Abstract: A driving apparatus for moving an object. The apparatus includes a first actuator which drives the object in X and Y directions, a second actuator which drives a reaction force counter, which receives a reaction force generated when the first actuator drives the object, and a controller which calculates X- and Y-direction reaction forces and a moment reaction force on the basis of X- and Y-direction positions of the object and X- and Y-direction accelerations of the object, which are to be received by the reaction force counter when the object is driven by the first actuator, and controls the second actuator so as to cancel the reaction forces and the moment reaction force.

Abstract: A controller includes a rotating direction detecting unit 34 to detect the rotating direction of a servo motor 6, a reversing distance computing unit 31 to compute a rotating angle of the servo motor 6, a rotation resistance computing unit 35 to compute rotation resistance on the servo motor side 6, and an elastic deformation error amount computing unit 21 to compute a deformation error amount of a ball screw 3. In the controller, when the rotating direction detecting unit 34 detects reverse of the servo motor 6, the rotation resistance computing unit 35 computes rotation resistance based on a rotating angle ?? of the servo motor 6 after the servo motor is reversed. The elastic deformation error amount computing unit 21 computes the elastic deformation error amount ? based on the computed rotation resistance. Thereby, a position command value inputted into the position control unit 14 can be corrected.

Abstract: A control axis is subordinated to a plurality of position-controlled successive axes. It is determined, while an adjusting stroke, an initial theoretical position value for each successive axis by means of the position value or the temporal derivation of the position value of the control axis, in detecting for each successive axis a real position value, in determining a train interval by means of the real position value and the initial value position, in determining a deviation value which is valid for all successive axes by means of the train interval thereof and in determining again a final theoretical position value by means of the deviation value in connection with the real position value and in adjusting the position value for each successive axis by means of said final theoretical position value.

Abstract: Apparatus and method for compensating for positional indicia misplacements in the positioning of a control object, such as with servo seam misplacements on a data storage device storage medium. An actual position for the control object is determined in relation to a corrected commanded position of the control object and a corrected position error of the control object. The corrected commanded position is determined in relation to a gain error and an actual commanded position, and the corrected position error determined in relation to the gain error and an actual position error. Preferably, an actual position error of the control object is next determined in relation to the actual position, and the control object is moved to reduce the actual position error. The positional indicia preferably comprise AB and CD seams of ABCD servo dibit patterns on a recording surface.

Abstract: A motor controlling method according to the present invention involves causing rotation of a motor to commence by applying an initial power that can cause movement of an object to be transported to commence, to the motor; obtaining a position of the object to be transported after the motor has been controlled so as to cause the object to be transported to move to a target position based on a signal outputted in response to the rotation of the motor; and correcting an initial power to be used when movement of the object to be transported is caused to commence a next time in response to a difference between the target position and the obtained position of the object to be transported.

Abstract: A programming device for making a program for returning a robot to its waiting position when the robot is stopped by an error. A robot control device is connected to the programming device via a network line. When the robot during operation is stopped by the error, information including data of a position where the robot is stopped is transferred to the programming device. The programming device makes the returning program, based on layout data, the received information and data including teaching positions and attribute data of the positions, by which the robot may be returned from the stop position to the waiting position without interfering with peripheral devices. The returning program is executed by using an offline simulation function of the programming device. The program is transferred to the robot control device after it is judged that interference will not occur. The robot may be safely returned to the waiting position by executing the returning program.

Abstract: A motor position signal processing apparatus electrically connected to a signal processor and an optical encoder of a motor control system includes a first switch, a second switch, a first signal integration amplifier, a first separator, a second signal integration amplifier, a second separator, a third signal integration amplifier, a third separator, a fourth separator and an inverter. An enable signal outputted by the signal processor is processed by the inverter to switch the operation to the first switch or the second switch. An incremental signal outputted by the optical encoder, a motor mechanical position and a reset correction signal are processed by the first, second and third signal integration amplifiers and transmitted to the signal processor for controlling the operation of a motor.

Abstract: An electric motor controller for controlling an electric motor that includes a rotor and a stator that faces the rotor.

Abstract: A numerical controller is capable of foreseeing the occurrence of interference during operation of a machine and securely preventing the interference. An advanced position calculating section determines advanced time for the next interference check, based on an end time point of an interference check by an interference checking device and the sum of a time required for the interference check, a time required for communication, a time required for decelerating and stopping a movable part, and a predetermined float. If an interference checking device detects interference, the interference checking device delivers an axis stop signal the movable part.

