US3667383A

US3667383A - Print and transport belt synchronizer

Info

Publication number: US3667383A
Application number: US887605A
Authority: US
Inventors: Ronald H Mack; Nicholas Kondur Jr; James A Mitchell
Original assignee: Burroughs Corp
Current assignee: Unisys Corp
Priority date: 1969-12-23
Filing date: 1969-12-23
Publication date: 1972-06-06
Anticipated expiration: 1989-06-06
Also published as: GB1307775A; FR2073044A5; NL7017997A; DE2063189A1; JPS514736B1

Abstract

A high-speed serial printer including a continuously rotating print drum having characters on its periphery, a hammer and carrier, and a belt for transporting the hammer and carrier parallel to the axis of drum along a line of print. A control system, including two timing discs, operates in synchronism with the drum. The first disc is indicative of the angular position of the drum and the second disc is to signal the hammer carrier to engage the transport belt at the start of each line of print. A double-ended transducer responds to the two timing discs to provide the appropriate signals for the printer.

Description

15] 3,667,383 1451 June6, 1972 United States Patent Mack et a].

3,117,514 1/1964 Doersam,.lr.................

Foley [54] PRINT AND TRANSPORT BELT SYNCHRONIZER [72] Inventors: Ronald R. Mack, Plymouth; Nicholas Konm S m y m m d .& u no or... m m cm m m WM $4 a Em mi dur, Jr., Plymouth Township, both of Mich.; Janis A. Mitchell, Paris, France [73] Assignee: Burroughs Corporation, Detroit, Mich.

print. A double-ended transducer responds to the two timin discs to provide the appropriate signals for the printer.

9 Clairm, 5 Drawing Flgures x We 93 Wm DKR PATENTEDJUN 6 I972 SHEET 10F 3 FIG.

DIFFERENTIAL AMPLIFIER INVENTO S RONALD H. MACK,

NICHOLAS KONDUR,Jr. 8. JAMES A. MYITCHELL AGENT PATENTEUJun 6 m2 SHEET 2 BF 3 A mm r" m d TK. 3E T NC EAUC N VMDT E m mm m H K A DS LAE Mu 7 H Y B 1 NQE PATENTEDJun s 1912 SHEET 3 OF 3 FIG.4.

R HM mK L 16 E N UH EADC w Nw Hm D A S MAS 6N t OM l-l w m m Na In Hlb .H q

PRINT AND TRANSPORT BELT SYNCHRONIZER BACKGROUND OF THE INVENTION This invention relates to high-speed serial printers and, more particularly, to the control system for such a printer.

High-speed printers find many applications as, for example, in connection with electronic computers, electronic desk calculators and the like. Many of these high-speed printers utilize continuously moving type faces carried on the surface of rotating drums, chains, or belts. The prior art high-speed printers employing continuously moving type provide one of two printing hammer arrangements; a row of printing hammers, one for each character position along the line of print, or a single hammer which is transported along the line of print from one character position to the next.

In the latter type of highspeed printer, the transport mechanism which moves the hammer along the line of print may be a threaded shaft, as is common in strip printers, or a toothed belt. A detailed explanation of the operation of a high-speed serial printer employing a toothed belt transport mechanism may be seen, for example, in US. Pat. No. 3,472,352 to Nicholas Kondur, Jr., assigned to the assignee of 'the present invention.

In high-speed printers using a single print hammer and a rotating drum in conjunction with a computer, one or more types of timing signals may be necessary to coordinate drum rotation, hammer movement and flow of data from the central processor. For example, signals (1) to initiate the movement of the print hammer and carrier at the start of each line of print, (2) to indicate the position of the print hammer along the line of print, and (3) to cause the hammer to print, i.e., force the paper against the drum, may be necessary for the correct operation of a printer.

In the prior art devices, such as the aforementioned patent to Kondur, the central processor or data source signals the initiation of each line of print. This causes the drum to start rotating and the print hammer and its associated hardware to engage the transport belt. However, if the angular position of the drum varies slightly the synchronism between the drum the print hammer may be lost.

