Abstract: A method of operating a four quadrant motor involves (a) monitoring a motor voltage magnitude request signal which varies between zero and a maximum value and (b) monitoring a motor direction request input. In step (c), based upon the request signal and input monitored in steps (a) and (b), a voltage request reference signal is established. In a step (d) a current magnitude request signal is monitored and in a step (e) a first current request reference signal and a second current request reference signal are established based upon the signal monitored in step (d). In a step (f) a voltage across a current sense resistor of a bus connected for powering the motor is monitored and in a step (g) a sense resistor reference signal is established based upon the signal monitored in step (f). In a step (h) the first current request reference signal is compared with a feedback current signal and in a step (i) the second current request reference signal is also compared with the feedback current signal.

Abstract: The present invention relates to an electronic circuit that interrupts the application of electrical power to a motor after a predetermined period of time. The electronic circuit is disposed between a motor which drives a device from an initial position to a final position and a switch movable from a first position to a second position. A battery which supplies the electrical power for the motor is engaged with the switch. The control circuit includes at least two energy storage devices. Depending on the position of the switch, one of the energy storage devices will be fully charged by the battery source. Altering the position of the switch will cause the fully charged energy storage device to begin its discharge and the alternate energy storage device will be “instantly” charged. During the time that both energy storage devices have a significant charge on them, a control signal is generated.

Abstract: A motor for a power tool adapted to be powered by either an AC power source or a DC power source. The motor 12 includes a permanent magnet field 30 having an armature 34 disposed within the field. The armature 34 includes a shaft 36 having a DC commutator 38 disposed at one end of the shaft. The DC commutator is coupled to a first armature winding. An AC commutator 42 is disposed coaxially over a portion of the DC commutator 38 and is coupled to a second armature winding 44. A first pair of brushes 46 are disposed on the DC commutator 38 for coupling power from a DC power source to the first armature winding 40. A second pair of brushes 48 couple rectified AC power to the second armature winding 44. A power module including an AC/DC selector switch 26 enables a user to select whether AC or DC power is to be used to power the tool.

Abstract: A device for determining a rotational number of an electric dc motor which drives a moving body of an automobile accessory such a sunroof, or a glass pane of a power window includes a switched capacitance filter for eliminating noise from the motor, a cutoff frequency of the switched capacitance filter being dependent on a clock input thereof; a pulse shaping circuit for generating a ripple pulse signal indicative of the rotational number of the motor by wave-shaping an output of the switched capacitance filter; and a pulse generating circuit providing an output pulse signal so as to establish a condition wherein the frequency of the ripple pulse signal is equalized to the cutoff frequency of the a switched capacitance filter.

Abstract: An apparatus and method for driving a motor with a reduced current flowing in the motor, as well as reduced vibrations of the motor at a start-up is provided. The motor driving apparatus has a position detector for detecting a position of a rotor of a brushless DC motor, a DC/AC converter for converting a DC voltage derived from a DC power supply into an AC voltage, and a controller for controlling the DC/AC converter to control the conduction of a stator winding of the motor. For a start-up of the motor, the controller positions the rotor by supplying a current to a first conduction phase of the stator winding, and then once turns off the conduction. After that, the controller controls the DC/AC converter to rotate the rotor by supplying current to a second conduction phase of the stator winding, and to start a position detecting operation after a specified time elapses since the rotor starts rotation.

Abstract: A full wave signal E is compared with a trapezoidal wave signal G in a comparator to output a second comparison signal H. The full wave signal E is obtained through full wave conversion applied to a sine wave signal of a Hall element. The trapezoidal wave signal G is obtained by sampling and holding an attenuated signal F, obtained by attenuating the full wave signal E, at a trailing end of a first comparison signal D, and nulling the attenuated signal F at a subsequent leading end thereof. Then, the first and second comparison signals D, H are added up in an OR circuit to output an addition signal K, so that no drive current IL flows through the driving coils at a point near the former and latter halves of a phase changeover point. Near the former half of a phase changeover a point, the drive current IL is nulled before counter electromotive force Ec becomes small, enabling motor noise reduction.

