Abstract: A mechanical system includes a plurality of amplifier groups each having a common power source unit connected to a higher-level power source and a plurality of power supply units for supplying power to servo motors from the common power source unit. A servo motor drive control device of the mechanical system includes a plurality of amplifier group electric power detection units each determining an electric energy of the corresponding one of the amplifier groups.

Abstract: The invention relates to a device for actuating an electrical switchgear comprising at least one mobile contact point driven by a rotary shaft. According to the invention, an electric motor comprising a rotating drive shaft can be coupled to the rotary shaft by means of a transmission, in order to drive the same.

Abstract: A driving force transmitting device for driving a driven unit includes a first driving unit, a second driving unit, a driving force-transmitted portion which is attached to the driven unit and to which driving forces of the first and second driving units are transmitted, and a controlling unit for separately controlling the first and second driving units, wherein driving force transmitting portions of the first and second driving units transmit the driving forces to the driving force-transmitted portion at its different positions, and wherein when the driven unit being driven is to be stopped, the controlling unit causes the first driving unit to drive in a direction reverse to a driving direction while the second driving unit continues to drive, then causes the first and second driving units to stop in a state in which the driving forces of the first and second driving units are balanced with each other.

Abstract: A method according to an example of the present invention is a servo control method to be applied to a feed drive mechanism configured to drive an object to be driven by using a plurality of motors, in which velocity control of the object to be driven is carried out by using a signal obtained by mixing velocity feedback signals of the motors with each other, and a torque instruction obtained by the velocity control is used for drive of all the motors. By this example, there is provided a servo control system capable of preventing a phenomenon in which a transfer function changes depending on the position of the object to be driven, and the phase abruptly lags to make the operation unstable, thereby making it difficult to increase the gain, from occurring.

Abstract: A motor control device includes at least one operating unit that is provided corresponding to at least one motor to operate the at least one motor, and a control unit that, each time at least one control cycle arrives in which the at least one motor is operated, sets a manipulated variable of the at least one motor to the at least one operating unit that operates the at least one motor of which the at least one control cycle arrives.

Abstract: A fractional boost system including a boost converter, responsive to the base level voltage of a power supply, for providing a boost level voltage to a load and a control system for sensing the current to the boost converter and limiting the boost function of the boost converter when the current to the boost converter exceeds a predetermined level, while applying the power supply base level voltage and supplying current exceeding the predetermined level to the load.

Abstract: A disclosed moving body controlling device includes a first moving body driven by a first motor that is controlled by a first control unit, a second moving body driven by a second motor that is controlled by a second control unit and affecting movement of the first moving body, a memory unit storing a relationship between the second motor rotational speed and an indicating value for driving the first and second motors when the second control unit changes the second motor rotational speed while the first control unit controls a first motor rotational speed to cause a first rotational body surface speed to be a predetermined speed in a mode of setting a second motor target rotational speed, whereby a reference point at which the surface speed starts to exceed the predetermined speed is detected, and based on the reference point the second motor target rotational speed is set.

Abstract: A switch is provided which is dynamically configurable via a network port thereon. One switch is employed to establish point-to-point electrical connections between devices under test (DUTs) and host devices coupled to upstream ports and downstream ports on the switch respectively. Two switches coupled to a network are employed to facilitate a distributed test lab. DUTs are coupled to upstream ports on a first switch which, based on communication with a test controller over the network, establishes a logical connection between the upstream port coupled to a particular DUT and the network. Host devices are coupled to downstream ports on a second switch which, based on communication with the test controller over the network, establishes a logical connection between the downstream port coupled to a particular host device and the network. A logical connection is also established across the network between the particular DUT and host device.

Abstract: A synchronous control apparatus to synchronously control a plurality of motors with respect to a control subject includes a command device and a plurality of motor control devices. The control subject includes the motors, a plurality of position detectors configured to detect a plurality of position information of the motors respectively, and at least one coupler connecting movable axes of the motors. The command device includes a first position controller which is configured to compute a work position based on the position information detected by the position detectors and which is configured to compute, based on a difference between a position command and the work position, a new position command. Each of the motor control devices includes a second position controller configured to compute commands to drive the plurality of motors based on a difference between the new position command and the position information.

