GB2072388A - Printing apparatus - Google Patents

Abstract

A daisy wheel printer which accommodates different print wheel fonts has switchable ROMs each containing print position and instruction information for each character on an associated print wheel. The possible number of printing positions is substantially double the number of characters carried on a print wheel <IMAGE>

Description

SPECIFICATION Printing apparatus This invention relates to impact character printers of the kind known as daisy wheel printers.

Known daisy wheel printers are designed to accept substantially one basic type of print wheel character font. This is because the printer, either by a read only memory or by supplementary externally programmed instructions, must provide with each particular character font, instructions as to the hammer intensity, ribbon increment and carriage displacement. The carriage displacement is especially important when proportional spacing is utilized.

One attempted solution which has been tried in the past where it was desired to use print wheels, one of which has an English alphabet and the other an Arabic alphabet, was a double read only memory together with a toggle switch on the frame of the printer which would switch between either of the memories depending on which character font was being used, English or Arabic. Rather than using a switch it was also possible to cut or reconnect a jumper wire or for that matter merely to replace one ROM with another.

In the specific case of the Arabic alphabet the ROM utilized only even printing positions leaving seven possible character positions blank in order to provide for extra space larger than usual for adjacent Arabic characters.

However, all of the foregoing was done on the basis of 96 printing positions, and of course, this is a standard in the industry for daisy wheel printers.

Because of the above 96 character print wheel standard and the associated 96 printing positions provided by the daisy wheel drive system of the printer, print wheel designers have been severely constrained.

in U.S. Patent 4118129 there is described a print wheel system which includes a print wheel drive which is capable of 1 92 printing positions. This 1 92 printing position system has actually been used with a so-called "documentary print wheel" where in order to provide proportional spacing, odd printing positions as well as even were used. However, this documentary printing wheel was never used in a switchable mode. On contrary, the use of the documentary system severely restricted the use of any other wheel on this particular printer.

As is apparent from the foregoing, the capability of a daisy wheel print system where the print wheel may be driven to substantially double the number of printing positions as the typical maximum number of characters on the print wheel has never been fully utilized.

It is, therefore, an object of the present invention to provide an improved daisy wheel printer which accommodates different type wheel fonts.

It is another object of the invention to provide a printer as above where the available print positions are fully utilized in order to enhance the flexibility of the print wheel designer.

It is yet another object of the invention to provide a printer as above where print wheels with different type fonts can easily be changed without requiring extensive and expensive software reprogramming in order to define new character locations, hammer intensities and degrees of ribbon advancement.

According to the invention in its broadest aspect, there is provided a daisy wheel printer where the maximum number of characters on the wheel is limited by mechanical constraints but where the daisy print wheel drive system, which intermittently moves the print wheel to printing positions, is capable of substantially double the number of printing positions, compared to the maximum number of characters, the printer comprising a plurality of selectively replaceable print wheels each with a different type font, a plurality of read only memories (ROMs) is uniquely associated with each one of the print wheels for storing printing position decoding information for printing selected characters and for storing printing instructions associated with each of such characters, at least some of the printing positions which are utilized in one ROM being different from those utilized in another ROM so that substantially more printing positions than the maximum number is utilized, and switching means for enabling a selected one of the ROF9ns which corresponds to the associated print wheel placed in the printer.

Various embodiments od the invention will now be described with reference to the ac companying drawings in which: Figure 1 is a block diagram of a printer system embodying the present invention; Figure 2 is a table useful in understanding the configuration of Fig. 1; Figure 3 is a diagrammatic view of a docu mentary print wheel which is old per se but can effectively be used in the context of the present invention; Figure 4 is a table useful in understanding the documentary print wheel of Fig. 3; Figure 5 is a diagrammatic view of a "Courier" print wheel which is old per se but is useful in understanding the effectiveness of the present invention; Figure 6 is a block diagram of the logic circuitry embodying the present invention; and Figure 7 is a flow chart which is helpful in explaining the operation of Fig. 6.

Fig. 1 in many respects illustrates a typical daisy wheel printer logic system as disclosed in U.S. Patent Specification No. 4118129 where a data source 10 interfaces with a character register 11 to provide an ASCII character code output on line 1 2 which in turn is connected to a ROM 1 3. Portion 1 3a decodes the ASCII characters into a relative print wheel location or position. For example, assuming the print wheel has 96 characters, which is the normal maximum number of characters on such wheel as discussed above, ROM 1 3a would decode the ASCII character to tell the print wheel to turn to, say, its thirteenth character.

