Abstract: The invention relates to a circuit arrangement (100) for evaluating at least two switching states of an actuating element, having a moveable contact means (110) which is connectable to the actuating element, a first evaluation circuit (140a) with a first voltage divider, which has first node points (K1a, K2a, K3a, K4a, K5a) and a first tap (150a) for tapping off a first output signal (A1, A3, A5) of the first evaluation circuit (140a), at least one second evaluation circuit (140b) with a second voltage divider, which has second node points (K1b, K2b, K3b, K4b, K5b) and a second tap (150a) for tapping off a second output signal (A2, A4, A6) of the second evaluation circuit (140b), first contact surfaces (121a, 122a, 123a, 124a, 125a) which are each electrically connected to one of the first node points (K1a to K5a), and second contact surfaces (121b, 122b, 123b, 124b, 125b) which are each electrically connected to one of the second node points (K1b to k5b), wherein via the movable contact means (110), dependin

Abstract: An improved electromechanical Blade Clutch Actuator (BCA) that employs an electric gear motor system to provide more economical, convenient and reliable user control with an electric switch to engage/disengage the cutting blades. The user control may be a switch remotely mounted anywhere on the mower for greater design freedom due to the removal of the manual interface. The BCA also incorporates a novel slip clutch for overload protection.

Abstract: An illustrative example method of maintaining an elevator drive includes determining whether a humidity condition near the elevator drive is outside a desired range. When the humidity condition is outside the desired range and the elevator drive is idle, reactive power is provided to at least one component of the elevator drive to increase a temperature of the at least one component without using the elevator drive to operate an associated elevator system.

Abstract: In the method for increasing the availability of an elevator standing unused at a landing the ambient temperature of at least one electrical device of the elevator is measured; and when the ambient temperature falls below a threshold value, electric current is conducted to at least one electrical device of the elevator for warming the electrical device in question. The patent application also includes an independent claim for a system for increasing the availability of an elevator standing unused at a landing.

Abstract: A variable frequency drive motor system includes a variable frequency drive motor and a controller coupled to the motor. The controller includes a rectifier, a direct current (DC) link bus, and an inverter. The controller is configured to determine that a brake has failed. In response to the determination that the brake has failed, the controller is configured to determine that power to the controller from a power supply has been interrupted. In response to the determination that power to the controller has been interrupted and a determination that a DC voltage across the DC link bus is below a first threshold value, the controller is configured to drive the motor at a faster speed.

Abstract: A control system is provided for an electric machine having a rotor and a stator. The control system has a converter circuit in electrical communication with the stator and a controller in electrical communication with the converter circuit. The controller is configured to receive a first signal indicating a torque applied to or output by the rotor and receive a second signal indicating a rotational speed of the rotor. The controller is also configured to determine at least one characteristic of a pulse signal based on at least one of the first or second signal. The controller is also configured to inject the pulse signal into one or more phases of the stator via the converter circuit according to the determined at least one characteristic. The controller is also configured to determine a position of the rotor based on the injected pulse signal.

Abstract: The invention relates to a method for actuating inverter stages (2) switched in parallel, wherein each inverter stage (2) comprises several switching elements (3) with two switching states each. In accordance with the invention, the actuation of the inverter stages (2) occurs via a central control unit (6) which is connected to each inverter stage (2) via a serial data transmission path (5). Measures are proposed for transmitting the selected switching states from the central control unit (6) to the respective inverter stage (2) in order to ensure secure operation of the inverter stages (2) over a plurality of switching processes on the one hand and to reliably prevent functional impairments of the switching elements (3) by erroneous actuation, but to also carry out the actuation of the switching elements (3) of the inverter stages (2) in a sufficiently rapid way on the other hand in order to avoid impairing the quality of the output current formed by the inverter stage (2).

Abstract: A motor control apparatus includes: a driving control unit that performs driving control of a motor in accordance with a drive command; an interrupt control unit that starts and executes interrupt processing for performing the driving control at an interrupt cycle; a first processing unit that executes same first processing every time the interrupt processing starts; and a second processing unit that selects and executes a different piece of processing from second processing every time the interrupt processing starts. The interrupt control unit executes at least one piece of the first processing before executing the second processing in the interrupt processing.

