US3872788A

US3872788A - Hammer flight time aligning system for impact printers

Info

Publication number: US3872788A
Application number: US409024A
Authority: US
Inventors: Gaston Albert Palombo
Original assignee: HONEYWELL BULL SA
Current assignee: HONEYWELL BULL Cie SA; HONEYWELL BULL SA
Priority date: 1972-10-26
Filing date: 1973-10-23
Publication date: 1975-03-25
Anticipated expiration: 1992-03-25
Also published as: GB1441007A; FR2205003A5; IT1027515B; JPS4995538A; DE2353825A1

Abstract

A closed loop system is provided in an impact printer wherein a variable delay circuit is introduced into the command input to a hammer of the printer. The introduced delay time between the command input for the hammer to strike and the time at which the hammer actually is released or actuated to travel during its flight time from its normal position into impacting relation with the printer anvil, is adjustable so that the time of impact may be corrected to coincide with a desired timing relation, i.e. the hammer may be ''''aligned.'''' All hammers of the printer are similarly aligned and in order to accommodate for the fact that the actual flight time of any hammer will vary from strike-tostrike, provision is made for determining the average of several actual flight times and for correcting the delay time in accord with this average.

Description

Unite States Palombo HAMMER FLIGHT TIME ALIGNING SYSTEM FOR IMPACT PRINTERS Primary Examiner-Edgar S. Burr Assistant Examiner-Edward M. Coven [75] Inventor. Gaston Albert Palombo, Dan outm, Attorney Agent or Firm Fred Jacob France [73] Assignee: Compagnie Honeywell Bull (Societe [57] ABSTRACT Anonyme), Paris, France I d A closed oop system is provi ed in an impact printer [22] 1973 wherein a variable delay circuit is introduced into the [21] Appl. No.: 409,024 command input to a hammer of the printer. The introduced delay time between the command input for the 30 hammer to strike and the time at which the hammer 1 Forelgn Apphcatm Pnomy Dam actually is released or actuated to travel during its Oct. 26, 1972 France 72.38060 time from its normal p iti n into impacting relation with the printer anvii, is adjustable so that the Cl 101/9114, time of impact'may be corrected to coincide with a [51] Ill. Cl 134M 7/08 dggirgd timing relation, i e, the hammer may be Fleld of Search aligned." All hammers of the printer are similarly 340/1725 aligned and in order to accommodate for the fact that the actual flight time of any hammer will vary from References Cited strike-to-strike, provision is made for determining the UNITED STATES PATENTS average of several actual flight times and for correct- 3,312.174 4/1967 Cunningham 101/93 c ing the delay time in accord with average- 3.602,i38 8/1971 Batomb 101/93 C 3.662.389 5/1972 Janis 340/365 23 Clams 7 Drawmg F'gms Q D E L iDEP mock 83 HF 7L 1 i +22 66 i w Bey |CAR1 T P Counter Shopen PATENIEBMARZSIBYS (SHEETIDFG cw U FiG-1 HAMMER FLIGHT TIME ALIGNING SYSTEM FOR IMPACT PRINTERS BACKGROUND OF THE INVENTION Modern impact printers include a writing medium in front of which passes a type carrier (i.e. a rotating drum, a linear support for the characters) which carry out a periodical movement so that each character to be printed is offered to each printing position of a print line. A strike organ is associated with each printing position which releases an associated print hammer at the desired moment, i.e. when the character to be printed is in the corresponding printing position. Generally this release occurs due to the action upon the hammer by an electromagnetic or electrodynamic activator.

The hammers of the impact printers are usually freeflight ones, so as to avoid too long an impact time and early wear of the contact material The real flight time t of the hammer is that time from the instant in which the activator is ordered to release the hammer and the exact moment at which the hammer strikes the character support.

For the same hammer this time t,. changes from strike to strike. For this reason, a mean flight time is defined as z,.,,,. This time t,.,,, is different for different hammers and varies for the same hammer in the course of time. As the main reasons for these variations one may cite:

wear of the hammer faces entailing a change of the distance to be covered.

variation of the impact forces of the activator due to mechanical frictions, variation of the electrical voltage, of the temperature, etc,;

friction effects if the hammer is guided in flight;

- expansions;

sticking of the activator on the hammer, etc.

One must, however, realize that the mean flight time changes slowly so that over a period of a few days, it essentially remains constant and that this is characteristic of each hammer.

However, the means flight time will change significantly over longer periods of time so that if it were not corrected, an ensuing disalignment of the strike will result.

In current practice, an alignment operation is carried out during manufacture of the printer, and subsequently during maintenance of the machine.

In the alignment during manufacture a first alignment operation consists of ascertaining by means of a bar provided with a shock absorber, functioning as the printer anvil, if the time intervals of the flight I in relation to a mean value I, are not too great.

