Common to all is that all are made as flat and thin discs from plastic material [usually polyearbonate. The recording is done by visual or magnetic excitation of a sensitive substrate embedded in the plastic substrate.

While initially all such discs were supplied as discs with pre recorded data, more and more these devices are such that can be used to record, as well as erase and record again digital data. At this time commercially available recordable discs are known as CD-R, where data is recorded once, and not erased, or as CD-WR which enable a very large number of write and read as well erase operations.

Other, new types of writable discs which are on the initial stage of marketing are magneto optical recording discs and DVD-Ram discs.

In view of their very high data storage capacity [CD-R or CD-WR have a 650 MB capacity, DVD-Ram a 5.2 GB storage, and new magneto-optical discs with 17GB memory have been announced], they will soon replace the older technology for dynamic storage known as Floppy Discs (FD), which have, only a tiny fraction (1.44 Mega Bytes) of storage space.

High capacity storing discs will thus assume the same role that FD had. They will be used among other things to archives computer files, as storing of certain items of data is more convenient when handled separately from the hard disc in the computer, as well as providing a low cost back up storage. In addition privacy and security considerations will make such storage devices useful in many cases.

Therefore, such new flexible storage devices, in particular the low cost CD-R and the slightly more expensive CD-RW are already getting strong presence in the PC market. Furthermore, as manufacturers are planning universal drives that can accommodate all types of discs, they will become useful and common.

Pre recorded discs, such as CD-Rom are sold with a marking of their content printed on the plastic disc. All such discs have one side which is used to read and write data with a laser beam, therefore not accessible to external markings that may block the beam, and another side which is not used to access data and is printable therefore.

It is a matter of common sense that discs which are recorded on a PC such as the above mentioned devices, should be marked so that the user can inspect visually what type of content is stored in them.

Currently, if one wants to mark on a disc as to what was stored inside, he faces three marking alternatives: a pen, a label or a printer. From point of appearance, hand-writing is the least attractive solution for apparent reasons.

Self adhesive labels can be printed remotely and then applied to the plastic disc.

This can be done nearly everywhere, as nearly any PC is connected to a printer. However, labels are not so desirable, as they can peel off and damage the very delicate recording device. A stronger objection to use of labels is that CD spin at very high rate, and require a very high precision during read and write operations. If the labels are not attached precisely so that an even slight imbalance occur, the read and write operations will be impaired. Thus direct printing on the disc might be the best solution, but only if it is simple and affordable.

Currently, several companies offer stand-alone printers that can print directly on discs. Fargo Electronics from Minnesota, offer the Signature, an ink jet CD printer. Similar products are offered also by two other USA companies (Superimage's Media Printer, and Affex's Multimedia printer). Another ink jet printer, Opal7 is offered by a Japanese company, Chugai-Boyeki. These products, essentially modified standard ink jet printers are sold for $800-$2000. A relatively expensive (about $3,000) monochrome thermal transfer printer is made by Rimage (USA).

The present invention propose a much cheaper, simpler and smaller ink jet printing mechanism designed specifically to print markings Getters, characters or graphics) directly on discs.

The mechanism of the invention is designed in such a way that it can be also incorporated into the space occupied by standard CD drives of a PC rather than being offered only as a stand alone printer as the other products mentioned above.

Furthermore, in order to simplify assembly and lower costs, the present invention utilizes some of the inherent existing components of the disk drive mechanism as part of the print mechanism drive, contrast to stand alone printers which require their own motors and drives for an X-Y movement of the printing head over the disc.

Summary of the Invention The apparatus for printing desired information on digital discs, according to the invention, comprises an ink jet printing head, comprising a linear movement mechanism for driving the head along a radial axis and a mechanism for rotating the disc, positioned on the side of the disc opposite to that on which read/write operations are carried on or intended to be carried on by laser means.

