JPS6254623B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates in particular to a tool holding spindle arrangement for a grinding machine.

In grinding machines, the shaft of the tool-holding spindle is mounted in a radial bearing by means of rollers. In this type of device, the circumferential speed of the spindle shaft is limited by the maximum permissible value of the rollers. Therefore, in order to drive the spindle at as high a rotational speed as possible, the diameter of the shaft of the spindle and therefore its inertia must be limited. This limitation results in a reduction in the stiffness of the spindle, particularly at the free end of the spindle that holds the tool. This lack of stiffness is manifested in particular by a displacement of the axis of rotation of the tool when the tool is in operation, and thus results in considerable defects in machining accuracy.
Moreover, since the rollers are subject to frictional wear and this wear becomes increasingly rapid as the rotational speed of the spindle increases, the unnecessary amplitude of the radial movement of the tool will tend to increase over time. Attempts have been made to circumvent the above-mentioned drawbacks by limiting the mechanical friction of the spindle shaft on its support bearing by using hydraulic bearings as a known solution, in which the spindle shaft is moved with a viscous fluid. Some structures are supported in filled, sealed bearings, which reduce friction and maintain spindle axis stiffness at relatively low rotational speeds, but It is not possible to provide the rotating spindle with the desired stiffness in order to avoid radial displacements and obtain extremely high machining precision. Furthermore, it is true that at high rotational speeds the friction becomes significant.

The object of the invention is to provide a support device for holding a tool which avoids the above-mentioned drawbacks of known devices.

Another object of the present invention is to provide a support device for holding a tool that makes it possible to precisely control the displacement of the tool with a controlled swing width.

The tool-holding spindle according to the invention comprises: (a) a jacket 13; (b) a shaft with a large diameter; and (c) a tool-holding device with a smaller diameter than said shaft achieved at the front free end of said shaft. (d) in the end region of said shaft, two electromagnetic motors each comprising an annular stator wound with an excitation stator coil and an annular rotor mounted on said shaft surrounded by said annular stator; a radial bearing; (e) an inductor fixed within the jacket at a location substantially equidistant from each electromagnetic radial bearing and surrounding the shaft, the inductor of the shaft; (f) an electric motor for driving the shaft at high speed with an armature disposed on an outer peripheral portion corresponding to the shaft; (f) for supplying a signal indicating the radial position of the shaft in the vicinity of the two electromagnetic radial bearings; At least one of an electromagnetic type comprising a stator made of two pairs of ferromagnetic materials arranged in two different radial directions, and a ring made of a cylindrical conductive material provided on the shaft. (o) a magnetic field consisting of a ferromagnetic material having a disc-shaped rotor mounted on the shaft and coils arranged axially apart on each side of the circumferential edge of the rotor; (h) at least one electromagnetic thrust bearing comprising a yoke; (h) a disc-shaped rotor comprising a disc-shaped conductor attached to the shaft, and a front end of the outer sheath, at the front part of the shaft; at least one electromagnetic thrust position sensor for providing a signal indicative of the axial displacement of the forward part of the spindle, comprising: a coil carried in an annular ring mounted on the outside of a covering annular lid; In response to signals from a radial position detector, a thrust position detector, and a second electromagnetic thrust position detector provided at the rear end of the shaft for detecting axial displacement of the rear end of the shaft, each of the electromagnetic an electric control circuit provided between each of the detectors and the coil of each of the bearings for controlling the excitation current of the radial bearing and the electromagnetic thrust bearing so that the shaft always takes the reference position; j) reference position change signals respectively connected between the detector and the control circuit for modifying at least one of the signals from the detector to change the reference position of the axis depending on the machining purpose; and a detection signal changing circuit comprising a circuit for outputting and adding to the algebraic sum of the signals from the detector, and further comprising a disc-shaped rotor of an electromagnetic thrust bearing disposed at the rear of the shaft. Each is characterized by

The first advantage of the invention thus represented is obtained by the fact that the shaft of the spindle is rotated without undergoing any mechanical friction, this shaft being supported on an electromagnetic bearing and mounted on an armature. is driven by a directly mounted electric motor. Furthermore, since the electromagnetic support system does not impose any restrictions on the spindle shaft diameter, the spindle shaft exhibits high inertia and considerable stiffness, which makes it possible to avoid vibrations at high speeds. Moreover, the control of each radial bearing by the detector cooperates with the stiffness of the shaft to reduce the radial displacement of the axis of rotation of the spindle and achieve high machining accuracy. Furthermore, selective modification of the signal generated by the at least one position sensor allows precise control of the position of the tool and its displacement during the machining operation, thereby allowing the radial and/or axial movement of the spindle. It is possible to perform special operations such as controlling directional displacement and correcting conicity.

The device includes two electromagnetic radial bearings, each controlled by an electromagnetic radial position sensor and located in close proximity to the end section of the spindle shaft, the armature of the motor being substantially disposed from the two electromagnetic radial bearings. mounted on the spindle axis equidistant from the Therefore, the spindle axes are separated from each other by two
radially aligned in one place, any wobbling or precession of the axis of rotation is quickly eliminated.

The electromagnetic thrust bearing is controlled by an electrical control circuit operated by signals received from the electromagnetic thrust position sensor to maintain the spindle against axial displacement.

The electromagnetic radial position sensor may be of the type consisting of a tubular electrically conductive rotor mounted on the shaft of a spindle and a stator surrounding the rotor.