Abstract: A method and apparatus for driving a decelerating a multi-phase wound electric motor having a rotor and multiple phase coils arranged as a stator, wherein each phase coil has a first terminal and a second terminal, and the first terminals of the phase coils are connected together at a center tap. Commutation signals in response to BEMF voltages in the phase coils select a first and a second coil in each commutation state, such that when energized the first and second coils are capable of providing forward torque to the rotor based on the rotational position of the rotor relative to the phase coils. In each commutation state, the second terminal of the first is electrically connected to an upper voltage supply. For applying forward torque to the rotor, the second coil is electrically connecting the second terminal of the second coil to a lower voltage supply, wherein the upper voltage supply is at a higher voltage than the lower voltage supply.

Abstract: A direct current motor for use in a closed-loop control system is disclosed that includes a rotating commutator having a plurality of slots, a plurality of windings, the number of windings that conduct current corresponding to one less than the number of slots of the commutator, and a plurality of brushes that are configured so that application of a direct current voltage across the brushes results in a current flow in at least one of the windings which causes the commutator to rotate. Continuous application of the direct current voltage across the brushes causes the current to flow in a varying number of the current conducting windings as the commutator continues to rotate, the number periodically varying from all of the current conducting windings to the at least one current conducting winding.

Abstract: A control method and an apparatus for precisely driving a motor of a head drum assembly by using impulse generation magnets in a video cassette recorder is disclosed. While a displacement of a hall sensor installed on a stator side is produced with respect to magnetic fluxes generated from impulse generation magnets installed on frequency generator magnets of a rotor, an impulse detection signal is supplied from the hall sensor. After a zero-crossing signal obtained by executing a zero-crossing detecting process with respect to the impulse detection signal is compared by a driving controller with a count signal obtained by counting a pulse number of the impulse detection signal, a next drive order of a switching section for driving the motor with reference to a present position of rotary magnets of the rotor is determined, and a rotational position of the motor is precisely controlled according to the rotational speed control signal which is computed on the basis of the determined drive order.

Abstract: A speed control device particularly adapted for use with electrical motor-driven apparatus, stationary tools and hand tools having digital operator input controls. A semiconductor switching device controls a percentage of ON time for the electric motor in the electric motor-driven apparatus. Discrete and repeatable settings are selectable to a user through digital input switches.

Abstract: As stated earlier, the technical purpose of the present invention is to solve inconvenience in use and installation of the AC motor with a controller, and to provide the AC motor available for mass production at a low cost by installing an airtight and compact controller within the case of the AC motor and by setting the sensing wheel in one part of the driving shaft making it possible for the rotative speed primary means integrated to the said controller to sense the driving speed.

Abstract: An electric motor (10,110,210) comprises a TRIAC (16, 116, 216) for controlling the application power to the motor and a switch (18,118,215a) for controlled cut-off of the power supply. Upon operation of a switch (15b, 115B, 215B) for short-circuiting of motor from a power supply (13, 14; 113,114; 213,214) armature the power is supported to the field windings (12,112,212) with at least one predetermined braking voltage. Upon exhaustion of a braking period, the switch mechanism operates to cut off power completely from the motor.

Abstract: An electric motor (10, 110, 210) is coupled to a TRIAC (16, 116, 216) for controlling the application of power to the motor from a power supply (13, 14; 113, 114; 213, 214) and a switch (18, 118, 215a) for controlled cut-off of the power supply. Upon operation of a switch (15b, 115b, 215b) for short-circuiting an armature (11, 111, 211) of the motor, power is supplied to field windings (12, 112, 212,) of the motor with at least one predetermined braking voltage. A braking period can be established following short-circuiting of the motor by (1) a prescribed delay, (2) comparing the changing voltage level across the TRIAC (16, 116) and cutting the power off when the voltage level rises to a prescribed level, or (3) monitoring the decreasing speed of the motor to cut off the power when the speed decreases below a prescribed level.

Abstract: A rotating field, synchronized electric generator or motor in which the magnetic field that the armature produces can rotate relative to the stator at a speed significantly different from that of the armature, under electronic or other control that obviates the need for a mechanical torque-carrying gearbox that can be used for a similar purpose in a synchronized generator or motor.

Abstract: A braking circuit for braking an electric motor having an armature and run and brake windings, which includes a switching circuit disposed between a source of electrical power and the run winding, this circuit being operable to disconnect the run winding from the source of electrical power. The braking circuit further includes a switching mechanism operable to connect the brake winding in order to brake the electric motor. The switching mechanism preferably connects the brake winding after a predetermined period of time has elapsed from the disconnection of the run winding. This braking circuit can be used in a saw for braking the saw's blade.