Abstract: A radar antenna device is provided for rotating an antenna unit which successively emits transmission signals. It is configured to reduce the capacity of an electric power source for supplying electric power to a transmission circuit, a drive unit and the like. A radar antenna device is comprised with an antenna unit and a control unit. The antenna unit is driven by a drive unit to rotate and emits successively transmission signals generated by a transmission circuit into an outer space. After electric power is supplied to the drive unit to be driven, the control unit controls the transmission circuit in response to the transmission start signal from the transmission start signal producer so that the electric power for the transmission will be supplied to the transmission circuit.

Abstract: Tubular actuator (1) for driving a windable element in a building, comprising: in a tube (3) having a longitudinal axis (X-X?), a reduction gear and an output shaft (4) at a first end of the tube and a fixed-point (2) in two portions at a second end of the tube, the fixed-point comprising a first portion (20; 20?) at least partially outside the tube and a second portion (40; 40?) assembled in the tube, wherein the first portion comprises at least one torque and weight-bearing axial extension, this torque and weight-bearing axial extension being capable of being inserted into at least one recess of the second portion and being locked in translation along the longitudinal axis relative to the tube of the actuator by a first locking means (35, 37, 38).

Abstract: A vehicle 10 includes an electric actuator system 11 that operates according to a method 12 to move the vehicle 10 from an un-level condition to a level condition. The system 11 includes electric actuators 22-25 disposed substantially near the four corners of the vehicle 10 and a controller 32, 33 in electric communication with each of the actuators. The method 12 includes providing electric power at a first predetermined power level to two of the actuators to level the vehicle 10 along one of its X and Y axes. The method 12 further includes simultaneously sensing the attitude of the vehicle 10 along the other of its axes, and changing the power level provided to at least one of the powered actuators to a second predetermined power level to maintain the attitude along the other axis within a predetermined range.

Abstract: A powered screwdriver system includes an electric ratchet. In accordance with one aspect, the powered screwdriver system includes a driver housing and includes a motor disposed within the housing. A working end provides a rotational output and is mechanically coupled to the rotor. A power source provides power to the motor. A controller receives signals representative of a motor condition and, based on the received signals, controls the motor in a manner providing the electric ratchet.

Abstract: A trash can with a power operated lid can include a lifting mechanism with a motor, a lifting member, and a variable gear. In some embodiments, the motor is operably connected with the variable gear such that the motor can drive the variable gear and/or the lifting member. In certain implementations, the variable gear includes one or more teeth with varying tooth radii. In some variants, the variable gear and a clutch member are engageable and are configured to allow manual operation of the lid.

Abstract: In a motor, a stationary member is provided with a number M (M is a positive integer) of first poles within 360 electrical degrees at spaces therebetween. A plurality of windings are at least partly wound in the spaces, respectively. A movable member is movably arranged relative to the stationary member and provided with a number K (K is a positive integer) of second poles. The number K of second poles is different from the number M of first poles. A unidirectional current supply unit supplies a unidirectional current to at least one of the windings so as to create an attractive force between at least one of the first poles and a corresponding at least one of the second poles to thereby move the movable member relative to the stationary member.

Abstract: An ECU that controls a motor includes: a target current value setting unit setting a target current; a voltage detecting unit detecting a detected voltage on the basis of a detection signal from a voltage sensor; a voltage calculation unit calculating an estimated voltage on the basis of a power supply voltage of a battery; and an induced voltage observer calculating an induced voltage generated at the motor using an inter-terminal voltage based on the estimated voltage when the target current is set to a value other than zero; whereas the induced voltage observer calculates the induced voltage using an inter-terminal voltage based on the detected voltage when the target current is set to zero.

Abstract: Embodiments of the present disclosure relate to methods, systems and apparatus for mapping torque to current to generate current commands used to control operation of an electric machine. Based on a DC input voltage, lookup tables (LUTs) are selected. Each of the selected LUTs includes a plurality (B) of first entries that correspond a particular input value of an angular rotation speed of the electric machine, and a set of coefficients are output from each of the selected LUTs that can be applied within a first polynomial function to generate a plurality of first polynomial functions each having a different sets of coefficients. A plurality of particular output values for a first current command are generated via the plurality of first polynomial functions. The particular output values for the first current command can be interpolated to generate a final output value for the first current command.

