DE2806360A1 - PROCEDURE AND CIRCUIT FOR IMPROVING PRINT QUALITY IN INKJET PRINTERS - Google Patents

Description

SA 976 017/022

Applicant: International Business Machines

j Corporation, Armonk, N.Y. 10504

I ki / bm

Method and circuit for improving print quality in inkjet printers

The invention relates to a type of method specified in the preamble of claim 1 for the ongoing determination of the Default time in inkjet printers and a circuit for carrying out the method. The invention is particularly for Inkjet printers intended in which greater printing speed is achieved by the displacement between Recording medium and printing unit with variable, e.g. non-linear Speed takes place, and being electronic circuitry for correcting the trajectories of the ink droplets are provided so that they impinge in the intended positions on the paper. The invention can also can be used for other variable-speed devices that require the correction of a similar Operation arrives.

JThe technology of the inkjet printer has now reached a level

at which under precisely controlled conditions ! excellent print results can be achieved. The development therefore tends to maintain the high print quality ! Simultaneous increase in printing speed.

jSupercharger printers for on-the-fly printing are available for very large ones ! Speeds, however, the print quality can in most

Today one is no longer far removed from printing units for large print volumes of high quality, whereby the attention j The focus is particularly on the relative displacement of the recording medium used by the printing unit

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Ι -δ

supporting beam is traversed.

Conventional inkjet printers that use high

Working at speed, the moving parts of the carrier are subjected to a great deal of stress, which can lead to undesirable effects Changes in the relative speed of the inkjet printing unit running back and forth over the recording medium to lead. U.S. Patents 3,181,403, 3,539,895, 3,657,627, and 3,940,675 are machine tool controls described in which by means of electronic digital circuits, the pulse generators, digital registers and comparator circuits on v / iron, the relative movements of one or two machine elements are tracked and the speed of movement of one is controlled in such a way that it leads to the arrives at a predetermined time at a predetermined location. The! Calculation of the default time and the interpolation of the current Position can not be found in these patents.

U.S. Patent 3,912,913 relates to a computer control wherein a desired condition is represented by a digital number. It becomes a digital input variable which represents a change to be carried out within a time predetermined by the programming is. The change is subtracted from the first digital number! And the difference compared to the number that j corresponds to the current condition, from which a control variable j is derived. The interpolation of the edge steepness that corresponds to the digital number which represents the specified change! is not difficult for the person skilled in the art; but the ! By definition, calculation of the standard time is missing in this patent specification.

U.S. Patent 3,938,163 relates to the deflection of drops of ink directed onto a recording medium and indicates the correction of the skew in the vertical direction caused by the horizontal displacement of the carrier occurs during the vertical excursion of the ink jet over a plurality of drop positions. This skewing

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is supported by an additional set of electrostatic baffles achieved, which are arranged at a suitable angle. A gradual correction is not sought and the default time does not matter in this context.

U.S. Patent 3,898,671 relates to a conventional constant speed printer with no compensation for

the changes in the carrier speed, although a compensation ^! sation circuit is provided, which ensures that no unintentional change in the carrier speed can occur at the time of printing.

U.S. Patent 3,911,818 is believed to be closest to the invention and relates to a computer controlled ink jet printer for aligning a loosely inserted sheet of paper, e.g. by hand, to a predetermined position or within a given margin with respect to this position. Except for clock signals that indicate the speed of the sheet of paper a "top margin" signal is generated to which the printing is aligned. A requirement is not mentioned, nor does the interpolation of the current carrier position and the corresponding clock signals.

It is the object of the invention specified in claim 1, that of inkjet printers with variable relative speed between printing unit and recording medium as a result of the dependence of the trajectory of the ink droplets on the Lateral speed of the nozzle to avoid resulting uneven pressure.

A circuit designed according to the invention for measuring and calculating the instantaneous speed of the printing unit contains at least one phase stabilized loop, a phase comparator / detector and a voltage controlled Includes square wave generator and a frequency divider. Position information is fed to the loop, and to it analog output signal (speed) is via a

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Knalog / digital converter and a register, your digital output signal (Position) fed via counter to an arithmetic unit in which the default time is calculated.

