Security System for Electronic Printing Systems

The invention relates to electronic printers and printing systems, and more particularly, to a security system for electronic printers and printing systems.

In conventional light/lens copiers, document security has generally been grounded on physical possession of the document originals and the copies made while copier access and use has been based on billing considerations. In the case of document security, security for a user's originals and copies was attended to by the fact that the originals from which the copies were made as well as the copies themselves normally remained in the possession and control of the owner or in the hands of someone known to the owner and trusted to make copies. Control over copier access on the hand, if it existed at all, was generally based on assuring that the person using the copier and making copies was correctly billed or charged for the copies made. This for example led in the past to development and introduction of copy charge counters or meters which limited use of a copier to those persons having an account against which the cost of the copies could be charged. But generally, in the copier environment, little or no attention was given to security, and particularly to the security of the owner's files.

With the advent of electronic printing systems however, where the image is in the form of electrical signals or pixels, a user's electronic files, programs, etc., which may be confidential or personal in nature, are at least temporarily stored in the system. As a result, the owner's files may be available to anyone having access to the system for reading, copying, tampering, etc. A similar situation occurs with data that is transmitted to a communication channel to or from the system. Anyone having access to the system can intercept and gain access to the transmitted data for his own purposes.

In the prior art, security in the past has focused on computer systems as evidenced by U.S. Pat. No. 4,713,753 to Boebert el al wherein there is disclosed a secure system architecture for a data processor in which a predefined security policy, stored in a secure processor, uses format control to prevent alteration of a program. U.S. Pat. Nos. 4,525,780 to Bratt et al and 4,498,132 to Ahlstrom et al (which relies on U.S. Pat. No. 4,525,780 for its description) disclose a data processing system having an addressing system for processing object based information with a protection scheme for controlling access rights to the information. And U.S. Pat. No. 4,799,258 to Davies discloses a dual key system for controlling access to computers to assure a tamper resistant store.

Further in computer applications, a User Identification Code (UIC) technique has been used to control file access. In this technique, two numbers are provided per user, a group number and a member number. Each user accordingly is represented as a member of a group which may span a number of other users with a common need to share information. Further, each file has certain attributes associated with it, such as the UIC of the owner and the protection settings controlling READ and WRITE access. The UIC system however is limited in the levels of security that it can provide and has limited extensibility.

A second prior art technique of the type discussed in U.S. Pat. Nos. 4,498,132 and 4,525,780 above is based upon access lists where each operation on a file is controlled by a list maintained by the file's owner of users who are granted or denied access. The list additionally may contain pre-defined group names and object enablements or restrictions. The disadvantages of this technique are the large amount of memory required and large amounts of processing overhead needed to maintain and verify the list.

In contrast, the present invention provides a security process for an electronic reprographic printer, comprising the steps of: providing a security administrator; providing a security profile with discrete security levels for different classes of users under the control of the security administrator; giving the administrator power to assign user identification numbers at less secured sites, and enable use of passwords by the users at more secure sites; providing a site administrator; giving the site administrator control over user job programming options for the printer; isolating functions of the site administrator from user functions by assigning special identification number and password to the site administrator to prevent users from accessing the site administrator functions; and providing user file security by enabling users, to protect user files by user passwords, to limit access to others to user files, and to assign a non-removable security label to a user's files which prevent printing or displaying of the files without the security label.

FIG. 1 is a view depicting an electronic printing system incorporating the security system of the present invention;

FIG. 2 is a block diagram depicting the major elements of the printing system shown in FIG. 1;

FIG. 3 is a plan view illustrating the principal mechanical components of the printing system shown in FIG. 1;

FIG. 4 is a schematic view showing certain construction details of the document scanner for the printing system shown in FIG. 1;

FIGS. 5A, 5B, and 5C comprise a schematic block diagram showing the major parts of the control section for the printing system shown in FIG.1;

FIG. 6 is a block diagram of the Operating System, together with Printed Wiring Boards and shared line connections for the printing system shown in FIG. 1;

FIG. 7 is a view depicting an exemplary job programming ticket and job scorecard displayed on the User Interface (UI) touchscreen of the printing system shown in FIG. 1;

FIG. 8 is a view of the User Interface touchscreen on which is displayed a SECURITY card file having "Users", "Security Profile", and "Access Lists" icons, with the "Users" icon actuated to display a listing of users by name;