In high-speed printers of the type described there must be synchronization between the drum and print hammer to cause the correct character to be printed. For this purpose the prior art devices have favored a rotating timing disc having teeth thereon corresponding to the characters on the periphery of the drum. The teeth cooperate with a transducer to generate pulses indicative of the angular position of the drum. These pulses serve as one input to a comparator. The other input to the comparator is from the central processor and represents the character to be printed. When these two inputs to the comparator match, the appropriate signal is given by the comparator and the printing hammer is actuated to print the character. After a character is printed, an irregular spacing of one tooth may be used to reset the comparator. This type of timing apparatus may be seen, for example, in US. Pat. No. 3,117,514, to C. Doersam, Jr. However, in this arrangement, any deviation in the speed of the rotating drum may defeat the precise timing required to interpret the irregular teeth spac- To overcome this problem, the prior art devices have suggested two alternatives; either two timing discs, each having its own transducer or a single timing disc having two transducers. An example of the apparatus using a single timing disc and two transducers may be seen in US. Pat. No. 3,291,909, to Clark et al.

As can be appreciated from a review of these prior art devices, the cost of these devices may be reduced by eliminating duplicate circuitry, such as two transducers, and by permitting the same timing pulses to perform plural functions without a loss of synchronism.

SUMMARY OF THE INVENTION Accordingly, with these prior art problems in mind, the invention contemplates. the solution to these problems by providing a new and improved serial printer control system including more reliable synchronization.

In addition, it is an object of the present invention to provide a new double-ended transducer for responding to multiple timing means.

It is a further object of this invention to maintain synchronism in a high-speed drum printer regardless of the initial position of the print drum.

It is yet another object of this invention to eliminate the timing problems which arise with the use of irregular spacing of the timing teeth for resetting a comparator in a high-speed printing operation.

These and other objects are accomplished in a high-speed serial printer including two timing discs driven in synchronism with the rotating drum of the printer. The first timing disc generates pulses to engage the print hammer with a hammer transport belt and the second timing disc generates pulses indicative of the location of the character on the periphery of the drum. A double-ended transducer responds to both timin discs.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing objects and advantages of our invention, together with other advantages which may be attained by its use, will be apparent from the following detailed description of the invention when read in conjunction with the drawings. In the drawings, wherein like numerals refer to the same feature:

FIG. 1 is an overall perspective view of a high-speed serial printer including the features of our invention;

FIG. 2 is an illustration of the two timing discs, the doubleended transducer, and associated control circuitry;

FIG. 3 is a block diagram of the logic circuitry for demodulating the signals from the double-ended transducer;

FIG. 4, comprising FIGS. 4A 4C, is a schematic diagram of part of the logic circuitry of FIG. 3; and

FIG. 5, comprising FIGS. 5A 5G, is a timing diagram illustrating the operation of the control circuitry.

DESCRIPTION OF THE PREFERRED EMBODIMENT and belt 31. A carrier 25 is mounted forwardly of the drum for carrying hammer is along a print line 27 parallel to the axes of both drum 13 and shaft 23. I

The drum is driven by electric motor 29 through a toothed drive belt 31. The drum is driven continuously by the motor to move print elements or type on the periphery of the drum past the print line 27. The print elements, which may include letters, numerals and any other symbols (hereinafter referred to as characters), are arranged on the periphery of the drum in rows which are parallel to the drum axis and in columns which extend part way around the drum. The columns of type extend part way to allow time for the hammer 15 to be retracted after a character is printed. The printing type are arranged such that the characters of each column are in a predetermined sequence and the sequence is repeated twice in each column with a dwell or blank area between the sequences. Furthermore the print elements for each column are oriented such that at a given time the same character appears in each column along the line of print 27.

I-Iammer 15 is pivotably mounted on carrier 25. The hammer is conventionallybiased away from drum l3 and solenoid 33 operates to fire the hammer forward against paper 35 and drum 13. The characters in a line of print are printed serially from right to left.

v Shaft 37, located at the right side of the printer 11 and perpendicular to shaft 23, is driven by motor 29 in synchronism with drum 13. Drive pulley 39 is mounted on the front end of shaft 37 and guide pulley 41 is mounted at the left side of the printer. Each pulley has its axis of rotation horizontally disposed. Transport belt 17, an endless belt, is passed around the pulleys 39 and 41 and is driven in a counterclockwise direction by the rotation of shaft 37 which drives pulley 39.

In the aforementioned Kondur, Jr. patent, there is a detailed description of the clutch means for engaging the carrier with the transport belt. In the present invention the location of such a clutch means in designated 43. The clutch means 43, which includes a solenoid 45 for activating the clutch (FIG. 2), is attached to carrier 25. When the solenoid 45 is activated the clutch means 43 engages the teeth of the belt 17 and the hammer and carrier are transported from right to left along the line of print 27. Spring 47 urges the carrier 25 to a rest position which is defined as the extreme right side of .the line of print 27.