The apparatus may be incorporated in the space occupied by a standard CD-RW or CD-R drive. Preferably, at least part of the linear movement mechanism is part of the mechanism for driving the laser head in the read/write operations and/or the mechanism for rotating the-disc-is part of the mechanism for driving the disc in the read/write operations.

In a preferred embodiment, the ink jet printing head comprises the nozzles and ink containers, and is in the form of a replaceable cartridge, slidingly and removably mounted on a sliding rod.

The invention further comprises a method of printing desired information on digital discs by means of an ink jet printing head, which comprising placing the printing head on the side of the disc opposite to that on which read/write operations are carried on or intended to be carried on by laser means and activating the head to eject ink drops onto the disc while linearly displacing said head along a radial axis and for rotating the disc.

Before printing the desired information, at least one coordinate point is printed on the disc, for determining the sectorial coordinates of the ink jet printing head during the printing of the desired information. The coordinate point or points are preferably printed on the inner or outer boundary of the annular configuration of the disc.

Brief Description of the Drawings The above and other characteristics and advantages of the invention will be better understood through the following illustrative and non-limitative detailed description of preferred embodiments thereof, with reference to the appended drawings, wherein: -Fig. 1 is a schematic drawing of such mechanism which contain two motors, and a laser read/write head, according to a preferred embodiment of the invention; -Fig. 2 shows the other side of disc surface which is used for printing, according to a preferred embodiment of the invention; -Fig. 3 shows the ink jet head with row of nozzles and ink containers on its sides, according to a preferred embodiment of the invention; -Fig. 4 shows several of the possibilities to place such markings-a single marker, a 4 mark compass and a ring of markers, according to a preferred embodiment of the invention; -Fig. 5 schematically illustrates an arrangement for pulling out an emptied cartridge and inserting a new one into its place.

Detailed description of preferred embodiments The drive mechanism of discs is structured so that it permit movements of the read/write laser element in relation to the disc in a spiral mode in CD-ROM, or in concentric circles in writable devices. That is achieved by two relational movements-a rotatory (circular) one and a linear one, which allow to laser read and write element to reach any point on the disc surface under software control.

The arrangement allows also that this access ability can be instantaneous.

Figure 1 is a schematic drawing of such mechanism which contain two motors, and a laser read/write head. The disc data surface 1 is scanned by laser head 5.

This laser head is moving linearly along the radial axis on a sliding rod 4 by linear stepping motor 3, while the disc is rotated by rotatory motor 2.

Figure 2 shows the other side of disc surface 1 which is used for printing. The ink jet print head 6 has a line of nozzles 7 arranged on the radial axis. The ink jet head is moved along this axis by sliding rod 8 which is actuated by linear stepping motor 9.

The two types of operations, of read/write and of printing are carried in different times, and not concurrently. However, in order to supply certain data about the spatial coordinates of the disc, one specific read operation is performed by the laser head during printing. The laser head is kept stationary at a predetermined known point along the radius of the disc and read the track data which give sectorial information.

The circular fixed rate movement of the disc is executed by a continuous dc motor rotating at a constant speed, or in a speed which is related to its angular position, and which is an inherent part of any CD drive. In the data read and write modes this rotation allows access of the laser head into all sectors of the disc. The same movement and the same motor are used to allow access of the print head into any sector of the printable surface of the disc. In the read and write data mode the linear movement is achieved by a high precision stepping motor that execute a movement along the radius of the disc that allows positioning of the laser head at any point along the radius of the disc. The combination of the two movements allows thus access of the laser head to any point on the surface of the disc.

The precise control of the spatial positioning of the head is achieved by the use of an encoding mechanism that feeds back the linear position, and by the feedback from track data embedded on the disc that supply the sectorial information.

The degree of mechanical precision required for such laser beam is very high, measured in sub micron units both in the rotatory and in the linear directions.