The present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows a tool-holding spindle 10 of a grinding machine, the shaft 11 of which is housed in a cylindrical jacket 13 and whose distal end carries a mandrel 14 on which a grinding wheel 15 is attached.

The outer cover 13 is provided with an annular abutment shoulder 13a on its front inner surface located on the side of the grinding wheel 15, and a ring 17 screwed onto the inner surface of the outer cover 13 allows the electronic radial bearing 16 to Annular stator 16
The ferromagnetic part a comes into contact with it. Annular stator 16
a surrounds the annular rotor 16b made of ferromagnetic material of the electromagnetic radial bearing 16, and
b is fixed to the shaft 11. As can be further seen in FIG. 2, the annular stator 16a consists of one pole piece 16c including an outer annular portion and a branch portion projecting radially inward and each wound by a coil 16e, with adjacent coils The winding directions are opposite.

The front side of the jacket 13 is closed with an annular lid 18 which is fixed to the jacket 13 with screws 19. The lid 18 acts as a front auxiliary bearing for the shaft 11 by the roller bearing 20, providing a clearance between the inner surface of the roller bearing 20 and the outer surface of the shaft 11. The roller bearing 20 is prevented from moving in the axial direction by abutting against the inner shoulder of the lid 18 using an annular ring 21 coaxially fixed to the lid 18 by a screw 22.

The jacket 13 has at its rear an inner abutment shoulder 13b against which the ferromagnetic part of the annular stator 23a of the second electrode radial bearing 23 rests. The structure of the electromagnetic radial bearing 23 is similar to that of the radial bearing 16, and includes an annular rotor 23b made of a ferromagnetic material attached to the shaft 11. Similar to the annular stator 16a of the electromagnetic radial bearing 16, the annular stator 23a of the electromagnetic radial bearing 23 has a coil 23e.
have.

The rear part of the jacket 13 is closed by a lid 24 fixed to the jacket 13 with screws 25. Lid 24
The roller bearing 26 acts as a rear auxiliary bearing for the shaft 11, and a gap is provided between the inner surface of the roller bearing 26 and the outer surface of the shaft 11. The roller bearing 26 is fixed in contact with the inner shoulder of the lid 24 using a ring 27 that is screwed into the lid 24.

At the rear of the shaft 11 and at its free end, there is a disk-shaped rotor 28 made of a ferromagnetic material with an electromagnetic thrust bearing 28.
b is installed. The disk-shaped rotor 28b is interposed between a ring 29 that contacts the shoulder of the shaft 11 and a ring 30 that is fixed with a nut 31, and is prevented from moving in the axial direction. Rings 29 and 30 are constructed of an insulative plastic material, with ring 30 having a radial surface 30a which is normally spaced from roller bearing 26 and which is connected to electromagnetic thrust bearing 28.
When the roller bearing 26 is not in an operating state, it is separated from the rear auxiliary roller bearing 26 and is in an idling state. The stator 28a of the thrust bearing 28 includes two annular ferromagnetic field yokes 28c and 28d having a coil 28e. Field yokes 28c and 28d are respectively disposed on either side of disk-shaped rotor 28b and are each slightly axially spaced from the periphery of the radial surface of the rotor. The field yoke 28c is housed in a groove provided in the lid 24, and the field yoke 28d is connected to the side surface of the ferromagnetic portion of the stator 23a of the electromagnetic radial bearing 23 with an insulating ring 32 interposed on one side. , and the other side is held in the axial direction by an insulating ring 34 and a ring 33 screwed into the jacket 13.

Stator 1 of electromagnetic radial bearings 16 and 23
A tube body 35 is attached to the intermediate portion of the jacket between 6a and 23a. Electromagnetic radial position detector 36 combined with electromagnetic radial bearing 16
A stator 36a made of a ferromagnetic material, an inductor 37a of an electric motor 37, and an electromagnetic radial bearing 23.
The stator 38a, also made of ferromagnetic material, of the electromagnetic radial position detector combined with the tube body 3
5 in the above order from front to rear. These three elements are tube body 3
5 and a nut 39 screwed into the tube body 35.

An electromagnetic radial position detector 3 is located at the intermediate portion of the shaft 11 between the annular rotors 16b and 23b made of ferromagnetic material of the electromagnetic radial bearings 16 and 23.
A ring 36b made of conductors of No. 6 to form a cylindrical rotor, an armature 37b of the electric motor 37, and a ring 38b made of conductors of the electromagnetic radial position detector 38 to form a cylindrical rotor are attached in sequence. There is. The device consisting of annular rotors 16b and 23b, rings 36b and 38b and motor armature 37b is held axially by two nuts 40 and 41 screwed onto shaft 11.

An electromagnetic thrust position detector 4 is installed in the front part of the shaft 11.
A disk-shaped rotor 42b made of two conductive materials is attached, and its coil 42a is housed in an annular groove of an annular ring 21 attached to the outside of the annular lid 18. The disc-shaped rotor 42b is connected to the shoulder of the shaft 11 and the shaft 1.
It is held in the axial direction with a nut 42 screwed on the shaft 1.

At the rear end of the shaft 11, there is a coil 53a housed in the lid 24, and a flat conductive member 53b facing the coil 53a and housed in a recess formed in the rear radial end surface of the shaft 11. Two electromagnetic thrust position detectors 53 are arranged.

