Abstract: An apparatus for controlling an end-effector assembly is provided. The apparatus includes a elongated element configured to engage the end-effector assembly and a drive assembly. A first motion transfer mechanism is disposed at an end of the elongated element. The first motion transfer mechanism is configured to transfer a rotational motion of the elongated element to a motion of the end-effector assembly. A second motion transfer mechanism is disposed at the second end of the elongated element. The second motion transfer mechanism is configured to transfer a motion of the drive assembly to the rotational motion of the elongated element.

Abstract: A system and methods are disclosed for precision placement or insertion of an object using robotic manipulation. A robotic tool includes at least three members, including a first member and a second member that grip the object between opposing faces and a third member that exerts a force on a proximate end of the object to push the object out of the robotic tool. A series of maneuvers is performed with the robotic tool in order to place the object on a surface or insert the object in a hole. The maneuvers include positioning the object against the surface, rotating the object around a contact point between the object and the surface, rotating the robotic tool around a contact point between the object and either the first or second member of the robotic tool, sliding the object horizontally along a surface, and tucking the object into a final desired position.

Abstract: An apparatus for controlling an end-effector assembly is provided. The apparatus includes a elongated element configured to engage the end-effector assembly and a drive assembly. A first motion transfer mechanism is disposed at an end of the elongated element. The first motion transfer mechanism is configured to transfer a rotational motion of the elongated element to a motion of the end-effector assembly. A second motion transfer mechanism is disposed at the second end of the elongated element. The second motion transfer mechanism is configured to transfer a motion of the drive assembly to the rotational motion of the elongated element.

Abstract: A workpiece conveying device capable of correctly positioning and conveying a workpiece that has a burr having an indefinite shape by means of a robot. A robot hand has first and second claws configured to move toward and away from each other. The first claw has a first contacting portion configured to come into contact with a lower surface of the burr, and a first clamping portion arranged at a front end of the first contacting portion and configured to come into contact with a main body of the workpiece. The second claw has a second contacting portion configured to come into contact with the lower surface of the burr, and a second clamping portion arranged at a front end of the second contacting portion and configured to come into contact with the main body. The first and second clamping portions cooperatively position and clamp the main body.

Abstract: A mechanical capstan amplifier. The mechanical capstan amplifier (60) having a first tensioner (64) with a first actuating rod (72) extending therefrom. The first tensioner (64) is configured to rotate the first actuating rod (72). The amplifier (60) also includes a drive motor (62) having a drive rod (78) extending therefrom. The drive motor (62) is configured to rotate the drive rod (78). A first cord (66), extending between the first actuating rod (72) and a first load to be moved also extends at least partially around the drive rod (78). Actuation of the first tensioner (64) causes the first cord (66) to tighten around the drive rod (78) and moves the load.

Abstract: According to one embodiment, a gripping device grips a rim of a workpiece by opening and closing gripping plates. The device includes a gripping unit, a hoisting and lowering unit and a motion control unit. The gripping unit includes a first and a second gripping plate. The first gripping plate has a first gripper to contact the rim. The second gripping plate has a second gripper to contact the rim. At least one of the first and second gripping plates is moved and the first and second gripper are spaced from each other. The hoisting and lowering unit is configured to hoist and lower the gripping unit. The motion control unit is configured to control open/close operations and hoisting and lowering operations. The motion control unit mechanically controls first first hoisting and lowering operations, controls second the open/close operations, and controls third second hoisting and lowering operations.

Abstract: A robotic finger assembly can include a base for mounting the finger to a robotic hand, with the base having a motor, and at least three links. The links of the robotic hand are connected to each other and to the base by a series of joints. A joint shaft and a pivot shaft, where the pivot shaft can freely move within its respective joint shaft, is connected to a preceding link. The motor is activated for opening or closing the finger. The finger closes on an object with a distributed force across the links. Grasping also can mean engaging an object like a human hand, by closing the first finger link until it engages the object, then closing the second finger link until it engages the object, then closing the third link until it engages the object. A robotic hand assembly is also disclosed.

