Inkjet printing apparatus

Disclosed is an inkjet printing apparatus including a connection switching device in a housing having external suction ports and an internal suction port being disposed at an equal distance from the center of rotation of a switching section, the external suction ports being connectable to a plurality of lines, the internal suction port being connected to a suction path for sucking the interior of the housing. The connection switching device selectively connects any of the plurality of external suction ports to the suction device by rotating the switching section Consequently, when the switching section is connected to the internal suction port, the interior of the housing is sucked, whereby ink is sucked from all the inkjet nozzles.

BACKGROUND

1. Field of the Invention

This invention relates to an inkjet printing apparatus with a plurality of inkjet heads.

2. Description of the Related Art

A conventional inkjet printing apparatus having an inkjet head with many inkjet nozzles performs cleaning to the inkjet head by suction (suction purge) so as to eliminate printing failure, so-called nozzle clogging, resulting from partial clogging of the inkjet nozzles.

For instance, Japanese Patent Publication No. 2008-213216 discloses an inkjet recorder. The inkjet recorder includes caps covering ejection port groups (an inkjet head) individually, and a pump supplying ink from the ejection ports (inkjet nozzles) into the caps. The inkjet recorder further includes a connection channel connecting the caps to the pumps, respectively, and on/off valves provided on the channel individually. In the inkjet recorder, the on/off valves on the connection channel in communication with each of the caps of the group of ejection ports (inkjet heads) are selectively opened, whereby suction purge can be achieved in which only a cap covering the inkjet nozzle with no ink being ejected therefrom is connected to the pump to be sucked individually.

Another inkjet printing apparatus has also been proposed. The inkjet printing apparatus includes a cleaning mechanism that allows overall suction for sucking collectively a plurality of inkjet heads and individual suction for sucking every inkjet head individually. See International Publication WO2007/058139. The cleaning mechanism includes an individual suction cap that connects one cap, selected from caps covering a plurality of inkjet heads, to a pump via a tube; the caps connected to the pump via a tube branched to the caps; a first on/off valve switching suction of the plurality of caps simultaneously; and a second on/off valve switching suction of only the individual suction cap. Overall suction is performed while the plurality of inkjet heads are all covered with the caps to open the first and second on/off valves. Individual suction is performed while only one inkjet head is covered with the individual suction cap to close the first on/off valve and to open the second on/off valve. This allows individual suction for the inkjet head to be sucked.

The apparatus disclosed in Japanese Patent Publication No. 2008-213216 has a drawback as under. That is, many electromagnetic on/off valves corresponding to the number of caps have to be disposed, resulting in an enlarged apparatus and increased production costs. The apparatus has another drawback as under. That is, many electromagnetic on/off valves are driven, resulting in increased power consumption and running costs.

Moreover, the apparatus of WO2007/058139 performs cleaning to every inkjet unit having a plurality of inkjet heads being arranged in one direction. Consequently, when individual suction is performed to the inkjet heads, it takes longer time to move the inkjet unit to align the inkjet heads with the individual suction cap depending on arrangement of the inkjet heads to be sucked in the inkjet unit. This causes a drawback that longer time is required for cleaning the inkjet heads.

In order to solve the above-mentioned drawbacks, one object of this invention is to provide an inkjet printing apparatus with a simple construction that allows reduction in ink consumption and rapid cleaning of inkjet heads.

SUMMARY

This invention is constituted as stated below to achieve the above object. One example of this invention discloses an inkjet printing apparatus with a plurality of inkjet heads having a plurality of inkjet nozzles being arranged in a row; a plurality of caps for the plurality of inkjet heads respectively; a plurality of lines in communication with the plurality of caps respectively; and a suction device sucking ink from the plurality of inkjet nozzles via the plurality of caps and the plurality of lines. The inkjet printing apparatus includes a draw-off port connecting to the suction device; a switching section having an internal communication path in communication with the draw-off port and being supported rotatably while being connected to a driving device; a housing accommodating the switching section and having external suction ports and an internal suction port being disposed at an equal distance from the center of rotation of the switching section, the external suction ports being connectable to the plurality of lines, the internal suction port being connected to a suction path for sucking an interior of the housing; further including a connection switching device for selectively connecting the suction port to the suction device by rotating the switching section to a position where the communication path is brought into communication with any of the plurality of external suction ports.