The electromagnetic support effect during rotation of the spindle 10 is carried out by the electromagnetic radial bearings 16, 23 and the electromagnetic thrust bearing 28. Electromagnetic radial position sensors 36 and 38 have the same construction as shown in detail in FIG. Stator 36a
is the magnetic pole branch portion 36 around which the coil 36e is wound.
It is equipped with d. Electromagnetic radial position detector 36
and 38, it is preferable to adopt a structure similar to that described in British Patent No. 1418261 "Radial position detection device for electromagnetic bearing". The currents exciting coils 16e and 23e of electromagnetic radial bearings 16 and 23 are controlled by signals emitted by electromagnetic radial position sensors 36 and 38. To this end, control of bearings 16 and 23 from electromagnetic radial position sensing 36 and 38, respectively, can be implemented using a circuit such as that described in U.S. Pat. No. 3,787,100, described below with reference to FIGS. 4 and 5.

The axial position of the spindle is regulated by the signals transmitted by the electromagnetic thrust position sensors 42 and 53, the coils 42a and 53a of these sensors which adjust the excitation circuit of the coil 28e of the electromagnetic thrust bearing. It is noted that the axial control of the spindle is carried out mainly using only one electromagnetic thrust position sensor located at the front end of the shaft 11, so as to minimize the influence of the expansion of the hot part of the shaft 11. Should. However, the function of the two electromagnetic thrust position detectors 42 and 53 is that the detector 42 detects sudden displacements and vibrations of the shaft 11 during grinding work at the front part of the shaft, while the detector 53 detects sudden displacements and vibrations of the shaft 11 due to thermal expansion. It is set to detect positional displacement at the rear end of the shaft.

The spindle 11 is rotated by an electric motor 37. This motor is an asynchronous motor, and its inductor 37a including an iron core and an excitation coil is fixed, and its armature 37b is composed of a copper rod 37c extending parallel to the axis of the shaft 11 and housed in the periphery of said shaft. . The rod 37c is electrically connected by welding its ends. Inductor 37a of motor 37
is similar to the pole pieces of the stators of the electromagnetic radial bearings 16, 23 and the stators of the radial detectors 36, 38 in that the electromagnetic radial bearings 16 and 23 are constructed of sheet metal bundles or stacked iron plates. The inductor 37a of the motor 37 is cooled by circulating a cooling fluid such as water in a spiral groove 44 provided on the outer cylindrical surface of the tube body 35. This outer surface abuts the inner surface of the jacket 13 and the groove 44 forms a closed circuit. This helical groove communicates with the outside through a supply orifice 45 and a discharge orifice 46 (see FIG. 3) for the cooling fluid, which orifices are provided in the wall of the jacket 13. For further details, please refer to these orifices 4.
5 and 46 open toward the groove 44 substantially in the tangential direction.

Similarly to the power supply cable of the inductor 37a of the motor 37, the coils 16e, 23e, 28e, 36e, 3
The ends of the conductors and cables connected to 8e, 42a and 53a are integrated into a junction box 47 fixed to the lid 24. Passages such as 48 are made in the jacket 13, tube body 35 and lids 18 and 24 for passing these electrical conductors and cables. Circuit that controls the electromagnetic bearing (4th
(see figure) is arranged outside the jacket 13 so as not to be affected by the temperature occurring inside this jacket.

In order to avoid the ingress of dust and debris resulting from machining operations on the outside of the housing 13, a protective lid 49 is fixed in front of the housing 13 by a screw 50 screwed to the lid 18 on the one hand, and on the other hand. Lid 1
At least one orifice 51 is provided at 8 and coupled to a source of pressurized air (not shown) for blowing compressed air onto the inside of the jacket 13. The jacket is hermetically closed at its rear and the pressurized air introduced into the jacket escapes in front of the orifice to prevent dust and debris from entering.

As already mentioned, the manner in which the spindle is supported and driven in the device according to the invention allows extremely high rotational speeds of 60,000 rpm to be reached, without any restriction on the diameter of the spindle shaft. This axis therefore has high inertia and considerable stiffness. Moreover, the sensor control of the position of the spindle axis corrects any displacement of the spindle axis with respect to its normal position, and together with the rigidity of the axis, high machining accuracy can be obtained.

During the machining operation, the radial and axial position of the spindle is controlled by signals conveyed by an electromagnetic radial position sensor and an electromagnetic thrust position sensor, so that these positions relative to the jacket 13 The shaft 11 is held constant and perfectly aligned within the gap between the stator 28a and the disc-shaped rotor 28b of the electromagnetic radial bearings 16, 23 and the electromagnetic thrust bearing 28. In this case, the positioning and movement of the tool is carried out simply by moving a carriage (not shown) to which the jacket 13 is fixed by means of a bush 52.

However, tool holding spindle devices such as those described above provide a very useful auxiliary action for controlling the positioning and movement of tools for machining operations since the shaft itself is also displaceable.

In fact, when the shaft 11 is located in a certain axial and radial reference position, for example perfectly aligned in the jacket 13, there is a There is a gap of about 0.10 to 0.20 mm. As soon as the shaft is displaced axially or radially from this reference position, this displacement is detected by an electromagnetic thrust position detector and an electromagnetic radial position detector, and the excitation current of the electromagnetic thrust and electromagnetic radial bearings is is changed as a function of the signal transmitted by the shaft 11 to return the shaft 11 to its reference position. It is therefore possible to adjust the axial direction or It is contemplated that the radial reference position may be intentionally varied to provide a predetermined amplitude and direction displacement.

Of course, the displacement of the tool electrically controlled in this way is of a limited maximum amplitude of the order of 0.10 mm, but is of much greater precision than can be obtained by mechanically controlled displacement. Obviously, this offers the great advantage of providing special processing control.