Abstract: A tendon-driven robotic gripper is disclosed for performing fingertip and enveloping grasps. One embodiment comprises two fingers, each with two links, and is actuated using a single active tendon. During unobstructed closing, the distal links remain parallel, creating exact fingertip grasps. Conversely, if the proximal links are stopped by contact with an object, the distal links start flexing, creating a stable enveloping grasp. The route of the active tendon and the parameters of the springs providing passive extension forces are optimized in order to achieve this behavior. An additional passive tendon is disclosed that may be used as a constraint preventing the gripper from entering undesirable parts of the joint workspace. A method for optimizing the dimensions of the links in order to achieve enveloping grasps of a large range of objects is disclosed and applied to a set of common household objects.

Abstract: A clamp (1) is described for manipulators including a body (2) provided with two coplanar seats (21, 22) for housing the respective jaws (G1, G2). The jaws (G1, G2) are translatable in parallel in the respective seats (21, 22) alternately in the two ways, between a retracted position and an extended position, with average- or long-stroke. The clamp further includes an electrical motor (M) for activating the jaws and an electronic unit (CPU) for controlling the electric motor, inside the body (2) of the clamp (1). A transmission assembly is operatively interposed between the electric motor and the jaws, and includes in its turn two pushing screws (V1, V2) and respective translation assemblies (GT1, GT2). The rotation given by the electric motor (M) to the counter rotating pushing screws (V1, V2) causes the translation in opposite directions of the translation assemblies (GT1, GT2), which trail the jaws (G1, G2).

Abstract: An object is to provide a robot hand and a robot that are compact and lightweight and can reliably hold various types of workpieces. To achieve this object, the robot hand and the robot include: a plurality of joint portions that rotates about respective rotation axes parallel with each other; a plurality of links that is connected via each of the joint portions in sequence from a distal end; a linking member that links rotations of the joint portions adjacent to each other; and a single drive source that drives only the joint portion at a proximal end to rotate the joint portion.

Abstract: A gripper apparatus for removing and replacing objects such as containers or vials in an array of containers has a gripper head which extends downward from a support arm, a planetary gear assembly mounted in the gripper head including at least three planet gears, and at least one gripping grip extending downward from each planet gear and projecting beyond a lower end of the gripper head. A drive motor drives the planetary gear assembly to rotate the planet gears in opposite directions, moving the grips inward and outward along predetermined paths to grip and carry an object and release the object when in a desired location.

Abstract: A drive device includes plural moving portions, piezoelectric motors that move the moving portions, at least one drive circuit that drives the piezoelectric motors, and a connection/disconnection portion that connects and disconnects the piezoelectric motors and the drive circuit. The number of drive circuits is fewer than the number of piezoelectric motors.

Abstract: A tendon-driven robotic gripper is disclosed for performing fingertip and enveloping grasps. One embodiment comprises two fingers, each with two links, and is actuated using a single active tendon. During unobstructed closing, the distal links remain parallel, creating exact fingertip grasps. Conversely, if the proximal links are stopped by contact with an object, the distal links start flexing, creating a stable enveloping grasp. The route of the active tendon and the parameters of the springs providing passive extension forces are optimized in order to achieve this behavior. An additional passive tendon is disclosed that may be used as a constraint preventing the gripper from entering undesirable parts of the joint workspace. A method for optimizing the dimensions of the links in order to achieve enveloping grasps of a large range of objects is disclosed and applied to a set of common household objects.

Abstract: A robot finger driving module is driven by a driving motor installed in a robot hand. The robot finger driving module receives a driving force of the driving motor by a pulley gear connected to the driving motor through a driving belt. When the robot finger driving module is fixed, a driving direction of a first output gear is opposite to a rotation-driving direction of a second output gear. When the robot finger driving module rotates, even though any one of the first output gear and the second output gear is fixed, the other is driven to rotate in the rotating direction of the robot finger driving module, thereby exhibiting differential gear characteristics.

Abstract: A robot hand that changes a space between finger members provided apart from each other includes: moving members on which the finger members are vertically provided; a palm member including a moving mechanism for moving the moving members in a predetermined axial direction; and guide members that guide the movement of the moving members in the predetermined axial direction.

Abstract: A robot hand, which has an arbitrary object grasping function in the same manner as a human hand and a high precision and stable grasping function in the same manner as an industrial gripper and performs a pose similar to a human hand while having complete opposability without any increase in complexity or degree of freedom. The robot hand includes a base part, and a plurality of finger connection parts, and a plurality of finger modules connected to the plurality of finger connection parts. The finger connection parts connected to the base part are connected to adjacent finger connection parts by roll joints such that each pair the finger connection parts connected by the roll joints is driven together, and the finger connection parts adjacent to the finger connection parts connected to the base part are driven separately from the finger connection parts connected to the base part.