Abstract: The present invention relates to a control system of multi-shaft servo motor, wherein, comprises a position loop module (400) for receiving a position loop given value and a position feedback value of respective shelves and figuring out a velocity loop given value; a velocity loop module (500) for receiving the velocity loop given value and a velocity feedback value of respective shelves and figuring out a current loop given value; a current loop module (200) for receiving the current loop given value and a current feedback value of respective shelves and outputting a current loop output value; a PWM signal generation module (300) for receiving the current loop output value from the current loop module (200) and generating a PWM signal for controlling respective shelves of the servo motor; and a multi-shaft time sequence control module (700) for controlling the position loop module (400), the velocity loop module (500), the current loop module (200) and the PWM signal generation module to receive and process

Abstract: A multi-actuator motion control system includes a control methodology that coordinates the motion of multiple actuators while limiting the force-fight between the actuators. Control logic is provided in a relative coordinate system that allows control of the mean actuator position. Force-fight between the actuators is decoupled from the actuator position by estimating load forces on the actuator using reduced-order observers.

Abstract: A motor speed control system includes a pulse outputting device capable of outputting a pulse each time a motor rotates, a pulse interval determining device capable of determining a pulse interval between the pulses outputted, and a comparative value calculating device capable of obtaining a comparative value as the product of a first value and a second value. The first value can correspond to the pulse interval determined, and the second value can correspond to a set rotational speed of the motor. The system can further include a set value calculating device capable of obtaining a set value as the product of the second value and a third value and a controller capable of controlling a supply of power to the motor such that a difference between the set value and the comparative value decreases.

Abstract: A numerical controller capable of performing axis reconfiguration of control axes in at least two paths without need for the paths to wait. A program block is read and it is determined whether or not the read block includes an axis detachment command. If the block includes the axis detachment command block, an action axis attribute of an control axis designated by the axis detachment command is altered to a non-action axis attribute. Further, if the read block includes an axis allocation command, it is determined whether or not an control axis designated by the axis allocation command becomes a non-action axis, and when the control axis has the non-action axis attribute, the non-action axis attribute of the control axis is altered to a designated path's action axis attribute. Thus, the axis reconfiguration processing in one path can be performed separately from axis reconfiguration processing in another path.

Abstract: Initial speeds in the move commands for respective control axes at servo-on are determined according to parameter setting, or the comparative relationship or difference in speed among the actual speeds of the control axes so that difference in position between the control axes does not increase as the move commands are executed after the servo-on. The actual speeds of the control axes are set as initial speeds in the move commands, and a target axis is specified on the basis of the comparative relationship among their actual speeds and the other control axes are accelerated or decelerated at the acceleration or deceleration rate specified in the move commands to attain the position and speed of the target axis, so that differences in position and speed among the control axes are gradually decreased as the move commands are executed after the servo-on, thereby preventing abrupt speed changes and suppressing mechanical shocks.

Abstract: An apparatus and method for servomotors of an electric injection molding machine includes a motion controlling unit, two driving amplifying units, and two servomotors respectively connected to the driving amplifying units. The motion controlling unit includes two servomotor position controllers both for receiving a first position command, and the driving amplifying units are respectively connected to the servomotor position controllers for receiving a second and third position command. Two position detectors are respectively received in the two screw caps that are mounted to the servomotors for detecting absolute positions of the corresponding screw caps. The screw caps are respectively connected to inputs of the first and second servomotor position controllers to form two screw cap position feedback circuits.

Abstract: Disclosed is an assembly comprising at least two electric drive units (4) for respectively driving one of at least two drawers (2) which are movably mounted within a common furniture carcass (3). A measuring instrument (10) is assigned to each drive unit (4) in order to detect a force (F) that a user applies to the respective drawer (2). The inventive assembly further comprises at least one control or regulation device (9) for controlling or regulating the drive units (4). The measuring signals of the measuring instrument (10) can be fed to the control or regulation device (9) while the control or regulation device (9) can trigger the associated drive unit (4) after receiving a predetermined measuring signal from one of the measuring instruments (10).

Abstract: A servomotor control system includes: an integrated control unit for integrally controlling servomotors; and servomotor units coupled with the integrated control unit and the servomotors. Each servomotor unit includes: a motor driver; a rotation detector of the servomotor; an original point detector for detecting an original point of the servomotor; a communication element for obtaining control information including rotation position instruction information from the integrated control unit; a rotation position calculator for calculating a current rotation position of the servomotor based on a rotation detection signal; a motor drive instruction element for outputting driving instruction information to the motor driver according to the control information and the current rotation position; and a current rotation position correction element for resetting the current rotation position to a predetermined original point when the original point detector detects the original point.

Abstract: A driving control apparatus for driving a controlled object. The apparatus includes first and second interferometers, each of which (i) detects a position of the controlled object in a predetermined direction and (ii) produces a respective detection value. A control unit obtains a rotation amount of the controlled object based on the detection values produced by the first and second interferometers, at a predetermined measurement timing, to calculate a controlled variable based on the rotation amount and a target value, and to output the controlled variable.