The example of this invention includes the connection switching device for selectively connecting any of the plurality of external suction ports to the suction device by rotating the switching section in the housing having the external suction ports and the internal suction port being disposed at an equal distance from the center of rotation of the switching section. Here, the external suction ports are connectable to the plurality of lines, and the internal suction port is connected the suction path for sucking the interior of the housing. When the switching section is connected to any of the external suction ports, ink is sucked from any of the plurality of inkjet nozzles. When the switching section is connected to the internal suction port, the interior of the housing is sucked, whereby ink is sucked from all the inkjet nozzles. Consequently, reduction in ink consumption due to suction purge of the inkjet head in no need of suction purge can be achieved. Moreover, rapid cleaning can be performed to the plurality of inkjet heads selectively.

In addition, the housing in the example of this invention preferably includes the draw-off port of the suction path on the bottom of the housing, the suction path sucking the interior of the housing.

In addition, the housing in the example of this invention preferably includes the plurality of external suction ports arranged radially.

In addition, the housing in the example of this invention preferably includes the plurality of external suction ports arranged coaxially.

In addition, the housing in the example of this invention preferably includes the suction path sucking the interior of the housing.

In addition, the switching section in the example of this invention has an L-shape. A first end of the switching section rotates by the driving device, whereas a second end thereof is communicated with each of the plurality of external suction ports. Such a construction is preferable.

In addition, the switching section in the example of this invention has a crank shape. A first end of the switching section rotates by the driving device, whereas a second end thereof is communicated with each of the plurality of external suction ports. Such a construction is preferable.

In addition, the housing in the example of this invention preferably includes a closed bearing at the center of rotation of the switching section.

In addition, the plurality of inkjet heads is provided for every single-color ink.

The inkjet printing apparatus in the example of this invention includes the connection switching device for selectively connecting any of the plurality of external suction ports to the suction device by rotating the switching section in the housing having the external suction ports and the internal suction port being disposed at an equal distance from the center of rotation of the switching section. Here, the external suction ports are connectable to the plurality of lines, and the internal suction port connects the suction path for sucking the interior of the housing. When the switching section is connected to any of the external suction ports, ink is sucked from any of the plurality of inkjet nozzles. When the switching section is connected to the internal suction port, the interior of the housing is sucked, whereby ink is sucked from all the inkjet nozzles. Consequently, reduction in ink consumption due to suction purge of the inkjet head in no need of suction purge can be achieved. Moreover, rapid cleaning can be performed to the plurality of inkjet heads selectively.

Moreover, the housing includes inside thereof the draw-off port of the suction path sucking the interior of the housing. This ensures suction of ink accumulated in the interior of the housing.

Moreover, the housing has the suction path formed therein for sucking the interior of the housing. This achieves a compact housing.

DETAILED DESCRIPTION

Description will be given hereinafter of examples of this invention with reference to the drawings.

FIG. 1illustrates an inkjet printing apparatus100according to one example of this invention. The inkjet printing apparatus100performs printing by ejecting ink onto a roll sheet to be transported. The inkjet printing apparatus100includes a controller1, a transporting section2, an ejector3, a drying section4, and an inspecting section5.

The controller1controls the inkjet printing apparatus1entirely. The controller1controls transportation of a sheet9by the transporting section2, ejection of ink onto the sheet9by the ejector3or cleaning in the ejector3, drying of the sheet9with the ink ejected thereon by the drying section4, imaging of a printing image on the sheet9by the inspecting section5. Such control achieves printing onto the sheet9by the inkjet printing apparatus100.

The transporting section2transports the sheet9in the inkjet printing apparatus100. The transporting section2includes a sheet accommodating section20, a drive roller21, and a support roller22.

The sheet accommodating section20accommodates the sheet9as a roll sheet to be printed. A sheet accommodating section20aaccommodates the printing sheet9prior to printing, and a sheet accommodating section20baccommodates the sheet9subsequent to the printing.

The sheet9fed out from the sheet accommodating section20ais transported to the ejector3, the drying section4, and the inspecting section5with drive rollers21aand21bwhile being supported by the support roller22. Then the sheet9is wound up in the sheet accommodating section20b.

The ejector3receives ink from an ink tank, not shown. The ejector3ejects the ink in response to drive signals generated by the controller1in accordance with image information, thereby performing printing onto the sheet9.