Abstract: A robot hand is provided, the robot hand including three finger sections, a supporting section which supports a proximal end of each of the three finger sections, and a circumferential movement section which circumferentially moves a second finger section and a third finger section of the three finger sections about a position where the three finger sections are supported on the supporting section is provided. The circumferentially moving second finger section and third finger section are circumferentially movable in a range of 180 degrees or greater in a circumferential direction substantially around a hand axis of the robot hand, about the position where the three finger sections are supported on the supporting section.

Abstract: A robot hand that changes a space between finger members provided apart from each other includes: moving members on which the finger members are vertically provided; a palm member including a moving mechanism for moving the moving members in a predetermined axial direction; and guide members that guide the movement of the moving members in the predetermined axial direction.

Abstract: Embodiments are directed to a robot hand including a frame, a link member moving relative to the frame, a joint unit provided between the frame and the link member, a drive unit supplying power to the joint unit so as to rotate the link member, and a backlash removal unit supplying constant torque to the joint unit, even if a relative position of the link member to the frame is changed as the link member is rotated.

Abstract: A tendon tensioning system includes a tendon having a proximal end and a distal end, an actuator, and a motor controller. The actuator may include a drive screw and a motor, and may be coupled with the proximal end of the tendon and configured to apply a tension through the tendon in response to an electrical current. The motor controller may be electrically coupled with the actuator, and configured to provide an electrical current having a first amplitude to the actuator until a stall tension is achieved through the tendon; provide a pulse current to the actuator following the achievement of the stall tension, where the amplitude of the pulse current is greater than the first amplitude, and return the motor to a steady state holding current following the conclusion of the pulse current.

Abstract: A programmable robot system includes a robot provided with a number of individual arm sections, where adjacent sections are interconnected by a joint. The system furthermore includes a controllable drive mechanism provided in at least some of the joints and a control system for controlling the drive. The robot system is furthermore provided with user a interface mechanism including a mechanism for programming the robot system, the user interface mechanism being either provided externally to the robot, as an integral part of the robot or as a combination hereof, and a storage mechanism co-operating with the user interface mechanism and the control system for storing information related to the movement and further operations of the robot and optionally for storing information relating to the surroundings.

Abstract: Artificial hand suitable for robotic applications or as a prosthesis, comprising a frame with a thumb and at least two fingers, and having a motor drive for adjusting the thumb and the fingers with respect to the frame, wherein the motor drive has a housing and an axle which is rotatably positioned within the housing, and wherein the housing is mounted in a first bearing supported by the frame to enable that the housing may rotate with regard to the frame, and that the thumb and fingers are drivingly connected with the housing and the axle respectively.

Abstract: A motor includes a vibrating plate having a projection part to be pressed against a driven member and a piezoelectric material provided on the vibrating plate, wherein a Young's modulus EL in the pressing direction of the vibrating plate and a Young's modulus ES in a direction crossing the pressing direction are different.

Abstract: A robot hand includes a first finger unit and a second finger unit, a driving unit that causes the finger units to perform an opening and closing action, and a finger-unit moving mechanism that changes a direction in which the opening and closing action of the first finger unit and the second finger unit is performed. The finger-unit moving mechanism includes a worm wheel, a motor, and a worm. A first gear that rotates in a direction different from the rotating direction of the worm in association with the rotation of the worm is provided in the first finger unit. A second gear that rotates in a direction opposite to the rotating direction of the first gear in association with the rotation of the worm is provided in the second finger unit.

Abstract: Disclosed herein are a robot actuator and a humanoid robot having the same. The robot actuator includes a rotation driving source, a ball screw member including a ball screw part connected to the rotation driving source and a nut part connected to the ball screw part, a guide member separated in parallel from the ball screw part, a slider member movably supported by the guide member, and a connection member connecting the slider member and the nut part to move the slider member in connection with movement of the nut part, and the connection member is relatively movably connected to at least one of the nut part and the slider member. Therefore, efficiency in force reflection and back-drivability of the actuator is improved.