FIG. 9 is a view in which a user is selected by highlighting and opening a SYSTEM ADMINISTRATOR window providing processing selections;

FIG. 10 is a view displaying the User Profile for the user selected;

FIG. 11 is a view displaying the "Privileges" card file for the user selected;

FIG. 12 is a view showing the "Delete User?" options window opened;

FIG. 13 is a view showing the "Assign New Owner" options window opened;

FIG. 14 is a view showing the user "Profile Options" window opened to display the "New User Template" selections;

FIG. 15 is a view of the User Interface touchscreen showing the "New User Template" following selection;

FIG. 16 is a view showing the "Security Profile" card file for the site;

FIG. 17 is a view showing the "Activity Log" for the site;

FIG. 18 is a view showing the "Activity Log" in FIG. 17 with the "Audit Trail Options" window opened;

FIG. 19 is a view of the User Interface touchscreen depicting the "Access Lists" card file;

FIG. 20 is a view showing the "Access Lists" card file of FIG. 19 with a file window opened to display list selections:

FIG. 21 is a view showing the "Access Lists" card file of FIG. 19 with the "Delete List?" window opened;

FIG. 22 is a view showing the "Member Name" file with names of members in a selected access list;

FIG. 23 is a view showing the "Remove from list" selection window for removing members from the selected access list;

FIG. 24 is a view showing the "Add Member" window for adding a member's name to the access list selected;

FIG. 25 is a view showing the "Job Access Control" card enabling a file owner to set the access rights to the owner's files; and

FIG. 26 is a plane view of a second embodiment in which the security system is externally administered.

Referring to FIGS. 1 and 2, there is shown an exemplary image printing system 2 for processing print jobs in accordance with the teachings of the present invention. Printing system 2 for purposes of explanation is divided into image input section 4, controller section 7, and printer section 8. In the example shown, image input section 4 has both remote and on-site image inputs, enabling system 2 to provide network, scan, and print services. Other system combinations may be envisioned such as a stand alone printing system with on-site image input (i.e., a scanner), controller, and printer; a network printing system with remote input, controller, and printer; etc. While a specific printing system is shown and described, the present invention may be used with other types of printing systems. For example, printer section 8 may instead use a different printer type such as ink jet, ionographic, etc.

Referring particularly to FIGS. 2-4, for off-site image input, image input section 4 has a network 5 with a suitable communication channel such as a telephone line enabling image data in the form of image signals or pixels from one or more remote sources to be input to system 2 for processing. Where the Page Description Language (PDL) of the incoming imaging data is different than the PDL used by system 2, suitable conversion means (not shown) are provided. Other remote sources of image data such as streaming tape, floppy disk, etc. may be envisioned.

For on-site image input, section 4 has a document scanner 6 with a transparent platen 20 on which documents 22 to be scanned are located. One or more linear arrays 24 are supported for reciprocating scanning movement below platen 20 by motor 21. Lens 26 and mirrors 28, 29, 30 cooperate to focus array 24 on a line like segment of platen 20 and the document being scanned thereon. A lamp 170 and reflector 172 cooperate to illuminate the line-like segment being scanned through scan slit 174. Image data in the form of image signals or pixels from net 5 or array 24 are input to processor 25 for processing. After processing, the image signals are output to controller section 7.

Processor 25 converts the analog image signals output by array 24 to digital. Processor 25 further processes image signals as required to enable system 2 to store and handle the image data in the form required to carry out the job programmed. Processor 25 also provides enhancements and changes to the image signals such as filtering, thresholding, screening, cropping, scaling, etc.

Documents 22 to be scanned may be located on platen 20 for scanning by automatic document handler (ADF) 35 operable in either a Recirculating Document Handling (RDH) mode or a Semi-Automatic Document Handling (SADH) mode. A manual mode including a Book mode and a Computer Forms Feeder (CFF) mode are also provided, the latter to accommodate documents in the form of computer fanfold. For RDH mode operation, document handler 35 has a document tray 37 in which documents 22 are arranged in stacks or batches. The documents 22 in tray 37 are advanced by vacuum feed belt 40 and document feed rolls 41 and document feed belt 42 onto platen 20 where the document is scanned by array 24. Following scanning, the document is removed from platen 20 by belt 42 and returned to tray 37 by document feed rolls 44.