Abstract: An aircraft user interface haptic feedback system includes a user interface, a position sensor, a cogless motor, and a control circuit. The user interface is movable to a position. The position sensor senses the position of the user interface and supplies a user interface position signal. The cogless motor is coupled to the user interface, and receives motor drive signals. The cogless motor, in response to the motor drive signals, supplies feedback force to the user interface. The control circuit receives at least the user interface position signal and a signal representative of the motor current and is operable, in response to at least these signals, to control the motor current supplied to the cogless motor using a non-trapezoidal motor commutation scheme.

Abstract: A movement control apparatus for a moving member, includes: a drive unit that moves a moving member by rapid traverse on a first axis and a second axis intersecting the first axis, and overlaps the rapid traverse movements in the two axis directions to thereby allow the moving member to move around the periphery of a given area; a reference arc setting unit that sets a reference arc inscribed in the first and second axes; a timing setting unit that sets an overlap movement start timing for the rapid traverse of the moving member based on the reference arc when switching the moving member from the first axis to the second axis; and a control unit that controls the operation of the drive unit to move the moving member at a timing set by the timing setting unit.

Abstract: A display apparatus includes a base, a display screen part supported on the base turnably, a driving part for turning the display screen part in accordance with an inputted control signal, a turning prevention mechanism for preventing turning of the display screen part, a judgment part for judging on the basis of the inputted control signal whether the display apparatus is operated or not, and a controller for producing a signal for operating the turning prevention mechanism to prevent turning of the display screen part when it is judged that there is no operation to the display screen part and producing a signal for releasing operation of the turning prevention mechanism when it is judged that there is operation to the display screen part.

Abstract: A “construction set” consisting of active and passive parts connected by joints that can be manipulated to form an movable articulated assembly representing things like animals and skeletons. Each active part includes a position sensor for acquiring and storing position data specifying a sequence of positions assumed by the active part as the assembly is reshaped, and a controllable drive motor for moving the active part relative to a connected part in accordance with the position data.

Abstract: A system and method of command signal conditioning in high response systems is disclosed. The system includes a central digital controller having a digital controller frame rate, a motor, a motor controller in communication with the digital controller and the motor, the motor controller having a motor controller frame rate higher than the digital controller frame rate, and a signal conditioner adapted to condition the command signal to produce a modified command signal at the motor controller frame rate. The signal conditioner is preferably implemented in software. In one embodiment, the signal conditioner is adapted to calculate a moving average at the frame rate of the motor controller. In another embodiment, the signal conditioner comprises a first order hold and a filter in communication therewith. A method of command signal conditioning in accordance with the foregoing is also disclosed.

Abstract: A servo control apparatus includes a motor including a motor shaft, the motor for driving a drive subject; a detecting section that detects a rotation position of the motor shaft; and a control system configured to generate a motor torque command for the motor using the rotation position. The control system includes an observer configured to estimate friction torque occurring in the vicinity of the motor shaft on the basis of the rotation position and an application voltage to the motor. The observer is configured to generate a compensation voltage to be added to the application voltage on the basis of the friction torque.

Abstract: The invention includes a system and method for generating simulated encoder outputs in a control system. An output pulse width between reference position inputs is computed, the output pulse width being based upon a difference between an updated reference position input and a previous reference position input, and upon a time interval between the reference position inputs. Next, a plurality of simulated encoder pulses is output between updates of the reference position input based upon the computed output pulse width. The output pulse is thereafter adjusted in a closed loop manner between updates of the reference position input.

Abstract: A motor control amplifier for position feedback control is provided utilizing the inherent inductor and/or resistor dynamics of the motor. The motor control amplifier applies a voltage to the motor equivalent to the electrical motor resistance multiplied by the current of the motor, canceling out the electrical motor resistance, and thereby providing position feedback control through motor inductance. A command term/voltage could be added to make the position feedback control relative to a setpoint. Further, a motor control amplifier for feedback control to arbitrary dynamics is provided. The motor amplifier applies a voltage proportional to a wave command signal. The motor amplifier has a sensing component to provide a wave return signal to construct a wave transformer from the electrical motor resistance.