One records the flight times, i.e. with an instrument which has a Gauss curve for the flight times t as wellas the mentioned intervals. The strike motors whose hammers display intervals which are too large are eliminated and one proceeds with the second alignment operation.

The second alignment operation consists of manually changing the physical parameters which affect the actual flight times of the selected hammers, measuring the mean flight time by means of a bar functioning as the printer anvil, and repeating these steps until a satisfactory alignment is achieved. It is obvious that this procedure is iterative and can only be performed ap proximately for it is very difficult to determine accurately the average of a time with instruments used habitually for this type of measurement (i.e. an oscilloscope) and a shock absorber bar. To align a machine completely several hours are required which is obviously costly.

BRIEF SUMMARY OF THE INVENTION Since it is next to impossible to modify or control the mechanical and physical causes of the variation of the mean time of flight directly, the present invention involves the introduction of a new value, namely, the mean fictitious flight timeT which may be adjusted for each hammer and may be made identical for the system. The mean fictitious flight is defined as the sum T t,.,,, r where 2 is the actual mean flight time and I is a delay time which is adjustable for each hammer.

This delay time is encompassed within that time period between the instant at which the logic control circuitry of the printer commands the strike and the instant at which the activator in fact receives the energy necessary to release or actuate the hammer. The invention involves a system in which the time of the fictitious flight T is identical for all hammers by individual control of the time t for each hammer.

The type support may be either a rotating cyllindrical drum or an endless type-carrying chain, mounted between two pulleys rotating on parallel axes, said hammer impacting against an anvil during each strike through the intervening selected type'carrying finger and the writing medium.

In a particular mode of embodiment of the invention. the impact detector, in the case of chain printers. consists of a series of piezoelectrical crystals positioned in the anvil. The impact signal produced by a crystal is shaped by a suitable wave shaping circuit before being sent to the mean flight time measuring device.

The invention will be better understood in the course of the following description, with reference to the attached drawings and offering for purposes of explanation, without limitation, a mode of embodiment according to the invention.

BRIEF DESCRIPTION OF THE DRAWING FIGURES FIG. 1 represents in diagram form an example of the character support of a printer whose hammers are aligned by the device according to the invention;

FIG. 2 is a block diagram of the device according to the invention;

FIG. 3 is a timing diagram of signals describing the operation of the device of FIG. 2;

FIG. 4 exhibits more in detail the block diagram of FIG. 2;

FIG. 5 is a timing diagram of signals illustrating the operation of the device of FIG. 4-;

FIG. 6 is a timing diagram showing a possible division of the timer'pulse as a pulse of fixed delay" and a pulse of variable delay; and

FIG. 7 illustrates a modification of the invention.

DETAILED DESCRIPTION OF THE INVENTION 7 The invention will be better understood when the principles of construction and the operation of a printer of a type-carrying chain are called to mind.

FIGS. 1a and lb show respectively a perspective and a plan view of an impact printer including such a typecarrying chain 100. The chain is illustrated mounted in the printing machine on two pulleys 101A and 1013 whose axes Yl Y'l and Y2 and Y'2 are verti- I cal. To facilitate the understanding of FIG. 1a, only a part of the chain 100 is shown with its type-carrying tongues 111 to 120, (ten in the case of this illustration). The latter are intentionally oversized in relation to the chain 100 so as to make FIG. la more distinct. In the same manner, a certain number of hammers 120 to 130 are shown in a very schematic form in FIG. 1b together with associated actuators 120 to 130'. This endless belt 100 passes in a linear manner with constant speed between the hammers 120 to 130, on the one hand, and the writing medium 102 and a fixed anvil 103 on the other hand. I

The speed of the chain 100 is adjustable and depends on the required printing speed for the printing machine. Synchronization apertures 131 to 140 are associated with the respective fingers 111 to 120, in such fashion that each finger corresponds with a single synchronization aperture.

As shown in FIG. la, the synchronization holes are located between the type-carrying fingers. Thus the aperture 131 is positioned between the fingers 110 and 111, the hole 132 between the

fingers

111 and 112 and so on. If the chain 100 passes in the direction of the arroes F1 and F2, as illustrated, the aperture 131 is associated with the finger 111, the hole 132 with the finger 112 and so on.

The type-carrying chain 100 further provides an initial chain hole 104, positioned on a different alignment level than thatof the synchronization holes.

A synchronization pickup C1 is disposed at the level of the synchronization holes and furnishes a pulse whenever a synchronization hole 131-140 passes before it. This pulse is sent to the conventional strikeorder logic circuits of the printer.

