US3712212A

US3712212A - Variable printer intensity control

Info

Publication number: US3712212A
Application number: US00198156A
Authority: US
Inventors: J Beery
Original assignee: Burroughs Corp
Current assignee: Unisys Corp
Priority date: 1971-11-12
Filing date: 1971-11-12
Publication date: 1973-01-23
Anticipated expiration: 1990-01-23

Abstract

Apparatus for printing characters with an impact intensity varying according to the surface area of the character being printed. Included in the apparatus is a cyclically movable character bearing member, such as a rotary print wheel or drum or an endless belt and one or more print hammers cooperable with the member forming a printing couple for printing characters. An electromagnetic field produced by a solenoid initiates the flight of the hammer against a document which may be moved relatively thereto as the printing operation is performed. The current through the solenoid coil is limited by resisters of different values which are controlled by electrical gates for selectively varying the amount of current supplied to the coil for driving the hammer. The timing of the printing is kept in synchronization with the document movement by means of an electromechanical clock capable of dividing each character position into an equal number of zones. During the operation of the printing apparatus, the sequence of accessing the digits to be printed, positioning the print wheel, and firing the hammer continues as the document moves through the apparatus. Associated with the print wheel and jointly rotatable therewith is a disk having a plurality of coded positions represented by apertures therein each position representing a printing character position on the print wheel.

Description

United States Patent Beery v 3,712,212 Jan. 23, 1973 VARIABLE PRINTER INTENSITY CONTROL [5 6] References Cited UNITED STATES PATENTS 2,935,935 5/1960 Preston et a1. ..101/93 R 3,172,353 3/1965 Helms ..101/93 C 3,218,965 11/1965 Simons et a1 ..101/93 R 3,513,774 5/1970 Pawletko et al. ..10l/93 C Primary ExaminerWilliam B. Penn Att0rneyPaul W. Fish et al.

[57] ABSTRACT Apparatus for printing characters with an impact intensity varying according to the surface area of the character being printed. Included in the apparatus is a cyclically movable character bearing member, such as a rotary print wheel or drum or an endless belt and one or more print hammers cooperable with the member forming a printing couple for printing characters. An electromagnetic field produced by a solenoid initiates the flight of the hammer against a document which may be moved relatively thereto as the printing operation is performed. The current through the solenoid coil is limited by resisters of different values which are controlled by electrical gates for selectively varying the amount of current supplied to the coil for driving the hammer. The timing of the printing is kept in synchronization with the document movement by means of an electromechanical clock capable of divid' mg each character position into an equal number of zones. During the operation of the printing apparatus, the sequence of accessing the digits to be printed, positioning the print wheel, and firing the hammer continues as the document moves through the apparatus. Associated with the print wheel and jointly rotatable therewith is a disk having a plurality of coded positions represented by apertures therein each position representing a printing character position on the print wheel.

6 Claims, 3 Drawing Figures PATENTEDJAH23 I975 SHEEI 1 OF 2 24 VDC FIG. 1. fiao 28 26 1332 I l l I l l i l iv "villi.

22 FFREG INVENTOR.

JACK BE ERY V3. i /Q ATTORNEY.

UZZQMJ PATENTEDJAN 23 I873 SHEET 2 BF 2 MEI EMESZI v wZON N mZON MZON FEE-m 50 6 :82 o ow m N GI 1 VARIABLE PRINTER INTENSITY CONTROL CROSS REFERENCE TO RELATED PATENTS AND PATENT APPLICATIONS Reference may be made to the patent to Jack Beery U.S. Pat No. 3,573,589 entitled POSITION SERVO SYSTEM FOR A MOTOR INCLUDING DETENT- ING AT DESTINATION and also to the co-pending application of Richard M. Williams Ser. No. 72,921, filed Sept. 1?, 1970, and entitled DOCUMENT EN- CODING APPARATUS.