For operation in the SADH mode, a document entry slot 46 provides access to the document feed belt 42 between tray 37 and platen 20 through which individual documents may be inserted manually for transport to platen 20. Feed rolls 49 behind slot 46 form a nip for engaging and feeding the document to feed belt 42 and onto platen 20. Following scanning, the document is removed from platen 20 and discharged into catch tray 48.

For operation in the CFF mode, computer forms material is fed through slot 46 and advanced by feed rolls 49 to document feed belt 42 which in turn advances a page of the fanfold material into position on platen 20.

Referring to FIGS. 2 and 3, printer section 8 comprises a laser type printer and for purposes of explanation is separated into a Raster Output Scanner (ROS) section 87, Print Module Section 95, Paper Supply section 107, and Finisher 120. ROS 95 has a laser 91, the beam of which is split into two imaging beams 94. Each beam 94 is modulated in accordance with the content of an image signal input by acousto-optic modulator (MOD) 92 to provide dual imaging beams 94. Beams 94 are scanned across a moving photoreceptor 98 of Print Module 95 by the mirrored facets of a rotating polygon 100 to expose two image lines on photoreceptor 98 with each scan and create the latent electrostatic images represented by the image signal input to modulator 92. Photoreceptor 98 is uniformly charged by corotrons 102 at a charging station preparatory to exposure by imaging beams 94. The latent electrostatic images are developed by developer 104 having a developer supply 105 and transferred at transfer station 106 to a print media 108 delivered by Paper Supply section 107. Media 108 as will appear may comprise any of variety of sheet sizes, types, and colors. For transfer, the print media is brought forward in timed registration with the developed image on photoreceptor 98 from either a main paper tray 110 or from auxiliary paper trays 112, or 114. The developed image transferred to the print media 108 is permanently fixed or fused by fuser 116 and the resulting prints discharged to either output tray 118, or to finisher 120. Finisher 120 includes a stitcher 122 for stitching or stapling the prints together to form books 121 and a thermal binder 124 for adhesively binding the prints into books 121.

Referring to FIGS. 1, 2 and 5, controller section 7 is, for explanation purposes, divided into an image input controller 50, User Interface (UI) 52, system controller 54, main memory 56, image manipulation section 58, and image output controller 60.

The image data input from processor 25 of image input section 4 to controller section 7 is compressed by image compressor/processor 51 of image input controller 50 on PWB 70-3. As the image data passes through compressor/processor 51, it is segmented into slices N scanlines wide, each slice having a slice pointer. The compressed image data together with slice pointers and any related image descriptors providing image specific information (such as height and width of the document in pixels, the compression method used, pointers to the compressed image data, and pointers to the image slice pointers) are placed in an image file. The image files, which represent different print jobs, are temporarily stored in system memory 61 which comprises a Random Access Memory or RAM pending transfer to main memory 56 where the data is held pending use.

As best seen in FIG. 1, UI 52 includes a combined operator controller/CRT display consisting of an interactive touchscreen 62, keyboard 64, and mouse 66. UI 52 interfaces the operator with printing system 2, enabling the operator to program print jobs and other instructions, to obtain system operating information, instructions, programming information, diagnostic information, etc. Items displayed on touchscreen 62 such as files and icons are actuated by either touching the displayed item on screen 62 with a finger or by using mouse 66 to point cursor 67 to the item selected and keying the mouse.

Main memory 56 has plural hard disks 90-1, 90-2, 90-3 for storing machine Operating System software, machine operating data, and the scanned image data currently being processed.

When the compressed image data in main memory 56 requires further processing, or is required for display on touchscreen 62 of UI 52, or is required by printer section 8, the data is accessed in main memory 56. Where further processing other than that provided by processor 25 is required, the data is transferred to image manipulation section 58 on PWB 70-6 where the additional processing steps such as collation, make ready, decomposition, etc. are carried out. Following processing, the data may be returned to main memory 56, sent to UI 52 for display on touchscreen 62, or sent to image output controller 60.

Image data output to image output controller 60 is decompressed and readied for printing by image generating processors 86 of PWBs 70-7, 70-8 (seen in FIG. 5A). Following this, the data is output by dispatch processors 88, 89 on PWB 70-9 to printer section 8. Image data sent to printer section 8 for printing is normally purged from memory 56 to make room for new image data.

