Abstract: Embodiments of the invention provide a way to accurately detect the position of a spindle motor. In a spindle motor startup process according to one embodiment, a parameter setup section acquires from a parameter table a sense time value corresponding to an input voltage that is acquired from an ADC. The parameter setup section sets the sense time value in a register. A position determination section, which is within an SPM driver, performs an induced voltage detection process for rotor position detection purposes during the time corresponding to the sense time value that is set in the register. Even when the input voltage is decreased, rotor position detection can be properly achieved by changing the sense time value in accordance with a change in the input voltage.

Abstract: Latch control methods and systems are disclosed, including a latch that receives power from a motor associated with a latch. A sensor can be provided for monitoring the current consumption of the motor. A microcontroller can control the latch and/or the motor, based on the current consumption data received from the sensor concerning the current consumption of the motor. Monitoring of the current waveform of the motor therefore provides speed and direction feedback data for control of the latch. Additionally, a microprocessor can process instructions for controlling the interaction of the motor, the latch, the sensor and/or the microcontroller. Such a current monitoring control system is made possible by variation in current consumption of the motor during rotation as a result of commutation, which can be interrogated by measuring the voltage drop across the motor or a shunt resistor, or through the use of other current sensors, such as, for example, a Hall-effect type current sensor.

Abstract: Provided herewith is an improved scheme for parking a load such as an indicator pointer and calibrating its position in a system for controlling the position of the load. The system also has a stopper for physically impeding the load when it is to be parked. In one embodiment, a parking method involves driving the motor in a reduced torque mode to move the load toward the stopper, stopping the load at the stopper while the motor is driven in the reduced torque mode, and maintaining the motor in a reduced torque mode until transitioning to an insignificant torque mode.

Abstract: The present invention provides a motor control system and method thereof. The motor control system comprises a motor controller and a compensation device. The motor controller is used for generating a motor control output according to a reference signal and a first signal. The compensation device is used for generating a compensated motor control output according to the motor control output and a second signal. Moreover, the compensation device utilizes the compensated motor control output to reduce the steady-state phase error between the first signal and the reference signal.

Abstract: An object is to provide an inverter device capable of realizing exact protection of the winding of a motor. An inverter device for generating a pseudo alternating current by switching a direct current to drive a motor, comprises a controller that executes vector control on the basis of a secondary current applied to the motor. The controller calculates a current density from the secondary current to execute a predetermined protection operation on the basis of the calculated current density. The controller imposes a restriction on the operation frequency of the motor on the basis of the current density.

Abstract: An electronic control unit for producing a sufficiently boosted voltage even when a supply voltage becomes high includes an inverter that drives switching elements and converts a DC voltage into an AC voltage, and booster means which boosts a DC voltage that is input into a voltage to lie within a voltage range in which a voltage necessary for driving the switching elements is a lower-limit value and a maximum boosted voltage is an upper-limit value, and outputs the boosted voltage to the inverter.

Abstract: A servo motor with a built-in drive circuit in which a sensor circuit portion, a drive control circuit portion, and a motor drive circuit are collectively provided on two boards, thereby achieving simplification and a reduction in the size of the circuit configuration. In the servo motor with the built-in drive circuit, the sensor circuit portion and the drive control circuit portion are formed on a sensor circuit board, and the motor drive circuit is formed on a motor drive board, thereby achieving a reduction in size.

Abstract: A method and control system to control a brushless DC motor to a preferred position is provided. The advantages that accrue to a system employing the method and apparatus to control the brushless DC motor to a preferred position include optimizing response time, energy usage, coil heating, and ability to hold to a fix position. The method to control the brushless DC motor to a position comprises monitoring actual position of the brushless DC motor, monitoring energy used by the brushless DC motor, and determining a commanded position of the brushless DC motor. A zero torque commutation method is employed to control the brushless DC motor to the commanded position only when a time-rate change in the commanded position is less than a first threshold, a difference between the commanded position and actual position is less than a second threshold, and, the monitored energy used is less than a third threshold.

Abstract: A servo motor with a built-in drive circuit is provided in which, when power is off, positional data including multiple-rotation counting values is stored in a nonvolatile memory to thereby eliminate battery back-up, and in which the CPU of a drive control circuit portion is in charge of the multiple-rotation counting itself to thereby eliminate the circuit for multiple-rotation counting. Due to a reduction in the number of lines involved and an elimination of battery back-up, a reduction in size is achieved. The servo motor with a built-in drive circuit includes an absolute encoder for detecting rotation of a servo motor portion and an electromagnetic mechanical brake, in which, when the power is off, the positional data at that time is stored in a nonvolatile memory.

