Mounting shaft fixture, mounting head and surface mounting device

Abstract

Mounting shaft device (120) configured to mount an electronic component, the mounting shaft device (120) comprising: a splined shaft (121) having a supply passage for air pressure and extending through a shaft bore in a support element (171); an inlet element (161) communicating with a valve (90) and allowing air pressure to be introduced from the valve (90) to the supply passage of the splined shaft (121); a component holder (250) located at an axial end of the splined shaft (121) and configured to receive air pressure through the supply passage of the splined shaft (121) to hold an electronic component; a wedge nut (151) connected to the splined shaft (121) by a wedge mechanism;and a bearing (181) which supports the splined shaft (121) in the shaft bore in the support element (171) so that it is linearly movable in an axial direction and rotatable about its axis, wherein the bearing (181), the insertion element (161) and the wedge nut (151) are arranged on an axis of the splined shaft (121) in that order, starting from the component holder (250), the splined shaft (121) has a ball raceway (123) which extends in an axial direction of the splined shaft (121) and receives a ball (143), so that the splined shaft (121) and the wedge nut (151) are connected to each other by a wedge mechanism, and the ball raceway (123) is provided only on the upper section of the splined shaft (121) in which the wedge nut (151) is arranged, and not on a section corresponding to the insertion element (161) and a section corresponding to the bearing (181) corresponds to the wedge nut (151) located below it.

Description

TECHNICAL FIELDThe technology disclosed herein relates to a structure of a mounting shaft device installed in, for example, a mounting head of a surface mount apparatus.GENERAL STATE OF THE ARTIn a known technique, splined coupling is used to move a shaft linearly in the axial direction and to rotate the shaft about the axis. Such a technique is used, for example, in a mounting head of a surface mount apparatus configured to mount an electronic component on a circuit board. More specifically, the technique is applied to a shaft that moves and rotates the pickup nozzles up / down.In Patent Document 1 below, a pickup head is made up of separate members including a lower nozzle shaft and an upper nozzle shaft detachably attached to the upper end of the lower nozzle shaft by a shaft coupling. This configuration makes it possible to exchange components such as a pickup nozzle and a lower nozzle shaft as needed, and to shorten the time required for exchanging the components.Moreover, in Patent Document 1, the lower nozzle shaft and the upper nozzle shaft each have an air passage at the core thereof. The air passage extends through the lower and upper nozzle shafts in the axial direction. At the upper end of the upper nozzle shaft, an air conduit is connected. Air pressure is applied to the pick-up nozzle through the air line and the air passages in the shafts.PRIOR ART DOCUMENTPatent DocumentPatent Document 1: Japanese Patent Application Publication JP 2005-327 774 A US 2001 / 0 049 874 A1 discloses an apparatus for holding a component and an apparatus for mounting a component. The electronic component mounting apparatus has a first air-conveying device connected to an air duct at one end portion of a spline shaft, and a second air-conveying device connected to the air duct near the other end of the spline shaft. The first and second air supplies serve to supply air to the air duct to make the interior equal to the atmospheric pressure.JP 2011-98 413 A describes a component suction head used for various component mounting apparatuses, for example, a chip mounting apparatus for mounting an electronic component on an electronic circuit board. The component is held and arranged at a predetermined position.JP H11-97 893 A describes an electronic component mounting apparatus having an adhesive head for clamping, transferring and mounting an electronic component to a circuit board.JP 2011-029 527 A describes a component mounting apparatus having a plurality of suction nozzle units concentrically arranged at equal intervals on a rotating body.JP 2013-135 150 A discloses a suction head for a surface mounting machine.DISCLOSURE OF THE PRESENT INVENTIONProblem to be Solved by the InventionElectronic components to be mounted on circuit boards have recently undergone further miniaturization, so that improvements in the mounting accuracy of electronic components are required. In addition, it is important to shorten the response time required when switching air pressures to be applied to the pickup nozzles in order to shorten the mounting stroke time. Thus, it is desired to improve the mounting accuracy of electric components and to shorten the response time required in switching air pressures.The technology disclosed in this document has been developed in view of the above-described problem, and an object is to improve the mounting accuracy of an electronic component and to shorten the response time required in switching air pressures.means for achieving the objectA mounting shaft device disclosed herein includes a spline shaft including an air pressure supply passage inside and extending through a shaft bore in a support member, an introduction member in communication with a valve and allowing air pressure to be introduced from the valve to the spline shaft supply passage, a component holder attached to an axial end of the spline shaft and configured to receive the air pressure applied through the spline shaft supply passage to hold an electronic component, a spline nut connected to the spline shaft through a spline mechanism, and a bearing linearly movable in the shaft bore in the support member in both an axial direction and rotatable about the axis thereof. The bearing, the introduction member, and the spline nut are disposed on an axis of the spline shaft in this order from the component holder. The spline shaft has a ball track groove extending in an axial direction of the spline shaft and receiving a ball that connects the spline shaft and the spline nut to each other through a spline mechanism. The ball track groove is provided only at the upper portion of the spline shaft in which the spline nut is disposed, and is not provided at a portion corresponding to the introduction member and a portion corresponding