Method for Dot Matrix Printing at Selected Uniform Dot Column Spacing

This invention relates to matrix printers; more particularly it relates to matrix printers in which characters are printed column serially by a columnar array of print wires mounted for movement with a carrier; and specifically to a method for printing dot columns at any selected uniform column spacing.

To print at uniformly spaced positions the prior art, e.g. U.S. Pat. Nos. 3,703,949, 3,905,463 and 4,024,941, among others, have employed high resolution devices in the form of discs or tapes with sensible marks or openings at the desired spacing to control the energization of print wires at the proper time to effect uniformly spaced printing regardless of irregularity in carrier motion. Such high resolution devices have been found to be relatively expensive to manufacture.

In accordance with the invention uniformly spaced printing at selected spacings, regardless of irregular print carrier motion, is achieved with a low resolution pulse source which generates control pulses at intervals corresponding to carrier movement through a given distance greater than the print spacing selected. The control pulses are utilized in conjunction with the known distance between pulses and the selected spacing between print columns to establish, relative to control pulses, all the printing positions, spaced selected distances apart, possible between two control pulses. Thus in each interval between control pulses printing positions are defined. In order that the print wires will be energized at the established print positions, the velocity of the carriage in a preceding interval between control pulses is calculated from the given distance between control pulses, and from the measured time between two preceding control pulses. The velocity so calculated and the distances from a control pulse to established print positions, are utilized to calculate times of energization.

An object of the invention is to provide a control for a matrix printer to enable dot columns to be printed at selected uniformly spaced distances notwithstanding irregular motion of a carrier supporting print elements.

Other objects, features and advantages of the present invention will become known to those skilled in the art from a reading of the following detailed description when taken in conjunction with the accompanying drawing wherein like reference numerals designate like or corresponding parts throughout the several views thereof, and wherein:

FIG. 1 is a block schematic diagram of elements of a control system in accordance with the invention;

FIG. 2 is a diagram illustrating relationships between a low resolution electronically generated grid and an established high resolution printing grid with printing positions uniformly spaced; and

FIG. 3 is a curve showing carriage velocity against position.

Referring now to the drawing there is shown in FIG. 1 a system wherein only those logic elements of a micro computer necessary to an understanding of the invention are depicted. The system includes a carriage 11 carrying a printer 12 comprising a column array of print wires 13 adapted to be driven to print by solenoids 14. As will be appreciated and explained further hereinafter, selectively conditioned print solenoids 14 will be energized by print signals on a line 15. Selected ones of the print solenoids 14 will be conditioned, column serially, over lines 16 from a memory 17 which receives character information of character width Z (FIG. 2) from data lines 18.

A motor 19 is adapted when energized to drive a pulley 21. Trained around pulley 21 and a spaced pulley 22 is a cable 23 connected at opposite ends to the carriage 11 to effect movement of the carriage 11 across a printing line. The motor 19 will be energized to initiate the printing of a line of stored data applied to data lines 18 in response to a start pulse on line 24 to a motor start circuit 25. Motor 19 is preferably a brushless D.C. motor which is caused to be driven by output pulses from commutater logic or pulse generator circuitry 26. The output pulses from generator 26 serve also as control pulses R.sub.1, R.sub.2, R.sub.3, etc. which, with reference to FIG. 2, issue at intervals t.sub.1, t.sub.2, t.sub.3 corresonding to carriage movement through a given fixed distance S. As shown in FIG. 2 the motor is assumed to be up to speed and thus velocity changes from interval to interval are assumed to be negligible. Pulses R.sub.1, R.sub.2, R.sub.3 etc. define a coarse printing grid generally designated by reference numeral 27.

As shown in FIG. 1 a memory 28 stores the fixed distance S between control pulses R.sub.1 and a memory 29 stores the selected dot column spacing, S.sub.z, i.e. the desired distance between print positions. With reference to FIG. 2, the selected spacings S.sub.z define a printing grid 31.

In a logic circuit 32 to which are applied pulses R, the known distance S between pulses R, and the selected distance S.sub.z between dot columns, as stored in memory locations 28 and 29, the printing grid 31 is established with reference to the coarse grid 27. As viewed in FIG. 2, distances S.sub.n i.e. S.sub.10 -S.sub.14 measured from a pulse R.sub.n to all the possible printing positions 33 which can be accomodated between two pulses R.sub.n and R.sub.n +1 are calculated.

Also in a logic circuit 34 the time t.sub.n-1 between a pulse R.sub.n and its preceding pulse R.sub.n-1 is measured and conveyed to a logic circuit 35 to which the known distance S in memory 29 is also supplied, whereby a calculation of the velocity of the carriage 11 in the previous interval is calculated. In a logic circuit 36, the established printing positions S.sub.n i.e. S.sub.10-14 at the output of logic circuit 32, and the carriage velocity V.sub.n-1 calculated in logic circuit 35 over the interval between pulses R.sub.n-1 and R.sub.n, are utilized to calculate the times t.sub.10 -t.sub.14 for application on line 15 to energize the conditioned print solenoids to assure that printing of dot columns constituting a character 37 will occur at the established print positions 33 of printing grid 31.

It is to be noted that known distance S is not a multiple of the distance S.sub.z selected and in memory. Thus the logic circuit 32 is designed to be capable of keeping track of the distance between the last print position in a given interval between pulses, e.g. position 5 in interval t.sub.5, and a following pulse R so that the first print position following a pulse R will always be spaced from the last print position in an earlier interval by the distance S.sub.z. Thus with reference to FIG. 2 the print position 1 following pulse R.sub.6 occurs at a distance S.sub.10 from R.sub.6 which is the sum of a remainder distance d and twice the distance S.sub.z.

With reference to FIG. 3 there is shown a plot of carriage velocity v versus carriage travel s.sub.D divided into equal distances .DELTA.S which contain an integral multiple of the distances S between two pulses R. As carriage velocity following motor energization, before it achieves constant velocity, increases at a particularly high rate, nonuniformly spaced printing columns would result. To avoid this the average speeds V.sub.1, V.sub.2, V.sub.3 in a travel distance .DELTA.S between pulses R.sub.1 and R.sub.4, as calculated in logic circuit 35; are conveyed to a shift register 38 and used in a further logic circuit 39, to which the known distance S is also applied, to carry out a tendency calculation to furnish a correction signal K for application to logic circuit 36 to vary the times of issuance of signals t.sub.10 -t.sub.14 in the next .DELTA.S interval between pulses R.sub.4 and R.sub.7 so that the velocity changes .DELTA.V.sub.u, .DELTA.V.sub.n, .DELTA.V.sub.w between pulses R.sub.4, R.sub.5 -R.sub.5, R.sub.6 -R.sub.6, R.sub.7 are appropriately equalized. Between pulses R.sub.4 and R.sub.7 a new tendency calculation will be carried out and utilized to correct printing times in the travel distance .DELTA.S between pulse R.sub.7 and R.sub.10. Note is made that the changes .DELTA.V shown are exaggerated and are in reality very small. As will be appreciated printing will be delayed until a tendency calculation, to correct times in the next distance .DELTA.S, is accomplished. It should also be understood that the above applies also to carriage decelleration.