BACKGROUND OF THE INVENTION This invention is directed to that field of art pertaining to printing of data on record media and more particularly to the varying of the printing impact on such media in accordance with the surface area of the characters being printed.

SUMMARY OF THE INVENTION An important object of the invention is to provide an improved control system for modifying the impaction of a print hammer or the like upon record media and particularly in accordance with the surface area of the characters to be printed.

A further important object of the invention is to provide a printer of the aforesaid character which includes an electronic circuit of improved character for controlling the hammer by appropriately selected electrical signals for varying the impact thereof upon record media.

Another important object of the invention is to provide an improved printer of this character which is economical to manufacture and is rugged and durable in use.

In carrying out these objects, the present invention contemplates a printing apparatus which in its broader aspects employs electrical signals of varying energy for modifying the operation of the printing couple composed of a print hammer and a cyclically movable member between which record media are fed. More particularly, the invention contemplates a control circuit associated with printing apparatus and particularly with a document encoding station including an impact print member cooperable with a character bearing cyclically movable member for printing on documents moving at relatively high speeds. Included in the control circuit is means which, depending upon the surface area of the selected character to be printed, can modify the current supplied by the circuit to the energy producing means for impacting the hammer against a document interposed between the hammer and the character bearing member. Further included in such control circuit are a plurality of electronic gates variably controlled and operated to modify the amount of current supplied to the hammer to vary its impact intensity.

The above'listed objects and advantages, other objects, advantages, and aspects of the invention will be more fully explained in the following detailed description. For a more complete understanding of the invention, reference may be had to the following detailed description in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a preferred circuit for varying the amount of current supplied to a print hammer driving solenoid for impacting the latter upon record media, the circuit including an electromechanical clock generator for determining the firing time of the print hammer;

FIG. 2 is a chart illustrating the timing diagrams for firing the print hammer; and

FIG. 3 is a schematic view of the separate driver circuits associated with each hammer arid showing their connections to the hammer driving solenoid.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION The printing apparatus to be described hereinafter may be used to encode information on record media, such as bank checks, either in magnetic ink or conventional ink but with the characters so shaped as to be recognized by a machine. More specifically, such printings may be in magnetic ink character recognition form, referred to as MICR, or in optical character recognition form, referred to as OCR, depending upon the nature of the equipment for machine reading these characteristics. If desired, the printing may be performed with magnetic ink in a font capable of being readily sensed by an optical recognition device. The amount of intensity with which the print hammer impinges upon a record member or document not only has an effect on the appearance of the characters to the eye but also on the machine readability thereof.

The printing couple of the illustrated embodiment of the invention comprises a print wheel or disk 10 rotatable about an axis 12 and having one column of characters circularly arranged around the periphery of the wheel. One or more such sets of printing characters may be included in the column depending upon the peripheral dimension of the wheel and other factors. Associated with the type wheel and forming the opposite member of the couple is any suitable shaped print hammer 14. A shank member 16, which as shown may be directly connected to the hammer, is surrounded and controlled by a coil 18 of an'electromagnetic device such as a solenoid. In normal operation the type wheel is rotated to bring a selected character into position to be struck by the hammer 14 in the absence of a document therebetween. In the normal operation of the printing couple, successive documents would be fed between the hammer and the print wheel and the impact of the hammer on the document would cause the transfer of an ink image of the selected character onto the document.