Mounted on one end of shaft 23 is a character timing disc 19 having a series of flux producing points, such as teeth 49, on its periphery. The flux producing points or teeth correspond to the location of the various type elements on the periphery of the drum 13. Since there are two sets of type elements on the periphery of the drum 13, which are separated by blank areas or dwells, there are two corresponding sets of teeth 49 on the'periphery of disc 19 and two corresponding dwells. The use of two sets of type elements or characters will be more fully explained hereinafter. A bevel gear 51 is mounted on the right end of shaft 23. Shaft 53 is mounted on the printer 1 l to the right of shaft 23 and perpendicular thereto. (Shaft 53 is parallel to shaft 37.) Bevel gear 55 is 'mounted on the front end of shaft 53 and is oriented to mesh with bevel gear 51. Transport timing or belt engage disc 21 is rotatably mounted on the rear of shaft 53. Disc 21 has a single flux producing point, such as stud 63, thereon. Therefore, when motor 29 rotates drum 13, character disc 19 and transport disc 21 rotate in synchronism therewith.

A double-ended transducer 57 is located intermediate the two

discs

19 and 21. The front end 59 of the double-ended transducer responds to the flux producing points or teeth 49 on the character disc 19. The rear end 61 of the transducer 57 responds to the flux producing point or stud 63 on the second disc 21.

The structure of the double-ended transducer can be understood by referring to FIG. 2. The front and

rear ends

59, 61, respectively, of transducer 57 are two pole pieces of ferromagnetic material. A permanent magnet 65, which may be a ceramic magnet, is disposed between and in contact with both

pole pieces

59, 61. A coil 67 is wound around one pole piece (e.g., 59) and then around the other pole piece (e.g., 61) in the same direction. Hence the two ends of the transducer are wound in series. One end of coil 67 is grounded and the other end isconnected to a control circuit 69 via lead 71. Altematively, both ends of coil 67 could be connected to the control circuit 69 as though the coil were the secondary of a transfonner.

The control circuit 69 includes a phase demodulator 73, a two input comparator 75, a data source 77, a three input AND-gate 79 and an SCR (Silicon Controlled Rectifier) 81. The output of phase demodulator 73 is connected as one input to comparator 75, via lead 83, and as one input to three-input AND-gate 79, via lead 85. The output of data source 77 is the Second input to comparator 75, via lead 87, and the second input to AND-gate 79 via lead 89.

When carrier 25 is in the rest or home" position, as defined previously, magnetic shunt 91 is prevented from entering the magnetic path between magnet 93 and magnetic switch 95 and switch 95 is closed. Lead 96 connects switch 95 to the third input of AND-gate 79. Therefore, only when switch 95'is closed can AND-gate 79 be enabled. Once carrier 25 starts to move along the line of print 27 the shunt 91 moves between magnet 93 and switch 95 opening the switch 95 and inhibiting AND-gate 79. A fuller explanation of the operation of the printer, including the cooperation between carrier 25 and shunt 91, may be found in US. Pat. No. 3,472,352, Kondur, Jr., assigned to the assignee of the present invention.

The output of AND-gate 79 is connected to the gate of SCR 8]. The cathode of the SCR is grounded and the output of the SCR is taken from the anode and connected to a tum off or timer 97. The output of timer 97 is connected via lead 98 to clutch-engage solenoid 45. When AND-gate 79 is enabled the output therefrom fires SCR 81. The output from the SCR activates the clutch solenoid 45 via lead 98 to permit the belt clutch 43 to engage the toothed transport belt 17. Since one input to AND-gate 79 occurs only when switch 95 is closed, the clutch can only be energized when the carrier 25 is at the rest position. At the completion of a line of print, conventional timer 97 will deactivate SCR 81 and de-energize solenoid 45. Clutch 43 will release the toothed belt 17 and spring 47 will return the carrier to its rest position. v

