JPH0993989A - Torque control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a torque control device in which an electromagnetic brake can make control torque dot to zero over the wide range of the number of revolutions and at the same time torque can be kept nearly constant even when the number of revolutions is changed. SOLUTION: This device is two sets of systems comprising coils disposed at a plurality of intervals of equal angle, and is provided with independently constituted coil systems 5a, 5b, 5c, 6a, 6b, 6c, a magnet relatively rotatably disposed relative to each coil of the coil systems and amplifiers 7a, 7b, 7c connected between coils paired with each other in each of the coil systems to amplify an induced voltage generated in the coils of one-side system and to apply it to the coils of the other-side system so that the paired coils of each system donot interfere with each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotational force control device for controlling the tension of a wire rod in winding work such as a coil.

[0002]

2. Description of the Related Art As a conventional device for controlling torque,
There is a motor for rotation drive or an electromagnetic brake for braking.

[0003]

However, in the motor exclusively used for rotational driving, the control range of the rotational speed is limited and there is a possibility that reverse rotation may occur. Further, the electromagnetic brake dedicated to braking is not suitable for operation involving deceleration. For this reason, the number of revolutions is generally proportional to the voltage and inversely proportional to the torque, so that it is difficult to rotate the conventional torque control device at high speed with high torque. Therefore, for example, in winding work of a coil or the like, it is difficult to control the tension of the wire or the torque over a wide range of rotation speeds by the conventional rotation force control device. Further, in the conventional torque control device, the basic characteristics of the rotation speed and the torque with respect to the voltage are fixed. Therefore, in order to keep the rotational force constant with respect to the rotational speed, it was necessary to make the applied voltage variable.

In view of the above points, the present invention makes it possible to perform electromagnetic braking up to a braking torque of zero over a wide range of rotation speeds, and to keep the torque substantially constant even when the rotation speed changes. The purpose is to provide a control device.

[0005]

According to the present invention, the above object is to provide a system for controlling a rotational force, which comprises two sets of coils each having a plurality of coils arranged at equal angular intervals.
A coil system independently configured so that the coils forming each pair do not interfere with each other, and a magnet rotatably disposed so as to face each coil of the coil system.
Connected between the coils forming a pair of the respective coil systems,
This is achieved by including an amplifier that amplifies the induced voltage generated in the coil of one system and applies it to the coil of the other system.

According to the above structure, each coil system is configured as an independent rotating system, and when a driving voltage is supplied from the outside, each coil system works as an electric motor in cooperation with the magnet. When driven to rotate, each coil system will act as a generator in cooperation with the magnet. Then, an induced voltage is generated in each coil of the coil system acting as the generator by rotational driving, and this induced voltage is amplified by the amplifier and applied to the coil which should be a pair of the other coil system.

Here, the counter electromotive force of the electric motor is canceled by the coils to be paired in each coil system, or controlled by the gain adjustment of the amplifier. This allows
Below the rotational speed determined by the drive voltage, the torque is related only to the gain of the amplifier and not the drive voltage, so that a substantially constant torque can be obtained even if the rotational speed changes.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. The embodiments described below are preferred specific examples of the present invention,
Although various technically preferable limitations are given, the scope of the present invention is not limited to these forms unless there is a description to limit the present invention in the following description.

1 to 4 show the operating principle of an embodiment of a torque control device according to the present invention. 1 and 2 are two generators (or electric motors) of four poles and three phases, which are used in the torque control device 1 and are configured independently of each other.
A few. As shown in FIG. 1, the generator 2 includes a rotor 4 rotatably supported around a rotating shaft 4a, three coils 5a arranged around the rotor 4 at equal angular intervals,
And a coil system 5 composed of 5b and 5c. Also,
As shown in FIG. 2, the generator 3 includes a rotor 4 rotatably supported around a rotating shaft 4a, and three coils 6a, 6b, 6c arranged at equal angular intervals around the rotor 4. And a coil system 6 consisting of

Here, the rotor 4 is
S-pole and N-pole magnets are alternately arranged side by side. In the case shown, it has a four-pole configuration. Coil system 5,
As shown in FIG. 3, 6 are arranged at rotational positions which are offset from each other by 60 degrees so as to be alternately arranged with respect to the rotation shaft 4a. As shown in FIG. 4, each of the coils 5a, 5b, 5c forming the coil system 5 has one end connected to each other and the other end having a pair of coils 6a, 6b, The other end of 6c is connected via amplifiers 7a, 7b, and 7c, respectively. One ends of the coils 6a, 6b, 6c are connected to each other.

