Abstract: The invention discloses an overcurrent protection circuit, coupled to a DC bus between first and second DC ends, the DC bus including positive bus and negative bus, and the circuit including: a main protection branch connected in series with the positive or negative bus, and including first and second protection switches connected in series and connected to a first node; a freewheeling switch branch having two ends, one end being connected to the first node, the other end being connected to an opposite bus to the main protection branch; a detection unit coupled to the DC bus for detecting a voltage or a current of the DC bus to output an overcurrent detection signal; and a control unit coupled to the detection unit and the main protection branch, and configured to control the main protection branch according to the overcurrent detection signal.

Abstract: A method of diagnosing an open phase fault condition comprising the steps of: determining the q axis motor current in the motor, the motor speed, the q axis motor current demand, and the demanded phase voltage from the controller and outputting a signal indicative of that an open phase fault condition of motor is present when the following conditions are met: (1) the q axis current demand amplitude is above a threshold; (2) the q axis motor current is below a first predefined fraction of the demanded q axis motor current; (3) the demanded phase voltage is greater than a second predefined fraction of the saturated phase voltage value of the motor circuit; and (4) the motor speed is below a threshold speed.

Abstract: The present invention addresses the problem of providing a method for detecting a magnetic field location in an electric motor, said method making it possible to lower costs using simple hardware and software, and instantaneously detect permanent-magnet field location. As a means for solving said problem, an MPU (51) sequentially selects one from six conduction patterns using a phase at which one-phase conduction occurs without branching at a neutral point among three-phase coils as a phase to be measured, applies a sensing current to the three-phase coils, and uses a timer (56) to measure a pulse-width time until the coil current detected by a current sensor (53) reaches a current threshold, and stores the same as measurement data.

Abstract: A coil arrangement for an inductive power transfer system comprising a core (32, 33) having a region of decreased permeability (34), a coil (45) associated with the core, and a tuning slug (35) which is moveable along an axis adjacent the region of decreased permeability in order to adjust the inductance of the coil arrangement, the tuning slug (35) having an effective permeability which varies along said axis.

Abstract: Systems and configurations for open phase detection of a motor in a vehicle by a current detection module having a logic gate configuration. In one embodiment, a detection unit coupled to a control unit includes a current detection module configured to measure at least one current value of each phase of the multi-phase electric motor the vehicle. The current detection module compares current values of each phase to at least one reference value to determine an open phase condition. Current values are compared by digital logic components of the current detection module, and the control unit is configured to control operation of the motor in response to the open phase condition. An open phase condition is detected based on at least one phase current having a near zero level and an unchanged current component for one phase.

Abstract: A control device includes an estimation module configured to repeatedly calculate an angle estimation value correlated with a magnetic pole position of a rotating electric machine, and a storage module configured to store the angle estimation value. The estimation module includes a response information calculation module configured to calculate response information indicating a current change resulting from a change in an output voltage to the rotating electric machine or a voltage change resulting from a change in an output current to the rotating electric machine, a coefficient calculation module configured to calculate an interference coefficient correlated with electromagnetic mutual interference between coordinate axes of an orthogonal coordinate system of the rotating electric machine based on a past angle estimation value stored in the storage module, and an angle calculation module configured to calculate an angle estimation value based on the response information and the interference coefficient.

Abstract: The current subject matter provides a tool and user interface for estimating a velocity at which a plunger of a rod lift pump system will impact a fluid within a well when the rod lift pump system is altered to operate under various conditions of pump fillage. In some embodiments, the estimated impact velocity can be determined using a velocity pattern characterizing a velocity and position of a plunger of a rod lift pump system operating under a condition of complete pump fillage. The estimated impact velocity can provide a user with useful insight into potential operation of the rod lift pump system when operating under various conditions of pump fillage.

Abstract: The invention relates to a device and to a method for monitoring an electrical network in a rail vehicle. The electrical network includes at least one converter, at least one drive motor, at least one first phase line for electrical connection of the at least one converter and the at least one drive motor. A magnitude of a current change of a first phase current is determined. A network error in a partial network on the machine side is detected if at least one criterion based on the current change is met. The criterion based on a current change is met when the magnitude of the current change of the first phase current is greater than a predetermined current change threshold.