In the present invention, an additional and nearly identical linear movement mechanism is used. This additional mechanism is placed however in the opposite side of the disc to the laser head. The data side of the disc which is used by the laser source, is conventionally the bottom side. The opposite, printable side is the top of the disc. Such arrangement is very advantageous for drop of demand ink jet mechanism. In such mechanism the preferred way to eject and place ink droplets on a substrate is from top to down, the ink jet nozzle is place above the substrate and droplets are being injected perpendicularly down toward the substrate. This increases the ejection velocity, a parameter necessary for accurate placement of the droplet.

Figure 3 shows the ink jet head 6 with row of nozzles 10, and ink containers 11 on its sides. Rows of nozzles could consist each in a single nozzle. In addition, the head is flash mounted with optical sensor 12. In order to achieve high degree of droplet placement accuracy, all nozzles in a first preferred embodiment of the invention are placed on a single line along the radius of the disc. Such arrangement allows an easy calculation of droplet ejection time so that precise positioning is achieved, as the distance between adjacent nozzles is known, the exact positioning of any and all along the radius is also known from the encoding mechanism incorporated in the linear movement mechanism, the sector information is available from the track data read by stationary laser beam during printing, and the time needed for the droplet to reach the surface is known from drop velocity and distance of the nozzle from the substrate. Since the tracks are arranged as a continuous spiral, or concentric rings, additional information is needed for determining the exact sectorial coordinates on the disc. Such information can be provided by first printing an encoding at least one coordinate point on either the outside or the inside circumference of the annular disc, reading such coordinate point by an optical sensor mounted on the inner or outer edge of the print head at a point radially centered as the nozzles are. Once the coordinate point or points are detected, track data is counted and calculated.

Figure 4 shows several of the possibilities to place such markings-a single marker, a 4 mark compass and a ring of markers. Thus, detection of the printed coordinate (s), coupled with track data is sufficient for exact determination of the spatial location of any nozzle with respect to the printed surface at any time during the rotation of the disc.

Two prerequisites are needed for this operation. First the coordinate point (s) have to be printed on a new disc prior to any other print operation. Second, the optical sensor that detect the coordinate point (s) must be placed stationary on radial axis along the circumference line where such points are printed. All such data are used to calculate precisely when to eject a drop so that it reaches the rotating substrate at a predetermined point.

To illustrate such a situation in a drop on demand ink jet mechanism, reference is made to actual typical parameters. The maximal distance between nozzle and substrate is 1 millimeter, and typical drop velocity is 6 meter per second. This means that the travel duration of the droplet is 1/6000 of a second, or 0.15 microsecond. Proper placement for good printing of a 600 dpi drop that have a diameter of 43 microns, requires that the deviation of the droplet will not exceed 5-10 microns. The radial position is guaranteed by the linear stepping motor, but the sectorial positioning is a matter of correct detection of the rotatory movement. The sectorial information is derived from data bits that are arranged along the spiral tracks of the discs (such bits are either physical pits and through or optically modified points) and are 1 micron of width, and 3 microns of length along the track. Based on the 10 microns the margin error of droplet placement timing with respect to the rotatory movement is three times the accuracy of the sectorial track data. Thus it is possible to read the track data with an accuracy in excess of that needed to minimize placement errors.

Other factors contributing to possible errors might be due to delays in reading, transmitting and processing of the track data. However, since the speed of rotation is controllable, it is possible to calculate the maximum speed allowed so that not more than the allowable error will occur.

In the extreme case, the preferred embodiment is a case in which the rotation of the disc during droplet ejection is zero or above it. The zero case is a situation defined as stop and go mode, where the disc is rotated until precise alignment of the sector is achieved, then stops, and ejection occurs. However, this extreme case is not anticipated, and speed which allow efficient rotation for fast printing speeds can be reached.

As stated above, the present invention aims primarily, but not exclusively to incorporate the ink jet print head into a standard CD drive mechanism. Such drive offer a very narrow space above-the disc. It is necessary therefore to keep the ink jet mechanism in a very low profile.