The invention differs from the device according to the , last described USA patent in that the carrier of the inkjet printer in accordance with a Speed / position profile is transported, which is used for acceleration and deceleration for the moving parts reasonable burden with favorable work performance results. For each position at which a picture element is to be generated, a position pulse is generated that is used for control. Furthermore, between every two consecutive image ^ element impulses generate an interpolation quantity which ent- ■ (neither has an analog form nor occurs as a predetermined number of i interpolation pulses. Analog quantities converted into digital impulses. The default is calculated in the form of interpolation pulses and to the picture element pulses that correspond to the current position count! A comparison circuit compares this count

I;

with the count value for the print position of the next pixel, and if there is a match, the Inkjet printer printed a pixel.

According to the invention, a position scanner is provided which generates electrical signals, or at least one signal transition for each pixel position along a print line which ink droplets are to be deposited as dots i (or at which ink droplets are to be deflected in such a way that they create spaces, i.e. the opposite of pixels). The position signals, or their transitions, are called addresses used for the pixel positions and also as trigger pulses for the generation of interpolation transitions between) the position pulses and based on the time when the last position transition occurred. This interpolation

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! transitions are spaced apart substantially of the same order of magnitude as the nominal error, the; ivon due to the speed variation of the pressure along the line [! progressive printing carrier.

If the other parameters kept within the desired or by ^1, the design of the machine required tolerances
;, the change in the picture element positioning is reduced to: 'a corresponding tolerance range in which the
'Ink drops for imprinting the data on the desired
'Position can be selected on the basis of the algebraic sum of the position of: the carrier and the specification, from which the ' ,! Address of the desired print position results. The address of the \ print position is generated with the speed that the
; Takes support at a given pixel position and projected onto J ■ the next pixel position wished by the overall \ pixel print position to the calculated target
away. ^:

i;

| The address of the desired picture element position is shown under
Control of the processor is entered in a register, the calculated position is also entered in a second register under control of the processor and the contents
each register compared in a comparator. The content of the
; second register is updated each time the carrier
a printing position happened. If the contents of the two
Registers are identical, the printing unit sets a drop
on the recording medium or this is converted into a
'. catching device deflected.

: i

It can be advantageous to print in both directions of movement of the medium relative to the recording medium. In a ' : Circuit that scans the carrier direction becomes a bista- j tical signal level is generated, which is fed to the arithmetic unitJ to add the specification to the position address or to add it to! subtract. I.

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Details of the invention are described below with reference to exemplary embodiments illustrated in the drawings. Show it:

1 is a speed diagram of a conventional printer;

Figs. 2 speed diagrams of exemplary embodiments and 3 games of the invention,

Figs. 4 functional diagrams of the electronic switching to 8 circuits according to the invention for the calculation of the Specification and for the control of the inkjet printer.

A paper carrier is arranged in a housing, with the paper moving by a preselected one in each case in the longitudinal direction Number of pixels transported. A stepper motor is preferably used for this purpose. In the case is a carrier for an inkjet printer is arranged, which is laterally guided back and forth over the paper. Apparently The inkjet printing unit can also be arranged in a stationary manner and the recording medium on a paper trolley be transported both laterally and longitudinally, but in the preferred embodiment it is assumed that that the inkjet printing mechanism on a laterally displaceable Carrier is arranged. The lateral transport speed of the inkjet printer is 254 cm / s, ! the distance between its nozzle and the recording medium is 1.27 cm. The ink is ejected from the nozzle in a continuous stream of drops at a speed of 1270 cm / s. Printing takes place by selective deflection of the 'drops away from the recording medium into a collecting device, ! as well as by depositing the drops on the paper in accordance with the character information. For each to be recorded

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In the image point, the time is provided for four drops, with three drops being printed and the time for the fourth drop being used to actuate the deflection circuit. Other times can of course be selected for other printing units or other applications. Typically, an ink flow of around 380 drops per cm will give the desired resolution. In the embodiment described, the resolution is 27.25 pixels per cm. The mentioned distance and the mentioned speed result in a time interval of 41.7 Jas between the drops, corresponding to a pulse repetition frequency of 12.5 kHz. The printing unit is equipped with a position scanner, which can be an opto-electrical device, for example, which delivers a pulse sequence with 95 transitions per cm, which corresponds to the positions at which the drops are to be deposited. The transport direction of the carrier in relation to the recording medium is determined by a further scanning device.