Associated with and at the level of the initial opening 104 of the chain is a pickup C2 that emits a pulse when this aperture 104 passes before it, which pulse is also sent to the logic circuits. I,

The combination of the two signals emitted by the pickups Cl and C2 makes it possible in a known manner to identify by said logic circuits all the synchronization openings and, consequently, all the fingers. When one keeps in mind the relative geometrical constellation formed of the pickups, the hammers and the fingers, one knows always the relative positions of the hammers with respect to this or that type-carrying finger so that one may order the desired strike accordingly, all as is conventional and well known in the art.

The device according to the invention is represented in the form of a block diagram in FIG. 2.

vIn FIG. 2 there may be seen the different essential composing elements of the device according to the invention, i.e.:

l. The timer generator 1 which is a digital monostable;

. The strike amplifier 2;

. The hammer 3;

. The impact detector 4;

. The means flight time measuring device 5; The subtracting circuit 6;

. The order corrector circuit 7; and

. The time base 8.

To better appreciate the principle of operation of the present device of flight time alignment, it is necessary to call to mind the the operation of a hammer in the course of a strike, with the understanding that this function is the same for all the others.

When one of the synchronization openings 131 to passes in front of the synchronization pickup C1, the strike-order logic circuits send the pulse DEP to the delay monostable l which corresponds with the hammer chosen by the said circuits. This pulse DEP, represented in FIG. 2, rises to logic 1 at the instant T., and drops again to zero logic at the moment T 'at which time the delay monostable 1 outputs. The latter supplies the pulse DEL which rises to logic 1 at the instant T and falls again down to logic zero in the instant t, at which the strike amplifier 2 furnishes the order pulse MART to the hammer 3 which order pulse drops again to zero in the instant t The hammer 3 is actuated at the time t and strikes the character at the instant When recapitulating the notations initially used one may write that the actual flight time of the hammer is t, -1 while the fictitious flight time of the hammer IS is the adjustable duration of the pulse supplied by the monostable 1, also called delay time.

Since the flight time I for the same hammer changes from strike to strike the mean flight time I,.,,, is introduced.

This value t,.,,, not only changes from hammer to hammer but also varies in time for the same hammer, as was explained above.

The mean fictitious flight time is, therefore, introduced The automatic alignment operation performed by the device according to the invention thus consists in rendering identical the quantity T for all hammers by ad justment of the variable quantity (r I t,,.

The theoretical alignment operation schedule consists in the following for each hammer:

I. perform the same number n of strikes in each schedule; and

2. measure in each strike the corresponding t,,.

If i is the order of the order of the strike (1' n) and 1,, (i) is the corresponding fictitious flight time, the mean fictitious flight time will be after n strikes .3. in calculating T; 4. in comparing it with a reference flight time T and in computing the difference;

T TR e;

5. in adding or subtracting T.. from 1,

In practice, the device of FIG. 1 accomplishes the alignment operation of the hammer 3 in the following way.

The time base 8 delivers from the moment t on to the digital monostable 1 a series of it set pulses H whose duration is roughly longer than the maximum time T assumed, in such a manner that between the instant in which the hammer strikes the anvil and the instant in which the following pulse l-I begins, there is sufficient time to permit stabilization of the hammer. One examines what occurs during each pulse H The monostable 1 supplies the pulse DEL of a duration r,, to the strike amplifier 2 which delivers the pulse MART, permitting by means of an actuator of a known type (i.e., electromechanical) to release or actuate the tan.

Each flight time 1,;(1') and consequently T is expressed in binary form in time units h of the signal UTI furnished by the time base 8 to the device 5. The value of T is sent to the subtractor circuit 6 where the reference flight time T is subtracted from T. T is also expressed in binary form as units of h (see FIG. 3) with t T where 1 is defined as the instant of the strike of a perfect hammer of the flight time t equal to T Thereafter, when one speaks about the flight times r,.,(i); T, T of the delay time I it will have to be understood that they are expressed in time units h. The difference T-T (expressed in binary form) is sent to the ordercorrector circuit 7 which transforms it into a signal E (see FIG. 2) which is a sequency of very short pulses whose period is equal to that of signal UT2, supplied by the time base 8 (usually different and below h) and whose number is equal to the duration of the error which one has to add or deduct to (from) the delay time 1,, according to the flight time T of the hammer being too short or too long in relation to T (T is represented too long in FIG. 3) The corrector circuit 7 modifies by the sending of signal E to the triggered monostable 1 the adjustment of the latter in such a fashion that the mean flight time T be henceforth equal to T To better facilitate the understanding of this correction operation the signals DEL. H1, MART, IMP, TVR are represented on the right side of FIG. 3 from the moment 1'0. Once the correction is achieved and the prime" index has been attached to the variable t to show that the series of n pulses H1, hence of n strikes, is terminated and that the correction of the delay time r has been accomplished by the device according to the invention, the values of the variable r equal to 1' 1' the value of the time interval I' correspond tothe values 1,, r One will find that the delay time and that the impact instant t' coincides with the instant 1' According to the above, it may be seen that the time base 8 delivers the signal U TI. supplying the reference time h to the measuring device 5, the sequence of pulses H, to the digital monostable I and the signal & T2 to the corrector circuit 7. This time base 8 has thus an essential function in the operation of the device according to the invention. The different elements which make it up may be seen in FIG. 4. They are a first clodk 81, a bistable 82, an AND gate 83, a strike counter 84, a second clock 85 and an AND gate circuit 86.