Abstract: A method of optimizing a servo controller power required in the operation of two-dimensional flexure (Microelectronic Memory Storage) MEMS devices. Furthermore, provided is an arrangement for optimizing servo controller power in a two-dimensional flexure MEMS storage device through a utilization of the inventive method.

Abstract: A driving apparatus (100p, 100s) is provided with: a base portion (110); a stage portion (130) on which a driven object (12) is mounted and which can be displaced; an elastic portion (120) which has elasticity to displace the stage portion in one direction (Y axis); a first applying device (151-2, 152-2, 22) for applying an excitation force for displacing the stage portion such that the stage portion is resonated in the one direction at a resonance frequency determined by the stage portion and the elastic portion; and a second applying device (151-1, 152-1, 22) for applying a driving force for displacing, in a stepwise manner or in a continuous manner, the stage portion or the driven object mounted on the stage portion in other direction (X axis), wherein the stage portion or another stage portion mounted on the stage portion as the driven object is divided into a plurality of stage fractions.

Abstract: A robotic system is provided that enables easy manipulation and various operations. A walking operation allocated to a manipulated switch operation section is performed. Meanwhile, the right ankle roll axis control motor, the left ankle roll axis control motor, right hip joint roll axis control motor, and the left hip joint roll axis control motor are driven according to the operation amount of a manipulated analog operation section. Thus, the barycentric position of the robot is shifted to change the traveling direction of walking.

Abstract: A method for estimating joint load at a joint of a segment. The method comprises the steps of receiving kinematic data, determining a modified acceleration using at least the kinematic data, estimating a joint load using at least the modified acceleration; and determining simulated kinematic data for the segment using at least the joint load. The present disclosure thus addresses the problems with conventional inverse dynamics analysis by providing a forward dynamics solution for estimation of joint loads that is stable, guaranteed to converge, computationally efficient, and does not require acceleration computations. According to one embodiment, a joint load is estimated using an approach of closed form dynamics.

Abstract: A lithographic apparatus includes a projection system to project a patterned beam of radiation onto a substrate, which is held on a substrate support and a drive system to move the substrate support along a trajectory. In the drive system, set-point data, including set-point coordinates, are generated for moving the substrate support relative to the projection system in a first and second directions. The set-point coordinates of the first and second directions are transformed into set-point coordinates of third and fourth directions. Motion data, including motion coordinates, are generated for moving the substrate support relative to the projection system in the third and fourth directions, limiting the velocity in the third and fourth directions to a maximum velocity. The motion coordinates of the third and fourth directions are transformed into motion coordinates of the first and second directions for driving the first and second drive motors.

Abstract: An actuator controller includes an actuator body to be driven in a predetermined driven range, an actuator driving unit; and a controller body for controlling the driven position of the actuator body. The controller body includes an instructing signal outputting zone configured to outputting a position instructing signal for instructing the driven position of the actuator body according to a bid, excluding arbitrary two bits among the predetermined bit counts, an normal direction forcedly driving signal for instructing a normal direction forcedly driving to drive the actuator body in a predetermined direction with the one of the arbitrary two bits, and a reverse direction forcedly driving signal for instructing a reverse direction forcedly driving to drive the actuator body in a direction reverse to the predetermined direction with the other arbitrary bit.

Abstract: A first determining section determines whether a recording medium is conveyed in a first direction. A setting section sets a first current value as a current initially outputted to a DC motor each time the first determining section determines that the recording medium is conveyed in the first direction. A first current outputting section outputs a current at the first current value, and subsequently outputs by steps a current gradually higher than the first current value motor until the first determining section again determines that the recording medium is conveyed in the first direction. A second determining section determines whether the recording medium is conveyed in a second direction opposite the first direction after the first current outputting section outputs a current at the first current value.

Abstract: In controlled mechanical hardware, such as servo-controlled hardware, data from the control algorithm is obtained and logged for possible later analysis. Loss-less compression is provided without increasing the size of the storage memory. Instead of continuously storing the complete (absolute) value of a monitored control parameter, an absolute value is stored in an absolute entry and one or more values of the parameter which are relative to each preceding value are stored in a sequence of associated relative entries. The space required to store a relative value is less than the space required to store an absolute value. Updated absolute values and groups of associated relative values may also be recorded periodically or when a relative value is too large for the allotted space. The size of relative values may be variable and appropriate information data entries may be generated to indicate the size of associated relative entries.