The ejector3includes a plurality of inkjet nozzle groups30k,30c,30m, and30y. The inkjet nozzle groups30k,30c,30m, and30yextend perpendicularly relative to a transport direction of the sheet9. Arrangement of many nozzles in a row achieves a width of ejection more than a width of the sheet9to be transported. Such a construction of the ejector3achieves printing by one-time ejection without performing reciprocated scanning in a width direction of the sheet9to be transported.

Here, the number of inkjet nozzle groups in the ejector3is limited to four, but may be one for single-color ejection. Moreover, the number of inkjet nozzle groups may be five or more for additional special-color ejection.

The drying section4heats the sheet9subsequent to printing by the ejector3with use of a heater, a dryer, and the like, to evaporate solvent of ink (mainly, water). Consequently, the ink is fixed.

The drying section4includes a construction of oscillating radiation. Consequently, when radiation-curable ink, such as an ultraviolet-curable ink, is ejected from the ejector3, the ink is fixed (cured) on the sheet9.

The inspecting section5takes printing images so as to determine whether or not the controller1performs printing onto the sheet9satisfactorily. The inspecting section5takes a printing image5printed on the sheet9to be transported with use of a CCD line sensor or a CCD camera, and then transmits information on the image to the controller1. The controller1compares the image information used for ink ejection with photographic information to determine an ejection failure in the ejector3. This enables to determine whether or not the printing is performed satisfactorily.

Here, the ejection failure is, for example, no-ink ejection from the nozzle, failure in spraying of ink droplets, or failure in size of ink droplets. When the controller1determines such an ejection failure in the ejector3, the controller1performs cleaning of the ejector3.

FIGS. 2 and 3are schematic views of the ejector3to which cleaning is performed.FIG. 2illustrates the ejector3performing printing onto the sheet9, whereasFIG. 3illustrates the ejector3to which the cleaning is performed.

The ejector3includes a cleaning section31for cleaning an inkjet nozzle group. The cleaning section31has a suction cap311, a suction tube312, an electromagnetic on/off valve313, a suction pump314, a connection switching section315, and a suction line316.

Here, description will be given assuming that eight inkjet heads30ato30hare arranged in a row to form one inkjet nozzle group30. Of course, the number of inkjet heads arranged in a row to form the inkjet nozzle group30of is limited to eight.

Moreover, for explanation purposes, the ejector3includes one cleaning section31for one inkjet nozzle group30. In actual, the ejector3includes a plurality of cleaning sections31for a plurality of inkjet nozzle groups30, respectively.

The suction cap311covers the inkjet nozzle group30so as to prevent the nozzles from being dried or contaminated. The suction cap311includes the suction tube312connected to the suction pump314. The suction cap311performs covering as illustrated inFIG. 3while the controller1controls the inkjet nozzle group30to move downward. This allows suction for eliminating ink clogging in the inkjet nozzle group30.

The suction tube312is connected to the suction cap311as noted above. The suction pump314sucks ink via the suction tube312from the inkjet nozzle group30covered with the suction cap311.

Here, suction tubes312ato312hare provided for the suction caps311ato311h, respectively, and are connected to the connection switching section315so as to allow suction.

In addition, a suction tube312zis not connected to the suction cap311directly, but is connected to the switching section315so as to suck the interior of the connection switching section315.

This achieves suction of ink from the suction caps311ato311h. Details thereof are to be mentioned later.

The electromagnetic on/off valve313is disposed on the suction line316via which the suction pump314and the connection switching section315are connected. As illustrated inFIG. 2, the controller1controls the electromagnetic on/off valve313to close the suction line316while the inkjet nozzle group30performs ejection to the sheet9. As illustrated inFIG. 3, when the ink is sucked from the inkjet heads30ato30hwhile the suction cap311covers the inkjet nozzle group30and the connection switching section315switchingly connects the suction pump314to the suction tubes312ato312h, the controller1controls the electromagnetic on/off valve313to open the suction line316. Details thereof are to be mentioned later.

In addition, when the suction pump314collectively sucks ink from the inkjet heads30ato30hwhile the switching section315switchingly connects the suction tube312z, the controller1controls the electromagnetic on/off valve313to open the suction line316. Details thereof are to be mentioned later.