Abstract: A controller controls an electric motor to provide assist power corresponding to steering operation for an electric power steering apparatus. The controller comprises a detecting device, a filtering device, a judging device and a determining device. The detecting device detects present voltage of a power source for the electric motor. The filtering device filters the present voltage based on a small time-constant when the voltage of the power source increases and based on a large time-constant when the voltage of the power source decreases. The judging device judges whether the filtered voltage is lower than a predetermined threshold. And, the determining device determines being abnormality of the power source when it is judged that the filtered voltage is lower than the threshold.

Abstract: A method for determining the mass moment of inertia of an electric motor drive system of a machine, having a drive motor and further drive elements arranged downstream of the drive motor. The method includes a) determining a compensation current, which compensates losses occurring at a constant speed of the motor, so that a motor speed of the drive motor remains constant and b) determining an acceleration current, which generates a defined acceleration of the drive motor when the losses occurring at the constant speed of the drive motor are compensated. The method further entails c) calculating a mass moment of inertia of the electric motor drive system based on the determined acceleration current.

Abstract: In a motor control device controlling a motor by a state feedback control, high control accuracy is maintained regardless of fluctuations in a motor load so as to improve control performance of the state feedback control. A control signal (manipulation amount) outputted from a feedback calculator for controlling the motor is compared to a manipulation threshold set to a manipulation threshold setting register so as to determine the magnitude of a load amount of the motor. The feedback calculator includes an observer and performs the state feedback control of the motor. When the load amount is in normal level, a normal load observer matrix set in an observer table is selected to configure a normal load observer. When the load amount is increased, a high load observer matrix is selected to configure a high load observer.

Abstract: A disk drive is disclosed wherein a BEMF speed error is measured during a BEMF spindle speed control mode, and a spindle control current is updated in response to the BEMF speed error to drive the disk at an operating speed. A reference time period (RTP) is calibrated, and a sinusoidal error in a wedge time period (WTP) due to eccentricity in the disk rotating is estimated to generate an eccentricity compensation value. After switching to a wedge spindle speed control mode, an actual WTP is detected and a wedge speed error is generated in response to the RTP, the detected actual WTP, and the eccentricity compensation value. The disk is then maintained at the operating speed by updating the spindle control current in response to the wedge speed error.

Abstract: An apparatus monitors performance of a power inverter to detect malfunctions. A first signal indicates the direction that electric current exists between a first voltage bus and an output terminal of the power inverter. A second signal indicates the direction that electric current exists between a second voltage bus and the output terminal. A third signal indicates the direction that electric current occurs between the output terminal and a load. Other signals designate a commanded conductivity of switches that control the current within the power inverter. A controller analyzes the values of those signals to determine whether a malfunction has occurred.

Abstract: In a holding arrangement (101) for a medical-optical instrument (103), an electric motor is provided in a rotational joint (111, 119) to compensate a load torque occurring in this rotational joint. This electric motor is supplied with current in correspondence to a detected position of the rotational joint (111, 119). A current control curve required for this purpose is stored in a memory. This current control curve can be determined in that the rotational joints are deflected with the electric motor into predetermined positions and the current demand needed therefor is detected.

Abstract: A motor driving circuit includes an induced voltage detecting circuit for detecting induced voltages in a motor; a rotation speed/phase detecting circuit and an output matrix circuit for generating a plurality of control signals in response to the detection result of the voltage detecting circuit; a current control circuit for generating current control command values in response to the control signals; and a current detecting circuit for detecting output currents that are driving the motor, and for controlling output transistors in response to its detection result and the current control command values. The motor driving circuit can sharply reduce the driving noise of the motor with improving the efficiency of the motor drive by shaping the output currents in a sinusoidal waveform.

Abstract: A robust current loop controller for a servo system is provided. The robust current loop controller includes a model reference controller and a current controller. The model reference controller generates a velocity command signal from a current command reference signal of the servo system and generates a current command signal through comparing the velocity command signal with a feedback velocity command signal of the servo system. The current controller generates a control signal from the current command signal, the current command reference signal and a current feedback signal in order to drive the servo system.