Abstract: Taught herein is a controller for a direct current brushless motor connected to a high voltage control system, comprising a microprocessor and an input/output interface circuit connected between the high voltage control system and the microprocessor; wherein the input/output interface circuit is a step-down circuit for transforming a high voltage control signal into a low-voltage control signal. The controller enables the high voltage control system to cooperate with motor, therefore a user is not necessary to design a new high voltage control system when replacing the conventional AC motor with the DC brushless motor, which saves time, and reduces cost.

Abstract: A machine includes an operator seat and an armrest adjacent the operator seat. The machine may also include a control system, which may include a control handle extending at least partially upward from the armrest. The control system may also include a force feedback device drivingly connected to the control handle and operable to supply feedback force to the control handle. The force-feedback device may include at least one of an actuator or a brake. Additionally, the control system may automatically adjust the magnitude of the feedback force supplied to the control handle by the force feedback device in at least some circumstances.

Abstract: An image sensing apparatus, which has a constant-voltage driven stepping motor, comprises a PWM waveform generation part that generates pulse signals to be applied to switching devices; and a PWM waveform determination section that determines a PWM waveform to be generated by the PWM waveform generation section. The PWM waveform determination section determines, in accordance with the determined rotation speed value and output torque value of the stepping motor, a duty ratio range that is a range extending from the minimum to the maximum of the duty ratio of the pulse signals. It is designed that the higher the rotational speed value is, the wider the duty ratio width is.

Abstract: A servo device is provided which includes a drive source made of a brushless motor. A DC motor driving integrated circuit produces output signals and controls the output of a three-phase brushless motor driving integrated circuit to drive the brush less motor. A selection switching section detects information regarding the rotational speed of the brushless motor. The selection switching section extracts the counter electromotive voltage of the brushless motor, feeds the voltage back to the DC motor driving integrated circuit and PWM controls a drive signal output from the three-phase brushless motor driving integrated circuit. This allows the brushless motor to be easily applied to the servo device.

Abstract: A driving apparatus for a DC brushless motor of a ceiling fan is provided. By setting at least one coder and one sensor outside the DC brushless motor, the driving apparatus can sense the position of magnetic poles of the motor for driving the motor. Meanwhile, a controller set with the motor stores the rotation speed of the motor before being turned off by detecting the turn-off time of a turn-on/off signal.

Abstract: A servo control apparatus for a linear motor comprises a position feedback device, a driver and a position compensating device that are connected with one another. The servo control apparatus is electrically connected to the linear motor. By such arrangements, it can not only improve the precision of the displacement of the linear motor, but also make the movement of the linear motor relatively smooth.

Abstract: A circuit is adapted to activate a writer head of a data storage media drive during both the boost periods as well as the steady state periods. The current supplied to the writer head during the boost periods exceeds the steady state current and flows between positive and negative voltage supplies so as to provide the required magnetic flux change in the inductor disposed in the write head. During the steady state periods, a switch circuit is turned on to provide a second current path across the writer head. During the steady state periods, the current flows between the positive voltage supply and the ground to reduce power consumption. The switch circuit is turned off during the boost periods.

Abstract: A method for detecting and controlling output characteristics of a DC motor is provided in the present invention, wherein an input impedance related to the DC motor is measured for analyzing the output characteristics of the DC motor so that the output characteristics of the DC motor is capable being controlled according to the requirement of usage. By means of the foregoing method, the present invention further provides a self-propelled apparatus which functions to detect and control the output of the DC motor for maintaining the moving speed according to the environment status and road condition.

Abstract: A disk drive system including retract logic for control of the voice coil motor in a retract operation, in which the voice coil motor positions the read/write head actuator arm in a safe place in a loss-of-power event, is disclosed. The retract logic includes circuitry for controlling the application of power to the voice coil motor from an external capacitor in a pulse-width modulated manner. Current from the capacitor is coupled to the voice coil motor in a drive phase of the pulse-width modulation cycle, and is recirculated through the voice coil motor in a complementary phase of the pulse-width modulation cycle. The recirculation is accomplished by a recirculation transistor that is smaller than the pull-down transistor used in the drive phase.

