Electric-component mounting system including movable substrate-holding device

An electric-component mounting system including component-mounting devices arranged in an array and each having a component-holding head for holding an electric component, and a head-moving device to move the head, and a substrate-transferring device to move at least one substrate on which electric components are to be mounted, and wherein the substrate-transferring device stops each substrate at at least one stop position which corresponds to at least one of the component-mounting devices and at which operations of the component-mounting devices are concurrently performed on the at least one substrate. The substrate-transferring device includes a first transferring device to move each substrate along a path parallel to the array of the component-mounting devices and stop each substrate at least once during its movement along the path, and a second transferring device having a substrate-holding device to hold each substrate at each stop position and a holding-device moving device to reciprocate the substrate-holding device by a maximum distance smaller than a maximum distance of movement of each substrate by the first transferring device, so that each substrate is moved together with the substrate-holding device.

The present application is based on Japanese Patent Application No. 2001-373983 filed Dec. 7, 2001, the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to an electric-component mounting system provided with a component-mounting device arranged to mount electric components (including electronic components) on a circuit substrate, and more particularly to techniques for improving mounting accuracy of the electric components on a circuit substrate which is larger than a component mountable area of the component-mounting device.

2. Discussion of Related Art

One type of known electric-component mounting system includes a plurality of component-mounting devices arranged in series with each other along a line, and a substrate-transferring device disposed so as to extend along the line of the component-mounting devices. Each component-mounting device includes a component-holding head operable to hold an electric component, and a head moving device arranged to move the component-holding head. The substrate-transferring device is arranged to transfer at least one circuit substrate on which electric components are to be mounted. Each circuit substrate is stopped at a predetermined component-mounting position aligned with a corresponding one of the component-mounting devices, so that operations to mount the electric components on the circuit substrates are concurrently performed by the respective component-mounting devices. Usually, the substrate-transferring device is of a chain track type or endless track type including a conveyor, for example. When the component mounting operations are performed on a circuit substrate which is larger than a component mountable area of the component-holding head of the corresponding component-mounting device in the electric-component mounting system of the type described, some of the predetermined electric components are first mounted in a portion of the component-mounting area of the circuit substrate which corresponds to the component mountable area of the component-holding head, and then the other electric components are mounted in the other portion of the component-mounting area of the circuit substrate, after the circuit substrate is fed downwards by an appropriate distance. In some electric-component mounting systems of this type, a fiducial-mark imaging device arranged to take images of a plurality of fiducial marks provided on each circuit substrate is disposed upstream of the most upstream one of the component-mounting devices, so that the images of the fiducial marks are taken before the circuit substrate is transferred to the component-mounting position aligned with the corresponding component-mounting device. In most cases, the fiducial marks which are provided to accurately detect positioning errors of each circuit substrate are disposed at respective positions on the circuit substrate, which are spaced from each other, for instance, in the direction of transfer of the circuit substrate, or at two positions which are located in respective two diagonally opposed corner portions of the rectangular circuit substrate. The fiducial-mark imaging device is movable to simultaneously take the images of the spaced-apart fiducial-marks, without having to move the circuit substrate. Image data representative of the images of the fiducial marks thus taken are compared with stored reference image data representative of the nominal positions of the fiducial marks, to calculate positioning errors of the circuit substrate. The calculated positioning errors are fed to the component-mounting devices as the circuit substrate is transferred, so that positions to which the component-holding head of each component-mounting device is moved to mount the electric components on the circuit substrate are adjusted so as to eliminate the positioning errors of the circuit substrate when the electric components are mounted at the predetermined mounting positions.

However, the positioning accuracy of the electric components mounted on the circuit substrates is influenced by accuracy of feeding of the circuit substrates by a feeding mechanism of the substrate-transferring device after the imaging of the fiducial marks. Accordingly, the electric-component mounting system including a plurality of component-mounting devices arranged in series with each other suffers from difficulty in maintaining a high degree of positioning accuracy of the electric components mounted on the circuit substrates. To improve the positioning accuracy of each circuit substrate at the component-mounting position, the circuit substrate may be transferred downwards together with a pallet while the circuit substrate is fixed in position on the pallet. In this case, however, a pallet transferring device for transferring the pallet downwards with high positioning accuracy is required as well as the pallet. In addition, a device for returning the pallet to the original position upstream of the component-mounting devices is also required, so that the substrate-transferring device tends to be complicated in construction.

Each of the plurality of component-mounting devices of the electric-component mounting system may be provided with a fiducial-mark imaging device, which is arranged to be moved by the head moving device, to take the images of the fiducial marks on each circuit substrate each time the circuit substrate is stopped at the component-mounting position corresponding to each component-mounting device. In this case, the errors of positioning of the circuit substrate relative to the component-mounting device are detected on the basis of the images of the fiducial marks, and the component-mounting accuracy can be improved. However, an area in which the fiducial-mark imaging device is movable almost entirely overlaps the component mountable area of the component-holding head of the component-mounting device. When the electric components are mounted on a circuit substrate which is larger than the component mountable area of the component-holding head, the fiducial-mark imaging device is not able to take the images of all of the mutually spaced-apart fiducial marks provided on the circuit substrate. Therefore, the electric-component mounting system wherein each component-mounting device is provided with the fiducial-mark imaging device is not capable of dealing with the circuit substrates which are larger than the component mountable area of the component-mounting device.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an electric-component mounting system which permits electric components to be mounted with high accuracy on a circuit substrate which is larger than the component mountable area of its component-holding head. This object may be achieved according to any one of the following modes of the present invention, each of which is numbered like the appended claims and depends from the other mode or modes, where appropriate, for easier understanding of technical features disclosed in the present application and possible combinations of those features. However, it is to be understood that the invention is not limited to those technical features or combinations thereof, and that any one of a plurality of technical features described below with respect to any one mode of the invention may be a subject matter of the present invention, without the other technical feature or features being combined with that one technical feature.

(1) An electric-component mounting system for mounting electric components on at least one circuit substrate, comprising:a plurality of component-mounting devices which are arranged in series with each other and each of which includes a component-holding head operable to hold an electric component, and a head-moving device operable to move the component-holding head; anda substrate-transferring device disposed so as to extend along an array of the plurality of component-mounting devices and operable to move the at least one circuit substrate and stop the at least one circuit substrate at at least one stop position which respectively corresponds to at least one of the plurality of component-mounting devices and at which the at least one component-mounting device mounts the electric components on the at least one circuit substrate,and wherein the substrate-transferring device includes (a) a first transferring device operable to move the at least one circuit substrate, along at least a path from an upstream end to a downstream end of the array of the plurality of component-mounting devices, and stop the at lest one circuit substrate at least once during movement thereof along the path, and (b) a second transferring device comprising a substrate-holding device operable to fixedly hold the at least one circuit substrate at each of the at least one stop position established by the first transferring device, and a holding-device moving device operable to reciprocate the substrate-holding device in a direction of movement of the at least one circuit substrate by the first transferring device, by a maximum distance smaller than a maximum distance of movement of the at least one circuit substrate by the first transferring device, so that the at least one circuit substrate held by the substrate-holding device is moved together with the substrate-holding device.

In the electric-component mounting system constructed according to the above mode (1) of the present invention, the plurality of component-mounting devices are arranged in series with each other, and each circuit substrate is moved by the first transferring device along a path from the upstream end to the downstream end of the array of the component-mounting devices. The first transferring device stops each circuit substrate at least once during its movement along the path, and the substrate-holding device of the second transferring device holds each circuit substrate stopped by the first transferring device, such that the circuit substrate is not movable relative to the substrate-holding device. The substrate-holding device fixedly holding each circuit substrate is reciprocated by the holding-device moving device of the second transferring device, to move each circuit substrate in the direction of movement of the substrate by the first transferring device. Although each circuit substrate is movable by the first and second transferring devices in the direction parallel to the array of the plurality of component-mounting devices, the these two transferring devices are transferring devices of different types, which cooperate with each other to improve a freedom in the movement of each circuit substrate. For instance, the first transferring device which is provided to move each circuit substrate along the path extending from the upstream end to the downstream end of the array may be arranged to stop each circuit substrate with a comparatively low degree of positioning accuracy at each stop position, while the second transferring device may be arranged to position and hold each circuit substrate with a comparatively high degree of positioning accuracy and stop each circuit substrate at a desired position with a comparatively high degree of positioning accuracy, so that the electric components can be accurately mounted on the circuit substrate accurately positioned by the second transferring device, by the component-mounting devices.