The type wheel 10 may be rotated different angular distances in opposite directions or continuously in one direction. In the former case, the wheel may be driven by a servo stepping motor which may be of the character disclosed in the aforesaid U.S. Pat. No. 3,573,589, so that the type wheel may be stepped in opposite directions and stopped at very fast rates. The rotatable positioning of the type wheel is accomplished by induction coils energized by a set of coil drivers for bringing the selected type on the wheel into print position at which time the wheel is stopped to receive the impact of the hammer disposed on the opposite side of the transport path along which the documents are fed. As described in the patent, the print wheel may be adjustably rotated in either direction and selectively controlled to rotate the wheel in the shortest direction to bring the selected type'on the wheel into printing position. I

Associated with the type wheel and jointly rotatable therewith on the axis 12 thereof is a control plate or disk having a plurality of coded positions thereon which may be a plurality of apertures through which light from a set of lamps generally indicated at 22 are projected and received by a corresponding set of photocell units each including an amplifier generally indicated at 24. Each coded position represents a printing position on the type wheel 10. The four photocell units 24 represent the binary values of 1, 2, 4 and 8 the purpose of which will be described in more detail hereinafter.

The timing of the operation of the illustrated embodiment of the invention is performed by an electromechanical clock including a rotatable member or disk 26 rotatable about axis 28 and separate and apart from the print wheel 10 and disk 20. A circular portion of the disk is disposed in intercepting relation between a lamp 30 and a photocell 32. The circular portion is provided with a series of equally spaced apart apertures (not shown) which alternately admit and intercept the passage of light from the lamp to the photocell. Usually, the disk is rotated at a constant speed but this is not essential for the illustrated embodiment of the invention. The current generated in the photocell as a result of the successive impingements of light therein is increased by the amplifier 34 and then fed to a shift register 36 which serves as a character zone counter arranged to emit pulses on channels 38, 40 and 42 designated by the legends Z1, Z2 and Z4 respectively.

forming three inputs of a NAND gate 44. A fourth input to the NAND gate, that indicated at 46, bears the legend Encode. The single output of the NAND gate is connected to an inverter 48 and its output in turn is connected to a conductor 50 along which the hammer firing signals are conducted.

As previously mentioned the intensity of the impact of the hammer is determined by the amount of current delivered to the solenoid coil 18. Variations in this current are provided by the series of gating circuits illustrated in the balance of FIG. 1 and by the electrical parallel relationship of the solenoid drivers and associated resistances of different values which are connected to a common lead extending to the coil 18. With more specific reference to this portion of FIG. I, it is noted that the coil is connected to a plus 24 volts do. from which variable amounts of current are derived for activating the coil and thereby imparting motion to the hammer 14. One lead of the coil is connected by a common conductor 51 to two or more driver circuits which are designated 52 and 54 and are respectively illustrated in detail in FIG. 3. The output of each

driver

52 and 54 is connected to a

resistance

56 and 58 respectively, each of different resistive value, and these in turn are directly connected to the common lead 5] previously mentioned. Each

driver circuit

52 and 54 is respectively connected to a

NAND gate

60 and 62. These two gates have one of their inputs connected in common to the output 50 of the clock circuit for receiving hammer firing signals therefrom. Each of the remaining inputs to the

NAND gates

60 and 62 are connected to a separate series of NAND gates, certain ones of which have inputs connected to the photocell outputs PCl, PC2, lfC4 and PC8 and their respective inverted outputs PCl, W2, I 64 and W as identified by the legends thereon.

More specifically with reference to the respective series of gating devices connected to the hammer driver it is noted that NAND gate 60 has one of its inputs connected to the output of gate 64 which in turn has one of its inputs being served by the output of NAND gate 66 and which in turn is connected to an inverter 68 and that in turn to NAND gate 70. In this gate series,

NAND gates

66 and 70 have inputs connected to certain of the outputs or inverted outputs of the photocell units 24 previously mentioned. In a similar fashion, NAND gate 62 associated with driver circuit 54 has the second of its inputs being served by the output of NAND gate 72 and this gate in turn is connected to the output of gate 74 and the latter has its input connected to the output of NAND gate 76. In this series of connected gates, it is noted that

NAND gate

72 and 76 have NAND gates connected to the remaining outputs and inverted outputs of the photocell units 24 previously mentioned. In addition, the second input of gate 64 is served by the output of gate 72 and similarly the second input of gate 74 is served by the output of gate 70 to complete the logic formulas.