1 is a graphic representation of the printing cycle of a conventional inkjet printer, the printing mechanism of which crosses the recording medium once per cycle. At t _Q , the carrier begins to cross the record carrier and is accelerated until time t ₁ , where it

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reached its full speed. The time interval between t and t " , referred to as t, serves to calm the system, whereupon in the time between t and t, ie during the interval T, printing

can be done at constant speed, usually with some Difficulties can be maintained, which is necessary for precise placement of the impression, since the motor has a fixed default time conditional. Usually, printing is stopped shortly before the end of the constant speed range at time t to

3 ι

ensure linear operation. Between t. and t the carrier is decelerated and t, - its direction of movement is reversed for the following print cycle. . At time t _fi , the acceleration then takes place in the opposite direction. The time T required for reversing

ta

So the delay time T speaks from t to t and a subsequent one Acceleration time T from t to t. As you can see, this is the reversal time

3. J D

relatively long, which reduces the printing speed accordingly.

With the aid of the invention it is possible to precisely determine the printing position both in the case of printers with a constant carrier speed and also in the case of printers with a non-constant speed. Printers with non-constant speed are also ready to print during at least parts of the acceleration and deceleration process of a print cycle, and in the case of printers with constant speed, the requirements for strict adherence to constant speed are very liberal, which means that the particularly high costs associated with maintaining the exact constant speed are very liberal are to be avoided. A print position clock is connected to the electronic circuit, which determines the actual speed of the carrier at the location of the last print, as well as the specification _/ which is required for the optimal positioning at the next print location. The speed profile according to Fig.l can be used to advantage with the present invention, but other profiles are preferred because of its sharp kinks.

2 shows a graphic representation of a speed profile for a printing cycle of a printer with a non-constant speed, with which a significantly higher printing speed is possible than with the flatter profile according to Fig.l. The curve according to Fig.2 consists essentially of an acceleration phase, which extends from time t to time t, which is followed by a Delay phase from t to t ,, and where the printing time T from t to

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t is sufficient with a relatively short reversal time T, which is the same

J-O - L ti

the sum of T from t "to t, and T, from t to t for each Halba" Oil d 13 14

cycle.

A speed profile according to FIG. 3 is preferably used in connection with the present invention. The acceleration and Delay phases from t to t or t to t are shorter and relatively constant, the phase of constant speed extends from t to t ",, whereby, however, unintentional changes in speed, as in any other part of the cycle, 'relatively harmless are.

For example, but not by way of limitation, a stepper motor can be used because its torque characteristics make it appear particularly suitable for this application. The torque of a stepper motor falls exponentially with the speed, as can be seen from FIG. During the acceleration phase T and during the pressure phase T

a ρ

is the speed at a given moment:

v = v _f (le ^{t / r} ), (1)

where ν is the final speed, t is the time and τ is the transport time constant. The deceleration of the stepper motor is approximate linear, so that during the deceleration phase T

v = -at, (2)

where a is the acceleration constant:

According to the invention, the transport time constant T becomes equal to the delay time T made to eliminate any tendency for discontinuity at d

to eliminate zero speed. Preferably the reverse

time (T + T
ac

makes, where

time (T + T) equal to the switching time of the recording medium

α. Cl

T / T, = 1.2 (3)

a Q

The distance traveled during acceleration and deceleration are the same, and if the line length is constant, the return time can begin at the speed

v = 0.7v _f , (4)

and there is no waiting time for either accelerating or decelerating the settling is required. It will be easy for a person skilled in the art to apply the statements made above to lines of different lengths.

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4 shows a functional diagram of the circuit according to the invention for depositing a drop of liquid for pressure or for deflecting the drop into a catcher corresponding to the character information, for a Printing unit that is not necessarily guided over the recording medium at a constant speed. The circuit is for measuring the Speed and to calculate the default time for the Output of the print signal to the control circuits of the inkjet printer. A position encoder 50 supplies a sequence of at its output 52 Impulses that result in the passing of the print carrier on successive Print positions are assigned along a print line. A second Encoder 54 delivers a pulse train that determines the carrier position as a function of the speed and direction of rotation of the continuously revolving Stepper motor is assigned, which drives the carrier. This pulse sequence is available at output 56. It controls in a known way the stepper motor. The encoder 54 serves as a source of pulses with a bandwidth (up to 24 picture elements) which is sufficient for the set time to bring the frequency at which the phase between the transitions on which the trigger signal is based can be compared with the output signal of the interpolation circuits to be described. A The input of a phase comparator 58 is connected to the output 52 of the position encoder 50 connected, while another input in a cascade connection to the output of a voltage-controlled square wave generator 64 is connected, so that together with an amplifier and compensation circuit 62, a phase-stabilized loop 60 is formed is. The loop 60 operates as an interpolation circuit and is connected to an analog phase comparator 68, which is part of another phase stabilized loop 70, which has a second amplifier and. Compensation circuit 72, a voltage controlled square wave generator 74 and a frequency divider 76 belong. The direction signals are applied to the inputs of the phase comparator 68. The loop 60 acts as an analog tachometer and is used to control the phase position at which the default time loop 70 is synchronized with the encoder 54. In In this arrangement, the encoder 54 provides at its output 56 pulses which indicate the direction of movement of the carrier, as well as in time and phase pulse transitions occurring over a range of 4ir, the coincidence at the phase comparator 68 results in the uncorrected default time. The analog voltage at the input de, Rochteck wave generator 64 is the interpolation,