Where the required accuracy of positioning of each circuit substrate by the first transferring device is comparatively low, as described above, the construction of the first transferring device may be simplified, and the required cost of manufacture of the first transferring may be accordingly reduced. For example, the first transferring device includes a belt conveyor or any other type of conveyor arranged to move each circuit substrate along an endless path. A transferring device of this endless or chain track type is capable of moving each circuit substrate by a maximum distance almost equal to its length. On the other hand, the second transferring device which is arranged to move the substrate-holding device fixedly holding each circuit substrate permits a comparatively high degree of accuracy of positioning of each circuit substrate at a desired position. However, the second transferring device requires a space for permitting a movement of the substrate-holding device, in addition to an installation space for the substrate-holding device. In this respect, it is desirable to minimize the maximum distance of reciprocating movement of the substrate-holding device. Although the maximum distance of reciprocating movement of the substrate-holding device may be made large enough to move each circuit substrate between the upstream and downstream ends of the array of the component-mounting devices, this arrangement requires the length of the second transferring device in the direction of transfer of each circuit substrate, to be considerably larger than the length of the first transferring device and the length of the array of the component-mounting devices. In view of this drawback, the maximum distance of reciprocation of the substrate-holding device by the holding-device moving device of the second transferring device is made smaller than the maximum distance of movement of each circuit substrate by the first transferring device, according to the principle of the present invention.

In summary, the first and second transferring devices of the substrate-transferring device provided in the present electric-component mounting system are constructed and arranged so as to make up for their drawbacks, and cooperate to not only increase the maximum distance of movement of each circuit substrate of the substrate-transferring device and but also improve the accuracy of positioning of the circuit substrate by the substrate-transferring device.

(2) An electric-component mounting system according to the above mode (1), wherein the first transferring device comprises a belt conveyor arranged to move the at least one circuit substrate while supporting each of the at least one circuit substrate in contact with a lower surface of each circuit substrate.

(3) An electric-component mounting system according to the above mode (2), wherein the substrate-holding device includes a holder portion arranged to grip each circuit substrate in a vertical direction, at a first portion of each circuit substrate which is spaced from a second portion thereof at which each circuit substrate is supported on its lower surface by the belt conveyor of the first transferring device, the first portion being spaced from the second portion in a direction perpendicular to the direction of movement of the at least one circuit substrate by the first transferring device.

The belt conveyor preferably includes two sets of a conveyor belt, a belt guide and a belt drive device, as described below. However, the belt conveyor may include a single conveyor belt which has a comparatively large width and which is arranged to move each circuit substrate while supporting each circuit substrate in contact with a portion of its lower surface which is intermediate in the width direction perpendicular to the direction of movement of each circuit substrate. In this case, the substrate-holding device of the second transferring device is required to hold two portions of each circuit substrate which are located on the opposite sides of the conveyor belt. Where the belt conveyor includes the two sets of conveyor belt, belt guide and belt drive devices as indicated above, the substrate-holding device is arranged to grip portions of each circuit substrate which are located either inwardly or outwardly of the portions at which each circuit substrate is supported by the two conveyor belts. In either of these two cases, the holder portion of the substrate-holding device is preferably arranged to grip each circuit substrate in the vertical direction, at lateral end portions of the substrate opposite to each other in the width direction. In this arrangement in which the each circuit substrate is fixedly held at its relatively narrow lateral end portions, each circuit substrate has a relatively large area in which the electric components can be mounted.

In the electric-component mounting system according to the above mode (3) in which the holder portion of the substrate-holding device grips each circuit substrate in the vertical direction, it is possible to effectively prevent an undesirable displacement of each circuit substrate relative to the substrate-holding device. However, the arrangement of the substrate-holding device according to the above mode (3) is not essential. For instance, the substrate-holding device may include at least one support member which is located below each circuit substrate to support the circuit substrate and which is provided with a sucker capable of holding the circuit substrate by suction under a negative pressure. This arrangement also prevents a displacement of each circuit substrate relative to the substrate-holding device.

(4) An electric-component mounting system according to the above mode (2), wherein the belt conveyor includes two conveyor units each including a conveyor belt, a belt guide and a belt drive device operable to rotate the conveyor belt, the two conveyor units supporting respective opposite lateral portions of each circuit substrate parallel to the direction of movement of the at least one circuit substrate, and cooperating with each other to move the each circuit substrate.

Where the belt conveyor includes the two conveyor units each including a conveyor belt, a belt guide and a belt drive device according to the above mode (4), each circuit substrate is supported at its opposite lateral portions by the respective two conveyor belts, so that at least one support member described below with respect to the following mode (5) may be provided, and a distance between the two conveyor belts can be adjusted depending upon the width of the at least one circuit substrate.

(5) An electric-component mounting system according to the above mode (4), wherein the substrate-holding device of the second transferring device includes at least one support member which is located between said two conveyor units and each of which supports said each circuit substrate in contact with said lower surface, at a corresponding one of at least one local position of said each circuit substrate between said two conveyor units.

Where each circuit substrate has a relatively large width, the circuit substrate is desirably supported at an intermediate portion of its width, as well as at its opposite lateral portions, in order to prevent deflection or flexure of the circuit substrate at its intermediate portion. However, the electric components are often mounted on both of the upper and lower surfaces of each circuit substrate. When each circuit substrate is supported on its lower surface after the electric components have been mounted on the lower surface, the circuit substrate must be supported at a local portion or portions, while avoiding an interference of the support member or members with the electronic components mounted on the lower surface. In this respect, the substrate-holding device according to the above mode 5) is suitable to prevent the interference.

(6) An electric-component mounting system according to the above mode (4) or (5), wherein the substrate-holding device of the second transferring device includes two holder portions arranged to grip each circuit substrate in a vertical direction, at respective portions of each circuit substrate which are inwardly spaced from the opposite end portions thereof at which each circuit substrate is supported on its lower surface by the two conveyor units.

Where each circuit substrate is supported at its opposite end portions by the relatively narrow conveyor belts, the circuit substrate is desirably supported by the two holder portions at the respective portions inwardly spaced from the opposite end portions.

(7) An electric-component mounting system according to the above mode (4) or (5), wherein the substrate-holding device of the second transferring device includes two holder portions arranged to grip said each circuit substrate in a vertical direction, at respective opposite end portions of each circuit substrate which extend outwardly from the opposite lateral portions thereof at which each circuit substrate is supported on its lower surface by the two conveyor units.

(8) An electric-component mounting system according to any one of the above modes (1)–(7), wherein the first transferring device is moved together with the substrate-holding device by the holding-device moving device.

In the electric-component mounting system according to the above mode (8), the first transferring device and the substrate-holding device of the second transferring device may include a common main body. In this case, the substrate-holding device can be made relatively simple in construction.

(9) An electric-component mounting system according to any one of the above modes (1)–(7), wherein the first transferring device includes a main body disposed immovably relative to the plurality of component-mounting devices, and the substrate-holding device is disposed movably relative to the main body of the first transferring device.

Where the main body of the first transferring device is separate from the main body of the substrate-holding device and is not moved together with the substrate-holding device by the holding-device moving device, it is not necessary to provide a space for permitting the first transferring device to be moved. Accordingly, the required overall installation space for the electronic-component mounting system including the substrate-transferring device according to the above mode (9) can be reduced. Where two substrate-transferring devices are provided on the upstream and downstream sides of the substrate-transferring device of the present electric-component mounting system, the arrangement according to the above mode (9) does not require spaces between those two other substrate-transferring devices and the substrate-transferring device of the present system, for permitting the movement of the main body of the first transferring device. Accordingly, a transfer of a circuit substrate from the upstream substrate-transferring device onto the first transferring device and a transfer of another circuit substrate from the first transferring device onto the downstream substrate-transferring device can be effected concurrently.

