Component mounting method

In accordance with a component mounting method, a component stored in a component feeder is held by a component holding member and then is mounted in a mounting position on n object. The method includes, when a mounting posture of the component in which the component is mounted onto the object is inclined with respect to a basic posture of the component by a mounting angle, the operation of holding the component from the component feeder by the component holding member that has preliminarily been rotated to the mounting angle in such a direction as to depart from a reference posture of the component holding member prior to the mounting of the component on the object. And afterwards, the component holding member is rotated in a specified direction to finally return the component holding member to the reference posture, and then the component is mounted on the object.

BACKGROUND OF THE INVENTION
 The present invention relates to component mounting method and apparatus
 for mounting, for example, a component such as an electronic, mechanical,
 or optical component to a specified position on an object to be mounted
 such as a printed circuit board. More particularly, the invention relates
 to component mounting method and apparatus which make it possible to mount
 the component on the object with high precision, by driving a rotating
 mechanism so that the component will be rotated in one direction, with a
 view to suppressing the occurrence of lost motions of the rotating
 mechanism in correcting the postural angle of the component during the
 mounting operation.
 FIG. 14 is a perspective view of a conventional electronic component
 mounting apparatus 100 for mounting electronic components. A conveyor 132
 conveys circuit boards to and from the electronic component mounting
 apparatus 100, and further holds the circuit boards during production.
 Electronic component feeders 133 and 134 store and feed electronic
 components to be mounted on the circuit boards. The electronic component
 feeder 133 is a reel type electronic component feeder in which electronic
 components are stored on a reel, and the electronic component feeder 134
 is a tray type electronic component feeder in which electronic components
 are stored on a tray. A component pickup head 136, which is equipped with
 a nozzle 138 for picking up an electronic component from the electronic
 component feeders 133, 134, performs up and down motions, rotating motion
 and other motions of the nozzle 138. The rotating motion is effected by a
 rotating mechanism connected to the component pickup head 136. The
 component pickup head 136 is provided with a second component recognition
 camera 11 for capturing an image of the electronic component from above. A
 component recognition camera 137 is provided for capturing from blow, an
 image of the posture of the electronic component picked up by the nozzle
 138. An X-Y robot 135 moves the component pickup head 136 in X and Y
 directions.
 The electronic component mounting apparatus 100 performs the following
 operations. For picking up an electronic component, the X-Y robot 135
 moves the component pickup head 136, i.e. the nozzle 138, to an
 electronic-component pickup position in the electronic component feeder
 133 or 134 and then lowers the nozzle 138 to pick up an electronic
 component. The nozzle 138 is lifted after the pickup.
 Next, as shown at Step ("S" in the drawings) 101 of FIG. 16, the nozzle
 138, after picking up the electronic component is rotated by the rotating
 mechanism circumferentially of the nozzle 138 about the center axis of the
 nozzle 138, according to a mounting angle preset for the picked-up
 electronic component. Subsequently, at Step 102, the X-Y robot 135 moves
 the component pickup head 136 to the location of the component recognition
 camera 137, where the posture of the electronic component picked up by the
 nozzle 138 is recognized by the component recognition camera 137. Next, at
 Step 103, a difference between the actual angle of the picked-up
 electronic component and the mounting angle is determined based on the
 recognition result, and an angular correction for the picked-up electronic
 component is performed so that the difference value becomes zero. This
 correction is performed by rotating the nozzle 138, which is effected by
 again driving the rotating mechanism. Then, at Step 104, the electronic
 component, picked up by the nozzle 138, is moved to a specified position
 on the electronic circuit board in the X- and Y-directions by the
 component pickup head 136, which is moved by the X-Y robot 135. Further
 with an operation of the component pickup head 136, the nozzle 138 is
 lowered so that the electronic component is mounted to the specified
 component mounting position on the electronic circuit board, where the
 electronic component is released from the pickup head. By iterating these
 operations, electronic components are removed one after another from the
 electronic component feeder 133 or 134 and mounted onto the electronic
 circuit board.
 The aforementioned rotating mechanism for the nozzle 138 is shown in FIG.
 15. The nozzle 138 is fixed to a gear 102 so as to be inserted through
 center part of the gear 102. The gear 102 is connected to a motor output
 shaft 105 via a timing belt 101. Accordingly, rotation of the output shaft
 105 is transferred to the pickup nozzle 138 via the gear 102 by the timing
 belt 101, by which the electronic component picked up by the pickup nozzle
 138 is rotated to the specified mounting angle.
 However, the timing belt 101 or the gear 102 has a backlash. Moreover,
 depending on whether the angle of the electronic component is too large or
 too small relative to the target mounting angle, the direction in which
 the nozzle 138 is rotated differs. Therefore, by rotating the nozzle 138
 clockwise, or counterclockwise, or clockwise and counterclockwise together
 with the gear 102 or the like, there can occur an error in the final
 mounting angle of the electronic component due to the backlash.