Abstract: A method and system are disclosed for heating of robots in cold environments, whereby the robot possesses permanent magnet brushless or three-phase synchronous motors with three motor phases including three stator coils (L1, L2, L3) connected to an inverter controllable by a control-unit and with a rotor with permanent magnet excitation. A current can be applied to at least one phase of the stator coil (L1, L2, L3) of the motor such that, if the motor stands still, a directed magnetic flux (?) is created which interacts with the permanent magnets of the rotor in such a way that the resulting torque will be close to zero.

Abstract: A compressor apparatus includes a power source (26), a shell (12; 42), an electric motor (28; 52; 100; 200) having motor windings, and a control assembly (106; 206). The electric motor (28; 52; 100; 200) is located within the shell (12; 42). The control assembly a control assembly (106; 206) provides power to the motor windings from the power source (26) in two modes. A first mode provides power to the motor windings to generate heat without producing force output with the motor (28; 52; 100; 200). A second mode provides power to the motor windings to produce force output with the motor (28; 52; 100; 200). The control assembly (106; 206) activates the first mode for a selected time period prior to activation of the second mode in order to drive out a fluid (36) to reduce a risk of a flooded compressor start.

Abstract: An electrically driven mooring winch is provided. The mooring winch includes a winding drum, an AC motor configured to drive the winding drum, a frequency conversion unit connected to the AC motor, and a control unit configured to control the frequency conversion unit on the basis of an indicator for tension of the mooring rope. The control unit is configured to set a reference value of rotational speed of the AC motor to a predetermined value, drive the AC motor in one direction for a predetermined time interval, define a first value of a torque of the AC motor, drive the AC motor in an opposite direction for the predetermined interval, define a second value of the torque of the AC motor, and compute a torque estimate using the first and second values of the torque.

Abstract: Method and systems for testing an electric motor are provided. A switching circuit coupled to the motor is operated in a first mode causing current to flow through the motor such that the motor is actuated with near zero torque. A magnitude of the current is repeatedly adjusted between first and second values. The current flow through the motor is monitored.

Abstract: A move-sled-home device is used in an optical disc drive. The move-sled-home device includes a processing unit, a motor actuator, a sled, a sled motor, and a current-detecting unit. The processing unit outputs a control signal. The motor actuator generates a driving voltage according to the control signal. The sled motor generates a driving current according to the driving voltage to move the sled. The current-detecting unit is used for receiving and converting the driving current into an indicating signal, and issuing the indicating signal to the processing unit. During a move-sled-home action, the processing unit realizes a magnitude of the driving current according to the indicating signal, thereby determining whether the move-sled-home action is finished.

Abstract: An active pilot inceptor system includes a pilot inceptor, a multi-phase motor, and a motor control. The pilot inceptor is configured to receive user input and is operable, in response to the user input, to move to a control position. The multi-phase motor is coupled to the pilot inceptor to selectively supply haptic feedback thereto. The motor control is operable to selectively energize the multi-phase motor in a manner that causes the multi-phase motor to generate torque and supply the haptic feedback to the inceptor, and to selectively energize the multi-phase motor in a manner that the multi-phase motor does not generate torque.

Abstract: In a torque motor driving device for wire cut electrical discharge machines, a voltage waveform rectified by a full-wave rectifying circuit, not using a high-capacitance electrolytic capacitor, is applied as an AC voltage to a single-phase torque motor by a bridge circuit including semiconductor switches. A PWM signal whose duty is adjusted so that the current flowing through the torque motor matches an instructed value is generated and the generated PWM signal is used for the operation of the bridge circuit.

Abstract: An HVAC actuator configured to function in cold environments by providing a supplemental current component to an HVAC actuator in order to generate supplemental heat to warm the HVAC actuator.

Abstract: A motor control device includes a dq-axis current control unit for generating a dq-axis voltage reference based on a dq-axis current reference and a dq-axis current signal, an initial magnetic pole position estimation unit for estimating a magnetic pole position of the motor upon power-on to generate a magnetic pole position signal, and a magnetic pole position estimation precision confirming unit for supplying a current in a d-axis direction after generation of the magnetic pole position signal with the initial magnetic pole position estimation unit, and checking an error of the magnetic pole position signal based on an angle of movement of the motor.

Abstract: To reduce a leakage current when a motor for driving a compressor is energized, with the compressor unoperated. Setting the carrier frequency of an inverter at a value lower than that used during normal operation to cause phase interruption electrification of the motor.

Abstract: The present invention relates a motor controller and a motor control method of controlling a motor having a stator coil and a rotator.

