More particularly, the invention relates to an electronic device for controlling the positioning and activation of a print-head of a dot matrix printer, of the ink jet type for example, or of a sensor in equipment for the scanning of text and/or images.

Background Art Dot printing, for example printing with ink jet printers, is effected by making a print-head translate transversally to a medium, generally paper, and selectively exciting a plurality of nozzles, placed orthogonally to the direction of movement of the head, for printing on the paper medium or the sheet through the emission of ink.

The times at which to excite the nozzles of the head are calculated by taking as the reference in cyclical fashion an interval of space or step P which, in cases where the head is moved by a step motor, corresponds to one step of the motor and, where the head is controlled by an optical or magnetic encoder, corresponds to the minimum interval detected by the encoder.

To effect printing, each step P is divided into a plurality of elementary steps P/n and the excitation of the nozzles

of the head is effected upon the completion of each elementary step P/n.

The elementary step P/n is calculated by taking as the reference the interval Tp, corresponding to the time taken by the print-head to travel the step P, and dividing the interval Tp by the number n.

In the known art, the excitation of the nozzles is performed at the time Tp/n and subsequently at each successive elementary step P/n by repeatedly adding Tp/n until the reference period Tp is reached.

The number n of excitations of the print-head in the step P is strictly related to the printing resolution which is calculated in"points per inch" (ppi) and corresponds to the number of excitations of the print-head per unit length of one inch or, in metric terms, 25.4 mm; the step P is in actual fact a sub-multiple of the unit length and the division of the step P into elementary steps P/n therefore gives the printing resolution.

Naturally the printing resolution in some printers can be selected from a range of discrete values between a minimum and a maximum printing resolution, for example 600 ppi or 1200 ppi.

A first problem in the known art comes from the method of calculating the value Tp/n corresponding to the elementary step P/n.

In actual fact, as the division of the value Tp by the number n generally gives a value having an integral part ti and a decimal part tr corresponding to the remainder, the result is that, it being impossible in a binary system such as an electronic printer to take into account the time tr, the latter is neglected and only the value ti which corresponds to the integral part of Tp/n is used to excite the print nozzles.

A second problem in the known art comes from the fact that, on adding instant by instant the value ti and exciting the print nozzles in correspondence with the instants of time thus calculated, it occurs that the error due to tr continues to rise until a maximum of n times tr, a value which in some cases may even correspond to a few elementary printing steps P/n.

From the practical viewpoint, and assuming that ti is approximated up or down to the theoretical value TP/n, dot printing is of varying intensity in correspondence with the extremities of each step P.

A further technical problem, linked to the previous one, consists of the fact that, as n and accordingly the corresponding printing resolution increase, the error due to tr also increases, with the result that the uniformity of printing, and therefore the printing quality, worsens, exactly under the conditions where it should be maximal when the printing resolution is maximal.

Disclosure of the Invention The object of this invention is to resolve the range of technical problems described. above and which may be resumed as a lack of uniformity observed in particular in dot matrix printers, but which is also present in scanning equipment and, in general, in text and/or image processing equipment using a movable element to be positioned and activated with precision in an interval of space P.

This technical problem is solved by the electronic device for the control of moving elements in text and/or image processing equipment characterised by control means associated with the timing means and with the activating means and suitable for controlling the activating means by way of a predefined plurality of numerical values, selectively associable with the time interval Tp, whereby the activation of the moving element is effected in the

interval of space P at n instants of time uniformly distributed inside the time interval Tp.

In accordance with a further characteristic of this invention, a method is also described for the control of moving elements in text and/or image processing equipment characterised by the technique of associating in the time interval Tp a plurality of predefined numerical values such that the combination of the time interval Tp with the predefined numerical values guarantees a uniform spacing in the interval of space P.

Brief Description of Drawings This and other characteristics of the present invention will become apparent from the following description of a preferred embodiment, provided by way of a non-limiting example and with reference to the accompanying drawings, wherein: Fig. 1 represents a general block diagram of the device according to the invention; and Fig. 2 represents one embodiment of the device of Fig. 1.