 To suppress the occurrence of such errors, the resolution of the timing
 belt 101 or the gear 102 is enhanced or a mechanism which directly,
 transforms rotation of the motor output shaft into rotation of the pickup
 nozzle is adopted, responsive to the required precision. However, this
 increases the manufacturing costs and requires a large space for the
 installation of the motor and the nozzle 138.
 SUMMARY OF THE INVENTION
 The present invention has been accomplished to solve these and other
 issues. An object of the present invention is therefore to provide a
 component mounting method and apparatus which allow a component to be
 mounted at a mounting angle with good precision.
 In accomplishing these and other objects, according to a first aspect of
 the present invention, there is provided a component mounting method by
 which a component stored in a component feeder is held by a component
 holding member for holding the component and is then mounted in a mounting
 position on an object. The method comprising: when a mounting posture of
 the component in which the component is mounted onto the object is
 inclined with respect to a basic posture of the component by a mounting
 angle, holding the component from the component feeder by the component
 holding member that has preliminarily been rotated to the mounting angle
 in such a direction as to depart from a reference posture of the component
 holding member prior to the mounting of the component to the object, and
 afterwards, rotating the component holding member in a specified direction
 to finally return the component holding member to the reference posture,
 and then mounting the component on the object.
 According to a second aspect of the present invention, there is provided a
 component mounting method by which a component stored in a component
 feeder is held by a component holding member for holding the component and
 then mounted to a mounting position on an object to be mounted. The method
 comprising: when a mounting posture of the component in which the
 component is mounted onto the object is inclined with respect to a basic
 posture of the component by a mounting angle, detecting that the posture
 of the component in the component feeder is inclined with respect to an
 ideal position by a component posture angle by recognizing by a
 recognition device the component fed by the component feeder; based on the
 mounting angle and the component posture angle, calculating a pre-holding
 rotational angle, which is an angle for preliminarily rotating the
 component holding member before holding the component; holding the
 component from the component feeder by the component holding member that
 has preliminarily been rotated to the pre-holding rotational angle in such
 a direction as to depart from a reference posture of the component holding
 member; and rotating the component holding member in a specified direction
 to finally return the component holding member to the reference posture,
 and then mounting the component on the object.
 According to a third aspect of the present invention, there is provided a
 component mounting method according to the first aspect, wherein the
 component holding member is rotated circumferentially of the component
 holding member by a driving device via a transfer member which causes an
 error to occur in a rotational angle of the component holding member only
 when the component holding member is rotated in one direction and not to
 occur when the component holding member is rotated in the other direction
 that is opposite to the one direction and corresponding to the specified
 direction. The component holding member works to mount the component to
 the object in the reference posture in the rotational direction about a
 center axis of the component holding member, and the transfer member
 being, when gears are fitted to an output shaft of the driving device and
 the component holding member, respectively, a toothed belt for coupling
 the gear of the output shaft and the gear of the component holding member
 with each other, in which constitution arrangement that an error occurs to
 the rotational angle of the component holding member only when the
 component holding member is rotated in one direction and does not occur
 when the component holding member is rotated in the other direction means
 that the gear of the component holding member is normally urged in the
 other direction against the toothed belt, so that when the component
 holding member is rotated in the one direction, an error corresponding to
 a backlash between the gear of the component holding member and the
 toothed belt occurs, while when the component holding member is rotated in
 the other direction, no backlash takes place between the gear of the
 component holding member and the toothed belt so that no error occurs to
 the rotational angle of the component holding member.
 According to a fourth aspect of the present invention, there is provided a
 component mounting method according to the second aspect. In particular,
 the component holding member is rotated circumferentially of the component
 holding member by a driving device via a transfer member which causes an
 error to occur in the rotational angle of the component holding member
 only when the component holding member is rotated in one direction and not
 to occur when the component holding member is rotated in the other
 direction that is opposite to the one direction and corresponding to the
 specified direction. The component holding member works to mount the
 component to the object in the reference posture in the rotational
 direction about a center axis of the component holding member, and the
 transfer member being, when gears are fitted to an output shaft of the
 driving device and the component holding member, respectively, a toothed
 belt for coupling the gear of the output shaft and the gear of the
 component holding member with each other, in which constitution
 arrangement that an error occurs to the rotational angle of the component
 holding member only when the component holding member is rotated in one
 direction and does not occur when the component holding member is rotated
 in the other direction means that the gear of the component holding member
 is normally urged in the other direction against the toothed belt. Thus,
 when the component holding member is rotated in the one direction, an
 error corresponding to a backlash between the gear of the component
 holding member and the toothed belt occurs, while when the component
 holding member is rotated in the other direction, no backlash takes place
 between the gear of the component holding member and the toothed belt so
 that no error occurs to the rotational angle of the component holding
 member.