Abstract: A rotary speed control circuit for feeding a dc universal motor for driving a washing machine. A rectifier and a smoothing capacitor derive the operating voltage of the motor from the mains ac voltage and provided for control of the rotary speed is a regulating device (R) which controls a power stage for the motor, the power stage including a power switch (TR1) and a commutation diode (D1) in the topology of a low-setting device. The power stage feeding the motor includes a high-setting inductor (L) and can be switched over from the topology of a low-setting device to the topology of a high-setting device.

Abstract: A braking circuit for a universal motor is proposed, in which, during braking, the at least one field winding is connected in series with the armature by means of a semi-conductor switch, preferably a field effect transistor or a thyristor. Since the semiconductor switch can also be switched intermittently and with a time delay, not only is it possible to regulate the braking current simply, but there is also a reduced formation of sparks at the collector. The reduction in the contact erosion lengthens the service life and increases the reliability of the motor.

Abstract: A drive current and a regenerative current are alternately applied to a motor during a PWM (pulse width modulation) time period. The regenerative current is produced by an electromagnetic induction of an armature and flows in the opposite direction as the drive current. Therefore, a rotating speed of the motor is reduced, so that a speed-reduction following characteristic for the motor is improved. By varying the duty factor, the lengths of time during which the drive current and the regenerative current are flowing can be controlled. Thus, the speed of the motor can be controlled.

Abstract: In a series-wound motor with electric brake, which comprises an armature provided with an armature winding and at least two exciter coils mounted on pole shoes as well as switchgear which, in the operative phase of the motor, serially connect the exciter coils with the armature winding and connect the serial connection to terminal clamps for the operating voltage and which, in the braking phase, interrupt the connection to the terminal clamps and short-circuit the armature winding by the parallel connection of a winding, an independent optimization of the braking behavior is made possible in that at least one of the exciter coils is subdivided into two part windings and in that, when braking, one of the part windings has its polarity changed and is short-circuited with the armature winding.

Abstract: An H-Bridge motor controller having a floating, electrically isolated high side FET driver design where the motor driver circuity is electrically isolated from the logic circuitry. Back EMF generation during motor operation is minimized by employing a "fifth" power transistor to the H-Bridge that connects the motor coil to ground when the other transistors in the H-Bridge are turned off, so as to provide a direct path for the unused energy to be removed from the driver circuit without interfering with the normal switching of the FETs. Alternatively, back EMF generation is minimized by applying switching signals to the H-Bridge where, instead of turning the low side FET drivers between motor clocks, the low side FET drivers are both turned on during the "off time" period, so as to connect both ends of the motor coil to ground during the "off" period, thereby draining the coil of unused energy.

Abstract: An improved phase controller is operatively connected to the operating lever or trigger of an electrically powered tool for supplying its motor with electric power from an ac power supply. It includes a device for establishing a divisional voltage derived from the ac voltage across the electric power supply. A variable resistor-and-capacitor series-connection is connected across the motor-and-power supply series-connection. A device provided for supplying the ac motor with electric power when the charging voltage across the capacitor rises above the divisional voltage. The variable resistor is operatively connected to the operating lever, and the capacitor can be charged with electricity at a charging rate which is determined by the variable resistance and the fixed capacitance under the control of the operating lever.

Abstract: A circuit and method for controlling the speed of a universal motor driven by an AC source is disclosed. The method includes the steps of measuring a value of a temporal property of a current through the motor and determining a speed of rotation of the universal motor using the temporal property. The method for controlling the speed of the universal motor further includes comparing the determined speed of rotation with a desired speed of rotation and adjusting the current through the motor so that the speed of the motor approaches the desired speed of rotation.

Abstract: A hybrid DC motor controller is provided for driving a DC motor. A switch is connected in series with the DC motor, and a capacitor is coupled in parallel with the DC motor and the switch. The speed of the DC motor is controlled by the capacitor voltage and the duty cycle of a pulse-width modulated (PWM) signal supplied to the switch. The hybrid controller combines a motor speed control loop with a PWM optimization loop. The motor speed control loop generates a PWM signal in response to the speed of the DC motor and conducts that PWM signal to the switch to control the DC motor. The PWM optimization loop includes a controller that is responsive to the PWM signal and an AC voltage signal. This controller compares the PWM signal with a PWM signal setpoint, and drives the PWM signal toward the PWM signal setpoint by adjusting the capacitor voltage in response to the comparison between the PWM signal and the PWM signal setpoint.