Referring particularly to FIGS. 5A-5C, control section 7 includes a plurality of Printed Wiring Boards (PWBs) 70, PWBs 70 being coupled with one another and with System Memory 61 by a pair of memory buses 72, 74. Memory controller 76 couples System Memory 61 with buses 72, 74. PWBs 70 include system processor PWB 70-1 having plural system processors 78; low speed I/O processor PWB 70-2 having UI communication controller 80 for transmitting data to and from UI 52; PWBs 70-3, 70-4, 70-5 having disk drive controller/processors 82 for transmitting data to and from disks 90-1, 90-2, 90-3 respectively of main memory 56 (image compressor/processor 51 for compressing the image data is on PWB 70-3); image manipulation PWB 70-6 with image manipulation processors of image manipulation section 58; image generation processor PWBs 70-7, 70-8 with image generation processors 86 for processing the image data for printing by printer section 8; dispatch processor PWB 70-9 having dispatch processors 88, 89 for controlling transmission of data to and from printer section 8; and boot control-arbitration-scheduler PWB 70-10.

Referring particularly to FIG. 6, system control signals are distributed via a plurality of printed wiring boards (PWBs). These include EDN core PWB 130, Marking Imaging core PWB 132, Paper Handling core PWB 134, and Finisher Binder core PWB 136 together with various Input/Output (I/O) PWBs 138. A system bus 140 couples the core PWBs 130, 132, 134, 136 with each other and with controller section 7 while local buses 142 serve to couple the I/O PWBs 138 with each other and with their associated core PWB.

On machine power up, the Operating System software is loaded from memory 56 to EDN core PWB 130 and from there to the remaining core PWBs 132, 134, 136 via bus 140, each core PWB 130, 132, 134, 136 having a boot ROM 147 for controlling downloading of Operating System software to the PWB, fault detection, etc. Boot ROMs 147 also enable transmission of Operating System software and control data to and from PWBs 130, 132, 134, 136 via bus 140 and control data to and from I/O PWBs 138 via local buses 142. Additional ROM, RAM, and NVM memory types are resident at various locations within system 2.

Referring to FIG. 7, jobs are programmed in a Job Program mode in which there is displayed on touchscreen 62 a Job Ticket 150 and a Job Scorecard 152 for the job being programmed. Job Ticket 150 displays various job selections programmed while Job Scorecard 152 displays the basic instructions to the system for printing the job.

To control access to printing system 2 at a site and protect any sensitive data and files stored in the system memory, the security system of the present invention is provided. When invoked, a user in order to gain access to printing system 2 must authenticate himself by a special User Identification number (User ID). Where a password option is enabled, the user is also required to enter his password. As will appear, a Security administrator assigns the User ID while the user creates his own password when allowed to do so.

The site, which is the business location for the printing system 2, has the ability to define the level of security desired. Generally, the levels of security are:

(1) no security except for administrative functions controlled by either a site administrator or a security administrator. These administrative functions are the type which require access controls to protect sensitive information and performance variables for the system. At this security level, no user would be required to log onto printing system and each user would have full access to any function available on the system

(2) a partially secure site would allow User IDs to be assigned to some users at the Security Administrator's discretion. This would give these users access to certain privileged system functions.

(3) a fully secured site where all users are assigned a User ID by the Security administrator.

(4) fully secured site with passwords would allow some or all users, at the discretion of the Security administrator, to employ their own password to control access to the user's own files that are in the system.

A Site administrator is normally provided (although one administrator may serve in both Site and Security Administrator capacities). The site administrator is considered a privileged user and as such has certain privileges over and above those of either a secure or non-secure user. The Site administrator typically establishes the programming features and functions that the site will have, the system default settings, i.e., restricting access to complex printer programming features to avoid printer downtime, restricting user access to pre-selected printer programming features to reduce personal use of the printer, etc., and has shared operating functions such as billing, accounting, etc.

A Security administrator is a trusted individual charged with the responsibility for creating and implementing the security rules of printing system 2 consistent with the security level desired by the site. In this capacity, the Security administrator controls access to the programming features, administration, and service of printing system 2. Programming functions and features comprise the different level of system job programming choices that are made available to a user by the Site administator. Security administration relates to the process by which security at the site is administered while service refers to the security that governs access by service or repair personnel (referred to herein as Tech Reps.).