In addition, the ROM contains a portion 1 3b which contains associated information related to each specific character stored in the ROM such as ribbon increment, how far the ribbon should be advanced for each character, and also the proper hammer intensity for that character. In addition, carriage displacement which may be utilized in the case of proportional spacing, may be stored in the ROM instead of ribbon increment. Then the ribbon increment can be computed from the carriage displacement information. However, in the present invention, carriage displacement is preferably provided by the external program.

The output of the ROM on line 14 is connected to the printer logic 1 5.

The table of Fig. 2 indicates the contents of ROM 1 3 where the bytes contain eight bits. A typical eight bit print wheel position which is related to a specific ASCII character is illustrated. Since there are 1 92 possible printing positions eight bits must be used. This is opposed to the normal seven bits in the 96 position printer. In addition, an associated print instruction would include three bits for hammer intensity, while the other four bits are used in the preferred embodiment for ribbon incrementing but could theoretically be used for carriage displacement.

The actual information of the table of Fig. 2 could include print wheel position information such as for the wheel of Fig. 3 which illustrates a fragmentary documentary print wheel where the letters and their relative character position (relative to the 1 92 possible) are illustrated. Fig. 4 shows the proportional spacing units relating to the size of the various characters. Such proportional spacing units are greater in number for D, B, O, E, T as reflected in Fig. 3 where the spokes are further apart. From a design standpoint they are made further apart by utilizing both even and odd print positions (with respect to the 192). Fig. 5 is a more typical print wheel termed "Courier" which utilizes just the even positions with the letters shown.

The block diagram of Fig. 6 illustrates the concept of the present invention. Rather than the single ROM 1 3 shown in Fig. 1 and as also illustrated in Fig. 6 there is a special character ROM 1 6. A central processing unit 1 8 is connected via a data bus 1 9 to the standard ROM and to the special character ROM. Input/output ports are provided. A switch 22 is provided on the feature panel 23 of the printer which may be actuated between its standard print wheel position and special print wheel position.When actuated it causes CPU 1 8 by means of data bus 1 9 to address the special character ROM 1 6 via address bus 24 and read the character information into the CPU instead of reading the character information from the standard character table in ROM 1 3. It should be mentioned parenthetically that standard ROM 1 3 also includes a program storage portion for overall operation of the printer. Thus in summary, the special character ROM 1 6 is actuated by the user activating switch 22 when they have placed the special character print wheel in the printer.

Fig. 7 illustrates a flow chart illustrating the operation of the activation of switch 22. Such switch is shown in the operational block 22' where when it is "off" a standard character table is looked up and when "on" the special character table is enabled.

Switch 22 could alternatively, of course, be activated by an associated computer.

To summarize the present invention, it is useful to refer to the documentary print wheel of Fig. 3 and the standard print wheel of Fig.

5. When a change is made from, for example, the standard print wheel to the documentary one a switch need merely be actuated rather than extensive reprogramming as needed in the prior art. Moreover, since the documentary print wheel contains odd printing positions as well as even, the full 1 92 printing position capacity of the printer can be utilized giving the print wheel designer greater flexibility. In general the ability to use both odd and even printing positions allows the designer to maximize the total number of characters on a print wheel at the same time maintaining even weight distribution. Print wheel design becomes especially difficult when standard alpha-numeric characters are mixed with special symbols. The technique of the present invention is of significant help in solving this design problem.

Claims (4)

1. A daisy wheel type printer where the maximum number of characters on the wheel is limited by mechanical constraints but where the daisy print wheel drive system, which intermittently moves the print wheel to printing positions, is capable of substantially double the number of printing positions compared to the maximum number of characters, said printer comprising a plurality of selectively replaceable print wheels each with a different type font, a plurality of read only memories (ROMs) each uniquely associated with one of the print wheels for storing printing position decoding information for printing selected characters and for storing printing instructions associated with each of such characters at least some of the printing positions which are utilized in one ROM being different from those utilized in another ROM so that substantially more printing positions than the maximum number is utilized, and switching means for enabling a selected one of the ROMs which corresponds to the associated print wheel placed in the printer.

2. A printer as claimed in Claim 1 which includes a feature panel and where the switching means includes a mechanical switch mounted on the feature panel.

3. A printer as claimed in Claim 1 where the printing instructions include print hammer intensity and carriage or ribbon increment information.

4. A daisy wheel printer substantially as described with reference to Figs. 6 and 7 of the accompanying drawings.