Abstract: A robotic gripper (10) has fingers (12) that are configured to grasp an object, and an actuator (20) for driving the fingers. The actuator has a drive train (30) connected to the fingers for driving the fingers, an impact mechanism (40) mechanically connected to the drive train for driving the drive train, and a motor (50) connected to the impact mechanism for driving the impact mechanism. The impact mechanism generates a series of impacts that are delivered to the drive train when the impact mechanism is loaded beyond a threshold torque. The drive train is a back-drive inhibited drive train provided by a worm drive (32, 34) that is mechanically coupled to the impact mechanism.

Abstract: A robot has a structure in which finger joints do not interfere with each other. The robot includes a first actuator driving the finger joint, a first power transmission, a second actuator driving the finger joint, and a second power transmission. The first actuator and the first power transmission are coupled with a wrist joint so that the position of the first actuator and the first power transmission is changed. Accordingly, even if the wrist joint operates, the distance between the first actuator and the finger joint is constantly maintained.

Abstract: A gripper apparatus for removing and replacing objects such as containers or vials in an array of containers has a gripper head which extends downward from a support arm, a planetary gear assembly mounted in the gripper head including at least three planet gears, and at least one gripping pin extending downward from each planet gear and projecting beyond a lower end of the gripper head. A drive motor drives the planetary gear assembly to rotate the planet gears in opposite directions, moving the pins inward and outward along predetermined paths to grip and carry an object and release the object when in a desired location.

Abstract: An industrial gripper includes a base plate, at least three finger units to be moved relative to the base plate, a supporting unit to support the finger units, a first drive unit coupled to the supporting unit to allow simultaneous angular displacement of the finger units toward an object, and a second drive unit coupled to the supporting unit to adjust orientation angles between the finger units. Each of the finger units includes an intermediation member to be moved in a first direction by the first drive unit, a grip member to grip the object by being moved in a second direction different from the first direction as a movement direction of the intermediation member, and a connection member to convert the first direction movement of the intermediation member into the second direction movement of the grip member.

Abstract: A holding system includes a force control module configured to generate a force signal to cause a holding device to perform at least one of a hold stroke and a release stroke. The hold stroke includes transitioning a gripping element of the holding device to a first position to grip an object. The release stroke includes transitioning the gripping element to a second position to release the object. The holding device is non-backdrivable. A stall detection module is configured to (i) monitor a sensor signal received from a sensor of an electric motor assembly of the holding device and (ii) detect a first stall condition of an electric motor based on the sensor signal. A shut off module is configured to shut off current to the electric motor based on the detection of the first stall condition during or at an end of the release stroke.

Abstract: A piezoelectric actuator includes a vibrating body including a piezoelectric device; a driving circuit that supplies a driving signal to the piezoelectric device; a phase difference detecting circuit that detects a phase difference between the driving signal and a detection signal detected based on vibration of the vibrating body; and a frequency controller that controls the frequency and power of the driving signal, wherein the frequency controller sets the power to an upper limit voltage value when the frequency is changed so that the phase difference falls within a predetermined range and sets the voltage to a lower limit voltage value smaller than the upper limit voltage value when the phase difference is outside the predetermined range.

Abstract: An actuator having a two-parameters energy converter is coupled to a transducer and is driven by a controller. Prior to assembly and operation of the actuator, a calibration procedure is performed. The calibration procedure, together with the unique controller, enable accurate control of the output parameters of the actuator. In one example, the parameters are rate and force, and the calibration and controller enable accurate control of the rate and force at the output of the actuator by measuring only the rate at the output of the energy converter. Consequently, no sensors are needed at the output of the actuator, i.e., at the output of the transducer, where the load is applied.

Abstract: A motor including a driven unit; an actuator including a vibrating plate having, at an end thereof, a protrusion which is biased toward the driven unit and a piezoelectric body stacked on the vibrating plate; and a biasing unit biasing the actuator toward the driven unit, wherein an axis in a direction in which the biasing unit biases the actuator toward the driven unit intersects with a plane containing a vibrating surface of the vibrating plate.

Abstract: A drive mechanism and a gripper mechanism equipped with the drive mechanism are provided. An electrical gripper includes a drive mechanism equipped with a motor, a feed screw that transmits a rotary drive force from the motor to a feed nut capable of displacement in an axial direction, and a gripper section that grips a workpiece by coupling to the feed nut and being displaced thereby. The drive mechanism further is constituted by a self-locking mechanism, which prevents the feed nut from being retracted as a result of a reactive force received in the event that the feed nut is advanced and the workpiece is gripped by the gripper section.

