of the longitudinal position of the draw bar by detecting the amount of elastic deformation that is the tensile stress of the draw bar before and after the tool is mounted by providing the gauge sensing part on the draw bar. . As a result, even when a failure occurs and the tool is fixed with a small holding force, it can be detected reliably, and the tool can be prevented from rotating with a weak holding force.
Furthermore, when the tensile stress falls below the allowable range of the tool holding force, a command is issued to the machine tool control device such as issuing a warning, disabling the spindle, or limiting the spindle speed. By doing so, it is possible to easily avoid the problem that the tool comes off during rotation.
[0017]
In addition, since the tool holding force can be measured via a piston that does not rotate, it can be measured with a simple configuration. The gauge sensing device strain amount measuring device and the tool holding force determining device used at this time are also known electronic devices. Since it can be easily configured by combining circuits and machine accuracy is not required, it can be configured at a lower cost than a measuring device that accurately detects the longitudinal position of the draw bar, and the entire system can be configured at a lower cost.
[0018]
In the above embodiment, the gauge sensing part is provided in the vicinity of the front end of the draw bar, but it may not be the front end, and the draw bar is elastically deformed from the compression spring locking part of the rear part to the front end. Just stick. However, when there is a thin part compared to other parts as in the above-described embodiment, the elastic deformation amount of the part is larger than that of the large-diameter portion, so it is preferable to provide the part.
[0019]
【The invention's effect】
As described above in detail, according to the present invention, the tool holding force can be measured regardless of the longitudinal position of the draw bar. As a result, even when a failure occurs and the tool is fixed with a small holding force, it can be detected reliably, and the tool can be prevented from rotating with a weak holding force.
[0020]
In addition, since the tool holding force can be measured via a piston that does not rotate, it can be measured with a simple configuration. In addition, since the strain amount measuring device and the tool holding force determining device of the gauge sensitive part used at this time can be configured relatively inexpensively, the entire measuring system can also be configured inexpensively.
[Brief description of the drawings]
FIG. 1 shows an example of an embodiment of a spindle device for a machine tool according to the present invention, and is a longitudinal sectional explanatory view of a spindle portion which is a main part thereof.
FIG. 2 is a longitudinal sectional view of a conventional spindle device.
[Explanation of symbols]
1 .... Spindle, 2 .... Through hole, 3 .... Drawbar, 4 .... Holder gripper, 5 .... Tool holder, 6 .... Piston unit, 7 .... Piston, 9 .... Gauge sensing part, 10, 11. Contact point.

Claims (1)

In the spindle device of a machine tool having a draw bar for operating the tool holder on the spindle in the spindle hollow cylindrical portion,
Attaching a gauge sensitive part at an arbitrary position of the draw bar, and allowing the elastic deformation of the draw bar to be measured by a resistance change of the gauge sensitive part ,
The wire that detects the resistance change of the gauge sensor is connected to the contact provided at the rear part of the draw bar, while the draw bar contact part of the piston that moves the draw bar back and forth is provided with a contact that can contact the draw bar side contact. A spindle device for a machine tool, characterized in that both contact points are brought into contact with each other when the pressure is pressed, and the resistance change amount of the gauge sensing part can be measured via a piston .

Images