Best mode for Carrying Out the Invention With reference to Fig. 1 the electronic device for the control of moving elements in text and/or image processing equipment (device) 10 comprises an encoder circuit 11, of known type, suitable for detecting, by means of a sensor of, for example, the optical or magnetic type, unitary distances or steps P travelled by a movable element, for example a print-head or movable head 30, and for outputting predefined electrical signal levels in correspondence with the beginning and end of each step P.

The device 10 also comprises a shunt circuit (shunt) 12 and a timer circuit 14, of known type, cascade connected to the encoder 11 and respectively suitable, the shunt 12 for outputting a pulse in correspondence with the changes of level of the electrical signal coming from the encoder 11,

and the timer 14, for measuring the time or period Tp between two like pulses generated by the shunt 12; the period Tp therefore corresponds to the time taken by the head 30 to travel the step P.

The device 10 also comprises a register (Tp register) 15, connected in a known way to the output of the timer 14 and to the output of the shunt 12 and suitable for cyclically storing the period Tp.

Finally the device 10 comprises an optimising logic circuit 20 which, in the most general embodiment, comprises a divider circuit (divider) 21, an equals comparator circuit (comparator) 22, having two inputs and one output, and a plurality of registers (values register) 25.

The values register 25 is suitable for storing, in a like number of registers, numerical values predefined in the stage of designing the device 10.

The number of registers depends on the printing resolution and is equal to or slightly less than the number of parts into which the period Tp is subdivided.

The known type values register 25 has an input connected to the output of the comparator 22 and an output connected to a first input of the divider 21.

The divider 21, of known type, has a second input connected to the output of the Tp register 15 and an output connected to the first input of the comparator 22 and is suitable for dividing selectively and in sequence the period Tp by the value contained in each of the registers of the values register 25.

The comparator 22, of known type, has its second input connected to the output of the timer 14 and its output connected to the print-head 30 and to the values register 25; the comparator 22 is suitable for generating an electrical signal output when the configurations of the signals on the two inputs are identical.

The signal output by the comparator 22 is suitable both for causing the excitation of the print-head 30, and for commanding the values register 25 to select a new register for calculating the division of the time Tp.

The operation of the device 10 described up to now is as follows.

When the encoder 11 detects the start of a printing step P, the shunt 12 transmits the timer 14 a first pulse which enables the timer 14 to start the counting of the period Tp until the time at which the shunt 12 transmits a second similar pulse corresponding to the end of the step P.

The second pulse is interpreted by the timer 14 as indicative of the end of the step P and enables the register Tp 15 to store the period Tp and the timer 14 to resume the counting of a new period Tp.

The divider 21 divides the period Tp stored in the register Tp 15 by the first value stored in the values register 25 and presents the configuration to the first input of the comparator 22.

The timer 14 presents the configuration corresponding to the current count of the period Tp to the second input of the comparator 22; this count lets the comparator 22 generate an electric signal output when the signals presented by the timer 14 and the divider 21 are of identical configurations.

The signal output by the comparator 22 is transmitted to the print-head 30 to activate the printing of points and to the values register 25 so that it presents the divider 21 with the next value in sequence.

The divider 21 effects a new division of the time period Tp and presents this value to the comparator 22 which, under the same conditions as described above, generates a new signal for the activation of printing and so on until the end of the period Tp.

By means of the device 10, it is therefore possible to activate the movable head 30 uniformly in the step P, the print pulses being generated by adding to the initial time, on each occasion, a time calculated in absolute fashion on the basis of the numerical values predefined in relation to the desired resolution.

In accordance with a further, optimised embodiment, in particular, in the case where the step P has to be divided into elementary steps corresponding to values having a power of 2, for example into 8 elementary steps or into sub-multiple parts of this value, the optimising logic circuit 20 may be built in the following way.