Abstract: A harmonic current attenuating device of a motor for attenuating a harmonic current generated from the motor by controlling the rotation speed by varying a sine wave voltage into a non-sinusoidal wave by phase-controlling the sine wave voltage, comprises a reactor having an E shape core, a coil wound to the E shape core and an I shape core.

Abstract: The invention relates to a method for driving an electric motor (1) which is employed, in particular, in manually guided electric tools, such as drilling machines, screwing machines or the like. Variable pulses of an electric voltage are applied to the electric motor (1) in such a way that the rotor of the electric motor (1) moves at a rotational speed which can be set. In order that the rotor of the electric motor (1) moves intermittently or abruptly, at least parts of at least individual pulses are blanked by superposition of a pulse interval having a zero voltage. A circuit arrangement for a method of this type has control electronics (5) and an electronic power switch (4), such as a triac, a transistor, an IGBT or the like, which is switched by the control electronics (5) in such a way that the variable pulses can be applied to the electric motor (1) via the electronic power switch (4).

Abstract: A circuit and method to clamp a node of a power device connected to a driving node of a polyphase d-c motor to a reference potential during a powering off of the drive includes a current mirror and a comparator. A first input of the comparator is connected to the reference potential, and a second input is connected to the driving node. The reference potential may be a ground potential, or, preferably, the potential at another driving node of the motor. An output of the comparator is connected to a first side of the current mirror. A circuit is connected to apply a current reflecting the output of the comparator to a low side driver connected to the node.

Abstract: Current control apparatus of DC motor includes current amplifying means for detecting the current amount at the rear end of the motor and amplifying the current value; on-off control means for comparing the input current with the current supplied from the current amplifying means and outputting an on-off control signal according to the current amount; and microcomputer for controlling the duty value of the pulse wave of a predetermined frequency occurring in accordance with the on-off control signal from the on-off control means and controlling the on-off time of the chopper transistor.

Abstract: A universal motor which operates an electric tool is controlled by a phase-gating controller for determining variable rotational speeds. The phase-gating controller can be switched over to wave-packet-controlled phase-gating control mode in order to be able to switch over between a continuous speed-torque characteristic and pulsating operation.

Abstract: In an ordinary DC motor in a windshield wiper, operating speed tends to increase as the motor brushes become seated. The invention counteracts this tendency by providing a brush geometry which causes the effective angular position of a brush to change during seating. The change is in a direction which tends to reduce speed.

Abstract: An apparatus for driving an electric motor, including a full-wave rectifier which rectifies an alternating current supplied from an alternating-current power supply, and supplies a full-wave rectified current to the motor, a chopper which chops the full-wave rectified current supplied from the rectifier to the motor so that the chopped current is applied to the motor, and a control device which generates a chopping pulse signal having a first signal characteristic corresponding to a given motor control target and a second signal characteristic to reduce an alternating-current component of the full-wave rectified current supplied to the motor, the control device supplying the chopping pulse signal to the chopper so that the chopper chops the full-wave rectified current according to the chopping pulse signal.

Abstract: A control system for a three phase brushless motor suitable for use in a three and a half inch flexible magnetic disk drive. The control system needs but one Hall effect sensor for providing a rotor position signal indicative of the angular position of the rotor relative to stator windings. Comparators compare the rotor position signal with reference voltages and provide moment signals indicative of the moments the rotor position signal crosses the reference voltage levels. Three phase motor excitation control signals are produced by counters which count clock pulses for preset periods in response to the moment signals. Motor speed is controlled on the basis of not only the actual motor speed but also the phase difference between the clock pulses and a signal indicative of the moments the rotor position signal crosses zero.

Abstract: A speed control method for controlling an electric motor by varying the supply duration of the motor, comprises the steps of:initially storing, for a constant speed to be obtained, the curve of the current in the motor as a function of the supply duration;selecting a supply duration;measuring the resulting current in the motor; andcorrecting the supply duration so that the point defined by the supply duration and the resulting measured current converges towards a point of the curve.