The first clock sends out from the moment t in which the pulse DEP drops down to zero an endless sequence of pulses H, (see FIGS. 3 and which is sent to the first input of the circuit ET 83.

The bistable circuit 82 furnishes a pulse BIS which rises to logic 1 at the instant t and falls down again to logic zero in the instant 1 in which the nth pulse of the sequence III drops to zero logic. Thus pulse BIS is sent to the second input of the AND circuit 83. One receives in the output of the AND circuit 83 the sequence of pulses I'll, sent to the first input of the AND circuit 86, to an input II of the digital monostable l and finally to the input of the strike counter 84. The latter registers a strike whenever one of the n pulses of the sequence I-lll arrives there. The capacity of counting of the counter 84 is equal to n 2", i.e. at the nth pulse the counter sends a pulse CAR I to the second input of the bistable 82. This pulse CAR 1, when it drops again to zero logic in the instant t causes the pulse BIS to fall again to zero, while the pulse BTS rises to logic I. This pulse is sent to the input H of the order corrector circuit 7.

The clock supplies a signal U TI giving the time unit h of reference to the measuring device of the flight time 5, and to the second input of the ANd circuit 86. The signal U T Hll is received in the output of the AND circuit 86 (see FIG. 5) which is sent to the input 12 of the digital monostable ll.

In view of the fact that the functioning of the triggered monostable 3, of the impact detector 4, and of the measuring device of the means flight time 5 is anal ogous, one considers from strike to strike of one pulse Hi to another one pulse H, i.e., the first. Furthermore, to facilitate the understanding of FIG. 5 only two series of signals are represented, the one corresponding with the first pulse H the other corresponding with the nth pulse H the instants t t,, l 1 being relative to the first pulse, the corresponding times t 1, I 1 1 being relative to the nth pulse.

As was mentioned previously, the monostable I delivers the pulse DEL to the strike amplifier 2 which supplies by the pulse MART the force necessary for the release or actuation of the hammer 3. The description and a detailed operation of the monostable I will be given later on, the understanding of the functioning of the latter is much easier if the operation of the detector 4 of the mean flight time measuring device 5, the subtractor 6 and of the circuit 7 will have been explained.

The impact detector 4 includes the transducer 11 and the wave shaping circuit 42.

The transducer 41 is positioned inside the anvil 103 of the printer and is of the type which permits accurate determination of the instant of impact. The transducer may take any conventional form such as a piezoelectrical crystal, microphone, strain guage, etc. The transducer ll delivers a signal 'CIIOC which is shaped by the circuit 82 which emits in its output the pulse IMP (FIGS. 3 and 6).

The mean flight time measuring device 5 includes the flip-flop circuit 51 and the AND gate 52 with two inputs, the counter accumulator 53 of a capacity 2""*". the division circuit which performs n 2'".

The flip-flop circuit 81 receives at its first input the signal IMF and at its second input the pulse Hi to produce the output signal TVM. a pulse which rises to logic l in the instant t (i.e. at the same moment as the rise of the pulse III) and drops again to zero logic in the instant 1 in which the pulse IMP rises to logic. I. The duration of that pulse TVM is thus equal to 1 t um)- The signal TVM is sent to the first input of the AND gate 52, while the second input of this gate receives the signal U T1. In the output of the gate 52 a sequence TVM of qi U Tl pulses is thus received and this sequence is sent to the counter accumulator 53 which records the number qi.

What was described with respect to the first strike (and the signals which concern it) applies to the (n-l) other strikes and one receives for example:

At the end of n trikes, the counter 53 will have totaled the number (ql-q,-+ q,,) (t,.,(l) t5,

Obviously, the counting capacity of the counter 53 is such that the preceding number does not completely fill it. The capacity of the counter 53 is equal to 2 2"X2" in which the number 2 is chosen so that 2 h be higher than the maximum fictitious flight time t assumed for the hammers of the printer.

Thus, the counter 53 supplies the dividing circuit 54 in its (m-l-p) parallel outputs the number (q q, q,,). The circuit 54 performs the division of this number by 2'" n and delivers, thereafter, a number t,.(i)/(n lz) equal to the mean flight time T of the hammer under consideration. This number is sent from p outputs of the circuit 54 to the subtractor 5 in p bits; the latter receives in binary form the number equal to the reference flight time T delivers the number Te to its p outputs if T, (T, T is positive or the complement of T if T,, is negative, i.e., 2" T The order-corrector circuit 7 includes the AND gate 72 having two inputs, the error abstractor 75 of a capacity of 2" and the monostable of delay transfer 76.