The logic of these series of gates and their respective connections to the outputs of the photocell units 24 is such that the hammer driving circuits are kept informed of the position of the type wheel and particularly each printing character thereon so that regardless of direction of rotation of the wheel and the position at which it is stopped -to perform the printing operation the driving circuits corresponding to the characters to be printed are either independently energized or simultaneously energized to provide different current values for energizing the solenoid coil 18. In other words, either one or both of the

drivers

52 and 54 can be turned on individually or simultaneously. In this manner, three intensities of current can be obtained for the solenoid coil circuit from two driver circuits. The following chart shows the driver configurations, the driver current being selected to provide the desired hammer force found necessary for good MICR or OCR ink transfer without embossment for each character position on the wheel.

Medium Driver Light Driver Wheel Position waqauaunw-c l0 AMOUNT 12 ACCT NO.

13 DASH l4 OBLITERATE imum amount of current is supplied when both drivers are turned for printing a large surface area character such as 8" is printed. All of the remaining characters may be printed using the medium current driver. The characters printed may be in fonts suitable for MlCR or OCR characters. The energy noted in the above chart is for E 13 B printing only. Such fonts differ from the conventionally shaped characters normally used for printing and thus their respective surface areas forming the image differ from their corresponding conventionally shaped characters.

The circuits so far described will provide three different hammer impact values as indicated in the above chart. For more impact intensity values an additional driver circuit and its associated gating elements similar to those previously described and shown may be provided as indicated in dotted outline at the right of FIG. 1. Such a driver circuit indicated at 78 will be similar to the

circuits

52 and 54 illustrated in FIG. 3 and will include a resistance 80 which will differ in its resistive value from either of the two previously described

resistances

56 and 58. Associated with the driver circuit 78, as previously described in connection with

driver circuits

52 and 54, is a NAND gate 82 having its output connected to the driver circuit 78 and having two inputs, one of which is connected to the common lead 50 from the zone counter 36 which serves to deliver the hammer firing signals. The other input to NAND gate 82 is connected to the output of NAND gate 84 whose several inputs are connected to the photocell outputs PCl, PC2, PC4 and PC8 and their respective inverted outputs either directly or through one or more NAND gates in the manner previously described in connection with the gating circuitry for the

hammer driver circuits

52 and 54. With the addition ofa third driver circuit 78 and its associated resistance and gating devices it is possible, by judicial selection of any one or a combination of any two or all three driver circuits for energizing the solenoid coil 18, to expand the print impact intensity capability to eight different values so that from three parallely related driver circuits a larger number of impact intensity values are available.

The clock generator illustrated in the upper left portion of FIG. 1 is designed to provide eight pulses for each character position of the type wheel and thus divide each character position into eight zones. The clock signals which are received by the zone counter 36 provide three signals of different time durations for regulating the operation of the different parts of the printing apparatus including the firing of the print hammer. In the illustrated embodiment of the invention, the encoding is a digit-by-digit operation. The information to be encoded on the document is withdrawn from the memory in the system and transferred digit by digit to an encode register where it is used to position the print wheel 10 in the manner described in the aforesaid US. Pat. No. 3,573,589. The firing of the print hammer is accomplished in the last or eighth zone counted by the zone counter 36 at which time the selected character is already in position for printing and the document is moving to bring the print receiving area thereof into printing position to receive the image of the selected character.