In a preferred embodiment, the ink jet mechanism is such as produced by Scitex Corporation of Israel. The mechanism of this ink jet is shaped as thin wafer, 1.8 mm thick, with nozzles occupying the bottom surface of the wafer, and piezo elements the top surface. The width and length of the wafer are determined by the number of nozzles employed. Since the nozzle-to-nozzle distance in this mechanism is 2.3 mm, a single row of nozzles (wherein each row may consist of a single nozzle) require a wafer width of 3 mm. An 8 nozzle row will require a wafer length of 20 mm. Such dimensions are small enough to allow placing such ink jet in a space very close to the one available in standard CD drive and also allow travel of the mechanism in and out along the radius of the disc. However the present invention is not limited to Scitex'ink jet heads, as other ink jet mechanisms can be adopted to be structured in a similar manner.

In a preferred embodiment, on each side of the bar shaped mechanism a small ink container having the same thickness and length of the bar is attached. The ink jet mechanism and the ink container are sealed together to form a complete ink jet cartridge in the shape of a 3 mm thick wafer, which can have length and width useful and practical to meet space constraints as well as ink capacity requirements.

The advantage of such arrangement is not only the very small space, but also that the ink jet head and its ink supply are constituting a complete, wafer thin, cartridge.

For example, the print capacity in the case of eight nozzles Scitex'device, and with 0.15 ml ink capacity (enough to print an area of 6x6 cm in 50 discs at 10% black density such as conventional text), the total surface of the wafer will measure 20 x 40 mm, with ink containers depth of 2mm.

These figures illustrate that such cartridge will suffice for printing on discs in many user sites. To those who will have higher printing duties, or will print more ink consuming graphics, such as grayscale or halftones, the present invention provide a solution by a cartridge replacement.

In the preferred embodiment, the cartridge described above, is being held in holder designed so that it holds the cartridge along a sliding rod, in a way similar to the way the laser element is held along a sliding rod in CD drives. With an opening engineered in the top front of the CD drive case, it is possible to insert in or pull out a cartridge. Thus, when the cartridge in use is emptied of ink, it can be pulled out, and a new one is inserted in its place. Figure 5 depict this arrangement. However, the invention is not limited to the wafer thin cartridges.

In case that more space is made available in the CD drive, other configurations, including a configuration with a separate ink supply connected to the head by flexible tube can be considered.

Printing on a circularly shaped substrate poses problems not encountered in a rectangular shaped substrate used in almost all office and PC printers. Simply there are no orienting coordinates. In case of one time printing this is not a problem as the reader will orient the disc so he can read the printed text.

However, as the aim is to allow for more than one time printing, a solution and means for that are also offered in the present invention. It should be apparent to those familiar with data storing operations that printing of the content can be repetitive and occurring in the different times. For example, whenever a file is written into the disc, the user will like to print on he disc the name of the file. The present invention includes therefore a software mean, by which whenever a new disc is used it will be first be printed with orientation coordinates.

Preferably, these coordinates will be printed along the outer or the inner circumference of the-annular boundaries of the disc surface (the disc have a central hole). Such coordinates will then be scanned by the photo-sensitive element of the optical sensor mount at the edge of the holder of the ink jet cartridge. Miniature photo-sensitive elements which contain an emitter and a sensor are commercially available from many manufacturers such as HP, Motorola and others, and some are sufficiently small to be used.

Prior to any subsequent printing, the disc will be rotated, the cartridge holder will be gradually moved along the radius, and the orientation markings, as well as all other already printed information will be scanned. The scanned information will then be displayed on the computer screen. The user will then type in the new information, select a font and size and the print location he deems suitable. A software program will display the desired appearance. Once confirme, it will be then processed by software and sent to the print mechanism under location control derived from the linear movement encoder and the track decoder information.

Those familiar with the art can see that creating such software is a routine matter. They can also see that as the total disc surface can be scanned according to the mean provided by the present invention, that on subsequent printings, it is possible to display not only the coordinates, but all information that was printed before. Such display provides the user with tools to decide where to put the new information, to avoid undesired over printing and also to erase prior printed information by printing over it lines or any other graphics.