The following items are some examples of special processing operations performed as described above.

1. Control of the radial displacement of the spindle.

By modifying the signal transmitted by the electromagnetic radial position detector, the radial reference position of the axis of the spindle can be adjusted to the forward and backward bearings 1.
A radial displacement of a predetermined amplitude is applied and changed by simultaneous action on each of 6 and 23. Through this control, the grinding of the workpiece is
A radial displacement on the order of microns is imparted to the tool for extremely precise termination.

2 Control of axial displacement of spindle.

The axial reference position of the spindle is changed by modifying the signal transmitted by the electromagnetic thrust position sensor. This modification is carried out in a linearly controlled manner and, when carried out simultaneously with the radial movement of the spindle, allows machining of inclined or curved surfaces, such as the surfaces of grooves or passages.

3 Correction of conicity.

of the workpiece by selectively changing the radial reference position of the front electromagnetic radial bearing 16 or the rear electromagnetic radial bearing 23 by imparting a change to the signal transmitted by the corresponding detector. Conicity can be compensated or corrected during machining.

Such a selection change of the radial reference position of the electromagnetic radial bearing can also be used for the purpose of adjusting the rotational position of the shaft of the spindle.

4 Compensation for thermal effects.

Changing the radial and axial reference position of the spindle makes it possible to compensate for deviations in the spindle position caused by expansion or contraction of the heat generating part.

5. Geometrical shape processing of the ground surface.

If the grinding surface exhibits a specific cross-section, for example if this surface is to be ovalized, the continuous displacement of the axial and/or radial reference position of the spindle is electrically controlled during the machining operation to achieve the desired cross-section. You can get the shape directly.

6. Micro-vibration of tools.

During grinding operations, it is advantageous to provide the tool with a reciprocating linear motion in conjunction with its forward motion. Such a reciprocating linear motion can be obtained in the form of minute vibrations, for example by periodic changes in the excitation current of an electromagnetic thrust bearing.

The processing examples described above are all based on controlling the excursion of the radial and/or axial reference position of the spindle. As previously mentioned, this control is accomplished by modifying the signals transmitted by one or more of the electromagnetic thrust position detectors and the electromagnetic radial position detectors.

For example, consider an electromagnetic radial position sensor and an electromagnetic radial bearing below. Each electromagnetic radial position detector, such as 36, is composed of coils 36e (FIG. 3) that are grouped into two sets of coils, each set of coils being arranged diametrically opposite each other and having two sets of coils.
The sets of coils are arranged along two perpendicular diameters. Each electromagnetic radial bearing such as 16 includes a plurality of electromagnets including a coil 16e (FIG. 2);
These electromagnets are grouped into sets, each set containing diametrically opposed electromagnets. Control of the radial position of the shaft 11 is performed by a control circuit as described in the above-mentioned U.S. Pat. Provides control signals to the circuit. axis 1
1 occupies a perfectly aligned radial reference position within the bearing 16, the pair of detectors produces response signals of equal absolute value, and the excitation current of the electromagnet of the armature of the bearing 16 is Not changed. On the contrary, as soon as the shaft 11 is displaced from its radial reference position, a control signal is issued to change the excitation current of at least one electromagnet in order to return the shaft 11 to its radial reference position.

If it is desired to control a predetermined amplitude and directional displacement of the shaft 11 from its radial reference position, it is therefore possible to use the signal transmitted by the detector to cause the shaft to move from its reference position. It is sufficient to give a value of the same distance but in the opposite direction as when it is displaced. To this end, a control circuit is provided which is connected to the sensor group of electromagnetic radial position sensors 36 and 38, and which control circuit includes a device for selectively modifying the signals transmitted by the sensor group. Containing and electromagnetic radial bearings 16 and 2
3 is connected to the input side to the circuitry controlling the circuit.

Controlling the displacement of the axial reference position of the spindle includes a device capable of selectively modifying the signals transmitted by the electromagnetic thrust position detectors 42, 53 and to the circuitry controlling the axial position of the spindle. Electromagnetic thrust position detector 4 connected to the input side of
2 and 53, said control circuitry controls the excitation current supply circuit of the electromagnetic thrust bearing 28.

4 and 5, the aforementioned U.S. patent no.
3787100 shows the general electrical control circuit including the known electrical control circuitry shown in the patent specification 3787100, as well as the schematic arrangement of the detector group and the bearing group with respect to the shaft 11 of the spindle device shown in FIG. 1; ing.

In FIG. 5, the electromagnetic radial position detector 36
The coil 36e is shown in more detail as the lateral windings X ₁ and X' ₁ and the vertical windings Y' and Y' ₁ , as well as the lateral windings _{2 , and _}
A ₁ and A′ ₁ and the vertical windings are B ₁ and
B' ₁ , and the lateral windings of the other electromagnetic radial bearing 23 are designated A ₂ and A' ₂ , and the vertical windings are designated B ₂ and B' ₂ . In this arrangement, the output signals of the horizontally arranged detector group collectively control the windings of the horizontal electromagnetic radial bearing, and the output signals of the vertically arranged detector group control the vertical direction. Figure 4 shows that the windings of the electromagnetic radial bearing are centrally controlled, and the windings of the electromagnetic thrust bearing (not shown) are controlled by the output signal of the corresponding electromagnetic thrust position detector. This should be kept in mind in understanding the control circuit shown.