Comparator is a conventional logic device which provides an output only when the two inputs agree or match. One

input to comparator 75 is the character to be printed (from data source 77 via lead 87) and the other input is the character on the drum in position to be printed (from teeth 49 via demodulator 73 and lead 83).'The output of comparator 75 is connected via lead 99 to one input of a two input AND- gate 101. The other input of AND-gate 101 has an inverted leg 111. The output of switch is also connected via lead 1 13 to this inverted leg 111 of the AND-gate 101. Hence, AND-gate 101 functions to indicate the presence of a signal from the comparator 75 and, an open switch 95. (The absence of a closed switch 95.) Recalling the earlier discussion, open switch 95 indicates that the carrier is not at rest but has engaged transport belt 17 and is moving along the line of print 27. When gate 101 is enabled, itsoutput, via lead 115, activates hammer solenoid 33 to fire the print hammer 15.,

Referring next to FIG. 3, the logic circuitry of the phase demodulator 73 will be explained. The demodulation circuit 73 includes a differential amplifier 117, having two outputs designated A and B. The A output of the differential amplifier is connected to an amplifier or driver 119 and the driver is connected to an AC coupled timing circuit 121. The output of timing circuit 121 isconnected as one input to each of the AND-

gates

123 and 125.

The B output of the differential amplifier 117 is connected to a first inverter 127. The output of inverter 127 is connected through a diode 129, which is poled with its anode toward inverter 127, to a second inverter 131. One terminal of a capacitor 133 is connected to the junction 130 of the cathode of diode 129 and inverter 131.'The other terminal of the capacitor is biased negative. The second inverter 131 has its output connected to the other input of AND-gate 123. The output of inverter 131 also serves as an input to a third inverter 135. The output of inverter 135 is the second input to AND-gate 125.

Since a magnetic transducer responds to the rate of change of reluctance, the output voltage of the magnetic transducer is the first derivative of the amount of activating mass in front of the pole piece of the transducer. When a character pulse tooth 49 from character disc 19 passes the front pole piece 59, the slope or rate of change of the voltage output of the transducer is positive on the leading edge, zero in the center, and negative on the trailing edge. When the belt engage stud 63 passes the rear pole piece 61 the reverse output waveform occurs since the stud passes the opposite pole piece of the transducer and the pole pieces are wound in series. The output is negative on the leading edge, zero in the center, and positive on the trailing edge. This is seen from Lenzs Law for magnetically inducing current into a coil.

The various circuits employed in the logic circuit of FIG. 3 are well known in the art. However, in order to provide a complete disclosure, illustrative schematic circuits are shown. FIG. 4A is representative of the differential amplifier 1 17. The two inputs may be obtained from the transducer 57 using a conventional transformer. (Alternatively both ends of coil 67 could be used instead of grounding one side of the coil.) The two PNPotransistors have their bases connected through two equal resistors R (1,000 ohms each). At the junction of the two resistors a negative bias is provided by voltage V, (V l4 volts). The emitters of the transistors are connected together and a bias is provided to the emitters via voltage V (V 28 volts) connected through resistor R (5,100 ohms). The collector of each transistor is connected to ground through a resistor R; (6,200 ohms) and the outputs of the amplifier are taken from the collector of each transistor.

Amplifier or driver 1 19 is noninverting merely shapes the A output of the differential amplifier and does not contribute to the logic considerations.

FIG. 48 illustrates a typical inverter such as

inverters

127, 131, and 135. The input to the inverter passes through resistor R (30 kilohms) and then to the base of a PNP-transistor. Negative potential is provided at the junction of resistor R and the base of the transistor via voltage V through resistor R (270 kilohms). The emitter of the transistor is biased negative (V,) and the collector of the transistor is connected to ground through resistor R The output is taken from the collector.

Referring to FIG. 4C a representative schematic circuit for the AC coupled timing circuit 121 will be explained. The input to the timing circuit is connected to one terminal of a coupling capacitor C (470 picofarads). At this input a negative bias is provided from voltage V coupled through resistor R, (2,000 ohms). The other terminal of the capacitor is coupled through an equal resistor R to the base of a PNP-transistor. The junction of the capacitor and the second resistor R is connected via resistor R (47 kilohms) to ground. The emitter of the transistor is connected to a source of negative potential V and the collector of the transistor is coupled via resistor R to ground. The output of the timing circuit is taken from the collector. I I

Referring to FIGS. 2, 3, and 5, the timing sequence of the control circuitry will be explained. FIG. 5A illustrates the output waveform of the transducer 57. FIG. 5B represents the'A output of the differential amplifier 117. FIG. 5C represents the output signals from the timing circuit 121 and, as can be seen by comparison with FIGS. 5A and 5B, the timing circuit generates an output signal on the negative-going portion of each output pulse from the A output of the differential amplifier. FIG. 5D represents the B output of the differential amplifier 117 and FIGS. 5E, 50, and SF represent the pulse trains taken from the output of

inverters

127, 131, and 135, respectively. When an inverter (e.g., inverter 135) is referred to as high its output will enable the circuit to which it is connected (e.g., AND-gate 125) and when an invertor is referred to as low" its output will inhibit the gate to which it is connected.