Abstract: A robotic gripper. Each of two gripper fingers is attached to a bearing carriage. Each bearing carriage defines a rack gear and is adapted to ride on a bearing rail. A single pinion gear has two gear elements. Each of the two gear elements are meshed with one of the two rack gears so as to drive the two bearing carriages in opposite direction upon rotation of the pinion gear. A worm gear is fixed to the single pinion gear. A worm screw is meshed to the worm gear and adapted to cause rotation of the worm gear and the single pinion gear and a gripping action or a releasing action of the two gripping fingers, depending on the rotation of the worm screw. A motor is adapted to drive the worm screw in a first rotary direction and a second rotary direction.

Abstract: An exemplary system for sensing the state and position of a robot is provided. The system measures the acceleration and angular velocity of the robot and calculates a velocity, and a displacement of the robot. The state of the robot according to the acceleration and the velocity vector, of the robot, is determined. The system includes an alarm that activates according to the state of the robot. The system also compensates for any inaccuracy of the measured displacements.

Abstract: A jointed mechanical device is provided. The device includes at least one element (204) having a fixed end and a deflectable end. The device also includes at least one actuating structure (206) having a first end coupled to at least the deflectable end of the element, where the actuating structure includes at least one elastic element (214) in series with at least one non-elastic element. The device further includes at least one force actuator (202) configured to apply an actuator force to a second end of the actuating structure. Additionally, the device includes a control system (315) for adjusting an operation of the force actuator based at least one actuation input, an amount of the actuator force, and an amount of displacement generated by the force actuator.

Abstract: A multi-joint finger unit (1) has first and second joint sections (3, 5) constructed by using bevel gears. In each joint section (3, 5), the section where a driving bevel gear (10, 44) and a driven bevel gear (14, 56) mesh with each other and also a bearing section of a joint shaft (15, 57) are assembled in a tubular housing (13, 51) whose forward end is closed. Rear end openings (13A, 52) of the tubular housings (13, 51) are closed by a tubular housing (7) at a finger root and a tubular housing (41) at a finger body section. The section where the gears of the joint sections (3, 5) mesh and the bearing section are substantially sealed, so that a foreign matter is prevented from entering from the outside to these sections and lubricant does not leaks from these sections. The multi-joint finger unit is suitable for use in place where thick powder dust is present and in a clean room.

Abstract: A robot includes a base unit, at least two link mechanisms arranged on the base unit, drive units capable of bending and expanding the link mechanisms, and a control unit controlling the drive units. At least one drive unit has a drive force larger than those of the other drive units, and the other drive units are passively displaced by external forces larger than their own drive forces.

Abstract: In a controller, a first switch unit establishes electrical connection between a power-off brake and a power source when a servomotor is energized. The electrical connection causes the power-off brake to be released. A second switch unit is provided between the power-off brake and the power source. The second switch unit establishes electrical connection between the power-off brake and the power source upon being manually operated during the servomotor being deenergized. A calculating unit calculates a driving speed of the joint by the servomotor. A determining unit determines whether the calculated driving speed of the joint is greater than a predetermined threshold speed. An interrupting unit interrupts a supply of electrical power from the power source to the power-off brake through the electrical connection established by the second switch unit when it is determined that the calculated driving speed of the joint is greater than the predetermined threshold speed.

Abstract: A robot hand equipped with a function of gently pinching an object may include a single degree of freedom joint for allowing bending or stretching at a connecting portion between a distal phalange section and a middle phalange section. The robot hand may further include a driving mechanism for causing this joint to make a rotating motion within a predetermined angular range. This driving mechanism is constituted by a motor and a speed reducer. The joint and the driving mechanism are configured so that the distal phalange section is rotated relative to the middle phalange section in two directions, namely, an inward direction and an outward direction within the predetermined angular range from a state where the distal phalange section is arranged in a straight line with the middle phalange section.

Abstract: An apparatus and associated method is provided for individually positioning first and second input links of a four-bar linkage to move first and second follower links pivotally joined therebetween in order to move a chuck supported by one of the follower links between a retracted position and an extended position.