to the bearing located below the spline nut.In this configuration, the bearing, the introduction member, and the spline nut are mounted on the axis of the spline shaft in this order from the component holder. Thereby, the mounting accuracy of an electronic component is improved, and the time required for switching air pressures is shortened.The following embodiments embody preferred aspects of the mounting shaft device disclosed herein.The introduction member may have a tubular shape. The introducing member and the spline define therebetween an air chamber communicating with the supply passage. The introduction member may include a communication hole in a peripheral wall of the air chamber. The communication bore is in communication with the valve. This configuration enables the air pressure from the valve to the supply passage to be introduced into the spline shaft through the communication bore and the air chamber.The spline shaft may include a limiter at an end portion of the ball track groove. The limiter is configured to prevent the ball from sticking in an incomplete raceway. The "incomplete raceway" is a groove having an incomplete groove shape having a width or a depth smaller than a normal groove shape of the ball raceway. By the above-described configuration, the ball is prevented from being caught in the incomplete raceway. Thus, functional disturbances of the spline shaft during the linear axial movement are reduced.The spline shaft may have an annular groove having an annular shape at the boundary between the incomplete raceway and the ball raceway. The restrictor may be a ball stopper mounted in the annular groove at the boundary between the incomplete raceway and the ball raceway. The ball stopper may be configured to prevent the ball from moving from the ball raceway to the incomplete raceway. With this configuration, the ball stopper prevents the ball from moving from the ball raceway into the incomplete raceway, so that the ball is prevented from being caught in the incomplete raceway.The limiter may be a step at the boundary between the incomplete raceway and the ball raceway. With this configuration, the step prevents the ball from moving from the ball raceway into the incomplete raceway, so that the ball is prevented from being caught in the incomplete raceway.The limiter may be a filling material that fills the incomplete raceway. In this configuration, the filler prevents the ball from moving from the ball raceway into the incomplete raceway, so that the ball is prevented from being caught in the incomplete raceway.A mounting head disclosed herein includes the above-described mounting shaft device, a base having a through bore in which the introduction member and the support member are mounted one above the other and through which the spline shaft extends in the axial direction, the valve in a mounting bore in the base and in communication with the introduction member, an axial drive unit configured to move the spline shaft in the axial direction, and a rotational drive unit configured to transmit torque to the spline nut to rotate the spline shaft about an axis thereof.Advantageous Effects of the InventionBy the technology disclosed herein, the mounting accuracy of electronic components is improved, and the response time required in switching air pressures is shortened.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is a plan view of a surface mount apparatus adopted as an embodiment. FIG. 2 is a perspective view of a mounting head. FIG. 3 is an enlarged perspective view of a portion of the mounting head. FIG. 4 is a perspective view illustrating a structure of a rotating body. FIG. 5 is an enlarged view of a portion A of FIG. 4. FIG. 6 is a cross-sectional view of main components of the mounting head. FIG. 7 is an enlarged view of a portion (a lower half) of FIG. 6. FIG. 8 is a perspective view of a mounting shaft device. FIG. 9 is an exploded perspective view of the mounting shaft device. FIG. 10 is a cross-sectional view taken along line B-B of FIG. 9. FIG. 11 is a cross-sectional view of the mounting shaft device. FIG. 12 is a perspective view of a ball cage. FIG. 13 is an enlarged view of a portion of FIG. 10. FIG. 14 is a vertical sectional view of a rotating body. FIG. 15 is a cross-sectional view taken along line E-E in FIG. 14 (for indicating the positional relationship between a mounting head device and a switching device). FIG. 16 is a view showing how the ball groove is formed. FIG. 17 is an enlarged view of the portion C of FIG. 9. FIG. 18 is an enlarged view of the portion D of FIG. 10. FIG. 19 is a cross-sectional view illustrating another embodiment of a spline shaft. FIG. 20 is a cross-sectional view illustrating another embodiment of the spline shaft.EMBODIMENT OF THE INVENTION(Overall Configuration of Surface Mount Apparatus)Referring to the drawings, an embodiment will be described. In this embodiment, a surface mount apparatus 1 shown in FIG. 1 will be described as an example. The surface mount apparatus 1 includes, for example, a base 10, a transport conveyor 20 configured to mount a circuit board (an example of a board) B 1, a component mounting device 30 configured to mount an electronic component (an example of a component) E 1 on the circuit board B 1, and component feeding portions 40.The base 10 has an elongated shape in plan view and has a planar upper surface. Below the transport conveyor 20, a support device for supporting the circuit board B 1 during mounting of the electronic component E 1 on the circuit board B 1 is provided on the base 10. In the following description, the longitudinal direction of the base 10 (the left-right direction in FIG. 1 ) and the conveying direction of the conveying conveyor 20 are referred to as an X direction. The width direction of the base 10 (the up / down direction in FIG. 1 ) is referred to as a Y direction. The up / down direction of the base 10 (the up / down direction in FIG. 2 ) is referred to as a Z direction.The conveyance conveyor 20 is located substantially at the center of the base 10 in the Y direction, and is configured to convey the circuit board B 1 in the conveyance direction (the X-axis direction). The transport conveyor 20 includes a pair of conveyor belts 22 configured to circulate in the X direction. The circuit board B 1 is positioned above the conveyor belts 22. The circuit board B 1 is transported from one side in the transport direction (the right side in FIG. 1 ) along the conveyor belts 22 to an operation position (a region surrounded by a two-dot chain line in FIG. 1 ) on the base 10 where the circuit board B 1 is stopped for the mounting operation of the electronic component E 1. Then, the circuit board B 1 is transported to the other side (the left side in FIG. 1 ) along the conveyor belts 22 and discharged.On each side of the transport conveyor 20 (each side in the up / down direction in FIG. 1 ), two component feeding portions 40 are arranged side by side in the X direction, i.e., there are four component feeding portions 40 in total. the component feeding portions 40 each include a plurality of conveyors 42. The conveyors 42 each include, for example, a drum (not shown) on which a component supply tape (not shown) holding the electronic components E 1 is wound, and an electric supply device (not shown) configured to supply the component supply tape from the drum. The conveyor 42 feeds the electronic components E 1 one by one from component feeding positions located at the end adjacent to the transport conveyor.The component mounting device 30 includes a pair of support frames 32, a rotatable mounting head 50, and a mounting head driving mechanism configured to drive the mounting head 50. The support frames 32 are positioned on both sides of the base 10 in the X direction and extend in the Y direction.A Y-axis servo mechanism includes Y-axis guide rails 33Y, a Y-axis ball screw 34Y on which a ball nut (not shown) is screwed, and a Y-axis servo motor 35Y. A head rest 36 fixed to the ball nut is fixed to each Y-axis guide rail 33Y. When the Y-axis servo motor 35Y is operated, the ball nut moves forward or backward along the Y-axis ball screw 34Y. Thereby, the headrest 36 fixed to the ball nut and the mounting head 50 described later is moved in the Y direction along the Y-axis guide rails 33Y.The X-axis servo mechanism includes an X-axis guide rail (not shown), an X-axis ball screw 34X on which a ball nut (not shown) is screwed, and an X-axis servo motor 35X. The mounting head 50 is fixed to the X-axis guide rail so as to be movable in the axial direction of the X-axis guide rail. When the X-axis servo motor 35X is operated, the ball nut moves forward or backward along the X-axis ball screw 34X. Thereby, the mounting head 50 fixed to the ball nut is moved in the X direction along the X-axis guide rail.As described above, the mounting head 50 is movable in the X direction and the Y direction by the X-axis servo mechanism and the Y-axis servo mechanism within a predetermined range of movement.(Structure of Mounting Head)Next, the structure of the mounting head 50 will be described in detail. The mounting head 50 is configured to hold the electronic component E 1 supplied from the conveyor 42 by suction and mount the electronic component E 1 on the circuit board B 1. As shown in FIGS. 2 to 4, the mounting head 50 of this embodiment includes a head body 60, a head support member 52 that supports the head body 60, and covers 53 and 54.As shown in FIGS. 4 and 6, the head body 60, which is a rotatable head body, includes a shaft 62 of cylindrical shape extending in the Z direction, a rotating body (corresponding to a "base" of this invention) 64, eighteen mounting shaft devices 120, and an N-axis drive unit 45.The shaft 62 has a two-layer structure, and includes an outer shaft 62B and an inner shaft 62A located inside the outer shaft 62B. The inner shaft 62A is supported by the head support member 52 rotatably about the axis of the shaft 62A.The rotating body 64 has a substantially cylindrical shape and a larger diameter than the shaft 62. The rotating body 64 is fixed to the lower portion of the inner shaft 62A. The rotating body 64 has eighteen through-holes 65. The eighteen through holes 65 are arranged in the circumferential direction with an equal distance therebetween. The mounting shaft devices 120 are fixed in the respective through holes 65.At the upper portion of the shaft 62, an N-axis driven gear 62N and an R-axis driven gear 62R are superposed on each other (see FIG. 4 ). The N-axis driven gear 62N and the R-axis driven gear 62R are respectively engaged with the inner shaft 62A and the outer shaft 62B.The N-axis drive unit 45 includes an N-axis servo motor 35N and an N-axis drive gear (not shown) mounted around the output shaft of the N-axis servo motor 35N. The N-axis drive gear and the N-axis driven gear 62N are meshed with each other. When the N-axis servomotor 35N is operated, the driving force of the motor 35N is transmitted to the inner shaft 62A through the N-axis drive gear and the N-axis driven gear 62N. Thereby, the rotating body 64 rotates together with the inner shaft 62A, and thus the eighteen mounting shaft devices 120 supported by the rotating body 64 are rotated together with the rotating body 64.The outer shaft 62B is supported by the inner shaft 62A and the rotating body 64 at axial end portions thereof by bearings. The outer shaft 62B is rotatable with respect to the inner shaft 62A and the rotating body 64.(Mounting Shaft Device)As shown in FIGS. 8 to 11, the mounting shaft device 120 includes a spline shaft 121, a ball holder 141, a spline nut 151 which is an outer cylinder, a first shaft tube (corresponding to an "introduction member" of the invention) 161, a second shaft tube (corresponding to a "support member" of the invention) 171, a ball cage (a "bearing" of the invention) 181, and a coil spring 230.The first shaft tube 161 has a tubular shape having a through hole extending in the Z direction (the up / down direction). The first shaft tube 161, which is formed in a stepped shape, includes a shaft body 162 having a small diameter and a housing portion 164 having a large diameter.As shown in FIG. 7, the shaft body 162 of the first shaft tube 161 is located in the upper portion of the through hole 65 in the rotating body 64, and the first shaft tube 161 is fixed to the through hole 65 in a rotationally fixed manner.The second shaft tube 171 has a tubular shape having a through hole extending in the Z direction (the up / down direction). As shown in FIG. 7, the second shaft tube 171 is located at the lower portion of the through hole 65 in the rotating body 64 and is fixed in the through hole 65 in a non-rotatable manner. The end portion (the lower end portion) of the second shaft tube 171 protrudes from the lower surface of the rotating body 64.As shown in FIGS. 