In the quiescent state t, the differential amplifier 117 is biased to hold the output of amplifier or driver 119 high and inverter 127 low. Amplifier 1 19 being high" holds the output of timing circuit 121 low which inhibits both AND-

gates

123 and 125. Inverter 127 low holds inverter 131 high, and, inverter 131 high holds inverter 135 low. As a character tooth 49 starts past pole piece 59 of transducer 57, the output of the transducer (FIG. 5A) causes an output from the differential amplifier (FIGS. 5B, 5D). This output causes inverter 127 (FIG. SE) to go high", capacitor 133 to charge, inverter 131 (FIG. 5G) to go low, and inverter 135 (FIG. 5F) to go high. This is shown, for example, as time I in FIG. 5.

As the center of this tooth passes the transducer, at time inverter 127 goes low", but the charge on the capacitor 133 causes a delay which holds inverter 131 low and inverter 131 low holds inverter 135 high. With the passing of the center of the tooth the output of amplifier or driver 119 also goes "low. When the output of the driver goes low, it triggers the AC coupled timing circuit 121. The timing circuit is a conventional circuit which responds to the negative-going edge of a pulse to generate an output. Since the output of the timing circuit 121 is used to sample or enable the

gates

123 and 125 it is often referred to as a pulse sampling circuit."

At time when a pulse sample signal is generated by timing circuit 121, inverter 127 has just gone "low" but capacitor 133 will hold junction 130, the input of inverter 131, high.

The presence of the high" at the input of inverter 131 will cause its output to remain low" which in turn holds the output of inverter 135 high. Since inverter 131 is low it inhibits AND-gate 123. This prevents a signal from being generated along lead to AND-gate 79 and inhibits engaging the carrier 25 to the transport belt. However, since the output of inverter 135 remains high", AND-gate 125 is enabled. This permits a signal to be passed via lead 83 to the comparator 75.

At time when capacitor 133 discharges, inverter 131 goes high and inverter 135 goes on. The logic circuitry is now in the prevents the output along lead 83 from serving as an input to the comparator 75. But since inverter 131 is high, AND-gate 123 is satisfied and the output on lead 85 permits the carrier 25 to engage the transport belt 17.

As the middle of the stud 63 passes the pole piece (1,, inverter 127 will go high and charge capacitor 133. However, the timing circuit will not trigger again'until a new tooth (or stud) passes a pole piece. Hence, the delay in discharging the capacitor until time i when the quiescent condition is reached, will not affect the output of

gates

123 or 125.

Additional aspects of the operation of this invention will now be described. Assume that motor 29 is operating and, via belt 31, is driving the drum 13. The first condition is to initiate a line of print. The carrier 25 is at the extreme right hand position, that 'is, at the rest position. When this occurs the magnetic shunt 91 will not be between magnet 93 and switch 95; therefore, the switch contacts will be closed." By virtue of switch 95 being closed an input will be presented, via lead 96 to one of the three inputs of AND-gate 79. An appropriate signal will be presented from data source 77 via lead 89 to a second input of AND-gate 79. Since a line of print is to be initiated, as distinguished from printing various characters,- there is no signal from data source 77 to comparator 75 on lead 87 at this time.

The rotation of shaft 23 by the motor 29 causes disc 19 to rotate and the teeth 49 to pass pole piece 59 of double-ended transducer 57. A series of output pulses are generated similar to those shown in FIG. 5A beginning at These pulses will each enable AND-gate 125, but, since one input is missing to comparator 75 (there is no input at lead 87) the hammer will not fire and no character will be printed. In addition, via in verted leg 111 of AND-gate 101, the hammer is precluded from firing. Belt engage disc 21 is also rotating, and, when belt engage stud 63 passes the right pole piece 61 of transducer 57, a waveform similar to that shown at times 1 -1 in FIG. 5A is generated. This will enable AND-gate 123 and a signal is sent via lead 85 to AND-gate 79. Since all three inputs are now applied to AND-gate 79 the gate is enabled and this fires the SCR 81. When SCR 81 fires, a signal via lead 98 energizes the belt engage clutch solenoid 45 and the carrier 25 engages the belt 17. This starts the carrier 25 moving along the line of print 27 from right to left.