Abstract: A speed control method for a brushless DC (BLDC) motor capable of solving the phases distortion problem generated between an applied voltage and a winding current of the motor during a high speed rotation of the motor. According to the method, the present revolution per minute (RPM) of the motor is detected, and an output control wave of a new pattern is obtained utilizing a value of an advance phase angle determined according to the detected RPM of the motor. Accordingly, the rotation of the motor is controlled by the new pattern control wave in response to the motor rotation of a high, intermediate or low speed, and thus the phase distortion generated between the applied voltage and the winding current of the motor can be prevented, resulting in the improvement of the motor efficiency. The method may be applied to a typical sensorless BLDC motor.

Abstract: A motor braking circuit arrangement, for use with a series/universal motor and a power supply for supplying power to the motor, including two separately actuable switches electrically interconnecting a separate braking winding with the motor to effect braking when either of the two switches are deactuated. The circuit arrangement includes a field winding wound about the motor stator and electrically connected in series with the motor armature winding. The separate brake winding is wound about the stator. The two switches are series-connected, and each switch is capable of assuming a first position associated with normal motor operation and a second position associated with motor braking wherein the separate brake winding is electrically connected in parallel with the motor armature. The switches may be single-pole, double-pole or combinations thereof.

Abstract: A series-wound motor, wherein, for braking purposes, the polarity of the armature of the motor is reversed for the opposite direction of rotation. The current supply for the motor is maintained until the armature comes substantially to a standstill and subsequently, the current supply to the motor is interrupted. The braking time is controlled in dependence upon operating parameters. For example, the braking time can be controlled by a predetermined time constant for the interruption of the current supply. To prevent running in the opposite direction, a reversal preventing device can be provided.

Abstract: The series field winding of a compound or series motor includes a plurality of taps and, connected in parallel therewith, a transient storage element such as a capacitor, and a flywheel diode. The taps are controlled by switches in the form of transistors or thyristors which are turned on and off by a central control unit in response to setting of the speed and, optionally, various feedback devices such as a motor speed detector, an armature EMF detector, or a load current detector. The transient storage device replaces conventional linear impedance or linear power elements in order to prevent loss of power as the armature voltage is increased.

Abstract: The method and the arrangement for temperature monitoring of universal motors based upon a resistance measurement of a field winding, wherein a DC current component of low magnitude is superimposed upon the motor current for elimination of the complex values of the AC current impedance, and wherein the voltage drop in the field winding is amplified and freed from the AC voltage component and is compared as a DC voltage component proportional to the ohmic resistance of the field winding to a temperature independent DC voltage component, which is obtained in an analogous manner from a current measuring shunt, through which the motor AC current, including the superimposed DC current component, flows.

Abstract: A low voltage power supply which uses a low voltage transistor in conjunction with a winding of an electric motor and the high voltage motor commutation transistors. The motor winding is energised by the commutation transistors for example during use of the motor, and the low voltage transistor is used to divert current from the energised motor winding at desired intervals to provide the low voltage power supply. The low voltage supply may be used in an appliance such as a laundry machine for supplying the motor control circuitry and auxiliary devices for example, a drainage pump and water supply control valves.

Abstract: An electric powered bicycle having a dip sensor or switch and/or a gradient sensor or switch. The bicycle comprises front and rear wheels each rotatably supported by its frame; a chain slung between said wheels and a chain set for transferring manual power to said wheels; an electric motor coupled to one of said wheels for driving said wheel directly; and a power supply capable of supplying electric power to said motor. The dip or gradient sensors are associated with a pulse width modulation circuit.

Abstract: An electric motor for portable machine tools, comprising an output shaft for operating, means for sensing the speed of said output shaft; means for sensing the magnitude and the phase of the input voltage of the electric motor itself; means for sensing the electric current absorbed by the load, microprocessor means programmed for processing the detected values sensed by said means for sensing; means for generating an acceleration ramp at the starting; means for generating a deceleration ramp at the stopping, as well as means for generating the cruise speed of the tool, voltage controlled by said microprocessor in response to said detected values processed by itself, and means for controlling the forward running, reverse running and the run storing.

Abstract: A new instrument for monitoring the condition and speed of an operating electric motor from a remote location. The slip-poles component is derived from a motor current signal. The magnitude of the slip-poles component provides the basis for a motor condition monitor, while the frequency of the slip-poles component provides the basis for a motor speed monitor. The result is a simple-to-understand motor health monitor in an easy-to-use package. Straightforward indications of motor speed, motor running current, motor condition (e.g., rotor bar condition) and synthesized motor sound (audible indication of motor condition) are provided. With the device, a relatively untrained worker can diagnose electric motors in the field without requiring the presence of a trained engineer or technician.