 According to a fifth aspect of the present invention, there is provided a
 component mounting method by which a component stored in a component
 feeder is held by a component holding member for holding a component and
 then mounted to a mounting position on an object to be mounted. The
 component holding member is rotated circumferentially by a driving device
 via a transfer member which causes an error to occur in the rotational
 angle of the component holding member only when the component holding
 member is rotated in one direction and not to occur when the component
 holding member is rotated in the other direction that is opposite to the
 one direction. The component holding member works to mount the component
 to the object in a reference posture in the rotational direction about a
 center axis of the component holding member; and that when a mounting
 posture of the component in which the component is mounted onto the object
 is inclined with respect to a basic posture of the component by a mounting
 angle with an origin of a coordinate system on the object taken as a
 center. The method comprises: detecting that the posture of the component
 in the component feeder is inclined with respect to an ideal position by a
 component posture angle with an origin of a coordinate system of the
 component feeder taken as a center, by recognizing by a recognition device
 the component fed by the component feeder; based on the mounting angle and
 the component posture angle, calculating a pre-holding rotational angle,
 which is an angle for preliminarily rotating the component holding member
 before holding the component; on condition that a direction of rotation in
 which the component holding member is rotated in the one direction from
 the reference posture is regarded as being of positive angle, while a
 direction of rotation in which the component holding member is rotated in
 the other direction is regarded as being of negative angle, calculating
 the pre-holding rotational angle and then deciding whether the pre-holding
 rotational angle is positive or negative; if the pre-holding rotational
 angle is zero or positive, holding the component from the component feeder
 by the component holding member that has preliminarily been rotated to the
 pre-holding rotational angle in the one direction from the reference
 posture, and then rotating the component holding member in the other
 direction to the pre-holding rotational angle via the transfer member to
 return the component holding member to the reference posture, and then
 mounting the component on the object; and meanwhile, if the pre-holding
 rotational angle is negative, holding the component from the component
 feeder by the component holding member that has preliminarily been rotated
 to the pre-holding rotational angle in the other direction from the
 reference posture, and then rotating the component holding member in the
 one direction to an angle resulting from adding a return angle to the
 pre-holding rotational angle to return the component holding member to the
 reference posture, and afterwards rotating the component holding member in
 the other direction to the return angle to return the component holding
 member to the reference posture, and then mounting the component on the
 object.
 According to a sixth aspect of the present invention, there is provided a
 component mounting method according to the fifth aspect. The transfer
 member is, when gears are fitted to an output shaft of the driving device
 and the component holding member, respectively, a toothed belt for
 coupling the gear of the output shaft and the gear of the component
 holding member with each other, in which constitution the arrangement that
 an error occurs to the rotational angle of the component holding member
 only when the component holding member is rotated in one direction and
 does not occur when the component holding member is rotated in the other
 direction means that the gear of the component holding member is normally
 urged in the other direction against the toothed belt, so that when the
 component holding member is rotated in the one direction, an error
 corresponding to a backlash between the gear of the component holding
 member and the toothed belt occurs, while when the component holding
 member is rotated in the other direction, no backlash takes place between
 the gear of the component holding member and the toothed belt so that no
 error occurs to the rotational angle of the component holding member.
 According to a seventh aspect of the present invention, there is provided a
 component mounting apparatus by which a component stored in a component
 feeder is held by a component holding member for and then mounted on a
 mounting position of an object. The apparatus comprising: a controller for
 performing control operations of, when a mounting posture of the component
 in which the component is mounted onto the object is inclined with respect
 to a basic posture of the component by a mounting angle, holding the
 component from the component feeder by the component holding member that
 has preliminarily been rotated to the mounting angle in such a direction
 as to depart from a reference posture of the component holding member
 prior to the mounting of the component to the object, and afterwards,
 rotating the component holding member in a specified direction to finally
 return the component holding member to the reference posture, and then
 mounting the component on the object.
 According to an eighth aspect of the present invention, there is provided a
 component mounting apparatus by which a component stored in a component
 feeder is held by a component holding member for holding the component and
 then mounted in a mounting position on an object. The apparatus
 comprising: a controller for performing control operations of, when a
 mounting posture of the component in which the component is mounted onto
 the object is inclined with respect to a basic posture of the component by
 a mounting angle, detecting that the posture of the component in the
 component feeder is inclined with respect to an ideal position by a
 component posture angle by recognizing by a recognition device the
 component fed by the component feeder; based on the mounting angle and the
 component posture angle, calculating a pre-holding rotational angle, which
 is an angle for preliminarily rotating the component holding member before
 holding the component; holding the component from the component feeder by
 the component holding member that has preliminarily been rotated to the
 pre-holding rotational angle in such a direction as to depart from a
 reference posture of the component holding member; and rotating the
 component holding member in a specified direction to finally return the
 component holding member to the reference posture, and then mounting the
 component on the object.