Once the carrier 25 has engaged transport 17 and is travelling along the line of print the second condition, i.e., the characters to be printed, is communicated from the data source 77 via lead 87 to comparator 75. As the teeth 49 of demodulator 73. These pulses are sampled on the negative'or trailing edge, and each pulse enables AND-gate 125 as explained previously. Each time gate 125 is enabled, a signal is passed to comparator 75 via lead 83. When and only when the signals in comparator 75 match, an output is provided via lead 99 as one input to AND-gate 101. When the carrier 25 starts to move from the rest position the magnetic shunt 91 moves between magnet 93 and switch 95. This operation was more fully described in the aforementioned Kondur patent. Moving the magnetic shunt between the magnet and the switch causes the switch contacts to open and provides an open circuit along lead 113. This open circuit is converted via inhibit leg 111 at the second input of AND gate'l01. Consequently, when the comparator 75 indicates the appropriate signal, via lead 99, AND-gate 101 is enabled and a signal via lead 115 fires hammer solenoid 33 causing the hammer 15 to strike the drum 13 and print the appropriate character along the line of print 27 Switch 95 opens as the carrier moves from the rest position since shunt 91 enters the path between magnet 93 and the switch. Lead 96 connects the output of switch 95 to one input of AND-gate 79, and, when switch 95 is open AND-gate 79 is inhibited. This prevents a second belt engage signal from being transmitted to the clutch solenoid 45 once the belt has been engaged for a given line of print. As the drum 13 continues to rotate, the stud 63 will again pass the right end 61 of transducer 57. However, absent information from the data source 77 to AND-gate 79 requiring a new line of print and absent the closing of switch 95, this signal has no effect. As character disc 19 continues to rotate, the second set of characters on the wheel pass through the print area and, simultaneously, the second set of teeth 49 pass pole piece 59 of transducer 57. Again the appropriate signals are sent through the phase demodulator to the comparator and, when the signals in comparator 75 match, a second character is printed.

Thus it may be seen that when the carrier is at rest the print pulses are inhibited via the closed circuit in switch 95 and the only pulse which can activate the system is a belt engage pulse generated by stud 63 on disc'21. Similarly, once the carrier has started its travel, belt engage pulses are inhibited by the open switch 95 and only the print pulses can activate the system. At the conclusion of a line of print, based on the tim ing considerations of a given line, timer 97 turns off the SCR 81 and de-energizes clutch solenoid'45to release the carrier 25" from the belt.l7. Spring 47 brings the carrier back to rest position ready to print a new line of print.

Various modifications of this system will be obvious to those skilled in the art. For example, since there are two sets of type elements on drum 13 and two sets of teeth 49 on disc 19, for

each revolution of the drum two characters may be printed. Since the print engage pulse is used only once for a single line of print the speed of disc 21 may be reduced without a loss of synchronism. Therefore, by the use of a 2:1 reduction bevel gears the speed of disc 21 may be halved.

In addition, if the comparator 75 is not internally reset after each character is printed, the output via lead 83 may be used for this purpose since the number of teeth 49 correspond to the number of characters which could be printed in a given print position. To accomplish this, one of two alternatives is necessary. First, two studs 63 could be used on disc 21. The studs would be l80 apart. Then, one stud 63 would pass the pole piece'6l after each set of character teeth 49. Second, using only one stud 63, the bevel gears 51, 55 would be required to have a l:2 speed increase. Therefore disc 21 would rotate twice as fast as character disc 19.

Furthermore, pulses from stud 63 may be used as an input to data source 77 to indicate the print positions along a line of print 27. In addition, stud 63 may be replaced by a slot and the direction of the winding 67 on pole piece 61 would be reversed. The opposite polarity waveform would still be obtained from disc 21.

Therefore, it will be appreciated that those skilled in the art may make various changes and modifications and still remain within the spirit and scope of this invention.