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which has to be added algebraically to the default time to produce the square wave generator 74 at the right time to affect the ink drop deflection. When the speed increases, she hurries Phase of the output pulse of the square wave generator 74 at the output 80 before, and the loop gain is readjusted so that the lead just coincides with the target time. The distance of the pulses generated by the encoder 54 is necessarily a multiple η or a part l / n of the pixel spacings.

A similar arrangement is shown in Figure 5. The speedometer loop 60 is connected to one input of a differential amplifier 82. A direction scanner 84 is used to add the specified time to the current position in accordance with the direction of movement of the carrier or subtract from it. The two output signals of the differential amplifier 82 are fed to a tapped winding 86, 88 on a magnetic core 90 which is part of an electromechanical arrangement of which only the essential parts are shown. The differential excitation the winding 86, 88 deflects a feromagneti see armature 92 from an intermediate position in which it is held by conventional means such as a pair of lightweight springs (not shown). The anchor 92 carries a mask 94 which has an opening 96. This electromechanical arrangement is mounted on a printing unit carrier, which is indicated by the dashed rectangle 100. The magnetic core 90 and the winding 86, 88 are fixedly arranged with respect to the carrier 100, while the armature 92 with the mask 94 is freely movable in the arrangement by -0.038 mm. The carrier 100 is operated by a continuously Stepper motor driven transversely to the paper feed direction. The paper is held in a conventional paper guide, which is not is shown. A scale 110 is attached to the machine frame, which works together with optical scanning means arranged on the carrier 100, which are part of the position encoder 50. The light / dark transitions on the scale 110 there are exactly one pixel position from one another away, namely 0.21 mm. An optoelectronic transducer, which is indicated by a rectangle 98, generates a when the scale 110 is scanned Pulse sequence that occurs at the output terminals 80 and, as previously described, is used to trigger the printing process. The movement of the mask 94 leaves advance the phase of the position dicreres, as already described above Embodiment was the case, and a readjustment of the

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Reinforcement leads to a match between the phase lead and the required default time for the ink drops to charge.

6 shows a further embodiment of a control circuit. Again an analog tachometer is used, which has a phase-stabilized oscillator. This tachometer loop 220 includes a Phase comparator 222, an amplifier and compensation circuit 224, a voltage controlled square wave generator 226 and a frequency divider 228. A train of electrical pulses indicative of the current position of the carrier is applied to the input terminals 230 of the phase comparator 222 supplied. The 2 frequency divider 228 is part of the tachometer loop 220 and increases its resolution by a factor of 2. An upward and downward counting counter 232 (M-Bit) is used to determine the absolute carrier position with respect to a fixed reference, with the direction of movement of the carrier in the form of a voltage is applied to the input terminals 234, which determines the counting direction up or down. That The analog output signal of the loop 220 runs to an analog / digital converter 236, which generates a digital default value, which always then is transferred to a Q-bit register 238 when on terminals 230 Impulse occurs which indicates the new position of the carrier 100 with respect to the paper. One connected to the square wave generator 226 Counter 240 (N-bit) and counter 232 supply carrier position data to Arithmetic unit 242, which also receives the direction information, and the default value from register 238 is added to or from the position specification subtracted, depending on the result of the interpolation. For printing in only one direction, the output of the interpolation loop 220 is used fed directly to the arithmetic unit 242, it being possible to dispense with the counter 240. Between the arithmetic unit 242 and the output terminals 280 which trigger pulse for the inkjet printer occurs, a comparator 244 (M-bit) is arranged in this embodiment, which blocks the printing process until a first printing position based on data from the central unit via input 248 into a Counter 246 is loaded.