(10) An electric-component mounting system according to any one of the above modes (1)–(9), wherein each of the plurality of component-mounting devices includes an imaging device operable to obtain image data of fiducial marks provided on each of the at least one circuit substrate held by the substrate-holding device, the electric-component mounting system further comprising an image data processing device operable to positioning errors of the at least one circuit substrate as held by the substrate-holding device, on the basis of the image data of the fiducial marks obtained by the imaging device.

In the electric-component mounting system according to the above mode (10), the fiducial marks provided on each circuit substrate held by the substrate-holding device are imaged by the imaging device, to obtain the positioning errors of the circuit substrate as held by the substrate-holding device, so that the obtained positioning errors are eliminated when the electric components are mounted on the circuit substrate by the component-mounting devices. Since the positioning errors of each circuit substrate will not vary due to a movement of the substrate-holding device, the electric components can be mounted on the circuit substrate with high positioning accuracy after the circuit substrate is moved with the substrate-holding device, provided the movement of the substrate-holding device is controlled with high positioning accuracy.

Where the substrate-holding device is provided with a positioning device capable of positioning each circuit substrate with high accuracy, the imaging device is not essential according to the principle of the present invention. Where the imaging device is provided, on the other hand, the substrate-holding device is not required to be provided with such a positioning device, or the positioning device is not required to position each circuit substrate with high accuracy. Generally, the electric components can be mounted on each circuit substrate with higher accuracy, where the positioning errors of the imaging device are detected by the imaging device to eliminate the positioning errors upon mounting of the electric components, than where the circuit substrate is accurately positioned by the positioning device.

(11) An electric-component mounting system according to the above mode (10), wherein the imaging device is moved with the component-holding head by the head-moving device.

Where the imaging device is moved by a suitable moving device, the two or more fiducial marks can be imaged by the same imaging device. In the electric-component mounting system according to the above mode (11), the head-moving device is used as the moving device for moving the imaging device, so that the system is available at a reduced cost.

(12) An electric-component mounting system according to any one of claims (1)–(11), wherein the substrate-holding device has a length larger than a distance between a downstream end of a component mountable area of a most downstream one of the plurality of component-mounting devices and an upstream end of a component mountable area of a most upstream one of the component-mounting devices.

In the electric-component mounting system according to the above mode (12) in which the length of the substrate-holding device is larger than the distance between the opposite ends of the array of the component-mounting devices, the substrate-holding device is able to hold a plurality of circuit substrates arranged in series with each other, so that the component-mounting devices can concurrently perform operations to mount the electric components on those circuit substrates. Alternatively, the substrate-holding device is able to hold a long single circuit substrate having a plurality of component-mounting areas in which the electric components are concurrently mounted by the respective component-mounting devices.

(13) An electric-component mounting system according to any one of the above modes (1)–(12), wherein the plurality of component-mounting devices consist of at least three component-mounting devices arranged in series with each other.

While the principle of the present invention is applicable to an electric-component mounting system comprising two component-mounting devices, the present invention is more advantageously applicable to an electric-component mounting system comprising three or more component-mounting devices arranged in series with each other.

(14) An electric-component mounting system according to claim13, wherein said at least three component-mounting devices are arranged at a predetermined constant pitch.

Although it is not essential that the at least three component-mounting devices be arranged at a predetermined constant pitch, the at least three component-mounting devices are desirably arranged at a constant pitch, for simplification of control of the component-mounting operations performed by the component-mounting devices.

(15) An electric-component mounting system according to any one of the above modes (1)–(14), wherein the maximum distance of movement of the substrate-holding device by the holding-device moving device is not larger than a center-to-center distance of adjacent ones of the plurality of component-mounting devices.

While the maximum distance of movement of the substrate-holding device by the holding-device moving may be larger than the center-to-center distance of the adjacent component-mounting devices, an advantage to be obtained by the maximum distance of movement larger than the center-to-center distance does not usually justify an increase in the cost of manufacture of the holding-device moving device which is required to obtain that advantage.

(16) An electric-component mounting system according to the above mode (15), wherein the maximum distance of movement of the substrate-holding device by the holding-device moving device is not larger than a spacing distance between component mountable areas of adjacent ones of the plurality of component-mounting devices.

Where the maximum distance of movement of the substrate-holding device by the holding-device moving device is equal to the spacing distance between the component mountable areas of the adjacent component-mounting devices, the electric components can be mounted in any area of each circuit substrate held by the substrate-holding device. However, this arrangement is not essential, and the principle of this invention can be practiced even where the maximum distance of movement is smaller than the spacing distance between the component mountable areas of the adjacent component-mounting devices.

(17) An electric-component mounting system according to any one of the above modes (10)–(16), wherein the fiducial marks consist of a plurality of fiducial marks provided at respective positions on each circuit substrate, which positions which are spaced apart from each other, the electric-component mounting system further comprising an imaging control device operable to operate the imaging device to image at least one first fiducial mark selected from the plurality of fiducial marks before a movement of the substrate-holding device by the holding-device moving device, and at least one second fiducial mark selected from the plurality of fiducial marks after the movement of the substrate-holding device, the at least one second fiducial mark being different from the at least one first fiducial mark, and wherein the image data processing device includes a positioning-error obtaining portion operable to obtain the positioning errors of each circuit substrate as held by the substrate-holding device, on the basis of positioning errors of the at least one first fiducial mark and the at least one second fiducial mark which have been imaged by the imaging device.

In the electric-component mounting system according to the above mode (17), a plurality of fiducial marks selected from the plurality of fiducial marks provided on each circuit substrate can be imaged by the imaging device even where the imaging device is stationary. Further, fiducial marks which are not located within a movable area of the movable imaging device can be imaged by the imaging device. Accordingly, the positioning errors of each circuit substrate can be obtained on the basis of the positioning errors of the fiducial marks imaged by the imaging device.

(18) An electric-component mounting system according to any one of the above modes (10)–(12), wherein the image data processing device includes a positioning-error obtaining portion operable to obtain the positioning errors of the each circuit substrate as held by the substrate-holding device, on the basis of image data of a plurality of fiducial marks which are provided on each circuit substrate and which are imaged by at least two adjacent imaging devices of the plurality of component-mounting devices.

In the electric-component mounting system according to the above mode (18), the positioning errors of each circuit substrate can be obtained on the basis of the positioning errors of a plurality of fiducial marks which are located within movable areas of the adjacent imaging devices, or within an area which is larger than a sum of the movable areas of the adjacent imaging devices and a movable area of the substrate-holding device.

(19) An electric-component mounting system according to any one of the above modes (1)–(18), wherein the holding-device moving device includes a feedscrew and a nut which are held in engagement with each other and fixed axially immovably to one and the other of a main body of the substrate-holding device and a main body of the electric-component mounting system which movably supports the main body of the substrate-holding device, the holding-device moving device further including a motor whose operating angle is controlled with high accuracy and which is operated to rotate one of the feedscrew and the nut while the other of the feedscrew and the nut is prevented from being rotated.

While the holding-device moving device may use a linear motor, for instance, the holding-device moving device preferably includes a feedscrew, a nut and a motor as in the above mode (19).

(20) An electric-component mounting system for mounting electric components on a circuit substrate, comprising:at least one component-mounting device each including a component-holding head operable to hold an electric component, and a head-moving device operable to move the component-holding head;a substrate-transferring device operable to move the circuit substrate to a stop position corresponding to each of the at least one component-mounting device, and to move the circuit substrate from said position;a substrate-holding device operable to fixedly hold the circuit substrate which has been moved to the stop position by the substrate-transferring device; anda holding-device moving device operable to move the substrate-holding device in a direction of movement of the circuit substrate by the substrate-transferring device,and wherein a plurality of areas of the circuit substrate held by the substrate-holding device are located at respective positions corresponding to the at least one component-mounting device.

(21) An electric-component mounting system according to the above mode (20), further comprising a control device for controlling the holding-device moving device to move the substrate-holding device, for successively moving the circuit substrate held by the substrate-holding device, such that the plurality of areas are located at the respective positions at which at least one component-mounting device is successively operated to mount the electric components on the respective areas.