Abstract: A pumpjack is operated continuously over a sequence of two adjacent pump stroke cycles, by energizing an electric motor to operate the pumpjack over a first pump stroke cycle according to a motor speed profile over a plurality of discrete control periods within the cycle, while receiving sensory feedback from one or more sensors. In response to the feedback, and while continuing to operate the pumpjack, one or more speed adjustments are made to specific control periods, so as to alter the motor speed profile while continuing to operate the electric motor to drive the pump jack. The intra-cycle control optimizes flow while reacting to detrimental and changing conditions.

Abstract: A motor driving apparatus includes a driving circuit that drives a motor based on a driving instruction signal at a first state of the first state and a second state which are binarized, a current feedback circuit including a latch circuit, and a controller that outputs the driving instruction signal and a current command signal. The latch circuit latches a third state of the third state and a fourth state which are binarized if a motor current value exceeds a current command value. When the driving instruction signal becomes the second state, the latch circuit releases the latching of the third state and outputs a signal of the fourth state. The controller outputs the driving instruction signal of the second state along with the current command signal so as to release the latching of the latch circuit when outputting the current command signal with the current command value changed.

Abstract: A method of operating an uninterruptible power supply (UPS) includes generating, during a portion of an output cycle, a substantially sinusoidal output voltage responsive to a plurality of pulse width modulation (PWM) control signals provided to a power conversion circuit of the UPS, comparing the output voltage to a reference root mean square (RMS) voltage at each of a plurality of time intervals during the portion of the output cycle, calculating a PWM control signal scaling factor based on each of the comparisons to the reference RMS voltage, and maintaining the output voltage at substantially the reference RMS voltage by applying the calculated PWM control signal scaling factor to at least one of the plurality of PWM control signals. The method may include detecting that the output voltage has reached a maximum output voltage level and clamping the output voltage to a steady state output voltage reference level.

Abstract: An abnormality diagnosis apparatus for an electric pump prevents an erroneous decision that a normally functioning electric pump has an abnormality. When a motor is driven by a current of the driving motor using an upper limit current I? before a predetermined time T1 passes, it is decided that there is a probability that an abnormality occurs in the pump and the decision is reported to an external device when the number of rotations of the motor is less than the lower limit number of rotations set under lower limit temperature of a hydraulic oil. When the motor is driven by limiting the current of the motor by I? and I? (<I?) after T1 passes, it is decided that there is a probability of occurrence of an abnormality when rotation of the motor stops and the decision is reported to the external device.

Abstract: A device for regulating an increase in the output torque over time of an electric drive motor, including a monitoring unit for monitoring an operating variable of the electric drive motor, a regulating unit for regulating the operating variable for regulating the increase in output torque over time, a control unit for activating the regulating unit as a function of a time derivation of the monitored operating variable, the regulating unit being designed to be deactivated after a predetermined period of time. A method for regulating an increase in the output torque over time of an electric drive motor is also described. A corresponding tool and a computer program having program code for carrying out the method are also described.

Abstract: An motor drive controller may include: A mode control unit calculating a pulse frequency of a pulse width modulation (PWM) signal provided from an outside and generating an operating signal according to the calculated pulse frequency of the PWM signal, a regulator receiving the operating signal, transitioning to an enable state based on the operating signal, and generating a driving voltage and a motor control module receiving the driving voltage from the regulator and controlling an operation of a motor. The mode control unit is configured to set up a sleep mask time using a clock signal provided from the outside and control the regulator to maintain the enable state during the sleep mask time.

Abstract: A motor-driven appliance of one aspect of the present disclosure includes a motor and a controller. The controller includes a physical quantity detector, a variation deriving portion, a loaded condition detector, and driving output portion. The physical quantity detector detects a physical quantity related to an operating state of the motor. The variation deriving portion derives a variation in the physical quantity based upon the physical quantity detected by the physical quantity detector. The loaded condition detector detects that the motor is under a loaded condition in which the motor is applied with a load based upon the variation derived by the variation deriving portion. The driving output portion generates the driving output corresponding to whether the loaded condition is detected by the loaded condition detector.

Abstract: Disclosed are alternate embodiments of various components of a barrier operator system. and methods of operation, including of the mechanical drive subsystem with segmented and self-locking rail unit, rail mounting supports, belt and chain drive tensioning, and drive assembly carriage and interface; the electronics and software routines for controlled operation of the various barrier operator functions; wall console communications with the barrier operator; encryption and decryption of access codes; establishment and monitoring of travel limits and barrier speed and force profiles; thermal protection of barrier operator drive motors; and establishment and control of communications from the barrier operator to accessories by way of a wireless adapter.