Abstract: A system, in one embodiment, includes a drive having a housing, a stator disposed in the housing, a rotor disposed in the stator, and a programmable logic controller disposed inside, mounted on, or in general proximity to the housing. In another embodiment, a system includes a network, a first motor having a first integral programmable logic controller coupled to the network, and a second motor having a second integral programmable logic controller coupled to the network. In a further embodiment, a system includes a rotary machine having a rotor and a stator disposed concentric with one another, a microprocessor, memory coupled to the microprocessor, a power supply coupled to the microprocessor and the memory, and a machine sensor coupled to the microprocessor.

Abstract: A pointing apparatus and method of operation for an antenna mount provided with a base frame and an antenna mount rotatably coupled together. A first wheel rigidly coupled to one of the base frame and the antenna mount driven by a mechanical linkage with a first drive wheel and a second drive wheel mounted to the base frame or the antenna mount not rigidly coupled to the first wheel. The first drive wheel and the second drive wheel driven against one another in opposite directions; a torque level unbalance applied between the first motor and the second motor operative to rotate the base frame and the antenna mount with respect to one another in a first desired direction.

Abstract: A disclosed moving body controlling device includes a first moving body driven by a first motor that is controlled by a first control unit, a second moving body driven by a second motor that is controlled by a second control unit and affecting movement of the first moving body, a memory unit storing a relationship between the second motor rotational speed and an indicating value for driving the first and second motors when the second control unit changes the second motor rotational speed while the first control unit controls a first motor rotational speed to cause a first rotational body surface speed to be a predetermined speed in a mode of setting a second motor target rotational speed, whereby a reference point at which the surface speed starts to exceed the predetermined speed is detected, and based on the reference point the second motor target rotational speed is set.

Abstract: The invention relates to a drive system comprising a control unit (1), which is connected to drive units (3a, 3b, 3c, 3d, 3e, 3f, 3g) via a data bus (2) for the exchange of data. According to the invention, one drive unit (3a, 3b) is connected to the drive motor (7a, 7b) in order to control the latter (7a, 7b) and an additional drive unit (3c, 3d, 3e, 3f, 3g) is connected to a magnetic bearing (11c, 11d, 11e, 11f, 11g) of a magnetic spindle bearing arrangement (23) in order to control said bearing (11c, 11d, 11e, 11f, 11g). The invention thus provides a drive system, in which a magnetic spindle bearing arrangement (23) is integrated.

Abstract: Servo controller for controlling a plurality of motors including a master motor and a slave motor cooperatively driving a movable member. The servo controller is configured to control the master motor and the slave motor based on position references for the master motor. The servo controller includes a master speed controller configured to calculate a reference torque for the master motor based on speed errors for the master motor. The slave speed controller is configured to calculate reference torques for the slave motor based on speed errors for the slave motor. Each of the reference torques includes a proportional torque part and an integral torque part. The servo controller is configured to calculate each of the integral torque parts based on the speed errors of the master motor and the speed errors of the slave motor, such that the torques due to the integral torque parts will be distributed equally between the master and slave motors or according to a predefined ratio.

Abstract: A numerical controller capable of performing axis reconfiguration of control axes in at least two paths without need for the paths to wait. A program block is read and it is determined whether or not the read block includes an axis detachment command. If the block includes the axis detachment command block, an action axis attribute of an control axis designated by the axis detachment command is altered to a non-action axis attribute. Further, if the read block includes an axis allocation command, it is determined whether or not an control axis designated by the axis allocation command becomes a non-action axis, and when the control axis has the non-action axis attribute, the non-action axis attribute of the control axis is altered to a designated path's action axis attribute. Thus, the axis reconfiguration processing in one path can be performed separately from axis reconfiguration processing in another path.

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: The control apparatus 10 of a servo motor of the present invention has a position control unit 11 controlling the position of a servo motor 33, a speed control unit 12 controlling a speed of the servo motor 33, a distributing unit 13 dividing the speed command output by the position control unit 11 into a filtered part Vf which is filtered to suppress vibration and a nonfiltered part Vnf, a filtering unit 14 receiving as input the filtered part Vf and filtering and outputting the filtered part Vf, and an adder unit 15 adding the filtered part Vf filtered by the filtering unit 14 and the nonfiltered part Vnf and outputting the result to the speed control unit 12.

Abstract: In a first aspect, a substrate loading station is served by a conveyor which continuously transports substrate carriers. A substrate carrier handler that is part of the substrate loading station operates to exchange substrate carriers with the conveyor while the conveyor is in motion. A carrier exchange procedure may include moving an end effector of the substrate carrier handler at a velocity that substantially matches a velocity of the conveyor. Numerous other aspects are provided.