 According to a ninth aspect of the present invention, there is provided a
 component mounting apparatus according to the seventh aspect. In
 particular, the component holding member is rotated circumferentially of
 the component holding member by a driving device via a transfer member
 which causes an error to occur in a rotational angle of the component
 holding member only when the component holding member is rotated in one
 direction and not to occur when the component holding member is rotated in
 the other direction that is opposite to the one direction and
 corresponding to the specified direction. The component holding member
 works to mount the component to the object in the reference posture in the
 rotational direction about a center axis of the component holding member,
 and the transfer member being, when gears are fitted to an output shaft of
 the driving device and the component holding member, respectively, a
 toothed belt for coupling the gear of the output shaft and the gear of the
 component holding member with each other, in which constitution the
 arrangement that an error occurs in the rotational angle of the component
 holding member only when the component holding member is rotated in one
 direction and does not occur when the component holding member is rotated
 in the other direction means that the gear of the component holding member
 is normally urged in the other direction against the toothed belt, so that
 when the component holding member is rotated in the one direction, an
 error corresponding to a backlash between the gear of the component
 holding member and the toothed belt occurs, while when the component
 holding member is rotated in the other direction, no backlash takes place
 between the gear of the component holding member and the toothed belt so
 that no error occurs to the rotational angle of the component holding
 member.
 According to a tenth aspect of the present invention, there is provided a
 component mounting apparatus according to the eighth aspect. In
 particular, the component holding member is rotated circumferentially of
 the component holding member by a driving device via a transfer member
 which causes an error in the occur to rotational angle the component
 holding member only when the component holding member is rotated in one
 direction and not to occur when the component holding member is rotated in
 the other direction that Is opposite to the one direction and
 corresponding to the specified direction. The component holding member
 works to mount the component on the object in the reference posture in the
 rotational direction about a center axis of the component holding member,
 and the transfer member being, when gears are fitted to an output shaft of
 the driving device and the component holding member, respectively, a
 toothed belt for coupling the gear of the output shaft and the gear of the
 component holding member with each other, in which constitution the
 arrangement that an error occurs to the rotational angle of the component
 holding member only when the component holding member is rotated in one
 direction and does not occur when the component holding member is rotated
 in the other direction means that the gear of the component holding member
 is normally urged in the other direction against the toothed belt, so that
 when the component holding member is rotated in the one direction, an
 error corresponding to a backlash between the gear of the component
 holding member and the toothed belt occurs, while when the component
 holding member is rotated in the other direction, no backlash takes place
 between the gear of the component holding member and the toothed belt so
 that no error occurs to the rotational angle of the component holding
 member.
 According to an eleventh aspect of the present invention, there is provided
 a component mounting apparatus by which a component stored in a component
 feeder is held by a component holding member for holding a component and
 then mounted in a mounting position on an object. The component holding
 member is rotated circumferentially of the component holding member by a
 driving device via a transfer member which causes an error to occur in the
 rotational angle of the component holding member only when the component
 holding member is rotated in one direction and not to occur when the
 component holding member is rotated in the other direction that is
 opposite to the one direction. The component holding member works to mount
 the component on the object in a reference posture in the rotational
 direction about a center axis of the component holding member; and that
 when a mounting posture of the component in which the component is mounted
 onto the object is inclined with respect to a basic posture of the
 component by a mounting angle with an origin of a coordinate system on the
 object taken as a center. The apparatus comprises: a controller for
 performing control operations of, detecting that the posture of the
 component in the component feeder is inclined with respect to an ideal
 position by a component posture angle with an origin of a coordinate
 system of the component feeder taken as a center, by recognizing with a
 recognition device the component fed by the component feeder; based on the
 mounting angle and the component posture angle, calculating a pre-holding
 rotational angle, which is an angle for preliminarily rotating the
 component holding member before holding the component; on condition that a
 direction of rotation in which the component holding member is rotated in
 the one direction from the reference posture is regarded as being of
 positive angle, while a direction of rotation in which the component
 holding member is rotated in the other direction is regarded as being of
 negative angle, calculating the pre-holding rotational angle and then
 deciding whether the pre-holding rotational angle is positive or negative;
 if the pre-holding rotational angle is zero or positive, holding the
 component from the component feeder with the component holding member that
 has preliminarily been rotated to the pre-holding rotational angle in the
 one direction from the reference posture, and then rotating the component
 holding member in the other direction to the pre-holding rotational angle
 via the transfer member to return the component holding member to the
 reference posture, and then mounting the component on the object, and, if
 the pre-holding rotational angle is negative, holding the component from
 the component feeder with the component holding member that has
 preliminarily been rotated to the pre-holding rotational angle in the
 other direction from the reference posture, and then rotating the
 component holding member in the one direction to an angle resulting from
 adding a return angle to the pre-holding rotational angle to return the
 component holding member to the reference posture, and afterwards rotating
 the component holding member in the other direction to the return angle to
 return the component holding member to the reference posture, and then
 mounting the component on the object.