Abstract: An apparatus for driving an electric motor according to a given control target, including a control circuit which generates a control command signal corresponding to the control target, a chopping signal generator which generates a chopping signal based on the control command signal generated by the control circuit, a full-wave rectifier which rectifies an alternating current supplied from an alternating-current power supply, and supplies a full-wave rectified current to the motor, and a chopper which is connected in series to a series circuit including the motor and the full-wave rectifier and which chops the full-wave rectified current supplied to the motor according to the chopping signal generated by the chopping signal generator.

Abstract: A control system for controlling the excitation of a DC motor or generator activates an auxiliary power source to increase the magnetic field intensity in one or more field windings of the motor or generator when the intensity falls below a desired level, especially during a low voltage mode of operation. The system includes an excitation control system which generates a feedback signal for controlling a subexciter circuit included in the auxiliary power source in response to signals generated from detection elements that monitor various operational conditions of the motor or generator.

Abstract: A control circuit is proposed, which can be used for the phase-shift control of an electric motor in an a.c. voltage supply line. The ground connector of the control circuit, together with the cathode of a semiconductor switch (triac), is directly connected with load current circuit. Because of this, it is possible to do without potential-separating means when it is intended to feed signals at the load current circuit directly into the control circuit. An auxiliary voltage source is connected between the synchronization input and the ground connector to maintain the function of the synchronization input.

Abstract: A series universal AC/DC motor is controlled by switching the phase angle of an AC signal with a triac power switch in response to a motor control providing a phase-locked loop velocity control. A speed command circuit provides a reference frequency corresponding to a selected motor speed. The reference frequency is compared to a feedback frequency representing actual motor speed. An error signal representing the phase difference between the reference and feedback frequencies is compared to a ramp signal produced by the AC power source, and a resulting trigger pulse is used to control the triac power switch, thereby regulating the speed of the motor.

Abstract: Sub-excitation of a series-type excitation magnetic field winding for a DC motor or generator is provided by an auxiliary power supply which, when the voltage in the main circuit is low, supplies voltage through a diode to the main series field winding in order to keep the voltage at or near saturation and thereby improve motor efficiency.

Abstract: This invention is for incrementally controlling energizing and de-energizing of at least two electrical motors in which motor armatures are mechanically coupled to a single mechanical member and in which motor stators are mechanically referenced to a second mechanical member. By energizing and deenergizing two or more electric motors of different force and torque capability coupled in this manner it is possible to provide increments of force and torque as small as the incremental capability of the smallest motor and to provide a large number of force and torque increments which can approximate a smooth control of force and torque in forward and reverse directions. The type of motor used for this invention is a multiple-two-node-open-circuit-armature-winding motor as disclosed in the referenced patents. This type of motor offers various levels of energizing the motor to the full force and torque capability.

Abstract: Dynamic current feedback for a main motor-generator is provided by an auxiliary generator which supplies power directly to the main excitation field winding of the main motor-generator, rather than to an auxiliary shunt field winding as in a prior design, the main auxiliary generator in turn being driven by a current-follower type DC motor whose speed depends on the amount of current passing through the main motor-generator armature or the voltage drop across the main motor-generator series winding in the case of a series or compound main motor-generator. The current supplied by the auxiliary generator to the main excitation field winding of the main motor-generator can have either the same polarity as the main excitation field winding of the main motor-generator, or an inverse polarity, to provide positive or negative feedback.

Abstract: A governor circuit for limiting the top speed of a universal series or compound motor. The governor circuit includes a voltage detector for detecting a selectable threshold voltage across the armature of the motor, and a current shunting circuit which is triggered by the voltage detector when the armature voltage of the motor reaches the threshold level to thereby shunt current through an auxiliary field winding and around the armature and/or main field winding, thereby limiting the speed of the motor. A plurality of embodiments is disclosed which accommodate various conventional power supply types.

Abstract: A universal electric motor having an arbor mounted on a rotating armature with a run winding for generating a magnetic field having a polarity relative to the armature and for rotating the arbor, a first switch for connecting the run winding to a power source, and a brake winding for generating a counter magnetic field opposed with respect to the armature winding to that generated by the run winding.