According to the torque control device 1 thus constructed, the induced voltage generated in each coil 5a, 5b, 5c of the one coil system 5 by the rotation of the rotor 4 is
Via amplifiers 7a, 7b and 7c,
Coils 6a, 6b, 6 to be a pair of the other coil system 6
will be applied to c. As a result, the coil systems 5 and 6 having the double and three-phase structure are treated independently of each other, so that the coil systems 5 and 6 are respectively generators / generators.
It is used as a generator / motor or an electric motor / motor, and the rotational force is easily controlled by adjusting the gains of the amplifiers 7a, 7b, 7c.

By the way, when each coil system 5, 6 is used as a generator / motor, the coil system 5 is set to G (generator).
When the phase and the coil system 6 are M (motor) phases, the induced voltage generated in each coil 5a, 5b, 5c of the coil system 5, which is the G phase, is amplified by the amplifiers 7a, 7b, 7c and the M phase is used. Each coil 6a, 6b, 6c of a certain coil system 6
Apply to. As a result, the M phase is driven. Here, in a general motor, the torque T is
Assuming the applied voltage V, the constant Kt, and the rotating load Z,

[Equation 1] Since the basic structure of the torque control device 1 is the same as that of the motor, in the M phase, if the counter electromotive force E is set, the applied voltage V is

[Equation 2] Becomes In the G phase, the applied voltage V = 0. Therefore, the rotational torque T of the rotational force control device 1 at this time is M
It is the sum of the phase motor torque (positive) and the G phase braking torque (negative). Therefore, assuming that the gain Kg of the amplifier, the rotational load Zg of the G phase, and the rotational load Zm of the M phase,

(Equation 3) Becomes In this case, the amplifiers 7a, 7b, 7c
Since Zg> Zm by the connection of, if Z = Zm except for the first term,

[Equation 4] Becomes Solving this for the number of revolutions N,

(Equation 5) Becomes

Therefore, the condition for generating the rotational torque is Kg>
It becomes 1 and does not depend on the applied voltage V and the counter electromotive force E. The starting torque is zero when E = 0. Further, the rotation speed N increases in proportion to the torque T regardless of the external voltage. Thereby, the amplifiers 7a, 7b, 7c
By appropriately adjusting the gain of, by balancing the motor torque and the brake torque,
It is possible to realize a motor that can freely rotate with zero torque or any torque without load torque. Thus, stable control of high-speed rotation and low torque can be performed, and for example, high-speed winding of an ultrafine wire in an automatic winding machine can be easily performed.

Furthermore, in the above description, the amplifiers 7a, 7b and 7c are replaced by the coils 5a, 5b and 5c.
This is so-called one-way driving, in which the induced voltage of c is amplified to drive the coils 6a, 6b, 6c, but the invention is not limited to this, and the induced voltage of each coil of the G-phase coil system 5 is amplified to obtain the M-phase. In addition to driving each coil of the coil system 6 of No. 2, at the same time, a bidirectional drive (a so-called twin drive motor) in which the induced voltage of the M-phase coil system 6 is amplified to drive the G-phase coil system 5 is also possible. Is. In this case, the torque T is

(Equation 6) Therefore, in principle, twice the torque can be obtained.

By the way, the amplifiers 7a, 7a
Although b and 7c are based on an amplifier having a linear characteristic, when the gain Kg is increased, E is proportional to the rotation speed, so the amplifier easily becomes a clip state, and the above equation is no longer valid. Will end up. Here, assuming that the amplifier has a linear characteristic when E ≦ V / Kg and clips to the upper limit voltage V when E> V / Kg, a linear characteristic when E ≦ V / Kg. Therefore, the above equation holds, but E> V / Kg
Then, since the second term in Expression 3 differs depending on the condition of E, the torque T is

(Equation 7) Is represented by That is, the relationships of the above formulas 1 and 4 are mixed in one cycle. Where E = KvN,
Since Z = KiN, if E / Z = Kv / Ki,

(Equation 8) Becomes Therefore, when E ≦ V / Kg, the torque T
Has a constant value determined only by the structure of the amplifier and the motor, and when E> V / Kg, the torque-rotational speed characteristic shows a curve that changes from indeterminate to concave to convex.