FIG. 2 is a timing diagram illustrating the timing of the pulses produced by the clock generator and by the zone counter with particular reference to the firing of the print hammer in the last counted zone. The constant frequency clock generator 26-32 produces the equally spaced apart pulses shown at 86. When the arrival of a document between the print wheel and the hammer is sensed, such as by an appropriately located photocell, a start signal is generated which is shown at 88 runs for the period of the time that the document is in the printing station. The output 38 of the zone counter 36 represented by the legend Z1 delivers a series of pulses switching or alternating between two voltage levels each having a time duration equal to the time span between two adjacent clock pulses as illustrated at in FlG. 2. The output 40 represented by the legend Z2 delivers pulses 92 of twice the time duration and half the frequency of the pulses 90. The third output 42 represented by the legend Z4 produces pulses each having a time duration of four clock pulses as illustrated at 94 in FIG. 2. It is apparent from the darker area in each of the graphs represented by 90, 92 and 94 that a coincidence of a plus voltage occurs, which is an encode signal of like sign is received on the fourth input to the NAND 44 44, will produce, a signal such as represented at 96 on the hammer firing channel 50 leading to the

NAND gates

60, 62 and 82 of the circuit for energizing the solenoid coil 18. Unless inhibited by other components in the circuitry of the apparatus, the encode signal on input channel 46 of NAND gate 44 continues active or high so that when Z1, Z2 and Z4 in FIG. 2 are all high at one time, which is represented by time zone 7, a print signal 96 is delivered by channel 50 to one of the inputs of each of the

NAND gates

60, 62 and 82 and enabling their respective driver circuits for hammer activation depending upon the signals received on the remaining inputs of these gates.

The

driver circuits

52 and 54 shown in FIG. 3 and the one not illustrated therein for driver circuit 78 are of conventional design and need not be described in detail. Suffice to say that when an input pulse going from a value of +5 volts to ground is switched at input points, A or B, the transistors Q1 or Q2 respectively will swing from +24 volts to less than +2.0 volts allowing the load to conduct, which load in this instance is the solenoid coil 18 and either or both of the

resistors

56 or 58. When the points A or B of the driver circuits are moved from ground to +5 volts, the transistors Q1 or Q2 turn off, and if all such transistors associated with the driver circuits are similarly effected, then the coil 18 is also switched off. When the coil is cut off it wants to continue to conduct and goes to +24 volts plus an additional surge from the coil which may reach 400 to 500 volts. Under normal conditions such high voltage surges would impair if not destroy the transistors which may be only good for about 60 volts. To protect against such happenings, provision is made in the coil circuit for limiting this inductive surge or kick" which as shown in FIGS. 1 and 3 is accomplished by means of a diode 98 and zener diode 100 arranged as shown in FIGS. 1 and 3. The diode 98 suppresses the inductive surge and the zener diode is the controlling element allowing the voltage to go a limited distance above the source voltage of 24 volts but below the destructive voltage of the transistors before switching off the coil.

The operation of the embodiment of the invention illustrated herein is believed to be self-evident from the drawings and the above recited description. First, it may be understood that one of the driver circuits, such as 52, has a relatively high resistance 56 which renders this driver circuit as a low or light intensity driver, and that a second of the driver circuits, such as 54, has a lower valued resistance 58 which renders it as a medium intensity driver, and so forth for the remaining driver circuits in the system. The trains of logical gates leading to the set of

gates

60, 62 and 82 translate the characters successively brought into printing position by the print wheel into the signals which not only identify each such character but activate a selected one or selected two or more of the driver circuits for supplying different currents for energizing the solenoid coil 18. The electrical parallel relationship of the driver circuits and their respective resistors provide a larger selection of impact intensities for the different characters on the print wheel than there are drivers for propelling the single print hammer. The addition of more driver circuits, such as represented in phantom at 78 and 80, multiplies the number of impact intensities available not only for printing the decimal characters illustrated on the print wheel 10 but also a full alphabet and additional symbols.

Although the illustrated embodiment of the invention herein employs a stepping type of rotary print member capable of being reversely driven, it is to be understood that the invention is also applicable to a printer having a character type bearing member which is continuously movable or rotatable in one direction. In the latter type of printing apparatus, suitable control means would be provided for signifying each character on the type bearing member as it approaches the print position and also for controlling the energization of the solenoid coil 18 proportional to the surface area of the character being printed and thus propel the print hammer with the proper amount of energy for providing uniform printing of the characters on a record medium and while both type bearing member and record medium are moving. ln other words as each character on the print member moves into printing position not only is the nature of this character recognized but also the area of its print face so that a proper amount of energy is supplied to the solenoid coil for initiating the flight of the print hammer against the record medium with the desired impact so that all characters printed are all of substantially the same degree of intensity.