8 to 10, the spline shaft 121 is long in the Z direction (the up / down direction) and is a single shaft that is divided in the Z direction. As shown in FIG. 11, the spline shaft 121 has a supply passage 131 extending in the Z direction at the core. The supply passage 131 extends in the spline shaft 121 over a lower portion located slightly below the center of the spline shaft 121 in the Z direction.The supply passage 131 extends to the lower end of the spline shaft 121 and in communication with the pickup nozzle 250 located at the axial end of the spline shaft 121. As described above, the supply passage 131 is included only in the lower portion of the spline shaft 121, and is not included in the upper portion thereof.Moreover, the spline shaft 121 includes a through hole 133 and a ball groove 123. As shown in FIG. 11, the through hole 133 is located at the upper end of the supply passage 131. The through hole 133 extends through the core of the spline shaft 121 in the horizontal direction (in the radial direction) and in communication with the supply passage 131 located on the core.As shown in FIG. 10, the ball track groove 123 is provided at the upper portion of the spline shaft 121 and extends in the Z direction (the up / down direction). In the Z direction, the ball track groove 123 is not aligned with the supply passage 131.As shown in FIGS. 7 and 11, the spline shaft 121 extends through a shaft hole 163 of the first shaft tube 161 and a shaft hole 173 of the second shaft tube 171, which are stacked in this order. The spline shaft 121 is provided in the first and second shaft pipes 161 and 171.The lower portion of the spline shaft 121 protrudes downward from the lower surface of the rotating body 64, and the upper portion thereof protrudes upward from the upper surface of the rotating body 64.The ball cage 181 is located in the second shaft tube 171. As shown in FIG. 13, the ball cage 181 includes a plurality of balls 183 and a tubular holding member 185. The retainer 185 holds the balls 183 so as to be rollable. More specifically, the retainer 185 holds the balls 183 so as to be rollable and arranged with the same pitch therebetween in the circumferential direction and arranged with a predetermined pitch in the Z direction.The balls 183 held by the holder 185 are in contact with both the inner surface of the second shaft tube 171 and the outer surface of the spline shaft 121 to support the spline shaft 121. In other words, the balls 183 arranged with the circumferentially equally large distance therebetween are rolled according to the rotation of the spline shaft 121 while simultaneously contacting the inner surface of the second shaft tube 171 and the outer surface of the spline shaft 121. This allows the spline shaft 121 to be rotatably supported with respect to the second shaft tube 171.In addition, the balls 183 arranged in the Z direction are rolled according to the linear movement of the spline shaft 121 in the Z direction (the axial direction) while simultaneously contacting the inner surface of the second shaft tube 171 and the outer surface of the spline shaft 121. This makes it possible to support the spline shaft 121 linearly movable with respect to the second shaft tube 171 in the Z direction.As described above, the ball cage 181 supports the spline shaft 121 to be linearly movable both rotatably about the axis L of the spline shaft 121 and in the Z direction (the axial direction) with respect to the second shaft tube 171.Moreover, the shaft body 162 of the first shaft tube 161 is in communication with a switching device (corresponding to a "valve" of the invention) 90 configured to switch air pressures to introduce the air pressure from the switching device 90 into the supply passage 131 of the spline shaft 121.More specifically, the shaft body 162 and the spline shaft 121 define therebetween an air chamber 165 as shown in FIG. 13. The air chamber 165 extends over the entire circumference of the spline shaft 121. At the upper and lower ends of the air chamber 165, seal walls 166 in contact with the outer surface of the spline shaft 121 are fitted without gaps to prevent air from leaking outside the air chamber 165.As shown in FIG. 13, the through hole 133 of the spline shaft 121 is located in the air chamber 165. The air chamber 165 is in communication with the supply passage 131 of the spline shaft 121 through the through hole 133.The shaft body 162 has a communication hole 167 in the peripheral wall of the air chamber 165 (see FIG. 9 ). The communication bore 167 is in communication with an outlet port 94C of the switching device 90 through an inner passage 68 in the rotating body 64 (see FIG. 14 ). The air pressure from the switching device 90 is introduced into the air chamber 165 through the inner passage 68 and the communication bore 167. In this configuration, the air pressure is introduced from the switching device 90 through the air chamber 165 to the supply passage 131 of the spline shaft 121.As shown in FIG. 13, the air chamber 165 has a predetermined dimension in the Z direction (indicated by "F" in FIG. 13 ) that allows the through hole 133 to be located in the air chamber 165 when the spline shaft 121 moves in the Z direction within a predetermined range of movement. In this configuration, even when the spline 121 moves in the Z direction in a predetermined range of movement, the air pressure from the switching device 90 is continuously applied to the supply passage 131 of the spline 121.In addition, since the air chamber 165 extends over the entire circumference of the spline shaft 121, the air pressure from the switching device 90 is constantly applied to the supply passage 131 of the spline shaft 121 even when the spline shaft 121 rotates about its axis.The position of the upper end of the supply passage 131 of the spline shaft 121 is set depending on the position of the air chamber 165. More specifically, the upper end of the supply passage 131 is flush with the upper end of the air chamber 165 when the spline shaft 121 is at the end of the upward movement, as shown in FIGS. 6 and 13.The housing portion 164 of the first shaft tube 161 is not located in the through hole 65, but is located above the upper surface of the rotating body 64.As shown in FIGS. 8 to 10, the spline nut 151 has a tubular shape having a through hole extending in the Z direction (an outer cylinder), and has a ball groove (not shown) extending in the up / down direction in the inner surface. On the outer surface of the spline nut 151, a gear 155 is attached.The spline nut 151 is disposed coaxially with a portion of the spline shaft 121 that protrudes upward from the first shaft tube 161. The spline nut 151 has a lower portion 157 fitted into the housing portion 164 of the first shaft tube 161. Through a bearing 200, the spline nut 151 is rotatably supported in the housing portion 164 of the first shaft tube 161. The key nut 151 is prevented from coming off the housing portion 164 by a pin 159.The ball retainer 141 is located between the spline shaft 121 and the spline nut 151. The ball retainer 141 includes a plurality of balls 143 arranged in a predetermined arrangement and a tubular retainer 145 that retains the balls 143 so as to be rollable.The balls 143 arranged in rows partially rollably fit into holes 145A in the retainer 145. The holes 145A are linearly arranged in the Z direction (the up / down direction) with a predetermined distance therebetween at a predetermined angular distance. The holes 145A in the holder 145 each have a circular inner opening 145b having a diameter slightly smaller than the diameter of the ball 143. In this configuration, the balls 143 are held by the retainer 145. The ball retainer 141 prevents the balls 143 from jumping out of the retainer 145 alone. The linear balls 143 fit into both the ball groove 123 in the spline shaft 121 and the ball groove (not shown) in the spline nut 151.The balls 183 are not only disposed on the front side of the spline shaft 121 as shown in FIG. 9, but are also disposed on the rear side, i.e., in the concrete configuration, they are arranged in two rows. Accordingly, the outer surface of the spline shaft 121 and the inner surface of the spline nut 151 precisely each have two ball running grooves.The spline shaft 121 is connected to the spline nut 151 through a ball-and-groove mechanism via the ball holder 141, and thus torque is transmitted to the spline shaft 121 through the spline nut 151. Moreover, the spline shaft 121 is capable of sliding (linear movement) in the Z direction with respect to the spline nut 151.Moreover, as shown in FIGS. 7 and 11, at the lower portion of each spline shaft 121 protruding downward from the rotary body 64 through a nozzle holder 240, a pickup nozzle (corresponding to a "component holder" of the invention) 250 configured to hold an electronic component E 1 by suction is provided.The pickup nozzle 250 is supplied with a negative pressure or a positive pressure through the supply passage 131. The pickup nozzles 250 are each configured to hold an electronic component E 1 at the end portion by suction using a negative pressure, and discharge the electronic component E 1 held at the end portion by a positive pressure.As shown in FIGS. 8 to 10, the coil spring 230 is disposed at the upper portion of the spline shaft 121. As shown in FIG. 11, the coil spring 230 is mounted between a spring lock nut 235 mounted on the upper end of the spline shaft 121 and a circular spring lock washer 158 disposed on the inner surface of the upper portion of the spline shaft 151.The distance between the spring washer 158 and the spring lock nut 235 in the Z direction is the largest when the spline shaft 121 has been moved to the end of the upward movement as shown in FIG. 6. The coil spring 230 in such a state is still compressed and constantly biases the spline shaft 121 in the upward direction.As shown in FIG. 11, on the axis of the spline shaft 121, the above-described mounting shaft device 120 includes the ball cage 181, the first shaft tube 161, and the spline nut 151 in this order from the pickup nozzle 250 which is a component holder (i.e., from the lower side in FIG. 11 ). In other words, the ball cage 181 configured to support the spline shaft 121 is closest to the pickup nozzle 250 configured to hold an electronic component by suction. This configuration improves the mounting accuracy of an electronic component and shortens a response time required in switching air pressures (the time between switching air pressures at the switching device and receiving the air pressure at the pickup nozzle 250).More specifically, the displacement of the pickup nozzle 250 caused by tilting of the spline shaft 121 is substantially proportional to the distance between a fulcrum on the spline shaft 121 and the pickup nozzle 250. Thus, the displacement of the pickup nozzle 250 decreases as the distance between the ball cage 181 supporting the spline shaft 121 and the pickup nozzle 250 decreases. The above-described configuration improves the mounting accuracy of an electronic component.The response time required when the switching device 90 switches air pressures increases as the sub volume of the switching device 90 increases. In this example, on the axis of the spline shaft 121, the ball cage 181, the first shaft tube 161, and the spline nut 151 are arranged in this order from the pickup nozzle 250. The first shaft tube 161 is closer to the pickup nozzle 250 than the spline nut 151.With this arrangement, the length of the supply passage 131 in the spline shaft 121 is short compared to the case where the first shaft tube 161 and the spline nut 151 are arranged reversely. Thereby, the sub-volume of the switching device 90 is reduced, and the response time required for switching air pressures, which is performed by the switching device 90, is shortened.(R-axis drive unit and Z-axis drive unit)As shown in FIGS. 2 and 6, the mounting head 50 includes an R-axis drive unit 70 and two Z-axis drive units 80. The R-axis drive unit (corresponding to a "rotational drive unit" of the invention) 70 is configured to simultaneously rotate the spline shafts 121 in the same direction about the axis L.The R-axis drive unit 70 includes an R-axis servo motor 35R (see FIG. 2 ), an R-axis drive gear 72R (see FIG. 3 ) that is mounted on the output shaft of the R-axis servo motor 35R and engages with an R-axis driven gear 62R, and a common gear 55.The common gear 55 is mounted on the lower portion of the outer shaft 62B. As shown in FIG. 5, the common gear 55 is meshed with the gears 155 of the spline nuts 151. When the R-axis servomotor 35R is operated, the driving force of the motor 35R is transmitted to the outer shaft 62B and through the R-axis drive gear 72R and the R-axis driven gear 62R to the common gear 55, so that the outer shaft 62B and the common gear 55 are