US 3833761 A
A fluorescent lamp for facsimile copy scanning is provided with regulated constant current for constant illumination; all solid state starter circuitry; and automatic current direction reversal once for each scanning line to prevent uneven darkening due to prolonged DC passing through the lamp in one direction.
Claims available in
Description (OCR text may contain errors)
Unlted States Patent 1 1 1111 3,833,761
Houck Sept. 3, 1974 [5 FLUORESCENT LAMP SYSTEM FOR 3,341,737 9/1967 Rosa 315/DIG. 2 FACSIMILE 3,486,069 12/1969 Mahler..... 7 3,486,070 12/1969 Engel 7 Inventor: Deward J. Houck, Mastlc Beach, 3,505,562 4/1970 Engel 315/DIG. 7 N.Y. 3,514,667 5/1970 Dessoulavy et a1. 3l5/DIG. 5
 Assignee: International Scanatron Systems FOREIGN PATENTS OR APPLICATIONS 1 Central 1 1,118,357 11/1961 Germany 315/DIG.7  Filed: July 12, 1971 Primary ExaminerRichard Murray  Appl L685 Assistant ExaminerJoseph A. Orsino, Jr.
Attorney, Agent, or FirmAlfred W. Barber  US. Cl. 178/7.1, 315/97  Int. Cl. H04n l/24 57 ABSTRACT  Fleld of Search 8 A fluorescent lamp for facsimile copy scanning is provided with regulated constant current for constant il- 56 R f Ct d lumination; all solid state starter circuitry; and auto- 1 e erences matic current direction reversal once for each scan- UNITED STATES PATENTS ning line to prevent uneven darkening due to pro- 2,871,409 1/1959 Aldrich et a1 SIS/DIG. 7 longed DC passing through the lamp in one direction. 3,198,982 8/1965 Benson et al. 3l5/97 3,263,123 2/1966 Leeder 315/131(;. 3 5 Chums 2 Drawmg Flgures +100ov. V
PAIENIEUSEP 3 3.833.761
SIEEI 2 BF 2 CDG) FIG. 2
INVENTOR. EWARD HOUOK D WWWIM ATTORNEY FLUORESCENT LAMP SYSTEM FOR FACSIMILE Facsimile scanners which scan copy to be transmitted a line at a time require a long linear light source of very even illumination along the length of the line and very constant illumination with time. The linear fluorescent lamp is a convenient source of such illumination. However, a number of problems have arisen with these lamps and their operation. For one thing operating on direct current over a long period of time the lamps blacken more at one end than at the other. This has been partially corrected by reversing the direction of current flow from time to time. This, on the other hand, permits the lamp to extinguish momentarily during the process of reversing causing a black line to appear in the facsimile copy. Starting the lamps has also been a problem since ordinarily a fluorescent lamp fires sporadically on starting making the usually desired instant starting problematical. Again, attempts to provide a very constant illumination by regulating the voltage across the lamp have not been completely successful.
SUMMARY In accordance with the present invention starting of the fluorescent lamp is provided by an all solid state circuit eliminating the usual ballast transformer. The lamp is operated on constant current providing an improved uniform illumination over long periods of time. Furthermore, the polarity of the direct current feeding the lamp is automatically reversed at each scanning line during the blanking pulse interval so that not only is uneven blackening of the lamp prevented but no lines are produced in the copy. The lamp current is regulated by a power transistor in a constant current circuit. The direction of current flow through the lamp is determined by which pair of two oppositely connected pair of silicon controlled rectifiers is conducting. At each scanning line the blanking pulse of the facsimile signal triggers the constant current transistor off thereby dropping the SCR current to zero allowing the previously conducting pair to go off and the current reversal to pick up in the second pair.
IN THE DRAWING FIG. 1 is a schematic circuit diagram of a portion of the present invention and is used to help explain its operation.
FIG. 2 is a schematic circuit diagram of the complete system of the present invention.
FIG. 1 is a schematic circuit diagram of a portion of the complete system (see FIG. 2) to clearly show the basic circuit for energizing the fluorescent lamp with constant current and how it is turned on and off. Lamp 1 includes filaments 2 and 3 at opposite ends of the lamp cylinder. Lamp current is supplied from a suitable 100 volt direct current source represented by battery 4 connected with negative to ground G and positive on lead 5. This positive potential is applied over lead 5 to anode 7 of silicon controlled rectifier 6 and assuming it is conducting, the current flows out of cathode 9 and over lead 10 to one side of lamp filament 3. SCR 6 also has a gate 8 for tum-on purposes as will be described in connectionwith FIG. 2. Continuing, current leaves filament 3 over lead 11 to cathode 12 of zener diode 12-13 and through this zener diode leaves anode 13 over lead 14 to one side of filament 2. From the other side of filament 2, the current passes over lead 15 to anode 17 of the second SCR 16. Assuming SCR 16 is conducting, the current leaves cathode l9 and flows over lead 20 to collector 23 of power transistor 22 and with transistor 22 in a conducting state, leaves by emitter 24 and flows through resistor 25 back to the negative end of battery 4 at ground G. Pulse transformer 21 is part of the circuit for turning on SCRs 6 and 16 and its function will be fully described in connection with FIG. 2.
The circuit outlined in the above paragraph provides a constant current to lamp 1. With a regulated voltage drop across zener diode 29 supplied through resistor 32 from a source of positive 12 volts, base 25 to which the cathode of zener diode 29 is connected is maintained at the zener regulating voltage, say 4.7 volts, with respect to ground G. With this connection emitter 24 must assume the base voltage minus the base to emitter drop, say 0.7 volt, or 4.0 volts and the current through transistor 22 must therefore be the emitter voltage divided by the resistance of the emitter series resistor 33 say 24 ohms or 166 milliamperes. Thus, since current regulating transistor 22 is in series with lamp 1, the current through lamp 1 is kept constant.