Abstract: A detent mechanism includes: a control member to be operated rotationally; a rotary member including a pair of magnetic poles adapted to rotate in conjunction with the control member; a plurality of electromagnets provided along a rotational path of the magnetic poles of the rotary member; and a detent controller that has a detent energization pattern in which a current energization direction and an energization amount are determined for the plurality of electromagnets. The detent controller gives a detent in operation of the control member by applying an electromagnetic force between at least one of the plurality of electromagnets and the rotary member by energization control for the plurality of electromagnets according to the detent energization pattern.

Abstract: An electric jack load balancing method and device for reducing the difference in load carried by each jack of a pair of electric jacks while adjusting the attitude of a platform. The device includes a controller configured to reduce the difference in load carried by each jack of a pair of electric jacks. The method includes monitoring the power draws of the jack motors of the pair of electric jacks, comparing the ratio of the power draws of the jack motors to a predetermined desirable power draw ratio, and when the jack motor power draw ratio differs from the desirable power draw ratio, modifying the operation of the jacks in such a way as to decrease the difference between their actual power draw ratio and the predetermined desirable power draw ratio.

Abstract: A method and device for detecting the stroke limit of an electric motor-driven jack while the jack is being used to adjust the attitude of a mobile platform. A controller is programmed to detect when an electric jack motor has driven a jack to a jack stroke limit by monitoring one or more jack motor power draw characteristics and comparing those values to known values associated with the driving of a jack at or near the end of a jack stroke.

Abstract: An electric jack ground contact detection method and device for detecting ground contact of an electric motor-driven jack as the jack is being extended to adjust the attitude of a mobile platform. The device includes a controller that monitors the electrical power draw of an electric motor-driven jack while the jack is being extended for use in adjusting the attitude of a mobile platform. The controller recognizes jack ground contact when the monitored power draw value exceeds a ground contact power draw value consistent with jack ground contact. The controller calculates the ground contact power draw value as equaling the sum of a dynamically-adjusted threshold power draw value associated with jack extension before ground contact and a power draw increase value equaling an amount of additional power that the jack is known to draw as a result of jack ground contact.

Abstract: A control apparatus for an electric railcar that provides control so that when rotational speed of a motor decreases below a required value, torque of the motor will decrease at a required rate of change, a current limiter for limiting a torque current command “(A)Iqp” output from a current command arithmetic unit is provided to ensure that when the rotational speed of the motor decreases below the required value, the torque current command will be limited to a command value “(B)Iqp” smaller than that command value, and to ensure that a carrier frequency at which PWM signals are created when switching elements of the electric power converter are controlled by carrier generator is controlled to become lower than a carrier frequency existing when the rotational speed of the motor decreases below the required value.

Abstract: A detector (20) detects the position of a motor, and a differentiator (26) calculates the speed of the motor from the position of the motor. An command generation section (11) fixes a position command to a current position. A position control section (12) generates a speed command such that the position command matches the position of the motor. A speed control section (13) generates such a torque command that the speed command coincides with the speed of the motor. An adder (16) adds a high-speed sweep waveform generated by a random signal generation section (15) as torque random to a torque command output from a torque filter section (14), thereby outputting a new torque command. A current control section (17) converts the torque command into a current command, thereby driving a motor (18). A frequency response measurement section (21) receives a torque command output from the adder (16) and a motor speed calculated by a differentiator (26) and measures a frequency response.

Abstract: A motor controller includes DC motor, driving mechanism, voltage generator circuit and control unit. The driving mechanism moves an object having a predetermined mass against a load applied to the object and by transmitting a rotational force of the motor to the object. The voltage generator circuit generates first and second voltages. The first voltage is high enough to rotate the motor to such a degree as to get the object moved by the driving mechanism. The second voltage has the same polarity as the first voltage and has such amplitude as to prevent the motor from rotating either in a backward direction due to a cogging torque or in a forward direction. The control unit controls the voltage generator circuit in such a manner that the voltage generator circuit applies the second voltage to the motor after having applied the first voltage to the motor.