As a result, in a bidirectional drive (so-called twin drive motor), a characteristic similar to that of an AC hysteresis motor can be obtained. It becomes gentle and becomes the same as the drooping characteristic of the DC motor. Thus, the twin drive motor can be driven by direct current as a motor, and the rotation speed N can be freely set by adjusting the gain Kg of the amplifiers 7a, 7b, 7c and the voltage V. This allows it to be used like a DC brushless motor. Further, since the coils to be paired act to cancel the counter electromotive force, high-speed rotation can be obtained even in the case of a high torque motor.

On the other hand, the above twin drive motor can be used as an electromagnetic brake (generator), an electric motor, or a generator / electric motor as a rotational force control actuator by appropriately switching the connection state of each coil. At the same time, when the gain Kg of the amplifier is set near 1, a motor that does not rotate despite the motor torque being generated is configured, so that an electromagnetic brake with an extremely small constant torque can be configured. Become.

5 and 6 show a first embodiment of the torque control device according to the present invention. 5 and 6, the rotational force control device 10 is a hollow cylindrical yoke 1
1, covers 12 and 13 for closing both ends of the yoke 11,
The covers 12 and 13 are rotatable around the center of the yoke 11.
The rotor 14 supported by the coil 11, the coils 15 arranged at equal angular intervals on the inner surface of the yoke 11, the iron core 16 inserted into the coil 15, and the intermediate frame 17 for positioning the coil 15 at a predetermined position. , A holding plate 18 for holding the coil 15 with respect to the intermediate frame 17.

The yoke 11 also serves as a case and is made of a magnetic material. Also, the covers 12 and 13 are
A bearing 1 attached to both ends of the yoke 11 and rotatably supporting the rotor 14 at the center thereof.
2a and 13a are provided. As a result, the rotor 14
Will be disposed near the center of the yoke 11.

As shown in FIG. 7, the rotor 14 has a rotating shaft 14a rotatably supported by the bearings 12a and 13a of the covers 12 and 13, and an equal angle around the rotating shaft 14a near the center of the rotating shaft 14a. It is provided with a rotor magnet 14b mounted at intervals or magnetized with multiple poles.
Here, the rotor magnet 14b is configured so that the direction of its magnetic flux extends in the radial direction with respect to the rotating shaft 14a, and has four poles in the illustrated case. The rotor magnet 14b of the rotor 14 may have six poles as shown in FIG. 8 or eight poles as shown in FIG.

As shown in FIG. 1, a plurality of coils 15 are provided around the rotary shaft 14a at equal angular intervals (in the case shown,
Six coils 15 are provided. In this case, each coil 15 has its winding wound around the bobbin in advance.

The iron core 16 is made of a magnetic material and has one end (the outer end in the radial direction) greatly expanded, and the other end slightly expanded, and the other end is each coil 15 It is inserted in the hollow part of the bobbin.

As shown in FIGS. 10 and 11, the intermediate frame 17 is formed of a non-magnetic material in a hollow cylindrical shape, and has holes 17a for positioning the coils 15. The holes 17a are arranged at equal angular intervals with respect to the central axis, and in the illustrated case, six holes 17a are provided. As a result, as shown on the left side of FIG.
The coil 15 in which the iron core 16 is inserted is the intermediate frame 17
By being inserted into the holes 17a from the outside in the radial direction, the coils 15 are positioned at predetermined positions at equal angular intervals with respect to the intermediate frame 17.

As shown in FIG. 12, the holding plate 18 is formed of a substantially rectangular flat plate, and has a hole 18a at the center thereof into which the iron core 16 can be inserted. This hole 18a is open on one side via a slit 18b. Thus, as shown on the left side of FIG. 10, the pressing plate 18 is laterally inserted between the coil 15 and the iron core 16 inserted in the coil 15 between the lower side of the enlarged one end and the coil 15. Can be done. Here, when the coil 15 is inserted into the hole 17a of the intermediate frame 17, the pressing plate 18 has its periphery abutting the periphery of the hole 17a of the intermediate frame 17,
The position of the coil 15 in the radial direction will be restricted.

