A ball screw, including: a spindle supported for rotation around an axis of rotation; a ball nut radially disposed around the spindle, axially displaceable with respect to the spindle, and including a helical protrusion, the helical protrusion defining a helical groove; a plurality of balls disposed in the helical groove and in contact with the spindle; a reset spring including a portion located in the helical groove and an end portion extending past the helical groove in a circumferential direction around the axis of rotation; and a retaining device directly connected to the ball nut and arranged to limit displacement of the end portion of the reset spring in a first axial direction parallel to the axis of rotation. For a first circumferential position of the spindle around the axis of rotation, the reset spring urges the plurality of balls in a second axial direction, opposite the first axial direction.

A ball screw device includes: a screw shaft that has a first screw groove on an outer circumferential surface thereof; a cylindrical nut member that has a second screw groove on an inner circumferential surface thereof; plural rolling elements that can roll in a rolling path formed between the first screw groove and the second screw groove; and a lubricant applied to the rolling path, wherein the lubricant has a loss tangent tanδ larger than 0.11, which is measured by dynamic viscoelasticity measurement performed at a temperature of 25° C., an angular frequency of 10 rad/s, and an amount of strain of 0.01%.

In a ball screw apparatus, a ball train including a plurality of main balls is housed in a raceway between a ball track of a ball nut and a ball track of a ball screw shaft. A coil spring housed in the raceway includes a first end that engages with an end of the ball train and a second end supported by a stopper (a first recessed portion, a protruding portion, or the like) of the ball nut. A stopper ball having a diameter larger than the diameter of the main ball is interposed between the stopper and the second end of the coil spring.

A ball screw device includes a screw shaft that has a first helical groove on an outer circumference, a nut that has a second helical groove on an inner circumference, a plurality of balls, a stopper provided at an end portion of the second helical groove, and a spring body that is placed between an end portion ball closest to the stopper and the stopper. The spring body is configured of a plurality of coil springs arrayed along the first helical groove and the second helical groove. The coil springs that are adjacent each have a spring end portion of which rigidity is higher than rigidity of a spring middle portion.

A ball screw device includes a screw shaft; a nut having a second helical groove; and a plurality of balls. When the screw shaft is rotated about an axis of the screw shaft while being subjected to the external force, the balls are displaced from positions under no load condition toward one side in an axial direction. A second helical groove of the nut includes a stopping member configured to prevent the balls from falling off from the second helical groove. A plurality of coil springs are arranged in series along the second helical groove. An angle in a circumferential direction occupied by each of the coil springs about the axis is 180 degrees or less when the coil springs are disposed in the second helical groove.

A ball screw, including: a spindle supported for rotation around an axis of rotation; a ball nut radially disposed around the spindle, axially displaceable with respect to the spindle, and including a helical protrusion, the helical protrusion defining a helical groove; a plurality of balls disposed in the helical groove and in contact with the spindle; a reset spring including a portion located in the helical groove and an end portion extending past the helical groove in a circumferential direction around the axis of rotation; and a retaining device directly connected to the ball nut and arranged to limit displacement of the end portion of the reset spring in a first axial direction parallel to the axis of rotation. For a first circumferential position of the spindle around the axis of rotation, the reset spring urges the plurality of balls in a second axial direction, opposite the first axial direction.

An actuator has: a motor section; a ball spline having a finite stroke and equipped with a shaft capable of moving along its axis; an external screw thread formed on the shaft; a nut section having an internal screw thread engaging the external screw thread and operating to transmit the rotary force of the motor section to the shaft; and a case housing the motor section and the ball spline. The shaft has a contact section at its front end, the contact section being designed to make contact with the driven object. The contact section is lower than the shaft in thermal conductivity. Due to heat generated by the motor section, the shaft elongates along the axis of the shaft in a first direction, and the case elongates along the axis of the shaft in a second direction opposite to the first direction.

A ball screw assembly includes a guider, an open nut, an open shield, a first circulator, a second circulator, and a ball circulating assembly. The open nut is slidably fitted over the guider and includes an axial cylinder having an axial opening. An inner spiral channel of the axial cylinder and a spiral channel of the guider form an inner ball race. The open shield is coaxially fitted over the axial cylinder. An inner peripheral wall of the open shield and an outer annular wall of the axial cylinder form an outer ball race. The first circulator and the second circulator are disposed on the axial cylinder. The inner ball race, a first curve of the first circulator, the outer ball race, and a second curve of the second circulator form a ball circulating race, and the ball circulating assembly rolls in the ball circulating race.

A ball screw assembly includes a guider, an open nut, an open shield, a first circulator, a second circulator, and a ball circulating assembly. The open nut is slidably fitted over the guider and includes an axial cylinder having an axial opening. An inner spiral channel of the axial cylinder and a spiral channel of the guider form an inner ball race. The open shield is coaxially fitted over the axial cylinder. An inner peripheral wall of the open shield and an outer annular wall of the axial cylinder form an outer spiral ball race. The first circulator and the second circulator are disposed on the axial cylinder. The inner ball race, a first curve of the first circulator, the outer spiral ball race, and a second curve of the second circulator form a ball circulating race, and the ball circulating assembly rolls in the ball circulating race.

A ball screw assembly includes a guider, an open nut, open shields, a first circulator, a second circulator, and ball circulating assemblies. The open nut is slidably fitted over the guider and includes an axial cylinder having an axial opening. Inner spiral channels of the axial cylinder and spiral channels of the guider form inner ball races. The open shields are coaxially fitted over the axial cylinder. An inner peripheral wall of each of the open shields and an outer annular wall of the axial cylinder form an outer ball race. The first circulator and the second circulator are disposed on the axial cylinder corresponding to the open shields. The inner ball races, first curves of the first circulator, the outer ball races, and second curves of the second circulator form ball circulating races, and the ball circulating assemblies roll in the ball circulating races.