 According to a twelfth aspect of the present invention, there is provided a
 component mounting apparatus according to the eleventh aspect. In
 particular, the transfer member is, when gears are fitted to an output
 shaft of the driving device and the component holding member,
 respectively, a toothed belt for coupling the gear of the output shaft and
 the gear of the component holding member with each other, in which
 constitution the arrangement that an error occurs in the rotational angle
 of the component holding member only when the component holding member is
 rotated in one direction and does not occur when the component holding
 member is rotated in the other direction means that the gear of the
 component holding member is normally urged in the other direction against
 the toothed belt, so that when the component holding member is rotated in
 the one direction, an error corresponding to a backlash between the gear
 of the component holding member and the toothed belt occurs. However, when
 the component holding member is rotated in the other direction, no
 backlash takes place between the gear of the component holding member and
 the toothed belt so that no error occurs to the rotational angle of the
 component holding member.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 Before the description of the present invention proceeds, it is to be noted
 that like parts are designated by like reference numerals throughout the
 accompanying drawings.
 A component mounting method and a component mounting apparatus, which are
 one embodiment of the present invention, are described below with
 reference to the accompanying drawings. The present component mounting
 method is to be executed by the present component mounting apparatus.
 Throughout the drawings including FIGS. 14 and 15 mentioned above, like
 constituent parts are designated by like reference numerals and their
 description is omitted. In addition, one embodiment that fulfills the
 function of the transfer member corresponds to the timing belt 101. Also,
 one embodiment that fulfills the function of the component recognition
 device corresponds to the second component recognition camera 11. Also,
 one direction corresponds to direction I while the specified direction and
 the other direction correspond to direction II.
 In order to prevent the occurrence of errors in the final mounting angle of
 an electronic component due to the backlash as described above, the
 component mounting method and apparatus of this embodiment are arranged so
 that the rotational direction in which the rotational angle of the pickup
 nozzle 138 is finally adjusted for mounting the component by the pickup
 nozzle 138. The rotational direction is at all times in a direction such
 that rotational errors will never occur at the pickup nozzle 138, as
 detailed later. That rotational errors will never occur means that there
 will occur no mounting trouble in relation to the mounting precision at
 which the electronic component is mounted onto the circuit board, serving
 as an object to be mounted, by the pickup nozzle 138.
 As shown in FIG. 2, the component mounting apparatus 1 of this embodiment
 comprises a conveyor equipment 132, electronic component feeders 133, 134,
 an X-Y robot 135, a component pickup head 10 and a component recognition
 camera 137. The construction of these constituent members is principally
 the same as that of the component mounting apparatus 100 of the
 conventional art as described with reference to FIG. 14, and so its
 description is omitted. In addition, the component pickup head 10, which
 is generally equivalent to the aforementioned component pickup head 136 of
 the conventional art, is identical in its basic construction to the
 component pickup head 136, with the difference being that the gear 102 is
 provided with urging means as described below. Further, the component
 mounting apparatus 1 of this embodiment differs from the conventional
 electronic component mounting apparatus 100 in that a controller 2 is
 provided to perform operational control, as described in detail below,
 primarily for the component pick-up head 10, and that the gear 102 fitted
 to the pickup nozzle 138 is normally urged in such a direction so as to be
 rotated in a later-described direction II, as shown in FIG. 13, in the
 component pickup head 10. In addition, the device for urging the gear 102
 may be a known device, such as a spiral spring 20 as shown in the figure,
 for example, in the gear 102.
 As a result of the arrangement in which the gear 102 is urged in direction
 II as seen above, even if, for example, the belt 101 moves along a
 direction III such that a tooth 110a of the belt 101 and a tooth 102a of
 the gear 102 have separated from each other, the gear 102 will be rotated
 in the II direction due to the urging force when the movement of the belt
 101 along direction III has stopped or when its moving speed has dropped
 below a specified value, so that the tooth 102a of the gear 102 comes into
 contact with the tooth 101a of the belt 101 once again. Accordingly, in
 the component pickup head 10, when the pickup nozzle 138 rotates in
 direction II, there will occur no backlash between the tooth 101a of the
 belt 101 and the tooth 102a of the gear 102 so that no errors will occur
 in the rotational angle of the pickup nozzle 138. Conversely, when the
 pickup nozzle 138 rotates in direction I, the aforementioned urging force
 will not act, so that a backlash will occur between the tooth 101a of the
 belt 101 and the tooth 102a of the gear 102, in which case an error will
 occur in the rotational angle of the pickup nozzle 138.
 Next described is the operation of the component mounting apparatus 1 of
 this embodiment. Operations of the conveyor equipment 132, the electronic
 component feeders 133, 134, the X-Y robot 135 and the component
 recognition camera 137 are the same as in the conventional component
 mounting apparatus 100, and so their description is omitted. Accordingly,
 below described in detail is the rotational operation of the pickup nozzle
 138 in the component pickup head 10, which is a characteristic operation
 of this embodiment. Before the detailed description, preconditions will
 first be explained.
 As described in connection with the conventional device, and as shown in
 FIG. 3, the pickup nozzle 138 picks up an electronic component 4 placed in
 a component pickup position 3 of the component feeder 133 or 134
 (hereinafter, the component feeder 133 is taken as an example). An X-Y
 coordinate system 5 is assumed here to represent the posture of the
 electronic component 4 in the component pickup position 3 of the component
 feeder 133. Also, as shown in FIG. 4, an X-Y coordinate system 8 in the
 circuit board 6 is assumed to represent the mounting posture of the
 electronic component 4 that has been mounted in a mounting position 7 on
 the circuit board 6, which is conveyed by the conveyor equipment 132.