While a particular embodiment of the invention has been shown and described, it will be understood, of course, that it is not desired that the invention be limited thereto since modifications may be made, and it is therefore contemplated by the appended claims to cover any such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A printing device including, in combination;

a cyclically movable printing member carrying a plurality of printing characters, said characters varying to printing areas from a relatively low to a relatively high degree,

a hammer assembly including a hammer predisposed to strike a printing character brought into alignment with its path of movement and to print an image of the struck character upon a record medium interposed therebetween and further including electrically powered means for propelling the hammer toward the printing member,

means for moving said printing member to bring characters carried thereby successively into alignment with the path of movement of said hammer,

circuit means for delivering varying amounts of current to the hammer propelling means for operating the same including a set of logic gates each having two inputs which when concurrently signalled will activate the gate, said gates each being capable when individually activated of causing the delivery of a distinctive amount of current to the hammer propelling means for operating the same which differs from the amount of current caused to be delivered by other gates in said set of gates and also capable when two or more of the gates of said set are concurrently activated for causing the delivering of still different amounts of current to the hammer propelling means for operating the same,

means responding to the aligning of each printing character carried by said printing member with the path of movement of said hammer for delivering a first electrical signal to one of the two inputs of one or more of said logic gates, and

means also responding to the positioning of each printing character in alignment with the path of movement of said hammer for delivering an electrical signal to the other one of the two inputs of one or more of said logic gates concurrently with the delivery ofsaid first signals for selectively activating said one or more gates in accordance with the degree of the printing area of the character brought into alignment with the hammer with the result that the intensity with which the hammer will strike a selected printing character can be proportioned to its printing area.

.2. A printing device as defined in claim 1 characterized in that the electrically powered means for propelling the hammer comprises a solenoid coil which is energized by the activation of any one or more of said logic gates.

3. A printing device as defined in claim 2 characterized in that said circuit means further includes resistance components electrically connected individually to each of said logic gates which differ in resistive value from one another.

4. A printingdevice as defined in claim 3 characterized in that said resistance components are connected in electrical series relation with their respective logic gates and connected to the solenoid coil in electrical parallel relation to one another.

5. A printing device including, in combination;

a cyclically movable printing member carrying a plurality of printing characters, said characters varying in printing areas from a relatively small extent to a relatively large extent,

a hammer assembly including a hammer operable to strike anyone of the printing characters and to print an image of the struck character upon a record medium interposed therebetween,

means for moving said printing member to bringthe characters on the member successively into alignment with the path of movement of said hammer,

electrically powered means for propelling the hammer against the printing member with varying degrees of intensity including a circuit having a plurality of resistors of different resistive values disposed in the circuit in electrical parallel relationship to one another,

control means for said hammer propelling means including switching means individually associated with each of said resistors and operable to either permit or cut-off the flow of current through its associated resistor, and

means responding to the movement of each printing character into alignment with the hammers striking path of movement for activating an individual one or simultaneously activating at least two of said switching means depending upon the extent of the printing area of the aligning character.

6. A printing device including, in combination;

a rotatable circularly shaped printing member having a plurality of printing characters circumferentially arranged on the periphery thereof, said characters varying in printing areas from a relatively small extent to a relatively large extent,

a hammer assembly including a hammer operable to strike anyone of the printing characters and to print an image of the struck character upon a record medium interposed there-between,

means for rotating said printing member to move the characters on the member successively into alignment with the striking path of movement of said hammer,

electromagnetic means for propelling the hammer against the rotary member,

means for energizing said hammer propelling means including a plurality of logic gates each capable when separately activated of delivering a different amount of current to the hammer propelling means and also capable when two or more of the gates are concurrently activated of delivering still further different amounts of current to the hammer propelling means, and

means responding to the positioning of each printing character in alignment with the path of movement of the hammer for activating an individual one or concurrently activating at least two of said logic gates in accordance with the extent of the printing area of each printing character.