In place of the values register 25 and the divider 21, the optimising circuit 20 comprises a first and a second selector circuit (multiplexer), 26a and 26b, (Fig. 2) an adding circuit (adder) 27 and an 8's counter 28, all of known type.

Each of the two multiplexers, 26a and 26b, is connected to the input of the register Tp 15 and to the output of the adder 27 and is controlled by the counter 28 through a pair of control connections, 29a and 29b respectively, in a way described below in detail.

Each of the multiplexers 26a and 26b, of known type, is suitable for outputting to the adder 27 the contents of the register Tp 15"split"by the shifting of a number of bits that varies from 0 to numerous bits.

In particular, each of the two multiplexers 26a or 26b is suitable for presenting to the adder 27: - the period Tp via the connection 15a; - the period Tp/8 via the connection 15b which effects a shift of 3 bits, which, as is known, corresponds to a division by 8 of the period Tp ;

- the period Tp/4 via the connection 15c which effects a shift of 2 bits, corresponding to the division by 4 of the period Tp ; - the period Tp/2 via the connection 15d which effects a shift of 1 bit corresponding to the division by 2 of the period Tp ; and - the value zero (0), via the connection 15e.

The adder 27 is suitable for effecting the algebraic sum, including the sign, of the values selectively presented by the multiplexers 26a and 26b and for generating this value on its output.

The adder 27 has its output connected to the first input of the comparator 22 and is controlled, with regard to the sign of the adding operations, by the counter 28 by means of a control connection 29c.

The counter 28 has its input connected to the output of the comparator 22 and is programmed to control, by way of the control connections, 29a and 29b, each of the two multiplexers 26a and 26b to select, for each elementary step P/n, a given value, derived from the contents of the register Tp 15, to be presented at the inputs of the adder 27, as will be described in detail later.

The operation of the device in this particular embodiment is as follows.

Assuming, for instance, that each printing step P corresponds to a fraction equal to 1/150 of an inch (1 inch = 25. 4 mm), and assuming that it is desired to print with a printing resolution of 1200 points per inch (ppi), that is to say equal to 1/8 of the step P, the shunt 12 transmits the timer 14 a first pulse to start the count of the period Tp and a second pulse in correspondence with the completion of the step P of 1/150 of an inch.

The period Tp thus measured is stored in the register Tp 15 and the counter 28 controls the multiplexers 26a and 26b

with the control connections 29a and 29b in such a way that the value Tp/8 is associated with the first input of the adder 27 and the value 0 with the second input of the adder 27. Once the print pulse has been generated, in the way already described, the counter 28 in the same way associates the value Tp/4 and the value 0 and presents them to the adder 27. Subsequently the counter 28 associates, in the order, the values Tp/2 and Tp/8 and controls the adder 27 with the control connection 29c so that the difference is obtained between the two values (control by subtraction), then the values Tp/2 and 0; then again Tp/2 and TP/8, and then Tp and Tp/4 and effects the control by subtraction, then Tp and Tp/8 and effects once again the control by subtraction.

By way of this technique, the excitation of the print-head is again effected on each occasion on the basis of the values calculated by taking as the reference the period Tp and adding the value calculated to the step P start time, without incrementing an approximated value for each elementary step P/n.

Naturally by using a part of the connections from 15a to 15e and by suitably programming the counter 28, a printing resolution of 600 or 300 ppi may be obtained.

It will also be obvious that, for example, to obtain a resolution of 2400 ppi all that is required is to arrange for a connection to the multiplexers 26a and 26b that effects a shift of 4 bits which, as is known, corresponds to a division by 16 of the period Tp, and so on for proportionally larger resolutions.

Naturally, the embodiments do not change in the case of equipment effecting the scanning by points of documents comprising texts and/or images, since this type of equipment generally also comprises a movable element that

has to be activated uniformly in predefined intervals of space P.

Changes may be made to the dimensions, shapes, materials, components, circuitry components, connections and contacts, as also to the circuitry and construction details illustrated, and to the method of operation without departing from the scope of the invention.