Abstract: A motor controller includes DC motor, driving mechanism, voltage generator circuit and control unit. The driving mechanism moves an object having a predetermined mass against a load applied to the object and by transmitting a rotational force of the motor to the object. The voltage generator circuit generates first and second voltages. The first voltage is high enough to rotate the motor to such a degree as to get the object moved by the driving mechanism. The second voltage has the same polarity as the first voltage and has such amplitude as to prevent the motor from rotating either in a backward direction due to a cogging torque or in a forward direction. The control unit controls the voltage generator circuit in such a manner that the voltage generator circuit applies the second voltage to the motor after having applied the first voltage to the motor.

Abstract: In an air conditioner having a control unit receiving a power from a switching power supply, a supplied voltage for the control unit is reduced to a possible lowest voltage for the unit to operate. This arrangement provides the air conditioner with less electromagnetic wave noise of the switching power supply, with a quick check and repair, and with having a motor-driven compressor quick start.

Abstract: The motor-generator circuitry of a flywheel energy conversion device can be utilized to preheat the rotor of the flywheel device. It may be desirable to preheat the rotor prior to normal operation because a rotor operating in cold temperature may be more susceptible to brittle fracture or other damage than a rotor operating at a specified operating temperature. The present invention may utilize the principle of induction heating to preheat the rotor. In preferred embodiments, high frequency current may be passed through armature windings of the motor-generating circuitry to induce surface currents into the periphery of the rotor. Heat may then be generated in portions of the rotor receiving the induced currents and then radiate from those portions to raise the rotor temperature to a desired level.

Abstract: The present invention relates to a motor and especially to a technique for maintaining constant power consumption in preheating a compressor motor in an air conditioner. An object thereof is to permit constant preheating of the motor irrespective of variations in receiving voltage. To accomplish this object, switching control of an inverter (15) that applies a three-phase current to a motor (30) is performed by a control circuit (20) in accordance with a duty based on detected values of voltage (Vm) and current (Im). This duty decreases with increasing receiving voltage.

Abstract: To make it possible to provide high quality heating or warming with low environmental pollution for a low environmental pollution vehicle such as an electric vehicle or a hybrid vehicle, an automotive air-conditioning apparatus has a hot water circuit that includes a hot water heater (heat source unit), a hot water circulating pump and a heater core to thereby perform a heating operation for heating passenger compartment air wherein, an electric motor is excited under the condition that the rotation thereof is fixed to thereby generate heat in the electric motor. The generated heat is utilized as a heat source for the hot water heater. The restricting mechanism may include two electric motors which are rotated in opposite directions to each other or a lock mechanism.

Abstract: A control device for a diaphragm pump to feed a filter press or similar user unit comprising a three-phase electric driving motor for the pump which is connected to a supply main via a variable-frequency converter, which frequency converter has an analogue output at which a signal will appear which corresponds to the respective motor torque, a standard r.p.m. set-point adjuster to the input of which the actual signal is provided via an inverter and in which a graph is stored which produces an interdependences between the motor torque and the speed such that if the actual-signal rates are small the graph for the speed runs along a constant maximum value and if a preset rate is reached for the actual signal it gradually declines to a minimum value, and an attenuation member for the actual signal.

Abstract: A laboratory centrifuge, whose centrifuge rotor is mounted in a bowl (6) which can be brought to the correct temperature and which is set up in particular for the setting of temperatures below the ambient temperature, is provided with a drive means comprising at least one electric motor (1) which is equipped with standstill heating means to maintain the temperature within the motor above a dew point temperature independent of a material-specific cooling temperature within the bowl (6). The standstill heating is provided by the winding system of the stator and/or of the rotor of the electric motor (1) and is connected to a control device (21). The formation of condensation within the motor and the consequential adverse effects arising from this, such as for example corrosion damage to electrical contacts as well as to the bearings of the motor shaft, can be avoided by this means. Also, no additional components are needed for the actual standstill heating.

Abstract: A control device for a DC motor driving a diaphragm pump including a pulse generating integral circuit and a variable voltage setting integral circuit. The variable voltage setting integral circuit sets a pulse-base voltage at a level such that the DC motor is not rotated when no pulse is applied, thereby a high voltage overshoot generated at the rising and the falling point of an electrical pulse is restricted. Discharge of the diaphragm pump is accurately regulated by means of modifying frequency, voltage, and duty ratio of the pulse.