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: A robot control apparatus comprises a servo amplifier having an AC/DC converter and used for driving a servo motor of a robot, and performs control so that power for driving the robot is supplied to the servo amplifier through a capacitor inrush current preventing resistor until precharging of a capacitor provided for the AC/DC converter is completed. The robot control apparatus has a first operation mode in which the power is supplied by bypassing the resistor, a second operation mode in which power is supplied through the resistor thereby controlling the servo motor in the robot to a lower driving speed than the driving speed in the first operation mode, and a selector switch SW for effecting switching from the first operation mode to the second operation mode or from the second operation mode to the first operation mode. With this configuration, a power supply circuit for supplying power to the servo amplifier for limiting the driving of the robot is reliably implemented by hardware.

Abstract: In position tandem control in which one movable member is driven by two motors, an output of the integral element of the velocity control unit in the control system for one motor is copied to the integral element of the velocity control unit in the control system for the other motor. A preload is added to a torque command output from each of the velocity control units in the motor control systems for two motors so that torques in mutually opposite directions are generated to suppress backlash between gears.

Abstract: A servo controller which drives one movable member 1 by means of a plurality of motors including one main motor 31 and at least one sub motor 41 includes: a main-motor controlling unit 30 for controlling driving of the main motor 31; and at least one sub-motor controlling unit 40 for controlling driving of the at least one sub motor 41. The sub-motor controlling unit 40 includes a sub-motor position controlling unit 44 and a sub-motor velocity controlling unit 45. Both the sub-motor position controlling unit 44 and the sub-motor velocity controlling unit 45 do not have an integral characteristic.

Abstract: The present invention discloses a servo control circuit comprising: a first node for receiving a control voltage; a second node for receiving a feedback voltage; an operational amplifier controlling a current on a path according to the voltages at the first and second nodes, the path including an internal voltage node thereon; an analog to digital converter (ADC) for converting the voltage at the internal voltage node to a digital signal; and a control logic circuit for generating a servo control signal according to the digital signal.

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: There are included a plurality of actuators, an instruction generator for generating instructions of plural degrees of freedom, a position arithmetic unit for calculating positions of plural degrees of freedom from signals of a plurality of sensors, a control arithmetic unit for calculating operation amounts of plural degrees of freedom from the instructions of plural degrees of freedom and the positions of plural degrees of freedom, a thrust force conversion arithmetic unit for calculating thrust force instructions of the plurality of actuators from the operation amounts of the plural degrees of freedom, a current instruction unit for calculating current instructions which should be flowed to the plurality of actuators, and a sensor configuration input device for selecting a desired sensor configuration from among a plurality of sensor configurations. The positions of plural degrees of freedom are calculated by using a position arithmetic expression corresponding to a selected sensor configuration.

Abstract: A hybrid backplane uses multiple, parallel serial communication channels to provide flexibility and robustness in a motor drive control requiring high-speed data communication for the real-time control of motor waveforms.

Abstract: Electronic control system for a submarine actuator, said actuator comprising a container body, from which a drive shaft projects that is suitable for inserting in a seat of said submarine device. The system comprises an electronic control board for at least one electric motor arranged inside said container body suitable for moving said drive shaft.

Abstract: A method for determining accuracy of an actual position of a plurality of independent motors in a printing press is provided. The method includes commanding each of the plurality of motors in the printing press via a controller to move a desired initial position, comparing an actual position of each motor to the desired initial position of each motor, determining if the actual position of each motor is within a predetermined tolerance of the desired initial position, and resetting any motor outside the predetermined tolerance to be within the predetermined tolerance. A printing press is also provided. The printing press includes a plurality of printing press components and a plurality of motors. Each motor drives at least one of the printing press components and each of the motors has a desired initial position. The printing press also includes a position detector for determining an actual position of the motor with respect to the desired initial position of the motor.

Abstract: In a first aspect, a wafer loading station adapted to exchange wafer carriers with a wafer carrier transport system comprises a biasing element adapted to urge the end effector of the wafer loading station away from a moveable conveyor of the wafer carrier transport system upon the occurrence of a unscheduled event such as a power failure or an emergency shutdown. In a second aspect, an uninterruptible power supply commands a controller to cause the wafer carrier handler to retract the end effector from the wafer carrier transport system upon the occurrence of the unscheduled event, and provides the power necessary for the same. Numerous other aspects are provided.