The monostable 76 receives the signal m of the bistable of the bistable 82 and delivers a signal TRANSF which rises to logic 1 in the i instant i (at the same time as m5) and falls back to zero in the instant t defined arbitrarily. This signal TRANSF is sent to one of the AND gate 72 of which the p other inputs receive the number Te (or its complement 2 Te if Te It may be seen then that this gate 72 is validated by the signal TRANSF from the moment t i.e. when the hammer has finished'its series of'n strikes. This difference Te is sent by the gate 72 in parallel to all p inputs of the up-down counter 75. The signal TRANSF is also sent to the first input of the corrector flip-flop 73, while the other input receives the signal BOR which is produced when the counter 75 is emptied. The flip-flop 73 delivers the correction signal COr which increases to logic 1 in the instant t and falls again to zero logic as soon as the pulse BOR is received. This signal COR is sent at the same time as the signal U T2 (whose period is generally below h so that the correction operations may be carried out very rapidly) to the AND gate 74 at whose output the signal Eis received, a sequence of very short pulses. This signal, sent to the down counteinput of the counter 75 causes the latter to move back a digit at each E pulse received until the counter 75 is emptied. Since the latter, before receiving the signal E, contained the value Te of the difference of the flight times (or its complement to 2", as could be seen above), one realized that the signal COR is of such duration that the number of E pulses is equal to Te if Te is positive or its complement 2' Te is negative.

The digital monostable 1 includes the delay counter of the gate 17 to the storage counter 14. This presettingnumber is arbitrarily chosen between 0 and 2". The counter 14 presets in turn the counter 13 at the value PP by means of the AND circuit 16 because at this time the signal DEE is high.

b. lntermediate phase (during each pulse H The counter 13 receives the signal UT H, at its conductor 12 stemming from the AND circuit 86 and consisting of a predetermined number of pulses from the clock 85. At each pulse received it moves forward one unit until its capacity 2" is filled by the preset number PP plus the predetermined number of clock pulses (instant t,). In this instant I, the counter sends out the pulse CAR which is sent to an input of the delay bistable 15 which receives in the other input the pulse H The bistable 15 changes its state and the pulse DEE goes up to logic 1, enabling the AND circuit 16 to reinsert the presetting number PP into the counter 13. It thus may be seen that since the capacity of the counter 13 is 2" the number 2" PP is equal to the time of the delay 1 0)- c. Final phase (after the n pulses H1). At this time the signal EB goes low and the signal BIS goes high (FIG. 5) so that the gate 83 no longer is enabled and the monostable 76 is actuated to produce the pulse output signal TRANSF which is of a duration sufficiently long as to enable the ensuing transfer of the accumulated or averaged error 'signal Te to be transferred to the counter 75. This transfer is effected by the gate 72. At the same time, the signal TRANSF sets the bistable 73 such that its state changes to produce the output signal COR, thereby allowing the pulses from the clock 85 to down-count the counter 75. The number of clock pulses (clock 85) required to empty the counter 75 is also applied to the counting input of the counter 14 to modify its store so that the counter 14 will now store that number which either is PP Te or PP Te dependent upon whether the number Te 0 or whether Te 0, in which latter case the complement of Te is present in the counter 75 at the end of the nth strike. The delay T is therefore either increased or decreased to the new value I' (FIG. 3) so that the corresponding hammer will be henceforth actuated at that new time ['2 which in the average assures that the moment of hammer impact occurs at t'4. As noted. the counter 75 when emptied produces the output signal BOR which changes the state of the binary 73 to terminate the gateenabling signal COR.

Two cases must be examined:

1. If Te 0, the counter 14 counts then the number (PP Te): The delay becomes then 2" PP Te and T is thus reduced.

2. If Te 0 the counter stores PP 2" Te or PP Te and the delay-t becomes 2 PP Te. It has, therefore, increased.

In the two cases, the new value of delay is immediately transferred to the delay counter 13 (by validation by DEE of the gate 16).

In a preferred version of realization of the invention, the signal DEL is divided in two signal DELV and DELF, as is shown in FIG. 6, of respective duration (t t and t and one receives always 2. After the n strikes: the counter 13 receives the signal E at its input conductor 132 thus to change the count stored therein. The operation-of the counter 13 is then exactly identical with that of the storage counter 5 14 of the first version (see above).