To enable the Security administrator to carry out his duties, the Security administrator establishes and maintains a User Profile for each user. The User Profile allows the Security administrator to establish a security profile for each user to whom the Security administrator assigns a User ID plus other security enablements such as user passwords, rights to access different system programming functions, etc. depending upon the security level of the site. As will be understood, access to the user profile is limited to whatever rights the Security administrator has.

Referring to FIGS. 8-12 and APPENDIX A "UserProfile Module", on entering the "Administration" mode, there is displayed on touchscreen 62 certain card files including a "SECURITY" card file 200 on which are displayed "Users", "Security Profile", and "Access Lists" icons 201, 202, 203 respectively. Actuation of "Users" icon 201 causes a "User Name" file 205 to be displayed listing the names of all users at the site to whom a User ID has been assigned, the user's ID, and whether the user is "Active" or "Inactive". Up and down scrolling icons 207, 208 permit scrolling of file 205 to allow reading of all the user names.

Where the Security administrator desires to view the User Profile for a particular user, a "Users" icon 210 in "Users Name" file 205 is actuated to display a "SYSTEM ADMINISTRATION" window 212 having "Open Profile", "Activate", "Delete", and "Close" selections. Moving window 212 so that the window pointer 212' is opposite the name of the user whose User Profile is to be viewed and actuating "Open Profile" displays the User Profile 215 for the user name selected. As shown in FIG. 10, User Profile 215 identifies the "User Status", "User Name", "User ID", whether the user has a password or not, and the user's "Default Account". Additionally, a "Job Access Control" icon 217 and a "Privileges" icon 219 are displayed.

Selecting "Privileges" 219 displays the privileges granted to the user as shown in FIG. 11. These consist of "Administration", "Service", and "Feature Access".

The Security administrator ordinarily has "Administration" privileges for "Security" while the Site administrator has privileges for "Site". A single person may have privileges for "Both". Special ID numbers prevent users from gaining access to the security and administration functions performed by the administrator or administrators.

Referring to FIGS. 9, 12, and 13, actuating "Delete" in window 212 displays a "Delete User?" window 221 with "Yes" and "No" options. Actuation of "Yes" deletes the current user and displays an "Assign New Owner" window 223 through which the Security administrator can assign a new owner for the former user's jobs currently in the system if desired. For this, and referring to FIGS. 14-15, a "Profile Options" window 225 is opened displaying a "New User Template" selection 226. Actuation of the "New User Template" 226 displays the template 228 seen in FIG. 15 by which a User Profile 215 for the new user is created.

A similar procedure is followed where a "New User" is to be added to the users given access to printing system 2. In that case, the "New User" icon 230 in "Users Name" file 205 (FIG. 8) is actuated.

The Security administrator may also be given the ability to set up certain user independent functions such as the number of attempts a user can make to logon before lockout, minimum User ID length, minimum password length, etc. depending on the security level of the site. For this, and referring to FIGS. 8 and 16, the Security Profile icon 202 is actuated to display "Security Profile" scorecard 232 showing the current security setup of the site. These include whether or not user logon is required ("Logon Required"), the minimum number of characters in the user's ID ("Minimum User ID Length"), the length of a sessions ("Session Timeout"), the maximum number of logon attempts by a user that are allowed ("Maximum Failed Logons"), if a password is required ("Password required for"), the "Minimum Password Length", "Password History Length", and "Password Expiration".

An "Activity Log" icon 235 enables the Security administrator to access data when auditing security relevant functions and to activate auditing functions which will monitor and log system data, user logon/off, access to secure items, power on/off, etc. Actuating icon 235 displays an "Activity Log" scorecard 237 (FIG. 17) with a series of system auditing options for monitoring the number of times certain activities such as "Logon/Logoff", etc. take place. The site security enablements such as "Security Configuration" are also displayed for selection together with an option to print out a hard copy of the activity log ("Print Activity Log") and to reset the log ("Reinitialize Activity Log") as shown in FIG. 18.

Referring to FIGS. 8 and 19-24, the Security administrator may also set up access lists grouping users who have security access to a common file. Actuating "Access List" icon 203 displays a card file 239 of names for a specific job with a selection window 240. As in the case of individual users discussed previously, the Security administrator may select a list for deletion (FIG. 21), or open a list to display the members names (FIG. 22), or remove individual members from the list (FIG. 23), or add new members to the list (FIG. 24).