rotated.When the common gear 55 rotates, the nuts 151 are rotated due to the engagement of the common gear 55 with the gears 155. Further, since the nuts 151 are connected to the associated shafts 121 through a ball-and-groove mechanism, the eighteen shafts 121 are simultaneously rotated in the same direction about the respective axes by the same angle due to the rotation of the common gear 55.The Z-axis drive units (corresponding to an "axial drive unit" of the invention) 80 are configured to stroke in the Z direction in two of the eighteen spline shafts 121 located at predetermined positions (left and right sides in FIG. 6 ).The Z-axis drive units 80 are symmetrically mounted on the left and right sides of the head body 60 with the shaft 62 therebetween at positions above the spline shafts 121 (see FIG. 6 ).As shown in FIGS. 2, 4, and 6, the Z-axis driving units 80 each include a box-like body 82 and a Z-axis movable portion 84 configured to move in the Z direction (the up / down direction). In the body 82, a Z-axis linear motor (not shown) for driving the Z-axis movable portion 84 by a linear force is mounted.As shown in FIGS. 4 and 6, a Z-axis eccentric roller 86 is rotatably attached to the lower portion of each of the Z-axis movable portions 84.When the Z-axis movable portion 84 is moved downward from a basic position shown in FIG. 6, the Z-axis eccentric roller 86 comes into contact with the upper end of the spline shaft 121 located at a predetermined position (left and right sides in FIG. 6 ), so that the spline shaft 121 moves downward against the spring force of the coil spring 230.Thereby, the pickup nozzle 250 is moved downward, allowing the end portion of the pickup nozzle 250 to approach the circuit board B 1 located at a component feeding position of the conveyor 42 or at the operating position. When the Z-axis movable portion 84 is moved upward in this state, the spline shaft 121 and the pickup nozzle 250 are moved upward by the spring restoring force of the coil spring 230.The Z-axis eccentric roller 86 in the basic position shown in FIG. 6 is located away from the upper end of the spline shaft 121. Thus, when the Z-axis movable portions 84 are at the basic positions shown in FIG. 6, the entire rotating body including the eighteen spline shafts 121 is capable of rotating about the shaft 62 without coming into contact with the Z-axis eccentric roller 86.(Shifting Device and V-axis Driving Unit)As shown in FIGS. 4 and 6, the mounting head 50 includes switching devices 90 configured to switch the pressure applied to the pickup nozzles 250 between a negative pressure and a positive pressure, and V-axis drive units 100 configured to trigger the switching devices 90.More specifically, as shown in FIG. 15, the rotating body 64 has eighteen mounting holes 66 with the same circumferential distance therebetween. The mounting holes 66 are long in the Z direction and open into the upper surface of the rotating body 64, and the switching devices 90 are mounted in the respective mounting holes 66, and accordingly, eighteen switching devices 90 are mounted on the rotating body 64 with the same circumferentially-sized interval therebetween.As shown in FIG. 15, the mounting holes 66 are adjacent to the corresponding through-holes 65, in which the mounting shaft devices are mounted, on the outer sides of the through-holes 65, and thus the switching devices 90 adjacent to the corresponding mounting shaft devices 120 are located on the outer sides of the corresponding mounting shaft devices 120. More specifically, the switching devices 90 are adjacent to the first shaft pipes 161 of the associated mounting shaft devices 120 on the outer sides of the first shaft pipes 161.As shown in FIG. 14, the switching devices 90 each include a slider 92 and a cylindrical sleeve 94. the slider 92 has a contact portion 93 having a laterally facing U-like shape at the upper portion. As shown in FIG. 14, the sleeve 94 has a negative pressure inlet port 94A, a positive pressure inlet port 94B, and an outlet port 94C.As shown in FIG. 15, the outlet port 94C is connected to the communication bore 167 of the first shaft tube 161 of the associated mounting shaft device 120 through the inner passage 68 in the rotating body 64. Thus, the outlet port 94C is in communication with the air chamber 165 in the first shaft tube 161 through the inner passage 68 and the communication bore 167.The spool 92 is configured to switch the flow paths in the sleeve 94 to change the port in communication with the outlet port 94C. In this example, when the spool 92 is at the end of the upward movement (hereinafter referred to as the pressurization position"), in the sleeve 94, the vacuum inlet port 94A and the outlet port 94C are in communication with each other.On the other hand, when the spool 92 is at the end of the downward movement (hereinafter referred to as "pressurizing position"), the positive pressure inlet port 94B and the outlet port 94C are in communication with each other. As described above, the pressure applied to the pickup nozzle 250 through the inner passage 68, the communication bore 167, the air chamber 165, and the supply passage 131 is switched between negative pressure and positive pressure by moving the spool 92.The negative pressure inlet port 94A of each switching device 90 is supplied with negative pressure from a negative pressure source (not shown) through the negative pressure supply passage 63 in the inner shaft 62A and the negative pressure supply passage 69 in the rotating body 64 Moreover, the positive pressure inlet port 94B of each switching device 90 is supplied with positive pressure from a positive pressure source (not shown) through the positive pressure supply passage 111 in an outer ring member 110 surrounding the outer surface of the rotating body 64. The rotating body 64 and the outer ring member 110 are rotatable relative to each other.Next, the V-axis drive units 100 will be described. The V-axis drive units 100 are each configured to move the slider 92 in the Z direction (the axial direction) between the pressurizing position and the pressurizing position. The V-axis drive units 100 are symmetrically disposed on the left and right sides of the mounting head 50 with the shaft 62 of the rotating body 60 interposed therebetween, as in the two Z-axis drive units 80.The two V-axis drive units 100 are mounted at positions matched with the two Z-axis drive units 80 in