Abstract: A speed region of a motor is divided into a region lower than a first switch speed VS1, a region higher than a second switch speed VS2 and a region between the first and second switch speeds. An abnormal load determination level to be compared with an estimated load obtained by an observer is set for each of the regions. An abnormal load determination level AL4 applied when an acceleration exceeds a threshold value is set. The abnormal load determination level AL4 is used for comparison with the estimated load until a predetermined period of time elapses after the acceleration to be commanded to the motor, which once exceeded the threshold level, drops. In other cases, the estimated load is compared with the abnormal load determination level having a value according to the speed. If the estimated load exceeds the compared abnormal load determination level, it is judged that a collision is detected.

Abstract: A velocity control loop of a motor control apparatus including a notch filter. The notch filter attenuates a signal component at a central frequency from a motor driving command, and outputs the attenuated motor driving command. The driving of a motor is controlled based on the attenuated motor driving command. The central frequency of the notch filter is set equal to a frequency at which a phase of open loop frequency characteristics of the velocity control loop that does not include a notch filter is a value obtained by subtracting 180 degrees from a preset phase margin. An attenuation factor of the notch filter by which the signal component at the central frequency is attenuated is set so that a gradient of a phase diagram of the open loop frequency characteristics of the velocity control loop including the notch filter is substantially zero.

Abstract: The present invention is a rotary indexing table driven by an induction motor. The rotary indexing table includes a rotatable work supporting platform, an AC induction motor including a motor shaft coupled to the rotatable work supporting platform; and a controller operatively coupled to the AC induction motor. The AC induction motor is equipped with a high resolution positional feedback device. The high-resolution positional feedback device may be an encoder or a resolver. The controller is configured to drive the AC induction motor in a direct drive manner. The high-resolution positional feedback device is operatively coupled to the controller, and the controller is configured to filter a signal provided by the high-resolution positional feedback device. The signal provided by the high-resolution positional feedback device may be a square wave or a sine wave. The present invention is also directed to a method precisely driving and positioning a rotary indexing table.

Abstract: A reference position detecting apparatus includes an electric motor and a motor control unit. The electric motor includes a plurality of first coils and a plurality of second coils. The electric motor further includes a rotor that rotates when at least one of the plurality of first coils and the plurality of second coils is supplied with electricity. The motor control unit controls electricity supplied to either one of the plurality of first coils and the plurality of second coils to rotate the rotor to a limit position in a movable range of an object.

Abstract: A control device for a stepping motor is provided that can reduce torque generated by a motor and control the expansion of a speed deviation when the rotational speed of a rotor exceeds a speed command. The control device includes first judging means (27) for judging whether a positional deviation of a rotor is within a predetermined range, second judging means (28) for judging whether a sign of the positional deviation and a sign of a speed deviation coincide with each other, and phase setting means (34 to 35) for setting a winding current command phase.

Abstract: A method for estimating joint load at a joint of a segment. The method comprises the steps of receiving kinematic data, determining a modified acceleration using at least the kinematic data, estimating a joint load using at least the modified acceleration; and determining simulated kinematic data for the segment using at least the joint load. The method addresses the problems with conventional inverse dynamics analysis by providing a forward dynamics solution for estimation of joint loads that is stable, guaranteed to converge, computationally efficient, and does not require acceleration computations. According to one embodiment, a joint load is estimated recursively.

Abstract: Embodiments of the invention provide a disk device and a method of controlling the device which is capable of suppressing peak current, even for serial communication, that is required when initiating rotation of a spindle motor down to a level equivalent to that of parallel communication, without prolonging elapsed time before reaching the steady rotation speed. In one embodiment, an HDD includes a serial communication circuit which executes serial communication with a host, an SPM which rotates a disk, an HDC/MPU which controls the SPM and the serial communication circuit. The HDC/MPU, after shutting down the serial communication circuit once, starts up the serial communication circuit again when rotation speed of the SPM reached the specified standard value, and establishes serial communication with the host by means of the serial communication circuit.

Abstract: A method for providing independent static and dynamic models in a prediction, control and optimization environment utilizes an independent static model (20) and an independent dynamic model (22). The static model (20) is a rigorous predictive model that is trained over a wide range of data, whereas the dynamic model (22) is trained over a narrow range of data. The gain K of the static model (20) is utilized to scale the gain k of the dynamic model (22). The forced dynamic portion of the model (22) referred to as the bi variables are scaled by the ratio of the gains K and k. The bi have a direct effect on the gain of a dynamic model (22). This is facilitated by a coefficient modification block (40). Thereafter, the difference between the new value input to the static model (20) and the prior steady-state value is utilized as an input to the dynamic model (22). The predicted dynamic output is then summed with the previous steady-state value to provide a predicted value Y.