While the electric-component mounting system according to the above mode (20) preferably includes a plurality of component-mounting device, the principle of the invention according to the above mode (20) can be practiced even where the system is provided with only one component-mounting device. For example, the system according to the above mode (20) permits mounting of the electric components on a circuit substrate which is larger than the movable area of the component-holding head of the component-mounting device. Further, the present system permits the substrate-transferring device to function as a first transferring device operable to move the circuit substrate between upstream and downstream substrate-transferring devices respectively disposed on the upstream and downstream sides of the present system, and permits the holding-device moving device to function as a second transferring device operable to position the circuit substrate, and move the circuit substrate for mounting the electric components on the circuit substrate. The electric-component mounting system according to the above mode (20) is particularly effective to mount a comparatively small number of kinds of the electric components on a comparatively large area of the circuit substrate.

It is noted that the electric-component mounting system according to the above mode (20) or (21) may incorporate any one of the technical features of the above modes (2)–(11), (17) and (19), except in that the provision of a plurality of component-mounting devices is not essential in the system of the mode (20).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first toFIG. 1there is schematically shown an electric-component mounting system in the form of an electronic-component mounting system constructed according to one embodiment of this invention, which includes a machine base10serving as a main body of the system. On the machine base10, there are mounted four component-mounting devices12which are arranged in series with each other at a predetermined pitch in a direction of transfer of circuit substrates in the form of printed-wiring boards14. The direction of transfer of the printed-wiring boards14is parallel to an X-axis direction indicated inFIG. 1. In the present electronic-component mounting system, each printed-wiring board14is transferred from a position upstream of an array of the component-mounting devices12to a position downstream of this array, such that each printed-wiring board14is stopped at each of component-mounting positions corresponding to the component-mounting devices12, so that electric components in the form of electronic components16(shown inFIG. 3) are successively or sequentially mounted and provisionally fixed on each printed-wiring board14.

Upstream of the most upstream one of the component-mounting devices12in the direction of transfer of the printed-wiring boards14, there is disposed another or upstream electronic-component mounting system. Upstream of this upstream electronic-component mounting system there is disposed a high-viscosity-fluid applying system in the form of a screen-printing system arranged to apply a highly viscous fluid in the form of a solder paste to the circuit substrates in the form of the printed-wiring boards14. Further, a re-flow furnace system is disposed downstream of the most downstream component-mounting device12. The re-flow furnace system is arranged to heat the solder paste into a molten state for electrically connecting the already mounted electronic components to the printed-wiring boards14.

As shown inFIG. 1, the present electronic-component mounting system further includes a substrate-transferring device in the form of a printed-wiring-board transferring device18(hereinafter referred to as “PWB transferring device18”) and a component-supplying device30, which are both mounted on the machine base10. The PWB transferring device18is provided with a substrate conveyor in the form of a printed-wiring-board conveyor20(hereinafter referred to as “PWB conveyor20”) disposed so as to extend in the X0axis direction and arranged to transfer the printed-wiring boards14in the X-axis direction. The electronic-component mounting system further includes four stopper devices22and a substrate holding device in the form of a printed-wiring-board holding device24(hereinafter referred to as “PWB holding device24”). Each printed-wiring board14is stopped by the corresponding stopper device22at the component-mounting position of each component-mounting device12, and held by the PWB holding device24. The four stopper devices22are provided for the respective component-mounting devices12, and each stopper device22includes a stopper member26, and a stopper elevating and lowering device28(shown inFIG. 8) operable to elevate and lower the stopper ember26. The stopper elevating and lowering device28includes a drive source in the form of a fluid-operated actuator such as an air cylinder. The stopper member26is vertically movable by the stopper elevating and lowering device28, between an operated position in which the stopper member26projects above an upper surface of each conveyor belt122(described below by reference toFIG. 5), to stop the printed-wiring board14, and a non-operated position in which the stopper member26is retracted below the upper surface of each conveyor belt122, to permit the printed-wiring board14to be moved through the corresponding component-mounting device12. The PWB conveyor20of the PWB transferring device18and the PWB holding device24of each component-mounting device12will be described below in detail.

On one of opposite sides of the PWB conveyor20as seen in a Y-axis direction perpendicular to the X-axis direction in the horizontal plane of the PWB conveyor20, there are disposed four component-supplying devices30corresponding to the respective four component-mounting devices12. The component-supplying devices30are arranged in series with each other in the X-axis direction (direction of transfer of the printed-wiring boards14). As shown inFIG. 2, each component-supplying device30includes a stationary feeder support block32, and a multiplicity of tape feeders34mounted on the feeder support block32such that the tape feeders34are arranged in the X-axis direction. Each tape feeder34accommodates a succession of electric components in the form of electronic components16(FIG. 3), and is arranged to feed the electronic components16to its predetermined component-supply portion one after another. In the present electronic-component mounting system, each tape feeder34is arranged to feed a carrier tape, which has a multiplicity of recesses which are equally spaced apart from each other in the longitudinal direction and accommodate the respective electronic components16. As the carrier tape is fed, the electronic component16located at the leading end of the unused portion of the carrier tape is located at the component-supply portion of the tape feeder34at which the electronic component16is picked up by a component-holding head40of the component-mounting device12, as described below. Alternatively, the component-supplying device30may use parts feeders each of which is arranged to feed electronic components from a storage container or casing to the component-supply portion, by suitable feeding means such as an air stream, a ramp way, an oscillating motion, or a combination of these feeding means.

In each component-mounting device12, the above-indicated component-holding head40is movable in the X-axis and Y-axis directions, to receive the electronic component16from the component-supplying device40and move the electronic component16to a predetermined component-mounting spot on the printed-wiring board14held at the component-mounting position by the PWB holding device24. At the component-mounting spots, the component-holding device40releases the electronic component16and mount it onto the printed-wiring board14. To this end, the component-mounting device12is provided with an XY robot42held by an upper frame46which is supported by upper parts of support posts44and disposed above the machine base10, as shown inFIGS. 2 and 3. On the underside of the upper frame46, there are fixed two parallel guide rails48extending in the Y-axis direction in the horizontal plane. A Y-axis slide52is held in engagement at its guide blocks50with the guide rails48such that the Y-axis slide52is slidably movable in the Y-axis direction. The Y-axis slide52is provided with a nut54held in engagement with a feedscrew56extending in the Y-axis direction. With the feedscrew56rotated by a Y-axis drive motor (servomotor)58(shown inFIG. 8), the Y-axis slide52is moved in the horizontally extending Y-axis direction. It will be understood that the nut54, the feedscrew56and the Y-axis slide motor58cooperate to constitute a Y-axis slide drive device operable to move the Y-axis slide52, while the guide rails48and the guide blocks50cooperate to constitute a Y-axis slide guiding device for guiding the Y-axis slide52.

On the Y-axis slide52, an X-axis slide60is mounted such that the X-axis slide60is slidably movable on the Y-axis slide53in the horizontally extending X-axis direction perpendicular to the Y-axis direction. The X-axis slide60is provided with a nut (not shown) held in engagement with a feedscrew62extending in the X-axis direction. With the feedscrew62rotated by an X-axis drive motor (servomotor)64, the X-axis slide60is moved in the X-axis direction while being guided by guide rails66and guide blocks (not shown). It will be understood that the feedscrew62, the nut and the X-axis drive motor64cooperate to constitute an X-axis slide drive device operable to move the X-axis slide60, while the guide rails66and the guide blocks cooperate to constitute an X-axis slide guiding device for guiding the X-axis slide60. It will also be understood that the XY robot is constituted by the Y-axis slide52, the X-axis slide60, the Y-axis slide drive device, the X-axis drive device, the Y-axis slide guiding device and the X-axis slide guiding device. On the X-axis slide60, there is mounted the above-indicated component-holding device40, which is movable by the XY robot42to a desired position in the horizontal plane, that is, in the XY plane. The component-holding head40has a suction nozzle58removably mounted thereon and operable to hold the electronic component16by suction under a negative pressure.

The component-holding head40of each component-mounting device12is moved to desired positions within a component mountable area70indicated inFIG. 1, to mount the predetermined electronic components16at the respective predetermined component-mounting spots on the printed-wiring board14, according to a predetermined mounting program, while the printed-wiring board14transferred by the PWB conveyor20is held at the component-mounting position by the PWB holding device24. Upon completion of the operation of the component-holding head40to mount the electronic components16in the component mountable area70in each component-mounting device12, each printed-wiring board14is fed from the present component-mounting device12to the component mountable area70in the next downstream component-mounting device12, and the operations of the component-holding heads40to mount the electronic components16are initiated on the printed-wiring boards14thus loaded onto the respective component-mounting devices12. With these component mounting operations being performed repeatedly, the four component-mounting devices12cooperate to mount the predetermined electronic components16on each of the successively fed printed-wiring boards14.