Fig.7 is a functional diagram of a circuit used in exchange can be used for the just described analog-to-digital converter 236 and register 238 (although not limited to this use), which is desirable because of the cost of the analog / digital converter. The circuit shown in Fig. 7 calculates a digital speed

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worth directly from time measurements. For a split operation, a iterative addition (or subtraction) process is used. The circuit comprises an accumulator 260 which has an N-bit adder 262 and a Sum register 266, which is connected to a data selector 268. The accumulator 260 has a capacity of 2 -2. The time interval between two position pulses that occur at the input 254 ', a square wave generator 270 and a counter 272 measured. The measured value is meanwhile stored in a register 274 saved. The pulse repetition frequency of the generator is selected according to the desired resolution and should preferably be quartz stabilized to guarantee the required frequency constancy. The quartz frequency can for example be 5 MHz.

A switching mechanism 276, which is connected to the generator 270, to the input 254 ' and is connected to the carry output of the adding unit 262, has an output data line which is connected to an adding cycle counter 278 is, as well as control lines which lead to the sum register 266 and to a count register 238 '. From the contents of the accumulator 260 a constant distance d is subtracted by dividing the inverse of the number d is added.

The value

y = 2 ^{n + 1} -d (5)

is fed to the adder 262 as ADDEND A, while the previously im Sum register 266 stored time measurement value T is supplied as ADDEND B will. The sum y + T then appears at the output of the adder, which is called up by the data selector 268 under the control of the switching unit 276 and is transferred to the sum register 266. When register 266 is loaded, ADDEND A assumes the value y + T and the value y + 2T appears at the input of the register 266. Each supply of a default pulse to the sum register 266 leads to an adding cycle, and after m-1 such Accumulator 260 overflows adding cycles. This results in

y ₊ mT = 2 ^{m + 1,.} (6)

where m is the value of the speed sought. This value appears at the output of the adder cycle counter 278 and is transferred 238 ^thousand in the count register.

Another embodiment of the invention is shown in Figure 8, wherein a phase stabilized oscillator includes a phase detector 222, a voltage controlled square wave generator 326 and a frequency divider

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328 includes. For the resolution required in this application, a resolution factor of 8 is used. To change the resolution you can either the frequency divider 328 can be changed, or an additional frequency divider 329 can be switched on. The loop 320 is used to track the position of the wearer. When the carrier is transported along a print line, a sequence of position pulses is generated which enter the loop 320 via the input 330 and the phase detector 322. Input 334 is given a direction of movement voltage characterizing the carrier supplied. The frequency divider

329 and a 12-bit counter 336, which is connected to the square wave generator 326 is connected, serve as position counter, with the frequency divider

329, as an interpolation circuit, the pixel resolution between the print positions divides into eight parts. Since printing is in both directions, the voltage characterizing the transport direction at the input 334 in the frequency divider 329 and the counter 336 as well as in the Arithmetic unit 342 fed in, the arithmetic unit also receiving the output signals from the frequency divider 329 and from the counter 336.

A circuit 346 determines the default time with respect to the current one Speed. The circuit 346 comprises a generator 348, and a counter 350, which is connected to the generator 348 and to the input

330 for the position signals is connected. The pulse repetition frequency of generator 348 is set at 5 MHz and is preferably crystal stabilized. The counter 350 counts the between the position signals pulses from generator 348 appearing at input 330, and this count is transferred to a register 352 which is cascaded with an address register of a programmable read-only memory 354. The count value serves as the current address for the permanent memory. This supplies the default time, which is transmitted to the arithmetic unit 342.

The carrier position indicated by the output signals on the "coarse" and "Fine" output lines of counter 336 and frequency divider 329 are represented is, as well as the default time, which is supplied by the read-only memory 354, are algebraically added in the arithmetic unit 342 and one Comparator 356 is supplied, on whose output line 380 a reversible Counter 358 is connected, the counting direction of which is controlled by the direction signal at input 334. · The output signals of the counter 358 run into comparator 356.

The arithmetic unit 342 is zx ^ isch successive position pulses

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tracked eight times. The default time is between two position impulses tracked. Therefore, the speed and the assigned default time are calculated for the position in front of the position at which the current recording takes place.