the Z direction (see FIG. 6 ). The two V-axis drive units 100 are configured to move the sliders 92 of the switching devices 90 associated with the pickup nozzles 250 of the mounting shaft devices 120 located at the predetermined positions (left and right sides in FIG. 6 ) between the pressurizing position and the pressurizing position.As shown in FIGS. 3, 4, and 6, the V-axis drive units 100 each include a box-like shape body 102 and a V-axis movable portion 104 configured to move in the Z direction (the up / down direction). A V-axis linear motor (not shown) is mounted in the body 102.As shown in FIGS. 4 and 6, an eccentric roller 106 (hereinafter referred to as "V-axis eccentric roller 106") is rotatably fixed to the V-axis movable portion 104 by means of an eccentric roller support portion 105.When the V-axis eccentric roller 106 is moved upward from the middle position by activating the V-axis drive unit 100, the V-axis eccentric roller 106 pushes up the contact portion, so that the slider 92 is moved to the pressurizing position. In contrast, when the V-axis eccentric roller 106 is moved downward from the intermediate position, it pushes down the contact portion, so that the slider 92 is moved to the pressurizing position.(Approach to Preventing Ball Trapping)For a spline mechanism, the spline shaft 121 is required to have the ball track 123. When the ball track groove 123 is in the air chamber 165 in the first shaft tube 161, air escapes from the air chamber 165 to the outside through the ball track groove 123. In order to prevent such leakage, the ball track groove 123 needs to be located away from the air chamber 165. In this example, the ball track groove 123 is provided in a region indicated by "G" in FIG. 10.Moreover, the spline shaft 121 has a cut end portion 125 at the end of the ball track 123. The cut end portion 125 is an incomplete raceway. More specifically, the cut end portion 125 is a groove having a depth decreasing toward the distal end (the lower end in FIG. 18 ). The cut end portion 125 is formed when the ball track groove 123 is formed only over a part of the spline shaft 121 but not over the entire length of the spline shaft 121.More specifically, as shown in FIG. 16, the ball track groove 123 is formed by a cutting tool having a rotatable circular rotary blade 300. Thus, when the formation of the ball groove 123 is finished before it is formed over the entire length of the shaft 121, an unfinished groove is formed at the end portion of the groove, i.e., the cut end portion 125 is formed. FIG. 16(A) shows an example in which the raceway 123 is formed over the entire length of the spline shaft 121 (the cut end portion 125 is not formed). FIG. 16(B) shows an example in which the ball groove 123 is formed over a part of the spline shaft 121 (forming the cut end portion 125).When the ball 143 enters the cut end portion 125 having a gradually decreasing depth, it would stick therein, which would result in a malfunction. The cut end portion 125 is an example of "incomplete raceway" of the invention.In this embodiment, as shown in FIGS. 17 and 18, the spline shaft 121 has an annular groove 127 and a ball stopper 128 mounted in the annular groove 127. The annular groove 127 has an annular shape with the axial line L of the spline shaft 121 as a center. The annular groove 127 is located at the boundary between the cut end portion 125 and the ball running groove (a full groove) 123.The annular groove 127 is a groove deeper than the cut end portion 125, and thus a step is formed between the annular groove 127 and the cut end portion 125. The ball stopper (an example of a "restrictor" of the invention) 128 mounted in the annular groove 127 is an open ring-shaped resin member. The ball stopper 128, which is in the form of an open ring, can be fixed to the annular groove 127 from the lateral side.When the ball 143 rolls along the ball track groove 123 toward the end of the ball track groove 123 (toward the lower end in FIG. 18 ), the ball 143 comes into contact with the ball stopper 128, which prevents the ball 143 in the ball track groove 123 from moving into the cut end portion 125. Therefore, the ball 143 is unlikely to be stuck in the cut end portion 125. Thereby, the malfunction of the spline shaft 121 in the linear movement in the Z direction (the axial direction) is reduced.Moreover, as shown in FIG. 18, the outer diameter of the ball stopper 128 is smaller than the outer diameter of the spline shaft 121. This configuration prevents the ball stopper 128 from coming into contact with the limiter 145 of the ball holder 141.(Advantages of Embodiment)In the mounting shaft device 120 of the embodiment, on the axis of the spline shaft 121, the ball cage 181, the first shaft tube 161, and the spline nut 151 are arranged in this order from the pickup nozzle 250 which is a component holder (i.e., from the lower side in FIG. 11 ). This configuration improves the mounting accuracy of an electronic component and shortens the response time required in switching air pressures.< Embodiments>The technology disclosed in this document is not limited to the embodiment described above and illustrated by the drawings. For example, the following embodiments are also intended to be included in the technical scope.(1) In the above-described embodiment, as an example of the mounting head, a rotatable mounting head including mounting shaft devices 120 arranged in the circumferential direction has been described. However, the mounting head may be, for example, a linear mounting head including mounting shaft devices 120 arranged in a straight line in an axial direction. Moreover, the mounting head may include only one mounting shaft device 120 and not a plurality of mounting shaft devices 120.(2) In the above-described embodiment, as an example of a component holder, the pickup nozzle 250 has been described, but the component holder may be a chuck holder configured to be opened or closed using compressed air.(3) In the example of the above-described embodiment, the ball stopper 128 is used to prevent the ball 143 from being caught in the cut end portion 125 of the spline shaft 121. However, a filling material 270 (see FIG. 19 ) formed of, for example, synthetic resin may fill the cut end portion 125 to prevent the ball 143 from being stuck in the cut end portion 125.