In FIG. 4, one radial position detector 3
_The output signals _resulting from _the 6 transverse windings X _{1 and} An operating reference position change signal Δx ₁ is applied and connected to an input terminal of a known control network S, and in a similar manner output signals resulting from the transverse windings X ₂ and X' ₂ of the other radial position sensor 38. are likewise added algebraically, and the summation value X ₂ is added to the operating reference position change signal Δx ₂ of the axis controlled by the potentiometer Px ₂ in the adder circuit Ax ₂ to the input terminal of the known control network S. Connected.
What is noteworthy here is that the composite values x ₁ and x ₂ are theoretically x ₁ = x ₂ when the shaft 11 is rotating at the reference position, and the value of the operation reference position change signal is also has the relationship Δx ₁ = Δx ₂ . Said x ₁
When a load is actually applied to the shaft 11, Δx 1 and Δx 2 naturally take different values, but Δx ₁ and Δx ₂ remain at _their initially set values. What can be said from these operations is that the values of Δx ₁ and Δx ₂ must initially be set to values for centering the shaft 11 when rotating without load. However, this centering state, ie, the reference position rotation state, does not mean a rotation state at the geometric center, but a rotation state at the mechanical center. That is, these center positions usually differ depending on the balance of the rotor and the strength of the magnetic field. For example, the above-mentioned "device for selectively changing the transmitted signal" is based on these Δx ₁ , Δx ₂ , Δ
It means _a device for separately setting a reference position by changing _{y 1 ,} Δy ₂ and _{Δz ,} and in _FIG . , Px ₂ , Py ₁ , Py ₂ and Pz ₁
It also means Pz ₂ . This also means that the mechanical center position is relative, and the position of the spindle or shaft can be tilted or moved axially back and forth by adjusting the potentiometer. It also means something that can be done.

Next, the known network S, namely U.S. Pat.
The control circuit shown in the specification of No. 3787100 will be schematically explained.

The three groups of output signals from the adder circuits Ax ₁ , Ax ₂ , Ay ₁ , Ay ₂ and the two differential amplifiers 115 and 116 are respectively input to the three groups of circuit networks S, and the outputs from Ax ₁ and Ax ₂ , for example, To explain the circuit network that receives the signal, the signal output from Ax ₁ is divided into two, one is directly sent to one input terminal of the adder circuit 121, and the other is inverted in phase by the inverter 124 and then sent to Ax _2. The signal output from Ax 2 is directly input to the other terminal of the adder circuit 125, and the other input terminal of the adder circuit 121 is directly connected to the output from _Ax2 . The output of the adder circuit 121 is connected to the input side of a phase advance network 122, which is composed of an integrator-differentiator/amplifier circuit. Furthermore, the output of the network is added to the adder circuit 1.
23 and the selection amplifier 101 to the winding A ₁ of the stator coil 16e of the radial bearing 16 or
_A'1 , and the signal from the network 122 is simultaneously sent to the adder circuit 128 and the selection amplifier 1.
02 to the winding A ₂ or A' ₂ of the stator coil 23e of the other radial bearing 23. Further, the output from the adder circuit 125 is input to a wideband phase advancer circuit 126, and the wideband phase advancer circuit 1
The output from 26 is output to the winding A ₁ or A' ₁ via the circuit 123 and the selection amplifier 101, and at the same time, the output from the adder circuit 125 is converted in phase by 180 degrees by the inverter 127. , the winding A ₂ via the selection amplifier 102
Alternatively, it is output to _A'2 . Note that the addition circuit 123
One input terminal of the adder circuit 128 is directly connected to the output of the broadband phase advance circuit 126, and at the same time, one input terminal of the adder circuit 128 is directly connected to the output of the phase advance network 122.

For convenience, the correspondence between each circuit is listed below.

Addition circuit 121 → 131, phase advance network 1
22→132, addition circuit 123→133, inverter 124→134, addition circuit 125→135,
Wideband phase advancing circuit 126 → 136, inverter 12
7→137, addition circuit 128→138, selection amplifier 101→103, selection amplifier 102→104.

Regarding the control of the electromagnetic thrust bearing 28, the output signals from the windings Za and Zb of the respective coils of the electromagnetic thrust position detectors 42 and 53 are algebraically added in advance in the comparator circuit 118 to obtain a thrust position change signal. Potentiometers Pz ₁ and Pz ₂
and algebraically add the output signal from the coil winding Za to the operation reference position change signal Δz ₁ from the potentiometer Pz ₁ , and input the output to the known control circuit S. do.
Note that in this case, the configuration of the circuit network is different from that in the case of radial direction control; the output is simply input to the phase advance circuit 114, and then selected to the two windings of the coil 28e of the electromagnetic thrust bearing via the selection amplifier 105. It is possible to control the shaft 11 in the axial direction by simply outputting the signal.

The details of the control method and circuit of the electromagnetic thrust bearing will become clearer from the following explanation with reference to FIGS. 6 to 13.

6 to 11 show the shaft 11 of the electromagnetic thrust bearing 28 and the electromagnetic thrust position detectors 42, 53.
FIG. 3 is an explanatory diagram showing a change in the gap during the operation. FIG. 12 is a schematic diagram showing the positions of the gaps shown in FIGS. 6 to 11 in the tool holding spindle device for a grinding machine according to the present invention;
Figure 3 shows the control circuit for the electromagnetic thrust bearing.

In FIG. 15, reference numeral 11 indicates a shaft suspended by electromagnetic radial bearings 16, 23 controlled by electromagnetic radial position detectors 36, 38. An electric motor 37 for rotating the shaft 11 is provided at an intermediate position between the electromagnetic radial bearings 16 and 23. The electric motor 37 is the largest source of heat in such a device and the shaft 1
It must be kept in mind that the source of expansion heat of 1 is essentially this electric motor 37.