Abstract: A motor control device includes a drive circuit that supplies drive electric power in three phases to a motor, according to turning on or off of FETs; a microcomputer that generates control signals for turning on or off the FETs. The microcomputer detects a current-carrying failure in a U phase when all of (i) a condition that an absolute value of a U phase current value is less than a current determination value, (ii) a condition that a duty value corresponding to the U phase voltage command value is equal to or greater than a first duty determination value, or equal to or less than a second duty determination value; and (iii) a condition that the U phase voltage command value is deviated from the V phase and W phase voltage command values are satisfied.

Abstract: A method for sensing and compensating for variances in load and voltage in a closed loop voice coil system is described. A load in a system which included a supply voltage and the load, which includes an inductive element, is excited with a known duty cycle for a time interval. At an end time, at the end of the time interval, the current which flows through the load is sensed. A lumped term based at least in part on the time interval and a change in the load current during the time interval is calculated. The lumped term is representative of the supply voltage and one or more electrical characteristic of the load. A control signal to control a voltage applied to the load may be generated based at least in part on the lumped term. Apparatus and computer-readable media are also described.

Abstract: In an electric power steering system, a drain terminal side of a semiconductor relay is positioned to face a heat sink through an insulation film layer. The semiconductor relay has a source terminal between a gate terminal and a drain terminal. The source terminal is provided between the gate terminal and the drain terminal with respect to parts of the gate terminal, the drain terminal and the source terminal, which extend generally in parallel each other on the same plane.

Abstract: A variable speed power converter controls the speed of a load in a material handling system as a function of the torque required to move the load. While the power converter is running, the torque being produced in the motor is determined. The power converter then determines the maximum rotational speed of the motor as a function of the torque currently being produced and of the torque-speed curve of the motor. The power converter then commands the motor to rotate at this maximum rotational speed. The power converter periodically monitors the torque being produced and adjusts the maximum rotational speed of the motor throughout the run.

Abstract: A method for monitoring at least one subsea electric machine supplied by a system for electric power transmission. The system has a power supply, a controller and an AC power line connecting the at least one machine with the power supply. The method includes the steps of: receiving at the controller, high speed data from at least one subsea sensor arranged between the subsea side of the AC power line and the at least one subsea electric machine, wherein the high speed data includes measurements of an electrical parameter for the at least one machine; and comparing the one or more measurements to a predetermined value. A system for electric power transmission arranged for operating at least one subsea load or electric machine is also described.

Abstract: The present invention relates to a motor drive overcurrent blocking circuit, a motor driving circuit, and a method for blocking an overcurrent in a motor driving circuit. The motor drive overcurrent blocking circuit includes: a motor driving unit switched according to a driving control signal to drive a motor; an overcurrent sensing unit connected between a lower end of the sink switching element group and a ground to sense a current flowing in the turned-on switching element of the sink switching element group in the sensing terminal; and an overcurrent blocking unit turned on according to a voltage due to an overcurrent sensed by the overcurrent sensing unit and blocking the overcurrent by sinking the driving control signal applied to the turned-on switching element of the sink switching element group to the ground is provided.

Abstract: A ripple extraction device extracts ripple components contained in a current signal of a motor. The ripple extraction device is provided with a current-voltage converter that converts a current signal of the motor into a voltage signal; a filter that filters the voltage signal converted by the current-voltage converter, and attenuates the ripple components; and a differential amplifier that obtains the difference between the voltage signal converted by the current-voltage converter and an output signal of the filter.

Abstract: In the case of a method for automatically controlling an electrohydraulic pressing tool, in particular for producing pipe connections, to actuate the pressing tool a hydraulic piston is moved, in that fluid is pumped into a hydraulic cylinder by a hydraulic pump driven by an electric motor. When a limiting pressure in the hydraulic cylinder is reached, a pressure relief valve opens, and so the hydraulic fluid can flow into a reservoir. With the aid of a control device, a current drop at the motor is detected when the valve opens. The electric motor is switched off when the current falls by a predetermined value (?I) and/or decreases over a predetermined time period (?t) after reaching a limiting current.

Abstract: A technique for providing a user with effective information in performing an operation is provided in a power tool having a speed change mechanism. A power tool has a speed change mechanism that switches a tool bit 113 from first drive mode in which the tool bit is driven at high speed and low torque to second drive mode in which the tool bit is driven at low speed and high torque, according to load on the tool bit 113. The power tool includes detecting and indicating device 161, 163, 167 that detect a predetermined status condition of the first drive mode and indicate switching from the first drive mode to the second drive mode before switching to the second drive mode.