(4) In the example of the above-described embodiment, the ball stopper 128 has the shape of an open ring. However, the ball stopper 128 may be in the form of a closed ring having no gap. In such a case, the ball stopper 128 may be disposed at the annular groove 127 from the axial end of the spline shaft 121. Moreover, the material of the ball stopper 128 is not limited to resin, and may be, for example, rubber.(5) In the example of the above-described embodiment, the ball stopper 128 is used to prevent the ball 143 from being caught in the cut end portion 125 of the spline shaft 121. Specifically, as shown in FIG. 20, a step 280 may be used at the boundary between the cut end portion 125 and the ball raceway groove 123 to prevent the ball 143 from being stuck in the cut end portion 125 of the spline shaft 121. FIG. 20 shows an example in which the step 280 is used to prevent the ball 143 from being caught in the cut end portion 125. The step 280 extends without interruption from the cut end portion 125 to the ball running groove 123. When the ball 143 comes into contact with the step 280, the ball 143 in the ball track groove 123 is prevented from moving into the cut end portion 125.(6) In the above-described embodiment, the second shaft tube 171 is described as an example of the support member. However, for example, the rotating body 64 may be a support member. More specifically, the second shaft tube 171 can be eliminated, and the spline shaft 121 can be supported in the through hole 65 of the rotating body 64. When the second shaft tube 171 is eliminated, the ball cage 181 may be fitted between the through hole 65 in the rotating body 64 and the spline shaft 121 to support the spline shaft 181.EXPLANATION OF REFERENCE NUMERALS1 Surface mounter 20 Transport conveyor (transport device) 30 Component mounting device 42 Conveyor 50 Mounting head 60 Head body 62 Shaft 64 Rotatable body (base) 70 R-axis drive unit (rotational drive unit) 80 Z-axis drive unit (axial drive unit) 90 Switching device (valve) 120 Mounting shaft device 121 Spline shaft 123 Ball raceway 125 Cut end portion (incomplete raceway) 127 Ring groove 128 Ball stopper (limiter) 151 Spline nut 161 First shaft pipe (introduction member) 171 Second shaft pipe (support member) 181 Ball cage (bearing) 230 Coil spring 250 Pick-up nozzle (component holder)

Claims

A mounting shaft device (120) configured to mount an electronic component, the mounting shaft device (120) comprising: a spline shaft (121) having a supply passage for air pressure therein and extending through a shaft hole in a support member (171); an introduction member (161) in communication with a valve (90) and allowing air pressure to be introduced from the valve (90) to the supply passage of the spline shaft (121); a component holder (250) located at an axial end of the spline shaft (121) and configured to receive the air pressure through the supply passage of the spline shaft (121) to hold an electronic component; a spline nut (151) connected to the spline shaft (121) through a spline mechanism; and a bearing (181), the spline shaft (121) is linearly movable in the shaft hole in the support member (171) in both an axial direction and rotatably supported about the axis thereof, wherein the bearing (181), the introduction member (161) and the spline nut (151) are disposed on an axis of the spline shaft (121) in this order from the component holder (250), the spline shaft (121) has a ball running groove (123) extending in an axial direction of the spline shaft (121) and receiving a ball (143) such that the spline shaft (121) and the spline nut (151) are connected to each other by a spline mechanism, and the ball running groove (123) is provided only at the upper portion of the spline shaft (121) in which the spline nut (151) is disposed, and not at a portion thereof, which corresponds to the introduction member (161), and a portion corresponding to the bearing (181) located below the spline nut (151) is provided.The mounting shaft device (120) according to claim 1, wherein the introduction member (161) has a tubular shape, the introduction member (161) and the spline shaft (121) define an air chamber therebetween which is in communication with the supply passage, and the introduction member (161) has a communication bore in a circumferential wall of the air chamber, the communication bore being in communication with the valve (90).The mounting shaft device (120) according to claim 1 or 2, wherein the spline shaft (121) has the ball raceway groove (123) and a limiter (128) at an end portion of the ball raceway groove (123), the limiter (128) being configured to prevent the ball (143) from being stuck in an incomplete raceway groove (125) having a depth gradually decreasing toward the distal end.The mounting shaft device (120) according to claim 3, wherein the spline shaft (62) has an annular groove (127) having an annular shape at the boundary between the incomplete raceway (125) and the ball raceway (123), and the limiter (128) is a ball stopper located in the annular groove (127) at the boundary between the incomplete raceway (125) and the ball raceway (123), the ball stopper being configured to prevent the ball (143) from moving from the ball raceway (123) to the incomplete raceway (125).The mounting shaft device (120) according to claim 3, wherein the limiter (128) is a step at the boundary between the incomplete raceway (125) and the ball raceway (123).The mounting shaft device (120) according to claim 3, wherein the restrictor (128) is a filling material filling the incomplete raceway (125).A mounting head (50) comprising: the mounting shaft device (120) according to any one of claims 1 to 6; a base (64) having a through hole (65) in which the introduction member (161) and the support member (171) are located one above the other and through which the spline shaft (121) extends in the axial direction; the valve (90), in a mounting hole in the base (64) and in communication with the introduction member (161); 23 / 1, an axial drive unit (80) configured to move the spline shaft (121) in the axial direction; and a rotational drive unit (70) configured to transmit torque to the spline nut (151) to rotate the spline shaft (121) about an axis thereof.A surface mount apparatus (1) comprising the mounting head (50) according to claim 7, wherein the surface mount apparatus (1) is configured to mount an electronic component held by the component holder (250) of the mounting head (50) on a board.

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