Further, as shown in FIG. 13, the coil 15 is one of the coils 15 arranged along the circumferential direction.
Every third coil constitutes one coil system, and one coil system is the G phase and three coils G
1, G2, G3, and the other coil system has three coils M1, M2, M3 as the M phase. In this case, the G-phase coil is omitted in FIG. As shown in FIG. 14, one end of each of these coils is connected to each other, and the other ends of the coils G1 and M1, G2 and M2, G3 and M3 to be paired with each other are amplified as described later. Connected by. Incidentally, in the case of a general so-called SRM motor, as shown in FIG. 15, each coil 15 constitutes an A-phase, B-phase and C-phase coil system composed of coils on opposite sides. At the same time, as shown in FIG. 16, the coils of each phase are connected to each other in series and one ends thereof are connected to each other, which is a configuration different from that of the torque control device 10.

FIG. 17 shows the positional relationship between each coil 15 and the rotor magnet 14b of the rotor 14, the direction of the magnetic field, and the induced voltage generated in each coil M1, M2, M3 of the M-phase coil system. Thereby, when the rotor 14 rotates, the coils G1, G2, G3, M1, M2,
The change in the induced voltage of M3 can be seen. FIG. 18 shows each coil 1
5 shows changes in the direction of the magnetic field in the usage mode of 5 (generator / motor). That is, the first stage is the direction of the magnetic field in the case of forward rotation of motor drive braking, the second stage is the direction of the magnetic field in the case of reverse rotation, and the third stage is the direction of the magnetic field in the case of unidirectional drive in a twin drive motor. The fourth row shows the change in the direction of the magnetic field in the case of bidirectional driving.

FIG. 19 shows the coils G1 and M1 and G2.
And M2 and G3 and M3 are connected to each other. In FIG. 19, the amplifier 1
Reference numeral 9 denotes a first amplifier 19a to which an induced voltage of the coil G1 is input, a second amplifier 19b to which an induced voltage of the coil G2 is input, and a third amplifier 19a to which an induced voltage of the coil G3 is input. And 19c. Each amplifier 19a, 19b, 1
Since 9c has the same configuration, only the amplifier 19a will be described below. The amplifier 19a includes an operation amplifier 20, gain setting resistors R1, R2, R3 and R4 of the operation amplifier 20, and a complementary SE that amplifies an output signal of the operation amplifier 20.
It is provided with two transistors Q1 and Q2 forming PP and an oscillation preventing capacitor C. As a result, the induced voltage input from the coil G1 is
It is amplified by 9a and applied to the coil M1. In this case, the gain of the amplifier 19a is
It can be adjusted by changing the resistance value of the variable resistor R3. The amplifier 19a is configured as a so-called ± power source reverse-phase amplifier circuit, but is not limited to this.
Obviously, for example, it may be configured as an in-phase amplifier or a single power supply amplifier.

The torque control device 10 according to the embodiment of the present invention is configured as described above, and each coil 15
As shown in FIG. 15, the rotor 1 is arranged at equal angular intervals with respect to the rotation shaft 14a of the rotor 14, and the other end of the iron core 16 is
4 may be arranged at a predetermined distance from the surface.
As a result, the torque control device 10 is configured in a double, four-pole, three-phase structure.

Here, when the rotor 14 is rotating,
Of each coil 15, coils G1 and G of a G-phase coil system
An induced voltage is generated by the magnetic field of the rotor magnet 14b of the rotor 14 acting on G2 and G3. Then, the induced voltages are respectively generated by the amplifier 19
Are amplified by the individual amplifiers 19a, 19b and 19c of
Applied to M3. As a result, the M-phase coils M1 and M
The counter electromotive force generated by the rotation of the motors 2 and M3 is offset, and the electromagnetic brake operates with low torque.