Abstract: A steering control apparatus includes a direct current power source, a three-phase alternating current motor, and a motor driving circuit. An emergency switching element is provided on at least two phases of a three-phase power supply line connected to the three-phase alternating current motor within the motor driving circuit, and the emergency switching element is turned off when an abnormality occurs such that the motor driving circuit is disconnected from the three-phase alternating current motor. The emergency switching element is a MOSFET, and the MOSFETs are provided in pairs in each of the two phases of the three-phase power supply line. Further, parasitic diodes of the pairs of MOSFETs are disposed in opposite orientations to each other.

Abstract: An open phase detection system and method for a three-phase motor is provided. The open phase detection system comprises: a signal generating unit coupled to the three-phase motor and configured to generate a driving signal for driving the three-phase motor; a detecting unit coupled to the signal generating unit, and configured to detect whether the signal generating unit generates the driving signal and to detect three-phase current values of the three-phase motor; and a determining unit coupled to the detecting unit, and configured to determine whether the three-phase motor has open phase according to the three phase current values detected by the detecting unit when the driving signal is detected.

Abstract: The invention relates to a method for controlling the movement of a wiper blade over a wiping surface, including the steps of moving the wiper blade up and down over the wiping surface between a lower turning position and an upper turning position, detecting a requirement to stop the wiper blade, moving the wiper blade downward into a lower end position and from there upward into a first parking position in the event that a reversing signal is present, and stopping the wiper blade. To this end, the wiper blade is moved into the lower end position only if previously thereto low mechanical resistance against the movement of the wiper blade over the wiping surface was determined.

Abstract: A method and a device for monitoring the startup of an electric drive, which has a polyphase machine, a pulse-controlled inverter and a control unit. The control unit is provided to compare rotational speed values that are successive in time to one another during the startup of the drive, and when recognizing a non-increase in the rotational speed of the rotor shaft, to detect a mixup of phase lines or pulse-controlled inverter lines.

Abstract: A motor control device that has a high-frequency component, and a DC bias component that has a magnitude which causes a motor to be magnetically saturated and take on a certain value over a predetermined period, and is positively and negatively symmetrical are impressed as an observation command on a d-axis current command. The polarity of the magnetic pole of a permanent magnet is identified based on a relationship of large and small magnitudes between a first amplitude, which is attained during a period during which a DC bias component takes on a positive certain value, among amplitudes of a high-frequency component contained in a d-axis response voltage computed based on a feedback current respondent to the observation command, and a second amplitude attained during a period during which the DC bias component takes on a negative certain value.

Abstract: A device for regulating an increase in the output torque over time of an electric drive motor, including a monitoring unit for monitoring an operating variable of the electric drive motor, a regulating unit for regulating the operating variable for regulating the increase in output torque over time, a control unit for activating the regulating unit as a function of a time derivation of the monitored operating variable, the regulating unit being designed to be deactivated after a predetermined period of time. A method for regulating an increase in the output torque over time of an electric drive motor is also described. A corresponding tool and a computer program having program code for carrying out the method are also described.

Abstract: Apparatus, having multiple motor modules, has an MCU module. Each motor module has an electronically controlled motor. The MCU module has an MCU and an interface for connecting to a bus from a CPU. In use the MCU module receives control signals from the CPU and in turn instructs a selected one of the motors to operate.

Abstract: The invention relates to a motor arrangement (1) comprising a motor (4) on which a transmitter device (6) is arranged, a regulating device (2) which is spatially separated from the motor, communicates with the motor (4) via at least one motor line/connection line (10), and controls the movement of the motor, and at least one sensor device (8) which is arranged on the motor (4), detects at least one physical property of the motor, and emits a signal characterising said physical property, the transmitter device (6) being connected to the regulating device (2) via the connection line. According to the invention, there is a direct communication connection (9) between the sensor device (8) and the transmitter device (6), by which means the sensor device (8) transmits the characteristic signal directly to the transmitter device (6).