Abstract: A finger unit of a robot hand has a first rotational actuator, a first finger joint part, a first finger linkage, a second finger joint part, and a second finger linkage that are connected in this order. A second rotational actuator is attached to the first finger linkage. The first finger linkage swivels about the first finger joint part by the first rotational actuator, and the second finger linkage swivels about the second finger joint part by the second rotational actuator. The second rotational actuator is attached to the first finger linkage so as to be in a slantwise orientation relative to a straight line connecting a center of rotation of the first finger joint part and a center of rotation of the second finger joint part. With this configuration, an axial length of the finger unit of a robot hand can be shortened.

Abstract: A multi-finger grasping mechanism (300), comprising three two-joint finger units (1-1 to 1-3). Each two-joint finger unit further comprises a finger root part (2), a finger root side joint part (5), a finger intermediate part (3), a finger tip side joint part (6), and a finger tip part (4). The finger intermediate part (3) can be swung about the joint axis (5a) of the finger root side joint part (5), and the finger tip part (4) can be swung about the joint axis (6a) of the finger tip side joint part (6). The finger tip part (4) can be swung about the center axis thereof. When a bolt (W) is held by the finger tip part (4) and the finger part (4) is rotated, the tightening operation of the bolt (W) can be performed.

Abstract: A micro actuator including a translationally driving section having a moving portion which is incorporated in a case and moves translationally, and a displacement enlarging member having one end portion connected to the moving portion of the translationally driving section and another end portion connected to the case, wherein as the one end portion is pulled on the basis of the translational movement, the amount of displacement of its distal end is enlarged.

Abstract: A workpiece-gripping chuck includes a converting mechanism provided in a body, which converts a driving force from a rotary driving source into a displacement in the axial direction. First and second pistons of the converting mechanism are displaced in the axial direction under a rotary action of a pinion gear. Further, the first and second pistons are displaced in the axial direction, respectively, by supplying a pressure fluid from a first or second port formed in the body. A workpiece may be positioned by means of a pair of gripping members under the driving action of the rotary driving source, and the workpiece is further gripped by the gripping members by applying a pressing force of the pressure fluid in addition to the driving force.

Abstract: A manipulator comprises an operation command unit provided with an attitude adjusting unit and an end effector control unit, a connecting unit having one end connected to the operation command unit, a working unit connected to the other end of the connecting unit and provided with an end effector and a support unit supporting the end effector for motions, and a control unit that transmits an operation command provided by the attitude adjusting unit to the support unit to adjust the attitude of the end effector and transmits an operation command provided by the end effector control unit to the end effector to operate the end effector. The support unit includes a first joint capable of turning about a first axis perpendicular to the center axis of the connecting unit, and a second joint capable of turning about a second axis perpendicular to the first axis. The end effector can be turned for rolling about an axis substantially parallel to the second axis of the second joint.

Abstract: An apparatus for convening a liquid crystal display panel for moving various size unit liquid crystal display panels. The present invention includes a horizontal driving unit controlling a revolution of a motor, a plurality of screw shafts protruding out of the horizontal driving unit. A pair of robot arms having first and second ends, the first ends are supported by corresponding screw shafts and extend from the screw shafts, and a plurality of clamping units connected to the second ends of the robot arms.

Abstract: A robotic device has a base and at least one finger having at least two links that are connected in series on rotary joints with at least two degrees of freedom. A brushless motor and an associated controller are located at each joint to produce a rotational movement of a link. Wires for electrical power and communication serially connect the controllers in a distributed control network. A network operating controller coordinates the operation of the network, including power distribution. At least one, but more typically two to five, wires interconnect all the controllers through one or more joints. Motor sensors and external world sensors monitor operating parameters of the robotic hand. The electrical signal output of the sensors can be input anywhere on the distributed control network. V-grooves on the robotic hand locate objects precisely and assist in gripping. The hand is sealed, immersible and has electrical connections through the rotary joints for anodizing in a single dunk without masking.

Abstract: A gripper comprises a motor 25, contained within a case 32, for driving a translational nut 23 that is moved in translation, a finger 20 having one end connected to the translational nut 23, with the other end being connected to the case 32, in which when the one end is pulled upon a movement of the translational nut, the finger is expanded in the amount of displacement at a top end, a plate-like stopper member 26 connected to one end of the finger 20 and having a projecting piece 26b around the outer periphery thereof, a holder member 22 for inserting loosely the projecting piece 26b, a locating nut 28 for adjusting a predetermined gap from the stopper member 26 by being threadingly engaged with a threaded portion of the holder member 22, and a spring 29 for pressing the locating nut 28.