After the nth pulse H1, the previously stored count PP in the counter 13 is altered to a new value dependent upon the error term E, as described above in conjunction with FIG. 4. Since the period of the signal DELF is fixed and since the total time represented by according to the invention which is shown on the right side of FIG. 6. As in FIG. 3, the prime index attached to a variable E, means that a series of n pulses H hence of it strikes, is terminated, and that the duration n, of the delay time had been modified from its value Te by the device according to the invention, to render the values of 1 equal to t,, t' t corresponding with the preceding value I t t If one has (t, 1' t,, =t,,-Te=(t t )-Te=(t' t' )+(t -t' with To accomplish the divison of the signal DEL in DELV and DELF and to carry out the correction of the signal DELV, the time base 8 and the digital monostable 1 are modified as indicated in FIG. 7; the other elements of the correction device according to the invention remain unchanged in relation to the first described version.

The time base 8 includes always the

elements

81, 82, 83, 84, 85. One adds to it the pulse generator 87 which receives the signal U T1 supplied by the clock 85 and furnishes a sequence UT H2 of n 2* pulses during the time duration of the signal U T1, the time duration of the signal H1. The triggered monostable 1 comprises besides the delay counter 13 of the counting capacity the sequential periods of DELV and DELF determine the delay time r it is possible that the error term E will be so great as to indicate that the initial count in the counter 13 should be equal to or greater than 2". This, of course, represents an ambiguity and indicates simply that the period of the signal DELF is too little. in other words, the monostable 18 must be adjusted to increase the period of the signal DELF, which may be effected 20 by manual adjustment.

in order to provide means by which a correction due to the error term E would cause the capacity 2 of the counter 13 to be exceeded, the master clock 9 is employed as shown in F IG. 7. The master clock 9 provides the basis timing format for the system from which all CG whose output at AL provides a suitable alarm such 2p, the delay bistable 15 and the analogue monostable 18. Obviously compared to the first version of the invention the storage counter 14 is omitted.

The operation of the digital monostable is now the following: W

1. During each of n strikes: The counter 13 is preset to start its count at some number PP. The value of the variable delay (r t is, therefore, 2" PP. The counter 13 receives at the input conductor 131 the pulse sequence UT H2. It thus advances by one unit at each pulse received. It will be recalled that the pulse generator 87 produces 2 pulses during the period of the pulses H1 so that at some time t the counter is filled and at the instant r produces the pulse CAR 2 to the first input of the delay bistable 15 whose second input receives the signal H The delay bistablev 15 transmits the pulse DELV to the monostable 18 which delivers in response to the latter the pulse DELF of the fixed duration (l -I In the meantime the signal H1 is still up so that the counter 13 continues to receive the pulses UT H2 after being filled and emptied and theirby counts toward the number PP. Since the capacity of the counter is equal to the number of pulses of the signal UT H2 and since the period of the signal UT 1 is approximately equal to that of H1, the counter 13, at the end of each of the n pulses l-l,, is again preset to the count PP, without being filled again by the time the signal H1 goes low.

as a bell, a light, etc. which informs the operator that manual adjustment of the monostable 18 is required to increase the period of the signal D'ELF.

The

elements

1, 5, 6, 7 and 8 of either system as described above, in other words the logical system of computation and correction of the quantity T, are preferably common to all hammers, the alignment operations carried out during the periods of upkeep and maintenance of the printing machine being affected by the one system and the hammers are aligned one after another. However, it is evident that an alignment system could be aligned simultaneously. It is also possible to perform the alignment of the hammers while the printer carriers on its normal work.

What is claimed is:

1. in an impact printer having a printing anvil, a plurality of hammers normally spaced from said anvil, type carrier means disposed between said hammers and said anvil and including means for causing relative movehammer impact against the anvil is desired, actuator means for causing each said hammer selectively to travel into impacting relation to said anvil, and timing means for initiating actuation of each said actuator means in response to attainment of a predetermined relative position of such hammer and the type carrier means which is in advance of attainment of a corresponding particular alignment the improvement wherein;

said timing means includes variable delay means for selectively varying the time of initiating movement of each said hammer with respect to the time of attaining the corresponding relative position of such hammer and the anvil;

ing the time of impact of a selected hammer with said anvil; and

correction means connecting each detector means with an associated variable delay means for controlling said time of initiating movement of the selected hammer to cause such hammer to impact the anvil with essentially a predetermined time delay with respect to the attainment of said predetermined relative position between such hammer and the anvil whereby all hammers may be actuated to impact at the desired times.

2. ln an impact printer as defined in claim 1 wherein said correction means includes means for averaging the flight time of the selected hammer over a number of actuations thereof and, means for controlling said variable delay means according to such time average.

3. An impactjprinter as defined in claim 2 wherein said detector means includes an impact detecting transducer for each hammer, each such transducer being mounted in said anvil.

4. An impact printer as defined in claim 3 wherein said means for averaging includes a count accumulator, a count pulse generator, and a gate, said count pulse generator being connected to said count accumulator through said gate and said gate being controlled by said detector means to pass pulses from said pulse generator in dependence upon the actual time required for the selected hammer to impact the anvil.