Abstract: A motor controller comprises a processor selectively outputting an on-signal to either one of an upper arm switching element and a lower arm switching element based upon a detected position by the position sensor, gate drivers inputting a driving voltage to the gates of the switching elements by shifting a level of the on-signal from the processor to the upper arm switching element and a bootstrap capacitor configured to be charged while the upper arm switching element is turned off and to behave as a voltage supply for the gate driver while the upper arm switching element is turned on. The processor is configured to reduce a set duty ratio when the set duty ratio is equal to or larger than a predetermined value (e.g. 80 percents) and a rotational position of the motor does not change for a first predetermined time. This motor controller can prevent the switching element from a burnout even if the motor is locked.

Abstract: The present invention provides a riding work vehicle that includes a vehicle body having a driver seat; a driving wheel unit supporting the vehicle body; a working electric motor that drives a work unit having a work device; an electric motor controller controlling an operation of the working electric motor in a steady mode or a power saving mode in which consumed power is smaller than the steady mode; and a work load evaluator that evaluates load of the working electric motor. In the riding work vehicle, the electric motor controller operates the working electric motor in the power saving mode in a case where the load of the working electric motor evaluated by the work load evaluator is low load lower than a threshold value.

Abstract: An open phase detection system and method for a three-phase motor is provided. The open phase detection system comprises: a signal generating unit coupled to the three-phase motor and configured to generate a driving signal for driving the three-phase motor; a detecting unit coupled to the signal generating unit, and configured to detect whether the signal generating unit generates the driving signal and to detect three-phase current values of the three-phase motor; and a determining unit coupled to the detecting unit, and configured to determine whether the three-phase motor has open phase according to the three phase current values detected by the detecting unit when the driving signal is detected.

Abstract: The invention relates to a processing unit of a measuring signal related to conditions of an object controlled by power electronics. The processing unit comprises an interface with digital terminals, wherein the interface is provided with at least one terminal for a sensor which generates the measuring signal. Further, the processing unit comprises a calculating unit to which the interface is connected. The calculating unit is equipped with a real-time control system. In addition, the calculating unit comprises a general-purpose processor.

Abstract: A control system aims at converting, via a switching circuit, a direct current voltage into an alternating current voltage to be applied to multiphase windings of a multiphase rotary machine to thereby control rotation of the multiphase rotary machine. In the control system, a command voltage determiner determines a command voltage value for an alternating current voltage to be applied to the multiphase windings based on a zero crossing of a line-to-line current and a zero crossing of the amount of change in the line-to-line current. A driving unit drives the switching circuit on and off based on the determined command voltage value to thereby modulate the direct current voltage to the alternating current voltage to be applied to the multiphase windings.

Abstract: A method for testing an electric motor which is connected to a valve element by at least one component comprises starting the motor, measuring a movement parameter of at least one of the motor and the component without moving the valve element, and stopping the motor when the measured movement parameter indicates that the valve element is about to move.

Abstract: Disclosed is a circuit arrangement for electrically controlling and/or regulating the movement of an electrically driven unit (2), especially a window lifter or sliding roof of a motor vehicle, and to a method for operating said circuit arrangement. According to the invention, a jamming protection System is characterized in that a correlation variable (K) for the adjusting force of the unit (2) is measured and the adjusting movement is stopped or reversed in order to prevent jamming if the correlation variable (K) for the adjusting force exceeds a threshold value that corresponding to a predetermined jamming force. A filter (140) is used for temporally filtering the correlation variable (K) for the adjusting force of the unit. The invention is characterized in that the filter parameters (142, 143), especially the cutoff frequency (fg) and/or the order of the filter (140), can be controlled.

Abstract: A method of detecting one or more failed current sensor and estimating a phase current for the failed current sensor on a three-phase machine is disclosed. The method may include detecting one or more failed current sensor by determining if an absolute value of a sum of the phase currents of the motor is below an open circuit value. The method may also include determining which phase currents are approximately zero, for each phase current associated with each phase of the motor, if the sum of the phase currents of the motor is not below the open circuit value. The method may further include estimating the phase current for the failed current sensor by determining the phase current value for the failed current sensor, that when added to the phase currents of the remaining current sensors, will make the sum of all the phase currents equal to approximately zero.

Abstract: A motor controlling device and a motor controlling method are provided. The motor controlling device includes a first sensor, a second sensor and a signal switching circuit. The signal switching circuit is electrically connected to the first and second sensors, respectively. The signal switching circuit is switched to the first sensor to output a first switching phase signal to drive a motor when the motor starts to operate. The signal switching circuit is switched to the second sensor to output a second switching phase signal to drive the motor when a predetermined switching condition is satisfied with a predetermined value during the motor operation.