In actual operation, control transistor 26 is initially on or conducting as by applying a logic 1 (positive bias) to base 30 over lead 31. With transistor 26 conducting, collector 27 is in saturation and the collector 27 to emitter 28 circuit is a substantial short circuit, shorting the voltage across zener diode 29 and hence the voltage from base 25 to ground G to a low value. With a very low bias on base 25, transistor 22 becomes substantially non-conducting and the lamp current is reduced to a very low value or substantially zero. In other words, the
lamp 1 is turned off. To turn lamp 1 on, control lead 31 is switched to logic 0 (ground) and transistor 26 with no bias opens allowing full zener voltage across zener diode 29 and between base 25 and ground G. This turns on transistor 22 which now supplies a regulated current (166 ma) to the lamp filaments 2 and 3 as described above. When filaments 2 and 3 become heated the presence of the high voltage (1,000 volts) on wire 34 close to the lamp causes the lamp to ionize or fire. In the ionized state the voltage across the lamp between filaments 2 and 3 drops to a low value, well below the regulating voltage of zener diode 12-13 (for example 68 volts) and all of the constant regulated current flows through the lamp. The lamp is now operating at constant current and will supply a very constant illumination over a long period of time.
FIG. 2, the complete circuit diagram of the preferred form of the present invention, incorporates the portion shown in FIG. 1 and described above. The numbers correspond for corresponding circuit components and similar functions. Facsimile scanner 34 supplies two signals in any suitable manner and well known in the art. One is a starting signal which is logic 0 for lamp off 1 As described abovethis logic 1 applied to base 30 of transistor 26 through resistor 42 and over lead 31, causes transistor 26 to conduct shorting zener diode 29 and the input to current regulating transistor 22 so that little or no current is supplied to lamp 1 and it is in an off condition. When lamp 1 is to be turned on, a logic 1 is applied to terminal 36 over lead 35 and to input 38 of NAND gate 37. This causes NAND gate 37 to change state and the resulting pulse applied through capacitor 45 causes the flip-flop made up of crossconnected NAND gates 43 and 44 to change condition. Since outputs 46 and 47 are coupled to primary 50 of pulse transformer 51 through resistors 48 and 49 respectively, the flipping of the flip-flop induces a pulse in primary 50 which in turn induces pulses in secondary windings 52, 53 and 54. These secondaries being coupled to the gates of SCRs 6, 16, 55 and 56 causes one pair to fire. Assuming for purposes of this description that SCRs 6 and 16 fire, the on condition for lamp 1 is provided as described above in conjunction with FIG. 1. The logic now provided at output 41 of NAND gate 37 places logic 0 on base 30 turning transistor 26 off and allowing the zener 26 to receive a voltage and to turn on current control transistor 22. Now, the coniplete condition described above in connection with FIG. 1 has been established and lamp 1 is turned on.
Now, between each scan line there is a blanking pulse, logic 0 applied to terminal 57 over lead 58 and through capacitor 59 and diode 60 to input terminal 39 of NAND gate 37. This causes NAND gate 37 at output 41 to go momentarily to logic 1, transistor 26 to turn on (shorting zener diode 29) and transistor 22 to turn off. The lamp goes out and without conduction current SCRs 6 and 16 turn off. Now, NAND gates 37 and 62 are cross-coupled by lead 63 and capacitor 61 to form a one-shot which in turn limits the duration of the logic 1 at output 41 to approximately 50 microseconds. At the end of the 50 microsecond interval NAND gate 37 returns to output logic 0 state turning off transistor 26 and turning on transistor 22 restoring the constant lamp current. This return of output 41 to zero causes flip-flop 43-44 to again reverse its state triggering SCRs 55 and 56 which in turn conduct current through lamp 1 in the opposite direction. The lamp immediately turns on since over the very short off time, sufficient ions remain to cause it to strike again. This action continues, reversing the direction of the lamp current flow in response to each blanking pulse, until the end of the transmission and thereby providing precisely equal lamp current in each direction and preventing unequal blackening of the lamp envelope.
At the end of the transmission an off signal (logic 0) is again applied over lead 35 to terminal 36, output 41 goes to logic 1, transistor 26 conducts and transistor 22 goes off, and lamp 1 goes out.
1. In a facsimile scanning system including line by line copy scanning means and means for providing blanking pulses for each scanned line, the combination of;
a fluorescent lamp for illuminating facsimile copy to be scanned;
a source of constant current connected in series with said lamp and four silicon controlled rectifier s in turn connected to provide current reversing switching to said lamp;
and means responsive to the line frequency blanking pulses of said facsimile system for actuating said switching means and thereby reversing the direction of current flow through said lamp for each scanning line of said facsimile copy.
2. In a facsimile scanning system the combination of;
a fluorescent lamp including two filaments for illuminating facsimile copy to be scanned; means for supplying constant current to said lamp through said filaments; and means for starting said lamp including two backto-back zener diodes connected in shunt with said lamp for conducting said constant current through said filaments prior to firing of said lamp and a source of static-high voltage in proximity to the main body of said lamp. 3. A facsimile scanning lamp system as set forth in claim 1, and including;
means for holding said constant current at a value substantially below a normal operating current prior to starting. 4. A facsimile scanning lamp system as set forth in claim 1;
wherein said switching is fast enough to reverse the current through said lamp before deionization can take place. 5. A facsimile scanning lamp system as claim 2;
set forth in wherein the zener voltage of said zener diodes is substantially greater than the voltage drop across said lamp while conducting.