Abstract: A voltage regulator controls an output of an automotive alternator by controlling an amount of excitation current supplied to a field winding of the alternator. The amount of the excitation current is sensed by a sensing resistor as a sensed voltage appearing across the sensing resistor. The sensed voltage is amplified by an amplifier to obtain a detected voltage, an amplifying factor of which is adjusted based on an reference voltage precisely corresponding to the amount of the excitation current, and thereby the detected voltage is equalized to the reference voltage. In this manner, the excitation current is precisely detected without mechanically adjusting a resistance of the sensing resistor by function-trimming or the like.

Abstract: Verification system logic operates PWM motor drivers for DC motors of a tape drive, and verifies the on time duty cycle period and offset of the PWM motor drivers; verifies DAC current reference and amplifier sense signals against thresholds; and verifies Hall sensor state sequence of the DC motors during rotation. If the verifications are successful, the logic rotates the DC motors, and, for each motor, verifies the time of acceleration at a desired torque; verifies a computed velocity based on a measured velocity to a reference velocity; and verifies an actual rotation rate to a computed velocity.

Abstract: A permanent magnet rotating machine control system and method includes an estimator that calculates an estimate of the machine's rotor speed. The estimator receives energization feed back from the machine in a first rotating reference frame and outputs the rotor speed estimate in a second rotating reference frame. A controller receives a rotor speed demand and the rotor speed estimate, and outputs control signals for controlling energization of the machine in response to the rotor speed demand and rotor speed estimate signals. The first rotating reference frame rotates at the commanded rotor speed, and the second rotating reference frame rotates at the estimated actual rotor speed.

Abstract: The invention in the simplest form is a technique to provide for sharing of power and signal pins on a motor controller. The switching simply follows the magnetic switching detected by the Hall sensor as the motor magnet passes and uses a diode or resistor instead of a switch. The power transistors are respectively connected to a voltage regulator through a diode or resistor and there are no switches in the circuit. To avoid simultaneous switching, one embodiment is designed by turning “On” slowly and turn “Off” quickly. Slow “On” is accomplished by using a resistor/capacitor (RC) delay such that the gate drive ramps slowly. Fast “OFF” is obtained by discharging the gate capacitance with an N-CH transistor that bypasses the RC delay.

Abstract: A system for controlling an electric motor includes a controller and a position indicator that provides position information regarding at least one motor component to the controller. The controller utilizes phase relationships indicative of the position information to determine the actual position of the component of interest. The phase information in one example is derived from the output of a resolver that provides two output signals corresponding to sin (&thgr;) and cos (&thgr;), where &thgr; is the angular position. Utilizing the phase relationship simplifies the task of determining accurate position information that is useful to modify motor control signals to compensate for latency when making position determinations, velocity calculations or both. The inventive system makes it possible to use less expensive electronics to arrive at more reliable results.

Abstract: Conventional position-sensorless motor drive control circuits start a motor by a method that has the disadvantage that the motor is not always started in the forward direction or by a method that has the disadvantage that a current detection resistor produces a power loss. According to the invention, a motor drive control circuit that controls, with drive signals, a drive portion that feeds drive currents to the stator coils of a motor has a drive signal output circuit that outputs rotor position detection drive signals to the drive portion before the starting of the motor and a detection circuit that receives the common-terminal voltage of the stator coils when the drive signal output circuit is outputting the rotor position detection drive signals and that detects, according to the common-terminal voltage of the stator coils, the position of the rotor before the starting of the motor.

Abstract: A magnetic disk drive that drives and positions an actuator using a voice coil motor, includes a current sensing resistor connected in series to a terminal on current input side of the voice coil motor, a first operational amplifier and a second operational amplifier. The magnetic disk drive further includes one of a third operational amplifier and a microcomputer.

Abstract: A vacuum cleaner operates via power supplied from either an on-board battery or an AC power outlet. When the vacuum cleaner is operating by using the battery a controller monitors the voltage level in the battery and automatically shuts down the vacuum cleaner when the battery voltage has decreased below a preset level. This prevents a full drainage of the battery and increases its longevity. The controller that monitors the battery voltage level can be used with batteries of different voltages. The controller automatically determines which type of battery is being used and shuts down power to the vacuum cleaner motor after the appropriate amount of battery drainage.