Abstract: An imaging system that includes a radiation source. An image receptor is located to receive radiation emitted by the radiation source. The imaging system further has a servo system that includes a computer operationally coupled to a motor-load element. The servo system is configured to position the radiation source, the image receptor and the object to be scanned. The servo system is configured to measure at set time intervals in real-time a position of the radiation source, the image receptor, and the object. The measured position is used to predict a native hardware motion parameter value for the servo system.

Abstract: There is provided a motor driving apparatus in which variations in individual circuit constants have a small effect even when a drive current is small. An error amplifier circuit amplifies a difference between a current detection signal showing a current value of a drive current that flows in the motor and a drive command signal controlling the drive current and converts an amplified difference into a current to output the current as an error amplifier current signal. A D/A conversion circuit generates a sinusoidal signal from the error amplifier current signal based on a digital signal sequence outputted from a rotational position detecting unit. It is preferable that a transfer coefficient of the error amplifier circuit is inversely proportional to the resistance value of the D/A conversion circuit.

Abstract: An electronic cam using a servo motor is controlled such that its motion including its acceleration will be connected between synchronized and non-synchronized control sections. A controlled object is moved at a fixed speed during the synchronized control section. A fifth-order function for position control of the electronic cam, a fourth-order function for speed control of the electronic cam and a third-order function for acceleration control of the electronic cam are used in the non-synchronized control section such that operation of the electronic cam at transition points between the synchronized control section and the non-synchronized control section is smoothly controlled.

Abstract: An arrangement having at least one movable furniture part, in particular having a drawer or the like, having at least one drive unit and at least one regulating device for regulating the at least one drive unit, wherein the arrangement (7) has at least one, preferably analog, acceleration measuring device (2), with the at least one acceleration measuring device (2) generating an acceleration signal that is characteristic of accelerations caused by forces applied to the at least one movable furniture part (3) from the outside and that may be supplied to the at least one regulating device (1).

Abstract: A motor drive control unit includes a chip in which everything about a control system is provided and controls a spindle motor which rotates magnetic disks at a constant speed. When a measurement instruction is received from a disturbance generating unit and the upper-level device, sine wave disturbance is generated in the revolution speed of the spindle motor which depends on the motor drive control unit. A speed detecting unit detects the revolution speed of the spindle motor as measured data while the disturbance is being generated by the disturbance generating unit. A measured data transferring unit transfers the detected measured data detected by the speed detecting unit to the upper-level device, wherein control characteristics such as gains and phases with respect to frequencies of the motor control unit are computed.

Abstract: A dustbin, adapted to be opened/closed automatically by induction actuated, includes a container body, cover, motor and actuating device, wherein the motor is connected to the driven element of the cover through the actuating device. The dustbin includes a sensing and controlling device of the stroke of the cover, wherein a cover stroke perception and a shut off circuit, the cover stroke perception is connected with the shut off circuit, and the shut off circuit is connected with the motor, the shut off circuit receives the activating signal from the cover stroke perception and then controls the motor to actuate correspondingly, the cover's stroke inducted by the trigger; point of the cover stroke perception is less than the whole stroke during the closing of the cover. The noise of the crash between the cover and the container body is low, and closing of the cover is rapid and spiffy.

Abstract: A shock detection circuit housed in an electronic device includes an output shock signal that is indicative of vibration amplitude. To compensate for vibrations that are experienced by the electronic device, the output shock signal is analyzed. The analysis of the output shock signal allows a vibration frequency of the output shock signal to be identified and used in vibration compensation.

Abstract: There are provided two kinds of nuts of a ball thread nut 20 and a non-ball thread nut 30 which is rotatable in synchronization with the ball thread nut 20 and in which a thread groove in rectangular or trapezoidal shape in section is formed. In a thread rod 10, two kinds of thread grooves are formed at the same pitch, one 11 of the thread grooves being in an arc shape in section so as to be meshed with the ball thread nut 20 through balls B and the other thread groove 12 being in a rectangular or trapezoidal shape in section so as to be meshed with the non-ball thread nut 30. When load is less than a predetermined value, the thread ridge of the non-ball thread nut 20 and the thread ridge 13 of the thread rod 10 are separated and are out of contact with each other so that the thread rod 10 is moved in the axial direction thereof by only the ball thread nut 20.