What is claimed is: 1. In a high-speed serial printer including a print drum having characters thereon, said drum being rotatable about its axis, a print hammer mounted on a hammer carrier, said hammer carrier having a rest position, and means for continu: ously transporting said carrier along a line of print, said line of print being parallel to said axis, a control system comprising:

timing means coupled to said drum for synchronous rotation therewith, I

a single double-ended transducer having a first transducing means at one end thereof and a second transducing means at the opposite end thereof, said first andsecond transducing means being responsive to said timing means for generating first and second signals respectively, means responsive to said first signal for engaging said hammer carrier with said transporting means, and

means responsive to said second signal for firing said print of said drum relarest position for enabling said engaging means and responsive to said carrier being in other than said rest ing said engaging means.

3. The control system of claim 1 wherein said firing means position for inhibitincludes means responsive to said carrier being in said rest position for inhibiting said firing means.

4. The control system of claim 1 wherein said timing means includes: v

a character disc having flux producing points thereon corresponding to the angular location of the characters on said drum, and an engage disc having at least one flux producing point thereon. i 5. The control circuit of claim 1 wherein said first and second transducer means includes first and second magnetic pole pieces, respectively, and coil means wound on said pole pieces for connecting said first transducer means in series with said second transducer means. 7 i 6. The control system of claim 5 further including circuit means for differentiating between said first and second signals. 7. The control circuit of claim 6 wherein said circuit means includes:

a differential amplifier having an input coupled to said coil means,

logic means coupled to the output of said differential amplifier for differentiating between said first and second signals, and

means coupled to said logic means for transmitting said first signal to said engaging means and for transmitting said second signal to said firing means. 8. The control system of claim 4 wherein said timing means further includes:

means for positioning said engage disc and enabling said at least one flux producing point to pass in proximity to said first transducer means for generating said first signal, and means for positioning said character disc and enabling said flux producing points thereon to pass in proximity to said second transducer means for generating said second signal. 7 9. The control system of claim 8 wherein said character disc includes at least one blank area devoid of flux producing points and wherein at least one of said positioning means includes means for orienting said discs with respect to one another and insuring that said at least one flux producing point of said engage disc passes in proximity to said first transducer means only when said blank area of said character disc passes in proximity to said second transducer means.

Claims

1. In a high-speed serial printer including a print drum having characters thereon, said drum being rotatable about its axis, a print hammer mounted on a hammer carrier, said hammer carrier having a rest position, and means for continuously transporting said carrier along a line of print, said line of print being parallel to said axis, a control system comprising: timing means coupled to said drum for synchronous rotation therewith, a single double-ended transducer having a first transducing means at one end thereof and a second transducing means at the opposite end thereof, said first and second transducing means being responsive to said timing means for generating first and second signals respectively, means responsive to said first signal for engaging said hammer carrier with said transporting means, and means responsive to said second signal for firing said print hammer at the correct angular position of said drum relative to said line of print.

2. The control system of claim 1 wherein said engaging means includes means responsive to said carrier being in said rest position for enabling said engaging means and responsive to said carrier being in other than said rest position for inhibiting said engaging means.

3. The control system of claim 1 wherein said firing means includes means responsive to said carrier being in said rest position for inhibiting said firing means.

4. The control system of claim 1 wherein said timing means includes: a character disc having flux producing points thereon corresponding to the angular location of the characters on said drum, and an engage disc having at least one flux producing point thereon.

5. The control circuit of claim 1 wherein said first and second transducer means includes first and second magnetic pole pieces, respectively, and coil means wound on said pole pieces for connecting said first transducer means in series with said second transducer means.

6. The control system of claim 5 further including circuit means for differentiating between said first and second signals.

7. The control circuit of claim 6 wherein said circuit means includes: a differential amplifier having an input coupled to said coil means, logic means coupled to the output of said differential amplifier for differentiating between said first and second signals, and means coupled to said logic means for transmitting said first signal to said engaging means and for transmitting said second signal to said firing means.

8. The control system of claim 4 wherein said timing means further includes: means for positioning said engage disc and enabling said at least one flux producing point to pass in proximity to said first transducer means for generating said first signal, and means for positioning said character disc and enabling said flux producing points thereon to pass in proximity to said second transducer means for generating said second signal.

9. The control system of claim 8 wherein said character disc includes at least one blank area devoid of flux producing points and wherein at least one of said positioning means includes means for orienting said discs with respect to one another and insuring that said at least one flux producing point of said engage disc passes in proximity to said first transducer means only when said blank area of said character disc passes in proximity to said second transducer means.