Abstract: Torque is distributed by calculating first and second torque commands using a requested torque and a ratio of speeds of first and second wheels and limiting them in accordance with respective torque command approved ranges and approved change rates; converting the limited torque commands to horsepower commands and limiting them in accordance with respective horsepower command approved ranges and approved change rates; and converting the limited horsepower commands to present torque commands. Maximum horsepower available is determined by using an engine speed to determine a nominal amount of available horsepower; applying a desired load status signal and an actual engine load status signal to a proportional-integral A regulator; and using the nominal amount of available horsepower and an output signal of the regulator to determine the maximum amount of available horsepower.

Abstract: A method for removing moisture from an induction motor having at least two phase windings with each phase winding coupled by a first respective parallel combination of a first switch and a first diode to a positive voltage line and a second respective parallel combination of a second switch and a second diode to a negative voltage line includes supplying voltage to the positive and negative voltage lines and switching ON and OFF selected ones of the first and second switches to provide a current to preheat the induction motor. The provided current can be a substantially DC current or a substantially sinusoidal current.

Abstract: The present invention is a temperature control system for a motor coupled to a power source. The motor has at least one winding which serves as a heater and temperature sensor as well as producing torque during normal operation. The mathematical relationship between temperature and resistance in the motor winding is used to determine the winding temperature. The actual winding temperature is then compared to a desired operating temperature, and the current to the motor winding is controlled so as to keep the motor temperature within a desired range.

Abstract: A reaction force generating apparatus is provided which generates a reaction force for a rotationally operated member to be manually or mechanically operated. An alternating motor is provided that has a stator with three-phase coils; a rotor including permanent magnets; and a rotational axle extending from the center of the rotor and having a rotationally operated member attached to its one end. A direct voltage is supplied to the three-phase coils of the alternating motor, thereby producing a magnetic field on the stator. The magnetic field is oriented in one direction and cooperates with the permanent magnets to generate an electromagnetic attraction force for maintaining the operated member in a predetermined angular position. When the operated member is moved, a torque, or reaction force, is generated to restore the initial position of the operated member.

Abstract: A limited angle torque motor and control circuit are adapted to convert an electrical demand signal of varying magnitude into a motor shaft position relating to the magnitude of the demand signal. More particularly, a bidirectional motor is provided having two stator coils wound in phase opposition, so that the torques produced by the currents in the opposedly wound coils are summed such that the coil having the greater current controls the direction of rotor rotation. A position sensor provides feedback of the present shaft position; the magnitude of the feedback signal being indicative of motor shaft position. Finally, an electronic control circuit which is responsive to both the demand signal and the shaft position signal is provided and has two outputs for simultaneously driving the current in each respective stator coil. A summing means is included in the control circuit for combining the shaft position signal and demand signal so as to produce an error signal.

Abstract: A motor control method and apparatus for a hoist is disclosed in which a drive motor is connected to an adjustable frequency power supply in which the frequency of the power supplied to the motor can be selectively varied. At the initiation of a hoist operation, when the hoist brake is holding the motor and an object constituting a load on the motor stationary, power is supplied to the motor at a predetermined low frequency which is sufficient to provide load holding torque upon release of the brake. The actual current level of the power supplied to the motor is sensed at the initiation of the hoist operation and a signal representative of that current level is compared with a reference signal representative of a current level which is sufficient to provide the load holding torque. If the signal representative of the actual current level of the power supplied to the motor exceeds the reference signal, an output signal is provided which will result in the release of the hoist brake from its holding condition.

Abstract: There is disclosed a method of controlling a voltage-to-frequency inverter which controls an induction motor by the use of an open-loop system. The motor drives a machine such as a crane, and is braked by a mechanical brake. When the machine is started or stopped, a low-frequency voltage is supplied to the motor so that the motor may produce a torque necessary to hold the load, until the actuation of the mechanical brake ends completely.

Abstract: An actuator comprises a housing; a permanent magnet arranged in the housing to be rotatable; an output shaft coupled to the permanent magnet; a stator fixed in the housing in such manner to be separated from the outer peripheral surface of the permanent magnet in diametrical directions, the stator having its inner peripheral surface provided with alternately projections and spaces; coils on the stator, and excitation switching means for switching the excitation of the coils; wherein the number of the projections and the number of the spaces in the stator is three times that of the pole pairs of the permanent magnet, and wherein the excitation switching means is connected to the coils so that the magnetic field which attracts the permanent magnet is developed by the coils which lie at the respective sides of the space opposite to the magnetic pole reversing portion of the permanent magnet, the space being corresponding to the position where the magnetic pole reversing portion of the permanent magnet is desired