On the X-axis slide60, the component-holding head40is mounted such that the component-holding head40is vertically movable and rotatable about its axis. Each component-mounting device12is provided with a head elevating and lowering device80(shown inFIG. 8) operable to elevate and lower the component-holding head40, and a head rotating device82(also shown inFIG. 8) operable to rotate the component-holding head40about its axis. Each of these devices80,82includes a drive source in the form of an electric motor. As shown inFIGS. 1 and 3, the X-axis slide60also carries a fiducial-mark imaging device in the form of a fiducial-mark camera86operable to take images of two fiducial marks84provided on each printed-wiring board14, as shown inFIG. 9. The fiducial-mark camera86is a CCD camera, which is movable with the component-holding head40by the XY robot42, within an area which substantially entirely overlaps the component mountable area (movable area)70of the component-holding head40.

Each component-mounting device12is provided with a component imaging device in the form of a component camera90, which is located between the component-supplying device30and the PWB transferring device18(PWB conveyor20) in the Y-axis direction, as indicated inFIG. 2. When the component-holding head40which has received the electronic component16from the component-supply device30is moved in the Y-axis direction, past this component camera90toward the printed-wiring-board14as held by the PWB holding device24. The component camera90is a CCD camera operable to take an image of the electronic component16as held by the component-holding head40, in an upward direction. Near the component camera90, there is provided an illuminating device operable to irradiate the electronic component16and its vicinity when the image of the electronic component16is taken by the component camera90. The component camera90may be a line scan camera.

As shown inFIG. 5, the PWB conveyor20includes a pair of parallel guides100,102. The guides100,102have respective elongate main bodies104,106each having a rectangular shape in transverse cross section. The main bodies104,106extend in the X-axis direction in the horizontal plane. The guide100is a stationary guide, while the other guide102is a movable guide movable in the Y-axis direction toward and away from the stationary guide100.

Each one of the main bodies104,106of the two guides100,102is provided with two driven pulleys120rotatably supported on its surface opposed to the corresponding surface of the other main body104, as schematically shown inFIG. 6with respect to the main body104of the guide100by way of example. The two driven pulleys120are located at the respective opposite longitudinal ends which are spaced from each other in the X-axis direction. The endless conveyor belt122indicated above is held in engagement with the driven pulleys120. Thus, the PWB conveyor20used in the present system is a belt conveyor. The conveyor belt122is guided by two guide pulleys124also rotatably supported by the main body104. The conveyor belt122provided on the guide100is also held in engagement with a driving pulley128, which is fixed to an output shaft of a drive source or an electric motor in the form of a conveyor motor132. The driving pulley128is fixed to one end of a spline shaft134which is rotatably supported at its opposite ends by the main body104and a frame (not shown). One of the driven pulleys120of the guide102is splined to the other end of the spline shaft134. This driven pulley120of the guide102is rotatably and axially immovably supported by the main body106of the guide102. In this arrangement, a rotary motion of the conveyor motor132causes the driving pulley128and the driven and guide pulleys120,124of the guide100to be rotated, and at the same time causes the spline shaft135to be rotated, thereby rotating the driven pulleys120of the guide102, so that the two conveyor belts122are rotated in synchronization with each other through the spline shaft134.

As shown inFIG. 5, two belt guides140,142are provided integrally with the respective opposed surfaces of the main bodies104,106such that the belt guides140,142extend in the X-axis direction in the horizontal plane. The belt guides140,142support the respective conveyor belts122in contact with the lower surfaces of their straight portions144. The printed-wiring board14is supported by the belt guides140,142, at its opposite end portions extending in the X-axis direction, in contact with the upper surfaces of the straight portions144. With the conveyor belts122being rotated, the printed-wiring board14is transferred in the X-axis direction. That is, the belt conveyors122supported by the horizontal guides100,102support and transfer the printed-wiring board14while the board14is held in its horizontally extending attitude. As shown inFIG. 5, the main bodies104,106of the guides100,102have respective vertical guiding surfaces146which are opposed to each other in the Y-axis direction and which are provided to guide the printed-wiring board14, in sliding contact with the opposite side surfaces of the board14. In the present embodiment, the main bodies104,106are provided commonly for all of the four component-mounting devices12, and the conveyor belts122have a length considerably larger than the length of the array of the four component-mounting devices12. Namely, the length of the conveyor belts122permits the printed-wiring board14to be transferred from a position a predetermined distance upstream of the upstream end of the array of the component-mounting devices12, to a position a predetermined distance downstream of the downstream end of the array.

The guide102is movable by a width changing device148shown inFIG. 7, toward and away from the other guide100, to adjust a distance between the guides100,102, that is, an effective width of the PWB conveyor20, depending upon the specific width of the printed-wiring board14. The main body106of the guide102is supported by the machine base10, through a pair of support portions149formed integrally with the longitudinally opposite end portions of the main body106which are spaced from each other in the X-axis direction. The main body106is movable relative to the machine base10in the Y-axis direction (perpendicular to the X-axis direction). InFIG. 7, only one of the two support portions149is shown. A pair of feedscrews150are attached to the machine base10such that each feedscrew150is rotatable and axially immovable relative to the machine base10. A pair of nuts152are fixed to the respective support portions149, and are held in engagement with the respective feedscrews150. When the feedscrews150are rotated by a drive source or electric motor in the form of a width changing motor154(shown inFIG. 8), the guide102is moved in the Y-axis direction. Each of the two feedscrews150has a sprocket wheel160fixed at its one end, and the two sprocket wheels160fixed to the two feedscrews150are connected to each other by a chain162. These sprocket wheels160and the chain162cooperate to constitute a rotation transmitting device operable to transmit a rotary motion of one of the two feedscrews150to the other feedscrew150. In this arrangement, the two feedscrews150are rotated in synchronization with each other by the width changing motor154. The guide102is guided by a guiding device, which includes a pair of guide blocks156fixed to the respective support portions149, and a pair of guide rails158fixed to the side surfaces of the machine base10. The width changing device148includes the above-indicated rotation transmitting device, and the feedscrews150, nuts152, width changing motor154.

As shown inFIGS. 4 and 5, the PWB holding device includes a pair of parallel holder members170,172, each of which is an elongate member having a generally rectangular shape in transverse cross section. The holder members170,172are supported by a main body of the PWB holding device in the form of a support block176, such that the holder members170,172extend in the X-axis direction. The holder members170,172have respective integrally formed presser portions177,178extending toward each other in the Y-axis direction. These holder members170,172are provided commonly for all of the four component-mounting devices12.

The support block176is mounted on the machine base10such that the support block176is movable relative to the machine base.10in the X-axis direction. As shown inFIG. 5, the machine base10is provided with a feedscrew180fixed thereto such that the feedscrew180is rotatable and axially immovable relative to the machine base10. The support block176is provided with a nut182fixed thereto such that the nut182is neither axially movable nor rotatable relative to the support block176. The nut182is held in engagement with the feedscrew180. When the feedscrew180is rotated by a drive source or electric motor in the form of a support-block drive motor184(shown inFIG. 8), the support block176is moved in the X-axis direction, while being guided by a guiding device including a plurality of guide blocks186and a pair of guide rails188. The feedscrew180and the nut182cooperate to constitute a motion converting device operable to convert a rotary motion of the support-block drive motor184into a linear motion of the support block176, while the support block176, feedscrew180, nut182, support-block drive motor184, guide blocks186and guide rails188cooperate to constitute a holding-device moving device operable to move the PWB holding device24in the X-axis direction by a maximum distance shorter than the maximum distance of movement of the printed-wiring board14by the PWB conveyor20. In the present embodiment, the feedscrew180of the holding-device moving device is fixed to the machine base10, while the nut182of the same device is fixed to the main body of the PWB holding device24in the form of the support block176, such that the feedscrew180and the nut182are not axially movable.