 Also, as shown in FIG. 5, an X-Y coordinate system 9 of the pickup nozzle
 138 is assumed with the rotational center of the pickup nozzle 138 taken
 as the origin. In such a case, generally, because each of the X-Y
 coordinate systems 5, 8, 9 is an independent coordinate system, it would
 be necessary to consider shifts of the coordinate axes between the X-Y
 coordinate systems 5, 8, 9 in order to execute the operations of picking
 up the electronic component 4 from the component feeder 133 and mounting
 it to the circuit board 6 by the pickup nozzle 138. However, for an easier
 understanding, it is assumed hereinbelow that coordinate axes and origins
 of the X-Y coordinate system 5, the X-Y coordinate system 8 and the X-Y
 coordinate system 9 are perfectly coincident with one another,
 respectively. Further, a posture of the pickup nozzle 138 in the direction
 of rotation about the center axis of the pickup nozzle 138 in which
 posture the pickup nozzle 138 mounts the electronic component 4 to the
 mounting position 7 of the circuit board 6 will hereinafter be referred to
 as reference posture. Also, the X-Y coordinate system 9 of the pickup
 nozzle 138 positioned in the reference posture is assumed to be coincident
 with the X-Y coordinate system 5 and the X-Y coordinate system 8. Further,
 as shown in FIG. 5, with the pickup nozzle 138 positioned in the reference
 posture, a position of the pickup nozzle 138 along the X-axis in the X-Y
 coordinate system 9 is represented by numeral 12. When the pickup nozzle
 138 picks up the electronic component 4, the pickup nozzle 138 is set to
 the reference posture. Therefore, it is assumed that the pickup nozzle 138
 is positioned in the Reference posture when the pickup nozzle 138 picks up
 the electronic component 4 in the component pickup position 3, and when
 the pickup nozzle 138 mounts it on the mounting position 7.
 Now the operation is explained in detail. Assume that the current time
 point is a time point when the circuit board 6 has been conveyed and held
 in the component mounting apparatus 1 by the conveyor equipment 132, where
 the component mounting operation is going to be started. At Step ("S" in
 the drawings) 1 in FIG. 1, before the pickup nozzle 138 picks up the
 electronic component 4 from the component feeder 133, an image of the
 electronic component 4 in the component pickup position 3 of the component
 feeder 133 is first captured by a second component recognition camera 11
 equipped in the component pickup head 10. Based on this image information,
 the controller 2 recognizes the posture of the electronic component 4 in
 the component pickup position 3, and detects a component posture angle
 .alpha., which is an angle representing a shift from the ideal position of
 the electronic component 4 placed in the component pickup position 3 as
 shown in FIG. 3. Since the X-Y coordinate system 5 and the X-Y coordinate
 system 9 are coincident with each other as described above, the component
 posture angle a coincides with an angle to which the pickup nozzle 138
 should be rotated from the reference posture of the pickup nozzle 138.
 Meanwhile, as shown in FIG. 4, the mounting angle .theta., which is an
 angle representing a shift from the basic posture to the mounting posture
 of the electronic component 4 that has been mounted to the mounting
 position 7 on the circuit board 6, from data which has previously been
 recognized by the controller 2 as in the conventional component mounting
 apparatus 100. In this connection, since the X-Y coordinate system 8 and
 the X-Y coordinate system 9 are coincident with each other as described
 above, the mounting angle .theta. coincides with an angle through which
 the pickup nozzle 138 should be rotated from the reference posture of the
 pickup nozzle 138.
 Accordingly, at Step 2, the controller 2 calculates a pre-pickup rotational
 angle .theta..sub.PRE which is a value resulting from adding the component
 posture angle .alpha. and the mounting angle .theta. together. In FIGS. 3,
 4 and 9, it is assumed that the angle goes positive counterclockwise
 beyond the border of the X-axis and negative clockwise. Therefore, the
 component posture angle .alpha. and the mounting angle .theta. in FIGS. 3
 and 4 are positive values while the mounting angle .theta. in FIG. 9 is a
 negative value. For example, in the case of FIGS. 3 and 4, since both the
 component posture angle .alpha. and the mounting angle .theta. are
 positive, the pre-pickup rotational angle .theta..sub.PRE becomes a
 positive value. Meanwhile, in the case of FIGS. 3 and 9, the component
 posture angle .alpha. is a positive value but the mounting angle .theta.
 is a negative value, so that if the mounting angle .theta. has a value
 beyond the component posture angle .alpha., the pre-pickup rotational
 angle .theta..sub.PRE becomes a negative value.
 At Step 3, it is decided whether the pre-pickup rotational angle
 .theta..sub.PRE is zero, positive or negative. If the pre-pickup
 rotational angle .theta..sub.PRE is decided to be zero or positive, then
 the program moves to Step 4. If the mounting angle .theta..sub.PRE is
 decided to be negative, then the program moves to Step 7. It is noted that
 if the pre-pickup rotational angle .theta..sub.PRE is decided to be zero
 or positive, the pickup nozzle 138 is rotated in direction I as shown in
 FIG. 6, which is clockwise as an example, from the reference posture.