As will be understood, the set of operations and program selections which an user is allowed to perform on a particular job or directory object is a direct consequence of the user's clearance. Control over access to jobs and data stored in printing system 2 originates with the data creator or owner and governs the operations which a user is allowed to perform on files resident in the system.

Referring to FIGS. 10 and 25, actuation of "Job Access Control" icon 217 displays a "Job Access Control" scorecard 241 allowing a user to impose security restrictions on the user's files or jobs that are resident in printing system 2. The security limitations fall into two general classes: "COPIED and MODIFIED" and "COPIED" only. Each class is subdivided into: "All Users" 242, "Job Owner" 244, "Access List" 246, and "None" 248. "All Users" allows anyone to modify and/or copy the user's jobs, "Job Owner" allows only the job owner to modify and/or copy the user's jobs, "Access List" lists the names of users who are allowed to modify and/or copy the user's jobs, and "None" prevents anyone, including the job owner, from modifying and/or copying the user's jobs.

Tech Reps have their own security protection in the form of a Tech Rep ID number which is assigned either when printing system 2 is manufactured or when system 2 is installed. The Tech Rep ID number can be used to control down to the work support group level or any other service control level desired.

Once the Tech Rep ID number is assigned, the service organization to which the Tech Rep belongs can assign a password to protect both the service organization and the site by limiting access to only Tech Reps who have the correct password. The Tech Rep password can be changed at any time by the service organization. Further the service organization can assign special Tech Rep passwords to each site to further enhance site and/or the service organization security requirements.

Additionally, the service organization can also assign advanced levels of servicing access to selected personnel at individual sites. Typically this would be to site personal who have attended special training courses enabling them to perform more difficult and complex service operations on printing system 2 than the typical user would be able to do. The Site administrator normally would decide the site personal to be selected for this purpose with the Security administrator controlling special service access rights through "Service" selection under "PRIVILEGE" as shown in FIG. 11.

While files are protected through the password mechanism and/or by the ability of a user to decide the appropriate access rights of others to the user's files as described, the operator also has the ability to assign a security label to a file. To enable the use of security labels, the system described and claimed in copending application Ser. No. 07/590,633, filed on Sept. 28, 1990, entitled "Process For Merging Logos With Prints Produced By Electronic Printing Machines" in the names of Hengst et al (Attorney Docket No. D/89288) and incorporated by reference herein may be used for this purpose. A folder for security labels is stored in the system Merge Library into which the operator places his security label(s). In doing so, the user can identify the location of the security label on the page and the page side on which the security label is to appear. Printing system 2 assures that once selected, the user's file will never be displayed on touchscreen 62 or printed by printer section 8 without the security label selected by the user being present. In addition, printing system 2 provides the operator with the option of placing the security label in the background of the image displayed on touchscreen 62 or printed by printer section 8. This prevents anyone from removing the label since the security label will appear associated directly with the image itself.

In addition to security labels, printing system 2 provides the capability of printing other label types such as labels with an automatic date-time stamp along the edge or edges of the image displayed or printed, a label identifying the site of the printing system making the prints, a label identifying the image owner, etc.

Referring to FIG. 26, while a security system internal to a printing system 2 has been shown and described, control over the security of one or more sites may be established from a remote site, referred to herein as security center 300. Center 300 is coupled to the printing system site or sites by a communication channel 305 such as a telephone wire. An external data base or memory 308 at security center 300 serves as a storage medium for the users' User Profiles 215 and ID numbers following establishment by the Security administrator. The users individual passwords are stored in the internal data base or memory 56 of the printing system that is used by the user.

In order to gain access to one or more of the printing systems 2, the user enters his user ID number and password using keyboard 64. The user ID number is transmitted via channel 305 to the external data base 308 where a comparison is made with the user ID numbers held in data base 308. Where the user ID number entered at the site by the user matches a number held in data base 308, an authentication signal is sent via channel 305 to the printing system controller section 7, authenticating the user. Concurrently, the password entered by the user is compared with passwords held in the system internal data base and where a match is found, a second authentication signal is generated and sent to controller section 7 of the printing system. On receipt of user authentication, controller section 7 enables the user to access the printing system.

While the invention has been described with reference to the structure disclosed, it is not confined to the details set forth, but is intended to cover such modifications or changes as may come within the scope of the following claims. ##SPC1##