The holder member172is disposed on the support block176such that the holder member172is movable in the Y-axis direction toward and away from the other holder member170. The holder member172is moved by two latching devices190(one of which is shown inFIG. 7), toward and away from the holder member170, together with the guide102, so that a distance between the two holder members170,172is adjusted when the distance between the two guides100,102is adjusted. In the present embodiment, the latching devices190are disposed on the opposite sides of the holder member172and are spaced apart from each other in the X-axis direction. Each latching device190is constituted by a movable engaging member192supported by the support portion149movably in the X-axis direction, a drive source or fluid-operated actuator in the form of an air cylinder194for moving the engaging member192, and an engaging recess196which is formed on the holder member172and which is engageable with an engaging end portion196of the engaging member192. The engaging end portion196has a conical or tapered shape with its diameter continuously decreasing in a direction toward the extreme end, while the engaging recess198has a conical or tapered shape with its diameter continuously deceasing in a direction toward the bottom. In the present embodiment, the engaging member192is formed integrally with a piston rod of the air cylinder194. Normally, the engaging member192is located at its retracted position at which the engaging end portion196is spaced apart from the engaging recess198. When the width of the printed-wiring board14to be transferred by the PWB conveyor20is changed, the engaging member192is moved to its advanced position for engagement of the engaging end portion196with the engaging recess198. To change the width of the PWB conveyor20, the guide102(and the belt conveyor122supported by this guide102) and the holder member172are moved in the Y-axis direction. Before this movement, the air cylinder194of each latching device190is activated to advance the engaging member192to its advanced position for engagement of the engaging end portion196with the engaging recess198of the holder member172. In this condition, the guide102is moved in the Y-axis direction by the width changing device148, while at the same time the holder member172now connected to the guide102through the latching device190and the support portion149is moved together with the guide102. While the engaging members192of the latching devices190are located at their retracted positions, the movements of the holder members170,172are not disturbed by the latching devices190. In the present embodiment, the guide102and the holder member172are both moved by the drive source in the form of the width changing motor154of the width changing device148, the guide102and the holder member172may be moved by respective drive sources in synchronization with each other.

As shown inFIG. 5, the holder members170,172have respective support members200supported on their opposed surfaces such that the support members200are vertically movable. These support members200constitute a part of the PWB holding device24. Each support member200takes the form of a plate which is elongated in the X-axis direction and located on an inner side of the corresponding conveyor belt122remote from the outer side surface of the holder member170,172as seen in the Y-axis direction. The support members200are normally held at their lower positions under biasing actions of suitable biasing devices such as spring members (not shown), so that the support members200are spaced apart from the printed-wiring board14transferred by the conveyor belts122. When the support members200are moved to their upper positions in synchronization with an elevator drive device210(which will be described), the support members200come into contact with the lower surface of the printing-wiring board14, push up the board14away from the conveyor belts122, and eventually force the board14against the presser portions177,178of the holder members170,172. Thus, the printed-wiring board14is gripped by and between the support members200and the presser portions177,178, at the lateral ends of the board14which are opposed to each other in the Y-axis direction perpendicular to the direction of transfer of the board14. Described more specifically, the board14is gripped by and between the support members200and the presser portions177,178, at their portions which are slightly inwardly spaced from the lateral end portions at which the board14is supported by the conveyor belts122. An example of the structure for gripping the printed-wiring board14is disclosed in JP-A-11-204995.

The PWB holding device24is provided with a plurality of support members in the form of support pins206, as schematically shown inFIG. 5. These support pins206are supported by an elevator plate208, which is elevated and lowered by the above-indicated elevator drive device210. When the support pins206are located at their upper position, the support pins206are held in contact with the lower surface of the printed-wiring board14, while forcing the board14onto the presser portions177,178with a vertical spacing distance left between the conveyor belts122and the lower surface of the board14. In the present embodiment, the elevator drive device210uses a drive source or fluid-operated actuator in the form of an air cylinder212(shown inFIG. 8). While the elevator plate208and the elevator drive device210are commonly used for all of the four component-mounting devices12in the present embodiment, one set of the elevator plate208and the elevator drive device210may be used commonly for each set of two adjacent ones of the component-mounting devices12. In this case, the two elevator plates208are elevated and lowered by the respective two elevator drive devices210, in synchronization with each other. Alternatively, each of the four component-mounting devices12is provided with a set of the elevator plate208and the elevator drive device210.

In the present electronic-component mounting system, the four printed-wiring boards14are movable by a movement of the support block176in the X-axis direction by a maximum distance shorter than the maximum distance of movement of the boards14by the PWB conveyor20, while the boards14are held upwardly apart from the conveyor belts122and gripped by and between the presser portions177,178, and the support members200and support pins206in the vertical direction.

While the four stopper devices22to stop the printed-wiring boards14are provided in the present electronic-component mounting system, sensors for detecting deceleration-start positions and sensors for detecting stop positions may be provided in place of or in addition to the stopper devices22, so that deceleration of each printed-wiring board14is initiated at the detected deceleration-start position, and the board14is stopped at the detected stop position. Each of these sensors may be a photoelectric sensor of reflection type or light-transmitting type including a light-emitting portion and a light-receiving or photosensitive portion, or alternatively a proximity switch or a limit switch.

The present electronic-component mounting system includes a control device240.FIG. 8shows this control device240and some elements of the mounting system which relate to the present invention. The control device240is principally constituted by a computer241incorporating a processing unit (PU)242, a read-only memory (ROM)244, a random-access memory (RAM)246, an input port248and an output port250, which are interconnected to each other through a bus line.

To the input port248, there are connected various detectors and computers including the above-described fiducial-mark cameras86and component cameras90, an image data processing computer260for processing image data obtained by those cameras86,90, and encoders262,264,266and268for detecting the amounts of operation of the above-indicated Y-axis drive motors58, X-axis drive motors64, conveyor motor132and support-block drive motor184. To the output port250, there are connected through driver circuits270various actuators including the above-described stopper elevating and lowering device28, Y-axis drive motors58, X-axis drive motors64, head elevating and lowering devices80, head rotating devices82, conveyor motor132, width changing motor154, support-block drive motor184, control valves for the air cylinders194,212. As described above, the operating amounts or angles of the Y-axis drive motors58, X-axis drive motors64, conveyor motor132and support-block drive motor184are detected by the respective encoders262,264,266,268, and these motors58,64,132,184are controlled with high accuracy on the basis of the detected operating amounts. The ROM244stores control programs for controlling a component-mounting operation of the present system in general, and the RAM246stores various programs including: a program for transferring the printed-wiring boards14onto the individual component-mounting devices12; a program for positioning the component-holding heads40of the component-mounting devices12according to kinds of the electronic components16, mounting spots and order at and in which the electronic components16are to be mounted on the printed-wiring boards14; and a program for positioning the fiducial mark cameras86of the component-mounting devices12.

Referring next toFIG. 9, there will be described the component-mounting operation of the present electronic-component mounting system to mount the electronic components16on the printed-wiring boards14. It is noted thatFIG. 9schematically shows the component-mounting devices12and the printed-wiring boards14, for easy understanding of the relative positions between the component-mounting devices12and the printed-wiring boards14.

Initially, the four printed-wiring boards14are transferred by the conveyor belts122of the PWB conveyor20, and stopped by the respective stopper devices22provided in the respective component-mounting devices12. The four printed-wiring boards14are positioned such that one of the two fiducial marks84which is located downstream of the other in the X-axis direction (direction of transfer of the boards14) is located within the movable area of the fiducial-mark camera86. This fiducial mark84located within the movable area of the fiducial-mark camera86will be referred to as the “downstream fiducial mark84”. InFIG. 9, the movable area of the fiducial-mark camera86, which entirely overlaps the component mountable area of the component-holding head40, is indicated by hatching lines (inclined upwards as they extend rightwards). After the four printed-wiring boards14are thus positioned in place in the respective component-mounting devices12, the air cylinder212is activated to elevate the elevator plate208to its elevated position, so that the boards14are lifted by the support members200, away from the conveyor belts122, and forced against the presser portions177,178, whereby the boards14are concurrently gripped or held in the vertical direction at their lateral end portions. At the same time, each board14is supported at local portions of its lower surface between the two support members200, by the plurality of support pins206located at the upper position as a result of the activation of the air cylinder212.