 Meanwhile, if the pre-pickup rotational angle .theta..sub.PRE is decided
 to be negative, the pickup nozzle 138 is rotated in direction II as shown
 in FIG. 6, which is counterclockwise as an example, from the reference
 posture.
 For example, if the pre-pickup rotational angle .theta..sub.PRE is decided
 to be positive as in the case of FIGS. 3 and 4, the controller 2 at Step 4
 preliminarily rotates the pickup nozzle 138 in direction I from the
 reference posture to an extent of the absolute value of the pre-pickup
 rotational angle .theta..sub.PRE, i.e., to an extent of
 .vertline.(+.alpha.)+(+.theta.).vertline., as shown in FIG. 7, before the
 suction of the component 4. In FIG. 7, the position 12 after rotation of
 the pickup nozzle 138 is indicated by numeral 13. Also, when the pickup
 nozzle 138 is rotated in the direction I, an error corresponding to the
 backlash is included in the rotational angle of the pickup nozzle 138 as
 described above.
 Then at Step 5, the electronic component 4 is picked up in the component
 pickup position 3 of the component feeder 133 by the pickup nozzle 138
 that has been rotated as described above.
 Next at Step 6, as shown in FIG. 8, the controller 2 rotates the pickup
 nozzle 138 in direction II from the position 13 to an extent of the
 absolute value of the pre-pickup rotational angle .theta..sub.PRE, i.e.,
 to an extent of .vertline.(+.alpha.)+(+.theta.).vertline.. As described
 before, when the pickup nozzle 138 is rotated in direction II, an error
 corresponding to the backlash is not included in the rotational angle of
 the pickup nozzle 138. Accordingly, at a time point when the operation of
 Step 6 is completed, the pickup nozzle 138 is at a position that is
 coincident with the reference posture again.
 Therefore, at Step 11, which is the step succeeding Step 6, the component
 pickup head 10 is moved to the mounting position 7 of the circuit board 6
 by the X-Y robot 135, and then the pickup nozzle 138 is lowered so that
 the electronic component 4 held by the pickup nozzle 138 in the state of
 Step 6, is mounted on the circuit board 6. Through these operations, the
 electronic component 4 is mounted in the mounting position 7 of the
 circuit board 6.
 Meanwhile, when the pre-pickup rotational angle .theta..sub.PRE is
 determined to be negative, for example as shown in FIGS. 3 and 9, the
 controller 2 at Step 7, before the pickup (suction) of the electronic
 component 4, preliminarily rotates the pickup.) nozzle 138 in the
 direction II from the reference posture to an extent of the absolute value
 of the pre-pickup, rotational angle .theta..sub.PRE i.e., to an extent of
 .vertline.(+.alpha.)+(-.theta.).vertline., as shown in FIG. 10. In FIG.
 10, the position where the position 12 comes after the rotation of the
 pickup nozzle 138 is indicated by numeral 14.
 Then, at Step 8, the electronic component 4 is picked up in the component
 pickup position 3 of the component feeder 133 by the pickup nozzle 138
 that has been rotated as described above.
 With regard to the pickup nozzle 138 that has been rotated in direction II
 from the reference posture as described above, when the pickup nozzle 138
 is rotated merely in direction I so as to be returned to the reference
 posture for the mounting of the electronic component 4 to the circuit
 board 6, a rotational error would be included in the rotation of the
 pickup nozzle 138 in direction I as described before, such that the
 electronic component 4 would not coincide with the mounting position 7 on
 the circuit board 6 in the rotational direction of the pickup nozzle 138.
 Therefore, operations of the following Step 9 and Step 10 are executed
 when the pre-pickup rotational angle .theta..sub.PRE is negative.
 At Step 9, as shown in FIG. 11, the controller 2 rotates the pickup nozzle
 138 in direction I from the position 14 through an angle resulting from
 further adding a return angle .beta. to the absolute value of the
 pre-pickup rotational angle .theta..sub.PRE, i.e.
 .vertline.(+.alpha.)+(-.theta.).vertline.. In this case, the return angle
 .beta. is an angle having a positive value which is sufficiently smaller
 than the component posture angle .alpha.. In FIG. 11, the position where
 the position 12 comes after the rotation of the pickup nozzle 138 is
 indicated by numeral 15.
 Next at Step 10, as shown in FIG. 12, the controller 2 rotates the pickup
 nozzle 138 in direction II from position 15 through the return angle
 .beta.. With the rotation in direction II at Step 10, an error
 corresponding to the backlash will not be included in the rotational angle
 of the pickup nozzle 138 as described before. Accordingly, the position of
 the pickup nozzle 138 is again coincident with the reference posture at a
 time point when the operation of Step 10 is completed.