5. An impact printer as defined in claim 4 wherein said means for averaging also includes means for dividing the total number of accumulated pulses by said number of actuations of the selected hammer.

6. An impact printer as defined in claim 1 wherein said means for averaging includes a count accumulator, a count pulse generator, and a gate, said count pulse generator being connectedto said count accumulator through said gate being controlled by said detector means to pass pulses from said pulse generator in dependence upon the actual time required for the selected hammer to impact the anvil.

7. An impact printer as defined in claim 2 wherein said means for averaging includes a count accumulator,

.a count pulse generator, and a gate, said count pulse generator being connected to said count accumulator through said gate and said gate being controlled by said detector means to pass pulses from said pulse generator in dependence upon the actual time required for the selected hammer to impact the anvil.

8. An impact printer as defined in claim 7 wherein said means for averaging also includes meansfor dividing the total number of accumulated pulses by said number of actuations of the selected hammer.

9. In an impact printer having a set of hammers, an anvil spaced from said hammers and actuator means for the hammers whereby inherently to provide an arrangement in which different hammers may required different time periods in which to reach impact with the anvil with respect to a command signal input time to said actuator means, the combination of:

clock input means for providing a series of clock pulses in response to said command signal input;

delay counter means connected to said actuator means and having said series of clock pulses as an input thereto for delaying energization of the actuator means until a particular number of clock pulses occur; and

means for selectively altering said particular number of clock pulses which must occur before energization of said actuator means is effected. 7

10. In an impact printer as defined in claim 9 wherein said clock input means includes a free running clock and gate means enabled by said command signal to pass said series of clock pulses to said delay counter means.

11. ln an impact printer as defined in claim 10 wherein said delay counter means has a selected count capacity and energizes said actuator means upon attainment of said count capacity, and wherein said means for selectively altering comprises means for inserting a variable count into said delay counter means.

12. In an impact printer as defined in claim 11 including detector means carried by said anvil for detecting the moment of impact of a hammer with the anvil, gate means connected to said clock input means and to said detector means for averaging the number of clock pulses produced between the instant of actuator means energization and detector means actuation over a selected number of actuations of a particular hammer, and wherein said means for inserting includes sub tractor means connected to said means for averaging for producing an error signalwhich is the difference between the average number of clock pulses and a reference number of clock pulses.

13. In an impact printer as defined in claim 12 wherein said delay counter means is updated by said subtractor means after every actuation of said particular hammer during said selected number of actuations thereof.

14. In an impact printer as defined in claim 12 wherein said means for inserting includes a storage counter connected to said delay counter means and gate means connecting said subtractor means to said storage counter for updating the storage counter at the end of said selected number of actuations of a particular hammer.

15. A closed loop system for aligning the flight time of the hammer of an impact printer, said closed loop system including said hammer, detector means for determining the moment of impact of said hammer with an associated anvil, logic circuit imput means for commanding energization of said hammer at a successive number n of particular times, delay means connected to said logic circuit input means for delaying actuation of said hammer with respect to each said particular time by a delay time period r averaging means connected to said detector means for determining the average actual time period between actuation of said hammer and impact thereof over said successive number n of hammer actuations, subtractor means connected to said averaging means for determining the difference between said average actual time period and a predetermined reference time period, and corrector means connecting said subtractor means to said delay means for changing said delay time period t such that the period of time between the instant of command signal input and the instant of hammer impact approaches a selected correct value.

16. A closed loop system as defined in claim 15 wherein said delay means includes a counter, said logic circuit input means includes clock means connected to said counter in response to command input, and wherein said counter is of fixed capacity and includes an output terminal for actuating said hammer upon reaching a count corresponding to said fixed capacity.

17. A closed loop system as defined in claim 16 wherein said corrector means is connected to said counter to insert a count therein.

18. A closed loop system as defined in claim wherein said delay means includes a counter and said corrector means is connected to said counter to preset same to a predetermined count which controls the delay time t 19. A closed loop system as defined in claim 18 wherein said delay means also includes a monostable connected to said counter and actuated thereby when said counter reaches its count capacity.

20. A closed loop system as defined in claim 19 wherein said logic circuit input means includes clock means connected to said counter in response to command input.

21. A closed loop system as defined in claim 18 wherein said delay means also includes a bistable device connected to said counter and actuated thereby when said counter reaches its count capacity.

22. A closed loop system as defined in claim 21 wherein said delay means also includes a bistable device connected to said counter and actuated thereby when said counter reaches its count capacity.

23. A closed loop system as defined in claim 15 wherein said delay means includes a counter of selected count capacity and said corrector means is connected to said counter to preset same to a predetermined count after the nth hammer actuation, said logic circuit input means including clock means connected to said counter in response to command input for causing said counter to count, said delay time 1,, being controlled in dependence upon the time required for said counter to reach said selected capacity from said predetermined count.