The four printed-wiring boards14thus held by the PWB holding device24are shown in the uppermost view ofFIG. 9. In this state, the fiducial-mark camera86of each component-mounting device12is moved by the XY robot42, to a nominal position of the downstream fiducial mark84. Images of the downstream fiducial marks84on the four boards14are simultaneously taken by the respective fiducial-mark cameras86of the component-mounting devices12. Then, the support block176is moved relative to the fiducial-mark camera86by the support-block drive motor184in the downstream direction in the X-axis direction by a predetermined short distance L1so that the other fiducial mark84(hereinafter referred to as the “upstream fiducial mark84”) is located within the movable area of the fiducial-mark camera86, as shown in the intermediate view ofFIG. 9. In this state, the fiducial-mark cameras86are moved to nominal positions of the upstream fiducial marks84, and the images of these upstream fiducial marks84are simultaneously taken by the fiducial-mark camera86. Image data thus obtained by the fiducial-mark cameras86are processed by the image data processing computer260, to obtain the actual positions of the fiducial marks84on the four printed-wiring boards14. The obtained image data of the fiducial marks84are stored in the RAM246, in relation to the four fiducial-mark cameras86. The image data processing computer260compares the positions of the fiducial marks84represented by the obtained image data, with the nominal positions stored in the RAM246, to calculate actual positioning errors of the fiducial marks84with respect to the nominal positions. On the basis of the thus calculated positioning errors of the fiducial marks84, the movement distance L1of the support block176and a movement distance of the fiducial-mark camera86, the PU242calculates positioning errors in the X-axis and Y-axis directions of each printed-wiring board14as held by the PWB holding device24.

Then, the four component-holding heads40of the four component-mounting devices12are moved by the XY robots42are moved to respective positions right above the component-supply portions of the selected tape feeders34of the respective component-supplying devices30, and the suction nozzles68are lowered by the head elevating and lowering devices80, to receive the electronic components16from the selected tape feeders34. Then, the component-holding heads40are moved to component-imaging positions, at which images of the electronic components16as held by the suction nozzles68are taken by the component cameras90. Subsequently, the component-holding heads40are moved by the XY robots40, to positions right above the nominal positions of the component-mounting spots on the printed-wiring boards14. For accurate positioning of the electronic components16on the boards14, however, the positions to which the component-holding heads40are moved to mount the electronic components16on the printed-wiring boards14are adjusted for compensation for the positioning errors of the boards14and positioning errors of the electronic components16, and for other reasons. After the images of the electronic components16are taken by the component cameras90and during the movements of the component-holding heads40toward the component-mounting spots on the boards14, obtained image data of the electronic components16are processed to obtain horizontal positioning errors (X-axis and Y-axis positioning errors) and an angular positioning error of each electronic component16as held by the corresponding suction nozzle68. The component-holding head40(suction nozzle68) is rotated by a suitable angle by the head rotating device82, to eliminate the angular positioning error of the electronic component16. Where the angular position of the electronic component16as held by the suction nozzle68is different from that of the electronic component16as mounted on the board14, the component-holding head40is rotated by an angle required to eliminate the angular positioning error of the component16and to mount the component16on the board14in the predetermined angular position. The positions at which the component-holding heads40(suction nozzles68) are moved to mount the electronic components16are adjusted by adjusting the nominal distances of movements of the heads40in the X-axis and Y-axis directions, so as to eliminate the obtained positioning errors of the boards14, the obtained horizontal positioning errors of the electronic components16, and horizontal positioning errors of the electronic components16which are generated as a result of rotation of each component-holding head40to eliminate the angular positioning error of the electronic component16and to establish the predetermined the angular position in which the electronic component16is mounted on the board14. The component-holding heads40are moved by the adjusted distances of movements, and the suction nozzles68are lowered to mount the electronic components16on the boards14. The operations to eliminate the positioning errors of the boards14and the electronic components16and the operations to mount the electronic components16on the boards14are concurrently performed in the four component-mounting devices12.

After a set of predetermined electronic components16has been mounted in an area of each printed-wiring board14corresponding to the component mountable area of the corresponding component-mounting device12, the support block176is moved in the upstream direction by the above-indicated distance L1relative to the component-mounting devices12, so that the component-holding heads40are movable in an area of the boards14in which the electronic components16have not been mounted. This area is indicated by cross-hatching lines in the lowermost view ofFIG. 9. Then, another set of predetermined electronic components16is mounted in this area of the board14. In this case, too, the distances of movements of the suction nozzles68(component-holding heads40) are adjusted to eliminate the positioning errors of the boards14, the horizontal positioning errors of the electronic components16as held by the suction nozzles68, and the horizontal positioning errors of the electronic components16generated as a result of rotation of each component-holding head40to eliminate the angular positioning error of the electronic component16and to establish the predetermined the angular position of the electronic component16as mounted on the board14.

It will be understood from the foregoing description of the present embodiment that the XY robots42function as a head-moving device operable to move the component-holding heads44, and that the PWB transferring device18functions as a substrate-transferring device operable to transfer circuit substrates in the form of the printed-wiring boards14. It will also be understood that the PWB conveyor20functions as a first transferring deice operable to transfer the circuit substrates, while the PWB holding device24and the holding-device moving device189cooperate to constitute a second transferring device operable to transfer the circuit substrates. It will further be understood that the presser portions177,178of the holder members170,172, the support members200and the support pins206cooperate to constitute a holder portion for fixedly holding the circuit substrates. It is noted that the support pins206as well as the support members200function as support members for supporting each circuit substrate in the form of the printed-wiring board14, at one or more points on its lower surface. It will also be understood that the guides100,102constitute a main body of the first transferring device, and that the fiducial-mark cameras86function as an imaging device operable to image the fiducial marks84, while the image data processing computer260functions as an image data processing device operable to obtain the positioning errors of the circuit substrates as held by the PWB holding device24, on the basis of a result of imaging of the fiducial marks84. It will further be understood that a portion of the control device240assigned to operate the fiducial-mark cameras86to image one and the other of the two fiducial marks84before and after the movement of the PWB holding device24, respectively, provides an imaging control device. It will also be understood that the image data processing computer260which functions as the image data processing device includes a first positioning-error obtaining portion operable to the positioning errors of the printed-wiring boards14as held by the PWB holding device24, on the basis of the positioning errors of the plurality of fiducial marks84obtained before and after the movement of the PWB holding device.

In the present embodiment, the printed-wiring boards14held and positioned by the PWB holding device24can be linearly reciprocated in the X-axis direction by a relatively short maximum distance, so that the fiducial marks84provided on each printed-wiring board14can be imaged by the fiducial-mark camera86provided in each component-mounting device12, when the electronic components16are mounted on the printed-wiring board14, even where the size of the board14is larger than that of the component mountable area of the component-mounting device12. Accordingly, the electronic components16can be mounted on each printed-wiring board14with high positioning accuracy. Further, the distance of movement of the printed-wiring boards14held by the PWB holding device24is relatively small, so that the time required for moving the boards14is accordingly short, and the mounting operation can be performed with high efficiency with a reduced non-productive time. In the present embodiment, the maximum distance of movement of the PWB holding device24is not larger than a center-to-center distance of the adjacent component-mounting devices12. Described more specifically, the maximum distance L1(indicated inFIG. 9) of the PWB holding device24is not larger than a distance L2(indicated inFIG. 9) between the mutually opposed ends of the component mountable areas of the two adjacent component-mounting devices12. The maximum distance of movement of the PWB holding device24may be selected within a range between L1and L2. Since the PWB holding device24is moved by only a short distance to move the printed-wiring boards14, the accuracy of positioning of the boards14relative to the component-mounting devices12can be easily enhanced. Thus, the component-mounting devices12permit accurate mounting of the electronic components16on the printed-wiring boards14even where the dimension of the component mountable area of each component-mounting device12in the X-axis direction is smaller than the corresponding dimension of the printed-wiring boards14. Accordingly, the present electronic-component mounting system can be made relatively compact in construction and small-sized, so that the required installation space of the system can be reduced.

In the present electronic-component mounting system, the upstream fiducial mark84is first imaged, and then the downstream fiducial mark84is imaged after a movement of the printed-wiring boards14in the upstream direction by a short distance L1back to the original positions, at which the component mounting operations on the boards14are initiated. This order of imaging of the two fiducial marks84is different from that shown inFIG. 9.