Reference numeral 28 designates an electromagnetic thrust bearing consisting of a disk-shaped rotor 28b attached to the shaft 11 and a field yoke provided with an excitation coil 28d.
The rear clearance E of the electromagnetic thrust bearing 28 is limited by the free space formed by the radial plane A of the field yoke and the rear radial plane A' of the disc-shaped rotor 28b.

The electromagnetic thrust position detector 42 is located at the front end of the shaft 11, has a radial plane B', and has a coil 42a.
A radial plane B is defined by the outer end surface of the annular ring 21 having a diameter. Radial planes B and B' are the gaps of the first electromagnetic thrust position detector 42
forming e ₁ .

The electromagnetic thrust position detector 53 disposed at the rear end of the shaft 11 has a flat conductor 53b disposed on the end surface of the shaft to define a radial plane C.
The lid No. 3 accommodates a coil 53a in its inner end surface, and the end surface forms a radial plane C. These radial planes C and C' form a gap e ₂ of the second electromagnetic thrust position detector 53.

It must be noted that this second electromagnetic thrust position detector 53 is arranged very close to the electromagnetic thrust bearing 28. Therefore, the change in the gap e ₂ is detected by the electromagnetic thrust position detector 53, and the gap e ₂ is also directly detected since the thermal expansion of the shaft between the bearing 28 and the detector is almost negligible. It changes in direct proportion to the clearance E of the bearing 28.

A first electromagnetic thrust position detector 42 disposed near the front end of the shaft 11 is connected to the shaft (mandrel 1
It is possible to detect all changes in the thrust position of the tool mounted on the tool (located at 4) as a value with respect to a fixed radial plane B. Of course, this thrust position change also includes thermal expansion of the shaft 11 due to heat generated by the electric motor 37.

If the thrust position control of the shaft is performed by a single electromagnetic thrust position detector, this detector 42 detects the position of the actual tool on the shaft as precisely as possible. Whatever position it is in, it must be placed at the front end of the shaft. Conversely, the second electromagnetic thrust position detector 53
Even if a chisel is used, the change in the gap between the rear end of the shaft 11 and the inner end surface of the cover provided on the outer sheath 13 does not correspond accurately to the change in the position of the tool (grinding wheel speed wheel or milling tool). The result will be unsatisfactory and the precision machining of the workpiece will not be possible.

The purpose of electromagnetic thrust position sensors 42 and 53 will be more readily understood by considering the description of FIGS. 6-11.

FIG. 6 shows the position of each gap when the shaft 11 is in a normal position. In this state, gaps e ₁ and e ₂ of each of the detectors 42 and 53 have reference values of e ₁₀ and e ₂₀ , and gap E also has a reference value of E ₀ .

FIG. 7 shows the shaft 11 rotated by the motor 37.
The figure shows a state in which thermal expansion is occurring throughout. Further, the shaft 11 is not subjected to any external perturbation. As shown in FIG.
The thermal expansion effect generated on the shaft due to the heat generation effect of the electric motor installed in the center of the shaft increases the gap _e1 of the thrust position detector 42 by a certain value a. Gap E between thrust bearing 28 and electromagnetic thrust position detector 53 and
e ₂ is reduced by a certain value a. Of course, it is a prerequisite that the electric motor 37 is located substantially centrally with the detectors 42 and 53 and that the detector 53 is arranged in close proximity to the bearing 28.

If the electromagnetic thrust bearing 28 is controlled by the electromagnetic thrust position detector 53, the detector detects a decrease in the gap _e2 and increases the gap E of the bearing 28.
to move the shaft 11 and the disk rotor 28b forward by a value a toward the steady state value E ₀ , so that the disk rotor 42b of the electromagnetic thrust position sensor 42 (and the mandrel 14 ) moves further to the left, and the gap e ₁ becomes the value e ₁₀ +2a, resulting in the mandrel 14 being moved to the left by this value.

On the other hand, in FIG. 7, when the electromagnetic thrust bearing 28 is controlled by the electromagnetic thrust position detector 42, the detector 42 detects that the gap _e1 has increased by the value a, and the An attempt is made to reduce the clearance E by moving the shaft 11 to the right (backward) by a value a, and the disk-shaped rotor 4 of the electromagnetic thrust position detector 42
2b (and the mandrel 14) return to their original positions (Fig. 9), whereas the gap E of the bearing 28
The value becomes E ₀ −2a, and the electromagnetic thrust position detector 5
The gap e ₂ in No. 3 has a value of e ₂₀ -2a. In this case, the mandrel 14 returns to its original position despite the expansion of the shaft 11, and the gaps between the bearing 28 and the electromagnetic thrust position detector 53 are different from the original reference values _E0 and _e20, respectively. Takes a value.

Figure 8 shows that the shaft 11 is moved to the left due to the heat generated by the electric motor.
It shows a state in which it has expanded to the right by a value a and has further moved overall to the left by a value b due to external perturbation. In this case, the electromagnetic thrust position detector 42
The gap has a value of e ₁₂ = e ₁₀ + a + b, the bearing 28 has a gap of E ₂ = E ₀ - a + b, and the electromagnetic thrust position detector 53 has a gap of e ₂₂ = e ₂₀
The gap has a value of −a+b.