The suction pump314sucks the ink from the inkjet nozzle group30through the suction line316, the connection switching section315, the suction tube312ato312hor312z, and the suction cap311under the state as inFIG. 3. When the suction pump314generates negative pressure, ink is discharged from the inkjet nozzle group30. The ink discharged due to negative pressure is accumulated in a drain tank, not shown, of the inkjet printing apparatus100through the suction cap311, the suction tube312, the connection switching section315, the suction line316, and the suction pump314.

When the suction pump314sucks the ink in the inkjet nozzle group30, the controller1controls the connection switching section315to switch the suction line316and the suction tube312ato312hor312zso as to individually suck the inkjet heads30ato30hforming the inkjet nozzle group30or collectively suck the inkjet heads30ato30h.

The connection switching section315is to be described in detail hereinafter with reference toFIGS. 4 and 5.

FIG. 4illustrates an external construction of the connection switching section315. The switching section315includes a housing315for sealingly accommodating therein a switching section315k(not shown in this drawing) communicated with the suction line316. The housing315hincludes a plurality of suction ports315ifor connecting the suction tubes312ato312h, and312z.

The housing315hincludes a sealed bearing315jthat enables to rotate the switching section315k. The bearing315jallows rotating the switching section315kby a motor, not shown, while the interior of the housing315his kept sealed.

The plurality of suction ports315iare disposed radially along the outer periphery of the housing315hso as to correspond to the suction tubes312ato312h, and312z.

Specifically, a suction port315iais connected to be in communication with the suction tube312a. A suction port315ibis connected to be in communication with the suction tube312b. Hereinafter, similar connection is performed, and the suction port315ihis similarly connected to be in communication with the suction tube312h.

Moreover, the suction port315izis connected to be in communication with the suction tube312z. Here, the suction tube312zis connected to be in communication not with the inkjet nozzle group30but with an ink draw-off port315oprovided on the housing315h.

The ink draw-off port315odraws off the ink accumulated in the housing315hwhen the inkjet nozzle group30is entirely sucked, which is to be mentioned later. The ink draw-off port315ois preferably disposed on the bottom of the housing315hfor a suitable position of drawing off the accumulated ink, the position being in a negative (−) Y-axis direction when the direction is represented by X-, Y-, and Z-axes.

The housing315hcan be made from stainless steel, titanium, or fluorocarbon resin, the material having resistance to pressure upon suction by the suction pump314and resistance to corrosion from ink.

FIG. 5is an explanatory view of an internal construction of the connection switching section315. The connection switching section315includes inside thereof a rotatable switching section315kcommunicated with the suction line316.

The switching section315khas a substantially L-shape. The controller1controls the switching section315kto rotate by the motor, not shown, whereby the switching section315kis slidingly engaged in each of the plurality of suction ports315i. When the switching section315kis engaged in the suction port315i, the suction tube312is brought into communication with the suction line316. Consequently, the suction pump314enables to suck the ink from the inkjet nozzle group30covered with the suction cap311.

The site where the switching section315kis engaged in the suction port315ipreferably has a sealing construction, such as a grease seal, a rubber seal, or a metal seal, for obtaining efficient suction or entire suction of the inkjet nozzle group30, to be mentioned later.

The plurality of suction ports315iato315ihis connected to be in communication with the suction tubes312ato312h, respectively. The suction tube312zconnected to the suction port315izis connected to be in communication with the ink draw-off port315oprovided on the bottom of the housing315has illustrated. Such connection causes the switching section315kto be slidingly engaged in the suction port315iz, thereby bringing the suction tube312zto be in communication with the suction line316. Consequently, the suction pump314enables to suck the interior of the housing315h.

FIG. 6is an explanatory view of suction of the inkjet nozzle group30by the connection switching section315.

FIG. 6(a)illustrates an interior housing315hfor explanation of sucking the inkjet heads30ato30hindividually when the cleaning section31performs cleaning to the inkjet nozzle group30. Here, the switching section315performs operations for sucking the ink in the inkjet head30a.

The controller1controls the switching section315kto rotate and be slidingly engaged in the suction port315iawhile the ejector3is in the state as illustrated inFIG. 3. Accordingly, the suction tube312ais brought into communication with the suction line316. Thereafter, the electromagnetic on/off valve313is made “open” so as the suction pump314to start suction, whereby a sliding engaged portion is sealed and the suction line316has negative pressure. The negative pressure causes the ink to be discharged from the inkjet head30acovered with the suction cap311avia the suction tube312acommunicated with the suction line316. The discharged ink is sucked by the suction pump314through the suction cap311aand the suction tube312ato be accumulated in the drain tank, not shown, of the inkjet printing apparatus100.