Abstract: Disclosed herein is a system for applying a power-supply voltage to the voice coil control circuit provided in a disk drive and designed to drive the head actuator provided in the disk drive. The power supply circuit of the disk drive outputs a voltage that corresponds to the power-supply voltage applied from a host system. A voltage step-up circuit is provided, which increases the output voltage of the power supply circuit. A switching circuit is provided, which selects the increased voltage output from the voltage step-up circuit when a large current needs to be supplied to the voice coil motor incorporated in the disk drive. The switching circuit selects the output voltage of the power supply circuit when a relatively small current needs to be supplied to the voice coil motor.

Abstract: A system for providing DC current to a rotating superconducting winding is provided. The system receives current feedback from the superconducting winding and determines an error signal based on the current feedback and a reference signal. The system determines a control signal corresponding to the error signal and provides a positive and negative superconducting winding excitation voltage based on the control signal.

Abstract: A DC motor drive circuit includes a switching circuit that drives the coils of a small permanent magnetic DC motor. The drive circuit is preferably implemented in an integrated circuit device, such as a silicon CMOS device. Integrated into the same integrated circuit device is a magnetic sensor arranged to detect the position of the permanent magnet as it passes a defined point, or points, in its revolution, and control circuitry to derive the timing waveforms for driving the coils. The integrated power devices for driving the coils are also arranged to limit the rise and fall times of the applied voltages and currents so as to reduce or eliminate the generation of unwanted RFI. Additional circuitry is also integrated into the same integrated circuit device to derive the necessary power to operate the magnetic sensor, the control circuitry and the switching circuitry from the connections between the switching circuitry and the coils so as to remove the need for a separate power supply connection.

Abstract: A deviation between a target value of a quantity of state and an actual value of the quantity of state that is caused to follow the target value or a time-integral of the deviation is filtered. Based on the filtered value, a switching surface &sgr; is calculated. Based on a value of the switching surface &sgr;, a control input value u is outputted. The filter is set through comparison in Bode diagrams between a design model of a control system based on an ordinary sliding mode control method and a characteristic variation model of the control system, and by performing compensation in such a direction as to cancel out the variation. The filtering process makes it possible to properly control the control system having a dead time by the sliding mode control method.

Abstract: An object is to realize acoustic noise reduction under a wide range of rotating speeds and together with PWM control. A signal (VCTL1) is generated as a trapezoidal wave repeatedly rising and falling in each given electrical angle section extending before and after the current-supply pattern is switched in accordance with the electrical angle of a rotor of a motor, and a signal (VCTL2) is generated in the opposite phase. A control circuit (22) appropriately selects among the signals (VCTL1 and VCTL2) and a given signal (SCTL) and inputs them to comparators (59 to 61). The comparators (59 to 61) compare the input signals with a carrier signal (B6) provided as a triangular wave. Switch elements for controlling the current-supply pattern to the motor turn on/off on the basis of output signals (C1 to C6) from the comparators (59 to 61). As a result, the current-supply pattern is switched softly by PWM control in the electrical angle section mentioned above.

Abstract: A driving system has a driving mechanism for producing a driving force, a drive controlling device for controlling the driving mechanism, and a temperature adjusting mechanism for collecting heat from the driving mechanism, wherein a cooling amount of the temperature adjusting mechanism is controlled on the basis of a signal applied from the drive controlling device to the driving mechanism. The cooling amount required for the driving mechanism or the amount of heat generation in the driving mechanism is predicted, on the basis of a signal applied to the driving mechanism, and the cooling amount is then controlled.

Abstract: A controller for a system has two or more operating modes. The controller operates according to a different control algorithm in each operating mode. A manually operable switch typically used for sending a reset signal to the controller, may also be used to change operating modes. The controller changes operating mode when it detects that the switch is manually operated during a preselected phase of controller operation, typically when power is first applied. The disclosed embodiment allows up to four different operating modes to be selected. A first selection of operating modes can occurs if the switch is held closed during startup and then immediately released. A second selection of operating mode occurs if the switch is pressed within a preselected time interval after power is first applied to the controller. Both selections can be made during a single start-up event.

Abstract: An on-line monitor for electrical faults in the stator of an ac motor has a single di/dt current transformer or three separate di/dt current transformers coupled to the three phase conductors of the ac supply. The windings of the transformer, or transformers, are selected to generate a single sensed signal containing a linear combination of components of current in the three phase conductors weighted relatively so that algebraic differences between components from any two phase conductors is non-zero, such as preferably 2A+B-C or 3A+2B+C. The single sensed current signal is bandpass filtered to generate a pulse signal which is applied to an analyzer. The analyzer, preferably implemented by a microcontroller, generates an output based upon a combination of the amplitude and frequency of occurrence of the current pulse signal including a time attenuated accumulation of the pulses.