Claims

1. In an impact printer having a printing anvil, a plurality of hammers normally spaced from said anvil, type carrier means disposed between said hammers and said anvil and including means for causing relative movement of said type carrier means between said hammers and said anvil periodically to effect particular alignments of the type carrier means relative to the hammers and the anvil at the times of which alignments hammer impact against the anvil is desired, actuator means for causing each said hammer selectively to travel into impacting relation to said anvil, and timing means for initiating actuation of said actuator means in response to attainment of a predetermined relative position of such hammer and the type carrier means which is in advance of attainment of a corresponding particular alignment the improvement wherein: said timing means includes variable delay means for selectively varying the time of initiating movement of each said hammer with respect to the time of attaining the corresponding relative position of such hammer and the anvil; detector means associated with said anvil for detecting the time of impact of a selected hammer with said anvil; and correction means connecting each detector means with an associated variable delay means for controlling said time of initiating movement of the selected hammer to cause such hammer to impact the anvil with essentially a predetermined time delay with respect to the attainment of said predetermined relative position between such hammer and the anvil whereby all hammers may be actuated to impact at the desired times.

2. In an impact printer as defined in claim 1 wherein said correction means includes means for averaging the flight time of the selected hammer over a number of actuations thereof and means for controlling said variable delay means according to such time average.

3. An impact printer as defined in claim 2 wherein said detector means includes an impact detecting transducer for each hammer, each such transducer being mounted in said anvil.

6. An impact printer as defined in claim 1 wherein said means for averaging includes a count accumulator, a count pulse generator, and a gate, said count pulse generator being connected to said count accumulator through said gate being controlled by said detector means to pass pulses from said pulse generator in dependence upon the actual time required for the selected hammer to impact the anvil.

7. An impact printeR as defined in claim 2 wherein said means for averaging includes a count accumulator, a count pulse generator, and a gate, said count pulse generator being connected to said count accumulator through said gate and said gate being controlled by said detector means to pass pulses from said pulse generator in dependence upon the actual time required for the selected hammer to impact the anvil.

8. An impact printer as defined in claim 7 wherein said means for averaging also includes means for dividing the total number of accumulated pulses by said number of actuations of the selected hammer.

9. In an impact printer having a set of hammers, an anvil spaced from said hammers and actuator means for the hammers whereby inherently to provide an arrangement in which different hammers may required different time periods in which to reach impact with the anvil with respect to a command signal input time to said actuator means, the combination of: clock input means for providing a series of clock pulses in response to said command signal input; delay counter means connected to said actuator means and having said series of clock pulses as an input thereto for delaying energization of the actuator means until a particular number of clock pulses occur; and means for selectively altering said particular number of clock pulses which must occur before energization of said actuator means is effected.

11. In an impact printer as defined in claim 10 wherein said delay counter means has a selected count capacity and energizes said actuator means upon attainment of said count capacity, and wherein said means for selectively altering comprises means for inserting a variable count into said delay counter means.

12. In an impact printer as defined in claim 11 including detector means carried by said anvil for detecting the moment of impact of a hammer with the anvil, gate means connected to said clock input means and to said detector means for averaging the number of clock pulses produced between the instant of actuator means energization and detector means actuation over a selected number of actuations of a particular hammer, and wherein said means for inserting includes subtractor means connected to said means for averaging for producing an error signal which is the difference between the average number of clock pulses and a reference number of clock pulses.

15. A closed loop system for aligning the flight time of the hammer of an impact printer, said closed loop system including said hammer, detector means for determining the moment of impact of said hammer with an associated anvil, logic circuit imput means for commanding energization of said hammer at a successive number n of particular times, delay means connected to said logic circuit input means for delaying actuation of said hammer with respect to each said particular time by a delay time period td, averaging means connected to said detector means for determining the average actual time period between actuation of said hammer and impact thereof over said successive number n of hammer actuations, subtractor means connected to said averaging means for determining the difference between said average actual time period and a predetermined reference time period, and corrector means connecting said subtractor means to said delay means for changing said delay time period td such that the period of time between the instant of command signal input and the instant of hammer impact approaches a selected correct value.

18. A closed loop system as defined in claim 15 wherein said delay means includes a counter and said corrector means is connected to said counter to preset same to a predetermined count which controls the delay time td.

19. A closed loop system as defined in claim 18 wherein said delay means also includes a monostable connected to said counter and actuated thereby when said counter reaches its count capacity.

23. A closed loop system as defined in claim 15 wherein said delay means includes a counter of selected count capacity and said corrector means is connected to said counter to preset same to a predetermined count after the nth hammer actuation, said logic circuit input means including clock means connected to said counter in response to command input for causing said counter to count, said delay time td being controlled in dependence upon the time required for said counter to reach said selected capacity from said predetermined count.