Abstract: A system and method are disclosed for turning off the voltage to a pump jack electric motor during predetermined periods of time to save energy. In the method, the motor's response to closed-loop control may be evaluated over several pump strokes. The periods of the pump stroke when it is feasible to turn off the motor may be identified. The consistency of the measurements over several strokes may be evaluated. The motor may be turned off during predetermined periods on subsequent pump strokes when each pump stroke shows sufficiently similar behavior to that predicted during the closed-loop control process. The system may return to the closed-loop control process after a predetermined period of time to adjust to any changes in the system.

Abstract: In a motor controller, in the case that occurrence of a failure of electric current flow is detected in any phase of a motor, a phase electric current command value changing in accordance with a secant curve or a cosecant curve with an asymptotic line at a predetermined rotation angle corresponding to the phase in which the failure of electric current flow has occurred is calculated. The calculated phase electric current command value is limited in such a manner as to become within a predetermined range. In the case that a rotation angle of the motor exists in a range in which the phase electric current command value is limited, the execution of an anomaly detection of a control system utilizing an electric current deviation of a d/q coordinate system is inhibited.

Abstract: The following invention is an electromechanical system (1) that is to be connected to an electricity supply (7), comprising: an electric machine (2) that can operate as an independent generator with a rotating shaft, and a switching system (9) allowing i) in the first configuration, the electric machine to operate as a motor in the case where the connected device (4) is normally driven or as a generator in the case where the coupled device is normally driving, and ii) in the second configuration, the electric machine to operate as an independent generator, the electrical energy generated by the electric machine (2; 22) being dissipated in the machine and in a dissipative load (13).

Abstract: An electric centrifugal pump for conveying a fluid, in particular for conveying fuel to an aircraft engine, is disclosed. The pump includes a housing in which a rotor shaft is rotationally mounted and an impeller for conveying the fuel which is arranged on the rotor shaft. A motor arrangement is provided for driving the rotor shaft in a rotary manner around a rotor axis. The impeller includes at least one rotor, and at least one stator is arranged in the housing in a plane-parallel manner adjacent to the rotor such that the rotor and the stator form the motor arrangement.

Abstract: The inverter device contains the following structure: an inverter circuit which has upper-arm switching elements that are connected on a positive side of a DC power source and lower-arm switching elements that are connected on a negative side of the DC power source; a current sensor that detects current flowing between the DC power source and the inverter circuit; and a control circuit that controls the inverter circuit by a PWM driving so that the inverter circuit outputs AC current to the motor. The control circuit provides a carrier cycle with a first correction and provides the successive cycle with a second correction, by which the current sensor can detect phase current of the motor. A ripple current caused by the first correction and a ripple current caused by the second correction are opposite in polarity.

Abstract: A programmable logic controller is disclosed. The programmable logic controller includes control circuitry integrally arranged with a current path and at least one micro electromechanical system (MEMS) switch disposed in the current path. The programmable logic controller further includes a hybrid arcless limiting technology (HALT) circuit connected in parallel with the at least one MEMS switch facilitating the opening of the at least one MEMS switch. The programmable logic controller also may include a MEMS switch and a voltage sensor for measuring the voltage across the MEMS switch. The MEMS switches are arranged to transmit or receive logic signals.

Abstract: A method for starting a blower motor with a locked rotor condition, the motor having one or more speed settings, each speed setting having a reference voltage and reference current value associated therewith, the method comprising, from a motor off condition, applying the reference voltage to the motor, the reference voltage associated with a desired speed setting; measuring current flowing through the motor to define a measured current value; comparing the measured current value to the reference current value associated with the desired speed setting to determine if a locked rotor condition exists; if a locked rotor condition exists, increasing the motor speed from the desired speed setting until either the output speed is at a maximum speed or the locked rotor condition ceases to exist; and adjusting the motor output speed value to the desired speed setting.

Abstract: The invention relates to a power tool, which comprises a motor for driving a tool bit rotating, the motor attains a rotational speed, a source for supplying an electric current to said motor, a sensor for measuring said current, and a control device. The control device fulfills the task of detection of a variation of the slope of the current in the course of time, and generates a control signal. The rotational speed of the tool is reduced in response to the control signal. The present invention automatically detects whether the work piece operated by the tool bit reaches a predetermined position by providing electronic control means. It may make sure that the screw is driven into a piece of wood and does not go beyond the predetermined position once detect that the work piece reaches the position and carries out the changing action.