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Claims (1)

SA 976 017/022 PATENT CLAIMS ': Method for the ongoing determination of the default time in inkjet printers, in which the Print unit carrying carrier and a recording medium a relative displacement takes place at a variable speed, characterized in that the current position of the carrier as well as its instantaneous speed are scanned, and that from these Samples as well as the drop speed and the distance between the nozzle of the printing unit and the recording medium the default time for triggering the printing process is calculated. Method according to claim 1, characterized in that: that the speed of the carrier according to a selectable speed / time profile (FIGS. 1 to 3) is controlled depending on the carrier position. Circuit for performing the method according j to claim 1, in an inkjet printer having transversely to 'one to the feed direction of the recording [carrier variable speed slidably * arranged the printing unit supporting carrier, characterized i marked by a position encoder (50) for lauryl j for scanning the position of the carrier and for generating the passage of successive printing | Positions of the carrier characterizing pulses' · means (54) for detecting the instantaneous speed of the carrier as it passes the printing ^positions: and at least one phase-stabilized loop j (60, 70, 220, 320) having means for calculating the standard time from the position information and the Instantaneous speed of the wearer, which 8 0983 5/0618 * r ~ ORIGINAL INSPECTED SA 976 017/022 time to control the printing process is fed to the printing unit. Circuit according to Claim 3, characterized by a first phase-stabilized tachometer loop (60) for measuring the relative speed between printing unit and carrier, with one with its first input the first phase comparator (58) connected to the position encoder (50) and one in series therewith switched first square wave generator (64), the output of which connects to the second input of the phase comparator (58) is connected by a second phase stabilized loop (70) consisting of a second phase comparator (68), the first input of which is connected to a motor encoder (54), a second square wave generator (74) connected to the output of this phase comparator (68) and a frequency divider (76) connected to its output (80), the output of which is connected to the second Input of the second phase comparator (68) is connected, and by a connection from the output of the first Phase comparator (58) to a third input of the second phase comparator (68), the whole in such a way, that when the carrier speed increases, the phase of the signal at the output (80) of the generator (40) leads, so that in the second loop (70) through an amplifier (72) the control voltage of the generator (74) is increased until the required default time is reached. Circuit according to claim 3, characterized by a phase stabilized tachometer loop (60) with a with its first input to the position encoder (50) connected phase comparator (58) and one with this series-connected square wave 809835/0618 SA 976 017/022 generator (64), the output of which is connected to the second input of the phase comparator (58), through a differential amplifier (82), the first of which Input to the output of the phase comparator (58), and its second input to a motor encoder (54) is connected, and its outputs with the windings (86, 88) of an electromechanical Converter (90, 92, 94) are connected, which converter (90, 92, 94) is arranged on the printing unit carrier (100) is, the armature (92) of the transducer (90, 92, 94) having a mask (94) connected to it in accordance with the differential supply of the windings (86, 88) pivoted so that one arranged on the mask (94) electro-optical scanning device (96, 98) when sweeping over phase-controlled pulses of a scale (110) arranged stationary on the machine frame which are used to determine the standard time. 6. A circuit according to claim 3, characterized by a phase-stabilized tachometer loop (220), for measuring the relative speed between the printing unit and a carrier, having a first input (230) connected to the position encoder (50) Phase comparator (222) and a square wave generator (226) connected in series with this, whose The output is connected to the second input of the phase comparator (222) via a frequency divider (228), an analog / digital converter (236) which digitizes the analog output signal of the loop (220) and A register (238) feeds (B) an arithmetic unit (242), one to the output of the square wave generator (226) connected first counter (240) and one connected to the position encoder (50) 8 0 9835/0618 SA 976 017/022 'second counter (232), the outputs of which with the arithmetic factory (242) are connected (A). 7. A circuit according to claim 3, characterized by a phase-stabilized loop (320) for measuring the relative speed between printing unit and recording medium, with a phase detector (322), the first input of which to the position encoder (50) is connected, and its output to a first voltage controlled square wave generator (326) is connected, the output of which is connected via a first frequency divider (328) to the second input of the : Phase detector (322), as well as a frequency divider i (329) is connected to an arithmetic unit (342), a j: second square wave generator (348), the output of which i is connected to the first input of a counter (350), the second input of which is connected to the position I encoder (50) is connected, and its outputs j • via a register (352) and a permanent memory (354) \ are connected to the arithmetic unit (342) to whose j j output a signal representing the default time | I occurs. ! 809835/0618