If the electromagnetic thrust bearing 28 is controlled by the electromagnetic thrust position detector 42, the disc-shaped rotor 4
2b (and mandrel 14) return to their original position with a gap of value _e10 . When the position of the bearing 28 is modified as a function of the output of the electromagnetic thrust position detector 42, the clearance of the bearing 28 and the clearance of the electromagnetic thrust position detector 53 will be as shown in FIG. 9 once the modification occurs. They have values of E ₃ and e ₂₃ , respectively.

The axis control in the thrust direction described above is implemented by the circuit configuration shown in FIG. Windings Za and Zb of electromagnetic thrust position detectors 42 and 53,
Therefore, in reality, the signals e' ₁ and e' ₂ generated from 42a and 53a correspond to the potentials that generate the gaps e ₁ and e ₂ in FIG. 12, respectively. These signals e′ ₁ and e′ ₂ are each first connected to comparator circuit 1.
It is input to non-inverting input terminals 15 and 116. The inverting input terminal of the circuit receives the reference position signal e' ₁₀ or e' ₂₀ from the potentiometers P _z1 and P _z2 , respectively.
is input. These reference position signals correspond to the potential generated in the gap e ₁₀ or e ₂₀ of the thrust position detectors 42, 53 during normal operation. The outputs E ₁ and E ₂ of the comparison circuits 115 and 116 are both input to an addition circuit 117 and a comparison circuit 118. The circuit 117 outputs a value E 1 +E 2 /2 corresponding to the movement value b of the axis 11 due to external perturbation (high frequency perturbation), and the comparator circuit 118 outputs a value E ₁ +E ₂ /2 corresponding to the movement value b of the axis 11 due to external perturbation (high frequency perturbation), and the comparison circuit 118
A value E ₁ −E ₂ /2 corresponding to the movement value a of the front end portion of No. 1 is output.

The output of the adder circuit 117 is input to the display circuit 119, and the output of the comparator circuit 118 is input to the arithmetic _{circuit 113} . A value for feeding back a correction value corresponding to the movement value a to the output side is calculated.

The output E ₁ of the comparator circuit 115 is input to the phase advance circuit 114 and then to the selection amplifier 105 . (See FIG. 4) This means that, as mentioned above, a sudden change in the axial direction at the front of the spindle 10 during actual operation is detected by the electromagnetic thrust position detector 42, and the output signal is mainly transmitted to the electromagnetic thrust bearing 28.
will be controlled. Output of comparison circuit 116
E ₂ is input to, for example, a limit setting circuit 120 and compared with a limit value, and the circuit is further connected to an alarm circuit 121.
Alternatively, it is connected to a circuit for readjusting operating parameters. Actually, E ₂ represents the amount of displacement of the gap e ₂ of the detector 53 or the amount of displacement of the gap E of the bearing 28. Since these displacements E ₂ are different from the displacement E ₁ of the first electromagnetic thrust position sensor, the gap e ₁ can be enlarged, but the gap e ₂ is narrowed.
(See Figure 9) This means that the gaps E and _e2 must be kept below the above-mentioned limit values to avoid the rotating parts of the electromagnetic thrust bearing 28 and the electromagnetic thrust position detector 53 coming into contact with the fixed parts. Furthermore, an alarm must be activated when E ₂ exceeds the above-mentioned limit value.

The output of the comparator circuit 118, which indicates the thermal expansion value a in both the left and right directions of the shaft 11, is
A correction value a/k taking into account the thermal expansion of the shaft 11 between B' and the outer end of the mandrel 14 (l) is simultaneously input to the arithmetic circuit 113. As a practical matter, if axis 1
1 expands left and right from the center of the shaft by a value a, the shaft between the tip of the tool attached to the mandrel 14 and the disc-shaped rotor 42b also expands further leftward by a value a/k. It ends up. in this case,
The value a/k is a function of the thermal expansion value a, and this value is usually calculated based on the amount of expansion of the axial length L between the first and second thrust position detectors. The output from the arithmetic circuit 113 calculated in this manner and added with the thermal expansion value is fed back to the inverting input terminals of the comparison circuits 115 and 116 to correspond to the change in the thrust position of the shaft due to thermal expansion, taking into account the correction value. Operation reference position change signals Δ _z1 and Δ _z2 are sequentially output to comparison circuits 115 and 116. As shown in Fig. 10, in actual machining, the tool tip must not be moved in the axial direction except in special cases, so the shaft 11 must be further moved to the right by a/k. No.

Figures 11 and 13 are potentiometer P.
The arithmetic circuit 113 for outputting the total correction value to be added to the operation reference position change signals Δ _z1 and Δ _z2 generated from _z1 and P _z2 and the state of each gap at that time are shown, respectively. circuit 113
can also be input for parameters other than thermal expansion correction. That is, the arithmetic circuit 113 can add a value T to the operation reference position according to the machining purpose, and this value T is an operation value that compensates for tool wear or moves the shaft 11 slightly to the left. It means. Of course, by regularly changing the value of T in a short period of time, it is possible to transmit minute vibrations to the tool.

From the above, the functions of the first and second electromagnetic thrust position detectors 42 and 53 have been clarified, but to put it more simply, the first electromagnetic thrust position detector 42 is A second electromagnetic thrust position detector 53 provided at the rear end of the other shaft detects a relatively large axial displacement of the shaft 1.
The entire axial change including the thermal expansion of 1 is detected, and the difference between the two detected values means the thermal expansion value.
becomes indispensable, and as a result, the function of the detector is to detect thermal expansion.

As can be seen from the above description, the control network described above makes it possible to set the reference position of the shaft 11 in any direction, thereby making it easy to achieve a very wide variety of grinding operations. be understood.