Claims

1. A printing device including, in combination; a cyclically movable printing member carrying a plurality of printing characters, said characters varying to printing areas from a relatively low to a relatively high degree, a hammer assembly including a hammer predisposed to strike a printing character brought into alignment with its path of movement and to print an image of the struck character upon a record medium interposed therebetween and further including electrically powered means for propelling the hammer toward the printing member, means for moving said printing member to bring characters carried thereby successively into alignment with the path of movement of said hammer, circuit means for delivering varying amounts of current to the hammer propelling means for operating the same including a set of logic gates each having two inputs which when concurrently signalled will activate the gate, said gates each being capable when individually activated of causing the delivery of a distinctive amount of current to the hammer propelling means for operating the same which differs from the amount of current caused to be delivered by other gates in said set of gates and also capable when two or more of the gates of said set are concurrently activated for causing the delivering of still different amounts of current to the hammer propelling means for operating the same, means responding to the aligning of each printing character carried by said printing member with the path of movement of said hammer for delivering a first electrical signal to one of the two inputs of one or more of said logic gates, and means also responding to the positioning of each printing character in alignment with the path of movement of said hammer for delivering an electrical signal to the other one of the two inputs of one or more of said logic gates concurrently with the delivery of said first signals for selectively activating said one or more gates in accordance with the degree of the printing area of the character brought into alignment with the hammer with the result that the intensity with which the hammer will strike a selected printing character can be proportioned to its printing area.

2. A printing device as defined in claim 1 characterized in that the electrically powered means for propelling the hammer comprises a solenoid coil which is energized by the activation of any one or more of said logic gates.

4. A printing device as defined in claim 3 characterized in that said resistance components are connected in electrical series relation with their respective logic gates and connected to the solenoid coil in electrical parallel relation to one another.

5. A printing device including, in combination; a cyclically movable printing member carrying a plurality of printing characters, said characters varying in printing areas from a relatively small extent to a relatively large extent, a hammer assembly including a hammer operable to strike anyone of the printing characters and to print an image of the struck character upon a record medium interposed therebetween, means for moving said printing member to bring the characters on the member successively into alignment with the pAth of movement of said hammer, electrically powered means for propelling the hammer against the printing member with varying degrees of intensity including a circuit having a plurality of resistors of different resistive values disposed in the circuit in electrical parallel relationship to one another, control means for said hammer propelling means including switching means individually associated with each of said resistors and operable to either permit or cut-off the flow of current through its associated resistor, and means responding to the movement of each printing character into alignment with the hammer''s striking path of movement for activating an individual one or simultaneously activating at least two of said switching means depending upon the extent of the printing area of the aligning character.

6. A printing device including, in combination; a rotatable circularly shaped printing member having a plurality of printing characters circumferentially arranged on the periphery thereof, said characters varying in printing areas from a relatively small extent to a relatively large extent, a hammer assembly including a hammer operable to strike anyone of the printing characters and to print an image of the struck character upon a record medium interposed therebetween, means for rotating said printing member to move the characters on the member successively into alignment with the striking path of movement of said hammer, electromagnetic means for propelling the hammer against the rotary member, means for energizing said hammer propelling means including a plurality of logic gates each capable when separately activated of delivering a different amount of current to the hammer propelling means and also capable when two or more of the gates are concurrently activated of delivering still further different amounts of current to the hammer propelling means, and means responding to the positioning of each printing character in alignment with the path of movement of the hammer for activating an individual one or concurrently activating at least two of said logic gates in accordance with the extent of the printing area of each printing character.