Abstract: A power window apparatus is provided for detecting pinching in accordance with the opened/closed position of the window and a state of rotation of a motor, the apparatus having a position sensor which detects a safety-control suspension region of the window and which is an accurate sensor. A spiral guide groove is formed in the inner surface of a housing opposite to a rotational plate which is rotated by an output shaft of a motor which opens/closes a window. A follower which is guided by the spiral guide groove is able to move along a straight guide groove provided for the rotational plate in the radial direction. Terminals in the form of conductive films are provided for a printed circuit board accommodated in the housing. When the rotational plate has been rotated, the follower is guided by the spiral guide groove so as to be moved in the straight guide groove. Thus, a slide member provided for the follower is brought into contact with the terminals so that the terminals are conducted with each other.

Abstract: A control system is provided for a limited angle torque motor used as a rotary position control device. A motor for which the system is intended would consist of a rotor and a stator. The system uses an analog Hall-effect sensor to sense the position of the rotor. Rather than attempting to shield the Hall-effect sensor from the influences of magnetic fields generated by the field windings in the stator during motor operation, the system allows the output signal from the Hall effect sensor to contain elements of both the angular position and the extraneous magnetic field generated by the field windings of the motor. Current feedback from a circuit which independently senses the motor current is then combined with this signal to eliminate the influence of the motor coil magnetic field. The system is applicable to a number of limited angle torque motor designs.

Abstract: A conventional method for driving a servo-motor carried out control by means of a current feedback loop, using a current sensor and an A/D converter; therefore, the number of parts was great, cost reduction was difficult and it was difficult to avoid control errors caused by errors in the precision of the current sensor.A method for driving a servo-motor of the present invention comprises detecting a power voltage (V) of a servo-motor (4), controlling a voltage command (Vcmd) to a power converter (3) by numeric calculation using a detected value (Vcc) of this power voltage (V), and controlling power of a drive current (Iu, Iv, Iw).

Abstract: A brushless motor having at least one current influence detector (10a, 10b, 10c) for detecting influence of an induced voltage caused by variations of current flowing in an armature winding (3). Furthermore, a positional signal detecting circuit means (11) detects a positional signal corresponding to rotational position of the rotor (2) in accordance with the voltage signal appearing at the armature winding (3) and the output signal issued from the at least one current influence detector (10a, 10b, 10c).

Abstract: Apparatus for electronically producing a torque dependent signal for a plural drive phase synchronous step motor, without the use of an accelerometer or other external feedback device, includes a circuit for detecting respective instantaneous terminal voltage signals for at least two phases of the motor; another circuit for detecting respective instantaneous phase current signals for said at least two phases; and a signal processing circuit for combining the detected signals to produce said torque dependent signal.

Abstract: This invention relates to a suction inlet/discharge outlet opening or closing apparatus for an air conditioner having a function to close a suction inlet and a discharge outlet at the time of recovery of electric power, with reference to a time duration retrieved from an appropriate storage containing the time duration counted during a closing/opening of the suction inlet and discharge outlet, and a method therefor.

Abstract: A system for increasing the efficiency of single and multi-phase induction motors. The system is comprised of a microcontroller which combines a time when the AC line current reaches zero amps with a time when AC line voltage to the AC motor reaches zero volts and with a digital measurement provided by an A/D converter to determine a servo error. The servo error determines whether the A/C motor needs more or less power. The microprocessor provides a control signal to a switching means to supply the minimum power required based on the servo error.

Abstract: The driving apparatus for a power antenna, e.g. an extensible-retractable automotive radio antenna, is provided with stability function which controls the operation of the motor driving the power antenna until the power antenna is varied into a state for performing normal operation, and provides hysteresis to prevent a state of the controlling signal from being varied too often by a voltage drop generated in rotation of the motor.

Abstract: A servo-drive device is provided for an actuating of, for example, ventilation dampers in motor-vehicle air-conditioning installations element which can be stably positioned in a plurality of positions, d.c. motors with a gear mechanism are used for servo-drive devices of this type. A mechanical system which is moved at the same time and has potential energy varying along its path of movement is coupled to the servo drive such that it influences the current of the servo motor to permit the respective position of the actuating element to be identified by a control device on the basis of the evaluation of the motor current characteristically which depends on the force exerted by the mechanical system on the actuating element.