In the illustrated embodiment, each printed-wiring board14is larger than the component mountable area of each component-mounting device12and the dimension of the printed-wiring board14in the X-axis direction is not larger than a distance between the component mountable areas of the adjacent component-mounting devices12. Namely, the two fiducial marks84provided on each printed-wiring board14are not located within the movable area of the corresponding fiducial-mark camera86, but the two fiducial marks84can be imaged one after the other by moving the PWB holding device24to move the printed-wiring boards14. However, the electronic components16can be mounted on the basis of the positioning errors of the printed-wiring boards14as held by the PWB holding device24, even where the size of each board14is smaller than the component mountable area of each component-mounting device12, or the dimension of the board14in the X-axis direction is larger than the distance between the component mountable areas of the adjacent component-mounting devices12.

In an example ofFIG. 10, the dimension of each printed-wiring board400in the X-axis direction is larger than a distance between the component mountable areas of the adjacent two component-mounting devices12(between the movable areas of the adjacent two fiducial-mark cameras86. In this case, two fiducial marks402provided on each printed-wiring board400are imaged by the respective adjacent two fiducial-mark cameras86, and the obtained image data are processed by the image data processing computer260. The example ofFIG. 10will be described with respect to the operations of the two fiducial mark cameras86and the corresponding two component-mounting devices12. InFIG. 10, the component mountable areas of the component-mounting devices12(movable areas of the fiducial-mark cameras86) are indicated by hatching lines (inclined upwards as they extend rightwards).

In the example ofFIG. 10wherein the adjacent two fiducial-mark cameras86are operated to image the respective two fiducial marks402provided on one printed-wiring board400, it is desirable to obtain relative positioning errors of these two fiducial-mark cameras86. To this end, a test or reference board (which may be a printed-wiring board) having at least three fiducial marks is prepared. These fiducial marks are positioned relative to each other such that at least two of these fiducial marks can be imaged by one fiducial-mark camera86while at least one other fiducial mark can be imaged by the adjacent fiducial-mark camera86. The relative positions of these at least three fiducial marks on the test board should be known. This test board is transferred by the PWB conveyor20and positioned and held by the PWB holding device24, such that the at least two fiducial marks can be imaged by one fiducial-mark camera86while the at least one other fiducial mark86can be imaged by the adjacent fiducial-mark camera86. In this state, the two fiducial-mark cameras86are moved and operated to take the images of the fiducial marks on the test board. On the basis of the thus obtained image data, positioning errors of one of the two fiducial-mark cameras86relative to the other fiducial-mark camera86(positioning errors of the downstream fiducial-mark camera86relative to the upstream fiducial-mark camera86) in the X-axis and Y-axis directions are obtained and stored in the RAM246of the control device240. The relative positioning errors of the adjacent two fiducial-mark cameras86may be obtained in the following manner, for example. Initially, positioning errors of the test board as held by the PWB holding device24are calculated on the basis of the positioning errors of the at least two fiducial marks imaged by one of the two fiducial-mark cameras86, for instance, by the downstream camera86. Then, positioning errors of the at least one fiducial mark imaged by the other (upstream) fiducial-mark camera86. On the basis of the thus obtained positioning errors of the at least one fiducial mark and the previously obtained positioning error of the test board, the positioning errors of the upstream fiducial-mark camera86with respect to the downstream fiducial-mark camera86are obtained. For improving the accuracy of detection of the positioning errors of the test board as held by the PWB holding device24, the at least two fiducial marks imaged by one of the two fiducial-mark cameras86are desirably spaced apart from each other by a distance or distances as large as possible to permit simultaneous imaging of these at least two fiducial marks by the one fiducial-mark camera86.

When the electronic components16are actually mounted on the printed-wiring boards400, these boards400are transferred by the PWB conveyor20, and positioned and held by the PWB holding device24. In the example ofFIG. 10, each of the two printed-wiring boards400is stopped by the stopper device22of the downstream one of the adjacent two component-mounting devices12corresponding to that board400. The thus stopped board400is held by the PWB holding device24. Then, the adjacent two fiducial-mark cameras86are moved to respective positions right above the two fiducial marks402which are spaced apart from each other, as indicated in the upper view ofFIG. 10. At this time, the distance of movement of the upstream fiducial-mark camera86is adjusted to eliminate the positioning errors of the upstream fiducial-mark camera86with respect to the downstream fiducial-mark camera86. The thus moved fiducial-mark cameras86are operated to image the respective two fiducial marks402, and the thus obtained image data are processed by the image data processing computer250, to obtain the actual positions of the fiducial marks402. The thus obtained positions of the fiducial marks402are compared with reference or nominal positions stored in the RAM246, to obtain positioning errors of the fiducial marks402. On the basis of the thus obtained positioning errors of the fiducial marks402, the X-axis and Y-axis positioning errors and angular positioning error of the printed-wiring board400are calculated. The angular positioning error of the board400is an error of angular positioning about an axis normal to the plane of the board400. On the basis of the X-axis and Y-axis and angular positioning errors of the board400, the distances of movement (stop positions) of the two component-holding heads40are adjusted, and the component-holding heads40are moved by the adjusted distances of movements to mount the electronic components16in an area of the printed0-wiring board400corresponding to the component mountable areas of the component-mounting devices12. In the position of the board400indicated in the upper view ofFIG. 10, the upstream end portion of the board400lies within the component mountable area of the upstream component-mounting device12. The electronic components may or may not be mounted in this upstream end portion of the board400. In the former case, the preparation of a component-mounting program is complicated, but the efficiency of the component-mounting operation on the board400can be improved.

After a set of predetermined electronic components16has been mounted in the areas of the board400lying within the component mountable areas of the adjacent two component-mounting devices12, the PWB holding device24is moved in the upstream direction to move the board400by a predetermined distance, as indicated in the lower view ofFIG. 10, so that another set of predetermined electronic components is mounted in an area of the board400in which the electronic components have not been mounted and which is now located within the component mountable area of the upstream component-mounting device12. As in the mounting of the electronic components on the board400located as indicated in the upper view ofFIG. 10, the distance of movement of the upstream component-holding head40is adjusted for compensation for the horizontal and angular positioning errors of the board400.

In the mode of operation of the electronic-component mounting system shown inFIG. 10, the image data processing computer260functions as a second positioning-error obtaining portion operable to obtain the positioning errors of the each printed-wiring board400as held by the PWB holding device24, on the basis of the image data of the two fiducial marks402obtained by the two fiducial-mark cameras86.

In the modes of operation of the system ofFIGS. 9 and 10, the electronic components16are mounted, in the first mounting operation, in the entire portion of the predetermined component-mounting region of the board14,400which portion is located within the component mountable area or areas of the component-mounting device or devices12, and in the second mounting operation, in the other area of the board14,400in which the electronic components16have not been mounted. However, the component-mounting program may be prepared so that the first mounting operation is performed in one half of the component-mounting region of the board14,400, while the second mounting operation is performed in the other half of the component-mounting region. Alternatively, the component-mounting program may be prepared so that the two areas of the board14,400in which the first and second component-mounting operations are performed, respectively, partially overlap each other.

In the embodiment described above, the PWB holding device24is movable relative to the component-mounting devices12and the PWB conveyor20. However, the PWB conveyor20may be moved together with the PWB holding device24relative to the component-mounting devices12, by the holding-device moving device189. In this case, each of the guides100,102which constitute the main body of the PWB conveyor20, and each of the holder members170,172which constitute the main body of the PWB holding device24can be provided by a common structure, so that the PWB conveyor20can be simplified in construction. An example of this modification is shown inFIG. 11as a second embodiment of this invention, wherein the belt guides140,142of the PWB conveyor20are formed integrally with the holder members170,172of the PWB holding device24. In this second embodiment wherein the PWB conveyor20is moved together with the PWB holding device24, it is necessary to provide spacing distances L between the present electronic-component mounting system and the adjacent devices, for permitting the movements of the PWB conveyor20and the PWB holding device24as a unit.

While the two preferred embodiments of the present invention have been described in detail, for illustrative purpose only, it is to be understood that the present invention may be embodied with various changes and improvements, such as those described in the SUMMARY OF THE INVENTION, which may occur to those skilled in the art.