When the ink is sucked from each of the inkjet heads30bto30h, the controller1controls the switching section315kto rotate and be slidingly engaged in each of the suction ports315ibto315ih, thereby opening the electromagnetic on/off valve313and performing suction by the suction pump314. Consequently, similar to the inkjet head30a, the ink can be sucked from each of the inkjet heads30bto30h.

FIG. 6(a)illustrates ink suction. The suction is preferable for cleaning the inkjet nozzle group30by the cleaning section31, especially for cleaning each of the inkjet heads30ato30hin a defective condition.

On the other hand, many number of inkjet heads forming the inkjet nozzle group30requires much time to repeatedly perform the operation as inFIG. 6(a)for sucking the ink from all of the inkjet heads. This is because the ink has to be sucked from every inkjet head.

For instance, when ink is sucked in a manner as illustrated inFIG. 6(a), it needs time until pressure within the suction cap311returns into atmospheric pressure in order to eliminate redundant ink ejection due to the negative pressure. Assuming that the time is around ten seconds for one inkjet head and the number of inkjet heads is eight, idling time of eighty seconds occurs during a cleaning process.

In order to solve the problem above, the housing315hof the cleaning section31includes the ink draw-off port315ofor sucking the interior of the housing315h.

FIG. 6(b)illustrates an interior housing315hfor explanation of sucking the inkjet heads30ato30hcollectively when the cleaning section31performs cleaning to the inkjet nozzle group30. Here, the switching section315performs operations for sucking the ink entirely from the inkjet nozzle group30.

The controller1controls the switching section315kto rotate and be slidingly engaged in the suction port315izwhile the ejector3is in the state as illustrated inFIG. 3. Accordingly, the suction tube312zis brought into communication with the suction line316, the suction tube312zbeing connected to be in communication with the ink draw-off port315o. Thereafter, the electromagnetic on/off valve313is made “open” so as the suction pump314to start suction, whereby a sliding engaged site is sealed and the suction line316has negative pressure. Accordingly, the interior of the housing315hwhere the ink draw-off port315opasses also has negative pressure.

Here, the housing315hhas a sealed construction. Consequently, negative pressure within the housing315his also applied to the suction caps311ato311hvia the suction tubes312ato312hconnected to the suction ports315ia, respectively. This causes the ink to be discharged from the inkjet heads30ato30h.

The ink discharged from the inkjet heads30ato30hflows into the housing315hvia the suction caps311ato311h, the suction tubes312ato312h, and the suction ports315iato315ih.

The ink flown into the housing315his discharged through the ink draw-off port315ointo the suction port315iz. Here, the ink draw-off port315odisposed on the bottom of the housing315hcollects the ink accumulated within the housing315hnaturally, resulting in efficient ink suction.

Thereafter, the ink is sucked by the suction pump314from the ink draw-off port315othrough the suction tube312zand then through the switching section315kslidingly engaged in the suction port315iz. Accordingly, the ink is accumulated in the drain tank, not shown, of the inkjet printing apparatus100.

As noted above, ink suction illustrated inFIG. 6(b)causes all the inkjet heads30ato30hto be cleaned for a short period of time when the cleaning section31performs cleaning to the inkjet nozzle group30.

As noted above, the cleaning section31inFIG. 2of the inkjet printing apparatus.100inFIG. 1includes the connection switching section315inFIGS. 4 and 5. Consequently, when the switching section315kis connected to any of the suction ports315iato315ih, the ink is sucked from any of the inkjet heads30ato30h. When the switching section315kis connected to the suction port315iz, the interior of the housing315his sucked via the ink draw-off port315o, whereby the ink is sucked from the entire inkjet nozzle group30. As a result, reduction in ink consumption due to the suction purge of the inkjet head in no need of suction purge can be achieved. Moreover, rapid cleaning can be performed selectively to the plurality of inkjet heads.