Abstract: A voltage mode drive for a servo system builds a drive matrix from an error signal, which is the difference between a measured value for a parameter of the servo system, such as the position of a rotating drum, and a reference signal, a voltage control signal for the servo system, and an estimated set of parameters for the servo system, the parameters including drive current. The outputs from the drive matrix are a new estimated set of parameters for the servo system which are multiplied by appropriate system constants to produce the voltage control signal. The voltage control signal is amplified by a voltage amplifier and applied to drive the servo system.

Abstract: The shift quality of an automated mechanical transmission is improved and transmission wear is reduced by controlling the armature current of the motor driving the transmission shifting mechanism. The current is monitored by a microcontroller to determine if the shifting mechanism has encountered a snag or has stalled during a shift operation. The microcontroller is programmed to control the duty cycle of a pulse width modulated (PWM) voltage signal, applied to the motor, in accordance with an algorithm which provides both proportional and derivative control of the error between the measured current and a target current. The rapid reduction in current spikes through PWM control reduces the force applied to the shifting mechanism and thus the sliding clutch and transmission gearing.

Abstract: The determination of the position of a tape thread-in and thread-out mechanism in a cassette recorder is carried out using contact paths together with a slider contact that form position switches. Output signals of the position switches are coupled via a resistor network that combines the output signals and produces an output signal on a single conductor. The resistor network output signal is coupled to an input of an analog -to-digital converter. To improve the reliability of determining the position of the mechanism without requiring the use of highly accurate resistors in the resistor network, the voltage value assigned to each individual position is measured at the output of the network during a calibration operation. The voltage values are stored in a memory and used as the desired values during normal operation.

Abstract: An apparatus and a method for discriminating position information in a position control system. The apparatus includes a position detector for detecting information regarding a current position of a motor, a position counter for counting the motor current position information from the position detector at a fixed period, a central processing unit for reading a counted value from the position counter, comparing the read value with a normal position command value stored therein, compensating for a difference value as a result of the comparison and outputting a position control value based on the compensated value, and a digital/analog converter for converting the position control value from the central processing unit into an analog signal and outputting the analog signal as a position control signal for the motor.

Abstract: A speed control device for a DC motor controls the rotational speed of the DC motor through adjustment of a duty cycle of a semiconductor switching element. The rotational speed to be obtained is determined by an amount of operation of an operation member. A second contact switch is arranged to bypass the semiconductor switching element and is turned on to eliminate influence of the internal resistance of the semiconductor switching element. A power source contact switch is provided between a power source and the DC motor and is turned on and off through operation of the operation member.

Abstract: A system for inverter control of a servo motor where in the inverter is connected to a velocity control section and a position detection section is connected to the servo motor. Primary and back-up power for operating the velocity control section and the position detection section is provided by power sources that are located in the velocity control section and are connected to the position detection section by cables. The cables used to provide signal transmission between the position detecting section and the velocity control section are switched by relays to transmit the power of a power failure back-up power supply at the time of a power failure. Also, a transmission signal transmitted from one of the position detecting section and the velocity control section to the other via a first cable connection is returned via a second cable connection and a connection fault may be judged depending on whether or not the return signal matches the transmission signal.

Abstract: An electronic sensing circuit, which can be used in place of a linear variable differential transformer (LVDT) has four piezoresistor elements in a Wheatstone bridge configuration. A source voltage is applied across a first pair of bridge points, and the resulting junction voltages appearing at a second pair of bridge points are applied to a pair of inverting amplifiers in balanced configuration which provide first and second output voltages which change relative to each other depending upon the direction and amount of pressure applied to the piezoresistor elements in a manner similar to the output voltages provided by an LVDT.

Abstract: An automatic offset adjusting apparatus for current detectors in a digital controller for a servo motor is constructed so that, when errors occur in offset correction values due to a temperature change and the like while the servo motor is in operation, an electrical angle detecting unit detects a ripple of the torque of the servo motor, on the basis of a ripple of a torque command value, and detects a first electrical angle, where the torque command value becomes maximum, and a second electrical angle, where the torque command value becomes minimum, based on an electrical angle signal of the servo motor, a judgement unit judges whether or not offset correction errors have occurred on the basis of a difference between the first and second electrical angles, and, if the judgement unit judges that the offset correction errors have occurred, a correction unit adds adjustment values for the offset correction values corresponding to the first electrical angle to the respective offset correction values to update th