[Brief explanation of the drawing]

FIG. 1 is an explanatory view of a tool holding spindle of a grinding machine according to the present invention, and is an axial sectional view taken along the line - in FIG. 2; Fig. 2 is a partial explanatory view taken along the line - of Fig. 1; Fig. 3 is a partial explanatory view taken along the line - of Fig. 1; Fig. 4 is an explanatory diagram of the electrical control circuit; FIG. 5 shows the schematic arrangement of the electrical control elements. Explanatory diagram;
6 to 11 are explanatory diagrams showing changes in the gap between the electromagnetic thrust bearing and the first and second electromagnetic thrust position detectors; FIG. 12 is a schematic diagram showing the gap position of the device according to the present invention; FIG. 13 is a control circuit diagram of an electromagnetic thrust bearing. In the figure; code; 10... spindle for tool holding;
11...shaft, 13...outer cover, 13a, 13b...
Inner contact shoulder, 14... mandrel, 15... grinding wheel, 16... electromagnetic radial bearing, 16a...
Annular stator, 16b... Annular rotor, 16c...
...Magnetic pole piece, 16d... Branch part, 16e... Coil, 17... Ring, 18... Annular lid, 19...
Screw, 20...Roller bearing, 21...
Annular ring, 22... Screw, 23... Electromagnetic radial bearing, 23a... Annular stator, 23b...
...Annular rotor, 23e...Coil, 24...Lid,
25... Screw, 26... Roller bearing,
27...Ring, 28...Electromagnetic thrust bearing, 2
8a... Stator, 28b... Disc-shaped rotor, 2
8c...Field yoke, 28d...Field yoke, 2
9, 30...ring, 30a...radial surface,
32... Insulating ring, 33... Ring, 34...
Insulating ring, 35...Tube body, 35a...Cylindrical surface, 35b...Inner abutment shoulder, 36...Electromagnetic radial position detector, 36a...Stator, 3
6b...Ring, 36d...Magnetic pole branch part, 36
e...Coil, 37...Electric motor, 37a...
Inductor, 37b...armature, 37c...copper rod, 3
8... Electromagnetic radial position detector, 38a... Stator, 38b... Ring, 38e... Coil, 3
9...Natsuto, 40, 41...Natsuto, 42...
Electromagnetic thrust position detector, 42a...Coil, 4
2b... Disk-shaped rotor, 43... Nut, 44...
... Helical groove, 45 ... Supply orifice, 46 ...
...Drainage orifice, 47...Connection box, 48...Passage, 49...Protective lid, 50...Screw, 51...
... Orifice, 52 ... Bush, 53 ... Electromagnetic thrust position detector, 53a ... Coil, 53b ...
... Flat conductor, 53e... Coil, X ₁ , X' ₁ ,
X ₂ , X' ₂ , Y ₁ , Y' ₁ , Y ₂ Y' ₂ ...... Electromagnetic radial position detector stator coil winding, Za, Zb ... Electromagnetic thrust position detector coil winding, Px ₁ ...... Pz...
Potentiometer, A ₁ . . . B' _{2 .} . . shows the electromagnetic radial bearing stator coil windings, respectively.

Claims (1)

[Scope of Claims] 1 (a) a jacket 13; (b) a shaft 11 having a large diameter; and (c) a shaft 11 connected to a front free end of the shaft 11 and having a smaller diameter than the shaft 11. (d) Annular stators 16a and 23a around which excitation stator coils 16e and 23e are wound, respectively, in the end region of the shaft 11; two electromagnetic radial bearings 16, 23 consisting of attached annular rotors 16b, 23b; (e) each of the electromagnetic radial bearings 16, 23;
an inductor 3 fixed within said jacket at a position substantially equidistant from and surrounding said axis 11;
(f) the two electromagnetic radial bearings 16; and (f) the two electromagnetic radial bearings 16. . A ring 36 made of a cylindrical conductor provided on 11
(g) a disk-shaped rotor 28 attached to the shaft 11;
b and field yokes 28c and 28d made of ferromagnetic material having coils 28e arranged axially apart from each other on both sides of the peripheral edge of the rotor; h) At the front part of the shaft 11, a disc-shaped rotor 42b made of a disc-shaped conductor attached to the shaft and an annular lid 1 covering the front end of the jacket 13;
at least one electromagnetic thrust position sensor 42 providing a signal indicative of the axial displacement of the forward part of the spindle 10, consisting of a coil 42a carried in an annular ring 21 mounted on the outside of the spindle 10; (i) The electromagnetic radial position detectors 36, 38, the thrust position detector 42, and a second electromagnetic thrust position detector 5 provided at the rear end of the shaft 11 for detecting axial displacement of the rear end of the shaft.
coils 16e and 2 of each of the detectors and each of the bearings for controlling the excitation current of each of the electromagnetic radial bearings and the electromagnetic thrust bearing in response to signals from 3 so that the shaft always takes the reference position;
3e, 28e; (j) changing at least one of the signals from the detectors 36, 38, 42, 53 to adjust the reference of the axis 11 according to the processing purpose; a sensing signal changing circuit comprising a circuit for outputting and adding to an algebraic summation of the signals from the detector a reference position change signal connected between the detector and the control circuit, respectively, for changing the position; A tool holding spindle device for a grinding machine, comprising: 2 Disc-shaped rotor 28b of electromagnetic thrust bearing 28
2. Device according to claim 1, characterized in that the is arranged at the rear of the shaft (11).