 Therefore, at Step 11, which is the step succeeding Step 10, the component
 pickup head 10 is moved to the mounting position 7 of the circuit board 6
 by the X-Y robot 135, and then the pickup nozzle 138 is lowered so that
 the electronic component 4, held by the pickup nozzle 138 in the state of
 Step 10, is mounted on the circuit board 6. Through these operations, the
 electronic component 4 is mounted in the mounting position 7 of the
 circuit board 6.
 As described above, in this embodiment, before the electronic component 4,
 which is an object to be mounted, is picked up by the pickup nozzle 138
 from the component feeder 133, the posture of the electronic component 4
 in the component pickup position 3 of the component feeder 133 is
 recognized by the second recognition camera 11. Then, the pickup nozzle
 138 is preliminarily rotated through a pre-pickup rotational angle
 .theta..sub.PRE that results from adding a component posture angle .alpha.
 obtained by this recognition and the mounting angle .theta. together, and
 afterwards the electronic component 4 is picked up. Further, when the
 picked-up electronic component 4 is finally rotated to the mounting angle,
 it will be rotated in direction II in which no error will occur in the
 rotation of the pickup nozzle 138. Through these operations, the
 electronic component 4 can be mounted correctly in the mounting position 7
 without any lost motion of the pickup nozzle 138 in the rotational
 direction.
 Also when the rotation of the pickup nozzle 138 is fulfilled by means of a
 ball screw, high precision positioning is enabled by a mounting method
 similar to that of this embodiment.
 Although the pickup nozzle 138 moves thicknesswise of the circuit board 6
 so that the direction of movement of the pickup nozzle 138 is coincident
 with the direction of the rotational axis of the pickup nozzle 138 in this
 embodiment, there are some cases where these are not coincident. In such a
 case, when the electronic component 4 is rotated to the mounting angle,
 the center of the electronic component 4 would move in the (X, Y)
 directions, in which case the quantity of the movement should additionally
 be corrected by a known method.
 In addition, in the above-described embodiment, the posture of the
 electronic component 4 is recognized by the component recognition camera
 137 before the electronic component 4 is picked up from the component
 feeder 133 by the pickup nozzle 138. However, without being limited to
 this, the posture of the electronic component 4 may be recognized by the
 component recognition camera 137 after the electronic component 4 has been
 picked up from the component feeder 133 by the pickup nozzle 138, where
 the resulting angle is taken as the component posture angle .alpha..
 Furthermore, the component posture angle .alpha. may be obtained by
 recognizing the posture of the electronic component 4 both before and
 after the pickup to determine component posture angles .alpha.-1 and
 .alpha.-2, and by adding up these values to determine the component
 posture angle .alpha..
 Also, this embodiment has been described to show a case where the component
 posture angle .alpha. is taken into consideration. However, when the
 posture of the electronic component 4 in the component pickup position 3
 of the component feeder 133 is undoubtedly coincident with its ideal
 posture, there is no need of taking into consideration the component
 posture angle .alpha..
 As described in detail above, according to the component mounting method of
 the first aspect of the invention and to the component mounting apparatus
 of the fourth aspect of the invention, a controller is provided so that
 the following operations are executed by the controller. That is, before
 the mounting of the component on the circuit board, the nozzle is rotated
 to a mounting angle in such a direction so as to depart from the reference
 posture of the nozzle, and afterwards, the nozzle is rotated in a
 specified direction so as to be finally returned to the reference posture,
 in which state the component is mounted on the circuit board. Like this,
 the nozzle is rotated in such a specified direction that no rotational
 errors occur with respect to the nozzle, so that a component mounting
 operation at a high-precision mounting angle can be accomplished.
 Also, according to the component mounting method of the second and third
 aspects of the invention and to the component mounting apparatus of the
 fifth and sixth aspects of the invention, a controller is provided so that
 the following operations are executed by the controller. That is, a
 component posture angle is obtained by recognizing the posture of the
 component in the component feeder with a component recognition device.
 Then, a pre-pickup rotational angle is determined based on the component
 posture angle and a mounting angle, and the nozzle is rotated to the
 pre-pickup rotational angle in such a direction as to depart from the
 reference posture of the nozzle, and afterwards, the nozzle is rotated in
 a specified direction so as to be finally returned to the reference
 posture, in which state the component is mounted on the circuit board.
 Like this, the component posture angle, based on the posture of the
 component in the component feeder, is considered and, just before the
 mounting of the component, the nozzle is rotated in such a specified
 direction so as to cause no errors in the nozzle, so that a component can
 be mounted with a higher-precision mounting angle.
 The entire disclosure of Japanese Patent Application No. 3-347593 filed on
 Dec. 26, 1996, including specification, claims, drawings, and summary are
 incorporated herein by reference in its entirety.
 Although the present invention has been fully described in connection with
 the preferred embodiments thereof with reference to the accompanying
 drawings, it is to be noted that various changes and modifications are
 apparent to those skilled in the art. Such changes and modifications are
 to be understood as included within the scope of the present invention as
 defined by the appended claims unless they depart therefrom.