FIG. 20 shows another example of the electrical configuration of the torque control device 10. In FIG. 20, the individual amplifiers 19a and 19a of the amplifier 19 are
Switching circuits 21, 22, and 23 are connected between b and 19c and the M-phase coils M1, M2, and M3. The changeover circuits 21, 22, 23 are configured as double-headed three-pole changeover switches.
1, M2 and M3 can be connected in reverse phase. The switching circuits 21, 22, 23 are adapted to perform a switching operation in conjunction with each other, and at one side, that is, in the switching position shown in the drawing, each coil M1, M is switched.
By connecting the coils 2 and M3 in phase with the coils G1, G2 and G3, the coils 2 and M3 act as a generator and drive the rotor 14. In this case, amplifier 1
By properly adjusting the gain of 9, it is possible to follow an arbitrary rotation speed with zero torque. further,
By appropriately adjusting the relationship between the external drive voltage and the gain, a substantially constant torque can be obtained in a wide range of rotation speeds. In addition, the switching circuit 21,
When 22 and 23 are switched to the other side, each coil M
1, M2, M3 are connected to the coils G1, G2, G3 in opposite phase to act as an electromagnetic brake to brake the rotor 14.

21 and 22 show a second embodiment of the torque control device according to the present invention. 21 and 22, the rotational force control device 30 is configured as a flat type that does not use an iron core, and includes a stator substrate 31 and a plurality of annularly arranged on the stator substrate 31 (in the case of the drawing). , 6) coils 32 (see FIG. 23), a disk-shaped rotor 33 that is rotatably supported facing the stator substrate 31, and covers 34 and 35 that cover both surfaces of the stator substrate 31, respectively. ing.

The stator substrate 31 is formed in a flat plate shape, and on one surface (the right surface in the case shown) of the stator substrate 31, the coils 32 are arranged at equal angular intervals around the center.

As shown in FIG. 23, a plurality of coils 32 are provided at equal angular intervals around the central axis (6 coils in the case shown).
Individual) coils 32 are provided. In this case, each coil 32 has a flat outer shape, and its winding is wound around the bobbin in advance.

The rotor 33 has a rotating shaft 33a rotatably supported by the covers 34 and 35, and, as shown in FIG. 24, has a multi-pole attachment around the center of the rotating shaft 33a at equal angular intervals. And a magnetized rotor magnet 33b. Here, the rotating shaft 33a is attached to the magnet 33b by, for example, press fitting. In the case shown in the figure, the rotor magnet 33b is alternately magnetized with N poles and S poles (black portions in the drawing) so as to have 8 poles in total.

Further, the covers 34 and 35 are attached to both surfaces of the stator substrate 31, and bearings 34a and 3 for rotatably supporting the rotor 33 at the centers thereof.
5a. As a result, the rotor 33 is
As shown in FIG. 5, the stator substrate 11 is arranged near the center.

Here, the coil 32 is one of the coils 15 arranged along the circumferential direction, as shown in FIG.
Every third coil constitutes one coil system, and one coil system is the G phase and three coils G
1, G2, G3, and the other coil system has three coils M1, M2, M3 as the M phase. These coils G1, G2, G3 and M1, M2, M3 are shown in FIG.
As shown in FIG. 6, the coils G1 and M1 and G2 and M which are to be paired with each other are connected to each other at one end.
The other ends of 2, G3 and M3 are connected by amplifiers A1, A2 and A3, respectively.

The rotational force control device 30 configured as described above
According to this, when the rotor 33 is rotating, each coil 3
Among them, the induced voltage is generated by the magnetic field of the rotor magnet 33b of the rotor 33 acting on the coils G1, G2, G3 of the G-phase coil system. Then, the induced voltages are respectively generated by the amplifiers A1, A2, A
Amplified by 3, each coil M1 of the M-phase coil system
It is applied to M2 and M3. As a result, the M-phase coil M
1, M2 and M3 cancel the counter electromotive force generated by rotation, and the electromagnetic brake acts.

In the above embodiment, the coil 1
In each case, 5 and 32 are provided, but
Not limited to this, it is obvious that the present invention can be applied to a rotational force control device provided with a large number of coils of 6 or more.

[0039]

As described above, according to the present invention,
By adjusting the gain of the amplifier, a substantially constant torque can be obtained in a wide range of rotation speeds, so that the torque becomes almost zero at any rotation speed, and an electromagnetic brake corresponding to a high rotation speed can be obtained. Further, a constant torque can be obtained even at a low rotation speed, and a more stable torque can be obtained than at a motor even at a high rotation speed.

[Brief description of drawings]

FIG. 1 is a schematic view of a first coil system showing the principle of an embodiment of a torque control device according to the present invention.