Abstract: A machine has a basic body and a machine element. The machine element can be moved relative to the basic body by an electric working drive which is connected to an electric supply system via a working converter. An electric buffer drive is connected to the electric supply system via a buffer converter. The working converter and the buffer converter are controlled by a control device in line with a predetermined travel movement of the machine element in a coordinated manner. The coordination is such that a total load on the supply system by both converters together during the total travel movement of the machine element remains below a maximum load prompted by the working converter alone. The buffer drive has a drive shaft which has no flywheel connected to it.

Abstract: A servo motor controlling method includes: directly or indirectly detecting a position of a moving body which performs a circular-arc interpolation feeding motion by a servo motor; performing a feedback control for enabling the position of the moving body to comply with a position command; and at a quadrant changing time when a moving direction of the moving body is changed, performing torque correction on a torque command value according to a distance from a position where the moving direction is changed. By this method, a quadrant protrusion and a torque change with respect to a friction caused from a free zone at a time of reversion of a ball screw can be appropriately corrected. Especially, by performing a first torque correction for a static friction at the position where the moving direction is changed, and by performing a second torque correction for a moving friction after movement by the distance corresponding to the free zone, more appropriate correction can be obtained.

Abstract: A method for controlling the movement of axles whose drives are connected for exchanging energy, in particular by connecting intermediate circuits of the converters respectively comprised by the drives, prior to the start of the movement, a predictive determination of the sequence of movements being performed, in the process of which first the time-critical axle is determined, then the travel profile of the time-critical axle is defined, then a respective total energy consumption is assigned to the possible travel profiles of additional axles, from these, the profile is selected that has the smallest total energy requirement associated with it, and then the movement is carried out.

Abstract: A servomotor controller by which a load on a machine device can be reduced, and control capability can be stabilized as well as the resistance property for a temporary blackout or a temporary voltage drop can be more secured in accordance with driving conditions of the machine device and a motor load. The servomotor controller includes: a bus voltage detector for measuring a bus voltage, and a current detector for detecting current passing through a servomotor. A controller 9 switches, depending on the bus voltage, a position control operation with a velocity control operation, to decrease the current supplied to the servomotor in a case where the bus voltage is lower than a first predefined reference voltage.

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 control system for placing controlled members in required positions including two control columns assigned to the controlled members to be moved, each control column having two degrees of freedom. Two actuators controlled by two control circuits apply to their associated control column either a resisting torque or a displacement torque. Each control column is provided with a mechanical spring system spring-loading the associated control column into its neutral position and adapted to provide, in the event of manipulation of the corresponding control column, a resisting torque in support of the resisting torque supplied by the associated actuator.

Abstract: A vision system and method for calibrating motion of a robot disposed in a processing system is provided. In one embodiment, a vision system for a processing system includes a camera and a calibration wafer that are positioned in a processing system. The camera is positioned on the robot and is adapted to obtain image data of the calibration wafer disposed in a predefined location within the processing system. The image data is utilized to calibrate the robots motion.

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: Certain exemplary embodiments comprise a system comprising a plurality of Active Front End units adapted to be electrically coupled to a direct current (DC) bus. Each of the plurality of Active Front End units can be adapted to be electrically coupled to a separate winding of a transformer of a plurality of transformers. Each of the plurality of Active Front End units can be adapted to convert alternating current (AC) voltage to a DC voltage. Each of the plurality of Active Front End units can be adapted to supply the DC voltage to the DC bus. The DC bus can be adapted to be electrically coupled to a plurality of inverters.

Abstract: A synchronization device for an engine is provided that has a first active sensor and a second active sensor. The first active sensor is adapted to determine an angular position of a first shaft and the second active sensor is adapted to determine the angular position of a second shaft. The first active sensor and the second active sensor are adapted to provide information on the state of the angular position of the first shaft and the second shaft or the angular position of the first shaft and the phase position between the first shaft and the second shaft to the control device. In addition, the control device is adapted to provide a control signal for setting a given phase difference between the first and the second shaft.

Abstract: A motor control device includes: a first motor that provides a driving force for rotating a roll on which a roll paper is wound to supply the roll paper from the roll; a second motor that provides a driving force for driving a transport driving roller which is provided on a downstream side than the roll along a supply direction of the roll paper and used for transporting the roll paper; a load measuring unit that measures a relationship between a load on the first motor and a driving speed of the first motor when the second motor is not driven and the first motor is driven; and a motor control unit that simultaneously drives the first and second motors at a certain timing, provides to the first motor an interpolation output based on the measurement result of the load measurement unit and a driving speed of the second motor during the control, and transports the roll paper to the downstream side by driving the second motor.

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.