Moreover, ink accumulated in the suction caps311ato311is sucked as inFIG. 6(b)not only by ink suction from the inkjet nozzle group30but also by flushing or pressure purge performed to the inkjet nozzle group30by the controller1. Consequently, the ink can be prevented from flowing out of the suction cap311.

Description has been given of the housing315hof the connection switching section315, the housing being substantially cylindrical and having a plurality of suction ports315ialong the outer periphery thereof. The location of the plurality of suction ports315iin the housing315his not limited to this.

FIG. 7is an explanatory view of another aspect of the connection switching section315.

In a housing3150hof the connection switching section315illustrated inFIG. 7(a), a plurality of suction ports3150iis not arranged along the outer periphery of the housing3150hbut is arranged coaxially and parallel to the center axis of the housing3150hhaving a substantially cylindrical shape. The plurality of suction ports3150iis arranged in a direction opposite to the suction line316. In this case, an ink ejection port3150oalso enables to be disposed on the bottom of the housing3150h.

FIG. 7(b)illustrates the connection switching section315seen from the suction line316. Here, a disk and an outer peripheral surface of the suction line316in a suction side of the housing3150hare illustrated by dotted lines for explanation purposes.

The switching section3150kinFIG. 7(b)differs from that inFIG. 5in shape. That is, the switching section3150khas a substantially crank shape. The switching section3150kis also in communication with the suction line316. The controller1controls a motor, not shown, to rotate, thereby engaging the switching section3150kin a plurality of suction ports3150iformed in the housing3150h.

The site where the switching section3150kis slidingly engaged in the suction port3150ipreferably has a sealing construction, such as a grease seal, a rubber seal, or a metal seal, for obtaining efficient suction or entire suction of the inkjet nozzle group30.

In the connection switching section315inFIG. 7, the suction line316and the plurality of suction ports3150iare arranged substantially coaxially. This reduces a storage space in a Y-axis direction. In the inkjet printing apparatus100, reduction in ink consumption due to the suction purge of the inkjet head in no need of suction purge can be achieved. Moreover, rapid cleaning can be performed selectively to the plurality of inkjet heads.

Description has been given of the housing315hor3150hof the connection switching section315including ink draw-off port315oor3150oand suction port315izor3150izbeing connected to the suction tube312zcommunicated with the ink draw-off port315oor3150o. Alternatively, the housing315hor3150hitself may include a suction path achieving the same function as the suction tube312z.

FIG. 8illustrates a housing315′kof a connection switching section315′. The housing315′hincludes a plurality of suction port315′iformed by suction ports315′iato315′ihon suction tubes312ato312h. Here, an ink draw-off port315′ois communicated with the suction port315′izvia a suction path315′vformed on the housing315′h.

In the inkjet printing apparatus100, such a construction as above allows reduction in ink consumption due to the suction purge of the inkjet head having no need for suction purge can be achieved. Moreover, rapid cleaning can be performed selectively to the plurality of inkjet heads.

Modification

Description has been given of the housing315hof the connection switching section315having a substantially cylindrical shape. Alternatively, the housing315hmay have a substantially cone, spherical zone, or spherical crown shape. Specifically, the housing315hmay have a shape with a plurality of suction ports315ibeing arranged at an equal distance from the center of rotation of the switching section315k. In this case, the similar effect as above can be produced.

In addition, description has been given of the connection switching section315disposed in the cleaning section31such that the switching section315khas the center of rotation in a substantially horizontal direction. Alternatively, the connection switching section315may be disposed such that the switching section315khas the center of rotation in a substantially vertical direction.

In this case, the ink draw-off port315oon the bottom of the housing315hcauses the ink to be flown naturally and to be further accumulated. Consequently, the ink can be sucked efficiently from the entire inkjet nozzle group30. Especially, the housing315hhaving a substantially cone or spherical crown shape enables to increase efficiency.

Here, the solvent of ink to be cleaned by use in the inkjet printing apparatus100is not limited to water.

Moreover, the ink to be cleaned by use in the inkjet printing apparatus100may be not only dye ink used for general inkjet printing but also pigment ink.

Moreover, the ink to be cleaned by use in the inkjet printing apparatus100may be not only ink used for general printing but also functional ink used for circuit-pattern formation, biological tissue preparation, or three-dimensional shaping.

INDUSTRIAL UTILITY

As noted above, this invention is suitable to an inkjet printing apparatus.

DESCRIPTION OF REFERENCES