FIG. 2 is a schematic diagram showing a second coil system in the torque control device of FIG.

FIG. 3 is a schematic front view showing the overall configuration of the torque control device of FIG.

FIG. 4 is a schematic perspective view showing an electrical configuration of the torque control device of FIG.

FIG. 5 is a cross-sectional view showing a first embodiment of the torque control device according to the present invention.

6 is a partially cutaway side view of the torque control device of FIG.

7A and 7B are a front view and a side view of a rotor in the torque control device of FIG.

FIG. 8 is a front view showing a modified example of the rotor of FIG.

9 is a front view showing a second modified example of the rotor of FIG. 7. FIG.

10 is a sectional view of an intermediate frame in the torque control device of FIG.

11 is a side view of the intermediate frame of FIG.

12A and 12B are a side view and a plan view showing a pressing plate in the torque control device of FIG.

13 is a schematic front view showing a relationship among a rotor, a coil, and an iron core in the torque control device of FIG.

14 is a circuit diagram showing a connection state of each coil in the torque control device of FIG.

FIG. 15 is a schematic front view showing a relationship between a rotor, a coil, and an iron core in a conventional double four-pole three-phase small motor.

16 is a circuit diagram showing a connection state of each coil in the small motor of FIG.

17 is a diagram showing a direction of a magnetic field and an induced voltage accompanying rotation of a rotor in a generator / motor mode in the torque control device of FIG.

18 is a diagram showing the direction of a magnetic field associated with rotation of the rotor in another operation mode of the torque control device of FIG.

19 is a circuit diagram showing a configuration example of an amplifier connected between coils to be paired in the torque control device of FIG.

20 is a circuit diagram showing a configuration example of a switching circuit for each coil system in the torque control device of FIG.

FIG. 21 is a front view showing a second embodiment of the torque control device according to the present invention.

22 is a side view of the torque control device of FIG. 21. FIG.

23 is a schematic front view showing an arrangement example of each coil in the torque control device of FIG. 21. FIG.

FIG. 24 is a schematic front view showing the configuration of a rotor magnet in the torque control device of FIG. 21.

FIG. 25 is a circuit diagram and a connection diagram showing a connection state of coils in the torque control device of FIG. 21.

FIG. 26 is a schematic diagram showing a configuration as a twin drive motor in the torque control device of FIG. 21.

[Explanation of symbols]

 1 Rotational Force Control Device 2,3 Generator 4 Rotor 5,6 Coil System 5a, 5b, 5c, 6a, 6b, 6c Coil 7a, 7b, 7c Amplifire 10 Rotational Force Control Device 11 Yoke (Case) 12, 13 Cover 12a, 13a Bearing 14 Rotor 14a Rotating shaft 14b Magnet 15 Coil 16 Iron core 17 Intermediate frame 17a Positioning hole 18 Suppression plate 18a Hole 18b Slit 19 Amplifire 19a, 19b, 19c Individual amplifier 20 Operation amplifier 21,22,22 23 Switching Circuit 30 Flat Type Rotational Force Control Device 31 Stator Substrate 32 Coil 33 Rotor 33a Rotating Shaft 33b Magnet 34, 35 Cover 34a, 35a Bearing

Claims (6)

[Claims] 1. A device for controlling a rotational force, comprising two sets of coils each having a plurality of coils arranged at equal angular intervals, the coils being independent from each other so that coils forming a pair do not interfere with each other. A coil system configured as described above, a magnet that is rotatably disposed so as to face each coil of the coil system, and is connected between a pair of coils of each coil system,
A rotational force control device comprising: an amplifier that amplifies an induced voltage generated in a coil of one system and applies the amplified voltage to a coil of the other system. 2. The torque control device according to claim 1, wherein each of the coil systems is used as a generator and an electric motor, respectively. 3. The torque control device according to claim 1, wherein each of the coil systems is used as a generator together. 4. The torque control device according to claim 1, wherein the amplifier is configured so that gain can be adjusted. 5. The torque control device according to claim 1, wherein each of the amplifiers comprises a plurality of amplifiers having different gains, and one amplifier is selectively used by the switching means. 6. The torque control device according to claim 1, further comprising switching means for inverting the polarity of one of the coil systems.